scholarly journals Addressing a lattice of rotatable molecular dipoles with the electric field of an STM tip

2021 ◽  
Vol 23 (8) ◽  
pp. 4874-4881
Author(s):  
Timo Frauhammer ◽  
Lukas Gerhard ◽  
Kevin Edelmann ◽  
Marcin Lindner ◽  
Michal Valášek ◽  
...  
Keyword(s):  
Electric Field ◽  
Electrostatic Interactions ◽  
Head Groups

Electrostatic interactions within a lattice of freestanding rotatable head groups mounted on tripodal molecular platforms.

scholarly journals Separation of water–ethanol solutions with carbon nanotubes and electric fields

2016 ◽  
Vol 18 (48) ◽  
pp. 33310-33319 ◽  
Author(s):  
Winarto Winarto ◽  
Daisuke Takaiwa ◽  
Eiji Yamamoto ◽  
Kenji Yasuoka
Keyword(s):  
Carbon Nanotubes ◽  
Electric Field ◽  
Electric Fields ◽  
Electrostatic Interactions ◽  
Water Molecules ◽  
Ordered Structure

Under an electric field, water prefers to fill CNTs over ethanol, and electrostatic interactions within the ordered structure of the water molecules determine the separation effects.

Physical and chemical model of ion stability and movement within the dynamic and voltage-gated STM tip–surface tunneling junction

2017 ◽  
Vol 204 ◽  
pp. 159-172 ◽  
Author(s):  
Brandon E. Hirsch ◽  
Kevin P. McDonald ◽  
Steven L. Tait ◽  
Amar H. Flood
Keyword(s):  
Electric Field ◽  
Experimental Evidence ◽  
Electrostatic Interactions ◽  
Scanning Tunneling ◽  
Chemical Transformations ◽  
Tunneling Microscopy ◽  
Mobility Of Ions ◽  
Negative Surface ◽  
Ion Stability ◽  
And Migration

The interaction and mobility of ions in complex systems are fundamental to processes throughout chemistry, biology, and physics. However, nanoscale characterization of ion stability and migration remains poorly understood. Here, we examine ion movements to and from physisorbed molecular receptors at solution–graphite interfaces by developing a theoretical model alongside experimental scanning tunneling microscopy (STM) results. The model includes van der Waals forces and electrostatic interactions originating from the surface, tip, and physisorbed receptors, as well as a tip–surface electric field arising from the STM bias voltage (Vb). Our model reveals how both the electric field and tip–surface distance, dtip, can influence anion stability at the receptor binding sites on the surface or at the STM tip, as well as the size of the barrier for anion transitions between those locations. These predictions agree well with prior and new STM results from the interactions of anions with aryl-triazole receptors that order into functional monolayers on graphite. Scanning produces clear resolution at large magnitude negative surface biases (−0.8 V) while resolution degrades at small negative surface biases (−0.4 V). The loss in resolution arises from frequent tip retractions assigned to anion migration within the tip–surface tunneling region. This experimental evidence in combination with support from the model demonstrates a local voltage gating of anions with the STM tip inside physisorbed receptors. This generalized model and experimental evidence may help to provide a basis to understand the nanoscale details of related chemical transformations and their underlying thermodynamic and kinetic preferences.

scholarly journals Transferable Gaussian Attractive Potentials for Organic/oxide Interfaces

2021 ◽  
Author(s):  
Jérôme Rey ◽  
Sarah Blanck ◽  
Paul Clabaut ◽  
Sophie Loehlé ◽  
Stephan Steinmann ◽  
...  
Keyword(s):  
Electrostatic Interactions ◽  
Organic Molecules ◽  
Surface Films ◽  
Oxide Interfaces ◽  
Gaussian Potential ◽  
Adsorbed Films ◽  
Head Groups ◽  
Strong Structuration ◽  
The Common ◽  
Dynamics Simulations

Organic/oxide interfaces play an important role in many areas of chemistry, and in particular for lubrication and corrosion. Molecular dynamics simulations are the method of choice for providing complementary insight to experiments. However, the force fields used to simulate the interaction between molecules and oxide surfaces tend to capture only weak physisorption interactions, discarding the stabilizing Lewis acid/base interactions. We here propose an improvement of the usual molecular mechanics description (based on Lennard-Jones and electrostatic interactions) by addition of an attractive Gaussian potential between reactive sites of the surface and heteroatoms of adsorbed organic molecules, leading to the GLJ potential. The interactions of four oxygenated and four amine molecules with the typical and widespread hematite and γ-alumina surfaces are investigated. The total RMSD for all probed molecules decreases from 29.2 to 5.7 kcal/mol, and the corresponding percentage from 107.4 to 22.6% over hematite, while on γ-alumina the RMSD decreases from 21.5 to 7.6 kcal/mol, despite using a single parameter for all five chemically inequivalent surface aluminum atoms. Applying GLJ to the simulation of n-octadecanamine and N-tetradecyldiethanolamine adsorbed films on hematite and alumina respectively demonstrates that mobility of the surfactants is overestimated by the common LJ potential, while GLJ shows a strong structuration and slow dynamics of the surface films, as could be expected from the first-principles adsorption energies for model head-groups.

scholarly journals A Preorganized Electric Field Leads to Minimal Geometrical Reorientation in the Catalytic Reaction of Ketosteroid Isomerase

2020 ◽  
Author(s):  
Yufan Wu ◽  
Stephen Fried ◽  
Steven Boxer
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Ground State ◽  
Active Site ◽  
Electrostatic Interactions ◽  
Stark Effect ◽  
Structural Changes ◽  
Enzymatic Catalysis ◽  
Ketosteroid Isomerase ◽  
Computational Enzyme Design

<div><p>Electrostatic interactions play a pivotal role in enzymatic catalysis and are increasingly modeled explicitly in computational enzyme design; nevertheless, they are challenging to measure experimentally. Using vibrational Stark effect (VSE) spectroscopy, we have measured electric fields inside the active site of the enzyme ketosteroid isomerase (KSI). These studies have shown that these fields can be unusually large, but it has been unclear to what extent they specifically stabilize the transition state (TS) relative to a ground state (GS). In the following, we use crystallography and computational modeling to show that KSI’s intrinsic electric field is nearly perfectly oriented to stabilize the geometry of its reaction’s TS. Moreover, we find that this electric field adjusts the orientation of its substrate in the ground state so that the substrate needs to only undergo minimal structural changes upon activation to its TS. This work provides evidence that the active site electric field in KSI is preorganized to facilitate catalysis and provides a template for how electrostatic preorganization can be measured in enzymatic systems. <br></p></div>

scholarly journals Different Head Group Dependence on The Lipid Thermodynamic Property of Myelin Basic Protein in the Lipid Monolayer

2021 ◽  
Author(s):  
Lei Zhang ◽  
Ming Zhang ◽  
Runguang Sun
Keyword(s):  
Myelin Basic Protein ◽  
Electrostatic Interactions ◽  
Basic Protein ◽  
Second Virial Coefficient ◽  
Virial Equation ◽  
Lipid Monolayer ◽  
Statistical Thermodynamic ◽  
Head Group ◽  
Myelin Lipid ◽  
Head Groups

Abstract The interaction between the role of 18.5 KDa myelin basic protein (MBP) isoform and phospholipids has been thought to maintain the stability and compactness of the myelin sheath structure. In this study, we describe the statistical thermodynamic theory of different concentrations’ effects on MBP in the major myelin lipid (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE)，and 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-L-serine (POPS)) monolayers at the air/subphase interface via Langmuir-Blodgett (LB) technique. A simple statistical mechanical theory is established that predicts the interaction between proteins and phosphate head groups at low surface pressures and the second virial coefficient dependences for the PC, PE, and PS head groups are illustrated. In addition, the surface pressure(π)-mean molecular area(mma) curves were also analyzed using two-dimensional virial equation of state (2D-VES). The positively charged showed that MBP may integrate into different lipid monolayers via hydrophobic and electrostatic interactions, which was found to be consistent with AFM observations of domain and aggregate structures as well as with changes in the surface morphology induced by MBP. These analyses pertaining to membrane structure will provide better insight into membrane modeling systems, especially the interaction between membrane molecules.

scholarly journals Fluorinated Surfactant Adsorption on Mineral Surfaces: Implications for PFAS Fate and Transport in the Environment

Surfaces ◽  
2020 ◽  
Vol 3 (4) ◽  
pp. 516-566 ◽  
Author(s):  
Anthony V. Alves ◽  
Marina Tsianou ◽  
Paschalis Alexandridis
Keyword(s):  
Electrostatic Interactions ◽  
Hydrophobic Interactions ◽  
Mineral Surfaces ◽  
Product Packaging ◽  
Fluorinated Surfactants ◽  
Fluorinated Surfactant ◽  
Kinetics Of Adsorption ◽  
Head Groups ◽  
Underlying Mechanisms ◽  
Kinetics Of

Fluorinated surfactants, which fall under the class of per- and polyfluoroalkyl substances (PFAS), are amphiphilic molecules that comprise hydrophobic fluorocarbon chains and hydrophilic head-groups. Fluorinated surfactants have been utilized in many applications, e.g., fire-fighting foams, paints, household/kitchenware items, product packaging, and fabrics. These compounds then made their way into the environment, and have been detected in soil, fresh water, and seawater. From there, they can enter human bodies. Fluorinated surfactants are persistent in water and soil environments, and their adsorption onto mineral surfaces contributes to this persistence. This review examines how fluorinated surfactants adsorb onto mineral surfaces, by analyzing the thermodynamics and kinetics of adsorption, and the underlying mechanisms. Adsorption of fluorinated surfactants onto mineral surfaces can be explained by electrostatic interactions, hydrophobic interactions, hydrogen bonding, and ligand and ion exchange. The aqueous pH, varying salt or humic acid concentrations, and the surfactant chemistry can influence the adsorption of fluorinated surfactants onto mineral surfaces. Further research is needed on fluorinated surfactant adsorbent materials to treat drinking water, and on strategies that can modulate the fate of these compounds in specific environmental locations.

Quantification of Electric Field inside the Protein Active Sites and Fullerenes

2021 ◽  
Author(s):  
Ambuj Dhakad ◽  
Subhrakant Jena ◽  
Dipak Kumar Sahoo ◽  
Himansu S. Biswal
Keyword(s):  
Electric Field ◽  
Electrostatic Field ◽  
Electrostatic Interactions ◽  
Active Sites ◽  
Biological Functions ◽  
Simple Method ◽  
Protein Active Sites

While electrostatic interactions are exceedingly accountable for biological functions, no simple method exists to directly estimate or measure the electrostatic field in the protein active sites. The electrostatic field inside...

Dynamics and Transport of Molecules in Polymer and Colloidal-Rod Networks

2007 ◽  
Vol 1060 ◽  
Author(s):  
Kyongok Kang
Keyword(s):  
Electric Field ◽  
Electrostatic Interactions ◽  
Polymer Network ◽  
Mesh Size ◽  
Limited Range ◽  
Correlation Spectroscopy ◽  
Relaxation Dynamics ◽  
Screening Length ◽  
Cholesteric Phase ◽  
Hydrodynamic Screening

ABSTRACTRe-orientational dynamics of liquid crystal molecules in a polymer network subjected to an electric field is studied by means of light diffraction [1]. When the optical pitch of the electric-field induced cholesteric phase is small compared to the optical wavelength of light, dynamic light scattering (DLS) can be performed to extract the relaxation dynamics of the chiral nematic molecules in the presence of the polymer network. Intriguingly, the reactive mesogenic type of polymer network exhibits a confinement effect, which can be probed within the limited range of scattering angles that comply with the structural correlation length in the system [2].Diffusive mass transport of molecules through a rod network can be studied via fluorescence correlation spectroscopy (FCS) and DLS. Long time self-diffusion of tracer spheres (silica and proteins) in isotropic and nematic colloidal-rod networks (fd-viruses) is systematically studied for various tracer-sphere sizes as compared to the mesh size of the network [3]. In addition, by varying the salt concentration, the relative contribution of electrostatic interactions can be varied. A theory is developed where the diffusion coefficient is expressed in terms of the hydrodynamic screening length of the highly entangled rod-network. The hydrodynamic screening length of rod networks is extracted from diffusion data as a function of the rod concentration both for isotropic and nematic networks [4-5].

ELECTROSTATIC INTERACTIONS FOR PARTICLE ARRAYS IN ELECTRORHEOLOGICAL FLUIDS II: MEASUREMENTS

1994 ◽  
Vol 08 (20n21) ◽  
pp. 2895-2902 ◽  
Author(s):  
YING CHEN ◽  
H. CONRAD
Keyword(s):  
Shear Modulus ◽  
Electric Field ◽  
Shear Strain ◽  
Enhancement Factor ◽  
Shear Force ◽  
Electrostatic Interactions ◽  
Silicone Oil ◽  
Electrorheological Fluids ◽  
Proportionality Constant ◽  
Er Fluids

The force required to shear one-, two- and three-chain clusters of 230 µm dia. glass beads in silicone oil was measured. In each case the shear force was proportional to the shear strain, the proportionality constant increasing with electric field and number n of chains in the cluster. The derived shear modulus G also increased with n. An extrapolation of the present results suggests that a cluster of 4–5 chains would give the stress enhancement factor of 10–20 observed for real ER fluids.

scholarly journals Many-body effects and simulations of potassium channels

2009 ◽  
Vol 465 (2106) ◽  
pp. 1701-1716 ◽  
Author(s):  
Christopher J. Illingworth ◽  
Carmen Domene
Keyword(s):  
Potassium Channels ◽  
Electric Field ◽  
Electrostatic Interactions ◽  
Force Fields ◽  
Interatomic Interaction ◽  
Additive Interaction ◽  
Interaction Potentials ◽  
Polarization Effects ◽  
Normal Shape ◽  
Classical Computer

The electronic polarizability of an ion or a molecule is a measure of the relative tendency of its electron cloud to be distorted from its normal shape by an electric field. On the molecular scale, in a condensed phase, any species sits in an electric field due to its neighbours, and the resulting polarization is an important contribution to the total interaction energy. Electrostatic interactions are crucial for determining the majority of chemical–physical properties of the system and electronic polarization is a fundamental component of these interactions. Thus, polarization effects should be taken into account if accurate descriptions are desired. In classical computer simulations, the forces required to drive the system are typically based on interatomic interaction potentials derived in part from electronic structure calculations or from experimental data. Owing to the difficulties in including polarization effects in classical force fields, most of them are based just on pairwise additive interaction potentials. At present, major efforts are underway to develop polarizable interaction potentials for biomolecular simulations. In this review, various ways of introducing explicit polarizability into biomolecular models and force fields are reviewed, and the progress that might be achieved in applying such methods to study potassium channels is described.

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