J. Heyrovský, Japan, and organic polarography.

Polarography is an electroanalytical technique based on recording current-voltage curves using a dropping mercury as the working electrode. It can be used for investigations of both reductions and oxidations of inorganic and organic species. Before WWII the developments of this technique linked Prague (in the then Czechoslovakia) with Kyoto (in Japan, where reductions of organic compounds were first observed).

Nucleophilic attack by bromide ions as a first step of conversion of Se(VI) to Se(IV).

Numerous commonly used analytical methods allow only determination of a total amount of selenium in a given sample. Electroanalytical methods as well as those based on hydride generation or on formation of piazselenol allow only determination of Se(IV). To determine Se(VI) by these procedures, present alone or in mixtures with Se(IV), it is first necessary to convert Se(VI) to Se(IV).

Polarographic and voltammetric behavior of selenious acid and its use in analysis.

Solution chemistry of Se(IV), in particular the acid-base properties, salt and complex formation, chemical reduction and reaction of Se(IV) with organic and inorganic sulfur compounds are briefly summarized. The electrochemical reduction of Se(IV) on dropping and stationary mercury electrodes is dealt with in some detail. The effects of antecedent acid-base equilibria and of consecutive reactions of the reduction product, Se(2-), adsorption of their products, and effects of added metal ions are discussed.

Reactions of orthophthalaldehyde with ammonia and 2-aminoethanol.

Reactions of orthophthalaldehyde (OPA) with amines are used in the determination of amino acids and in applications of OPA as a biocide. To contribute to the understanding of processes involved, the reactions of OPA with ammonia, which are conveniently slow, were studied. In a set of rapidly established equilibria, the 1,3-dihydroxyindole and the product of its dehydration are formed (Scheme 1).

Electrochemical determination of HIV drug Abacavir based on its reduction.

Abacavir (I), a drug used in the treatment of HIV, is electrochemically reduced at the dropping mercury electrode in a four-electron process, similar to structurally related adenine (III) and adenosine triphosphate (IV). To undergo the reduction, the species is protonated in the vicinity of the electrode. The protonations take place on the 6-amino group and on one of the pyrimidine ring nitrogens.

Equilibrium constants in reactions of 2-aminoethanol and ammonia with isophthalaldehyde and terephthalaldehyde.

Equilibria established in reactions between isophthalaldehyde (IPA) and terephthalaldehyde (TPA) on one side and 2-aminoethanol and NH3 on the other side were followed in solutions, where these amines acted both as reagents and as buffers. The equilibrium between TPA and 2-aminoethanol was followed spectrophotometrically; all others, of reactions of TPA with NH3 and of IPA with both NH3 and H2N-CH2CH2-OH, were followed by using polarography. Separate limiting reduction currents of the dialdehyde and its imine enable simultaneous determination of the starting material and the product.

Existence and reactivity of three forms of orthophthalaldehyde in aqueous solutions. Polarographic, voltammetric, and spectrophotometric study.

Orthophthalaldehyde (1,2-dicarboxaldehyde) (OPA) forms in the presence of a strong nucleophile with amino acids isoindole derivatives. The reaction is used in fluorometric determination of amino acids. The mechanism of these processes is not understood.

Comparison of solution chemistries of orthophthalaldehyde and 2,3-naphthalenedicarboxaldehyde.

Polarography was used to obtain the concentrations of the dialdehydic (10%), monohydrated acyclic (5%), and cyclic hemiacetal form (85%) of orthophthalaldehyde (OPA). For 2,3-naphthalenedicarboxaldehyde (NDA) these values were estimated to be 15, 7, and 78%. Addition of water in unbuffered solutions followed first-order kinetics with rate constants 0.

Strong covalent hydration of terephthalaldehyde.

Spectrophotometric and electroanalytical studies indicate that one of the formyl groups of terephthalaldehyde in aqueous solution is present in about 23% as a geminal diol. Stronger covalent hydration of CHO in terephthalaldehyde than in p-nitrobenzaldehyde is attributed to a strong resonance interaction between the two formyl groups.

Electroreduction of aromatic oximes: diprotonation, adsorption, imine formation, and substituent effects.

Aromatic oximes are reduced in aqueous solution in a four-electron process. The reducible species in the pH range 5-8 is a diprotonated form of the oxime. This species is generated in the course of electrolysis in the vicinity of the electrode surface from the adsorbed neutral form of the oxime.

Acid hydrolysis of 1,6-dihydro-4-amino-3-methyl-6-phenyl-1,2, 4-triazin-5(4H)-one (1,6-dihydrometamitron).

Metamitron (1) does not undergo hydrolysis at pH 1-8 and up to 5 M H(2)SO(4). The product of its two-electron reduction, 1, 6-dihydrometamitron (2), on the other hand, undergoes at pH <3 relatively fast hydrolysis. The dependence of the measured rate constant on acidity indicates that the completely protonated form (AH(2)(2+)) predominating in strongly acidic media undergoes hydrolysis slower than the species bearing one less proton (AH(+)).

Interaction of iron(II) with bile salts.

Iron(II) ions react with small aggregates of cholate, glycocholate, chenodeoxycholate, and deoxycholate to form soluble and colloidal compounds. Taurocholate under conditions used does not react with the Fe2+ ion. Small aggregates of dihydroxy bile salts (predominating in the premicellar region, at concentrations of the bile salt above 1 mmol dm-3) have a larger affinity for Fe2+ compared to those formed from cholate anions.

Interaction between Cu2+ ions and cholic acid derivatives followed by polarography.

Interaction of bile salts with Cu2+ ions in unbuffered systems containing 0.15 M NaNO3 was followed by measuring polarographic limiting currents and half-wave potentials. Whereas taurocholate forms neither soluble complexes nor compounds of limited solubility, cholate, glycocholate, and dehydrocholate from both soluble complexes and slightly soluble salts of copper(II) with small aggregates of bile salts.

Chemical properties of bile acids. V. Interaction with concentrated sulfuric acid.

The reaction between concentrated sulfuric acid and steroid hydroxy compounds, previously studied for a series of sterols, was used to develop an analytical method for bile acids. The reaction generates species absorbing in the wavelength ranges 300-320 and 370-390 nm, corresponding to isomeric allylic and dienylic carbocations. Eleven bile acids were examined and influence of time, temperature and sulfuric acid concentration on the chromogenic reaction was studied.

Electroreduction of nifedipine.

At pH greater than 6, the nitro group of nifedipine is reduced in a four-electron step to a hydroxylamino group. At pH less than 6, the hydroxylamino derivative undergoes an acid-catalyzed dehydration, and the rate of this reaction governs the limiting current. Resulting quinonemethide is further reduced, and a six-electron reduction step results.

Diffusion of naproxen in presence of beta-cyclodextrin across a silicone rubber membrane.

The diffusion of Naproxen through a silicone rubber membrane has been studied for four different release systems: solution and suspension both of Naproxen and Naproxen beta-cyclodextrin coprecipitates. Differences in transport between the two forms indicate the existence of an interaction between the acid and beta-cyclodextrin in solution. Independence of the transport on pH in the case of the coprecipitate indicates rapid liberation of Naproxen from the complex prior to entering the membrane.

Effect of pretreating samples with boric acid before liquid-chromatographic determination of urinary catecholamines.

Isolation of catecholamines on prepacked gravity-fed ion-exchange columns in conjunction with liquid-chromatographic separation is occasionally subject to disturbances of unknown origin, especially after injection of H3BO3 eluates from the ion-exchange columns onto the chromatography column. Peak spreading, sometimes even peak splitting, has been observed in many laboratories--effects easily confused with those sometimes caused by voided columns or by impurities. To elucidate the origins of these interferences, we performed a combined voltammetric and chromatographic investigation.

Development and publication of new polarographic and related methods of analysis.

A review is made of the factors that should be investigated in the development of new polarographic methods of analysis. Recommendations are made concerning the preparation for publication of the results of such investigations.

Effect of pH on concentration of species present in aqueous solutions of carbonyl compounds affected by hydration-dehydration and keto-enol equilibria.

Equations have been derived for hydration-dehydration and keto-enol equilibria of carbonyl compounds, showing the changes, with pH, of individual species present in aqueous solutions. An Egtran computer program has been constructed, so that the pH-variation of individual species for widely varying values of equilibrium constants can be evaluated. The treatment enables isolation of individual equilibrium constants from experimental data and identification of the system involved.