Glutamic acid adsorption

Surface faceting may be particularly significant in chiral heterogeneous catalysis, particularly in the N i/P-ketoester system. The adsorption of tartaric add and glutamic acid onto Ni is known to be corrosive and it is also established that modifiers are leached into solution during both the modification and the catalytic reaction [28]. The preferential formation of chiral step-kink arrangements by corrosive adsorption could lead to catalytically active and enantioselective sites at step-kinks with no requirement for the chiral modifier to be present on the surface. 

The residue was diluted in water (5 mL) and, if necessary, the pH adjusted to 7.0 with 1 M KOH before adsorption of the product on a column of Dowex 1X8 resin (200-400 mesh, AcO form, 2 cm x 10 cm). The column was washed with water (50 mL) and then eluted with AcOH aqueous solutions (50 mL of 0.1 m, 50 mL of 0.2 m and 50 mL of 0.5 M AcOH). The ninhydrin-positive fractions were combined and dried under reduced pressure to afford (25,4/ )-4-methyl glutamic acid 2 isolated as a white solid (192 mg, 41 %) and with a high purity (>98 %). 

The mechanism of interaction of amino acids at solid/ aqueous solution interfaces has been investigated through adsorption and electrokinetic measurements. Isotherms for the adsorption of glutamic acid, proline and lysine from aqueous solutions at the surface of rutile are quite different from those on hydroxyapatite. To delineate the role of the electrical double layer in adsorption behavior, electrophoretic mobilities were measured as a function of pH and amino acid concentrations. Mechanisms for interaction of these surfactants with rutile and hydroxyapatite are proposed, taking into consideration the structure of the amino acid ions, solution chemistry and the electrical aspects of adsorption. 

Adsorption and ElectroKlnetic Behavior of Rutile. Isotherms for the adsorption of lysine, prollne and glutamic acid on rutile (1102) are given in Figure 1. There is no simple relationship between the adsorption density and the equilibrium concentration. The adsorption does not obey the Langmiur, Freundllch or Stern-Grahame relationships. The leveling-off of the adsorption... 

Below the PZC of Ti02 (pH < 6.7) adsorption of glutamic acid makes the electrophoretic mobility more negative as anticipated. At pH s... 

Adsorption and Electrokinetic Behavior of Hydroxyapatite. The adsorption densities of glutamic acid and lysine on hydroxyapatite are shown in Flgures b and 7. The change in slope of the adsorption isotherm at 10 M glutamic acid is considered to be due to a... 

Figure 2. The effect of pH on the adsorption of glutamic acid, lysine and proline on rutile.

Figure 6. The isotherm for adsorption of glutamic acid on hydroxyapatite.

The adsorption of amino acids on rutile and hydroxyapatite exhibits some characteristics of specific adsorption. The results can be interpreted in terms of electrostatic models of adsorption, however, if reorientation of adsorbed molecules is taken into consideration. The electrokinetic behavior of hydroxyapatite in glutamic acid is complicated because of a chemical reaction, possibly involving calcium ions. The study shows that it is necessary to take into consideration the orientation of adsorbed molecules, particularly for zwitterionic surfactants. 

The effect increased with increasing concentration of thiosulphate. Above pH 7, thiosulphate suppressed adsorption of Ag by holding the cation as a complex in solution. Adsorption of Ag on ferrihydrite was also enhanced by glutamic acid and that of Cu was promoted by both glutamic acid and by 2.3-pyrazidinedicarboxylic acid. 

Bioactive macromolecules like peptides, proteins, and nucleic acids have been successfully embedded in planar LbL films. An important question is the retention of the bioactivity of the film-embedded biomolecules. The structural properties and stability of the LbL films formed from synthesized polypeptides of various amino acid sequences were recently reported [50]. The authors showed that control over the amino acid sequence enables control over non-covalent interpolypeptide interaction in the film, which determines the film properties. Haynie and coworkers showed by circular dichroism spectroscopy that the extent of adsorption of poly(L-glutamic acid) (PGA) and poly(L-lysine) (PLL) in the LbL films scales with the extent of secondary structure of the polypeptides in solution [51]. Boulmedais demonstrated that the secondary structure of the film composed of these polypeptides is the same as the peptide structure in the complex formed in solution [52], as found by Fourier transform IR spectroscopy (FUR). 

Figure 7. Experimental data and model calculations of glutamic acid adsorption on amorphous iron oxyhydroxide as a function of pH and total glutamate added. For model calculations a surface site coverage of 18 sites/adsorbed glutamate molecule was assumed, Fe(OH)s(am), lO M O.IM NaNOs, 25°C. Glutamic (O) acid 1.1 X added (A) (----) Model calculation.

In our previous works [1-3], we reported experimental and theoretical equilibrium isotherms for adsorption of L-glutamic acid in the single component system on polyaminated highly porous chitosan (hereafter called PEl-CH), weakly basic ion exchanger, and crosslinked chitosan fiber. We found that the adsorption of L-glutamic acid, which is a kind of acidic amino acid, was controlled by the acid/base neutralization reaction between neutral L-glutamic acid (zwitterion, A and those adsorbents. 

Due to the difference of the polymer adsorption onto different faces of different crystal forms, polymer adsorption onto the crystal face has played an important role in crystal polymorphic transformationJ Garti and Zour have studied the effects of surfactants on the polymorphic transformation of glutamic acid. Glutamic acid has two crystal forms, a and p, with the p-form being more stable than the ot-form. Those surfactants that preferentially adsorb onto the surface of the ot-growing crystals retard the transformation of the ot-form to the p-form. A Langmuir analysis indicates that the kinetic coefficient of crystal polymorphic transformation is related to the volume of the surfactant adsorbed at the crystal surface. 

Niwa M, Matsui M, Koide K, Higashi N. Enantioselective adsorption of ferrocene-modified glutamic acids on helical poly(L-glutamic acid) self-assemblies at gold electrodes. J Mater Chem 1997 7 2191-2192. 

However, not only the kinetics but also the morphology of precipitated HAp nanocrystals will be modified by structure-mediated (epitaxial) adsorption of organic constituents such as poly(amino acids) at prominent lattice planes of HAp. For example, adsorption of poly(l-lysine) on (0 0 1) planes causes formation of polycrystalline nanocrystals of HAp whereas adsorption of poly(l-glutamic acid) leads to precipitation of large flat micron-sized single crystals of HAp (Stupp and Braun, 1997). Similar relations have been found in experiments involving adsorption of recombinant human-like collagen (Zhai and Cui, 2006) and bovine serum albumin (BSA) (Liu et al., 2003) on hydroxyapatite surfaces. 

Black and Davey used Eq. (3.22) to study the effect of the tailor-made additive L-glutamic acid on L-asparagine monohydrate crystals. With the use of a linear adsorption isotherm, Eq. (3.22) fit the crystal growth rate data. Consistent with a structural model in which impurities are embedded in the growing crystal surface, the growth rate of the crystals tended to zero at a high L-glutamic level. 

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