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Title: Stabilizing a different cyclooctatetraene stereoisomer

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Journal Article: Published Article
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Volume: 114; Journal Issue: 37; Related Information: CHORUS Timestamp: 2017-11-28 14:34:52; Journal ID: ISSN 0027-8424
Proceedings of the National Academy of Sciences
Country of Publication:
United States

Citation Formats

Li, Longfei, Lei, Ming, Xie, Yaoming, Schaefer, III, Henry F., Chen, Bo, and Hoffmann, Roald. Stabilizing a different cyclooctatetraene stereoisomer. United States: N. p., 2017. Web. doi:10.1073/pnas.1709586114.
Li, Longfei, Lei, Ming, Xie, Yaoming, Schaefer, III, Henry F., Chen, Bo, & Hoffmann, Roald. Stabilizing a different cyclooctatetraene stereoisomer. United States. doi:10.1073/pnas.1709586114.
Li, Longfei, Lei, Ming, Xie, Yaoming, Schaefer, III, Henry F., Chen, Bo, and Hoffmann, Roald. 2017. "Stabilizing a different cyclooctatetraene stereoisomer". United States. doi:10.1073/pnas.1709586114.
title = {Stabilizing a different cyclooctatetraene stereoisomer},
author = {Li, Longfei and Lei, Ming and Xie, Yaoming and Schaefer, III, Henry F. and Chen, Bo and Hoffmann, Roald},
abstractNote = {},
doi = {10.1073/pnas.1709586114},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
number = 37,
volume = 114,
place = {United States},
year = 2017,
month = 8

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  • In the present paper they report the first determination of the heat of combustion c//sup 0/ of bis(eta/sup 8/-cyclooctatetraene)thorium (thorocene), and also a refinement of the measurement of c//sup 0/ for bis(eta/sup 8/-cyclooctatetraene)uranium (uranocene). These measurements, along with the results of tensimetric experiments, have been used to calculate the standard enthalpies of formation of these compounds both in the condensed and vapor phase, as well as the average dissociation energies of the actinide-cyclooctatetraene bonds. The metal-ligand chemical bonds in these compounds have been found to be among the strongest of the known sandwich compounds. Comparative estimates of themore » values of the average dissociation energies of all of the bonds in thorocene and uranocene have revealed that the determining factor controlling the thermal destabilization of these molecules is the average carbon-hydrogen bond energy.« less
  • (-)-N6-(R-4-Hydroxyphenylisopropyl)adenosine (HPIA) was iodinated with NaI and trace /sup 125/I. Mono- and diiodinated reaction products and the starting material were separated by high pressure liquid chromatography and the structures of the reaction products were verified by NMR. (-)-N6-(R-Phenylisopropyl)adenosine (PIA), IHPIA, and I2HPIA decreased rat atrial contractility with ED50 values of 24, 28, and 33 nM, respectively. The contractile effects of these compounds were competitively blocked by theophylline (KI . 7.9 microM), but were not affected by adenosine deaminase. IHPIA also inhibited (-)isoproterenol-stimulated cyclic AMP accumulation in adipocytes with an ED50 (10 nM) and to an extent (83%) nearly identical tomore » PIA. (/sup 125/I)HPIA prepared using carrier-free /sup 125/I bound to adenosine receptors on membranes from rat cerebral cortex, adipocyte ghosts, and heart ventricles. Binding was inhibited stereospecifically by PIA and by other adenosine analogues and alkylxanthines. The KD of (/sup 125/I)HPIA determined kinetically using brain membranes at 21 degrees was 0.94 nM in good agreement with the equilibrium determination of 1.94 nM. The density of adenosine receptors in brain membranes was found to be 871 fmol/mg of protein. When normalized to protein, the density of receptors in heart membranes and adipocyte ghosts, respectively, was found to be 39- and 2.3-fold less than in brain membranes. It was concluded that (/sup 125/I)HPIA can be rapidly synthesized and purified, binds to adenosine R-sites and is an agonist radioligand resistant to adenosine deaminase. Computer modeling of the equilibrium binding resulting from the use of mixed stereoisomers of a radioligand indicates that the combined use of (-)(/sup 125/I)HPIA and (+)(/sup 125/I)HPIA would result in the generation of nonlinear Scatchard plots.« less
  • Oligonucleotides containing site-specifically-modified N{sup 2}-guanine (+)-trans-, (-)-trans-, (+)-cis-, and (-)-cis-BPDE adducts into 50-base-pair DNA fragments. These substrates were used in reactions with the Escherichia coli UvrABC nuclease system. The interaction of the UvrA{sub 2} and UvrA{sub 2}B complexes with these four stereoisomers was probed using DNase I footprinting and gel mobility shift assays. DNase I digestion of substrates containing each stereoisomer of BPDE displayed a unique pattern which was consistent with the known structure of these DNA adducts. UvrA and UvrA{sub 2}B appeared to interact very similarly with all four substrates. Binding of UvrA{sub 2} to these substrates produced amore » 33-bp footprint, and the UvrB-DNA complex resulted in footprint of 24 bp. The UvrABC nuclease system produced bimodal incisions at the eighth phosphate 5{prime} and the fifth, sixth, or seventh phosphate 3{prime} to the modified guanine. The variation of the 3{prime} incision site was linked to the stereochemistry and orientation of the BPDE adduct. For example, the 3{prime} incision of the 50-bp duplex containing (-)-trans-BPDE-N{sup 2}-guanine was inhibited at the fifth phosphate. UvrABC nuclease incision kinetics revealed a hierarchy of specificity. The intercalative cis isomers were incised more efficiently than the corresponding trans isomers which lie in the minor groove. The (+) enantiomers were incised more efficiently than the (-) form for both cis and trans isomers. These observations reveal that UvrABC nuclease recognition and incision are directly influenced by the conformation of the DNA adduct. 59 refs., 10 figs.« less
  • This paper reports on NMR-molecular mechanics structural studies of the (-)-trans-anti-benzo[c]phenanthrene-dA adduct positioned opposite dT in the sequence context of the d(C1-T2-C3-T4-C5-[BPh]A6-C7-T8-T9-C10-C11){center_dot}d(G12-G13-A14-A15-G16-T17-G18-A19-G20-A21-G22) duplex (designated as the (-)-trans-anti-[BPh]dA6{center_dot}dT 11-mer duplex). This adduct is derived from the covalent binding of (-)-1,2-dihydroxy-3,4-epoxy- 1,2,3,4-tetrahydro-benzo[c]phenanthrene[(-)-anti-BPhDE] to N{sup 6} of dA6 in this duplex sequence. The benzo[c]phenanthrenyl and nucleic acid exchangeable and nonexchangeable protons were assigned in the predominant conformation following analysis of two-dimensional NMR data sets in H{sub 2}O and D{sub 2}O buffer solution. The solution structure of the (-)-trans-anti-[BPh]dA{center_dot}dT 11-mer duplex has been determined by incorporating intramolecular and carcinogen-DNA proton-proton distances defined by lowermore » an upper bounds deduced from NOESY data sets as restraints in molecular mechanics computations in torsion angle space. 52 refs., 9 figs., 2 tabs.« less