Stoffwechselprodukte von Mikroorganismen. 218. Mitteilung. Versuche zur Strukturaufklärung von Niphimycin, 1. Teil. Reinigung und Charakterisierung der Niphimycine Iα und Iβ sowie Abbau mit Salpetersäure

On the Structure Elucidation of Niphimycin, Part I. Purification and Characterization of the Niphimycins Iα and Ib?; Degradation by Nitric Acid From a sample of niphimycin the pure components, niphimycin Iα and Ib?, were isolated by column chromatography and droplet counter-current chromatography. They were characterized by UV., IR., ¹H-NMR. (300 MHz) and ¹³C-NMR. spectra. A vigorous degradation of niphimycin with nitric acid, followed by esterification with diazomethane, gave a complex mixture, from which many components could be isolated and identified. Several of the degradation products were synthesized, one of them (dimethyl 2,4-dimethyladipate) in a stereospecific manner, establishing the configuration of two of the centers of chirality of niphimycin. Niphithricin was identified with copiamycin and yielded with nitric acid a degradation mixture very similar to that from niphimycin. The structures of the degradation products are in good agreement with a macrolide-type structure of niphimycin and copiamycin. Further work for structure elucidation of niphimycin and copiamycin is in progress.     

Orientation of benzene in supersonic expansions, probed by IR-laser absorption and by molecular beam scattering

This work represents the first experimental demonstration that planar molecules tend to travel as a "frisbee" when a gaseous mixture with lighter carriers expands into a vacuum, the orientation being due to collisions. The molecule is benzene, the prototype of aromatic chemistry. The demonstration is via two complementary experiments: interrogating benzene by IR-laser light and controlling its orientation by selective scattering on rare gas targets. The results cast new light on the microscopic mechanisms of collisional alignment and suggest a useful way to produce intense beams of aligned molecules, permitting studies of steric effects in gas-phase processes and in surface catalysis.     

Neutron scattering length of terbium structure refinement and magnetic moments of terbium iron garnet

The neutron scattering length of terbium was redetermined from powder data on terbium iron garnet (TbIG) and TbO₂ by the profile analysis technique. The mean value obtained is b (Tb) = 0.735(10) x 10^?12cm. Furthermore the positional and thermal parameters of TbIG have been refined from single crystal X-ray and neutron powder data. The results from both experiments agree well. The X-ray data from a sphere of diameter φ = 282μm were collected by MoKα radiation. The refinement was carried out including an extinction parameter which was also applied to correct for anomalous transmission. The powder data were treated by the profile analysis technique where the structural parameters and the magnetic moments were refined simultaneously. Two slightly different form factor curves were applied for Fe³⁺ in the crystallographic sites. The magnetic moments for the iron ions were found to be μ = 3.69(10)μ_B for the octahedral and 3.65(10)μ_B for the tetrahedral site at room temperature. The moment for terbium is μ = 1.15(09)μ_B and the whole magnetisation for one formula unit is 0.12(0.40)μ_B. The observed moments of Fe³⁺ are considerably reduced as compared to the free ion spin only value which was calculated from a Brillouin function for $\text{S =}\text{5}\text{2}$ to be 4.34μ_Bat 300 K.     

The Conway-Kochen Argument and Relativistic GRW Models

In a recent paper, Conway and Kochen proposed what is now known as the “Free Will theorem” which, among other things, should prove the impossibility of combining GRW models with special relativity, i.e., of formulating relativistically invariant models of spontaneous wavefunction collapse. Since their argument basically amounts to a non-locality proof for any theory aiming at reproducing quantum correlations, and since it was clear since very a long time that any relativistic collapse model must be non-local in some way, we discuss why the theorem of Conway and Kochen does not affect the program of formulating relativistic GRW models.     

Phantom validation and in vivo application of an inversion procedure for retrieving the optical properties of diffusive layered media from time-resolved reflectance measurements

An experimental validation of an inversion procedure for retrieving the optical properties of layered media from multidistance time-resolved reflectance measurements is presented. The results cover a wide range of optical properties, showing excellent effectiveness and reliability of the procedure in reconstructing the optical properties of a two-layered medium. The optical properties of the first layer and the absorption of the second layer could be retrieved with excellent precision, whereas the reduced scattering coefficient of the second layer was reconstructed with a large error. The first layer thickness could be retrieved with an error less than 50%. An example of retrieval of the optical properties of muscle from in vivo measurements during an arterial occlusion is shown.     

Polymerization of Methacrylamide Initiated by Ceric Ion-Citric Acid Redox System

Homogeneous polymerization of methacrylamide initiated by the ceric ammonium sulfate-citric acid (CA) redox pair has been investigated and reported at 35 ± 0.2°C under nitrogen atmosphere. The initiation was caused by the free radical generated by the decomposition of the complex formed between ceric ion and citric acid. The rate of monomer disappearance was found to be proportional to [CA]^0.4, [Ce^0.4+]^0.65, and [Monomer]¹ The rate of ceric ion disappearance was directly proportional to the ceric ion concentration but independent of the monomer concentration. The initial rate was independent of [H₂SO₄]. The activation energy of the system was found to be 21.4 kJ/mol.     

On the flexibility of agglomeration based physical space discontinuous Galerkin discretizations

In this work we show that the flexibility of the discontinuous Galerkin (dG) discretization can be fruitfully exploited to implement numerical solution strategies based on the use of elements with very general shapes. Thanks to the freedom in defining the mesh topology, we propose a new h-adaptive technique based on agglomeration coarsening of a fine mesh. The possibility to enhance the error distribution over the computational domain is investigated on a Poisson problem with the goal of obtaining a mesh independent discretization.The main building block of our dG method consists of defining discrete polynomial spaces directly on physical frame elements. For this purpose we orthonormalize with respect to the L²-product a set of monomials relocated in a specific element frame and we introduce an easy way to reduce the cost related to numerical integration on agglomerated meshes. To complete the dG formulation for second order problems, two extensions of the BR2 scheme to arbitrary polyhedral grids, including an estimate of the stabilization parameter ensuring the coercivity property, are here proposed.     

A continuum thermodynamical approach to electrochemical systems

This work focuses on formulating constitutive models for the bulk and double layer regions of an electrochemical system based on the fundamentals of modern continuum thermodynamics. Particularly, the constitutive models proposed accounting for transport phenomena in electrochemical systems by emphasizing the possibility of cross-coupling between two or more phenomena. Upon deriving a set of thermodynamic restrictions from the Müller-Liu approach of the second law of thermodynamics and axioms of constitutive theory, non-equilibrium quantities are examined in detail, and constitutive answers of the bulk and double layer regions are discussed. Moreover, the conditions for the thermodynamic equilibrium are evaluated for each region as well as the occurrence of dissipative mechanisms. Besides offering a proper formulation for non-equilibrium electrochemical systems, the approach described in this work can be easily extended to more complex chemical systems.     

Mössbauer effect studies on alkali tris (malonato) ferrates(III)

Mössbauer spectra of alkali tris(malonato) ferrates(III) i.e. M₃[Fe(C₃H₂O₄)₃].4H₂O(M=Li, Na, K, NH₄) at 298±2K display a single broad absorption band due to spin lattice relaxation effect. The isomer shift values indicate these complexes to be high spin with octahedral symmetry. The isomer shift shows a decreasing trend with the increase in electronegativity/polarizing power of the substituent cation (Li⁺, Na⁺, K⁺, NH₄ ⁺). A linear correlation between isomer shift values and the (Fe-O) stretching freguencies has also been observed.