A measurement of the electromagnetic form factor of the eta meson and of the branching ratio for the eta Dalitz decay

In an optical spark chamber experiment we have obtained a sample of 80 eta Dalitz decays (η → e⁺e^?γ) and have measured the eta electromagnetic form factor to be F(X) = 1.0?(0.22 ±0.45)X, where X=M_ee²/M_η², and the branching ratio (η→e⁺e^?γ/(η→π⁺π^?π⁰)= (0.0082 ± 0.0020).     

‘Confined coherence’ in strongly correlated anisotropic metals

We present a detailed discussion of both theoretical and experimental evidence in favour of the existence of states of ‘confined coherence’ in metals of sufficiently high anisotropy and with sufficiently strong correlations. The defining property of such a state is that single electron coherence is confined to lower dimensional subspaces (planes or chains) so that it is impossible to observe interference effects between histories which involve electrons moving between these subspaces. The most dramatic experimental manifestation of such a state is the coexistence of incoherent non-metallic transport in one or two directions (transverse to the lower dimensional subspaces) with coherent transport in at least one other direction (within the subspaces). The magnitude of the Fermi surface warping due to transverse (intersubspace) momentum plays the role of an order parameter (in a state of confined coherence, this order parameter vanishes) and the effect can occur in a pure system at zero temperature. Our theoretical approach is to treat an anisotropic two (2D)- or three (3D)-dimensional electronic system as a collection of one (1D)- or two-dimensional electron liquids coupled by weak interliquid single-particle hopping. We find that a necessary condition for the destruction of coherent interliquid transport is that the intraliquid state be a non-Fermi liquid. We present a very detailed discussion of coupled 1D Luttinger liquids and the reasons for believing in the existence of a phase of confined coherence in that model. This provides a paradigm for incoherent transport between weakly coupled 2D non-Fermi liquids, the case relevant to the experiments of which we are aware. Specifically, anomalous transport data in the (normal state of the) cuprate superconductors and in the low temperature metallic state of the highly anisotropic organic conductor (TMTSF)₂PF₆ cannot be understood within a Fermi liquid framework, and, we argue, the only plausible way to understand that transport is in terms of a state of confined coherence.     

Structure of 6α-methyl-17α-hydroxyprogesterone butanoate,C26H38O4

The title compound crystallizes in space groupP2₁2₁2₁ with lattice constantsa=16.253(3),b=17.107(3), andc=8.486(2) Å. The A ring has 1,2-half-chair conformation. The calculated steric energy of a 6-methyl-17-ester progesterone molecule is lower by about 4 kJ/mol for the normal A-ring conformation. The progesterone side chain has typical conformation for 17-ester steroids; the C(16)-C(17)-C(20)-O(20) torsion angle is –24.9(4)°.     

Structure of 3α,12β-dihydroxy-2β-morpholino-5α-pregnan-20-one,C25H41O4N

The crystal and molecular structure of 3,12-dihydroxy-2-morpholino-5-pregnan-20-one, C₂₅H₄₁O₄N, has been determined:M _r =419.6,P2₁,a=13.5778(8),b=14.4340(8),c=5.8943(5) Å,=94.32(1)°,V _c =1151.9(3) ų,Z=2,D _x =1.21 g cm^–3, (CuK) = 1.5418 Å, =5.6 cm^–1,F(000)=460,R=0.039,R _w =0.040 for 2421 unique observed reflections. All six-membered rings have chair conformations, and theD ring has a 13-envelope conformation. The progesterone side chain has an unusual conformation, and the C16-C17-C20-O20 torsion angle, which defines the conformation, is –152.6(3)°. The unusual conformation seems to be forced by the intramolecular hydrogen bond between the hydroxyl group at C12 and the O20 atom from the side-chain.     

Ruthenium-Catalyzed C−C Coupling of Terminal Alkynes with Primary Alcohols or Aldehydes: α,β-Acetylenic Ketones (Ynones) via Oxidative Alkynylation

The first metal-catalyzed oxidative alkynylations of primary alcohols or aldehydes to form α,β-acetylenic ketones (ynones) are described. Deuterium labelling studies corroborate a novel reaction mechanism in which alkyne hydroruthenation forms a transient vinylruthenium complex that deprotonates the terminal alkyne to form the active alkynylruthenium nucleophile.     

Microbial evasion of the immune system: structural modifications of enterobactin impair siderocalin recognition

The mammalian protein siderocalin binds and inactivates the ferric complex of the bacterial siderophore enterobactin with a Kd value similar to that of the bacterial receptor FepA. However, microorganisms can evade this immune response by structural modifications of the siderophore. The binding of siderophores by siderocalin relies in part on electrostatic interactions and does not depend greatly on what metal is in the complex. It is also sterically limited by the rigid conformation of the protein calyx; methylation of the three catecholate rings of enterobactin hinders siderocalin recognition. The siderocalin binding has been probed for a series of enterobactin analogues in order to investigate in detail the specificity of siderocalin recognition.