Studies on the Reaction of Iron(II) with NO in a Noncoordinating Ionic Liquid

A review: Biological technologies for nitrogen monoxide abatement

Nitrogen oxides (NOx), including nitrogen monoxide (NO) and nitrogen dioxide (NO2), are among the most important global atmospheric pollutants because they have a negative impact on human respiratory health, animals, and the environment through the greenhouse effect and ozone layer destruction. NOx compounds are predominantly generated by anthropogenic activities, which involve combustion processes such as energy production, transportation, and industrial activities. The most widely used alternatives for NOx abatement on an industrial scale are selective catalytic and non-catalytic reductions; however, these alternatives have high costs when treating large air flows with low pollutant concentrations, and most of these methods generate residues that require further treatment. Therefore, biotechnologies that are normally used for wastewater treatment (based on nitrification, denitrification, anammox, microalgae, and combinations of these) are being investigated for flue gas treatment. Most of such investigations have focused on chemical absorption and biological reduction (CABR) systems using different equipment configurations, such as biofilters, rotating reactors, or membrane reactors. This review summarizes the current state of these biotechnologies available for NOx treatment, discusses and compares the use of different microorganisms, and analyzes the experimental performance of bioreactors used for NOx emission control, both at the laboratory scale and in industrial settings, to provide an overview of proven technical solutions and biotechnologies for NOx treatment. Additionally, a comparative assessment of the advantages and disadvantages is performed, and special challenges for biological technologies for NO abatement are presented.

Iron(II/III) Halide Complexes Promote the Interconversion of Nitric Oxide and S-Nitrosothiols through Reversible Fe-S Interaction

Heme and non-heme iron in biology mediate the storage/release of NO^• from S-nitrosothiols as a means to control the biological concentration of NO^•. Despite their importance in many physiological processes, the mechanisms of N-S bond formation/cleavage at Fe centers have been controversial. Herein, we report the interconversion of NO^• and S-nitrosothiols mediated by Fe^II/Fe^III chloride complexes. The reaction of 2 equiv of S-nitrosothiol (Ph₃CSNO) with [Cl₆Fe^II₂]^2- results in facile release of NO^• and formation of iron(III) halothiolate. Detailed spectroscopic studies, including in situ UV-vis, IR, and Mössbauer spectroscopy, support the interaction of the S atom with the Fe^II center. This is in contrast to the proposed mechanism of NO^• release from the well-studied "red product" κ¹-N bound S-nitrosothiol Fe^II complex, [(CN)₅Fe(κ¹-N-RSNO)]^3-. Additionally, Fe^III chloride can mediate NO^• storage through the formation of S-nitrosothiols. Treatment of iron(III) halothiolate with 2 equiv of NO^• regenerates Ph₃CSNO with the Fe^II source trapped as the S = 3/2 {FeNO}⁷ species [Cl₃FeNO]^-, which is inert toward further coordination and activation of S-nitrosothiols. Our work demonstrates how labile iron can mediate the interconversion of NO^•/thiolate and S-nitrosothiol, which has important implications toward how Nature manages the biological concentration of free NO^•.

Simultaneous Removal of NO and SO2 from Flue Gas Using [Bmim]2FeCl4/Sulfolane Binary Mixtures

NO and SO2 are the major pollutants of coal combustion. As superior absorbents, ionic liquids are environmentally friendly, are reusable, and can clean flue gases, such as CO2, SO2, and NO x . However, NO and SO2 absorption with low concentration in flue gases under normal conditions is rarely studied. In this work, [Bmim]2FeCl4 was synthesized and mixed with sulfolane for NO and SO2 removal from flue gas. The investigated concentrations of NO and SO2 were 1100 and 2500 ppm, respectively, which are close to real fuel gas conditions. Results showed that 30 wt % [Bmim]2FeCl4/sulfolane mixture performed the best absorption behavior. The presence of SO2 could promote NO absorption by [Bmim]2FeCl4/sulfolane mixture. The 30 wt % [Bmim]2FeCl4/sulfolane mixture had removal efficiencies of 93.6 and 76.2% for NO and SO2, respectively. This mixture also showed great reusability for NO and SO2 after six cycles of absorption. Fourier transform infrared (FTIR) spectrum indicated that SO2 and NO removal by [Bmim]2FeCl4/sulfolane binary mixture was due to the chemical reaction between NO and [Bmim]2FeCl4 and the physical absorption between SO2 and sulfolane.

Inorganic reaction mechanisms. A personal journey

This review covers highlights of the work performed in the van Eldik group on inorganic reaction mechanisms over the past two decades in the form of a personal journey. Topics that are covered include, from NO to HNO chemistry, peroxide activation in model porphyrin and enzymatic systems, the wonder-world of Ru^III(edta) chemistry, redox chemistry of Ru(iii) complexes, Ru(ii) polypyridyl complexes and their application, relevant physicochemical properties and reaction mechanisms in ionic liquids, and mechanistic insight from computational chemistry. In each of these sections, typical examples of mechanistic studies are presented in reference to related work reported in the literature.

A Structural Model for the Iron-Nitrosyl Adduct of Gentisate Dioxygenase

We present the synthesis, properties, and characterization of [Fe(T1Et4iPrIP)(NO)(H₂O)₂](OTf)₂ (1) (T1Et4iPrIP = Tris(1-ethyl-4-isopropyl-imidazolyl)phosphine) as a model for the nitrosyl adduct of gentisate 1,2-dioxygenase (GDO). The further characterization of [Fe(T1Et4iPrIP)(THF)(NO)(OTf)](OTf) (2) which was previously communicated (Inorg. Chem. 2014, 53, 5414) is also presented. The weighted average Fe-N-O angle of 162° for 1 is very close to linear (≥ 165°) for these types of complexes. The coordinated water ligands participate in hydrogen bonding interactions. The spectral properties (EPR, UV-vis, FTIR) for 1 are compared with 2 and found to be quite comparable. Complex 1 closely follows the relationship between the Fe-N-O angle and NO vibrational frequency which was previously identified for 6-coordinate {FeNO}⁷ complexes. Liquid FTIR studies on 2 indicate that the ν(NO) vibration position is sensitive to solvent shifting to lower energy (relative to the solid) in donor solvent THF and shifting to higher energy in dichloromethane. The basis for this behavior is discussed. The K _eq for NO binding in 2 was calculated in THF and found to be 470 M^-1. Density functional theory (DFT) studies on 1 indicate donation of electron density to the iron center from the π* orbitals of formally NO^-. Such a donation accounts for the near linearity of the Fe-N-O bond and the large ν(NO) value of 1791 cm^-1.

Ionic liquid promotes N2 coordination to titanocene(iii) monochloride

Coordination of N₂ to [(Cp₂TiCl)₂] in a non-coordinating ionic liquid, Pyr₄FAP, was studied by UV-vis/NIR and EPR spectroscopies. [(Cp₂TiCl)₂] is in equilibrium between monomeric [Cp₂TiCl] and dimeric species [(Cp₂TiCl)₂]. The frozen solution EPR spectrum revealed the coordination of N₂ to [Cp₂TiCl], suggesting that Pyr₄FAP promotes N₂ coordination to the Ti(iii) center.

Alkyl Grignard cross-coupling of aryl phosphates catalyzed by new, highly active ionic iron(ii) complexes containing a phosphine ligand and an imidazolium cation

Ionic iron(ii) complexes, [HL][Fe(PR₃)X₃], showed high catalytic activities in alkyl Grignard cross-coupling of aryl phosphates, and the corresponding reductive cross-coupling.