Hydrolysis thermodynamic parameters

Most of the reported thermodynamic parameters refer to a single ionic medium and a single ionic strength. Hydrolysis of [MeiSnirV)] " was performed... 

The formation of 1 1 complexes between ethylenediamine-N, N1 -diacetic acid (edda) and Zn11 or Cd11 have been studied by calorimetric (AH) and potentiometric techniques.389 Earlier studies had omitted to allow for protonation reactions of the ethanoato groups in the ligand. Thermodynamic parameters for edda lie between those of nitrilotriacetate and triethylenetetra-mine. Edda appears to undergo a slow metal-ion-catalyzed hydrolysis in aqueous acid solution. 

Similar considerations apply to complexes of methyl 2,3-diaminopropionate.73 Thermodynamic parameters AH and ASjg for the base hydrolysis of the [CuE2]2+ and [CuEA]+ complexes of methyl L-histidinate72 and methyl DL-2,3-diaminopropionate73 indicate that AH values are ca. 4-8 kJ mol-1 higher for the metal complexes compared with the free ligands. The rate increases are due to more positive values of AS5>8 for the complexes. 

Some interesting conclusions can be drawn from the thermodynamic parameters for base hydrolysis of the MA+ complexes (Table 19). The rate enhancements in the metal ion-promoted reactions arise from more positive values of AS41 and, in general, lower enthalpies of activation. In addition, there is a close correspondence between values of log XMA+ and AG (Figure 5). The general trends in AH and AS in the metal-promoted reactions can be rationalized in terms... 

The thermodynamic parameters were calculated and are summarized in Table III. Both enthalpy and entropy decrease considerably with complex formation. Such a large decrease in enthalpy and entropy has not been found in other complex formation systems. For example, the change in enthalpy with the complex formation because of hydrophobic interactions generally is not so large and change in entropy is positive (23,24) and change in enthalpy with the complex formation in enzymatic hydrolysis of cellulose is slightly positive (25). These unusual decreases in enthalpy and entropy are inferred to be characteristics of the present complex formation system. 

The aim of this section is to demonstrate how reaction calorimetry in combination with IR-ATR spectroscopy can be used for the determination of kinetic and thermodynamic parameters. Several examples of chemical reactions will be discussed, each highlighting a different aspect in the application of reaction calorimetry. The reactions considered are the hydrolysis of acetic anhydride, the sequential epoxidation of 2,5-di-ferf-butyl-l,4-benzoquinone and the hydrogenation of nitrobenzene. The results discussed in this section were obtained using a new calorimetric principle presented below. 

As pointed out in Section 8.2, most physical and chemical processes, not just the chemical transformation of reactants into products, are accompanied by heat effects. Thus, if calorimetry is used as an analytical tool and such additional processes take place before, during, or after a chemical reaction, it is necessary to separate their effects from that of the chemical reaction in the measured heat-flow signals. In the following, we illustrate the basic principles involved in applying calorimetry combined with IR-ATR spectroscopy to the determination of kinetic and thermodynamic parameters of chemical reactions. We shall show how the combination of the two techniques provides extra information that helps in identifying processes additional to the chemical reaction which is the primary focus of the investigation. The hydrolysis of acetic anhydride is shown in Scheme 8.1, and the postulated pseudo-first-order kinetic model for the reaction carried out in 0.1 M aqueous hydrochloric acid is shown in Equation 8.22 ... 

A wide range of kinetic and thermodynamic parameters have been measured for the formation and hydrolysis of Schiff bases derived from pyridoxal S -phosphalc and L-tryptophan over a range of pH and temperature.22... 

Commercial yeast invertase (Bioinvert ) was immobilized by adsorption on anion-exchange resins, collectively named Dowex (1x8 50-400,1x4 50-400, and 1x2 100-400). Optimal binding was obtained at pH 5.5 and 32°C. Among different polystyrene beads, the complex Dowex-1x4-200/invertase showed a yield coupling and an immobilization coefficient equal to 100%. The thermodynamic and kinetic parameters for sucrose hydrolysis for both soluble and insoluble enzyme were evaluated. The complex Dowex/inver-tase was stable without any desorption of enzyme from the support during the reaction, and it had thermodynamic parameters equal to the soluble form. The stability against pH presented by the soluble invertase was between 4.0 and 5.0, whereas for insoluble enzyme it was between 5.0 and 6.0. In both cases, the optimal pH values were found in the range of the stability interval. The Km and Vmax for the immobilized invertase were 38.2 mM and 0.0489 U/mL, and for the soluble enzyme were 40.3 mM and 0.0320 U/mL. 

H. Flodgaard and P. Fleron (1974). Thermodynamic parameters for the hydrolysis of inorganic pyrophosphate at pH 7.4 as a function of Mg2+, K+ and ionic strength determined from equilibrium studies of the reaction. J. Biol. Chem., 249, 3465-3469. 

Thermodynamic Parameters for Hydrolysis Reactions0 in Aqueous Solution... 

The kinetics of hydrolysis of energetic material precursors - mono- and dinitro derivatives of pyrazole, imidazole, 1,2,4-triazole, and isoxazole has been studied by the polarographic and photometric methods [647], The alkaline hydrolysis rate constants experimentally determined depend on the nature of the heterocycle. A possible mechanism for hydrolytic transformations of nitroazoles is proposed on the basis of the calculated thermodynamic parameters of the reaction. 

Kinetic investigations of the effects of urea and similar denaturing agents on rates and thermodynamic parameters of micelle catalyzed reactions have been suggested to be more sensitive probes for the nature and extent of hydrophobic interactions than CMC determinations. Thus, Monger and Portnoy (1968) have taken advantage of the base catalyzed hydrolysis of micellar -nitrophenyl dodecanoate. The rate constant for the hydrolysis of -nitrophenyl dodecanoate decreases rapidly with increasing initial concentration of the ester (10 to 10 m), and the second-order rate constant for the base-catalyzed hydrolysis of this ester... 

The H /ATP ratio (the number of protons ejected per ATP hydrolysed) was originally also determined by a pulse method and found to be 2 [118]. Again, later experiments indicated a higher value of 3 or 4 [119], As discussed in Section If (i), in the case of ATP synthesis or hydrolysis the transport of substrates and products may be accompanied by net movement of a proton across the membrane, so that more protons are involved than those transported via the ATPase complex itself. H /ATP ratios have also been calculated via equations containing thermodynamic parameters a stoichiometry of around 2.5-3 was deduced [120-122]. 

Having substituted values of a number of parameters [5, 29] in the equation (10), we shall receive dependence of an effective constant of speed of hydrolysis of ether links on temperature and thermodynamic parameters of the media ... 

It has to be pointed out that, with a few exceptions, the acceleration by polyelectrolytes was associated with decreases and Table IV gives the thermodynamic parameters for the aquation reactions of Co(NH3)5Br induced by Ag". Similar decreases in and AS were found for various reactions the Hg -induced aquation of Co(NH3)5Br , the SpjAr reaction of dinitrochlorobenzoic acid with OH [51], the hydrolysis of 2,4-dinitrophenyl phosphates [reaction (E)] [33], the outer-sphere electron-transfers between Co-complexes [Co(NH3)5N3, Co(NH3)5Br , Co(en)2Cl2 ] and Ru(NH3)6 or [8, 20] [en ethylenediamine], the polyvinyl-imidazole-accelerated solvolysis of p-nitrophenylacetate [52], the coupling reactions of dinitrofluorobenzene with aminoacids [53], dipeptides [53] and aniline [54], the lignin sulfonic acid-accelerated hydrolysis of methyl acetate [55], and the hydrolysis of nitrophenyl esters [37]. The opposite tendency (acceleration caused by increases... 

Deschrevel, B., Vincent, J. C., Ripoll, C., andThellier, M., Thermodynamic parameters monitoring the equilibrium shift of enzyme-catalyzed hydrolysis/synthesis reactions in favor of synthesis in mixtures of water and organic solvent, Bioeng. Biotech., 81 167-177, 2002. 

Mild acidic hydrolysis (5mM HCl at 100 C) of cyclohepta-amylose gave an 8% yield of maltoheptaose. The first-order rate constant increased during hydrolysis because the a-(l - 4)-linkages of cyclohepta-amylose and linear dextrins are cleaved at different rates. Various thermodynamic parameters and the dependence of the rate of hydrolysis on pH and on complexation of cyclohepta-amylose with toluene were determined. 

A number of reports have appeared outlining the effects of ion-pairing upon the rates of hydrolysis of complex ions of the type [Co(NH3)5X] +. When X = Cl ( =2), ion pairs formed with maleate and phthalate ions increase the rate of aquation, and the equilibrium constants and associated thermodynamic parameters for ion-pair formation were obtained along with the rate constants at 313—323 K, When X is unidentate oxalate ion (ox ), SO - and HSO " ions accelerate the rate of acid hydrolysis through the formation of the ion pairs [Co(NH3)50x] +,S04 and... 

As indicated in Chapter III, step 1 of the fibrinogen-fibrin conversion is an example of a limited proteolytic reaction in which hydrolysis does not go to completion. Side-chain hydrogen bonding may stabilize the peptide bond in the manner indicated in Chapter III. We shall therefore discuss the reversibility of step 1 and the thermodynamic parameters for the equilibrium (Laskowski et al., 1960b). As in the case of the kinetic experiments discussed in Section 5b, the medium used was 1 molar NaBr at pH 5.3 to prevent polymerization of fibrin monomer, and the analysis for f was carried out using TAMe as a thrombin inhibitor, as already mentioned The equilibrium position was approached from both directions. 

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