... conventional nuclear power stations that consume uranium will, over the same time scale as th... more ... conventional nuclear power stations that consume uranium will, over the same time scale as the loss of oil and gas supplies, run ... 10 years: - Elucidation of the basic catalytic mechanism of PSII water splitting and hydrogenase function interfaced with research on (i) biomimetic ...
Magic angle spinning (MAS) NMR with Lee–Goldburg cross-polarization (LG-CP) is used to promote lo... more Magic angle spinning (MAS) NMR with Lee–Goldburg cross-polarization (LG-CP) is used to promote long-range heteronuclear transfer of magnetization and to constrain a structural model for uniformly labeled chlorophyll a/H 2 O. An effective maximum transfer range d max can be determined experimentally from the detection of a gradually decreasing series of intramolecular correlations with the 13 C along the molecular skeleton. To probe intermolecular contacts , d max can be set to ∼4.2 ˚ A by choosing an LG-CP contact time of 2 ms. Long-range 1 H– 13 C correlations are used in conjunction with carbon and proton aggregation shifts to establish the stacking of the chlorophyll a (Chl a) molecules. First, high-field (14.1 T) 2-D MAS NMR homonuclear (13 C– 13 C) dipolar correlation spectra provide a complete assignment of the carbon chemical shifts. Second , proton chemical shifts are obtained from 1 H– 13 C heteronuclear dipolar correlation spectroscopy in high magnetic field. The shift constraints and long-range 1 H– 13 C intermolecular correlations reveal a 2-D stacking homologous to the molecular arrangement in crystalline solid ethyl-chlorophyllide a. A doubling of a small subset of the carbon resonances, in the 7-methyl region of the molecule, provides evidence for two marginally different well-defined molecular environments. Evidence is found for the presence of neutral structural water molecules forming a hydrogen-bonded network to stabilize Chl a sheets. In line with the microcrystalline order observed for the rings, the long T 1 's, and absence of conformational shifts for the 13 C in the phytyl tails, it is proposed that the Chl a form a rigid 3-D space-filling structure. Probably the only way this can be realized with the sheets is by forming bilayers with interpen-etration of elongated tails. Such a 3-D space-filling organization of the aggregated Chl a from MAS NMR would match existing models inferred from electron microscopy and low-resolution X-ray powder diffraction, while a micellar model based on neutron diffraction and antiparallel stacking observed in solution can be discarded. C 2002 Elsevier Science (USA)
In water electrocatalytic systems, stability and robustness of the catalytic materials for long-t... more In water electrocatalytic systems, stability and robustness of the catalytic materials for long-term performance are the key parameters which determine their deployment on large terrestrial scale. We present here a neutral HCO3–/CO2 as a new electrolyte system for the in-situ assembling of highly robust and efficient cobalt(II)-derived electrocatalysts for water oxidation under benign conditions. The electrodeposited cobalt catalyst in an easy accessible near-neutral HCO3–/CO2 (Co-Ci) system, shows remarkable oxygen evolution current efficiency as compared to the Co-phosphate (Co-Pi) type catalytic system. The oxygen onset is just at 1.29 V (vs. NHE) and peak current density (J) for oxygen evolution approaching 4.0 mA cm–2 on an ITO anode, and 9.0 mA cm–2 on a GC substrate are obtained at just 1.59 V (vs. NHE) in a neutral pH solution. During long-term controlled-potential electrolysis (CPE) of water, the Co-Ci system shows a very high oxygen evolution current density of ca. 2.0 mA ...
ABSTRACT This chapter presents some recent applications of enrichment with stable 13C isotopes an... more ABSTRACT This chapter presents some recent applications of enrichment with stable 13C isotopes and magic angle spinning (MAS) nuclear magnetic resonance (NMR) studies of rhodopsin. Comprehensive information about the electronic and spatial structure of the ligand can be obtained when bound to the membrane with isotope labeling and MAS NMR. The chapter provides an overview of the labeling and MAS NMR studies aiming at a characterization of ligand-protein interactions for rhodopsin via the determination of chemical shifts. To illustrate the capabilities of MAS NMR for studying photoproducts, shift data on the ligand–protein interactions in bathorhodopsin, structural data for the pre-discharge metarhodopsin I, and shift data for the discharged metarhodopsin II photointermediate is also reviewed. MAS NMR, in conjunction with selective isotope enrichment, is the method of choice for NMR investigations of membrane protein receptors when in the membrane in their natural environment. It is a technique for obtaining high-resolution NMR data from solids. In a MAS NMR experiment, the chemical shift anisotropy broadening of the NMR response in the solid state is suppressed by macroscopic sample rotation around an axis at the magic angle βm = 54°44′ with respect to the applied magnetic field.
The visible absorption of bacteriorhodopsin (bR) is highly sensitive to pH, the maximum shifting ... more The visible absorption of bacteriorhodopsin (bR) is highly sensitive to pH, the maximum shifting from 568 nm (pH 7) to approximately 600 nm (pH 2) and back to 565 nm (pH 0) as the pH is decreased further with HCl. Blue membrane is also formed by deionization of neutral purple membrane suspensions. Low-temperature, magic angle spinning 13C and 15N NMR was used to investigate the transitions to the blue and acid purple states. The 15N NMR studies involved (epsilon-15N)lysine bR, allowing a detailed investigation of effects at the Schiff base nitrogen. The 15N resonance shifts approximately 16 ppm upfield in the neutral purple to blue transition and returns to its original value in the blue to acid purple transition. Thus, the 15N shift correlates directly with the color changes, suggesting an important contribution of the Schiff base counterion to the opsin shift. The results indicate weaker hydrogen bonding in the blue form than in the two purple forms and permit a determination of t...
Using solid-state nuclear magnetic resonance (NMR), structure and its underlying details, such as... more Using solid-state nuclear magnetic resonance (NMR), structure and its underlying details, such as the rigidity, order, dynamics or electrostatic heterogeneity of the large membrane protein complexes involved in photosynthesis can be resolved at specifi c spots with a resolution well beyond the capabilities of X-ray and other diffraction methods. Following a brief explanation of the theoretical background of the magic
This paper presents the synthesis and characterization by mass spectrometry and NMR spectroscopy ... more This paper presents the synthesis and characterization by mass spectrometry and NMR spectroscopy of [2-13C]- and [3-13C]ubiquinone-0 and of [5-13C]- and [6-13C]ubiquinone-10. A scheme based on the synthetic approach to [5-13C]ubiquinone-10 has been worked out for the synthesis of ubiquinones 13C-labeled at any individual position and at every combination of positions in the quinone ring. The [5-13C]- and [6-13C]ubiquinone-10 isotopomers were incorporated into the QA-site of the photosynthetic reaction center of Rhodobacter sphaeroides R-26. Magic angle spinning NMR subsequently revealed an unperturbed 6-position, while the signal of the 5-position was absent. These results corroborate the recently reported detection of an asymmetric binding of QA with a dynamic perturbation involving the 4-carbonyl functionality.
ABSTRACT Abundant low-frequency motions in the poly(methyl methacrylate) (PMMA) phase of polymer ... more ABSTRACT Abundant low-frequency motions in the poly(methyl methacrylate) (PMMA) phase of polymer blends of poly(propylene oxide) epoxy and thermoplastic PMMA with submicron morphologies are revealed by solid-state NMR measurements. The presence of this mobility is in line with the depression of glass temperatures in thin polymer films. The modified polymer dynamics induced by microscopic morphology is potentially important for research on frequency-dependent polymer conductivity, dynamics in polymeric glasses, physical aging, and models for polymer fracture dynamics.
We investigate the electron injection from a terrylene-based chromophore to the TiO2 semiconducto... more We investigate the electron injection from a terrylene-based chromophore to the TiO2 semiconductor bridged by a recently proposed phenyl-amide-phenyl molecular rectifier. The mechanism of electron transfer is studied by means of quantum dynamics simulations using an extended Hückel Hamiltonian. It is found that the inclusion of the nuclear motion is necessary to observe the photoinduced electron transfer. In particular, the fluctuations of the dihedral angle between the terrylene and the phenyl ring modulate the localization and thus the electronic coupling between the donor and acceptor states involved in the injection process. The electron propagation shows characteristic oscillatory features that correlate with interatomic distance fluctuations in the bridge, which are associated with the vibrational modes driving the process. The understanding of such effects is important for the design of functional dyes with optimal injection and rectification properties.
ABSTRACT Domain walls (narrow solitons) in the Ising-type quasi 1-d antiferromagnet RbFeCl3.2H2O ... more ABSTRACT Domain walls (narrow solitons) in the Ising-type quasi 1-d antiferromagnet RbFeCl3.2H2O have been studied by means of Mössbauer relaxation experiments in magnetic fields strong enough (1.5 T) to suppress the 3-d long-range ordering. Excellent agreement is obtained with the Blume - Tjon model, assuming stochastic relaxation due to the propagation of wall-. In still higher fields (6 T) the excitation of walls is found to be suppressed by the generation of a staggered field on the (slightly canted) antiferromagnetic chains.
... conventional nuclear power stations that consume uranium will, over the same time scale as th... more ... conventional nuclear power stations that consume uranium will, over the same time scale as the loss of oil and gas supplies, run ... 10 years: - Elucidation of the basic catalytic mechanism of PSII water splitting and hydrogenase function interfaced with research on (i) biomimetic ...
Magic angle spinning (MAS) NMR with Lee–Goldburg cross-polarization (LG-CP) is used to promote lo... more Magic angle spinning (MAS) NMR with Lee–Goldburg cross-polarization (LG-CP) is used to promote long-range heteronuclear transfer of magnetization and to constrain a structural model for uniformly labeled chlorophyll a/H 2 O. An effective maximum transfer range d max can be determined experimentally from the detection of a gradually decreasing series of intramolecular correlations with the 13 C along the molecular skeleton. To probe intermolecular contacts , d max can be set to ∼4.2 ˚ A by choosing an LG-CP contact time of 2 ms. Long-range 1 H– 13 C correlations are used in conjunction with carbon and proton aggregation shifts to establish the stacking of the chlorophyll a (Chl a) molecules. First, high-field (14.1 T) 2-D MAS NMR homonuclear (13 C– 13 C) dipolar correlation spectra provide a complete assignment of the carbon chemical shifts. Second , proton chemical shifts are obtained from 1 H– 13 C heteronuclear dipolar correlation spectroscopy in high magnetic field. The shift constraints and long-range 1 H– 13 C intermolecular correlations reveal a 2-D stacking homologous to the molecular arrangement in crystalline solid ethyl-chlorophyllide a. A doubling of a small subset of the carbon resonances, in the 7-methyl region of the molecule, provides evidence for two marginally different well-defined molecular environments. Evidence is found for the presence of neutral structural water molecules forming a hydrogen-bonded network to stabilize Chl a sheets. In line with the microcrystalline order observed for the rings, the long T 1 's, and absence of conformational shifts for the 13 C in the phytyl tails, it is proposed that the Chl a form a rigid 3-D space-filling structure. Probably the only way this can be realized with the sheets is by forming bilayers with interpen-etration of elongated tails. Such a 3-D space-filling organization of the aggregated Chl a from MAS NMR would match existing models inferred from electron microscopy and low-resolution X-ray powder diffraction, while a micellar model based on neutron diffraction and antiparallel stacking observed in solution can be discarded. C 2002 Elsevier Science (USA)
In water electrocatalytic systems, stability and robustness of the catalytic materials for long-t... more In water electrocatalytic systems, stability and robustness of the catalytic materials for long-term performance are the key parameters which determine their deployment on large terrestrial scale. We present here a neutral HCO3–/CO2 as a new electrolyte system for the in-situ assembling of highly robust and efficient cobalt(II)-derived electrocatalysts for water oxidation under benign conditions. The electrodeposited cobalt catalyst in an easy accessible near-neutral HCO3–/CO2 (Co-Ci) system, shows remarkable oxygen evolution current efficiency as compared to the Co-phosphate (Co-Pi) type catalytic system. The oxygen onset is just at 1.29 V (vs. NHE) and peak current density (J) for oxygen evolution approaching 4.0 mA cm–2 on an ITO anode, and 9.0 mA cm–2 on a GC substrate are obtained at just 1.59 V (vs. NHE) in a neutral pH solution. During long-term controlled-potential electrolysis (CPE) of water, the Co-Ci system shows a very high oxygen evolution current density of ca. 2.0 mA ...
ABSTRACT This chapter presents some recent applications of enrichment with stable 13C isotopes an... more ABSTRACT This chapter presents some recent applications of enrichment with stable 13C isotopes and magic angle spinning (MAS) nuclear magnetic resonance (NMR) studies of rhodopsin. Comprehensive information about the electronic and spatial structure of the ligand can be obtained when bound to the membrane with isotope labeling and MAS NMR. The chapter provides an overview of the labeling and MAS NMR studies aiming at a characterization of ligand-protein interactions for rhodopsin via the determination of chemical shifts. To illustrate the capabilities of MAS NMR for studying photoproducts, shift data on the ligand–protein interactions in bathorhodopsin, structural data for the pre-discharge metarhodopsin I, and shift data for the discharged metarhodopsin II photointermediate is also reviewed. MAS NMR, in conjunction with selective isotope enrichment, is the method of choice for NMR investigations of membrane protein receptors when in the membrane in their natural environment. It is a technique for obtaining high-resolution NMR data from solids. In a MAS NMR experiment, the chemical shift anisotropy broadening of the NMR response in the solid state is suppressed by macroscopic sample rotation around an axis at the magic angle βm = 54°44′ with respect to the applied magnetic field.
The visible absorption of bacteriorhodopsin (bR) is highly sensitive to pH, the maximum shifting ... more The visible absorption of bacteriorhodopsin (bR) is highly sensitive to pH, the maximum shifting from 568 nm (pH 7) to approximately 600 nm (pH 2) and back to 565 nm (pH 0) as the pH is decreased further with HCl. Blue membrane is also formed by deionization of neutral purple membrane suspensions. Low-temperature, magic angle spinning 13C and 15N NMR was used to investigate the transitions to the blue and acid purple states. The 15N NMR studies involved (epsilon-15N)lysine bR, allowing a detailed investigation of effects at the Schiff base nitrogen. The 15N resonance shifts approximately 16 ppm upfield in the neutral purple to blue transition and returns to its original value in the blue to acid purple transition. Thus, the 15N shift correlates directly with the color changes, suggesting an important contribution of the Schiff base counterion to the opsin shift. The results indicate weaker hydrogen bonding in the blue form than in the two purple forms and permit a determination of t...
Using solid-state nuclear magnetic resonance (NMR), structure and its underlying details, such as... more Using solid-state nuclear magnetic resonance (NMR), structure and its underlying details, such as the rigidity, order, dynamics or electrostatic heterogeneity of the large membrane protein complexes involved in photosynthesis can be resolved at specifi c spots with a resolution well beyond the capabilities of X-ray and other diffraction methods. Following a brief explanation of the theoretical background of the magic
This paper presents the synthesis and characterization by mass spectrometry and NMR spectroscopy ... more This paper presents the synthesis and characterization by mass spectrometry and NMR spectroscopy of [2-13C]- and [3-13C]ubiquinone-0 and of [5-13C]- and [6-13C]ubiquinone-10. A scheme based on the synthetic approach to [5-13C]ubiquinone-10 has been worked out for the synthesis of ubiquinones 13C-labeled at any individual position and at every combination of positions in the quinone ring. The [5-13C]- and [6-13C]ubiquinone-10 isotopomers were incorporated into the QA-site of the photosynthetic reaction center of Rhodobacter sphaeroides R-26. Magic angle spinning NMR subsequently revealed an unperturbed 6-position, while the signal of the 5-position was absent. These results corroborate the recently reported detection of an asymmetric binding of QA with a dynamic perturbation involving the 4-carbonyl functionality.
ABSTRACT Abundant low-frequency motions in the poly(methyl methacrylate) (PMMA) phase of polymer ... more ABSTRACT Abundant low-frequency motions in the poly(methyl methacrylate) (PMMA) phase of polymer blends of poly(propylene oxide) epoxy and thermoplastic PMMA with submicron morphologies are revealed by solid-state NMR measurements. The presence of this mobility is in line with the depression of glass temperatures in thin polymer films. The modified polymer dynamics induced by microscopic morphology is potentially important for research on frequency-dependent polymer conductivity, dynamics in polymeric glasses, physical aging, and models for polymer fracture dynamics.
We investigate the electron injection from a terrylene-based chromophore to the TiO2 semiconducto... more We investigate the electron injection from a terrylene-based chromophore to the TiO2 semiconductor bridged by a recently proposed phenyl-amide-phenyl molecular rectifier. The mechanism of electron transfer is studied by means of quantum dynamics simulations using an extended Hückel Hamiltonian. It is found that the inclusion of the nuclear motion is necessary to observe the photoinduced electron transfer. In particular, the fluctuations of the dihedral angle between the terrylene and the phenyl ring modulate the localization and thus the electronic coupling between the donor and acceptor states involved in the injection process. The electron propagation shows characteristic oscillatory features that correlate with interatomic distance fluctuations in the bridge, which are associated with the vibrational modes driving the process. The understanding of such effects is important for the design of functional dyes with optimal injection and rectification properties.
ABSTRACT Domain walls (narrow solitons) in the Ising-type quasi 1-d antiferromagnet RbFeCl3.2H2O ... more ABSTRACT Domain walls (narrow solitons) in the Ising-type quasi 1-d antiferromagnet RbFeCl3.2H2O have been studied by means of Mössbauer relaxation experiments in magnetic fields strong enough (1.5 T) to suppress the 3-d long-range ordering. Excellent agreement is obtained with the Blume - Tjon model, assuming stochastic relaxation due to the propagation of wall-. In still higher fields (6 T) the excitation of walls is found to be suppressed by the generation of a staggered field on the (slightly canted) antiferromagnetic chains.
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