Theoretical Investigations on Thermal Rearrangement Reactions of (Aminomethyl)silane

Thermal rearrangement reactions of (aminomethyl)silane H3SiCH2NH2 were studied by ab initio calculations at the G3 level. The results show that two dyotropic reactions could happen when H3SiCH2NH2 is heated. In one reaction, the silyl group migrates from the carbon to the nitrogen atom while a hydrogen atom shifts from the nitrogen to the carbon atom, forming (methylamino)silane CH3NHSiH3 (reaction A). This reaction can proceed via three paths:  a path involving two consecutive steps with two transition states and one intermediate metastable carbene species (A-1); and two concerted paths (A-2 and A-3). In the other reaction, the amino group migrates from the carbon to the silicon atom while a hydrogen atom shifts from the silicon to the carbon atom, via a double three-membered ring transition state, forming aminomethylsilane CH3SiH2NH2 (reaction B). Reaction rate constants, changes (ΔS⧧, ΔH, and ΔG) in thermodynamic functions and equilibrium constants of the reactions were calculated with the MP2(full)/6-311G(d,p) optimized geometries, harmonic vibrational frequencies and G3 energies of reactants, transition states, intermediates and products with statistical mechanical methods and the conventional transition-state theory (TST) with Wigner tunneling approximation over a temperature range 400−1800 K

Correction to “Effect of Counterions on Micellization of Pyrrolidinium Based Silicone Ionic Liquids in Aqueous Solutions”

Correction to “Effect of Counterions on Micellization of Pyrrolidinium Based Silicone Ionic Liquids in Aqueous Solutions

Theoretical Study on the Substitution Reactions of Silylenoid H₂SiLiF with CH₄, NH₃, H₂O, HF, SiH₄, PH₃, H₂S, and HCl

DFT calculations at the B3LYP/6-31G(d,p) level have been performed to explore the substitution reactions of silylenoid H2SiLiF with XHn hydrides, where XHn = CH4, NH3, H2O, HF, SiH4, PH3, H2S, and HCl. We have identified a previously unreported reaction pathway on each reaction surface, H2SiLiF + XHn → H3SiF + LiXHn-1, which involved the initial formation of an association complex via a five-membered cyclic transition state to form an intermediate followed by the substituted product H3SiF with LiXHn-1 dissociating. These theoretical calculations suggest that (i) there is a very clear trend toward lower activation barriers and more exothermic interactions on going from left to right along a given row in the periodic table, and (ii) for the second-row hydrides, the substitution reactions are more exothermic than for the first-row hydrides and the reaction barriers are lower. The solvent effects were considered by means of the polarized continuum model (PCM) using THF as a solvent. The presence of THF solvent disfavors slightly the substitution reaction. Compared to the previously reported insertions and H2-elimination reactions of H2SiLiF and XHn, the substitution reactions should be most favorable

Computational Modeling Study on Formation of Acyclic Clavulanate Intermediates in Inhibition of Class A β-Lactamase: Water-Assisted Proton Transfer

Molecular dynamics (MD) simulation and quantum chemical (QC) calculations were used to investigate the reaction mechanism of the formation of acyclic clavulanate intermediates in the inhibition of class A β-lactamase. The initial model for QC calculations was derived from an MD simulation. It was composed of a substrate clavulanate and four residues (Ser70, Gln237, Ser130, and Ser216), which form hydrogen bonds with the substrate. The QC calculation results indicate that the oxazolidine ring can undergo cleavage by proton transfer, which yields not only imine but also enamine products. A new mechanism involving hydrogen transfer from C6 to O1 has been suggested. Besides, MD simulation provided evidence that the water molecule can catalyze the proton transfer, and QC calculation shows water assistance can decrease the energy barrier greatly

An ab Initio Study on Thermal Rearrangement Reactions of 1-Silylprop-2-en-1-ol H₃SiCH(OH)CHCH₂

The thermal rearrangement reactions of 1-silylprop-2-en-1-ol H3SiCH(OH)CHCH2 were studied by ab initio calculations at the G2(MP2) and G3 levels. The reaction mechanisms were revealed through ab initio molecular orbital theory. On the basis of the MP2(full)/6-31G(d) optimized geometries, harmonic vibrational frequencies of various stationary points were calculated. The reaction paths were investigated and confirmed by intrinsic reaction coordinate (IRC) calculations. The results show that the thermal rearrangements of H3SiCH(OH)CHCH2 happen in two ways. One is via the Brook rearrangement reactions (reaction A), and the silyl group migrates from carbon atom to oxygen atom passing through a double three-membered ring transition state, forming allyloxysilane CH2CHCH2OSiH3. In the other, the reactant undergoes a dyotropic rearrangement; the hydroxyl group migrates from carbon atom to silicon atom coupled with a simultaneous migration of a hydrogen atom from silicon atom to carbon atom, forming allylsilanol CH2CHCH2SiH2OH (reaction B). The barriers for reactions A and B were computed to be 343.5 and 203.7 kJ/mol, respectively, at the G3 level. The changes of the thermodynamic functions, entropy (ΔS), entropy (ΔS⧧) for the transition state, enthalpy (ΔH), and free energy (ΔG) were calculated by using the MP2(full)/6-31G(d) optimized geometries, and harmonic vibrational frequencies of reactants, transition states, and products with statistical mechanical methods, and equilibrium constant K(T) and reaction rate constant k(T) in canonical variational transition-state theory (CVT) with centrifugal-dominant small-curvature tunneling approximation (SCT) were calculated over a temperature range 400−1300 K. The conventional transition-state theory (TST) rate constants were also calculated for the purposes of comparison. The influences of the vinyl group attached to the center carbon of the α-silyl alcohols on reactions were discussed

Synthesis and Solution Behavior of Sulfonate-Based Silicone Surfactants with Specific, Atomically Defined Hydrophobic Tails

A series of sulfonate-based silicone surfactants with different hydrophobic groups were synthesized. Two synthetic strategies are introduced to permit exquisite control over the hydrophobic moieties. Solution behavior of these surfactants was investigated by surface tensiometry, electrical conductivity, transmission electron microscopy, and dynamic light scattering. The results indicate that the aqueous behavior of the surfactants was distinctly influenced by the hydrophobic groups. Subtle distinctions in surfactant-related properties, which can be attributed to the three-dimensional molecular structures of the surfactants, can be seen for compounds with different hydrophobic moieties. Contact angle results of these surfactants indicate that they have super dispersal ability with the potential value in agriculture

3D Macroporous and Mesoporous Sponge for Selective Pollutant Removal

Three-dimensional (3D) hierarchically porous materials are widely used owing to their unique pore structures and rich specific surface areas. Herein, we design a 3D macroporous and mesoporous silicone sponge via a one-pot efficient thiol oxidative coupling reaction between polysiloxanes and HS-modified mesoporous polymers. The diameters of the macropores and mesopores are higher and lower than 50 nm, respectively. The sponge possesses a surface area of 20.72 m2 g–1, a porosity of 61.39%, and good compression and thermal insulation properties. A dye adsorption evaluation confirmed that the sponge selectively removed cation dyes from a mixed dye solution. This synthesis method for 3D macroporous and mesoporous sponges can potentially synthesize composites of other mesoporous materials

DataSheet1_Tannic Acid as a Natural Crosslinker for Catalyst-Free Silicone Elastomers From Hydrogen Bonding to Covalent Bonding.docx

The construction of silicone elastomers crosslinked by a natural crosslinker under a catalyst-free method is highly desirable. Herein we present catalyst-free silicone elastomers (SEs) by simply introducing tannic acid (TA) as a natural crosslinker when using poly (aminopropylmethylsiloxane-co-dimethylsiloxane) (PAPMS) as the base polymer. The crosslinked bonding of these SEs can be easily changed from hydrogen bonding to covalent bonding by altering the curing reaction from room temperature to heating condition. The formability and mechanical properties of the SEs can be tuned by altering various factors, including processing technique, the amount of TA and aminopropyl-terminated polydimethylsiloxane, the molecular weight and -NH2 content of PAPMS, and the amount of reinforcing filler. The hydrogen bonding was proved by the reversible crosslinking of the elastomers, which can be gradually dissolved in tetrahydrofuran and re-formed after removing the solvent. The covalent bonding was proved by a model reaction of catechol and n-decylamine and occurred through a combination of hydroxylamine reaction and Michael addition reaction. These elastomers exhibit good thermal stability and excellent hydrophobic property and can bond iron sheets to hold the weight of 500 g, indicating their promising as adhesives. These results reveal that TA as a natural product is a suitable “green” crosslinker for the construction of catalyst-free silicone elastomers by a simple crosslinking strategy. Under this strategy, TA and more natural polyphenols could be certainly utilized as crosslinkers to fabricate more organic elastomers by selecting amine-containing polymers and further explore their extensive applications in adhesives, sealants, insulators, sensors, and so forth.</p

Catalytic and Thermal 1,2-Rearrangement of (α-Mercaptobenzyl)trimethylsilane

The mechanisms of catalytic and thermal 1,2-rearrangement of (α-mercaptobenzyl)trimethylsilane were studied by using density functional theory (DFT) at the MP2/6-31+G(d,p)//B3LYP/6-31G(d) levels. The results show that (α-mercaptobenzyl)trimethylsilane rearranges to (benzylthio)trimethylsilane through a trimethylsilyl group migration from C to S atom via a transition state of pentacoordinate Si atom with or without radical initiators. The low reaction activation energy (15.1 kcal/mol) is responsible for the fast rearrangement in the presence of radical initiators. Both radical and nonradical thermal rearrangement mechanisms were suggested, and the radical mechanism dominates through its self-catalyzing. These results are consistent with the experiment results. The activation energy (ΔHact = 15.1 kcal/mol) for the rate-determining step within the self-catalytic cycle is low enough to make (trimethylsilylbenzyl)thiyl radical be a reasonable catalyst for the thermal rearrangement. The catalytic and thermal 1,2-rearrangement mechanisms of (α-mercaptobenzyl)trimethylsilane, especially the self-catalytic radical mechanism, were revealed for the first time. The comparison of the rearrangement mechanisms between (α-mercaptobenzyl)trimethylsilane and silylmethanethiol discloses the factors in determining the reaction mechanism of such kinds of mercaptoalkyl-functionalized organosilanes. The phenyl group is found to be favorable for the radical rearrangement, thus making (α-mercaptobenzyl)trimethylsilane instable