One-dimensional displacement of active matter on curved substrates

We analytically find the diffusion of overdamped active Brownian particles (ABPs) constrained to move along curved one-dimensional channels. The autonomous motion of these particles is achieved by a projection of their internal propulsion force along the channels' long section. In particular, the diffusion of ABPs moving on one-dimensional channels with a form of a circle, an ellipse, and a limacon of second order is analysed. To characterise the effect of substrate's geometry and self-propulsion on their diffusion, analytical expressions for the ABPs short- and long-time variances, as well as their steady angular probability density functions are offered. Curvature effects are found to reduce the time an ABP reaches its steady state. Our theoretical results are validated using Brownian dynamics simulations. This model may be relevant for experiments dealing with catalytic driven systems, bacteria, and tumour cell dispersion in one-dimensional channels.     

HTMoL: full-stack solution for remote access,visualization, and analysis of molecular dynamics trajectory data

Research on biology has seen significant advances with the use of molecular dynamics (MD) simulations. The MD methodology enables explanation and discovery of molecular mechanisms in a wide range of natural processes and biological systems. The need to readily share the ever-increasing amount of MD data has been hindered by the lack of specialized bioinformatic tools. The difficulty lies in the efficient management of the data, i.e., in sending and processing 3D information for its visualization. In this work, we present HTMoL, a plug-in-free, secure GPU-accelerated web application specifically designed to stream and visualize MD trajectory data on a web browser. Now, individual research labs can publish MD data on the Internet, or use HTMoL to profoundly improve scientific reports by including supplemental MD data in a journal publication. HTMoL can also be used as a visualization interface to access MD trajectories generated on a high-performance computer center directly. Furthermore, the HTMoL architecture can be leveraged with educational efforts to improve learning in the fields of biology, chemistry, and physics.     

Electrochemical C−H/N−H Activation by Water‐Tolerant Cobalt Catalysis at Room Temperature

Electrochemistry enabled C?H/N?H functionalizations at room temperature by external oxidant‐free cobalt catalysis. Thus, the sustainable cobalt electrocatalysis manifold proceeds with excellent levels of chemoselectivity and positional selectivity, and with ample scope, thus allowing electrochemical C?H activation under exceedingly mild reaction conditions at room temperature in water.     

On the influence of fatty acid chain unsaturation on supramolecular gelation of aminocarbohydrate-based supra-amphiphiles

Supramolecular gels are soft materials formed mainly by low molecular weight units held together by intermolecular interactions. Stabilizing these kinds of materials is quite a challenge due to the influence of multiple factors interfering with the integrity of the supramolecular structure. In our previous studies, we have shown that the aminocarbohydrate meglumine (MEG) interacts with organic acids by ion-pairing leading to the formation of MEG–carboxylate adducts. These adducts undergo supramolecular polymerization by heat treatment, but the macromolecular assembly was stable for a short period due to hydrogen bond (H-bond) breakup. Herein, we attempt to study the influence of hydrophobic building blocks on the formation of these compounds aiming to stabilize H-bonds to produce polymerizable supra-amphiphiles in water. Oleic acid and stearic acid are two analogous fatty acids differing only in the presence of unsaturation that were used in our studies. Results demonstrated that the presence of unsaturation hinders gelation in water by interfering with the self-assembly behavior of supra-amphiphiles. Thus, unsaturated supra-amphiphiles behave like traditional surfactants and gelify water at high concentrations (above 30% w/w). On the other hand, supramolecular gels with a polymer-like behavior could be produced with a saturated supra-amphiphile in water (above 4% w/w). The material was characterized by a lamellar arrangement that facilitates the alignment of H-bonds necessary to stabilize the self-assembled structure. These results have pivotal importance on the design of polymerizable supra-amphiphiles and demonstrate that the double bond of hydrophobic building blocks is an important design factor to be considered by scientists studying similar materials.     

Transport coefficients, Raman spectroscopy, and computer simulation of lithium salt solutions in an ionic liquid

Lithium salt solutions of Li(CF3SO2)2N, LiTFSI, in a room-temperature ionic liquid (RTIL), 1-butyl-2,3-dimethyl-imidazolium cation, BMMI, and the (CF3SO2)2N(-), bis(trifluoromethanesulfonyl)imide anion, [BMMI][TFSI], were prepared in different concentrations. Thermal properties, density, viscosity, ionic conductivity, and self-diffusion coefficients were determined at different temperatures for pure [BMMI][TFSI] and the lithium solutions. Raman spectroscopy measurements and computer simulations were also carried out in order to understand the microscopic origin of the observed changes in transport coefficients. Slopes of Walden plots for conductivity and fluidity, and the ratio between the actual conductivity and the Nernst-Einstein estimate for conductivity, decrease with increasing LiTFSI content. All of these studies indicated the formation of aggregates of different chemical nature, as it is corroborated by the Raman spectra. In addition, molecular dynamics (MD) simulations showed that the coordination of Li+ by oxygen atoms of TFSI anions changes with Li+ concentration producing a remarkable change of the RTIL structure with a concomitant reduction of diffusion coefficients of all species in the solutions.     

Photophysical characterization of a highly conjugated bipyridyl-based dye synthesized by a unique two-step approach

In this article, we present a new and simple, yet efficient, two-step approach to synthesize 4,4'-bis(dibutylaminostyrylstyryl)-2,2'-bipyridine with high yield, as well as its linear and nonlinear optical characterizations in THF and toluene solutions. We show that its one- and two-photon absorption spectra are similar in both solvents. Nevertheless, the relaxation processes of this compound exhibit dependence on the solvent polarity. The one- and two-photon induced fluorescence signal of this molecule in solution reveals that its excited state is highly stabilized in THF solution rather than in toluene. Analysis of the fluorescence quantum yield, lifetime, and radiative and nonradiative decay rates are in agreement with Lippert's model for solute-solvent interactions. The optical measurements demonstrate that this dye is a promising candidate for multiphoton fluorescence imaging, optical limiting, and dye lasers.