Predicting the Relative Stabilities of Mu ltiparti cle Hydrogen - Bonded Aggregates Based on the llumber of Hydrogen Bonds and the ilumbet of Particles and Measuting These Stabilities with Titrations Using Dimethyl Sulfoxide

This paper describes an experimental method for determining the relative stabilities of hydrogen-bonded aggregates in terms of the mole fraction of dimethyl sulfoxide (DMSO) in chloroform solutioo, /DMSo, required to cause their dissociation. It also describes three indices-ft-, /6, rrnd I1J(Nl)-that estimate the relative stabilities of hydrogen-bonded aggregates. Each of these indices depend on two variables: HB and N. FIB is the number of hydrogen bonds holding the aggregate together: N is the number of particles in the aggregate. The melting-point index, lrrn: HB/(N-1), corresponds conceptually to a "melting point" for the aggregate, that is. a temperature at which it would dissociate into separate particles. This index is the most useful of the three for "rule of thumb" estimation of relative stability if assembly occurs cooperatiuely. The free energy index, 1c:2.8HB 16(N-1). corresponds to a free energy of assembly, AG, with units kcaVmol. The index Ic/(N-l):2'8HBl(N-l) l6 corresponds conceptually to a free energy of association per particle, AGI(N-1). This third index is most useful if assembly occurs noncooperatiuely.