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We have obtained and analyzed the absorption, fluorescence, and fluorescence excitation spectra of indole vapor, N-acetyl-L-tryptophan vapor, and 3-indole aldehyde vapor. From analysis of the dependence of the fluorescence spectrum of the free indole molecules on the wavelength of the exciting radiation λ ex , it follows that emission of fluorescence occurs when the molecules undergo a transition from the one electronically excited state 1 L b . The fluorescence spectra of the studied compounds are insignificantly different, suggesting a major role for the indole chromophore in formation of the compounds. The absorption spectrum of N-acetyl-L-tryptophan, in which the group of atoms is added to the indole ring through a -C-C bond, is similar to the spectrum of indole, while the spectrum of 3-indole aldehyde is significantly different from the indole spectrum due to the effect of the C=O group conjugated with the indole ring. The fluorescence excitation spectra are considerably different from the absorption spectra. This is associated with the strong dependence of the quantum yield for the free molecules on λ ex . Qualitatively, they are mirror-symmetric to the fluorescence spectra of the stodied compounds. Analysis of the data obtained provides a basis for assuming that in the case of free molecules of indole and its derivatives, the 1 L a absorption in the extreme long-wavelength region of the spectrum does not overlap 1 L b absorption.Introduction. Indole is a chromophore in the amino acid series including tryptophan, the luminescence of which is used when studying complex biological systems. It is well known that the medium has a strong effect on the photophysical properties of indole. Accordingly, broad studies have been conducted on different solutions of indole and its derivatives. The results obtained are covered in monographs [1-3] and many other publications, including theoretical papers [4,5]. It is important to study these molecules in the gas phase (where they do not interact with a medium but rather are free molecules), especially rarefied vapor, where they do not interact with each other during the lifetime of the molecules in the excited electronic state. However, there have only been isolated studies of indole and its derivatives in the gas phase.The first data on the absorption spectrum of indole vapor are found in [6], where the authors associate the longest wavelength band in the spectrum with the electronic transition 1 L b , and the maximum of this band at λ max = 283.7 nm is assumed to correspond to a purely electronic transition. A group of weak bands is also assigned to the same electronic transition. The absorption band with maximum wavelength λ max = 274.1 nm, like the subsequent bands at λ max = 260 and 255 nm, is assigned to the second electronic transition 1 L a . This absorption spectrum of indole vapor is given in the monographs [1,2]. In [6], the absorption spectrum of 3-methylindole vapor is obtained, while [7] gives the spectrum of 5-methoxyindole. A problem with these papers was ...

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UDC 547;535.34;543.42.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 CH 3 , CH 2 , 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 CHCl 3 and CDCl 3 ) 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.Introduction. Brassinosteroids are a new class of natural and synthetic steroidal phytohormones [1] which play a key role in regulation of the growth and development of plants, and also have good prospects for use in medicine and veterinary practice as new pharmacological agents. A condition for high biological activity of brassinosteroids is the presence in the B ring of a 6-keto (castasterone and related compounds) or 7-oxa-6-keto (brassinolide and other lactones) structural moiety, and also a 2α,3α-diol group on the A ring and a trans fusion for the A/B rings (see structural formulas). Along with these structural features, the biological activity of brassinosteroids is determined by the structure of the side chain: the presence and configurations of hydroxyl groups at the carbon atoms C 22 and C 23, and also the nature of the substituent at the carbon atom C 24 [2][3][4]. It has been established that the greatest biological activity in many test systems is shown by brassinolide, first obtained from pollen of the plant Brassica napus [5]. However, a clear interconnection between the structure and the biological properties of brassinosteroids has not yet been established. This makes large-scale use of brassinosteroids in agriculture as plant growth stimulators difficult, and limits their advance into other areas of application.Despite the fact that the IR spectra provide considerable information about the structure and interactions of molecules, in study of brassinosteroids, IR spectroscopy methods have been used mainly to confirm the course of chemical reactions in synthesis of new compounds in this class.In this work, we used IR spectroscopy methods to study the structure and intermolecular interactions of 24-epibrassinolide (1), 24-epicastasterone (2), 28-homobrassinolide (3), and 28-homocastasterone (4), the structural formulas of which have the form:

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