Selective chemical modification

Cysteine is the most frequently used residue for selective chemical modification of proteins due to its relatively low abundance in proteins and the increased nucleophilicity of the thiol group relative to other natural amino acid side chains. The intrinsic selectivity is low unless no cysteine is present or unless all unwanted cysteines... 

Selective chemical change of the serine—OH group to cysteine—SH in enzymes can be performed with extremely reactive serine residues in the active sites by the use of phenylmethylsulfonyl fluoride and, subsequently, thioacetic acid (Polgar and Bender, 1966). This selective chemical modification demonstrates the essential role of an—OH... 

Encapsulation of other material into carbon nanotubes would also open up a possibility for the applications to electrodevices. By applying the template method, perfect encapsulation of other material into carbon nanotubes became possible. No foreign material was observed on the outer surface of carbon nanotubes. The metal-filled uniform carbon nanotubes thus prepared can be regarded as a novel onedimensional composite, which could have a variety of potential applications (e.g novel catalyst for Pt metal-filled nanotubes, and magnetic nanodevice for Fe304-filled nanotubes). Furthermore, the template method enables selective chemical modification of the inner surface of carbon nanotubes. With this technique, carbon... 

The chemical synthesis of the Amanita toxins has presented several problems, in particular those related to the formation of the sulfur bridge. The latter has been explored with model compounds.[2 31 It has been found that the synthesis of the (sulfanyl)indole moiety can be achieved by reacting an indole compound with an alkanesulfenyl chloride. A model tryptathionine compound has been prepared by reacting A-acyl-L-cysteine and /V-acyl-L-tryptophan in the presence of A-chlorosuccinimide in glacial acetic acid at room temperature.[4] The sulfanylation reaction has been subsequently exploited for the selective chemical modification of tryptophan residues in proteins using 2-nitrophenylsulfenyl chlorideJ5 ... 

The understanding and prediction of such effects and the development of milder and more selective synthetic transformations, applicable to the synthesis of highly complex structures or to the selective chemical modification of proteins, DNA, or even living cells will continue to be the challenge for current and future generations of chemists. 

M15. Mahley, R. W., Innerarity, T. L., Weisgraber, K. H., and Oh, S. Y., Altered metabolism (in vivo and in vitro) of plasma lipoproteins after selective chemical modification of lysine residues of the apoproteins. J. Clin. Invest. 64, 743-750 (1979). 

Chemical modification of CNTs changes or improves their chemical and electrical properties, thereby expanding their application fields. All of the efforts for the chemical modification have been directed toward the outer surface of CNTs. No one has, however, attempted to differentiate between the outer and inner surfaces or to modify only the inner one while leaving the outer one as it is. One of the reasons for this is that both ends are generally closed for most CNTs, but even if they were open, such differentiation would be essentially impossible any chemical treatment to the inner surface always affects the outer one. Only the template technique enables such selective chemical modification of the inner surface of nanotubes. With this technique, CNTs with outer and inner surfaces that have different properties can be prepared, and unique adsorption behaviors and electrical properties can be expected from such CNTs with heteroproperties. 

Clearly, the phenomenon of pH memory has the potential to be utilized as a means of achieving selective chemical modification of ionizable fimctional groups, even for those within the same class, by controlling the pH of lyophilization. 

Selective chemical modification studies demonstrated that lysyl and arginyl residues were important in the interaction of apoE, as well as of apoBlOO, with the LDL receptor (Mahley et al., 1977a Weisgraber et ai, 1978). Thus, there are close parallels in the binding of both apoli-... 

The reactivity of conjugated double bonds is significantly different from that of isolated double bonds in the polymer backbone of polydienes. This difference can be used for selective chemical modification of the dienes with reactions such as the Diels—Alder reaction. With maleic anhydride as an enophile, selective addition to the terminal pair of conjugated double bonds in a chloroprene oligomer is complete in a few hours to give 102.391... 

Secondly, selective chemical modification may be performed because the carbohydrate residues have a distinct low reactivity. This can be done by periodate oxidation which cleaves C-C bonds bearing adjacent hydroxyl groups and converts them to aldehydes [25,26]. The generated dialdehyde can react with a variety of nucleophiles - usually primary amino groups on the surface of carrier materials. The resulting Schiff bases can be further stabilized by sodium boro-hydride, sodium cyanoborohydride or pyridine-borane reduction [27]. 

Two approaches were used for the initial studies of this problem. One involves selective chemical modification ofthe FeS-cluster followed by an examination ofthe effects on the electron-transfer pathways. The other is the specific alteration ofthe FeS-cluster(s) by site-directed mutagenesis. Results from these studies will be discussed here in their chronological order. 

Selective chemical modification. The usefulness of this technique is also limited to those residues, such as lysine, methionine and tyrosine, for which modification reactions are known. In some cases assignment of spectral lines to specific residues by this technique has been possible, but more often the selectivity of the reaction in situ is inadequate to permit an unequivocal interpretation. 

The face of the molecule as shown in Figs. 21-24 is probably the one seen by reductase and oxidase molecules, with entry and egress of electrons through the exposed edge of the heme. This, at least, is the simplest assumption in the absence of compelling evidence to the contrary. Which part of the crevice encounters each of the two molecules—oxidase and reductase—or whether or not they bind in the same region, are questions which can only be answered by selective chemical modification of residues on the surface of the cytochrome molecule or by physical chemical characterization of intermolecular complexes with cytochrome c. 

For some time, we have been interested in designing selective chemical modification reactions for coal with a particular emphasis upon characterizing the carbon skeleton of coal (2). The strategy for the approach starts with the working hypothesis that coal can be viewed as a three-dimensional macromolecule in which aromatic and hydroaromatic clusters are cross-linked to one another by various functional groups such as methylene units and polymethylene chains. In addition, the aromatic and hydroaromatic clusters, at least in bituminous coals, are assumed to be derived from polynuclear aromatic compounds (3, 4). 

The condensation of dimethyl diglycolate and aryl glyoxylates in the presence of potassium tert-butoxide as base provided a series of 4-arylfuran-3-ols bearing one tert-butyl ester and one methyl ester. As such, this furandicarboxylate allowed an easy differentiation of the two esters for selective chemical modifications <01TL6429>. 

TABLE 5.1 Selected Chemical Modification of Chitosan Toward Bioactive Intermediates of Chitosan Derivatives for Coupling with Peptides or Proteins... 

Scheme 3 Selective chemical modification of an MIP that targets specific classes of sites either (a) low affinity sites (as denoted as the more shallow imprints), or (b) sites with a specific selectivity.

Scheme 8 Representation of the guest directed selective chemical modification strategy. The depth of the imprint in these models corresponds to the binding affinity of that site.

Scheme 9 Selective chemical modification using the template molecule to mask one specific class of sites.

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