High-resolution ultrasound spectroscopy and isothermal titration calorimetry were used to characterize interactions between hyaluronan and arginine oligomers. The molecular weight of arginine oligomer plays an important role in interactions with hyaluronan. Interactions were observable for arginine oligomers with eight monomer units and longer chains. The effect of the ionic strength and molecular weight of hyaluronan on interactions was tested. In an environment with increased ionic strength, the length of the arginine oligomer was crucial. Generally, sufficiently high ionic strength suppresses interactions between hyaluronan and arginine oligomers, which demonstrated interactions in water. From the point of view of the molecular weight of hyaluronan, the transition between the rod conformation and the random coil conformation appeared to be important.
This
work is focused on the study of the effect of cholesterol
on the properties of vesicular membranes of ionic amphiphilic pairs
at different temperatures. The hexadecyltrimethylammonium-dodecyl
sulfate ionic amphiphilic pair system with the addition of 10 mol
% dioctadecyldimethylammonium chloride was chosen for a detailed study
of vesicle properties. A large range of cholesterol concentrations
(0–73 mol %) in the temperature range 10–80 °C
was studied. Under these conditions, the size distribution, the membrane
fluidity, and the surface layer were monitored together with the change
in the mobility of water in the surface layer. Obtained quantities
were correlated with each other and combined into appropriate graphs.
It was found that in stable systems that meet the condition of unimodal
size distribution with a PDI value lower than 0.3, temperature has
virtually no effect on the size of vesicular systems. On the contrary,
when studying the hydration and fluidity of the membrane, significant
changes in these parameters were found, which, however, do not affect
the short-term stability of these vesicular systems. The presented
results thus indicate the possibility of adjusting the composition
of the vesicular system in terms of fluidity and membrane hydration
while maintaining short-term stability and size distribution.
High-resolution ultrasound spectroscopy (HR-US), size and ζpotential titrations, and isothermal titration calorimetry (ITC) were used to characterize the interactions between hyaluronan and catanionic ion pair amphiphile vesicles composed of hexadecyltrimethylammonium-dodecylsulphate (HTMA-DS), dioctadecyldimethylammonium chloride (DODAC), and cholesterol. In addition to these methods, visual observations were performed with the selected molecular weight of hyaluronan. A very good correlation was obtained between data from size titration, HR-US, and visual observation, which indicated in lower charge ratios the formation of hyaluronan-coated vesicles. On the contrary, at higher charge ratios, coated vesicles disintegrated to a size of around 2000 nm. The intensity of these interactions and the disaggregation were dependent on the molecular weight of hyaluronan. All interactions studied by ITC showed strong exothermic behavior, and these interactions between vesicles and hyaluronan were confirmed from the first addition, independently of the molecular weight of hyaluronan.
In this study, the high-resolution ultrasonic spectroscopy
(HR-US)
technique was applied to examine interpolyelectrolyte neutralization.
The mentioned method was tested on the example of complexation between
poly(allylammonium) cations and poly(acrylate) anions in aqueous solutions
at pH = 7. It was confirmed by HR-US that the type of titration (stepwise
or abrupt), the direction of titration, and the type of background
salt affect the outcome of interpolyelectrolyte neutralization. The
obtained results were explained on the basis of ultrasonic velocity
and attenuation changes in the context of suspension compressibility,
a parameter that is extremely sensitive to molecular organization
and intermolecular interactions. Moreover, the results of HR-US measurements
proved to be consistent with previous results obtained by more traditional
methods such as dynamic light scattering, microcalorimetry, and electrokinetics.
This research demonstrates that HR-US is a convenient and reliable
method that can be employed for the investigation of interpolyelectrolyte
neutralization and polyelectrolyte-related processes.
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