One-step precipitation

Approximately 0.7-pm diameter MIP beads with hydroquinone recognition sites have been prepared using similar one-step precipitation polymerization (Table 6) [183], These beads were immobilized in an agarose gel film deposited on GCE. The resulting MIP-modified electrode has been used as a chronoamperometric chemosensor for determination of hydroquinone. The current response of the chemosensor linearly increased with the hydroquinone concentration in the range of 2-100 pM and LOD for hydroquinone was 1 pM. 

Chen [16] studied experimentally the preparation of ultrafine white carbon black by the common (one-step) precipitation process with the submerged circulative impinging stream reactor (SCISR) developed by Wu [15] as the reaction-precipitation equipment and obtained satisfactory results. 

The development of techniques and methods for protein purification has been an essential pre-requisite for many of the advancements made in biotechnology. This booklet provides advice and examples for a smooth path to protein purification. Protein purification varies from simple one-step precipitation procedures to large scale validated production processes. Often more than one purification step is necessary to reach the desired purity. The key to successful and efficient protein purification is to select the most appropriate techniques, optimise their performance to suit the requirements and combine them in a logical way to maximise yield and minimise the number of steps required. 

It should be pointed out that although most of the research works used silica as a model material, fluorinated surfactants can be used for the preparation of a very wide variety of different mesoporous materials, including TiOj [70], aluminophos-phates and Fe- aluminophosphates [71], and Fe-Si oxides [72]. Organic functionalizations can also be obtained in direct synthesis processes. An example is the preparation in a one-step precipitation process, by Rankin et al., of vinyl-functionalized porous silica materials using mixtures ofTEOS and vinyltriethox-ysilane in aqueous solutions of cationic fluorinated surfactants [73]. 

Yue and Cohen prepared (ZnCd)S2 colloids by multiple loading experiments [164]. The carboxylic acid coordination sites are regenerated and can be re-used to make onion-type binary clusters. This technique allows for the possibility of cluster-size control and the synthesis of core-shell clusters through multiple metal-loading and reduction cycles. Recharging leads to ZnCdS colloids. In a similar fashion, bimetallic Au/Pd nanocolloids have been synthesized as catalysts for hydrogenation of dienes [244]. Eisenberg and coworkers used this method to increase the size of CdS colloids [267]. A one step precipitation approach was used to prepare the bicomponent particles Cd and Se in the presence of polyvinyl alcohol (PVA) [268]. 

The overall rainfall rate and amoimt depend on these microphysical processes and even more greatly on the initial amount of water vapor present, and on the vertical motions that transport water upward, cool the air, and cause supersaturation to occur in the first place. Thus the delivery of water to the Earth s surface as one step in the hydrologic cycle is controlled by both microphysical and meteorologic processes. The global average precipitation amounts to about 75 cm/yr or 750 L/(m yr). 

The mono-silylated or free acetamides, which are liberated during silylation with 22 a, can, furthermore, interfere with any subsequent reaction, e.g. with electrophiles. Thus in the one-pot/one-step silylation, Friedel-Crafts catalyzed, nucleoside synthesis starting from protected sugar derivatives and pyrimidine or purine bases, the mono- or bis-silylated amides such as 22 a can compete with less reactive silylated heterocycHc bases for the intermediate electrophilic sugar cation to form protected 1-acetylamino sugars in up to 49% yield [42, 47]. On silylation with trimethylsilylated urea 23 a the Hberated free urea is nearly insoluble in most solvents, for example CH2CI2, and thus rapidly precipitated [43]. 

Ferrous sulfide acts as a reducing agent at pH 8 to 9 for reduction of hexavalent chromium and then precipitates the trivalent chromium as a hydroxide in one step without pH adjustment.5162 So, the hexavalent chromium in the nickel-chromium plating wastewater does not have to be isolated and pretreated by reduction to the trivalent form. The new process is applicable for removal of all heavy metals. All heavy metals other than chromium are removed as insoluble metal sulfides, M(II)S. 

To determine the efficiency of aminoacylation of [14C]Phe-tRNA, 5 fil aliquots of the aminoacylation mixture are withdrawn before and after the reaction the samples taken from the reaction mixture at the end of the incubation are spotted onto 3-MM paper discs (Schleicher Schuell) and processed by the cold TCA precipitation method, while the sample taken before the reaction is spotted on a paper disc pretreated empty by the same cold TCA procedure. Determination of the radioactivity present on these filters by liquid scintillation counting allows one to calculate the aminoacylation efficiency of the reaction (which, for phenylalanine, should be >2% of total tRNA). The specific activity of the [14C] Phe-tRNA can be determined after one-step purification of Phe-tRNA by BD cellulose chromatography (Gillam et al., 1968), followed by determination of the radioactivity and of the A260. 

Although not completely characterized, this yellow solid was assumed to be a dicopper diene derivative. In order to dissolve the yellow precipitate, DMPU (dimethylpropylene urea) was required. The dicopper diene species 34a is unstable in solution and gradually decomposes to undefined compounds. Therefore, all reactions involving transmetalation to copper are performed in situ in a one-pot or one-step process. 

Cocaine can be extracted from the leaves with almost any organic solvent. Moisten the dried, powdered leaves with Na carbonate solution and extract with cold benzene or petroleum ether. Extract the organic solution with small amounts of dilute sulfuric acid and basify the extract with Na carbonate (the alkaloids precipitate). Dissolve the precipitate in ether, separate the ether from the aqueous Na carbonate and dry and evaporate in vacuum the ether. Dissolve the residue in methanol and heat with sulfuric acid or methanol-HCl dilute with water and extract with CHC13. Concentrate and neutralize the aqueous layer and cool to precipitate methylecgonine sulfate, which is converted to cocaine in one step. The alkaloids can also be extracted directly from the powder with dilute sulfuric acid. 

A typical condensation procedure involves a one-step reaction where the monomer and suitable catalyst/initiator are mixed and heated to the required reaction temperature. To accomplish a satisfactory conversion, the low molar mass condensation products formed throughout the reaction have to be removed. This is most often accomplished by using a flow of inert gas and/or by reducing the pressure in the reaction vessel. The resulting polymer is generally used without any purification or, in some cases, after precipitation of the dissolved reaction product from a nonsolvent. 

To find out what cations are in a solution using precipitation reactions, chemists carry out reactions according to a scheme that incorporates tests for each component that may be present. One example of such a scheme is shown in Figure 9.9. This scheme shows how a chemist would analyze an unknown solution that may contain all, some, or none of the following ions silver, Ag" " cadmium, Cd and aluminium, Al ". The analysis uses selective, step by step precipitation. 

Kaneda et al. synthesized [61] a series of high molecular weight extended chain copolyimides (XV) by the reaction of PMDA and 3,3, 4,4 -biphenyltetra-carboxylic dianhydride (PPDA) with 3,3 -dimethyl-4,4 -diaminobiphenyl. Solvents used for the one-step synthesis to the fully cyclized imide structure were phenol, p-chlorophenol, m-cresol, p-cresol and 2,4-dicholorophenol. The polycondensations were performed at 180°C for 2h with a monomer concentration of 6% by weight and p-hydroxybenzoic acid used as a catalytic accelerator. A maximum of 50 mol % of PMDA could be used before the copolymer precipitated from solution. Reconstituted copolymers as isotropic dopes (8-10% by weight) in p-chlorophenol were dry-jet wet spun between 80 and 100 °C [62]. 

Ferrous sulfate (FeS04) or ferrous sulfide (FeS) reduces and precipitates hexavalent chromium in one step. This eliminates the two-step reduction and precipitation required when sulfur dioxide or sodium bisulfite is used. 

Azetidine-2-carboxylic acid (2) is commercially available. It is readily prepared as the racemate by refluxing 2,4-dibromobutyric acid ester with benzhydrylamine in acetonitrile. If benzyl 2,4-dibromobutyrate is treated with benzhydrylamine, the resulting benzyl TV-benz-hydryl-D,L-azetidine-2-carboxylate is hydrogenolytically processed to D,L-azetidine-2-car-boxylic acid in a one-step reaction. 101,107 Resolution of the racemate can be performed by the method of Vogler 108 via fractional crystallization of the Z-D,L-Aze-OH-H-Tyr-N2H3 salt thereby the salt of the D-imino acid precipitates first from methanol. 96 A stereoselective synthesis of A-tosyl-L-azetidine-2-carboxylic acid can be achieved by a two-step reaction from N-tosyl-L-homoserine lactone. 94 ... 

A one-step synthesis of flavylium salts is similar in nature. A mixture of an o-hydroxyacetophenone, an aromatic aldehyde and ethyl orthoformate in perchloric acid is maintained at room temperature, whereupon the salt gradually precipitates (81CHE115). 

One of the key steps in any isotope dilution analysis concerns the isolation and purification of the diluted activity, plus the measurement of its specific activity. Two techniques are usually preferred for the separation precipitation and solvent extraction. As a purification step, precipitation has the advantage that the precipitate can easily be weighed at the time of separation, thereby allowing a quick determination of the specific activity. The main problem with the use of precipitation techniques involves the occurrence of co-precipitation phenomena, in which unwanted materials are precipitated along with the desired substance, thus altering the sample specific activity. Precipitation techniques are used for the isolation of inorganic components. 

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