硝酰氯的大气化学

硝酰氯(nitryl chloride,ClNO₂)是大气中一种重要的气态污染物,对大气氧化性、一次污染物的降解和二次污染物的生成具有重要影响,并在全球氮循环和氯循环中扮演着不可忽视的角色。本文归纳了ClNO₂的基本物理化学性质及其在大气中的生成和去除机制,并介绍了实验室研究和外场观测中ClNO₂的主要测量方法。在此基础上,本文总结了过去十几年报道的ClNO₂在实际大气中的时空分布特征,通过分析实验室模拟和外场观测的研究结果系统讨论了ClNO₂非均相生成的机制、产率及其影响因素,探讨了ClNO₂对氯自由基、大气氧化性以及臭氧和硝酸盐形成的影响。我们指出,ClNO₂既耦合了气相化学和非均相化学,又耦合了夜间大气化学和日间光化学,在我国大气复合污染中可能起着非常重要的作用。最后,本文提出了ClNO₂大气化学研究中尚待解决的关键科学问题,并简要讨论了该领域的未来发展方向。     

Atmospheric aerosols: composition, transformation, climate and health effects

Aerosols are of central importance for atmospheric chemistry and physics, the biosphere, climate, and public health. The airborne solid and liquid particles in the nanometer to micrometer size range influence the energy balance of the Earth, the hydrological cycle, atmospheric circulation, and the abundance of greenhouse and reactive trace gases. Moreover, they play important roles in the reproduction of biological organisms and can cause or enhance diseases. The primary parameters that determine the environmental and health effects of aerosol particles are their concentration, size, structure, and chemical composition. These parameters, however, are spatially and temporally highly variable. The quantification and identification of biological particles and carbonaceous components of fine particulate matter in the air (organic compounds and black or elemental carbon, respectively) represent demanding analytical challenges. This Review outlines the current state of knowledge, major open questions, and research perspectives on the properties and interactions of atmospheric aerosols and their effects on climate and human health.     

Competing C-4 and C-5-Acyl Stabilization of Uronic Acid Glycosyl Cations

Uronic acids are carbohydrates carrying a terminal carboxylic acid and have a unique reactivity in stereoselective glycosylation reactions. Herein, the competing intramolecular stabilization of uronic acid cations by the C-5 carboxylic acid or the C-4 acetyl group was studied with infrared ion spectroscopy (IRIS). IRIS reveals that a mixture of bridged ions is formed, in which the mixture is driven towards the C-1,C-5 dioxolanium ion when the C-5,C-2-relationship is cis, and towards the formation of the C-1,C-4 dioxepanium ion when this relation is trans. Isomer-population analysis and interconversion barrier computations show that the two bridged structures are not in dynamic equilibrium and that their ratio parallels the density functional theory computed stability of the structures. These studies reveal how the intrinsic interplay of the different functional groups influences the formation of the different regioisomeric products.     

Adsorbed Intermediates in Oxygen Reduction on Platinum Nanoparticles Observed by In Situ IR Spectroscopy

The sluggish kinetics of oxygen reduction to water remains a significant limitation in the viability of proton‐exchange‐membrane fuel cells, yet details of the four‐electron oxygen reduction reaction remain elusive. Herein, we apply in situ infrared spectroscopy to probe the surface chemistry of a commercial carbon‐supported Pt nanoparticle catalyst during oxygen reduction. The IR spectra show potential‐dependent appearance of adsorbed superoxide and hydroperoxide intermediates on Pt. This strongly supports an associative pathway for oxygen reduction. Analysis of the adsorbates alongside the catalytic current suggests that another pathway must also be in operation, consistent with a parallel dissociative pathway.     

Elucidation of the CO‐Release Kinetics of CORM‐A1 by Means of Vibrational Spectroscopy

CO‐releasing molecules (CORMs) are developed for investigations of the interaction between the signaling molecule carbon monoxide (CO) and cells or tissue. Prior to their application these molecules must be fully characterized with respect to their CO‐release mechanism. One widely used CORM for biological application is sodium boranocarbonate (CORM‐A1), which shows pH‐dependent CO liberation. The complete reaction mechanism of CORM‐A1 is not fully understood yet. Therefore, in this contribution time‐resolved gas‐phase IR spectroscopy is used to monitor the headspace above decaying CORM‐A1 solutions at four different pH values (5.8 to 7.4). Borane carbonyl is found as an intermediate in the gas phase, which is formed during CORM degradation and further decays to CO. Concentration profiles of a pseudoconsecutive first‐order reaction are successfully fitted to specific band areas of the measured gas‐phase spectra, and the rate constants are obtained. The production of borane carbonyl is strongly pH dependent (half‐lives between 5 and 106 min), whereas the decay of borane carbonyl in the gas phase is nearly constant with a half‐life of about 33 min. The ratio of liberated CO molecules per CORM‐A1 is determined to be 0.91±0.09, and boric acid is identified as further end product.     

Thinner,Smaller, Faster: IR Techniques To Probe the Functionality of Biological and Biomimetic Systems

New techniques in vibrational spectroscopy are promising for the study of biological samples as they provide exquisite spatial and/or temporal resolution with the benefit of minimal perturbation of the system during observation. In this Minireview we showcase the power of modern infrared techniques when applied to biological and biomimetic systems. Examples will be presented on how conformational changes in peptides can be traced with femtosecond resolution and nanometer sensitivity by 2D IR spectroscopy, and how surface‐enhanced infrared difference absorption spectroscopy can be used to monitor the effect of the membrane potential on a single proton‐transfer step in an integral membrane protein. Vibrational spectra of monolayers of molecules at basically any interface can be recorded with sum‐frequency generation, which is strictly surface‐sensitive. Chemical images are recorded by applying scanning near‐field infrared microscopy at lateral resolutions better than 50 nm.     

Ab Initio Study on the Mechanism of the Atmospheric Reaction OH+O3→HO2+O2

The atmospheric reaction (1) OH + O₃→HO₂ + O₂ was investigated theoretically by using MP2, QCISD, QCISD(T), and CCSD(T) methods with various basis sets. At the highest level of theory, namely, QCISD, the reaction is direct, with only one transition state between reactants and products. However, at the MP2 level, the reaction proceeds through a two‐step mechanism and shows two transition states, TS1 and TS2 , separated by an intermediate, Int . The different methodologies employed in this paper consistently predict the barrier height of reaction (1) to be within the range 2.16–5.11 kcal mol^?1, somewhat higher than the experimental value of 2.0 kcal mol^?1.     

Interaction of NO2 with Model NSR Catalysts: Metal–Oxide Interaction Controls Initial NOx Storage Mechanism

Using scanning tunneling microscopy (STM), molecular‐beam (MB) methods and time‐resolved infrared reflection absorption spectroscopy (TR‐IRAS), we investigate the mechanism of initial NO_x uptake on a model nitrogen storage and reduction (NSR) catalyst. The model system is prepared by co‐deposition of Pd metal particles and Ba‐containing oxide particles onto an ordered alumina film on NiAl(110). We show that the metal–oxide interaction between the active noble metal particles and the NO_x storage compound in NSR model catalysts plays an important role in the reaction mechanism. We suggest that strong interaction facilitates reverse spillover of activated oxygen species from the NO_x storage compound to the metal. This process leads to partial oxidation of the metal nanoparticles and simultaneous stabilization of the surface nitrite intermediate.     

Discovering the Active Sites for C3 Separation in MIL‐100(Fe) by Using Operando IR Spectroscopy

A reducible MIL‐100(Fe) metal–organic framework (MOF) was investigated for the separation of a propane/propene mixture. An operando methodology was applied (for the first time in the case of a MOF) in order to shed light on the separation mechanism. Breakthrough curves were obtained as in traditional separation column experiments, but monitoring the material surface online, thus providing evidences on the adsorption sites. The qualitative and quantitative analyses of Fe^II and, to some extent, Fe^III sites were possible, upon different activation protocols. Moreover, it was possible to identify the nature and the role of the active sites in the separation process by selective poisoning of one family of sites: it was clearly evidenced that the unsaturated Fe^II sites are mainly responsible for the separation effect of the propane/propene mixture, thanks to their affinity for the unsaturated bonds, such as the C?C entities in propene. The activity of the highly concentrated Fe^III sites was also highlighted.     

An Ab Initio Study on the Mechanism of the Atmospheric Reaction NH2+O3→H2NO+O2

The atmospheric reaction NH₂+O₃→H₂NO+O₂ has been investigated theoretically by using MP2, QCISD, QCISD(T), CCSD(T), CASSCF, and CASPT2 methods with various basis sets. At the MP2 level of theory, the hypersurface of the potential energy (HPES) shows a two step reaction mechanism. Therefore, the mechanism proceeds along two transition states (TS1 and TS2), separated by an intermediate designated as Int. However, when the single‐reference higher correlated QCISD and the multiconfigurational CASSCF methodologies have been employed, the minimum structure Int and TS2 are not found on the HPES, which thus confirms a direct reaction mechanism. Single‐reference high correlated and multiconfigurational methods consistently predict the barrier height of the reaction to be within the range of 3.9 to 6.6 kcal mol^?1, which is somewhat higher than the experimental value. ¹ The calculated reaction enthalpy is ?67.7 kcal mol^?1.     

Lithium Choreography: Intramolecular Arylations of Carbamate‐Stabilised Carbanions and Their Mechanisms Probed by In Situ IR Spectroscopy and DFT Calculations

Deprotonation of O‐allyl, O‐propargyl or O‐benzyl carbamates in the presence of a lithium counterion leads to carbamate‐stabilised organolithium compounds that may be quenched with electrophiles. We now report that when the allylic, propargylic or benzylic carbamate bears an N‐aryl substituent, an aryl migration takes place, leading to stereochemical inversion and C‐arylation of the carbamate α to oxygen. The aryl migration is an intramolecular S_NAr reaction, despite the lack of anion‐stabilising aryl substituents. Our in situ IR studies reveal a number of intermediates along the rearrangement pathway, including a “pre‐lithiation complex,” the deprotonated carbamate, the rearranged anion, and the final arylated carbamate. No evidence was obtained for a dearomatised intermediate during the aryl migration. DFT calculations predict that during the reaction the solvated Li cation moves from the carbanion centre, thus freeing its lone pair for nucleophilic attack on the remote phenyl ring. This charge separation leads to several alternative conformations. The one having Li⁺ bound to the carbamate oxygen gives rise to the lowest‐energy transition structure, and also leads to inversion of the configuration. In agreement with the IR studies, the DFT calculations fail to locate a dearomatised intermediate.     

Base‐Free Non‐Noble‐Metal‐Catalyzed Hydrogen Generation from Formic Acid: Scope and Mechanistic Insights

The iron‐catalyzed dehydrogenation of formic acid has been studied both experimentally and mechanistically. The most active catalysts were generated in situ from cationic Fe^II/Fe^III precursors and tris[2‐(diphenylphosphino)ethyl]phosphine ( 1 , PP₃). In contrast to most known noble‐metal catalysts used for this transformation, no additional base was necessary. The activity of the iron catalyst depended highly on the solvent used, the presence of halide ions, the water content, and the ligand‐to‐metal ratio. The optimal catalytic performance was achieved by using [FeH(PP₃)]BF₄/PP₃ in propylene carbonate in the presence of traces of water. With the exception of fluoride, the presence of halide ions in solution inhibited the catalytic activity. IR, Raman, UV/Vis, and EXAFS/XANES analyses gave detailed insights into the mechanism of hydrogen generation from formic acid at low temperature, supported by DFT calculations. In situ transmission FTIR measurements revealed the formation of an active iron formate species by the band observed at 1543 cm^?1, which could be correlated with the evolution of gas. This active species was deactivated in the presence of chloride ions due to the formation of a chloro species (UV/Vis, Raman, IR, and XAS). In addition, XAS measurements demonstrated the importance of the solvent for the coordination of the PP₃ ligand.