Topological Surface Research Articles

Synthesis, Antimalarial, Antileishmanial, and Cytotoxicity Activities and Preliminary In Silico ADMET Studies of 2-(7-Chloroquinolin-4-ylamino)ethyl Benzoate Derivatives.

A series of heterocyclic chloroquine hybrids, containing a chain of two carbon atoms at position four of the quinolinic chain and acting as a link between quinoline and several benzoyl groups, is synthesized and screened in vitro as an inhibitor of β-hematin formation and in vivo for its antimalarial activity against chloroquine-sensitive strains of Plasmodium berghei ANKA in this study. The compounds significantly reduced haeme crystallization, with IC50 values < 10 µM. The values were comparable to chloroquine's, with an IC50 of 1.50 ± 0.01 µM. The compounds 4c and 4e prolonged the average survival time of the infected mice to 16.7 ± 2.16 and 14.4 ± 1.20 days, respectively. We also studied the effect of the compounds 4b, 4c, and 4e on another important human parasite, Leishmania mexicana, which is responsible for cutaneous leishmaniasis, demonstrating a potential leishmanicidal effect against promasigotes, with an IC50 < 10 µM. Concerning the possible mechanism of action of these compounds on Lesihmania mexicana, we performed experiments demonstrating that these three compounds could induce the collapse of the parasite mitochondrial electrochemical membrane potential (Δφ). The in vitro cytotoxicity assays against mammalian cancerous and noncancerous human cell lines showed that the studied compounds exhibit low cytotoxic effects. The ADME/Tox analysis predicted moderate lipophilicity values, low unbound fraction values, and a poor distribution for these compounds. Therefore, moderate bioavailability was expected. We calculated other molecular descriptors, such as the topological polar surface area, according to Veber's rules, and except for 2 and 4i, the rest of the compounds violated this descriptor, demonstrating the low antimalarial activity of our compounds in vivo.

Topological electronic structure and spin texture of quasi-one-dimensional higher-order topological insulator Bi4Br4

The notion of topological insulators (TIs), characterized by an insulating bulk and conducting topological surface states, can be extended to higher-order topological insulators (HOTIs) hosting gapless modes localized at the boundaries of two or more dimensions lower than the insulating bulk. In this work, by performing high-resolution angle-resolved photoemission spectroscopy (ARPES) measurements with submicron spatial and spin resolution, we systematically investigate the electronic structure and spin texture of quasi-one-dimensional (1D) HOTI candidate Bi4Br4. In contrast to the bulk-state-dominant spectra on the (001) surface, we observe gapped surface states on the (100) surface, whose dispersion and spin-polarization agree well with our ab-initio calculations. Moreover, we reveal in-gap states connecting the surface valence and conduction bands, which is a signature of the hinge states inside the (100) surface gap. Our findings provide compelling evidence for the HOTI phase of Bi4Br4. The identification of the higher-order topological phase promises applications based on 1D spin-momentum locked current in electronic and spintronic devices.

Synergistic boost of catalytic activity in ZrTe topological catalyst via multiple topologically-electronic states

Topological materials feature highly-active topological surface states and high carrier mobility, making them promising catalysts. While ongoing research centers on topological catalysis, most topological semimetal catalysts tend to showcase either a singular topological electronic state or a lone highly catalytic surface, imposing limitations on overall efficiency. Our study highlights ZrTe as a standout catalyst for hydrogen evolution, boasting multiple topological states that excel across various surfaces. ZrTe exhibits a Weyl nodal ring and a triple degenerate nodal point near the Fermi energy, resulting in topological surface states on multiple surfaces. Notably, the (010) and (001) surfaces exhibit remarkable catalytic performance, with Gibbs free energy (ΔGH*) values surpassing that of the Pt metal. Our work establishes a robust and unequivocal link between catalysis and topological properties on the catalytic surfaces, revealing a linear correlation between ΔGH* and topological surface state density. ZrTe emerges as an exceptional topological catalyst, with both of its topological states significantly contributing to the catalytic performance on distinct surfaces. This pioneering discovery offers a valuable platform for advancing catalyst research in the concept of topological catalysts.

Intrinsically large effective mass and multi-valley band characteristics of n-type Bi2[sbnd]Bi2Te3 superlattice-like films

Thermoelectric superlattices are expected to decouple the strong correlation between various thermoelectric parameters, and are an important strategy for excellent thermoelectric performances. The superlattices of (Bi2)m(Bi2Te3)n homologous series are well-known for low lattice thermal conductivity and intriguing topological surface states. However, the impacts of electronic structure on the thermoelectric performance were still not well-understood in (Bi2)m(Bi2Te3)n. To cope with this issue, Bi2Bi2Te3 superlattice-like films with adjustable Bi2/(Bi2+Bi2Te3) molar ratio (R) were successfully fabricated by the molecular beam epitaxy technique. Angle-resolved photoemission spectroscopy measurements combined with theoretical calculations revealed the conduction band evolution from single-valley to multi-valley as R ≥ 0.30, leading to intrinsically high carrier effective mass and improved thermoelectric power factor. Also, the superlattice film (R = 0.46) with the structure close to Bi4Te3 possesses the topological surface state feature around the high symmetry point. As a result of the high effective mass of 3.9 m0 and very high electron density of 2.31 × 1021 cm−3, the film with R = 0.46 acquired the highest power factor of 1.49 mW·m−1·K−2 at 420 K, outperforming that of other (Bi2)m(Bi2Te3)n superlattices. This work lays an essential foundation on understanding the electronic structure and further improving thermoelectric performances of (Bi2)m(Bi2Te3)n homologous series.

Simultaneous Fine-Tuning of Hirshfeld Topological Surfaces, Volumes, and their Voids to Optimize the Radiation Shielding Properties: A Case Study of Silicon Carbide (SiC)

Simultaneous Fine-Tuning of Hirshfeld Topological Surfaces, Volumes, and their Voids to Optimize the Radiation Shielding Properties: A Case Study of Silicon Carbide (SiC)

Probing surface states: A study of UCF and WAL in Bi1.9Sb0.1Te2Se topological insulator

In the exploration of three-dimensional quaternary topological insulators, understanding surface states has become pivotal for unraveling the underlying physics and tapping into potential applications. Our study delves into the temperature and magnetic field-angle dependence of universal conductance fluctuations (UCF) and weak anti-localization (WAL) effects in a Bi1.9Sb0.1Te2Se topological insulator-based mesoscopic device. Conventionally, other low-temperature transport phenomena in probing surface states may inevitably face interference from three-dimensional bulk conductance. However, we experimentally demonstrate that, at low temperatures, UCF reflects the properties of two-dimensional topological surface states more accurately, thereby providing a more reliable and distinct way to confirm their existence. Moreover, we carefully analyze the temperature-dependent WAL using the Hikami–Larkin–Nagaoka model, proposing a crucial role for charge puddles associated with electrostatic fluctuations in the electron dephasing process. Our findings not only emphasize the key role of UCF in unveiling the underlying behavior of topological surface states but also offer a deeper understanding of phase-coherent transport in quaternary topological insulators.

Regiodivergent sp3 C-H Functionalization via Ni-Catalyzed Chain-Walking Reactions.

The catalytic translocation of a metal catalyst along a saturated hydrocarbon side chain constitutes a powerful strategy for enabling bond-forming reactions at remote, yet previously unfunctionalized, sp3 C-H sites. In recent years, Ni-catalyzed chain-walking reactions have offered counterintuitive strategies for forging sp3 architectures that would be difficult to accomplish otherwise. Although these strategies have evolved into mature tools for advanced organic synthesis, it was only recently that chemists showed the ability to control the motion at which the catalyst "walks" throughout the alkyl chain. Specialized ligand backbones, additives and a judicious choice of noninnocent functional groups on the side chain have allowed the design of "a la carte" protocols that enable regiodivergent bond-forming scenarios at different sp3 C-H sites with distinct topological surface areas. Given the inherent interest in increasing the fraction of sp3 hybridized carbons in medicinal chemistry, Ni-catalyzed regiodivergent chain-walking reactions might expedite the access to target leads in drug discovery campaigns.

Vibrational spectra, molecular level solvent interaction, stabilization, donor- acceptor energies, thermodynamic, non-covalent interaction and electronic behaviors of 6-Methoxyisoquinoline- anti tubercular agent

The present research is a theoretical examination of 6-methoxyisoquinoline implementing Density Functional Theory quantum mechanical approach. Structural optimization was performed to achieve a stable molecular structure with the least amount of energy. Several protic and aprotic solvent interactions were performed using the IEF polarization continuum model to examine the reactivity and stability of the molecules. Molecular interactions with solvents were investigated using UV–Visible, HOMO-LUMO, MEP, NBO, and NLO properties, which shows some changes in the compound activity at solvent phases against gas phase. The molecular interaction of π*C1–N2 to π*C5 - C10 shows the higher stabilizing energy. DMSO solvent exhibits a very low band gap energy, favors the molecule's high stability. Molecular reactivity, interactions, and optical behavior were all readily apparent. The chemical reactivity of the compound was found good in water. The percentage of PED contributions was evaluated for each mode of vibrations using vibrational spectral investigation. Topological surface analysis was used for better understanding of molecular electron density, reactive center, and steric effect. ELF, LOL, and RDG was generated for compounds with different solvents. The distance of transition and the overlapping of electron and hole were calculated using electron hole analysis. Pharmacological assessments include drug likeness, ADME, toxicity, and a pre-ADMET online tool, which supports the biological capability of the compound. Finally, molecular docking with anti-tubercular protein was performed, and a Ramachandran plot of chosen protein was shown to explore stability.

Crossover from gapped-to-gapless Dirac surface states in magnetic topological insulator MnBi2Te4

Intrinsic magnetic topological insulators (MTIs) host exotic topological phases such as quantized anomalous Hall insulating phase, arising due to the large magnetic exchange gap. However, the interplay of magnetism and topology in these systems in different temperature regimes remains elusive. In this work, we present the logarithmic temperature-dependence of conductivity for sub-100 nm thick exfoliated flakes of MTI MnBi2Te4 in the presence of out-of-plane magnetic fields and extracted the linear slope, κ. We observed a characteristic change, in the low-temperature regime, indicating the gapped Dirac surface state according to Lu–Shen theory. We also report the recovery of topological properties in the system via the weak-antilocalization effect in the vicinity of antiferromagnetic to paramagnetic transition and in the paramagnetic regime. Hikami–Larkin–Nagaoka analysis suggested the presence of topological surface states. Therefore, our study helps in understanding how intrinsic magnetism masks topological properties in an MTI as long as magnetic ordering persists.

Multi-cavity molecular descriptor interconnections: Enhanced protocol for prediction of serum albumin drug binding

The role of human serum albumin (HSA) in the transport of molecules predicates its involvement in the determination of drug distribution and metabolism. Optimization of ADME properties are analogous to HSA binding thus this is imperative to the drug discovery process. Currently, various in silico predictive tools exist to complement the drug discovery process, however, the prediction of possible ligand-binding sites on HSA has posed several challenges. Herein, we present a strong and deeper-than-surface case for the prediction of HSA-ligand binding sites using multi-cavity molecular descriptors by exploiting all experimentally available and crystallized HSA-bound drugs. Unlike previously proposed models found in literature, we established an in-depth correlation between the physicochemical properties of available crystallized HSA-bound drugs and different HSA binding site characteristics to precisely predict the binding sites of investigational molecules. Molecular descriptors such as the number of hydrogen bond donors (nHD), number of heteroatoms (nHet), topological polar surface area (TPSA), molecular weight (MW), and distribution coefficient (LogD) were correlated against HSA binding site characteristics, including hydrophobicity, hydrophilicity, enclosure, exposure, contact, site volume, and donor/acceptor ratio. Molecular descriptors nHD, TPSA, LogD, nHet, and MW were found to possess the most inherent capacities providing baseline information for the prediction of serum albumin binding site. We believe that these associations may form the bedrock for establishing a solid correlation between the physicochemical properties and Albumin binding site architecture. Information presented in this report would serve as critical in provisions of rational drug designing as well as drug delivery, bioavailability, and pharmacokinetics.

Magnetotransport Signatures of Superconducting Cooper Pairs Carried by Topological Surface States in Bismuth Selenide.

As topological insulators (TIs) are becoming increasingly intriguing, the community is exploring transformative applications that require interfacing TIs with other materials such as ferromagnets or superconductors. Herein, we report on the manifestations of superconducting electrons carried by topological surface states (TSS) in Bi2Se3 films. As key signatures of TSS-carried Cooper pairs, we uncover the hysteresis of magnetoresistance (MR) and the switching behavior of anisotropic magnetoresistance (AMR). For in-plane fields perpendicular to the injected current, AMR shows negative switching (resistance drop) when the contacts become superconducting, which is consistent with a cooperative Zeeman effect enabled by the spin-momentum locking of TSS. The MR and AMR behaviors are robust, occurring reliably in multiple samples, from different sources, and with different defect concentrations. Our findings can guide novel developments in superconductor/TI quantum devices relying on supercurrent detection as well as lead to more refined transport signatures of Majorana zero-modes in the future.

NiAs-type vanadium sulfides: Topological surface and abundant electroactivity as a bi-functional material in Mg/Li batteries

Rechargeable Mg battery (RMB) is a new type of next-generation secondary battery. The unique NiAs-type V3S4 is capable of achieving high electrochemical performance due to its bi-functional effect of electroactive and anchoring ability to the discharge products of polysulfides. Herein, the first-principles calculations were conducted to explore the electronic properties, dynamic and absorption behavior of Mg/Li-ions in the bulk and crystal plane of V3S4 to reveal the bi-functional mechanism in Mg/Li batteries. First, the stable surface adsorption and rapid diffusion kinetics of Mg/Li ions render the high-rate capability for V3S4. Second, the Mg/Li polysulfides could effectively anchor on the V3S4 (111) plane and retain their structural stability during the discharge–charge process for Mg/Li batteries. Even after Li2Sn/MgSn adsorption, the metallic property of V3S4 is still preserved to realize the redox electrochemistry of Li2Sn/MgSn and ameliorates the effect of the insulated low-order polysulfides. Meanwhile, the low Gibbs energy differences for Mg and Li polysulfides on V3S4 (111) plane gives the evidence of electrocatalytic property. As bi-functional material, the V3S4 has striking characteristics of low diffusion barrier, benificial adsorption and preeminent electrocatalytic ability of Li/Mg species, which can be leveraged for designing vanadium sulfides as high-conductivity cathode materials for RMBs.

DDDR-31. TARGETING CANCER STEM CELLS WITH A CDK2 INHIBITOR IN GLIOBLASTOMA

Abstract Glioblastoma (GB) is the most common and aggressive adult brain tumor with no cure. Brain tumor stem cells (BTSCs) are a rare population of self-renewing multipotent stem cells in GB that contribute to tumorigenesis, therapeutic resistance and tumour recurrence. Here, we report a CDK2 inhibitor that suppresses BTSCs via OSM/OSMR/STAT3 signalling pathway. To begin with we performed high throughput screening (HTS) of ~8400 compounds including FDA-approved drugs in patient derived human BTSCs that naturally harbour EGFRvIII mutation and elevated STAT3 phosphorylation, in search of compounds that can suppress EGFRvIII/OSMR/STAT3 oncogenic pathway. The screen led to the identification of a panel of CDK inhibitors that possessed important characteristics including a) ability to cross the blood-brain barrier with mall molecular weights of 277-566 kDa, b) low Topological Polar Surface Area (TPSA) of 76-115 A°, c) a low number of Hydrogen Bond Donors (HBDs) (1-4), and d) cLogP values ranging from 2-4. Following counter screens, we focused on a CDK2 inhibitor that significantly and most efficiently reduced OSM/OSMR signalling and STAT3 activation. Importantly, we found that the compound inhibited the self-renewal and growth of BTSCs in EGFRvIII subtype of BTSCs. This research has led to future investigation on in vivo assessment of this CDK2 inhibitor in combination with ionizing radiation and chemotherapy in preclinical models of GB.

Experimental investigation of the effect of topological insulator on the magnetization dynamics of ferromagnetic metal: and heterostructure

We have studied the spin-pumping phenomenon in ferromagnetic metal (FM) ()/topological insulator (TI) () bilayer system to understand magnetization dynamics of FM in contact with a TI. TIs embody a spin–momentum-locked surface state that spans the bulk band gap. Due to this special spin texture of the topological surface state, the spin-charge interconversion efficiency of TI is even higher than that of heavy metals. We evaluated the parameters like effective damping coefficient (), spin-mixing conductance () and spin current density () to demonstrate an efficient spin transfer in heterostructure. To probe the effect of the topological surface state, a systematic low-temperature study is crucial as the surface state of TI dominates at lower temperatures. The exponential increase of for all different thickness combinations of FM/TI bilayers and the enhancement of effective damping coefficient () with lowering temperature confirms that the spin chemical potential bias generated from spin-pumping induces spin current into the TI surface state. Furthermore, low-temperature measurements of effective magnetization () and magnetic anisotropy field (Hk ) showed anomaly around the same temperature region where the resistivity of TI starts showing metallic behavior due to the dominance of conducting TI surface state. The anomaly in Hk can result from the emerging exchange coupling between the TI surface state and the local moments of the FM layer at the interface without any long-range ferromagnetic order in TI at the interface.

Terahertz Plasmon Polaritons in Large Area Bi2Se3 Topological Insulators

AbstractAssessing the nature of topological quantum materials, and in particular probing the existence of topological surface states, is a very challenging task. Terahertz (THz) frequency scattering near‐field optical microscopy has emerged as an effective technique to investigate the presence of massless surface carriers by locally probing collective surface excitations, i.e., plasmon polaritons, whose dispersion critically depends on the density and nature of surface carriers. Here, thin (14–19 nm) films of Bi2Se3 are experimentally investigated through a combination of x‐ray diffraction, Hall‐bar magneto‐transport, and near‐field detectorless optical holography at THz frequencies, from 2 to 4.3 THz. The dispersion of surface plasmon polaritons are determined for different Bi2Se3 film thicknesses, proving the presence of massless surface carriers. The results open intriguing opportunities in THz nano‐plasmonics and topological nano‐photonics including the development of superlenses and metasurfaces, making use of plasmon polaritons.

Quantum magnetotransports derived from the topological Dirac fermions in single-crystalline Pt3Te4 semimetal: Observations of chiral anomaly, quantum interference, and surface helical spin textures

This study investigated exotic quantum magnetotransports and magnetization properties of Pt3Te4 single crystals to probe the topological properties of the mitrofanovite Pt3Te4. The signature of helical spin texture from the topological surface state and the chiral anomaly associated with a linear-like energy dispersion of electronic states were detected. At low temperatures, the negative magnetoresistance in the low-field region could be explained with the transport formula containing the chiral-anomaly effect as well as the quantum interference of weak localization/antilocalization transports. Moreover, the high-field transverse magnetoresistance at temperatures below 60 K showed a non-saturating, linear-like behavior. This was examined using the theory of Abrikosov’s quantum magnetoresistance. The findings indicate a Dirac-cone-like dispersion in Pt3Te4 at low temperatures. This study's findings reveal the significant impact of the concept that the magnetotransport in Pt3Te4 can be dominated by the topological Dirac fermions in a surface state, which reveal the signatures of quantum magnetotransport, being a new candidate of Dirac semimetal.

Non-trivial topological phases in transition metal rich half-Heusler oxides

Topological insulators with gapless surface states and insulating bulk in non-centrosymmetric cubic systems have been extensively explored following the discovery of two-dimensional quantum spin hall effect in zincblende HgTe. In such systems the negative band inversion strength E (= E E 0) governs the robustness of the non-trivial topological states at ambient conditions. Hence, realizing large negative values of E has been a guiding motivation of several investigations reported in literature. Here, we present a material design approach which can be employed to realize large negative values of E in cubic materials such as half-Heusler (HH) oxides with 18 valence electron configurations. We explore 27 HH oxides of the form ABO (A = Li, K, Rb; B = Cu, Ag, Au) in α-, β-, and γ-phase (by placing transition metal atom at different Wyckoff positions) for their non-trivial topological phase. Off these three phases, we found that, the α-phase of nine HH oxides (wherein the transition metal atoms occupy 4a Wyckoff positions in the crystal structure) is the most promising with non-trivial topological phase which is governed by the mass-Darwin fully-relativistic effects enhancing E. Whereas the other phases were found to be either trivial semiconductors or semimetals or metals and most of them being dynamically unstable. We focus on RbAuO in α-phase with E of −1.29 eV and the effect of strain fields on the topological surface states of this compound. We conclude that the α-phase of HH oxide presented here can be synthesized experimentally for diverse room temperature applications in spintronics and nanoelectronics.

Synthesis of prussian blue analog (Co/TCNi/HCCr) nanoparticles using a facile co-precipitation approach and evaluation of their dielectric characteristics for electronic applications

The Prussian blue analog Co0.4/(TCNi)0.2/(HCCr)0.6 (PBA) nanoparticles were synthesized via a chemical co-precipitation approach. The structural characteristics of the nanocomposite (NCp) were investigated using the XRD technique, which revealed that the synthetic PBA has a tiny crystallite size and poor crystallinity. The XRD analysis suggests that the fabricated NCp has a face-centered cubic structure with space group Fm-3 m. For deep microstructure analysis, SEM, EDX, and AFM were employed to describe the topological nature and surface architecture. It is observed that the PBA nanocomposite has a small crystallite size of ~13.66 ± 0.32 nm. The particles’ surface displays a high degree of homogeneity, while the grain boundaries are clearly discernible, presenting a spherical morphology with an average diameter of 22 ± 2.1 nm. The porosity was ascertained from an AFM image of approximately 140. Furthermore, the value of the average roughness (Rs) is 6.86 nm. The AC conductivity of PBA in disc form was calculated at various temperatures and frequencies. The results indicate that the dielectric constant (ɛ′) of PBA nanoparticles exhibits a rise from 163 to 3464 throughout the frequency range of 10–100 kHz at ambient temperature and from 27 to 6000 at 293 K. This finding provides confirmation that the dielectric characteristics of PBA nanoparticles are enhanced during the process of annealing. The values of the exponent factor (s) range from 0 to 1; this behavior is connected to the correlated barrier hopping model (CBHM) for AC conductivity. The value of WM was ascertained to be 1.69 eV. Furthermore, the values of activation energy were calculated, and these values decreased from 0.20 to 0.17 eV with annealing. The change in loss tangent (tanδ) as a function of angular frequency at various temperatures is also shown. The investigation of the dielectric characteristics was measured over a wide range of frequencies and temperatures to get valuable data about the dissipation properties of the prospective electronic applications.

Topological Transitions and Surface Umklapp Scattering in Weakly Modulated Periodic Metasurfaces.

Controlling and manipulating surface waves is highly beneficial for imaging applications, nanophotonic device design, and light-matter interactions. While deep-subwavelength structuring of the metal-dielectric interface can influence surface waves by forming strong effective anisotropy, it disregards important structural degrees of freedom such as the interplay between corrugation periodicity and depth and its effect on the beam transport. Here, we unlock these degrees of freedom, introducing weakly modulated metasurfaces, structured metal-dielectric surfaces beyond effective medium. We utilize groove-structuring with varying depths and periodicities to demonstrate control over the transport of surface waves, dominated by the depth-period interplay. We show unique backward focusing of surface waves driven by an umklapp process-momentum relaxation empowered by the periodic nature of the structure and discover a yet unexplored, dual-stage topological transition. Our findings can be applied to any type of guided wave, introducing a simple and versatile approach for controlling wave propagation in artificial media.

Giant lattice softening at a Lifshitz transition in Sr2RuO4.

The interplay of electronic and structural degrees of freedom in solids is a topic of intense research. More than 60 years ago, Lifshitz discussed a counterintuitive possibility: lattice softening driven by conduction electrons at topological Fermi surface transitions. The effect that he predicted, however, was small and has not been convincingly observed. Using a piezo-based uniaxial pressure cell to tune the ultraclean metal strontium ruthenate while measuring the stress-strain relationship, we reveal a huge softening of the Young's modulus at a Lifshitz transition of a two-dimensional Fermi surface and show that it is indeed driven entirely by the conduction electrons of the relevant energy band.