Manabu Nakazono

Cyclobutane pyrimidine dimers (CPDs) in DNA are produced by UV photoirradiation. When electrons are supplied, these lesions are cleaved and can be converted back to native thymine bases. Electrons play a crucial role in the repair of CPDs. Five synthetic oligonucleotides harboring DNAs were synthesized and purified by reversed-phase HPLC. Efficient cleavage required a compound bearing both an electron donor and a positive charge. Indole is a strong electron donor, and the structures of unsymmetrical indolylmaleimides contain an indole moiety. Positively charged unsymmetrical indolylmaleimides generated via N-methylation of the quinoline ring were investigated for their ability to repair CPDs in double-stranded DNA. The fluorescence intensities of indolylmaleimides increased in the presence of double-stranded DNAs containing CPDs, testing binding interactions. The repair efficiency of these CPD-containing substrates was approximately 30% after 30 min of UV photoirradiation in the presence of indolylmaleimides. Extending photoirradiation to 60 min further increased the repair yield. A novel small-molecule was identified that efficiently repaired CPDs in double-stranded DNA.

Enhancement effect on the chemiluminescence of acridinium ester derivatives under neutral conditions was investigated. Additions of phenols did not enhance the chemiluminescence intensities of acridinium ester derivatives in the presence of horseradish peroxidase and hydrogen peroxide. Additions of cetyltrimethylammonium bromide apparently enhanced the chemiluminescence intensities of phenyl 10‐methyl‐10λ⁴‐acridine‐9‐carboxylate derivatives with electron‐withdrawing groups at the 4‐position of the phenyl group. In particular, the chemiluminescence intensity of 4‐(trifluoromethyl)phenyl 10‐methyl‐10λ⁴‐acridine‐9‐carboxylate trifluoromethanesulfonate salt was 5.5 times stronger in the presence of cetyltrimethylammonium bromide than in its absence at pH 7. The chemiluminescence intensity of 3,4‐dicyano‐phenyl 10‐methyl‐10λ⁴‐acridine‐9‐carboxylate trifluoromethanesulfonate salt was 46 times stronger in the presence of cetyltrimethylammonium bromide at pH 7 than in its absence at pH 10.

Various novel acridinium ester derivatives having phenyl and biphenyl moieties were synthesized, and their optimal chemiluminescence conditions were investigated. Several strongly chemiluminescent acridinium esters under neutral conditions were found, and then these derivatives were used to detect hydrogen peroxide and glucose. Acridinium esters having strong electron-withdrawing groups such as cyano, methoxycarbonyl, and nitro at the 4-position of the phenyl moiety in phenyl 10-methyl-10λ⁴-acridine-9-carboxylate trifluoromethanesulfonate salt showed strong chemiluminescence intensities. The chemiluminescence intensity of 3,4-dicyanophenyl 10-methyl-10λ⁴-acridine-9-carboxylate trifluoromethanesulfonate salt was approximately 100 times stronger than that of phenyl 10-methyl-10λ⁴-acridine-9-carboxylate trifluoromethanesulfonate salt at pH 7. The linear calibration ranges of hydrogen peroxide and glucose were 0.05–10 mM and 10–2000 μM using 3,4-(dimethoxycarbonyl)phenyl 10-methyl-10λ⁴-acridine-9-carboxylate trifluoromethanesulfonate salt at pH 7 and pH 7.5, respectively. The proposed chemiluminescence reaction mechanism of acridinium ester via a dioxetanone structure was evaluated via quantum chemical calculation on density functional theory. The proposed mechanism was composed of the nucleophilic addition reaction of hydroperoxide anion, dioxetanone ring formation, and nonadiabatic transition due to spin–orbit coupling around the transition state (TS) to the triplet state (T₁) following the decomposition pathway. The TS which appeared in the thermal decomposition would be a rate-determining step for all three processes.

On-the-fly nonadiabatic ab initio molecular dynamics simulations have been carried out for three anionic species of indolylmaleimides (3-(1H-3-indolyl)-2,5-dihydro-1H-2,5-pyrroledione, IM) to clarify the mechanisms of photochemical reactions. The results are obtained for (i) a monovalent anion with a deprotonated indole NH group (IM⁻′), (ii) a monovalent anion with a deprotonated maleimide NH group (IM⁻′′) and (iii) a divalent anion with doubly deprotonated indole and the maleimide NH groups (IM²⁻). Quantum chemical calculations are treated at the three state averaged complete-active space self-consistent field level for 6 electrons in 5 orbitals with the cc-pVDZ basis set (CAS (6, 5) SCF/cc-pVDZ). Molecular dynamics simulations are performed with electronically nonadiabatic transitions included using the Zhu–Nakamura version of the trajectory surface hopping (ZN-TSH) method. It is found that the nonadiabatic transitions occur accompanied by the stretching and shrinking motions of the N(7)–C(8) bond in the case of IM⁻′ and the C(11)–N(12) bond in IM²⁻ rather than the twisting motion of the dihedral angle. We also found that the ultrafast S₂ → S₁ nonadiabatic transitions occur through the conical intersection (CoIn) right after photoexcitation to S₂ in IM⁻′ and IM²⁻. Furthermore, the S₁ → S₀ nonadiabatic transitions are found to take place in IM⁻′. It is concluded that IM²⁻ would mainly contribute to the photoemission, because the S₁ ← S₀ and S₂ ← S₀ transitions of IM⁻′′ are dipole-forbidden transitions and, moreover, IM²⁻ is found to be the only species to stay in the S₁ state without non-radiative decay.

Various indolylmaleimides (IMs) were synthesized, and their fluorescence (FL) and chemiluminescence (CL) were measured. The substitution at the 2-position of the indole ring and the 3- or 4-position of the maleimide moiety caused an obvious change in the FL and CL of the IMs. An almost on–off switching of the FL of the IMs was observed. The intramolecular charge transfer from the indole moiety to the maleimide moiety occurred in 3-(1H-3-indolyl)-2,5-dihydro-1H-2,5-pyrroledione. In the FL of the IMs, CASPT2 calculations showed deprotonation of the NH group of the indole ring and the maleimide moiety at the excited state. The CC bond in the maleimide moiety was needed for strong CL in the IMs without substitution at the 2-position of the indole ring. The relationships between the FL or CL properties and the structures of the IMs were clarified. These results provide significant information on the rational design of IMs as FL and CL probes.

Fluorescence (FL), chemiluminescence (CL) and bioluminescence (BL) have been extensively focused on luminescence assays. Various FL and CL compounds have been synthesized and evaluated their FL and CL properties. This review describes development of highly selective and sensitive FL and CL reagents by derivatizing luminol, indole and polyphenol. Luminol derivatives were used for measuring enzyme activities and ultraviolet ray power. Indole derivatives with large stokes shift and long-lasting CL properties were developed. Compound which had enhancement effect on polyphenol CL was found. Highly sensitive CL polyphenol dendrimers were synthesized.