Structural and mechanistic insights into C-P bond hydrolysis by phosphonoacetate hydrolase

Bacteria have evolved pathways to metabolize phosphonates as a nutrient source for phosphorus. In Sinorhizobium meliloti 1021, 2-aminoethylphosphonate is catabolized to phosphonoacetate, which is converted to acetate and inorganic phosphate by phosphonoacetate hydrolase (PhnA). Here we present detailed biochemical and structural characterization of PhnA that provides insights into the mechanism of C-P bond cleavage. The 1.35?? resolution crystal structure reveals a catalytic core similar to those of alkaline phosphatases and nucleotide pyrophosphatases but with notable differences, such as a longer metal-metal distance. Detailed structure-guided analysis of active site residues and four additional cocrystal structures with phosphonoacetate substrate, acetate, phosphonoformate inhibitor, and a covalently bound transition state mimic provide insight into active site features that may facilitate cleavage of the C-P bond. These studies expand upon the array of reactions that can be catalyzed by enzymes of the alkaline phosphatase superfamily.     

Effect of Bi2O3 on spectroscopic and structural properties of Er3+ doped cadmium bismuth borate glasses

Glasses with composition 20CdO·xBi(2)O(3)·(79.5-x)B(2)O(3) (15≤x≤35, x in mol%) containing 0.5 mol% of Er(3+) ions were prepared by melt-quench technique (1150°C in air). The amorphous nature of the glasses was confirmed by X-ray diffraction. The spectroscopic properties of the glasses were investigated using optical absorption spectra and fluorescence spectra. The phenomenological Judd-Ofelt intensity parameters Ω(λ) (λ=2, 4, 6) were determined from the spectral intensities of absorption bands in order to calculate the radiative transition probability (A(R)), radiative life time (τ(R)), branching ratios (β(R)) for various excited luminescent states. Using the near infrared emission spectra, full width at half maxima (FWHM), stimulated emission cross-section (σ(e)) and figure of merit (FOM) were evaluated and compared with other hosts. Especially, the numerical values of these parameters indicate that the emission transition (4)I(13/2)→(4)I(15/2) at 1.506 μm in Er(3+)-doped cadmium bismuth borate glasses may be useful in optical communication.     

Phosphonate-Modified UiO-66 Brønsted Acid Catalyst and Its Use in Dehydra-Decyclization of 2-Methyltetrahydrofuran to Pentadienes

Phosphorus-modified all-silica zeolites exhibit activity and selectivity in certain Brønsted acid catalyzed reactions for biomass conversion. In an effort to achieve similar performance with catalysts having well-defined sites, we report the incorporation of Brønsted acidity to metal–organic frameworks with the UiO-66 topology, achieved by attaching phosphonic acid to the 1,4-benzenedicarboxylate ligand and using it to form UiO-66-PO₃H₂ by post-synthesis modification. Characterization reveals that UiO-66-PO₃H₂ retains stability similar to UiO-66, and exhibits weak Brønsted acidity, as demonstrated by titrations, alcohol dehydration, and dehydra-decyclization of 2-methyltetrahydrofuran (2-MTHF). For the later reaction, the reported catalyst exhibits site-time yields and selectivity approaching that of phosphoric acid on all-silica zeolites. Using solid-state NMR and deprotonation energy calculations, the chemical environments of P and the corresponding acidities are determined.     

Synthesis,characterization and evaluation of novel benzothiazole clubbed chromene derivatives for their anti-inflammatory potential

Abstract

A series of chromene derivatives (5a–f) were prepared by multistep synthesis process using 2-[3-phenyl prop-2-ene nitrile] 1,3-benzothiazole and dimedone using piperidine as catalyst in ethanol. The reaction was found to proceed via Knoevenagel condensation of aldehydes with benzothiazole, followed by the elimination to afford the 2-(benzo[d]thiazol-2-yl)-3-(aryl)acrylonitrile, which then undergoes Michael addition with 5,5-dimethyl-1,3-cyclohexanedione, followed by intramolecular O-cyclization to give the products. The structures of all novel constructed derivatives were corroborated by elemental analysis and spectral data (FT-IR, ¹H-NMR, ¹³C-NMR and Mass). Subsequently, the compounds were tested for their in-vivo anti-inflammatory activity. This study revealed that these synthesized derivatives tend to have significantly anti inflammatory activity and shall prove as structural templates in the design and development of new anti inflammatory drugs.     

Cell model for hydromagnetic axial flow over a cylinder. Part I. transverse magnetic field

Using cell model initiated by Happel, the filtration problem across a membrane composed of an aggregate of parallel circular cylinders subject to a uniform transverse magnetic field is studied. The system is simulated by a single cylinder enveloped by a concentric cylindrical enveloping surface with axial flow. The analysis leads to the evaluation of the permeability parameter. The results are then graphically presented and discussed. The effect of magnetic field is seen to increase the permeability.     

Probing the Selectivity and Protein⋅Protein Interactions of a Nonreducing Fungal Polyketide Synthase Using Mechanism-Based Crosslinkers

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Vanadium complexes with quadridentate Schiff bases

The Schiff base ligands N,N′-(±)-trans-bis(3,5-dichloro-2-hydroxyacetophenone)-1,2-cyclohexanediamine (H₂L¹) and N,N′-(±)-trans-bis(5-chloro-4-methyl-2-hydroxyacetophenone)-1,2-cyclohexanediamine (H₂L²) were derived from the condensation of trans-1,2-diaminocyclohexane with 3,5-dichloro-2-hydroxyacetophenone or 5-chloro-4-methyl-2-hydroxyacetophenone, respectively. Both these ligands formed well-defined complexes with vanadium (IV) and (V) under suitable experimental conditions. These complexes have been characterized by elemental analysis, molar conductivity, magnetic moments, infrared, electronic spectra, ESR, X-ray diffraction, and thermogravimetric analysis. X-ray diffraction study of [VO(L²)]·H₂O complex indicated its monoclinic crystal system with a = 9.8525, b = 23.6271, c = 9.0904 Å, and β = 97.87°. The complexes [VO(L¹)]·H₂O and [VO(L²)]·H₂O have been examined as catalysts for epoxidation of styrene in the presence of hydrogen peroxide as oxidant. The IR spectral data suggest that both the ligands behave as dibasic tetradentate chelating agent with ONNO donor atoms sequence toward cental metal ion.     

Giant gain enhancement in surface‐confined resonant Stimulated Brillouin Scattering

The notion that Stimulated Brillouin Scattering (SBS) is primarily defined by bulk material properties has been overturned by recent work on nanoscale waveguides. It is now understood that boundary forces of radiation pressure and electrostriction appearing in such highly confined waveguides can make a significant contribution to the Brillouin gain. Here, this concept is extended to show that gain enhancement does not require nanoscale or subwavelength features, but generally appears where optical and acoustic fields are simultaneously confined near a free surface or material interface. This situation routinely occurs in whispering gallery resonators (WGRs), making gain enhancements much more accessible than previously thought. To illustrate this concept, the first full‐vectorial analytic model for SBS in WGRs is developed, including optical boundary forces, and the SBS gain in common silica WGR geometries is computationally evaluated. These results predict that gains 10⁴ times greater than the predictions of scalar theory may appear in WGRs even in the 100 μm size range. Further, trapezoidal cross‐section microdisks can exhibit very large SBS gains approaching 10² m⁻¹W⁻¹. With resonant amplification included, extreme gains on the order of 10¹² m⁻¹W⁻¹ may be realized, which is 10⁸ times greater than the highest predicted gains in linear waveguide systems.

     

Persistent spin oscillations in a spin-orbit-coupled superconductor

Quasi-two-dimensional superconductors with tunable spin-orbit coupling are very interesting systems with properties that are also potentially useful for applications. In this Letter we demonstrate that these systems exhibit undamped collective spin oscillations that can be excited by the application of a supercurrent. We propose to use these collective excitations to realize persistent spin oscillators operating in the frequency range of 10 GHz-1 THz.     

A block monotone iterative method for numerical solutions of nonlinear elliptic boundary value problems

The aim of this article is to develop a new block monotone iterative method for the numerical solutions of a nonlinear elliptic boundary value problem. The boundary value problem is discretized into a system of nonlinear algebraic equations, and a block monotone iterative method is established for the system using an upper solution or a lower solution as the initial iteration. The sequence of iterations can be computed in a parallel fashion and converge monotonically to a maximal solution or a minimal solution of the system. Three theoretical comparison results are given for the sequences from the proposed method and the block Jacobi monotone iterative method. The comparison results show that the sequence from the proposed method converges faster than the corresponding sequence given by the block Jacobi monotone iterative method. A simple and easily verified condition is obtained to guarantee a geometric convergence of the block monotone iterations. The numerical results demonstrate advantages of this new approach. © 2009 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2011