Macro-N-heterocyclic compounds: X-ray photoelectron spectra and structure

Bi-, tri-, and tetradentate macroheterocylic ligands, i.e., structural analogs of phthalocyanine, are studied by X-ray photoelectron spectroscopy. The X-ray photoelectron spectra of N1s lines of the nitrogen atoms of these compounds are analyzed. The binding energies and integrated intensities of N1s lines of the nitrogen atoms are determined and the effective charges on the nitrogen atoms are calculated. The structures of bi-, tri-and tetradentate macroheterocyclic ligands containing isoindole, benzene, and pyridine fragments are established on the basis of the data obtained.     

Methyl rotational tunneling dynamics of p-xylene confined in a crystalline zeolite host

The methyl rotational tunneling spectrum of p-xylene confined in nanoporous zeolite crystals has been measured by inelastic neutron scattering (INS) and proton nuclear magnetic resonance (NMR), and analyzed to extract the rotational potential energy surfaces characteristic of the methyl groups in the host-guest complex. The number and relative intensities of the tunneling peaks observed by INS indicate the presence of methyl-methyl coupling interactions in addition to the methyl-zeolite interactions. The INS tunneling spectra from the crystals (space group P2(1)2(1)2(1) with four crystallographically inequivalent methyl rotors) are quantitatively interpreted as a combination of transitions involving two coupled methyl rotors as well as a transition involving single-particle tunneling of a third inequivalent rotor, in a manner consistent with the observed tunneling energies and relative intensities. Together, the crystal structure and the absence of additional peaks in the INS spectra suggest that the tunneling of the fourth inequivalent rotor is strongly hindered and inaccessible to INS measurements. This is verified by proton NMR measurements of the spin-lattice relaxation time which reveal the tunneling characteristics of the fourth inequivalent rotor.     

HeI photoelectron spectroscopic study of the electronic structure of SSF2 and FSSF compounds

HeI photoelectron (PE) spectra are re-recorded for SSF₂ and FSSF. The assignment of bands has been made with the aid of band shapes, band intensities and ab initio calculations. In the PE spectrum of SSF₂, two sharp peaks at 10.48 and 11.22 eV are considered to result from through-space interaction of lone-pair orbitals in the two S atoms and two sharp peaks at 12.50 and 12.90 eV from through-space interaction of lone-pair orbitals in the two F atoms. The larger splitting of the S atoms can be attributed to the larger 3p orbital of S. The lack of sharp peaks in the PE spectrum of FSSF shows that there is no orbital which embodies the character of a lone-pair. So the PE spectra of SSF₂ and FSSF are examples embodying through-space interaction of lone-pair orbitals.     

Uracil on Cu(110): a quantitative structure determination by energy-scanned photoelectron diffraction

The local adsorption site of the nucleobase uracil on Cu(110) has been determined quantitatively by energy-scanned photoelectron diffraction (PhD). Qualitative inspection of the O 1s and N 1s soft x-ray photoelectron spectra, PhD modulation spectra, and O K-edge near-edge x-ray adsorption fine structure indicate that uracil bonds to the surface through its nitrogen and oxygen constituent atoms, each in near atop sites, with the molecular plane essentially perpendicular to surface and aligned along the close packed [110] azimuth. Multiple scattering simulations of the PhD spectra confirm and refine this geometry. The Cu-N bondlength is 1.96 ± 0.04 ?, while the Cu-O bondlengths of the two inequivalent O atoms are 1.93 ± 0.04 ? and 1.96 ± 0.04 ?, respectively. The molecule is twisted out of the [110]direction by 11 ± 5°.     

Beiträge zur Chemie der Pyrrolpigmente, 21. Mitt.: Röntgenphotoelektronenspektrometrische Untersuchungen des N1s-Niveaus von Gallenpigmenten

N_1s-X-ray photoelectron spectra of bilatrienes-abc exhibit two peaks with intensities of 3:1 and differing in bonding energy by approximatly two eV. By comparison with the spectra of model compounds representing certain bile pigment partial structures these peaks could be assigned to the lactam-, pyrrole- and the pyrrolenine type nitrogen atoms. From these results it could be established that bilatrienes-abc exist in the crystalline state as bis-lactam forms, having an unsymmetrical canonical dipyrromethene partial structure. By the same procedure the bis lactam structure of biladienes-ac (e.g. bilirubin) was deduced.

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20. Mitt.:H. Falk undA. Leodolter, Mh. Chem.109, 883 (1978).     

Investigation of diterpenoid isosteviol ammonium derivatives by matrix-assisted laser desorption/ionization mass spectrometry

Matrix-assisted laser desorption/ionization (MALDI) mass spectra of diterpenoid isosteviol ammonium derivatives have been analyzed. The compounds were synthesized as antibacterial agents. It has been found that peaks of salt cations were detected in positive ion MALDI mass spectra of mono-quaternary derivatives. The fragmentation of bis-quaternary salts depended on the distance between the ammonium centers. Clusters containing dication and acidic matrix anion have been observed for compounds with two quaternized nitrogen atoms connected by a nonanomethylene or a longer spacer. Similar clusters did not form for compounds containing pentamethylene or a shorter spacer between two quaternized nitrogen atoms.     

Electronic structure and specroscopic properties of norfloxacin,enoxacin, and nalidixic acid

The X-ray photoelectron spectra (XPS) of the core electrons of the carbon, oxygen, nitrogen, and fluorine atoms of antibiotics from the class of quinolones (nalidixic acid, norfloxacin, and enoxacin), having different antibacterial activities, were measured and interpreted. The integrated intensities of the π-π* and n-π* transition bands in the absorption spectra of the compounds were analyzed. The maxima of the luminescence spectral bands are given along with the lifetimes of the excited states and quantum yields of the protolytic forms of the compounds in aqueous media. The XPS data were compared with the Mulliken charges on heteroatoms obtained by quantum-chemical calculations.     

High-resolution HeI and HeII photoelectron spectra of the zinc and cadmium dihalide valence bands

We have recorded high-resolution HeI and HeII photoelectron spectra of the valence bands of six MX₂ compounds (M = Zn, Cd: X = Cl, Br, I) in the gas phase. Transition-state Xα SW calculations on all six compounds confirm the assignments. For the first time, we have clearly resolved the spin-orbit splitting of the II_g and II_u states in the bromide and iodide spectra: and calculated Π_u splittings, using a simple MO LCAO model and the D_xh double group, are in very good agreement with the experimental values. The relative intensities of the photoelectron peaks change markedly from HeI to HeII spectra, and Xα SW cross section calculations on ZnCl₂ predict these intensity changes rather well.     

Satellites and loss structures of core-electron peaks in x-ray photoelectron spectra of alkali fluorides

Structures consisting of several peaks were clearly observed in the loss band regions of core electron peaks in the X-ray photoelectron spectra of KF, NaF and LiF. It is shown that, although these structures very much resemble the electron energy loss spectra of the salts obtained using an externally produced electron beam, the energies and intensities of some peaks are dependent upon the ionizing core levels. One peak definitely attributable to an intrinsic satellite was found in the loss band region of F 1s spectrum of each salt, which was concluded to be due to the shake-up process associated with F 2p → F 3p excitation.     

Electron emission from naphthacene crystal due to the impact of argon and krypton metastable atoms

Energy distributions of electrons emitted from polycrystalline naphthacene due to the impact of metastable argon or krypton atoms were measured. The energy distribution peaks, except for large peaks appearing near zero eV, correspond to the kinetic energies estimated from photoelectron spectra on the assumption that the excitation energies of the metastable atoms are transferred to the electrons in the valence bands. The results are interpreted as the occurrence of Penning ionization (Auger de-excitation) on the naphthacene surface.     

Carbon 1s excitation spectroscopy of propyne, trifluoropropyne, and propargyl alcohol

The C 1s excitation spectra of propyne (HC2CH3), 3,3,3-trifluoropropyne (HC2CF3), and propargyl alcohol (HC3CH3OH) have been studied using synchrotron radiation and ion time-of-flight mass spectrometry. Discrete peaks below the carbon 1s ionization thresholds are compared and assigned, aided in part by ab-initio calculations incorporating an explicit C 1s hole. Calculated C 1s ionization potentials are in good agreement with previously reported experimental values. Calculated absolute excitation energies consistently underestimate the transition term values, but calculated relative excitation energies and intensities are in good agreement with the experimental results. The spectra are dominated by intense C 1s --> pi transitions. In the case of propyne, C 1s excitations from each of the three chemically inequivalent carbon atoms are observed. The effect of electronegative substitution is found to be different for the C 1s --> Rydberg transitions than for transitions to unoccupied valence levels, with Rydberg transition energies shifting with changes in the C 1s ionization potentials but valence transition energies showing only small changes with electronegative substitution. The C 1s (3a1,4a1) --> pi (6e) transitions of trifluoropropyne are shifted to lower energy relative to propyne even though the electronegative fluorine atoms cause a significant shift to higher energy in the corresponding C 1s IPs.     

Mass spectra of cyclic oxyethylenethioureas

Conclusions In contrast to cyclic polyethers, the peaks for ions containing the sulfur atoms have the greatest intensity in the mass spectra of oxyethylenethioureas. The presence of a peak for an ion with m/z 86 is an analytical characteristic of the mass spectra of these compounds.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2801–2803, December, 1984.Deceased.     

A conversational mass spectral search and retrieval system—II: Combined search options

An interactive, conversational mass spectral search system based on 8782 uncertified electron-impact mass spectra and accessible over ordinary telephone lines, is described. Compounds whose mass spectra are in the file can be immediately identified and very useful structural inferences can be obtained for compounds that are not represented in the file. The file may be searched in a number of ways, including by peaks and intensities, molecular weight, complete and partial molecular formula, molecular weight plus peaks/intensities, molecular formula plus peaks/intensities and molecular weight plus molecular formula. Lastly, the complete spectrum of any compound in the file can be printed out.     

Final-state intensities in photoelectron spectra of 4f electrons as predicted by relativistic calculations

Relativistic calculations have been performed for the intensities of the various photoelectron signals expected in ionisation of a partly filled 4f subshell in lanthanoid ions. The results account for discepancies found between the predictions of non-relativistic theory and the 4f photoelectron spectra of ytterbium (III)compounds.     

Low energy satellites in X-ray emission and X-ray photoelectron spectra of some transition metal ions: The identification of multiplet splitting effects

X-ray emission and X-ray photoelectron spectra from manganese and nickel compounds are compared. It is suggested that a comparison of the satellite structure of Kβ_1,3 X-ray peaks and photoelectron 3p peaks can be used to determine their origin since identical features would only be expected to arise from multiplet effects. Shake-up, shake-off and other multi-electron effects should therefore give rise to low (kinetic) energy satellites unique to the photoelectron spectrum.     

Secondary ion mass spectra of organic cationic dyestuffs

Rules for the behavior under fast atom bombardment (FAB) have been established for 15 cationic dyes — quaternary ammonium salts of heterocyclic amines and heterocycles containing quaternary nitrogen atoms with aliphatic substituents. Intense peaks corresponding to the molecular mass of the cationic part of the dyes [M-Hal]⁺ are observed in the spectra of all the derivatives. Fragmentation of the azodyes is determined by the azo group and the heterocyle. The base peaks in the case of compounds containing a quaternary nitrogen atom with aliphatic substituents correspond to the ammonium ion and a fragment of amine type. The results obtained can be used to identify dyes of unknown structure from their secondary ion mass spectra (SIMS).DeceasedTranslated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, 1411–1417, October, 1992     

Electronic structure of intercalation compounds of molybdenum disulfide MMoS2 (M = Cu, Ag) studied by X-ray emission and X-ray photoelectron spectroscopies

Electronic structures of intercalation compounds of molybdenum disulfide in which the MoS2 layers alternate with layers formed by the metal atoms (Cu, Ag) were studied by X-ray emission and photoelectron spectroscopies. The character of participation of these or other valence states of atoms in the construction of occupied and unoccupied energy bands of the substances studied was considered on the basis of the X-ray spectra of various series.     

Ammonia/desorption chemical ionization mass spectrometry of some cyclopentane iridoid glucosides

The ammonia/desorption chemical ionization (DCI) mass spectra of nine cyclopentane iridoid glucosides were measured. The dependences cf the intensities of different peaks on the structures and stereochemistries of the compounds investigated is discussed.     

X-ray spectral and quantum chemical study of the electronic structure of thiacalix[4]-arenes and their acyclic analogs

An X-ray photoelectron and X-ray emission study of the charge state of thiacalix[4]arenes is performed with a comparison with the data of quantum chemical calculations. Relaxation corrections between the Kohn-Sham orbital energies calculated by the DFT method and experimental parameters of the X-ray emission and photoelectron spectra of the studied compounds are estimated. It is shown that the formation of a cyclic aromatic system in thiacalixarenes results in a decrease in the energy of orbitals involving p-π interactions of the bridging sulfur atoms and aromatic moieties, which determines the features of the X-ray emission spectra of the studied compounds.