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Articles 1 - 13 of 13
Full-Text Articles in Physical Sciences and Mathematics
Computational Quantum Chemistry Studies Of The Stabilities Of Radical Adducts Formed During The Oxidation Of Melatonin Derivatives, James Horne
Electronic Theses and Dissertations
Melatonin is a natural antioxidant that has been investigated for properties as a potential spin trap to identify short-lived free radicals. Computational quantum chemistry studies have been performed for the oxidation of melatonin to N1-acetyl-N2-formyl-5-methoxykynuramine. This research focused on modification of melatonin into derivatives and analyzing the change in total molecular energy from melatonin to its oxidation product, as well as the corresponding derivatives. Each of the molecular geometries were optimized at the DFT/B3LYP/6-31G(d), DFT/B3LYP/cc-pVXZ (X = D, T), HF/6-31G(d), HF/cc-PVXZ (X = D, T), MP2/6-31G(d), and MP2/cc-PVXZ (X = D, T) levels of theory. …
Computational Quantum Study Of Intermediates Formed During The Partial Oxidation Of Melatonin, Oladun Oladiran
Computational Quantum Study Of Intermediates Formed During The Partial Oxidation Of Melatonin, Oladun Oladiran
Electronic Theses and Dissertations
Melatonin is a neurohormone produced by the pineal gland in the brain. It functions as an antioxidant to scavenge free radicals. Free radicals are reactive species; they often oxidize the cells leading to oxidative stress which may lead to severe health complications. Reaction of melatonin with free radicals is known to be stepwise, as such the stability of the intermediates can be examined. Thus, the possibility of using melatonin as an in vivo spin trap can be determined. Spin traps allow characterization of unstable radical species using electron spin resonance spectroscopy. In this research, ab initio quantum chemistry techniques were …
Computational Quantum Chemistry Studies Of The Stabilities Of Radical Intermediates Formed During The Oxidation Of Melatonin, Constance E. Warden
Computational Quantum Chemistry Studies Of The Stabilities Of Radical Intermediates Formed During The Oxidation Of Melatonin, Constance E. Warden
Electronic Theses and Dissertations
Melatonin, a nontoxic natural antioxidant, is of interest as a possible spin trap for use in spectroscopic methods to observe and identify short-lived free radicals, which have been linked to oxidative stress that may result in serious health problems. However, the reaction mechanisms for the oxidation of melatonin to form the product N1-acetyl-N2-formyl-5-methoxykynuramine are still not well understood. Computational quantum chemistry studies have been done on four proposed reaction mechanisms, involving the following major intermediate structures: a dioxetane, an epoxide, a melatonin radical cation, and a spin radical adduct. Molecular geometries were optimized at the …
Satellite Observations Of Stratospheric Hydrogen Flouride And Comparisons With Slimcat Calculations, Jeremy J. Harrison, Martyn P. Chipperfield, Christopher D. Boone, Sandip S. Dhomse, Peter F. Bernath, Lucien Froidevaux
Satellite Observations Of Stratospheric Hydrogen Flouride And Comparisons With Slimcat Calculations, Jeremy J. Harrison, Martyn P. Chipperfield, Christopher D. Boone, Sandip S. Dhomse, Peter F. Bernath, Lucien Froidevaux
Chemistry & Biochemistry Faculty Publications
The vast majority of emissions of fluorine-containing molecules are anthropogenic in nature, e.g. chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs). Many of these fluorine-containing species deplete stratospheric ozone and are regulated by the Montreal Protocol. Once in the atmosphere they slowly degrade, ultimately leading to the formation of hydrogen fluoride (HF), the dominant reservoir of stratospheric fluorine due to its extreme stability. Monitoring the growth of stratospheric HF is therefore an important marker for the success of the Montreal Protocol. We report the comparison of global distributions and trends of HF measured in the Earth's atmosphere by the satellite remote-sensing …
Technical Note: A Trace Gas Climatology Derived From The Atmospheric Chemistry Experiment Fourier Transform Spectrometer (Ace-Fts) Data Set, A. Jones, K. A. Walker, J. J. Jin, J. R. Taylor, C. D. Boone, P. F. Bernath, S. Brohede, G. L. Manney, S. Mcleod, R. Hughes, W. H. Daffer
Technical Note: A Trace Gas Climatology Derived From The Atmospheric Chemistry Experiment Fourier Transform Spectrometer (Ace-Fts) Data Set, A. Jones, K. A. Walker, J. J. Jin, J. R. Taylor, C. D. Boone, P. F. Bernath, S. Brohede, G. L. Manney, S. Mcleod, R. Hughes, W. H. Daffer
Chemistry & Biochemistry Faculty Publications
The Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) aboard the Canadian satellite SCISAT (launched in August 2003) was designed to investigate the composition of the upper troposphere, stratosphere, and mesosphere. ACE-FTS utilizes solar occultation to measure temperature and pressure as well as vertical profiles of over thirty chemical species including O3, H2O, CH4, N2O, CO, NO, NO2, N2O5, HNO3, HCl, ClONO2, CCl3F, CCl2F2, and HF. Global coverage for each species is obtained approximately over a three month …
Potential Energy Surface Around The Tropylium Ion., Kenneth Wayne Bullins
Potential Energy Surface Around The Tropylium Ion., Kenneth Wayne Bullins
Electronic Theses and Dissertations
The formation of the tropylium ion, C7H7+, in the mass spectrum of toluene is a chemical process that has been studied extensively in the past. The advances in computational power of personal computers have made the investigation of the pathway to form this ion and its subsequent decomposition feasible at a fairly high level of theory. The calculations that we performed were at the HF/6-31G (d, p) and the B3LYP/6-311++G (2d) levels. This work will show areas of the potential energy surface around the highly symmetric tropylium ion to give a glance of possible mechanisms …
Nonadditive Effects In Hf And Hcl Trimers, G. Chalasinski, S. M. Cybulski, M. M. Szczesniak, Steve Scheiner
Nonadditive Effects In Hf And Hcl Trimers, G. Chalasinski, S. M. Cybulski, M. M. Szczesniak, Steve Scheiner
Steve Scheiner
Nonadditive effects are calculated for (HF)3 and (HCl)3 complexes and analyzed via the combination of perturbation theory of intermolecular forces with Møller–Plesset perturbation theory (MPPT). In both systems the nonadditivity is dominated by the self‐consistent field (SCF) deformation effect, i.e., mutual polarization of the monomer wavefunctions. Heitler–London exchange and correlation effects are of secondary importance. Three‐body terms exhibit much lesser basis set dependence than the two‐body effects and even quite moderate basis sets which are not accurate enough for treatment of two‐body forces can yield three‐body effects of quantitative quality. This is due in large measure to the …
Nonadditive Effects In Hf And Hcl Trimers, G. Chalasinski, S. M. Cybulski, M. M. Szczesniak, Steve Scheiner
Nonadditive Effects In Hf And Hcl Trimers, G. Chalasinski, S. M. Cybulski, M. M. Szczesniak, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
Nonadditive effects are calculated for (HF)3 and (HCl)3 complexes and analyzed via the combination of perturbation theory of intermolecular forces with Møller–Plesset perturbation theory (MPPT). In both systems the nonadditivity is dominated by the self‐consistent field (SCF) deformation effect, i.e., mutual polarization of the monomer wavefunctions. Heitler–London exchange and correlation effects are of secondary importance. Three‐body terms exhibit much lesser basis set dependence than the two‐body effects and even quite moderate basis sets which are not accurate enough for treatment of two‐body forces can yield three‐body effects of quantitative quality. This is due in large measure to the …
Vibrational Frequencies And Intensities Of H-Bonded Systems. 1:1 And 1:2 Complexes Of Nh3 And Ph3 With Hf, I. J. Kurnig, M. M. Szczesniak, Steve Scheiner
Vibrational Frequencies And Intensities Of H-Bonded Systems. 1:1 And 1:2 Complexes Of Nh3 And Ph3 With Hf, I. J. Kurnig, M. M. Szczesniak, Steve Scheiner
Steve Scheiner
Frequencies and intensities are calculated by ab initio methods for all vibrational modes of the 1:1 H3X–HF and 1:2 H3X–HF–HF complexes (X=N,P). The HF stretching frequencies are subject to red shifts, roughly proportional to the strength of the H bond, and to manyfold increases in intensity. Although the intramolecular frequency shifts within the proton acceptors are relatively modest, the intensities of the NH3 stretches are magnified by several orders of magnitude as a result of H bonding (in contrast to PH3 which exhibits little sensitivity in this regard). …
Vibrational Frequencies And Intensities Of H-Bonded Systems. 1:1 And 1:2 Complexes Of Nh3 And Ph3 With Hfvibrational Frequencies And Intensities Of H‐Bonded Systems. 1:1 And 1:2 Complexes Of Nh3 And Ph3 With Hf, I. J. Kurnig, M. M. Szczesniak, Steve Scheiner
Vibrational Frequencies And Intensities Of H-Bonded Systems. 1:1 And 1:2 Complexes Of Nh3 And Ph3 With Hfvibrational Frequencies And Intensities Of H‐Bonded Systems. 1:1 And 1:2 Complexes Of Nh3 And Ph3 With Hf, I. J. Kurnig, M. M. Szczesniak, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
Frequencies and intensities are calculated by ab initio methods for all vibrational modes of the 1:1 H3X–HF and 1:2 H3X–HF–HF complexes (X=N,P). The HF stretching frequencies are subject to red shifts, roughly proportional to the strength of the H bond, and to manyfold increases in intensity. Although the intramolecular frequency shifts within the proton acceptors are relatively modest, the intensities of the NH3 stretches are magnified by several orders of magnitude as a result of H bonding (in contrast to PH3 which exhibits little sensitivity in this regard). …
Contribution Of Dispersion To The Properties Of H2s‐‐Hf And H2s‐‐Hcl, M. M. Szczesniak, Steve Scheiner
Contribution Of Dispersion To The Properties Of H2s‐‐Hf And H2s‐‐Hcl, M. M. Szczesniak, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
Ab initio calculations are carried out using a doubly polarized basis set. Dispersion, evaluated by second‐order Møller–Plesset perturbation theory (MP2), is found to have a profound influence on the stabilities and structures of the H‐bonded complexes. The contribution of dispersion to the H‐bond energies of H2S‐‐HF and H2S‐‐HCl is 44% and 69%, respectively, placing this attractive term second in magnitude only to electrostatics. Reductions of the intermolecular distance of 0.17 and 0.34 Å result from inclusion of correlation effects. Nevertheless, the influence of dispersion upon the angular characteristics of the …
Ab Initio Comparison Of H Bonds And Li Bonds. Complexes Of Lif, Licl, Hf, And Hcl With Nh3, Z. Latajka, Steve Scheiner
Ab Initio Comparison Of H Bonds And Li Bonds. Complexes Of Lif, Licl, Hf, And Hcl With Nh3, Z. Latajka, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
Ab initio calculations are carried out on the complexes H3N–LiF, H3N–LiCl and their analogs H3N–HF and H3N–HCl as well as the isolated subunits. Double‐zeta basis sets, augmented by two sets of polarization functions, are used in conjunction with second‐order Moller–Plesset perturbation theory (MP2) for evaluation of electron correlation effects. The Li bonds are found to be substantially stronger than their H‐bonding counterparts, due in large measure to the greater dipole moments of the LiX subunits. Correlation has a large effect on the geometry and energetics of …
Role Of D Functions In Ab Initio Calculation Of The Equilibrium Structure Of H2s–Hf, Steve Scheiner
Role Of D Functions In Ab Initio Calculation Of The Equilibrium Structure Of H2s–Hf, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
Full geometry optimizations are performed to determine the equilibrium geometry of the hydrogen‐bonded complex H2S–HF. The angle between the plane of the H2S moiety and the H‐bond axis calculated with the 4–31 G basis set is 106° as compared to the experimental value of 91±5°. This quantity is reduced significantly when d orbitals are added to the basis set, yielding an angle within experimental error of 91°. (AIP)