Structures and energetics of darunavir and active site amino acids of native and mutant HIV–1 protease: a computational study

Structural Chemistry - Quantum chemical calculations have been performed at the M06–2X/6–31G(d,p) level of theory to investigate the strength and nature of interactions between the...     

Alkaline oxygen evolution: exploring synergy between fcc and hcp cobalt nanoparticles entrapped in N-doped graphene

Herein, we report a Mott-Schottky catalyst by entrapping cobalt nanoparticles inside the N-doped graphene shell (Co@NC). The Co@NC delivered excellent oxygen evolution activity with an overpotential of merely 248 mV at a current density of 10 mA cm^–2 with promising long-term stability. The importance of Co encapsulated in NC has further been demonstrated by synthesizing Co nanoparticles without NC shell. The synergy between the hexagonal close-packed (hcp) and face-centered cubic (fcc) Co plays a major role to improve the OER activity, whereas the NC shell optimizes the electronic structure, improves the electron conductivity, and offers a large number of active sites in Co@NC. The density functional theory calculations have revealed that the hcp Co has a dominant role in the surface reaction of electrocatalytic oxygen evolution, whereas the fcc phase induces the built-in electric field at the interfaces with N-doped graphene to accelerate the H⁺ ion transport.     

Meshless method for nonlinear heat conduction analysis of nano-composites

Carbon nanotubes (CNTs) may become ideal reinforcing materials for high-performance nano-composites due their exceptional properties. Still, much work is needed to be done before the potentials of CNT based composites can be fully realized. The evaluation of effective material properties of nano-composites is one of many difficult tasks. Simulations using continuum mechanics approach can play a significant role in the analysis of these composites. In the present work, nonlinear heat conduction analysis of CNT based composites has been carried out using continuum mechanics approach. Element free Galerkin method has been applied as a numerical tool. Thermal conductivities of nanotube and polymer matrix are assumed to vary quadratically with temperature. Picard and quasi-linearization schemes have been utilized to obtain the solution of a system of nonlinear equations. Cylindrical representative volume element has been used to evaluate the thermal properties of nano-composites. Present simulations show that the temperature dependent matrix thermal conductivity has a significant effect on the equivalent thermal conductivity of the composite, whereas temperature dependent nanotube thermal conductivity has a small effect on the equivalent thermal conductivity of the composite. The results obtained by Picard method have been found almost similar with those obtained by quasi-linearization approach.     

Apparent Molar Volume and Isentropic Compressibility for the Binary Systems {Methyltrioctylammonium Bis(trifluoromethylsulfonyl)imide + Methyl Acetate or Methanol} and (Methanol + Methyl Acetate) at <Emphasis Type="Italic">T</Emphasis>=298.15, 303.15, 308.15 and 313.15 K and Atmospheric Pressure

The densities and speeds of sound for binary mixtures containing the solute ionic liquid (IL) methyltrioctylammonium bis(trifluoromethylsulfonyl)imide ([MOA]⁺[Tf₂N]⁻), solute/solvent methanol, and solvent methyl acetate have been measured at 298.15, 303.15, 308.15 and 313.15 K at atmospheric pressure. The binary mixtures studied are ([MOA]⁺[Tf₂N]⁻ + methyl acetate or methanol), and (methanol + methyl acetate). The apparent molar volume, V _φ and the apparent molar isentropic compressibility, k _φ , have been evaluated from the experimental density and speed of sound data, respectively. The parameters of a Redlich–Mayer type equation were fitted to the apparent molar volume and apparent molar isentropic compressibility data. The apparent molar volume and apparent molar isentropic compressibility at infinite dilution, V_f⁰V_{\phi}^{0} and k_f⁰k_{\phi}^{0}, respectively, of the binary solutions have also been calculated at each temperature. The infinite dilution apparent molar volume indicates that intermolecular interactions for (IL + methyl acetate) mixtures are stronger than for (IL + methanol) mixtures at all temperatures except at 298.15 K, and that V_f⁰V_{\phi}^{0} for the (IL + methyl acetate or methanol) binary systems increases with an increase in temperature. For the (methanol + methyl acetate) system the intermolecular interaction are weaker and V_f⁰V_{\phi}^{0} also increases with an increase in temperature. Values of the infinite dilution apparent molar expansibility, E_f⁰E_{\phi}^{0}, indicate that the interaction between (IL + methyl acetate) is greater than for (IL + methanol) and (methanol + methyl acetate).     

Diterpene glycosides from Stevia rebaudiana

Three novel diterpene glycosides were isolated for the first time from the commercial extract of the leaves of Stevia rebaudiana, along with several known steviol glycosides, namely stevioside, rebaudiosides A-F, rubusoside and dulcoside A. The new compounds were identified as 13-[(2-O-β-D-glucopyranosyl-3-O-β-D-glucopyranosyl-β-D-glucopyranosyl)oxy] ent-kaur-15-en-19-oic acid, 13-[(2-O-β-D-glucopyranosyl-3-O-β-D-glucopyranosyl-β-D-glucopyranosyl)oxy]-16β-hydroxy-ent-kauran-19-oic acid and 13-methyl-16-oxo-17-nor-ent-kauran-19-oic acid-β-D-glucopyranosyl ester on the basis of extensive 2D NMR and MS spectroscopic data as well as chemical studies.     

Chemical modification of L-glutamine to alpha-amino glutarimide on autoclaving facilitates Agrobacterium infection of host and non-host plants: A new use of a known compound

Background

Accidental autoclaving of L-glutamine was found to facilitate the Agrobacterium infection of a non host plant like tea in an earlier study. In the present communication, we elucidate the structural changes in L-glutamine due to autoclaving and also confirm the role of heat transformed L-glutamine in Agrobacterium mediated genetic transformation of host/non host plants.

Results

When autoclaved at 121°C and 15 psi for 20 or 40 min, L-glutamine was structurally modified into 5-oxo proline and 3-amino glutarimide (α-amino glutarimide), respectively. Of the two autoclaved products, only α-amino glutarimide facilitated Agrobacterium infection of a number of resistant to susceptible plants. However, the compound did not have any vir gene inducing property.

Conclusions

We report a one pot autoclave process for the synthesis of 5-oxo proline and α-amino glutarimide from L-glutamine. Xenobiotic detoxifying property of α-amino glutarimide is also proposed.     

Possible role of Lewis acid catalysis in the oxidation of alkenes and α,β-unsaturated ketones using bleomycin-zn(ii) and bleomycin-fe(iii)-iodosylbenzene in aqueous methanol

C₆H₅IO in CH₃OH-H₂0 is activated towards electrophilic attack upon various alkenes by Fe(ClO₄).9H₂O, FE(III) bleomycin and ZN(II) bleomycin. The results imply that direct transfer of oxygen from an Fe(V)=0 intermediate is not required in the mechanism of oxygenation by iron-containing species, and that much earlier work is questionable as models for biological oxygenation.     

Some polishing experiments on copper in a hyperbolic cell

Some polishing experiments have been carried out on copper anodes in a hyperbolic cell designed by Gilmont and Walton, using orthophosphoric acid as the electrolyte. The results obtained have been compared to those obtained in similar experiments in a Hull cell. It has been found that very similar bands of different reflectivity and polishes are found to form in both the cells. These bands shift with time and a study of such displacements has been made. The results are briefly discussed.     

Degradation Studies of Polycaprolactone in Banana Fibers Reinforced Thermoplastics Composites

In this paper we report the fabrication, properties and degradation studies of banana fibers–reinforced thermoplastic polymers. In order to impart hydrophobicity to the fibers and also to concomitantly increase interfacial bond strength, which is a critical factor for obtaining better mechanical properties of composites, banana fibers were treated with sodium hydroxide (5% and 10% for 4 h), sebacoyl chloride (SC) (0.5 g, 4 h), or toluene diisocyanate (TDl) (1.5 mL, 4 h). Mechanical properties of banana fibers treated with TDl were not affected to any significant extent, but there was an increase in tensile strength of fibers treated with sodium hydroxide (NaOH). Deterioration in mechanical properties was observed upon SC treatment. In thermograssimetre analogue (TGA) studies fibers showed initial mass loss (6.5%–9.5%) in the 50–150°C temperature region. Major weight loss occurred above 200°C. Scanning electron microscope (SEM) studies revealed an increase in surface roughness after alkali treatment. High density polyethylene (HDPE) modified by blending with poly (ε‐caprolactone) (80:20 w/w) was used as a thermoplastic matrix. Composites were fabricated by using 1 cm long banana fibers; the weight fraction of fibers was varied from 0.05–0.13. An increase in weight fraction of fibers resulted in an increase in tensile strength and modulus and decrease in elongation at break. Thin sheets and dumbbells were used for enzymatic and chemical hydrolysis degradation tests. The degradation of the material was monitored by weight change and loss of mechanical properties. The enzymatic degradation in (PCL) presence of Pseudomonas cepacia lipase (PCL) gave appreciable weight loss in PCL and blended materials.     

Structures and energetics of complexation of metal ions with ammonia,water, and benzene: A computational study

Quantum chemical calculations have been performed at CCSD(T)/def2‐TZVP level to investigate the strength and nature of interactions of ammonia (NH₃), water (H₂O), and benzene (C₆H₆) with various metal ions and validated with the available experimental results. For all the considered metal ions, a preference for C₆H₆ is observed for dicationic ions whereas the monocationic ions prefer to bind with NH₃. Density Functional Theory–Symmetry Adapted Perturbation Theory (DFT‐SAPT) analysis has been employed at PBE0AC/def2‐TZVP level on these complexes (closed shell), to understand the various energy terms contributing to binding energy (BE). The DFT‐SAPT result shows that for the metal ion complexes with H₂O electrostatic component is the major contributor to the BE whereas, for C₆H₆ complexes polarization component is dominant, except in the case of alkali metal ion complexes. However, in case of NH₃ complexes, electrostatic component is dominant for s‐block metal ions, whereas, for the d and p‐block metal ion complexes both electrostatic and polarization components are important. The geometry (M⁺–N and M⁺–O distance for NH₃ and H₂O complexes respectively, and cation–π distance for C₆H₆ complexes) for the alkali and alkaline earth metal ion complexes increases down the group. Natural population analysis performed on NH₃, H₂O, and C₆H₆ complexes shows that the charge transfer to metal ions is higher in case of C₆H₆ complexes. © 2016 Wiley Periodicals, Inc.