Phosphate surface complex structures

Figure 8. The phosphate surface complex structures on goethite in relation with the actual CD value found by modelling (Hiemstra and VanRiemsdijk 1996). The ligand charge is indicated on the various oxygens (italic).

Kwon, K.D. and Kubicki, J.D., Molecular orbital theory study on surface complex structures of phosphates to iron hydroxides Calculation of vibrational frequencies and adsorption energies, Langmuir, 20, 9249, 2004. 

Figure 9. The Cd surface complexes structure on goethite found for low affinity sites (Spadini et al.l994) and the calculated charge on the ligands, based on the actual CD value found by modelling (Venema et al. 1996b). The Cd surface complex has a hydroxyl as bridging ligand in contrast to the complexes of phosphate (figure 8).

The molecular geometry of phospholipid membranes is thus structurally analogous to inorganic phosphate minerals in that corrugated layers of metal ion-phosphate coordination complexes exist in membranes and minerals. In Fig. 5, the structure of a typical phosphate mineral is shown to reveal the type of molecular pattern that is exposed at the ionic surface of phospholipid membranes64,6S. For a recent review on membrane structure see66. ... 

The existence of clathrate-like water structure adjacent to the hydrophobic surfaces of macromolecules is an attractive hypothesis. Models have been proposed which have received some support from thermodynamical arguments [808]. However, this concept has proved ineffective as a basis for the interpretation of the structure associated with the many electron density solvent peaks, separated by 2.8 A to 3.0 A, which are frequently observed on the Fourier X-ray maps close to the surface of a protein [809, 810], Recently, however, some local clathrate-like water has been observed in special cases in the high-resolution studies of the small plant protein, crambin [811], in a hydrated deoxydinucleoside-phosphate drug complex [812], in (Phe4Val6) antamanide hydrate [8131 and in an oligodeoxy-nucleotide duplex [814],... 

Surface nuclei are to be distinguished structurally from mere surface clusters. For surface nuclei, accretion and rearrangement of constituent ions are needed to present a kernel on which a surface precipitate can grow successfully (7). A case in point is the formation of calcium phosphate nuclei on the surface of calcite after rearrangement of adsorbed phosphate clusters (68). The transition from surface complexes to clusters to precipitate was reviewed in detail by Charlet and Manceau (62). They stressed the important interre-... 

Surface Reaction Mechanism. In terms of reaction mechanism, we have no direct evidence for a particular mechanism of surface complex formation. However, in view of the very strong 0-Ta bond, it is not likely that free Ta ions are available at the surface under ambient conditions. Rather, we have to assume that an oxide ion has to be replaced by phosphate(s). Again this is not likely to be directly possible, and we assume that a low activation energy path is only feasible through intermediate structures such as those proposed in Figure 12. 

Palladium oxide 80 Partial charges model 183 Peptization 267. 269 Perovskites oxides 174 structure 175 synthesis 175 Phosphate 30 complexation 149 Phosphatoanlimonales 151 Phosphaiotungstates 152 7i-bond 15. 108, 112, 131, 137, 149, 193 Platinum oxide 80 Poisson-Boltzman equation 237 Point of zero surface tension 278 Polymers... 

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