Molecular interactions in solution

Tomasi, J. and M. Persico. 1994. Molecular Interactions in Solution An Overview of Methods Based on Continuous Distributions of the Solvent. Chemical Reviews 94, 2027. 

J. Tomasi and M. Persico, Molecular interactions in solution An overview of methods based on continuous distributions of the solvent, Chem. Rev. 94 2027 (1994). 

However, there are exceptions where a is not proportional to the concentration33,36 due to molecular interactions in solution, e.g., a nonlinear dependence was observed for 2-phenyl-propanal37. In the case of the specific rotation of aqueous malic acid, a change of sign occurs... 

Gakh, E.G., Dougall, D.K., and Baker, D.C., 1998. Proton nuclear magnetic resonance studies of monoacylated anthocyanins from the wild carrot Part 1. Inter- and intra-molecular interactions in solution. Phytochem. Anal. 9 28-34. 

Other molecular interactions in solution between herbicide molecules and surfactant micelles have been suggested (58), but no direct evidence exists for this assumption, although the cleaning action of detergents has been explained in this way (20). 

Table 7.8 shows the thermal diffusion ratios and thermal diffusion coefficients obtained from Onsager s reciprocal rules for toluene, chlorobenzene, and bromobenzene at 1 atm and at 298 and 308 K. Thermal diffusion or heats of transport may be extremely sensitive to the molecular interactions in solutions (Rowley et al., 1988). 

Intensive studies of the molecular interactions in solutions (e.g. [1]) have allowed to formulate general rules conditioning the proton transfer between the "neutrd" and "ion-pair" add-base complex in these media ... 

A semiempirical approach, similar, for examples, to the Hammett equation, does not require full understanding of complex molecular interactions in solution. A standard reaction or phenomenon is chosen, and the parameters of this reaction or phenomenon during changes in the solvent are examined. These parameters may be represented by the rate of equilibrium constants of the reaction, but also by, for example, shifts of the maxima in various spectra. The relations of this type most frequently used are the Grunwald-Winstein (50), Swain-Scott (57), Gielen-Nasielski (52), Berson (55), and Drougard-Decroocq (54) equations. 

For a number of assays, fluorescent-labeled analogues of a hgand are used. Some of those assays are of a quantitative nature, such as in fluorescence correlation spectroscopy (FCS), where the fluorescent-labeled analogue is used to determine binding kinetics (Fig. 5.5) [36]. FCS allows the direct detection of molecular interactions in solution. FCS monitors the random motion of a fluorescent molecule... 

Four spectroscopic techniques are particularly useful for the identification of molecular interactions in solution and/or in the solid state UV/vis, fluorescence, infrared, and nuclear magnetic resonance (NMR). They shall be discussed very briefly here, and some examples will be given later in the book. 

Concentration effects on the heats of transport and the thermal diffusion ratio of chloroform with various alkanes at 30 °C and 1 atm are seen in Table 7.2. Table 7.3 shows the experimental heats of transport at various concentrations and at temperatures 298 and 308 K for binary mixtures of toluene (1), chlorobenzene (2), and bromobenzene (3) at 1 atm (Rowley and Hall, 1096 Yi and Rowley, 1989). The absolute values of heats of transport decrease gradually as the concentrations of the alkane increase. Thermal diffusion or heats of transport may be sensitive to the molecular interactions in solutions. The heat of transport of component i is a measure of the local heat addition or removal required to maintain isothermal conditions as molecular diffusion of component i takes place from a higher chemical potential to a lower one. 

In order to give an idea of the usefulness of gas-liquid chromatography in checking the main theories of solutions and to establish its performance in the quantitative treatment of molecular interactions in solutions through deviations from ideality, some thermodynamic data which are particularly useful in the determination of activity coefficients will be considered schematically. At the same time, models of solutions applied in the deduction of activity coefficients will be presented. The expressions of these quantities will be considered for the case of infinite dilution, according to the requirements of chromatographic conditions. In practice the limita-... 

The characteristics of perfect solutions composed of molecules of similar chemical structure and size directly affect the approach to molecular interactions in solutions and justify the simple form assigned to the chemical potentials of components and to other partial molar quantities derived from the chemical potential. 

Clearly, ITC is a very versatile, sensitive, destruction-free, label-free, and very rapid (takes 1-3 h) instrumental method that requires typically less than micromolar amounts of material to learn about the thermodynamic parameters of reversible molecular associations. The accuracy and reliability of ITC for this purpose is unsurpassed, making it the gold standard in the characterization of inter-molecular interactions in solution. 

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