Molecular Liquids Research Articles

Improved data analysis for molecular dynamics in liquid CCl4

Previously reported inelastic x-ray scattering spectra of a typical van der Waals molecular liquid CCl4 were reanalyzed using a generalized Langevin formalism with a memory function including a thermal and two viscoelastic relaxation processes and simple sparse modeling. The obtained excitations of longitudinal acoustic phonons show a largely positive deviation from the hydrodynamic value by about 57%, much larger than about 37% by the previously reported damped harmonic oscillator result. Such large values of fast sounds in molecular liquids larger than 15-20% of typical liquid metals are interpreted as extra energy losses for terahertz phonons by molecules' vibrational and rotational motions. The rates of the fast and slow viscoelastic relaxations in the memory function at low Q indicate large values, about 0.5 and 2 ps, which correspond to the vibrational and rotational motions of CCl4 molecules, respectively. These values are larger than those of the typical polar molecular liquid acetone, which may reflect the heavier atomic mass of CCl4. The Q dependences of the viscoelastic relaxation rates are discussed in terms of the lifetime and propagating length of the terahertz phonon oscillations. The microscopic kinematic longitudinal viscosity was obtained from the viscoelastic relaxation magnitudes and times, rapidly decreasing with Q from a macroscopic value at Q→0.

LiNO3-assisted electrochemical extraction of metallic Sm from a molecular liquid-based electrolyte

Developing efficient, green, and cost-effective methods for extracting rare earth (RE) metals is essential to accelerate breakthroughs in critical technologies in the field of RE-based functional materials. In this study, a low-cost aprotic polar molecular liquid, N,N-Dimethylformamide (DMF), was used for electrowinning metallic Sm with upstream SmCl3 as the raw material, inspired by previous applications of diverse specialised ionic liquids for the electrochemical recovery of RE metals. Cyclic voltammetry and electrodeposition experiments demonstrated that metallic Sm cannot be obtained from the binary DMF-SmCl3 system, but can be electrodeposited with LiNO3. Therefore, the mechanism underlying the observed electrochemical behaviour is elucidated and discussed in detail. Sm and Sm–Co metallic elements were successfully electrodeposited on an Al substrate at a relatively high current density, characterised, and evaluated using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. Moreover, a unique two-step method involving electrodeposition and direct smelting is prospectively described for the continuous preparation of bulk RE-containing alloys to stabilise highly active RE elements. Therefore, this study provides valuable insights into practical solvometallurgical processes for RE metal extraction, refinement, and recycling.

Guest Editorial: Special Issue on Multi-Functional Molecular Liquids, Solids, and Crystals for Materials Engineering & Manufacturing — Part I

Guest Editorial: Special Issue on Multi-Functional Molecular Liquids, Solids, and Crystals for Materials Engineering & Manufacturing — Part I

Aqueous Humor Liquid Biopsy as a Companion Diagnostic for Retinoblastoma: Implications for Diagnosis, Prognosis, and Therapeutic Options: Five Years of Progress

To define the prospective use of the aqueous humor (AH) as a molecular diagnostic and prognostic liquid biopsy for retinoblastoma (RB). This is a prospective, observational study wherein an AH liquid biopsy is performed at diagnosis and longitudinally through therapy for patients with RB. Tumor-derived cell-free DNA is isolated and sequenced for single nucleotide variant analysis of the RB1 gene and detection of somatic copy number alterations (SCNAs). The SCNAs are used to determine tumor fraction (TFx). Specific SCNAs, including 6p gain and focal MycN gain, along with TFx, are prospectively correlated with intraocular tumor relapse, response to therapy, and globe salvage. A total of 26 eyes of 21 patients were included with AH taken at diagnosis. Successful ocular salvage was achieved in 19 of 26 (73.1%) eyes. Mutational analysis of 26 AH samples identified 23 pathogenic RB1 variants and 2 focal RB1 deletions; variant allele fraction ranged from 30.5% to 100% (median 93.2%). At diagnosis, SCNAs were detectable in 17 of 26 (65.4%) AH samples. Eyes with 6p gain and/or focal MycN gain had significantly greater odds of poor therapeutic outcomes (odds ratio = 6.75, 95% CI = 1.06-42.84, P = .04). Higher AH TFx was observed in eyes with vitreal progression (TFx = 46.0% ± 40.4) than regression (22.0 ± 29.1; difference: -24.0; P = .049). Establishing an AH liquid biopsy for RB is aimed at addressing (1) our inability to biopsy tumor tissue and (2) the lack of molecular biomarkers for intraocular prognosis. Current management decisions for RB are made based solely on clinical features without objective molecular testing. This prognostic study shows great promise for using AH as a companion diagnostic. NOTE: Publication of this article is sponsored by the American Ophthalmological Society.

Simple elaboration of drug-SPION nanocapsules (hybridosomes®) by solvent shifting: Effect of the drug molecular structure and concentration

Drug nanocapsules coated with iron oxide nanoparticles (SPION) were elaborated by the simultaneous nanoprecipitation of the drug and the nanoparticles, through solvent shifting. We examined four drugs: sorafenib, sorafenib tosylate, α-tocopherol and paclitaxel, to cover the cases of molecular solids, ionic solids, and molecular liquids. We first investigated the formation of the drug core in the final mixture of solvents at different concentrations. A Surfactant-Free Micro-Emulsion domain (SFME, thermodynamically stable) was observed at low drug concentration and an Ouzo domain (metastable) at high drug concentration, except for the case of paclitaxel which crystallizes at high concentration without forming an Ouzo domain. When co-nanoprecipitated with the molecular drugs in the Ouzo domain (sorafenib or α-tocopherol), the SPION limited the coalescence of the drug particles to less than 100 nm, forming capsules with a drug encapsulation efficiency of ca 80 %. In contrast, larger capsules were formed from the SFME or when using the ionic form (sorafenib tosylate). Finally, the sorafenib-SPION capsules exhibit a similar chemotherapeutic effect as the free drug on the hepatocellular carcinoma in vitro.

Comments on the calculation of thermodynamic adsorption equilibrium constant using the distribution coefficient in Journal of Molecular Liquids 380 (2023) 121725

This comment discussed the calculation of the standard equilibrium constant thermodynamic parameters about the paper published in Journal of Molecular Liquids 380 (2023) 121725. Recently, Khankhasaeva et al. (2023) published a high academic paper to reveal the adsorption kinetic and thermodynamic regularities of diclofenac (DCF) on Fe2O3-pillared montmorillonites (Fe-PMts). Although the author tries to convert the distribution coefficient (Kd) to the standard equilibrium constant (Ko), the calculation formula is incorrect due to the confusion of adsorbate and adsorbent. This creates dimension for Ko obtained from Eq. (2). In this comment, the origin and background of this kind of error is analyzed and the method for correcting the error is presented. We hope this comment clarifies the essence of calculating the standard equilibrium constant by using the distribution coefficient, so others avoid the propagation of this kind of error.

A Second Glass Transition Observed in Single-Component Homogeneous Liquids Due to Intramolecular Vitrification.

On supercooling a liquid, the viscosity rises rapidly until at the glass transition it vitrifies into an amorphous solid accompanied by a steep drop in the heat capacity. Therefore, a pure homogeneous liquid is not expected to display more than one glass transition. Here we show that a family of single-component homogeneous molecular liquids, titanium tetraalkoxides, exhibit two calorimetric glass transitions of comparable magnitude, one of which is the conventional glass transition associated with dynamic arrest of the bulk liquid properties, while the other is associated with the freezing out of intramolecular degrees of freedom. Such intramolecular vitrification is likely to be found in molecules in which low-frequency terahertz intramolecular motion is coupled to the surrounding liquid. These results imply that intramolecular barrier-crossing processes, typically associated with chemical reactivity, do not necessarily follow the Arrhenius law but may freeze out at a finite temperature.

The shift of excitation spectra at blue edge of emission (BEEmS) as a new methodology to probe heterogeneity

Many current methods for detecting molecular-level heterogeneity are complex and require stringent data analysis, limiting their widespread use. Herein, we propose a novel edge effect, i.e., the shift of excitation spectra at the blue edge of emission (which we termed as Blue Edge Emission Shift, BEEmS), to perceive the structural heterogeneity. This method is simple and can be easily implemented with commonly available fluorimeter. Red edge excitation shift (REES), a related technique, is already in use, but like most other known techniques, its usefulness is constrained by its dependence on environmental rigidity. Our method does not suffer from this drawback significantly. We showed the generality of the proposed method taking various chemically and biologically heterogenous systems including molecular liquid, deep eutectic solvents, organic cavitand, micelle and protein. BEEmS certainly comes out as a more effective sensor of heterogeneity than REES in certain cases (like denatured protein, hydrophobic deep eutectic solvent and SDS micelle) where solvation time is not sufficiently slow to be detected by REES, but can be measured though BEEmS. Furthermore, unlike most existing techniques, domain-specific heterogeneity of a model multi-domain protein is successfully measured.

Discrete Modeling Approach for Cluster-Based Excess Gibbs-Energy of Molecular Liquids.

The excess Gibbs-energy of a two-component liquid molecular mixture is modeled based on discrete clusters of molecules. These clusters preserve the three-dimensional geometric information about local molecule neighborhoods that inform the interaction energies of the clusters. In terms of a discrete Markov-chain, the clusters are used to hypothetically construct the mixture using sequential insertion steps. Each insertion step and, therefore, cluster is assigned a probability of occurring in an equilibrium system that is determined via the constrained minimization of the Helmholtz free energy. For this, informational Shannon entropy based on these probabilities is used synonymously with thermodynamic entropy. A first approach for coupling the model to real molecules is introduced in the form of a molecular sampling algorithm, which utilizes a force-field approach to determine the energetic interactions within a cluster. An exemplary application to four mixtures shows promising results regarding the description of a variety of excess Gibbs-energy curves, including the ability to distinguish between structural isomers.

Glass formation processes in fullerene mixtures

The local structural features of the A20B80 fullerene mixture (where A = C60 and B = C70) are studied by the molecular dynamics simulations for a wide temperature range, including the phase of an equilibrium liquid phase and a supercooled melt, in order to elucidate the mechanism of formation of the icosahedral short-range order in binary molecular liquids. Structural and cluster analyzes revealed the presence of icosahedral clusters in the supercooled melt phase and determined the critical glass transition temperature.

Modification of the Stefan’s Rule for the Surface Tension Coefficients of Liquids

A modification of the “Stefan’s rule” for the surface tension coefficients of liquids has been proposed, with the modification consisting in choosing a liquid as a system of comparison with respect to its surface. An expression for the surface tension coefficients has been derived and employed to interpret their temperature dependences for a number of molecular liquids with different physicochemical properties.

Water-induced changes in choline chloride-carboxylic acid deep eutectic solvents properties

Deep eutectic solvents (DES) have become a promising alternative to molecular organic solvents and ionic liquids in a variety of scientific applications. Their customizable physicochemical properties make them attractive for extraction, catalysis, electrochemistry and drug delivery. Recently, the study of not so much DES themselves, as their mixtures with water, has attracted particular interest. In this study, six widely used DESs based on choline chloride and carboxylic acids (citric, tartaric, malic, glycolic, malonic and lactic) with a water content of 0–50 wt% were analyzed. Properties such as density, viscosity, conductivity and spectral properties of DES (IR spectroscopy and refractive index) were studied. The results show that in the entire range of water content under study, there are no abrupt changes in properties for all the studied parameters, which allows us to conclude that water is gradually incorporated into the DES structure without its destruction. However, within this class of eutectic solvents, subclasses can be distinguished, due to various changes in the studied properties. These results provide important information for optimizing the performance of DES in practical applications and highlight their potential as sustainable green solvents in modern science and technology.

Polymer gel electrolytes containing sodium salts with BF4−, ClO4− and CF3SO3− anions immobilized in TEGDME molecular liquid for sodium battery and electric double layer capacitor

The present study reports synthesis and analysis of different characteristics of sodium ion conducting polymer gel electrolytes (PGEs) containing sodium salts with BF4−, ClO4− and CF3SO3− anions dissolved in tetraethylene glycol dimethyl ether and immobilized in a copolymer matrix consisting of polymethyl methacrylate and poly(vinylidene fluoride-co-hexafluoropropylene). The PGE containing the NaBF4 salt could deliver an ionic conductivity of 1.4 × 10−3 S cm−1 at room temperature along with superior dielectric properties as compared to the electrolytes with NaClO4 and NaCF3SO3 salts. The feasibility of designing sodium-based batteries and EDLCs has been demonstrated using the optimized PGE containing NaBF4 salt. The prototype sodium‑sulfur (NaS) battery designed by utilizing the optimized PGE, sodium amalgam anode and sulfur cathode provides open circuit voltage of ∼2.4 V and initial discharge capacity of ∼163 mA h g−1 and 126 mA h g−1 at discharge currents of 33 mA g−1 and 66 mA g−1, respectively. This optimized PGE also demonstrate good compatibility with AC electrodes in electric double layer capacitor (EDLC) application and delivered a significant specific capacity ∼64 F g−1 at 0.5 mA cm−2 current.

Laboratory equipment for practice learning in the framework of educational course “Molecular Physics and Thermodynamics”

This article presents laboratory equipment for practice learning of physics specialties students in the framework of educational course “Molecular Physics and Thermodynamics”. The presented laboratory equipment allows measuring the temperature dependence of the thermal conductivity coefficient of molecular liquids under atmospheric pressure and saturated vapors pressure in the temperature range from 150K to 400K. A general scheme of the developed experimental setup for measuring the thermal conductivity of liquids by the steady-state method under isobaric condition has been described. The created laboratory setup uses general design solutions of the coaxial cylinder method, preserving its features and measurement precision in general. The measurements are carried out on coaxial-geometry cell under atmospheric pressure. A modified heat potentiometer method with one thermometer was used, which allowed us to minimize the error in the estimation of the thermal conductivity coefficient due to the uncontrollable heat flows and different calibration of thermometers. The total systematic error in the measurement of the molecular liquids thermal conductivity does not exceed 3%. The procedures for direct measurement and calculation of the thermal conductivity coefficient of molecular liquids using the developed laboratory equipment are described.

A possible origin of the very fast sound in terahertz region in liquid benzene

Previously reported inelastic X-ray scattering spectra of molecular liquid benzene were reanalyzed by a generalized Langevin formalism (GLF) with a memory function including a thermal and two viscoelastic relaxation processes. A new algorithm was containing a simple sparse modeling to smooth Q dependences of dynamical parameters used in the present GLF analysis. The obtained excitation energies of longitudinal acoustic phonons show a largely positive deviation from the hydrodynamic value by about 50%, the same as that by previous analysis and similar to existing results of several molecular liquids. Such a large deviation of dynamical sound velocity in liquid benzene is interpreted as extra energy-losses for terahertz phonons by vibrational and rotational motions of benzene molecules. The rates of the fast and slow viscoelastic relaxations in the memory function at low Q are undetectable and 0.4-0.8 ps, respectively. These can be explained by the vibrational and anisotropic rotational motions of benzene molecules. The microscopic kinematic longitudinal viscosity rapidly decreases with Q from a reasonable macroscopic value.

Bridging organic, molecular, macromolecular, supramolecular and biological sciences to create functions via fluorine chemistry and fluorinated reagents

After a brief introduction highlighting the challenges of fluorine chemistry and the latest developments in the field, this Perspective will discuss how a combination of fluorine and fluorous chemistry together with fluorinated reagents helped to bridge between organic, molecular, macromolecular, supramolecular and biological sciences to create functions in the laboratory of the corresponding author. The reactivity of fluoride as a leaving group is best illustrated by SNAr reactions when it helped to demonstrate single electron transfer-mediated side reactions and through molecular design replaced activated aryl fluorides with aryl chlorides in the synthesis of poly(etherketone)s. Subsequently it was demonstrated how Ni(II) sigma complexes provided an orthogonal approach to the Suzuki-type cross-coupling of arylfluorides, other halides and all aryl C–O based electrophiles. Fluorinated reagents facilitated cylotrimetrization vs cyclotetramerization of bis(methoxy)benzyl chloride and alcohol and the synthesis of the simplest molecular liquid crystals. Triflic acid, methyl triflate facilitated the most tolerant living polymerizations including of cyclic siloxanes, functional vinyl ethers and oxazolines to generate self-organizable dendronized polymers while fluorine, trifluoromethyl and trifluoromethoxy groups facilitated disassembly and reassembly of liquid crystal polyethers and poly(p-phenylenes). Fluorinated stereocenters accessed the first heterochiral recognition in side-chain liquid crystal poly(vinyl ether)s and their model compounds. Alkali metal triflates mediated self-organization of supramolecular nonfluorinated and fluorinated self-assembling minidendrons, dendrons, dendrimers and self-organizable dendronized polymers. The role of fluorinated alkyl groups and of alkali metal triflates in the self-assembly, disassembly and isomorphic replacement analysis, of supramolecular helical columns, of the assembly of helical cogwheel coat and of spherical supramolecular dendrimers forming Frank-Kasper periodic and quasiperiodic arrays was highlighted. A brief discussion of fluorinated amino acids, peptides and peptoids and their potential role in the self-assembly and functions resulted from dendritic dipeptides followed by a discussion of semifluorinated amphiphilic Janus dendrimers as models of biological membranes, including for cell fusion and fission, concludes this Perspective.

Dynamical coarse-grained models of molecular liquids and their ideal and non-ideal mixtures.

Coarse-grained (CG) simulation models of condensed-phase systems can be derived with well-established methods that perform coarse-graining in space and provide an effective Hamiltonian with which some of the structural and thermodynamic properties of the underlying fine-grained (FG) reference system can be represented. Coarse-graining in time potentially provides CG models that furthermore represent dynamic properties. However, systematic efforts in this direction have so far been limited, especially for moderately coarse-grained, chemistry-specific systems with complicated conservative interactions. With the aim of representing structural, thermodynamic, and dynamic properties in CG simulations of multi-component molecular systems, we investigated a recently introduced method in which the force on a CG particle originates from conservative interactions with surrounding particles and non-Markovian dissipative interactions, the latter introduced by means of a colored-noise thermostat. We examined two different methods to derive isotropic memory kernels required for integrating the corresponding generalized Langevin equation (GLE) of motion, based on the orthogonal dynamics of the FG forces and on an iterative optimization scheme. As a proof of concept, we coarse-grain single-component molecular liquids (cyclohexane, tetrachloromethane) and ideal and non-ideal binary mixtures of cyclohexane/tetrachloromethane and ethanol/tetrachloromethane, respectively. We find that for all systems, the FG single particle velocity auto-correlation functions and, consequently, both the short time and long time diffusion coefficients can be quantitatively reproduced with the CG-GLE models. We furthermore demonstrate that the present GLE-approach leads to an improved description of the rate with which the spatial correlations decay, which is artificially accelerated in the absence of dissipation.

Photothermal Imaging of Transient and Steady State Convection Dynamics in Primary Alkanes

This paper presents a photothermal spectroscopy technique that effectively images convective heat flow in molecular liquids resulting from localized laser-induced heating. The method combines aspects of thermal lensing and photothermal deflection. A high-energy infrared laser is used to induce a thermal lens in the sample, and a divergent visible laser is used to probe the entire region of the excitation beam within the sample. This approach allows for the observation of the convective flow of the liquid above the excitation beam. The study focuses on the liquid primary alkanes, from n-pentane to n-pentadecane. The paper provides experimental results, including dynamical data for the propagation of the thermal plume, a transient feature, in these alkanes and the exploration of dependence on excitation laser power.

Computational Analysis of Excited-State Properties of MoS2 Nanosheet Modified with a Pyrene Derivative

MoS2, a representative transition metal dichalcogenides (TMD), is known to undergo the hydrogen evolution reaction in the exfoliated state, and its use as an auxiliary catalyst in place of platinum has been widely reported. Recently, the exfoliation of bulk MoS2 and efficient covalent modification of MoS2 nanosheets with N-bromobenzylmaleimide was successfully achieved using a planetary ball mill. For the photofunctionalization of MoS2, further coupling reaction with a pyrene derivative produced pyrene-benzyl-maleimide-MoS2 (Py-Bn-Mal-MoS2) nanosheet. The absorption spectrum of Py-Bn-Mal-MoS2 shows peaks similar to that of 1-phenylpyrene. On the other hand, the emission spectrum of Py-Bn-Mal-MoS2 is much different from that of 1-phenylpyrene. Furthermore, the emission peak of Py-Bn-Mal-MoS2 is more redshifted with increasing solvent polarity. However, the detailed mechanism is unclear. In this study, we investigated the excited-state properties of Py-Bn-Mal-MoS2 with theoretical methods. First, we constructed model systems of Py-Bn-Mal-MoS2 nanosheet and performed time-dependent density functional theory (TDDFT) calculations. The calculated molecular orbitals and dipole moment changes demonstrated that the emission is a charge transfer transition from the pyrene moiety to MoS2 nanosheet. Next, we performed three-dimensional reference interaction site model (3D-RISM) calculations, which is based on the integral equation theory of molecular liquids, to assess the solvent dependence of emission energies. The calculated results reproduced the experimental solvent dependence well. The distributions of polar solvent molecules showed strong interaction between the excited state of Py-Bn-Mal-MoS2 and solvent molecules. This study supports the potential of covalent modification of MoS2 for photocatalytic applications.

Soft pinning: Experimental validation of static correlations in supercooled molecular glass-forming liquids.

Enormous enhancement in the viscosity of a liquid near its glass transition is a hallmark of glass transition. Within a class of theoretical frameworks, it is connected to growing many-body static correlations near the transition, often called "amorphous ordering." At the same time, some theories do not invoke the existence of such a static length scale in the problem. Thus, proving the existence and possible estimation of the static length scales of amorphous order in different glass-forming liquids is very important to validate or falsify the predictions of these theories and unravel the true physics of glass formation. Experiments on molecular glass-forming liquids become pivotal in this scenario as the viscosity grows several folds (), and simulations or colloidal glass experiments fail to access these required long-time scales. Here we design an experiment to extract the static length scales in molecular liquids using dilute amounts of another large molecule as a pinning site. Results from dielectric relaxation experiments on supercooled Glycerol with different pinning concentrations of Sorbitol and Glucose, as well as the simulations on a few model glass-forming liquids with pinning sites, indicate the versatility of the proposed method, opening possible new avenues to study the physics of glass transition in other molecular liquids.