Pyrrole, detection

Pyrroles and Pyridines. In the three model systems, pyrroles were found in a minute amount, and 2-acetylpyrrole and pyrrole-2-caiboxaldehyde were the only pyrroles detected. 2-Acetylpyridine was found in a minute quantity in the three model systems. The sensory properties of 2-acetylpyridine have been associated with popcorn, bread, cracker and coffee aromas (4). 

Analytical and Test Methods. In addition to the modem spectroscopic methods of detection and identification of pyrroles, there are several chemical tests. The classical Runge test with HCl yields pyrrole red, an amorphous polymer mixture. In addition, all pyrroles with a free a- or P-position or with groups, eg, ester, that can be converted to such pyrroles under acid conditions undergo the Ehrlich reaction with p-(dimethylamino)henzaldehyde to give purple products. 

Both pyrrole and indole react with selenium dioxide in the presence of nitric acid to give a deep violet solution. Very small quantities (ca 4 of pyrrole can be detected by this method. 

Whereas the cycloaddition of arylazirines with simple alkenes produces A -pyrrolines, a rearranged isomer can be formed when the alkene and the azirine moieties are suitably arranged in the same molecule. This type of intramolecular photocycloaddition was first detected using 2-vinyl-substituted azirines (75JA4682). Irradiation of azirine (54) in benzene afforded a 2,3-disubstituted pyrrole (55), while thermolysis gave a 2,5-disubstituted pyrrole (56). Photolysis of azirine (57) proceeded similarly and gave 1,2-diphenylimidazole (58) as the exclusive photoproduct. This stands in marked contrast to the thermal reaction of (57) which afforded 1,3-diphenylpyrazole (59) as the only product. 

Aminoglycoside antibiotics and / -substituted indoles are stained red. Pyrrole derivatives with free / -positions react at room temperature to yield blue-colored zones [11]. Exposure to the vapors of aqua regia deepens the colors. This reaction sometimes produces fluorescence [3]. The detection limit for monomethylhydrazine is 200 pg per chromatogram zone [3]. 

When the original reaction between the 1-methylpyrrole and dimethyl acetylenedicarboxylate was carried out on a larger scale with inadequate cooling, an exothermic reaction took place and none of the dihydroindole (48) could be detected among the products. However these included the mellitic ester (49) and the pyrrole (50), indicating that some of the dihydroindole (48) had formed and had combined with more of the acetylenic ester as already described. A decomposition product of the dihydroindole as yet unidentified, tetramethyl l-methylindole-2,3,6,7-tetracarboxylate (52), and tetramethyl prehnit-... 

Because the complex is formed even when the pyridine used initially contains less than 0.0001 vol. % of pyrrole, it seemed that some pyrrole must be formed from pyridine under the influence of the catalyst. A search for pyrrole among the reaction products revealed that traces of pyrrole could be detected within minutes of the beginning of the reaction but even after refluxing over the catalyst for 5 days the recovered pyridine contained only about 1 vol. % of pyrrole. 

Pyridine, pyrrole, indole, quinoline and isoquinoline alkaloids Silica gel G Detection by two-dimensional TLC [11]... 

Fig. 3.19 Sequence-specific fluorescence detection of DNA. (Top) Model of polyamide-TMR conjugate bound to DNA. In aqueous solutions, the hairpin polyamide-fluorophore displays fluorescence enhancement only upon binding to its match DNA site. Black and white spheres represent imidazole and pyrrole...

H NMR spectroscopy studies of iron(IIl) a-alkyl and o-aryl porphyrins have been very important in elucidating spin states. Alkyl and most aryl complexes with simple porphyrin ligands (OEP, TPP, or TTP) are low spin, S — I /2 species. NMR spectra for the tetraarylporphyrin derivatives show upheld resonances for the porphyrin pyrrole protons (ca. — 18 to —35 ppm), and alternating upfield and downfield hyperfine shifts for the axial alkyl or aryl resonances. For -alkyl complexes, the a-protons show dramatic downfield shifts (to ca. 600 ppm), upfield shifts for the /3-protons (—25 to — 160 ppm) and downfield shifts for the y-protons (12 ppm). The cr-protons of alkyliron porphyrins are not usually detected as a result of their large downfield shift and broad resonance. These protons were first detected by deuterium NMR in the dcuterated complexes Fe(TPP)CD3 (532 ppm) and Fe(TPP)CD2CDi (562, -117 ppm). ... 

When porphyrins dissolved in strong mineral acids or in organic solvents are illuminated by ultraviolet hght, they emit a strong red fluorescence. This fluorescence is so characteristic that it is often used to detect small amounts of free porphyrins. The double bonds joining the pyrrole rings in the porphyrins are responsible for the characteristic absorption and fluorescence of these compounds these double bonds are absent in the porphyrinogens. 

HydroxyNPYR [ ] has been identified as a urinary metabolite of NPYR in the rat (up to 1% of the dose), but was not detected when NPYR was incubated with subcellular fractions from rat liver and lung (13, 20). It has been proposed that further metabolism of leads to dimethy 1 amine, [ ], another urinary metabolite of NPYR, 2-Pyrrolidinone [3 ] has also been detected in the urine of rats treated with NPYR. Its origin has not been conclusively established, but it may form from pyrrol id inone-2-oxime (i6). 

T. Konry, A. Novoa, Y. Shemer-Avni, N. Hanuka, S. Cosnier, A. Lepellec, and R.S. Marks, Optical fiber immunosensor based on a poly(pyrrole-benzophenone) film for the detection of antibodies to viral antigen. Anal. Chem. 77, 1771-1779 (2005). 

Electron Transfer Type of Dehydrogenase Sensors To fabricate an enzyme sensor for fructose, we found that a molecular interface of polypyrrole was not sufficient to realize high sensitivity and stability. We thus incorporated mediators (ferricyanide and ferrocene) in the enzyme-interface for the effective and the most sensitive detection of fructose in two different ways (l) two step method first, a monolayer FDH was electrochemically adsorbed on the electrode surface by electrostatic interaction, then entrapment of mediator and electro-polymerization of pyrrole in thin membrane was simultaneously performed in a separate solution containing mediator and pyrrole, (2) one-step method co-immobilization of mediator and enzyme and polymerization of pyrrole was simultaneously done in a solution containing enzyme enzyme, mediator and pyrrole as illustrated in Fig.22. 

The chemical structure of 2,5-hexanedione suggested that it could react with lysine side-chain amino groups in proteins to form pyrroles (see Figure 2-7). In vitro experiments showed that this was, in fact, the case, and that the modified proteins can undergo secondary reactions to yield oxidized and polymeric products (DeCaprio et al. 1982 Graham et al. 1982). Oral administration of 2,5-hexanedione produced evidence that this process can take place in vivo as demonstrated by the detection of 2,5-dimethylpyrrole adducts in serum and axonal cytoskeletal proteins (DeCaprio and O Neill 1985). When a series of... 

Studies by Heinze etal. on donor-substituted thiophenes or pyrroles [33] such as methylthio (= methylsulfonyl) or methoxy-substituted derivatives provide further clear evidence for this reaction pathway. They found, for instance, that 3-methylthiothiophene or 3-methoxythio-phene (2) undergo a fast coupling reaction. However, deposition processes or insoluble film formation could not be detected in usual experiments with these compounds, even at high concentrations. Similarly, the corresponding 3,3 -disubstituted bithiophenes (2a) do not polymerize, but the anodic oxidation of 4,4 -disubstituted bithiophenes (2c) produces excellent yields of conducting polymers. 

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