TITLE:
Redshift of Excitation Wavelength Caused by the Concentration of L-Tryptophan in Water: A Theoretical and Experimental Study
AUTHORS:
Diana Milena Uriza-Prias, Antonio Méndez-Blas, Juan Francisco Rivas-Silva
KEYWORDS:
Excitation Spectra, Tryptophan Concentration, Polar Solvent, Molecular Clusters, Time-Dependent Density Functional Theory (TD-DFT) Methods, Electronic Transitions, Fluorescence
JOURNAL NAME:
Open Journal of Physical Chemistry,
Vol.11 No.2,
May
26,
2021
ABSTRACT: A redshift in the wavelength of excitation spectra is experimentally
measured as a function of the concentration parameter for tryptophan solutions
in water. To understand the microscopic causes of this behavior, theoretical
calculations obtained from four model clusters are carried out: (Trp)1 - (H2O)9, (Trp)2 - (H2O)18, (Trp)3 - (H2O)27 and (Trp)4 - (H2O)36, where there are interactions among 1, 2, 3 and 4
molecules of tryptophan. According to the literature, each interaction occurred
with nine molecules of water to stabilize its expected zwitterionic form. In
these models, the molecules of tryptophan appear at an adjacent distance among
them to generate an analogous behavior when there is an experimental increase
in the concentration. It is evident that the
distance between adjacent molecules of tryptophan decreases as their
concentration increases. The optical properties of these clusters are
obtained by studying the corresponding excited states and the molecular
orbitals involved, showing charge transfers by using time-dependent density
functional theory (TD-DFT) methods. The experimental spectroscopic data are
obtained by using the clusters proposed, and good agreement is found by drawing
a comparison with the theoretical data.