jp3073798_si_001.pdf (431.69 kB)
Condensation, Complex Coacervation, and Overcharging during DNA–Gelatin Interactions in Aqueous Solutions
journal contribution
posted on 2012-11-08, 00:00 authored by Najmul Arfin, H. B. BohidarInteraction between DNA (effective hydrodynamic radius, RDNA ≈ 140 nm) and Gelatin A (GA) (effective
hydrodynamic radius, RGA ≈ 55 nm)
with charge ratio (DNA:GA = 16:1) and persistence length ratio (5:1)
was studied by using fixed DNA concentration (5 × 10–3 % (w/v)) and varying GA concentration (CGA = 0–0.25% (w/v)). Experimentally, three interesting regions
of interaction were observed from dynamic light scattering, turbidity,
zeta potential, and viscosity data: (i) CGA < 0.05% (w/v), GA binds to DNA forming soluble complexes of size Rcomplex ≈ 60 nm < RDNA (primary binding causing condensation); (ii) 0.05%
< CGA < 0.1% (w/v), Rcomplex ≈ 60 to 180 nm was observed up to charge-neutralization
point (secondary binding); and (iii) CGA > 0.1% (w/v) showed interesting overcharging behavior of DNA–GA
complexes, followed by liquid–liquid phase separation (complex
coacervation). Aforesaid regions of interaction were further examined
theoretically by modeling the problem using electrostatic and van
der Waals interaction potentials treating GA molecules as counterions
to DNA macroion. Region (i) was explained on the basis of electrostatic
screening, followed by reduction in persistence length, which resulted
in condensation of DNA–GA complex. In region (ii), the dominance
of van der Waals forces led to the formation of large soluble complexes
through selective binding. This was possible due to closer proximity
between GA and DNA–GA complexes and the absence of strong electrostatic
forces. In region (iii), these oversized and overcharged complexes
coarsened, leading to complex coacervation. Here the interaction energy
profile showed that a greater number of counterions was required over
and above the usual charge neutralization requirement for low-energy
configurations to be achieved.