Circular Dichroism
Introduction:
Circular Dichroism (CD) is a spectroscopic technique widely used in biochemistry and molecular biology to study the secondary structure of biological molecules such as proteins and nucleic acids. This technique is based on measuring the differences in light absorption between right-handed and left-handed circularly polarized light, which provides valuable information about molecular structure and biological interactions.
CD is considered a powerful and useful tool in scientific research, as it contributes to understanding the structure and function of biological molecules, offering deeper insights into their interactions and roles in biological processes.
Quantitative analysis and computational modeling are used to interpret the results and determine the secondary structure of the studied molecules.
Measurement Definition:
Circular dichroism relies on the property of selective absorption of circularly polarized light by molecules. When a substance is exposed to circularly polarized light, a difference in absorption occurs between the right and left circularly polarized light. This difference depends on the spatial structure of the molecules, as asymmetric molecules (such as proteins) absorb light in a way that varies based on their structural arrangement.
Benefits of Measurement:
1. Secondary Structure Analysis: CD is used to determine the proportions of alpha helices and beta sheets in proteins, aiding in understanding the general structure of molecules.
2. Molecular Interactions: CD can be used to study protein interactions with drugs or other molecules, providing information on how these interactions affect the structure.
3. Non-destructive: CD can measure small samples without destroying them, making it ideal for biochemical research.
4. Fast and Efficient: Results are obtained in a short time, helping accelerate research.
Types of Measurable Samples:
1. Proteins: The most common model due to their complex structure.
2. Nucleic Acids (DNA and RNA): Can be analyzed to study secondary structures.
3. Small Molecules: Such as drugs and chemical compounds.
4. Molecular Complexes: Such as protein-ligand or protein-nucleic acid complexes.
Measurement Conditions:
1. Concentration: The sample concentration should be appropriate, typically between 0.1 and 1 mmol/l.
2. Purity: The sample must be free of impurities and be pure.
3. Temperature: The sample temperature must be kept constant, as changes can affect the structure.
4. External Conditions: Measurement conditions should be free from external influences (e.g., stray light or vibrations).
Result Analysis:
Analyzing CD results requires understanding the relationship between absorption values and the resulting spectrum. The basic steps include:
Data Collection: Data is collected at different wavelengths, typically from 190 to 250 nm.
CD Calculation: The difference in absorption between right and left circularly polarized light is calculated to obtain CD values.
Spectrum Comparison: The resulting spectrum is compared with a reference or known model to determine the proportions of alpha helices and beta sheets.