Raman and infrared spectra of liquid dimethylsulphoxide (DMSO) and DMSO-water mixtures in a wide range of concentrations are reported and discussed. It is found that changes in the vibrational spectra can be related to a gradual insertion of water molecules in the cluster structure of liquid DMSO. In the more dilute aqueous solutions a gradual lowering of the vsz0 stretching frequency is observed and this can be related to the cooperative character of DMSO-water interactions. The interpretation of the spectra is in agreement with the capacity of DMSO for 'breaking' the structure of water in the more concentrated aqueous solutions and 'enhancing' it in very dilute solutions. INTRODUCTIONThe structure of liquid water and aqueous solutions of polar and apolar solutes has been the subject of many investi ations,'"-' including a number from this laboratory.The current models of water structure can be broadly divided into several categories: the 'continuum which considers water to be completely hydrogen bonded, but having a continuous distribution of molecular geometries and hydrogen bond strengths; the 'cluster m~d e l ' , '~-'~ in which water is regarded as being a mixture of clusters of H 2 0 molecules, each molecule being linked to four others, in equilibrium with single H2O molecules included in the clusters. More recent 'mixture m o d e l~' '~-'~ consider liquid water to be a mixture of a small numbers of distinct species of molecular aggregates, with a different number of hydrogen bonds for each molecule. Experimental evidence for the mixture models arises from both spectroscopic data (IR2' and Raman2*) and from radial diffusion function (RDF) data.22In considering the structure of aqueous solutions, a clear distinction must be made between dilute and concentrated solutions. Dilute aqueous solutions can be suitably treated by dividing solutes into 'structuremaking' or 'structure-breakin ' on the basis of their effects on solvent structures. ","'Structure-making' solutes cause an 'enhancement' or a 'rigidification' of water structure, whereas 'structure-breaking' solutes cause a disruption of solvent structures. This model is not applicable to concentrated aqueous solutions, where the concept of 'structure of water' becomes meaningless. We have considered this point in a recent paper.6 On the basis of earlier work on the structure of concentrated aqueous solutions of strong inorganic acids, bases and their salts, and on the cooperative character of hydrogen bond^,^ we have proposed a structural model for concentrated aqueous solutions of electrolytes as a function of the ionic electrostatic field of the solute. 2-FThe interest in structural characterization of aqueous solutions of dimethylsulphoxide (DMSO) arises not only because of its extensive use as an industrial solvent, but also because of its unusual chemi~o-physical~~ and biological25 properties.The radial diffusion function (RDF) obtained from X-ray diffraction26 and neutron inelastic scattering (NIS)26 studies of aqueous solutions of DMSO showed an 'enh...

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Dimethylsulphoxide (DMS0)-hydrogen chloride interactions have been studied by means of Raman and infrared spectroscopy both in solid 1 : 1 adducts and in liquid mixtures with DMSO : HCl molar ratios >2. The deuterated analogue solid 1: 1 (DMSO-d&DCl was also prepared and studied. Vibrational data suggest the presence of a (DMSOHOSMD)' cation with strong (0-H-O)+ hydrogen bonds both in the solid adducts and in the liquid mixtures. In the solid adducts the (CIHC1)-anion may be present. A relation between some biological properties of DMSO and its protonation is suggested.

Examples of a class of glassy biomaterials with chemical composition similar to that of bone have been prepared by beating mixtures of calcium metaphosphate and hydroxylapatite. The Raman and infrared spectra of these materials are reported and discussed in relation to glass structure, which is of the linear polymeric type with chain length depending on the molar ratio R = [Ca0]/[P20,]. The products of the thermal decomposition of hydroxylapatite have also been characterized spectroscopically.