10-Methyl-9-(phenoxycarbonyl)acridinium trifluoromethanesulfonates bearing alkyl substituents at the benzene ring were synthesized, purified, and identified. In the reaction with OOH(-) in basic aqueous media, the cations of the compounds investigated were converted to electronically excited 10-methyl-9-acridinone, whose relaxation was accompanied by chemiluminescence (CL). The kinetic constants of CL decay, relative efficiencies of light emission, chemiluminescence quantum yields, and resistance toward alkaline hydrolysis were determined experimentally under various conditions. The mechanism of CL generation is considered on the basis of thermodynamic and kinetic parameters of the reaction steps predicted at the DFT level of theory. The chemiluminescence efficiency is the result of competition of the electrophilic center at C(9) between nucleophilic substitution by OOH(-) or OH(-) and the ability of the intermediates thus formed to decompose to electronically excited 10-methyl-9-acridinone. Identification of stable and intermediate reaction products corroborated the suggested reaction scheme. The results obtained, particularly the dependency of the "usefulness" parameter, which takes into account the CL quantum yield and the susceptibility to hydrolysis, on the cavity volume of the entity removed during oxidation, form a convenient framework within which to rationally design chemiluminescent 10-methyl-9-(phenoxycarbonyl)acridinium cations.

A series of 10-methyl-9-(phenoxycarbonyl)acridinium trifluoromethanesulfonates (XAEs), bearing substituents of various characteristics in the lateral benzene ring (2-halogen, 2,6-dihalogen, 2-trifluoromethyl, 2-nitro, 2-methoxy, 3-halogen and 4-halogen) were synthesized with high yields, identified and subjected to a physicochemical and theoretical investigation. The main task of the work was to assess the mechanism and optimal conditions of light emission in various liquid systems based on the above salts in order to evaluate their potential usefulness as chemiluminescence (CL) labels and indicators in ultra-sensitive analyses. Density functional theory (DFT) calculations were performed to investigate the detailed mechanism of the oxidation of 9-substituted 10-methylacridinium cations involved in XAEs by hydrogen peroxide in alkaline media. Three general pathways were drawn, which are termed the "light path" (chemiluminogenic) and there were two "dark paths" (non-chemiluminogenic): hydrolytic and "pseudobase". The CL time profiles, triggered in alkaline solutions containing hydrogen peroxide, enabled us to establish crucial physicochemical parameters, including pseudo-first order kinetic constants of CL decay and relative efficiencies of emission. In order to optimize the systems' luminogenic performance, different bases, such as sodium hydroxide, tetrabutylammonium hydroxide (TBAOH) and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), as well as enhancers, such as cationic, zwitterionic and neutral surfactants (cetyltrimethylammonium chloride (CTAC), N,N-dimethyldodecylammonio-1,3-propane sulfonate (DDAPS) and Triton X-100, respectively) were tested. The results revealed the optimal CL systems, which enabled us to obtain substantially higher emissions than typical ones, based on acridinium esters or luminol. The derived parameters, characterizing the potential utility of the acridinium esters, such as stability in aqueous environments and usefulness (the product of emission efficiency and stability at a given pH), enabled us to reveal the best candidates and their practical applications. The post-reaction mixtures, analyzed by means of chromatography (RP-HPLC) and mass spectrometry (ESI-MS), allowed us to verify the occurrence and population of the products that were theoretically predicted, i.e. 10-methyl-9-acridinone (NMAON), 10-methylacridinium-9-carboxylic acid (NMACA) and substituted phenols (RPhOHs).

1,3-Diphenylisobenzofuran (DPBF) has been developed as a selective probe for the detection and quantitative determination of hydrogen peroxide in samples containing different reactive nitrogen and oxygen species (RNOS). DPBF is a fluorescent probe which, for almost 20 years, was believed to react in a highly specific manner toward some reactive oxygen species (ROS) such as singlet oxygen and hydroxy, alkyloxy or alkylperoxy radicals. Under the action of these individuals DPBF has been rapidly transformed to 1,2-dibenzoylbenzene (DBB). In order to check if DPBF can act as a unique indicator of the total amount of different RNOS, as well as oxidative stress caused by an overproduction of these individuals, a series of experiments was carried out, in which DPBF reacted with peroxynitrite anion, superoxide anion, hydrogen peroxide, hypochlorite anion, and anions commonly present under biological conditions, namely nitrite and nitrate. In all cases, except for hydrogen peroxide, the product of the reaction is DBB. Only under the action of HO 9-hydroxyanthracen-10(9H)-one (oxanthrone) is formed. This product has been identified with the use of fluorescence spectroscopy, NMR spectroscopy, high performance liquid chromatography coupled with mass spectrometry, infrared spectroscopy, elemental analysis, and cyclic voltammetry (CV). A linear relationship was found between a decrease in the fluorescence intensity of DPBF and the concentration of hydrogen peroxide in the range of concentrations of 0.196-3.941 mM. DPBF responds to hydrogen peroxide in a very specific way with the limits of detection and quantitation of 88 and 122.8 μM, respectively. The kinetics of the reaction between DBBF and HO was also studied.

The chemiluminogenic (CL) properties of aryl esters of 9-carboxy-10-methylacridinium acid and 9-carboxy-2-methoxy-10-methylacridinium acid (AE), variously substituted in the benzene ring (2-H, 2-CH(3), 2-Cl) were investigated in aliphatic alcohols, acetonitrile, and dimethyl sulfoxide in the presence of hydrogen peroxide and different bases-potassium hydroxide, tetra-n-butylammonium hydroxide, and 1,8-diazabicyclo[5.4.0]undec-7-ene. The dependence of their CL properties (decay rate constants (k(CL)) and relative efficiencies (RE)) on solvent parameters, the nature and concentration of base, as well as H(2)O(2) concentration were investigated. Comparison of the various AE revealed that substituents at the benzene ring strongly influence the reaction kinetics, while 2-OCH(3) substitution of the acridine nucleus is manifested, in general, by a red shift in the emission spectrum and slight increase in CL efficiency. The values of k(CL) depend linearly on polarity and acid-base properties of solvents as well as on concentration of bases (over certain concentration ranges) and demonstrate a nonlinear dependence on H(2)O(2) concentration. RE values depend on solvent polarity and nucleophilicity but are rather weakly dependent on base and oxidant concentrations. The CL properties of the above systems are discussed in the context of their physicochemical features gained from fluorescence spectroscopy, spectrophotometric titration, MS, and HPLC. Electronically excited 10-methyl-9-acridinones are the light-emitting entities in both organic and aqueous environments. It was also found that the tendency for an unwanted side-process, the production of a pseudobase form of AE, to take place was similar in alcoholic and aqueous media, although 2-methoxy ring-substituted derivatives seemed to be less susceptible to this dark-type conversion. On the basis of these results new CL systems are postulated that are more efficient than their aqueous counterparts.