Fluorescence isooctane

Isooctane porphyrin methyl esters reactivation of faded fluorescence benzene and petroleum ether can be employed in the same way [233, 289]... 

The conformation of bovine myelin basic protein (MBP) in AOT/isooctane/water reversed micellar systems was studied by Waks et al. 67). This MBP is an extrinsic water soluble protein which attains an extended conformation in aqueous solution 68 but is more density packed at the membrane surface. The solubilization of MBP in the AOT reversed micelles depends on the water/AOT-ratio w0 68). The maximum of solubilization was observed at a w0-value as low as 5.56. The same value was obtained for another major protein component of myelin, the Folch-Pi proteolipid 69). According to fluorescence emission spectra of MBP, accessibility of the single tryptophane residue seems to be decreased in AOT reversed micelles. From CD-spectra one can conclude that there is a higher conformational rigidity in reversed micelles and a more ordered aqueous environment. 

Dunn and Stich [78] and Dunn [79] have described a monitoring procedure for polyaromatic hydrocarbons, particularly benzo[a]pyrene in marine sediments. The procedures involve extraction and purification of hydrocarbon fractions from the sediments and determination of compounds by thin layer chromatography and fluorometry, or gas chromatography. In this procedure, the sediment was refluxed with ethanolic potassium hydroxide, then filtered and the filtrate extracted with isooctane. The isooctane extract was cleaned up on a florisil column, then the polyaromatic hydrocarbons were extracted from the isoactive extract with pure dimethyl sulphoxide. The latter phase was contacted with water, then extracted with isooctane to recover polyaromatic hydrocarbons. The overall recovery of polyaromatic hydrocarbons in this extract by fluorescence spectroscopy was 50-70%. 

The experimentally obtained values show larger divergence based on alkane fluorescence measurement. Walter et al. [148] and Luthjens et al. [65,128] published 0.8-0.9. Later the latter authors modified their value to 0.65 [149]. In solutions of isooctane, cyclohexane, or -hexane with naphthalene, Sauer and Jonah established this value as 0.5 0.1 this singlet formation probability is approximately constant during the decay of charged species up to 70 nsec [150]. In final product experiments/ = 0.34 [151], 0.53, and 0.47 [84] was estimated for cyclohexane, cix-decalin, and trans-6eca m, respectively. The low value for cyclohexane is due to the ionic reactions before recombination. 

AOT/isooctane Recombinant Cutinase Fluorescence study of cutinase in RMs to evaluate its structure and protein unfolding [54]... 

AOT/isooctane [304],refolding of recombinant proteins such as lysozyme [305], and refolding studies on triosephosphate isomerase using fluorescence resonance energy transfer [306]. 

In the presence of excess of cadmium ions, [Cd2+]/[S2-] = 2, Figures 3.4.3A and 3.4.3B show the fluorescence spectra at various water content. The unchanged spectra with the excitation wavelengths indicate a lower size distribution of the particles formed in mixed reverse micelles than that obtained in the case of the Cd(N03)2/ HMP/AOT/isooctane/water reverse micellar system. The shift of the emission maximum with the water content, w, can be related to the increase of the average size of the particles. For a sample synthesized for a given experimental... 

This phenomenon appears to be quite general since triethylamine quenches acenaphthene singlets in acetonitrile at the rate of 2 x 109 M-1 sec-1 as determined by intensity and lifetime measurements. Quenching of triphenylene fluorescence also occurs at this rate in acetonitrile but is two orders of magnitude slower in isooctane. P. S. Engel, Unpublished results. 

AOT-isooctane-H20 reversed micelles 50-A-diameter CdS particles generated in situ in reversed micelles from CdCl2 or Cd(N03)2 by H2S Reversed-micelle-entrapped CdS was fluorescence quenched by methylviologen band-gap excitation in the presence of Rh as catalyst and PhSH as sacrificial electron donor resulted in water photoreduction 611... 

AOT-isooctane-H20 reversed micelles Monodispersed CdS particles generated in situ in reversed micelles Size of CdS depended on the ratio of Cd2+ to S2 strong fluorescence was observed in the presence of excess Cd2+ high yield of CdS-mediated MV2+ photoreduction 612... 

Fig. 13 HPLC of vitamin E. (A) Standards of vitamin E vitamers. Column, 5-p.m Supelcosil LC-Si (250 X 4.6-mm ID) mobile phase, isooctane/ethyl acetate (97.5 2.5), 1.6 ml/min fluorescence detection, excitation 290 nm, emission 330 nm. Peaks (1) a-tocopherol (2) a-tocotrienol (3) /3-tocopherol (4) y-tocopherol (5) /3-tocotrienol (6) y-tocotrienol (7) 5-tocopherol (8) 5-tocotrienol. (B) Saponified rice bran sample. Chromatographic conditions as in (A) except for mobile phase isooctane/ethyl acetate/2,2-dimethoxypropane (98.15 0.9 0.85 0.1). (From Ref. 228. AOCS Press.)...

Figure 2. (Top) Stern-Volmer plots for the quenching of the fluorescence of colloi fcl CdS in AOT-entrapped water pools in isooctane by RMV + (0), MV2+ 4Q), and PhSH (0) (Bottom) Absorption and emission spectra of colloidal CdS in AOT entrapped water pools in isooctane. The shoulder observed at 400 nm is due to a spectrometer artifact.

Fig. 26. Increased fluorescent yield (arbitrary scale) per Tb3+ ion at 545 nm as produced by decreasing the volume of solubilizate in each micelle. V = volume of mixture (1 1 by volume) of 0.5M TbCl3 and 0.5M HPA (= hydroxy-phenylacetic acid) solutions which has been solubilized in 1 ml of 2 10 2mol dm-3 AOT in isooctane. [J. Colloid Interface Sci. 56, 168 (1976))...

FIGURE 5-52. Examples of normal phase separations, (a) Corn-oil tocopherols. Sample 10 /xL of corn oil in 100 /xL of mobile phase. Column Nova Pak Silica (4 jam), 3.9 mm ID x 150 mm. Mobile phase 0.3% isopropyl alcohol in isooctane. Flow rate 1.0 mL/min. Detection fluorescence 290 nm excitation and 335 nm emission. (b) Separation of vitamin E from vitamin A. Mobile phase 0.5% isopropyl alcohol in isooctane. Other conditions are the same as those in a with the exception that retinol was detected with 365 nm excitation and 510 nm emission, (c) Structures of compounds. 

Quinolones are amphoteric compounds that are soluble in polar organic solvents such as acetonitrile, methanol, ethanol, dimethylformamide, dichloromethane, and ethyl acetate.They are slightly soluble in water and are insoluble in nonpolar solvents such as hexane, petroleum ether, and isooctane. Most of these dmgs are fluorescent and quite stable in aqueous solution and toward light, except miloxacin, which is reported to be unstable. These inherent characteristics have made quinolones difficult to analyze by chromatographic methods. 

Fluorescence (, 3, 247 nm in neat p-dioxane) occurs with a quantum yield of 0.029 (184) in the liquid state only (183). Addition of water effects a diminution and a red shift while isooctane causes a blue shift, as well as a reduction in intensity. O2 (183) and N2O (187) are quenchers. It is thought that the fluorescence is from some form of excited aggregate whose composition varies with dilution, and that monomeric p-dioxane does not fluoresce (183). It has also been suggested that photodetachment of an electron might occur, and fluorescence might be a consequence of charge recombination (187). 

Fluorescent naphthol-based polymers were prepared by HRP-catalyzed polymerization of 2-naphthol in AOT/isooctane reverse micelles to give the polymer microspheres.31 The precipitated polymer was soluble in a range of polar and nonpolar organic solvents and possessed quinonoid structure. The reverse micellar system induced the peroxidase-catalyzed copolymerization of p-hydroxythiophenol and />ethylphenol, yielding the thiol-containing polyphenol particles.32 The attachment of CdS to the particles gave the CdS—polymer nanocomposite showing fluorescence characteristics. 

P>MA Particles. PIB-stabilized PbWA particles were prepared containing naphthalene [N] groups covalently attached to the fTWA chains. This was effected quite simply by adding l naphthylmethyl methacrylate to the NWA polymerization step of the particle synthesis. From reactivity ratios, one knows that the N groups are randomly distributed along the P>MA chains. The particles were purified by repeated centrifugation, replacement of the supernatant serum with fresh solvent (isooctane) and redispersion. A fluorescence spectrum of the dispersion was typical of that of a 1-alkyl-naphthalene. Chemical analysis indicated a particle composition IB/NWA/N of 13/100/10. 

Figure I. Fluorescence decay profile of N (lower curve, measured at 337 nm) and Ant (upper curve, 450 nm) for dispersions of PIB-stabilized F MA particles, labelled with N in the F MA phase, in isooctane containing 2 x 10 M Ant.

Figure 4. The decay of recombination fluorescence for solution of 10 M p-terphenyl-i/u and 3x10 M diphenylsulphide-c io in isooctane in various magnetic fields [23]. For convenience, the curves are shifted relative to each other. The oscillating component comes from the recombination of the singlet-bom pairs (diphenylsulphide-r io)V(p-terphenyl-(/i4). ...

Figure 6. The ratio between the fluorescence decay curves in high (9600 G) and weak (170 G) magnetic fields for recombination of (diphenylsulphide- fio) /(p-terphenyl- fi4) pairs in isooctane [29]. The concentration of />-terphenyl- fi4 is 10 M. It is seen that as the concentration of the hole acceptor, diphenylsulphide- fio, decreases from 0.12 M (curve a) to 0.012 M (curve b), the phase shift in oscillations appears and the oscillation amplitude decreases. Circles the theoretical fit to curve (a).

Even more important are reactions of radiolytic products with the precursors of these excited states. Results from recent experiments in which the solute luminescence and magnetic field effect were compared for radiolysis of cyclohexane or isooctane with 0.5-2.2 MeV electrons, 1-5 MeV protons, and 2-20 MeV a-particles suggested that the decrease in the solute luminescence and the magnetic field effect was due to both the increasing importance of crossrecombination and the "intervention of radicals or other transient species with the precursors" with the fluorescent states [63]. The effects of spin relaxation and ion-radical reactions in dense spurs were identified as likely causes for reduced magnetic field effects, fluorescence yields, and probabilities 0 in spurs from 17-40 keV x-rays as compared to the spurs from fast electrons [80]. 

Structural dependence on temperature is now best illustrated by example. Optically inactive poly(hexyl-2-methylpropylsilane) has an a parameter of 1.29 in THF indicating a rigid rod-like structure. Furthermore, in isooctane solution at ambient temperature the peaks of the UV absorption and fluorescence spectra are narrow, they mirror each other, and the Stokes shift is only 3 nm. These are indicative of an almost homogeneous photoexcited energy state with minimal structural variation in the main chain. Notwithstanding this conclusion, when the solution is cooled to -80 °C, the absorptivity increases, the peaks narrow, and the Stokes shift drops to 2.2 nm. It is thus assumed that the polymer attains a perfectly extended rod shape at this temperature. ... 

Tocopherols are analy2ed in their vmesterified form and separations are very easy by HPLC. The use of fluorescence detection provides very accmate results. The oil is diluted with eluent (3% tetrahydrofuran in isooctane) to 10 mg ml Pure standards are analy-... 

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