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11.
Sullens TA Jensen RA Shvareva TY Albrecht-Schmitt TE 《Journal of the American Chemical Society》2004,126(9):2676-2677
Novel open-framework alkali metal uranyl periodates, having the formula A[(UO2)3(HIO6)(OH)(O)(H2O)].1.5H2O (A = Li, Na, K, Rb, Cs), have been prepared through mild hydrothermal synthesis. These isostructural compounds contain distorted UO7 pentagonal bipyramids that are linked through a uranyl (UO22+) to uranyl cation-cation interaction. This interaction arises from a single axial uranyl oxygen coordinating at an equatorial site of an adjacent uranyl unit. These uranium oxide polyhedra are further bound by IO6 distorted octahedra creating an open-framework structure whose channels contain the alkali metal cations. 相似文献
12.
Nathaniel L SegravesSuzette Lopez Tyler A JohnsonSadri A Said Xiong FuFrancis J Schmitz Halina PietraszkiewiczFrederick A Valeriote Phillip Crews 《Tetrahedron letters》2003,44(17):3471-3475
The structural variations and bioactivity properties of the alkaloids in the fascaplysin (1) and the reticulatine (3) families were examined. Four organisms were analyzed consisting of two collections of the sponge Fascaplysinopsis reticulata and two collections of the tunicate Didemnum sp. Reported are the isolation of three new compounds: 3-bromofascaplysin (2), 14-bromoreticulatine (4), and 14-bromoreticulatate (6) along with reticulatate (5) previously known as a semi-synthetic product of 1. Compounds 1 and 5 showed selectivity in a cell based cytotoxicity assay. 相似文献
13.
Broadwater SJ Hickey MK McQuade DT 《Journal of the American Chemical Society》2003,125(37):11154-11155
Herein, we report a highly sensitive luminescent thin film chemosensor constructed out of a small-molecule donor/acceptor system. Two types of films were compared: one using a small-molecule crystalline donor/acceptor pair and the other using a donor-graft polymer/small-molecule acceptor pair. The acceptor selected for this proof of concept responds to acid, causing its absorption and emission bands to red-shift, which increases spectral overlap with the donor. This increase in overlap greatly enhances energy transfer from the acceptor to the donor. Signal amplification was ascertained by measuring the ratio of acceptor fluorescence when the donor was excited versus direct excitation of the acceptor. Both types of films exhibited large amplification. For the polymeric system, the mechanism of energy migration was investigated by the use of steady-state fluorescence spectroscopy. The mechanism was determined to be dominated by an exciton-hopping process. 相似文献
14.
Heteronuclear diethylcarbamato complexes of the form Co(n)()Mg(6)(-)(n)()(Et(2)NCO(2))(12) were prepared from the isostructural homonuclear precursors Mg(6)(Et(2)NCO(2))(12), 1, and Co(6)(Et(2)NCO(2))(12), 2, via a solvothermal methodology. Two materials were selected for single-crystal X-ray diffraction analysis: Co(1.6)Mg(4.4)(Et(2)NCO(2))(12) and Co(2.7)Mg(3.3)(Et(2)NCO(2))(12). Both compounds crystallize in the orthorhombic space group Ccca, as do 1 and 2. The molecular structure is best described as two trinuclear M(3) units cross-linked by diethylcarbamate ligands and twisted about one another, so that the complex has overall D(2) symmetry and is chiral. Each trinuclear unit consists of two terminal pentacoordinate metal ions and one central hexacoordinate metal ion. The X-ray diffraction data were unambiguous that the Co(2+) ions migrate exclusively to the pentacoordinate sites in the heteronuclear complexes, thus demonstrating that metal ion scrambling at the molecular level must occur. The composition of individual crystals can be continuously varied for Co(2+) mole fractions chi(Co) < 0.5, and the a and c unit cell distances are linearly related to chi(Co). This indicates that the compounds behave as solid solutions. There appears to be either a chemical or crystallographic phenomenon inherent in the synthetic methodology that prevents isolation of heteronuclear materials having chi(Co) > 0.5. Solution electronic spectroscopy and molecular weight measurements show that 2 can dissociate in chloroform and cyclohexane solution to give a dimeric complex 2'. This behavior contrasts with the stability of 1 in solution, as shown by NMR. The kinetic rate profile for formation of Co(n)Mg(6-n)(Et(2)NCO(2))(12) reveals saturation kinetics and is consistent with direct attack by 2' on 1 to give the heteronuclear complex via a higher nuclearity intermediate. This study illustrates a general method for the preparation of solids based on heteronuclear Werner-type complexes of the M(6)(Et(2)NCO(2))(12) structure type, and the mechanism by which such compounds can be formed from isostructural homonuclear precursors. 相似文献
15.
Thale Z Johnson T Tenney K Wenzel PJ Lobkovsky E Clardy J Media J Pietraszkiewicz H Valeriote FA Crews P 《The Journal of organic chemistry》2002,67(26):9384-9391
A reinvestigation of sponge natural products from additional Indo-Pacific collections of Xestospongiacf. carbonaria and X. cf. exigua has provided further insights on the structures, biological activities, and biosynthetic origin of bisannulated acridines. These alkaloids include one known pyridoacridine, neoamphimedine (2), and three new analogues, 5-methoxyneoamphimedine (4), neoamphimedine Y (5), and neoamphimedine Z (6). A completely new acridine, alpkinidine (7), was also isolated. A disk diffusion soft agar assay, using a panel of five cancer cell lines (solid tumors and leukemias) and two normal cells, was used to evaluate the differential cytotoxicity (solid tumor selectivity) of the sponge semipure extracts and selected compounds including amphimedine (1), 2, 4, and 7. While all four compounds were solid tumor selective, 1 and 2 were the most potent and 4 was the most selective. The rationale used to characterize the new structures is outlined along with the related biosynthetic pathways envisioned to generate 2 and 7. 相似文献
16.
[reaction: see text] Cyclic ene-N-p-toluenesulfonamides tethered to an electron-deficient alkyne undergo cycloisomerizations readily under the influence of catalytic Pt(II) salts (PtCl2 or [dppbPtmu-OH]2(BF4)2) or AgOTf. Yields for this process range from 47% to 99%. The resulting functionalized 2-azahydrindans can be reacted further using the Diels-Alder reaction. Tandem cycloisomerization-cycloaddition reactions in one pot generate highly functionalized 1-azadecalin ring systems in a highly stereocontrolled manner. 相似文献
17.
A fast centroid molecular dynamics (CMD) methodology is proposed in which the effective centroid forces are predetermined through a force-matching algorithm applied to a standard path integral molecular dynamics simulation. The resulting method greatly reduces the computational cost of generating centroid trajectories, thus extending the applicability of CMD. The method is applied to the study of liquid para-hydrogen at two state points and liquid ortho-deuterium at one state point. The static and dynamical results are compared to those obtained from full adiabatic CMD simulations and found to be in excellent agreement for all three systems; the transport properties are also compared to experiment and found to have a similar level of agreement. 相似文献
18.
Rajendiran TM Kirk ML Setyawati IA Caudle MT Kampf JW Pecoraro VL 《Chemical communications (Cambridge, England)》2003,(7):824-825
Binuclear manganese complexes Mn2(III/IV)(dtsalpn)2DCBI, 1, Mn2(III/III)(dtsalpn)2HDCBI, 2, containing the ligand dicarboxyimidazole (DCBI) have been prepared in order to address the issue of imidazole bridged and ferromagnetically coupled Mn sites in high oxidation states of the OEC in Photosystem II (PS II). Temperature dependent magnetic susceptibility studies of 1 indicates that the interaction between the two Mn(III)/Mn(IV) ions is ferromagnetic (J = +1.4 cm(-1)). Variable temperature EPR spectra of 1 shows that a g = 2 multiline is as an excited state signal corresponding to S = 1/2. 相似文献
19.