Heterolysis of H−X Bonds by Pentamethylcyclopentadienyl−Aminoborole Complexes of Zirconium and Hafnium

The pentamethylcyclopentadienyl−aminoborole chloro complexes Cp*{η^5-C_4H_4BN(CHMe_2)_2}MCl·LiCl (Cp* = (η^5-C_5Me_5); M = Zr, Hf) heterolytically cleave H−X bonds to form Cp*{η^5-C_4H_4BNH(CHMe_2)_2}MCl(X) (X = OR, SR, C⋮CR). Control experiments using deuterium-labeled substrates show heterolysis occurs with no incorporation of deuterium into the 2,5 positions of the borole heterocycle. Cp*{η^5-C_4H_4BNH(CHMe_2)_2}Hf(C⋮CSiMe_3)_2 is prepared from Cp*{η^^5-C_4H_4BN(CHMe_2)_2}Hf(η^3-C_3H_5) and 2 equiv of (trimethylsilyl)acetylene. Treatment of Cp*{η^5-C_4H_4BN(CHMe_2)_2}MCl·LiCl (M = Zr, Hf) with donor ligands L yields the LiCl-free complexes Cp*{η^5-C_4H_4BN(CHMe_2)_2}MCl(L) (M = Zr, L = NMe2H; M = Hf, L = PMe_3). Cp*{η^5-C_4H_4BN(CHMe_2)_2}HfCl(PMe_3) reacts with (trimethylsilyl)acetylene with loss of HN(CHMe_2)_2 to form Cp*{η^5-C_4H_4B(C⋮CSiMe_3)}HfCl(PMe_3), resulting from formal migration of acetylide from hafnium to boron. X-ray structure determinations of Cp*{η^5-C_4H_4BNH(CHMe_2)_2}HfCl(C⋮CSiMe_3), Cp*{η^5-C_4H_4BN(CHMe_2)_2}HfCl(PMe_3), and Cp*{η^5-C_4H_4B(C⋮CSiMe_3)}HfCl(PMe_3) are reported

Heterolysis of H−X Bonds by Pentamethylcyclopentadienyl−Aminoborole Complexes of Zirconium and Hafnium

The pentamethylcyclopentadienyl−aminoborole chloro complexes Cp*{η^5-C_4H_4BN(CHMe_2)_2}MCl·LiCl (Cp* = (η^5-C_5Me_5); M = Zr, Hf) heterolytically cleave H−X bonds to form Cp*{η^5-C_4H_4BNH(CHMe_2)_2}MCl(X) (X = OR, SR, C⋮CR). Control experiments using deuterium-labeled substrates show heterolysis occurs with no incorporation of deuterium into the 2,5 positions of the borole heterocycle. Cp*{η^5-C_4H_4BNH(CHMe_2)_2}Hf(C⋮CSiMe_3)_2 is prepared from Cp*{η^^5-C_4H_4BN(CHMe_2)_2}Hf(η^3-C_3H_5) and 2 equiv of (trimethylsilyl)acetylene. Treatment of Cp*{η^5-C_4H_4BN(CHMe_2)_2}MCl·LiCl (M = Zr, Hf) with donor ligands L yields the LiCl-free complexes Cp*{η^5-C_4H_4BN(CHMe_2)_2}MCl(L) (M = Zr, L = NMe2H; M = Hf, L = PMe_3). Cp*{η^5-C_4H_4BN(CHMe_2)_2}HfCl(PMe_3) reacts with (trimethylsilyl)acetylene with loss of HN(CHMe_2)_2 to form Cp*{η^5-C_4H_4B(C⋮CSiMe_3)}HfCl(PMe_3), resulting from formal migration of acetylide from hafnium to boron. X-ray structure determinations of Cp*{η^5-C_4H_4BNH(CHMe_2)_2}HfCl(C⋮CSiMe_3), Cp*{η^5-C_4H_4BN(CHMe_2)_2}HfCl(PMe_3), and Cp*{η^5-C_4H_4B(C⋮CSiMe_3)}HfCl(PMe_3) are reported

Kinetics of superoxide reactions with dissolved organic matter in tropical Atlantic surface waters near Cape Verde (TENATSO)

The decay kinetics of superoxide (O2−) reacting with organic matter was examined in oligotrophic waters at, and nearby, the TENATSO ocean observatory adjacent to the Cape Verde archipelago. Superoxide is the short-lived primary photochemical product of colored dissolved organic matter (CDOM) photolysis and also reacts with CDOM or trace metals (Cu, Fe) to form H2O2. In the present work we focused our investigations on reactions between CDOM and superoxide. O2− decay kinetics experiments were performed by adding KO2 to diethylenetriaminepentaacetic acid (DTPA) amended seawater and utilizing an established chemiluminescence technique for the detection of O2− at nM levels. In Cape Verdean waters we found a significant reactivity of superoxide with CDOM with maximal rates adjacent to the chlorophyll maximum, presumably from production of new CDOM from bacteria/phytoplankton. This work highlights a poorly understood process which impacts on the biogeochemical cycling of CDOM and trace metals in the open ocean

Multi Component Self-Assembly: Supramolecular Organic Frameworks Containing Metal-Rotaxane Subunits (RSOFs)

A facile, one-pot synthesis of rotaxanated supramolecular organic frameworks (RSOFs) is reported. These systems consist of bis-carboxylate anions threaded through the core of tetraimidazolium macrocycles. Trivalent metal cations, yttrium(III) and smaller lanthanides, are used to "lock" the threaded strut in place. This results in the formation of three-dimensional RSOFs.National Science Foundation CHE 1057904, 0741973Robert A. Welch Foundation F-1018Korean World Class University (WCU) R32-2010-000-10217-0Chemistr

Decoherence control in microwave cavities

We present a scheme able to protect the quantum states of a cavity mode against the decohering effects of photon loss. The scheme preserves quantum states with a definite parity, and improves previous proposals for decoherence control in cavities. It is implemented by sending single atoms, one by one, through the cavity. The atomic state gets first correlated to the photon number parity. The wrong parity results in an atom in the upper state. The atom in this state is then used to inject a photon in the mode via adiabatic transfer, correcting the field parity. By solving numerically the exact master equation of the system, we show that the protection of simple quantum states could be experimentally demonstrated using presently available experimental apparatus.Comment: 13 pages, RevTeX, 8 figure

Human cultured dendritic cells show differential sensitivity to chemotherapy agents as assessed by the MTS assay

Assessment of the chemosensitivity of dendritic cells (DC) may allow more rational development of combined chemotherapy and immunotherapy protocols. Human monocyte-derived DC generated reproducible results in the MTS (Owen’s reagent) assay, which was then used to study DC survival after treatment with four different chemotherapy agents. DC preparations from three different donors were used per drug. DC were sensitive to doxorubicin (concentration range 0.1–50 μM) with variation in sensitivity between donors (IC50 244–1100 nM). The most extreme variation was seen for vinblastine (concentration range 250–0.025 μM with IC50 0.15–17.25 μM). In contrast, there was relative resistance to etoposide (concentration range 0.2–200 μM) and 5-fluorouracil (concentration range 0.7–7700 μM) with no toxicity seen until 50 μM and 770 μM respectively. The function of DC in allogeneic mixed leucocyte reactions closely paralleled results from the MTS assays. The differential sensitivity to chemotherapy agents did not appear to be due to expression of P-glycoprotein. These results suggest that etoposide or 5-fluorouracil is less likely to reduce the immunotherapeutic potential of DC and may be valuable in the design of prodrug activation therapy. © 1999 Cancer Research Campaig

Cell-Autonomous Alterations in Dendritic Arbor Morphology and Connectivity Induced by Overexpression of MeCP2 in Xenopus Central Neurons In Vivo

Methyl CpG binding protein-2 (MeCP2) is an essential epigenetic regulator in human brain development. Mutations in the MeCP2 gene have been linked to Rett syndrome, a severe X-linked progressive neurodevelopmental disorder, and one of the most common causes of mental retardation in females. MeCP2 duplication and triplication have also been found to affect brain development, indicating that both loss of function and gain in MeCP2 dosage lead to similar neurological phenotypes. Here, we used the Xenopus laevis visual system as an in vivo model to examine the consequence of increased MeCP2 expression during the morphological maturation of individual central neurons in an otherwise intact brain. Single-cell overexpression of wild-type human MeCP2 was combined with time-lapse confocal microscopy imaging to study dynamic mechanisms by which MeCP2 influences tectal neuron dendritic arborization. Analysis of neurons co-expressing DsRed2 demonstrates that MeCP2 overexpression specifically interfered with dendritic elaboration, decreasing the rates of branch addition and elimination over a 48 hour observation period. Moreover, dynamic analysis of neurons co-expressing wt-hMeCP2 and PSD95-GFP revealed that even though neurons expressing wt-hMeCP2 possessed significantly fewer dendrites and simpler morphologies than control neurons at the same developmental stage, postsynaptic site density in wt-hMeCP2-expressing neurons was similar to controls and increased at a rate higher than controls. Together, our in vivo studies support an early, cell-autonomous role for MeCP2 during the morphological differentiation of neurons and indicate that perturbations in MeCP2 gene dosage result in deficits in dendritic arborization that can be compensated, at least in part, by synaptic connectivity changes

Meeting Report: Consensus Statement—Parkinson’s Disease and the Environment: Collaborative on Health and the Environment and Parkinson’s Action Network (CHE PAN) Conference 26–28 June 2007

BackgroundParkinson's disease (PD) is the second most common neurodegenerative disorder. People with PD, their families, scientists, health care providers, and the general public are increasingly interested in identifying environmental contributors to PD risk.MethodsIn June 2007, a multidisciplinary group of experts gathered in Sunnyvale, California, USA, to assess what is known about the contribution of environmental factors to PD.ResultsWe describe the conclusions around which they came to consensus with respect to environmental contributors to PD risk. We conclude with a brief summary of research needs.ConclusionsPD is a complex disorder, and multiple different pathogenic pathways and mechanisms can ultimately lead to PD. Within the individual there are many determinants of PD risk, and within populations, the causes of PD are heterogeneous. Although rare recognized genetic mutations are sufficient to cause PD, these account for < 10% of PD in the U.S. population, and incomplete penetrance suggests that environmental factors may be involved. Indeed, interplay among environmental factors and genetic makeup likely influences the risk of developing PD. There is a need for further understanding of how risk factors interact, and studying PD is likely to increase understanding of other neurodegenerative disorders

Non-bee insects are important contributors to global crop pollination

Wild and managed bees are well documented as effective pollinators of global crops of economic importance. However, the contributions by pollinators other than bees have been little explored despite their potential to contribute to crop production and stability in the face of environmental change. Non-bee pollinators include flies, beetles, moths, butterflies, wasps, ants, birds, and bats, among others. Here we focus on non-bee insects and synthesize 39 field studies from five continents that directly measured the crop pollination services provided by non-bees, honey bees, and other bees to compare the relative contributions of these taxa. Non-bees performed 25–50% of the total number of flower visits. Although non-bees were less effective pollinators than bees per flower visit, they made more visits; thus these two factors compensated for each other, resulting in pollination services rendered by non-bees that were similar to those provided by bees. In the subset of studies that measured fruit set, fruit set increased with non-bee insect visits independently of bee visitation rates, indicating that non-bee insects provide a unique benefit that is not provided by bees. We also show that non-bee insects are not as reliant as bees on the presence of remnant natural or seminatural habitat in the surrounding landscape. These results strongly suggest that non-bee insect pollinators play a significant role in global crop production and respond differently than bees to landscape structure, probably making their crop pollination services more robust to changes in land use. Non-bee insects provide a valuable service and provide potential insurance against bee population declines