Ascorbic acid in dimethyl-and diethylsulfoxide solutions has been studied using vibrational (Fourier transform IR and Raman) spectroscopy. Noticeable changes observed in the range of S=O-group vibrations can be explained by the presence of a hydrogen bond between ascorbic acid and sulfoxides. Various types of ascorbic acid/sulfoxide hydrogen-bonded complexes were revealed based on spectral analysis data. The results showed that the ascorbic acid/dimethylsulfoxide system has predominantly one type of complexes whereas the ascorbic acid/diethylsulfoxide system can contain three types of complexes.Introduction. Ascorbic acid (AA) is better known as vitamin C and is the focus of several scientific research groups [1][2][3][4][5][6]. Dimethylsulfoxide (DMSO) is widely used in both biology and medicine [7,8]. The biological significance of diethylsulfoxide (DESO) has been demonstrated [9, 10]. The urgency for investigating AA-DMSO (DESO) systems stems from the fact that AA acts as a cryoprotector, like DMSO and DESO. Furthermore, it has been shown [11] that AA in combination with DMSO enhances the effective cryopreservation of cells. It is noteworthy that DMSO and DESO can penetrate living tissue without causing damage [9] and that AA maintains skin elasticity. Thus, it was expected based on the known property of DMSO as an effective drug transporter [7,8] that DMSO (or DESO) solutions of AA would increase its transport. Recently Fourier-transform IR spectroscopy with attenuated total internal reflectance (ATIR) was used to find the transport effectiveness of AA through skin [1]. The study of AA-DMSO (DESO) solutions is also important for revealing the nature of the intermolecular interaction and understanding the mechanism of their biological activity.Herein the existence of various intermolecular AA-DMSO (DESO) complexes is proven using IR and Raman spectroscopy.Experimental. DESO was prepared and purified according to the literature method [12]. The purity of the product was tested using GC >99.5% purity, <0.01% water content after drying over molecular sieves). DMSO (Aldrich Chemical Co.) was dried over molecular sieves and distilled at reduced pressure. Ascorbic acid (Aldrich Chemical Co., 99.5%) was used as received.IR spectra of pure AA were obtained using a mineral oil mull and drops between KBr plates. Solutions were prepared by direct mixing of a known quantity of DESO, DMSO, and AA at concentrations of 0.25, 0.50, and 1.00 M. IR spectra of pure AA and solutions in DESO and DMSO were recorded using a Fourier-transform Nicolet/NEXUS spectrometer with a CsJ beam divider in the range 4000-220 cm -1 with resolution 4 cm -1 and 32 scans.Raman spectra were recorded on an IFS66-FRA106 (Bruker Instrument Co.) Fourier-transform spectrometer. The laser power on the sample was ≈200 mW at λ = 1064 nm. Each Raman spectrum was the average of 2000 scans with spectrometer resolution 2 cm -1 . Measurements were made in a cell with a thermostatted holder at sample temperature 25 o C (±1 o C). The reproducibility of the Raman...