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. In this paper, we present a short review of easy, fast, and inexpensive preliminary tests for the detection of transient triplet carbonyls in chemical and biological systems. This paper covers direct and indirect methods to look for triplet carbonyls based on their spectral distribution of chemiluminescence, photoproduct analysis, quenching of light emission by conjugated dienes, and enhancement of light emission by the sensitizer 9,10-dibromoanthracence-2-sulfonate ion (DBAS).

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. This paper reports on the co-oxidation of aminoacetone and oxyhemoglobin in normally aerated phosphate buffer, leading to structural changes in hemoglobin, which can be attributed to the addition of aminoacetone-produced methylglyoxal to the protein. Hydroxyl radical-promoted chemical damage to hemoglobin may also occur in parallel, which is suggested by EPR-spin trapping studies with 5,5-dimethyl-1-pyrroline-N-oxide and ethanol. Concomitantly, oxyhemoglobin is oxidized to methemoglobin, as indicated by characteristic CD spectral changes in the Soret and visible regions. Overall, these findings may contribute to elucidate the molecular mechanisms underlying human diseases associated with hemoglobin dysfunctions and with aminoacetone in metabolic alterations related to excess glycine and threonine.

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 (Ac3* ). Accordingly, quenching of Ac3* by tryptophan (Trp) unveiled parallel enzyme damage and inactivation, likely explained by scavenging of IBAL tertiary radical reaction intermediate and Ac3* -derived 2-hydroxy-i-propyl radical. Quenching constants were calculated from Stern-Volmer plots, and the structure of radical adducts was revealed by mass spectrometry. As expected, a concurrent Schiff-type adduct was found to be one of the reaction by-products. These findings draw attention to potential structural and functional changes in enzymes involved in the electronic chemiexcitation of their products.

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. In contrast to typical Re(i) polypyridyl complexes, the substitution of Cl with the et-isonic ligand showed a bathochromic shift of the emission maxima, relatively low emission quantum yield and fast lifetime. Photophysical investigation of the fac-[ReCl(et-isonic)2(CO)3] compound provided meaningful information on the excited state manifold of the fac-[Re(L)(Am2phen)(CO)3]0/+ complexes. As shown in the absorption profile, a remarkable inversion of the lowest-lying excited state takes place from the usually observed MLCTRe→Am2phen to the unusual MLCTRe→et-isonic. The lipophilicity of the positive-complex was higher than that of the non-charge compound and the same trend for the activity against cells was observed, in the absence of light. In addition, flow cytometry and Western Blot analyses showed an overexpression of pro-caspase-9, suggesting a caspase proteolytic cascade through an intrinsic-pathway apoptosis mechanism. The photophysical properties of these compounds reported herein provide new fundamental insights into the understanding of substituent groups on polypyridyl ligands which are relevant to practical development.