Motion Of Aqueous Solutions Research Articles

Spectroscopic mapping of the gold complex oligomers (dimer, trimer, tetramer, and pentamer) by excited-state coherent nuclear wavepacket motion in aqueous solutions.

We investigate the excited-state dynamics of the [Au(CN)2-] oligomers following photo-initiated intermolecular Au-Au bond formation by carrying out femtosecond time-resolved absorption and emission measurements at various concentrations (0.080-0.6 mol dm-3) with different photoexcitation wavelengths (290-340 nm). The temporal profiles of the time-resolved absorption signals exhibit clear oscillations arising from the Au-Au stretch coherent wavepacket motion of the excited-state oligomers, which is initiated with the photo-induced Au-Au bond formation. The frequency of the observed oscillation is changed with the change of the concentration, excitation wavelength, and wavelength of the excited-state absorption monitored, reflecting the change in the size of the oligomers detected. Fourier transforms (FTs) of the oscillations provide 2D plots of the FT amplitude against the oscillation frequency versus the detected wavelengths. Because the FT amplitude exhibits a node at the peak wavelength of the absorption of the species that gives rise to the oscillation, the 2D plots enabled us to determine the peak wavelength of the excited-state absorption of the dimer, trimer, tetramer, and pentamer. We also performed femtosecond time-resolved absorption measurements for the 0.3 mol dm-3 solution with 260 nm photoexcitation, which is the condition employed in previous time-resolved X-ray studies (e.g., K. H. Kim et al. Nature, 2015, 518 (7539), 385-389). It was found that various excited-state oligomers, including the dimer, were simultaneously generated under this condition, although the analysis of the previous time-resolved X-ray studies was made by assuming that only the excited-state trimer was generated. The obtained results show that the excited-state dynamics of the trimer claimed based on the time-resolved X-ray data is questionable and that re-analysis and re-examining of its data are necessary.

Plasmon Induced Photocatalysts for Light-Driven Nanomotors.

Micro/nanomachines (MNMs) correspond to human-made devices with motion in aqueous solutions. There are different routes for powering these devices. Light-driven MNMs are gaining increasing attention as fuel-free devices. On the other hand, Plasmonic nanoparticles (NPs) and their photocatalytic activity have shown great potential for photochemistry reactions. Here we review several photocatalyst nanosystems, with a special emphasis in Plasmon induced photocatalytic reactions, as a novel proposal to be explored by the MNMs community in order to extend the light-driven motion of MNMs harnessing the visible and near-infrared (NIR) light spectrum.

Fluorescent self-propelled covalent organic framework as a microsensor for nitro explosive detection

Covalent-organic-frameworks (COFs) are an emerging class of porous materials with fascinating structural features desired for a wide spectrum of applications. However, the potential sensing applications of COFs are hindered by their hydrophobic nature, as well as limited detection speed and sensing sensitivity. We report a fluorescent self-propelled COF as a microsensor for highly efficient nitro explosive detection. Together with MnO2 microsphere catalysts and magnetic Fe3O4 nanoparticles, the fluorescent COF is built in biodegradable polymeric spheres. The resulting microsensors can exhibit magnetically guided autonomous motion in aqueous solution. Fluorescence quenching of the microsensors is observed upon their navigation in solutions with trace amounts of explosives. Continuous mixing induced by the bubble propulsion of microsensors greatly shortens the sensing time to several minutes. We anticipate the presented strategy would provide implications for sensing applications of COFs.

Identifying Water-Anion Correlated Motion in Aqueous Solutions through Van Hove Functions.

Electrolyte solutions are ubiquitous in materials in daily use and in biological systems. However, the understanding of their molecular and ionic dynamics, particularly those of their correlated motions, are elusive despite extensive experimental, theoretical, and numerical studies. Here we report the real-space observations of the molecular/ionic-correlated dynamics of aqueous salt (NaCl, NaBr, and NaI) solutions using the Van Hove functions obtained by high-resolution inelastic X-ray scattering measurement and molecular dynamics simulation. Our results directly depict the distance-dependent dynamics of aqueous salt solutions on the picosecond time scale and identify the changes in the anion-water correlations. This study demonstrates the capability of the real-space Van Hove function analysis to describe the local correlated dynamics in aqueous salt solutions.

Erratum: Local correlated motions in aqueous solution of sodium chloride [Phys. Rev. Materials 3, 065604 (2019)

Received 29 August 2019DOI:https://doi.org/10.1103/PhysRevMaterials.3.109902©2019 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasDiffusionInterparticle interactionsPhysical SystemsCollective dynamicsWaterPropertiesViscosityBiological PhysicsPolymers & Soft MatterCondensed Matter, Materials & Applied Physics

Local correlated motions in aqueous solution of sodium chloride

Real-space motions of molecules and ions in an aqueous solution of sodium chloride are studied with high-resolution inelastic x-ray scattering. We focus on the correlated dynamics of water molecules and salt ions, instead of the instantaneous structure and the rotational and reorientation dynamics that have been studied using scattering techniques and optical spectroscopy, respectively. The real-space analysis in terms of the Van Hove function illustrates the effect of salt ions to slow down the local correlated dynamics of surrounding water in the hydration shells.

Diffracted X-ray Blinking Tracks Single Protein Motions

Single molecule dynamics studies have begun to use quantum probes. Single particle analysis using cryo-transmission electron microscopy has dramatically improved the resolution when studying protein structures and is shifting towards molecular motion observations. X-ray free-electron lasers are also being explored as routes for determining single molecule structures of biological entities. Here, we propose a new X-ray single molecule technology that allows observation of molecular internal motion over long time scales, ranging from milliseconds up to 103 seconds. Our method uses both low-dose monochromatic X-rays and nanocrystal labelling technology. During monochromatic X-ray diffraction experiments, the intensity of X-ray diffraction from moving single nanocrystals appears to blink because of Brownian motion in aqueous solutions. X-ray diffraction spots from moving nanocrystals were observed to cycle in and out of the Bragg condition. Consequently, the internal motions of a protein molecule labelled with nanocrystals could be extracted from the time trajectory using this diffracted X-ray blinking (DXB) approach. Finally, we succeeded in distinguishing the degree of fluctuation motions of an individual acetylcholine-binding protein (AChBP) interacting with acetylcholine (ACh) using a laboratory X-ray source.

Seeing Molecules in Motion in Aqueous Solutions

Hydrogen bonds play critical roles in determining the structural, thermodynamic and dynamical behavior of water and aqueous solutions. In solutions of ions in water, the hydrogen bonded network can be perturbed significantly by the presence of ions. This perturbation, in turn, changes many of the equilibrium and dynamical properties of water in the solutions compared to those in pure water. The network of hydrogen bonds is dynamic in nature. It fluctuates at a very fast rate due to breaking and reformation of hydrogen bonds. In the present article, a brief review is made of some of the recent computer simulation studies to ‘see’ these hydrogen bonded molecules in motion in aqueous solutions. Connections of the simulation results are also made to some of the recent experimental studies on aqueous solutions using the method of time dependent infrared spectroscopy.

Dielectrophoretic behavior of a single cell when manipulated by optoelectronic tweezers: A study based on COMSOL ALE simulations

Abstract Optoelectronic tweezers uses optically induced dielectrophoretic (DEP) force for manipulating cells in aqueous solution, which has shown potential applications in biology and tissue engineering among other possibilities. To effectively design the optoelectronic tweezers (OETs) chip, detailed knowledge about the behavior of cells in response to DEP force in an aqueous layer is needed. In this paper, the trajectories of an SMMC-77721 cell, simulated as a rigid dielectric sphere, in the induced electric field of optical trapping are studied using both an Arbitrary Lagrangian-Eulerian (ALE) method and a particle-tracing method (PTM) available within the COMSOL multiphysics software platform. Because the ALE method involves solving the distorted electric field around the cell and taking a full account of the Maxwell stress tensor (MST), it is expected to provide more accurate predictions about the spherical cell velocity than PTM that involves dipole moment approximation. Our ALE results show noticeably greater cell velocity than that predicted by the classical DEP expression based on dipole moment approximation. The ALE model can help gain new insights for analyzing cell motions in aqueous solution under sophisticated optical spot patterns.

Group analysis of equations of motion of aqueous solutions of polymers

Group analysis of equations of motion of aqueous solutions of polymers

Solvation shell resolved THz spectra of simple aqua ions - distinct distance- and frequency-dependent contributions of solvation shells.

Hydration of ions is a topic of broad relevance in chemistry and biology. Liquid-state terahertz spectroscopy has been demonstrated to be able to detect even small solute-induced changes in the hydrogen bond network dynamics at the solute-water interface. Here, we apply ab initio molecular dynamics simulations to study the solvation of Na(+) and Cl(-) in bulk water in the context of their far-infrared responses. Spatial decomposition schemes for infrared spectra down to the THz regime reveal the importance of both dipolar couplings and correlations in particle motion in these aqueous solutions. The explicit representation of the electronic structure properly captures the solute-solvent polarization effects that are crucial for the interpretation of recent experimental data. This demonstrates that theoretical spectroscopy significantly complements experimental measurements and provides most detailed insights by selectively monitoring the spectral activity due to distinct hydration spheres.

Polarization-based immunoassay in aqueous solution using Au nanoparticle-labeled antibody

Here we describe an ultrasensitive antigen-antibody immunoassay using gold nanoparticles (AuNPs). Polarization microscopy is used to discriminate individual AuNP dimers from isolated single AuNPs by means of their Brownian motion in aqueous solution. The optical anisotropy and rotational diffusion time were measured to provide accurate and robust discrimination. Since the size of a naked antibody is comparable to that of an AuNP, the distance between two AuNPs (inter-dimer distance) is rather large, and therefore the optical anisotropy is seriously degraded. To address this problem, we digested the antibody with the protease pepsin to reduce the distance. Autocorrelation analysis allowed discrimination of the difference in optical anisotropy and rotational diffusion time. Setting an appropriate threshold for the measurement enabled sufficient accuracy in the discrimination.

Three-Dimensional Picometer-Scale Motions in Aqueous Solution Visualized by Diffracted Electron Tracking

Diffracted X-Ray tracking (DXT) method has been developed for obtaining dynamical information at single protein molecule level. The motion of an individual single gold nanocrystal can be observed by this method, which is linked to specific site in the molecule, using a time resolved Laue diffraction technique. This method needs a very strong X-ray source, so we continue to develop a compact instrument with use of the electron beam instead of the X-ray. The Electron Back-Scattered Diffraction (EBSD) is adopted to monitor the Three-dimensional (3D) crystal orientation of the gold nanocrystal. We call this the Diffracted Electron Tracking (DET). For this purpose, we have developed the wet cell using the very thin carbon sealing film for maintained atmospheric pressure from high vacuum surroundings of a scanning electron microscope (SEM), and confirmed that the EBSD pattern (EBSP) can be obtained from the gold nanocrystals through the carbon sealing film of the wet cell. When the gold nanocrystal moved by the motion of labeled molecules, the change of the EBSP is observed. Moreover, we confirmed EBSP can be obtained from 40nm diameter of commercial colloidal gold instead of gold nanocrystal. The colloidal gold was more sensitive and more accurate to detect the motion of linked molecule by reason of its good sphericity and well-regulated particle size. Recently, we developed new configuration of the wet cell that might be able to obtain EBSP without intensive electron damages. This method may contribute to develop as a single molecular technology for fragile molecules by electron irradiation. using this method, we are planning to detect rotational motion of the chaperonin protein in the presence of ATP.

Complexity of polypeptide dynamics: chaos, Brownian motion and elasticity in aqueous solution

Is the dynamics in solution of flexible molecules Brownian and chaotic? And, could it be related to the elastomeric properties of macromolecules? In this framework molecular dynamics simulations and nonlinear theory analysis was used to examine the complexity of polypeptide motions in aqueous solutions. Global indicators of classical chaos and self-organised criticality are investigated and a model for elasticity of rubber proteins is proposed. The glycine-rich polypeptide Ac-Phe-Gly-Gly-Met-Gly-Gly-Gly-Asn-Ala-Gly-NMe, the repeat motif of the rubber protein Abductin, has been modelled in aqueous solution by nearly 30 ns of parallel molecular dynamics simulations and motions carefully analysed using nonlinear theory of complex systems. The most important conformational lengths describing the peptide size as end-to-end distance, gyration radius and the longest interatomic distance have been considered. Moreover, the configurational 3 N-dimensional vector R, whose components are the Cartesian coordinates of peptide atoms, was considered as the global motion descriptor at the molecular scale. The system complexity was analysed in terms of time correlation functions, fast Fourier transforms, attractor dimension, Hurst and Lyapunov critical exponents. The global dynamics of R is Brownian with typical autocorrelation function and Fourier spectrum and Hurst exponent H=1/2 was estimated. In contrast, the conformational lengths undergo anomalous diffusion with antipersistent fractional Brownian motion ( H=1/3) according to the Self-Organised Criticality—SOC—theory. The delay coordinate embedding shows the existence of a low dimensional chaotic attractor with five positive Lyapunov exponents typical of dissipative and chaotic systems. In the framework of the chaotic hypothesis, which assumes that the properties of statistical mechanics can be predicted by treating the systems as chaotic, and the Gaspard's microscopic motion observations, the Brownian dynamics of the peptide appear to be an emergent behaviour due to the chaos of an unstable state. The SOC regime of the polypeptide defines the metastable chaotic region of poor-solvent, observed for macromolecules between ideal θ solvation and phase separation, in agreement to the soft solution and protein rubber state. The proposed soft solution model can be crucial in the expression of the entropic elastic force exhibited by rubber proteins as Elastin and Abductin.

Diffusion in Surfactant Systems Studied by Forced Rayleigh Scattering

The technique of forced Rayleigh scattering (FRS) was used to obtain information on the microstructure of two surfactant systems: i.e. bis(2-ethylhexyl) sulfosuccinate (AOT)/octanol/water and tetradecyldimethylammonium oxide (TDMAO)/tetradecyltrimethylammonium bromide (TTMAB)/hexanol/water. Diffusion coefficients of the dye molecules congo red and methyl red, and of surfactant aggregates labeled with these dye probes, have been determined. In the L 2 (microemulsion) phase of AOT/octanol/water stained with congo red, diffusion coefficients have been found to decrease with increasing water content. In contrast, at the transition from the L 2 to the cubic phase, a continuous increase was observed. Although submicroscopically bicontinuous structures may exist in the microemulsion, the interconnectivity of the rodlike aggregates is not sufficient to enable free diffusion of the water soluble dye over the distance range investigated by FRS. Thus the determined diffusion coefficients reflect the motion of dynamic structural units. The situation is different in the cubic phase: here the long range order makes it possible for the dye molecules to diffuse in the water channels. Compared to unhindered motion in aqueous solution, the diffusion coefficient is reduced to about 20% by steric obstruction effects. The continuous increase of the diffusion coefficient at the phase transition reflects the close structural relationship between the two phases near the phase boundary, whilst there is a remarkable difference in the L 2 phase further away. For the system TDMAO/TTMAB/hexano1/water the transition from the micellar L 1 to the vesicular L α phase with increasing alcohol content has been investigated. The lipophilic dye methyl red is anchored in the surfactant layers, as is verified by polarization microscopy. In the L 1 phase there is a transition from spherical to rodlike micelles. Self-diffusion coefficients of these spheres and rods have been measured, and the results have been compared to theoretical values, calculated by the model of Edwards and Doi for concentrated solutions of rodlike molecules. In the L α phase the vesicles are densely packed, so that the diffusion coefficients originate from the motion of the dye probe within the surfactant bilayers and from an exchange between different bilayers. In complementary experiments, the mobility of the vesicles in an electric field has been probed.

Monte Carlo simulations of the counter ion effect on the conformational equilibrium of the N, N′-diphenyl-guanidinium ion in aqueous solution

Results of calculations for the equilibrium of the syn–syn, anti–syn, and anti–anti conformers of the N, N′-diphenyl-guanidinium ion in aqueous solution are sensitive to whether a counter ion is considered. Relative internal free energies were calculated upon MP2/6-31G*//HF/4-31G energies (second order Mo/ller–Plesset energies obtained when using the 6-31G* basis set at geometries optimized at the Hartree–Fock level and using the 4-31G basis set) and relative solvation free energy terms were obtained by Monte Carlo simulations. Without considering a counter ion only a small fraction of the solute has been predicted to adopt the anti–anti conformation in the solution. When considering acetate and chloride counter ions with salt concentration of 0.11 mol/ℓ at 310 K, mimicking physiological conditions, the counter ion close to the cation stabilizes the anti–anti form significantly. Though there are not local free energy minima for the present systems with close counter ions because of the relatively weak ion–ion interaction due to the largely delocalized total charge and atomic charge alternation in the cation, the constraint for the C(guanidinium)...C(carboxylate) separation of 4.6 Å allows an insight into the arginine...aspartate or glutamate interactions commonly found in peptides. The N–H(guanidinium)...O(carboxylate) hydrogen bonds are not stable due to thermal motion in aqueous solution. The neighboring water molecules, however, move into the space in-between the charged groups and comprise a hydrogen bonded network. Interactions with a chloride counter ion may be significant for the drug delivery process to the receptor site. Close contact between the N, N′-diphenyl guanidinium and a chloride ion is also not favored, though it may occur temporarily and then would favor the anti–anti conformer. Deviation from the relative solvation free energy obtained for the conformational change of the single cation is still some tenths of a kcal/mol with ions separated as much as 12.4 Å. While solvation energetics is affected even at such a separation, solution structure around the ions can be basically characterized without considering the effect of a remote counterpart.

Electrically Driven Polymer Gel Finger Working in the Air

Using ionic polymer gel that demonstrated an electric field-associated bending mo tion in aqueous solutions, an electrically driven polymer gel finger has been constructed. The material used for the finger was a hybrid gel of a cylindrical poly(vinyl alcohol)-poly(sodium acrylate) composite gel (PVA-PAA gel) rod and PVA gel film containing sodium carbonate as a skin. The working gel finger has been designed by equipping the PVA gel film of the hybrid gel with two platinum wires as electrodes. When a dc voltage was applied, the finger bent smoothly toward the positive electrode at a relatively high speed in the air. The bending of the finger occurred through a differential swelling of the PVA-PAA gel in the hybrid gel. A prototype of a microrobot hand with two gel fingers has also been designed. The hand grasped or released a piece of paper in response to electric signals.

Velocity profiles in rectangular channel flow of liquid crystalline polymer solutions

The motion of aqueous solutions of hydroxypropylcellulose in a shallow channel was visualized by means of an electrochemical technique. Isotropic and anisotropic solutions of approximately the same viscosity were used. The velocity profiles of the liquid crystalline solution were found to be qualitatively very different from those of the isotropic one. In particular, anomalous maxima in the velocity near the side walls were observed.

Theory of nonstationary flows of Maxwell fluids in aqueous solutions of polymers

One proves theorems of existence “in the small” for the classical solutions of a periodic initial-boundary-value problem and of the Cauchy problem for the system of integrodifferential equations describing the motion of Maxwell fluids of order N=1, 2, ... and also theorems of existence “in the small” for weak (relative to t) solutions of a periodic intial-boundary-value problem and of the Cauchy problem for the system of differential equations describing the motion of aqueous solutions of polymers.

Molecular dynamics of polyglutamic acid studied by perturbed angular correlation of gamma rays

The technique of perturbed angular correlations of gamma rays has been used to study the motion in aqueous solution of two molecular weight species of polyglutamic acid (M.W.=14 700 and 98 000). The rotational correlation times were determined to be τc(14 700) =14+5−3 ns and τc(98 000) =145+45−30 ns. Using a simple model, the mean molecular radii were found to be R (14 700) =19±2 Å and R (98 000) =32±3 Å. Values were also determined for the quadrupole interaction frequencies and asymmetry parameters.