Sulfur Atoms Research Articles

Rapidly and simply detecting Cr (VI) in aqueous media via a diketopyrrolopyrrole-based chemosensor with both high selectivity and low LOD

BackgroundThe high toxicity of hexavalent chromium [Cr (VI)] could not only cause harmful effects on humans, including carcinogenicity, respiratory issues, genetic damage, and skin irritation, but also contaminate drinking water sources, aquatic ecosystems, and soil, impairing the reproductive capacity, growth, and survival of organisms. Due to these harmful effects, detecting toxic Cr (VI) is of great significance. However, the rapid, simple, and efficient detection at a low Cr (VI) concentration is extremely challenging, especially in an acidic condition (existing as HCrO4−) due to its low adsorption free energy. ResultsA diketopyrrolopyrrole-based small molecule (DPPT-PhSMe) is designed and characterized to act as a chemosensor, which allows a high selectivity to Cr (VI) at an acidic condition with a low limit of detection to 10−8 M that is two orders of magnitude lower than the cut of limit (1 μM) recommended by World Health Organization (WHO). Mechanism study indicates that the rich sulfur atoms enhance the affinity to HCrO4−. Combining with favorable features of diketopyrrolopyrrole, DPPT-PhSMe not only allows dual-mode detection (colorimetric and spectroscopic) to Cr (VI), but also enables disposable paper-based sensor for naked-eye detection to Cr (VI) from fully aqueous media. The investigation of DPPT-PhSMe chemosensor for the quantification of Cr (VI) in real life samples demonstrates a high reliability and accuracy with an average percentage recovery of 102.1 % ± 4 (n = 3). SignificanceDPPT-PhSMe represents the first diketopyrrolopyrrole-derived chemosensor for efficient detection to toxic Cr (VI), not only providing a targeted solution to the bottleneck of Cr (VI) detection in acidic conditions (existing as HCrO4−) caused by its low adsorption free energy, but also opening a new scenario for simple, selective, and efficient Cr (VI) detection with conjugated dye molecules.

Tetrathiafulvalene Carboxylate-Based Anode Material for High-Performance Sodium-Ion Batteries.

Organic electrode materials are promising to be applied in sodium ion batteries (SIBs) due to their low cost and easily modified molecular structures. Nevertheless, low conductivity and high solubility in electrolytes still limit the development of organic electrodes. In this work, a carboxylate small molecule (BDTTS) based on tetrathiafulvalene is developed as anode material for SIBs. BDTTS has a large rigid π-conjugated planar structure, which may reduce solubility in the electrolyte, meanwhile facilitating charge transporting. Experimental results and theoretical calculations both support that apart from the four carbonyl groups, the sulfur atoms on tetrathiafulvalene also provide additional active sites during the discharge/charge process. Therefore, the additional active sites can well compensate for the capacity loss caused by the large molecular weight. The as-synthesized BDTTS electrode renders an excellent capacity of 230 mAh g-1 at a current density of 50 mA g-1 and an excellent long-life performance of 128 mAh g-1 at 2 C after 500 cycles. This work enriches the study on organic electrodes for high-performance SIBs and paves the way for further development and utilization of organic electrodes.

Influence of electron irradiation on the band gap and microhardness of TlInS2, TlInSSe and TlIn0.99Cr0.01S2 single crystals

ABSTRACT This work investigated the effect of partial replacement of sulphur atoms with selenium atoms (TlInSSe) and indium atoms with chromium atoms (TlIn0.99Cr0.01S2) on the band gap and microhardness of TlInS2 single crystals irradiated with electrons with energy of 2 MeV and a fluence of up to 1.5 × 1017 el/cm2. The band gap from the measured absorption spectra was determined using the Tauc method. It has been established that this irradiation leads to a decrease in the band gap in TlInS2, TlInSSe and TlIn0.99Cr0.01S2 crystals. It has been shown that after electron irradiation the microhardness of these crystals increased due to an increase in the size of crystallites on their surface.

Effects of Curing Agents on the Adhesion of Epoxy Resin to Copper: A Density Functional Theory Study.

Epoxy resins are widely used adhesives in industrial fields. To use epoxy resin as an adhesive, it is necessary to mix the epoxy resin with a hardener. Hardeners have various functional groups and skeletons, and the properties of epoxy resins vary depending on the hardener. Although the adhesion of epoxy resins has been extensively studied using density functional theory (DFT) calculations, few studies have evaluated the effect of hardener molecules. Therefore, in this study, DFT calculations of adhesion energies and bonding structures on Cu (111) and Cu2O (111) surfaces are performed for model molecules of adducts of epoxy resin with hardeners having various functional groups and skeletons to evaluate the influence of the hardeners on the adhesion of epoxy resin to the metal surface. The adhesion energy to the Cu (111) surface is governed by the energy due to dispersion forces. Hardeners of the thiol type, which contain relatively heavy sulfur atoms, and hardeners with aromatic rings, displaying high planarity, enable the entire molecule to approach the metal surface, resulting in a relatively high adhesion strength. The calculations for the Cu2O (111) surface show the adhesion strength is more strongly influenced by interactions such as hydrogen bonds between the surface and adhesive molecules than by dispersion forces. Therefore, in adhesion to Cu2O (111), the benzylamine-epoxy adduct with hydrogen bonding and OH-π interactions with the surface, in addition to having a relatively flexible framework, shows a high adhesion strength.

Circularly Polarized Electroluminescence from Intrinsically Axial Chiral Materials Based on Bidibenzo[b,d]furan/bidibenzo[b,d]thiophene

AbstractHerein, by connecting chiral bidibenzo[b,d]furan/bidibenzo[b,d]thiophene and multi‐resonance thermally activated delayed fluorescence (MR‐TADF) units, two pairs of intrinsically axial chiral MR‐TADF materials (R/S‐BDBF‐BNO and R/S‐BDBT‐BNO) realize mirror‐symmetric circularly polarized luminescence (CPL) and narrowband emission. The chiral moieties effectively engage in frontier molecular orbital distributions through the establishment of covalent bonds with boron atoms. The proportions of (1,1′‐bidibenzo[b,d]furan)‐2,2′‐diol in the highest occupied and lowest unoccupied natural transition orbitals (HONTO/LUNTO) are 25.3% and 64.7%, respectively. In addition, BDBT‐BNO processes a dual‐channel transition mode, thus the (1,1′‐bidibenzo[b,d]thiophene)‐2,2′‐diol constitutes 22.8%, 24.3% and 54.0%, 46.9% of the distributions of HONTO, HONTO‐1 and LUNTO, LUNTO+1, respectively. The high proportions endow R/S‐BDBF‐BNO and R/S‐BDBT‐BNO with good CPL properties with dissymmetry factors (|gPL|) of 1.7/1.8 × 10−3. Correspondingly, the circularly polarized organic light‐emitting diodes based on the enantiomers exhibit mirror symmetrical circularly polarized electroluminescence with |gEL| factors of 1.5/1.6 × 10−3. Furthermore, the introduction of sulphur atoms enables BDBT‐BNO to have a high maximum external quantum efficiency of 35.7% in device.

Stereospecific Synthesis and Biological Evaluation of KRN7000 Analogues with Thio-modifications at the Acyl Moiety.

α-Galactosylceramide (KRN7000 or α-GalCer) analogues terminated with phenyl (Ph) groups at the acyl moiety possess more potency than KRN7000 to activate invariant natural killer T (iNKT) cells for inducing a T helper 1 (Th1)-biased immune response. However, biological activities of phenyl glycolipids with thio-modifications at the acyl moiety remain unknown, and facile approaches for highly stereoselective synthesis of KRN7000 and its analogues are rather scarce. Herein, we exploited 4,6-di-O-tert-butylsilylene (DTBS)-directed stereospecific galactosylation to efficiently synthesize various α-GalCer analogues bearing thioamide, terminal thiophenyl and dual modifications at the acyl moiety. Biological evaluations suggest that a new analogue S34 featuring a terminal Ph-S-Ph-F group exhibits a more superior Th1-biased immune response in mice. Molecular docking analysis revealed that the introduction of a sulfur atom influences vital hydrogen bonding interactions between glycolipids and the cluster of differentiation 1d (CDld), thus adjusting the stability of the glycolipid-CDld complex.

LATTICE DYNAMICAL STUDY OF THORIUM SULPHIDE

Thorium sulfide (ThS) is a chemical compound composed of thorium and sulfur atoms, with the chemical formula ThS. It belongs to the class of sulfides. To understand the dimensional stability and thermal behaviour of thorium sulphide (ThS), a lattice dynamical research issued to investigate its vibrational characteristics. We study the density of states (DOS) and phonon dispersion in the 50–60 GHz frequency region using computational techniques. Important information about the stability of the ThS crystal structure are given by the phonon dispersion curves, namely the presence of imaginary phonon frequencies that point to dynamical stability. We identify the major modes of vibration and their contributions to the thermodynamic properties of ThS through studying the phonon density of states.Van der Waals' three-body force shell model is used in this study to theoretically investigate the lattice dynamical behaviour of (ThS...). Elastic constants, pressure derivatives, dispersion relation curve, combined density of states, equation of state, and specific ultrasonic properties of the ThS are among the parameters for which calculated values are gave.The stability of the structure and vibrational properties of thorium sulphide are now better known by lattice dynamical study, which provides the way to its effective application in a range of technological uses, from nuclear reactors to the production of creative materials. Keywords: lattice, dynamics, thermal, vibrational

Stabilizing Layered BiOBr Photoelectrocatalyst by Van Der Waals Heterojunction Strategy

AbstractThe photoelectrocatalytic (PEC) hydrogen evolution reaction (HER) holds immense promise as a clean and sustainable method for hydrogen production. However, finding a suitable catalyst which is efficient, stable and scalable still remains an open challenge. BiOBr is a 2D layered material studied as photoelectrocatalyst because of its suitable band gap for light absorption and potential for up‐scalable production. However, its application in HER is not commonly reported, because of instability in a cathodic PEC environment, driven by a strong tendency to reduction to metallic bismuth. To solve this problem, 2D MoS2 is used to induce the formation of a van der Waals (vdW) layered heterojunction (HJ) to stabilize the lattice of BiOBr during HER. By performing PEC HER with the HJs containing different ratios of MoS2, it is found that the HJ with 1 % MoS2 can increase the stability of BiOBr, while the one with 50 % MoS2 can even accelerate the reduction of BiOBr to metallic bismuth. DFT calculations reveal that the interface between BiOBr and MoS2 in the HJ with 1 % MoS2 tends to push active electrons on the sulfur atoms, thus favoring HER. On the other hand, in the 50 % HJ, active electrons are prone to react with BiOBr to induce reduction. In situ wide‐angle X‐ray diffraction (WAXD) on the MoS2/BiOBr HJs with 1 % and 50 % of MoS2 allows to track the phase change and the phase transfer speed of BiOBr during PEC HER. Interestingly, when the HJ is illuminated with UV light, a lower amount of BiOBr is reduced to Bi under negative potential, due to the presence of photogenerated holes reacting with the extra electrons derived from the negative bias and preventing the BiOBr photon absorber to be further reduced.

High-Refractive-Index Cross-Linked Cyclic Olefin Polymers with Excellent Transparency via Thiol-Ene Click Reaction.

High-refractive-index polymers are important optical materials in optoelectronics. Conventional cyclic olefin polymers (COPs), possessing many excellent optical properties, are a class of highly promising optical materials; however, one of the greatest obstacles is their low refractive index of n = 1.52-1.54. Here, one efficient strategy of first incorporating high molar refraction groups, including carbazolyl and indolyl moieties, into unsaturated COPs via ring-opening metathesis polymerization (ROMP) and then introducing another high molar refraction sulfur atom by a subsequent thiol-ene click reaction is presented. The obtained cross-linked COPs bearing both an aromatic group and sulfur possess significantly higher refractive indices (n = 1.611-1.684 at 589 nm) and highly optical transparency (approximately 95%) in the range of vis-NIR. This provides a way toward potential applications of new-generation optical materials.

Effect of Metal Coordination Environment on the Stability of Zinc Complexes and Their Reactivity with NaSH

AbstractMetal complexes with multidentate ligands are frequently used as model compounds to shed light on the (bio)‐inorganic chemistry of H2S. Zinc complexes bearing salen‐type ONNO ligands with different bridging groups are particularly relevant in this respect. Here, we describe the use of zinc complexes with the sulfur‐analogues of the ONNO ligands with the S‐donors replacing either the neutral nitrogen donors or the anionic oxygen atoms of the classical salen ligands. In addition, we studied a hexadentate cyclic ligand, with four neutral sulfur atoms and two anionic oxygens. Having two coordinative pockets this ligand is able to form a bimetallic zinc complex. We report how the different coordinative environments of the explored ligands influence the stability of the zinc complexes and their abilities to form the related hydrosulfide species.

High-confidence placement of low-occupancy fragments into electron density using the anomalous signal of sulfur and halogen atoms.

Fragment-based drug design using X-ray crystallography is a powerful technique to enable the development of new lead compounds, or probe molecules, against biological targets. This study addresses the need to determine fragment binding orientations for low-occupancy fragments with incomplete electron density, an essential step before further development of the molecule. Halogen atoms play multiple roles in drug discovery due to their unique combination of electronegativity, steric effects and hydrophobic properties. Fragments incorporating halogen atoms serve as promising starting points in hit-to-lead development as they often establish halogen bonds with target proteins, potentially enhancing binding affinity and selectivity, as well as counteracting drug resistance. Here, the aim was to unambiguously identify the binding orientations of fragment hits for SARS-CoV-2 nonstructural protein 1 (nsp1) which contain a combination of sulfur and/or chlorine, bromine and iodine substituents. The binding orientations of carefully selected nsp1 analogue hits were focused on by employing their anomalous scattering combined with Pan-Dataset Density Analysis (PanDDA). Anomalous difference Fourier maps derived from the diffraction data collected at both standard and long-wavelength X-rays were compared. The discrepancies observed in the maps of iodine-containing fragments collected at different energies were attributed to site-specific radiation-damage stemming from the strong X-ray absorption of I atoms, which is likely to cause cleavage of the C-I bond. A reliable and effective data-collection strategy to unambiguously determine the binding orientations of low-occupancy fragments containing sulfur and/or halogen atoms while mitigating radiation damage is presented.

Mechanochemical and Microwave Multistep Organic Reactions

Abstract: The development of more sustainable chemical reactions and processes has been the focus of recent research activities. Advances in the field of organic synthesis have led to the emergence of new methodologies and techniques involving non-conventional energy sources. These include the applications of mechanical energy (mechanochemistry) and microwave radiation (MW) methods. This article reviews the advances in multistep organic synthesis of biologically relevant organic molecules using mechanochemistry and microwave techniques. Among them, various heterocyclic molecules (with nitrogen, oxygen, and sulphur atoms), amides, and peptides have been synthesized by multistep mechanochemical or MW reactions. Performing multiple synthetic steps using more sustainable methods shows cumulative advantages over multistep processes under conventional conditions in terms of reduced solvent use, shorter reaction times, better turnovers, and reaction yields. Simplification of protocols by carrying out two or more reaction steps in the same reaction vessel is another advantage of multistep syntheses.

Platinum(II) phosphoryl-substituted thiourea complexes with bis-phosphine ligands and some triphenylarsine and triphenylstibine analogues

Reactions between the phosphorylthiourea ligands (EtO)2PONHC(S)NHPh (L1), (EtO)2PONHC(S)NHCH(CH3)3) (L2) and (EtO)2PONHC(S)NHCH2CH3 (L3) and cis-[PtCl2(PPh3)2] gave complexes in which the ligands bind to the platinum(II) centre as dianionic ligands. For ligands L1 and L3, the ligand binds through the thiourea sulfur and the N-alkyl nitrogen atoms, giving the distal isomer. In contrast, the ligand L2, on account of the bulky t-butyl substituent on the ligand, coordinates via the sulfur and N-phosphoryl nitrogen atoms, giving the proximal isomer. The identities of the isomers were confirmed by single crystal X-ray analysis and 31P{1H} NMR spectroscopy. The latter showing that the appearance or absence of 3J(PP) couplings between the ligand and ancillary ligands provides indicative isomeric information. Further reactions between the ligand L1 and a series of bis-phosphine, triphenylarsine and triphenylstibine platinum(II) starting complexes gave the corresponding products also as the distal linkage isomer. Computational analysis reveals a possible chalcogen bond non-covalent interaction that may be responsible for the preference for the distal isomer.

Sulfur atom effect on the photochemical release of benzylamine from caged amines

Abstract Carbamate linkers are commonly used to attach photolabile protecting groups (PPGs) to amine functional groups. However, the release of amines from the carbamate linkage has low photochemical quantum yields because of the low leaving ability of the carbamic anion. In this study, we synthesized a new coumarin-based thiocarbamate-containing caged amine as a model to study the effect of sulfur on the photocleavage of the amine from the PPG. The release of the amine from the thiocarbamate (−SC(O)NHCH2Ph) linkage was ∼20 times faster than from the carbamate (−OC(O)NHCH2Ph) linkage.

Synthesis, spectral, antibacterial and NLO properties of organotin(IV) complexes of Thiosemicarbazones and Semicarbazones

In this study, the antimicrobial and nonlinear optical (NLO) response of thiosemicarbazone, semicarbazone, and their organotin(IV) compounds have been investigated. Organotin(IV) complexes of various types, namely [R2Sn(PhTscz)2], [R2Sn(Tscz)2], [R2Sn(Scz)2], [Bu3Sn(PTscz)], [Bu3Sn(PTscz)], and [Bu3Sn(Scz)] (where R = n-Butyl; methyl; PhTsczH = (±) 2-isopropyl-5-methyl-cyclohexylidene)-N-phenylhydrazine-carboxamide, TsczH = (±) 2-isopropyl-5-methylcyclo-hexylidene)hydrazinecarbothioamide, SczH = (±) 2-isopropyl-5-methylcyclohexyli-dene)hydrazine-carboxamide), were synthesized and characterized by CHN analysis, molar conductivity, UV-Vis, FTIR, and NMR (1H, 13C, 119Sn) spectroscopy, along with theoretical evidence obtained through density functional theory (DFT) simulations. The results showed that the Schiff base (HL) ligands acts as a bidentate NO/NS donor with azomethine nitrogen (N) and deprotonated ketonic oxygen/thionic sulphur (O, S) atoms. [R2Sn(L)2] complexes are assigned a distorted octahedral structure, while Bu3Sn(L) complexes have distorted trigonal bipyramidal structures. The B3LYP/LanL2DZ programme theoretically discussed the electronic structure and nonlinear optical (NLO) properties of the synthesized compounds. The synthesised compounds were evaluated for antibacterial activity using the zone inhibition method. Antibacterial activity of the ligands and its metal complexes against Gram(+) and Gram(-) bacteria demonstrated that the organotin complexes are more potentially resistant to microbial activities than the free ligands. According to the reactivity parameter factors, compound Bu2Sn(Scz)2 (3) is less reactive and more stable. Nonlinear optical (NLO) study revealed that compound (3) had greater linear polarizability (α) values, whereas compound Me2Sn(Scz)2 (9) had higher first hyperpolarizability (βtot) values of 244.29 a.u. Because of their high initial hyperpolarizability values, these molecules have excellent non-linear optical properties and can be exploited as innovative materials in the construction of optoelectronic devices.

Synthesis, structural characterization, density functional theory, anticancer, and antimicrobic studies of Ni2+ and Cu2+ complexes encompassing tridentate ONS‐donor azo‐thiosemicarbazone

This study focuses on the synthesis of azo‐thiosemicarbazone ligand, which is designed by reacting 2‐hydroxy‐5‐(phenyldiazenyl)benzaldehyde with hydrazine carbothioamide. Hence, this ligand was exploited for chelation with nickel and cupric salts in (1 M:1 L) molar ratio. These synthetics were structurally investigated using a variety of physical, analytical, and spectroscopic (1D/2D‐NMR, UV–Vis, FT‐IR, and E‐mass) tools as well as theoretically. The finding demonstrated that the resulting azo‐thiosemicarbazone (H4Azo‐TSC) bonded with the nickel and cupric ions as mono/di‐basic tridentate chelators, binding them via deprotonated phenolic oxygen, imino nitrogen, and thionic/thiol sulfur atoms adopting square planar geometry. The theoretical investigation was examined by DFT/B3LYP/LanL2dZ, including energetic parameters, HOMO‐LUMO energy gap, dipole moment, and geometrical optimization, which were applied to support the complexes' geometrical structure. The in vitro microbicidal activities of the azo‐thiosemicarbazone, compared with its Ni2+ and Cu2+ complexes, display superior activity over the metal complexes against different bacterial and fungal species. The anticancer efficacy of the synthetics was tested against human lung fibroblast (WI38) and mammary gland breast cancer (MCF‐7) compared with Doxorubicin as a standard drug. The cytotoxic efficiency of metallic complexes exceeded that of un‐chelated azo‐thiosemicarbazone. The most effective complex is Ni2+ complex with IC50 equal to 11.75 and 14.05 μg/ml, respectively. It has been demonstrated that Ni2+ and Cu2+ complexes are more biocompatible than free azo‐thiosemicarbazone; this finding may be related to the chelation process.

Unveiling the potential of graphene and S-doped graphene nanostructures for toxic gas sensing and solar sensitizer cell devices: insights from DFT calculations.

In this work, we explore the potential of 2D materials, particularly graphene and its derivatives, for eco-friendly electricity generation and air pollution reduction. Leveraging the significant surface area of graphene nanomaterials, the susceptibility of these graphene-based nanostructures to hazardous substances and their applicability in clean solar cell (SSC) devices were systematically investigated using density functional theory (DFT), as implemented within Gaussian 5.0 code. Time-dependent DFT (TD-DFT) was employed to characterize the UV-visible spectrum of unstrained nanostructures. Herein, we considered three potentially harmful gases-CO, NH3, and Br2. Adsorption calculations revealed a notable interaction between the pure graphene nanostructure and Br2 gas, while the S-doped counterpart exhibited reduced interaction. Saturated S-doped nanostructures demonstrated an enhanced affinity for NH3 and CO gases compared to their pure S-doped counterparts, attributed to the sulfur (S) atom facilitating gas molecule binding to the nanostructure's surface. Furthermore, simulations of the SSC device architecture indicated the superior performance of the pure graphene nanostructure in terms of light-harvesting efficiency, injection energy, and electron injection into the lower conduction band of CBM titanium dioxide (TiO2). These findings suggest a potential avenue for developing nanostructures tailored for SSC devices and gas sensors, offering a dual solution to address air pollution concerns. Density function theory was used to compute the ground and excited state properties for pure and sulfur-doped graphene nanostructures. The hybrid function B3LYP with a 6-31G* basis set was utilized to describe the exchange correlation. Gauss Sum 2.2 software is used to estimate the density of state (DOS) for all structures under investigation.

Temporal dynamics and metagenomics of phosphorothioate epigenomes in the human gut microbiome.

Epigenetic regulation of gene expression and host defense is well established in microbial communities, with dozens of DNA modifications comprising the epigenomes of prokaryotes and bacteriophage. Phosphorothioation (PT) of DNA, in which a chemically-reactive sulfur atom replaces a non-bridging oxygen in the sugar-phosphate backbone, is catalyzed by dnd and ssp gene families widespread in bacteria and archaea. However, little is known about the role of PTs or other microbial epigenetic modifications in the human microbiome. Here we optimized and applied fecal DNA extraction, mass spectrometric, and metagenomics technologies to characterize the landscape and temporal dynamics of gut microbes possessing PT modifications. Exploiting the nuclease-resistance of PTs, mass spectrometric analysis of limit digests of PT-containing DNA reveals PT dinucleotides as part of genomic consensus sequences, with 16 possible dinucleotide combinations. Analysis of mouse fecal DNA revealed a highly uniform spectrum of 11 PT dinucleotides in all littermates, with PTs estimated to occur in 5-10% of gut microbes. Though at similar levels, PT dinucleotides in fecal DNA from 11 healthy humans possessed signature combinations and levels of individual PTs. Comparison with a widely distributed microbial epigenetic mark, m6dA, suggested temporal dynamics consistent with expectations for gut microbial communities based on Taylor's Power Law. Application of PT-seq for site-specific metagenomic analysis of PT-containing bacteria in one fecal donor revealed the larger consensus sequences for the PT dinucleotides in Bacteroidota, Firmicutes, Actinobacteria, and Proteobacteria, which differed from unbiased metagenomics and suggested that the abundance of PT-containing bacteria did not simply mirror the spectrum of gut bacteria. PT-seq further revealed low abundance PT sites not detected as dinucleotides by mass spectrometry, attesting to the complementarity of the technologies. The results of our studies provide a benchmark for understanding the behavior of an abundant and chemically-reactive epigenetic mark in the human gut microbiome, with implications for inflammatory conditions of the gut.

Amorphous MoS2 from a machine learning inter-atomic potential.

Amorphous molybdenum disulfide has shown potential as a hydrogen evolution catalyst, but the origin of its high activity is unclear, as is its atomic structure. Here, we have developed a classical inter-atomic potential using the charge equilibration neural network method, and we have employed it to generate atomic models of amorphous MoS2 by melting and quenching processes. The amorphous phase contains an abundance of molybdenum and sulfur atoms in low coordination. Besides the 6-coordinated molybdenum typical of the crystalline phases, a substantial fraction displays coordinations 4 and 5. The amorphous phase is also characterized by the appearance of direct S-S bonds. Density functional theory shows that the amorphous phase is metallic, with a considerable contribution of the 4-coordinated molybdenum to the density of states at the Fermi level. S-S bonds are related to the reduction of sulfur, with the excess electrons spread over several molybdenum atoms. Moreover, S-S bond formation is associated with a distinctive broadening of the 3s states, which could be exploited for experimental characterization of the amorphous phases. The large variety of local environments and the high density of electronic states at the Fermi level may play a positive role in increasing the electrocatalytic activity of this compound.

Synthesis of Thionated Perylenediimides: State of the Art and First Investigations of an Alternative to Lawesson's Reagent.

Perylenediimides (PDIs) are composed of a central perylene ring, on which are grafted two imide groups at the peri positions. Thionated PDIs are characterized by the substitution of one or more oxygen atoms of these imide functions with sulfur atoms. This structural modification alters the electronic properties with a redshift of the optical absorption accompanied by modification of the charge transport characteristics compared to their non-thionated counterparts. These properties make them suitable candidates for applications in optoelectronic devices, such as organic light-emitting diodes and organic photovoltaics. Moreover, the presence of sulfur atom(s) can favor the promotion of reactive oxygen species production for photodynamic and photothermal therapies. These thionated PDIs can be synthesized through the post-functionalization of PDIs by using a sulfurizing reagent. Nevertheless, the main drawbacks remain the difficulties in adjusting the degree of thionation and obtaining tri- and tetrathionated PDIs. Up to now, this thionation reaction has been described almost exclusively using Lawesson's reagent. In the current study, we present our first investigations into an alternative reagent to enhance selectivity and achieve a greater degree of thionation. The association of phosphorus pentasulfide with hexamethyldisiloxane (Curphey's reagent) clearly demonstrated higher reactivity compared with Lawesson's reagent to attain multi-thionated PDIs.