Influence of the charge transport layers on charge extraction and interface recombination in quasi-two-dimensional perovskite solar cells.

The identification of electronic processes at the charge-selective contact buried interface is very important for photovoltaic research. The main loss of perovskite solar cell (PeSCs) is generally bound up with its charge transfer layer. Especially, the current record for the highest power conversion efficiency of quasi-two-dimensional (quasi-2D) PeSCs is achieved by inverted device configurations, compared with the efficiency of upright structures. This study investigated, the carrier recombination and charge extraction in quasi-2D PeSCs by leveraging scanning probe microscope technology, steady-state photoluminescence (PL) measurements, and time-resolved PL spectroscopy. The built-in potential in quasi-2D bulk perovskite can be regarded as a budget to hinder energy loss in inverted device configurations. Interface photogenerated recombination in quasi-2D PeSCs can be fully comprehended only when the complete device is under consideration. Our work underlines the significance of considering restructuring loss from the perspective of the complete device instead of individual layers or interfaces in quasi-2D PeSCs.

Synthesis of globotriose-modified peptides for the preparation of a colorimetric biosensor to detect Shiga toxins.

Globotriose (Gal-α1, 4-Gal-ß1, 4-Glc) is involved in binding with Shiga toxins (Stxs) produced by Shigella dysenteriae and certain pathogenic Escherichia coli strains which could cause severe gastroenteritis and hemolytic uremic syndrome (HUS). Thus, this trisaccharide group and its derivatives provide potentials in the development of carbohydrate-based diagnostic and therapeutic reagents against bacterial infection. Instead of the tedious chemical synthesis of globotriose or its glycoconjugates, we reported a multi-step (step-wise) enzymatic synthesis system containing glucosyltransferase (ApNGT, E.C. 4.3.3.5), ß-1, 4-galactosyltransferase (LgtB, E.C. 2.4.1.22) and α-1, 4-galactosyltransferase (LgtC, E.C. 2.4.1.44) to produce globotriose-containing glycopeptides. In addition, based on the specific binding between Stxs and globotriose, a cost-efficient, convenient, ultra-sensitive and specific colorimetric biosensor was further constructed to detect Stxs using glycoconjugated Au@Fe-TFPA-COP (globotriose@Au@Fe-TFPA-COP) as a nanoenzyme catalyst. We estimate that this method conveniently applied in the detection of Stx-producing bacteria and associated infectious diseases.

Dependence of the Heterogeneity of Grain Boundaries on Adjacent Grains in Perovskites and Its Impact on Photovoltage.

In polycrystalline perovskites, grain boundaries (GBs) that isolate grains determine the optoelectronic properties of a semiconductor, and hence affect the photovoltaic performance of a solar cell. Photocurrent and photovoltage are affected by the microscopic structure of perovskites but are difficult to quantify on the intragrain length scale and are often treated as homogeneous within the photoactive layer. Here, the nanoscale through-film and lateral photoresponse of large-grained perovskite are studied by photoconductive atomic force microscopy. Photocurrent collection along GBs relies on the formation of adjacent grains, exhibiting GB to GB heterogeneity. Regarding to the spatially correlated heterogeneity, the photovoltage of grains deduced from the photoresponse curves at specific positions is larger than that of GBs by up to 0.4 V, suggesting that the photovoltage loss mainly originates from the shunting of GBs through the whole perovskite layer. These spatial heterogeneities are alleviated by depositing a capping layer onto the perovskite layer, highlighting the role of the inserted layer between the perovskite and electrode in real solar cells. This research reveals the heterogeneity of GBs and its influence on photovoltage that actually occurs in virtual solar cells, which is crucial for optimizing perovskite-based solar cells.

Aged sol-gel solution-processed texture tin oxide for high-efficient perovskite solar cells.

Mesoporous n-i-p perovskite solar cells (PeSCs) demonstrate attractive potential for obtaining high power conversion efficiencies (PCEs), by employing inorganic electron transport layers (ETLs). However, these ETLs composed of dual layers (a condense layer and a mesoporous layer) suffer the composite process and high sintering temperature. Here, we demonstrate a simple and efficient process to improve the device performance of PeSCs by using a textured SnO2 film. Self-aged sol-gel SnO2 solution after spin coating results in a textured structure without sacrificing the surface coverage. Excellent light trapping ability is achieved by optimizing the aged time of sol-gel SnO2 solution, which mimics the evolution of the conventional mesoporous layer. Such a SnO2 textured structure provides a large contact area for rapid charge extraction, and alleviates interfacial recombination loss. Therefore, this PeSC yields an optimal PCE of 19%, which is prominent in state-of-the-art SnO2-based devices. These results indicate that one-step solution processed SnO2 with a textured structure offers a simple and efficient way to improve the device performance of PeSCs without a complex process.

Integration of Zn-Ag and Zn-Air Batteries: A Hybrid Battery with the Advantages of Both.

We report a hybrid battery that integrates a Zn-Ag battery and a Zn-air battery to utilize the unique advantages of both battery systems. In the positive electrode, Ag nanoparticles couple the discharge behaviors through the two distinct electrochemical systems by working as the active reactant and the effective catalyst in the Zn-Ag and Zn-air reactions, respectively. In the negative electrode, in situ grown Zn particles provide large surface areas and suppress the dendrite, enabling the long-term operating safety. The battery first exhibits two-step voltage plateaus of 1.85 and 1.53 V in the Zn-Ag reaction, after which a voltage plateau of 1.25 V is delivered in the Zn-air reaction, and the specific capacity reaches 800 mAh gZn-1. In addition, excellent reversibility and stability with maintaining high energy efficiency of 68% and a capacity retention of nearly 100% at 10 mA cm-2 are demonstrated through 100 cycles, outperforming both conventional Zn-air and Zn-Ag batteries. This work brings forth a conceptually novel high-performance battery, and more generally opens up new vistas for developing hybrid electrochemical systems by integrating the advantages from two distinct ones.

Production of human blood group B antigen epitope conjugated protein in Escherichia coli and utilization of the adsorption blood group B antibody.

BACKGROUND: In the process of ABO-incompatible (ABOi) organ transplantation, removal of anti-A and/or B antibodies from blood plasma is a promising method to overcome hyperacute rejection and allograft loss caused by the immune response between anti-A and/or B antibodies and the A and/or B antigens in the recipient. Although there are commercial columns to do this work, the application is still limited because of the high production cost. RESULTS: In this study, the PglB glycosylation pathway from Campylobacter jejuni was exploited to produce glycoprotein conjugated with Escherichia coli O86:B7 O-antigen, which bears the blood group B antigen epitope to absorb blood group B antibody in blood. The titers of blood group B antibody were reduced to a safe level without changing the clotting function of plasma after glycoprotein absorption of B antibodies in the plasma. CONCLUSIONS: We developed a feasible strategy for the specific adsorption/removal of blood group antibodies. This method will be useful in ABOi organ transplantation and universal blood transfusion.

L-Rhamnose Enhances the Immunogenicity of Melanoma-Associated Antigen A3 for Stimulating Antitumor Immune Responses.

Vaccines based on melanoma-associated antigens (MAGEs) present a promising strategy for tumor immunotherapy, albeit with weak immunogenicity. In this study, the xenoantigen L-rhamnose (Rha) was chemically conjugated with truncated MAGE-A3 (tMAGE-A3) to generate Rha-tMAGE-A3. The product showed good antigenicity with anti-Rha antibodies purified from human serum. FITC-labeled Rha-tMAGE-A3 was detected in THP-1 human macrophage cells via the anti-Rha antibody-dependent antigen uptake process. Furthermore, peripheral blood mononuclear cells (PBMCs) stimulated with Rha-tMAGE-A3 in the presence of anti-Rha antibodies showed better cytotoxicity toward A375 human melanoma cells surfaced by MAGE-A3 antigen compared to PBMCs stimulated with tMAGE-A3. All data reveal that linking of Rha epitopes to MAGE enhances the immunogenicity of MAGE by harnessing the immune effector functions of human naturally existing anti-Rha antibodies. Rha epitopes could become immunogenicity enhancers of tumor associated antigens in the development of tumor immunotherapies.

Facile Enzymatic Synthesis of Ketoses.

Studies of rare ketoses have been hampered by a lack of efficient preparation methods. A convenient, efficient, and cost-effective platform for the facile synthesis of ketoses is described. This method enables the preparation of difficult-to-access ketopentoses and ketohexoses from common and inexpensive starting materials with high yield and purity and without the need for a tedious isomer separation step.

Bioconversion of D-galactose to D-tagatose: continuous packed bed reaction with an immobilized thermostable L-arabinose isomerase and efficient purification by selective microbial degradation.

The continuous enzymatic conversion of D-galactose to D-tagatose with an immobilized thermostable L-arabinose isomerase in packed-bed reactor and a novel method for D-tagatose purification were studied. L-arabinose isomerase from Thermoanaerobacter mathranii (TMAI) was recombinantly overexpressed and immobilized in calcium alginate. The effects of pH and temperature on D-tagatose production reaction catalyzed by free and immobilized TMAI were investigated. The optimal condition for free enzyme was pH 8.0, 60°C, 5 mM MnCl(2). However, that for immobilized enzyme was pH 7.5, 75°C, 5 mM MnCl(2). In addition, the catalytic activity of immobilized enzyme at high temperature and low pH was significantly improved compared with free enzyme. The optimum reaction yield with immobilized TMAI increased by four percentage points to 43.9% compared with that of free TMAI. The highest productivity of 10 g/L h was achieved with the yield of 23.3%. Continuous production was performed at 70°C; after 168 h, the reaction yield was still above 30%. The resultant syrup was then incubated with Saccharomyces cerevisiae L1 cells. The selective degradation of D-galactose was achieved, obtaining D-tagatose with the purity above 95%. The established production and separation methods further potentiate the industrial production of D-tagatose via bioconversion and biopurification processes.

Characterization and synthetic application of a novel beta1,3-galactosyltransferase from Escherichia coli O55:H7.

A beta1,3-galactosyltransferase (WbgO) was identified in Escherichia coli O55:H7. Its function was confirmed by radioactive activity assay and structure analysis of the disaccharide synthesized with the recombinant enzyme. WbgO requires a divalent metal ion, either Mn(2+) or Mg(2+), for its activity and is active between pH 6.0-8.0 with a pH optimum of 7.0. N-acetylglucosamine (GlcNAc) and oligosaccharides with GlcNAc at the non-reducing end were shown to be its preferred substrates and it can be used for the synthesis of type 1 glycan chains from these substrates. Together with a recombinant bacterial GlcNAc-transferase, benzyl beta-lacto-N-tetraoside was synthesized with the purified WbgO to demonstrate the synthetic utility of WbgO.

Structural basis and catalytic mechanism for the dual functional endo-beta-N-acetylglucosaminidase A.

Endo-beta-N-acetylglucosaminidases (ENGases) are dual specificity enzymes with an ability to catalyze hydrolysis and transglycosylation reactions. Recently, these enzymes have become the focus of intense research because of their potential for synthesis of glycopeptides. We have determined the 3D structures of an ENGase from Arthrobacter protophormiae (Endo-A) in 3 forms, one in native form, one in complex with Man(3)GlcNAc-thiazoline and another in complex with GlcNAc-Asn. The carbohydrate moiety sits above the TIM-barrel in a cleft region surrounded by aromatic residues. The conserved essential catalytic residues - E173, N171 and Y205 are within hydrogen bonding distance of the substrate. W216 and W244 regulate access to the active site during transglycosylation by serving as "gate-keepers". Interestingly, Y299F mutation resulted in a 3 fold increase in the transglycosylation activity. The structure provides insights into the catalytic mechanism of GH85 family of glycoside hydrolases at molecular level and could assist rational engineering of ENGases.

[Construction of the Man8 GlcNAc2 glycosylation Saccharomyces cerevisiae mutant strain].

In Saccharomyces cerevisiae, protein glycosylation passed two different N-linked modification pathways after the export of predominantly Man8 GlcNAc2-containing glycoproteins from ER to the Golgi. The core oligosaccharide undergoes maturation in the Golgi resulting in a Man8-13 GlcNAc2 structure. Alternatively, core structures may be hypermannosylated with up to 200 mannose residues composing of a backbone of alpha1,6-mannosyl residues with branched alpha1, 2- and alpha1,3-mannosyl side chains. Mnn1p and Och1p play an important role in this process. The null disruption of MNN1, OCH1 was replaced by the S. cerevisiae URA3, HIS3, respectively. To characterize the N-glycosylation in the mnn1 och1 mutant, mannoproteins were obtained by hot citrate buffer extraction after the mnn1 och1 cells were crumbled. The extracted mannoprotein was precipitated by ethanol, and further purified by concanavalin A-sepharose 4B. The N-oligomannose saccharides were released from mannoprotein by PNGase F digestion, and then peptides and detergents were removed by passage through ion exchange columns. For desalting, glycans were applied to porous graphitic-carbon cartridge. 2-aminopyridine pyridylaminated sugars were profiled and purified by size fractionation HPLC with Shim-pack cle-NH2 column, and result showed dominantly a single peak. MALDI TOF/MS analysis ofthis peak revealed that its molecular weight was 1796.5Da, which corresponds to the calculated mass of Man8 GlcNAc2-PA. These results indicated that disruptions of MNN1 and OCH1 eliminated the hypermannosylation of the N-linked glycans, and glycoproteins were glycosylated with a single core type glycan, Man8 GlcNAc2, in the mnn1 och1 mutant.

Cloning and characterization of GDP-perosamine synthetase (Per) from Escherichia coli O157:H7 and synthesis of GDP-perosamine in vitro.

GDP-perosamine synthetase (Per, E.C. not yet classified) is important to the synthesis of Escherichia coli O157:H7 O-antigen. The mutant in per gene can disrupt the synthesis of O157 O-antigen. In this study, GDP-perosamine synthetase was cloned from E. coli O157:H7 and over-expressed in E. coli BL21 (DE3). The recombinant His-tagged Per fusion protein was a decamer with molecular weight of 431 kDa. The optimal pH value of this recombinant protein was 7.5. The divalent ions had no significant effect on Per-catalyzed reaction. The K(m) and K(cat)/K(m) for GDP-4-keto-6-deoxy-d-mannose were 0.09 mM and 2.1 x 10(5)M(-1)S(-1), and those for l-glutamate were 2mM and 0.52 x 10(5)M(-1)S(-1), respectively. Per was used to synthesize GDP-perosamine from GDP-mannose together with recombinant GDP-mannose dehydratase (GMD, E.C. 4.2.1.47). The purified GDP-perosamine was identified by MS and NMR. In summary, this work provided a feasible approach for the synthesis of GDP-perosamine which can lead to the study of LPS biosynthesis of pathogenic E. coli O157:H7.

Influence of N-glycosylation on Saccharomyces cerevisiae morphology: a golgi glycosylation mutant shows cell division defects.

The N-glycosylation mutants (mnn1 and mnn1 och1) show different morphological characteristics at the restrictive and nonpermissive temperature. We deleted the MNN1 to eliminate the terminal alpha1, 3-linked mannose of hypermannosylation and deleted the OCH1 to block the elongation of the main backbone chain. The mnn1 cells exhibited no observable change with respect to the wild-type strain at 28 degrees C and 37 degrees C, but the mnn1 och1 double mutant exhibited defects in cell cytokinesis, showed a slower growth rate, and became temperature-sensitive. Meanwhile, the mnn1 och1 mutant tended to aggregate, which was probably due to the glycolsylation defect. Loss of mannosyl-phosphate-accepting sites in this mutant migth result in reduced charge repulsion between cell surfaces. Pyridylaminated glycans were profiled and purified through an NH(2) column by size-fractionation high-performance liquid chromatography. Matrix assisted laser desoption/ionization time of flight mass spectrometry (MALDI TOF/MS) analysis of the N-glycan structure of the mnn1 och1 mutant revealed that the main component is Man(8)GlcNAc(2).

A new fermentation process allows large-scale production of tetra-N-acetyl-chitotetraosyl allosamizoline.

A new compound 2, possessing a tetra-N-acetyl-chitotetraosyl moiety as a constituent, was synthesized by bacterial fermentation, which used allosamizoline 1 as the initial acceptor. A 2-binding chitinase assay, indicated that the chitinase was inactivated by 2 with IC50 = 0.03 microg/mL.

Immobilization of UDP-galactose 4-epimerase from Escherichia coli on the yeast cell surface.

UDP-galactose 4-epimerase (EC 5.1.3.2, Gal E) from Escherichia coli catalyzes the reversible reaction between UDP-galactose and UDP-glucose. In this study, the Gal E gene from E. coli, coding UDP-galactose 4-epimerase, was cloned into pYD1 plasmid and then transformed into Saccharomyces cerevisiae EBY100 for expression of Gal E on the cell surface. Enzyme activity analyses with EBY100 cells showed that the enzyme displayed on the yeast cell surface was very active in the conversion between UDP-Glc and UDP-Gal. It took about 3 min to reach equilibrium from UDP-galactose to UDP-glucose.

Structure-function relations of carbohydrates by neoglycolipid arrays.

The work presented herein is a new noncovalent glycoarray assembly method for microplates created by simply mixing together a carbohydrate and a tetradecylamine. alpha-D-Mannopyranoside, alpha-D-glucopyranoside, and alpha-D-galactopyranoside were utilized in model studies and product formations were detected by lectin binding. The method can be extended to study the steric hindrance effect of carbohydrate-protein interactions, namely the structure-function relations of carbohydrates.

Chemo-enzymatic synthesis of tetra-N-acetyl-chitotetraosyl allosamizoline.

A new compound 7, possessing a tetra-N-acetyl-chitotetraosyl moiety as a constituent, was synthesized by bacterial fermentation which used allosamizoline 6 as the initial acceptor.