Strong Substrate Research Articles

Substrate Specificity of Aglaia loheri Active Isolate towards P-glycoprotein in Multidrug-Resistant Cancer Cells

Multidrug resistance (MDR) is a major contributory factor in the failure of chemotherapy. Concrete interpretation of P-glycoprotein (P-gp) substrate specificity, whether a substance is a substrate or an inhibitor, represents an important feature of a compound's pharmaceutical profiling in drug design and development. In this work, the P-gp substrate specificity of Maldi 531.2[M+H](+), a phenol ester from Aglaia loheri Blanco leaves was investigated. This study focuses on the effect of Maldi 531.2[M+H](+) on P-gp ATPase activity, which was examined by measuring the amount of inorganic phosphates (Pi) released as a result of ATP hydrolysis. To test the effects of Maldi 531.2[M+H](+) on MDR activity, an attempt to combine Maldi 531.2[M+H](+) with a potent P-gp substrate such as verapamil was performed. As a result of this combination treatment, two distinct patterns of interaction with P-gp activity were determined by a calcein-acetoxymethyl ester (AM) assay. Depending on the concentratgion, both stimulation and inhibition of MDR activity were observed at certain drug concentrations suggesting biphasic reactions, which can be understood as cooperative stimulation and competitive inhibition, respectively. Verapamil is a strong substrate to P-gp. Substrate specificity of Maldi 531.2[M+H](+) may be less than the substrate specificity of verapamil, but it acts additively together with low concentrations of verapamil in stimulating ATPase activity. On the one hand, verapamil and Maldi 531.2[M+H](+) exerted cooperative stimulation on P-gp. On the other hand, Maldi 531.2[M+H](+) acts as competitive inhibitor at higher concentrations.

Discovery of a Xylooligosaccharide Oxidase from Myceliophthora thermophila C1

By inspection of the predicted proteome of the fungus Myceliophthora thermophila C1 for vanillyl-alcohol oxidase (VAO)-type flavoprotein oxidases, a putative oligosaccharide oxidase was identified. By homologous expression and subsequent purification, the respective protein could be obtained. The protein was found to contain a bicovalently bound FAD cofactor. By screening a large number of carbohydrates, several mono- and oligosaccharides could be identified as substrates. The enzyme exhibits a strong substrate preference toward xylooligosaccharides; hence it is named xylooligosaccharide oxidase (XylO). Chemical analyses of the product formed upon oxidation of xylobiose revealed that the oxidation occurs at C1, yielding xylobionate as product. By elucidation of several XylO crystal structures (in complex with a substrate mimic, xylose, and xylobiose), the residues that tune the unique substrate specificity and regioselectivity could be identified. The discovery of this novel oligosaccharide oxidase reveals that the VAO-type flavoprotein family harbors oxidases tuned for specific oligosaccharides. The unique substrate profile of XylO hints at a role in the degradation of xylan-derived oligosaccharides by the fungus M. thermophila C1.

Digital pH Test Strips for In-Field pH Monitoring Using Iridium Oxide-Reduced Graphene Oxide Hybrid Thin Films

While pH test strips are not decimally accurate and only semiquantitative, the more accurate and automated laboratory-based pH meters lack disposability and portability. Benefiting from advantages of both sides and filling the gap of unmet needs in between, we integrated a miniaturized paper-fluidic electrochemical pH platform coupled with a portable pH device powered by consumer batteries to make digital pH test strips for truly in-field measurements. To overcome the inability to form the smooth and uniform pH-sensitive functionality on screen-printed carbon, i.e., anodically electrodeposited iridium oxide thin films (AEIROFs), reduced graphene oxide was used as substrate for synthesis of homogeneous metal oxide–nanocarbon hybrid thin films, IrO2-reduced graphene oxide (IrO2-rGO), as the sensing moiety with strong substrate adhesion. A hydrophobic barrier-patterned paper micropad (μPAD) with programmed flow rates can locally accelerate linear wicking speed to boost delivery and response time. IrO2-rGO sh...

Low-temperature anharmonic phonon properties of supported graphene

Temperature-dependent Raman studies of anharmonic phonon-phonon processes in supported graphene are presented. Different G peak position temperature dependencies for graphene on glass and copper substrates were observed. Having calculated graphene-substrate total interaction energy taking into account substrate-induced strain, we estimated E2g mode energy changes due to anharmonic phonon-phonon interaction as the temperature decreases from room temperature to a value close to absolute zero for both substrates. For graphene on glass, the obtained value was about 1.8 times greater than the theoretical one for suspended graphene. For graphene on copper, the value was about 2.9 times greater. This result demonstrates a strong substrate influence on anharmonic phonon-phonon processes in graphene.

Characterizing fluorocarbon assisted atomic layer etching of Si using cyclic Ar/C4F8 and Ar/CHF3 plasma.

With the increasing interest in establishing directional etching methods capable of atomic scale resolution for fabricating highly scaled electronic devices, the need for development and characterization of atomic layer etching processes, or generally etch processes with atomic layer precision, is growing. In this work, a flux-controlled cyclic plasma process is used for etching of SiO2 and Si at the Angstrom-level. This is based on steady-state Ar plasma, with periodic, precise injection of a fluorocarbon (FC) precursor (C4F8 and CHF3) and synchronized, plasma-based Ar+ ion bombardment [D. Metzler et al., J. Vac. Sci. Technol., A 32, 020603 (2014) and D. Metzler et al., J. Vac. Sci. Technol., A 34, 01B101 (2016)]. For low energy Ar+ ion bombardment conditions, physical sputter rates are minimized, whereas material can be etched when FC reactants are present at the surface. This cyclic approach offers a large parameter space for process optimization. Etch depth per cycle, removal rates, and self-limitation of removal, along with material dependence of these aspects, were examined as a function of FC surface coverage, ion energy, and etch step length using in situ real time ellipsometry. The deposited FC thickness per cycle is found to have a strong impact on etch depth per cycle of SiO2 and Si but is limited with regard to control over material etching selectivity. Ion energy over the 20-30 eV range strongly impacts material selectivity. The choice of precursor can have a significant impact on the surface chemistry and chemically enhanced etching. CHF3 has a lower FC deposition yield for both SiO2 and Si and also exhibits a strong substrate dependence of FC deposition yield, in contrast to C4F8. The thickness of deposited FC layers using CHF3 is found to be greater for Si than for SiO2. X-ray photoelectron spectroscopy was used to study surface chemistry. When thicker FC films of 11 Å are employed, strong changes of FC film chemistry during a cycle are seen whereas the chemical state of the substrate varies much less. On the other hand, for FC film deposition of 5 Å for each cycle, strong substrate surface chemical changes are seen during an etching cycle. The nature of this cyclic etching with periodic deposition of thin FC films differs significantly from conventional etching with steady-state FC layers since surface conditions change strongly throughout each cycle.

Cube texture evolution of Ni5W alloy substrates and La–Zr–O buffer layer of YBCO-coated conductors

The cube texture evolution of Ni-5 at%W alloy deformed up to a very high strain was thoroughly investigated by X-ray diffraction (XRD) and electron back-scattered diffraction (EBSD) during the process of deformation, recrystallization and grain growth. A typical copper-type rolling texture, mainly consisting of components of S, copper and brass orientations, is obtained after heavy cold rolling. The fraction of rolling texture is slightly strengthened during recovery and then strongly reduced during recrystallization process. The cube texture is formed by consuming the rolling texture components during the discontinuous recrystallization process. The cube grains have a size advantage with respect to the non-cube grains. A strong cube-textured Ni5W alloy substrate with cube texture area fraction of 98.2 % (<10°) is obtained after annealing at 1050 °C for 1 h. The full width half maximum (FWHM) values for the X-ray (111) φ-scan and the (002) ω-scan of this substrate are 5.84° and 4.76°, respectively. Furthermore, the area fraction of {001} 〈110〉 orientation of the epitaxially grown La2Zr2O7 buffer layer is 97.1 % (<10°), and the FWHM values of (111) φ-scan and (002) ω-scan are 5.22° and 5.00°, respectively.

Highly Enantioselective Synthesis of Chiral Succinimides via Rh/Bisphosphine-Thiourea-Catalyzed Asymmetric Hydrogenation

We have successfully developed a highly enantioselective hydrogenation of various 3-aryl and 3-methyl maleinimides to access enantiomerically pure 3-substituted succinimides catalyzed by Rh/bisphosphine-thiourea (ZhaoPhos). This efficient catalytic system furnished the desired 3-substituted succinimide products with high yields and enantioselectivities (up to 99% yield, full conversions, almost all 3-aryl succinimide products up to 99% ee, and 3-methyl succinimide with 83% ee). Our catalytic system has a strong substrate tolerance and generality. Whether the N-substituted group of maleinimides is H or other protecting groups, the maleinimides were hydrogenated well (up to >99% ee, 99% yield). Moreover, the hydrogenation succinimide products can be readily utilized for the construction of biologically active molecules, such as chiral amides and pyrrolidines.

3D nanoporous gold scaffold supported on graphene paper: Freestanding and flexible electrode with high loading of ultrafine PtCo alloy nanoparticles for electrochemical glucose sensing

Recent advances in on-body wearable medical apparatus and implantable devices drive the development of light-weight and bendable electrochemical sensors, which require the design of high-performance flexible electrode system. In this work, we reported a new type of freestanding and flexible electrode based on graphene paper (GP) supported 3D monolithic nanoporous gold (NPG) scaffold (NPG/GP), which was further modified by a layer of highly dense, well dispersed and ultrafine binary PtCo alloy nanoparticles via a facile and effective ultrasonic electrodeposition method. Our results demonstrated that benefited from the synergistic effect of the electrocatalytically active PtCo alloy nanoparticles, the large-active-area and highly conductive 3D NPG scaffold, and the mechanically strong and stable GP electrode substrate, the resultant PtCo alloy nanoparticles modified NPG/GP (PtCo/NPG/GP) exhibited high mechanical strength and good electrochemical sensing performances toward nonenzymatic detection of glucose, including a wide linear range from 35 μM– to 30 mM, a low detection limit of 5 μM (S/N = 3) and a high sensitivity of 7.84 μA cm−2 mM−1 as well as good selectivity, long-term stability and reproducibility. The practical application of the proposed PtCo/NPG/GP has also been demonstrated in in vitro detection of blood glucose in real clinic samples.

Lipid-based oral delivery systems for skin deposition of a potential chemopreventive DIM derivative: characterization and evaluation.

The objective of this study was to explore the oral route as a viable potential for the skin deposition of a novel diindolylmethane derivative (DIM-D) for chemoprevention activity. Various lipid-based oral delivery systems were optimized and compared for enhancing DIM-D's oral bioavailability and skin deposition. Preformulation studies were performed to evaluate the log P and solubility of DIM-D. Microsomal metabolism, P-glycoprotein efflux, and caco-2 monolayer permeability of DIM-D were determined. Comparative evaluation of the oral absorption and skin deposition of DIM-D-loaded various lipid-based formulations was performed in rats. DIM-D showed pH-dependent solubility and a high log P value. It was not a strong substrate of microsomal degradation and P-glycoprotein. SMEDDs comprised of medium chain triglycerides, monoglycerides, and kolliphor-HS15 (36.70±0.42nm). SNEDDs comprised of long chain triglycerides, cremophor RH40, labrasol, and TPGS (84.00±14.14nm). Nanostructured lipid carriers (NLC) consisted of compritol, miglyol, and surfactants (116.50±2.12nm). The blank formulations all showed >70% cell viability in caco-2 cells. Differential Scanning Calorimetry confirmed the amorphization of DIM-D within the lipid matrices while Atomic Force Microscopy showed particle size distribution similar to the dynamic light scattering data. DIM-D also showed reduced permeation across caco-2 monolayer that was enhanced (p<0.05) by SNEDDs in comparison to SMEDDs and NLC. Fabsolute for DIM-D SNEDDs, SMEDDs, and NLC was 0.14, 0.04, and 0.007, respectively. SNEDDs caused 53.90, 11.32, and 15.08-fold more skin deposition of DIM-D than the free drug, SMEDDs, and NLC, respectively, at 2h following oral administration and shows a viable potential for use in skin cancer chemoprevention. Graphical Abstract ᅟ.

Effective immobilization of tyrosinase via enzyme catalytic polymerization of l-DOPA for highly sensitive phenol and atrazine sensing

The facile preparation of poly(l-DOPA)-tyrosinase (PDM-Tyr) composite and its application both in substrate (phenol) and inhibitor (atrazine) sensing is reported here for the first time. Effective immobilization of enzyme is realized via in-situ entrapping Tyr in poly(l-DOPA) (PDM), which is formed by Tyr catalytic polymerization of l-DOPA. The Tyr modified electrode is simply prepared by dipping the PDM-Tyr composite on an Au electrode and then covered by Nafion. The thus-prepared Tyr-immobilized electrode exhibits excellent performance superior to most Tyr-based electrochemical biosensors, the sensitivity to phenol is as high as 5122 μA mM−1 in the linear range of 10nM~1.25 μM, the apparent Michaelis-Menten constant (KMapp) determined as low as 3.13μM indicates strong substrate binding and high catalytic activity of the immobilized Tyr. The biosensor also works well in atrazine biosensing, with a linear detection range of 50ppb~30ppm and a low detection limit of 10ppb obtained. In addition, the biosensor shows excellent stability, precision, high sensitivity and fabrication simplicity.

Substrate effect on the growth of monolayer dendritic MoS2 on LaAlO3 (100) and its electrocatalytic applications

In accommodating the rapid development of two-dimensional (2D) nanomaterials, chemical vapor deposition (CVD) has become a powerful tool for their batch production with desirable characteristics, such as high crystal quality, large domain size, and tunable domain shape. The crystallinity and morphology of the growth substrates usually play a crucial role in the CVD synthesis of high-quality monolayer MoS2, a kind of 2D layered material which has ignited huge interest in nanoelectronics, optoelectronics and energy harvesting, etc. Herein, by utilizing a low-pressure chemical vapor deposition (LPCVD) system, we demonstrate a regioselective synthesis of monolayer MoS2 on the corrugated single-crystal LaAlO3 (100) with twin crystal domains induced by the second-order phase transition. Unique dendritic morphologies with tunable nucleation densities were obtained in different regions of the undulated substrate, presenting a strong substrate modulation effect. Interestingly, the exposure of abundant active edge sites along with the rather high nucleation density makes the monolayer dendritic MoS2 a good electrocatalyst for hydrogen evolution reaction (HER), particularly featured by a rather high exchange current density (70.4 μA cm−2). Furthermore, uniform monolayer MoS2 films can also be obtained and transferred to arbitrary substrates. We believe that this work provides a new growth system for the controllable synthesis of 2D layered materials with unique dendritic morphologies, as well as its great application potential in energy conversion and harvesting.

Isolation and characterization of Dehalobacter sp. strain UNSWDHB capable of chloroform and chlorinated ethane respiration.

Dehalobacter sp. strain UNSWDHB can dechlorinate up to 4 mM trichloromethane at a rate of 0.1 mM per day to dichloromethane and 1,1,2-trichloroethane (1 mM, 0.1 mM per day) with the unprecedented product profile of 1,2-dichloroethane and vinyl chloride. 1,1,1-trichloroethane and 1,1-dichloroethane were slowly utilized by strain UNSWDHB and were not completely removed, with minimum threshold concentrations of 0.12 mM and 0.07 mM respectively under growth conditions. Enzyme kinetic experiments confirmed strong substrate affinity for trichloromethane and 1,1,2-trichloroethane (Km = 30 and 62 µM respectively) and poor substrate affinity for 1,1,1-trichloroethane and 1,1-dichloroethane (Km = 238 and 837 µM respectively). Comparison of enzyme kinetic and growth data with other trichloromethane respiring organisms (Dehalobacter sp. strain CF and Desulfitobacterium sp. strain PR) suggests an adaptation of strain UNSWDHB to trichloromethane. The trichloromethane RDase (TmrA) expressed by strain UNSWDHB was identified by BN-PAGE and functionally characterized. Amino acid comparison of homologous RDases from all three organisms revealed only six significant amino acid substitutions/deletions, which are likely to be crucial for substrate specificity. Furthermore, strain UNSWDHB was shown to grow without exogenous supply of cobalamin confirming genomic-based predictions of a fully functional cobalamin synthetic pathway.

Sorafenib metabolism, transport, and enterohepatic recycling: physiologically based modeling and simulation in mice.

This study used uncertainty and sensitivity analysis to evaluate a physiologically based pharmacokinetic (PBPK) model of the complex mechanisms of sorafenib and its two main metabolites, sorafenib glucuronide and sorafenib N-oxide in mice. A PBPK model for sorafenib and its two main metabolites was developed to explain disposition in mice. It included relevant influx (Oatp) and efflux (Abcc2 and Abcc3) transporters, hepatic metabolic enzymes (CYP3A4 and UGT1A9), and intestinal β-glucuronidase. Parameterization of drug-specific processes was based on in vitro, ex vivo, and in silico data along with plasma and liver pharmacokinetic data from single and multiple transporter knockout mice. Uncertainty analysis demonstrated that the model structure and parameter values could explain the observed variability in the pharmacokinetic data. Global sensitivity analysis demonstrated the global effects of metabolizing enzymes on sorafenib and metabolite disposition and the local effects of transporters on their respective substrate exposures. In addition, through hypothesis testing, the model supported that the influx transporter Oatp is a weak substrate for sorafenib and a strong substrate for sorafenib glucuronide and that the efflux transporter Abcc2 is not the only transporter affected in the Abcc2 knockout mouse. Translation of the mouse model to humans for the purpose of explaining exceptionally high human pharmacokinetic variability and its relationship with exposure-dependent dose-limiting toxicities will require delineation of the importance of these processes on disposition.

MTH1 Substrate Recognition--An Example of Specific Promiscuity.

MTH1 (NUDT1) is an oncologic target involved in the prevention of DNA damage. We investigate the way MTH1 recognises its substrates and present substrate-bound structures of MTH1 for 8-oxo-dGTP and 8-oxo-rATP as examples of novel strong and weak binding substrate motifs. Investigation of a small set of purine-like fragments using 2D NMR resulted in identification of a fragment with weak potency. The protein-ligand X-Ray structure of this fragment provides insight into the role of water molecules in substrate selectivity. Wider fragment screening by NMR resulted in three new protein structures exhibiting alternative binding configurations to the key Asp-Asp recognition element of the protein. These inhibitor binding modes demonstrate that MTH1 employs an intricate yet promiscuous mechanism of substrate anchoring through its Asp-Asp pharmacophore. The structures suggest that water-mediated interactions convey selectivity towards oxidized substrates over their non-oxidised counterparts, in particular by stabilization of a water molecule in a hydrophobic environment through hydrogen bonding. These findings may be useful in the design of inhibitors of MTH1.

High-speed thermal plasma deposition of copper coating on aluminum surface with strong substrate adhesion and low transient resistivity

Abstract Copper and aluminum are widespread materials and have many applications, especially in the electrical engineering, and their coupling is an important issue. The direct connection of these materials without special preparation leads to increasing the transient resistance and energy loses in the contact place. This paper shows the possibility of copper deposition on aluminum substrates using high-speed thermal plasma jet, generated by a coaxial magnetoplasma accelerator. This method allows forming the uniform coating, having the thickness from 50 to 100 μm, with the strong adhesion to the substrate. It is found that in the considered system the adhesion strength depends on the speed of the material deposition and varies from 1540 MPa to 2520 MPa. Such a strong coupling is achieved due to the presence of the mixing material zone near the interface. The material mixing and the absence of clearly-seen boundary between coating and substrate provides not only the strong adhesion but also allows reducing the transient contact resistance. The value of the transient resistance can be decreased at 2.8 times in comparison with the direct connection of copper and aluminum. The surface roughness of synthesized samples and its influence on the transient contact resistance is also investigated using profilometry analysis. It is shown that increasing the compression force can positively decrease the surface roughness that leads to increasing the contact area and, respectively, to decreasing the transient resistance.

Deposition of a TiC/Ti coating with a strong substrate adhesion using a high-speed plasma jet

Titanium carbide coatings have many applications due to their large number of useful properties such as the increase of the resistance to wear, corrosion, and oxidation of the substrate. However, poor adhesion of TiC coatings to metal substrates is known as one of the main problems. This paper shows the possibility of depositing TiC/Ti coating with a thickness of 10 to 30 μm on copper substrates using a high-speed plasma jet, which is generated by a coaxial magneto-plasma accelerator. The formation of cubic titanium carbide with a small amount of pure titanium is confirmed by XRD and SAED results. EDX analysis indicates both the presence of an intermixing zone near the boundary between the substrate and coating, where their particles mix together during the crystallization process, and the deep penetration of titanium particles into the substrate structure due to the high speed of the plasma flow (~ 3 km/s). These processes lead to the formation of a coating with a strong adhesion to substrate. The critical adhesion strength is equal to 5200 MPa. However, the presence of pure titanium particles influences the hardness of the coating, slightly decreasing the coating hardness to ~ 1900 HV and increasing the hardness of the substrate top layers up to 95 HV.

Substrate Specificity in Photocatalytic Degradation of Mixtures of Organic Contaminants in Water

TiO2-induced photocatalytic decomposition of methyl orange (MO) and atrazine in aqueous solutions was investigated using a top illumination reactor and LC-MS analysis. TiO2 P25 was determined to be the most favorable catalyst when compared to TiO2 Hombikat or Pt-promoted P25 (0.5% Pt/P25). For all catalysts, a strong substrate specificity was observed when simultaneous decomposition was attempted at neutral pH or acidic conditions: MO decomposition was largely preferred over decomposition of atrazine. For TiO2 P25, several process parameters were varied (catalyst loading, MO initial concentration, pH) to determine that the cause of this observation is preferential adsorption. Atrazine decomposition was no longer inhibited by MO at (i) large catalyst concentrations, (ii) at a low MO over atrazine ration, and (iii) at basic conditions (pH 11). Apparently the surface charge of illuminated TiO2 significantly affects the degradation behavior of contaminants when present in mixtures. Surface specificity is not limited to a combination of MO and atrazine, but for P25, this is also shown to occur in decomposition of a mixture of MO and acid orange (AO), compounds with similarity in molecular structure. Consequences of the results for practical application of photocatalysis for water decontamination are briefly discussed.

Quasi one-dimensional band dispersion and surface metallization in long-range ordered polymeric wires.

On-surface covalent self-assembly of organic molecules is a very promising bottom–up approach for producing atomically controlled nanostructures. Due to their highly tuneable properties, these structures may be used as building blocks in electronic carbon-based molecular devices. Following this idea, here we report on the electronic structure of an ordered array of poly(para-phenylene) nanowires produced by surface-catalysed dehalogenative reaction. By scanning tunnelling spectroscopy we follow the quantization of unoccupied molecular states as a function of oligomer length, with Fermi level crossing observed for long chains. Angle-resolved photoelectron spectroscopy reveals a quasi-1D valence band as well as a direct gap of 1.15 eV, as the conduction band is partially filled through adsorption on the surface. Tight-binding modelling and ab initio density functional theory calculations lead to a full description of the band structure, including the gap size and charge transfer mechanisms, highlighting a strong substrate–molecule interaction that drives the system into a metallic behaviour.

Green access to chiral Vince lactam in a buffer-free aqueous system using a newly identified substrate-tolerant (−)-γ-lactamase

A novel (−)-γ-lactamase with high catalytic efficiency, strong substrate tolerance and environmental friendliness was identified for green access to chiral Vince lactam.

Dunnione ameliorates cisplatin-induced small intestinal damage by modulating NAD+ metabolism

Although cisplatin is a widely used anticancer drug for the treatment of a variety of tumors, its use is critically limited because of adverse effects such as ototoxicity, nephrotoxicity, neuropathy, and gastrointestinal damage. Cisplatin treatment increases oxidative stress biomarkers in the small intestine, which may induce apoptosis of epithelial cells and thereby elicit damage to the small intestine. Nicotinamide adenine dinucleotide (NAD+) is a cofactor for various enzymes associated with cellular homeostasis. In the present study, we demonstrated that the hyper-activation of poly(ADP-ribose) polymerase-1 (PARP-1) is closely associated with the depletion of NAD+ in the small intestine after cisplatin treatment, which results in downregulation of sirtuin1 (SIRT1) activity. Furthermore, a decrease in SIRT1 activity was found to play an important role in cisplatin-mediated small intestinal damage through nuclear factor (NF)-κB p65 activation, facilitated by its acetylation increase. However, use of dunnione as a strong substrate for the NADH:quinone oxidoreductase 1 (NQO1) enzyme led to an increase in intracellular NAD+ levels and prevented the cisplatin-induced small intestinal damage correlating with the modulation of PARP-1, SIRT1, and NF-κB. These results suggest that direct modulation of cellular NAD+ levels by pharmacological NQO1 substrates could be a promising therapeutic approach for protecting against cisplatin-induced small intestinal damage.