Dr Victor Chechik
Nanoscale chemistry, free radicals and EPR spectroscopy
Chemists have excelled at making small molecules and understanding their properties. However, most processes in nature and many industrial reactions include large ordered molecular assemblies, eg protein aggregates, cell membranes, catalyst surfaces etc. We are interested in understanding the factors which determine the structure and properties of such nanometre-scale molecular aggregates. We are often using free radicals and electron paramagnetic resonance (EPR) to characterise the properties and reactivity of nanostructures. We are also interested in the mechanistic chemistry of free radicals in other systems.
Many research projects in our group use ligand-protected inorganic nanoparticles as easy-to-make, well-defined and versatile nanostructures. For instance, gold nanoparticles could be easily prepared by reduction of Au(III) salts in the presence of a good ligand. Organic thiols are particularly good at coating Au nanoparticles, as they adsorb to the gold surface very strongly and are compatible with a large variety of functional groups.
We are interested in preparing functional nanostructures. Materials containing only a few hundred atoms often have unique physical and chemical properties. The aim of our research is to understand and exploit these properties. For instance, we are developing nanoparticle-based contrast agents for Magnetic Resonance Imaging (MRI). We are also interested in other medicinal applications of nanoparticles, nanoparticle-based drugs, nanoparticle toxicity.
EPR studies of nanostructured materials
We are applying the electron paramagnetic resonance (EPR) spectroscopy to study the organisation and properties of nanostructured materials. For instance, stable organic free radicals (eg nitroxides) could be used as spin probes to report on the molecular environment at the nanoscale. A number of features make ERP particularly suitable for studying nanostructured materials:
- EPR spectra can provide information about the distances between adjacent spin labels in the 1-3 nm range (up to 8 nm with special modern techniques). These distances are within the typical range of nanostructured material dimensions (e.g., nanoparticles).
- EPR provides information about the dynamics of the spin label on the nanosecond (ns) time scale. This time scale is very useful for nanoparticle studies, as characteristic tumbling rates for spin-labelled nanostructures often fall within this range.
Our projects in this area include:
- Chemical reactions at the nanoparticle surface: mechanism of ligand exchange reaction, catalysis by the inorganic core etc.
- Spin-labelled nanoparticles: dynamics and distribution of ligands on the nanoparticle surface
- Other spin-labelled supramolecular systems, including host-guest complexes, and colloidal aggregates.
Free radical intermediates
EPR spectroscopy is ideally suited for studying free radicals, and several projects in our group are focused on detecting the free-radical intermediates in organic reactions with the view of developing mechanistic understanding. Free radicals are common intermediates in a surprisingly large number of processes, and understanding and controlling their role is important for many industrial processes. Examples of projects in this area include:
- Catalytic free-radical oxidations and reductions
- Prevention of spontaneous polymerisation of important monomers and oxidation of organic compounds; development of antioxidants and polymer inhibitors
- Understanding the radical chemistry involved in hair-dye formation
- Gd-functionalised Au nanoparticles as targeted contrast agents in MRI: relaxivity enhancement by polyelectrolyte coating.
M F Warsi, R W Adams, S B Duckett, V Chechik, Chem Commun, 2010, 46, 451-453.
- Spin Trapping of Au−H Intermediate in the Alcohol Oxidation by Supported and Unsupported Gold Catalysts.
M Conte, H Miyamura, S Kobayashi, V Chechik, J Am Chem Soc, 2009, 131, 7189-7196.
- Studying Supramolecular Assemblies by ESEEM Spectroscopy: Inclusion Complexes of Cyclodextrins.
G Ionita, M Florent, D Goldfarb, V Chechik, J Phys Chem B, 2009, 113, 5781-5787.
- Self-assembly of cross-linked β-cyclodextrin nanocapsules.
L C Jones, W M Lackowski, Y Vasilyeva, K Wilson, V Chechik, Chem Commun, 2009, 1377-1379.
- TEMPO-inhibited polymerisation: simultaneous determination of oxygen and inhibitor concentrations by EPR.
M Conte, Y Ma, C Loyns, P Price, D Rippon, V Chechik, Org Biomol Chem, 2009, 7, 2685-2687.
- Lateral Diffusion of Thiol Ligands on the Surface of Au Nanoparticles: An Electron Paramagnetic Resonance Study.
P Ionita, A Volkov, G Jeschke and V Chechik, Anal Chem, 2008, 80, 95-106.
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