Interaction between methylene blue and calf thymus deoxyribonucleic acid by spectroscopic technologies

Area of Science:

• Biophysical Chemistry
• Molecular Interactions
• Spectroscopy

Background:

• Methylene blue (MB) is a versatile dye with potential applications in photodynamic therapy and diagnostics.
• Understanding the interaction between small molecules like MB and DNA is crucial for developing targeted therapies and molecular probes.

Purpose of the Study:

• To characterize the binding modes of methylene blue (MB) to calf thymus deoxyribonucleic acid (ctDNA).
• To investigate the influence of molar ratio (gamma) on MB-ctDNA interaction mechanisms.
• To elucidate the underlying mechanisms of spectroscopic changes and fluorescence quenching.

Main Methods:

• UV-Vis absorption spectroscopy to monitor spectral shifts and hypochromicity.
• Fluorescence spectroscopy and polarization measurements to assess MB's microenvironment and binding.
• Fluorescence quenching experiments using ferrocyanide to differentiate binding modes.

Main Results:

• At low MB:ctDNA ratios (gamma < 4), MB binds electrostatically to DNA phosphates and surface stacks, showing hypochromism without spectral shifts.
• At high MB:ctDNA ratios (gamma > 6), MB intercalates between DNA base pairs, evidenced by spectral red shifts and increased fluorescence polarization.
• Ferrocyanide quenching experiments corroborated the distinct binding modes at different molar ratios.

Conclusions:

• The binding mode of MB to ctDNA is dependent on the MB:ctDNA molar ratio.
• Electrostatic binding and surface stacking dominate at low ratios, while intercalation becomes preferred at high ratios.
• Spectroscopic and fluorescence techniques effectively distinguish these binding mechanisms.