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151.
R. Wadsworth P. Regan S. M. Mullins G. J. Gyapong D. L. Watson P. J. Nolan M. J. Godfrey I. Jenkins Y. J. He B. J. Varley W. Gelletly J. Simpson 《Zeitschrift für Physik A Hadrons and Nuclei》1989,333(4):409-410
A rotational band of nine γ-rays has been observed in133Sm. The moment of inertia of the band indicates that it has a higher deformation than expected for states in nuclei in this region. The properties are such that it can be interpreted as being due to the odd neutron occupying the ν i2/13 nn intruder orbital. This is the first evidence for the occupation of this orbital in nuclei with neutron number N<73. 相似文献
152.
The novel complex trans-[PdCl2(η1-N-2-ethyl-2-oxazoline)2] is shown to be an active and oxidatively robust catalyst for C-C bond-forming reactions (Heck, Sonogashira, Ullman, Suzuki), which can be carried out in air without rigorous solvent/substrate purification and in the absence of additional free ligand. 相似文献
153.
Antoniazzi L Arenton M Cao Z Chen T Conetti S Cox B Delchamps S Fortney L Guffey K Haire M Ioannou P Jenkins CM Judd DJ Kourkoumelis C Manousakis-Katsikakis A Kuzminski J LeCompte T Marchionni A He M Mazur PO Murphy CT Pramantiotis P Rameika R Resvanis LK Rosati M Rosen J Shen C Shen Q Simard A Smith RP Spiegel L Stairs DG Tan Y Tesarek RJ Turkington T Turnbull L Turkot F Tzamarias S Voulgaris G Wagoner DE Wang C Yang W Yao N Zhang N Zhang X Zioulas G Zou B 《Physical review D: Particles and fields》1992,46(11):4828-4835
154.
Geoffrey R. County Ron S. Dickson Susan M. Jenkins Julian Johnson Olga Paravagna 《Journal of organometallic chemistry》1997,530(1-2)
Treatment of (η5-C5H5)2Rh2(CO)η1-Ph2P(CH2)n PPh2(μ-η1:η1-CF3C2CF3) (I) with (η5-CH3C5H4)Mn(CO)2(thf) or Cr(CO)5(thf) gives the hetero-trinuclear products (η-C5H5)2Rh2(CO)(μ-CF3C2CF3)μ:η1:η1-Ph2P(CH2)nPPh2(η-CH3C5H3C4)Mn(CO2) (II, n = 1–4) and (η5-C5H5)2Rh2(CO)(μ-CF3C2CF3)μ:η1:η1-Ph2P(CH2)nPPh2Cr(CO)5 (IV, n = 1–4) in good yields. In these products, the configuration of the CO and bisphosphine units on the Rh-Rh bond is trans. Related reactions between (η5:η5-C5H4CH2C5H4)Rh2(CO)η1-Ph2P(CH2)nPPh2(μ-η1:η1- (V) and the same solvated manganese and chromium complexes give (η5:η5-C5H4CH2C5H4)Rh2(CO)(μ-CF3C2CF3)μ:η1:η1-Ph2P(CH2) (VI, n = 1, 2 or 4) and (η5:η5-C5H4CH2C5H4)Rh2(CO)(μ-CF3C2CF3)μ:η1:η1-Ph2P(CH2) (VIII). The complexes (VI) and (VIII) have a mutually cis arrangement of CO and the bisphosphine on the Rh-Rh bond. Attempts to induce the complexes (IV), (V), (VI), and (VIII) to form clusters by loss of CO and Rh-M bond formation were not successful. Treatment with trimethylamine oxide or sunlight irradiation generally resulted in loss of the hetero-metal and formation of the dirhodium phosphine oxide complexes (III, n = 2 or 4) and (VII, n = 2, 3). 相似文献
155.
Dr. Laurence R. Doyle Dr. Ashley J. Wooles Lucy C. Jenkins Dr. Floriana Tuna Prof. Eric J. L. McInnes Prof. Stephen T. Liddle 《Angewandte Chemie (International ed. in English)》2018,57(21):6314-6318
Catalytic reduction of N2 to NH3 by a Ti complex has been achieved, thus now adding an early d‐block metal to the small group of mid‐ and late‐d‐block metals (Mo, Fe, Ru, Os, Co) that catalytically produce NH3 by N2 reduction and protonolysis under homogeneous, abiological conditions. Reduction of [TiIV(TrenTMS)X] (X=Cl, 1A ; I, 1B ; TrenTMS=N(CH2CH2NSiMe3)3) with KC8 affords [TiIII(TrenTMS)] ( 2 ). Addition of N2 affords [{(TrenTMS)TiIII}2(μ‐η1:η1‐N2)] ( 3 ); further reduction with KC8 gives [{(TrenTMS)TiIV}2(μ‐η1:η1:η2:η2‐N2K2)] ( 4 ). Addition of benzo‐15‐crown‐5 ether (B15C5) to 4 affords [{(TrenTMS)TiIV}2(μ‐η1:η1‐N2)][K(B15C5)2]2 ( 5 ). Complexes 3 – 5 treated under N2 with KC8 and [R3PH][I], (the weakest H+ source yet used in N2 reduction) produce up to 18 equiv of NH3 with only trace N2H4. When only acid is present, N2H4 is the dominant product, suggesting successive protonation produces [{(TrenTMS)TiIV}2(μ‐η1:η1‐N2H4)][I]2, and that extruded N2H4 reacts further with [R3PH][I]/KC8 to form NH3. 相似文献
156.
Solid-phase synthesis and biochemical studies of O-boranophosphopeptides and O-dithiophosphopeptides
Jenkins KE Higson AP Seeberger PH Caruthers MH 《Journal of the American Chemical Society》2002,124(23):6584-6593
Signal transduction cascades maintain control over important cellular processes such as cell growth and differentiation by orchestrating protein phosphorylation and dephosphorylation. Specific control of these processes in vivo and in vitro can be achieved with peptide analogues that mimic the binding properties of phosphoproteins. We present here the solid-phase synthesis of two novel classes of phosphopeptide mimetics, O-boranophosphopeptides and O-dithiophosphopeptides, derivatized on tyrosine, serine, and threonine. The use of H-phosphonate and H-phosphonothioate monoesters containing the base labile 9-fluorenemethyl protecting group was key to the synthesis of both phosphopeptide mimetics. O-Boranophosphopeptides were synthesized by condensing O-(9-fluorenemethyl)-H-phosphonate to the peptide hydroxylic component (tyr, ser, or thr) followed by oxidation with borane complexes. Similarly, the synthesis of O-dithiophosphopeptides used the O-(9-fluorenemethyl)-H-phosphonothioate synthon and oxidation with elemental sulfur. Base elimination of the Fmol protecting group and cleavage from the solid support with concentrated ammonium hydroxide afforded the boranophosphopeptide and dithiophosphopeptide target compounds. Ac-YIIPLPG-NH2, having either dithiophosphoryl tyrosine or boranophosphoryltyrosine but no sequence specificity for Yersinia protein tyrosine phosphatase (PTP), was found to competitively inhibit this enzyme with KI values of 430 +/- 50 and 670 +/- 50 microM, respectively. In addition, both phosphopeptide analogues were resistant toward Yersinia PTP enzymatic hydrolysis. Under conditions (pH 8.0) where the phosphopeptide was rapidly dephosphorylated, the boranophosphopeptide hydrolyzed slowly (t1/2 = 15 h) and the dithiophosphopeptide was completely stable over 24 h. 相似文献
157.
The viscoelastic behavior of a semidilute hydrophobically modified alkali-soluble emulsion (HASE)-C20 polymer in NaCl and NaCl/SDS (sodium dodecyl sulfate) solutions was determined using a Rheometric fluids rheometer and the data were converted to relaxation spectra. The dynamic moduli can be fitted with a multiple modes Maxwell model. In the presence of increasing amounts of NaCl, the moduli decrease, where G', decreases more rapidly than G". However, in the presence of SDS and 0.4 M NaCl, the dynamic moduli increase to a maximum at a critical concentration and decrease thereafter. The relaxation spectra suggest that the structure of the polymer network is complex and it contains two to six relaxation times, depending on the NaCl or SDS/0.4 M NaCl concentrations. With increasing NaCl concentrations, the fastest peak shifts to longer times while the slowest peak decreases. This corresponds to the destruction of the network as the polymer backbone collapses to form clusters with a larger aggregation number. For HASE in SDS/0.4 M NaCl solutions, the lifetime of both the hydrophobic junction (fastest peak) and network relaxation (slowest peak) shift to longer times, which suggests the strengthening of active junctions by bound SDS molecules. However, beyond a critical SDS concentration, the relaxation time of the polymer and hydrophobic junction decreases to an asymptotic value. Copyright 2000 Academic Press. 相似文献
158.
Nakamura T Busfield WK Jenkins ID Rizzardo E Thang SH Suyama S 《The Journal of organic chemistry》2000,65(1):16-23
The thermolysis of a series of tert-alkyl peroxypivalates 1 in cumene has been investigated by using the nitroxide radical-trapping technique. tert-Alkoxyl radicals generated from the thermolysis underwent the unimolecular reactions, beta-scission, and 1,5-H shift, competing with hydrogen abstraction from cumene. The absolute rate constants for beta-scission of tert-alkoxyl radicals, which vary over 4 orders of magnitude, indicate the vastly different behavior of alkoxyl radicals. However, the radical generation efficiencies of 1 varied only slightly, from 53 (R = Me) to 63% (R = Bu(t)()), supporting a mechanism involving concerted two-bond scission within the solvent cage to generate the tert-butyl radical, CO(2), and an alkoxyl radical. The thermolysis rate constants of tert-alkyl peroxypivalates 1 were influenced by both inductive and steric effects [Taft-Ingold equation, log(rel k(d)) = (0.97 +/- 0. 14)Sigmasigma - (0.31 +/- 0.04)SigmaE(s)(c), was obtained]. 相似文献
159.
Frederick S. Richardson Gary Hilmes Jacqueline J. Jenkins 《Theoretical chemistry accounts》1975,39(1):75-91
The influence of vibronic interactions on the chiroptical spectra associated with a threesome of nearly degenerate electronic excited states in a dissymmetric molecular system is examined on a formal theoretical model. The model considers two vibrational modes to be effective in promoting pseudo Jahn-Teller (PJT) type interactions between the three closely spaced electronic excited states. Formal expressions are developed for the rotatory strengths of individual vibronic levels derived from the coupled electronic states. Two mode (vibrational)-three state (electronic) vibronic Hamiltonians are constructed (basis set size, 63–108, depending upon interaction parameters used) and diagonalized for a large number of different parameter sets representative of various vibronic coupling strengths, electronic energy level spacings, oscillator (vibrational mode) frequencies, and electronic rotatory strengths. Diagonalization of these vibronic Hamiltonians yields vibronic wave functions and energies which are then used to calculate rotatory strength spectra for the model system. The calculated results demonstrate the profound influence which vibronic interactions of the PJT type may have on the sign patterns and intensity distributions within the rotatory strength spectrum associated with a set of nearly degenerate electronic states. The implication of these results for the interpretation of circular dichroism spectra of chiral transition metal complexes with pseudo tetragonal symmetry are discussed. 相似文献
160.
Summary Column characteristics affecting the chromatographic behavior of glass and siliceous glass (fused silica) capillary columns include the dimensional uniformity of the column, the physical and chemical characteristics of the column wall and the characteristics of the liquid phase. In the case of the coated column the uniformity and thickness of the liquid phase film are the most important criteria affecting column reproducibility. The paper discusses these factors and their influence on column performance.Presented in part at the Symposium on Standardized Materials for Chromatography, 181 st National American Chemical Society Meeting, Atlanta, Georgia, March 29–April 3, 1981. 相似文献