Electron Impact Mass Spectrometry Research Articles

Formation of Previously Undescribed Δ7-Phytosterol Oxidation Products and Tocopherylquinone Adducts in Pumpkin Seed Oil during Roasting, Screw-Pressing, and Simulated Culinary Processing at Elevated Temperatures.

The influence of pumpkin seed roasting conditions (110-140 °C) and screw-pressing on the formation of previously undescribed Δ7-phytosterol oxidation products and tocopherylquinone adducts with nucleophilic phosphatidylethanolamine species was investigated. The roasting process of pumpkin seed paste at a temperature above 120 °C for 30 min considerably enhanced the formation of Δ7-oxysterols. Targeted analysis [electron impact mass spectrometry (MS), 1D-nuclear magnetic resonance] led to the identification of five novel markers of pumpkin paste roasting, among which (3β,5α,22E,24S)-stigmasta-7,22-dien-6-one-3-ol (6-oxo-α-spinasterol), stereoisomers of (3β,5α,22E)-7,8-epoxystigmast-22-en-3-ol (7,8-epoxy-α-spinasterol), and (3β,5α)-22,23-epoxystigmast-7-en-3-ol (7,8-epoxy-α-spinasterol) were reported in edible oils for the first time. Simulated culinary processing provided novel stereoisomers of (3β,5α,22E)-stigmasta-7,22-dien-3,6-diol, unusual (3β,5α,22E)-stigmasta-7,22-dien-6,15-dione-3-ol, and (5α,22E)-stigmasta-7,22-dien-3-one accompanied by minor stereoisomers of (3β,5α)-7,8;22,23-diepoxystigmastan-3-ol. Moreover, a clear relationship between the pumpkin seed oil stability index and synergistic effect of glycerophospholipids with present tocochromanols was found. High-resolution atmospheric pressure chemical ionization-MS experiments clearly demonstrated the formation of various γ-tocopherylquinone adducts with primary amines, namely, octylamine. The mitigation strategy of potentially detrimental oxysterols from pumpkin seed oil included optimization of processing parameters while maintaining the formation of desirable sensory-active compounds.

Highly Photosensitive Lead Sulfide Thin Films Grown by H2 S Free MOCVD Using a Single Source Metal-Organic Precursor.

High-quality lead sulfide (PbS)films are deposited on selected substrate chemistries by an H2 S-free metal-organic chemicalvapordeposition (MOCVD) process using a single-source metal-organic complex (Pb(dmampS)2 ). The complex is synthesized via a salt metathesis reaction betweenPbCl2 andlithium1-(dimethylamino)-2-methylpropane-2-thiolate (Li(dmampS))in diethyl ether. Subsequent film deposition is conducted by a simple thermolysis process in the absence of H2 S, yet chemical and structural analysis confirm chemically stoichiometric and homogenous films. Mechanistic studies with electron impact mass spectroscopy (EIMS) and gas chromatography mass spectroscopy (GCMS) suggest the selective cleavage of C-S bonds in the complex as the reason for the facile PbS formation with negligible impurity incorporation. The high crystallinity, low hole concentrations, and charge transport properties comparable and in many cases superior to films produced by atomic layer deposition (ALD) testify to the quality of the films. Lastly, rigid and flexible photodetectors fabricated with the PbS films exhibit considerably high photocurrents, reliable switching characteristics, and high sensitivity over a broad spectral bandwidth, highlighting the potential for realizing practical broadband photodetectors.

Isolation and characterization of β-sitosterol, oleanolic, 19- dehyroursolic and yarumic acids, from Plectranthus esculentus leaves and tubers

Plectranthus esculentus N.E.Br. (family Lamiaceae) also known as Livingstone potato (vat or rizga in Nigeria), is a dicotyledonous perennial shrub growing up to 2 m tall. While it is cultivated mainly for its edible tubers, the plant is potentially valuable as phytomedicine. Three varieties (vat-long’at, vat-riyom and vat-bebot) are well known among the Berom of Plateau State, Nigeria. The vat-bebot variety (which showed good promise in bioactivity studies) was used in this study. The leaves and tubers were extracted successively with hexane, ethyl acetate, methanol and water. Fractionation of the active ethyl acetate extracts was carried out using open column and preparative High Performance Liquid Chromatography (prep HPLC). This led to the isolation of β-sitosterol and oleanolic acid from the leaves; while 19-dehydroursolic acid and yarumic acid, as well as β-sitosterol were isolated from the tubers. Nuclear Magnetic Resonance (NMR) and Electron Impact Mass Spectroscopy (EIMS) were used to characterize isolated compounds. Comparing acquired spectral data of isolated compounds with those from literature helped to confirm the identity of the compounds. The isolation and characterisation of these compounds, from Plecthranthus esculentus, have not been hitherto reported in literature.

Antimicrobial and anti-biofilm activity of manuka essential oil against Listeria monocytogenes and Staphylococcus aureus of food origin.

The activity of manuka (Leptospermum scoparium) essential oil (EO) on biofilms of foodborne Listeria monocytogenes and Staphylococcus aureus has been studied. Seven strains of L. monocytogenes and 7 of S. aureus (5 methicillin-resistant) were tested. EO minimal inhibitory concentration (MIC), EO minimal bactericidal concentration (MBC) and biofilm production quantification were determined for each strain by microtiter methods. Moreover, EO Minimum Biofilm Inhibitory Concentration (MBIC) and Minimum Biofilm Eradicating Concentration (MBEC) were determined on 2 L. monocytogenes and 3 S. aureus that showed the best biofilm production. Finally, on 4 strains out of 5 (2 L. monocytogenes and 2 S. aureus) EO Biofilm Reduction Percentage (BRP) vs. untreated controls was assessed after a treatment with EO subinhibitory concentrations. The chemical composition of manuka essential oil was determined by Gas Chromatography- Electron Impact Mass Spectrometry (GCEIMS). The manuka EO demonstrated good antimicrobial activity: L. monocytogenes MIC and MBC were 0.466 mg/ml and 0.933 mg/ml, respectively, whereas S. aureus MIC and MBC were 0.233 mg/ml and 0.466 mg/ml, respectively. Furthermore, L. monocytogenes showed a MBIC of 0.933 mg/ml and a MBEC in the range of 0.933–1.865 mg/ml, whereas S. aureus had a MBIC in the range of 7.461–14.922 mg/ml and a MBEC of 14.922 mg/ml. L. monocytogenes revealed no significant BRP after the treatment with manuka EO, whereas S. aureus showed a BRP higher than 50% with MIC/2 and MIC/4 EO concentrations. These results provide information for feasible manuka EO applications in food production systems.

Development of conditions for Pyrazidol identification in the urine in the presence of its biotransformation products by thin layer chromatography and mass spectrometry

For the analytical diagnosis of drug poisoning, it is important to develop conditions for the detection of both native compounds and products of their biotransformation in biological samples. Aim. To develop a method for isolating the antidepressant drug Pyrazidol from the human urine in the presence of its biotransformation products and determine the conditions that are suitable for analytical diagnostics of thymoleptic intoxication for their detection by thin layer chromatography. Materials and methods. The study was conducted with the human urine samples collected after taking a single therapeutic dose of Pyrazidol. The urine was subjected to the acid hydrolysis, and the antidepressant and its metabolites were extracted from the hydrolysate with chloroform from an alkaline medium at pH 8-9. Concomitant endogenous admixtures were removed by extraction with diethyl ether from an acidic medium at pH 1. For the chromatographic study of the extracts, four mobile phases recommended by the International Association of Forensic Toxicologists for TLC screening of drugs, and Merck chromatographic plates were used. Color reactions were performed on pieces of chromatographic plates with a number of chromogenic reagents most commonly used in chemico-toxicological analysis. Metabolites were identified by electron impact mass spectrometry. Results and discussion. The native substance and dehydropyrazidol were detected in the urine hydrolysates by TLC, their chromatographic mobility parameters in four TLC screening systems, as well as the results of their color reactions with the chromogenic reagents were determined. Conclusions. Conditions for isolating Pyrazidol and its biotransformation product from the urine have been proposed. The method for detecting the native compound and dehydropyrazidol in the urine extracts by TLC and mass spectrometry after taking a single therapeutic dose of the drug has been developed. The method is recommended for use in the practice of forensic and clinical toxicology.

Copper(II) Perfluorinated Carboxylate Complexes with Small Aliphatic Amines as Universal Precursors for Nanomaterial Fabrication.

Copper(II) carboxylate compounds with ethylamine and isopropylamine of the general formula [Cu2(RNH2)2(µ-O2CRf)4], where R = Et, iPr, and Rf = CnF2n+1, n = 1–6, were characterised in the condensed and gas phases by electron impact mass spectrometry (EI MS), IR spectroscopy, and thermal analysis. A mass spectra analysis confirmed the presence of metallated species in the gas phase. Among the observed fragments, the pseudomolecular ions [Cu2(RNH2)2(µ-O2CRf)3]+ were found, which suggests the dimeric structure of the studied complexes with axially N-coordinated ethyl- or isopropylamine molecules and bridging perfluorinated carboxylates. TGA studies demonstrated that copper transfer to the gas phase occurs even under atmospheric pressure. The temperature range of the [Cu2(RNH2)2(µ-O2CRf)4] and other copper carriers detection, observed in variable temperature infrared spectra, depends on the type of amine. The possible mechanisms of the decomposition of the tested compounds are proposed. The copper films were produced without additional reducing agents despite using Cu(II) CVD precursors in the chemical vapor deposition experiments. The layers of the gel-like complexes were fabricated in both spin- and dip-coating experiments, resulting in copper or copper oxide materials when heated. Dinuclear copper(II) carboxylate complexes with ethyl- and isopropylamine [Cu2(RNH2)2(µ-O2CRf)4] can be applied for the formation of metal or metal oxide materials, also in the nanoscale, by vapour and ‘wet’ deposition methods.

Microhardness and Fluoride Release of Glass Ionomer Cement Modified with a Novel Al+3 Complex to Enhance Its Antimicrobial Activity.

Objectives To synthesize and characterize a novel Al+3 complex with 2-(2-hydroxyphenyl)-1H-benzimidazole (HL) to be added to a restorative glass ionomer cement (GIC) to enhance its antimicrobial activities and to evaluate the Vickers microhardness (HV) and fluoride release (FR) of the modified GIC. Materials and Methods Al+3 complex was synthesized by the addition of 1 mmol (0.210 g) of HL to 1 mmol (0.342 g) of aluminum sulfate in ethanol. The resulting solution was then refluxed under stirring for 24 h and then collected by filtration and dried in a vacuum desiccator over an anhydrous CaCl2. Characterization of Al+3 complex was carried out by Fourier transform infrared spectroscopy (FTIR), elemental microanalysis, thermal gravimetric analysis (TGA), molar conductance, 1H NMR spectra, and electron impact-mass spectrometry. The antimicrobial activity of Al+3 complex-modified GIC (Al-GIC) was studied by the “cut plug method” against Gram-negative bacteria (Acinetobacter baumannii) and Gram-positive bacteria (Staphylococcus aureus, Enterococcus, and Streptococcus mutants) and fungi (Candida albicans). HV was evaluated by a digital microhardness tester (Zwick/Roell, Indentec, ZHVμ-S, West Midlands, England). Fluoride levels in ppm were obtained using the ion-selective electrode connected to a digital meter. A one-way ANOVA and Bonferroni test were used to analyze the data with the significance level established at p ≤ 0.05. Results Synthesis of Al+3 complex was confirmed by FTIR, elemental microanalysis TGA, molar conductance, 1H NMR spectra, and electron impact-mass spectrometry. Al-GICs exhibited an enhanced antibacterial activity against all studied microorganisms as confirmed by the growth of inhibition zones compared to control GIC (C-GIC). Though there was a slight reduction in HV and FR with increasing the added percent of Al+3 complex, no significant differences were found between the studied groups. Conclusions Addition of Al+3 complex to GIC powder enhanced the antimicrobial activity of GIC materials. As there was a negligible insignificant reduction in HV and FR upon the addition of Al+3 complex, Al-GICs can be used with a guaranteed degree of clinical success.

A 1D silver(I) coordination polymer of a new hydrozone-hydrazide ligand: Spectral, structural, emission, and anti-bacterial properties and its application as a solid source precursor for silver oxide nanoparticles

A new one-dimensional (1D) coordination polymer of composition [Ag(L)(NO3)]n was synthesized by a reaction of silver(I) nitrate with a new hydrazone-hydrazide ligand (L) derived from 2-acetyl furan and ethyl hydrazine carboxylate. Both the ligand, L, and the silver(I) complex were characterized using elemental analysis, electron impact mass spectrometry (EI-Mass), infrared (IR), proton nuclear magnetic resonance (1H NMR), ultraviolet–visible (UV–Vis) spectroscopy, and emission spectroscopy analyses. Single-crystal X-ray diffraction study shows that the structure of the silver(I) complex consists of 1D polymeric chains in which silver(I) ion is in four coordination complexes arising from one N, O-chelating L and two O, O′-bridging nitrate anions. The complex emitted energy around 360 nm and was used as a single precursor for synthesis of silver oxide nanoparticles (Ag2O NPs). From transmission electron microscopy (TEM) and higher-resolution TEM (HR-TEM) images, the as-prepared Ag2O NPs were nearly spherical in shape with average particle sizes of approximately 22–24 nm. Anti-bacterial properties of both the ligand and the metal complex were studied.

English

In the search for new drugs possessing the activities we have sought to synthesize new quinoline derivatives which constitute a basic heterocyclic support of some drugs such as quinine, chloroquine marketed under the name Nivaquine®, Mefloquine®, used in the treatment of malaria. The objective of this work is to contribute to the synthesis of new derivatives of quinoline. It consists in introducing heterocycles such as benzimidazole in its 3-position. The introduction of heterocyclics, aryls or alkyls on the pyrrolic nitrogen of benzimidazole, allowed us to obtain compounds 3a-f. The chemical structures of all these compounds were determined by NMR (1H, 13C) and electron impact mass spectrometry. Key words: Quinoline, benzimidazole, aryls, alkyls.

Substituent Effects on EI-MS Fragmentation Patterns of 5-Allyloxy-1-aryl-tetrazoles and 4-Allyl-1-aryl-tetrazole-5-ones; Correlation with UV-Induced Fragmentation Channels.

1,4- and 1,5-disubstituted tetrazoles possess enriched structures and versatile chemistry, representing a challenge for chemists. In the present work, we unravel the fragmentation patterns of a chemically diverse range of 5-allyloxy-1-aryl-tetrazoles and 4-allyl-1-aryl-tetrazolole-5-ones when subjected to electron impact mass spectrometry (EI-MS) and investigate the correlation with the UV-induced fragmentation channels of the matrix-isolated tetrazole derivatives. Our results indicate that the fragmentation pathways of the selected tetrazoles in EI-MS are highly influenced by the electronic effects induced by substitution. Multiple pathways can be envisaged to explain the mechanisms of fragmentation, frequently awarding common final species, namely arylisocyanate, arylazide, arylnitrene, isocyanic acid and hydrogen azide radical cations, as well as allyl/aryl cations. The identified fragments are consistent with those found in previous investigations concerning the photochemical stability of the same class of molecules. This parallelism showcases a similarity in the behaviour of tetrazoles under EI-MS and UV-irradiation in the inert environment of cryogenic matrices of noble gases, providing efficient tools for reactivity predictions, whether for analytical ends or more in-depth studies. Theoretical calculations provide complementary information to articulate predictions of resulting products.

Submersion of rubidium clusters in helium nanodroplets

Alkali atoms and small clusters are known to reside on the surface of a helium droplet rather than its inside as most other dopant species. A theoretical investigation suggested that alkali clusters (Li–Rb) exceeding a certain critical size can become submerged in the droplet, which was experimentally confirmed for sodium and potassium. Here, we report an analogous experimental study of rubidium cluster submersion by means of electron impact mass spectrometry. We recorded size distributions of Rb cluster ions at various electron energies between 8 and 160 eV. Our data suggest that Rb clusters attached to helium droplets undergo a gradual submersion transition similar to potassium, ultimately leading to the full submersion of clusters larger than sim 100~hbox {Rb} atoms. Our findings are consistent with previous theoretical and experimental studies.Graphic abstract

GC-MS of some lycorine-type Amaryllidaceae alkaloids.

The search for novel bioactive compounds and the identification of known ones in the plant kingdom are a challenge for the scientists working in different fields of plant science. In the recent years, mass spectrometry is the most frequently applied method for analysis of complex mixtures of plant metabolites. Twenty-two alkaloids of different lycorine skeleton subtypes (with a Δ3,4 double bond, with a Δ4,11 double bond, with saturated rings C and D, and with aromatic ring C) were subjected to separation with gas chromatography and studied with electron impact mass spectrometry including single quadropole (GC-EIMS), tandem mass (GC-EIMS/MS) and high resolution mass (EI-HRMS) detectors in order to determine their fragmentation pattern. The compounds showed excellent separation and specific MS fragmentation allowing structural determination. The GC-MS can be successfully applied for searching new and identification of known bioactive molecules, chemotaxonomical and chemoecological studies, among others, within the Amaryllidoideae subfamily.

A new experimental method for investigations on microstructure of liquid-vapor interface

Many physical, chemical, and biological processes happen in liquid-vapor interface and are profoundly influenced with the local microstructures. In contrast to the liquid bulk, molecular orientation is the remarkable one of asymmetric structural features of the interface. Here we report an experimental method, namely, electron-impact time-delayed mass spectrometry and give a brief review about our recent progresses. This brand-new method not only enables us to have more insights into the interfacial structures, as done with small-angle X-ray and neutron scatterings and vibrational sum frequency generation spectroscopy, but also provides opportunity to explore the electron-driven chemical reactions therein.

On the mass spectrometric fragmentations of the bacterial sesterterpenes sestermobaraenes A-C.

A 13C-labelling was introduced into each individual carbon of the recently discovered sestermobaraenes by the enzymatic conversion of the correspondingly 13C-labelled isoprenyl diphosphate precursors with the sestermobaraene synthase from Streptomyces mobaraensis. The main compounds sestermobaraenes A, B, and C were analysed by gas chromatography–mass spectrometry (GC–MS), allowing for a deep mechanistic investigation of the electron impact mass spectrometry (EIMS) fragmentation reactions of these sesterterpene hydrocarbons.

The study and comparison of power-dependent nonlinear optical behaviours of α-mangostin with Sheik-Bahae formalism and thermal lens model using Z-Scan technique

The pericarp of Garcinia mangostana (mangosteen) contains α -mangostin (α -MG), which is an essential compound derived from the family of xanthone. This study aimed to determine the nonlinear optical response of the extracted α -MG using Z-scan technique (532 nm, 0.5–1.0 W). A series of characterisations were also done by using 1H &13C nuclear magnetic resonance (NMR), electron impact mass spectrometry (EIMS), ultraviolet-visible (UV–vis) and Fourier transform infrared (FTIR) to validate the identity of the extracted α -MG. The results showed that only nonlinear refraction (NLR) was successfully captured and measured by the closed-aperture signal. The localized absorption across the media enabled the α -MG to exhibit a self-defocusing effect. The recorded values of the nonlinear refractive index, which were denoted as n2, were then compared with two different theoretical fitting curves, which were Sheikh-Bahae Formalism (SBF) and Thermal Lens Model (TLM). The values of n2 obtained were in the order of 10−9 and 10-10 for SBF and TLM, respectively. The NLO characteristics of the α -MG were observed at the excitation wavelength of 532 nm.

Study on Structural and Thermal Characteristics of Heteroleptic Yttrium Complexes as Potential Precursors for Vapor Phase Deposition

Yttrium oxide (Y2O3) thin films are implemented as a functional component in a broad field of applications such as optics, electronics or thermal barrier coatings. Atomic layer deposition (ALD) is a promising technique to fabricate high‐quality thin films with atomic level precision in which the precursor choice plays a crucial role in process development. The limited number of suitable yttrium precursors available for ALD of Y2O3 has triggered increasing research activity seeking new or modified precursors. In this study, heteroleptic compounds of yttrium bearing the cyclopentadienyl (Cp) ligand in combination with the chelating amidinate or guanidinate ligands were targeted as potential precursors for ALD. In this context, a systematic and comparative study of the structure and thermal characteristics of (bis‐cyclopentadienyl‐(N,N'‐diisopropyl‐2‐methyl‐amidinato)yttrium) [YCp2(dpamd)] 1 and (bis‐cyclopentadienyl‐(N,N'‐diisopropyl‐2‐dimethylamido‐guanidinato)yttrium) [YCp2(dpdmg)] 2 was performed. Complementary characterization tools such as 1H‐NMR, elemental analysis, electron‐impact mass spectrometry (EI‐MS) and single‐crystal X‐ray diffraction (XRD) confirmed the spectroscopic purity and the monomeric nature of the metalorganic compounds. Hirshfeld surface analysis revealed influence of the ligand choice on the intermolecular interactions of the compounds. The important figures of merit for a precursor, namely the thermal properties were investigated via thermogravimetric analysis. Thus, the volatility, transport behavior and thermal stability were examined and compared to their homoleptic counterparts [YCp3], [Y(dpamd)3] or [Y(dpdmg)3].

An Experimental and Theoretical Study of Laser Postionization of Femtosecond-Laser-Desorbed Drug Molecules.

Femtosecond laser desorption postionization mass spectrometry using 7.9 eV single-photon ionization (7.9 eV fs-LDPI-MS) detected three of four drug compounds previously found to have very low ionization efficiencies by secondary ion mass spectrometry. Electronic structure calculations of the ionization energies and other properties of these four drug compounds predicted that all display ionization energies below the 7.9 eV photon energy, as required for single-photon ionization. The 7.9 eV fs-LDPI-MS of carbamazepine, imipramine, and verapamil all showed significant precursor (M+) ion signal, but no representative signal was observed for ciprofloxacin. Furthermore, 7.9 eV fs-LDPI-MS displayed higher M+ signals and mostly similar fragment ions compared with 70 eV electron impact mass spectrometry. Ionization and fragmentation patterns are discussed in terms of calculated wave functions for the highest occupied molecular orbitals. The implications for improving lateral resolution and sensitivity of MS imaging of drug compounds are also considered.

Effects of nanoemulsion and essential oil from the leaves of Ocotea elegans against Dysdercus peruvianus

The Dysdercus peruvianus Guérin-Méneville is commonly known as the cotton stainer bug. In this study, it was evaluated the insecticide activity and mode of action of the essential oil from leaves of Ocotea elegans Mez and its nanoemulsion against D. peruvianus. Leaves of O. elegans were extracted by hydrodistillation. The essential oil obtained was analyzed by gas chromatography coupled with electron impact mass spectrometry and flame ionization detector. The essential oil toxicity measured by lethal dose 50 (LD50) and survival rate of insects were recorded. Lastly, an assay was carried out to assess the inhibition of the enzyme acetylcholinesterase to determine a possible mechanism of action of insecticidal activity. The sesquiterpene sesquirosefuran was the major compound detected and corresponds to 92% of the components of the essential oil. The nanoemulsion more stable showed hydrophilic lipophilic balance (HLB 11.74), droplet size 92±1.80 nm, and polydispersity index (PDI of 0.215±0.015). After the topical application of the O. elegans essential oil, significant decreases in the survival of D. peruvianus occurred in a dose-response manner with LD50 = 162.18 μg and the survival rate of the nanoemulsion in D. peruvianus was 10.0±5.47, a better value than in pure essential oil. The acetylcholinesterase inhibition presented inhibition concentration (IC50 = 1.37mg/mL) and mixed type of inhibition. This indicates that the essential oil of leaves from O. elegans and its nanoemulsion are promising candidates for use in integrated pest management programs.

A first report on the synthesis of a complex of unsubstituted 1,2,3-triazolo[1,5-a]pyridine formed in situ via oxidative N–N bond coupling: Structural, photoluminescent, and biological properties of a new Cu(II) complex and its use as a single-source precursor for Cu and CuO nanoparticles

New copper(II) complexes [Cu(Pytc)(Cl)2]·2H2O (1) and [Cu2(tzp)2(CH3COO)4] (2) (Pytc = tert-butyl 2-(pyridine-2yl-methylene)hydrazinecarboxylate; tzp = 1,2,3-triazolo[1,5-a]pyridine) were prepared and were characterized by elemental analysis, electron impact mass spectrometry, UV–visible spectroscopy, infrared spectroscopy, and photoluminescence studies. A single-crystal X-ray diffraction study of 2 revealed a paddle-wheel copper(II) acetate structure with tzp acting as a monodentate ligand coordinated axially. Pytc and the metal complexes showed emissive, antibacterial, and antifungal properties. Furthermore, 2 was demonstrated to be a solid-state single-source precursor to form Cu and CuO nanoparticles (NPs) under different atmospheric conditions. By transmission electron microscopy, the as-prepared nanoparticles were observed to be roughly spherical with average particle sizes of approximately 10–12 nm for Cu NPs and approximately 20–22 nm for CuO NPs. Furthermore, high crystallinity, high purity, and the single-phase nature of the as-prepared NPs were revealed by the powder X-ray diffraction pattern.

Identifying the Molecular Orientation and Clusters in the Liquid-Vapor Interface of 1-Propanol by Time-Delayed Mass Spectrometry.

Structural inhomogeneity of the liquid-vapor interface, such as the spatial orientation of molecular specific groups and the non-uniform distribution of hydrogen-bonded (HB) clusters, is crucial for understanding the physicochemical processes therein. Although the molecular orientation at the outermost layer was authenticated, to date, direct experimental evidence of the in situ existence of different-sized HB clusters, as a long-standing theoretical argument, is still lacking. Here we report time-delayed electron-impact tandem mass spectrometry, and its powerful ability to identify the local structures of the liquid-vapor interface of 1-propanol is demonstrated not only by mapping the molecular orientations both in the outermost layer and in the subsurface but also by validating the existence of the HB molecular dimers in the subsurface by detecting their protonated ions. We further distinguish two different sources of the protonated dimer: the gas-phase protonation of the neutral dimer that evaporates in advance and the time-lag evaporation of the protonated dimer produced in the subsurface. This methodology is a brand-new way to explore the microstructures and the electron-driven chemical reactions in different local regions of the liquid-vapor interface.