Complexation enthalpy

Stability constants as a function of temperature and the calculated complexation enthalpies and entropies of the associated reactions are given in Table II. The results of duplicate experiments at 2.0 M acidity and ionic strength are shown as the last entry in the table. Comparison of the results at 25°C, and 1.0 and 2.0 M acidity indicate an approximate inverse first order stoichiometry in [IT "] for the Kj and acid independence for K2. 

DeCarvalho and Choppin (10, 11) previously have reported the stability constants, complexation enthalpies, and entropies for a series of trivalent lanthanide and actinide sulfates. As their work was conducted a pH 3, the dominant sulfate species was S0 and the measured reaction was as in equation 12. 

H20, CH3OH-. . H20, CN-. . HzO, HCC-. . H20, HCOCT. . H20. The DFT(B3LYP) and the DFT(BLYP) results were in a fair agreement with the MP2 results. The root mean square deviation of the DFT and the MP2 complexation enthalpies amounted to 0.7 and 1.1 kcal/mol, for B3LYP and BLYP, respectively. From the basis set dependence of the DFT results, it was concluded that the nonlocal DFT calculations require diffuse atomic functions. 

Laugel N, Betscha C, Winterhalter M et al (2006) Relationship between the growth regime of polyelectrolyte multilayers and the polyanion/polycation complexation enthalpy. J Phys ChemB 110 19443-19449... 

It is evident from stability-constant measurements that the monoglyceride of tetradecanoic acid forms the most stable complex. Enthalpies of melting of the complex increase proportionally with the length of the carbon chain of the fatty acid residue. Binding parameters (Table LII)717 show that the complexes are weak and they can be readily decomposed by other competing agents. As shown by Kim and Hill,863 cyclomaltoheptaose forms binary complexes with lysolecithin and ternary complexes with lysolecithin and amylose. The complex of lysolecithin with amylose is disrupted by cyclomaltoheptaose. 

According to the t-scores, Vmin is the most important parameter also for this correlation. However, the relative importance of Is,min is much larger than in the correlation with the phenol-base complexation enthalpies, consistent with the larger effect of charge transfer on frequency shifts compared to enthalpies. 

Factors Influencing Solution Stabilities of Complexes Enthalpy Effects ... 

The emphasis of work by French researchers has been the use of soft-donor extractants and complexants to enhance actinide/lanthanide group separation (Vitorge 1985, Musikas et al. 1980, Musikas 1985). The relative stability constants for lanthanide and actinide azide complexes reported by Musikas etal. (1980) suggest that hydrazoic acid could function as a useful reagent for this separation. This is confirmed in a later report for Am/Eu separation (Musikas 1985) in which americium extraction is suppressed by complex formation with azide. The separation factors are not very different from those reported by Sekine (1965) using SCN as the complexant in TBP extraction. However, Choppin and Barber (1989) find that, while the trivalent actinide-azide stability constants are somewhat larger than those of the trivalent lanthanides, the complexation enthalpies calculated from the temperature coefficient of the / s do not support the existence of a covalent bonding contribution. 

Fundamental properties are revealed in kinetic acidity studies (the kinetic acidity of m-CF3CgH4SMe is greater than that of the selenium analogue by a factor of 1.38), polarography (RSCH2CH2COCO2R is protonated at a carbonyl group rather than at sulphur), voltammetry (three successive anodic peaks for Ph2Se at Pt in MeCN), and complexation enthalpies of l,cu-bis-(n-butylthio)alkanes with... 

The thermodynamics of complex formation of PMAA and PAA with PEG were studied by Papisov et al. [34] using calorimetry, potentiometry and viscometry. Complexation enthalpy and entropy values were obtained from titration and calorimetric measurements. The enthalpy of complexation of PMAA and PEG was 0.33 kcal/mole and the entropy of complexation 1.32 cal/mole°K. Both values are higher than for complexes involving PAA, indicating a stronger hydrophobic association in the PMAA complex than in PAA. The equimolar complex of PMAA and PEG as measured by viscometry started to dissociate between pH=5.1 and pH=5.4, with no complex detected at pH=5.9. Here, PMAA concentrations of O.lg/dl were used. 

The two most commonly employed techniques for obtaining complexation enthalpies are based on the temperature dependence of equilibrium constants or calorimetric procedures. In the latter, the heat evolved when the acid and base are mixed in the reaction cell of a calorimeter is measured. The molar enthalpy of complexation, AH°, is related to the measured heat output, Q, corrected for the heats of dilution, the equilibrium concentration of the complex, [AB], and the volume of the solution in litres, V, by the relation... 

Many correlations between the complexation enthalpy and the Gibbs energy of complexation have been proposed, for example the SbCls complexes [78], the diiodine complexes [4] or the hydrogen-bonded complexes [84]. They have been explained either by a quasi-isoentropic behaviour of the complexation reaction or by an enthalpy-entropy compensation effect (Equation 1.90) ... 

It is well known that the equilibrium constant and complexation enthalpy are usually widely affected by intermolecular interactions of the species A, B and AB with the solvent... 

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