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231223s2008 xx |||||o 00| ||eng c |
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|a pubmed24n0585.xml
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|a (DE-627)NLM175549249
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|a (NLM)18058864
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|a DE-627
|b ger
|c DE-627
|e rakwb
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|a eng
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1 |
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|a Alstrup Lie, Mette
|e verfasserin
|4 aut
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|a A DFT study of solvation effects on the tautomeric equilibrium and catalytic ylide generation of thiamin models
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|c 2008
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| 336 |
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|a Text
|b txt
|2 rdacontent
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|a ƒaComputermedien
|b c
|2 rdamedia
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|a ƒa Online-Ressource
|b cr
|2 rdacarrier
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|a Date Completed 11.06.2008
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|a Date Revised 21.11.2013
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|a published: Print
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|a Citation Status MEDLINE
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|a Copyright 2007 Wiley Periodicals, Inc.
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|a Thiamin diphosphate (ThDP) is the biologically active form of vitamin B1 and an essential cofactor for a number of enzymes. The effect of solvent polarity on the tautomeric equilibria of ThDP using three model systems of the 4'-aminopyrimidine ring is studied by density functional theory calculations (B3LYP/6-311+G(d,p)//B3LYP/6-31G(d)) in the gas phase and selected solvents (cyclohexane, ether, dichloroethane, and water). Solvation effects are investigated using three different schemes: implicit solvation by a continuum model, explicit solvation by inclusion of three water molecules mimicking the first solvation shell of the enzymatic environment, and by a mixed implicit/explicit solvation model. The 4'-aminopyrimidine tautomer is more stable than the 1',4'-iminopyrimidine tautomer in all solvation schemes employed; however, the trend for the stabilities of the 1',4'-iminopyrimidine tautomer in the solvents depends on the specific ThDP-model. Formation of the catalytic important ylide for ThDP-dependent enzymes by deprotonation of ThDP(C2) is also investigated by localization of transition states for two possible pathways. Only the less stable tautomer, 1',4'-iminopyrimidine ThDP, is able to form the catalytic active ylide. Generation of the ylide through a direct intramolecular proton transfer from ThDP(C2) to the ThDP(N4') nitrogen lone pair is favored by 6 kcal/mol in the gas phase, as compared to a water-mediated ylide generation. However, inclusion of a dielectric medium reduces this difference dramatically. Furthermore, inclusion of two water molecules to model the apoenzymatic environment lowers the activation energies of both direct and water-mediated ylide generation
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|a Journal Article
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|a Research Support, Non-U.S. Gov't
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7 |
|a Cyclohexanes
|2 NLM
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7 |
|a Ethers
|2 NLM
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| 650 |
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7 |
|a Ethylene Dichlorides
|2 NLM
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7 |
|a Gases
|2 NLM
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| 650 |
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|a Solvents
|2 NLM
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|a Water
|2 NLM
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| 650 |
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|a 059QF0KO0R
|2 NLM
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|a Cyclohexane
|2 NLM
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| 650 |
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7 |
|a 48K5MKG32S
|2 NLM
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| 650 |
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|a Thiamine Pyrophosphate
|2 NLM
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| 650 |
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|a Q57971654Y
|2 NLM
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| 700 |
1 |
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|a Schiøtt, Birgit
|e verfasserin
|4 aut
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| 773 |
0 |
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|i Enthalten in
|t Journal of computational chemistry
|d 1984
|g 29(2008), 7 vom: 30. Mai, Seite 1037-47
|w (DE-627)NLM098138448
|x 1096-987X
|7 nnns
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| 773 |
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|g volume:29
|g year:2008
|g number:7
|g day:30
|g month:05
|g pages:1037-47
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|a AR
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|d 29
|j 2008
|e 7
|b 30
|c 05
|h 1037-47
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