Electrodeposition of BiVO4 with needle-like flower architecture for high performance photoelectrochemical splitting of water

Photoelectrochemical (PEC) water splitting is a green and sustainable approach capable of driving mass hydrogen production in the future. To realize this vision, development of a well-performing photoelectrode is highly demanded. In this comprehensive study, electrodeposition technique was applied for fabricating BiVO₄ films by regulating the deposition time from 1 min until 9 min. Interestingly, the morphology, crystallinity, chemical structure, and optical properties of BiVO₄ films depend strongly on the deposition time. It is found that BiVO₄ layer deposited for 7 min with a cross-section thickness of around 321.1–326.5 nm showed the optimum performance, whereby the photocurrent reached up to ~0.32 mA/cm^?2 at 1.23 V vs. RHE. The deposited BiVO₄ represents tiny and long petals, similar to “needle” nanostructures, which is embedded closely into compact agglomerates. Such morphology enables the BiVO₄ films to perform efficiently as photoanode in PEC cells. Besides, high crystallinity is detected from the sharp peaks of XRD and Raman analysis, as well as good light absorption capability that are the main contributors to the enhancement of PEC performance. In addition to the facile fabrication offered by electrodeposition method, the non-toxic attributes and the impressive PEC performance of the optimum BiVO₄ layer could serve as an interesting option for other applications such as gas sensors, solar cells, degradation of pollutants and photocatalytic water splitting.     

Mass transfer and current distribution on a metallic wire

The current and copper deposit distribution on a metallic fibre (stainless steel, diameter of 2 mm) was studied numerically and experimentally. The experimental copper deposit was measured with an optical microscope and the current distribution was deduced. The influence of electrolysis time on copper deposit distribution was also studied. A typical current tertiary distribution was observed. The experiment with a longer electrolysis time exhibited a larger current variation around the wire. A numerical study of this problem was also carried out. The simulation involved a laminar and turbulent flow solver together with a numerical model for the mass transfer of ionic species due to diffusion, migration and convection. A good correlation was found between simulated and experimental results for experiments with a short electrolysis time. This numerical model was then used to study the influence of the flow velocity and the diffusion coefficient on the current density and on the average mass transfer around a wire a few microns in diameter. The general relation: for 0.02 < Re_p < 14.22 and 1000 < Sc < 12,000 was obtained. Comparison with data available in the literature demonstrates good agreement between our model and previous results.     

Mesoporous beta zeolite obtained by desilication

Zeolite beta crystals (Si/Al = 35) synthesized in fluoride medium were treated in aqueous 0.2 M NaOH solution for mesopore formation by selective extraction of framework silicon. A 16 parallel-batch reactor was used to study the influence of the treatment time and temperature on the physico-chemical properties of the zeolites, which were characterized by ICP-OES, XRD, N₂ adsorption at 77 K, SEM, TEM, DRIFTS, and in situ ATR-IR. Alkaline treatment of H-beta within the optimal window of Si/Al ratios identified for other zeolite families leads to extensive silicon extraction at mild treatment conditions. This originates substantial mesoporosity and presumably improved transport, but negatively impacts on the microporous and acidic properties of the resulting sample. Consequently, the alkaline-treated beta zeolites show lower catalytic activity in the acid-catalyzed liquid-phase benzene alkylation than the purely microporous parent material. The relatively low stability of framework aluminum in BEA, compared to MFI and MOR, is detrimental for the controlled mesopore formation by Si dissolution, since aluminum cannot optimally exert its pore-directing role.     

A Cactus‐Derived Toxin‐Like Cystine Knot Peptide with Selective Antimicrobial Activity

Naturally occurring cystine knot peptides show a wide range of biological activity, and as they have inherent stability they represent potential scaffolds for peptide‐based drug design and biomolecular engineering. Here we report the discovery, sequencing, chemical synthesis, three‐dimensional solution structure determination and bioactivity of the first cystine knot peptide from Cactaceae (cactus) family: Ep‐AMP1 from Echinopsis pachanoi. The structure of Ep‐AMP1 (35 amino acids) conforms to that of the inhibitor cystine knot (or knottin) family but represents a novel diverse sequence; its activity was more than 500 times higher against bacterial than against eukaryotic cells. Rapid bactericidal action and liposome leakage implicate membrane permeabilisation as the mechanism of action. Sequence homology places Ec‐AMP1 in the plant C6‐type of antimicrobial peptides, but the three dimensional structure is highly similar to that of a spider neurotoxin.     

4“-O-Alkylated α-Galactosylceramide Analogues as iNKT-Cell Antigens: Synthetic,Biological, and Structural Studies

Invariant natural killer T-cells (iNKT) are a glycolipid-responsive subset of T-lymphocytes that fulfill a pivotal role in the immune system. The archetypical synthetic glycolipid, α-galactosylceramide (α-GalCer), whose molecular framework is inspired by a group of amphiphilic natural products, remains the most studied antigen for iNKT-cells. Nonetheless, the potential of α-GalCer as an immunostimulating agent is compromised by the fact that this glycolipid elicits simultaneous secretion of Th1- and Th2-cytokines. This has incited medicinal chemistry efforts to identify analogues that are able to perturb the Th1/Th2 balance. In this work, we present the synthesis of an extensive set of 4“-O-alkylated α-GalCer analogues, which were evaluated in vivo for their cytokine induction. We have found that conversion of the 4”-OH group to ether moieties decreases the immunogenic potential in mice relative to α-GalCer. Yet, the benzyl-modified glycolipids are able to produce a distinct pro-inflammatory immune response. The crystal structures suggest an extra hydrophobic interaction between the benzyl moiety and the α2-helix of CD1d.     

Structures of the Apo and FAD‐Bound Forms of 2‐Hydroxybiphenyl 3‐monooxygenase (HbpA) Locate Activity Hotspots Identified by Using Directed Evolution

The FAD‐dependent monooxygenase HbpA from Pseudomonas azelaica HBP1 catalyses the hydroxylation of 2‐hydroxybiphenyl (2HBP) to 2,3‐dihydroxybiphenyl (23DHBP). HbpA has been used extensively as a model for studying flavoprotein hydroxylases under process conditions, and has also been subjected to directed‐evolution experiments that altered its catalytic properties. The structure of HbpA has been determined in its apo and FAD‐complex forms to resolutions of 2.76 and 2.03 Å, respectively. Comparisons of the HbpA structure with those of homologues, in conjunction with a model of the reaction product in the active site, reveal His48 as the most likely acid/base residue to be involved in the hydroxylation mechanism. Mutation of His48 to Ala resulted in an inactive enzyme. The structures of HbpA also provide evidence that mutants achieved by directed evolution that altered activity are comparatively remote from the substrate‐binding site.     

Characterization of Aptamer-Protein Complexes by X-ray Crystallography and Alternative Approaches

Aptamers are oligonucleotide ligands, either RNA or ssDNA, selected for high-affinity binding to molecular targets, such as small organic molecules, proteins or whole microorganisms. While reports of new aptamers are numerous, characterization of their specific interaction is often restricted to the affinity of binding (K(D)). Over the years, crystal structures of aptamer-protein complexes have only scarcely become available. Here we describe some relevant technical issues about the process of crystallizing aptamer-protein complexes and highlight some biochemical details on the molecular basis of selected aptamer-protein interactions. In addition, alternative experimental and computational approaches are discussed to study aptamer-protein interactions.     

Kinetic studies of alkyl formate hydrolysis using formic acid as a catalyst

BACKGROUND: The hydrolysis of methyl formate is the major industrial process for the production of formic acid. The aim of the work is to determine the reaction kinetics quantitatively in the presence of formic acid catalyst, develop a mathematical model for the reaction system and estimate the kinetic parameters for the purpose of optimization. RESULTS: Liquid phase hydrolysis kinetics of alkyl formates (ethyl and methyl formate) was studied in an isothermal batch reactor at 80–110 °C and 20 bar nitrogen pressure. The catalyst of choice was formic acid. The reaction rate was enhanced but the formic acid product yield was slightly suppressed relative to the uncatalysed system. A kinetic model comprising mass balances and rate equations was developed and the kinetic and equilibrium parameters included in the rate equations were estimated from the experimental data with non‐linear regression analysis. CONCLUSION: The model was able to predict the experimental results successfully. The results obtained were compared quantitatively with an earlier model involving alkyl formate hydrolysis in a neutral aqueous solution. Copyright © 2011 Society of Chemical Industry     

Evolution of Flavylium-Based Color Systems in Plants: What Physical Chemistry Can Tell Us

Anthocyanins are the basis of the color of angiosperms, 3-deoxyanthocyanins and sphagnorubin play the same role in mosses and ferns, and auronidins are responsible for the color in liverworts. In this study, the color system of cyanidin-3-O-glucoside (kuromanin) as a representative compound of simpler anthocyanins was fully characterized by stopped flow. This type of anthocyanin cannot confer significant color to plants without intra- or intermolecular interactions, complexation with metals or supramolecular structures as in Commelina communis. The anthocyanin’s color system was compared with those of 3-deoxyanthocyanins and riccionidin A, the aglycone of auronidins. The three systems follow the same sequence of chemical reactions, but the respective thermodynamics and kinetics are dramatically different.