Halogen Bond-Assisted Supramolecular Dimerization of Pyridinium-Fused 1,2,4-Selenadiazoles via Four-Center Se2N2 Chalcogen Bonding

The synthesis and structural characterization of α-haloalkyl-substituted pyridinium-fused 1,2,4-selenadiazoles with various counterions is reported herein, demonstrating a strategy for directed supramolecular dimerization in the solid state. The compounds were obtained through a recently discovered 1,3-dipolar cycloaddition reaction between nitriles and bifunctional 2-pyridylselenyl reagents, and their structures were confirmed by the X-ray crystallography. α-Haloalkyl-substituted pyridinium-fused 1,2,4-selenadiazoles exclusively formed supramolecular dimers via four-center Se···N chalcogen bonding, supported by additional halogen bonding involving α-haloalkyl substituents. The introduction of halogens at the α-position of the substituent R in the selenadiazole core proved effective in promoting supramolecular dimerization, which was unaffected by variation of counterions. Additionally, the impact of cocrystallization with a classical halogen bond donor C6F3I3 on the supramolecular assembly was investigated. Non-covalent interactions were studied using density functional theory calculations and topological analysis of the electron density distribution, which indicated that all ChB, XB and HB interactions are purely non-covalent and attractive in nature. This study underscores the potential of halogen and chalcogen bonding in directing the self-assembly of functional supramolecular materials employing 1,2,4-selenadiazoles derived from recently discovered cycloaddition between nitriles and bifunctional 2-pyridylselenyl reagents.

Perturbation of autophagy pathways in murine alveolar macrophage by 2D TMDCs is chalcogen-dependent

Increasing risks of incidental and occupational exposures to two-dimensional transition metal dichalcogenides (2D TMDCs) due to their broad application in various areas raised their public health concerns. While the composition-dependent cytotoxicity of 2D TMDCs has been well-recognized, how the outer chalcogenide atoms and inner transition metal atoms differentially contribute to their perturbation on cell homeostasis at non-lethal doses remains to be identified. In the present work, we compared the autophagy induction and related mechanisms in response to WS2, NbS2, WSe2 and NbSe2 nanosheets exposures in MH-S murine alveolar macrophages. All these 2D TMDCs had comparable physicochemical properties, overall cytotoxicity and capability in triggering autophagy in MH-S cells, but showed outer chalcogen-dependent subcellular localization and activation of autophagy pathways. Specifically, WS2 and NbS2 nanosheets adhered on the cell surface and internalized in the lysosomes, and triggered mTOR-dependent activation of autophagy. Meanwhile, WSe2 and NbSe2 nanosheets had extensive distribution in cytoplasm of MH-S cells and induced autophagy in an mTOR-independent manner. Furthermore, the 2D TMDCs-induced perturbation on autophagy aggravated the cytotoxicity of respirable benzo[a]pyrene. These findings provide a deeper insight into the potential health risk of environmental 2D TMDCs from the perspective of homeostasis perturbation.

Synthesis, computational and experimental pharmacological studies for (thio)ether-triazine 5-HT6R ligands with noticeable action on AChE/BChE and chalcogen-dependent intrinsic activity in search for new class of drugs against Alzheimer's disease

Alzheimer's disease is becoming a growing problem increasing at a tremendous rate. Serotonin 5-HT6 receptors appear to be a particularly attractive target from a therapeutic perspective, due to their involvement not only in cognitive processes, but also in depression and psychosis. In this work, we present the synthesis and broad biological characterization of a new series of 18 compounds with a unique 1,3,5-triazine backbone, as potent 5-HT6 receptor ligands. The main aim of this research is to compare the biological activity of the newly synthesized sulfur derivatives with their oxygen analogues and their N-demethylated O- and S-metabolites obtained for the first time. Most of the new triazines displayed high affinity (Ki < 200 nM) and selectivity towards 5-HT6R, with respect to 5-HT2AR, 5-HT7R, and D2R, in the radioligand binding assays. For selected, active compounds crystallographic studies, functional bioassays, and ADME-Tox profile in vitro were performed. The exciting novelty is that the sulfur derivatives exhibit an agonistic mode of action contrary to all other compounds obtained to date in this chemical class herein and previously reported. Advanced computational studies indicated that this intriguing functional shift might be caused by presence of chalcogen bonds formed only by the sulfur atom. In addition, the N-demethylated derivatives have emerged highly potent antioxidants and, moreover, show a significant improvement in metabolic stability compared to the parent structures. The cholinesterase study present micromolar inhibitory AChE and BChE activity for both 5-HT6 agonist 19 and potent antagonist 5. Finally, the behavioral experiments of compound 19 demonstrated its antidepressant-like properties and slight ability to improve cognitive deficits, without inducing memory impairments by itself. Described pharmacological properties of both compounds (5 and 19) allow to give a design clue for the development of multitarget compounds with 5-HT6 (both agonist and antagonist)/AChE and/or BChE mechanism in the group of 1,3,5-triazine derivatives.

Understanding base and backbone contributions of phosphorothioate DNA for molecular recognition with SBD proteins

Bacterial DNA phosphorothioate (PT) modification provides a specific anchoring site for sulfur-binding proteins (SBDs). Besides, their recognition patterns include phosphate links and bases neighboring the PT-modified site, thereby bringing about genome sequence-dependent properties in PT-related epigenetics. Here, we analyze the contributions of the DNA backbone (phosphates and deoxyribose) and bases bound with two SBD proteins in Streptomyces pristinaespiralis and coelicolor (SBDSco and SBDSpr). The chalcogen-hydrophobic interactions remained constantly at the anchoring site while the adjacent bases formed conditional and distinctive non-covalent interactions. More importantly, SBD/PT-DNA interactions were not limited within the traditional "4-bp core" range from 5'-I to 3'-III but extended to upstream 5'-II and 5'-III bases and even 5''-I to 5''-III at the non-PT-modified complementary strand. From the epigenetic viewpoint, bases 3'-II, 5''-I, and 5''-III of SBDSpr and 3'-II, 5''-II, and 5''-III of SBDSco present remarkable differentiations in the molecular recognitions. From the protein viewpoint, H102 in SBDSpr and R191 in SBDSco contribute significantly while proline residues at the PT-bound site are strictly conserved for the PT-chalcogen bond. The mutual and make-up mutations are proposed to alter the SBD/PT-DNA recognition pattern, besides additional chiral phosphorothioate modifications on phosphates 5'-II, 5'-II, 3'-I, and 3'-II.

On the Importance of Halogen and Chalcogen Bonds in the Solid State of Nucleic Acids: A Combined Crystallographic and Theoretical Perspective

In this work, intra- and intermolecular halogen and chalcogen bonds (HlgBs and ChBs, respectively) present in the solid state of nucleic acids (NAs) have been studied at the RI-MP2/def2-TZVP level of theory. To achieve this, a Protein Data Bank (PDB) survey was carried out, revealing a series of structures in which Br/I or S/Se/Te atoms belonging to nucleobases or pentose rings were involved in noncovalent interactions (NCIs) with electron-rich species. The energetics and directionality of these NCIs were rationalized through a computational study, which included the use of Molecular Electrostatic Potential (MEP) surfaces, the Quantum Theory of Atoms in Molecules (QTAIM), and Non Covalent Interaction plot (NCIplot) and Natural Bonding Orbital (NBO) techniques.

5'-Chalcogen-Substituted Nucleoside Pyrophosphate and Phosphate Monoester Analogues: Preparation and Hydrolysis Studies

Novel sulfur and selenium substituted 5',5'-linked dinucleoside pyrophate analogues were prepared in a vibration ball mill from the corresponding persilylated monophosphate. The chemical hydrolysis of pyrophosphorochalcogenolate-linked dimers was studied over a wide pH-range. The effect of the chalcogeno-substitution on the reactivity of dinucleoside pyrophosphates was surprisingly modest, and the chemical stability is promising considering the potential therapeutic or diagnostic applications. The chemical stability of the precursor phosphorochalcogenolate monoesters was also investigated. Hydrolytic desilylation of these materials was effected in aqueous buffer at pH 3, 7 or 11 and resulted in phosphorus-chalcogen bond scission which was monitored using ³¹P NMR. The rate of dephosphorylation was dependent upon both the nature of the chalcogen and the pH. The integrity of the P-S bond in the corresponding phosphorothiolate was maintained at high pH but rapidly degraded at pH 3. In contrast, P-Se bond cleavage of the phosphoroselenolate monoester was rapid and the rate increased with alkalinity. The results obtained in kinetic experiments provide insight on the reactivity of the novel pyrophosphates studied as well as of other types of thiosubstituted biological phosphates. At the same time, these results also provide evidence for possible formation of unexpectedly reactive intermediates as the chalcogen-substituted analogues are metabolised.

Facile Access to 2-Selenoxo-1,2,3,4-tetrahydro-4-quinazolinone Scaffolds and Corresponding Diselenides via Cyclization between Methyl Anthranilate and Isoselenocyanates: Synthesis and Structural Features

A practical method for the synthesis of 2-selenoxo-1,2,3,4-tetrahydro-4-quinazolinone was reported. The latter compounds were found to undergo facile oxidation with H2O2 into corresponding diselenides. Novel organoselenium derivatives were characterized by the 1H, 77Se, and 13C NMR spectroscopies, high-resolution electrospray ionization mass spectrometry, IR, elemental analyses (C, H, N), and X-ray diffraction analysis for several of them. Novel heterocycles exhibited multiple remarkable chalcogen bonding (ChB) interactions in the solid state, which were studied theoretically.

Stereoselective Processes Based on σ-Hole Interactions

The σ-hole interaction represents a noncovalent interaction between atoms with σ-hole(s) on their surface (such as halogens and chalcogens) and negative sites. Over the last decade, significant developments have emerged in applications where the σ-hole interaction was demonstrated to play a key role in the control over chirality. The aim of this review is to give a comprehensive overview of the current advancements in the use of σ-hole interactions in stereoselective processes, such as formation of chiral supramolecular assemblies, separation of enantiomers, enantioselective complexation and asymmetric catalysis.

Achieving Efficient NIR-II Type-I Photosensitizers for Photodynamic/Photothermal Therapy upon Regulating Chalcogen Elements

Second near-infrared (NIR-II) window type-I photosensitizers have intrinsic advantages in photodynamic/photothermal therapy (PDT/PTT) of some malignant tumors with deep infiltration, large size, complicated location, and low possibility of surgery/radiotherapy. Herein, three chalcogen-element-based donor-acceptor-type semiconducting polymers (poly[2,2″-((E)-4,4″-bis(2-octyldodecyl)-[6,6″-bithieno[3,2-b]pyrrolylidene]-5,5″(4H,4″H)-dione)-alt-2,5-(thiophene)] (PTS), poly[2,2″-((E)-4,4″-bis(2-octyldodecyl)-[6,6″-bithieno[3,2-b]pyrrolylidene]-5,5″(4H,4″H)-dione)-alt-2,5-(selenophene)] (PTSe), and poly[2,2″-((E)-4,4″-bis(2-octyldodecyl)-[6,6″-bithieno[3,2-b]pyrrolylidene]-5,5″(4H,4'H)-dione)-alt-2,5-(tellurophene)] (PTTe)) are synthesized and fully characterized, demonstrating strong absorption in the NIR-II region. Upon adjusting the chalcogen elements, the intramolecular charge-transfer characteristics and the heavy-atom effect are tuned to enhance the intersystem crossing rate, improving the photodynamic effect. Moreover, the energy levels and Gibbs free energies are tuned to facilitate the type-I photodynamic process. As a result, PTTe nanoparticles (NPs) produce superoxide anion radicals (O₂ ^•- ) more efficiently and demonstrate higher photothermal conversion efficiency than PTS and PTSe NPs upon NIR-II (1064 nm) laser irradiation, exhibiting unprecedented NIR-II type-I PDT/PTT performance in vitro and in vivo. This work provides ideas for achieving high-performance NIR-II type-I PDT/PTT semiconducting polymers for hypoxic oncotherapy.

Effects of azole rings with different chalcogen atoms on ESIPT behavior for benzochalcogenazolyl-substituted hydroxyfluorenes

ESIPT behavior has attracted a lot of eyes of researchers in recent years because of its unique optical properties. Due to its large Stokes shift and double emission fluorescence, white light can be generated in the fluorophore based on the excited state intramolecular proton transfer (ESIPT) principle. The excited state proton transfer behavior of hydroxylated benzoxazole (BO-OH), benzothiazole (BS-OH) and benzoselenazole (BSe-OH) have been investigated in heptane, chloroform and DMF solvents. By comparing the infrared vibration spectra and the variation of bond parameters from the S₀ to S₁ states, and analyzing the frontier molecular orbitals, the influence of hydrogen bond dynamics, the solvent polarity, charge redistribution and the effects of different proton acceptors on proton transfer were observed. The only structural difference among the three substituted hydroxyfluorenes is the heteroatom in the azole ring (oxygen, sulfur and selenium, respectively). We have scanned the potential energy curve of the ESIPT process, and compared the potential barrier, it is found that the heavier chalcogen atoms are more favorable for proton transfer. At the same time, the potential application of changing heteroatoms in the azole ring by walking down the chalcogenic group in crystal luminescence color regulation is also discussed.

Highly Active Halogen Bonding and Chalcogen Bonding Chloride Transporters with Non-Protonophoric Activity

Synthetic anion transporters show much promise as potential anti-cancer agents and therapeutics for diseases associated with mis-regulation of protein anion channels. In such applications high activity and anion selectivity are crucial to overcome competing proton or hydroxide transport which dissipates cellular pH gradients. Here, highly active bidentate halogen bonding and chalcogen bonding anion carriers based on electron deficient iodo- and telluromethyl-triazole derivatives are reported. Anion transport experiments in lipid bilayer vesicles reveal record nanomolar chloride transport activity for the bidentate halogen bonding anion carrier, and remarkably high chloride over proton/hydroxide selectivity for the chalcogen bonding anionophore. Computational studies provide further insight into the role of sigma-hole mediated anion recognition and desolvation at the membrane interface. Comparison with hydrogen bonding analogues demonstrates the importance of employing sigma-hole donor motifs in synthetic anionophores for achieving both high transport activity and selectivity.

Ultralong Organic Phosphorescent Nanocrystals with Long-Lived Triplet Excited States for Afterglow Imaging and Photodynamic Therapy

The development of novel applications of ultralong organic phosphorescent (UOP) materials is highly desired. Herein, a series of UOP materials (EDCz, E = O, S, Se, and Te) for bacterial afterglow imaging and photodynamic therapy (PDT) is reported. By structurally bonding with the chalcogen atoms with π-conjugated scaffolds, EDCz not only absorbs visible light but also emits UOP with an efficiency of ca. 0.01-6.8% and a long lifetime of 0.08-0.318 s under ambient conditions. Benefiting from the long-lived triplet excited states, the SeDCz nanocrystals (NCs) possessed the best optical properties in the series, generating ¹O₂ under white light irradiation and performing as an agent for Staphylococcus aureus afterglow imaging and PDT at a low concentration (98 ng mL^-1). The SeDCz NCs are also utilized as real-time UOP imaging agents and promoted healing of infected wounds in living mice. To the best of our knowledge, this study presents the first example of UOP-based bacterial photodynamic theranostic agents and creates a platform for the next-generation efficient UOP-based photosensitizers for bioimaging and skin regeneration.

A 2D transition-metal dichalcogenide MoS2 based novel nanocomposite and nanocarrier for multiplex miRNA detection

Nanoscale MoS2 has attracted extensive attention for sensing due to its superior properties. This study outlines a microfluidic and electrochemical biosensing methodology for the multiplex detection of paratuberculosis-specific miRNAs. Herein, we report the synthesis of MoS2 nanosheets decorated with a copper ferrite (CuFe2O4) nanoparticle composite and molecular probe immobilized MoS2 nanosheets as nanocarriers for the electrochemical detection of miRNAs. Paratuberculosis is a bacterial infection of the intestinal tract of dairy cattle, and is a cause of substantial economic and animal losses all over the world. The designed biosensing electrode was modified with the synthesized MoS2-CuFe2O4 nanocomposites for a highly amplified signal generation. Additionally, selective detection of miRNAs was accomplished by functionalizing the MoS2 nanosheets with a miRNA-specific biotin-tagged thiolated molecular probe and ferrocene thiol. The presence of target miRNA triggered the opening of the molecular probe present on the nanocarriers. The interaction of the molecular probe and miRNA resulted in an increase in the electrochemical signal from ferrocene. The optimized microfluidic biosensor was employed to detect a range of miRNA concentrations from the target analyte. Using square wave voltammetric analysis, a detection limit of 0.48 pM was calculated, with a detection range of 1 pM to 1.5 nM. The application of the biosensor was also assessed by detecting miRNAs in spiked serum and positive clinical samples. The developed nanomaterial enabled biosensor easily discriminated between the target miRNAs and other interfering molecules. The developed microfluidic biosensor has the potential to be used as a point-of-care, miRNA based diagnostic tool for paratuberculosis in dairy cows.

Review on Chalcogenide 3D Nano-structured Crystals: Synthesis and Growth Mechanism

Three dimensional (3D) nano-structured crystals have received extensive attention for their superior properties over zero dimensional (0D), one dimensional (1D), or two dimensional (2D) nanomaterials in many areas. This review is generalized for the group of chalcogenide nanoflowers (NFs) by the synthetic techniques, such as solvothermal, wet chemical, sol-gel, surface oxidation, microwave, coating, electrochemical, and several other methods. The formation mechanism was also described for the purpose of opening up new food for thoughts to bring up new functionality of materials by tuning the morphology of crystals. The pH value or the template plays fundamental role in forming the nano-flowered structure. Moreover, the correlations between the surface area (SA), contact angle (CA), and the NFs are also discussed within the context. Here, we also discussed some patents relevant to the topic.

Effect of KI/AgI on the thermal and optical properties of the GeS₂-In₂S₃ chalcogenide glasses

GeS₂-In₂S₃-KI/AgI chalcohalide glasses were prepared by traditional melt-quenching method and the glass-forming region was determined. The dependence of glass properties on composition as formula of (100 - x)(0.75GeS₂-0.25In₂S₃) - x(In₂S₃-KI/AgI) was investigated. The allowed indirect transition of samples was calculated according to the classical Tauc equation. The results show that 50 mol% AgI can be introduced in the glassy matrix while only 40 mol% of KI can be incorporated in the GeS₂-In₂S₃-KI glass system. GeS₂-In₂ S₃-AgI glass system has larger density, higher refractive index and better thermal stability, while GeS₂-In₂S₃-KI glass system has shorter visible cut-off wavelength and higher optical band gap.

A new generation of cyanide ion-selective membranes for flow injection application

Using induced cathodic electrodeposition a number of silver chalcogenide thin layer membranes of non-trivial composition have been synthesized and their performance as ion-selective flow-injection potentiometric detectors (FIPDs) for free cyanide has been critically estimated in the context of the stringent requirements for toxic cyanide environmental monitoring. AgSCN/Ag2S, Ag2S, Ag(2+delta)Se, Ag(2+delta)Se(1-x)Te(x) (0<delta<0.25 and x approximately = 0.13), Ag2Se and Ag2Se(1-x)Te(x) electroplated membranes were selected for the present performance-based comparative study in order to obtain a feedback information about the effect of membrane composition. Both silver selenide and Te-doped silver selenide membranes, irrespective of their stoichiometry with respect to silver, exhibit the lowest detection limit for CN- (52 ppb) with linear double-Nernstian response down to 130 ppb. The type of chalcogene anion in the membrane composition proves to exert dominant effect on the general performance characteristics of the newly developed FIPDs. The silver stoichiometry (intrinsic defects factor) and the inclusion of Te-dopant (extrinsic defects factor) have more pronounced effect on the profile of the output signal and exert moderate control on the detectors selectivity and baseline stability. This new generation of CN(-)-ion-selective membranes for FIPDs exhibits high selectivity against the common interferents present in cyanide effluents such as SCN-, S2O3(2-), Cl- and do not get poisoned in the presence of S2-. Moreover, their long-term stability and signal reproducibility, which make redundant the regular day-to-day calibration, coupled with the cost-effective technology for membranes preparation and easy re-generation make them attractive candidates for incorporation into automated in-field devices for in situ cyanide toxic species monitoring.

Tunable optically pumped lead-chalcogenide mid-infrared emitters on Si-substrates

Two types of novel lead-chalcogenide mid-IR emitters grown by molecular beam epitaxy (MBE) on Si or BaF(2) substrates are described:PbSe/PbEuSe edge emitting double heterostructure (DH) and quantum well (QW) lasers are pumped optically with low-cost III-V laser-diodes. They emit in the 3-6 microm range with powers up to 200 mW. Tuning is performed by temperature change and/or mechanically if bars with slightly tapered composition are used. A "wavelength transformer", a PbSe/PbEuSe active resonant cavity with top and bottom Bragg mirror transforms the incoming 0.8 microm pump radiation to e.g. 4.2 microm wavelength. It operates at room temperature, width and value of the emission line is determined by design.

A multi-technique surface study of the mercury(II) chalcogenide ion-selective electrode in saline media

X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), rotating disc electrode-electrochemical impedance spectroscopy (RDE-EIS) and synchrotron radiation-grazing incidence X-ray diffraction (SR-GIXRD) have been used to study the response mechanism of the mercury(II) chalcogenide ion-selective electrode (ISE) in saline media. XPS and SIMS have shown that the chalcogenide surface is poisoned by silver chloride, or a mixture of silver halides, on continuous exposure to synthetic and real seawater. Significantly, the in-situ SR-GIXRD study demonstrated that electrode fouling in synthetic seawater is linked to the formation of poorly crystalline or amorphous silver chloride, and that the low level of free mercury(II) in a calibration buffer (i.e., 10(-14) M) is able to undergo metathesis with silver(II) sulfide in the membrane generating mercury(II) sulfide. Significantly, the results of this detailed surface study have shown that silver chloride fouling of the electrode is ameliorated in real seawater comprising natural organic ligands, and this has been attributed to the peptization of silver chloride by the surfactant-like nature of seawater ligands at pH 8. RDE-EIS aging studies have revealed that the chalcogenide membrane experiences a sluggish charge transfer reaction in seawater, and contrary to a previous report for a static electrode, the seawater matrix does not passivate the RDE. The results of this XPS, SIMS, RDE-EIS and SR-GIXRD study have elucidated the response mechanism of the mercury(II) ISE in saline media.