Precipitation by organic solvents

Water miscible organic solvents, such as ethanol, isopropanol and acetone, reduce the solubility of proteins by decreasing the dielectric constant of aqueous solution and taking away water from around the proteins. Also, these organic solvents can remove the lipids bound to a protein. Precipitation by organic solvents is affected by temperature, ionic strength and the pH of the buffer solution. 

Solvent extraction techniques are useful in the quantitative analysis of niobium. The fluoro complexes are amenable to extraction by a wide variety of ketones. Some of the water-insoluble complexes with organic precipitants are extractable by organic solvents and colorimetry is performed on the extract. An example is the extraction of the niobium—oxine complex with chloroform (41). The extraction of the niobium—pyrocatechol violet complex with tridodecylethylammonium bromide and the extraction of niobium—pyrocatechol—sparteine complex with chloroform are examples of extractions of water-soluble complexes. Colorimetry is performed on the extract (42,43). Colorimetry may also be performed directly on the water-soluble complex, eg, using ascorbic acid and 5-nitrosahcyhc acid (44,45). 

The primary polymerization product ia these processes has a relatively wide molecular weight distribution, and a separate step is often used to narrow the polydispersity. Such a narrowkig step may consist of high vacuum stripping to remove volatile polymer chains, often followed by a solvent fractionation step (35,36), sometimes a solvent fractionation step alone (37,38), or a fractional precipitation from organic solvent (32). The molecular weight distribution can also be narrowed by depolymerization at elevated temperatures ia the presence of a depolymerization catalyst (217—220). 

Quantitative. Classically, silver concentration ia solution has been determined by titration with a standard solution of thiocyanate. Ferric ion is the iadicator. The deep red ferric thiocyanate color appears only when the silver is completely titrated. GravimetricaHy, silver is determined by precipitation with chloride, sulfide, or 1,2,3-benzotriazole. Silver can be precipitated as the metal by electro deposition or chemical reduciag agents. A colored silver diethjldithiocarbamate complex, extractable by organic solvents, is used for the spectrophotometric determination of silver complexes. 

Grace and Co.) is added to the mixture which is refluxed for 5-10 min or until the gas evolution is complete. The product, often an aziridine, is obtained by pouring the reaction mixture into water and either by filtering or by extracting the precipitate with organic solvent followed by a water wash and drying. 

When appreciable amounts of pectin, proteins, lipids, unwanted polyphenols, or other compounds are suspected to be present in anthocyanin-containing extracts, some of them can be precipitated or the anthocyanins may be crystalhzed and separated from the others. Pectin and proteins can be removed by organic solvents such as methanol and acetone in order to reduce their solubility, then precipitated and separated by centrifugation. Gelatin was used to remove proanthocyanidin due to its high molecular weight. Anthocyanins were reported to be precipitated early by lead acetate to achieve isolation from other materials. ... 

Exudate collection in trap solutions usually requires subsequent concentration steps (vacuum evaporation, lyophilization) due to the low concentration of exudate compounds. Depending on the composition of the trap solution, the reduction of sample volume can lead to high salt concentrations, which may interfere with subsequent analysis or may even cause irreversible precipitation of certain exudate compounds (e.g., Ca-citrate, Ca-oxalate, proteins). Therefore, if possible, removal of interfering salts by use of ion exchange resins prior to sample concentration is recommended. Alternatively, solid-phase extraction techniques may be employed for enrichment of exudate compounds from the diluted trap solution (11,22). High-molecular-weight compounds may be concentrated by precipitation with organic solvents [methanol, ethanol, acetone 80% (v/v) for polysaccharides and proteins] or acidification [trichloroacetic acid 10% (w/v), per-... 

DCC is a waxy solid that is often difficult to remove from a bottle. Its vapors are extremely hazardous to inhalation and to the eyes. It should always be handled in a fume hood. The isourea by-product of a DCC-initiated reaction, dicyclohexyl urea (DCU) (Figure 3.5), is also water-insoluble and must be removed by organic solvent washing. For synthesis of peptides or affinity supports on insoluble matrices this is not a problem, because washing of the support material can be done without disturbing the conjugate coupled to the support. For solution phase chemistry, however, reaction products must be removed by solvent washings, precipitations, or recrystallizations. 

Elimination of Cellulases from Xylanases. Classical methods of protein fractionation can be used for to separate cellulases and xylanases on a large scale only when they differ considerably in molecular weight or isoelectric point. The Tricho-derma harzianum enzymes were separated by ultrafiltration because the xylanase was smaller and passed through the membrane into the ultrafiltrate 18). Fractional precipitation with organic solvents is another possibility (7). 

The possibility of obtaining higher surlacc-area precipitates from organic solvents is described by Desmond et al. [20] polar compounds such as alcohols. 

If polymerization catalysts, for instance for alkenc polymerization (Zicglcr-Natta-type catalysts), are prepared by precipitation methods, they can be formed by precipitation from organic solvents, as claimed in several patents [22], In these patents the precipitation of titanium-magnesium compounds in THF with hexane as precipitating agent is used for the formation of the catalyst. Many important Zicgler-Natta initiators are solids, and heterogeneous initiator systems seem to be necessary for the production of isotactic polyalkenes [23]. However, not much information on the details of catalyst preparation is available in the open literature. 

The coil-globule transition can also be observed by PL (from changes in the IMM of the polymer), when polymers are precipitated in organic solvents. These data were obtained for PMMA in toluene precipitated with octane or other non-solvents. Figure 9 shows the dependence Tw on the concentration of octane used as the precipitant for PMMA fractions of various molecular weights. Naturally, for PMMA in... 

ADP-ribosylation of tfie samples is carried out in glass tubes (approximate volume 5 ml) in case the reaction has to be followed by precipitation with organic solvents. Therefore, the markings on the tubes should withstand solvents. Each tube contains 10 (xl of preactivated toxin (100 ng PT/tube) and 20 [il of membrane suspension. The reaction is readily started by addition of 30 1 of the P-NAD" -containing buffer, resulting in a total volume of 60 (il per tube. ADP-ribosylation of the thoroughly vortexed sample is conducted for 30 min at 30°C or tor 20 min at 37°C while the tubes are agitated con-tinously. 

Derivation By nitrating mannitol with mixed acid, purifying the precipitate from organic solvents and stabilizing. 

AMPS is a water-soluble monomer it is also soluble in polar organic solvents such as methanol, dimethyl formamide (DMF), and dimethyl sulfoxide (DMSO). MPDMA is soluble in similar polar solvents. Because of the solubility characteristics of these two species, the reactions (that is, the formation of the ion pairs) were conducted in water, methanol, or DMF. The product, MPDMA AMPS, was very hygroscopic and apparently had a tendency to polymerize spontaneously during the course of isolation (solvent stripping and precipitation by non-solvents). The preferred medium for preparation was found to be anhydrous THF which also had been used for other ionic monomer pairs (13). In addition, a slight excess of MPDMA was used to ensure complete reaction of AMPS. The excess base, MPDMA, was removed using cold THF (which did not dissolve the product). 

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