Secondary organic aerosol formation from limonene ozonolysis: homogeneous and heterogeneous influences as a function of NO(x)

Limonene has a high emission rate both from biogenic sources and from household solvents. Here we examine the limonene + ozone reaction as a source for secondary organic aerosol (SOA). Our data show that limonene has very high potential to form SOA and that NO(x) levels, O(3) levels, and UV radiation all influence SOA formation. High SOA formation is observed under conditions where both double bonds in limonene are oxidized, but those conditions depend strongly on NO(x). At low NO(x), heterogeneous oxidation of the terminal double bond follows the initial limonene ozonolysis (at the endocyclic double bond) almost immediately, making the initial reaction rate limiting. This requires a high uptake coefficient between ozone and the first-generation, unsaturated organic particles. However, at high NO(x), this heterogeneous processing is inhibited and gas-phase oxidation of the terminal double bond dominates. Although this chemistry is slower, it also yields products with low volatility. UV light suppresses production of the lowest volatility products, as we have shown in earlier studies of the alpha-pinene + ozone reaction.     

Mechanisms of Cysteine-Lysine Covalent Linkage—The Role of Reactive Oxygen Species and Competition with Disulfide Bonds**

Recently, a new naturally occurring covalent linkage was characterised, involving a cysteine and a lysine, bridged through an oxygen atom. The latter was dubbed as the NOS bond, reflecting the individual atoms involved in this uncommon bond which finds little parallel in lab chemistry. It is found to form under oxidising conditions and is reversible upon addition of reducing agents. Further studies have identified the bond in crystal structures across a variety of systems and organisms, potentially playing an important role in regulation, cellular defense and replication. Not only that, double NOS bonds have been identified and even found to be competitive in relation to the formation of disulfide bonds. This raises several questions about how this exotic bond comes to be, what are the intermediates involved in its formation and how it competes with other pathways of sulfide oxidation. With this objective in mind, we revisited our first proposed mechanism for the reaction with model electronic structure calculations, adding information about the reactivity with alternative reactive oxygen species and other potential competing products of oxidation. We present a network with more than 30 reactions which provides one of the most encompassing pictures for cysteine oxidation pathways to date.     

Oxidation of oleic acid and oleic acid/sodium chloride(aq) mixture droplets with ozone: changes of hygroscopicity and role of secondary reactions

The heterogeneous reactions of oleic acid (OL) and oleic-acid/sodium-chloride(aq) (OL/NaCl(aq)) mixture droplets with ozone are studied at two relative humidities (RH). The reactions were monitored concomitantly using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FT-IR) for the organic species and UV-vis spectrometry for the ozone concentration in order to investigate reaction rate discrepancies reported in literature as well as the oxidation mechanism. The less volatile products were identified and resolved by a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR-MS). This led to identification of 13 organic molecules (up to 45 carbons). Identified products were predominantly composed by nananoic acid and azelaic acid. Our results suggest that the propagation reaction is possibly initiated by a secondary reaction such as the stabilized Criegee intermediates reacting with oleic acid. For hygroscopic properties, the ATR-IR spectra at high RH (87 +/- 5%) showed that the hydrophobic oleic acid droplets can take up water slightly when exposed to ozone. For internally mixed OL/NaCl(aq) droplets, the hygroscopic properties of the droplets upon ozone exposure were found to be complex; hygroscopic properties or the growth factors of the droplets are altered as the oxidation products of oleic acid exist concurrently with NaCl(aq). Furthermore, the concentration of ozone was monitored to examine the kinetics of the oxidation reaction. The integrated ozone profile recorded by UV-vis spectrometry showed the consumed ozone represents only 30 +/- 2% of total oleic acid and hence confirmed the existence of secondary reactions. A kinetic model was used to simulate an ozone temporal profile that could only be described if the secondary reactions were included. The discrepancy of ozone uptake coefficients according to the OL and ozone measurements as well as their atmospheric implications are herein discussed.     

Dry synthesis of triple cumulative double bonds (C=C=C=N) on Si(111)-7 x 7 surfaces

The interactions of cyanoacetylene and diacetylene with a Si(111)-7 x 7 surface have been studied as model systems to mechanistically understand the chemical binding of unsaturated organic molecules to diradical-like silicon dangling bonds. Vibrational studies show that cyanoacetylene mainly binds to the surface through a diradical reaction involving both cyano and C[triple bond]C groups with an adjacent adatom-rest atom pair at 110 K, resulting in an intermediate containing triple cumulative double bonds (C=C=C=N). On the other hand, diacetylene was shown to the covalently attached to Si(111)-7 x 7 only through one of its C[triple bond]C groups, forming an enynic-like structure with a C=C-C[triple bond]C skeleton. These chemisorbed species containing triple cumulative double bonds (C=C=C=N) and C=C-C[triple bond]C may be employed as precursors (or templates) for further construction of bilayer organic films on the semiconductor surfaces.     

Adsorption of unsaturated hydrocarbon moieties on H:Si(111) by Grignard reaction

Grafting of unsaturated hydrocarbon moieties (-CH(2)-CH=CH(2), -CH=CH(2), -CH(2)-CH=CH-CH(3), and -CCH) by a C-Si covalent bond was attempted by the Grignard reaction on hydrogen-terminated Si(111) in tetrahydrofuran solutions. The product adsorbates were monitored by vibrational methods of high-resolution electron energy loss spectroscopy and multiple internal infrared reflection absorption spectroscopy, as well as Auger electron spectroscopy. The temperature and the period of reaction were adjusted so as to preserve the unsaturated carbon-carbon bonds. The -CH(2)-CH=CH(2) group was introduced by a mild reaction condition, with the reservation of the C=C double bond confirmed. The unsaturated bonds in -CH(2)-CH=CH-CH(3) and -CCH were also reserved. Only in the case of -CH=CH(2) was the reservation of the C=C double bond not realized. Unsaturated hydrocarbon moieties are applicable for further organic modification to introduce functional groups, and are prospective materials in nanofabrication and biological application on silicon wafer surfaces.     

Heterogeneous uptake of ozone on reactive components of mineral dust aerosol: an environmental aerosol reaction chamber study

We have undertaken a kinetic study of heterogeneous ozone decomposition on alpha-Fe2O3 (hematite) and alpha-Al2O3 (corundum) aerosols under ambient conditions of temperature, pressure, and relative humidity in order to better understand the role of mineral dust aerosol in ozone loss mechanisms in the atmosphere. The kinetic measurements are made in an environmental aerosol reaction chamber by use of infrared and ultraviolet spectroscopic probes. The apparent heterogeneous uptake coefficient, gamma, for ozone reaction with alpha-Fe2O3 and alpha-Al2O3 surfaces is determined as a function of relative humidity (RH). The uptake of ozone by the iron oxide surface is approximately an order of magnitude larger than that by the aluminum oxide sample, under dry conditions. At the pressures used, alpha-Fe2O3 shows clear evidence for catalytic decomposition of ozone while alpha-Al2O3 appears to saturate at a finite ozone coverage. The measured uptake for both minerals decreases markedly as the RH is increased. Comparison with other literature reports and the atmospheric implications of these results are discussed.     

Assembly of the Entire Carbon Backbone of a Stereoisomer of the Antitumor Marine Natural Product Hemicalide

A strategy for the assembly of the entire carbon backbone of a stereoisomer of the antitumor marine natural product hemicalide has been investigated. The devised convergent approach relies on Horner–Wadsworth–Emmons and Julia–Kocienski olefination reactions for the construction of the C6=C7 and C34=C35 double bonds, respectively, an aldol reaction to create the C27−C28 bond, and a Suzuki–Miyaura cross-coupling as the endgame to form the C15−C16 bond.     

Intermolecular amidation of unactivated sp2 and sp2 C-H bonds via palladium-catalyzed cascade C-H activation/nitrene insertion

This communication describes the Pd(OAc)2-catalyzed intermolecular amidation reactions of unactivated sp2 and sp3 C-H bonds using primary amides and potassium persulfate. The substrates containing a pendent oxime or pyridine group were amidated with excellent chemo- and regioselectivities. It is noteworthy that reactive C-X bonds were well-tolerated and a variety of primary amides can be effective nucleophiles for the Pd-catalyzed C-H amidation reactions. For the reaction of unactivated sp3 C-H bonds, beta-amidation of 1 degrees sp3 C-H bonds versus 2 degrees C-H bonds is preferred. The catalytic reaction is initiated by chelation-assisted cyclopalladation involving C-H bond activation. Preliminary mechanistic study suggested that the persulfate oxidation of primary amides should generate reactive nitrene species, which then reacted with the cyclopalladated complex.     

C_(70)与臭氧反应机理的理论研究

用半经验AM1方法研究了C_(70)与臭氧环加成反应的反应机理。采用Berny梯度 法优化得到反应的过滤度，并进行了振动分析确诊。计算结果表明：臭氧在C_(70) 6－6单、双键上的环加成反应均为复杂反应，由三步组成：第一步是O_3分子与C_ (70)的6-6单、双键发生1,3-偶极环加成反应，生成分子臭氧化物（即中间体I）， 6－6双键加成为放热反应，6－6单键加成为吸热反应，活化势垒分别为84.7和181. 2 kJ·mol~(-1)；第二步是中间体I的加成，C－C键断裂，生成两性离子中间体II 的放热反应，其势垒分别为61.3和13.3 kJ·mol~(-1)；第三步是中间体II脱去一 个Q_2分子生成具有环氧结构的C_(70)O，均为放热反应，活化势垒分别为169.3和 101.2 kJ·mol~(-1)；第三步是中间体I脱去一个O_2分子生成具有环氧结构的C_ (70)O，均为放热反应，活化势垒分别为169.3和101.2 kJ·mol~(-1)，从反应机理 和动力学角度解释了6－6双键加成优于6-6双键加成优于6-6双键加成优于6-6单键 加成的原因。O_3分子与C_(70)6-6双键的加成反应是协同且同步进行的，与6－6单 键的加成反应是协同但不同步的过程。     

Mechanism of the addition of nonenolizable aldehydes and ketones to (Di)metallenes (R(2)X=YR(2), X = Si,Ge Y = C,Si, Ge): a density functional and multiconfigurational perturbation theory study

The mechanism of the addition of nonenolizable aldehydes and ketones to group 14 (di)metallenes has been examined through a theoretical study of the addition of formaldehyde to Si=C, Ge=C, Si=Si, Si=Ge, and Ge=Ge bonds at the B3LYP/6-311++G(d,p) and CAS-MCQDPT2/6-31++G(d,p) levels of theory. The reaction pathways located can be grouped as either involving the formation of singlet diradical or zwitterionic intermediates or as concerted processes. Within each group of reaction pathways, several different mechanisms have been located, with not all mechanisms being available to all of the (di)metallenes. It was found that for reactions in which a Si-O bond results (i.e., addition to Si=C, Si=Si, and Si=Ge) both diradical and zwitterionic intermediates are possible; however, the formation of diradical intermediates was not found for reactions that result in the formation of a Ge-O bond (addition to Ge=C and Ge=Ge). The underlying cause of this pathway selectivity is examined, as well as the effect of solvent on the relative energies of the pathways. The results of the study shed light on the cause of experimentally obtained results regarding the mechanism of the reaction of (di)metallenes with nonenolizable ketones and aldehydes.     

Factors influencing the reductive cleavage of C-x multiple bonds in their reactions with meal-meal multiple bonds (X = C, N, O, S)

Though metal-metal multiple bonds of the transition elements are redox active, their reactivity towards C-X multiple bonds (X = C, N, O, S) vary greatly depending principally on: 1. The coordination geometry of the metal. 2. The oxidation state of the metal and the electronic configuration of the M-M bond. 3. The nature of the attendant ligands. Specific examples of C-X multiple bond activation at dimolybdenum and ditungsten centers are presented that illustrate the importance of these factors. Evidence is presented to support the view that reductive cleavage of a C-X multiple bond can be considered to be equivalent to an intramolecular redox reaction within a [M2CX] "cluster complex," for which the frontier orbital energies of the C-X and M-M multiple bonds are of paramount importance. Some applications of these C-X reductive cleavage reactions toward organic synthesis are described.     

Effect of contact surfaces on the thermal and photooxidation of dehydrated castor oil

The effect of stainless steel, glass, zirconium and titanium enamel surfaces on the thermal and photooxidative toughening mechanism of dehydrated castor oil films deposited on these surfaces was investigated using different analytical and spectroscopic methods. The conjugated and non-conjugated double bonds were identified and quantified using both Raman spectroscopy and 1D and 2D NMR spectroscopy. The disappearance of the double bonds in thermally oxidised oil-on-surface films was shown to be concomitant with the formation of hydroperoxides (determined by iodometric titration). The type of the surface had a major effect on the rate of thermal oxidation of the oil, but all of the surfaces examined had resulted in a significantly higher rate of oxidation compared to that of the neat oil. The highest effect was exhibited by the stainless steel surface followed by zirconium enamel, titanium enamel and glass. The rate of thermal oxidation of the oil-on-steel surface (at 100 °C, based on peroxide values) was more than five times faster than that of oil-on-glass and more than 21 times faster than the neat oil when compared under similar thermal oxidative conditions. The rate of photooxidation at 60 °C of oil-on-steel films was found to be about one and half times faster than their rate of thermal oxidation at the same temperature. Results from absorbance reflectance infrared microscopy with line scans taken across the depth of thermally oxidised oil-on-steel films suggest that the thermal oxidative toughening mechanism of the oil occurs by two different reaction pathways with the film outermost layers, i.e. furthest away from the steel surface, oxidising through a traditional free radical oxidation process involving the formation of various oxygenated products formed from the decomposition of allylic hydroperoxides, whereas, in the deeper layers closer to the steel surface, crosslinking reactions predominate.     

NR transfer reactivity of azo-compound I of P450. How does the nitrogen substituent tune the reactivity of the species toward C-H and C=C activation?

We studied electronic structures and reactivity patterns of azo-compound I species (RN-Cpd I) by comparison to O-Cpd I of, e.g., cytochrome P450. The study shows that the RN-Cpd I species are capable of C=C aziridination and C-H amidation, in a two-state mechanism similar to that of O-Cpd I. However, unlike O-Cpd I, here the nitrogen substituent (R) exerts a major impact on structure and reactivity. Thus, it is demonstrated that Fe=NR bonds of RN-Cpd I will generally be substantially longer than Fe=O bonds; electron-withdrawing R groups will generate a very long Fe=N bond, whereas electron-releasing R groups should have the opposite effect and hence a shorter Fe=N bond. The R substituent controls also the reactivity of RN-Cpd I toward C=C and C-H bonds by exerting steric and electronic effects. Our analysis shows that an electron-releasing substituent will lower the barriers for both bond activation reactions, since the electronic factor makes the reactions highly exothermic, while an electron-withdrawing one should raise both barriers. The steric bulk of the substituent is predicted to inhibit more strongly the aziridination reactions. It is predicted that electron-releasing substituents with small bulk will create powerful aziridination reagents, whereas electron-withdrawing substituents like MeSO(2) will prefer C-H bond activation with preference that increases with steric bulk. Finally, the study predicts (i) that the reactions of RN-Cpd I will be less stereospecific than those of O-Cpd I and (ii) that aziridination will be more stereoselective than amidation.     

Reaction pathways of Sc+ (3D, 1D) and Fe+ (6D, 4F) with acetone in the gas phase: metal ion oxidation and acetone deethanization

The reactions of Sc⁺ (³D, ¹D) and Fe⁺ (⁶D, ⁴ F) with acetone have been investigated in both high‐ and low‐spin states using density functional theory. Our calculations have indicated that oxidation of Sc⁺ by acetone can take place by (1) metal‐mediated H migration, (2) direct methyl‐H shift and/or (3) C = O insertion. The most energetically favorable pathway is metal‐mediated H migration followed by intramolecular ScO⁺ rotation and dissociation. For the deethanization of acetone mediated by Fe⁺, the reaction occurs on either the quartet or sextet surfaces through five elementary steps, i.e. encounter complexation, C–C bond activation, methyl migration, C–C coupling and non‐reactive dissociation. The rate‐determining step along the quartet‐state potential‐energy surface (PES) is similar to that in the case of Ni⁺ (² F, 3d⁹), namely the methyl‐migration step. For the sextet‐state PES, however, the energy barrier for methyl migration is lower than that for C–C bond activation, and the rate‐determining step is C–C coupling. In general, the low‐spin‐state pathways are lower in energy than the high‐spin‐state pathways; therefore, the reaction pathways for the oxidation of Sc⁺ and the Fe⁺‐mediated deethanization of acetone mostly involve the low‐spin states. Copyright © 2012 John Wiley & Sons, Ltd.     

Contributions of organic electrosynthesis to green chemistry

In organic electrosynthesis C–C bond formation and functional group interconversion proceed via reactive intermediates that are generated by electron transfer at the anode and cathode. Electron transfer combined with a chemical reaction provides conversions that are not available in non-electrochemical reactions. These are potential selectivity, redox-umpolung, and the substitution of a hydrogen atom for a nucleophile or the addition of two nucleophiles to a double bond in one-pot reactions. Furthermore electrolysis is well suited for oxidation and reduction of functional groups. Electrochemical syntheses need mostly fewer steps, produce less waste, provide a cheaper reagent, require less auxiliaries and allow often an easier scale-up than non-electrochemical syntheses. In addition, they can be conducted at ambient temperature and pressure. All these qualities agree well with the rules of green chemistry. This statement is substantiated with examples of C–C bond formation and functional group interconversion at the anode and cathode.     

Dibora[2]ferrocenophane: A Carbene-Stabilized Diborene in a Strained cis-Configuration

Unsaturated bridges that link the two cyclopentadienyl ligands together in strained ansa metallocenes are rare and limited to carbon–carbon double bonds. The synthesis and isolation of a strained ferrocenophane containing an unsaturated two-boron bridge, isoelectronic with a C=C double bond, was achieved by reduction of a carbene-stabilized 1,1′-bis(dihaloboryl)ferrocene. A combination of spectroscopic and electrochemical measurements as well as density functional theory (DFT) calculations was used to assess the influence of the unprecedented strained cis configuration on the optical and electrochemical properties of the carbene-stabilized diborene unit. Initial reactivity studies show that the dibora[2]ferrocenophane is prone to boron–boron double bond cleavage reactions.     

Acetone oxidation using ozone on manganese oxide catalysts

Supported manganese oxide catalysts were prepared by the impregnation of alumina foam blocks washcoated with alumina and silica. The manganese content based on the weight of the washcoats was 10 wt % calculated as MnO2. Fourier transform profiles of the Mn K-edge EXAFS spectra for these samples gave three distinctive peaks at 0.15, 0.25, and 0.32 nm and were close to the profiles of Mn3O4 and beta-MnO2. The number of surface active sites was determined through oxygen chemisorption measurements at a reduction temperature (Tred = 443 K) obtained from temperature-programmed reduction (TPR) experiments. Acetone catalytic oxidation was studied from room temperature to 573 K, and was found to be highly accelerated by the use of ozone on both catalysts with substantial reductions in the reaction temperature. The only carbon-containing product detected was CO2. The alumina-supported catalyst was found to be more active than the silica-supported catalyst in acetone and ozone conversion, with higher turnover frequencies (TOFs) for both reactions. The pressure drop through the foam was low and increased little (0.003 kPa/10 000 h(-1)) with space velocity. In situ steady-state Raman spectroscopy measurements during the acetone catalytic oxidation reaction showed the presence of an adsorbed acetone species with a C-H bond at 2930 cm(-1) and a peroxide species derived from ozone with an O-O bond at 890 cm(-1).     

Probes of spin conservation in heavy metal reactions: experimental and theoretical studies of the reactions of Re+ with H2, D2, and HD

A guided ion beam tandem mass spectrometer is used to examine the kinetic energy dependence of reactions of the third-row transition metal cation, Re(+), with molecular hydrogen and its isotopologues. A flow tube ion source produces Re(+) in its (7)S(3) electronic ground state. Reaction with H(2), D(2), and HD forms Re H(+)(Re D(+)) in endothermic processes. Modeling of the endothermic reaction cross sections yields the 0 K bond dissociation energy of D(0)(Re(+)-H)=2.29+/-0.07 eV (221+/-6 kJ/mol). The experimental thermochemistry is consistent with ab initio calculations, performed here and in the literature. Theory also provides the electronic structures of these species and is used to examine the reactive potential energy surfaces. Results from reactions with HD provide insight into the reaction mechanisms and indicate that the late metal ion, Re(+), reacts largely via a statistical mechanism. This is consistent with the potential energy surfaces which locate a stable Re H(2) (+)((5)B(2)) complex. Results for this third-row transition metal system are compared with the first-row congener (Mn(+)) and found to have much higher reactivity towards dihydrogen and stronger M(+)-H bonds. These differences can be attributed to efficient coupling among surfaces of different spin along with lanthanide contraction and relativistic effects.     

Measurements of ambient ozone using indigo blue-coated filters

Ozone monitoring techniques utilize expensive instruments that are often large and heavy. These instruments are not easy to handle in the field, and their size also limits some sampling schemes, principally for indoor ozone determination. We have developed a lightweight, inexpensive, and sensitive method that offers flexibility to undertake measurements of ambient ozone in many environments, both indoor and outdoor. The method is based on the reaction of ozone with indigo blue dye. The indigo molecule contains 1 carbon double bond (C = C) that reacts with ozone and results in nearly colorless reaction products. During sample collection, 2 cellulose filters coated with 40 micro of 1.0 x 10(-3) M indigo blue were used. The determinations were done spectrophotometrically at 250 and 600 nm. The analytical parameters studied were sampling time and flow rate. Analytical curves were constructed with concentrations ranging from 37 to 123 parts per billion by volume (ppbv) of standard ozone, at 0.4 L/min and 15 min sampling time. The detection limits achieved were 6 and 9 ppbv, respectively, at 250 and 600 nm. Considering interferences, measurements made at 250 nm gave more reliable and specific values for ozone.     

Formation of a C–C double bond from two aliphatic carbons. Multiple C–H activations in an iridium pincer complex

The search for novel, atom-economic methods for the formation of C–C bonds is of crucial importance in synthetic chemistry. Especially attractive are reactions where C–C bonds are formed through C–H activation, but the coupling of unactivated, alkane-type C_sp³–H bonds remains an unsolved challenge. Here, we report iridium-mediated intramolecular coupling reactions involving up to four unactivated C_sp³–H bonds to give carbon–carbon double bonds under the extrusion of dihydrogen. The reaction described herein is completely reversible and the direction can be controlled by altering the reaction conditions. With a hydrogen acceptor present a C–C double bond is formed, while reacting under dihydrogen pressure leads to the reverse process, with some of the steps representing net C_sp³–C_sp³ bond cleavage. Mechanistic investigations revealed a conceptually-novel overall reactivity pattern where insertion or deinsertion of an Ir carbene moiety, formed via double C–H activation, into an Ir–C bond is responsible for the key C–C bond formation and cleavage steps.