Gravitational redshift experiments with the high-resolution Mössbauer resonance in67Zn

A gravitational tedshift (GRS) experiment using the high-resolution Mössbauer resonance in⁶⁷Zn is described. The tiny Doppler motion of the source can be checked by a dc-SQUID based displacement sensor. The results on the GRS strongly indicate that solid-state effects, which are difficult to control experimentally, finally limit the accuracy that Mössbauer measurements can provide in determining the GRS. We argue that for this reason conventional Mössbauer experiments most probably will not be able to compete with other methods in future GRS measurements of very high precision.     

An adaptive moving mesh approach for hyperbolic conservation laws on time-dependent domains

The general idea of moving mesh approaches is to improve the approximation quality and the numerical performance by redistributing a fixed number of discretization points. This is called rrefinement. The classical approaches are applied to partial differential equations on fixed domains. An extension to time-dependent (expanding) domains is presented. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Zaubervorlesung mit Salvador Dalí. Chemie‐Edutainment

During the past 10 years the “Magic chemistry” lecture was conducted in Erlangen. Due to an increasing professionalization of the lecture and especially the underlying information concept, we could emphasize the seriousness of this event. We combine scientific education and entertainment to an “edutainment” concept. We hope to show in an exemplary way, how fun and experimental natural sciences can be combined in a big live event.     

67Zn Mössbauer study of Zn metal and Cu−Zn alloys at high pressure

A high pressure Mössbauer spectrometer for the 93.3keV resonance in⁶⁷Zn has been used to investigate Zn metal and two Cu?Zn alloys with Zn concentrations of 41.9at% and 48.0at% at 4.2K and pressures up to ～58kbar. For Zn metal the c/a-ratio plays an important role to describe the change of the Mössbauer parameters with pressure. Most striking is the increase of the recoil-free fraction by a factor of ～3. In the brass alloys a new phase is observed at 4.2K and high pressures which we tentatively identify with a martensitic α₁-phase.     

High pressure studies of actinide intermetallics

Hyperfine Interactions - Magnetic properties of NpOs2,NpAl2. NpCo2Si2, NpAs, and NpSn3 are investigated by high pressure Mössbauer spectroscopy using the 60 keV transition in237Np. A wide...     

67Zn Mössbauer study of Cu−Zn alloys at high pressure

The high-resolution 93.3-keV Mössbauer resonance in⁶⁷Zn was used to investigate Cu?Zn alloys (brass) containing 16.6 wt.% Zn (α-phase) and 50.5 wt.% Zn (β'-phase) at pressures up to 6.2 GPa and at 4.2 K. The recoil-free fraction and the center shift change linearly with reduced volume. The decrease of the center shift is due to the second-order Doppler effect which is partially compensated by the increase of the s-electron density at the⁶⁷Zn nucleus when the conduction electrons are compressed. In α-brass short-range order leads to four different Cu?Zn configurations. One of them exhibits a center shift which nearly coincides with that of the β'-phase.     

Quantum path interference in the wavelength dependence of high-harmonic generation

We investigate the dependence of the intensity of radiation due to high-harmonic generation as a function of the wavelength lambda of the fundamental driver field. Superimposed on a smooth power-law dependence observed previously, we find surprisingly strong and rapid fluctuations on a fine lambda scale. We identify the origin of these fluctuations in terms of quantum path interferences with up to five returning orbits significantly contributing.     

Thermodynamic and kinetic studies on reactions of Pt(II) complexes with biologically relevant nucleophiles

The effect of different N-N spectator ligands on the reactivity of platinum(II) complexes was investigated by studying the water lability of [Pt(diaminocyclohexane)(H2O)2]2+ (Pt(dach)), [Pt(ethylenediamine)(H2O)2]2+ (Pt(en)), [Pt(aminomethylpyridine)(H2O)2]2+ (Pt(amp)), and [Pt(N,N'-bipyridine)(H2O)2]2+ (Pt(bpy)). Some of the selected N-N chelates form part of the coordination sphere of Pt(II) drugs in clinical use, as in Pt(dach) (oxaliplatin), or are models, regarding the nature of the amines, with higher stability in terms of substitution and hydrolysis of the diamine moiety, as in Pt(en) (cisplatin) and Pt(amp) (AMD473). The effect of pi-acceptors on the reactivity was investigated by introducing one (Pt(amp)) or two pyridine rings (Pt(bpy)) in the system. The pK(a) values for the two water molecules (viz., Pt(dach) (pK(a1) = 6.01, pK(a2) = 7.69), Pt(en) (pK(a1) = 5.97, pK(a2) = 7.47), Pt(amp) (pK(a1) = 5.82, pK(a2) = 6.83), Pt(bpy) (pK(a1) = 4.80, pK(a2) = 6.32) show a decrease in the order Pt(dach) > Pt(en) > Pt(amp) > Pt(bpy). The substitution of both coordinated water molecules by a series of nucleophiles (viz., thiourea (tu), L-methionine (L-Met), and guanosine-5'-monophosphate (5'GMP-) was investigated under pseudo-first-order conditions as a function of concentration, temperature, and pressure using UV-vis spectrophotometric and stopped-flow techniques and was found to occur in two subsequent reaction steps. The following k1 values for Pt(dach), Pt(en), Pt(amp), and Pt(bpy) were found: tu (25 degrees C, M(-1) s(-1)) 21 +/- 1, 34.0 +/- 0.4, 233 +/- 5, 5081 +/- 275; L-Met (25 degrees C) 0.85 +/- 0.01, 0.70 +/- 0.03, 2.15 +/- 0.05, 21.8 +/- 0.6; 5'GMP- (40 degrees C) 5.8 +/- 0.2, 3.9 +/- 0.1, 12.5 +/- 0.5, 24.4 +/- 0.3. The results for k2 for Pt(dach), Pt(en), Pt(amp), and Pt(bpy) are as follows: tu (25 degrees C, M(-1) s(-1)) 11.5 +/- 0.5, 10.2 +/- 0.2, 38 +/- 1, 1119 +/- 22; L-Met (25 degrees C, s(-1)) 2.5 +/- 0.1, 2.0 +/- 0.2, 1.2 +/- 0.3, 290 +/- 4; 5'GMP- (40 degrees C, M(-1) s(-1)) 0.21 +/- 0.02, 0.38 +/- 0.02, 0.97 +/- 0.02, 24 +/- 1. The activation parameters for all reactions suggest an associative substitution mechanism. The pK(a) values and substitution rates of the complexes studied can be tuned through the nature of the N-N chelate, which is important in the development of new active compounds for cancer therapy.