Studies on collective behaviour of gap junction channels

Gap junction provides low resistance pathways for cell-to-cell passive diffusion of ions, metabolites, second messengers etc. and thus, controls development, differentiation in embryonic tissues, and communication in adult tissues. It has been pointed out in our previous work that these passive diffusion channels behave cooperatively which in turn depends on the structural parameters and also membrane potentials. In the present paper, we have analyzed the multichannel bilayer electrophysiological data of rat liver gap junction Connexin 32 (Cx32) hemichannels. Through the measurements of relaxation time it has been demonstrated that one of the relaxation time constants follows a decay pattern with the number of channels open at various potentials applied across the bilayer membrane. This leads to the conclusion that the collective behaviour of rat liver gap junction hemichannels is cooperative in multichannel ensembles.     

Effect of interactions on molecular fluxes and fluctuations in the transport across membrane channels

Transport of molecules across membrane channels is investigated theoretically using exactly solvable one-dimensional discrete-state stochastic models. An interaction between molecules and membrane pores is modeled via a set of binding sites with different energies. It is shown that the interaction potential strongly influences the particle currents as well as fluctuations in the number of translocated molecules. For small concentration gradients, the attractive sites lead to largest currents and fluctuations, while the repulsive interactions yield the largest fluxes and dispersions for large concentration gradients. Interaction energies that lead to maximal currents and maximal fluctuations are the same only for locally symmetric potentials, where transition states are equally distant from the neighboring binding sites, while they differ for the locally asymmetric potentials. The conditions for the most optimal translocation transport with maximal current and minimal dispersion are discussed. It is argued that, in this case, the interaction strength is independent of local symmetry of the potential of mean forces. In addition, the effect of the global asymmetry of the interaction potential is investigated, and it is shown that it also strongly affects the particle translocation dynamics. These phenomena can be explained by analyzing the details of the particle entering and leaving the binding sites in the channel.     

Nonequilibrium electronic transport of 4,4'-bipyridine molecular junction

The electronic transport properties of a 4,4'-bipyridine molecule sandwiched between two Au(111) surfaces are studied with a fully self-consistent nonequilibrium Green's-function method combined with the density-functional theory. The 4,4'-bipyridine molecule prefers to adsorb near the hollow site of the Au(111) surface and distorts slightly. The modifications on the electronic structure of the molecule due to the presence of the electrodes are described by the renormalized molecular orbitals, which correspond well to the calculated transmission peaks. The average Fermi level lies close to the lowest unoccupied renormalized molecular orbital, which determines the electronic transport property of the molecular junction under a small bias voltage. The total transmission is contributed by a single channel. The transmission peaks shift with the applied bias voltage, and this behavior depends on the spatial distribution of the renormalized molecular orbitals and the voltage drop along the molecular junction. The shape of the calculated conductance curve of the equilibrium geometric configuration reproduces the main feature of the experimental results, but the value is larger than the measured data by about 6 times. Good agreement with the experimental measurements can be obtained by elongating the molecular junction. The electronic transport behaviors depend strongly on the interface configuration.     

Metal-mediated transport of electrons across molecular films

Electron transfer (ET) to a redox probe in solution across the self-assembled monolayers (SAMs) of a tris-(2-pyridylmethyl)amine-based ligand on gold electrodes is greatly enhanced by Cu-binding.     

The special features of molecular transport in nanosized channels

The molecular theory of the transport of pure substances and mixtures of molecules of different shapes in narrow slit-like pores, in which the potential of surface forces creates a strongly anisotropic distribution of molecules across pores and thereby makes the hydrodynamics equation inapplicable, is considered. The new microhydrodynamic approach is based on the lattice gas model, which takes into account the intrinsic volume of molecules and intermolecular interactions in the quasi-chemical approximation. Self-consistent calculations of dissipative coefficients taking nonlocal fluid properties into account were performed on the basis of the transition state model including information about equilibrium adsorbate distribution. Changes in fluid concentrations from the gaseous to liquid state and a broad temperature range, including the critical region, are analyzed. This allows vapor, liquid, and vapor-liquid fluid flows to be considered in the presence of capillary condensation. An increase in the size of pores transforms the equations of the theory into hydrodynamic transfer equations for gas or liquid flows, while preserving the relation of transfer coefficients to intermolecular potentials. The use of microhydrodynamic approach equations in numerical calculations and the possibility of applying this approach are discussed.     

n-Pentane and isopentane in one-dimensional channels

Molecular dynamics studies of n-pentane and isopentane in one-dimensional channels of AlPO(4)-5 and a carbon nanotube are reported. Variation of the structure and energetics in AlPO(4)-5 along the channel axis of isopentane is similar to what has been found for other rigid molecular systems. In n-pentane, these properties exhibit more frequent undulations along the channel due to flexibility. The end-to-end distance of n-pentane is a function of its position along the channel in AlPO(4)-5, suggesting that n-pentane has to alternately stretch in the narrow part and destretch or coil in the broader part of the channel. n-Pentane lies flat instead of upright on the inner surface of the carbon nanotube. Both of the species exhibit diffusive motion in AlPO(4)-5, and the self-diffusivity is higher than that in bulk. Isopentane has a higher diffusivity than does n-pentane. This is attributed to the higher cross section of isopentane, which is closer to the void cross section. Further, the coupling of the translational motion with the slower dihedral angle reorientation in the case of n-pentane decreases its mobility. Superdiffusive motion is seen for both species in the carbon nanotube. These results can be understood in terms of the levitation effect.     

Light-regulated ion transport through artificial ion channels based on TiO2 nanotubular arrays

Light-responsive artificial ion channels are created using self-organized TiO(2) nanotubular arrays, whose ion transport properties can be regulated by external ultraviolet light. The formation of electrostatic traps within TiO(2) nanotubes by UV light contributes to the light-regulated ion transport.     

Cell docking inside microwells within reversibly sealed microfluidic channels for fabricating multiphenotype cell arrays

We present a soft lithographic method to fabricate multiphenotype cell arrays by capturing cells within an array of reversibly sealed microfluidic channels. The technique uses reversible sealing of elastomeric polydimethylsiloxane (PDMS) molds on surfaces to sequentially deliver various fluids or cells onto specific locations on a substrate. Microwells on the substrate were used to capture and immobilize cells within low shear stress regions inside channels. By using an array of channels it was possible to deposit multiple cell types, such as hepatocytes, fibroblasts, and embryonic stem cells, on the substrates. Upon formation of the cell arrays on the substrate, the PDMS mold could be removed, generating a multiphenotype array of cells. In addition, the orthogonal alignment and subsequent attachment of a secondary array of channels on the patterned substrates could be used to deliver fluids to the patterned cells. The ability to position many cell types on particular regions within a two dimensional substrate could potentially lead to improved high-throughput methods applicable to drug screening and tissue engineering.     

Colorimetric sensor arrays for molecular recognition

The development of colorimetric sensor arrays for the detection of volatile organic compounds is reported. Using an array of chemo-responsive dyes, enormous discriminatory power is created in a simple device that can imaged easily with an ordinary flat-bed scanner. High sensitivities (ppb) have been demonstrated for the detection of biologically important analytes, including amines, carboxylic acids, and thiols. By the proper choice of dyes and substrate, the array can be made essentially non-responsive to changes in humidity.     

Long-range light-modulated charge transport across the molecular heterostructure doped protein biopolymers

Biological electron transfer (ET) across proteins is ubiquitous, such as the notable photosynthesis example, where light-induced charge separation takes place within the reaction center, followed by sequential ET via intramolecular cofactors within the protein. Far from biology, carbon dots (C-Dots) with their unique optoelectronic properties can be considered as game-changers for next-generation advanced technologies. Here, we use C-Dots for making heterostructure (HS) configurations by conjugating them to a natural ET mediator, the hemin molecule, thus making an electron donor–acceptor system. We show by transient absorption and emission spectroscopy that the rapid intramolecular charge separation happens following light excitation, which can be ascribed to an ultrafast electron and hole transfer (HT) from the C-Dot donor to the hemin acceptor. Upon integrating the HS into a protein matrix, we show that this HT within the HS configuration is 3.3 times faster compared to the same process in solution, indicating the active role of the protein in supporting the rapid light-induced long-range intermolecular charge separation. We further use impedance, electrochemical, and transient photocurrent measurements to show that the light-induced transient charge separation results in an enhanced ET and HT efficiency across the protein biopolymer. The charge conduction across our protein biopolymers, reaching nearly 0.01 S cm⁻¹, along with the simplicity and low-cost of their formation promotes their use in a variety of optoelectronic devices, such as artificial photosynthesis, photo-responsive protonic–electronic transistors, and photodetectors.

This work reports on a chimeric protein matrix with C-Dot–hemin heterostructures as cofactors. We show how the protein environment facilitates an ultrafast charge separation, resulting in long-range electron conduction across the protein matrix.     

Geometry in digital molecular arrays

The development of digital molecular devices arises through the appropriate geometric positioning of a molecular assay. A detailed evaluation of the digital media reveals the critical aspects of geometric positioning in terms of developing an analytically-robust system for molecular analysis. This study reveals an explicit digital compact disc based assay for molecular affinity events.     

Polarization energies,transport gap and charge transfer states of organic molecular crystals

A self-consistent calculation of electronic polarization in organic molecular crystals and thin films is presented in terms of charge redistribution in nonoverlapping molecules in a lattice. The polarization energies P₊ and P₋ of a molecular cation and anion are found for anthracene and perelynetetracarboxylic dianhydride (PTCDA), together with binding energies of ion pairs and transport gaps of PTCDA films on metallic substrates. The 500 meV variation of P₊+P₋ with film thickness agrees with experiment, as do calculated dielectric tensors. Comparisons are made to submolecular calculations in crystals.     

Selective transport of ATP across a phospholipid bilayer by a molecular umbrella

Acylation of each primary group of spermidine with cholic acid, followed by acylation of the secondary amino group using an activated form of Nalpha,Ndelta,Nomega-tri-CBZ-l-arginine, and subsequent hydrogenolysis, afforded a conjugate (i.e., 1) which readily transports adenosine 5-triphosphate, but not glutathione, across phospholipid bilayers made from 1-palmitoyl-2-oleyol-sn-glycero-3-phosphocholine and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylglycerol.     

Lead-free molecular one-dimensional perovskite for efficient X-ray detection

<正>In recent years,great progress has been achieved for organicinorganic halide perovskites due to their excellent optoelectronic properties and stability for photovoltaics,light emitting diodes,and high-energy radiation detection [1-5].One-dimensional(1 D)perovskites,as an important derivative of three-dimensional(3 D)perovskites,exhibit low exciton dissociation efficiency,     

Molecular transport in narrow channels

The micro-hydrodynamic method is applid to the calculation of the molecular transport in narrow channels in case of capillary condensation, at the flow anisotropy resulted from the potential of the wall surface and/or of boundary vapor and fluid phases. The mechanisms of molecular transport in the one-phase and two-phase fluid flows as a dependence of fluid density and adsorption potential of channel walls are discussed.     

Design of pi-conjugated organic materials for one-dimensional energy transport in nanochannels

Various end-substituted distyrylbenzenes have been synthesized to serve as guest molecules in inclusion compounds to promote efficient energy transport along one-dimensional channels. Their optical and photophysical properties have been characterized at both experimental and theoretical levels. All molecules display a large transition dipole moment between the ground state and lowest excited state and hence a short radiative lifetime (on the order of 1-2 ns). They also exhibit a large spectral overlap between the emission and absorption spectra, which enables efficient energy transport between molecules arranged in a head-to-tail configuration in nanochannels. Hopping rates on the order of 10(12) s(-1) are calculated at a full quantum-chemical level; this is much larger than the radiative lifetimes and opens the way for energy migration over large distances. Changes in the nature of the terminal substituents are found to modulate the optical properties weakly but to impact significantly the energy transfer rates.     

Diffusion in one-dimensional channels with zero-mean time-periodic tilting forces

We investigate the motion of overdamped Brownian particles in a one-dimensional channel under a zero-mean time-periodic tilting force F(t). By introducing a simple harmonic signal, strong enhancement of diffusion is possible for relatively large values of the Peclet number. Direct numerical simulations over the corresponding Fokker-Planck equation show that the diffusion enhancement is induced by a type of nonlinear resonance effect involving the tilting force and the density gradient.