264 research outputs found
Calculations of the Relative Energies of the 2
Article on a proposed experimental test of the prediction of a triplet ground state for (CO)4
Action spectroscopy of gas-phase carboxylate anions by multiple photon IR electron detachment/attachment
We report on a form of gas-phase anion action spectroscopy based on infrared
multiple photon electron detachment and subsequent capture of the free
electrons by a neutral electron scavenger in a Fourier Transform Ion Cyclotron
Resonance (FTICR) mass spectrometer. This method allows one to obtain
background-free spectra of strongly bound anions, for which no dissociation
channels are observed. The first gas-phase spectra of acetate and propionate
are presented using SF6 as electron scavenger and a free electron laser as
source of intense and tunable infrared radiation. To validate the method, we
compare infrared spectra obtained through multiple photon electron
detachment/attachment and multiple photon dissociation for the benzoate anion.
In addition, different electron acceptors are used, comparing both associative
and dissociative electron capture. The relative energies of dissociation (by
CO2 loss) and electron detachment are investigated for all three anions by DFT
and CCSD(T) methods. DFT calculations are also employed to predict vibrational
frequencies, which provide a good fit to the infrared spectra observed. The
frequencies of the symmetric and antisymmetric carboxylate stretching modes for
the aliphatic carboxylates are compared to those previously observed in
condensed-phase IR spectra and to those reported for gas-phase benzoate,
showing a strong influence of the solution environment and a slight substituent
effect on the antisymmetric stretch.Comment: Revised version, Submitted to J Phys Chem
ApoE Receptor 2 Regulates Synapse and Dendritic Spine Formation
Apolipoprotein E receptor 2 (ApoEr2) is a postsynaptic protein involved in long-term potentiation (LTP), learning, and memory through unknown mechanisms. We examined the biological effects of ApoEr2 on synapse and dendritic spine formation-processes critical for learning and memory.In a heterologous co-culture synapse assay, overexpression of ApoEr2 in COS7 cells significantly increased colocalization with synaptophysin in primary hippocampal neurons, suggesting that ApoEr2 promotes interaction with presynaptic structures. In primary neuronal cultures, overexpression of ApoEr2 increased dendritic spine density. Consistent with our in vitro findings, ApoEr2 knockout mice had decreased dendritic spine density in cortical layers II/III at 1 month of age. We also tested whether the interaction between ApoEr2 and its cytoplasmic adaptor proteins, specifically X11α and PSD-95, affected synapse and dendritic spine formation. X11α decreased cell surface levels of ApoEr2 along with synapse and dendritic spine density. In contrast, PSD-95 increased cell surface levels of ApoEr2 as well as synapse and dendritic spine density.These results suggest that ApoEr2 plays important roles in structure and function of CNS synapses and dendritic spines, and that these roles are modulated by cytoplasmic adaptor proteins X11α and PSD-95
Through-Bond Interactions in the Diradical Intermediates Formed in the Rearrangements of Bicyclo[ n
Article on through-bond interactions in the diradical intermediates formed in the rearrangements of bicyclo[n.m.0]alkatetraenes
The Biochemistry, Ultrastructure, and Subunit Assembly Mechanism of AMPA Receptors
The AMPA-type ionotropic glutamate receptors (AMPA-Rs) are tetrameric ligand-gated ion channels that play crucial roles in synaptic transmission and plasticity. Our knowledge about the ultrastructure and subunit assembly mechanisms of intact AMPA-Rs was very limited. However, the new studies using single particle EM and X-ray crystallography are revealing important insights. For example, the tetrameric crystal structure of the GluA2cryst construct provided the atomic view of the intact receptor. In addition, the single particle EM structures of the subunit assembly intermediates revealed the conformational requirement for the dimer-to-tetramer transition during the maturation of AMPA-Rs. These new data in the field provide new models and interpretations. In the brain, the native AMPA-R complexes contain auxiliary subunits that influence subunit assembly, gating, and trafficking of the AMPA-Rs. Understanding the mechanisms of the auxiliary subunits will become increasingly important to precisely describe the function of AMPA-Rs in the brain. The AMPA-R proteomics studies continuously reveal a previously unexpected degree of molecular heterogeneity of the complex. Because the AMPA-Rs are important drug targets for treating various neurological and psychiatric diseases, it is likely that these new native complexes will require detailed mechanistic analysis in the future. The current ultrastructural data on the receptors and the receptor-expressing stable cell lines that were developed during the course of these studies are useful resources for high throughput drug screening and further drug designing. Moreover, we are getting closer to understanding the precise mechanisms of AMPA-R-mediated synaptic plasticity
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