Base association constant

Acid-base reactions in hydrocarbon oil formulations and low polar media can be formulated as acid-base association constants between an acid and base ... 

Simplificaion of the acidity or basicity scale in low polar media consists of a series of equilibrium constants corresponding to the reaction above, with either B or HA being the reference compound. The acid-base association constants for the equilibria of substances interacting within these solvents, will be seen to fall mainly in the range logKBHA = 2 to 7 (Davies, 1968). 

Singh, P. P. Malik, R. Maken, S. Acree Jr., W. E. Zvaigzne, A. L Thermochemical investigations of associated solutions. 12. Mole fraction versus volume fraction based association constants for predicting excess molar enthalpies of acetone-bromoform-alkane mixtures Thermochim. Acta 1990,165,113-127... 

One can write acid-base equilibrium constants for the species in the inner compact layer and ion pair association constants for the outer compact layer. In these constants, the concentration or activity of an ion is related to that in the bulk by a term e p(-erp/kT), where yp is the potential appropriate to the layer [25]. The charge density in both layers is given by the algebraic sum of the ions present per unit area, which is related to the number of ions removed from solution by, for example, a pH titration. If the capacity of the layers can be estimated, one has a relationship between the charge density and potential and thence to the experimentally measurable zeta potential [26]. 

The DNA base pairs guanine (G), cytosine (C), adenine (A) and thymine (T). The uracil-2,6-diaminopyridine pair can also form three hydrogen bonds but has a much lower association constant than G-C. 

Table 6-4. Association constants for complexes between carboxylic acids and nitrogen bases in aprotic solvents and corresponding association constants and site densities for binding of the base to a molecu-larly imprinted polymer.

The commonly used method for the determination of association constants is by conductivity measurements on symmetrical electrolytes at low salt concentrations. The evaluation may advantageously be based on the low-concentration chemical model (lcCM), which is a Hamiltonian model at the McMillan-Mayer level including short-range nonelectrostatic interactions of cations and anions [89]. It is a feature of the lcCM that the association constants do not depend on the physical... 

In contrast to points (l)-(3) of discussion, the effect of ion association on the conductivity of concentrated solutions is proven only with difficulty. Previously published reviews refer mainly to the permittivity of the solvent or quote some theoretical expressions for association constants which only take permittivity and distance parameters into account. Ue and Mori [212] in a recent publication tried a multiple linear regression based Eq. (62)... 

The main conclusions from this study are that the electron-drawing fluorine substituent produces a decrease in the association constant by a factor of about 3 for PC-based solutions and of 5.5 for solutions in DME [81] (cf. also Fig. 5). The consequence is an increase in the maximum of conductivity by about 30 percent (PC) and about 80 percent (DME). 

A prerequisite condition for the increase in conductivity being caused by added ligands is a high association constant of the salt in the absence of added ligand. If the association constant is low, as it is for AN-based solutions, a decrease of conductivity may occur, because the Stokes radius of the solvated Li+ ion is increased by ligands with molecular diameters larger than that of AN, entailing lower cation mobility [214],... 

The results are in accordance with those obtained by Taft and colleagues80,81. These authors have measured the 19F NMR chemical shifts of p-FC6H4OH in the presenceof 60 bases including sulphoxides (DMSO, methyl phenyl, methyl p-nitrophenyl, diphenyl, tetramethylene sulphoxide) and determined the association constants K for the hydrogen bond shown in equation 15. 

This reaction reduces the concentration of the free polystyryl anions, the only species capable of propagating the reaction in this system. The association constant of the above reaction deduced from the kinetics of retardation 78) agrees well with that reported previously 79) based on the results of conductance studies. 

Purcell and coworkers obtained good correlations between the IR and H NMR methods by the use of 1,1,1,3,3,3-hexafluoropropanol and phenol as acids . Taddei and colleagues have reported that with CHCI3 as the donor, a free energy relationship is established between the association constants and the H NMR chemical shift values of CHCI3 in the presence of Lewis bases. However, a non-linear relationship has been observed for several other Lewis bases and CHCI3 by other authors . 

On the other hand, Arnett and his coworkers have reported both the enthalpies of the protonation (AHJ and the hydrogen bond (AHf) for acid-base reactions. They calculated Hj by measuring the association constants for the proton transfer (ionization) in a number of bases by using FSO3H as the acid and determined Ai/j by calorimetric measurements of the heat of dissolution of P-FC6H4OH in various hydrogen bond acceptors, including sulphoxides, in They have also tried to correlate and... 

Significantly, it has been shown that coordination of nucleobases can enhance base pairing interactions (115). These findings confirm previous theoretical calculations (116). The association constant for Watson-Crick interactions between 9-EtG and 1-MeC was 6.9 M 1, determined... 

Metal-modified base pairs have been reported some time ago for identical (119), complementary (120), and non-complementary bases (59,121-126). These may assemble into a type I quartet through dimerization, as seen for trassociation constant of 59.1 M 1 in d6-DMSO (123). Rather unusual is the involvement of the aromatic C-H5 proton in the hydrogen bond-... 

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