Mechanism of AMPPD Chemiluminescence in a Different Voice

Abstract

The chemiluminescence phenomenon of 3-(2'-spiroadamantyl)-4-methoxy-4-(3″-phosphoryloxy)-phenyl-1,2-dioxetane (AMPPD or m-AMPPD) has been routinely applied in clinical diagnostics. Although the AMPDD chemiluminescence immunoassay is one of the most successful immunoassays, the mechanism of AMPPD chemiluminescence remains largely unknown. The AMPPD chemiluminescence process is composed of three steps: AMPPD is enzymatically triggered to produce 3-(2'-spiroadamantyl)-4-methoxy-4-(3″-hydroxyphenyl)-1,2-dioxetane (m-AMPD); m-AMPD decomposes into the excited-state methyl m-oxybenzoate anion (m-MOB(-)); the excited-state m-MOB(-) relaxes to its ground state and emits light. Obviously, the middle step is critical for the chemiluminescence and has not been well understood because of both experimental and theoretical difficulties. We performed the first theoretical study on the chemiluminescent decomposition mechanism of m-AMPD and its para isomer, p-AMPD, using the complete active space self-consistent field and the second-order multiconfigurational perturbation methods in addition to the density functional method. This investigation revealed that (1) neither the intramolecular chemical initiated electron exchange luminescence (CIEEL) nor the concerted charge transfer (CT) mechanism can describe the decomposition of m- and p-AMPD well. Instead, their decomposition occurs according to our previously proposed mechanism of gradually reversible CT-initiated luminescence. (2) The different stabilities of the m- and p-AMPD chemiexcited states might be the basis for the large difference in their chemiluminescence efficiencies. (3) The relationship between the chemiluminescence efficiency and the position of the electron donor on the aromatic ring, the so-called "odd/even selection rule," does not fully explain the chemiluminescence efficiency of dioxetanes. The odd/even selection rule is only correct for partial dioxetanes, because it does not capture the origin of the relationship between the chemiluminescence and the donor. We revealed that the origin consists of a combination of conjugation, induction, and steric effects. On the basis of this combination of effects, we theoretically designed some 1,2-dioxetanes to guide experimentalists in the synthesis of these excellent chemiluminescent molecules.

Interstate Crossing-Induced Chemiexcitation Mechanism as the Basis for Imidazopyrazinone Bioluminescence

“…Thus, here we have employed a long‐rang‐corrected hybrid exchange‐correlation density functional (in this case, ωB97XD), which performs well in predicting CT excitations . Such strategy has been gaining traction in chemi‐/bioluminescent studies, as such functionals can provide a quite accurate qualitative picture for these systems . This is also the case for our study, in which both the PES of both S 0 and S 1 of I–Diox − are well in line with the results obtained recently for a Cypridina dioxetanone analog …”

“…In implicit water, this gap is slightly smaller and wider, as between IRCs of 2.83 and 4.08 amu 1/2 bohr, the energy difference varies between 14.9 and 12.1 kcal mol −1 . It should be noted that the results obtained in previous works indicate that calculations of a higher‐level (multi‐reference ones) will surely predict a small energy gaps between these states . The importance of these higher‐level calculations has been reported in several studies, due to role of multi‐reference correlation in these systems .…”

“…As already referred, when one deals with a chemi‐/bioluminescent system that is characterized by an inefficient light output, it is generally thought that this is the result of an inefficient chemiexcitation step ,‐,‐ That is, chemi‐/bioluminescent reactions are only regarded as light‐emitting state producing processes (which are singlet ones), and other non‐emitting states (triplet ones) are not considered. However, simple dioxetanones and dioxetanes are known for producing triplet states, besides singlet excited states .…”

Synthesis of 1,2‐Dioxetanes as Thermochemiluminescent Labels for Ultrasensitive Bioassays: Rational Prediction of Olefin Photooxygenation Outcome by Using a Chemometric Approach

“…2a, 2k cf. [21] To the best of our knowledge,v ery few examples are present in the literature that describe the behavior of EWG-substituted 1,2-dioxetanes, [22] and no studies have been reportedo nf luorine-bearing aryl dioxetanes or concerning the dependenceo f1 ,2-dioxetanesp roperties on the EWG distribution on the acridan system.I nparticular,opposite effects on fluorescencequantum yield as af unctiono ft he substituent positionh ave never been observed. These unexpected and intriguing resultss uggested that the emitting performances of F-substituted acridane-based ketones were mostly affectedb yt he position rather than the electronic features of the substituents on the aromatic rings.…”

Persistent Chemiluminescent Glow of Phenoxy‐dioxetane Luminophore Enables Unique CRET‐Based Detection of Proteases

“…This is mostly because of the lack of experimental evidence regarding the intermediates formed prior to the formation of the final electronically excited species. Current mechanistic investigations have relied primarily on computational considerations . Although this subject is outside the scope of the described research, we note that the unique kinetic behavior of 7‐HC‐CL, and the inferred presence of a long‐lived intermediate formed during chemiexcitation, may constitute an exceptional opportunity for experimental investigation of the chemiexcitation mechanism.…”