Revisiting the Aqueous Solutions of Dimethyl Sulfoxide by Spectroscopy in the Mid- and Near-Infrared: Experiments and Car–Parrinello Simulations

Abstract

The infrared and near-infrared spectra of the aqueous solutions of dimethyl sulfoxide are revisited. Experimental and computational vibrational spectra are analyzed and compared. The latter are determined as the Fourier transformation of the velocity autocorrelation function of data obtained from Car-Parrinello molecular dynamics simulations. The experimental absorption spectra are deconvolved, and the excess spectra are determined. The two-dimensional excess contour plot provides a means of visualizing and identifying spectral regions and concentration ranges exhibiting nonideal behavior. In the binary mixtures, the analysis of the SO stretching band provides a semiquantitative picture of the formation and dissociation of hydrogen-bonded DMSO-water complexes. A maximum concentration of these clusters is found in the equimolar mixture. At high DMSO concentration, the formation of rather stable 3DMSO:1water complexes is suggested. The formation of 1DMSO:2water clusters, in which the water oxygen atoms interact with the sulfoxide methyl groups, is proposed as a possible reason for the marked depression of the freezing temperature at the eutectic point.

Unsupervised Screening of Vibrational Spectra by Principal Component Analysis for Identifying Molecular Clusters

“…Again, the third PC has an extremum around x DMSO =0.5 indicating that it corresponds to 1:1 water‐DMSO dimers. This is in concert with the existing literature, in which experimental and theoretical studies confirmed that hydrogen‐bonded dimers are the predominant interspecies configuration …”

“…16 scans were averaged to obtain an appropriate signal‐to‐noise ratio. For further details on the data acquisition and treatment, for example, how the excess spectra were obtained, see the references …”

“…This is in concert with the existing literature, in which experimental and theoretical studies confirmed that hydrogenbonded dimers are the predominant interspecies configuration. [14][15][16][17][18][19][20] Using the full spectrum (500-4000 cm À1 )i sv ery attractive and efficient, as this means that the approachw orks completely unsupervised. In the next step, we tested whether or not the PCA results are sensitive to the spectralr egion.F or this purpose, the fingerprint region (900-1900 cm À1 ), the CH and OH stretching region (2700-3800 cm À1 ), and the region around .…”

Infrared Spectroscopy as Molecular Probe of the Macroscopic Metal-Liquid Interface

“…The broad and strong hydroxyl (OH) stretching band of water dominates the high wavenumber region, i.e., 2800 to 3800 cm −1 . This band is commonly deconvolved into several sub-bands, indicating the different hydrogen-bonding states of water molecules [29,30]: The lower the wavenumber, the stronger the hydrogen bonding [31]. However, even with the naked eye, systematic differences between the three cases can be observed.…”

Proton Transfer Reaction Dynamics of Pyranine in DMSO/Water Mixtures

“…[14] These uniquea ttributes of DMSO/waterm ixtures have motivated ag ood number of investigations on them. [12,15,16] Various experimental techniques have been employed to address these aqueousD MSO systems, such as dielectric relaxation spectroscopy, [17,18] vibrational spectroscopy, [19][20][21][22] neutron diffraction, [23] fluorescences pectroscopy, [24] molecular dynamics simulations, [25][26][27][28] etc. Al arge majority of these studies suggest that DMSO significantly impacts the donor/acceptor balance in water by participation of its oxygen lone pairs for accepting two hydrogen bonds.…”