Bond Polarizability Research Articles

Chlorophyll Films for Radiation Dosimetry: A Feasibility Study

Abstract Novel Chlorophyll-PVA composite films have been prepared and tested for the dosimetry of therapeutic radiation. The radiation response has been quantified using UV-Vis spectroscopy. FTIR and XRD spectroscopies have been used to characterize the physical properties and irradiation response of the films. The films have shown response towards the therapeutic x-rays beams of 6 MV nominal energy in the tested dose range of 0.25 Gy to 32 Gy in discrete dose levels occurring in the geometric progression series of 2. The dosimeter has been found to exhibit sensitivity at a low dose of 0.25 Gy. The dose response curve of the dosimeter exhibits an exponential relationship of the absorbance and absorbed dose. A region of saturated absorbance has been observed beyond 4 Gy. The peak intensities of the FTIR spectra have been found to decrease with increasing doses as compared to the unirradiated samples, because of the changes in the bond polarities and molecular geometries. The XRD spectra indicates a change in the molecular orientation resulting in a decrease in peak intensity with increasing dose. This study indicates the feasibility of chl-PVA films in the dosimetry of therapeutic radiation. This film dosimeter can be processed locally with minimum resources and standardized against a known standard before clinical use. The chlorophyll molecules need careful handling owing to their sensitivity to light and temperature.

Growth, characterization and cognition of 2-cyanopyridinium perchlorate single crystals for nonlinear optical applications.

The fascinating electronic applications attracted researchers to explore the field of nonlinear optical (NLO) materials. The slow evaporation of solvent technique (SEST) was employed to grow the 2-cyanopyridinium perchlorate (2-CPPC) NLO single crystals. The cell parameters of the grown 2-CPPC crystal are confirmed by the single crystal X-ray diffraction (SCXRD) study. The powder X-ray diffraction studies confirm the crystallinity of 2-CPPC crystals, and the peaks were indexed. The computation for the geometry optimization, HOMO-LUMO energy gap, global reactivity parameters, natural bond orbital (NBO) analysis, polarizability, and hyperpolarizability of the 2-CPPC molecule was done using B3LYP (6-311G basis set) functional of DFT method. The experimental FTIR and UV-Vis results of the 2-CPPC compound were compared with the simulated results. The second harmonic generation (SHG) study for the 2-CPPC crystal was employed using Kurtz-Perry powder technique. Single beam Z-scan technique using He-Ne laser is used to study the third-order NLO properties.

The use of 1D carbon nanotube interacting with caffeine molecules for applications in solar cells: structure optimisation, Raman analysis and optoelectronic properties

This study proposes a promising candidate for organic solar cells through the creation of a novel nano-hybrid system composed of caffeine molecules encapsulated within a semiconducting single-walled carbon nanotube known as NT14 (14,0). The stability and optoelectronic properties of this hybrid system, designated as CA@NT14, were thoroughly investigated. We determined the optimal diameter for the NT14 nanotube using molecular mechanics, Density Functional Theory, spectral moment’s method, and bond polarizability model, finding it to be approximately 1.18 nm. The encapsulation’s impact on the Raman-active modes, specifically the radial breathing mode and tangential mode, was analyzed through Raman spectra calculations, revealing structural stability and charge transfer from CA to NT14. Notably, the NT14’s Fermi level position increased upon encapsulation, indicating charge transfer and a type-II band alignment. The study further examined the bandgap characteristics of the hybrid system, finding that the encapsulation of CA within semiconducting NT14 nanotubes minimally impacts the nanotube’s bandgap, thus retaining its excellent visible light absorption properties. Conversely, encapsulating CA within metallic nanotubes significantly reduces their bandgap, limiting their light absorption range. The nonresonant Raman responses of NT14 pre- and post-encapsulation corroborated the charge transfer between CA and NT14. Future research will focus on computing the electronic transport characteristics, transmission spectra, I-V characteristics, and yield of CA@NT14 using DFT and Non-Equilibrium Green’s Function ( formalism. An experimental study will be conducted to validate these theoretical findings. These results indicate the potential of CA@NT14 hybrids as effective active layers in organic solar cells, highlighting their significance in advancing optoelectronic applications.

Tip-like copper sites on high curvature supports for non-covalent to covalent interaction tuning in CO2 photoreduction

Single-atom engineering offers a promising method to transform CO2 into high-value chemicals. The local coordination structure design of the metal-support is crucial for overcoming slow reaction kinetics. In this study, Cu single atoms are immobilized on curved Bi12O17Br2 surface to create a tip-like metal site structure named Cutip-Bi12O17Br2. Due to the high curvature Bi12O17Br2 surface with tensile strain, the tip Cu creates significant electronegativity differences between adjacent Bi atomic sites, creating the vigorous polarization centers. The strong charge redistribution character of tip asymmetric Cu-Bi site favor the polarization of CO bond in nonpolar CO2 and adjust the noncovalent to covalent interaction of reaction intermediates. Benefiting from these features, the optimized Cutip-Bi12O17Br2 enhance the CO production rate by a factor of 34 relative to bulk-Bi12O17Br2, reaching a rate of 96.99 μmol g−1 h−1. This work provides a comprehensive understanding of the structural regulation of single-atom on high curvature surface for CO2 photoreduction.

IPr*F - Highly Hindered, Fluorinated N-Heterocyclic Carbenes.

The introduction of fluorine atom has attracted considerable interest in molecular design owing to the high electronegativity and the resulting polarization of carbon-fluorine bonds. Simultaneously, sterically-hindered N-heterocyclic carbenes (NHCs) have received major interest due to high stabilization of the reactive metal centers, which has paved the way for the synthesis of stable and reactive organometallic compounds with broad applications in main group chemistry, inorganic synthesis and transition-metal-catalysis. Herein, we report the first class of sterically-hindered, fluorinated N-heterocyclic carbenes. These ligands feature variable fluorine substitution at the N-aromatic wingtip, permitting to rationally vary steric and electronic characteristics of the carbene center imparted by the fluorine atom. An efficient, one-pot synthesis of fluorinated IPr*F ligands is presented, enabling broad access of academic and industrial researchers to the fluorinated ligands. The evaluation of steric, electron-donating and π-accepting properties as well as coordination chemistry to Au(I), Rh(I) and Se is presented. Considering the unique properties of carbon-fluorine bonds, we anticipate that this novel class of fluorinated carbene ligands will find widespread application in stabilizing reactive metal centers.

Pursuing Extreme Descriptive Power and Generality in Chemical Bond Theories: A Method to Decipher "Interatomic Genomes" from Interatomic Electron Structures.

The description and analysis of chemical bonds have been difficult following the popularization of electronic structure calculations. Although many attempts have been made from the perspective of electronic structure, the sheer volume of information in the electronic structure has left contemporary chemical bond analysis methods grappling with an inescapable "Trilemma" where the model briefness, generality, and descriptiveness (descriptive power) cannot be obtained simultaneously. To push the generality and descriptiveness to their extremes, herein a general machine learning-based framework is introduced to compact chemical bonds into a detailed residue-by-residue "genome" with matched encoding/decoding tools. The framework fuses the quantum mechanical aspects, auto feature extraction, nanostructures and/or simulations, and generative models. The encoded genomes are information-dense and decodable, where 100% generality is guaranteed. The descriptiveness of genomes appears to be broader than most known models. As a proof of concept, the realization presented in this work compacts the complete information regarding two critical chemical bonds in thiolate-protected gold nanoclusters, the S-Au and Au-Au bonds, from a Bosonic-Fermionic character perspective into 8-valued genomes. The machine learning component is trained based on 26,528 density functional theory simulated electron localization function images. With an exploration of the space span for the genome, bond polarization, hybridization, intrusion of other atoms, alignments, crystal orientation, atomic motions, and more details are observed. Furthermore, it has emerged from extensive generation tests that molecules and solids can be integrated in such a concise manner than is typically achieved with purely geometric representations. To showcase the intraclass complexity of S-Au and Au-Au bonds visually, a roadmap is plotted by summarizing and correlating the similarities of 8-value-genomes. Furthermore, genomes can be associated with realistic indices easily with a simple multilayer perception architecture as a simple calculating tool. Besides, there are 3 sets of applications, including a set of chemisorption, a set of molecular dynamical analysis, and a set of ultrafast processes, showcasing the interpretability potentials of interatomic genomes in the geometric structures, kinetic properties, and vibration characteristics of molecular systems. As the framework rose to the challenge of nanoclusters from a complicated mesoscopic family of material, the displayed generality and comprehensiveness indicate that the model may "understand" chemical bonds in a machine's way.

AIM/NBO Analysis of the Geminal Coupling Constants in the Stabilization of A-Type Dimeric Proanthocyanidin: Angular Dependence.

The angular dependence of the indirect short-range spin-spin coupling constants (SSCC), the geminal , , and in A-type dimeric proanthocyanidin, was investigated using density functional theory. We studied the rotation of ring B around the bond. Therefore, we calculated hyperconjugative charge transfers and bond polarizations within the natural bond orbital (NBO) approach, performing a topological study based on Bader's theory, AIM (atoms in molecules), and analyzing the angular dependence of AIM/NBO parameters. The results describe a relationship between the geminal coupling that changes with angular variation and NBO charge transfers to the bonds involved in the coupling pathways that can explain the behavior of the former property. Based on AIM/NBO data, inductive and mesomeric effects were described and quantified, showing a clear correlation with the stabilization of the structure, demonstrating a resonance-assisted inductive effect. We also set out strong hyperconjugative interactions (anomeric effect) involving nonbonding electron pairs of oxygen atoms. This analysis of coupling constants supports previous models by other authors and shows the application in this particular case. Moreover, the SSCCs studied herein are used for identifying stable structures and conformational search analysis of flavonoids. Finally, our results show the relationship between SSCCs and the structure stabilization and charge delocalization effects.

Ultrahigh Stability and Operation Performance in Bi-doped GeTe/Sb2Te3 Superlattices Achieved by Tailoring Bonding and Structural Properties.

Changes in bond types and the reversible switching process between metavalent and covalent bonds are related to the operating mechanism of the phase-change (PC) behavior. Thus, controlling the bonding characteristics is the key to improving the PC memory performance. In this study, we have controlled the bonding characteristics of GeTe/Sb2Te3 superlattices (SLs) via bismuth (Bi) doping. The incorporation of Bi into the GeTe sublayers tailors the metavalent bond. We observed significant improvement in device reliability, set speed, and power consumption induced upon increasing Bi incorporation. The introduction of Bi was found to suppress the change in density between the SET and RESET states, resulting in a significant increase in device reliability. The reduction in Peierls distortion, leading to a more octahedral-like atomic arrangement, intensifies electron-phonon coupling with increased bond polarizability, which are responsible for the fast set speed and low power consumption. This study demonstrates how the structural and thermodynamic changes in phase change materials alter phase change characteristics due to systematic changes of bonding and provides an important methodology for the development of PC devices.

Effect of rGO synthesis on Mg-C interaction-induced hydrogen uptake by Mg-rGO nanocomposites

Reduced graphene oxide (rGO) is synthesized electrochemically (erGO), chemically (crGO) and thermally (trGO). These are eventually used for synthesizing Mg-erGO, Mg-crGO and Mg-trGO nanocomposites by ball-milling (ball:powder = 40:1, 20 h, 450 rpm) for hydrogen storage. Upon H-uptake (PH2 = 15 bar, 320 °C), Mg-erGO exhibits fastest and highest H-uptake (∼6 wt%) with lowest incubation time (∼2 h). Mg-crGO and Mg-trGO yield lower H-uptake (∼5 wt%) and larger incubation times (∼7, ∼20 h). The erGO is highly wrinkled offering easy access to its surface and highest extent of sp2 carbon (XPS). Contrarily, crGO and trGO possess lower wrinkling and heavy stacking, respectively. Mg-erGO is least defective as estimated from Raman (ID/IG∼1.11) versus Mg-crGO and Mg-trGO (ID/IG∼1.22, 1.46). This least defective erGO enhances Mg → C electron transfer in Mg-erGO, inducing H-H bond polarization and subsequent Mg-H bond formation. Thus, it leads to the best H-uptake performance.

Enantiospecificity in NMR enabled by chirality-induced spin selectivity

Spin polarization in chiral molecules is a magnetic molecular response associated with electron transport and enantioselective bond polarization that occurs even in the absence of an external magnetic field. An unexpected finding by Santos and co-workers reported enantiospecific NMR responses in solid-state cross-polarization (CP) experiments, suggesting a possible additional contribution to the indirect nuclear spin-spin coupling in chiral molecules induced by bond polarization in the presence of spin-orbit coupling. Herein we provide a theoretical treatment for this phenomenon, presenting an effective spin-Hamiltonian for helical molecules like DNA and density functional theory (DFT) results on amino acids that confirm the dependence of J-couplings on the choice of enantiomer. The connection between nuclear spin dynamics and chirality could offer insights for molecular sensing and quantum information sciences. These results establish NMR as a potential tool for chiral discrimination without external agents.

Efficient microwave induction to modify surface for high-rate lithium/fluorinated carbon battery with ultra-high power density

The practical application of high-rate lithium/fluorinated carbon (Li/CFx) primary batteries faces challenge of relatively slow electrode reaction kinetics limited by inert C-F bond and strong polarity. Herein, an effective microwave-induction strategy was developed to regulate C-F bond for 80C high-rate Li/CFx battery with suppressed polarization. The as-mentioned microwave method was carried out in the alcohol-based solvent for uniformly modify CFx, including precise defluorination, C-F bond regulation, surface functional groups and carbon quantum dots. Precise defluorination contains the conversion of C-F bond to semi-ionic C-F bond while preserving C-F2 and C-F3. During the process of C-F bond regulation, hydroxyl groups is grafted onto the surface of CFx to increase the wettability and electronegativity of the electrode. Compared with raw CFx, the Li/CFx batteries using microwave-modified CFx achieved high discharge rate of 80C possessing a high power density of 134.091 kW/kg. In addition, the optimal Li/CFx battery possesses a large specific capacity increase ratio of 142.6 % at 50C. This microwave-induction approach for modifying CFx in ethanol-based solvent provides a facile and effective pathway to design high-rate Li/CFx battery.

Accuracy and limitations of the bond polarizability model in modeling of Raman scattering from molecular dynamics simulations.

Calculation of Raman scattering from molecular dynamics (MD) simulations requires accurate modeling of the evolution of the electronic polarizability of the system along its MD trajectory. For large systems, this necessitates the use of atomistic models to represent the dependence of electronic polarizability on atomic coordinates. The bond polarizability model (BPM) is the simplest such model and has been used for modeling the Raman spectra of molecular systems but has not been applied to solid-state systems. Here, we systematically investigate the accuracy and limitations of the BPM parameterized from the density functional theory results for a series of simple molecules, such as CO2, SO2, H2S, H2O, NH3, and CH4; the more complex CH2O, CH3OH, CH3CH2OH, and thiophene molecules; and the BaTiO3 and CsPbBr3 perovskite solids. We find that BPM can reliably reproduce the overall features of the Raman spectra, such as shifts of peak positions. However, with the exception of highly symmetric systems, the assumption of non-interacting bonds limits the quantitative accuracy of the BPM; this assumption also leads to qualitatively inaccurate polarizability evolution and Raman spectra for systems where large deviations from the ground state structure are present.

Hydrogen Bond Strengthens Acceptor Group: The Curious Case of the C-H···O=C Bond.

An H-bond involves the sharing of a hydrogen atom between an electronegative atom to which it is covalently bound (the donor) and another electronegative atom serving as an acceptor. Such bonds represent a critically important geometrical force in biological macromolecules and, as such, have been characterized extensively. H-bond formation invariably leads to a weakening within the acceptor moiety due to the pulling exerted by the donor hydrogen. This phenomenon can be compared to a spring connecting two masses; pulling one mass stretches the spring, similarly affecting the bond between the two masses. Herein, we describe the opposite phenomenon when investigating the energetics of the C-H···O=C bond. This bond underpins the most prevalent protein transmembrane dimerization motif (GxxxG) in which a glycine Cα-H on one helix forms a hydrogen bond with a carbonyl in a nearby helix. We use isotope-edited FT-IR spectroscopy and corroborating computational approaches to demonstrate a surprising strengthening of the acceptor C=O bond upon binding with the glycine Cα-H. We show that electronic factors associated with the Cα-H bond strengthen the C=O oscillator by increasing the s-character of the σ-bond, lowering the hyperconjugative disruption of the π-bond. In addition, a reduction of the acceptor C=O bond's polarity is observed upon the formation of the C-H···O=C bond. Our findings challenge the conventional understanding of H-bond dynamics and provide new insights into the structural stability of inter-helical protein interactions.

N-Heterocyclic Carbene Enabled Functionalization of Inert C(Sp3)-H Bonds via Hydrogen Atom Transfer (HAT) Processes.

Developing methods to directly transform C(sp3) -H bonds is crucial in synthetic chemistry due to their prevalence in various organic compounds. While conventional protocols have largely relied on transition metal catalysis, recent advancements in organocatalysis, particularly with radical NHC catalysis have sparked interest in the direct functionalization of "inert" C(sp3) -H bonds for cross C-C coupling with carbonyl moieties. This strategy involves selective cleavage of C(sp3) -H bonds to generate key carbon radicals, often achieved via hydrogen atom transfer (HAT) processes. By leveraging the bond dissociation energy (BDE) and polarity effects, HAT enables the rapid functionalization of diverse C(sp3)-H substrates, such as ethers, amines, and alkanes. This mini-review summarizes the progress in carbene organocatalytic functionalization of inert C(sp3)-H bonds enabled by HAT processes, categorizing them into two sections: 1) C-H functionalization involving acyl azolium intermediates; and 2) functionalization of C-H bonds via reductive Breslow intermediates.

Formation, Structure and Reactivity of a Beryllium(0) Complex with Mgδ+-Beδ- Bond Polarization.

Attempts to create a novel Mg-Be bond by reaction of [(DIPePBDI*)MgNa]2 with Be[N(SiMe3)2]2 failed; DIPePBDI*=HC[(tBu)C=N(DIPeP)]2, DIPeP=2,6-Et2C-phenyl. Even at elevated temperatures, no conversion was observed. This is likely caused by strong steric shielding of the Be center. A similar reaction with the more open Cp*BeCl gave in quantitative yield (DIPePBDI*)MgBeCp* (1). The crystal structure shows a Mg-Be bond of 2.469(4) Å. Homolytic cleavage of the Mg-Be bond requires ΔH=69.6 kcal mol-1 (cf. CpBe-BeCp 69.0 kcal mol-1 and (DIPPBDI)Mg-Mg(DIPPBDI) 55.8 kcal mol-1). Natural-Population-Analysis (NPA) shows fragment charges: (DIPePBDI*)Mg +0.27/BeCp* -0.27. The very low NPA charge on Be (+0.62) compared to Mg (+1.21) and the strongly upfield 9Be NMR signal at -23.7 ppm are in line with considerable electron density on Be and the formal oxidation state assignment of MgII-Be0. Despite this Mgδ+-Beδ- polarity, 1 is extremely thermally stable and unreactive towards H2, CO, N2, cyclohexene and carbodiimide. It reacted with benzophenone, azobenzene, phenyl acetylene, CO2 and CS2. Reaction with 1-adamantyl azide led to reductive coupling and formation of an N6-chain. The azide reagent also inserted in the Cp*-Be bond. The inertness of 1 is likely due to bulky ligands protecting the Mg-Be unit.

Formation, Structure and Reactivity of a Beryllium(0) Complex with Mgδ+−Beδ− Bond Polarization

Formation, Structure and Reactivity of a Beryllium(0) Complex with Mg^δ+−Be^δ− Bond Polarization

Vibrational Spectra Simulations in Amino Acid-Based Imidazolium Ionic Liquids.

We present maximally localized Wannier functions and Voronoi tessellation to obtain dipole moment distributions for vibrational spectra in several important ionic liquids calculated by using ab initio molecular dynamics simulations. IR and Raman spectra of various imidazolium-based ionic liquids (ILs) paired with six amino acid anions are shown herein. For IR spectra, two approaches (Wannier and Voronoi) are in agreement with respect to the relative intensities and the overall shapes for the main peaks. Under Raman spectra, the polarizability of the covalent bonds is shown to affect the strength of the Raman scattering signal. The advantage of the Voronoi tessellation method, being that it does not have strong spikes in its time development, is demonstrated by the comparison of two theoretical methods (Wannier and Voronoi) with experimental data. We analyze the errors between theoretical and experimental spectroscopic data, with the Voronoi method shown to accurately reproduce experimental values. In addition, theoretical spectroscopy shows the ability to accurately separate components of a mixture. The combination of theoretical and experimental methods is utilized to understand the spectroscopic properties of amino acid-based imidazolium ILs.

Strain-Dependent Effects on Confinement of Folded Acoustic and Optical Phonons in Short-Period (XC)m/(YC)n with X,Y (≡Si, Ge, Sn) Superlattices.

Carbon-based novel low-dimensional XC/YC (with X, Y ≡ Si, Ge, and Sn) heterostructures have recently gained considerable scientific and technological interest in the design of electronic devices for energy transport use in extreme environments. Despite many efforts made to understand the structural, electronic, and vibrational properties of XC and XxY1-xC alloys, no measurements exist for identifying the phonon characteristics of superlattices (SLs) by employing either an infrared and/or Raman scattering spectroscopy. In this work, we report the results of a systematic study to investigate the lattice dynamics of the ideal (XC)m/(YC)n as well as graded (XC)10-∆/(X0.5Y0.5C)∆/(YC)10-∆/(X0.5Y0.5C)∆ SLs by meticulously including the interfacial layer thickness ∆ (≡1-3 monolayers). While the folded acoustic phonons (FAPs) are calculated using a Rytov model, the confined optical modes (COMs) and FAPs are described by adopting a modified linear-chain model. Although the simulations of low-energy dispersions for the FAPs indicated no significant changes by increasing ∆, the results revealed, however, considerable "downward" shifts of high frequency COMs and "upward" shifts for the low energy optical modes. In the framework of a bond polarizability model, the calculated results of Raman scattering spectra for graded SLs are presented as a function of ∆. Special attention is paid to those modes in the middle of the frequency region, which offer strong contributions for enhancing the Raman intensity profiles. These simulated changes are linked to the localization of atomic displacements constrained either by the XC/YC or YC/XC unabrupt interfaces. We strongly feel that this study will encourage spectroscopists to perform Raman scattering measurements to check our theoretical conjectures.

Asymmetric Bond Delta‐Polarization at the Interfacial Se─Ru─O Bridge for Efficient pH‐Robust Water Electrolysis

AbstractThe rationalization of pH‐robust catalysis is highly desired but challengeable for overall water electrolysis (WE). It requests a metal active site that can make an efficient adaption with both cathodic hydrogen and anodic oxygen evolution reactions (HER/OER). Herein, a RuO2‐x/RuSe2 heterostructure electrocatalyst is profiled with interfacial Se─Ru─O bridge for the pH‐robust water splitting studies. An asymmetric bond delta‐polarization (Δp) is found at the interfacial Se─Ru─O bridge, including the Δp > 0 at the Ru─O part and Δp < 0 at the Ru─Se side by both experiment and calculation results. The enlarged Ru─O bond polarizability (Δp > 0) can in principle trigger the lattice oxygen mediated (LOM) pathway for OER; meanwhile, the reduced Ru─Se bond polarizability can benefit the HER due to the strengthened d‐p band hybridization. Resultantly, the heterostructure can deliver ultralow overpotentials of 25/10 mV for Pt‐beyond HER and 210/255 mV for OER at 10 mA cm−2 in acidic/alkaline media, respectively. In especial, the acidic overall WE can be stably operated for 200 h with a low cell voltage of 1.478 V at 10 mA cm−2. This research clarifies the asymmetric bond polarization as the criterion for the rational design of efficient WE catalysts.

Low-frequency Raman active modes of twisted bilayer MoS2

We study the low-frequency Raman active modes of twisted bilayer MoS2 for several twist angles using a force-field approach and a parametrized bond polarizability model. We show that twist angles near high-symmetry stacking configurations exhibit stacking frustration that leads to significant buckling of the moiré superlattice. We find that atomic relaxation due to the twist is of prime importance. The periodic displacement of the Mo atoms shows the realization of a soliton network, and in turn, leads to the emergence of a number of frequency modes not seen in the high-symmetry stacking systems. Some of the modes are only seen in the XZ Raman polarization setup while others are seen in the XY setup. The symmetry of the normal modes, and how this affects the Raman tensors is examined in detail.