Solute-Solvent Interactions in Biological Molecules: L-Cysteine
Year: 2008
Type: article
Abstract: The cyclic voltammetric behavior of L-cysteine at different pH values in the absence and presence of ions such as chloride from hydrochloric acid or sodium chloride, bromide from sodium bromide, and phosphate from the buffer made from potassium dihydrogen phosphate and sodium hydroxide have been investigated. In the active region, the cathodic current depended on the starting potential as well as the L-cysteine concentration. Also if the starting potential was more anodic, the cathodic and anodic active regions extended much more into both cathodic and anodic regions. While scans 2 and 3 gave nearly the same current, scan 1 always gave higher cathodic current especially in the presence of counter-ions. With the scanning potential starting at 0.0 V, cathodic current oscillations were observed in the presence of counter-ions and high concentrations of L-cysteine. Admittance data in the absence as well as the presence of counter-ions indicated a competing influence of orientational effects of water with decreasing frequencies, indicating a characteristic of the self-assembly behavior. In the absence of counter-ions, admittance increased continuously from 1000 Hz to 10 Hz. In the presence of counter-ions this trend changed the direction at different frequencies, depending on the concentration of the counter-ion. The admittance data indicated strong interactions between α-COO-and α-NH3+ groups of L-cysteine. Impedance data indicated oscillations at high frequencies. Capacitance data suggested the presence of two species in the absence and the presence of 5 mM NaCl or 5 mM NaBr but not in 0.1 M HCl or 0.059 M phosphate buffer. Cyclic voltammetry and admittance data suggested the need to investigate the electrochemical behaviour of molecules without any background electrolytes, whenever possible, in order to gain information on solute-solvent interactions near the double layer. This finding is contrary to the accepted practice in electrochemistry.
Authors: C.V. Krishnan, M. Garnett, B. Chu
Institution: Stony Brook University
Language: English
Subfield: Physical and Theoretical Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,670
OpenAlex ID: W4382140761