RHAMNOLIPIDS AS MODULATORS OF PARTITIONING BEHAVIOR IN AQUEOUS TWO PHASE MICELLAR SYSTEMS OF ALCOHOL ETHOXYLATE SURFACTANTS

MARTINI, GEORGINA; HAIDAR, CARLA; PELLEGRINI MALPIEDI, LUCIANA; NERLI, BIBIANA

Guaruja

Conferencia; 20th Biopartitioning & Purification Conference 2019 (BPP 2019); 2019

Non-ionic surfactants are able to form aqueous two phase micellar systems (ATPMSs) above a critical temperature, named cloud point (CP). The ATPMS selectivity lies in the difference of hydrophobicity between their micellar-rich and micellar-poor phases. However, the inclusion of a co-surfactant with electrical charge may affect the system physicochemical properties and its partitioning performance. Mixtures formed by tergitol 15-s-7 (Tg7), an alcohol ethoxylate synthetic surfactant, and rhamnolipids (RLs), biosurfactants produced by Pseudomonas aeruginosa, were studied. The use of biosurfactants as co-surfactants was evaluated since they are biodegradable and sustainably produced. The partitioning behavior of cibacron blue (CB), a negatively charged dye, was also determined. Water (W) and sodium citrate 100mM pH 5.00 (CitpH5) and pH 7.00 (CitpH7) were used as surfactant mixtures media. The CPs of Tg7 3% wt/wt in CitpH7 and CitpH5 (32.4 and 35.0 °C) were significantly lower than that obtained in W (41.1 °C). The kosmotropic character of the citrate anion would be responsible for favoring the phase separation. The addition of RL to Tg7 systems at mass ratios Tg7/RL of 12, 18 and 24 affected differently the CPs according to the medium. The CP of Tg7 in W was increased by RL up to 55.5 °C while it was decreased until 29.5 °C at pH 5.00. The CP was not practically affected by the RL presence in CitpH7. When the RL was not charged (pH < pKa 6), its presence favored the phase separation while at pH>pKa, the RL was negatively charged, and the opposite behavior took place. Micellar critical concentration and hydrodynamic diameter of micelles, determined by fluorescence and dynamic light scattering measurements, respectively, were correlated with the CP values. On the hand, drastic changes in CB partitioning were observed with/without RL at the different media. In the presence of RL, partitioning coefficients (Kr), defined as the ratio between micellar and aqueous CB concentrations, increased from 13.2 to 18.0 at pH5 and decreased from 15.2 to 8.2 at pH7. Hydrophobic interaction would prevail when RL was not charged (pH5), thus displacing the partitioning equilibrium to the micellar phase, while a repulsion effect between CB and RL, both negatively charged, would be responsible of decreasing the Kr at pH7. These results demonstrated the modulator effect of RL on the CB partitioning behavior, thus representing a potential tool to optimize a purification strategy.