Substituent effects on the rate of carbene formation by the pyrolysis of rigid aryl substituted diazomethanes

Rate constants for the pyrolysis of 1-diazo-4,4-dimethyl-1,4-dihydronaphthalenes, 4a–4e, have been measured in methanol : 6% triethylamine. In contrast to non-rigid cases, like diphenyldiazomethanes, where all para substituents show a rate increase compared to hydrogen, these rates show a linear Hammett correlation for para substituents with σ⁺ = — 0.84. This observation is rationalized by a non-linear process for loss of nitrogen leading directly to the ground-state singlet of the carbene, 17. This carbene is then trapped to give the ether 11.     

The energy calibration of LEP in the 1993 scan

This report summarizes the procedure for providing the absolute energy calibration of the LEP beams during the energy scan in 1993. The average beam energy around the LEP ring was measured in 25 calibrations with the resonant depolarization technique. The time variation of this average beam energy is well described by a model of the accelerator based on monitored quantities. The absolute calibration of the centre of mass energies of the off-peak points is determined with a precision of 2 parts in 10⁵ resulting in a systematic error on the Z-mass of about 1.4 MeV and on the Z-width of about 1.5 MeV.     

Preparation of Pd/ceramic composite membrane 1. Improvement of the conventional preparation technique

The Pd/ceramic composite membrane made is reported in this paper. The thin palladium film was deposited on the surface of a porous ceramic substrate by the conventional and improved electroless plating technique, respectively. The rate of palladium deposition increases and especially the sensitization and activation steps in the conventional electroless plating process has been omitted by an improved technique.     

ULTRAVIOLET RADIATION IN ANTARCTICA: INHIBITION OF PRIMARY PRODUCTION

With the seasonal formation of the ozone hole over Antarctica, there is much concern regarding the effects of increased solar UV-B radiation (280–320 nm) on the marine ecosystem in the Southern Ocean. In situ incubations of natural phytoplankton assemblages in antarctic waters indicate that under normal ozone conditions UV-B radiation is responsible for a loss of approximately 4.9% of primary production in the euphotic zone, whereas UV radiation with wavelengths between 320 and 360 nm causes a loss of approximately 6.2%. When combined with data on the action spectrum for photoinhibition by UV radiation, our data suggest that the enhanced fluence of UV-B radiation under a well-developed ozone hole (150 Dobson units) would decrease daily primary productivity by an additional amount of 3.8%. Calculations that take into consideration the extent and duration of low stratospheric ozone concentrations during September to November indicate that the decrease in total annual primary production in antarctic waters due to enhanced UV-B radiation would be 0.20%.     

Analytical construct resins for analysis of solid-phase chemistry

Rapid and unambiguous analysis of reactions performed on resin supports can be achieved by using "analytical constructs". These resins allow the synthesis of materials using solid-phase methods in the usual manner, but they also contain functionality enabling cleavage of analytically enhanced derivatives of the resin-bound products. This is possible due to the use of two linkers bound in series to the polymer. Cleavage at the first linker yields the products attached to an analytical enhancer that facilitates detection. Orthogonal cleavage at the second linker yields the desired products in the usual manner.     

SPIN TRAPPING OF THE SUPEROXIDE RADICAL BY 4-(N-METHYLPYRIDINIUM) t-BUTYL NITRONE

The synthesis of 4-(N-methylpyridinium) t-butyl nitrone (4-MePyBN) and its use as a spin trap for superoxide radicals produced in aqueous solutions is reported (a^N= 13.78 G, a^H_ß= 1.65 G, and g = 2.0091). The half-life of the spin adduct as a function of pH (83 s at pH 5.5, 78 s at pH 7.0, and 65 s at pH 8.0) the effects of iron salts, diethylenetriaminepentacetic acid (DETAPAC), and superoxide dismutase were examined, and comparisons made between 4-MePyBN and 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as spin trapping agents for the superoxide radical.     

Metallohelices emulate the properties of short cationic α-helical peptides

Naturally occurring peptides in many living systems perform antimicrobial and anticancer host defence roles, but their potential for clinical application is limited by low metabolic stability and relatively high costs of goods. Self-assembled helical metal complexes provide an attractive synthetic platform for non-peptidic architectures that can emulate some of the properties of short cationic α-helical peptides, with tuneable charge, shape, size and amphipathicity. Correspondingly there is a growing body of evidence demonstrating that these supramolecular architectures exhibit bioactivity that emulates that of the natural systems. We review that evidence in the context of synthetic advances in the area, driven by the potential for biomedical applications. We note some design considerations for new biologically-relevant metallohelices, and give our outlook on the future of these compounds as therapeutic peptidomimetics.

Advances in metal–organic self-assembly have unearthed an area of chemical space containing peptide-emulating molecules. Comparison with natural systems indicates future directions in terms of synthesis, disease areas and mechanistic understanding.     

Synthesis and structural assignment of 5,6-dihydro-8-hydroxy-9-methoxy-1H,7H-benzo[ij] quinolizine-1,7-dione

The compound 5,6-dihydro-8-hydroxy-9-methoxy-1H,7H-benzo[ij]quinolizine-1,7-dione ( 4a ) was synthesized from 3-(1,4-dihydro-6,7-dimethoxy-4-oxo-1-quinolyl)propionic acid ( 3a , free base), involving spontaneous demethylation with ring closure. The structural assignment of 4a was based on an analogous, unequivocal synthesis of 5,6-dihydro-9-ethoxy-8-hydroxy-1H,7H-benzo[ij]quinolizine-1,7-dione hydrochloride ( 4b ).