Conformational behavior and magnetic properties of a nitroxide amino acid derivative in vacuo and in aqueous solution(339 views) D'Amore M, Improta R, Barone V
Dipartimento di Chimica, Universita Federico II, Complesso Univ. Monte S.Angelo, via Cintia, I-80126 Napoli, Italy
Ist. di Biostrutture e Bioimmagini, CNR, via Mezzocannone 6, I-80134 Naples, Italy
References: Not available.
Conformational behavior and magnetic properties of a nitroxide amino acid derivative in vacuo and in aqueous solution
The conformational behavior and magnetic properties of the α-acetylamino, N′-methylamide derivative of TOAC (4-amino-2, 2, 6.6-tetramethylpiperidine-l-oxyl-4-carboxylic acid) have been investigated in vacuo and in aqueous solution by an integrated computational approach including density functional, post-Hartree Fock, and continuum solvent models. According to our computations, piperidine rings with an equatorial placement of the nitroxide moiety are more stable by about 1 kcal/mol than their axial counterparts both in vacuo and in aqueous solution. With respect to natural residues, TOAC shows a marked preference for helical conformers, which is further enhanced by polar solvents. A comparison with other C α-tetrasubstituted residues points out the difference between cyclic and open-chain substituents. The nitrogen isotropic hyperfine coupling constants (AN) of folded TOAC conformers are similar to those of other nitroxides involving six-membered rings and are well reproduced by a composite QM/QM/PCM model. The AN values of extended TOAC conformers are significantly lower because of the constrained nearly planar structure of the piperidine ring.
Conformational behavior and magnetic properties of a nitroxide amino acid derivative in vacuo and in aqueous solution
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