Shape fluorescence

T Tubular fluorescent lamp TC Tubular fluorescent compact lamp H High pressure HM High pressure mercury HI High pressure iodide HS High pressure sodium L Low pressure LS Low pressure sodium Q Quartz (halogen) lamp . T Tubular lamp . E Elliptical form (2) -D Double tube compact lamp -DE Double ended -L Long compact lamp -SE Self ballasted electronic -U U-shaped fluorescent lamp -Us U-shaped fluorescent lamp, short -EL Compact fluorescent lamp for external electronic ballast -with key letter T Tube diameter (in mm) (3) Lamp rated power (without ballast), in W. 

In view of the data obtained when extracts from P. sylvestris and D. dolichopetala were purified by immunoaffinity chromatography and analysed by ion-suppression, reverse phase HPLC, it would have been very tempting to assume that the application of these procedures to the analysis of extracts from dwarf-1 Zea mays, and other tissues, would also provide accurate quantitative estimates of endogenous lAA. The HPLC trace illustrated in Fig. 8B, in which a Gaussian-shaped fluorescent lAA-like peak is a major component, would appear to support this belief. However, the data in Fig. 8C show that such an assumption would have been incorrect and led to an inaccurate overestimate of lAA. 

We have previously pointed out that, under the appropriate conditions, the sigmoidally shaped fluorescence induction curves should also be observed when the PS II reaction centers are partially closed by short, pulsed light flashes and when the fluorescence yield is measured with a weak probe light flash delivered at some time 6t (30 - 100 ps) after the variable - intensity pump flash (3). This follows from the assumption that under either steady-state or flash-excitation conditions, the fraction of closed reaction centers q should depend simply on the number of photons absorbed by PS II In both cases. However, using pump flashes of less than 1 /is in duration, the fluorescence induction curves measured by the pump-probe technique have been shown to be exponential in shape [3.4]. Similar obsenrations have been made by Mauzerall and his co-workers [5.6] who concluded that the probability of escape of an exciton from a PS II unit with a closed reaction center to a unit with an open one. is less than 0.25 and that the apparent optical cross-section of PS II with open and closed traps is constant to within + 10 % [7]. The exponentiaiity of the pump-probe fluorescence Induction curves implies that the variable fluorescence Fy = (F[l ] - Fo)/(Fmax " Fq) is proportional to q under these conditions, where 1 represents the fiuence of the pump flash expressed in units of incident photons/cm. ... 

In the next section, methods based on the modification of phosphine oxides to provide novel phosphine oxides are discussed. New star-shaped and rod-shaped fluorescent phosphine oxides were obtained by the Pd-catalyzed Sonogashira couplings of the corresponding P=0-functionalized arylacetylenes with appropriate arylhalogenides. The elegant syntheses are shown in Schemes 10 and 11. ... 

Fig. IV-19. Fluorescence micrographs showing the shape transitions in monolayers of dimyristoylphosphatidylcholine (DMPC) (84%) and dihydrocholesterol (15%) and a lipid containing the dye, Texas Red. (From Ref. 228.)...

Micellar structure has been a subject of much discussion [104]. Early proposals for spherical [159] and lamellar [160] micelles may both have merit. A schematic of a spherical micelle and a unilamellar vesicle is shown in Fig. Xni-11. In addition to the most common spherical micelles, scattering and microscopy experiments have shown the existence of rodlike [161, 162], disklike [163], threadlike [132] and even quadmple-helix [164] structures. Lattice models (see Fig. XIII-12) by Leermakers and Scheutjens have confirmed and characterized the properties of spherical and membrane like micelles [165]. Similar analyses exist for micelles formed by diblock copolymers in a selective solvent [166]. Other shapes proposed include ellipsoidal [167] and a sphere-to-cylinder transition [168]. Fluorescence depolarization and NMR studies both point to a rather fluid micellar core consistent with the disorder implied by Fig. Xm-12. 

An important extension to the simplest upconversion experiment at a single detection frequency M2 is the practice of measuring time-resolvedfluorescence spectra, that is, the shape of the fluorescence spectrum... 

Loring R F, Van Y J and Mukamel S 1987 Time-resolved fluorescence and hole-burning line shapes of solvated molecules longitudinal dielectric relaxation and vibrational dynamics J. Chem. Phys. 87 5840-57... 

The shape of the broad absorption curve in Figure 9.17 is typical of that of any dye suitable for a laser. It shows an absorption maximum to low wavelength of the Og band position, which is close to the absorption-fluorescence crossing point. The shape of the absorption curve results from a change of shape of the molecule, from Sq to 5i, in the... 

Figure 9.46 Rotational structure of the Ojj bands in the fluorescence excitation spectra of s-tetrazine dimers at about 552 run. Bottom Ojj band of planar dimer. Middle Ojj band of T-shaped dimer with transition in monomer unit in stem of T. Top Ojj band of T-shaped dimer with transition in monomer unit in top of T. (Reproduced, with permission, from Haynam, C. A., Brumbaugh, D. V and Levy, D. H., J. Chem. Phys., 79, f58f, f983)...

Solvent Influence. Solvent nature has been found to influence absorption spectra, but fluorescence is substantiaHy less sensitive (9,58). Sensitivity to solvent media is one of the main characteristics of unsymmetrical dyes, especiaHy the merocyanines (59). Some dyes manifest positive solvatochromic effects (60) the band maximum is bathochromicaHy shifted as solvent polarity increases. Other dyes, eg, highly unsymmetrical ones, exhibit negative solvatochromicity, and the absorption band is blue-shifted on passing from nonpolar to highly polar solvent (59). In addition, solvents can lead to changes in intensity and shape of spectral bands (58). 

When sublimed, anthraquinone forms a pale yeUow, crystalline material, needle-like in shape. Unlike anthracene, it exhibits no fluorescence. It melts at 286°C and boils at 379°—381°C. At much higher temperatures, decomposition occurs. Anthraquinone has only a slight solubiUty in alcohol or benzene and is best recrystallized from glacial acetic acid or high boiling solvents such as nitrobenzene or dichlorobenzene. It is very soluble in concentrated sulfuric acid. In methanol, uv absorptions of anthraquinone are at 250 nm (e = 4.98), 270 nm (4.5), and 325 nm (4.02) (4). In the it spectmm, the double aUyflc ketone absorbs at 5.95 p.m (1681 cm ), and the aromatic double bond absorbs at 6.25 p.m (1600 cm ) and 6.30 pm (1587 cm ). 

Lamp types (a) incandescent and tungsten-halogen lamp shapes (b) fluorescent and compact fluorescent lamp shapes (c) typical high-pressure sodium lamp (d) typical metal halide lamp. 

Both compounds were non-fluorescent. Compound KM-1 was similar to PMs in the absorption maximum (A.max 488 nm) but not in the spectral shape, whereas KM-2 was similar to PMs in the spectral shape but not in the absorption maximum at 515 nm (Fig. 9.10). The chemical structures of KM-1 and KM-2 have been determined by high-resolution mass spectrometry and NMR spectrometry (Fig. 9.11 Stojanovic, 1995). 

After extraction, each phase may be studied independently in order to obtain a useful qualitative evaluation of the components in the original sample. The selectivity and specificity of fluorescence analysis can be especially beneficial in identification of PAHs. For example, some components could be identified by examining the fluorescence spectra of the organic and aqueous phases. Characteristic peak shapes may reveal identities of the components. For more complicated systems in which the spectra overlap, lifetime measurements may be used to identify components (27). 

Depolarization measurements, coupled with fluorescence lifetimes, are correlated with rates of molecular rotation to obtain estimates of molecular conformation, volume, and shape. 

This chapter presents new information about the physical properties of humic acid fractions from the Okefenokee Swamp, Georgia. Specialized techniques of fluorescence depolarization spectroscopy and phase-shift fluorometry allow the nondestructive determination of molar volume and shape in aqueous solutions. The techniques also provide sufficient data to make a reliable estimate of the number of different fluorophores in the molecule their respective excitation and emission spectra, and their phase-resolved emission spectra. These measurements are possible even in instances where two fluorophores have nearly identical emission specta. The general theoretical background of each method is presented first, followed by the specific results of our measurements. Parts of the theoretical treatment of depolarization and phase-shift fluorometry given here are more fully expanded upon in (5,9-ll). Recent work and reviews of these techniques are given by Warner and McGown (72). 

Any factor that affects the size or shape of a molecule, the hindered movement of a fluorophore within a molecule, or the energy transfer within the molecule will affect the measured depolarization of its fluorescence emission. Therefore, the conformation of humic fractions in solution can be studied as a function of pH, ionic strength, temperature, and other factors by depolarization measurements. The principle of the method is that excitation of fluorescent samples with polarized light stimulates... 

---