dorsal/arxiv
View SchemaDFT 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
| Authors | Larissa N. Ikryannikova, Leila Yu. Ustynyuk, Alexander N. Tikhonov |
|---|---|
| Categories | |
| ArXiv ID | physics/0312130 |
| URL | https://arxiv.org/abs/physics/0312130 |
| DOI | 10.1021/jp037943d |
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 physico-chemical 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 (n = 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 ≥ 41 water molecules could be considered as an appropriate model for simulation of ATI hydration effects.
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"abstract": "Imidazoline-based nitroxide radicals are often used as spin probes for medium\nacidity and polarity in different systems. In this work, using the density\nfunctional theory (DFT) approach, we have studied how physico-chemical\ncharacteristics (geometry, atomic charges and electron spin density\ndistribution) of pH-sensitive spin label\n4-amino-2,2,5,5-tetramethyl-3-imidazoline-N-oxyl (ATI) depend on protonation\nand aqueous surroundings. Our calculations demonstrate that ATI protonation\nshould occur at the nitrogen atom of the imidazoline ring rather than at the\namino group. Protonation of ATI leads to a decrease in a spin density on the\nnitrogen atom of the nitroxide fragment \u003eN-O. For simulation of ATI hydration\neffects, we have constructed a water shell around a spin label molecule by\nmeans of gradual (step-by-step) surrounding of ATI with water molecules (n =\n2-41). Calculated spin density on the nitrogen atom of the nitroxide fragment\nincreased with an extension of a water shell around ATI. Both protonation and\nhydration of ATI caused certain changes in calculated geometric parameters\n(bond lengths and valence angles). Investigating how structural and energy\nparameters of a system ATI-(H2O)n depend on a number of surrounding water\nmolecules, we came to the conclusion that a hydrogen-bonded cluster of n\n\u0026#8805; 41 water molecules could be considered as an appropriate model for\nsimulation of ATI hydration effects.",
"arxiv_id": "physics/0312130",
"authors": [
"Larissa N. Ikryannikova",
"Leila Yu. Ustynyuk",
"Alexander N. Tikhonov"
],
"categories": [
"physics.atm-clus",
"physics.chem-ph"
],
"doi": "10.1021/jp037943d",
"title": "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",
"url": "https://arxiv.org/abs/physics/0312130"
},
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