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Titolo:
Kinetics and mechanism of the Cu2+ induced hydrolysis of nitrile groups inthe side chain of tetraazamacrocycles. Models for nitrilases
Autore:
Siegfried, L; Kowallick, R; Kaden, TA;
Indirizzi:
Inst Inorgan Chem, CH-4056 Basel, Switzerland Inst Inorgan Chem Basel Switzerland CH-4056 , CH-4056 Basel, Switzerland
Titolo Testata:
SUPRAMOLECULAR CHEMISTRY
fascicolo: 2, volume: 13, anno: 2001,
pagine: 357 - 367
SICI:
1061-0278(2001)13:2<357:KAMOTC>2.0.ZU;2-#
Fonte:
ISI
Lingua:
ENG
Soggetto:
MACROCYCLIC LIGANDS; ZINC(II) COMPLEX; METAL-COMPLEXES; CU-2+-PROMOTED HYDROLYSIS; CATALYTIC HYDROLYSIS; COPPER(II) COMPLEX; PHOSPHATE DIESTER; ESTER HYDROLYSIS; CU-2+ COMPLEXES; DINUCLEAR;
Keywords:
Cu2+ complexes; tetraazamacrocycles; hydrolysis; nitrile; kinetics; mechanism;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
42
Recensione:
Indirizzi per estratti:
Indirizzo: Kaden, TA Inst Inorgan Chem, Spitalstr 51, CH-4056 Basel, Switzerland InstInorgan Chem Spitalstr 51 Basel Switzerland CH-4056 erland
Citazione:
L. Siegfried et al., "Kinetics and mechanism of the Cu2+ induced hydrolysis of nitrile groups inthe side chain of tetraazamacrocycles. Models for nitrilases", SUPRAMOL CH, 13(2), 2001, pp. 357-367

Abstract

A series of mono-N-functionalized tetraaza macrocycles having a nitrile group in their side chain have been synthesized and the kinetics and mechanism of the Cu2+ induced hydrolysis has been studied. Two factors were systematically varied: the length of the side chain and thus the distance between Cu2+ and the nitrile group, as well as the rigidity of the macrocycle by introducing an additional ethylene bridge. The mechanism of the hydrolysis proceeds by an intramolecular attack of a coordinated OH- onto the nitrile group in a five or six center transition state. The intramolecular nature of the reaction has been proven (a) by the pH dependence of the hydrolysis, which in some cases has a plateau at high pH values, (b) by the competitive inhibition with SCN-, and (c) by the spectral changes observed at high PH. The sequence of Cu2+ induced hydrolysis rates is the following: flexible macrocycle with a short chain > rigid macrocycle with a short chain > flexiblemacrocycle with a longer chain similar to rigid macrocycle with a longer chain. The length of the side chain, which determines whether a five or six center transition state is formed, is the most important factor. The fastest hydrolysis has a half-life time of about 50 ms at pH 12.5 and 25 degreesCand indicates the efficiency of the metal ion. The rigidity of the macrocycle also influences the reactivity since in the rigid complexes on one sidethe Cu2+ ion is less accessible for OH- to give the reactive intermediate and on the other side the transition state is less reactive because of topological aspects.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 27/09/20 alle ore 07:13:54