A. Schrimpf

Thermally stimulated luminescence and conductivity of doped Ar solids

Solid Ar samples doped with the noble metal atoms Au or Ag as well as with molecules have been exposed to synchrotron and x-ray irradiation. Impurity trapping of excitons generated by the irradiation partly led to an ionization; the impurities formed deep traps for one type of charge carrier, the complementary ones were promoted into band states and subsequently captured into shallow traps. These charge carriers could be thermally released giving rise to thermally stimulated luminescence (TSL) and conductivity (TSC) signals, which were recorded simultaneously. The glow curves of both, TSL and TSC, clearly revealed the existence of intrinsic and extrinsic electron traps. Using a step-like temperature increase it could be demonstrated that traps exist with a broad distribution of binding energies. A first-order kinetics model was developed to extract binding energies from the temperature dependence of the thermally stimulated luminescence.

Thermally activated processes in Li doped Ar matrices studied by electronic spin-lattice relaxation

Optical absorption and ESR spectra were taken simultaneously of Li doped Ar matrices. The measurements showed that the broad absorption near the free atom D1, D2 transitions is in reality a superposition of two spectra, the so‐called blue and red triplet, well known from other alkali rare gas systems. Both triplets could be correlated with corresponding ESR spectra. Longitudinal and transversal electronic relaxation times T1 and T2 were determined by carefully analyzing the saturation of the ESR signal amplitudes and the line broadening. The temperature dependence of T1 and T2 suggests that the relaxation is caused by thermally activated local structural changes with an extremely low activation enthalpy of the order of 1 meV. Similar results were obtained in K, Ag, and Au doped Ar matrices.

On the ESR spectra and bonding of lithium complexes of acetylene, ethylene and benzene: a matrix isolation study

Abstract Electron spin resonance (ESR) and optical absorption spectra of 6LiC2H2, 7LiC2H2, 7LiC2H4, 7LiC2D4, 6LiC2D4, LiC6H6 and LiC6D6 complexes embedded in solid argon have been measured at low temperature. Lithium—acetylene and lithium—ethylene complexes exhibit hyperfine structures due to both lithium and equivalent hydrogen nuclear spins. g tensors, alkali-metal atom and proton hyperfine coupling tensors were determined with help of computer simulation of the powder spectra. It is shown that both these complexes have a 2B2 ground state thus correlating with the Li2P atomic state. The polyligand Li(C2H4)2 and Li(C2H4)3 complexes have also been observed and their ESR spectra are consistent with D2h and D3h symmetry structures. In contrast, LiC6H6 presents no lithium hyperfine structure but a hyperfine splitting of unequivalent hydrogen spins. This confirms that LiC6H6 has lost the six-fold symmetry of the benzene ring resulting from the complete or near complete transfer of the lithium valence electron into one of the formerly degenerate unoccupied molecular orbitals of benzene, and has C2v symmetry.

Correlation of electron spin resonance and optical absorption of K atoms in solid Ar

Electron spin resonance (ESR) and optical absorption spectra of K atoms embedded in Ar matrices have been measured simultaneously. ESR and optical spectra could be correlated comparing the effects of annealing and light induced site modifications. Electron spin relaxation times were estimated by saturation measurements. A large variety of ESR spectra was found which could be arranged into four groups according to their A and g factor matrix shifts. Two of these groups could be correlated with optical absorptions namely with the so-called red and blue triplet bands. The other two groups belong to K-(H2O)n complexes. Part of the absorption disappeared irreversibly upon annealing at about 12 K. There is considerable experimental evidence that this annealing process indicates the transition from an amorphous to a microcrystalline structure at about 12 K.

Two opposing D-amino acids give zigzag hairpin epitopes an additional kink to create antibody selective peptide antigens.

We have developed peptides that are able to distinguish between subgroups of polyclonal antibodies. These β‐hairpin peptides act as conformational epitopes with specific shape and flexibility; they have been analyzed by NMR and CD spectroscopy, and have been shown to identify known disease markers. As a standalone mini β‐sheet, a hairpin is stabilized by alternating pairs of hydrogen‐bonded and non‐bonded amino acids on its two opposing peptide strands. A single d mutation disrupts this secondary structure, the correlated double‐d mutation of two opposing amino acids compensates for this destabilizing effect. The designed kink was introduced into both hydrogen‐bonded and ‐non‐bonded positions of an all‐l hairpin that is a known conformational epitope in molecular recognition. Our peptides enabled the discrimination of different human rheumatoid arthritis autoantibodies in an ELISA assay.

An international campaign of the 19th century to determine the solar parallax - The US Naval expedition to the southern hemisphere 1849–1852

AbstractnIn 1847 Christian Ludwig Gerling, Marburg (Germany), suggested the solar parallax to bendetermined by measuring the position of Venus close to its inferior conjunction,nespecially at the stationary points, from observatories on nearly the same meridian butnwidely differing in latitude. James M. Gilliss, astronomer at the newly founded U.S. NavalnObservatory, enthusiastically adopted this idea and procured a grant for the youngnastronomical community of the United States for an expedition to Chile. There they were tonobserve several conjunctions of Venus and oppositions of Mars, while the accompanyingnmeasurements were to be taken at the US Naval Observatory in Washington D.C. and thenHarvard College Observatory at Cambridge, USA. This expedition was supported by A.V.nHumboldt, C.F. Gauß, J.F. Encke, S.C. Walker, A.D. Bache, B. Peirce and others. From 1849nto 1852 not only were astronomical, but also meteorological and magnetic observations andnmeasurements recorded, mainly in Santa Lucia close to Santiago, Chile. By comparing thesenmeasurements with those taken simultaneously at other observatories around the world thensolar parallax could be calculated, although incomplete data from the correspondingnnorthern observatories threatened the project’s success. In retrospect this expedition cannbe recognized as the foundation of the Chilean astronomy. The first director of the newnNational Astronomical Observatory of Chile was Dr. C.W. Moesta, a Hessian student ofnChristian Ludwig Gerling’s. The exchange of data between German, American and othernastronomers during this expedition was well mediated by J.G. Flügel, consul of the UnitednStates of America and representative of the Smithsonian Institution in Europe, whonaltogether played a major role in nurturing the relationship between the growingnscientific community in the U.S. and the well established one in Europe at that time.n

Site modification of K atoms in solid Ar by X-ray and light irradiation

The influence of X-ray irradiation on the optical absorption of K-atoms in Ar-matrices was studied as a function of time and temperature. Exponential decrease of the so-called red and blue triplet absorptions was observed. Simultaneously a new absorption in the range of the red triplet was built up. The new absorption could alternatively be produced by light irradiation into the red or the blue triplet, as was shown in a second experiment studying correlated optical and ESR-absorption. After annealing at 15 K the new absorption disappeared, and the original absorptions were largely restored. All experimental results can well be understood in terms of exciton production, self-trapping, and deexcitation, and are described by a master equation system.

Simultaneous ESR and optical absorption measurements of K in solid Ar

Abstract An apparatus was developed for simulataneous electron spin resonance (ESR) and optical absorption experiments on atoms imbedded in rare gas matrices. In a first application the temperature dependence of ESR signals and of optical absorption spectra of K atoms in Ar matrices were studied. One of the numerous ESR lines could be unambiguously assigned to the so-called red triplet absorption due to their identical annealing behaviour at 12–14 K. The correspondence of other ESR lines to optical absorptions is discussed.

Excitonic energy transfer in Au doped and undoped Kr solids

Abstract Excitons were produced in Au doped and undoped Kr by VUV irradiation. The dependence of exciton self-trapping as well as trapping (at the Au atoms) on excitation energy and sample temperature has been studied via fluorescence yield spectroscopy. An exciton diffusion model describes the measured spectra quantitatively.

A set of conformationally well-defined L/D-peptide epitopes provides a serological bar code for autoantibody subtypes

Which conformational parameters lead to an antibody-affine peptide antigen? And in how many different conformations can we actually present the respective conformational epitope? To provide answers from a chemical point of view, we direct the bending and tethering of peptide backbones by the utilisation of a hydrophobic cluster, disulfides, and d-amino acids. Each mutation is employed pairwise on directly opposite sides of a β-hairpin. In combination, these synthetic modules guide the formation of complementary β-sheet-like structures, whereby the oppositely configured (l/d-)bi-disulfide pairs form with high regioselectivity. The conformational properties of the peptides are assessed by NMR spectroscopy and correlated with their antibody affinity in ELISA. From a pool of thus designed peptide antigens with distinctive complementary affinities against known rheumatoid arthritis (RA) autoantibodies, we select a set of epitopes for an immunoassay with sera of RA patients. We want to put emphasis on the idea, that the different conformational properties of the chosen antigens, containing the same epitope sequence, are mirrored in the distribution of autoantibody subtypes (or of the antibody polyclonality, respectively). Such directly comparable information can only be delivered by a set of peptides, rather than a single one. The hairpin-restriction technology of l/d-configured bi-disulfide amino acid pairs is not limited to RA but applicable to other shape-persistent hairpin motifs which are supposed to identify subgroups of protein receptors.