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Complex formation between benzene carboxylic acids and β-cyclodextrin in aqueous solutions at 290-300 K was studied using UV spectroscopy. The formation of 1:1 supramolecular inclusion compounds β-cyclodextrinbenzene and β-cyclodextrin-salicylic acid was found. Stability constants (K s ) of the complexes and thermodynamic parameters for formation of the inclusion compounds (∆G, ∆H, and ∆S) were calculated.Introduction. Cyclodextrins (cyclic oligosaccharides) form inclusion complexes with many drugs that have increased solubility, bioavailability, and stability to hydrolysis and oxidation [1][2][3][4][5]. The drugs are encapsulated during formation of supramolecular "host-guest" inclusion compounds within the inner cavity consisting of α-(1 → 4)-glucopyranose rings bonded to each other [6]. This can prolong the action of the drugs.Herein complex formation between benzene carboxylic acids (BCA) (benzoic and 2-hydroxybenzoic or salicylic) and β-cyclodextrin (β-CD) is studied using UV spectroscopy. Benzoic acid is used in medicine as an antiseptic and antirheumatic agent. Salicylic acid possesses anti-inflammatory activity and is used to treat cardiological and skin diseases. However, these BCA are poorly soluble in water and also cause irritation of mucus membranes and affect gastrointestinal blood circulation [7,8].Experimental. β-CD (Fluka, MW = 1135, 99% pure) and BCA (Reakhim, analytically pure; benzoic acid, MW = 122.1, T mp = 395 K, pK a = 4.20; salicylic acid (MW = 138.1, T mp = 432.5 K, T boil = 484 K, pK a = 2.97) were used without further purification. UV absorption spectra of BCA in water and n-hexane and aqueous solutions of BCA containing β-CD were recorded on a Specord M-40 spectrophotometer at 200-350 nm in quartz cuvettes (l = 0.1 cm). Solutions of BCA containing given amounts of β-CD were stored beforehand for 4 days at T = 291, 293, 295, 298, and 300 K for the complex formation to reach equilibrium. IR spectra of samples in KBr disks (1:1 ratio) were recorded on a Thermo Nicolet NEXUS single-beam IR Fourier-transform spectrometer using the NEXUS Smart Collector diffuse reflectance attachment.Results and Discussion.

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