Microscopic and spectroscopic analysis of chitosan–DNA conjugates

• The conjugation of chitosan of different sizes on DNA compaction and particle formation is studied here.
• Chitosan binds DNA via electrostatic and hydrophilic interactions.
• Chitosan-100 forms stronger DNA conjugate than chitosan-200 ad chitosan-15 kD.
• Major DNA compaction and particle formation occurred with chitosan-100 and chitosan-200 kD.
• A partial B to A-DNA transition was observed in the presence of chitosan-100 and chitosan-200 kD.

Conjugations of DNA with chitosans 15 kD (ch-15), 100 kD (ch-100) and 200 kD (ch-200) were investigated in aqueous solution at pH 5.5–6.5. Multiple spectroscopic methods and atomic force microscopy (AFM) were used to locate the chitosan binding sites and the effect of polymer conjugation on DNA compaction and particle formation. Structural analysis showed that chitosan–DNA conjugation is mainly via electrostatic interactions through polymer cationic charged NH2 and negatively charged backbone phosphate groups. As polymer size increases major DNA compaction and particle formation occurs. At high chitosan concentration major DNA structural changes observed indicating a partial B to A-DNA conformational transition.