Comparison of the mechanisms of DNA damage following photoexcitation and chemiexcitation.

In this review, we compare the mechanisms and consequences of electronic excitation of DNA via photon absorption or photosensitization, as well as by chemically induced generation of excited states. The absorption of UV radiation by DNA is known to produce cyclobutane pyrimidine dimers (CPDs) and thymine pyrimidone photoproducts. Photosensitizers are known to enable such transformations using UV-A and visible light by generating triplet species able to transfer energy to DNA.

Mining reactive triplet carbonyls in biological systems.

Aliphatic triplet carbonyls can be treated as short-lived radicals, since both species share similar reactions such as hydrogen atom abstraction, cyclization, addition, and isomerization. Importantly, enzyme-generated triplet carbonyls excite triplet molecular oxygen to the highly reactive, electrophilic singlet state by resonance energy transfer, which can react with proteins, lipids, and DNA. Carbonyl triplets, singlet oxygen, and radicals are endowed with the potential to trigger both normal and pathological responses.

Aerobic co-oxidation of hemoglobin and aminoacetone, a putative source of methylglyoxal.

Aminoacetone (1-aminopropan-2-one), a putative minor biological source of methylglyoxal, reacts like other α-aminoketones such as 6-aminolevulinic acid (first heme precursor) and 1,4-diaminobutanone (a microbicide) yielding electrophilic α-oxoaldehydes, ammonium ion and reactive oxygen species by metal- and hemeprotein-catalyzed aerobic oxidation. A plethora of recent reports implicates triose phosphate-generated methylglyoxal in protein crosslinking and DNA addition, leading to age-related disorders, including diabetes. Importantly, methylglyoxal-treated hemoglobin adds four water-exposed arginine residues, which may compromise its physiological role and potentially serve as biomarkers for diabetes.

l-Tryptophan Interactions with the Horseradish Peroxidase-Catalyzed Generation of Triplet Acetone.

Triplet carbonyls generated by chemiexcitation are involved in typical photobiochemical processes in the absence of light. Due to their biradical nature, ultraweak light emission and long lifetime, electronically excited triplet species display typical radical reactions such as isomerization, fragmentation, cycloaddition and hydrogen abstraction. In this paper, we report chemical reactions in a set of amino acid residues induced by the isobutanal/horseradish peroxidase (IBAL/HRP) system, a well-known source of excited triplet acetone (Ac ).

Understanding the photophysical properties of rhenium(I) compounds coordinated to 4,7-diamine-1,10-phenanthroline: synthetic, luminescence and biological studies.

In the present study, the photophysical properties and preliminary time-dependent density functional theory (TD-DFT) data of new rhenium(i) polypyridyl compounds, fac-[Re(L)(Am2phen)(CO)3]0/+, where Am2phen = 4,7-diamine-1,10-phenanthroline and L = Cl and ethyl isonicotinate (et-isonic), provided new insights into excited-state deactivation through an unusual inversion between two metal-to-ligand charge-transfer excited states. In addition, their cellular uptake using breast cancer (MCF-7) and melanoma (SkMel-147 and SkMel-29) cell lines and bioactivity were investigated and their cell-killing mechanism and protein expression were also studied. Preliminary TD-DFT results showed that both compounds exhibited a strong and broad absorption band around 300-400 nm which corresponds to a combination of ILAm2phen and MLCTRe→Am2phen transitions, and a strong contribution of charge transfer transition MLCTRe→et-isonic for fac-[Re(et-isonic)(Am2phen)(CO)3]+ is also observed.

Photophysical properties of rhenium(i) complexes and photosensitized generation of singlet oxygen.

fac-[Re(ampy)(CO)(NN)] complexes (ampy = 2-aminomethylpyridine and NN = 1,10-phenanthroline (phen), and 2,2'-bipyridine (bpy)) were synthesized, purified and characterized by proton nuclear magnetic resonance (H NMR), UV-visible and Fourier-transformed infrared (FT-IR) spectroscopies, and their photophysical properties were investigated using steady state and time-resolved emission spectroscopies. The electronic absorption spectra exhibit two main absorption bands: the higher energy band, which was assigned to intraligand transition (IL), and the lower energy band assigned to metal-to-ligand charge transfer (MLCT). Both complexes showed emission at room temperature in a CHCN solution (λ = 560 nm, ϕ = 0.