Raman and infrared study on the effects of dimethylsulphoxide (DMSO) on water structure

Abstract

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...

Polarizability anisotropy relaxation in pure and aqueous dimethylsulfoxide

“…4 -14 The prevailing view is that most of these effects are associated with DMSO's strong hydrophilic nature, which leads to the formation of stoichiometrically well-defined DMSO-water aggregates, with the concomitant formation of a hydrogen bond network and pronounced structural microheterogeneities. 10,[15][16][17][18] No evidence of hydrophobic association between DMSO molecules, as suggested by early experiments, 19,20 has been found by neutron diffraction analyses. 17 More recently, DMSO-water systems have been studied by experimental techniques such as time-resolved Kerr spectroscopy, 21 quasi-elastic neutron scattering, 22,23 timeresolved fluorescence upconversion spectroscopy, 23 and mass spectrometry, 24 devised to investigate molecular clustering.…”

Excess properties and spectral studies for binary system tri-ethylene glycol + dimethyl sulfoxide

“…The stretching vibration of S_O (1055 cm −1 ) [45] in DMSO was split into two new absorption bands at 1028 cm −1 and 1055 cm −1 . The former could be assigned to the interaction of S_O with hydroxyl in TEG, while the latter to the free S_O groups or S_O groups forming cyclic dimmer with another DMSO molecule [46]. Although FTIR results showed that there were hydrogen bonding between the intramolecular molecules of TEG, the interaction of hydroxyl hydrogen in TEG with oxygen in DMSO was much stronger, which was similar to that between DMSO and methanol [47].…”

Interfacial Molecular Organization at Aqueous Solution Surfaces of Atmospherically Relevant Dimethyl Sulfoxide and Methanesulfonic Acid Using Sum Frequency Spectroscopy and Molecular Dynamics Simulation

“…55 For pure DMSO, a broad band peaked at 1043 cm -1 is observed for the SdO stretch mode. 26 The asymmetric band shape ranges from 1000 to 1100 cm -1 and has a shoulder at ∼1055 cm -1 . This broad shape of SdO stretch shows the existence of different aggregates in pure DMSO.…”