Biomedical subjects
Publications and source records attributed to J D Roberts.
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Lanthanide-induced shfits of (13)C nuclear magnetic resonances are reported for several amines and n-butyl isocyanide. Contact contributions to such shifts, especially of beta carbons, are clearly important for the chelates of Eu(+3) and Pr(+3). The importance of contact terms is shown to change in a rather predictable manner with the structure of the amine.
The pattern of (13)C and (1)H nuclear magnetic resonance (NMR) shift changes produced by complexation of cobalt and nickel acetylacetonates with amines and alcohols indicates that there is more than one mode of operation of the contact interaction. A large effect with alternating signs is important at the alpha and beta carbons, but this effect seems to be overlaid by another influence that appears to fall off monotonically as one proceeds away from the site of complexation.
Carbon-13 nuclear magnetic resonance spectra have been taken of Delta(8)- and Delta(9)-tetrahydrocannabinol. The absorptions have been assigned to specific carbons with the aid of off-resonance and selective proton-decoupling experiments, as well as by chemical-shift comparison with model compounds.
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Studies of product compositions and deuterium-label rearrangements at various concentrations of tri-n-butyltin hydride in the reductions of exo-and endo-5-bromonorbornene and 2-bromonortricyclcne to mixtures of norbornene and nortricyclene lead to three main conclusions: (i) at least two radical intermediates contribute to product formation; (ii) each intermediate yields predominantly (80% or more) one product; and (iii) nortricyclene is predominantly derived from a symmetrical intermediate. This constitutes strong evidence for hydrogen abstraction by classical (i.e., single-product) norbornenyl and nortricyclyl radicals. It is argued that the norbornenyl-nortricyclyl system is exceptionally well suited for the generation of a nonclassical (dual-product) radical; hence, the existence of a nonclassical radical in any other system is rather unlikely.
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The early changes induced by a carcinogenic nitrosoquinoline compound (NTDQ) have been studied in the subcutaneous tissues of 88 rats. An initial acute infiammatory response is quickly replaced by a distinctive granuloma which is established by 10 days and persists indefinitely-a sequence which takes place both in adult and in newborn animals. Its main components-histiocytes, multinucleate giant cells and granulation tissue-are described in detail and the formation of giant cells by fusion from adjacent histiocytes has been traced. Autoradiographic studies with tritiated thymidine show heavy nuclear labelling in the histiocytes and fibroblasts during the first 10 days; this later declines but raised levels of nuclear labelling persist up to the end of the experiment. No proliferative activity is seen in the giant cells and these cells show only feeble phagocytic activity, tested by their ability to take up carbon particles. The experiments in which colloidal carbon was injected locally also provided some information on the lymphatic vessels in the vicinity of NTDQ-induced granulomata. It appears that, initially, the lesions contain large dilated lymphatic vessels. Later, a dense connective tissue barrier develops and lymphatic connections with the surrounding dermis are progressively reduced.The properties of granulomata induced by NTDQ are discussed and some possible relationships between the formation of granulomata and eventual tumour developed are considered. Particular emphasis is given to two related features: the sustained proliferative activity of the fibroblasts and the resulting semi-isolation of the injection site lesion by the formation of a dense connective tissue barrier.
Natural-abundance (13)C nuclear magnetic resonance spectra of ten common nucleotides in neutral, aqueous solutions have been determined and interpreted. The spectra of two of these substances were also determined in acidic solutions, and several of the carbon chemical shifts were found to depend markedly on pH. Within the limited range of concentrations employed, there were observed no carbon chemical-shift changes which could be ascribed to base-stacking or base-pairing phenomena.