The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform
Marcel Mayor - One of the best experts on this subject based on the ideXlab platform.
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single molecule spin switch based on voltage triggered distortion of the Coordination Sphere
Angewandte Chemie, 2015Co-Authors: Gero D. Harzmann, Riccardo Frisenda, Herre S. J. Van Der Zant, Marcel MayorAbstract:Here, we report on a new single-molecule-switching concept based on the Coordination-Sphere-dependent spin state of Fe(II) species. The perpendicular arrangement of two terpyridine (tpy) ligands within heteroleptic complexes is distorted by the applied electric field. Whereas one ligand fixes the complex in the junction, the second one exhibits an intrinsic dipole moment which senses the E field and causes the distortion of the Fe(II) Coordination Sphere triggering the alteration of its spin state. A series of complexes with different dipole moments have been synthesized and their transport features were investigated via mechanically controlled break-junctions. Statistical analyses support the hypothesized switching mechanism with increasing numbers of junctions displaying voltage-dependent bistabilities upon increasing the Fe(II) complexes' intrinsic dipole moments. A constant threshold value of the E field required for switching corroborates the mechanism.
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Single‐Molecule Spin Switch Based on Voltage‐Triggered Distortion of the Coordination Sphere
Angewandte Chemie (International ed. in English), 2015Co-Authors: Gero D. Harzmann, Riccardo Frisenda, Herre S. J. Van Der Zant, Marcel MayorAbstract:Here, we report on a new single-molecule-switching concept based on the Coordination-Sphere-dependent spin state of Fe(II) species. The perpendicular arrangement of two terpyridine (tpy) ligands within heteroleptic complexes is distorted by the applied electric field. Whereas one ligand fixes the complex in the junction, the second one exhibits an intrinsic dipole moment which senses the E field and causes the distortion of the Fe(II) Coordination Sphere triggering the alteration of its spin state. A series of complexes with different dipole moments have been synthesized and their transport features were investigated via mechanically controlled break-junctions. Statistical analyses support the hypothesized switching mechanism with increasing numbers of junctions displaying voltage-dependent bistabilities upon increasing the Fe(II) complexes' intrinsic dipole moments. A constant threshold value of the E field required for switching corroborates the mechanism.
Theodore R. Holman - One of the best experts on this subject based on the ideXlab platform.
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Spectroscopic characterization of soybean lipoxygenase-1 mutants: the role of second Coordination Sphere residues in the regulation of enzyme activity.
Biochemistry, 2003Co-Authors: Gerhard Schenk, Theodore R. Holman, Michael L. Neidig, Jing Zhou, Edward I. SolomonAbstract:Lipoxygenases are non-heme iron enzymes, which catalyze the stereo- and regiospecific hydroperoxidation of unsaturated fatty acids. Spectroscopic studies on soybean lipoxygenase have shown that the ferrous form of the enzyme is a mixture of five- and six-coordinate species (40 and 60%, respectively). Addition of substrate leads to a purely six-coordinate form. A series of mutations in the second Coordination Sphere (Q697E, Q697N, Q495A, and Q495E) were generated, and the structures of the mutants were solved by crystallography [Tomchick et al. (2001) Biochemistry 40, 7509-7517]. While this study clearly showed the contribution of H-bond interactions between the first and the second Coordination Spheres in catalysis, no correlation with the Coordination environment of the Fe(II) was observed. A recent study using density-functional theory [Lehnert and Solomon (2002) J. Biol. Inorg. Chem. 8, 294-305] indicated that Coordination flexibility, involving the Asn694 ligand, is regulated via H-bond interactions. In this paper, we investigate the solution structures of the second Coordination Sphere mutants using CD and MCD spectroscopy since these techniques are more sensitive indicators of the first Coordination Sphere ligation of Fe(II) systems. Our data demonstrate that the iron Coordination environment directly relates to activity, with the mutations that have the ability to form a five-coordinate/six-coordinate mixture being more active. We propose that the H-bond between the weak Asn694 ligand and the Gln697 plays a key role in the modulation of the Coordination flexibility of Asn694, and thus, is crucial for the regulation of enzyme reactivity.
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Structural and functional characterization of second-Coordination Sphere mutants of soybean lipoxygenase-1.
Biochemistry, 2001Co-Authors: Diana R. Tomchick, Phuc Phan, Marcin Cymborowski, Wladek Minor, Theodore R. HolmanAbstract:Lipoxygenases are an important class of non-heme iron enzymes that catalyze the hydroperoxidation of unsaturated fatty acids. The details of the enzymatic mechanism of lipoxygenases are still not well understood. This study utilizes a combination of kinetic and structural probes to relate the lipoxygenase mechanism of action with structural modifications of the iron's second Coordination Sphere. The second Coordination Sphere consists of Gln495 and Gln697, which form a hydrogen bond network between the substrate cavity and the first Coordination Sphere (Asn694). In this investigation, we compared the kinetic and structural properties of four mutants (Q495E, Q495A, Q697N, and Q697E) with those of wild-type soybean lipoxygenase-1 and determined that changes in the second Coordination Sphere affected the enzymatic activity by hydrogen bond rearrangement and substrate positioning through interaction with Gln495. The nature of the C−H bond cleavage event remained unchanged, which demonstrates that the mutation...
Andrew S. Borovik - One of the best experts on this subject based on the ideXlab platform.
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Coordination Chemistry within a Protein Host: Regulation of the Secondary Coordination Sphere
Chemical Communications, 2018Co-Authors: Samuel I. Mann, Tillmann Heinisch, Thomas R Ward, Andrew S. BorovikAbstract:Secondary Coordination Spheres of metal complexes are instrumental in controlling properties that are linked to function. To study these effects in aqueous solutions artificial Cu proteins have been developed using biotin–streptavidin (Sav) technology and their binding of external azide ions investigated. Parallel binding studies were done in crystallo on single crystals of the artificial Cu proteins. Spectroscopic changes in solution are consistent with azide binding to the Cu centers. Structural studies corroborate that a Cu–N3 unit is present in each Sav subunit and reveal the composition of hydrogen bonding (H-bonding) networks that include the coordinated azido ligand. The networks involve amino acid residues and water molecules within the secondary Coordination Sphere. Mutation of these residues to ones that cannot form H-bonds caused a measurble change in the equilibrium binding constants that were measured in solution. These findings further demonstrate the utility of biotin–Sav technology to prepare water-stable inorganic complexes whose structures can be controlled within both primary and secondary Coordination Spheres.
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Role of the secondary Coordination Sphere in metal-mediated dioxygen activation.
Inorganic chemistry, 2010Co-Authors: Ryan L. Shook, Andrew S. BorovikAbstract:Alfred Werner proposed nearly 100 years ago that the secondary Coordination Sphere has a role in determining the physical properties of transition-metal complexes. We now know that the secondary Coordination Sphere impacts nearly all aspects of transition-metal chemistry, including the reactivity and selectivity in metal-mediated processes. These features are highlighted in the binding and activation of dioxygen by transition-metal complexes. There are clear connections between control of the secondary Coordination Sphere and the ability of metal complexes to (1) reversibly bind dioxygen or (2) bind and activate dioxygen to form highly reactive metal−oxo complexes. In this Forum Article, several biological and synthetic examples are presented and discussed in terms of structure−function relationships. Particular emphasis is given to systems with defined noncovalent interactions, such as intramolecular H-bonds involving dioxygen-derived ligands. To further illustrate these effects, the homolytic cleavage o...
Gero D. Harzmann - One of the best experts on this subject based on the ideXlab platform.
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single molecule spin switch based on voltage triggered distortion of the Coordination Sphere
Angewandte Chemie, 2015Co-Authors: Gero D. Harzmann, Riccardo Frisenda, Herre S. J. Van Der Zant, Marcel MayorAbstract:Here, we report on a new single-molecule-switching concept based on the Coordination-Sphere-dependent spin state of Fe(II) species. The perpendicular arrangement of two terpyridine (tpy) ligands within heteroleptic complexes is distorted by the applied electric field. Whereas one ligand fixes the complex in the junction, the second one exhibits an intrinsic dipole moment which senses the E field and causes the distortion of the Fe(II) Coordination Sphere triggering the alteration of its spin state. A series of complexes with different dipole moments have been synthesized and their transport features were investigated via mechanically controlled break-junctions. Statistical analyses support the hypothesized switching mechanism with increasing numbers of junctions displaying voltage-dependent bistabilities upon increasing the Fe(II) complexes' intrinsic dipole moments. A constant threshold value of the E field required for switching corroborates the mechanism.
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Single‐Molecule Spin Switch Based on Voltage‐Triggered Distortion of the Coordination Sphere
Angewandte Chemie (International ed. in English), 2015Co-Authors: Gero D. Harzmann, Riccardo Frisenda, Herre S. J. Van Der Zant, Marcel MayorAbstract:Here, we report on a new single-molecule-switching concept based on the Coordination-Sphere-dependent spin state of Fe(II) species. The perpendicular arrangement of two terpyridine (tpy) ligands within heteroleptic complexes is distorted by the applied electric field. Whereas one ligand fixes the complex in the junction, the second one exhibits an intrinsic dipole moment which senses the E field and causes the distortion of the Fe(II) Coordination Sphere triggering the alteration of its spin state. A series of complexes with different dipole moments have been synthesized and their transport features were investigated via mechanically controlled break-junctions. Statistical analyses support the hypothesized switching mechanism with increasing numbers of junctions displaying voltage-dependent bistabilities upon increasing the Fe(II) complexes' intrinsic dipole moments. A constant threshold value of the E field required for switching corroborates the mechanism.
Edward I. Solomon - One of the best experts on this subject based on the ideXlab platform.
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Spectroscopic characterization of soybean lipoxygenase-1 mutants: the role of second Coordination Sphere residues in the regulation of enzyme activity.
Biochemistry, 2003Co-Authors: Gerhard Schenk, Theodore R. Holman, Michael L. Neidig, Jing Zhou, Edward I. SolomonAbstract:Lipoxygenases are non-heme iron enzymes, which catalyze the stereo- and regiospecific hydroperoxidation of unsaturated fatty acids. Spectroscopic studies on soybean lipoxygenase have shown that the ferrous form of the enzyme is a mixture of five- and six-coordinate species (40 and 60%, respectively). Addition of substrate leads to a purely six-coordinate form. A series of mutations in the second Coordination Sphere (Q697E, Q697N, Q495A, and Q495E) were generated, and the structures of the mutants were solved by crystallography [Tomchick et al. (2001) Biochemistry 40, 7509-7517]. While this study clearly showed the contribution of H-bond interactions between the first and the second Coordination Spheres in catalysis, no correlation with the Coordination environment of the Fe(II) was observed. A recent study using density-functional theory [Lehnert and Solomon (2002) J. Biol. Inorg. Chem. 8, 294-305] indicated that Coordination flexibility, involving the Asn694 ligand, is regulated via H-bond interactions. In this paper, we investigate the solution structures of the second Coordination Sphere mutants using CD and MCD spectroscopy since these techniques are more sensitive indicators of the first Coordination Sphere ligation of Fe(II) systems. Our data demonstrate that the iron Coordination environment directly relates to activity, with the mutations that have the ability to form a five-coordinate/six-coordinate mixture being more active. We propose that the H-bond between the weak Asn694 ligand and the Gln697 plays a key role in the modulation of the Coordination flexibility of Asn694, and thus, is crucial for the regulation of enzyme reactivity.