A study of the effects of the polarity of the solvents acetone and cyclohexane on the luminescent properties of tryptophan.

Autor: Uriza-Prias DM; Instituto de Física, Benemérita Universidad Autónoma de Puebla, Apdo. Postal J -48, 72570 Puebla, Pue, Mexico. Electronic address: duriza@ifuap.buap.mx., Méndez-Blas A; Instituto de Física, Benemérita Universidad Autónoma de Puebla, Apdo. Postal J -48, 72570 Puebla, Pue, Mexico., Rivas-Silva JF; Instituto de Física, Benemérita Universidad Autónoma de Puebla, Apdo. Postal J -48, 72570 Puebla, Pue, Mexico.
Jazyk: angličtina
Zdroj: Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy [Spectrochim Acta A Mol Biomol Spectrosc] 2022 Feb 05; Vol. 266, pp. 120434. Date of Electronic Publication: 2021 Sep 29.
DOI: 10.1016/j.saa.2021.120434
Abstrakt: The luminescent properties of tryptophan in solvents less polar than water, such as acetone, and non-polar ones, such as cyclohexane, are experimentally studied and compared with theoretical calculations using time-dependent density functional theory (TD-DFT) methods. Since tryptophan may present different configurations and charge distributions, the most stable conformer is analyzed for both solvents, including its neutral and zwitterionic forms. To perform the simulation two clusters are proposed with the Zpt conformer in acetone: [Formula: see text] and [Formula: see text] , and four clusters with the Nag + conformer in cyclohexane: (Trp) 1 -(C 6 H 12 ), (Trp) 2 -(C 6 H 12 ), (Trp) 3 -(C 6 H 12 ) and (Trp) 4 -(C 6 H 12 ), in order to conveniently emulate the concentration in each solvent by reducing the distance between adjacent tryptophan molecules as the concentration increases, since there is no control over the volume parameter. In each case, the UV-vis absorption is computed and compared with the experimental excitation spectra; the results show a good agreement. This calculation allows a more detailed analysis of the experimental results based on the properties of the molecular orbitals involved in electronic transitions. In the present work, a strong effect of the solvent acetone on tryptophan is observed; for this solvent, a charge transfer from the solute to solvent happens. This behavior does not occur with water (polar solvent) or cyclohexane (non-polar solvent). Finally, experimental spectroscopic data of Trp in cyclohexane are explained through the hydrogen bonds between amino acid molecules present in the fluorescent states. In this case, the theoretical and experimental results are compared and also show good agreement.
Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
(Copyright © 2021 Elsevier B.V. All rights reserved.)
Databáze: MEDLINE
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