DFT study of nitroxide radicals. 1. Effects of solvent on structural and electronic characteristics of 4-amino-2,2,5,5-tetramethyl-3-imidazoline-N-oxyl

Larissa N. Ikryannikova, Leila Yu Ustynyuk, Alexander N. Tikhonov

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

Imidazoline-based nitroxide radicals are often used as spin probes for medium acidity and polarity in different systems. In this work, using the density functional theory (DFT) approach, we have studied how physicochemical characteristics (geometry, atomic charges, and electron spin density distribution) of pH-sensitive spin-label 4-amino-2,2,5,5-tetramethyl-3- imidazoline-N-oxyl (ATI) depend on protonation and aqueous surroundings. Our calculations demonstrate that ATI protonation should occur at the nitrogen atom of the imidazoline ring rather than at the amino group. Protonation of ATI leads to a decrease in a spin density on the nitrogen atom of the nitroxide fragment >N-O. For simulation of ATI hydration effects, we have constructed a water shell around a spin-label molecule by means of gradual (step-by-step) surrounding of ATI with water molecules (nH2O = 2-41). Calculated spin density on the nitrogen atom of the nitroxide fragment increased with an extension of a water shell around ATI. Both protonation and hydration of ATI caused certain changes in calculated geometric parameters (bond lengths and valence angles). Investigating how structural and energy parameters of a system ATI-(H2O)n depend on a number of surrounding water molecules, we came to the conclusion that a hydrogen-bonded cluster of n H2O ≥ 41 water molecules could be considered as an appropriate model for simulation of ATI hydration effects.

Original languageEnglish
Pages (from-to)4759-4768
Number of pages10
JournalJournal of Physical Chemistry A
Volume108
Issue number21
DOIs
Publication statusPublished - May 27 2004
Externally publishedYes

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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