Surface protonated phosphates

Fig. 5.38 Reduction of 10-3m phenylglyoxylic acid at the mercury streaming electrode in acetate and phosphate buffers containing 1 m KN03 (1) pH 5.02, (2) pH 5.45, (3) pH 5.85, (4) pH 6.25. The curves 2, 3 and 4 are shifted by 0.2 V, 0.4 V and 0.6 V with respect to curve 1. The first wave is controlled by the surface protonation reaction while the second is a direct reduction of the acid anion. (According to J. Koryta)...

Phosphate. The binding of phosphate to hydrous oxides, especially AI2O3 and FeOOH, is also characterized by a proton release and a shift of lEP to lower pH values. With goethite (a-FeOOH) dispersed in phosphate solutions, the fixed charge was computed as a function of pH from titration curves (surface proton balance) and from analytic information (phosphate adsorbed) (18) (Figure 8). Reasonable agreement with electrokinetic data was obtained. 

Dehydration of alcohols is catalyzed by zirconium phosphate. The activity for dehydration of cydohexanol is nearly proportional to the number of surface hydroxyl groups for zirconium phosphates of varying crystallinity. The activity is poison by the exchange of surface proton with Cs or introduction of quinoline. The active sites are monohydrogen protons. ... 

The effects of organic molecules and phosphate on the adsorption of acid phosphatase on various minerals, and kaolinite in particular, have been investigated by Huang et al. [97]. The Langmuir affinity constant for AcP adsorption by kaolinite follows the series tartrate (K — 97.8) > phosphate (K= 48.6) > oxalate (K — 35.6) > acetate (K= 13.4). At low concentration, acetate even promoted the adsorption of acid phosphatase. It was considered that competitive interactions between anionic adsorbates can occur directly through competition for surface sites and indirectly through effects of anion adsorption on the surface charge and protonation. 

Murakami and Kondo (1975) reported that the cationic micelle is quite effective for the pyridoxal-catalyzed elimination of S-phenylcysteine. The significant rate acceleration was explained by the binding of the Schiff s base to the micelle phase, followed by the efficient proton abstraction by hydroxide ion at the micelle surface. According to Gani et al. (1978), mixed micelles of CTAB and dodecylamine hydrochloride are good models for the site accommodating pyridoxal 5 -phosphate in glycogen phosphorylase, since the micelles can imitate well the formation of SchifT s bases in hydrophobic environments. 

This may be due to the higher acidity of the surface sites (see Kint) values in Table I) and hence higher activation energy of proton adsorption for the silica-alumina and Y-zirconium phosphate. 

Dissolved metals and metal-containing surfaces play an important role in the transformation of organic contaminants in the subsurface environment. Metal ions can catalyze hydrolysis in a way similar to acid catalysis. Organic hydrolyzable compounds susceptible to metal ion catalysis include carboxylic acids, esters, amides, anilides, and phosphate-containing esters. Metal ions and protons... 

When particles or large molecules make contact with water or an aqueous solution, the polarity of the solvent promotes the formation of an electrically charged interface. The accumulation of charge can result from at least three mechanisms (a) ionization of acid and/or base groups on the particle s surface (b) the adsorption of anions, cations, ampholytes, and/or protons and (c) dissolution of ion-pairs that are discrete subunits of the crystalline particle, such as calcium-oxalate and calcium-phosphate complexes that are building blocks of kidney stone and bone crystal, respectively. The electric charging of the surface also influences how other solutes, ions, and water molecules are attracted to that surface. These interactions and the random thermal motion of ionic and polar solvent molecules establishes a diffuse part of what is termed the electric double layer, with the surface being the other part of this double layer. 

Tejedor-Tejedor, M.L Anderson, M.A. (1990) Protonation of phosphate on the surface of goethite as studied by CIR-FTIR and electrophoretic mobility. Langmuir 6 602-611... 

Zhang, X. Zhang, F. Mao, D. (1999) Effect of iron plaque outside roots on nutrient uptake by rice Oryza sativa L.) Phosphate uptake. Plant and Soil 209 187-192 Zhang,Y Charlet, L. Schindler, P.W. (1992) Adsorption of protons, Fe(II) and Al(IIl) on lepidocrocite (y-FeOOH). Colloids Surfaces 63 259-268... 

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