Comparison between fluorescence

A Comparison Between Fluorescence Spectroscopy and Molecular Dynamics Results... 

Knutson, B. L., D. L. Tomasko, C. A. Eckert, P. G. Debenedetti, and A. A. Chiavlo. 1992. Local density augmentation in supercritical solutions A comparison between fluorescence spectroscopy and molecular dynamics results. In ACS Symp. Ser., 488 60-72. 

XRF is closely related to the EPMA, energy-dispersive X-Ray Spectroscopy (EDS), and total reflection X-Ray Fluorescence (TRXF), which are described elsewhere in this encyclopedia. Brief comparisons between XRF and each of these three techniques are given below. 

In a comparison of fluorescence spectra between the ester and thioester derivative crystals of PDA, the ester crystal shows a strong emission whereas the thioester crystal fluoresces much more weakly. For example, the intensity of a PDA methyl thioester crystal is about one-thousandth of that of a PDA methyl ester crystal. Furthermore, the fluorescence lifetime of mixed crystals which consist of a large amount of PDA methyl ester and a small amount of the corresponding thioester moiety is much shortened, compared to the lifetime of pure PDA methyl ester crystals. In quenching experiments in solutions of PDA ester, the fluorescence of the PDA ester is dramatically quenched by thioacetate. Similar behaviour has been obtained with several types of diolefin derivatives having a thioester moiety, where crystal structures are isomorphous with the corresponding ester derivatives. 

Second, the technology has mediocre reproducibility. Software is available to morph images so that spots can be lined up such software is expensive, difficult to use, and not always accurate in its alignment. To overcome this problem and to simplify quantitative comparisons between samples, Unlu et al. (1997) developed differential gel electrophoresis (DIGE), where two samples are each labeled with different fluorescent tags, pooled, separated on the same gel, and scanned at characteristic wavelengths to resolve the components. This technology has been commercialized by Amersham. 

Problems related to the use of a guest dye can be reduced if the polymer contains a fluorescent chemical group. Gohil and Salem [70] took advantage of such intrinsic fluorescence to characterize the in-plane distribution of orientation in biaxially drawn PET films. In these experiments, the chain-intrinsic fluorescent label is due to the formation of dimers by two terephthalic moieties, exclusively within the noncrystalline regions. A comparison between sequential and simultaneous drawing along the MD and TD directions was undertaken for a fixed MD draw ratio of 3.5 and various TD draw ratios. The orientational order was characterized by two "orientation ratios" Rmd and RTD such that... 

In Fig. 3.5A a comparison between time-gated detection and TCSPC is shown. The time-gated detection system was based on four 2 ns wide gates. The first gate opened about 0.5 ns after the peak of the excitation pulse from a pulsed diode laser. The TCSPC trace was recorded using 1024 channels of 34.5 ps width. The specimen consisted of a piece of fluorescent plastic with a lifetime of about 3.8 ns. In order to compare the results, approximately 1700-1800 counts were recorded in both experiments. The lifetimes obtained with TG and TCSPC amounted to 3.85 0.2 ns and 3.80 0.2 ns respectively, see Fig. 3.5B. Both techniques yield comparable lifetime estimations and statistical errors. 

Fig. 7.1. Cross section of X-ray fluorescence as a function of electron energy showing a comparison between calculated and measured values (from [36])...

Steady-state method 2 comparison between the absorption spectrum and the excitation spectrum (through observation of the acceptor fluorescence) The corrected excitation spectrum is represented by... 

It is now clear that in the absence of molecular oxygen most proteins phosphoresce in aqueous solutions at ambient temperature.(10) In this chapter we discuss the use of phosphorescence of tryptophan to study proteins, with emphasis on measurements at room temperature. Comparisons between phosphorescence and the more commonly used fluorescence spectroscopy are made. Comprehensive reviews of protein luminescence have been written by Longworth.(n 12 1 A discussion on the use of phosphorescence at room temperature for the study of biological materials was given by Horie and Vanderkooi.(13)... 

Hubert, C.L., Sherling, S.E., Johnston, P.A., and Stancato, L.R, Data concordance from a comparison between filter binding and fluorescence polarization assay formats for identification of ROCK-II inhibitors, /. Biomol. Screen., 8, 399, 2003. 

The question is similar to asking how many times one can strip and reuse a microarray before performance deteriorates. An alternative approach is provided by Hessner et al. (2003a) in which the cDNA probes are permanently labeled using fluorescein-labeled primers to the clone s vector insert region. Fluorescein is excited at 488 nm and emits at 508 nm, while Cy3 may be excited at 543 nm to reduce any spectral overlap with fluorescein. Thus, fluorescein-labeled cDNA probes may be printed down and the slide scanned for QC/QA purposes prior to hybridization. Since the same region is primer-labeled in each cDNA, a direct comparison between the relahve fluorescence units (RFUs) and the amount of cDNA probe can be defermined. 

The samples were excited at 549 nm and the resultant fluorescence emission spectra were digitized. The emission spectra of i-2 differed only in relative intensity. A direct comparison between the integrated and normalized fluorescence spectra of i-2 was made with that of ZnTPP. The data normalized to the known fluorescence quantum yield of ZnTPP(ii) are listed in Table II. Fluorescence lifetimes were determined on 10 M solutions of... 

Boatman, J. F., M. Luria, C. C. Van Valin, and D. L. Wellman, Continuous Atmospheric Sulfur Gas Measurements Aboard an Aircraft A Comparison between the Flame Photometric and Fluorescence Methods, Atmos. Environ., 22, 1949-1955 (1988). 

Doll, T. E., F. H. Frimmel, M. U. Kumke, and G. Ohlenbusch, Interaction between natural organic matter (NOM) and polycyclic aromatic compounds (PAC) - comparison of fluorescence quenching and solid phase micto extraction (SPME) , Fresenius J. Anal. Chem., 364, 313-319 (1999). 

Figure 12.4—Fluorescence intensity. Depending on the point from which fluorescence is emitted in solution, a variable light intensity will reach the detector. By specific positioning of the excitation and emission windows, it is possible to estimate the re-absorption of fluorescence radiation (by comparison between sectors a and c in the figure) and the absorption of the incident radiation (by comparison between sectors a and b). In practice, fluorescence emitted from the central region of the cell is collected.

RAPID Sand Filtration. A comparison between raw water and sand-filtered water is shown in Figure 3. Three main fractions are typically recovered with Sephadex G25 from low-TOC surface waters. These fractions will be referred to as Gl, G3, and G5, which correspond to the fraction numbers by order of elution. The apparent MWs for these fractions are as follows >5000 daltons for Gl, 1000-5000 daltons for G3, and <1000 daltons for G5. During RSF, G5 exhibits a decrease in TOC, fluorescence, and UV260, whereas Gl shows a decrease only in TOC. The distribution by MW of organic carbon after sand filtration is as follows >5000 daltons, 17 (Gl) 1000-5000 daltons, 29 (G3) and <1000 daltons, 54 (G5). 

Table II. Comparison between XRF and EPMA analysis of Tyre coin 9463 (all values are in weight percent). EPMA analysis of 3 other coins is included for comparison. Results show that the Fe levels detected using the XRF are likely all from detector fluorescence in the instrument The difference in Pb may well be due to a poorly polished Pb standard...

Substantial evidence suggests that in highly asymmetric supercritical mixtures the local and bulk environment of a solute molecule differ appreciably. The concept of a local density enhancement around a solute molecule is supported by spectroscopic, theoretical, and computational investigations of intermolecular interactions in supercritical solutions. Here we make for the first time direct comparison between local density enhancements determined for the system pyrene in CO2 by two very different methods-fluorescence spectroscopy and molecular dynamics simulation. The qualitative agreement is quite satisfactory, and the results show great promise for an improved understanding at a molecular level of supercritical fluid solutions. 

Figure 6 shows a comparison between the density enhancements deduced from experiments and those calculated via simulation (the latter at R = 1.94). The reduced temperature in both cases is 1.02. This very good agreement suggests that the density augmentation measured in the fluorescence spectra corresponds to the first solvation shell. 

Figure 6 Comparison between local density augmentation deduced from fluorescence spectroscopy ( ), and the corresponding molecular dynamics simulations at R = 1.94 (Q). Both curves are for a reduced temperature of 1.02. The arrow denotes the critical density of carbon dioxide.

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