Electron Density Shifts Research Articles

Spectroscopic, computational, docking, and cytotoxicity investigations of 5-chloro-2-mercaptobenzimidazole as an anti-breast cancer medication

The vibrations were attributed to 5-chloro-2-mercaptobenzimidazole using FTIR and FT-Raman spectroscopy. The optimized geometrical parameters, IR intensity, and the Raman activity of the vibrational bands were estimated using the Becke three-parameter Lee-Yang-Parr functional and the 6-311++G(d,p) level of theory. These findings are compared with the experimental data. The molecule’s HOMO-LUMO energy gap is found to be 4.418 eV. UV-Vis analysis reveals that the π→π* transition, which happens when electron density shifts from nitrogen, sulfur, and chlorine atoms in the molecule, to the electrons of the C-C bonds of the ring. Total density of states was used to assess the molecular orbital contributions. There are 47α and 47β electrons totaling 94 electrons in the DOS spectrum. NBO investigations indicate that a considerable stabilizing energy of 30.37 and 30.90 Kcal/mol was revealed by the lone pair transition of N1 and N3 atoms to π*(C7-C8) and π*(C4-C9). The more electrophilic region, as seen by the red zone in MEP mapping, lies in the vicinity of the nitrogen and sulfur atoms. The molecule’s hydrogen atoms are found in the blue nucleophilic area. The theoretical chemical shifts for 1H and 13C NMR ranged from 7.03 to 8.23 ppm and 113.10 to 207.31 ppm, respectively. The docking research showed that the molecule attached to protein 1AQU with a greater binding energy of −6.8 Kcalmol−1. The cytotoxicity of the sample was evaluated against a MCF-7 cell line (IC50 = 16.54 µg/ml) and exhibited a good breast cancer action. In addition, ADMET prediction has been used to estimate the medicinal applicability of the chemical.

Effects of Static Electric Fields on the Excitations of Silver Nanowire Dimers.

We theoretically studied the introduction of static electric fields to Ag10 nanowire dimer systems, including the effects of this field on optical absorption characteristics and the orbitals responsible for these excitations. Linear-response time-dependent density functional theory computations were performed on three distinct dimer systems: end-to-end, parallel, and 90° angle dimer systems separated by a closest interparticle distance of 7.0 Å. The calculations were performed in the presence of a 0.1 V/Å electric field strength applied in the z and y directions. The orientation of the dimer system and the direction of the applied static electric field each play a significant role in the resulting absorption spectra and the electronic structure of the nanowires. As a result, a dimer system can exhibit a blue shift for the longitudinal excitation and a red shift for the transverse excitation in the presence of one direction of the static electric field but not for the other direction. Notably, the electron density shifts from one nanowire to the other in the presence of the static electric field. Changes in optical characteristics and electronic structure suggest that the usage of a static electric field with a particular spatial configuration of nanowires provides a way to tune the optical properties of the system.

Multiple Representations Analysis of Chemical Bonding Concepts in General Chemistry Books

This research aimed to analyze the use of the concept of the three levels of chemical representation in eight general chemistry books. It was qualitative research with an evaluative descriptive design. The concepts analyzed included the concepts of ionic, covalent, and metallic bonds. The analysis focused on two main criteria: the use of macroscopic, sub-microscopic, and symbolic levels of representation and the relationship between the three levels. The results of the analysis showed that in the concept of ionic bonding, there were pictures of some salts or reactions for the formation of ionic compounds from their elements at the macroscopic level, explanations at the sub-microscopic level, and models of the arrangement of ions in the ionic crystal lattice for the symbolic level. In the concept of covalent bonds, there were images of gasses or covalent compounds at the macroscopic level, explanations at the sub-microscopic level, and models of electron density shifts at the symbolic level. In the concept of metallic bonds, there were pictures of some metals at the macroscopic level, explanations at the sub-microscopic level, and electron cloud models at the symbolic level. The relationship between the levels of representation was found in five of the eight general chemistry books analyzed. General chemistry books present the relationship between the three levels of representation in images that include energy level diagrams, atomic or ionic arrangement models, reaction equations, and explanations of the molecular level.
 Keywords: concept, chemical representation, general chemistry, books

Single atom catalysts supported on cyclo[18]carbon and its allotropes (B9N9 and Al9N9) for the hydrogen evolution and oxygen evolution reactions

The scientific community is actively searching for a cost-effective, easily available and exceptionally efficient catalyst to substitute expensive and scarce catalysts based on transition metals (TMs), in order to meet the increasing demand for renewable and clean energy resources. Recently, single-atom catalysts (SACs) are specifically engineered to achieve impressive catalytic performance while minimizing the need for expensive noble TMs in electrochemical energy conversion applications. In this study, we have studied the potential of cyclo[18]carbon (C18 nanocluster), along with its analogous structures (B9N9 and Al9N9 nanoclusters), as supports for TMs (Ni, Pd, and Pt) SACs in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The strong binding between TMs and nanoclusters was confirmed by high binding energy, structural changes, Mulliken charge transfer, induced dipole moments, and shifts in HOMO and LUMO electron density. Introduction of Ni, Pd, and Pt onto the nanoclusters decreased the HOMO-LUMO gap, indicating improved conductivity of the support. Notably, the Gibbs free energy of H adsorption (ΔGH) was measured as 0.07 eV and -0.07 eV for Pt/B9N9 and Pt/Al9N9 SACs, respectively, indicating their potential as HER catalysts. These findings serve as a compelling inspiration for experimentalists in their pursuit of designing highly efficient and cost-effective HER catalysts.

Computer aided design and evaluation of benzothiadiazole based non-fullerene acceptors for organic solar cells applications

Herein, we report the end-capped modification of the recently reported acceptor CH1007. Considering the importance of non-fullerene acceptors, we theoretically designed a series of benzo-thiadiazole core-based acceptors (MS1-MS8) to enhance the photophysical, and photovoltaic properties of the acceptors. In this study, properties like frontier molecular orbitals, maximum absorption, transition density matrix, open-circuit voltage, binding and excitation energies, dipole moment, and partial density of states were estimated by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) using B3LYP functional with bases set 6-31G(d,p). When studied computationally, all engineered compounds exhibited red-shift in the absorption spectrum and λmax lie in the range of 734–900 nm, compared to the reference compound (λmax = 735 nm). The designed acceptors exhibited low reorganizational energies (better charge transfer property), low binding and excitation energies besides narrow HOMO-LUMO bandgap. Moreover, the donor–acceptor complexes of the designed acceptors MS1 and MS4 have been studied with well-known standard donors PTB7-Th & PM6. The distribution of electron density in the resultant donor–acceptor complexes showed successful shift of electron density from donor moiety to acceptor moiety. The results revealed that such type of end-capped modifications in acceptors can lead to better photophysical and optoelectronic properties. So, designed compounds have potential to enhance the capacity of acceptor molecules and are therefore, suggested for the development of more efficient organic solar cells (OSCs).

Unveiling the gemcitabine drug complexation with cucurbit[n]urils (n = 6–8): a computational analysis

In this work, we have investigated the complex formation capability of gemcitabine drug with host cucurbit[n]urils, Q[n] (n = 6, 7, and 8) using density functional theory (DFT). The DFT studies demonstrate that the most stable configuration is a fully encapsulated complex. In the encapsulated gemcitabine@Q[6] and gemcitabine@Q[7] complexes, the gemcitabine amino -NH2 and the alcoholic groups bond with the carbonyl units of Q[n]. The addition of sodium ions leads to the partial exclusion of the gemcitabine molecule and the sodium atoms lie close to the carbonyl portal of Q[7]. Thermodynamic parameters computed for the complexation process exhibit high negative Gibbs free energy change, implying that the encapsulation process is spontaneous and is an enthalpy-driven process. Frontier molecular orbitals are located mainly on the gemcitabine uracil ring, before and after encapsulation, indicating that the encapsulation occurs by pure physical adsorption. Quantitative molecular electrostatic potentials demonstrate a shift in electron density during the complex formation and are more pronounced in gemcitabine@Q[7]. Atoms-in-molecule (AIM) topological analysis illustrate that these complexes are stabilized by various non-covalent interactions including hydrogen bonding (HBs) and C···F interactions. The reduced density gradient (RDG) graph exhibits the presence of strong HBs and weak van der Waals interactions and the presence of steric repulsion. The isosurface non-covalent interactions (NCI) diagram shows predominant steric interaction in the gemcitabine@Q[6] complex. The NCI isosurface for gemcitabine encapsulated complexes with Q[7] and Q[8] host displays that the green patches are uniformly distributed in all directions. Finally, EDA results demonstrate Pauling’s repulsive energy is predominant in gemcitabine@Q[6] complex, while the orbital and dispersion energies stabilize the gemcitabine@Q[7] complex.

First principle study of hybrid materials based on conjugated polymers and zirconium oxide as a proficient sensor for H2S gas

A density functional-based study of polymer/zirconium oxide composites has been carried out to explore their optical and electronic properties for developing an efficient sensor for the HS analyte. Composites of Zirconium oxide (ZrO) with three different conjugated polymers; polythiophene (PTh), polypyrrole (PPy), and polyaniline (PAni) have been designed. Narrowing of the band gap, favorable interaction, and shift of charge density from the polymer unit to the metal oxide evidenced the stability and suitability of designed composites for sensing applications. The natural bond orbital (NBO) analysis, frontier orbital pictures, and configuration establish that electron density shifts from the polymer unit to the ZrO in optimised composites. Perturbation in electronic and optical properties after binding of HS on composite surfaces supports the sensing ability of composites toward H. The high magnitude of binding energy and significant blue shifts in absorption spectra confirm the sensing of the H analyte by the designed composites.

Investigation of the Geometric and Spectroscopic Properties of Four Twisted Triphenylpyridinium Donor-Acceptor Dyes.

The geometric and spectroscopic properties of four cationic N-aryl-2,4,6-triphenylpyridinium-based donor-acceptor dyes─1-[4-(9H-carbazol-9-yl)phenyl]-2,4,6-triphenylpyridinium, 1-[4-(N,N-diphenylamino)phenyl]-2,4,6-triphenylpyridinium, 1-(9-phenyl-9H-carbazol-3-yl)-2,4,6-triphenylpyridinium, and 1-(9-ethyl-9H-carbazol-3-yl)-2,4,6-triphenylpyridinium─are reported. The four dyes exhibited a twisted, quasi-perpendicular geometry about the central donor-acceptor bond, shown by X-ray crystallography and supported by Raman spectroscopy and DFT calculations. The electronic absorption spectra show weak charge transfer (CT) transitions at about 400 nm (ε ∼ 3000 L mol-1 cm-1). Time dependent (TD) DFT supported the nature of the CT transition, displaying an 89-97% shift in electron density from the donor to the acceptor upon electronic excitation. Excited state geometry calculations revealed significant geometry changes upon electronic excitation. Enhancement of vibrational modes attributable to this transition was also recognized in the resonance Raman spectra. Emission spectroscopies showed two distinct emission bands. The lower energy band, resulting from radiative decay of the CT excited state, exhibited large anomalous Stokes shifts of ∼9000 cm-1. Much of the Stokes shift was a consequence of geometry changes between the ground and excited states. This was confirmed by variable temperature emission studies, with Stokes shifts reducing by up to 3000 cm-1 upon cooling from 293 to 80 K. Additionally, a high energy aggregation induced emission band was present for two of the dyes, resulting from the inhibition of excited state geometry reorganization and supported by solid-state emission spectra. These phenomena exemplify the importance of geometry in short range donor-acceptor dyes such as these.

Anion complexes of diborane derivatives inserted to benzene

AbstractThe complexes formed between three molecules where the diboryl units (HBH2BH) replace the C2H2 moiety in benzene (B6H12, C2B4H10, and C4B2H8) and 10 anions (H−, F−, Cl−, Br−, OH−, CCH−, CH3−, CN−, N3−, and CNO−) have been studied using MP2 computational methods with the complete basis set (CBS) extrapolation scheme. The stability of the complexes for a given anion increases with the number of diborane units in the molecules, and these energy values are correlated with the presence of different anions and number of diborane units. The electron density of the complexes has been characterized and analyzed using the quantum theory of atoms in molecules (QTAIM) and electron density shift (EDS) models.

Intermolecular interactions between cyclo[18]carbon and XCN (X = H, F, Cl, Br, I): a theoretical study.

In this article, the intermolecular interactions of cyclo[18]carbon with XCN (X = H, F, Cl, Br, I) were investigated in detail by quantum chemistry calculations and wavefunction analyses. The electrostatic potential and van der Waals potential of cyclo[18]carbon were examined, then the structures of the complexes, the interaction energies of the intermolecular interactions were studied. Quantum theory of atoms in molecules analysis was performed to help understand the specific interactions. The XCN molecules can insert into the cyclo[18]carbon ring, and ClCN, BrCN, and ICN could also bind with cyclo[18]carbon from outside. Charge transfer in the inner complex is more prominent than that of the outer complex. Plots of electron density difference revealed that electron density shift was significantly different when the X atom changed. The main driving force for molecular binding is dispersion attraction, which is disclosed by interaction region indicator analysis and energy decomposition calculations.

On predicting bonding patterns of small clusters of alkaline-earth (Be, Mg) and triel (B, Al) fluorides: a balance between atomic size and electron-deficient character

The structures, bonding and stability of (MF2)m:(M´F3)n (M = Be, Mg; M´ = B, Al; m = 0,1,2; n = 0,1,2) clusters were obtained at the B3LYP/aug-cc-pVTZ level of theory. To understand trends across this set of closely related atoms, an analysis of the results obtained using atoms in molecules (AIM), electron localisation function (ELF) and electron density shift (EDS) approaches, permits to identify subtle dissimilarities when the first-row elements, Be and B, are replaced by the second-row counterparts, Mg and Al. For dimers this replacement involves an increase in the bonding enthalpies as a direct consequence of a much larger ionic character of the derivatives including second-row elements. For trimers and tetramers, rather stable structures involving penta-coordinated aluminium atoms are formed, which are not found for the B-containing analogues. In all clusters investigated the electronic environment around each monomer does not change significantly neither with nature of the monomers interacting with it or with the size of the cluster, though some small cooperative effects are observed when analyzing the binding enthalpies. The important consequence is that the stability of larger clusters can be easily predicted through a statistical treatment of the values obtained for the smaller ones.

Insight into Spodium-π Bonding Characteristics of the MX2⋯π (M = Zn, Cd and Hg; X = Cl, Br and I) Complexes-A Theoretical Study.

The spodium–π bonding between MX2 (M = Zn, Cd, and Hg; X = Cl, Br, and I) acting as a Lewis acid, and C2H2/C2H4 acting as a Lewis base was studied by ab initio calculations. Two types of structures of cross (T) and parallel (P) forms are obtained. For the T form, the X–M–X axis adopts a cross configuration with the molecular axis of C≡C or C=C, but both of them are parallel in the P form. NCI, AIM, and electron density shifts analyses further, indicating that the spodium–π bonding exists in the binary complexes. Spodium–π bonding exhibits a partially covalent nature characterized with a negative energy density and large interaction energy. With the increase of electronegativity of the substituents on the Lewis acid or its decrease in the Lewis base, the interaction energies increase and vice versa. The spodium–π interaction is dominated by electrostatic interaction in most complexes, whereas dispersion and electrostatic energies are responsible for the stability of the MX2⋯C2F2 complexes. The spodium–π bonding further complements the concept of the spodium bond and provides a wider range of research on the adjustment of the strength of spodium bond.

Raman Spectroscopy and Chemical Bonding of BaFCl, BaFBr, and BaFl

We investigated in detail the Raman scattering of barium fluorohalides BaFX (X = Cl, Br, I) in an effort to characterize changes in structure and chemical bonding. The overall picture that emerges from the BaFX Raman data is that with the compositional change from X = Cl → Br → I, electron density shifts from the axial Ba-X bond to the equatorial Ba-X bonds with compositional change to the heavier halide, and that the charge distribution becomes more delocalized in the halide layers. This change in electron density indicates an increase in covalency of the Ba-X bonds from Cl to I.

Structural changes of 1-(phenylethynyl)naphthalene upon electronic excitation from Franck–Condon fits of several fluorescence emission spectra

The structural changes of 1-(Phenylethynyl)naphthalene (1-PEN) upon excitation from the ground state to the lowest excited singlet state have been assessed from a combined Franck–Condon-Fit of fluorescence emission spectra after excitation of several vibronic bands of 1-PEN and ab initio calculations. An analysis of the infrared spectrum, the laser induced fluorescence (LIF) spectrum and the fluorescence emission spectra is given on the basis of the approximate coupled cluster singles and doubles model (CC2) within the resolution-of-identity approximation and taking spin-component scaling into account. The excited state structure of 1-PEN is found to be planar, with the major geometry changes upon excitation localized in the naphthalene moiety. Electron density shifts from the naphthyl ring to the phenyl ring upon electronic excitation, leading to an increase of the permanent dipole moment of 1-PEN. The lowest electronically excited state of 1-PEN can be labeled as 1Lb-state, with the 1La-state energetically quasi-degenerate. The geometry changes, determined from the Franck–Condon analysis are in agreement with this assignment.

Superacid ZrO2–SiO2–SnO2 Mixed Oxide: Synthesis and Study

Superacid ternary ZrO2 SiO2 SnO2 oxide has been synthesized by the sol-gel method with a different atomic ratio Zr:Si:Sn. The highest strength of acid sites has been observed in the ranges of 20 ≤ Zr4+ ≤ 29, 60 ≤ Si4+ ≤ 67, 11 ≤ Sn4+ ≤ 20 at.%. According to the XPS spectra and 119Sn, 29Si MAS NMR spectra of ZrO2 SiO2 SnO2 a partial shift of electron density from zirconium to silicon ions was observed resulting in the formation of superacid Lewis sites. It was shown that superacid Zr29Si60Sn11 mixed oxide efficiently catalyzes acylation of toluene with acetic anhydride at 423 K in a flow reactor with 45% conversion of anhydride at 100% selectivity towards p-methylacetophenone.

Evaluation of Electron Density Shifts in Noncovalent Interactions.

In the present paper, we report the quantitative evaluation of the electron density shift (EDS) maps within different complexes. Values associated with the total EDS maps exhibited good correlation with different quantities such as interaction energies, Eint, intermolecular distances, bond critical points, and LMOEDA energy decomposition terms. Besides, EDS maps at different cutoffs were also evaluated and related with the interaction energies values. Finally, EDS maps and their corresponding values are found to correlate with Eint within systems with cooperative effects. To our knowledge, this is the first time that the EDS has been quanitatively evaluated.

Element-specific investigations of ultrafast dynamics in photoexcited Cu2ZnSnS4 nanoparticles in solution

Ultrafast, light-induced dynamics in copper–zinc–tin–sulfide (CZTS) photovoltaic nanoparticles are investigated through a combination of optical and x-ray transient absorption spectroscopy. Laser-pump, x-ray-probe spectroscopy on a colloidal CZTS nanoparticle ink yields element-specificity, which reveals a rapid photo-induced shift of electron density away from Cu-sites, affecting the molecular orbital occupation and structure of CZTS. We observe the formation of a stable charge-separated and thermally excited structure, which persists for nanoseconds and involves an increased charge density at the Zn sites. Combined with density functional theory calculations, the results provide new insight into the structural and electronic dynamics of CZTS absorbers for solar cells.

Tailoring Electronegativity of Bimetallic Ni/Fe Metal–Organic Framework Nanosheets for Electrocatalytic Water Oxidation

The performance-limiting half reaction of electrochemical water splitting is the anodic oxygen evolution reaction (OER). The increased adsorption, especially chemical adsorption capacity, of the OER intermediate *O on anode materials is one of the key factors to improve the performance of the anodic electrocatalysts. In this research, we tuned the electronegativity of anode materials to tailor their chemical adsorption capacity in OER by modulating the metal ion composition in the secondary building unit in metal–organic frameworks (MOFs). Nanosheet Fe(III)-MIL-88A has been prepared as a parent catalyst in this research due to its high charger transfer capability and stability. Ni2+ ions with lower electronegativity have been introduced to exchange Fe3+ sites in Fe(III)-MIL-88A, which would lead to decrease of the overall electronegativity of the MOF anode, accompanied by the electron density shift from Ni2+ to Fe3+ via bridge oxygen. Porous MOFs with lower overall electronegativity significantly improved their adsorption capacity for *O intermediate, thereby accelerating the OER performance during operation. Our research hints at the potential that the electronegativity of porous anodes could be fine-tuned to optimize their adsorption capability for the high-efficient hydrogen production during electrocatalytic water splitting.

3d‐metal (Cr to Zn) Nitrilotris(Methylenephosphonate)s with different coordination symmetries: Electronic Structure and Chemical Bond

AbstractIn this study, we present a comparative study of two parallel isostructural series of the 3d‐metal coordination complexes with nitrilotris(methylenephosphonic acid) H6{N(CH2PO3)3} (NTP, H6L) as a ligand. The series were analyzed by comparing their complexes in the spatial distribution of electron density and electron‐energy spectrum extracted from the XRD and XPS data, respectively. The first isostructural series (M=CrII, MnII, FeII, CoII, NiII, CuII, ZnII) contains a fourfold (four‐times) protonated ligand (H4L2−) and has a slightly distorted octahedral coordination of 3d‐metal atom by three O atoms of PO3 groups and three water molecules. The second isostructural series (M=MnII, CoII, CuII, ZnII) with the fully deprotonated ligand (L6−) has a distorted trigonal‐bipyramidal coordination of 3d‐metal atom with four O atoms of PO3 groups and N atom in the vertex. The complex of L6− with NiII, which is structurally close to the second series complexes, has a slightly distorted octahedral coordination of Ni atom with four O atoms of PO3 groups, N atom and an additional water molecule. For fully deprotonated PO3 groups, considerable shift of electron density is observed away from the center of the phosphorus atom to all the three P−O bonds. The protonation of only one of the oxygen atoms causes the shift of electron density from all the three P−O bonds to the center of the phosphorus atom and localization of P3s electron pair.

Probing Bias-Induced Electron Density Shifts in Metal-Molecule Interfaces via Tip-Enhanced Raman Scattering.

Surface charging effects at metal-molecule interfaces, for example, charge transfer, charge transport, charge injection, and so on, have a strong impact on the performance of organic electronics. Only having molecules bound or adsorbed on different metals results in a doping-like behavior at the interface by the different work functions of the metals and creates hybrid surface states, which strongly affect the efficiencies. With the ongoing downsizing and thinning of the organic components, the impact of the interface will even further increase. However, most of the investigations only monitor the interface without the additional charging effects from applying a voltage to the interface. In this work we present a spectroscopic approach based on tip-enhanced Raman spectroscopy (TERS) to study metal-molecule interfaces with an applied voltage simulating the electric field strength in real devices. We monitor how an intrinsic inductive effect of partial functional groups in molecules can shift the molecular electron density (ED) distribution when a bias voltage is applied. Therefore, we choose two molecules as model systems, which are similar in size and binding condition to a smooth gold surface, but with different electronic structure. By placing the tip 1 nm over the molecular surface at a fixed position and changing the applied bias voltage, we record electric-field-dependent tip-enhanced Raman spectra. Specific vibrational bands exhibit voltage-dependent intensity changes related to the shift of the local ED inside the molecules. We believe this experiment is valuable to gain deeper insights into charged metal-molecule interfaces.