Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “electrostatics”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,063 records · Page 59Linked to original sources
PubMed2004

Surface micromachined electrostatically actuated micro peristaltic pump.

An electrostatically actuated micro peristaltic pump is reported. The micro pump is entirely surface micromachined using a multilayer parylene technology. Taking advantage of the multilayer technology, the micro pump design enables the pumped fluid to be isolated from the electric field. Electrostatic actuation of the parylene membrane using both DC and AC voltages was demonstrated and applied to fluid pumping based on a 3-phase peristaltic sequence. A maximum flow rate of 1.7 nL min(-1) and an estimated pumping pressure of 1.6 kPa were achieved at 20 Hz phase frequency. A dynamic analysis was also performed with a lumped-parameter model for the peristaltic pump. The analysis results allow a quantitative understanding of the peristaltic pumping operation, and correctly predict the trends exhibited by the experimental data. The small footprint of the micro pump is well suited for large-scale integration of microfluidics. Moreover, because the same platform technology has also been used to fabricate other devices (e.g. valves, electrospray ionization nozzles, filters and flow sensors), the integration of these different devices can potentially lead to versatile and functional micro total analysis systems (microTAS).

Equipment Design↗
PubMed2005

Modeling the electric field third-order nonlinear responses of an infinite aggregate of hexatriene chains using the electrostatic interaction model.

A classical electrostatic polarization scheme using the additive distribution procedure has been applied to determine the static longitudinal polarizability and second hyperpolarizability of a all-trans hexatriene molecule in an infinite stretched fiber. The parameters have been derived from ab initio coupled-perturbed Hartree-Fock calculations and the electrostatic scheme has been validated via comparison with ab initio results on small clusters. Upon packing, the polarizability of all-trans hexatriene increases by 7% whereas the second hyperpolarizability increases by as much as 61%. These increases result from the balance between the enhancement of the (hyper)polarizability due to collinear packing and the reduction associated with lateral packing.

Algorithms↗
PubMed2006

Intermolecular electrostatic interactions and Brownian tumbling in protein solutions.

It is often implicitly assumed that the long-range intermolecular electrostatic interactions in homogeneous protein solutions either are negligible for affecting protein Brownian tumbling or cause its deceleration without changing the shape of rotational auto-correlation function. This review presents a wide set of experimental data (NMR relaxation, dielectric spectroscopy and Brownian dynamics simulations) demonstrating that the interprotein electrostatic steering leads to a complication of the rotational correlation function. The key point of this effect is the rotational anisotropy caused by the interaction of the electric dipole moment of a protein with the external electric field produced by charges of neighboring proteins. Taking this effect into account in some cases might be of critical importance for the correct interpretation of various experimental data.

Anisotropy↗
PubMed2006

Electrophoresis of electrostatically assembled fullerene-porphyrin conjugates.

The formation of electrostatically coupled assemblies of a series of anionic dendritic fullerene derivatives and cationic porphyrins in buffered aqueous media was studied with gel electrophoresis. Of central interest in these investigations was the variation of the amount of charge carried by the molecules, their size, shape and self-aggregation. Ferric cytochrome c 1 and the more rigid zinc porphyrin served as octacationic species. The two new anionic fullerene derivates 3 and 6 were synthesized. The formation of electrostatic complexes of the fullerene polyelectrolytes 3 and 4 with 1and 2 was clearly evident in the gel electrophoresis experiment. Compounds and showed a similar behaviour towards 2. The electrophoresis experiments confirmed previous results obtained with other techniques on a qualitative level and gave new insights into aggregation phenomena.

Dendrimers↗
PubMed2002

Modulation of the electrostatic charge at the active site of foot-and-mouth-disease-virus leader proteinase, an unusual papain-like enzyme.

The leader proteinase (L(pro)) of foot-and-mouth-disease virus is an unusual papain-like cysteine proteinase. Synthesized without an N-terminal pro precursor region, it frees itself from the growing polypeptide chain by cleavage at its own C-terminus. It also possesses a unique electrostatic environment around the active site, essentially due to Asp(163), which orients the catalytic histidine residue, and Asp(164); the equivalent residues in papain are Asn(175) and Ser(176). The importance of these residues for L(pro) activity was examined by site-directed mutagenesis. Replacement of Asp(163) with asparagine reduced activity by five-fold towards a hexapeptide substrate and slightly delayed self-processing when expressed in rabbit reticulocyte lysates. However, no effect on the cleavage of the only known cellular substrate of L(pro), eukaryotic initiation factor 4GI (eIF4GI), was observed. In contrast, replacement of Asp(164) by either alanine, asparagine or lysine abrogated activity towards the hexapeptide. Furthermore, in all cases, the onset of both self-processing and eIF4GI cleavage were significantly delayed; the reaction rates were also diminished compared with those of the wild-type enzyme. The alanine-substituted enzyme was least affected, followed by those substituted with asparagine and lysine. The double mutant protein in which both aspartate residues were replaced by asparagine was most severely affected; it failed to complete either self-processing or eIF4GI cleavage within 3 h, compared with the 8 min required by the wild-type enzyme. Hence, we propose that the electrostatic charge of Asp(164), and to a lesser extent that of Asp(163), is extremely important for L(pro) to attain full activity upon synthesis.

Amino Acid Substitution↗
PubMed1965

The influence of sialic acid residues on the ability of glycoproteins toi nteract electrostatically with chondromucoprotein.

1. Although glycoproteins with less than 1% of sialic acid (fibrinogen, lipoproteins, gamma-globulins) interact electrostatically with chondromucoprotein to form insoluble complexes, interaction with glycoproteins containing larger amounts of sialic acid (orosomucoid, urine glycoprotein, seromucoid, fraction VI) was electrostatically impossible. Reasons for this are discussed. 2. The latter glycoproteins interacted with chondromucoprotein after mild acid hydrolysis or neuraminidase treatment, complex-formation being inversely related to their sialic acid content. 3. Complex-formation with sialic acid-deficient orosomucoid was maximum at pH3.6 and negligible above its isoelectric point of pH5, and was inhibited by Ca(2+) ions and EDTA. 4. These results are discussed in relation to the carbohydrate composition and biological activities of euglobulin fractions, and of complexes formed by adding chondromucoprotein to abnormal plasmas which may contain sialic acid-deficient glycoproteins owing to faulty carbohydrate metabolism.

Journal Article↗
PubMed1975

Electrostatic effects on the kinetics of bound enzymes.

1. The effect of the interaction between the charged matrix and substrate on the kinetic behaviour of bound enzymes was investigated theoretically. 2. Simple expression is derived for the apparent Km. 3. The apparent Km can only be used for the characterization of the electrostatic effect of the ionic strength does not vary with the substrate concentration. 4. The deviations from Michaelis-Menton kinetics are graphically illustrated for cases when the ionic strength varies with the substrate concentration. 5. The inhibition of the bound enzyme by a charged inhibitor at constant ionic strength is characterized by an apparent Ki. 6. When both the inhibitor concentration and the ionic strength change there is no apparent Ki, and the inhibition profile is graphically illustrated for this case. 7. Under certain conditions the electrostatic effects manifest thenselves in a sigmoidal dependence of the enzyme activity on the concentration of the substrate or inhibitor.

Binding Sites↗
PubMed2002

Evidence for crucial electrostatic interactions between Bcl-2 homology domains BH3 and BH4 in the anti-apoptotic Nr-13 protein.

Nr-13 is an anti-apoptotic member of the Bcl-2 family previously shown to interact with Bax. The biological significance of this interaction was explored both in yeast and vertebrate cells and revealed that Nr-13 is able to counteract the pro-apoptotic activity of Bax. The Bax-interacting domain has been identified and corresponds to alpha-helices 5 and 6 in Nr-13. Site-directed mutagenesis has revealed that the N-terminal region of Nr-13 is essential for activity and corresponds to a genuine Bcl-2 homology domain (BH4). The modelling of Nr-13, based on its similarity with other Bcl-2 family proteins and energy minimization, suggests the possibility of electrostatic interactions between the two N-terminal-conserved domains BH4 and BH3. Disruption of these interactions severely affects Nr-13 anti-apoptotic activity. Together our results suggest that electrostatic interactions between BH4 and BH3 domains play a role in the control of activity of Nr-13 and a subset of Bcl-2 family members.

Amino Acid Sequence↗
PubMed2003

Variation in the pH-dependent pre-steady-state and steady-state kinetic characteristics of cysteine-proteinase mechanism: evidence for electrostatic modulation of catalytic-site function by the neighbouring carboxylate anion.

The acylation and deacylation stages of the hydrolysis of N -acetyl-Phe-Gly methyl thionoester catalysed by papain and actinidin were investigated by stopped-flow spectral analysis. Differences in the forms of pH-dependence of the steady-state and pre-steady-state kinetic parameters support the hypothesis that, whereas for papain, in accord with the traditional view, the rate-determining step is the base-catalysed reaction of the acyl-enzyme intermediate with water, for actinidin it is a post-acylation conformational change required to permit release of the alcohol product and its replacement in the catalytic site by the key water molecule. Possible assignments of the kinetically influential p K (a) values, guided by the results of modelling, including electrostatic-potential calculations, and of the mechanistic roles of the ionizing groups, are discussed. It is concluded that Asp(161) is the source of a key electrostatic modulator (p K (a) 5.0+/-0.1) in actinidin, analogous to Asp(158) in papain, whose influence is not detected kinetically; it is always in the 'on' state because of its low p K (a) value (2.8+/-0.06).

Acylation↗
PubMed1984

Electrostatic screening stimulates rate-limiting steps in mitochondrial electron transport.

The effect of electrostatic screening of fixed negative charges on uncoupled mitochondrial electron transport was investigated with substrates with different charge and different sites of donation of electrons to the electron-transport chain of Jerusalem-artichoke (Helianthus tuberosus L.) mitochondria. Duroquinol (neutral substrate) was oxidized with a pH optimum of 7.6-7.8. The addition of cations caused a doubling of Vmax. (order of efficiency C3+ greater than C2+ greater than C+) through electrostatic screening, whereas the Km was unaffected. Screening stimulated (by 150%) the Vmax. for the oxidation of reduced cytochrome c (positive substrate; to O2), but in this case the Km doubled. The Vmax. of the oxidation of exogenous NADH (negative substrate) was also stimulated by screening when the acceptor was O2, but unaffected when duroquinone was the acceptor. In both cases, the Km for NADH was considerably decreased. The effect of screening on the Km for the different substrates can be explained by the changes in the effective concentration of substrate near the active site due to the lowering in the size of the surface potential. The effect of screening on the Vmax. of the different partial processes indicates that increasing the salt concentration of the medium enhances the maximal activity of cytochrome c oxidase. However, the results also point at the existence of other rate-limiting steps, which are affected by screening and may involve ubiquinone, in electron transport in plant mitochondria.

Cell Membrane↗
PubMed2005

Reversible - through calmodulin - electrostatic interactions between basic residues on proteins and acidic lipids in the plasma membrane.

The inner leaflet of a typical mammalian plasma membrane contains 20-30% univalent PS (phosphatidylserine) and 1% multivalent PtdIns(4,5)P(2). Numerous proteins have clusters of basic (or basic/hydrophobic) residues that bind to these acidic lipids. The intracellular effector CaM (calmodulin) can reverse this binding on a wide variety of proteins, including MARCKS (myristoylated alanine-rich C kinase substrate), GAP43 (growth-associated protein 43, also known as neuromodulin), gravin, GRK5 (G-protein-coupled receptor kinase 5), the NMDA (N-methyl-D-aspartate) receptor and the ErbB family. We used the first principles of physics, incorporating atomic models and the Poisson-Boltzmann equation, to describe how the basic effector domain of MARCKS binds electrostatically to acidic lipids on the plasma membrane. The theoretical calculations show the basic cluster produces a local positive electrostatic potential that should laterally sequester PtdIns(4,5)P(2), even when univalent acidic lipids are present at a physiologically relevant 100-fold excess; four independent experimental measurements confirm this prediction. Ca(2+)/CaM binds with high affinity (K(d) approximately 10nM) to this domain and releases the PtdIns(4,5)P(2). MARCKS, a major PKC (protein kinase C) substrate, is present at concentrations comparable with those of PtdIns(4,5)P(2) (approx. 10 microM) in many cell types. Thus MARCKS can act as a reversible PtdIns(4,5)P(2) buffer, binding PtdIns(4,5)P(2) in a quiescent cell, and releasing it locally when the intracellular Ca(2+) concentration increases. This reversible sequestration is important because PtdIns(4,5)P(2) plays many roles in cell biology. Less is known about the role of CaM-mediated reversible membrane binding of basic/hydrophobic clusters for the other proteins.

Animals↗
PubMed2000

Reducing electrostatic charge on spacer devices and bronchodilator response.

AIMS: Plastic spacers are widely used with pressurized metered dose inhalers (pMDI). Reducing electrostatic charge by washing spacers with detergent has been shown to greatly improve in vitro and in vivo drug delivery. We assessed whether this finding is associated with an improved bronchodilator response in adult asthmatics. METHODS: Twenty subjects (age 18-65 years) with a known bronchodilator response inhaled in random order salbutamol from a pMDI (Ventolin) through an untreated new spacer (Volumatic) and through a detergent washed spacer. Patients received the following doses of salbutamol via pMDI at 20 min intervals: 100 microg, 100 microg, 200 microg, 400 microg, 800 microg. Spirometry, heart rate and blood pressure were checked prior to each dose and 20 min after the last dose. RESULTS: There were no differences between baseline forced expiratory volume in 1 s (FEV1) using either spacer (2.61+/-0.56 and 2.52+/-0.45 l, untreated and treated with detergent, respectively; mean +/- s.d.). The provocation dose required to cause a clinically significant improvement of 10% in FEV1 (PD10) was significantly lower when the detergent treated spacer was used (1505 +/-1335 and 430+/-732 microg, untreated and treated, respectively, P<0.002). CONCLUSIONS: We have demonstrated an improvement in bronchodilator response, in adult asthmatics, after reducing the electrostatic charge in a spacer device by washing it with ordinary household detergent. This finding stresses the importance of an optimal choice of delivery device for asthma medication.

Adolescent↗
PubMed2002

Electrostatic properties of the structure of the docking and dimerization domain of protein kinase A IIalpha.

The structure of the N-terminal docking and dimerization domain of the type IIalpha regulatory subunit (RIIalpha D/D) of protein kinase A (PKA) forms a noncovalent stand-alone X-type four-helix bundle structural motif, consisting of two helix-loop-helix monomers. RIIalpha D/D possesses a strong hydrophobic core and two distinct, exposed faces. A hydrophobic face with a groove is the site of protein-protein interactions necessary for subcellular localization. A highly charged face, opposite to the former, may be involved in regulation of protein-protein interactions as a result of changes in phosphorylation state of the regulatory subunit. Although recent studies have addressed the hydrophobic character of packing of RIIalpha D/D and revealed the function of the hydrophobic face as the binding site to A-kinase anchoring proteins (AKAPs), little attention has been paid to the charges involved in structure and function. To examine the electrostatic character of the structure of RIIalpha D/D we have predicted mean apparent pKa values, based on Poisson-Boltzmann electrostatic calculations, using an ensemble of calculated dimer structures. We propose that the helix promoting sequence Glu34-X-X-X-Arg38 stabilizes the second helix of each monomer, through the formation of a (i, i +4) side chain salt bridge. We show that a weak inter-helical hydrogen bond between Tyr35-Glu19 of each monomer contributes to tertiary packing and may be responsible for discriminating from alternative quaternary packing of the two monomers. We also show that an inter-monomer hydrogen bond between Asp30-Arg40 contributes to quaternary packing. We propose that the charged face comprising of Asp27-Asp30-Glu34-Arg38-Arg40-Glu41-Arg43-Arg44 may be necessary to provide flexibility or stability in the region between the C-terminus and the interdomain/autoinhibitory sequence of RIIalpha, depending on the activation state of PKA. We also discuss the structural requirements necessary for the formation of a stacked (rather than intertwined) dimer, which has consequences for the orientation of the functionally important and distinct faces.

Binding Sites↗
PubMed2002

Electrostatic role of aromatic ring stacking in the pH-sensitive modulation of a chymotrypsin-type serine protease, Achromobacter protease I.

Achromobacter protease I (API) has a unique region of aromatic ring stacking with Trp169-His210 in close proximity to the catalytic triad. This paper reveals the electrostatic role of aromatic stacking in the shift in optimum pH to the alkaline region, which is the highest pH range (8.5-10) among chymotrypsin-type serine proteases. The pH-activity profile of API showed a sigmoidal distribution that appears at pH 8-10, with a shoulder at pH 6-8. Variants with smaller amino acid residues substituted for Trp169 had lower pH optima on the acidic side by 0-0.9 units. On the other hand, replacement of His210 by Ala or Ser lowered the acidic rim by 1.9 pH units, which is essentially identical to that of chymotrypsin and trypsin. Energy minimization for the mutant structures suggested that the side-chain of Trp169 stacked with His210 was responsible for isolation of the electrostatic interaction between His210 and the catalytic Asp113 from solvent. The aromatic stacking regulates the low activity at neutral pH and the high activity at alkaline pH due to the interference of the hydrogen bonded network in the catalytic triad residues.

Alcaligenes↗
PubMed2000

The role of individual lysine residues in the basic patch on turnip cytochrome f for electrostatic interactions with plastocyanin in vitro.

The role of electrostatic interactions in determining the rate of electron transfer between cytochrome f and plastocyanin has been examined in vitro with mutants of turnip cytochrome f and mutants of pea and spinach plastocyanins. Mutation of lysine residues Lys58, Lys65 and Lys187 of cytochrome f to neutral or acidic residues resulted in decreased binding constants and decreased rates of electron transfer to wild-type pea plastocyanin. Interaction of the cytochrome f mutant K187E with the pea plastocyanin mutant D51K gave a further decrease in electron transfer rate, indicating that a complementary charge pair at these positions could not compensate for the decreased overall charge on the proteins. Similar results were obtained with the interaction of the cytochrome f mutant K187E with single, double and triple mutants of residues in the acidic patches of spinach plastocyanin. These results suggest that the lysine residues of the basic patch on cytochrome f are predominantly involved in long-range electrostatic interactions with plastocyanin. However, analysis of the data using thermodynamic cycles provided evidence for the interaction of Lys187 of cytochrome f with Asp51, Asp42 and Glu43 of plastocyanin in the complex, in agreement with a structural model of a cytochrome f-plastocyanin complex determined by NMR.

Aspartic Acid↗
PubMed2006

Preparation of nano-sized particles from collagen II by a high-voltage electrostatic field system.

The pilot study describes a novel method for preparing nano-sized particles from collagen II using a high-voltage electrostatic field system. Observations from transmission electron microscopy showed that, in one of the cases, the nano-sized collagen II particles exhibited good sphericity, and the particles were in the range of 23.3+/-1.7 nm in diameter at the experimental setting of 3 kV cm(-1), for a 3 h treatment period and at 25 degrees C (with a collagen concentration of 0.2 mg ml(-1)). When the treatment temperature increased to 30 degrees C, the collagen II began to lose the tendency to form individually separated spherically shaped nano-particles. Moreover, a fibrous structure of collagen II was formed instead of a nano-particle shape at the temperature of 37 degrees C. This result is probably contributed to by an entropy-driven process that is termed fibrillogenesis, a larger force causing the collagen molecules to self-assemble and then form collagen fibrils. It is interesting to note that this is practically the first attempt to produce nano-particles directly from collagen II solution under the treatment of a high-voltage electrostatic field, together with a set of working parameters for the collagen concentration and low-temperature setting.

Biocompatible Materials↗
PubMed2004

The effects of solute-solvent electrostatic interactions on solvatochromic shifts in supercritical CO2.

Solvent clustering around attractive solutes is an important feature of supercritical solvation. We examine here the effects of the local density enhancement on solvatochromic shifts in electronic absorption and emission spectra in supercritical CO2. We use molecular dynamics (MD) simulation to study the spectral line shifts for model diatomic solutes that become more polar upon electronic excitation. The electronic transition is modeled as either a change from a quadrupolar to a dipolar solute charge distribution or as an increase in the magnitude of the solute dipole. Our main focus is on the density dependence of the line shifts at 320 K, which corresponds to about 1.05 times the solvent critical temperature, Tc, but results for higher temperatures are also obtained in order to determine the behavior of the line shifts in the absence of local density enhancement. We find that the extent of local density enhancement at 1.05Tc is strongly correlated with solute-solvent electrostatic attraction and that the density dependence of the emission line shifts resembles the behavior of the effective local densities, rho(eff), obtained from the first-shell coordination numbers. The differences that are seen are shown to be due to solute-solvent orientational correlations which provide an additional source of enhancement for electrostatic solvation energies and spectral line shifts.

Journal Article↗
PubMed2004

Molecular electrostatic potentials and electron densities in nitroazacubanes.

Successive introduction of nitrogen atoms in the cubyl corners instead of C-NO2 groups of octanitrocubane (CNO2)8, the most powerful explosives known to date, leads to a class of energy-rich compounds known as nitroazacubanes. In present work the ab initio Hartree-Fock and hybrid density functional calculations have been carried out on the possible conformers of (CNO2)(8-alpha)Nalpha (with alpha=0-8), nitroazacubanes. The charge distributions in these systems have been derived using the topography of the molecular electrostatic potential and electron density. Molecular electrostatic potential investigations reveal that of different nitroazacubane conformers, the electron-rich regions around nitro oxygens of the lowest energy conformer having face opposite nitrogen atoms within a cube are more delocalized. These conformers are predicted to have the largest difference of the energies of the highest occupied molecular orbital and lowest unoccupied molecular orbital relative to the other conformers. The dipole moments of nitroazacubanes are dependent on the nitrogen sites within a cube, caused by the resultant of C-N bond moments and nearly insensitive to position of the NO2 groups. The lowest frequency vibration (522 cm(-1)) suggests octa-azacubane having robust structure in the nitroazacubane series. Substitution of nitrogen atom instead of C-NO2 group leads to increase in electron density at the bond critical point of the X-N (X=C or N) bonds in a cube. The heats of formation of different nitroazacubanes were calculated by using the isodesmic reaction approach. The present calculation has shown that for the di- though hexanitroazacubanes the most destabilized conformer possess largest dipole moment and the heat of formation as well. A linear correlation of the electron density at the bond critical point of X-N bonds and the heat of formation has been obtained.

Journal Article↗