Fluorescence Excitation and Dispersed Fluorescence Spectra of the First Electronic Excited (S1) State of peri-Hexabenzocoronene (C42H18) Isolated in Solid para-Hydrogen.

Large polycyclic aromatic hydrocarbons (PAH) and their cationic, hydrogenated, and protonated derivatives have long been considered as promising candidates for the carriers of the diffuse interstellar bands. peri-Hexabenzocoronene (peri-HBC, C42H18) is a large, compact PAH, and, to the best of our knowledge, the largest centrosymmetric all-benzenoid PAH for which electronic spectroscopy data has been published. In this work, we present the dispersed fluorescence and fluorescence excitation spectra of the first electronic excited (S1) state of peri-HBC isolated in solid para-H2 and provide the first detailed vibronic analysis of observed features. The observed spectra agree with the emission and absorption spectra simulated according to optimized geometries and scaled harmonic vibrational frequencies calculated at the density functional theory (DFT) level using a Franck-Condon Herzberg-Teller approach; the spectral bands are associated solely with vibrational normal modes of approximate e2g symmetry and their combinations with vibrational modes of approximately a1g symmetry. We clearly observed the position of the S1-S0 electronic transition origin of peri-HBC at 22,088 cm-1 (452.7 nm), which was unreported previously. The matrix shift of ∼110 cm-1 to the red relative to the gas-phase value was estimated by comparison of two reported gas-phase bands with our work. Because of the significant deviation from the reported wavelengths of DIB, the weakness of the S1-S0 electronic transitions, and the lack of reported DIB at <400 nm where the intense S4 ← S0 band of peri-HBC is located, peri-HBC is unlikely to contribute to DIB.

Infrared and Laser-Induced Fluorescence Spectra of Sumanene Isolated in Solid para-Hydrogen.

The para-hydrogen (p-H2) matrix-isolation technique has been scarcely used to record electronic absorption and emission spectra. It is expected that its small matrix shifts due to diminished molecular interactions and the softness of the lattice might be advantageous to help identify the carriers of the diffuse interstellar bands. In this article, we present infrared, fluorescence excitation, and dispersed fluorescence spectra of sumanene (C21H12), a bowl-shaped polycyclic aromatic hydrocarbon and a fragment of C60, isolated in solid p-H2. The recorded vibrational wavenumbers from infrared and dispersed fluorescence agree with the scaled harmonic vibrational wavenumbers calculated with the B3PW91/6-311++G(2d,2p) and B3LYP/6-311++G(2d,2p) methods. The recorded fluorescence excitation spectra are consistent with the spectra of jet-cooled gas-phase C21H12 reported previously by Kunishige et al. We found a rather small matrix shift of 55 cm-1 for the S1-S0 electronic transition origin located at 27 888 cm-1. Vibrational wavenumbers associated with the S1 state of C21H12 inferred from the experimental spectrum can be assigned mostly to fundamental normal modes; they are in satisfactory agreement with scaled harmonic vibrational wavenumbers calculated at the TD-B3PW91/6-311++G(2d,2p) level of theory. Significantly more vibrational modes of the S1 state were identified as compared with those in the reported gas-phase work. The potential of p-H2 matrix-isolation spectroscopy to provide electronic excitation spectra suitable for comparison to astronomical observations is discussed by comparing the spectra of C21H12 isolated in solid p-H2 and in solid Ne, a matrix host commonly employed in astrochemistry.

Fluorescence Excitation and Dispersed Fluorescence Spectra of the 1-Hydronaphthyl Radical (1-C10H9) in Solid para-Hydrogen.

Matrix isolation spectroscopy with para-hydrogen (p-H2) has previously been employed to record IR absorption spectra of hydrogenated and protonated polycyclic aromatic hydrocarbons (PAHs), prospective carriers of unidentified infrared and diffuse interstellar bands. Despite the promising prospects of p-H2 as matrix host, especially the rather weak interaction with the guest molecules and the resulting small matrix shifts, p-H2 matrix isolation spectroscopy has rarely been applied to study electronic transitions of guest molecules. Here, we present the dispersed fluorescence and fluorescence excitation spectrum of the 1-hydronaphthyl radical (1-C10H9) isolated in solid p-H2. We observed a strong 000 band associated with the electronic transition to the first excited electronic state at 18881 cm-1, red-shifted by ∼68 cm-1 relative to a value reported for jet-cooled 1-C10H9. From a comparison of our experimental results to simulated vibrationally resolved electronic absorption and emission spectra computed on the basis of (TD-)DFT geometry optimizations and scaled harmonic vibration calculations using the FCclasses code, we derived assignments for observed vibronic transitions. The dispersed fluorescence spectrum of 1-C10H9 is new; it complements the infrared spectrum and identified many vibrational modes unidentifiable with infrared. The excitation spectrum covers a much wider spectral range than previous reports. We compare the excitation spectrum in solid p-H2 to the reported electronic absorption spectrum of jet-cooled gaseous 1-C10H9 and that of 1-C10H9 isolated in solid Ne to assess the influence of p-H2 as a matrix host on the electronic transition of 1-C10H9 and discuss a potential contribution of 1-C10H9 to the diffuse interstellar bands.

Temperature- and pressure-dependent kinetics of the competing C-O bond fission reactions of dimethoxymethane.

Oxymethylene ethers are often considered as promising fuel additives to reduce the emissions of soot and NOx from diesel engines. Dimethoxymethane (DMM) is the smallest member of this class of compounds and therefore particularly suitable to study the reactivity of the characteristic methylenedioxy group (O-CH2-O). In this context, we investigated the pyrolysis of DMM behind reflected shock waves at temperatures between 1100 and 1600 K and nominal pressures of 0.4 and 4.7 bar by monitoring the formation of H atoms with time-resolved atom resonance absorption spectroscopy. Rate coefficients for the C-O bond fission reactions of DMM were inferred from the recorded [H](t) profiles, and a pronounced temperature and pressure dependence of the rate coefficients was found. To rationalize this finding, we characterized the relevant parts of the potential energy surface of DMM by performing quantum chemical calculations at the CCSD(F12*)(T*)/cc-pVQZ-F12//B2PLYP-D3/def2-TZVPP level of theory. On the basis of the results, a two-channel master equation accounting for the two different C-O bond-fission reactions of DMM was set up and solved. Specific rate coefficients were calculated from the simplified Statistical Adiabatic Channel Model. The branching between the two reaction channels was modeled, and the CH3OCH2O + CH3 product channel was found to be clearly dominating. A Troe parameterization for the pressure dependence of this channel was derived. To enable implementation of both channels into kinetic mechanisms for combustion modeling, 'log p' parameterizations of the rate coefficients for both reaction channels are also given and were implemented into a literature mechanism for DMM oxidation. With this slightly modified mechanism, the results of our experiments could be adequately modeled. The role of competing molecular (i.e. nonradical) decomposition channels of DMM was also quantum-chemically checked, but no indications for such channels could be found.

Water does not catalyze the reaction of OH radicals with ethanol.

Recent experiments suggested that water catalyzes the reaction of OH radicals with alcohols, while another work showed the opposite result. Here, we resolve this disagreement and show that heterogeneous oxidation systematically biased the work showing the catalytic effect and corroborate that water does not catalyze the reaction of OH with alcohols.

Pyrolysis of Furan and Its Methylated Derivatives: A Shock-Tube/TOF-MS and Modeling Study.

In this study, the pyrolysis of furan (F) and its two methyl-substituted derivatives 2-methylfuran (2-MF) and 2,5-dimethylfuran (2,5-DMF) was investigated behind reflected shock waves at pressures near 1 bar in Ne as the bath gas. Concentration-time profiles of different stable species (reactants, intermediates, and products) were recorded simultaneously with high-repetition time-of-flight mass spectrometry and compared to results from simulations with a recently published, combined F/2-MF/2,5-DMF oxidation mechanism that was slightly modified already in another publication to describe the formation of H atoms in these pyrolysis systems. The temperature ranges covered in our experiments were chosen in line with the different thermal stabilities of the three reactants (F: T = 1050-1920 K; 2-MF: T = 1060-1900 K; 2,5-DMF: T = 1000-1800 K). In general, we obtained satisfactory agreement of the experimental and modeling results. To clarify the most important reaction routes for the formation of the detected species, we performed extensive sensitivity and rate-of-production analyses. The influence of increasing methylation of the furan ring on the formation and consumption of the different species is discussed in detail. Experimental concentration-time profiles are given in tabular form in the Supporting Information to enable tests of future mechanism developments.

H-Atom-Forming Reaction Pathways in the Pyrolysis of Furan, 2-Methylfuran, and 2,5-Dimethylfuran: A Shock-Tube and Modeling Study.

The methyl-substituted furan derivatives 2-methylfuran (2-MF) and 2,5-dimethylfuran (2,5-DMF) are often discussed as alternative fuels. Despite the large number of mechanistic studies on the pyrolysis and oxidation of 2-MF, 2,5-DMF, and unsubstituted furan (F), detailed kinetic investigations of the initial reaction steps are scarce. In this work, we report on shock-tube studies with detection of hydrogen atoms by atom resonance absorption spectroscopy to investigate the thermal decomposition of F, 2-MF, and 2,5-DMF. Hydrogen atom concentration-time profiles were recorded behind reflected shock waves at temperatures between 1200 and 1900 K and pressures between 0.7 and 1.6 bar with Ar as the bath gas. The recorded profiles were compared with results from kinetic simulations performed on the basis of a joint F/2-MF/2,5-DMF oxidation mechanism recently published. Kinetic parameters for a small number of reactions with high sensitivities for the formation and consumption of H atoms were adapted by taking values from other references to improve the agreement of the experimentally determined and simulated concentration-time profiles. In this way, an adequate description of the H atom concentration-time profiles for all three furan derivatives with the joint mechanism could be achieved. On the basis of this adapted mechanism, the formation pathways of H atoms in the pyrolysis of all three furan derivatives were identified and analyzed. It turned out that the formation of H atoms in the case of 2-MF and 2,5-DMF is governed by a competition between H split-off from the methyl group(s) of the reactant molecule as well as from the primary ring-opening product. In the case of F, only decomposition steps of the ring-opening product are relevant. The adapted mechanism is given in machine-readable form for modeling purposes, and the alterations made are discussed.

TLR9 agonism differentially impacts human NK cell-mediated direct killing and antibody-dependent cell-mediated cytotoxicity.

There are two known mechanisms by which natural killer (NK) cells recognize and kill diseased targets: (i) direct killing and (ii) antibody-dependent cell-mediated cytotoxicity (ADCC). We investigated an indirect NK cell activation strategy for the enhancement of human NK cell killing function. We did this by leveraging the fact that toll-like receptor 9 (TLR9) agonism within pools of human peripheral blood mononuclear cells (PBMCs) results in a robust interferon signaling cascade that leads to NK cell activation. After TLR9 agonist stimulation, NK cells were enriched and incorporated into assays to assess their ability to kill tumor cell line targets. Notably, differential impacts of TLR9 agonism were observed-direct killing was enhanced while ADCC was not increased. To ensure that the observed differential effects were not attributable to differences between human donors, we recapitulated the observation using our Natural Killer-Simultaneous ADCC and Direct Killing Assay (NK-SADKA) that controls for human-to-human differences. Next, we observed a treatment-induced decrease in NK cell surface CD16-known to be shed by NK cells post-activation. Given the essential role of CD16 in ADCC, such shedding could account for the observed differential impact of TLR9 agonism on NK cell-mediated killing capacity.

Development and implementation of natural killer cell simultaneous ADCC and direct killing assay.

Assays to quantify natural killer (NK) cell killing efficacy have traditionally focused on assessing either direct killing or antibody dependent cell-mediated cytotoxicity (ADCC) independently. Due to the probability that immunotherapeutic interventions affect NK cell-mediated direct killing and NK cell-mediated ADCC differently, we developed an assay with the capacity to measure NK cell-mediated direct killing and ADCC simultaneously with cells from the same human donor. Specifically, this design allows for a single NK cell population to be split into several experimental conditions (e.g., direct killing, ADCC), thus controlling for potential confounders associated with human-to-human variation when assessing immunotherapy impacts. Our Natural Killer cell Simultaneous ADCC and Direct Killing Assay (NK-SADKA) allows researchers to reproducibly quantify both direct killing and ADCC by human NK cells. Furthermore, this optimized experimental design allows for concurrent analysis of the NK cells via flow cytometric immunophenotyping of NK cell populations which will facilitate the identification of relationships between NK cell phenotype and the subsequent killing potential. This assay will be valuable for assessing the broader impact(s) of immunotherapy strategies on both modes of NK cell killing.

Adverse cutaneous drug reactions to ibandronate.

Bisphosphonates are frequently used to treat bone diseases characterized by increased osteoclastic bone resorption. Adverse skin reactions to bisphosphonates are rare and range from benign to severe. Different cutaneous skin reactions have been reported with ibandronate in clinical and pharmacovigilance studies, from macula-papular rashes to toxic epidermal necrolysis. We report two new cases of erythematous and oedematous skin lesions to oral monthly ibandronate, appearing after multiple intakes of the drug. Prick tests were positive in both cases at 48 or 96 hours, and one could be confirmed histologically. Lesions did not relapse after substituting the culprit bisphosphonate with another one. A wide range of rare-to-very-rare adverse skin reactions exist with bisphosphonates, and especially ibandronate. We review the reported cases of adverse cutaneous drug reactions to bisphosphonates and illustrate the polymorphism and variety of the skin lesions. These reactions are not well known and may be misdiagnosed as they do not always suggest drug-induced eruptions. Furthermore, delays between drug intake and the first lesions can be misleading. The absence of cross-reactions among bisphosphonates allows substitution.