The dipole potential of phospholipid membranes and methods for its detection

The dipole potential is an electrical potential within phospholipid membranes, which arises because of the alignment of dipolar residues of the lipids and/or water dipoles in the region between the aqueous phases and the hydrocarbon-like interior of the membrane. For a fully saturated phosphatidylcholine membrane, its value is believed to be in the range 220–280 mV, positive in the membrane interior. This results in an enormous electric field strength within the membrane of 10⁸–10⁹ Vm⁻¹. The dipole potential is thus likely to have great significance in controlling the conformation of ion-translocating membrane proteins and so in regulating enzyme function. Because of its location within the membrane, quantification of the dipole potential is extremely difficult and presents a great challenge to the experimentalist and theoretician alike. Both electrical and spectroscopic methods developed for the determination of the dipole potential on lipid bilayers and monolayers are presented and possible causes for differences in the values derived are discussed.     

Size selective and volume exclusion effects on ion transfer at the silicalite modified liquid-liquid interface

The modification of the liquid/liquid interface with membranes of silicalite, a neutral framework zeolite, is used to extend the potential window. This feature allows the observation of the transfer of extremely hydrophilic ions, due to the size-exclusion of organic ions from the interior of the zeolitic framework. Similarly, volume exclusion effects are shown to affect facilitated ion transfer processes involving alkali metal cations. In contrast, proton transfer is largely unaffected by the presence of the zeolite, which is suggestive of more rapid diffusion processes within the interior of the framework. The technique of liquid/liquid electrochemistry should allow the measurement of solution phase transport parameters for ions within microporous hosts.     

Acentric 2-D ensembles of D-br-A electron-transfer chromophores via vectorial orientation within amphiphilic n-helix bundle peptides for photovoltaic device applications

We show that simply designed amphiphilic 4-helix bundle peptides can be utilized to vectorially orient a linearly extended donor-bridge-acceptor (D-br-A) electron transfer (ET) chromophore within its core. The bundle's interior is shown to provide a unique solvation environment for the D-br-A assembly not accessible in conventional solvents and thereby control the magnitudes of both light-induced ET and thermal charge recombination rate constants. The amphiphilicity of the bundle's exterior was employed to vectorially orient the peptide-chromophore complex at a liquid-gas interface, and its ends were tailored for subsequent covalent attachment to an inorganic surface, via a "directed assembly" approach. Structural data, combined with evaluation of the excited state dynamics exhibited by these peptide-chromophore complexes, demonstrate that densely packed, acentrically ordered 2-D monolayer ensembles of such complexes at high in-plane chromophore densities approaching 1/200 ?(2) offer unique potential as active layers in binary heterojunction photovoltaic devices.     

Modifying metal nanoparticle placement on carbon supports using an aerosol-based process, with application to the environmental remediation of chlorinated hydrocarbons

A facile aerosol-based process (ABP) is developed to vary the placement of iron nanoparticles on the external surface of carbon microspheres or within the interior. This is accomplished through the competitive mechanisms of sucrose carbonization and the precipitation of soluble iron salts, in an aerosol droplet passing through a high temperature heating zone. At lower aerosolization temperatures, carbonization occurs first leading to iron salt precipitation on the external surface, while at higher temperatures interior placement occurs through concurrent iron salt precipitation and sucrose carbonization. The resulting composites are highly conducive to the reductive dechlorination of compounds such as trichloroethylene (TCE) as the carbon support is a strong adsorbent, and zerovalent iron effectively reduces TCE to innocuous gases such as ethane. Since both iron and carbon are widely used catalysts and catalyst supports, the simple process of modifying iron placement has significant potential applications in heterogeneous catalysis.     

Bulk conductivity of soft surface layers: experimental measurement and electrokinetic implications

Conductivity measurements were carried out on a family of polyacrylamide-co-sodium acrylate gels cross-linked with N,N'-methylenebisacrylamide in a homemade electrokinetic cell. The conductivity data allowed the equilibrium Donnan potential difference between the bulk gel and the bulk electrolyte solution to be estimated at various ionic strengths. The data were fit to a simple model assuming full dissociation of functional groups as well as to a more complete model (Dukhin, S. S.; Zimmerman, R.; Werner, C. J. Colloid Interface Sci. 2004, 274, 309) that accounts for the weak electrolyte nature of the acrylate groups fixed within the gel structure. The conductivity of the gel layers was observed to be significantly larger than the conductivity of the bulk electrolyte solutions at low ionic strengths. The increased conductivity reflects the enhanced concentration of ions within the gel structure due to Donnan equilibrium and the mobility of ions within the high water content gel layers. The electrokinetic implications of the bulk conductivity of gel-like soft surface layers are discussed in terms of the influence of the gel conductance on the resulting streaming potential.     

Charge Transport in Mesomorphic Phthalocyanines Studied by Pulse-Radiolysis Time-Resolved Microwave Conductivity

The pulse-radiolysis time-resolved microwave conductivity (PR-TRMC) technique has been used to obtain information on the transport of charge within columnarly stacked, peripherally octaalkoxy-substituted phthalocyanines. Data are presented on the one-dimensional, intracolumnar charge mobility and on the timescale of quasi-two-dimensional intercolumnar electron tunnelling. Particular attention is paid to materials that are liquid-crystalline at room temperature, because of their potential technological importance in optoelectric charge transport layers and molecular semiconductor devices. The relevance of the data to channeled charge transport in aligned thin layers is discussed.     

Au(111)-离子液体界面层状结构与温度关联的原位AFM力曲线研究

本文针对BMIPF6 和OMIPF6两种离子液体,在电极表面远离零电荷电位且以负电荷表面电位下,运用AFM力曲线详细地研究了其与Au(111)单晶电极界面所形成的层状结构与温度的关联. 在15 ~ 40 ^oC的温度范围内,温度越低其离子液体层状结构越稳定. 温度对OMIPF₆离子液体层状结构的稳定性和数目的影响较BMIPF₆缓和：温度变化5 ^oC,OMIPF₆靠近表面第一层层状结构的力值变化仅为1 ~ 2 nN,而BMIPF6第一层层状结构的力值变化为3 ~ 5 nN;较低温下,BMIPF₆中层状结构的数目有所增加,而OMIPF₆的层状数目始终保持两层,且随温度的变化并不敏感. 这可归因于两种离子液体的阳离子尺寸以及与电极表面的作用方式和强度不同;同时,OMIPF₆较粘稠,其热运动受温度的影响不甚敏感.     

Structure of a cyclodextrin functionalized anionic clay: XRD analysis, spectroscopy, and computer simulations

Carboxy-methyl beta-cyclodextrin (CMCD) cavities have been intercalated within the galleries of anionic clay, Mg-Al layered double hydroxide (LDH). The cyclodextrin functionalized LDH has been reported to adsorb neutral and nonpolar guest molecules. X-ray diffraction, IR, and Raman vibrational spectroscopy and (13)C CPMAS NMR have been used to characterize the confined CMCD molecules, whereas molecular dynamics simulations have been used to probe the interlayer arrangement and orientation of the intercalated species. Spectroscopic measurements as well as MD simulations show that there is no significant change in the geometry of the CMCD cavity on intercalation. Within the galleries of the anionic clay, the CMCD anions are arranged as bilayers with the carboxy methyl substituents, located at the narrower opening of the bucket-like cyclodextrin toroid, anchored to the LDH sheet. This arrangement leaves the wider opening of the CMCD anion facing away from the layers allowing the interior of the cyclodextrin cavity to be accessible to guest molecules. Finally, the hydrophobicity of the anchored cyclodextrin cavity has been characterized using fluorescence from pyrene included within it.     

Crystallinity and the effect of ionizing radiation in polyethylene. I. Crosslinking and the crystal core

An extensive study has been carried out on the effect of ionizing radiation on polyethylene in the form of solution-grown single crystals to follow up preceding investigations which had indicated that the radiation-induced effects along the fold surfaces could be significantly different from those within the crystal interior. In this first part of the series, radiation-induced crosslinking was investigated in the case of “crystal core” material. This material, obtained by removal of the fold surface by oxidative degradation with ozone, consists of isolated foldfree crystal layers of dicarboxylic acids of uniform length, the length itself depending on the fold length of the starting crystal. This “core material” was irradiated by γ rays and the effect of crosslinking was followed by GPC analysis by recording the development of dimer, trimer, etc., peaks in the chromatograms. For a given dose, the fractional amount of crosslinked material is independent of the chain length. This, together with other effects described, provides unambiguous evidence that crosslinking occurs at the chain ends or, in other words, that there is no crosslinking within the interior of the paraffinoid lattice. Further, no permanent scission was observed to occur within the lattice, at least in amounts detectable by the present molecular weight measurements. The obvious significance of these effects for radiation studies on paraffinoid substances in general, beyond those of the present long-chain dicarboxylic acids, is discussed prior to utilizing them in the study of chain-folded polyethylene crystals in the following parts of the series.     

A method to enhance porosity of micro-particles

The nuclear track technique (NTT) is used to enhance the porosity of silica micro-particles. The enhanced porosity is a result of the formation of surface and interior pores or tracks in the silica by the action of external and internal fission fragments. The fission tracks produced at the surface and within the interior of the micro-particles are a result of coating the particles with trace quantitities of uranium, instead of having trace quantities of uranium incorporated within the silica matrix.     

Preparation of synthons for carborane containing macromolecules

The modification of para-carborane with appropriate functionalities for incorporation within a dendrimer framework was accomplished by functionalizing the carbon centers with protected alcohol and free acid groups. These compounds are excellent candidates for utilization as functional linkers between two generations of an aliphatic polyester dendrimer structure. Future assembly of these structures will result in dendritic macromolecules containing carboranes within their interior and will be enveloped by hydrophilic groups (hydroxyls) to maintain their water solubility and biocompatibility. These structures have potential applications in Boron Neutron Capture Therapy and Synovectomy. Additionally, carboranes were coupled to polymerizable acrylate structures, and it was shown that the resulting carborane monomers could be polymerized using living free-radical polymerization techniques.     

Particle‐in‐a‐Frame Nanostructures with Interior Nanogaps

Designing plasmonic hollow colloids with small interior nanogaps would allow structural properties to be exploited that are normally linked to an ensemble of particles but within a single nanoparticle. Now, a synthetic approach for constructing a new class of frame nanostructures is presented. Fine control over the galvanic replacement reaction of Ag nanoprisms with Au precursors gave unprecedented Au particle‐in‐a‐frame nanostructures with well‐defined sub‐2 nm interior nanogaps. The prepared nanostructures exhibited superior performance in applications, such as plasmonic sensing and surface‐enhanced Raman scattering, over their solid nanostructure and nanoframe counterparts. This highlights the benefit of their interior hot spots, which can highly promote and maximize the electric field confinement within a single nanostructure.     

Functionalizing the interior of dendrimers: Synthetic challenges and applications

Chemists' fascination with dendrimers mainly originates from their unique architecture and its exploitation for the design of well‐defined functional macromolecules. Depending on the nature of the synthesis, functionalization is traditionally introduced at the core, the periphery, or both. However, the specific incorporation of functional groups at the interior layers, i.e., generations, represents a considerable synthetic hurdle that must be overcome for the full potential of dendrimers to be realized. This review covers recent advances in this emerging frontier of dendrimer science with a particular focus on covalent modifications. Monomer design, syntheses, and properties of various dendritic backbone types are discussed. Internal functionalization dramatically increases the degree of complexity that can be implemented into a dendrimer macromolecule and, therefore, promises to lead to smart materials for future applications in bio‐ and nanotechnologies. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1047–1058, 2003     

Janus Composite Nanotubes

We propose a facile method to achieve paramagnetic Janus nanotubes with two compositions compartmentalized onto the interior and exterior surfaces, respectively. A sulfonated polydivinylbenzene (PDVB) nanotube is prepared by simple sulfonation of the exterior surface of a PDVB nanotube. Silica@FeOOH dual layers are sequentially grown onto the sulfonated PDVB nanotube surface. The composite nanotubes become paramagnetic after calcination and can be broken into shorter pieces under vigorous ultrasonication. After selective modification of the interior and exterior surfaces of the paramagnetic nanotubes, the nanotube shell becomes Janus in wettability. Desired hydrophobic species can be selectively captured inside the cavity. The paramagnetic Janus composite nanotubes can align into parallel chains under a magnetic field, which is self‐disassembled upon removal of the magnetic field.     

Polymeric vesicles with a hydrophobic interior formed by a thiophene-based all-conjugated amphiphilic diblock copolymer

The diblock copolymer, BP26, assembled into polymeric vesicles with double layers that formed a hydrophobic crystalline interior and a hydrophilic amorphous exterior in methanol, a selective solvent for the PEGT block. The vesicles were demonstrated to encapsulate a hydrophobic guest polyfluorene (PF).     

Kinetics of interior loop formation in semiflexible chains

Loop formation between monomers in the interior of semiflexible chains describes elementary events in biomolecular folding and DNA bending. We calculate analytically the interior distance distribution function for semiflexible chains using a mean field approach. Using the potential of mean force derived from the distance distribution function we present a simple expression for the kinetics of interior looping by adopting Kramers theory. For the parameters, that are appropriate for DNA, the theoretical predictions in comparison with the case are in excellent agreement with explicit Brownian dynamics simulations of wormlike chain (WLC) model. The interior looping times (tauIC) can be greatly altered in the cases when the stiffness of the loop differs from that of the dangling ends. If the dangling end is stiffer than the loop then tauIC increases for the case of the WLC with uniform persistence length. In contrast, attachment of flexible dangling ends enhances rate of interior loop formation. The theory also shows that if the monomers are charged and interact via screened Coulomb potential then both the cyclization (tauc) and interior looping (tauIC) times greatly increase at low ionic concentration. Because both tauc and tauIC are determined essentially by the effective persistence length [lp(R)] we computed lp(R) by varying the range of the repulsive interaction between the monomers. For short range interactions lp(R) nearly coincides with the bare persistence length which is determined largely by the backbone chain connectivity. This finding rationalizes the efficacy of describing a number of experimental observations (response of biopolymers to force and cyclization kinetics) in biomolecules using WLC model with an effective persistence length.     

Polymeric sodium 3,5‐di­carboxy­benzene­sulfonate–urea–water (1/1/1)

In the title compound, poly­[sodium‐μ₄‐3,5‐di­carboxy­benzene­sulfonato‐κ⁴O:O′:O′′:O′′′‐μ₂‐urea‐κ²O:N] monohydrate], {[Na(C₈H₅O₇S)(CH₄N₂O)]·H₂O}_n, the organic anions are arranged almost vertically within (001) monolayers, with the sulfonate and carboxylic acid groups pointing into the interlayer region. The inversion‐related aromatic rings of the anions inside the layers are arrayed via offset face‐to‐face interactions into molecular stacks along the crystallographic a axis. The `up' and `down' arrangement of the aromatic portions makes both faces of the layers ionic and hydro­philic, whereas the interiors of the layers are primarily hydro­phobic. The interleaving of the anions is such that the carboxylic acid groups are oriented more toward the interior than are the sulfonate groups. The aromatic rings in neighbouring layers are arranged in a herring‐bone fashion. The coordination sphere of the Na⁺ ions contains two sulfonate and two carboxylic acid O atoms, from a total of four different acid anions belonging to two neighbouring anionic monolayers. The urea mol­ecules are positioned between translation‐related anionic stacks inside the (001) layers, serving a triple function, viz. they fill in the large meshes (empty cavities) formed within the anionic–cationic network, and they provide additional Na⁺ coordination and hydrogen‐bond sites.     

Hollow Carbon Nanobubbles: Synthesis,Chemical Functionalization,and Container‐Type Behavior in Water

Thin‐walled, hollow carbon nanospheres with a hydrophobic interior and good water dispersability can be synthesized in two steps: First, metal nanoparticles, coated with a few layers of graphene‐like carbon, are selectively modified on the outside with a covalently attached hydrophilic polymer. Second, the metal core is removed at elevated temperature treatment with acid, leaving a well‐defined carbon‐based hydrophobic cavity. Loading experiments with the dye rhodamine B and doxorubicin confirmed the filling and release of a cargo and adjustment of a dynamic equilibrium (cargo‐loaded versus release). Rhodamine B preferably accumulates in the interior of the bubbles. Filled nanobubbles allowed constant dye release into pure water. Studies of the concentration‐dependent loading and release show an unusual hysteresis.     

Bilayered cyclofusene

Multiply-connected monolayered cyclofusene (MMC) is a fused hexacyclic system with at least two interior empty regions called holes. Multiply-connected bilayered cyclofusene (MBC) is a structure derived from an MMC by replacing each layer of hexacycles by two layers. Various properties of the equitability of these bipartite graphs are examined.     

Targeting of cancer cells with ferrimagnetic ferritin cage nanoparticles

Protein cage architectures such as virus capsids and ferritins are versatile nanoscale platforms amenable to both genetic and chemical modification. Incorporation of multiple functionalities within these nanometer-sized protein architectures demonstrate their potential to serve as functional nanomaterials with applications in medical imaging and therapy. In the present study, we synthesized an iron oxide (magnetite) nanoparticle within the interior cavity of a genetically engineered human H-chain ferritin (HFn). A cell-specific targeting peptide, RGD-4C which binds alphavbeta3 integrins upregulated on tumor vasculature, was genetically incorporated on the exterior surface of HFn. Both magnetite-containing and fluorescently labeled RGD4C-Fn cages bound C32 melanoma cells in vitro. Together these results demonstrate the capability of a genetically modified protein cage architecture to serve as a multifunctional nanoscale container for simultaneous iron oxide loading and cell-specific targeting.