Christian Roth

The CCP4 (Collaborative Computational Project, Number 4) software suite for macromolecular structure determination by X-ray crystallography groups brings together many programs and libraries that, by means of well established conventions, interoperate effectively without adhering to strict design guidelines. Because of this inherent flexibility, users are often presented with diverse, even divergent, choices for solving every type of problem. Recently, CCP4 introduced CCP4i2, a modern graphical interface designed to help structural biologists to navigate the process of structure determination, with an emphasis on pipelining and the streamlined presentation of results. In addition, CCP4i2 provides a framework for writing structure-solution scripts that can be built up incrementally to create increasingly automatic procedures.

Counterintuitive: The preformation of ion pairs can explain the low melting points of imidazolium-based ionic liquids (ILs) and the resulting expanded range of working temperatures. This quasi-ion-pair formation is possible for ILs having cations with only one interaction site leading to local and directional hydrogen bonds with the corresponding anion (see structure; O red, N blue, F green, S yellow).

The low-frequency motions in ionic liquids can be studied by transmission and attenuated total reflection spectroscopy in the THz region (see spectrum for 1). These motions involve flexing of individual ions and intermolecular interactions by hydrogen bonding. Combined measurements show that the degree of hydrogen bonding is crucial for the solid structures of this material.

Three imidazolium-based ionic liquids of the type [Cnmim][NTf2] with varying alkyl chain lengths (n = 1, 2 and 8) at the 1 position of the imidazolium ring were studied applying IR, linear Raman, and multiplex CARS spectroscopy. The focus has been on the CH-stretching region of the imidazolium ring, which is supposed to carry information about a possible hydrogen bonding network in the ionic liquid. The measurements are compared to calculations of the corresponding anharmonic vibrational spectra for a cluster of [C2mim][NTf2] consisting of four ion pairs. The results support the hypothesis of weak hydrogen bonding involving the C(4)-H and C(5)-H groups and somewhat stronger hydrogen bonds of the C(2)-H groups.