Fluorescence steady-state measurements

The fluorescence decrease in Figure 1 can be attributed to the consumption of the anthracene photosensitizer during the photosensitization reaction. The photosensitization proceeds by an electron transfer reaction from the anthracene to the initiator, resulting in loss of aromaticity of the of the central ring.17 Therefore, the photosensitization reaction leads to a disruption in the n electron structure of the anthracene, and the resulting molecule does not absorb at 364 nm (nor fluoresce in the 420 - 440 nm region). Hence, the steady-state fluorescence measurements allow the anthracene concentration to be monitored in situ while the photosensitization reaction takes place. 

Pitfalls in steady-state fluorescence measurements inner filter effects and polarization effects... 

In this final section, we summarize the operation and characteristics of the principal vacuum tube and solid state detectors that are available for red/near-IR fluorescence studies. These include conventional photomultipliers, microchannel plate versions, streak cameras, and various types of photodiodes. Detector applicability to both steady-state and time-resolved studies will be considered. However, emphasis will be placed on photon counting capabilities as this provides the ultimate sensitivity in steady-state fluorescence measurements as well as permitting lifetime studies. 

The importance of comparing time-dependent and steady-state fluorescence measurements is well illustrated by the difficulty of resolving purely static from purely dynamic quenching. In either case, the basic relationship between the steady-state fluorescence intensity and quencher concentration is the same. The Stem-Volmer relationship for static quenching due to formation of an intermolecular complex is i... 

The steady-state fluorescence measurements of pyrene in supercritical CO2 were made with a spectrometer assembly consisting mainly of Kratos optical parts. The custom built high pressure optical cell is equipped for detection at 90°. The emission was detected with a Hammamatsu IP-28 photomultiplier tube. The... 

Staab and coworkers have prepared stacked Q-P-Q triad 28 [80-83]. An X-ray structure determination of the molecule shows that the quinones are situated directly above and below the plane of the porphyrin, with their planes parallel to the porphyrin plane and 3.4 A from it. Steady state fluorescence measurements demonstrate strong quenching of the porphyrin first excited singlet state, which in turn suggests rapid electron transfer. Additional data were obtained from fluorescence lifetime measurements [83]. In dichloromethane, for instance, the lifetime of an analog of 28 in which the quinones were replaced with redox inactive dimethoxyphenyl substituents was 9.0 ns. In 28, this lifetime was reduced to 2 ) ps. 

As described in the previous section, we incorporated Et as an artificial DNA base at specific sites in duplex DNA (Fig. 12.12) [44-46]. Temperature-dependent absorption and steady-state fluorescence measurements prove the intercalation of the Et moiety in duplex DNA [44], The intercalation properties of the Et moiety do not depend significantly on the local duplex environment. Interestingly, the optical properties of Et seem not to interfere with the presence of the different counterbases T, G, C or A [45]. This result is remarkable with respect to the steric demand of the Et heterocycle and indicates a bulged position of the counterbase. 

Kong, K., Bers, M. W., and Tromberg, B. J (1997). Time-resolved and steady-state fluorescence measurements of beta-nicotinamide adenine dinucleotide-alcohol dehydrogenase complex during UVA exposure. Photochem. Photobio. B Biol. 37 91-95. 

To illustrate the capabilities of the system shown in Fig. 16.12, we present new, previously unpublished results from our laboratory. In Fig. 16.13, we illustrate results for three fluorescent probe molecules (pyrene, DCM [4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran], and PRODAN [6-propionyl-2-(/V,/V-dimethylamino)naphthalene]) that were doped within a series of PFFA/Pluronic P104 BP blends. In the initial experiments, 16 BP formulations were prepared manually using micropipettes, while subsequent experiments utilized the ALHS to prepare 21 BP formulations. These formulations were spun cast into thin films employing quartz microscope slides as substrates. To characterize the local microenvironment surrounding each probe within a given formulation, steady-state fluorescence measurements using a conventional spectrofluorometer were performed. 

The remainder of this chapter is organized as follows. Steady-state fluorescence measurements are reviewed briefly in Section 2. Time-resolved fluorescence measurements performed in our laboratory are discussed in some detail and are related to other work in Section 3. A discussion of processes other than injection which might contribute to the decay of D is given in Section 4. In order to give the reader some feeling for the evolution of our views on this complex problem, the presentation is roughly chronological. 

Kogej K, Vrhovsek A, Skerjanc J. Interactions between anionic polyelectrolyte and cationic surfactant steady-state fluorescence measurements. In Noda I, Kokufuta E, eds. Polyelectrolytes. Osaka Yamada Science Foundation, 1999 288-291. 

Figure 7. The variation of the rate of proton dissociation from excited hydroxypyrene trisulfonate on the molar concentration of the salt (O, ) time-resolved fluorescence measurements ( , ) steady-state fluorescence measurements (A) proton diffusion coefficient, normalized for pure water (data from Glietenberg et al. 1968). Open symbols, MgCl2 closed symbols, LiC104.

The enhanced emission of the neutral form recorded in these two examples may originate either from rapid recombination of H+ with 4>CT (see Scheme II) or from slow dissociation of 4>OH due to reduced activity of water in the cavity (see Figure 9). The contribution of each mechanism to the overall observation cannot be deduced from steady-state fluorescence measurements and necessitate kinetic analysis according to Equation (18). 

In steady-state fluorescence measurements on a specimen containing multiple types of fluorophores, the expected intensity is given by... 

The value of trilinear models is clearest in steady-state fluorescence measurements. They are also valuable in time-resolved fluorescence spectroscopy in situations where the appropriateness of a specific parametric equation for time decay, such as a sum of a few exponentials, is unclear. Although we are unaware of any work using trilinear models with other kinds of excited-state spectroscopy, trilinear models will be a valuable means of achieving component resolution whenever the absence of reliable parametric equations makes global analysis impossible. 

The interaclion between g and g was investigated through laser pumped dye laser spectroscopy at X=430 nm and steady state fluorescence measurements. Rgure 2 clearly shows that the thioether moiety is mostly responsible for the deactivation process occuring in the S. state and which is admittedly related to a back electron transfer. 

The light-harvesting system of green bacteria consists of BChl c containing chlorosomes attached to the cell membrane by a baseplate containing BChl a. The cell membrane contains the B 808-866 antenna complex and the reaction center. We report here a comparison of the properties of chlorosome preparations obtained by different treatments. Energy transfer in these preparations was studied by picosecond absorbance recovery and steady-state fluorescence measurements. The results are used to propose a new model for the structure of chlorosomes. 

The steady state fluorescence measurements were performed at 665 nm. The emission from our sample was then scanned from 670 to 750 nm. This resulted in an emission spectrum with a maximum around 684 nm.If one takes the small Stokes shift into account, clearly this must be the emission from the PS 2 core chlorophylls. It is thus reasonable to assume that we have indeed achieved an effective energy transfer from the LHC-II to the PS 2 core, i.e. the system seems to be intact.The experiment was then continued by adding small amounts of Triton X-100. As a result of this titration we could see a spectral shift of the emission maximum towards shorter wavelengths. The total fluorescence yield seemed to increase dramatically compared to the yield measured before the addition of Triton X-100. Furthermore, the fluorescence anisotropy increased from a value of below 0.1 to... 

Fluorimetry has experienced an explosive growth since the early 1980s, much of which has been driven by the use of fluorescence as a noninvasive technique for biology and biochemistry. Fluorescence techniques are widely used to quantify molecular parameters of different chemical, biochemical, and biological processes because of their inherent sensitivity, specificity and temporal resolution. In fact, the luminescence lifetime is an important characteristic of a fluorescent molecule and its environment. Many intra- and intermolecular processes are able to modulate the molecule emission which cannot be investigated by steady-state fluorescence measurements. For example, rotational diffusion,... 

Fluorescence analysis methods are now widely used because of their extreme sensitivity, which provides detection limits at picomolar levels and below, and the great variety of sample presentation methods available. Flowing liquids, soHd surfaces, concentrated solutions, and suspensions can all be studied in addition to measurements in dilute solution. This article is concerned with the quantitative relationships underpinning steady-state fluorescence measurements time resolved fluorescence is considered separately. 

---