The interfacial coupling of a nanoscale oxide material to a metal surface creates a hybrid system... more The interfacial coupling of a nanoscale oxide material to a metal surface creates a hybrid system with novel and often unprecedented physical and chemical properties that are not shared by the individual components of the system. The dimensionality of the oxide phase adds a further parameter to a oxide-metal hybrid system, which may be used as a tunable model for the study of emergent phenomena of low-dimensional (low-D) materials. Low-D oxide nanostructures on well-defined metal surfaces can be fabricated with atomic-scale design control using bottom-up directed self-assembly and a surface science methodology. Here we discuss the elastic and electronic effects introduced by the oxide-metal interface and how they determine the novel structure concepts that are encountered in low-D oxide nanophases on metal surfaces. The systems of interest are the oxides of Mn, Co, and Ni, which in monoxide form share a common rock-salt structure in the bulk and antiferromagnetic ordering behaviour....
The development of robust and cheap photocatalyst systems for visible-light induced organic subst... more The development of robust and cheap photocatalyst systems for visible-light induced organic substrate transformations is a significant uprising research topic at the crossroads of green chemistry and modern synthetic methodology. Atom economy, efficiency and selectivity are key parameters for the future practical applicability of the specific processes catalyzed. In this context, we report a simple and sustainable oxygen-dependent route for oxidizing various aromatic and aliphatic aldehydes to the corresponding carboxylic acids at room temperature under visible light and sunlight irradiation mediated by cobalt phthalocyanine tetrasulfonic acid (CoPcS) supported on reduced graphene oxide (RGO). Remarkably, products are obtained with (81-100)% conversion and 100% selectivity.
The spectroscopic and photochromic properties of the dinuclear rhodium complex Rh2L10X4 (L = CH3 ... more The spectroscopic and photochromic properties of the dinuclear rhodium complex Rh2L10X4 (L = CH3 CN, X− = BF−4 ) have been studied in acetonitrile solution. A reversible wavelengthdependent photoredox disproportionation of the dark-equilibrated dirhodium(II) compound occurs upon irradiation with quantum yields of φ = 0.04 at 254 nm and φ = 0.60 at 436 nm, respectively. While the photolysis products show conspicuous aggregation phenomena at higher concentrations, a straightforward pseudo-bimolecular recombination of the metastable fragments following second-order kinetics was observed in 5 × 10−5 M solution with k = 0.18 l mol−1 s−1 at 295 K. Both spectroscopic and kinetic results are consistent with the heterolytic formation of mononuclear rhodium(I) and rhodium(III) acetonitrile complexes in the course of the photochemical reaction.
The new bis(bidentate) tetraphosphane cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphanyl)buta-1,3-... more The new bis(bidentate) tetraphosphane cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphanyl)buta-1,3-diene (dppbd) (7) was obtained by applying a photochemical synthetic protocol. The key step of the photochemical reaction consisted of an intramolecular [2+2] cycloaddition involving a CC double and triple bond of the Pt-dimer species of the formula [Pt 2 Cl 4 (dppa)(trans-dppen)] (2) {dppa = 1,2-bis(diphenylphosphanyl)acetylene and dppen = 1,2-bis(diphenylphosphanyl)-ethene} leading to [Pt 2 Cl 4 (dppbd)] (5). The asymmetrically bridged precursor complex 2 was obtained by combinatorial
Proton diffusion along biological membranes is vitally important for cellular energetics. Here we... more Proton diffusion along biological membranes is vitally important for cellular energetics. Here we extended previous time-resolved fluorescence measurements to study the time and temperature dependence of surface proton transport. We determined the Gibbs activation energy barrier ΔG (‡)r that opposes proton surface-to-bulk release from Arrhenius plots of (i) protons' surface diffusion constant and (ii) the rate coefficient for proton surface-to-bulk release. The large size of ΔG (‡)r disproves that quasi-equilibrium exists in our experiments between protons in the near-membrane layers and in the aqueous bulk. Instead, non-equilibrium kinetics describes the proton travel between the site of its photo-release and its arrival at a distant membrane patch at different temperatures. ΔG (‡)r contains only a minor enthalpic contribution that roughly corresponds to the breakage of a single hydrogen bond. Thus, our experiments reveal an entropic trap that ensures channeling of highly mobil...
Chemistry (Weinheim an der Bergstrasse, Germany), Jan 22, 2016
The reaction of 2,3,5,6-tetracyanopyridine (TCNPy) and Cr(C6 H6 )2 forms diamagnetic σ-[TCNPy]2 (... more The reaction of 2,3,5,6-tetracyanopyridine (TCNPy) and Cr(C6 H6 )2 forms diamagnetic σ-[TCNPy]2 (2-) possessing a 1.572(3) Å intrafragment sp(3) -sp(3) bond. This is in contrast to the structurally related 1,2,4,5-tetracyanobenzene and 1,2,4,5-tetracyanopyrazine that form π-dimer dianions possessing long, multicenter bonds.
Pyridine (1) and pyridazine (2) are investigated as electrocatalysts for the reduction of CO 2 to... more Pyridine (1) and pyridazine (2) are investigated as electrocatalysts for the reduction of CO 2 to methanol in aqueous electrolyte solution by E. Portenkirchner et al. on p. 1543. The picture shows the cyclic voltammogram of the one-electron reduction of pyridinium at different scan rates.
The palladium-catalyzed SuzukieMiyaura cross-coupling reaction has been investigated on mesosubst... more The palladium-catalyzed SuzukieMiyaura cross-coupling reaction has been investigated on mesosubstituted trans-A 2 B-corrole using tailored Pd-catalyst systems. We present the first examples of SuzukieMiyaura cross-coupling reactions on meso-substituted trans-A 2 B-corrole derivatives with neutral, sterically hindered, inactivated and heteroaromatic boronic acids and esters, alkenylboronic acids, as well as quickly deboronating aryl boronic acids and benzocondensated five membered heterocyclic boronic acids. In addition, we established a high-yield procedure for the SuzukieMiyaura cross-coupling reaction of corroles with neutral boronic acids. Due to the lability of the free-base corrole macrocycles, functionalization of the corrole periphery was performed with the corresponding Cu-metallated species. meso-Substituted trans-A 2 B-corrole can hence be regarded as highly versatile platform towards more sophisticated corrole systems. X-ray structure analysis of a functionalized meso-substituted trans-A 2 B copper corrole exhibited the typical features of such a Cu-complex: short NeCu distances and a saddled corrole configuration. Moreover, we observed a sensitivity of the formal oxidation state of the coordinated copper ions towards SuzukieMiyaura cross-coupling reaction conditions, where the central copper(III) ion approaches the characteristic features of a copper(II) species. This redox behaviour was examined by UV/vis absorption spectra, nuclear magnetic resonance (NMR) experiments and time-dependent density functional theoretical calculations.
A constant-time TOCSY difference experiment for the determination of 3 J(1 H3-31 P) coupling cons... more A constant-time TOCSY difference experiment for the determination of 3 J(1 H3-31 P) coupling constants in non-isotope-labelled DNA oligonucleotides is presented. The method is tested on a DNA octamer and compared with the established constant-time NOESY difference method. Each 3 J(1 H3-31 P) coupling constant is determined from amplitude changes caused by phosphorous decoupling, which are observable on multiple cross-peaks, thus leading to a high accuracy of the value of the 3 J(1 H3-31 P) coupling constant. The new experiment delivers up to three times the sensitivity compared with previously reported methods.
The rhenium complex fac-(5,5 0-bisphenylethynyl-2,2 0-bipyridyl)Re(CO) 3 Cl was used as a novel c... more The rhenium complex fac-(5,5 0-bisphenylethynyl-2,2 0-bipyridyl)Re(CO) 3 Cl was used as a novel catalyst for the electro-and photochemical reduction of CO 2 to CO in homogeneous solution. The results were compared to (2,2 0-bipyridyl)Re(CO) 3 Cl as a benchmark compound. Cyclic voltammetric studies as well as bulk controlled potential electrolysis experiments were performed using a CO 2 saturated solution in acetonitrile. (5,5 0-bisphenylethynyl-2,2 0-bipyridyl)Re(CO) 3 Cl showed a 6.5-fold increase in current density under CO 2 at À1750 mV versus normal hydrogen electrode (NHE) as compared to the operation without CO 2. Quantitative analysis by gas chromatography (GC) and infrared spectroscopy showed a Faradaic efficiency of around 45% for the formation of CO.
The synthesis, structure, photophysics, and spectroscopic characterization of two novel organomet... more The synthesis, structure, photophysics, and spectroscopic characterization of two novel organometallic rhodium and rhenium multichromophore photosensitizers carrying a central 2,2′-bipyridyl acceptor moiety are reported. Due to the presence of rigid phenylethynyl substituents in their 5,5′-position acting as intramolecular antenna groups, these compounds display perturbed excited state properties and a modified luminescence behaviour compared to the unsubstituted parent systems. The rhodium
Bimolecular reactions of the antimony(V) porphyrin complexes SbO(tpp)OH, 1 and SbO(oep)OH, 2 with... more Bimolecular reactions of the antimony(V) porphyrin complexes SbO(tpp)OH, 1 and SbO(oep)OH, 2 with tetra-n-butylammonium hydroxide were investigated at 298 K in acetonitrile solution (tpp, dianion of 5,10,15,20-tetraphenylporphyrin and oep, dianion of 2,3,7,8,12,13,17,18-octaethylporphyrin). Spontaneous nucleophilic addition of hydroxide ions to the non-oxidized porphyrin macrocycle leads to novel hydroxyphlorin derivatives, which contain a saturated meso-carbon bridge. While this process is a reversible equilibrium reaction for the TPP derivative, the OEP complex undergoes subsequent demetallation and oxidative ring cleavage in the presence of dioxygen. Possible implications for the competitive inhibition of heme-oxygenase by high-valent metalloporphyrin therapeutics are discussed.
JBIC Journal of Biological Inorganic Chemistry, 2009
The novel gold porphyrin complex (5,10,15-tris(N-methylpyridinium-4-yl)-20-(1-pyrenyl)-porphyrina... more The novel gold porphyrin complex (5,10,15-tris(N-methylpyridinium-4-yl)-20-(1-pyrenyl)-porphyrinato)gold(III) chloride, [Au(III)(TMPy3Pyr1P)]Cl4, was prepared and characterized by optical spectroscopy, high-resolution nuclear magnetic resonance (NMR), and electrospray mass spectrometry. This cationic multichromophore compound exhibits excellent water solubility and does not form aggregates under physiological conditions. Binding interactions of this complex and related model compounds with nucleic acid substrates have been studied and characterized by NMR and circular dichroism spectroscopy. The photoreactivity of [Au(III)(TMPy3Pyr1P)]Cl4 was investigated under anaerobic and aerobic conditions in the presence of an excess of purine nucleoside, guanosine, and plasmid DNA. Photocatalytic oxidative degradation of guanosine and the change from supercoiled to circular plasmid DNA upon monochromatic irradiation and polychromatic blue-light exposure with a maximum at 420 nm was explored. The potential of the novel water-soluble cationic metallointercalator complex [Au(III)(TMPy3Pyr1P)]Cl4 to serve as a catalytic photonuclease for the cleavage of DNA has been demonstrated.
Four new compounds of the general formula [M(L)(CH3COO)][PF6], where L is a tetradentate tripodal... more Four new compounds of the general formula [M(L)(CH3COO)][PF6], where L is a tetradentate tripodal ligand such as tris[2-(dimethylamino)ethyl]amine (L1) or (2-aminoethyl)bis(2-pyridylmethyl)amine (L2) and M is Co(II), Ni(II) or Cu(II), have been prepared employing a simple two-step synthesis. The compounds have been characterised by elemental analysis, mass spectroscopy, IR spectroscopy and X-ray diffraction. The catalytic properties of the derivatives containing the aliphatic ligand L1 have been investigated in particular toward the oxidation of cyclohexane and adamantane in the presence of the sacrificial oxidant m-CPBA (meta-chloroperbenzoic acid). Good TONs and selectivity have been determined for the cobalt and nickel compounds.
An efficient photocatalytic two-electron reduction and protonation of nicotine amide adenine dinu... more An efficient photocatalytic two-electron reduction and protonation of nicotine amide adenine dinucleotide (NAD +), as well as the synthetic nucleotide co-factor analogue N-benzyl-3-carbamoyl-pyridinium (BNAD +), powered by photons in the long-wavelength region of visible light (λ irr > 610 nm), is demonstrated for the first time. This functional artificial photosynthetic counterpart of the complete energy-trapping and solar-to-fuel conversion primary processes occurring in natural photosystem I (PS I) is achieved with a robust water-soluble tin(IV) complex of meso-tetrakis(N-methylpyridinium)chlorin acting as the light-harvesting sensitizer (threshold wavelength of λ thr = 660 nm). In buffered aqueous solution, this chlorophyll-like compound photocatalytically recycles a rhodium hydride complex of the type [Cp*Rh-(bpy)H] + , which is able to mediate regioselective hydride transfer processes. Different one-and two-electron donors are tested for the reductive quenching of the irradiated tin complex to initiate the secondary dark reactions leading to nucleotide co-factor reduction. Very promising conversion efficiencies, quantum yields, and excellent photosensitizer stabilities are observed. As an example of a catalytic dark reaction utilizing the reduction equivalents of accumulated NADH, an enzymatic process for the selective transformation of aldehydes with alcohol dehydrogenase (ADH) coupled to the primary photoreactions of the system is also demonstrated. A tentative reaction mechanism for the transfer of two electrons and one proton from the reductively quenched tin chlorin sensitizer to the rhodium co-catalyst, acting as a reversible hydride carrier, is proposed.
Observations of the photoredox reactivity of antimony(II1) porphyrin complexes are reported. Upon... more Observations of the photoredox reactivity of antimony(II1) porphyrin complexes are reported. Upon irradiation with visible light under ambient conditions, a photooxidation to the corresponding dihydroxoantimony(V) porphyrins occurs. At the same time a two-electron or four-electron reduction of molecular oxygen takes place, depending on the experimental conditions. In the absence of suitable electron acceptors, a photoinduced disproportionation reaction occurs. The photolysis of antimony(II1) porphyrins shows a pronounced wavelength dependence. The reactive excited state is concluded to be of the metal-centered sp type. An extended model for the electronic structure of p-type hyper metalloporphyrins is suggested.
The interfacial coupling of a nanoscale oxide material to a metal surface creates a hybrid system... more The interfacial coupling of a nanoscale oxide material to a metal surface creates a hybrid system with novel and often unprecedented physical and chemical properties that are not shared by the individual components of the system. The dimensionality of the oxide phase adds a further parameter to a oxide-metal hybrid system, which may be used as a tunable model for the study of emergent phenomena of low-dimensional (low-D) materials. Low-D oxide nanostructures on well-defined metal surfaces can be fabricated with atomic-scale design control using bottom-up directed self-assembly and a surface science methodology. Here we discuss the elastic and electronic effects introduced by the oxide-metal interface and how they determine the novel structure concepts that are encountered in low-D oxide nanophases on metal surfaces. The systems of interest are the oxides of Mn, Co, and Ni, which in monoxide form share a common rock-salt structure in the bulk and antiferromagnetic ordering behaviour....
The development of robust and cheap photocatalyst systems for visible-light induced organic subst... more The development of robust and cheap photocatalyst systems for visible-light induced organic substrate transformations is a significant uprising research topic at the crossroads of green chemistry and modern synthetic methodology. Atom economy, efficiency and selectivity are key parameters for the future practical applicability of the specific processes catalyzed. In this context, we report a simple and sustainable oxygen-dependent route for oxidizing various aromatic and aliphatic aldehydes to the corresponding carboxylic acids at room temperature under visible light and sunlight irradiation mediated by cobalt phthalocyanine tetrasulfonic acid (CoPcS) supported on reduced graphene oxide (RGO). Remarkably, products are obtained with (81-100)% conversion and 100% selectivity.
The spectroscopic and photochromic properties of the dinuclear rhodium complex Rh2L10X4 (L = CH3 ... more The spectroscopic and photochromic properties of the dinuclear rhodium complex Rh2L10X4 (L = CH3 CN, X− = BF−4 ) have been studied in acetonitrile solution. A reversible wavelengthdependent photoredox disproportionation of the dark-equilibrated dirhodium(II) compound occurs upon irradiation with quantum yields of φ = 0.04 at 254 nm and φ = 0.60 at 436 nm, respectively. While the photolysis products show conspicuous aggregation phenomena at higher concentrations, a straightforward pseudo-bimolecular recombination of the metastable fragments following second-order kinetics was observed in 5 × 10−5 M solution with k = 0.18 l mol−1 s−1 at 295 K. Both spectroscopic and kinetic results are consistent with the heterolytic formation of mononuclear rhodium(I) and rhodium(III) acetonitrile complexes in the course of the photochemical reaction.
The new bis(bidentate) tetraphosphane cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphanyl)buta-1,3-... more The new bis(bidentate) tetraphosphane cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphanyl)buta-1,3-diene (dppbd) (7) was obtained by applying a photochemical synthetic protocol. The key step of the photochemical reaction consisted of an intramolecular [2+2] cycloaddition involving a CC double and triple bond of the Pt-dimer species of the formula [Pt 2 Cl 4 (dppa)(trans-dppen)] (2) {dppa = 1,2-bis(diphenylphosphanyl)acetylene and dppen = 1,2-bis(diphenylphosphanyl)-ethene} leading to [Pt 2 Cl 4 (dppbd)] (5). The asymmetrically bridged precursor complex 2 was obtained by combinatorial
Proton diffusion along biological membranes is vitally important for cellular energetics. Here we... more Proton diffusion along biological membranes is vitally important for cellular energetics. Here we extended previous time-resolved fluorescence measurements to study the time and temperature dependence of surface proton transport. We determined the Gibbs activation energy barrier ΔG (‡)r that opposes proton surface-to-bulk release from Arrhenius plots of (i) protons' surface diffusion constant and (ii) the rate coefficient for proton surface-to-bulk release. The large size of ΔG (‡)r disproves that quasi-equilibrium exists in our experiments between protons in the near-membrane layers and in the aqueous bulk. Instead, non-equilibrium kinetics describes the proton travel between the site of its photo-release and its arrival at a distant membrane patch at different temperatures. ΔG (‡)r contains only a minor enthalpic contribution that roughly corresponds to the breakage of a single hydrogen bond. Thus, our experiments reveal an entropic trap that ensures channeling of highly mobil...
Chemistry (Weinheim an der Bergstrasse, Germany), Jan 22, 2016
The reaction of 2,3,5,6-tetracyanopyridine (TCNPy) and Cr(C6 H6 )2 forms diamagnetic σ-[TCNPy]2 (... more The reaction of 2,3,5,6-tetracyanopyridine (TCNPy) and Cr(C6 H6 )2 forms diamagnetic σ-[TCNPy]2 (2-) possessing a 1.572(3) Å intrafragment sp(3) -sp(3) bond. This is in contrast to the structurally related 1,2,4,5-tetracyanobenzene and 1,2,4,5-tetracyanopyrazine that form π-dimer dianions possessing long, multicenter bonds.
Pyridine (1) and pyridazine (2) are investigated as electrocatalysts for the reduction of CO 2 to... more Pyridine (1) and pyridazine (2) are investigated as electrocatalysts for the reduction of CO 2 to methanol in aqueous electrolyte solution by E. Portenkirchner et al. on p. 1543. The picture shows the cyclic voltammogram of the one-electron reduction of pyridinium at different scan rates.
The palladium-catalyzed SuzukieMiyaura cross-coupling reaction has been investigated on mesosubst... more The palladium-catalyzed SuzukieMiyaura cross-coupling reaction has been investigated on mesosubstituted trans-A 2 B-corrole using tailored Pd-catalyst systems. We present the first examples of SuzukieMiyaura cross-coupling reactions on meso-substituted trans-A 2 B-corrole derivatives with neutral, sterically hindered, inactivated and heteroaromatic boronic acids and esters, alkenylboronic acids, as well as quickly deboronating aryl boronic acids and benzocondensated five membered heterocyclic boronic acids. In addition, we established a high-yield procedure for the SuzukieMiyaura cross-coupling reaction of corroles with neutral boronic acids. Due to the lability of the free-base corrole macrocycles, functionalization of the corrole periphery was performed with the corresponding Cu-metallated species. meso-Substituted trans-A 2 B-corrole can hence be regarded as highly versatile platform towards more sophisticated corrole systems. X-ray structure analysis of a functionalized meso-substituted trans-A 2 B copper corrole exhibited the typical features of such a Cu-complex: short NeCu distances and a saddled corrole configuration. Moreover, we observed a sensitivity of the formal oxidation state of the coordinated copper ions towards SuzukieMiyaura cross-coupling reaction conditions, where the central copper(III) ion approaches the characteristic features of a copper(II) species. This redox behaviour was examined by UV/vis absorption spectra, nuclear magnetic resonance (NMR) experiments and time-dependent density functional theoretical calculations.
A constant-time TOCSY difference experiment for the determination of 3 J(1 H3-31 P) coupling cons... more A constant-time TOCSY difference experiment for the determination of 3 J(1 H3-31 P) coupling constants in non-isotope-labelled DNA oligonucleotides is presented. The method is tested on a DNA octamer and compared with the established constant-time NOESY difference method. Each 3 J(1 H3-31 P) coupling constant is determined from amplitude changes caused by phosphorous decoupling, which are observable on multiple cross-peaks, thus leading to a high accuracy of the value of the 3 J(1 H3-31 P) coupling constant. The new experiment delivers up to three times the sensitivity compared with previously reported methods.
The rhenium complex fac-(5,5 0-bisphenylethynyl-2,2 0-bipyridyl)Re(CO) 3 Cl was used as a novel c... more The rhenium complex fac-(5,5 0-bisphenylethynyl-2,2 0-bipyridyl)Re(CO) 3 Cl was used as a novel catalyst for the electro-and photochemical reduction of CO 2 to CO in homogeneous solution. The results were compared to (2,2 0-bipyridyl)Re(CO) 3 Cl as a benchmark compound. Cyclic voltammetric studies as well as bulk controlled potential electrolysis experiments were performed using a CO 2 saturated solution in acetonitrile. (5,5 0-bisphenylethynyl-2,2 0-bipyridyl)Re(CO) 3 Cl showed a 6.5-fold increase in current density under CO 2 at À1750 mV versus normal hydrogen electrode (NHE) as compared to the operation without CO 2. Quantitative analysis by gas chromatography (GC) and infrared spectroscopy showed a Faradaic efficiency of around 45% for the formation of CO.
The synthesis, structure, photophysics, and spectroscopic characterization of two novel organomet... more The synthesis, structure, photophysics, and spectroscopic characterization of two novel organometallic rhodium and rhenium multichromophore photosensitizers carrying a central 2,2′-bipyridyl acceptor moiety are reported. Due to the presence of rigid phenylethynyl substituents in their 5,5′-position acting as intramolecular antenna groups, these compounds display perturbed excited state properties and a modified luminescence behaviour compared to the unsubstituted parent systems. The rhodium
Bimolecular reactions of the antimony(V) porphyrin complexes SbO(tpp)OH, 1 and SbO(oep)OH, 2 with... more Bimolecular reactions of the antimony(V) porphyrin complexes SbO(tpp)OH, 1 and SbO(oep)OH, 2 with tetra-n-butylammonium hydroxide were investigated at 298 K in acetonitrile solution (tpp, dianion of 5,10,15,20-tetraphenylporphyrin and oep, dianion of 2,3,7,8,12,13,17,18-octaethylporphyrin). Spontaneous nucleophilic addition of hydroxide ions to the non-oxidized porphyrin macrocycle leads to novel hydroxyphlorin derivatives, which contain a saturated meso-carbon bridge. While this process is a reversible equilibrium reaction for the TPP derivative, the OEP complex undergoes subsequent demetallation and oxidative ring cleavage in the presence of dioxygen. Possible implications for the competitive inhibition of heme-oxygenase by high-valent metalloporphyrin therapeutics are discussed.
JBIC Journal of Biological Inorganic Chemistry, 2009
The novel gold porphyrin complex (5,10,15-tris(N-methylpyridinium-4-yl)-20-(1-pyrenyl)-porphyrina... more The novel gold porphyrin complex (5,10,15-tris(N-methylpyridinium-4-yl)-20-(1-pyrenyl)-porphyrinato)gold(III) chloride, [Au(III)(TMPy3Pyr1P)]Cl4, was prepared and characterized by optical spectroscopy, high-resolution nuclear magnetic resonance (NMR), and electrospray mass spectrometry. This cationic multichromophore compound exhibits excellent water solubility and does not form aggregates under physiological conditions. Binding interactions of this complex and related model compounds with nucleic acid substrates have been studied and characterized by NMR and circular dichroism spectroscopy. The photoreactivity of [Au(III)(TMPy3Pyr1P)]Cl4 was investigated under anaerobic and aerobic conditions in the presence of an excess of purine nucleoside, guanosine, and plasmid DNA. Photocatalytic oxidative degradation of guanosine and the change from supercoiled to circular plasmid DNA upon monochromatic irradiation and polychromatic blue-light exposure with a maximum at 420 nm was explored. The potential of the novel water-soluble cationic metallointercalator complex [Au(III)(TMPy3Pyr1P)]Cl4 to serve as a catalytic photonuclease for the cleavage of DNA has been demonstrated.
Four new compounds of the general formula [M(L)(CH3COO)][PF6], where L is a tetradentate tripodal... more Four new compounds of the general formula [M(L)(CH3COO)][PF6], where L is a tetradentate tripodal ligand such as tris[2-(dimethylamino)ethyl]amine (L1) or (2-aminoethyl)bis(2-pyridylmethyl)amine (L2) and M is Co(II), Ni(II) or Cu(II), have been prepared employing a simple two-step synthesis. The compounds have been characterised by elemental analysis, mass spectroscopy, IR spectroscopy and X-ray diffraction. The catalytic properties of the derivatives containing the aliphatic ligand L1 have been investigated in particular toward the oxidation of cyclohexane and adamantane in the presence of the sacrificial oxidant m-CPBA (meta-chloroperbenzoic acid). Good TONs and selectivity have been determined for the cobalt and nickel compounds.
An efficient photocatalytic two-electron reduction and protonation of nicotine amide adenine dinu... more An efficient photocatalytic two-electron reduction and protonation of nicotine amide adenine dinucleotide (NAD +), as well as the synthetic nucleotide co-factor analogue N-benzyl-3-carbamoyl-pyridinium (BNAD +), powered by photons in the long-wavelength region of visible light (λ irr > 610 nm), is demonstrated for the first time. This functional artificial photosynthetic counterpart of the complete energy-trapping and solar-to-fuel conversion primary processes occurring in natural photosystem I (PS I) is achieved with a robust water-soluble tin(IV) complex of meso-tetrakis(N-methylpyridinium)chlorin acting as the light-harvesting sensitizer (threshold wavelength of λ thr = 660 nm). In buffered aqueous solution, this chlorophyll-like compound photocatalytically recycles a rhodium hydride complex of the type [Cp*Rh-(bpy)H] + , which is able to mediate regioselective hydride transfer processes. Different one-and two-electron donors are tested for the reductive quenching of the irradiated tin complex to initiate the secondary dark reactions leading to nucleotide co-factor reduction. Very promising conversion efficiencies, quantum yields, and excellent photosensitizer stabilities are observed. As an example of a catalytic dark reaction utilizing the reduction equivalents of accumulated NADH, an enzymatic process for the selective transformation of aldehydes with alcohol dehydrogenase (ADH) coupled to the primary photoreactions of the system is also demonstrated. A tentative reaction mechanism for the transfer of two electrons and one proton from the reductively quenched tin chlorin sensitizer to the rhodium co-catalyst, acting as a reversible hydride carrier, is proposed.
Observations of the photoredox reactivity of antimony(II1) porphyrin complexes are reported. Upon... more Observations of the photoredox reactivity of antimony(II1) porphyrin complexes are reported. Upon irradiation with visible light under ambient conditions, a photooxidation to the corresponding dihydroxoantimony(V) porphyrins occurs. At the same time a two-electron or four-electron reduction of molecular oxygen takes place, depending on the experimental conditions. In the absence of suitable electron acceptors, a photoinduced disproportionation reaction occurs. The photolysis of antimony(II1) porphyrins shows a pronounced wavelength dependence. The reactive excited state is concluded to be of the metal-centered sp type. An extended model for the electronic structure of p-type hyper metalloporphyrins is suggested.
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Papers by Günther Knör