Fluorescence intensity table

With increasing concentration of DHB, the photoproduct forms more slowly, as evidenced by decreasing loss of fluorescence intensity (Table I, entries 1-3). Nevertheless, the concentration of photoproduct(s) and RET from the polymer to photoproduct(s) are expected to increase with time, and stabilization of the polymer will eventually depend upon the capability of the photoproduct(s) to dissipate excitation energy imparted in the RET process. The observed decrease in stabilization efficiency by DHB (based on film discoloration) with exposure time in an accelerometer indicates that DHB is more effective than the photoproduct(s) in dissipating the light energy. Similar spectroscopic studies on polystyrene have led to the same conclusion in this case, as well.6... 

Further examples pf fluorescence stabilization and intensity augmentation as a result of treatment of the chromatogram with viscous, lipophilic liquids are listed in Table 22. The alteration of the pH [293] or the addition of organic acids or bases [292] have also been found to be effective. Wintersteiger [291] has also described the effect that the TLC layer itself (binder) can influence the fluorescence intensity. 

Table I. Relative Fluorescence Intensities Obtained from Various Types of Nucleic Acids...

Table II. Relative Fluorescence Intensities Obtained Using DNA s from Various Sources...

In practice it is much simpler to determine the relative quantum yield of fluorescence than the absolute quantum yield (see Table 2.1). This is done by comparing the fluorescence intensity of a given sample to that of a compound whose fluorescence quantum yield is known. For this one must... 

Shell Chemical Company), exhibits a maximum at 300 nm, corresponding to that of the model chromophore anisole. The fluorescence intensity decreases monotonically with increasing concentration of 2,4-dihydroxybenzophenone (DHB) and, furthermore, decreases with time on continued excitation (274 nm) in the spectrophotometer. The fluorescence loss with time may be resolved into two exponential decays. Initially, a relatively rapid fluorescence loss is observed within 20 sec, followed by a slower loss. Loss constants for the initial (k ) and secondary (kj) exponential decays for 1.5 ym films (on glass slides) containing varying concentrations of DHB are provided in Table I (entries 1-3). The initial loss constants are seen to decrease more markedly with increasing DHB concentration than the secondary constants. 

The importance of phenol formation by the proposed pathway was probed by irradiating l,3-diphenoxy-2-methyl-2-propanol (5) under the same conditions. Compared to 3, the rate of phenol formation was approximately 2 times slower. Since the 11-transfer step in Scheme II is not available to 5, the results provide support for the scheme as an important, but not sole, pathway for phenol formation. Irradiation of and 5 with an air purge resulted in faster rates of phenol formation (ca. 5-fold) relative to N2. These findings parallel the accelerated fluorescence intensity loss from polymer 1 films in air as compared to the results in vacuo (see Table I). 

The conversion of squaraine 19a to the rotaxane 18 D 19a causes a modest red-shift only in both absorption (10 nm) and emission (7 nm) but an approximately threefold decrease in quantum yield. The addition of two triazole rings (dye 19b) did not significantly alter the quantum yield of 17b (Table 4). A macrocycle-induced quenching effect was verified by fluorescence titration experiments adding aliquots of 18 to a solution of squaraine 17b in methylene chloride [58]. Treatment of the 18 d 17b psuedorotaxane system with the tetrabutylammonium salts of chloride, acetate, or benzoate leads to the displacement of squaraine 17b from the macrocyclic cavity and the nearly complete restoration of its fluorescence intensity. The 18-induced quenching of 17b does not support the utility of this system as a bioimaging probe however, the pseudorotaxane system 18 Z> 17b acts as an effective and selective anion sensor with NIR fluorescence. 

This relation shows that the fluorescence intensity is proportional to the concentration only for low absorbances. Deviation from a linear variation increases with increasing absorbance (Table 3.2). 

The ratiometric measurements are preferable because the ratio of the fluorescence intensities at two wavelengths is in fact independent of the total concentration of the dye, photobleaching, fluctuations of the source intensity, sensitivity of the instrument, etc. The characteristics of some fluorescent pH indicators allowing ratiometric measurements are given in Table 10.1. 

The fluorescence decay parameters of tyrosine and several tyrosine analogues at neutral pH are listed in Table 1.2. Tyrosine zwitterion and analogues with an ionized a-carboxyl group exhibit monoexponential decay kinetics. Conversion of the a-carboxyl group to the corresponding amide results in a fluorescence intensity decay that requires at least a double exponential to fit the data. While not shown in Table 1.2, protonation of the carboxyl group also results in complex decay kinetics.(38)... 

Fluorometric methods have been developed for determining the concentrations of more than 50 elements in the periodic table. These methods depend on the measurement of changes in the fluorescence intensity of a fluorescent dye on interaction with the species to be analysed. The concentration of the substance being analysed is proportional to the fluorescence intensity, determined from calibration curves. The interactions can take the form of ionic associates between a dye cation and a metal complex anion, e.g. AgBrj with a rhodamine cation, or alternatively with a fluorescent dye anion, e.g. fluorescein and a complex cation. In another method, the changes... 

Relative fluorescence intensities and spectra at a series of pH values are shown in Fig. 12, and some pertinent parameters are summarized in Table IX. At a specific pH the fluorescence intensity as a function of wavelength has been expressed as relative to the intensity at the maximum at the same pH. The maximum intensities were different at different PH values. Nevertheless, the ratio of intensities of dimer and monomer, ID//M, being independent of polymer concentration, may be compared for all the samples and pH values. 

Kropp and Windsor (105,107) studied extensively the effects of deutera-tion on the luminescence characteristics of some rare-earth complexes. Solutions of europium and terbium salts in heavy water give fluorescence intensities and lifetimes many times greater than the corresponding solutions in ordinary water. Table X gives the results of their studies on europium... 

By measuring fluorescence intensity as a function of [Q] at fixed [S], we can find the average number of molecules of S per micelle if we know the critical micelle concentration (which is independently measured in solutions of S). The table below gives data for 3.8 (jlM pyrene in a micellar solution with a total concentration of sodium dodecyl sulfate [S] = 20.8 mM. 

The xanthenes exist in solution in several different forms depending on pH, as shown in Figure 2 and Table 1 [18]. The emission quantum yield of fluorescein depends on the acidity of the solution, the fluorescence intensity decreasing as the protonated forms of the dye come to predominate with decreasing pH. This pH sensitivity allows fluorescein derivatives to be employed as pH indicators, to measure the pH inside living cells [19-22], at water-lipid interfaces [23], and in the interior of phospholipid vesicles [24]. The sensitivity of fluorescein emission to the pH of the medium has also been used to measure lateral proton conductances at water-lipid interfaces [25-28] and proton translocation across phospholipid vesicles [29] and to determine the electrostatic potential of macromolecules [30, 31]. The pheno-... 

Standardize the spectrofluorimeter in the following way. Pipet 2.0 mL of the pH 7.5, ethidium bromide-Tris buffer into a cuvette. Add 1.0 mL of Tris buffer I and 20 fiL of standard DNA solution. Mix and place in the fluorimeter. Adjust the fluorescence intensity to 100. Clean the cuvette as described in part A and repeat the assay using various concentrations of spermine. Prepare a table displaying the amount of each component to be added. Four reagents must be in the table pH 7.5, ethidium bromide-Tris buffer, DNA solution, spermine, and Tris buffer I. Maintain the volume of DNA at 20 fiL and ethidium bromide solution at 2.0 mL for all assays. Use 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, and 1.0 mL of spermine in the assays. Remember that the total volume of all constituents in the cuvette must remain constant at 3.02 mL for all the assays. Therefore, the amount of Tris buffer I must change with the amount of spermine added. Prepare each assay separately by adding the proper amount of each component to the cuvette. Mix well and record the fluorescence intensity of each cuvette. 

A significant increase of the lifetime (t) and fluorescence intensity (tq) has been demonstrated [605—608] by using deuterated solvents and a summary [607] of the results for Eu3+ is given in Table 48. The chloride and nitrate show significant enhancement of intensity in D2O compared to H2O whereas for sulphate, acetate and EDTA the OdI Oh ratio is low. Solvents other than water may increase the fluorescence yield but the... 

Table 48. The ratios of fluorescence intensities (rjDlrjHF and lifetimes (tdIth) in deuterated and nondevterated solvents of some europium compounds [607]...

Under ultraviolet light milkweed and rabbit hair fibers that had been dyed with bloodroot fluoresced in a pale yellow/orange and a bright yellow/orange respectively. Because the commercially obtained undyed rabbit hair yam fluoresced intensely, untreated rabbit hair obtained directly from a breeder was used for testing and to use as control (Table III). 

The results in Table I show that, in the presence of plant material, the standard GA3 is spread over a considerably wider range than is usual. However, after the sample is further purified by the second run, the mobility of GA3 returns to normal. The same pattern of distribution, with zone III as maximum, is manifest in the natural run, although at considerably lower fluorescent intensities. For both fractions, the presence of GA3 is confirmed by the capryl system. A portion of zone III of the natural extract gave positive response proportional to concentration in the pinto bean seedling assay and in the dwarf maize mutants I and V assay. The relative activity on both mutants was approximately equal, as is required for GA3 (26). The correlation of relatively specific biological growth activity with chromatographic and chemical behavior affirms the presence of a GA3-like substance in kudzu vine. 

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