TY - JOUR
T1 - Surface adsorption and solution aggregation of a novel lauroyl-L-carnitine surfactant
AU - Liu, Huayang
AU - Hu, Xuzhi
AU - Li, Zongyi
AU - Fa, Ke
AU - Gong, Haoning
AU - Ma, Kun
AU - Liao, Mingrui
AU - Li, Peixun
AU - Webster, John R.P.
AU - Petkov, Jordan T.
AU - Thomas, Robert K.
AU - Ren Lu, Jian
N1 - Funding Information:
We thank Lonza for funding this project (P121881), ISIS Neutron Facility, STFC for neutron beam time on LOQ (RB 1810241), LARMOR (RB 1910578) and SURF (RB 1920496). This work benefited from the SasView software developed under NSF award DMR-0520547 and Igor pro.
Publisher Copyright:
© 2021
PY - 2021/6/1
Y1 - 2021/6/1
N2 - Hypothesis: L-carnitine plays a crucial role in the cellular production of energy by transporting fatty acids into mitochondria. Acylated L-carnitines are amphiphilic and if appropriate physical properties were demonstrated, they could replace many currently used surfactants with improved biocompatibility and health benefits. Experiments: This work evaluated the surface adsorption of lauroyl-L-carnitine (C12LC) and its aggregation behavior. The size and shape of the aggregates of C12LC surfactant were studied at different temperatures, concentrations, pH and ionic strength by dynamic light scattering (DLS) and small-angle neutron scattering (SANS). Surface tension measurements were carried out to determine the critical micellar concentration (CMC) of C12LC. Combining with the Gibbs equation, the surface excess at different concentrations could be determined. Neutron reflection (NR) was used to determine the structure of the adsorbed layer at the air/water interface with the help of isotopic contrast variations. Findings: At pH 7, the limiting area per molecule (ACMC) of the zwitterionic C12LC adsorbed layer at the air/water interface was found to be 46 Å2 from surface tension and neutron reflection, smaller than the values of C12PC, C12E5, DTAB, C12C4betaine and C12C8betaine but close to that of SDS. A pronounced surface tension minimum at pH 2 at the low ionic strength was linked to a minimum value of area per molecule of about 30 Å2, indicating the competitive adsorption from traces of lauric acid produced by hydrolysis of C12LC. As the concentration increased, area per molecule reached a plateau of 37–39 Å2, indicating the dissolution of the more surface-active lauric acid into the micelles of C12LC. DLS and SANS showed that the size and shape of micelles had little response to temperature, concentration, ionic strength or pH. The SANS profiles measured under 3 isotopic contrasts could be well fitted by the core–shell model, giving a spherical core radius of 15.7 Å and a shell thickness of 10.5 Å. The decrease of pH led to more protonated carboxyl groups and more positively charged micelles, but the micellar structures remained unchanged, in spite of their stronger interaction. These features make C12LC potentially attractive as a solubilizing agent.
AB - Hypothesis: L-carnitine plays a crucial role in the cellular production of energy by transporting fatty acids into mitochondria. Acylated L-carnitines are amphiphilic and if appropriate physical properties were demonstrated, they could replace many currently used surfactants with improved biocompatibility and health benefits. Experiments: This work evaluated the surface adsorption of lauroyl-L-carnitine (C12LC) and its aggregation behavior. The size and shape of the aggregates of C12LC surfactant were studied at different temperatures, concentrations, pH and ionic strength by dynamic light scattering (DLS) and small-angle neutron scattering (SANS). Surface tension measurements were carried out to determine the critical micellar concentration (CMC) of C12LC. Combining with the Gibbs equation, the surface excess at different concentrations could be determined. Neutron reflection (NR) was used to determine the structure of the adsorbed layer at the air/water interface with the help of isotopic contrast variations. Findings: At pH 7, the limiting area per molecule (ACMC) of the zwitterionic C12LC adsorbed layer at the air/water interface was found to be 46 Å2 from surface tension and neutron reflection, smaller than the values of C12PC, C12E5, DTAB, C12C4betaine and C12C8betaine but close to that of SDS. A pronounced surface tension minimum at pH 2 at the low ionic strength was linked to a minimum value of area per molecule of about 30 Å2, indicating the competitive adsorption from traces of lauric acid produced by hydrolysis of C12LC. As the concentration increased, area per molecule reached a plateau of 37–39 Å2, indicating the dissolution of the more surface-active lauric acid into the micelles of C12LC. DLS and SANS showed that the size and shape of micelles had little response to temperature, concentration, ionic strength or pH. The SANS profiles measured under 3 isotopic contrasts could be well fitted by the core–shell model, giving a spherical core radius of 15.7 Å and a shell thickness of 10.5 Å. The decrease of pH led to more protonated carboxyl groups and more positively charged micelles, but the micellar structures remained unchanged, in spite of their stronger interaction. These features make C12LC potentially attractive as a solubilizing agent.
KW - Aggregation
KW - Antimicrobial
KW - Biocompatible surfactants
KW - Carnitine surfactants
KW - Healthcare materials
KW - Personal care
KW - pH responsive
KW - Surface adsorption
U2 - 10.1016/j.jcis.2021.01.106
DO - 10.1016/j.jcis.2021.01.106
M3 - Article
C2 - 33592522
AN - SCOPUS:85100722887
SN - 0021-9797
VL - 591
SP - 106
EP - 114
JO - Journal of Colloid and Interface Science
JF - Journal of Colloid and Interface Science
ER -