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Electrostatic Interactions (electrostatic + interaction)
Kinds of Electrostatic Interactions Terms modified by Electrostatic Interactions Selected AbstractsSelf-Assembly of Nanotriangle Superlattices Facilitated by Repulsive Electrostatic Interactions,ANGEWANDTE CHEMIE, Issue 38 2010David Aufräumen hilft: Die Kristallisation dreieckiger Goldnanoprismen in dichtest gepackte Mono- und Multischichten wird durch elektrostatische Abstoßung erleichtert, und sie erhöht die Intensität in der oberflächenverstärkten Raman-Spektroskopie (SERS) um eine Größenordnung gegenüber der ungeordneter Proben. [source] Synthesis and Reactivity of Enediynyl Amino Acids and Peptides: A Novel Concept in Lowering the Activation Energy of Bergman Cyclization by H-Bonding and Electrostatic Interactions.CHEMINFORM, Issue 7 2004Amit Basak No abstract is available for this article. [source] Chiral Induction, Memory, and Amplification in Porphyrin Homoaggregates Based on Electrostatic InteractionsCHEMPHYSCHEM, Issue 6 2009LiXi Zeng Dr. Abstract Supramolecular chirality in two configurational homoaggregates of anionic meso -tetrakis(4-sulfonatophenyl)porphyrin (TPPS) can be induced by D - and L -alanine in acidic water (see picture). The chirality can be further memorized and enforced through strong electrostatic interactions between TPPS aggregates and achiral poly(allylamine) [PAA]. Supramolecular chirality in two configurational homoaggregates of anionic meso -tetrakis(4-sulfonatophenyl)porphyrin (TPPS) can be induced by D - and L -alanine (Ala) in acidic water, respectively. The induced supramolecular chirality can be further memorized and enforced, even after complete removal of Ala or in the presence of excess Ala with the opposite configuration, through strong electrostatic interactions with achiral poly(allylamine) [PAA]. The ionic chiral interactions between TPPS and Ala or PAA are characterized by means of UV/Vis absorption and circular dichroism spectrometry. Fluorescence spectroscopy and atomic force microscopy are used as complementary techniques. On the basis of the comprehensive experimental results, a possible mechanism for chiral induction, memory, and amplification of TPPS homoaggregates by chiral amino acids and achiral PAA is proposed. Thus, we demonstrate a novel strategy to realize chiral memory in supramolecular systems by polyelectrolytes through hierarchical electrostatic self-assembly. [source] Multichromophores for Nonlinear Optics: Designing the Material Properties by Electrostatic Interactions,CHEMPHYSCHEM, Issue 17 2007Francesca Terenziani Dr. Abstract To fully exploit the promise of molecular materials for NLO applications, inter- and supramolecular interactions must be accounted for. We review our recent work on electrostatic interchromophore interactions in multichromophores for NLO applications. The discussion is based on a bottom-up modeling strategy: each chromophore is described in terms of an essential state model, validated and parameterized against spectroscopic data for solvated chromophores. The relevant information is then used to build a model for clusters of chromophores interacting through electrostatic forces. Exact NLO responses and spectra calculated within this model fully account for collective and cooperative interchromophore interactions, which can either amplify or suppress NLO responses; supramolecular engineering of multichromophores is a powerful tool for the design of NLO materials. Moreover, new features emerge in multichromophores with no counterpart at the single-chromophore level, offering new exciting opportunities for applications. [source] A model of a gp120 V3 peptide in complex with an HIV-neutralizing antibody based on NMR and mutant cycle-derived constraintsFEBS JOURNAL, Issue 3 2000Anat Zvi The 0.5, monoclonal antibody is a very potent strain-specific HIV-neutralizing antibody raised against gp120, the envelope glycoprotein of HIV-1. This antibody recognizes the V3 loop of gp120, which is a major neutralizing determinant of the virus. The antibody,peptide interactions, involving aromatic and negatively charged residues of the antibody 0.5,, were studied by NMR and double-mutant cycles. A deuterated V3 peptide and a Fab containing deuterated aromatic amino acids were used to assign these interactions to specific V3 residues and to the amino acid type and specific chain of the antibody by NOE difference spectroscopy. Electrostatic interactions between negatively charged residues of the antibody Fv and peptide residues were studied by mutagenesis of both antibody and peptide residues and double-mutant cycles. Several interactions could be assigned unambiguously: F96(L) of the antibody interacts with Pro13 of the peptide, H52(H) interacts with Ile7, Ile9 and Gln10 and D56(H) interacts with Arg11. The interactions of the light-chain tyrosines with Pro13 and Gly14 could be assigned to either Y30a(L) and Y32(L), respectively, or Y32(L) and Y49(L), respectively. Three heavy-chain tyrosines interact with Ile7, Ile20 and Phe17. Several combinations of assignments involving Y32(H), Y53(H), Y96(H) and Y100a(H) may satisfy the NMR and mutagenesis constraints, and therefore at this stage the interactions of the heavy-chain tyrosines were not taken into account. The unambiguous assignments [F96(L), H52(H) and D56(H)] and the two possible assignments of the light-chain tyrosines were used to dock the peptide into the antibody-combining site. The peptide converges to a unique position within the binding site, with the RGPG loop pointing into the center of the groove formed by the antibody complementary determining regions while retaining the ,-hairpin conformation and the type-VI RGPG turn [Tugarinov, V., Zvi, A., Levy, R. & Anglister, J. (1999) Nat. Struct. Biol.6, 331,335]. [source] Inorganic Materials and Ionic Liquids: Large-scale Nanopatterning of Single Proteins used as Carriers of Magnetic Nanoparticles (Adv. Mater.ADVANCED MATERIALS, Issue 5 20105/2010) Ricardo Garcia, Eugenio Coronado, and co-workers demonstrate on p. 588 large-scale patterning of single ferritin molecules by sequential (atomic force microscopy local oxidation) and parallel approaches (lithographically controlled wetting). The nanopattern size matches the size of the protein (,10 nm). Electrostatic interactions, capillary forces, surface functionalization, and nanolithography are used to achieve the desired protein organization. [source] Large-scale Nanopatterning of Single Proteins used as Carriers of Magnetic NanoparticlesADVANCED MATERIALS, Issue 5 2010Ramsés V. Martínez Patterning of single ferritin molecules by sequential (atomic force microscopy local oxidation) and parallel approaches (lithographically controlled wetting). The nanopattern size matches the size of the protein (,10 nm). Electrostatic interactions, capillary forces, surface functionalization, and nanolithography are used to achieve the desired protein organization. [source] Kinetics and mechanism for oxime formation from benzoylformic acid: Electrostatic interactions in the dehydration of carbinolaminesINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 9 2008A. Malpica The evidence establishes that oxime formation from benzoylformic acid in the pH range from 0.25 to 5.5 occurs with acid-catalyzed dehydration of carbinolamines derived from the acid and its anion. The pH-rate profile shows in order of decreasing pH in two regions: (1) In the pH range from 5.5 to ,2.2 the second-order rate constants are linearly dependent on the concentration of hydronium ion and (2) from pH ,2.2 to 0.25 the rate constants deviate slightly from the line of slope = ,1. This slight deviation is a consequence of the very similar values of limiting rate constants of the two forms of the substrate. Electrostatic interactions between charged carbinolamines and hydronium ions are analyzed. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 554,558, 2008 [source] Prediction of pKa and redox properties in the thioredoxin superfamilyPROTEIN SCIENCE, Issue 10 2004Efrosini Moutevelis Abstract Electrostatic interactions play important roles in diverse biological phenomena controlling the function of many proteins. Polar molecules can be studied with the FDPB method solving the Poisson-Boltzmann equation on a finite difference grid. A method for the prediction of pKas and redox potentials in the thioredoxin superfamily is introduced. The results are compared with experimental pKa data where available, and predictions are made for members lacking such data. Studying CxxC motif variation in the context of different background structures permits analysis of contributions to cysteine ,pKas. The motif itself and the overall framework regulate pKa variation. The reported method includes generation of multiple side-chain rotamers for the CxxC motif and is an effective predictive tool for functional pKa variation across the superfamily. Redox potential follows the trend in cysteine pKa variation, but some residual discrepancy indicates that a pH-independent factor plays a role in determining redox potentials for at least some members of the superfamily. A possible molecular basis for this feature is discussed. [source] Elongation of the BH8 ,-hairpin peptide: Electrostatic interactions in ,-hairpin formation and stabilityPROTEIN SCIENCE, Issue 7 2001Marina Ramírez-Alvarado Abstract An elongated version of the de novo designed ,-hairpin peptide, BH8, has allowed us to gain insight into the role of electrostatic interactions in ,-hairpin stability. A Lys,Glu electrostatic pair has been introduced by adding a residue at the beginning and at the end of the N-terminal and C-terminal strands, respectively, of the ,-hairpin structure, in both orientations. The two resulting peptides and controls having Ala residues at these positions and different combinations of Ala with Lys, or Glu residues, have been analyzed by nuclear magnetic resonance (NMR), under different pH and ionic strength conditions. All of the NMR parameters, in particular the conformational shift analysis of C, protons and the coupling constants, 3JHN,, correlate well and the population estimates are in reasonable agreement among the different methods used. In the most structured peptides, we find an extension of the ,-hairpin structure comprising the two extra residues. Analysis of the pH and salt dependence shows that ionic pairs contribute to ,-hairpin stability. The interaction is electrostatic in nature and can be screened by salt. There is also an important salt-independent contribution of negatively charged groups to the stability of this family of ,-hairpin peptides. [source] Weak interactions and molecular recognition in systems involving electron transfer proteinsTHE CHEMICAL RECORD, Issue 4 2001Shun Hirota Abstract Electrostatic interactions and other weak interactions between amino acid side chains on protein surfaces play important roles in molecular recognition, and the mechanism of their intermolecular interactions has gained much interest. We established that charged peptides are useful for investigating the molecular recognition character of proteins and their molecular interaction induced structural changes. Positively charged lysine peptides competitively inhibited electron transfer from reduced cytochrome f (cyt f) or cytochrome c (cyt c) to oxidized plastocyanin (PC), due to neutralization of the negatively charged site of PC by formation of PC,lysine peptide complexes. Lysine peptides also inhibited electron transfer from cyt c to cytochrome c peroxidase. Likewise, negatively charged aspartic acid peptides interacted with the positively charged sites of cyt f and cyt c, and competitively inhibited electron transfer from reduced cyt f or cyt c to oxidized PC and from [Fe(CN)6]4, to oxidized cyt c. Changes in the geometry and a shift to a higher redox potential of the active site Cu of PC on oligolysine binding were detected by spectroscopic and electrochemical measurements, owing to the absence of absorption in the visible region for lysine peptides. Structural and redox potential changes were also observed for cyt f and cyt c by interaction with aspartic acid peptides. ©2001 John Wiley & Sons, Inc. and The Japan Chemical Journal Forum Chem Rec 1:290,299, 2001 [source] The anionic coordination polymer {K2[PtII2AgI8(2,2,-bipyridine)2(O2CCF3)14]}nACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2009Zachary M. Hudson The trimetallic compound catena -poly[dipotassium(I) [bis(2,2,-bipyridine)di-,3 -trifluoroacetato-dodeca-,2 -trifluoroacetato-diplatinum(II)octasilver(I)]], K2[Pt2Ag8(C2F3O2)14(C10H8N2)2], forms an extended structure in the solid state. Electrostatic interactions involving the K+ ions play a key role in the formation of the extended structure in three dimensions. The AgI ions form one-dimensional coordination polymers, with alternating Ag2 and Ag6 units linked by CF3CO2, ligands. Pt...Pt interactions perpendicular to the one-dimensional polymerization axis provide another element of long-range order, and electrostatic interactions with K+ ions provide connectivity between adjacent polymeric structures. [source] Electrostatic interactions with histone tails may bend linker DNA in chromatinBIOPOLYMERS, Issue 1 2006Angelo Perico Abstract Is linker DNA bent in the 30-nm chromatin fiber at physiological conditions? We show here that electrostatic interactions between linker DNA and histone tails including salt condensation and release may bend linker DNA, thus affecting the higher order organization of chromatin. © 2005 Wiley Periodicals, Inc. Biopolymers 81: 20,28, 2006 This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] 2261: Development and evaluation of PLGA nanoparticles with cyclosporine and the inclusion of HP,CD for ocular useACTA OPHTHALMOLOGICA, Issue 2010K HERMANS Ocular delivery of peptides requires new concepts in order to optimize the bioavailability and its therapeutic effect. The first peptide selected in present research project is Cyclosporine A (CyA) used in the treatment of the dry eye syndrome and against corneal graft rejection. The aim of the project is the development of nanoparticles with physicochemical properties for a suitable and prolonged release of CyA, using a factorial design. These drug delivery systems will be produced employing PLGA using the emulsification solvent evaporation method. Positively charged polymers as chitosan or Eudragit® will be incorporated to obtain nanoparticles with a positive particle charge. Electrostatic interactions with the negatively charged mucins lead to a prolonged residence time at the precorneal area. Nanoparticles will be evaluated on zeta potential, particle size and their in vitro drug release properties. CyA and CyA complexed with HP,CD will be compared. The most suitable preparations will be selected in a next phase of the project for an in vivo study using an animal model. [source] Electroanalysis of Bisphenol A at a Multiwalled Carbon Nanotubes-gold Nanoparticles Modified Glassy Carbon ElectrodeELECTROANALYSIS, Issue 22 2009Xinman Tu Abstract A sensitive electrochemical method was developed for the determination of bisphenol A (BPA) at a glassy carbon electrode (GCE) modified with a multiwalled carbon nanotubes (MWCNTs)-gold nanoparticles (GNPs) hybrid film, which was prepared based on the electrostatic interaction between positively charged cetyltrimethylammonium bromide (CTAB) and negatively charged MWCNTs and GNPs. The MWCNT-GNPs/GCE exhibited an enhanced electroactivity for BPA oxidation versus unmodified GCE and MWCNTs/GCE. The experimental parameters, including the amounts of modified MWCNTs and GNPs, the pH of the supporting electrolyte, scan rate and accumulation time, were examined and optimized. Under the optimal conditions, the differential pulse voltammetric anodic peak current of BPA was linear with the BPA concentration from 2.0×10,8 to 2×10,5 mol L,1, with a limit of detection of 7.5,nmol L,1. The proposed procedure was applied to determine BPA leached from real plastic samples with satisfactory results. [source] CE-ESI-MS/MS as a rapid screening tool for the comparison of protein,ligand interactionsELECTROPHORESIS, Issue 7 2010Thomas Hoffmann Abstract In drug development, the combinatorial synthesis of drug libraries is common use, therefore efficient tools for the characterization of drug candidates and the extent of interaction between a drug and its target protein is a central question of analytical interest. While biological activity is tested today by enzyme assays, MS techniques attract more and more attention as an alternative for a rapid comparison of drug,target interactions. CE enables the separation of proteins and drug,enzyme complexes preserving their physiological activity in aqueous media. By hyphenating CE with ESI-MS/MS, the binding strength of enzyme inhibitors can be deduced from MS/MS experiments, which selectively release the inhibitor from the drug,target complex after CID. In this study, ,-chymotrypsin (CT), a serine protease, was chosen as a model compound. Chymostatin is a naturally occurring peptide aldehyde binding to CT through a hemiacetal bond and electrostatic interaction. First, a CE separation was developed, which allows the analysis of ,-CT and a chymotrypsin,chymostatin complex under MS-compatible conditions. The use of neutral-coated CE capillaries was mandatory to reduce analyte,wall interactions. ESI-quadrupole ion trap-MS was worked out to demonstrate the selective drug release after CID. Fragmentation of the drug,enzyme complex was monitored in dependence from the excitation energy in the ion trap, leading to the V50 voltage that enables 50% complex fragmentation as a reference value for chymotrypsin,chymostatin complex. A stable CE-ESI-MS/MS setup was established, which preserves the drug,enzyme complexes during ionization,desolvation processes. With this optimized setup, different CT inhibitors could be investigated and compared. [source] Methacrylate-based monolithic column with mixed-mode hydrophilic interaction/strong cation-exchange stationary phase for capillary liquid chromatography and pressure-assisted CECELECTROPHORESIS, Issue 19 2008Jian Lin Abstract A novel porous polymethacrylate-based monolithic column by in situ copolymerization of 3-sulfopropyl methacrylate (SPMA) and pentaerythritol triacrylate in a binary porogenic solvent consisting of cyclohexanol/ethylene glycol was prepared. The monolith possessed in their structures bonded sulfonate groups and hydroxyl groups and was evaluated as a hydrophilic interaction and strong cation-exchange stationary phases in capillary liquid chromatography (cLC) and pressure-assisted CEC using small polar neutral and charged solutes. While the SPMA was introduced as multifunctional monomer, the pentaerythritol triacrylate was used to replace ethylene glycol dimethacrylate as cross-linker with much more hydrophilicity due to a hydroxyl sub-layer. The different characterization of monolithic stationary phases were specially designed and easily prepared by altering the amount of SPMA in the polymerization solution as well as the composition of the porogenic solvent for cLC and pressure-assisted CEC. The resulting monolith showed the different trends about the effect of the permeabilities on efficiency in the pressure-assisted CEC and cLC modes. A typical hydrophilic interaction chromatography mechanism was observed at higher organic solvent content (ACN%>70%) for polar neutral analytes. For polar charged analytes, both hydrophilic interaction and electrostatic interaction contributed to their retention. Therefore, for charged analytes, selectivity can be readily manipulated by changing the composition of the mobile phase (e.g., pH, ionic strength and organic modifier). With the optimized monolithic column, high plate counts reaching greater than 170,000,plates/m for pressure-assisted CEC and 105,000 plates/m for cLC were easily obtained, respectively. [source] Macrocyclic polyamine-modified poly(glycidyl methacrylate- co -ethylene dimethacrylate) monolith for capillary electrochromatographyELECTROPHORESIS, Issue 11 2008Yun Tian Abstract 1,4,10,13,16-Pentaazatricycloheneicosane-9,17-dione (macrocyclic polyamine)-modified polymer-based monolithic column for CEC was prepared by ring opening reaction of epoxide groups from poly(glycidyl methacrylate- co -ethylene dimethacrylate) (GMA- co -EDMA) monolith with macrocyclic polyamine. Conditions such as reaction time and concentration of macrocyclic polyamine for the modification reaction were optimized to generate substantial EOF and enough chromatographic interactions. Anodic EOF was observed in the pH range of 2.0,8.0 studied due to the protonation of macrcyclic polyamine at the surface of the monolith. Morphology of the monolithic column was examined by SEM and the incorporation of macrocyclic polyamine to the poly(GMA- co -EDMA) monolith was characterized by infrared (IR) spectra. Successful separation of inorganic anions, isomeric benzenediols, and benzoic acid derivatives on the monolithic column was achieved for CEC. In addition to hydrophobic interaction, hydrogen bonding and electrostatic interaction played a significant role in the separation process. [source] Separation of cationic polymer particles and characterization of avidin-immobilized particles by capillary electrophoresisELECTROPHORESIS, Issue 5-6 2006Yukihiro Okamoto Abstract Cationic polymer microparticles have received much attention especially in the field of biotechnology, such that their analysis and separation have become important. So far, the separation of cationic polymer particles with different size using CE has not been achieved and the cationic particles migrated as if they are negatively charged, probably due to electrostatic interaction between capillary wall and cationic polymer particles. In this paper, the separation of cationic polymer microparticles by CE was investigated in detail. The separation of cationic particles with different size was achieved in CE by taking into account the interaction between sample particles and the inner surface of capillaries. By employing a poly(vinyl alcohol)-coated capillary, a better size separation of amine-modified latex particles was obtained compared to a Polybrene-coated capillary. It was elucidated that the composition, concentration, and pH of the background solution were also important factors in the separation of colloidal particles to avoid the surface adsorption and the characteristic aggregation of polymer particles. Furthermore, the CE analysis was applied to the characterization of cationic protein-immobilized particles. [source] Impact of surface thermodynamics on bacterial transportENVIRONMENTAL MICROBIOLOGY, Issue 4 2001Gang Chen Microbial surface thermodynamics correlated with bacterial transport in saturated porous media. The surface thermodynamics was characterized by contact-angle measurement and the wicking method, which was related to surface free energies of Lifshitz,van der Waals interaction, Lewis acid,base interaction, and electrostatic interaction between the bacteria and the medium matrix. Transport of three different strains of bacteria present at three physiological states was measured in columns of silica gel and sand from the Canadian River Alluvium (Norman, OK, USA). Microorganisms in stationary state had the highest deposit on solid matrix, compared with logarithmic and decay states. The deposition correlated with the total surface free energy (,G132TOT) and the differences in ,G132TOT were mainly controlled by the Lewis acid,base interaction. Infrared spectroscopy showed that the increased deposition correlated with an increase in the hydrogen-bonding functional groups on the cell surfaces. [source] Pyrrolidino DNA with Bases Corresponding to the 2-Oxo Deletion Mutants of Thymine and Cytosine: Synthesis and Triplex-Forming PropertiesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 24 2007Alain Mayer Abstract The dual recognition properties of pyrrolidino DNA species as parallel triplex-forming oligonucleotides were previously found to be strongly dependent upon the nature of the pyrimidine bases. In the structure,activity study presented here we were able to exclude this differential binding being due to their 2-oxo function. We had previously reported on the incorporation of pyrrolidino C -nucleosides into triplex-forming 2,-deoxyoligonucleotides (TFOs). The basic nitrogen atom that replaces the 4,-oxygen atom of the 2,-deoxysugar in such modified units introduces a positive charge in the third strand, and this is able to produce favourable electrostatic interaction with the negatively charged DNA target duplex. A first series of pyrrolidino pseudonucleosides with the bases isocytosine and uracil proved successful for GC base-pair recognition, but was unsuccessful for AT base-pair recognition within the parallel triplex binding motif. Here we report on the synthesis of the two novel 2,-deoxypyrrolidino nucleosides carrying the bases pyridin-2-one and 2-aminopyridine, their phosphoramidite building blocks and theirincorporation into TFOs. Pyrrolidinylpyridin-2-one (dp2P) and -2-aminopyridine (dp2AP), prepared as part of a structure,activity profiling of pyrrolidino DNA in triplex binding, are deletion mutants of T and C, respectively. We found by Tm measurements that neither modification increased triplex binding efficiency relative to the iso-C- and -U-containing pyrrolidino TFOs. These experiments clearly show that the C4 carbonyl function, although important for triplex binding through indirect contributions in general, is not responsible for the differential binding of the latter two aminonucleosides and suggest that TFO conformation is more important. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Tris(8-hydroxyquinoline-5-sulfonate)aluminum Intercalated Mg,Al Layered Double Hydroxide with Blue Luminescence by Hydrothermal SynthesisADVANCED FUNCTIONAL MATERIALS, Issue 17 2010Shuangde Li Abstract Blue luminescent hybrid materials (DDS,AQS(x%)/LDH) are successfully prepared by co-intercalating tris(8-hydroxyquinoline-5-sulfonate)aluminum anions (AQS3,) and dodecyl sulfonate (DDS,) with different molar ratios into Mg,Al layered double hydroxides (LDHs) by the hydrothermal and solution co-precipitation methods. A film of the material on a quartz substrate is obtained by the solvent evaporation method. The results show the blue luminescence is remarkably different from the pristine Na3AQS, which has cyan luminescence (ca. 450,470 nm vs. 495 nm). Furthermore, the hydrothermal product of DDS,AQS(66.67%)/LDH exhibits optimal luminous intensity and a significantly enhanced fluorescence lifetime. Nuclear magnetic resonance and Fourier-transform infrared spectroscopy indicate that the cyan,blue luminescence transition is due to the isomerization of meridianal to facial AQS via ligand flip caused by a host,guest electrostatic interaction, in combination with the dispersion and pre-intercalation effect of DDS. The hydrothermal conditions can promote a more ordered alignment of the intercalated fac -AQS compared with alignment in the solution state, and the rigid LDHs environment can confine the internal mobility of AQS to keep the facial configuration stable. This stability allows a facile preparation of large amounts of blue luminous powder/film, which is a new type of inorganic,organic hybrid photofunctional material. [source] Identification of domains on the extrinsic 23 kDa protein possibly involved in electrostatic interaction with the extrinsic 33 kDa protein in spinach photosystem IIFEBS JOURNAL, Issue 5 2004Akihiko Tohri To elucidate the domains on the extrinsic 23 kDa protein involved in electrostatic interaction with the extrinsic 33 kDa protein in spinach photosystem II, we modified amino or carboxyl groups of the 23 kDa protein to uncharged methyl ester groups with N -succinimidyl propionate or glycine methyl ester in the presence of a water-soluble carbodiimide, respectively. The N -succinimidyl propionate-modified 23 kDa protein did not bind to the 33 kDa protein associated with PSII membranes, whereas the glycine methyl ester-modified 23 kDa protein completely bound. This indicates that positive charges on the 23 kDa protein are important for electrostatic interaction with the 33 kDa protein associated with the PSII membranes. Mapping of the N -succinimidyl propionate-modified sites of the 23 kDa protein was performed using Staphylococcus V8 protease digestion of the modified protein followed by determination of the mass of the resultant peptide fragments with MALDI-TOF MS. The results showed that six domains (Lys11,Lys14, Lys27,Lys38, Lys40, Lys90,Lys96, Lys143,Lys152, Lys166,Lys174) were modified with N -succinimidyl propionate. In these domains, Lys11, Lys13, Lys33, Lys38, Lys143, Lys166, Lys170 and Lys174 were wholly conserved in the 23 kDa protein from 12 species of higher plants. These positively charged lysyl residues on the 23 kDa protein may be involved in electrostatic interactions with the negatively charged carboxyl groups on the 33 kDa protein, the latter has been suggested to be important for the 23 kDa binding [Bricker, T.M. & Frankel, L.K. (2003) Biochemistry42, 2056,2061]. [source] Biodegradable Dextran Nanogels for RNA Interference: Focusing on Endosomal Escape and Intracellular siRNA DeliveryADVANCED FUNCTIONAL MATERIALS, Issue 9 2009Koen Raemdonck Abstract The successful therapeutic application of small interfering RNA (siRNA) largely relies on the development of safe and effective delivery systems that are able to guide the siRNA therapeutics to the cytoplasm of the target cell. In this report, biodegradable cationic dextran nanogels are engineered by inverse emulsion photopolymerization and their potential as siRNA carriers is evaluated. The nanogels are able to entrap siRNA with a high loading capacity, based on electrostatic interaction. Confocal microscopy and flow cytometry analysis reveal that large amounts of siRNA-loaded nanogels can be internalized by HuH-7 human hepatoma cells without significant cytotoxicity. Following their cellular uptake, it is found that the nanogels are mainly trafficked towards the endolysosomes. The influence of two different strategies to enhance endosomal escape on the extent of gene silencing is investigated. It is found that both the application of photochemical internalization (PCI) and the use of an influenza-derived fusogenic peptide (diINF-7) can significantly improve the silencing efficiency of siRNA-loaded nanogels. Furthermore, it is shown that an efficient gene silencing requires the degradation of the nanogels. As the degradation kinetics of the nanogels can easily be tailored, these particles show potential for intracellular controlled release of short interfering RNA. [source] Dextran Microgels for Time-Controlled Delivery of siRNA,ADVANCED FUNCTIONAL MATERIALS, Issue 7 2008Koen Raemdonck Abstract To apply siRNA as a therapeutic agent, appropriate attention should be paid to the optimization of the siRNA gene silencing effect, both in terms of magnitude and duration. Intracellular time-controlled siRNA delivery could aid in tailoring the kinetics of siRNA gene knockdown. However, materials with easily tunable siRNA release properties have not been subjected to thorough investigation thus far. This report describes cationic biodegradable dextran microgels which can be loaded with siRNA posterior to gel formation. Even though the siRNAs are incorporated in the hydrogel network based on electrostatic interaction, still a time-controlled release can be achieved by varying the initial network density of the microgels. To demonstrate the biological functionality of the siRNA loaded gels, we studied their cellular internalization and enhanced green fluorescent protein (EGFP) gene silencing potential in HUH7 human hepatoma cells. [source] Electrostatic analysis of charge interactions in proteinsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 1 2010G. P. Tsironis Abstract We model proteins as continuous electrostatic media immersed in water to investigate charge mediated processes in their interior. We use a Green's function formalism and find analytical expressions for the electrostatic energy in the vicinity of the protein surfaces. We find that due to image charges generated by the protein dielectric medium embedded in water, the effective electrostatic interaction between the two charges in the interior of the protein has an energy larger than the thermal energy. We focus specifically on kinesin to asses the strength of the electrostatic interaction between ATP and ADP molecules. It is known experimentally that ADP expulsion is correlated to ATP kinesin binding while both processes are essential for the kinesin walk. We estimate that the Bjerrum length in the interior of the kinesin dimer protein is of the order of 4 nm and that the pure electrostatic ATP,ADP interaction is of the order of 3,5 kBT. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] Effects of magnetic field and rare-earth ions on properties of polyaniline nanoparticlesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2007Shuling Zhang Abstract The uniform polyaniline nanoparticles with the size of about 50 nm were electropolymerized using the method of constant potential of 0.8 V. The effects of rare-earth cations and magnetic field on the preparation and properties of polyaniline were investigated. It was found that the addition of rare-earth cations could enhance the effect of magnetic field on the properties of polyaniline. The resulting products were characterized by FTIR spectra, UV,vis spectra and scanning electron microscope (SEM); the conductivity and cyclic voltammetry (CV) were also investigated. The experimental results show that the magnetic field has an orientation effect on polyaniline chain and there exists the interaction between rare-earth cations and polyaniline chain because of the electrostatic interaction. The addition of rare-earth cations can increase electrical conductivity, moreover, the effect of NdCl3 and ErCl3 on properties of polyaniline is more remarkable than LaCl3 and SmCl3. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2286,2294, 2007 [source] Graph-theoretical identification of dissociation pathways on free energy landscapes of biomolecular interactionJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 4 2010Ling Wang Abstract Biomolecular association and dissociation reactions take place on complicated interaction free energy landscapes that are still very hard to characterize computationally. For large enough distances, though, it often suffices to consider the six relative translational and rotational degrees of freedom of the two particles treated as rigid bodies. Here, we computed the six-dimensional free energy surface of a dimer of water-soluble alpha-helices by scanning these six degrees of freedom in about one million grid points. In each point, the relative free energy difference was computed as the sum of the polar and nonpolar solvation free energies of the helix dimer and of the intermolecular coulombic interaction energy. The Dijkstra graph algorithm was then applied to search for the lowest cost dissociation pathways based on a weighted, directed graph, where the vertices represent the grid points, the edges connect the grid points and their neighbors, and the weights are the reaction costs between adjacent pairs of grid points. As an example, the configuration of the bound state was chosen as the source node, and the eight corners of the translational cube were chosen as the destination nodes. With the strong electrostatic interaction of the two helices giving rise to a clearly funnel-shaped energy landscape, the eight lowest-energy cost pathways coming from different orientations converge into a well-defined pathway for association. We believe that the methodology presented here will prove useful for identifying low-energy association and dissociation pathways in future studies of complicated free energy landscapes for biomolecular interaction. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 [source] Accuracy of distributed multipoles and polarizabilities: Comparison between the LoProp and MpProp modelsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 6 2007P. Söderhjelm Abstract Localized multipole moments up to the fifth moment as well as localized dipole polarizabilities are calculated with the MpProp and the newly developed LoProp methods for a total of 20 molecules, predominantly derived from amino acids. A comparison of electrostatic potentials calculated from the multipole expansion obtained by the two methods with ab initio results shows that both methods reproduce the electrostatic interaction with an elementary charge with a mean absolute error of ,1.5 kJ/mol at contact distance and less than 0.1 kJ/mol at distances 2 Å further out when terms up to the octupole moments are included. The polarizabilities are tested with homogenous electric fields and are found to have similar accuracy. The MpProp method gives better multipole moments unless diffuse basis sets are used, whereas LoProp gives better polarizabilities. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007 [source] Exploration of ionic modification in dual-layer hollow fiber membranes for long-term high-performance protein separationAICHE JOURNAL, Issue 2 2009Yi Li Abstract Two types of ionic modification approaches (i.e., sulfonation and triethylamination) were applied with the aid of dual-layer hollow fiber technology in this work to fine tune the pore size and pore size distribution, introduce the electrostatic interaction, and reduce membrane fouling for long-term high-performance protein separation. A binary protein mixture comprising bovine serum albumin (BSA) and hemoglobin (Hb) was separated in this work. The sulfonated fiber exhibits an improved BSA/Hb separation factor at pH = 6.8 compared with as-spun fibers but at the expense of BSA sieving coefficient. On the other hand, the triethylaminated fiber reveals the best and most durable separation performance at pH = 4.8. Its BSA/Hb separation factor is maintained above 80 for 4 days and maximum BSA sieving coefficient reaches 33%. Therefore, this study documents that an intelligent combination of both size-exclusion and electrostatic interaction can synergistically enhance protein separation performance in both purity and concentration. © 2008 American Institute of Chemical Engineers AIChE J, 2009 [source] | ||||||||||||||||||||||||||||||||||||||||||||||