Crystal and Molecular Structure of the [6-Deoxy-6-[(2-(4-imidazolyl)ethyl)amino]- cyclomaltoheptaose]copper(II) Ternary Complex with L-Tryptophanate. Role of Weak Forces in the Chiral Recognition Process Assisted by a Metallocyclodextrin.
The ternary copper(II) complex of 6-deoxy-6-[(2-(4-imidazolyl)ethyl)amino]cyclomaltoheptaose (CDhm) and L-tryptophanate (L-TrpO(-)) was characterized by ESR and X-ray diffraction. The solid state structure of [Cu(CDhm)(L-TrpO)](+) shows that the aromatic side chain of TrpO(-) is outside the cavity and that the two amino nitrogen atoms, one from the histamine molecule and one from the amino acidate, are in a cis disposition. The two amino nitrogens, the imidazole nitrogen, and the carboxylate oxygen atoms form the base of a square pyramid, which surrounds the copper(II) ion, a water molecule occupying an apical position. Atomic distances suggest for this complex that pi-pi and d-pi interactions could occur in the solid state. Morover, the [Cu(CDhm)(L-TrpO)](+) has a self-assembled structure in which a CDhm molecule behaves as host and as guest. The imidazole and the indole ring are directed into the cavity of an adjacent CDhm molecule from the wider cyclodextrin rim, thus forming a polymeric column structure. ESR spectra were run on the copper(II) ternary complexes with L- or D-tryptophanate and L- or D-alaninate in frozen aqueous solution and on the former pair of enantiomers in the solid state, as well. While in the case of the ternary complex with L- or D-alaninate no differences are observed in their frozen solution spectra, in the case of complexes with TrpO(-) subtle differences are found. These differences, which disappear when excess methanol is used, are ascribed to the presence of weak forces, such as hydrophobic or d-pi interactions.
Bonomo
Raffaele P.
RP
Dipartimento di Scienze Chimiche, Università di Catania, v.le A. Doria 6, 95125 Catania, Italy, Dipartimento di Chimica, Università della Basilicata, via N. Sauro 85, 85100 Potenza, Italy, Dipartimento di Chimica, Centro di Studio di Biocristallografia del CNR, via Mezzocannone 4, 80134 Napoli, Italy, Facoltà di Scienze Ambientali, Seconda Università di Napoli, via Arena 22, 81100 Caserta, Italy, and Istituto per lo Studio delle Sostanze Naturali di Interesse Alimentare e Chimico Farmaceutico, CNR, v.le A. Doria 6, 95125 Italy.
Di Blasio
Benedetto
B
Maccarrone
Giuseppe
G
Pavone
Vincenzo
V
Pedone
Carlo
C
Rizzarelli
Enrico
E
Saviano
Michele
M
Vecchio
Graziella
G