Heterogeneous hydrolysis

Related applications include peptide/protein hydrolysis, heterogeneous catalysis reactions, acid digestion of samples, (e.g. tissue, implants, catalysts, drugs, etc), for AA / ICP / ICP-MS analysis, solvent extractions, processing and/or destruction of toxic chemicals, chemotherapy and anti-neoplastic agents. 

Additionally, metal fluorides are extremely sensitive to traces of water. Probably due to a combination of specific surface area and susceptibility to hydrolysis, heterogeneous acid catalysts for use in large-scale fluorination processes are usually based on either chromia or 7-alumina, which become fluorinated in situ. 

Heterogeneous Catalysis. The main discovery of the 1980s was the use of titanium sihcaUte (TS-1) a synthetic zeoHte from the ZSM family containing no aluminum and where some titanium atoms replace siUcon atoms in the crystalline system (Ti/Si = 5%) (33). This zeoHte can be obtained by the hydrolysis of a siUcate and an alkyl titanate in the presence of quaternary ammonium hydroxide followed by heating to 170°C. Mainly studies have been devoted to the stmcture of TS-1 and its behavior toward H2O2 (34). The oxidation properties of the couple H2O2/TS-I have been extensively developed in... 

Hardness on the Mohs scale is often above 8 and sometimes approaches 10 (diamond). These properties commend nitrides for use as crucibles, high-temperature reaction vessels, thermocouple sheaths and related applications. Several metal nitrides are also used as heterogeneous catalysts, notably the iron nitrides in the Fischer-Tropsch hydriding of carbonyls. Few chemical reactions of metal nitrides have been studied the most characteristic (often extremely slow but occasionally rapid) is hydrolysis to give ammonia or nitrogen ... 

P-Lactamases are enzymes that hydrolyze the P-lactam ring of P-lactamantibiotics (penicillins, cephalosporins, monobactams and carbapenems). They are the most common cause of P-lactam resistance. Most enzymes use a serine residue in the active site that attacks the P-lactam-amid carbonyl group. The covalently formed acylester is then hydrolyzed to reactivate the P-lacta-mase and liberates the inactivated antibiotic. Metallo P-lactamases use Zn(II) bound water for hydrolysis of the P-lactam bond. P-Lactamases constitute a heterogeneous group of enzymes with differences in molecular structures, in substrate preferences and in the genetic localizations of the encoding gene (Table 1). 

Nonmuscle/smooth muscle myosins-Il are structurally similar to striated muscle myosin-II, but they have slower rates of ATP hydrolysis than do their striated muscle counterparts. Nonmuscle/smooth muscle myosin-II is also regulated differently than striated muscle myosin-II. Nonmuscle myosin-II is divided into the invertebrate and vertebrate branches (Cheney et al., 1993). This group is ubiquitous because it is present in most lower organisms, such as slime molds, amoeba, sea urchins, etc., and in virtually all mammalian nonmuscle cells. Smooth muscle myosin-II is also somewhat heterogeneous in that at least three separate forms of smooth muscle heavy chains, with molecular weights of 196,000, 200,000, and 204,000 have been identified (Kawamoto and Adelstein, 1987). The physiological properties of these separate myosin heavy chains are not yet known. 

Bertrand and Santelli (89) have investigated the hydrolysis, under apparently heterogeneous conditions, of 4,5-hexadien-2-yl tosylate, 114, and 4-methyl4,5-hexadien-2-yl tosylate, 115. After 90 min at 80°, 114 upon steam distillation yields a mixture consisting of 3% hydrocarbon 67% of cis- and rrans-2-methylcyclopropyl methyl ketone, 116 and 30% of 4,5-hexadien-2-ol, 117. When optically active 114 was treated under similar conditions, the resulting rrans-2-methylcyclopropyl methyl ketone had an inverted configuration at the reaction center, whereas the dienol 117 was found to be racemic (90). This... 

An intriguing influence of a cosolvent immiscible with water on the enantioselec-tivity of the enzyme-catalyzed hydrolysis was observed. It was proven that enzyme enantioselectivity is directly correlated with the cosolvent hydrophobicity. In the best example, for ethyl ether as cosolvent, the reaction proceeded with E = 55, and the target compound was obtained in 33% yield with 92.7% ee. This finding may be of great practical importance, particularly in industrial processes [24], since it will enable better optimization of enzyme-catalyzed processes. It is clear that, in future, immobilized enzymes, as heterogeneous catalysts, wiU be widely used in most industrial transformations, especially in the preparation of pharmaceuticals [25]. 

A brief summary of current and potential processes is given in Table 8.1. As shown in the table, most of the reactions are hydrolysis, hydrogenolysis, hydration, hydrogenation, oxidation, and isomerization reactions, where catalysis plays a key role. Particularly, the role of heterogeneous catalysts has increased in this connection in recent years therefore, this chapter concerns mostly the application of heterogeneous solid catalysts in the transformation of biomass. An extensive review of various chemicals originating from nature is provided by Maki-Arvela et al. [33]. 

The coupling of solute transport in the GI lumen with solute lumenal metabolism (homogeneous reaction) and membrane metabolism (heterogeneous reaction) has been discussed by Sinko et al. [54] and is more generally treated in Cussler s text [55], At the cellular level, solute metabolism can occur at the mucosal membrane, in the enterocyte cytosol, and in the endoplasmic reticulum (or microsomal compartment). For peptide drugs, the extent of hydrolysis by lumenal and membrane-bound peptidases reduces drug availability for intestinal absorption [56], Preferential hydrolysis (metabolic specificity) has been targeted for reconversion... 

Under basic conditions, the hydrolysis rates of R4 nSi(OMe)n decrease with an increasing number of alkyl or aryl substituents [3], By using RSi(OMe)3/Si(OMe)4 mixtures and appropriate reaction conditions, a quasi two-step sol-gel process provides particles of a controlled heterogeneity, having a SiC>2 core, and organyl substituents mainly on their surface [2],... 

Heterogeneous catalysts, particularly zeolites, have been found suitable for performing transformations of biomass carbohydrates for the production of fine and specialty chemicals.123 From these catalytic routes, the hydrolysis of abundant biomass saccharides, such as cellulose or sucrose, is of particular interest. The latter disaccharide constitutes one of the main renewable raw materials employed for the production of biobased products, notably food additives and pharmaceuticals.124 Hydrolysis of sucrose leads to a 1 1 mixture of glucose and fructose, termed invert sugar and, depending on the reaction conditions, the subsequent formation of 5-hydroxymethylfurfural (HMF) as a by-product resulting from dehydration of fructose. HMF is a versatile intermediate used in industry, and can be derivatized to yield a number of polymerizable furanoid monomers. In particular, HMF has been used in the manufacture of special phenolic resins.125... 

C. Moreau, J. Lecomte, S. Mseddi, and N. Zmimita, Stereoelectronic effects in hydrolysis and hydrogenolysis of acetals and thioacetals in the presence of heterogeneous catalysts, J. Mol. Catal. A Chem., 125 (1997) 143-149. 

R. Shukla, X. E. Verykios, and R. Mutharasan, Isomerization and hydrolysis reactions of important disaccharides over inorganic heterogeneous catalysts,... 

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