Silica freeze-drying

C. Isolation and purification of XK-62-2 100 g of the white powder obtained in the above step B are placed to form a thin, uniform layer on the upper part of a 5 cm0X 150 cm column packed with about 3 kg of silica gel advancely suspended in a solvent of chloroform, isopropanol and 17% aqueous ammonia (2 1 1 by volume). Thereafter, elution is carried out with the same solvent at a flow rate of about 250 ml/hour. The eluate is separated in 100 ml portions. The active fraction is subjected to paper chromatography to examine the components eluted. XK-62-2 is eluted in fraction Nos. 53-75 and gentamicin Cja is eluted in fraction Nos. 85-120. The fraction Nos. 53-75 are combined and concentrated under reduced pressure to sufficiently remove the solvent. The concentrate Is then dissolved in a small amount of water. After freeze-drying the solution, about 38 g of a purified preparate of XK-62-2 (free base) is obtained. The preparate has an activity of 950 units/mg. Likewise, fraction Nos. 85-120 are combined and concentrated under reduced pressure to sufficiently remove the solvent. The concentrate is then dissolved in a small amount of water. After freeze-drying the solution, about 50 g of a purified preparate of gentamicin Cja (free base) is obtained. 

In this case some of the Sll silica was freeze-dried and degassed at 10-3 Torr and 150°C and then reacted with trichloromethylsilane in the vapour phase this replaced the surface hydroxyl groups by chloro groups. The particles were then redispersed (with the aid of ultrasonics) in a 4 1 volume ratio toluene THF solvent mixture. "Living" polystyrene (PS19), in a similar solvent mixture was then introduced and the grafting reaction allowed to proceed for 24 hr at room temperature. 

In the first freeze drying plant [2.9] phosphorous pentoxide has been used to absorb the water vapor, but to day this technique is outdated. The development of refrigeration technology with compressors or NH3 absorption and the availability of LN2 has replaced water absorption by silica gel or similar products. Some trials aiming to revive this technology are detailed in Section 1.2.6. 

The RM of the dried product was measured at 50 °C over P205 or in an oven with circulating air at 50 °C, or in the same oven at 90 °C over silica gel. Identical measurements were made with fresh bones. For NMR measurements, a known amount of D20 was added to the bone in a glass container. After equilibrium between DzO and H20 was reached, a known amount of the product was taken from the solution and studied in a Perkin Elmer NMR-spectrometer. In Fig. 3.23 the water contents of fresh and freeze dried bones are listed measured by NMR and the gravimetric methods at 90 °C. The data show that only a certain amount of the total water can be removed at 90 °C, while another amount is so... 

Molecular imprinting is not limited to organic polymer matrices, but can also be applied to silica-based materials and even proteins. Proteins freeze-dried in the presence of a transition state analogue as template have been used successfully as catalysts, e.g., for the dehydrofluorination of a fluorobutanone. For instance, lyophilized 3-lactoglobulin imprinted in this manner with N-isopropyl-N-ni-trobenzyl-amine could accelerate the dehydrofluorination by a factor of 3.27 compared to the non-imprinted protein see Table 5 [62]. In a similar procedure, BSA was imprinted with N-methyl-N-(4-nitrobenzyl)-S-aminovaleric acid and showed an enhancement of the catalytic effect by a factor of 3.3 compared to the control protein for the same reaction see Table 5 [113]. 

The migration order of wine anthocyanins in CE has been studied in detail and the results have been compared with those obtained by RP-HPLC-MS. Wines were filtered and used for the analyses without any other pretreatment. Wine samples of 10 ml were freeze-dried, redissolved in methanol and applied for semi-preparative fractionation. CZE measurements were carried out in a fused-silica capillary (46 cm effective length, 75 /an i.d.). The capillary was conditioned with 0.1 M NaOH (2 min), water (2 min) and running buffer (5 min). The buffer consisted of 50 mM sodium teraborate (pH = 8.4) containing 15 per cent (v/v)... 

To estimate the recovery of cell walls as dry weight, remove a small aliquot, record weight, freeze dry and then further dry to a constant weight over desiccant (e.g., silica... 

Extraction and extract separation. The freeze dried samples were ground and extracted with chloroform for one hour at 55°C. Free sulfur was removed by percolating the extracts over an activated copper column. Resulting extracts were separated using thin layer chromatography (Merck precoated T.L.C. Silica-gel 60f-254) with cyclohexane as the eluting solvent. Three fractions were obtained an immobile polar fraction, an "intermediate fraction, and a saturated/unsaturated hydrocarbon fraction. 

Method C Freeze-dried extract mixed with silica gel and heated, 10 min at 150 °C. n.d., not detected. 

In analyses of extract from freeze-dried fish [89] gel chromatography on Bio-Beads S-X3 with cyclohexane/ethyl acetate (1/1) was used for removal of neutral fat. Then adsorption column chromatography on silica gel (1.5% water) according to the multi-residue procedure of Specht and Tillkes [93] was applied. Elution with n-hexane separated TCBTs and PCBs from the main portion of organochlorine pesticides and other more polar compounds. The hexane extract was evaporated to 0.5 ml for GC-MS determination [89,90]. 

At the onset of our research work, we tried to operate in the same way with freeze-dried products that had received a strong gamma irradiation (40-60 kGy) at room temperature. The results were disappointing because we were limited to rather low temperatures (below 100°C) and, even so, when the material could stand high temperatures like freeze-dried silica. This is why we attempted to apply to these products the same methodology that we used previously for our investigation on water and solutions. 

Additional studies done on freeze-dried silica gels (microbeads gels from Rhodia, Salindres) give some support to this idea. In Figure 23, for instance, we can see that when we shift from a largely hydrated material (like the fresh starting material at around 40% residual moisture) to the low residual moisture freeze-dried gels, the -120°C/-40°C emission is first almost completely erased and then disappears (for 2% residual moisture). At the same time the low-temperature peak increases and sharpens. 

Moisture, and Ash Content. For Skeletonema, the wet basis moisture content In batches one through four were 88.9%, 87.5%, 90.3%, and 87.6%, respectively. The average wet basis moisture content of the freeze dried material was 5%. The average ash content of all batches was 30% dry weight basis. The high ash level Is due to the silica skeleton of Skeletonema costatum. 

Add the sintered-glass funnel to the Buchner filter system and attach the vacuum source. Fill the funnel to a depth of 2 cm using anhydrous silica. Filter the aqueous polymer solution through the silica. A blue colour will appear, indicating the Cud I) species that is formed in the presence of oxygen. The solution of polymer must be freeze-dried overnight to remove all water and leave a white solid polymer product. Yields >90% are typical. 

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