Application of the Kwei equation to model the Tg behavior of binary blends of sugars and salts.

Vitrification of sugar-based solutions plays an important role in cryopreservation, lyophilization, and the emerging field of anhydrous preservation. An understanding of the glass transition characteristics of such formulations is essential for determining an appropriate storage temperature to ensure an extended shelf life of vitrified products. To better understand the effect of salts on the glass transition temperature (T(g)) of glass-forming sugars, we investigated several data-fitting models (Fox, Gordon-Taylor and Kwei) for sugar-salt formulations using data from the literature, as well as new data generated on blends of trehalose and choline dihydrogen phosphate (CDHP). CDHP has recently been shown to have promise as a stabilizing agent for proteins and DNA. The Kwei equation, which has a specific parameter characterizing intermolecular interactions, provides good fits to the T(g) data for sugar-salt blends, and complements other commonly used models that are frequently used to model T(g) data.

Bioenergetics for the growth of Staphylococcus lentus in biocompatible choline salts.

Choline-based biocompatible salts were used as "nutrients" for the growth of Staphylococcus lentus bacteria. Increase in the growth rate of bacteria was observed, compared to conventional carbon sources. In the case of the ionic liquid, choline lactate, the increase was pronounced. Bacterial growth was correlated with power-time curve in an investigation monitored online by reaction calorimetry. From the power-time curve, three phases of the growth can be distinctly seen. Heat yield coefficients estimated for the growth of S. lentus were found to match well with those reported hitherto. A comparative study of heat yields (catabolic) between glucose and choline lactate revealed significant information; the heat yield due to choline lactate (Y (Q/S)) consumption and oxygen (Y (Q/O)) were 23.4 kJ/g and 435 kJ/mol and whereas that for glucose with oxygen were 9.6 kJ/g and 427 kJ/mol, respectively, showing clearly the preferential affinity of choline lactate by the bacteria rather than glucose. This study also established that the use of ionic liquids as nutrients can be monitored using bioreaction calorimetry.

Structure and function of proteins in hydrated choline dihydrogen phosphate ionic liquid.

Ionic liquids are being intensely studied as promising media for the stabilization of proteins and other biomolecules. Choline dihydrogen phosphate (CDHP) has been identified as one of the most promising candidates for this application. In this work we have probed in more detail the effects that CDHP may have on the thermodynamics, structure, and stability of proteins, including one of therapeutic interest. Microcalorimetry and circular dichroism spectropolarimetry (CD) were used to assess the thermal stability of protein solutions in CDHP/water mixtures at various concentrations. Increasing thermal stability of lysozyme and interleukin-2 in proportion to CDHP concentration was observed. Isothermal titration calorimetry (ITC) was used to quantify binding interactions, and indicate that the mechanism for stability does not appear to be dependent upon CDHP binding to protein. CD and small angle X-ray scattering (SAXS) analyses were used to probe for structural changes due to the presence of CDHP. SAXS indicates charge effects on the surface of the protein play a role in protein stability in ionic liquids, and no significant alteration of the overall tertiary conformation of lysozyme was observed at 25 °C. However, after incubation at 37 °C or at higher concentrations of CDHP, small changes in protein structure were seen. Effects on protein activity were monitored using turbidity assays, and CDHP decreases protein activity but does not eliminate it. Protein solubility was also monitored using a turbidity assay and was found to be inversely proportional to the concentration of CDHP in solution.

Group transfer polymerisation in hydrophobic ionic liquids.

For the first time, group transfer polymerisation of methyl methacrylate (MMA) has been successfully carried out at ambient temperatures in an ionic liquid to produce living polymers of improved polydispersity.