Interfacial behavior of a reacting alkoxysilane monolayer system

We report here the results on the investigations of the dynamic interfacial behavior of a trifunctional alkoxysilane, octadecyltrimethoxysilane (OTMS) as it is reacting at the air-water interface. We have investigated both the II-A isotherms and A(t) isobars of OTMS at acidic subphases. An attempt to analyze the kinetics of the reaction in the monolayer was limited to the early stages of the reactions and only describes the kinetics of hydrolysis. We also confirmed by rheological measurements that this system does indeed form a network inefficiently and the resulting structure most likely consists of extensive linear segments as has been suggested in earlier reports. The general rheological characteristic indicates the product to have high molecular weight. The product also exhibited a 2D sol-gel transition that has general features of a percolating network. However, the scaling behavior does not follow exactly that predicted; several reasons for this are discussed. (Figure Presented) A(t) isobars of OTMS at various subphase pH

Mesoporous TMOS-MTMS copolymer silica gels catalyzed by fluoride

Mesoporous HF-catalyzed tetramethoxysilane-methyltrimethoxysilane (TMOS-MTMS) copolymer silica gels with average pore diameter from 80 to 100 Å and narrow pore size distribution have been obtained. Mesoporous TMOS-MTMS copolymer gels with tetramethoxysilane ranging from 10% to 100% were also produced with tetrabutylammonium fluoride (TBAF) catalyst. The pore sizes of TBAF-catalyzed copolymer gels were controlled over a range from 25 to 194 Å. Their pore sizes increased with increasing fluoride content to R2=0.112 (R2, molarratio of F/Si) and then level off. The catalytic effect of fluoride on the sol-gel process was investigated. The results suggest that multi-fluorinated silicon species catalyze the silica polymerization. © 2001 Elvier Science B.V. All rights reserved

Grazing incidence synchrotron x-ray diffraction of polymerizing Langmuir monolayers

Octadecyltrimethoxysilane (OTMS) was spread on the water surface of a Langmuir trough. Utilizing the high-intensity synchrotron X-ray radiation at the Advanced Photon Source at Argonne National Laboratory, the kinetics of film growth of OTMS as a function of the subphase pH was studied. In situ grazing incidence X-ray diffraction experiments at the air/water interface revealed that OTMS self-assembles into small domains and that the number of these ordered domains increases as OTMS undergoes hydrolysis/condensation reactions. The hexagonal packing of alkyl chains found in the OTMS monolayer is consistent with the ordering found in bulk OTMS by powder X-ray diffraction

Oil-filled silica nanocapsules for lipophilic drug uptake: Implications for drug detoxification therapy

Oil-filled nanocapsules were synthesized using the oil droplets of an O/W microemulsion as templates. A polysiloxane/silicate shell was formed at the surface of the oil droplet by cross-linking n-octadecyltrimethoxysilane and tetramethoxysiloxane. The shell imparted stability to the oil droplets against coalescence. The nanocapsules can be used in a number of applications (i.e., biomedical or environmental) where the free concentration of lipophilic compounds must be reduced. As a proof, the nanocapsules (1.4% w/v oil content in saline) were shown to sequester quinoline (8μM) from saline in \u3c15 min. The removal process was followed in real time using the UV absorbance of free quinoline in solution. Our primary goal is to produce a system for drug detoxification therapy. As a proof of concept for sequestering drugs, the nanocapsules were used in the removal of free bupivacaine from normal saline solution. The free bupivacaine concentration was determined in the aqueous phase after contact with such nanocapsules using HPLC. The results showed a rapid removal of bupivacaine. The nanocapsules at a concentration of 0.1% w/v oil content showed a maximum removal capacity of ≈1900 μM bupivacaine

Aggregation and surface morphology of a poly(ethylene oxide)-block-polystyrene three-arm star polymer at the air/water interface studied by AFM

The behavior of a three-arm star amphiphilic copolymer, PEO3-b-PSD3 were investigated at the air/water interface through atomic force microscopy (AFM) images of the monolayer on mica. The Langmuir-Blodgett (LB) films were prepared on the KSV 5000 system with a platinum Wilhelmy plate. The PEO3-b-PS3 three arm star used were prepared by the anionic polymerization of ethylene oxide followed by the ATRP synthesis of styrene. It was assumed that the characteristics of the monolayer at the air/water interface remained unchanged upon transfer to the mica surface

Crystallization and Solid-State Characterization of the Hemihydrate of Albuterol Hemisulfate

Comprehensive solid-state characterization and development of a controlled crystallization process of the recently discovered hemihydrate of albuterol hemisulfate (ASH) are presented. The ASH is physically stable when stored at ambient conditions for at least 3 months and at 0% relative humidity for at least 2 months. The thermal dehydration of the hydrate occurs at ∼100 °C and proceeds without a loss of crystallinity. The dehydrated crystal structure persists up to decomposition temperature (∼160–185 °C). An inspection of the single-crystal X-ray structure revealed an isolated-site (class A) hydrate with a complex three-dimensional supramolecular network sustained via multiple strong hydrogen bonds. Thermodynamic stability studies established that the hydrate is more-stable relative to the nonsolvated form at <i>a</i>_w > 0.63 at 5 °C, <i>a</i>_w > 0.65 at 20 °C, and <i>a</i>_w > 0.80 at 40 °C. The constructed phase diagram for the anhydrate–hydrate system guided the development of a controlled crystallization process at a 0.5 g scale with a yield of ∼92 wt % using a combination of cooling and antisolvent addition crystallizations

Perioperative Interventions to Reduce Pancreatic Fistula Following Pancreaticoduodenectomy: Meta-Analysis

BACKGROUND: Data on interventions to reduce postoperative pancreatic fistula (POPF) following pancreatoduodenectomy (PD) are conflicting. The aim of this study was to assimilate data from RCTs. METHODS: MEDLINE and Embase databases were searched systematically for RCTs evaluating interventions to reduce all grades of POPF or clinically relevant (CR) POPF after PD. Meta-analysis was undertaken for interventions investigated in multiple studies. A post hoc analysis of negative RCTs assessed whether these had appropriate statistical power. RESULTS: Among 22 interventions (7512 patients, 55 studies), 12 were assessed by multiple studies, and subjected to meta-analysis. Of these, external pancreatic duct drainage was the only intervention associated with reduced rates of both CR-POPF (odds ratio (OR) 0.40, 95 per cent c.i. 0.20 to 0.80) and all-POPF (OR 0.42, 0.25 to 0.70). Ulinastatin was associated with reduced rates of CR-POPF (OR 0.24, 0.06 to 0.93). Invagination (versus duct-to-mucosa) pancreatojejunostomy was associated with reduced rates of all-POPF (OR 0.60, 0.40 to 0.90). Most negative RCTs were found to be underpowered, with post hoc power calculations indicating that interventions would need to reduce the POPF rate to 1 per cent or less in order to achieve 80 per cent power in 16 of 34 (all-POPF) and 19 of 25 (CR-POPF) studies respectively. CONCLUSION: This meta-analysis supports a role for several interventions to reduce POPF after PD. RCTs in this field were often relatively small and underpowered, especially those evaluating CR-POPF