Circular dichroism (CD) spectroscopy is a technique used to study the secondary structure of proteins and nucleic acids. CD spectroscopy is based on the differential absorption of left- and right-circularly polarized light by molecules that exhibit chirality, such as proteins and nucleic acids.
Here are the basic principles of CD spectroscopy:
- Chirality: Chiral molecules are molecules that are not superimposable on their mirror images. Proteins and nucleic acids are chiral molecules that exhibit optical activity, meaning that they can rotate the plane of polarized light.
- Circular polarization: Circularly polarized light is produced by passing linearly polarized light through a quarter-wave plate. The resulting circularly polarized light has a clockwise (right-circularly polarized) or counterclockwise (left-circularly polarized) rotation.
- Absorption: Proteins and nucleic acids absorb circularly polarized light differently depending on their secondary structure. Alpha helices, beta sheets, and random coils all have characteristic CD spectra, allowing for determination of protein and nucleic acid secondary structure.
CD spectroscopy can be used to study a wide range of biological molecules, including proteins, nucleic acids, lipids, and carbohydrates. CD spectroscopy is often used in conjunction with other techniques, such as X-ray crystallography and nuclear magnetic resonance (NMR) spectroscopy, to provide complementary information about protein and nucleic acid structure and function.
CD spectroscopy has a wide range of applications in biological research, such as studying protein folding and stability, identifying ligand binding sites, and monitoring protein-protein interactions. CD spectroscopy can also be used in drug discovery and development to screen compounds for binding to specific proteins or to monitor protein-ligand interactions.