Interaction of yeast alcohol dehydrogenase with protoberberine alkaloids.

Oxidation of ethanol and reduction of aldehyde catalysed by yeast alcohol dehydrogenase is inhibited by several naturally occurring as well as semi-synthetic protoberberine alkaloids. The affinity of these compounds for the enzyme depends essentially on their hydrophobicity. Corysamine and coptisine are the most potent inhibitors among the natural alkaloids of this group.

Organic complexing agents in atomic-absorption spectrometry-a review.

The influence of organic completing agents on the determination of a particular element by atomic-absorption spectrometry (AAS) with flame or electrothermal atomization may increase the sensitivity and selectivity. The effect of the structure and properties of the organic ligand in connection with the particular atomization mechanism is discussed.

Spectrophotometric determination of thallium with 4-(2-pyridylazo)resorcinol and 4-(2-thiazolylazo)resorcinol.

Thallium(III) gives sensitive reactions with PAR and TAR (epsilon = 2 x 10(4) at 520 nm), forming 1:1 complexes at pH approximately 1-2, and a mixture of 1:1 and 1:2 complexes at higher pH values; hydrolysis sets in above pH approximately 3. The stability constants are evaluated.

Complexation of uranium by 2-(2-thiazolylazo)-4-methoxyphenol and 2-(2-thiazolylazo)-5-methoxyphenol.

A comparative study has been made of the complexation of uranium(VI) by 2-(2-thiazolyl)-4-methoxyphenol (TAMH) and 2-(2-thiazolylazo)-5-methoxyphenol(TAMR). The complexes are less stable and have lower molar absorptivities than the PAR and TAR complexes but are still useful for determination of uranium. The TAMH chelate can be extracted into isobutyl methyl ketone.

Extraction of metals from metal ion-catechol-quaternary base systems.

Methods are given for the extraction of iron(III), molybdenum(VI), titanium(IV), niobium(V), vanadium(IV), uranium(VI) and tungsten(VI) as ternary complexes with catechol and a quaternary cation such as n-butyltriphenylphosphonium, n-propyltriphenylphosphonium, tetraphenylarsonium, cetylpyridinium, cetyltrimethylammonium and 2,3,5-triphenyltetrazolium, the solvent being chloroform. By use of masking agents and pH control, some of these elements can be separated from each other by this means.

Complexation of aluminium, yttrium, lanthanum and lanthanides with 4-(2-pyridylazo)resorcinol (par).

The sensitive reactions between 4-(2-pyridylazo)resorcinol (PAR) and yttrium, lanthanum and the lanthanides can be used for the spectrophotometric determination of these elements. The method has no advantage over other methods for the determination of aluminium and lanthanum. Only M(PAR)H and M(PAR) complexes are formed in solutions where the molarity of the metal ion is greater than or nearly equal to the molarity of the ligand at pH < 7-5.

The reaction of uranyl ions with 4-(2-pyridylazo)resorcinol.

The uranyl ion and 4-(2-pyridylazo)resorcinol (PAR) form only 1:1 chelates in solutions of pH < 8.5, UO(2),(PAR)H(+) being formed at pH > 3 and UO(2),(PAR) at pH > 5.5.

Spectrophotometric study of the reaction of the uranyl ion with 4-(2-thiazolylazo) resorcinol.

The uranyl ion forms only 1:1 chelates with 4-(2-thiazolylazo) resorcinol (TAR) in solution, UO(2)(TAR)H(+) being formed below pH 3 and UOS(TAR) above pH 3-5. The latter complex may also be precipitated at pH > 3. The quantitative formation of UO(2)(TAR) at pH 7.

Electron Microscopy of Ultrathin Sections of Sporosarcina ureae.

Mazanec, K. (J. E.