Cation acidic properties

Carboxylate exchangers contain —COOH groups which have weak acidic properties and will only function as cation exchangers when the pH is sufficiently high (pH > 6) to permit complete dissociation of the —COOH site. Outside this range the ion exchanger can be used only at the cost of reduced capacity. 

ACID DYES Commercial acid dyes contain one or more sulfonate groups, thereby providing solubility in aqueous media. These dyes are apphed in the presence of organic or mineral acids (pH 2—6). Such acids protonate any available cationic sites on the fiber, thereby making possible bonding between the fiber and the anionic dye molecule. Wool, an animal fiber, is an amphoteric coUoid, possessing both basic and acidic properties because of the amino and carboxylic groups of the protein stmcture. In order to dye such a system, coulombic interactions between the dye molecule and the fiber must take place ie, H2N" -wool-COO + H2N" -wool-COOH. The term acid dye is appHed to those that are capable of such interactions. Acid dyes... 

Cations which are covalently attached to the allyl anion part by a cr-bond and have sufficient Lewis acid properties offer the broadest versatility and highest levels of stereocontrol, since the C—C bond-forming step can occur in a pericyclic process9 accompanied by allylic inversion. It is reasonable to assume the prior assembly of both reaction partners in an open-chain complex, in which usually the (F )-oxonium ion, avoiding allylic 1,3-strain10, is predominant. 

As far as investigated77, most reactions of the allyllithium-sparteine complexes with electrophiles proceed antarafacially, either as SE2 or anti-SE2 reactions. As a working hypothesis it is assumed that the bulky ligand obliterates the Lewis acid properties of the lithium cation. 

The pillaring process also affected the concentration and the strength of acid sites, as confirmed by NH3-TPD (Table 1). Also, the ion exchange with Ni2+ cations modified the acid properties of surfaces new Lewis (nickel cations) and Bronsted (H+) acid sites have been created during the ion exchange and thermal activation (eq. 1), respectively. 

Separation is based on the reversible chelate-complex formation between the chiral selector covalently bonded to the chromatographic support, and the chiral solute with transition metal cations. Chelation properties of both the chiral selector and the chiral solute are required. Compounds therefore need to have two polar functional groups in a favorable arrangement to each other, like a )3-amino acids, amino alcohols and a-hydroxy acids, which can form rings membered with central chelating metal ions, like Cu(II), Zn(II), Cyclic... 

The introduction of silicon into hypothetical phosphorus sites produces negatively charged frameworks with cation-exchange properties and weak to mild acidic catalytic properties. Again, as in the case of the aluminophosphate molecular sieves, they exhibit excellent thermal and hydrothermal stability. 

A review considering the generation and characterization of radical ions, their reactions, formation of species with three-electron bonds, and radical cations of strained systems has been published." The redox and acidity properties of a number of substituted benzene radical cations were smdied by pulse radiolysis. ... 

Elimination of coextracted materials and concentration of tetracyclines have also been accomplished using mixed-phase extraction membranes with both re-versed-phase and cation-exchange properties (294,295), or solid-phase extraction columns packed with cation-exchange materials such as CM-Sephadex C-25 (301), aromatic sulfonic acid (310), and carboxylic acid (283, 300). For the same purpose, metal chelate affinity chromatography has also been employed. In this technique, the tetracyclines are specifically absorbed on the column sorbent by chelation with copper ions bound to small chelating Sepharose fast flow column (278-281, 294-296). 

Qynthetic and natural zeolites are becoming increasingly important as catalysts, carriers of catalysts, and adsorbents. Zeolites are especially suited to these purposes because their properties can be modified by cation exchange. The literature describes several studies which show characteristic changes in physicochemical properties resulting from cation exchange— e.g., catalytic activity (1,2), acidic properties (3), adsorption behavior (4), structure of solid (5,6), and thermal stability (7,8). 

The acidic properties of coordinated water in aquo cations vary enormously with the cation. Table 10 contains p KX values,19-226 where KX = [M(OH)(OH2 ) r,1)+][H+ (aq)]/M(OH2 )nx+ ][H20], with [H20] taken as unity.7 There is an approximate correlation with electrostatics (charges and ionic radii), but such properties as oxidizing power and softness complicate the pattern.227... 

Condensation between phenol and selenium oxychloride in ether or chloroform solution produces two isomeric selenonium chlorides, [(HO.CeH4)3Se]Cl, each containing chlorine precipitable as silver chloride and replaceable by other acid radicals. The three phenolic hydroxyl groups of the complex cation impart acidic properties to the chlorides, causing them to be soluble in aqueous caustic alkali. From such solutions carbonic or acetic acid precipitates the amphoteric oxide [(H0.C6H4)8Se]20, which redissolves in alkalis and reacts with acids to give a bromide, nitrate, sulphate and chloroplatinate. The following scheme shows the compounds obtained ... 

Fraenkel et al. (17), who isolated mutant strains which had lost the ability to grow on glycerol, succinate, or acetate but grew normally on hexoses or pentoses. These organisms were shown to be deficient in a specific FDPase, which could be distinguished from the nonspecific acid hexosephosphatase present in both mutant or wild-type strains by the fact that the latter was present in the periplasmic space (86) and did not require a divalent metal cation. The properties of the specific FDPase were confirmed with a partially purified preparation (87) the E. coli enzyme was shown to be highly specific for FDP and to be active with very low concentrations of this substance. The requirement for a divalent cation was satisfied by Mg2+, which was far more effective than Mn2+ other divalent cations were either inactive or inhibitory. The partially purified enzyme showed optimum activity at pH 7.8, with very little activity below pH 7 or above pH 9. The enzyme resembled mammalian and Candida FDPases in its sensitivity to low concentrations of AMP it was approximately 50% inhibited at an AMP concentration of 2.5 X 10-° M. 

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