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Título:
RHAMNOLIPIDS AS MODULADORS OF PARTITIONING BEHAVIOR IN AQUEOUS TWO PHASE MICELLAR SYSTEMS OF ALCOHOL ETOXILATE SURFACTANTS
Autor/es:
GEORGINA MARTINI; CARLA N. HAIDAR; LUCIANA P. MALPIEDI; BIBIANA B. NERLI
Lugar:
Campos Ville - Araraquara, Sao Paulo
Reunión:
Conferencia; BPP 2019 Biopartitioning and Purification Conference; 2019
Institución organizadora:
Faculdade de Ciências Farmacêuticas - Câmpus de Araraquara, UNESP
Resumen:
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 on 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 behavior 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. 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 citrate 100mM pH 5,00 (CitpH5) and pH 7,00 (CitpH7) were used as media for surfactant mixtures. 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 of 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 at pH5 until 29.5 °C. 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 a fluorescence probe and by dynamic light scattering measurements respectively, were correlated with the CP values. Drastic changes in CB partitioning were observed with/without the co-surfactant 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. This shows a modulator effect of RL on the CB partitioning behavior, thus representing a potential tool to optimize a purification strategy.