Correction: Transient coarsening and the motility of optically heated Janus colloids in a binary liquid mixture.

Correction for 'Transient coarsening and the motility of optically heated Janus colloids in a binary liquid mixture' by Juan Ruben Gomez-Solano et al., Soft Matter, 2020, DOI: 10.1039/d0sm00964d.

Transient coarsening and the motility of optically heated Janus colloids in a binary liquid mixture.

A gold-capped Janus particle suspended in a near-critical binary liquid mixture can self-propel under illumination. We have immobilized such a particle in a narrow channel and carried out a combined experimental and theoretical study of the non-equilibrium dynamics of a binary solvent around it - lasting from the very moment of switching illumination on until the steady state is reached. In the theoretical study we use both a purely diffusive and a hydrodynamic model, which we solve numerically. Our results demonstrate a remarkable complexity of the time evolution of the concentration field around the colloid. This evolution is governed by the combined effects of the temperature gradient and the wettability, and crucially depends on whether the colloid is free to move or is trapped. For the trapped colloid, all approaches indicate that the early time dynamics is purely diffusive and characterized by composition layers travelling with constant speed from the surface of the colloid into the bulk of the solvent. Subsequently, hydrodynamic effects set in. Anomalously large nonequilibrium fluctuations, which result from the temperature gradient and the vicinity of the critical point of the binary liquid mixture, give rise to strong concentration fluctuations in the solvent and to permanently changing coarsening patterns not observed for a mobile particle. The early time dynamics around initially still Janus colloids produces a force which is able to set the Janus colloid into motion. The propulsion due to this transient dynamics is in the direction opposite to that observed after the steady state is attained.

Aging phenomena during phase separation in fluids: decay of autocorrelation for vapor-liquid transitions.

We performed molecular dynamics simulations to study relaxation phenomena during vapor-liquid transitions in a single component Lennard-Jones system. Results from two different overall densities are presented: one in the neighborhood of the vapor branch of the coexistence curve and the other being close to the critical density. The nonequilibrium morphologies, growth mechanisms and growth laws in the two cases are vastly different. In the low density case growth occurs via diffusive coalescence of droplets in a disconnected morphology. On the other hand, the elongated structure in the higher density case grows via advective transport of particles inside the tube-like liquid domains. The objective in this work has been to identify how the decay of the order-parameter autocorrelation, an important quantity to understand aging dynamics, differs in the two cases. In the case of the disconnected morphology, we observe a very robust power-law decay, as a function of the ratio of the characteristic lengths at the observation time and at the age of the system, whereas the results for the percolating structure appear rather complex. To quantify the decay in the latter case, unlike the standard method followed in a previous study, here we have performed a finite-size scaling analysis. The outcome of this analysis shows the presence of a strong preasymptotic correction, while revealing that in this case also, albeit in the asymptotic limit, the decay follows a power-law. Even though the corresponding exponents in the two cases differ drastically, this study, combined with a few recent ones, suggests that power-law behavior of this correlation function is rather universal in coarsening dynamics.

Phase separation around a heated colloid in bulk and under confinement.

We study the non-equilibrium coarsening dynamics of a binary liquid solvent around a colloidal particle in the presence of a time-dependent temperature gradient that emerges after a temperature quench of a suitable coated colloid surface. The solvent is maintained at its critical concentration and the colloid is fixed in space. The coarsening patterns near the surface are shown to be strongly dependent on the colloid surface adsorption properties and on the temperature evolution. The temperature gradient alters the morphology of the binary solvent near the surface of the colloid as compared to the coarsening proceeding at a constant temperature everywhere. We also present results for the evolution of coarsening in thin films with confining surfaces preferring one species of the binary liquid mixture over the other. Confinement leads to a faster phase segregation process and formation of a bridge connecting the colloid and both confining walls.

Bio-activity of aminosulfonyl ureas in the light of nucleic acid bases and DNA base pair interaction.

The quantum chemical descriptors based on density functional theory (DFT) are applied to predict the biological activity (log IC50) of one class of acyl-CoA: cholesterol O-acyltransferase (ACAT) inhibitors, viz. aminosulfonyl ureas. ACAT are very effective agents for reduction of triglyceride and cholesterol levels in human body. Successful two parameter quantitative structure-activity relationship (QSAR) models are developed with a combination of relevant global and local DFT based descriptors for prediction of biological activity of aminosulfonyl ureas. The global descriptors, electron affinity of the ACAT inhibitors (EA) and/or charge transfer (ΔN) between inhibitors and model biosystems (NA bases and DNA base pairs) along with the local group atomic charge on sulfonyl moiety (∑QSul) of the inhibitors reveals more than 90% efficacy of the selected descriptors for predicting the experimental log (IC50) values.

Solvent coarsening around colloids driven by temperature gradients.

Using mesoscopic numerical simulations and analytical theory, we investigate the coarsening of the solvent structure around a colloidal particle emerging after a temperature quench of the colloid surface. Qualitative differences in the coarsening mechanisms are found, depending on the composition of the binary liquid mixture forming the solvent and on the adsorption preferences of the colloid. For an adsorptionwise neutral colloid, the phase next to its surface alternates as a function of time. This behavior sets in on the scale of the relaxation time of the solvent and is absent for colloids with strong adsorption preferences. A Janus colloid, with a small temperature difference between its two hemispheres, reveals an asymmetric structure formation and surface enrichment around it, even if the solvent is within its one-phase region and if the temperature of the colloid is above the critical demixing temperature T_{c} of the solvent. Our phenomenological model turns out to capture recent experimental findings according to which, upon laser illumination of a Janus colloid and due to the ensuing temperature gradient between its two hemispheres, the surrounding binary liquid mixture develops a concentration gradient.

Comparative analyses of polyphenolic composition of Fragaria spp. color mutants.

White-fruited mutants of Fragaria vesca, and one of F. x ananassa, were studied to determine the identity and quantity of major flavonols (FVLs), flavan-3-ols (FV3Ls), hydroxycinnamic acids (HCAs), and ellagic acid (EA)-derived compounds, by using HPLC-MS. The content of 22 compounds across the major groups were used to assess the possibility of unique mutations among the mutant gentoypes. Total HCAs were lower in the white than the red cultivars of both species, except for 2 white F. vesca cultivars. Total FVLs were comparable in white fruit of both species, although a red F. x ananassa had more than a red F. vesca. Total FV3Ls were higher in red than white cultivars of both species. Total EA-derived content was generally higher in white than in red F. vesca. Principal component analysis and a combined heatmap and hierarchical cluster analysis clearly discriminated among the five white F. vesca genotypes.

Optical activity of Co-porphyrin in the light of IR and Raman spectroscopy: A critical DFT investigation.

A critical investigation on the structure, electronic properties and optical activities of a series of transition metal doped porphyrins (TMP; TM=Fe, Co, Ni) in the light of infrared and Raman spectroscopy is performed, under density functional formalism. The structure and electronic properties are studied in terms of ionization potential, electron affinity, chemical hardness (η), binding energies of the transition metals (BETM) etc. The origin of the optical activities, especially the visibly active cobalt porphyrin is addressed through critical study on their infrared and Raman spectra. The information availed from the spectral analysis will certainly ease their possible synthesis and useful applications in the sensor and optoelectronic domains.

Effects of Phenolic Compounds on Growth of Colletotrichum spp. In Vitro.

Colletotrichum acutatum is responsible for anthracnose fruit rot, one of the most devastating diseases in strawberry. Phenolic compounds have been described as contributors to anthracnose resistance in strawberry (Fragaria x ananassa, Duch.). Six isolates of Colletotrichum acutatum and four isolates of three other Colletotrichum species, C. gloeosporioides, C. fragariae, and C. graminicola, associated with disease symptoms were investigated in this study. The potential inhibitory effect of phenolic acids (gallic acid, caffeic acid, chlorogenic acid, ferulic acid, trans-cinnamic acid, p-coumaric acid, salicylic acid), flavonoids (catechin, quercetin, naringenin), and ellagic acid, which are naturally found in strawberry, were screened against two different spore suspension concentrations of the Colletotrichum isolates at 5, 10, 50 mM in vitro. Among the phenolic acids and flavonoids tested in this study, only trans-cinnamic acid, ferulic acid, and p-coumaric acid inhibited fungal growth. The inhibitory effects were concentration-dependent but also varied with the spore suspension concentration of the isolates. The results demonstrated that trans-cinnamic acid had the greatest inhibitory effect on all Colletotrichum spp. isolates tested.

Levofloxacin capped Ag-nanoparicles: A new highly selective sensor for cations under joint experimental and DFT investigation.

A very new and alternate function of an antibiotic drug levofloxacin (Lv), as a highly selective, colorimetric turn-OFF/turn-ON chemosensor for metal-ions Hg2+ and Fe3+, has been reported in this study. An extremely easy, very less time consuming, economical one-pot method of synthesis has been developed for the production of silver nanoparticles (AgNPs). The AgNPs that are stabilized and surface functionalized by Lv. Functionalization of AgNPs by antibiotic drug Lv has been thoroughly confirmed using FTIR spectrophotometry. Two carbonyl oxygen moieties, one belongs to the pyridine oxygen group and another one from the carboxylate oxygen group of Lv together form the binding site over the nanoparticle surface. The Lv-AgNPs system has shown naked eye detectable colour change, as well as significant change via both UV-Vis and fluorescence spectroscopy. The limits of detection (LODs) are predicted to be 6.86×10-8M for Hg2+ and 2.52×10-9M for Fe3+ using UV-Vis spectroscopy and 2.35×10-9M for Fe3+ using fluorescence spectroscopy. UV-Vis spectroscopy, fluorescence spectroscopy, FTIR, TEM, DLS etc. have been used for the physico-chemical characterization of Lv-AgNPs system and the nanoparticle mediated sensing process. Detailed experimental and theoretical studies employing FTIR spectrophotometry and density functional theory (DFT) studies have been used for the elucidation of drug-nanoparticle based sensing mechanism. It is also demonstrated that the Lv-AgNPs system can show real time application using Test-Paper Kit to establish the drug-nanoparticle assembly as a potential colorimetric turn-OFF/turn-ON sensing system for Hg2+ and Fe3+ respectively.

Structure and dynamics of binary liquid mixtures near their continuous demixing transitions.

The dynamic and static critical behavior of a family of binary Lennard-Jones liquid mixtures, close to their continuous demixing points (belonging to the so-called model H' dynamic universality class), are studied computationally by combining semi-grand canonical Monte Carlo simulations and large-scale molecular dynamics (MD) simulations, accelerated by graphic processing units (GPU). The symmetric binary liquid mixtures considered cover a variety of densities, a wide range of compressibilities, and various interactions between the unlike particles. The static quantities studied here encompass the bulk phase diagram (including both the binodal and the λ-line), the correlation length, and the concentration susceptibility, of the finite-sized systems above the bulk critical temperature Tc, the compressibility and the pressure at Tc. Concerning the collective transport properties, we focus on the Onsager coefficient and the shear viscosity. The critical power-law singularities of these quantities are analyzed in the mixed phase (above Tc) and non-universal critical amplitudes are extracted. Two universal amplitude ratios are calculated. The first one involves static amplitudes only and agrees well with the expectations for the three-dimensional Ising universality class. The second ratio includes also dynamic critical amplitudes and is related to the Einstein-Kawasaki relation for the interdiffusion constant. Precise estimates of this amplitude ratio are difficult to obtain from MD simulations, but within the error bars our results are compatible with theoretical predictions and experimental values for model H'. Evidence is reported for an inverse proportionality of the pressure and the isothermal compressibility at the demixing transition, upon varying either the number density or the repulsion strength between unlike particles.

Study of critical dynamics in fluids via molecular dynamics in canonical ensemble.

With the objective of understanding the usefulness of thermostats in the study of dynamic critical phenomena in fluids, we present results for transport properties in a binary Lennard-Jones fluid that exhibits liquid-liquid phase transition. Various collective transport properties, calculated from the molecular dynamics (MD) simulations in canonical ensemble, with different thermostats, are compared with those obtained from MD simulations in microcanonical ensemble. It is observed that the Nosé-Hoover and dissipative particle dynamics thermostats are useful for the calculations of mutual diffusivity and shear viscosity. The Nosé-Hoover thermostat, however, as opposed to the latter, appears inadequate for the study of bulk viscosity.

Toxicity prediction of PHDDs and phenols in the light of nucleic acid bases and DNA base pair interaction.

The applicability of Density Functional Theory (DFT) based descriptors for the development of quantitative structure-toxicity relationships (QSTR) is assessed for two different series of toxic aromatic compounds, viz., polyhalogenated dibenzo-p-dioxins (PHDDs) and phenols (PHs). A series of 20 compounds each for PHDDs and PHs with their experimental toxicities (IC50 and IGC50) is chosen in the present study to develop DFT based efficient quantum chemical parameters (QCPs) for explaining the toxin potential of the considered compounds. A systematic analysis to find out the electron donation/acceptance nature of these selected compounds with the considered model biosystems, viz., nucleic acid (NA) bases and DNA base pairs, is performed to identify potential QCPs. Accordingly, PHDDs is found to be electron acceptors whereas phenols as donors, during their interaction with biosystems. Two parameter regression model is carried out comprising global charge transfer (ΔN), and local Fukui Function's for nucleophilic attack (fk(+)) for PHDDs and the same for electrophilic attack (fk(-)) in case of PHs. It is heartening to note that our chosen descriptors, viz, charge transfer (ΔN) and Fukui Function (fk(±)) plays a crucial role by explaining more than 90% of the observed toxic behavior (in terms of correlation-coefficient, R) of PHDDs and PHs. The developed QCPs, viz., ΔN and fk(±) can be added as the new descriptors in the QSTR parlance.

Bioimaging application of a novel anion selective chemosensor derived from vitamin B6 cofactor.

The detection of intracellular fluoride was achieved by a novel Schiff base chemosensor derived from vitamin B6 cofactor (L) using fluorescence imaging technique. The sensor L was synthesized by condensation of pyridoxal phosphate with 2-aminothiophenol. The anion recognition ability of L was explored by UV-Vis and fluorescence methods in DMSO and mixed DMSO-H2O system. The sensor L showed both naked-eye detectable color change from colorless to light green and remarkable fluorescence enhancement at 500 nm in the presence of F(-) and AcO(-). The anion recognition was occurred through the formation of hydrogen bonded complexes between these anions and L, followed by the partial deprotonation of L. The detection limit of L for the analysis of F(-) and AcO(-) was calculated to be 1.88 µM and 9.10 µM, respectively. Finally, the detection of cytoplasmic fluoride was tested using human cancer cell HeLa through fluorescence imaging.

Finite-size scaling study of shear viscosity anomaly at liquid-liquid criticality.

We study the equilibrium dynamics of a symmetrical binary Lennard-Jones fluid mixture near its consolute criticality. Molecular dynamics simulation results for the shear viscosity, η, from a microcanonical ensemble are compared with those from a canonical ensemble with various thermostats. It is observed that the Nosé-Hoover thermostat is a good candidate for this purpose, and is therefore adopted for the quantification of the critical singularity of η, to avoid the temperature fluctuations (or even drifts) that are often encountered in microcanonical simulations. Via a finite-size scaling analysis of our simulation data we have been able to confirm that the shear viscosity exhibits a weak critical singularity in agreement with the theoretical predictions.

Simulation of transport around the coexistence region of a binary fluid.

We use Monte Carlo and molecular dynamics simulations to study phase behavior and transport properties in a symmetric binary fluid where particles interact via Lennard-Jones potential. Our results for the critical behavior of collective transport properties, with particular emphasis on bulk viscosity, is understood via appropriate application of finite-size scaling technique. It appears that the critical enhancements in these quantities are visible far above the critical point. This result is consistent with an earlier report from computer simulations where, however, the authors do not quantify the critical singularity.

Effects of domain morphology on kinetics of fluid phase separation.

Kinetics of phase separation in a three-dimensional single-component Lennard-Jones fluid, that exhibits vapor-liquid transition, is studied via molecular dynamics simulations after quenching homogeneous systems, of different overall densities, inside the coexistence region. For densities close to the vapor branch of the coexistence curve, phase separation progresses via nucleation of liquid droplets and collisions among them. This is different from the evaporation-condensation mechanism proposed by Lifshitz and Slyozov, even though both lead to power-law growth of average domain size, as a function of time, with an exponent α = 1∕3. Beyond a certain threshold value of the overall density, we observe elongated, percolating domain morphology which suddenly enhances the value of α. These results are consistent with some existing theoretical expectations.

Nucleation and growth of droplets in vapor-liquid transitions.

Results for the kinetics of vapor-liquid transitions, following temperature quenches with different densities, are presented from molecular dynamics simulations of a Lennard-Jones system. For a critical density, bicontinuous liquid and vapor domains are observed which grow with time, obeying the predictions for the hydrodynamic mechanism. On the other hand, for quenches with density significantly below the critical one, phase separation progresses via nucleation and growth of liquid droplets. In the latter case, the Brownian diffusion and collision mechanism for the droplet growth is confirmed. We also discuss the possibility of interdroplet interaction leading to a different amplitude in the growth law. Arguments for faster growth, observed at early times, are also provided.

Effect of lipid molecule headgroup mismatch on non steroidal anti-inflammatory drugs induced membrane fusion.

Membrane fusion is an essential process guiding many important biological events, which most commonly requires the aid of proteins and peptides as fusogenic agents. Small drug induced fusion at low drug concentration is a rare event. Only three drugs, namely, meloxicam (Mx), piroxicam (Px), and tenoxicam (Tx), belonging to the oxicam group of non steroidal anti-inflammatory drugs (NSAIDs) have been shown by us to induce membrane fusion successfully at low drug concentration. A better elucidation of the mechanism and the effect of different parameters in modulating the fusion process will allow the use of these common drugs to induce and control membrane fusion in various biochemical processes. In this study, we monitor the effect of lipid headgroup size mismatch in the bilayer on oxicam NSAIDs induced membrane fusion, by introducing dimyristoylphosphatidylethanolamine (DMPE) in dimyristoylphosphatidylcholine (DMPC) small unilamellar vesicles (SUVs). Such headgroup mismatch affects various lipid parameters which includes inhibition of trans-bilayer motion, domain formation, decrease in curvature, etc. Changes in various lipidic parameters introduce defects in the membrane bilayer and thereby modulate membrane fusion. SUVs formed by DMPC with increasing DMPE content (10, 20, and 30 mol %) were used as simple model membranes. Transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) were used to characterize the DMPC-DMPE mixed vesicles. Fluorescence assays were used to probe the time dependence of lipid mixing, content mixing, and leakage and also used to determine the partitioning of the drugs in the membrane bilayer. How the inhibition of trans-bilayer motion, heterogeneous distribution of lipids, decrease in vesicle curvature, etc., arising due to headgroup mismatch affect the fusion process has been isolated and identified here. Mx amplifies these effects maximally followed by Px and Tx. This has been correlated to the enhanced partitioning of the hydrophobic Mx compared to the more hydrophilic Px and Tx in the mixed bilayer.

Membrane fusion induced by small molecules and ions.

Membrane fusion is a key event in many biological processes. These processes are controlled by various fusogenic agents of which proteins and peptides from the principal group. The fusion process is characterized by three major steps, namely, inter membrane contact, lipid mixing forming the intermediate step, pore opening and finally mixing of inner contents of the cells/vesicles. These steps are governed by energy barriers, which need to be overcome to complete fusion. Structural reorganization of big molecules like proteins/peptides, supplies the required driving force to overcome the energy barrier of the different intermediate steps. Small molecules/ions do not share this advantage. Hence fusion induced by small molecules/ions is expected to be different from that induced by proteins/peptides. Although several reviews exist on membrane fusion, no recent review is devoted solely to small moleculs/ions induced membrane fusion. Here we intend to present, how a variety of small molecules/ions act as independent fusogens. The detailed mechanism of some are well understood but for many it is still an unanswered question. Clearer understanding of how a particular small molecule can control fusion will open up a vista to use these moleucles instead of proteins/peptides to induce fusion both in vivo and in vitro fusion processes.