We show that all existing methods quantifying rotational motion in molecular fluids eventually have severe limitations in systems undergoing complex rotational motion characterized by slow, heterogeneous, or intermittent dynamics. This impacts, in particular, the study of rotational dynamics in molecular supercooled liquids near their glass transition, as well as discussions of the decoupling between rotational and translational motion and violations of the Debye-Stokes-Einstein relation. We present a brief overview of existing methods and explain why none of them can accurately capture the evolution of rotational dynamics from a diffusive fluid to an arrested solid, thus resolving inconsistent literature results. We then introduce an empirical method that efficiently solves all issues. We benchmark our method by devising a family of continuous-time random walk models for rotational dynamics. Our method correctly quantifies the statistics of free and caged rotational motion, as well as non-Gaussian and non-Fickian rotational dynamics, and should allow a better characterization of dynamic heterogeneity in the rotational motion of supercooled molecular fluids.

Fluids, characterized by broken time-reversal and parity symmetries, exhibit odd transport phenomena where longitudinal drivings can induce transverse fluxes. Recently, a mesoscale model called chiral stochastic rotation dynamics (CSRD) has been developed to simulate odd fluids with high computational efficiency. In this work, we verify the Green-Kubo relations for both normal and odd transport coefficients in this model, confirming that this model correctly captures the underlying statistical relationship between macroscopic transport and microscopic fluctuations in odd fluids. This work solidifies the physical foundation of the CSRD model, paving the way for its application in studying the statistical physics and nonequilibrium behavior of odd fluids.

Tuning thermal conductivity (κ) of metal-organic frameworks (MOFs) is pivotal for advancing their emerging thermoelectric applications and addressing the heat dissipation bottleneck in gas adsorption processes, yet heat conduction mechanisms in MOFs, particularly from the perspective of intrinsic lattice vibrations, remain elusive, limiting rational thermal engineering. Here, we focus on organic ligand rotational dynamics and elucidate their critical but long-overlooked modulations on thermal transport. Through elaborate atomistic simulations on prototypical MIL-47, we report that low-frequency, anharmonic linker librations dramatically intensify phonon scattering, inducing an over 2-fold reduction in κ. Such a suppression effect is further confirmed to be universal across diverse flexible frameworks featuring rotatable ligands, including the known zeolitic imidazolate and covalent organic families. Accordingly, we evaluate multiple practical strategies to regulate κ by tailoring linker rotational dynamics. These insights open vast avenues for the flexible design of MOFs' thermal performance to meet their energy-related applications.

Coupling and decoupling between translational and rotational dynamics in a tetrahedral molecular liquid

Type V deep eutectic solvents (DESs) are composed exclusively of nonionic molecular species, in contrast to type I-IV DESs, which contain at least one ionic component. In the absence of ionic constituents, the cohesive energy of type V DESs is governed primarily by hydrogen bonding and van der Waals interactions. Such an intermolecular framework imparts distinct physicochemical properties, such as increased hydrophobicity and relatively low viscosity (compared to their ionic counterparts), substantially broadening the application potential of DESs. Owing to their fundamental distinction from ionic DESs and ionic liquids (ILs), it is imperative to understand how the nonionic nature of type V DESs influences their microstructure and dynamic behavior for their rational and strategic utilization. To address this, we examined the microenvironment of a thymol/camphor-based type V DES using three molecular probes: Coumarin-153, a neutral benchmark probe widely employed for investigating dynamics in solutions, and two fluorescent molecular rotors, Thioflavin T and Auramine O, whose fluorescence quantum yield is sensitive to the microviscosity of the local environment. Absorption and steady-state fluorescence measurements reveal that the local micropolarity experienced by Coumarin-153 in the DES is comparable to that of acetonitrile. A slight red-edge excitation shift observed in the steady-state fluorescence spectra with varying excitation wavelengths points to the presence of subtle spatial heterogeneity within the solvent. Time-resolved emission spectra (TRES) were recorded over the temperature range of 278-333 K and used to construct the solvent correlation function, which describes the solvent's reorganization in the excited state following the electronic excitation of Coumarin-153. The solvation dynamics were found to be bimodal, with a dominant, markedly slow component indicative of a highly sluggish solvent response. Correlating the solvation dynamics with the shear viscosity of the solvent reveals significant decoupling (p ≈ 0.62, where p is the decoupling parameter), suggesting decoupling of the solvation dynamics from the viscosity of the medium. Furthermore, a dynamic crossover was observed at approximately 308 K or 35 °C, showing temperature-dependent modulation in the structural features of the thymol/camphor-based DES. In contrast, the rotational dynamics of Coumarin-153 closely follow the Stokes-Einstein-Debye hydrodynamic model (p ≈ 0.8), indicating that despite heterogeneity, Coumarin-153 experiences an effectively homogeneous local environment. In the thymol/camphor-based DES, the temperature-dependent evolution of fluorescence quantum yield for both Thioflavin T and Auramine O reveals a nonuniform response across the studied range, manifesting as two distinct friction regimes separated by a well-defined crossover at 308 K. Microviscosity determination of both probes reveals decoupling of the torsional relaxation from the bulk viscosity of the solvent, which is complemented by the disparity in the activation energy values of viscous flow and nonradiative transition obtained by utilizing Arrhenius-type curves. This observation suggests that the photophysical behavior of molecular rotors like Thioflavin T and Auramine O is not governed solely by the bulk viscosity of the DES; rather, the local microstructure of the solvent plays a dominant role. These findings underscore how variations in local polarity and specific solute-solvent interactions drive preferential solvation, revealing the presence of microscopically heterogeneous domains within the nonionic, hydrogen-bonded framework of the DES.

Controlling the spin state of single molecules is central to the next-generation molecular electronics and spintronic architectures. Using first-principles computational methods, we systematically investigate the geometrical, electronic structures, magnetic properties, and transport behaviors of the sandwich-like [Cp-M(cyclo-E5)M-Cp]x (E = Sb, Bi; M = V, Ta, Nb) nanoclusters (NCs), which feature a unique "metal-ring-metal" topology. We demonstrate that mechanical perturbations─specifically the vertical translation and in-plane rotation of the central E5 ring─ effectively modulate the localized coordination field to enable robust, reversible high-spin to low-spin (HS ↔ LS). Moreover, in specific oxidation states, these distinct spin states are coupled with unique magnetic correlations, where the HS state exhibits ferromagnetic (FM) alignment and the LS state manifests antiferromagnetic (AFM) coupling. Crucially, the rotational dynamics of the central ring realize a temperature-dependent, conformationally switchable magnetic phase, while electronic charge modulation provides a highly sensitive, orthogonal axis for gating these magnetic characteristics. These combined mechanical and electrical degrees of freedom yield highly distinctive magnetic signatures and spin-polarized electronic transport profiles. By mapping out specific candidate molecules, highlighting the antimony-based [Cp-V(cyclo-Sb5)V-Cp]x NCs framework as an exceptional candidate for multimode mechanical control, our findings deliver a rigorous, structure-driven blueprint for molecular spin regulation, positioning this class of nanoclusters as highly promising platforms for single-molecule memory, nanoscale spin valves, and molecular spintronic applications.

Higher-order nucleic acid structures have garnered attention nowadays in the field of active cancer research owing to their wide range of applications in gene regulation and targeted gene therapy. Chelerythrine (CHL), a benzophenanthridine plant alkaloid, exhibits important biological activities and has therapeutic applications. In this article, we endeavour to elucidate the comparative binding interactions of chelerythrine (CHL) with the triplex (T.A*T) and duplex (A.T) structures of DNA by performing a series of spectroscopic studies and theoretical calculations. UV-visible absorption spectrophotometric studies and spectrofluorimetric studies showed stronger binding affinity of CHL towards T.A*T compared with its parent duplex form, i.e. A.T. Thermal melting experiments revealed a substantial thermal stabilization of the Hoogsteen base-paired strand of the T.A*T triplex (up to ∼31.4 °C), while the Watson-Crick base-paired strands of both triplex and duplex forms were moderately stabilized (up to ∼9 °C). Fluorescence quenching studies, steady-state anisotropy studies, competitive displacement assays, and circular dichroism studies confirmed an intercalative binding mode in both cases, and the extent of intercalation was found to be stronger in the case of the triplex compared with the parent duplex form. Fluorescence lifetime measurements and time-resolved anisotropy decay studies demonstrated significant alteration in the excited-state behaviour and rotational dynamics of CHL within the DNA triplex- and duplex-bound environments, respectively. Analysis of the thermodynamic parameters revealed that the complexation of CHL with both forms of DNA helices was characterized by negative enthalpy changes and negative entropy changes. Theoretical calculations using DFT and TD-DFT methods validated the experimental optical spectroscopic behaviour of the ligand CHL, as obtained from both absorption and fluorescence studies. Elucidation of such structural and energetic facets involved in the association of CHL with the DNA triplex and duplex forms may offer new scope for strategic nucleic acid-targeted drug design.

Chiral active Brownian particles (CABPs) are self-propelled agents with intrinsic rotational dynamics, giving rise to circular trajectories commonly observed in biological and synthetic microswimmers. Understanding how CABPs explore confined environments and locate targets is crucial for characterizing transport, search efficiency, and reaction processes in physical and biological systems. We study the escape dynamics of CABPs from one- and two-dimensional confined domains. In one dimension, we consider intervals with either two absorbing boundaries or a reflecting boundary on one side and an absorbing boundary on the other, and derive closed-form asymptotic solutions in the high-chirality regime, revealing the quantitative scaling of the mean first passage time (MFPT) as a function of particle rotation speed (chirality). In two dimensions, we analyze escape from a disk containing one absorbing arc or two symmetric absorbing arcs. By numerically solving the governing partial differential equations, we compute the MFPT for CABPs to escape the domains as a function of the particle's initial orientation, self-propulsion speed, angular velocity, and domain geometry. Our results show that, depending on the parameters and geometry, the MFPT can exhibit non-monotonic behavior as a function of chirality. A minimal escape time exists at an intermediate value of chirality, where the rotational time scale balances the active swimming time scale, redirecting a particle towards the exit which would otherwise be blocked due to unfavorable initial orientation. Our work offers a comprehensive characterization of CABP escape dynamics in canonical confinements and identifies chirality as a key control parameter for transport and search in confined physical and biological systems.

Recent studies have shown that metal-organic frameworks (MOFs) can enable ultralow rotational barriers for molecular rotors in the solid state. In this near-free-rotor regime, elucidating how molecules behave within an ordered lattice becomes central to both a fundamental understanding and the design of crystalline molecular machines. Here, using a series of structurally simple, isoreticular MOF-5 homologues as a common platform, we present a systematic computational investigation of the rotational dynamics of five highly symmetric, rigid cage-like hydrocarbon rotators─bicyclo[1.1.1]pentane (BCP), cubane (CUB), bicyclo[2.2.2]octane (BCO), barrelene (BAR), and diamantane (DIA)─over a broad temperature range of 30-300 K. We show that under nearly barrierless conditions, these molecular rotators can exhibit inertia-dominated, continuous unidirectional rotations, which we quantify by the frequency of 360° turnover events. Temperature dependence of the 360° turnover frequency reveals clear differences among the rotors in how their dominant dynamical mechanisms transition with temperature. Furthermore, we introduce a Langevin description to quantitatively analyze the time evolution of the mean squared net angular displacement of the rotors in their rotational coordinate. We show that on long time scales all rotors enter the Brownian diffusion regime. The extracted rotational damping coefficients η reveal pronounced differences among the five rotors in both the strength of rotor-lattice coupling and its temperature dependence.

The paddle-wheel mechanism has long been invoked to explain ion transport in organic ionic plastic crystals (OIPCs), wherein rotational motion of matrix ions is assumed to facilitate ion hopping. Here, we critically examine the paddle-wheel mechanism using molecular dynamics (MD) simulations combined with hop function analysis for a representative OIPC, Li-doped 1,3-dimethylimidazolium hexafluorophosphate ([MMIM][PF6]). While matrix ions ([MMIM]+ and PF6-) exhibit translation-rotation coupling consistent with the paddle-wheel mechanism, Li+ ion transport, central to the ion conductivity of solid-state electrolytes (SSEs), is decoupled from the rotational dynamics of neighbor ions. Instead, the hop function analysis reveals that the collective rearrangement of the third, fourth, and fifth nearest PF6- anions around Li+ forms the transition-state configuration governing Li+ hopping. This process constitutes the primary Li+ ion transport mechanism, replacing the conventional paddle-wheel mechanism. Our results establish the hop function analysis as a robust framework for disentangling ion transport mechanisms in complex solid-state electrolytes and call for a reassessment of long-standing mechanistic assumptions in OIPCs.

Water confined in zeolite-templated carbons (ZTCs) exhibits properties fundamentally different from those of bulk liquid, with profound implications for energy storage, separation technologies, and catalysis. Despite the technological importance of water behavior in ZTC nanopores, molecular-level understanding remains limited. This work presents comprehensive molecular dynamics (MD) simulations investigating the structure, dynamics, and hydrogen bonding characteristics of water confined within faujasite-derived ZTC. Classical MD simulations were developed with validated force fields to characterize radial and spatial distribution functions, hydrogen bond networks and lifetimes, cluster size distributions, domain formation, translational and rotational dynamics, and velocity autocorrelation functions. Systematic comparison with bulk liquid water reveals confinement-induced modifications to tetrahedral hydrogen bonding networks, spatial organization into discrete domains, hydrogen bond dynamics, and transport properties. The three-dimensional hierarchical pore topology of ZTC creates unique confinement environments distinct from one-dimensional nanotubes or two-dimensional slit pores. These findings provide molecular-level insights essential for the rational design of ZTC-based materials for electrochemical energy storage, water desalination membranes, proton exchange systems, and aqueous-phase catalysis, thereby advancing fundamental understanding of water confinement in complex carbon nanostructures.

Entropic crystallization of Brownian squares through pathways governed by orientational dynamics.

This work examines molecular dynamics and interactions in ethylene glycol-choline chloride (EG-ChCl) mixtures across 0-33 mol % ChCl, spanning the true eutectic region near 17-20 mol % and the commonly used 1:2 formulation. We combine pulsed-field-gradient (PFG) diffusion, fast-field-cycling (FFC) relaxometry, temperature-dependent 13C T1, and nuclear Overhauser effect spectroscopy (NOESY) to disentangle local from macroscopic dynamics. PFG and FFC show that both translational and average rotational motions largely track the strong increase in viscosity with ChCl content, with ethylene glycol consistently diffusing faster than the choline cation and no global dynamical anomaly at the eutectic composition. More subtle, site-specific composition effects nevertheless emerge. The ratio of the diffusion coefficient of the hydroxyl group of choline to the diffusion coefficient of the methyl group of choline displays a shallow minimum in the 17-25 mol % region, indicating a modest change in how the hydroxyl-bearing end of choline samples the underlying translational motion relative to the methyl groups. 13C T1 analysis shows that rotational correlation times at 25 °C generally increase with ChCl, reflecting viscosity-coupled slowing, while the CH2-Nα site exhibits a small but reproducible deviation from this monotonic trend near the eutectic. NOESY spectra at similar compositions reveal enhanced cross-relaxation between EG and choline protons, consistent with increased headgroup-solvent contact density rather than a wholesale structural rearrangement. Overall, our multitechnique study demonstrates that EG-ChCl dynamics are predominantly viscosity-dominated, with the eutectic region acting as a subtle dynamical crossover where specific choline segments become maximally coupled to the hydrogen-bond network. These insights refine the structure-dynamics picture of choline-chloride DESs and provide practical guidance for tuning composition in electrochemical, separation, and catalytic applications.

Isotope-selective rotational control of asymmetric-top molecules is a challenging task owing to their complex rotational dynamics. Here, we extend a simulation framework for isotope-selective rotational control to the water isotopologues H2O and T2O, and numerically identify pulse conditions that maximize isotope contrast in an equimolar gas-phase mixture driven by nonresonant, linearly polarized double pulses. We examine three characteristic rotational periods associated with ΔJ = 1 transitions from the ground state and find that TrotB+C=1/B+C provides the strongest synchronization for isotope contrast. To quantify isotope-selective rotational contrast, we define a rotational contrast metric based on the three-dimensional alignments of H2O and T2O. When the pulse delay is synchronized to TrotB+C, the metric reaches a maximum value of 1.99 at 10K; further optimization of the pulse delay and intensity ratio increases the metric to 2.20. These results demonstrate that appreciable isotope-selective contrast can be achieved even in the H2O/T2O system, where the small polarizability anisotropy makes alignment control inherently difficult, and establish a versatile route toward isotope-selective rotational control of more complex asymmetric-top molecules.

The vibration problem caused by milling is a key factor restricting high-precision and high-efficiency machining. Traditional passive vibration suppression methods are limited by fixed structural parameters and lack sufficient adaptability to dynamic operating conditions, making it difficult to achieve effective broadband vibration control. Magnetic bearings, with their non-contact characteristics and active controllability, provide a new idea for milling vibration suppression. To overcome these limitations, this paper proposes a novel hybrid magnetic-ball-supported flexible rotor system that combines active magnetic bearings with mechanical ball bearings, thereby achieving both controllable dynamic stiffness and stable rigid support. Based on the milling force model and the hybrid support rotor dynamics model, a coupled mathematical model is established, and the vibration suppression effect of the magnetic bearing on milling induced vibration is investigated by magnetic force regulation under PID control. Furthermore, milling force signals were generated using a simulation platform and applied to the rotor test bench to conduct numerical simulations and experimental validation. The results demonstrate that the proposed hybrid support strategy can significantly reduce milling-induced vibration amplitude, improve rotor dynamic stability, and enhance vibration suppression performance over a wide operating range. This study proposes a new hybrid vibration control scheme for high-speed, high-precision milling systems and provides a method for intelligent vibration reduction in advanced machining equipment.

Direct measurements of molecular motion during chemical reactions are essential to understand how molecular machines perform work. In most systems, however, the reaction rate is dictated by the probability of reaching the transition geometry by thermal fluctuations, thereby masking the underlying molecular motions. Here, we study the dynamics of rotation around the central double bond of an artificial light-driven molecular motor by femtosecond transient absorption and fluorescence spectroscopy. We observe a first rotation step, assigned to a rotation of ∼28° which occurs synchronously across the motor ensemble and without an activation barrier, such that the measurements are representative of molecular dynamics. We can thus estimate the rotation speed and the relative importance of inertia, friction and strain, and propose a simplified nanomechanical model for the molecular motor. The results suggest a new framework to investigate work at the nanoscale and provide tools to analyze the mechanics of molecular machines, both synthetic or biological.

Controlling water structure and dynamics at silica interfaces are central to a wide range of technologies, including protective oxide layers for solar water splitting and nanoporous membranes. In this work, we develop a machine learning interatomic potential, trained via active learning, to achieve ab initio accuracy for water confined between hydroxylated silica surfaces over a range of silanol coverages and slit widths. We find that partially hydroxylated surfaces (50 and 75% OH) support stronger water-surface hydrogen bonding and more extended interfacial density profiles than fully hydroxylated (100% OH) surfaces, indicating that increasing OH coverage does not necessarily strengthen interfacial hydrogen-bond networks. Translational diffusion decreases approximately linearly with slit width and OH coverage, whereas rotational dynamics respond nonlinearly. In particular, at the smallest slit width of 5 Å, 75% OH coverage produces an enhanced local tetrahedral ordered interfacial network that strongly suppresses reorientation, while 100% coverage yields a crowded, disordered interfacial layer that also hinders rotation. In contrast, the 50% OH coverage is sufficiently sparse that it does not markedly alter water structure or dynamics under confinement. These results show that coupled control of pore size and surface chemistry enables nonlinear tuning of interfacial water structure and transport, providing a design strategy for optimizing porous silica for either enhanced interfacial stability and controlled reactivity or rapid and selective transport.

Hydridoborates have emerged as a distinct class of inorganic solid electrolytes with exceptional potential for solid-state batteries. Their lithium and sodium salts with polyhedral closo- and closo-carba-hydridoborate anions offer low crystallographic density, mechanical softness suitable for cold pressing, and broad electrochemical stability, enabling integration with alkali metal anodes and high-voltage cathodes. Superionic transport arises from order-disorder transitions and the resulting rotational dynamics of the cage anions, which create a highly connected and dynamically accessible network of Li+ and Na+ migration pathways. So far, electrolyte synthesis is costly, due to the close chemical relationship among boron-hydrogen clusters that leads to low selectivity and often produces mixtures of hydridoborates that are difficult to separate. Most reported routes are multistep procedures involving elevated temperatures, extended reaction times, solvent handling, and purification steps. Synthetic routes based on inexpensive NaBH4 precursors, and direct synthesis of mixed-anion electrolytes instead of pure hydridoborate salts showcase promising paths toward scalable cost-effective synthesis. Finally, recently discovered mechanisms of hydridoborate oxidation and reduction are outlined, and their integration into solid-state batteries is summarized. By linking structural chemistry, transport mechanisms, and device-level behavior, this Feature Article outlines key design principles and future directions for hydridoborate solid electrolytes in next-generation solid-state batteries.

A novel predictive controller is introduced for rendezvous with non-cooperative tumbling targets in active debris removal applications, based on the model predictive control for tracking (MPCT) framework, which improves the robustness and computational efficiency of conventional MPC by optimizing the system toward artificial equilibrium points rather than fixed references. This paper aims to provide a computationally efficient and theoretically sound control strategy that enables reliable proximity operations around tumbling objects, despite their complex rotational motion. The target’s nonperiodic rotational dynamics and state and control constraints are considered. The approach is based on applying an intermediate coordinate transformation that eliminates the time dependency due to rotations in the constraints. The proposed algorithm leverages feasible trajectories, obtained through the conservation of momentum and energy of rotating bodies, to obtain strong convergence guarantees on arbitrary horizons. A control law is then found as the solution to a quadratic programming problem that provides feasibility and stability guarantees by means of a terminal virtual controller. The main result is an MPCT-based controller for linear time-varying systems induced by rotational dynamics, with provable feasibility and stability guarantees. A near-rendezvous simulation with the Envisat spacecraft confirms the practical relevance and performance of the proposed controller.

Experimental Investigation of the directional collapse and microjet dynamics of single acoustic bubbles in confined tubes.