Inclusion complexes of serotonin and dopamine with a dioxa-pentaaza-cyclophane  

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Orozco Valencia, Yedith Soberanes, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5405399/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 14 Jan, 2025 Read the published version in Journal of Inclusion Phenomena and Macrocyclic Chemistry → Version 1 posted 10 You are reading this latest preprint version Abstract In attempt to find new type of artificial receptors towards neurotransmitters, NMR studies were carried out on the supramolecular complexation of serotonin and dopamine with a dioxa-pentaaza-cyclophane derived from diethylenetriaminepentaacetic acid (known as DTPA); at the pH 7.2, the macrocycle composed of three phenylene groups is negatively charged with three anionic -CH 2 CO 2 − arms, whereas the aromatic neurotransmitters carry a cationic -NH 3 + group. Aromatic protons in the cyclophane exhibit up-field shifts due to the ring current effect of the neurotransmitters in NMR titration; the through-space interaction is confirmed by NOESY (Nuclear Overhauser Enhancement and Exchange Spectroscopy). Geometry optimization shows that the macrocycle can encapsulate either neurotransmitter molecule to form a 1:1-inclusion complex in which electrostatic and hydrogen-bonding interaction operate between the functional groups of the component molecules. The through-space interaction is stronger for serotonin because of its better fitness to the macrocyclic cavity. The thermodynamic stabilities of the complexes are about 20 M − 1 in D 2 O, and are very slightly decreased in the coexistence of electrolytes. The complexation is promoted by the electrostatic and hydrogen bonds. The resulting ion-pair is stabilized by the successive encapsulation, which protects the weak bonds against the electrostatic field of the electrolyte. The combination of multiple types of interacting sites may be crucial in the design of receptors that can function under isotonic conditions. Serotonin Dopamine Cyclophane Supramolecular complexes Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Introduction The human brain relies on neurotransmitters to perform many important functions. Serotonin (see Scheme 1 ) is, for example, distributed throughout the central nervous system [ 1 ] and is essential for the regulation of various cardiological, neuropsychological and behavioral processes [ 2 – 6 ]. An imbalance in serotonin can lead to mental health problems such as Alzheimer's disease, childhood autism and schizophrenia [ 7 , 8 ]. Another typical example is dopamine (Scheme 1 ), which plays a role in the central and peripheral nervous system in the regulation of brain functions related to motivation, learning and movement control [ 9 ]; dysfunction of dopamine can lead to neurological and neuropsychiatric disorders [ 10 ]. Since abnormal levels of the above-mentioned biogenic amines are associated with various psychiatric disorders and neurodegenerative diseases [ 8 – 13 ], the method to detect them is of great importance for the clinical and pharmacological fields. In addition, the creation of artificial receptors for specific neurotransmitters helps understand substrate‒receptor interactions in neurobiology, as is frequently observed in medicinal chemistry [ 14 ]. From these points of view, the extensive efforts have been made to develop artificial receptors. Cyclophane with definite cavity provides a hydrophobic pocket, and potentially encapsulates a guest molecule inside the cavity through various non-covalent interactions to protect the guests from harmful environments. Many cyclophane derivatives have been synthesized with differently charged functional groups that may enhance solubility in water as well as efficiency for binding guests [ 15 , 16 ]. A series of functional cyclophanes have been synthesized by the cyclization of diethylenetriaminepentaacetic anhydride (DTPA) with aromatic diamines [ 17 , 18 ]. Among them, a cyclophane consisting of four p -phenylene rings has been found to interact with serotonin and dopamine in aqueous solution [ 18 ]. However, the stoichiometry of the resulting complex remains undetermined, probably because the macrocyclic frame is too rigid to adapt the conformation to the encapsulation of a transmitter molecule. It is expected that this problem is solved with the cyclophane shown in Scheme 1 , as the macrocyclic frame composed of o - and p -phenylene groups is expected to have a suitable shape and size for encapsulating an aromatic molecule without a large change in the conformation [ 19 ]. The pD-variation NMR has shown that the central amino nitrogen in the DTPA moiety is protonated in the pD range 6‒8 (see Figure S1 in Supporting Information). The resulting ionic cyclophane, abbreviated as CyH 2− , can interact electrostatically with cationic serotonin (SrH + ) and dopamine (DpH + ). The present NMR study has demonstrated the formation of 1:1 inclusion complexes based on the titrimetric method and NOESY (Nuclear Overhauser Enhancement and Exchange Spectroscopy). The geometry optimization suggests that the complexes are formed as a result of multiple intermolecular interactions, including electrostatic interactions, hydrogen bonding, and a van der Waals contact within the macrocyclic cavity. Results Complexation detected by NMR The NMR spectrum of the cyclophane (at a constant total concentration [Cy] t ) was observed by varying the total concentration of serotonin [Sr] t in D 2 O at a pD of 7.65 (corresponding to pH 7.2). As shown in Figure 1, the signals of protons b1 and b2 adjacent to amino nitrogen are shifted up-field (or decreases in δ) with increasing serotonin concentration, suggesting the intermolecular interaction at the functional groups capable of having electrostatic interactions and/or hydrogen bonding with SrH + . Notably, protons d and i in the aromatic moiety also exhibit significant up-field shifts. Since these protons are located far apart from the functional groups, the observed up-field shifts are attributable to the ring current effect of serotonin; i.e ., protons d and i reside in the up-field shift region above the molecular plane of the serotonin ring, which generates angle-dependent local fields around the nearby protons [20]. Therefore, the observed NMR shifts suggest the presence of a van der Waals contact between the aromatic groups of the cyclophane and serotonin molecules. The through-space interaction has been confirmed by NOESY; Figure 2 presents a NOESY diagram observed for an equimolar mixture of CyH 2− and SrH + . A correlation peak is detected between the p -disubstituted CH 2 ( d ) fraction of cyclophane and proton 7 belonging to the indole ring of serotonin, whereas proton 6 does not show a correlation peak. This correlation demonstrates the presence of van der Waals face-to-face contact between the reactant molecules in such a way that CH( 7 ) resides inside the ring-current field induced by the p -phenylene ring of the cyclophane. The binding sites in serotonin are located by observing 1 H NMR of serotonin with varying the concentration of the cyclophane. Figure 3 demonstrates that ring protons 2 and 6 as well as aliphatic α proton exhibit up-field shifts with increasing concentration of the cyclophane. These spectral changes of serotonin result from the van der Waals contact and hydrogen bonding of OH and NH groups towards the functional groups of the cyclophane. The cyclophane, when titrated with DpH + , shows similar spectral changes (See Figure S2 in supplementary). The up-field shifts of the aromatic protons d and i are very small compared with those of serotonin. On the other hand, clear up-field shifts are presented by the aliphatic and aromatic protons of dopamine in the titration with the cyclophane (Figure 4). These titration results suggest the formation of DpH + ‒ CyH 2− complex associated with hydrogen-bonding and a close contact between the aromatic groups. The NOESY showed diffuse peaks that could be due to a correlation of the cyclophane proton d with the dopamine protons 2 , 5 , and 6 (Figure S3 in Supplementary). The possible correlation peaks are too weak to be convinced, in contrast to the SrH + ‒CyH 2− system; the through-space interaction of serotonin is much stronger than that of dopamine. Optimized geometries of complexes The close contact between the aromatic groups is supposed to result from the encapsulation of a neurotransmitter molecule in the cavity of the cyclophane in their complex. The molecular geometry of the complex was optimized with the DFT (Density Functional Theory) method [21] using the exchange-correlation functional ωB97XD [22] together with the atomic orbital base 6-311G(d,p). An implicit solvation with water via the polarizable continuum model (PCM) [23] was used in the optimization process. The optimized molecular geometry was verified to correspond to the global minima on the potential energy surface by the frequency analysis. All calculations were performed with the computational package Gaussian 09 (G09) [24]. Figure 5 presents the geometry optimized for a SrH + ‒CyH 2− pair. The shape and size of the macrocyclic cavity are suited to a SrH + molecule to yield a 1:1-inclusion complex. The p -phenylene group of CyH 2− and the indole ring of SrH + are stacked each other with a face-to-face distance of 3.49 Å, which is nearly equal to double the van der Waals radius 1.70 Å of phenyl group (or half-thickness of aromatic molecule). Distances between protons d and 7 are 4.21 and 4.60 Å, while those between d and 6 are 5.41 and 6.29 Å. Since the cyclophane consists of two chemically equivalent moieties, the encapsulated molecule reorients in such a way that the complex takes another equivalent molecular geometry. Usually, the exchange between two equivalent geometries is much faster than the frequency of the chemical shift difference [23]. Consequently, NMR observes a time-averaged geometry so that the chemically equivalent protons present a single signal, and the correlation peak is given by the pair with the stronger correlation. Thus, the optimized geometry consistently explains why the NOESY exhibits a correlation peak between d and 7 but not between d and 6 , giving evidence for the presence of the through-space interaction. In addition to the van der Waals contact, three types of interactions are operative between the host and guest molecules: electrostatic interaction between NCH 2 CO 2 − of the CyH 2− and –CH 2 NH 3 + of SrH + , with an O‒H distance of 1.60 Å; hydrogen bonding between amide oxygen of CyH 2− and the OH proton of SrH + , with an O‒H distance of 1.90 Å; hydrogen bonding between a terminal carboxylate oxygen of CyH 2− and ring NH proton of SrH + , with an O‒H distance of 1.78 Å. This binding scheme is consistent with that predicted from the NMR shifts of protons adjacent to the functional groups of CyH 2− and SrH+ in their titrations (Figures 1 and 3). Notably, the non-covalent bonds are formed within the macrocyclic cavity so that they are protected form the environment. The DFT optimization of a DpH + ‒CyH 2− pair also demonstrates the formation of an inclusion complex with multiple intermolecular interactions (Figure 6): electrostatic interaction between NCH 2 CO 2 − of CyH 2− and CH 2 NH 3 + of DpH + ; hydrogen bonding between amide oxygen of CyH 2− and the OH proton of DpH + ; hydrogen bonding between a carboxylate oxygen atom of CyH 2− and second OH proton of DpH + . This scheme of inter- molecular interaction is consistent with the NMR titration results (Figure 4). The phenyl rings of the reactant molecules are stacked each other with a face-to-face distance of 3.75 Å, which is very long compared with the van der Waals contact 3.40 Å of aromatic molecules. The closer contact (3.49 Å) in the serotonin complex suggests the macrocyclic cavity better suits serotonin molecule to result in the stronger through-space interaction that is detectable in NOESY. Thermodynamic stability In the titration of CyH 2− with SrH + , some signals are shifted with increasing total concentration of the titrant [Sr] t (Figure 1). Among them, the sharp signals of protons d and i do not interfere with the neighboring signals so as to give reliable δ values. Moreover, these protons are far apart from the functional groups so that their signals are sensitive to the through-space interaction, and little influenced by effects other than complexation ( e.g ., solvation and protonation) when compared with the proton signals of the DTPA moiety. For these reasons, protons d and i were chosen for the determination of the thermodynamic stability constants. Figure 7 plots changes in δ , Δ = δ ([Sr] t ) – δ (0), against the total concentration [Sr] t of added serotonin (plots for the other protons are shown in Figure S4). The observed asymptotic titration curves suggest the formation of a complex between the reactants. When a 1:1-complex SrH·CyH is formed as suggested by the DFT calculation, the thermodynamic stability constant is defined by the equilibrium constant of the complexation, K = [SrH·CyH]/[SrH][CyH]. The titration curve (or Δ versus [Sr] t plot) is formulated by Equation 1 in the rapid-exchange case of NMR. Δ = Δ c { b – ( b 2 – 4[Cy] t [Sr] t ) 1/2 }/{2[Cy] t } (1) b = [Cy] t + [Sr] t + 1/ K (1a) Here, Δ c is the δ change intrinsic of the resonant proton in the complex. Least-squares calculations based on Equation 1 gave good fitness of the titration curves (Figure 7), while any other stoichiometry like (SrH) 2 ·(CyH) did not interpret the titration curves. This fact is consistent with the DFT calculation. The stability constant of the 1:1-complex was determined by least-squares fitting of the linear combination of curves of protons d and i ; along with the Δ c values. The obtained stability constant is shown in Table 1. Similar spectral changes were observed in the titration with dopamine; the changes in δ of protons d and i exhibit asymptotic titration curves (Figure 8), from which the stability constant is determined by least-squares fitting, as shown in Table 1. To examine the effect of electrolytes on the complexations, the titrations were carried out in the presence of Li + , Na + , or K + ion, as the effects of the cations on the protonation have been found by the UV spectrometry of the cyclophane [20]. The observed titration curves are essentially the same type of curves shown in Figures 7 and 8. The obtained stability constants are of the same order of magnitude as in the absence of electrolyte, but tend to decrease in the coexistence of alkali metal ions (Table 1). The electrolytes studied affect the intermolecular interactions very slightly. Table 1. Stability constants K /M −1 of the complexes of cyclophane with serotonin (SrH + ) and dopamine (DpH + ) at pD ≈ 7.65 and T = 25 °C, in the absence of electrolytes and in the coexistence of alkali metal ions at the concentration of [R]/M; standard deviations are given in the parentheses Added electrolyte Stability constant, K /M −1 Cation [R]/M SrH + DpH + none 23 (1) 20 (1) Li + 0.02 22 (1) 16 (2) Na + 0.02 15 (2) 13 (3) K + 0.01 20 (1) 15 (2) K + 0.02 21 (1) 13 (2) K + 0.03 13 (1) 17 (2) K + 0.06 10 (1) 12 (1) K + 0.10 10 (1) 15 (1) Discussion The present NMR and DFT studies give evidence for the formation of an inclusion complex between the anionic DTPA-derived cyclophane and serotonin cation at pH 7.2. The size and shape of the macrocyclic cavity suits serotonin molecule so well that van der Waals contact is formed between the aromatic rings of the reactant molecules. The complexation is supposed to be motivated by electrostatic interaction between the oppositely charged groups, and the resulting ion-pair is stabilized by the encapsulation accompanied by multiple intermolecular interactions including electrostatic interaction, hydrogen-bonding and van der Waals contact. These intermolecular interactions are enclosed within the macrocyclic cavity so that the thermodynamic stability is little affected by the static field from coexisting electrolytes even in a concentration as high as 0.1 M. Such protection from electrolytes is important in use as a receptor under isotonic conditions. The macrocyclic cavity is less favorable for dopamine cation to form a close van der Waals constant, but it still works for encapsulation to protect intermolecular interactions from the environmental effects. The present study exemplifies that the arrangement of multiple binding sites of different types is crucial in the molecular design of receptors, despite necessity for enhancing the thermodynamic stability. Experimental Materials The cyclophane CyH 3 was synthesized by the method reported previously and confirmed by 1 H NMR [20]. The hydrochloride of serotonin and dopamine were supplied from Sigma-Aldrich. NMR spectroscopy NMR spectra were recorded with a Bruker Avance 400 spectrometer in D 2 O at a probe temperature of 25 °C. The internal reference was sodium 3-(trimethyl)-1-propane sulfonate (DSS), the concentration was minimized to avoid possible electrostatic effects. Sodium 3-(trimethyl)-1-propane sulfonate (DSS) was used as an internal reference at a minimized concentration, to avoid possible electrostatic effects. Cyclophane was dissolved by adding a minimal amount of solid sodium carbonate, and the pD was adjusted with diluted DCl. The pD value was set to 7.65 (corresponding to pH 7.2), at which the reactants formed mono-protonated species CyH 2− , SrH + , and DpH + , respectively (Scheme 1); the species of the cyclophane was identified based on the pD dependence of the NMR spectrum (see Figure S1 in the Supplementary Information) [19]. The pD was determined based on the relationship pD = pH meas + 0.45 from a pH value determined with a glass electrode [26]. 1 H NMR titrations were performed in NMR tubes containing 0.5 mL of a 0.002 M cyclophane solution by adding successively 0.005 mL aliquots of serotonin or dopamine up to the accumulated concentration of 0.02 M. To investigate the effect of electrolytes, titrations were carried out with solutions of different alkaline ions. In the NMR observation of the neurotransmitters with the variation of cyclophane concentration, a series of sample solutions were prepared individually in NMR tubes because of the low solubility of the cyclophane; the appropriate solutions were pipetted into a batch of NMR tubes in such a way that the concentration of a neurotransmitter was constant at 0.002 M and the concentration of the cyclohane was varied up to 0.014 M. 2D NOESY experiments were performed using a solvent suppression sequence with a mixing time of 400 ms and a relaxation time of 2 s. In all experiments, the pH value was measured before and after the measurement to confirm the constancy. Declarations Acknowledgment Sabbatical scholarship of CONAHCYT (I1200/320/2022) is awarded to R.E.N. (CVU No.33703), T. M.-P thanks CONAHCYT for the support to accomplish graduate studies The authors thank the Supramolecular Chemistry Thematic Network, the University of Sonora research fund for supporting the NMR facility, the ACARUS-UNISON supercomputer center for computational resources, and Dra. Lorena Armenta-Villegas for technical assistance with NMR experiments. Funding This work was supported in part by Consejo Nacional de Humanidades Ciencias y Tecnologias, Mexico (Proyecto No. CF-2023-I-2251). Author Contribution T. M.-P: Investigation, Conceptualization, Validation, Figures; A. U. O. V.: Theoretical Optimization; Y. S. Methodology; R. R. S. M.: Supervision, Resources; M. I.: Writing – review & editing, Writing – original draft, Supervision, Methodology, Formal analysis, Data curation; H. S.: Methodology, Formal analysis; R.E. N.: Supervision, Figures, Data analysis, Resources. References Hernández-Mendoza, G. 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Available: https://pubs.acs.org/sharingguidelines Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 14 Jan, 2025 Read the published version in Journal of Inclusion Phenomena and Macrocyclic Chemistry → Version 1 posted Editorial decision: Revision requested 08 Dec, 2024 Reviews received at journal 08 Dec, 2024 Reviewers agreed at journal 02 Dec, 2024 Reviews received at journal 17 Nov, 2024 Reviewers agreed at journal 12 Nov, 2024 Reviewers agreed at journal 10 Nov, 2024 Reviewers invited by journal 07 Nov, 2024 Editor assigned by journal 06 Nov, 2024 Submission checks completed at journal 06 Nov, 2024 First submitted to journal 06 Nov, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Orozco Valencia","email":"","orcid":"","institution":"Universidad de Sonora","correspondingAuthor":false,"prefix":"","firstName":"Ángel","middleName":"U. Orozco","lastName":"Valencia","suffix":""},{"id":387674181,"identity":"0f44e869-0729-4171-b12a-0779f078ee3d","order_by":2,"name":"Yedith Soberanes","email":"","orcid":"","institution":"Universidad de Sonora","correspondingAuthor":false,"prefix":"","firstName":"Yedith","middleName":"","lastName":"Soberanes","suffix":""},{"id":387674182,"identity":"4f77098e-87d1-4291-8a50-da82139f5401","order_by":3,"name":"Rogerio R. Sotelo-Mundo","email":"","orcid":"","institution":"Centro de Investigación en Alimentación y Desarrollo","correspondingAuthor":false,"prefix":"","firstName":"Rogerio","middleName":"R.","lastName":"Sotelo-Mundo","suffix":""},{"id":387674183,"identity":"1632ae6e-eff3-4762-8fce-83d2c4ae3c98","order_by":4,"name":"Motomichi Inoue","email":"","orcid":"","institution":"Universidad de Sonora","correspondingAuthor":false,"prefix":"","firstName":"Motomichi","middleName":"","lastName":"Inoue","suffix":""},{"id":387674184,"identity":"701791c2-5ac7-4966-9b54-7f56aaa4129b","order_by":5,"name":"Hisila Santacruz","email":"","orcid":"","institution":"Universidad de Sonora","correspondingAuthor":false,"prefix":"","firstName":"Hisila","middleName":"","lastName":"Santacruz","suffix":""},{"id":387674185,"identity":"36581793-1872-4ed6-82e4-4c39e5fa5bc7","order_by":6,"name":"Rosa E. Navarro","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABDklEQVRIiWNgGAWjYNCCAmQOewMDQwJBLQbIHJ4DJGuRIKDevL394YcPBjZ5/A28Bz/z1NzL55d8Y/bgwR+bPAaxMwbYtMicOWMsOcMgrVjiAF+yNM+xYsuZs3PMDRLb0ooZpNOw2ichkcMgzWNwOLHhAI+B5Ay2BAOD2zlmEokNQBHp5APYtaQ//v3H4H/i/AM8xj9n/ANquXnGTCLhD0hLYgN2LQlm0gwGBxI3HOAxk/jYBtRyA8hIYMNjC88ZM8seg+TEjYd5zCw+9iUYSPaklUkA/ZLYhssv7O2Pb/yosEucd7zH+EbCtwQDfvbD2yR//LFJ7JfOwRpiCMCMLsCGX/0oGAWjYBSMAjwAACTHXJ4HFMvfAAAAAElFTkSuQmCC","orcid":"","institution":"Universidad de Sonora","correspondingAuthor":true,"prefix":"","firstName":"Rosa","middleName":"E.","lastName":"Navarro","suffix":""}],"badges":[],"createdAt":"2024-11-06 21:23:16","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5405399/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5405399/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s10847-024-01274-w","type":"published","date":"2025-01-14T15:57:58+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":71203738,"identity":"432e657b-e72b-49ff-9004-2f54e6097634","added_by":"auto","created_at":"2024-12-12 06:42:18","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":52152,"visible":true,"origin":"","legend":"\u003cp\u003eChanges in \u003csup\u003e1\u003c/sup\u003eH NMR spectrum of the cyclophane (Cy) with increasing serotonin (Sr) concentration at the ratio [Cy]\u003csub\u003et\u003c/sub\u003e:[Sr]\u003csub\u003et\u003c/sub\u003e up to 1:10 (for labelling of protons, see Scheme 1): [Cy]t = 0.002 M; pD = 7.65; no additional electrolyte; \u003cem\u003eT \u003c/em\u003e= 25 °C.\u0026nbsp;\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-5405399/v1/612ea29ca4e9ee08b1cefe86.png"},{"id":71203741,"identity":"2a7dae5e-2f63-4d9f-a37e-00f27b9c0025","added_by":"auto","created_at":"2024-12-12 06:42:19","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":100109,"visible":true,"origin":"","legend":"\u003cp\u003eNOESY of CyH‒SrH (0.01M) system in D\u003csub\u003e2\u003c/sub\u003eO at pD = 7.65 without additional electrolyte. Spectrum conditions: pulse, 90°; mixing time, 400 ms; 1td, 256; 2td, 2048; power level, 60 dB; duration, 2 s; number of scans, 16. Correlation is observed between proton \u003cstrong\u003ed\u003c/strong\u003e of the cyclophane and proton \u003cstrong\u003e7\u003c/strong\u003e of serotonin. The negative phase is removed for better visualization of the correlations.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-5405399/v1/80095ba740bfbfece55c30c5.png"},{"id":71203917,"identity":"6c7831f6-0a00-4f52-b0f3-34ec3b4e8286","added_by":"auto","created_at":"2024-12-12 06:50:18","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":97413,"visible":true,"origin":"","legend":"\u003cp\u003e\u003csup\u003e1\u003c/sup\u003eH NMR spectra of serotonin (Sr) at different concentrations of the cyclophane (Cy) in the range of [Sr]\u003csub\u003et\u003c/sub\u003e:[Cy]\u003csub\u003et\u003c/sub\u003e up to 1:7 (for\u0026nbsp;labelling of protons, see Scheme 1): [Sr]t = 0.002 M; pD = 7.65; no additional electrolyte; \u003cem\u003eT \u003c/em\u003e= 25 °C.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5405399/v1/aa749a13531370147e2375c2.png"},{"id":71203736,"identity":"00d1d14b-043c-4ca3-befe-f85f6027ecf5","added_by":"auto","created_at":"2024-12-12 06:42:18","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":103576,"visible":true,"origin":"","legend":"\u003cp\u003e\u003csup\u003e1\u003c/sup\u003eH NMR spectra of dopamine (Dp)\u0026nbsp; at different concentrations of the cyclophane (Cy) in the range of [Dp]\u003csub\u003et\u003c/sub\u003e:[Cy]\u003csub\u003et\u003c/sub\u003e up to 1:7 (for\u0026nbsp;labelling of protons, see Scheme 1): [Dp]\u003csub\u003et\u003c/sub\u003e = 0.002 M; pD = 7.65; no additional electrolyte; \u003cem\u003eT \u003c/em\u003e= 25 °C.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-5405399/v1/5f596bcf1deebacbc2e9ce13.png"},{"id":71203740,"identity":"a6a5265f-64f9-44ef-a549-aa18d7a2028a","added_by":"auto","created_at":"2024-12-12 06:42:19","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":86983,"visible":true,"origin":"","legend":"\u003cp\u003eGeometry optimized for CyH\u003csup\u003e2−\u003c/sup\u003e‒SrH\u003csup\u003e+\u003c/sup\u003e complex. Interatomic distances (in Å) are shown for four types of intermolecular interactions.\u0026nbsp;\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-5405399/v1/8285fa2f1ee4e5c2098ae460.png"},{"id":71203918,"identity":"477e6830-61ef-4208-949c-9de144da3489","added_by":"auto","created_at":"2024-12-12 06:50:19","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":87352,"visible":true,"origin":"","legend":"\u003cp\u003eGeometry optimized for CyH\u003csup\u003e2−\u003c/sup\u003e‒DpH\u003csup\u003e+\u003c/sup\u003e complex. Interatomic distances (in Å) are shown for four types of intermolecular interactions.\u0026nbsp;\u0026nbsp;\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-5405399/v1/68888cecdbfb1a2c73dfd85f.png"},{"id":71203920,"identity":"071bc4fb-d9df-4336-9e1d-76aa10901a75","added_by":"auto","created_at":"2024-12-12 06:50:19","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":48492,"visible":true,"origin":"","legend":"\u003cp\u003eChange in NMR shift \u003cem\u003eδ\u003c/em\u003e, \u003cem\u003eΔ\u003c/em\u003e = \u003cem\u003eδ\u003c/em\u003e([Sr]t) – \u003cem\u003eδ\u003c/em\u003e(0), of protons \u003cstrong\u003ed\u003c/strong\u003e (●) and \u003cstrong\u003ei\u003c/strong\u003e (■) of the cyclophane (0.002 M) as a function of the total concentration of serotonin [Sr]t/M; the solid lines are the best fits based on Equation 1 for 1:1-complexation; the obtained stability is shown in Table 1; for labels of the protons, see Scheme 1.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-5405399/v1/485fdef3566b8e3326b5890c.png"},{"id":71204975,"identity":"1aa7b6f6-02bc-4b46-ad0d-4ece9086046e","added_by":"auto","created_at":"2024-12-12 06:58:19","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":51307,"visible":true,"origin":"","legend":"\u003cp\u003eChange in NMR shift \u003cem\u003eδ, Δ\u003c/em\u003e = \u003cem\u003eδ\u003c/em\u003e([Dp]\u003csub\u003et\u003c/sub\u003e) \u003cem\u003e–\u003c/em\u003e \u003cem\u003eδ\u003c/em\u003e(0), of protons \u003cstrong\u003ed\u003c/strong\u003e (●) and \u003cstrong\u003ei\u003c/strong\u003e (■) of the cyclophane (0.002 M) as a function of the total concentration of dopamine [Dp]\u003csub\u003et\u003c/sub\u003e/M; the solid lines are the best fits based on Equation 1 for 1:1-complexation; the obtained stability is shown in Table 1; for labels of the protons, see Scheme 1.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-5405399/v1/a2040e19d737e18e994853a5.png"},{"id":74284708,"identity":"69397f1b-af36-4010-bf5d-d51627b33b72","added_by":"auto","created_at":"2025-01-20 16:11:20","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1237655,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5405399/v1/5e39a376-293f-4316-8347-85c03a551c99.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Inclusion complexes of serotonin and dopamine with a dioxa-pentaaza-cyclophane ","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe human brain relies on neurotransmitters to perform many important functions. Serotonin (see Scheme \u003cspan refid=\"Sch1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) is, for example, distributed throughout the central nervous system [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e] and is essential for the regulation of various cardiological, neuropsychological and behavioral processes [\u003cspan additionalcitationids=\"CR3 CR4 CR5\" citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. An imbalance in serotonin can lead to mental health problems such as Alzheimer's disease, childhood autism and schizophrenia [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Another typical example is dopamine (Scheme \u003cspan refid=\"Sch1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), which plays a role in the central and peripheral nervous system in the regulation of brain functions related to motivation, learning and movement control [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]; dysfunction of dopamine can lead to neurological and neuropsychiatric disorders [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eSince abnormal levels of the above-mentioned biogenic amines are associated with various psychiatric disorders and neurodegenerative diseases [\u003cspan additionalcitationids=\"CR9 CR10 CR11 CR12\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], the method to detect them is of great importance for the clinical and pharmacological fields. In addition, the creation of artificial receptors for specific neurotransmitters helps understand substrate‒receptor interactions in neurobiology, as is frequently observed in medicinal chemistry [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. From these points of view, the extensive efforts have been made to develop artificial receptors. Cyclophane with definite cavity provides a hydrophobic pocket, and potentially encapsulates a guest molecule inside the cavity through various non-covalent interactions to protect the guests from harmful environments. Many cyclophane derivatives have been synthesized with differently charged functional groups that may enhance solubility in water as well as efficiency for binding guests [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eA series of functional cyclophanes have been synthesized by the cyclization of diethylenetriaminepentaacetic anhydride (DTPA) with aromatic diamines [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Among them, a cyclophane consisting of four \u003cem\u003ep\u003c/em\u003e-phenylene rings has been found to interact with serotonin and dopamine in aqueous solution [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. However, the stoichiometry of the resulting complex remains undetermined, probably because the macrocyclic frame is too rigid to adapt the conformation to the encapsulation of a transmitter molecule. It is expected that this problem is solved with the cyclophane shown in Scheme \u003cspan refid=\"Sch1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, as the macrocyclic frame composed of \u003cem\u003eo\u003c/em\u003e- and \u003cem\u003ep\u003c/em\u003e-phenylene groups is expected to have a suitable shape and size for encapsulating an aromatic molecule without a large change in the conformation [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. The pD-variation NMR has shown that the central amino nitrogen in the DTPA moiety is protonated in the pD range 6‒8 (see Figure S1 in Supporting Information). The resulting ionic cyclophane, abbreviated as CyH\u003csup\u003e2\u0026minus;\u003c/sup\u003e, can interact electrostatically with cationic serotonin (SrH\u003csup\u003e+\u003c/sup\u003e) and dopamine (DpH\u003csup\u003e+\u003c/sup\u003e). The present NMR study has demonstrated the formation of 1:1 inclusion complexes based on the titrimetric method and NOESY (Nuclear Overhauser Enhancement and Exchange Spectroscopy). The geometry optimization suggests that the complexes are formed as a result of multiple intermolecular interactions, including electrostatic interactions, hydrogen bonding, and a van der Waals contact within the macrocyclic cavity.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cstrong\u003e\u003cem\u003eComplexation detected by NMR\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp skip=\"true\"\u003eThe NMR spectrum of the cyclophane (at a constant total concentration [Cy]\u003csub\u003et\u003c/sub\u003e) was observed by varying the total concentration of serotonin [Sr]\u003csub\u003et\u003c/sub\u003e in D\u003csub\u003e2\u003c/sub\u003eO at a pD of 7.65 (corresponding to pH 7.2). As shown in Figure 1, the signals of protons \u003cstrong\u003eb1\u003c/strong\u003e and \u003cstrong\u003eb2\u003c/strong\u003e adjacent to amino nitrogen are shifted up-field (or decreases in \u0026delta;) with increasing serotonin concentration, suggesting the intermolecular interaction at the functional groups capable of having electrostatic interactions and/or hydrogen bonding with SrH\u003csup\u003e+\u003c/sup\u003e. Notably, protons \u003cstrong\u003ed\u003c/strong\u003e and \u003cstrong\u003ei\u003c/strong\u003e in the aromatic moiety also exhibit significant up-field shifts. Since these protons are located far apart from the functional groups, the observed up-field shifts are attributable to the ring current effect of serotonin; \u003cem\u003ei.e\u003c/em\u003e., protons \u003cstrong\u003ed\u003c/strong\u003e and \u003cstrong\u003ei\u003c/strong\u003e reside in the up-field shift region above the molecular plane of the serotonin ring, which generates angle-dependent local fields around the nearby protons [20]. Therefore, the observed NMR shifts suggest the presence of a van der Waals contact between the aromatic groups of the cyclophane and serotonin molecules. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe through-space interaction has been confirmed by\u0026nbsp;NOESY; Figure 2 presents a NOESY diagram observed for an equimolar mixture of CyH\u003csup\u003e2\u0026minus;\u003c/sup\u003e and SrH\u003csup\u003e+\u003c/sup\u003e. A correlation peak is detected between the \u003cem\u003ep\u003c/em\u003e-disubstituted CH\u003csub\u003e2\u003c/sub\u003e(\u003cstrong\u003ed\u003c/strong\u003e) fraction of cyclophane and proton \u003cstrong\u003e7\u003c/strong\u003e belonging to the indole ring of serotonin, whereas proton \u003cstrong\u003e6\u003c/strong\u003e\u0026nbsp; does not show a correlation peak. This correlation demonstrates the presence of van der Waals face-to-face contact between the reactant molecules in such a way that CH(\u003cstrong\u003e7\u003c/strong\u003e) \u0026nbsp;resides inside the ring-current field induced by the \u003cem\u003ep\u003c/em\u003e-phenylene ring of the cyclophane.\u003c/p\u003e\n\u003cp\u003eThe binding sites in serotonin are located by observing \u003csup\u003e1\u003c/sup\u003eH NMR of serotonin with varying the concentration of the cyclophane. Figure 3 demonstrates that ring protons \u003cstrong\u003e2\u0026nbsp;\u003c/strong\u003eand \u003cstrong\u003e6\u003c/strong\u003e as well as aliphatic \u003cstrong\u003e\u0026alpha;\u003c/strong\u003e proton exhibit up-field shifts with increasing concentration of the cyclophane. These spectral changes of serotonin result from the van der Waals contact and hydrogen bonding of OH and NH groups towards the functional groups of the cyclophane.\u003c/p\u003e\n\u003cp\u003eThe cyclophane, when titrated with DpH\u003csup\u003e+\u003c/sup\u003e, shows similar spectral changes (See Figure S2 in supplementary). The up-field shifts of the aromatic protons \u003cstrong\u003ed\u003c/strong\u003e and \u003cstrong\u003ei\u003c/strong\u003e are very small compared with those of serotonin. On the other hand, clear up-field shifts are presented by the aliphatic and aromatic protons of dopamine in the titration with the cyclophane (Figure 4). These titration results suggest the formation of DpH\u003csup\u003e+\u003c/sup\u003e‒ CyH\u003csup\u003e2\u0026minus;\u003c/sup\u003e complex associated with hydrogen-bonding and a close contact between the aromatic groups. The NOESY showed diffuse peaks that could be due to a correlation of the cyclophane proton \u003cstrong\u003ed\u003c/strong\u003e with the dopamine protons \u003cstrong\u003e2\u003c/strong\u003e, \u003cstrong\u003e5\u003c/strong\u003e, and \u003cstrong\u003e6\u003c/strong\u003e (Figure S3 in Supplementary). The possible correlation peaks are too weak to be convinced, in contrast to the SrH\u003csup\u003e+\u003c/sup\u003e‒CyH\u003csup\u003e2\u0026minus;\u003c/sup\u003e system; the through-space interaction of serotonin is much stronger than that of dopamine.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eOptimized geometries of complexes\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe close contact between the aromatic groups is supposed to result from the encapsulation of a neurotransmitter molecule in the cavity of the cyclophane in their complex. The molecular geometry of the complex was optimized with the DFT (Density Functional Theory) method [21] using the exchange-correlation functional \u0026omega;B97XD [22] together with the atomic orbital base 6-311G(d,p). An implicit solvation with water via the polarizable continuum model (PCM) [23] was used in the optimization process. The optimized molecular geometry was verified to correspond to the global minima on the potential energy surface by the frequency analysis. All calculations were performed with the computational package Gaussian 09 (G09) [24].\u003c/p\u003e\n\u003cp\u003eFigure 5\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003epresents the geometry\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eoptimized for a SrH\u003csup\u003e+\u003c/sup\u003e‒CyH\u003csup\u003e2\u0026minus;\u0026nbsp;\u003c/sup\u003epair. \u003csup\u003e\u0026nbsp;\u003c/sup\u003eThe shape and size of the macrocyclic cavity are suited to a SrH\u003csup\u003e+\u003c/sup\u003e molecule to yield a 1:1-inclusion complex. The \u003cem\u003ep\u003c/em\u003e-phenylene group of CyH\u003csup\u003e2\u0026minus;\u0026nbsp;\u003c/sup\u003eand the indole ring of SrH\u003csup\u003e+\u003c/sup\u003e are stacked each other with a face-to-face distance of 3.49 \u0026Aring;, which is nearly equal to double the van der Waals radius 1.70 \u0026Aring; of phenyl group (or half-thickness of aromatic molecule). Distances between protons \u003cstrong\u003ed\u003c/strong\u003e and \u003cstrong\u003e7\u003c/strong\u003e are 4.21 and 4.60 \u0026Aring;, while those between \u003cstrong\u003ed\u003c/strong\u003e and \u003cstrong\u003e6\u003c/strong\u003e are 5.41 and 6.29 \u0026Aring;. Since the cyclophane consists of two chemically equivalent moieties, the encapsulated molecule reorients in such a way that the complex takes another equivalent molecular geometry. Usually, the exchange between two equivalent geometries is much faster than the frequency of the chemical shift difference [23]. Consequently, NMR observes a time-averaged geometry so that the chemically equivalent protons present a single signal, and the correlation peak is given by the pair with the stronger correlation. Thus, the optimized geometry consistently explains why the NOESY exhibits a correlation peak between \u003cstrong\u003ed\u003c/strong\u003e and \u003cstrong\u003e7\u003c/strong\u003e but not between \u003cstrong\u003ed\u003c/strong\u003e and \u003cstrong\u003e6\u003c/strong\u003e, giving evidence for the presence of the through-space interaction. In addition to the van der Waals contact, three types of interactions are operative between the host and guest molecules: electrostatic interaction between NCH\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e of the CyH\u003csup\u003e2\u0026minus;\u0026nbsp;\u003c/sup\u003eand \u0026ndash;CH\u003csub\u003e2\u003c/sub\u003eNH\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e of SrH\u003csup\u003e+\u003c/sup\u003e, with an O‒H distance of 1.60 \u0026Aring;; hydrogen bonding between amide oxygen of CyH\u003csup\u003e2\u0026minus;\u003c/sup\u003e and the OH proton of SrH\u003csup\u003e+\u003c/sup\u003e, with an O‒H distance of 1.90 \u0026Aring;; hydrogen bonding between a terminal carboxylate oxygen of CyH\u003csup\u003e2\u0026minus;\u003c/sup\u003e and ring NH proton of SrH\u003csup\u003e+\u003c/sup\u003e, with an O‒H distance of 1.78 \u0026Aring;. This binding scheme is consistent with that predicted from the NMR shifts of protons adjacent to the functional groups of CyH\u003csup\u003e2\u0026minus;\u003c/sup\u003e and SrH+ in their titrations (Figures 1 and 3). \u0026nbsp; Notably, the non-covalent bonds are formed within the macrocyclic cavity so that they are protected form the environment. \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe DFT optimization of a DpH\u003csup\u003e+\u003c/sup\u003e‒CyH\u003csup\u003e2\u0026minus;\u0026nbsp;\u003c/sup\u003epair also demonstrates the formation of an inclusion complex with multiple intermolecular interactions (Figure 6): electrostatic interaction between NCH\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e of CyH\u003csup\u003e2\u0026minus;\u003c/sup\u003e and CH\u003csub\u003e2\u003c/sub\u003eNH\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e of DpH\u003csup\u003e+\u003c/sup\u003e; hydrogen bonding between amide oxygen of CyH\u003csup\u003e2\u0026minus;\u003c/sup\u003e and the OH proton of DpH\u003csup\u003e+\u003c/sup\u003e; hydrogen bonding between a carboxylate oxygen atom of CyH\u003csup\u003e2\u0026minus;\u003c/sup\u003e and second OH proton of DpH\u003csup\u003e+\u003c/sup\u003e. This scheme of inter- molecular interaction is consistent with the NMR titration results (Figure 4). The phenyl rings of the reactant molecules are stacked each other with a face-to-face distance of 3.75 \u0026Aring;, which is very long compared with the van der Waals contact 3.40 \u0026Aring; of aromatic molecules. The closer contact (3.49 \u0026Aring;) in the serotonin complex suggests the macrocyclic cavity better suits serotonin molecule to result in the stronger through-space interaction that is detectable in NOESY.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eThermodynamic stability\u003c/em\u003e\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn the titration of CyH\u003csup\u003e2\u0026minus;\u003c/sup\u003e with SrH\u003csup\u003e+\u003c/sup\u003e, some signals are shifted with increasing total concentration of the titrant [Sr]\u003csub\u003et\u003c/sub\u003e (Figure 1). Among them, the sharp signals of protons \u003cstrong\u003ed\u003c/strong\u003e and \u003cstrong\u003ei\u003c/strong\u003e do not interfere with the neighboring signals so as to give reliable \u003cem\u003e\u0026delta;\u003c/em\u003e values. Moreover, these protons are far apart from the functional groups so that their signals are sensitive to the through-space interaction, and little influenced by effects other than complexation (\u003cem\u003ee.g\u003c/em\u003e., solvation and protonation) when compared with the proton signals of the DTPA moiety. For these reasons, protons \u003cstrong\u003ed\u003c/strong\u003e and \u003cstrong\u003ei\u003c/strong\u003e were chosen for the determination of the thermodynamic stability constants. Figure 7 plots changes in\u003cem\u003e\u0026nbsp;\u0026delta;\u003c/em\u003e, \u003cem\u003e\u0026Delta;\u003c/em\u003e = \u003cem\u003e\u0026delta;\u003c/em\u003e([Sr]\u003csub\u003et\u003c/sub\u003e) \u003cem\u003e\u0026ndash;\u003c/em\u003e \u003cem\u003e\u0026delta;\u003c/em\u003e(0), against the total concentration [Sr]\u003csub\u003et\u003c/sub\u003e of added serotonin (plots for the other protons are shown in Figure S4). The observed asymptotic titration curves suggest the formation of a complex between the reactants. When a 1:1-complex SrH\u0026middot;CyH is formed as suggested by the DFT calculation, the thermodynamic stability constant is defined by the equilibrium constant of the complexation, \u003cem\u003eK\u003c/em\u003e = [SrH\u0026middot;CyH]/[SrH][CyH]. The titration curve (or \u003cem\u003e\u0026Delta;\u003c/em\u003e versus [Sr]\u003csub\u003et\u003c/sub\u003e plot) is formulated by Equation 1 in the rapid-exchange case of NMR.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e\u0026Delta;\u003c/em\u003e = \u003cem\u003e\u0026Delta;\u003csub\u003ec\u003c/sub\u003e\u003c/em\u003e{\u003cem\u003eb\u003c/em\u003e \u0026ndash; (\u003cem\u003eb\u003c/em\u003e\u003csup\u003e2\u003c/sup\u003e \u0026ndash; 4[Cy]\u003csub\u003et\u003c/sub\u003e[Sr]\u003csub\u003et\u003c/sub\u003e)\u003csup\u003e1/2\u003c/sup\u003e}/{2[Cy]\u003csub\u003et\u003c/sub\u003e} \u0026nbsp; (1)\u003csub\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/sub\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eb\u003c/em\u003e = [Cy]\u003csub\u003et\u003c/sub\u003e + [Sr]\u003csub\u003et\u003c/sub\u003e + 1/\u003cem\u003eK\u003c/em\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;(1a)\u003c/p\u003e\n\u003cp\u003eHere,\u003cem\u003e\u0026nbsp;\u0026Delta;\u003csub\u003ec\u003c/sub\u003e\u003c/em\u003e is the \u003cem\u003e\u0026delta;\u003c/em\u003e change intrinsic of the resonant proton in the complex. Least-squares calculations based on Equation 1 gave good fitness of the titration curves (Figure 7), while any other stoichiometry like (SrH)\u003csub\u003e2\u003c/sub\u003e\u0026middot;(CyH) did not interpret the titration curves. This fact is consistent with the DFT calculation. The stability constant of the 1:1-complex was determined by least-squares fitting of the linear combination of curves of protons \u003cstrong\u003ed\u003c/strong\u003e and\u003cstrong\u003e\u0026nbsp;i\u003c/strong\u003e; along with the\u003cem\u003e\u0026nbsp;\u0026Delta;\u003csub\u003ec\u003c/sub\u003e\u003c/em\u003e values. The obtained stability constant is shown in Table 1. Similar spectral changes were observed in the titration with dopamine; the changes in \u003cem\u003e\u0026delta;\u003c/em\u003e of protons \u003cstrong\u003ed\u003c/strong\u003e and \u003cstrong\u003ei\u003c/strong\u003e exhibit asymptotic titration curves (Figure 8), from which the stability constant is determined by least-squares fitting, as shown in Table 1.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTo examine the effect of electrolytes on the complexations, the titrations were carried out in the presence of Li\u003csup\u003e+\u003c/sup\u003e, Na\u003csup\u003e+\u003c/sup\u003e, or K\u003csup\u003e+\u003c/sup\u003e ion, as the effects of the cations on the protonation have been found by the UV spectrometry of the cyclophane [20]. The observed titration curves are essentially the same type of curves shown in Figures 7 and 8. The obtained stability constants are of the same order of magnitude as in the absence of electrolyte, but tend to decrease in the coexistence of alkali metal ions (Table 1). The electrolytes studied affect the intermolecular interactions very slightly. \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cdiv align=\"center\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"4\" valign=\"top\" style=\"width: 100%;\"\u003eTable 1. \u0026nbsp;Stability constants \u003cem\u003eK\u003c/em\u003e/M\u003csup\u003e\u0026minus;1\u003c/sup\u003e of the complexes of cyclophane with serotonin (SrH\u003csup\u003e+\u003c/sup\u003e) and dopamine (DpH\u003csup\u003e+\u003c/sup\u003e) at pD \u0026asymp; 7.65 and\u0026nbsp;\u003cem\u003eT\u003c/em\u003e = 25 \u0026deg;C, in the absence of electrolytes and in the coexistence of alkali metal ions at the concentration of [R]/M; standard deviations are given in the parentheses \u0026nbsp;\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 42.7873%;\"\u003eAdded electrolyte\u003cbr\u003e\u003c/td\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 57.2127%;\"\u003eStability constant, \u003cem\u003eK\u003c/em\u003e/M\u003csup\u003e\u0026minus;1\u003c/sup\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 19.8044%;\"\u003eCation\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 22.9829%;\"\u003e[R]/M\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 27.8729%;\"\u003eSrH\u003csup\u003e+\u003c/sup\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 29.3399%;\"\u003eDpH\u003csup\u003e+\u003c/sup\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 19.8044%;\"\u003enone\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 22.9829%;\"\u003e\u0026nbsp;\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 27.8729%;\"\u003e23 (1)\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 29.3399%;\"\u003e20 (1)\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 19.8044%;\"\u003eLi\u003csup\u003e+\u003c/sup\u003e \u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 22.9829%;\"\u003e0.02\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 27.8729%;\"\u003e22 (1)\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 29.3399%;\"\u003e16 (2)\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 19.8044%;\"\u003eNa\u003csup\u003e+\u003c/sup\u003e \u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 22.9829%;\"\u003e0.02\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 27.8729%;\"\u003e15 (2)\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 29.3399%;\"\u003e13 (3)\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 19.8044%;\"\u003eK\u003csup\u003e+\u003c/sup\u003e \u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 22.9829%;\"\u003e0.01\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 27.8729%;\"\u003e20 (1)\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 29.3399%;\"\u003e15 (2)\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 19.8044%;\"\u003eK\u003csup\u003e+\u003c/sup\u003e \u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 22.9829%;\"\u003e0.02\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 27.8729%;\"\u003e21 (1)\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 29.3399%;\"\u003e13 (2)\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 19.8044%;\"\u003eK\u003csup\u003e+\u003c/sup\u003e \u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 22.9829%;\"\u003e0.03\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 27.8729%;\"\u003e13 (1)\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 29.3399%;\"\u003e17 (2)\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 19.8044%;\"\u003eK\u003csup\u003e+\u003c/sup\u003e \u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 22.9829%;\"\u003e0.06\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 27.8729%;\"\u003e10 (1)\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 29.3399%;\"\u003e12 (1)\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 19.8044%;\"\u003eK\u003csup\u003e+\u003c/sup\u003e \u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 22.9829%;\"\u003e0.10\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 27.8729%;\"\u003e10 (1)\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 29.3399%;\"\u003e15 (1)\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe present NMR and DFT studies give evidence for the formation of an inclusion complex between the anionic DTPA-derived cyclophane and serotonin cation at pH 7.2. The size and shape of the macrocyclic cavity suits serotonin molecule so well that van der Waals contact is formed between the aromatic rings of the reactant molecules. The complexation is supposed to be motivated by electrostatic interaction between the oppositely charged groups, and the resulting ion-pair is stabilized by the encapsulation accompanied by multiple intermolecular interactions including electrostatic interaction, hydrogen-bonding and van der Waals contact. These intermolecular interactions are enclosed within the macrocyclic cavity so that the thermodynamic stability is little affected by the static field from coexisting electrolytes even in a concentration as high as 0.1 M. Such protection from electrolytes is important in use as a receptor under isotonic conditions. The macrocyclic cavity is less favorable for dopamine cation to form a close van der Waals constant, but it still works for encapsulation to protect intermolecular interactions from the environmental effects. The present study exemplifies that the arrangement of multiple binding sites of different types is crucial in the molecular design of receptors, despite necessity for enhancing the thermodynamic stability.\u003c/p\u003e"},{"header":"Experimental","content":"\u003cp\u003e\u003cstrong\u003e\u003cem\u003eMaterials\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe cyclophane CyH\u003csub\u003e3\u003c/sub\u003e was synthesized by the method reported previously and confirmed by \u003csup\u003e1\u003c/sup\u003eH NMR [20]. The hydrochloride of serotonin and dopamine were supplied from Sigma-Aldrich.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eNMR spectroscopy\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNMR spectra were recorded with a Bruker Avance 400 spectrometer in D\u003csub\u003e2\u003c/sub\u003eO at a probe temperature of 25 \u0026deg;C. The internal reference was sodium 3-(trimethyl)-1-propane sulfonate (DSS), the concentration was minimized to avoid possible electrostatic effects.\u003c/p\u003e\n\u003cp\u003eSodium 3-(trimethyl)-1-propane sulfonate (DSS) was used as an internal reference at a minimized concentration, to avoid possible electrostatic effects. Cyclophane was dissolved by adding a minimal amount of solid sodium carbonate, and the pD was adjusted with diluted DCl. The pD value was set to 7.65 (corresponding to pH 7.2), at which the reactants formed mono-protonated species CyH\u003csup\u003e2\u0026minus;\u003c/sup\u003e, SrH\u003csup\u003e+\u003c/sup\u003e, and DpH\u003csup\u003e+\u003c/sup\u003e, respectively (Scheme 1); the species of the cyclophane was identified\u0026nbsp;based on\u0026nbsp;the pD dependence of the NMR spectrum (see Figure S1 in the Supplementary Information) [19]. The pD was determined based on the relationship pD = pH\u003csub\u003emeas\u003c/sub\u003e + 0.45 from a pH value determined with a glass electrode [26].\u003c/p\u003e\n\u003cp skip=\"true\"\u003e\u003csup\u003e1\u003c/sup\u003eH NMR titrations were performed in NMR tubes containing 0.5 mL of a 0.002 M cyclophane solution by adding successively 0.005 mL aliquots of serotonin or dopamine up to the accumulated concentration of 0.02 M. To investigate the effect of electrolytes, titrations were carried out with solutions of different alkaline ions. In the NMR observation of the neurotransmitters with the variation of cyclophane concentration, a series of sample solutions were prepared individually in NMR tubes because of the low solubility of the cyclophane; the appropriate solutions were pipetted into a batch of NMR tubes in such a way that the concentration of a neurotransmitter was constant at 0.002 M and the concentration of the cyclohane was varied up to 0.014 M. 2D NOESY experiments were performed using a solvent suppression sequence with a mixing time of 400 ms and a relaxation time of 2 s. In all experiments, the pH value was measured before and after the measurement to confirm the constancy. \u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgment\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSabbatical scholarship of CONAHCYT (I1200/320/2022) is awarded to R.E.N. (CVU No.33703), T. M.-P thanks CONAHCYT for the support to accomplish graduate studies\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe authors thank the Supramolecular Chemistry Thematic Network, the University of Sonora research fund for supporting the NMR facility, the ACARUS-UNISON supercomputer center for computational resources, and Dra. Lorena Armenta-Villegas for technical assistance with NMR experiments.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported in part by Consejo Nacional de Humanidades\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eCiencias y Tecnologias, Mexico (Proyecto No. CF-2023-I-2251).\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eT. M.-P: Investigation, Conceptualization, Validation, Figures; A. U. O. V.: Theoretical Optimization; Y. S. Methodology; R. R. S. M.: Supervision, Resources; M. I.: Writing \u0026ndash; review \u0026amp; editing, Writing \u0026ndash; original draft, Supervision, Methodology, Formal analysis, Data curation; H. S.: Methodology, Formal analysis; R.E. N.: Supervision, Figures, Data analysis, Resources.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eHern\u0026aacute;ndez-Mendoza, G. A., \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Fluorescence of serotonin in the visible spectrum upon multiphotonic photoconversion,\u0026rdquo; \u003cem\u003eBiomed Opt Express\u003c/em\u003e, vol. 11, no. 3, p. 1432, Mar. 2020, doi: 10.1364/boe.380412.\u003c/li\u003e\n\u003cli\u003eMarioara, O. M. N., Ghenea, A. E., Vladoianu, C. N., Carsote, M. and Popescu, M. \u0026ldquo;The relationship between serotonine, histamine and the brain`s electrical activity in patients with depression and endocrine disorders,\u0026rdquo; \u003cem\u003eRo Med J.\u003c/em\u003e, vol. 68, no. 2, pp. 273\u0026ndash;277, 2021, doi: 10.37897/RMJ.2021.2.22.\u003c/li\u003e\n\u003cli\u003eCarhart-Harris, R. L. and Nutt, D. J. \u0026ldquo;Serotonin and brain function: A tale of two receptors,\u0026rdquo; Sep. 01, 2017, \u003cem\u003eSAGE Publications Ltd\u003c/em\u003e. doi: 10.1177/0269881117725915.\u003c/li\u003e\n\u003cli\u003eDilworth, M. V., Findlay, H. E. and Booth, P. 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Available: https://pubs.acs.org/sharingguidelines\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-inclusion-phenomena-and-macrocyclic-chemistry","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jiph","sideBox":"Learn more about [Journal of Inclusion Phenomena and Macrocyclic Chemistry](http://link.springer.com/journal/10847)","snPcode":"10847","submissionUrl":"https://submission.nature.com/new-submission/10847/3","title":"Journal of Inclusion Phenomena and Macrocyclic Chemistry","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Serotonin, Dopamine, Cyclophane, Supramolecular complexes","lastPublishedDoi":"10.21203/rs.3.rs-5405399/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5405399/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn attempt to find new type of artificial receptors towards neurotransmitters, NMR studies were carried out on the supramolecular complexation of serotonin and dopamine with a dioxa-pentaaza-cyclophane derived from diethylenetriaminepentaacetic acid (known as DTPA); at the pH 7.2, the macrocycle composed of three phenylene groups is negatively charged with three anionic -CH\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e arms, whereas the aromatic neurotransmitters carry a cationic -NH\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e group. Aromatic protons in the cyclophane exhibit up-field shifts due to the ring current effect of the neurotransmitters in NMR titration; the through-space interaction is confirmed by NOESY (Nuclear Overhauser Enhancement and Exchange Spectroscopy). Geometry optimization shows that the macrocycle can encapsulate either neurotransmitter molecule to form a 1:1-inclusion complex in which electrostatic and hydrogen-bonding interaction operate between the functional groups of the component molecules. The through-space interaction is stronger for serotonin because of its better fitness to the macrocyclic cavity. The thermodynamic stabilities of the complexes are about 20 M\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in D\u003csub\u003e2\u003c/sub\u003eO, and are very slightly decreased in the coexistence of electrolytes. The complexation is promoted by the electrostatic and hydrogen bonds. The resulting ion-pair is stabilized by the successive encapsulation, which protects the weak bonds against the electrostatic field of the electrolyte. The combination of multiple types of interacting sites may be crucial in the design of receptors that can function under isotonic conditions.\u003c/p\u003e","manuscriptTitle":"Inclusion complexes of serotonin and dopamine with a dioxa-pentaaza-cyclophane ","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-12-12 06:42:14","doi":"10.21203/rs.3.rs-5405399/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-12-08T20:01:04+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-12-08T19:57:00+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"168269645963144472610357763725866628399","date":"2024-12-02T12:14:52+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-11-18T02:19:17+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"199802384065784315366056138422331205360","date":"2024-11-12T08:35:29+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"304183238110819090800327716102287425229","date":"2024-11-10T13:55:32+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-11-07T10:07:19+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-11-07T04:08:21+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-11-07T04:06:10+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Inclusion Phenomena and Macrocyclic Chemistry","date":"2024-11-06T21:15:19+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-inclusion-phenomena-and-macrocyclic-chemistry","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jiph","sideBox":"Learn more about [Journal of Inclusion Phenomena and Macrocyclic Chemistry](http://link.springer.com/journal/10847)","snPcode":"10847","submissionUrl":"https://submission.nature.com/new-submission/10847/3","title":"Journal of Inclusion Phenomena and Macrocyclic Chemistry","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"32b97d00-15bc-4829-906c-f1682214be22","owner":[],"postedDate":"December 12th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-01-20T16:04:28+00:00","versionOfRecord":{"articleIdentity":"rs-5405399","link":"https://doi.org/10.1007/s10847-024-01274-w","journal":{"identity":"journal-of-inclusion-phenomena-and-macrocyclic-chemistry","isVorOnly":false,"title":"Journal of Inclusion Phenomena and Macrocyclic Chemistry"},"publishedOn":"2025-01-14 15:57:58","publishedOnDateReadable":"January 14th, 2025"},"versionCreatedAt":"2024-12-12 06:42:14","video":"","vorDoi":"10.1007/s10847-024-01274-w","vorDoiUrl":"https://doi.org/10.1007/s10847-024-01274-w","workflowStages":[]},"version":"v1","identity":"rs-5405399","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5405399","identity":"rs-5405399","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}