Exchange Methods

Another method of fractionating peptides according to their charge is by the use of ion exchange materials. These have frequently been 

Under suitable conditions it is possible to obtain separations on an ion exchange column by elution analysis. The pH of the developing solution should be such that the solutes are distributed between the resin and solvent so that they move down the column as definite bands. 

In this way Consden et al. (1948) and Drake (1947) separated glutamic and aspartic acid on columns of Amberlite IR.-4 (polyamine anion exchanger) maintained at pH 2.5, and this type of column has been used to separate acidic peptides from a wool hydrolyzate (Consden et al., 1949). More recently Stein and Moore (1949) have obtained excellent fractionations of amino acids on columns of Dowex-50 (cation exchanger, sulfonic acid groups) developed with 1.5-4 N HCl. The separations obtained are almost certainly due to differences in adsorption affinity for the resin, as well as to charge effects. At the pH used the only partially 

Group Separation of Amino Acids and Peptides according to Jutisz and Lederer [1947) 

Cysteine Simple dipeptides other than those in group 3 5,8 +  

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The rapid fission of a mass of or another heavy nucleus is the principle of the atomic bomb, the energy liberated being the destructive power. For useful energy the reaction has to be moderated this is done in a reactor where moderators such as water, heavy water, graphite, beryllium, etc., reduce the number of neutrons and slow those present to the most useful energies. The heat produced in a reactor is removed by normal heat-exchange methods. The neutrons in a reactor may be used for the formation of new isotopes, e.g. the transuranic elements, further fissile materials ( °Pu from or of the... 

The O-S exchange method in presence of a-halogenated carbonyl compound is a very good one for thiazole compounds. The thioamide is prepared in situ by the action of amide upon phosphorus pentasulphide with solvent. The a-halogenated aldehyde reacts directly. But the O-Se exchange cannot be performed with a-halogenated carbonyl compounds because of the apparition of phosphoric acid. (Scheme 3), The C-Se bond is very sensitive to add pH. 

Ion-exchange methods are based essentially on a reversible exchange of ions between an external liquid phase and an ionic solid phase. The solid phase consists of a polymeric matrix, insoluble, but permeable, which contains fixed charge groups and mobile counter ions of opposite charge. These counter ions can be exchanged for other ions in the external liquid phase. Enrichment of one or several of the components is obtained if selective exchange forces are operative. The method is limited to substances at least partially in ionized form. 

Spectroscopic methods for the deterrnination of impurities in niobium include the older arc and spark emission procedures (53) along with newer inductively coupled plasma source optical emission methods (54). Some work has been done using inductively coupled mass spectroscopy to determine impurities in niobium (55,56). X-ray fluorescence analysis, a widely used method for niobium analysis, is used for routine work by niobium concentrates producers (57,58). Paying careful attention to matrix effects, precision and accuracy of x-ray fluorescence analyses are at least equal to those of the gravimetric and ion-exchange methods. 

The batch and fed-batch procedures are used for most commercial antibiotic fermentations. A typical batch fermentor may hold over 150,000 Hters. When a maximum yield of antibiotic is obtained, the fermentation broth is processed by purification procedures tailored for the specific antibiotic being produced. Nonpolar antibiotics are usually purified by solvent extraction procedures water-soluble compounds are commonly purified by ion-exchange methods. Chromatography procedures can readily provide high quaHty material, but for economic reasons chromatography steps are avoided if possible. 

Another approach, the so-called seeding technique, provides preferential sites for the nucleation of scale, which permits the heat-transfer surfaces to remain clean of scale. Extensive studies of this technique have been conducted, and field use was reported ia the former USSR as early as the mid-1960s (42). The use of ion-exchange methods is another possible approach. Eor calcium, the exchange can be represented as... 

Fig. 6. Size-distribution of metal crystallites on the surface of Co-silica made by precipitalion-ion-exchange method.

Isolation of Inosine by Ion Exchange Method Half of the above clear centrifugate (1.15 liters) is treated with 250 cc of anion exchange (bicarbonate form) and stirred together therewith for 16 hours at room temperature. The pH value is increased thereby to about 4 to 5. The ion exchanger is filtered off under suction and washed 3 times, each time with 150 cc of water. The solution is brought to a pH value of 7 by means of normal sodium hydroxide (total volume of the solution about 1.55 liters), and concentrated to a volume of about 100 cc under vacuum. 

The following example describes the preperation of 2-methyl-2-sec-butyl-1,3-propenediol dicarbamate using the urethane exchange method ... 

Nonionic surfactants, including EO-PO block copolymers, may be readily separated from anionic surfactants by a simple batch ion exchange method [21] analytical separation of EO-PO copolymers from other nonionic surfactants is possible by thin-layer chromatography (TLC) [22,23] and paper chromatography [24], and EO-PO copolymers may themselves be separated into narrow molecular weight fractions on a preparative scale by gel permeation chromatography (GPC) [25]. 

This is usually prepared by either a base-exchange method using sodium zeolite, by a lime-soda ash process, or by the addition of sodium hexametaphosphate. In addition to the bacteria derived from fhe mains water, additional flora of Bacillus spp. and Staphylococcus aureus may be introduced into systems which use brine for regeneration and from the chemical filter beds which, unless treated, can act as a reservoir for bacteria. 

The radioisotope Cr was used to tag the species and the separation of Cr from CrX " was achieved using an ion-exchange method, after oxidation of the Cr to Cr with Fe(III) or oxygen. The reactions were carried out in the absence of oxygen in perchlorate media. For the systems involving chloride, fluoride, and azide . King et al. have found a rate law... 

Separation of the products was achieved using an ion-exchange method, the reaction taking place in sealed vessels with the Cr(Vl) labelled ( Cr). Under various conditions only 40% of the Cr appears in the product Cr2(OH)2. This led these workers to propose a modified mechanism in which the step involving Cr(V) proceeds in two ways... 

Platinum catalysts were prepared by ion-exchange of activated charcoal. A powdered support was used for batch experiments (CECA SOS) and a granular form (Norit Rox 0.8) was employed in the continuous reactor. Oxidised sites on the surface of the support were created by treatment with aqueous sodium hypochlorite (3%) and ion-exchange of the associated protons with Pt(NH3)42+ ions was performed as described previously [13,14]. The palladium catalyst mentioned in section 3.1 was prepared by impregnation, as described in [8]. Bimetallic PtBi/C catalysts were prepared by two methods (1) bismuth was deposited onto a platinum catalyst, previously prepared by the exchange method outlined above, using the surface redox reaction ... 

Na-ZSM-5(a molar SiOz/AlaOa ratio=23.8) provided by Tosoh Corp. was used. ln(4wt%)/H-ZSM-5 and lr(1wt%)/H-ZSM-5 catalysts were prepared by the ion exchange method using NH4-ZSM-5 derived from the Na-ZSM-5 with aqueous solutions of ln(NOs)3 at 368 K for 8 h and lrCI(NH3)sCl2 at room temperature for 24 h, respectively. Addition of precious metals, 1wt% platinum and iridium to ln/H-ZSM-5 was carried out by impregnating the ln/NH4-ZSM-5 in aqueous solutions of Pt(NH3)4Cl2 and lrCI(NH3)5Cl2, respectively. The catalysts were calcined at 813 K for 3 h. 

Dufresne, C., Isolation by ion-exchange methods, in Methods in Biotechnology, vol. 4, in Natural Products Isolation, R. J. P. Cannell, Ed., Humana Press, Totowa, NJ, 1998, 141. 

Shifflet, M. J. and Shapiro, M., Validation of a cation-exchange method to test for residual amounts of a cleaning and sanitizing solution on pharmaceutical process equipment, BioPharm, 51, Jan. 2000. 

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