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Strong Electrostatic Interaction (strong + electrostatic_interaction)
Selected AbstractsBiphasic Resorbable Calcium Phosphate Ceramic for Bone Implants and Local Alendronate Delivery,ADVANCED ENGINEERING MATERIALS, Issue 5 2010Shashwat S. Banerjee A novel biphasic calcium phosphate ceramic composed of tricalcium phosphate (TCP) and calcium pyrophosphate (CP) is synthesized in order to tailor the biodegradation behavior of the ceramic. The results show that biphasic TCP/CP ceramic has a strength of 62.2,±,2.1 MPa, which is superior to single-phase TCP and CP ceramics, which show strengths of 44.3,±,3.0 and 53.0,±,4.8 MPa, respectively. In addition, biphasic TCP/CP ceramic displays a controlled strength degradation from 62.2,±,2.1 to 40.5,±,1.0 MPa in stimulated body fluid over a period of 28 d. An in vitro cell materials interaction study using human fetal osteoblast cells indicates that TCP/CP ceramic is cytocompatible. TCP/CP ceramic also show a good loading capacity for alendronate. Adsorption of alendronate (AD) on the TCP/CP surface is found to proceed via ligand exchange mechanism and the in vitro release profile of AD from TCP/CP surface is characterized by an initial fast release followed by a slow and sustained release. Strong electrostatic interactions between AD groups and surface Ca2+ ions enable the slow and sustained release of AD. These results demonstrate that the newly developed biphasic ceramic, with its controlled strength degradation and drug release, shows promise for use in orthopedic and tissue engineering applications. [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] Antimicrobial peptides from the skin of the Japanese mountain brown frog, Rana ornativentrisCHEMICAL BIOLOGY & DRUG DESIGN, Issue 5 2001J.B. Kim Abstract: Six peptides with antimicrobial activity were isolated from an extract of freeze-dried skin of the Japanese mountain brown frog Rana ornativentris. Two structurally related peptides (brevinin-20a GLFNVFKGALKTAGKHVAGSLLNQLKCKVSGGC, 11 nmol/g dried tissue, and brevinin-20b GIFNVFKGALKTAGKHVAGSLLNQLKCKVSGEC, 170 nmol/g) belong to the brevinin-2 family, previously identified in Asian and European, but not North American, Ranid frogs. Four peptides (temporin-1Oa FLPLLASLFSRLL.NH2, 13 nmol/g; temporin-1Ob FLPLIGKILGTI L.NH2, 350 nmol/g; temporin-1Oc FLPLLASLFSRLF.NH2, 14 nmol/g; and temporin-1Od FLPLLASLFSGLF.NH2, 8 nmol/g) are members of the temporin family first identified in the European common frog Rana temporaria but also found in the skins of North American Ranids. The brevinin-2 peptides showed broad-spectrum activity against the gram-positive bacterium, Staphylococcus aureus, the gram-negative bacterium, Escherichia coli and the yeast Candida albicans, whereas the temporins showed potent activity only against S. aureus. The brevinins and temporins belong to the class of cationic antimicrobial peptides that adopt an amphipathic ,-helical conformation but it is significant that temporin-1Od, which lacks a basic amino acid residue, is still active against S. aureus (minimum inhibitory concentration=13 µm compared with 2 µm for temporin-1Oa). This suggests that strong electrostatic interaction between the peptide and the negatively charged phospholipids of the cell membrane is not an absolute prerequisite for antimicrobial activity. [source] Adsorption of Insulin Peptide on Charged Single-Walled Carbon Nanotubes: Significant Role of Ordered Water MoleculesCHEMPHYSCHEM, Issue 8 2009Jia-Wei Shen Abstract Ordered hydration shells: The more ordered hydration shells outside the charged CNT surfaces prevent more compact adsorption of the peptide in the charged CNT systems (see picture), but peptide binding strengths on the charged CNT surfaces are stronger due to the electrostatic interaction. Studies of adsorption dynamics and stability for peptides/proteins on single-walled carbon nanotubes (SWNTs) are of great importance for a better understanding of the properties and nature of nanotube-based biosystems. Herein, the dynamics and mechanism of the adsorption of the insulin chain B peptide on different charged SWNTs are investigated by explicit solvent molecular dynamics simulations. The results show that all types of surfaces effectively attract the model peptide. Water molecules play a significant role in peptide adsorption on the surfaces of charged carbon nanotubes (CNTs). Compared to peptide adsorption on neutral CNT surfaces, the more ordered hydration shells outside the tube prevent more compact adsorption of the peptide in charged CNT systems. This shield effect leads to a smaller conformational change and van der Waals interaction between the peptide and surfaces, but peptide binding strengths on charged CNT surfaces are stronger than those on the neutral CNT surface due to the strong electrostatic interaction. The result of these simulations implies the possibility of improving the binding strength of peptides/proteins on CNT surfaces, as well as keeping the integrity of the peptide/protein conformation in peptide/protein,CNT complexes by charging the CNTs. [source] The SAAP force field: Development of the single amino acid potentials for 20 proteinogenic amino acids and Monte Carlo molecular simulation for short peptides,JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2009Michio Iwaoka Abstract Molecular simulation by using force field parameters has been widely applied in the fields of peptide and protein research for various purposes. We recently proposed a new all-atom protein force field, called the SAAP force field, which utilizes single amino acid potentials (SAAPs) as the fundamental elements. In this article, whole sets of the SAAP force field parameters in vacuo, in ether, and in water have been developed by ab initio calculation for all 20 proteinogenic amino acids and applied to Monte Carlo molecular simulation for two short peptides. The side-chain separation approximation method was employed to obtain the SAAP parameters for the amino acids with a long side chain. Monte Carlo simulation for Met-enkephalin (CHO-Tyr-Gly-Gly-Phe-Met-NH2) by using the SAAP force field revealed that the conformation in vacuo is mainly controlled by strong electrostatic interactions between the amino acid residues, while the SAAPs and the interamino acid Lennard-Jones potentials are predominant in water. In ether, the conformation would be determined by the combination of the three components. On the other hand, the SAAP simulation for chignolin (H-Gly-Tyr-Asp-Pro-Glu-Thr-Gly-Thr-Trp-Gly-OH) reasonably reproduced a native-like ,-hairpin structure in water although the C-terminal and side-chain conformations were different from the native ones. It was suggested that the SAAP force field is a useful tool for analyzing conformations of polypeptides in terms of intrinsic conformational propensities of the single amino acid units. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009 [source] Magnetic field effects on the copolymerization of water-soluble and ionic monomersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2009Ignacio Rintoul Abstract The effect of magnetic field (MF) on the radical copolymerization of a series of water-soluble and ionic monomers is presented including acrylamide (AM), acrylic acid (AA), its ionized form acrylate (A,), and diallyldimethylammonium chloride (DADMAC). The following combinations have been studied: AM/AA, AM/A,, AM/DADMAC, and AA/DADMAC. In addition to the MF, strong electrostatic interactions are present for the majority of monomer combinations and conditions. Although the monomer consumption rate (Rp) increased up to 65% applying a MF of 0.1 Tesla, the composition of the resulting copolymers was not affected under such conditions. Despite this increase of Rp by MF, the electrostatic repulsion between ionic monomers and charged growing radicals dominates Rp and governs the copolymer composition with and without MF. The order of the experimentally obtained reactivity ratios reflects the extent of electrostatic interaction: rAM/AA (1.41) < r (3.10) < rAA/DADMAC (4.25) < rAM/DADMAC (6.95) and rAA/AM (2.20) > rDADMAC/AA (0.25) > r (0.17) > rDADMAC/AM (0.03). Overall, weak MF offers to reduce the production time without modifying the product composition. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 373,383, 2009 [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] | |||||||||||||