Water oxidation kinetics of nanoporous BiVO4 photoanodes functionalised with nickel/iron oxyhydroxide electrocatalysts

In this work, spectroelectrochemical techniques are employed to analyse the catalytic water oxidation performance of a series of three nickel/iron oxyhydroxide electrocatalysts deposited on FTO and BiVO₄, at neutral pH. Similar electrochemical water oxidation performance is observed for each of the FeOOH, Ni(Fe)OOH and FeOOHNiOOH electrocatalysts studied, which is found to result from a balance between degree of charge accumulation and rate of water oxidation. Once added onto BiVO₄ photoanodes, a large enhancement in the water oxidation photoelectrochemical performance is observed in comparison to the un-modified BiVO₄. To understand the origin of this enhancement, the films were evaluated through time-resolved optical spectroscopic techniques, allowing comparisons between electrochemical and photoelectrochemical water oxidation. For all three catalysts, fast hole transfer from BiVO₄ to the catalyst is observed in the transient absorption data. Using operando photoinduced absorption measurements, we find that water oxidation is driven by oxidised states within the catalyst layer, following hole transfer from BiVO₄. This charge transfer is correlated with a suppression of recombination losses which result in remarkably enhanced water oxidation performance relative to un-modified BiVO₄. Moreover, despite similar electrocatalytic behaviour of all three electrocatalysts, we show that variations in water oxidation performance observed among the BiVO₄/MOOH photoanodes stem from differences in photoelectrochemical and electrochemical charge accumulation in the catalyst layers. Under illumination, the amount of accumulated charge in the catalyst is driven by the injection of photogenerated holes from BiVO₄, which is further affected by the recombination loss at the BiVO₄/MOOH interface, and thus leads to deviations from their behaviour as standalone electrocatalysts.

Elucidating the role of charge accumulation and reaction kinetics in governing the performance of Ni/Fe oxyhydroxides as electrocatalysts and as co-catalysts on BiVO₄ photoanodes water oxidation.     

Enzymes produced by soil fungi following microaerobic growth on lignocellulosic materials

Four fungal strains able to grow under low oxygenation conditions were selected and used in studies to determine the production of enzymes (endoglucanases, exoglucases, β-glucosidase, and peroxidases) that promote the degradation of lignocellulosic materials. The capacity of the fungi to ferment lignocellulosic materials was also investigated. Avicel, xylan, Whatman no. 1 filter paper, or agroindustrial residues were used as carbon sources in a medium containing mineral salts, vitamins, and cysteine as a reducing agent, under either microaerophilic or combined conditions (aerobic followed by microaerophilic conditions). The results obtained with strains Q10, H2, and LH5 suggest that they prefer a low oxygen concentration for growth and enzyme production. However, strain F20 seems to need higher levels of oxygenation. Lignocellulolytic activities were detected in all strains but varied with the carbon source used for growth. In general, the highest levels of these activities were produced by strain H2 under microaerophilic conditions. Ethanol and other nongaseous fermentation products were detected following high-performance liquid chromatography analysis using a Supelcogel C-610H column, demonstrating the fermentative capability of these strains.     

Characterization of aromatic-thiol π-type hydrogen bonding and phenylalanine-cysteine side chain interactions through ab initio calculations and protein database analyses

In this study, the aromatic-thiol π hydrogen bonding and phenylalanine-cysteine side chain interactions are characterized through both molecular orbital calculations on a C₆H₆-HSCH₃ model complex and database analyses of 609 X-ray protein structures. The aromatic-thiol π hydrogen bonding interaction can achieve a stabilization energy of 2.60 kcal mol^?1, and is stronger than the already documented aromatic-hydroxyl and aromatic-amino hydrogen bonds. However, the occurrence of the aromatic-thiol hydrogen bond is rather rare in proteins. This is because most of the thiol groups participate in the formation of either disulphide bonds or stronger S—H…O (or N) ‘normal’ hydrogen bonds in a protein environment. Interactions between the side chains of phenylalanine and cysteine residues are characterized as the phenyl(Phe)(HSCH₂-)(Cys) interaction. The bonding energy for such interactions is approximately 3.71 kcal mol-¹ and is achieved in a geometric arrangement with an optimal phenyl(Phe)-(HS-)(Cys) π-type hydrogen bonding interaction. The interaction is very sensitive to the orientation of the two lone electron pairs on the sulphur atom relative to the π electron cloud of the phenyl ring. Accordingly, the interaction configurations that can accomplish a significant bonding energy exist only within a narrow configurational space. The database analysis of 609 experimental X-ray protein structures demonstrates that only 268 of the 1620 cysteine residues involve such phenylalanine-cysteine side chain interactions. Most of these interactions occur in the form of π (aromatic)-lone pair(sulphur) attractions, and correspond to a bonding energy less than 1.5 kcal mol^?1. A few were identified as the aromatic-thiol hydrogen bond with a bonding energy of 2.0–3.6 kcal mol^?1.     

Comments on the effects of overstimulation on microphonic sensitivity

Utilizing the differential recording technique, microphonic isopotential measurements were carried out before and after overstimulation. Recordings were made in the first and third turns of guinea pig cochleas. The exposure stimuli were pure tones of frequencies near the best frequency of the recording site. The results were suggestive of differences in the effects of overstimulation in different turns of the cochlea, at least as they are manifested electrophysiologically.     

Dynamics of photogenerated holes in nanocrystalline α-Fe2O3 electrodes for water oxidation probed by transient absorption spectroscopy

Transient absorption spectroscopy on the μs-s time scale is used to monitor the yield and decay dynamics of photogenerated holes in nanocrystalline hematite photoanodes. In the absence of a positive applied bias, these holes are observed to undergo rapid electron-hole recombination. The application of a positive bias results in the generation of long-lived (3 ± 1 s lifetime) photoholes.     

Short-Chain Branching in Polyethylene and Poly(vinyl Chloride) Using Pyrolysis Hydrogenation Gas Chromatography and 13C Nuclear Magnetic Resonance Analysis

This study compares the use of pyrolysis hydrogenation gas chromatography (PHGC) and ¹³C Fourier transform nuclear magnetic resonance (FTNMR) methods for the analysis of reference polyethylene (PE) samples, ethylene-α-olefin copolymers, and specially prepared poly(vinyl chloride) (PVC) samples which were reduced to their PE skeletal structures. The nature and relative quantities of the short branches along the polymer chains were determined using both techniques. Improved high-resolution PHGC data, obtained with a fused silica capillary separation column, gave results which were in satisfactory agreement with the ¹³C FTNMR data. This approach confirms that detailed microstructural information can be obtained with these methods by using carefully controlled experimental conditions and appropriate reference systems.     

Thieno[3,2-b]thiophene-diketopyrrolopyrrole-containing polymers for high-performance organic field-effect transistors and organic photovoltaic devices

We report the synthesis and polymerization of a novel thieno[3,2-b]thiophene-diketopyrrolopyrrole-based monomer. Copolymerization with thiophene afforded a polymer with a maximum hole mobility of 1.95 cm(2) V(-1) s(-1), which is the highest mobility from a polymer-based OFET reported to date. Bulk-heterojunction solar cells comprising this polymer and PC(71)BM gave a power conversion efficiency of 5.4%.