Rapid identification and quantification of chlorpheniramine maleate or pheniramine maleate in pharmaceutical preparations by thin-layer chromatography-densitometry

Thin-layer chromatography (TLC)-densitometry was used to separate, identify, and quantitate chlorpheniramine maleate (CPM) and pheniramine maleate (PM) when present in combination with other drugs in pharmaceutical preparations of tablets, syrups, eye and ear drops, etc. CPM or PM was extracted (tablets, capsules, etc.) or diluted (liquid preparations, if needed) with 80% ethanol and isolated from other ingredients by TLC on silica gel G using cyclohexane-chloroform-methanol-diethylamine (4.5 + 4.0 + 0.5 + 1.0, v/v) as the mobile phase. Separated CPM and PM were detected under shortwave ultraviolet light and quantitated by scanning densitometry at 260 nm. Recoveries of CPM and PM were 100.09+/-0.77% and 100.09+/-0.87%, respectively.     

First principles study of CO oxidation on TiO2(110): the role of surface oxygen vacancies

The reactivities of the stoichiometric and partially reduced rutile TiO2(110) surfaces towards oxygen adsorption and carbon monoxide oxidation have been studied by means of periodic density functional theory calculations within the Car-Parrinello approach. O2 adsorption as well as CO oxidation are found to take place only in the presence of surface oxygen vacancies (partially reduced surface). The oxidation of CO by molecularly adsorbed O2 at the O-vacancy site is found to have an activation energy of about 0.4 eV. When the adsorbed O2 is dissociated, the resulting adatoms can oxidize incoming gas-phase CO molecules with no barrier. In all studied cases, once CO is oxidized to form CO2, the resulting surface is defect-free and no catalytic cycle can be established.     

Enzymatic synthesis of oligosaccharides, alkyl and terpenyl glucosides, by recombinant Escherichia coli-expressed Pichia etchellsii β-glucosidase II

The biosynthetic activity of yeast Pichia etchellsii β-glucosidase II (BglII) expressed in recombinant Escherichia coli was utilized for synthesis of cellooligosaccharides, alkyl and terpene glucosides. Cellooligosaccharides with a degree of polymerization of 3 and greater were resolved by thin-layer chromatography (TLC) using an ethyl acetate: 1-propanol:2-propanol:water (8:5:1:1) solvent system followed by visualization with 0.2% naphthoresorcinol reagent. Using 2M cellobiose and 15 IU of partially purified BglII, 57 mmol/L of oligosaccharides (comprising mostly cellotriose and cellopentaose) was synthesized in 16 h. Similarly, alkyl glucosides with chain lengths from 6 to 10 carbons were synthesized and products extracted to near purity by ethylacetate extraction. The same extraction method was employed to separate, to near purity, various monoterpenyl (nerol, geraniol, citronellol) glucosides. A reliable and simple method for separation of cellooligosaccharides using a combination of Bio-Gel P-2 gel filtration and charcoal celite adsorption chromatography was developed. The cellooligosaccharides were separated to purity as confirmed by TLC. The enzyme was among the very few that could synthesize a wide variety of glycoconjugates.     

Analysis of current-voltage characteristics of inhomogeneous Schottky diodes at low temperatures

Two approaches of Gaussian distribution of barrier heights in inhomogeneous Schottky diodes have been analyzed by comparing the results for consistency between the two. For this the current-voltage characteristics of inhomogeneous Schottky diodes have been generated by using analytically solved thermionic-emission diffusion equation incorporating Gaussian distribution of barrier heights and by direct numerical integration over a barrier height range. The differences in the results obtained in two approaches are discussed and it is shown that the two approaches yield current-voltage characteristics with slightly different features. The discrepancies in the results obtained in two approaches are attributed to the same series resistance assumed for all elementary barriers of the distribution. It is shown that assigning same series resistance to all barrier of the distribution in numerical integration approach causes current saturation at low bias and inhibits intersection of current-voltage curves from being observable which otherwise occurs in the curves obtained using analytical equation. The paper deals with these aspects in details.     

Dynamical signatures of ‘phase transitions’: Chaos in finite clusters

Finite clusters of atoms or molecules, typically composed of about 50 particles (and often as few as 13 or even less) have proved to be useful prototypes of systems undergoing phase transitions. Analogues of the solid-liquid melting transition, surface melting, structural phase transitions and the glass transition have been observed in cluster systems. The methods of nonlinear dynamics can be applied to systems of this size, and these have helped elucidate the nature of the microscopic dynamics, which, as a function of internal energy (or ‘temperature’) can be in a solidlike, liquidlike, or even gaseous state. The Lyapunov exponents show a characteristic behaviour as a function of energy, and provide a reliable signature of the solid-liquid melting phase transition. The behaviour of such indices at other phase transitions has only partially been explored. These and related applications are reviewed in the present article.     

Synthesis,Spectroscopy, Semi‐empirical and Biological Activities of Organotin(IV) Complexes with o‐Isopropyl Carbonodithioic Acid

New organotin(IV) complexes have been synthesized by treating potassium o‐isopropyl carbonodithioate with R₂SnCl₂/R₃SnCl in 1 : 2/1 : 1 M/L ratio. All complexes have been characterized by IR and NMR (¹H, ¹³C) spectroscopy. IR results shows that ligand acts as bidentate which is also confirmed by semi‐empirical study. NMR data reveals four coordinated geometry in solution. Computed positive heat of formation shows that complex 5 is thermodynamically unstable. UV/visible spectroscopy was used to assess the mode of interaction and binding of the complexes with DNA which shows that complex 5 exhibits higher binding constant as compared to complex 3 . In protein kinase inhibition assay, compound 3 was found most active, while other biological activities shows that triorganotin(IV) complexes are biologically more active as compared to diorganotin(IV) complexes.     

Applying green analytical chemistry for development and validation of RP-HPLC stability indicating assay method for estimation of fenoverine in bulk and dosage form using quality by design approach

A green and robust reverse-phase liquid chromatographic method has been developed for the determination of fenoverine (FEN), by applying combined principles of green analytical chemistry and quality by design approaches on a Spherisorb C18 column (150?×?4.6?mm, 3?µm) with UV detection at 262?nm. A two level fractional factorial design (2^^7-3) Res IV was used for screening of influential chromatographic factors. The critical method parameters actively affecting critical quality attributes (CQAs) were identified and further optimized using Box–Behnken design. The predicted optimum assay conditions comprised of methanol and ammonium acetate buffer 20?mM, in an extent of 81:19% v/v individually having a flow rate of 1.0?mL/min with a column oven temperature of 33°C. The drug was stressed in hydrolytic, oxidative, reductive, thermal, and photolytic conditions. The developed method was validated successfully. The detector response was linear in the concentration of 0.5–160?µg/mL with a limit of detection (LOD) and limit of quantitation (LOQ) as 0.1 and 0.3?µg/mL, respectively. The % recovery was found to be 99.7%. The analytical method volume intensity value for developed method was 45?mL and the environment assessment tool (EAT) score was 41.07. The method is simple, environmentally benign, rapid, and robust for the determination of FEN in bulk and in its dosage form.     

Cu(II) catalyzed imine C-H functionalization leading to synthesis of 2,5-substituted 1,3,4-oxadiazoles

A direct access to symmetrical and unsymmetrical 2,5-disubstituted [1,3,4]-oxadiazoles has been accomplished through an imine C-H functionalization of N-arylidenearoylhydrazide using a catalytic quantity of Cu(OTf)(2). This is the first example of amidic oxygen functioning as a nucleophile in a Cu-catalyzed oxidative coupling of an imine C-H bond. These reactions can be performed in air atmosphere and moisture making it exceptionally practical for application in organic synthesis.     

Ligand exchange chromatography: a vital dimension for the reliable characterization of heterocycles in crude oils and refined products

In the present study, we established a statistical distribution pattern of indigenous sulfur, nitrogen, and oxygen species in Arabian Heavy crude oil and its distilled fractions: naphtha, gas oil, and vacuum gas oil (VGO) using chemical derivatization with methyl iodide and subsequent characterization by positive electrospray Fourier transform mass spectrometry. It was observed that sulfur species for naphtha and gas oil were accumulated at lower double bond equivalent values and at lower carbon numbers compared to VGO, whereas crude oil encompassed a complete range of the sulfur species detected in all distilled fractions. Moreover, the use of alumina column chromatography and ligand exchange chromatography (LEC) on a palladium-bonded silica stationary phase revealed additional structural features of sulfur heterocycles in terms of condensed and non-condensed thiophenes. During LEC separation, in addition to sulfur heterocycles, interesting results were obtained for oxygen-containing compounds. Ortho-substituted alkyl phenols were separated from meta- and para-substituted alkyl phenols on a palladium-bonded silica stationary phase.     

Nonlinear distribution function for a plasma obeying Vlasov-Maxwell system of equations

The nonlinear distribution function of Allis, generalised to include the transverse electromagnetic waves in a plasma, is used to set up the coupled wave equations for the longitudinal and the transverse modes. These are solved, keeping terms up to the cubic order of nonlinearity, by using the method of multiple scales. The equations of wave modulation are derived, which are solved to discuss the nature of the modulational instability and solitary wave propagation. It is found that the solutions so obtained satisfy conditions which are very similar to the well known Lighthill criterion for stability, appropriately modified due to the coupling of the two modes. The role of the average constant current due to any flow of the resonant and trapped electrons in determining the stability, is also discussed.