Melamine-Bridged Bis(porphyrin-Zn^II) Receptors: Molecular Recognition Properties

Abstract

Dimeric metalloporphyrin hosts with tweezer-like structures have been synthesized by reacting the cyanuric chloride scaffold, CC, with 5-(4-aminophenyl)-10,15,20-triphenylporphyrin, P, and 5-(4-aminophenyl)-10,15,20-trimesitylporphyrin, M, to yield the homoconjugates free bases PP and MM and the heterodyad PM. Metalation with Zn(II), gives three structurally related ditopic receptors P(Zn)P(Zn), P(Zn)M(Zn), and M(Zn)M(Zn) with differential steric hindrance and conformational rigidity. The solution structure and supramolecular properties of these porphyrin dimers have been investigated as isolated molecules and in the presence of aliphatic alpha,omega-diamines of general formula H(2)N-(CH(2))(n)-NH(2) (n = 4-8) by spectroscopic and theoretical studies including multidimensional NMR, UV-vis, molecular modeling, and computational NMR methods. Binding constants in the range 4.2 x 10(6) to 3.4 x 10(7) M(-1) are observed in dichloromethane at 298 K, with a 3 orders of magnitude increase as compared to monodentate nBuNH(2), thus indicating the occurrence of a host-guest ditopic interaction. Linear correlation graphs are obtained by plotting the Soret band shift (Delta nu, cm(-1)) of the complex as a function of the diamine chain length. Combined NMR evidence and OPLS 2005 Force Field conformational analysis point to a mutual adaptation of both the binding partners in the host-guest complex, whose geometry is mainly dictated by the steric impact of the bulky substituents at the porphyrin periphery.

Bulky melamine‐based Zn‐porphyrin tweezer as a CD probe of molecular chirality

“…As described in previous studies 25 of B/PP, syn, syn conformer represents a cofacial arrangement of porphyrin rings along the triazine-aminoporphyrin CÀ ÀN bond of the melamine bridge (Fig. 3).…”

“…1) has been developed by some of us. [23][24][25] The aryl groups in the B tweezer, designated as B/TT, B/MM, and B/PP, have, respectively, 3,5-tert-butylphenyl, 2,4,6-trimethylphenyl, and phenyl as substituents in the meso-position of the porphyrin moieties. The B tweezer family combines the advantageous features of previously developed tweezers by having a sterically encumbered periphery and a melamine bridge between the porphyrin units, which is shorter and more rigid.…”

Syn–anti conformational switching: Synthesis and X-ray structures of tweezer and anti form in a zinc porphyrin dimer induced by axial ligands

“…A supramolecular tweezer arising from the insertion of a guest molecule between two binding sites of a molecular host that leads to a fascinating spatial architecture resembles a pincer holding an object. Although bis-porphyrin derivatives are well suited to serve as host compounds for the tweezers [18,19,[24][25][26][27][28][29][30], only a few complexes have been structurally characterized so far [18,19,27].…”

Synthesis, heterogenization and sensing properties of melamine-bridged bis-porphyrin dimers

“…To this aim, we have used nucleophilic aminophenyl-substituted porphyrins such as 5-(4-aminophenyl)-10,15,20-triphenylporphyrin, P, and 5-(4-aminophenyl)-10,15,20-trimesitylporphyrin M. Scheme 2 exemplifies the preparation of a small library of three bis(porphyrin) receptors starting from the two aminoporphyrin derivatives P and M [15,16].…”