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Excited singlet molecular O₂(¹Δg) is generated enzymatically from excited carbonyls in the dark.

Mano CM, Prado FM, Massari J, Ronsein GE, Martinez GR, Miyamoto S, Cadet J, Sies H, Medeiros MH, Bechara EJ, Di Mascio P - Sci Rep (2014)

Bottom Line: This involves thermolysis of 3,3,4,4-tetramethyl-1,2-dioxetane, a chemical source, and horseradish peroxidase-catalyzed oxidation of 2-methylpropanal, as an enzymatic source.This corroborates formation of O2 ((1)Δg).Altogether, photoemission and chemical trapping studies clearly demonstrate that chemically and enzymatically nascent excited carbonyl generates (18)O2 ((1)Δg) by triplet-triplet energy transfer to ground state oxygen O2 ((3)Σg(-)), and supports the long formulated hypothesis of O2 ((1)Δg) involvement in physiological and pathophysiological events that might take place in tissues in the absence of light.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, CEP 05513-970, CP 26077, São Paulo, SP, Brazil.

ABSTRACT
In mammalian tissues, ultraweak chemiluminescence arising from biomolecule oxidation has been attributed to the radiative deactivation of singlet molecular oxygen [O2 ((1)Δg)] and electronically excited triplet carbonyl products involving dioxetane intermediates. Herein, we describe evidence of the generation of O2 ((1)Δg) in aqueous solution via energy transfer from excited triplet acetone. This involves thermolysis of 3,3,4,4-tetramethyl-1,2-dioxetane, a chemical source, and horseradish peroxidase-catalyzed oxidation of 2-methylpropanal, as an enzymatic source. Both sources of excited carbonyls showed characteristic light emission at 1,270 nm, directly indicative of the monomolecular decay of O2 ((1)Δg). Indirect analysis of O2 ((1)Δg) by electron paramagnetic resonance using the chemical trap 2,2,6,6-tetramethylpiperidine showed the formation of 2,2,6,6-tetramethylpiperidine-1-oxyl. Using [(18)O]-labeled triplet, ground state molecular oxygen [(18)O2 ((3)Σg(-))], chemical trapping of (18)O2 ((1)Δg) with disodium salt of anthracene-9,10-diyldiethane-2,1-diyl disulfate yielding the corresponding double-[(18)O]-labeled 9,10-endoperoxide, was detected through mass spectrometry. This corroborates formation of O2 ((1)Δg). Altogether, photoemission and chemical trapping studies clearly demonstrate that chemically and enzymatically nascent excited carbonyl generates (18)O2 ((1)Δg) by triplet-triplet energy transfer to ground state oxygen O2 ((3)Σg(-)), and supports the long formulated hypothesis of O2 ((1)Δg) involvement in physiological and pathophysiological events that might take place in tissues in the absence of light.

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Effect of pure O2 purging on the chemiluminescence intensity elicited by TMD.(A) UV-visible light emission time course of triplet excited acetone during the thermolysis of 5 mM TMD in CCl4 at 70°C, and (B) Monomol light emission of O2 (1Δg) recorded during the decomposition of 5 mM TMD in CCl4 at 70°C. The arrow in both graphs indicates the time elapsed in O2 purging.
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f2: Effect of pure O2 purging on the chemiluminescence intensity elicited by TMD.(A) UV-visible light emission time course of triplet excited acetone during the thermolysis of 5 mM TMD in CCl4 at 70°C, and (B) Monomol light emission of O2 (1Δg) recorded during the decomposition of 5 mM TMD in CCl4 at 70°C. The arrow in both graphs indicates the time elapsed in O2 purging.

Mentions: Since the concentration of O2 in solution can limit the generation of O2 (1Δg) by TMD thermolysis, additional luminescence experiments were performed using CCl4. Ten minutes after starting the reaction, pure O2 was purged inside the cuvette in an attempt to enhance O2 (1Δg) generation (Fig. 2). As expected, the influx of molecular O2 into the system decreased the intensity of UV-visible light (Fig. 2A) due to energy transfer of the generated triplet acetone to molecular oxygen, although a slight decrease in NIR monomol light emission of O2 (1Δg) was observed (Fig. 2B). In this respect, we note that, although triplet molecular oxygen is known to be a triplet carbonyl suppressor18, McGarvey et al.61 reported an inverse correlation between molecular oxygen quenching of different triplet naphthalenes in benzene and the generation of O2 (1Δg). This finding was then correlated to structural differences in naphthalene, and not to changes in O2 concentration.


Excited singlet molecular O₂(¹Δg) is generated enzymatically from excited carbonyls in the dark.

Mano CM, Prado FM, Massari J, Ronsein GE, Martinez GR, Miyamoto S, Cadet J, Sies H, Medeiros MH, Bechara EJ, Di Mascio P - Sci Rep (2014)

Effect of pure O2 purging on the chemiluminescence intensity elicited by TMD.(A) UV-visible light emission time course of triplet excited acetone during the thermolysis of 5 mM TMD in CCl4 at 70°C, and (B) Monomol light emission of O2 (1Δg) recorded during the decomposition of 5 mM TMD in CCl4 at 70°C. The arrow in both graphs indicates the time elapsed in O2 purging.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4120373&req=5

f2: Effect of pure O2 purging on the chemiluminescence intensity elicited by TMD.(A) UV-visible light emission time course of triplet excited acetone during the thermolysis of 5 mM TMD in CCl4 at 70°C, and (B) Monomol light emission of O2 (1Δg) recorded during the decomposition of 5 mM TMD in CCl4 at 70°C. The arrow in both graphs indicates the time elapsed in O2 purging.
Mentions: Since the concentration of O2 in solution can limit the generation of O2 (1Δg) by TMD thermolysis, additional luminescence experiments were performed using CCl4. Ten minutes after starting the reaction, pure O2 was purged inside the cuvette in an attempt to enhance O2 (1Δg) generation (Fig. 2). As expected, the influx of molecular O2 into the system decreased the intensity of UV-visible light (Fig. 2A) due to energy transfer of the generated triplet acetone to molecular oxygen, although a slight decrease in NIR monomol light emission of O2 (1Δg) was observed (Fig. 2B). In this respect, we note that, although triplet molecular oxygen is known to be a triplet carbonyl suppressor18, McGarvey et al.61 reported an inverse correlation between molecular oxygen quenching of different triplet naphthalenes in benzene and the generation of O2 (1Δg). This finding was then correlated to structural differences in naphthalene, and not to changes in O2 concentration.

Bottom Line: This involves thermolysis of 3,3,4,4-tetramethyl-1,2-dioxetane, a chemical source, and horseradish peroxidase-catalyzed oxidation of 2-methylpropanal, as an enzymatic source.This corroborates formation of O2 ((1)Δg).Altogether, photoemission and chemical trapping studies clearly demonstrate that chemically and enzymatically nascent excited carbonyl generates (18)O2 ((1)Δg) by triplet-triplet energy transfer to ground state oxygen O2 ((3)Σg(-)), and supports the long formulated hypothesis of O2 ((1)Δg) involvement in physiological and pathophysiological events that might take place in tissues in the absence of light.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, CEP 05513-970, CP 26077, São Paulo, SP, Brazil.

ABSTRACT
In mammalian tissues, ultraweak chemiluminescence arising from biomolecule oxidation has been attributed to the radiative deactivation of singlet molecular oxygen [O2 ((1)Δg)] and electronically excited triplet carbonyl products involving dioxetane intermediates. Herein, we describe evidence of the generation of O2 ((1)Δg) in aqueous solution via energy transfer from excited triplet acetone. This involves thermolysis of 3,3,4,4-tetramethyl-1,2-dioxetane, a chemical source, and horseradish peroxidase-catalyzed oxidation of 2-methylpropanal, as an enzymatic source. Both sources of excited carbonyls showed characteristic light emission at 1,270 nm, directly indicative of the monomolecular decay of O2 ((1)Δg). Indirect analysis of O2 ((1)Δg) by electron paramagnetic resonance using the chemical trap 2,2,6,6-tetramethylpiperidine showed the formation of 2,2,6,6-tetramethylpiperidine-1-oxyl. Using [(18)O]-labeled triplet, ground state molecular oxygen [(18)O2 ((3)Σg(-))], chemical trapping of (18)O2 ((1)Δg) with disodium salt of anthracene-9,10-diyldiethane-2,1-diyl disulfate yielding the corresponding double-[(18)O]-labeled 9,10-endoperoxide, was detected through mass spectrometry. This corroborates formation of O2 ((1)Δg). Altogether, photoemission and chemical trapping studies clearly demonstrate that chemically and enzymatically nascent excited carbonyl generates (18)O2 ((1)Δg) by triplet-triplet energy transfer to ground state oxygen O2 ((3)Σg(-)), and supports the long formulated hypothesis of O2 ((1)Δg) involvement in physiological and pathophysiological events that might take place in tissues in the absence of light.

Show MeSH
Related in: MedlinePlus