title: Vinyl polymers based on L-histidine residues. Part 1. The thermodynamics of poly(ampholyte)s in the free and in the cross-linked gel form.
abstract: Amphiphilic vinyl polymers (in the free and cross-linked forms), carrying carboxyl and imidazole groups, were prepared by a radical polymerization of the purposely synthesized N-acryloyl-L-histidine. The protonation thermodynamic studies (at 25 degrees C in 0.15 M NaCl) showed high polyelectrolyte character of the soluble polymer. Unlike the linear decreasing trend of the basicity constant, over the whole range of alpha (degree of protonation), the enthalpy changes for the protonation of the imidazole nitrogen in the polymer showed a decreasing pattern only at alpha > 0.5. This was ascribed to the formation of hydrogen bonds between protonated and free neighboring monomer units. Viscometric data revealed a minimum hydrodynamic volume of the polymer at its isoelectric point (pH 5), whereas at higher or lower pHs, the macromolecule expanded greatly as a consequence of the charged sites formation. This produced a preferential solvation of the protonated imidazole and carboxylate ions, the latter being surrounded by more water molecules in the hydration shell. The peculiar hydration behavior was confirmed in the cross-linked polymer. The hydrogel showed an equilibrium degree of swelling (EDS), strongly dependent on pH, in a similar manner as viscometric data of the soluble polymer. A linear relationship between the reduced viscosity and the EDS was found. The polymer was non toxic against the RAW264 cell line.
authors.affiliation: Dipartimento di Scienze e Tecnologie Chimiche e dei Biosistemi, Via Aldo Moro, Università di Siena, I-53100 Siena, Italy.
authors.forename: Mario
authors.initials: M
authors.lastname: Casolaro
authors.forename: Severino
authors.initials: S
authors.lastname: Bottari
authors.forename: Andrea
authors.initials: A
authors.lastname: Cappelli
authors.forename: Raniero
authors.initials: R
authors.lastname: Mendichi
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Ito
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D003432:Cross-Linking Reagents / Q000737:chemistry*; D005782:Gels / Q000138:chemical synthesis / Q000737:chemistry*; D006639:Histidine / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D051379:Mice; D015394:Molecular Structure; D009000:Monocytes / Q000187:drug effects; D011108:Polymers / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology; D013816:Thermodynamics; D014753:Vinyl Compounds / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology
chemical_list: D003432:Cross-Linking Reagents; D005782:Gels; D011108:Polymers; D014753:Vinyl Compounds; D006639:Histidine