Imaging membrane protein helical wheels

Resonance patterns have been observed in 2D solid-state NMR spectra of the transmembrane segment of M2 protein from Influenza A virus in oriented samples reflecting the helical wheel of this alpha-helix. The center of this pattern uniquely defines the helical tilt with respect to the bilayer normal without a need for resonance assignments. The distribution of resonances from amino acid specific labels around the "PISA wheel" defines the rotational orientation of the helix and yields preliminary site-specific assignments. With assignments high-resolution structural detail, such as differences in tilt and rotational orientation along the helical axis leading to an assessment of helical coiling, can be obtained.     

The determination of bromine in biological material by thermal neutron activation analysis

The determination of bromine in biological material by thermal neutron activation analysis using instrumental [Ge(Li)] and radiochemical separation techniques is described. The radiochemical method is ten times more sensitive (0.4 ng) than the instrumental technique but both may be used for analysis of the majority of human tissue samples. Both techniques are rapid, simple, accurate and may be used for batch analysis.     

Thermal fracture of plastics

The extension and fracture under tension of poly(vinyl chloride) strips of different lengths have been studied. It was found that, in spite of decreasing strain rate, long pieces are subject to a type of brittle fracture (necking rupture) occurring immediately after neck formation. This result, which could be expected from previous work, is shown to depend on the elastic energy stored in the longer test pieces. This energy is converted to heat under conditions of neck formation, leading to a temperature rise of 24 ± 4°C, determined by a thermal imaging system. With short test pieces the rise in temperature is much smaller, and a transition to stable neck propagation occurs. Optical and electron micrographs provide additional evidence of heating at the fracture surface. A semiquantitative treatment of the adiabatic process gives upper and lower limits for the predicted temperature change neglecting thermal losses. It is also possible to estimate a minimum length for the initiation of adiabatic deformation. Both calculations give results in reasonable agreement with experiments. Observations with polycarbonate show a similar length effect at low temperatures.     

Bridgehead substitutions. Preparation of 7-chloro-, 7-bromo- and 7-methylsulphinyl-gibberellins

7-Hydroxygibberellins react with nucleophiles in the presence of fluoroamine to give bridgehead substitution products.