Chemical modification of sheep plasma glycoprotein

Glycoprotein isolated from sheep plasma was chemically modified, and the effect of chemical modification on biological activities and immunological cross reactions has been studied. The removal of sialic acid resulted in a change in the “overall conformation” of the glycoprotein as evidenced by a decrease in viscosity of the glycoprotein solution and an increased susceptibility of the glycoprotein to proteolytic enzymes. Sialic acid-free glycoprotein no longer inhibited the tryptic activity or prolonged the clotting time of plasma. However, it could react with the antiserum to sheep plasma glycoprotein. The periodate oxidation of sheep plasma glycoprotein resulted in a complete loss of inhibition of trypsin activity, prolongation of plasma clotting time, and the ability to cross-react with the rabbit antiserum. The significance of periodate oxidation in relation to the possible sequence of sugars in the carbohydrate prosthetic group in the glycoprotein is discussed. Iodination and heating in buffers of acid and alkaline pH values of sheep plasma glycoprotein resulted in complete loss of trypsin activity and ability to prolong plasma clotting time. Iodination of the glycoprotein did not affect the immunological cross-reactivity.

The Role of Interface Modification on Thermal Degradation and Crystallization Behavior of Composites from Commingled Polypropylene Fiber and Banana Fiber

The thermal degradation behavior of banana fiber and polypropylene/banana fiber composites has been studied by thermogravimetric analysis. Banana fiber was found to be decomposing in two stages, first one around 320 degrees C and the second one around 450 degrees C. For chemically treated banana fiber, the decomposition process has been at a higher temperature, indicating thermal stability for the treated fiber. Activation energies for thermal degradation were estimated using Coats and Redfern method. Calorific value of the banana fiber was measured using a constant volume isothermal bomb calorimeter. rystallization studies exhibited an increase in the crystallization temperature and crystallinity of polypropylene upon the addition of banana fiber. POLYM. COMPOS., 31:1113-1123, 2010. (C) 2009 Society of Plastics Engineers.

In situ surface modification of molybdenum-doped organic-inorganic hybrid TiO2 nanoparticles under hydrothermal conditions and treatment of pharmaceutical effluent

Molybdenum-doped TiO2 organic-inorganic hybrid nanoparticles were synthesized under mild hydrothermal conditions by in situ surface modification using n-butylamine. This was carried out at 150 degrees C at autogeneous pressure over 18 h. n-Butylamine was selected as a surfactant since it produced nanoparticles of the desired size and shape. The products were characterized using powder X-ray diffraction, Fourier transform infrared spectrometry, dynamic light-scattering spectroscopy, UV-Vis spectroscopy and transmission electron microscopy. Chemical oxygen demand was estimated in order to determine the photodegradation efficiency of the molybdenum-doped TiO2 hybrid nanoparticles in the treatment of pharmaceutical effluents. It was found that molybdenum-doped TiO2 hybrid nanoparticles showed higher photocatalytic efficiency than untreated TiO2 nanoparticles.

Beta-turns in nascent procollagen are sites of posttranslational enzymatic hydroxylation of proline

The selective hydroxylation of proline residues in nascent procollagen chains by prolyl hydroxylase (EC 1.14.11.2) can be understood in terms of the conformational feature of the -Pro-Gly-segments in linear peptides and globular proteins. The folded beta-turn conformation in such segments appears to be the conformational requirement for proline hydroxylation. The available data on the hydroxylation of native and synthetic substrates of prolyl hydroxylase are explained on the basis of the extent of beta-turn formation in them. Taken in conjunction with the conformational features of the hydroxyproline residue, our results bring out the conformational reason for the posttranslational proline hydroxylation which, it is proposed, leads to the "straightening" of the beta-turn segments into the linear triple-helical conformation.

Proteolytic susceptibility and methionine modification of monodeamidated ribonuclease A

The susceptibility of a monodeamidated RNAaseA (RNAaseAa1) towards carboxypeptidaseA , alpha-chymotrypsin and pepsin has been studied. Similar to RNAaseA, the C-terminal of RNAaseAa1 is not available for carboxypeptidaseA hydrolysis. The thermal stability of RNAaseAa1 as probed through chymotryptic digestion is found to be less than that of RNAaseA. Preliminary chromatographic analysis of the digested material, however, suggests that the nature of thermal transition might be the same in the two proteins. Pepsin inactivates RNAaseAa1 more slowly than does RNAaseA. Accordingly, less peptide bonds, almost half that of RNAaseA, are cleaved by pepsin in RNAaseAa1. The accumulation of RNAase-P type intermediates is not evident during peptic digestion of RNAaseAa1. Reaction with O-benzoquinone at low pH shows that methionines of the deamidated protein seem to have higher reactivities. These observations indicate a different structure for RNAaseAa1 at elevated temperature and low pH.

Effect of La modification on antiferroelectricity and dielectric phase transition in sol-gel grown PbZrO3 thin films

Antiferroelectricity of sol-gel grown pure and La modified PbZrO3 thin films, with a maximum extent of 6 mol%, has been characterized by temperature dependent P-E hysteresis loops within the applied electric field of 60 MV/m. It has been seen that on extent of La modification electric field induced phase transformation can be altered and at 40 degrees C its maximum value has been observed at +/- 38 MV/m on 6 mol% modifications whereas the minimum value is +/- 22 MV/m on 1 mol%. On La modification the variation of electric field induced phase transformations at 40 degrees C has been correlated with the temperature of ntiferroelectric phase condensation on cooling. The critical electric fields for saturated P-E hysteresis loops have been defined from field dependent maximum polarizations and their variations on La modification show a similar trend as found in their dielectric phase transition temperatures. (C) 2010 Elsevier Ltd. All rights reserved.

Wide Ranged La Modification in CCTO Ceramics Through Sol-Gel: Effect on Microstructure and Dielectric Properties

Sol-Gel method was employed to synthesize pure and wide ranged La-modified CaCu3Ti4O12 ceramics using mixed acetate-nitrate-alcoxide individual metal-ion precursors. SEM pictures revealed that grain size monotonously decreases with the extent of La incorporation. All the prepared ceramics manifested dielectric constant in the range similar to 10(3)-10(4). Dielectric loss was found to decrease with La incorporation and got optimized for 20% La3+ while retaining its high dielectric constant which may be industrially important. Room temperature Impedance spectroscopy suggested that decrease in grain resistance is responsible for reduction in dielectric loss according to Internal Barrier Layer Capacitor (IBLC) model.

Chemical toughening of epoxies. I. Structural modification of epoxy resins by reaction with hydroxy-terminated poly (butadiene-co-acrylonitrile)

In an attempt to toughen the epoxy resin matrix for fiber-reinforced composite applications, a chemical modification procedure of a commercially available bisphenol-A-based epoxy resin using reactive liquid rubber HTBN [hydroxy-terminated poly(butadiene-co-acrylonitrile)] and TDI (tolylene diisocyanate) is described. The progress of the reaction and the structural changes during modification process are studied using IR spectroscopy, viscosity data, and chemical analysis (epoxy value determination). The studies support the proposition that TDI acts as a coupling agent between the epoxy and HTBN, forming a urethane linkage with the former and an oxazolidone ring with the latter. The chemical reactions that possibly take place during the modification are discussed.

Chemical toughening of epoxies. I. Structural modification of epoxy resins by reaction with hydroxy-terminated poly(butadiene-co-acrylonitrile)

In an attempt to toughen the epoxy resin matrix for fiber-reinforced composite applications, a chemical modification procedure of a commercially available bisphenol-A-based epoxy resin using reactive liquid rubber HTBN [hydroxy-terminated poly(butadiene-co-acrylonitrile)] and TDI (tolylene diisocyanate) is described. The progress of the reaction and the structural changes during modification process are studied using IR spectroscopy, viscosity data, and chemical analysis (epoxy value determination). The studies support the proposition that TDI acts as a coupling agent between the epoxy and HTBN, forming a urethane linkage with the former and an oxazolidone ring with the latter. The chemical reactions that possibly take place during the modification are discussed.

Modification of the sugar specificity of a plant lectin: structural studies on a point mutant of Erythrina corallodendron lectin

A mutant of Erythrina corallodendron lectin was generated with the aim of enhancing its affinity for N-acetylgalactosamine. A tyrosine residue close to the binding site of the lectin was mutated to a glycine in order to facilitate stronger interactions between the acetamido group of the sugar and the lectin which were prevented by the side chain of the tyrosine in the wild-type lectin. The crystal structures of this Y106G mutant lectin in complex with galactose and N-acetylgalactosamine have been determined. A structural rationale has been provided for the differences in the relative binding affinities of the wild-type and mutant lectins towards the two sugars based on the structures. A hydrogen bond between the O6 atom of the sugars and the variable loop of the carbohydrate-binding site of the lectin is lost in the mutant complexes owing to a conformational change in the loop. This loss is compensated by an additional hydrogen bond that is formed between the acetamido group of the sugar and the mutant lectin in the complex with N-acetylgalactosamine, resulting in a higher affinity of the mutant lectin for N-acetylgalactosamine compared with that for galactose, in contrast to the almost equal affinity of the wild-type lectin for the two sugars. The structure of a complex of the mutant with a citrate ion bound at the carbohydrate-binding site that was obtained while attempting to crystallize the complexes with sugars is also presented.

Interaction of EcoP1 modification methylase with S-adenosyl-L-methionine: a UV-crosslinking study

EcoP1 modification methylase was radioactively labeled when incubated with S-adenosyl-L-[methyl-3H]methionine in the presence of ultraviolet light. Crosslinking of the enzyme as detected by electrophoresis on sodium dodecyl sulfate-polyacrylamide gel followed by fluorography and autoradiography, was shown to be specific by a number of criteria. More importantly, EcoP1 modification methylase was also radioactively labeled with S-adenosyl-L-[carboxyl-14C]methionine demonstrating that labeling involved binding of the entire AdoMet molecule rather than methylation of the protein. Further, c2 EcoP1 mutant DNA modification methylases which show negligible or very little methylation activity, correspondingly formed a weak or no adduct upon crosslinking. These results suggest that photolabeling of EcoP1 DNA modification methylase occurs at the AdoMet binding site.

Modification of photochemical reactivity on formation of inclusion complexes: photorearrangement of benzyl phenyl ethers and methyl phenoxyacetates

The photorearrangement of benzyl phenyl ethers and methyl phenoxyacetates was investigated in methanol and in complexes with cyclodextrin in both the solid state and aqueous solutions. Irradiation in cyclodextrin media leads to a large change in product distribution with a very significant ortho selectivity different from that found in methanol where the reaction is non-selective. For meta-substituted ethers and phenoxyacetates, an impressive regioselectivity between the two ortho-rearranged isomers is observed and this is significantly enhanced by increasing the substituent chain length which acts as a spacer to induce a tight fit between the host and the guest. The observed results are rationalized on the basis of specific orientations of the unsubstituted and meta-substituted ethers and phenoxyacetates in the cyclodextrin cavity.

DNA recognition by the EcoP15I and EcoPI modification methyltransferases

The DNA-binding properties of the EcoP15I DNA methyltransferase (M . EcoP15I; MTase) were studied using electrophoretic mobility shift assays. We show by molecular size-exclusion chromatography and dimethyl suberimidate crosslinking that M . EcoP15I is a dimer in solution. While M . EcoP15I binds approx. threefold more tightly to its recognition sequence, 5'-CAGCAG-3', than to non-specific sequences in the presence of AdoMet or its analogs, the discrimination between specific and non-specific sequences significantly increases in presence of ATP. These results suggest for the first time a role for ATP in DNA recognition by type-III restriction-modification enzymes. Furthermore, we show that although c2 EcoPI mutant MTases are defective in AdoMet binding, they are still able to bind DNA in a sequence-specific manner.