Synthesis of Melting Gels Using Mono-Substituted and Di-Substituted Alkoxysiloxanes

Hybrid organic-inorganic sol-gel materials containing silica were first called “ORMOSILs” in 1984.1 Since then, the number of hybrid organicinorganic combinations has increased rapidly.2 Hybrid materials have remarkable features resulting from the synergistic combination of both inorganic and organic components that make them suitable for a wide range of applications such as electrochemical devices, biomedical applications including drug delivery, and electronic and optoelectronic applications including light-emitting diodes, photodiodes, solar cells, gas sensors and field effect transistors. Generally, organic-inorganic materials are classified in two broad categories: Class I materials where the organic and inorganic components are embedded one within the other and display weak bonds, and Class II materials where there are strong covalent bonds between the inorganic and organic components.3 For more than 25 years hybrid gels have been grown by sol-gel process.4 Since sol-gel processing is a low temperature method, it is only natural that sol-gel processing has been extended to hybrid materials with retained organic content. Ordinarily, the outcome of the sol-gel process with the precursor tetraethylorthosilicate (TEOS) (Aldrich Prod. No. 333859) is a 3-dimensional network. TEOS, with 4 identical groups attached to Si, undergoes hydrolysis and polycondensation reactions. The 4 identical groups can be changed to, for example, 3 identical groups and one group with a direct Si-C bond. While the remaining 3 ethoxy groups are reactive to hydrolysis, the substituted group, for example, methyl, is not

Phenyl-Substituted Siloxane Hybrid Gels that Soften Below 140[degrees]C

A characteristic of so-called melting gels is that the gels, which are rigid at room temperature, are able to soften and resoften at temperatures around 110 [degrees]C. However, after consolidation at temperatures higher than 150 [degrees]C, the gels no longer resoften. Two systems of melting gels were investigated: phenyltrimethoxysilane (PhTMS)–diphenyldimethoxysilane (DPhDMS) and phenyltriethoxysilane (PhTES)–diphenyldiethoxysilane (DPhDES). The influence of disubstituted versus monosubstituted alkoxide on the softening behavior and the temperature of decomposition was studied. The consolidation temperature increased as the amount of disubstituted alkoxide increased, while the decomposition temperature increased only slightly. In general, the ethoxy-containing gels (maximum at 150[degrees]C) consolidated at lower temperatures than the methoxy-containing gels (maximum at 180[degrees]C)

Carbonic Anhydrase Inhibitors. Part 541: Metal Complexes of Heterocyclic Sulfonamides: A New Class of Antiglaucoma Agents

Metal complexes of heterocyclic sulfonamides possessing carbonic anhydrase (CA) inhibitory properties were recently shown to be useful as intraocular pressure (IOP) lowering agents in experimental animals, and might be developed as a novel class of antiglaucoma drugs. Here we report the synthesis of a heterocyclic sulfonamide CA inhibitor and of the metal complexes containing main group metal ions, such as Be(II), Mg(II), Al(III), Zn(II), Cd(II) and Hg(II) and the new sulfonamide as well as 5-amino-1,3,4-thiadiazole-2-sulfonamide as ligands. The new complexes were characterized by standard physico-chemical procedures, and assayed as inhibitors of three CA isozymes, CA I, II and IV. Some of them (but not the parent sulfonamides) strongly lowered IOP in rabbits when administered as a 2% solution into the eye

Hybrid Sol–Gel Glasses with Glass-Transition Temperatures below Room Temperature

Melting gels are hybrid gels that have the ability to soften and flow at around 100 ° C for some combinations of mono- and di-substituted alkoxysiloxanes, where substitutions are either all aromatic or all aliphatic. In this study, melting gels were prepared using phenyltriethoxysilane (PhTES) and dimethyldiethoxysilane (DMDES), meaning both an aromatic and aliphatic substitution. Differential scanning calorimetry was performed to identify glass-transition temperatures, and thermal gravimetric analysis coupled with differential thermal analysis (TGA-DTA) was performed to measure weight loss. The glass-transition temperatures ( T g ) ranged from – 61 ° C to + 5.6 ° C, which are between the values in the methyl only system, where all T g values are less than 0 ° C, and those values in the phenyl only system, where T g values are greater than 0 ° C. The T g decreased with an increase in the DMDES fraction. Below 450 ° C, the gels lost little weight, but around 600 ° C there was a drop in weight. This temperature is lower than the temperature for gels prepared with only aromatic substitutions, but higher than that for gels prepared with only aliphatic substitutions. Final heat treatment was carried out at 150 ° C for the gel with 80%PhTES-20%DMDES (in mol%), and the consolidation temperature increased with increasing DMDES content to 205 ° C for the gel with 50%PhTES-50%DMDES. After this heat treatment, the melting gels no longer soften

Thermal analysis of organically modified siloxane melting gels

Hybrid melting gels were prepared by a sol–gel process, starting with a mono-substituted siloxane and a disubstituted siloxane, methyltrimethoxysilane (MTES) together with dimethyldimethoxysilane (DMDES). Five gel compositions were prepared with concentrations between 50% MTES–50% DMDES and 75% MTES–25% DMDES (in mol.%)

Carbonic Anhydrase Inhibitors. Part 551 Metal Complexes of 1,3,4-Thiadiazole-2-Sulfonamide Derivatives: In Vitro Inhibition Studies With Carbonic Anhydrase Isozymes I, II and IV

Coordination compounds of 5-chloroacetamido-1,3,4-thiadiazole-2-sulfonamide (Hcaz) with V(IV), Cr(lll), Fe(ll), Co(ll), Ni(ll) and Cu(ll) have been prepared and characterized by standard procedures (spectroscopic, magnetic, EPR, thermogravimetric and conductimetric measurements). Some of these compounds showed very good in vitro inhibitory properties against three physiologically relevant carbonic anhydrase (CA)isozymes, i.e., CA I, II, and IV. The differences between these isozymes in susceptibility to inhibition by these metal complexes is discussed in relationship to the characteristic features of their active sites, and is rationalized in terms useful for developing isozyme-specific CA inhibitors

Complexes With Biologically Active Ligands. Part 91 Metal Complexes of 5-Benzoylamino- and 5-(3-Nitrobenzoyl-Amino)-1,3,4-Thiadiazole-2-Sulfonamide as Carbonic Anhydrase Inhibitors

Complexes containing the anions of 5-benzoylamido-1,3,4-thiadiazole-2-sulfonamide and 5-(3-nitro-benzoylamido)-1,3,4-thiadiazole-2-sulfonamid as ligands, and V(IV); Cr(III); Fe(III); Co(II); Ni(II); Cu(II) and Ag(I) were synthesized and characterized by standard procedures (elemental analysis; IR, electronic, and EPR spectroscopy; TG, magnetic and conductimetric measurements). The original sulfonamides and their metal complexes are strong inhibitors of two carbonic anhydrase (CA) isozymes, CA I and II

Study of the Gelling Process in the La-Co-Citric Acid System

The gelling process in the aqueous lanthanum-cobalt-citric acid system was studied using UV-VIS and IR spectroscopic methods, as well as viscosity measurements, to establish the gelling mechanism of transition metal ions (La3+ and Co2+) in the presence of chelating agent. Lanthanum and cobalt nitrates and lanthanum and cobalt acetates, respectively, were used as starting reagents, and the citric acid was used as chelating agent. The gelation process was investigated at room temperature and at 80°C. At elevated temperature, the gels were obtained after 30 h, whereas at room temperature, these were obtained in 1 month. Complex gels were formed for the both studied systems. The Co2+ ions mainly present an octahedral symmetry during the whole gelation process, whereas the citric acid acts as monodentate or bridging ligand depending on the metal precursors used. The mechanism of formation of the La- Co-CA based gels with the coordinative structures was proposed

Thickness-properties synergy in organic–inorganic consolidated melting-gel coatings for protection of 304 stainless steel in NaCl solutions

Homogeneous and crack-free methyl-substituted organic–inorganic hybrid glass coatings (thickness up to 10 μm) were deposited on AISI 304 stainless steel. Different hybrid glasses obtained fromconsolidation of the diluted melting gels with various methyltriethoxysilane (MTES)/dimethyldiethoxysilane (DMDES) ratios were evaluated considering chemical structure, coating adhesion and corrosion protection. The 70MTES/30DMDES (molar%) melting-gel coating provided improved corrosion protection for this steel due to the synergy of different properties: a highly cross-linked inorganic structure, a coating plasticity based on the hybrid network, and a good adhesion to the substrate through hydroxyl groups. Electrochemical results showa good barrier film with a passive range of 500 mV, a lowanodic current density (0.03 nA cm−2) and impedance values of 109.5Ωcm2 after two months of immersion in 3.5 wt.% NaCl solution

Corrosion Protection of 304 Stainless Steel with Melting Gels Coatings

Methyl-substituted melting gels were used to coat AISI 304 stainless steel substrates. Crack-free coatings up to 1 mm in thickness were obtained. SEM micrographs of cross-sections con fi rm good adhesion to the surface. Samples were subjected to structural characterization using FT-IR, and Raman spectroscopy. Mechanical properties were investigated by micro-scratch tests. Electrochemical analyses (anodic polarization and electrochemical impedance spectroscopy) were performed in 3.5% NaCl solutions. Electrochemical tests show excellent performance of the coatings against corrosion with no sign of degradation after several months of immersion