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PubMed1996

Electrostatic interaction between two domains of isocitrate dehydrogenase from Thermus thermophilus is important for the catalytic function and protein stability.

The role of electrostatic interaction between Lys96 and Glu147 of isocitrate dehydrogenase from Thermus thermophilus was investigated by site-directed mutagenesis. These two residues are located near the active site and involved in the interdomain interaction. Analyses of the catalytic properties and thermostability of the Glu147Gln mutant revealed that this interaction plays important roles in catalytic function and protein stability.

Amino Acid Sequence↗
PubMed1999

Electrostatic attraction at the core of membrane fusion.

SNARE proteins appear to be involved in homotypic and heterotypic membrane fusion events [Sollner et al. (1993) Nature 362, 318-324]. The crystal structure of the synaptic SNARE complex exhibits a parallel four-helical bundle fold with two helices contributed by SNAP-25, a target SNARE (t-SNARE), and the other two by a different t-SNARE, syntaxin, and a donor vesicle SNARE (v-SNARE), synaptobrevin. The carboxy-terminal boundary of the complex, predicted to occur at the closest proximity between the apposed membranes, displays a high density of positively charged residues. This feature combined with the enrichment of negatively charged phospholipids in the cytosolic exposed leaflet of the membrane bilayer suggest that electrostatic attraction between oppositely charged interfaces may be sufficient to induce dynamic and discrete micellar discontinuities of the apposed membranes with the transient breakdown at the junction and subsequent reformation. Thus, the positively charged end of the SNARE complex in concert with Ca2+ may be sufficient to generate a transient 'fusion pore'.

Calcium↗
PubMed2003

Inhibition of oxidized LDL aggregation with the calcium channel blocker amlodipine: role of electrostatic interactions.

Atherogenic low-density lipoproteins (LDL) are characterized by elevations in cholesterol content and increased electronegativity, factors that contribute to aggregation and foam cell formation. This study was designed to test the effect of the positively charged calcium channel blocker (CCB) amlodipine on the aggregation properties of oxidized LDL lipids. Large unilamellar vesicles (LUVs) (100 nm diameter) labeled with a non-exchangeable marker [3H]cholesteryl hexadecyl ether were prepared with lipids extracted from human LDL following oxidation. The LUVs were shown to bind, in a reversible fashion, to charged diethylaminoethyl Sephadex columns. The addition of amlodipine inhibited binding of the oxidized LDL lipids in a dose-dependent fashion with an IC(50) in the nanomolar range as a result of its high lipophilicity and positively charged amino group (pK(a) of 9.02). The activity of amlodipine was reproduced in model membranes that contained fixed amounts of charged phospholipid (glycerophospholipid) in a concentration-dependent manner. By contrast, drugs lacking a formal positive charge, including CCBs (felodipine, nifedipine, diltiazem, verapamil) and an angiotensin-converting enzyme-inhibitor (ramiprilate) had no effect on the column binding of the modified, electronegative lipids. These effects of amlodipine on LDL lipid aggregation and electrostatic properties may represent a novel antiatherosclerotic mechanism of action.

Amlodipine↗
PubMed2000

Elution mechanism in electrostatic ion chromatography with histidine as an isoelectric ampholytic mobile phase.

Electrostatic ion chromatography (EIC) using a zwitterionic stationary phase (formed by coating a C18 material with a hydrophobic zwitterionic surfactant) was studied with a mobile phase comprising an aqueous solution of histidine at the pH of its isoelectric point, together with non-suppressed conductometric detection. Anions and cations were found to be eluted as separate peaks, unlike the elution behaviour observed on the same system when pure water was used as mobile phase. An explanation was suggested in terms of protonation equilibria of the overall uncharged histidine to form small amounts of histidine cations and anions in the mobile phase which could act as counterions for analyte anions and cations. This suggestion was supported by measured pH changes occurring in the bands of eluted analyte anions (a decreased pH compared to the mobile phase) and cations (an increased pH compared to the mobile phase). The analytical potential of this type of EIC is discussed.

Chromatography, Liquid↗
PubMed2000

Suppressed electrostatic ion chromatography with tetraborate as eluent and its application to the determination of inorganic anions in snow and rainwater.

Tetraborate is investigated as the eluent ion for suppressed electrostatic ion chromatography (EIC) using a zwitterionic stationary phase. Good separation of a range of inorganic anions (SO4(2-), Cl-, NO3-, Br-, NO3-, ClO3-, and I-) was obtained, with detection limits for highly conducting ions (SO4(2-), Cl-, NO2-, Br- , and NO3-) being less than 8 x 10(-8) M, and for weakly conducting anions (ClO3- and I-) being 2.7 x 10(-7) and 5.8 x 10(-7) M, respectively. Calibration curves were linear up to 1.8 mM of each analyte. Retention times were found to increase with increasing eluent concentration and a linear relationship was observed between log k' and log[Na2B4O7] for all analytes. This behaviour is attributed to the progressive formation of a binary electrical double layer at the surface of the zwitterionic stationary phase. Retention times of analytes could be manipulated by varying the concentration of the eluent. This new suppressed-EIC system was applied to the determination of inorganic anions (SO4(-2) , CI-, NO3-, NO2-, and Br-) in snow and rainwater samples.

Anions↗
PubMed2001

Manipulation of separation selectivity of inorganic anions in electrostatic ion chromatography by the use of mixed cationic-zwitterionic micelles as the column coating solution.

This paper describes an electrostatic ion chromatographic system in which the separation selectivity for inorganic anions, especially for sulfate and phosphate, could be manipulated by altering the molar ratio of the zwitterionic and cationic surfactants in the column coating solution used to prepare the stationary phase. The zwitterionic surfactant used for this study was 3-(N,N-dimethyltetradecylammonio)propanesulfonate (Zwittergent-3-14) and the cationic surfactant was tetradecyltrimethylammonium (TTA). Using a reversed-phase C18 column (250x4.6 mm I.D.) coated with 10/10 (mM/mM) of TTA/Zwittergent-3-14 mixed micelles as the stationary phase and either NaHCO3 or Na2CO3 aqueous solution as the eluent, together with suppressed conductivity detection, baseline separation of seven model inorganic anions was obtained. The elution order for those anions was found to be F+ < HPO4(2-) < Cl- < SO4(2-) < NO2- < Br- < NO3-. Under the same conditions but using 1/10 (mM/mM) of TTA/Zwittergent-3-14 mixed micelles as the column coating solution, the elution order for these model ions was F- < HPO4(2-) < SO4(2-) < Cl- < NO2- < Br- < NO3-. The early elution of phosphate and sulfate is a unique attribute of this system. Detection limits for F-, HPO4(2-), Cl-, SO4(2-), NO2-, Br- and NO3- (S/N=3, sample injection volume 100 microl) were 0.11, 0.12, 0.12, 0.18, 0.49, 0.49, 0.52 microM, respectively.

Anions↗
PubMed2001

Simultaneous control of electrostatic micellar partition and electroosmotic flow-rate by anion-dominated partition into zwitterionic micelles.

The zeta potentials of zwitterionic micelles and capillary walls have been evaluated with capillary electrophoresis. The zeta potential of the micelles is predominantly determined by the nature of anions, while cations of identical valence have marginal effects; the linear relation has been found between the induced zeta potential and the hydration energy of an anion. The zeta potential of the capillary wall is also varied with anionic natures, and there is a good correlation between micellar and capillary wall zeta potential. This strongly suggests that the zeta potential of capillary walls is determined by the partition of anions into the surfactant layer formed on the capillary wall. Thus, we can simultaneously control both the electroosmotic flow-rate and micellar surface potential (in turn electrostatic interaction between micelles and ionic solutes) by varying the type and concentration of electrolytes. This idea has been applied to the separation of aromatic cationic solutes.

Anions↗
PubMed2002

Rapid and direct determination of iodide in seawater by electrostatic ion chromatography.

An electrostatic ion chromatographic (IC) method for rapid and direct determination of iodide in seawater is reported. Separation was achieved using a reversed-phase ODS packed column (250x4.6 mm I.D.) modified by coating with Zwittergent-3-14 micelles, with an eluent comprising an aqueous solution containing 0.2 mM NaClO4 and 0.3 mM Zwittergent-3-14 and using UV detection at 210 nm. Samples prepared by dissolving NaIO3, NaNO2, NaBr, NaBrO3, NaNO3, NaI, and NaSCN in artificial or real seawaters were analyzed using this IC system. Nitrite, iodate, bromide, bromate, and nitrate showed very little or no retention, while iodide and thiocyanate were well separated, being eluted within 6 and 16 min, respectively. The detection limit for iodide obtained by injecting 400 microL of sample was 0.011 microM (S/N = 3), and the precision values obtained by analyzing samples containing 0.1 or 0.3 microM iodide in real seawater samples were 2.3% RSD and 1.2% RSD, respectively. Direct determination of iodide in real seawater samples was possible using this proposed IC system.

Chromatography, Liquid↗
PubMed1999

Electrostatic ion chromatography of polarizable anions in saline waters with N-[2-[acetyl(3-sulfopropyl)amino]ethyl]-N,N-dimethyldodecanaminium hydroxide (ammonium sulfobetaine-1) as the stationary phase and a dilute electrolytic solution as the mobile phase.

A new type of zwitterionic surfactant, N-{2-[acetyl(3-sulfopropyl)amino]ethyl}-N,N-dimethyldodecanaminium hydroxide (ammonium sulfobetaine-1), with a greater distance between the two charged groups, was used as the stationary phase for electrostatic ion chromatography (EIC) of polarizable anions (e.g., thiocyanate, iodide and nitrate) in saline water samples. The targeted species (polarizable anions) were baseline separated using this type of zwitterionic surfactant as the stationary phase, but the highly polarizable species (iodide and thiocyanate) were eluted faster (compared with the results obtained using N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate, C12N3S, with a shorter distance between the two charged groups, as the stationary phase). In other words, the extent of binding of the highly polarizable anion (iodide and thiocyanate) was found to be smaller when using ammonium sulfobetaine-1 as the stationary phase. This provides a rapid but effective method for the analysis of highly polarizable anions in saline water samples. The results for the successful detection of iodide in seawater demonstrates the usefulness of this new type of zwitterionic surfactants for EIC.

Betaine↗
PubMed1999

Retention modelling of electrostatic and adsorption effects of aliphatic and aromatic carboxylic acids in ion-exclusion chromatography.

The retention mechanism of aliphatic and aromatic carboxylic acids in ion-exclusion chromatography has been investigated with consideration of simultaneous electrostatic repulsion effects and hydrophobic adsorption effects. A mathematical relationship between the retention factor of the analyte and the mobile-phase composition (sulfuric acid concentration and percentage of methanol), the type of analyte (pKa and hydrophobicity) and some physical characteristics of the stationary phase has been derived. Thirteen carboxylic acids (comprising mono- and divalent, aliphatic and aromatic acids) were chosen and used to acquire retention data on three different cation-exchange stationary phases (in which the sulfonate functional groups are bound to polystyrene-divinylbenzene, polymethacrylate or silica) using 14 mobile-phase compositions of varying pH and percent methanol. These retention data were used to derive the parameters necessary to solve the retention model using non-linear regression. In this way, a quantitative measure of the effects of adsorption phenomena on analyte retention were obtained. The model was then used to optimise the separation of nine carboxylic acids.

Carboxylic Acids↗
PubMed2003

Electrostatic interaction between ion-penetrable membranes in a salt-free medium.

A set of coupled equations is given which determines the distributions of the electric potential and counterions in a system of two interacting identical ion-penetrable membranes of thickness d at separation h immersed in a salt-free medium containing only counterions. The solution to these coupled equations also gives the electrostatic repulsive force between the membranes. It is shown that the interaction force remains finite at h-->0, unlike the case of the interaction between two planar charged surfaces (d-->0), and that the interaction force becomes independent of the membrane fixed charge and membrane thickness d at very large h. Finally, an approximate single transcendental equation giving the solution to the coupled equations is derived.

Journal Article↗
PubMed2003

Application of the method of images on electrostatic phenomena in aqueous Al2O3 and ZrO2 suspensions.

A new solution for the Poisson equation for the diffuse part of the double layer around spherical particles will be presented. The numerical results are compared with the solution of the well-known DLVO theory. The range of the diffuse layer differs considerably in the two theories. Also, the inconsistent representation of the surface and diffuse layer charge in the DLVO theory do not occur in the new theory. Experimental zeta potential measurements were used to determine the charge of colloidal Al2O3 and ZrO2 particles. It is shown that the calculated charge can be interpreted as a superposition of independent H+ and OH- adsorption isotherms. The corresponding Langmuir adsorption isotherms are taken to model the zeta potential dependence on pH. In the vicinity of the isoelectric point the model fits well with the experimental data, but at higher ion concentrations considerable deviations occur. The deviations are discussed. Furthermore, the numerical results for the run of the potential in the diffuse part of the double layer were used to determine the electrostatic interaction potential between the particles in correlation with the zeta potential measurements. The corresponding total interaction potentials, including the van der Waals attraction, were taken to calculate the coagulation half-life for a suspension with a particle loading of 2 vol%. It is shown that stability against coagulation is maintained for Al2O3 particles in the pH region between 3.3 and 7 and for ZrO2 only around pH 5. Stability against flocculation can be achieved in the pH regime between 4.5 and 7 for Al2O3, while the examined ZrO2 particles are not stable against flocculation in aqueous suspensions.

Journal Article↗
PubMed2003

Electrostatic interactions in leucine zippers: thermodynamic analysis of the contributions of Glu and His residues and the effect of mutating salt bridges.

Electrostatic interactions play a complex role in stabilizing proteins. Here, we present a rigorous thermodynamic analysis of the contribution of individual Glu and His residues to the relative pH-dependent stability of the designed disulfide-linked leucine zipper AB(SS). The contribution of an ionized side-chain to the pH-dependent stability is related to the shift of the pK(a) induced by folding of the coiled coil structure. pK(a)(F) values of ten Glu and two His side-chains in folded AB(SS) and the corresponding pK(a)(U) values in unfolded peptides with partial sequences of AB(SS) were determined by 1H NMR spectroscopy: of four Glu residues not involved in ion pairing, two are destabilizing (-5.6 kJ mol(-1)) and two are interacting with the positive alpha-helix dipoles and are thus stabilizing (+3.8 kJ mol(-1)) in charged form. The two His residues positioned in the C-terminal moiety of AB(SS) interact with the negative alpha-helix dipoles resulting in net stabilization of the coiled coil conformation carrying charged His (-2.6 kJ mol(-1)). Of the six Glu residues involved in inter-helical salt bridges, three are destabilizing and three are stabilizing in charged form, the net contribution of salt-bridged Glu side-chains being destabilizing (-1.1 kJ mol(-1)). The sum of the individual contributions of protonated Glu and His to the higher stability of AB(SS) at acidic pH (-5.4 kJ mol(-1)) agrees with the difference in stability determined by thermal unfolding at pH 8 and pH 2 (-5.3 kJ mol(-1)). To confirm salt bridge formation, the positive charge of the basic partner residue of one stabilizing and one destabilizing Glu was removed by isosteric mutations (Lys-->norleucine, Arg-->norvaline). Both mutations destabilize the coiled coil conformation at neutral pH and increase the pK(a) of the formerly ion-paired Glu side-chain, verifying the formation of a salt bridge even in the case where a charged side-chain is destabilizing. Because removing charges by a double mutation cycle mainly discloses the immediate charge-charge effect, mutational analysis tends to overestimate the overall energetic contribution of salt bridges to protein stability.

Amino Acid Sequence↗
PubMed2003

The fastest global events in RNA folding: electrostatic relaxation and tertiary collapse of the Tetrahymena ribozyme.

Large RNAs can collapse into compact conformations well before the stable formation of the tertiary contacts that define their final folds. This study identifies likely physical mechanisms driving these early compaction events in RNA folding. We have employed time-resolved small-angle X-ray scattering to monitor the fastest global shape changes of the Tetrahymena ribozyme under different ionic conditions and with RNA mutations that remove long-range tertiary contacts. A partial collapse in each of the folding time-courses occurs within tens of milliseconds with either monovalent or divalent cations. Combined with comparison to predictions from structural models, this observation suggests a relaxation of the RNA to a more compact but denatured conformational ensemble in response to enhanced electrostatic screening at higher ionic concentrations. Further, the results provide evidence against counterion-correlation-mediated attraction between RNA double helices, a recently proposed model for early collapse. A previous study revealed a second 100 ms phase of collapse to a globular state. Surprisingly, we find that progression to this second early folding intermediate requires RNA sequence motifs that eventually mediate native long-range tertiary interactions, even though these regions of the RNA were observed to be solvent-accessible in previous footprinting studies under similar conditions. These results help delineate an analogy between the early conformational changes in RNA folding and the "burst phase" changes and molten globule formation in protein folding.

Animals↗
PubMed1983

Converting structural changes upon oxidation of cytochrome c to electrostatic reorganization energy.

The observed X-ray structural differences between reduced and oxidized cytochrome c are converted to electrostatic energy. This conversion is used to estimate the protein reorganization energy which determines the protein contribution to the activation barrier for the electron transfer reaction. It is shown that the reorganization energy of cytochrome c is much smaller than the corresponding energy for electron transfer in water and that this is consistent with the role for cytochromes as electron transfer catalysts.

Cytochrome c Group↗
PubMed2005

Peptide and protein folding and conformational equilibria: theoretical treatment of electrostatics and hydrogen bonding with implicit solvent models.

Since biomolecules exist in aqueous and membrane environments, the accurate modeling of solvation, and hydrogen bonding interactions in particular, is essential for the exploration of structure and function in theoretical and computational studies. In this chapter, we focus on alternatives to explicit solvent models and discuss recent advances in generalized Born (GB) implicit solvent theories. We present a brief review of the successes and shortcomings of the application of these theories to biomolecular problems that are strongly linked to backbone H-bonding and electrostatics. This discussion naturally leads us to explore existing areas for improvement in current GB theories and our approach towards addressing a number of the key issues that remain in the refinement of these models. Specifically, the critical importance of balancing solvation forces and intramolecular forces in GB models is illustrated by examining the influence of backbone hydrogen bond strength and backbone dihedral energetics on conformational equilibria of small peptids.

Computer Simulation↗
PubMed1980

Controlled trial of an electrostatic precipitator in childhood asthma.

A cross-over trial was conducted on 10 children with moderate to severe asthma, who had positive skin tests to Dermatophagoides pteronyssinus and nocturnal wheeze. An electrostatic precipitator was used during the night to remove airborne particles from the bedroom. During use of the precipitator peak expiratory flow rates were no better than in a control period.

Adolescent↗
PubMed2004

Influence of precursor solution parameters on chemical properties of calcium phosphate coatings prepared using Electrostatic Spray Deposition (ESD).

A novel coating technique, referred to as Electrostatic Spray Deposition (ESD), was used to deposit calcium phosphate (CaP) coatings with a variety of chemical properties. The relationship between the composition of the precursor solutions and the crystal and molecular structure of the deposited coatings was investigated by means of X-ray diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR) and Energy Dispersive Spectroscopy (EDS). It was shown that the relative Ca/P ratio in the precursor solution, the absolute precursor concentration, the acidity of the precursor solution and the type of Ca-precursor strongly influenced the chemical nature of the deposited CaP coatings. Various crystal phases and phase mixtures were obtained, such as carbonate apatite, beta-TCP, Mg-substituted whitlockite, monetite, beta/gamma-pyrophosphate, and calcite. It was shown that carbonate plays an essential role in the chemical mechanism of coating formation. Carbonate is formed due to a decomposition reaction of organic solvents. Depending on deposition conditions, carbonate anions (a) react with acidic phosphate groups, (b) are incorporated into apatitic calcium phosphate phases, and (c) react with excessive Ca(2+) cations in case of phosphate-deficient precursor solutions.

Adsorption↗