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Updated: Apr 18, 2026
CD Spectroscopy to Study DNA-Protein Interactions
Published on: February 10, 2022
Study on the Interaction between Isatin-β-Thiosemicarbazone and Calf Thymus DNA by Spectroscopic Techniques
Parvaneh Pakravan1, Shahla Masoudian2
1Department of Chemistry, Zanjan Branch, Islamic Azad University, Zanjan, Iran.
Insights
Isatin-β-thiosemicarbazone (IBT) intercalates into calf thymus DNA (CT-DNA), displacing Neutral Red dye. This DNA binding interaction is enthalpy-favored, confirmed by spectral and viscosity studies.
Area of Science:
- Biophysical Chemistry
- Molecular Interactions
- Spectroscopy
Background:
- Understanding drug-DNA interactions is crucial for developing new therapeutic agents.
- Isatin derivatives have shown potential biological activities, warranting investigation into their molecular mechanisms.
- Calf thymus DNA (CT-DNA) serves as a standard model for studying DNA-ligand interactions.
Purpose of the Study:
- To investigate the binding mechanism of isatin-β-thiosemicarbazone (IBT) with calf thymus DNA (CT-DNA).
- To characterize the thermodynamic and structural changes associated with IBT-CT-DNA complex formation.
- To explore the potential of IBT as a DNA-interacting agent.
Main Methods:
- UV-Vis absorption spectroscopy
- Fluorescence spectroscopy (including quenching studies)
- Viscosity measurements
- Circular dichroism (CD) spectroscopy
Main Results:
- IBT binds to CT-DNA via intercalation, with a binding constant K = 1.03×10(5) M⁻¹.
- IBT displaces the Neutral Red (NR) dye from the NR-DNA complex.
- Fluorescence quenching studies revealed binding constants (Kf) and approximately one binding site (n≈1).
- Thermodynamic analysis indicated an enthalpy-favored and entropy-disfavored binding process.
- CD spectral studies showed alterations in CT-DNA base stacking, supporting intercalation.
Conclusions:
- Isatin-β-thiosemicarbazone (IBT) exhibits significant intercalation into calf thymus DNA (CT-DNA).
- The binding process is primarily driven by enthalpy, suggesting favorable interactions within the DNA structure.
- These findings provide insights into the molecular basis of IBT-DNA interactions, relevant for medicinal chemistry applications.
Abstract:
The interaction between isatin-β-thiosemicarbazone (IBT) and calf thymus DNA (CT-DNA) was investigated in physiological buffer (pH 7.4) using Neutral Red (NR) dye as a spectral probe by UV-Vis absorption and fluorescence spectroscopy, as well as viscosity measurements. The IBT is stabilized by intercalation in the DNA (K [IBT -DNA] = 1.03×10(5) M(-1)), and displaces the NR dye from the NR-DNA complex. The binding constants Kf and number of binding sites (n≈1) of IBT with DNA were obtained by fluorescence quenching method at different temperatures. Furthermore, the enthalpy and entropy of the reaction between IBT and CT-DNA showed that the reaction is enthalpy-favored and entropy-disfavored. The changes in the base stacking of CT-DNA upon the binding of IBT are reflected in the circular dichroic (CD) spectral studies. The viscosity increase of CT-DNA solution is another evidence to indicate that, IBT is able to be intercalated in the DNA base pairs.
