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171.
The bis(diamine)palladium(II) cations (diamine = ethane-1,2-diamine, propane-1,3-diamine, or butane-1,4-diamine) all undergo condensation reactions with formaldehyde and nitroethane to produce macromonocycles where each pair of cis-disposed primary amines has been converted to a -NH-CH(2)-C(CH(3))(NO(2))-CH(2)-NH- strap. The 14-membered-ring macrocycle has been previously prepared by condensation around copper(II) and nickel(II), but this does not permit synthesis of the larger ring macrocycles. The macrocyclic complex (6,13-dimethyl-6, 13-dinitro-1,4,8,11-tetraazacyclotetradecane)palladium(II) perchlorate crystallizes in the triclinic space group P&onemacr;, a = 8.105(3) ?, b = 8.370(2) ?, c = 9.437(4) ?, alpha = 69.04(3) degrees, beta = 68.60(3), gamma = 71.53(3) degrees. Complexes of the 16- and 18-membered macrocycles (3,11-dimethyl-3,11-dinitro-1,5,9,13-tetraazacyclohexadecane)palladium(II) perchlorate and (3,12-dimethyl-3,12-dinitro-1,5,10,14-tetraaazacyclooctadecane)palladium(II) perchlorate crystallize in the monoclinic space group P2(1)/c, with a = 8.391(2) ?, b = 12.816(3) ?, c = 23.925(9) ?, and beta = 93.18(2) degrees, and the triclinic space group P&onemacr;, with a = 7.746(5) ?, b = 9.912(5) ?, c = 18.96(2) ?, alpha = 91.76(6) degrees, beta = 101.73(7) degrees, and gamma = 112.83(5) degrees respectively. The larger macrocycles are "swollen" by incorporating longer methylene chains, "swelling" leading to an increase in Pd-N distance and in tetrahedral distortion, with the dominant geometric isomer apparently changing with macrocycle size from anti-disposed nitro pendants (14-membered) to the syn isomer (16-, 18-membered). An irreversible Pd(II/IV) oxidation occurs at ca +1 V (vs Ag/AgCl), varying slightly with ring size, with a multi-electron nitro group reduction observed near -0.8 V in each case. Electronic spectra also vary slightly with ring size. 相似文献
172.
X-ray crystal structures are reported for the following complexes: [Ru(2)Cl(3)(tacn)(2)](PF(6))(2).4H(2)O (tacn = 1,4,7-triazacyclononane), monoclinic P2(1)/n, Z = 4, a = 14.418(8) ?, b = 11.577(3) ?, c = 18.471(1) ?, beta = 91.08(5) degrees, V = 3082 ?(3), R(R(w)) = 0.039 (0.043) using 4067 unique data with I > 2.5sigma(I) at 293 K; [Ru(2)Br(3)(tacn)(2)](PF(6))(2).2H(2)O, monoclinic P2(1)/a, Z = 4, a = 13.638(4) ?, b = 12.283(4) ?, c = 18.679(6) ?, beta = 109.19(2) degrees, V = 3069.5 ?(3), R(R(w)) = 0.052 (0.054) using 3668 unique data with I > 2.5sigma(I) at 293 K; [Ru(2)I(3)(tacn)(2)](PF(6))(2), cubic P2(1)/3, Z = 3, a = 14.03(4) ?, beta = 90.0 degrees, V = 2763.1(1) ?(3), R (R(w)) = 0.022 (0.025) using 896 unique data with I > 2.5sigma(I) at 293 K. All of the cations have cofacial bioctahedral geometries, although [Ru(2)Cl(3)(tacn)(2)](PF(6))(2).4H(2)O, [Ru(2)Br(3)(tacn)(2)](PF(6))(2).2H(2)O, and [Ru(2)I(3)(tacn)(2)](PF(6))(2) are not isomorphous. Average bond lengths and angles for the cofacial bioctahedral cores, [N(3)Ru(&mgr;-X)(3)RuN(3)](2+), are compared to those for the analogous ammine complexes [Ru(2)Cl(3)(NH(3))(6)](BPh(4))(2) and [Ru(2)Br(3)(NH(3))(6)](ZnBr(4)). The Ru-Ru distances in the tacn complexes are longer than those in the equivalent ammine complexes, probably as a result of steric interactions. 相似文献
173.
Selenium (10–80 μg kg?1) is determined by hydride-generation atomic absorption spectrometry in mixed diet, faecal and urine samples and in standard reference materials (bovine liver, rice flour, wheat flour and horse kidney) after two digestion procedures. No difference was found in digestion efficiency between a nitric/sulphuric acid mixture and a nitric/sulphuric/perchloric acid mixture. The results suggest that the digestion of most biological materials for the determination of selenium does not require the use of perchloric acid. 相似文献
174.
Resonance Raman Spectroscopy,and Its Application to Inorganic Chemistry. New Analytical Methods (27)
Robin J. H. Clark Trevor J. Dines 《Angewandte Chemie (International ed. in English)》1986,25(2):131-158
Resonance Raman spectra are obtained when the wave number of the exciting radiation is close to, or coincident with, that of an electronic transition of the scattering species. Such spectra are usually characterized by a very large enhancement of the intensities of particular Raman bands, sometimes with the appearance of intense overtone and combination tone progressions. The technique provides detailed information about excited electronic states because it is only the vibrational modes associated with the chromophore that are resonance-Raman active. Additionally, the high sensitivity is such that compounds at concentrations as low as 10?6 mol/L may be detected, enabling resonance Raman spectroscopy to be used as an analytical tool and for the study of chromophores in molecules of biological interest. 相似文献
175.
Kelso MJ Beyer RL Hoang HN Lakdawala AS Snyder JP Oliver WV Robertson TA Appleton TG Fairlie DP 《Journal of the American Chemical Society》2004,126(15):4828-4842
Alpha-Helices are key structural components of proteins and important recognition motifs in biology. Short peptides (相似文献
176.
Trevor J. Broxton 《Journal of mass spectrometry : JMS》1977,12(6):375-378
The mass spectra of aryl sulfonamides of some 2-aminopyridines and 2-aminopyrimidine show abundant peaks corresponding tothe loss of SO2 and HSO2 from the molecular ion. Evidence in favour of a cyclization-elimination reaction involving bond formation between the pyridine ring nitrogen and the ortho position of the benzene ring is presented. 相似文献
177.
M. Gardner Judith Dobson Brian Miller Colin Allchin David McMullan Trevor Oliver David Wells R. Hudson Richard Toft Mike Jessep 《Accreditation and quality assurance》2002,7(2):60-65
The implementation of a strategy for the assessment of the validity of environmental monitoring data – a ”data filter”– is
described. The approach was developed through the UK National Marine AQC Scheme for application to data collected during the
UK National Marine Monitoring Programme. Data reported for the year 1999, by nine laboratories, for 74 determinand-matrix
combinations were assessed on the basis of the completeness of their supporting quality assurance and quality control information.
The approach to the establishment of criteria of acceptability for quality information is described.
Received: 28 August 2001 Accepted: 29 November 2001 相似文献
178.
Electrophilic cobalt(III) mediates an unprecedented two-carbon ring expansion of coordinated five-membered rings, leading to a remarkably general new strategy for the synthesis of seven-membered carbocycles from readily available five-membered ring substrates. The reaction, a metal-mediated [5 + 2] cyclopentenyl/alkyne cycloaddition, proceeds via initial protonation of a cobalt(I) cyclopentadiene complex, followed by rearrangement to an agostic eta3-cyclopentenyl intermediate. The cyclic eta3-allyl residue then undergoes migratory coupling with alkyne followed by carbon-carbon bond activation of the unstrained five-membered ring and recyclization to the ring expanded product, although the order of events and intimate mechanism has not been conclusively established. The reaction is highly selective with respect to which five-membered ring ligand undergoes activation, presumably a consequence of rapid cobalt-mediated interannular hydride transfer and kinetic preference for alkyne insertion into the less substituted cyclopentenyl ring. The alkyne insertion is itself highly regioselective, proceeding via migration to the sterically smaller end of the alkyne. The reaction is sensitive to both the cobalt counterion and the ancillary eta5-cyclopentadienyl substituent but proceeds for a considerable range of alkyl-, aryl-, and trialkylsilyl-substituted terminal and internal alkynes. 相似文献
179.
Marine toxins targeting the actin cytoskeleton represent a new and promising class of anti-cancer compounds. Here we present a 2.0 A resolution structure of swinholide A, a marine macrolide, bound to two actin molecules. The structure demonstrates that the actin dimer in the complex does not represent a physiologically relevant entity, for the two actin molecules do not interact with each other. The swinholide A actin binding site is the same as that targeted by toxins of the trisoxazole family and numerous actin binding proteins, highlighting the importance of this site in actin polymerization. The observed structure reveals the mechanism of action of swinholide A and provides a structural framework about which to design new agents directed at the cytoskeleton. 相似文献
180.
Anniefer N. Magpusao Kelli Rutledge Dr. Trevor A. Hamlin Jean‐Marc Lawrence Dr. Brandon Q. Mercado Prof. Nicholas E. Leadbeater Prof. Mark W. Peczuh 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(17):6001-6011
Shape is an inherent trait of a molecule that dictates how it interacts with other molecules, either in binding events or intermolecular reactions. Large‐ring macrocyclic compounds in particular leverage their shape when they are selectively bound by biomolecules and also when they exhibit macrocyclic diastereoselectivity. Nonetheless, rules that link structural parameters to the conformation of a macrocycle are still rudimentary. Here we use a structural investigation of a family of [13]‐macrodilactones as a case study to develop rules that can be applied generally to macrocycles of different sizes and with a variety of functionality. A characteristic “ribbon” shape is adopted by the [13]‐macrodilactones in the absence of stereogenic centres, which exhibits planar chirality. When one stereogenic centre at key positions on the backbone is incorporated into the structure, the planar chirality is dictated by the configuration of the centre. In cases where two stereogenic centres are present, their relationships can either reinforce the characteristic ribbon shape or induce alternative shapes to be adopted. The rules established in the case study are then applied to the analysis of a structure of the natural product migrastatin. They lay the groundwork for the development of models to understand macrocycle‐biomolecule interactions and for the preparation of macrocycles with designed properties and activities. 相似文献