HPLC enantioseparation of racemic bupropion,baclofen and etodolac: modification of conventional ligand exchange approach by pre‐column formation of chiral ligand exchange complexes

Separation of racemic mixture of (RS)‐bupropion, (RS)‐baclofen and (RS)‐etodolac, commonly marketed racemic drugs, has been achieved by modifying the conventional ligand exchange approach. The Cu(II) complexes were first prepared with a few l ‐amino acids, namely, l ‐proline, l ‐histidine, l ‐phenylalanine and l ‐tryptophan, and to these was introduced a mixture of the enantiomer pair of (RS)‐bupropion, or (RS)‐baclofen or (RS)‐etodolac. As a result, formation of a pair of diastereomeric complexes occurred by ‘chiral ligand exchange’ via the competition between the chelating l ‐amino acid and each of the two enantiomers from a given pair. The diastereomeric mixture formed in the pre‐column process was loaded onto HPLC column. Thus, both the phases during chromatographic separation process were achiral (i.e. neither the stationary phase had any chiral structural feature of its own nor did the mobile phase have any chiral additive). Separation of diastereomers was successful using a C₁₈ column and a binary mixture of MeCN and TEAP buffer of pH 4.0 (60:40, v/v) as mobile phase at a flow rate of 1 mL/min and UV detection at 230 nm for (RS)‐Bup, 220 nm for (RS)‐Bac and 223 nm for (RS)‐Etd. Baseline separation of the two enantiomers was obtained with a resolution of 6.63 in <15 min. Copyright © 2016 John Wiley & Sons, Ltd.     

Influence of sulphur atom on the qualitative behavior of electron impact total cross sections of some sulphur containing molecules

Absolute elastic differential cross sections (DCS) have been measured experimentally for several sulphur containing molecules such as SF₆, CS₂, DMS and DMSO using a novel high resolution electron spectrometer. The measured DCS’s were extrapolated in the forward and backward angles using a tenth order legendre polynomial based least squares fitting technique. Total cross sections (TCS) were determined by integrating the DCS over all angles for each incident energy. The influence of the sulphur atom on the molecular TCS is studied by comparing the qualitative behavior of electron impact cross sections for the sulphur containing molecules against the TCS of the sulphur atom at each incident energy. Theoretical calculations based on independent atom model are also presented as a guide to understand the nature of the electron-molecule collision processes measured in this study.     

Application of Hydrazino Dinitrophenyl-Amino Acids as Chiral Derivatizing Reagents for Liquid Chromatographic Enantioresolution of Carbonyl Compounds

A new series of chiral derivatizing reagents (CDRs) consisting of five hydrazino dinitrophenyl (HDNP)-amino acids (CDR 1?C5) was prepared by a two-step synthesis procedure starting from 1,5-difluoro-2,4-dinitrobenzene (DFDNB). In the first step, five fluoro-dinitrophenyl (FDNP)-reagents, namely FDNP-l-Leu, FDNP-l-Val, FDNP-l-Phe, FDNP-l-Ala and FDNP-d-Phg were synthesized by substituting one of the fluorine atoms in DFDNB moiety with amino acids l-Leu, l-Val, l-Phe, l-Ala and d-Phg, respectively. In the following step, the remaining fluorine atom of the FDNP reagents was substituted with hydrazine hydrate to obtain five HDNP reagents (i.e. CDR 1?C5; HDNP-l-Leu, HDNP-l-Val, HDNP-l-Phe, HDNP-l-Ala and HDNP-d-Phg). These five CDRs were used for synthesis of diastereomers of six racemic carbonyl compounds which were resolved by high-performance liquid chromatography using C18 column and gradient eluting mixture of acetonitrile or methanol with triethylammonium phosphate buffer with UV detection at 348 nm. Microwave irradiation was used for synthesis of both the CDRs and the diastereomers. The newly synthesized CDRs were observed to be superior in comparison to their counterparts having amino acid amides as chiral auxiliaries in terms of cost effectiveness and providing better resolution of diastereomers. The method was validated for limit of detection, linearity, accuracy and precision.     

Bismuth Chloride–Sodium Nitrite: A Novel Reagent for Chemoselective N-Nitrosation

Bismuth(III) chloride–sodium nitrite was used as a mild and efficient reagent for N-nitrosation of various tetrazoles, secondary amines, and amides under ambient conditions. Nitrosation took place chemoselectively at the nitrogen atom, giving corresponding N-nitroso derivatives in good to excellent yield.     

Removal of p-aminophenol and p-nitrophenol from aqueous solution through adsorption on bismuth,lead, and manganese ferrocyanides and their relevance to environmental issues

Removal of p-aminophenol (PAP) and p-nitrophenol (PNP) from aqueous solution have been studied through adsorption on bismuth, lead and manganese ferrocyanides (125 μm British Sieve Standard mesh size) at pH range 1.0–10.0 and room temperature (27 ± 1°C). The progress of adsorption was followed spectrophotometrically by measuring the absorbance of PAP and PNP solutions at their corresponding λ_max = 220 and 330 nm, respectively. At neutral pH, PNP was found to more adsorbed than PAP on all three metal ferrocyanides studied. Manganese ferrocyanide and bismuth ferrocyanide were found to have maximum and minimum adsorption, respectively for both adsorbents. The adsorption followed the Langmuir type of adsorption in the concentration range of 10^?4 to 10^?5 mol/L of PAP and PNP solutions.     

A new approach to the design of biorthogonal triplet half-band filter banks using generalized half-band polynomials

This paper presents a novel approach to design a class of biorthogonal triplet half-band filter banks based on the generalized half-band polynomials. The filter banks are designed with the help of three-step lifting scheme (using three kernels). The generalized half-band polynomial is used to construct these three kernels by imposing the number of zeros at \(z=-1\) . The maximum number of zeros imposed for the three kernels is half of the order of half-band polynomial ( \(K/2\) for \(K\) order polynomial). The three kernels give a set of constraints on the coefficients of half-band polynomial by imposing the zeros. In addition to structural perfect reconstruction and linear phase, the proposed filter banks provide better frequency selectivity, more similarity between analysis and synthesis filters (measure of near-orthogonality), and good time–frequency localization. The proposed technique offers more flexibility in the design of filters using two degrees of freedom. Some examples have been presented to illustrate the method.     

Silicon nitride processing for control of optical and electronic properties of silicon solar cells

Thin films of SiN are well suited as antireflection (AR) coatings for Si solar cells because their optical properties, such as refractive index and absorption coefficient, can be tailored during deposition to match those of Si solar cells. The SiN layers, particularly those deposited by a plasma-enhanced chemical vapor deposition (PECVD) process, can serve other functions in Si solar-cell fabrication. They can be excellent buffer layers through which the front metal contact can be fired. The PECVD nitridation also introduces H into the Si surface, which diffuses deep into the solar cell and passivates residual impurities and defects during metal-contact firing. The optimization of SiN properties and processing conditions may have conflicting demands based on its multifunctional role. To fully exploit these multiple functions, the SiN processing sequence must be optimized based on the properties of the nitride, the diffusion behavior of H, and the interactions of metal with the SiN/Si composite substrate.     

Dehydrogenation studies of dihydronicotinamide adenine dinucleotide (NADH) with methylene blue in the presence of the copper hexcyanoferrate(II) complex and light

The effects of copper ferrocyanide and light on the dehydrogenation rate of NADH by methylene blue is studied. The results suggest that the dehydrogenation rate of NADH with methylene blue is enhanced by copper ferrocyanide. Light also affects the reaction rate.     

Time-stretched analogue-to-digital conversion

A new concept for analogue-to-digital (ADC) conversion is proposed and demonstrated. The analogue signal is stretched in time prior to sampling and quantisation. Time stretching increases the input bandwidth and sampling rate of the ADC and is best implemented using optoelectronic techniques