Covalent chemical modifications

Neoglycosylation of proteins was also applied to the modification of the psychrophilic Atlantic cod trypsin the applicability of psychrophilic enzymes is limited because of their lower thermodynamic stability, despite their higher catalytic rate. It has been shown that the thermodynamic stability could be enhanced appreciably by covalent chemical modification with an oxidized sucrose polymer without affecting the enzymatic activity. The acquired stability of cod trypsin was found to be on par with the mesophilic porcine trypsin.40... 

Adding polar functional groups to cross-linked, apolar polymeric resins by covalent chemical modification has developed particularly for generation of SPE sorbents suitable for recovery of polar compounds. Hydrophilic functional groups such as acetyl, benzoyl, o-carboxybenzoyl, 2-carboxy-3/4-nitrobenzoyl, 2,4-dicarboxybenzoyl, hydroxymethyl, sulfonate, trimethyl-ammonium, and tetrakis(/>-carboxyphenyl)porphyrin have been chemically... 

More recently, covalent chemical modification has been used as a powerful tool to enhance the functionality and stability of enzymes, for example, the covalent link of flavin to papain turned a protease into an oxido-reductase [107]. The use of this methodology was rekindled as a result of the explosion in the interest in commercial and synthetic applications of enzymes [108]. As a consequence, enzymes with new properties such as stability at extreme pH conditions, temperature, or solubility in organic solvents are being generated. 

Thioredoxin, reduced with mercaptoethylamine, has been subjected to covalent chemical modifications employing monofunctional organoarsenical reagents, HjNPhAsO and HO(CH2)4AsCl2, specific for spatially close thiols. The modifications resulted in the formation of stable 15-membered cyclic dithioarsenite ring structures,... 

Enzyme activity can be regulated by covalent modification or by noncovalent (allosteric) modification. A few enzymes can undergo both forms of modification (e.g., glycogen phosphorylase and glutamine synthetase). Some covalent chemical modifications are phosphorylation and dephosphorylation, acetylation and deacetylation, adeny-lylation and deadenylylation, uridylylation and deuridyly-lation, and methylation and demethylation. In mammalian systems, phosphorylation and dephosphorylation are most commonly used as means of metabolic control. Phosphorylation is catalyzed by protein kinases and occurs at specific seryl (or threonyl) residues and occasionally at tyrosyl residues these amino acid residues are not usually part of the catalytic site of the enzyme. Dephosphorylation is accomplished by phosphoprotein phosphatases ... 

It was shown that the polyribosomal form of mRNP complexes is actively translated, whereas the free form is not. One mi t expect that a covalent chemical modification of some of the mRNA proteins, such as ADP-ribosylation, will render the mRNA available for translation. We characterized the mRNA-associated ADP-iibosyl transferase in plasmac) oma, in Krebs II, ascite tumor cells, and in liver. Several auto(ADP-ribosylated) proteins could be obtained when mRNP particles were incubated with NAD. It is unlikely that we are dealing with a contamination of chromatin since in plasmocytoma the enzymatic activity in mRNP represent 34% of the total cellular activity, while the maximum DNA contamination is only 4%. Moreover, after DNAse hydrolysis the enzymatic activity remains unchanged and addition of DNA is without effect [31]. More information on these mRNP particles will be given by Thomassin et al. (this volume). 

Abiman, P, Wildgoose, G., and Compton, R. (2008) Investigating the mechanism for the covalent chemical modification of multiwalled carbon nanotubes using aryl diazonium salts. Int.. Electrochem. Sci, 3 (2), 104-117. 

We have designed and/or studied several families of mono- and polynuclear organometallic complexes aimed at the selective and covalent chemical modification of proteins through their lysine residues. Chronologically, the first reagents included an N-hydroxysuccinimide ester function that is known from classical... 

The salt washed thylakoid membranes from spinach chloroplasts were treated with a primary amine-specific fluorescent chemical modifier, Fluorescamine (4-Phenylspiro furan-2 lQ 1-phthalan 3t3 dione). The effects of this covalent chemical modification on various processes of energy transduction were studied. It is suggested that the chemical modification by fluorescamine of free amino group of coupling factor 1 results in different conformations of CFi ... 

The chemical bonding theory of adhesion applied to silicones involves the formation of covalent bonds across an interface. This mechanism strongly depends on both the reactivity of the selected silicone cure system and the presence of reactive groups on the surface of the substrate. Some of the reactive groups that can be present in a silicone system have been discussed in Section 3.1. The silicone adhesive can be formulated so that there is an excess of these reactive groups, which can react with the substrate to form covalent bonds. It is also possible to enhance chemical bonding through the use of adhesion promoters or chemical modification of the substrate surface. 

The chemical modification techniques refer to the treatments used to modify the chemical compositions of polymer surfaces. Those can also be divided into two categories modification by direct chemical reaction with a given solution (wet treatment) and modification by covalent bonding of suitable macromolecular chains to the polymer surface (grafting). Among these techniques, surface grafting has been widely used to modify the surface of PDMS. 

The new phases were discovered by the combination of exploratory synthesis and a phase compatibility study. As commonly practised, the new studies were initially made through the chemical modification of a known phase. Inclusion of salt in some cases is incidental, and the formation of mixed-framework structures can be considered a result of phase segregation (for the lack of a better term) between chemically dissimilar covalent oxide lattices and space-filling, charge-compensating salts. Limited-phase compatibility studies were performed around the region where thermodynamically stable phases were discovered. Thus far, we have enjoyed much success in isolating new salt-inclusion solids via exploratory synthesis. 

As neutral carriers for the chemical modification, 16-crown-5 and calix[4]arene derivatives possessing a triethoxysilyl group (7) and (8) were designed for Na sensors. Triethoxysilylethyl-16-crown-5(7) was then mixed with a silicone-rubber precursor for the membrane fabrication accompanying covalent bonding of the neutral carrier. Comparison of IR spectra before and after extraction of the nonbonded neutral carrier... 

The in situ bulk polymerization of vinyl monomers in PET and the graft polymerization of vinyl monomers to PET are potential useful tools for the chemical modification of this polymer. The distinction between in situ polymerization and graft polymerization is a relatively minor one, and from a practical point of view may be of no significance. In graft polymerization, the newly formed polymer is covalently bonded to a site on the host polymer (PET), while the in situ bulk polymerization of a vinyl monomer results in a polymer that is physically entraped in the PET. The vinyl polymerization in the PET is usually carried out in the presence of the swelling solvent, thereby maintaining the swollen PET structure during polymerization. The swollen structure allows the monomer to diffuse in sufficient quantities to react at the active centers that have been produced by chemical initiation (with AIBM) before termination takes place. 

A qualitatively new approach to the surface pretreatment of solid electrodes is their chemical modification, which means a controlled attachment of suitable redox-active molecules to the electrode surface. The anchored surface molecules act as charge mediators between the elctrode and a substance in the electrolyte. A great effort in this respect was triggered in 1975 when Miller et al. attached the optically active methylester of phenylalanine by covalent bonding to a carbon electrode via the surface oxygen functionalities (cf. Fig. 5.27). Thus prepared, so-called chiral electrode showed stereospecific reduction of 4-acetylpyridine and ethylph-enylglyoxylate (but the product actually contained only a slight excess of one enantiomer). 

In a concurrently published report [160] Crooks and coworkers reported similar MUA-SAMs modified by covalent linking of hyperbranched macromolecules. These films containing a high density of surface carboxylic acid groups could selectively bind metal ions or undergo chemical modification. 

Covalent immobilization is performed through a chemical reaction between the protein molecule and the solid support (matrix). While the reactive moieties on the support can be chosen relatively freely, chemical modification of the protein tends to result in a decrease of its biological activity. Therefore, immobilization via reactive residues of the amino acids is preferred. To design suitable immobilization methods some guidelines should be followed. 

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