Role of Electronegativity on the Elemental Diversity in High-Entropy Alloys.

High-entropy alloys (HEAs) or multi-principal element alloys (MPEAs) have found extensive applications in high-precision devices. While the increased configurational entropy for HEAs favors more elemental diversity, it also increases the possibility of phase separation into multiple heterogeneous systems. This article reports that these two mutually competing effects are balanced for 3- and 4-component alloys. Analysis of all of the n-component ABCD···-type (∼5 × 105) available compounds in the materials' database shows that more than 70% are either 3- or 4-component ones. Their high propensity is explained on the basis of their optimal average difference of electronegativity (EN) ∼0.5-1.0 and the average sum of electronegativity (EN) ∼5.0-6.5 between the constituent atoms in the Oganov scale. Effectively, these 3- and 4-component alloys lie in the intermediate (centroid) region of the van Arkel-Ketelaar triangle, indicating their metalloid nature.

Oriented External Electric Field Controls the Rupture Forces in Mechanophores.

Controlling the reactivity of molecules under a mechanical pull has generated significant interest in organic and polymer chemistry. Inducing mechano-lability for otherwise rigid molecules has been possible through structural alterations like adjusting the pulling group, ring strain, and electron density of the scissile bond. In this article, we report that an oriented external electric field (OEEF) can significantly assist in mechanochemical transformations. Using a structurally diverse set of ring-opening reactions, 1(a)-4(a), we show that the critical force required for bond-cleavage, Frup, gets appreciably reduced when the OEEF acts in-phase with the bond-polarity direction. The primary condition for utilizing OEEF along with mechanochemistry is the requirement of structural asymmetry along the target bond. Effectively therefore, any polar ring-opening reaction might be manipulated by OEEF. The versatility of the strategy of using OEEF and mechanical force together can also be appreciated by the enhanced rupture force when the direction of the OEEF is flipped. We show that mechanical pulling and electric field can act as entwined twins toward mechano-lability.

Unlocking Enantioselectivity: Synergy of 2-Pyridone and Chiral Amino Acids in Pd-Catalyzed ß-C(sp3)-H Transformations.

Enantioselective C(sp3)-H activation has garnered significant attention in synthetic and computational chemistry. Chiral transient directing groups (TDGs) hold promise for enabling Pd(II)-catalyzed enantioselective C(sp3)-H functionalization. Despite the interest in this strategy, it presents a challenge because the stereogenic center on the chiral TDG is frequently distant from the C-H bond, leading to a mixture of functionalized products. Our computational study on Pd(II)-catalyzed enantioselective ß-C(sp3)-H arylation of aliphatic ketone with chiral amino acids provides a sustainable route to synthesizing complex chiral molecular scaffolds. The cooperative action of 2-pyridone derivatives and chiral amino acids is crucial in promoting the enantio-discriminating C-H activation, oxidative addition, and reductive elimination steps. Using 5-nitro-2-pyridone as the optimal external ligand demonstrates its ability to achieve the highest level of enantioselection. In contrast, the modeled 3,5-di((trifluoromethyl)sulfonyl)-2-pyridone ligand facilitates the most straightforward C-H activation. This study underscores the pivotal role of the alkyl substituent at the α-position of the amino acid (TDG) in altering enantioselectivity.

A non-B DNA binding peptidomimetic channel alters cellular functions.

DNA binding transcription factors possess the ability to interact with lipid membranes to construct ion-permeable pathways. Herein, we present a thiazole-based DNA binding peptide mimic TBP2, which forms transmembrane ion channels, impacting cellular ion concentration and consequently stabilizing G-quadruplex DNA structures. TBP2 self-assembles into nanostructures, e.g., vesicles and nanofibers and facilitates the transportation of Na+ and K+ across lipid membranes with high conductance (~0.6 nS). Moreover, TBP2 exhibits increased fluorescence when incorporated into the membrane or in cellular nuclei. Monomeric TBP2 can enter the lipid membrane and localize to the nuclei of cancer cells. The coordinated process of time-dependent membrane or nuclear localization of TBP2, combined with elevated intracellular cation levels and direct G-quadruplex (G4) interaction, synergistically promotes formation and stability of G4 structures, triggering cancer cell death. This study introduces a platform to mimic and control intricate biological functions, leading to the discovery of innovative therapeutic approaches.

Ultrafast symmetry-breaking charge separation in Perylenemonoimide-embedded multichromophores: impact of regioisomerism.

Symmetry-breaking charge separation (SB-CS) has recently evolved as an emerging concept offering its potential to the latest generation of organic photovoltaics. However there are several concerns that need to be addressed to reach the state-of-the-art in SB-CS chemistry, for instance, the desirable molecular geometry, interchromophoric distance and extent of electronic coupling. To shed light on those features, it is reported herein, that ortho-functionalized perylene monoimide (PMI) constituted regioisomeric dimer and trimer derivatives with varied molecular twisting and electronic conjugation have been synthesized. In steady-state photophysical studies, all the dimers and trimer derivatives exhibit a larger bathochromic shift in the emission spectra and a significant reduction of fluorescence quantum yield in polar DMF. Among the series of multichromophores, ortho- and self-coupled dimers display the strikingly different optical feature of SB-CS with a very fast charge separation rate (τCS = 80.2 ps) upon photoexcitation in DMF, which is unveiled by femtosecond transient absorption (fs-TA) studies. The SB-CS for two dimers is well-supported by the formation of PMI˙+ and PMI˙- bands in the fs-TA spectra. Further analysis of fs-TA data revealed that, among the other multichromophores the trimer also exhibits a clear charge separation, whereas SB-CS signatures are less prominent, but can not be completely disregarded, for the meta- and para-dimers. Additionally, the charge separation dynamics of those above-mentioned PMI derivatives are devoid of a kinetically favorable excimer or triplet formation. The evidence of a profound charge transfer phenomenon in the ortho-dimer is characterized by density functional theory (DFT) calculations on excited state electronic structures. The excitonic communications in the excited state electronic arrangements unravel the key role of dihedral twisting in SB-CS. The thermodynamic feasibility of CS (ΔGCS) and activation barrier (ΔG≠) of the derivatives in DMF are established from the Rehm-Weller equation and Marcus's theory, respectively. This work is an in-depth study of the effect of mutual orientation of PMIs and regioisomerism in determining sustainable guidelines for using SB-CS.

Screening 2D Materials for Their Nanotoxicity toward Nucleic Acids and Proteins: An In Silico Outlook.

Since the discovery of graphene, two-dimensional (2D) materials have been anticipated to demonstrate enormous potential in bionanomedicine. Unfortunately, the majority of 2D materials induce nanotoxicity via disruption of the structure of biomolecules. Consequently, there has been an urge to synthesize and identify biocompatible 2D materials. Before the cytotoxicity of 2D nanomaterials is experimentally tested, computational studies can rapidly screen them. Additionally, computational analyses can provide invaluable insights into molecular-level interactions. Recently, various "in silico" techniques have identified these interactions and helped to develop a comprehensive understanding of nanotoxicity of 2D materials. In this article, we discuss the key recent advances in the application of computational methods for the screening of 2D materials for their nanotoxicity toward two important categories of abundant biomolecules, namely, nucleic acids and proteins. We believe the present article would help to develop newer computational protocols for the identification of novel biocompatible materials, thereby paving the way for next-generation biomedical and therapeutic applications based on 2D materials.

First-principles design of heavy-atom-free singlet oxygen photosensitizers for photodynamic therapy.

In photodynamic therapy (PDT) treatment, heavy-atom-free photosensitizers (PSs) are a great source of singlet oxygen photosensitizer. Reactive oxygen species (ROS) are produced by an energy transfer from the lowest energy triplet excited state to the molecular oxygen of cancer cells. To clarify the photophysical characteristics in the excited states of a few experimentally identified thionated (>C=S) molecules and their oxygenated congeners (>C=O), a quantum chemical study is conducted. This study illustrates the properties of the excited states in oxygen congeners that render them unsuitable for PDT treatment. Concurrently, a hierarchy is presented based on the utility of the lowest-energy triplet excitons of thionated compounds. Their non-radiative decay rates are calculated for reverse-ISC and inter-system crossover (ISC) processes. In addition, the vibronic importance of C=O and C=S bonds is clarified by the computation of the Huang-Rhys factor, effective vibrational mode, and reorganization energy inside the Marcus-Levich-Jörtner system. ROS generation in thionated PSs exceeds their oxygen congeners as kf ≪ kISC, where radiative decay rate is designated as kf. As a result, the current work offers a calculated strategy for analyzing the effectiveness of thionated photosensitizers in PDT.

Pressure Induces Six-fold Coordination for the Lighter Pnictides Phosphorus and Arsenic Triiodide.

In this study, we employ an evolutionary algorithm in conjunction with first-principles density functional theory (DFT) calculations to comprehensively investigate the structural transitions, electronic properties, and chemical bonding behaviors of XI3 compounds, where X denotes phosphorus (P) and arsenic (As), across a range of elevated pressures. Our computational analyses reveal a distinctive phenomenon occurring under compression, wherein the initially trigonal structures of PI3 (P 63) and AsI3 (R-3) undergo an intriguing transformation, leading to the emergence of six-coordinated monoclinic phases (C2/m) at 6 GPa and 2 GPa for PI3 and AsI3, respectively. These high-pressure phases exhibit their stability up to 10 GPa for PI3 and 12 GPa for AsI3. Notably, the resulting structures at elevated pressures bear striking resemblance to the widely recognized six-coordinated octahedral BiI3 crystal configuration observed at ambient conditions. Our investigation further underscores the pivotal role of pressure-induced reactivity of the lone-pair electrons in PI3 and AsI3, facilitating their enhanced stereochemical reactivity and thereby enabling higher six-fold coordination. Complementary analyses employing electron localization function (ELF) and density of states (DOS) effectively delineate the progression towards augmented coordination in PI3 and AsI3 with increasing pressure. While the phenomenon of heightened coordination is conventionally associated with heavier pnictide iodides such as SbI3 and BiI3 under ambient conditions due to heightened ionic character and relativistic effects in bismuth (Bi) and antimony (Sb), our findings accentuate that analogous structural transformations can also be induced in lighter elements like phosphorus (P) and arsenic (As) under the influence of pressure.

Computational Assessment of the Biocompatibility of Two-Dimensional g-C3N3 Toward Lipid Membranes.

One of the most recent additions to the family of two-dimensional (2D) materials, graphitic C3N3 (g-C3N3), has been considered a viable contender for biomedical applications, although its potential toxicity remains elusive. We perform all-atom molecular dynamics simulations to decipher the interactions between model lipid membranes and g-C3N3 as a first step toward exploring the cytotoxicity induced at the nanoscale. We show that g-C3N3 can easily insert into the cellular membranes following a multistage mechanism consisting of simultaneous desolvation of the 2D material along with enrichment of nanomaterial-lipid interactions. Free energy calculations indicate that g-C3N3 is more stable in a membrane-bound state compared to an aqueous solution; however, the insertion of the material does not disturb the structural integrity of lipid membranes. After being inserted into a membrane, g-C3N3 is unlikely to be released into the cellular environment and is incapable of extracting lipid molecules from the membrane. The nature of interaction between the 2D material and membranes is found to be independent of the nanomaterial size. Also, the performance of g-C3N3 toward biomolecular delivery is shown to be significantly improved compared to the state-of-the-art 2D materials graphene and hexagonal boron nitride (h-BN). It is revealed that, the affinity of g-C3N3 toward lipid membranes is weaker compared to the nanotoxic graphene and h-BN, while being marginally higher than h2D-C2N, which in turn, increases the biocompatibility of the material, thereby brightening its future as a noncytotoxic material for forthcoming biomedical applications.

Pressure Induced Alteration and Stabilization of Intermolecular Stacking in Square-planar Osmium tetracarbonyl.

Osmium carbonyls are well known to form stable 18-electron complexes like Os(CO)5 , Os2 (CO)9 and Os3 (CO)12 having both bridging and terminal carbonyls. For osmium tetra-carbonyl, Os(CO)4 solid-state packing significantly alters the ground-state structure. The gas-phase stable see-saw geometry converts to a square-planar structure in solid state. Highly efficient intermolecular stacking between Os(CO)4 units assists this transformation. Each Os(CO)4 molecule is stacked in a staggered orientation with respect to each other. Pressure induces a [Xe]4f14 5d6 6s2 (S=2)→[Xe]4f14 5d8 (S=0) electronic transition in osmium stabilize a square planar osmium tetra-carbonyl. Under the influence of isotropic pressure, the molecules not only come closer to each other but their relative orientations also get significantly altered. Calculations show that at P=1 GPa and above, the eclipsed orientation for the intermolecular stacking gets preferred over the staggered form. The staggered→eclipsed intermolecular stacking orientation under pressure is shown to be controlled by London dispersion interactions.

Low Potential CO2 Reduction by Inert Fe(II)-Macrobicyclic Complex: A New Concept of Cavity Assisted CO2 Activation.

The advantage of a pre-organized π-cavity of Fe(II) complex of a newly developed macrobicycle cryptand is explored for CO2 reduction by overcoming the problem of high overpotential associated with the inert nature of the cryptate. Thus, a bipyridine-centered tritopic macrobicycle having a molecular π-cavity capable of forming Fe(II) complex as well as potential for CO2 encapsulation is synthesized. The inert Fe(II)-cryptate shows much lower potential in cyclic voltammetry than the Fe(II)-tris-dimethylbipyridine (Fe-MBP) core. Interestingly, this cryptate shows electrochemical CO2 reduction at a considerably lower potential than the Fe-MBP inert core. Therefore, this study represents that a well-structured π-cavity may generate a new series of molecular catalysts for the CO2 reduction reaction (CO2 RR), even with the inert metal complexes.

Modulation of Delayed Fluorescence Guided by Conformational Effect-Mediated Thermally Enhanced Phosphorescence in Phenothiazines-Quinoline-Cl Conjugates.

Triplet energy harvesting via thermally activated delayed fluorescence (TADF) from pure organic systems has attracted great attention in organic light-emitting diodes, sensing, and photocatalysis. However, the realization of thermally enhanced phosphorescence (TEP)-guided efficient TADF with a high rate of reverse intersystem crossing (kRISC) still needs to be discovered. Herein, we report two phenothiazine-quinoline conjugates (P2QC, P2QMC) comprising two phenothiazine donors covalently attached to the chlorine-substituted quinolinyl acceptor. Spectroscopic analysis in conjunction with quantum chemistry calculations reveals that TEP in P2QC originated due to slow internal conversion from higher-lying triplet to lowest triplet (T2' → T1') of the quasi-axial (QA) conformer and TADF (kRISC = 1.44 × 108 s-1) originated from the quasi-equatorial (QE) conformer caused by a low singlet-triplet gap (ΔES1-T1 = 0.11 eV) and triplet energy transfer from QA to QE owing to the degenerate ground state of the conformers. In contrast, TADF (kRISC = 0.74 × 108 s-1) and dual phosphorescence under ambient conditions are observed in P2QMC. This study provides a sustainable guideline for developing efficient TADF emitters via conformation effects and energy transfer mechanisms.

Autonomous self-healing organic crystals for nonlinear optics.

Non-centrosymmetric molecular crystals have a plethora of applications, such as piezoelectric transducers, energy storage and nonlinear optical materials owing to their unique structural order which is absent in other synthetic materials. As most crystals are brittle, their efficiency declines upon prolonged usage due to fatigue or catastrophic failure, limiting their utilities. Some natural substances, like bone, enamel, leaf and skin, function efficiently, last a life-time, thanks to their inherent self-healing nature. Therefore, incorporating self-healing ability in crystalline materials will greatly broaden their scope. Here, we report single crystals of a dibenzoate derivative, capable of self-healing within milliseconds via autonomous actuation. Systematic quantitative experiments reveal the limit of mechanical forces that the self-healing crystals can withstand. As a proof-of-concept, we also demonstrate that our self-healed crystals can retain their second harmonic generation (SHG) with high efficiency. Kinematic analysis of the actuation in our system also revealed its impressive performance parameters, and shows actuation response times in the millisecond range.

Microwave synthesis of molybdenene from MoS2.

Dirac materials are characterized by the emergence of massless quasiparticles in their low-energy excitation spectrum that obey the Dirac Hamiltonian. Known examples of Dirac materials are topological insulators, d-wave superconductors, graphene, and Weyl and Dirac semimetals, representing a striking range of fundamental properties with potential disruptive applications. However, none of the Dirac materials identified so far shows metallic character. Here, we present evidence for the formation of free-standing molybdenene, a two-dimensional material composed of only Mo atoms. Using MoS2 as a precursor, we induced electric-field-assisted molybdenene growth under microwave irradiation. We observe the formation of millimetre-long whiskers following screw-dislocation growth, consisting of weakly bonded molybdenene sheets, which, upon exfoliation, show metallic character, with an electrical conductivity of ~940 S m-1. Molybdenene when hybridized with two-dimensional h-BN or MoS2, fetch tunable optical and electronic properties. As a proof of principle, we also demonstrate applications of molybdenene as a surface-enhanced Raman spectroscopy platform for molecular sensing, as a substrate for electron imaging and as a scanning probe microscope cantilever.

Supramolecular Barrel-Rosette Ion Channel Based on 3,5-Diaminobenzoic Acid for Cation-Anion Symport.

The structural tropology and functions of natural cation-anion symporting channels have been continuously investigated due to their crucial role in regulating various physiological functions. To understand the physiological functions of the natural symporter channels, it is vital to develop small-molecule-based biomimicking systems that can provide mechanistic insights into the ion-binding sites and the ion-translocation pathways. Herein, we report a series of bis((R)-(-)-mandelic acid)-linked 3,5-diaminobenzoic acid based self-assembled ion channels with distinctive ion transport ability. Ion transport experiment across the lipid bilayer membrane revealed that compound 1 b exhibits the highest transport activity among the series, and it has interesting selective co-transporting functions, i.e., facilitates K+ /ClO4 - symport. Electrophysiology experiments confirmed the formation of supramolecular ion channels with an average diameter of 6.2±1 Šand single channel conductance of 57.3±1.9 pS. Selectivity studies of channel 1 b in a bilayer lipid membrane demonstrated a permeability ratio of P C l - / P K + = 0 . 053 ± 0 . 02 ${{P}_{{Cl}^{-}}/{P}_{{K}^{+}}=0.053\pm 0.02}$ , P C l O 4 - / P C l - = 2 . 1 ± 0 . 5 ${{P}_{{ClO}_{4}^{-}}/{P}_{{Cl}^{-}}=2.1\pm 0.5}$ , and P K + / P N a + = 1 . 5 ± 1 , ${{P}_{{K}^{+}}/{P}_{{Na}^{+}}=1.5\pm 1,}$ indicating the higher selectivity of the channel towards KClO4 over KCl salt. A hexameric assembly of a trimeric rosette of 1 b was subjected to molecular dynamics simulations with different salts to understand the supramolecular channel formation and ion selectivity pattern.

Dual Single-Atomic Co-Mn Sites in Metal-Organic-Framework-Derived N-Doped Nanoporous Carbon for Electrochemical Oxygen Reduction.

Synthesizing dual single-atom catalysts (DSACs) with atomically isolated metal pairs is a challenging task but can be an effective way to enhance the performance for electrochemical oxygen reduction reaction (ORR). Herein, well-defined DSACs of Co-Mn, stabilized in N-doped porous carbon polyhedra (named CoMn/NC), are synthesized using high-temperature pyrolysis of a Co/Mn-doped zeolitic imidazolate framework. The atomically isolated Co-Mn site in CoMn/NC is recognized by combining microscopic as well as spectroscopic techniques. CoMn/NC exhibited excellent ORR activities in alkaline (E1/2 = 0.89 V) as well as in acidic (E1/2 = 0.82 V) electrolytes with long-term durability and enhanced methanol tolerance. Density functional theory (DFT) suggests that the Co-Mn site is efficiently activating the O-O bond via bridging adsorption, decisive for the 4e- oxygen reduction process. Though the Co-Mn sites favor O2 activation via the dissociative ORR mechanism, stronger adsorption of the intermediates in the dissociative path degrades the overall ORR activity. Our DFT studies conclude that the ORR on an Co-Mn site mainly occurs via bridging side-on O2 adsorption following thermodynamically and kinetically favorable associative mechanistic pathways with a lower overpotential and activation barrier. CoMn/NC performed excellently as a cathode in a proton exchange membrane (PEM) fuel cell and rechargeable Zn-air battery with high peak power densities of 970 and 176 mW cm-2, respectively. This work provides the guidelines for the rational design and synthesis of nonprecious DSACs for enhancing the ORR activity as well as the robustness of DSACs and suggests a design of multifunctional robust electrocatalysts for energy storage and conversion devices.

Biaxial negative thermal expansion in carbon nets - graphyne and derivatives.

Materials that shrink during heating are important for advanced applications. Graphene has shown negative thermal expansion (NTE) up to 1000 K, which drives further research towards new two-dimensional allotropes of carbon to achieve higher performance. In this article, we have shown high NTE for Graphynes having sp-sp connectivity and that are stable at high temperature. The effect of heteroatom substitution in NTE for some graphynes and their periodic trends are also studied. Quasi-harmonic approximation (QHA) calculations show that thermal expansion remains negative at least until 1000 K for some graphynes. The results are in good agreement with ab-initio molecular dynamics (AIMD) simulations. The high NTE in the graphynes is understood based on their rigid unit modes (RUMs).

First-principles Calculations Reveal Frictional Advantage for C2 N/C6 N6 van der Waals Heterostructures.

Friction at the atomic scale is determined for three different carbon nitride structures namely C2 N/C2 N, C6 N6 /C6 N6 and C6 N6 /C2 N employing ab-initio density functional theory (DFT). The sliding path along the lowest energy corrugations determines the static frictional forces. Both the homo-layer structures (C2 N/C2 N and C6 N6 /C6 N6 ) have higher corrugation energy and correspondingly higher static lateral forces with respect to the hetero-layer structure (C2 N/C6 N6 ). The corrugation energy for the C2 N/C6 N6 heterostructure ( δ c o r r ${{\delta }_{corr}}$ =0.29 meV/atom) is one-order lower than C2 N/C2 N ( δ c o r r ${{\delta }_{corr}}$ =2.08 meV/atom) and C6 N6 /C6 N6 ( δ c o r r ${{\delta }_{corr}}$ =4.37 meV/atom). Such a significantly lower corrugation energy for the heterostructure arises due to the reduced fluctuation in the interfacial charge density along the sliding pathway. Moreover, the change in the interlayer distance along the sliding pathway is only 0.2 Šfor the heterostructure while its 0.3 Šand 0.4 Šfor C2 N and C6 N6 homo-layers respectively. The friction coefficients (FL /FN , FL =static lateral force; FN =normal force) decrease with increasing load for all the systems with the lowest value (0.04) for C2 N/C6 N6 at 2 GPa. The van der Waals heterostructures are, therefore, predicted to be highly efficient lubricant materials for reducing friction at the atomic scale.

London Dispersion Interactions Imitate Pressure for Molecular Crystals.

The packing of molecular crystals, in which the constituent molecular units have no directional forces, is primarily controlled by weak London dispersion (LD) forces. These forces assist in stabilizing the system by bringing the molecular units into the proximity of each other. In this paper, the same effect is shown to be externally induced by pressure. The minimal pressure required to correctly describe the crystal structure without LD interactions (PLD) provides a quantifiable measure for the weak intermolecular interactions. LD forces are shown to be essential for an accurate description of the pressure-induced phase transitions across examples of linear, trigonal-planar, square-planar, tetrahedral, trigonal bipyramidal, and octahedral molecules.

Redox-Triggered Activation of Heavy-Atom-Free Photosensitizer and Implications in Targeted Photodynamic Therapy.

A strategy for a redox-activatable heavy-atom-free photosensitizer (PS) based on thiolated naphthalimide has been demonstrated. The PS exhibits excellent reactive oxygen species (ROS) generation in the monomeric state. However, when encapsulated in a disulfide containing bioreducible amphiphilic triblock copolymer aggregate (polymersome), the PS exhibits aggregation in the confined hydrophobic environment, which results in a smaller exciton exchange rate between the singlet and triplet excited states (TDDFT studies), and consequently, the ROS generation ability of the PS was almost fully diminished. Such a PS (in the dormant state)-loaded redox-responsive polymersome showed excellent cellular uptake and intracellular release of the PS in its active form, which enabled cell killing upon light irradiation due to ROS generation. In a control experiment involving aggregates of a similar block copolymer, but lacking the bioreducible disulfide linkage, no intracellular reactivation of the PS was noticed, highlighting the importance of stimuli-responsive polymer assemblies in the area of targeted photodynamic therapy.