| 1. |
- Coates, C. G., et al.
(författare)
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Picosecond time-resolved resonance Raman probing of the light-switch states of Ru(Phen)(2)dppz (2+)
- 2001
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 105:50, s. 12653-12664
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Tidskriftsartikel (refereegranskat)abstract
- Picosecond time-resolved resonance Raman (picosecond-TR3) spectroscopy has been used to conduct an extensive photophysical characterization of the light- switch complex [Ru(phen)(2)dppz](2+) as a function of environment, in which studies have been carried out in aqueous and nonaqueous media and in DNA. The results are considered in rotation to a previous report describing environment-sensitive lowest triplet MLCT states. Vibrational marker features and enhancement patterns were used to determine the rapid progression (< 20 ps) between two triplet MLCT states in aqueous environment, followed by subnanosecond, nonradiative deactivation to the ground state. In nonaqueous environment, the long-lived, emissive triplet MLCT state is spectrally identified as the short-lived first triplet MLCT state observed in water, in agreement with the earlier proposed mechanism. The present data are shown to correlate well with previous nanosecond RR findings for the complex in each environment. Interestingly, a precursor state has been identified upon excitation in both nonaqueous solvent and in DNA, which precedes the triplet MLCT state, and the lifetime of which appears to be environment dependent. Observation of this state is discussed in relation to other recent femtosecond spectroscopic studies on this complex.
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| 2. |
- Dunsby, C., et al.
(författare)
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An electronically tunable ultrafast laser source applied to fluorescence imaging and fluorescence lifetime imaging microscopy
- 2004
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Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 37:23, s. 3296-3303
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Tidskriftsartikel (refereegranskat)abstract
- Fluorescence imaging is used widely in microscopy and macroscopic imaging applications for fields ranging from biomedicine to materials science. A critical component for any fluorescence imaging system is the excitation source. Traditionally, wide-field systems use filtered thermal or arc-generated white light sources, while point scanning confocal microscope systems require spatially coherent (point-like) laser sources. Unfortunately, the limited range of visible wavelengths available from conventional laser sources constrains the design and usefulness of fluorescent probes in confocal microscopy. A 'hands-off' laser-like source, electronically tunable across the visible spectrum, would be invaluable for fluorescence imaging and provide new opportunities, e.g. automated excitation fingerprinting and in situ measurement of excitation cross-sections. Yet more information can be obtained using fluorescence lifetime imaging (FLIM), which requires that the light source be pulsed or rapidly modulated. We show how a white light continuum, generated by injecting femtosecond optical radiation into a micro-structured optical fibre, coupled with a simple prism-based tunable filter arrangement, can fulfil all these roles as a continuously electronically tunable (435-1150 nm) visible ultrafast light source in confocal, wide-field and FLIM systems.
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| 3. |
- Eleme, K., et al.
(författare)
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Cell surface organization of stress-inducible proteins ULBP and MICA that stimulate human NK cells and T cells via NKG2D
- 2004
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Ingår i: Journal of Experimental Medicine. - : Rockefeller University Press. - 0022-1007 .- 1540-9538. ; 199:7, s. 1005-1010
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Tidskriftsartikel (refereegranskat)abstract
- Cell surface proteins major histocompatibility complex (MHC) class I-related chain A (MICA) and UL16-binding proteins (ULBP) 1, 2, and 3 are up-regulated upon infection or tumor transformation and can activate human natural killer (NK) cells. Patches of cross-linked raft resident ganglioside GM1 colocalized with ULBP1, 2, 3, or MICA, but not CD45. Thus, ULBPs and MICA are expressed in lipid rafts at the cell surface. Western blotting revealed that glycosylphosphatidylinositol (GPI)-anchored ULBP3 but not transmembrane MICA, MHC class I protein, or transferrin receptor, accumulated in detergent-resistant membranes containing GM1. Thus, MICA may have a weaker association with lipid rafts than ULBP3, yet both proteins accumulate at an activating human N-K cell immune synapse. Target cell lipid rafts marked by green fluorescent protein-tagged GPI also accumulate with ULBP3 at some synapses. Electron microscopy reveals constitutive clusters of ULBP at the cell surface. Regarding a specific molecular basis for the organization of these proteins, ULBP1, 2, and 3 and MICA are lipid modified. ULBP1, 2, and 3 are GPI anchored, and we demonstrate here that MICA is S-acylated. Finally, expression of a truncated form of MICA that lacks the putative site for S-acylation and the cytoplasmic tall can be expressed at the cell surface, but is unable to activate NK cells.
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| 4. |
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| 5. |
- Olofsson, J., et al.
(författare)
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Picosecond Kerr-gated time-resolved resonance Raman spectroscopy of the Ru(phen)(2)dppz (2+) interaction with DNA
- 2002
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Ingår i: Journal of Inorganic Biochemistry. - 0162-0134 .- 1873-3344. ; 91:1, s. 286-297
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Tidskriftsartikel (refereegranskat)abstract
- To investigate the basis of the 'light-switch' effect, the solvent dependence of the Kerr-gated picosecond-time resolved resonance Raman (TR3) spectra of [Ru(bpy),dppz](2+), [Ru(phen)(2)dppz](2+), and the modified complex [Ru(phen)(2)cpdppzOMe](2+) and a dimer [mu-C4(cpdppz)(2)-(phen)(4)Ru-2](4+) were studied. The investigation focussed on comparing the behaviour of [Ru(phen)(2)dppz](2+) in acetonitrile, ethanol, H2O, D2O, and DNA. The data are consistent with a model wherein excitation induces metal-to-ligand charge transfer (MLCT) to any of the ligands (termed the 'precursor' state) which, by interligand electron transfer (ILET), produces an excited state localised on the dppz ligand, MLCT1. In water this state relaxes with a characteristic time of similar to6 ps to a non-emissive state (MLCT2). The TR3 spectra in water, acetonitrile and DNA are all distinctly different. However. the early (4 ps) water spectrum resembles the spectrum in DNA. This interesting observation suggests that the DNA-bound excited state of the complex can be thought of as a model for the initial, poorly solvated state in water.
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| 6. |
- Olofsson, J., et al.
(författare)
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Three-state light switch of Ru(phen)(2)dppz (2+) : Distinct excited-state species with two, one, or no hydrogen bonds from solvent
- 2004
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 108:20, s. 4391-4398
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Tidskriftsartikel (refereegranskat)abstract
- The ruthenium complexes of dppz (dipyrido[3,2-a:2',3'-c]phenazine) have found wide interest due to their environment-sensitive luminescence and are used, for example, as spectroscopic probes for DNA. The deactivation process for the excited state of the light-switch complex [Ru(phen)(2)dppz](2+) (phen = 1,10-phenanthroline) has been studied in water, glycerol, ethylene glycol, and 1,2- and 1,3-propandiol by using fluorescence spectroscopy and single photon counting. In all solvents anomalous temperature dependence is found (increasing quantum yield and excited-state lifetime with increasing temperature). Model-independent analysis shows that only two emissive species, with solvent- and temperature-invariant emission spectral profiles, are sufficient to account for all the data in the polyol solvents. Van't Hoff plots of the ratio of the two species are linear at higher temperatures in all solvents, indicating rapid thermal equilibration of the two species, except for lower temperatures in the most viscous solvent glycerol. Kinetic modeling of the system with microscopic rate constants with positive Arrhenius activation energies requires a third nonemissive species, which is assigned to an excited state with two hydrogen bonds from the solvent, whereas the first two species are assigned to the mono-hydrogen-bonded and non-hydrogen-bonded excited-state species. This assignment is supported by the observation of a growing luminescence intensity as temperature is increased, but no wavelength shift, of high-purity [Ru(phen)(2)dppz](2+) in water solution.
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| 7. |
- Taner, S. B., et al.
(författare)
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Control of immune responses by trafficking cell surface proteins, vesicles and lipid rafts to and from the immunological synapse
- 2004
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Ingår i: Traffic. - : Wiley. - 1398-9219 .- 1600-0854. ; 5:9, s. 651-661
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Forskningsöversikt (refereegranskat)abstract
- Supramolecular clusters at the immunological synapse provide a mechanism for structuring complex communication networks between cells of the immune system. Regulating intra- and intercellular trafficking of proteins and lipids to and from the immunological synapse provides an additional level of complexity in determining the functional outcome of immune cell interactions. An emergent principle is that molecules requiring tightly regulated cell surface expression, e.g. negative regulators of cell activation or molecules promoting cytotoxicity, are trafficked to the immunological synapse from intracellular secretory as required lysosomes. Many molecules required for the early stages of the intercellular communication are already present at the cell surface, sometimes in lipid rafts, and are rapidly translocated laterally to the intercellular contact. Our understanding of these events critically depends on utilizing appropriate technologies for probing supramolecular recognition in live cells. Thus, we also present here a critical discussion of the technologies used to study lipid rafts and, more broadly, a map of the spatial and temporal dimensions covered by current live cell physical techniques, highlighting where advances are needed to exceed current spatial and temporal boundaries.
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| 8. |
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| 9. |
- Tuite, E., et al.
(författare)
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Probing DNA conductivity with photoinduced electron transfer and scanning tunneling microscopy
- 2000
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Ingår i: Journal of Biomolecular Structure and Dynamics. - : Informa UK Limited. - 0739-1102 .- 1538-0254. ; , s. 277-283
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Tidskriftsartikel (refereegranskat)abstract
- The possibility that the stacked DNA bases can mediate vectorial electron transfer has been examined using two different approaches. Experiments on photoinduced electron transfer with intercalated donors and accepters (either randomly bound or linked dyads of ruthenium complex and viologen) indicate that while DNA may be a better medium than acetonitrile for electron transfer over short distances (2-3-base pair, equivalent to 10-14 Angstrom centre-to-centre separation), it is a poor medium for transport over larger separations. Attempts to measure conductivity of individual DNA molecules using scanning tunneling microscopy to image mixed monolayers of mercaptohexanol (MCH) and 30-mer or 10-mer DNAs with alkanethiol linkers also indicate that DNA in its native state is a poor conductor. AFM images of the DNA/MCH mixed monolayers show that the DNA molecules extend vertically upward from the surface in such surface architectures.
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| 10. |
- Önfelt, Björn, et al.
(författare)
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Can membrane nanotubes facilitate communication between immune cells?
- 2004
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Ingår i: Biochemical Society Transactions. - 0300-5127 .- 1470-8752. ; 32, s. 676-678
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Tidskriftsartikel (refereegranskat)abstract
- Recent observations have revealed that intercellular connections can be formed through membrane nanotubes. These delicate structures could facilitate transport of organelles and membrane proteins between cells. The sharing of cell surface and cytoplasmic components between cells could be commonplace in biology, but an important physiological role for membrane nanotubes between immune cells is difficult to test with current technology.
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