Vitamin fluorescence quenching

This factor is particularly significant in OFBD since biological samples or isolates are used. In addition to background interference, fluorescence quenching has been demonstrated in a variety of biomolecules such as thiamine (vitamin Bi),(27) nicotinamide/28 nucleosides/nucleotides,(29) and pyruvate/30 To circumvent the obvious limitations associated with the use of UV or visible fluorophores in OFD, the potential... 

Fluorescence determinations are important to analyze cysteine, guanidine, proteins, (LSD), steroids, a number of enzymes and coenzymes, and some vitamins, as well as several hundred more substances. A fluorometer can be used to verify conformational changes in multipartite operator recognition by. -repressor as explained in a journal article by Deb et al. (2000). Upon titration with single operators site, the tryptophan fluorescence quenches to different degrees, suggesting different conformations of the DNA-protein complexes. 

D. S. Chatellier and H. B. White III, What Color Is Egg White A Biochemical Demonstration of the Formation of a Vitamin-Protein Complex Using Fluorescence Quenching, J. Chem. Ed. 1988,65, 814. 

Other studies have brought out the ambivalent characteristics of many porphyrins in charge-transfer adducts [189-192]. Porphyrin fluorescence quenching, a characteristic of complexation, occurs for a variety of aromatic donors and acceptors. The porphyrins are known [189-192] to form charge-transfer complexes with some amino acids and the indole tryptophan [193], some steroids [194], and some vitamins [194]. 

Additional support for the nonequivalence of the two subunits has been claimed by Everse 360) from fluorescence quenching studies of the stoichiometry of vitamin A acid binding. The nonlinear nature of such quenching Section II,F) might, however, require more direct binding studies for confirmation, especially since the results were obtained in the absence of coenzyme. 

Energy transfer experiments with factor V, factors Va and VaLC. Similar experiments have been performed with another factor involved in prothrombin activation but which is not vitamin K-dependent, namely factor V. The experiments were done with PC-PS (50-50) mixture labelled with 5 % PDPC or PDPA, at a single phospholipid-to-protein molar ratio, = 530. Fluorescence quenching values are reported in Table III. They are of the same magnitude with both probes, for factor V, factor Va and for factor VaLC in the absence of calcium. We conclude, therefore, that no significant selectivity for a particular class of lipid occurs. 

CdSe QDs have been used as an optical probe for the analysis of vitamin Bi concentration (Sun et al. 2008). The technique comprises the fluorescence quenching of light emitted by the CdSe QDs in presence of vitamin Bi under alkaline conditions. Vitamin Bi is an efficient quencher and can interrupt the radiative recombination process by adsorbing on the surface of CdSe QDs. The QDs produced an emission at 591 nm with excitation at 380 nm. Thus, vitamin Bi was determined from the linear relationship between concentration of vitamin Bi and fluorescence quenching of QDs. The obtained LOD was achieved at nanogram scale. The concentration of vitamin Bi in tablet and injection samples was determined by this method. 

A detailed discussion of fluorescence quenching, fluorescence, and other non-destructive TLC detection methods such as the use of reagents giving reversible color reactions and various biological methods was published by Barrett (1974). Although visualization with UV light is nondestructive with most substances and, therefore, well suited for preparative purposes, rearrangement of structure can sometimes occur—for example, with some steroid and vitamin molecules. 

Perisic-Janjic, N. U., Popovic, M. R., and Djakovic, T. Lj. (1995). Quantitative determination of vitamin B complex constituents by fluorescence quenching after TLC separation. Acta Chromatogr. 5 144-150. 

Vitamin K-related compounds can be visualized in a non-destructive way by fluorescence quenching of dichlorofluorescein or rhodamine B. This procedure, however, is not very sensitive and is suited only to localize the zones of interest after a preparative fractionation step. More specific and sensitive detection methods using spray reagents to visualize K vitamins have been reviewed by Lefevere et al. (73). These color reactions result in lower detection limits than fluorescence quenching, but they are destructive for the quinones. 

Nondestructive detection of K vitamins can be performed either by elution of separated bonds (localized by a standard spot) with chloroform and following determination of K vitamin concentration by UV detection (53) or mass selective detection (54,58). Densitometric scanning of TLC plates, based on either absorption, fluorescence, or fluorescence quenching of coated plates (55), is another method for nondestructive detection and can be used with external as well as internal standardization. The introduction of this quantitation method resulted in an improvement in terms of speed, sensitivity, and precision of TLC but could not prevent the advance of HPLC applications in past decades. 

TLC was used for both qualitative (26-28) and quantitative analysis (29-31) of flavins in different matrices. The separation and quantitative determination by fluorescence quenching of the B-complex vitamins in some pharmaceutical products was performed using a newly synthesised carbamide formaldehyde polymer aminoplast with solvent systems 1-butanol/water/acetone (25 9 5, v/v) and 1-butanol/methanol/benzene/water (20 10 10 8, v/v) (29). 

Fluorimetric methods of analysis make use of the natural fluorescence of the analyte, the formation of a fluorescent derivative or the quenching of the fluorescence of a suitable compound by the analyte. Fluorescence cannot occur unless there is light absorption, so that all fluorescent molecules absorb, but the reverse is not true only a small fraction of all absorbing compounds exhibits fluorescence. The types of molecule most likely to show useful fluorescence are those with delocalised ji-orbital systems. Often, the more rigid the molecule the stronger the fluorescence intensity. Naturally fluorescent compounds include Vitamin A, E (tocopherol). 

A protein of similar molecular weight to that of rat oncomodulin, rat and rabbit parvalbumins, S100, and the vitamin D-dependent calcium-binding proteins has been isolated from chicken gizzard smooth muscle. In this case, however, the fluorescence emission from the four tyrosine residues is quenched by Ca2+ binding.(160) The decrease in fluorescence intensity was used to suggest that there are two different classes of Ca2+binding sites. 

The riboflavin binding protein that occurs in eggs has been exploited for the radio-ligand binding assay of riboflavin. Because binding to the protein quenches the native fluorescence of riboflavin, it can be exploited for a direct titrimetric fluorescence assay of the vitamin in urine and other biological samples (Kodentsova et al., 1995). 

Photoinduced electron transfer quenching of a porphyrin-cored dendrimer was first reported in compound 52, where the fluorescence of the Zn core is quenched in acetonitrile by vitamin K3 (2-methyl-1,4-naphtoquinone) [123]. 

The dendritic molecule 12 with an integrated porphyrin core and a catechol surface could be dissolved in acetonitrile. Its fluorescence was easily quenched by vitamin K3, which presumably finds accommodation within the micellar core. Attempts to dissolve a porphyrin within the porphyrin micelle failed. They are too large and cannot interact with the dendritic porphyrin . 

NH4OH in water as solvent. When adsorbents containing fluorescent indicators are used, all forms and derivatives of vitamin Bs can be detected through fluorescence, or through quenching of indicator fluorescence in ultraviolet (UV) light (254 nm). 

Flavins are vitamine B2 and bind to proteins as coenzyme. Some photoreceptors contain flavins which receive photons. Iso-alloxazine nucleus being chromophore of various flavins is yellow dye and intensely emits greenish fluorescence in organic and aqueous solutions. The fluorescence of flavins is remarkably quenched when they bind to protein moiety. Among amino acid... 

The rapid decay of the excited state of pyrene P in micelles of hexadecyl pyridinium chloride, which is a known quencher of fluorescence, is in contrast to the lifetimes of P in nonquencher micelles such as Brij 35 and NaLS where lifetimes are of the order of 300 to 350 ns. In mixed Brij 35-CPC micelles, even when there are only a few molecules of CPC per micelle the net lifetime of pyrene falls to around 80 ns [75]. Preliminary experiments on quenching of photochemical reactions using menadione (vitamin K3) as solute show that on photolysis in aerated methanol this compound produces a fluorescent product. Photolysis at about 350 nm of menadione solubilized in NaLS or hexadecylpyri-dinium chloride micelles produces different results anionic surfactant solutions containing menadione exhibit fluorescence after photolysis, whereas the cationic solutions do not. Decomposition of menadione in NaLS was estimated to be 3.5 times higher than in hexadecylpyridinium chloride solutions. 

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