47 research outputs found
High frequency of inadequate test requests for antiphospholipid antibodies in daily clinical practice
Abstract Background: We have empirically noted that many physicians routinely request anti-phospholipid antibodies (aPL) without a correct clinical indication. The aim of this study was to evaluate retrospectively whether aPL testing at our Thrombosis Centre was justified. Methods: Medical records from 520 subjects for aPL screening tests for various clinical conditions were reviewed. The aPL screening tests were: lupus anticoagulant (LA), anti-cardiolipin antibodies (aCL) and anti-β(2) glycoptotein I (aβ(2) GPI). Requests for aPL screening were divided into justified, potentially justified or not adequately justified. Results: aPL testing requests were considered justified in 358 (69%) patients, potentially justified in 66 (12.6%) and not adequately justified in 96 (18.4%). LA was positive in 65 (18%) of justified requests and in only one (1%) of the 96 potentially justified requests. None of the 66 not adequately justified for aPL testing was positive for LA. aβ(2) ..
A molecular approach to 4',6-diamidine-2-phenylindole (DAPI) photophysical behaviour at different pH values.
Fluorescence anisotropy of DNA/DAPI complex: torsional dynamics and geometry of the complex.
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The fluorescence properties of a DNA probe. 4'-6-Diamidino-2-phenylindole (DAPI).
Steady-state and dynamic fluorescence measurements have been performed on DAPI in solution and in complexes formed with a number of synthetic and natural polydeoxynucleotides. The decay of DAPI in buffer at pH 7 was decomposed using two exponentials having lifetime values of approximately 2.8 ns and 0.2 ns. The double exponential character of the decay was maintained over a large pH range from 3 to 9. At pH 1 the short component dominated, whereas at pH 12, only the long component was detectable. Two distinct spectra were associated with the two lifetime components; the short component was shifted to the red. The short lifetime component occurs in the presence of water. In water the excitation spectra depended on the emission wavelength and there was no viscosity dependence of the two forms. To explain these results we propose that there is a ground state conformer in which preferential solvation of the indole ring allows proton transfer in the excited state. DAPI complexed with polydeoxynucleotides retained most of the features of the decay of DAPI in solution. However, the complexes with fully AT-containing polymers stabilized the longer lifetime form of DAPI because the stronger binding enhanced solvent shielding. A gradual increase of the short lifetime component, which monitors dye solvent exposure, was obtained as the AT content was decreased. For polyd(GC) the decay was similar to that of free DAPI
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A molecular approach to 4',6-diamidine-2-phenylindole (DAPI) photophysical behaviour at different pH values.
The photophysical mechanisms which determine the spectral properties and decay rates of 4',6-diamidine-2-phenylindole (DAPI) in solution and in association with nucleic acids have not yet been fully elucidated. We have performed steady-state and time-resolved fluorescence experiments on DAPI in a wide pH range to investigate the hypothesis that different ground-state conformations are responsible for the photophysical properties of the probe. Several excited-state mechanisms are investigated and it is concluded that among the proposed models, the hypothesis of ground-state heterogeneity with rapid interconversion among conformations is the only one consistent with the experiments in the entire pH range investigated
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Fluorescence lifetime distributions of DNA-4',6-diamidino-2-phenylindole complex.
Time-resolved fluorescence of 4',6-diamidino-2-phenylindole (DAPI) complexes show that for a homogeneous polymer (polyd(AT) or polyd(A).polyd(T)) at high P/D (phosphate/dye) ratio, a single exponential component adequately describes the fluorescence decay. For the AT polymers at low P/D ratio or for native DNA, the decay cannot be described by a single-exponential term. A continuous distribution of lifetime values of Gaussian shape gives a good fit to the decay data. We propose that the lifetime distribution method for the analysis of the fluorescence decay of DNA-DAPI complexes provides a useful method of characterizing the microheterogeneity of site binding
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The fluorescence properties of a DNA probe. 4'-6-Diamidino-2-phenylindole (DAPI).
Steady-state and dynamic fluorescence measurements have been performed on DAPI in solution and in complexes formed with a number of synthetic and natural polydeoxynucleotides. The decay of DAPI in buffer at pH 7 was decomposed using two exponentials having lifetime values of approximately 2.8 ns and 0.2 ns. The double exponential character of the decay was maintained over a large pH range from 3 to 9. At pH 1 the short component dominated, whereas at pH 12, only the long component was detectable. Two distinct spectra were associated with the two lifetime components; the short component was shifted to the red. The short lifetime component occurs in the presence of water. In water the excitation spectra depended on the emission wavelength and there was no viscosity dependence of the two forms. To explain these results we propose that there is a ground state conformer in which preferential solvation of the indole ring allows proton transfer in the excited state. DAPI complexed with polydeoxynucleotides retained most of the features of the decay of DAPI in solution. However, the complexes with fully AT-containing polymers stabilized the longer lifetime form of DAPI because the stronger binding enhanced solvent shielding. A gradual increase of the short lifetime component, which monitors dye solvent exposure, was obtained as the AT content was decreased. For polyd(GC) the decay was similar to that of free DAPI
Recommended from our members
A molecular approach to 4',6-diamidine-2-phenylindole (DAPI) photophysical behaviour at different pH values.
The photophysical mechanisms which determine the spectral properties and decay rates of 4',6-diamidine-2-phenylindole (DAPI) in solution and in association with nucleic acids have not yet been fully elucidated. We have performed steady-state and time-resolved fluorescence experiments on DAPI in a wide pH range to investigate the hypothesis that different ground-state conformations are responsible for the photophysical properties of the probe. Several excited-state mechanisms are investigated and it is concluded that among the proposed models, the hypothesis of ground-state heterogeneity with rapid interconversion among conformations is the only one consistent with the experiments in the entire pH range investigated