Rotational energy transfer in NO (A2Σ+, v = 0 and 1) studied by two-color double-resonance spectroscopy

Collision-induced rotational relaxation in the A²Σ⁺, v = 0 and 1 states of NO has been measured by using step-wise double-resonant ionization spectroscopy. Multiple quantum rotational energy transfer is occurring to at least |ΔJ| = 6 and the observed cross sections ranging from tens to hundreds of A² are larger than the gas-kinetic collisional cross section. The energy-transfer efficiency is slightly enhanced by the vibrational excitation. Energy-based scaling laws are successfully applied to reproduce the observed rotational distribution.     

Statistical models in the study of stereospecific polymerization

Triad tacticity data obtained by NMR analysis have previously been interpreted in terms of two basic statistical models in order to elucidate the stereospecific polymerization mechanism. In this paper the characteristics of these two basic models for stereospecific polymerization, the enantiomorphic-sites (EMS) model, and the polymer-end control (PEC) model, are examined and compared. The tacticity values accessible to the two-parameter EMS model, which includes the influence of the chain end unit, are shown to be highly restricted. Only about 20% of the isotacticity versus syndiotacticity plot is accessible to this model. To this extent the consistency of a set of triad tacticity data with the model can be tested. No such tacticity limits are exhibited by the two-parameter PEC model, which includes the influence of the penultimate unit. Any set of tacticity values which can be interpreted in terms of the two-parameter EMS model can also be interpreted in terms of the two-parameter PEC model.     

Experimental evidence of core modification in the near drip-line nucleus 23O

The longitudinal momentum (P(axially)) distributions of one- and two-neutron removal fragments ((21,22)O) of 23O from the reaction with a C target at 72 A MeV have been measured for the first time using a new direct time-of-flight method with nearly full acceptance for the breakup fragments. The unexpectedly narrow width of 21O ( 115 +/- 34 MeV/c in FWHM) is consistent with two neutrons occupying the 2s(1/2) orbital in 23O. This indicates modification of core (22O) structure for neutron halo-like sd shell nuclei near the drip line. This also suggests the lowering of the s orbital providing a justification for the N = 16 magic number.     

Synthesis and structure of the first 1,2sigma5-selenaphosphirane

A 1,2sigma5-selenaphosphirane bearing the Martin ligand was synthesized. Its structure in both the solid and the solution state was established by X-ray crystallographic analysis and NMR measurements, respectively. The selenaphosphirane has a polar P-Se bond, and the selenium atom is negatively charged. In the solution state, the degree of polarization of the P-Se bond depends on the acceptor number of the solvents.     

A new drimane from the heartwood of the Japanese yew, Taxus cuspidata

A new drimane sesquiterpenoid was isolated from the heartwood of the Japanese yew, Taxus cuspidata Sieb. et Zucc. Its structure was established as 1beta-acetoxyisodrimeninol (1beta-acetoxy-11,12-epoxy-7-drimen-11-ol, 1). This compound was gradually oxidized to give y-lactone (1beta-acetoxy-8-drimeno-11,12-lactone, 4).     

Unimodular Triangulations and Coverings of Configurations Arising from Root Systems

Existence of a regular unimodular triangulation of the configuration , where ⁺ is the collection of the positive roots of a root system and where (0, 0,...,0 ) is the origin of , will be shown for = B _n , C _n , D _n and BC _n . Moreover, existence of a unimodular covering of a certain subconfiguration of the configuration A _n+1 ⁺ will be studied.     

Synthesis of [Gly-1]RA-VII, [Gly-2]RA-VII, and [Gly-4]RA-VII. Glycine-containing analogues of RA-VII, an antitumor bicyclic hexapeptide from Rubia plants

Three analogues of RA-VII (1), an antitumor bicyclic hexapeptide from Rubia plants, were synthesized. Three analogues, [Gly-1]RA-VII (4), [Gly-2]RA-VII (5), and [Gly-4]RA-VII (6), in which one of the three alanine residues in 1 was replaced by a glycine residue, were prepared by linking of the cycloisodityrosine unit, obtained by degradation of 1, to three different glycine-containing tetrapeptides followed by macrocyclization. Of these three analogues, analogue 4 showed the highest cytotoxic activity. The NMR study revealed that in solution the conformer structures and their ratios of analogue 4 were very similar to those of natural peptide 1, suggesting that the methyl groups at Ala-2 and Ala-4 should be essential for producing the bioactive conformation, whereas that at D-Ala-1 is not essential.     

Photo-reversible Pb2+-complexation of thermosensitive poly(N-isopropyl acrylamide-co-spiropyran acrylate) in water

Photo-reversible Pb2+-complexation in a purely aqueous environment exhibiting a thermosensitive phase transition at a lower critical solution temperature was achieved using a synthetic copolymer composed of N-isopropyl acrylamide and spiropyran acrylate.