Silicon Moiety Research Articles

Methoxydioxasilepane: A Versatile and Stable Synthetic Precursor of Trimethoxysilane

AbstractThis study introduces aryl(methoxy)dioxasilepane as a versatile and stable precursor for aryl(trimethoxy)silanes. We conducted a quantitative assessment of the stability of this silicon moiety under acidic and basic conditions, demonstrating its superior stability compared to triethoxysilane, and methyl- or (trifluoroethoxy)dioxasilepanes. The synthetic utility of the methoxydioxasilepane unit was further elucidated through an examination of its orthogonality and selective functionalization capabilities. Notably, we developed an efficient method for the conversion of methoxydioxasilepane into trimethoxysilane. This method underscores the potential of a methoxydioxasilepane as a surrogate in multistep syntheses of silanetriols, which offer advantages in the development of silicon-based bioisosteres for medicinal chemistry applications.

Silicon-Containing Thiol-Specific Bioconjugating Reagent.

A new bioconjugation reagent containing silicon has been developed for the selective reaction with thiols. The inclusion of silicon significantly improves chemoselectivity and suppresses retro processes, thereby exceeding the capabilities of traditional reagents. The method is versatile and compatible with a broad range of thiols and unsaturated carbonyl compounds and yields moderate to high results. These reactions can be conducted under biocompatible conditions, thereby making them suitable for protein bioconjugation. The resulting conjugates display good stability in the presence of various biomolecules, which suggests their potential application for the synthesis of antibody-drug conjugates. Furthermore, the presence of a silicon moiety within the conjugated products opens up new avenues for drug release and bridging inorganics with other disciplines. This new class of silicon-containing thiol-specific bioconjugation reagents has significant implications for researchers working in bioanalytical science and medicinal chemistry and leads to innovative opportunities for advancing the field of bioconjugation research and medicinal chemistry.

Thiol-Specific Silicon-Containing Conjugating Reagent: β-Silyl Alkynyl Carbonyl Compounds.

Site-specific modification of thiol-containing biomolecules has been recognized as a versatile and powerful strategy for probing our biological systems and discovering novel therapeutics. The addition of lipophilic silicon moiety opens up new avenues for multi-disciplinary research with broad applications in both the medicinal and material sciences. However, adhering to the strict biocompatibility requirements, and achieving the introduction of labile silicon handle and high chemo-selectivity have been formidable. In this paper, we report silicon-based conjugating reagents including β-trialkylsilyl and silyl ether-tethered alkynones that selectively react with thiols under physiological conditions. The pH-neutral, metal-free and additive-free reaction yields stable products with broad substrate compatibility and full retention of silicon handles in most cases. Besides simple aliphatic and aromatic thiols, this approach is applicable in the labeling of thiols present in proteins, sugars and payloads, thereby expanding the toolbox of thiol conjugation.

Thiol‐Specific Silicon‐Containing Conjugating Reagent: β‐Silyl Alkynyl Carbonyl Compounds

AbstractSite‐specific modification of thiol‐containing biomolecules has been recognized as a versatile and powerful strategy for probing our biological systems and discovering novel therapeutics. The addition of lipophilic silicon moiety opens up new avenues for multi‐disciplinary research with broad applications in both the medicinal and material sciences. However, adhering to the strict biocompatibility requirements, and achieving the introduction of labile silicon handle and high chemo‐selectivity have been formidable. In this paper, we report silicon‐based conjugating reagents including β‐trialkylsilyl and silyl ether‐tethered alkynones that selectively react with thiols under physiological conditions. The pH‐neutral, metal‐free and additive‐free reaction yields stable products with broad substrate compatibility and full retention of silicon handles in most cases. Besides simple aliphatic and aromatic thiols, this approach is applicable in the labeling of thiols present in proteins, sugars and payloads, thereby expanding the toolbox of thiol conjugation.

A novel approach to achieve semi-sustained drug delivery to the eye through asymmetric loading of soft contact lenses

Soft contact lenses are increasingly being explored as a vehicle for controlled delivery of ophthalmic drugs. However, traditional methods of drug-loading by soaking have limitations such as burst delivery and the release of drugs at the front side of the lens, leading to poor drug efficacy and systemic side effects. This study introduces a new methodology, termed asymmetric drug loading, whereby the ophthalmic drug ‘Rebamipide’ is attached to and released from the post-lens (=cornea-contacting) surface exclusively. The methodology involves using polymeric microparticles that carry a lipophilic crystalline ophthalmic drug at their surface. These drug-loaded microparticles first transfer the drug to the concave surface of the contact lens, and when worn, the drug is transferred again, now from the lens to the cornea. This is achieved through the diffusion of the drug from one hydrophobic microenvironment (the silicone moieties of the contact lens polymer network) to another hydrophobic microenvironment (the corneal epithelium) over a short pathway. The second drug transfer was observed and studied in experiments using an ex vivo porcine eye model. The results show that the drug amount that was absorbed by the cornea after applying the rebamipide-loaded contact lenses is approximately 3× (10.7 ± 3.1 μg) as much as the amount of rebamipide that gets transferred after the instillation of one eye drop (1% solution (p < 0.001). The new drug-loading method offers a practical and reproducible means of delivering ophthalmic drugs to the cornea through soft contact lenses. The drug payloads achieved are comparable to dosages used during eye drop therapy.

Silicone-specific identification of trace polydimethylsiloxanes in wines with 2D-diffusion-ordered nuclear magnetic resonance spectroscopy (DOSY-NMR)

Present work stresses a novel analytical approach for increasing the specificity of standard NMR approaches for identifying polydimethylsiloxane (PDMS) and further silicone moieties in wines’ organic extracts, by including a second dimension that correlates chemical shifts with diffusion coefficients by means of pulsed-field gradient diffusion ordered spectroscopy (DOSY-NMR). Each silicone source in wines is unambiguously assigned by correlation of both local chemical environments and by a unique diffusion coefficient value, in turn related to a hydrodynamic radius (RH) that can be obtained with respect proper internal standards. Obtained PDMS diffusion coefficient values and hydrodynamic radii in wines’ extracts, in agreement with expected values, present a selectivity and specificity so far not reported, that positions DOSY-NMR spectroscopy as an alternative in oenology for controlling PDMS limits.

Diastereoselective and Synergistic Gold‐Catalyzed Bispropargylation of Xanthones and Thioxanthones: An Access to Xanthene Derivatives

AbstractA gold‐catalyzed bispropargylation of xanthone derivatives is described. The use of propargylsilanes permits to achieve a deoxygenative bispropargylation through a double catalytic addition of the corresponding allenylgold intermediate to the synergistically activated carbonyl moiety. This methodology works in a diastereoselective manner either with xanthone or thioxanthone derivatives. Monopropargylated xanthydrol silyl ethers were isolated as reaction intermediates and these species could be transformed into symmetrical and non‐symmetrical bispropargylated xanthenes. The formation of non‐symmetrical bispropargylated xanthenes could also be achieved through an one‐pot procedure. Finally, other interesting structures, such as propargylxanthylidenes, propargylxanthenes and bispropargylated xanthenes replacing the silicon moiety, were accessible following different one‐pot synthetic methodologies. In addition, bispropargylated xanthenes could perform a carbonylative [2+2+1] formal cycloaddition.magnified image

Novel phosphorus-containing silazanes as flame retardants in epoxy resins

Molecules containing different elements and moieties like P-N and P-O-Si have high impact on flame retardant properties. In this study, a novel group of flame retardants based on phosphasilazanes containing a P-N-Si structure is established. Due to introduction of the silazane moiety to various phosphorus environments, further properties, like mechanical or thermal, besides flame retardancy can be altered. The influence of phosphorus or silicon moieties and their mode of action on flame retardant properties is examined. In formulations with a high-performance epoxy resin, thermal properties (glass transition temperature and moisture absorption) and flame retardant performance (UL94 vertical burning test, cone calorimetry) are investigated. Alteration of chemical environment at the phosphorus atom determines various implications on burning behavior. For example, phosphorus-containing moieties promoting char generation and intumescence enhance char yields and other parameters describing flame retardant properties of phosphasilazanes in thermo-analysis as well as in cone calorimetry. On the other hand, higher concentration of silazane groups in the structure leads to higher flammability. Phosphorus moieties acting in gaseous phase cause poor flame retardant properties because they antagonize the char generation of silazanes.

Li8 Si8 , Li10 Si9 , and Li12 Si10 : Assemblies of Lithium-Silicon Aromatic Units.

We report the global minima structures of Li8 Si8 , Li10 Si9 , and Li12 Si10 systems, in which silicon moieties maintain structural and chemical bonding characteristics similar to those of their building blocks: the aromatic clusters Td -Li4 Si4 and C2v -Li6 Si5 . Electron counting rules, chemical bonding analysis, and magnetic response properties verify the silicon unit's aromaticity persistence. This study demonstrates the feasibility of assembling silicon-based nanostructures from aromatics clusters as building blocks.

Brief descriptions of the principles of prominent methods used to study the penetration of materials into human hair and a review of examples of their use.

Consumers are attracted to the latest fashion trends and different looks. This drives the search for novel hair treatments. Some chemicals present in hair treatment products can penetrate the hair shaft. These materials can either nourish or injure the hair cortex. Different techniques have been used to investigate the mechanism of molecule penetration and the conditions under which penetration occurs. This article reviews the techniques applied for this purpose. Various microscopy techniques are used to capture clear and colourful images to determine the diffusion pathways and the exact location of the molecules under study. However, the laborious sample preparation often leads to sample destruction since cross-sectioning is often required. While various other techniques have been successfully used for investigating the penetration methods, most of these require different amounts of work to be put in for sample preparation and instrumentation. Several spectroscopic techniques have been used to study the penetration of the molecules because of the high levels of accuracy and the quick response time of these techniques. Moreover, the samples are not damaged during the investigation.

Chromium(III) catalysts based on tridentate silicon-bridged tris(diphenylphosphine) ligands for selective ethylene tri-/tetramerization

The chromium(III) catalysts based on tridentate silicon-bridged tris(diphenylphosphine) ligands of the form RSi(CH2PPh2)3 (L1: R = Me; L2: R = Cy; L3: R = Ph) were investigated for selective ethylene tri-/tetramerization. The steric and electronic properties of the substituents attached to the silicon moiety have been observed to have a great impact on the catalytic performance of these catalysts. Single-crystal analysis, high-resolution mass spectrometry (HR-MS), and elemental analysis revealed that these complexes may adopt mononuclear tridentate coordination mode (k3-P, P, P) with Cr center. However, one of the phosphorus atoms in these complexes may act as a hemilabile donor and presumably loses its coordination with chromium in the presence of a competent donor which consequently transformed the tridentate complexes to bidentate (k2-P, P) coordination mode. Backbone modification of L1 of the precatalyst 1 via successive abstraction of methylene spacers may offer MeSi(CH2)n(PPh2)3 (L4: n = 2; L5: n = 1; L6: n = 0) type chromium(III) complexes. Ethylene oligomerization of these systems suggested that the methylene spacers may effectively tune the complex structure and catalytic performance. Precatalyst 1 and 4 respectively based on L1 and L4 deliver 70% C8 selectivity in the liquid oligomeric fraction and considerable activity under experimental conditions. DFT investigations based on catalyst 4 revealed that the catalyst may simultaneously facilitate the single and double coordination pathways for C8 formation, however, the single coordination pathway is thermodynamically more favorable for this system.

Divergent Gold‐Catalyzed Rearrangement of 1‐Alkenyl‐2‐alkynylcyclopropanes: Enyne Transformation Controlled by a Silicon Moiety

AbstractHere we report a gold(I)‐catalyzed rearrangement for a special type of alkynylcyclopropanes, such as (6‐ethynylbicyclo[3.1.0]hex‐2‐en‐6‐yl)silanes. These enynes evolved through an isomerization reaction towards the formation of isomeric alkynylcyclopropanes instead of the expected alkynylcyclohexadienes. A computational study on the reaction mechanism revealed the participation of a polycyclic gold(I) carbene complex as intermediate instead of a σ‐allylic gold cation which is in agreement with the expected influence in the energy of those intermediates due to the presence of the silyl group. Finally, this gold(I) carbene intermediate could be experimentally intercepted through intramolecular cyclopropanations.magnified image

Investigation of the migration ability of silicone and properties of waterborne polyurethanes

A series of silicone–waterborne polyurethanes (WPU) are prepared by a pre–polymer method based on poly(tetramethylene ether glycol), isophorone diisocyanate, and polydimethylsiloxane (PDMS). The effect of the molecular weight of PDMS and film–forming temperature on the properties of WPU are investigated. The hydrophobicity of the films is characterized by X–ray photoelectron spectroscopy, contact angle and water absorbed measurements. With increasing molecular weight of PDMS in the WPU films, the contact angles increase, surface free energies decrease, and a substantial enrichment of silicon moieties at the film–air interface is observed. As the film–forming temperature increases, more silicone migrates to the film–air interface, which improves the hydrophobicity of the film bulk. The extent of variable phase separation caused by the mobility and incompatibility between silicone and the WPU segment is observed in the matrix of the WPU films by scanning electron microscopy. The degree of phase separation increases with the molecular weight of PDMS and film–forming temperature.

Copper-Catalyzed Enantioselective and Exo-Selective Addition of Silicon Nucleophiles to 7-Oxa- and 7-Azabenzonorbornadiene Derivatives.

An enantioselective formal hydrosilylation of 7-oxa- and 7-azabenzonorbornadiene derivatives is reported. The exo-selective addition of the silicon moiety across these strained alkenes is achieved under copper catalysis, employing Si-B reagents as silicon pronucleophiles in the presence of an alkoxide base. No ring opening is observed. While successful for those substrates, the same procedure cannot be applied to benzonorbornadiene, norbornadiene, or norbornene.

PQ Group Holdings expands polyolefin catalysts portfolio through an agreement with INEOS

The chromium(III) catalysts based on tridentate silicon-bridged tris(diphenylphosphine) ligands of the form RSi(CH2PPh2)3 (L1: R = Me; L2: R = Cy; L3: R = Ph) were investigated for selective ethylene tri-/tetramerization. The steric and electronic properties of the substituents attached to the silicon moiety have been observed to have a great impact on the catalytic performance of these catalysts. Single-crystal analysis, high-resolution mass spectrometry (HR-MS), and elemental analysis revealed that these complexes may adopt mononuclear tridentate coordination mode (k3-P, P, P) with Cr center. However, one of the phosphorus atoms in these complexes may act as a hemilabile donor and presumably loses its coordination with chromium in the presence of a competent donor which consequently transformed the tridentate complexes to bidentate (k2-P, P) coordination mode. Backbone modification of L1 of the precatalyst 1 via successive abstraction of methylene spacers may offer MeSi(CH2)n(PPh2)3 (L4: n = 2; L5: n = 1; L6: n = 0) type chromium(III) complexes. Ethylene oligomerization of these systems suggested that the methylene spacers may effectively tune the complex structure and catalytic performance. Precatalyst 1 and 4 respectively based on L1 and L4 deliver 70% C8 selectivity in the liquid oligomeric fraction and considerable activity under experimental conditions. DFT investigations based on catalyst 4 revealed that the catalyst may simultaneously facilitate the single and double coordination pathways for C8 formation, however, the single coordination pathway is thermodynamically more favorable for this system.

Understanding hydrogen bonding in calcium silicate hydrate combining solid-state NMR and first principle calculations

Mechanisms of hydrogen bonding and molecular structure in the C-S-H are investigated by combining results of 29Si, 1H solid SSNMR analysis and first principle calculations. First principle calculations for 1H chemical shifts are used to correlate the observed 1H SSNMR spectra with the underlying structure of various hydrogen bonds between different silicon moieties and hydrogen groups in the C-S-H gels. The results show that strong hydrogen bonds are formed between water and terminal silicate sites or silanols, between adjacent terminal silanols and terminal silicate sites, between water or terminal silanols and hydroxyl groups bonded with interlayer calcium ions. Strong hydrogen bonds are favored to form in C-S-H with high Ca/Si molar ratios. The hydrogen bonding in terminal silicate sites is stronger than those in the paring or bridging silicate sites. New insights into the changes of basal spacing, Ca/Si ratio and H2O/Si ratio of in the molecular structure of C-S-H are presented based on the mechanism of hydrogen bonding.

Vinyl Cation Stabilization by Silicon Enables a Formal Metal-Free α-Arylation of Alkyl Ketones.

The ability of silicon to stabilize vinyl cationic species leads to a redox arylation of alkynes whereby the stringent limitations of reactivity and regioselectivity of alkyl‐substituted alkynes are lifted. This allows the synthesis of a range of α‐silyl‐α′‐arylketones under mild conditions in good to excellent yields and with high functional group tolerance, whereby the silicon moiety in the final products can either be removed for a formal acetone monoarylation transform, or capitalized upon for subsequent electrophilic substitutions at either side of the carbonyl group.

Highly Bent 1,3-Digerma-2-silaallene.

A 1,3-digerma-2-silacyclopenta-1,2-diene, that is, a 1,3-digerma-2-silaallene incorporated into a five-membered ring system, was synthesized and obtained as a stable orange solid. Owing to incorporation into a cyclic framework, the 1,3-digerma-2-silaallene moiety is highly bent, exhibiting a Si0 character for the central silicon moiety.

Highly Bent 1,3‐Digerma‐2‐silaallene

AbstractA 1,3‐digerma‐2‐silacyclopenta‐1,2‐diene, that is, a 1,3‐digerma‐2‐silaallene incorporated into a five‐membered ring system, was synthesized and obtained as a stable orange solid. Owing to incorporation into a cyclic framework, the 1,3‐digerma‐2‐silaallene moiety is highly bent, exhibiting a Si0 character for the central silicon moiety.

Synthesis and Characterisation of Organosilicon and Organotin Complexes derived from DHA Ligand

Organosilicon(IV) and organotin(IV) complexes with dehydroacetic acid and amino ether Schiff base ligand have been described with the help of elemental analyses, electronic, infrared, multinuclear magnetic resonance spectroscopy. Analysis of data suggested that the Schiff base provides two bidentate NO domains and was coordinated to silicon and tin moiety through the imine nitrogen and hydroxyl oxygen atom forming penta coordinated and hexa coordinate complexes in 1: 2 and 1: 1 molar ratio. Thermal studies of the synthesized organotin compounds shows that they are stable and decomposition of the complexes occur in two steps with the formation of metal oxides as the end product.