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The absorption of millimeter electromagnetic radiation (v = 1.4, 1.71, and 5 cm -1) by aqueous solutions of ~ycine (pH 6.t--6.2) in the concentration range of 0.5--2.5 tool L -1 was measured. It was found that the absorbing ability of the water present in the solutions, is higher than that of pure water. This phenomenon is explained by the presence of a center of negative hydration in the structure of the glycine zwitterion, which results in an increase in the rotational mobility of water molecules immobilized in the hydrate shell of the glycine zwitterion.Key words: glycine zwitterion, negative and positive hydration, aqueous solution, absorption of millimeter radiation.The biological rote of c~-amino acids evokes great interest in the molecular mechanisms of their interaction with an aqueous medium. In an aqueous medium at neutral pH values, c~-amino acids exist in the form of NH3+CHRCOO -zwitterions. Both charged groups can play the role of centers of the formation of H bonds with water molecules. The comparatively short distance between the withdrawing and donating centers is noticeably reflected in the acid-base and other physicochemical properties of a-amino acids. In particular, the IR spectra in the overtone region showed the formation of a stable I : 1 a-amino acid--water molecular complex, z The authors of this work assumed that in these complexes, a water molecule simultaneously forms two H bonds with the donor and acceptor groups of the a-amino acid, respectively. This mechanism of complex formation was not confirmed either in other experimental studies, or in a simulation of the hydration of glycine by the Monte-Carlo method. 3 Ab initio quantum-mechanical calculations of the glycine--water system showed, however, that this complex can exist. 4To obtain additional information on the character of intermolecular interactions of water molecules with the zwitterion of an cL-amino acid, we used absorption millimeter spectroscopy (AMS). The AMS experiment and its interpretation are considered in detail in Ref. 5. In this review, in particular, some problems that appear in the study of the hydration of c~-amino acids are discussed.The absorption of millimeter (MM) radiation by aqueous systems is a smooth function of frequency. Nevertheless, the AMS method allows one to study the action of a dissolved substance on the aqueous component of the solution, detecting the number of water molecules that change their dynamic state in the hydrate shell of the dissolved substance. 5 ExperimentalThe absorption coefficient* ct (dB mm -1) of the MM radiation (1.4--5 cm -l) of aqueous solutions of glycine (pH 6.1--6.2; C 2 = 0.5--2.5/mol L -l) was measured on quasioptical and waveguide type setups in ceils with variable thickness. 5 The absorption =exp (~ < 0.003) was measured at a frequency of 5 cm -1 at 20 and 60 ~ measurements at frequencies of 1.71 and 1.40 cm -1 were performed only at 20 ~ Bidistilled water and twice recrystallized glycine (Reanal) were used for the preparation of solutions. Results and DiscussionAs ...

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