Self-association of rifamycin B: Possible effects on molecular recognition

The macrocyclic antibiotic rifamycin B was found to be highly surface-activ e and to aggregate in aqueous solution. The aggregational behavior was stud ied using small-angle neutron scattering (SANS), Aqueous solutions of rifam ycin B showed pronounced scattering at both small-length scales (Q greater than or equal to 0.1 Angstrom(-1)) and at large-length scales ( Q less than or equal to 0.1 Angstrom(-1)). The larger association colloids appear to b e rather open low-density aggregates. The addition of 10% 2-propanol greatl y reduces the number and size of the aggregates. Somewhat higher amounts of alcohol appear to completely suppress or eliminate aggregation. The suppre ssion of aggregation coincides with the appearance and enhancement of enant ioselective association between rifamycin B and a variety of chiral amino a lcohols, It appears that the self-aggregation of rifamycin B may be a facto r that controls its ability to differentiate between enantiomers in aqueous and hydro-organic solutions.