The linearly polarized light emitted by the light source of the vibrating circular dichroism spectrometer is the basis. Subsequently, it is decomposed into left-handed and right-handed circularly polarized light using specific optical elements such as quarter wave plates. The polarization direction of these two types of circularly polarized light moves along a circle, but the rotation direction is opposite. When these two beams of circularly polarized light pass through a chiral sample, there is a difference in their absorption of left-handed and right-handed circularly polarized light due to the special structure of chiral molecules. This absorption difference is the source of the circular dichroism signal. The instrument obtains information about the sample by detecting this absorption difference. The detector in the instrument will capture the changes in light intensity after passing through the sample and convert them into electrical signals. These electrical signals undergo a series of processing and analysis to generate circular dichroism spectra. By interpreting the spectrum, detailed information about the secondary structure, folding process, and interactions of molecules in the sample can be inferred.

Vibration circular dichroism spectrometer (VCD) is an important tool for studying the molecular configuration and optical activity of chiral substances. The following are the measurement steps:

1. Instrument calibration: Use standard solutions to calibrate the instrument to determine the absorption wavelength and intensity of left-handed and right-handed circularly polarized light. This is to ensure the accuracy of subsequent measurements.

2. Sample preparation: Dissolve or prepare the sample to be tested in solution form for circular dichroism spectroscopy analysis. Choosing the appropriate solvent is crucial to ensure that it does not interfere with VCD testing, or its impact can be eliminated through subsequent data processing. For solid samples, methods such as compression molding, solid film, or spray coating can be used; If it is a solution small molecule sample, the commonly used colorimetric cell path length is 100 μ m, and typical solvents include CCl2, CDCl2, DMSO-D2, etc.

3. Sample measurement: Inject the prepared sample solution into the sample chamber, start the light source, and the detector begins to detect the absorption differences of different polarized light by the sample. Obtain relevant data by changing the polarization state of light at a specific temperature. For example, for solid testing, a rotating sample holder should be used to eliminate VCD false signals caused by birefringence and other factors.

4. Data collection: Record the electrical signal output by the detector to obtain the circular dichroism spectrum of the sample. This spectrum reflects the optical activity characteristics of the sample at different wavelengths.

5. Data processing and analysis: Firstly, eliminate background noise and other interference factors, and then use specialized software to deconvolve the spectral lines to obtain the intensity and frequency of each vibration mode. Finally, compare the results with the theoretical model to infer the structure and dynamic information of the sample. When determining a sample with an unknown configuration, compare the measured VCD test spectrum with the VCD calculated spectrum obtained by quantifying the preset absolute configuration. If the two correspond, the unknown configuration can be determined as the preset configuration.