Intermolecular Interactions and Chiral Recognition in Water

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Complexation of p-methylbenzoate (p-CH_3-Ph-CO_2^-) and alkanoate anions (CnCO_2^-) with cyclodextrins (CDs) through hydrogen bonding in an aprotic polar solvent, DMSO-d_6, has been studied by means of ^1H NMR spectroscopy. Although undissociated p-methylbenzoic acid, p-CH_3-Ph-CO_2H, does not interact with CDs, p-CH_3-Ph-CO_2^- is bound to native CDs such as α-, β-, and γ-CDs with fairly large binding constants (K) through hydrogen-bonding interactions. Addition of small amounts of D_2O suppresses the formation of the hydrogen-bonded complexes, suggesting that hydrogen-bonding interactions between simple host having dense OH groups as hydrogen-bond donors and guest having the CO_2^- group as a hydrogen-bond acceptor hardly occur in aqueous solution.Thermodynamic parameters for complexation of polyvalent cyclodextrin cation and anion with oppositely charged guests have been determined in D_2O containing 0.02 M NaCl by means of ^1H NMR spectroscopy. Protonated heptakis (6-amino-6-deoxy) … More -β-CD (per-NH_3^+-β-CD) forms stable inclusion complexes with monovalent guest anions. The enthalpy (ΔH) and entropy changes (ΔS) for complexation of per-NH_3^+-β-CD with p-methylbenzoate anion (p-CH_3-Ph-CO_2^-) are 3.8±0.7 kJ mol^<-1> and 88.6±2.2 J mol^<-1>K^<-1>, respectively. The thermodynamic parameters clearly indicate that dehydration from both the host and guest ions accounts for the entropic gain in inclusion process of p-CH_3-Ph-CO_2^- into the per-NH_3^+-β-CD cavity. The acetate anion is not included into the per-NH_3^+-β-CD cavity, while the butanoate and hexanoate anions form the inclusion complexes. The complexation of the alkanoate anions is entropically dominated. Judging from these results, it may be concluded that Coulomb interactions cooperated with inclusion are required for realizing the large entropic gain due to extended dehydration.Tetrakis (p-sulfonatophenyl) porphyrin tetraanion (TPPS) forms an extremely stable 1 : 2 inclusion complex of permethylated β-CD (TMe-β-CD)(porphyrin : CD=1 : 2). The K value for this system in water is too large to be determined. Such a system is expected to act as a good model for hemoglobin and/or myoglobin. The we studied the system composed of Fe (III) TPPS and TMe-β-CD.The Fe (III) complex of TPPS also form a very stable 1 : 2 complex of TMe-β-CD in water at pH>5, while the stoichiometry of the CD inclusion complex is altered to 1 : 1 because of the effort of the net charge of the porphyrin ring. The CD-porphyrin complex shows a novel behavior of axial ligation of Cl^- and ClO_4^-. Less