MECHANISMS FOR MOLECULAR COMPLEX FORMATION AND FACTORS WHICH DOMINATE MOLECULAR ORIENTATION IN MOLECULAR COMPLEXES

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^1H NMR spectra of tetrakis [4- (N-methyl) pyridinium] porphyrin (TMPyP) in D_2O was compared with those of prophyrins having three pyridinium groups and one phenyl group (TriMPyP) and two pyridinium groups and two phenyl groups (DiMPyP) at the peri positions. The spectra indicate that both TriMPyP and DiMPyP form their dimers through van deb Waals interaction in spite of the electrostatic repulsion between the positive charges of the porphyrins. It might be concluded that the pi-piinteraction between the porphyrin rings in wateris so strong that the attractive force to form the dimers overcomes the electrostatic repulsive force. On the other hand, TMPyP exists as the monomer form in water even at high concentrations and/or in the presence of inorganic salt. In such a case, the electrostatic repulsive force overcomes the van der Waals attractive force.Tetraarylporphyrins were used as probes to study the mechanism for inclusion of ionic guest molecules into the hydrophobic cyclodextrin … More (CDx) cavities. The phenyl groups having anionic or nonionic substituents at the peripositions of the porphyrins are loosely included by native-beta-cyclodextrin (beta-CDx) while the cationic peripheries are hardly included into the beta-CDx cavity. Anionic and nonionic porphyrins form very stable inclusion complexes with heptakis (tri-O-methyl) -beta-CDx (TMe-beta-CDx). Meanwhile, cationic porphyrins do not form the complexes with TMe-beta-CDx at all. These phenomena can be intepreted in terms of the microscopically polarized CDx cavity where anionic guest is preferable to stay but cationic guest forms very unstable complex because of electrostatic repulsion between the host and the guest.It has been known that CDx are poor hosts to recognize central chirality. Indeed, native and alkylated CDxs have very weak ability to recognize the chirality of amino acids and their derivatives. Then we tried to use coulomb interaction by using protonated aminated CDxs. Protonated amino-beta-CDxs can discriminate between the (R) -and (S) -enantiomers of N-acetyl amino acids and mandelic acid and its related acids in their dissociated forms. The coulomb interaction between the host and the guest as well as inclusion of the guest into the CDx cavity needs to achieve the chiral recognition. Less