H-1-NMR STUDY OF SELF-ASSOCIATION OF ACTINOMYCIN-D IN AN AQUEOUS-SOLUTION

This paper presents the results of a proton magnetic resonance study ( 500 MHz) of self-association of actinomycin D (AMD) antibiotic in an a queous solution. The equilibrium constants and thermo- dynamic paramet ers (Delta H, Delta S) of molecular association as well as the limitin g values of proton chemical shifts of associate molecules were determi ned from the concentration and temperature dependences of (1)X NMR che mical shifts of AMD. The results were analyzed using dimeric and infin ite-dimensional cooperative models of molecular self-association. The value of the cooperativity parameter indicates that AMD self-associati on is anticooperative, i.e., formation of aggregates larger than dimer s is energetically unfavorable. The values of induced proton chemical shifts were used to determine the most probable mutual orientation of chromophores in AMD structure.