No abstract

Flavodiiron nitric oxide reductases (FNORs), found in many pathogenic bacteria, are able to detoxify NO by reducing it to N2O. In this way, FNORs equip these pathogens with immunity to NO, which is a central immune defense agent in humans. Hence, FNORs are thought to promote infection of the human body, leading to chronic diseases. Despite this importance of FNORs for bacterial pathogenesis, the mechanism of NO reduction by these enzymes is not well understood. Here we present the synthesis and spectroscopic characterization of the diiron dinitrosyl model complex [Fe2(BPMP)(OPr)(NO)2](BPh4)2. The crystal structure of this complex shows two end-on-coordinated {FeNO}(7) units that, based on spectroscopic and electrochemical results, are only weakly electronically coupled. Importantly, reduction of this complex by two electrons leads to the clean formation of N2O in quantitative yield. This complex therefore represents the first example of a functional model system for FNORs. The results provide key mechanistic insight into the mechanism of FNORs and, in particular, represent strong support for the proposed "super-reduced" mechanism for these enzymes.

No abstract

Wax deposition in subsea pipelines is a problem of enormous economic consequences. The carbon number distribution (CND) is an important characteristic of the deposit because it significantly affects the yield stress of wax deposit , which is important in the design of the remediation technique of pigging. In this study, the recent theories for wax thermodynamic modeling are coupled with heat and mass transport modeling to identify the critical factors that determine the carbon number distribution of wax deposits. It is found that the deposit carbon number distribution is closely related to the diffusion of different n-alkane components and their respective concentration driving forces. The impact of molecular diffusion of the multiple components on the evolution of deposit carbon number distribution is quantified by evaluating of the mass driving force for each n-paraffin component. In addition, the effects of operating conditions on the deposit carbon number distribution are investigated by modeling and are validated by series of flow-loop experiments.