Structural features of interfacially adsorbed acyl-l-carnitines

[Display omitted] Acyl-l-carnitines (CnLCs) are potentially important as biosurfactants in drug delivery and tissue engineering due to their good biocompatibility. However, little is currently known about the basic interfacial behavior underlying their technological applications. Following our previ...

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Bibliographic Details
Published in:Journal of colloid and interface science 2022-10, Vol.623, p.368-377
Main Authors: Liu, Huayang, Fa, Ke, Hu, Xuzhi, Li, Zongyi, Zhang, Lin, Ma, Kun, Fragneto, Giovanna, Li, Peixun, Webster, John R.P., Petkov, Jordan T., Thomas, Robert K., Ren Lu, Jian
Format: Article
Language:English
Subjects:
acyl-l-carnitine
Antimicrobial surfactant
Biosurfactant
Compatibility
Interfacial adsorption
Neutron reflection
pH responsive
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Summary:[Display omitted] Acyl-l-carnitines (CnLCs) are potentially important as biosurfactants in drug delivery and tissue engineering due to their good biocompatibility. However, little is currently known about the basic interfacial behavior underlying their technological applications. Following our previous characterization of their solution aggregation and adsorption at the air/water interface, this work examines how they adsorb at the hydrophilic solid/liquid interface. As the SiO2/water interface has served as the model substrate for many interfacial adsorption studies, so it has been used in this work as the solid substrate to facilitate dynamic adsorption by spectroscopic ellipsometry (SE) and structural determination of the adsorbed layers by neutron reflection (NR) under different conditions at the SiO2/water interface from a group of CnLC (n = 12, 14, and 16). CnLC surfactants are zwitterionic at neutral pH. They reached saturated adsorption above their critical micellar concentrations (CMCs) and formed a sandwich bilayer with a head–tail-head structure at the hydrophilic SiO2/water interface. The total thicknesses of the adsorbed layers at CMC were found to be 33 ± 2, 35 ± 2, and 37 ± 2 Å for C12LC, C14LC, and C16LC, respectively, with their inner and outer head layers remaining similar but the thickness of the interdigitated middle layer increasing with acyl chain length. As the solution becomes acidic, the carboxyl groups become protonated and the l-carnitine heads are net positively charged, resulting in increased repulsion between the head groups. In this situation, the CnLC surfactants are adsorbed as distinct aggregates to reduce repulsive interaction, resulting in reduced surfactant volume fraction and layer thickness. However, a high ionic strength can screen the repulsive interaction and enhance the adsorbed amount, effectively diminishing the impact of pH. This information provides a useful basis for exploring the technological applications of CnLCs involving a solid substrate.
ISSN:0021-9797
1095-7103
DOI:10.1016/j.jcis.2022.05.024