Functionally graded fluoridated apatites.

M Okazaki; Y Miake; H Tohda; T Yanagisawa; T Matsumoto; J Takahashi

doi:10.1016/s0142-9612(99)00049-6

Home/Archive/PubMed

PubMed · 10454014

Functionally graded fluoridated apatites.

M Okazaki·Y Miake·H Tohda·T Yanagisawa·T Matsumoto·J Takahashi

View original source ↗Export metadata ↓

Abstract

Fluoridated hydroxyapatite was synthesized at 80 +/- 1 degree C and pH 7.4 +/- 0.2 using a gradient fluoride supply system. X-ray diffraction analysis showed a typically apatitic pattern, although the (3 0 0) reflection was broader than that of homogeneous fluorapatite. Scanning electron micrographic observation indicated that the apatite was composed of rod-like crystals similarly to fluorapatite. High-resolution transmission electron microscopy showed electron damage in the core of the crystal. When the apatite pellet was prepared, electron spectroscopy for chemical analysis showed a negative gradient of fluoride concentration with depth in the crystals. The apparent solubility in 0.5 mol/l acetate buffer solution (37 degrees C and pH 4.0) was 9.16 +/- 0.39 mmol/l, much less than that of homogeneous hydroxyapatite 32.3 +/- 1.9 mmol/l, and less than that of heterogeneous two-layer fluoridated apatite with an outer fluoride-rich layer 12.5 +/- 0.6 mmol/l, which was synthesized previously by supplying fluoride during the latter half of the experimental period. These results suggest that graded fluoridated apatite may be formed by this process and have higher acid resistance than two-layer fluoridated apatite.

Explore related subjects

Crystallography, X-Ray Hydroxyapatites Hydroxyl Radical Microscopy, Electron Microscopy, Electron, Scanning Models, Chemical Thermodynamics Journal Article Research Support, Non-U.S. Gov't

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

M Okazaki, Y Miake, H Tohda, T Yanagisawa, T Matsumoto, J Takahashi. 1999. Functionally graded fluoridated apatites.. https://doi.org/10.1016/s0142-9612(99)00049-6

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed2001

A new concept for multidimensional selection of ligand conformations (MultiSelect) and multidimensional scoring (MultiScore) of protein-ligand binding affinities.

In this work, eight different scoring functions have been combined with the aim of improving the prediction of protein-ligand binding conformations and affinities. The obtained scores were analyzed using multivariate statistical methods to generate expressions, with the ability (1) to select the best candidate between different docked conformations of an inhibitor (MultiSelect) and (2) to quantify the protein-ligand binding affinity (MultiScore). By use of the docking program GOLD, 40 different inhibitors were docked into the active site of three matrix metalloproteinases (MMP's), yielding a total of 120 enzyme-inhibitor complexes. For each complex, a single conformation of the inhibitor was selected using principal component analysis (PCA) for the scores obtained by the eight functions SCORE, LUDI, GRID, PMF_Score, D_Score, G_Score, ChemScore, and F_Score. Binding affinities were estimated based on partial least-squares projections onto latent structures (PLS) on the eight scores of each selected inhibitor conformation. By use of this procedure, R(2) = 0.78 and Q(2) = 0.78 were obtained when comparing experimental and calculated binding affinities. MultiSelect was evaluated by applying the same method for selecting docked conformations for 18 different protein-ligand complexes of known three-dimensional structure. In all cases, the selected ligand conformations were found to be very similar to the experimentally determined ligand conformations. A more general evaluation of MultiScore was performed using a set of 120 different protein-ligand complexes for which both the three-dimensional structures and the binding affinities were known. This approach allowed an evaluation of MultiScore independently of MultiSelect. The generality of the method was verified by obtaining R(2) = 0.68 and Q(2) = 0.67, when comparing calculated and experimental binding affinities for the 120 X-ray structures. In all cases, LUDI, SCORE, GRID, and F_Score were included as important functions, whereas the fifth function was PMF_Score and ChemScore for the MMP and X-ray models, respectively.

Crystallography, X-Ray↗

PubMed2001

Unexpected nitrosyl-group bending in six-coordinate [M(NO)](6) sigma-bonded aryl(iron) and -(ruthenium) porphyrins.

The six-coordinate nitrosyl sigma-bonded aryl(iron) and -(ruthenium) porphyrin complexes (OEP)Fe(NO)(p-C(6)H(4)F) and (OEP)Ru(NO)(p-C(6)H(4)F) (OEP = octaethylporphyrinato dianion) have been synthesized and characterized. Single-crystal X-ray structure determinations reveal an unprecedented bending and tilting of the MNO group for both [MNO](6) species as well as significant lengthening of trans axial bond distances. In (OEP)Fe(NO)(p-C(6)H(4)F) the Fe-N-O angle is 157.4(2) degrees, the nitrosyl nitrogen atom is tilted off of the normal to the heme plane by 9.2 degrees, Fe-N(NO) = 1.728(2) A, and Fe-C(aryl) = 2.040(3) A. In (OEP)Ru(NO)(p-C(6)H(4)F) the Ru-N-O angle is 154.9(3) degrees, the nitrosyl nitrogen atom is tilted off of the heme normal by 10.8 degrees, Ru-N(NO) = 1.807(3) A, and Ru-C(aryl) = 2.111(3) A. We show that these structural features are intrinsic to the molecules and are imposed by the strongly sigma-donating aryl ligand trans to the nitrosyl. Density functional-based calculations reproduce the structural distortions observed in the parent (OEP)Fe(NO)(p-C(6)H(4)F) and, combined with the results of extended Hückel calculations, show that the observed bending and tilting of the FeNO group indeed represent a low-energy conformation. We have identified specific orbital interactions that favor the unexpected bending and tilting of the FeNO group. The aryl ligand also affects the Fe-NO pi-bonding as measured by infrared and (57)Fe Mössbauer spectroscopies. The solid-state nitrosyl stretching frequencies for the iron complex (1791 cm(-)(1)) and the ruthenium complex (1773 cm(-)(1)) are significantly reduced compared to their respective [MNO](6) counterparts. The Mössbauer data for (OEP)Fe(NO)(p-C(6)H(4)F) yield the quadrupole splitting parameter +0.57 mm/s and the isomer shift 0.14 mm/s at 4.2 K. The results of our study show, for the first time, that bent Fe-N-O linkages are possible in formally ferric nitrosyl porphyrins.

Crystallography, X-Ray↗

PubMed2001

Factors determining the orientation of axially coordinated imidazoles in heme proteins.

Factors determining conformations of imidazole axially coordinated to heme in heme proteins were investigated by analyzing 693 hemes in 432 different crystal structures of heme proteins from the Protein Data Bank (PDB), where at least one histidine is ligated to heme. The results from a search of the PDB for protein structures were interpreted with molecular force field computations. Analysis of data from these crystal structures indicated that there are two main factors that determine the orientations of imidazole ligated to heme. These are the interactions of imidazole with the propionic acid side chains of heme and with the histidine backbone. From the analysis of the crystal structures of heme proteins, it turned out that the hydrogen bonding pattern is often not decisive, though it is probably used by nature to fine-tune the orientation of imidazole axially ligated to heme. We found that in many heme proteins the NdeltaH group of imidazole ligated to heme can assume a number of different hydrogen bonds and that in mutant structures the orientation of the ligated imidazole often does not change significantly, although the mutant altered the hydrogen bonding scheme involving the imidazole. Data from crystal structures of heme proteins show that there are preferred orientations of imidazoles with respect to heme. Generally, the NdeltaH group of imidazole is oriented toward the propionic acid groups of the heme. In some cases, the NdeltaH group of imidazole is close to only one of the propionic acid groups, but it is practically never oriented in the opposite direction. The imidazole also adopts a preferred orientation with respect to its histidine backbone such that the plane of the imidazole ring is practically never parallel to the Calpha-Cbeta bond of its histidine backbone. For a given conformation of histidine backbone with respect to heme, as well as imidazole with respect to histidine backbone, the orientation of the imidazole with respect to heme is uniquely determined, since the three orientations depend on each other. Hence, the interaction of the imidazole with the backbone also influences the orientation of the imidazole with respect to the heme. Force field computations are in agreement with experimental data. With this method, we showed that there is an energy minimum when the NdeltaH group of the imidazole is oriented toward the propionic acid groups and that there are minima of energy for orientations where the imidazole ring is orthogonal to the plane defined by the Calpha-Cbeta and Cbeta-Cgamma bonds of the histidine. The computations also demonstrated that these interactions are mainly of electrostatic origin. By taking into account these two major factors, we were able to understand the orientations of axially coordinated imidazoles for all groups of heme proteins, except for the group of cytochrome c peroxidase. In this group, the orientation of the imidazole is determined by a strong hydrogen bond of the NdeltaH group with Asp235.

Crystallography, X-Ray↗