Tetramethylsilane Research Articles

Tetrakis(trimethylsilyl)silane as a standard compound for fast spinning Solid-State NMR experiments

The development of magic angle spinning (MAS) at rates ranging from 30 kHz to greater than 100 kHz has substantially advanced solid-state nuclear magnetic resonance (SSNMR) spectroscopy 1H-detection methods. The small rotors required for such MAS rates have a limited sample volume and low 13C-detection sensitivity, rendering the traditional set of standard compounds for SSNMR insufficient or highly inconvenient for shimming and magic-angle calibration. Additionally, the reproducibility of magic angle setting, chemical shift referencing, and probe position can be especially critical for SSNMR experiments at high fields. These conditions suggest the need for a high signal-to-noise ratio (SNR) 1H-detection standard compound, which is preferably multi-purpose, to simplify instrument set up for ultra-fast MAS SSNMR instruments at high magnetic fields. In this study, we present the results for setting magic angle and shimming using tetrakis(trimethylsilyl)silane (TTMSS, or TKS), a tetramethylsilane (TMS) analogue, at near 40 kHz and demonstrate that we can achieve favorable results in less time but with equal or superior precision as traditional KBr and adamantane standards. The high SNR and TMS-like chemical shift of TKS also opens the possibilities for using TKS as an internal standard with biological samples. A single rotor containing a four-component mixture of TKS, adamantane, uniformly 13C, 15N-labeled N-acetyl valine and KBr was used to perform a complete configuration and calibration of a SSNMR probe without sample changes. We anticipate TKS as a standard compound to be especially effective at very high MAS conditions and to greatly simplify the instrument set up for high and ultra-high field SSNMR instruments.

Bias voltage influence on the a-SiCx:H interlayer deposition using tetramethylsilane: Decorative applications of a-C:H thin films on steel

Hydrogenated amorphous carbon (a-C:H) is a type of coating vastly applied on steel alloys due to its low friction coefficient, high hardness, and chemical inertness. Also, its characteristic brilliant black color like onyx stone is desirable for decorative applications. Despite the beneficial properties conferred to ferrous substrates, the adhesion of a-C:H films is weakened by its residual stress. In order to improve the adhesion of a-C:H films/steel alloy structures, one adopted strategy is the addition of an interlayer. This research investigated the influence of the bias voltage applied on the deposition of hydrogenated amorphous silicon carbide (a-SiCx:H) interlayers, with tetramethylsilane (TMS) as the precursor, to promote adhesion in a-C:H/a-SiCx:H/ferrous alloy structures for decorative applications. The thicker interlayer was achieved at −600 V. Two regimes were proposed to explain this behavior considering ionization rates and resputtering rates and chemical reactions in plasma. The chemical structure in different regions of the a-SiCx:H interlayer was analyzed in detail. An increase in the applied bias voltage leads to oxygen incorporation at the a-C:H/a-SiCx:H interface. Higher bias voltages result in lower silicon content at the a-SiCx:H/steel interface, which is correlated to the −800 V sample’s poor adhesion. Finally, we have included a discussion about a new range of loads when a decorative piece is held by the hand where the critical loads for delamination of a-C:H coatings measured here are good enough for decorative applications.

Improving the Through-Thickness Thermal Conductivity of Carbon Fiber/Epoxy Laminates by Direct Growth of SiC/Graphene Heterostructures on Carbon Fibers.

Poor thermal conductivity in the through-thickness direction is a critical limitation in the performance of carbon fiber-reinforced polymer (CFRP) composites over a broad range of applications in the aviation industry, where heat dissipation is required (e.g., battery packs, electronic housing, and heat spreaders). In this work, it is demonstrated for the first time that a hierarchical network of vertically oriented graphene nanoflakes (GNFs), with nanoconfined silicon carbide (SiC) nanocrystals, self-assembled on carbon fibers (CFs) can provide significant improvement to the thermal conductivity (TC) of CFRPs in the through-thickness direction. The vertically aligned SiC/GNF heterostructures were grown directly on CFs for the first time by single-step plasma-enhanced chemical vapor deposition (PECVD) employing tetramethylsilane (TMS) and methane (CH4) gases at temperatures of 800 and 950 °C. At the deposition temperature of 950 °C, the controlled introduction of SiC/GNF heterostructures induced a 56% improvement in through-thickness TC over the bare CFRP counterparts while simultaneously preserving the tensile strength. The increase in thermal conductivity is accomplished by SiC nanocrystals, which serve as linkage thermal conducting paths between the vertical graphene layers, further enhancing the smooth transmission of phonons in the vertical direction. The work demonstrates for the first time the unique potential of novel SiC/GNF heterostructures for attaining strong and thermally conductive multifunctional CFRPs.

Revisiting the initial reaction rates for TMS combustion and a new evidence for metastable silica nanoparticles in the gas-phase synthesis

Nanomaterials from gas-phase synthesis are tapping into new fields of application in research and industry due to their unique size-dependent properties. To produce tailored nanoparticles, the synthesis starting from the precursor decomposition to the particle formation must be fully understood. Tetramethylsilane is used as a precursor for the synthesis of silica nanomaterials in flames. The precursor starts to decompose by H-abstraction. Reaction rates for H-abstraction of tetramethylsilane (TMS) by +O/+H/+OH radicals are determined by means of quantum chemical calculations. The rate expressions are obtained in the temperature range from 300 to 1400 K: kH = 6,025,735 (T/K)2.1731exp(-(+2613.840 K)/T) cm3mol−1s−1 for the total bimolecular reaction coefficient of TMS with hydrogen atoms, kOH = 10,179,818 (T/K)1.7790 exp(-(+152.739 K)/T) cm3mol−1s−1 for TMS with OH radicals, and kO = 93,100 (T/K)2.4797 exp(-(+889.166 K)/T) cm3mol−1s−1 for TMS with O(3P) radicals, respectively. The reaction rates are implemented into the TMS reaction mechanism of Janbazi et al. [1], and a better agreement of the TMS reactivity in the flame is achieved. Experiments are conducted to obtain the mass deposition rates with a Quartz-Crystal-Microbalance (QCM) in a wide range of different equivalence ratios. The equivalence ratio is varied between ϕ = 0.6–1.2, and precursor amounts of 400, 600 and 800 ppm are used. These QCM-experiments are complementary to the MBMS-studies from Karakaya et al. [1–3] but use the same flame conditions to extend the data set. The results reveal that metastable particles exist in the reaction zone of the flame. Depending on flame conditions, their concentration decreases towards the end of the reaction zone, but particles subsequently grow again in the recombination zone of the flame. The mechanisms, which describe the reactivity of the metastable nanoparticles, are tentatively proposed. The understanding of the mechanisms can open up the way for tailored nanoparticles with different structures and stoichiometries.

Controlling of Chemical Bonding Structure, Wettability, Optical Characteristics of SiCN:H (SiC:H) Films Produced by PECVD Using Tetramethylsilane and Ammonia Mixture

PECVD SiC:H (SiCN:H) films were produced using tetramethylsilane (TMS) as a precursor in a mixture with inert helium or ammonia as a source of nitrogen. Mild plasma conditions were chosen in order to prevent the complete decomposition of the precursor molecules and promote the incorporation of the fragments of precursor into the film structure. The effect of deposition temperature and composition of gas mixture on the chemical bonding structure, elemental composition, deposition rate, and optical properties (transmittance, optical bandgap, and refractive index) of films have been examined. Use of the chosen deposition conditions allowed them to reach a relatively high deposition rate (up to 33 nm/min), compared with films produced in high plasma power conditions. Use of ammonia as an additional gas led to effective incorporation of N atoms in the films. The composition of the films moved from SiC:H to SiN:H with increasing of ammonia content to P(NH3)/P(TMS) = 1. The refractive index and optical bandgap of the films varied in the range of 1.55–2.08 and 3.0–5.2 eV, correspondingly, depending on the film composition and chemical bonding structure. The effect of treatment of SiCN films deposited at 400 °C by plasma of He, O2 or NH3 were studied by X-ray photoelectron spectroscopy, atomic force microscopy, and contact angle measurements. It was shown that plasma treatment significantly changes the surface characteristics. The water contact angle of the film was changed from 71 to 37° after exposure in the plasma conditions.

Robust Nuclear Magnetic Resonance (NMR) Spectroscopy Method for the Identification and Quantification of Phthalates in Fragments of Polyvinyl Chloride (PVC) Toys

An efficient nuclear magnetic resonance (NMR)-based method was developed to detect and quantify the presence of phthalates in plastic fragments obtained from a children’s toy and cosmetic product containers. Bis-2-ethyl hexyl phthalate (BEHP) was present at a concentration of 8.5% w/w in the plastic toy residue. This indicates levels of phthalates above the permitted threshold (e.g., <0.1% w/w) imposed by EU and USA regulations restricting the use of plasticizers in plastic toys for children aged 0 to 3 years. An added value of this method is that the tetramethylsilane (TMS) internal standard present at a concentration of 2.2 mmol/L in commercially available CDCl3 solvents may be conveniently used for the quantitative nuclear magnetic resonance (qNMR) analysis. The protocol described here is highly reproducible and may be easily applied to large scale investigations of plasticizers content into polyvinyl chloride (PVC) polymers.

Synthesis, vibrational spectra, Hirshfeld surface analysis, DFT calculations, and in silico ADMET study of 3-(2-chloroethyl)-2,6-bis(4-fluorophenyl)piperidin-4-one: A potent anti-Alzheimer agent

This study included experimental analysis, FT-Raman, FT-IR, UV-Vis and NMR with theoretical investigations of 3-(2-chloroethyl)-2,6-bis(p-fluorophenyl)piperidin-4-one [abbreviated as CEFP] molecule. To support experimental results, the DFT approach using the functional B3LYP and the basis set 6-311++G(d,p) performed theoretical quantum calculations (optimized structure and technical analyses). In gas phase, infrared and optimized calculations have been performed, whereas the NMR calculation was carried out using tetramethylsilane (TMS) solvation. The DFT/TD-DFT method was used to investigate the excited states of the CEFP compound's UV-Visible spectrum using the basis set 6-311++G(d,p). The Potential Energy Distribution Analysis (PED) of the title chemical was performed using VEDA4 software, and the findings were verified and matched to the FT-IR experimental spectral data. The surface of Hirshfeld on CEFP compound was performed utilizing the Crystal Explorer program. Topological (AIM, RDG) investigations were performed to investigate molecular characteristics. Furthermore, HOMO, LUMO, and MEP investigations of the title molecule were performed. The Molecular docking investigation among CEFP compound with the protein PDB: 6LVM was performed employing AutoDockVina software. Finally, the SwissADME web tool was used to investigate the CEFP molecule's physicochemical and pharmacokinetic properties.

Silicon-Carbide Nanocrystals from Nonthermal Plasma: Surface Chemistry and Quantum Confinement

Silicon-carbide (SiC) nanocrystals (NCs) of controlled 2–4 nm size are produced in low-pressure nonthermal plasma from the simple alkylsilane precursor tetramethylsilane (TMS). Generating material on the slightly carbon-rich side of 50/50 Si/C, we establish a process for thermally removing residual carbon, which in turn promotes a degree of intrinsic solubility in polar solvents such as isopropanol (IPA). Using the size-dependent Tauc gap of luminescent silicon NCs (Si NCs) as a point of reference, we demonstrate quantum confinement in nanocrystalline β-SiC but without measurable luminescence. Surface-sensitive spectroscopic techniques reveal an oxide shell surrounding a nanocrystalline SiC core, where negative surface charge groups promote solubility while likely acting as efficient trap states for nonradiative recombination. An analytical model is presented that combines electrostatic repulsion with van der Waals attraction to explain experimental observations of concentration-dependent cluster formation and reversible NC aggregation. We anticipate that these materials will be of interest for use as nanofillers in polymer composites and in specialty coatings, while providing a foundation for exploring routes to band gap emission from nanocrystalline SiC.

Determination of drug release profile of doxorubicin encapsulated in SLN with NMR spectroscopy

Solid lipid nanoparticles (SLN) have many various properties such as controlled drug release, elimination of side effects of drugs, etc. In this study, drug release study of SLN formulations was performed with Nuclear Magnetic Resonance (NMR) spectroscopy. Results obtained from NMR experiments were compared with other studies in the literature in which drug release of doxorubicin encapsulated in SLN formulations was carried out using High Pressure Liquid Chromatography (HPLC) and UV-VIS spectrophotometer. In NMR experiments, d6-DMSO and tetra methyl silane (TMS) were used as solvent and internal standard materials, respectively. Moreover, ferrocene was used as internal standard material in qNMR experiments. Doxorubicin was encapsulated in SLNs and after investigating the physicochemical properties of SLN formulations, specificity and selectivity of the qNMR method were evaluated by ratio of S/N ratio (signal/noise ratio) of singlet signal of doxorubicin to ratio of S/N ratio signal of ferrocene (internal standard material). Moreover, accuracy and precision of the qNMR method were evaluated. Results of qNMR method were validated. The results obtained from the qNMR method have been shown to be compatible with the results obtained from other traditional methods such as HPLC, UV-VIS, etc. It was also shown that the qNMR method is a simple and easy method for release of drugs encapsulated in SLNs. As a result, qNMR method is a suitable characterization method for determination of drug release of SLN formulations.

Supramolecular Nanohelix Fabricated by Pillararene-Based Host–Guest System for Chirality Amplification, Transfer, and Circularly Polarized Luminescence in Water

Supramolecular Nanohelix Fabricated by Pillararene-Based Host–Guest System for Chirality Amplification, Transfer, and Circularly Polarized Luminescence in Water

Comparative investigation on tetramethylsilane and neopentane combustion: Jet-stirred reactor pyrolysis and kinetic modeling

This work reports a comparative study on jet-stirred reactor (JSR) pyrolysis of tetramethylsilane (TMS) and neopentane at 1.04 bar and 770–1070 K. Gas chromatography (GC) was used to detect pyrolysis products and measure their mole fraction profiles versus heating temperature. TMS was observed to decompose about 70 K later than neopentane, showing a slower reactivity than its hydrocarbon counterpart. Hydrocarbon products such as methane, ethylene, ethane and propene were detected in the TMS pyrolysis, while besides TMS, no other Si-containing species was observed. Methane, acetylene, ethylene and isobutene were observed as dominant products in the neopentane pyrolysis. The pyrolysis models of TMS and neopentane were developed and validated against the present data, as well as the previous pyrolysis data of TMS. The available rate constants of SiC bond dissociation reaction were evaluated based on the mole fraction profiles of TMS in the present and previous pyrolysis work over a wide temperature region. The influence of methane-elimination reactions on the decomposition of TMS and neopentane was also discussed. Rate of production (ROP) analysis and sensitivity analysis were performed to provide insight into the fuel decomposition chemistry in both the TMS and neopentane pyrolysis. The SiC/CC bond dissociation reactions and methane-elimination reactions were concluded to be the crucial fuel consumption pathways in both the TMS and neopentane pyrolysis.

Diradicals or Zwitterions: The Chemical States of m -Benzoquinone and Structural Variation after Storage of Li Ions

Diradicals or Zwitterions: The Chemical States of <i>m</i> -Benzoquinone and Structural Variation after Storage of Li Ions

Synthesis of Silicon and Silicon Carbide Nanoparticles by Pulsed Electrical Discharges in Dielectric Liquids

Silicon carbide (SiC) has been widely used in many applications, which require high mechanical endurance or high electrical resistance. It also serves as a basic material for light emitting diodes. Here, we present an in-liquid plasma method to produce SiC nanoparticles. A sustained spark-discharge in a dielectric liquid, which is energized by a nanosecond pulsed power supply, is established for the synthesis. To provide Si and C, we employed graphite and silicon as electrodes and cyclohexane (CHX) and tetramethylsilane (TMS) as dielectric liquids. For a reasonable comparison, we tested various combinations of electrode and liquid, namely Si-to-C in CHX, Si-to-Si in CHX, and C-to-C in TMS. We found that discharges in CHX produce Si particles encapsulated in C-shell and Si nanoparticles in C-matrix. Meanwhile, discharges in TMS consistently produce SiC nanoparticles with an average size of ~ 10 nm, regardless of the electrode material.

Fabrication of Diamond Nanoneedle Arrays Containing High‐Brightness Silicon‐Vacancy Centers

AbstractThe optically active silicon‐vacancy (SiV) center in diamonds is an excellent candidate for quantum photonics and sensing applications. To date, optimizing the photoluminescence (PL) collection efficiency of SiV centers has proven difficult. To address this issue, the current study presents a simple two‐step method for preparing single‐crystalline diamond nanoneedle arrays. In the first step, silicon‐doped (001) textured diamond films are deposited with a mixture of microcrystalline and nanocrystalline grains in a microwave plasma CVD (MPCVD) system, using tetramethylsilane (TMS) gas as the dopant source. Subsequently, air annealing is used to selectively etch nanocrystalline diamond and sp2 amorphous carbon phases, while retaining the [001]‐oriented diamond nanoneedles with a curved top surface. In comparison to the as‐deposited films, the PL emission of SiV centers in these diamond nanoneedles is enhanced by a factor of up to 12.1. The finite‐difference time‐domain simulations further demonstrate that removing the nanocrystalline diamond and sp2 carbon from the sidewall of the diamond nanoneedles results in a remarkable increase in photoluminescence collection. Therefore, the findings have established for the first time the constraint effect of sp2 carbon on the optical collection of color centers at the sidewall rather than the top surface.

An Aggregation-Induced Emission Optical Highlighter for the Studies of Endoplasmic Reticulum-Lipid Droplet Content Dynamics

An Aggregation-Induced Emission Optical Highlighter for the Studies of Endoplasmic Reticulum-Lipid Droplet Content Dynamics

An Integration Strategy to Develop Dual-State Luminophores with Tunable Spectra, Large Stokes Shift, and Activatable Fluorescence for High-Contrast Imaging

An Integration Strategy to Develop Dual-State Luminophores with Tunable Spectra, Large Stokes Shift, and Activatable Fluorescence for High-Contrast Imaging

Bisindole [3]arenes—Indolyl Macrocyclic Arenes Having Significant Iodine Capture Capacity

Bisindole [3]arenes—Indolyl Macrocyclic Arenes Having Significant Iodine Capture Capacity

Multistimuli-Responsive Fluorescent Organometallic Assemblies Based on Mesoionic Carbene-Decorated Tetraphenylethene Ligands and Their Applications in Cell Imaging

Multistimuli-Responsive Fluorescent Organometallic Assemblies Based on Mesoionic Carbene-Decorated Tetraphenylethene Ligands and Their Applications in Cell Imaging

Separation and identification of impurities from intermediates of istradefylline

伊曲茶碱是一种新型选择性腺苷A2A受体拮抗剂,用于治疗帕金森氏病和改善帕金森氏病初期运动障碍。在伊曲茶碱中间体A1(6-氨基-1,3-二乙基-2,4-(1H,3H)-嘧啶二酮)的合成过程中,碱性条件或高温条件下会伴随生成至少2种副产物,在前期研究中我们已经对该中间体合成过程中的其中一种副产物进行过研究,确定其结构为(E)-N-乙基-2-氰基-3-乙氨基-2-丁烯酰胺。本文采用高效液相色谱(HPLC)对中间体A1的另外一种杂质进行分析:称取0.4 g中间体放入50 mL的烧杯中,依次加入8 mL水、8 mL乙腈,超声溶解,经0.45 μm有机膜过滤,得到测试样品溶液。采用Agilent Zorbax C18色谱柱(150 mm×4.6 mm, 5 μm)分离,柱温35 ℃,流动相为乙腈(A)和水(B),梯度洗脱(tmin/A∶B)=t0/20∶80, t15/60∶40, t20~t50/90∶10;流速1.0 mL/min;检测波长268 nm。然后通过Ceres B制备色谱柱分离,以乙腈-水(30/70, v/v)为流动相,流速为30 mL/min,在268 nm波长下检测,洗脱得到杂质纯品。通过高分辨率质谱(HRMS)、一维核磁共振(NMR)、二维核磁共振(2D NMR)对杂质进行了结构确认,并通过单晶X射线衍射(XRD)进行了表征。杂质经分析确认为1-(1,3-二乙基-2,6-二氧-1,2,3,6-四氢嘧啶-4-基)-3-乙基脲。根据杂质的化学结构推测其生成机理为:在碱性条件或高温条件下合成中间体A1时,过量的二乙基脲继续与中间体A1发生酰胺化反应而得到此副产物。此杂质与伊曲茶碱中间体A1结构相似,会伴随A1参与到伊曲茶碱合成的后续反应中,并对伊曲茶碱的安全性和有效性产生潜在的影响。因此,为了确保伊曲茶碱的质量,在生产过程中需要对该杂质的含量进行控制。

Synthesis and structural elucidation of a series of isoflavones-based on FPR antagonists

Synthesis and structural elucidation of a series of isoflavones-based on FPR antagonists