Time-resolved Crystallographic Developments Utilising Detector Gating Techniques

The X-ray scattering process occurs on the time scale of about 10-18 seconds; the complete data collection is in the order of hours at synchrotron sources and consequently gives a time-averaged structure of the crystalline material. Previously on beamline I19 at Diamond Light Source we have used a method which involves mechanically chopping the X-ray beam to produce a pulsed source. The pulsed X-ray beam can then be used to probe the crystal a short period after the sample has been photo-activated by a laser beam. This method can be repeated changing the period between the laser (pump) and X-ray pulse (probe) until the entire time series is obtained. Beamline I19 in collaboration with the Dynamic Structural Sciences Consortium at the Research Complex at Harwell have designed a novel strategy to collect an entire time-series (zero to 100 ms) in one data collection utilising the fast image collection time of the Pilatus detector. The 300K Pilatus detector has a readout out time of 2.7 ms and can be gated down to 200 ns. This means that we can use this gating (instead of the mechanical chopper) to obtain single crystal time-resolved structures. This technique shortens the data collection time and as the entire series is obtained from one crystal during the same data collection, this reduces decay and scaling issues.

Towards continuous crystallisation of layered and disordered solid forms

Crystallisation is a vital step in the manufacture of many pharmaceuticals and fine chemicals, producing solids in a form ideal for downstream processes. Unlike others, these industries have not kept pace with advances in continuous production and for centuries industrial crystallisation has operated as a batch process, relying heavily on stirred tank reactors which bring batch to batch variations and limited control over particle attributes. Continuous crystallisation can offer improved product quality, less waste and access to new products more efficiently. One such particle attribute is the presence of molecular disorder in crystalline materials where different ratios of disordered components may show different physical properties [1]. However, disorder can be difficult to control and characterise so has not to date been widely exploited for achieving optimised properties. Multi-component crystallisation can be used to encourage orientational disorder and layering within the crystal lattice by appropriate choice of co-former and by utilising the principles of crystal engineering. The research being presented aims to systematically study disordered and layered materials. Systems that exhibit these characteristics will be discussed structurally, together with results from transferring production of these materials from evaporative to cooling crystallisation, frequently a key first step in achieving crystallisation in a continuous flow environment. In addition, the structural attributes of the particles produced will be correlated with different physical properties such as solubility and compressibility [2].

Single crystal synchrotron X-ray diffraction for imaging hydrogen bond evolution

Hydrogen bonding is a valuable intermolecular interaction in "engineering" solid-state materials. This is because of the directionality and relative strength (1) of these bonds. Hydrogen bonds enable charge and energy transfer, via H-bond evolution, in a range of biological and chemical systems (2). Recent work has demonstrated that single crystal X-ray diffraction can be used to image the evolution of hydrogen bonds, including variable temperature proton migration and proton disorder processes. In particular, in a recent study of the temperature dependent proton disorder in hydrogen bonded 3,5-dinitrobenzoic acid (3,5-DNBA) dimers, the proton disorder deduced from data collected on an X-ray laboratory source is in agreement with that found from neutron data (3). This work focuses on variable temperature single crystal synchrotron X-ray diffraction, for the imaging of evolving hydrogen bonds. The development of appropriate methodology is important here, particularly as previous studies have involved laboratory X-ray sources only. Results will be presented from variable temperature data collections on I19, at the Diamond Light Source, and on beamline 11.3.1, at the Advanced Light Source (ALS), on systems such as 3,5-DNBA and co-crystals of benzimidazole, both exhibiting proton disorder across hydrogen bonding interactions. Synchrotron X-ray diffraction measurements have also been used to follow the change in the position of a proton within an intramolecular [N-H···N]+ hydrogen bond across a range of proton-sponge molecular complexes. Importantly, it has been possible to visualise the evolving hydrogen atom position in Fourier difference electron density maps generated from the synchrotron data. In particular, for the 35-DNBA study, the clearest picture of the evolving hydrogen atom position is observed in those generated from data collected at the ALS; even clearer than that observed in X-ray laboratory and neutron measurements on the same system.

Tuning colour in multi-component complexes: Molecular disorder as a design tool

The key aim of multi-component crystallisation is modification of the physicochemical properties for a specific task.[1] Tuning colour using molecular components is a relatively unexplored area, which is surprising given the possible advantages in pigment development. In crystalline materials, the optical characteristics are not solely dependent on the molecules but also on the crystal packing;[2] it follows that the optical properties could be modified using crystal engineering techniques. We have systematically investigated co-crystallising haloanilines with dinitrobenzoic acids to build an understanding of the intermolecular interactions. Molecular disorder of one or more of the components tends to lead to layered crystal structures that include stacking interactions and therefore strong colour, indicating that molecular disorder is desirable. Defects in inorganic systems are routinely exploited as a route to enhancing or introducing physical properties but similar effects in organic systems are yet to be properly exploited. We will discuss the methods by which disorder can be designed into molecular complexes, and the local ordering effects which give rise to strong diffuse scattering. Additionally we have identified a pair of thermochromic molecular complexes, 2-iodoaniline/2-bromoaniline 3,4-dinitrobenzoic acid, where disorder appears to be crucial in lending the materials their properties. Both complexes undergo a temperature-induced colour change from red to yellow corresponding to a significant molecular rearrangement. The thermochromic transition is a single-crystal to single-crystal effect; the role of molecular disorder as a facilitator for the molecular rearrangement, maintaining the crystal integrity, will be discussed. Despite the complexes being isostructural, only the bromoaniline complex shows reversible thermochromic behaviour; subtleties in the manifestation of this disorder can explain the differences in the reversibility of the transition.

Crystallography for the People

The British Crystallographic Association (BCA) has engaged in public outreach projects over the past two years, aimed at communicating the basic principles and applications of crystallography to the general public, especially in light of the Bragg Centenary Celebrations and the International Year of Crystallography. Based on an activity developed by the Young Crystallographers group of the BCA called "The Structure of Stuff is Sweet", we have developed a pack which can be used as a walk-up stand at science fairs and festivals, workshops and as science busking in pubs. The activities all focus on highlighting the relevance of crystallography to everyday life and are eye-catching to attract an audience. The biggest of the activities has been the UK Big Bang Fair which took place in both March 2013 and March 2014 in London and Birmingham, respectively. This is a very large science fair for schools and families to learn about different aspects of Science and Engineering, with over 75,000 people attending. The Science and Technology Facilities Council in the UK and the BCA funded a crystallography stand in collaboration with Diamond and ISIS. The stand had appeal to both young and old alike, and there was the opportunity to make unit cells from marshmallows, crystallise lysozyme, and to learn about the principles of diffraction using a lego beamline! We had a team of around 40 volunteers from Universities and institutions across the UK covering biological, chemical and physical crystallography. An outline of the events, pictures and comments from participants are presented, as well as our plans for future events building on these foundations to further strengthen the BCA's engagement with the wider community and to raise the profile of crystallography in the public domain. Please come to the poster to find out more about the BCA, and what we do.

Unravelling the nanostructure of cellulose microfibrils

Cellulose is the most abundant naturally occurring polymer and has diverse applications in biology, energy and engineering. The cellulose nanostructure has implications on the mechanical strength of natural materials such as wood and nanocelluloses are also being used to create high-performance composite materials with properties comparable to aramid fibres and carbon nanotubes. The efficiency of breakdown of cellulose into ethanoic alcohols for biofuels is also strongly linked to the aggregation of cellulose fibres into microfibrils. Despite this, the nanostructure of cellulose microfibrils is not well understood. Neutron scattering is a powerful way to distinguish order and disorder in biological fibres, wherever the disordered regions are accessible to deuterium exchange. The aggregation of microfibrils in plant cell walls, coupled to the benefits of deuterium exchange and increased scattering contrast using neutrons gives rise to a small-angle Bragg reflection allowing the size of microfibrils to be deduced. Applying these measurements with a range of spectroscopic techniques and wide-angle X-ray and neutron scattering (WAXS, WANS) has enabled us to develop a model for the structure for the microfibrils of cellulose microfibrils in a range of plant species. The scattering data were consistent with 3nm fibrils with both hydrophobic and hydrophilic surfaces exposed. Disorder in chain packing and hydrogen bonding were shown to increase outwards from the microfibril centre. Axial disorder could be explained in terms of twisting of the microfibrils, with implications for their biosynthesis. The disorder aspects of these microfibrils are directly related to the mechanical strength of wood and the natural variation in microfibril angle reflects this. We will present the outcome of in-situ stretching measurements of cellulose microfibrils with insights into the mechanism of the absorption of strain to further probe this mechanical strength.