RESUMO
Transport is a key parameter in air quality research and plays a dominant role in the Colorado Northern Front Range Metropolitan Area (NFRMA), where terrain induced flows and recirculation patterns can lead to vigorous mixing of different emission sources. To assess different transport processes and their connection to air quality in the NFRMA during the FRAPPÉ and DISCOVER-AQ campaigns in summer 2014, we use the Weather Research and Forecasting Model with inert tracers. Overall, the model represents well the measured winds and the inert tracers are in good agreement with observations of comparable trace gas concentrations. The model tracers support the analysis of surface wind and ozone measurements and allow for the analysis of transport patterns and interactions of emissions. A main focus of this study is on characterizing pollution transport from the NFRMA to the mountains by mountain-valley flows and the potential for recirculating pollution back into the NFRMA. One such event on 12 August 2014 was well captured by the aircraft and is studied in more detail. The model represents the flow conditions and demonstrates that during upslope events, frequently there is a separation of air masses that are heavily influenced by oil and gas emissions to the North and dominated by urban emissions to the South. This case study provides evidence that NFRMA pollution not only can impact the nearby Foothills and mountain areas to the East of the Continental Divide, but that pollution can "spill over" into the valleys to the West of the Continental Divide.
RESUMO
The Convective Transport of Active Species in the Tropics (CONTRAST) experiment was conducted from Guam (13.5° N, 144.8° E) during January-February 2014. Using the NSF/NCAR Gulfstream V research aircraft, the experiment investigated the photochemical environment over the tropical western Pacific (TWP) warm pool, a region of massive deep convection and the major pathway for air to enter the stratosphere during Northern Hemisphere (NH) winter. The new observations provide a wealth of information for quantifying the influence of convection on the vertical distributions of active species. The airborne in situ measurements up to 15 km altitude fill a significant gap by characterizing the abundance and altitude variation of a wide suite of trace gases. These measurements, together with observations of dynamical and microphysical parameters, provide significant new data for constraining and evaluating global chemistry climate models. Measurements include precursor and product gas species of reactive halogen compounds that impact ozone in the upper troposphere/lower stratosphere. High accuracy, in-situ measurements of ozone obtained during CONTRAST quantify ozone concentration profiles in the UT, where previous observations from balloon-borne ozonesondes were often near or below the limit of detection. CONTRAST was one of the three coordinated experiments to observe the TWP during January-February 2014. Together, CONTRAST, ATTREX and CAST, using complementary capabilities of the three aircraft platforms as well as ground-based instrumentation, provide a comprehensive quantification of the regional distribution and vertical structure of natural and pollutant trace gases in the TWP during NH winter, from the oceanic boundary to the lower stratosphere.
RESUMO
We have developed a chemical ionization mass spectrometry technique for precise in situ measurements of hydrochloric acid (HCl) from a high-altitude aircraft. In measurements at subtropical latitudes, minimum HCl values found in the upper troposphere (UT) were often near or below the detection limit of the measurements (0.005 parts per billion by volume), indicating that background HCl values are much lower than a global mean estimate. However, significant abundances of HCl were observed in many UT air parcels, as a result of stratosphere-to-troposphere transport events. We developed a method for diagnosing the amount of stratospheric ozone in these UT parcels using the compact linear correlation of HCl with ozone found throughout the lower stratosphere (LS). Expanded use of this method will lead to improved quantification of cross-tropopause transport events and validation of global chemical transport models.
RESUMO
In situ measurements of the relative humidity with respect to ice (RHi) and of nitric acid (HNO3) were made in both natural and contrail cirrus clouds in the upper troposphere. At temperatures lower than 202 kelvin, RHi values show a sharp increase to average values of over 130% in both cloud types. These enhanced RHi values are attributed to the presence of a new class of HNO3-containing ice particles (Delta-ice). We propose that surface HNO3 molecules prevent the ice/vapor system from reaching equilibrium by a mechanism similar to that of freezing point depression by antifreeze proteins. Delta-ice represents a new link between global climate and natural and anthropogenic nitrogen oxide emissions. Including Delta-ice in climate models will alter simulated cirrus properties and the distribution of upper tropospheric water vapor.
RESUMO
The molecular structure of didemnin A, the parent compound of a series of antiviral cytotoxic depsipeptides extracted from a marine tunicate Trididemnum solidum of the family of Didemnidae, has been determined by single-crystal X-ray diffraction. In the crystal, didemnin A molecules form pseudo-symmetric dimeric pair. The two molecules in the dimer are held together by strong N--H center dot center dot center dot O and N--H center dot center dot center dot N hydrogen bonds. A chloride ion, placed almost symmetrically between the dimeric pair, forms N--H center dot center dot center dot Cl hydrogen bonds (3.19 and 3.23 Angstrom) with both the molecules. The two independent molecules in the structure have closely similar geometry. For each molecule, the 23-membered depsipeptide ring assumes a folded conformation in the shape of a 'bent figure-of-eight' similar to that observed in the didemnin B crystal structure. The major conformational differences in the macrocycle of didemnin A and didemnin B are around the Hip residue. The root mean-square (RMS) difference of 20 of the 23 endocyclic torsion angles for the two structures is less than 10 degrees, while the three bond torsions in the Hip residue vary by about 50 degrees. The macrocycle conformation is stabilized by a transannular N--H center dot center dot center dot O hydrogen bond linking the isostatine amide group with the leucine carbonyl group. The truncated linear chain is folded back toward the macrocyclic ring and is held by a N--H center dot center dot center dot O hydrogen bond between the leucine amide group and Me-Leu carbonyl group. The transannular hydrogen bond in the didemnin A structure (N4--H center dot center dot center dot O3 = 2.83 Angstrom in both molecule a and molecule b) is noticeably stronger than that observed in the didemnin B structure (3.02 Angstrom). The X-ray structure of didemnin A is generally consistent with that obtained by NMR studies. Within the crystal, the molecules are packed in zig-zag chains formed by intermolecular O--H center dot center dot center dot O hydrogen bonds. The crystal structure and packing of didemnin A are quite different from that of the didemnin B structure.
Assuntos
Antivirais/química , Depsipeptídeos , Peptídeos Cíclicos/química , Ligação de Hidrogênio , Modelos Moleculares , Estrutura Molecular , Conformação Proteica , Difração de Raios XRESUMO
A novel epoxy sterol isolated from the marine mollusc Planaxis sulcatus has been identified as 9 alpha,11 alpha-epoxycholest-7-ene-3 beta,5 alpha,6 beta-triol by spectrometric methods.
Assuntos
Colestenos/isolamento & purificação , Citotoxinas/isolamento & purificação , Toxinas Marinhas/isolamento & purificação , Moluscos/análise , Animais , Colestenos/farmacologia , Citotoxinas/farmacologia , Leucemia L1210/tratamento farmacológico , Toxinas Marinhas/farmacologiaRESUMO
Didemnin B, a highly active depsipeptide isolated from a Caribbean tunicate, crystallizes from chloroform/benzene in the orthorhombic space group C2221, with cell parameters a = 14.990 +/- 0.003 A, b = 22.574 +/- 0.004 A, c = 41.112 +/- 0.009 A, V = 13911.7 A3 at 138 K and a calculated density of 1.143 g/cm3 based on C57H89N7O15, 1.5C6H6.H2O and eight formula units per cell. The overall agreement factor R = 0.052 for 7699 reflections, 20 theta max = 150 degrees, Cu K-alpha radiation. The structure determination revealed that didemnin B contains an isostatine residue instead of a statine residue. The conformation of the 23-membered depsipeptide ring is stabilized by one transannular hydrogen bond. The ring does not show the antiparallel beta-pleated-sheet structure but, instead, has a fold in the shape of a bent figure-eight. The linear peptide moiety, containing N-methylleucine and lactylproline, forms a beta (II)-bend and is folded back toward the cyclic backbone, giving the overall molecule a globular character. Comparison with the structure of cyclosporin A shows distinct stereochemical differences between the two molecules. It is suggested that didemnin B and cyclosporin A are unlikely to have a common receptor binding site.
Assuntos
Antivirais , Depsipeptídeos , Modelos Moleculares , Peptídeos Cíclicos , Conformação Proteica , Difração de Raios XRESUMO
Marine mollusks have been identified as a rich source of novel compounds. The diversity of the chemical nature of these compounds can be partially attributed to the dietary sources inasmuch as mollusks are known to concentrate selectively compounds present in their diet. Although cembranolide diterpenses have been isolated in ever-growing numbers from a variety of marine as well as terrestrial sources, there is only one report about their presence in a marine mollusk. In this communication, we report the isolation of dihydrosinularin and 11-epi-sinulariolide from the mollusk Planaxis sulcatus Born. Dihydrosinularin and 11-epi-sinulariolide acetate have been isolated previously from soft corals which, together with gorgonians, are the richest sources of marine cembranoids. It should be pointed out that this is the first report on the occurrence of the parent 11-epi-sinulariolide in a marine invertebrate. It is expected these diterpenes are of dietary origin although the possibility of biotransformation of a precusor by the mollusk cannot be ruled out at this time. Both dihydrosinularin and 11-epi-sinulariolide have been reported to have marginal antineoplastic activity against P-388 lymphocytic leukemia.
Assuntos
Diterpenos/isolamento & purificação , Moluscos/análise , Antineoplásicos/isolamento & purificaçãoRESUMO
Anisotropic reorientation of 3 alpha-substituted steroids has been well documented. Assignment of the 13C-nmr spectrum of Hippurin, a novel furospirostane and the measurement of the spin-lattice (T1) relaxation times has established both points in the molecule through which the axis of anisotropic reorientation passes, specifically the 3- and 24-positions.
Assuntos
Esteróis , Cinética , Espectroscopia de Ressonância Magnética/métodos , Conformação MolecularAssuntos
Transformação Celular Neoplásica/induzido quimicamente , Imunidade/efeitos dos fármacos , Toxinas Marinhas/efeitos adversos , Animais , Carbono/metabolismo , Transformação Celular Neoplásica/efeitos dos fármacos , Cnidários , Imunidade Celular/efeitos dos fármacos , Macrófagos/imunologia , Papiloma/induzido quimicamente , Tartarugas , UrocordadosAssuntos
Adenosina/isolamento & purificação , Arritmias Cardíacas/induzido quimicamente , Desoxiadenosinas/isolamento & purificação , Parada Cardíaca/induzido quimicamente , Poríferos/análise , Adenosina/farmacologia , Animais , Cromatografia , Desoxiadenosinas/farmacologia , Cobaias , Técnicas In VitroRESUMO
Crassin acetate, a lactonic cembrane diterpene, has been shown to be the principal antineoplastic agent present in the marine invertebrates (gorgonians) Pseudoplexaura porosa, P. flagellosa, P. wagenaari and P. crucis.