Showing papers on "Substrate (chemistry) published in 2015"
TL;DR: In this paper, the morphology of PbI2 was found to be of crucial importance for the performance of CH3NH3PbI3 perovskite solar cells under high relative humidity.
Abstract: We report here an efficient method for preparing high efficiency CH3NH3PbI3 perovskite solar cells under high relative humidity, where the morphology of PbI2 was found to be of crucial importance. CH3NH3PbI3 was formed on a mesoporous TiO2 layer by a two-step spin coating method. During the first-step spin-coating procedure to form a PbI2 layer, an FTO glass substrate was pre-heated at temperatures ranging from room temperature (without pre-heating) to 60 °C. An average power conversion efficiency (PCE) of 11.16% was achieved without pre-heating, which was improved to 15.31% as the temperature of the substrate (Tsub) was raised to 50 °C. The pre-heated substrate led to higher photocurrent and voltage than the non-pre-heated one. When Tsub increased to 60 °C, the PCE declined to 10.49% due to the large portion of unreacted PbI2. Compared to the non-pre-heated substrate, unreacted PbI2 was present on the pre-heated substrates after the second-step spin-coating of CH3NH3I as confirmed by X-ray diffraction and time-of-flight secondary ion mass spectroscopy (TOF-SIMS) depth profile analyses. The improved crystallinity of PbI2 induced by substrate pre-heating was responsible for incomplete conversion of PbI2 to CH3NH3PbI3. Nevertheless, the increase in photocurrent and voltage by pre-heating was attributed to better pore filling and surface coverage of the perovskite layer, as observed by focused ion beam assisted scanning electron microscopy (FIB-SEM) images, which was associated with the morphology of the PbI2 layer. According to a study on the effect of CH3NH3PbI3 thickness controlled by the concentration of PbI2, the substrate temperature was found to play a predominant role in determining the photovoltaic performance rather than thickness. A best PCE of 15.76% was achieved along with a photocurrent density of 21.27 mA cm−2, a voltage of 1.033 V and a fill factor of 0.718 from the perovskite solar cell prepared under 50% relative humidity.
294 citations
TL;DR: The green synthesis of palladium nanoparticles using Hippophae rhamnoides linn leaf extract and their application as heterogeneous catalysts for the Suzuki-Miyaura coupling in water was reported in this paper.
Abstract: During this study, we report the green synthesis of palladium nanoparticles using Hippophae rhamnoides Linn leaf extract and their application as heterogeneous catalysts for the Suzuki–Miyaura coupling in water. The synthesized nanoparticles are characterized by XRD, SEM, TEM and UV–vis techniques. This method has the advantages of high yields, simple methodology, and elimination of ligand, organic solvent and homogeneous catalysts and easy work-up. Furthermore, the catalyst exhibits high catalytic activity, superior cycling stability and excellent substrate applicability.
235 citations
TL;DR: Ultrathin printable graphene supercapacitors are demonstrated, based on solution-processed electrochemically exfoliated graphene hybrid films on an ultrathin poly(ethylene terephthalate) substrate, exhibiting an unprecedented volumetric capacitance, an ultrahigh scan rate, and AC line-filtering performance.
Abstract: Ultrathin printable graphene supercapacitors are demonstrated, based on solution-processed electrochemically exfoliated graphene hybrid films on an ultrathin poly(ethylene terephthalate) substrate, exhibiting an unprecedented volumetric capacitance of 348 F cm(-3) , an ultrahigh scan rate of 2000 V s(-1) , and AC line-filtering performance.
230 citations
TL;DR: The synthesis and study of self-propelled microparticles powered by enzymatic reactions and their directed movement in substrate concentration gradient is reported.
Abstract: Active biocompatible systems are of great current interest for their possible applications in drug or antidote delivery at specific locations. Herein, we report the synthesis and study of self-propelled microparticles powered by enzymatic reactions and their directed movement in substrate concentration gradient. Polystyrene microparticles were functionalized with the enzymes urease and catalase using a biotin-streptavidin linkage procedure. The motion of the enzyme-coated particles was studied in the presence of the respective substrates, using optical microscopy and dynamic light scattering analysis. The diffusion of the particles was found to increase in a substrate concentration dependent manner. The directed chemotactic movement of these enzyme-powered motors up the substrate gradient was studied using three-inlet microfluidic channel architecture.
220 citations
TL;DR: Progress on immobilization and microarray techniques of peptides has facilitated the progress and commercial application of chip-based peptide biosensors in clinical diagnosis, and peptides may play a generalist role in peptide-based bios Sensors.
199 citations
TL;DR: This study describes high-yield enzymatic hydrogen production from biomass sugars and an engineered reaction rate increase achieved through the use of kinetic modeling.
Abstract: The use of hydrogen (H2) as a fuel offers enhanced energy conversion efficiency and tremendous potential to decrease greenhouse gas emissions, but producing it in a distributed, carbon-neutral, low-cost manner requires new technologies. Herein we demonstrate the complete conversion of glucose and xylose from plant biomass to H2 and CO2 based on an in vitro synthetic enzymatic pathway. Glucose and xylose were simultaneously converted to H2 with a yield of two H2 per carbon, the maximum possible yield. Parameters of a nonlinear kinetic model were fitted with experimental data using a genetic algorithm, and a global sensitivity analysis was used to identify the enzymes that have the greatest impact on reaction rate and yield. After optimizing enzyme loadings using this model, volumetric H2 productivity was increased 3-fold to 32 mmol H2⋅L−1⋅h−1. The productivity was further enhanced to 54 mmol H2⋅L−1⋅h−1 by increasing reaction temperature, substrate, and enzyme concentrations—an increase of 67-fold compared with the initial studies using this method. The production of hydrogen from locally produced biomass is a promising means to achieve global green energy production.
198 citations
TL;DR: The substrate scope and the ability to accept chemically different types of substrates are shown to be reflected in conserved patterns of amino acids around the active site, which facilitates annotation and identification of biocatalytically relevant enzymes and protein engineering thereof.
183 citations
TL;DR: Cy5 labeled corresponding functional ssDNA for different analytes associated with graphene oxide (ssDNA-GO) were employed as core detection sensors to sensitively report the presence of the different type of chemicals as well as enlarge the chemical compatibility, which made it possible to simultaneous detect multiple chemicals under a same chemical microenvironment.
178 citations
TL;DR: By plasma-enhanced chemical vapor deposition, a molybdenum disulfide (MoS2) thin film is synthesized directly on a wafer-scale plastic substrate at below 300 °C, revealing its potential for flexible sensing devices.
Abstract: By plasma-enhanced chemical vapor deposition, a molybdenum disulfide (MoS2 ) thin film is synthesized directly on a wafer-scale plastic substrate at below 300 °C. The carrier mobility of the films is 3.74 cm(2) V(-1) s(-1) . Also, humidity is successfully detected with MoS2 -based sensors fabricated on the flexible substrate, which reveals its potential for flexible sensing devices.
174 citations
TL;DR: Key to success was a subsequent direct ring-opening oligomerization of in situ formed ε-CL in the aqueous phase by using lipase A from Candida antarctica, thus efficiently solving the product inhibition problem and leading to the formation of oligo-ε-CL.
Abstract: Poly-e-caprolactone (PCL) is chemically produced on an industrial scale in spite of the need for hazardous peracetic acid as an oxidation reagent. Although Baeyer-Villiger monooxygenases (BVMO) in principle enable the enzymatic synthesis of e-caprolactone (e-CL) directly from cyclohexanone with molecular oxygen, current systems suffer from low productivity and are subject to substrate and product inhibition. The major limitations for such a biocatalytic route to produce this bulk chemical were overcome by combining an alcohol dehydrogenase with a BVMO to enable the efficient oxidation of cyclohexanol to e-CL. Key to success was a subsequent direct ring-opening oligomerization of in situ formed e-CL in the aqueous phase by using lipase A from Candida antarctica, thus efficiently solving the product inhibition problem and leading to the formation of oligo-e-CL at more than 20 g L(-1) when starting from 200 mM cyclohexanol. This oligomer is easily chemically polymerized to PCL.
164 citations
TL;DR: The production of fungal laccase was optimized from local isolate of Pleurotus ostreatus using solid state fermentation using Factorial design to study the effect of several nutrients on enzyme production.
TL;DR: LOX structures combine to explain how similar enzymes with conserved catalytic machinery differ in product, but not substrate, specificities.
Abstract: Many intriguing facets of lipoxygenase (LOX) catalysis are open to a detailed structural analysis. Polyunsaturated fatty acids with two to six double bonds are oxygenated precisely on a particular carbon, typically forming a single chiral fatty acid hydroperoxide product. Molecular oxygen is not bound or liganded during catalysis, yet it is directed precisely to one position and one stereo configuration on the reacting fatty acid. The transformations proceed upon exposure of substrate to enzyme in the presence of O2 (RH + O2 → ROOH), so it has proved challenging to capture the precise mode of substrate binding in the LOX active site. Beginning with crystal structures with bound inhibitors or surrogate substrates, and most recently arachidonic acid bound under anaerobic conditions, a picture is consolidating of catalysis in a U-shaped fatty acid binding channel in which individual LOX enzymes use distinct amino acids to control the head-to-tail orientation of the fatty acid and register of the selected pentadiene opposite the non-heme iron, suitably positioned for the initial stereoselective hydrogen abstraction and subsequent reaction with O2 . Drawing on the crystal structures available currently, this review features the roles of the N-terminal β-barrel (C2-like, or PLAT domain) in substrate acquisition and sensitivity to cellular calcium, and the α-helical catalytic domain in fatty acid binding and reactions with O2 that produce hydroperoxide products with regio and stereospecificity. LOX structures combine to explain how similar enzymes with conserved catalytic machinery differ in product, but not substrate, specificities.
TL;DR: The proposed SERS system may open up a new opportunity for chemical and biological assay applications by effectively concentrating analytes in close proximity to the Raman hot spots domains between the adjacent AgNPs.
Abstract: Surface-enhanced Raman scattering (SERS) signals are intensively dominated by the Raman hot spots and distance between analyte molecules and metallic nanostructures. Herein, an efficient SERS substrate was developed by in situ synthesis of silver nanoparticles (AgNPs) on the surface of MIL-101 (Fe), a typical metal-organic framework (MOF). The as-prepared SERS substrate combines the numerous Raman hot spots between the high-density Ag NPs and the excellent adsorption performance of MOFs, making it an excellent SERS substrate for highly sensitive SERS detection by effectively concentrating analytes in close proximity to the Raman hot spots domains between the adjacent AgNPs. The resulting hybrid material was used for ultrasensitive SERS detection of dopamine based on the peroxidase-like activity of MIL-101 (Fe) by utilizing the enzyme-linked immunosorbent assay (ELISA) colorimetric substrate, 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) diammonium salt (ABTS) as a SERS marker. This new developed method showed good linearity in the range from 1.054 pM to 210.8 nM for dopamine with the correlation coefficient of 0.992, detection limit of approximately 0.32 pM [signal-to-noise ratio (S/N) = 3], and acceptable recoveries ranging from 99.8% to 108.0% in human urine. These results predict that the proposed SERS system may open up a new opportunity for chemical and biological assay applications.
TL;DR: Results indicate that the initial mechanism for alkene formation, which does not result from oxygen rebound, is similar to that widely suggested for P450 monooxygenation reactions.
Abstract: OleTJE, a cytochrome P450, catalyzes the conversion of fatty acids to terminal alkenes using hydrogen peroxide as a cosubstrate. Analytical studies with an eicosanoic acid substrate show that the enzyme predominantly generates nonadecene and that carbon dioxide is the one carbon coproduct of the reaction. The addition of hydrogen peroxide to a deuterated substrate–enzyme (E–S) complex results in the transient formation of an iron(IV) oxo π cation radical (Compound I) intermediate which is spectroscopically indistinguishable from those that perform oxygen insertion chemistries. A kinetic isotope effect for Compound I decay suggests that it abstracts a substrate hydrogen atom to initiate fatty acid decarboxylation. Together, these results indicate that the initial mechanism for alkene formation, which does not result from oxygen rebound, is similar to that widely suggested for P450 monooxygenation reactions.
TL;DR: Preliminary mechanistic studies were conducted, suggesting that C-H activation is the turnover limiting step, and the efficiency of this reaction was demonstrated by the rapid total synthesis of three natural products herniarin, xanthyletin, and seselin.
TL;DR: A user-friendly Ni-catalyzed reductive cyclization/carboxylation of unactivated alkyl halides with CO2 is described, which operates under mild conditions with an excellent chemoselectivity profile and a divergent syn/anti selectivity pattern that can be easily modulated by the substrate utilized.
Abstract: A user-friendly Ni-catalyzed reductive cyclization/carboxylation of unactivated alkyl halides with CO2 is described. The protocol operates under mild conditions with an excellent chemoselectivity profile and a divergent syn/anti selectivity pattern that can be easily modulated by the substrate utilized.
TL;DR: Photon upconversion lithography is demonstrated for the patterning of proteins using near-infrared light using an upconverting-nanoparticle-decorated substrate via blue-light-cleavable Ru complexes.
Abstract: Photon upconversion lithography is demonstrated for the patterning of proteins using near-infrared light. Proteins and an upconverting-nanoparticle-decorated substrate are linked via blue-light-cleavable Ru complexes. The substrate is irradiated using near-infrared light with a photomask. In the exposed areas, upconverting nanoparticles convert the near-infrared light into blue light, which induces cleavage of the Ru complexes and release of the proteins.
TL;DR: It is demonstrated that addition of protein effecting a seven‐fold decrease in the specific activity of cellulases enables a ten‐fold reduction in enzyme loading while maintaining a high level of cellulose hydrolysis in pretreated hardwood.
Abstract: Fundamental characterization of pretreated hardwood and its interactions with cellulolytic enzymes has confirmed that a pathway exists for dramatically reducing the loading of cellulase required for hydrolysis of pretreated biomass. We demonstrate that addition of protein effecting a seven-fold decrease in the specific activity of cellulases enables a ten-fold reduction in enzyme loading while maintaining a high level of cellulose hydrolysis in pretreated hardwood. While use of protein and other additives that adsorb on lignin have been reported previously, the current work demonstrates the effect in a dramatic manner and brings the rationale for this change into clear focus. The key to this result is recognizing and mitigating the pretreatment conundrum where increasingly severe pretreatment conditions enhance accessibility of the enzymes not only to cellulose, but also to lignin. The lignin adsorbs enzyme protein causing loss of cellulase activity. More enzyme, added to compensate for this lost activity, results in a higher cellulase loading. The addition of a different protein, such as BSA, prevents cellulase adsorption on lignin and enables the enzyme itself to better target its glucan substrate. This effect dramatically reduces the amount of cellulase for a given level of conversion with enzyme loadings of 15 FPU and 1.3 FPU/g solids both achieving 80% conversion. The understanding of this phenomenon reinvigorates motivation for the search for other approaches that prevent cellulase adsorption on lignin in order to achieve high glucose yields at low enzyme loadings for pretreated lignocellulose. Biotechnol. Bioeng. 2015;112: 677–687. © 2014 Wiley Periodicals, Inc.
TL;DR: In this article, a double-bladed casted mixed matrix substrate membrane was used for flat-sheet silica-polysulfone mixed matrix membrane fabrication, and a series of standardized characterization techniques, including ATR-FTIR, contact angle, zeta potential, pore size distribution, FESEM and EDX have been utilized to characterize the substrate membranes and resultant TFC-FO membranes.
TL;DR: In this article, the aqueous stem extract of Salvadora persica was used as reducing and capping agent for the synthesis of silver nanoparticles (AgNPs).
TL;DR: The results demonstrate that the diffusional limitation induced by the aggregation of carbon nanoparticles cannot be ignored because it can lead to increased reaction times, low efficiency, and high economic costs when low concentrations of environmental contaminants are used.
TL;DR: Ultrathin ZIF-8 membranes with a thickness of around 200 nm were prepared by chemical vapour modification of surface chemistry and nanopores of an asymmetric bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) substrate and exhibited exceptional H2 permeance as high as 2.05 × 10(-6) mol m(-2) s(-1) Pa(-1).
TL;DR: NMR spin relaxation studies of the enzymes ribonuclease HI from mesophilic and thermophilic bacteria, E. coli AlkB, and Saccharomyces cerevisiae triosephosphate isomerase are reviewed to illustrate the contributions of conformational flexibility and dynamics to diverse steps in enzyme mechanism.
Abstract: CONSPECTUS: Biological activities of enzymes, including regulation or coordination of mechanistic stages preceding or following the chemical step, may depend upon kinetic or equilibrium changes in protein conformations. Exchange of more open or flexible conformational states with more closed or constrained states can influence inhibition, allosteric regulation, substrate recognition, formation of the Michaelis complex, side reactions, and product release. NMR spectroscopy has long been applied to the study of conformational dynamic processes in enzymes because these phenomena can be characterized over multiple time scales with atomic site resolution. Laboratory-frame spin-relaxation measurements, sensitive to reorientational motions on picosecond-nanosecond time scales, and rotating-frame relaxation-dispersion measurements, sensitive to chemical exchange processes on microsecond-millisecond time scales, provide information on both conformational distributions and kinetics. This Account reviews NMR spin relaxation studies of the enzymes ribonuclease HI from mesophilic (Escherichia coli) and thermophilic (Thermus thermophilus) bacteria, E. coli AlkB, and Saccharomyces cerevisiae triosephosphate isomerase to illustrate the contributions of conformational flexibility and dynamics to diverse steps in enzyme mechanism. Spin relaxation measurements and molecular dynamics (MD) simulations of the bacterial ribonuclease H enzymes show that the handle region, one of three loop regions that interact with substrates, interconverts between two conformations. Comparison of these conformations with the structure of the complex between Homo sapiens ribonuclease H and a DNA:RNA substrate suggests that the more closed state is inhibitory to binding. The large population of the closed conformation in T. thermophilus ribonuclease H contributes to the increased Michaelis constant compared with the E. coli enzyme. NMR spin relaxation and fluorescence spectroscopy have characterized a conformational transition in AlkB between an open state, in which the side chains of methionine residues in the active site are disordered, and a closed state, in which these residues are ordered. The open state is highly populated in the AlkB/Zn(II) complex, and the closed state is highly populated in the AlkB/Zn(II)/2OG/substrate complex, in which 2OG is the 2-oxoglutarate cosubstrate and the substrate is a methylated DNA oligonucleotide. The equilibrium is shifted to approximately equal populations of the two conformations in the AlkB/Zn(II)/2OG complex. The conformational shift induced by 2OG ensures that 2OG binds to AlkB/Zn(II) prior to the substrate. In addition, the opening rate of the closed conformation limits premature release of substrate, preventing generation of toxic side products by reaction with water. Closure of active site loop 6 in triosephosphate isomerase is critical for forming the Michaelis complex, but reopening of the loop after the reaction is (partially) rate limiting. NMR spin relaxation and MD simulations of triosephosphate isomerase in complex with glycerol 3-phosphate demonstrate that closure of loop 6 is a highly correlated rigid-body motion. The MD simulations also indicate that motions of Gly173 in the most flexible region of loop 6 contribute to opening of the active site loop for product release. Considered together, these three enzyme systems illustrate the power of NMR spin relaxation investigations in providing global insights into the role of conformational dynamic processes in the mechanisms of enzymes from initial activation to final product release.
TL;DR: The results indicate that the reaction proceeds at the hypervalent iodine moiety of Togni reagent, which is activated by Cu(II) species acting as a Lewis acid catalyst, and this transformation exhibited a remarkable rate enhancement upon addition of Et3N.
Abstract: We examined the mechanism of our previously reported aminotrifluoromethylation reaction, which proceeds via intramolecular cyclization of alkenylamines in the presence of the combination of copper catalyst and Togni reagent (1). Kinetic studies revealed that the initial rate of the reaction was first order with respect to Togni reagent and CuI, as well as the substrate. Changes of the 19F NMR chemical shift of Togni reagent during the reaction suggested the existence of a dynamic equilibrium involving coordination of not only Togni reagent, but also the substrate amine and the product aziridine to copper. ESI-MS analysis provided evidence of involvement of reactive Cu(II) intermediates in the catalytic cycle. Overall, our results indicate that the reaction proceeds at the hypervalent iodine moiety of Togni reagent, which is activated by Cu(II) species acting as a Lewis acid catalyst. On the basis of these mechanistic considerations, we developed an efficient synthesis of trifluoromethylated pyrrolidine de...
TL;DR: This is the first reported 3D COF functional membrane fabricated successfully on a common porous α-Al2O3 ceramic support, and the gas permeation results indicate that the gas transport behavior is mainly governed by the predicted Knudsen diffusion process.
TL;DR: A concentration gradient controlled (CGC) kinetics model is proposed to explain the combined effects of lead-free soldering on Cu substrates and it is found that a larger Cu concentration gradient results in smaller Cu6Sn5 grains and more consumption of Cu substrate.
Abstract: Size effect model on kinetics of interfacial reaction between Sn-xAg-yCu solders and Cu substrate
TL;DR: It is shown that the presence of heavy metal ions in the tested solution causes an inhibition of the enzymatic reactions catalyzed by glucose oxidase and urease, which results in a restoration of the photoluminescence quantum yield of porous silicon.
TL;DR: In this paper, a novel thin film nanocomposite (TFN) FO membrane consisting of a polyetherimide (PEI) nanofibrous substrate reinforced by functionalized multi-walled carbon nanotubes (f-CNTs) and an ultrathin polyamide rejection layer was successfully fabricated.
TL;DR: In this paper, a set of monolayer WS2 films, either directly grown on sapphire and SiO2 substrates by CVD or transferred onto SiO 2 substrate, was investigated.
Abstract: This study reveals that the interaction between a 2D material and its substrate can significantly modify its electronic and optical properties, and thus can be used as a means to optimize these properties. High-temperature (25–500 °C) optical spectroscopy, which combines Raman and photoluminescence spectroscopies, is highly effective for investigating the interaction and material properties that are not accessible at the commonly used cryogenic temperature (e.g., a thermal activation process with an activation of a major fraction of the bandgap). This study investigates a set of monolayer WS2 films, either directly grown on sapphire and SiO2 substrates by CVD or transferred onto SiO2 substrate. The coupling with the substrate is shown to depend on the substrate type, the materialsubstrate bonding (even for the same substrate), and the excitation wavelength. The inherent difference in the states of strain between the as-grown and the transferred films has a significant impact on the material properties.
TL;DR: The chemical absorption of CO2 into a monoethanolamine solvent is currently the most widely accepted commercial approach to carbon dioxide capture, but the subsequent desorption from the solvents is extremely energy intensive and the use of a carbonic anhydrase enzyme as a reaction promoter can potentially overcome this obstacle.
Abstract: The chemical absorption of CO2 into a monoethanolamine solvent is currently the most widely accepted commercial approach to carbon dioxide capture. However, the subsequent desorption of CO2 from the solvents is extremely energy intensive. Alternative solvents are more energy efficient, but their slow reaction kinetics in the CO2 absorption step limits application. The use of a carbonic anhydrase (CA) enzyme as a reaction promoter can potentially overcome this obstacle. Native, engineered and artificial CA enzymes have been investigated for this application. Immobilization of the enzyme within the gas absorber or in a membrane format can increase enzyme stability and avoid thermal denaturation in the stripper. However, immobilization is only effective if the mass transfer of carbon dioxide through the liquid phase to reach the immobilization substrate does not become rate controlling. Further research should also consider the process economics of large-scale enzyme production and the long-term performance of the enzyme under real flue gas conditions. © 2014 Society of Chemical Industry