A comparison of orbital interactions in the additions of phosphonyl and acyl radicals to double bonds

Krenske, Elizabeth H.; Schiesser, Carl H.

doi:10.1039/b714597g

Cited by 10 publications

(9 citation statements)

References 15 publications

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“…Single-point energy calculations using the BH and HLYP and ROMP2 methods, and B3LYP/6-31G* optimized geometries gave the least accurate energies contrary to that previously reported28 for the prediction of energy barriers in which BHandHLYP provided good agreement with the highest levels of theory used in that study. Moreover, single-point energy calculations at the CCSD(T)/cc-pVDZ, CCSD/aug-cc-pVDZ, QCISD/cc-pVDZ, and QCISD/aug-cc-pVDZ levels of theory with the B3LYP/6-31G* optimized geometries gave 1.2-2.1 kcal/mol energy difference compared to that obtained with CBS-QB3.…”

Section: Benchmark Studiescontrasting

confidence: 99%

Superoxide Radical Anion Adduct of 5,5-Dimethyl-1-pyrroline N-Oxide. 4. Conformational Effects on the EPR Hyperfine Splitting Constants

2008

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Spin trapping has been commonly employed in the detection of superoxide radical anion in chemical and biological systems; hence, accurate interpretation of the hyperfine splitting constants (hfsc's) arising from the O 2 ·-adducts (also referred to as hydroperoxyl (HO 2 · ) radical adducts) of various nitrones is important. In this work, the nature of the relevant hfsc's was investigated by examining the effect of conformational changes in the hydroperoxyl moiety of the O 2 ·-adducts of 5,5-dimethyl-1-pyrroline N-oxide (DMPO), 5-ethoxycarbonyl-5-methyl-1-pyrroline N-oxide (EMPO), 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide (DEPMPO), 5-carbamoyl-5-methyl-1-pyrroline N-oxide (AMPO), and 7-oxa-1-azaspiro[4.4]non-1-en-6-one N-oxide, (CPCOMPO) on the magnitude of a N , a β-H , and a γ-H . Conformational change around the substituents and their effect on the hfsc's were also explored. Results indicate that a β-H is most sensitive to conformational changes of the hydroperoxyl and substituent groups relative to hfsc's of other nuclei. The orbital overlap between the C-H σ-orbital and the SOMO of the nitroxyl nitrogen plays a crucial factor in determining the magnitude of the a β-H . The hfsc values for the O 2 ·-adducts were predicted with high accuracy by using a low-cost computational method at the PCM(water)/BHandHLYP/EPR-III//B3LYP/ 6-31G* level of theory without taking into account the explicit water interaction.

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Section: Benchmark Studiescontrasting

confidence: 99%

Superoxide Radical Anion Adduct of 5,5-Dimethyl-1-pyrroline N-Oxide. 4. Conformational Effects on the EPR Hyperfine Splitting Constants

2008

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“…Variations in energetics as a function of basis set and method was assessed using B3LYP/6-31G* geometries and single-point energies at B3LYP/6-31+G**, B3LYP/6-311++G**, B3LYP/aug-cc-pVDZ, BHandHLYP/6-31+G**, mpw1pw91/6-31+G** and PBE1PBE/6-31+G** levels of theory. Reaction energy at the B3LYP/6-31+G**//B3LYP/6-31G* is within ∼1 kcal/mol difference of the energetics calculated at the B3LYP/aug-cc-pVDZ and BHandHLYP/6-31+G** levels (see Table S1 of Supporting Information), therefore, B3LYP/6-31+G**//B3LYP/6-31G* offers a reasonable approximation to the higher-level basis set and BHandHLYP/6-31+G** which is effective in approximating barrier height energies (29, 30). Density functional theory (DFT) (31, 32) was applied in this study to determine the optimized geometry, vibrational frequencies, and single-point energy of all stationary points (33–36).…”

Section: Methodsmentioning

confidence: 75%

Theoretical and Experimental Studies of Tyrosyl Hydroperoxide Formation in the Presence of H-Bond Donors

Field

Villamena

2008

Chem. Res. Toxicol.

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Oxidative damage to biomolecules such as lipids, proteins, nucleotides and sugars has been implicated in the pathogenesis of various diseases. Superoxide radical anion (O 2•− ) addition to nitrones bearing an amide N-H has been shown to be more favored compared to other nitrones (Villamena, F. A., et al., J. Am. Chem. Soc., 2007, 129, 8177-8191). It has also been demonstrated by others (Winterbourn, C. C., et al., Biochem. J. 2004, 381, 241-248) that O 2•− addition to tyrosine to form hydroperoxide is favored in the presence of basic amino groups but the mechanism for this observation remains obscure. We, therefore, hypothesized that the α-effect resulting from the interaction of O 2•− with N-H can play a crucial role in the enhancement of hydroperoxide formation. Understanding this phenomenon is important in the elucidation of mechanisms leading to oxidative stress in cellular systems. Computational (PCM/B3LYP/6-31+G**//B3LYP/6-31G level of theory) as well as experimental studies were carried out to shed insights into the effect of amide or amino N-H on the enhancement (or stabilization) of hydroperoxide formation in tyrosine. H-bond interaction of amino acid group with O 2•− results in the perturbation of the spin and charge densities of O 2•− . Similar phenomenon has been predicted for non-amino acids bearing H-bond donor groups. Using FOX assay, tyrosyl hydroperoxide formation was enhanced in the presence of H-bond donors from amino acids and non-amino acids. The role of H-bonding in either stabilizing the hydroperoxide adduct, or facilitation of O 2•− addition via α-effect was further theoretically investigated, and results show that the latter mechanism is more thermodynamically preferred. This study provides new mechanistic insights in the initiation of oxidative modification to tyrosyl radical.

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“…The B3LYP/6-31+G(d,p) and ROMP2/6-311G(d,p) levels gave the lowest estimate of the energy barriers while the BHandHLYP/6-311G(d,p)//B3LYP/6-31G(d) and ROMP2/cc-PVDZ//B3LYP/6-31G(d) gave bottom-of-the-well energy barrier estimates that are close to those of the more accurate QCISD/cc-PVDZ//B3LYP/6-31G(d) level. Moreover, a reasonable estimate was also obtained with PCM/BHandHLYP/6-311G(d,p)//BHandHLYP/6-31G(d) and a slighty lower estimate was obtained with the BHandHLYP/6-311G(d,p)/BHandHLYP/6-31G(d) level, which was preferred by Krenske and Schiesser . Therefore, the use of both BHandHLYP/6-311G(d,p)//B3LYP/6-31G(d) and ROMP2/cc-PVDZ//B3LYP/6-31G(d) levels of theory should justify calculation of approximated energetics of decomposition in this study.…”

Section: Resultsmentioning

confidence: 93%

“…It has been shown by Krenske and Schiesser that B3LYP-based approaches using small basis sets (cc-pVDZ or 6-31G(d)) gave lower estimates of the energy barriers for the addition of phosphonyl or acyl radicals to double bonds, and that the BHandHLYP functional provided reasonable estimates to the higher level barriers. They also found that BHandHLYP, using the basis sets cc-pVDZ or 6-311G(d,p), gave similar estimates as the QCISD or CCSD(T) single-point calculations.…”

Section: Resultsmentioning

confidence: 99%

Superoxide Radical Anion Adduct of 5,5-Dimethyl-1-pyrroline N-Oxide. 5. Thermodynamics and Kinetics of Unimolecular Decomposition

Villamena

2009

J. Phys. Chem. A

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The unimolecular decomposition of the superoxide radical anion adducts of 5,5-dimethyl-1-pyrroline N-oxide (DMPO), 5-carbamoyl-5-methyl-1-pyrroline N-oxide (AMPO), 5-ethoxycarbonyl-5-methyl-1-pyrroline N-oxide (EMPO), and 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide (DEPMPO) were computationally investigated by using PCM/BHandLYP/6-311G(d,p)//B3LYP/6-31G(d) and PCM/ROMP2/cc-PVDZ//B3LYP/6-31G(d) levels of theory. Results indicate that the O-O bond scission for nitrone-O(2)H to form the hydroxyl radical and the biradical is endoergic, and that the ring-opening step to form the nitrosoaldehyde is highly exoergic. The energy barriers for the O-O bond scission and ring-opening processes indicate that the former is the rate-limiting step of the reaction. The overall energetics for DMPO-O(2)H decomposition in the presence and absence of explicit water interactions was found to be the most preferred; however, no significant differences in the energetics of decomposition among the various isomers of AMPO-O(2)H, EMPO-O(2)H, and DEPMPO-O(2)H were observed.

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A comparison of orbital interactions in the additions of phosphonyl and acyl radicals to double bonds

Cited by 10 publications

References 15 publications

Superoxide Radical Anion Adduct of 5,5-Dimethyl-1-pyrroline N-Oxide. 4. Conformational Effects on the EPR Hyperfine Splitting Constants

Superoxide Radical Anion Adduct of 5,5-Dimethyl-1-pyrroline N-Oxide. 4. Conformational Effects on the EPR Hyperfine Splitting Constants

Theoretical and Experimental Studies of Tyrosyl Hydroperoxide Formation in the Presence of H-Bond Donors

Superoxide Radical Anion Adduct of 5,5-Dimethyl-1-pyrroline N-Oxide. 5. Thermodynamics and Kinetics of Unimolecular Decomposition

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