[Conformational transition within the A-form of complementary nucleic acids in solution]

Area of Science:

• Biophysics
• Molecular Biology
• Spectroscopy

Context:

• Investigating the structural dynamics of nucleic acids (A-DNA and tRNA) under varying ionic conditions.
• Examining the influence of solvent composition (water vs. ethanol) on nucleic acid conformation.
• Utilizing Circular Dichroism (CD) spectroscopy to probe secondary and tertiary structures.

Purpose:

• To elucidate the differential effects of sodium ion (Na+) concentration on the CD spectra of A-DNA and tRNA in aqueous and ethanol solutions.
• To understand how solvent environment modulates the interaction between cations and nucleic acids.
• To investigate the mechanisms by which ions and ethanol affect the helical structure and groove dimensions of DNA and tRNA.

Summary:

• Circular dichroic spectra of A-DNA in 78% ethanol and tRNA in water/ethanol solutions were analyzed with varying NaCl concentrations.
• Increased Na+ concentration shifted A-DNA's positive CD band (264 nm to 272 nm) and decreased the 210 nm band magnitude.
• Conversely, tRNA in water showed opposite spectral shifts, but in ethanol, it behaved like A-DNA, suggesting solvent-dependent ion interactions.

Impact:

• Demonstrates that cation concentration and solvent composition critically influence nucleic acid conformation.
• Highlights distinct ion-nucleic acid interactions in aqueous versus high-ethanol environments.
• Provides insights into the stabilization of wound helical conformations in aqueous solutions and potential unwinding effects in ethanol-rich media.