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Electron Laser (electron + laser)

Distribution by Scientific Domains
Chemistry100%

Kinds of Electron Laser

  • free electron laser
    		•

    Selected Abstracts

    Direct Probe of NO Vibration in the Naked Ferric Heme Nitrosyl Complex

    CHEMPHYSCHEM, Issue 6 2008
    Barbara Chiavarino Dr.
    Vibrational features: The coupling of a free electron laser to a mass spectrometer measures the IR spectrum of iron porphyrin complexes of nitric oxide (see figure). Comparison of the photo-dissociation spectra, identifies the NO vibration at 1842 cm,1. [source]

    Alkali Metal Complexes of the Dipeptides PheAla and AlaPhe: IRMPD Spectroscopy,

    CHEMPHYSCHEM, Issue 4 2008
    Nick C. Polfer, Prof.
    Abstract Complexes of PheAla and AlaPhe with alkali metal ions Na+ and K+ are generated by electrospray ionization, isolated in the Fourier-transform ion cyclotron resonance (FT,ICR) ion trapping mass spectrometer, and investigated by infrared multiple-photon dissociation (IRMPD) using light from the FELIX free electron laser over the mid-infrared range from 500 to 1900 cm,1. Insight into structural features of the complexes is gained by comparing the obtained spectra with predicted spectra and relative free energies obtained from DFT calculations for candidate conformers. Combining spectroscopic and energetic results establishes that the metal ion is always chelated by the amide carbonyl oxygen, whilst the C-terminal hydroxyl does not complex the metal ion and is in the endo conformation. It is also likely that the aromatic ring of Phe always chelates the metal ion in a cation-, binding configuration. Along with the amide CO and ring chelation sites, a third Lewis-basic group almost certainly chelates the metal ion, giving a threefold chelation geometry. This third site may be either the C-terminal carbonyl oxygen, or the N-terminal amino nitrogen. From the spectroscopic and computational evidence, a slight preference is given to the carbonyl group, in an ROaOt chelation pattern, but coordination by the amino group is almost equally likely (particularly for K+PheAla) in an ROaNt chelation pattern, and either of these conformations, or a mixture of them, would be consistent with the present evidence. (R represents the , ring site, Oa the amide oxygen, Ot the terminal carbonyl oxygen, and Nt the terminal nitrogen.) The spectroscopic findings are in better agreement with the MPW1PW91 DFT functional calculations of the thermochemistry compared with the B3LYP functional, which seems to underestimate the importance of the cation,, interaction. [source]

    Overview and new developments in softer X-ray (2Å < , < 5Å) protein crystallography

    JOURNAL OF SYNCHROTRON RADIATION, Issue 1 2004
    John R. Helliwell
    New methodologies with synchrotron radiation and X-ray free electron lasers (XFELs) in structural biology are being developed. Recent trends in harnessing softer X-rays in protein crystallography for phase determination are described. These include reference to a data-collection test at 2.6 Å wavelength with a lysozyme crystal on SRS station 7.2 (Helliwell, 1983) and also use of softer X-rays (2,Å wavelength) to optimise f," at the xenon L1 absorption edge in the Single Isomorphous Replacement Optimised Anomalous Scattering ('SIROAS') structure determination of apocrustacyanin A1 with four, partially occupied, xenon atoms (Cianci et al., 2001; Chayen et al., 2000). The hand of the protein was determined using the f," enhanced sulphur anomalous signal from six disulphides in the protein dimer of 40,kDa. In a follow-up study the single wavelength xenon L1 -edge f," optimised data set alone was used for phase determination and phase improvement by solvent flattening etc. (CCP4 DM) (Olczak et al., 2003). Auto-tracing of the protein was feasible but required additional diffraction data at higher resolution. This latter could be avoided in future by using improved tilted detector settings during use of softer X-rays, i.e. towards back-scattering recording (Helliwell, 2002). The Olczak et al. study has already led to optimisation of the new SRS beamline MPW,MAD,10 (see www.nwsgc.ac.uk) firstly involving the thinning of the beryllium windows as much as possible and planning for a MAR Research tilted detector `desk top beamline' geometry. Thus the use of softer, i.e. 2 to 3,Å wavelength range, X-rays will allow optimisation of xenon and iodine L -edge f," and enhancing of sulphur f," signals for higher throughput protein crystallography. Softer X-rays utilisation in protein crystallography includes work done on SRS bending-magnet station 7.2 in the early 1980s by the author as station scientist (Helliwell, 1984). In the future development of XFELs these softer X-ray wavelengths could also be harnessed and relax the demands to some extent on the complexity and cost of an XFEL. Thus, by use of say 4,Å XFEL radiation and use of a back-scattering geometry area detector the single molecule molecular transform could be sampled to a spatial resolution of 2,Å, sufficient, in principle, for protein model refinement (Miao et al., 1999). Meanwhile, Miao et al. (2003) report the first experimental recording of the diffraction pattern from intact Escherichia coli bacteria using coherent X-rays, with a wavelength of 2,Å, at a resolution of 30,nm and a real-space image constructed. The new single-particle X-ray diffraction-imaging era has commenced. [source]

    Infrared multiple photon dissociation spectroscopy of ions in Penning traps

    MASS SPECTROMETRY REVIEWS, Issue 3 2009
    John R. Eyler
    Abstract The ability of Paul and Penning traps to contain ions for time periods ranging from milliseconds to minutes allows the trapped ions to be subjected to laser irradiation for extended lengths of time. In this way, relatively low-powered tunable infrared lasers can be used to induce ion fragmentation when a sufficient number of infrared photons are absorbed, a process known as infrared multiple photon dissociation (IRMPD). If ion fragmentation is monitored as a function of laser wavelength, a photodissociation action spectrum can be obtained. The development of widely tunable infrared laser sources, in particular free electron lasers (FELs) and optical parametric oscillators/amplifiers (OPO/As), now allows spectra of trapped ions to be obtained for the entire "chemically relevant" infrared spectral region. This review describes experiments in which tunable infrared lasers have been used to irradiate ions in Penning traps. Early studies which utilized tunable carbon dioxide lasers with a limited output range are first reviewed. More recent studies with either FEL or OPO/A irradiation sources are then covered. The ionic systems examined have ranged from small hydrocarbons to multiply charged proteins, and they are discussed in approximate order of increasing complexity. © 2009 Wiley Periodicals, Inc., Mass Spec Rev 28:448,467, 2009 [source]