Biophysical and Biochemical Characterization of a Hyperthermostable and Ca<Superscript>2+</Superscript>-independent α-Amylase of an Extreme Thermophile <Emphasis Type="Italic">Geobacillus thermoleovorans</Emphasis>

alpha-Amylases reported from various microbial sources have been shown to be moderately thermostable and Ca2+ dependent. The bacterial strain used in this investigation is an extremely thermophilic bacterium Geobacillus thermoleovorans that produces a novel alpha-amylase (26 kDa; alpha-amylase gt), which is hyperthermostable (Topt 100 degrees C) and does not require Ca2+ for its activity/stability. These special features of alpha-amylase gt make it applicable in starch saccharification process. The structural aspects of alpha-amylase gt are, therefore, of significant interest to understand its structure-function relationship. The circular dichroism spectroscopic data revealed the native alpha-amylase gt to contain 25% alpha-helix, 21% beta-sheet, and 54% random coils. The addition of urea, at high concentration (8 M), appeared to expose the buried Trp residues of the native alpha-amylase gt to the aqueous environment and thus showed low fluorophore. Fluorescence-quenching experiments using KI, CsCl, N-bromosuccinimide, and acrylamide revealed interesting features of the tryptophan microenvironment. Analysis of Ksv and fa values of KI, CsCl, and acrylamide suggested the overall Trp microenvironment in alpha-amylase to be slightly electropositive. Fluorescence-quenching studies with acrylamide revealed the occurrence of both collisional as well as static quenching processes. There was no change in the alpha-helix content or the enzyme activity with an increase in temperature (60-100 degrees C) that suggested a critical role of the alpha-helix content in maintaining the catalytic activity.     

Tandem one-pot synthesis of flavans by recyclable silica-HClO4 catalyzed Knoevenagel condensation and [4 + 2]-Diels-Alder cycloaddition

An efficient one-pot multi-component synthesis of flavans using perchloric acid supported on silica as a recyclable heterogeneous catalyst has been described. This is the first report of direct one-step construction of a flavan skeleton from a phenolic precursor. The method involves a Knoevenagel-type condensation leading to in situ formation of transient O-quinone methide which further undergoes [4 + 2]-Diels-Alder cycloaddition with styrene to yield a flavan skeleton. The method provides easy access to a wide range of bio-active natural products viz. flavonoids, anthocyanins and catechins.     

A domino palladium-catalyzed C-C and C-O bonds formation via dual O-H bond activation: synthesis of 6,6-dialkyl-6H-benzo[c]chromenes

An efficient Pd-catalyzed domino reaction of α,α-dialkyl-(2-bromoaryl)methanols to 6,6-dialkyl-6H-benzo[c]chromenes is presented. Their formation can be explained via a five membered Pd(II)-cycle that efficiently involves a domino homocoupling with the second molecule, β-carbon cleavage, and finally intramolecular Buchwald-Hartwig cyclization. This domino process effectively involves breaking of five σ-bonds (2C-Br, 2O-H, and a C-C) and formation of two new σ-bonds (C-C and C-O). This mechanistic pathway is unprecedented and further illustrates the power of transition metal catalysis.     

Production of Acid-Stable and High-Maltose-Forming α-Amylase of Bacillus acidicola by Solid-State Fermentation and Immobilized Cells and Its Applicability in Baking

Among matrices used for immobilizing Bacillus acidicola cells [calcium alginate, chitosan + alginate, scotch brite, and polyurethane foam (PUF)], ??-amylase production was highest by PUF-immobilized cells (9.1?U?ml^?1), which is higher than free cells (7.2?U?ml^?1). The PUF-immobilized cells could be reused over seven cycles with sustained ??-amylase production. When three variables (moisture, starch, and ammonium sulfate), which significantly affected enzyme production in solid-state fermentation (SSF), were optimized using response surface methodology, 5.6-fold enhancement in enzyme production was attained. The enzyme production in SSF is 3.8-fold higher than that in submerged fermentation. The bread made by supplementing dough with ??-amylase of B. acidicola scored better than those with the xylanase of Bacillus halodurans and thermostable ??-amylase of Geobacillus thermoleovorans.     

Diverse organo-peptide macrocycles via a fast and catalyst-free oxime/intein-mediated dual ligation

Macrocyclic Organo-Peptide Hybrids (MOrPHs) can be prepared from genetically encoded polypeptides via a chemoselective and catalyst-free reaction between a trifunctional oxyamino/amino-thiol synthetic precursor and an intein-fusion protein incorporating a bioorthogonal keto group.     

Separation and inductively coupled plasma optical emission spectrometric (ICP-OES) determination of trace impurities in nuclear grade uranium oxide

A simple and rapid inductively coupled plasma optical emission spectrometric method for the determination of trace level impurities like REEs, Y, Cd, Co, V, Mg, B, Ca, Cr, Mn, Ni, Cu, Zn and Al in uranium oxide samples is described. The method involves solvent extraction separation of uranium from 6 M HNO₃ acid medium using di (2-ethyl hexyl) phosphoric acid in toluene, which selectively separates uranium leaving behind the trace impurities in the aqueous media, for quantification by ICP-OES. The method has been applied to few synthetic samples and five certified reference U₃O₈ standards. The results are compared with other methods such as TBP-TOPO-CCl₄ and 1,2 diaminocyclohexane N,N,N′,N′-tetra acetic acid (CyDTA)–ammonium hydroxide (NH₄OH) separation techniques. Different experimental parameters like contact time, acidity, aqueous to organic ratio etc., are optimized for better and accurate results. The method is simple, rapid, accurate and precise for all the studied elements, showing a relative standard deviation of 1.5–12.0% at trace levels studied (5.5–12% at 0.2 μg/mL and 1.5–6.0% at 0.5 μg/mL), on the synthetic samples prepared from high purity oxides.     

Steady state dynamics of a moving model cell

Crawling cell motility results due to treadmilling of a polymerized actin network at the leading edge. Steady state dynamics of a moving cell are governed by actin concentration profiles across the cell. Branching of new filaments implicating Arp2/3 and capping of existing filaments with capZ or Gelsolin are central to the robust functioning of the actin network. Using computer simulations, steady state concentration profiles of globular actin (G actin) and filamentous actin (F actin) are computed. The profiles are in agreement with experimentally observed ones. Simulations unveil that there is an optimal capping and branching rate for which the velocity of the model cell is maximum. Our simulations also indicate that the capping of actin filaments results in an increase in nucleation of new filaments by Arp2/3-induced branching and is in agreement with a recently observed monomer gating model. We observe that Arp2/3 and capping protein exhibit a functional antagonism with respect to the actin network treadmilling.     

A Dark Energy Model in a Scale Covariant Theory of Gravitation

An axially symmetric Bianchi type-I space time with variable equation of state (EoS) parameter and constant deceleration parameter has been investigated in scale covariant theory of gravitation formulated by Canuto et al. (Phys. Rev. Lett. 39:429, 1977). With the help of special law of variation for Hubble’s parameter proposed by Bermann (Nuovo Cimento 74B:182, 1983) a dark energy cosmological model is obtained in this theory. Some physical and kinematical properties of the model are also discussed.     

Adsorption studies of cesium on a new inorganic exchanger ammonium molybdophosphate-alumina (AMP-Al2O3)

The applicability of ammonium molybdophosphate-alumina (AMP-Al₂O₃) for the efficient removal of Cs from aqueous solution by adsorption has been investigated. The kinetics of adsorption of cesium ions has been studied by using radioanalytical procedure over a concentration range of 10⁻⁴−10⁻² mol.dm⁻³ and in the temperature range of 303–318 K. The results showed that the uptake follows the first order rate law with respect to cesium concentration and obeys Langmuir and modified Freundlich adsorption isotherm in the concentration range studied. Equilibrium adsorption values at different temperatures have been utilised to evaluate change in standard thermodynamic parameters (ΔH ⁰, ΔG ⁰ and ΔS ⁰). From the thermodynamic parameters it is found that the process is exothermic in nature.