Sachiko Sakura

Chemiluminescence of tryptophan enhanced by electrochemical energy

Electrochemiluminescence (ECL) was used to detect tryptophan in aqueous solutions in the presence of a brominating agent. Using platinum and glassy carbon electrodes, the ECL mechanism of tryptophan was studied. Tryptophan was oxidized at 0.78 V vs. sce in 0.1 M NaOH aqueous solution to the excited intermediate at a platinum electrode (0.44 V at a glassy carbon electrode). The intermediate was further oxidized and emitted light. The ECL signal was clearly observed when the applied potential was enough to oxidize the tryptophan. The ECL spectrum was measured, showing maximum emission peaks at 544 nm, 434 nm and 404 nm. Above 1.0 V, the brominating agent was oxidized which results in suppression of the ECL signal. A weak ECL signal was observed at an applied potential below 0.5 V, which indicates that this reaction is chemiluminescence (CL), enhanced by the applied potential. This method cannot be used for routine analysis because of the high detection limit of tryptophan (1.0 μmol), but can be used to obtain emission mechanism information.

Solvation effect of the cation of the supporting electrolyte in hexamethylphosphoramide

Abstract Polarographic reductions of sodium and potassium ions in hexamethylphosphoramide (HMPA) have been examined in various supporting electrolytes. The supporting electrolytes, which have much the same solvated radii and much the same electrocapillary curves, sometimes have a significantly different influence on the polarographic reductions of metal ions. The Li + and Hex 4 N + ions provide a typical example. Their effective radii are seen to have much the same characteristics. However, the polarographic reduction of the sodium ion shows a difference in shape between that occurring in Li + solution and that in Hex 4 N + solution. Another example is found in the case of Et 4 N + , Me 4 N + and 5N6 + , whose r eff and the electrocapillary curves are much the same. However, the polarographic reductions of the sodium and potassium ions are different in these solutions. The solvation number of the solvent molecule of the supporting electrolyte cation seems to exert a great influence on these reductions. The electrocapillary curves were also examined with the tetradodecylammonium ion, tetradecylammonium ion and tetraphenylphosphonium ion used as the supporting electrolytes. The inhibition of the reduction of metal ion for these cations is evidence for their lack of solvation. The effects of the solvated asymmetrical tetraalkylammonium ions on the polarographic behaviour were also examined. When some methyl groups cooperate with the tetraalkylammonium ion, the chemical character is between that of the Et 4 N + ion and that of the Me 4 N + ion.

Polarography in hexamethylphosphoramide: Effect of supporting electrolyte cations

Abstract Polarographic reductions of various metal ions such as the silver, cupric, zinc, cobaltous, nickel, ferric, ferrous ions and hydrogen ion in hexamethylphosphoramide (HMPA), have been investigated in the supporting electrolytes with various perchlorates. The reduction of most of these ions is strongly influenced by the cation of the supporting electrolyte. In the presence of the tetraethylammonium ion, when the size of the cation of the supporting electrolyte is small and easily adsorbed on the negatively charged electrode surface, the reductions of metal ions are controlled by some preceding processes and are naturally irreversible. The rate of reduction becomes more rapid with the increase of the size of the cation. Thus, in Hex4NClO4 or LiClO solutions, the reduction of these various metal ions takes place almost totally under diffusion control, although the waves of most of metal ions show a maximum. These effects of the cation of the supporting electrolytes on reduction can be explained as a phenomenon occurring on the electrode surface. This phenomenon has been reported in previous papers [1] on the reductions of the alkali and alkaline earth metal ions. The difference in the electrocapillary curves in these solutions is rarely shown at the potential around the electrocapillary maximum, but it is very obviously shown at more negative potential. The difference in the effect of the size of the cation of the supporting electrolyte on reduction of metal ion coincides well with the difference in the electrocapillary curves in these solutions: the effect of the size of the supporting electrolyte cation on the polarographic reduction is rarely shown at the potential around the electrocapillary maximum, but it is very obviously shown at more negative potential; therefore this effect is due to the electrode double-layer difference.

Voltammetric study of organic metals. II: The effect of solvent variation on electrochemically grown crystals of organic charge-transfer complexes

Abstract Crystals of organic charge-transfer complexes were grown by electrochemical oxidation of bis(ethylenedithio)-tetrathiafulvalene (BEDT-TTF) in the presence of trihalide anions in various solvents. In order to find the optimal conditions to grow the large, good quality crystals necessary for the study of solid-state electronic properties of these “organic metals”, the electrochemical behaviors of BEDT-TTF and several trihalide anions in various organic solvents were studied by means of cyclic voltammetry. The oxidation potential of BEDT-TTF, stability of the BEDT-TTF monocation radical and the redox behavior of various anions at the oxidation potential of BEDT-TTF in various solvents were studied. The cv data along with data from the crystal growth experiments were used to understand the solvent effect on the electrochemical synthesis of organic metals.

Effect of protic solvents on the polarographic reduction of the alkali metal ions in hexamethylphosphoric triamide

Sodium and lithium ions are not reduced at the dropping mercury electrode in hexamethylphosphoric triamide containing 0.05 mol dm−3 tetraethylammonium perchlorate while rubidium and caesium ions show diffusion controlled, l-electron reduction waves. The reduction of potassium ion is partially kinetic. When increasing amount of water is added to the solution, reduction waves of sodium and lithium begin to appear, and the kinetic contribution of potassium wave gradually disappears to give a diffusion controlled wave. The diffusion controlled waves of rubidium and caesium ions are essentially unaffected. The addition of methanol, ethanol, l-buthanol and dimethyl sulfoxide also has similar enhancing effects, which is attributed to the acceleration of the desolvation process by protons. These effects of protic solvent are apparently similar to that of the cation size of the supporting electrolytes, but of different origin, as indicated by the different behavior of the electrocapillary curves.