Publications by authors named "Tatyana E Shubina"

22 Publications

  • Page 1 of 1

Redox behavior and biological properties of ferrocene bearing porphyrins.

J Inorg Biochem 2017 06 21;171:76-89. Epub 2017 Mar 21.

Department of Chemistry & Pharmacy, Friedrich-Alexander University Erlangen-Nuremberg, Egerlandstraße 1, D-91058 Erlangen, Germany. Electronic address:

In order to improve antimicrobial effects of previously studied meso-tetrakis(4-ferrocenylphenyl)porphyrin 1, we have modified its structure by replacing two trans-positioned ferrocenylphenyl moieties with methoxy methylene substituted tert-butylphenyl moieties. Newly synthesized 5,15-bis-(ferrocenyl)-10,20-bis-(tert-butyl)-10,10,20,20-tetrakis-(methoxy-methylene)-5,10,15,20-tetraphenylporphyrin 4 was chemically characterized in detail (by NMR, UV/Vis, IR, MALDI-TOF and ESI MS spectrometry, cyclic voltammetry, prediction of the relative lipophilicity as well as computational methods) and its biological effects were studied in terms of its antibacterial and antifungal activity (both with and without photoactivation), cytotoxicity, hemolysis and DNA cleavage. New ferrocene bearing porphyrin 4 has demonstrated a broader antimicrobial spectrum and modified effects on eukaryotic cells compared to 1. This was discussed in terms of its i) increased lipophilicity, while exhibiting lower toxicity, and ii) the redox potential of a two-electron process that is shifted to lower values, in comparison to ferrocene, thus, entering the physiologically available range and being activated towards redox interactions with biomolecules.
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http://dx.doi.org/10.1016/j.jinorgbio.2017.03.002DOI Listing
June 2017

A Stable Crystalline Triarylphosphine Oxide Radical Anion.

Angew Chem Int Ed Engl 2016 10 27;55(43):13597-13601. Epub 2016 Sep 27.

Chair of Organic Chemistry I, Department of Chemistry and Pharmacy, University of Erlangen-Nürnberg, Henkestrasse 42, 91054, Erlangen, Germany.

Triarylphosphine oxides (Ar P=O) are being intensely studied as electron-accepting (n-type) materials. Despite the widespread application of these compounds as electron conductors, experimental data regarding the structural and electronic properties of their negatively charged states remain scarce owing to their propensity for follow-up chemistry. Herein, a carefully designed triarylphosphine oxide scaffold is disclosed that comprises sterically demanding spirofluorenyl moieties to shield the central phosphoryl (P=O) moiety. This compound undergoes chemical one-electron reduction to afford an exceptionally stable radical anion, which was isolated and characterized by X-ray crystallography for the very first time. The experimental data, corroborated by computational studies, shall allow for the construction of phosphine oxide materials with enhanced stability.
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http://dx.doi.org/10.1002/anie.201605963DOI Listing
October 2016

Does perthionitrite (SSNO(-)) account for sustained bioactivity of NO? A (bio)chemical characterization.

Inorg Chem 2015 Oct 26;54(19):9367-80. Epub 2015 Jun 26.

Department of Chemistry and Pharmacy, Friedrich-Alexander University of Erlangen-Nuremberg , Egerlandstrasse 1, 91058 Erlangen, Germany.

Hydrogen sulfide (H2S) and nitric oxide (NO) are important signaling molecules that regulate several physiological functions. Understanding the chemistry behind their interplay is important for explaining these functions. The reaction of H2S with S-nitrosothiols to form the smallest S-nitrosothiol, thionitrous acid (HSNO), is one example of physiologically relevant cross-talk between H2S and nitrogen species. Perthionitrite (SSNO(-)) has recently been considered as an important biological source of NO that is far more stable and longer living than HSNO. In order to experimentally address this issue here, we prepared SSNO(-) by two different approaches, which lead to two distinct species: SSNO(-) and dithionitric acid [HON(S)S/HSN(O)S]. (H)S2NO species and their reactivity were studied by (15)N NMR, IR, electron paramagnetic resonance and high-resolution electrospray ionization time-of-flight mass spectrometry, as well as by X-ray structure analysis and cyclic voltammetry. The obtained results pointed toward the inherent instability of SSNO(-) in water solutions. SSNO(-) decomposed readily in the presence of light, water, or acid, with concomitant formation of elemental sulfur and HNO. Furthermore, SSNO(-) reacted with H2S to generate HSNO. Computational studies on (H)SSNO provided additional explanations for its instability. Thus, on the basis of our data, it seems to be less probable that SSNO(-) can serve as a signaling molecule and biological source of NO. SSNO(-) salts could, however, be used as fast generators of HNO in water solutions.
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http://dx.doi.org/10.1021/acs.inorgchem.5b00831DOI Listing
October 2015

Nitrogen Oxide Atom-Transfer Redox Chemistry; Mechanism of NO(g) to Nitrite Conversion Utilizing μ-oxo Heme-Fe(III)-O-Cu(II)(L) Constructs.

J Am Chem Soc 2015 May 14;137(20):6602-15. Epub 2015 May 14.

†Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21211, United States.

While nitric oxide (NO, nitrogen monoxide) is a critically important signaling agent, its cellular concentrations must be tightly controlled, generally through its oxidative conversion to nitrite (NO2(-)) where it is held in reserve to be reconverted as needed. In part, this reaction is mediated by the binuclear heme a3/CuB active site of cytochrome c oxidase. In this report, the oxidation of NO(g) to nitrite is shown to occur efficiently in new synthetic μ-oxo heme-Fe(III)-O-Cu(II)(L) constructs (L being a tridentate or tetradentate pyridyl/alkylamino ligand), and spectroscopic and kinetic investigations provide detailed mechanistic insights. Two new X-ray structures of μ-oxo complexes have been determined and compared to literature analogs. All μ-oxo complexes react with 2 mol equiv NO(g) to give 1:1 mixtures of discrete [(L)Cu(II)(NO2(-))](+) plus ferrous heme-nitrosyl compounds; when the first NO(g) equiv reduces the heme center and itself is oxidized to nitrite, the second equiv of NO(g) traps the ferrous heme thus formed. For one μ-oxo heme-Fe(III)-O-Cu(II)(L) compound, the reaction with NO(g) reveals an intermediate species ("intermediate"), formally a bis-NO adduct, [(NO)(porphyrinate)Fe(II)-(NO2(-))-Cu(II)(L)](+) (λmax = 433 nm), confirmed by cryo-spray ionization mass spectrometry and EPR spectroscopy, along with the observation that cooling a 1:1 mixture of [(L)Cu(II)(NO2(-))](+) and heme-Fe(II)(NO) to -125 °C leads to association and generation of the key 433 nm UV-vis feature. Kinetic-thermodynamic parameters obtained from low-temperature stopped-flow measurements are in excellent agreement with DFT calculations carried out which describe the sequential addition of NO(g) to the μ-oxo complex.
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http://dx.doi.org/10.1021/jacs.5b02174DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4469181PMC
May 2015

Synthesis and properties of arylvinylidene-bridged triphenylamines.

J Org Chem 2015 Feb 3;80(4):2418-24. Epub 2015 Feb 3.

Lehrstuhl für Organische Chemie I, Department Chemie und Pharmazie, Friedrich-Alexander-Universität Erlangen-Nürnberg , Henkestrasse 42, D-91054 Erlangen, Germany.

A series of arylvinylidene-bridged triphenylamines were efficiently synthesized through the thionation/Barton-Kellogg olefination sequence from their corresponding carbonyl precursors. The electrochemical investigations identified these highly distorted scaffolds as fairly strong electron donors capable of several reversible oxidation steps with the first oxidation occurring at a potential comparable to that of ferrocene for the n-hexyl-substituted diphenylvinylidene-bridged compound.
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http://dx.doi.org/10.1021/jo502605eDOI Listing
February 2015

Multiply bonded metal(II) acetate (rhodium, ruthenium, and molybdenum) complexes with the trans-1,2-bis(N-methylimidazol-2-yl)ethylene ligand.

Inorg Chem 2014 Dec 13;53(23):12305-14. Epub 2014 Nov 13.

Inorganic Chemistry and Interdisciplinary Center for Molecular Materials, Department of Chemistry and Pharmacy, Friedrich-Alexander-Universität Erlangen-Nürnberg , Egerlandstraße 1, 91058 Erlangen, Germany.

The synthesis and structural characterization of new coordination polymers with the N,N-donor ligand trans-1,2-bis(N-methylimidazol-2-yl)ethylene (trans-bie) are reported. It was found that the acetate-bridged paddlewheel metal(II) complexes [M2(O2CCH3)4(trans-bie)]n with M = Rh, Ru, Mo, and Cr are linked by the trans-bie ligand to give a one-dimensional alternating chain. The metal-metal multiple bonds were analyzed with density functional theory and CASSCF/CASPT2 calculations (bond orders: Rh, 0.8; Ru, 1.7; Mo, 3.3).
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http://dx.doi.org/10.1021/ic501435aDOI Listing
December 2014

Reverse spin-crossover and high-pressure kinetics of the heme iron center relevant for the operation of heme proteins under deep-sea conditions.

Angew Chem Int Ed Engl 2014 Oct 11;53(43):11452-7. Epub 2014 Sep 11.

Lehrstuhl für Bioanorganische Chemie, Department Chemie und Pharmazie, Universität Erlangen-Nürnberg (Germany).

By design of a heme model complex with a binding pocket of appropriate size and flexibility, and by elucidating its kinetics and thermodynamics under elevated pressures, some of the pressure effects are demonstrated relevant for operation of heme-proteins under deep-sea conditions. Opposite from classical paradigms of the spin-crossover and reaction kinetics, a pressure increase can cause deceleration of the small-molecule binding to the vacant coordination site of the heme-center in a confined space and stabilize a high-spin state of its Fe center. This reverse high-pressure behavior can be achieved only if the volume changes related to the conformational transformation of the cavity can offset the volume changes caused by the substrate binding. It is speculated that based on these criteria nature could make a selection of structures of heme pockets that assist in reducing metabolic activity and enzymatic side reactions under extreme pressure conditions.
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http://dx.doi.org/10.1002/anie.201406954DOI Listing
October 2014

Integrating metalloporphycenes into p-type NiO-based dye-sensitized solar cells.

Chem Commun (Camb) 2014 Oct;50(77):11339-42

Friedrich-Alexander-University Erlangen-Nuremberg, Department of Chemistry and Pharmacy & Interdisciplinary Center for Molecular Materials, Egerlandstr. 3, 91058 Erlangen, Germany.

In the current work, we have explored a novel synthetic route towards metalated porphycenes and their use in p-type NiO-based dye-sensitized solar cells. Particular emphasis is placed on the influence that the relative positioning of the anchoring group exerts on the DSSC performance.
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http://dx.doi.org/10.1039/c4cc04523hDOI Listing
October 2014

Fullerene van der Waals oligomers as electron traps.

J Am Chem Soc 2014 Aug 24;136(31):10890-3. Epub 2014 Jul 24.

Computer-Chemie-Centrum and Interdisciplinary Center for Molecular Materials, Department Chemie und Pharmazie, Friedrich-Alexander-Universität Erlangen-Nürnberg , 91052 Erlangen, Germany.

Density functional theory calculations indicate that van der Waals fullerene dimers and larger oligomers can form interstitial electron traps in which the electrons are even more strongly bound than in isolated fullerene radical anions. The fullerenes behave like "super atoms", and the interstitial electron traps represent one-electron intermolecular σ-bonds. Spectroelectrochemical measurements on a bis-fullerene-substituted peptide provide experimental support. The proposed deep electron traps are relevant for all organic electronics applications in which non-covalently linked fullerenes in van der Waals contact with one another serve as n-type semiconductors.
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http://dx.doi.org/10.1021/ja505949mDOI Listing
August 2014

Optically active tetra-tert-butyl-P(5)-deltacyclene epimers: preparation, spectroscopy, dynamic equilibriums, H/D exchange, and transition-metal complex chemistry.

Chemistry 2014 May 27;20(19):5708-20. Epub 2014 Mar 27.

Department Chemie and Pharmazie, Universität Erlangen-Nürnberg, Egerlandstrsee 1, 91058 Erlangen (Germany), Fax: (+49) 9131-852-7367.

On the basis of isolated diastereomeric triorganylstannyl-P5 -deltacyclenes 7' and 7'', almost pure enantiomers of their destannylation products 8' and 8'' are now available. These stereochemically inert cage chiral species contain a configurationally labile P1H1 group that defines two epimers 8 a and 8 b of each of the enantiomers, which are connected by a rapid equilibrium. Mirror-symmetric circular dichroism (CD) spectra of the enantiomeric cages are compatible with the identification of epimers. A simulation of the CD spectrum of the major epimer 8'a relates the cage chirality of the system to the observed chiroptical effects. Both cage epimers and two of the phosphorus cage atoms are active as ligands with respect to [M(CO)5 ] fragments of Cr, Mo, and W. Four almost isoenergetic regio- and stereoisomers of the resulting mononuclear complexes are formed for these metals, but only one of the isomers per metal crystallized in the case of the racemic series of the complexes. The enantiopure versions of cages and cage complexes, however, did not crystallize at all, a well-known phenomenon for chiral compounds. CD spectra of the optically active complex isomer mixtures are close to identical with the CD spectra of the related free cages and point again to the chiral cages as the dominant source of the CD effects of the complexes. [(Benzene)RuCl2 ] complexes of the cage ligand 8 behave totally differently. Only a single species 12=[(benzene)RuCl2 ⋅8 b] is formed in almost quantitative yield and the minor epimer 8 b plays the role of the ligand exclusively. The reaction works as well for the separated enantiomeric cage versions to yield the highly enriched enantiomers 12' and 12'' separately. An efficient kinetic resolution process was identified as the main reason for this finding. It is based on a high stereo- and regiochemical flexibility of the PC cage ligand that is capable of adjusting to the specific requirements of a suitable transition-metal complex fragment. Such ligand flexibility is regularly observed in metalloenzymes, but is a very rare case in classical and organometallic complex chemistry.
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http://dx.doi.org/10.1002/chem.201303821DOI Listing
May 2014

Electrophilic monoiodination of terminal alkenes.

Org Biomol Chem 2013 May 21;11(17):2891-7. Epub 2013 Mar 21.

University of Minnesota, Natural Resources Research Institute, 5013 Miller Trunk Highway, Duluth, MN 55811, USA.

An excess of elemental iodine in N,N-dimethylacetamide enables effective 3/iodanylium-de-hydronation of terminal alkenes with 3-iodopropene derivatives and hydrogen iodide formation within minutes at room temperature. The optimal molar ratio of iodine to substrate was decreased to 1 : 1 when hydrogen iodide formed was oxidized on a platinum anode. The electrolytic oxidation recovers iodine as a reagent and diminishes the hydrogen iodide inhibitory action to accomplish the monoiodination. The proposed reaction mechanism is based on kinetic measurements and quantum mechanics calculations.
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http://dx.doi.org/10.1039/c3ob27348bDOI Listing
May 2013

Synthesis and evaluation of new guanidine-thiourea organocatalyst for the nitro-Michael reaction: Theoretical studies on mechanism and enantioselectivity.

Beilstein J Org Chem 2012 7;8:1485-98. Epub 2012 Sep 7.

Computer Chemistry Center and Interdisciplinary Center for Molecular Materials, University of Erlangen-Nuremberg, Nägelsbachstr. 25, 91052 Erlangen, Germany.

A new guanidine-thiourea organocatalyst has been developed and applied as bifunctional organocatalyst in the Michael addition reaction of diethyl malonate to trans-β-nitrostyrene. Extensive DFT calculations, including solvent effects and dispersion corrections, as well as ab initio calculations provide a plausible description of the reaction mechanism.
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http://dx.doi.org/10.3762/bjoc.8.168DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3458773PMC
October 2012

Coordination and metalation bifunctionality of Cu with 5,10,15,20-tetra(4-pyridyl)porphyrin: toward a mixed-valence two-dimensional coordination network.

J Am Chem Soc 2012 Apr 28;134(14):6401-8. Epub 2012 Mar 28.

Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China.

We investigated the coordination self-assembly and metalation reaction of Cu with 5,10,15,20-tetra(4-pyridyl)porphyrin (2HTPyP) on a Au(111) surface by means of scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory calculations. 2HTPyP was found to interact with Cu through both the peripheral pyridyl groups and the porphyrin core. Pairs of pyridyl groups from neighboring molecules coordinate Cu(0) atoms, which leads to the formation of a supramolecular metal-organic coordination network. The network formation occurs at room temperature; annealing at 450 K enhances the process. The interaction of Cu with the porphyrin core is more complex. At room temperature, formation of an initial complex Cu(0)-2HTPyP is observed. Annealing at 450 K activates an intramolecular redox reaction, by which the coordinated Cu(0) is oxidized to Cu(II) and the complex Cu(II)TPyP is formed. The coordination network consists then of Cu(II) complexes linked by Cu(0) atoms; that is, it represents a mixed-valence two-dimensional coordination network consisting of an ordered array of Cu(II) and Cu(0) centers. Above 520 K, the network degrades and the Cu atoms in the linking positions diffuse into the substrate, while the Cu(II)TPyP complexes form a close-packed structure that is stabilized by weak intermolecular interactions. Density functional theory investigations show that the reaction with Cu(0) proceeds via formation of an initial complex between metal atom and porphyrin followed by formation of Cu(II) porphyrin within the course of the reaction. The activation barrier of the rate limiting step was found to be 24-37 kcal mol(-1) depending on the method used. In addition, linear coordination of a Cu atom by two CuTPyP molecules is favorable according to gas-phase calculations.
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http://dx.doi.org/10.1021/ja300593wDOI Listing
April 2012

Influence of electron doping on the hydrogenation of fullerene C60 : a theoretical investigation.

Chemphyschem 2011 Oct 31;12(14):2581-9. Epub 2011 Aug 31.

Computer-Chemie-Centrum and Interdisciplinary Center for Molecular Materials, Fachbereich Chemie und Pharmazie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany.

The influence of electron attachment on the stability of the mono- and dihydrogenated buckminsterfullerene C(60) was studied using density functional theory and semiempirical molecular orbital techniques. We have also assessed the reliability of computationally accessible methods that are important for investigating the reactivity of graphenic species and surfaces in general. The B3LYP and M06L functionals with the 6-311+G(d,p) basis set and MNDO/c are found to be the best methods for describing the electron affinities of C(60) and C(60)H(2) . It is shown that simple frontier molecular orbital analyses at both the AM1 and B3LYP/6-31G(d) levels are useful for predicting the most favourable position of protonation of C(60)H(-) , that is, formation of the kinetically controlled product 1,9-dihydro[60]fullerene, which is also the thermodynamically controlled product, in agreement with experimental and previous theoretical studies. We have shown that reduction of exo- and endo-C(60)H makes them more stable in contrast to the reduction of the exo,exo-1,9-C(60)H(2) , reduced forms of which decompose more readily, in agreement with experimental electrochemical studies. However, most other dihydro[60]fullerenes are stabilized by reduction and the regioselectivity of addition is predicted to decrease as the less stable isomers are stabilized more by the addition of electrons than the two most stable ones (1,9 and 1,7).
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http://dx.doi.org/10.1002/cphc.201100529DOI Listing
October 2011

Conformationally restricted GABA analogs: from rigid carbocycles to cage hydrocarbons.

Future Med Chem 2011 Feb;3(2):223-41

National Technical University of Ukraine Kiev Polytechnic Institute, Department of Organic Chemistry, Kiev, Ukraine.

GABA was discovered to play an important role as the major inhibitory neurotransmitter in the adult mammalian CNS 60 years ago. The conformational flexibility of GABA is important for its biological function, as it has been found to bind to different receptors with different conformations. In an effort to increase the lipophilicity and to reduce conformational flexibility of GABA itself, a polycyclic or cage hydrocarbon framework can be introduced into the 3D structure of GABA in order to better control the binding. This article explores the available synthetic methods, properties and activity of carbocyclic (cyclopropanes, cyclobutanes and cyclohexanes) and cage (adamantane and others) hydrocarbons - analogs of GABA with conformationally rigid carbon skeletons.
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http://dx.doi.org/10.4155/fmc.10.287DOI Listing
February 2011

Water exchange on manganese(III) porphyrins. Mechanistic insights relevant for oxygen evolving complex and superoxide dismutation catalysis.

J Am Chem Soc 2010 Jun;132(21):7282-4

Friedrich-Alexander-Universität Erlangen-Nürnberg, Department Chemie und Pharmazie, Egerlandstr. 1, 91058 Erlangen, Germany.

In this work the rate constants (k(ex)) and the activation parameters (DeltaH(double dagger), DeltaS(double dagger), and DeltaV(double dagger)) for the water exchange process on Mn(III) centers have experimentally been determined using temperature and pressure dependent (17)O NMR techniques. For the investigations the Mn(III) porphyrin complexes [Mn(III)(TPPS)S(2)](n-) and [Mn(III)(TMpyP)S(2)](n+) (S = H(2)O and/or OH(-)) have been selected due to their high solution stability in a wide pH range, enabling the measurements of water exchange in the case of both diaqua and aqua-hydroxo complexes. We have experimentally demonstrated that the water exchange on Mn(III) porphyrins is a fast process (k(ex) approximately = 10(7) s(-1)) of an I(d) to I mechanism, strongly influenced by a Jahn-Teller effect and as such almost independent of a porphyrin charge and a trans ligand. This is also supported by our DFT calculations which show only a slight difference in an average Mn(III)-OH(2) bond found for a positively charged model porphyrin with protonated pyridine groups (2.446 A) and for a simple model without any substituents on the porphyrin ring (2.437 A). The calculated effective charge on the Mn center, which is significantly lower than its formal +3 charge (ca. +1.5 for diaqua; +1.4 for aqua-hydroxo), also contributes to its substitution lability. The herein presented results are discussed in connection to a possible fast exchanging substrate binding site in photosystem II and corresponding inorganic model complexes, as well as in the context of a possible inner-sphere catalytic pathway for superoxide dismutation on Mn centers.
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http://dx.doi.org/10.1021/ja1014585DOI Listing
June 2010

Computational and QSAR study of the alkylnaphthyl ketones adsorption on silver-ion stationary phase.

J Mol Model 2010 Mar 9;16(3):513-22. Epub 2009 Aug 9.

Department of Organic Chemistry, Kiev Polytechnic Institute, 03056, Kiev, Ukraine.

The chromatographic behaviour of alpha- and beta- alkylnaphthyl ketones at different temperatures on the silver-loaded stationary phase is described based on the QSRR model. Complexation via an oxygen atom is favoured over the interaction through the aromatic fragment. The QSRR model and DFT/MP2 studies suggest that retention times of alkylnaphthyl ketones on silver-containing stationary phases are determined primarily by the dipole moment, length of the alkyl substituent and concentration of modifier in the mobile phase.
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http://dx.doi.org/10.1007/s00894-009-0568-0DOI Listing
March 2010

Evidence for an enol mechanism in a highly enantioselective Mannich-type reaction catalyzed by primary amine-thiourea.

Angew Chem Int Ed Engl 2008 ;47(35):6624-8

Department of Chemistry and Pharmacy, University of Erlangen-Nürnberg, Henkestrasse 42, 91054 Erlangen, Germany.

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http://dx.doi.org/10.1002/anie.200800849DOI Listing
September 2008

Principle and mechanism of direct porphyrin metalation: joint experimental and theoretical investigation.

J Am Chem Soc 2007 Aug 11;129(30):9476-83. Epub 2007 Jul 11.

Computer-Chemie-Centrum, Universität Erlangen-Nürnberg, Nägelsbachstrasse 25, Erlangen, Germany.

The direct metalation of tetraphenylporphyrin with bare metal atoms (Co and Zn) was studied with X-ray photoelectron spectroscopy, scanning tunneling microscopy, and temperature-programmed reaction measurements on ordered monolayer films of the molecules adsorbed on a Ag(111) surface. The mechanism of this novel type of surface reaction was investigated using density functional theory (DFT) calculations for the related gas-phase reactions of the unsubstituted porphyrin with the metals Fe, Co, Ni, Cu, and Zn. The reaction starts with the formation of an initial complex, in which the metal atom is coordinated by the intact unreduced porphyrin. This complex resembles the sitting-atop complex proposed for porphyrin metalation with metal ions in solution. In two subsequent steps, the pyrrolic hydrogen atoms are transferred to the metal atom, forming H2, which is eventually released. The activation barriers of the H-transfer steps vary for the different metal atoms. DFT calculations suggest that metalations with Fe, Co, and Ni show two-state reactivity, while those with Cu and Zn proceed on a single potential energy surface. For metalation with Zn, we calculated a barrier of the first hydrogen transfer step of 32.6 kcal mol(-1), in good agreement with the overall experimental activation energy of 31 kcal mol(-1).
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http://dx.doi.org/10.1021/ja072360tDOI Listing
August 2007

Nitrite impurities are responsible for the reaction observed between vitamin B12 and nitric oxide in acidic aqueous solution.

Inorg Chem 2006 Sep;45(19):7869-76

Institute for Inorganic Chemistry, University of Erlangen-Nürnberg, Egerlandstrasse 1, 91058 Erlangen, Germany.

The reaction between aquacobalamin, Cbl(H2O), and NO was studied at low pH. As previously reported, the final product of the reaction is the same as that obtained in the reaction of NO and reduced Cbl(H2O), viz. Cbl(NO-). Nevertheless, this reductive nitrosylation is preceded by a faster reaction (accompanied by small absorbance changes) that depends on the HNO2 concentration but not on the NO concentration. Kinetic and UV-vis spectroscopic data show that Cbl(NO2-) is generated during this reaction. Spectroscopic data show that the dimethylbenzimidazole group trans to the NO2- ligand is protonated and partially dechelated at pH 1, by which a reaction with NO is induced. DFT calculations were performed to compare the ability of NO and NO2- to bind to cobalamin and their influence on the stability of the dimethylbenzimidazole group. The reductive nitrosylation reaction shows a quadratic dependence on the HNO2 concentration and an inverse dependence on the NO concentration. It also strongly depends on pH and is no longer observed at pH > 4. On the basis of earlier work performed on a series of Co(III) porphyrins, a mechanism is proposed that can quantitatively account for the HNO2 and NO dependencies. The reductive nitrosylation reaction is practically dominated by a back reaction, i.e., the reaction between Cbl(NO-) and HNO2, which accounts for the strange NO and HNO2 concentration dependencies observed.
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http://dx.doi.org/10.1021/ic061151rDOI Listing
September 2006

Oxidation of formic acid and carbon monoxide on gold electrodes studied by surface-enhanced Raman spectroscopy and DFT.

Chemphyschem 2005 Dec;6(12):2597-606

Schuit Institute of Catalysis, Laboratory of Inorganic Chemistry and Catalysis, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands.

The oxidation of formic acid and carbon monoxide was studied at a gold electrode by a combination of electrochemistry, in situ surface-enhanced Raman spectroscopy (SERS), differential electrochemical mass spectrometry, and first-principles DFT calculations. Comparison of the SERS results and the (field-dependent) DFT calculations strongly suggests that the relevant surface-bonded intermediate during oxidation of formic acid on gold is formate HCOO- ad*. Formate reacts to form carbon dioxide via two pathways: at low potentials, with a nearby water to produce carbon dioxide and a hydronium ion; at higher potentials, with surface-bonded hydroxyl (or oxide) to give carbon dioxide and water. In the former pathway, the rate-determining step is probably related to the reaction of surface-bonded formate with water, as measurements of the reaction order imply a surface almost completely saturated with adsorbate. The potential dependence of the rate of the low-potential pathway is presumably governed by the potential dependence of formate coverage. There is no evidence for CO formation on gold during oxidation of formic acid. The oxidation of carbon monoxide must involve the carboxyhydroxyl intermediate, but SERS measurements do not reveal this intermediate during CO oxidation, most likely because of its low surface coverage, as it is formed after the rate-determining step. Based on inconclusive spectroscopic evidence for the formation of surface-bonded OH at potentials substantially below the surface oxidation region, the question whether surface-bonded carbon monoxide reacts with surface hydroxyl or with water to form carboxyhydroxyl and carbon dioxide remains open. The SERS measurements show the existence of both atop and bridge-bonded CO on gold from two distinguishable low-frequency modes that agree very well with DFT calculations.
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http://dx.doi.org/10.1002/cphc.200500198DOI Listing
December 2005

H-coupled electron transfer in alkane C-h activations with halogen electrophiles.

J Am Chem Soc 2002 Sep;124(36):10718-27

Department of Organic Chemistry, Kiev Polytechnic Institute, 37 Pobeda Avenue, 03056 Kiev, Ukraine.

The mechanisms for the reactions of isobutane and adamantane with polyhalogen electrophiles (HHal(2)(+), Hal(3)(+), Hal(5)(+), and Hal(7)(+), Hal = Cl, Br, or I) were studied computationally at the MP2 and B3LYP levels of theory with the 6-31G (C, H, Cl, Br) and 3-21G (I) basis sets, as well as experimentally for adamantane halogenations in Br(2), Br(2)/HBr, and I(+)Cl(-)/CCl(4). The transition structures for the activation step display almost linear C...H...Hal interactions and are characterized by significant charge transfer to the electrophile; the hydrocarbon moieties resemble the respective radical cation structures. The regiospecificities for polar halogenations of the 3-degree C-H bonds of adamantane, the high experimental kinetic isotope effects (k(H)/k(D) = 3-4), the rate accelerations in the presence of Lewis and proton (HBr) acids, and the high kinetic orders for halogen (7.5 for Br(2)) can only be understood in terms of an H-coupled electron-transfer mechanism. The three centered-two electron (3c-2e) electrophilic mechanistic concept based on the attack of the electrophile on a C-H bond does not apply; electrophilic 3c-2e interactions dominate the C-H activations only with nonoxidizing electrophiles such as carbocations. This was shown by a comparative computational analysis of the electrophilic and H-coupled electron-transfer activation mechanisms for the isobutane reaction with an ambident electrophile, the allyl cation, at the above levels of theory.
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http://dx.doi.org/10.1021/ja0265512DOI Listing
September 2002