A microfluidic diffusion chamber for reversible environmental changes around flaccid lipid vesicles

The reversible environmental changes around flaccid lipid vesicles represent a considerable experimental challenge, particularly because of remarkable softness of flaccid membranes, which can warp irreversibly under the slightest hydrodynamic flow. As a result, we have developed a microfluidic device for the controlled analysis of individual flaccid, giant lipid vesicles in a changing chemical environment. The setup combines the advantages of a flow-free microfluidic diffusion chamber and optical tweezers, which are used to load the sample vesicles into the chamber. After a vesicle is loaded into the diffusion chamber, its chemical environment is controllably and reversibly changed solely by means of diffusion. The chamber is designed as a 250 micrometres-long and 100 micrometres-wide dead-end microchannel, which extends from a T-junction of the main microchannels. Measurements of the flow-velocity profile in the chamber show that the flow rate decreases exponentially and scales linearly with the flow rate in the main channel. The characteristic length of the exponential decrease is 15 (1 ± 0.13) micrometres, meaning that a large part of the diffusion chamber is effectively flow-free. The diffusion properties are assessed by monitoring the diffusion of a dye into the chamber. It was found that a simple 1D diffusion model fits well to the experimental data. The time needed for the exchange of solutes in the chamber is of the order of minutes, depending on the solute's molecular weight. Here, we demonstrate how the diffusion chamber can be used for reversible environmental changes around flaccid, giant lipid vesicles and membrane tethers (nanotubes).     

Microwave assisted synthesis and magnetic properties of octanuclear and enneanuclear Ni(II) complexes: an unprecedented coordination mode for the NO(2)(-) ligand

Octanuclear and enneanuclear Ni(II) complexes have been synthesized using a microwave reactor. The octanuclear complex Ni(8) presents a new triply bridging coordination mode for the NO(2)(-) ligand.     

Mechanism Insights into Second-Order Nonlinear Optical Responses of Anionic Metal Clusters

We present the first-principle calculations on the electronic excitations and second-order properties in solution phase of two typical inorganic trinuclear anionic clusters, [MoCu₂S₄(SPh)₂]²⁻ and [Mo₂CuS₄]¹⁻(edt)₂(PPh₃) (edt=1,2-ethanedithiolato) in the framework of density functional theory (DFT). The computed excitation energies are in good agreement with the outcome of the measurements. The predicted values of the molecular quadratic hyperpolarizabilities are of the comparable order of those of the typical organometallic chromophores. We demonstrate the significant contributions to the second-order responses from the charge transfers between the metal centers (MMCT) which are ascribed to the direct metal–metal bonding interactions in these two charged clusters. This meaningful ligand-independent mechanism for the second-order response largely relates to metal–metal bonding strength, and the understanding will benefit to the future design of the new-generation molecular based nonlinear optical materials and optoelectronic devices by means of the conscious tuning of metal–metal interactions and metal-core structures of inorganic polynuclear clusters.     

Rational assembly of soluble copper(II) phosphonates: synthesis, structure and magnetism of molecular tetranuclear copper(II) phosphonates

The reactions of the dinuclear copper complexes [Cu(2)(L)(OAc)] [H(3)L = N,N'-(2-hydroxypropane-1,3-diyl)bis(salicylaldimine) or [Cu(2)(L')(OAc)] (H(3)L' = N,N'-(2-hydroxypropane-1,3-diyl)bis(4,5-dimethylsalicylaldimine)] with various phosphonic acids, RPO(3)H(2) (R = t-Bu, Ph, c-C(5)H(9), c-C(6)H(11) or 2,4,6-i-Pr(3)-C(6)H(2)), leads to the replacement of the acetate bridge affording tetranuclear copper(II) phosphonates, [Cu(4)(L)(2)(t-BuPO(3))](CH(3)OH)(2)(C(6)H(6)) (1), [Cu(4)(L)(2)(PhPO(3))(H(2)O)(2)(NMe(2)CHO)](H(2)O)(2) (2), [Cu(4)(L')(2)(C(5)H(9)PO(3))](CH(3)OH)(2) (3), [Cu(4)(L')(2)(C(6)H(11)PO(3)](MeOH)(4)(H(2)O)(2) (4) and [Cu(4)(L')(2)(C(30)H(46)P(2)O(5))](PhCH(3)) (5). The molecular structures of 1-4 reveal that a [RPO(3)](2-) ligand is involved in holding the four copper atoms together by a 4.211 coordination mode. In 5, an in situ formed [(RPO(2))(2)O](4-) ligand bridges two pairs of the dinuclear subunits. Magnetic studies on these complexes reveal that the phosphonate ligand is an effective conduit for magnetic interaction among the four copper centers present; a predominantly antiferromagnetic interaction is observed at low temperatures.     

Colloidal stability of oleic- and ricinoleic-acid-coated magnetic nanoparticles in organic solvents

Polyacrylic acid (PAA) and polyacrylamide (PAAm) double network (DN) hydrogels with high mechanical strength (about 1.5 MPa) are obtained when two kinds of monomer solutions of 4M AA with 5 mol% crosslinker and 4M AAm with 0.1 mol% crosslinker are used for the optimal preparation. Their high mechanical strength can be maintained even at high water content (above 50%) and at external stimuli (solvent and pH). This optimized DN hydrogel is used to develop the PAA/PAAm inverse opal hydrogel with DN structure by twice infiltration-polymerization and colloidal templating. Its photonic stop band can be tuned by controlling the solvent and pH. It first shows a small red-shift (about 20 nm), and then a large blue-shift (about 180 nm) with the increased ethanol content. For pH response, the DN inverse opal hydrogel has a large stop-band shift of about 140 nm when the pH increases from 1.2 to 5.6. Moreover, the DN inverse opal hydrogel also shows rapid recovery ability without hysteresis phenomenon in strong acidic environment, good reproducibility and durability. The interaction between the independently crosslinked PAA network and PAAm network plays a significant role in determining the response performance.     

Boundary value problems on planar graphs and flat surfaces with integer cone singularities, II: The mixed Dirichlet-Neumann problem

In this paper we continue the study started in Hersonsky (in press) [16]. We consider a planar, bounded, m-connected region Ω, and let ∂Ω be its boundary. Let T be a cellular decomposition of Ω∪∂Ω, where each 2-cell is either a triangle or a quadrilateral. From these data and a conductance function we construct a canonical pair (S,f) where S is a special type of a (possibly immersed) genus (m−1)singular flat surface, tiled by rectangles and f is an energy preserving mapping from T(1) onto S. In Hersonsky (in press) [16] the solution of a Dirichlet problem defined on T(0) was utilized, in this paper we employ the solution of a mixed Dirichlet-Neumann problem.     

Effects of ageing on the electrical characteristics of Cd/CdS/n-Si/Au–Sb structure deposited by SILAR method

Cd/CdS/n-Si/Au–Sb structure has been fabricated by the Successive Ionic Layer Adsorption and Reaction (SILAR) method and the influence of the time dependent or ageing on the characteristic parameters are examined. The current–voltage (I–V), capacitance–voltage (C–V) and capacitance–frequency (C–f) characteristics of the structure have been measured immediately, 1, 3, 5, 15, 30, 45, 60, 75, 90, 105, 120, 135, 150 and 165 days after fabrication of the structure. The characteristic parameters of the structure such as barrier height, ideality factor, series resistance are calculated from the I–V measurements and the barrier height, carrier concentration values are calculated from reverse bias C^?2–V measurements at 500 kHz and room temperature. Furthermore, the density distribution and time constant of the interface states have been calculated from the C–f measurements using the Schottky Capacitance Spectroscopy method as a function of ageing time. It has been seen that the changes of characteristic parameters such as barrier height, ideality factor and series resistance of Cd/CdS/n-Si/Au–Sb structure have lightly changed with increasing ageing time. At the same time, the rectifying ratio of the device increases with ageing time. It can be clearly said that the I–V characteristics of device get better with time.     

Polarizable simulations with second order interaction model (POSSIM) force field: Developing parameters for protein side‐chain analogues

A previously introduced polarizable simulations with second‐order interaction model (POSSIM) force field has been extended to include parameters for small molecules serving as models for peptide and protein side‐chains. Parameters have been fitted to permit reproducing many‐body energies, gas‐phase dimerization energies, and geometries and liquid‐phase heats of vaporization and densities. Quantum mechanical and experimental data have been used as the target for the fitting. The POSSIM framework combines accuracy of a polarizable force field and computational efficiency of the second‐order approximation of the full‐scale induced point dipole polarization formalism. The resulting parameters can be used for simulations of the parameterized molecules themselves or their analogues. In addition to this, these force field parameters are currently being used in further development of the POSSIM fast polarizable force field for proteins. © 2012 Wiley Periodicals, Inc.     

Graft Copolymerization of Methyl Methacrylate onto Poly(Ethylene Terephthalate) Fibers Using Benzoyl Peroxide

Abstract

The graft copolymerization of methyl methacrylate onto poly(ethylene terephthalate) fibers has been studied using benzoyl peroxide as initiator. The grafting reactions were carried out within the 70 to 90°C temperature range, and the variations of graft yield with monomer and initiator concentrations were also investigated. The overall activation energy for grafting was calculated as 34.1 kcal/mol. The results of dyeability with the disperse dye suggested that diffusion into the fiber structure was moderately difficult when the graft yield reached 14?15%. The maximum graft yield was obtained at a benzoyl peroxide concentration of 4.00 × 10^?3 M. The decomposition temperature values obtained from thermogravimetric analysis show that the thermal stability of poly(ethylene terephthalate) fibers decreased as a result of grafting. Further, such change in the properties of methyl methacrylate grafted fibers as density, diameter, and moisture regain were also determined.