MACROMOLECULAR BIOSCIENCE, Issue 1 2010
Ronak Maheshwari
Abstract Multivalent, glycopolymer inhibitors designed for the treatment of disease and pathogen infection have shown improvements in binding correlated with general changes in glycopolymer architecture and composition. We have previously demonstrated that control of glycopolypeptide backbone extension and ligand spacing significantly impacts the inhibition of the cholera toxin B subunit pentamer (CT B5) by these polymers. In the studies reported here, we elucidate the role of backbone charge and linker length in modulating the inhibition event. Peptides of the sequence AXPXG (where X is a positive, neutral or negative amino acid), equipped with the alkyne functionality of propargyl glycine, were designed and synthesized via solid-phase peptide synthetic methods and glycosylated via Cu(I)-catalyzed alkyne-azide cycloaddition reactions. The capacity of the glycopeptides to inhibit the binding of the B5 subunit of cholera toxin was evaluated. These studies indicated that glycopeptides with a negatively charged backbone show improved inhibition of the binding event relative to the other glycopeptides. In addition, variations in the length of the linker between the peptide and the saccharide ligand also affected the inhibition of CT by the glycopeptides. Our findings suggest that, apart from appropriate saccharide spacing and polypeptide chain extension, saccharide linker conformation and the systematic placement of charges on the polypeptide backbone are also significant variables that can be tuned to improve the inhibitory potencies of glycopolypeptide-based multivalent inhibitors. [source]

Development of Nanothermite Composites with Variable Electrostatic Discharge Ignition Thresholds

PROPELLANTS, EXPLOSIVES, PYROTECHNICS, Issue 6 2007
Timothy Foley
Abstract A brief description of an apparatus for testing the electrostatic discharge ignition threshold for sensitive materials is presented. This apparatus was used to demonstrate how fluorocarbons could alter the propensity of a nanothermite to ignite. In addition to these findings, the effect of the fluorocarbon on the pressure output of the material is reported. [source]

Monte Carlo Simulations of the Electron Currents Collected by Electrostatic Probes

CONTRIBUTIONS TO PLASMA PHYSICS, Issue 7-8 2004
D. Trunec
Abstract We have carried out Monte Carlo simulation of the motion of electrons in the space charge sheath surrounding a cylindrical Langmuir (electrostatic) probe. The electron currents to the probe have been calculated from these simulations for different conditions (pressure of neutral gas, presence of magnetic field). The results of the simulations have been compared with recent Langmuir probe measurements made in cylindrical DC magnetron plasmas. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Electrochemical Behavior of Catecholamines and Related Compounds at In Situ Surfactant Modified Carbon Paste Electrodes

ELECTROANALYSIS, Issue 2-3 2007
M.Carmen Blanco-López
Abstract The voltammetric characteristics of catecholamines: epinephrine (E) and norepinephrine (NE) and related compounds: isoproterenol, metanephrine, L -dopa, methyldopa, vanillylmandelic acid (VMA), and homovanillic acid (HVA) at unmodified and in situ surfactant- modified carbon paste electrodes were comparatively evaluated. For the basic and amphoteric compounds the modification of the electrode surface with submicellar concentrations of anionic surfactants (sodium dodecylsulfate, sodium decylsulfate or sodium dodecylsulfonate) produce an important current enhancement in its oxidation and reduction peak current together with the improvement in the reversibility of the processes. These effects were explained in basis on electrostatic and hydrophobic interactions. On the other hand, the oxidation of acidic metabolites, HVA and VMA, was studied at electrodes modified in situ with cationic surfactants. Under certain conditions the surfactant could stabilise some of the electrochemical reaction intermediates, thus explaining the different voltammetric behaviour of HVA and VMA. [source]

Preparation and evaluation of the highly cross-linked poly(1-hexadecane-co-trimethylolpropane trimethacrylate) monolithic column for capillary electrochromatography

ELECTROPHORESIS, Issue 20 2009
Minghua Lu
Abstract In this paper, a novel highly cross-linked porous monolithic stationary phase having a long alkyl chain ligand (C16) was introduced and evaluated in CEC. The monolithic stationary phase was prepared by in situ copolymerization of 1-hexadecene, trimethylolpropane trimethacrylate, and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) in the presence of ternary porogenic solvent (cyclohexanol/1,4-butanediol/water). In preparing monoliths, the ternary cross-linker trimethylolpropane trimethacrylate was usually applied to preparing molecularly imprinted polymers or molecularly imprinted solid-phase extraction, instead of binary cross-linker ethylene dimethacrylate. 1-Hexadecene was introduced to provide the non-polar sites (C16) for chromatographic retention, while AMPS was used to generate the EOF for transporting the mobile phase through the monolithic capillary. Monolithic columns were prepared by optimizing proportion of porogenic solvent and AMPS content in the polymerization solution as well as the cross-linkers. The monolithic stationary phases could generate a strong and stable EOF in various pH values and exhibit an RP-chromatographic behavior for neutral compounds. For charged compounds, the separation was mainly based on the association of hydrophobic, electrostatic and electrophoretic interaction. [source]

Open-tubular capillary electrochromatography using a capillary coated with octadecylamine-capped gold nanoparticles

ELECTROPHORESIS, Issue 4 2008
Qishu Qu Dr.
Abstract Octadecylamine-capped gold nanoparticles (ODA-Au-NPs) were prepared and characterized by using UV,Vis adsorption spectrum, transmission electron chromatography (TEM), SEM, and FT-IR. A simple but robust hydrophobic coating was easily developed by flushing a capillary with a solution of ODA-Au-NPs, because the positive charges were carried by the nanoparticles which strongly adsorb to the negatively charged inner surface of a fused-silica capillary via electrostatic and hydrophobic interactions. The chromatographic characteristics of the coated capillary was investigated by varying the experimental parameters such as buffer pH, buffer concentration, and percentage of organic modifier in the mobile phase. The results show that (i) resolution between thiourea and naphthalene is almost the same when comparing the electrochromatograms obtained using pH,7 buffer as mobile phase after and before the capillary column was operated using pH,11 and 3 mobile phase; (ii) no significant changes in retention time and deterioration in peak efficiency were found after 60,runs of test aromatic mixtures; and (iii) column efficiency up to 189,000 theoretical plates/meter for testosterone was obtained. All of the results indicated that the coating could act as a stable stationary phase for open tubular CEC as well as for bioanalysis. [source]

Capillary electrochromatography with zwitterionic stationary phase on the lysine-bonded poly(glycidyl methacrylate- co -ethylene dimethacrylate) monolithic capillary column

ELECTROPHORESIS, Issue 12 2006
Xiaoli Dong
Abstract A polymer-based neutral monolithic capillary column was prepared by radical polymerization of glycidyl methacrylate and ethylene dimethacrylate in a 100,,m id fused-silica capillary, and the prepared monolithic column was subsequently modified based on a ring opening reaction of epoxide groups with 1,M,lysine in solution (pH,8.0) at 75°C for 10,h to produce a lysine chemically bonded stationary phases in capillary column. The ring opening reaction conditions were optimized so that the column could generate substantial EOF. Due to the zwitterionic functional groups of the lysine covalently bonded on the polymer monolithic rod, the prepared column can generate cathodic and anodic EOF by varying the pH values of running buffer during CEC separation. EOF reached the maximum of ,2.0×10,8,m2v,1s,1 and 2.6×10,8,m2v,1s,1 with pH of the running buffer of 2.25 and 10, respectively. As a consequence, neutral compounds, ionic solutes such as phenols, aromatic acids, anilines, and basic pharmaceuticals were all successfully separated on the column by CEC. Hydrophobic interaction is responsible for separation of neutral analytes. In addition, the electrostatic and hydrophobic interaction and the electrophoretic migration play a significant role in separation of the ionic or ionizable analytes. [source]

The Role of C,H···H,B Interactions in Establishing Rotamer Configurations in Metallabis(dicarbollide) Systems

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2010
Emilio José Juárez-Pérez
Abstract The aim of this work is to explore the self-interaction capability of the anion [3,3,-Co(1,2-C2B9H11)2], through Ccluster,H···H,B (Cc,H···H,B) dihydrogen bonds. A set of theoretical and empirical data aiming to establish the main rules that account for the binding mode between the negatively charged borane framework made by [3,3,-Co(1,2-C2B9H11)2], and the [NMe4]+ ions have been compiled. The interaction between cation and anion is mainly electrostatic but the covalent contribution is also proven and quantified. The existing intermolecular H···H short contacts have been studied and are compared with available data from the Cambridge Structural Database. The results show that the electronic configuration of the transition metal atom in the sandwich complex is not enough to define the preferred rotamer due to the influence of the anion environment and the H···H interactions present in the solid state. We present a methodology with widely used theoretical tools to study cation···cobaltabisdicarbollide interactions in the solid state. [source]

The Assembling of Semiconductor Nanocrystals

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2005
Alexey Shavel
Abstract Recent accomplishments in arranging semiconductor nanoparticles in a desired manner are reviewed. Coupling mechanisms utilized for this purpose include electrostatic and covalent interactions, methods like layer-by-layer assembly, solvent-controlled precipitation and surface amination for covalent attachment of nanoparticles are employed. Dipole,dipole interactions are operative in nanocrystal solids and fast Förster energy transfer is observed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Effect of earthworm activity (Aporrectodea giardi) on atrazine adsorption and biodegradation

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2006
T. Alekseeva
Summary We investigated the influence of earthworm (Aporrectodea giardi) activity on soil properties and on atrazine (AT) adsorption and biodegradation by comparing a coarse-textured smectite-free wetland soil (Brittany, France) with the earthworm casts derived from the top horizon of this soil. Casts are characterized by lower pH, are enriched in organic carbon (OC) and clay content, have a larger cation exchange capacity, and a greater exchangeable Ca content. The clay mineralogy of the soil studied and casts is characterized by a muscovite,kaolinite,chlorite association. In addition, the clay fraction of the soil contains lepidocrocite (,-FeOOH), which was not found in the casts. Atrazine adsorption isotherms were reasonably well described by the Freundlich equation and were all non-linear. The mean amounts of adsorbed AT for starting concentrations of 3,30 mg litre,1 ranged from 8 to 34%, being largest in earthworm casts. Soil AT adsorption capacity was well correlated with OC content. Non-decomposed organic matter present in the coarse size fractions and specific compounds present in earthworm casts (proteins, mono- and polysaccharides, polyphenols, sugars, lignin) and microbial and fungal biomass contribute to AT adsorption. Weak electrostatic (physical) sorption of AT on organic compounds and on mineral surfaces prevails. For casts, the formation of additional hydrophobic interactions between AT and SOM is proposed. We also studied AT biodegradation by the model bacterium Pseudomonas sp. strain ADP in the presence of soils or earthworm casts. An enhancement of the AT disappearance rate was observed in the presence of all the solid matrices tested compared with that obtained in an aqueous medium. The biodegradation rate was shown to be dependent not only on the OC content of the solid matrix, but mainly on its composition and structure. [source]

Pseudobilayer Vesicle Formation via Layer-by-Layer Assembly of Hydrophobically Modified Polymers on Sacrificial Substrates,

ADVANCED FUNCTIONAL MATERIALS, Issue 7 2005
J. Khopade
Abstract A bilayer of a hydrophobically modified polyelectrolyte, octadecyl poly(acrylamide) (PAAm), sandwiched between the layers of a hydrophilic polyelectrolyte, poly(ethyleneimine) (PEI), is prepared by the sequential electrostatic,hydrophobic,electrostatic-interaction-driven self-assembly on planar and colloid substrates. This process results in a PEI/[PAAm]2/PEI-multilayer-coated substrate. The removal of a PAA/PEI/[PAAm]2/PEI-multilayer-coated decomposable colloidal template produces hollow capsules. Irregular hydrophobic domains of the [PAAm]2 bilayer in the PEI/[PAAm]2/PEI-multilayer capsule are infiltrated with a lipid to obtain a uniform, distinct hydrophobic layer, imparting the capsule with a pseudobilayer vesicle structure. [source]

Drug,Membrane Interaction on Immobilized Liposome Chromatography Compared to Immobilized Artificial Membrane (IAM), Liposome/Water, and Octan-1-ol/Water Systems

HELVETICA CHIMICA ACTA, Issue 2 2010
Xiangli Liu
Abstract The objective of this study was to investigate drug,membrane interaction by immobilized liposome chromatography (ILC; expressed as lipophilicity index log,Ks) and the comparison with lipophilicity indices obtained by liposome/H2O, octan-1-ol/H2O, and immobilized artificial membrane (IAM) systems. A set of structurally diverse monofunctional compounds and drugs (nonsteroidal anti-inflammatory drugs and , -blockers) were selected in this study. This set of solutes consists of basic or acidic functionalities which are positively or negatively charged at physiological pH,7.4. No correlation was found between log,Ks from ILC and lipophilicity indices from any of the other membrane model systems for the whole set of compounds. For structurally related compounds, significant correlations could be established between log,Ks from ILC and lipophilicity indices from IAM chromatography and octan-1-ol/H2O. However, ILC and liposome/H2O systems only yield parallel partitioning information for structurally related large molecules. For hydrophilic compounds, the balance between electrostatic and hydrophobic interactions dominating drug partitioning is different in these two systems. [source]

Molecules on Si: Electronics with Chemistry

ADVANCED MATERIALS, Issue 2 2010
Ayelet Vilan
Abstract Basic scientific interest in using a semiconducting electrode in molecule-based electronics arises from the rich electrostatic landscape presented by semiconductor interfaces. Technological interest rests on the promise that combining existing semiconductor (primarily Si) electronics with (mostly organic) molecules will result in a whole that is larger than the sum of its parts. Such a hybrid approach appears presently particularly relevant for sensors and photovoltaics. Semiconductors, especially Si, present an important experimental test-bed for assessing electronic transport behavior of molecules, because they allow varying the critical interface energetics without, to a first approximation, altering the interfacial chemistry. To investigate semiconductor-molecule electronics we need reproducible, high-yield preparations of samples that allow reliable and reproducible data collection. Only in that way can we explore how the molecule/electrode interfaces affect or even dictate charge transport, which may then provide a basis for models with predictive power. To consider these issues and questions we will, in this Progress Report, review junctions based on direct bonding of molecules to oxide-free Si. describe the possible charge transport mechanisms across such interfaces and evaluate in how far they can be quantified. investigate to what extent imperfections in the monolayer are important for transport across the monolayer. revisit the concept of energy levels in such hybrid systems. [source]

Artificial Vasculature: Rapid Fabrication of Bio-inspired 3D Microfluidic Vascular Networks (Adv. Mater.

ADVANCED MATERIALS, Issue 35 2009
35/2009)
The cover depicts a 3D microchannel network embedded inside an acrylic polymer substrate. The network is created using an electrostatic discharge method that instantaneously vaporizes and fractures the substrate, leaving behind a tree-like fractal arrangement of microchannels bearing a remarkable similarity to naturally occurring vasculature. The ability to rapidly construct microchannel networks incorporating a wide range of diameters (,10,500 µm) may help enable production of organ-sized engineered tissue scaffolds containing embedded vasculature, as reported by Arul Jayaraman, Victor Ugaz, and co-workers on p. 3567. [source]

Rapid Fabrication of Bio-inspired 3D Microfluidic Vascular Networks

ADVANCED MATERIALS, Issue 35 2009
Jen-Huang Huang
A new method to embed branched 3D microvascular fluidic networks inside plastic substrates by harnessing electrostatic discharge phenomena is introduced. This nearly instantaneous process reproducibly generates highly branched tree-like microchannel architectures that bear remarkable similarity to naturally occurring vasculature. This method can be applied to a variety of polymers, and may help enable production of organ-sized tissue scaffolds containing embedded vasculature. [source]

Magnetically Tunable Colloidal Photonic Structures in Alkanol Solutions,

ADVANCED MATERIALS, Issue 18 2008
Jianping Ge
Magnetically tunable photonic structures are prepared in alkanol solutions by using silica-modified superparamagnetic Fe3O4 colloids as building blocks. Repulsive electrostatic and solvation forces and magnetically induced attractive forces contribute to the ordering of the Fe3O4@SiO2 colloids. The ability to form tunable photonic structures in nonaqueous solutions allows the fabrication of field-responsive polymer composite films for potential applications as displays and sensors. [source]

Effect of self-assemblies of various surfactants in their single and mixed states on the BZ oscillatory reaction

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2010
Muzaffar Hussain Najar
Micelles of different surfactants are well known to affect chemical equilibria and reactivities by selectively sequestering the reagent substrates through electrostatic and hydrophobic interactions. In this article, the effects of micelles of various surfactants on different parameters of the Ce(IV)-catalyzed Belousov,Zhabotinsky (BZ) oscillatory reaction at 35°C in nonstirred closed conditions are studied by employing spectrophotometry and tensiometry. Surfactants used in this study are the cationics hexadecyltrimethylammonium bromide (CTAB) and pentamethylene-1,5-bis(N -hexadecyl- N,N -dimethylammonium)bromide gemini (Gemini), anionic sodium dodecylbenzene sulfonate (SDBS), and nonionic Brij58, whereas the binary surfactant systems used are cationic,nonionic CTAB+Brij58 and anionic,nonionic SDBS+Brij58. The results revealed that the induction period shows a definite variation with increasing concentration of different surfactants above their critical micelle concentration (cmc). The amplitudes of oscillation and absorbance maxima and minima are enhanced in the presence of micelles of CTAB and Gemini surfactants, whereas micelles of SDBS and Brij58 have almost no effect on the nature of the oscillations. However, mixed micelles of CTAB+Brij58 and SDBS+Brij58 binary mixtures show a quite different effect on the overall behavior of the oscillations. The enhanced effect of CTAB and Gemini surfactants on the overall nature of oscillations has been attributed to the positive charge on the surface of their micelles and to some extent on the presence of nitrogen in their head group. The effect of mixed binary micelles may be attributed to their synergistic nature. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 659,668, 2010 [source]

Intra and intermolecular hydrogen bonding in formohydroxamic acid,

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 1 2008
Damanjit Kaur
Abstract The presence of hydrogen bonding interactions in several tautomeric forms of formohydroxamic acid (FHA) and 1:1 association among the tautomeric forms and water-coordinated tautomeric forms of FHA is explored theoretically. Out of the seven equilibrium structures, four tautomeric forms have been selected for aggregation with single water molecule and dimer formation. Fifteen aggregates of FHA with H2O have been optimized at MP2/AUG-cc-PVDZ level and analyzed for intramolecular and intermolecular H-bond interactions. Twenty-seven dimers of the four tautomeric forms have been obtained at MP2/6-31+G* level. The stabilization energies associated with dimerization and adduct formation with water are the result of H-bond interactions and range from very weak to medium. The atomic charges and NBO analysis indicate that the electrostatic and the charge transfer are the important components favoring H-bond formation. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source]

Intramolecular proton transfer induced by divalent alkali earth metal cation in the gas state

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2003
Hongqi Ai
Abstract Interactions between divalent alkali earth metal (DAEM) ions M (MBe, Mg, Ca, Sr, Ba) and the second stable glycine conformer in the gas phase, which can transfer into the ground-state glycine-M2+ (except the glycine,Be2+) among each corresponding isomers when these divalent metal ions are bound, are studied at the hybrid three-parameter B3LYP level with three different basis sets. Proton transfers from the hydroxyl to the amino nitrogen of the glycine without energy barriers have been first observed in the gas phase in these glycine,M2+ systems. The interaction between the glycine and these DAEM ions except beryllium and magnesium ion only create an amino hydrogen pointing to the original hydroxyl due to their weaker interaction relative to those divalent transition metal (DTM) ion-bound glycine derivatives, being obviously different from that between the glycine and DTM ions, in which two amino hydrogens point to the original hydroxyl oxygen when these metal-chelated glycine derivatives are produced. The interaction energy between the glycine and divalent magnesium would be the boundary of one or two amino hydrogens pointing to the hydrogyl oxygen, i.e., the ,170.3 kcal/mol of binding energy is a critical point. Similar intramolecular proton transfer has also been predicted for those DTM ion-chelated glycine systems; however, that in the gas state has not been observed in the monovalent metal ion-coordinated glycine systems. The binding energy between some monovalent TM ion and the glycine is similar to that of the glycine,Ba2+, which has the lowest binding strength among these DAEM,ion chelated glycine complexes. The difference among them only lies in the larger electrostatic and polarized effects in the latter, which favor the stability of the zwitterionic glycine form in the gas phase. According to these observations, we predict that the zwitterionic glycine would exist in the field of two positive charges in the gas phase. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 205,214, 2003 [source]

Molecular surface electrostatic potentials in relation to noncovalent interactions in biological systems

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2001
Peter Politzer
Abstract Noncovalent interactions are predominantly electrostatic in nature. It follows that an effective tool for their investigation and elucidation is the electrostatic potential on the molecular surface. We have shown that a variety of condensed phase macroscopic properties can be expressed quantitatively in terms of certain site-specific and global statistical quantities that characterize the overall pattern of the surface potential. We are now extending this approach to interactions in biological systems. Several applications will be discussed, including initial qualitative studies of dioxins, a series of anticonvulsants and some tetracyclines, the nucleotide bases, and a recent quantitative treatment of the anti-HIV activities of three groups of reverse transcriptase inhibitors. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001 [source]

H-bond donor strength;

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 9 2009
Abraham parameter;
A quantum chemical model is introduced to predict the H-bond donor strength of monofunctional organic compounds from their ground-state electronic properties. The model covers OH, NH, and CH as H-bond donor sites and was calibrated with experimental values for the Abraham H-bond donor strength parameter A using the ab initio and density functional theory levels HF/6-31G** and B3LYP/6-31G**. Starting with the Morokuma analysis of hydrogen bonding, the electrostatic (ES), polarizability (PL), and charge transfer (CT) components were quantified employing local molecular parameters. With hydrogen net atomic charges calculated from both natural population analysis and the ES potential scheme, the ES term turned out to provide only marginal contributions to the Abraham parameter A, except for weak hydrogen bonds associated with acidic CH sites. Accordingly, A is governed by PL and CT contributions. The PL component was characterized through a new measure of the local molecular hardness at hydrogen, ,(H), which in turn was quantified through empirically defined site-specific effective donor and acceptor energies, EEocc and EEvac. The latter parameter was also used to address the CT contribution to A. With an initial training set of 77 compounds, HF/6-31G** yielded a squared correlation coefficient, r2, of 0.91. Essentially identical statistics were achieved for a separate test set of 429 compounds and for the recalibrated model when using all 506 compounds. B3LYP/6-31G** yielded slightly inferior statistics. The discussion includes subset statistics for compounds containing OH, NH, and active CH sites and a nonlinear model extension with slightly improved statistics (r2 = 0.92). © 2008 Wiley Periodicals, Inc. J Comput Chem 2009 [source]

How resonance assists hydrogen bonding interactions: An energy decomposition analysis

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 1 2007
John Frederick Beck
Abstract Block-localized wave function (BLW) method, which is a variant of the ab initio valence bond (VB) theory, was employed to explore the nature of resonance-assisted hydrogen bonds (RAHBs) and to investigate the mechanism of synergistic interplay between , delocalization and hydrogen-bonding interactions. We examined the dimers of formic acid, formamide, 4-pyrimidinone, 2-pyridinone, 2-hydroxpyridine, and 2-hydroxycyclopenta-2,4-dien-1-one. In addition, we studied the interactions in ,-diketone enols with a simplified model, namely the hydrogen bonds of 3-hydroxypropenal with both ethenol and formaldehyde. The intermolecular interaction energies, either with or without the involvement of , resonance, were decomposed into the Hitler-London energy (,EHL), polarization energy (,Epol), charge transfer energy (,ECT), and electron correlation energy (,Ecor) terms. This allows for the examination of the character of hydrogen bonds and the impact of , conjugation on hydrogen bonding interactions. Although it has been proposed that resonance-assisted hydrogen bonds are accompanied with an increasing of covalency character, our analyses showed that the enhanced interactions mostly originate from the classical dipole,dipole (i.e., electrostatic) attraction, as resonance redistributes the electron density and increases the dipole moments in monomers. The covalency of hydrogen bonds, however, changes very little. This disputes the belief that RAHB is primarily covalent in nature. Accordingly, we recommend the term "resonance-assisted binding (RAB)" instead of "resonance-assisted hydrogen bonding (RHAB)" to highlight the electrostatic, which is a long-range effect, rather than the electron transfer nature of the enhanced stabilization in RAHBs. © 2006 Wiley Periodicals, Inc. J Comput Chem 28: 455,466, 2007 [source]

Dispersion and repulsion contributions to the solvation free energy: Comparison of quantum mechanical and classical approaches in the polarizable continuum model

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 15 2006
Carles Curutchet
Abstract We report a systematic comparison of the dispersion and repulsion contributions to the free energy of solvation determined using quantum mechanical self-consistent reaction field (QM-SCRF) and classical methods. In particular, QM-SCRF computations have been performed using the dispersion and repulsion expressions developed in the framework of the integral equation formalism of the polarizable continuum model, whereas classical methods involve both empirical pairwise potential and surface-dependent approaches. Calculations have been performed for a series of aliphatic and aromatic compounds containing prototypical functional groups in four solvents: water, octanol, chloroform, and carbon tetrachloride. The analysis is focused on the dependence of the dispersion and repulsion components on the level of theory used in QM-SCRF computations, the contribution of those terms in different solvents, and the magnitude of the coupling between electrostatic and dispersion,repulsion components. Finally, comparison is made between the dispersion,repulsion contributions obtained from QM-SCRF calculations and the results determined from classical approaches. © 2006 Wiley Periodicals, Inc. J Comput Chem, 2006 [source]

Global physicochemical properties as activity discriminants for the mGluR1 subtype of metabotropic glutamate receptors

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 16 2001
Marta Filizola
Abstract Metabotropic glutamate receptors (mGluRs) are important as candidate therapeutic targets for many neurological disorders. In the present work, the focus has been on the mGluR1 subtype, where agonists have a proconvulsant profile while antagonists exert anticonvulsant activity. Identification of molecular determinants for the inhibition of mGluR1 provides a new avenue for the discovery and development of novel anticonvulsant drugs. Spatial configuration of key groups alone cannot explain activation selectivity at this specific receptor subtype. In fact, all known agonists and antagonists acting at mGluR1 can accommodate the same critical moieties in a similar geometric arrangement that corresponds to the extended conformation of glutamate. Therefore, other factors must account for the differences in activation. This study presents the results of an analysis of a large suite of steric, topological, electrostatic, and thermodynamic molecular properties calculated for a representative set of potent mGluR1 agonists and antagonists. Global steric parameters and the total nonpolar area provide discrimination between the mGluR1 agonists and antagonists considered in the present work. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 2018,2027, 2001 [source]

Electric field controlled electrospray deposition for precise particle pattern and cell pattern formation

AICHE JOURNAL, Issue 10 2010
Jingwei Xie
Abstract Photolithography, soft lithography, and ink jetting have been used for automated micropattern fabrication. However, most of the methods for microfabrication of surface pattern are limited to the investigation of material properties of substrates with high-cost and complex procedures. In the present study, we show a simple (single-step) yet versatile and robust approach to generate biodegradable polymeric particle patterns on a substrate using electrospray deposition through a mask. Various particle patterns including patterned dots, circles, squares, and bands can be easily formed and the features of particle patterns could also be tailored using different masks and electrostatic focusing effects. Furthermore, cell patterns can be achieved on the surface of particle patterns by blocking the areas without particle deposition on the substrate and culturing cells on the substrate. Polymeric particle patterns and cell patterns developed in this study could be used in the high throughput screening of sustained release formulations, cell-based sensing, and drug discovery. In addition to experimental results, an analysis of the associated electric field is used to investigate quantitatively the nature of focusing effect. Scaling analysis is also applied to obtain the dominate terms in electrospray deposition process. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source]

Probing the limits of molecular imprinting: strategies with a template of limited size and functionality

JOURNAL OF MOLECULAR RECOGNITION, Issue 1 2009
Miruna Petcu
Abstract A series of polymers molecularly imprinted with the general anaesthetic propofol were synthesized using both semi- and non-covalent approaches. The polymers were evaluated with respect to template rebinding in both aqueous and organic media. In aqueous media, the observed propofol binding in these polymer systems was largely hydrophobic and non-specific in nature. In non-polar solvents such as hexane, electrostatic (hydrogen bonding) interactions dominate resulting in some selectivity. The implication of these results, in conjunction with those obtained using structures of similar size in other studies, is that propofol, a template possessing limited functionality and size, appears to define the lower limit for template size and degree of functionalization that can be used for the creation of ligand-selective recognition sites in molecularly imprinted polymers. Furthermore, studies with alternative ligands indicate that the steric crowding of a ligand's functionality to the polymer contributes to the extent of polymer,ligand recognition. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Determination of cubic equation of state parameters for pure fluids from first principle solvation calculations

AICHE JOURNAL, Issue 8 2008
Chieh-Ming Hsieh
Abstract A new method for estimation of parameters in cubic equations of state from ab initio solvation calculations is presented. In this method, the temperature-dependent interaction parameter a(T) is determined from the attractive component of solvation free energy, whereas the volume parameter b is assumed to be that of solvation cavity. This method requires only element-specific parameters, i.e., atomic radius and dispersion coefficient, and nine universal parameters for electrostatic and hydrogen-bonding interactions. The equations of state (EOS) parameters so determined allow the description of the complete fluid phase diagram, including the critical point. We have examined this method using the Peng,Robinson EOS for 392 compounds and achieved an accuracy of 43% in vapor pressure, 17% in liquid density, 5.4% in critical temperature, 11% in critical pressure, and 4% in critical volume. This method is, in principle, applicable to any chemical species and is especially useful for those whose experimental data are not available. © 2008 American Institute of Chemical Engineers AIChE J, 2008 [source]

Ketoprofen nanoparticle gels formed by evaporative precipitation into aqueous solution

AICHE JOURNAL, Issue 7 2006
Xiaoxia Chen
Abstract Aqueous nanoparticle gels of a poorly-water soluble drug, ketoprofen, were produced by evaporative precipitation into aqueous solution (EPAS). Liquid droplets of surfactant stabilized ketoprofen containing residual solvent were dispersed in water from 60 to 90°C below the melting point of pure ketoprofen. The carboxylic acid group in ketoprofen dissociates in pure water, providing electrostatic stabilization of the droplets to complement steric stabilization. Stable amorphous ketoprofen particles with a mean size of 135 nm, measured by dynamic light scattering, were formed with only 0.1% w/v poloxamer 407, resulting in an exceptionally high drug-to-surfactant ratio of 10:1. For 5% w/v poloxamer 407, interactions with ketoprofen produced a bluish, transparent gel composed of ,50 nm particles. In 2 min, 98% of the ketoprofen in the gel nanoparticles dissolved. The favorable interactions between the ketoprofen and poloxamer 407, along with the electrostatic and steric stabilization, lead to gelation, which further stabilizes the unusually small particles. The rapidly dissolving wet gels with extremely small particle sizes, one month stability, and relatively low viscosities, are of interest in transdermal and parenteral delivery; furthermore, the gels may be dried for oral delivery. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source]

Vapor,liquid equilibria of mixtures containing alkanes, carbon dioxide, and nitrogen

AICHE JOURNAL, Issue 7 2001
Jeffrey J. Potoff
New force fields for carbon dioxide and nitrogen are introduced that quantitatively reproduce the vapor,liquid equilibria (VLE) of the neat systems and their mixtures with alkanes. In addition to the usual VLE calculations for pure CO2 and N2, calculations of the binary mixtures with propane were used in the force-field development to achieve a good balance between dispersive and electrostatic (quadrupole,quadrupole) interactions. The transferability of the force fields was then assessed from calculations of the VLE for the binary mixtures with n-hexane, the binary mixture of CO2/N2, and the ternary mixture of CO2 /N2/propane. The VLE calculations were carried out using configurational-bias Monte Carlo simulations in either the grand canonical ensemble with histogram,reweighting or in the Gibbs ensemble. [source]

An investigation of the factors controlling the adsorption of protein antigens to anionic PLG microparticles

JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 11 2005
James Chesko
Abstract This work examines physico-chemical properties influencing protein adsorption to anionic PLG microparticles and demonstrates the ability to bind and release vaccine antigens over a range of loads, pH values, and ionic strengths. Poly(lactide-co-glycolide) microparticles were synthesized by a w/o/w emulsification method in the presence of the anionic surfactant DSS (dioctyl sodium sulfosuccinate). Ovalbumin (OVA), carbonic anhydrase (CAN), lysozyme (LYZ), lactic acid dehydrogenase, bovine serum albumin (BSA), an HIV envelope glyocoprotein, and a Neisseria meningitidis B protein were adsorbed to the PLG microparticles, with binding efficiency, initial release and zeta potentials measured. Protein (antigen) binding to PLG microparticles was influenced by both electrostatic interaction and other mechanisms such as van der Waals forces. The protein binding capacity was directly proportional to the available surface area and may have a practical upper limit imposed by the formation of a complete protein monolayer as suggested by AFM images. The protein affinity for the PLG surface depended strongly on the isoelectric point (pI) and electrostatic forces, but also showed contributions from nonCoulombic interactions. Protein antigens were adsorbed on anionic PLG microparticles with varying degrees of efficiency under different conditions such as pH and ionic strength. Observable changes in zeta potentials and morphology suggest the formation of a surface monolayer. Antigen binding and release occur through a combination of electrostatic and van der Waals interactions occurring at the polymer-solution interface. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:2510-2519, 2005 [source]