Hydration fluorescence

Post-column in-line photochemical derivatization permits fluorescence detection of the common aflatoxins Bl, B2, Gl, and G2 (60). Chromatographic evidence indicates that photolysis causes the hydration of the nonfluorescent Bl and Gl components to B2a and G2a components, respectively. Analysis of naturally contaminated com samples show no interfering peaks and permits the deterrnination of 1 and 0.25 ppb for Bl and B2, respectively. 

Principal component analysis has been used in combination with spectroscopy in other types of multicomponent analyses. For example, compatible and incompatible blends of polyphenzlene oxides and polystyrene were distinguished using Fourier-transform-infrared spectra (59). Raman spectra of sulfuric acid/water mixtures were used in conjunction with principal component analysis to identify different ions, compositions, and hydrates (60). The identity and number of species present in binary and tertiary mixtures of polycycHc aromatic hydrocarbons were deterrnined using fluorescence spectra (61). 

Naphthionic acid (4-aminonaphthalene-l-sulfonic acid) [84-86-6] M 223.3, m > 300°(dec), pK 2.68. It crystallises from H2O as needles of the 0.5 hydrate. Salt solns fluoresce strongly blue. 

Stilbenes that are used as fluorescent whitening agents are photolytically degraded by reactions involving cis-trans isomerization followed by hydration of the double bond, or oxidative fission of the double bond to yield aldehydes (Kramer et al. 1996). 

Duportail G, Klymchenko A, Mely Y, Demchenko AP (2002) On the coupling between surface charge and hydration in biomembranes experiments with 3-hydroxyflavone probes. J Fluoresc 12(2) 181-185... 

In order to confirm the large hydration behavior of phospholipid LB films only around their Tc, two-dimensional morphology of DMPE monolayers was observed by a fluorescence microscope. The two-... 

A short excursion into the physics and spectroscopy of intermolecular interactions is intended to illustrate the effects of fluorescence spectra change on the transition of dye molecules from liquid solvents to solid environments, on the change of polarity and hydration in these environments, and on the formation of excited-state complexes (excimers and exciplexes). 

Room temperature phosphorescence can be observed from dried proteins. Sheep wool keratin(47) has a phosphorescence lifetime of 1.4 s. Six lyophilized proteins were shown to exhibit phosphorescence at room temperature.(48) The spectra were diffuse, and the lifetime was non-single-exponential, which the authors interpreted as due to inhomogeneous distribution of tryptophans. As the protein was hydrated, the phosphorescence lifetime decreased. This decrease occurred over the same range of hydration where the tryptophan fluorescence becomes depolarized. Hence, these results are consistent with the idea that rigidity of the site contributes to the lifetimes. 

Use of the pH-sensitive membrane-impermeable flurophore pyranine based on the ratiometric method, which determines directly level of dissociation of pyranine from the ratio between the charged (nnprotonated) pyranine and total pyranine in the intraliposome aqneons phase Addition of impermeable DPX, which acts as a quencher to pyranine fluorescence, into the liposome external medium ensures lack of contribution of extraliposome medium pyranine fluorescence (18,22). This method is considered invasive as the pyranine has to be added in the hydration medium prior to liposome preparation and cannot be used for pH determination of intraliposome aqueous phase... 

We foimd that the ratiometric method is superior because it is not dependent on pyranine concentration and therefore free of error in pipeting (18,22,54). Calibration curves were constructed by preparing liposomes in which the hydration of the lipids to form MLV was done using solutions of high concentration at the desired pH in the range of 3.0 to 10.0. Gel-exclusion chromatography on a Sephadex column, as mentioned above, yielded a series of liposome preparations with a fixed external pH (pH 7.5), but different internal pH values determined by the buffer used for lipid hydration. Neither KI nor DPX, which quench the fluorescence of aqueous solutions of pyranine, has much effect on the fluorescence intensity of pyranine in the void volume after gel-exclusion chromatography, which indicates the complete removal of the pyranine from the extraliposomal medium. 

The most common assay uses 3a-hydroxysteroid dehydrogenase to form the 3-keto bile acid that is trapped by, for example, hydrazine hydrate, causing the reaction to go to completion. The co-factor NAD is reduced stoichiometrically and can be measured by ultraviolet absorption or more commonly by fluorescence at an activation of 345 nm and emission of 450 nm. Use of this enzyme measures all bile acids with a 3a-hydroxyl but not cholesterol, which has a 3p-hydroxyl, and does not measure bile acids with a sulphate or glucuronide group conjugated to the 3a-hydroxyl. 

A number of studies on the fluorescence decay of tyrosine, tyrosine derivatives, and small tyrosyl peptides have been carried out. 36-38 Whereas the tyrosine zwitterion and tyrosine derivatives with an ionized a-carboxy group exhibited monoexponential fluorescence decay (x = 3.26-3.76 ns), double- or triple-exponential decay was observed in most other cases. As in the case of the tryptophan model compounds, the complex decay kinetics were again interpreted in terms of rotamer populations resulting from rotation around the C —Cp bond. There is evidence to indicate that the shorter fluorescence lifetimes may arise from rotamers in which the phenol ring is in close contact with a hydrated carbonyl group 36 37 and that a charge-transfer mechanism may be implicated in this quenching process. 39 ... 

Tits, J., Stumpf, Th., Rabung, Th., Wieland, E. Fanghanel, Th. 2003. Uptake of trivalent actinides (Cm(III)) and lanthanides (Eu(III)) by Calcium silicate hydrates a wet chemistry and time-resolved laser fluorescence spectroscopy (TRLFS) study. Environmental Science and Technology, 37, 3568-3573. 

Irradiation of frozen aqueous thymine solutions produces the cis head-to-head (chh) dimer, the high quantum yield (0.5-1.0) being attributed to the preferred orientation of adjacent molecules in the microcrystalline thymine hydrate. The gradual isolation of substrate molecules in the photodimer matrix is associated135 with the appearance and increase in intensity of molecular fluorescence as photodimerization proceeds identical behavior... 

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