Surface Charge Potential Research Articles

Chitosan/PLA nanoparticles as a novel carrier for the delivery of anthraquinone: Synthesis, characterization and in vitro cytotoxicity evaluation

Designing novel materials for biomedical applications generally require the use of biodegradable materials. This study aims to engineer a biodegradable [chitosan (CS) and poly (lactic acid) (PLA)] as AQ carrier with nanometer dimensions and to evaluate the anticancer potency of the prepared CS/PLA–AQ NPs in human carcinoma (HepG2) cells. CS–PLA complex, which are well dispersed and stable in aqueous solution, was prepared by the precipitation of lactic acid in chitosan solution by dropping method and characterized by SEM, TEM, DLS and FTIR. The results thus displayed that the prepared nanoparticles carried a positive charge and showed the size in the range from 100 to 200nm. The in vitro (AQ) release study showed that these nanoparticles provided a continuous release of the entrapped AQ for 10 days, and the release behavior was influenced by the pH value of the medium thereby making feasible to develop CS–PLA for enhanced and sustained release of AQ. MTT assay revealed higher cytotoxic efficacy of CS/PLA–AQ NPs than Free AQ in HepG2 cells. Further, the mitochondrial membrane damage indicated by loss of mitochondrial membrane potential and necrotic cell death could be attributed to the increased reactive oxygen species production. Our results also suggest that upon CS/PLA–AQ NPs exposure the cell viability decreased due to apoptosis, as demonstrated by the formation of apoptotic bodies, sub-G1 hypodiploid cells, and DNA fragmentation. Henceforth, CS/PLA–AQ NPs demonstrated a strong antitumor activity in vitro by reducing cell viability, inducing cell necrosis, decreasing the negative surface charge and mitochondrial membrane potential, and fragmenting DNA.

금 표면 위에 형성된 글루타싸이온 층의 표면 물성

이산화티탄 표면에 흡착되는 금 입자의 분포 또는 그 반대 경우의 분포에 영향을 끼칠 수도 있는 정전기적 상호작용과 금 입자를 코팅한 Glutathione 층의 표면물성을 규명하였다. 이를 위하여, 원자힘현미경(AFM)으로 Glutathione 층표면과 이산화티탄표면 사이의 표면힘을 염 농도와 pH 값에 따라 측정하였다. 측정된 힘은 Derjaguin-Landau-Verwey-Overbeek(DLVO) 이론으로 해석되어 표면의 정전기적인 특성들이 정량적으로 산출되었다. 이 특성들이 염 농도와 pH에 대하여 나타내는 의존성을 질량보존의 법칙으로 기술하였다. pH 8과 11에서 실험으로 산출된 표면 특성의 염 농도 의존성은 이론적으로 예측했던 결과와 일치하는 것으로 관찰되었다. pH 8과 11에서 Glutathione 층의 표면이 이산화티탄 표면보다 높은 정전기적 특성을 갖는 것이 발견되었는데, 이는 Glutathione 층의 이온화-기능-그룹에 기인한 것으로 생각된다. It is investigated that that the physical properties of Glutathione layer formed on gold surfaces may make an effect on the distribution of either gold particle adsorbed to the <TEX>$TiO_2$</TEX> surface or vice versa with the adjustment of the electrostatic interactions. For the investigation, the atomic force microscope (AFM) was used to measure the surface forces between the surfaces as a function of the salt concentration and pH value. With the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, the forces were quantitatively analyzed to acquire the surface potential and charge density of the surfaces for each salt concentration and each pH value. The surface potential and charge density dependence on the salt concentration was described with the law of mass action, and the pH dependence was explained with the ionizable groups on the surface. The salt concentration dependence of the surface properties, found from the measurement at pH 8 and 11, was consistent with the prediction from the law. It was found that the Glutathione layer had higher values for the surface charge densities and potentials than the titanium dioxide surfaces at pH 8 and 11, which may be attributed to the ionized-functional-groups of the Glutathione layer.

Fluorescence of Colloidal Gold Nanoparticles is Controlled by the Surface Adsorbate

AbstractFluorescent gold nanoparticles are important biological labels, in particular for combined optical and electron microscopy. It is reported that density and type of surface ligands have key influence on the dominant UV‐vis fluorescence band in positively and negatively charged gold nanoparticles capped with citrate, gold oxide, and cetyltrimethyl ammonium bromide (CTAB). The peak excitation and emission energies and fluorescence intensities vary with nanoparticle size, reflecting changes in surface charge and surface potential as well as a varying density of surface adsorbates. The fluorescence peak shifts, the evolution of zeta potentials, and fluorescence intensity trends are explained by a model of the principal fluorescence transitions that takes into account the nanoparticle surface conditions, such as the adhesion of ligands. Varying surface ligands is a simple strategy to optimize fluorescence intensity and to design spectral properties of gold nanoparticles.

Cytotoxicity Induced by Engineered Silver Nanocrystallites Is Dependent on Surface Coatings and Cell Types

Due to their unique antimicrobial properties silver nanocrystallites have garnered substantial attention and are used extensively for biomedical applications as an additive to wound dressings, surgical instruments and bone substitute materials. They are also released into unintended locations such as the environment or biosphere. Therefore it is imperative to understand the potential interactions, fate and transport of nanoparticles with environmental biotic systems. Numerous factors including the composition, size, shape, surface charge, and capping molecule of nanoparticles are known to influence cell cytotoxicity. Our results demonstrate that the physical/chemical properties of the silver nanoparticles including surface charge, differential binding and aggregation potential, which are influenced by the surface coatings, are a major determining factor in eliciting cytotoxicity and in dictating potential cellular interactions. In the present investigation, silver nanocrystallites with nearly uniform size and shape distribution but with different surface coatings, imparting overall high negativity to high positivity, were synthesized. These nanoparticles included poly(diallyldimethylammonium) chloride-Ag, biogenic-Ag, colloidal-Ag (uncoated), and oleate-Ag with zeta potentials +45 ± 5, -12 ± 2, -42 ± 5, and -45 ± 5 mV, respectively; the particles were purified and thoroughly characterized so as to avoid false cytotoxicity interpretations. A systematic investigation on the cytotoxic effects, cellular response, and membrane damage caused by these four different silver nanoparticles was carried out using multiple toxicity measurements on mouse macrophage (RAW-264.7) and lung epithelial (C-10) cell lines. Our results clearly indicate that the cytotoxicity was dependent on various factors such as surface charge and coating materials used in the synthesis, particle aggregation, and the cell-type for the different silver nanoparticles that were investigated. Poly(diallyldimethylammonium)-coated Ag nanoparticles were found to be the most toxic, followed by biogenic-Ag and oleate-Ag nanoparticles, whereas uncoated or colloidal silver nanoparticles were found to be the least toxic to both macrophage and lung epithelial cells. Also, based on our cytotoxicity interpretations, lung epithelial cells were found to be more resistant to the silver nanoparticles than the macrophage cells, regardless of the surface coating.

Solution NMR structures reveal a distinct architecture and provide first structures for protein domain family PF04536.

The protein family (Pfam) PF04536 is a broadly conserved domain family of unknown function (DUF477), with more than 1,350 members in prokaryotic and eukaryotic proteins. High-quality NMR structures of the N-terminal domain comprising residues 41-180 of the 684-residue protein CG2496 from Corynebacterium glutamicum and the N-terminal domain comprising residues 35-182 of the 435-residue protein PG0361 from Porphyromonas gingivalis both exhibit an α/β fold comprised of a four-stranded β-sheet, three α-helices packed against one side of the sheet, and a fourth α-helix attached to the other side. In spite of low sequence similarity (18%) assessed by structure-based sequence alignment, the two structures are globally quite similar. However, moderate structural differences are observed for the relative orientation of two of the four helices. Comparison with known protein structures reveals that the α/β architecture of CG2496(41-180) and PG0361(35-182) has previously not been characterized. Moreover, calculation of surface charge potential and identification of surface clefts indicate that the two domains very likely have different functions.

Nano-cluster-enhanced high-performance perfluoro-polymer electrets for energy harvesting

Development of high-performance electret materials is required to obtain a large power output of the electrostatic vibration-driven energy harvesters. In this study, by introducing aminosilane derivatives into CYTOP-based perfluorinated polymer film, we have successfully formed nano-clusters containing the organic siloxanes in the polymer electrets. Using small-angle x-ray scattering, tapping mode AFM and SEM analysis, the existence of such nano-clusters has been directly observed in the CYTOP film. It is suggested that the observed nano-clusters serve as the charge trap site and enhance the surface charge density and the thermal stability of the trapped charges. As a polymer electret, an extremely high surface charge potential of −1.6 kV with the 15 µm thick film has been obtained under the optimum condition of corona charging.

Solar wind access to lunar polar craters: Feedback between surface charging and plasma expansion

[1] Determining the plasma environment within permanently shadowed lunar craters is critical to understanding local processes such as surface charging, electrostatic dust transport, volatile sequestration, and space weathering. In order to investigate the nature of this plasma environment, the first two-dimensional kinetic simulations of solar wind expansion into a lunar crater with a self-consistent plasma-surface interaction have been undertaken. The present results reveal how the plasma expansion into a crater couples with the electrically-charged lunar surface to produce a quasi-steady wake structure. In particular, there is a negative feedback between surface charging and ambipolar wake potential that allows an equilibrium to be achieved, with secondary electron emission strongly moderating the process. A range of secondary electron yields is explored, and two distinct limits are highlighted in which either surface charging or ambipolar expansion is responsible for determining the overall wake structure.

Physical Properties of Mercaptopyruvic-acid Layer Formed on Gold Surfaces

E-mail: jwpark@seoultech.ac.krReceived June 7, 2011, Accepted June 24, 2011We studied the physical properties of the mercaptopyruvic-acid layer formed on gold surfaces, which has theinteractions with the titanium dioxide surface for design of gold- titanium dioxide distribution. Surface forcemeasurements were performed, using the atomic force microscope (AFM), between the surfaces as a functionof the salt concentration and pH value. The forces were analyzed with the DLVO (Derjaguin-Landau-Verwey-Overbeek) theory, to evaluate the potential and charge density of the surfaces quantitatively for each saltconcentration and each pH value. The difference in the properties reflected the effect of the isoelectric point onthe surface forces. The forces were interpreted for the evaluation with the law of mass action and the ionizablegroups on the surface. The salt concentration dependence of the surface properties, found from themeasurement at pH 8.0, was consistent with the prediction from the law. It was found that the mercaptopyruvic-acid layer had higher values for the surface charge densities and potentials than the titanium dioxide surfacesat pH 8, which may be attributed to the ionized-functional-groups of the mercaptopyruvic-acid layer.Key Words : Mercaptopyruvic-acid, Gold surface, TiO

Surface chemical properties and pedogenesis of tropical soils derived from basalts with different ages in Hainan, China

Abstract Limited information is available on the changes of surface chemical properties of tropical soils with time during the pedogenesis. Soil samples of three profiles derived from basalts of 10, 1330 and 2290 kilo annum (ka) in age were collected from adjacent locations in a tropical region of Hainan Province, China. The changes in soil surface chemical properties and the mineralogy of the soil clay fraction with time were investigated using ion adsorption, micro-electrophoresis, and X-ray diffraction analysis. The content of 2:1-type clay minerals decreased, while those of kaolinite and gibbsite increased with increasing basalt age and degree of soil development. The content of pedogenic free iron (Fe) oxides and the ratio of free Fe oxides/total Fe oxides increased with soil development stage, while soil poorly crystalline Fe and aluminum (Al) oxides had an opposite trend. The positive surface charge of the soils increased with increasing basalt age and degree of soil development; this was consistent with the change in their contents of free Fe/Al oxides. However, the value of negative surface charge had an opposite behavior. The soil derived from 10-ka-basalt had much more negative charge than soils derived from 1330- and 2290-ka-basalt. Soil net surface charge and zeta potential of the soil clay-fraction decreased with the increase in basalt age. Both net charge–pH curves and zeta potential–pH curves shifted to positive values with increased basalt age and degree of soil development. Increasing age also elevated the point of zero net charge of the soil and the isoelectric point of soil colloids.

Dynamical effects and fluctuations of interaction-matrix elements for a ballistic quantum dot

We study matrix element fluctuations of the two-body screened Coulomb interaction and of the one-body surface charge potential in ballistic quantum dots, comparing behavior in actual chaotic billiards with analytic results previously obtained in a normalized random-wave model. We find that the matrix element variances in actual chaotic billiards typically exceed by a factor of 3 or 4 the predictions of the random-wave model, for dot sizes commonly used in experiments. We discuss dynamical effects that are responsible for this enhancement. These dynamical effects have an even more striking effect on the covariance, which changes sign when compared with random-wave predictions. In billiards that do not display hard chaos, an even larger enhancement of matrix element fluctuations is possible. These enhanced fluctuations have implications for peak spacing statistics and spectral scrambling for quantum dots in the Coulomb blockade regime.

Formulation development and systematic optimization of solid lipid nanoparticles of quercetin for improved brain delivery

This study aims at formulating solid lipid nanoparticles (SLNs) of quercetin, a natural flavonoid with established antioxidant activity, for intravenous administration in order to improve its permeation across the blood-brain barrier into the CNS, and eventually to improve the therapeutic efficacy of this molecule in Alzheimer's disease. The SLNs of quercetin were formulated using Compritol as the lipid and Tween 80 as the surfactant through a microemulsification technique, and optimized employing a 3(2) central composite design (CCD). Selection of the optimized SLN formulation, using brute-force methodology and overlay plots, was based on its efficiency of entrapping quercetin inside the lipophilic core, particle size, surface charge potential and ability of the SLNs to release the entrapped drug completely. The optimized formulation was subjected to various in-vivo behavioral and biochemical studies in Wistar rats. The optimized formulation exhibited a particle size of less than 200 nm, 85.73% drug entrapment efficiency and a zeta potential of 21.05 mV. In all the in-vivo behavioral and biochemical experiments, the rats treated with SLN-encapsulated quercetin showed markedly better memory-retention vis-à-vis test and pure quercetin-treated rats. The studies demonstrated successful targeting of the potent natural antioxidant, quercetin, to brain as a novel strategy having significant therapeutic potential to treat Alzheimer's disease.

Progress of marine biofouling and antifouling technologies

Adhesion of marine fouling organisms on artificial surfaces such as ship hulls causes many problems, including extra energy consumption, high maintenance costs, and increased corrosion. Therefore, marine antifouling is an important issue. In this review, physical and biochemical developments in the field of marine biofouling, which involves biofilm formation and macro-organism settlement, are discussed. The major antifouling technologies based on traditional chemical methods, biological methods, and physical methods are presented. The chemical methods include self-polishing types such as tributyltin (TBT) self-polishing copolymer coatings, which despite its good performance has been banned since 2008 because of its serious environmental impact. Therefore, other methods have been encouraged. These include coatings with copper compounds and biocide boosters to replace the TBT coatings. Biological extracts of secreted metabolites and enzymes are anticipated to act as antifoulants. Physical methods such as modification of surface topography, hydrophobic properties, and charge potential have also been considered to prevent biofouling. In this review, most of the current antifouling technologies are discussed. It is proposed that the physical antifouling technologies will be the ultimate antifouling solution, because of their broad-spectrum effectiveness and zero toxicity.

Polymer-Caged Nanobins for Synergistic Cisplatin−Doxorubicin Combination Chemotherapy

Multicomponent chemotherapy has increasingly become a strategy of great importance in clinical cancer treatments. However, this type of chemotherapy has not been demonstrated in nanoscale delivery vehicles where two cytotoxic agents can be packaged together, potentially leading to synergistic drug activities. Herein, we present the codelivery of doxorubicin and cisplatin via a single polymer-caged nanobin (PCN) and show that copackaging can yield strong synergy in the efficacy of these agents. Such a PCN comprises a doxorubicin-encapsulated liposomal core protected by a pH-responsive cisplatin prodrug-loaded polymer shell with tunable drug ratios and surface charge potentials. This dual-agent Pt-PCN(DXR) formulation dramatically enhances the overall cytotoxicity of each drug against cancer cells at reduced doses and exhibits higher synergy than combinations of either the free drugs or separately nano-packaged drugs. These results clearly indicate that the polymer-caged nanobin platform can offer new means for building synergy into combination chemotherapy regimens.

Impact of Environmental Conditions (pH, Ionic Strength, and Electrolyte Type) on the Surface Charge and Aggregation of Silver Nanoparticles Suspensions

The impact of capping agents and environmental conditions (pH, ionic strength, and background electrolytes) on surface charge and aggregation potential of silver nanoparticles (AgNPs) suspensions were investigated. Capping agents are chemicals used in the synthesis of nanoparticles to prevent aggregation. The AgNPs examined in the study were as follows: (a) uncoated AgNPs (H(2)-AgNPs), (b) electrostatically stabilized (citrate and NaBH(4)-AgNPs), (c) sterically stabilized (polyvinylpyrrolidone (PVP)-AgNPs), and (d) electrosterically stabilized (branched polyethyleneimine (BPEI)-AgNPs)). The uncoated (H(2)-AgNPs), the citrate, and NaBH(4)-coated AgNPs aggregated at higher ionic strengths (100 mM NaNO(3)) and/or acidic pH (3.0). For these three nanomaterials, chloride (Cl(-), 10 mM), as a background electrolyte, resulted in a minimal change in the hydrodynamic diameter even at low pH (3.0). This was limited by the presence of residual silver ions, which resulted in the formation of stable negatively charged AgCl colloids. Furthermore, the presence of Ca(2+) (10 mM) resulted in aggregation of the three previously identified AgNPs regardless of the pH. As for PVP coated AgNPs, the ionic strength, pH and electrolyte type had no impact on the aggregation of the sterically stabilized AgNPs. The surface charge and aggregation of the BPEI coated AgNPs varied according to the solution pH.

Formation of Crystalline-Oriented Titania Thin Films on ITO Glass Electrodes by EPD in a Strong Magnetic Field

Crystal-oriented and crack-free thin TiO2 films with a good interfacial adhesion on indium-tin oxide (ITO) glass substrates for photoelectrodes were fabricated by the electrophoretic deposition (EPD) method in a 12 T strong magnetic field. A binder-free suspension for the EPD was prepared by dispersing TiO2 in the mixture of 2-propanol and 2,4-pentanedione. The electrophoretic mobility and the sedimentation rate were measured at various ratios of the mixed solution. The optimized state of the suspension exhibiting the highest surface charge potential and producing deposits with the highest green density was obtained at the 50:50 mixing ratio. The TiO2 films were characterized by XRD and SEM analyses. The photo-current measurement was also conducted to investigate the relation between the photo-anode characteristics of a dye-sensitized solar cell and the plane orientation of the TiO2 films

Preparation of Crystalline‐Oriented Titania Photoelectrodes on ITO Glasses from a 2‐Propanol–2,4‐Pentanedione Solvent by Electrophoretic Deposition in a Strong Magnetic Field

Crystal‐oriented and crack‐free thin TiO2 films with a good interfacial adhesion on indium–tin oxide glass substrates for photoelectrodes of dye‐sensitized solar cells were fabricated by the constant voltage electrophoretic deposition (EPD) method in a strong magnetic field of 12 T generated by a superconducting magnet. A binder‐free suspension for the EPD was prepared by dispersing TiO2 in a mixture of 2‐propanol and 2,4‐pentanedione (acetylacetone). The electrical conductivity, sedimentation rate, and the electrophoretic mobility were measured at varying ratios of the mixed solution. The optimized state of the suspension exhibiting the highest surface charge potential and producing deposits with the highest green density was obtained at the 50:50 mixing ratio. The TiO2 films were characterized by X‐ray diffraction and scanning electron microscopic analyses.

Effect of Dipole Potential Variations on the Surface Charge Potential of Lipid Membranes

When the dipole potential of dimyristoylphosphatidylcholine (DMPC) monolayers was decreased, either by the insertion of phloretin or by the elimination of carbonyl groups at the interphase, the surface charge potential was displaced to lower negative values. At low ionic strength, the decrease of the negative charge density can be ascribed to a different exposure of the phosphate to water, as there is a good correlation to an increase in the area per lipid. At high ionic strength, the magnitude of the changes in the zeta potential produced by the effects on the dipole potential was found to be dependent on the type of anions present in the subphase. Differences between Cl- and ClO4- were ascribed to the adsorption of anions according to their different hydrations and polarizabilities. The influence of a low dipole potential on the anion adsorption can be ascribed to a less positive image charge at the membrane interior, resulting from an increase in the hydrocarbon core permittivity. This is congruent with the neutralization of interfacial dipoles and the area increase, as well as with the decrease in packing of the hydrocarbon groups. Phloretin did not cause changes in the dipole potential of dimyristoylphosphatidylethanolamine (DMPE), and in consequence, no effects on the zeta potential were measured. It is concluded that changes in the inner water/hydrocarbon plane affect the electrostatic potential measured in the outer plane of the polar headgroup region.

Some kinetic aspects of the charging of dielectric targets by a (1–50)-keV electron beam

The electron-emission characteristics of dielectrics irradiated with electron beams with a current density of about 10−5 A cm−2 have been experimentally investigated. An ambiguous relationship between the secondary electron-emission properties, the charged-surface potential, and the positive and negative charges accumulated in the surface region of dielectric targets is demonstrated. The character and values of various experimentally observed time charging constants, inconsistent with a number of theoretical models and estimates, are qualitatively explained.

Probing Surface Charge Potentials of Clay Basal Planes and Edges by Direct Force Measurements

The dispersion and gelation of clay suspensions have major impact on a number of industries, such as ceramic and composite materials processing, paper making, cement production, and consumer product formulation. To fundamentally understand controlling mechanisms of clay dispersion and gelation, it is necessary to study anisotropic surface charge properties and colloidal interactions of clay particles. In this study, a colloidal probe technique was employed to study the interaction forces between a silica probe and clay basal plane/edge surfaces. A muscovite mica was used as a representative of 2:1 phyllosilicate clay minerals. The muscovite basal plane was prepared by cleavage, while the edge surface was obtained by a microtome cutting technique. Direct force measurements demonstrated the anisotropic surface charge properties of the basal plane and edge surface. For the basal plane, the long-range forces were monotonically repulsive within pH 6-10 and the measured forces were pH-independent, thereby confirming that clay basal planes have permanent surface charge from isomorphic substitution of lattice elements. The measured interaction forces were fitted well with the classical DLVO theory. The surface potentials of muscovite basal plane derived from the measured force profiles were in good agreement with those reported in the literature. In the case of edge surfaces, the measured forces were monotonically repulsive at pH 10, decreasing with pH, and changed to be attractive at pH 5.6, strongly suggesting that the charge on the clay edge surfaces is pH-dependent. The measured force profiles could not be reasonably fitted with the classical DLVO theory, even with very small surface potential values, unless the surface roughness was considered. The surface element integration (SEI) method was used to calculate the DLVO forces to account for the surface roughness. The surface potentials of the muscovite edges were derived by fitting the measured force profiles with the surface element integrated DLVO model. The point of zero charge of the muscovite edge surface was estimated to be pH 7-8.

Electrostatic Behavior of the Charge-Regulated Bacterial Cell Surface

The electrostatic behavior of the charge-regulated surfaces of Gram-negative Escherichia coli and Gram-positive Bacillus brevis was studied using numerical modeling in conjunction with potentiometric titration and electrophoretic mobility data as a function of solution pH and electrolyte composition. Assuming a polyelectrolytic polymeric bacterial cell surface, these experimental and numerical analyses were used to determine the effective site numbers of cell surface acid-base functional groups and Ca(2+) sorption coefficients. Using effective site concentrations determined from 1:1 electrolyte (NaCl) experimental data, the charge-regulation model was able to replicate the effects of 2:1 electrolyte (CaCl(2)), both alone and as a mixture with NaCl, on the measured zeta potential using a single Ca(2+) surface binding constant for each of the bacterial species. This knowledge is vital for understanding how cells respond to changes in solution pH and electrolyte composition as well as how they interact with other surfaces. The latter is especially important due to the widespread use of the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory in the interpretation of bacterial adhesion. As surface charge and surface potential both vary on a charge-regulated surface, accurate modeling of bacterial interactions with surfaces ultimately requires use of an electrostatic model that accounts for the charge-regulated nature of the cell surface.