Potentiometric studies of dithiooxamide with a sulphide-selective membrane electrode

The sulphide-selective electrode is applicable to the determination of dithiooxamide by titration with silver nitrate. The effect of the alkali content of the solutions on the reaction has been studied. The reaction products are silver sulphide, oxalic acid, and nitric acid. If the alkali concentration of the solution is lower than that equivalent to the acid formed during the titration, the amount of sulphide produced by hydrolysis decreases and the equilibrium potential is established more slowly.The determination is rapid and accurate in the presence of 1 M sodium hydroxide.     

Interaction of adenine and thymine with aqueous sugar solutions

The solubility of the nucleic acid bases, adenine and thymine, in aqueous erythritol, xylose, glucose, and sucrose solutions has been studied. The solubility of adenine increases linearly with glucose and sucrose concentration, whereas with the other reagents a nonlinear increase is observed. Below 1.5M reagent concentration, the solubility of adenine increases in the order erythritol < robose, xylose < glucose < sucrose. The solubility of thymine in these solutions, on the other hand, decreases, increases, or does not change depending upon the reagent. The effect of temperature on the solubility of adenine and thymine in sugar solution indicates that the transfer of these molecules from water to sugar solution is exothermic.Presented in part at the VIIth All-India Symposium in Biophysics held at Visva Bharati University during October 1976.     

Adsorption Peculiarities of Carbon Monoxide on Iridium Electrodeposits

The transients of current and open-circuit potential observed at CO adsorption on Ir/Pt electrodes in solutions of sulfuric and hydrochloric acids are shown to adequately agree with those theoretically expected. From voltammetric curves of electrooxidation of chemisorbed CO, the values of its adsorption are estimated by making a proper double-layer correction. It is concluded that CO is preferentially adsorbed in the bridge form. During CO adsorption from sulfuric acid solutions on an electrode with a preliminarily accumulated monolayer of copper adatoms (Cu_ad), small negative current are observed and Cu_ad are displaced by 50%. To explain these results, it is assumed that CO is reduced by copper adatoms.     

Atomic Absorption Assay of Noble Metals in Ores with the Use of Sample Decomposition by Ultrasound

An atomic absorption assay of gold, silver, and palladium in various types of ores is performed with the use of ultrasound at the fire assay stage. It is shown that ultrasound can reduce the temperature and duration of fusion and increase the recovery of noble metals into the lead button.     

Organic synthesis on the microgram scale. V

Summary This paper describes a method for theg synthesis of flavone acetates in a sealed capillary tube. The reaction products are separated and purified on a thin-layer plate. The esters are then hydrolyzed on the plate and the parent flavones regenerated. A simple heating device is used which allows for observation of the reaction.

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Zusammenfassung Beschreibung der Mikrogrammsynthese von Flavonacetaten in einem verschmolzenen Kapillarröhrchen. Die Reaktionsprodukte werden auf einer Dünnschichtplatte getrennt und gereinigt. Dann verseift man die Ester auf der Platte und stellt die freien Flavone dar. Ein einfaches Heizgerät ermöglicht die Beobachtung der Reaktion.

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For part IV of this series see Mikrochim. Acta [Wien]1969, 352.     

A family of multiderivative methods for the numerical solution of the Schrödinger equation

A family of multiderivative methods with minimal phase-lag are introduced in this paper, for the numerical solution of the Schrödinger equation. The methods are called multiderivative since uses derivatives of order two, four or six. Numerical application of the new obtained methods to the Schrödinger equation shows their efficiency compared with other similar well known methods of the literature.Active Member of the European Academy of Sciences and Arts     

Continuous flow thin layer headspace (TLHS) analysis

Summary The paper presents a new method of a continuous isolation and determination of volatile organic halogens (VOX) in drinking waters based on so-called thin layer headspace (TLHS) isolation technique. The liberated volatile compounds are mineralized in an empty quartz tube at 850°C and absorbed in a buffered washing solution. After separation of air the halogen ions are determined potentiometrically in a flow-through cell using a silver/silver choride indicating electrode. The potential of the electrode is a linear function of the halogen ion concentration in the washing solution within the VOX concentration range usually encountered in drinking waters. The estimated detection limit of the method is ca. 0.1 g/l VOX and can be further improved by increasing the concentration factor. The theory of the TLHS isolation method has been further developed and verified. The derived dependences enable a simultaneous determination of the effective partition coefficients in the system, thus enabling calculation of the optimal gas flow rate.Part I and II, see [1, 2]     

Wannier-Stark effect on surface states

A recursive Green-function (RGF) technique is used to study the surface states of an electrified solid. The concatenating nature of the method leads to a continued-fraction form of the RGF, which can be expressed as a ratio of Bessel functions. The surface density of states (SDOS), derived from the RGF, reveals a quasi-Stark-ladder distribution of the energy levels at the surface atom. The dependence of the SDOS on the applied field and surface perturbation parameters is discussed.     

Phosphinofenchol or metastable phosphorane? Phosphorus derivatives of fenchol

Not the expected phosphinofenchol 1 but phosphorane 2 is obtained after reaction of 2-lithio(diphenylphosphino)benzene with (-)-fenchone. Surprisingly, ONIOM(B3LYP/6-31G*:UFF) computations of 1 and 2 as well as B3LYP analyses of smaller model systems point to a lower thermodynamic stability of phosphoranes relative to their isomeric alkoxyphosphines. An analogue inherent instability is computed for the methylphosphorane 10, which is also synthesized and characterized by X-ray analysis. Decreasing ring size in cyclic phosphoranes, that is, from five- to four-membered ring systems, destabilizes cyclic phosphoranes even more. This computational prediction is verified experimentally by reaction of lithiomethyl(diphenylphosphine) with (-)-fenchone and subsequent isolation of the corresponding phosphinofenchol. Protonation or alkylation of phosphoranide intermediates can account for the formation of metastable phosphoranes.     

Studies in polyphenol chemistry and bioactivity. 4.(1) Synthesis of trimeric,tetrameric, pentameric,and higher oligomeric epicatechin-derived procyanidins having all-4beta,8-interflavan connectivity and their inhibition of cancer cell growth through cell cycle arrest

We report an improved synthesis of bis(5,7,3',4'-tetra-O-benzyl)epicatechin 4beta,8-dimer (3) from 5,7,3',4'-tetra-O-benzylepicatechin (1) and 5,7,3',4'-tetra-O-benzyl-4-(2-hydroxyethoxy)epicatechin (2) by replacing the previously employed Lewis acid, titanium tetrachloride, with the clay mineral Bentonite K-10. Under the same conditions, the benzyl-protected all-4beta,8-trimer, -tetramer, and -pentamer were obtained regioselectively from their lower homologues, albeit in rapidly decreasing yields. Reaction of 2 with an organoaluminum thiolate generated from 2-mercaptobenzothiazole and trimethylaluminum followed by acetylation produced 3-O-acetyl-4-[(2-benzothiazolyl)thio]-5,7,3',4'-tetra-O-benzylepicatechin (12). Medium-sized protected oligomers with 4beta,8-interflavan linkages are obtained in improved yields by using this compound as the electrophile and silver tetrafluoroborate as activator and are isolated by reversed-phase HPLC. Their deprotection by ester saponification followed by hydrogenolysis yielded the free procyanidins, which were characterized as their peracetates. The synthetic procyanidins are identical by normal-phase HPLC with fractions isolated from cocoa. The principle of chain extension by two members was demonstrated using a dimeric electrophile obtained by self-condensation of compound 12. Both the synthetic and natural pentamer 32 inhibit the growth of several breast cancer cell lines. Using the MDA MB 231 line, it was established that this outcome is based on the induction of cell cycle arrest in the G0/G1 phase. Subsequent cell death is more likely necrotic rather than apoptotic. Control experiments demonstrate that the polyphenol itself, rather than hydrogen peroxide potentially formed by its autoxidation, is the causative agent.