Insolubilization bonds

C. Oligo- and Poly-nucleotides.—The stepwise enzymatic synthesis of internucleotide bonds has been reviewed. A number of polynucleotides containing modified bases have been synthesised " in the past year from nucleoside triphosphates with the aid of a polymerase enzyme, and the enzymatic synthesis of oligodeoxyribonucleotides using terminal deoxynucleotidyl transferase has been studied. Primer-independent polynucleotide phosphorylase from Micrococcus luteus has been attached to cellulose after the latter has been activated with cyanogen bromide. The preparation of insolubilized enzyme has enabled large quantities of synthetic polynucleotides to be made. The soluble enzyme has been used to prepare various modified polycytidylic acids. ... 

Hargreaves has suggested that the insolubilization of some closely related polymers is due to photolytic homolysis of the endoperoxide 0-0 bond and subsequent generation of carbon-centered radicals from the O radicals (19). There are several facts that make this an extremely unlikely explanation for the data described here these include the quantitative insufficiency of the maximum amount of endoperoxide reaction obtainable with a few hundred mJ/cm2 dose (homolysis quantum yield <0.5 (46), and extinction coefficient 1 (M cm)-1 (47)), and the synthetic utility of such homolysis reactions in related molecules in the presence of good hydrogen atom donors (implying facile epoxide formation) (48). Clearly the crosslinking observed under N2 is not accounted for by this mechanism. 

Iwayanagi (40) recently extended this system into the mid-UV range by changing the sensitizer to an aromatic monoazide compound (4-azidochalcone). Insolubilization of this mid-UV resist does not result in a cross-linked matrix as occurs with the bisazide sensitized MRS. The primary reaction appears to be insertion of the reactive nitrene into a C-H bond on the ring, forming a secondary amine. 

These results led to the conclusion that denaturation and/or insolubilization of actomyosin and myosin during frozen storage is a result of aggregation caused by the progressive increase in intermolecular crosslinkages due to formation of hydrogen bonds, ionic bonds, hydrophobic bonds and disulfide bonds. 

Figure I. Effect of heating of soy milk before drying and effect of addition of N-ethylmaleimide (NEMI) to heated soy milk on the insolubilization of protein after drying. The curves are (a), dried without adding NEMI (b), dried after adding SEMI and (C), the values of (a) minus the values of (b). Curve (a) indicates total amount of insolubilized protein curve (b) indicates the amount of protein insolubilized by mechanisms other than by intermolecular disulfide bond formation and curve (c) indicates the amount of protein insolubilized through disulfide bond polymerization (3).

Since part of the insolubilization of heated soy milk protein during drying occurs through the sulfhydryl/disulfide bond interchange reaction, experiments were carried out so as to distinguish... 

Figure 7. Increase in the insolubilization of soybean protein during frozen storage at —5°C by the addition of small amounts of mercaptoethanol (ME), indicating the promotion of a sulfhydryl/disulfide interchange reaction by a disulfide bond splitting agent (lOj...

Irreversible insolubilization of proteins may occur mainly through formation of both intermolecular disulfide and hydrophobic bonds. The product can be quite different depending on the relative contribution of these two types of bonds. The hydrophobic bonds are formed among the hydrophobic amino acid side chains contributed by valine, leucine, isoleucine, phenylalanine, etc. 

Needless to say, the fixation of inorganic chemicals in wood by interaction with the wood substrate and extractives is beneficial and greatly improves the durability of these preservatives. Contrarily, other interactions provide less desirable reactions. For example, under certain circumstances copper and zinc can become so tightly bound to the wood that their efficacy as wood preservatives is reduced. This result occurs when copper acetate and zinc acetate are used to treat wood (53). In this form, these elements are salts of acetic acid and they form ion-exchange bonds with the wood components that are stable in the weak acid environment and cannot be ionized readily by water. Conversely, this reduction in efficacy does not occur when copper sulfate and zinc chloride are used because they are salts of strong acids and the pH of the environment prevents insolubilization of these elements by the wood. 

The G values (chemical events/100 ev absorbed) are also indications of the tendency of a polymer to degrade or insolubilize under any form of radiation in excess of bond energies. In Table XI, a compilation of the G values is noted along with the expended energy for each bond broken or formed. In the case of... 

Nakamura, Sakata and Kichuchi 48> have compared the thermal and photochemical crosslinking of poly (vinyl cinnamate). The critical hardening value required is approximately 1.3 crosslinks per macromolecule possessing a degree of polymerization of 1400. The minute amount of crosslinking required to insolubilize poly(vinyl cinnamate) makes the study of the process difficult insight can be obtained only by inference. Furthermore, Nakamura and Kikuchi 44> reported that the quantum yield of the disappearance of the double bonds in poly(vinyl cinnamate) decreased rapidly with irradiation time. Extrapolation to zero time of exposure indicated a quantum yield of 0,34. It therefore seems hazardous to base conclusions on observations of products which result from long irradiation times. 

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