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A new additive for better crystals

Researchers explore solid-supported ionic liquids for protein crystallization

Ionic liquids are remarkable solvents with multiple applications, tailored by the chemists’ skills in the synthesis design. These solvents have been used for protein crystallization, an essential step for determining protein structures by x-ray, but applications have been limited to water miscible ionic liquids. Now, chemists from the Molecular Thermodynamics Lab, in collaboration with crystallographers from FCT-UNL, have shown how hydrophobic ionic liquids can be immobilized in hydrophilic solid carriers and how these functionalized particles improve the protein crystallization process. The details of the design of the new particles are published in Materials Chemistry and Physics and the proof of concept for protein crystallization is described in Crystal Growth & Design.

Ionic liquids are substances composed almost exclusively of ions that are usually liquid at room temperature. With applications in numerous fields, ionic liquids present particular advantages in protein-based processes, such as protein extraction, solubilisation, crystallization or their enzymatic activity. But because water is the natural reaction environment for proteins, ionic liquids used in bio-inspired processes are usually hydrated. An alternative is to explore the interface between hydrophobic ionic liquids and water (e.g., as biphasic enzyme-catalysed reactions), which requires the formation of extended undisturbed liquid/liquid contacts. Experiments developed at the Laboratory of Molecular Thermodynamics have shown that the immobilization of ionic liquids on hydrophilic solid carriers (such as barium sulphate) enables the dispersion of otherwise water-immiscible ionic liquids in aqueous media and the creation of extensive ionic liquid/water interfaces.

The immobilization of hydrophobic ionic liquids on a solid carrier can extend their applications in aqueous media and researchers explored this new possibility in the field of protein crystallization for the first time. A collaboration with researchers from FCT-UNL demonstrated that these solid-supported ionic liquids can be successfully used to scavenge proteins from solution, to induce protein crystallization at lower concentrations (than those needed to obtain crystals in control conditions) and to improve the crystal morphology. These features allowed obtaining X-ray diffraction data in cases where the production of good quality protein crystals was found unsuccessful without the aid of the IL-functionalized particles.

Ionic liquids immobilized in solid carriers can be handled as solids, which may offer advantages for specific purposes. Novel applications, emerging for example from suggested enhanced ionicity of the ionic liquids at the solid/liquid interface are yet to be explored.

Original Articles

Materials Chemistry and Physics, 2015, doi:10.1016/j.matchemphys.2015.04.042

Ionic liquid - functionalized crystals of barium sulfate: A hybrid organic-inorganic material with tuned hydrophilicity and solid-liquid behaviour

Kowacz, M., Marchel, M., Esperança, J. M. S. S. and Rebelo, L. P. N.


Crystal Growth & Design, 2015, DOI: 10.1021/acs.cgd.5b00403

Ionic liquid-functionalized mineral particles for protein crystallization

Kowacz, M., Marchel, M., Juknaitė, L., Esperança, J. M. S. S., Romão, M. J., Carvalho A. L. and Rebelo, L. P. N.


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