This paper reports on the switching characteristics of a spiropyran−cyclodextrin inclusion complex on a Au(111) surface. The switching behavior in acetone/water and ethanol/water solution is compared ...with that of the complex as thin film (∼100 layers) on gold and with the complex in a microcrystalline form. For the inclusion complex, we find a significantly increased switching time from the closed spiro to the open merocyanine conformation as compared to a solution of pure spiropyran. The thin film has a similar switching time as the solution of the inclusion complex. For the microcrystalline form, on the other hand, the switching times are considerably shorter. The back reaction exhibits a switching time for the solution of the inclusion complex which is similar to the pure spiropyran solution whereas the microcrystalline sample switches faster and the thin film of the inclusion complex slower than all the other ones. Furthermore, reversible switching of an adsorbed layer of the complex on gold could be observed. The switching characteristics can be explained in a model considering steric and compressive strain.
Pulsed electron−electron double resonance (ELDOR) has been used to obtain structural information from a FAD-dependent sulfhydryl oxidase, Augmenter of Liver Regeneration (ALR). ALR is a homodimer ...with each subunit containing a noncovalently bound FAD cofactor. Both FADs may be converted into the blue neutral radical form by aerobic treatment with DTT. From three-pulse and four-pulse ELDOR experiments, a distance of 26.1 ± 0.8 Å could be determined between the FAD cofactors in human ALR. Taking into account the electron spin density distribution in a neutral flavin radical obtained from density functional theory calculations, a distance of 26.9 Å could be estimated for the separation of the spin centers in the X-ray structure of rat ALR. The good agreement confirms that rat ALR may be used as a model for mechanistic discussions of human ALR. The experiments also demonstrate that neutral flavin radicals have the appropriate properties to be used as intrinsic spin labels for distance determinations in proteins.
Orientation of spin labels in de novo peptides Elsäßer, Celine; Monien, Bernhard; Haehnel, Wolfgang ...
Magnetic resonance in chemistry,
11/2005, Letnik:
43, Številka:
S1
Journal Article
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► Fischer patterns are used to enhance the function of photosystem I. ► Fischer patterns of Ag and Au show vanishing auto-luminescence. ► Coupling of photosystem I to these ...nanostructures modifies the protein function. ► Dark states of photosystem I become accessible using plasmonic interactions.
Single-molecule spectroscopy has been used to investigate the plasmonic interaction effects of nanometer-sized hexagonal arrays of Au- and Ag-triangles on the fluorescence properties of photosystem I (PSI) – a key component of the photosynthetic apparatus. The fluorescence emission of PSI is intensified upon coupling with these nanostructures. For single PSI trimers, enhancement factors of up to 10.5 (Au) and 15 (Ag) were observed. The average enhancement is 2.2/5.7 for Au/Ag, respectively. Comparison of the emission spectra shows that the enhancement depends on the wavelength. This wavelength dependence can be explained by the multichromophore composition of PSI. Furthermore, plasmonic interaction increases the fluorescence emission of spectral components, which are barely visible under natural conditions. The metal nanostructures produced via nanosphere lithography turned out to be beneficial tools for signal enhancement due to the very low intensity of their autoluminescence signal.
The interaction between two paramagnetic metal centers, a 3Fe−4S+ cluster and a NiFe center, is investigated in the hydrogenase from Desulfovibrio vulgaris Miyazaki F by pulsed ELDOR ...(electron−electron double resonance). The distance between the metal centers is known from X-ray crystallography. The experimental dipolar spin−spin interaction deviates from the value expected for two point-dipoles located at the centers of the metal clusters. An extended spin-coupling model accounting for the spin coupling in the 3Fe−4S+ cluster yields the observed interaction under the assumption of a particular magnetic coupling scheme for the three Fe ions. These results demonstrate that pulsed ELDOR can be used to gain insight into the inner structure of a multinuclear metal cluster.
Orientation of spin labels inde novo peptides Elsäßer, Celine; Monien, Bernhard; Haehnel, Wolfgang ...
Magnetic resonance in chemistry,
12/2005, Letnik:
43, Številka:
S1
Journal Article
