Se-Se Bonds Research Articles

Visible-Light-Induced Diselenide-Crosslinked Polymeric Micelles for ROS-Triggered Drug Delivery.

To synthesize an effective and versatile nano-platform serving as a promising carrier for controlled drug delivery, visible-light-induced diselenide-crosslinked polyurethane micelles were designed and prepared for ROS-triggered on-demand doxorubicin (DOX) release. A rationally designed amphiphilic block copolymer, poly(ethylene glycol)-b-poly(diselenolane diol-co-isophorone diisocyanate)-b-poly(ethylene glycol) (PEG-b-PUSe-b-PEG), which incorporates dangling diselenolane groups within the hydrophobic PU segments, was initially synthesized through the polycondensation reaction. In aqueous media, this type of amphiphilic block copolymer can self-assemble into micellar aggregates and encapsulate DOX within the micellar core, forming DOX-loaded micelles that are subsequently in situ core-crosslinked by diselenides via a visible-light-triggered metathesis reaction of Se-Se bonds. Compared with the non-crosslinked micelles (NCLMs), the as-prepared diselenide-crosslinked micelles (CLMs) exhibited a smaller particle size and improved colloidal stability. In vitro release studies have demonstrated suppressed drug release behavior for CLMs in physiological conditions, as compared to the NCLMs, whereas a burst release of DOX occurred upon exposure to an oxidation environment. Moreover, MTT assay results have revealed that the crosslinked polyurethane micelles displayed no significant cytotoxicity towards HeLa cells. Cellular uptake analyses have suggested the effective internalization of DOX-loaded crosslinked micelles and DOX release within cancer cells. These findings suggest that this kind of ROS-triggered reversibly crosslinked polyurethane micelles hold significant potential as a ROS-responsive drug delivery system.

Sr2MnO2Na1.6Se2: A Metamagnetic Layered Oxychalcogenide Synthesized by Reductive Na Intercalation to Break [Se2]2- Perselenide Dimer Units.

Recent advances in anion-redox topochemistry have enabled the synthesis of metastable mixed-anion solids. Synthesis of the new transition metal oxychalcogenide Sr2MnO2Na1.6Se2 by topochemical Na intercalation into Sr2MnO2Se2 is reported here. Na intercalation is enabled by the redox activity of [Se2]2- perselenide dimers, where the Se-Se bonds are cleaved and a [Na2-x Se2](2+x)- antifluorite layer is formed. Freshly prepared samples have 16(1) % Na-site vacancies corresponding to a formal oxidation state of Mn of +2.32, a mixed-valence between Mn2+ (d5) and Mn3+ (d4). Samples are highly prone to deintercalation of Na, and over two years, even in an argon glovebox environment, the Na content decreased by 4(1) %, leading to slight oxidation of Mn and a significantly increased long-range ordered moment on the Mn site as measured using neutron powder diffraction. The magnetic structure derived from neutron powder diffraction at 5 K reveals that the compound orders magnetically with ferromagnetic MnO2 sheets coupled antiferromagnetically. The aged sample shows a metamagnetic transition from bulk antiferromagnetic to ferromagnetic behavior in an applied magnetic field of 2 T, in contrast to the Cu analogue, Sr2MnO2Cu1.55Se2, where there is only a hint that such a transition may occur at fields exceeding 7 T. This is presumably due to the higher ionic character of [Na2-x Se2](2+x)- layers compared to [Cu2-x Se2](2+x)- layers, reducing the strength of the antiferromagnetic interactions between MnO2 sheets. Electrochemical Na intercalation into Sr2MnO2Se2 leads to the formation of multiphase sodiated products. The work shows the potential of anion redox to yield novel compounds with intriguing physical properties.

Chemo-photothermal nanoplatform with diselenide as the key for ferroptosis in colorectal cancer

Colorectal cancer (CRC) is a prevalent clinical malignancy of the gastrointestinal system, and its clinical drug resistance is the leading cause of poor prognosis. Mechanistically, CRC cells possess a specific oxidative stress defense mechanism composed of a significant number of endogenous antioxidants, such as glutathione, to combat the damage produced by drug-induced excessive reactive oxygen species (ROS). We report on a new anti-CRC nanoplatform, a multifunctional chemo-photothermal nanoplatform based on Camptothecin (CPT) and IR820, an indocyanine dye. The implementation of a GSH-triggered ferroptosis-integrated tumor chemo-photothermal nanoplatform successfully addressed the poor targeting ability of CPT and IR820 while exhibiting significant growth inhibitory effects on CRC cells. Mechanistically, to offset the oxidative stress created by the broken SeSe bonds, endogenous GSH was continuously depleted, which inactivated GPX4 to accumulate lipid peroxides and induce ferroptosis. Concurrently, exogenously administered linoleic acid was oxidized under photothermal conditions, resulting in an increase in LPO accumulation. With the breakdown of the oxidative stress defense system, chemotherapeutic efficacy could be effectively enhanced. In combination with photoacoustic imaging, the nanoplatform could eradicate solid tumors by means of ferroptosis-sensitized chemotherapy. This study indicates that chemotherapy involving a ferroptosis mechanism is a viable method for the treatment of CRC.

Tridentate NacNac Tames T-Shaped Nickel(I) Radical.

The reaction of a nickel(II) chloride complex containing a tridentate β-diketiminato ligand with a picolyl group [2,6-iPr2 -C6 H3 NC(Me)CHC(Me)NH(CH2 py)]Ni(II)Cl (1)] with KSi(SiMe3 )3 conveniently afforded a nickel(I) radical with a T-shaped geometry (2). The compound's metalloradical nature was confirmed through electron paramagnetic resonance (EPR) studies and its reaction with TEMPO, resulting in the formation of a highly unusual three-membered nickeloxaziridine complex (3). When reacted with disulfide and diselenide, the S-S and Se-Se bonds were cleaved, and a coupled product was formed through carbon atom of the pyridine-imine group. The nickel(I) radical activates dihydrogen at room temperature and atmospheric pressure to give the monomeric nickel hydride.

Seleno-relaxin analogues: effect of internal and external diselenide bonds on the foldability and a fibrosis-related factor of endometriotic stromal cells.

Human relaxin-2 (H2 relaxin) is a peptide hormone of about 6 kDa, first identified as a reproductive hormone involved in vasoregulation during pregnancy. It has recently attracted strong interest because of its diverse functions, including anti-inflammatory, anti-fibrotic, and vasodilatory, and has been suggested as a potential peptide-based drug candidate for a variety of diseases. Mature H2 relaxin is constituted by the A- and B-chains stabilized by two interchain disulfide (SS) bridges and one intrachain SS linkage. In this study, seleno-relaxins, SeRlx-α and SeRlx-β, which are [C11UA,C11UB] and [C10UA,C15UA] variants of H2 relaxin, respectively, were synthesized via a one-pot oxidative chain assembly (folding) from the component A- and B-chains. The substitution of SS bonds in a protein with their analogue, diselenide (SeSe) bonds, has been shown to alter the physical, chemical, and physiological properties of the protein. The surface SeSe bond (U11A-U11B) enhanced the yield of chain assembly while the internal SeSe bond (U10A-U15A) improved the reaction rate of the folding, indicating that these bridges play a major role in controlling the thermodynamics and kinetics, respectively, of the folding mechanism. Furthermore, SeRlx-α and SeRlx-β effectively reduced the expression of a tissue fibrosis-related factor in human endometriotic stromal cells. Thus, the findings of this study indicate that the S-to-Se substitution strategy not only enhances the foldability of relaxin, but also provides new guidance for the development of novel relaxin formulations for endometriosis treatment.

Structure, bonding and electronic characteristics of amorphous Se.

Ovonic threshold switching (OTS) selectors can effectively improve the storage density and suppress the leakage current of advanced phase-change memory devices. As a prototypical OTS material, amorphous GeSe is widely investigated. But the attention paid to amorphous Se (i.e., the functional constituent in amorphous GeSe) has been very limited up to now. Here we have explored the structure, bonding and electronic characteristics of amorphous Se using ab initio molecular dynamics simulations. The results reveal that the Se atoms in amorphous Se tend to form 2-coordinated configurations, and they connect with each other to form long chains. The fraction of the vibrational density of state located in the high frequency range is relatively large, and the formation energy of the Se-Se bond is as large as 4.44 eV, hinting that the Se-Se bonds in chains possess high stability. In addition, the mid-gap state related to the OTS behavior is also found in amorphous Se despite the small proportion. Our findings enrich the knowledge of amorphous Se, which aids the applications of Se-based OTS selectors.

The Ambiguous Origin of Thermochromism in Molecular Crystals of Dichalcogenides: Chalcogen Bonds versus Dynamic Se─Se/Te─Te Bonds.

We report thermochromism in crystals of diphenyl diselenide (dpdSe) and diphenyl ditelluride (dpdTe), which is at variance with the commonly known mechanisms of thermochromism in molecular crystals. Variable temperature neutron diffraction studies indicated no conformational change, tautomerization or phase transition between 100 K and 295 K. High-pressure crystallography studies indicated no associated piezochromism in dpdSe and dpdTe crystals. The evolution of the crystal structures and their electronic band structure with pressure and temperature reveal the contributions of intramolecular and intermolecular factors towards the origin of thermochromism - especially the intermolecular Se⋅⋅⋅Se and Te⋅⋅⋅Te chalcogen bonds and torsional modes of vibrations around the dynamic Se─Se and Te─Te bonds. Further, a co-crystal of dpdSe with iodine (dpdSe-I2) and an alloy crystal of dpdSe and dpdTe implied a predominantly intramolecular origin of the observed thermochromism associated with vibronic coupling.

Dual-stimulus phototherapeutic nanogel for triggering pyroptosis to promote cancer immunotherapy.

Pyroptosis is a highly inflammatory programmed cell death that activates inflammatory response, reverses immunosuppression and promotes systemic immune response for solid tumors treatment. However, the uncontrollable and imprecise process of pyroptosis stimulation leads to a scanty therapeutic effect. Here, we report a GSH/ROS dual response nanogel system (IMs) that can actively target the overexpressed mannose receptor (MR) of cancer cells, serve ultra-stable photothermal capacity of indocyanine green (ICG), induce cell pyroptosis and achieve enhanced tumor immune response. Photo-triggered IMs induce cytoplasmic Ca2+ introgression and activate caspase-3 through photo-activated ICG. The disconnect of SeSe bonds could breaks the oxidation and reduction balance of tumor cells, causing oxidative stress and synergistically enhances caspase-3 cleavage, and regulates cell pyroptosis ultimately. Combined with anti-programmed death receptor 1 (anti-PD-1), the nanogel system not only effective suppressed both primary tumor and distance tumor but also prolonged the survival period of mice. This work introduces a strategy to optimize the photothermal performance of ICG and enhance tumor immune response mediated by triggering pyroptosis, which provides an impressive option for immune checkpoint blockade therapy.

Structural & thermal study of Sb14Se(86-x)Sn(x) chalcogenide glassy system

The structural and thermal analyses of Sb14Se(86-x)Sn(x) (x = 3 and × = 6) glassy system generated by the usual melt-quenching approach are presented in this study. Using the differential scanning calorimeter (DSC) technology, the crystallisation mechanism of the produced glass samples were investigated. With increasing Sn content there is increase in glass transition temperature Tg. The less difference in melting temperature and crystallisation temperature makes prepared glasses suitable for memory switching devices. At room temperature the infrared transmission spectra of Sb14Se(86-x)Sn(x) (x = 0, 3, 6, 9, 12 and 15) chalchogenide glasses were acquired in the 2000–2500 cm−1 spectral range. With Sn addition, far IR spectra are shifted towards the high frequency side and some new bonds appear. Because it was evident that Se atoms were being replaced by Sn atoms, a corresponding rise in the production of Sn-Sn bonds and a subsequent fall in Se-Se bonds were seen. The glasses produced in this manner exhibit improved glass forming capability and strong thermal stability. There was good agreement between experimental data and theoretical estimations of bond energy, relative likelihood of bond formation, and wave number. [copyright information to be updated in production process]

Pressure induced bands convergence and strength enhancement in thermoelectric semiconductor β-InSe

The semiconductor InSe possesses an exceptional ductility at room temperature, but its weak electronic transport properties leads to the low thermoelectric properties, limiting its applications in flexible thermoelectric devices. In this work, we applied first principles to find that the hydrostatic pressure can remarkably improve the thermoelectric and mechanical properties of β-InSe. The multiple conduction bands convergence is observed at the hydrostatic pressure of 5 GPa, resulting in a maximum zT value of 0.235 at 300 K, which is 170 % higher than the intrinsic zT value of 0.087. The point defect calculations suggest that In0.96Pb0.04Se or InSe0.96Cl0.04 could obtain the optimal carrier concentration of 7.65 × 1019 cm−3 with the highest zT value. In addition, we find that the (001)/<110>slip system of InSe exhibits the lowest ideal shear strength of 0.68 GPa, due to the weak interlayered van der Waals SeSe bonds. While the hydrostatic pressure can reduce the bond lengths and strengthen the van der Waals SeSe bonds. At 5 GPa, a maximum stretching force constant of van der Waals SeSe bond is obtained, giving rise to a maximum shear ideal strength of 1.45 GPa, which is 113 % higher than that without pressure. This hydrostatic pressure induced strain engineering strategy provides a theoretical guidance to synthesize high-performance thermoelectric β-InSe with robust mechanical properties.

Preparation of Co-S/NixSey/C@TiO2 composite electrode and the performance improvement strategies for the electrooxidation of H2O2

BackgroundThe cleanliness and ease of storage and transportation of H2O2 make it a promising fuel of fuel cell, but improving the catalytic activity of H2O2 electrooxidation is a prerequisite. MethodThe Co-S/NixSey/C@TiO2 electrode was prepared by “vapor deposition” and “two-step electrodeposition”, and the electrode was scaled up and fabricated into a rotating cylinder electrode to improve the catalytic performance of H2O2 electrooxidation. Significant findingsThe presence of Se-Se bonds and the synergistic effect of Co-S compound and NixSey gave the electrode a reduced oxidation potential for the electrooxidation of H2O2. The three-dimensional (3D) structure of the electrode facilitated the exposure of the catalyst active site, and the loading of Co-S compound improved the hydrophilicity of electrode. It's important to note that an original rotating cylinder electrode system was fabricated using an enlarged Co-S/NixSey/C@TiO2 electrode to weaken concentration polarization and reduce bubble adsorption on the electrode surface. Through the study, rotation of electrode and circulation of reaction solution exhibit positive effect for the electrooxidation reaction. Especially with a rotation speed of 37 r min−1 of electrode, the performance was improved by 85%. This study provides new strategies for improving the performance of H2O2 electrooxidation, which is of high research significance.

Remarkable plasticity and softness of polymorphic InSe van der Waals crystals

Indium selenide (InSe) crystals are reported to show exceptional plasticity, a new property to two-dimensional van der Waals (2D vdW) semiconductors. However, the correlation between plasticity and specific prototypes is unclear, and the understanding of detailed plastic deformation mechanisms is inadequate. Here three prototypes of InSe are predicted to be plastically deformable by calculation, and the plasticity of polymorphic crystals is verified by experiment. Moreover, distinct nanoindentation behaviors are seen on the cleavage and cross-section surfaces. The modulus and hardness of InSe are the lowest ones among a large variety of materials. The plastic deformation is further perceived from chemical interactions during the slip process. Particularly for the cross-layer slip, the initial In-Se bonds break while new In-In and Se-Se bonds are newly formed, maintaining a decent interaction strength. The remarkable plasticity and softness alongside the novel physical properties, endow InSe great promise for application in deformable and flexible electronics.

A novel bifunctional thioarsenate based on unprecedented molecular [Cd4As8Se16(Se2)2]8- cluster anions.

Exploring and developing new functional inorganic chalcogenides with unique structures is always one of the most important missions in solid-state chemistry, especially those with molecular structures. Herein, a novel quaternary thioarsenate, Cs2CdAsSe5, is found to be based on an unprecedented molecular (poly)chalcogenide cluster architecture, which has never been discovered in inorganic chalcogenide systems. This rare windmill-like [Cd4As8Se16(Se2)2]8- cluster is made of four [CdSe4] and [As(V)Se4] tetrahedra via corner-sharing Se atoms and Se-Se bonds. Specifically, Cs2CdAsSe5 exhibits a remarkable photocurrent response and a large computationally predicted birefringence, and the origin of the optoelectronic performance and optical anisotropy is confirmed by detailed theoretical investigation.

Metal-free synthesis of diselenides and ditellurides by using TMSCN

A metal-free protocol is disclosed for C-Se and Se-Se bonds forming reactions between boronic acids and elemental selenium to synthesize diselenides by using TMSCN as an organic catalyst. Meanwhile, a series of ditellurides were obtained from boronic acids and elemental tellurium with TMSCN. Preliminary mechanistic studies reveal that the reaction involved a radical way.

Dual Glutathione Depletion Enhanced Enzyme Catalytic Activity for Hyperthermia Assisted Tumor Therapy on Semi-Metallic VSe2/Mn-CS.

Semimetallic nanomaterials as photothermal agents for bioimaging and cancer therapy have attracted tremendous interest. However, the poor photothermal stability, low biocompatibility, and single component limit their therapeutic efficiency in cancer treatment. Here, manganese-doped VSe2 semimetallic nanosheets were prepared and subsequently modified with chitosan (named VSe2/Mn-CS NSs) for combined enzyme catalytic and photothermal therapy. VSe2/Mn-CS NSs show high photothermal property with a photothermal conversion efficiency of 34.61% upon 808 nm near-infrared laser irradiation. In the tumor microenvironment, VSe2/Mn-CS NSs can convert endogenous H2O2 into lethal hydroxyl radicals (•OH) to induce cancer cell apoptosis. The interaction between glutathione (GSH) and Se-Se bonds in VSe2/Mn-CS NSs results in the depletion of GSH level, and the valence states transition of manganese ions is also beneficial for the GSH consumption. This dual depletion of GSH markedly enhances the peroxidase (POD) activity, leading to the high •OH production and the improved therapeutic effect. What is more, the T1-weighted magnetic resonance and photoacoustic imaging endow VSe2/Mn-CS NSs with the ability to guide and track the treatment process. Our study provides a research strategy for the application of semimetallic nanomaterials in cancer diagnosis and treatment.

Stabilized Synthesis of 2D Verbeekite: Monoclinic PdSe2 Crystals with High Mobility and In-Plane Optical and Electrical Anisotropy.

PdSe2 has a layered structure with an unusual, puckered Cairo pentagonal tiling. Its atomic bond configuration features planar 4-fold-coordinated Pd atoms and intralayer Se-Se bonds that enable polymorphic phases with distinct electronic and quantum properties, especially when atomically thin. PdSe2 is conventionally orthorhombic, and direct synthesis of its metastable polymorphic phases is still a challenge. Here, we report an ambient-pressure chemical vapor deposition approach to synthesize metastable monoclinic PdSe2. Monoclinic PdSe2 is shown to be synthesized selectively under Se-deficient conditions that induce Se vacancies. These defects are shown by first-principles density functional theory calculations to reduce the free energy of the metastable monoclinic phase, thereby stabilizing it during synthesis. The structure and composition of the monoclinic PdSe2 crystals are identified and characterized by scanning transmission electron microscopy imaging, convergent beam electron diffraction, and electron energy loss spectroscopy. Polarized Raman spectroscopy of the monoclinic PdSe2 flakes reveals their strong in-plane optical anisotropy. Electrical transport measurements show that the monoclinic PdSe2 exhibits n-type charge carrier conduction with electron mobilities up to ∼298 cm2 V-1 s-1 and a strong in-plane electron mobility anisotropy of ∼1.9. The defect-mediated growth pathway identified in this work is promising for phase-selective direct synthesis of other 2D transition metal dichalcogenides.

Remote Manipulation of ROS-Sensitive Calcium Channel Using Near-Infrared-Responsive Conjugated Oligomer Nanoparticles for Enhanced Tumor Therapy In Vivo.

The regulation of reactive oxygen species (ROS)-sensitive calcium (Ca2+) channels is of great significance in the treatment of tumors. Here, a simple ROS generation system is developed to activate ROS-sensitive ion channels for enhancing calcium-cascade-mediated tumor cell death under near-infrared (NIR) light irradiation. Upon irradiation with an 808 nm laser, a low-lethality amount of ROS facilitates plasmid transient potential receptor melastatin-2 (pTRPM2) gene release via cleavage of the Se-Se bonds, which contributed to enhancing the expression of TRPM2 in tumor cells. Meanwhile, ROS could potently activate TRPM2 for Ca2+ influx to inhibit early autophagy and to further induce intracellular ROS production, which ultimately led to cell death in TRPM2 expressing tumor cells. Both in vitro and in vivo data show that nanoparticles have an excellent therapeutic effect on cancer upon NIR light. This work presents a simple modality based on NIR light to remotely control the ROS-sensitive ion channel for cancer therapy.

Improving the electrochemical activity of PdSe2 by constructing P/T structural interfaces

Palladium diselenide (PdSe2) is acknowledged as a potential electrocatalyst for hydrogen evolution reaction (HER), but its large-scale basal plane is catalytically inert, which enormously limits its application in electrochemical efficiency. Here we employ the phase interface in PdSe2 to activate sites on the basal plane and improve the HER activity. Five P/T interface structures in PdSe2 are constructed and optimized by density functional theory (DFT) calculations. The interface boundaries consist of triangle, pentagonal and hexagonal rings with the formation of more Se-Se bonds. The structural stability and HER activity for these interface structures are evaluated, and the optimal sites for HER are confirmed, which are mostly located on Se atoms. Our proposed strategy proves the formation of interface in PdSe2 could successfully enhance its HER performance and could be also applicable to the other two-dimensional materials.

Dynamical and mechanical stability, electronic properties, bonding and weak interactions analysis of new compounds MgS2 and MgSe2 in [formula omitted] space group structure: Ab initio study

The main objective of this work is to highlight several physical behaviors of two new compounds (MgS2 and MgSe2) in the cubic structure of the Pa-3 space group, particularly their mechanical and dynamical stabilities, their electronic behaviors and to provide a detailed analysis of bonding between the different atoms and the identification of weak interactions that occur between unbonded atoms. The found results have shown that the two studied compounds are mechanically and dynamically stable, which confirms their presence in the Pa-3 space group structure. The values of the lattice parameter of both compounds are close to the theoretical comparison ones. 3D directional analysis of several mechanical quantities (E, G and υ) has shown that both compounds are elastically anisotropic. The study of the electronic properties has been carried out by TB-mBJ potential, which accurately estimates the band gap energy. The found results have shown that the value of the direct band-gap is close to that of the indirect one, which highlights the optoelectronic importance of these two new compounds. QTAIM analysis has shown that S-S and Se-Se bonds have a strong covalent character, while Mg-S and Mg-Se are ionic. Using the NCI method, weak interactions analysis has made it possible to locate all weak/strong interactions that exist in the structure of the two studied compounds and to identify their attractive/repulsive natures.

Study of optical bandgap and other related optical properties in amorphous thin films of some optical materials of Se-Te-Sn-Ag system

Recently, the STSA samples of Se78-xTe20Sn2Agx (x = 0, 2, 4, 6) system were synthesized by the classical melt-quench route to get them in bulk form in our laboratory for electrical/thermal characterization. Now, we have prepared their thin films (TFs) using physical vapor deposition for their optical characterization. The optical properties of as-prepared TFs have been examined through their experimental transmission spectra by choosing 400 nm to 2500 nm spectral range. Initially, we have determined the indices of refraction and the absorption of TFs. Next, we have calculated the optical band gap Egopt by applying Tauc’s theory. The outcomes indicate that the value of Egopt is influenced intensely by the film composition. The linear dependency of photon energy that exists upon the absorption coefficient for the film gives Urbach energy Ee. The other parameters like loss functions of volume/surface energy, optical/electrical conductivity, and complex dielectric constant, were also determined. The increment in the value of the optical band gap with Ag incorporation in the parent SeTeSn (STS) system can be clarified by the binding energy of Se-Se and Se-Ag bonds.