Acridine cation-radicals

One very intriguing work on benz[c]acridines and benzo[a]phenothiazines establishes a connection between their carcinogenicity and radical production (Kurihara et al. 1998). It would be interesting to check for a connection between the carcinogenicity and electron structures of the corresponding cation radicals too. 

The results of potential-dependent chronocoulometric measurements suggested the mechanism of Scheme 4 for the reaction sequence, where ArH is acridine and (ArHAr)+ is 101 or 102.347 The rate constant for the addition of acridine to its cation-radical was determined as 1.3 x 105 liter mol-1 sec-1. 

Such polycyclic aromatic hydrocarbons as anthracene or heteroaromatics as acridine, phenazine and 2,4,5-triphenyl oxazole act as Jt-donors for the Jt-acceptors AN and alkyl methacrylates [50-53]. Again, the interaction of the donor excited states with vinyl monomers leads to exciplex formation. But, the rate constants (k ) of these quenching processess are low compared to other quenching reactions (see Table 1). The assumed electron transfer character is supported by the influence of the donor reduction potential on the k value (see Table 1), and the detection of the monomer cation radicals with the anthracene-MMA system. Then, the ion radicals initiate the polymerization, the detailed mechanism of which is unsolved,... 

Acridine and phenothiazine cocrystallized to give two kinds of hydrogen-bonded CT crystals. Both crystals showed some photoreactivity and appear to have given many photoproducts (Scheme 18) [44]. Although this crystalline complex is complicated in terms of stoichiometry, crystal structure, and photoreaction, a transient study by femtosecond diffuse reflectance spectroscopy was carried out, as had been done for durene-pyromellitic dianhydride cocrystal [45]. For the yellow cocrystal, a transient absorption spectrum with maxima around 600 and 520 nm was obtained, which decayed biexponentially with lifetimes of 2 and 50 ps. The two absorption maxima were ascribed to the acridine anion radical and the phenothiazine cation radical, respectively. 

Absorbed dose 0.15 Mrad at 77°K. A = radical anion of acridine C = radical cation of acridine R = neutral radical [175],... 

Coupling reactions of the electrogenerated cation radicals can also occur. If the parent molecule is a good nucleophile, this can be considered as a nucleophilic attack by parent on its own cation radical. The nature of the electrochemical responses in CV and coulometry depend upon whether the coupled product can undergo further oxidation. For example, in the oxidation of aromatic aza-hydrocarbons such as acridine (AcH), studied by Marcoux and Adams (1974), the CV was characterized by an irreversible one-electron wave and coulometry showed an napp-value of one. An analysis of rotating disk voltammograms demonstrated that the reaction sequence (79)-(81) was more probable them that involving... 

Photopolymerization reactions are widely used for printing and photoresist appHcations (55). Spectral sensitization of cationic polymerization has utilized electron transfer from heteroaromatics, ketones, or dyes to initiators like iodonium or sulfonium salts (60). However, sensitized free-radical polymerization has been the main technology of choice (55). Spectral sensitizers over the wavelength region 300—700 nm are effective. AcryUc monomer polymerization, for example, is sensitized by xanthene, thiazine, acridine, cyanine, and merocyanine dyes. The required free-radical formation via these dyes may be achieved by hydrogen atom-transfer, electron-transfer, or exciplex formation with other initiator components of the photopolymer system. 

The rate constants for these relatively short range hole transfer reactions generally decrease exponentially with distance. Yet, characterizing these DNA-mediated reactions with the parameter (3 is a simplification and is certainly inappropriate in cases where the Frank-Condon factor varies with distance (such as has been observed for the acridine photooxidant). Keeping these limitations in mind, however, /i-values for DNA-mediated hole transfer of -0.6-0.7 A-1 have been suggested using several different oxidant-DNA assemblies (Ap, St, Ap radical cation). 

When acridane 1 is oxidized by dibenzoyl peroxide in propanol/ water in acid or neutral medium, there occurs chemiluminescence whose emission spectrum matches the fluorescence spectrum of acridinium cation (protonated acridine) 2. As radical scavengers have no influence... 

Oxidation of acridine in anhydrous acetonitrile leads to a dimer 65 formed by reaction of the nitrogen in one molecule of the substrate with the point of highest positive charge density in a radical-cation [208]. Anodic oxidation of neat pyridine... 

Both quinoline and isoquinoline molecular ions lose HCN to yield radical cation (109), while loss of HCN from acridine gives structure (110) (B-71MS364). 

Hydrogenase, HyD, includes a Fe-S cluster as active site. Photogenerated N,A -dimethyl-4,4 -bipyridinium radical cation, MV+, mediates H2-evolution in the presence of HyD [201-203], see Fig. 40. Different photosensitizers such as Ru(bpy) +, Zn-TMePyP4+ or acridine orange and sacrificial electron donor, i.e. ethylenediamine tetraacetic acid, EDTA, mercaptoethanol or cysteine, have been... 

The electrochemical behavior of the A-D compounds (selected structures are shown in Fig. 16) agrees well with that expected on the basis of the electrochemical properties of both the donor and the acceptor moieties [134-138]. That they can be reversibly reduced and oxidized to the corresponding radical cation and anion has been ascertained by cyclic voltammetry. The standard reduction potentials, are close to the values found for the parent aromatic hydrocarbons or acridine [124]. In a similar way, the standard oxidation potentials, °, are congruent with those found for the corresponding amines [148]. The electrochemical reaction of A-D compounds can be formulated as follows ... 

The product (183) is formed on irradiation of acridine (184) phenothiazine (185) crystals in which the ratio of the reactants is 3 4," This reactivity is different from the solution phase (in acetonitrile) process which affords both (183) and the dihydro dimer (186). The photoinduced electron transfer reactions of some a-silyl ethers has been investigated." The sensitizing system uses DCA/ biphenyl and irradiation at A, > 345 nm in acetonitrile/methanol. The irradiation brings about the formation of the radical cation (187) of the ether which undergoes cleavage to yield the radical (188), a hydroxymethyl equivalent. When these are generated in the presence of a,P-unsaturated esters such as (189) addition takes place affording the adducts (190). Additions to dimethyl maleate were also carried out successfully." ... 

To the more usual homolytic fragmentation of aryl halides (from the excited state or from the radical anion, the well known SrnI reaction, for a recent example see the arylation of aromatics), the heterolytic version of the reaction which produces phenyl cations has more recently joined. A theroretic study on the photodissociation of fluorinated iodobenzenes has been published. The perfluoroallgrlation of various alkenes has been obtained by irradiation in the presence of iodoperfluorobutane. The formation of phenyl cations is exemplified in many arylation reactions and, in the case of o-chlorostannane, also a benzyne has been reported. In the field of polymer chemistry, iodonium salts are model cationic photoinitiators. In particular the truxene-acridine/diphenyl iodonium salt/9-vinylcarbazole combination is able to promote the ringopening polymerization of an epoxide, whereas the truxene AD/allq l halide/amine system is very efficient in initiating the radical photopolymerization of an acrylate. ... 

Among condensed heterocyclic compounds formation of radical ions have been proved for the following compounds radical anions of acridine [117], phthalazine [126], phenazine [70, 126], 1,4,5,8-tetraazanaphthalene [131], 9,10-diazaphenanthrene [129], 2,2 -biiso-benzimidazolidine [129], and phenothiazone [108] radical cations for... 

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