Nonhydrolytic

Figure C2.17.1. Transmission electron micrograph of a Ti02 (anatase) nanocrystal. The mottled and unstmctured background is an amorjihous carbon support film. The nanocrystal is centred in die middle of die image. This microscopy allows for die direct imaging of die crystal stmcture, as well as the overall nanocrystal shape. This titania nanocrystal was syndiesized using die nonhydrolytic niediod outlined in [79].

Nonhydrolytic methods for the formation of siUcon dioxide from tetraalkoxysilanes have been reported (14—15). Others have been reinvestigated... 

Cyclodextrin stationary phases utilize cyclodextrins bound to a soHd support in such a way that the cyclodextrin is free to interact with solutes in solution. These bonded phases consist of cyclodextrin molecules linked to siUca gel by specific nonhydrolytic silane linkages (5,6). This stable cyclodextrin bonded phase is sold commercially under the trade name Cyclobond (Advanced Separation Technologies, Whippany, New Jersey). The vast majority of all reported hplc separations on CD-bonded phases utilize this media which was also the first chiral stationary phase (csp) developed for use in the reversed-phase mode. 

Some advantages of the Fmoc protective group are that it has excellent acid stability thus BOC and benzyl-based groups can be removed in its presence. It is readily cleaved, nonhydrolytically, by simple amines, and the protected amine is liberated as its free base. The Fmoc group is generally considered to be stable to hydrogenation conditions, but it has been shown that under some circumstances it can be cleaved with H2/Pd-C, AcOH, MeOH, (t /2 = 3-33 h). ... 

MejSil, CHCI3 or CH3CN, 25°, 6 min, 100% yield. Me3SiI also cleaves carbamates, esters, ethers, and ketals under neutral, nonhydrolytic conditions. Some selectivity can be achieved by control of reaction conditions. 

If the carbonyl group must be regenerated under nonhydrolytic conditions, (3-halo alcohols such as 3-bromopropane-l,2-diol or 2,2,2-trichloroethanol can be used for acetal formation. These groups can be removed by reduction with zinc, which leads to (3-elimination. 

Formation of 2-propanol and propene was confirmed by GC/MS. Chemisorption of Ti(0 Pr)4 is therefore suggested to be a consequence of nonhydrolytic condensation of the 2-propoxide ligands, which generates V-O-Ti bridges in the absence of surface hydroxyl groups. After removal of volatiles and desorption of physisorbed metal complexes, analysis reveals the presence of two equiv. Ti per V site on the surface, Table 1 (experiments 3 and 4). 

Alivisatos, A.P. (1999) A new nonhydrolytic single-precursor approach to surfactant-capped nanocrystals of transition metal oxides. Journal of the American Chemical Society, 121 (49), 11595-11596. 

Lyases decarboxylase, dehydratase, deoxyribose-phosphate aldolase nonhydrolytic bond cleavage... 

A few nonhydrolytic enzymes are able to catalyze the hydrolysis of some xenobiotics. These are briefly mentioned in the present context, and will be given greater attention in Chapt. 3, in regard to catalytic mechanism. 

Two major pathways are recognized to be of great pharmacological significance in the nonhydrolytic cleavage of nitrates, namely the thiol-dependent pathway and the hemoprotein-dependent pathway. A thiol-dependent pathway is also apparent for organic nitrites [5][30][31]. Before discussing... 

As early as 1855, the oxidation of guaiacol by peroxidase with hydrogen peroxide was observed by Schonbein [22]. Furthermore, the introduction of the PZ number (Purpurogallinzahl) by Willstatter and Stoll in 1917 [23] was probably the first attempt to define the catalytic activity for a nonhydrolytic enzyme. 

In nonhydrolytic sol-gel processing, by low-temperature thermolysis of the precursor (A1 compound in Scheme 3) in solution [110]... 

Nonhydrolytic sol-gel synthesis is a more recent variation on the sol-gel method. A metal halide is reacted with an oxygen derivative of the metal (Eq. 2-234). The reaction is catalyzed by Lewis acids such as FeCl3 and alkyl halide is a by-product [Hay and Raval, 2001], The reaction has been used to produce alumina (A1203) and titania (Ti02) as well as silica [Corriu and Leclercq, 1996]. 

Kriesel JW, Sander MS, et al (2001) Block copolymer-assisted synthesis of mesoporous, multicomponent oxides by nonhydrolytic, thermolytic decomposition of molecular precursors in nonpolar media. Chemistry of Materials 13(10), 3554-3563... 

One of the experimental limitations on the electron donor is that it must not catalyze the hydrolysis of the RBAX. It cannot, therefore, be a highly basic amine. We have chosen, therefore, to study the photoreduction of RBAX in the presence of a soluble nonhydrolytic donor, triphenyl n-butyl borate. 

Jpe selective, nonhydrolytic cleavage of glycosidic linkages [Eq. (8) 13]. This process is HtSeful in detennining structures of complex carbohydrates [14]. 

The role of ATP and S-adenosylmethionine in the reaction remains an intriguing but as yet unresolved question. Recently Yuan and Meselson have reported that in the presence of magnesium ion, ATP and S-adenosylmethionine the R-K endonuclease forms a specific complex with its DNA substrate (55). Complex formation is, however, observed at ATP concentrations (4 X 10-8 M) at which nucleolytic activity is not detectable. This result suggests that ATP may be involved in at least two steps (1) formation of a nonhydrolytic complex at low ATP levels and (2) formation of more stable (or more numerous) complexes and nucleolytic action at higher concentrations of ATP. The S-adenosylmethionine requirement for complex formation is in the same concentration range as observed for restriction. 

IMP does not accumulate in the cell but is converted to AMP, GMP, and the corresponding diphosphates and triphosphates. The two steps of the pathway from IMP to AMP (fig. 23.11) are typical reactions by which the amino group from aspartate is introduced into a product. The 6-hydroxyl group of IMP (tautomeric with the 6-keto group) is first displaced by the amino of aspartate to give adenylosuccinate, and the latter is then cleaved nonhydrolytically by adenylosuccinate lyase to yield fumarate and AMP. In the condensation of aspartate with IMP, cleavage of GTP to GDP and phosphate provides energy to drive the reaction. 

Alkyl ethers can act as nucleophiles in cyclofunctionalization reactions,17 and recently acetal oxygens have been shown to be excellent nucleophiles for participation in heteroatom cyclizations (Scheme 9). This reaction has been used as a nonhydrolytic procedure for unraveling complex acetals (conversion of 9 to 10),180 for specific liberation of an anomeric center (conversion of 11 to 12),181a for preparation of glycosyl bromides18115 and for saccharide coupling (reaction of 13 and 14 to give 15).182... 

Under nonhydrolytic conditions, 2-amino-1,8-naphthyridines (82) do, however, undergo the normal cyclization reactions with a-bromo ketones. Thus, imidazo[l,2- ]naphthyridines (83) are readily obtained.45... 

Since essentially all of the protein in the cellulose-grown culture or the sophorose-incubation mixture can be accounted for by the three principal proteins and the / -glucosidase, it seems reasonable to conclude that the multiplicity of enzymes seen after several days of culture growth are caused by degradation. This may be attributable either to inherent instability (3) or to the presence of hydrolytic enzymes (16). There seems to be no evidence for the Ci enzyme as a nonhydrolytic or affinity factor, since all known enzymes of the system are hydrolytic. That the sophorose-stimulated system (with no possible loss of the Ci ... 

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