Hydrolysis complexes formed

Plutonium(III) in aqueous solution, Pu " ( 4)> is pale blue. Aqueous plutonium(IV) is tan or brown the nitrate complex is green. Pu(V) is pale red-violet or pink in aqueous solution and is beUeved to be the ion PuO Pu(VI) is tan or orange in acid solution, and exists as the ion PuO. In neutral or basic solution Pu(VI) is yellow cationic and anionic hydrolysis complexes form. Pu(VII) has been described as blue-black. Its stmcture is unknown but may be the same as the six-coordinate NpO (OH) (91). Aqueous solutions of each oxidation state can be prepared by chemical oxidants or reductants... 

Hydrolysis. Complexes formed by Pu ions with OH represent hydrolysis reactions. There is extensive interaction between Pu + and water. Pu(Ill) hydrolyzes at ca pH 7 (105) the first hydrolysis equiUbrium is as follows ... 

An analysis of the RDF for the acid solution shows that the In3+ ion is bonded to six water molecules at 2.17 A (Fig. 28). The same In—H20 distance is found for octahedrally coordinated In3+ in crystal structures (223, 224). According to the difference curve this coordination is not changed by the hydrolysis. A possible model for a tetranuclear complex with four octahedrally coordinated In atoms occupying the four corners of a regular tetrahedron and joined by single hydroxo bridges is shown in Fig. 28. It is consistent with the experimental data and seems to be a likely model for the hydrolysis complexes formed in solution, but has not yet been found in crystal structures. 

Niobic Acid. Niobic acid, Nb20 XH2O, includes all hydrated forms of niobium pentoxide, where the degree of hydration depends on the method of preparation, age, etc. It is a white insoluble precipitate formed by acid hydrolysis of niobates that are prepared by alkaH pyrosulfate, carbonate, or hydroxide fusion base hydrolysis of niobium fluoride solutions or aqueous hydrolysis of chlorides or bromides. When it is formed in the presence of tannin, a volurninous red complex forms. Freshly precipitated niobic acid usually is coUoidal and is peptized by water washing, thus it is difficult to free from traces of electrolyte. Its properties vary with age and reactivity is noticeably diminished on standing for even a few days. It is soluble in concentrated hydrochloric and sulfuric acids but is reprecipitated on dilution and boiling and can be complexed when it is freshly made with oxaHc or tartaric acid. It is soluble in hydrofluoric acid of any concentration. 

Commercial condensed phosphoric acids are mixtures of linear polyphosphoric acids made by the thermal process either direcdy or as a by-product of heat recovery. Wet-process acid may also be concentrated to - 70% P2O5 by evaporation. Liaear phosphoric acids are strongly hygroscopic and undergo viscosity changes and hydrolysis to less complex forms when exposed to moist air. Upon dissolution ia excess water, hydrolytic degradation to phosphoric acid occurs the hydrolysis rate is highly temperature-dependent. At 25°C, the half-life for the formation of phosphoric acid from the condensed forms is several days, whereas at 100°C the half-life is a matter of minutes. 

The mono- and dialkan olamine titanates are water-soluble and slowly hydrolyze at pH 9.0. Loweting the pH iacreases the rate of hydrolysis, which is shown by the development of turbidity. Turbidity also occurs above pH 11. The tetrahydroxyalkylethylenediarnine titanate complexes form much more stable water solutions and can be used as dispersiag agents for aqueous Ti02 slurries (114). 

The kinetics of vinyl acetate emulsion polymeriza tion in the presence of alkyl phenyl ethoxylate surfactants of various chain lengths indicate that part of the emulsion polymerization occurs in the aqueous phase and part in the particles (115). A study of the emulsion polymerization of vinyl acetate in the presence of sodium lauryl sulfate reveals that a water-soluble poly(vinyl acetate)—sodium dodecyl sulfate polyelectrolyte complex forms, and that latex stabihty, polymer hydrolysis, and molecular weight are controlled by this phenomenon (116). 

Compounds of Tl have many similarities to those of the alkali metals TIOH is very soluble and is a strong base TI2CO3 is also soluble and resembles the corresponding Na and K compounds Tl forms colourless, well-crystallized salts of many oxoacids, and these tend to be anhydrous like those of the similarly sized Rb and Cs Tl salts of weak acids have a basic reaction in aqueous solution as a result of hydrolysis Tl forms polysulfldes (e.g. TI2S3) and polyiodides, etc. In other respects Tl resembles the more highly polarizing ion Ag+, e.g. in the colour and insolubility of its chromate, sulfide, arsenate and halides (except F), though it does not form ammine complexes in aqueous solution and its azide is not explosive. 

An alternative method for generating enriched 1,2-diols from meso-epoxides consists of asymmetric copolymerization with carbon dioxide. Nozaki demonstrated that a zinc complex formed in situ from diethylzinc and diphenylprolinol catalyzed the copolymerization with cyclohexene oxide in high yield. Alkaline hydrolysis of the isotactic polymer then liberated the trans diol in 94% yield and 70% ee (Scheme 7.20) [40]. Coates later found that other zinc complexes such as 12 are also effective in forming isotactic polymers [41-42]. 

The conformations of L-adenylyl-(3 5 )-L-adenosine (28) and L-adenylyl-(2 -> 5 )-L-adenosine (29), as deduced from circular dichroic spectra, are different from the corresponding DD-dinucleotides. < The n.m.r. and u.v. absorption spectra of (28) and (29) are the same as the DD-dimers and their chromatographic and electrophoretic properties appear identical. While (28) and (29) are resistant to enzymic hydrolysis they form complexes with polyU. 

The zinc complex formed with V,V -diphenylformamidinate is structurally analogous to the basic zinc acetate structure, as [Zn4(/i4-0)L6], and the basic beryllium acetate structure. It is prepared by hydrolysis of zinc bis(diphenylformamidinate).184 Mixed metal zinc lithium species were assembled from dimethyl zinc, t-butyl lithium, V.iV -diphenylbenzamidine and molecular oxygen. The amidinate compounds formed are dependent on the solvent and conditions. Zn2Li2 and... 

Bimetallic zinc complexes formed with hexaazamacrocycles were studied in the hydrolysis of activated carboxyesters. Potentiometric titration demonstrated the dominant presence of a dinuclear hydroxo bridged species at pH >7. /)-Nitrophenyl acetate is hydrolyzed with no loss of catalytic activity for at least 2.7 catalytic cycles 4... 

Previous workers (130, 259) had used a model in which the only complexes formed were BeL and Be2L2 for L = mp BeHL3- and Be2L2 for L = mdp. The discrepancy between the old results and the new ones may be traced to the influence of two factors incorrect allowance made for hydrolysis and unsophisticated methods of calculation, both of which are characteristic of the time when the old work was done. In any case there is no evidence in the recent work for the presence of dimeric species. 

The reaction mechanism of a-amylases is referred to as retaining, which means that the stereochemistry at the cleaved bond of the carbohydrate is retained. Hydrolysis of the glycosidic bond is mediated by an acid hydrolysis mechanism, which is in turn mediated by Aspl97 and Glu233 in pig pancreatic amylase. These interactions have been identified from X-ray crystallography. The aspartate residue has been shown to form a covalent bond with the Cl position of the substrate in X-ray structure of a complex formed by a structurally related glucosyltransferase. " The glutamate residue is located in vicinity to the chloride ion and acts as the acidic catalyst in the reaction. The catalytic site of a-amylases is located in a V-shaped depression on the surface of the enzyme. 

It seems worth pointing out, that 137 and human semm albumin contain no pendant phosphines and the donor atoms in the complexes formed with rhodium can be only O (137) or O, N and perhaps S (HSA), which are not the most suitable for stabilizing low oxidation state metal ions. Still these macroligands gave active and stable catalysts with rhodium, which shows that perhaps in the high local concentration provided by the polymer even these hard donor atoms are able to save the metal ion against hydrolysis or other deterioration. 

The interactions between transmitters and their receptors are readily reversible, and the number of transmitter-receptor complexes formed is a direct function of the amount of transmitter in the biophase. The length of time that intact molecules of acetylcholine remain in the biophase is short because acetylcholinesterase, an enzyme that rapidly hydrolyzes acetylcholine, is highly concentrated on the outer surfaces of both the prejunctional (neuronal) and postjunctional (effector cell) membranes. A rapid hydrolysis of acetylcholine by the enzyme results in a lowering of the concentration of free transmitter and a rapid dissociation of the transmitter from its receptors little or no acetylcholine escapes into the circulation. Any acetylcholine that does reach the circulation is immediately inactivated by plasma esterases. 

Another very instructive case concerns the alleged initiation of a cationic polymerisation by a charge-transfer complex formed by the compound chloranil (2,3,5,6-tetrachloroquinone) with the monomer N-vinyl-carb-azole. It was shown (Natsuume et al., 1969 1970) that this compound is not an initiator, but that the polymerisations were caused by a hydrolysis product, 2-hydroxy-3,5,6-trichloroquinone, which is a strong acid. One has learnt from this finding to be extremely suspicious of any claims for charge-transfer catalysis and to test one s suspicions by appropriate experiments involving progressive purification of the putative catalyst. 

Metal ion catalysis of salicyl phosphate hydrolysis is much more complicated than that of Sarin, since the former substrate can combine with metal ions to give stable complexes, and some of the complexes formed do not constitute pathways for the reaction. In addition the substrate undergoes intramolecular acid-base-catalyzed hydrolysis which is dependent on pH because of its conversion to a succession of ionic species having different reaction rates. Therefore a careful and detailed equilibrium study of proton and metal ion interactions of salicyl phosphate would be required before any mechanistic considerations of the kinetic behavior in the absence and presence of metal ions can be undertaken. 

Complexation228 of Zn2+ with the quadridentate 1,5-diazacyclooctane-N, A -diacetic acid (H2L) leads to formation of the trigonal prismatic [Zn(L)H20] species. The hydrolysis constant of the coordinated H20 (pKa = 8.6) is much lower than that of the coordinated H20 in the octahedral complex formed by ethylenediaminediacetate (pXa = 10.5). This increased acidity of coordinated H20 with decreasing coordination number has also been previously noted in the [Zn(Me6tren)H20]2+ cation,229 and has been attributed in part to the hydrophobic environment provided by the Me groups. This finding has important implications for the role of the... 

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