Related Experiment Video
Updated: Jul 15, 2026
06:48
CD Spectroscopy to Study DNA-Protein Interactions
Published on: February 10, 2022
Wavelength shifts in solid-state circular dichroism spectra: a possible explanation
Ettore Castiglioni1, Sergio Abbate, Giovanna Longhi
1JASCO Corporation, Hachioji-shi, Tokyo, Japan. ettore.castiglioni@jasco-europe.com
Chirality
|April 18, 2007
Summary
Artificial sampling created "absorption flattening" (AF) in UV-Vis spectra of chiral Tris(ethylenediamine)cobalt(III) chloride, causing a CD spectral red shift. This AF effect distorts CD spectra in inhomogeneous samples.
Area of Science:
- Analytical Chemistry
- Spectroscopy
- Chiroptical Methods
Background:
- Chiral compounds exhibit unique spectral properties.
- UV-Vis and Circular Dichroism (CD) spectroscopy are crucial for characterizing chiral molecules.
- Sample inhomogeneity can lead to spectral artifacts.
Purpose of the Study:
- To investigate the effect of artificial sampling-induced absorption flattening (AF) on UV-Vis and CD spectra.
- To understand how AF influences spectral data of chiral compounds.
- To identify AF as a source of CD spectral distortions.
Main Methods:
- Devised an artificial sampling approach to induce absorption flattening.
- Measured UV-Vis and CD spectra of Tris(ethylenediamine)cobalt(III) chloride.
- Calculated reference spectra from homogeneous solutions for comparison.
- Performed spectral simulations using bandshape analysis.
Main Results:
- Observed absorption flattening (AF) in the UV-Vis spectrum.
- Concomitant red shift in Circular Dichroism (CD) maxima was detected.
- Calculated spectra from homogeneous solutions validated experimental findings.
- Simulations confirmed AF as the cause of the CD spectral red shift.
Conclusions:
- Absorption flattening (AF) is a significant factor causing distortions in CD spectra of inhomogeneous samples.
- The observed red shift in CD spectra is directly attributable to AF.
- Strategies to compensate for or account for AF effects in spectral analysis are proposed.
Related Concept Videos
01:02¹H NMR: Interpreting Distorted and Overlapping Signals
Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...
02:32The de Broglie Wavelength
In the macroscopic world, objects that are large enough to be seen by the naked eye follow the rules of classical physics. A billiard ball moving on a table will behave like a particle; it will continue traveling in a straight line unless it collides with another ball, or it is acted on by some other force, such as friction. The ball has a well-defined position and velocity or well-defined momentum, p = mv, which is defined by mass m and velocity v at any given moment. This is the typical...
01:15NMR Spectroscopy: Chemical Shift Overview
The position of the absorption signal of a sample is reported relative to the position of the signal of tetramethylsilane (TMS), which is added as an internal reference while recording spectra. The difference between the absorption frequencies of the sample and TMS (in Hz) is divided by the spectrometer operating frequency (in MHz) to obtain a dimensionless quantity called the chemical shift. It is reported on the δ (delta) scale and expressed in parts per million.
For instance, the proton...
For instance, the proton...
01:14π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds
In aromatic compounds, such as benzene, the circulation of (4n + 2) π-electrons sets up a diamagnetic or diatropic ring current around the perimeter of the molecule. This current induces a magnetic field that opposes the external field inside the ring and reinforces it on the outside. The protons in benzene are deshielded and exhibit high chemical shifts in the range 6.5–8.5 ppm. The shielding effect at the center of the ring is evident in complex aromatic molecules, such as annulenes. In...
01:16UV–Vis Spectroscopy: Molecular Electronic Transitions
In Ultraviolet–Visible (UV–Vis) spectroscopy, the absorption of electromagnetic radiation is used to probe the electronic structure of molecules. This technique provides insights into molecular electronic transitions, particularly the movement of electrons between different molecular orbitals. Radiation is absorbed if the energy of the electromagnetic radiation passing through the molecule is precisely equal to the energy difference between the excited and ground states. During this process,...
01:27π Electron Effects on Chemical Shift: Overview
An applied magnetic field causes loosely bound π-electrons in organic molecules to circulate, producing a local or induced diamagnetic field over a large spatial volume. As the molecules tumble in solution, the field generated by π-electrons in spherical substituents results in a zero net field. However, the net field generated by π-electrons in non-spherical substituents is not zero. The effect of this induced field depends on the orientation of the molecule with respect to B0, resulting in...