RESUMO
Plant volatiles are emitted by plants in response to several forms of stress, including interaction with energetic photons. In the present work, we discuss the interaction of extreme UV and soft X-ray photons with a plant volatile, vanillin. The single and double (multiple) ionization of the vanillin molecule have been studied for the first time using time-of-flight mass spectrometry and VUV and soft X-ray photons (synchrotron radiation, at 12.0 eV, 21.2 eV, 130 eV, 310 eV, 531 eV, and 550 eV). At 12.0 and 21.2 eV, only singly charged species are observed and the parent ion, C8H8O3 (+), is the dominant species. Energy differences for some selected fragments were calculated theoretically in this energy region. At 130 eV, direct double and triple ionization of the valence electrons may occur. The fragmentation increases and CHO(+) becomes one of the main cations in the mass spectrum. The molecular ion is still the dominant species, but other fragments, such as C6H5O(+), begin to present similar intensities. At 310 eV, C 1s electrons may be ionized and Auger processes give rise to dissociative doubly ionized cations. Ionization around the O 1s edge has been studied both at the 531 eV resonance and above the ionization edge. Resonant and normal Auger processes play a significant role in each case and a large fragmentation of the molecule is observed at both photon energies, with intense fragments such as CHO(+) and CH3 (+) being clearly observed. A near edge X-ray absorption fine structure spectrum of the vanillin molecule was obtained around the O 1s ionization threshold. In addition, the fragmentation of vanillin has also been studied using a fast beam of electrons (800 eV), for the sake of comparison.
Assuntos
Benzaldeídos/efeitos da radiação , Compostos Orgânicos Voláteis/efeitos da radiação , Benzaldeídos/química , Espectrometria de Massas , Modelos Químicos , Fótons , Espectrofotometria , Raios Ultravioleta , Compostos Orgânicos Voláteis/química , Raios XRESUMO
Electronic excitation and ionic dissociation of dimethylsulfide (DMS) and dimethyldisulfide (DMDS) have been studied around the S 2p edge using synchrotron radiation and time-of-flight mass spectrometry techniques. Mass spectra were obtained for both molecules, below, on and above the well defined resonances observed in the S 2p photoabsorption spectrum and centered at approximately 166 eV photon energy. Ab initio IS-CASSCF calculations were performed for a better understanding of the photoabsorption spectra. Similar calculations were also performed for the H(2)S molecule, in order to establish a bench mark. For both molecules, a higher fragmentation degree is observed with increasing photon energy. In the DMDS case, selective fragmentation was observed in the formation of the [CH(n)S](+) ions at the first S 2p resonance (corresponding to excitation to a σ*SS state) and in the formation of the [S(2)](+) and [S](+) ions at the third S 2p resonance (corresponding to excitation to a σ*CS state). Previously unreported doubly charged ([S](2+), [CH(3)](2+)) are observed for DMS and DMDS.
Assuntos
Dissulfetos/química , Elétrons , Sulfetos/química , Absorção , Espectrometria de Massas , Modelos Moleculares , Conformação Molecular , Teoria QuânticaRESUMO
INTRODUCTION: Airway management is the most critical and potentially life-saving intervention performed by emergency medical service (EMS) providers. Invasive airway management often is required in non-cardiac-arrest patients who are combative or otherwise uncooperative. The success of prehospital invasive airway management in this patient population was evaluated. METHODS: A retrospective review was undertaken of the records of all such patients requiring endotracheal intubation over a three-year period (1987-1989). The study population included 278 patients enrolled by five advanced life support (ALS) units serving a suburban population of 425,000. Field trip sheets were reviewed for diagnosis, intubation method and success, number of intubation attempts, provider experience, reasons for unsuccessful intubations, and complications. RESULTS: A total of 394 invasive airway management attempts were performed on 278 patients. The overall successful intubation rate was 75% (41% orotracheal, 52% nasotracheal, 7% other or unknown). The most common diagnoses were COPD and pulmonary edema (30%) and trauma (24%). Experienced providers were successful on the first attempt in 57% of cases compared to 50% by inexperienced providers (p=.24). Multiple intubation attempts were required in 33% of the patients. There was no statistically significant difference in success rates between the orotracheal and nasotracheal methods (p=.51). The most common reason for unsuccessful intubation was altered level of consciousness. Complications occurred with 7% of successful attempts and in 18% of unsuccessful attempts (p less than .001). Forty-six percent of the patients who were not intubated successfully in the field and required intubation in the emergency department (ED) received a neuromuscular blocking agent prior to successful intubation. CONCLUSION: Prehospital providers can intubate a high but improvable proportion of non-cardiac-arrested patients by both the orotracheal and nasotracheal routes. The use of pharmacologic adjuncts to facilitate the prehospital intubation of selected, non-cardiac-arrested patients is a promising adjunct that needs further evaluation.