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Crystallisation and Directed Assembly

The theme of this group is the application of assembly-based approaches for the generation of new functional materials.  When we look at Nature, a fundamental feature of many of the materials or matter formed – which range from crystalline solids such as salt, to tightly-packed DNA in chromosomes, functional proteins, bio-membranes which enable the function of all life-on-earth, and even macroscopic structures such as bone, which shows a remarkable seven levels of hierarchical ordering – is that they display highly organized structures.  Interestingly, such materials are often generated by the self-assembly of smaller sub-units, where the composition and geometry of the sub-units dictates how they interact and then assemble.  In this way, Nature can construct complex materials with remarkable properties that go far beyond that achievable with small molecules.

Our research takes inspiration from these processes, and is investigating how assembly occurs over length scales ranging from the molecular to the mesoscale. Addressing topics ranging from crystallization, supramolecular assembly, crystal engineering and the assembly of bio-molecules we are developing an understanding of the physico-chemical interactions which govern assembly processes.  Armed with this insight, we are then able to design and build new structures/ materials, with tailor-made properties, where targets can include new molecular devices, catalytic materials, drug therapies, or batteries.

Crystal Engineering

In this research grouping, we are interested in directing self-assembly to generate functional molecular crystals and coordination polymers. One set of projects involves switchable materials based on spin-crossover metal complexes, which reversibly change their magnetic moment, colour and conductivity in response to a physical stimulus like a change in temperature or laser irradiation. These switching events can be gradual or abrupt, and sometimes exhibit thermal hysteresis. These properties are controlled by the way each switching site interacts with its nearest neighbours in the crystal, and we are leading efforts to understand these phenomena. Coordination polymers, in contrast, are crystalline metal-ligand systems with infinite structures such as chains, helices, grids and 3D lattice which find application in areas including molecular separations, catalysis and gas storage. Our ultimate goal is to be able to build these types of molecular material – by design – from the bottom-up using strategies of “host-guest control” where interactions between the host and simple guest molecules manipulate the overall self-assembly outcomes.

Supramolecular Assembly

The same principles of self-assembly can also be used to produce discrete molecules with three-dimensional topologies and cage structures. One active project focuses on unusually large metal/organic molecular cages with dimensions in the nm range. These hollow molecules are the size of a small protein and the dynamics of guest binding within their cavities, and of the cages themselves, are being studied by a combination of spectroscopic and molecular dynamics methods. The structures of the cages can be systematically modified by appropriate substitution of the walls of the cavities, allowing us to vary the hydrophobicity and steric properties of their internal cavities. Specific host-guest interactions can thus be designed into the cage structures, enabling them to be used as nano-scale reaction vessels and in a wide range of other applications.  In a new project, the same principles of self-assembly are being applied using redox-active components, to produce new molecular architectures exhibiting strong optical absorptions in the infra-red that are switchable by guest binding.

Crystallization

Crystallization is a hugely important subject which lies at the heart of a vast array of natural phenomena and technological processes, including weathering and frost heave, scaling phenomena, the formation of ice in the atmosphere and applications such as the fabrication of nano-materials, mineral-based biomaterials, pharmaceuticals and food-stuffs.  In the School of Chemistry, we have particular interests in biomineralization – the formation of structures such as bones, teeth and seashells.  Biominerals are characterized by many remarkable features, such as complex morphologies and superior mechanical properties, and yet are formed in water under ambient conditions.  Using the strategies by which Nature forms biominerals as an inspiration, we are developing new methods of controlling synthetic crystallization processes.  In this way we can, for example, generate crystals with composite structures whose hardnesses are superior even to biominerals, we can gain control over polymorph, and we can form single crystals with sponge-like morphologies.  This will enable us to form new materials, or indeed to prevent unwanted crystallization events such as the formation of kidney stones, or scaling, and is thus highly important to fundamental research and technology across many disciplines.

Biomolecular Self-Assembly

Molecular self-assembly is an integral component of the formation and function of biological systems.  Researchers in the School of Chemistry, University of Leeds are interested in many aspects of these processes, where a principal goal is to build an improved understanding of biological systems, and then apply this new knowledge to the development of novel, functional nanostructured materials and devices.  The research carried out covers many topics, including the biophysical properties of lipid membranes, the applications of membrane-based materials, and nanotoxicology – where we are developing high throughput toxicity sensors.  In collaboration with local SMEs we are engaged in an intense activity to commercialise these devices. Looking to nanomedicine, we are interested in topics such as targeted drug delivery, while biologically-inspired self-assembly is being used as a route to engineer structures such as nanotapes, ribbons and fibres, which have found application in regenerative dentistry.  Finally, theoretical, computational methods are being used to investigate the phase behaviour and transitions of complex systems of biomolecules, with the expectation that this will enable us to bridge our understanding of colloidal systems, polymers, and proteins. Such an approach is being used to study the aggregation of proteins into amyloid fibrils. In this context, we have innovated methods of directing  biomembrane assembly through the use of applied electric field. These methods use simulation techniques in concert with detailed experimental methods.

These research interests are supported by the University of Leeds Centre for Crystallization, which brings together researchers with interests in crystallization from across the university, and the Centre for Molecular Nanoscience (CMNS) which is an interdisciplinary university centre focussing primarily on so-called 'bottom-up' nanoscience, including molecular self-assembly and self-organization, directed molecular assembly, and related application areas including nanomedicine and nanotoxicology.

The group has access to excellent research facilities that include:

  • A new single crystal diffractometer and  a new high resolution Scanning Electron microscope in the School of Chemistry
  • New laboratories enabling electrochemistry, biochemistry, and chemical synthesis.  
  • New research laboratories for crystallization studies equipped with a wide range of analytical equipment including Raman microscopy, BET, TGA and DSC.
  • Further access to state-of-the-art electron microscopy is provided through university centres located in Engineering (LEMAS) and Biology.
  • SoC staff also have access to  bio-imaging facilities (Biology), dynamic light scattering, powder diffraction and zeta-potential particle measurements (Engineering), variable temperature X-ray powder diffraction (Earth Sciences and Engineering), a SQUID magnetometer (Physics) and a Scanning Probe Microscope facility (Physics).


A wide range of PhD projects are available, where these are described on the Project Opportunities page and on individual staff research pages.

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