Multi-angle in situ dynamic light scattering at a neutron spin echo spectrometer

A new sample environment, called Bio-Oven, has been built for the Neutron Spin Echo (NSE) Spectrometer J-NSE Phoenix. It provides active temperature control and the possibility to perform Dynamic Light Scattering (DLS) measurements during the neutron measurement. DLS provides diffusion coefficients of the dissolved nanoparticles, and thus one can monitor the aggregation state of the sample on a time scale of minutes during the spin echo measurement times on the order of days. This approach helps to validate the NSE data or to replace the sample when its aggregation state influences the spin echo measurement results. The new Bio-Oven is an in situ DLS setup based on optical fibers decoupling the free space optics around the sample cuvette in a lightproof casing from the laser sources and the detectors. It collects light from three scattering angles simultaneously. Six different values of momentum transfer can be accessed by switching between two different laser colors. Test experiments were performed with silica nanoparticles with diameters ranging from 20 nm up to 300 nm. Their hydrodynamic radii were determined from DLS measurements and compared with the ones obtained by a commercial particle sizer. It was demonstrated that also the static light scattering signal can be processed and gives meaningful results. The protein sample apomyoglobin was used for a long-term test and in a first neutron measurement using the new Bio-Oven. The results prove that the aggregation state of the sample can be followed using in situ DLS along with the neutron measurement.

Uniaxial Pressure Dependence of Magnetic Order in MnSi

We report comprehensive small angle neutron scattering measurements complemented by ac susceptibility data of the helical order, conical phase, and Skyrmion lattice phase (SLP) in MnSi under uniaxial pressures. For all crystallographic orientations uniaxial pressure favors the phase for which a spatial modulation of the magnetization is closest to the pressure axis. Uniaxial pressures as low as 1 kbar applied perpendicular to the magnetic field axis enhance the Skyrmion lattice phase substantially, whereas the Skyrmion lattice phase is suppressed for pressure parallel to the field. Taken together we present quantitative microscopic information on how strain couples to magnetic order in the chiral magnet MnSi.

Band Structure of Helimagnons in MnSi Resolved by Inelastic Neutron Scattering

A magnetic helix realizes a one-dimensional magnetic crystal with a period given by the pitch length λh. Its spin-wave excitations-the helimagnons-experience Bragg scattering off this periodicity, leading to gaps in the spectrum that inhibit their propagation along the pitch direction. Using high-resolution inelastic neutron scattering, the resulting band structure of helimagnons was resolved by preparing a single crystal of MnSi in a single magnetic-helix domain. At least five helimagnon bands could be identified that cover the crossover from flat bands at low energies with helimagnons basically localized along the pitch direction to dispersing bands at higher energies. In the low-energy limit, we find the helimagnon spectrum to be determined by a universal, parameter-free theory. Taking into account corrections to this low-energy theory, quantitative agreement is obtained in the entire energy range studied with the help of a single fitting parameter.

Long-wavelength helimagnetic order and skyrmion lattice phase in Cu2OSeO3

We report a long-wavelength helimagnetic superstructure in bulk samples of the ferrimagnetic insulator Cu2OSeO3. The magnetic phase diagram associated with the helimagnetic modulation inferred from small-angle neutron scattering and magnetization measurements includes a skyrmion lattice phase and is strongly reminiscent of MnSi, FeGe, and Fe(1-x)Co(x)Si, i.e., binary isostructural siblings of Cu2OSeO3 that order helimagnetically. The temperature dependence of the specific heat of Cu2OSeO3 is characteristic of nearly critical spin fluctuations at the helimagnetic transition. This provides putative evidence for effective spin currents as the origin of enhancements of the magnetodielectric response instead of atomic displacements considered so far.

The myelin basic protein-specific T cell repertoire in (transgenic) Lewis rat/SCID mouse chimeras: preferential V beta 8.2 T cell receptor usage depends on an intact Lewis thymic microenvironment

In the Lewis rat, myelin basic protein (MBP)-specific, encephalitogenic T cells preferentially recognize sequence 68-88, and use the V beta 8.2 gene to encode their T cell receptors. To analyze the structural prerequisites for the development of the MBP-specific T cell repertoire, we reconstituted severe-combined immunodeficient (SCID) mice with fetal (embryonic day 15-16) Lewis rat lymphoid tissue, and then isolated MBP-specific T cell lines from the adult chimeras after immunization. Two types of chimera were constructed: SCID mice reconstituted with rat fetal liver cells only, allowing T cell maturation within a chimeric SCID thymus consisting of mouse thymic epithelium and rat interdigitating dendritic cells, and SCID mice reconstituted with rat fetal liver cells and rat fetal thymus grafts, allowing T cell maturation within the chimeric SCID and the intact Lewis rat thymic microenvironment. Without exception, the T cell lines isolated from MBP-immunized SCID chimeras were restricted by MHC class II of the Lewis rat (RT1.B1), and none by I-Ad of the SCID mouse. Most of the T cell lines recognized the immunodominant MBP epitope 68-88. In striking contrast to intact Lewis rats, in SCID mice reconstituted by rat fetal liver only, MBP-specific T cell clones used a seemingly random repertoire of V beta genes without a bias for V beta 8.2. In chimeras containing fetal Lewis liver plus fetal thymus grafted under the kidney capsule, however, dominant utilization of V beta 8.2 was restored. The migration of liver-derived stem cells through rat thymus grafts was documented by combining fetal tissues from wild-type and transgenic Lewis rats. The results confirm that the recognition of the immunodominant epitope 68-88 by MBP-specific encephalitogenic T cells is a genetically determined feature of the Lewis rat T cell repertoire. They further suggest that the formation of the repertoire requires T cell differentiation in a syngeneic thymic microenvironment.

[Pachydermoperiostosis]

Pachydermoperiostosis (Friedreich-Erb-Arnold syndrome, Touraine-Solente-Golé syndrome) is a rare disease with an autosomal dominant mode of inheritance; it occurs almost exclusively in men. A report of typical pachydermoperiostosis in a 31-year-old man is presented. Associated features were clubbed digits of the hands and feet with watch-crystal nails, thickening of the skin and soft tissues, hyperhidrosis of hands and feet, hyperplasia of the sebaceous glands with seborrhoea, gynaecomastia, and ophthalmic abnormalities that had been present since puberty. Radiological examination revealed periosteal hyperostosis of the short and long bones. Endocrine disturbances were not detected. Skin biopsies showed hypertrophy of the skin and skin appendages. Primary (idiopathic, hereditary) pachydermoperiostosis should be distinguished from secondary (symptomatic) forms of the disease, which are often associated with lung tumours.

Dibenzo[a,g]quinolizin-8-ones: synthesis, estrogen receptor affinities, and cytostatic activity

A number of acetoxy-substituted dibenzo[a,g]quinolizin-8-ones were synthesized by the reaction of 1-oxoisoquinolines with substituted homophthalic acid anhydride. All of the derivatives with acetoxy groups in positions 3 and 10 bind to the estrogen receptor. Relative binding affinities (RBA) ranged from 1.8 to 5.6 (estradiol: RBA = 100) when the substituent at C-6 was a short alkyl group. Introduction of additional oxygen functions in the 2- and/or 11-position decreased binding affinities. Analyses of the enantiomers of 6-methyl (6b) and 6-ethyl (6c) derivatives revealed that the receptor binding is mainly due to one optical isomer (e.g. (-)-6b, 9.9; (+)-6b, 0.6). In hormone-sensitive human MCF-7 breast cancer cells, compounds with one acetoxy group in each aromatic ring strongly inhibited cellular growth. Despite marked differences in receptor affinity, the enantiomers displayed similar activities in this cell culture. In hormone-independent MDA-MB 231 mammary tumor cells, only a weak cytostatic effect was recorded at 10(-5) M. In the immature mouse uterine weight test, minimal estrogenic activity was observed. At higher doses, a significant anti-estrogenic effect became evident. It is assumed that the estrogen antagonism is responsible for the specific cytostatic effect in MCF-7 breast cancer cells.

6-Alkyl-12-formylindolo[2,1-a]isoquinolines. Syntheses, estrogen receptor binding affinities, and stereospecific cytostatic activity

A number of 6-alkyl-12-formyl-5,6-dihydroindolol[2,1-a]isoquinolines were synthesized by the Bischler-Napieralski reaction from the respective 1-alkyl-2-(3-methoxyphenyl)ethylamines and bromo-substituted (methoxyphenyl)acetic acid chlorides followed by a second ring closure reaction involving a base-generated benzyne intermediate. The methoxy functions in positions 3 and 9 or 10 were cleaved with BBr3 and the free hydroxy groups converted into the acetates. The enantiomers of the most potent derivatives were separated by liquid chromatography on triacetylcellulose. All of the compounds tested bind to the calf uterine estrogen receptor. The relative binding affinities (RBA) ranged from 0.5 to 3.9 (17 beta-estradiol: RBA = 100) and were dependent on the position of the oxygen function in the indole moiety. The 3,10-diacetoxy derivatives showed higher RBA values than the corresponding 3,9-substituted tetracycles. There was no major difference in binding affinity between (+)- and (-)-enantiomers. Computer-assisted molecular modeling studies showed that the chiral carbon atom 6 of the indoloisoquinoline is likely to mimic the C-11 atom of estradiol. In the mouse uterine weight test, only the 3,10-diacetoxy series exhibited weak estrogenic activity at higher doses. The antiestrogenic effects found with all the compounds varied considerably. Maximum inhibition of estrone-stimulated uterine growth was found for the ethyl derivative 7d (80% with 250 micrograms/animal per day). All derivatives strongly inhibited the growth of human breast cancer cells in vitro. There was no significant difference between hormone-sensitive MCF-7 cells and hormone-independent MDA-MB 231 cells. Cytostatic activity was higher for the 3,9-substituted indoloisoquinolines than for the 3,10-analogues and dependent on the length of the alkyl group at C-6. The maximum effect was found with the butyl derivative 7g. When the enantiomers of the ethyl (7c), propyl (7e), and butyl derivative were studied, a strong difference in activity was observed between the stereoisomers. The IC50 values of the (+)-forms were usually only a tenth of those of the levorotatory isomers. Maximum cytostatic activity was found with (+)-7g: 85% inhibition at 1 x 10(-7) M in MCF-7 cells and 94% inhibition at 2.5 x 10(-7) M in MDA-MB 231 cells. This stereospecificity indicates a selective action on a biochemical target. Since no interaction with DNA was observed, the precise mode of action still remains to be elucidated.