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81.
82.
The principal decomposition routes of molecular ions of cis, cis, cis-2,4,6-octatriene, cis, cis, trans-2,4,6-octatriene, trans, cis, trans-2,4,6-octatriene, trans-5,6-dimethyl-1,3-cyclohexadiene and cis-5,6-dimethyl-1,3-cyclohexadiene were studied using ion kinetic spectroscopy. The loss of radicals from [M]+· appears to proceed via a ground state, while loss of a neutral molecule appears to involve either complete equilibration of structure within the system or both ground state and excited state pathways. 相似文献
83.
Guelev V Sorey S Hoffman DW Iverson BL 《Journal of the American Chemical Society》2002,124(12):2864-2865
We have been investigating a modular, threading DNA polyintercalator design based upon the 1,4,5,8-naphthalene tetracarboxylic diimide (NDI) intercalating unit. Previously, we have reported the NMR analysis of a bis-intercalator-DNA complex in which the peptide linker between NDI units was found to occupy the DNA major groove (Guelev, Lee, Sorey, Hoffman, Iverson, Chem. Biol. 2001, 8, 415-425). Here we describe the NMR analysis of a complex between a related bis-intercalator known to display altered DNA sequence specificity. In this case, the linker resides in the DNA minor groove. We have thus shown that within this set of sequence specific bis-intercalators, both DNA grooves can be accessed, setting the stage for longer threading polyintercalators designed to have linkers occupying both grooves in an alternating fashion. 相似文献
84.
Charles M. Lindsay Keith Smith Charles Allan Brown Kathleen Betterton-Cruz 《Tetrahedron letters》1984,25(9):995-998
Unsymmetrical hexathioorthooxalates of types () and () undergo elimination of dialkyl disulfide on heating in an organic solvent; the reaction, which is catalyzed by acid, proceeds without fission of the central C:C bond and provides the first general, high yield synthesis of unsymmetrical benzotetrathiafulvalenes of types () and (). 相似文献
85.
Salvador Puig-Torres Gary E. Martin Keith Smith Paul Cacioli James A. Reiss 《Journal of heterocyclic chemistry》1982,19(4):879-882
The reaction of 2-chloro-3-thiocyanatopyridine with a substituted spiroepoxycyclohexadienone, which served as a masked phenol with reversed polarity, led to the first reported synthesis of an analog of the 4-azaphenoxathiin ring system. Confirmation of the structure was obtained from the assignment of the 13C-nmr spectrum. 相似文献
86.
Keith B. Oldham Terence J. Cardwell Jose H. Santos Alan M. Bond 《Journal of Electroanalytical Chemistry》1997,430(1-2)
Voltammetric studies in solutions of high resistivity are facilitated by the use of microelectrodes under steady-state conditions. Such solutions are encountered with solvents of low permittivity because of the very sparing solubility of electrolytes. Moreover, in such media the supporting electrolyte, as well as the electroactive ionic species, is usually extensively ion paired. Here we predict the limiting current that will flow in these circumstances, when a monovalent ion undergoes a one-electron transfer at a hemispherical microelectrode to form a neutral product. The ion pairing equilibria are assumed to be fast but all diffusion coefficients are treated as distinct. An analytical solution is elusive in the general case, but a simple numerical procedure allows the limiting current to be predicted for any combination of the system parameters. Several special cases are also discussed, some of which yield explicit formulae for the limiting current. In a companion paper, experimental data are compared with the theoretical predictions. 相似文献
87.
Armbruster P Agarwal YK Brüchle W Brügger M Dufour JP Gaggeler H Hessberger FP Hofmann S Lemmertz P Münzenberg G Poppensieker K Reisdorf W Schadel M Schmidt K Schneider JH Schneider WF Sümmerer K Vermeulen D Wirth aG Ghiorso A Gregorich KE Lee D Leino M Moody KJ Seaborg GT Welch RB Wilmarth P Yashita S Frink C Greulich N Herrmann G Hickmann U Hildebrand N Kratz JV Trautman N Fowler MM Hoffman DC Daniels WR von Gunten HR Dornhöfer H 《Physical review letters》1985,54(5):406-409
88.
Predicting the performance of molecularly imprinted polymers: Selective extraction of caffeine by molecularly imprinted solid phase extraction 总被引:2,自引:0,他引:2
A rational design approach was taken to the planning and synthesis of a molecularly imprinted polymer capable of extracting caffeine (the template molecule) from a standard solution of caffeine and further from a food sample containing caffeine. Data from NMR titration experiments in conjunction with a molecular modelling approach was used in predicting the relative ratios of template to functional monomer and furthermore determined both the choice of solvent (porogen) and the amount used for the study. In addition the molecular modelling program yielded information regarding the thermodynamic stability of the pre-polymerisation complex. Post-polymerisation analysis of the polymer itself by analysis of the pore size distribution by BET yielded significant information regarding the nature of the size and distribution of the pores within the polymer matrix. Here is proposed a stepwise procedure for the development and testing of a molecularly imprinted polymer using a well-studied compound—caffeine as a model system. It is shown that both the physical characteristics of a molecularly imprinted polymer (MIP) and the analysis of the pre-polymerisation complex can yield vital information, which can predict how well a given MIP will perform. 相似文献
89.
Clorobiocin (clo) and novobiocin (nov) are potent inhibitors of bacterial DNA gyrase. The two substances differ in the substitution pattern at C-8' of the aminocoumarin ring, carrying a chlorine atom or a methyl group, respectively. By gene inactivation, clo-hal was identified as the gene of the halogenase responsible for the introduction of the chlorine atom of clorobiocin. Inactivation of cloZ did not affect clorobiocin formation, showing that this ORF is not essential for clorobiocin biosynthesis. Expression of the methyltransferase gene novO in the clo-hal(-) mutant led to the very efficient formation of a hybrid antibiotic containing a methyl group instead of a chlorine atom at C-8'. Comparison of the antibacterial activity of clorobiocin analogs with -Cl, -H, or -CH(3) at C-8' showed that chlorine leads to 8-fold higher activity than hydrogen and to 2-fold higher activity than a methyl group. 相似文献
90.
The noble metals are inhomogeneously distributed in sulphide ores and their host rocks. It is therefore necessary to analyse large sample sizes to obtain representative analyses. A nickel sulphide fire assay technique has been adapted to extract the noble metals from a large sample size (50 g) into a nickel sulphide button. Subsequently the fire assay button is dissolved in hydrochloric acid and the solution is filtered. The noble metal residue retained on the filter paper is analysed quantitatively by i.n.a.a. techniques. This method is rapid, relatively inexpensive and has better sensitivities for all the noble metals than other analytical techniques. 相似文献