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101.
Claisen rearrangement induced by low-energy collision of ESI-generated, protonated benzyloxy indoles
Crotti S Stella L Munari I Massaccesi F Cotarca L Forcato M Traldi P 《Journal of mass spectrometry : JMS》2007,42(12):1562-1568
The Claisen rearrangement is a well-known process occurring in condensed phase. In the gas-phase protonated allyl phenyl ethers, propargyl phenyl ethers, and N-allyl aniline produced by positive ion chemical ionization undergo Claisen rearrangement. This reaction has been observed even in the case of odd-electron molecular ions. Phenyl allenyl ether molecular ions actually undergo Claisen rearrangement, producing intense [M - CO](+*) ions. In this investigation, the behavior of protonated benzyloxy indole and some of its derivatives, obtained in electrospray conditions, is described. Low-energy MS/MS experiments carried out on [M + H](+) species show CO loss and an unexpected water loss: both can be justified only by the occurrence of Claisen rearrangement. Deuterium labeling experiments confirm this mechanism. The influence of different substituents in the indole moiety is discussed. 相似文献
102.
Wind M Gebhardt K Grunwald H Spickermann J Donzelli M Kellenberger L Muller M Fullhardt P Schmitt-Hoffmann A Schleimer M 《Rapid communications in mass spectrometry : RCM》2007,21(7):1093-1099
The in vitro metabolic pattern of BAL19403, a novel macrolide antibiotic, was investigated by capillary liquid chromatography/quadrupole time-of-flight mass spectrometry (LC/QTOF-MS) in incubations with human microsomes. For the elucidation of the metabolic pathway, BAL19403 labeled with four deuterium atoms (D4) was used, and detection of metabolites performed using mixtures of the unlabeled (H4) BAL19403 and its D4 analogue (1:1) as substrate. All metabolites appeared with similar chromatographic behavior. MS/MS spectra of BAL19403 and its metabolites are dominated by non-informative fragment ions. Therefore, the structure of the metabolites was elucidated mainly by accurate mass measurements with subsequent proposals of elemental compositions. Main biotransformations were N-demethylation, lactone ring hydrolysis, and oxidation. Additionally, N-dealkylation of the aromatic moiety was identified. This dealkylation results not only in formation of an aldehyde, according to the classical pathway, but also in formation of the corresponding alcohol and carboxylic acid. Final elucidation of their structures was possible, since this dealkylation takes place vicinal to the deuterium-labeled part of BAL19403 and interferes with D/H exchange. The degree of D/H exchange, determined by analysis of the metabolite isotopic pattern, was used to elucidate the adjacent functional group. 相似文献
103.
Dionigi C Stoliar P Porzio W Destri S Cavallini M Bilotti I Brillante A Biscarini F 《Langmuir : the ACS journal of surfaces and colloids》2007,23(4):2030-2036
We demonstrate field effect transistors based on organic semiconductor molecules dispersed in a self-organized polystyrene (PS) latex bead matrix. An aqueous colloidal composite made of PS and tetrahexylsexithiophene (H4T6) is deposited with a micropipet into the channel of a bottom-contact field effect transistor. The beads self-organize into a network whose characteristic distances are governed by their packing. The semiconductor molecules crystallize in the interstitial voids, leading to the growth of large interconnected domains. Depending on the bead size and the ratio between H4T6 and PS, the fraction of the different phases in the polymorph can be controlled. In the transistors where the H4T6 metastable "red phase" is the largest, the device response and the charge mobility are comparable to those of sexithienyl thin films grown by high-vacuum sublimation. 相似文献
104.
The N-terminal 30-amino acid tail of histone H4, a nuclear protein, was studied as a model for the interaction of this protein with Ni(ii) ions. The behaviour of the ends-blocked Ac-SGRGKGGKGLGKGGA(15)K(16)R(17)H(18)R(19)KVLRDNIQGIT-Am fragment towards Ni(ii) was analyzed with multidimensional NMR (1D, 2D TOCSY, NOESY) and UV-Vis spectroscopy. As expected, the coordination involved the imidazolic nitrogen of the His(18) residue and the three deprotonated amidic nitrogens of the His(18), Arg(17) and Lys(16) residues, respectively. A model for the structure of the complex was calculated from the inter-residual NOEs recorded in 2D NOESY spectra. The structure obtained shows that the interaction with the metal is responsible for deep changes in the conformation of the peptide, blocking the side chain of Arg(17) and Lys(16) residues above the coordination plane. These structural modifications may be physiologically relevant to the mechanism of nickel carcinogenesis. 相似文献
105.
Diffusion data from pulsed‐field gradient spin‐echo (PGSE) methods are shown to be qualitatively useful in the investigation of problems involving unknown molecular aggregation and/or the nature of inter‐ionic interactions in metal complexes. For charged species possessing anions such as PF, BF, CF3SO or BArF−, both 19F‐ and 1H‐PGSE methods offer a valid alternative and, sometimes, unique view of gross and subtle solution molecular structure and dynamics. Problems associated with solvents, concentration, and reproducibility are discussed. 相似文献
106.
107.
Massimiliano Aschi Mark Brnstrup Martin Diefenbach Jeremy N. Harvey Detlef Schrder Helmut Schwarz 《Angewandte Chemie (International ed. in English)》1998,37(6):829-832
What exactly are the elementary steps in the Pt-catalyzed coupling of methane and ammonia (Degussa process) shown on the right? Mass spectrometry and ab initio theory have been used to probe the mechanistic details of this technically important synthesis of hydrogen cyanide. 相似文献
108.
Giovanni Grassi Massimiliano Cordaro Giuseppe Bruno Francesco Nicol 《Helvetica chimica acta》2002,85(1):196-205
The structures of 6‐methyl‐4,8,9‐triphenyl‐2‐oxa‐3,7‐diazaspiro[4.4]nona‐3,6‐dien‐1‐one ( 3 ) and N‐[(2‐Methyl‐4,5‐diphenyl‐1H‐pyrrole‐3‐carbonyl)oxy]benzamide ( 4 ) were established by X‐ray crystal‐structure analysis. A significant improvement in the procedure currently available for the synthesis of these compounds is described. Ab initio and DFT calculations were carried out on the compound 4 and its precursor 3 , and compared with X‐ray results. In particular, to relate structural features to biological properties, the conformational characteristics and rotational barrier of compound 4 were studied. 相似文献
109.
Philip C. Andrews Tobias Beck Benjamin H. Fraser Peter C. Junk Massimiliano Massi Boujemaa Moubaraki Keith S. Murray Morry Silberstein 《Polyhedron》2009
The controlled hydrolysis of lanthanoid trichloride hexahydrate (Ln = Nd, Eu, Ho) in methanol with the β-diketone ligands dibenzoylmethane and 1,3-bis(4-ethoxyphenyl)propane-1,3-dione yielded tetranuclear and pentanuclear hydroxo clusters for Eu and Ho. In contrast, performing the reaction in the presence of 1,3-bis(4-methoxyphenyl)propane-1,3-dione yielded a mononuclear complex for Nd. The compounds were structurally characterised by means of single crystal X-ray diffraction, showing that the increased bulkiness of the ligand due to the ethoxy functionalities does not affect the capability of the diketonate to stabilize the cluster core. Variable temperature dc susceptibility magnetic measurements were made on the clusters and were indicative of very weak to zero antiferromagnetic, intra-cluster coupling. Variable frequency ac data recorded at low temperatures did not show any evidence for single molecule magnet (SMM) behaviour, unlike the recent reported case of the analogue [Dy5(OH)5(Ph2acac)10], where Ph2acac− is the dibenzoylmethanide ligand. 相似文献
110.
Serena Silvi Dr. Edwin C. Constable Prof. Catherine E. Housecroft Prof. Jonathon E. Beves Dr. Emma L. Dunphy Dr. Massimiliano Tomasulo Dr. Françisco M. Raymo Prof. Alberto Credi Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(1):178-185
Molecular logic gates process physical or chemical “inputs” to generate “outputs” based on a set of logical operators. We report the design and operation of a chemical ensemble in solution that behaves as integrated AND, OR, and XNOR gates with optical input and output signals. The ensemble is composed of a reversible merocyanine‐type photoacid and a ruthenium polypyridine complex that functions as a pH‐controlled three‐state luminescent switch. The light‐triggered release of protons from the photoacid is used to control the state of the transition‐metal complex. Therefore, the two molecular switching devices communicate with one another through the exchange of ionic signals. By means of such a double (optical–chemical–optical) signal‐transduction mechanism, inputs of violet light modulate a luminescence output in the red/far‐red region of the visible spectrum. Nondestructive reading is guaranteed because the green light used for excitation in the photoluminescence experiments does not affect the state of the gate. The reset is thermally driven and, thus, does not involve the addition of chemicals and accumulation of byproducts. Owing to its reversibility and stability, this molecular device can afford many cycles of digital operation. 相似文献