In this work, low molecular weight (17 kDa) hyaluronan was modified by dodecanoyl substituents. The activation of dodecanoic acid was mediated by benzoyl chloride towards the preparation of a mixed anhydride, which reacts in a second step with HA in water mixed with an organic solvent. The effect of the cosolvent was studied and showed an even distribution of substituents and higher reaction rate in water: 1,4-dioxane compared to water:tert-butanol where substituents occupy adjacent positions. The chemical characterization of the prepared derivatives was elucidated by NMR, FTIR spectroscopy, thermal analyses, and gas chromatography, while the distribution of substituents was evaluated by enzymatic degradation. Molecular-dynamics simulations reveal opposite solvent separations around HA and dodecanoyl chains, that is stronger in water:tert-butanol solution. The resulting incompatibility of solvation-shells of the two entities repels the reaction intermediates from the HA chain and drives them towards the already bound substituents, explaining the observed differences in the distribution evenness. Thus, the influence of the solvent on the reaction selectivity is observed by shielding reactive sites around HA. Therefore, a control of the distribution of the substituents was obtained by defining the concentration of HA and used cosolvent.

Contipro a s Dolní Dobrouč 401 561 02 Dolní Dobrouč Czech Republic

Tomas Bata University in Zlín Faculty of Technology Department of Physics and Materials Engineering Nám T G Masaryka 5555 76001 Zlín Czech Republic

Tomas Bata University in Zlín Faculty of Technology Department of Physics and Materials Engineering Nám T G Masaryka 5555 76001 Zlín Czech Republic; Charles University Faculty of Science Department of Biochemistry Hlavova 8 2030 12843 Praha 2 Czech Republic

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Insight into the Lubrication and Adhesion Properties of Hyaluronan for Ocular Drug Delivery