Ligand Control of Dinitrosyl Iron Complexes for Selective Superoxide-Mediated Nitric Oxide Monooxygenation and Superoxide-Dioxygen Interconversion.

Through nitrosylation of [Fe-S] proteins, or the chelatable iron pool, a dinitrosyl iron unit (DNIU) [Fe(NO)2] embedded in the form of low-molecular-weight/protein-bound dinitrosyl iron complexes (DNICs) was discovered as a metallocofactor assembled under inflammatory conditions with elevated levels of nitric oxide (NO) and superoxide (O2-). In an attempt to gain biomimetic insights into the unexplored transformations of the DNIU under inflammation, we investigated the reactivity toward O2- by a series of DNICs [(NO)2Fe(µ-MePyr)2Fe(NO)2] (1) and [(NO)2Fe(µ-SEt)2Fe(NO)2] (3). During the superoxide-induced conversion of DNIC 1 into DNIC [(K-18-crown-6-ether)2(NO2)][Fe(µ-MePyr)4(µ-O)2(Fe(NO)2)4] (2-K-crown) and a [Fe3+(MePyr)x(NO2)y(O)z]n adduct, stoichiometric NO monooxygenation yielding NO2- occurs without the transient formation of peroxynitrite-derived •OH/•NO2 species. To study the isoelectronic reaction of O2(g) and one-electron-reduced DNIC 1, a DNIC featuring an electronically localized {Fe(NO)2}9-{Fe(NO)2}10 electronic structure, [K-18-crown-6-ether][(NO)2Fe(µ-MePyr)2Fe(NO)2] (1-red), was successfully synthesized and characterized. Oxygenation of DNIC 1-red leads to the similar assembly of DNIC 2-K-crown, of which the electronic structure is best described as paramagnetic with weak antiferromagnetic coupling among the four S = 1/2 {FeIII(NO-)2}9 units and S = 5/2 Fe3+ center. In contrast to DNICs 1 and 1-red, DNICs 3 and [K-18-crown-6-ether][(NO)2Fe(µ-SEt)2Fe(NO)2] (3-red) display a reversible equilibrium of "3 + O2- ⇋ 3-red + O2(g)", which is ascribed to the covalent [Fe(µ-SEt)2Fe] core and redox-active [Fe(NO)2] unit. Based on this study, the supporting/bridging ligands in dinuclear DNIC 1/3 (or 1-red/3-red) control the selective monooxygenation of NO and redox interconversion between O2- and O2 during reaction with O2- (or O2).

Multifunctional microchip-based distillation apparatus II - Aerated distillation for sulfur dioxide detection.

A multifunctional microchip-based distillation apparatus is presented for the distilled of sulfur dioxide (SO2) in food products. The microchip is fabricated on poly(methyl methacrylate) (PMMA) substrates, and comprises a sample zone, a buffer zone, a serpentine distillation column, and a collection zone. In the process, the sample is introduced into the sample zone and is heated under carefully controlled temperature and time conditions. The resulting SO2 and water vapor are carried by nitrogen (N2) gas to the distillation column, where the SO2 is separated from the water vapor via the condensing effects of a continuous cold water flow. Finally, the SO2 is transported to the collection zone, where it is collected with hydrogen peroxide (H2O2) and its concentration determined using an alkali-based titration and paper-based detection method. A distillation efficiency of 90.5% is obtained under the optimal distillation conditions at concentrations of 20-4000 ppm. Moreover, a linear correlation (R2 = 0.9997) is observed between the experimental measurements of the SO2 concentration and the known concentration. The validity of the presented microchip-based distillation apparatus is further investigated by distilling the SO2 concentrations of 25 commodity samples. The detection results show that the deviation does not exceed 5.4% compared with the traditional official method.