Dowex 30 cation exchanger

Two approaches were used (i) the selective adsorption of free (only) DOX to Dowex cation exchanges either in polycarbonate tips of pipetors (range 0.1-... 

Studies on purine metabolism For the measurement of the de novo purine synthesis 10 juCi glycine-Cl4 (U) were administered orally in the morning to the patients who were on a low purine diet Following glycine-Cl4 administration the urines were collected in 3 portions on the first day and in one portion on the remaining days 5 rol urine were applied to a Dowex cation-exchange column (Dowex 50 fX 4, 200 - 400 mesh ... 

Dowex 50W-X2 0.6 0.70 Strongly acidic cation exchanger with S-DVB matrix for separation of peptides, nucleotides, and cations. Molecular weight exclusion <2700. 

Accurately weigh about 6 g NaCl and dissolve in distilled water. Pass the solution through a well-rinsed cation exchange column (Dowex 50W) in the hydrogen form. The equivalent amount of HCl is washed from the column (in 10 column volumes) into a volumetric flask and made up to volume. Equivalent weight is the formula weight. 

Ion-exchange separations can also be made by the use of a polymer with exchangeable anions in this case, the lanthanide or actinide elements must be initially present as complex ions (11,12). The anion-exchange resins Dowex-1 (a copolymer of styrene and divinylben2ene with quaternary ammonium groups) and Amherlite IRA-400 (a quaternary ammonium polystyrene) have been used successfully. The order of elution is often the reverse of that from cationic-exchange resins. 

Deamidation of soy and other seed meal proteins by hydrolysis of the amide bond, and minimization of the hydrolysis of peptide bonds, improves functional properties of these products. For example, treatment of soy protein with dilute (0.05 A/) HCl, with or without a cation-exchange resin (Dowex 50) as a catalyst (133), with anions such as bicarbonate, phosphate, or chloride at pH 8.0 (134), or with peptide glutaminase at pH 7.0 (135), improved solubiHty, whipabiHty, water binding, and emulsifying properties. 

Recovery and Purification. The dalbaheptides are present in both the fermentation broth and the mycelial mass, from which they can be extracted with acetone or methanol, or by raising the pH of the harvested material, eg, to a pH of 10.5—11 for A47934 (16) (44) and A41030 (41) and actaplanin (Table 2) (28). A detailed review on the isolation of dalbaheptides has been written (14). Recovery from aqueous solution is made by ion pair (avoparcin) or butanol (teicoplanin) extraction. The described isolation schemes use ion-exchange matrices such as Dowex and Amberlite IR, acidic alumina, cross-linked polymeric adsorbents such as Diaion HP and Amberlite XAD, cation-exchange dextran gel (Sephadex), and polyamides in various sequences. Reverse-phase hplc, ion-exchange, or affinity resins may be used for further purification (14,89). 

J mol ). This is additional evidence in favor of rate limitation by inner diffusion. However, the same reaction in the presence of Dowex-50, which has a more open three-dimensional network, gave an activation energy of 44800 J mol , and closely similar values were obtained for the hydrolysis of ethyl acetate [29] and dimethyl seb-acate [30]. The activation energy for the hydrolysis of ethyl acetate on a macroreticular sulphonated cationic exchanger [93] is 3566 J mol . For the hydrolysis of ethyl formate in a binary system, the isocomposition activation energy (Ec) [28,92] tends to decrease as the solvent content increases, while for solutions of the same dielectric constant, the iso-dielectric activation energy (Ed) increases as the dielectric constant of the solvent increases (Table 6). 

The rate of hydrolysis of sarin on Dowex-50 cation exchange resin is insensitive to the stirring rate. However, with a more active catalyst (Amberlite-IRA 400), the rate constant at 20°C was 5.3, 7.5, and 8.5 h at 60,800 and 1000 revolutions/min , respectively, suggesting that film diffusion was the rate-limiting. step. Thus, the mechanism of the rate-limiting step depends on the nature of the catalyst [34]. 

Strong acid cation exchangers Duolite C225 Duolite C255 Duolite C26C Amberlite 120 Amberlite 200 Dowex 50 AG50W AGMP-50 ... 

Fig. 14. Selective bonding of oxytetracycline vs its molar fraction (Nj) in Dowex 50 x 1 sulfonated cation exchangers with different exchange capacity 1) 5.0 mg-equiv/g 2) 2.3 mg-equiv/g...

Fig. 29. Effect of the extent of crosslinking of sulfonated cation exchangers (quantity of cross-linking agent) on diffusion coefficient of tetracycline in sorbent grains 1) SDMDMA, 2) SHMDMA, i) SEDMA, 4) Dowex-50W...

Studies by Deathrage ef a/.137 139 revealed that most of dipeptides were hydrolyzed 100 times faster with cation exchange resins (Dowex-50) than with HC1. Deathrage etal.139 also found that the entropy of activation was significantly less than in the case of hydrolysis of the same compounds by HC1, while the enthalpies of activation for the two cases were practically the same. While the entropy changes associated with catalysis by the cationic exchange resins remain obscure, presumably the mechanism of the catalysis follows that for homogeneous acids as described here later. 

Sakurada et al.88, 145, 146 hydrolyzed aliphatic esters having various hydrophobicities with cation-exchange resins, Dowex 50 w, and found a close correlation between the accelerating factor and the degree of ester adsorption toward the resins. 

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