Breaking the barrier to fast electron transfer

A study of the electron transfer for a non-glycosylated redox variant of GOx is reported, immobilised onto an electrode via a polyhistidine tag. The non-glycosylated variant allows the enzyme to be brought closer to the electrode, and within charge transfer distances predicted by Marcus' theory. The enzyme-electrode-hybrid shows direct very fast reversible electrochemical electron transfer, with a rate constant of ~ 350 s^− 1 under anaerobic conditions. This is 2 orders of magnitude faster than the enzyme-free flavin adenine dinucleotide (FAD). These results are discussed in the context of the conformation of FAD in the active site of GOx. Further data, presented in the presence of oxygen, show a reduced electron transfer rate (~ 160 s^− 1) that may be associated with the oxygen interaction with the histidines in the active site. These residues are implicated in the proton transfer mechanism and thus suggest that the presence of oxygen may have a profound effect in attenuating the direct electron transfer rate and thus moderating ‘short-circuit’ incidental electron transfer between proteins.     

Stable configurations in hybrid nematic cells in relation to thickness and surface order

The phase diagram of equilibrium configurations in thin hybrid nematic cells has been investigated in the framework of Landau-de Gennes theory extended to include weak surface anchoring. Surface interactions linear in the tensor order parameter were assumed and biaxiality was induced by the surfaces. It was found that in addition to the usual configuration where the director bends continuously from one plate to the other, there is also a possible configuration where bend does not occur, but where there is an eigenvalue exchange; i.e. the eigenvector of the tensor order parameter associated with the eigenvalue of the largest magnitude is different in different regions of the cell. Furthermore, for very small cell thickness a third possibility occurs: the eigenvector corresponding to the eigenvalue with the largest magnitude is uniform throughout the cell; it is either parallel or perpendicular to both plates depending upon the dominant surface interaction. Continuous transitions occur between the different configurations.     

Biocatalysis made to order

Recombinant DNA technology is now being explored to engineer enzyme molecules. It has many far-reaching applications in biocatalytic processes of enzyme engineering. The facts have pursued certain important industrial, biomedical, and environmental problems. These current excitements are mainly focused on the basis of gene cloning and in vitro mutagenesis for overproduction and redesigning of enzymes, as well as their probable implications in industry, antibiotic research, and waste degradation.     

Fluidity of water confined down to subnanometer films

A surface force balance with extremely high sensitivity and resolution for measuring shear forces across thin films has been used to investigate directly the dynamic properties of salt-free water (so-called conductivity water) in a gap between two atomically smooth solid surfaces. Our results reveal that no shear stress can be sustained by water (within our resolution and shear rates) down to films of thickness D = D0 = 0.0 +/- 0.3 nm. At short range (D < 3.5 +/- 1 nm), an attractive van der Waals (vdW) force between the surfaces causes a jump into a flat adhesive contact at D0, at which the surfaces rigidly couple. Analysis of the jump behavior reveals that the viscosity of water remains within a factor of 3 or so of its bulk value down to D0. This contrasts sharply with the case of confined nonassociating liquids, whose effective viscosity increases by many orders of magnitude at film thicknesses lower than about five to eight monolayers. We attribute this to the fundamentally different mechanisms of solidification of organic liquids and of water. In the former case, the density increase induced in the films by the confinement promotes solidification, while, in the case of water, such densification (due to vdW attraction between the liquid molecules and the confining walls), in agreement with bulk behavior, suppresses the tendency of the water to solidify.     

Donor-acceptor oligorotaxanes made to order

Five donor–acceptor oligorotaxanes made up of dumbbells composed of tetraethylene glycol chains, interspersed with three and five 1,5‐dioxynaphthalene units, and terminated by 2,6‐diisopropylphenoxy stoppers, have been prepared by the threading of discrete numbers of cyclobis(paraquat‐p‐phenylene) rings, followed by a kinetically controlled stoppering protocol that relies on click chemistry. The well‐known copper(I)‐catalyzed alkyne–azide cycloaddition between azide functions placed at the ends of the polyether chains and alkyne‐bearing stopper precursors was employed during the final kinetically controlled template‐directed synthesis of the five oligorotaxanes, which were characterized subsequently by ¹H NMR spectroscopy at low temperature (233 K) in deuterated acetonitrile. The secondary structures, as well as the conformations, of the five oligorotaxanes were unraveled by spectroscopic comparison with the dumbbell and ring components. By focusing attention on the changes in chemical shifts of some key probe protons, obtained from a wide range of low‐temperature spectra, a picture emerges of a high degree of folding within the thread protons of the dumbbells of four of the five oligorotaxanes—the fifth oligorotaxane represents a control compound in effect—brought about by a combination of C? H???O and π–π stacking interactions between the π‐electron‐deficient bipyridinium units in the rings and the π‐electron‐rich 1,5‐dioxynaphthalene units and polyether chains in the dumbbells. The secondary structures of a foldamer‐like nature have received further support from a solid‐state superstructure of a related [3]pseudorotaxane and density functional calculations performed thereon.     

Protein modulators made to order

Small molecules were created by diversity-oriented synthesis and subsequently subjected to microarray-based screening for their ability to bind a protein of interest. This general two-step method proved powerful in generating highly specific modulators of protein function.     

Breaking of ketene bonds during HCl addition to trimethylsilylketene

IR spectroscopy is coupled with the matrix isolation technique to study the reaction of trimethylsilylketene with HCl. From 50 K trimethylsilylketene reacts with hydrogen chloride, leading to the cleavage of the Si-C bond and the formation of trimethylsilyl chloride and acetyl chloride, through intermediate trimethylsilylacetyl chloride which was identified. A reaction profile for this result is proposed based on a theoretical study carried out at the DFT level.     

Determination of phenols by HPLC down to PPT levels

Summary A mixture of eleven priority pollutant phenols (PPP) have been separated using a Dionex 4000 chromatograph; VAL-U-PAK ODS (250 × 4.6 mm I.D.) column; eluents A: CH₃CN/0.2M NaH₂PO₄/CH₃COOH 40/60/1 and B: CH₃CN with/without gradient; detectors: UV-254 nm and Pulse Amperometric Detector (PAD) with glassycarbon electrode (+1.20V). With preconcentration unit (guard RP-18 column) on line and PAD, detectability limit at ten ppt was achieved. The method has been applied for determination of PPP in tap-water and in leachates from sanitary and industrial landfill sites.     

Breaking 12% efficiency in flexible organic solar cells by using a composite electrode

The performance of flexible organic solar cells(OSCs)significantly relies on the quality of transparent flexible electrode.Here,we used silver nanowires(AgNWs)with various weight ratios to dope high-conductive poly(3,4-ethylenedioxythiophene):polystyrene sulfonate(PH1000)to optimize the optical and electronic properties of PH1000 film.A high-quality flexible composite electrode PET/Ag-mesh/PH1000:AgNWs-20 with smooth surface,a low sheet resistance of 6Ω/sq and a high transmittance of 86%at 550-nm wavelength was obtained by doping 20 wt%AgNWs to PH1000(PH1000:AgNWs-20).The flexible OSCs based on the PET/Ag-mesh/PH1000:AgNWs-20 electrode delivered a power conversion efficiency(PCE)of12.07%with an open circuit voltage(V_(oc))of 0.826 V,a short-circuit current density(J_(sc))of 20.90 m A/cm~2and a fill factor(FF)of69.87%,which is the highest reported PCE for the flexible indium-tin oxide(ITO)-free OSCs.This work demonstrated that the flexible composite electrodes of PET/Ag-mesh/PH1000:AgNWs are promising alternatives for the conventional PET/ITO electrode,and open a new avenue for developing high-performance flexible transparent electrode for optoelectronic devices.     

Electrochemical hydrogen evolution in hydroxide hydrate down to 110 K

Electrochemical hydrogen evolution was studied at an Au electrode in liquid and solid tetramethylammonium hydroxide hydrate (CH₃)₄NOH·10H₂O (m.p. 253 K) down to almost 110 K. The current–potential relationships were obtained by slow scan voltammetry. The lowering of temperature causes substantial decrease of the slope of linear Tafel plots. This was interpreted as a decrease of charge transfer coefficient from 0.37 at room temperature to 0.01 at 113 K. The activation energy of the electrochemical hydrogen evolution at temperatures below 200 K is equal to 0.25±0.03 eV and is larger than the activation energy of the electrolyte conductivity.     

A simple method to selectively scale down the self-interaction correction

The method of Perdew and Zunger is commonly used to correct the self-interaction error of approximate density functionals. However, it has been shown that this orbital-based self-interaction correction (SIC) tends to overcorrect and often impairs molecular properties. We have recently proposed a method to improve the performance of the SIC by scaling it down in many-electron regions. In this communication, we present a simplification of this scheme. For every occupied orbital, we introduce a scaling factor determined by the ratio of the orbital density to the total spin-density. Thus, the magnitude of the correction is adjusted depending on how much orbital densities overlap with one another. Such a modification of the Perdew-Zunger SIC does not add any appreciable time to the computation, but significantly improves the accuracy for a number of benchmark properties.     

Mass‐biased partitioning to enhance middle down proteomics analysis

A strategy is presented for enhancing the middle‐down analysis of higher mass peptides recovered from complex protein mixtures. Following a 30‐min digestion of multiple myeloma cell lysate by an acid cleavage reaction that is selective for aspartic acid, a 3000 Da membrane filter is used to bifurcate the peptide product mixture, and the heavier fraction is subjected to collisional activation with precursor selection that excludes charge states below +4. Filtration and charge state selection are shown to provide significant increases in the number of peptides identified in the mass range above 3000 Da and in information about protein sequences. Copyright © 2013 John Wiley & Sons, Ltd.     

Determination of vapour pressures down to 0.01 Pa by headspace gas-chromatography

Summary The application of automated headspace gaschromatography for the determination of vapour pressures is described. The vapour pressures determined at different temperatures for 1-chloronaphthalene, anthracene, -hexachlorocyclohexane and hexachlorobenzene agree well with the data from literature. The lower limit of applicability of the method is in the range of 0.01 Pa.

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Bestimmung von Dampfdrucken bis hinab zu 0,01 Pa durch Dampfraum-GC

Zusammenfassung Die Anwendung der automatischen Dampfraumanalyse zur Dampfdruckbestimmung wird beschrieben. Die bei verschiedenen Temperaturen ermittelten Dampfdrucke von 1-Chlornaphthalin, Anthracen, -Hexachlorocyclohexan und Hexachlorbenzol befinden sich in guter Übereinstimmung mit den Literaturangaben. Die untere Grenze der Anwendbarkeit liegt bei 0,01 Pa.

     

Enhancement of the nematic order of polar liquid crystals in thin cells

Experimental observations show that the nematic order parameter (S) is significantly enhanced as the thickness of the cell is reduced. However, calculations based on earlier theories are not in good agreement with the experimental data. We earlier developed a molecular mean field model that assumes that the medium with polar molecules consists of inter-converting anti-parallel and parallel pairs, to explain the molecular origin of the ‘two lengths’ model. The model has been used to explain effects such as double re-entrance and the effect of electric field on the nematic–isotropic transition temperature, T _NI. We have recently extended the Maier–Saupe (M–S) theory using an empirical variation of surface potential, to account for the enhancement in which a molecule near the surface is assumed to feel the mean field potential (M–S type) and also the surface-induced potential. Variation in the density of the medium due to variation of S has been ignored. In the present paper, the change in the relative proportion of the parallel pairs due to changes in the density of the medium is included in the M–S theory with the surface potential. This results in improved agreement with the experimental data.     

Tuning up or down the UV-induced apoptosis in Chinese hamster ovary cells with cell cycle inhibitors

Exposure to UVC induces apoptosis in Chinese hamster ovary (CHO.K1) cells. While studying the underlying mechanism, we found that a variety of cell cycle inhibitors, including colcemid, hydroxyurea and mimosine, enhance the UV-induced apoptosis in these cells. Such enhancement was not dependent on the cell cycle progression nor was it related to the difference in UV sensitivity at different phases of the cell cycle. The expression of p21(waf1/cip1), a general cyclin-dependent kinase (CDK) inhibitor, was deficient in CHO.K1 cells. Ectopic overexpression of the human p21 markedly increased the survival rates of the UV-irradiated cells in the presence of colcemid. In addition, roscovitine, a small-molecule inhibitor of CDK, also inhibited the UV-induced apoptosis. These observations suggest that deregulation of CDK activity may be critical in the UV-induced apoptosis in CHO.K1 cells.