Linked Life Data

16853941

Source:http://linkedlifedata.com/resource/pubmed/id/16853941

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
47
pubmed:dateCreated
2006-7-20
pubmed:abstractText
Tautomeric equilibria have been studied for five-member N-heterocycles and their methyl derivatives in the gas phase and in different solvents with dielectric constants of epsilon = 4.7-78.4. The free energy changes differently for tautomers upon solvation as compared to the gas phase, resulting in a shift of the equilibrium constant in solution. Solvents with increasing dielectric constant produce more negative solute-solvent interaction energies and increasing internal energies. The methyl-substituted imidazole and pyrrazole form delicate equilibria between two tautomeric forms. Depending on the solvent, the methyl-substituted triazoles and tetrazole have one or two major tautomers in solution. When estimating the relative solvation free energies by means of an explicit solvent model and using the FEP/MC method, one observes that the preferred tautomers differ in several cases from those predicted by the continuum solvent model. The 1,2-prototropic shift, as an intramolecular tautomerization path, requires about 50 kcal/mol activation energy for imidazole in the gas phase, and this route is also disfavored in a solution. The calculated activation free energy along the intramolecular path is 48-50 kcal/mol in chloroform and water as compared to a literature value of 13.6 kcal/mol for pyrrazole in DMSO. A molecular dynamics computer experiment favors the formation of an imidazole chain in chloroform, making the 1,3-tautomerization feasible along an intermolecular path in nonprotic solvents. In aqueous solution, one strong N-H...Ow hydrogen bond is formed for each species, whereas all other nitrogens in the ring form weaker, N...HwOw type hydrogen bonds. The tetrahydrofuran solvent acts as a hydrogen bond acceptor and forms N-H... Oether bonds. Molecules of the dichloromethane solvent are in favorable dipole-dipole interactions with the solute. The results obtained are useful in the design of N-heterocyclic ligands forming specified hydrogen bonds with protein side chains.
pubmed:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Dec
pubmed:issn
1520-6106
pubmed:author
pubmed:issnType
Print
pubmed:day
1
pubmed:volume
109
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
22588-602
pubmed:dateRevised
2009-11-3
pubmed:meshHeading
pubmed:year
2005
pubmed:articleTitle
Theoretical studies of the tautomeric equilibria for five-member N-heterocycles in the gas phase and in solution.
pubmed:affiliation
Center for Drug Design and Development, The University of Toledo, Toledo, Ohio 43606-3390, USA. pnagy@utnet.utoledo.edu
pubmed:publicationType
Journal Article, Research Support, N.I.H., Extramural