Three new cholinesterase-inhibiting cis-clerodane diterpenoids from Otostegia limbata

Three new tricyclic cis-clerodane type diterpenoids trivially named as limbatolide A (1), limbatolide B (2) and limbatolide C (3) have been isolated from the roots of Otostegia limbata along with two known compounds; oleanic acid and beta-sitosterol. The structure elucidation of the new compounds was based primarily on two-dimensional (2D) NMR techniques. Compounds 1-3 displayed inhibitory potential in a concentration-dependent manner against acetylcholinesterase (AChE; EC 3.1.1.7) and butyrylcholinesterase (BChE; EC 3.1.1.8) enzymes, respectively.     

Structure determination of bioactive galloyl derivatives by NMR spectroscopy

The investigation of the chemical constituents of Symplocos racemosa Roxb led to the isolation of two new glycosides, symcomoside A (1) and symcomoside B (2), together with one known glycoside, tortoside C (3), which is reported for the first time from this plant. The structures of the new compounds were determined by 1D and 2D homonuclear and heteronuclear NMR spectroscopy, from chemical evidence and by comparison with published data for closely related compounds. Symcomoside B (2) showed potent inhibitory activity against alpha-glucosidase in a concentration-dependent fashion with an IC50 value of 0.733 +/- 0.033 mM whereas symcomoside A (1) showed very weak inhibitory activity against alpha-glucosidase (9.90% in 0.70 mM).     

Speciation of arsenic in ground water samples: A comparative study of CE-UV, HG-AAS and LC-ICP-MS

The performance of capillary electrophoresis-ultraviolet detector (CE-UV), hydride generation-atomic absorption spectrometry (HG-AAS) and liquid chromatography-inductively coupled plasma mass spectrometry (LC-ICP-MS) have been compared for the speciation of arsenic (As) in groundwater samples. Two inorganic As species, arsenite (As^III), arsenate (As^V) and one organo species dimethyl arsenic acid (DMA) were mainly considered for this study as these are known to be predominant in water. Under optimal analytical conditions, limits of detection (LD) ranging from 0.10 (As^III, AsT) to 0.19 (DMA) μg/l for HG-AAS, 100 (As^III, DMA) to 500 (As^V) μg/l for CE-UV and 0.1 (DMA, MMA) to 0.2 (As^III, As^V) μg/l for LC-ICP-MS, allowed the determination of the above three species present in these samples. Results obtained by all the three methods are well correlated (r² = 0.996*** for total As) with the precision of <5% R.S.D. except CE-UV. The effect of interfering ions (e.g. Fe²⁺, Fe³⁺, SO₄²⁻ and Cl⁻) commonly found in ground water on separation and estimation of As species were studied and corrected for. Spike recovery was tested and found to be 80-110% at 0.5 μg/l As standard except CE-UV where only 50% of the analyte was recovered. Comparison of these results shows that LC-ICP-MS is the best choice for routine analysis of As species in ground water samples.     

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Synthesis and Characterization of Uniform Fine Particles of Iron(III) Hydroxide/Oxide

Iron(III) hydroxide was precipitated from the homogeneous solutions, containing variuos amounts of iron(III) nitrate, potassium sulfate, and urea, by heating at 85 °C for different periods of time (5‐30 min). The precipitated solids were either in the form of gel or dispersed particles of different shapes and sizes, depending upon the composition of the reactant mixtures. The as‐prepared solids were amorphous in nature and were formulated as Fe(OH)₃.H₂O. On calcinations at 800 °C for 1 h, the latter converted into crystalline compound, composed of α‐Fe₂O₃ (hematite). The calcined particles retained the original features of their precursors to a maximum extent.     

Extraordinary Changes in the Electronic Structure and Properties of CdS and ZnS by Anionic Substitution: Cosubstitution of P and Cl in Place of S

Unlike cation substitution, anion substitution in inorganic materials such as metal oxides and sulfides would be expected to bring about major changes in the electronic structure and properties. In order to explore this important aspect, we have carried out first‐principles DFT calculations to determine the effects of substitution of P and Cl on the properties of CdS and ZnS in hexagonal and cubic structures and show that a sub‐band of the trivalent phosphorus with strong bonding with the cation appears in the gap just above the valence band, causing a reduction in the gap and enhancement of dielectric properties. Experimentally, it has been possible to substitute P and Cl in hexagonal CdS and ZnS. The doping reduces the band gap significantly as predicted by theory. A similar decrease in the band gap is observed in N and F co‐substituted in cubic ZnS. Such anionic substitution helps to improve hydrogen evolution from CdS semiconductor structures and may give rise to other applications as well.     

New developments in the dye-doped polymer dispersed liquid crystals gratings: A review

In this study, the dye-doped polymer dispersed liquid crystals (PDLC) gratings techniques performed by the various research groups or being developed are briefly reviewed. Especially, the electrically switched diffraction and holographic gratings, have attained much attention by various research groups working in the PDLC-related display studies. The fabrication methodologies used for such grating texture, include like the conventional dye-doped PDLC grating, Azo-dye doped PDLC gratings, and lasing techniques etc., adopted for dye-doped PDLC gratings. The useful features and characteristics of their fabrication process of such gratings are discussed. Finally, some of the future perspectives on this particular research field are presented.     

Speciation of arsenic by ion chromatography inductively coupled plasma mass spectrometry using ammonium eluents

A method based on ion chromatography (IC) and inductively coupled plasma MS (ICP-MS) was developed for the speciation of arsenic in water and soil extracts. An anion-exchange column (G3154A/101) was used to separate As(III), As(V), dimethylarsinic acid (DMA), and monomethylarsonic acid (MMA) with excellent resolution. Various ammonium salts, including NH4H2PO4, (NH4)2HPO4, (NH4)2CO3, and NH4HCO3, were examined as eluents to reduce matrix interference from chloride and to solve clogging problems. The best arsenic speciation was obtained within 9 min with excellent resolution and without interference from high chloride concentrations using an eluent containing 7.5 mM (NH4)2HPO4 at pH 7.9. The detection limits for the target arsenic species ranged from 0.1 to 0.4 microg/L with direct injection of sample without matrix elimination. The proposed method was effectively demonstrated by determining arsenic species in contaminated waters and soils of Bangladesh.     

Two new rare-class tetracyclic diterpenoids from Otostegia limbata

Two new tetracyclic diterpenoids trivially named as limbatenolide D (1) and limbatenolide E (2) have been isolated from Otostegia limbata. The structure elucidation of the compounds was based primarily on two-dimensional (2D) NMR techniques and on comparison with the literature data.