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.     

Physicochemical modification of nanodiamonds

Thermal modification of nanodiamonds in the atmosphere of argon and hydrogen and their chemical modification with oleum and chlorine at different temperatures were studied. The effect of the modification conditions on the catalytic activity of palladium catalysts supported by nanodiamonds in the reaction of nitrobenzene hydrogenation and on the adsorption properties of nanodiamonds with respect to benzene, chloroform, and water was analysed.     

Xyloglucan in cellulose modification

Xyloglucans are the principal polysaccharides coating and crosslinking cellulose microfibrills in the majority of land plants. This review summarizes current knowledge of xyloglucan structures, solution properties, and the mechanism of interaction of xyloglucans with cellulose. This knowledge base forms the platform for new biomimetic methods of cellulose surface modification with applications within the fields of textile manufacture, papermaking, and materials science. Recent advances using the enzyme xyloglucan endo-transglycosylase (XET, EC 2.4.1.207) to introduce varied chemical functionality onto cellulose surfaces are highlighted.     

Electrochemical modification of lignins

The results of the electrochemical sililation, phosphorylation, and fluorination of lignin are described. Lignin is a natural polymer, a large-scale side product of the hydrolysis and pulp-and-paper industries. The electrochemical modification processes and mechanisms of some reactions are presented. Applications of electrochemically obtained lignin derivatives are considered Deceased.     

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.     

Protein modification by arginylation

The modification of protein by arginine catalyzed by arginyltransferases (ATE1) described by the Kashina group in this issue shows that arginylation of protein occurs widely in biology and is being recognized as a key regulatory reaction such as phosphorylation of proteins (Wang et?al., 2011).     

Tautomeric modification of GlcNAc-thiazoline

The potent O-GlcNAcase (OGA) inhibitor GlcNAc-thiazoline has been modified by buffer- or acylation-induced imine-to-enamine conversion and then electrophile or radical addition (Xn = D3, F, N3, OH, SMe, COCF3, CF3). Several functionalized GlcNAc-thiazolines show highly selective inhibition of OGA vs human hexosaminidase and thus have promise as tools for targeted investigations of OGA, an enzyme linked to diabetes and neurodegeneration. A new radical addition/fragmentation reaction of the N-(trifluoroacetyl)enamine has been discovered.     

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.     

Plasmochemical modification of polymer surfaces

Influence of low-temperature plasma on the polymer surface was studied with the aim of preparing polymers with required surface properties.     

Surface modification in microchip electrophoresis

Different approaches and techniques for surface modification of microfluidic devices applied for microchip electrophoresis are reviewed. The main focus is on the improved electrophoretic separation by reducing analyte-wall interactions and manipulation of electroosmosis. Approaches and methods for permanent and dynamic surface modification of microfluidic devices, manufactured from glass, quartz and also different polymeric substrates, are described.     

Morphological modification of UHMPE fibers

UHMPE fibers can display several morphological features, including skin-core, microfibrillar and shish-kebab structures. In this work, an attempt was made to eliminate these morphologies by treating the UHMPE in a two-roll mill, at temperatures ranging from ambient to 145°C. Up to 130°C the tensile strength and modulus of the fiber were retained, and thermal analysis and crystallographic data showed that ordering in the fiber remained intact. The shish-kebab and microfibrillar morphologies were greatly reduced and the fiber cross-section was altered from circular to a flat ribbon.     

Mechanochemical modification of V-P-Bi-O catalysts

It has been shown that mechanochemical treatment of a V-P-Bi-O catalyst increases the surface area of the specimens and the surface concentration of phosphorus. The treatment also changes the ratio between concentrations of planes in the VOHP0₄·0.5H₂O phase, increasing the content of the plane of paired vanadyls, and lowers the crystallization temperature of the vanadyl pyrophosphate. All of these changes result in higher conversions in the oxidation of n-butane and higher selectivities of maleic anhydride formation.Translated from Teoreticheskaya i Éxperimental'naya Khimiya, Vol. 31, No. 5, pp. 313–315, September–October, 1995.     

Nematic-nematic modification in side-on-fixed polysiloxanes

Abstract

A series of side-chain liquid crystal polymers has been synthesized with mesogenic groups laterally branched to a polysiloxane backbone (the so-called side-on-fixed). An anomaly of the diamagnetic anisotropy in the nematic state was shown to be very sensitive to a number of structural parameters such as the length of the aliphatic tails, the length of the spacer and the fixation rate of the mesogenic groups on the backbone. On the basis of accurate density measurements, microscopic observations and X-ray diffraction experiments on aligned samples, the occurrence of a nematic-nematic transition connected to this anomaly is questionned.     

Drug delivery from hydrophobic-modified mesoporous silicas: Control via modification level and site-selective modification

Dimethylsilyl (DMS) modified mesoporous silicas were successfully prepared via co-condensation and post-grafting modification methods. The post-grafting modification was carried out by the reaction of the as-synthesized MCM-41 material (before CTAB removal) with diethoxydimethylsinale (DEDMS). N₂ adsorption-desorption and ²⁹Si MAS NMR characterization demonstrated that different amount of DMS groups were successfully incorporated into the co-condensation modified samples, and the functional DMS groups were placed selectively on the pore openings and external pore surfaces in the post-grafting modified samples. Subsequently, the controlled drug delivery properties from the resulting DMS-modified mesoporous silicas were investigated in detail. The drug adsorption experiments showed that the adsorption capacities were mainly depended on the content of silanol group (CSG) in the corresponding carriers. The in vitro tests exhibited that the incorporation of DMS groups greatly retarded the ibuprofen release rate. Moreover, the ibuprofen release profiles could be well modulated by varying DMS modification levels and site-selective distribution of functional groups in mesoporous carriers.     

Hydrothermal modification of carbon adsorbents

The effects of high-pressure autoclave treatments on porous structure and surface properties were studied for a variety of activated carbons (AC, synthetic and produced from plum stones) treated with water vapour, hydrogen peroxide (10–50%) or 10% aqueous ammonia solution at relatively low temperatures (250, 350, 400^○C). Surface and structural parameters of modified ACs were determined using nitrogen, water, ammonia and benzene adsorption isotherms. It was found that the effects of AC modification resulting in changes in their porous structure and surface chemistry depend on the kind of initial ACs, modifier type and concentration of modifier and treatment temperature. At the same conditions synthetic ACs are modified to a larger extent than ACs prepared using natural raw materials. Repeated treatment of a given carbon intensifies changes in its porous structure.     

Nematic-nematic modification in side-on-fixed polysiloxanes

A series of side-chain liquid crystal polymers has been synthesized with mesogenic groups laterally branched to a polysiloxane backbone (the so-called side-on-fixed). An anomaly of the diamagnetic anisotropy in the nematic state was shown to be very sensitive to a number of structural parameters such as the length of the aliphatic tails, the length of the spacer and the fixation rate of the mesogenic groups on the backbone. On the basis of accurate density measurements, microscopic observations and X-ray diffraction experiments on aligned samples, the occurrence of a nematic-nematic transition connected to this anomaly is questionned.     

Surface modification of waterborne polyurethane

Fluorinated urethane oligomers (SMAs) having repeat unit identical to the hard segment of base polyurethane (PU) have been synthesized and blended with base PU prior to dispersion. XPS and static contact angle measurements showed that surfaces of dispersion cast film are significantly enriched with SMA although SMA and base PU were miscible in bulk phase showing a single glass transition temperature. AFM showed that surface roughness of the dispersion cast film increased over 13 times with the addition of SMA (15%) providing possible mechanism of increased water and oil resistance as well as low friction coefficient of the film.     

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 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.