1.7.6: Compressions- Isentropic- Neutral Solutes
Granted that \(\phi\left(K_{\mathrm{Sj}} ; \text { def }\right)\) has been measured for solutions containing neutral solutes (at defined \(\mathrm{T}\) and \(\mathrm{p}\)), interesting patterns emerge for the dependences of \(\phi\left(\mathrm{K}_{\mathrm{Sj}} ; \operatorname{def}\right)\) on molality \(\mathrm{m}_{j}\) and on solute \(j\). Further these dependences are readily extrapolated (geometrically) to infinite dilution to yield estimates of \(\phi\left(K_{\mathrm{S}_{j}} ; \operatorname{def}\right)^{\infty}\). These comments apply to solutions of neutral solutes in both aqueous and non-aqueous solutions; e.g. solutions in propylene carbonate [1] and aqueous solutions of carbohydrates [2].
For dilute solutions of neutral solutes \(\phi\left(K_{\mathrm{Sj}} ; \text { def }\right)\) is often approximately a linear function of the molality \(\mathrm{m}_{j}\).
\[\text { Thus } \phi\left(\mathrm{K}_{\mathrm{S}_{\mathrm{j}}} ; \text { def }\right)=\phi\left(\mathrm{K}_{\mathrm{S}_{\mathrm{j}}} ; \text { def }\right)^{\infty}+\mathrm{b}_{\mathrm{KS}} \,\left(\mathrm{m}_{\mathrm{j}} / \mathrm{m}^{0}\right) \nonumber \]
For aqueous solutions containing ureas, acetamides and \(\alpha,\omega\)-alkanediols, the slope \(b_{\mathrm{KS}}\) is positive. For dextrose(aq), sucrose(aq), urea(aq) and thiourea(aq) φ(; ) K def Sj ∞ is negative. In contrast φ(; ) K def Sj ∞ is positive for dioxan(aq) and acetamide(aq). In other words \(\phi\left(K_{\mathrm{S}_{j}} ; \operatorname{def}\right)^{\infty}\) is characteristic of the solute [3,4]. Group additivity schemes are discussed for \(\phi\left(K_{\mathrm{S}_{j}} ; \operatorname{def}\right)^{\infty}\) with respect to glycylpeptides(aq) [5], amino acids(aq) [6-8] and alcohols [9-11]. With increase in temperature \(\phi\left(K_{\mathrm{S}_{j}} ; \operatorname{def}\right)^{\infty}\) for amino acids(aq) [8] and glycyl dipeptides(aq) [12,13] increases. Particularly interesting in terms of solute-water interactions is the study reported by Galema et al [14, 15] who comment on the calculation of \(\phi\left(K_{\mathrm{Sj}} ; \text { def }\right)\) for solute-\(j\) using equation (b).
\[\mathrm{K}_{\mathrm{sj}}(\mathrm{aq} ; \operatorname{def})=\phi\left(\mathrm{K}_{\mathrm{sj}} ; \operatorname{def}\right)+\mathrm{m}_{\mathrm{j}} \,\left[\partial \phi\left(\mathrm{K}_{\mathrm{s} j} ; \operatorname{def}\right) / \partial \mathrm{m}_{\mathrm{j}}\right]_{\mathrm{T}, \mathrm{p}} \nonumber \]
This study confirmed the importance of the stereochemistry of carbohydrates on their hydration. A clear contrast is drawn between those solutes where the hydrophilic groups match and mismatch into the three dimensionally hydrogen - bonded structure of liquid water. With increase in solute concentration, the dependence of \(\mathrm{K}_{\mathrm{Sj}}(\mathrm{aq} ; \text { def })\) on composition is non-linear [16]. For amines(aq) \(\mathrm{K}_{\mathrm{Sj}}(\mathrm{aq} ; \text { def })\) passes through minima [16].
Chalikian discusses the isentropic compression of a wide range of solutes with reference to group contributions [17], the discussion being extended to proteins [18] and oligopeptides[19].
Footnotes
[1] H. Høiland, J. Solution Chem., 1977, 6 , 291.
[2] P. J. Bernal and W. A. Van Hook, J. Chem. Thermodyn., 1986, 18 ,955.
[3] A. Lo Surdo, C. Shin and F. J. Millero, J. Chem. Eng. Data, 1978, 23 , 197.
[4] F. Franks, J. R. Ravenhill and D. S. Reid, J Solution Chem.,1972, 1 ,3.
[5] M. Iqbal and R. E. Verrall, J.Phys.Chem.,1987, 91 ,967.
[6] D. P. Kharakoz, J.Phys.Chem.,1991, 95 ,5634.
[7] F. J. Millero, A. Lo Surdo and C. Shin, J.Phys.Chem.,1978, 82 ,784.
[8] T. V. Chalikian, A. P. Sarvazyan, T. Funck, C. A. Cain and K. J. Breslauer, J. Phys. Chem., 1994, 98 , 321.
[9] M. Kikuchi, M. Sakurai and K. Nitta, J. Chem. Eng. Data, 1995, 40 ,935
[10] M. Sakurai, K. Nakamura, K. Nitta and N. Takenaka, J. Chem. Eng. Data, 1995, 40 ,301.
[11] T. Nakajima, T. Komatsu and T. Nakagawa, Bull. Chem. Soc Jpn., 1975, 48 ,788.
[12] G. R. Hedwig, H. Hoiland and E. Hogseth, J. Solution Chem.,1996, 25 ,1041.
[13] G. R. Hedwig, J. D. Hastie and H. Hoiland, J. Solution Chem.,1996, 25 ,615.
[14] S. A. Galema and H. Høiland, J. Phys. Chem., 1991, 95 , 5321.
[15] S. A. Galema, J. B. F. N. Engberts, H. Hoiland and G. M. Forland, J. Phys. Chem., 1993, 97 , 6885.
[16] M. Kaulgud and K. J. Patil, J. Phys. Chem., 1974, 78 ,714.
[17] T. V. Chalikian, J. Phys. Chem.B,2001, 105 ,12566.
[18] N Taulier and T.V. Chalikian, Biochem. Biophys. Acta, 2002, 1595 ,48.
[19] A. W.Hakin, H. Hoiland and G. R. Hedwig, Phys. Chem. Chem. Phys.,2000, 2 ,4850.