Gyromagnetic ratios of excited states in186W

The gyromagnetic ratios of the 4 ₁ ⁺ , 6 ₁ ⁺ , and 2 ₂ ⁺ states in¹⁸⁶W were measured relative to that of the 2 ₁ ⁺ level by means of the transient field implantation perturbedγ-ray angular distribution technique. The nuclei in the states of interest were Coulomb excited using a beam of 220-MeV⁶³Cu projectiles and recoiled swiftly through a thin, polarized Fe foil. The present measurements yielded ratiosg(4 ₁ ⁺ )/g(2 ₁ ⁺ )=1.04±0.07,g(6 ₁ ⁺ )/g(2 ₁ ⁺ )=1.03 ±0.20 andg(2 ₂ ⁺ )/g(2 ₁ ⁺ )=0.63±0.13. The sizable disparity between the measuredg-factors of the ground- and excited-band is examined within the context of the interacting boson approximation model.     

Nuclear orientation as a tool for studying the structure of very unstable nuclei

With the availability of modern isotope separator on-line systems it has become possible to make broad and systematic studies of low-energy low-spin nuclear structure. A vital ingredient in such a program is unique spin-parity assignments to all low-lying levels. A most desirable complement to spin-parity information is detailed spectroscopic information. Obtaining such information far from stability is difficult because of low activity production. Nuclear orientation provides a means for obtaining spin assignments usingsingles measurements. This is less demanding on source intensities than - angular correlation coincidence measurements. Further, nuclear orientation can provide information on magnetic moments and on multipole mixing ratios. A number of structural problems are discussed: the need for unique spin assignments in systematics schemes; the need to distinguish between E2+E0 and M1 transitions; the importance of measuring E2-M1 mixing ratios; and the value of magnetic moment information. Particular emphasis is placed on the desirability of obtaining such information in the neutron-deficient Pt, Au, Hg, Tl, Pb and Bi isotopes, based upon the experimental program at the UNISOR facility.Work supported in part by U.S.Dept. of Energy, Contract No. DE-AS05-80ER10599.     

A stereocontrolled route to protected isocyanates from alcohols

Full details are given for a modified Mitsunobu approach to the formation of N-alkylated 1,2,4-dithiazolidine-3,5-diones 2 from a wide range of alcohols 10 with predominantly, inversion of configuration. The resulting products 2 can be regarded as protected isocyanates 6.     

Free radical rearrangements of organocobaloximes: alkynyl to cycloalkylidene and hexenyl to cyclopentylmethyl

Under irradiation by tungsten light in pyridine solution, several substituted alkylcobaloximes undergo rearrangement to more stable substituted alkyl- or alkenyl-cobaloximes. When the same reactions are carried out in the presence of carbon tetrachloride or chloroform, no rearranged organocobaloximes are obtained, but a variety of organic products are obtained derived from the interception of transient organic radicals by the halogenated solvent. The rearrangements are rationalised in terms of a reversible homolysis of the carbon-cobalt bond, rearrangement of the organic radical and recapture by the cobalt(II) fragment to give complexes that are more stable to irradiation than their precursors.     

Regioselectivity in palladium-catalyzed C-H activation/oxygenation reactions

[reaction: see text] Palladium-catalyzed directed C-H activation/oxygenation reactions have been explored in a series of meta-substituted aryl pyridine and aryl amide derivatives. These transformations tolerate a diverse array of electron-donating and electron-withdrawing meta-substituents and generally proceed with high levels of regioselectivity for functionalization of the less sterically hindered ortho-C-H bond.     

Individually addressable recessed gold microelectrode arrays with monolayers of thio-cyclodextrin nanocavities

Four, individually addressable 30 microm diameter, e-beam deposited, gold microelectrodes recessed by 6 microm were suitably spaced on a single substrate to avoid diffusional overlap between each microelectrode. The single substrate device was functionalised with thiolated alpha-, beta-, and gamma-cyclodextrin nanocavities without spacer groups to ensure close proximity of the cavities to the electrode surface. The microelectrodes were assessed in two stages. The e-beam deposited micron sized electrodes were characterized using models for recessed and inlaid microdisk electrodes. Subsequently, each individually addressable, atomically flat, micro-patterned gold electrode with thiolated CD ensembles was treated as a nanoporous electrode assembly. Theoretical and experimental results were compared using cyclic voltammetry. Atomic force microscopy was also used to characterise the modified microelectrodes. Comparisons were made with thiolated CDs deposited on macroelectrodes. This is the first report of the behaviour of immobilized CD nanocavities ensembles on atomically flat gold microelectrodes.     

International Review of Science Solid State Chemistry,Inorganic Chemistry Series Two,Vol. 10 : Consultant Editor H.J. Emeleus FRS,Volume Editor L.E.J. Roberts,Butterworths, London, 1975, pp. 264, price £13.00

Complexes of nicotinic and isonicotinic acids and their deuterated analogues with pyridine, 4-Me pyridine and N Me imidazole have been examined by IR spectroscopy. Strong hydrogen bonding between an O atom of the acid and the N atom of the base with the H atom lying closer to the O atom, is present in all systems.     

EFFECT OF BASE SEQUENCE ON THE ULTRAVIOLET IRRADIATION PRODUCTS OF DOUBLE-STRANDED POLYNUCLEOTIDES CONTAINING BROMOURACIL AND ADENINE

Abstract —The effects of ultraviolet irradiation of double-stranded synthetic polynucleotides containing BrU and A have been investigated. Homopolymer pairs and alternating copolymers composed of either ribo- or deoxyribo-nucleotides were prepared and were irradiated with either 313 nm or ˜ 285 nm light. Strand separation and a modest amount of strand breakage followed irradiation of the homopolymer pairs. Changes in the ultraviolet absorption spectra of the polymers during irradiation reflected the sum of hyperchromic increases caused by progressive strand separation and loss of absorbance caused by photoproduct formation. Extensive debromination occurred. An RNase digest of irradiated poly(rA)–poly¹⁴C(rBrU), analysed by column chromatography, showed components similar to those found previously upon irradiation of single-stranded poly(rBrU). Little photoproduct was released by RNase digestion as mononucleotides. The major photoproduct was in the dinucleotide fraction, and may be 5,5'-diuracil. Base sequence had a profound effect on the sensitivity of the polynucleotides. Irradiation of alternating copolymers with doses of light comparable to those that produced major photochemical changes in the homopolymer pairs brought about little if any change in the copolymers of alternating base sequence.