ΔG° and TΔS° - Charge relationships for the binding of inorganic and organic anions by open chain polyammonium cations: A short review

The dependence on charge of Delta G degrees and T Delta S degrees for the formation of several open-chain polyammonium cation-inorganic and organic anion complexes has been reviewed. Generally quite a good linear fit is obtained for both Delta G degrees and T Delta S degrees vs. zeta [zeta = \anion charge\x(cation charge)] when considering single systems, such as C2(n-1)NnH(6n . 2)(n+) (n = 2...6) with atp(4-) By considering different systems together, a fairly good linear fit is obtained for both thermodynamic parameters vs, zeta, with a sharp difference between T Delta S degrees and Delta G degrees, whose fit is significantly better than that of T Delta S degrees, i.e., the entropic term is the most specific one. Some general relationships are reported. The most general relationships, valid for all the systems considered are : -Delta G degrees = 7 +/- 1 kJ mol(-1) n(-1), T Delta S degrees = 9.2 +/- 2.4 kJ mol(-1) n(-1), where n is the number of possible salt bridges, calculated by the crude approximation n = zeta/2. More sophisticated equations, including a term for the effect of the basicity of amines, give a significantly better fit. The possibility of using these relationships as predictive tools, is discussed.