Circular dichroism (CD) is the differential absorption of left- and right-handed circularly polarized light. It is a form of spectroscopy used to determine the optical isomerism and secondary structure of molecules, and to study a wide variety of chiral materials in solution, particularly biologically important molecules such as proteins, nucleic acids, carbohydrates, lipids and drugs. It is an ideal technique to investigate protein/ligand binding interactions, such as those involved in signal transduction of normal and tumour cells, without the need for labelling or immobilising any of the components.
IR spectroscopy is a widely used and versatile method for analysis at the molecular scale. In fact single molecular species are identified, and their amount quantified, by specific vibrational spectra with several characteristic absorption bands in the mid-IR range. The high information content of such spectra lends itself to the operation of data bases and the "fingerprint" approach especially to organic and biological material identification, as well as condensed matter studies.
Hard X-ray imaging allow detailed information to be gathered from below the surface of a material through either full-field imaging, where the whole sample is illuminated, or through scanning, where the beam is focused to a small spot which is scanned across the sample. The high intensity and energy of synchrotron X-rays makes it possible to image a much larger range of materials and sample thicknesses than conventional X-ray sources, and the brilliance of the synchrotron source produces very high resolution images.
Often called Non-crystalline diffraction (NCD), Small Angle X-ray Scattering provides essential information on the structure and dynamics of large molecular assemblies in low ordered environments. These are characteristic of living organisms and many complex materials such as polymers and colloids. Small angle scattering covers the angular range up to 1° while WAXS typically covers 5 - 60°. Anomalous SAXS (ASAXS) takes advantage of the tuneable nature of synchrotron X-rays, using X-rays with energies close to the absorption edges of the element under study. This provides information on the specific composition and density fluctuation of the sample.
Spectroscopic experiments allow researchers to reveal elemental composition, chemical state and physical properties of both inorganic material and biological systems. By sweeping through a range of photon energies the absorption, reflectivity or fluorescence of the sample is measured. In the X-ray region all atoms absorb X-rays sharply at certain wavelengths (called absorption edges) that are characteristic of that atomic species, so element-specific information can be obtained.
Diamond Light Source is the UK's national synchrotron science facility, located at the Harwell Science and Innovation Campus in Oxfordshire.
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