PREDICTING THE RELATIVE STABILITIES OF MULTIPARTICLE HYDROGEN-BONDED AGGREGATES BASED ON THE NUMBER OF HYDROGEN-BONDS AND THE NUMBER OF PARTICLES AND MEASURING THESE STABILITIES WITH TITRATIONS USING DIMETHYL-SULFOXIDE

This paper describes an experimental method for determining the relati ve stabilities of hydrogen-bonded aggregates in terms of the mole frac tion of dimethyl sulfoxide (DMSO) in chloroform solution, chi(DMSO), r equired to cause their dissociation. It also describes three indices-I -Tm, I-G, and I-G/(N-1)--that estimate the relative stabilities of hyd rogen-bonded aggregates. Each of these indices depend on two variables : HB and N. HB is the number of hydrogen bonds holding the aggregate t ogether; N is the number of particles in the aggregate. The melting-po int index, I-Tm = HB/(N-1), corresponds conceptually to a ''melting po int'' for the aggregate, that is, a temperature at which it would diss ociate into separate particles. This index is the most useful of the t hree for ''rule of thumb'' estimation of relative stability if assembl y occurs cooperatively. The free energy index, I-G = 2.8HB - 16(N-1), corresponds to a free energy of assembly, Delta G, with units kcal/mol . The index I-G/(N-1) = 2.8HB/(N-1) - 16 corresponds conceptually to a free energy of association per particle, Delta G/(N-1). This third in dex is most useful if assembly occurs noncooperatively.