Infrared Spectroscopy of Bilberry Extract Water-in-Oil Emulsions: Sensing the Water-Oil Interface.

Water-in-oil (w/o) emulsions are of great interest in many areas of the life sciences, including food technology, bioprocess engineering, and pharmaceuticals. Such emulsions are complex multi-component systems and the molecular mechanisms which lead to a stable emulsion are yet to be fully understood. In this work, attenuated total reflection (ATR) infrared (IR) spectroscopy is applied to a series of w/o emulsions of an aqueous anthocyanin-rich bilberry extract dispersed in a medium chain triglyceride (MCT) oil phase. The content of the emulsifier polyglycerin-polyricinoleat (PGPR) has been varied systematically in order to investigate whether or not its concentration has an impact on the molecular stabilization mechanisms. The molecular stabilization is accessed by a careful analysis of the IR spectrum, where changes in the vibrational frequencies and signal strengths indicate alterations of the molecular environment at the water/oil interface. The results suggest that adding emulsifier in excess of 1% by weight does not lead to an enhanced stabilization of the emulsion.

Molecular Solution Behaviour of an Intermediate Biofuel Feedstock: Acetone-Butanol-Ethanol (ABE).

Mixtures of acetone, butanol, and ethanol (ABE) are common intermediate products in the production of biofuels via biomass fermentation. Their separation to yield, for example, bio-butanol, is still difficult due to the lack of a fundamental understanding of these mixtures at the molecular level. In order to bridge this gap, a detailed analysis of characteristic features of the vibrational spectrum is carried out. A systematic study of the binary solutions of acetone with ethanol and butanol does not only reveal a universal behaviour at the molecular level when acetone is mixed with short-chain alcohols, it also shows that the phenomena at a length scale between the molecules and in the macroscopic solution need to be taken into account to understand the structure-property relationships. The size of self-associated molecule clusters seems to determine whether or not a system exhibits an azeotrope. When a second alcohol is added to an acetone/alcohol solution, no additional non-idealities are induced, which is advantageous for modelling ternary ABE mixtures and for improving their processing in the production of biofuels.

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

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.

Fluorescence spectroscopy of Rhodamine 6G: concentration and solvent effects.

Rhodamine 6G (R6G), also known as Rhodamine 590, is one of the most frequently used dyes for application in dye lasers and as a fluorescence tracer, e.g., in the area of environmental hydraulics. Knowing the spectroscopic characteristics of the optical emission is key to obtaining high conversion efficiency and measurement accuracy, respectively. In this work, solvent and concentration effects are studied. A series of eight different organic solvents (methanol, ethanol, n-propanol, iso-propanol, n-butanol, n-pentanol, acetone, and dimethyl sulfoxide (DMSO)) are investigated at constant dye concentration. Relatively small changes of the fluorescence spectrum are observed for the different solvents; the highest fluorescence intensity is observed for methanol and lowest for DMSO. The shortest peak wavelength is found in methanol (568 nm) and the longest in DMSO (579 nm). Concentration effects in aqueous R6G solutions are studied over the full concentration range from the solubility limit to highly dilute states. Changing the dye concentration provides tunability between ∼550 nm in the dilute case and ∼620 nm at high concentration, at which point the fluorescence spectrum indicates the formation of R6G aggregates.

Probing the balance of attraction and repulsion in binary mixtures of dimethyl sulfoxide and n-alcohols.

Published volumetric mixing data for DMSO-n-alcohol systems show a transition from attractive to repulsive interaction dominance for increasing alkyl chain length. A spectroscopic marker for the relative dominance of these interactions is investigated by FTIR measurements. While most vibrational modes show very similar behavior for the alcohols (C3-C5) studied, the CO torsion mode reveals a strong correlation between maximum red-shift and the balance of attraction and repulsion.