Magnetic order in Y6(57Fe:Mn)23H26

The ferrimagnetic compound Y₆Mn₂₃ and its hydride Y₆Mn₂₃H₂₆, both doped with 0.5%⁵⁷Fe, have been investigated using the ⁵⁷Fe Mössbauer resonance and dc field magnetization measurements. For the hydride a small ⁵⁷Fe magnetic hyperfine field is observed to increase abruptly below 110 K whereas the bulk magnetization results suggest antiferromagnetic ordering at T_N≈ 180 K.     

Polarization-dependent EXAFS in bromine-doped polyacetylene

The local dopant structure was investigated in stretch-oriented (CHBr_y)_x at 77 K by polarization dependent EXAFS measurements at the Br-K edge. Definite nn Br-C and Br-Br distances are derived and nnn distances are tentatively assigned. The data clearly show that a large portion of Br intercalates in form of linear Br^-₃ (or longer Br^-_2n+1) molecules with the molecular axis parallel to the (CH)_x chains. Two models for the local dopant structure are proposed and discussed on the basis of other experimental results.     

Mössbauer determination of the E2/M1 mixing ratio of the 77 keV transition in197Au and of the sign of the electric field gradient in KAu(CN)2

A Mössbauer measurement of the E2/M1 mixing ratio of the 77 KeV transition in¹⁹⁷Au yielded δ=?0.352±0.005. With this result, Mössbauer absorption spectra of KAu(CN)₂ single crystals show that the electric field gradient at¹⁹⁷Au in this compound is negative. This implies that the field gradient is mainly produced by 6p_z electrons. The data also indicate a large vibrational anisotropy of Au in KAu(CN)₂.     

Dimerization of merocyanine dyes. Structural and energetic characterization of dipolar dye aggregates and implications for nonlinear optical materials

Aggregation of polar merocyanine dyes has been identified as an important problem in the fabrication of organic materials for photonic applications. In this work, a series of merocyanine dyes is synthesized, and their aggregation is investigated by a combination of several experimental techniques to reveal structure-property relationships. These studies provide clear evidence for the formation of centrosymmetric dimers for all investigated merocyanines in concentrated solution and in the solid state. The thermodynamics of dimerization in liquid solution is studied by concentration-dependent permittivity measurements, UV-vis spectroscopy, and electrooptical absorption experiments. A centrosymmetric dimer structure with antiparallel ordering of the dipole moments is observed in solution by 2D NMR spectroscopy as well as in the solid state by X-ray crystallography and interpreted in terms of dipolar and pi-pi interactions. The optical properties of the dimer aggregates are satisfactorily explained by an excitonic coupling model. The effect of an external electric field on the dimerization equilibrium is considered and quantitatively determined by electrooptical absorption measurements. Implications of the observed findings on the design of nonlinear optical and photorefractive materials are discussed.     

Effect of pressure on the M?ssbauer isomer shift and quadrupole splitting in Au(I)-cyanides

The effect of pressure on the Mössbauer isomer shift and quadrupole splitting was studied with the 77 keV resonance of¹⁹⁷Au in the Au(I)-cyanides AuCN and KAu(CN)₂ at 4.2 K under pressures up to 80 kbar. We observe an increase of the electron density and a decrease of the absolute value of the electric field gradient at the Au nuclei in both compounds with pressure. This variation is different from the correlation that has been established for these parameters within the chemical series of Au(I) compounds at ambient pressure. It indicates that the-bonding increases strongly under pressure. X-ray diffraction studies on AuCN under pressures up to 115 kbar together with investigations of the Goldanskii-Karyagin-effect on AuCN at ambient pressure support the previous assumption that the sign of the electric field gradient at the Au(I) sites is negative.     

Binding constant determination of high-affinity protein-ligand complexes by electrospray ionization mass spectrometry and ligand competition

We describe an approach for the determination of binding constants for protein-ligand complexes with electrospray ionization mass spectrometry, based on the observation of unbound ligands competing for binding to a protein target. For the first time, dissociation constants lower than picomolar could be determined with good accuracy by electrospray ionization mass spectrometry. The presented methodology relies only on the determination of signal intensity ratios for free ligands in the low mass region. Therefore, all the advantages of measuring low masses with mass spectrometry, such as high resolution are preserved. By using a reference ligand with known binding affinity, the affinity of a second ligand can be determined. Since no noncovalently bound species are observed, assumptions about response factors are not necessary. The method is validated with ligands binding to avidin and applied to ligands binding to p38 mitogen-activated protein kinase.     

Crystalline-electric field interactions in DyBa2Cu3O7−δ and TmBa2Cu3O7−δ from161Dy- and169Tm-Mössbauer spectroscopy

¹⁶¹Dy- and¹⁶⁹Tm-Mössbauer spectroscopy is employed to measure the temperature dependence of the electric quadrupole interaction at the rare earth nucleus in orthorhombic and tetragonal phases of DyBa₂Cu₃O_7?δ and TmBa₂Cu₃O_7?δ. Analyses of the quadrupole splittings in terms of the crystalline-electric field parametersB _n ^m are compared with available data from inelastic neutron scattering and¹⁵⁵Gd-Mössbauer measurements.     

The toughening transition in hair keratin

In a recent paper, Milczarek et al. [1] describe the observation of a toughening transition in keratin by DSC. On the basis of their results it is shown that the hypothesis of the existence of this transition is based on the misinterpretation of the evaporation peak of residual water, still present in keratin fibers after mild drying procedures.