Tritiated water, formation

Hydrogenation reactions in which H2/D2/T2 gases are replaced by various formates proceed very rapidly under MW irradiation conditions (Scheme 6.54) [182]. The pattern of labeling can be easily modified and the advantages are especially noteworthy in the case of tritium where high specific activity tritiated water is hazardous to use. 

The formation of surface oxides on the prism faces of graphite single crystals was shown by Hennig (67). The experiments have been described on page 191. Adsorption studies with tritiated water by Montet (68) confirmed this result. 

The most direct route towards functionalized aliphatic polyesters is based on the functionalization of polyester chains. This approach is a very appealing because a wide range of functionalized aliphatic polyesters could then be made available from a single precursor. This approach was implemented by Vert and coworkers using a two-step process. Eirst, PCL was metallated by lithium diisopropylamide with formation of a poly(enolate). Second, the poly(enolate) was reacted with an electrophile such as naphthoyl chloride [101], benzylchloroformate [101] acetophenone [101], benzaldehyde [101], carbon dioxide [102] tritiated water [103], ot-bromoacetoxy-co-methoxy-poly(ethylene oxide) [104], or iodine [105] (Fig. 26). The implementation of this strategy is, however, difficult because of a severe competition between chain metallation and chain degradation. Moreover, the content of functionalization is quite low (<30%), even under optimized conditions. 

The formation of 76a is essential, as the enol 76 would not be expected to be decarboxylated. When allowed to react in tritiated water, both L-ascorbic acid and D-amfomo-hexulosonic acid produced 2-furaldehyde having an activity approximately 60% of that of the solvent most of the activity was situated at the a-carbon atom. The failure to detect any pentose is probably ascribable to the high reactivity of the 1,2-enediol (77). 

The present work was undertaken in an attempt to shed light on the mechanism of hydroxyproline formation in collagen biosynthesis and on the site of action of ascorbate. It was recognized that these phenomena were very likely to be closely interrelated. Proline labeled with tritium was used because it was anticipated that tritium released from proline during hydroxylation would appear in the tissue water as tritiated water. The use of tritiated proline in such a system might then provide a new parameter for following the hydroxylation reaction, provided that the formation of tritiated water was stoichiometrically related to the formation of hydroxyproline. Such an approach might conceivably permit the demonstration of hydroxylation and peptide bond formation as separate chemical steps. 

The data given in Table VI show that there was a considerable increase in formation of tritiated water upon in vitro addition of ascorbic acid. Addition of ascorbic acid failed to increase tritiated water for mation with minces of normal granuloma, and no effect was observed... 

Figure 3. Formation of tritiated water from tritiated proline by granuloma from normal and scorbutic guinea pigs...

Despite the divergent results obtained with different preparations of tritiated proline, we have found that the ratio of the tritiated water formed to the tritiated hydroxyproline formed is constant for a given batch of tritiated proline. Since in the carrageenin tumor system there is a definite relationship between the formation of tritiated water and tritiated hydroxyproline, this system should be of value in obtaining definitive results when appropriately labeled prolines are available. This is apparently not true for the chick embryo, in which there is a considerable metabolism of proline to other products and therefore a much greater formation of tritiated water (23). 

It is conceivable that the reduced formation of tritiated water observed in scurvy could be due to a general reduction in protein synthesis, but this would not explain the marked differences between the specific activities of proline and hydroxyproline observed, nor would it explain observations in our laboratory that glycine and tyrosine are incorporated at rates similar to that of incorporation of proline into the collagen of granuloma obtained from scorbutic animals. 

The striking increases in the formation of tritiated water and tritiated hydroxyproline on in vitro addition of ascorbate are consistent with a function of this vitamin in hydroxylation—probably at step 3. The present results do not support a systemic ascorbic acid-mediated effect, the belief that ascorbic acid functions in the maintenance of collagen, or acts by stimulating maturation of the fibroblasts in the system under study here. The present data do not support the possibility that intermediates containing hydroxyproline accumulate in scurvy. The proposal that ascorbic acid is involved in the hydroxylation reaction itself is consistent with studies on the nonenzymatic hydroxylation of proline (4) and on enzymatic hydroxylation of other compounds (5, 20, 21, 44, 51). 

If this scheme is correct, it should be possible to obtain conditions under which protein synthesis but not hydroxylation is blocked. That this may be possible experimentally is suggested by the results of recent experiments (24) in our laboratory, which have shown that in the presence of puromycin, the formation of collagen hydroxyproline determined in carageenin tumors as described here is markedly reduced, but that hydroxylation (as determined by the formation of tritiated water and tritiated hydroxyproline) continues. Further work—especially efforts directed at isolation of intermediates—are in progress. 

Tritium-labelled CI-921 (16b) has been obtained in an exchange reaction with tritiated water and unlabelled 76, catalysed by platinum black in HOAc. Any labile tritium has been removed in vacuo using MeOH as a solvent. The product had, after preparative silica-gel plate chromatography of 76b and after TLC of the formate salt of 76b, a specific activity of 4.2Ci/mmol, with radiochemical purity greater than 99%. The tritiated salt of high specific activity had, after converting it to the free base and dilution with the 2-hydroxyethanesulphonate salt of unlabelled CI-921 and purification, a final specific activity of 59.3 mCi/mmol. 

The lower graph of Figure 2 relates to the flood with the same chemical slug and formation brine, but with oil at waterflood residual saturation in the core. This time, the tritium concentration in the effluent liquids peaked at 0.82 pore volumes of total chemical slug injected—0.17 pore volumes earlier than when there was no oil in the core. The tritiated water peaked earlier when there was oil in the core due to the pore volume occupied by the oil. According to the oil production curve, 16 percent of the pore volume of the core was occupied by oil when the tritium peaked. 

The flood history is summarized in Table 3. First baseline pressure drops were determined across the 1.8 m core during simultaneous injection of brine (without surfactant) and gas at a fixed frontal advance rate and varying gas fractional flows. A frontal advance rate of 4.0 m/day was selected to ensure a flow rate higher than the critical rate for effective foam formation and propagation. A non-adsorbing tracer, tritiated water, was added to the brine so that the breakthrough of the tracer could be compared with the breakthrough of the gas. 

The formation of 2-furaldehyde on acid-catalysed dehydration, etc., of 1-benzyl-amino-l-deoxy-D-f/ireo-pentulose and l-benzylamino-l-deoxy-o-fructuronic acid has been studied in isotopically labelled water (either acidified deuterium oxide or tritiated water).The pattern of labelling of the 2-furaldehyde derived from the latter compound is consistent with a mechanism involving the decarboxylation of a Py-unsaturated carboxylic acid intermediate (see also p. 136). 

A series of reported studies provide some insights into the nature and the role of bound water in the passivity of austenitic stainless steels [4-6]. The studies primarily focused on the passivity of t)rpe 304 stainless steel, passivated in deaerated 0.5 M H2SO4. Radiotracer studies were conducted with tritiated water in order to determine the quantity of water bound into the lattice following the formation of the passive film. In addition, the rate of desorption of bound water from the film was determined by dioxane solvent extraction. Dynamic rupture and self-repair of the passive film were seen to be critically influenced by the nature of the bound water. Two classes of bound water were determine from XPS, radiotracer, Coulombic titration, pitting incubation, and noise analysis [4-6]. The two classes of bound water were of the following types (a) M-H2O and M-OH (aquo and ola-tion groups) and (b) M-0 or M-OOH with 0X0 and olation bridges. 

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