In the study, various water clusters were explored from the point of view of the proton transfer between H-bonded neighbors. A relatively modest approach--the MP26-31++G(d,p) level--was chosen as acceptable considering the fact that also larger systems have to be included. The tight ion-pair model (with usually three fixed O-O distances) was adopted for the autodissociation process. First, cluster-estimated pH values rapidly decrease as cluster size increases from 2 to 6. For larger clusters in gas phase, the topology of H bonds plays an important role, varying pH from 7 to 13 in hexamers and from 5 to 15 in octamer clusters. The relationship energy/distance was quantified, too. Enhancing our model with the conductorlike screening model (COSMO) approach brought significant improvement in description of the autodissociation reaction with a stable zwitterionic structure. However, when the O-O restrictions were released, the small barrier for backward reaction disappeared, reforming neutral cluster spontaneously. Also Boltzmann weighting procedure was applied, and for the explored clusters in vacuo, the series of pH 25-18-14-13-10 was obtained for cluster sizes n=2, 3, 4, 6, 8. Using the COSMO approach, the analogous series is 15-14-12-10-9. The limit of the series is still about two to three units above the experimentally known pH. In order to reach the size-independent (bulk) value, larger clusters are needed. However, the situation is far from hopeless since (as it was proven in the study) four-coordinated molecules are not involved in the proton transfer process directly; they can only be a part of the surrounding environment.

The evaporation of thin solution layers is an important process taking place in fields such as distillation, coating, or thin film manufacturing. Under suitable conditions, evaporation can induce convective flow by creating gradients in surface tension (Bénard–Marangoni instability) or density. These phenomena have been studied by many authors, but detailed and illustrative visualizations of real experiments are surprisingly scarce compared to simulation results and drawn schemes. Therefore, detailed and representative visualizations of regular Bénard–Marangoni convective cell patterns are provided in solution‐casted films from acylated hyaluronan. The visualizations agree with predictions made in the literature, thus providing important experimental validation. Most importantly, structures resulting from both horizontal and vertical convective flow are clearly visible. In a subsequent parametric study, the effects of selected parameters on the size of the convective cells are elucidated. The results suggest that the cell size increases with increasing solution layer height and increasing polymer concentration, while no statistically significant effect is observed for the degree of hyaluronan substitution.

Hyaluronan (HA) represents an interesting polymer for nanoparticle coating due to its biocompatibility and enhanced cell interaction via CD44 receptor. Here, we describe incorporation of oleatecapped b-NaYF 4 :Yb 3? , Er 3? nanoparticles (UCNP-OA) into amphiphilic HA by microemulsion method. Resulting structures have a spherical, micelle-like appearance with a hydrodynamic diameter of 180 nm. UCNP-OA-loaded HA micelles show a good stability in PBS buffer and cell culture media. The intensity of green emission of UCNP-OA-loaded HA micelles in water is about five times higher than that of ligand-free UCNP, indicating that amphiphilic HA effectively protects UCNP luminescence from quenching by water molecules. We found that UCNP-OA-loaded HA micelles in concentrations up to 50 lg mL -1 increase cell viability of normal human dermal fibroblasts (NHDF), while viability of human breast adenocarcinoma cells MDA-MB-231 is reduced at these concentrations. The utility of UCNP-OA-loaded HA micelles as a bio-imaging probe was demonstrated in vitro by successful labelling of NHDF and MDA-MB-231 cells overexpressing the CD44 receptor. NHDF (d) incubated with UCNP-OA-loaded oleyl-HA micelles and excess of oleyl-HA (2 mg mL -1 ) served as controls. Green and blue colours represent upconversion emission and Hoechststained cell nuclei, respectively. (Color figure online)