Abstract
Bacterial lipopolysaccharides (LPS) are designated as endotoxins, because they cause fever and a wide range of pathologies in humans. It is important to develop effective methodologies to detect trace quantities of LPS in aqueous systems. The present study develops a fine-tuning procedure for the entrapment of trace quantities of LPS from E. coli EH100. The capture agents are self-assemblies (tectomers) formed by synthetic four-antennary oligoglycine (C-(CH2-NH-Gly7)4, T4). Based on previously performed investigations of bulk and adsorption-layer properties of aqueous solutions containing T4 and LPS, the optimal conditions for the entrapment interactions are further fine-tuned by the pH regulation of aqueous systems. A combined investigation protocol is developed, including dynamic light scattering, profile analysis tensiometry, microscopic thin-liquid-film techniques, and transmission electron microscopy. The key results are: (1) two types of complexes between T4 and LPS are generated—amphiphilic species and “sandwich-like” hydrophilic entities; the complexes are smaller at lower pH, and larger at higher pH; (2) an optimum range of pH values is established within which the whole quantity of the LPS is entrapped by the tectomers, namely pH = 5.04–6.30. The obtained data substantiate the notion that T4 may be used for an effective capture and the removal of traces of endotoxins in aqueous systems.
Highlights
The detection and capture of lipopolysaccharides (LPS) in aqueous media are important challenges, related to human health issues
The black dots in the middle are related to secondary thinner film portions on top of the tectomeric aggregates
In the cases of buffered T4+LPS solutions (C(T4) = 2 × 10-4 mol/L, C(LPS) = 0.5 μg/L), the films drain rapidly within ~20 s; the respective snapshots evidence rather inhomogeneous film thicknesses, with the onset of dimples and black dots (Figure 7c). These outcomes are in contrast with the ‘native-pH’ case, where the films have welloutlined characteristic white patterns, with black dots in the middle of the white formations, and the obtained foam films are unstable, draining very quickly in less than 3 s (Figure 7a)
Summary
The detection and capture of lipopolysaccharides (LPS) in aqueous media are important challenges, related to human health issues. LPS are the key components of the outer surface layer of the cell walls in Gram-negative bacteria, like the human pathogens. LPS are known to be highly immunogenic, because they carry antigenic determinants capable to activate the innate immunity. This alerts the host about the invasion of Gram-negative bacteria at very early stages; sometimes the results are uncontrolled pathological responses such as fever, hypotension, and septic shock (the tenth leading cause of death in high-income countries) [12].
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