Manifestation of structure and intermolecular interactions of biologically active brassinosteroids in infrared spectra

We have analyzed the IR spectra obtained for steroidal phytohormones 24-epibrassinolide, 24-epicastasterone, 28-homobrassinolide, and 28-homocastasterone. The characteristic frequencies of the stretching vibrations of the hydrocarbon groups CH3, CH2, and CH and also the C=O groups in the spectra of brassinolides are higher than in the spectra of castasterones, which makes it possible to identify them from the IR spectra. Study of the spectra of these brassinosteroids in different media (pressed samples in KBr, films, solutions in CHCl3 and CDCl3) allowed us to establish the presence of intermolecular interactions in which C=O and OH groups, OH-OH groups participate, and also the possible formation of intramolecular hydrogen bonds between the OH groups of the molecules.