: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Five new MnII coordination polymers, namely [Mn2(tbip)2(bix)] (1), [Mn3(tbip)3(bix)2] (2), [Mn3(tbip)2(Htbip)2(bib)2]·4H2O (3), [Mn4(tbip)4(bbp)2(H2O)2] (4), and [Mn4(tbip)4(bip)]·2H2O (5), were prepared by hydrothermal reactions of Mn(II) acetate with H2tbip (5-tert-butyl isophthalic acid) in the presence of different di-imidazolyl coligands (bix =1,4-bis(imidazol-1-ylmethyl)benzene, bib =1,4-bis(imidazol) butane, bbp =1,3-bis(benzimidazol)propane, bip =1,3-bis(imidazol)propane). All complexes were characterized by elemental analysis, IR spectra, thermogravimetric analysis, single-crystal X-ray crystallography, and powder X-ray diffraction. Single crystal X-ray studies show that these coordination polymers contain homometallic clusters varying from dimeric, trimeric, and tetrameric motifs to polymeric chains depending upon the coligands used. Complex 1 has a 3D 6-connected polycatenane network with dinuclear [Mn2O2] secondary building units. Complex 2 possesses a 3D 8-connected structure with trinuclear ...

MnII Coordination Polymers Based on Bi-, Tri-, and Tetranuclear and Polymeric Chain Building Units: Crystal Structures and Magnetic Properties

Recent advances in the synthesis and properties of 4-, 5-, 6- or 7-azaindoles

https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=900170

Catalytic inhibition of laminar flames by transition metal compounds

We show by experiments that nonheme Fe IV O species react with cyclohexene to yield selective hydrogen atom transfer (HAT) reactions with virtually no CC epoxidation. Straightforward DFT calculations reveal, however, that CC epoxidation on the S = 2 state possesses a low-energy barrier and should contribute substantially to the oxidation of cyclohexene by the nonheme Fe IV O species. By modeling the selectivity of this two-site reactivity, we show that an interplay of tunneling and spin inversion probability (SIP) reverses the apparent barriers and prefers exclusive S = 1 HAT over mixed HAT and CC epoxidation on S = 2. The model enables us to derive a SIP value by combining experimental and theoretical results.

Determination of Spin Inversion Probability, H-Tunneling Correction, and Regioselectivity in the Two-State Reactivity of Nonheme Iron(IV)-Oxo Complexes.

The mechanism and dynamics of double proton transfer dependence on hydrogen-bonding of solvent molecules to the bridging water in a water wire were studied by a direct ab initio dynamics approach with variational transition-state theory including multidimensional tunneling. Long-range proton transfers in solution and within enzymes may have very different mechanisms depending on the pKa values of participating groups and their electrostatic interactions with their environment. For end groups that have acidic or basic pKa values, proton transfers by the classical Grotthuss and “proton-hole” transfer mechanisms, respectively, are energetically favorable. This study shows that these processes are facilitated by hydrogen-bond accepting and donating solvent molecule interactions with the water wire in the transition state (TS), respectively. Tunneling also depends very much on the hydrogen bonding to the water wire. All molecules hydrogen bonded to the water wire, even if they raised and narrowed energy barrie...

Proton transfer dependence on hydrogen-bonding of solvent to the water wire: a theoretical study.

Type-III copper-containing enzymes have dicopper centers in their active sites and exhibit a novel capacity for activating aliphatic C–H bonds in various substrates by taking molecular oxygen. Dicopper enzyme models developed by Tolman and co-workers reveal exceptionally large kinetic isotope effects (KIEs) for the hydrogen transfer process, indicating a significant tunneling effect. In this work, we demonstrate that variational transition state theory allows accurate prediction of the KIEs and Arrhenius parameters for such model systems. This includes multidimensional tunneling based on state-of-the-art quantum-mechanical calculations of the minimum-energy path (MEP). The computational model of bis(μ-oxo)dicopper enzyme consists of 70 atoms, resulting in a 204-dimensional potential energy surface. The calculated values of EaH – EaD, AH/AD, and the KIE at 233 K are −1.86 kcal/mol, 0.51, and 28.1, respectively, for the isopropyl ligand system. These values agree very well with experimental values within th...

Large Tunneling Effect on the Hydrogen Transfer in Bis(μ-oxo)dicopper Enzyme: A Theoretical Study

The rule of the geometric mean in rates and kinetic isotope effects has long been used as a criterion for identifying the reaction mechanism, e.g., stepwise vs. concerted, for double proton transfer reactions. Potential energy surfaces of double proton transfers for excited state tautomerization in a 1:1 7-azaindole:H 2 O complex were generated at the MRPT2//CASSCF(10,9)/6-31G(d,p) level. Variational transition state theory, including multidimensional tunneling approximation, was used to calculate rates and kinetic isotope effects. No intermediates were present along the reaction coordinate. Two protons in the excited state tautomerization were transferred concertedly, albeit asynchronously. Positions of the variational transition states depend very much on the isotopic substitution. The asynchronicity of two protons in flight breaks the underlying assumption of the rule of the geometric mean so that the relation, k HH / k HD  ≈  k HD / k DD , is no longer valid in the excited state double proton transfer. Breakdown of the geometric mean rule does not necessarily entail that the reaction mechanism is stepwise; therefore this rule should be used very carefully as a criterion for identification of the mechanism.

Excited state double proton transfer of a 1:1 7-azaindole:H2O complex and the breakdown of the rule of the geometric mean: Variational transition state theory studies including multidimensional tunneling

It has been shown that methane has the longest ignition delay time among the simple aliphatic hydrocarbons. 1-3 This phenomenon can be explained by the fact that the C-H bond in methane is considerably stronger than the C-C bond in larger hydrocarbons. 2 It was also shown that by adding small amounts of ethane or propane to methane, it was possible to shorten its ignition delay time. 4 Whereas it is rather simple to shorten the ignition delay of methane, we are not aware of any attempt to increase its delay. Recently, flame studies have shown that metal-containing compounds are promising candidates for replacing halons as fire suppression agents. In particular, flame velocity studies indicate that Fe(CO) 5 can be up to sixty times more efficient a flame inhibitor than CF 3Br. Reinelt and Linteris 6 studied the flame inhibition effect of iron pentacarbonyl in premixed flames by measuring the burning velocity, and in counterflow diffusion flames by measuring the extinction strain rate. They found that at low Fe(CO) 5 mole fraction, the burning velocity was strongly dependent on inhibitor mole fraction, whereas at high Fe(CO) 5 mole fraction, the burning velocity was nearly independent of inhibitor mole fraction. A chemical interpretation of flame inhibiting effect of Fe(CO)5 has been developed by Rumminger et al. on the basis of burning velocity measurements on CH 4-O2-N2 and H2-CO-O2-N2 premixed and counterflow flames of varying composition. Up to date, most of the works on the flame inhibition by iron pentacarbonyl have been done by measuring the burning velocity in flames. Therefore, we undertook to charac-

http://koreascience.or.kr:80/article/JAKO200202727363808.pdf

The addition effect of Fe(CO)5 on methane ignition

O, formic acid dimer, formamidine dimer, formamide dimer, formic acid + formamide, formicacid + formamidine, formamide + formamidine, and barrier heights for the double proton transfer in thesecomplexes. Various ab initio, density functional theory, multilevel methods have been used. Geometries andenergies depend very much on the level of theory. In particular, the transition state symmetry of the protontransfer in formamidine dimer varies greatly depending on the level of theory, so very high level of theory mustbe used to get any reasonable results.Key Words : Double proton transfer, Tautomerization, Hydrogen-bonded complex, Asynchronous mecha-nism, MulilevelIntroductionProton transfer is one of the simplest and the mostfundamental reaction in chemistry and biology. Protontransfer involving many protons is also an important phen-omenon. Most multiproton transfers occur, either concerted-ly or stepwise, through a hydrogen-bonded chain. A protonrelay is thought to account for the high mobility of theproton in water. There are many examples of multiprotontransfer such as proton relay systems in enzymes, certainproton transfers in hydrogen-bonded water complexes, andproton transfers in prototropic tautomerisms. H-bondingcomplexes of formic acid (FA), formamide (FM), and form-amidine (FN), such as FA-water, FM-water, and FN-water,can serve as model systems for protein-water and protein-solvent interactions. Due to the simplicity of this model, thecharacterization of the hydrogen-bonding interactions bet-ween water and FA, FM, and FN, and prototropic tautomeri-zation in these complexes have been of considerable interestto experimentalists and theoreticians.FA dimer is one of the most extensively studied systemsboth experimentally and theoretically, since it is one of thesimplest examples of a multiproton transfer system in whichthe constituents are held together by two hydrogen bonds.Therefore, it can be used as a model of many chemically andbiologically important multiproton transfers. All high levelab initio calculations that have been performed for the gasphase suggest that the protons in formic acid are transferredconcertedly and synchronously via the transition state posse-ssing D

Kisoo Park

Papers

Proton transfer dependence on hydrogen-bonding of solvent to the water wire: a theoretical study.

Large Tunneling Effect on the Hydrogen Transfer in Bis(μ-oxo)dicopper Enzyme: A Theoretical Study

Excited state double proton transfer of a 1:1 7-azaindole:H2O complex and the breakdown of the rule of the geometric mean: Variational transition state theory studies including multidimensional tunneling

The addition effect of Fe(CO)5 on methane ignition

Quantum Mechanical Studies for Structures and Energetic of Double Proton Transfer in Biologically Important Hydrogen-bonded Complexes