Electrostatic Interactions In Water Research Articles

On-off-on fluorescence detection for biomolecules by a fluorescent cage through host-guest complexation in water

Detection of nucleoside derivatives has paramount importance because they are the essential biomolecular units for all life. Herein, we report a host-guest approach by using a fluorescent tetraphenylethene-based octacationic cage as host and 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) as guest and fluorescent indicator to form non-fluorescent 1:1:1 host-(endo-exo)guest complex in water. This new host-(endo-exo)guest complex can be successfully used for detecting nucleosides (e.g., ATP and GTP), DNA (e.g., sm-DNA), and antibiotics (e.g., Penicillin G) with off-on fluorescence response via a competitive host-guest exchange with HPTS as exo-guest in water. Furthermore, this on-off-on fluorescent host-guest complex is also used for cell imaging based on ATP concentration in HeLa cells. Therefore, this study not only provides insight into the construction of a supramolecular probe with on-off-on fluorescence via host-guest complexation and exchange in solution, but also realizes a universal method for detecting and monitoring biomolecules.

Electrostatic interactions in water: a nonlocal electrostatic approach

Can we avoid molecular dynamics simulations to estimate the electrostatic interaction between charged objects separated by a nanometric distance in water? To answer this question, we develop a continuous model for the dielectric properties of water based on a functional of the polarisation. A phenomenological Landau–Ginzburg Hamiltonian for the electrostatic energy of water is parameterised to capture the dipolar correlations in the fluid at the nanometric scale. We show that in this framework, the effective interactions of simple objects such as point charges are analytically tractable. In particular, the derivation of the interaction energy between a solvated charge and a surface can be reduced to a system of linear equations of electrostatic potentials and analytically solved. This approach could thus give access in few calculation lines to data that necessitate long and costly simulations.

Synthesis of γ-alumina (Al2O3) nanoparticles and their potential for use as an adsorbent in the removal of methylene blue dye from industrial wastewater.

Non-toxic nanomaterials have gained significant importance recently in the treatment of industrial wastewater that sometimes contains organic dyes such as methylene blue. We report here an easy approach for the synthesis of γ-alumina (Al2O3) nanoparticles via a method that incorporates the use of formamide and the non-ionic surfactant Tween-80. Together, formamide and Tween-80 serve as an effective precipitating agent and a convenient synthetic template, respectively, in directing the growth of the alumina nanoparticles. The morphology and structure of the nanoparticles were investigated by FT-IR, XRD, TGA, SEM, EDX, elemental mapping and TEM methods. The sizes of the nanoparticles are in the 30–50 nm range. The maximum pore size is 4.13 nm and the surface area is 112.9 m2 g−1 as determined by the Brunauer–Emmett–Teller (BET) method. The nanomaterials are excellent adsorbents for the cationic methylene blue dye from aqueous solution. The effects of pH, time, temperature and concentration on the adsorption have been examined and the adsorption capacity increased from 490 to 2210 mg g−1 as the initial concentration was increased from 50 to 400 mg L−1 under the following conditions: pH 9, 10 min reaction time, and 60 °C. The adsorption mechanism is considered to encompass electrostatic interactions in water between the Al2O3 nanoparticles and the cationic methylene blue dye. These readily made nanoparticles may well prove useful in both wastewater treatment and industrial catalysis.

Hydrophobic Surface Enhances Electrostatic Interaction in Water.

A high dielectric constant is one of the peculiar properties of liquid water, indicating that the electrostatic interaction between charged substances is largely reduced in water. We show by molecular dynamics simulation that the dielectric constant of water is decreased near the hydrophobic surface. We further show that the decrease in the dielectric constant is due to both the decreased water density and the reduced water dipole correlation in the direction perpendicular to the surface. We finally demonstrate that electrostatic interaction in water is actually strengthened near the hydrophobic surface.

Biocompatible and colloidally stabilized mPEG-PE/calcium phosphate hybrid nanoparticles loaded with siRNAs targeting tumors.

Calcium phosphate nanoparticles are safe and effective delivery vehicles for small interfering RNA (siRNA), as a result of their excellent biocompatibility. In this work, mPEG-PE (polyethylene glycol-L-α-phosphatidylethanolamine) was synthesized and used to prepare nanoparticles composed of mPEG-PE and calcium phosphate for siRNA delivery. Calcium phosphate and mPEG-PE formed the stable hybrid nanoparticles through self-assembly resulting from electrostatic interaction in water. The average size of the hybrid nanoparticles was approximately 53.2 nm with a negative charge of approximately −16.7 mV, which was confirmed by dynamic light scattering (DLS) measurements. The nanoparticles exhibited excellent stability in serum and could protect siRNA from ribonuclease (RNase) degradation. The cellular internalization of siRNA-loaded nanoparticles was evaluated in SMMC-7721 cells using a laser scanning confocal microscope (CLSM) and flow cytometry. The hybrid nanoparticles could efficiently deliver siRNA to cells compared with free siRNA. Moreover, the in vivo distribution of Cy5-siRNA-loaded hybrid nanoparticles was observed after being injected into tumor-bearing nude mice. The nanoparticles concentrated in the tumor regions through an enhanced permeability and retention (EPR) effect based on the fluorescence intensities of tissue distribution. A safety evaluation of the nanoparticles was performed both in vitro and in vivo demonstrating that the hybrid nanoparticle delivery system had almost no toxicity. These results indicated that the mPEG-PE/CaP hybrid nanoparticles could be a stable, safe and promising siRNA nanocarrier for anticancer therapy.

Amphiphilic pillar[5]arenes: influence of chemical structure on self-assembly morphology and application in gas response and λ-DNA condensation

In order to investigate the influence of chemical structures on self-assembly morphology, six amphiphilic pillar[5]arenes C1, C2, C3, C4, D, and E with different hydrophilic and hydrophobic groups were synthesized. When they were dissolved in water, they all self-assembled into vesicles first. The amine groups on C1 and C2 can reversibly react with CO2 in water, so vesicles self-assembled from them could reversibly transform into micelles by bubbling CO2 and N2. More interestingly, C1, C2, C3, and C4 with the same N-(2-aminoethyl)acetamide units as the hydrophilic groups all further self-assembled into microtubes, on the other hand, E with acetohydrazide units as the hydrophilic groups further self-assembled into nanosheets in water. Amphiphilic pillar[5]arene D could not further self-assemble into any other morphology in water itself, but the carboxylate groups on D can coordinate with silver ions so it could further self-assemble into dendritic structures in water. Dynamic light scattering, transmission electron microscopy, scanning electron microscopy, UV-Vis spectroscopy, and FT-IR spectroscopy were employed to characterize the self-assembly processes of these six amphiphilic pillar[5]arenes and the resultant self-assemblies. The acidified microtubes, which have ammonium ions on their surfaces, could capture negatively charged DNA through electrostatic interactions in water.

Dispersion of Single-Walled Carbon Nanotubes in Water by a Conjugated Surfactant

Stable water dispersions of single wall carbon nanotubes (SWCNTs) have important implications for their applications in biomedical and composites field. In this work, a water-soluble optical brightener bearing benzene ring and sodium sulfonate groups was employed as surfactant for SWCNTs in water. The surfactant molecules were absorbed on graphene nanotube surfaces via π-π interaction, Van Der Waals interaction and electrostatic interactions in water under ultrasonic treatment. The functionalized carbon nanotubes were stably dispersed in water for several months without sedimentation. The carbon nanotubes/organic conjugated molecules nanohybrids have potential application in nanocomposites, biomedical engineering, and photovoltaic devices.

Driving Force for the Association of Hydrophobic Peptides: The Importance of Electrostatic Interactions in Coarse-Grained Water Models

The hydrophobic effect plays a central role in many biological processes, including protein folding and aggregation. The hydrophobic interaction between solutes, such as helical peptides, is believed to be of entropic origin and driven by the increase in the entropy of water due to association. In this work, we examine the association between peptides in water using several coarse-grained (CG) models, such as MARTINI (MAR), polarizable MARTINI (POL), and big multipole water (BMW) models, where four atomistic water molecules are grouped into a single CG unit. All models predict that a pair of helical peptides (Ala20 and Leu20) has favorable association free energy. The BMW model is the only model, however, in which this association is entropy-driven, as has been previously established with atomistic simulations and experiments. The MAR and POL models, where the CG water particles do not have a quadrupole moment, predict an enthalpy-driven association, with a negligible entropy change upon association. Similarly, the association of two rigid cylinders in water is found to be enthalpy-driven when the water is described with the CG model of Shinoda et al. that includes a soft-core nonelectrostatic interaction, while BMW predicts an entropy-driven association. These results emphasize the importance of electrostatic interactions in water for the qualitative features of the thermodynamics of biophysical systems.

An empirical potential based quasicontinuum theory for structural prediction of water

An empirical potential based quasicontinuum theory (EQT) is proposed to predict the structure, concentration, and various potential profiles of water in confined environments. EQT seamlessly unifies the continuum theory given by the Nernst-Planck equation and the atomistic theory governed by interatomic potentials. In particular, the interatomic potentials describing various interactions in water are directly incorporated into the Nernst-Planck theory. We introduce a new empirical potential to compute electrostatic interactions in water. The results from the EQT formalism are compared with molecular dynamics simulations and a good match is observed for channels with widths ranging from 2sigma(ow) to 20sigma(ow), where sigma(ow) is the water-oxygen Lennard-Jones distance parameter. While molecular dynamics can be limited to small length scales, EQT can be used at various length scales to effectively and accurately capture both the interfacial structure and bulk properties of water making it a robust and fast method that can predict properties in widths ranging from the macroscale down to the nanoscale.

Electrostatic potentials of proteins in water: a structured continuum approach

Electrostatic interactions play a crucial role in many biomolecular processes, including molecular recognition and binding. Biomolecular electrostatics is modulated to a large extent by the water surrounding the molecules. Here, we present a novel approach to the computation of electrostatic potentials which allows the inclusion of water structure into the classical theory of continuum electrostatics. Based on our recent purely differential formulation of nonlocal electrostatics [Hildebrandt, et al. (2004) Phys. Rev. Lett., 93, 108104] we have developed a new algorithm for its efficient numerical solution. The key component of this algorithm is a boundary element solver, having the same computational complexity as established boundary element methods for local continuum electrostatics. This allows, for the first time, the computation of electrostatic potentials and interactions of large biomolecular systems immersed in water including effects of the solvent's structure in a continuum description. We illustrate the applicability of our approach with two examples, the enzymes trypsin and acetylcholinesterase. The approach is applicable to all problems requiring precise prediction of electrostatic interactions in water, such as protein-ligand and protein-protein docking, folding and chromatin regulation. Initial results indicate that this approach may shed new light on biomolecular electrostatics and on aspects of molecular recognition that classical local electrostatics cannot reveal.

Selenium-Mediated Micellar Catalyst: An Efficient Enzyme Model for Glutathione Peroxidase-like Catalysis

Mimicking the properties of the selenoenzyme glutathione peroxidase (GPx) has inspired great interest. In this report, a selenium-containing micellar catalyst was successfully constructed by the self-assembly of the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) with benzeneseleninic acid (PhSeO2H) through hydrophobic and electrostatic interaction in water. The selenium-containing micellar catalyst demonstrated substrate specificity for both 3-carboxy-4-nitrobenzenethiol (ArSH, 2) and cumene hydroperoxide (CUOOH), and their complexation was confirmed by UV and fluorescence spectra. More importantly, it demonstrated high GPx activity in two assay systems. It is about 126 times more effective than the well-known GPx mimic ebselen in the classical coupled reductase assay system; however, by using hydrophobic substrate ArSH (2) as an alternative of glutathione (GSH, 1), the micellar catalyst exhibited remarkable 500-fold and 94 500-fold rate enhancements compared with that of PhSeO2H and PhSeSePh.

Polarization of Water near Dipolar Surfaces: A Simple Model for Anomalous Dielectric Behavior

A model for the electrostatic interactions in water in the vicinity of a surface is suggested, which accounts, within the Poisson-Boltzmann mean field approach, for the screening of the charges and for the coupling interactions between neighboring dipoles. When the water molecules near a solid surface are assumed to be organized in icelike layers, the polarization is not a continuous function but exists only at the discrete positions of the water molecules. The particular positions of the water molecules in the icelike structure govern the manner in which the average water dipoles align with each other. On the basis of this model, one could explain the nonmonotonic behavior of the polarization and the electrical potential as well as the anomalous dielectric response of water (the nonproportionality of the polarization and the macroscopic electric field), which were obtained recently via molecular dynamics simulations.

Nonracemic Dopant-Mediated Hierarchical Amplification of Macromolecular Helicity in a Charged Polyacetylene Leading to a Cholesteric Liquid Crystal in Water

Here we show the first example of a helical polyacetylene that forms a lyotropic liquid crystal (LC) through a hierarchical amplification of a macromolecular helicity process in water. The macromolecular helicity with an excess of one helical sense was first induced in the positively charged polyacetylene upon complexation with an extremely small oppositely charged nonracemic dopant through electrostatic interaction in water. Subsequently, the helicity was significantly amplified in the polymer backbone as an almost perfect single-handed helix through self-assembly into supramolecular helical arrays in a lyotropic cholesteric state. The present results will allow the detection of a tiny imbalance in chiral molecules and also provide new approaches for the design of novel water-soluble helical architectures and the construction of new chiral materials in areas such as biotechnology and materials science.

Steady-State and Time-Dependent Fluorescence Quenching Studies of the Binding of Anionic Micelles to Polycation

Soluble complex formation between poly(N-methyl-4-vinylpyridinium chloride) (QPVP) and mixed micelles of dodecyl octa(ethylene glycol) monoether (C12E8) and sodium dodecyl sulfate (SDS), driven by electrostatic interactions in water, was investigated by turbidimetric, quasielastic light scattering, and fluorescence techniques. The polymer−micelle interaction was monitored through quenching of fluorescence of pyrene probes solubilized in C12E8/SDS mixed micelles, the quenching occurring upon binding of the micelles to QPVP. Unlike the case in which fluorescence-labeled polyelectrolytes are employed in conjunction with quencher-carrying micelles to monitor polymer−micelle interactions, QPVP plays a dual role as a polycation to interact with anionic micelles and a quencher for fluorescence of a probe solubilized in the micelle. Thus, hydrophobic contribution from fluorescence labels, an additional complexity in the former case, can be eliminated by employing QPVP, making it possible to monitor polymer−micell...

Characterization of lactate–guanidinium and lactate–lactate interactions in aqueous solution by spectropolarimetry

Spectropolarimetry has been used to quantify the lactate–guanidinium and lactate–lactate equilibrium interactions in aqueous solution. Association constants for the lactate–guanidinium and lactate–lactate formations are 6.11 dm3 mol–1 and 1.12 dm3 mol–1, respectively, in aqueous solution; 6.11 dm3 mol–1 is a high value for an electrostatic interaction in water. This stability, however, cannot account for the extremely strong lactate–protein binding, observed earlier by NMR spectroscopy. The molar rotation coefficients for both the heteroassociation and homoassociation complexes are also calculated.The homoassociative lactate–lactate binding is the first such interaction, whose constant has been determined by spectropolarimetry in aqueous solution.

Design and synthesis of intramolecular ion-pairing cis-bicyclo[4.4.0]decane (cis-decalin) amino acids: conformation-based probes of electrostatic interactions in water

The design strategy and synthesis of cis-bicyclo[4.4.0]decane (cis-decalin) derivatives as conformation-based probes of electrostatic interactions in H 2 O are described. The molecules were designed so that formation of an intramolecular electrostatic interaction occurs in only one of two low-energy conformers; hence, the conformational equilibrium of a given molecule is under control of the electrostatic interaction, which can be determined accurately with NMR studies