Chemoselective one-pot access to benzo[e]indole-4,5-diones and naphtho[2,1-b]thiophene-4,5-diones via copper-catalyzed oxidative [3 + 2] annulation of α-oxoketene N,S-acetals/β-ketothioamides with α-/β-naphthols

An operationally simple and efficient one-pot method for the synthesis of 1-aroyl (or alkanoyl)-2-thioalkyl-3-aryl (or alkyl)-3H-benzo[e]indole-4,5-diones and naphtho[2,1-b]thiophene-4,5-diones has been devised by copper-catalyzed cross-coupling of α-oxoketene N,S-acetals/β-ketothioamides with α-/β-naphthols in open air for the first time. The key to the success of this transformation is the room temperature oxidation of α-/β-naphthol to 1,2-naphthoquinone as a reactive species, which undergoes formal [3 + 2] annulation with α-oxoketene N,S-acetals/β-ketothioamides via cascade sequence of Michael addition/tautomerization/oxidation/cyclization/aromatization reactions, enabling addition of a pyrrole/thiophene ring onto naphthoquinone moiety. Further, benzo[e]indole-4,5-diones were transformed to pentacyclic fused phenazine derivatives under solvent-free conditions. Based on our experimental outcomes, a tentative mechanistic rationale for this chemoselective protocol is proposed, which is well validated and supported by the control experiments.     

Multielemental analysis of vegetarian human diets and dietary components by neutron activation

Two vegetarian diet samples representative of the Indian sub-continent were prepared (in raw form) by the proportionate blending method for adolescent and adult age groups. These along with its components, viz. wheat, rice flours and pulses, were analyzed for 12 minor and trace elements by instrumental neutron activation analysis (INAA) and high resolution -ray spectrometry. Bowen's kale was also analyzed to check the accuracy of the method. The concentrations of Br, Co, Cu, Fe, K, Mn and P are comparable to the non-vegetarian American and European diets. Zinc concentrations are however lower than the recommended dietary allowances (RDA) and the western non-vegetarian diets.     

Effect of chain stiffness and entanglements on the elastic behavior of end-linked elastomers

The effect of chain stiffness and entanglements on the elastic behavior and microscopic structure of cross-linked polymer networks was studied using Monte Carlo simulations. We investigated the behavior of entangled and entanglement-free networks at various degrees of chain stiffness and densities. Based on previous results that indicated that trapped entanglements prevent strain-induced order-disorder transitions in semiflexible chain networks, we prepared the entangled networks by end-linking the chains in very dilute conditions so as to minimize the extent of trapped entanglements. We also considered the entanglement-free case by using a "diamond" structure. We found that the presence of even a very small amount of trapped entanglements is enough to prevent a discontinuous strain-induced transition to an ordered phase. In these mildly entangled networks, a nematiclike order is eventually attained at high extensions but the elastic response remains continuous and the cross-links remain uniformly distributed through the simulation box. The entanglement-free diamond networks on the other hand show discontinuities in their stress-strain data. Networks at higher densities exhibit a more stable ordered phase and show an unusual staircaselike stress-strain curve. This is the result of a stepwise extension mechanism in which the chains form ordered domains that exclude the cross-links. Extension is achieved by increasing the number of these ordered domains in the strain direction. Cross-links aggregate in the spaces between these ordered domains and form periodic bands. Each vertical upturn in the stress-strain data corresponds to the existence of an integer number of ordered domains. This stepwise elastic behavior is found to be similar to that exhibited by some tough natural materials.     

Development and validation of a reversed phase liquid chromatographic method for separation and determination of related-substances of modafinil in bulk drugs

A reversed-phase high-performance liquid chromatographic (RP-HPLC) method for determination and evaluation of purity of modafinil in bulk drugs using Kromasil C₁₈ column with acetonitrile: 0.02 M ammonium acetate as a mobile phase in gradient elution mode at 30 °C and detection at 225 nm using photodiode array detector has been developed. The effects of pH, temperature and the percent of organic modifier on resolution were studied. Related substances, viz, sulphide, sulphoxide, sulphones of the modafinil, acid and ester derivatives, were separated and quantified. The method was found to be simple, rapid, selective and capable of detecting all process related impurities at trace levels in the finished products of modafinil with detection limits of 0.6-2.4 × 10⁻⁸ g. The method was validated with respect to accuracy, precision, linearity, ruggedness, and limits of detection and quantification. It was found to be suitable not only for monitoring the reactions during the process development but also quality assurance of modafinil.     

A Specific Spray Reagent for the Identification and Detection of Carbaryl in Biological Materials

JPC – Journal of Planar Chromatography – Modern TLC -     

Surface modification and aging studies of addition-curing silicone rubbers by oxygen plasma

Poly(dimethyl siloxane) (PDMS) has been focused on recently due to its variety of applications specifically in microsystems technology. Many companies market two-component PDMS, which is comprised of a base component and a curing agent. Widely known and used for microsystems applications is Sylgard 184 from Dow Corning. Present work deals with two-component Room Temperature Vulcanized (RTV) PDMS from three different companies. They are Sylgard 184 from Dow Corning, RTV 615 from GE Silicones and RTV 141 from Rhodia Chemicals. Temporary increase in wettability of these three different types of PDMS by oxygen plasma by varying the plasma power and exposure time has been studied and compared with results available in literature. The hydrophobic recovery of the modified surfaces was monitored as a function of time and quantified. The surfaces were characterized using contact angle measurements and ATR-FTIR and XPS spectroscopy, their behavior analyzed in term of free surface energy and work of adhesion.     

Structure, stability, and dynamics of canonical and noncanonical base pairs: quantum chemical studies

The importance of non-Watson-Crick base pairs in the three-dimensional structure of RNA is now well established. The structure and stability of these noncanonical base pairs are, however, poorly understood. We have attempted to understand structural features of 33 frequently occurring base pairs using density functional theory. These are of three types, namely (i) those stabilized by two or more polar hydrogen bonds between the bases, (ii) those having one polar and another C-H...O/N type interactions, and (iii) those having one H-bond between the bases and another involving one of the sugars linked to the bases. We found that the base pairs having two polar H-bonds are very stable as compared to those having one C-H...O/N interaction. Our quantitatively analysis of structures of these optimized base pairs indicates that they possess a different amount of nonplanarity with large propeller or buckle values as also observed in the crystal structures. We further found that geometry optimization does not modify the hydrogen-bonding pattern, as values of shear and open angle of the base pairs remain conserved. The structures of initial crystal geometry and final optimized geometry of some base pairs having only one polar H-bond and a C-H...O/N interaction, however, are significantly different, indicating the weak nature of the nonpolar interaction. The base pair flexibility, as measured from normal-mode analysis, in terms of the intrinsic standard deviations of the base pair structural parameters are in conformity with those calculated from RNA crystal structures. We also noticed that deformation of a base pair along the stretch direction is impossible for all of the base pairs, and movements of the base pairs along shear and open are also quite restricted. The base pair opening mode through alteration of propeller or buckle is considerably less restricted for most of the base pairs.     

Gradient HPLC of antibiotics in urine, ground water, chicken muscle, hospital wastewater, and pharmaceutical samples using C-18 and RP-amide columns

A simple and highly sensitive high pressure liquid chromatographic (HPLC-UV) method has been developed for the determination of ofloxacin, lomefloxacin, cinoxacin, and nalidixic acid, in mobile phase citrate buffer (0.001 M) of pH 4.5 prepared in water (X), methanol (Y), and ACN (Z) using gradient at a flow rate of 1.0 mL/min by direct UV absorbance detection at lambda = 280 nm. Separation of analytes was studied on the C-18 and RP-amide columns and best results were observed on the RP-amide column with LODs (3.3 x S/m) 0.89, 0.55, 0.67, and 1.41 ng/mL for ofloxacin, lomefloxacin, cinoxacin, and nalidixic acid, respectively, and better RSD than the C-18 column. The recovery of Fluoroquinolones (FQs) in urine, ground water, hospital wastewater, and chicken muscle using this method is more than 90%. The method was successfully applied to the analysis of ofloxacin, lomefloxacin, cinoxacin, and nalidixic acid in urine, ground water, pharmaceutical dosage forms, hospital wastewater, and chicken muscle.     

Evaluation of genotoxic and modulatory effects of Nyctanthes arbor-tristis calyx extract and the isolated crocin in Ames’ assay

Flowers of the plant Nyctanthes arbor-tristis (NAT) are widely used in the traditional medicinal systems of several Asian countries. In the present study, potential genotoxicity and modulatory effects of ethanolic extract of NAT flower calyx (NAT FCE) and crocin, a carotenoid principle were evaluated employing standard Salmonella assay. Experiments evaluating the genotoxic potential of NAT FCE and crocin, with and without the S9-activation in TA 98, TA 100 and TA 102 showed a lack of increase in revertant mutants. Evaluation of modulatory effects of NAT FCE and crocin, without the S9, showed significant decrease in the number of 4-nitro-o-phenylenediamine-, sodium azide- and ethyl methanesulfonate-induced revertants. However, with S9, NAT FCE and crocin moderately increased the 2-aminoanthracene-induced revertants in TA 98; they moderately decreased revertants in TA 100 and TA 102. Both NAT FCE and crocin have been shown to be non-genotoxic and to be able to modulate responses of standard mutagens.