TY - JOUR

T1 - An experimental and theoretical study of l-tryptophan in an aqueous solution, combining two-layered ONIOM and SCRF calculations

AU - Leyton, Patricio

AU - Brunet, Juan

AU - Silva, Viviana

AU - Paipa, Carolina

AU - Castillo, María Victoria

AU - Brandán, Silvia Antonia

N1 - Funding Information:
This work was subsidized with grants from CIUNT (Consejo de Investigaciones, Universidad Nacional de Tucumán R. Argentina) . The authors thank Prof. Tom Sundius for his permission to use MOLVIB. Proyecto Bicentenario de Ciencia y Tecnología PSD 82-2006 is also acknowledged for its help.

PY - 2012/3

Y1 - 2012/3

N2 - ONIOM and SCRF calculations were performed to study the most stable theoretical structure of l-tryptophan in an aqueous solution phase and to observe the changes occurring in the structural and vibrational properties of l-tryptophan in the aqueous media. l-Tryptophan was characterized by infrared and Raman spectroscopies in the solid state and as an aqueous solution. Optimized geometries and relative stabilities for the l-tryptophan zwitterion were calculated while taking into account solvent effects using the self-consistent reaction field (SCRF) theory. The obtained results in the aqueous solution were compared with those calculated for the zwitterion in the gas phase by means of two-layered ONIOM calculations. For the complete assignments of the IR and Raman spectra of l-tryptophan in the aqueous solution phase, density functional theory (DFT) calculations were combined with Pulay's scaled quantum mechanical force field (SQMFF) methodology in order to fit the theoretical wavenumber values to the experimental values. Additionally, the roles of specific and bulk contributions from solvent effects on the properties of l-tryptophan were analyzed. Furthermore, bands corresponding to the normal modes of vibration were localized and assigned, and they served as the bases for the calculations of the corresponding force constants. Significant effects on the geometrical and vibrational frequencies were found for the studied zwitterion.

AB - ONIOM and SCRF calculations were performed to study the most stable theoretical structure of l-tryptophan in an aqueous solution phase and to observe the changes occurring in the structural and vibrational properties of l-tryptophan in the aqueous media. l-Tryptophan was characterized by infrared and Raman spectroscopies in the solid state and as an aqueous solution. Optimized geometries and relative stabilities for the l-tryptophan zwitterion were calculated while taking into account solvent effects using the self-consistent reaction field (SCRF) theory. The obtained results in the aqueous solution were compared with those calculated for the zwitterion in the gas phase by means of two-layered ONIOM calculations. For the complete assignments of the IR and Raman spectra of l-tryptophan in the aqueous solution phase, density functional theory (DFT) calculations were combined with Pulay's scaled quantum mechanical force field (SQMFF) methodology in order to fit the theoretical wavenumber values to the experimental values. Additionally, the roles of specific and bulk contributions from solvent effects on the properties of l-tryptophan were analyzed. Furthermore, bands corresponding to the normal modes of vibration were localized and assigned, and they served as the bases for the calculations of the corresponding force constants. Significant effects on the geometrical and vibrational frequencies were found for the studied zwitterion.

KW - DFT calculations

KW - Force field

KW - Molecular structure

KW - Vibrational spectra

KW - l-Tryptophan

UR - http://www.scopus.com/inward/record.url?scp=84856222547&partnerID=8YFLogxK

U2 - 10.1016/j.saa.2011.12.023

DO - 10.1016/j.saa.2011.12.023

M3 - Article

C2 - 22226676

AN - SCOPUS:84856222547

SN - 1386-1425

VL - 88

SP - 162

EP - 170

JO - Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy

JF - Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy

ER -