Crystal and molecular structure of diaquobis(1,1′-dimethyl-2,2′-diimidazolylsulfide)copper(II) methylsulfate, (C8H10N4S)2Cu(II)(OH2)2(CH3OS03)2

The crystal and molecular structure of the title complex has been determined. The space group isP2₁/n, witha=8.460(3),b=8.503(3),c=20.341 (8) Å,=98.41(3) andZ=2. The ligand molecules chelate the Cu^II such that the metal has a tetragonally distorted octahedral geometry; four N atoms occupy the equatorial plane and two H₂O molecules occupy the axial positions. The average Cu-N and Cu-O distances are 2.005(6) and 2.47(1) Å, respectively. The novel ligand, 1,1-dimethyl-2,2-diimidazolylsulfide was formedin situ from a methanolic solution of copper(II) sulfate pentahydrate and 1-methylimidazole-2-thiol. The measured spectral parameters (visible, EPR, and photoelectron spectroscopy) correlate well with the molecular structure.     

A novel oxidative rearrangement of 6-methoxypyran-2-ones

As part of our continuing studies of pyrone-containing natural products, a series 6-methoxypyran-2-ones were synthesized. These were found to react with molecular oxygen at 20 degrees C, and this novel reaction yielded a series of highly functionalized alpha,beta-butenolides. [reaction: see text]     

One nanosecond photon correlation spectroscopy on smectic liquid crystal films

We have extended photon correlation spectroscopy down to a one-nanosecond time scale, and applied it to a study of layer undulations in freestanding smectic-A films of two cyanobiphenyl liquid crystals. Temporal correlations in the intensity of scattered light reveal an interesting combination of under- and overdamped modes. The underdamped mode is accurately described by a recently calculated correlation function of the smectic layer displacement, although its frequency and damping rate exhibit stronger dispersion at large optical wave vectors than expected from current dynamical models for smectic films.     

Biomimetic synthesis of the pyrrolobenzoxazine core of paeciloxazine

Starting from a protected L-tryptophan derivative the pyrrolobenzoxazine core unit of paeciloxazine can be synthesized in two oxidation steps.     

Electron correlation in the second Landau level: a competition between many nearly degenerate quantum phases

At a very low-temperature of 9 mK, electrons in the second Landau level of an extremely high-mobility two-dimensional electron system exhibit a very complex electronic behavior. With a varying filling factor, quantum liquids of different origins compete with several insulating phases leading to an irregular pattern in the transport parameters. We observe a fully developed nu=2+2/5 state separated from the even-denominator nu=2+1/2 state by an insulating phase and a nu=2+2/7 and nu=2+1/5 state surrounded by such phases. A developing plateau at nu=2+3/8 points to the existence of other even-denominator states.     

Expedient synthesis of a highly substituted tropolone via a 3-oxidopyrylium [5+2] cycloaddition reaction

An expedient ten-step synthesis of a substituted tropolone is described. The synthesis involves a 3-oxidopyrylium [5+2] cycloaddition reaction with acrylonitrile as the key step, affording a highly functionalized [3.2.1]-bicycle 10 as a single regioisomer. The nitrile substituent of the reduced cycloadduct 12 permits efficient ether-bridge cleavage and tropolone 15 is obtained after a final bis-oxidation procedure. The pyranulose acetate cycloaddition precursor was derived from 3-methyl-2-furoate.     

Biomimetic synthesis of biatractylolide and biepiasterolide

[reaction: see text] The biomimetic synthesis of the bisesquiterpenoids biatractylolide 1 and biepiasterolide 2 is reported.     

Total synthesis of panepophenanthrin

[reaction: see text] The biomimetic synthesis of the racemic dimer panepophenanthrin was achieved in good yield employing a tandem reaction sequence.     

Reorientation of anisotropy in a square well quantum hall sample

We have measured magnetotransport at half-filled high Landau levels in a quantum well with two occupied electric subbands. We find resistivities that are isotropic in perpendicular magnetic field but become strongly anisotropic at nu = 9/2 and 11/2 on tilting the field. The anisotropy appears at an in-plane field, B(ip) approximately 2.5 T, with the easy-current direction parallel to B(ip) but rotates by 90 degrees at B(ip) approximately 10 T and points now in the same direction as in single-subband samples. This complex behavior is in quantitative agreement with theoretical calculations based on a unidirectional charge density wave state model.     

Changes in modal parameters of a bridge during fatigue testing

The effects of high-cycle fatigue on the dynamic modal properties of a full-scale bridge test section are examined in this study. A span 30.5 m (100 ft) in length was salvaged from an interstate bridge for experimental testing to establish the fatigue performance of the retrofit procedures which could be used for future field repairs of the fatigue cracks. Horizontal cracks had formed in the webs of the twin bridge girders in the vicinity of the web-flange weld at or near the connections of the girders to the floor beams. An electrohydraulic vibration shaker was used to excite the test span in the torsional and bending modes to promote fatigue crack growth. In addition to the experimental evaluation of the retrofit procedures, the dynamic response characteristics of the test span during the high-cycle fatigue test were monitored. Experimental data have been used to establish mode shapes and modal damping ratios during the four-million-cycle fatigue test. Damping ratios ranged from 1.09 percent to 0.53 percent. Modal stiffnesses were calculated based on the experimental mode shapes. There is a modest correlation between the changes in stiffness and the observed cracking of the steel girders and the subsequent repairs. Paper was presented at the 1988 SEM Spring Conference on Experimental Mechanics held in Porland, OR on June 5–10.