Quinoxaline fluorescence

Jaung JY (2006) Synthesis and halochromism of new quinoxaline fluorescent dyes. Dyes Pigments 71 245-250. doi 10.1016/j.dyepig.2005.07.008... 

The formation of relatively stable fluorescent products by the reaction of adrenaline with ethylenediamine (and certain other primary amines) in air, first reported in 1948 by Natelson et was adapted by Weil-Malherbe and Bone in 1952 for the assay of catecholamines.197 198 Since 1952 much work, largely of an empirical nature, has been carried out to improve the analytical procedure since often apparently minor variations of the reaction conditions have a significant effect on the fluorescence observed (see Section V, E, 4). Paper chromatographic examination of the reaction mixtures obtained from adrenaline and noradrenaline suggested that more than one product could be formed in each case.199-205 The main fluorescent product of the interaction of adrenochrome (1) (obtained by oxidation of adrenaline) and ethylenediamine in air has been obtained as a crystalline solid by Harley-Mason and Laird and shown to be 2,3-dihydro-3-hydroxy-l-methylpyrrolo[4,5-g]quinoxaline (94) (7% yield).206,207 This compound has two hydrogen atoms less than... 

The fluorescence spectra of quinoxalin-2-one and 3-substituted quinoxalin-2-ones have been reported and correlated with the absorption spectra.252 253... 

The detection of the individual C vitamers is complicated by their distinctly different properties. Although AA and DHAA are both ultraviolet (UV) absorbers, the absorbance maximum of DHAA is between 210 and 230 nm (15,18,42,43). For practical detection purposes, this makes DHAA particularly susceptible to interferences from a number of naturally occurring food constituents and limits the choice of reagents and solvents. In contrast, AA exhibits a pH-dependent absorbance maximum of 245-265 nm, which makes UV absorbance an ideal choice for detection. On the strength of its reducing capacity, AA can be detected electrochemically, but DHAA is electrochemically inactive. Neither AA nor DHAA fluoresce naturally. However, DHAA readily forms a fluorescent quinoxaline derivative upon reaction with o-phenylenediamine. As a result, chemical derivatization is often used to achieve the sensitivity needed to detect the naturally occurring vitamin C in food. 

The X-ray crystal structures of pyrazine V.JV -dioxide (134) <02AX(E)1253>, the P-polymorph of phenazine (135) <02AX(C)181>, cobalt(III) complexes of pyrazine-2,6- and pyridine-2,6-dicarboxylic acids <02JIC458>, and bis-urea-substituted phenazines <02ZN(B)937> were reported. Fluorescent pyrido[l,2-a]quinoxalines 136 prepared as pH indicators were examined by X-ray crystallography <02JCS(P2)181>, as were macrocyclic quinoxaline-bridged porphyrinoids obtained from the condensation of dipyrrolylquinoxalines 137 and 1,8-diaminoanthracene... 

The fluorescence and phosphorescence of quinazoline, 6-chloro-4-phenyl-and 6-chloro-l-methyl-4-phenylquinazolin-2(lH)-one were recorded in ethanol containing 1% of concentrated sulfuric acid. The luminescence of these compounds on thin-layer chromatography (TLC) plates saturated with ethanol was reported. 4-Morpholino- and 4-piperidino-6-methoxy-2-phenyl-quinazoline also have luminescent properties, and the ultraviolet fluorescence in the crystals and in hexane or benzene solution was discussed. The time and wavelength resolved emission from quinazoline vapor at low pressures was studied with a pulsed frequency double-dye laser and were compared with those of quinoxaline and cinnoline. ... 

Since modern structural determination depends heavily upon H and C NMR analysis, information from IR and UV spectroscopies is less abundant than formerly. However, these spectroscopies are still useful to study photophysical properties, chemical behavior, and electronic orientation of the substituents in heteroaromatics. The pH dependence of both electronic and IR spectra of pyrazine has been examined to obtained p. values and information about the solute-solvent interactions, respectively <84JST(i 14)367). Electronic absorption taken in conjunction with fluorescence spectra indicate that 1,4-dihydro-2,3-quinoxalinedione exists in its diketo form irrespective of the nature of the solvent, by comparison with the spectra of the parent quinoxaline and 1,4-dimethyl-2,3-quinoxalinedione <87MI 603-01). New measurements of the singlet-triplet absorption spectra of pyrazine and pyrazine-d 4 at longer pathlengths and higher vapor pressures have been recorded <93aci537). 

An alternative approach is to utilise the fluorescence which is exhibited by the product of the condensation ofdehydroascorbic acid with o-phenylenediamine. The quinoxaline produced fluoresces at 427 nm when irradiated at 350 nm. Generally the procedure consists of oxidising any L-ascorbic acid present to dehydroascorbic acid, so that the total may be determined spectrofluorimetrically. 

Detailed examination of the ultraviolet absorbing properties of quinoxalin-2-one as a function of pH and solvent has been carried out, and the fluorescence spectra of various quinoxalin-2-ones have been reported. The fluorescence of quinoxalin-2-one has been explored for analytical purposes. 

The fluorescence spectra of certain pyrrolo[l,2-a]quinoxalines have been recorded and compared with those of various quinoxaline derivatives. ... 

The tetracyclic compound 90, a photoaddition product of flavoquinone and acetylenic enzyme inhibitors, decomposes in alkali to give the highly fluorescent pyrrolo[l,2-a]quinoxaline 91." °... 

Bazzar M, Ghaemy M, Alizadeh R. Novel fluorescent light-emitting polymer composites bearing 1,2,4-triazole and quinoxaline moieties reinforcement and thermal stabilization with silicon carbide nanoparticles by epoxide functionalization. Polym Degrad Stab 2012 97(9) 1690-703. 

Vitamin C is another soluble vitamin frequently determined in foodstuffs using fluorimetric detection. It is most often oxidized to dehydroascorbic acid with HgCl2 or 2,6-dichloroindophenol, which is subsequently reacted with p-phenylenediamine to form a fluorescent quinoxaline derivative (Figure 1). The method can be implemented in an automated fashion. The determination of total vitamin C (ascorbic and dehydroascorbic acid) in foods (vegetables and fruits) is also of great interest. The recommended method uses reversed-phase ion-pair LC and fluorimetric detection. Total vitamin C and total isovitamin C (erythorbic and dehydroerythorbic acids) can be determined similarly by prior extraction with trichloroacetic acid and precolumn derivatization, wherein ascorbic and erythorbic acids are oxidized enzymatically and total dehydroascorbic and dehydroerythorbic acids are treated with o-phenyl-enediamine. 

The physicochemical properties of the water-soluble vitamins are extensively utilized in chemical methods. A method for quantitative vitamin C (ascorbic acid, AA) measurement in food and physiological samples is based on a reaction of the keto groups in dehydroascorbic acid (DHA) with o-phenylenediamine (OPD) to give a fluorescent quinoxaline. This method involves the oxidation of AA to DHA, followed by the measurement of total AA in the sample. The reductive capabilities of AA can especially be utilized for direct electrochemical (amperometric or coulometric) measurement when coupled with HPLC separation. 

In the absence of collisions, no emission in the phosphorescence region has been detected, but the pronounced triplet character of the excited system may be evidenced by the T T absorption or the T-T energy transfer. In quinoxaline, a strong T-T absorption appears (its intensity is practically the same in the presence and absence of collisions) at a time scale much shorter than the long fluorescence decay (Soep and Tramer, 1975). A triplet yield of the order of one has been found for pyrazine and pyrimidine by the biacetyl... 

In contrast to thiophene-5,5 -dioxide, the non-aromatic character of which limits the stability of the derived materials, the aromatic dibenzothiophene-5,5 -dioxide is very stable and topologically equivalent to a fluorene moiety. Its LUMO energy level is 1 eV Iowct than that in fluorene [168], and several highly fluorescent molecular and oligomeric materials based on dibenzothiophene-5, 5 -dioxide have been synthesized and studied (125 and 126). Diphenylamino end-capped dibenzothiophene-5,5-dioxide derivatives 125a-c were used as emitters [73a, 169, 170], the dibenzothiophene-5,5-dioxide-quinoxaline derivative 126 was used as an electron-transporting material [171], and multilayer OLEDs based on these compounds demonstrated excellent performance (Table 19.5). 

Eight heterocyclic aromatic amine carcinogens were extracted from cooked meats. A Cjg column and a complex 30-min 95/5- 45/55 water (lOmM triethylamine phosphate at pH 3.6)/acetonitrile resolved 2-amino-1-methyl-, 2-amino-3,8-dimethyl-, and 2-amino-3,4,8-trimethylimidazo[4,5-/]quinoxaline with monitoring by UV (A = 262 nm) and fluorescence (A = 307 nm, ex 370 nm, em). A 40-min 95/5—>-20/80 water (25 mM triethylamine phosphate at pH 3.6)/acetonitriIe gradient on the same column resolved 2-amino-1,6-dimethylimi-... 

In this way, generally after localisation through the fluorescence of the substances themselves, determinations have been carried out of coumarin derivatives, following chromatographic separation from lemon and grapefruit oils [729] quinoxaline derivatives of 2-ketoacids [651] benzo-(a)-pyrene [599] and vitamin Bg factors [702]. Cortisol [228] and aldosterone [229] which had been extracted from urine and purified by TLC, have been localised with the help of a reference chromatogram and then determined fluorometrically after treatment with sulphuric acid. After extraction from the thin layer, nicotine, nomicotine and anabasine could be determined phosphorimetrically (see p. 141) with a relative standard deviation of 6% [761]. 

Ktnetec (48) determined ascorbic acid, DHA, acetylsalicylic acid, and its degradation product, salicylic acid, from pharmaceuticals. He used UV detection for the measurement of ascorbic acid, acetylsalicylic acid, and fluorescence detection with the exitation wavelength set at 350 nm and emission wavelength set at 430 nm for measurement of the quinoxaline derivative of o-phenylenediamine and DHA. The o-phenylenediamine reagent was eluted as an unretained compound in the amino column thus causing no interference with other compounds in either UV or fluorescence detection. The detection limit was about 0.002 mg/ mL of sample, the injection volume was 20 pL. 

To gain a better understanding of the vase-kite transition the Diederich group subsequently synthesized quinoxaline-bridged velcrands bearing one or two (48, Fig. 9.19) fluorescent (BODIPY) labels for single molecule spectroscopic studies [127]. The introduction of the BODIPY labels had little effect on the switching... 

AA samples were loaded into two serial sample injection valves and injected into a carrier system containing mercuric chloride and o-phenylenediamine. The formation of a fluorescent quinoxaline was monitored at 435 nm (excitation at 366 nm) 0.6 30 2.0 Pharmaceuticals 1991 145 CO o o S o > o... 

Enzymatic kinetic spectrofluorometric procedure combining the merging zones based on the oxidation of AA to dehydroascorbic acid, which reacts with o-phenylenediamine to form a fluorescent quinoxaline No data 30 2.0-4.1 Pharmaceuticals, beverages, urine 1995 146 CL < 5> 3... 

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