Fluorescence in ethanol

UV absorption maxima occur at 236, 274 and 316 nm. The molecular formula of zearalenone is C18H22Os, its molecular weight is 318.4 g/mol and its melting point is 162-163°C (Blackwell et al. 1985 Josephs et al. 2003). The maximum fluorescence in ethanol occurs with irradiation at 314 nm and with emission at 450 nm. Its solubility in water is about 0.002 g/100 ml. In an aqueous solution of inositol, the presence of zearalenone can change the crystal structure of this alcohol, which indicates the possibility of interaction between both substances (our observations). Moreover, zearalenone is slightly soluble in hexane and progressively more so in benzene, acetonitrile, methylene chloride, methanol, ethanol and acetone. However, it is readily soluble in aqueous alkali. 

Effect of Anthracene Concentration on the Intensity of Delayed Fluorescence in Ethanol° b... 

This structure for sempervirine was soon disproved by two syntheses of the compound XXV, which was shown to possess properties quite different from those reported for sempervirine (88, 89). In particular, the compound XXV was a weak base, pKa 5.0, which exhibited only a faint fluorescence in ethanol solution. Its UV-spectrum in acid solution was markedly different from that in neutral solution. This was in contrast to sempervirine, which exhibits virtually identical spectra in neutral and acid solutions, but a markedly different spectrum in alkaline solution (88, 89). 

P. C. J. H. W. Offen. Pyrene Fluorescence in ethanol and cyclohexane under pressure The journal of Chemical Physics, 1973, 59, 801-806. 

FIGURE 4. Absorption and fluorescence soectra of HNA, curve 1 absorption in absolute ethanon° curve 2 absorption in cyclohexane=° curve 3 fluorescence in ethanol, 77°K, excitation at 25,600 cm" 42 curve... 

Most of the thiazoles studied absorb in the ultraviolet above 254 nm, and the best detection for these compounds is an ultraviolet lamp (with plates containing a fluorescent indicator). Other indicator systems also exist, among which 5% phosphomolybdic acid in ethanol, diazotized sulfanilic acid or Pauly s reagent (Dragendorff s reagent for arylthiazoles), sulfuric anisaldehyde, and vanillin sulfuric acid followed by Dragendorff s reagent develop alkylthiazoles. Iodine vapor is also a useful wide-spectrum indicator. 

Polyethylene glycol 4000 silymann enhancement 5% in ethanol, optimum for fluorescence after 24 h [274]... 

Note A 5% solution of polyethylene glycol 4000 in ethanol can be sprayed onto the chromatogram [2, 4] for the purpose of increasing and stabilizing the fluorescence instead of dipping it in liquid paraffin - -hexane (1 - - 2). If this alternative is chosen the plate should not be analyzed for a further 30 min since it is only then that the full intensity of the fluorescence develops [6]. 

Extraction and purification of luciferin and luciferase (Viviani etal., 2002a) To isolate luciferin, the lanterns of the Australian A. flava were homogenized in hot 0.1 M citrate buffer, pH 5, and the mixture was heated to 95°C for 5 min. The mixture was acidified to pH 2.5-3.0 with HCl, and luciferin was extracted with ethyl acetate. Upon thin-layer chromatography (ethanol-ethyl acetate-water, 5 3 2 or 3 5 2), the active fraction of luciferin was fluorescent in purple (emission Lav 415 nm when excited at 290 nm). To isolate the luciferase, the cold-water extract prepared according to Wood (1993 see above) was chromatographed on a column of Sephacryl S-300. On the same... 

Shimomura and Johnson, 1969). The blue fluorescent substance showed an ultraviolet absorption maximum at 350 nm (in ethanol) thus, it was named AF-350 (renamed coelenteramine later). We obtained about 1 mg of AF-350 from 125 mg of pure aequorin that had been extracted and purified from 2.5 tons of Aequorea, and then determined its structure as shown in Fig. 4.1.9 (Shimomura and Johnson, 1972). 

Fig. 9.13 Absorption spectrum of one of the luciferin precursors of Mycena cit-ricolor in methanol (dash-dot line, A.max 369 nm). The absorption and fluorescence emission spectra of the decylamine-activation product of the same precursor in neutral aqueous solution (solid lines abs. Amax 372 nm and fl. Xmax 460 nm), and in ethanol (broken lines abs. Amax 375 nm and fl. Amax 522 nm). The chemiluminescence spectrum of the same activation product (dotted line, A.max 580 nm). The dotted line (7max 320 nm) is the absorption spectrum of M. citricolor natural luciferin reported by Kuwabara and Wassink (1966).

Properties of the activation product. The two decylamine-activation products (luciferins) showed similar absorption characteristics (A.max 372 nm in water, and 375 nm in ethanol), which clearly differ from the absorption peak of the natural luciferin (320 nm) reported by Kuwabara and Wassink (1966). The fluorescence emission of the activation products varied significantly by solvents, showing a peak at 460 nm in neutral aqueous solution and a broad peak at 485-522 nm in ethanol. They emitted chemiluminescence (A.max 580 nm) in the presence of CTAB, H2O2 and Fe2+ (Fig. 9.13), in resemblance to the (NH4)2S04-activation product of panal (A.max 570 nm). 

When a photoprotein solution (1.3 ml) was shaken with ethanol (0.7 ml) containing one drop of concentrated HC1 and then the mixture was extracted twice with 2 ml each of ethyl acetate, about 75% of the chromophore was extracted into the ethyl acetate extract. The chromophore isolated showed an absorption peak at 398 nm in neutral methanol (Fig. 10.2.5). The isolated chromophore was practically non-fluorescent, like the native photoprotein. However, the acidification of a methanolic solution with HC1 resulted in a sharpening and two-fold increase of the 398 nm absorption peak, accompanied by the appearance of fluorescence. In aqueous 0.1 M HC1, two fluorescence emission peaks (595 nm and 650 nm) were found, together with a corresponding excitation peak (400 nm). Treatment of the 398 nm absorbing chromophore with 0.1 M NaOH resulted in a rapid loss of the 398 nm absorption peak. Dithionite did not affect the 398 peak, suggesting that the chromophore does not contain Fe3+. 

Figure 7. Dependence of the fluorescence quamum yield of BMPC on solvent viscosity ( ) in linear alcohols, from methanol to dccanol, at 25°C, (o) in absolute ethanol between 200 and 298 K. The quantum yields were measured on optically thin samples (Am <0.2). The value in ethanol, 5.7x10, was determined relative to quinine sulfate in 0.5 mol 1" HjSO ((j)p=0.55 [62]) and 9,10-diphenylanthracene in cyclohexane (4ip=0.90 [63]). It was then used as a reference for the determinations in the other alcohols.

The synthetic alkaloid coralyne (Scheme 1) on the other hand is a planar molecule and is not readily soluble in aqueous buffers. It is highly soluble in ethanol and methanol. Coralyne is characterized by strong absorption maxima at 219, 300, 311, 326 and 424 nm with characteristic humps at 231, 360 and 405 nm in 30% (v/v) ethanol. It is highly fluorescent and gives an emission spectrum with a maximum at 460 nm when excitation was done either at 310 or 424 nm. It was observed that both absorbance and the fluorescence pattern of coralyne remained unaltered in buffer of various pH values ranging from 1.0 to 13.0 and also with salt concentration ranging from 4.0 to 500 mM. This implied that hydrophobic environment favoured the increment of their fluorescence properties [144]. 

FIGURE 10.13 The TLC profiles of labeled peaks isolated from [U- C]ascorbic-acid-modified calf lens protein obtained from Bio-Gel P-2 chromatography. Peaks 2 to 7 were spotted on a preparative silica gel TLC plate and developed with ethanol/ammonia (7 3, v/v). The fluorescence in each lane was detected by irradiation with a Wood s lamp at 360 nm, and the pattern of radioactivity was determined by scanning the plate with AMBIS imaging system. (Reprinted with permission from Cheng, R. et al., Biochim. Biophys. Acta, 1537, 14-26, 2001. Copyright (2001) Elsevier.)... 

Figure 4. Absorption and emission of TIN and MT in different solvents (I) absorption of TIN in methylcyclohexane/isopentane at 150 K (II) absorption of TIN in ethanol/methanol at 150 K (III) absorption of MT in hexane at 296 K (IV) (a) fluorescence and (b) phosphorescence of TIN or MT in 20 20 1 ethanol/ether/pyridine at 90 K (V) fluorescence of TIN in methylcyclohexane/isopentane at 90 K.

Using picosecond flash spectroscopy Gupta et al. 2k) reported for 2-hydroxyphenylbenzotriazole in ethanol a short-lived transient (6 ps) followed by a transient absorption whose lifetime is estimated to be 600 ps. The authors assigned the short-lived transient to the "vertical singlet" while the long-lived transient is presumably the "proton transferred species". These measurements of transient absorptions with the picosecond flash method confirm our results derived from the fluorescence emission using the phase fluorimetric method. 

Nanosecond flash spectroscopic studies showed that II fluoresces in CH2CI2 and ethanol solutions at room temperature. The emission has a lifetime less than 1.0 nsec in either solvent and cannot be resolved from the laser profile. Quantum yield of... 

In a less polar solvent, 951 ethanol, absorptions at 241 and 286 nm were reported with the A - B transition being obscured by solvent absorption. Also in HFIP, DMT displays a fluorescence approximately 100 times as intense as in ethanol solution was reported. 

The quantum yields are 0.15-0.21 in ethanol and 0.01-0.02 in an aqueous medium, but in micelles, the quantum yields are five to tenfold increased. The aggregation of these dyes was studied in [53]. The amphiphilic squaraines 4 combine favorable photophysical properties and good solubility in aqueous media and in addition interact efficiently with micelles, and therefore have the potential to be used as NIR fluorescent sensors. However, our own investigations show that aniline-based squaraines lack chemical and photochemical stability when compared to oxo-squaraines with heterocyclic end-groups. 

In most cases, the linear absorption is measured with standard spectrometers, and the fluorescence properties are obtained with commercially available spectrofluo-rometers using reference samples with well-known <1>F for calibration of the fluorescence quantum yield. In the ultraviolet and visible range, there are many well-known fluorescence quantum yield standards. Anthracene in ethanol (Cresyl Violet in methanol (commonly used reference samples for wavelengths of 350-650 nm. For wavelengths longer than 650 nm, there is a lack of fluorescence references. Recently, a photochemically stable, D-ji-D polymethine molecule has been proposed as a fluorescence standard near 800 nm [57]. This molecule, PD 2631 (chemical structure shown in Fig. 5) in ethanol, has linear absorption and fluorescence spectra of the reference PD 2631 in ethanol to... 

Gramicidin exhibits strong fluorescence in 95% ethanol. The excitation maximum is at 286 nm and the emission maximum is at 337 nm. The fluorescence intensity was linear with respect to concentration in solution51. 

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