scholarly journals Bypassing the Multi-reference Character of Singlet Molecular Oxygen. Part 2: Ene-reaction

2021 ◽  
Author(s):  
Kurt Mikkelsen ◽  
Malte Jespersen ◽  
Matthew Johnson ◽  
Solvejg Jørgensen ◽  
Emma Petersen-Sonn
Keyword(s):  
Singlet Oxygen ◽  
Molecular Oxygen ◽  
Theoretical Calculations ◽  
Singlet Molecular Oxygen ◽  
Ene Reaction ◽  
Calculated Rate ◽  
Trans Butene ◽  
Oxygen Addition ◽  
Concerted Reaction

Theoretical calculations involving singlet molecular oxygen (O2(1g)) are challeng- ing due to their inherent multi-reference character. We have tested the quality of re- stricted and unrestricted DFT geometries obtained for the reaction between singlet oxy- gen and a series of alkenes (propene, 2-methylpropene, trans-butene, 2-methylbutene and 2,3-dimethylbutene) which are able to follow the ene-reaction. The electronic en- ergy of the obtained geometries are rened using 3 dierent methods which account for the multi-reference character of singlet oxygen. The results show that the mechanism for the ene-reaction is qualitatively dierent when either one or two allylic-hydrogen groups are available for the reaction. When one allylic-hydrogen group is available the UDFT calculations predict a stepwise addition forming a biradical intermediate, while, the RDFT calculations predict a concerted reaction where both hydrogen abstrac- tion and oxygen addition occur simultaneously. When two allylic-hydrogen groups are available for the reaction then UDFT and RDFT predict the same reaction mechanism, namely that the reaction occurs as a stepwise addition without a stable intermediate between the two transition states. The calculated rate constants are in reasonable agreement with experimental data, except for trans-butene where the calculated rate constant is three orders of magnitude lower than the experimental one. In conclusion we nd that the simple bypassing scheme tested in this paper is a robust approach for calculations of reaction involving singlet oxygen in the limit that the transition state processes low multi-reference character. 2

Singlet oxygen and natural substrates: functional polyunsaturated models for the photooxidative degradation of carotenoids

2015 ◽  
Vol 87 (7) ◽  
pp. 639-647 ◽  
Author(s):  
Axel G. Griesbeck ◽  
Margarethe Kleczka ◽  
Alan de Kiff ◽  
Moritz Vollmer ◽  
Angelika Eske ◽  
...  
Keyword(s):  
Singlet Oxygen ◽  
Research Report ◽  
Secondary Products ◽  
Model Compounds ◽  
Singlet Molecular Oxygen ◽  
Ene Reaction ◽  
Stabilizing Effect ◽  
Oxygen Addition ◽  
Tandem Reactivity ◽  
Singlet Oxygen Reaction

AbstractThe primary chemical reactions of singlet molecular oxygen with polyunsaturated carotenoids are the focus of this research report. Model compounds that exhibit electronic properties and substituent pattern similar to natural carotenes, xanthophylls or apocarotenoids, respectively, were investigated with regard to photooxygenation reactivity. For dienes and trienes as substrates, high tandem reactivity was observed and hydroperoxy-endoperoxides were isolated as the secondary products of singlet oxygen reaction. The electronic gem-effect on the regioselectivity of the ene reaction is conserved also in vinylogous positions and thus appears to originate from a radical-stabilizing effect. In an attempt to combine different peroxide groups derived from natural products as a tool for new pharmaceutically active products, a dyade synthesis of an artemisinine-safranol with subsequent singlet oxygen addition was realized.

Intermediates in the Formation and Thermolysis of Peroxides from Oxidations with Singlet Oxygen

2014 ◽  
Vol 67 (3) ◽  
pp. 320 ◽  
Author(s):  
Werner Fudickar ◽  
Torsten Linker
Keyword(s):  
Singlet Oxygen ◽  
Theoretical Work ◽  
Ene Reaction ◽  
Experimental Findings ◽  
Zwitterionic Intermediate ◽  
Concerted Reaction

Herein we describe the recent mechanistic understandings of the singlet oxygen ene reaction to give hydroperoxides and the [4+2] cycloaddition affording endoperoxides. Both experimental findings and theoretical work conclude in the formation of intermediates structurally similar to perepoxides during the ene reaction. Such intermediates mainly control the regio- and stereoselectivities of this reaction class. For the [4+2] cycloaddition, both a synchronous concerted reaction (benzene, naphthalenes) and a stepwise reaction with a non-symmetric zwitterionic intermediate (larger acenes) have been found. The thermolysis of endoperoxides derived from acenes proceeds stepwise for anthracenes, but in a concerted manner for less stable adducts such as naphthalene.

Synthesis, crystal structure and physicochemical characterization of a Hg(II) complex with 6-methoxyquinoline as ligand

2015 ◽  
Vol 70 (10) ◽  
pp. 719-725 ◽  
Author(s):  
Cristian Villa-Pérez ◽  
Isabel C. Ortega ◽  
Angélica M. Payán-Aristizábal ◽  
Gustavo Echeverría ◽  
Gloria C. Valencia-Uribe ◽  
...  
Keyword(s):  
Molecular Oxygen ◽  
Theoretical Calculations ◽  
Physicochemical Characterization ◽  
Spectroscopic Studies ◽  
Monoclinic Space Group ◽  
Oxygen Production ◽  
X Ray Diffraction ◽  
Singlet Molecular Oxygen ◽  
X Ray

AbstractA new complex of Hg(II) with 6-methoxyquinoline (C10H9NO-6MQ) has been synthesized and characterized. The structure of the complex Hg(6MQ)Cl2 was determined by single crystal X-ray diffraction. It crystallizes in the monoclinic space group P21/c with a = 3.9139(3), b = 26.3400(2), c = 10.9090(9) Å, β = 89.833(6)°, V = 1124.6(1) Å3 and Z = 4 molecules per unit cell. The coordination geometry of the mercury(II) center can be described as a distorted square pyramid formed by one nitrogen atom of the 6MQ and four chlorine atoms. Fourier transform infrared, Raman and UV/Vis spectroscopic studies have been carried out to characterize the compound, using theoretical calculations for the assignment of the experimentally observed bands. The thermal behavior was investigated by thermogravimetric analysis. The quantum yield of singlet molecular oxygen production ΦΔ was measured with steady-state methods in ethanol, using 9,10-dimethylanthracene (DMA) as actinometer and Bengal rose as reference photosensitizer. The resultant singlet molecular oxygen was detected indirectly by photooxidation reactions of DMA. The luminescence properties have also been studied.

Singlet Molecular Oxygen Triggers the soxRS Regulon of Escherichia coli

2001 ◽  
Vol 382 (7) ◽  
pp. 1071-1075 ◽  
Author(s):  
Lucymara F. Agnez-Lima ◽  
Paolo Di Mascio ◽  
Bruce Demple ◽  
Carlos F.M. Menck
Keyword(s):  
Escherichia Coli ◽  
Singlet Oxygen ◽  
Molecular Oxygen ◽  
Singlet Molecular Oxygen ◽  
Signal Molecule ◽  
Present Evidence ◽  
Oxidative Stresses ◽  
Electronically Excited ◽  
Soxrs Regulon ◽  
Intercellular Signal

AbstractThe electronically excited molecular oxygen (singlet oxygen, [1]O[2]) can be detrimental to cells in several ways, although recent reports indicate that it may play a role as an intercellular signal in eukaryotes. Here we present evidence that [1]O[2], generated by thermodissociation of disodium 3,3(1,4-naphthylidene) diproprionate endoperoxide, activates transcription of genes of the soxRS regulon, and that this induction is paralleled by induction of a soxS::lacZ operon fusion. The inductions were dependent on a functional soxR gene. These data imply that protective responses, such as induction of the soxRS regulon, may be triggered by diverse environmental oxidative stresses, and that [1]O[2] may also function as a signal molecule in prokaryotes.

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