Joze Koller

University of Strathclyde, Glasgow, SCT, United Kingdom

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Publications (11)64.57 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Protonated dihydrogen trioxide (HOOOH) has been postulated in various forms for many years. Protonation can occur at either the terminal (HOOO(H)H(+)) or central (HOOH(OH)(+)) oxygen atom. However, to date there has been no definitive evidence provided for either of these species. In the current work we have employed ab initio methods, CCSD(T) and MP2, with a large basis set (6-311++G(3df,3pd)) to determine the relative stabilities of these species. It is shown that the terminally protonated species is strongly favored relative to the centrally protonated species (DeltaE = 15.8 kcal/mol, CCSD(T)//MP2). The mechanism of formation of HOOO(H)H(+) was determined to occur with a low barrier with the H(3)O(+) occurring in a thermoneutral reaction (DeltaE = -0.3 kcal/mol, CCSD(T)//MP2). Although HOOO(H)H(+) exists as a stable intermediate, it is extremely short-lived and rapidly decomposes (DeltaE* = 8.6 kcal/mol, MP2) to H(3)O(+) and O(2)((1)Delta(g)). The decomposition reaction is stabilized by solvent water molecules. The short-lived nature of the intermediate implies that the intermediate species can not be observed in (17)O NMR spectra, which has been demonstrated experimentally.
    The Journal of Physical Chemistry A 08/2010; 114(30):8003-8. · 2.77 Impact Factor
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    ABSTRACT: We demonstrate in this work by theory and experiment that benzaldehyde hydrotrioxide (PhC(O)OOOH), the intermediate most likely formed in the low-temperature ozonation of benzaldehyde, is too unstable to be detected by NMR (1H, 13C, and 17O) spectroscopy in various organic solvents at temperatures > or = -80 degrees C and that its previous detection must have been erroneous. Several plausible mechanisms for the formation of this polyoxide were explored by using density functional theory. We found that the formation of the hydrotrioxide involves the facile 1,3-dipolar insertion of ozone into the C-H bond (deltaH(double dagger) = 11.1 kcal/mol) in a strongly exothermic process (deltaH(R) = -57.0 kcal/mol). The hydrotrioxide then quickly decomposes in a second concerted, exothermic reaction involving an intramolecular H transfer to form benzoic acid and singlet oxygen (O2(1delta(g))) (deltaH(double dagger) = 5.6 kcal/mol), deltaH(R) = -14.0 kcal/mol). The equilibrium is thus expected to be shifted toward the products; therefore, this intermediate cannot be observed experimentally. Peroxybenzoic acid, still another major reaction product formed in the ozonation reaction, is formed as a result of the surprising instability of the RC(O)O-OOH bond (deltaH(R) = 23.5 kcal/mol), generating HOO* and benzoyloxyl radicals. Both of these radicals can then initiate the chain autoxidation reaction sequence--the abstraction of a H atom from benzaldehyde to form either a benzoyl radical and HOOH or a benzoyl radical and benzoic acid. Because only very small amounts of HOOH were detected in the decomposition mixtures, the recombination of the benzoyl radical with the HOO* radical (deltaH(R) = -80.7 kcal/mol) appears to be the major source of peroxybenzoic acid. A theoretical investigation of the mechanistic possibility of the involvement of still another intermediate, a cyclic tetraoxide (tetraoxolane) formed as a primary product in the 1,3-dipolar cycloaddition of ozone to the carbonyl group of the aldehyde, revealed that the tetraoxide is a "real" molecular entity with the five-membered ring adopting an envelope conformation. The tetraoxide is destabilized by 7.0 kcal/mol relative to the reactant complex, and the transition state for its formation is 17.4 kcal/mol above the reactant complex, which, although accessible under the reaction conditions, is not expected to be competitive with the reaction generating the hydrotrioxide.
    The Journal of Organic Chemistry 12/2008; 74(1):96-101. · 4.56 Impact Factor
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    ABSTRACT: Hydrogen-bonded gas-phase molecular clusters of dihydrogen trioxide (HOOOH) have been investigated using DFT (B3LYP/6-311++G(3df,3pd)) and MP2/6-311++G(3df,3pd) methods. The binding energies, vibrational frequencies, and dipole moments for the various dimer, trimer, and tetramer structures, in which HOOOH acts as a proton donor as well as an acceptor, are reported. The stronger binding interaction in the HOOOH dimer, as compared to that in the analogous cyclic structure of the HOOH dimer, indicates that dihydrogen trioxide is a stronger acid than hydrogen peroxide. A new decomposition pathway for HOOOH was explored. Decomposition occurs via an eight-membered ring transition state for the intermolecular (slightly asynchronous) transfer of two protons between the HOOOH molecules, which form a cyclic dimer, to produce water and singlet oxygen (Delta (1)O 2). This autocatalytic decomposition appears to explain a relatively fast decomposition (Delta H a(298K) = 19.9 kcal/mol, B3LYP/6-311+G(d,p)) of HOOOH in nonpolar (inert) solvents, which might even compete with the water-assisted decomposition of this simplest of polyoxides (Delta H a(298K) = 18.8 kcal/mol for (H 2O) 2-assisted decomposition) in more polar solvents. The formation of relatively strongly hydrogen-bonded complexes between HOOOH and organic oxygen bases, HOOOH-B (B = acetone and dimethyl ether), strongly retards the decomposition in these bases as solvents, most likely by preventing such a proton transfer.
    The Journal of Physical Chemistry A 10/2008; 112(35):8129-35. · 2.77 Impact Factor
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    ABSTRACT: Binding of a small molecule to a macromolecular target reduces its conformational freedom, resulting in a negative entropy change that opposes the binding. The goal of this study is to estimate the configurational entropy change of two minor-groove-binding ligands, netropsin and distamycin, upon binding to the DNA duplex d(CGCGAAAAACGCG).d(CGCGTTTTTCGCG). Configurational entropy upper bounds based on 10-ns molecular dynamics simulations of netropsin and distamycin in solution and in complex with DNA in solution were estimated using the covariance matrix of atom-positional fluctuations. The results suggest that netropsin and distamycin lose a significant amount of configurational entropy upon binding to the DNA minor groove. The estimated changes in configurational entropy for netropsin and distamycin are -127 J K(-1) mol(-1) and -104 J K(-1) mol(-1), respectively. Estimates of the configurational entropy contributions of parts of the ligands are presented, showing that the loss of configurational entropy is comparatively more pronounced for the flexible tails than for the relatively rigid central body.
    Biophysical Journal 09/2006; 91(4):1460-70. · 3.67 Impact Factor
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    ABSTRACT: Molecular dynamics simulations have been performed on netropsin in two different charge states and on distamycin binding to the minor groove of the DNA duplex d(CGCGAAAAACGCG).d(CGCGTTTTTCGCG). The relative free energy of binding of the two non-covalently interacting ligands was calculated using the thermodynamic integration method and reflects the experimental result. From 2 ns simulations of the ligands free in solution and when bound to DNA, the mobility and the hydrogen-bonding patterns of the ligands were studied, as well as their hydration. It is shown that even though distamycin is less hydrated than netropsin, the loss of ligand-solvent interactions is very similar for both ligands. The relative mobilities of the ligands in their bound and free forms indicate a larger entropic penalty for distamycin when binding to the minor groove compared with netropsin, partially explaining the lower binding affinity of the distamycin molecule. The detailed structural and energetic insights obtained from the molecular dynamics simulations allow for a better understanding of the factors determining ligand-DNA binding.
    Nucleic Acids Research 02/2005; 33(2):725-33. · 8.28 Impact Factor
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    ABSTRACT: Low-temperature (-78 degrees C) ozonation of 1,2-diphenylhydrazine in various oxygen bases as solvents (acetone-d(6), methyl acetate, tert-butyl methyl ether) produced hydrogen trioxide (HOOOH), 1,2-diphenyldiazene, 1,2-diphenyldiazene-N-oxide, and hydrogen peroxide. Ozonation of 1,2-dimethylhydrazine produced besides HOOOH, 1,2-dimethyldiazene, 1,2-dimethyldiazene-N-oxide and hydrogen peroxide, also formic acid and nitromethane. Kinetic and activation parameters for the decomposition of the HOOOH produced in this way, and identified by (1)H, (2)H, and (17)O NMR spectroscopy, are in agreement with our previous proposal that water participates in this reaction as a bifunctional catalyst in a polar decomposition process to produce water and singlet oxygen (O(2), (1)delta(g)). The possibility that hydrogen peroxide is, besides water, also involved in the decomposition of hydrogen trioxide is also considered. The half-life of HOOOH at room temperature (20 degrees C) is 16 +/- 1 min in all solvents investigated. Using a variety of DFT methods (restricted, broken-symmetry unrestricted, self-interaction corrected) in connection with the B3LYP functional, a stepwise mechanism involving the hydrotrioxyl (HOOO(*)) radical is proposed for the ozonation of hydrazines (RNHNHR, R = H, Ph, Me) that involves the abstraction of the N-hydrogen atom by ozone to form a radical pair, RNNHR(*) (*)OOOH. The hydrotrioxyl radical can then either abstract the remaining N(H) hydrogen atom from the RNNHR(*) radical to form the corresponding diazene (RN=NR), or recombines with RNNHR(*) in a solvent cage to form the hydrotrioxide, RN(OOOH)NHR. The decomposition of these very labile hydrotrioxides involves the homolytic scission of the RO-OOH bond with subsequent "in cage" formation of the diazene-N-oxide and hydrogen peroxide. Although 1,2-diphenyldiazene is unreactive toward ozone under conditions investigated, 1,2-dimethyldiazene reacts with relative ease to yield 1,2-dimethyldiazene-N-oxide and singlet oxygen (O(2), (1)delta(g)). The subsequent reaction sequence between these two components to yield nitromethane as the final product is discussed. The formation of formic acid and nitromethane in the ozonolysis of 1,2-dimethylhydrazine is explained as being due to the abstraction of a methyl H atom of the CH(3)NNHCH(3)(*) radical by HOOO(*) in the solvent cage. The possible mechanism of the reaction of the initially formed formaldehyde methylhydrazone (and HOOOH) with ozone/oxygen mixtures to produce formic acid and nitromethane is also discussed.
    Journal of the American Chemical Society 10/2003; 125(38):11553-64. · 10.68 Impact Factor
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    ABSTRACT: The HOOO(-) anion (1) can adopt a triplet state (T-1) or a singlet state (S-1), where the former is 9.8 kcal/mol (DeltaH(298) = 10.3 kcal/mol) more stable than the latter. S-1 possesses a strong O-OOH bond with some double bond character and a weakly covalent OO-OH bond (1.80 A) according to CCSD(T)/6-311++G(3df,3pd) calculations (the longest O-O bond ever found for a peroxide). In aqueous solution, S-1 adopts a geometry closely related to that of HOOOH (OO(O), 1.388 A; (O)OO(H), 1.509 A; tau(OOOH), 78.3 degrees ), justifying that S-1 is considered the anion of HOOOH. Dissociation into HO anion and O(2)((1)Delta(g)) requires 15.4 (DeltaH(298) = 14.3; DeltaG(298) = 8.9) kcal/mol. Structure T-1 corresponds to a van der Waals complex between HO anion and O(2)((3)Sigma(g)(-)) having a binding energy of 2.7 (DeltaH(298) = 2.1) kcal/mol. Modes of generating S-1 in aqueous solution are discussed, and it is shown that S-1 represents an important intermediate in ozonation reactions.
    Journal of the American Chemical Society 08/2002; 124(28):8462-70. · 10.68 Impact Factor
  • Journal of The American Chemical Society - J AM CHEM SOC. 04/2002; 113(13).
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    ABSTRACT: Low-temperature ozonation of cumene (1a) in acetone, methyl acetate, and tert-butyl methyl ether at -70 degrees C produced the corresponding hydrotrioxide, C(6)H(5)C(CH(3))(2)OOOH (2a), along with hydrogen trioxide, HOOOH. Ozonation of triphenylmethane (1b), however, produced only triphenylmethyl hydrotrioxide, (C(6)H(5))(3)COOOH (2b). These observations, together with the previously reported experimental evidence, seem to support the "radical" mechanism for the first step of the ozonation of the C-H bonds in hydrocarbons, i.e., the formation of the caged radical pair (R(**)OOOH), which allows both (a) collapse of the radical pair to ROOOH and (b) the abstraction of the hydrogen atom from alkyl radical R(*) by HOOO(*) to form HOOOH. The B3LYP/6-311++G(d,p) (ZPE) calculations revealed that HOOO radicals are considerably stabilized by forming intermolecularly hydrogen-bonded complexes with acetone (BE = 8.55 kcal/mol) and dimethyl ether (7.04 kcal/mol). This type of interaction appears to be crucial for the relatively fast reactions (and the formation of the polyoxides in relatively high yields) in these solvents, as compared to the ozonations run in nonbasic solvents. However, HOOO radicals appear to be not stable enough to abstract hydrogen atoms outside the solvent cage, as indicated by the absence of HOOOH among the products in the ozonolysis of triphenylmethane. The decomposition of alkyl hydrotrioxides 2a and 2b involves a homolytic cleavage of the RO-OOH bond with subsequent "in cage" reactions of the corresponding radicals, while the decomposition of HOOOH is most likely predominantly a "pericyclic" process involving one or more molecules of water acting as a bifunctional catalyst to produce water and singlet oxygen (Delta(1)O(2)).
    Journal of the American Chemical Society 02/2002; 124(3):404-9. · 10.68 Impact Factor
  • E Erzen, J Koller, B Plesnicar
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    ABSTRACT: The oxidation of thianthrene 5-oxide, i.e., a mechanistic probe for the assessment of the electronic character of various oxidants, with peroxybenzoic acids in various oxygen bases as solvents was investigated. The nucleophilicity (X(SO)) of peroxy acids was increasing with increasing basicity of the oxygen base. A good linear correlation was observed by plotting X(SO) values vs either the Kamlet-Taft beta values or the OOH (1)H NMR chemical shifts of m-chloroperoxybenzoic acid (m-CPBA) in solvents of various basicity. These observations, together with the results of IR and (1)H NMR spectroscopic studies of peroxybenzoic acids, and DFT (B3LYP/6-311++G) studies of the intramolecular hydrogen bonding in peroxyformic, peroxyacetic, and m-CPBA, as well as the intermolecular hydrogen bonding in the complexes of the these peroxy acids with dimethyl ether as a model oxygen base, support the involvement of the peroxy acid-oxygen base complexes in the transition states of these reactions. The increased nucleophilicity (X(SO)) of peroxy acids in basic solvents is most likely due to the increased negative charge on the terminal "electrophilic" peroxycarboxylic oxygen atom (OH), and/or the increased LUMO and HOMO energies of the peroxy acid in the complexes, as compared to those parameters in the intramolecularly hydrogen-bonded form of peroxy acids, believed to be operative in inert solvents.
    The Journal of Organic Chemistry 08/2001; 66(15):5155-62. · 4.56 Impact Factor
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    ABSTRACT: Low-temperature ozonation of isopropyl alcohol (1a) and isopropyl methyl ether (1b) in [D6]acetone, methyl acetate, and tert-butyl methyl ether at -78 degrees C produced the corresponding hydrotrioxides, Me2C(OH)(OOOH) (2a) and Me2C(OMe)(OOOH) (2b), along with hydrogen trioxide (HOOOH). All the polyoxides investigated were characterized for the first time by 17O NMR spectroscopy of highly 17O-enriched species. The assignment was confirmed by GIAO/MP2/6-31++G* calculations of 17O NMR chemical shifts, which were in excellent agreement with the experimental values. Ab initio density functional (DFT) calculations at the B3LYP/ 6-31G*+ZPE level have clarified the transition structure (TS1, deltaE = 7.4 and 10.6 kcalmol(-1), relative to isolated reactants and the complex 1a-ozone, respectively) for the ozonation of 1a: this, together with the formation of HOOOH and some other products, indicates the involvement of radical intermediates (R*, *OOOH) in the reaction. The activation parameters for the decomposition of the hydrotrioxides 2a and 2b (Ea, = 23.5+/-1.5 kcalmol(-1), logA = 16+/-1.8) were typical for a homolytic process in which cleavage of the ROOOH molecule occurs to yield a radical pair [RO* *OOH] and represents the lowest available energy pathway. Significantly the lower activation parameters for the decomposition of HOOOH (Ea = 16.5+/-2.2 kcalmol(-1), logA = 9.5+/-2.0) relative to those expected for the homolytic scission of the HO-OOH bond [bond dissociation energy (BDE) = 29.8 kcalmol(-1), CCSD(T)/6-311++G**] are in accord with the proposal that water behaves as a bifunctional catalyst and therefore participates in a "polar" (non-radical) decomposition process of this polyoxide. A relatively large acceleration of the decomposition of the hydrotrioxide 2a in [D6]acetone, accompanied by a significant lowering of the activation energies, was observed in the presence of a large excess of water. Thus intramolecular 1,3-proton transfer probably also involves the participation of water and is similar to the mechanism proposed for the decomposition of HOOOH. This hypothesis was further substantiated by the B3LYP/6-31++ G*+ZPE calculations for the participation of water in the decomposition of CH3OOOH, which revealed two stationary points on the potential energy surface corresponding to a CH3OOOH-HOH complex and a six-membered cyclic transition state TS2. The energy barriers were comparable with those calculated for HOOOH, that is, deltaE = 15.0 and 21.5 kcalmol(-1) relative to isolated reactants and the CH3OOOH-HOH complex, respectively.
    Chemistry 04/2000; 6(5):809-19. · 5.93 Impact Factor

Publication Stats

67 Citations
64.57 Total Impact Points

Institutions

  • 2010
    • University of Strathclyde
      • Department of Pure and Applied Chemistry
      Glasgow, SCT, United Kingdom
  • 2000–2008
    • University of Ljubljana
      • • Faculty of Chemistry and Chemical Technology
      • • Department of Chemistry and Biochemistry
      Ljubljana, Ljubljana, Slovenia