Dermal absorption of cyclic and linear siloxanes: a review

Cyclic and linear siloxanes are compounds synthesized from silicon consisting of alternating atoms of silicone and oxygen [Si-O] units with organic side chains. The most common cyclic siloxanes are octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6), while the most common linear siloxanes are high molecular weight polydimethylsiloxanes (PDMS) and low molecular weight volatile linear siloxanes known as hexamethyldisiloxane (L2), octamethyltrisiloxane (L3), decamethyltetrasiloxane (L4), dodecamethylpentasiloxane (L5). These compounds (1) exhibit low dermal toxicity, (2) are generally inert and non-reactive, and (3) are compatible with a wide range of chemicals offering beneficial chemical properties which include the following: wash-off or transfer resistance from the skin, sun protection factor (SPF) enhancement, emolliency in cleaning products). Because of these properties, these compounds are incorporated into multiple consumer products for use on the skin, such as cosmetics and health-care products, with over 300,000 tons annually sold into the personal care and consumer products sector. Because of their widespread use in consumer products and potential for human dermal exposure, a comprehensive understanding of the dermal absorption and overall fate of siloxanes following dermal exposure is important. This review summarizes available data associated with the dermal absorption/penetration as well as fate of the most commonly used siloxane substances.

Determination of solvation parameter model compound descriptors by gas chromatography

The solvation parameter model uses five system independent descriptors to characterize compound properties defined as excess molar refraction, E, dipolarity/polarizability, S, hydrogen-bond acidity, A, hydrogen-bond basicity, B, and the gas-liquid partition constant at 25 °C on n-hexadecane, L, to model transfer properties in gas-condensed phase biphasic systems. The E descriptor for compounds liquid at 20 °C is available by calculation using a refractive index value while E for solid compounds at 20 °C and the S, A, B, and L descriptors are determined by experiment. As a single-technique approach, it is shown that with up to 20 retention factor measurements on four columns comprising a poly(siloxane) containing methyloctyl or dimethyldiphenylsiloxane monomers (SPB-Octyl or HP-5), a poly(siloxane) containing methyltrifluoropropylsiloxane monomers (Rtx-OPP or DB-210), a poly(siloxane) containing bis(cyanopropylsiloxane) monomers (HP-88 or SGE BPX-90), and a poly(ethylene glycol) stationary phase (DB-WAXetr or HP-INNOWAX) are suitable for assigning the S, A, and L descriptors. Using the descriptors in the updated WSU compound descriptor database as target values the average absolute error in the descriptor assignments for 52 varied compounds in the temperature range 60-140 °C was 0.072 for E, 0.016 for S, 0.008 for A, and 0.022 for L corresponding to 30 %, 3.5 %, and 0.6 % as a relative average absolute error for E, S, and L, respectively. For the higher temperature range of 160-240 °C and 34 varied compounds that are liquid at 20 °C the average absolute error for the S, A and L descriptors was 0.026, 0.020, and 0.031, respectively, with the largest relative average absolute error for S of 3.2 % (< 1 % for the L descriptor). For 35 varied compounds that are solid at 20 °C the relative absolute error for the E, S, A, and L descriptors in the higher temperature range was 0.068, 0.035, 0.020, and 0.020, respectively, with a relative average absolute error for E (6.5 %), S (3.5 %) and L (0.88 %). The S, A, and L descriptor can be accurately assigned on the four-column system over a wide temperature range. The E descriptor for solid compounds at 20 °C exhibits greater variability than desirable. The B descriptor cannot be assigned by the four-column system, which lack hydrogen-bond acid functional groups, and is only poorly assigned on the weak hydrogen-bond acid ionic liquid column SLB-IL100.

Directed evolution for Si-C bond cleavage of volatile siloxanes in glass bioreactors

Volatile methylsiloxanes (VMS) are a class of non-biodegradable anthropogenic compounds with propensity for long-range transport and potential for bioaccumulation in the environment. As a proof-of-principle for biological degradation of these compounds, we engineered P450 enzymes to oxidatively cleave Si-C bonds in linear and cyclic VMS. Enzymatic reactions with VMS are challenging to screen with conventional tools, however, due to their volatility, poor aqueous solubility, and tendency to extract polypropylene from standard 96-well deep-well plates. To address these challenges, we developed a new biocatalytic reactor consisting of individual 2-mL glass shells assembled in conventional 96-well plate format. In this chapter, we provide a detailed account of the assembly and use of the 96-well glass shell reactors for screening biocatalytic reactions. Additionally, we discuss the application of GC/MS analysis techniques for VMS oxidase reactions and modified procedures for validating improved variants. This protocol can be adopted broadly for biocatalytic reactions with substrates that are volatile or not suitable for polypropylene plates.

New Ethynylphenylborasilsesquioxanes-Their Reactivity and Behavior during Thermal Decomposition

In this paper, a new type of borasilsesquioxanes was synthesized through a condensation process, and its reactivity in catalytic hydrosilylation reactions with silanes, siloxanes, and silsesquioxanes was investigated. The obtained compounds were mostly obtained in >90% yield. They were fully characterized using spectroscopic (1H, 13C, 29Si NMR) and spectrometric (MALDI-TOF-MS) methods. The next stage of the research involved studying the thermogravimetric properties of the borasilsesquioxanes. By analyzing the different stages of decomposition using spectroscopic techniques (NMR, ATR-FTIR, Raman) and microscopic imaging, it was found that the structure of the borasilsesquioxanes changed during the pyrolysis process and polymer compounds were formed.

Fabrication of Highly Thermally Resistant and Self-Healing Polysiloxane Elastomers by Constructing Covalent and Reversible Networks

The fabrication of self-healing elastomers with high thermal stability for use in extreme thermal conditions such as aerospace remains a major challenge. A strategy for preparing self-healing elastomers with stable covalent bonds and dynamic metal-ligand coordination interactions as crosslinking sites in polydimethylsiloxane (PDMS) is proposed. The added Fe (III) not only serves as the dynamic crosslinking point at room temperature which is crucial for self-healing performance, but also plays a role as free radical scavenging agent at high temperatures. The results show that the PDMS elastomers possessed an initial thermal degradation temperature over 380 °C and a room temperature self-healing efficiency as high as 65.7%. Moreover, the char residue at 800 °C of PDMS elastomer reaches 7.19% in nitrogen atmosphere, and up to 14.02% in air atmosphere by doping a small amount (i.e., 0.3 wt%) of Fe (III), which is remarkable for the self-healing elastomers that contain weak and dynamic bonds with relatively poor thermal stability. This study provides an insight into designing self-healing PDMS-based materials that can be targeted for use as high-temperature thermal protection coatings.

Are Si-C bonds formed in the environment and/or in technical microbiological systems?

Organosiloxanes are industrially produced worldwide in millions of tons per annum and are widely used by industry, professionals, and consumers. Some of these compounds are PBT (persistent, biaccumulative and toxic) or vPvB (very persistent and very bioaccumulative). If organosiloxanes react at all in the environment, Si-O bonds are hydrolyzed or Si-C bonds are oxidatively cleaved, to result finally in silica and carbon dioxide. In strong contrast and very unexpectedly, recently formation of new Si-CH3 bonds from siloxanes and methane by the action of microorganisms under mild ambient conditions was proposed (in landfills or digesters) and even reported (in a biotrickling filter, 30 °C). This is very surprising in view of the harsh conditions required in industrial Si-CH3 synthesis. Here, we scrutinized the pertinent papers, with the result that evidence put forward for Si-C bond formation from siloxanes and methane in technical microbiological systems is invalid, suggesting such reactions will not occur in the environment where they are even less favored by conditions. The claim of such reactions followed from erroneous calculations and misinterpretation of experimental results. We propose an alternative explanation of the experimental observations, i.e., the putative observation of such reactions was presumably due to confusion of two compounds, hexamethyldisiloxane and dimethylsilanediol, that elute at similar retention times from standard GC columns.

Occurrence of methylsiloxanes in indoor store dust in China and potential human exposure

Methylsiloxanes are synthetic molecules with versatile and extensive applications. Because of their volatile properties, they are easily released from manufactured products and contaminate indoor environments, causing high human exposure. However, available information on their presence in specific microenvironments, and on the related potential risks for human health, is limited. We conducted a survey of sixteen methylsiloxanes species, including three cyclic (D₄-D₆) and thirteen linear (L₄-L₁₆) chemicals, in indoor dust samples from twenty-eight stores representative of six store categories in Beijing, China. Total methylsiloxane concentrations in store dust were 176-54,825 ng/g, depending on the store, with a median of 2196 ng/g. Linear chemicals represented a median proportion of 90.8% of total methylsiloxanes. The measured methylsiloxane concentrations in this study were marginally higher than those reported previously for standard living and working environments. The highest linear and total methylsiloxane concentrations were measured in electronic stores, while the highest cyclic methylsiloxane concentrations were measured in department stores. The presence of methylsiloxanes in the store dust samples was attributed mainly to their release from chemical additives in marketed products. Estimated median total exposure doses under normal and worst-case exposure scenarios were 0.237 and 0.888 ng/kg bw/d, respectively. Further investigation is needed to characterize methylsiloxane distribution in other microenvironments and to evaluate the associated health risks.

Some Theoretical and Experimental Evidence for Particularities of the Siloxane Bond

The specific features of the siloxane bond unify the compounds based on it into a class with its own chemistry and unique combinations of chemical and physical properties. An illustration of their chemical peculiarity is the behavior of 1,3-bis(2-aminoethylaminomethyl)tetramethyldisiloxane (AEAMDS) in the reaction with carbonyl compounds and metal salts, by which we obtain the metal complexes of the corresponding Schiff bases formed in situ. Depending on the reaction conditions, the fragmentation of this compound takes place at the siloxane bond, but, in most cases, it is in the organic moieties in the β position with respect to the silicon atom. The main compounds that were formed based on the moieties resulting from the splitting of this diamine were isolated and characterized from a structural point of view. Depending on the presence or not of the metal salt in the reaction mixture, these are metal complexes with organic ligands (either dangling or not dangling silanol tails), or organic compounds. Through theoretical calculations, electrons that appear in the structure of the siloxane bond in different contexts and that lead to such fragmentations have been assessed.

Optically Triggering and Monitoring Single-Cell-Level Metabolism Using Ormosil-Decorated Ultrathin Fibers

The integration of biological components and artificial devices requires a bio-machine interface that can simultaneously trigger and monitor the activities in biosystems. Herein, we use an organically modified silicate (ormosil) composite coating containing a light-responsive nanocapsule and a fluorescent bioprobe for reactive oxygen species (ROS) to decorate ultrathin optical fibers, namely, ormosil-decorated ultrathin fibers (OD-UFs), and demonstrate that these OD-UFs can optically trigger and monitor the intracellular metabolism activities in living cells. The sizes and shapes of UF tips were finely controlled to match the dimension and mechanical properties of living cells. The increased elasticity of the ormosil coating of OD-UFs reduces possible mechanical damage during the cell membrane penetration. The light-responsive nanocapsule was physically absorbed on the surface of the ormosil coating and could release a stimulant to trigger the metabolism activities in cells upon the guided laser through OD-UFs. The fluorescent bioprobe was covalently linked with the ormosil matrix for monitoring the intracellular ROS generation, which was verified by the in vitro experiments on the microdroplets of a hydrogen peroxide solution. Finally, we found that the living cells could maintain most of their viability after being inserted with OD-UFs, and the intracellular metabolism activities were successfully triggered and monitored at the single-cell level. The OD-UF provides a new platform for the investigation of intracellular behaviors for drug stimulations and represents a new proof of concept for a bio-machine interface based on the optical and chemical activities of organic functional molecules.

Producing Fluorine- and Lubricant-Free Flexible Pathogen- and Blood-Repellent Surfaces Using Polysiloxane-Based Hierarchical Structures

High-touch surfaces are known to be a major route for the spread of pathogens in healthcare and public settings. Antimicrobial coatings have, therefore, garnered significant attention to help mitigate the transmission of infectious diseases via the surface route. Among antimicrobial coatings, pathogen-repellent surfaces provide unique advantages in terms of safety in public settings such as instant repellency, affordability, biocompatibility, and long-term stability. While there have been many advances in the fabrication of biorepellent surfaces in the past two decades, this area of research continues to suffer challenges in scalability, cost, compatibility with high-touch applications, and performance for pathogen repellency. These features are critical for high-touch surfaces to be used in public settings. Additionally, the environmental impact of manufacturing repellent surfaces remains a challenge, mainly due to the use of fluorinated coatings. Here, we present a flexible hierarchical coating with straightforward and cost-effective manufacturing without the use of fluorine or a lubricant. Hierarchical surfaces were prepared through the growth of polysiloxane nanostructures using n-propyltrichlorosilane (n-PTCS) on activated polyolefin (PO), followed by heat shrinking to induce microscale wrinkles. The developed coatings demonstrated repellency, with contact angles over 153° and sliding angles <1°. In assays mimicking touch, these hierarchical surfaces demonstrated a 97.5% reduction in transmission of Escherichia coli (E.coli), demonstrating their potential as antimicrobial coatings to mitigate the spread of infectious diseases. Additionally, the developed surfaces displayed a 93% reduction in blood staining after incubation with human whole blood, confirming repellent properties that reduce bacterial deposition.

Antibacterial Polysiloxane Polymers and Coatings for Cochlear Implants

Within this study, new materials were synthesized and characterized based on polysiloxane modified with different ratios of N-acetyl-l-cysteine (NAC) and crosslinked via UV-assisted thiol-ene addition, in order to obtain efficient membranes able to resist bacterial adherence and biofilm formation. These membranes were subjected to in vitro testing for microbial adherence against S. pneumoniae using standardized tests. WISTAR rats were implanted for 4 weeks with crosslinked siloxane samples without and with NAC. A set of physical characterization methods was employed to assess the chemical structure and morphological aspects of the new synthetized materials before and after contact with the microbiological medium.

Silicane Derivative Increases Doxorubicin Efficacy in an Ovarian Carcinoma Mouse Model: Fighting Drug Resistance

The development of cancer resistance continues to represent a bottleneck of cancer therapy. It is one of the leading factors preventing drugs to exhibit their full therapeutic potential. Consequently, it reduces the efficacy of anticancer therapy and causes the survival rate of therapy-resistant patients to be far from satisfactory. Here, an emerging strategy for overcoming drug resistance is proposed employing a novel two-dimensional (2D) nanomaterial polysiloxane (PSX). We have reported on the synthesis of PSX nanosheets (PSX NSs) and proved that they have favorable properties for biomedical applications. PSX NSs evinced unprecedented cytocompatibility up to the concentration of 300 μg/mL, while inducing very low level of red blood cell hemolysis and were found to be highly effective for anticancer drug binding. PSX NSs enhanced the efficacy of the anticancer drug doxorubicin (DOX) by around 27.8-43.4% on average and, interestingly, were found to be especially effective in the therapy of drug-resistant tumors, improving the effectiveness of up to 52%. Fluorescence microscopy revealed improved retention of DOX within the drug-resistant cells when bound on PSX NSs. DOX bound on the surface of PSX NSs, i.e., PSX@DOX, improved, in general, the DOX cytotoxicity in vitro. More importantly, PSX@DOX reduced the growth of DOX-resistant tumors in vivo with 3.5 times better average efficiency than the free drug. Altogether, this paper represents an introduction of a new 2D nanomaterial derived from silicane and pioneers its biomedical application. As advances in the field of material synthesis are rapidly progressing, novel 2D nanomaterials with improved properties are being synthesized and await thorough exploration. Our findings further provide a better understanding of the mechanisms involved in the cancer resistance and can promote the development of a precise cancer therapy.

Photocross-Linked Antimicrobial Amino-Siloxane Elastomers

Mechanically robust bulk antimicrobial polymers are one way to address disease transmission via contaminated surfaces. Here, we demonstrate the visible light photo-oxidative cross-linking of amine-containing PDMS using a single-component, solvent-free system where amines have a dual role as antimicrobial functionalities and cross-linking sites. Rose Bengal, a xanthene dye used as a fluorescent stain, is thermally reacted with the polymer to give a solvent-free liquid siloxane that can generate reactive singlet oxygen upon aerobic green light irradiation, coupling the amine functionalities into imine cross-links. Photorheological experiments demonstrate that light intensity is the largest kinetic factor in the photo-oxidative curing of these polymers. Room temperature irradiation under an ambient atmosphere results in free-standing elastic materials with mechanical properties that depend on the amount of Rose Bengal present. An ultimate elongation strain of 117% and Young's modulus of 2.15 MPa were observed for the highest dye loading, with both mechanical properties found to be higher than those for the same solution-based dye amounts. We demonstrate that the solvent-free nature of the material can be exploited to generate 3D structures using low-temperature deposition as well as direct-write patterning and photolithography on glass substrates. The antimicrobial activity was investigated, with the cross-linked material demonstrating greater efficacy against E. coli (Gram negative) compared with MRSA (Gram positive) bacterial strains and inducing complete cell lysis of incubated CHO-K1 mammalian cells, demonstrating applicability as a mechanically robust single-component antimicrobial elastomer.

Oligodimethylsiloxane-Oligoproline Block Co-Oligomers: the Interplay between Aggregation and Phase Segregation in Bulk and Solution

Discrete block co-oligomers (BCOs) assemble into highly ordered nanostructures, which adopt a variety of morphologies depending on their environment. Here, we present a series of discrete oligodimethylsiloxane-oligoproline (oDMS-oPro) BCOs with varying oligomer lengths and proline end-groups, and study the nanostructures formed in both bulk and solution. The conjugation of oligoprolines to apolar siloxanes permits a study of the aggregation behavior of oligoproline moieties in a variety of solvents, including a highly apolar solvent like methylcyclohexane. The apolar solvent is more reminiscent of the polarity of the siloxane bulk, which gives insights into the supramolecular interactions that govern both bulk and solution assembly processes of the oligoproline. This extensive structural characterization allows the bridging of the gap between solution and bulk assembly. The interplay between the aggregation of the oligoproline block and the phase segregation induced by the siloxane drives the assembly. This gives rise to disordered, micellar microstructures in apolar solution and crystallization-driven lamellar nanostructures in the bulk. While most di- and triblock co-oligomers adopt predictable morphological features, one of them, oDMS15-oPro6-NH2, exhibits pathway complexity leading to gel formation. The pathway selection in the complex interplay between aggregation and phase segregation gives rise to interesting material properties.

The Effects of Hydrophobicity and Textural Properties on Hexamethyldisiloxane Adsorption in Reduced Graphene Oxide Aerogels

To expand the applications of graphene-based materials to biogas purification, a series of reduced graphene oxide aerogels (rGOAs) were prepared from industrial grade graphene oxide using a simple hydrothermal method. The influences of the hydrothermal preparation temperature on the textural properties, hydrophobicity and physisorption behavior of the rGOAs were investigated using a range of physical and spectroscopic techniques. The results showed that the rGOAs had a macro-porous three-dimensional network structure. Raising the hydrothermal treatment temperature reduced the number of oxygen-containing groups, whereas the specific surface area (SBET), micropore volume (Vmicro) and water contact angle values of the rGOAs all increased. The dynamic adsorption properties of the rGOAs towards hexamethyldisiloxane (L2) increased with increasing hydrothermal treatment temperature and the breakthrough adsorption capacity showed a significant linear association with SBET, Vmicro and contact angle. There was a significant negative association between the breakthrough time and inlet concentration of L2, and the relationship could be reliably predicted with a simple empirical formula. L2 adsorption also increased with decreasing bed temperature. Saturated rGOAs were readily regenerated by a brief heat-treatment at 100 °C. This study has demonstrated the potential of novel rGOA for applications using adsorbents to remove siloxanes from biogas.

Synthesis of Silsesquioxanes with Substituted Triazole Ring Functionalities and Their Coordination Ability

A synthesis of a series of mono-T8 and difunctionalized double-decker silsesquioxanes bearing substituted triazole ring(s) has been reported within this work. The catalytic protocol for their formation is based on the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) process. Diverse alkynes were in the scope of our interest-i.e., aryl, hetaryl, alkyl, silyl, or germyl-and the latter was shown to be the first example of terminal germane alkyne which is reactive in the applied process' conditions. From the pallet of 15 compounds, three of them with pyridine-triazole and thiophenyl-triazole moiety attached to T8 or DDSQ core were verified in terms of their coordinating properties towards selected transition metals, i.e., Pd(II), Pt(II), and Rh(I). The studies resulted in the formation of four SQs based coordination compounds that were obtained in high yields up to 93% and their thorough spectroscopic characterization is presented. To our knowledge, this is the first example of the DDSQ-based molecular complex possessing bidentate pyridine-triazole ligand binding two Pd(II) ions.

Reliable Condensation Curing Silicone Elastomers with Tailorable Properties

The long-term stability of condensation curing silicone elastomers can be affected by many factors such as curing environment, cross-linker type and concentration, and catalyst concentration. Mechanically unstable silicone elastomers may lead to undesirable application failure or reduced lifetime. This study investigates the stability of different condensation curing silicone elastomer compositions. Elastomers are prepared via the reaction of telechelic silanol-terminated polydimethylsiloxane (HO-PDMS-OH) with trimethoxysilane-terminated polysiloxane ((MeO)3Si-PDMS-Si(OMe)3) and ethoxy-terminated octakis(dimethylsiloxy)-T8-silsesquioxane ((QMOEt)8), respectively. Two post-curing reactions are found to significantly affect both the stability of mechanical properties over time and final properties of the resulting elastomers: Namely, the condensation of dangling and/or unreacted polymer chains, and the reaction between cross-linker molecules. Findings from the stability study are then used to prepare reliable silicone elastomer coatings. Coating properties are tailored by varying the cross-linker molecular weight, type, and concentration. Finally, it is shown that, by proper choice of all three parameters, a coating with excellent scratch resistance and electrical breakdown strength can be produced even without an addition of fillers.

A Novel Glass Fiber Coated with Sol-Gel Poly-Diphenylsiloxane Sorbent for the On-Line Determination of Toxic Metals Using Flow Injection Column Preconcentration Platform Coupled with Flame Atomic Absorption Spectrometry

A novel simple and sensitive, time-based flow injection solid phase extraction system was developed for the automated determination of metals at low concentration. The potential of the proposed scheme, coupled with flame atomic absorption spectrometry (FAAS), was demonstrated for trace lead and chromium(VI) determination in environmental water samples. The method, which was based on a new sorptive extraction system, consisted of a microcolumn packed with glass fiber coated with sol-gel poly (diphenylsiloxane) (sol-gel PDPS), which is presented here for the first time. The analytical procedure involves the on-line chelate complex formation of target species with ammonium pyrrolidine dithiocarbamate (APDC), retention onto the hydrophobic sol-gel sorbent coated surface of glass fibers, and finally elution with methyl isobutyl ketone prior to atomization. All main chemical and hydrodynamic factors, which affect the complex formation, retention, and elution of the metal, were optimized thoroughly. Furthermore, the tolerance to potential interfering ions appearing in environmental samples was also explored. Enhancement factors of 215 and 70, detection limits (3 s) of 1.1 μg·L^-1 and 1.2 μg·L^-1, and relative standard deviations (RSD) of 3.0% (at 20.0 μg·L^-1) and 3.2% (at 20.0 μg·L^-1) were obtained for lead and chromium(VI), respec tively, for 120 s preconcentration time. The trueness of the developed method was estimated by analyzing certified reference materials and spiked environmental water samples.

Accuracy evaluation of 3D printed interim prosthesis fabrication using a CBCT scanning based digital model

OBJECTIVES

This study aimed to evaluate the marginal and internal gaps in 3D-printed interim crowns made from digital models of cone-beam computed tomography (CBCT) conversion data.

MATERIALS AND METHODS

Sixteen polyvinylsiloxane impressions were taken from patients for single crown restorations and were scanned using CBCT. The scanning data were converted to positive Standard Triangulation Language (STL) files using custom-developed software. The fabricated stone models were scanned with an intraoral optical scanner (IOS) to compare the surface accuracy with the STL data obtained by CBCT. The converted STL files were utilized to fabricate interim crowns with a photopolymer using a digital light-processing 3D printer. The replica method was used to analyze the accuracy. The marginal and internal gaps in the replica specimen of each interim crown were measured with a digital microscope. The Friedman test and Mann-Whitney U test (Wilcoxon-signed rank test) were conducted to compare the measurements of the marginal and internal gaps with a 95% level of confidence.

RESULTS

The root-mean-square values of the CBCT and IOS ranged from 41.00 to 126.60 μm, and the mean was 60.12 μm. The mean values of the marginal, internal, and total gaps were 132.96 (±139.23) μm, 137.86 (±103.09) μm, and 135.68 (±120.30) μm, respectively. There were no statistically significant differences in the marginal or internal gaps between the mesiodistal and buccolingual surfaces, but the marginal area (132.96 μm) and occlusal area (255.88 μm) had significant mean differences.

CONCLUSION

The marginal gap of the fabricated interim crowns based on CBCT STL data was within the acceptable range of clinical success. Through ongoing developments of high-resolution CBCT and the digital model conversion technique, CBCT might be an alternative method to acquire digital models for interim crown fabrication.

"Umbrella" Structure Trisiloxane Surfactant: Synthesis and Application for Reverse Flotation of Phosphorite Ore in Phosphate Fertilizer Production

Phosphorite is generally used in the manufacture of phosphate fertilizer and plays a vital role in the development of agricultural and food production. Nonetheless, how to obtain phosphorite concentrates efficiently and sustainably has become an urgent problem. In this study, a newly designed trisiloxane surfactant, N-(2-Aminoethyl)-3-aminopropyltrisiloxane (AATS), has been prepared and utilized as an emerging collector for reverse flotation of phosphorite ore. Its collecting ability was compared with the conventional surfactant 1-dodecamine (DDA). In the collector concentration tests, AATS with lower concentrations showed stronger collecting ability for quartz. In the pH tests, AATS always performed better than DDA in the acidic or alkaline condition. In bench-scale flotation experiments, the P₂O₅ recovery of phosphorite concentrates with 150 g/t AATS was 10.77% higher than that with 300 g/t DDA, which proved that AATS can be applied to the sustainable production of phosphorite concentrates. For a 4000 t/d phosphorite ore processing plant, the profit could be increased 7,014,702.07 USD every year by using AATS as the collector. Therefore, this work provides a promising approach to enhance the production efficiency of phosphate fertilizer and to promote the sustainable development of agriculture.

Performance and fungal diversity of bio-trickling filters packed with composite media of polydimethylsiloxane and foam ceramics for hydrophobic VOC removal

Bio-trickling filters (BTFs) can be used for the treatment of hydrophobic VOC-contaminated air. To improve treatment performance, two novel polydimethylsiloxane (PDMS) packing media were produced and trialled in BTFs inoculated with Cladophialophora fungus. The BTF packed with PDMS/foam ceramic composite filler showed superior performance: rapid start-up within 3 days, rapid restart within 7 days after starvation for 1 month, a maximum toluene elimination capacity (EC) of 264.4 g m^-3·h^-1 at an empty bed residence time of 10 s, and a pressure drop that was controllable by adjusting the nutrient supply regime. High-throughput sequencing was used to analyse the effect of spatial position on the microbial communities in the top and bottom filler layers. Meanwhile, by investigating the EC in the vertical direction of the BTF, spatial heterogeneity in the fungal degradation of a hydrophobic VOC was preliminarily explored.

Acetaldehyde gas removal by a nylon film-TiO2 composite sheet prepared on a paper surface using interfacial polymerization and electrostatic interactions

In this study, preparation of a nylon film-TiO₂ composite sheet with both physical durability under UV irradiation and TiO₂ photocatalysis functionality was investigated. First, a nylon film was directly prepared on paper by interfacial polymerization using ethylenediamine and terephthaloyl chloride in a cyclohexane-chloroform mixture (3:1, v/v). Next, the nylon-coated paper was treated with tetraethyl orthosilicate and 3-aminopropyltrimethoxysilane to prepare polysiloxane on its surface. This was followed by fixation of TiO₂ powder via electrostatic interactions with the polysiloxane. Although nylon films on paper usually decompose under TiO₂ photocatalysis, the nylon film-TiO₂ composite sheets prepared using 0.5%-1.0% (w/v) TiO₂ did not decompose under photocatalysis. The residual rate of strength of the sheet remained at almost 100% after 240 h, which could be attributed to protection of the sheet by the polysiloxane layer. The nylon film was fibrous and could effectively adsorb acetaldehyde gas. All of the nylon film-TiO₂ composite sheets prepared using 0.5%-5.0% TiO₂ photocatalytically removed acetaldehyde under UV irradiation and no acetaldehyde gas was detected after 240-300 min. These results show the nylon film-TiO₂ composite sheet can effectively remove acetaldehyde gas by photocatalysis and adsorption and could be applied to removal of volatile organic compounds in indoor air.

Dental composites - a low-dose source of bisphenol A?

Dental composite materials often contain monomers with bisphenol A (BPA) structure in their molecules, e.g. bisphenol-A glycidyl dimethacrylate (Bis-GMA). In this study, it was examined whether dental restorative composites could be a low-dose source of BPA or alternative bisphenols, which are known to have endocrine-disrupting effects. Bis-GMA-containing composites Charisma Classic (CC) and Filtek Ultimate Universal Restorative (FU) and "BPA-free" Charisma Diamond (CD) and Admira Fusion (AF) were examined. Specimens (diameter 6 mm, height 2 mm, n=5) were light-cured from one side for 20 s and stored at 37 °C in methanol which was periodically changed over 130 days to determine the kinetics of BPA release. BPA concentrations were measured using a dansyl chloride derivatization method with liquid chromatography - tandem mass spectrometry detection. The amounts of BPA were expressed in nanograms per gram of composite (ng/g). BPA release from Bis-GMA-containing CC and FU was significantly higher compared to "BPA-free" CD and AF. The highest 1-day release was detected with FU (15.4+/-0.8 ng/g), followed by CC (9.1+/-1.1 ng/g), AF (2.1+/-1.3 ng/g), and CD (1.6+/-0.8 ng/g), and the release gradually decreased over the examined period. Detected values were several orders of magnitude below the tolerable daily intake (4 microg/kg body weight/day). Alternative bisphenols were not detected. BPA was released even from "BPA-free" composites, although in significantly lower amounts than from Bis-GMA-containing composites. Despite incubation in methanol, detected amounts of BPA were substantially lower than current limits suggesting that dental composites should not pose a health risk if adequately polymerized.

Novel perspectives on stomatal impressions: Rapid and non-invasive surface characterization of plant leaves by scanning electron microscopy

Scanning electron microscopy (SEM) is widely used to investigate the surface morphology, and physiological state of plant leaves. Conventionally used methods for sample preparation are invasive, irreversible, require skill and expensive equipment, and are time and labor consuming. This study demonstrates a method to obtain in vivo surface information of plant leaves by imaging replicas with SEM that is rapid and non-invasive. Dental putty was applied to the leaves for 5 minutes and then removed. Replicas were then imaged with SEM and compared to fresh leaves, and leaves that were processed conventionally by chemical fixation, dehydration and critical point drying. The surface structure of leaves was well preserved on the replicas. The outline of epidermal as well as guard cells could be clearly distinguished enabling determination of stomatal density. Comparison of the dimensions of guard cells revealed that replicas did not differ from fresh leaves, while conventional sample preparation induced strong shrinkage (-40% in length and -38% in width) of the cells when compared to guard cells on fresh leaves. Tilting the replicas enabled clear measurement of stomatal aperture dimensions. Summing up, the major advantages of this method are that it is inexpensive, non-toxic, simple to apply, can be performed in the field, and that results on stomatal density and in vivo stomatal dimensions in 3D can be obtained in a few minutes.

Siloxanes-Versatile Materials for Surface Functionalisation and Graft Copolymers

Siloxanes are adaptable species that have found extensive applications as versatile materials for functionalising various surfaces and as building blocks for polymers and hybrid organic-inorganic systems. The primary goal of this review is to report on and briefly explain the most relevant recent developments related to siloxanes and their applications, particularly regarding surface modification and the synthesis of graft copolymers bearing siloxane or polysiloxane segments. The key strategies for both functionalisation and synthesis of siloxane-bearing polymers are highlighted, and the various trends in the development of siloxane-based materials and the intended directions of their applications are explored.

Fe3O4@Void@Microporous Organic Polymer-Based Multifunctional Drug Delivery Systems: Targeting, Imaging, and Magneto-Thermal Behaviors

Multifunctional drug delivery systems were designed and engineered by template synthesis of a microporous organic polymer (MOP) and by postsynthetic modification. Hollow MOP spheres bearing Fe₃O₄ yolks (Fe₃O₄@Void@MOP) were prepared by the synthesis of MOP on Fe₃O₄@SiO₂ nanoparticles and by successive silica etching. In addition to the magneto-thermal function of Fe₃O₄ yolks, an aggregation-induced emission (AIE) feature was incorporated into the Fe₃O₄@Void@MOP through a homocoupling of tetra(4-ethynylphenyl)ethylene to form Fe₃O₄@Void@MOP-TE. Folate groups were further introduced into Fe₃O₄@Void@MOP-TE through the postsynthetic modification based on the thiol-yne click reaction. The resultant Fe₃O₄@Void@MOP-TE-FA showed multifunctionality in antitumoral therapy via folate receptor targeting, doxorubicin delivery, AIE-based imaging, and the magneto-thermal feature.

Ultrastable Plasmonic Bioink for Printable Point-Of-Care Biosensors

Point-of-care biosensors are critically important for early disease diagnosis and timely clinical intervention in resource-limited settings. The real-world application of these biosensors requires the use of stable biological reagents and cost-effective fabrication approaches. To meet these stringent requirements, we introduce a generic encapsulation strategy to realize ultrastable plasmonic bioink by encapsulating antibodies with an organosiloxane polymer through in situ polymerization. Plasmonic nanostructures serve as sensitive nanotransducers, allowing for label-free biochemical detection. The plasmonic bioink with encapsulated antibodies exhibits excellent thermal, biological, and colloidal stabilities making it compatible with printing process. As a proof-of-concept, we demonstrate the printability of the ultrastable plasmonic bioinks on different types of substrates with direct writing techniques. The organosiloxane polymer preserves the biorecognition capabilities of the biosensors under harsh conditions, including elevated temperature, exposure to chemical/biological denaturants, and ultrasonic agitation. Plasmonic biochips fabricated with the ultrastable ink exhibit superior stability compared to the biochips with unencapsulated antibodies.

Development of a solid-phase microextraction method for fast analysis of cyclic volatile methylsiloxanes in water

Cyclic volatile methylsiloxanes (cVMS) are widely used in consumer products and commonly detected in the environment. There are challenges in the analysis of cVMS because of their ubiquitous use which can introduce high background contamination. The current study introduces a sample preparation method based on headspace of solid-phase microextraction (SPME) for monitoring the cVMS in waters. Efforts were made to reduce the background contamination during sample preparation and instrument analysis. A laboratory prepared MIL-101 coating was prepared using polysulfone instead of polydimethylsiloxane as adhesive to avoid the contamination. The extraction performance of the MIL-101 fiber was optimized and evaluated. The optimized extraction time and temperature were 60 min and 40 °C, respectively. The method quantification limits of the MIL-101 fiber for octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecylcyclohexasiloxane (D6) in water were 0.15 ng mL^-1, 0.14 ng mL^-1, and 0.27 ng mL^-1, respectively. The extraction efficiency of the proposed MIL-101 fiber was comparable to the commercial polydimethylsiloxane/divinylbenzene fiber. The developed method was applied to analyze the cVMS in wastewater treatment plant and the concentrations in the barscreen and in the aeration tank ranged from 0.73 to 3.3 ng mL^-1 and 7.74-85.1 ng mL^-1, respectively. The MIL-101 fiber was also applied to study the photodegradation of the cVMS in water under simulated sunlight. Approximately 25%, 20%, and 45% of D4, D5, and D6, respectively, were degraded after 10 h exposure.

Gaseous mercury capture by coir fibre coated with a metal-halide

Toxic gaseous elemental mercury (GEM) is emitted to the atmosphere through a variety of routes at rates estimated at over 5000 tonnes per annum, a large fraction of which is Anthropogenic. It is then widely disbursed atmospherically and eventually deposited, where it is subject to further biogeochemical cycling, including re-emission. Research into capture of point source mercury emissions revolves almost exclusively around the use of activated carbons, various catalytic oxidation substrates, or as a by-product of acidic treatments of flue gas during SOx and NOx reduction methods. GEM is very non-reactive in its native state, but capture rates are greatly enhanced if GEM is first oxidized, or at least where oxidation states play a role at the substrate GEM interface. Little research has been devoted to capture of GEM directly. However, presented here is a novel adaption of coir fibers for use as a substrate in capturing GEM emissions directly. Various coir modifications were investigated, with the most effective being fibers coated with CuI crystals dispersed in a non-crosslinked poly-siloxane matrix. Scanning electron microscopy was used to view surface morphologies, and sorption characteristics were measured using atomic absorption spectroscopy (AAS). These results indicate that coir fibers modified by CuI-[SiO₂] _n show great promise in their ability to efficiently sorb GEM, and could potentially be utilized in a variety of configurations and settings where GEM emissions need to be captured.

IMPLICATIONS

Highly toxic gaseous elemental mercury (GEM) has proved very difficult to capture, requiring complex catalytic oxidation or expensive gas scrubbing technologies. The modified coir fiber described in this work can effectively capture GEM without prior catalytic oxidation or any other physicochemical treatment of the gas. The solution provided here is made from renewable resources, is low cost, and the raw materials are readily available in bulk. Further, the mercury is bound in a stable and insoluble form that can be readily isolated from the substrate. This filtration device can be adapted to suit a variety of settings for GEM capture.

Feasibility of intratumoral 165Holmium siloxane delivery to induced U87 glioblastoma in a large animal model, the Yucatan minipig

Glioblastoma is the most aggressive primary brain tumor leading to death in most of patients. It comprises almost 50-55% of all gliomas with an incidence rate of 2-3 per 100,000. Despite its rarity, overall mortality of glioblastoma is comparable to the most frequent tumors. The current standard treatment combines surgical resection, radiotherapy and chemotherapy with temozolomide. In spite of this aggressive multimodality protocol, prognosis of glioblastoma is poor and the median survival remains about 12-14.5 months. In this regard, new therapeutic approaches should be developed to improve the life quality and survival time of the patient after the initial diagnosis. Before switching to clinical trials in humans, all innovative therapeutic methods must be studied first on a relevant animal model in preclinical settings. In this regard, we validated the feasibility of intratumoral delivery of a holmium (Ho) microparticle suspension to an induced U87 glioblastoma model. Among the different radioactive beta emitters, 166Ho emits high-energy β(-) radiation and low-energy γ radiation. β(-) radiation is an effective means for tumor destruction and γ rays are well suited for imaging (SPECT) and consequent dosimetry. In addition, the paramagnetic Ho nucleus is a good asset to perform MRI imaging. In this study, five minipigs, implanted with our glioblastoma model were used to test the injectability of 165Ho (stable) using a bespoke injector and needle. The suspension was produced in the form of Ho microparticles and injected inside the tumor by a technique known as microbrachytherapy using a stereotactic system. At the end of this trial, it was found that the 165Ho suspension can be injected successfully inside the tumor with absence or minimal traces of Ho reflux after the injections. This injection technique and the use of the 165Ho suspension needs to be further assessed with radioactive 166Ho in future studies.

Grafting polysiloxane onto ultrafiltration membranes to optimize surface energy and mitigate fouling

Conventional approaches to mitigate fouling of membrane surfaces impart hydrophilicity to the membrane surface, which increases the water of hydration and fluidity near the surface. By contrast, we demonstrate here that tuning the membrane surface energy close to that of the dispersive component of water surface tension (21.8 mN m^-1) can also improve the antifouling properties of the membrane. Specifically, ultrafiltration (UF) membranes were first modified using polydopamine (PDA) followed by grafting of amine-terminated polysiloxane (PSi-NH₂). For example, with 2 g L^-1 PSi-NH₂ coating solution, the obtained coating layer contains 53% by mass fraction PSi-NH₂ and exhibits a total surface energy of 21 mN m^-1, decreasing the adsorption of bovine serum albumin by 44% compared to the unmodified membrane. When challenged with 1 g L^-1 sodium alginate in a constant-flux crossflow system, the PSi-NH₂-grafted membrane exhibits a 70% lower fouling rate than the pristine membrane at a water flux of 110 L (m² h)^-1 and good stability when cleaned with NaOH solutions.

A 1,5-Oligosilanylene Dianion as Building Block for Oligosiloxane Containing Cages, Ferrocenophanes, and Cyclic Germylenes and Stannylenes

Starting out from dipotassium 1,5-oligosiloxanylene diide 2, a 3,7,10-trioxa-octasilabicyclo[3.3.3]undecane was prepared, which represents the third known example of this cage structure type. Reaction of 1,3-dichlorotetramethyldisiloxane with 1,1'-bis[bis(trimethylsilyl)potassiosilyl]ferrocene gave a ferrocenophane with a disiloxane containg bridge. The compound can be further derivatized by conversion into a 1,5-oligosilanyl diide. Reacting 1,5-oligosiloxanylene diide 2 with SnCl2 or GeCl2·dioxane in the presence of PMe3 gave cyclic disilylated tetrylene PMe3 adducts. Release of the base-free stannylene led to a dimerization process which gave a bicyclic distannene as the final product. Abstraction of the PMe3 from the cyclic disilylated germylene PMe3 adduct with B(C6F5)3 caused oxidative addition of the germylene into a para-C-F bond of Me3P·B(C6F5)3.

Polymer Stabilized Cholesteric Liquid Crystal Siloxane for Temperature-Responsive Photonic Coatings

Temperature-responsive photonic coatings are appealing for a variety of applications, including smart windows. However, the fabrication of such reflective polymer coatings remains a challenge. In this work, we report the development of a temperature-responsive, infrared-reflective coating consisting of a polymer-stabilized cholesteric liquid crystal siloxane, applied by a simple bar coating method. First, a side-chain liquid crystal oligosiloxane containing acrylate, chiral and mesogenic moieties was successfully synthesized via multiple steps, including preparing precursors, hydrosilylation, deprotection, and esterification reactions. Products of all the steps were fully characterized revealing a chain extension during the deprotection step. Subsequently, the photonic coating was fabricated by bar-coating the cholesteric liquid crystal oligomer on glass, using a mediator liquid crystalline molecule. After the UV-curing and removal of the mediator, a transparent IR reflective polymer-stabilized cholesteric liquid crystal coating was obtained. Notably, this fully cured, partially crosslinked transparent polymer coating retained temperature responsiveness due to the presence of non-reactive liquid-crystal oligosiloxanes. Upon increasing the temperature from room temperature, the polymer-stabilized cholesteric liquid crystal coating showed a continuous blue-shift of the reflection band from 1400 nm to 800 nm, and the shift was fully reversible.

Preliminary evaluation of application of a 3-dimensional network structure of siloxanes Dergall preparation on chick embryo development and microbiological status of eggshells

The spatial network structure of Dergall is based on substances nontoxic to humans and the environment which, when applied on solid surfaces, creates a coating that reduces bacterial cell adhesion. The bacteriostatic properties of siloxanes are based on a purely physical action mechanism which excludes development of drug-resistant microorganisms. The aims of the present study were to 1) evaluate a Dergall layer formed on the eggshell surface regarding the potential harmful effects on the chick embryo; 2) evaluate antimicrobial activity and estimate the prolongation time of Dergall's potential antimicrobial activity. Dergall at a concentration of 0.6% formed a layer on the eggshell surface. In vitro testing of the potential harmful effects of Dergall by means of a hen embryo test of the chorioallantoic membrane showed no irritation reaction at a concentration of 3% and lower. The hatchability of the groups sprayed with a Dergall water solution with a concentration of 0 to 5% was 89.1 to 93.8% for fertilized eggs (P > 0.05) but decreased to 63.7% (P < 0.05) in the group sprayed with a 6% concentration of the solution. This phenomenon was caused by embryo mortality in the first week of incubation. At the concentration of 0.6%, Dergall exhibited strong antibacterial properties against bacteria such as Staphylococcus aureus, Escherichia coli, Shigella dysenteriae, Shigella flexneri, and Salmonella typhimurium. For Streptococcus pyogenes, the highest antibacterial activity of Dergall was reported in the concentrations of 100 and 50%. For Pseudomonas aeruginosa, no antibacterial activity of Dergall was generally observed, but in vivo testing showed a strong decrease of all gram-negative bacteria growth. Moreover, a prolonged antimicrobial effect lasting until 3 D after disinfection was observed, which makes Dergall a safe and efficient disinfectant.

Hydroxyl radical oxidation of cyclic methylsiloxanes D4 ∼ D6 in aqueous phase

Cyclic methylsiloxanes (CMS) were listed as candidates of substances of very high concerns in 2018 by the REACH. These compounds can enter environmental waters, and potentially cause harmful effects to aquatic organisms and human beings. Until now, reaction mechanisms of these pollutants with hydroxyl radicals (HO) in aqueous phase were unknown. In this study, reaction mechanisms of three typical CMS (D4 ∼ D6) with HO in aqueous phase were investigated by employing both UV/H₂O₂ experiments and density functional theoretical calculations. Bimolecular reaction rate constants (k_HO·) of D4 ∼ D6 with HO were determined as k_HO·(D4) = 8k_HO·(D5) = 12k_HO·(D6) = 6.6 × 10⁸ L mol^-1 s^-1. Half-lives of HO oxiding D4 ∼ D6 ranged from 12 to 140 days at [HO] = 10^-15 mol L^-1 in sunlit surface water, and were comparable to (D4, D5) or much shorter (D6) than hydrolytic half-lives. The reactivity to HO decreased with the increasing size of siloxane ring in aqueous phase, in an order totally opposite to that in gaseous phase. Calculation results indicated that HO oxidation of the three CMS proceeded spontaneously through an exothermic H-abstraction process at the first step. Water molecules participated into H-abstraction of CMS and caused energy barrier of D5 higher than that of D4. Thus, H-bonds formed by water molecules were responsible for the reverse reactivity of CMS in aqueous phase. This work provided basic evidences suggesting environmental persistence of CMS in aqueous phase completely different from that in gaseous phase.

Lung cell exposure to secondary photochemical aerosols generated from OH oxidation of cyclic siloxanes

To study the fate of cyclic volatile methyl siloxanes (cVMS) undergoing photooxidation in the environment and to assess the acute toxicity of inhaled secondary aerosols from cVMS, we used an oxidative flow reactor (OFR) to produce aerosols from oxidation of decamethylcyclopentasiloxane (D5). The aerosols produced from this process were characterized for size, shape, and chemical composition. We found that the OFR produced aerosols composed of silicon and oxygen, arranged in chain agglomerates, with primary particles of approximately 31 nm in diameter. Lung cells were exposed to the secondary organosilicon aerosols at estimated doses of 54-116 ng/cm² using a Vitrocell air-liquid interface system, and organic gases and ozone exposure was minimized through a series of denuders. Siloxane aerosols were not found to be highly toxic.

Alkoxy- and Silanol-Functionalized Cage-Type Oligosiloxanes as Molecular Building Blocks to Construct Nanoporous Materials

Siloxane-based materials have a wide range of applications. Cage-type oligosiloxanes have attracted significant attention as molecular building blocks to construct novel siloxane-based nanoporous materials with promising applications such as in catalysis and adsorption. This paper reviews recent progress in the preparation of siloxane-based nanoporous materials using alkoxy- and silanol-functionalized cage siloxanes. The arrangement of cage siloxanes units is controlled by various methods, including amphiphilic self-assembly, hydrogen bonding of silanol groups, and regioselective functionalization, toward the preparation of ordered nanoporous siloxane-based materials.

Magnetic Resonance Imaging of Single Cells

This chapter discusses a methodology for simultaneously imaging stem cells and endothelial cells within polysaccharide-based scaffolds for tissue engineering. These scaffolds were then implanted into nude mice. Human mesenchymal stem cells (HMSCs) were labeled with the T₁-marker Gd(III)-DOTAGA-functionalized polysiloxane nanoparticles (GdNPs), whereas endothelial umbilical vein cells (HUVECs) were labeled with citrate-stabilized maghemite nanoparticles (IONPs), which predominantly shorten the T₂-relaxation times of the water molecules in scaffolds and tissue. Dual cell detection was achieved by performing T₁- and T₂-weighted MRI in both tissue scaffolds and in vivo.

A Study of the Influence of the HCl Concentration on the Composition and Structure of (Hydroxy)Arylsiloxanes from the Hydrolysis-Condensation Reaction of Aryltrichlorosilanes

The hydrolysis–condensation reactions of m-tolyl, m-chlorophenyl, and α-naphtyl-trichlorsilanes, (1, 2, and 3, respectively) in water-acetone solutions were examined for how they were influenced by the change in the concentration of HCl (C_HCl). The composition of the products was monitored by ²⁹Si NMR spectroscopy and atmospheric pressure chemical ionization mass spectrometry (APCI-MS). The acidity of the medium was shown to affect the yields of the products, and so, what products were formed. For 3, e.g., APCI-MS showed peaks of α-naphtyl-T₈ and α-naphtyl-T₁₀ as the most abundant in the spectra taken after 48 and 240 h for the reaction conducted at C_HCl = 0.037 mol L⁻¹. Unlike this, at C_HCl = 0.15 mol L⁻¹, those peaks were of [α-naphtyl(HO)₂SiO]₂(α-naphtyl)(HO)Si and/or [α-naphtyl(HO)Si]₃, [α-naphtyl(HO)Si]_4,5, and α-naphtyl-T₈ after 192 h. However, at both C_HCl values, the main product (and an intermediate) after 24 h was trans-1,1,3,3-tetrahydroxy-1,3-di-α-naphtyldisiloxane. It was isolated and its structure established by ¹H-, ²⁹Si-NMR, and X-ray powder diffraction.

Tailor-made PEG coated iron oxide nanoparticles as contrast agents for long lasting magnetic resonance molecular imaging of solid cancers

Magnetic resonance imaging (MRI) is the most powerful technique for non-invasive diagnosis of human diseases and disorders. Properly designed contrast agents can be accumulated in the damaged zone and be internalized by cells, becoming interesting cellular MRI probes for disease tracking and monitoring. However, this approach is sometimes limited by the relaxation rates of contrast agents currently in clinical use, which show neither optimal pharmacokinetic parameters nor toxicity. In this work, a suitable contrast agent candidate, based on iron oxide nanoparticles (IONPs) coated with polyethyleneglycol, was finely designed, prepared and fully characterized under a physical, chemical and biological point of view. To stand out the real potential of our study, all the experiments were performed in comparison with Ferumoxytol, a FDA approved IONPs. IONPs with a core size of 15 nm and coated with polyethyleneglycol of 5 kDa (OD15-P5) resulted the best ones, being able to be uptaken by both tumoral cells and macrophages and showing no toxicity for in vitro and in vivo experiments. In vitro and in vivo MRI results for OD15-P5 showed r₂ relaxivity values higher than Ferumoxitol. Furthermore, the injected OD15-P5 were completely retained at the tumor site for up to 24 h showing high potential as MRI contrast agents for real time long-lasting monitoring of the tumor evolution.

Preparation of polyoxometalate-doped aminosilane-modified silicate hybrid as a new barrier of chem-bio toxicant

Nanohybrid membranes based on the Keggin-type polyoxometalate (POM) H5PV2Mo10O40 and aminosilane-modified silicate (Ormosil and Ormosil(NR4+Cl-)) hybrids were synthesized as a new barrier to protect against simulants of chemical and biological toxicant. The 31P NMR and XPS results indicated that POM was bound to the Ormosil and Ormosil(NR4+Cl-) hybrids after impregnation. The antibacterial effects of the hybrids and hybrid-impregnated fabrics against Gram-negative and Gram-positive bacteria were investigated with zone of inhibition, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and plate-counting method. The MIC/MBC values of Ormosil(NR4+Cl-)/POM and Ormosil/POM against bacteria were 0.267/2.67 and 2.67/26.7, respectively, and the percentage reduction of bacteria was approximately 100% after 20 laundry cycles of their fabrics. The reaction products and mechanisms of the adsorptive degradation of 2-chloroethylethylsulfide (CEES) by hybrids were investigated with 13C NMR. The results of this study showed that POM-doped Ormosil systems are capable of destroying bacteria and CEES.

Hybrid Geopolymers from Fly Ash and Polysiloxanes

The preparation and characterization of innovative organic-inorganic hybrid geopolymers, obtained by valorizing coal fly ash generated from thermoelectric power plants, is reported for the first time. These hybrid materials are prepared by simultaneously reacting fly ash and dimethylsiloxane oligomers at 25 °C in a strongly alkaline environment. Despite their lower density, the obtained materials are characterized by highly improved mechanical properties when compared to the unmodified geopolymer obtained without the use of polysiloxanes, hence confirming the effectiveness of the applied synthetic strategy which specifically aims at obtaining hybrid materials with better mechanical properties in respect to conventional ones. This study is an example of the production of new materials by reusing and valorizing waste raw resources and by-products, thus representing a possible contribution towards the circular economy.

Amphiphilic calix[4]arenes as a highly selective gas chromatographic stationary phase for aromatic amine isomers

Efficient separation of aromatic amine isomers is a challenging issue in chemical industry and environmental analysis. Here we report the use of p-amino-tetradecyloxy-calix[4]arene (C4A-NH₂) as a novel stationary phase for gas chromatographic (GC) separations. The statically coated C4A-NH₂ capillary column showed a high column efficiency of 4332 plates/m for a 0.25 mm ID column and medium polarity. The C4A-NH₂ stationary phase exhibited an excellent separation performance both for aromatic amine isomers and a complex mixture of aliphatic analytes with a wide ranging polarity, showing distinct advantages over the commercial polysiloxane stationary phases via diversified molecular interactions covering H-bonding, π-π, van der Waals interactions and shape-fitting selectivity. The retention mechanisms of aromatic amine isomers on C4A-NH₂ column were further investigated by quantum chemistry calculations. In addition, the C4A-NH₂ column showed good column repeatability with relative standard deviation (RSD) values of 0.03%-0.07% for run-to-run, 0.10%-0.27% for day-to-day and 2.6%-5.7% for column-to-column, respectively, and thermal stability up to 240℃.

The consequences of overcoming the human skin barrier by siloxanes (silicones) Part 1. Penetration and permeation depth study of cyclic methyl siloxanes

Dynamic production of cyclic siloxanes: octamethylcyclotetrasiloxane D4, decamethylcyclopentasiloxane D5 and dodecamethylcyclohexasiloxane D6 increases their concentrations in environment. It is considered that both environmental pollution and the usage of personal care products and cosmetics containing cyclic siloxanes can be the main source of the human exposure by transdermal route. The aim of the study was to verify the possibility to overcome the skin barrier by cyclic siloxanes (ATR-FTIR and GC-FID), evaluation of diffusion pathway to stratum corneum SC (Fluorescence microscopy), and determination of depth of permeation to deeper skin layers: epidermis and dermis (ATR-FTIR) and also of potential interaction with SC lipids and proteins (Fluorescence microscopy, ATR-FTIR) and the cytotoxicity studies against HaCaT cells (MTT test). The results show that D4, D5 and D5 can penetrate to SC and permeate into the deeper layers of the skin: epidermis and dermis. The quantitative analysis (GC-FID) showed that total cumulative doses for D4, D5 and D6 were: 42.50; 95.37 and 77.19 μg/cm2/24 h, respectively. The microscopic analysis proved, transepidermal route through the lipid matrix as well as through the canyons (intercluster spaces) were a diffusion pathway to the SC as well as disruption of human SC lipid structure by: D4 (the most), D5 and D6 (the least). The cytotoxicity studies demonstrated that the tested range of concentrations of D5 and D6 (up to 300 mM, 111 300 mg and 133 500 mg respectively) did not impaired the HaCaT growth, while D4 had IC50 value of 40 098 mM ± 7.94 (10 906 ± 872,5 mg).

Long-range transport potential and atmospheric persistence of cyclic volatile methylsiloxanes based on global measurements

This study investigates persistence (P) and long-range transport potential (LRTP) of cyclic volatile methylsiloxanes (cVMS) based on the field measurements in the Northern Hemisphere. The field data consisted of published outdoor air concentrations of octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexasiloxane (D6) at urban, suburban, rural and remote locations excluding the point sources. Three major trends were observed. First, D4 and D6 concentrations were correlated with measured concentrations for D5 at the same times and locations in the majority of the datasets, reflecting the common sources and similar removal mechanism(s) for these compounds. Second, as the sampling sites changed from the source to remote locations along a south-to-north transect, average cVMS concentrations in air decreased in an exponential manner. The empirical characteristic travel distances (eCTD) extracted from these spatial patterns were smaller than model estimated values and differed in order among individual compounds (D4 ∼ D5 < D6). Finally, D5/D6 concentration ratios were also found to decrease exponentially along the same spatial gradient, contrary to model predictions of an increase based on current knowledge of mechanisms controlling atmospheric cVMS degradation. These findings suggest that there may be additional removal process(es) for airborne cVMS, currently not accounted for, that requires further elucidation.

Photo-oxidative degradation of doxorubicin with siloxane MOFs by exposure to daylight

Doxorubicin (DOX) is a chemotherapeutic agent from anthracycline class, which acts unselectively on all cells; thus, it may have genotoxic and/or mutagenic effects and cause serious environmental problems. Herein, the decomposition of a diluted solution of DOX hydrochloride for injection has been investigated under photo-oxidative conditions, in ambient light and without pH modification, using hydrogen peroxide as oxidizing agent and hydrophobic siloxane-based metal-organic frameworks (MOFs) as heterogeneous catalysts. The kinetics of the photodegradation process was followed by UV-Vis spectroscopy and by ESI-MS. According to UV-Vis data, two pseudo-first-order kinetic steps describe the process, with rate constants in the order of 10^-3-10^-2 min^-1 for the rate-determining one. ESI-MS provided more accurate information, with a rate constant of 2.6 · 10^-2 min^-1 calculated from the variation of DOX ion abundance. Complete decomposition of DOX was achieved after 120 min in the shade and after only 20 min by exposure to sunlight. The analysis of the residual waters by mass spectrometry and 1D and 2D NMR spectroscopy showed complete disappearance of DOX in all cases, excluded any anthracycline species, which are destroyed in the tested conditions, and proved formation of an un-harmful compound-glycerol, while no trace of metal was detected by XRF. Preliminary data also showed decomposition of oxytetracycline in similar conditions. By this study, we bring into attention a less-addressed pollution issue and we propose a mild and effective method for the removal of drug emerging pollutants.

Microbial fuel cell performance of graphitic carbon functionalized porous polysiloxane based ceramic membranes

Proton-conducting porous ceramic membranes were synthesized via a polymer-derived ceramic route and probed in a microbial fuel cell (MFC). Their chemical compositions were altered by adding carbon allotropes including graphene oxide (GO) and multiwall carbon nanotubes into a polysiloxane matrix as filler materials. Physical characteristics of the synthesized membranes such as porosity, hydrophilicity, mechanical stability, ion exchange capacity, and oxygen mass transfer coefficient were determined to investigate the best membrane material for further testing in MFCs. The ion exchange capacity of the membrane increased drastically after adding 0.5 wt% of GO at an increment of 9 fold with respect to that of the non-modified ceramic membrane, while the oxygen mass transfer coefficient of the membrane decreased by 52.6%. The MFC operated with this membrane exhibited a maximum power density of 7.23 W m^-3 with a coulombic efficiency of 28.8%, which was significantly higher than the value obtained using polymeric Nafion membrane. Hence, out of all membranes tested in this study the GO-modified polysiloxane based ceramic membranes are found to have a potential to replace Nafion membranes in pilot scale MFCs.

Novel polysiloxane-based rhodamine B fluorescent probe for selectively detection of Al3+ and its application in living-cell and zebrafish imaging

Polysiloxanes have excellent stability and biological relevance and are suitable for biological research. However, there were few polysiloxane-based fluorescent probes for bioimaging. This report successfully designed a new polysiloxane-based polymer fluorescent probe (RB-1) for the first time as a "turn-on" fluorescent probe response to Al³⁺ ion with highly sensitive and selectivity. Importantly, this probe could also apply both in cell and zebrafish imaging, indicating the huge application development prospects of polysiloxane-based fluorescent probes in future.

Trimethyl Chitosan/Siloxane-Hybrid Coated Fe3O4 Nanoparticles for the Uptake of Sulfamethoxazole from Water

The presence of several organic contaminants in the environment and aquatic compartments has been a matter of great concern in the recent years. To tackle this problem, new sustainable and cost-effective technologies are needed. Herein we describe magnetic biosorbents prepared from trimethyl chitosan (TMC), which is a quaternary chitosan scarcely studied for environmental applications. Core@shell particles comprising a core of magnetite (Fe3O4) coated with TMC/siloxane hybrid shells (Fe3O4@SiO2/SiTMC) were successfully prepared using a simple one-step coating procedure. Adsorption tests were conducted to investigate the potential of the coated particles for the magnetically assisted removal of the antibiotic sulfamethoxazole (SMX) from aqueous solutions. It was found that TMC-based particles provide higher SMX adsorption capacity than the counterparts prepared using pristine chitosan. Therefore, the type of chemical modification introduced in the chitosan type precursors used in the surface coatings has a dominant effect on the sorption efficiency of the respective final magnetic nanosorbents.

Siloxane in baking moulds, emission to indoor air and migration to food during baking with an electric oven

Linear and cyclic volatile methylsiloxanes (l-VMS and c-VMS) are man-made chemicals with no natural source. They have been widely used in cosmetics, personal care products, coatings and many other products. As a consequence of their wide use, VMS can be found in different environmental media, as well as in humans. We bought 14 new silicone baking moulds and 3 metallic moulds from the market and used them in different baking experiments. Four of the silicone baking moulds were produced in Germany, two in Italy, four in China, and for the other moulds were no information available. The metal forms were all produced in Germany. VMS were measured in the indoor air throughout the baking process and at the edge and in the center of the finished cakes using a GC/MS system. Additionally, the particle number concentration (PNC) and particle size distribution were measured in the indoor air. The highest median concentrations of VMS were observed immediately following baking: 301 μg/m³ of D7, 212 μg/m³ of D6, and 130 μg/m³ of D8. The silicone moulds containing the highest concentrations of c-VMS corresponded with distinctly higher concentrations of the compounds in indoor air. Using a mould for more than one baking cycle reduced the indoor air concentrations substantially. Samples collected from the edge of the cake had higher concentrations relative to samples from the center, with a mean initial concentration of 6.6 mg/kg of D15, 3.9 mg/kg of D9, 3.7 mg/kg of D12, and 4.8 mg/kg of D18. D3 to D5 were measured only at very low concentrations. Before starting the experiment, an average PNC of 7300 particles/cm³ was observed in the room's air, while a PNC of 140,000 particles/cm³ was observed around the electric stove while it was baking, but this PNC slowly decreased after the oven was switched off. Baking with 4 of the moulds exceeded the German indoor precaution guide value for c-VMS, but the health hazard guide value was not reached during every experiment. Compared to other exposure routes, c-VMS contamination of cake from silicone moulds seems to be low, as demonstrated by the low concentrations of D4 and D6 measured. For less volatile c-VMS > D6 the results of the study indicate that food might play a more important role for daily intake. As a general rule, silicone moulds should be used only after precleaning and while strictly following the temperature suggestions of the producers.