radical fragment
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Abstract. A new instrument for the measurement of atmospheric nitrous acid (HONO) and hydroxyl radicals (OH) has been developed using laser photofragmentation (LP) of HONO at 355 nm after expansion into a low-pressure cell, followed by resonant laser-induced fluorescence (LIF) of the resulting OH radical fragment at 308 nm similar to the fluorescence assay by gas expansion technique (FAGE). The LP/LIF instrument is calibrated by determining the photofragmentation efficiency of HONO and calibrating the instrument sensitivity for detection of the OH fragment. In this method, a known concentration of OH from the photo-dissociation of water vapor is titrated with nitric oxide to produce a known concentration of HONO. Measurement of the concentration of the OH radical fragment relative to the concentration of HONO provides a measurement of the photofragmentation efficiency. The LP/LIF instrument has demonstrated a 1σ detection limit for HONO of 9 ppt for a 10 min integration time. Ambient measurements of HONO and OH from a forested environment and an urban setting are presented along with indoor measurements to demonstrate the performance of the instrument.

Collision-induced dissociation (CID) is a common fragmentation strategy in mass spectrometry (MS) analysis. A conventional understanding is that fragment ions generated in low-energy CID should follow the even-electron rule. As such, (de)protonated precursor ions should predominately generate (de)protonated fragment ions with very few radical fragment ions (RFIs). However, the extent to which RFIs present in MS2 spectra has not been comprehensively investigated. This work uses the latest NIST 20 tandem mass spectral library to investigate of the occurrence of RFIs in CID MS2 experiments. In particular, RFIs were recognized using their integer double bond equivalent (DBE) values calculated from their annotated molecular formulas. Our study shows unexpected results as 65.4% and 68.8% of MS2 spectra contain at least 10% RFIs by ion-count (total number of ions) in positive and negative electrospray ionization (ESI) modes, respectively. Furthermore, we classified chemicals based on their compound classes and chemical substructures, and calculated the percentages of RFIs in each class. Results show that “Organic 1,3-dipolar compounds” and “Lignans, neolignans and related compounds” are the top 2 compound superclasses which tend to produce RFIs in their CID MS2 spectra. Moreover, aromatic, arylbromide, heteroaromatic, alkylarylether, phenol, and conjugated double bond-containing chemicals are more likely to produce RFIs. We also found four possible patterns of change in RFI percentages as a function of CID collision energy. Finally, we demonstrate that the inadequate consideration of RFIs in most conventional bioinformatic tools might cause problems during in silico fragmentation and de novo annotation of MS2 spectra. This work provides a further understanding of CID MS2 mechanism, and the unexpectedly large percentage of RFIs suggests a need for consideration in the development of bioinformatic software for MS2 interpretation.

Abstract. A new instrument for the measurement of atmospheric nitrous acid (HONO) and hydroxyl radicals (OH) has been developed using laser photofragmentation (LP) of HONO at 355 nm after expansion into a low-pressure cell, followed by resonant laser-induced fluorescence (LIF) of the resulting OH radical fragment at 308 nm similar to the fluorescence assay by gas expansion technique (FAGE). The LP/LIF instrument is calibrated by determining the photo-fragmentation efficiency of HONO. In this method, a known concentration of OH from the photo-dissociation of water vapor is titrated with nitric oxide to produce a known concentration of HONO. Measurement of the concentration of the OH radical fragment relative to the concentration of HONO provides a measurement of the photo-fragmentation efficiency. The LP/LIF instrument has demonstrated a 1σ detection limit of 9 ppt for a 10-min integration time. Ambient measurements of HONO and OH from a forested environment and an urban setting are presented along with indoor measurements to demonstrate the performance of the instrument.

The adsorption and decomposition of the FOX-7 molecule on Al13 clusters were investigated by generalized gradient approximation of the density functional theory. The strong attractive forces between the FOX-7 molecule and aluminum atoms induce the N−O bond breaking of FOX-7. Subsequently, the dissociated oxygen atoms and radical fragment of FOX-7 oxidize the aluminum clusters. The largest adsorption energy is −1020.4 kJ/mol. We also investigated three adsorption reaction paths of the FOX-7 molecule on the Al13 clusters in the A configuration. The activation energy for the adsorption steps are 0.2, 11.4, and 10.2 kJ/mol, respectively, and Al13 is more active than the Al(111) surface and the Al13 cluster performs better in decreasing the adsorption barrier of FOX-7 on the aluminum surface as well. The rate constants of three adsorption paths increase as temperature increases over the temperature range 275–500 K.

The surprising thing about ?Das ?lteste Systemprogramm des deutschen Idealismus. Ein handshriftliher Fund,? one of Rosenzweig?s best supported and most carefully detailed texts, is that he almost completely ignores one of the most stunning and mysterious fragments of this brief, two-page manuscript that he discovers in 1914 at the Prussian State Library in Berlin. Not only that: while discussing and justifying in detail every part of this manuscript, attempting to prove that just because it is in Hegel?s handwriting, does not necessarily mean that Hegel is its author, Rosenzweig completely sidelines the famous, completely anarchistic, and radical fragment about the state. My question then is, why does Rosenzweig leave out any argument about Schelling?s understanding of the state? Or more precisely, how have Schelling?s positions on the state been incorporated and transformed in Rosenzweig?s texts? How does Rosenzweig use these fragments? Why does he nowhere thematize Schelling?s thoughts on the state, or what in eine revolution?re Staatslehre Rosenzweig calls Schelling?s revolutionary teachings on the matter?

The photosensitized (electron transfer) carbon–carbon bond cleavage of 1,1,2,2-tetraphenylethane (1b), 2-(4-methoxy-phenyl)-1,1-diphenyl-2-niethylpropane (1c), 1,1,2-triphenyl-2-methylpropane (1d), and 2-(4-trifluoromethylphenyl)-1,1-diphenyl-2-methylpropane (1e) has been studied with 1,4-dicyanobenzene (2) serving as the electron-accepting sensitizer. The oxidation potential of 1b–e have been measured by cyclic voltammetry. Estimation of the free-energy associated with the electron transfer between these donors (1b–e) and the first excited singlet state of 2, using the Weller equation, indicates the process is favorable in every case. There is, in every case, a one-to-one correspondence of products derived from reaction of the carbocation fragment and from the carbanion derived from the initially formed radical fragment. The efficiency of the reaction of 1b, which gives a good yield of diphenylmethane (3) and methyl diphenylmethyl ether, has been studied as a function of temperature. The observed activation energy (7.2 kcal mol−1) is equated to the bond dissociation energy of the central bond of the radical cation (1b+•). The ratio of products from the unsymmetric compounds is dependent upon the redox potentials of the fragment radicals and carbocations.