Remarkable bismuth-gold alloy decorated on MWCNT for glucose electrooxidation: the effect of bismuth promotion and optimization via response surface methodology

In this study, the carbon nanotube supported gold, bismuth, and gold-bismuth(Au/MWCNT, Bi/MWCNT, and Au-Bi/MWCNT) nanocatalysts were prepared with NaBH₄ reduction method at varying molar atomic ratio for glucose electrooxidation (GAEO). The synthesized nanocatalysts at different Au: Bi atomic ratios are characterized via x - ray diffraction (XRD), transmission electron microscopy (TEM), and N₂ adsorption-desorption. For the performance of AuBi/MWCNT for GAEO, electrochemical measurements are performed by using different electrochemical techniques namely cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). Monometallic Au/MWCNT exhibits higher activity than Bi/MWCNT with 256.57 mA/mg (0.936 mA/cm²) current density. According to CV results, Au₈₀Bi₂₀/MWCNT nanocatalyst has the highest GAEO activity with the mass activity of 320.15 mA/mg (1.133 mA/cm²). For Au₈₀Bi₂₀/MWCNT, central composite design (CCD) is utilized for optimum conditions of the electrode preparation. Au₈₀Bi₂₀/MWCNT nanocatalysts are promising anode nanocatalysts for direct glucose fuel cells (DGFCs).     

Stress-Dependent Porosity and Permeability of Porous Rocks Represented by a Mechanistic Elastic Cylindrical Pore-Shell Model

The stress dependency of the porosity and permeability of porous rocks is described theoretically by representing the preferential flow paths in heterogeneous porous rocks by a bundle of tortuous cylindrical elastic tubes. A Lamé-type equation is applied to relate the radial displacement of the internal wall of the cylindrical elastic tubes and the porosity to the variation of the pore fluid pressure. The variation of the permeability of porous rocks by effective stress is determined by incorporating the radial displacement of the internal wall of the cylindrical elastic tubes into the Kozeny–Carman relationship. The fully analytical solutions of the mechanistic elastic pore-shell model developed by combining the Lamé and Kozeny–Carman equations are shown to lead to very accurate correlations of the stress dependency of both the porosity and the permeability of porous rocks.

     

Parameterization of Biot–Willis Effective-Stress Coefficient for Deformation and Alteration of Porous Rocks

Transport in Porous Media - The effective stress coefficient is an essential geomechanical parameter required for estimation of the effective stress acting upon the subsurface reservoir porous rock...     

Synthesis of thick TiO2 nanotube arrays on transparent substrate by anodization technique

A vertically aligned transparent TiO₂ nanotube array (tTNA) of significantly enhanced tube-length 6.3 ± 0.3 µm was successfully synthesized on glass substrates by anodization technique with ammonium fluoride and ethylene glycol-based electrolyte. Prior to anodization, Ti metal was deposited on glass substrate by facing-target sputtering technique with various sputtering pressures at substrate temperature 420 °C to find out the relation between the structural properties of the Ti layer and the corresponding growth mechanism of the TiO₂ nanotube. The study revealed that structural properties of Ti metal layers and its adhesion to the glass substrate, which can be tuned by deposition parameters, play an important role in the process of tTNA formation.     

Efficient intramolecular general acid catalysis of nucleophilic attack on a phosphodiester

The hydrolysis of methyl 8-dimethylamino-1-naphthyl phosphate 4 and its reactions with a representative range of nucleophiles are catalyzed by the dimethylammonium group at acidic pH with rate accelerations of the order of 106. The reaction persists up to pH 7 because the strong intramolecular hydrogen bond, which is the key to efficient general acid catalysis, is present also in the reactant. The sensitivity to the basicity of the nucleophile (Br?nsted beta(nuc) = 0.29) lies between values measured previously for mono- and triesters. The comparisons suggest that general acid catalyzed reactions of phosphate mono- or diesters with strongly basic oxyanion nucleophiles (like those derived from a serine oxygen or a bound water molecule in an enzyme active site) will be fastest when their negative charges are neutralized by protonation. Reactions with NH2OH and its N-methylated derivatives show an apparent alpha-effect, but NH2OMe reacts no faster than a primary amine of similar basicity. It is suggested that the reaction involving NH2OH as an oxygen nucleophile proceeds through the pre-equilibrium formation of the tautomer H3N+-O- as the active nucleophile: ab initio calculations support this idea.     

Electronic structure and spectro-structural correlations of Fe(III)Zn(II) biomimetics for purple acid phosphatases: relevance to DNA cleavage and cytotoxic activity

Purple acid phosphatases (PAPs) are a group of metallohydrolases that contain a dinuclear Fe(III)M(II) center (M(II) = Fe, Mn, Zn) in the active site and are able to catalyze the hydrolysis of a variety of phosphoric acid esters. The dinuclear complex [(H(2)O)Fe(III)(μ-OH)Zn(II)(L-H)](ClO(4))(2) (2) with the ligand 2-[N-bis(2-pyridylmethyl)aminomethyl]-4-methyl-6-[N'-(2-pyridylmethyl)(2-hydroxybenzyl) aminomethyl]phenol (H(2)L-H) has recently been prepared and is found to closely mimic the coordination environment of the Fe(III)Zn(II) active site found in red kidney bean PAP (Neves et al. J. Am. Chem. Soc. 2007, 129, 7486). The biomimetic shows significant catalytic activity in hydrolytic reactions. By using a variety of structural, spectroscopic, and computational techniques the electronic structure of the Fe(III) center of this biomimetic complex was determined. In the solid state the electronic ground state reflects the rhombically distorted Fe(III)N(2)O(4) octahedron with a dominant tetragonal compression aligned along the μ-OH-Fe-O(phenolate) direction. To probe the role of the Fe-O(phenolate) bond, the phenolate moiety was modified to contain electron-donating or -withdrawing groups (-CH(3), -H, -Br, -NO(2)) in the 5-position. The effects of the substituents on the electronic properties of the biomimetic complexes were studied with a range of experimental and computational techniques. This study establishes benchmarks against accurate crystallographic structural information using spectroscopic techniques that are not restricted to single crystals. Kinetic studies on the hydrolysis reaction revealed that the phosphodiesterase activity increases in the order -NO(2) ←Br ←H ←CH(3) when 2,4-bis(dinitrophenyl)phosphate (2,4-bdnpp) was used as substrate, and a linear free energy relationship is found when log(k(cat)/k(0)) is plotted against the Hammett parameter σ. However, nuclease activity measurements in the cleavage of double stranded DNA showed that the complexes containing the electron-withdrawing -NO(2) and electron-donating -CH(3) groups are the most active while the cytotoxic activity of the biomimetics on leukemia and lung tumoral cells is highest for complexes with electron-donating groups.     

The Use of 2,2,2-Trichloro-1-Arylethanones as Benzoylating Agents

The preparation of several amides and hydrazides from the reaction of the title compounds with different nitrogen nucleophiles is shown to be a general high-yield conversion of synthetic utility.     

Effects of Atmospheric Plasma Pretreatments on Pectinase Efficiency in Bioscouring of Linen Fabrics

Pectinase enzyme treatment subsequent to atmospheric air- or argon-plasma surface modification was applied in linen fabric preparation. Wettability by water drop test, wickability by thin layer wicking experiment, residual pectin content and colour of the fabrics were characterized. Results clearly proved that the efficiency of pectinase in improving linen water absorbency can be significantly enhanced by plasma pretreatment. Argon-plasma pretreatment followed by a Beisol PRO enzyme treatment reduced the wetting time considerably and resulted in a fabric surface that has been characterized by the lowest water contact angle (86.6??). All the applied treatments increased the energy of the fibre surface. The alkaline scoured, the argon-plasma treated and the argon-plasma-pectinase treated samples have been characterized by the highest $ \gamma_{S}^{total} $ values. Plasma treatment significantly decreased the whiteness and increased the yellowness of the raw fabrics. However, the enzyme treatment applied after the plasma treatment has overcome the colour differences.     

Polymers containing hydroxamate groups: nanoreactors for hydrolysis of phosphoryl esters

A polyhydroxamicalkanoate (PHA) polymer containing the functional groups hydroxamic acid and carboxylic acid with the ability to accelerate dephosphorylation reactions is proposed. The methodology used to prepare this polymer favored the position of the two functional groups next to each other, which allows for the cooperativity between these groups. This cooperative effect has an important role when one wants to mimic enzymes. The catalytic effect promoted by the polymer was evaluated on the cleavage of the bis(2,4-dinitrophenyl) phosphate (BDNPP) and diethyl 2,4-dinitrophenyl phosphate (DEDNPP) esters. Indeed, PHA was very efficient and promiscuous because it increased the rate of both reactions by a factor of up to 10(6)-fold. Isothermal titration calorimetry (ITC) experiments showed that the presence of PHA aids the formation of cetyltrimethylammonium bromide (CTABr) micelles. Thus, the effect of the cationic surfactant CTABr on the dephosphorylation of BDNPP by PHA was also investigated, and it was observed that, when CTABr is added to PHA, the reaction is ca. 15-fold faster compared to the reaction when only PHA is present.