High Refractive Index, Enantiopure Silicones Based on BINOL.

The high refractive index aromatic compound, binaphthol (BINOL), is readily incorporated into silicone polymer chains using the Piers-Rubinsztajn (PR) reaction; alternating and random linear copolymers, and elastomers are available. The highest refractive index (RI) materials are BINOL rich. It is not possible to directly make high refractive index linear polymers with very short HSi-capped, telechelic silicone chains, as they do not react cleanly. However, chain extending short vinyl-capped BINOL macromers with simple arylsilanes using hydrosilylation leads to polymers with a molar mass of up to 8000 and refractive indices of up to 1.58. Elastomers are prepared using similar processes. The reactions are facile to practice and suggest BINOL can be harnessed in these and other processes to augment RI.

Chelating Silicone Dendrons: Trying to Impact Organisms by Disrupting Ions at Interfaces.

The viability of pathogens at interfaces can be disrupted by the presence of (cationic) charge and chelating groups. We report on the synthesis of silicone dendrimers and linear polymers based on a motif of hexadentate ligands with the ability to capture and deliver metal ions. Mono-, di- or trialkoxysilanes are converted in G1 to analogous vinylsilicones and then, iteratively using the Piers-Rubinsztajn reaction and hydrosilylation, each vinyl group is transformed into a trivinyl cluster at G2. The thiol-ene reaction with cysteamine or 3-mercaptopropionic acid and the trivinyl cluster leads to hexadentate ligands 3 × N-S or 3 × HOOC-S. The compounds were shown to effectively capture a variety of metals ions. Copper ion chelation was pursued in more detail, because of its toxicity. On average, metal ions form chelates with 2.4 of the three ligands in a cluster. Upon chelation, viscous oils are converted to (very) soft elastomers. Most of the ions could be stripped from the elastomers using aqueous EDTA solutions, demonstrating the ability of the silicones to both sequester and deliver ions. However, complete ion removal is not observed; at equilibrium, the silicones remain ionically crosslinked.

Revisiting the System Silanes-Polysaccharides: The Cases of THEOS-Chitosan and MeTHEOS-Chitosan.

The glycol alkoxysilanes, tetrakis(2-hydroxyethyl)silane (THEOS), and tris(2-hydroxyethyl)methyl silane (MeTHEOS) are water soluble derivatives of tetraethoxysilane (TEOS) and methyltriethoxysilane (MeTEOS) and precursors of the system silane-chitosan reviewed in this work. The glycol modified alkoxysilanes are obtained by transesterification reaction of TEOS or MeTEOS with ethylene glycol. The reaction evolution is monitored by 29 Si NMR. It is possible to observe the formation of the various species of glycol alkoxysilanes in equilibrium as the reaction proceeds showing that the oligomers formation is favored at longer reaction times with the final product tendency to gel keeping the complete water solubility. The glycol alkoxysilanes are synthesized at moderated reaction conditions, by using the Piers-Rubinsztajn (PR) reaction. Additionally, it is already known that THEOS is compatible with different natural polysaccharides as chitosan and the same behavior has been demonstrated in this work for MeTHEOS. Several reports refer studies regarding the system THEOS-polysaccharides to synthesize hybrid materials. The system THEOS-chitosan is known but the characterization as well as the way silane-chitosan interact has not been studied in detail. In the present report, chemical evidence of the covalent interactions THEOS- and MeTHEOS-chitosan based on NMR studies (13 C and 29 Si) are presented as intended.

An Approach to the Use of Glycol Alkoxysilane-Polysaccharide Hybrids in the Conservation of Historical Building Stones.

Stone consolidants have been widely used to protect historical monuments. Consolidants and hydrophobic formulations based on the use of tetraethoxysilane (TEOS) and alkylalkoxysilanes as precursors have been widely applied, despite their lack of solubility in water and requirement to be applied in organic media. In the search for a "greener" alternative based on silicon that has potential use in this field, the use of tetrakis(2-hydroxyethyl)silane (THEOS) and tris(2-hydroxyethyl)methyl silane (MeTHEOS) as precursors, due their high water solubility and stability, is proposed in this paper. It is already known that THEOS and MeTHEOS possess remarkable compatibility with different natural polysaccharides. The investigated approach uses the water-soluble silanes THEOS-chitosan and MeTHEOS-chitosan as a basis for obtaining hybrid consolidants and hydrophobic formulations for the conservation of siliceous and calcareous stones. In the case of calcareous systems, their incompatibility with alkoxysilanes is known and is expected to be solved by the developed hybrid consolidant. Their application in the conservation of building stones from historical and archeological sites from Guanajuato, México was studied. The evaluation of the consolidant and hydrophobic formulation treatment was mainly conducted by determining the mechanical properties and contact angle measurements with satisfactory results in terms of the performance and compatibility with the studied stones.

One-step synthesis of amphiphilic copolymers PDMS-b-PEG using tris(pentafluorophenyl)borane and subsequent study of encapsulation and release of curcumin.

A series of amphiphilic block copolymer (BCP) micelles based on poly(dimethylsiloxane) (PDMS) and poly(ethylene glycol) (PEG) were synthesized by a one-step reaction in the presence of tris(pentafluorophenyl)borane (BCF) as a catalyst. The structural composition of PDMS-b-PEG (PR11) and PEG-b-PDMS-b-PEG (PR12) was corroborated by FTIR, 29Si NMR, and TGA. The BCPs were assembled in an aqueous solution, obtaining micelles between 57 and 87 nm in size. PR11 exhibited a higher (2.0 g L-1) critical micelle concentration (CMC) than PR12 (1.5 g L-1) due to the short chain length. The synthesized nano micelles were used to encapsulate curcumin, which is one of three compounds of turmeric plant 'Curcuma longa' with significant biological activities, including antioxidant, chemoprotective, antibacterial, anti-inflammatory, antiviral, and anti-depressant properties. The encapsulation efficiency of curcumin was 60% for PR11 and 45% for PR12. Regarding the release study, PR11 delivered 53% curcumin after five days under acidic conditions (pH of 1.2) compared to 43% at a pH of 7.4. The degradation products of curcumin were observed under basic conditions and were more stable at acidic pH. In both situations, the release process is carried out by breaking the silyl-ether bond, allowing the release of curcumin. PR11 showed prolonged release times, so it could be used to reduce ingestion times and simultaneously work as a nanocarrier for other hydrophobic drugs.