Self-Restructuring of Polyhydromethylsiloxanes by the Hydride Transfer Process: A New Approach to the Cross-Linking of Polysiloxanes and to the Fabrication of Thin Polysiloxane Coatings.

The branching and cross-linking of siloxane polymers are important processes in silicone technology. A new type of such a process has been developed, which is a self-restructuring of linear polyhydromethylsiloxane (PHMS). This process involves the reorganization of the PHMS to form a highly branched siloxane polymer or finally a cross-linked siloxane network. It occurs through the transfer of a hydride ion between silicon atoms catalyzed by tris(pentafluoromethyl)borane. Its advantage over existing branching and cross-linking reactions is that it runs at room temperature without a low-molecular-weight cross-linker in the absence of water, silanol groups, or other protic compounds and it does not use metal catalysts. The study of this process was carried out in toluene solution. Its course was followed by 1H NMR, 29Si NMR and FTIR, SEC, and gas chromatography. A general mechanism of this new self-restructuring process supported by quantum calculations is proposed. It has been shown that a linear PHMS self-restructured to a highly branched polymer can serve as a pure methylsiloxane film precursor.

Organosulfur Materials with High Photo- and Photo-Oxidation Stability: 10-Anthryl Sulfoxides and Sulfones and Their Photophysical Properties Dependent on the Sulfur Oxidation State.

While few studies show only symmetrical and poorly mono-SOn (n = 0-2) substituted acenes, in this study, we present a synthesis of a new group of unsymmetrical, significantly substituted derivatives, which revealed unique photophysical properties. Both sulfides (S), sulfoxides (SO) and sulfones (SO2) showed very high photochemical stabilities, unusual for these groups, during UV-irradiation at 254/365 nm (air O2 and Ar), which was higher than any found in the literature. For the (S)/(SO) series (254 nm), the stabilities of 80-519 min. (air O2 and Ar) were found. At 365 nm, stabilities of 124-812 min./(air O2) for (S)/(SO) and higher for (SO2) were observed. Photoluminescence lifetimes of (SOn) of the lower anthryl symmetry remained in the following order: (SO2) < (S) < (SO); those with full symmetry were in the following order: (S) < (SO) < (SO2). The enhanced photostability was explained with DFT/MS/Hammett's constants, which showed the leading role of the SOn groups in stabilization of HOMO/LUMO frontier orbitals. The SOn (n = 0-2) substituted acenes turned out to be tunable violet/blue/green emitters by oxidation of S atoms and the introduction of rich substitution.

Synthesis and characterization of bis(amine)palladium(II) carboxylate complexes as precursors of palladium nanoparticles.

The synthesis and characterization of the adducts of n-alkyl amine and palladium n-alkyl carboxylate, [Pd(R2NH2)2(R1COO)2] (R1 = 1, 7, and 11; R2 = 8, 12, and 16), as precursors for the synthesis of palladium nanoparticles (PdNPs) was carried out via differential scanning calorimetry, FT-IR, Raman and UV-Vis spectroscopy, NMR spectroscopy (1H, 13C pulsed field gradient spin-echo (PGSE), and 13C CP-MAS), and powder X-ray diffraction. Pd n-alkyl carboxylates were obtained by a ligand exchange reaction from palladium acetate and the appropriate aliphatic carboxylic acid. It is proposed that carboxyl moieties in the presence of amine ligands are bound to palladium ions via monodentate bonding as opposed to bridging bidentate coordination of pure palladium carboxylate which exists in the form of polymer aggregates. All the studied palladium carboxylate/amine complexes form bilayer lamellar structures and exhibit first-order melting transitions. The evidence presented in this study shows that the phase behavior of bivalent metal carboxylates is mainly controlled by the type of coordination of carboxylate head groups. For n-alkyl carboxylates, linear chain type aggregates replace the trimeric units of Pd acetate. In solution, in the presence of amine, palladium salt aggregates disintegrate and the Pd complex is isolated and stabilized by amine molecules. Using bis(amine) palladium carboxylate adducts as precursors, palladium nanoparticles were fabricated. During high temperature thermolysis, the bis(amine) Pd carboxylate complex decomposes to form small sized Pd nanoparticles. Combining NMR techniques with FTIR spectroscopy, it was possible to follow an original stabilization mechanism. PdNPs are stabilized by weakly interacting long chain aliphatic amide and carboxylic acid derived from the palladium precursor.

Reactions of Zirconium (IV) n-Propoxide with SiH-Functional Polysiloxanes as a Route to Siloxane-Zirconium Hybrid Materials with Enhanced Refractive Index.

The reaction of poly(hydromethylsiloxane-co-methylphenylsiloxane) with zirconium (IV) n-propoxide in dry toluene leads to extensive scission of the siloxane chain and conversion of Si-H groups. These processes produce oligomeric siloxanes and organosilanes containing moisture sensitive propoxy and siloxy-zirconate groups. The obtained post-reaction solution of zirconium containing heterosiloxane oligomers is stable under anhydrous conditions for several weeks. However, its exposure to moisture initiates the hydrolytic condensation of the reactive groups leading to cross-linking and the formation of a siloxane-zirconium composite. Spin coating of the siloxane-zirconium prepolymer followed by exposure to moisture produces thin films with excellent light transparency and increased refractive index. The final coatings are characterized by ellipsometry, UV-Vis, IR, and 29 Si MAS NMR spectroscopies.

Effect of temperature on B(C6F5)3-catalysed reduction of germanium alkoxides by hydrosilanes - a new route to germanium nanoparticles.

Reduction of Ge(OBu)4 with PhMe2SiH catalyzed by B(C6F5)3 at ambient temperature leads to GeH4. We discovered that a higher temperature (above 100 °C) completely changes the reaction course by producing germanium nanoparticles (Ge NPs) in high yield. This process provides a simple one-pot method for Ge NPs synthesis from readily available substrates under mild conditions.

Chlorambucil labelled with the phenosafranin scaffold as a new chemotherapeutic for imaging and cancer treatment.

Here we report the first of the phenosafranin-chlorambucil conjugate as a new type of a chemotherapeutic agent suitable for dual detection methods (spectrophotometric and fluorescence) in imaging systems and cancer treatment. The synthetic cationic dye (3,7-diamino-5-phenylphenazinium chloride) is used as a fluorescent light-triggered scaffold that acts as a carrier for an anti-cancer drug. The chlorambucil was attached covalently via amide bonds to the bifunctional fluorophore, which facilitates tracking with visible light. Our studies revealed that the new photosensitive compound exhibits improved intrinsic activity in vitro in HeLa cells culture experiments; thus it could be a potential anti-cancer candidate in theranostic drug-delivery systems. In light of the urgent need for in vivo monitoring of the biodistribution of anti-cancer drugs, this strategy for the synthesis of innovative conjugates based on the phenosafranin backbone offers a promising possibility for drug control in anti-cancer therapy and diagnosis. This aspect makes the phenosafranin-chlorambucil conjugate unique among currently available biomarkers.

Synthesis and characterization of silver nanoparticles from (bis)alkylamine silver carboxylate precursors.

A comparative study of amine and silver carboxylate adducts [R1COOAg-2(R2NH2)] (R1 = 1, 7, 11; R2 = 8, 12) as a key intermediate in NPs synthesis is carried out via differential scanning calorimetry, solid-state FT-infrared spectroscopy, 13C CP MAS NMR, powder X-ray diffraction and X-ray photoelectron spectroscopy, and various solution NMR spectroscopies (1H and 13C NMR, pulsed field gradient spin-echo NMR, and ROESY). It is proposed that carboxyl moieties in the presence of amine ligands are bound to silver ions via chelating bidentate type of coordination as opposed to bridging bidentate coordination of pure silver carboxylates resulting from the formation of dimeric units. All complexes are packed as lamellar bilayer structures. Silver carboxylate/amine complexes show one first-order melting transition. The evidence presented in this study shows that phase behavior of monovalent metal carboxylates are controlled, mainly, by head group bonding. In solution, insoluble silver salt is stabilized by amine molecules which exist in dynamic equilibrium. Using (bis)amine-silver carboxylate complex as precursor, silver nanoparticles were fabricated. During high-temperature thermolysis, the (bis)amine-carboxylate adduct decomposes to produce silver nanoparticles of small size. NPs are stabilized by strongly interacting carboxylate and trace amounts of amine derived from the silver precursor interacting with carboxylic acid. A corresponding aliphatic amide obtained from silver precursor at high-temperature reaction conditions is not taking part in the stabilization. Combining NMR techniques with FTIR, it was possible to follow an original stabilization mechanism. Graphical abstractThe synthesis of a series (bis)alkylamine silver(I) carboxylate complexes in nonpolar solvents were carried out and fully characterized both in the solid and solution. Carboxyl moieties in the presence of amine ligands are bound to silver ions via chelating bidentate type of coordination. The complexes form layered structures which thermally decompose forming nanoparticles stabilized only by aliphatic carboxylates.

Application of parylene for surface (polymer) enhanced laser desorption/ionization of synthetic polymers.

RATIONALE: Synthetic polymers of molecular masses up to a few kDa can be analyzed without the use of any matrix by direct laser desorption/ionization mass spectrometry (LDI-MS). In this technique, the surface of the sample plate plays a crucial role, and many attempts have been made to understand the influence of the surface on the ease of desorption. Since this technique requires no tedious sample pretreatment, it is a promising method for the rapid characterization of various synthetic polymers. METHODS: Parylene (poly(p-xylylenes), PPX) was tested as a surface support for studying the molecular masses of biocompatible polymers: poly(ethylene glycol) (PEG), poly(L-lactide) (PLLA), and poly(methyl methacrylate) (PMMA). The average molecular masses of the polymers were: PEG (600.0 Da and 3.5 kDa), PMMA (2.0 kDa), and PLLA (2.8 kDa). RESULTS: LDI mass spectra of polymers deposited on parylene were enhanced by a factor of two over those obtained directly from the gold target plate. CONCLUSIONS: Modification of the surface of the target plate by the addition of a PPX layer extended the functionality of LDI-TOF MS, especially for the analysis of low-mass compounds. The LDI analysis using the PPX-coated target plate provided details of polymers including: end-group, composition, monomer unit, and molecular mass distribution. The average molecular weights of four tested polymers on the gold target plate and the PPX support were unchanged, indicating that sample degradation was not occurring despite the high energy of the laser beam. The LDI investigations showed that the PPX support boosted ion yields by a factor of two compared with the gold target plate.

Synthesis and optoelectronic properties of hexahydroxylated 10-O-R-substituted anthracenes via a new modification of the Friedel-Crafts reaction using O-protected ortho-acetal diarylmethanols.

A new modification of the Friedel-Crafts type intramolecular cyclization involving O-protected ortho-acetal diarylmethanols as a new type of reactant, was carried out for the first time in a medium containing a large amount of water at room temperature and enabled synthesis of a series of electron-rich, hexahydroxylated 10-O-R-substituted anthracenes, where R is an alkyl (Me, nBu, n-C(16)H(33)) or arylalkyl group (CH(2)Ph, CH(2)-2-Napht, CH(2)C(6)H(4)CH(2)OAr) and also evaluation of their electronic and optoelectronic properties in solution, crystal, and solid thin film. In this transformation, a central 10-O-R-substituted benzene ring was formed, fused to rings originating from two independent aromatic aldehydes. The reaction proceeded via two identified mechanisms involving acetal and/or free aldehyde groups. The acid sensitive acetal and dibenzyl alkoxy functions have never been used together in the intramolecular Friedel-Crafts type cyclization. The new compounds revealed deep blue fluorescence and quantum yields in solution around 0.3. The electrical properties investigated for thin films obtained by vacuum deposition on glass were 10-O-R-substituent dependent and showed much faster transient current decay in the case of the 10-O-CH(2)Ph derivative than for the material with a 10-O-Me substituent (the lifetime of charge carriers was 25 times shorter in this case). The AFM images of thin films, Stokes shifts, and X-ray analysis of π-stacking interactions in crystals of the new materials have been also obtained.

First approach to nitrogen-containing fused aromatic hydrocarbons as targets for organoelectronics utilizing a new transformation of O-protected diaryl methanols.

A new concise approach for the construction of heteroatom analogues of polycyclic aromatic benzo[g]quinoline, benzo[b]carbazole, and pyrido[b]carbazole systems via diaryl methanols is described. This transformation involves formation of a central benzene ring fused to two aromatic 5- or 6-membered rings of pyrrole and/or pyridine by using a combination of two aromatic aldehydes, of which at least one contains a ring nitrogen. Analysis of the UV and fluorescent properties, Stokes shifts, quantum yields in solution, and pi-stacking interactions in the crystal structures of the new materials was performed. These polycyclic aromatic compounds show potential as small-molecule organoelectronic materials.

Aurophilic complexes as gold atom sources in organic media.

The decomposition, either thermal or under H2, of [O(AuIPR3)3](CF3SO3) (R = Ph 1, R = Me 2) in organic solvents has been studied by 31P(1H) NMR, UV-vis spectroscopy and TEM; during the reaction, the phosphine acts as an efficient oxygen trap and gold nanoparticles are produced which may be stabilized by PVP in acetonitrile (mean diameter 4.5 nm) or oleylamine in toluene (mean diameter 9 nm).