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Saccharides participate in the most vitally important biochemical processes involving the formation of molecular complexes. As components of glycoproteins and glycolipids, saccharides perform the receptor functions on a surface of the cell membranes as receptor with respect to medicines [1,2], viruses and bacteria [3,4]. Saccharides also participate in formation of enzyme-substrate complexes [5] and determine the antigen-antibody interactions [5,6]. All these processes include recognition of the reagent structure in the course of complex formation.The selective interactions of mono-and oligosaccharides with compounds of different nature and structure in solutions are of interest today [7][8][9][10][11]. The analysis of the literature data shows that these interactions occur due to noncovalent forces (van der Waals and electrostatic interactions, hydrogen bonds, etc.). The authors of [7][8][9] concluded that capability of saccharides to form complexes is determined by their structures. However, in many cases, the nature of intermolecular interactions in saccharide complexes, their peculiar features, and the role of a solvent in these processes remain still unclear. Some disaccharides were shown to give thermodynamically stable and entropystabilized complexes with 1,4,7,10,13,16-hexaoxacyclooctadecane ( 18-crown-6 ) [12,13].This paper reports the results of integrated study of interactions of two pentoses (D-xylose and L-arabinose) with 18-crow-6 in water at 298.15 K. Crown ethers are known to be models of cyclic antibiotics and enzymes [14]. Therefore, the study of complexation of monosaccharides with crown ethers is of special interest.EXPERIMENTAL 18-Crown-6 (ICN Biomedicals Co.), D-xylose, and L-arabinose (Fluka) with purity > 99% were used as received. All reagents were dried before experiments in vacuum at 323 K (crown ether) and 343 K (monosaccharides) for several days. The solutions were prepared using freshly twice-distilled degassed water by gravimetric method.Calorimetric titration. Heat effects of interactions in the systems under study were measured using automated differential titration calorimeter. Its design, parameters, and calibration are described in [15]. An aqueous solution of 18-crown-6 ( 2-3 × 10 -3 mol/dm 3 ) was placed in calorimetric cell and an aqueous solution of monosaccharide (0.2-0.3 mol/dm 3 ) was placed in injection syringer (the dose volume was 7.64 × 10 -5 dm 3 ). The procedure of calorimetric experiment and details of data collection and processing were similar to those in [12,13]. The titration curves of the systems under investigation at 289.15 K are presented in Fig. 1.Densimetry. The density of the studied solutions was measured on a magnetic-float densimeter with a design similar to that used in [16,17]. The values of a float volume and solenoid constant were found from calibration of a system against water ( ρ 298.15 (H 2 O) = 997.04 kg/m 3 [18]) using set of weights. The weight of platinum rings was chosen such that the working current was 0.05 ≤ i ≤ 0.13 A. The current wa...

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