Phosphates, modified characterization

Schafer, W.A. Carr, P.W. Funkenbusch, E.F. Parson, K.A. Physical and chemical characterization of a porous phosphate-modified zirconia substrate. J. Chromatogr. 1991, 5S7, 137-147. 

Schafer et al. used several spectroscopic techniques to characterize the surface species on phosphate-modified zirconia particles. Their results show that phosphate merely adsorbs on the surface of zirconia under the mildest phosphate concentration, i.e., neutral pH, room temperature, and short contact times. However, at acidic pH and higher temperarnres, esterification of the phosphate with surface hydroxyls takes place as the kinetic barriers are overcome. The solid NMR studies clearly show the presence of covalently bound phosphate. This phosphate modification effectively blocks the sites responsible for the strong interaction of certain Lewis bases with the zirconia surface, resulting in a more biocompatible stationary phase. Unlike fluoride-modified zirconia, phosphate-modified zirconia behaves as a classic cation exchanger and not as a mixed-mode medium analogous to hydroxyapatite, despite spectroscopic evidence of zirconium phosphate formation on the surface. This limits the applicability of the supports, as most proteins and enzymes are anionic at neutral pH. Nevertheless, its ability to separate proteins with high p/ values still deserves much attention. The preparative-scale separation of murine IgGs from a fermentation broth demonstrates the utiUty of the supports for solutes that are retained. 

The incorporation of POSS NHj enhances the corrosion resistance of the phosphate-modified epoxy system. System 1 dominates the corrosion resistance because of the presence of POSS-NHj, which acts as nanostructured crosslinking sites to form coatings characterized with high crosshnk density, thereby resulting in tough and relatively hard protective films on metals. 

The above flame retardants, HMPN and TMP, along with another commercially available alkyl phosphate, triethyl phosphate (TEP), were systematically characterized by Xu et al. To quantify the flammability of the electrolytes so that the effectiveness of these flame retardants could be compared on a more reliable basis, these authors modified a standard test UL 94 HB, intended for solid polymer samples, and measured the self-extinguishing time (SET) instead of the universally used flame propagation rate. Compared with the UL 94 HB, this new quantity is more appropriate for the evaluation of the electrolytes of low flammability, since the electrolytes that are determined to be retarded or nonflammable by this method all showed zero flame propa-... 

This technique is characterized by an activation of probe functionalities that easily react with the modified surface. The methods for activation are derived from protein chemistry and occur in the activation of the carboxyl group (carbodiimide method, active ester method, reactive anhydrides [13,14]). Due to the similarity to the carboxyl group the activation methods are applied to phosphate and sulfonate groups as well (Fig. 11). 

Conventional methods for the study of protein phosphorylation rely on radioactive labelling, 2D-GE protein mapping, and Edman degradation. Early studies in LC-MS characterization of protein phosphorylation involve MS-MS analysis of modified tryptic peptide to determine the phosphorylation site by complementary peptide mapping, e.g., [5-7]. In the LC-MS analysis of tryptic and V8-protease digests of a phosphorylated (ppl9) and nonphosphorylated (pl9) 19-kDa cytosolic protein, two sets of ions with a phosphate-characteristic mass difference of 80 Da were observed. Sequence analysis of the relevant peptides by MS-MS showed that phosphorylation occurs at Ser-25 and Ser-38 [7]. 

For the hydrosilylation reaction various rhodium, platinum, and cobalt catalysts were employed. For the further chain extension the OH-functionalities were deprotected by KCN in methanol. The final step involved the enzymatic polymerization from the maltoheptaose-modified polystyrene using (z-D-glucose-l-phosphate dipotassium salt dihydrate in a citrate buffer (pH = 6.2) and potato phosphorylase (Scheme 59). The characterization of the block copolymers was problematic in the case of high amylose contents, due to the insolubihty of the copolymers in THF. 

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