Circular Dichroism (CD) Spectroscopy

Circular dichroism (CD) is the difference in the absorption of left-handed circularly polarized light and right-handed circularly polarized light and occurs when a molecule contains one or more chiral chromophores (light-absorbing groups).

Circular dichroism spectroscopy is a useful technique for analyzing peptide and protein secondary structure and folding properties in solution using very small amounts of protein or peptides.  It is based on the differential absorbance of left and right circularly polarized light by a chromophore. The CD analysis of peptides and proteins is based on the amide chromophore in the far UV region (below 240 nm), as well as information from the aromatic side chains (260-320 nm). For example, α-helical proteins have negative bands at 222 nm and 208 nm and a positive band at 193 nm. Whereas, proteins with well-defined antiparallel β-pleated sheets (β-sheet) have negative bands at 218 nm and positive bands at 195 nm.

 

Buffers used for CD spectroscopy should be free of any optically active compounds and should be as transparent as possible. The total absorbance of the sample, including the buffer and cell, should be below one CD unit for high quality data.

The CD measurements are performed in high transparent quartz cuvettes,, with path lengths ranging from 0.01 to 1 cm.

The new Chirascan CD spectrometer (Applied Photophysics) is available for all faculty members and external users. Faculty members are requested to order using the device though BookIt system.