Dehydroxy lation

Given the large number of variables, Thomas et argued that it was important to carry out both univariate and multi-variate analyses of the data. Both types of analysis showed that LBTT, the activity of the 7a-dehydroxy-lation, and the distal colonic luminal pH were all significant risk factors for high proportions of DCA in serum (and by implication, in bile). Based on these results, the authors concluded that there was indeed prolonged colonic transit in conventional gallstone patients and that this, in turn, was likely to result in increased DCA formation, solubilisation (and therefore bioavailability) and absorption. 

Schwertmann, U. (1979) The influence of aluminum on iron oxides. V. Clay minerals as sources of aluminum. Soil Sci. 128 195-200 Schwertmann, U. (1984) The double dehydroxy-lation peak of goethite. Thermochim. Acta 78 39-46... 

In order to obtain different extent of lithiation in reaction (1) the following experimental variables were changed temperature of dehydroxy lation, the amount of butyl lithium used, temperature and time of the reaction. The palladium content of the catalyst was... 

Montmorillonite-Calcite (me) Mixture. Heated mixtures of montmorillonite and calcite yielded the phases given in Table I. Although the montmorillonite structure persisted through 400 °C, it underwent dehydroxy lation between 400 and 500 °C. Grim and Bradley (16) have shown that the general layered structure is able to survive the elimination of the (OH) water with moderate readjustments. This structure produces an X-ray diffraction pattern like that given in Table III. Table III represents data close to those observed in this study. This phase is called dehydroxylated montmorillonite in Table I. This phase disappeared between 700 and 800 °C as a result of the complete destruction of the montmorillonite crystal structure. Calcite decomposed between 500 and 600 °C to form lime that was present through 900 °C. 

Significant TS applications have been described by Butteridge et al., Bellchamber et al., and Shimada, " and one example is included here. Thermo-sonimetry has been applied to study the dehydroxy-lation behavior of kaolin, which show two regions of acoustic activity. The low temperature region corresponds to dehydroxylation and the high temperature region corresponds to recrystalization as metakaolinite. The relevant temperature regions of acoustic activity are defined by the coupled DTA analysis. 

The fact that the OH- positions can be occupied by mobile O2- ions or by vacancies is of vital importance for understanding the kinetics of the dehydroxy-lation reaction of HAp to oxyhydroxyapatite and oxyapatite, respectively. Rietveld refinements and spectroscopic studies of the structure of Ca-deficient synthetic apatite obtained from suspensions of monetite (DCPA, CaHP04) showed that crystalline products of the average composition Ca9303(PO4)6(OH)0606-1.97H2O were formed with a Ca/P ratio of 1.55 and a = 943.20 pm, c = 687.51 pm... 

Guggenheim S, Bailey SW (1978) Refinement of the margarite stractme in subgroup symmetiy Correction, further refinement, and comments. Am Mineral 63 186-187 Guggenheim S, Chang Y-H, Koster van Groos AF (1987) Muscovite dehydroxy lation High-temperature studies. Am Mineral 72 537-550... 

The higher the degassing temperature, the higher is the wavenumber of the absorbance diminution. This fact corresponds to a preferential dehydroxy-lation of the sUanols that interact the most strongly with neighbors. 

An investigation of the distribution of the dehydroxylation products of cholic and chenodeoxycholic acids by mixed human fecal microorganisms in vitro (27) has shown that lithocholic acid (formed by the bacterial dehydroxy lation of chenodeoxycholic acid) was recovered almost entirely in the... 

Mechanistie studies of the IspH (HMB-PP reduetase, 4-hydroxy-3-methylbut-2-enyl diphosphate reduetase) eatalysed reduetive dehydroxy-lation of 4-hydroxy-3-methyl-2-( )-l-diphosphate (130) to isopentenyl diphosphate (131) and rearranged dimethylallyl diphosphate (132), suggested that both the 4-OH group and the double bond of (130), may eon-tribute to the formation of a substrate-IspH complex (Scheme 34). ... 

It is highly probable that lattice vacancies created by removal of silicon may be filled up in the same way and under similar conditions as those remaining after release of aluminum. Thus, recrystallization of the desilicated products to particles with well-ordered crystal structure but traversed by nanopores is obviously effected by water steam present as reaction product of the dehydroxy-lation of hydroxyl nests . After the desihcation process, the zeolite is in the sodium (or potassium) form and this is known to be highly resistant towards hydrothermal effects. Therefore, it is to be expected that steaming represents the most effective method for the stabilization of desilicated zeolites avoiding the risk of concurrent dealumination. 

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