Virtual issue on absolute structure

Following the success of the inaugural virtual issue on polymorphism in December 2011 (http://journals.iucr.org/special_issues/2011/polymorphism/ ), Acta Crystallographica Section C is pleased to release its second virtual issue, which is on the topic of absolute structure (http://journals.iucr.org/special_issues/2012/absolutestructure/ ).The unambiguous determination of absolute structure, particularly where the absolute configuration of an enantiomerically pure chiral molecule is needed, is important not only for synthetic and natural-product chemists, who wish to fully characterize their products, but can be a critical step for the pharmaceutical industry, where opposite enantiomers of a drug can have quite different biological properties. One should also mention those crystal engineers endeavouring to prepare non-centrosymmetric crystals for applications such as second-harmonic generation.

A major impetus in enabling the study of absolute structure has been the advent of dual radiation CCD diffractometers. This means that more laboratories have routine access to Cu Kα radiation with the potential to successfully study light-atom structures. The latter have been viewed as one of the remaining difficulties in this field.

For the validation of absolute-structure determination, over the years there has been a heavy reliance on the statistics (values and standard uncertainties) of derived parameters or something equivalent, and little study of the fit of the model to the observed quantities. There has been little questioning of the quality of crystals, data collection and correction methodologies. Clearly, absolute-structure determination is still a rich field, wide open for development, especially for light-atom compounds of great importance to the pharmaceutical and chemical industries.

The concept of virtual issues of Section C is an initiative designed to make it easier for readers to find papers relevant to their field of interest, thus increasing the visibility and impact of those papers, and consequently the attractiveness of the journal to authors. This virtual issue has the ambition to present the results of crystal-structure determinations which demonstrate new successes and remaining limitations in absolute-structure evaluation.

The editors of Acta Crystallographica Section C hope that readers find this virtual issue interesting and beneficial. The next virtual issue, on the subject of metal-organic frameworks, will be published in late 2013.