Photoinduced Rearrangement of Dienones and Santonin Rerouted by Amines

The photoinduced rearrangement pathways of simple 2,5‐dienones and the natural product santonin were found to be effectively rerouted by amines, giving rise to unprecedented products. Either cis olefins or cyclobutenes were obtained from 4,4‐disubstituted 2,5‐dienone upon irradiation (365 nm) in the presence of various amines depending on the solvent. Previously undescribed [4.4.0] and [5.3.0] fused‐ring‐containing products were obtained when santonin was irradiated (365 nm) in the presence of methylamine. The amines present in these reactions were incorporated into the products by means of amide‐group formation.     

A Proof of Hozo's Conjecture on the Homology of a Class of Nilpotent Lie Algebras

LetPbe a rooted tree with rootrand vertex set {1, 2,…,n}. ConsiderPto be a poset by sayingu ≤ vifuis on the path fromrtov. LetZ[P] be the span of all matricesz_uvsuch thatu <_P v, wherez_uvis then × nmatrix with a 1 in theu, ventry and 0's elsewhere. Note thatZ[P] is a nilpotent Lie subalgebra of ?_n(). I. Hozo (Electron. J. Combin., to appear) studied the Laplacian of the Koszul complex for computing the Lie algebra homology ofZ[P]. He showed that the tree structure ofPforces significant simplifications in the Laplacian. He went on to conjecture that the eigenvalues of the Laplacian are indexed by certain labellings ofPby partitions. He gave a simple method for determining the eigenvalue indexed by a labelling. In this paper we prove Hozo's conjecture. As a consequence, we deduce that all eigenvalues of the Laplacian are integers.     

Molecular structures of neopentane and di-tert-butylmethane by vapor-phase electron diffraction

Although the present molecules are much less strained than the tri-t-butyl member of the series CH_n(t-Bu)_4–n studied previously, di-t-butylmethane nevertheless exhibits striking steric deformations due to its pair of inescapable GG' conformations. The two adjacent t-butyl groups respond to the steric stress by undergoing torsional displacements of 15 ± 6° (3σ), by tilting away from each other by 3–5°, and by opening up the central CCC bond angle to 125–128° (parameter value sensitive to assumptions in analysis). Carbon-carbon bonds, with mean lengths of 1.545 ± 0.005Å, are stretched on the average by about 0.008Åfrom the neopentane reference value. Derived molecular parameters are in substantial agreement with values calculated by molecular mechanics using model fields MUB-1 and MUB-2. The methylene¹³C-H nmr coupling constant was found to be 125 Hz, a value indistinguishable from those reported for unstrained alkanes but not in accord with predictions from the formulas of Foote or Mislow for severely distorted methylene groups.Molecular parameters for neopentane included r_g(C-C) = 1.534 ± 0.003Å, r_g(C-H) = 1.114 ± 0.008Åand ∠CCH = 112 ± 3°. The new value for the C-C bond satisfactorily resolves a discrepancy between previously reported bond lengths. These had disagreed significantly with each other but, to within their uncertainties, they are consistent with the new, intermediate value. Amplitudes of vibration were determined for both neopentane and di-t-butylmethane.     

Pulsed-field ionization electron spectroscopy and binding energies of alkali metal-dimethyl ether and -dimethoxyethane complexes

Lithium and sodium complexes of dimethyl ether (DME) and dimethoxyethane (DXE) were produced by reactions of laser-vaporized metal atoms with organic vapors in a pulsed nozzle cluster source. The mono-ligand complexes were studied by photoionization and pulsed field ionization zero electron kinetic energy (ZEKE) spectroscopy. Vibrationally resolved ZEKE spectra were obtained for Li(DME), Na(DME) and Li(DXE) and a photoionization efficiency spectrum for Na(DXE). The ZEKE spectra were analyzed by comparing with the spectra of other metal-ether complexes and with electronic structure calculations and spectral simulations. Major vibrations measured for the M(DME) (M=Li,Na) ions were M-O and C-O stretches and M-O-C and C-O-C bends. These vibrations and additional O-Li-O and O-C-C-O bends were observed for the Li(DXE) ion. The M(DME) complexes were in C2v symmetry with the metal atom binding to oxygen, whereas Li(DXE) was in a C2 ring configuration with the Li atom attaching to both oxygen atoms. Moreover, the ionization energies of these complexes were measured from the ZEKE or photoionization spectra and bond dissociation energies were derived from a thermodynamic cycle.     

Cyclic homology and the Macdonald conjectures

Summary LetA+(k) denote the ring [t]/t ^k+1 and letG be a reductive complex Lie algebra with exponentsm ₁, ...,m n. This paper concerns the Lie algebra cohomology ofGA ₊(k) considered as a bigraded algebra (here one of the gradings is homological degree and the other, which we callweight, is inherited from the obvious grading ofGA ₊(k)). We conjecture that this Lie algebra cohomology is an exterior algebra withk+1 generators of homological degree 2m _s +1 fors=1,2, ...,n. Of thesek+1 generators of degree 2m _s +1, one has weight 0 and the others have weights (k+1)m _s +t fort=1,2, ...,k.It is shown that this conjecture about the Lie algebra cohomology of A ₊(k) implies the Macdonald root system conjectures. Next we consider the case thatG is a classical Lie algebra with root systemA _n ,B _n ,C _n , orD _n. It is shown that our conjecture holds in the limit onn asn approaches infinity which amounts to the computation of the cyclic and dihedral cohomologies ofA+(k). Lastly we discuss the relevance of this limiting case to the case of finiten in this situation.Partially supported by NSF grant number MCS-8401718 and a Bantrell Fellowship     

Replication in UV-lrradiated Caenorhabditis elegans Embryos

Abstract— Replication continues in wild-type (but not rad mutant) Caenorhabditis elegans embryos even after exposure to massive fluences of UV radiation. It is of interest to elucidate the mechanism(s) for this "damage-resistant" DNA synthesis. In this study, DNA from unirradiated and UV-irradiated wild-type embryos was examined using the electron microscope. Large fluences of UV radiation (180 J m⁻²) had little effect on either replication bubble size or distances between bubbles in wild-type embryos, indicating that the damage-resistant DNA synthesis was not grossly aberrant. Conversely, UV irradiation significantly decreased center-to-center distances between bubbles in excision-repair-deficient rad-3 embryos. This suggests that the decreased DNA synthesis observed after UV irradiation in rad-3 embryos is due largely to blockage of elongation of DNA synthesis.     

Preparation of β′-phenylsulfonyl α,β-unsaturated ketones and unsymmetric dialkenyl ketones from 2-alkenyl-2-methoxycyclopropyl phenyl sulfones

β′-Phenylsulfonyl α,β-unsaturated ketones, which can be easily converted to unsymmetric dialkenyl ketones, were prepared via ring opening reactions of 2-alkenyl-2-methoxycyclopropyl phenyl sulfones.     

Absorption und Adsorption

Ohne Zusammenfassung     

Highly selective electrocatalytic conversion of CO2 to CO at -0.57 V (NHE) by carbon monoxide dehydrogenase from Moorella thermoacetica

We found that CODH is a fascinating enzyme for the electrochemical conversion of CO2 to CO. It could reduce CO2 to CO at -0.57 V vs NHE with approximately 100% current efficiency in 0.1 M phosphate buffer (pH 6.3). Nature's unique structure of C-cluster in CODH would be responsible for the low overpotential and the selective and fast conversion of CO2. The turnover number per C-cluster is 700 h-1, and the pH optimum is 6.3.