Small Net Charge Research Articles

Resistance of the antibacterial agent ceragenin CSA-13 to inactivation by DNA or F-actin and its activity in cystic fibrosis sputum

The goal of this study was to evaluate the effects of DNA and F-actin [polyanions present in high concentration in cystic fibrosis (CF) airway fluid] on the antibacterial activities of the cationic steroid antibiotic CSA-13 and the cationic peptides LL37, WLBU2 and HB71. Light scattering intensity was used to evaluate the aggregation of DNA and F-actin by the cationic antibacterial agents. Bacterial killing assays, atomic force microscopy, determination of MIC values and bacterial load of CF sputa were used to determine the bactericidal activity. Inhibition of nuclear factor-kappaB (NF-kappaB) translocation in human aorta endothelial cells (HAECs) was quantified as an assay of anti-inflammatory action. CSA-13 is significantly more effective than cationic antibacterial peptides against kanamycin-resistant Pseudomonas aeruginosa and less susceptible to inactivation by DNA or F-actin. The concentration of CSA-13 sufficient to decrease the CF sputa bacteria load by approximately 90% is at least 10 times lower than that at which CSA-13 formed aggregates with DNA or F-actin. Both CSA-13 and LL37 prevent lipopolysaccharide-induced translocation of NF-kappaB in HAEC, thereby suggesting that these antibacterial molecules might prevent systemic inflammation caused by bacterial wall components. Charge-based interactions that strongly inhibit the antibacterial activity of host cationic antibacterial peptides present in CF sputa have significantly less effect on molecules from the ceragenin family such as CSA-13 due in part to their smaller net charge and distribution of this charge over a hydrophobic scaffold. CSA molecules therefore have potential for the treatment of chronic infections and inflammation that occur in CF airways and other settings in which extracellular polyanions accumulate.

Effect of gelatin molecular charge heterogeneity on formation of intermolecular complexes and coacervation transition

AbstractWe investigate the molecular charge heterogeneity of gelatin molecules at three different pHs: isoelectric pH = 5 (pI), and at pHs = pI ± 1 by measuring the zeta potential distributions. Its effect on the formation of soluble intermolecular complexes induced by the presence of a nonsolvent, ethanol, was explored. The charge distributions were found to be symmetric at pH = 5, where the onset of binding, and formation of soluble complexes were observed to be facilitated by the presence of a small net charge (close to zero) with the molecules exhibiting polyampholyte (PA) behavior. These distributions turned asymmetric at pH = 6, yet complex formation and coacervation occurred. On the other hand, for pH = 4 samples, these distributions were found to be strongly asymmetric with the molecules possessing very high net positive charge, such a system did not yield coacervation. The PA to polyelectrolyte transition and its repercussion on coacervation has been discussed in the light of the experimental results obtained from electrophoresis, turbidimetry, atomic force microscopy, and nanoindentation studies. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1511–1520, 2007

Charge neutralization of dust particles in a plasma with negative ions

Charging of dust grains in a plasma with negative ions is studied experimentally. When the relatively mobile electrons are attached to heavy negative ions, their tendency to charge the grains negatively is reduced. In a plasma in which a substantial fraction of the electrons are eliminated (positive ion/negative ion plasma), the grain charge can be reduced in magnitude nearly to zero (“decharging” or charge neutralization). If the positive ions are lighter than the negative ions, dust grains having a small net positive charge can be produced.

Probe Diffusion in Concentrated Polyelectrolyte Solutions: Effect of Background Interactions on Competition between Electrostatic and Viscous Forces

We have used fluorescence recovery after photobleaching (FRAP) to measure the diffusion coefficient D of a small probe protein, green fluorescent protein (GFP), in solutions of the polyelectrolyte sodium polystyrenesulfonate (NaPSS) over a wide range of conditions. We covered a range of polyelectrolyte concentrations that resulted in solution viscosities η from 1 to 50−100 cP, contrasted the behavior of high molecular weight (1 × 106 Da) and low molecular weight (7 × 104 Da) NaPSS, and explored the effects of low and high salt concentrations. We worked at a solution pH of 5.5, slightly higher than the isoelectric point of the GFP, which therefore had a small net negative charge. We observed positive deviations as large as 10-fold from Stokes−Einstein (S−E) behavior in high molecular weight NaPSS at low ionic strength. However, in low molecular weight NaPSS, approximately the same molecular weight as the DNA from our previous studies, deviations from S−E behavior were more modest, less than 2-fold. For hig...

Thin Films of Polyethylenimine and Alkyltrimethylammonium Bromides at the Air/Water Interface

We have prepared and analyzed thin film structures formed by polyethylenimine and alkyltrimethylammonium bromide (CnTAB) surfactants at the air/water interface, using both surface and bulk sensitive techniques. In initial experiments it was observed that hexagonal arrays of rodlike micelles surrounded by the polymer were formed at the solution surface, with the principal axis of the micelles running parallel to the surface. In the studies reported here, the formation of these ordered mesostructured films was identified as being kinetically but not thermodynamically favored, with some of the systems examined showing a loss of structure from their neutron reflectometry profiles with time. The polymer was used in both an as-diluted state (with a small net positive charge) and a neutral state, through the addition of sodium hydroxide to the solution. The primary interaction in these systems was found to be that of a neutral polymer with a cationic surfactant; however, by modifying the charge on the polymer it is possible to alter the distance between micelles by up to 6 Å without destroying the structure of the films. Analysis of the bulk solution with small-angle neutron scattering showed that the micelles in solution are elliptical rather than rod-shaped, and so the assembly of the hexagonal mesostructure occurs at the air/water interface rather than adsorbing to the interface from the bulk.

Permeation Properties of an Engineered Bacterial OmpF Porin Containing the EEEE-Locus of Ca 2+ Channels

The selectivity filter of the bacterial porin OmpF carries a small net charge close to −1 e and is therefore only slightly cation-selective. Calcium channels, on the other hand, contain four negatively charged glutamates, the EEEE-locus, and are among the most selective cation channels known. We aimed to turn the essentially nonselective OmpF into a Ca 2+-selective channel. To that end, two additional glutamates (R42E and R132E) were introduced in the OmpF constriction zone that already contains D113 and E117. Mutant OmpF containing this DEEE-locus has a high Ca 2+ over Cl − selectivity and a Na + current with a strongly increased sensitivity to 1 mM Ca 2+. The charge/space competition model, initially applied to the L-type Ca 2+ channel, identifies the fixed charge and filter volume as key determinants of ion selectivity, with the precise atomic arrangement having only second-order effects. By implication, the reproduction of fixed charge and filter volume should transform two channels into channels of similar selectivity, even if the two belong to entirely different ion channel families, as is the case for OmpF and the L-type Ca 2+ channel. The results presented here fit quite well in the framework of charge/space competition theory.

Interaction of electrically neutral and cationic forms of imipramine with liposome and erythrocyte membranes

Imipramine (IP) is an amphiphilic amine that is clinically useful as a tricyclic antidepressant. In the present work, we have investigated the pH effects on (a) the micellization properties of IP, (b) IP-induced release of aqueous contents from artificial vesicles (liposomes), and (c) IP-induced haemolysis, under hypotonic and isotonic conditions, in the pH range 5.0–10.0. Our data show that IP-membrane interaction caused important membrane destabilisation. However, changes in pH modified strongly the effects of IP. We suggest that the parameters of IP-induced model and cell membrane lysis are sensitive to the changes in the charge of this amphiphile. IP interacts more strongly with the membrane at basic pH (smaller net charge) than at neutral or acidic pH. A simple interpretation of these data is that increasing pH causes a decrease in IP net charge, thus a decrease in the critical micellar concentration of IP, and an increased partition into the lipid bilayer. Concomitantly, pH variations both above and below 7 tend to destabilise the cell membrane, so that the protective effect of IP against hypotonic haemolysis has a maximum at neutral pH.

Drag Forces on a Stationary Particle in Flowing Two-Dimensional Ordered Particle Monolayers: Simulation and Measurement Using Optical Tweezers

Using a laser tweezer method, we have studied the drag force on a charged polystyrene latex particle adsorbed at the oil-water interface when an ordered 2D monolayer of identical particles is flowed around it. The drag force, measured as a function of the flow velocity and the lattice spacing in the particle monolayer, contains contributions from long-range electrostatic forces between the particles at the liquid interface. The interpretation of the experimental results is based on a model in which the repulsion arises primarily from the presence of a very small net electric charge at the particle-oil interface. This charge corresponds to a fractional ionization of the sulfate groups present at the particle surface exposed to the oil phase which is estimated from an independent experiment (see Aveyard, R.; Binks, B. P.; Clint, J. H.; Fletcher, P. D. I.; Horozov, T. S.; Neumann, B.; Paunov, V. N.; Annesley, J.; Botchway, S. W.; Nees, D.; Parker, A. W.; Ward, A. D.; Burgess, A. N. Phys. Rev. Lett. 2002, 88, 246102-1) to be approximately 3.3 x 10 - 4 for the latex sample used. The experimentally determined drag forces are in reasonable agreement with results from computer simulations for a range of values of the velocity and the lattice spacing of the particle monolayer.

Whey protein aggregation under shear conditions – effects of pH‐value and removal of calcium

The effects of pH‐value and a reduction in calcium content on the kinetics of whey protein denaturation and the aggregation behaviour, under shear in a scraped surface heat exchanger, were examined. The denaturation rate of β‐lactoglobulin at 80 °C is considerably retarded as the pH‐value decreases from pH 6.7 to 4.5. Aggregates which are produced under shear between pH 4 and 5.5 reveal a small particle size (<5 μm) irrespective of the lactose content and the heating temperature. This is attributed to the low reactivity of the thiol groups and the small net charge of the proteins in this pH‐range. At a reduced calcium concentration the heat‐ and shear‐treatment resulted in a gritty structure with large rubber‐like particles. These are not to be taken as primary whey protein aggregates but as fragments of a fine‐stranded gel.

Small-Angle Neutron-Scattering Studies on the Nature of the Incorporation of Polar Oils into Aggregates of N,N-Dimethyldodecylamine-N-oxide

The internal structure of oil-in-water microemulsion droplets has been studied by small-angle neutron scattering (SANS) using contrast variation. The single-chain surfactant used was N,N-dimethyldodecylamine-N-oxide (C12AO), and the oil phase was one of two semipolar ethyl esters, ethyl hexadecanoate or ethyl octanoate. Data from core−shell-drop neutron contrast series were simultaneously fitted to an interacting, polydisperse, core−shell, sphere model to investigate the possibility that the semipolar oils penetrate the curved surfactant film. For microemulsions containing a weight ratio of 1:5 ethyl hexadecanoate/surfactant, the data were most consistent with only a small extent of oil in the surfactant hydrocarbon (tail) region (∼4% v/v), whereas in microemulsions containing the same amount of ethyl octanoate, the oil concentration was ∼ 16% v/v. Increasing the relative amount of ethyl octanoate to 3:5 increased the extent of oil in the tail region to about 26% v/v. These results indicate that the extent of oil penetration into such positively curved monolayers depends on both the acyl chain length of the oil and its concentration. SANS data were also obtained for micelles of C12AO in D2O. Model fitting showed the micelles to be consistent with prolate ellipsoids having an axial ratio of around 1.6 to 1.7. Details of the model discussed do not entirely agree with models proposed in earlier literature. In both micelles and microemulsions, the surfactant behaves as if it has a small net charge, leading to repulsive rather than hard-sphere interactions.

Equilibria for intense ion beam transport in low-pressure gas or vacuum

Two fluid equilibrium solutions for intense ion beam transport in low-pressure gas or vacuum are derived. The equilibria that are most relevant to beam transport have neutralizing electrons drifting in the same direction as the beam. These solutions require a small net positive charge within the beam channel to support an equilibrium radial electric field to allow the electrons to E×B drift axially. At the extremes of the domain of allowable solutions this electric field approaches zero and complete charge neutrality is achieved. In this case, two solutions are obtained. The first describes ballistic beam transport with complete neutralization of the beam current by the electrons, and the second describes pinched beam transport with no neutralizing electron current. Equilibria between these two extremes exhibit both a small net positive charge within the beam channel and partial current neutralization.

Study of the electronic structure of Au–V bimetallics using X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure (XANES)

Core-level binding energy shifts and valence band behaviour for Au–V intermetallic compounds have been studied with X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure (XANES). It is found that both the Au 4f and V 2p core levels exhibit a positive binding energy shift, relative to the pure metals. These results can be explained with the charge compensation model (Watson et al., Phys. Rev. B4 (1971) 4139): there is an increase in the number of sp-like conduction electrons accompanied by a decrease in the d-electron count at the Au site resulting in a small net charge flow onto the Au site in accord with electronegativity and electroneutrality considerations. Au L-edge X-ray absorption near-edge structures (XANES) provide direct evidence for d-charge depletion at the gold site confirming the XPS results. V K-edge XANES indicate d-charge depletion at the V site, as well. These results are compared with those for Au–Ti and Au–Ta alloys.

OPTIMIZATION OF CATIONIC LIPOSOME-MEDIATED GENE TRANSFER TO HUMAN BRONCHIAL EPITHELIAL CELLS EXPRESSING WILD-TYPE OR ABNORMAL CYSTIC FIBROSIS TRANSMEMBRANE CONDUCTANCE REGULATOR (CFTR)

We determined optimum conditions for delivering DNA to transformed human bronchial epithelial cells expressing wild-type (BEAS) or abnormal (2CF) cystic fibrosis transmembrane conductance regulator (CFTR) using cationic liposomes (Lipofectin, [N-(N,N-dimethylaminoethane) carbamyl] cholesterol [DC-Chol] dioleoylphosphatidylethanolamine [DOPE], or LipofectAMINE) and reporter genes which measured overall transgene expression (luciferase) or the fraction of cells transfected (heat stable alkaline phosphatase). All liposomes showed dose-related toxicity. Optimal liposome and lipid: DNA ratios were different for BEAS than for 2CF cells. For all 3 liposome preparations, small particle size and net cationic charge related to transfection efficiency. Both LipofectAMINE and DC Chol/DOPE transfected a maximum of 3% of BEAS cells, but luciferase expression could be increased without increasing the fraction of cells transfected. LipofectAMINE transfected a maximum of 6% of 2CF cells, and luciferase expression could be increased with no further increase in fraction of transfected cells. DC-Chol/DOPE transfected over 12% of 2CF cells with relatively small increases in luciferase expression. We conclude that an optimal cationic liposome and lipid: DNA ratio for transfecting bronchial epithelial cells depends on: (1) small particle size and net cationic charge, (2) whether the cells have the cystic fibrosis defect, and (3) whether the desired outcome is transfection of the maximum fraction of the cells or maximum total expression of the transgene.

Electronic structure of Au–Ta alloys:: An X-ray spectroscopy study

Au–Ta alloys with the compositions of AuTa, AuTa 2 and AuTa 3, prepared by quenching from the melt, has been studied with X-ray diffraction, photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure (XANES) measurements. It was found that while AuTa 3 is a single-phase solid solution, AuTa 2 and AuTa have mixed phases and that the Au and Ta 4f levels of the alloys shift to higher binding energy, relative to the pure metal; this is accompanied by a narrowing of the Au 5d component of the alloy d-band, which moves away from the Fermi level. This observation is interpreted in terms of a charge compensation model in which Au loses d charge but is overcompensated by s–p charge gain, resulting in a small net charge flow from Ta to Au. The observed Ta 4f binding energy shift is as predicted by electronegativity and indicates charge depletion at the Ta site. The notion of d charge depletion at both Au and Ta sites upon alloying is confirmed independently by XANES measurements which showed that the L 2,3 edge whiteline intensity for both Au and Ta increases as they become more dilute in the host, indicating an increase in d hole count. The experimental results compare favorably with a recent linear-augmented Slater-type-orbital (LASTO) calculations. The implications of these results are discussed.

The electrodeposition of asphaltenes and implications for asphaltene structure and stability in crude and residual oils

Electrodeposition experiments have identified that colloidally stable asphaltene ‘micelles’ in crude oils possess little net charge and are apparently not affected by DC electric fields alone. However, upon destabilisation of the micelles (whether partial or total) with n-alkanes, electrodeposition occurs to extents which depend on the crude oil or residue, the alkane used and the relative dilution. Thus, at low dilutions, and hence incomplete destabilisation, the deposited material possesses a small net negative charge; higher dilutions result in a positively charged deposit. These findings are consistent with a structural model for asphaltene ‘micelles’ comprising negatively charged ‘peptising’ resins surrounding a positively charged central asphaltene core. In crude oils, the resins may be smaller and better able to stabilise the polar core, and are accordingly more difficult to displace. Electrical treatment therefore produces deposits with relatively weak charge. In thermally treated vacuum and visbroken residues, on the other hand, the deposits are highly positively charged and electrodeposition occurs much more readily, consistent with the reduced state of peptisation in these systems. This confirms earlier work indicating that the structure of asphaltene is thermally modified during distillation, a process which continues throughout visbreaking, resulting in lower degrees of asphaltene peptisation and the production of highly positively charged deposits. Flocculation between destabilised micelles is proposed to occur as a result of enhanced van der Waals' attractive forces as the distinction between resin-coated asphaltenes and the hydrocarbon oil is lost. This is reflected in an increase in the Hamaker interaction parameter as resins are stripped from the asphaltene.

Effect of the Net Charge Distribution on the Aqueous Solution Properties of Polyampholytes

The zwitterion nature of ampholytic polymers provides features that are useful in environmental and industrial applications, e. g. ion-exchange membrane, as flocculants in sewage treatment and in oil recovery processes. In the latter case, the increase in viscosity which is observed in the presence of brine (anti -polyelectrolyte behavior) make them ideal candidates for high salinity media. The aqueous solution properties of a series of ampholytic terpolymers based on sodium-2-acrylamido-2- rilethylpropanesulfonate (NaAMPS), Methacryloyloxyethyltrimethylammonium chloride (MADQUAT) and acrylamide (AM), prepared in inverse micro emulsions have been investigated by viscometry and light scattering experiments. The distribution of the net charge among the chains was varied by adjusting the initial monomer composition and the degree of conversion. The effect of this distribution on the solubility of the samples and on the chain conformation was studied. It was found that samples with a narrow distribution of net charges were soluble in water even if the average net charge is small. Addition of salt produces a transition from an extended conformation to a more compact one in qualitative agreement with theoretical predictions. A practically alternated NaAMPS- MADQUAT copolymer prepared in homogeneous solution and with a small average net charge shows a behaviour quite similar to that of the terpolymers.

Aqueous solution properties of polyampholytes: effect of the net charge distribution

Viscometric and light scattering studies have been performed on aqueous solutions of polyampholyte terpolymers based on sodium-2-acrylamido-2-methylpropanesulfonate (Na-AMPS), 2-(methacryloyloxy)-ethyltrimethylammonium chloride (MADQUAT), and acrylamide (AM), prepared by an inverse microemulsion polymerization technique. The distribution of net charges among the chains was varied by adjusting the initial monomer composition and the degree of conversion. The effect of this distribution on the solubility of the samples and on the chain conformation was studied. It was found that samples with a narrow distribution of net charges were soluble in pure water even if the average net charge is small. Addition of salt induces a transition from an extended conformation to a more compact one, in qualitative agreement with theoretical predictions. A practically alternated NaAMPS-MADQUAT copolymer prepared by polymerization in homogeneous solution and with a small average net charge shows a behavior quite similar to that of the terpolymers. © 1996 John Wiley & Sons, Inc.

Aqueous solution properties of polyampholytes: effect of the net charge distribution

Viscometric and light scattering studies have been performed on aqueous solutions of polyampholyte terpolymers based on sodium-2-acrylamido-2-methylpropanesulfonate (Na-AMPS), 2-(methacryloyloxy)-ethyltrimethylammonium chloride (MADQUAT), and acrylamide (AM), prepared by an inverse microemulsion polymerization technique. The distribution of net charges among the chains was varied by adjusting the initial monomer composition and the degree of conversion. The effect of this distribution on the solubility of the samples and on the chain conformation was studied. It was found that samples with a narrow distribution of net charges were soluble in pure water even if the average net charge is small. Addition of salt induces a transition from an extended conformation to a more compact one, in qualitative agreement with theoretical predictions. A practically alternated NaAMPS-MADQUAT copolymer prepared by polymerization in homogeneous solution and with a small average net charge shows a behavior quite similar to that of the terpolymers. © 1996 John Wiley & Sons, Inc.

Evidence for multipolar charge distribution in falling water drops

A method for producing water drops with very small net charge (few fC) was employed in conjunction with a sensing device, in order to identify the electric signals produced by falling water drops. The sensing device consists of a wire loop hooked to a patch-clamp amplifier set into voltage-clamp mode. Water drops with very small net charge produce a negligible signal at the sensing device but when falling through a horizontal charged capacitor they produce well-defined and reproducible signals which are proportional to the capacitor voltage. The experimental curves can be fitted to the theoretical ones considering the drop as possessing a multipolar charge distribution. There is evidence that this distribution is due to the contribution of the field-oriented water molecules multipoles.

Charge redistribution in ion-beam-mixed PdAg alloys

Charge flow and valence/d-band behavior in ion-beam-mixed (IBM) Pd 1− x Ag x ( x = 0.5–0.9) alloys have been studied by X-ray photoemission measurement of the valence bands and of core-level binding energy shifts and X-ray absorption near-edge structure. We correlated the observed Ag 3d 5 2 core-level shifts in these IBM alloys, relative to the elemental Ag, with the White Line area changes at the Pd and Ag L 3-edge to investigate the charge redistribution at the Ag site. The results indicate that there is a decrease in sp-like conduction electron and a negligible change in the number of d-electrons at the Ag site upon alloying. These results are in line with our previous results in which Pd gains d-charges and loses sp-type charges. This electron redistribution due to hybridization in the alloy leads small net charge transfer from the Ag site to the Pd site in accordance with electronegativity predictions. This result is consistent with the result of recent theoretical calculation of Lu et al. using the “special-quasi-random-structure” (SQS) concept in which Ag loses mainly sp-charge while Pd gains d-charge in forming the PdAg alloy.