Alkaline titrations of poly(dG-dC).poly(dG-dC): microemulsion versus solution behavior.

Area of Science:

• Biochemistry
• Physical Chemistry
• Materials Science

Background:

• Poly(guanosine-cytosine) (PolyGC) is a polynucleotide with unique structural and chemical properties.
• Understanding PolyGC's behavior in different environments is crucial for its applications.
• Reverse micelles offer a unique microenvironment for studying biomolecules.

Purpose of the Study:

• To investigate the deprotonation behavior of PolyGC under varying salt concentrations in both aqueous solutions and reverse micellar systems.
• To compare the influence of ionic strength on PolyGC denaturation in these two distinct media.
• To elucidate the role of the microenvironment in modulating PolyGC's acid-base properties.

Main Methods:

• Titration of PolyGC with a strong base in water and in cationic reverse micelles (CTAB/n-hexane/n-pentanol/water).
• Spectroscopic analysis using Circular Dichroism (CD) and UV-Vis spectroscopy.
• pH measurements for solution experiments to monitor deprotonation.
• Quantification of hydroxyl ions required for half-transition (R(OH)).

Main Results:

• PolyGC denaturation by base was observed in both media and was reversible by acid addition.
• In aqueous solution, the apparent pKa decreased with increasing NaCl concentration, showing a linear dependence.
• In reverse micelles, R(OH) was independent of NaCl concentration and significantly lower than in solution, suggesting pKa is also salt-independent.

Conclusions:

• The ionic strength significantly affects PolyGC deprotonation and denaturation in aqueous solution.
• Reverse micelles provide a buffered microenvironment, rendering PolyGC's deprotonation independent of external salt concentration.
• The positive charges of the micellar wall and counter-ions likely contribute to this observed buffering effect, explaining the discrepancy between the two media.