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The fundamental reaction pathways to the simplest dialkylsubstituted aromatics—xylenes (C6H4(CH3)2)—in high‐temperature combustion flames and in low‐temperature extraterrestrial environments are still unknown, but critical to understand the chemistry and molecular mass growth processes in these extreme environments. Exploiting crossed molecular beam experiments augmented by state‐of‐the‐art electronic structure and statistical calculations, this study uncovers a previously elusive, facile gas‐phase synthesis of xylenes through an isomer‐selective reaction of 1‐propynyl (methylethynyl, CH3CC) with 2‐methyl‐1,3‐butadiene (isoprene, C5H8). The reaction dynamics are driven by a barrierless addition of the radical to the diene moiety of 2‐methyl‐1,3‐butadiene followed by extensive isomerization (hydrogen shifts, cyclization) prior to unimolecular decomposition accompanied by aromatization via atomic hydrogen loss. This overall exoergic reaction affords a preparation of xylenes not only in high‐temperature environments such as in combustion flames and around circumstellar envelopes of carbon‐rich Asymptotic Giant Branch (AGB) stars, but also in low‐temperature cold molecular clouds (10 K) and in hydrocarbon‐rich atmospheres of planets and their moons such as Triton and Titan. Our study established a hitherto unknown gas‐phase route to xylenes and potentially more complex, disubstituted benzenes via a single collision event highlighting the significance of an alkyl‐substituted ethynyl‐mediated preparation of aromatic molecules in our Universe. [ABSTRACT FROM AUTHOR]

Glycinal (HCOCH2NH2) and acetamide (CH3CONH2) are simple molecular building blocks of biomolecules in prebiotic chemistry, though their origin on early Earth and formation in interstellar media remain a mystery. These molecules are formed with their tautomers in low temperature interstellar model ices upon interaction with simulated galactic cosmic rays. Glycinal and acetamide are accessed via barrierless radical‐radical reactions of vinoxy (⋅CH2CHO) and acetyl (⋅C(O)CH3), and then undergo keto‐enol tautomerization. Exploiting tunable photoionization reflectron time‐of‐flight mass spectroscopy and photoionization efficiency (PIE) curves, these results demonstrate fundamental reaction pathways for the formation of complex organics through non‐equilibrium ice reactions in cold molecular cloud environments. These molecules demonstrate an unconventional starting point for abiotic synthesis of organics relevant to contemporary biomolecules like polypeptides and cell membranes in deep space. [ABSTRACT FROM AUTHOR]

The simplest polycyclic aromatic hydrocarbon (PAH) carrying a five‐membered ring—9H‐fluorene (C13H10)—is produced isomer‐specifically in the gas phase by reacting benzyl (C7H7⋅) with phenyl (C6H5⋅) radicals in a pyrolytic reactor coupled with single photon ionization mass spectrometry. The unconventional mechanism of reaction is supported by theoretical calculations, which first produces diphenylmethane and unexpected 1‐(6‐methylenecyclohexa‐2,4‐dienyl)benzene intermediates (C13H12) accessed via addition of the phenyl radical to the ortho position of the benzyl radical. These findings offer convincing evidence for molecular mass growth processes defying conventional wisdom that radical‐radical reactions are initiated through recombination at their radical centers. The structure of 9H‐fluorene acts as a molecular building block for complex curved nanostructures like fullerenes and nanobowls providing fundamental insights into the hydrocarbon evolution in high temperature settings. [ABSTRACT FROM AUTHOR]

The simplest polycyclic aromatic hydrocarbon (PAH) carrying a five‐membered ring—9H‐fluorene (C13H10)—is produced isomer‐specifically in the gas phase by reacting benzyl (C7H7⋅) with phenyl (C6H5⋅) radicals in a pyrolytic reactor coupled with single photon ionization mass spectrometry. The unconventional mechanism of reaction is supported by theoretical calculations, which first produces diphenylmethane and unexpected 1‐(6‐methylenecyclohexa‐2,4‐dienyl)benzene intermediates (C13H12) accessed via addition of the phenyl radical to the ortho position of the benzyl radical. These findings offer convincing evidence for molecular mass growth processes defying conventional wisdom that radical‐radical reactions are initiated through recombination at their radical centers. The structure of 9H‐fluorene acts as a molecular building block for complex curved nanostructures like fullerenes and nanobowls providing fundamental insights into the hydrocarbon evolution in high temperature settings. [ABSTRACT FROM AUTHOR]

The simplest polycyclic aromatic hydrocarbon (PAH) carrying a five‐membered ring—9H‐fluorene (C13H10)—is produced isomer‐specifically in the gas phase by reacting benzyl (C7H7⋅) with phenyl (C6H5⋅) radicals in a pyrolytic reactor coupled with single photon ionization mass spectrometry. The unconventional mechanism of reaction is supported by theoretical calculations, which first produces diphenylmethane and unexpected 1‐(6‐methylenecyclohexa‐2,4‐dienyl)benzene intermediates (C13H12) accessed via addition of the phenyl radical to the ortho position of the benzyl radical. These findings offer convincing evidence for molecular mass growth processes defying conventional wisdom that radical‐radical reactions are initiated through recombination at their radical centers. The structure of 9H‐fluorene acts as a molecular building block for complex curved nanostructures like fullerenes and nanobowls providing fundamental insights into the hydrocarbon evolution in high temperature settings. [ABSTRACT FROM AUTHOR]

The simplest polycyclic aromatic hydrocarbon (PAH) carrying a five‐membered ring—9H‐fluorene (C13H10)—is produced isomer‐specifically in the gas phase by reacting benzyl (C7H7⋅) with phenyl (C6H5⋅) radicals in a pyrolytic reactor coupled with single photon ionization mass spectrometry. The unconventional mechanism of reaction is supported by theoretical calculations, which first produces diphenylmethane and unexpected 1‐(6‐methylenecyclohexa‐2,4‐dienyl)benzene intermediates (C13H12) accessed via addition of the phenyl radical to the ortho position of the benzyl radical. These findings offer convincing evidence for molecular mass growth processes defying conventional wisdom that radical‐radical reactions are initiated through recombination at their radical centers. The structure of 9H‐fluorene acts as a molecular building block for complex curved nanostructures like fullerenes and nanobowls providing fundamental insights into the hydrocarbon evolution in high temperature settings. [ABSTRACT FROM AUTHOR]

The hitherto elusive monobridged Ge(μ‐H)GeH (X1A′) molecule was prepared in the gas phase by bimolecular reaction of atomic germanium with germane (GeH4). Electronic structure calculations revealed that this reaction commenced on the triplet surface with the formation of a van der Waals complex, followed by insertion of germanium into a germanium‐hydrogen bond over a submerged barrier to form the triplet digermanylidene intermediate (HGeGeH3); the latter underwent intersystem crossing from the triplet to the singlet surface. On the singlet surface, HGeGeH3 predominantly isomerized through two successive hydrogen shifts prior to unimolecular decomposition to Ge(μ‐H)GeH isomer, which is in equilibrium with the vinylidene‐type (H2GeGe) and dibridged (Ge(μ‐H2)Ge) isomers. This reaction leads to the formation of cyclic dinuclear germanium molecules, which do not exist on the isovalent C2H2 surface, thus deepening our understanding of the role of nonadiabatic reaction dynamics in preparing nonclassical, hydrogen‐bridged isomers carrying main group XIV elements. [ABSTRACT FROM AUTHOR]

Extracorporeal life support (ECLS) is a means to support patients with acute respiratory failure. Initially, recommendations to treat severe cases of pandemic coronavirus disease 2019 (COVID‐19) with ECLS have been restrained. In the meantime, ECLS has been shown to produce similar outcomes in patients with severe COVID‐19 compared to existing data on ARDS mortality. We performed an international email survey to assess how ECLS providers worldwide have previously used ECLS during the treatment of critically ill patients with COVID‐19. A questionnaire with 45 questions (covering, e.g., indication, technical aspects, benefit, and reasons for treatment discontinuation), mostly multiple choice, was distributed by email to ECLS centers. The survey was approved by the European branch of the Extracorporeal Life Support Organization (ELSO); 276 ECMO professionals from 98 centers in 30 different countries on four continents reported that they employed ECMO for very severe COVID‐19 cases, mostly in veno‐venous configuration (87%). The most common reason to establish ECLS was isolated hypoxemic respiratory failure (50%), followed by a combination of hypoxemia and hypercapnia (39%). Only a small fraction of patients required veno‐arterial cannulation due to heart failure (3%). Time on ECLS varied between less than 2 and more than 4 weeks. The main reason to discontinue ECLS treatment prior to patient's recovery was lack of clinical improvement (53%), followed by major bleeding, mostly intracranially (13%). Only 4% of respondents reported that triage situations, lack of staff or lack of oxygenators, were responsible for discontinuation of ECLS support. Most ECLS physicians (51%, IQR 30%) agreed that patients with COVID‐19‐induced ARDS (CARDS) benefitted from ECLS. Overall mortality of COVID‐19 patients on ECLS was estimated to be about 55%. ECLS has been utilized successfully during the COVID‐19 pandemic to stabilize CARDS patients in hypoxemic or hypercapnic lung failure. Age and multimorbidity limited the use of ECLS. Triage situations were rarely a concern. ECLS providers stated that patients with severe COVID‐19 benefitted from ECLS. [ABSTRACT FROM AUTHOR]

The identification of silicon‐substituted, complex organics carrying multiple functional groups by classical infrared spectroscopy is challenging because the group frequencies of functional groups often overlap. Photoionization (PI) reflectron time‐of‐fight mass spectrometry (ReTOF‐MS) in combination with temperature‐programmed desorption (TPD) holds certain advantages because molecules are identified after sublimation from the matrix into in the gas phase based on distinct ionization energies and sublimation temperatures. In this study, we reveal the detection of 1‐silaglycolaldehyde (HSiOCH2OH), 2‐sila‐acetic acid (H3SiCOOH), and 1,2‐disila‐acetaldehyde (H3SiSiHO)—the silicon analogues of the well‐known glycolaldehyde (HCOCH2OH), acetic acid (H3CCOOH), and acetaldehyde (H3CCHO), in the gas phase after preparation in silane (SiH4)–carbon dioxide ices exposed to energetic electrons and subliming the neutral reaction products formed within the ices into the gas phase. [ABSTRACT FROM AUTHOR]

The silene molecule (H2SiCH2; X1A1) has been synthesized under single collision conditions via the bimolecular gas phase reaction of ground state methylidyne radicals (CH) with silane (SiH4). Exploiting crossed molecular beams experiments augmented by high‐level electronic structure calculations, the elementary reaction commenced on the doublet surface through a barrierless insertion of the methylidyne radical into a silicon‐hydrogen bond forming the silylmethyl (CH2SiH3; X2A′) complex followed by hydrogen migration to the methylsilyl radical (SiH2CH3; X2A′). Both silylmethyl and methylsilyl intermediates undergo unimolecular hydrogen loss to silene (H2SiCH2; X1A1). The exploration of the elementary reaction of methylidyne with silane delivers a unique view at the widely uncharted reaction dynamics and isomerization processes of the carbon–silicon system in the gas phase, which are noticeably different from those of the isovalent carbon system thus contributing to our knowledge on carbon silicon bond couplings at the molecular level. [ABSTRACT FROM AUTHOR]

A representative, low‐temperature gas‐phase reaction mechanism synthesizing polyacenes via ring annulation exemplified by the formation of pentacene (C22H14) along with its benzo[a]tetracene isomer (C22H14) is unraveled by probing the elementary reaction of the 2‐tetracenyl radical (C18H11.) with vinylacetylene (C4H4). The pathway to pentacene—a prototype polyacene and a fundamental molecular building block in graphenes, fullerenes, and carbon nanotubes—is facilitated by a barrierless, vinylacetylene mediated gas‐phase process thus disputing conventional hypotheses that synthesis of polycyclic aromatic hydrocarbons (PAHs) solely proceeds at elevated temperatures. This low‐temperature pathway can launch isomer‐selective routes to aromatic structures through submerged reaction barriers, resonantly stabilized free‐radical intermediates, and methodical ring annulation in deep space eventually changing our perception about the chemistry of carbon in our universe. [ABSTRACT FROM AUTHOR]

A unified low‐temperature reaction mechanism on the formation of acenes, phenacenes, and helicenes—polycyclic aromatic hydrocarbons (PAHs) that are distinct via the linear, zigzag, and ortho‐condensed arrangements of fused benzene rings—is revealed. This mechanism is mediated through a barrierless, vinylacetylene mediated gas‐phase chemistry utilizing tetracene, [4]phenacene, and [4]helicene as benchmarks contesting established ideas that molecular mass growth processes to PAHs transpire at elevated temperatures. This mechanism opens up an isomer‐selective route to aromatic structures involving submerged reaction barriers, resonantly stabilized free‐radical intermediates, and systematic ring annulation potentially yielding molecular wires along with racemic mixtures of helicenes in deep space. Connecting helicene templates to the Origins of Life ultimately changes our hypothesis on interstellar carbon chemistry. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons (PAHs) represent the link between resonance‐stabilized free radicals and carbonaceous nanoparticles generated in incomplete combustion processes and in circumstellar envelopes of carbon rich asymptotic giant branch (AGB) stars. Although these PAHs resemble building blocks of complex carbonaceous nanostructures, their fundamental formation mechanisms have remained elusive. By exploring these reaction mechanisms of the phenyl radical with biphenyl/naphthalene theoretically and experimentally, we provide compelling evidence on a novel phenyl‐addition/dehydrocyclization (PAC) pathway leading to prototype PAHs: triphenylene and fluoranthene. PAC operates efficiently at high temperatures leading through rapid molecular mass growth processes to complex aromatic structures, which are difficult to synthesize by traditional pathways such as hydrogen‐abstraction/acetylene‐addition. The elucidation of the fundamental reactions leading to PAHs is necessary to facilitate an understanding of the origin and evolution of the molecular universe and of carbon in our galaxy. [ABSTRACT FROM AUTHOR]

Theoretical calculations and experimental simulations indicate that the surprisingly low sulfur abundance on the surfaces of spacecraft visited S‐type asteroids 433 Eros and 25143 Itokawa may be due to space weathering. Two current missions, Osiris‐Rex and Hayabusa 2, are studing asteroids 101955 Bennu (B‐type) and 162173 Ryugu (C‐type), respectively. Understanding space weathering effects related to sulfur containing species is only in the beginning stages and has not been studied from the point of view of C‐type asteroids. This laboratory study details the formation of hydrogen sulfide (H2S) and hydrogen disulfide (H2S2) from conversion of nonvolatile‐sulfuretted species in the Murchison meteorite by exposure to energetic electrons and laser processing, which mimics the synergic effect of secondary electrons generated by galactic cosmic rays and high‐energy solar wind particles plus micrometeorite impact on airless bodies. The results indicate that space weathering processes likely induce depletion of sulfur on the surface of C‐type and undifferentiated S‐type asteroids. For keeping scientific integrity of these fragile species, cold/cryogenic curation of future collected samples from asteroids might be required. Plain Language Summary: The Near Earth Asteroid Rendezvous (NEAR) Shoemaker and Hayabusa spacecraft have detected surprisingly low sulfur abundance on the surfaces of asteroids 433 Eros and 25143 Itokawa. The physical and chemical properties of the surfaces of asteroids are affected by space weathering processes including irradiation by cosmic rays and bombardment of micrometeorites. However, understanding space weathering effects related to sulfur containing species is only in the beginning stages. Here we show that hydrogen sulfide (H2S) and hydrogen disulfide (H2S2) can be generated from conversion of nonvolatile sulfuretted species in the Murchison meteorite by simulated weathering processes. The Murchison meteorite is suggested to originate from asteroids. These volatile sulfur‐containing species sublimed at temperatures lower than the maximum surface temperatures (with the Sun overhead) on asteroids. These results indicate that space weathering likely induces depletion of sulfur on the surfaces of asteroids. Key Points: Murchison meteorite samples were irradiated with electrons and laser to model effects of space weatheringHydrogen sulfide (H2S) and hydrogen disulfide (H2S2) were generated from sulfur‐containing minerals at low temperatureConversion of sulfur‐containing mineral to volatile H2S may induce the surficial sulfur depletion on asteroids [ABSTRACT FROM AUTHOR]

The triafulvene molecule (c‐C4H4)—the simplest representative of the fulvene family—has been synthesized for the first time in the gas phase through the reaction of the methylidyne radical (CH) with methylacetylene (CH3CCH) and allene (H2CCCH2) under single‐collision conditions. The experimental and computational data suggest triafulvene is formed by the barrierless cycloaddition of the methylidyne radical to the π‐electron density of either C3H4 isomer followed by unimolecular decomposition through elimination of atomic hydrogen from the CH3 or CH2 groups of the reactants. The dipole moment of triafulvene of 1.90 D suggests that this molecule could represent a critical tracer of microwave‐inactive allene in cold molecular clouds, thus defining constraints on the largely elusive hydrocarbon chemistry in low‐temperature interstellar environments, such as that of the Taurus Molecular Cloud 1 (TMC‐1). [ABSTRACT FROM AUTHOR]

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The International Atomic Energy Agency (IAEA) jointly with the Elettra Sincrotrone Trieste (EST) operates a multipurpose X-ray spectrometry endstation at the X-ray Fluorescence beamline (10.1L). The facility has been available to external users since the beginning of 2015 through the peer-review process of EST. Using this collaboration framework, the IAEA supports and promotes synchrotron-radiation-based research and training activities for various research groups from the IAEA Member States, especially those who have limited previous experience and resources to access a synchrotron radiation facility. This paper aims to provide a broad overview about various analytical capabilities, intrinsic features and performance figures of the IAEA X-ray spectrometry endstation through the measured results. The IAEA--EST endstation works with monochromatic X-rays in the energy range 3.7-14 keV for the Elettra storage ring operating at 2.0 or 2.4 GeVelectron energy. It offers a combination of different advanced analytical probes, e.g. X-ray reflectivity, X-ray absorption fine-structure measurements, grazing-incidence X-ray fluorescence measurements, using different excitation and detection geometries, and thereby supports a comprehensive characterization for different kinds of nanostructured and bulk materials. [ABSTRACT FROM AUTHOR]

The 1,2,4,7-cyclooctatetraenyl radical (C8H7) has been synthesized for the very first time via the bimolecular gas-phase reaction of ground-state carbon atoms with 1,3,5-cycloheptatriene (C7H8) on the triplet surface under single-collision conditions. The barrier-less route to the cyclic 1,2,4,7-cyclooctatetraenyl radical accesses exotic reaction intermediates on the triplet surface, which cannot be synthesized via classical organic chemistry methods: the triplet non-aromatic 2,4,6-cyclooctatriene (C8H8) and the triplet aromatic 1,3,5,7-cyclooctatetraene (C8H8). Our approach provides a clean gas-phase synthesis of this hitherto elusive cyclic radical species 1,2,4,7-cyclooctatetraenyl via a single-collision event and opens up a versatile, unconventional path to access this previously largely obscure class of cyclooctatetraenyl radicals, which have been impossible to access through classical synthetic methods. [ABSTRACT FROM AUTHOR]

Due to their oxidizing properties, perchlorates (ClO4−) are suggested by the planetary science community to play a vital role in the scarcity of organics on the Martian surface. However, alternative oxidation agents such as hydrogen peroxide (H2O2) have received surprisingly little attention. In this study, samples of magnesium perchlorate hexahydrate (Mg(ClO4)2 · 6H2O) were exposed to monoenergetic electrons and D2+ ions separately, sequentially, and simultaneously to probe the effects of galactic cosmic ray exposure of perchlorates and the potential incorporation of hydrogen (deuterium) into these minerals. The experiments were carried out under ultrahigh-vacuum conditions at 50 K, after which the samples were slowly heated to 300 K while the subliming products were monitored by a quadrupole mass spectrometer. In all cases, molecular oxygen (O2) was detected upon the onset of irradiation and also during the warmup phase. In case of a simultaneous D2+-electron exposure, deuterated water (D2O) and deuterium peroxide (D2O2) were also detected in the warmup phase, whereas only small amounts of D2O2 were found after an exclusive D2+ irradiation. These experiments yield the first data identifying hydrogen peroxide as a potential product in the interaction of cosmic rays with perchlorates in the Martian regolith revealing that perchlorates are capable of producing multiple oxidizing agents (O2 and D2O2) that may account for the destruction of organics on the Martian surface. [ABSTRACT FROM AUTHOR]

The hydrogen-abstraction/acetylene-addition (HACA) mechanism has been central for the last decades in attempting to rationalize the formation of polycyclic aromatic hydrocarbons (PAHs) as detected in carbonaceous meteorites such as in Murchison. Nevertheless, the basic reaction mechanisms leading to the formation of even the simplest tricyclic PAHs like anthracene and phenanthrene are still elusive. Here, by exploring the previously unknown chemistry of the ortho-biphenylyl radical with acetylene, we deliver compelling evidence on the efficient synthesis of phenanthrene in carbon-rich circumstellar environments. However, the lack of formation of the anthracene isomer implies that HACA alone cannot be responsible for the formation of PAHs in extreme environments. Considering the overall picture, alternative pathways such as vinylacetylene-mediated reactions are required to play a crucial role in the synthesis of complex PAHs in circumstellar envelopes of dying carbon-rich stars. [ABSTRACT FROM AUTHOR]

The hitherto elusive disilavinylidene (H2SiSi) molecule, which is in equilibrium with the mono-bridged (Si(H)SiH) and di-bridged (Si(H2)Si) isomers, was initially formed in the gas-phase reaction of ground-state atomic silicon (Si) with silane (SiH4) under single-collision conditions in crossed molecular beam experiments. Combined with state-of-the-art electronic structure and statistical calculations, the reaction was found to involve an initial formation of a van der Waals complex in the entrance channel, a submerged barrier to insertion, intersystem crossing (ISC) from the triplet to the singlet manifold, and hydrogen migrations. These studies provide a rare glimpse of silicon chemistry on the molecular level and shed light on the remarkable non-adiabatic reaction dynamics of silicon, which are quite distinct from those of isovalent carbon systems, providing important insight that reveals an exotic silicon chemistry to form disilavinylidene. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons (PAHs) are omnipresent in the interstellar medium (ISM) and also in carbonaceous meteorites (CM) such as Murchison. However, the basic reaction routes leading to the formation of even the simplest PAH-naphthalene (C10H8)-via the hydrogen-abstraction/acetylene-addition (HACA) mechanism still remain ambiguous. Here, by revealing the uncharted fundamental chemistry of the styrenyl (C8H7) and the ortho-vinylphenyl radicals (C8H7)-key transient species of the HACA mechanism-with acetylene (C2H2), we provide the first solid experimental evidence on the facile formation of naphthalene in a simulated combustion environment validating the previously postulated HACA mechanism for these two radicals. This study highlights, at the molecular level spanning combustion and astrochemistry, the importance of the HACA mechanism to the formation of the prototype PAH naphthalene. [ABSTRACT FROM AUTHOR]

Silole (1-silacyclopenta-2,4-diene) was synthesized for the first time by the bimolecular reaction of the simplest silicon-bearing radical, silylidyne (SiH), with 1,3-butadiene (C4H6) in the gas phase under single-collision conditions. The absence of consecutive collisions of the primary reaction product prevents successive reactions of the silole by Diels- Alder dimerization, thus enabling the clean gas-phase synthesis of this hitherto elusive cyclic species from acyclic precursors in a single-collision event. Our method opens up a versatile and unconventional path to access a previously rather obscure class of organosilicon molecules (substituted siloles), which have been difficult to access through classical synthetic methods. [ABSTRACT FROM AUTHOR]

Silole (1-silacyclopenta-2,4-diene) was synthesized for the first time by the bimolecular reaction of the simplest silicon-bearing radical, silylidyne (SiH), with 1,3-butadiene (C4H6) in the gas phase under single-collision conditions. The absence of consecutive collisions of the primary reaction product prevents successive reactions of the silole by Diels- Alder dimerization, thus enabling the clean gas-phase synthesis of this hitherto elusive cyclic species from acyclic precursors in a single-collision event. Our method opens up a versatile and unconventional path to access a previously rather obscure class of organosilicon molecules (substituted siloles), which have been difficult to access through classical synthetic methods. [ABSTRACT FROM AUTHOR]

The hydrogen abstraction/acetylene addition (HACA) mechanism has long been viewed as a key route to aromatic ring growth of polycyclic aromatic hydrocarbons (PAHs) in combustion systems. However, doubt has been drawn on the ubiquity of the mechanism by recent electronic structure calculations which predict that the HACA mechanism starting from the naphthyl radical preferentially forms acenaphthylene, thereby blocking cyclization to a third six-membered ring. Here, by probing the products formed in the reaction of 1- and 2-naphthyl radicals in excess acetylene under combustion-like conditions with the help of photoionization mass spectrometry, we provide experimental evidence that this reaction produces 1- and 2-ethynylnaphthalenes (C12H8), acenaphthylene (C12H8) and diethynylnaphthalenes (C14H8). Importantly, neither phenanthrene nor anthracene (C14H10) was found, which indicates that the HACA mechanism does not lead to cyclization of the third aromatic ring as expected but rather undergoes ethynyl substitution reactions instead. [ABSTRACT FROM AUTHOR]

Contemporary mechanisms for the spontaneous formation of glycerol have not been able to explain its existence on early Earth. The exogenous origin and delivery of organic molecules to early Earth presents an alternative route to their terrestrial in situ formation since biorelevant molecules like amino acids, carboxylic acids, and alkylphosphonic acids have been recovered from carbonaceous chondrites. Reported herein is the first in situ identification of glycerol, the key building block of all cellular membranes, formed by exposure of methanol-based - interstellar model ices to ionizing radiation in the form of energetic electrons. These results provide compelling evidence that the radiation-induced formation of glycerol in low-temperature interstellar model ices is facile. Synthesized on interstellar grains and eventually incorporated into the 'building material' of solar systems, biorelevant molecules such as glycerol could have been dispensed to habitable planets such as early Earth by comets and meteorites. [ABSTRACT FROM AUTHOR]

Aims In patients after the Fontan procedure, assessment of a failing Fontan circuit is difficult. Natriuretic peptides failed to be reliable markers of functional status or systemic ventricular function in this patient cohort. The aim of the study was to assess the clinical utility of mid-regional pro-adrenomedullin ( MR-proADM) in patients after the Fontan procedure. Methods and results Plasma MR-proADM levels were measured in 53 patients after the Fontan procedure and compared with clinical status, echocardiographic, and laboratory parameters including NT-proBNP. Median MR-proADM levels were 0.668 nmol/L in patients with a failing Fontan circuit as compared with 0.357 nmol/L in those without Fontan failure ( P = 0.001). Levels of MR-proADM were significantly related to the presence of Fontan failure ( r = 0.444, P = 0.001), NYHA class ( r = 0.434, P < 0.001), and γ-glutamyltransferase levels ( r = 0.554, P < 0.001). According to receiver operating characteristic ( ROC) curve analysis, Fontan failure was best predicted by MR-proADM [area under the curve ( AUC) 0.985, P = 0.001], NT-proBNP ( AUC 0.947, P = 0.003), NYHA class ( AUC 0.962, P = 0.002), and the inspiratory/expiratory ratio of the inferior vena cava diameter ( AUC 0.973, P = 0.007). The optimal cut-off of MR-proADM for the prediction of Fontan failure was 0.520 nmol/L with a sensitivity of 100%, specificity of 93.9%, positive predictive value of 57.1%, negative predictive value of 100%, and overall accuracy of 94.3%. However, the data should also be validated in a larger cohort of patients. Conclusion Serial measurements of MR-proADM levels may help identify patients at risk for a failing Fontan circulation especially when exceeding 0.520 nmol/L. In these patients, intensified medical care should be considered to prevent further clinical deterioration. [ABSTRACT FROM AUTHOR]

For almost half a century, polycyclic aromatic hydrocarbons (PAHs) have been proposed to play a key role in the astrochemical evolution of the interstellar medium (ISM) and in the chemistry of combustion systems. However, even the most fundamental reaction mechanism assumed to lead to the simplest PAH naphthalene-the hydrogen abstraction-acetylene addition (HACA) mechanism-has eluded experimental observation. Here, by probing the phenylacetylene (C8H6) intermediate together with naphthalene (C10H8) under combustion-like conditions by photo-ionization mass spectrometry, the very first direct experimental evidence for the validity of the HACA mechanism which so far had only been speculated theoretically is reported. [ABSTRACT FROM AUTHOR]

Dicarbon (C2), the simplest bare carbon molecule, is ubiquitous in the interstellar medium and in combustion flames. A gas-phase synthesis is presented of the benzyl radical (C6H5CH2) by the crossed molecular beam reaction of dicarbon, C2(X1Σg+, a3Πu), with 2-methyl-1,3-butadiene (isoprene; C5H8; X1A′) accessing the triplet and singlet C7H8 potential energy surfaces (PESs) under single collision conditions. The experimental data combined with ab initio and statistical calculations reveal the underlying reaction mechanism and chemical dynamics. On the singlet and triplet surfaces, the reactions involve indirect scattering dynamics and are initiated by the barrierless addition of dicarbon to the carbon-carbon double bond of the 2-methyl-1,3-butadiene molecule. These initial addition complexes rearrange via multiple isomerization steps, leading eventually to the formation of C7H7 radical species through atomic hydrogen elimination. The benzyl radical (C6H5CH2), the thermodynamically most stable C7H7 isomer, is determined as the major product. [ABSTRACT FROM AUTHOR]

Dicarbon (C2), the simplest bare carbon molecule, is ubiquitous in the interstellar medium and in combustion flames. A gas-phase synthesis is presented of the benzyl radical (C6H5CH2) by the crossed molecular beam reaction of dicarbon, C2(X1Σg+, a3Πu), with 2-methyl-1,3-butadiene (isoprene; C5H8; X1A′) accessing the triplet and singlet C7H8 potential energy surfaces (PESs) under single collision conditions. The experimental data combined with ab initio and statistical calculations reveal the underlying reaction mechanism and chemical dynamics. On the singlet and triplet surfaces, the reactions involve indirect scattering dynamics and are initiated by the barrierless addition of dicarbon to the carbon-carbon double bond of the 2-methyl-1,3-butadiene molecule. These initial addition complexes rearrange via multiple isomerization steps, leading eventually to the formation of C7H7 radical species through atomic hydrogen elimination. The benzyl radical (C6H5CH2), the thermodynamically most stable C7H7 isomer, is determined as the major product. [ABSTRACT FROM AUTHOR]