Please use this identifier to cite or link to this item:
DC FieldValueLanguage
dc.contributor.authorKaczor, A.-
dc.contributor.authorReva, I. D.-
dc.contributor.authorProniewicz, L. M.-
dc.contributor.authorFausto, R.-
dc.description.abstractThe conformational behavior and infrared spectrum of l-phenylalanine were studied by matrix-isolation infrared spectroscopy and DFT [B3LYP/6-311++G(d,p)] calculations. The fourteen most stable structures were predicted to differ in energy by less than 10 kJ mol-1, eight of them with abundances higher than 5% at the temperature of evaporation of the compound (423 K). Experimental results suggest that six conformers contribute to the spectrum of the isolated compound, whereas two conformers (IIb3 and IIIb3) relax in matrix to a more stable form (IIb2) due to low energy barriers for conformational isomerization (conformational cooling). The two lowest-energy conformers (Ib1, Ia) differ only in the arrangement of the amino acid group relative to the phenyl ring; they exhibit a relatively strong stabilizing intramolecular hydrogen bond of the O−H···N type and the carboxylic group in the trans configuration (OC−O−H dihedral angle ca. 180°). Type II conformers have a weaker H-bond of the N−H···OC type, but they bear the more favorable cis arrangement of the carboxylic group. Being considerably more flexible, type II conformers are stabilized by entropy and the relative abundances of two conformers of this type (IIb2 and IIc1) are shown to significantly increase with temperature due to entropic stabilization. At 423 K, these conformers are found to be the first and third most abundant species present in the conformational equilibrium, with relative populations of ca. 15% each, whereas their populations could be expected to be only ca. 5% if entropy effects were not taken into consideration. Indeed, phenylalanine can be considered a notable example of a molecule where entropy plays an essential role in determining the relative abundance of the possible low-energy conformational states and then, the thermodynamics of the compound, even at moderate temperatures. Upon UV irradiation (λ > 235 nm) of the matrix-isolated compound, unimolecular photodecomposition of phenylalanine is observed with production of CO2 and phenethylamine.por
dc.publisherAmerican Chemical Societypor
dc.titleImportance of Entropy in the Conformational Equilibrium of Phenylalanine:  A Matrix-Isolation Infrared Spectroscopy and Density Functional Theory Studypor
degois.publication.titleJ. Phys. Chem. Apor
item.fulltextCom Texto completo-
item.grantfulltextopen- of Sciences and Technology- of Sciences and Technology- of Coimbra- of Coimbra- - Coimbra Chemistry Centre- - Coimbra Chemistry Centre- of Sciences and Technology- of Sciences and Technology-
Appears in Collections:FCTUC Química - Artigos em Revistas Internacionais
Files in This Item:
File Description SizeFormat
J.Physical Chemistry A, 110 (2006) 2360.pdf359.38 kBAdobe PDFView/Open
Show simple item record


checked on May 29, 2020

Citations 1

checked on Oct 2, 2021

Page view(s) 20

checked on Oct 8, 2021

Download(s) 50

checked on Oct 8, 2021

Google ScholarTM




Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.