Systematic of Alcohol-Induced Simple Coacervation in Aqueous Gelatin Solutions

Abstract

Turbidity measurements performed at 450 nm were used to follow the process of simple coacervation when 1% (w/v) aqueous alkali processed gelatin (type-B) solutions were titrated with methanol, ethanol, propanol, and tert-butyl alcohol at various pHs of the solution ranging from pH = 5 to 8 and ionic strengths varying from I = 0.01 to 0.1 M NaCl. The titration profiles clearly established the transition points in terms of the percentage of volume of alcohol added relative to that of solvent corresponding to the first occurrence of turbidity (Vt) and a point of turbidity maximum (Vp). Addition of more alcohol drove the system toward precipitation. The values of Vt and Vp characterized the initiation of intramolecular folding and intermolecular aggregate formation of the charge neutralized gelatin molecules and the subsequent micro coacervate droplet formation. The state of intermolecular aggregates and that of folded gelatin molecules could be characterized by dynamic laser light scattering experiments, which implied spontaneous segregation of particle sizes preceding coacervation. The aggregates constitute the coacervate phase while the folded gelatin molecules mostly stay dispersed in the supernatant. The data taken together reveal the role played by solution entropy in addition to that of electrostatic and solute-solvent interactions, which had been overlooked hitherto.

Collagen- vs. Gelatine-Based Biomaterials and Their Biocompatibility: Review and Perspectives

“…The gelatine sol undergoes a first order thermo-reversible gelation transition at temperatures lower then Tg with is ~30°C, during which gelatine molecules undergo an association-mediated conformational transition from random coil to triple helix. The sol has polydisperse random coils of gelatine molecules and aggregates, whereas in gel state there is propensity of triple helices stabilized through intermolecular hydrogen bonding, during which, three dimensional (3D) interconnected network connecting large fractions of the gelatine chains is formed (Mohanty & Bohidar, 2003. On cooling, gelatine chains can rewind, but not within the correct register, and small triplehelical segments formed may further aggregate during gel formation.…”

Coacervation in Biopolymers

“…A representative estimation of electrostatic interaction energy can be carried out in the pH window 4 to 9 where most of the kinetics is located. The apparent hydrodynamic radius R h of gelatin is 50 nm [30,62] and that of agar is 100 nm (measured). The intermolecular distance can be determined from concentration and molecular weight as The intermolecular distance d s was estimated to be ≈ 63 nm in this particular system.…”

“…This originates from the changes in degree of surface hydration in the free and complex molecules. If ∆C p has large positive values, the system leads to charge neutralization via ionization process (protein-polysaccharide systems), if ∆C p is negative, the system provokes hydrophobic interactions and if ∆C p is positive with negative ∆H at all temperatures, there is significant contribution of H-bonding [30]. In a recent study of gelatin-agar system done in our laboratory [12], no temperature effect was observed either on the critical pH of complex formation or on the pH where phase separation occurred.…”

Polysaccharides as safer release systems for agrochemicals

“…Tefft and Friend (1993) have prepared series of polymeric microsphere herbicide formulations by using spray-drying technique. The best example of simple coacervation is the encapsulation of core material in gelatin (Mohanty and Bohidar 2003). In ionotropic gelation, pesticide containing polymer solution is poured drop wise into solution of metal ions.…”