Synthetic studies toward biselides. Part 1: synthesis of the core carbon framework of biselides A,B, and E using Stille coupling

Biselides A and B are cytotoxic marine polyketides. We have achieved synthesis of the C-1–C-15 segment of biselides A and B by using Stille coupling and regioselective oxidative cleavage as key steps. Furthermore, we constructed the α,β-unsaturated lactone part of biselide E by using a similar strategy.     

Investigation of electronic states of infinite-layer SrFeO2 epitaxial thin films by X-ray photoemission and absorption spectroscopies

We investigated the electronic states of a single-crystal SrFeO₂ epitaxial thin film in the valence-band and conduction-band regions using synchrotron-radiation X-ray photoemission and absorption spectroscopies. Fe 2p–3d resonant photoemission measurements revealed that the Fe 3d states have higher densities of states at binding energies of 3–5 eV and 5–8.5 eV in the valence-band region. The O K-edge X-ray absorption spectrum exhibited three peaks in the Fe 3d-derived conduction band hybridized with O 2p states; these can be assigned to Fe 3d_xy, 3d_xz + 3d_yz, and 3d_x²_–y². In addition, the indirect bandgap value of the SrFeO₂ film was determined to be 1.3 eV by transmission and absorption spectroscopies.     

On the variation of the stability constants of EuCl2+ in the mixed system of dimethyl sulfoxide and water

The effect of water-miscible alcohols and acetone on the extraction and separation of Cd and Zn chlorides by TOPO was systematically investigated. The maximum extraction of Zn chloride with 0.1 M TOPO decreases in the order: acetone>methanol>ethanol>2-propanol>2-butanol. For alcohols, the sequence of decreasing extractability is thus parallel to the order of their dielectric constants. This can be explained by the increase of HCl extraction by TOPO in the same direction. The presence of additives in the polar phase prevents the formation of a bulky white precipitate encountered during extraction of ZnCl₂ from pure aqueous solutions. A decrease of Cd chloride extraction was generally noticed in presence of additives; this is more noticeable for the longer chain alcohols. The highest separation factor (E for ZnCl₂ and CdCl₂ in 0.48M HCl is obtained from 30% methanol (13.8 compared to about 3.8 in absence of methanol) and from 10–20% acetone where it reaches 30.     

The thermolysin-catalyzed condensation reactions of n-substituted aspartic and glutamic acids with phenylalanine alkyl esters

The title reactions occur with concurrent peptide synthesis and optical resolutions of racemic substrates. With this method, Z-L-Asp-L-Phe-OME, the precursor to the synthetic sweetner, could be obtained in high yield.     

Microwave spectrum of 3-bromopropene in the excited torsional states

The microwave spectra in the excited states of the CC torsion for the ⁷⁹Br and ⁸¹Br isotopic species of 3-bromopropene were measured in the frequency region 15.3–23.7 GHz. The a-type R-branch and b-type Q-branch rotational transitions in the first and second excited states of one conformer, skew, have been assigned and analyzed. Analysis of the spectrum yields the rotational constants and the nuclear quadrupole coupling constants. From relative intensity measurements the energy differences associated with the CC torsion, between the ground and first excited state, the ground and second excited state have been found to lie 109 and 206 cm^?1, respectively.     

Microwave spectrum of 3-iodopropene

The microwave spectra of 3-iodopropene were measured in the frequency region 12–18 GHz. The a-type R-branch and the b-type Q-branch rotational transitions of one conformer, skew, have been assigned and the rotational constants of the ground state have been obtained: A = 17 644.34, B = 1588.12, and C = 1538.64 MHz. The second-order quadrupole effects give rise to anomalous hyperfine splittings and are analyzed by taking into account χ_ab of the quadrupole coupling tensor. The nuclear quadrupole coupling constants have been determined to be χ_aa = ?1337, χ_bb = 387, χ_cc = 950, and ∥χ_ab∥ = 1081 MHz.     

Rotational analysis of the a3Π0+,1-X1Σ+ emission systems of GeH+

New emission systems have been observed from the helium afterglow reaction of GeH₄ in the 520–610 nm region. On the basis of the rotational analysis, they were assigned to the a ³Π_0⁺-X¹Σ⁺ and a³Π₁-X¹Σ⁺ subsystems of GeH⁺. Spectroscopic constants have been determined for the GeH⁺ (a³Π_0⁺, a³Π₁, X¹Σ⁺) states.     

Plumbing constructions of connected divides and the Milnor fibers of plane curve singularities

A divide is the image of a generic, relative immersion of a finite number of copies of the unit interval or the unit circle into the unit disk. N. A'Campo defined for each connected divide a link in S³ and proved that the link is fibered. In the present paper we show that the fiber surface of the fibration of a connected divide can be obtained from a disk by a successive plumbing of a finite number of positive Hopf bands. In particular, this gives us a geometric understanding of plumbing constructions of the Milnor fibers of isolated, complex plane curve singularities in terms of certain replacements of the curves of their real morsifications.     

On the fourth Johnson homomorphism of the automorphism group of a free group

In this paper we consider the Johnson homomorphism of the automorphism group of a free group with respect to the lower central series of the IA-automorphism group of a free group. In particular, we determine the rational cokernel of the fourth Johnson homomorphism, and show that there appears a new obstruction for the surjectivity of the Johnson homomorphism. Furthermore we characterize this obstruction using trace maps.