Intact Precursors Research Articles

Investigating the combined capability of confocal Raman microscopy and direct analysis in real time-mass spectrometry (DART-MS) for the analysis of intact explosives

The identification of organic and inorganic components used to produce homemade explosives (HMEs) remains a challenge for forensic analysts due to their diverse physicochemical properties that require different instrumentation. This study aims to explore the combined use of direct analysis in real time-mass spectrometry (DART-MS) and Raman microscopy to provide a rapid and reliable analysis of a variety of intact explosives with minimal sample preparation, including 2,4,6-trinitrotoluene (TNT), pentaerythritol tetranitrate (PETN), seven inorganic oxidizing salts, and five smokeless powder constituents. While both techniques were well-suited for the analysis of TNT and PETN, DART-MS had the advantage of being more sensitive compared to Raman spectroscopy for the identification of the organic components contained in smokeless powder. Even though the identification of ammonium-based salts using DART-MS could be achieved, the analysis of low-volatility compounds, such as the inorganic oxidizing salts, was more straightforward with Raman microscopy and did not require sample preparation. This study demonstrates the benefits and limitations of combining Raman microscopy and DART-MS for the analysis of intact explosives and precursors. Using this combined approach enabled the rapid identification of various organic and inorganic explosives and precursors with minimal sample preparation.

Thymectomy in Red Cell Aplasia - A Case Report

1.1. Background: Pure Red Cell Aplasia (PRCA) is a very rare syndrome responsible for severe anemia due to absence or significant reduction of erythroid precursors in the bone marrow. It’s etiology is variable, ranging from a congenital disease to an acquired one. Secondary acquired PRCA may be associated with several conditions, including Thymic Tumors. 1.2. Case Presentation: A 42-year-old male presented to the Internal Medicine department with constitutional symptoms: non-intentional weight-loss, palpitations, somnolence. Clinical investigation showed a severe normocytic normochromic anemia, with significant reticulocytopenia. Due to clinical status, several blood transfusions were needed. Further investigation with bone marrow biopsy showed intact precursors for platelets and leukocytes, with absence of erythroid precursors; the primary diagnostic hypothesis was Pure Red Cell Aplasia, with no etiology well defined, however. In order to rule out other conditions, imaging scans were performed; the chest CT showed a large mediastinal expansive formation, compatible with Thymoma. Patient was submitted to Thymectomy by the Thoracic Surgery team, with posterior improvement of clinical and hemodynamic status. Even so, for definitive remission of the PRCA, a bone marrow transplant was needed. The patient was successfully treated and remains healthy so far.

Symmetrical dehalogenation of 2, 7-dibromopyrene on Cu(1 1 1) with tunable intermediates and reaction paths

On-surface Ullmann coupling has attracted intensive attentions recently owing to its uniqueness at the tailor-made fabrication of conjugated nanostructures with high controllability. However, in-depth understanding of reaction mechanisms has not been fully established yet. Herein, symmetrical dehalogenation of 2, 7-dibromopyrene (Br2Py) on Cu(111) has been investigated in-detail via a combination of scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory. First, deposition of Br2Py onto the precooled Cu(111) results in the self-assembly of intact precursors, while the formation of organometallic (OM) chains is induced on Cu(111) kept at room temperature (RT) after symmetrical dehalogenation due to the relatively high reactivity of Cu at RT. Further, it has been intriguingly discovered that symmetrically debrominated residues can be bound either to copper atoms from substrate leading the formation of close packed species, or to surface adatoms forming the Kagome-like pattern when Cu(111) is held at elevated temperatures during deposition. Nevertheless, covalent organic chains are constructed ultimately from different OM intermediates after stepwise annealing with the fingerprint of structural transition clearly identified. Based on these findings, our report provides appealing insights for the comprehensive understanding of surface Ullmann coupling mechanisms.

Analysis of Intact Glycosidic Aroma Precursors in Grapes by High-Performance Liquid Chromatography with a Diode Array Detector.

Nowadays, the techniques for the analysis of glycosidic precursors in grapes involve changes in the glycoside structure or it is necessary the use of very expensive analytical techniques. In this study, we describe for the first time an approach to analyse intact glycosidic aroma precursors in grapes by high-performance liquid chromatography with a diode array detector (HPLC-DAD), a simple and cheap analytical technique that could be used in wineries. Briefly, the skin of Muscat of Alexandria grapes was extracted using a microwave and purified using solid-phase extraction combining Oasis MCX and LiChrolut EN cartridges. In total, 20 compounds were selected by HPLC-DAD at 195 nm and taking as a reference the spectrum of phenyl β-D-glucopyranoside, whose DAD spectrum showed a first shoulder from 190 to 230 nm and a second around 200–360 nm. After that, these glycosidic compounds were identified by High-performance liquid chromatography–quadrupole time-of-flight mass spectrometry (HPLC-qTOF-MS). Disaccharides hexose pentose were the most abundant group observed with respect to the sugars and monoterpendiols the main aglycones found.

The non-destructive separation of diverse astrobiologically relevant organic molecules by customizable capillary zone electrophoresis and monolithic capillary electrochromatography

AbstractThein situdetection of organic molecules in space is key to understanding the variety and the distribution of the building blocks of life, and possibly the detection of extraterrestrial life itself. Gas chromatography mass spectrometry (GC-MS) has been the most sensitive analytical strategy for organic analyses in flight, and was used on missions from NASA's Viking, Phoenix, Curiosity missions to ESA's Rosetta space probe. While pyrolysis GC-MS revealed the first organics on Mars, this step alters or degrades certain fragile molecules that are excellent biosignatures including polypeptides, oligonucleotides and polysaccharides, rendering the intact precursors undetectable. We have identified a solution tailored to the detection of biopolymers and other biomarkers by the use of liquid-based capillary electrophoresis and electrochromatography. In this study, we show that a capillary electrochromatography approach using monolithic stationary phases with tailor-made surface chemistry can separate and identify various polycyclic aromatic hydrocarbons, nucleobases and aromatic acids that could be formed under astrophysically relevant conditions. In order to simulate flyby organic sample capture, we conducted hypervelocity impact experiments which consisted of accelerating peptide-soaked montmorillonite particles to a speed of 5.6 km s−1, and capturing them in an amorphous silica aerogel of 10 mg cm−3bulk density. Bulk peptide extraction from aerogel followed by capillary zone electrophoresis led to the detection of only two stereoisomeric peptide peaks. The recovery rates of each step of the extraction procedure after the hypervelocity impact suggest that major peptide loss occurred during the impact. Our study provides initial exploration of feasibility of this approach for capturing intact peptides, and subsequently detecting candidate biomolecules during flight missions that would be missed by GC-MS alone. As the monolith-based electrochromatography technology could be customized to detect specific classes of compounds as well as miniaturized, these results demonstrate the potential of the instrumentation for future astrobiology-related spaceflight missions.

Synthesis of Selenoaziridines: A Study on Stereochemical Outcomes of the Reaction of Aziridine Radicals and Anions Generated from Iodoaziridines.

The synthesis of a new functional group in the form of selenyl-substituted aziridines is described. Selenoaziridines are stereoselectively prepared by functionalization of intact aziridine precursors involving radical and anionic intermediates. Radicals are generated from cis-N-Ts iodoaziridines by activation of the C–I bond using alkoxides as a source of single electrons. These form predominantly trans-substituted selenoaziridines dependent on the size of the diselenide. cis-Aziridinyllithiums generated by Li–I exchange also react with diselenides stereospecifically to form a range of cis-selenoaziridines. Proposals for the stereochemical outcome are presented.

A new era for understanding amyloid structures and disease.

The aggregation of proteins into amyloid fibrils and their deposition into plaques and intracellular inclusions is the hallmark of amyloid disease. The accumulation and deposition of amyloid fibrils, collectively known as amyloidosis, is associated with many pathological conditions that can be associated with ageing, such as Alzheimer disease, Parkinson disease, type II diabetes and dialysis-related amyloidosis. However, elucidation of the atomic structure of amyloid fibrils formed from their intact protein precursors and how fibril formation relates to disease has remained elusive. Recent advances in structural biology techniques, including cryo-electron microscopy and solid-state NMR spectroscopy, have finally broken this impasse. The first near-atomic-resolution structures of amyloid fibrils formed in vitro, seeded from plaque material and analysed directly ex vivo are now available. The results reveal cross-β structures that are far more intricate than anticipated. Here, we describe these structures, highlighting their similarities and differences, and the basis for their toxicity. We discuss how amyloid structure may affect the ability of fibrils to spread to different sites in the cell and between organisms in a prion-like manner, along with their roles in disease. These molecular insights will aid in understanding the development and spread of amyloid diseases and are inspiring new strategies for therapeutic intervention.

Novel archaeal tetraether lipids with a cyclohexyl ring identified in Fayetteville Green Lake, NY, and other sulfidic lacustrine settings.

The meromictic Fayetteville Green Lake (FGL) is of significant geobiological interest because of microbial cycling of sulfur within and below the permanent chemocline and in the euxinic deep waters. Studies of glycerol dibiphytanyl glycerol tetraethers (GDGTs) may help shed light on understanding the activity of archaeal communities in these habitats. Normal-phase and reversed-phase liquid chromatography/mass spectrometry (LC/MS) analysis on total lipid extracts of environmental samples revealed series of GDGTs with different biphytane structures. Comparison of the mass spectrum of biphytane obtained from separated novel GDGTs with that of a synthetic C40 biphytane confirms our structural assignments. A unique cyclohexyl ring configured in the middle of a C40 biphytane chain was identified in these novel GDGTs. We suggest the trivial name S-GDGTs for these compounds, where 'S' stands for 'sulfidic' and 'six-membered ring'. S-GDGT derivatives composed of biphytanes modified with double bonds and cyclopentane rings were also detected in the samples we analyzed. Intact polar lipid precursors of S-GDGT include compounds with mono- and diglycosyl head groups. The carbon isotopic composition of S-GDGTs and their occurrence in FGL, Messel Shale as well as Salt Pond and salt marshes on Cape Cod suggest that S-GDGTs may be produced by chemoautotrophic archaea that prefer sulfidic conditions. Copyright © 2016 John Wiley & Sons, Ltd.

Microbial biotransformation of polyphenols during in vitro colonic fermentation of masticated mango and banana

Mango and banana cell structures, which survived in vivo mastication and in vitro gastrointestinal digestion, were fermented in vitro for 48h. For both fruits, flavonoids and phenolic acids were liberated and underwent microbial metabolism involving ring fission, dehydroxylation and decarboxylation. UHPLC-PDA/Q-ToF-MS profiles revealed rapid degradation (72–78%) of most intact precursors (epicatechin and several unidentified compounds) within 10h, before the exponential phase of the cumulative gas production. Concomitant formation of catabolites (e.g. 4-hydroxyphenylacetic acid) occurred within 4–8h, while metabolism of catechin derivative and 3-(4-hydroxyphenyl)propanoic acid continued slowly for at least 48h, suggesting intact plant cell walls can be a controlling factor in microbial susceptibility. Untargeted PCA and OPLS-DA demonstrated clear classifications in the compositional fruit type and compound profiles as a function of time. Clusters and distinct discriminating compounds were recognised, which could lead to subsequent biomarker identification for establishing differences in polyphenol microbial metabolism of various fruit matrices.

Rapid identification and quantitative analysis of the chemical constituents in Scutellaria indica L. by UHPLC–QTOF–MS and UHPLC–MS/MS

Ultra high performance liquid chromatography (UHPLC) coupled with a hybrid quadrupole time-of-flight mass spectrometry (QTOF–MS) was used to separate and identify the compounds in Scutellaria indica L. Fragmentation patterns of these compounds were investigated by the UHPLC–QTOF–MS technique in both negative and positive ion modes. By using this strategy, both intact precursors and fragment ions information were obtained from a single injection. A total of 42 phenolic and other compounds were unequivocally or tentatively identified from S. indica for the first time. Among them, 8 phenolic compounds: scutellarin, luteolin, naringenin, wogonoside, apigenin, hispidulin, wogonin and chrysin were further quantified and used as marker substances by multiple-reaction monitoring in negative ionization mode. The results demonstrated that the calibration curves for all analytes showed good linearity (R2>0.9992) within the test ranges. The overall limits of detection and limits of quantification were 0.12–10.52ng/mL and 4.67–20.22ng/mL, respectively. The recovery was 96.02–102.88% with a relative standard deviation of less than 3.02%. It is proposed that the methods described here can be applied for rapid evaluation, quality control and authenticity establishment of S. indica.

Effects of growth phase on the membrane lipid composition of the thaumarchaeon Nitrosopumilus maritimus and their implications for archaeal lipid distributions in the marine environment

The characteristic glycerol dibiphytanyl glycerol tetraether membrane lipids (GDGTs) of marine ammonia-oxidizing archaea (AOA) are widely used as biomarkers for studying their occurrence and distribution in marine environments and for reconstructing past sea surface temperatures using the TEX86 index. Despite an increasing use of GDGT biomarkers in microbial ecology and paleoceanography, the physiological and environmental factors influencing lipid composition in AOA, in particular the cyclization of GDGTs, remain unconstrained. We investigated the effect of metabolic state on the composition of intact polar and core lipids and the resulting TEX86 paleothermometer in pure cultures of the marine AOA Nitrosopumilus maritimus as a function of growth phase. The cellular lipid content ranged from 0.9 to 1.9fgcell−1 and increased during growth but was lower in the stationary phases, indicating changes in average cell size in response to metabolic status. The relative abundances of monoglycosidic GDGTs increased from 27% in early growth phase to 60% in late stationary phase, while monohydroxylated GDGTs increased only slightly. The proportions of characteristic hexose-phosphohexose GDGTs were up to 7-fold higher during growth than in stationary phase, suggesting that they are valuable biomarkers for the metabolically active fraction of AOA assemblages in the environment. Methoxy archaeol was identified as novel, genuine archaeal lipid of yet unknown function; it is one of the most abundant single compounds in the lipidome of N. maritimus. TEX86 values of individual intact GDGTs and total GDGTs differed substantially, were generally lower during early and late growth phases than in stationary phase, and did not reflect growth temperature. Consequently, our results strongly suggest that biosynthesis is at least partially responsible for the systematic offsets in TEX86 values between different intact polar GDGT classes observed previously in environmental samples. Nevertheless, differences in degradation rates of intact polar GDGTs may influence the TEX86 index because the intact polar lipid precursors differ for individual core GDGTs and moreover their relative abundances change with growth stage, which may result in distinct release rates of core GDGTs from their polar precursors. Overall, our findings stress the need to accurately describe the factors influencing GDGT cyclization in thaumarchaea and thus paleotemperature reconstructions.

Isolation of intact glycosidic aroma precursors from grape juice by hydrophilic interaction liquid chromatography

Background and Aims Aroma precursors in grape juice include glycosylated terpenoids or benzenoids. The separation of these polar substances has been achieved by several chromatographic techniques but often after the esterification of the sugar hydroxyls. We aimed to develop a high-performance liquid chromatography method to isolate the glycoconjugates in their natural form. Methods and Results The glycoside fraction was extracted from fresh grape juice, treated with lead (II) acetate to precipitate phenolic compounds and finally separated by hydrophilic interaction liquid chromatography. Three compounds were isolated, and their structures elucidated by means of spectroscopic data; one revealed previously unreported structural features. Conclusions Our hydrophilic interaction liquid chromatography method has been proven effective for the purification of the complex blend of many chemical compounds that contribute to grape and wine flavour. Significance of the Study The present article proposes a new, straightforward procedure for the isolation of flavour glycoconjugates.

Identification of polar lipid precursors of the ubiquitous branched GDGT orphan lipids in a peat bog in Northern Germany

Two types of intact branched glycerol dialkyl glycerol tetraethers (GDGTs) were detected in peat bog samples from Bullenmoor, Northern Germany. Glucuronosyl and glucosyl branched GDGTs comprise on average ca. 4% of the microbial intact polar lipids in the anoxic, acidic peat layer ca. 20 cm below the surface of the bog, suggesting an important ecological role for the source microorganisms. No corresponding phospholipids were detected. Notably, glycosidic branched GDGTs are 5–10 times less abundant than their intact isoprenoid counterparts derived from Archaea, while branched GDGT core lipids exceed their isoprenoid analogues by about an order of magnitude. These contrasting relationships may reflect lower standing stocks of the biomass of producers of branched GDGTs, combined with higher population growth rates relative to soil Archaea. Search strategies for the microbial producers of these conspicuous orphan lipids should benefit from the discovery of their intact polar precursors.

Positive and negative tandem mass spectrometric fingerprints of lipids from the halophilic Archaea Haloarcula marismortui

Lipids from the extremely halophilic Archaea, Haloarcula marismortui, contain abundant phytanyl diether phospholipids, namely archaetidic acid (AA), archaetidylglycerol (AG), archaetidylglycerosulfate (AGS), with mainly archaetidylglycerophosphate methyl ester (AGP-Me). These were accompanied by a triglycosyl archaeol (TGA), lacking characteristic sulfate groups. Tandem-mass spectrometry was employed to provide fingerprints for identifying these known lipids, as well as small amounts of unsaturated phospholipids. These contained 3 and 6 double bonds in their archaeol moiety, suggested by negative tandem-MS of intact phospholipids, as indicated by differences between their pseudo-molecular ion and specific fragment ions designated as pi(2). The core ether lipids were confirmed by electrospray ionization mass spectrometry (ESI-MS) as 2,3-di-O-phytanyl-sn-glycerol (C20, C20), which gave rise to a precursor-ion at m/z 660 [M+Li](+), and its fragment ion at m/z 379 [M+Li](+), consistent with mono-O-phytanyl-glycerol. Furthermore, lithiated ions at m/z 654 (MS(1)), 379 (MS(2)) and m/z 648 (MS(1)), 373 (MS(2)), combined with (1)H/(13)C NMR chemical shifts at delta 5.31-121.6 (C2/2'-H2/2'), 5.08-124.9 (C6/6'-H6/6') and 5.10-126.0 (10/10'-H10/10') confirmed the presence of unsaturated homologs of archaeol. We carried out a comprehensive study on the lipids present in cells of H. marismortui. We used positive and negative ESI-MS with tandem-MS, which served as a fingerprint analysis for identifying the majority of component lipids.

Simultaneous tracing of multiple precursors each labeled with a different homo-elemental isotope by speciation analysis: Distribution and metabolism of four parenteral selenium sources

Abstract The availability, distribution, and metabolism of four typical selenium sources [inorganic selenite and selenate, and organic selenomethionine (SeMet) and methylselenocysteine (MeSeCys)] were compared by administering them simultaneously through a parenteral route. The four selenium sources were each labeled with a different enriched selenium isotope (82Se, 78Se, 77Se, and 76Se, respectively), and administered intravenously at the dose of 25 μg Se/kg body weight each to rats that had been depleted of natural abundance selenium with a single isotope, 80Se, by feeding 80Se-selenite in drinking water and a selenium-deficient diet. At 1 h post-injection, the amounts of the four tracers recovered from major organs and blood comprised around 70, 55, and 50 % of the doses for selenite, MeSeCys and SeMet, and selenate, respectively, being most abundant in the liver. The intact precursors, except for selenite, were recovered from all organs. 77Se and 76Se of SeMet and MeSeCys origin, respectively, were much more efficiently recovered from the pancreas than selenite and selenate, in forms mostly bound to proteins together with intact forms, suggesting that SeMet and MeSeCys are preferentially distributed directly to the pancreas. The incorporations of selenium into selenoprotein P (Sel P) and selenosugars were most efficient from selenite and less efficient from SeMet, suggesting that selenite was most efficiently utilized for the syntheses of selenoproteins and selenosugars. Although selenate was partly excreted into the urine in its intact form, it was retained longer in the plasma in its intact form than the other selenium sources. The advantage of simultaneous administration of multiple precursors each labeled with a different enriched isotope to depleted hosts followed by simultaneous tracing of the labeled isotopes over the conventional method with a single tracer is emphasized together with cautions that may occur with the new multiple tracer method.

Human cerebrospinal fluid peptidomics

Cerebrospinal fluid (CSF) has frequently been extensively studied to explore several different central nervous system (CNS) disorders because it contains proteins, enzymes, hormones, neuropeptides and neurotransmitters that play critical regulatory roles in many different physiological processes. Individual neuropeptidergic systems in CSF have been studied. In theory, peptidomics offers a bird's-eye, comprehensive and systems-level approach to analyze all of the peptidergic systems that have been expressed in CSF at any given time. In this study, low molecular mass (M(r) < 5 kDa) peptides were isolated by ultrafiltration. The isolated peptides, with or without trypsin digestion, were preferentially enriched with a solid-phase extraction cartridge, and the peptides were separated with capillary liquid chromatography and analyzed with on-line quadrupole time-of-flight mass spectrometry (MS). In this proof-of-principle study, the 20 representative MS-characterized peptides were shown to be derived from 12 proteins, among which four proteins, amyloid-like protein 1, secretogranin I, granin-like neuroendocrine peptide precursor and neurosecretory protein VGF, have been shown elsewhere to be either associated with CNS disorders or to play a central role in the CNS. The long-term goals of this peptidomics study are to monitor the changes (amount; modifications) of CSF peptides, clarify the aberrant processing of large intact protein precursors, elucidate the molecular mechanisms of CNS disorders and find biomarkers. This analytical method is effective for the analysis of the human lumbar CSF peptidome.

Plasma Deposition and Surface Characterization of Oligoglyme, Dioxane, and Crown Ether Nonfouling Films

Plasma-deposited PEG-like films are emerging as promising materials for preventing protein and bacterial attachment to surfaces. To date, there has not been a detailed surface analysis to examine the chemistry and molecular structure of these films as a function of both precursor size and structure. In this paper, we describe radio-frequency plasma deposition of a series of short-chain oligoglymes, dioxane, and crown ethers onto glass cover slips to create poly(ethylene glycol)-like coatings. The resultant films were characterized by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), dynamic contact angle goniometry, and radiolabeled fibrinogen adsorption. Detailed analysis of the high-mass (120-300 m/z) TOF-SIMS oligoglyme film spectra revealed six classes of significant fragments. Two new models are proposed to describe how these fragments could be formed by distinct film-building processes: incorporation of intact and fragmented precursor molecules. The models also provide for the incorporation of hydrocarbon--a species that is not present in the precursors but is evidenced in XPS C(1s) spectra of these films. Two additional models describe the effects of incorporating intact and fragmented cyclic precursors.

Sulfur and Nitrogen Availability Interact to Affect the Flavor Biosynthetic Pathway in Onion

To determine the extent to which sulfur (S) and nitrogen (N) fertility interact to influence the flavor biosynthetic pathway in onion (Allium cepa L.), `Granex 33' onions were grown in hydroponic solution culture with varying levels of S and N availability. Plants were grown at 5, 45, or 125 mg·L-1 sulfate (SO42-), and 10, 50, 90, or 130 mg·L-1 N, in a factorial combination. Total bulb S, total and individual flavor precursors and their peptide intermediates in intact onion tissue were measured. To measure the effect of S and N on alliinase activity, flavor precursors were also measured in onion macerates. Sulfur and N availability in the hydroponics solution interacted to influence all flavor compounds except S-methyl-L-cysteine sulfoxide. Levels of S-methyl-L-cysteine sulfoxide were influenced by N and S levels in the solutions; however, no interaction was present. At the lowest SO 42- or N levels, most precursors and peptides measured were present in very low concentrations. When SO 42- or N availability was adequate, differences among flavor compounds were small. Results indicated that S fertility had a greater influence on trans-S-1-propenyl-L-cysteine sulfoxide (1-PRENCSO) accumulation, while N availability had a greater influence on S-methyl-L-cysteine sulfoxide levels. Flavor precursors remaining in the onion macerates revealed that the percentage of intact precursors hydrolyzed by alliinase were not significantly influenced by either SO 42- or N levels in the solutions, except for 1-PRENCSO, which was affected by N levels. Nitrogen and S fertility interacted to influence the flavor biosynthetic pathway and may need to be considered together when manipulating onion flavor compounds.

New doser for chemical vapor deposition of low vapor-pressure solid precursors

In this article we describe a new ultrahigh vacuum compatible device to maximize the volatilization of low vapor-pressure precursors used in chemical vapor deposition processes while minimizing their dissociation. A differentially pumped system that places the precursor close to the target substrate was adopted to achieve this configuration; it also allows loading and unloading of the precursor reservoir without breaking vacuum. The device permits the volatilization of low vapor-pressure solid precursors by passing a preheated carrier gas through the precursor which is placed between two fritted disks. This device was also used without a carrier gas and proved its efficiency. The complexes (1,1,1,5,5,5-hexafluoropentanedionato)(1,5-cyclooctadiene) copper (I), [(hfac)Cu(COD)], and (1,1,1,2,2,3,3-heptafluoro-7, 7-dimethyl-4, 6-octanedionato) (trimethylphosphine) silver (I), [(fod)AgPMe3], proved the efficacy of this doser in delivering intact precursors to the substrate using reflection-absorption infrared spectroscopy and mass spectrometry techniques during the adsorption of these precursors on polished Al disks and on polyurethane thin films spun cast onto similar polished Al disks.

Further direct evidence for stepwise dissociation of acetone and acetone clusters

The (pre)dissociation of acetone and acetone clusters after excitation to states corresponding to upper {S1,T1} and 3s Rydberg states of the acetone monomer are investigated through femtosecond pump–probe experiments coupled with molecular beam time-of-flight mass spectrometry techniques. Upon excitation to either state, [(CH3)2CO]n* dissociates rapidly. Acetyl fragments, [(CH3)2CO]n−1CH3CO+ may arise from ionization of an excited species formed by (pre)dissociation of intact precursors or by dissociation after the intact species has been ionized. The method employed to separate these two channels is discussed herein; the resulting transients are fit to a kinetic model to elucidate intermediate lifetimes and dissociation mechanisms. The present experiments establish that a stepwise dissociation mechanism is operative upon excitation to the 3s Rydberg state for the acetone monomer and dimer, with their corresponding acetyl fragments having lifetimes on the order of picoseconds. Larger cluster species, [(CH3)2CO]n (n≳2), do not exhibit the predissociative behavior evident in the monomer and dimer. Conversely, dissociation upon excitation to the {S1,T1} state exhibits an initial loss of a methyl unit, with the acetyl intermediate being considerably more stable than those created by dissociation of acetone from higher lying states. A strong dependence on the internal energy available after the dissociation event is noted.