Native groups

Acylation reactions can be done at the nucleophilic sites on pyrimidines using activated forms of carboxylic acids. Acylation of functional groups in nucleotides typically is used for protection during synthesis (Reese, 1973). However, for bioconjugate applications, the reactivity of native groups on pyrimidines is not as great as that obtained using an amine-terminal spacer derivative, such as those described in Chapter 27, Section 2.1. Yields and reaction rates are typically low for direct acylation or alkylation of pyrimidine bases, especially in aqueous environments. 

The O-acetyl substituents of the native, group C polysaccharide were located by comparing its 13C-n.m.r. spectrum with that of the O-deacetylated, group C polysaccharide (see Fig. 2). The appearance of characteristic multiplets in some of the signals of the native polysaccharide showed that the O-acetyl groups are distributed exclusively between 0-7 and 0-8 of its sialic acid residues. 

Fig. 40.—Agar-diffusion pattern of the acid hydrolyzate of antigens and anti-group L Streptococci serum (S) acid hydrolyzate of group L polysaccharide (well A) native group L polysaccharide (well N), and enzyme hydrolyzate of group L polysaccharide (well E). Photograph of the paper chromatogram, showing release of carbohydrate from the polysaccharide by 1 h of acid hydrolysis, and of enzyme hydrolysis for 6-h periods.

A member of the platinum group, ruthenium occurs native with other members of the group in ores found in the Ural mountains and in North and South America. It is also found along with other platinum metals in small but commercial quantities in pentlandite of the Sudbury, Ontario, nickel-mining region, and in pyroxinite deposits of South Africa. 

Platinum occurs native, accompanied by small quantities of iridium, osmium, palladium, ruthenium, and rhodium, all belonging to the same group of metals. These are found in the alluvial deposits of the Ural mountains, of Columbia, and of certain western American states. Sperrylite, occurring with the nickel-bearing deposits of Sudbury, Ontario, is the source of a considerable amount of metal. 

Protein tertiary structure is also influenced by the environment In water a globu lar protein usually adopts a shape that places its hydrophobic groups toward the interior with Its polar groups on the surface where they are solvated by water molecules About 65% of the mass of most cells is water and the proteins present m cells are said to be m their native state—the tertiary structure m which they express their biological activ ity When the tertiary structure of a protein is disrupted by adding substances that cause the protein chain to unfold the protein becomes denatured and loses most if not all of Its activity Evidence that supports the view that the tertiary structure is dictated by the primary structure includes experiments m which proteins are denatured and allowed to stand whereupon they are observed to spontaneously readopt their native state confer matron with full recovery of biological activity... 

The significance of phenoxy anions is well recognized in the isolation of kraft and other water-insoluble technical lignins by acid precipitation. The ioniza tion of phenoHc hydroxyl groups coupled with the reduction of molecular size renders native lignin soluble in the aqueous pulping solution, thus enabling its separation from the polysaccharide components of wood. 

With the exception of peanuts, most of the important nuts from around the world are home on trees, many of them from native seedlings. Among the latter group are the beechnut, Bra2il nut, butternut, chestnut, filbert, hickory nut, pecan, pine nut, and black walnut. The pecan, Knglish walnut, filbert, and almond are the four principal edible tree nuts produced in the United States, where the term Knglish walnut is used synonymously with the Persian or Carpathian walnut (2). 

Gofactors. Frequendy proteins exist in their native state in association with other nonprotein molecules or cofactors, which are cmcial to their function. These may be simple metal ions, such as Fe " in hemerythrin or Ca " in calmodulin a heme group, as for the globins nucleotides, as for dehydrogenases, etc. 

Compared to native starches, monophosphate esters have a decreased gelatinization temperature range and swell in cold water at a DS of 0.07. Starch phosphates have increased paste viscosity and clarity and decreased retrogradation. Their properties are in many ways similar to those of potato starch, which naturally contains phosphate groups. 

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