Structure and ESR features of glycine radical

被引:38
作者
Barone, V
Adamo, C
Grand, A
Jolibois, F
Brunel, Y
Subra, R
机构
[1] UNIV BASILICATA, DIPARTIMENTO CHIM, I-85100 POTENZA, ITALY
[2] CEN, DRFMC, SERV ETUD SYST & ARCHITECTURES MOLEC, F-38041 GRENOBLE, FRANCE
[3] UNIV GRENOBLE 1, ETUD DYNAM & STRUCT SELECT LAB, F-38041 GRENOBLE, FRANCE
关键词
D O I
10.1021/ja00155a026
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
The structure, conformational behavior, and ESR features of the glycine radical have been investigated by an established quantum-mechanical protocol with the aim of better elucidating the role of intrinsic and environmental effects in determining the physicochemical properties of amino acid radicals involved in biological systems. From a structural point of view, extraction of a hydrogen atom from glycine modifies only the local environment of the C(alpha)atom. The conformational freedom of the radical is, however, severely restricted with respect to its closed-shell parent. In particular, only planar or nearly planar structures are energetically accessible. These are characterized by very similar hyperfine splittings, which ate in agreement with experiment for C-alpha and N, but are significantly too large for H-alpha. Although the average value of H(N) splittings is not far from the experimental value, the two protons are strongly not equivalent. The computed torsional barrier around the N-C-alpha bond is too high to allow an effective rotational averaging and also inversion of the NH2 moiety, which is governed by a low-energy barrier (approximate to 3 kJ/mol), cannot restore agreement with experiment. Inclusion of solvent-induced structural modifications significantly improves matters for H-alpha, whereas the equivalence of H(N) atoms in acidic solution can be explained in terms of a mixture between the neutral species and a nonclassical cationic form.
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页码:12618 / 12624
页数:7
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