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61.
J. Bauche H. Hühnermann D. N. Stacey V. Stacey M. Wilson 《Zeitschrift für Physik A Hadrons and Nuclei》1985,320(2):157-163
An interpretation is given of published measurements of optical isotope shifts in cadmium. This requires the evaluation of two electronic factors for each transition; these are found for the alkali-like transitions γγ226.5, 806.7 and 853.3 nm of Cd II using data from hyperfine structure and evidence from atomic calculations. The King relations then allow the electronic factors for γ1441.6 nm to be derived. Finally, the precise measurements of isotope shifts in this transition are analysed to investigate how the nuclear charge distribution changes over the range of stable isotopes. 相似文献
62.
C.J. Foot P.E.G. Baird M.G. Boshier D.N. Stacey G.K. Woodgate 《Optics Communications》1984,50(3):199-204
Intra-cavity second harmonic generation in a ring dye laser using lithium formate monohydrate has been observed to produce tunable cw UV radiation around 243 nm with single frequency powers of up to 1.4 mW. This wavelength region is of particular interest in the context of Doppler-free spectroscopy of atomic hydrogen. The radiation was used to excite an atomic beam of strontium to study the transition 5s2 1S0-4d5p 1P1 of Sr I. The isotope shifts were determined as follows: 88Sr-87Sr 123.7(8) MHz; 88Sr 285.0(8) MHz; 88Sr-84Sr 600.1(9) MHz. The values are compared with results for other lines and muonic isotope shifts to obtain the specific mass shift and field shift in this transition and to study the configuration mixing effects. The hyperfine structure of 87Sr was not resolved, the intervals being very much less than the measured linewidth of 25 MHz. 相似文献
63.
Brent Hawrylak Stacey Andrecyk Carrie-Ellen Gabriel Kim Gracie R. Palepu 《Journal of solution chemistry》1998,27(9):827-841
Solution properties of aqueous mixtures of isomeric butanediols have been investigated employing viscosity, surface tension, and index of refraction measurements as functions of temperature. The deviation of viscosity, surface tension, and molar refraction from ideal solution behavior is evaluated from the experimental data. The deviation from ideality is discussed in terms of molecular interactions between the components. Surface activity of the diols is evident from the surface tension measurements. It is found that the degree of hydrophobicity of the diols varies in the order 1,2 > 2,3 > 1,3 > 1,4. The strength of interaction of diols with the water varies in the order 2,3 > 1,4 1,3 > 1,2. 相似文献
64.
We report the synthesis and characterization of perchlorate salts containing the following three novel complex cations each with a bidentate thioether ligand: binuclear cis-[Pt(CH3SCH2CH2CH2SCH3)(mu-OH)]22+, mononuclear cis-[Pt(CH3SCH2CH2CH2SCH3)(H2O)2]2+, and mononuclear cis-[Pd(CH3SCH2CH2CH2SCH3)(H2O)2]2+. Despite their analogous compositions, the mononuclear Pt(II) and Pd(II) complexes differ in the selectivity with which they promote the hydrolysis of polypeptides. The complex cis-[Pt(CH3SCH2CH2CH2SCH3)(H2O)2]2+ promotes slow but selective cleavage of Met-Pro peptide bonds at pH 2.0. The selectivity of the complex cis-[Pd(CH3SCH2CH2CH2SCH3)(H2O)2]2+ is pH-dependent. At pH 2.0, this Pd(II) complex promotes residue-selective hydrolysis of the X-Y bond in X-Y-Met and X-Y-His sequences; the rate is enhanced when residue Y is proline. At pH 7.0, this kinetic preference becomes sequence-selective in that the Pd(II) complex exclusively cleaves the X-Pro bond in X-Pro-Met and X-Pro-His sequences. The enhanced reactivity of the X-Pro amide group is attributed to the high basicity of its carbonyl oxygen atom. Binding of the metal(II) atom enhances the electrophilicity of the carbonyl carbon atom and promotes nucleophilic attack by a solvent water molecule. The bidentate thioether ligand disfavors the formation of hydrolytically unreactive complexes, allowing the Pd(II) complex to promote the cleavage reaction. 相似文献
65.
Stacey A. Lomenzo Amy L. Bradley Naijue Zhu Cheryl L. Klein Mark L. Trudell 《Journal of heterocyclic chemistry》1997,34(4):1139-1146
A new synthetic approach for the regiospecific alkylation of the 6-position of the tropane ring system has been developed. Alkylation, desulfonylation and deprotection of tropanes 5 and 12 furnished a series of 6-endo-alkyltropan-2-one derivatives 8a-e, 15a-e and 16a-e (R = Me, Et, n-Pr, n-Bu, Bn) stereoselectively in good yields. The 6-endo isomers 15a-e and 6-exo isomers 16a-e were easily obtained as pure diastereoisomers. 相似文献
66.
Shenna M. LaPointe Craig A. Wheaton Stacey D. Wetmore 《Chemical physics letters》2004,400(4-6):487-493
Density-functional theory was used to study the properties (binding geometries and affinities for the natural DNA bases) of various degenerate nucleobases, which bind without discrimination to the purines or pyrimidines. The data for purine mimics (Z and K) indicates that although stronger binding strengths are calculated for pairs with cytosine compared with thymine, cytosine binds to a less stable tautomer of the nucleobase mimic. Indeed, the energy differences between the binding strengths and the tautomers effectively cancel and thereby provide a possible explanation for the observed degenerate properties of these molecules. Similar trends are found for the pyrimidine mimics (M and P); however, the energy differences do not cancel, even upon inclusion of environmental effects. 相似文献
67.
Turnbull WB Kalovidouris SA Stoddart JF 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(13):2988-3000
Carbohydrate-based dendritic structures composed of 21 and 27 monosaccharide residues have been synthesized in a convergent manner from trisaccharide building blocks. The oligosaccharide AB2 monomers are based on a maltosyl beta(1-->6)galactose structure, which has been modified to include two methylamino groups at the primary positions of the glucosyl residues. Reductive alkylation of the secondary amino groups, with the innate formyl function of a second oligosaccharide monomer, allows for the chemoselective construction of dendritic wedges, while employing a minimal number of protecting groups. The first-generation dendron can be coupled either to another AB2 monomer, to give a second-generation dendron, or to a tris[2-(methylamino)ethyl]amine-based core moiety, to provide a carbohydrate-based dendrimer. Alternating alpha- and beta-glucosyl residues in the monomers and dendrons, simplifies 1H NMR spectra as a consequence of spreading out the anomeric proton signals. Monomers and dendrons were characterized by extensive one- and two-dimensional NMR spectroscopy in addition to FAB, electrospray, and MALDI-TOF mass spectrometry. Molecular dynamics simulations revealed similar conformations in the dendrons as in the isolated trisaccharide repeating units. 相似文献
68.
R. Kloch P. E. G. Baird M. G. Boshier M. J. Macpherson C. W. P. Palmer D. N. Stacey V. Stacey 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1987,6(4):315-317
We have measured isotope shifts in λ326.1 nm of CdI using a pressure-scanned interferometer. The results are, in GHz: 116–106, ?2.222 (30); 113–108, ?1.052(10); 111–110, ?0.049 (12); 111–106, ?1.048 (10). Results for stable isotopes in λ326.1 nm are needed in the interpretation of existing measurements on radioactive cadmium isotopes. The new data are more precise than early atomic beam measurements but are reasonably consistent with them. 相似文献
69.
70.
Russell HF Bremner JB Bushelle-Edghill J Lewis MR Thomas SR Bates F 《Tetrahedron letters》2007,48(9):1637-1639
Reaction of primary aromatic amines with peroxidic tetrahydrofuran (THF) in the presence of hydrogen and 10% palladium on carbon catalyst results in THF ring opening to give 4-N-arylamino-1-butanols in a good yield. The reaction mechanism is believed to involve a free-radical sequence resulting in an imino alcohol subsequently reduced to product. 相似文献