Insight into the crystal facet-dependent Cr(VI) reduction: A comparative study of pyrite {100} and {111} facets.

The migration and transformation of hexavalent chromium (Cr(VI)) in the environment are regulated by pyrite (FeS2). However, variations in pyrite crystal facets influence the adsorption behavior and electron transfer between pyrite and Cr(VI), thereby impacting the Cr(VI) reduction performance. Herein, two naturally common facets of pyrite were synthesized hydrothermally to investigate the facet-dependent mechanisms of Cr(VI) reduction. The experimental results revealed that the {111} facet exhibited approximately 1.30-1.50 times higher efficiency in Cr(VI) reduction compared to the {100} facet. Surface analyses and electrochemical results indicated that {111} facet displayed a higher iron-sulfur oxidation level, which was affected by its superior electrochemical properties during the reaction with Cr(VI). Density functional theory (DFT) calculations demonstrated that the narrower band gap and lower work function on {111} facet were more favorable for the electron transfer between Fe(II) and Cr(VI). Furthermore, different adsorption configurations were observed on {100} and {111} surfaces due to the unique arrangements of Fe and S atoms. Specifically, O atoms in Cr2O72- directly bound with the S sites on {100} but the Fe sites on {111}. According to the density of states (DOS), the Fe site had better reactivity than the S site in the reaction, which appeared to be related to the fracture of S-S bonds. Additionally, the adsorption configuration of Cr2O72- on {111} surface showed a stronger adsorption energy and a more stable coordination mode, favoring subsequent Cr(VI) reduction process. These findings provide an in-depth analysis of facet-dependent mechanisms underlying Cr(VI) reduction behavior, offering new insights into studying environmental interactions between heavy metals and natural minerals.

Revisited UV- spectra of chlorohydroxoaurate anions.

The most important ionic precursor of gold, [AuCl4]-, is used in aqueous solution leading to chlorohydroxoaurates species, [AuCl4-x(OH)x]- (x = 1-4) due to partial hydrolysis. Their UV spectral signatures are still relatively unknown though very useful in many domains of application. Individual spectra of each of them are determined for the first time thanks to a thorough experimental investigation comprising the range 200-250 nm, surpringly ignored up to now. New isosbestic points useful for species partition analysis are evidenced. Electronic transition attribution is obtained from quantum chemical calculations based on TD-DFT. The prediction of the experimental blueshifted bands of the [AuCl4-x(OH)x]-1 anions was possible only after applying energy corrections calibrated on the full UV range two-band spectrum of the [AuCl4]- complex.

Toward understanding ammonia capture in two amino-functionalized metal-organic frameworks using in-situ infrared spectroscopy and DFT calculation.

Two isostructural, three-dimensional, interpenetrated amino-functionalized Metal-Organic Frameworks (Co-2AIN-MOF and Cd-2AIN-MOF) based on 2-aminoisonicotinic acid (2AIN) were synthesized, structurally characterized and determined. Based on the PXRD analysis, the solvent exchange hardly changed their framework structure, and the samples fully activated by methanol can be achieved and examined by infrared spectroscopy. Due to the presence of the carbonyl group and free amino groups in the pore of the framework, the NH3 uptakes of Co-2AIN-MOF and Cd-2AIN-MOF are 11.70 and 13.81 mmol/g and at 1 bar, respectively. In-situ Infrared spectroscopy and DFT calculations revealed the different adsorption sites and processes between Co-2AIN-MOF and Cd-2AIN-MOF.

A novel chemical probe based on the salamo-Co(II) complex for the highly selective fluorescence detection of tyrosine.

A new and rare Salamo-Co(II) complex probe L-Co2+ was designed and synthesised. The structure of the [Co3(L)2(µ-OAc)2(MeOH)2]⋅2H2O complex was obtained by X-ray diffraction experiments. Three Co(II) atoms are in a line in the complex, and all Co(II) atoms form a 6-coordinated octahedral configuration. The probe L-Co2+ selectively recognises tyrosine in DMF/H2O (8:2, v/v). Upon addition of tyrosine, the fluorescence intensity of L-Co2+ was enhanced in a short time. The probe showed high selectivity and sensitivity for tyrosine, detection limit is 4.27 × 10-8 M. The recognition mechanism of probe L-Co2+ for Tyr was inferred by FT-IR spectra, UV spectroscopy, ESI mass spectra and DFT calculations. Finally, due to the simplicity and specificity of the identification process, the probe was also subjected to a test paper experiment and a milk assay.

Metal Complexation for the Rational Design of Gemcitabine Formulations in Cancer Therapy.

Nanoformulation of chemotherapies represents a promising strategy to enhance outcomes in cancer therapy. Gemcitabine is a chemotherapeutic agent approved by the Food and Drug Administration for the treatment of various solid tumors. Nevertheless, its therapeutic effectiveness is constrained by its poor metabolic stability and pharmacokinetic profile. Nanoformulations of gemcitabine in lipid and polymer nanocarriers usually lead to poor loading capability and an inability to effectively control its release profile due to the physicochemical characteristics of the drug and matrices. Here, we propose metal-gemcitabine complexation with biorelevant metal cations as a strategy to alter the properties of gemcitabine in a noncovalent manner, paving the way for the development of novel nanoformulations. A speciation study on gemcitabine and Mn2+, Zn2+, and Ca2+ was performed with the aim of investigating the extent of the interaction between the drug and the proposed metal cations, and selecting the best conditions of temperature, pH, and drug-to-metal molar ratio that optimize such interactions. Also, a series of density functional theory calculations and spin-polarized ab initio molecular dynamics simulations were carried out to achieve insights on the atomistic modalities of these interactions. Mn2+-gemcitabine species demonstrated the ability to maintain gemcitabine's biological activity in vitro. The scientific relevance of this study lies in its potential to propose metal-gemcitabine as a valuable strategy for developing nanoformulations with optimized quality target product profiles. The work is also clinically relevant because it will lead to improved treatment outcomes, including enhanced efficacy and pharmacokinetics, decreased toxicity, and new clinical possibilities for this potent therapeutic molecule.

Shannon entropy variation as a global indicator of electron density contraction at interatomic regions in chemical reactions.

CONTEXT: The negative of the Shannon entropy derivative is proposed to account for electron density contraction as the chemical bonds are breaking and forming during a chemical reaction. We called this property the electron density contraction index, EDC, which allows identifying stages in a reaction that are dominated by electron contraction or expansion. Four different reactions were analyzed to show how the EDC index changes along the reaction coordinate. The results indicate that the rate of change of Shannon entropy is directly related to the rate of change of the electron density at the bond critical points between all the atomic pairs in the molecular systems. It is expected that EDC will complement the detailed analysis of reaction mechanisms that can be performed with the theoretical tools available to date. METHODS: Density functional theory calculations at the B3LYP/6-31G(d,p) level of theory were carried out using Gaussian 16 to analyze the reaction mechanisms of the four reactions studied. The reaction paths were obtained via the intrinsic reaction coordinate method, which served as the reaction coordinate to obtain the reaction force and the EDC profiles in each case. Shannon entropy and electron density at the bond critical points were calculated using the Multiwfn 3.7 package.

Observation on Switching Properties of WO3-Based H2 Sensor Regulated by Temperature and Gas Concentration.

Transition metal oxide semiconductors have great potential for use in H2 sensors, but in recent years, the strange phenomena about gas-sensitive performance associated with their special properties have been more widely discussed in research. In some cases, the resistance of transition metal oxide gas sensors will emerge with some changes contrary to their intrinsic semiconductor characteristics, especially in gas sensor research of WO3. Based on the hydrothermal synthesis of WO3, our work focuses on the abnormal change of tungsten oxide resistance to different gases at low temperature (80-200 °C) and high temperature (above 200 °C). Through in situ FT-IR and in situ XPS, combined with density functional theory calculations, a new reasonable explanation of WO3 is proposed for the abnormal resistance change caused by temperature and the strange response due to gas concentration. The occurrence of these findings can be attributed to the synergistic effect resulting from the presence of two contributing factors. One of them is attributed to the alteration in the surface valence state of WO3 induced by gas, resulting in the reduction of W6+. The other one is due to the reaction between gas and adsorbed oxygen on the surface of WO3. This work presents a novel and rational concept for addressing the reaction mechanism between gas and transition metal oxide semiconductors, thereby paving the way for the development of highly efficient gas sensors based on transition metal oxide semiconductors.

Designing a Novel C3-Fe-N Interface Local Coordination Microenvironment for Efficient Electrocatalytic Water Splitting.

Developing single-atomic electrocatalysts (SACs) with high activity and stability for electrocatalytic water-splitting has been challenging. Moreover, the practical utilization of SACs is still far from meeting the the theoretical prediction. Herein a facile and easy scale-up fabrication method is proposed for designing a novel carbon-iron-nitrogen (C-Fe-N) electrocatalyst with a single atom electron bridge (C-Fe-N SAEBs), which exhibits lower overpotential and impedance than previously reported electrocatalysts. 0.8-C-Fe-N SAEBs exhibits significant activity and excellent stability in the bi-functional decomposition of water. The excellent performance of the C-Fe-N SAEBs electrocatalyst can be attributed to the strong coupling effect at the interface owing to the formation of a single atom C3-Fe-N local coordination microenvironment at the interface, which enhance the exposure of active sites and charge transfer, and reduced the adsorption energy barrier of intermediates. Theoretical calculation and synchrotron radiation analysis are performed to understand the mechanistic insights behind the experimental results. The results reveal that the active C3-Fe-N local coordination microenvironment at the interface not only improves water-splitting behavior but also provides a deeper understanding of local-interface geometry/electronic structure for improving the electrocatalytic activity. Thus, the proposed electrocatalyst, as well as the mechanistic insights into its properties, presents a significant stride toward practical application.

A Stereoselective Synthesis of a Novel α,ß-Unsaturated Imine-Benzodiazepine through Condensation Reaction, Crystal Structure, and DFT Calculations.

The stereoisomers (E)-2,2-dimethyl-4-(4-subsitutedstyryl)-2,3-dihydro-1H-[1,5]-benzodiazepine 3(a-d) were synthesized via the condensation reaction of 2,2,4-trimethyl-2,3-dihydro-1H-1,5-benzodiazepine (BZD) 1 with the benzaldehyde derivatives 2(a-d) in ethanol. The chemical structure of the prepared products was confirmed by NMR (1H and 13C), HRMS, and X-ray analysis of the crystal structure 3d. The condensation reaction was examined using DFT calculations at the theoretical level of B3LYP/6-31G(d) to elucidate the chemo-, regio-, and stereoselectivity and the reaction mechanism of the produced isomer. Furthermore, we identified each reagent's reactive sites by the measurement of the reactivity indices. We also looked at how the electron-withdrawing groups (EWGs) of various aldehydes affected the reaction's mechanism and the stability of products 3(a-d).

Unveiling the Influence of Water Molecules for NF3 Removal by the Reaction of NF3 with OH: A DFT Study.

The removal of nitrogen trifluoride (NF3) is of significant importance in atmospheric chemistry, as NF3 is an important anthropogenic greenhouse gas. However, the radical species OH and O(1D) in atmospheric conditions are nonreactive towards NF3. It is necessary to explore possible ways to remove NF3 in atmosphere. Therefore, the participation of water molecules in the reaction of NF3 with OH was discussed, as water is abundant in the atmosphere and can form very stable complexes due to its ability to act as both a hydrogen bond donor and acceptor. Systemic DFT calculations carried out at the CBS-QB3 and ωB97XD/aug-cc-pVTZ level of theory suggest that water molecules could affect the NF3 + OH reaction as well. The energy barrier of the SN2 mechanism was decreased by 8.52 kcal/mol and 10.58 kcal/mol with the assistance of H2O and (H2O)2, respectively. Moreover, the presence of (H2O)2 not only reduced the energy barrier of the reaction, but also changed the product channels, i.e., formation of NF2O + (H2O)2-HF instead of NF2OH + (H2O)2-F. Therefore, the removal of NF3 by reaction with OH is possible in the presence of water molecules. The results presented in this study should provide useful information on the atmospheric chemistry of NF3.

Large Number of Direct or Pseudo-Direct Band Gap Semiconductors among A3TrPn2 Compounds with A = Li, Na, K, Rb, Cs; Tr = Al, Ga, In; Pn = P, As.

Due to the high impact of semiconductors with respect to many applications for electronics and energy transformation, the search for new compounds and a deep understanding of the structure-property relationship in such materials has a high priority. Electron-precise Zintl compounds of the composition A3TrPn2 (A = Li - Cs, Tr = Al - In, Pn = P, As) have been reported for 22 possible element combinations and show a large variety of different crystal structures comprising zero-, one-, two- and three-dimensional polyanionic substructures. From Li to Cs, the compounds systematically lower the complexity of the anionic structure. For an insight into possible crystal-structure band-structure relations for all compounds (experimentally known or predicted), their band structures, density of states and crystal orbital Hamilton populations were calculated on a basis of DFT/PBE0 and SVP/TZVP basis sets. All but three (Na3AlP2, Na3GaP2 and Na3AlAs2) compounds show direct or pseudo-direct band gaps. Indirect band gaps seem to be linked to one specific structure type, but only for Al and Ga compounds. Arsenides show smaller band gaps than phosphides due to weaker Tr-As bonds. The bonding situation was confirmed by a Mullikan analysis, and most states close to the Fermi level were assigned to non-bonding orbitals.

Quantum Chemical Stability Analysis of Phthalocyanine Metal One-Dimensional Polymers with Bidentate Ligands.

The combination of metal-phthalocyanine complexes and axially coordinated organic molecules into polymer chains presents a significant challenge in the synthesis of hybrid materials. A calculated structure for one-dimensional coordinate polymers with N-donor ligands using ab initio (PM6) and DFT (LanL2Dz) methods is presented. DFT methods have shown that there is a linear, one-dimensional structure without distorted geometry for the two bipyridine ligands. The components of the proposed polymers consist of square-planar Zn complexes of phthalocyanine (PcZn) connected via bridging ligands (L). Electronic properties of the monomer PcZnL of zinc phthalocyanine with bidentate ligands have been analyzed using calculations based on density functional theory (B3LYP6-31G(d,p)). Molecular orbital calculations show that this connection between the metallomacrocycle and the conjugated ligand results in a small energy gap, promising molecularly active materials as conductors. The crystallographic reports indicate that obtaining this kind of polymer with the participation of Pc Zn and bidentate ligands is possible.

Liquid phase transformation mechanism of ß-caryophyllonic acid initiated by hydroxyl radicals and ozone in atmosphere.

ß-caryophyllonic acid (BCA), as an important precursor of aqueous secondary organic aerosols (aqSOA), has adverse effects on the atmospheric environment and human health. However, the key atmospheric chemical reaction process in which BCA participates in the formation of aqueous secondary organic aerosols is still unclear. In this study, the reaction mechanism and kinetics of BCA with ·OH and O3 were investigated by quantum chemical calculations. The initiation reactions between BCA and ·OH include addition and H-abstraction reaction pathways, subsequent intermediates will also react with O2, ultimately undergo a cracking reaction to generate small molecular substances. The reaction of BCA with O3 can generate primary ozone oxides and the Criegee Intermediates oIM3, subsequent main reaction products include keto-BCA, as well as other small molecule aqSOA precursors. The entire reaction process increases the O/C ratio of aqSOA in the aqueous phase and generates products of small molecules such as 4-formylpropionic acid, which plays an important role in the formation of aqSOA. At 298K, the transformation rate constants of BCA initiated by ·OH and O3 are 1.47 × 1010 M-1 s-1 and 3.16 × 105 M-1 s-1, respectively, the atmospheric lifetimes of BCA reacting with ·OH range from 0.86 h-5.40 h, while the lifetimes of BCA reacting with O3 range from 0.44 h-10.04 years. This suggests that BCA primarily reacts with ·OH. However, under higher O3 concentrations, its ozonolysis becomes significant, promoting the formation of aqSOA. According to the risk assessment, the toxicity of most transformation products (TPs) gradually decreased, but the residual developmental toxicity could not be ignored. In this paper, the atmospheric liquid phase oxidation mechanisms of sesquiterpene unsaturated derived acid were studied from the microscopic level, which has guiding significance for the formation and transformation of aqSOA in atmosphere.

Enhancing the Sodium Storage Performance of Na4MnCr(PO4)3 through the Manipulation of Intrinsic Site Occupation Defects.

Manganese-based NASICON-type compounds are promising as high-energy-density cathodes for sodium-ion batteries. However, the structural defects of Mn ions inside the crystal framework reduce the sodium storage capacity, voltage plateau, and cyclic stability of the cathodes. Here, a strategy to inhibit the Mn ion defects of Na4MnCr(PO4)3 has been proposed by using different phosphate sources. It is found that Na4MnCr(PO4)3 prepared with NH4H2PO4 (NMCP-N) exhibits less noticeable voltage hysteresis than that of Na4MnCr(PO4)3 prepared with H3PO4 (NMCP-H), indicating that the site occupation defects of Mn ions in the Na4MnCr(PO4)3 crystal structure are successfully suppressed, as confirmed by theoretical calculations and structural refinements. In the case of NMCP-N, a capacity of 109.7 mAh g-1 is delivered at 0.01 A g-1, and 54.2% capacity retention can be kept after 500 cycles at 0.5 A g-1, which is much better than that of the counterpart of NMCP-H (a lower capacity of 96.1 mAh g-1 and poorer cyclability of only 22.8% capacity retention after 500 cycles), showing that the structure defects strongly affect the sodium storage properties of Na4MnCr(PO4)3 cathodes. This work provides an effective strategy to manipulate the structure defects of Mn-based NASICON-type cathode materials to enhance their electrochemistry.

Mechanism of adsorption and targeted degradation of antimicrobial micropollutant sulfamethoxazole in aquatic environments.

FHWSB as an integrated absorptive catalyst, based on Walnut shell biochar (WSB) via hydrochloric acid modification and ferrous chloride impregnation, was prepared, reacted with H2O2 to generate active free radicals •OH and •O2-, which oxidized and degraded about 80% of micro-pollutant sulfamethoxazole (SMX) from water, effectively resolving micro-pollutants' removal being inefficient because of high toxicity, persistence, and bioaccumulation in existed methods. It was clarified the specific degradation pathways and mechanisms of SMX by FHWSB synergistic H2O2 via characterization and analysis assisted DFT calculations. Furthermore, it was found that the toxicity of a series of intermediates produced by SMX degraded continued to decline, consistent with its direction of degradation via toxicological analysis. The work provides a simple and feasible strategy for the effective removal of antibiotic micro-pollutants in aquatic environments.

Electrospun Lithium Porous Nanosorbent Fibers for Enhanced Lithium Adsorption and Sustainable Applications.

Electrospun nanosorbent fibers specifically designed for efficient lithium extraction were developed, exhibiting superior physicochemical properties. These fibers were fabricated using a polyacrylonitrile/dimethylformamide matrix, with viscosity and dynamic mechanical analysis showing that optimal interactions were achieved at lower contents of layered double hydroxide. This meticulous adjustment in formulation led to the creation of lithium porous nanosorbent fibers (Li-PNFs-1). Li-PNFs-1 exhibited outstanding mechanical attributes, including a yield stress of 0.09 MPa, a tensile strength of 2.48 MPa, and an elongation at a break of 19.7%. Additionally, they demonstrated pronounced hydrophilicity and hierarchical porous architecture, which greatly favor rapid wetting kinetics and lithium adsorption. Morphologically, they exhibited uniform smoothness with a diameter averaging 546 nm, indicative of orderly crystalline growth and a dense molecular arrangement. X-ray photoelectron spectroscopy and density functional theory using Cambridge Serial Total Energy Package revealed modifications in the spatial and electronic configurations of polyacrylonitrile due to hydrogen bonding, facilitating lithium adsorption capacity up to 13.45 mg/g under optimal conditions. Besides, kinetics and isotherm showed rapid equilibrium within 60 min and confirmed the chemical and selective nature of Li+ uptake. These fibers demonstrated consistent adsorption performance across multiple cycles, highlighting their potential for sustainable use in industrial applications.

Highly Durable Chemoresistive Micropatterned PdAu Hydrogen Sensors: Performance and Mechanism.

Hydrogen (H2) is a promising alternative energy source for Net-zero, but the risk of explosion requires accurate and rapid detection systems. As the use of H2 energy expands, sensors require high performance in a variety of properties. Palladium (Pd) is an attractive material for H2 detection due to its high H2 affinity and catalytic properties. However, poor stability caused by volume changes and reliability due to environmental sensitivity remain obstacles. This study proposes a micropatterned thin film of PdAu with optimized composition (Pd0.62Au0.38) as a chemoresistive sensor to overcome these issues. At room temperature, the sensor has a wide detection range of 0.0002% to 5% and a fast response time of 9.5 s. Significantly, the sensor exhibits excellent durability for repeated operation (>35 h) in 5% H2 and resistance to humidity and carbon monoxide. We also report a negative resistivity change in PdAu, which is opposite to that of Pd. Density functional theory (DFT) calculations were performed to investigate the resistance change. DFT analysis revealed that H2 penetrates specific interstitial sites, causing partial lattice compression. The lattice compression causes a decrease in electrical resistance. This work is expected to contribute to the development of high-performance H2 sensors using Pd-based alloys.

Axial Coordination Engineering on Fe‒N‒C Materials for Oxygen Reduction: Insights from Theory.

Axial coordination engineering has emerged as an effective strategy to regulate the catalytic performance of metal‒N‒C materials for oxygen reduction reaction (ORR). However, the ORR mechanism and activity changes of their active centers modified by axial ligands are still unclear. Here, a comprehensive investigation of the ORR on a series of FeN4‒L moieties (L stands for an axial ligand) is performed using advanced density functional theory (DFT) calculations. The axial ligand has a substantial effect on the electronic structure and catalytic activity of the FeN4 center. Specially, FeN4‒C6H5 is screened as a promising active moiety with superior ORR activity, as further revealed by constant-potential calculations and kinetic analysis. The enhanced activity is attributed to the weakened *OH adsorption caused by the altered electronic structure. Moreover, microkinetic modeling shows that at pH = 1, FeN4‒C6H5 possesses an impressive theoretical half-wave potential of ~1.01 V, superior to the pristine Fe‒N‒C catalysts (~0.88 V) calculated at the same level. These findings advance the understanding of the ORR mechanism of FeN4‒L and provide guidance for optimizing the ORR performance of single-metal-atom catalysts.

Synthesis and Spectroscopic Properties of Diarylethene-Subporphyrinoid Hybrids.

Two novel diarylethene-fused subporphyrinoids were prepared and characterized. A mono diarylethene derivative was obtained via a statistical condensation reaction with 2 eq. of 1,2-dicyanobenzene and 1 eq. of thiophene-disubstituted butenedinitrile. The symmetric triply diarylethene-fused subporphyrazine was synthesized via a cyclotrimerization reaction of the thiophene-disubstituted butenedinitrile derivative. These compounds were characterized by NMR spectroscopy and high-resolution mass spectrometry. The spectroscopic properties have been measured in hexane and in chloroform. The mono diarylethene-fused-type compound showed photochromism at 580 nm and >700 nm wavelength, accompanied by degradation. According to DFT calculations, photoreactivity likely depends on the contribution of aromatic feature of pyrrole ring bonded to two thiophene rings.

Structural Insight on Interaction of NMDA receptor with fentanyl, ketamine and Isoflurane: A Computational Study to Unravel Mode of Binding.

NMDA receptors are considered targets for many anesthetics if they are modulated by the drugs at clinically relevant concentrations. Volatile anesthetics like isoflurane and ketamine interact with NMDA receptors, inhibiting channel activation and thus blocking NMDA neurotransmission at clinically relevant concentrations. The mode of binding of commonly used drugs like ketamine, isoflurane, and fentanyl is poorly understood. We used molecular docking, molecular dynamics simulations, and DFT calculation of these drugs against the NMDA receptor. Using well-defined computational methods, we identified that these drugs have high docking scores and significant interaction with receptors. These drugs bind to the substrate-binding pocket and form a remarkable number of interactions. We have found that these interactions are stable and have low HOMO-LUMO energy gaps. This study provides enough evidences of strong and stable interaction between drugs and NMDA receptor.