Validated spectrophotometric methods for the simultaneous determination of ciprofloxacin hydrochloride and metronidazole in tablets

A binary mixture of ciprofloxacin hydrochloride (CIP) and metronidazole (MET) was determined by five simple and accurate methods, without prior separation. In the first method, CIP was determined by second derivative spectrophotometric method ((2)D) by measuring the amplitude at 282 nm (zero ordinate value of MET). On the other hand, the determination of MET was based on isosbestic point technique, where the total content of the mixture was determined at 294.5 nm (isosbestic point), then the content of MET could be calculated by subtraction. The second method was first derivative ratio spectrophotometric method ((1)DD) where the total amplitude at 261 and 285 nm and the amplitude at 295.5 nm were selected to simultaneously determine CIP and MET in binary mixture, respectively. The third method was based on dual wavelength analysis, in which two wavelengths were selected, at which the absorbances of the other component were the same. The fourth method depends on using Q-analysis method (absorbance ratio) which involves the formation of Q-absorbance equation using the respective absorptivity values at 294.5 nm (isosbestic point) and 281.5 nm (λ(max) of CIP). The fifth method is partial least-squares (PLS) chemometric technique for determination of CIP and MET. The developed methods were successfully applied to the analysis of CIP and MET in laboratory prepared mixtures and tablets with good recoveries and their validation was carried out following the International Conference on Harmonization (ICH) guidelines. The results obtained were statistically compared with each other showing no significant difference with respect to accuracy and precision.     

Rational redesign of Candida antarctica lipase B for the ring opening polymerization of D,D-lactide

Based on molecular modelling, the enzyme Candida antarctica lipase B was redesigned as a catalyst for the ring opening polymerization of D,D-lactide. Two mutants with 90-fold increased activity as compared to the wild-type enzyme were created. In a preparative synthesis of poly(D,D-lactide) the mutants greatly improved the rate and the degree of polymerization.     

Direct experimental evidence for an enamine radical cation in SOMO catalysis

SOMO catalysis has lately obtained large interest as a new and powerful version of enantioselective organocatalysis which includes radical steps initiated by a one-electron oxidation. The intermediate enamine radical cation has been postulated, but has not been observed directly so far. This communication now reports the direct detection of this key intermediate.     

PHOTODYNAMIC ALTERATIONS OF THE CELL ENVELOPE OF PROTEUS MIRABILIS AND THEIR REPAIR

Abstract— Photodynamic treatment of Proteus mirabilis gives rise to changes in the cell envelope as can be detected by the behaviour of cells during lysis: lysis of cells proceeds more readily than that of untreated cells, measured by the liberation of labelled DNA. After photodynamic treatment the cell envelope is restored to the control levels. This repair process takes place within 5 min in broth as well as in buffer solutions.     

Organic transformations via metal silane reagents: syntheses of vinyl ethers from dimethyl ketals and (CO)5MnSi(CH3)3

The reaction of dimethyl ketals with (CO)₅MnSi(CH₃)₃ ($\text{1}$ at 50 °C in CH₃CN affords methyl enol ethers, generally in 75–95% yields.