Tetrasulfide Groups Research Articles

Open-Source and Reduced-Expenditure Nanosystem with ROS Self-Amplification and Glutathione Depletion for Simultaneous Augmented Chemodynamic/Photodynamic Therapy.

Reactive oxygen species (ROS)-induced cell apoptosis has emerged as an efficient strategy for cancer therapy. However, tumor hypoxia and insufficient amounts of endogenous hydrogen peroxide (H2O2) in the tumor microenvironment are currently the main limitations of photodynamic therapy (PDT) and chemodynamic therapy (CDT). Moreover, the glutathione (GSH) scavenging effect on ROS further hinders the efficiency of ROS-mediated therapy. Here, a CaO2-based nanosystem (named as CF@CO@HC) with ROS self-amplification and GSH-depletion abilities was developed by a bottom-up approach. This hybrid nanoparticle consisted of a photosensitizer-doped calcium peroxide (CaO2) core (CaO2-FM), a hybrid organosilica framework (Cu-ONS) incorporated with Fenton reagents (Cu2+) and tetrasulfide groups, and a local hydrophobic cage (HC) shell. The photosensitizer was fluorescein derivative 4-FM with a thermally activated delayed fluorescence (TADF) property. The HC shell was built to protect the CaO2 and the photosensitizer from being attacked by water. Upon being internalized into cancer cells, the nanosystem was decomposed through the reduction reactions of Cu2+ and the tetrasulfide bond-doped silica shell by GSH, thus releasing Cu+ for Cu+-mediated CDT. Meanwhile, the exposed CaO2-FM can react with H2O to liberate photosensitizer 4-FM and generate H2O2 and O2 to overcome barriers in CDT and PDT. Thus, our study provided an open-source and reduced-expenditure strategy via GSH depletion and ROS self-amplification behaviors for ROS generation and significantly achieved an improved synergistic PDT/CDT for cancers.

Synthesis of novel adsorbent based on tetrasulfide-functionalized fibrous silica KCC-1 for removal of Hg(II) cations

Hg(II) has been identified to be one of the extremely toxic heavy metals because of its hazardous effects and this fact that it is even more hazardous to animals than other pollutants such as Ag, Au, Cd, Ni, Pb, Co, Cu, and Zn. Accordingly, for the first time, tetrasulfide-functionalized fibrous silica KCC-1 (TS-KCC-1) spheres were synthesized by a facile, conventional ultrasonic-assisted, sol–gel-hydrothermal preparation approach to adsorb Hg(II) from aqueous solution. Tetrasulfide groups (–S–S–S–S–) were chosen as binding sites due to the strong and effective interaction of mercury ions (Hg(II)) with sulfur atoms. Hg(II) uptake onto TS-KCC-1 in a batch system has been carried out. Isotherm and kinetic results showed a very agreed agreement with Langmuir and pseudo-first-order models, respectively, with a Langmuir maximum uptake capacity of 132.55 mg g–1 (volume of the solution = 20.0 mL; adsorbent dose = 5.0 mg; pH = 5.0; temperature: 198 K; contact time = 40 min; shaking speed = 180 rpm). TS-KCC-1was shown to be a promising functional nanoporous material for the uptake of Hg(II) cations from aqueous media. To the best of our knowledge, there has been no report on the uptake of toxic Hg(II) cations by tetrasulfide-functionalized KCC-1 prepared by a conventional ultrasonic-assisted sol–gel-hydrothermal synthesis method.

Surface modification of oxidized carbon fibers by grafting bis(triethoxysilylpropyl) tetrasulfide (TESPT) and rubber sizing agent : Application to short carbon fibers/SBR composites

Bis(triethoxysilylpropyl) tetrasulfide (TESPT) with ethoxysilyl and tetrasulfide groups were grafted successfully on the oxidized short carbon fibers (CF) surface in order to create a strong continuous network between short CF and styrene butadiene rubber (SBR). The Hummer's method has been used for initial surface modification of short CF by solution oxidation (CF-OH) to establish hydroxyl groups required for the grafting process. Furthermore, a novel “rubber sizing agent” on the surface of short CF was applied by solution of SBR for the first time (CF-OH-g-TESPT-SBR). The surface of the modified short CF analyzed using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, thermal gravimetric analysis (TGA) and scanning electron microscopy (SEM) micrographs to confirm the oxidation, grafting of TESPT and rubber sizing agent onto the CF surface. Then the SBR reinforced with different loading of modified short CF composites were compounded in a two-roll mill. The highest value of electrical conductivity and thermal properties was achieved at 5 phr modified short CF in SBR composite. Tear strength was increased to 24.5% in the transverse direction of the modified short CF. This has agreement with the results of surface morphology of fracture and weight loss of the composites by SEM and TGA, respectively.

Tetrasulfide‐Functionalized Mesoporous Silica on Nanowire Ring Resonators for Detection of Aqueous Lead, Pb(II)

AbstractSilicon‐on‐insulator (SOI) microring resonators coated with tetrasulfide‐functionalized mesoporous silica (MPS) (S4‐MPS) are reported as sensors to detect Pb(II) ions in aqueous solutions from 10 ppb to 1 ppm. The sensors are based on the interaction of the evanescent field of the guided light with the functionalized mesoporous silica films. Upon absorption of metal ions, the resonant wavelengths of the microresonators shift due to the increased refractive index of the film. The sensors are exposed to aqueous solutions of Pb(II) ions at different concentrations and time‐resolved absorption–desorption curves are obtained. The concentrations of Pb(II) ions are determined using the Lorentz–Lorenz model. It is found that two distinct binding sites with different affinities for Pb(II) are present in the S4‐MPS silica films, corresponding to tetrasulfide groups and, likely, silanol groups. The number of available binding sites corresponds to 1/25 of the total number of S4‐groups. Equilibrium constants for absorption of Pb(II) to both binding sites are obtained from the rate constants for the absorption and desorption processes. The initial absorption rates depend linearly on the concentration of Pb(II) and are used to determine the 3σ limit of detection as 58 ppbm in deionized water and 350 ppbm in tap water.

Physicochemical effects of amino‐ or sulfur‐functional groups onto SBA‐15 sol‐gel synthesized mesoporous ceramic material

SBA‐15 mesoporous ceramics were synthesized by a sol‐gel method with some modifications and functionalized with ethylenediamine or tetrasulfide groups and using a sequential washing approach of organic solvent mixtures. The effects of the functional groups onto the physicochemical properties were characterized using XRD, TG/DTA, FTIR, N2 adsorption–desorption, TEM, SEM and NMR. These analyses showed that the SBA‐15 ceramic synthesized at low temperature shows a flat two‐dimensional hexagonal symmetry with pore diameters of 7.1 to 7.8 nm. In the meantime, the functionalized ethylenediamine SBA‐15 presented a narrow pore‐size distribution with diameter around 3.5 to 5.7 nm.A different behavior was observed on the tetrasulfide SBA‐15 showing a decrease in unit‐cell parameter, in pore size (∼ 2.5 nm) and an increase in pore wall size with loss in structural order and at high sulfur concentrations exhibited an amorphous structure. Results indicated that the lattice crystalline structure value of the SBA‐15 increased due to the amino‐functionalization process to a value of 13.48 nm respect to a value of 12.72 nm in SBA‐15 and decreased to 10.12 nm as an effect of the sulfur‐functionalization process, indicative of the effect of the amino and sulfur group into the well‐ordered hexagonal mesoporous structure of SBA‐15 ceramic materials.

Adhesion and Long-Term Barrier Restoration of Intrinsic Self-Healing Hybrid Sol-Gel Coatings.

Self-healing polymeric coatings aiming at smart and on-demand protection of metallic substrates have lately attracted considerable attention. In the present paper, the potential application of a dual network hybrid sol-gel polymer containing reversible tetrasulfide groups as a protective coating for the AA2024-T3 substrate is presented. Depending on the constituent ratio, the developed polymer exhibited a hydrophobic surface, high adhesion strength, and an effective long-term corrosion protection in 0.5 M NaCl solution. Upon thermal treatment, the healable hybrid sol-gel coating demonstrated full restoration of the barrier properties as well as recovery of the coating adhesion and surface properties (e.g., hydrophobicity and surface topology) necessary for lifetime extension of corrosion protective coatings. Excellent long-term barrier restoration of the coating was only obtained if the scratch width was less than the coating thickness.

Silica nanocapsules for redox-responsive delivery

Redox-responsive silica nanocapsules with a hydrophobic liquid core were synthesized by reactive templating of miniemulsion droplets with functional alkoxysilanes. Tetrasulfide bridges were successfully introduced into the inorganic shell and were found to be accessible for chemical reactions as shown by 31P-NMR spectroscopy. Indeed, the tetrasulfide groups could be reduced to yield thiol groups. A subsequent increase of permeability of the silica shell was observed upon reduction of the tetrasulfide groups.

Synthesis and properties of polysiloxane xerogels containing tetrasulfide groups

Polysiloxane xerogels with a functional group content of 1.1–1.9 mmol/g have been obtained by the hydrolytic condensation of the alkoxysilanes Si(OC2H5)4 and [(C2H5O)3Si(CH2)3S2]2 in the 2 : 1, 4 : 1, and 8 : 1 ratios. It has been demonstrated by 13C and 29Si CPMAS NMR spectroscopy that the xerogels have a polysiloxane framework with dipropyl tetrasulfide bridges, silanol groups, unhydrolyzed ethoxyl groups, and hydrogen-bonded water molecules on the surface. The xerogels have a porous structure. As the molar ratio of the reacting alkoxysilanes is increased in the above-specified range, the specific surface area of the xerogel increases (from 89 to 312 m2/kg) and the same is valid for other structure-adsorption characteristics. The synthesized polysiloxane xerogels readily sorb Hg2+ from acidified solutions. Their static sorption capacity can be as high as 1.5 g Hg per gram of sorbent. However, in the course of time, the 1 : 1 complexes forming on the xerogel surface undergo transformations accompanied by the release of mercury sulfide and/or Hg2+ reduction to mercury metal.

Clay modification and its effect on the physical properties of silicone rubber/clay composites

AbstractSodium montmorillonite (MMT) was modified with benzyldimethyltetradecylammonium* chloride (B13) to prepare M‐MMT. Treatment of MMT and M‐MMT with bis(3‐triethoxy silylpropyl) tetra sulfide (TEPTS) introduced tetra sulfide groups (TS) on the surface of the clays and yielded MMT‐TS and M‐MMT‐TS, respectively. A high temperature vulcanization silicone rubber (HTV) was compounded with MMT, MMT‐TS, M‐MMT, and M‐MMT‐TS, and the morphology of the resulting HTV/clay composites was analyzed by using the corresponding TEM images. The degree of swelling of the HTV composites in the toluene solution was measured to gauge their crosslinking density and thus to exclude the possibility that the enhanced mechanical properties came from increase in the crosslinking density. The greatly improved mechanical properties, as a result of the incorporation of the TEPTS‐modified clay into HTV, were attributed to the enhanced interaction owing to the plausible chemical reaction between the TEPTS‐modified clay and the HTV matrix. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Influence of clay modification on the reinforcement of vinyl‐terminated polydimethylsiloxane networks

AbstractA novel method was attempted to reinforce a vinyl‐terminated polydimethylsiloxane (PDMS) with two commercially available clays, sodium montmorillonite and Cloisite® 25A. The two clays were functionalized with bis(3‐triethoxysilylpropyl)tetrasulfide (TESPT) to prepare Na+MMTS4 and C25AS4, respectively. Incorporation of the tetrasulfide group‐containing clays, especially Na+MMTS4, was found to be effective for the enhancement of the interfacial interaction between PDMS and the clays by way of a plausible chemical reaction between the tetrasulfide groups (TSS) and the vinyl‐terminated PDMS. Compounding of PDMS with the TESPT‐modified clays improved the mechanical properties significantly. In particular, the elongation at break of PDMS/Na+MMTS4 composite was almost twice as high as that of neat PDMS, even if the silicate layers were not fully exfoliated in the PDMS matrix. The tear strength of PDMS was also improved greatly as a result of the incorporation of Na+MMTS4. According to toluene swelling test results, the crosslinking density of the composites was lower than that of neat PDMS, indicating that the improved mechanical properties of the composites arise from enhanced compatibility between the constituents and not from increased crosslinking density. Copyright © 2009 Society of Chemical Industry

Thermal stability and ablation properties of silicone rubber composites

AbstractEffects of incorporation of clay and carbon fiber (CF) into a high temperature vulcanized (HTV) silicone rubber, i.e., poly(dimethylsiloxane) (PDMS) containing vinyl groups, on its thermal stability and ablation properties were explored through thermogravimetric analyses (TGA) and oxy‐acetylene torch tests. Natural clay, sodium montmorillonite (MMT), was modified with a silane compound bearing tetra sulfide (TS) groups to prepare MMTS4: the TS groups may react with the vinyl groups of HTV and enhance the interfacial interaction between the clay and HTV. MMTS4 layers were better dispersed than MMT layers in the respective composites with exfoliated/intercalated coexisting morphology. According to TGA results and to the insulation index, the HTV/MMTS4 composite was more thermally stable than HTV/MMT. However, addition of CF to the composites lowered their thermal stability, because of the high thermal conductivity of CF. The time elapsed for the composite specimen, loaded with a constant weight, to break off after the oxy‐acetylene flame bursts onto the surface of the specimen was employed as an index for an integrated assessment of the ablation properties, simultaneously taking into consideration the mechanical strength of the char and the rate of decomposition. The elapsed time increased in the order of: HTV < HTV/CF ≈ HTV/MMTS4 < HTV/CF/MMTS4 ≈ HTV/MMT < HTV/CF/MMT. This order was different from the increasing order of the thermal stability determined by TGA results and the insulation index. The decreased degree of crosslinking of the composites with MMTS4 compared with that of the composite with MMT may be unfavorable for the formation of a mechanically strong char and could lead to early rupture of the HTV/MMTS4 specimen. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Stabilization of mesoporous silica films using multiple organosilanes

Mesoporous silica (MPS) thin films are attractive for electrically isolating Cu wiring in nanodevices. While porosity is conducive for realizing low-dielectric permittivity k necessary for low signal propagation delays, it renders the MPS susceptible to moisture uptake and metal diffusion. Here, we show that passivating MPS with more than one organosilane with different molecular termini provides several fold greater protection against such instabilities than improvements observed by functionalizing MPS with either type of organosilane individually. MPS films functionalized with bis[3-(triethoxysilyl)propyl] tetrasulfide (BTPTS) and trimethylchlorosilane (TMCS) exhibit at least three orders of magnitude greater time to dielectric breakdown. Bias thermal annealing and infrared spectroscopy measurements indicate that the increased stability is due to Cu blocking by the tetrasulfide groups in BTPTS and decreased moisture uptake is caused by hydrophobic passivation with TMCS. These findings are germane for realizing high-stability low k dielectrics for nanodevice architectures.

Preparation and mechanical properties of acrylonitrile‐butadiene‐styrene copolymer/clay nanocomposites

AbstractBis(3‐triethoxysilylpropyl) tetrasulfane (TSS) was reacted with the silanol groups of the commercially available clay, Closite®25A (C25A) to prepare TSS‐C25A, which was melt‐compounded with acrylonitrile‐butadiene‐styrene copolymer (ABS). The tetra sulfide groups of TSS‐C25A may chemically react with the vinyl groups of ABS to enhance the interaction between the clay and ABS. The ABS/clay composites exhibited much higher tensile strength and elongation at break than the neat ABS. Especially the elongation at break of ABS/TSS‐C25A composite was 5 times higher than that of neat ABS. The X‐ray diffraction patterns of the clay showed that the d001 basal spacing was enlarged from 1.89 nm to 2.71–2.86 nm as a result of the compounding with ABS. According to the thermogravimetric analysis, the thermal decomposition of the composite took place at a slightly higher temperature than that of neat ABS. Intercalated/exfoliated coexisting structures were observed by transmission electron microscopy for the ABS/clay composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008