Glycol substrate

The latter method, the template method, involves a reaction to produce a transition state similar to the desired product using a template. The template should have a shape similar to the space of the product. The template interacts with the substrate by forming noncovalent bonds such as coordination bonds (Fig. 3). The representative and most successful examples are found in crown ether chemistry. In the chemistry, alkali metals act as templates to create a crown-ether-like transition state with an ethylene glycol substrate by using metal-oxygen coordination bonds. 

Fig. 17. Doubly labelled ethylene glycol substrates used to investigate the stereospecificity of hydroxyl migration.

The use of secondary alcohols as reductants for DODH was first reported by Elhnan, Bergman, and coworkers, who employed Re-carbonyl compounds, e.g., Re2(CO)io, as pre-catalysts under aerobic conditions (Scheme 16) [36]. Optimized conditions used the glycol substrate with the mono-alcohol as the solvent, e.g., 3-octanol, at 150-175°C, with 1-2.5 mol% Re2(CO)io and TsOH as a co-catalyst (2-5 mol%). Good yields of the olefin (50-84%) were obtained with representative glycols. The sy -3,4-decanediol was converted highly selectively to trans-3-decene, implicating a sy -eUmination process in the diol to olefin conversion (Scheme 17). Erythritol was converted moderately efficiently to 2,5-dihydrofuran (62% yield), presumably the result of initial 1,4-diol dehydration followed by DODH of the THF-diol intermediate. The nature of the active catalyst was unknown at the time, but was speculated to be an oxidized Re species. 

Enzymatic synthesis offluorinated polyesters was demonstrated (133). Fluo-rinated diols such as 2,2,3,3-tetrafluoro-l,4-butanediol and 2,2,3,3,4,4-hexafluoro-1,5-pen tanediol were used as glycol substrate and polymerized with divinyl adipate using lipase CA catalyst. The enzymatic synthesis of polyester was also achieved in supercritical fluoroform solvent by the polymerization of bis(2,2,2-trichloroethyl) adipate and 1,4-butanediol (134). The molecular weight increased as a fiinction of the pressure. 

Further steps m glycolysis use the d glyceraldehyde 3 phosphate formed m the aldolase catalyzed cleavage reaction as a substrate Its coproduct dihydroxyacetone phosphate is not wasted however The enzyme triose phosphate isomerase converts dihydroxyacetone phosphate to d glyceraldehyde 3 phosphate which enters the glycol ysis pathway for further transformations... 

Stamp-Pad Inks. These inks are impregnated into a cloth or foam mbber pad and transferred by pressure to mbber type which is then stamped or impressed against the substrate. The inks must be completely nondrying in the pad and yet dry by rapid penetration into the paper. Since it is desirable that the total ink soak into the stock, dyes are used rather than pigments. The vehicles used are usually glycols. 

Water-Based Writing Inks. These consist of very fine pigment dispersions in aqueous media containing small amounts of glycol or glycerol and a dispersing aid. They dry mainly by evaporation and quick wetting of ceUulosic fibers in paper substrates. 

Formulas for representative floor poHshes are Hsted in References 3, 12, 13, and 25. An aqueous formula may contain 0—12 wt % polymer, 0—12 wt % resin, 0—6 wt % wax, 0.3—1.5 wt % tris(butoxyethyl)phosphate, 1—6 wt % glycol ether, and 0—1 wt % zinc, with water filling the rest. Water-clear floor finishes contain Htfle or no wax, whereas buffable products contain relatively large amounts of wax. Sealers contain Htfle wax and relatively large amounts of emulsion polymers (28). For industrial use, sealers are appHed to porous substrates to fiH the pores and prevent poHshes that are used as topcoats from soaking into the floor. 

Reactive (unsaturated) epoxy resins (qv) are reaction products of multiple glycidyl ethers of phenoHc base polymer substrates with methacrylic, acryhc, or fumaric acids. Reactive (unsaturated) polyester resins are reaction products of glycols and diacids (aromatic, aUphatic, unsaturated) esterified with acryhc or methacrylic acids (see POLYESTERS,unsaturated). Reactive polyether resins are typically poly(ethylene glycol (600) dimethacrylate) or poly(ethylene glycol (400) diacrylate) (see PoLYETPiERs). 

Polyalcohols, such as glycerol, sugar, sorbitol, and propylene glycol may prevent denaturation (28). Also substrates or substrate analogues often stabilize by conferring an increased rigidity to the enzyme stmcture. 

Mino and Kaizerman [12] established that certain. ceric salts such as the nitrate and sulphate form very effective redox systems in the presence of organic reducing agents such as alcohols, thiols, glycols, aldehyde, and amines. Duke and coworkers [14,15] suggested the formation of an intermediate complex between the substrate and ceric ion, which subsequently is disproportionate to a free radical species. Evidence of complex formation between Ce(IV) and cellulose has been studied by several investigators [16-19]. Using alcohol the reaction can be written as follows ... 

A final class of multifunctional initiators is based on the use a (muUi)functional polymer and a low molecular weight redox agent. Radicals on the polymer chain arc generated from the polymer bound functionality by a redox reaction. Ideally, no free initiating species are formed. The best known of this class are the polyol-redox and related systems. Polymers containing hydroxy or glycol and related functionality are subject to one electron oxidation by species such as ceric ions or periodate (Scheme 7.23).266,267 Substrates such as cellulose,... 

As would be expected in a substrate with a poor leaving group the predominant elimination process is of the Hofmann type. However, the authors did find some unexpected reactions. For example, the p-nitrophenyl sulphone was completely consumed within six hours of heating with the glycolate system, yet alkenes formed only a minor part of the products, the major part not being clearly identified. The p-dimethylaminophenyl sulphone was three to six times more reactive than the other sulphones, but it also underwent elimination at a significant rate with either solvent, even in the absence of alkoxides. The reasons for this are obscure. 

In concentrated NaOH, chitin becomes alkali chitin which reacts with 2-chloroethanol to yield 0-(2-hydroxyethyl) chitin, known as glycol chitin this compoimd was probably the first derivative to find practical use (as the recommended substrate for lysozyme). Alkali chitin with sodium monochloroacetate yields the widely used water-soluble 0-carboxymethyl chitin sodium salt [118]. The latter is also particularly susceptible to lysozyme, and its oUgomers are degraded by N-acetylglucosaminidase, thus it is convenient for medical appHcations, including bone regeneration. 

The simplest way to prepare a biocatalyst for use in organic solvents and, at the same time, to adjust key parameters, such as pH, is its lyophilization or precipitation from aqueous solutions. These preparations, however, can undergo substrate diffusion limitations or prevent enzyme-substrate interaction because of protein-protein stacking. Enzyme lyophilization in the presence of lyoprotectants (polyethylene glycol, various sugars), ligands, and salts have often yielded preparations that are markedly more active than those obtained in the absence of additives [19]. Besides that, the addition of these ligands can also affect enzyme selectivity as follows. 

Adsorption on solid matrices, which improves (at optimal protein/support ratios) enzyme dispersion, reduces diffusion limitations and favors substrate access to individual enzyme molecules. Immobilized lipases with excellent activity and stability were obtained by entrapping the enzymes in hydrophobic sol-gel materials [20]. Finally, in order to minimize substrate diffusion limitations and maximize enzyme dispersion, various approaches have been attempted to solubilize the biocatalysts in organic solvents. The most widespread method is the one based on the covalent linking of the amphiphilic polymer polyethylene glycol (PEG) to enzyme molecules [21]. 

Amorphous films of the (Zn,Fe)S semiconductor have been obtained by electrodeposition on TO substrates from a diethylene glycol solution containing Ss, FeCl2, and ZnCl2 reagents [102]. The films were annealed at 285 °C in argon to give sphalerite and pyrrhotite (Zn,Fe)S phases. A direct relationship was observed... 

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