Stochastic models (cooperative and non-cooperative) for NMR analysis of the hetero-association of aromatic molecules in aqueous solution

Abstract

STOCHASTIC MODELS (COOPERATIVE AND NON-COOPERATIVE) FOR NMR ANALYSIS OF THE HETERO-ASSOCIATION OF AROMATIC MOLECULESto take into account all physically-meaningful association reactions of molecules in which there are no limitations on the lengths of the aggregates and complexes. These algorithmical approaches are compared with previously published basic (BASE) and generalized (GEN) analytical statistical thermodynamical models of hetero-association of biologically-active aromatic molecules using the same sets of published NMR data measured under the same solution conditions (0.1М phosphate buffer, pD=7.1, T=298K). It is shown that, within experimental errors, the BASE analytical model may be used to describe molecular systems characterized by relatively small contributions of hetero-association reactions, whereas the GEN model may be applied to hetero-association reactions of any aromatic compound with different self-association properties. The STOCH-C computational algorithm enabled the effect on hetero-association of the interactions of molecules with different cooperativity parameters of self-association to be estimated for the first time and it is proposed that the algorithm for the stochastic models has great potential for detailed investigation and understanding of the interactions of aromatic molecules in solution.3

Effect of a mixture of caffeine and nicotinamide on the solubility of vitamin (B2) in aqueous solution

“…Using the basic Stochastic model [Evstigneev et al, 2005b] the calculations for FMN-CAF and FMN-NMD mixtures have been repeated for the quantity F s expressed in the form of equation (3), and the results gave the same intercept as in Fig.5a, which indicates that the effects under consideration do not depend on the criterion employed.…”

“…In this case the functional-analytical approach for describing the complex equilibrium for two components in solution was not considered appropriate (reviewed in [Veselkov et al, 2001b]) and a computer-based algorithmical approach was developed. Recently we have reported a Stochastic algorithmical model, which takes into account all possible distributions of homo-and hetero-stacks within a hetero-complex, and have successfully applied it to analyse the NMR data of two-component mixtures of aromatic molecules in solution [Evstigneev et al, 2005b].…”

“…The basic idea of the Stochastic algorithm is to represent the hetero-complex, formed from an arbitrary number of X and Y molecules, as a binary number in which X and Y correspond to 0 and 1 bits, respectively [Evstigneev et al, 2005b]. Hence, cycling over all binary numbers from zero up to the maximum number allowed by the length of a complex means that all statistically possible molecular complexes in solution are generated.…”

“…In the present work the computer algorithm developed for binary mixtures [Evstigneev et al, 2005b] has been modified for the cycling over ternary numbers and applied to the analysis of NMR data on the FMN-CAF-NMD mixture (Fig.3). In the analysis of the experimental data on the three-component mixture FMN-CAF-NMD, it is important to test both the modified Stochastic algorithm and the appropriateness of using hetero-association constants derived from previous studies on two-component systems (CAF-NMD, K XY ; FMN-CAF, K XZ ; FMN-NMD, Table 2).…”

“…Using the basic stochastic model [Evstigneev et al, 2005b] and equilibrium constants in Table 2 However, on increasing the concentration of CAF and NMD past the ca. 350mM point (Fig.5a), the F s curve in the FMN-CAF system goes beyond the F s curve in the FMN-NMD system, which means that at higher concentrations Nicotinamide becomes more effective in solubilising FMN than does Caffeine.…”