Highly Polarizable Research Articles

Deep Structure of Epithermal Deposits in Youxi Area: Insights from CSAMT and Dual-Frequency IP Data

Epithermal deposits represent a significant category of gold occurrences, with their subsurface structure playing a key role in reserve assessments. Fujian Province, characterized by extensive Mesozoic volcanic activities, stands out as a noteworthy region for shallow hydrothermal mineralization in China. This paper focus on the Youxi area within Fujian Province, employing the dual-frequency induced polarization method (DFIP) and controlled-source audio-frequency magnetotelluric method (CSAMT) to investigate the target ore. The DFIP results revealed predominant northeast-oriented zones with high polarizability and notable apparent resistivity. The CSAMT data were inverted using the SCS2D software. Two-dimensional resistivity profiles reveal a three-layer electrical structure, comprising subsurface banded rhyolites influenced by fault zones, intermediate-low resistivity sandstone layers, and deep-seated high-resistivity conglomerates. The resistivity gradient zones and highly polarizable locations align closely with known local faults. We interpreted these resistivity gradient zones as prospective target areas for mineralization, a hypothesis subsequently validated by drilling results. Combining geochemical analyses of epithermal gold deposits with the electrical resistivity structure, we propose an explanatory model for the mechanism of the formation of epithermal gold–silver deposits in the Youxi area. The magmatic hydrothermal fluids ascended along the fault, underwent convection-driven interaction with meteoric waters, and subsequently metasomatized the host rocks. This integrated approach provides valuable insights into the geological processes governing epithermal gold–silver deposit formation in the Youxi region.

Layered Perovskite Oxyiodide with Narrow Band Gap and Long Lifetime Carriers for Water Splitting Photocatalysis.

The development of semiconductors with narrow band gap and high stability is crucial for achieving solar to chemical energy conversion. Compounds with iodine, which has a high polarizability, have attracted attention because of their narrow band gap and long carrier lifetime, as typified by halide perovskite solar cells; however, they have been regarded as unsuitable for harsh photocatalytic water splitting because iodine is prone to self-oxidation. Here, we demonstrate that Ba2Bi3Nb2O11I, a layered Sillén-Aurivillius oxyiodide, not only has access to a wider range of visible light than its chloride and bromide counterparts, but also functions as a stable photocatalyst, efficiently oxidizing water. Density functional theory calculations reveal that the oxygen 2p orbitals in the perovskite block, rather than the fluorite Bi2O2 block as previously pointed out, anomalously push up the valence band maximum, which can be explained by a modified Madelung potential analysis that takes into account the high polarizability of iodine. In addition, the highly polarizable iodide contributes to longer carrier lifetime of Ba2Bi3Nb2O11I, allowing for a significantly higher quantum efficiency than its chloride and bromide counterparts. Visible-light-driven Z-scheme water splitting was achieved for the first time in an iodine-based system using Ba2Bi3Nb2O11I as an oxygen-evolution photocatalyst. The present study provides a novel approach for incorporating polarizable "soft" anions into building blocks of layered materials to manipulate the band structure and improve the carrier dynamics for visible-light responsive functions.

Linear Electro-Optic Modulation in Highly Polarizable Organic Perovskites.

Electrical-to-optical signal conversion is widely employed in information technology and is implemented using on-chip optical modulators. State-of-the-art modulator technologies are incompatible with silicon manufacturing techniques: inorganic nonlinear crystals such as LiNbO3 are integrated with silicon photonic chips only using complex approaches, and hybrid silicon-LiNbO3 optical modulators show either low bandwidth or high operating voltage. Organic perovskites are solution-processed materials readily integrated with silicon photonics; and organic molecules embedded within the perovskite scaffold allow in principle for high polarizability. However, it is found that the large molecules required for high polarizability also require an increase of the size of the perovskite cavity: specifically, using the highly polarizable DR2+ (R = H, F, Cl) in the A site necessitates the exploration of new X-site options. Only by introducing BF4 - as the X-site molecule is it possible to synthesize (DCl)(NH4 )(BF4 )3 , a material exhibiting a linear EO coefficient of 20 pm V-1 , which is 10 times higher than that of metal halide perovskites and is a 1.5 fold enhancement compared to reported organic perovskites. The EO response of the organic perovskite approaches that of LiNbO3 (reff ≈ 30 pm V-1 ) and highlights the promise of rationally designed organic perovskites for use in efficient EO modulators.

Improved methane/nitrogen separation properties of zirconium-based metal–organic framework by incorporating highly polarizable bromine atoms

The separation of methane, a commercially important fuel and greenhouse gas, from nitrogen is a very important and challenging issue. To address this problem, we systematically incorporated various functional groups (-H, -NH2, -NO2, -Br, and -Br2) into the pores of a hydrothermally stable zirconium-based metal–organic framework (MOF). Various adsorption experiments and molecular simulations confirmed that the CH4 uptake at low pressures could be clearly enhanced by incorporating functional groups due to the effect of the pore size and the functional group polarizability. Remarkably, UiO-66-Br2 exhibited the highest CH4/N2 selectivity (5.06 and 5.63 at 1 bar and 15 bar, respectively) under both vacuum-swing adsorption (VSA) and pressure-swing adsorption (PSA) conditions. Moreover, the UiO-66-Br2 showed efficient separation of CH4 from N2 under dynamic mixture flow conditions, good cyclic CH4 adsorption–desorption profile for 15 cycles and easy regeneration under mild conditions without increasing temperature. These results suggest that incorporation of functional groups with high polarizability, such as bromine, into the pores of MOFs is an efficient strategy for developing adsorbents for CH4/N2 separation.

Anomalous Complex Electrical Conductivity of a Graphitic Black Schist From the Himalayas of Central Nepal

AbstractWe analyzed in the laboratory the frequency‐dependent, complex‐valued, electrical conductivity of a graphitic black schist and an augen gneiss, both collected in the Main Central Thrust shear zone in the Himalayas of central Nepal, which was heavily affected by the deadly Mw7.8 Gorkha earthquake in 2015. We focused on anisotropy and salinity dependence of both cores and crushed material as well as the impact of CO2 on conductivity. This black schist possesses an extraordinarily high polarizability and a highly frequency‐dependent conductivity. Its anisotropy is very pronounced. The investigations can relate the main polarization feature to disseminated, aligned plates of graphite. By contrast, the augen gneiss shows low polarizability and a moderately anisotropic conductivity dominated by the pore‐filling brine. We further demonstrate that neglecting the complex and frequency‐dependent nature of conductivity can lead to serious misinterpretation of magnetotelluric data during inversion if highly polarizable rocks are present.

Nanoscopy reveals surface-metallic black phosphorus.

Black phosphorus (BP) is an emerging two-dimensional material with intriguing physical properties. It is highly anisotropic and highly tunable by means of both the number of monolayers and surface doping. Here, we experimentally investigate and theoretically interpret the near-field properties of a-few-atomic-monolayer nanoflakes of BP. We discover near-field patterns of bright outside fringes and a high surface polarizability of nanofilm BP consistent with its surface-metallic, plasmonic behavior at mid-infrared frequencies <1176 cm−1. We conclude that these fringes are caused by the formation of a highly polarizable layer at the BP surface. This layer has a thickness of ~1 nm and exhibits plasmonic behavior. We estimate that it contains free carriers in a concentration of n≈1.1 × 1020 cm−3. Surface plasmonic behavior is observed for 10–40 nm BP thicknesses but absent for a 4-nm BP thickness. This discovery opens up a new field of research and potential applications in nanoelectronics, plasmonics and optoelectronics.

Investigation on relationship between breakdown strength enhancement of composites and dielectric characteristics of nanoparticle

In this work, the relationship between dielectric characteristics of nanoparticle and its effects on dielectric breakdown strength of Epoxy was investigated. The dielectric characteristic was tailored through silica surface encapsulation on TiO2. It was found that in contrast to raw TiO2, addition of TiO2@SiO2 core-shell nanoparticle obviously improved the dielectric breakdown strength of epoxy resin. Meanwhile, peculiar increase of resistivity was also observed. Based on the results, a mechanism through barrier effect by electric double layer was proposed to explain this enhancement, which was regarded closely associated with the highly polarizable and surface insulating features of TiO2 after silica encapsulation. Experimental validation was also conducted with permittivity and space charge distribution measurement of composites. It was concluded that the high polarizability and surface insulativity firstly favored formation of the double layer, synergistically from which the resulted space charge in homo-pattern then suppressed excessive charge injection through Coulomb repulsive interaction, and improved electrical strength by retarding exorbitant localized field occurrence which had been found to be direct cause of breakdown when it exceed a critical value.

Achieving high electric energy storage in a polymer nanocomposite at low filling ratios using a highly polarizable phthalocyanine interphase

ABSTRACTPolymer nanodielectrics have become attractive for practical applications such as electric energy storage and electromechanical actuation. However, to enhance the apparent dielectric constant of polymer nanodielectrics, a significant amount (&gt;30 vol %) of spherical particles needs to be incorporated into the polymer matrix. As a consequence, melt‐processing of polymer nanodielectrics into uniform thin films becomes difficult at such a high filler content, and electric breakdown strength will greatly decrease. In this work, we describe a three‐phase composite approach towards high energy density nanodielectrics at low filling ratios. In this approach, a highly polarizable tetrameric metallophthalocyanine (TMPc) initiator is coated onto 68 nm BaTiO3 nanoparticles, from which poly(methyl methacrylate) (PMMA) brushes are grafted using atom transfer radical polymerization for the nanoparticles to be uniformly dispersed in a poly(vinylidene fluoride‐co‐hexafluoropropylene) [P(VDF‐HFP)] matrix. For comparison, two‐phase P(VDF‐HFP)/BaTiO3 composites without the TMPc interfacial layer are also prepared. Owing to the high polarizability of the TMPc interface layer, the three‐phase composite films exhibit higher dielectric constant and thus higher energy density than the two‐phase composite films at volume‐filling ratios below 5 vol %. Therefore, these high energy density three‐phase nanodielectrics with a low filling ratio are promising for melt‐processing into thin dielectric films. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 1669–1680

Structural Determinants of Tau Aggregation Inhibitor Potency

Small-molecule Tau aggregation inhibitors are under investigation as potential therapeutic agents against Alzheimer disease. Many such inhibitors have been identified in vitro, but their potency-driving features, and their molecular targets in the Tau aggregation pathway, have resisted identification. Previously we proposed ligand polarizability, a measure of electron delocalization, as a candidate descriptor of inhibitor potency. Here we tested this hypothesis by correlating the ground state polarizabilities of cyanine, phenothiazine, and arylmethine derivatives calculated using ab initio quantum methods with inhibitory potency values determined in the presence of octadecyl sulfate inducer under reducing conditions. A series of rhodanine analogs was analyzed as well using potency values disclosed in the literature. Results showed that polarizability and inhibitory potency directly correlated within all four series. To identify putative binding targets, representative members of the four chemotypes were added to aggregation reactions, where they were found to stabilize soluble, but SDS-resistant Tau species at the expense of filamentous aggregates. Using SDS resistance as a secondary assay, and a library of Tau deletion and missense mutants as targets, interaction with cyanine was localized to the microtubule binding repeat region. Moreover, the SDS-resistant phenotype was completely dependent on the presence of octadecyl sulfate inducer, but not intact PHF6/PH6* hexapeptide motifs, indicating that cyanine interacted with a species in the aggregation pathway prior to nucleus formation. Together the data suggest that flat, highly polarizable ligands inhibit Tau aggregation by interacting with folded species in the aggregation pathway and driving their assembly into soluble but highly stable Tau oligomers.

Ligand electronic properties modulate tau filament binding site density

Small molecules that bind tau-bearing neurofibrillary lesions are being sought for premortem diagnosis, staging, and treatment of Alzheimer's disease and other tauopathic neurodegenerative diseases. The utility of these agents will depend on both their binding affinity and binding site density (Bmax). Previously we identified polarizability as a descriptor of protein aggregate binding affinity. To examine its contribution to binding site density, we investigated the ability of two closely related benzothiazole derivatives ((E)-2-[[4-(dimethylamino)phenyl]azo]-6-methoxybenzothiazole) and ((E)-2-[2-[4-(dimethylamino)phenyl]ethenyl]-6-methoxybenzothiazole) that differed in polarizability to displace probes of high (Thioflavin S) and low (radiolabeled (E,E)-1-iodo-2,5-bis(3-hydroxycarbonyl-4-methoxy)styrylbenzene; IMSB) density sites. Consistent with their site densities, Thioflavin S completely displaced radiolabeled IMSB, but IMSB was incapable of displacing Thioflavin S. Although both benzothiazoles displaced the low Bmax IMSB probe, only the highly polarizable analog displaced near saturating concentrations of the Thioflavin S probe. Quantum calculations showed that high polarizability reflected extensive pi-electron delocalization fostered by the presence of electron donating and accepting groups. These data suggest that electron delocalization promotes ligand binding at a subset of sites on tau aggregates that are present at high density, and that optimizing this aspect of ligand structure can yield tau-directed agents with superior diagnostic and therapeutic performance.

Mesoporous germanium-rich chalcogenido frameworks with highly polarizable surfaces and relevance to gas separation

Mesoporous materials with tunable non-oxidic framework compositions can exhibit new kinds of functionality including internal surfaces with high polarizability. As the chemical and physical characteristics of the framework components can induce useful catalytic, absorption and optoelectronic features, the mesoporous structure can promote fast mass diffusion kinetics and size-selective transport of guest molecules. So far, synthetic efforts have resulted in mesoporous metal chalcogenides on using structure-directing moulds of soft or hard templates. These include ordered mesoporous II-VI semiconductors (such as CdS (refs 2,3), ZnS (ref. 4) and CdTe (ref. 5)). Recently, template-free synthetic routes for high-surface-area chalcogenide aerogels have been reported. Here, we describe a novel kind of porous materials based on germanium-rich chalcogenide networks and 'soft' highly polarizable surfaces. We demonstrate that these materials can exhibit excellent selectivity for separating hydrogen from carbon dioxide and methane. These highly polarizable mesoporous structures have important implications for membrane-based gas separation process technologies including hydrogen purification.

Optical characterization of xTiO2–(60−x)SiO2–40Na2O glasses

Abstract Different x TiO 2 –(60 − x )SiO 2 –40Na 2 O (5 ≤ x ≤ 20 wt.%) glasses are prepared in the form of plane parallel slabs. The optical constants of these optical glasses are determined over a wide spectral range, 0.2–3 μm, providing the complex dielectric constant to be calculated. The different dispersion parameters of the studied compositions are determined as well. Higher values for the refractive index and dispersion are recorded due to the high polarizability of Ti and the low preference of 4-coordination for titanium. The wavelength for zero material dispersion is evaluated. The second-order index of refraction and the third-order nonlinear optical susceptibility are computed from the measured linear refractive index data. These nonlinear properties of the present glass show one order of magnitude enhancement over some TiO 2 silicate glasses. The measured mid-IR-spectra of the different glasses are carried out to investigate the structure of the present glasses. It has been found that, the addition of titanium (i.e., highly polarizable element) not only acts as glass modifier but also behaves as intermediate and Ti 4+ exalts more the measured glass parameters.

Molecular dynamics study of water penetration in staphylococcal nuclease

The ionization properties of Lys and Glu residues buried in the hydrophobic core of staphylococcal nuclease (SN) suggest that the interior of this protein behaves as a highly polarizable medium with an apparent dielectric constant near 10. This has been rationalized previously in terms of localized conformational relaxation concomitant with the ionization of the internal residue, and with contributions by internal water molecules. Paradoxically, the crystal structure of the SN V66E variant shows internal water molecules and the structure of the V66K variant does not. To assess the structural and dynamical character of interior water molecules in SN, a series of 10-ns-long molecular dynamics (MD) simulations was performed with wild-type SN, and with the V66E and V66K variants with Glu66 and Lys66 in the neutral form. Internal water molecules were identified based on their coordination state and characterized in terms of their residence times, average location, dipole moment fluctuations, hydrogen bonding interactions, and interaction energies. The locations of the water molecules that have residence times of several nanoseconds and display small mean-square displacements agree well with the locations of crystallographically observed water molecules. Additional, relatively disordered water molecules that are not observed crystallographically were found in internal hydrophobic locations. All of the interior water molecules that were analyzed in detail displayed a distribution of interaction energies with higher mean value and narrower width than a bulk water molecule. This underscores the importance of protein dynamics for hydration of the protein interior. Further analysis of the MD trajectories revealed that the fluctuations in the protein structure (especially the loop elements) can strongly influence protein hydration by changing the patterns or strengths of hydrogen bonding interactions between water molecules and the protein. To investigate the dynamical response of the protein to burial of charged groups in the protein interior, MD simulations were performed with Glu66 and Lys66 in the charged state. Overall, the MD simulations suggest that a conformational change rather than internal water molecules is the dominant determinant of the high apparent polarizability of the protein interior.

Spiers Memorial Lecture. On the hypothesis of cathodic protection of genes.

Holes (electron vacancies) injected by oxidants are transferred across <50 base pair (bp) long dissolved DNA duplexes in homogeneous solutions by hopping between CG base pairs. The injected holes oxidize remote G-sites, particularly sites comprising sequences of multiple GC base pairs. When not aligned in parallel, condensed-phase DNA duplexes are electrically insulating, but when aligned their one-dimensional conductivity in the direction of the aligned long axes increases at least 103 fold. The conductivity of 600 nm long DNA “ropes” exceeds 103 Ω−1 cm−1, a value typical of degenerate semiconductors and only two orders of magnitude below that of conventional metals like iron. The increase is attributed to the high unidirectional polarizability of DNA, which has been theoretically estimated to be 1.5 × 10−27 F m−2, 13 orders of magnitude greater than that of water. It is proposed that the cause of the high unidirectional polarizability is the rapid and concerted shift of protons between primary amines of G-, C- and A-bases of neighboring pairs of the DNA stack. Even though the buildup of high concentrations of oxidants like H2O2 and NO is usually avoided in cells, their concentrations can exceed 1 nM, a value translating to >109 oxidant-molecules per copy of the genome. Thus, oxidative attack of a cell’s genome, which can be several centimeters long, is not unlikely. Some species may have evolved so that their essential chromosomal domains, including their transcribed genes, are cathodically protected against oxidative damage: When an essential element of the genome is attacked by an oxidizing agent, a less essential element of their genome is sacrificially oxidized. The sacrificially oxidized domain may have only a protective function, or it may have an essential function the transient loss of which does not lead to cellular damage within the characteristic period required for damage recognition, excision and repair. For cathodic protection of the essential parts of the genome, the sacrificially oxidized domain must be (a) in electronic contact with the protected domain and (b) more reducing and more rapidly oxidized than the protected domain. The redox potentials of the four bases of DNA s. NHE at pH 7 are G, 1.04 V; T, 1.29 V; A, 1.32 V; and C, 1.44 ± 0.02 V. Not only is G the most reducing of bases, but its catalytic one-electron oxidation kinetics in poly-GC sequences is particularly rapid. The redox potentials of the GC and AT base pairs, estimated by averaging the potentials of their constituent bases are, respectively, 1.24 and 1.31 V. There can be three types of sacrificially oxidized domains, differing in their electronic conductivity: (a) Long, highly polarizable, electronically conducting GC-rich sequences within the chromosomes, exemplified by the 1–2 kilobase (kb) long double-stranded CpG islands found at the 5′-end of genes in chromosomes of animals; (b) very short, single-stranded G-rich sequences, that are neither particularly polarizable nor conductive, but are proximal to, or terminating, the protected conductive double-stranded sequence. These are exemplified by the 12–20 base long G-rich telomeric overhang; and (c) organized, moderately polarizable and somewhat electronically conductive arrays of aligned G-rich single strands, exemplified by the K+-complexes of G-tetrads, the existence of which has been verified so far only in itro. In all three cases the protective process resembles that of steel by zinc, where the more reducing zinc is sacrificially oxidized while protecting the steel against corrosion, a process described by Humphrey Davy, who was assisted by Michael Faraday. If the hypothesis of cathodic protection of essential chromosomal domains is valid, then aging and genomic instability of cells may reflect the loss of protection against oxidative damage.

Theory of the energy spectrum of excess electrons in highly polarizable fluids.

The energy of the bottom of the conduction zone and the effective mass of excess electrons injected into a nonpolar fluid with high polarizability is considered. Pseudopotential theory of electrons in a cellular medium is extended to conditions where polarization attraction predominates over electron-fluid interaction. The solution is obtained in the Wigner-Seitz cell for the case where the scattering length of electron in the fluid is negative. The calculated density dependences of the conduction-zone bottom and effective mass of electron in noble fluids are in satisfactory agreement with available experimental data.

Charge Localization of Some Highly Polarizable Systems

AbstractIn this work we discuss some close analogies among various intramolecular charge‐transfer systems with high polarizability. They range from sudden‐polarization systems concerning two‐electron localization to valence‐hole and core‐hole systems involving only one‐electron localization, and the combined situation of valence electron‐core hole pair localization. The high polarizability of a two‐site (a, b) system is shown to be correlated to the weakness of the electronic coupling integral &lt;a|H|b&gt; between the sites. The hole localization in core‐hole states and van der waals ions is compared with that of molecular ions due to solvation effect. The electron‐hole pair localization in the core‐hole state of the mixed valence system is compared with that in the Πg,a state of H2 due to electron correlation behavior.