Pore Opening Process Research Articles

Effects of Salicylic and Acetylsalicylic Acids in Mitochondrial and Erythrocyte Membranes

For further clarification of the mechanisms of pharmacological effects of salicylic and acetylsalicylic acids, the interactions of these acids with mitochondrial and erythrocyte membranes were studied and the role of calcium ions in the effects of salicylic and acetylsalicylic acids was examined. Salicylic acid and to a lesser extent acetylsalicylic acid at 0.5−2.0 mM concentration effectively inhibited the respiratory activity of isolated rat liver mitochondria, by uncoupling respiration and phosphorylation processes, induced depolarization of the mitochondrial membrane and potentiated Ca2+-stimulated formation of mitochondrial permeability transition pores in EGTA-free media. Cyclosporine A and ruthenium red partially inhibited the mitochondrial pore opening process induced by salicylic and acetylsalicylic acids both in the absence and presence of Ca2+ ions. Salicylic acid (180–360 µM) markedly accelerated proton-induced lysis of human erythrocytes (at pH 3.2) and caused hyperpolarization of erythrocyte membranes (at pH 5.5, but not at pH 7.4), probably as a result of proton transfer to the cytoplasm of the cell. Thus, salicylic and acetylsalicylic acids interact with mitochondrial and plasma membranes, act as effective proton/Ca2+ ionophores and stimulate the mitochondrial calcium uniporter.

Multiple Modes of Fusion and Retrieval at the Calyx of Held Synapse.

Neurotransmitter in vesicles is released through a fusion pore when vesicles fuse with the plasma membrane. Subsequent retrieval of the fused vesicle membrane is the key step in recycling exocytosed vesicles. Application of advanced electrophysiological techniques to a large nerve terminal, the calyx of Held, has led to recordings of endocytosis, individual vesicle fusion and retrieval, and the kinetics of the fusion pore opening process and the fission pore closure process. These studies have revealed three kinetically different forms of endocytosis-rapid, slow, and bulk-and two forms of fusion-full collapse and kiss-and-run. Calcium influx triggers all kinetically distinguishable forms of endocytosis at calyces by activation of calmodulin/calcineurin signaling pathway and protein kinase C, which may dephosphorylate and phosphorylate endocytic proteins. Polymerized actin may provide mechanical forces to bend the membrane, forming membrane pits, the precursor for generating vesicles. These research advancements are reviewed in this chapter.

Pore-Opening Dynamics of Single Nanometer Biovesicles at an Electrified Interface.

Release from nanobiovesicles via a pore generated by membrane electroporation at an electrified interface can be monitored by vesicle impact electrochemical cytometry (VIEC) and provides rich information about the various vesicular content transfer processes, including content homeostasis, intraphase content transfer, or the transient fusion of vesicles. These processes are primarily influenced by the vesicular pore-opening dynamics at the electrified interface which has not been disclosed at the single nanobiovesicle level yet. In this work, after simultaneously measuring the size and release dynamics of individual vesicles, we employed a moving mesh-finite element simulation algorithm to reconstruct the accurate pore-opening dynamics of individual vesicles with different sizes during VIEC. We investigated the expansion times and maximal pore sizes as two characteristics of different vesicles. The pore expansion times between nanobiovesicles and pure lipid liposomes were compared, and that of the nanobiovesicles is much longer than that for the liposomes, 2.1 ms vs 0.18 ms, respectively, which reflects the membrane proteins limiting the electroporation process. For the vesicles with different sizes, a positive relationship of pore size (Rp,max) with the vesicle size (Rves) and also their ratio (Rp,max/Rves) versus the vesicle sizes is observed. The mechanism of the pore size determination is discussed and related to the membrane proteins and the vesicle size. This work accurately describes the dynamic pore-opening process of individual vesicles which discloses the heterogeneity in electroporation of different sized vesicles. This should allow us to examine the more complicated vesicular content transfer process between intravesicular compartments.

Multifunctional Coordination Polymer Exhibiting Reversible Mechanical Motion Allowing Selective Uptake of Guests and Leading to Enhanced Electrical Conductivity.

A remarkably flexible, multifunctional, 2D coordination polymer exhibiting an unprecedented mode of reversible mechanical motion, enabling pores to open and close, is reported. Such multifunctional materials are highly sought after, owing to the potential to exploit coexisting electronic and mechanical functionalities that underpin useful technological applications such as actuators and ultrasensitive detectors. The coordination polymer, of composition Mn(F4TCNQ)(py)2 (F4TCNQ = 2,3,5,6-tetrafluoro-7,7,8,8-tetracycanoquinodimethane; py = pyridine), consists of Mn(II) centers bridged by F4TCNQ dianions and coordinated by py molecules that extend above and below the 2D network. Exposure of Mn(F4TCNQ)(py)2, in its collapsed state, to carbon dioxide results in a pore-opening process at a threshold pressure for a given temperature. In addition to carbon dioxide, a variety of volatile guests may be incorporated into the pores, which are lined with electron-rich F4TCNQ dianions. The inclusion of electron-deficient guests such as 1,4-benzoquinone, nitrobenzene, maleic anhydride, and iodine into the pores is accompanied by a striking color change associated with a new host-guest charge-transfer interaction and an improvement in the semiconductor behavior, with the iodine adduct showing an increase in conductivity of almost 5 orders of magnitude. Experimental and density functional theory calculations on this remarkable multifunctional material demonstrate a reduction in the optical band gap with increasing electron affinity of the guest.

Tailoring Mesoporous Silicon Surface to Form a Versatile Template for Nanoparticle Deposition

Porous silicon (PS) can be used as a loading template in sensing or as a matrix to develop nanoparticle arrays. We present a comprehensive study of PS morphology and optical properties before and after the pore opening process, including the determination of thickness, pore size, and pore density of PS layers, its surface wettability, and reflectivity. The PS samples were fabricated by electrochemical anodization of monocrystalline silicon wafer in 5–20 wt.% hydrofluoric acid (HF) solution at a current density in the range of 20–200 mA/cm2. Anodization was followed by the pore opening process, i.e., the removal of a parasitic superficial layer with a “bottleneck” structure by reactive ion etching (RIE). The results illustrate that “bottleneck”-free PS allows to achieve a high pore density using a low HF concentration and a reduced current density. We established that this structure demonstrates higher hydrophobicity in comparison to the samples before RIE. The applicability of the developed “bottleneck”-free PS was tested via filling the pores with silver nanoparticles, indicating its potential use as a template for the fabrication of nanoparticle arrays.

Fabrication of nanopores and nanoslits with feature sizes down to 5 nm by wet etching method

This paper presents an improved three-step wet etching method for the fabrication of single-crystal silicon nanopores and nanoslists. A diffusion model was built to analyze the influence of the color-based feedback mechanism on the final pore size. Reference structures were added aside normal pore patterns, to obtain a more precise control of the pore size during the pore opening process. By using this method, square nanopores with the minimum size of 8 nm × 8 nm, rectangle nanopores and nanoslits with feature sizes down to 5 nm were successfully obtained. Focused ion beam cutting revealed that the nanopore profile keeps well the inverted-pyramid shape, with an included angle of 54.7°.

Comparative study of coal based catalysts for NO adsorption and NO reduction by CO

A series of Fe-Co catalysts supported on coal based activated semicoke were tested for the catalytic performance of NO adsorption and NO reduction by CO. The structural property, surface chemistry and reaction mechanism were then investigated by nitrogen adsorption, X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Raman scattering, and in situ diffuse reflectance infrared Fourier transform spectra (DRIFT). The catalysts were prepared by changing type of coal, carbonization temperature, and activation method. For type of coal, lignite and bitumite were used as the raw materials and the experimental results showed that catalyst based on lignite exhibited superior performance of both NO adsorption and reduction than the catalyst based on bitumite. It was explained that less volatile and moisture content and higher level of graphitization of bitumite inhibit its pore opening process, and further resulted in smaller surface area, less metal loading and less surface Oβ, which are determining for the catalytic behavior. Carbonization temperatures of 500, 700 and 900 °C were tried. Higher carbonization temperature could enhance pores-opening and increase surface area where adsorbed NOx could be stored, resulting in higher adsorption capacity. But higher carbonization temperature could lead to the depletion of surface oxygen and decrease the amount of loaded metals, lowering the catalytic activity. Carbonization temperature of 700 °C was found to the optimum one considering both NO adsorption and reduction. Three activation methods were studied, i.e., HNO3, KOH and vapor activation. Catalyst activated by KOH exhibited the best performance of both NO adsorption and reduction. It is explained that KOH activation could help to retain surface oxygen, and thus increase metal loading and vacancy Oβ, which are essential for the catalytic performance.

Effects of Barrier Layer Thinning and Pore Opening on Nanowire Growth in Nanoporous Aluminum Oxide Templates

Nanowires have garnered much interest in recent years for their potential in increasing performance of devices, such as solar cells, thermoelectrics, batteries, and piezoelectrics. Many methods exist for the fabrication of nanowires, but one of the most promising methods is the use of nanoporous aluminum oxide templates due to its extremely high density and self-ordering through a hexagonal close packed structure. However, fabricating uniform arrays of nanowires in contact with a conductive substrate still remains a challenge. A vital step in the process is removal of the barrier layer between the pore and the underlying substrate. This step is needed to establish direct contact from the pores to the substrate. The objective is to remove the barrier without sacrificing the pore walls. Several methods exist for barrier layer thinning, including stepping down the anodization voltage or ramping down the applied current. However, the thinning method will influence the outcome of the pore opening, which is the second and final step in creating direct contact between the pore and substrate. Here, different barrier layer thinning techniques will be discussed and their effect on the pore opening process examined. Both step-down voltage and ramped current methods were used to understand the barrier layer thinning process. These results were correlated to the amount of pore opening achieved, measured through a combination of electrochemical impedance spectroscopy and chronoamperometry. Finally, nanowires were grown within these aluminum oxide templates to study the effects of different barrier layer thinning and pore opening techniques on nanowire growth and uniformity. This research provides a comprehensive approach towards fabricating uniform, high-density nanowire arrays.

Large scale free-standing open-ended TiO2 nanotube arrays: stress-induced self-detachment and in situ pore opening

In this study, the free-standing and open-ended TiO2 nanotube arrays with large area are synthesized under high field anodization. The membrane is firstly self-detached from Ti foil during anodization followed by a pore opening process of in situ field-assisted chemical dissolution. A model of stress accumulation is proposed to explain the self-detachment of the as-formed TiO2 nanotube membrane from the underlying Ti substrate. It is believed that the stress accumulation in the membrane is the collective effects of the stress generation during tube growth and the stress release due to chemical dissolution. When the stress accumulates to a critical value, the TiO2 nanotube membrane would be self-detached from the Ti substrate. It is found that the magnitude of stress is associated with the thickness of a stressed layer rather than the thickness of the as-formed TiO2 membrane. By changing the anodization parameters, the stress accumulation rate can be facilely controlled, which finally determines the detaching time and thickness of the detached membrane.

Release kinetics of gold nanoparticles from collagen microcapsules by total reflection X-ray fluorescence

One of the main challenges in nanotechnology based drug delivery systems is the design of novel materials for patient specific therapeutic efficacy. This can be achieved taking into account changes in the expression profiles of related proteins. Here, we focus on collagen type I micro-capsules for releasing molecules using a biological stimulus elicited by over-expressed collagenolytic matrix metalloproteinase I (MMPI). We have carried out label-free real time monitoring of the release kinetics of gold nanoparticles induced by MMPI in order to define the pore opening process by synchrotron radiation based total reflection X-ray fluorescence. Scanning electron and confocal laser scanning microcopy investigations have been carried out in order to further characterize the interaction between collagen micro-capsules and MMP1. The results enable to predict and to engineer the release time for drug molecules of different sizes. Moreover, the proposed label-free approach can be adopted for the visualization of pore formation and of release kinetics for nano-engineered polymeric capsules.

Investigation of the Influence of Different Process Setting Parameters on the Surface Formation at Honing of Thermally Sprayed Layers

In the development of modern combustion engines, light metal alloys combined with cylinder bore coatings are increasingly used to reduce total car mass. These coatings require an adaption of the honing process to achieve the coating's full technological potential. In this study, the influence of different process setting parameters on the surface formation of thermally sprayed layers was investigated using two different coating materials. Emphasis of this study was on the investigation of the pore opening process and the formation of burr extending into the pore cavity. The mechanism of pore opening was simulated using an FEM-Model in Abaqus/explicit. In order to gain an improved fundamental understanding of the mechanism of pore opening, a single abrasive grain and exemplary pore geometry were used.

Pore-opening Process in Nanoporous AAO Membranes for Electrodeposition of Semiconducting Nanowires

ABSTRACTThe fabrication of nanoporous aluminum oxide (Al2O3) membranes for large scale production of nanowires is performed at room temperature by a two-step anodization of commercially available aluminum foil tapes. During the anodization process, an oxide barrier layer is formed at the interface with aluminum. In the present work, the removal of the barrier is performed by (i) ramping down the voltage with a rate in the range of 0.5 V per 60s to 2 V per 60s and (ii) immersing the substrate in 50% phosphoric acid for up to 5 minutes. Depending on the removal conditions, several morphologies at the oxide-aluminum interface are observed by Scanning Electron Microscopy (SEM). Ramping down the voltage at less than 0.3 V per 15s combined by immersion in 50% phosphoric acid for less than 3 minutes is found to open the barrier layer of the nanopores. The pores have root-like structure with branches as small as few nanometers due to the slow voltage ramping. Several amorphous anodized Al2O3 (AAO) templates with pore diameter ranging from 30 to 40 nm and with length up to 25 μm were prepared by two-step anodization for the cathodic electrodeposition of photoactive nanowire semiconductors such as copper indium diselenide and cadmium sulfide.

Selective Gas Adsorption in the Flexible Metal–Organic Frameworks Cu(BDTri)L (L=DMF, DEF)

Use of the ditopic ligand 1,4-benzenedi(1H-1,2,3-triazole) (H(2)BDTri) enabled isolation of two new three-dimensional metal-organic frameworks of formulae Cu(BDTri)L in which L=DMF (1) and diethylformamide (DEF; 2). These compounds have the same primary structure, featuring one-dimensional channels with the bridging DMF or DEF molecules pointing into the cavity. Upon exposure to solvent vapors, both display a reversible flexibility, as characterized by single-crystal to single-crystal phase transitions in 1. The O(2) adsorption isotherms for the compounds show a two-step adsorption behavior associated with a permanent microporosity and a pore-opening process. In the case of N(2) adsorption, only 1 exhibits a two-step adsorption isotherm, whereas 2 does not present any pore opening, demonstrating that design of a flexible framework cavity can control the pore opening and thereby possibly enhance O(2)/N(2) separation.

Ultrathin Alumina Membranes for Surface Nanopatterning in Fabricating Quantum‐Sized Nanodots

Using ultrathin alumina membranes (UTAMs) as evaporation or etching masks large-scale ordered arrays of surface nanostructures can be synthesized on substrates. However, it is a challenge for this technique to synthesize quantum-sized surface structures. Here an innovative approach to prepare UTAMs with regularly arrayed pores in the quantum size range is reported. This new approach is based on a well-controlled pore-opening process and a modulated anodization process. Using UTAMs with quantum-sized pores for the surface patterning process, ordered arrays of quantum dots are synthesized on silicon substrates. This is the first time in realizing large-scale regularly arrayed surface structures in the quantum size range using the UTAM technique, which is an important breakthrough in the field of surface nanopatterning.

Quantum dots: Small 5/2010

The cover picture illustrates regularly arrayed quantum-sized pores and surface nanostructures prepared using an innovative approach of surface patterning. This new approach is based on a well-controlled pore-opening process and a modulated anodization process of ultrathin alumina membranes (UTAMs). Using UTAMs with quantum-sized pores for surface-patterning processes, ordered arrays of quantum dots are synthesized on silicon substrates. This is the first time in realizing large-scale regularly arrayed surface structures in the quantum size range using the UTAM technique, which is an important breakthrough in the field of surface nanopatterning. The large-scale quantum-dot arrays are promising candidate structures for new types of optoelectronic and display devices on the basis of the quantum-confinement effect. For more information, please read the Full Paper “Ultrathin Alumina Membranes for Surface Nanopatterning in Fabricating Quantum-Sized Nanodots” by Y. Lei et al., beginning on page 695.

Preparation of aminated microfiltration membranes by degradable functionalization using plain PEI membranes with various morphologies

The work describes the functionalization of microporous poly(ether imide) membranes with ultrafiltration separation profile by degradative functionalization using a two-step treatment process, which leads to strongly aminated membranes with microfiltration properties. Membranes with different morphology and ultrafiltration separation profile were prepared. In the first step, the pore system was opened by treatment with diethylenetriamine (DETA) which was followed by a treatment with high molecular poly(ethylene imine) to increase the amount of amine groups. Results verify that macrovoidal structures are more beneficial than sponge-like structures because of their strongly opened pores while only a small reduction in membrane thickness occurred. The separation properties of the virgin membrane have only a marginal influence on the pore opening process because of the leveling off the separation properties after a short treatment time. The number of covalently bound amine functions could be strongly increased by a second step functionalization process using a high-molar volume polyamine as a modifier which indicates the presence of residual imide groups of the basic polymer after the primary DETA treatment. Moreover the prepared membranes are suited for steam sterilization. These characteristics suggest a beneficial application in adsorptive separation processes.

Numerical simulation of electroporation in spherical cells.

This article presents a numerical study of the electroporation process of spherical cells suspended in an electrolyte solution, using the equivalent circuit method (ECM) for field calculation proposed by Ramos et al. A model for the electric conductance of the cell membrane derived from the analytical and experimental results obtained by Glaser et al. for planar lipidic membranes was applied. The influence of the cell concentration and membrane properties (described in the model) on the membrane current, membrane potential, and dependence of the electrolyte conductivity on the applied electric field was studied. These results clarify the electric events connected with the pore opening process and allow the planning of experimental approaches to study reversible membrane rupture in real cells.

Fusion pathways of vesicles: A Brownian dynamics simulation

We studied the fusion dynamics of vesicles using a Brownian dynamics simulation. Amphiphilic molecules spontaneously form vesicles with a bilayer structure. Two vesicles come into contact and form a stalk intermediate, in which a necklike structure only connects the outer monolayers, as predicted by the stalk hypothesis. We have found a new pathway of pore opening from stalks at high temperature: the elliptic stalk bends and contact between the ends of the arc-shaped stalk leads to pore opening. On the other hand, we have clarified that the pore-opening process at low temperature agrees with the modified stalk model: a pore is induced by contact between the inner monolayers inside the stalk.

Fatty acid-promoted mitochondrial permeability transition by membrane depolarization and binding to the ADP/ATP carrier

The mechanism by which non-esterified long-chain fatty acids (FFA) promote mitochondrial permeability transition (MPT) is not clear. We examined with energized rat liver mitochondria the role of two possible actions of FFA in MPT, (i) the reduction of the transmembrane potential (Δψ) and (ii) the increase of the negative surface charge of the inner mitochondrial membrane [Broekemeier, K.M. and Pfeiffer, D.G., Biochemistry 43, (1995) 16440–16449]. It was found that the ability of FFA to stimulate large amplitude swelling is clearly related to their uncoupling activity. Moreover, compared with classical protonophores (FCCP) FFA increase the sensitivity of the pore opening process to Δψ changes. In addition, FFA interact like their thioester derivatives in a structure-dependent manner with the ADP/ATP carrier (measured as inhibition of [ 3H]atractyloside binding to the AAC protein). It is suggested that not only the protonophoric action of FFA, but also a presumable stabilization of the `cytosolic' conformation of AAC contribute to the FFA-promoted MPT.

The pore opening process of etching polymer films irradiated by single and multiple heavy ions. The etching process in the range of the track core radius (10 nm)

The technique of electrochemical etching of irradiated polymer films is an useful method to investigate structures of the track cores. In the case of the investigation of multiple track foils, the mean effective radius corresponds to the average of all synchron etching pores. On the other hand, the etching cones of all tracks do not break through to conducting micro channels coincidentally. The statistical character of this pore opening (break through) process is still unexplained, although several effects concerning this topic have been observed in the past. Another computer program simulates by way of the Monte Carlo Method the etching process of an ensemble of tracks within a thin polymer film. The conductivity of the multiple track etching foil can be described by the convolution between the conductivity of a single pore and the time dependent breakthrough rate. By way of the Laplace Transforms the measurements of the multiple and single track etching polymer films can be deconvoluted and yield the statistical nature of the pore opening process.