title: Nitric oxide-releasing fumed silica particles: synthesis, characterization, and biomedical application.
abstract: The preparation, characterization, and preliminary biomedical application of various nitric oxide (NO)-releasing fumed silica particles (0.2-0.3 microm) are reported. The tiny NO-releasing particles are synthesized by first tethering alkylamines onto the surface of the silica using amine-containing silylation reagents. These amine groups are then converted to corresponding N-diazeniumdiolate groups via reaction with NO(g) at high pressure in the presence of methoxide bases (e.g., NaOMe). N-Diazeniumdiolate groups were found to form more readily with secondary amino nitrogens than primary amino nitrogens tethered to the silica. Different alkali metal cations of the methoxide bases, however, have little effect on the degree of N-diazeniumdiolate formation. The N-diazeniumdiolate moieties attached on the silica surface undergo a primarily proton-driven dissociation to NO under physiological conditions, with an "apparent" reaction order somewhat greater than 1 owing to local increases in pH at the surface of the particles as free amine groups are generated. The rates of N-diazeniumdiolate dissociation are further related to the parent amine structures and the pH of the soaking buffer. The N-diazeniumdiolate groups also undergo slow thermal dissociation to NO, with zero-order dissociation observed at both -15 and 23 degrees C. It is further shown that the resulting NO-releasing fumed silica particles can be embedded into polymer films to create coatings that are thromboresistant, via the release of NO at fluxes that mimic healthy endothelial cells (EC). For example a polyurethane coating containing 20 wt % of NO-releasing particles prepared with pendant hexane diamine structure (i.e., Sil-2N[6]-N(2)O(2)Na) is shown to exhibit improved surface thromboresistivity (compared to controls) when used to coat the inner walls of extracorporeal circuits (ECC) employed in a rabbit model for extracorporeal blood circulation.
authors.affiliation: Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, USA.
authors.forename: Huiping
authors.initials: H
authors.lastname: Zhang
authors.forename: Gail M
authors.initials: GM
authors.lastname: Annich
authors.forename: Judiann
authors.initials: J
authors.lastname: Miskulin
authors.forename: Kelly
authors.initials: K
authors.lastname: Stankiewicz
authors.forename: Kathryn
authors.initials: K
authors.lastname: Osterholzer
authors.forename: Scott I
authors.initials: SI
authors.lastname: Merz
authors.forename: Robert H
authors.initials: RH
authors.lastname: Bartlett
authors.forename: Mark E
authors.initials: ME
authors.lastname: Meyerhoff
mesh_terms: D000588:Amines / Q000737:chemistry; D000818:Animals; D001391:Azo Compounds / Q000737:chemistry; D020099:Coated Materials, Biocompatible / Q000138:chemical synthesis / Q000737:chemistry*; D005112:Extracorporeal Circulation / Q000295:instrumentation / Q000379:methods; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D000432:Methanol / Q000737:chemistry; D020030:Nitric Oxide Donors / Q000097:blood / Q000138:chemical synthesis / Q000737:chemistry*; D009573:Nitrites / Q000737:chemistry; D010316:Particle Size; D011140:Polyurethanes / Q000737:chemistry; D011817:Rabbits; D012822:Silicon Dioxide / Q000097:blood / Q000138:chemical synthesis / Q000737:chemistry*; D012997:Solvents; D013329:Structure-Activity Relationship
chemical_list: D000588:Amines; D001391:Azo Compounds; D020099:Coated Materials, Biocompatible; D020030:Nitric Oxide Donors; D009573:Nitrites; D011140:Polyurethanes; D012997:Solvents; C452539:diazeniumdiolate; D012822:Silicon Dioxide; D000432:Methanol