Phenylarsine oxide (PAO) is a membrane-permeable trivalent arsenic compounds, which interfere the biochemical activity of intracellular enzymes or proteins through reacting specifically with sulfhydryl and vicinal dithiol groups in the protein structure. Although the deleterious effects of arsenic compounds in bioorganisms have been extensively studied, however its role in the synaptogenesis is still obscure. Here we test the role of PAO on the synaptic activity at developing Xenopus neuromuscular synapse by using whole-cell patch clamp recording. Bath application of PAO dose-dependently increases the frequency of spontaneous synaptic currents (SSC frequency) and reaches its maximal effect at 10 £gM. The SSC frequency is robustly facilitated in 10~15 minutes after PAO application and then the release of neurotransmitter were abruptly ceased due to the degenerative collapse of the presynaptic motoneuron. Pretreatment of the culture with Ca2+ chelator BAPTA-AM significantly blunted the SSC frequency facilitation induced by PAO, suggesting a rise in Ca2+ in presynaptic motoneuron is a prerequisite. The PAO-induced SSC frequency facilitation is unaffected even that Ca2+ is eliminated from culture medium or addition of pharmacological Ca2+ channel inhibitor cadmium, indicating the influx of extracellular Ca2+ is not needed for the rise of [Ca2+]i. Depletion of endoplasmic reticulum Ca2+ pool with thapsigargin effectively hampered the PAO-induced SSC frequency facilitation. Pretreatment of ryanodine receptor inhibitor TMB-8 but not IP3 receptor inhibitor XeC significantly occluded the increase of SSC frequency elicited by PAO. Furthermore, bath application of the culture with either mitochondria oxidative phosphorylation uncoupler FCCP or mitochondrial permeability transition pore inhibitor cyclosporin A significantly abolished the SSC facilitating effect of PAO. Pretreatment the culture with TMB-8 and cyclosporin A have no addictive effects on the occlusion of PAO-induced SSC frequency facilitation, suggesting a consecutively released Ca2+ from internal store through ryanodine receptor and mitochondria is responsible for PAO-induced SSC frequency facilitation. The synaptic facilitating effect of PAO is eliminated while incubated with free radical scavenger n-acetylcysteine. Furthermore, treating cultures with complex III of electron transport chain (ETC) inhibitor antimycin A, but not complex I inhibitor rotenone, abolished PAO-induced facilitation of synaptic transmission. PAO elicited no facilitation effects on SSC frequency when pretreatment the culture with either thiol-modifying agent NEM or thiol-reducing agent DTT. Overall, results from our current study provide evidences that reactive oxygen species derived from PAO inhibition on complex III of ETC induce the open of MPT pore in mitochondria, the accompanied Ca2+ leak from mitochondria and Ca2+-induced Ca2+ release from endoplasmic reticulum resulted in a robustly release of neurotransmitter and a destructive damage on the neuron.

Electronic devices, for logical and memory applications, are constructed based on bistable electronic units that can store binary information. Molecular electronics proposes the use of single molecules—with two distinctive states of conductance—as bistable units that can be used to create more complex electronic devices. The conductance of a molecule is strongly influenced by the contacts used to address it. The purpose of this work is to determine the electrical characteristics of several candidate molecular junctions, which are composed of a molecule and contacts. Specifically, we are interested in determining whether binary information, “0” or “1,” can be encoded in the low- and high-conductance states of the molecular junctions. First, we calculate quantum-mechanically the electronic structure of the molecular junction. Second, the continuous electronic states of the contacts, originated from their infinite nature, are obtained by solving the Schrödinger equation with periodic boundary conditions. Last, the electron transport through the molecular junctions is calculated based on a chemical interpretation of the Landauer formalism for coherent transport, which involves the information obtained from the molecule and the contacts. Metal-molecule-metal and metal-molecule-semiconductor junctions are considered. The molecule used is an olygo(phenylene ethynylene) composed of three benzene rings and a nitro group in the middle ring; this molecule is referred hereafter as the nitroOPE molecule. Gold, silicon, and metallic carbon nanotubes are used as contacts to the molecule. Results from the calculations show that the molecular junctions have distinctive states of conductance for different conformational and charge states. High conductance is found in the conformation in which all the benzene rings of the nitroOPE are coplanar. If the middle benzene ring is made perpendicular to the others, low conductance is found. Also, the negatively charged junctions (anion, dianion) show low conductance. Whenever a semiconducting contact is used, a flat region of zero current is found at low bias voltages. The results indicate that the use of Si contacts is possible; however, because of the flat region, the operating point of the devices needs to be moved to higher voltages.

This study has investigated the involvement of photosynthetic electron transport chain on the regulation of gene expression of methionine sulfoxide reductase (UfMSR) in the marine macroalga Ulva fasciata Delile.UfMSRA is from copper stress and UfMSRB ir from hypersalinity stress. UfMSRA is similar to Arabidopsis AtMSRA4 and UfMSRB is similar to AtMSRB1. UfMSRA is specific to the MetSO S-enantiomer and UfMSRB catalytically reduces the MetSO R-enantiomer. Both enzymes are required, since in the cell oxidation of Met residues at the sulfur atom results in a racemic mixture of the two stereoisomers. UfMSRA and UfMSRB transcripts were increased by white light, blue light and red light with the maximum at 1 h following a decline, but kept constant in the dark. The magnitude of UfMSRA and UfMSRB transcript increase showed a positive linear correlation to increasing light intensity from 0-1200 u mole¡Pm-2¡Ps-1. The treatment with linear electron transport chain inhibitors, hydroxylamine, 3-(3,4-dichlorophenyl) -1,1-dimethylurea (DCMU), 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB) and stigmatellin, effectively inhibited PS II activity under 300 u mole¡Pm-2¡Ps-1 irradiance. DBMIB and stigmatellin can increase UfMSRA transcript that was reversed by 2,6-dichlorophenolindophenol (DCPIP), a PS I electron donor. It indicates that the block of electron transport of the downstream of cytochrome b6f indeuces UfMSRA gene expression. Hydroxylamine, DCMU and DBMIB decreased UfMSRB transcript that was not reversed by DCPIP while stigmatellin increased UfMSRB mRNA level, reflecting a role of reduced state with Qo site located at cytochrome b6f on the induction of UfMSRB gene expression. The cyclic electron transport chain inhibitors, antimycin A that inhibited photosynthetic electron transport, can inhibit the increase of UfMSRA and UfMSRB transcripts by irradiance. UfMSRA and UfMSRB gene expression were both modulated by cyclic electron transport chain and linear electron transport chain. These results reveal that photosynthetic electron transport chain modulates UfMSRA and UfMSRB gene expression by change its redox state.

A theory of the carrier transport, optical emission, and photoconductivity from optoelectronic devices based on ambipolar long-channel carbon-nanotube (CNT) field-effect transistors (FETs) is presented in this dissertation. In optical emitters based on ambipolar long-channel CNT FETs, an analytic diffusive-transport model for various recombination mechanisms is provided for the first time. The relationship and the scaling of emitted light-spot size and emitted optical power are clearly depicted for the first time as well. We also implement a numerical diffusive-transport approach for the light emission, in which the focus is on the effects of radiative and nonradiative recombination in the channel, with the movement of the spatial recombination profile in response to the gate and drain voltages. For the first time, we find that the emitted light-spot size and the emitted optical power depend sensitively on the operative nonradiative recombination mechanisms. We implement a numerical diffusive-transport approach including exciton photogeneration as well for photoconductors based on ambipolar long-channel CNT FETs with uniform and near-field photoexcitation. We show that the photocurrents are typically much smaller than the dark currents, and explain some possible reasons. Moreover, the exciton densities in CNTs are calculated and the effect of exciton diffusion is presented.

The work presented in this thesis is primarily concerned with the synthesis and characterization of large, linear heteroacenes and their derivatives. We have been able to significantly expand on the types of materials available for application in organic electronic device architectures. In particular, the work focused on solution processible and novel derivatives of thiadiazoles, diazatetracenes, diazapentacenes, tetrazapentacences, and N,N-dihydrotetraazaheptacene. Extensive computational studies have been performed in order to better understand the optoelectronic properties of these materials. Although no devices have been fabricated that show appreciable hole or electron mobility, the properties of these materials are very promising. Besides our work on organic electronic materials for application in optoelectronic devices, we have also been able to develop, via the Click reaction, a series of aqueous metal sensors for copper (II), nickel (II), and silver (I) based upon fluorescence quenching. The use of a modified Stern-Volmer equation was necessary to fit the data in order to obtain binding constants. The exploration of new materials and their properties in the area of organic electronics is an exciting field for the synthetic organic chemist, as the goals associated with this work strive to impact humanity in a positive manner by reducing energy costs.

<p>Molecular electronics is envisioned as a possible next step in device miniaturization. It is usually taken to mean the design and manufacturing of electronic devices and applications where organic molecules work as the fundamental functioning unit. It involves the easurement and manipulation of electronic response and transport in molecules attached to conducting leads. Organic molecules have the advantages over conventional solid state electronics of inherent small sizes, endless chemical diversity and ambient temperature low cost manufacturing.</p><p> In this thesis we investigate the switching and conducting properties of photochromic dithienylethene derivatives. Such molecules change their conformation in solution when acted upon by light. Photochromic molecules are attractive candidates for use in molecular electronics because of the switching between different states with different conducting properties. The possibility of optically controlling the conductance of the molecule attached to leads may lead to new device implementations.</p><p> The switching reaction is investigated with potential energy calculations for different values of the reaction coordinate between the closed and the open isomer. The electronic and atomic structure calculations are performed with density functional theory (DFT). It is concluded that there is a large potential energy barrier separating the open and closed isomer and that switching between open and closed forms must involve excited states. </p><p>The conducting properties of the molecule inserted between gold leads is calculated within the Non Equilibrium Green Function theory. The transmission function is calculated for the two isomers with different basis sizes for the gold contacts, as well as the electrostatic potential, for finite applied bias voltages. We conclude that a Au 6s basis give qualitatively the same result as a Au spd basis close to the Fermi level. The transmission coefficient at the Fermi energy is around 10 times larger in the closed molecule compared to the open. This will result in a large difference in conductivity. It is also found that the large difference in conductivity will remain for small applied bias voltages. The results are consistent with earlier work.</p>

The electron transport through a molecular wire under the influence of an external laser field is studied using a reduced density matrix formalism. The full system is partitioned into the relevant part, i.e. the wire, electron reservoirs and a phonon bath. An earlier second-order perturbation theory approach of Meier and Tannor for bosonic environments which employs a numerical decomposition of the spectral density is used to describe the coupling to the phonon bath and is extended to deal with the electron transfer between the reservoirs and the molecular wire. Furthermore, from the resulting time-nonlocal (TNL) scheme a time-local (TL) approach can be determined. Both are employed to propagate the reduced density operator in time for an arbitrary time-dependent system Hamiltonian which incorporates the laser field non-perturbatively. Within the TL formulation, one can extract a current operator for the open quantum system. This enables a more general formulation of the problem which is necessary to employ an optimal control algorithm for open quantum systems in order to compute optimal control fields for time-distributed target states, e.g. current patterns. Thus, we take a fundamental step towards optimal control in molecular electronics. Numerical examples of the population dynamics, laser controlled current, TNL vs. TL and optimal control fields are presented to demonstrate the diverse applicability of the derived formalism.

Electron transport in nanoparticle single-electron transistors (SETs) is a fruitful method to explore a wide range of physical phenomena at the nanometer scale. In this thesis, we investigate electron transport in SETs incorporating various nanoparticles, including gold nanoparticles in both classical and quantum regimes and Pb nanoparticle in both superconducting and normal states. SETs have been successfully fabricated by incorporating individual gold nanoparticles into the gaps between two electrodes. Although single-electron tunneling behavior is prominent, quantized energy levels cannot be resolved in these SETs due to their relatively large particle sizes. A novel method has been developed to achieve SETs incorporating gold nanoparticles whose sizes are small enough to resolve discrete quantum energy levels. The devices consist of spontaneously-formed ultrasmall gold nanoparticles linked by alkanedithiols to gold electrodes. The devices reproducibly exhibit addition energies of a few hundred meV, which enables the observation of single electron tunneling at room temperature. At low temperatures, resonant tunneling through discrete energy levels in the Au nanoparticles is observed, which is accompanied by the excitations of molecular vibrations at large bias voltage. Having explored the SETs in normal state, we have extended the experiments to superconducting single-electron transistors (SSETs). We first fabricated and characterized Pb superconducting electrodes with nanometer-sized separation. Our observation clearly shows that conventional Barden-Cooper-Schrieffer theory remains valid to interpret the tunneling behavior between two nanometer-spaced Pb electrodes. Furthermore, by incorporating Pb nanoparticles between the two Pb electrodes, we have fabricated SSETs and investigated the transport properties of these devices. In the superconducting state, the conductance is suppressed by a combination of the single electron tunneling effect and the absence of density of states within the superconducting gap. In the suppression regime, the tunneling spectroscopy shows current features that arise from quasiparticle tunneling caused by singularity matching. At low temperature, the features can only be observed for odd charge states in SSETs. At high temperature, the odd-even parity effect is smeared out. Upon application of a magnetic field, the superconducting state is suppressed and single-electron tunneling behavior for normal metallic nanoparticles is recovered.

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We numerically investigate electron transport properties in an electron waveguide which can be constructed in 2DEG of the heterostructure of GaAs and AlGaAs. We apply R-matrix theory to solve a Schrödinger equation and construct a S-matrix, and we then calculate conductance of an electron waveguide. We study single impurity scattering in a waveguide. A [delta]-function model as a single impurity is very attractive, but it has been known that [delta]-function potential does not give a convergent result in two or higher space dimensions. However, we find that it can be used as a single impurity in a waveguide with the truncation of the number of modes. We also compute conductance for a finite size impurity by using R-matrix theory. We propose an appropriate criteria for determining the cut-off mode for a [delta]-function impurity that reproduces the conductance of a waveguide when a finite impurity presents. We find quantum scattering echoes in a ripple waveguide. A ripple waveguide (or cavity) is widely used for quantum chaos studies because it is easy to control a particle's dynamics. Moreover we can obtain an exact expression of Hamiltonian matrix with for the waveguide using a simple coordinate transformation. Having an exact Hamiltonian matrix reduces computation time significantly. It saves a lot of computational needs. We identify three families of resonance which correspond to three different classical phase space structures. Quasi bound states of one of those resonances reside on a hetero-clinic tangle formed by unstable manifolds and stable manifolds in the phase space of a corresponding classical system. Resonances due to these states appear in the conductance in a nearly periodic manner as a function of energy. Period from energy frequency gives a good agreement with a prediction of the classical theory. We also demonstrate wavepacket dynamics in a ripple waveguide. We find quantum echoes in the transmitted probability of a wavepacket. The period of echoes also agrees with the classical predictions. We also compute the electron transmission probability through a multi-ripple electron waveguide. We find an effect analogous to the Dicke effect in the multi-ripple electron waveguide. We show that one of the S-matrix poles, that of the super-radiant resonance state, withdraws further from the real axis as each ripple is added. The lifetime of the super-radiant state, for N quantum dots, decreases as [1/N] . This behavior of the lifetime of the super-radiant state is a signature of the Dicke effect. / text