Stability-Indicating HPTLC Method for Simultaneous Determination of Ezetimibe and Simvastatin

Simvastatin and ezetimibe are used to treat hyperlipidemia. A simple, selective and stability-indicating HPTLC method has been established for analysis of simvastatin and ezetimibe. The method has been validated so that both drugs can routinely be analyzed simultaneously. The method uses aluminum-backed silica gel 60F₂₅₄ TLC plates as stationary phase with n-hexane–acetone 6:4 (v/v) as mobile phase. Densitometric analysis of both drugs was carried out in absorbance mode at 234 nm. This system was found to give compact bands for simvastatin and ezetimibe (R _F 0.39 ± 0.05 and 0.50 ± 0.05, respectively). Linear relationships were obtained between response and amount of drug in the range 200–1,600 ng per band with high correlation coefficients (r ² = 0.9917 ± 0.0018 for simvastatin and r ² = 0.9927 ± 0.0021 for ezetimibe). The method was validated for precision, robustness, and recovery. The limits of detection and quantitation were 25 and 150 ng per band, respectively. Simvastatin and ezetimibe were subjected degradation by acid, pH 6.8 phosphate buffer, oxidation, dry heat, and wet heat. The degradation products were well resolved from the pure drug with significantly different R _F values. Because the method could effectively separate the drug from its degradation products, it can be used for stability-indicating analysis.     

Quantitative Analysis of Flavonoids in Annona squamosa Leaf Extracts and Its Pellet Formulation by Validated High-Performance Thin-Layer Chromatographic Technique

JPC – Journal of Planar Chromatography – Modern TLC - Annona squamosa, commonly known as custard apple, possesses various medicinal properties such as antimicrobial, insecticidal,...     

A nonafluoro nucleoside as a sensitive 19f NMR probe of nucleic acid conformation

A nucleoside carrying a perfluorinated tert-butyl group ( 4) was prepared by a Sonogashira coupling of 5-iodo-2'-deoxyuridine with 4,4,4-trifluoro-3,3-bis(trifluoromethyl)-1-butyne in nearly quantitative yield and subsequently incorporated into DNA oligomers. Thermal denaturation studies showed that 4 had a negligible effect on duplex stability when compared to thymidine. Transition from single strand to duplex was monitored by (19)F NMR spectroscopy at micromolar concentrations of oligomers, demonstrating the sensitivity of 4 as an NMR reporter nucleoside.     

Drop formation in aqueous two-phase systems

Extraction using aqueous two-phase systems (ATPSs) is a versatile technique for the downstream processing of various proteins/enzymes. The study of drop formation deals with the fundamental understanding of the behavior of liquid drops under the influence of various external body as well as surface forces. These studies provide a basis for designing of the extractions in column contactors in which liquid drops play a major role. Most of the drop formation studies reported so far is restricted to aqueous-organic systems. ATPSs, differ from aqueous-organic systems in their physical properties. In view of this, an attempt was made to develop a model for drop formation in ATPSs adopting the information available on aqueous-organic systems. In order to validate the model, experiments were performed by using polyethylene glycol (PEG)/salt systems of different phase compositions at various flow rates. At low flow rates the single stage model and at high flow rates the two stage model are able to predict the drop volume during its formation from tip of capillary. The experimental results were found to agree reasonably well with those predicted by the model.     

Catalytic asymmetric coupling of 2-naphthols by chiral tridentate oxovanadium (IV) complexes

A series of chiral oxovanadium(IV) complexes derived from tridentate N-3,5-substituted and N-3,4-benzo- and N-5,6-benzo-salicylidene-alpha-amino acids can serve as efficient catalysts for the enantioselective oxidative couplings of various 3-, 6-, and 7-substituted 2-naphthols under O(2). The best scenario involves the use of a vanadyl complex arising from 2-hydroxy-1-naphthaldehyde and valine (or phenylalanine) in CCl(4), leading to BINOLs in good yields (75-100%) and with enantioselectivities of up to 68%.     

Prelude to molecular dynamics: Topography-driven gaussian charge models

A new strategy to develop Gaussian charge models (GCMs) for molecules like ammonia, water, ethene, hydrogen sulfide, formaldehyde and benzene is presented. These molecular models comprising of positive point charges and negative Gaussian charge distributions (GCDs), which represent nuclei and continuous electron charge distribution, are found to correctly represent the ab initio Molecular Electrostatic Potential (MESP) and reproduce its essential topographical features of corresponding molecules. The models use optimized parameters: positive charges at nuclei, negative charges on GCDs, Gaussian exponent and centers. The Potential Energy Surface (PES) of water dimer has been explored using water GCMs. A good agreement has been found between PES obtained using GCMs and wave function. The Gaussian models correctly predict structure of benzene-water complex. It is thus recommended to use GCMs for molecular dynamic simulations.     

Chemical shifts of the LIII absorption discontinuity of rhenium

Chemical shifts of the X-ray L_III absorption discontinuities of rhenium in some of its binary and ternary compounds have been studied using a bent crystal X-ray spectrograph. The chemical shifts (ΔE) are found to be governed by the effective charges (q) on the absorbing ions, which have been calculated using Suchet's theory. For the compound ReCl₅, however, the effective ionic charge cannot be calculated since the pentavalent radius of rhenium is not known. The ΔE, q plot has been used to determine the charges on the rhenium ions in ReCl₅ as well as in two ternary compounds KReO₄ and NaReO₄. Our work has enabled us to determine the ionic radius of pentavalent rhenium.     

A study of EXAFS associated with the Re LIII discontinuity in metal and some compounds

The authors have reanalysed the data on the EXAFS associated with the rhenium L_III absorption discontinuity in the metal and in some of its compounds, and have interpreted them in the light of the recent theory proposed by Lytle, Sayers and Stern. It has been shown that the α parameter of EXAFS is a measure of valency and that the metallic valency of rhenium is two.