Reduced-molar-mass low-acyl gellan gum was obtained by the centrifugation of an aqueous solution of commercially available food-grade gellan gum. The derived sample was characterized by NMR, FTIR, ICPE, and viscometry methods. The characteristics were compared with commercially available gellan gum Gelzan™. The main focus of the investigation is on the rheological properties of low-molar-mass-gellan ion-induced gels and the influence of reduced molar mass on gelling of gellan. The gels were prepared by adding 0.2–0.3 M of NaCl or KCl to the 0.6 g/dL gellan gum aqueous solution in a 1:1 ratio. The kinetics of gelling at room temperature, studied by rheological methods, strongly depends on molar mass and is practically independent of the temperature (up to 37 °C) and the type of ions. Analysis of the mechanical spectra characterized the obtained gels as weak gels. The gelling temperature achieved upon cooling for low-molar-mass gellan with a 0.1 M NaCl concentration was 39.0 °C (rheology) and 43.5–42.5 °C (visual observation). In summary, this study complements the existing knowledge about how the reduced molar mass of low-acyl gellan gum influences its rheological properties and gelling behavior in ion-induced systems and provides insights into the formulation of gellan-based gels, which can be effectively utilized in various food and pharmaceutical applications.

In this work, we report our results on the hydrodynamic behavior of poly(2-methyl-2-oxazoline) (PMeOx). PMeOx is gaining significant attention for use as hydrophilic polymer in pharmaceutical carriers as an alternative for the commonly used poly(ethylene glycol) (PEG), for which antibodies are found in a significant fraction of the human population. The main focus of the current study is to determine the hydrodynamic characteristics of PMeOx under physiological conditions, which serves as basis for better understanding of the use of PMeOx in pharmaceutical applications. This goal was achieved by studying PMeOx solutions in phosphate-buffered saline (PBS) as a solvent at 37 °C. This study was performed based on two series of PMeOx samples; one series is synthesized by conventional living cationic ring-opening polymerization, which is limited by the maximum chain length that can be achieved, and a second series is obtained by an alternative synthesis strategy based on acetylation of well-defined linear poly(ethylene imine) (PEI) prepared by controlled side-chain hydrolysis of a defined high molar mass of poly(2-ethyl-2-oxazoline). The combination of these two series of PMeOx allowed the determination of the Kuhn–Mark–Houwink–Sakurada equations in a broad molar mass range. For intrinsic viscosity, sedimentation and diffusion coefficients, the following expressions were obtained: $\left[\eta \right]=0.015M^{0.77}$, $s_0=0.019M^{0.42}$ and $D_0=2600M^{-0.58}$, respectively. As a result, it can be concluded that the phosphate-buffered saline buffer at 37 °C represents a thermodynamically good solvent for PMeOx, based on the scaling indices of the equations. The conformational parameters for PMeOx chains were also determined, revealing an equilibrium rigidity or Kuhn segment length, (A) of 1.7 nm and a polymer chain diameter (d) of 0.4 nm. The obtained value for the equilibrium rigidity is very similar to the reported values for other hydrophilic polymers, such as PEG, poly(vinylpyrrolidone) and poly(2-ethyl-2-oxazoline), making PMeOx a relevant alternative to PEG.

The interaction of silver nitrate with star-shaped poly(2-ethyl-2-oxazoline) and poly(2-isopropyl-2-oxazoline) containing central thiacalix[4]arene cores, which proceeds under visible light in aqueous solutions at ambient temperature, was studied. It was found that this process led to the formation of stable colloidal solutions of silver nanoparticles. The kinetics of the formation of the nanoparticles was investigated by the observation of a time-dependent increase in the intensity of the plasmon resonance peak that is related to the nanoparticles and appears in the range of 400 to 700 nm. According to the data of electron and X-ray spectroscopy, scanning and transmission electron microscopy, X-ray diffraction analysis, and dynamic light scattering, the radius of the obtained silver nanoparticles is equal to 30 nm. In addition, the flow birefringence experiments showed that solutions of nanoparticles have high optical shear coefficients.

The optical, electro-optical, and dynamic characteristics of poly( N-acryloyl-11-aminoundecanoic acid) in organic solvents and of the sodium salt of its monomer in water were studied via the methods...