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Unusual, pH-induced, self-assembly of sophorolipid biosurfactants

Niki Baccile, Florence Babonneau, Jacques Jestin, Gerard Pehau-Arnaudet and Inge Van Bogaert (UGent)
(2012) ACS NANO. 6(6). p.4763-4776
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Abstract
An increasing need exists for simple, bioderived, nontoxic, and up-scalable compounds with stimuli-responsive properties. Acidic sophorolipids (SL) are glucose-based biosurfactants derived from the yeast broth of Candida bombicola (teleomorph: Starmerella bombicola). The specific design of this molecule, a sophorose head with a free end-COON group at the end of the alkyl chain, makes it a potentially interesting pH-responsive compound. We have specifically investigated this assumption using a combination of small angle neutron scattering (SANS), transmission electron microscopy under cryogenic conditions (Cryo-TEM), and nuclear magnetic resonance (NMR) techniques and found a strong dependence of SL self-assembly on the degree of ionization, alpha, of the COOH group at concentration values as low as Sand 03 wt %. At least three regimes can be identified where the supramolecular behavior of SL is unexpectedly different: (1) at low alpha values, self-assembly is driven by concentration, C and micelles are mainly identified as nonionic objects whose curvature decreases (sphere-to-rod) with C; (2) at mid alpha values, the formation of COO- groups introduces negative charges at the micellar surface inducing an increase in curvature (rod-to-sphere transition). Repulsive electrostatic long-range Interactions appear at this stage. In both regimes 1 and 2, the cross-section radius of the micelles is below 25 angstrom. This behavior is concentration independent. (3) At alpha = 1, individual micelles seem to favor the formation of large netlike tubular aggregates whose size is above 100 nm. Such a complex behavior is very unique as it is generally not observed for common alkyl-based surfactants in concentration ranges below 5-10 wt %.
Keywords
biosurfactants, self-assembly, ionization degree, pH-responsive, microbial-derived surfactants, sophorolipids, small angle neutron scattering, cryo-TEM, X-RAY, ENZYMATIC CONVERSION, MICROBIAL-PRODUCTION, AQUEOUS-SOLUTIONS, OLEIC-ACID, MICELLES, SCATTERING, BOLAAMPHIPHILE, BEHAVIOR, CHAINS

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MLA
Baccile, Niki, et al. “Unusual, PH-Induced, Self-Assembly of Sophorolipid Biosurfactants.” ACS NANO, vol. 6, no. 6, 2012, pp. 4763–76, doi:10.1021/nn204911k.
APA
Baccile, N., Babonneau, F., Jestin, J., Pehau-Arnaudet, G., & Van Bogaert, I. (2012). Unusual, pH-induced, self-assembly of sophorolipid biosurfactants. ACS NANO, 6(6), 4763–4776. https://doi.org/10.1021/nn204911k
Chicago author-date
Baccile, Niki, Florence Babonneau, Jacques Jestin, Gerard Pehau-Arnaudet, and Inge Van Bogaert. 2012. “Unusual, PH-Induced, Self-Assembly of Sophorolipid Biosurfactants.” ACS NANO 6 (6): 4763–76. https://doi.org/10.1021/nn204911k.
Chicago author-date (all authors)
Baccile, Niki, Florence Babonneau, Jacques Jestin, Gerard Pehau-Arnaudet, and Inge Van Bogaert. 2012. “Unusual, PH-Induced, Self-Assembly of Sophorolipid Biosurfactants.” ACS NANO 6 (6): 4763–4776. doi:10.1021/nn204911k.
Vancouver
1.
Baccile N, Babonneau F, Jestin J, Pehau-Arnaudet G, Van Bogaert I. Unusual, pH-induced, self-assembly of sophorolipid biosurfactants. ACS NANO. 2012;6(6):4763–76.
IEEE
[1]
N. Baccile, F. Babonneau, J. Jestin, G. Pehau-Arnaudet, and I. Van Bogaert, “Unusual, pH-induced, self-assembly of sophorolipid biosurfactants,” ACS NANO, vol. 6, no. 6, pp. 4763–4776, 2012.
@article{4094098,
  abstract     = {{An increasing need exists for simple, bioderived, nontoxic, and up-scalable compounds with stimuli-responsive properties. Acidic sophorolipids (SL) are glucose-based biosurfactants derived from the yeast broth of Candida bombicola (teleomorph: Starmerella bombicola). The specific design of this molecule, a sophorose head with a free end-COON group at the end of the alkyl chain, makes it a potentially interesting pH-responsive compound. We have specifically investigated this assumption using a combination of small angle neutron scattering (SANS), transmission electron microscopy under cryogenic conditions (Cryo-TEM), and nuclear magnetic resonance (NMR) techniques and found a strong dependence of SL self-assembly on the degree of ionization, alpha, of the COOH group at concentration values as low as Sand 03 wt %. At least three regimes can be identified where the supramolecular behavior of SL is unexpectedly different: (1) at low alpha values, self-assembly is driven by concentration, C and micelles are mainly identified as nonionic objects whose curvature decreases (sphere-to-rod) with C; (2) at mid alpha values, the formation of COO- groups introduces negative charges at the micellar surface inducing an increase in curvature (rod-to-sphere transition). Repulsive electrostatic long-range Interactions appear at this stage. In both regimes 1 and 2, the cross-section radius of the micelles is below 25 angstrom. This behavior is concentration independent. (3) At alpha = 1, individual micelles seem to favor the formation of large netlike tubular aggregates whose size is above 100 nm. Such a complex behavior is very unique as it is generally not observed for common alkyl-based surfactants in concentration ranges below 5-10 wt %.}},
  author       = {{Baccile, Niki and Babonneau, Florence and Jestin, Jacques and Pehau-Arnaudet, Gerard and Van Bogaert, Inge}},
  issn         = {{1936-0851}},
  journal      = {{ACS NANO}},
  keywords     = {{biosurfactants,self-assembly,ionization degree,pH-responsive,microbial-derived surfactants,sophorolipids,small angle neutron scattering,cryo-TEM,X-RAY,ENZYMATIC CONVERSION,MICROBIAL-PRODUCTION,AQUEOUS-SOLUTIONS,OLEIC-ACID,MICELLES,SCATTERING,BOLAAMPHIPHILE,BEHAVIOR,CHAINS}},
  language     = {{eng}},
  number       = {{6}},
  pages        = {{4763--4776}},
  title        = {{Unusual, pH-induced, self-assembly of sophorolipid biosurfactants}},
  url          = {{http://doi.org/10.1021/nn204911k}},
  volume       = {{6}},
  year         = {{2012}},
}
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