In the traditional view, covalently bound materials differ in a fundamental way from metallic substances. Though both are built from more basic units that are, in turn, constructed from a small number of atoms, for these two materials classes the nature of these units is thought to be quite different. For covalent solids and liquids, these units are considered to be molecular, meaning that they possess properties and bonding that are retained in the condensed phase and thus they continue to be identifiable within the larger system. For metallic materials, these basic units are considered to be mere constructs that are not observable against the delocalized bonding of metals or alloys. The perceived dissimilarity of metallic and covalently bound materials has fostered distinctly different approaches to their design and improvement. Here, the delocalized view of metallic bonding is examined. This examination suggests that much of the rationale used in the design of molecular materials my be applied to metals and alloys as well. 相似文献
A new organic hybrid holmium–germanate oxo-cluster [Ho8(phen)2Ge12(μ3-O)24(CH2CH2COO)12(H2O)16]·2H2O (1, phen = 1,10-phenanthroline) was prepared under mild hydrothermal conditions and structurally characterized by elemental analysis, UV/Vis, IR spectroscopy, thermogravimetric analysis, and powder X-ray diffraction. Compounds 1 contains cage clusters [Ho8(phen)2Ge12(μ3-O)24(CH2CH2COO)12(H2O)16] and free H2O molecules. The cage cluster is constructed by the combination of two [Ho(phen)(H2O)2] units, two [Ge6O12(CH2CH2COO)6] rings and one circular [Ho6O36] fragment via sharing O atoms. 1 is the rare example of organic hybrid holmium–germanate oxo-cluster decorated by phen ligands. 相似文献
The first organic–inorganic hybrid compound based on the Keggin polyoxometalate and alkali-N-heterocycle ligand [Na4(tib)2(H2O)2(α-HBW12O40)]·2H2O (1) (tib = 1,3,5-tris(1-imidazoly)benzene) was hydrothermally synthesized by utilizing a pH-dependent approach in the POM/Cu/tib reaction systems. X-ray structural analyses reveal that compound 1, formed in pH 5.2, possesses a (3,4,6)-connected 2D net with the (42·5)(46)(33·46·52·64) topology. In addition, electrochemical and electrocatalytic properties of compound 1 were studied by cyclic voltammograms. Compound 1 displayed electrocatalytic activities toward reduction of nitrite. 相似文献
We provide modeling and experimental data describing the dominant ion-loss mechanisms for differential mobility spectrometry (DMS). Ion motion is considered from the inlet region of the mobility analyzer to the DMS exit, and losses resulting from diffusion to electrode surfaces, insufficient effective gap, ion fragmentation, and fringing field effects are considered for a commercial DMS system with 1-mm gap height. It is shown that losses due to diffusion and radial oscillations can be minimized with careful consideration of residence time, electrode spacing, gas flow rate, and waveform frequency. Fragmentation effects can be minimized by limitation of the separation field. When these parameters were optimized, fringing field effects at the DMS inlet contributed the most to signal reduction. We also describe a new DMS cell configuration that improves the gas dynamics at the mobility cell inlet. The new cell provides a gas jet that decreases the residence time for ions within the fringing field region, resulting in at least twofold increase in ion signal as determined by experimental data and simulations.
With recent advances in understanding the genomic underpinnings and oncogenic drivers of pathogenesis in different subtypes, it is increasingly clear that proper pretreatment diagnostics are essential for the choice of appropriate treatment options for non-small cell lung cancer (NSCLC). Tumor tissue preservation in optimal cutting temperature (OCT) compound is commonly used in the surgical suite. However, proteins recovered from OCT-embedded specimens pose a challenge for LC-MS/MS experiments, due to the large amounts of polymers present in OCT. Here we present a simple workflow for whole proteome analysis of OCT-embedded NSCLC tissue samples, which involves a simple trichloroacetic acid precipitation step. Comparisons of protein recovery between frozen versus OCT-embedded tissue showed excellent consistency with more than 9200 proteins identified. Using an isobaric labeling strategy, we quantified more than 5400 proteins in tumor versus normal OCT-embedded core needle biopsy samples. Gene ontology analysis indicated that a number of proliferative as well as squamous cell carcinoma (SqCC) marker proteins were overexpressed in the tumor, consistent with the patient’s pathology based diagnosis of “poorly differentiated SqCC”. Among the most downregulated proteins in the tumor sample, we noted a number of proteins with potential immunomodulatory functions. Finally, interrogation of the aberrantly expressed proteins using a candidate approach and cross-referencing with publicly available databases led to the identification of potential druggable targets in DNA replication and DNA damage repair pathways. We conclude that our approach allows LC-MS/MS proteomic analyses on OCT-embedded lung cancer specimens, opening the way to bring powerful proteomics into the clinic.
The efficient formation of gaseous ions is the crucial step in all successful mass spectrometric experiments. The invention of electrospray ionization (ESI) has strongly facilitated this step by transferring preformed ions directly from solution to the gas phase – thereby circumventing the need to first convert analytes to the gas phase and then ionize them – and therefore ESI has become an extremely useful and widely applied MS technique. The invention of sonic spray ionization (SSI) has also allowed for the transfer of ions from solution into the gas phase, but without the assistance of a voltage or heating. Numerous ionization techniques, using similar principles to those applied in either ESI or SSI, have subsequently been developed. Although experimental conditions used in such techniques vary markedly, herein we argue that they are all based on either one of two basic principles by which ions can be transferred from solution to the gas phase, that is: via (1) neutralizing the counter ion, or (2) separating the ions. We have selected 35 such techniques and categorized them accordingly. This article thereby aims to establish the basic principles by which gaseous ions can be obtained from solvated ions. We further propose that any new ionization technique used to transfer solvated ions to the gas phase will similarly fall into one of these two mechanistic categories.
Radical activation methods, such as electron transfer dissociation (ETD), produce structural information complementary to collision-induced dissociation. Herein, electron transfer dissociation of 3-fold protonated DNA hexamers was studied to gain insight into the fragmentation mechanism. The fragmentation patterns of a large set of DNA hexamers confirm cytosine as the primary target of electron transfer. The reported data reveal backbone cleavage by internal electron transfer from the nucleobase to the phosphate linker leading either to a?/w or d/z? ion pairs. This reaction pathway contrasts with previous findings on the dissociation processes after electron capture by DNA cations, suggesting multiple, parallel dissociation channels. However, all these channels merely result in partial fragmentation of the precursor ion because the charge-reduced DNA radical cations are quite stable. Two hypotheses are put forward to explain the low dissociation yield of DNA radical cations: it is either attributed to non-covalent interactions between complementary fragments or to the stabilization of the unpaired electron in stacked nucleobases. MS3 experiments suggest that the charge-reduced species is the intact oligonucleotide. Moreover, introducing abasic sites significantly increases the dissociation yield of DNA cations. Consequently, the stabilization of the unpaired electron by π–π-stacking provides an appropriate rationale for the high intensity of DNA radical cations after electron transfer.
