Stereochemistry of organic sulfur compounds.: Part 15. The important role of protonation in the investigation of the interactions between the thioether and some amine functions in 1,2-disubstituted phenylethanes

Syntheses and conformational study of 1-X-2-phenylethyl methyl sulfide (X=NH₂, NHMe, NMe₂, and ⁺NMe₃ are reported. Conformational populations have been inferred mainly from the variations in vicinal coupling constants induced by protonation and solvent polarity changes. Steric factors are in general dominant. The dimethylami no group additionally showed a strong repulsive $\text{gauche}$ effect. However, when the nitrogen bore positive charge, the attractive ⁺N/SMe interaction dominated the equilibria except in the trimethylammonium derivative. Solvent polarity effects were very significant.     

Salicylaldehyde-1-phthalazinohydrazone as an analytical reagent

The synthesis, characteristics and analytical properties of salicylaldehyde-1-phthalazinohydrazone are described. Spectral characteristics, pK values, the effect of oxidizing and reducing agents, resistance to hydrolysis, and reactions with common cations are reported.     

Spectrophotometric determination of catecholamines with metaperiodate by flow-injection analysis

A flow-injection Spectrophotometric method for the determination of adrenaline and isoprenaline, based on the reaction with metaperiodate, is described. The calibration graphs are linear up to 2 × 10⁻⁴ M. Flow injection allows the measurement of 120 samples per hour. The method was successfully applied to the determination of both catecholamines in pharmaceuticals.     

Design of ultrasonic wedge transducer

Cones and wedges inserted between an ultrasonic transducer and the specimen provide the transducer (circular or rectangular shape) with enhanced capability for point or line contact with the specimen. Such an arrangement is useful in that the transducer can be used for transmitting to and receiving from a point (or line) source, and that it can eliminate the undesirable aperture effect that makes the transducer blind to waves traveling in certain directions and those of certain frequencies. In this paper, a comprehensive numerical analysis based on a wave propagation model is carried out for the study of characteristics and parameters of cones and wedges influencing their performance. We study the effect of the dimensions, shape and aperture on the frequency response and the angle of incidence of the wave. For computational accuracy and efficiency, the boundary element method is used in the analysis.     

Fast urinary screening for paracetamol using on-line microwave assisted hydrolysis and spectrophotometric detection

A fully automated urinary screening system for paracetamol and its metabolites is proposed. The method comprises on-line acid microwave assisted hydrolysis of the drug to p-aminophenol followed by reaction with o-cresol in alkaline medium. The indophenol blue dye formed can be continuously monitored at 620 nm. The detection limit achieved, 0.1 microgram ml-1, allows a high dilution of the samples, thus reducing potential interferences from the sample matrix (mainly protein degradation during urine hydrolysis). The proposed screening system also possesses an adequate selectivity, as the major interferent, epinephrine, is tolerated at concentrations higher than those that could be found in the positive urine samples. The reproducibility, expressed as relative standard deviation, was 3.0% and the sample frequency 20 h-1. The reliability of the method was established at five concentrations (between 0.5 and 4 times the detection limit). Finally, it was applied to the screening of several human urine samples. The results obtained were compared with those provided by batch acid hydrolysis, and were similar in all instances.     

Self-association of pyridine-2,6-dicarboxylic acid in aqueous solution as determined from ultraviolet hypochromic and hyperchromic effects

The self-association of pyridine-2,6-dicarboxylic acid (dipicolinic acid), was studied in aqueous solution at the pH values of 0.2, 3.5, 6.9 and 13.0, by ultraviolet spectroscopy. The variation in molar absorptivity with the concentration of this compound was measured for the band in the mid-ultraviolet region. Deviations from Beer-Lambert law with increasing concentration were found at the pH values of 0.2, 3.5 and 6.9. Hypochromic effects were detected at pH 0.2 and 6.9, while a hyperchromic effect was observed at pH 3.5. These results were interpreted in terms of self-association leading to the formation of dimers. From the fitting of the experimental curves of hypochromic or hyperchromic effects, self-association constants were calculated. The occurrence of hypochromic and hyperchromic effects was analyzed in terms of vertical and horizontal interactions, respectively, to elucidate the nature of the self-association processes, stacking or hydrogen bonding, relevant to each of the protolytic species of dipicolinic acid in aqueous solution.     

Structure–affinity relationships for the binding of actinomycin D to DNA

Molecular models of the complexes between actinomycin D and 14 different DNA hexamers were built based on the X-ray crystal structure of the actinomycin–d(GAAGCTTC)2 complex. The DNA sequences included the canonical GpC binding step flanked by different base pairs, nonclassical binding sites such as GpG and GpT, and sites containing 2,6-diamino- purine. A good correlation was found between the intermolecular interaction energies calculated for the refined complexes and the relative preferences of actinomycin binding to standard and modified DNA. A detailed energy decomposition into van der Waals and electrostatic components for the interactions between the DNA base pairs and either the chromophore or the peptidic part of the antibiotic was performed for each complex. The resulting energy matrix was then subjected to principal component analysis, which showed that actinomycin D discriminates among different DNA sequences by an interplay of hydrogen bonding and stacking interactions. The structure–affinity relationships for this important antitumor drug are thus rationalized and may be used to advantage in the design of novel sequence-specific DNA-binding agents.     

Distribution Free Procedures for Some Inventory Models

Stochastic inventory models, such as continuous review models and periodic review models, require information on the lead time demand. However, information about the form of the probability distribution of the lead time demand is often limited in practice. We relax the assumption that the cumulative distribution function, say F, of the lead time demand is completely known and merely assume that the first two moments of F are known and finte. The minmax distribution free approach for the inventory model consists of finding the most unfavourable distribution for each decision variable and then minimizing over the decision variable. We solve both the continuous review model and the periodic review model with a mixture of backorders and lost sales using the minmax distribution free approach.