Mechanical properties and structure of gel systems

Understanding the origins of the mechanical properties and its correlation withrnthe microstructure of gel systems is of great scientific and industrial interest. Inrngeneral, colloidal gels can be classified into chemical and physical gels, accordingrnto the life time of the network bonds. The characteristic di↵erences in gelationrndynamics can be observed with rheological measurements.rnAs a model system, a mixture of sodium silicate and low concentration sulfuric acidrnwas used. Nano-sized silica particles grow and aggregate to a system-spanning gelrnnetwork. The influence of the finite solubility of silica at high pH on the gelationrnwas studied with classical and piezo rheometer. The storage modulus of therngel grew logarithmically with time with two distinct growth laws. A relaxationrnat low frequency was observed in the frequency dependent measurements. I attributernthese two behaviors as a sign of structural rearrangements due to the finiternsolubility of silica at high pH. The reaction equilibrium between formation andrndissolution of bonds leads to a finite life time of the bonds and behavior similar tornphysical gel. The frequency dependence was more pronounced for lower water concentrations,rnhigher temperatures and shorter reaction times. With two relaxationrnmodels, I deduced characteristic relaxation times from the experimental data. Besidesrnrheology, the evolution of silica gels at high pH on di↵erent length scales wasrnstudied by NMR and dynamic light scattering. The results revealed that the primaryrnparticles existed already in sodium silicate and aggregated after the mixingrnof reactants due to a chemical reaction. Throughout the aggregation process thernsystem was in its chemical reaction equilibrium. Applying large oscillatory shearrnstrain to the gel allowed for modifying the gel modulus. The e↵ect of shear andrnshear history on the rheological properties of the gel were investigated. The storagernmodulus of the final gel increased with increasing strain. This behavior can be explained with (i) shear-induced aggregate compaction and (ii) combination ofrnbreakage and new formation of bonds.rnIn comparison with the physical gel-like behavior of the silica gel at high pH, typicalrnchemical gel features were exhibited by other gels formed from various chemicalrnreactions. Influences of the chemical structure modification on the gelation wererninvestigated with the piezo-rheometer. The external stimuli can be applied to tunernthe mechanical properties of the gel systems.

Aza-Michael addition of amines to activated alkenes catalyzed by Silica supported perchloric acid under a solvent-free condition

An efficient aza-Michael addition of amines to a series of ,-unsaturated ketones, carboxylic esters, nitriles and chalcones has been carried out using perchloric acid supported over silica gel (HClO4-SiO2) at room temperature in high yields under solvent-free reaction conditions.

Bioactive organic/inorganic hybrids with improved mechanical performance

New sol-gel functionalized poly-ethylene glycol (PEGM)/SiO2-CaO hybrids were prepared with interpenetrating networks of silica and PEGM through the formation of Si-O-Si bonds. Bioactive and mechanical properties were investigated for a series of hybrids containing varying organic/inorganic ratios and PEG molecular weights. In contrast to the unmodified PEG/SiO2-CaO hybrids, which rapidly dissolved and crumbled, the epoxy modified hybrids exhibited good mechanical properties and bioactivity. The compressive strength and Young's modulus were greater for higher molecular weight PEGM hybrids (PEGM600 compared to PEGM300). Compressive strengths of 138 MPa and 81 MPa were found for the 50: 50 and 60: 40 organic/inorganic hybrid samples respectively, which are comparable with cortical bone. Young's modulus values of ∼800 MPa were obtained for the 50 : 50 and 60 : 40 organic/inorganic hybrids. Bioactivity tests were conducted by immersing the hybrids into simulated body fluid and observing the formation of apatite. Apatite formation was observed within 24 hours of immersion. PEGM600 hybrids showed enhanced apatite formation compared to PEGM300 hybrids. Increased apatite formation was observed with increasing organic/inorganic ratio. 70 : 30 and 60 : 40 hybrids exhibited the greatest apatite formation. All PEGM hybrids samples had good cell viability and proliferation. The 60 : 40 PEGM600 hybrids displayed the optimal combination of bioactivity and mechanical strength. The bioactivity of these hybrids, combined with the enhanced mechanical properties, demonstrate that these materials have significant potential for bone regeneration applications.

Thermogravimetric analysis, PXRD, EDX and XPS study of chrysocolla (Cu,Al)2H2Si2O5(OH)4·nH2O : structural implications

Selected chrysocolla mineral samples from different origins have been studied by using PXRD, SEM, EDX and XPS. The XRD patterns show that the chrysocolla mineral samples are non-diffracting and no other phases are present in the minerals, thus showing the chrysocolla samples are pure. SEM analyses show the chrysocolla surfaces are featureless. EDX analyses enable the formulae of the chrysocolla samples to be calculated. The thermal decomposition of the mineral chrysocolla has been studied using a combination of thermogravimetric analysis and derivative thermogravimetric analysis. Five thermal decomposition mass loss steps are observed for the chrysocolla from Arizona (a) at 125 ◦C with the loss of water, (b) at 340 ◦C with the loss of hydroxyl units, (c) at 468.5 ◦C with a further loss of hydroxyls, (d) at 821 ◦C with oxygen loss and (e) at 895 ◦C with a further loss of oxygen. The thermal analysis of the chrysocolla from Congo shows mass losses at 125, 275.3, 805.6 and 877.4 ◦C and for the Nevada chrysocolla, mass loss steps at 268, 333, 463, 786.0 and 817.7 ◦C are observed. The thermal analysis of spertiniite is very different from that of chrysocolla and thermally decomposes at around 160 ◦C. XPS shows that there are two different copper species present, one which is bonded to oxygen and one to a hydroxyl unit. The O 1s is broad and very symmetrical suggesting two O species of equal number. The bond energy of 102.9 eV for the Si 2p suggests that it is in the form of a silicate. The bond energy is much higher for silicas around ∼103.5 eV. The reported value for silica gel has Si 2p at 103.4 eV. The combination of TG, PXRD, EDX and XPS adds to our fundamental knowledge of the structure of chrysocolla.

Studies of phosphazenes. Part 15. Chloro(phenoxy)cyclotetraphosphazenes, N4P4Cl8-n(OPh)n

The reaction of N4P4Cl8(1) with sodium phenoxide (or phenol in the presence of triethylamine) has been studied under a variety of experimental conditions. The chloro(phenoxy)-derivatives, N4P4Cl8-n(OPh)n[n= 1 or 2 (mixture of four non-geminal isomers), 3(mixture of non-geminal isomers), 4(mixture of isomers), 5(mixture of isomers), 6(mixture of four non-geminal isomers), or 8], have been isolated by column chromatography over silica gel. Attempts to separate geometric isomers were unsuccessful. Structural elucidation of the products is based on the 31P n.m.r. data for the chloro-precursors and 1H and 31P n.m.r. spectra of the dimethylamino- and/or methoxy-derivatives. The chlorine-replacement pattern is discussed.

Improving oncolytic adenoviral therapies for gastrointestinal cancers and tumor initiating cells

Although the treatment of most cancers has improved steadily, only few metastatic solid tumors can be cured. Despite responses, refractory clones often emerge and the disease becomes refractory to available treatment modalities. Furthermore, resistance factors are shared between different treatment regimens and therefore loss of response typically occurs rapidly, and there is a tendency for cross-resistance between agents. Therefore, new agents with novel mechanisms of action and lacking cross-resistance to currently available approaches are needed. Modified oncolytic adenoviruses, featuring cancer-celective cell lysis and spread, constitute an interesting drug platform towards the goals of tumor specificity and the implementation of potent multimodal treatment regimens. In this work, we demonstrate the applicability of capsid-modified, transcriptionally targeted oncolytic adenoviruses in targeting gastric, pancreatic and breast cancer. A variety of capsid modified adenoviruses were tested for transductional specificity first in gastric and pancreatic cancer cells and patient tissues and then in mice. Then, oncolytic viruses featuring the same capsid modifications were tested to confirm that successful transductional targeting translates into enhanced oncolytic potential. Capsid modified oncolytic viruses also prolonged the survival of tumor bearing orthotopic models of gastric and pancreatic cancer. Taken together, oncolytic adenoviral gene therapy could be a potent drug for gastric and pancreatic cancer, and its specificity, potency and safety can be modulated by means of capsid modification. We also characterized a new intraperitoneal virus delivery method in benefit for the persistence of gene delivery to intraperitoneal gastric and pancreatic cancer tumors. With a silica implant a steady and sustained virus release to the vicinity of the tumor improved the survival of the orthotopic tumor bearing mice. Furthermore, silica gel-based virus delivery lowered the toxicity mediating proimflammatory cytokine response and production of total and anti-adenovirus neutralizing antibodies (NAbs). On the other hand, silica shielded the virus against pre-excisting NAbs, resulting in a more favourable biodistribution in the preimmunized mice. The silica implant might therefore be of interest in treating intraperitoneally disseminated disease. Cancer stem cells are thought to be resistant to conventional cancer drugs and might play an important role in cancer relapse and the formation of metastasis. Therefore, we examined if transcriptionally modified oncolytic adenoviruses are able to kill these cells. Complete eradication of CD44+CD24-/low putative breast cancer stem cells was seen in vitro, and significant antitumor activity was detected in CD44+CD24-/low –derived tumor bearing mice. Thus, genetically engineered oncolytic adenoviruses have potential in destroying cancer initiating cells, which may have relevance for the elimination of cancer stem cells in humans.

Optimisation of in-cell accelerated solvent extraction technique for the determination of organochlorine pesticides in river sediments

Organochlorine pesticides (OCPs) are ubiquitous environmental contaminants with adverse impacts on aquatic biota, wildlife and human health even at low concentrations. However, conventional methods for their determination in river sediments are resource intensive. This paper presents an approach that is rapid and also reliable for the detection of OCPs. Accelerated Solvent Extraction (ASE) with in-cell silica gel clean-up followed by Triple Quadrupole Gas Chromatograph Mass Spectrometry (GCMS/MS) was used to recover OCPs from sediment samples. Variables such as temperature, solvent ratio, adsorbent mass and extraction cycle were evaluated and optimised for the extraction. With the exception of Aldrin, which was unaffected by any of the variables evaluated, the recovery of OCPs from sediment samples was largely influenced by solvent ratio and adsorbent mass and, to some extent, the number of cycles and temperature. The optimised conditions for OCPs extraction in sediment with good recoveries were determined to be 4 cycles, 4.5 g of silica gel, 105 ᴼC, and 4:3 v/v DCM: hexane mixture. With the exception of two compounds (α-BHC and Aldrin) whose recoveries were low (59.73 and 47.66 % respectively), the recovery of the other pesticides were in the range 85.35 – 117.97% with precision < 10 % RSD. The method developed significantly reduces sample preparation time, the amount of solvent used, matrix interference, and is highly sensitive and selective.

Catalytic cracking of acetic acid to acetic anhydride

Catalytic cracking of acetic acid using triethyl phosphate and silica gel catalysts was investigated. The desired reaction leading to ketene is accompanied by side reactions: two parallel with respect to acetic acid decomposition and the consecutive ketene decomposition reactions. Effect of temperature, catalyst concentration, space velocity, and pressure was studied in detail. Triethyl phosphate was found to be a much better catalyst than silica gel. The optimum yield of ketene was obtained at 750° C, 100 mm. of Hg pressure, and apparent contact time of 5.687 × 10-4 hour.

Hydrochlorination of methanol to methyl chloride in fixed catalyst beds

The vapor phase hydrochlorination of methanol to methyl chloride in fixed beds with silica gel-alumina (88 to 12) and γ-alumina catalysts was studied in a glass tubular reactor in the temperature range of 300° to 390°C. Of the two catalysts studied, γ-alumina gave nearly equilibrium conversions under the experimental conditions. The data are expressed in the form of second-order irreversible rate equations for both the catalysts studied.

cis-trans Enantiomerism in the Diels-Alder cycloadducts of 6-arylfulvenes with maleic anhydride: resolution of the exo adducts via the N-((1S)-1-(naphth-1-yl)ethyl)imide derivatives: assignment of the absolute configurations based on the crystal structure of an imide diastereomer

A new case of the uncommon cis-trans enantiomerism is presented. The titled anhydride adducts were prepared in good yields by the known reaction of three 6-arylfulvenes with maleic anhydride (aryl = phenyl, p-tolyl and p-anisyl). The exo adducts were converted to the corresponding imides by reaction with (1S)-1-(naphth-1-yl)ethylamine in similar to 80% yields, and the resulting diastereomeric imides separated by silica gel column chromatography. They were hydrolysed and recyclised to the chiral anhydrides, in `one-pot' with 10% NaOH-EtOH, followed by treatment with 2 M HCl, in similar to 40% yields. The titled anhydrides were thus obtained in homochiral form, in enantiomeric purities (generally) of similar to 90% as indicated by chiral HPLC. The chiral anhydrides were also converted to the corresponding imides (presumably stereospecifically), by treatment with ammonia solution in excellent yields. The crystal structure of one of the above diastereomeric imides (derived from 6-phenylfulvene) was determined, and based on the known (S)-configuration of the naphthylethylamine moiety, the `configurations' of the original anhydride adducts were assigned. (c) 2005 Elsevier Ltd. All rights reserved.

Chromatographic methods for determination of nimesulide and for stability studies

Simple and rapid HPLC, GC, and TLC procedures have been developed for detection and determination of nimesulide, a non-pharmacopeial drug, in preformulation and dosage form. Use of these techniques has enabled separation of impurities and the precursor in the bulk material and in formulations. Isocratic reversed-phase HPLC was performed on a C-18 column with methanol-water-acetic acid, 67:32:1 (v/v), as mobile phase and UV detection at 230 nm. Calibration curves were linear over the concentration range 100-1000 mug mL(-1) with a good correlation coefficient (0.9993) and a coefficient of variation of 1.5%. Gas chromatography was performed on an OV-17 packed column with temperature programming and flame-ionization detection. The lower limit of determination by HPLC and GC was 4 ppm. Thin-layer chromatography of nimesulide was performed on silica gel G with toluene-ethyl acetate, 8:2, as mobile phase. Stability testing of the drug was performed under different temperature, humidity, and UV-radiation conditions.

Reversible Formation of a Planar Chiral Ferrocenylboroxine and Its Supramolecular Structure

The boronic acid (pS)-1,2-NpFcB(OH)(2) (1) was obtained by treatment of the lithiated species (pS)-1,2-NpFcLi with B(O(i)Pr)(3), followed by acidic workup; subsequent dehydration gave the enantiomerically pure boroxine [(pS)-1,2-NpFcBO](3) (2) in 49% isolated yield. Multinuclear and 2D NMR spectroscopies, single-crystal X-ray diffraction, and elemental analysis served to confirm the structure of 2. In the solid-state structure, all three of the naphthyl groups point in one direction and all of the ferrocenyl moieties are placed on the opposite face of the boroxine ring, which is also the preferred conformation in solution according to a (1)H, (1)H-NOESY experiment. Cyclic voltammetry revealed three separate reversible oxidation events, which suggests significant communication between the ferrocenyl moieties. These redox processes experience a cathodic shift upon addition of 4-dimethylaminopyridine (DMAP) as a Lewis base. The six-membered ring is opened upon treatment with hot CHCl(3)/MeOH to form the methoxy species (pS)-1,2-NpFcB(OH)(OMe) (3), which can be converted back to the cycle 2 by dissolution in wet CHCl(3), followed by column chromatography on silica gel.

Solar driven Adsorption Desalination system

Desalination is one of the most traditional processes to generate potable water. With the rise in demand for potable water and paucity of fresh water resources, this process has gained special importance. Conventional thermal desalination processes involves evaporative methods such as multi-stage flash and solar distils, which are found to be energy intensive, whereas reverse osmosis based systems have high operating and maintenance costs. The present work describes the Adsorption Desalination (AD) system, which is an emerging process of thermal desalination cum refrigeration capable of utilizing low grade heat easily obtainable from even non-concentrating type solar collectors. The system employs a combination of flash evaporation and thermal compression to generate cooling and desalinated water. The current study analyses the system dynamics of a 4-bed single stage silica-gel plus water based AD system. A lumped model is developed using conservation of energy and mass coupled with the kinetics of adsorption/desorption process. The constitutive equations for the system components viz. evaporator, adsorber and condenser, are solved and the performance of the system is evaluated for a single stage AD system at various condenser temperatures and cycle times to determine optimum operating conditions required for desalination and cooling. (C) 2013 P. Dutta. Published by Elsevier Ltd.

Simulation study of a two-stage adsorber system

The present study simulates a two-stage silica gel + water adsorption desalination (AD) and chiller system. The adsorber system thermally compresses the low pressure steam generated in the evaporator to the condenser pressure in two stages. Unlike a standalone adsorption chiller unit which operates in a closed cycle the present system is an open cycle wherein the condensed desalinated water is not fed back to the evaporator. The mathematical relations formulated in the current study are based on conservation of mass and energy along with isotherm relation and kinetics for RD-type silica gel + water pair. Various constitutive relations for each component namely the evaporator, adsorber and condenser are integrated in the model. The dynamics of heat exchanger are modeled using LMTD method, and LDF model is used to predict the dynamic characteristic of the adsorber bed. The system performance indicators namely, specific cooling capacity (SCC), specific daily water production (SDWP) and coefficient of performance (COP) are used as objective functions to optimize the system. The novelty of the present work is in introduction of inter-stage pressure as a new parameter for optimizing the two-stage operation of AD chiller system. (C) 2014 Elsevier Ltd. All rights reserved.

Continuous vapour adsorption cooling system with three adsorber beds

In this paper, the design of a new solar operated adsorption cooling system with two identical small and one large adsorber beds, which is capable of producing cold continuously, has been proposed. In this system, cold energy is stored in the form of refrigerant in a separate refrigerant storage tank at ambient temperature. Silica gel water is used as a working pair and system is driven by solar energy. The operating principle is described in details and its thermodynamic transient analysis is presented. Effect of COP and SCE for different adsorbent mass and adsorption/desorption time of smaller beds are discussed. Recommended mass and number of cycles of operation for smaller beds to attain continuous cooling with average COP and SCE of 0.63 and 337.5 kJ/kg, respectively are also discussed, at a generation, condenser and evaporator temperatures of 368 K, 303 K and 283 K, respectively. (C) 2015 Elsevier Ltd. All rights reserved.