Bridging the gap between Molecular Dynamics and EPR spectroscopy: Application to Liquid Crystal systems

Liquid crystals (LCs) are an intermediate state of matter that combines both long range order, as found in crystals, and disorder, a characteristic of fluids. This combination of properties gives rise to unique optical and electrical properties that allow LCs to be switched rapidly by electric fields. These properties underlay their widespread application, for example, in displays as seen in flat TV screens and digital watches. The ordering of molecules in LC phases can be, for example, as parallel rods (termed nematic) or as stacks of discs (termed columnar discotics). The latter can conduct charge up and down the columns. This offers potential applications as organic electronic charge transport materials in devices such as light emitting diodes (LEDs), one-dimensional conductors, to provide new types of photoconductors, and photovoltaic solar cells. The underlying molecular organisation must be engineered to produce electron-hole recombination for luminescence or separation for solar cells. Molecular organisation can be by vacuum deposition or the formation of films. The growing demand for LCs with new properties is leading to the development of new mixtures of liquid crystals, new ways to align LC layers for holographic video projection, and the production of new polymeric liquid crystals. The exploitation of self-organising LCs is an important avenue of current research. In order to design novel materials with desired properties it is necessary to describe and predict their behaviour from the molecular level. Recently, major advances in both theoretical and experimental areas have emerged which promise progress in the studies of complex partially ordered molecular systems such as LCs. Firstly, spin labels, specially designed chemical agents that carry a stable unpaired electron, can be introduced within complex molecular systems in order to report on the order and dynamics of surrounding molecules. Because an electron has a magnetic moment it can interact with an external magnetic field. Electron Paramagnetic Resonance (EPR) measures this interaction in the form of spectral line shape. The orientation of the spin label to the magnetic field has a dramatic effect on this line shape and therefore molecular mobility, dynamics and distribution can be studied. EPR is a technique that acts as a snapshot of very fast molecular motions and can resolve molecular re-orientational dynamics of the introduced spin probe over times shorter than a billionth of a second. Recent advances in EPR instrumentation, using different frequencies with spin labels and probes has become an important method for studying structure and dynamics of complex phases such as LCs, of proteins and their complexes, DNA/RNA, polymers, lipids and nanostructures. Secondly, the huge increase in computer power over the last decade has led to an increase in the use of molecular dynamics (MD) simulations as a tool to understand complex chemical systems with the potential to predict various properties of complex self-organising systems such as LCs, LC mixtures and composite systems. Yet there is no general methodology and user-friendly computational tools which are able to link directly state-of-the art MD simulations of complex molecular systems with the simulation and analysis of EPR spectra.The aim of this proposal is to bridge the gap between MD simulations and EPR spectroscopy and to develop methodology, which would enable one to obtain a detailed description and reach unambiguous conclusions about molecular arrangement and interactions within complex molecular systems. In the proposed work, this methodology will be applied to different types of LCs, mixtures and hybrid systems. The output of this proposal will be available to the international scientific community in the form of user-friendly software.

Our proposal aims to develop a general advanced methodology, which will bring together EPR spectroscopy and state-of-the-art computer modelling techniques. Our methodology will contribute to the understanding of the order and dynamics of complex systems at molecular level and will be applied to LC systems. The methods developed could eventually be employed in both research and industry laboratories around the world as a research tool to pursue the design of new materials with useful properties. LC materials are widely used in numerous devices with wide application in many branches of science and technology: biology, science, medicine and also everyday life. A novel tool with enhanced possibility for a detailed analysis of molecular behaviour within LCs will foster the development of new materials with useful properties. Therefore, in the longer term, our proposed research will have impact in enhancing the quality of life. In the shorter term, beneficiaries from our research will be various industrial laboratories who use or are planning to use EPR spectroscopic tools and computer modelling for characterisation and design of novel LC materials. Since, spin labelling EPR approaches are widely used to characterise bio-molecular systems other beneficiaries would be biomedical laboratories and pharmaceutical laboratories who use or will use in the future site-directed mutagenesis with spin labelled EPR. Non-academic laboratories will benefit from our research through the application of novel methodology and user friendly software for MD-EPR simulations and analysis of data. In order to successfully achieve this we will focus on the following: a) making methodology convincing to non-academic users, b) making it easy to use and c) disseminating it as widely as possible by seeking efficient roots to deliver new knowledge to experimental and industrial laboratories in the UK and worldwide. Additional benefits would include: Design and synthesis of novel spin probes for discotic/columnar LCs as a result of collaboration with synthetic chemists and research and professional skills in different disciplines, which a PDRA will gain through working on the project and obtaining research training. We will develop a website, from which users will be able to download software and other supporting files and detailed instructions on how to use them. We plan to disseminate our new methodology as widely as possible. This will involve various knowledge transfer activities for engagement and communication with non-academic communities. This will include publication in non-specialist media, arranging day training workshop and developing links with industrial laboratories. VSO has experience in communication with media and dissemination research to people outside research community through his previous engagement with media and knowledge transfer activities. We also intend to take full advantage of our dedicated website in order to present successful examples of application using non-specialised language and video images. Collaborations with other research partners will play an important role in efficient dissemination and exploitation of our results. In order to disseminate our results as widely as possible and to achieve maximal impact we will integrate our codes with highly popular and widely used EPR simulation suite developed by Prof. Hanson's group from the Centre for Magnetic Resonance, University of Queenland, Australia. This EPR simulation suite has been distributed by Bruker Biospin, a world leading commercial manufacturer of EPR spectrometers. Our research will involve collaboration with the synthetic group at UEA led by Dr Andrew Cammidge. One of the outcomes of the proposed MD-EPR work will be the design and synthesis of novel spin probes. Those probes which will be most suitable for a combined MD-EPR approach, in terms of providing information about mobility and order in discotic/columnar systems, would be patented.