Hydrolysis divalent effect

Divalent Effect In the brine of low to medium sahnities (monovalent content), the viscosity of polyacrylamide solution increases as hydrolysis proceeds (increases). However, in the presence of divalents, the viscosity behavior will be determined largely by the divalent metal ion concentrations. As hydrolysis increases, more acrylic acid exists in the solution. Hydrolyzed polyacrylamides (negative carboxyl groups) interact strongly with divalent metal cations such as Csi and Mg ". This phenomenon is commonly associated with reduction in solution viscosity, formation of gels or precipitates. 

Sigel and co-workers have over a number of years investigated the hydrolysis of a variety of nucleoside 5 -triphosphates and the effects of divalent metal ions. A significant result is that for the hydrolysis of e-ATP (e-ATP is l,A -ethenoadenosine 5 -triphosphate) in the presence of both and Cu +, the most active species is a 2 1 complex metal ion e-ATP (122). It was also proposed that a metal ion bound OH ion effected the hydrolysis. The effect of a number of divalent metal ions on the rates of dephosphorylation of a number of nucleotide triphosphates has also been investigated (128). The ability to dephosphorylate ATP decreased in the order Cu " > Cd > Zn " >Ni >Mn + > Mg-It was suggested that since the pH maximum for the hydrolytic reaction for a particular metal ion paralleled the tendency for that metal ion to form hydroxo complexes (i.e., the p a of the coordinated water molecule) that a metal bound hydroxide ion was involved in the reaction. The most reactive species of the pyrimidine triphosphates could be formulated as [M2(NTP)(OH)J, although the structure of the active complex could only be speculated upon. The reactivity of the purine NTPs was attributed to the dimeric species [M2(NTP)2(0H)]. In both cases, however, two divalent metal ions and a bound hydroxide ion seem to be required to activate the NTPs to hydrolysis. 

Most biological environments contain substantial amounts of divalent and monovalent metal ions, including Mg, Ca, Na, K, and so on. What effect do metal ions have on the equilibrium constant for ATP hydrolysis and the... 

The running of parallel reactions of hydrolysis, ammonolysis and depolymerization of apple pectin in aqueous solution of ammonia (IM) at 25 C were investigated. It was examined the effects of monovalent cations (Na, K", NH4 ) and divalent cations (Ca, Mg ) when they were added as chloride salts. It was found that the relative rates of the above mentioned reactions, depend on the nature and concentration of the added salts as well. The chlorides of sodium, potassium and calcium accelerate hydrolysis and depolymerization, while magnesium chloride delays these reactions. Ammonolysis was increased in cases of ammonium chloride addition. 

The major mode of polyacrylamide decomposition at elevated temperature (in the absence of oxygen) is hydrolysis (319,320). Thus, the concentration of divalent metal ions has an effect on viscosity retention at high temperature. Chelating and sequestering agents have been used to reduce the adverse effect of... 

The chemistry of aluminium combines features in common with two other groups of elements, namely (i) divalent magnesium and calcium, and (ii) trivalent chromium and iron (Williams, 1999). It is likely that the toxic effects of aluminium are related to its interference with calcium directed processes, whereas its access to tissues is probably a function of its similarity to ferric iron (Ward and Crichton, 2001). The effective ionic radius of Al3+ in sixfold coordination (54 pm) is most like that of Fe3+ (65 pm), as is its hydrolysis behaviour in aqueous solution ... 

In 17, X may be POj (but COCH3, SO3 and other groups have also been examined by this means). In the type of structure shown in 18 we have already encountered the 2-nitrile hydrolyses. With X = POf in 18, divalent metal ions show a pronounced catalysis of the hydrolysis of the dianionic species. The metal is strongly chelated to the phenanthroline but in the product it is unlikely that the 0 is coordinated since a four-membered ring would result (see Sec. 6.8). The monoanionic form (X = POjH ) is the reactive species (Prob. 3). Reaction of the dianion in the absence of metal ion cannot be observed and with Cu +, for example, accelerating effects of >10 are estimated. ... 

The phosphate esters (81) and (82) are also subject to catalysis by metal ions275,276 and possible reactive complexes are illustrated. Metal complexes of adenosinediphosphoric acid and adenosinemonophosphoric acids have been studied277 and the effect of divalent metal ions on the hydrolysis of ADP and ATP has been investigated.278,279... 

Metal Ion Effects. The metal ion effects on the acid-catalyzed hydrolysis of PPS also were examined by Benkovic and Hevey (5). However, they observed that in water near pH 3, the rate enhancement in the presence of an excess of metal ion was at most only threefold (Mg2+, Ca2+, Al3+) and in some cases (Zn2+, Co2+, Cu2+) the rate was actually retarded. We thought that the substrate PPS and Mg2+ ion should be hydrated heavily in water so that their complexa-tion for rate enhancement is weak. If, however, the hydrolysis is carried out in a solvent of low water content, such complexation would not occur, and therefore, the rate enhancement might be more pronounced. This possibility appears to be supported by the fact that the active sites of many enzymes are hydrophobic. Of course, there is a possibility that the S—O fission may not require metal ion activation. In this connection, it is interesting to note that in biological phosphoryl-transfer reactions the enzymes generally require divalent metal ions for activity (7, 8, 9), but such metal ion dependency appears to be less important for sulfate-transfer enzymes. For example, many phosphatases require metal ions, but no sulfatase is known to be metal... 

First, there are inorganic pyrophosphatases (EC 3.6.1.1) which can hydrolyse tri- and tetraphosphate (Baykov et al, 1999). The ability of some pyrophosphatases to split these substrates depends on pH and divalent cations (Baykov et al, 1999). The most effective hydrolysis of low-molecular-weight PolyPs was observed for inorganic pyrophosphatase isolated from the archaeon Metanotrix soehgenii. This hydrolyses PolyP3 and PolyP4 for 44 and 8 %, respectively, of the PP, hydrolysis rate (Jetten et al, 1992) and may therefore be involved in their metabolism. 

Hydrolytic catalysis by metal ions is also important in the hydrolysis of nucleic acids, especially RNA (36). Molecules of RNA that catalyze hydrolytic reactions, termed ribozymes, require divalent metal ions to effect hydrolysis efficiently. Thus, all ribozymes are metalloenzymes (6). There is speculation that ribozymes may have been the first enzymes to evolve (37), so the very first enzymes may have been metalloenzymes Recently, substitution of sulfur for the 3 -oxygen atom in a substrate of the tetrahymena ribozyme has been shown to give a 1000-fold reduction in rate of hydrolysis with Mg2+ but no attenuation of the hydrolysis rate with Mn2+ and Zn2+ (38). Because Mn2+ and Zn2+ have stronger affinities for sulfur than Mg2+ has, this feature provides strong evidence for a true catalytic role of the divalent cation in the hydrolytic mechanism, involving coordination of the metal to the 3 -oxygen atom. Other examples of metal-ion catalyzed hydrolysis of RNA involve lanthanide complexes, which are discussed in this volume. 

The effects of divalent ions (Cu , Ni", Co" and Zn") on the hydrolysis of phthalate, succinate and acetate esters of 2-(hydroxymethyl)picolinic acid (54) have been studied to establish if strong bonding of the metal ion to the leaving group oxygen might enhance intramolecular carboxylate attack. With these esters, saturation conditions are observed at low metal ion concentrations... 

Divalent metal ions (Cu , Ni", Co and Zn ) have a significant catalytic effect in the hydrolysis of (132), although only limited complexation occurs and saturation effects were not observed. 

This effect has been known for quite some time [76-81] and used to influence the reaction rate between the charged particles. Examples include some hydrolysis reactions [80] where a small addition of polyelectrolyte causes a dramatic acceleration of the chemical reaction between equally charged divalent counterions in solution. The effect of a polyelectrolyte on ion-ion collision frequencies has also been used to probe the distribution of ions around the polyion. For example, Meares and coworkers [82] probed the electrosta-... 

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