17 research outputs found
Rationalizing Structure, Stability, and Chemical Bonding of Pure and Doped Clusters Isolated and Solvated Multiply Charged Anions, and Solid State Materials
Chemistry is the study of materials and the changes that materials undergo. One can tune the properties of the known materials and design the novel materials with desired properties knowing what is responsible for the chemical reactivity, structure, and stability of those materials. The unified chemical bonding theory could address all these questions, but we do not have one available yet. The most accepted general theory of chemical bonding was proposed by Lewis in 1916, though Lewis’s theory fails to explain the bonding in materials with delocalized electron density such as sub-nano and nanoclusters, as well as aromatic organic and organometallic molecules. The dissertation presents a set of projects that can be considered the steps towards the development of the unified chemical bonding theory by extending the ideas of Lewis. The dissertation also presents the studies of the properties of multiply charged anions, which tend to undergo Coulomb explosion in the isolated state and release the excess energy stored in them. It is shown how the properties of multiply charged anions can be tuned upon changing the chemical identity of the species or interaction with solvent molecules. Our findings led to the discovery of a new long-lived triply charged anionic species, whose metastability was explained by the existence of a repulsive Coulomb barrier. We also proposed two ways to restore high symmetry of compounds by suppression of the pseudo Jahn-Teller effect, which could lead to the design of new materials with the restored symmetry and therefore the novel properties
Photo-driven Molecular Wankel Engine B
We report a molecular Wankel motor, the dual-ring structure B13+, driven by
circularly-polarized infrared electromagnetic radiation, under which a guided
uni-directional rotation of the outer ring is achieved with rotational
frequency of the order of 300 MHz.Comment: 5 pages, 4 figure
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Photo-driven Molecular Wankel Engine B
We report a molecular Wankel motor, the dual-ring structure B13+, driven by
circularly-polarized infrared electromagnetic radiation, under which a guided
uni-directional rotation of the outer ring is achieved with rotational
frequency of the order of 300 MHz
B<sub>22</sub><sup>–</sup> and B<sub>23</sub><sup>–</sup>: All-Boron Analogues of Anthracene and Phenanthrene
Clusters of boron atoms exhibit intriguing size-dependent
structures
and chemical bonding that are different from bulk boron and may lead
to new boron-based nanostructures. We report a combined photoelectron
spectroscopic and ab initio study of the 22- and 23-atom boron clusters.
The joint experimental and theoretical investigation shows that B<sub>22</sub><sup>–</sup> and B<sub>23</sub><sup>–</sup> possess quasi-planar and planar structures, respectively. The quasi-planar
B<sub>22</sub><sup>–</sup> consists of fourteen peripheral
atoms and eight interior atoms in a slightly buckled triangular lattice.
Chemical bonding analyses of the closed-shell B<sub>22</sub><sup>2–</sup> species reveal seven delocalized π orbitals, which are similar
to those in anthracene. B<sub>23</sub><sup>–</sup> is a perfectly
planar and heart-shaped cluster with a pentagonal cavity and a π-bonding
pattern similar to that in phenanthrene. Thus, B<sub>22</sub><sup>–</sup> and B<sub>23</sub><sup>–</sup>, the largest
negatively charged boron clusters that have been characterized experimentally
to date, can be viewed as all-boron analogues of anthracene and phenanthrene,
respectively. The current work shows not only that boron clusters
are planar at very large sizes but also that they continue to yield
surprises and novel chemical bonding analogous to specific polycyclic
aromatic hydrocarbons
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Neuron-Subtype-Specific Expression, Interaction Affinities, and Specificity Determinants of DIP/Dpr Cell Recognition Proteins
Binding between DIP and Dpr neuronal recognition proteins has been proposed to regulate synaptic connections between lamina and medulla neurons in the Drosophila visual system. Each lamina neuron was previously shown to express many Dprs. Here, we demonstrate, by contrast, that their synaptic partners typically express one or two DIPs, with binding specificities matched to the lamina neuron-expressed Dprs. A deeper understanding of the molecular logic of DIP/Dpr interaction requires quantitative studies on the properties of these proteins. We thus generated a quantitative affinity-based DIP/Dpr interactome for all DIP/Dpr protein family members. This revealed a broad range of affinities and identified homophilic binding for some DIPs and some Dprs. These data, along with full-length ectodomain DIP/Dpr and DIP/DIP crystal structures, led to the identification of molecular determinants of DIP/Dpr specificity. This structural knowledge, along with a comprehensive set of quantitative binding affinities, provides new tools for functional studies in vivo
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Interactions between the Ig-Superfamily Proteins DIP-α and Dpr6/10 Regulate Assembly of Neural Circuits
Drosophila Dpr (21 paralogs) and DIP proteins (11 paralogs) are cell recognition molecules of the immunoglobulin superfamily (IgSF) that form a complex protein interaction network. DIP and Dpr proteins are expressed in a synaptic layer-specific fashion in the visual system. How interactions between these proteins regulate layer-specific synaptic circuitry is not known. Here we establish that DIP-α and its interacting partners Dpr6 and Dpr10 regulate multiple processes, including arborization within layers, synapse number, layer specificity, and cell survival. We demonstrate that heterophilic binding between Dpr6/10 and DIP-α and homophilic binding between DIP-α proteins promote interactions between processes in vivo. Knockin mutants disrupting the DIP/Dpr binding interface reveal a role for these proteins during normal development, while ectopic expression studies support an instructive role for interactions between DIPs and Dprs in circuit development. These studies support an important role for the DIP/Dpr protein interaction network in regulating cell-type-specific connectivity patterns