No abstract

As part of an investigation into the use of biological nitrogen fixation for fertilizer ammonia production, continuous culture studies of respiration and nitrogen fixation in the aerobic bacteria Azotobacter vinelandii under oxygen-limited conditions were conducted. Respiration and growth rates followed Monod forms with respect to dissolved oxygen concentration. However, specific nitrogen fixation rate and nitrogenase activity exhibited maximum values at dissolved oxygen concentrations of ca. 0.02 mM (10% of air saturation). These results suggest careful control of oxygen in the environment is necessary to optimize fixed nitrogen production by this organism.

Phenylpropanolamine (PPA) bound to ion-exchange resin was encapsulated in hollow fibers made of segmented polyurethane. This system was examined as an oral sustained-release delivery system. The fibers were spun by the phase inversion process and cut into different aspect ratios (length/diameter). The U.S.P. basket dissolution method was used to evaluate the in vitro drug release kinetics and the effect of the aspect ratio on the release. For in vivo evaluation, selected fibers were orally administered to dogs in gelatin capsules. The fiber delivery system provided a sustained-release profile of plasma PPA and a longer terminal half-life when compared to an oral immediate-release formulation.

The results suggest unique dynamics of water diffusion through the polymer matrix that may play a critical role in achieving controlled release properties. Furthermore, we suspect that the molecular interactions associated with this new synthetic absorbable material may find a critical utility in important medical applications.