Chemical modification of horseradish peroxidase with several methoxypolyethylene glycols

The chemical modification of ε-NH₂ lysine residues of horseradish peroxidase (E.C. 1.11.1.7) with several mPEG was carried out. The modified enzymes were studied through Chromatographic and electrophoretic methods; the extent of mPEG linking was determined using¹H-NMR. Peroxidase, modified with mPEG ranging from 350 to 5000, activated with 4-nitrophenylchloroformate (mPEGpn), showed a better thermal stability than the native, but there was no correlation between the length of the polymer adduct and the improvement. The enzyme was modified with mPEG (5000) activated by cyanuric chloride (mPEGcc). The number of modified lysine increased, but the thermal behavior of mPEGcc peroxidase was similar to those of mPEGpn enzymes. In all cases, the modification did not markedly change the stability in organic solvents.     

Chemical modification of E. coli L-asparaginase with polyethylene glycol grafted vinylpyrrolidone–maleic anhydride copolymer

A series of polyethylene glycol grafted vinylpyrrolidone–maleic anhydride copolymers [P(VMP)] was synthesized by radical copolymerization of vinylpyrrolidone, maleic anhydride and polyethylene glycol maleic acid monoester. Escherichia coli l -asparaginase was chemically modified with these copolymers. The modified l -asparaginase exhibited the complete loss of antigenicity towards anti-asparaginase serum from rabbit. The highest enzyme activity of the modified l -asparaginase without antigenicity was retained by 59% of the nonmodified one. The modified enzyme was also more resistant to trypsin in vitro. When tested in vivo, the native l -asparaginase was quickly cleared from the plasma of rabbits (half-life time: t_1/2=1.2 hr), whereas the modified enzyme showed prolonged clearance from plasma (t_1/2=53 hr). © 1997 John Wiley & Sons, Ltd.     

Chemical modification of polyvinyl chloride with thiourea

Russian Chemical Bulletin - The quasi-homogeneous (“synthesis in gel”) conditions for functionalization of polyvinyl chloride (PVC) with thiourea were experimentally selected. It was...     

Chemical modification of rolivsans with epoxy resins

New glassy network copolymers exhibiting enhanced heat resistance were prepared by thermochemical transformations of rolivsans modified with small amounts (5 ± 3%) of epoxy resins. The influence of the composition of these copolymers on their thermomechanical properties was evaluated by performing dynamic mechanical and thermal analysis and by studying the temperature dependences of the ultimate strength at three-point bending.     

Chemical modification of estafiatin

A high reactivity of the olefinic double bonds of the lignin (Lg) macromolecule in the reaction with molecular chlorine has been found which has permitted the chlorination of Lg to be carried out under cryogenic conditions at 150–250 K. The process takes place by a radical-chain mechanism with a length of the kinetic chain of approximately 1000 units. The bulk of the chlorine is consumed in the olefinic chains of the Lg. Other reaction products besides chlorolignin are hydrogen chloride and phenoxyl radicals, which have singlet ESR spectrum (H=1.0–1.2 mT) and are retained in the chlorinated samples of Lg to 250 K.Institute of Chemical Physics, Academy of Sciences of the USSR, Chernogolovka, Moscow Province. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 671–676, September–October, 1990.     

Chemical modification of estafiatin

The halogenation, epoxidation, acetylation, and oxidation of the sesquiterpene--lactone estafiatin (I) has given eight derivatives. It has been shown that during the epoxidation of estafiatone (IV) the formation of a -lactone takes place as the result of the Bayer-Villiger oxidation of the cyclopentanone fragment. A stereoselective conversion of estafiatin into the known natural guaianolide isozaluzanin C is described. The structures of the derivatives synthesized were established on the basis of their IR, UV, PMR, and mass spectra.Institute of Organic Synthesis and Coal Chemistry, Kazakh Academy of Sciences. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 648–653, September–October, 1991.     

Chemical modification of argolide

Chemical transformations have been made of argolide, a sesquiterpene lactone of the germacrane type, as a result of which new epoxy, amino, and hydroxy derivatives of it have been obtained.Institute of Phytochemistry, Academy of Sciences of the Republic of Kazakhstan, Karaganda, fax (3212) 433144, e-mail: arglabin@phyto, karaganda, su. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 188–192, March–April, 1999.     

Surface modification of nanoporous alumina surfaces with poly(ethylene glycol)

Nanoporous alumina surfaces have a variety of applications in biosensors, biofiltration, and targeted drug delivery. However, the fabrication route to create these nanopores in alumina results in surface defects in the crystal lattice. This results in inherent charge on the porous surface causing biofouling, that is, nonspecific adsorption of biomolecules. Poly(ethylene glycol) (PEG) is known to form biocompatible nonfouling films on silicon surfaces. However, its application to alumina surfaces is very limited and has not been well investigated. In this study, we have covalently attached PEG to nanoporous alumina surfaces to improve their nonfouling properties. A PEG-silane coupling technique was used to modify the surface. Different concentrations of PEG for different immobilization times were used to form PEG films of various grafting densities. X-ray photoelectron spectroscopy (XPS) was used to verify the presence of PEG moieties on the alumina surface. High-resolution C1s spectra show that with an increase in concentration and immobilization time, the grafting density of PEG also increases. Further, a standard overlayer model was used to calculate the thickness of PEG films formed using the XPS intensities of the Al2p peaks. The films formed by this technique are less than 2.5 nm thick, suggesting that such films will not clog the pores which are in the range of 70-80 nm.     

Chemical modification of silica surfaces

The formation of phenylaerosil via silica hydride in the gas phase and the subsequent introduction of nitro and amino groups in solution has been followed using IR and UV spectroscopy. The direct reaction of aminophenyltriethoxysilane (APhS) with the silica surface has also been investigated.     

Chemical modification of polyolefin blends

The effect of crosslinking on the properties of low density polyethylene / polypropylene blends was investigated. It was found that crosslinking results in much higher deformability of the blends compared to uncrosslinked materials. A decrease in crystalline portion determined by DSC leads to lower modulus in crosslinked samples. High drawability of crosslinked samples is mainly attributed to peculiar behaviour of PE part of the crosslinked blend where thicker lamellae are formed during drawing.     

Chemical modification of polymeric hydrocarbons

Although polymeric hydrocarbons (PCH) carry no functions, they can be modified in many ways. Unsaturated PCH undergo addition reactions as hydrogenation, halogenation, epoxidation and thiol addition. Saturated PCH can be substituted with various functions, notably halogen and chlorosulfonyl groups. All PCH can be modified, by a grafting mechanism, with functional monomers as maleic anhydride. Some modified PCH play a major role in multiphase systems as blends, rubber-modified thermoplastics and thermoplastic elastomers. Attractive grafting procedures involve in-situ grafting in PCH/monomer solutions and during reactive blending processes.     

Chemical modification of poly(acrylonitrile) with amines

The chemical modification of poly(acrylonitrile) was carried out using monoethanolamine and 1,2-ethylenediamine. The effect of the reaction conditions on the content of basic groups was studied. Polymer analogous reactions were carried out by varying the amount of the starting reagents and the temperature. The amino-containing polymers were characterized by elemental analysis. The obtained water-soluble polymers were used as carriers of low-molecular substances. © 1996 John Wiley & Sons, Inc.     

Chemical modification of crystal-like mesoporous phenylene-silica with amino group

Amination of phenylene moieties in crystal-like mesoporous silica hybridized with phenylene is successfully achieved with close to 28% conversion of phenylene by a two-step chemical transformation process while preserving both the ordered mesostructure and crystal-like molecular scale periodicity of the parent material.     

Chemical modification of natural clays

Natural clay samples and calcined clay varieties treated with hydrochloric acid of various strengths were characterized by X-ray diffraction, positron annihilation spectroscopy, and IR spectroscopy. The specific surfaces and pore sizes were determined by nitrogen adsorption. The constituent phases of the clay were found to be nontronite, muscovite, quartz, and hematite; after calcination, quartz, muscovite, hematite, and an amorphous phase remained in the samples. The Brilliant Green adsorption properties and tribotechnical properties of the modified clays were studied. The natural clay was surface-modified chemically by means of consecutive exposure to 36.5% hydrochloric acid and an alkaline hydrolyzate of rice hulls. Calcination at 700°С destroyed the amorphous phase to a greater extent; exposure to acid provided a greater recovery of aluminum and iron ions from the surface of calcined samples. Native clay composites with an alkaline hydrolyzate of rice hulls were shown to have enhanced tribotechnical characteristics.     

Chemical modification of oximes with N-protected amino acids

The modification of oximes, including 5α-steroids, with N-protected amino acids, in solution phase, using benzotriazole methodology is reported.     

Chemical modification of neodymium high cis-1,4 polybutadiene with styreneoxide

The polymerization of 1,3-butadiene (BD) was carried out in the presence of a catalyst composed of neodymium 2-ethylhexanoate, triisobutyl aluminum, diisobutyl aluminum hydride (DIBAH), ethylaluminum sesquichloride and acetylacetone. The molecular weight of the BR could be controlled with DIBAH. The reactive polymer was then chemically modified with styreneoxide (STO). The STO content of BR increased with the decrease in the molecular weight of the BR. This polymer was modified by the STO at the chain terminal end. The physical properties of the vulcanizates with the modified BR were measured. The abrasion resistance and the tensile strength were found to be improved.