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911.
Aaron P. Holm Susan M. Kauzlarich Simon A. Morton James G. Tobin 《Journal of solid state chemistry》2005,178(1):262-269
Measurements of core and valence electronic states of single crystals of the rare earth transition metal Zintl phases Yb14MnSb11 and Yb14ZnSb11 were performed using the X-ray photoelectron spectroscopy station of Beamline 7 at the Advanced Light Source. Sample surfaces of Yb14MnSb11 and Yb14ZnSb11 were measured as received, after Ar+ ion bombardment, and after cleaving in situ. The single crystal structure of Yb14ZnSb11 is also reported. Both compounds are air-sensitive and show Yb3+ due to surface oxidation. In the case of Yb14MnSb11, there is no evidence for Yb3+ that would be intrinsic to the sample, consistent with previously reported X-ray magnetic circular dichroism studies. Detailed analyses of the Yb14ZnSb11 surfaces reveal a significant contribution of both Yb3+ and Yb2+ 4f states in the valence band region. This result is predicted for the Zn analog by Zintl counting rules and support the mixed valency of Yb for Yb14ZnSb11. Further detailed analysis of the core and valence band structure of both Yb14MnSb11 and Yb14ZnSb11 is presented. 相似文献
912.
D. Chakravarti R. N. Chakravarti L. A. Cohen B. Dasgupta S. Datta H. K. Miller 《Tetrahedron》1961,16(1-4):224-250
On the basis of a critical study of the ultra-violet and the infra-red absorption spectra of arborine, dihydroarborine, 1,2-dimethylquinazol-4-one, 2-ethyl-1-methylquinazol-4-one, 2,3-dihydro-1,2-dimethylquinazol-4-one and 2,3-dihydro-2-ethyl-1-methylquinazol-4-one, it has been shown that arborine is 2-benzyl-1-methylquinazol-4-one and not the tautomeric form, 2-benzylidene-1-methylquinazol-4-one. This has been confirmed on the basis of the nuclear magnetic resonance spectrum of arborine. Incidentally, it has been shown that 'glycosine' of Chatterjee and Ghosh Majumdar is not a new alkaloid and this name should be deleted from the literature. 相似文献
913.
Dounay AB Overman LE Wrobleski AD 《Journal of the American Chemical Society》2005,127(29):10186-10187
A catalytic asymmetric method for the chemical synthesis of alkaloids containing the 1,2,3,4-tetrahydro-9a,4a-(iminoethano)-9H-carbazole (1) moiety is reported and verified by the enantioselective total synthesis of (+)-minfiensine (4). The central step in this total synthesis is the sequential catalytic asymmetric Heck-N-acyliminium ion cyclization of dienyl carbamate triflate 10, prepared in six steps from 1,2-cyclohexanedione, to give enantiopure 3,4-dihydro-9a,4a-(iminoethano)-9H-carbazole (12) in 75% yield. Iminoethano-9H-carbazole 12 is transformed in six steps to dienyl iodide 17, which undergoes diastereoselective intramolecular Heck cyclization to form pentacyclic intermediate 18. In eight additional steps, this latter intermediate is transformed to (+)-minfiensine (4). 相似文献
914.
Pfennig BW Mordas CJ McCloskey A Lockard JV Salmon PM Cohen JL Watson DF Bocarsly AB 《Inorganic chemistry》2002,41(17):4389-4395
The synthesis, characterization, electrochemical, photophysical, and photochemical properties of two hexanuclear mixed-valence compounds are reported. Each supramolecular species consists of two cyano-bridged [(NC)(5)Fe(II)-CN-Pt(IV)(NH(3))(3)L-NC-Fe(II)(CN)(5)] triads that are linked to each other through a Pt(IV)-L-Pt(IV) bridge, where L = 4,4'-dipyridyl (bpy) or 3,3'-dimethyl-4,4'-dipyridyl (dmb). The major difference between the two compounds is the electronic nature of the bridging ligand between the two Pt atoms. Both species exhibit a broad Fe(II) --> Pt(IV) intervalent (IT) absorption band at 421 nm with an oscillator strength that is approximately four times that for [(NC)(5)Fe(II)-CN-Pt(IV)(NH(3))(5)] and twice that for [(NC)(5)Fe(II)-CN-Pt(IV)(NH(3))(4)-NC-Fe(II)(CN)(5)].(4-) When L = bpy, the resonance Raman spectrum obtained by irradiating the IT band at 488 nm exhibits several dipyridyl ring modes at 1604, 1291, and 1234 cm(-1) which are not present in the spectrum when L = dmb. In addition, femtosecond pump-probe spectroscopy performed at 400 nm yields a transient bleach of the IT absorption band with a single exponential decay of 3.5 ps for L = bpy, compared with only 1.8 ps for L = dmb and 2.1 ps for [(NC)(5)Fe(II)-CN-Pt(IV)(NH(3))(4)-NC-Fe(II)(CN)(5)].(4-) Last, prolonged irradiation of the complexes at 488 nm leads to the formation of 4 equiv of ferricyanide with a quantum efficiency of 0.0014 for L = bpy and 0.0011 for L = dmb. The transient absorption, resonance Raman, and photochemical data suggest that the degree of excited electronic coupling in these compounds is tunable by changing the electronic nature of the Pt-L-Pt bridging ligand. 相似文献
915.
Introduction of metastatic heterogeneity by short-term in vivo passage of a cloned transformed cell line 总被引:2,自引:0,他引:2
J E Talmadge J R Starkey W C Davis A L Cohen 《Journal of supramolecular structure》1979,12(2):227-243
An experimental system for the study of metastasis has been developed using an epithelioid cell line of hepatic origin which had previously been chemically transformed in vitro. These metastatic cells were studied in the syngeneic rat strain. The cloned parent cell line metastasizes only to the lungs following intravenous, subcutaneous, or intraperitoneal injection. The metastatic phenotype is stable during in vitro passage, and subclones from the parent clone have a metastatic capacity statistically similar to that of the parent clone. Following ascites passage of the parent cell line, the cell population obtained exhibits the same metastatic ability as the parent clone. However, subclones obtained from the ascites-passaged population exhibit metastatic heterogeneity. This heterogeneity is introduced by the host passage and not by in vitro culture or subcloning. In the case of the two metastatic variants examined, the difference in the metastatic phenotype is found not to be due to differences in arrest or trapping of the cells but appears to be related to long-term survival and proliferation of the tumor cells following their arrest in the lungs. Morphologically the variants are very similar, and growth of the metastatic foci provokes a vigorous inflammatory response by the host. 相似文献
916.
The opportunistic protozoan Cryptosporidium parvum is highly resistant to disinfectants, including those specifically used for processing reused medical equipment in hospitals. C. parvum oocysts were dried onto glass and steel grooved penicylinders and challenged with 2.5% glutaraldehyde solution in the presence of 3 types of soil with exposures at 10 min, 90 min, and 10 h. The influence of organic soils on disinfection was measured with 5% fetal bovine serum (FBS), 10% FBS, and 5 mg mucin/mL. An in vitro excystation procedure and cell culture infection assay were used to determine survivability of oocysts after the germicide challenge. In the presence of organic soil, all oocysts removed from carriers excysted and infected cell monolayers after all germicide contact times. However, excystation was observed only from oocysts that received no protection from organic soil after 10 h exposure. In these samples, no infection was observed in the cell monolayers. The results of this research demonstrate the importance of thorough cleaning of medical equipment before disinfection. 相似文献
917.
A novel synthetic biodegradable oligomer based upon methacrylated aminocaproyl maleamic acid (MACMA), was synthesized and characterized. Injectable and in situ crosslinkable polymer networks were formulated by copolymerization of MACMA with triethyleneglycol dimethacrylate (TEGDMA). In addition, composites composed of MACMA, TEGDMA and beta-tricalcium phosphate (β-TCP) were prepared. The networks and composites were initiated by photo- and redox-polymerization, respectively. The initial compressive (CS) and diametral tensile strengths (DTS) of these materials were determined and used to evaluate the effects of MACMA/TEGDMA ratios on the degradation behavior of the materials. The neat resin networks exhibited initial CS values ranging from 6.7 to 284.2 MPa and the composites demonstrated initial DTS values ranging from 2.8 to 20.8 MPa and CS values ranging from 19.1 to 119.5 MPa. During the course of degradation the polymer neat resins lost 51%, 69% and 61% of their initial CS after 3 weeks for the MACMA/TEGDMA ratios at 25/75, 50/50 and 75/25, respectively. The resin with the MACMA/TEGDMA ratio of 75/25 completely degraded after 6 months. The composite with the MACMA/TEGDMA ratio of 25/75 exhibited a significant increase in CS after an initial decrease for 7 days and then lost 57% of its initial CS after 3 months. The composite composed of poly(MACMA) homopolymer showed a complete degradation after 21 days. 相似文献
918.
Aaron Nilsen Rebecca Braslau 《Journal of polymer science. Part A, Polymer chemistry》2006,44(2):697-717
Nitroxides bearing an α‐hydrogen decompose upon heating in a bimolecular reaction. A new mechanism is proposed for the decomposition of t‐butylisopropylphenyl nitroxide (TIPNO) involving the formation of a head‐to‐tail dimer, single electron transfer to form an oxammonium salt, epimerization to the corresponding nitrone, and elimination to form a conjugated oxime. This mechanism may provide insights into designing new nitroxides for use in controlled polymerization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 697–717, 2006 相似文献
919.
Derat E Cohen S Shaik S Altun A Thiel W 《Journal of the American Chemical Society》2005,127(39):13611-13621
The active species, Compound I, of horseradish peroxidase (HRP) has been investigated by quantum mechanical/molecular mechanical (QM/MM) calculations using 10 different QM regions. In accord with experimental data, the lowest doublet and quartet states are found to be virtually degenerate, with two unpaired electrons on the FeO moiety and one localized on the porphyrin in an a(2u)-dominant orbital with a minor, but nonnegligible, a(1u) component. The proximal ligand appears to be imidazole rather than imidazolate. The hydrogen-bonding network around the FeO moiety (i.e., Arg38 and His42) has significant influence on the axial bonds and the spin density distribution in the FeO moiety. Including this network in the QM region was found to be essential for reproducing the experimental M?ssbauer parameters. The protein environment shapes most of the subtle features of Compound I of HRP. 相似文献
920.
Fry HC Cohen AD Toscano JP Meyer GJ Karlin KD 《Journal of the American Chemical Society》2005,127(17):6225-6230
Time-resolved infrared (TRIR) flash photolytic techniques have been employed to initiate and observe the efficient dissociation of CO from a synthetic heme-CO/copper complex, [((6)L)Fe(II)(CO)..Cu(I)](+) (2), in CH(3)CN and acetone at room temperature. In CH(3)CN, a significant fraction of the photodissociated CO molecules transiently bind to copper (nu(CO)(Cu) = 2091 cm(-)(1)) giving [((6)L)Fe(II)..Cu(I)(CO)](+) (4), with an observed rate constant, k(1) = 1.5 x 10(5) s(-)(1). That is followed by a slower direct transfer of CO from the copper moiety back to the heme (nu(CO)(Fe) = 1975 cm(-)(1)) with k(2) = 1600 s(-)(1). Additional transient absorption (TA) UV-vis spectroscopic experiments have been performed monitoring the CO-transfer reaction by following the Soret band. Eyring analysis of the temperature-dependent data yields DeltaH(double dagger) = 43.9 kJ mol(-)(1) for the 4-to-2 transformation, similar to that for CO dissociation from [Cu(I)(tmpa)(CO)](+) in CH(3)CN (DeltaH(double dagger) = 43.6 kJ mol(-)(1)), suggesting CO dissociation from copper regulates the binding of small molecules to the heme within [((6)L)Fe(II)..Cu(I)](+)(3). Our observations are analagous to those observed for the heme(a3)/Cu(B) active site of cytochrome c oxidase, where photodissociated CO from the heme(a3) site immediately (ps) transfers to Cu(B) followed by millisecond transfer back to the heme. 相似文献