Synthesis of 9-(substituted phenoxycarbonyl)-10-methylacridinium trifluoromethanesulfonates: Effects of the leaving group on chemiluminescent properties

Various 9-(substituted phenoxycarbonyl)-10-methylacridinium trifluoromethanesulfonates possessing electron-withdrawing substituents have been synthesized. The effect of substituents on the stability of the acridinium esters (AEs) at various temperatures in different buffers and the chemiluminescent properties have been examined. There was little correlation between the chemiluminescent properties of AEs and the pKa values of their associated phenols, but the steric effects of the ortho-substituents in the phenoxy group, as well as their electron-withdrawing natures, seem to play an important role in determining the properties. In general, when two identical substituents are present in the 2- and 6-positions, the compound is significantly more stable than when only a single substituent is present, presumably because of greater steric hindrance from the second group. The exception is the 2,6-difluorophenyl ester, which is less stable than the 2-fluorophenyl ester, presumably because the fluoro group is small. Addition of a third electron-withdrawing substituent at the 4-position, where it has no steric influence, typically increases susceptibility to decomposition. The presence of a nitro group has a significant destabilizing effect on AEs. Of the AEs studied, the 4-chlorophenyl ester showed the greatest chemiluminescent yield, while the 2-iodo-6-(trifluoromethyl)phenyl ester group showed the greatest stability in low pH buffers.

Synthesis and chemiluminescent characteristics of two new acridinium esters

Two new acridinium esters with a 2-(succinimidyloxycarbonyl)ethyl side arm, namely, 9-(2,6-dibromophenoxycarbonyl)-10-methyl-2-(2-(succinimidyloxycarbonyl)ethyl)acridinium trifluoromethanesulfonate and 9-(4-(2-(succinimidyloxycarbonyl)ethyl)phenoxycarbonyl)-2,7-dimethoxy-10-methylacridinium triflate, have been produced and characterized. The chemiluminescent properties and hydrolytic stabilities of the new acridinium esters have been investigated.

What Other Than Acridinium Esters? Computational Search for New Acridinium-Based Chemiluminogens

The rapid increase in disease prevalence in the world makes it extremely important to search for new or develop existing diagnostic methods, for example, chemiluminescent labeling used in immunodiagnostics. At present, acridinium esters are willingly used as chemiluminogenic fragments of labels. However, the search for new chemiluminogens that are particularly efficient is the main task of our studies. The density functional theory (DFT) and time-dependent (TD) DFT methods were used to obtain thermodynamic and kinetic results concerning the chemiluminescence and competitive dark reactions, which indicated whether some of the scrutinized derivatives have better characteristics than the chemiluminogens used so far. Synthesis of these candidates for efficient chemiluminogens, followed by studies of their chemiluminescent properties, and ultimately in chemiluminescent labeling, are further steps to confirm their potential applicability in immunodiagnostics.

Synthesis, structure elucidation, and chemiluminescent activity of new 9-substituted 10-(ω-(succinimidyloxycarbonyl)alkyl)acridinium esters

Several new acridinium esters 2-9 having their central acridinium ring bearing a 9-(2,5-dimethylphenoxycarbonyl), 9-(2,6-bis(trifluoromethyl)phenoxycarbonyl) or 9-(2,6-dinitrophenoxycarbonyl) group, and a 10-methyl, 10-(3-(succinimidyloxycarbonyl)propyl), 10-(5-(succinimidyloxycarbonyl)pentyl), or 10-(10-(succinimidyloxycarbonyl)decyl) group, have been synthesized and their chemiluminescent properties have been tested. The 2,5-dimethylphenyl acridinium esters emit light slowly (glow) when treated with alkaline hydrogen peroxide, while the 2,6-dinitrophenyl and 2,6-bis(trifluoromethyl)phenyl esters emit light rapidly (flash). The substituent at the 10 position affects the hydrolytic stabilities of the compounds.

Direct and Indirect Chemiluminescence: Reactions, Mechanisms and Challenges

Emission of light by matter can occur through a variety of mechanisms. When it results from an electronically excited state of a species produced by a chemical reaction, it is called chemiluminescence (CL). The phenomenon can take place both in natural and artificial chemical systems and it has been utilized in a variety of applications. In this review, we aim to revisit some of the latest CL applications based on direct and indirect production modes. The characteristics of the chemical reactions and the underpinning CL mechanisms are thoroughly discussed in view of studies from the very recent bibliography. Different methodologies aiming at higher CL efficiencies are summarized and presented in detail, including CL type and scaffolds used in each study. The CL role in the development of efficient therapeutic platforms is also discussed in relation to the Reactive Oxygen Species (ROS) and singlet oxygen (1O2) produced, as final products. Moreover, recent research results from our team are included regarding the behavior of commonly used photosensitizers upon chemical activation under CL conditions. The CL prospects in imaging, biomimetic organic and radical chemistry, and therapeutics are critically presented in respect to the persisting challenges and limitations of the existing strategies to date.

Acridinium Ester Chemiluminescence: Methyl Substitution on the Acridine Moiety

Methyl groups were introduced on the acridine moiety in chemiluminescent acridinium esters that have electron-withdrawing groups (trifluoromethyl, cyano, nitro, ethoxycarbonyl) at the 4-position on the phenyl ester. The introduction of methyl groups at the 2-, 2,7-, and 2,3,6,7-positions on the acridine moiety shifted the optimal pH that gave relatively strong chemiluminescence intensity from neutral conditions to alkaline conditions. 4-(Ethoxycarbonyl)phenyl 2,3,6,7,10-pentamethyl-10λ⁴-acridine-9-carboxylate, trifluoromethanesulfonate salt showed long-lasting chemiluminescence under alkaline conditions. Acridinium esters to determine hydrogen peroxide concentration at pH 7-10 were newly developed.

Computational Insights on the Mechanism of the Chemiluminescence Reaction of New Group of Chemiluminogens-10-Methyl-9-thiophenoxycarbonylacridinium Cations

Immunodiagnostics, in which one of the promising procedures is the chemiluminescent labelling, is essential to facilitate the detection of infections in a human organism. One of the standards commonly used in luminometric assays is luminol, which characterized by low quantum yield in aqueous environments. Acridinium esters have better characteristics in this topic. Therefore, the search for new derivatives, especially those characterized by the higher quantum yield of chemiluminescence, is one of the aims of the research undertaken. Using the proposed mechanism of chemiluminescence, we examined the effect of replacing a single atom within a center of reaction on the efficient transformation of substrates into electronically excited products. The density functional theory (DFT) and time dependent (TD) DFT calculated thermodynamic and kinetic data concerning the chemiluminescence and competitive dark pathways suggests that some of the scrutinized derivatives have better characteristics than the chemiluminogens used so far. Synthesis of these candidates for efficient chemiluminogens, followed by studies of their chemiluminescent properties, and ultimately in chemiluminescent labelling, are further steps to confirm their potential applicability in immunodiagnostics.

A comparison of chemiluminescent acridinium dimethylphenyl ester labels with different conjugation sites

Chemiluminescent acridinium dimethylphenyl esters are highly sensitive labels that are used in automated assays for clinical diagnosis. Light emission from these labels and their conjugates is triggered by treatment with alkaline peroxide. Conjugation of acridinium ester labels is normally done at the phenol. During the chemiluminescent reaction of these acridinium esters, the phenolic ester is cleaved and the light emitting acridone moiety is liberated from its conjugate partner. In the current study, we report the synthesis of three new acridinium esters with conjugation sites at the acridinium nitrogen and compare their properties with that of a conventional acridinium ester with a conjugation site at the phenol. Our study is the first that provides a direct comparison of the emissive properties of acridinium dimethylphenyl esters (free labels and protein conjugates) with different conjugation sites, one where the light emitting acridone remains attached to its conjugate partner versus conventional labeling which results in cleavage of the acridone from the conjugate. Our results indicate that the conjugation at the acridinium nitrogen, which also alters how the acridinium ring and phenol are oriented with respect to the protein surface, has a minimal impact on emission kinetics and emission spectra. However, this mode of conjugation to three different proteins led to a significant increase in light yield which should be useful for improving the assay sensitivity.

Synthesis and properties of chemiluminescent acridinium esters with different N-alkyl groups

Acridinium esters containingN-alkyl groups with charge-neutral sulfobetaine zwitterions when compared toN-sulfopropyl groups exhibit faster light emission, improved chemiluminescence stability and lower non-specific binding.