Acridinium compounds

The best-known chemiluminescent acridinium derivative is lucigenin (10,10 -dimethyl-9,9 -biacridinium dinitrate). The reaction with alkahne peroxide produces iV-methylacridone, which emits light at 442 nm. 

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Combination of the hydroxyl ion with the mesomeric cation involves the removal of a double bond. For the quaternary pyridinium compounds this causes the total loss of the aromaticity. For quaternary quinolinium and isoquinolinium compounds, the aromatic character of one of the two rings is lost, and for the quaternary acridinium compounds that of one out of three. Hence., the order of stabilities of these compounds (determined by Hantzsch ) is explained. - Comparison of quaternary 3,4-dihydroisoquinolinium compounds and their isoquinolinium analogs with respect to the equilibrium (5) (4) shows that a much higher hydroxyl ion concentration is necessary for the isoquinolinium ions to form the carbinolamine. This is because the transition from the quaternary 3,4-dihydroisoquinolinium ions into the undissociated carbinolamine involves significantly smaller loss of mesomeric energy than that for the quaternary isoquinolinium hydroxides. ... 

Table 22 Rate Constants for Reductive Coupling of A -Substituted Pyridinium, Quinolinium, and Acridinium Compounds...

Matsuo and Mayer [33], on the other hand, found that the same reactant in acetonitrile solution, upon treatment with Ru O, quicMy generated the acridinium ion, as might have been anticipated for a simple hydride-transfer reaction, but in only 40-50% yield. Relatively slowly thereafter the acridinium compound and the remaining reactant were converted to the acridinium leuco-base (hydroxide-ion adduct). Matsuo and Mayer concluded that the process shovm in Eq. (4.5) was occurring ... 

ImmunO lSS iy. Chemiluminescence compounds (eg, acridinium esters and sulfonamides, isoluminol), luciferases (eg, firefly, marine bacterial, Benilla and Varela luciferase), photoproteins (eg, aequorin, Benilld), and components of bioluminescence reactions have been tested as replacements for radioactive labels in both competitive and sandwich-type immunoassays. Acridinium ester labels are used extensively in routine clinical immunoassay analysis designed to detect a wide range of hormones, cancer markers, specific antibodies, specific proteins, and therapeutic dmgs. An acridinium ester label produces a flash of light when it reacts with an alkaline solution of hydrogen peroxide. The detection limit for the label is 0.5 amol. 

Me Capra in particular proposed n> that the chemiluminescence reactions of a large number of organic compounds had this concerted dioxetane decomposition step as key reaction in the production of electronically excited products, namely acridinium salts 25,26,27) indolylperoxides 28>, activated oxalic esters 29>, diphenyl carbene 30>, tetrakis-dimethylamino-ethylene 31 32>, lucigenin 33>, and substituted imidazoles 23>. 

Chemiluminescence detection in capillary electrophoresis (CE) has attracted much attention as a promising way to offer excellent analytical selectivity and sensitivity. Several reagents, such as luminol, acridinium, peroxyoxalate, and tris(2,29-bipyridine)ruthenium(II) complex have been utilized. Since chemiluminescence detection is approximately 102—106 times more sensitive than spectrophotometric and fluorometric detections, its combination with isoelectric focusing may result in a highly sensitive analytical tool for amphoteric compounds, e.g., proteins and peptides. A detector using luminol-H202 chemiluminescence has been characterized in a very simple and inexpensive setup, but only pressure-driven mobilization of the zones was effective. [68],... 

The family of photoreducible dyes (e.g, acridinium, xanthene, thiazinium among other classes of dyes) produce excited states of essentially quinoidal structures which can act as efficient acceptors of electrons. Amines [59], sulfur compounds, especially sulfmate salts [60], heterocycles of low ionization potential [61], alkylcarboxylates and stable enolate anions [62], and several classes of organo-metallic compounds, notably allylic and benzylic organostannanes [63], represent classes of compounds which have proved efficacious as coinitiators in electron transfer sensitization with these dyes. Electron transfer with the organometallics was unambiguously established in a series of model studies involving electron acceptors of the anthracene class [64],... 

Signal antibodies have most often been radiolabeled (for immunoradiometric assays [IRMA]) with ( 25j) 7,62,i%,344,4i4 labeled with a chemiluminescent (for immunochemilummo-metric assays [ICMA]) compound, such as acridinium ester, or an enzyme (enzyme-linked immunosorbent assay [ELISA] or enzyme immunoassay [EIA]), such as ALP, converting a substrate (1,2-dioxetane phosphate) to a chemiluminescent product. 

Typical photosensitizers for diaryliodonium salts are condensed ring aromatic hydrocarbons, diaryl ketones, and acridinium dyes. Condensed ring aromatic hydrocarbons are particularly effective photosensitizers for triarylsulfonium salts. The use of photosensitizers in onium salt photolysis permits the photoimaging processes induced by these compounds to be optimally fitted to the specific irradiation source used for their exposure. 

Ironically, the synthesis and chemiluminescent properties of some of these important compounds were first reported in the 1920s i.e., acridine-9-carboxylic acid, a precursor of acridinium esters, was synthesized in 1928 (L7), which was the same year that Albrecht described the chemiluminescence of luminol (A8). The emission from lucigenin, a 6is-acridinium analog, was reported 7 years later by Gleu and Petsch (G7). 

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