The biological nitrogen fixation process is introduced. Discussion focusses on the 'Dominant Hypothesis' of nitrogenase composition and functioning. The enzyme system catalyzes the six-electron reduction of N2 to 2 NH3 concomitant with the evolution of H2. ATP hydrolysis drives the process. The two protein components of the enzyme, [Fe] and [FeMo], contain transition metal sulfide clusters. Recently, an alternative nitrogenase containing vanadium has also been reported. [FeMo] contains the unique FeMo-co site, which has been studied using microbiological, molecular genetic, biochemical, biophysical, chemical and synthetic modelling approaches. Alternative substrates for nitrogenase include a number of unsaturated small molecules. The inorganic chemical literature yields clues for the activation of relevant small molecules such as acetylenes. Substrate reactions of nitrogenase also implicate hydrogen activation as a key feature of nitrogenase turnover. The different ways in which hydrogen can interact with transition metal sulfide clusters are discussed. The need for application of sophisticated probes to distinguish structural and mechanistic possibilities is emphasized. Recent work is presented on the use of Electron Spin Echo Spectroscopy to probe the relation of the extracted cofactor to the center in the intact FeMo protein.
The pore structure of a microporous material H–SAPO-34 is modified using organometallic reagents such as dialkyl zinc (ZnR2, R = Me, Et) via both solution and vapor deposition techniques. After quenching with methanol and air calcination, the modified material is obtained (designated as H–SAPO-34/ZnMe2). H–SAPO-34/ZnMe2 is different compared with framework incorporated ZnAPSO-34 and zinc cation exchanged Zn/SAPO-34. Diffuse Reflectance UV/vis (DRUV) reveals a blue shift in the charge transfer band (202 nm → 195 nm) for H–SAPO-34/ZnMe2, indicating perturbations to the SAPO-34 framework as a result of ZnMe2 modification. Two new resonances (3717 and 924 cm–1) associated with dimethylzinc treatment are observed in FTIR and are attributed to a new Zn–OH moiety. A combination of solid-state 1H and 13C NMR analyses confirms that zinc is in the form of Zn–OH attaching to the framework oxygen in H–SAPO-34/ZnMe2. The reaction of ZnMe2 with H–SAPO-34 has been monitored by NMR following an in situ Chemical Vapor Deposition (CVD) treatment. On the basis of this study, a detailed reaction pathway is proposed: the Brønsted acid sites in H–SAPO-34 react with ZnMe2 upon contact, forming methane and anchoring the Zn-Me species to the framework oxygen; subsequent quenching with methanol converts Zn-Me into Zn-OMe, which is converted to Zn–OH upon air calcination. Presence of the Zn–OH species in the pores reduces the pore volume, as measured by the uptake capacity for methanol.
ABSTRACT Bioremediation, the stimulation of the natural process of biodegradation, played an important role in the cleanup of the oil spill from the Exxon Valdez in Prince William Sound, Alaska. Since there were already substantial indigenous populations of oil-degrading microbes in the area, it was apparent that degradation was likely to be nutrient—not microbial—limited. Bioremediation therefore involved the application of carefully selected fertilizers to provide assimilable nitrogen and phosphorus to the indigenous organisms, with the intent to stimulate their activity and enhance their numbers. We show here that the indigenous microbial populations were indeed substantially increased, throughout the sound, approximately one month after widespread fertilizer applications in both 1989 and 1990. Furthermore, while oil-degrading bacteria made up a significant fraction of the microbial populations on contaminated beaches in September and October 1989, they had declined to less than 1 percent by the summer of 1990, suggesting that the microbial populations on the shorelines were returning to their pre-spill conditions.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTProtein nitrogen coordination to the iron-molybdenum center of nitrogenase from Clostridium pasteurianumH. Thomann, T. V. Morgan, H. Jin, S. J. N. Burgmayer, R. E. Bare, and E. I. StiefelCite this: J. Am. Chem. Soc. 1987, 109, 25, 7913–7914Publication Date (Print):December 1, 1987Publication History Published online1 May 2002Published inissue 1 December 1987https://pubs.acs.org/doi/10.1021/ja00259a067https://doi.org/10.1021/ja00259a067research-articleACS PublicationsRequest reuse permissionsArticle Views122Altmetric-Citations32LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
Field trails were performed in the summer of 1997 on the island of Spitzbergen (approximately 78°N, 17’E). Approximately 5 L m -2 of an IF-30 intermediate fuel grade oil was applied to 140 meters of shoreline. The oiled shoreline was divided into four plots with one plot left untreated, and two plots tilled to a depth of approximately 20 cm. Four applications of fertilizer were applied over a two-month period to one of the tilled plots, and also to an untilled plot. The effect of bioremediation on the microbial community was evaluated using phospholipid fatty acid analysis, hydrocarbon degradation gene probes, and 16S rDNA gene based phylogenetic analysis. Clear differences were observed between fertilized and un-fertilized beaches indicating that bioremediation stimulated the hydrocarbon degrading community in an Arctic environment.
