Residual Hydroxyl Research Articles

Current insights into protease dynamics in human epithelial disease and barrier function

The fundamental importance of proteolytic enzymes to the biology of all living organisms is manifestly demonstrated by genomic analyses which demonstrate that genes encoding proteases and their inhibitors account for over 2 % of the coding sequences of most genomes sequenced to date. For example, over 500 protease genes have been annotated in the human genome. This extraordinary diversity reflects the wide range of biological functions performed by this family of enzymes: in addition to relatively non-specific degradative functions, characterized for example by digestive enzymes of the intestine, proteases also perform the selective and limited cleavage of a myriad of protein substrates which defines their subsequent biological functions and properties. In so doing, protease-dependent peptide bond hydrolysis ranks among the most significant of all posttranslational modification systems and underpins the processes of development, tissue homeostasis, turnover and remodelling, immune protection and healing. Given their central role in health, it is unsurprising that imbalances in protease activity are also intimately associated with both inherited and acquired human conditions. Proteases are generally classified on the basis of their mechanism of peptide bond cleavage. Four major families are well known. In the case of serine and cysteine enzymes, the hydroxyl and thiol residues respectively act as the nucleophilic groups in catalyzing hydrolytic peptide bond cleavage. Metalloenzymes, utilize a metal ion, frequently Zn, at their active site to activate a molecule of water to act as the nucleophile attack group. In aspartyl, sometimes referred to as acidic, proteases a similar mechanism of action to the metallo-enzymes is proposed in which a molecule of water is co-ordinated in the active site between two conserved aspartic acid residues, one of which causes activation of the water by removal of a proton and formation of the nucleophilic group required for peptide bond cleavage. In addition to these well known major catalytic classes, a number of additional mechanisms of peptide bond cleavage are now recognized leading to an expanded classification system which includes three additional classes. A subset of acidic proteases was originally identified based on their resistance to pepstatin, a broad spectrum inhibitor of proteases active at acidic pH. The unusual active sites of this pepstatin-insensitive subset proved difficult to characterise, but it is now recognized that some members of the subset were actually misclassified serine proteases, but with an acidic pH optimum, whilst the remainder represented a new class of protease containing glutamic acid/glutamine in their active site rather than aspartic acid. A further catalytic type of protease was identified following the elucidation of the crystallographic structure of the yeast proteasome which demonstrated the presence of an N-terminal threonine at the reactive centre fulfilling a similar nucleophilic role to the serine residue in the active sites of serine proteases. Once again this helped explain an inhibitor resistance phenomenon in that the proteasome was well known to be insensitive to inhibition by a wide range of standard protease inhibitors. The final and most recent addition to the list of classes is unusual in that members of this group are not proteases at all: they do not achieve peptide bond through hydrolysis, but instead act through the specific and unusual chemistry of asparagine. An asparagine residue at the active site is able to act as a nucleophile and cause autolytic cleavage of the peptide chain. In this instance the asparagine residue is destroyed and therefore the active site functions only once. The reader is referred to the MEROPS database (http://merops.sanger.ac.uk) which provides an excellent on M. A. Curtis :D. P. Kelsell (*) Blizard Institute, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, Whitechapel, London E1 2AT, UK e-mail: d.p.kelsell@qmul.ac.uk

Synthesis, molecular docking study, and anticancer activity of triaryl-1,2,4-oxadiazole

This study describes synthesis of a new group of triaryl-1,2,4-oxadiazole derivatives and their anticancer activities. The target compounds were prepared from reaction of different imines and 4-substituted benzohydroxyiminoyl chlorides. All the synthesized compounds were screened for antiproliferative activities against MCF7 and K562 cell lines using MTT assay at 50-μM concentration. Four compounds that showed more than 50 % cytotoxicity were selected for determination of IC50. Out of these, 6c-1y showed remarkable inhibitory cytotoxicity activity against MCF7 and K562 cell lines with IC50 6.50 and 21.66 μM, respectively. A molecular modeling study where 6c-1y was docked in the binding site of COX-2 showed a 2.3-A hydrogen bond forming via hydroxyl group of Ser516 residue and oxygen of central oxadiazole ring and triaryl moiety of 6c-1y oriented toward the hydrophobic pockets of COX-2. Our data indicate that these derivatives may present promising chemotherapeutic agents, possibly targeting COX-2 pathway.

Deoxynucleoside triphosphates bearing histamine, carboxylic acid, and hydroxyl residues – synthesis and biochemical characterization

Modified nucleoside triphosphates (dA(Hs)TP, dU(POH)TP, and dC(Val)TP) bearing imidazole, hydroxyl, and carboxylic acid residues connected to the purine and pyrimidine bases through alkyne linkers were prepared. These modified dN*TPs were excellent substrates for various DNA polymerases in primer extension reactions. Moreover, the combined use of terminal deoxynucleotidyl transferase (TdT) and the modified dNTPs led to efficient tailing reactions that rival those of natural counterparts. Finally, the triphosphates were tolerated by polymerases under PCR conditions, and the ensuing modified oligonucleotides served as templates for the regeneration of unmodified DNA. Thus, these modified dN*TPs are fully compatible with in vitro selection methods and can be used to develop artificial peptidases based on DNA.

Nanogranular Al2O3 proton conducting films for low-voltage oxide-based homojunction thin-film transistors

Nanogranular Al2O3 films were deposited by the plasma-enhanced chemical vapor deposition (PECVD) method using gas sources of trimethylaluminum and oxygen at 100 °C. Structural characterizations indicate that the as-deposited nanogranular Al2O3 film has an amorphous structure with excess oxygen due to ambient humidity and residual hydroxyl. As-deposited Al2O3 films show a mean pore size of 7.4 nm, and a high proton conductivity of 1.2 × 10−4 S cm−1 at room temperature with a 30% relative humidity. Low-voltage (1.5 V) indium-tin-oxide (ITO) thin-film transistors gated by such nanogranular Al2O3-based proton conductors exhibit a large current on/off ratio of 2.1 × 107 and a high field-effect mobility of 29 cm2 V−1 s−1. Our results demonstrate that nanogranular Al2O3-based films are promising gate dielectric candidates for portable biosensors.

Effects of Oxygen Plasma Post-Treatment on Ga-Doped ZnO Films Grown by Thermal-Mode ALD

Gallium-doped zinc oxide (GZO) thin films were grown via thermal-mode atomic layer deposition (TM-ALD) at different deposition temperatures. Diethylzinc (DEZ), triethylgallium (TEG), and H2O were used as zinc, gallium precursors, and oxygen source, respectively. ALD-GZO thin films are constituted as a layer-by-layer structure by stacking zinc oxides and gallium oxides. In order to eliminate the residual hydroxyl groups, we have employed the oxygen ion bombardment on ALD-GZO film surface. The influences of O2 plasma post-treatment on the surface morphology, surface chemical property, electrical, and optical characteristics of GZO films are investigated. With enhancing the O2 plasma power, the performance of GZO films would be improved. As a result of exposure to 200-W plasma power, the resistivity decreases from 6.7 × 10−4 to 4.5 × 10−4 Ω-cm, the carrier concentration increases from 9.7 × 1020 to 1.2 × 1021 cm−3, the specific contact resistance decreases from 4.4 × 10−4 to 7.5 × 10−5 Ω-cm2 for Ti/Al contact, the surface property changes from hydrophilic to hydrophobic behavior, the bandgap energy varies from 3.7 to 3.8 eV for Burstein-Moss shift phenomenon, and the mean optical transmittance keeps above 90% in the visible spectrum. On the other hand, the transmittance decreases with O2 plasma power in the near- and mid-infrared regions.

A novel biomass coated Ag–TiO2 composite as a photoanode for enhanced photocurrent in dye-sensitized solar cells

A novel biomass-coated Ag nanoparticle-modified TiO2 composite was prepared and used as a photoanode in a dye-sensitized solar cell with a high surface area, strong light scattering and efficient electron transport. It was found that syzygium extract has an appreciable effective function as a reducing and stabilizing agent simultaneously. The mean size of the synthesized silver nanoparticles is 4.0 ± 0.7 nm measured on the TEM images. Residual hydroxyl groups of the biomass on the photoanode improve dye absorption and electron injection efficiency. The syzygium-Ag–TiO2 DSSC exhibits the best performance with a short-circuit current of 11.8 mA cm−2 corresponding to a photoelectric conversion efficiency of 5.12%, which is higher than the glucose-Ag–TiO2 and UV-Ag–TiO2 DSSCs, and much higher than the blank DSSC.

Phosphonic Esters and their Application of Protease Control

α-Aminoalkylphosphonate diaryl esters are potent, irreversible, and highly selective site-directed inhibitors of serine proteases. The structure of the phosphonate group resembles the transition state observed during a peptide bond hydrolysis and therefore phosphonates are referred as transition state analogues. They react with the hydroxyl group of the active site serine residue leading to formation of a stable enzyme-inhibitor complex. Moreover, incorporation of a peptidyl chain at the N-terminus as well as an introduction of electron withdrawing or electron donating substituents within the ester ring structure allows for a generation of specific inhibitors that react only with target serine protease. The great advantage of the aminophosphonate diaryl esters over other classes of inhibitors is their stability in aqueous solutions, no toxicity and lack of reactivity with cysteine, threonine, aspartyl and metalloproteinases. The above resulted in their application as convenient tools to study proteases function and activity using in vivo and in vitro assays of different pathological disorders (diabetes, cancer metastasis, pulmonary diseases or hypertension); to determine the cellular localization of the proteinases (activity based probes), to be used in proteomic approach or as the reactive antigens to develop a catalytic function within the antibodies binding site. Herein we present the development of α-aminoalkylphosphonate diaryl esters as inhibitors of several serine proteases including dipeptidyl peptidase IV, cathepsin G, human neutrophil elastase, mast cell chymase and urokinase-type plasminogen activator. We have provided a historical perspective as well as a comprehensive report of the most recent studies in this field.

Oligonucleotide derivatives in nucleic acid hybridization analysis. III. Synthesis and investigation of properties of oligonucleotides, bearing bifunctional non-nucleotide insertion

Non-nucleotide phosporamidites were synthetized, having branched backbone with different position of functional groups. Obtained phosphoramidite monomers contain intercalator moiety--6-chloro-2-methoxyacridine, and additional hydroxyl residue protected with dimethoxytrityl group or with tert-butyldimethylsilyl group for post-synthetic modification. Synthesized oligothymidilates contain one or more modified units in different positions of sequence. Melting temperature and thermodynamic parameters of formation of complementary duplexes formed by modified oligonucleotides was defined (change in enthalpy and entropy). The introduction of intercalating residue causes a significant stabilization of DNA duplexes. It is shown that the efficiency of the fluorescence of acridine residue in the oligonucleotide conjugate significantly changes upon hybridization with DNA.

Functionalizing Biodegradable Dextran Scaffolds Using Living Radical Polymerization: New Versatile Nanoparticles for the Delivery of Therapeutic Molecules

Conferring biodegradability to nanoparticles is vitally important when nanomedicine applications are being targeted, as this prevents potential problems with bioaccumulation of byproducts after delivery. In this work, dextran has been modified (and rendered hydrophobic) by partial acetalation. A solid state NMR method was first developed to fully characterize the acetalated polymers. In a subsequent synthetic step, RAFT functionality was attached via residual unmodified hydroxyl groups. The RAFT groups were then used in a living free radical polymerization reaction to control the growth of hydrophilic PEG-methacrylate chains, thereby generating amphiphilic comblike polymers. The amphiphilic polymers were then self-assembled in water to form various morphologies, including small vesicles, wormlike rods, and micellar structures, with PEG at the periphery acting as a nonfouling biocompatible polymer layer. The acetalated dextran nanoparticles were designed for potential doxorubicin (DOX) delivery application based on the premise that in the cell compartments (endosome, lysozome) the acetalated dextran would hydrolyze, destroying the nanoparticle structure, releasing the encapsulated DOX. In-vitro studies confirmed minimal cytotoxicity of the (unloaded) nanoparticles, even after 3 days, proving that the hydrolysis products from the acetal groups (methanol and acetone) had no observable cytotoxic effect. An intriguing initial result is reported that in vitro studies of DOX-loaded dextran-nanoparticles (compared to free DOX) revealed an increased differential toxicity toward a cancer cell line when compared to a normal cell line. Efficient accumulation of DOX in a human neuroblastoma cell line (SY-5Y) was confirmed by both confocal microscopy and flow cytometry measurements. Furthermore, the time dependent release of DOX was monitored using fluorescence lifetime imaging microscopy (FLIM) in SY-5Y live cells. FLIM revealed bimodal lifetime distributions, showing the accumulation of both DOX-loaded dextran-nanoparticles and subsequent release of DOX in the living cells. From FLIM data analysis, the amount of DOX released in SY-5Y cells was found to increase from 35% to 55% when the incubation time increased from 3 h to 24 h.

Chemical recycling of PET using neopentyl glycol: Reaction kinetics and preparation of polyurethane coatings

Recycling of post-consumer poly(ethylene terephthalate) (PET) is a worldwide concern due to its environmental impact and large increasing volume of these materials produced by society. Current work aims at effective recycling of waste PET from soft drink bottles by glycolysis method and thereby utilization of the recycled product for coating application.In the investigation, we report neopentyl glycol (NPG), which till date is not studied much for chemical recycling of PET, as an effective diol for glycolysis reaction. NPG was used in a molar ratio of 1:6 (PET:NPG) and the glycolysis reaction was carried out at 200–220°C in presence of 0.5% zinc acetate as a trans-esterification catalyst. The progress of glycolysis reaction was studied by means of molecular weight of residual PET and hydroxyl value of the glycolyzed oligomer. The glycolyzed oligomer was also characterized using gel permeation chromatography (GPC) and differential scanning calorimetry (DSC) to study its molecular weight distribution and the thermal characteristics respectively. The glycolyzed monomeric product was purified and characterized by conventional method of hydroxyl and saponification number, Fourier transform infrared spectroscopy (FTIR), Proton NMR (1H NMR) spectroscopy, DSC, X-ray diffraction (XRD) and gas chromatography–mass spectroscopy (GC–MS). Further polyester (PE) polyol was successfully synthesized by polyesterification of glycolyzed monomeric product, adipic acid, isophthalic acid and trimethylol propane. Polyurethane coatings were prepared from the polyester polyol and different commercial polyisocyanate curing agents and applied on mild steel panels. The coated films were evaluated for their optical, mechanical and chemical properties. Thermal properties of coatings were investigated by DSC and thermogravimetric analysis (TGA).

Thermoplastic Cellulose Propionate-graft-Poly(L-lactide) Copolymers Homogeneously Synthesized by "One Pot" Process from Native Cellulose

Using native cellulose as the starting materials and 4-dimethylaminopyridine(DMAP) as the catalyst,a series of novel cellulose propionate-graft-poly(L-lactide) copolymers(CP-g-PLAs) was synthesized in an ionic liquid AmimCl via "one pot" process.DMAP can effectively catalyze the propionylation of cellulose with propionic anhydride and the subsequent ring-opening grafting copolymerization of L-lactide(LA) from residual hydroxyl groups in cellulose.The structure of CP-g-PLA copolymers could be well controlled by changing the molar ratio of propionate hydride/cellulose and LA/cellulose.When PLA content above 27.46%,the copolymers exhibited thermoplastic behavior and could be shaped by conventional melt processing methods,such as injection molding.

Improved chemical stabilities for end-capped high performance liquid chromatography stationary phases based on poly(methyloctadecylsiloxane) thermally immobilized onto metalized silicas

Endcapped stationary phases were prepared after thermal immobilization of poly(methyloctadecylsiloxane) (PMODS) onto zirconized and titanized silica supports. These new stationary phases have lower densities of residual hydroxyl groups, according to infrared spectroscopy and 29Si CP-MAS NMR and as shown by the symmetrical peaks of basic compounds from the Tanaka, Engelhardt and SRM 870 test mixtures. Stability tests for the endcapped stationary phases, measured using severe alkaline conditions (70:30 (v/v) methanol:0.05mol/L K2CO3/KHCO3, pH 10, 50°C), revealed that the stabilities of these phases are greater than the stabilities of similar nonendcapped phases. The stationary phases showed good performance for the separation of basic pharmaceuticals.

Polarity-dependent photoemission of in situ cleaved zinc oxide single crystals

Abstract

Preparation of waterborne hyperbranched polyurethane acrylate/LDH nanocomposite

A series of novel waterborne hyperbranched polyurethane acrylate (WHPUA)/layered double hydroxide (LDH) nanocomposites based on hyperbranched aliphatic polyester Boltorn H20 (H20) and MgAl-LDH were successfully synthesized by in situ polymerization approach. The MgAl-LDH was firstly modified by sodium dodecyl sulfate (SDS) through the coprecipitation method, and then grafted by isophorone diisocyanate (IPDI), forming a complex with NCO groups at the surface and interlayer of LDH (LDH-DS-NCO). The residual hydroxyl groups after modification with succinic anhydride were crosslinked by the semi-adduct of IPDI reacted with HEA, and LDH-DS-NCO, followed by a neutralization reaction with triethylamine. The resulting water dispersible hyperbranched polyurethane acrylate WHPUA/LDH hybrid oligomer was then exposed to a medium pressure mercury lamp, forming a partially exfoliated WHPUA/LDH nanocomposite in the presence of a fragmental photoinitiator. The chemical structure, crystal configuration, morphology of WHPUA/LDH nanocomposite were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and high resolution transmission electron microscopy. The experimental results indicated that both the intercalated and exfoliated structures were formed in the UV cured polymer/LDH nanocomposite. The TGA results showed that the thermal stability was improved. Moreover, the pencil hardness was greatly increased, and the flexibility remained at an acceptable level for the UV cured polymer/LDH nanocomposites.

Core–shell magnetic chitosan particles functionalized by grafting: Synthesis and characterization

A method for preparing magnetic composite particles with a core containing iron oxide encapsulated in crosslinked chitosan (CS) and a functionalized synthetic copolymer shell is proposed and optimized. The magnetic material is produced in situ. Surface vinyl groups are introduced by attaching glycidyl methacrylate (GMA) to the hydroxyl or amino chitosan residues via ether or N-alkyl bonds in acidic medium. These groups are used in a subsequent synthesis step as starting points for free radical copolymerization of GMA, ethylene glycol dimethacrylate (EGDMA) and poly(ethylene glycol methylmethacrylate) (PEG-MMA). The epoxy rings are opened in the final step with ethylenediamine (EDA). The results confirm that a grafted polymer layer has been anchored on the surface by covalent bonds. Sorption batch experiments using copper (II) ion solutions were conducted in order to compare the performance of the synthesized materials as heavy metal adsorbents. The functionalized particles show superior adsorption capacity compared to the ungrafted material.

Catalytic methanation reaction over alumina supported cobalt oxide doped noble metal oxides for the purification of simulated natural gas

A series of alumina supported cobalt oxide based catalysts doped with noble metals such as ruthenium and platinum were prepared by wet impregnation method. The variables studied were difference ratio and calcination temperatures. Pt/Co(10:90)/Al2O3 catalyst calcined at 700°C was found to be the best catalyst which able to convert 70.10% of CO2 into methane with 47% of CH4 formation at maximum temperature studied of 400°C. X-ray diffraction analysis showed that this catalyst possessed the active site Co3O4 in face-centered cubic and PtO2 in the orthorhombic phase with Al2O3 existed in the cubic phase. According to the FESEM micrographs, both fresh and spent Pt/Co(10:90)/Al2O3 catalysts displayed small particle size with undefined shape. Nitrogen Adsorption analysis showed that 5.50% reduction of the total surface area for the spent Pt/Co(10:90)/Al2O3 catalyst. Meanwhile, Energy Dispersive X-ray analysis (EDX) indicated that Co and Pt were reduced by 0.74% and 0.14% respectively on the spent Pt/Co(10:90)/Al2O3 catalyst. Characterization using FT-IR and TGA-DTA analysis revealed the existence of residual nitrate and hydroxyl compounds on the Pt/Co(10:90)/Al2O3 catalyst.

Microstructure evolution of ammonia‐catalyzed phenolic resin during thermooxidative aging

AbstractThe thermooxidative aging of ammonia‐catalyzed phenolic resin for 30 days at 60–170°C was investigated in this article. The aging mechanism and thermal properties of the phenolic resin during thermooxidative aging were described by thermogravimetry (TG)–Fourier transform infrared (FTIR) spectroscopy, attenuated total reflectance (ATR)–FTIR spectroscopy, and dynamic mechanical thermal analysis. The results show that the CN bond decomposed into ammonia and the dehydration condensation between the residual hydroxyl groups occurred during the thermooxidative aging. Because of the presence of oxygen, the methylene bridges were oxidized into carbonyl groups. After aging for 30 days, the mass loss ratio reached 4.50%. The results of weight change at high temperatures coincided with the results of TG–FTIR spectroscopy and ATR–FTIR spectroscopy. The glass‐transition temperature (Tg) increased from 240 to 312°C after thermooxidative aging for 30 days, which revealed the postcuring of phenolic resins. In addition, an empirical equation between the weight change ratio and Tg was obtained. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Impact resistance enhancement by adding epoxy ended hyperbranched polyester to DGEBA photocured thermosets

Epoxy-functionalized HBP was synthesized and used as toughening additive in epoxy based UV-curable formulations. The addition of the HBP-epox induced an increase of epoxy group conversion, probably through both an activated monomer mechanism, involving the residual hydroxyl groups, and a copolymerization reaction, involving the epoxy functionalities present on the surface of the HBP. Phase separation was reached during UV-Curing, which assured to maintain the good thermomechanical properties of the cured epoxy matrix improving the impact resistance.

Admittance and subthreshold characteristics of atomic-layer-deposition Al2O3 on In0.53Ga0.47As in surface and buried channel flatband metal-oxide-semiconductor field effect transistors

The admittances and subthreshold characteristics of capacitors and MOSFETs on buried and surface In0.53Ga0.47As channel flatband wafers, with a dielectric of Al2O3 deposited on In0.53Ga0.47As, are reported. The admittance characteristics of both wafers indicate the presence of defect states within the oxide, in common with a number of other oxides on In0.53Ga0.47As. The two wafers studied have not been hydrogen annealed, but do show some similar features to FGA treated oxides on n+ substrates. We discuss how the possible presence of residual hydroxyl ions in as-grown Al2O3 may explain these similarities and also account for many of the changes in the properties of FGA treated n+ samples. The issues around the comparison of subthreshold swing (SS) results and the impact of transistor design parameters on the energy portion of the defect state distribution affecting efficient device switching are discussed. The interface state model is applied to low source-drain voltage SS data to extract an effective interface state density (Dit) that includes interface and oxide traps. The logarithmic gate voltage sweep rate dependence of the SS Dit is used to extract an oxide trap density (Dot) and a simple method is used to estimate the Fermi level position within the band gap, Et. The Al2O3 Dit(Et) and Dot(Et) distributions are found to be similar to each other and to the results of our analysis of Gd0.25Ga0.15O0.6/Ga2O3 and HfO2/Al2O3 on In0.53Ga0.47As, adding weight to the suggestion of there being a common defect state distribution and perhaps a common cause of defects states for a number of oxides on In0.53Ga0.47As.

Sequential three-step three-photon near-infrared quantum splitting in β-NaYF4:Tm3+

We report on sequential three-step three-photon near-infrared (NIR) quantum splitting in Tm3+-doped β-NaYF4, where an incident blue photon around 470 nm is split into three NIR photons (1165, 1466, and 1800 nm). The underlying mechanism is analyzed by means of static and dynamic photoemission spectroscopy. Here, an experimental total quantum yield of ∼32% is obtained. When quenching due to residual hydroxyl groups and other defect species can be overcome, numerical analyses indicate a theoretical maximum quantum yield of 158%, suggesting application in efficient spectral converters.