Synthesis and polymerization of epoxymethacrylates, 1. Catalysis and kinetics of the addition reaction of methacrylic acid and 2,2-bis[4-(2,3-epoxypropoxy)phenyl]propane

The kinetics of the addition reaction of methacrylic acid (1) and 2,2-bis[4-(2,3-epoxypropoxy)-phenyl]propane catalyzed by tertiary aliphatic amines, aromatic N-heterocycles and quaternary ammonium salts, respectively, was studied in bulk with equimolar amounts of functional groups from room temperature to 120°C. A reaction order of 1,5 with regard to the conversion of epoxy as well as carboxylic groups was observed. This can be explained assuming the formation of an ammonium alkoxide ion pair by the equilibrium reaction of an epoxy group with ammonium carboxylate and the irreversible consecutive reaction of the ion pair with (1) under formation of 2-hydroxyester groups and regeneration of ammonium carboxylate. The reaction rate constants increase linearly with the concentration of the catalyst and increase with increasing basicity of alkylpyridines. The advantage of the aromatic N-heterocyclic catalysts consists in their stability to peroxides which are ingredients of preparations together with the epoxy methacrylate Bis-GMA, e. g. in dental composites and adhesives.     

Understanding the "lucky few": The conundrum of HIV-exposed, seronegative individuals

It has been known for many years that not all individuals who are repeatedly exposed to HIV-1 show evidence of viral replication, seroconvert, and eventually develop disease. Quite apart from those who seroconvert but progress slowly to AIDS (ie, slow progressors, longterm nonprogressors, elite controllers), these rare, exposed seronegatives either resist infection or harbor extremely low levels of virus that may be detected only using ultrasensitive methods (occult infection). The correlates of protection that confer this unique status to a tiny minority of HIV-exposed individuals remain a subject of intense interest, investigation, and controversy, as no single genetic or immunologic parameter has yet been able to fully explain this phenomenon. However, there is general consensus that studying these individuals may provide invaluable information to aid in the design of vaccines and therapeutic approaches. This review describes the major findings on this important topic, with a focus on immunologic studies.