Molecular Motion Research Articles

Unlocking Cage‐Confined Cations Molecular Dynamics toward High‐Tc Perovskite Ferroelectrics

Cage‐confinement effect that imposes great constriction on the dynamic behaviors of guest molecules is an established platform for tailoring physical properties. Herein, the strategy of enhancing cage‐confinement effect to control molecular motion has been probed for the first time to exploit new high‐Tc ferroelectrics of 2D hybrid perovskites. By fine‐tailoring of the confined cations inside the perovskite cavities, we have successfully obtained new homologous ferroelectrics of (BA)2(MA)2Pb3Cl10 (1; BA =n‐butylamine, MA = methylamine) and (BA)2(EA)2Pb3Cl10 (2; EA = ethylamine). Intriguingly, this dynamics modulation of cage‐confined cations leads to a remarkable promotion of Curie temperature (Tc), boosting from 340 K (for 1) to 402 K (for 2). In situ solid‐state NMR spectroscopy and theoretical simulations on energy barrier confirm that the larger EA cation in 2 is subject to stronger confinement effect, of which potential energy barrier of molecular motion is ~3.5 times that of MA cation. This dynamic behavior greatly suppresses the dynamic motions of EA cation, while MA cation can easily accelerate motion and reach a fast motion limit, thus accounting for an enhancement of Tc (ΔT~62 K) in 2. The finding sheds light on the understanding of cage‐confined electric orders and the precise design of high‐performance ferroelectrics.

Unlocking Cage-Confined Cations Molecular Dynamics toward High-Tc Perovskite Ferroelectrics.

Cage-confinement effect that imposes great constriction on the dynamic behaviors of guest molecules is an established platform for tailoring physical properties. Herein, the strategy of enhancing cage-confinement effect to control molecular motion has been probed for the first time to exploit new high-Tc ferroelectrics of 2D hybrid perovskites. By fine-tailoring of the confined cations inside the perovskite cavities, we have successfully obtained new homologous ferroelectrics of (BA)2(MA)2Pb3Cl10 (1; BA =n-butylamine, MA = methylamine) and (BA)2(EA)2Pb3Cl10 (2; EA = ethylamine). Intriguingly, this dynamics modulation of cage-confined cations leads to a remarkable promotion of Curie temperature (Tc), boosting from 340 K (for 1) to 402 K (for 2). In situ solid-state NMR spectroscopy and theoretical simulations on energy barrier confirm that the larger EA cation in 2 is subject to stronger confinement effect, of which potential energy barrier of molecular motion is ~3.5 times that of MA cation. This dynamic behavior greatly suppresses the dynamic motions of EA cation, while MA cation can easily accelerate motion and reach a fast motion limit, thus accounting for an enhancement of Tc (ΔT~62 K) in 2. The finding sheds light on the understanding of cage-confined electric orders and the precise design of high-performance ferroelectrics.

Probing the Hidden Photoisomerization of a Symmetric Phosphaalkene Switch

In this study, we present the synthesis and analysis of a novel, air‐stable, and solvent‐resistant phosphaalkene switch. Using this symmetric switch, we have demonstrated degenerate photoisomerization experimentally for the first time. With a combination of photochemical‐exchange NMR spectroscopy, ultrafast transient absorption spectroscopy, and quantum chemical calculations, we elucidate the isomerization mechanism of this symmetric phosphaalkene. Our findings highlight the critical role of the isolobal analogy between C=P and C=C bonds in governing nanoscale molecular motion and break new ground for our understanding of light‐induced molecular processes in symmetric heteroalkene systems.

Probing the Hidden Photoisomerization of a Symmetric Phosphaalkene Switch.

In this study, we present the synthesis and analysis of a novel, air-stable, and solvent-resistant phosphaalkene switch. Using this symmetric switch, we have demonstrated degenerate photoisomerization experimentally for the first time. With a combination of photochemical-exchange NMR spectroscopy, ultrafast transient absorption spectroscopy, and quantum chemical calculations, we elucidate the isomerization mechanism of this symmetric phosphaalkene. Our findings highlight the critical role of the isolobal analogy between C=P and C=C bonds in governing nanoscale molecular motion and break new ground for our understanding of light-induced molecular processes in symmetric heteroalkene systems.

Utilization of Electric Fields to Modulate Molecular Activities on the Nanoscale: From Physical Properties to Chemical Reactions.

As a primary energy source, electricity drives broad fields from everyday electronic circuits to industrial chemical catalysis. From a chemistry viewpoint, studying electric field effects on chemical reactivity is highly important for revealing the intrinsic mechanisms of molecular behaviors and mastering chemical reactions. Recently, manipulating the molecular activity using electric fields has emerged as a new research field. In addition, because integration of molecules into electronic devices has the natural complementary metal-oxide-semiconductor compatibility, electric field-driven molecular devices meet the requirements for both electronic device miniaturization and precise regulation of chemical reactions. This Review provides a timely and comprehensive overview of recent state-of-the-art advances, including theoretical models and prototype devices for electric field-based manipulation of molecular activities. First, we summarize the main approaches to providing electric fields for molecules. Then, we introduce several methods to measure their strengths in different systems quantitatively. Subsequently, we provide detailed discussions of electric field-regulated photophysics, electron transport, molecular movements, and chemical reactions. This review intends to provide a technical manual for precise molecular control in devices via electric fields. This could lead to development of new optoelectronic functions, more efficient logic processing units, more precise bond-selective control, new catalytic paradigms, and new chemical reactions.

Investigating Interaction Dynamics of an Enantioselective Peptide‐Catalyzed Acylation Reaction

Modern nuclear magnetic resonance (NMR) methods like carbon relaxation dispersion in the rotating frame (13C‐R1ρ) and proton chemical exchange saturation transfer (1H‐CEST) are key methods to investigate molecular recognition in biomacromolecules and to detect molecular motions on the µs to s timescale, revealing transient conformational states. Changes in kinetics can be linked to binding, folding, or catalytic events. Here, we investigated whether these methods allow detection of changes in the dynamics of a small, highly selective peptide catalyst during recognition of its enantiomeric substrates. The flexible tetrapeptide Boc‐l‐(π‐Me)‐His‐AGly‐l‐Cha‐l‐Phe‐OMe, used for the monoacetylation of cycloalkane‐diols, is probed at natural abundance using 13C‐R1ρ and 1H‐CEST. Indeed, we detected differences in dynamics of the peptide upon interaction with the diol. Importantly, these differ depending on the enantiomer of the substrate used. These enantiospecific influences of the substrates on the dynamics of the peptide are rationalized using computational techniques. We find that even though one enantiomer reacts faster, as confirmed by reaction monitoring, the other is more tightly bound in DCM (as confirmed by 1H‐saturation transfer difference (STD) measurements). These findings provide insights into the recognition of the substrates and explain the selectivity differences observed between the solvents toluene and DCM.

Investigating Interaction Dynamics of an Enantioselective Peptide‐Catalyzed Acylation Reaction

Modern nuclear magnetic resonance (NMR) methods like carbon relaxation dispersion in the rotating frame (13C‐R1ρ) and proton chemical exchange saturation transfer (1H‐CEST) are key methods to investigate molecular recognition in biomacromolecules and to detect molecular motions on the µs to s timescale, revealing transient conformational states. Changes in kinetics can be linked to binding, folding, or catalytic events. Here, we investigated whether these methods allow detection of changes in the dynamics of a small, highly selective peptide catalyst during recognition of its enantiomeric substrates. The flexible tetrapeptide Boc‐l‐(π‐Me)‐His‐AGly‐l‐Cha‐l‐Phe‐OMe, used for the monoacetylation of cycloalkane‐diols, is probed at natural abundance using 13C‐R1ρ and 1H‐CEST. Indeed, we detected differences in dynamics of the peptide upon interaction with the diol. Importantly, these differ depending on the enantiomer of the substrate used. These enantiospecific influences of the substrates on the dynamics of the peptide are rationalized using computational techniques. We find that even though one enantiomer reacts faster, as confirmed by reaction monitoring, the other is more tightly bound in DCM (as confirmed by 1H‐saturation transfer difference (STD) measurements). These findings provide insights into the recognition of the substrates and explain the selectivity differences observed between the solvents toluene and DCM.

Controlled migration of oleic acid amide through adsorption on TS-1 zeolite for long-lasting anti-adhesive rubber composites

The adhesion of materials on the surface can affect the appearance, durability, and performance stability of rubber composites. Incorporating anti-adhesive additives into composites is an effective strategy to improve anti-adhesive properties, as these additives migrate to the surface to form an anti-adhesive layer. However, excessive migration rates can result in poor durability of the anti-adhesive layer and significant powder adhesion on the surface. This study prepared titanium silicate zeolite adsorbed with acid amide composite filler (OAA@TS-1) by adsorbing OAA onto the active sites of TS-1, which was then incorporated into natural rubber (NR). The adsorption effect reduces the migration rate of OAA within the rubber composite, allowing more OAA to remain in the matrix. Additionally, the adsorption is reversible, and the adsorbed OAA can overcome the adsorption through molecular thermal motion, which can migrate to the surface. After the anti-adhesive layer is worn, OAA can persistently migrate outward, effectively repairing the layer and enhancing the durability of the anti-adhesive properties. In comparison to rubber composites filled solely with OAA, the OAA@(TS-1) filled rubber composite exhibits a remarkable reduction of 55% in the amount of adherent powder on the composite surface and a 24% decrease in the coefficient of friction after three friction cycles. After slicing and leaving for 3 days, the contact angle increases by 18%. The long-lasting anti-adhesive rubber composite developed in this study demonstrates significant application potential in areas such as material conveyance and power transmission.

Slip due to kink propagation at the liquid–solid interface

In Couette flow, the liquid atoms adjacent to a solid substrate may have a finite average tangential velocity relative to the substrate. This so-called slip has been observed frequently. However, the particular molecular-level mechanisms that give rise to liquid slip are poorly understood. It is often assumed that liquid slip occurs by surface diffusion whereby atoms independently move from one substrate equilibrium site to another. We show that under certain conditions, liquid slip is due not to singular independent molecular motion, but to localized nonlinear waves that propagate at speeds that are orders of magnitude greater than the slip velocity at the liquid–solid interface. Using non-equilibrium molecular dynamics simulations, we find the properties of these waves and the conditions under which they are to be expected as the main progenitors of slip. We also provide a theoretical guide to the properties of these nonlinear waves by using an augmented Frenkel–Kontorova model. The new understanding provided by our results may lead to enhanced capabilities of the liquid–solid interface, for heat transfer, mixing, and surface-mediated catalysis.

Pressure-Engineered Through-Space Conjugation for Precise Control of Clusteroluminescence.

Clusteroluminogens (CLgens) represent an innovative class of nonconjugated luminophores that address the limitations of conventional π-conjugated molecules. Different from the through-bond conjugation mechanism in π-conjugated luminophores, through-space conjugation (TSC) plays dominant roles in CLgens. However, precisely controlling TSC to customize the optical properties of CLgens remains a significant challenge. This work proposes a novel strategy of high pressure to engineer TSC within tetraphenylalkanes (TPAs)-based CLgens at molecular level. High-pressure exploration enables accurate manipulation of clusteroluminescence and elucidates the intrinsic structure-property relationships involved. Upon initial compression, the predominant molecular distortions marked by increased interfacial angles between benzene rings diminish TSC, resulting in anomalous hypochromatic shift in emission. Subsequently, considerable structural contraction enhances TSC and suppresses molecular motion, resulting in a pronouncedly enhanced and bathochromic-shifted emission. Notably, a series of TPAs-based CLgens exhibit intense white-light emission upon pressure release, attributed to irreversible structural distortion and destruction. This study not only advances the understanding of CLgens, but also underscores the crucial structural factors for effective TSC control, paving the way for establishing new photophysical theories for aggregate science.

Pressure‐Engineered Through‐Space Conjugation for Precise Control of Clusteroluminescence

Clusteroluminogens (CLgens) represent an innovative class of nonconjugated luminophores that address the limitations of conventional π‐conjugated molecules. Different from the through‐bond conjugation mechanism in π‐conjugated luminophores, through‐space conjugation (TSC) plays dominant roles in CLgens. However, precisely controlling TSC to customize the optical properties of CLgens remains a significant challenge. This work proposes a novel strategy of high pressure to engineer TSC within tetraphenylalkanes (TPAs)‐based CLgens at molecular level. High‐pressure exploration enables accurate manipulation of clusteroluminescence and elucidates the intrinsic structure‐property relationships involved. Upon initial compression, the predominant molecular distortions marked by increased interfacial angles between benzene rings diminish TSC, resulting in anomalous hypochromatic shift in emission. Subsequently, considerable structural contraction enhances TSC and suppresses molecular motion, resulting in a pronouncedly enhanced and bathochromic‐shifted emission. Notably, a series of TPAs‐based CLgens exhibit intense white‐light emission upon pressure release, attributed to irreversible structural distortion and destruction. This study not only advances the understanding of CLgens, but also underscores the crucial structural factors for effective TSC control, paving the way for establishing new photophysical theories for aggregate science.

Promoting mechanism of SO2 and NO adsorption on activated carbon at sub-zero temperature

The adsorption of SO₂ and NO on activated carbon (AC) was studied between −40 ℃ and 20 ℃. The results showed that the adsorption capacity of AC-2–750 (AC reacted with a 2:1 ratio of KOH at 750 °C) for SO2 and NO were 374.2 mg/g and 83.1 mg/g at −40 °C, respectively. As the temperature decreased, the van der Waals and electrostatic forces strengthened while molecular movements weakened, favouring low-temperature adsorption. During co-adsorption, SO2 was preferentially adsorbed in ultramicropores, whereas NO was primarily adsorbed in supermicropores. When NO was oxidised to NO2, it occupied the original adsorption sites of SO2, leading to a reduction in SO2 adsorption. The presence of NO2 favoured the adsorption of the entire system. This study provided directions for the design of activated carbon for LAS (low-temperature adsorption) technology and illustrated its mechanism at the microscopic level.

Three-arm polyrotaxanes with multidirectional molecular motions as the nanocarrier for nitric oxide-enhanced photodynamic therapy against bacterial biofilms in septic arthritis

Bacterial biofilms are one of the major contributors to the refractoriness of septic arthritis. Although nitric oxide (NO)-enhanced photodynamic (PDT) therapy has been involved in biofilm eradication, the anti-biofilm efficacy is usually hindered by the short half-life and limited diffusion distance of active molecules. Herein, we report a three-arm structure using the photosensitive core chlorin e6 to integrate three α-cyclodextrin (α-CD) polyrotaxane chains as the supramolecular nanocarrier of NO-enhanced PDT therapy, in which NO was loaded on the cationic rings (α-CDs). Beneficial from the enhanced permeability of the nanocarrier due to the collective act on biofilms by the molecular motions (slide and rotation of rings) of three chains in different directions, NO capable of inducing biofilm dispersal and reactive oxygen species were efficiently delivered deep inside biofilms under 660 nm laser irradiation, and reactive nitrogen species with stronger bactericidal ability was produced in-situ, further accomplishing bacteria elimination inside biofilms. In-vivo therapeutic performance of this platform was demonstrated in a rat septic arthritis model by eliminating the methicillin-resistant Staphylococcus aureus infection, and potentiating the immune microenvironment regulation and bone loss inhibition, also providing a promising strategy to numerous obstinate clinical infections caused by biofilms.Graphical

The potent PHL4 transcription factor effector domain contains significant disorder.

The phosphate-starvation response transcription-factor protein family is essential to plant response to low-levels of phosphate. Proteins in this transcription factor (TF) family act by altering various gene expression levels, such as increasing levels of the acid phosphatase proteins which catalyze the conversion of inorganic phosphates to bio-available compounds. There are few structural characterizations of proteins in this TF family, none of which address the potent TF activation domains. The phosphate-starvation response-like protein-4 (PHL4) protein from this family has garnered interest due to the unusually high TF activation activity of the N-terminal domain. Here, we demonstrate using solution nuclear magnetic resonance (NMR) measurements that the PHL4 N-terminal activating TF effector domain is mainly an intrinsically disordered domain of over 200 residues, and that the C-terminal region of PHL4 is also disordered. Additionally, we present evidence from size-exclusion chromatography, diffusion NMR measurements, and a cross-linking assay suggesting full-length PHL4 forms a trimeric or tetrameric assembly. Together, the data indicate the N- and C-terminal disordered domains in PHL4 flank a central folded region that likely forms the ordered oligomer of PHL4. This work provides a foundation for future studies detailing how the conformations and molecular motions of PHL4 change as it acts as a potent activator of gene expression in phosphate metabolism. Such a detailed mechanistic understanding of TF function will benefit genetic engineering efforts that take advantage of this activity to boost transcriptional activation of genes across different organisms.

Effect of fused deposition modeling bioprinting variables on damping factor in shape memory structures for in vitro applications

ABSTRACT The aim of this study is to investigate the variation in the shape memory effect in the Tan Delta output parameter of shape memory polymeric stents, fabricated by the bio-FDM process, during a reversible endothermic cycle with changes in the input parameters. Pure polycaprolactone polymer was directly used in this study. The Damping Factor, or Tan Delta, is a key factor in expressing the shape memory effect of the memory stents. For a more accurate evaluation of this effect, SEM tests, uniaxial tensile tests, and dynamic mechanical and thermal analyses were employed. The Tan Delta of the shape memory stents was approximately 18.81%. Surface morphology changes led to approximately a 14.18% variation in elastic properties, as the dynamic molecular motion and polymer chain constraints resulted in increased pressure. It was found that the fabrication input parameters led to approximately a 20% change in the shape memory effect.

Long-Lived Room-Temperature Phosphorescence from Silica Nanoparticles with In Situ Generated Carbonaceous Defects for Blue Organic Light-Emitting Diodes.

In this study, in situ formed silica nanoparticles (SNPs) emitting second-level phosphorescence at room temperature without a phosphorescent dopant have been achieved for the first time. This phosphorescence is achieved through the simple in situ formation of carbonaceous defects (CDs) within the SNPs, followed by passivation of the CDs by a robust silica matrix. The CD in the SNPs, termed CD@SNPs, are synthesized by cross-linking tetraethyl orthosilicate (TEOS) and (3-aminopropyl)triethoxysilane (APTES), and these cross-linked components create a porous structure within the silica matrix. Upon calcination, the carbon-related structures within the pores deform, leading to the formation of CDs. Confined within a robust silica matrix, the molecular motion of the CD is restricted, facilitating the generation of a stable triplet state and suppressing nonradiative decay. Moreover, the robust silica matrix passivates the CD confined in the SNPs at a nanoscale. These comprehensive effects enable prolonged phosphorescence emission from the SNPs. In addition, these phosphorescence-emitting SNPs have been applied as dopants in the emissive layer of organic light-emitting diodes to realize blue light emission. This feature suggests the possibility of utilizing luminescent SNPs as light emitters in display technologies.

Coupling Rotary Motion to Helicene Inversion within a Molecular Motor.

Towards complex coupled molecular motions, the remote handedness inversion of a helicene moiety was achieved by a rotary molecular motor. The use of a specifically engineered dynamic helicene stator in a novel overcrowded-alkene second-generation molecular motor based on a fluorinated dibenzofluorene fragment allows for an unprecedented control over helicity inversion. This is achieved by the mechanical coupling of the rotation of the rotor to the helicene inversion of the stator half via a remote chirality transmission process. Thus, the unidirectional rotary motion generated upon irradiation is used to invert the dynamic stereochemistry of a helicene, leading to a 6-steps cycle with eight intermediates. In this cycle, both alternation between P and M configurations of the helicene stator and dynamic thermal interconversion (paddling motion) can be achieved. In-depth computational and spectroscopic studies were performed to support the associated mechanism. The control over coupled motion and dynamic helicity offers prospects for the development of complex responsive systems.

Coupling Rotary Motion to Helicene Inversion within a Molecular Motor

Towards complex coupled molecular motions, the remote handedness inversion of a helicene moiety was achieved by a rotary molecular motor. The use of a specifically engineered dynamic helicene stator in a novel overcrowded‐alkene second‐generation molecular motor based on a fluorinated dibenzofluorene fragment allows for an unprecedented control over helicity inversion. This is achieved by the mechanical coupling of the rotation of the rotor to the helicene inversion of the stator half via a remote chirality transmission process. Thus, the unidirectional rotary motion generated upon irradiation is used to invert the dynamic stereochemistry of a helicene, leading to a 6‐steps cycle with eight intermediates. In this cycle, both alternation between P and M configurations of the helicene stator and dynamic thermal interconversion (paddling motion) can be achieved. In‐depth computational and spectroscopic studies were performed to support the associated mechanism. The control over coupled motion and dynamic helicity offers prospects for the development of complex responsive systems.

Cooperative and Local Molecular Motion of High-Density Water in Glycerol Aqueous Solutions.

The glass-to-liquid transition of water, particularly in high-density water (HDW), has long been a controversial topic due to challenges posed by inevitable crystallization. In this study, we addressed this issue by creating homogeneous high-density glass from a dilute glycerol aqueous solution under high pressure. Using dielectric spectroscopy, we explored the glass transition of HDW in glycerol solutions across the full concentration range under high pressures. HDW was found to exhibit two distinct relaxation modes: one linked to cooperative motion and the other to noncooperative local motion. The fragility index classification of HDW, derived from the cooperative motion of water, suggests that HDW behaves as a "fragile" liquid, contradicting previous suggestions. Extrapolation to pure HDW indicates that the dielectric relaxation observed in pure HDW originates from noncooperative local water motion.

Tribological properties of polyimide coating filled with solvent-free covalent carbon quantum dots nanofluids

Novel organic coatings were developed by incorporating solvent-free covalent carbon quantum dots nanofluids (CQDs NFs) into a polyimide (PI) matrix. The tribological properties of CQDs NFs/PI composite coatings were tested using a ball-on-disk tribometer, revealing that even a low loading of CQDs NFs significantly improved tribological performance of PI. Molecular dynamics (MD) simulations and nanoindentation tests showed that CQDs NFs restricted PI molecular chain movement, enhancing mechanical properties. Additionally, CQDs NFs promoted the formation of stable transfer films on steel surfaces, improving wear resistance. This study confirms CQDs NFs' effectiveness in modifying PI composite coatings' friction and wear properties.