Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Multinuclear nanoliter one-dimensional and two-dimensional NMR spectroscopy with a single non-resonant microcoil
    Fratila, R.M. ; Gomez, M.V. ; Sykora, S. ; Velders, A.H. - \ 2014
    Nature Communications 5 (2014). - ISSN 2041-1723
    nuclear-magnetic-resonance - liquid-state nmr - to-noise ratio - multidimensional nmr - probe - f-19 - design - chip - flow - h-1-nmr
    Nuclear magnetic resonance (NMR) spectroscopy is a powerful analytical technique, but its low sensitivity and highly sophisticated, costly, equipment severely constrain more widespread applications. Here we show that a non-resonant planar transceiver microcoil integrated in a microfluidic chip (detection volume 25¿nl) can detect different nuclides in the full broad-band range of Larmor frequencies (at 9.4¿T from 61 to 400¿MHz). Routine one-dimensional (1D) and two-dimensional (2D), homo- and heteronuclear experiments can be carried out using the broad-band coil set-up. Noteworthy, heteronuclear 2D experiments can be performed in a straightforward manner on virtually any combination of nuclides (from classical 1H–13C to more exotic combinations like 19F–31P) both in coupled and decoupled mode. Importantly, the concept of a non-resonant system provides magnetic field-independent NMR probes; moreover, the small-volume alleviates problems related to field inhomogeneity, making the broad-band coil an attractive option for, for example, portable and table-top NMR systems
    Fluorescence lifetime imaging by time-correlated single-photon counting
    Becker, W. ; Bergmann, A. ; Hink, M.A. ; Konig, K. ; Benndorf, K. ; Biskup, C. - \ 2004
    Microscopy Research and Technique 63 (2004)1. - ISSN 1059-910X - p. 58 - 66.
    to-noise ratio - multiphoton microscopy - resolved fluorescence - multiple fluorophores - protein interactions - 2-photon excitation - scanning microscope - femtosecond laser - live cells - ccd camera
    We present a time-correlated single photon counting (TCPSC) technique that allows time-resolved multi-wavelength imaging in conjunction with a laser scanning microscope and a pulsed excitation source. The technique is based on a four-dimensional histogramming process that records the photon density over the time of the fluorescence decay, the x-y coordinates of the scanning area, and the wavelength. The histogramming process avoids any time gating or wavelength scanning and, therefore, yields a near-perfect counting efficiency. The time resolution is limited only by the transit time spread of the detector. The technique can be used with almost any confocal or two-photon laser scanning microscope and works at any scanning rate. We demonstrate the application to samples stained with several dyes and to CFP-YFP FRET.
    LC-UV-solid-phase extraction-NMR-MS combined with a cryogenic flow probe and its application to the identification of compounds present in Greek oregano
    Exarchou, V. ; Godejohann, M. ; Beek, T.A. van; Gerothanassis, I.P. ; Vervoort, J.J.M. - \ 2003
    Analytical Chemistry 75 (2003)22. - ISSN 0003-2700 - p. 6288 - 6294.
    magnetic-resonance-spectroscopy - performance liquid-chromatography - high-resolution nmr - tandem mass-spectrometry - to-noise ratio - hplc-nmr - solvent-suppression - natural-products - plant-extracts - constituents
    Structure elucidation of natural products usually relies on a combination of NMR spectroscopy with mass spectrometry whereby NMR trails MS in terms of the minimum sample amount required. In the present study, the usefulness of on-line solid-phase extraction (SPE) in LC-NMR for peak storage after the LC separation prior to NMR analysis is demonstrated. The SPE unit allows the use of normal protonated solvents for the LC separation and fully deuterated solvents for flushing the trapped compounds to the NAIR probe. Thus, solvent suppression is no longer necessary. Multiple trapping of the same analyte from repeated LC injections was utilized to solve the problem of low concentration and to obtain 2D heteronuclear NMR spectra. In addition, a combination of the SPE unit with a recently developed cryoflow NMR probe and an MS was evaluated. This on-line LC-UV-SPE-NMR-MS system was used for the automated analysis of a Greek oregano extract. Combining the data provided by the UV, MS, and NMR spectra, the flavonoids taxifolin, aromadendrin, eriodictyol, naringenin, and apigenin, the phenolic acid rosmarinic acid, and the monoterpene carvacrol were identified. This automated technique is very useful for natural product analysis, and the large sensitivity improvement leads to significantly reduced NAIR acquisition times.
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