Complex formation and hydrolysis

This discussion shows that the empirical rate laws must be reexpressed, where necessary, as a collection of terms which are appropriate functions of the concentrations of species actually present in the solutions. The observed nonintegral dependences shown by some of the stoichiometric concentrations may be caused by (a) equilibria in which an appreciable fraction of one of the reactants is present as more than one species complex formation and hydrolysis are examples of such equilibria, (b) more than one kinetically important activated complex, or... 

Complex formation and hydrolysis of complexes. In acidic solutions, hydrolysis of group 5 elements is competing with complex formation. For group 5 complexes, it is described by the following equilibrium ... 

Reaction of [TcBrJ-" with citric acid is reported to yield polymeric mono- and dicitrates and monomeric dicitrates of Tc(IV). Complex formation and hydrolysis of Tc(lV) were shown to be competitive reactions. Brown to violet solutions occurred, depending on the molar ratio of citratc/technetium and on the reaction time [370,371], The complex formation of Tc(IV) with nitrilotriacctic acid (H3iita), ethylc-nediaminctetraacetic acid (H4edta), and cyclohexanediaminetctraacetic acid (f data) were studied in aqueous solution by means of ion exchange and electrophoresis [372] and the complex composition of solid di- and trinuclear compounds containing H jnta were analyzed [373]. 

The formation of complex ions in aqueous solutions with anionic ligands is an important feature of the aqueous chemistry of Pu. Complex formation and hydrolysis are competing reactions and may be looked upon as the displacement of the HgO molecules in the hydration sphere by the anionic ligand or by OH , respectively. The ability of an ion to form complexes is dependent on the magnitude of the ionic potential which may be defined by the equation... 

The calculations have shown that the theory of hydrolysis [279] based on the relation between the cation size and charge does not explain all the experimental behavior, like, e.g., the difference between Nb and Ta, or Mo and W. Only by performing relativistic calculations for real chemical equilibrium in solutions can complex formation and hydrolysis constants, as well as distribution coefficients between an aqueous and organic phases (or sorption coefficients) and their order in... 

Bob s research interests and knowledge across chemistry were great. Throughout his career he retained an interest in biomimetic chemistry, specifically the study of metal ion-promoted reactions and reactions of molecules activated by metal ion coordination. His early interests in carbohydrate chemistry inspired him to study metal ion catalysis of both peptide formation and hydrolysis as well as studies in inorganic reaction mechanisms. He was particularly interested in the mechanisms of base-catalyzed hydrolysis within metal complexes and the development of the so-called dissociative conjugate-base (DCB) mechanism for base-catalyzed substitution reactions at inert d6 metal ions such as Co(III). 

The various oxidation states of plutonium exhibit characteristic absorption spectra in the ultraviolet, visible and infrared regions. Each oxidation state is sufficiently distinct that its reaction can be monitored during hydrolysis and complex formation. Various research groups have studied the relationship between oxidation and absorption spectra (6-9). The absorption spectra may respond to complex formation or hydrolysis Nebel (10) has shown that the absorption peak of Pu(IV) shifts from 470 nm to 496 nm when Pu(IV) complexed with two molecules of citrate. 

The ability of metal ions to accelerate the hydrolysis of a variety of linkages has been a subject of sustained interest. If the hydrolyzed substrate remains attached to the metal, the reaction becomes stoichiometric and is termed metal-ion promoted. If the hydrolyzed product does not bind to the metal ion, the latter is free to continue its action and play a catalytic role. The modus operandi of these effects is undoubtedly as a result of metal-complex formation, and this has been demonstrated for both labile and inert metal systems. Reactions of nucleophiles other than HjO and OH will also be considered. 

The tendencies to complex ion formation and hydrolysis ordinarily increase in the series M+ < An02+ < An+ < An02+ < An+ and with decreasing ion size from Ac to Lr. For complexation with some univalent... 

Eichhom and his co-workers have thoroughly studied the kinetics of the formation and hydrolysis of polydentate Schiff bases in the presence of various cations (9, 10, 25). The reactions are complicated by a factor not found in the absence of metal ions, i.e, the formation of metal chelate complexes stabilizes the Schiff bases thermodynamically but this factor is determined by, and varies with, the central metal ion involved. In the case of bis(2-thiophenyl)-ethylenediamine, both copper (II) and nickel(II) catalyze the hydrolytic decomposition via complex formation. The nickel (I I) is the more effective catalyst from the viewpoint of the actual rate constants. However, it requires an activation energy cf 12.5 kcal., while the corresponding reaction in the copper(II) case requires only 11.3 kcal. The values for the entropies of activation were found to be —30.0 e.u. for the nickel(II) system and — 34.7 e.u. for the copper(II) system. Studies of the rate of formation of the Schiff bases and their metal complexes (25) showed that prior coordination of one of the reactants slowed down the rate of formation of the Schiff base when the other reactant was added. Although copper (more than nickel) favored the production of the Schiff bases from the viewpoint of the thermodynamics of the overall reaction, the formation reactions were slower with copper than with nickel. The rate of hydrolysis of Schiff bases with or/Zw-aminophenols is so fast that the corresponding metal complexes cannot be isolated from solutions containing water (4). 

Reactions involving the formation and hydrolysis of phosphate and polyphosphate esters are of vital importance in biological systems in which it is found that magnesium ions are almost invariably implicated. The formation and decomposition of adenosine triphosphate are the fundamental reactions involved in energy storage in living systems. In this context, it is perhaps relevant to note that the hydrolysis of ATP is enhanced, albeit in a very modest manner, by some cobalt(m) complexes. 

For the AIX separations at 4-8 M HC1, where no hydrolysis should occur at such high acidities, the data of Table 17 suggest that the trend in the complex formation and Kd values should definitely be continued with Rf Zr > Hf > Rf. The AIX separations [174] of group-4 elements from aqueous 4-8 M HC1 solutions have, however, shown an inverse sequence in Kd values Rf > Zr > Hf. Taking into account the above mentioned arguments, this result cannot find its theoretical explanation. 

Predicted trends in hydrolysis, complex formation and extraction of complexes at various experimental conditions in comparison with experimental results are summarized in Table 23. 

The formation and hydrolysis of monodentate salicylate complexes (230) parallels other car-boxylates (Tables 60 and 59, respectively). Metal-ion-accelerated hydrolysis (Fe3+ species,814... 

The two platelet membrane glycoproteins for which the strongest evidence exists at the present time that they are thrombin receptors are a specific form of the GPIb-DC-V conq>lex and PARI, the protease-activated thrombin receptor these will be discussed next in this review. Based on their apparent ability to form complexes with a hrombin, several other proteins had previously t en proposed as thrombin receptors but in only a few cases were the necessary further studies carried out to test these hypotheses. Protease nexin 1 was proposed as a thrombin receptor based on the similar time courses of complex formation and platelet activation but it was subsequently found that protease nexin 1 cannot be a receptor since it is an internal conq>onent of platelets that is expressed on the surface only ater activation. Glycoprotein V has also been proposed as a thrombin receptor based on the feet that it can be cleaved by low concentrations of a-thrombin but subsequent studies (reviewed in ) showed that there was no consistent relationship between the rate or extent of GPV hydrolysis and the extent of platelet activation induced by a-thrombin. Another thrombin-activatable receptor, PAW, has been identified in mouse platelets but not in human platelets using a reverse transcriptase/ polymerase chain reaction approach (unpublished data and S.Coughlin, personal communication). PAR3 has, however, been reported cloned from a human platelet cDNA library. ... 

Thus, the surface serves to accumulate both the ester (by complex formation and electrostatic attraction) and the nucleophile (by electrostatic attraction alone), facilitating reaction. In fact, the overall first-order rate constant for hydrolysis (Ar ) reflects this concentration effect Atj, reaches its highest value at the pH where the product [>Al-MPT][OH"ld is at a maximum. No other role of the oxide surface in promoting hydrolysis need be postulated. 

Irreversible inhibitors are effectively esteratic site inhibitors which, like true substrates, react with the hydroxyl group of serine at the catalytic active site. Such inhibitors, sometimes referred to as acid-transferring inhibitors, include the organophosphates, the organo-sulfonates, and the carbamates. All form acyl-enzyme complexes which, unlike substrate-enzyme intermediates, are relatively stable to hydrolysis. Indeed, the phosphorylated enzyme intermediates have half-lives from a few hours to several days (A12), whereas the sulfonated or carbamylated enzyme complexes have much shorter half-lives—several minutes to a few hours. Several strong lines of direct evidence point to the formation of an acyl complex—the isolation of phosphorylated serine from hydrolysates of horse cholinesterase (J2), complex formation and carbamylation (02), and the sulfonation of butyrylcholinesterase by methanesulfonyl fluoride in the presence of tubocurarine and eserine (P6). 

Since transition elements are known to be subject to strong hydrolysis, the latter influences both the complex formation and extraction. 

Table 10 Formation and hydrolysis constants of mononuclear hydroxo-complexes of aluminium (in)...

Predictions. To predict the hydrolysis and complex formation (and finally, the extraction behaviour) of Rf in HF and HCl solutions, the following reactions were considered in [219] the first hydrolysis step... 

This trend was then expected to be experimentally observed in the values. For the anion exchange ADC separations at 4-8 M HCl (chlorination process according to Eq. 35, no hydrolysis), the trend in the complex formation and Ki values will definitely be continued with Rf, i.e. 

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