Translational Motion Of Molecules Research Articles

A Pyrrole-Bridged Bis(oxa[5]helicene)-Based Molecular Semiconductor for Efficient and Durable Perovskite Solar Cells: Microscopic Insights

Exotic organic semiconductors based on helicenes are attractive because of their peculiar topology-related optoelectronic properties and good solution-processability. We herein construct pyrrole-bridged bis(oxa[5]helicene) and further employ it as the π-linker of a solution-processable molecular semiconductor (DOP-OMeDPA) with improved hole mobility and glass transition temperature compared with its oxa[5]helicene counterpart. A solution-processed, doped semiconducting composite of DOP-OMeDPA presents high conductivity and slow interfacial charge recombination in perovskite solar cells, enabling the fabrication of thermostable devices with 21.3% efficiency. The DOP-OMeDPA-based thin film exhibits excellent morphology stability at 60 °C and remarkably attenuates the thermal decomposition of perovskite. Molecular dynamics modeling uncovers the microscopic origin of glass transition, that is, the torsional vibration of electron-donor for pristine materials, compared with the translational motion of molecules in doped ones.

The Shape of (Intracellular) Water

The translational motion of molecules in cells deviates from what is observed in dilute solutions. Theoretical models provide explanations for this effect but with predictions that drastically depend on the nanoscale organization assumed for macromolecular crowding agents. A conclusive test of the nature of the translational motion in cells is missing owing to the lack of techniques capable of probing crowding with the required temporal and spatial resolution. Here we show that fluorescence-fluctuation analysis of raster scans at variable timescales can provide this information. By using green fluorescent proteins, we measure protein translational motion at the unprecedented timescale of 1 μs, unveiling unobstructed Brownian motion from 25 to 100 nm in the cell cytoplasm, and partially suppressed diffusion above 100 nm. By using experiments on model systems we attribute this effect to the presence of relatively immobile structures rather than to diffusing crowding agents. In a complementary way, these results can be used to infer about the intracellular organization of bulk water. We discuss the implications of our results for intracellular processes in general, also in light of the recent advancements in the field with the discovery, for instance, of membrane-less organelles as possible key regulators of intracellular biochemistry.

MD-modeling of the intermediate scattering function for argon-like liquids and water

The spectral densities of the intermediate scattering function (ISF) for argon-like liquids and water are studied with the help of computer simulations. In the case of water, only translational motions for the centers of mass of molecules are taken into account. The applicability region for the diffusion approximation (DA) for the ISF is investigated. It is shown that the upper limit kD(T) of DA for wave vectors k→ depends on temperature and satisfies the inequality: kD(T) < < 1/a, where a is the interparticle spacing. Analogously, the upper limit ωDk→T for frequencies depends on wave vector and temperature and it is surprisingly small: ωDk→T~γDk→2, where γDk→2 is the half-width for the Lorentzian: γDk→2~Dsk→2, and Ds is the self-diffusion coefficient. The possibility to estimate the ratio Dc/Ds, where Dc is the collective part of the self-diffusion coefficient, is discussed. It has been shown that k→-dependencies of the half-width γDk→2 for water and argon spectra are similar to each other. It means that the behavior of γDk→2 is mainly determined by translational motion of molecules.

Effect of the collective motions of molecules inside a condensed phase on fluctuations in the density of small bodies

An approach to calculating the effects of fluctuations in density that considers the collective motions of molecules in small condensed phases (e.g., droplets, microcrystals, adsorption at microcrystal faces) is proposed. Statistical sums of the vibrational, rotational, and translational motions of molecules are of a collective character expressed in the dependences of these statistical sums on the local configurations of neighboring molecules. This changes their individual contributions to the free energy and modifies fluctuations in density in the inner homogeneous regions of small bodies. Interactions between nearest neighbors are considered in a quasi-chemical approximation that reflects the effects of short-range direct correlations. Expressions for isotherms relating the densities of mixture components to the chemical potentials in a thermostat are obtained, along with equations for pair distribution functions.

Кінематична зсувна в'язкість води, водних розчинів електролітів та етанолу

The nature of the kinematic shear viscosity in associated (water and aqueous solutions of electrolytes) and strongly associated (alcohols) liquids has been studied. The behavior of the kinematic shear viscosity is shown to be governed by orientational correlations and the translational motion of molecules, which is characteristic of argon. The former mechanism dominates in the supercooled area and in normal states close to the triple point. The latter one is responsible for the viscosity at higher temperatures. The characteristic temperature tH separating those areas is found to be close to the triple point in the case of water and electrolyte aqueous solutions, and to the critical point in the case of ethanol. The agreement with experimental data is quite satisfactory.

Probing short-range protein Brownian motion in the cytoplasm of living cells.

The translational motion of molecules in cells deviates from what is observed in dilute solutions. Theoretical models provide explanations for this effect but with predictions that drastically depend on the nanoscale organization assumed for macromolecular crowding agents. A conclusive test of the nature of the translational motion in cells is missing owing to the lack of techniques capable of probing crowding with the required temporal and spatial resolution. Here we show that fluorescence-fluctuation analysis of raster scans at variable timescales can provide this information. By using green fluorescent proteins in cells, we measure protein motion at the unprecedented timescale of 1 μs, unveiling unobstructed Brownian motion from 25 to 100 nm, and partially suppressed diffusion above 100 nm. Furthermore, experiments on model systems attribute this effect to the presence of relatively immobile structures rather than to diffusing crowding agents. We discuss the implications of these results for intracellular processes.

Molecular dynamics simulation of the nematic liquid crystal phase in the presence of an intense magnetic field

The influence of an intense external field on the dynamics of the nematic liquid crystal phase is investigated using a molecular dynamics simulation for the Gay-Berne nematogen under isobaric-isothermal conditions. The molecular dynamics as a function of the second-rank orientational order parameter P<2> for a system consisting of a nematic liquid crystal in the presence of an intense magnetic field is compared with that of a similar system without the field. The translational motion of molecules is determined as a function of the translational diffusion coefficient tensor and the anisotropy and compared with the values predicted theoretically. The rotational dynamics of molecules is analyzed using the first- and the second-rank orientational time correlation functions. The translational diffusion coefficient parallel with respect to the director is constrained by the intense field, although the perpendicular one is decreased as the P<2> is increased, just as it is in the system without the field. However, no essential effect of the strong magnetic field is observed in the rotational molecular dynamics. Further, the rotational diffusion coefficient parallel with respect to the director obtained from the first-rank orientational time correlation function in the simulation is qualitatively in agreement with that in the real nematic liquid crystalline molecules. The P<2> dependence of the rotational diffusion coefficient for the system with the intense magnetic field shows a tendency similar to that for the system without the field.

Transient CARS spectroscopy of rotational transitions in H2: the statistical dependences of the Doppler and collision dephasing

The S0(0) and S0(1) rotational transitions in the H2 molecules are studied by the method of transient CARS spectroscopy at temperatures 296 and 80 K in a broad range of gas densities — from the density at which Doppler dephasing occurs to the density corresponding to collision dephasing. The slowest decay of the responses of the scattered probe pulse at the molar gas density ∼0.2 amagat corresponds to the Dicke line narrowing. It is shown that the dephasing of the S0(1) transition in the natural H2 mixture leads to a substantial discrepancy between the experimental results and the model of statistically independent perturbations of the rotational and translational motion of molecules at densities within a few tenths of amagat. This discrepancy becomes quite significant at liquid nitrogen temperature. At the same time, the dephasing of the S0(0) transition better corresponds to this model, as well as the dephasing of the S0(1) transition in the buffer He gas. The deviation from the model of statistically independent perturbations is described by introducing the correlation parameter. It is assumed that the features of the dephasing of the S0(1) transition observed in the natural H2 mixture are mainly caused by resonance dephasing collisions.

Spontaneous Polarization of a Gas of Two-Level Molecules and the Gibbs Quasi-Energy Distribution

We study the possibility of spontaneous formation of a polarization structure in a thermodynamically equilibrium gas of dipolarly interacting two-level molecules. Using the Maxwell-Bloch equations within the framework of the mean-field theory, we find that the antiferroelectric phase transition in a gas with a weak relaxation of the polarization is always a second-order transition. It is shown that if relaxation is neglected, then in the quasi-classical consideration of the translational motion of molecules in the polarization wave, the energy levels of a separate molecule coincide with its quasi-energies that are well known in quantum optics. Thus, to study the statistical properties of the antiferroelectric phase, we apply the generalized Gibbs distribution over quasi-energy states of the molecules. As a result, we determine the characteristic features and the possible parameters of the antiferroelectric state of a gas. In particular, it is found that, owing to the Doppler resonance of part of the molecules with the polarization wave, the properties of the gas antiferroelectrics behind the phase-transition point may radically differ from the properties of the conventional ferroelectrics in the Ginzburg-Landau theory. We also analyze the influence of polarization fluctuations for the case of a ferroelectric transition in a gas.

Helical motions of aliphatic chains in molecular crystals the incoherent quasi-elastic neutron scattering law

The incoherent quasi-elastic neutron scattering (IQNS) law for the restricted diffusive motion of a particle along a spiral (helical motion) is derived in order to model correlated rotational and translational motions of molecules in the dynamically disordered phases of organic molecular crystals. In addition, we present a unified formulation to calculate the scattering laws for restricted translational diffusion, uniaxial restricted rotational diffusion and uncorrelated restricted translations and rotations. We therefore discuss the various experimental geometries needed to analyse in detail these motions. Spectra are simulated and analysed on the basis of IQNS experiments performed to study the dynamics of n-nonadecane molecules in various crystalline environments. We also discuss the existence of correlated and uncorrelated rotational and translational motions in the ‘rotator’ phase of pure n-nonadecane samples.

Dielectric spectroscopy and molecular dynamics of CH3Cl/CCl4liquid solutions

Power absorption coefficient has been measured for CH3Cl/CCl4 solutions as a function of concentration and temperature over the 0-THz frequency range. The refractive index has also been measured for frequencies up to 400 GHz. The spectroscopic results are well described by the confined rotator model and the temperature and concentration dependence of the derived parameters is typical of polar solutes in non-polar solvents. The most interesting feature of the experimental results is the existence of some excess absorption over that predicted by the model. This additional band is situated in the millimetre wavelength range and intensifies with increasing fraction of non-polar molecules. It is postulated that this additional absorption is due to induced dipoles generated by translational motion of molecules.

On the Law of Equipartition for Translational Motion of Excited Molecules in Equilibrium with Thermal Radiation

Abstract Einstein’s radiation theory consists of two parts: the derivation of Planck's radiation law from a physical mechanism of absorption and emission of radiation by excited molecules that are in thermal equilibrium with the radiation field and a demonstration of the validity of the law of equipartition of energy for the translational motion of the molecules. Several incongruities are observed: Einstein could not have legitimately substituted back into his dynamical equilibrium condition, valid at any finite temperature, a limiting condition between the coefficients of absorption and stimulated emission that he obtained in the high temperature limit. His justification of the law of equipartition involves, on the one hand, treating the motion of the excited molecule as brownian motion while, on the other hand, employing special relativity to obtain an expression for the diffusion coefficient. In the former the velocity of the molecule is a stochastic variable while in the latter it is a uniform velocity. Hence equipartition does not hold for the translational motion.

Semiclassical representation method in statistical physics of interacting molecules

Abstract The description of the method of transition from the quantum-statistical theory of interacting subsystems to a semi-classical one is given, using interacting molecules as an example. The kinetic equation for the distribution function of the classical subsystem, i.e., a translational motion of molecules which interacts with a quantum subsystem, namely, the internal motions of the molecules, is derived. The physical interpretation of the classical intermolecular potential and the origin of irreversibility of translational motion of molecules are discussed.

The translational motion of molecules at short times: a study using molecular dynamic simulations and the model of itinerant oscillation

Abstract A newly developed version of the itinerant oscillator model for molecular translation in fluids is evaluated by means of data obtained from a molecular dynamics simulation of the fluid using an atom-atom potential. The data consists of: 1. Velocity ( v ) and force ( F ) autocorrelation functions. 2. Mean square displacements of molecular centres of mass and even moments thereof. 3. Autocorrelation of v2n and F2n (as a means of investigating the deviation of v and F from Gaussian behaviour). 4. The van Hove function Gs(R,t). The latter is matched against incoherent neutron scattering data observed by Dasannacharya and Rao [13] for liquid argon. The theoretical picture is realistic except that the neglect of cross-correlations and rotation-translation coupling is clearly affecting the agreement between the simulated and calculated mean square displacements. The self van Hove function Gs( R ,t) exhibits complicated non-Gaussian behaviour which will be difficult to follow using the theory of Brownian motion.

Ordered and disordered states of DOBHOP

Crystalline and liquid crystalline phases as well as the fast cooled state of the smectic liquid crystal compound p-n-decyloxybenzoic acid -p-n-hexyloxyphenyl ester (DOBHOP) are studied. On quenching from the liquid crystal phase a glassy state freezes out, exhibiting a structure similar to a smectic phase as measured by neutron diffraction. Raman spectra of the ordered and disordered states show that the change of the density of states of intermolecular vibration in a crystal-liquid crystal phase transition is mainly determined by the change of the structure, though the translational motion of molecules and anharmonicity also play a role. [Russian Text Ignored].

Self-diffusion and molecular motion in nematic and smectic liquid crystals

A molecular-dynamic simulation of nematic and smectic liquid crystals yields information about the characteristics of rotational and translational motion of molecules in these mesophases.

Kinetics of molecular motions in liquids and its correlation with kinetics of radical liquid–phase reactions

AbstractStable nitroxide radicals and ESR techniques have been used to investigate rotational and translational motions of molecules in the liquid state. It is found that for hydrocarbons and molecules with low polarity the rotational frequencies are about an order of magnitude faster than translational encounters. Arrhenius parameters are reported for the rates of both types of processes. A scheme is given for the relation of these motions to radical recombination in solution and also to reactions requiring activation energy. The consequences of this scheme are examined.Such important properties as hydrodynamic fluidity, thermal conductivity, processes of extraction and solution, occurring in the liquid phase as well as at the interface are determined by mobility of particles in the liquid. The problem of molecular mobility is of essential significance for the kinetics of chemical and chemico‐physical processes in the liquid phase.Application of both ESR techniques and stable nitroxide radicals for kinetic studies of molecular motions in liquids and the correlation between molecular mobility and the kinetic parameters of liquid‐phase radical reactions have been studied in the present paper.

The flow of compressible gas

The relations are derived between velocity, density and pressure in a flowing compressible gas on the basis of fundamental mechanical principles of the conservation of matter, of momentum and of energy. The results are checked by application to test data on the discharge of superheated steam, and are found to be in excellent agreement throughout the range of pressure ratios from 1.00 to 0.20. It is shown that below certain (critical) pressure ratio the polyatomic gas behaves as monatomic one, indicating that energy transfer ceased between rotational and translational motions of molecules. This phenomenon occurs apparently only in accelerating flow, and the change from acceleration to deceleration liberates the temporarily unavailable energy of rotation, and precipitates the sudden increase of pressure, known as “Compression Shock” in aerodynamics.

And new tea seed oil

The relations are derived between velocity, density and pressure in a flowing compressible gas on the basis of fundamental mechanical principles of the conservation of matter, of momentum and of energy. The results are checked by application to test data on the discharge of superheated steam, and are found to be in excellent agreement throughout the range of pressure ratios from 1.00 to 0.20. It is shown that below certain (critical) pressure ratio the polyatomic gas behaves as monatomic one, indicating that energy transfer ceased between rotational and translational motions of molecules. This phenomenon occurs apparently only in accelerating flow, and the change from acceleration to deceleration liberates the temporarily unavailable energy of rotation, and precipitates the sudden increase of pressure, known as “Compression Shock” in aerodynamics.