Showing papers by "National Chemical Laboratory published in 1998"

Molecular and Biotechnological Aspects of Microbial Proteases

Abstract: Proteases represent the class of enzymes which occupy a pivotal position with respect to their physiological roles as well as their commercial applications. They perform both degradative and synthetic functions. Since they are physiologically necessary for living organisms, proteases occur ubiquitously in a wide diversity of sources such as plants, animals, and microorganisms. Microbes are an attractive source of proteases owing to the limited space required for their cultivation and their ready susceptibility to genetic manipulation. Proteases are divided into exo- and endopeptidases based on their action at or away from the termini, respectively. They are also classified as serine proteases, aspartic proteases, cysteine proteases, and metalloproteases depending on the nature of the functional group at the active site. Proteases play a critical role in many physiological and pathophysiological processes. Based on their classification, four different types of catalytic mechanisms are operative. Proteases find extensive applications in the food and dairy industries. Alkaline proteases hold a great potential for application in the detergent and leather industries due to the increasing trend to develop environmentally friendly technologies. There is a renaissance of interest in using proteolytic enzymes as targets for developing therapeutic agents. Protease genes from several bacteria, fungi, and viruses have been cloned and sequenced with the prime aims of (i) overproduction of the enzyme by gene amplification, (ii) delineation of the role of the enzyme in pathogenecity, and (iii) alteration in enzyme properties to suit its commercial application. Protein engineering techniques have been exploited to obtain proteases which show unique specificity and/or enhanced stability at high temperature or pH or in the presence of detergents and to understand the structure-function relationships of the enzyme. Protein sequences of acidic, alkaline, and neutral proteases from diverse origins have been analyzed with the aim of studying their evolutionary relationships. Despite the extensive research on several aspects of proteases, there is a paucity of knowledge about the roles that govern the diverse specificity of these enzymes. Deciphering these secrets would enable us to exploit proteases for their applications in biotechnology.

Local Softness and Hardness Based Reactivity Descriptors for Predicting Intra- and Intermolecular Reactivity Sequences: Carbonyl Compounds

Abstract: The DFT-based reactivity descriptors “local softness” and “local hardness” are used as reactivity indices to predict the reactivity sequences (both intramolecular and intermolecular) of carbonyl compounds toward nucleophilic attack on them. The finite difference approximation is used to calculate local softness, whereas local hardness is approximated by −Vel/2N, where Vel is the electronic part of the molecular electrostatic potential. Both aldehydes and ketones, aliphatic and aromatic, have been selected as systems. Critical cases, e.g., C6H5CHCHCHO, CH3CHCHCHO, and CH2CHCHO, where a CC double bond is in conjugation with the CO group, are also considered. Two new reactivity descriptors are proposed, “relative electrophilicity” (sk+/sk-) and “relative nucleophilicity” (sk-/sk+), which will help to locate the preferable reactive sites. Our results show that local hardness can be used as a guiding parameter when constructing intermolecular reactivity sequences.

Effects of ozone on wild plants

Abstract: Although there is a great deal of concern about the effects of human activities on biodiversity, until recently there has been very little interest in the effects of ozone on the species that constitute the major part of the flora, the diverse herbaceous and shrubby species of natural and semi-natural communities. However, many wild species have been shown to be at least as sensitive to ozone as crops that show significant yield losses, so there is a pressing need for an evaluation of the risk to wild species posed by ozone. This review attempts to assess progress and highlight problems. It begins with a comment on semantics, discusses the difficulties involved in measuring relative ozone resistance and then proceeds to consider the effects of ozone on growth and resource allocation. The evidence for evolution of resistance is appraised and then the potential effects of several interactions (cutting/grazing, competition, soil water deficit and nutrition) are considered. The review ends with some remarks on observation of oxidant-induced changes in ecosystems.

The relationship between field-cooled and zero-field-cooled susceptibilities of some ordered magnetic systems

Abstract: Analysis of the irreversible field-cooled (FC) and the zero-field-cooled (ZFC) magnetic susceptibilities of one ferrimagnetic and three ferromagnetic systems, measured at different applied magnetic fields, shows that the irreversibility indicated by the difference between the FC and the ZFC susceptibilities arises from magnetic anisotropy. The two susceptibilities are related to each other through the coercivity which is a measure of the anisotropy. The ZFC susceptibility can be calculated from the FC susceptibility (or vice versa) and the coercivity.

Electrostatically controlled diffusion of carboxylic acid derivatized silver colloidal particles in thermally evaporated fatty amine films

Abstract: We have recently demonstrated that carboxylic acid derivatized silver colloidal particles can be incorporated in thermally evaporated fatty amine films by immersion of the films in the silver sol and that the process is controlled through electrostatic interactions [Sastry, M.; Patil, V.; Mayya, K. S. Langmuir 1997, 13, 4490]. In this paper, we analyze the influence of colloidal particle concentration, solution pH, and film thickness on the kinetics of cluster incorporation in thermally evaporated fatty amine films obtained from quartz-crystal microgravimetry (QCM) measurements in terms of a one-dimensional (1-D) Fickian-type diffusion model. Although it is found that 1-D diffusion adequately represents the cluster mass uptake kinetics observed using QCM, an interesting film-thickness dependence on the diffusivity was observed. The nature of the cluster-diffusion curves were quite different for amine films annealed prior to immersion in the colloidal solution. In these cases, the 1-D-diffusion model with ...

Chickpea Defensive Proteinase Inhibitors Can Be Inactivated by Podborer Gut Proteinases

Abstract: Developing chickpea (Cicer arietinum L.) seeds 12 to 60 d after flowering (DAF) were analyzed for proteinase inhibitor (Pi) activity. In addition, the electrophoretic profiles of trypsin inhibitor (Ti) accumulation were determined using a gel-radiographic film-contact print method. There was a progressive increase in Pi activity throughout seed development, whereas the synthesis of other proteins was low from 12 to 36 DAF and increased from 36 to 60 DAF. Seven different Ti bands were present in seeds at 36 DAF, the time of maximum podborer (Helicoverpa armigera) attack. Chickpea Pis showed differential inhibitory activity against trypsin, chymotrypsin, H. armigera gut proteinases, and bacterial proteinase(s). In vitro proteolysis of chickpea Ti-1 with various proteinases generated Ti-5 as the major fragment, whereas Ti-6 and -7 were not produced. The amount of Pi activity increased severalfold when seeds were injured by H. armigera feeding. In vitro and in vivo proteolysis of the early- and late-stage-specific Tis indicated that the chickpea Pis were prone to proteolytic digestion by H. armigera gut proteinases. These data suggest that survival of H. armigera on chickpea may result from the production of inhibitor-insensitive proteinases and by secretion of proteinases that digest chickpea Pis.

Synthesis of Nanophase TiO2 by Ion Beam Sputtering and Cold Condensation Technique

Abstract: Nanoparticles of TiO2 have been synthesized by an ion beam sputtering-cold condensation (IBS-CC) technique. A sintered TiO2 was sputtered by an ion beam (Kaufman source, 900 eV, Ar+ ions) and the e...

Selective Catalytic Transesterification, Transthiolesterification, and Protection of Carbonyl Compounds over Natural Kaolinitic Clay

Abstract: Transesterification and transthiolesterification of β-keto esters with variety of alcohols and thiols and selective protection of carbonyl functions with various protecting groups catalyzed by natural kaolinitic clay are described. The clay has been found to be an efficient catalyst in transesterifying long chain alcohols, unsaturated alcohols, and phenols to give their corresponding β-keto esters in high yields. For the first time, transthiolesterification of β-keto esters with a variety of thiols has been achieved under catalytic conditions. Clay also catalyzes selective transesterification of β-keto esters by primary alcohols in the presence of secondary and tertiary alcohols giving corresponding β-keto esters. A systematic study involving the reactivity of different nucleophiles (alcohols, amines, and thiols) toward β-keto esters is also described. Sterically hindered carbonyl groups as well as α,β-unsaturated carbonyl groups underwent protection without the deconjugation of the double bond. Chemosele...

Zeolite-encapsulated manganese(III)salen complexes

Abstract: Manganese(III) complexes of [ N , N ′-ethylenebis(salicylidene-aminato)] (salen), [ N , N ′-ethylenebis(5-chloro-salicylidene-aminato)] (Cl 2 Salen), [ N , N ′-ethylenebis(5-bromo-salicylidene-aminato)] (Br 2 Salen) and [ N , N ′-ethylenebis(5-nitro-salicylidene-aminato)] [(NO 2 ) 2 Salen] have been encapsulated in the supercages of zeolite X by the zeolite synthesis method. The catalysts have been characterized by FTIR, UV–Vis and EPR spectroscopic techniques, XRD, SEM, thermal and elemental analysis, as well as nitrogen adsorption and cyclic voltammetric studies. The extent of encapsulation of the Mn(III)Salen complexes in zeolite X varies with the nature of the substituent group on the aromatic ring. While bromo groups enhance encapsulation, substitution with –NO 2 groups decreases the amounts of Mn(III) complexes encapsulated in the cavities of the zeolites. Cyclic voltammetric data indicate that the zeolite matrix facilitates the reduction of Mn(III) to Mn(II), suggesting that it behaves like an electron-withdrawing substituent. The aerobic oxidation of styrene to benzaldehyde, styrene oxide and phenylacetaldehyde over these catalysts is also reported.

Identification of a STS marker linked to the Aegilops speltoides-derived leaf rust resistance gene Lr28 in wheat

Abstract: A sequence-tagged-site (STS) marker is reported linked to Lr28, a leaf rust resistance gene in wheat. RAPD (random amplified polymorphic DNA) analysis of near-isogenic lines (NILs) of Lr28 in eight varietal backgrounds was carried out using random primers. Genomic DNA enriched for low-copy sequences was used for RAPD analysis to overcome the lack of reproducibility due to the highly repetitive DNA sequences present in wheat. Of 80 random primers tested on the enriched DNA, one RAPD marker distinguished the NILs and the donor parent from the susceptible recurrent parents. The additional band present in resistant lines was cloned, sequenced, and STS primers specific for Lr28 were designed. The STS marker (Indian patent pending: 380 Del98) was further confirmed by bulk segregation analysis of F3 families. It was consistently present in the NILs, the resistant F3 bulk and the resistant F3 lines, but was absent in recurrent parents, the susceptible F3 bulk and the susceptible F3 lines.

Origin of the cluster-glass-like magnetic properties of the ferromagnetic system

Abstract: The magnetic behaviour of at low magnetic fields has been studied by ac susceptibility, and field cooled (FC) and zero field cooled (ZFC) magnetization measurements. The cluster-glass-like magnetic behaviour of the compound is found to originate from its magnetocrystalline anisotropy as similar properties are observed for ferromagnetic systems also. The cluster glass freezing temperature and its magnetic field dependence, the irreversibility between the FC and ZFC magnetization curves, the shape of the low-field susceptibility curves, etc are related to the magnitude and temperature variation of the coercivity which is a measure of the anisotropy, and the ratio where is the applied magnetic field.

Optical Absorption Study of the Biotin−Avidin Interaction on Colloidal Silver and Gold Particles

Abstract: The biotin−avidin reaction is well studied and is often used as a prototypical interaction in the development of immunoassays. In this paper, this reaction is studied on the surface of colloidal silver and gold particles as a first step in the development of a sol-based assay. More specifically, silver and gold colloidal particles were biotinylated by self-assembly of a biotin disulfide molecule, and the reaction of the surface-modified colloidal particles with avidin molecules was followed using optical absorption spectroscopy. The specific interaction of avidin, a tetrameric protein, with biotin leads to cross-linking of the colloidal particles (“flocculation”) and a consequent growth of a long wavelength absorption peak. The degree of flocculation was quantified using a semiempirical flocculation parameter, and the dependence of this parameter on the extent of biotinylation of the colloidal particle surface as well as the concentration of avidin in solution was studied to determine the optimum working ...

Surface basicity and acidity of alkaline earth‐promoted La2O3 catalysts and their performance in oxidative coupling of methane

Abstract: The catalytic activity and selectivity of La2O3 and alkaline earth (viz. Mg, Ca, Sr and Ba) promoted La2O3 (alkaline earth metal/La = 0.1) catalysts in the oxidative coupling of methane (OCM) to C2-hydrocarbons (at 800°C, CH4/O2 ratio = 4 or 8 and gas hourly space velocity = 102000 cm3 g-1 h-1) have been investigated. The acidity and basicity distributions on these catalysts are measured by the temperature programmed desorption (TPD) of NH3 and CO2 from 50°C to 950°C, respectively. Both the acidity and basicity of the La2O3 catalysts and their activity in the OCM are strongly influenced by the alkaline earth promoter and its concentration. Among the catalysts, Sr-promoted La2O3 (Sr/La = 0.1) is the most active and selective catalyst for the OCM process. This catalyst contains a larger number of strong basic sites and intermediate strength acid sites.

New Hydrotalcite-like Anionic Clays Containing Zr4+ in the Layers: Synthesis and Physicochemical Properties

Abstract: A new series of hydrotalcite (HT)-like anionic clays containing Zr4+ in the brucite-like layer has been synthesized by a simple coprecipitation method at constant pH. The incorporation of Zr in the layer has been investigated by various analytical methods, such as powder X-ray diffraction (PXRD), chemical analysis, FT-IR, ultraviolet−visible diffuse reflectance (UV−vis DR) spectra, and thermogravimetric analysis (TGA). The PXRD of as-synthesized samples showed that the crystallinity of the material decreased with increasing Zr content due to the distortions introduced by the incorporation of the larger cation, Zr. Thermal calcination at 723 K results in the formation of a poorly crystalline MgO phase in which some of the Zr4+ cations are dissolved. The crystallinity of the resulting MgO phase decreases with increasing Zr content and forms a ZrO2 phase, in addition to the MgO phase, at higher Zr content. Calcination at higher temperatures (>1000 K) yields a mixture of MgO, MgAl2O4 spinel, and ZrO2 phases. ...

Surface Modification of Polystyrene Using Nitrogen Plasma. An X-ray Photoelectron Spectroscopy Study

Abstract: A detailed X-ray photoelectron spectroscopy study of a plasma-modified polystyrene (PS) surface was carried out after N2 plasma treatment. PS surfaces were found to be highly hydrophilic and reactive as it readily picks up oxygen giving rise to oxyfunctionalities on the surface. The plasma treatment also led to a slow chain scission with carboxyl, forming carbonate linkage.

[3 + 2] Cycloaddition of Nonstabilized Azomethine Ylides. 7. Stereoselective Synthesis of Epibatidine and Analogues(,).

Abstract: Epibatidine (1) is synthesized by employing a [3 + 2] cycloaddition strategy as a key step via nonstabilized azomethine ylide 10, generated by one-electron oxidative double desilylation of N-benzyl-2,5-bis(trimethylsilyl)pyrrolidine (12). Cycloaddition of 10 with trans-ethyl-3-(6-chloro-3-pyridyl)-2-propenoate (22a) gives 26 in which the 6-chloro-3-pyridyl moiety is endo-oriented. Decarboxylation followed by debenzylation gives unnatural epimer 30 of 1. The required cycloadduct 33, in which 6-chloro-3-pyridyl moiety is exo-oriented, is obtained stereoselectively utilizing cis-ethyl-(6-chloro-3-pyridyl)-2-propenoate (22b) as dipolarophile. 30 is also converted to 1 by epimerization reaction using KOtBu. An alternative route involving conjugate addition of 6-chloro-3-iodo pyridine (37) to 36, obtained by cycloaddition of 10 with ethyl propiolate, is also suggested for the stereoselective synthesis of 1. A number of substituted epibatidines (38, 39, 40, 41, and 42) are synthesized through this strategy using...