Singlet molecular oxygen [O2(1Δg)]-mediated photodegradation of tyrosine derivatives in the presence of cationic and neutral micellar systems

Abstract

The kinetics of rose bengal-sensitized photooxidation of tyrosine and several tyrosine-derivatives (tyr-D) named tyrosine methyl ester, tyrosine ethyl ester and tyrosine benzyl ester was studied in buffered pH 11 water, and buffered pH 11 micellar aqueous solutions of 0.01 M cetyltrimethylammonium chloride (CTAC) and 0.01 M-octylphenoxypolyethoxyethanol [triton X100 (TX100)]. Through time-resolved phosphorescence detection of singlet molecular oxygen (O(2)((1)Delta(g))) and polarographic determination of oxygen consumption, the respective bimolecular rate constants for reactive (k(r)) and overall (k(t)) quenching of the oxidative species by tyr-D were evaluated. Both rate constants behave in different fashion depending on the particular reaction medium. k(r)/k(t) values, increase in the sense CTAC<<TX100 < water, indicating, for the tyr-D family studied, an excellent degree of self-protection against O(2)((1)Delta(g))-attack in the CTAC micellar system and a high photooxidability level in water. Results were interpreted in terms of a competition between solvent polarity effects, local substrate concentration and electron donating capabilities of the substrates in the different media that can contribute to predict the extent of photodynamic damage in biological environments.

Gum Arabic: More Than an Edible Emulsifier

“…Under photostationary conditions, the slopes of the linear plots of the consumption of dissolved oxygen are the observed pseudo-first order rate constant of the chemical quenchers, k obs (Criado et al, 2008), and the rate constant for the reactive quenching of 1 O 2 by GA is calculated with eqn. 12.…”

Isobaric Labeling Approach to the Tracking and Relative Quantitation of Peptide Damage at the Primary Structural Level

“…Nevertheless, currently holistic assays [such as the detection of carbonyl groups , , assays for specific oxidation products , , or physical changes in the substrate , ], which suffer from a lack of specificity and an inability to localize damage to specific proteins , remain the predominant methods for quantifying protein damage. Residue-level changes, which can impart significant changes in protein functionality, can be induced by diverse insults such as exposure to heat , light , cellular sensitizers , oxidants , and acids and are therefore important in both intra- and extracellular systems. The impact of residue-level damage on biological and product systems and the expanding field of redox proteomics demand accurate and sensitive tools for profiling and tracking damage at the molecular level.…”