Cosolute effects

Cosolute effects the presence of further organic solutes, as is the case in real waters, may significantly alter the solubility of the individual compounds. Suspended organic matter soil and sediment components (e.g. humic acids) may result in increased apparent solubilities by serving as a sink compartment due to sorption processes. 

Cosolute effects the presence of further organic or inorganic solutes, as is the case in real environments, may significantly alter the sorption of the individual compounds. 

Cosolute effects on hydrolysis reactions in water-rich aqueous media can be examined quantitatively by using a combined thermodynamic and kinetic analysis. The background theory shows that... 

Pairwise hydrophobic interactions can be used to alter the reactivity of organic molecules in water. For instance, the rate of hydrolysis reactions may be influenced significantly by the presence of hydrophobic cosolutes. The effect on reactivity has been analysed by comparirg the interactions between initial state and cosolute with those between transition state and cosolute. ... 

Li, A. and Doucette, W.J. The effect of cosolutes on the aqueous solubilities and octanol/water partition coefficients of selected polychlorinated biphenyl congeners. Environ. Toxicol. Chem., 12(ll) 2031-2035, 1993. 

Not surprisingly, it is rather difficult to separate the different contributions of the different interactions as they occur in the micellar Stern region. In an attempt to solve this problem, the group of Engberts used a series of hydrolysis reactions of activated esters and amides to probe the reaction environment offered by micelles. The reactions initially involved the water-catalyzed pH-independent hydrolysis reactions of i-methoxy-phenyl dichloroacetate 4 and l-benzoyl-3-phenyl-l,2,4-triazole 5, as extensive information on the rate retarding effects of added cosolutes on this reaction was available. ... 

Furthermore, for most compounds of interest to us, the octanol molecules present as cosolutes in the aqueous phase will have only a minor effect on the other organic compounds activity coefficients. Also, the activity coefficients of a series of apolar, monopolar, and bipolar compounds in wet versus dry octanol shows that, in most cases, Yu values changes by less than a factor of 2 to 3 when water is present in wet octanol (Dallas and Carr, 1992 Sherman et al., 1996 Komp and McLachlan, 1997a). Hence, as a first approximation, for nonpolar solvents, for w-octanol, and possibly for other solvents exhibiting polar groups, we may use Eq. 6-11 as a first approximation to estimate air- dry organic solvent partition constants for organic compounds as illustrated in Fig. 6.2. Conversely, experimental KM data may be used to estimate K,aw or Kitvi, if one or the other of these two constants is known. 

Klausen, J., S. B. Haderlein, and R. P. Schwarzenbach, Oxidation of substituted anilines by aqueous MnOz Effect of cosolutes on initial and quasi-steady-state kinetics , Environ. Sci. Technol., 31, 2642-2649 (1997). 

The experimental techniques available to determine AWPCs and their limitations have been discussed by Staudinger and Roberts [2]. These authors also evaluated the effects of pH, compound hydration, compound concentration, cosolvent, cosolute, and salt effects, suspended solids, dissolved organic matter, and surfactants. The experimental data have been compiled by a number of different authors [2-11]. 

Kim AI, Knopp S, Akers MJ, Nail SL. The physical state of mannitol after freeze-drying effects of mannitol concentration, freezing rate, and a noncrystallizing cosolute. J Pharm Sci 1998 87 931-935. 

Rao et al. (1990) investigated the effect of nonpolar cosolutes (trichloroethylene, toluene p-xylene), polar cosolutes (1-octanol, chlorobenzene, nitrobenzene, o-cresol) and polar cosolvents (methanol and dimethyl sulfoxide) on sorption of several polycyclic aromatic hydrocarbons (PAHs). The nonpolar cosolutes did not significantly influence PAH sorption, while the polar cosolutes (nitrobenzene, o-cresol), having sufficiently high aqueous solubilities, caused a significant decrease in PAH sorption. 

The next study on solution environment influences included the presence of another molecule in the solution. This cosolute was endowed with an attribute of nondissociation. Its lipophilicity was varied in a series of studies revealing that the dissociation of the acid decreased when the lipophilicity of the cosolute decreased. These results may present a new insight into this effect. 

Numerous experiments have been performed on the action of solutes on Ps formation in liquids. Parameters that have been examined are nature and concentration of the solutes, temperature, nature of the solvent, presence of cosolutes, electric and magnetic field effects. Due to the ease of dissolution of a large variety of compounds, the most studied solvent is water, which allows larger possibilities of comparison with data from pulse radiolysis. 

Onken, B.M. and Traina, S.J. 1997. The sorption of nonionic organic solutes to humic acid-mineral complexes effect of cosolutes. Journal of Environmental Quality, 26 132-8. 

Karlstrom, G. Carlsson, A. Lindman, B., "Phase Diagrams of Nonionic Polymer-Water Systems. Experimental and Theoretical Studies of the Effects of Surfactants and Other Cosolutes," J. Phys. Chem., 94, 5005 (1990). 

Lemieux and coworkers (3) obtained evidence that hydration may have an influence on the anomeric and exo-anomeric effects. Painter (18) has studied the influence of cosolutes upon the conformations of carbohydrates in aqueous solution and concluded that the observations made are in general accord with influences on the anomeric and exo-anomeric effects. As recently commented by Painter (18) in connection with the mounting body of evidence that steric preferences are not normally too large for the exo-anomeric effect to have an important influence upon conformation about the Ol-W bond, "If this is generally true, it is evident that the exo-anomeric effect must be a phenomenon of very considerable, if not profound, biological significance."... 

In sufficiently dilute aqueous solutions surfactants are present as monomeric particles or ions. Above critical micellization concentration CMC, monomers are in equilibrium with micelles. In this chapter the term micelle is used to denote spherical aggregates, each containing a few dozens of monomeric units, whose structure is illustrated in Fig. 4.64. The CMC of common surfactants are on the order of 10 " -10 mol dm . The CMC is not sharply defined and different methods (e.g. breakpoints in the curves expressing the conductivity, surface tension, viscosity and turbidity of surfactant solutions as the function of concentration) lead to somewhat different values. Moreover, CMC depends on the experimental conditions (temperature, presence of other solutes), thus the CMC relevant for the expierimental system of interest is not necessarily readily available from the literature. For example, the CMC is depressed in the presence of inert electrolytes and in the presence of apolar solutes, and it increases when the temperature increases. These shifts in the CMC reflect the effect of cosolutes on the activity of monomer species in surfactant solution, and consequently the factors affecting the CMC (e.g. salinity) affect also the surfactant adsorption. 

Turning next to the effect of cosolutes on the CMC, this is an important and broad issue that we will come back to later. A most important matter is the effect of added electrolyte on the CMCs of ionics. This is illustrated in Figure 19.7 for the simplest and generally most important case of adding a 1 1 inert electrolyte to a solution of a monovalent surfactant. The following features are noted ... 

Self-assembly and micelle formation have, however, a broader significance than this. Mixed polymer-surfactant solutions have many applications and it has become more and more evident that an important role of the polymer chains in many systems is to promote micelle formation. A macromolecular cosolute will be much more effective in reducing the CMC than a low-molecular-weight one. This is discussed in some detail in Chapter 20. 

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