Interaction between covalent DNA gels and a cationic surfactant.

Area of Science:

• Materials Science
• Polymer Chemistry
• Physical Chemistry

Background:

• Covalently cross-linked double-stranded (ds) DNA gels are complex polyelectrolyte networks.
• Cetyltrimethylammonium bromide (CTAB) is a cationic surfactant known to interact with negatively charged polymers.

Purpose of the Study:

• To investigate the interaction between dsDNA gels and CTAB.
• To study the volume transition of dsDNA gels upon CTAB absorption.
• To characterize the size and formation of CTAB aggregates within the DNA gel.

Main Methods:

• Preparation of covalently cross-linked dsDNA gels.
• Absorption of CTAB from aqueous solutions.
• Time-resolved fluorescence quenching (TRFQ) to determine surfactant aggregate size.
• Measurement of gel volume changes at varying CTAB concentrations.

Main Results:

• DNA gels form complexes with CTAB micelles at concentrations below the critical micelle concentration (cmc).
• Small CTAB micelles (160 < N < 210) form at low concentrations, while larger micelles (N > 500) form at 1 mM CTAB.
• Surfactant binding is nearly quantitative when DNA is in excess.
• Gel volume decreases by 90% as the surfactant to DNA charge ratio (beta) increases from 0 to 1.

Conclusions:

• The interaction between dsDNA gels and CTAB leads to significant gel volume collapse.
• The formation of CTAB-DNA complexes and the size of CTAB aggregates are dependent on surfactant concentration.
• This study provides insights into polyelectrolyte-surfactant interactions and their effect on network volume.