An observation-based, reduced-form model for oxidation in the remote marine troposphere.

The hydroxyl radical (OH) fuels atmospheric chemical cycling as the main sink for methane and a driver of the formation and loss of many air pollutants, but direct OH observations are sparse. We develop and evaluate an observation-based proxy for short-term, spatial variations in OH (ProxyOH) in the remote marine troposphere using comprehensive measurements from the NASA Atmospheric Tomography (ATom) airborne campaign. ProxyOH is a reduced form of the OH steady-state equation representing the dominant OH production and loss pathways in the remote marine troposphere, according to box model simulations of OH constrained with ATom observations. ProxyOH comprises only eight variables that are generally observed by routine ground- or satellite-based instruments. ProxyOH scales linearly with in situ [OH] spatial variations along the ATom flight tracks (median r2 = 0.90, interquartile range = 0.80 to 0.94 across 2-km altitude by 20° latitudinal regions). We deconstruct spatial variations in ProxyOH as a first-order approximation of the sensitivity of OH variations to individual terms. Two terms modulate within-region ProxyOH variations-water vapor (H2O) and, to a lesser extent, nitric oxide (NO). This implies that a limited set of observations could offer an avenue for observation-based mapping of OH spatial variations over much of the remote marine troposphere. Both H2O and NO are expected to change with climate, while NO also varies strongly with human activities. We also illustrate the utility of ProxyOH as a process-based approach for evaluating intermodel differences in remote marine tropospheric OH.

Extreme hydroxyl amounts generated by thunderstorm-induced corona on grounded metal objects.

Atmospheric electrical discharges are now known to generate unexpectedly large amounts of the atmosphere's primary oxidant, hydroxyl (OH), in thunderstorm anvils, where electrical discharges are caused by atmospheric charge separation. The question is "Do other electrical discharges also generate large amounts of oxidants?" In this paper, we demonstrate that corona formed on grounded metal objects under thunderstorms produce extreme amounts of OH, hydroperoxyl (HO2), and ozone (O3). Hundreds of parts per trillion to parts per billion of OH and HO2 were measured during seven thunderstorms that passed over the rooftop site during an air quality study in Houston, TX in summer 2006. A combination of analysis of these field results and laboratory experiments shows that these extreme oxidant amounts were generated by corona on the inlet of the OH-measuring instrument and that corona are easier to generate on lightning rods than on the inlet. In the laboratory, increasing the electric field increased OH, HO2, and O3, with 14 times more O3 generated than OH and HO2, which were equal. Calculations show that corona on lightning rods can annually generate OH that is 10-100 times ambient amounts within centimeters of the lightning rod and on high-voltage electrical power lines can generate OH that is 500 times ambient a meter away from the corona. Contrary to current thinking, previously unrecognized corona-generated OH, not corona-generated UV radiation, mostly likely initiates premature degradation of high-voltage polymer insulators.

Global airborne sampling reveals a previously unobserved dimethyl sulfide oxidation mechanism in the marine atmosphere.

Dimethyl sulfide (DMS), emitted from the oceans, is the most abundant biological source of sulfur to the marine atmosphere. Atmospheric DMS is oxidized to condensable products that form secondary aerosols that affect Earth's radiative balance by scattering solar radiation and serving as cloud condensation nuclei. We report the atmospheric discovery of a previously unquantified DMS oxidation product, hydroperoxymethyl thioformate (HPMTF, HOOCH2SCHO), identified through global-scale airborne observations that demonstrate it to be a major reservoir of marine sulfur. Observationally constrained model results show that more than 30% of oceanic DMS emitted to the atmosphere forms HPMTF. Coincident particle measurements suggest a strong link between HPMTF concentration and new particle formation and growth. Analyses of these observations show that HPMTF chemistry must be included in atmospheric models to improve representation of key linkages between the biogeochemistry of the ocean, marine aerosol formation and growth, and their combined effects on climate.

Constraints on Aerosol Nitrate Photolysis as a Potential Source of HONO and NO x.

The concentration of nitrogen oxides (NO x) plays a central role in controlling air quality. On a global scale, the primary sink of NO x is oxidation to form HNO3. Gas-phase HNO3 photolyses slowly with a lifetime in the troposphere of 10 days or more. However, several recent studies examining HONO chemistry have proposed that particle-phase HNO3 undergoes photolysis 10-300 times more rapidly than gas-phase HNO3. We present here constraints on the rate of particle-phase HNO3 photolysis based on observations of NO x and HNO3 collected over the Yellow Sea during the KORUS-AQ study in summer 2016. The fastest proposed photolysis rates are inconsistent with the observed NO x to HNO3 ratios. Negligible to moderate enhancements of the HNO3 photolysis rate in particles, 1-30 times faster than in the gas phase, are most consistent with the observations. Small or moderate enhancement of particle-phase HNO3 photolysis would not significantly affect the HNO3 budget but could help explain observations of HONO and NO x in highly aged air.

Highly functionalized organic nitrates in the southeast United States: Contribution to secondary organic aerosol and reactive nitrogen budgets.

Speciated particle-phase organic nitrates (pONs) were quantified using online chemical ionization MS during June and July of 2013 in rural Alabama as part of the Southern Oxidant and Aerosol Study. A large fraction of pONs is highly functionalized, possessing between six and eight oxygen atoms within each carbon number group, and is not the common first generation alkyl nitrates previously reported. Using calibrations for isoprene hydroxynitrates and the measured molecular compositions, we estimate that pONs account for 3% and 8% of total submicrometer organic aerosol mass, on average, during the day and night, respectively. Each of the isoprene- and monoterpenes-derived groups exhibited a strong diel trend consistent with the emission patterns of likely biogenic hydrocarbon precursors. An observationally constrained diel box model can replicate the observed pON assuming that pONs (i) are produced in the gas phase and rapidly establish gas-particle equilibrium and (ii) have a short particle-phase lifetime (∼2-4 h). Such dynamic behavior has significant implications for the production and phase partitioning of pONs, organic aerosol mass, and reactive nitrogen speciation in a forested environment.

Formation of Low Volatility Organic Compounds and Secondary Organic Aerosol from Isoprene Hydroxyhydroperoxide Low-NO Oxidation.

Gas-phase low volatility organic compounds (LVOC), produced from oxidation of isoprene 4-hydroxy-3-hydroperoxide (4,3-ISOPOOH) under low-NO conditions, were observed during the FIXCIT chamber study. Decreases in LVOC directly correspond to appearance and growth in secondary organic aerosol (SOA) of consistent elemental composition, indicating that LVOC condense (at OA below 1 µg m(-3)). This represents the first simultaneous measurement of condensing low volatility species from isoprene oxidation in both the gas and particle phases. The SOA formation in this study is separate from previously described isoprene epoxydiol (IEPOX) uptake. Assigning all condensing LVOC signals to 4,3-ISOPOOH oxidation in the chamber study implies a wall-loss corrected non-IEPOX SOA mass yield of ∼4%. By contrast to monoterpene oxidation, in which extremely low volatility VOC (ELVOC) constitute the organic aerosol, in the isoprene system LVOC with saturation concentrations from 10(-2) to 10 µg m(-3) are the main constituents. These LVOC may be important for the growth of nanoparticles in environments with low OA concentrations. LVOC observed in the chamber were also observed in the atmosphere during SOAS-2013 in the Southeastern United States, with the expected diurnal cycle. This previously uncharacterized aerosol formation pathway could account for ∼5.0 Tg yr(-1) of SOA production, or 3.3% of global SOA.

cis-Dichlorido(3,6,9-trithiabicyclo[9.3.1]pentadecane-κ2S3,S6)palladium(II) acetonitrile 0.8-solvate.

In the title complex, [PdCl2(C12H22S3)]·0.8CH3CN, a potentially tridentate thioether ligand coordinates in a cis-bidentate manner to yield a square-planar environment for the Pd(II) cation [mean deviation of the Pd from the Cl2S2 plane = 0.0406 (7) Å]. Each square-planar entity packs in an inverse face-to-face manner, giving pairs with plane-to-plane separations of 3.6225 (12) Šoff-set by 1.1263 (19) Å, with a Pd···Pd separation of 3.8551 (8) Å. A partial acetonitrile solvent molecule is present. The occupancy of this molecule was allowed to refine, and converged to 0.794 (10). The synthesis of the previously unreported 3,6,9-trithiabicyclo[9.3.1]pentadecane ligand is also outlined.

Selective formation of angular tricyclic compounds by ruthenium-mediated ring-rearrangement metathesis.

Unsaturated spirocyclic substrates bearing two alkenyl chains underwent ruthenium-mediated ring-rearrangement metathesis through relaying cyclohexene and cycloheptene moieties to give angularly fused tricyclics. In some instances where two products were expected, high degrees of selectivity were observed. In one instance the structural parameter leading to selectivity was very subtle; in others the transformation favoured the formation of products with a cis-fused cyclohexene moiety. An unusual transformation involving ring-opening, double-bond migration, and then ring-closing was observed.

Synthesis of 6H-dibenzo[b,d]pyran-6-ones using the inverse electron demand Diels-Alder reaction.

A set of coumarin-fused electron-deficient 1,3-dienes was synthesized, which differ in the nature of the electron-withdrawing group (EWG) at the terminus of the diene unit and (when EWG = CO(2)Me) the nature and position of substituents. These dienes reacted with the enamine derived from cyclopentanone and pyrrolidine to afford the corresponding cyclopenteno-fused 6H-dibenzo[b,d]pyran-6-ones, most likely via a domino inverse electron demand Diels-Alder (IEDDA)/elimination/transfer hydrogenation sequence. The parent diene (EWG = CO(2)Me, no substituents) was reacted with a range of electron-rich dienophiles (mostly enamines) to afford the corresponding 6H-dibenzo[b,d]pyran-6-ones or their nondehydrogenated precursors, which were aromatized upon treatment with a suitable oxidant. The enamines could either be synthesized prior to the reaction or generated in situ. The syntheses of 30 dibenzopyranones are reported.

Intramolecular Povarov reactions involving 3-aminocoumarins.

A series of pentacyclic heterocyclic systems (15 examples, 69-89%) have been synthesized using intramolecular Povarov reactions involving 3-aminocoumarins and O-cinnamylsalicylaldehydes. The Povarov adducts are formed with high selectivity for the trans,trans relative stereochemistry in the newly-formed [6,6] fused ring system. One example of a Povarov adduct featuring a new [6,5] fused ring system is reported. In this case, cis,trans relative stereochemistry was preferred.

Povarov reactions involving 3-aminocoumarins: synthesis of 1,2,3,4-tetrahydropyrido[2,3-c]coumarins and pyrido[2,3-c]coumarins.

Condensation of 3-aminocoumarin (5) with 4-nitrobenzaldehyde (8) afforded a 2-azadiene (9), which reacted with various electron-rich alkenes (10 examples) in the presence of Yb(OTf)3 to afford 1,2,3,4-tetrahydropyrido[2,3-c]coumarins. Yields were generally good, but the diastereomeric ratios were highly variable. The products arose through a formal [4 + 2] cycloaddition (inverse electron demand Diels-Alder reaction) followed by tautomerization. As such, these are examples of the Povarov reaction. A range of 1,2,3,4-tetrahydropyrido[2,3-c]coumarins was then synthesized using a three-component version of this reaction, which involves in situ formation of the 2-azadiene component. Some of these products were converted into the corresponding pyrido[2,3-c]coumarins upon treatment with various oxidants, the most effective of which proved to be nitrous gases.

Coordination "oligomers" in self-assembly reactions of some "tritopic" picolinic dihydrazone ligands-mononuclear, dinuclear, hexanuclear, heptanuclear, and nonanuclear examples.

"Tritopic" picolinic dihydrazone ligands with tridentate coordination pockets are designed to produce homoleptic [3 x 3] nonanuclear square grid complexes on reaction with transition-metal salts, and many structurally documented examples have been obtained with Mn(II), Cu(II), and Zn(II) ions. However, other oligomeric complexes with smaller nuclearities have also been discovered and identified structurally in some reactions involving Fe(II), Co(II), Ni(II), and Cu(II), with certain tritopic ligands. This illustrates the dynamic nature of the metal-ligand interaction and the conformationally flexible nature of the ligands and points to the possible involvement of some of these species as intermediates in the [3 x 3] grid formation process. Examples of mononuclear, dinuclear, hexanuclear, heptanuclear, and nonanuclear species involving Fe(II), Co(II), Ni(II), and Cu(II) salts with a series of potentially heptadentate picolinic dihydrazone ligands with pyrazine, pyrimidine, and pyridine end groups are described in the present study. Iron and cobalt complexation reactions are complicated by redox processes, which lead to mixed-oxidation-state Co(II)/Co(III) systems when starting with Co(II) salts, and reduction of Fe(III) to Fe(II) when starting with Fe(III). Magnetic exchange within the polynuclear structural frameworks is discussed and related to the structural features.

Electron-deficient dienes. 5. An inverse-electron-demand Diels-Alder approach to 2-substituted 4-methoxyxanthones and 3,4-dimethoxyxanthones.

Several 4-methoxyxanthones and 3,4-dimethoxyxanthones were synthesized in good yield via inverse-electron-demand Diels-Alder (IEDDA) driven domino reactions between a series of electron-deficient chromone-fused dienes with 1-(2,2-dimethoxyvinyl)pyrrolidine or tetramethoxyethene, respectively.

Photochemical cycloisomerizations via 7-exo-dig reactions on a calix[4]arene scaffold.

Narrow-rim 1,3-bis(phenylethynyl)-p-tert-butylcalix[4]arenes were found to be photolabile, producing unprecedented seven-membered oxacyclic systems formed via 7-exo-dig cyclizations and a new [3.2.1]bicyclic system via subsequent 1,8-H shifts. The calixarene provided a scaffold for these unprecedented photochemical reactions to occur.

Supramolecular 'flat' Mn9 grid complexes--towards functional molecular platforms.

Flat, quantum dot like arrays of closely spaced, electron rich metal centres are seen as attractive subunits for device capability at the molecular level. Mn(II)9 grids, formed by self-assembly processes using 'tritopic' pyridine-2,6-dihydrazone ligands, provide easy and pre-programmable routes to such systems, and have been shown to exhibit a number of potentially useful physical properties, which could be utilized to generate bi-stable molecular based states. Their ability to form surface monolayers, which can be mapped by STM techniques, bodes well for their possible integration into nanometer scale electronic components of the future. This report highlights some new Mn(II)9 grids, with functionalized ligand sites, that may provide suitable anchor points to surfaces and also be potential donor sites capable of further grid elaboration. Structures, magnetic properties, electrochemical properties, surface studies on HOPG (highly ordered pyrolytic graphite), including the imaging of individual metal ion sites in the grid using CITS (current imaging tunneling spectroscopy) are discussed, in addition to an analysis of the photophysics of a stable mixed oxidation state [Mn(III)4Mn(II)5] grid. The grid physical properties as a whole are assessed in the light of reasonable approaches to the use of such molecules as nanometer scale devices.

An octanuclear [Co(II)2-Co(III)2]2 interlocked grid--example of an inorganic [2]catenane.

An oxalic dihydrazide based flexible polydentate amidrazone ligand undergoes spontaneous [2 x 2] grid assembly, followed by partial disassembly, and then reassembly in the presence of Co(NO3)2.6H2O and NH4(NCS) to form a unique octanuclear [Co(II)2-Co(III)2]2 interlocked, single braided 4 + 4 [2]catenane.

Narrow-rim functionalization of calix[4]arenes via Sonogashira coupling reactions.

The narrow (or "lower")-rim hydroxyl groups of calixarenes are known to be resistant to substitution/displacement. The Sonogashira coupling reaction with TMSA and phenylacetylene, however, has now been extended to the bistriflate of p-tert-butylcalix[4]arene, previously known to be resistant to Stille, Neigishi, or Suzuki-Miyaura reactions. Under some of the reaction conditions investigated, the previously unknown narrow-rim mono- and diiodo-p-tert-butylcalix[4]arene products were also produced, in addition to the narrow-rim mono- and dialkynyl products. Homocoupling of the narrow-rim monoethynyl-p-tert-butyl-calix[4]arene produced a new narrow-rim rigid butadiyne-linked bis-p-tert-butylcalix[4]arene.

Synthesis and complexation properties of "zorbarene": a new naphthalene ring-based molecular receptor.

[picture: see text] The syntheses of the first 2,3-dialkoxy-substituted naphthalene ring-based macrocycles which have calixarene-like structures are reported. The complexation properties of these octahomotetraoxaisocalix[4]naphthalenes were investigated. These new members of the calixnaphthalene family did not demonstrate any appreciable complexation with C(60) or C(70) under the conditions studied, but did so with the tetramethylammonium cation, showing relatively strong association constants suggesting among other considerations that stronger cation-pi interactions versus pi-pi interactions are operative with these hosts. An X-ray crystal structure of the octa-O-ethoxy derivative revealed a structure having a "flattened partial-cone" conformation in which two acetonitrile guest molecules are trapped.

Self-assembly by ligand disassembly?--Formation of an unusual dodecanuclear [Co(II)6Co(III)6] cluster.

A sterically encumbered 'tritopic' picolinic-dihydrazone ligand reacts with cobalt(ii) nitrate in air to give a dodecanuclear [Co(ii)(6)Co(iii)(6)] cluster, in which six ligands are hydrolyzed to mono-carboxylate analogues.

Self-assembled polynuclear clusters derived from some flexible polydentate dihydrazide ligands.

Polynuclear manganese(II), cobalt(II)/(III), iron(II)/(III) and nickel(II) complexes of a group of flexible polydentate dihydrazone ligands, based on pyridine-2,6-dipicolinic (A), oxalic (B) and malonic (C) subunits are described. Structural details are reported for the linear dinuclear complexes [Ni2(2poap)2(H2O)2](NO3)4 . 2CH3OH . 2.5H2O (1), [Mn2(pttp)(NO3)2(CH3OH)2(H2O)2](NO3)2 . H2O (2) and [Mn2(mapttp)2(NO3)2(H2O)2](NO3)2 . 10H2O (3), a square tetranuclear complex [Co4(pttp)4]Br6 . 9H2O (4), a tetranuclear tetrahedral complex [Ni4(pttp)6](BF4)6F2 . 14H2O (7), and a mixed spin state tetranuclear Ni(II) complex [(2pyoap)2Ni4(CH3OH)4] . 1.5CH3OH (10), with a diamond-like arrangement of metal ions. The paramagnetic metal centers are well separated in each case, leading to weak antiferromagnetic coupling or non-existent spin exchange.