Effects of tetraalkylammonium salts on Brdieka and presodium currdnts of bovine - serum albumin ( polarography / adsorption / catalytic currents )

Tetraethyl-, tetrapropyl-, and tetrabutylammonium ions are capillary-active on the interface water-mercury. In the adsorbed state they increase Brdicka and presodium currents. These currents drop sharply at potentials where tetrabutylammonium ions are desorbed, these potentials being -1.60, -1.66, -1.72, and -1.79 V versus the saturated calomel electrode (SCE) at tetrabutylammonium concentrations of 0.1, 0.25, 1, and 5 mM, respectively. Indications are that tetraethylammonium ions at a concentration of 50 mM are desorbed at a potential of the order of -1.9 V (versus SCE). The increase of Brdicka currents is attributedat least in part-to a decrease in the rate of electroreduction of cobalt(II). In the desorbed state the effect-if any-of tetrabutylammonium ions on Brdicka and presodium currents is very small. Tetrabutylammonium ions also greatly increase Brdicka currents observed with cysteine, the effect disappearing after these ions attain their desorption potential. The effect of tetraphenylarsonium on Brdicka currents is very similar to that of tetrabutylammonium, while that of diphenylguanidine is similar to that of tetraethylammonium ions. Tetraethyl-, tetrapropyl-, and tetrabutylammonium salts are adsorbed from aqueous solutions on the surface of mercury. Mairanovskii and Churilina (1) report that these tetraalkylammonium ions have a significant effect on the kinetics and mechanism of electrode processes. Pungor and Farsang (2) found that at low concentrations tetraalkylammonium salts cause an increase in the catalytic hydrogen waves (comparable to "presodium" currents of bovine-serum albumin, BSA) of quinine, nicotinamide, and methylene blue in phosphate buffers. In order to explain the results by these authors, Mairanovskii et al. (1) studied the effect of tetraethylammonium perchlorate (TEAP) on catalytic hydrogen waves observed with pyridine and 2,6-lutidine in various buffers at the dropping mercury electrode. Under specified conditions they found an increase of the catalytic waves at concentrations of TEAP (10-40 mM). In general, they attribute the effect of TEAP to a retardation of electrochemical reactions by a film of cations adsorbed on the electrode, by a change in the electrokinetic potential, and by a specific action which is not completely understood. It appeared of interest to study the effects of tetraalkylammonium salts on Brdicka and presodium currents observed with BSA in various buffers. Characteristics of Brdicka currents (3-6) and of presodium currents (7) under various conditions, also in the presence of various concentrations of urea (8), have been presented in previous publications. A few experiments have also been carried out on the effects on Abbreviations: BSA, bovine-serum albumin; TEAP, tetraethylammonium perchlorate; TMAC, tetramethylammonium chloride; TEAC, tetraethylammonium chloride; TPAB, tetrapropylammonium bromide; TBAB, tetrabutylammonium bromide; SCE, saturated calomel electrode; DME, dropping mercury electrode; -ipL presodium current. Brdicka and presodium currents of BSA of tetraphenylarsonium ions, tetramethylguanidine, and diphenylguanidine, all capillary-active on the interface mercury-water. Finally, the effect of tetrabutylammonium ions on Brdicka currents of cysteine in the presence of cobalt(II) is described.