Structural Distortion Research Articles

Surface engineering of Li3V2(PO4)3-based cathode materials with enhanced performance for lithium-ion batteries working in a wide temperature range

Operating at extreme temperatures is the biggest challenge for lithium-ion batteries (LIBs) in practical applications, as both the capacity and cycling stability of LIBs are largely decreased due to the sluggish reaction kinetics of the cathodes. Therefore, developing suitable cathode materials is the key point to tackling this challenge. Lithium vanadium phosphate [Li3V2(PO4)3, LVP] is a promising cathode with good features of a high working voltage, high intrinsic ionic diffusion coefficiency, and stable olivine structure in a wide temperature range, although it is perplexed by the low electronic conductivity. To tackle this issue, a series of nitrogen-doped carbon network (NC) coated LVP composites were synthesized using a hydrothermal-assisted sol-gel method. Among them, the LVP@NC-0.8 sample exhibited a remarkable tolerance at a high charging cutoff voltage of 4.8 V in a wide temperature range. Full cells of LVP@NC-0.8||graphite exhibited superior performance at different current rates. Moreover, the reaction mechanism of the LVP@NC-0.8 electrode was proved by in-situ X-ray diffraction technique, demonstrating that temperature was a critical factor that contributed to the sluggish phase transformation with high voltage hysteresis at low temperature and severe crystal structure distortion at high temperature. Theoretical calculations further demonstrated the superiority of the NC for high electronic conductivity and reduced lithium transportation barriers. The enhanced electrochemical performances of LVP-based cathode materials have provided the possible application of LIBs in a wide temperature range.

Emergence of a potential charge-disproportionated insulating state in SrCrO3

We use a combination of density functional theory (DFT) and dynamical mean-field theory (DMFT) to investigate the potential emergence of a charge-disproportionated insulating phase in SrCrO3, whereby the Cr cations disproportionate according to 3Cr4+→2Cr3++Cr6+ and arrange in ordered planes perpendicular to the cubic [111] direction. We show that the charge disproportionation couples to a structural distortion where the oxygen octahedra around the nominal Cr6+ sites contract, while the octahedra surrounding the Cr3+ sites expand and distort. Our results indicate that the charge-disproportionated phase can be stabilized for realistic values of the Hubbard U and Hund's J parameters, but this requires a scaling of the DFT+DMFT double-counting correction by at least 35%. The disproportionated state can also be stabilized in DFT+U calculations for a specific magnetic configuration with antiparallel magnetic moments on adjacent Cr3+ sites and no magnetic moment on the Cr6+ sites. While this phase is higher in energy than other magnetic states that can arise in SrCrO3, the presence of an energy minimum suggests that the charge-disproportionated state represents a metastable state of SrCrO3. Published by the American Physical Society 2024

The role of Cu doped Ba0.5Sr0.5Fe0.95Zr0.05O3-δ: Local structure distortion, conductivity, and magnetization

The composition Ba0.5Sr0.5Fe1-xCuxZr0.05O3-δ (BSFCZ-x, x = 0–0.20) was successfully synthesized by the sol-gel self-combustion method using citric acid as fuel combustion. Structure, local structure, electrical, and magnetic properties are investigated. The X-ray diffraction revealed the oxides exhibit a cubic structure (Pm3 m), and the lattice parameter increases with x. The X-ray absorption data are analyzed to determine the oxidation state of B site metal transition Fe and Cu through edge-energy E0 evaluation. Fe performs the oxidation states Fe3+ and Fe4+, similarly to Cu2+ and Cu3+. Furthermore, the pre-edge was analyzed to determine the spin state configuration of the 3d subshell. The local lattice distortion was evaluated through EXAFS, resulting in a distorted FeO6 octahedron elongated to the z-axis, inducing the Jahn-Teller effect. The nonstoichiometric δ-value (3-δ) measurement leads to oxygen vacancy VO⦁⦁ defect. The electrical conductivity of semiconducting behavior increases significantly after Cu is dissolved in BSFZ up to 60 S/cm at 500 °C, from initially 5 S/cm. Furthermore, the magnetic properties show a slight magnetic saturation Ms for BSFZ related to the low spin state configuration of Fe 3d subshell, then significantly increased on BSFCZ samples due to Cu provoking spin state dragged partly to high spin state configuration.

Probing the metallic state, magnetic anisotropy, and large Curie temperature in CaCuFeReO[formula omitted]: Strain engineering

Rhenium-based double perovskite oxides (DPOs) are a particularly fascinating class of materials because of high carrier spin polarization, large magnetic anisotropy energy (MAE), and complex electrical behavior along with high Curie temperature (TC). Herein, we discussed the impact of biaxial ([110]) strain ranging from −5% to ＋ 5% along the ab-plane on the electronic and magnetic properties of CaCuFeReO6 (CCFRO) DPO using ab-inito calculations. The unstrained system exhibits a ferrimagnetic (FiM) spin ordering as an energetically stable magnetic ground state due to electron hopping between Fe+3/Re+5t2g and Cu+2eg orbitals along with a metallic electronic state. Moreover, [010] (b-axis) is the magnetic easy axis that produces the MAE of 5.36 meV, giving a giant MAE constant of 1.97×107 erg/cm3. The evaluated partial spin-magnetic moment on the Cu1/Cu2/Fe/Re ion is 0.14/0.44/4.04/−0.64μB, where “−” sign on the Re moment means that its spin is antiparallel to the other ions, verifying the FiM ordering in the system. Also, the eg, t2g/eg, and t2g orbital characteristics of Cu+2, Fe+3, and Re+5 ions are visible in the spin-magnetization density iso-surfaces plots, respectively. Using the classical Heisenberg model, the computed TC for the unstrained structure is 576 K, which is quite close to the experimentally reported value of 567 K. In addition, it is shown that the FiM metallic behavior in the motif is robust against biaxial ([110]) strain within the considered range. It has also been revealed that TC increased to 5.73%/3.30% for the considered range of −5% compressive/＋5% tensile strain due to improved structural distortions.

Crack propagation effects on the critical temperature degradation of superconducting Nb3Sn single crystal

The irreversible degradation of Nb3Sn critical performance caused by the crack propagation brings challenges to the reliability of Nb3Sn service equipment. In this paper, the crack propagation behavior of Nb3Sn single crystal was studied by molecular dynamics method. The results show that amorphous transformation occur in Nb3Sn samples with cracks under the applied loading conditions. On the basis of these results, the electronic structures of different regions in the cracked sample are studied by first principles method. The critical temperature response in this process is analyzed in combination with our proposed trans-scale electromechanical coupling model. The physical mechanism behind the critical temperature degradation caused by the transition between the cracked surface and the amorphous zone at the crack tip is discussed. Amorphous states and the crack surface destroy the special kind of bonding in the atom chain direction, inducing the electronic band structure distortions. The density of states curve of Nb3Sn no longer exhibits the characteristic peaks near the Fermi surface observed in cubic crystalline Nb3Sn. The intrinsic relationship between the crack propagation, the electronic structure evolution driven by the local atomic rearrangements, and the irreversible critical temperature degradation of cracked Nb3Sn is revealed by the given model. The results deepen the understanding of the electromechanical coupling behavior of Nb3Sn under complex deformation.

Elasto-plastic residual stress analysis of selective laser sintered porous materials based on 3D-multilayer thermo-structural phase-field simulations

Residual stress and plastic strain in additive manufactured materials can exhibit significant microscopic variation at the powder scale, profoundly influencing the overall properties of printed components. This variation depends on processing parameters and stems from multiple factors, including differences in powder bed morphology, non-uniform thermo-structural profiles, and inter-layer fusion. In this research, we propose a powder-resolved multilayer multiphysics simulation scheme tailored for porous materials through the process of selective laser sintering. This approach seamlessly integrates finite element method (FEM) based non-isothermal phase-field simulation with thermo-elasto-plastic simulation, incorporating temperature- and phase-dependent material properties. The outcome of this investigation includes a detailed depiction of the mesoscopic evolution of stress and plastic strain within a transient thermo-structure, evaluated across a spectrum of beam power and scan speed parameters. Simulation results further reveal the underlying mechanisms. For instance, stress concentration primarily occurs at the necking region of partially melted particles and the junctions between different layers, resulting in the accumulation of plastic strain and residual stress, ultimately leading to structural distortion in the materials. Based on the simulation data, phenomenological relation regarding porosity/densification control by the beam energy input was examined along with the comparison to experimental results. Regression models were also proposed to describe the dependency of the residual stress and the plastic strain on the beam energy input.

Theoretical investigation of gas sensing properties of a monolayer gallenene: First-principles insight

Two dimensional (2D) materials exhibit potential to be used in thin film electronic devices. In present paper, we explore 2D polymorphs of α-Ga by performing ab−initio calculations based on density functional theory. Phonon calculations show that Ga100 and Ga010 planes are dynamically stable at 6% and 2% bi-axial tensile strain. The ab-initio molecular dynamics calculations show that while Ga100 plane retain structural stability in a free standing state for temperature up to 500 K, Ga010 plane shows structure distortion which further increases with increase in temperature. We find total energy of Ga010 plane is smaller (−1.09 eV/f.u.) than Ga100 plane, indicating that Ga010 plane is energetically more stable. We next follow the adsorption of toxic gas molecule over Ga010 plane, referred as gallenene sheet. The negative adsorption energy shows that adsorption of phosgene (CCl2O), hydrogen cyanide (HCN), phosphine (PH3), and hydrogen selenide (H2Se) gas molecule over gallenene sheet is feasible. We find that (CCl2O) H2Se gas (weakly) strongly interact with gallenene with adsorption energy of (−0.39 eV) −0.52 eV. Bader charge calculation shows transfer of electronic charge between adsorbed gas molecule and gallenene sheet, which further confirmed by plot of electron localization function (ELF). The recovery time of desorption for CCl2O (PH3) gas comes 3.90×10−6 s (2.85×10−4 s) due to greater (smaller) out of plane distance of 2.93 Å (2.75 Å). The current–voltage (I–V) characteristic shows small deviation due to lower concentration of gases over gallenene, which further confirmed by transmission spectra. We hope that our theoretical predictions will help experimentalists to synthesize gallenene based gas sensors.

Management of Portal Hypertension in the Older Patient.

Aging is a process of physiological slowing, reduced regenerative capacity and inability to maintain cellular homeostasis. World Health Organisation declared the commencement of population aging globally, largely attributed to improvement in the healthcare system with early diagnosis and effective clinical management. Liver ages similar to other organs, with reduction in size and blood flow. In this review we aim to evaluate the effect of aging in liver disease. Aging causes dysregulation of major carbohydrate, fat and protein metabolism in the liver. Age is a major risk factor for liver fibrosis accelerated by sinusoidal endothelial dysfunction and immunological disharmony. Age plays a major role in patients with liver cirrhosis and influence outcomes in patients with portal hypertension. Transient elastography may be an useful tool in the assessment of portal hypertension. Hepatic structural distortion, increased vascular resistance, state of chronic inflammation, associated comorbidities, lack of physiological reserve in the older population may aggravate portal hypertension in patients with liver cirrhosis and may result in pronounced variceal bleed. Cut-offs for other non-invasive markers of fibrosis may differ in the elderly population. Non-selective beta blockers initiated at lower dose followed by escalation are the first line of therapy in elderly patients with cirrhosis and portal hypertension, unless contraindicated. Acute variceal bleed in the elderly cirrhotic patients can be life threatening and may cause rapid exsanguination due to poor reserve and associated comorbidities. Vasoactive drugs may be associated with more adverse reactions. Early endoscopy may be warranted in the elderly patients with acute variceal bleed. Role of TIPS in the elderly cirrhotics discussed. Management of portal hypertension in the older population may pose significant challenges to the treating clinician.

Excellent catalytic activity for NO decomposition on Rhn supported on grain-boundary terminations of the MgO (0 0 1) surface

In the present study, we first propose the grain-boundary termination of the MgO (001) surface (referred as GB@MgO(001)) as the substrate to support a series of Rhn clusters to trap and dissociate NO. Using van der Waals density functional theory calculations, we have studied the interaction between the Rhn (n = 1 ∼ 8) cluster and the MgOΣ5(210)GB@MgO(001) and the properties of the adsorption and dissociation of NO on Rhn/GB@MgO(001) systems. The Rhn clusters can tightly bond to the GB@MgO(001), with interfacial interactions comparable to those at the Rhn/MgO-nanotube interface. Stable quasi-two-dimensional Rhn clusters provide more active sites to NO. Moreover, NO dissociation is activated, with all the complete reaction paths occur below the reference state, indicating the possibility of the NO decomposition. An extremely small energy barrier of 0.037 eV was obtained for NO dissociating on the square-Rh4/GB@MgO(001) system. Molecular dynamic (MD) calculations reveal that NO can be completely decomposed at 527 K without obvious structure distortions of the complex. The adsorption of NO yields a change in the total magnetic moment of the Rhn/GB@MgO(001) system, but it has a minimal impact on the adsorption energy of NO. Our results also show that the optimal Rhn clusters that are good at trapping and dissociating NO are not the most stable structures, but rather clusters of relatively low dimension that are bound to the substrate with a moderate strength. As a result, the modification and tuning of the substrate structure can effectively enrich the structure of Rh cluster catalyst and improve its physical properties so that it can potentially play a greater role in other redox reactions, which motivates us to continue designing various types of GB@MgO(001) for different purposes.

Assessment of Iron-Based Spin-Orbit Coupling Effects in Pt-Fe Heterobimetallic Lantern Complexes via 57Fe Mössbauer Spectroscopy.

A series of heterobimetallic lantern complexes, [PtFe(SOCR)4(pyX)] where R = Me, X = H (1), X = NH2 (2), X = SMe (3); R = Ph, X = H (4), X = NH2 (5), X = SMe (6), have been prepared and characterized spectroscopically. Compounds 1, 4, and 5 are reported herein for the first time. The high-spin iron(II) sites of 1-6 have been investigated using 57Fe Mössbauer spectroscopy. Although the isomer shift of these species is nearly identical, their quadrupole splitting exhibits a much larger variation. Moreover, the zero-field Mössbauer spectra of 3-5 show surprising changes over time which are likely indicative of small structural distortions. The field dependent Mössbauer study of 1 and 6 revealed a zero field splitting (ZFS) characterized by a relatively large and positive D value. The combined Density Functional Theory (DFT) and ab initio Complete Active Space Self-Consistent Field (CASSCF) investigation of 1-6 indicates that their ground state is best described using a linear combination of {|xz⟩, |yz⟩} states. Our theoretical analysis suggests that the ZFSs and magnitude of the quadrupole splitting of 1-6 are determined by the spin-orbit coupling of the three lowest orbital states which have a T2g parentage.

Shielding unfavorable interaction by oxygen-mediated interlayer chemical bonding enables high-capacity and stable MoS2 cathode

Molybdenum disulfide (MoS2) as cathodes for aqueous zinc-ion batteries (AZIBs) typically undergoes sluggish kinetics and irreversible structure distortion because of the strong interaction between intensely electronegative sulfur and intercalated Zn2+, especially for thick electrodes. Herein, we propose a new oxygen-mediated interlayer chemical bonding strategy to achieve high-performance MoS2 cathode in thick electrode (5–15 mg cm−2). The oxygen-mediated interlayer chemical bonding is facilely formed by intercalating oxygen-rich β-cyclodextrin into MoS2 nanosheets (denoted as MoS2-β-CD), which not only expands the interlayer spacing (from 6.4 to 9.6 Å) but also effectively weakens the electrostatic interaction between Zn2+ and host frameworks, endowing it with fast electron/ion transport and robust structural stability. Consequently, even with 10 mg cm−2 loading, the MoS2-β-CD cathode delivers an impressive specific capacity of 228.0 mA h g−1 (2.3 mA h cm−2) at 4 mA cm−2, superior to most advanced MoS2-based electrodes. Additionally, the MoS2-β-CD electrode also possesses significantly enhanced durability (85.3 % vs. 28.6 % capacity retention after 5000 cycles). This work provides unique inspiration for rational design of AZIB cathodes for practical applications.

Numerical investigation of roping in multi-die meltblowing

This work aims at conducting a numerical investigation of the effect of the inter-die distance on the probability of roping during meltblowing. The results are qualitatively compared with the experimental data obtained by the present group in studies of roping in a model situation of solution blowing. The effectiveness of nonwoven products as filter membranes and others depends on the fiber size and geometrical fiber distributions in fiber mats. Jet roping in meltblowing results in a distortion of the laydown structure, which is detrimental to the product's efficiency. A quasi one-dimensional model is utilized here to predict the probability of jet–jet intersection in flight leading to roping, which was observed experimentally in the prior works of this group. The results of the present work are expected to be helpful in optimizing operating parameters to minimize roping in meltblown products.

Seeing the Unseen: The Structural Influence of the Lone Pair Electrons in PbWO4.

Pair distribution function (PDF) analysis of the scheelite-type material PbWO4 reveals previously unidentified short-range structural distortions in the PbO8 polyhedra and WO4 tetrahedra not observed in the similarly structured CaWO4. These local distortions are a result of the structural influence of the Pb2+ 6s2 lone pair electrons. These are not evident from the Rietveld analysis of synchrotron X-ray or neutron powder diffraction data, nor do they strongly influence the X-ray PDF (XPDF). This illustrates the importance of neutron PDF (NPDF) in the study of such materials. First-principles density function theory (DFT) calculations show that the Pb2+ 6s2 electrons are hybridized with the O2- 2p electrons near the Fermi level. The presence of local-scale distortions has previously been neglected in studies of structure-functionality relationships in PbWO4 and other scheelite-structured photocatalytic materials, including BiVO4, and this observation opens new avenues for their optimization.

Physicochemical characterization of rice straw before and after alkali-assist photocatalytic pretreatment: a comparative analysis.

The potential of alkali-assist photocatalytic (AAP) pretreatment to overcome the recalcitrant nature of lignocellulose biomass, i.e. rice straw (RS), was investigated in the present study. Box-Behenken Design (BBD) using standard response surface methodology (RSM) approach was considered to obtain optimal conditions for maximum delignification. The model was designed with three variables: alkali concentration (NaOH, 0-3% w/v), photocatalyst (TiO2 NPs (titania nanoparticles), 0-1g/L) and pretreatment time (30-240min). The availability of cellulose was increased by 96.73%, while the concentration of lignin and hemicellulose decreased by 73.89%, and 71.79%, respectively, at a combination of 1.5% NaOH, 0.5g/L TiO2 NPsand 135 min pretreatment time. The structural and morphological alterations in the RS were assessed via Fourier Transform Infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) both before and after AAPpretreatment. The FTIR measurement indicated that the original RS included a significant quantity of lignin, which was eliminated after the pretreatment procedure. The XRD pattern demonstrates that cellulose crystallinity is significantly affected by the pretreatment. The SEM analysis revealed structural distortion and surface porosity from the pretreatment procedure.

Joint dual-teacher distillation and unsupervised fusion for unpaired real-world image dehazing

AbstractExisting learning-based dehazing algorithms struggle to deal with real world hazy images for lack of paired clean data. Moreover, most dehazing methods require significant computation and memory. To address the above problems, we propose a joint dual-teacher knowledge distillation and unsupervised fusion framework for single image dehazing in this paper. First, considering the complex degradation factors in real-world hazy images, two synthetic-to-real dehazing networks are explored to generate two preliminary dehazing results with the heterogeneous distillation strategy. Second, to get more qualified ground truth, an unsupervised adversarial fusion network is proposed to refine the preliminary outputs of teachers with unpaired clean images. In particular, the unpaired clean images are enhanced to deal with the dim artifacts. Furthermore, to alleviate the structure distortion in the unsupervised adversarial training, we constructed an intermediate image to constrain the output of the fusion network. Finally, considering the memory storage and computation overhead, an end-to-end lightweight student network is trained to learn the mapping from the original hazy image to the output of the fusion network. Experimental results demonstrate that the proposed method achieves state-of-the-art performance on real-world hazy images in terms of no-reference image quality assessment and the parameters.

Interfacial bonding enhances MXene/Sb2Se3 composites toward cyclic stability and fast aluminum storage

Metal-chalcogenides have been extensively studied as electrode materials for rechargeable ion batteries due to their high theoretical specific capacity and high abundance. Although promising, these materials face challenges related to slow electrochemical kinetics, pronounced structural distortions, and severe shuttle effects. These issues have seriously hindered the practical application of metal-chalcogenides in ion batteries. This work presents a novel approach to form interfacial binding bonds and in situ generation of antimony selenide (Sb2Se3) on MXene by electrostatic adsorption. This innovative strategy enhances the reversible capacity and cycling stability of Sb2Se3 and effectively improves the electrochemical kinetics and shuttle effect. Ex-situ characterization elucidates the distinctive energy storage mechanism of the Ti3C2/Sb2Se3 cathode and the inhibitory effect of MXene on the dissolution of reaction intermediates into the electrolyte. Additionally, the improvement in charge transfer and ion diffusion due to the introduction of MXene was validated through density functional theory calculations. This work offers new insights into enhancing the stability of metal-chalcogenides and understanding the energy storage mechanism of antimony-based selenides in ion batteries.

Highly Stable MOF‐Type Lead Halide Luminescent Ferroelectrics

Lead halide molecular ferroelectrics represent an important class of luminescent ferroelectrics, distinguished by their high chemical and structural tunability, excellent processability and distinctive luminescent characteristics. However, their inherent instability, prone to decomposition upon exposure to moisture and light, hinders their broader ferroelectric applications. Herein, for the first time, we present a series of isoreticular metal‐organic framework (MOF)‐type lead halide luminescent ferroelectrics, demonstrating exceptional robustness under ambient conditions for at least 15 months and even when subjected to aqueous boiling conditions. Unlike conventional metal‐oxo secondary building units (SBUs) in MOFs adopting highly centrosymmetric structure with limited structural distortion, our lead halide‐based MOFs occupy structurally deformable [Pb2X]+ (X=Cl−/Br−/I−) SBUs that facilitate a c‐axis‐biased displacement of Pb2+ centers and substantially contribute to thermoinducible structural transformation. Importantly, this class of MOF‐type lead halide ferroelectrics undergo ferroelectric‐to‐paraelectric phase transitions with remarkably high Curie temperature of up to 505 K, superior to most of molecular ferroelectrics. Moreover, the covalent bonding between phosphorescent organic component and the light‐harvesting inorganic component achieves efficient spin‐orbit coupling and intersystem crossing, resulting in long‐lived afterglow emission. The compelling combination of high stability, ferroelectricity and afterglow emission exhibited by lead halide MOFs opens up many potential opportunities in energy‐conversion applications.

Electronic Couplings for Triplet-Triplet Annihilation Upconversion in Crystal Rubrene.

Triplet-triplet annihilation photon upconversion (TTA-UC) is a process able to repackage two low-frequency photons into light of higher energy. This transformation is typically orchestrated by the electronic degrees of freedom within organic compounds possessing suitable singlet and triplet energies and electronic couplings. In this work, we propose a computational protocol for the assessment of electronic couplings crucial to TTA-UC in molecular materials and apply it to the study of crystal rubrene. Our methodology integrates sophisticated yet computationally affordable approaches to quantify couplings in singlet and triplet energy transfer, the binding of triplet pairs, and the fusion to the singlet exciton. Of particular significance is the role played by charge-transfer states along the b-axis of rubrene crystal, acting as both partial quenchers of singlet energy transfer and mediators of triplet fusion. Our calculations identify the π-stacking direction as holding notable triplet energy transfer couplings, consistent with the experimentally observed anisotropic exciton diffusion. Finally, we have characterized the impact of thermally induced structural distortions, revealing their key role in the viability of triplet fusion and singlet fission. We posit that our approaches are transferable to a broad spectrum of organic molecular materials, offering a feasible means to quantify electronic couplings.

Highly Stable MOF-Type Lead Halide Luminescent Ferroelectrics.

Lead halide molecular ferroelectrics represent an important class of luminescent ferroelectrics, distinguished by their high chemical and structural tunability, excellent processability and distinctive luminescent characteristics. However, their inherent instability, prone to decomposition upon exposure to moisture and light, hinders their broader ferroelectric applications. Herein, for the first time, we present a series of isoreticular metal-organic framework (MOF)-type lead halide luminescent ferroelectrics, demonstrating exceptional robustness under ambient conditions for at least 15 months and even when subjected to aqueous boiling conditions. Unlike conventional metal-oxo secondary building units (SBUs) in MOFs adopting highly centrosymmetric structure with limited structural distortion, our lead halide-based MOFs occupy structurally deformable [Pb2X]+ (X=Cl-/Br-/I-) SBUs that facilitate a c-axis-biased displacement of Pb2+ centers and substantially contribute to thermoinducible structural transformation. Importantly, this class of MOF-type lead halide ferroelectrics undergo ferroelectric-to-paraelectric phase transitions with remarkably high Curie temperature of up to 505 K, superior to most of molecular ferroelectrics. Moreover, the covalent bonding between phosphorescent organic component and the light-harvesting inorganic component achieves efficient spin-orbit coupling and intersystem crossing, resulting in long-lived afterglow emission. The compelling combination of high stability, ferroelectricity and afterglow emission exhibited by lead halide MOFs opens up many potential opportunities in energy-conversion applications.

Helical reorganization in the context of membrane protein folding: Insights from simulations with bacteriorhodopsin (BR) fragments

Membrane protein folding is distinct from folding of soluble proteins. Conformational acquisition in major membrane protein subclasses can be delineated into insertion and folding processes. An exception to the “two stage” folding, later developed to “three stage” folding, is observed within the last two helices in bacteriorhodopsin (BR), a system that serves as a model membrane protein. We employ a reductionist approach to understand interplay of molecular factors underlying the apparent defiance. Leveraging available solution NMR structures, we construct, sample in silico, and analyze partially (PIn) and fully inserted (FIn) BR membrane states. The membrane lateral C-terminal helix (CH) in PIn is markedly prone to transient structural distortions over microsecond timescales; a disorder prone region (DPR) is thereby identified. While clear transmembrane propensities are not acquired, the distortions induce alterations in local membrane curvature and area per lipid. Importantly, energetic decompositions reveal that overall, the N-terminal helix (NH) is thermodynamically more stable in the PIn. Higher overall stability of the FIn arises from favorable interactions between the NH and the CH. Our results establish lack of spontaneous transition of the PIn to the FIn, and attributes their partitioning to barriers that exceed those accessible with thermal fluctuations. This work paves the way for further detailed studies aimed at determining the thermo-kinetic roles of the initial five helices, or complementary external factors, in complete helical folding and insertion in BR. We comment that complementing such efforts with the growing field of machine learning assisted energy landscape searches may offer unprecedented insights.