Development and Validation of a Fast Reversed-Phase Ion-Pairing Liquid Chromatographic Method for Simultaneous Determination of Eight Cephalosporin Antibiotics in Pharmaceutical Formulations

A fast and reliable single method was developed for rapid screening of cephalosporin oral dosage forms aimed to the detection of counterfeit and substandard drugs that might be illegally commercialised. Nine cephalosporin compounds, ceftibuten, cefatrizine, cefadroxil, cefaclor, cefprozil (Z) and (E)-isomers, cefixime, cephalexin and cefradine were separated in a six minutes chromatographic run by using a Symmetry^® C18 column (50 × 4.6 mm I.D., 3.5 μm particle size) and an UV detector set at 254 nm. The mobile phase consisted of a mixture of acetonitrile-methanol-phosphate buffer (50 mM) containing 1-pentanesulfonic acid sodium salt (7 mM) adjusted to pH=2.1 with phosphoric acid (9:13:78 v/v/v). Validation of the method showed it to be robust, precise, accurate and linear over the concentration range of analysis.     

The electronic structure of N4O62+ and the bonding interaction of NO+ and NO3−

The results are reported of an MO-SCF-CNDO/2 study of the experimental and optimal geometries of the N₄O₆²⁺ion cluster. The calculations are shown to support the stable existence of the N₄O₆²⁺ complex and the suggestion of its discoverers [1] on the role of NO⁺ in the N₂O₄ solutions. The proposed interpretation of the bonding interaction explains why the shortest N β O distances are found with the NO⁺ ions which have their nitrogen atoms displaced out of the NO₃^? plane.     

Dilute solution properties of sodium amylopectin xanthate

Sodium amylopectin xanthate, prepared by xanthation of potato amylopectin in alkaline medium, was fractionated and the fractions in 1M NaOH were characterized by viscometry and light scattering. The expansion factor α was determined from the expression due to Orofino and Flory. The value of a of the Mark-Houwink relation, [η] = KM^a, was also determined. Its weight-average molecular weight, end-to-end distance, branching, and other parameters in alkali solution were also evaluated. From the data, it was concluded that the sodium amylopectin xanthate molecule had a polydisperse random-coil chain configuration in 1M NaOH and had no tendency to aggregate in this medium.     

Biophysical and biochemical investigation on the binding of a manganese–cyanonitrosyl complex with DNA

The interaction of a cyanonitrosyl–manganate complex with DNA has been studied by u.v.–vis spectroscopy, circular dichroism, fluorescence and gel electrophoresis techniques. As the DNA 260 nm band remained insensitive to interaction, the interaction ratio was determined by monitoring the CN⁻→ Mn LMCT band observed at 222 nm, and the interaction ratio was found to be in the complex (D): DNA (P)=1:0.30 from the spectrophotometric titration. The above-mentioned physical measurements indicate that the binding mode is not intercalative and the cyanonitrosyl system is a groove binder.     

Kinetics and mechanism of the oxidation of aliphatic aldehydes by hexamethylenetetramine-bromine

Oxidation of aliphatic aldehydes by hexamethylenetetramine-bromine proceeds by a mechanism involving transfer of a hydride ion from the aldehyde to the oxidantvia an intermediate complex.     

The electronic structure of propiolic acid and propynal

A CNDO/2 calculation of ths total energy and electron distribution of propiolic acid and propynal shows that their dipole moment originates almost entirely from the charge distribution of the COOH and CHO groups and receives only a small contribution from the CCH group. These results provide a satisfactory explanation of very recent microwave dipole moment measurements on propiolic acid.     

A note on additively completely regular seminearrings

Semigroup Forum - In the endeavour of obtaining semigroup theoretic analogues i.e., the analogues of structure theorems of completely regular semigroups in the setting of additively regular...     

Kinetics of the oxidation of hypophosphite,deuteriohypophosphite, phosphite and neutralized phenyl phosphonous acid by tris(pyridine-2-carboxylato)manganese(III) in picolinate-picolinic acid buffer medium

Hypophosphite, deuteriohypophosphite, phosphite and neutralized phenyl phosphonous acid are oxidized by tris(pyridine-2-carboxylato)manganese(III) in Na(pic)–picH [where Na(pic) = sodium salt of picolinic acid and picH = picolinic acid] buffer in the 4.63–5.45 pH range. All the reactions appear to follow the same mechanistic pathway in which the substrate initially forms a 1:1 intermediate complex with the oxidant. The complex then breaks down in the rate-determining step to give a free radical intermediate which subsequently reacts with another molecule of oxidant to give the products. A deuterium isotope effect of k _H/k _D = 4.26 at 313 K, was observed in the oxidation of hypophosphite indicating that proton removal from phosphorus takes place in the rate-determining step. A mechanism consistent with the experimental observations has been proposed.     

Hydrogenation of acetylene–ethylene mixtures on Pd catalysts: study of the surface mechanism by computational approaches. Metal dispersion and catalytic activity

The hydrogenation mechanism of acetylene–ethylene mixtures on Pd catalysts under different experimental conditions was studied by employing a time-dependent Monte Carlo approach set to use a fixed series of event probabilities. The dependence of the catalyst activity and selectivity on the sizes of the metal particles was simulated at microscopic level and the results, also refined by fitting procedures, suggested proper explanations for the apparent nonuniformity of the related experimental findings. The use of the steric hindrance parameter of the surface species and the available surface energy on the metallic catalyst sites was decisive for reproducing the experimental results. Received: 16 September 1999 / Accepted: 3 February 2000 / Published online: 2 May 2000