Large electron polarization of H-like20Ne-ions traversing gd foils at very high velocities

It is shown that transient magnetic fields in Gd-host for²⁰Ne ions at a mean velocity of 12.5v₀(v₀=c/137), considerably beyond the Bohr velocity of 1s electrons of Ne ions (v_1s=10v₀), are dominated by the Fermi contact field of these electrons. The first excited 2⁺-state of²Ne was used as probe. The derived value for the mean degree of polarization p_1s=0.32(13), is surprisingly large, though still consistent with values obtained at lower velocities. Present calculations of spin exchange cross sections severely underestimate the observed polarization at this high velocity.The authors are grateful to the operating staff of the UNILAC for providing excellent beam conditions. They also thank Dr. P. Maier-Komor for preparing the delicate targets. Support by the BMFT is acknowledged.     

Darstellung,Ramanspektren und Kristallstrukturen von V2O3(SO4)2, K[VO(SO4)2] und NH4[VO(SO4)2]

Preparation, Raman Spectra, and Crystal Structures of V₂O₃(SO₄)₂, K[VO(SO₄)₂], and NH₄[VO(SO₄)₂] The oxo-sulfato-vanadates(V) V₂O₃(SO₄)₂, K[VO(SO₄)₂], and NH₄[VO(SO₄)₂] have been prepared as crystals suitable for X-ray structure determination. In all structures sulfate acts as an unidentate ligand only toward a single vanadium atom. The structure of V₂O₃(SO₄)₂ consists of a threedimensional network of pairs of cornershared VO₆ octahedra with one terminal oxygen atom each, and SO₄ tetrahedra. All oxygen atoms of the sulfate ions are coordinated. NH₄[VO(SO₄)₂] and K[VO(SO₄)₂] are isostructural. VO₆ octahedra with one terminal oxygen atom and pairs of sulfate tetrahedra form infinite chains by corner sharing. The chains are weakly interlinked to layers. The sulfate ions are distorted towards planar SO₃ molecules and single oxygen atoms attached to vanadium. This structural detail gives an explanation for the mechanism of the reversible reaction K[VO(SO₄)₂] ? K[VO₂(SO₄)] + SO₃ at 400°C. Raman spectra of the compounds have been recorded and interpreted with respect to their structures. Crystal data: V₂O₃(SO₄)₂, monoclinic, space group P2₁/a, a = 947.2(4), b = 891.3(3), c? 989.1(4) pm, β = 104.56(3)°, Z = 4, 878 unique data, R(R_w) = 0.039(0,033); K[VO(SO₄)₂], orthorhombic, space group P2₁2₁2₁, a = 495.3(2), b = 869.6(9), c = 1 627(1)pm, Z = 4, 642 unique data, R(R_w) = 0,11(0,10); NH₄[VO(SO₄)₂], orthorhombic, space group P2₁2₁2₁, a = 495.3(1), b = 870.0(2), c = 1 676.7(4)pm, Z = 4, 768 unique data, R(R_w) = 0.088(0.083).     

Rheology of gelling polymers in the Zimm model

In order to study rheological properties of gelling systems in dilute solution, we investigate the viscosity and the normal stresses in the Zimm model [B. H. Zimm, J. Chem. Phys. 24, 269 (1956)]. for randomly cross-linked monomers. The distribution of cluster topologies and sizes is assumed to be given either by Erdos-Renyi random graphs or three-dimensional bond percolation. Within this model the critical behavior of the viscosity and of the first normal stress coefficient is determined by the power-law scaling of their averages over clusters of a given size n with n. We investigate these scaling relations numerically and conclude that the scaling exponents are independent of the hydrodynamic interaction strength. The numerically determined exponents agree well with experimental data for branched polymers. However, we show that this traditional model of polymer physics is not able to yield a critical divergence at the gel point of the viscosity for a polydisperse dilute solution of gelation clusters. A generally accepted scaling relation for the Zimm exponent of the viscosity is thereby disproved.     

Investigation of the Chemo- and Stereoselectivity of the Ketene-Claisen Rearrangement

A novel type of ketene-Claisen rearrangement in which the precursor of the rearrangement is generated in situ by reaction of optically active allyl thioethers with dichloroketene is described. A characteristic feature of this rearrangement is the excellent chemoselectivity in favor of allyl thioethers vs. allyl ethers, i.e., exclusive chirality transfer of the allylic sulfur moiety is observed with 12, 13 , and 25--27 . The cyclic, optically active allyl thioethers (+)-(R)- 4 and (?)-(S)- 4 and the open-chain allyl thioethers 11--13 rearrange with in situ generated dichloroketene to the optically active thioesters (?)-(S)- 28 , (+)-(R)- 28 , and 31-33 , respectively. A chirality-transfer of > 99% in the cyclic cases (+)-(R)- 4 and (?)-(S)- 4 , and 96--98 % in the open-chain cases 11--13 is observed. Furthermore, the dichloroketene-Claisen rearrangement is characterized by a high asymmetric 1,2-induction. The chiral allylic sulfides 25--27 give the optically active thioesters 36--38 with a 1,2-induction > 99% as determined by NMR-shift experiments.     

6‐Aza‐2′‐deoxy­uridine and N3‐anisoyl‐6‐aza‐2′‐deoxy­uridine

In 2‐(2‐deoxy‐β‐d ‐erythro‐pentofuranosyl)‐1,2,4‐triazine‐3,5(2H,4H)‐dione (6‐aza‐2′‐deoxy­uridine), C₈H₁₁N₃O₅, (I), the conformation of the glycosylic bond is between anti and high‐anti [χ = −94.0 (3)°], whereas the derivative 2‐(2‐deoxy‐β‐d ‐erythro‐pentofuranosyl)‐N⁴‐(2‐methoxy­benzoyl)‐1,2,4‐triazine‐3,5(2H,4H)‐dione (N³‐anisoyl‐6‐aza‐2′‐deoxy­uridine), C₁₆H₁₇N₃O₇, (II), displays a high‐anti conformation [χ = −86.4 (3)°]. The furanosyl moiety in (I) adopts the S‐type sugar pucker (²T₃), with P = 188.1 (2)° and τ_m = 40.3 (2)°, while the sugar pucker in (II) is N (³T₄), with P = 36.1 (3)° and τ_m = 33.5 (2)°. The crystal structures of (I) and (II) are stabilized by inter­molecular N—H⋯O and O—H⋯O inter­actions.     

Electrospray-Ionization Mass Spectrometry: Detection of a radical cation present in solution: New results on the chemistry of (tetrahydropteridinone)-metal complexes

This paper marks the first reported detection of radical cations by Electrospray-Ionization Mass Spectrometry (ESI-MS). Electron Spin Resonance (ESR) measurements have proven that the detected radical cation existed already in solution and has not been generated by the electrospray ionization technique. However, we observed that the radical cation can be generated by changes in the ionization conditions. A molar mixture of 2-amino-5,6,7,8-tetrahydro-5-methylpterin-4(4H)-one dihydrochloride ( = 5,6,7,8-tetrahydro-N(5)-methylpterin-2 HCl, N(5)-MTHP-2 HCl), and tris(pentane-2,4-dionato)iron(III) in MeCN at pH 2–3 leads to the formation of a [bis(pentane-2,4-dionato)(2-amino-5,6,7,8-tetrahydro-5-methylpteridin-4 (4H)-one)]iron complex ( = [bis(pentane-2,4-dionato) (5,6,7,8-tetrahydro-N(5)-methylpteridin)]iron complex) which can be detected by ESI-MS. The results suggest that this complex might be an Fe^II radical cation, which could possibly be a suitable model complex for the active center of the phenylalanine hydroxylase. In the same solution, the stable radical cation of N(5)-MTHP is identified by ESI-MS and ESR.     

Wasserstoffbrücken in 1,1‐Bis(2‐hydroxyethyl)‐3‐benzoylthioharnstoff und seinen Nickel(II)‐ und Kupfer(II)‐Chelat‐Komplexen

Hydrogen Bonds in 1,1‐Bis(2‐hydroxyethyl)‐3‐benzoylthiourea and its Nickel(II)‐ and Copper(II)‐Chelate Complexes The ligand 1,1‐bis(2‐hydroxyethyl)‐3‐benzoylthiourea HL, ( 1 ), yields with nickel(II) and copper(II) ions neutral complexes [NiL₂], ( 2 ), and [CuL₂], ( 3 ). By X‐ray structure analysis and IR spectroscopy different intramolecular hydrogen bonds (OH…O) and (OH…N) could be identified in both equally coordinated ligands of the [NiL₂] molecule. For comparison X‐ray and IR data were also estimated for 1 and 3 .     

Solvothermal Synthesis and Characterization of the New Iron Thioantimonates(III) [Fe(C6H18N4)]FeSbS4 and [Fe(C4H13N3)2]Fe2Sb4S10 Containing FeII and FeIII and Protein‐Analogous [2FeIII‐2S]2+ Clusters

The two new compounds [Fe(tren)]FeSbS₄ ( 1 ) (tren = tris(2‐aminoethyl)amine) and [Fe(dien)₂]Fe₂Sb₄S₁₀ ( 2 ) (dien = diethylendiamine) were prepared under solvothermal conditions and represent the first thioantimonates(III) with iron cations integrated into the anionic network. In both compounds Fe³⁺ is part of a [2Fe^III‐2S] cluster which is often found in ferredoxines. In addition, Fe²⁺ ions are present which are surrounded by the organic ligands. In ( 1 ) the Fe²⁺ ion is also part of the thioantimonate(III) network whereas in ( 2 ) the Fe²⁺ ion is isolated. In both compounds the primary SbS₃ units are interconnected into one‐dimensional chains. The mixed‐valent character of [Fe(tren)]FeSbS₄ was unambiguously determined with Mössbauer spectroscopy. Both compounds exhibit paramagnetic behaviour and for ( 1 ) a deviation from linearity is observed due to a strong zero‐field splitting. Both compounds decompose in one single step.     

EVIDENCE FOR A MAGNESIUM DEPENDENT ATPase IN BOVINE ROD OUTER SEGMENT DISK MEMBRANES*†

Abstract—In the presence of Mg²⁺ and adenosine triphosphate (ATP), a rapid. light-induced, light-scattering transient is observed from bovine rod outer segments (ROS). This light-scattering transient we have labelled 'A'. Ca²⁺ cannot replace Mg²⁺. nor can guanosine triphosphate (GTP) replace ATP. 'A' is observed at ATP concentrations as low as a few μM.
The half-time of 'A', 60 ms at 20° and 20 ms at 37°, is consistent with a process possibly involved in visual transduction.
'A' has the action spectrum of rhodopsin bleaching and its amplitude is strictly proportional to the fraction of rhodopsin bleached per flash. 'A' can be regenerated by 11- cis retinal.
Inhibition studics with ATP analogues, which cannot be hydrolysed and fail to evoke an 'A' response, reveal that an ATP hydrolysis process has to precede illumination in order for 'A' to occur.
On the basis of the above findings. it is proposed that there is a Mg²⁺ dependent ATPase in ROS that allows the disk membrane to assume a new membrane state which, upon illumination, is altered. giving rise to the structural phenomenon monitored as light-scattering transient 'A'.