Interaction between a bisphosphonate, tiludronate, and biomimetic nanocrystalline apatites.

Bisphosphonates (BPs) are well established as successful antiresorptive agents for the prevention and treatment of bone diseases such as osteoporosis and Paget's disease. The aim of this work was to clarify the reaction mechanisms between a BP molecule, tiludronate, and the nanocrystalline apatite surface. The adsorption of tiludronate on well characterized synthetic biomimetic nanocrystalline apatites with homogeneous but different compositions and surface characteristics was investigated to determine the effect of the nanocrystalline apatite substrate on the adsorption behavior. The results show that the adsorption of tiludronate on nanocrystalline biomimetic apatite surfaces varies over a large range. The most immature apatitic samples exhibited the highest affinity and the greatest amount adsorbed at saturation. Maturation of the nanocrystals induces a decrease of these values. The amount of phosphate ion released per adsorbed BP molecule varied, depending on the nanocrystalline substrate considered. The adsorption mechanism, although associated with a release of phosphate ions, cannot be considered as a simple ion exchange process involving one or two phosphate ions on the surface. A two-step process is proposed consisting of a surface binding of BP groups to calcium ions associated with a proton release inducing the protonation of surface orthophosphate ions and their eventual solubilization

Modern NMR Approaches to the State of Water in Glasses

The state of water in volcanic and synthetic silkate glasses is characterized by a number of different modern solid state NMR techniques. ^1H solid echo NMR is used to quantitate total water contents reliably down to levels of 0.1 wt. %. Relative species concentrations of OH and H_2 are obtained either from an analysis of ^1H MAS-NMR spinning sideband patterns or by deuterium quadrupolar echo NMR difference spectroscopy, utilizing the different spin-lattice relaxation characteristics of OD and D_2O species. A distribution function of O-D···O distances, simulated on the basis of infrared results, yields good agreement with the experimental ^2H NMR lineshapes

Interactions between a symmetrical minor groove binding compound and DNA oligonucleotides: ^1H and ^(19)F NMR studies

High-resolution NMR techniques (proton and ^(19)F) have been used to study the interactions between several DNA oligonucleotides with varying length of AT base pairs and the synthetic pyrrole-containing compound (P1-F_4S-P1), which has properties similar to the DNA minor groove binding drug distamycin A. When this two-fold symmetrical DNA binding molecule is added to the self-complementary DNA oligomers, the resulting complex exhibits an NMR spectrum without any doubling of individual resonances, consistent with a two-fold symmetry of the complex. This is in contrast to all other complexes studied so far. The minimum length of an AT stretch for specific ligand binding is judged to be greater than 4 base pairs. Inter-molecular proton nuclear Overhauser effects between the ligand molecule and a DNA dodecamer d(CGCAAATTTGCG) provide evidence that P1-F_4S-P1 binds DNA in the minor groove and interacts with the middle AT base pairs. The presence of a specific interaction between P1-F_4S-P1 and DNA is conclusively demonstrated by ^(19)F NMR studies, in which four previously chemically equivalent fluorine nuclei in the free molecule become two non-equivalent pairs (yielding an AB quartet pattern) upon the binding of P1-F_4S-P1 to DNA duplex. A sequence-dependent binding behavior of P1-F_4S-P1 is evident by comparing the ^(19)F NMR spectra of the complexes between P1-F_4S-P1 and two different but related DNA dodecamers, d(CGCAAATTTGCG) and d(CGCTTTAAAGCG). P1-F_4S-P1 binds more strongly to the former dodecamer with an association constant of approximately 1 X 10^3 M^-1

Interactions between a symmetrical minor groove binding compound and DNA oligonucleotides: ^1H and ^(19)F NMR studies

High-resolution NMR techniques (proton and ^(19)F) have been used to study the interactions between several DNA oligonucleotides with varying length of AT base pairs and the synthetic pyrrole-containing compound (P1-F_4S-P1), which has properties similar to the DNA minor groove binding drug distamycin A. When this two-fold symmetrical DNA binding molecule is added to the self-complementary DNA oligomers, the resulting complex exhibits an NMR spectrum without any doubling of individual resonances, consistent with a two-fold symmetry of the complex. This is in contrast to all other complexes studied so far. The minimum length of an AT stretch for specific ligand binding is judged to be greater than 4 base pairs. Inter-molecular proton nuclear Overhauser effects between the ligand molecule and a DNA dodecamer d(CGCAAATTTGCG) provide evidence that P1-F_4S-P1 binds DNA in the minor groove and interacts with the middle AT base pairs. The presence of a specific interaction between P1-F_4S-P1 and DNA is conclusively demonstrated by ^(19)F NMR studies, in which four previously chemically equivalent fluorine nuclei in the free molecule become two non-equivalent pairs (yielding an AB quartet pattern) upon the binding of P1-F_4S-P1 to DNA duplex. A sequence-dependent binding behavior of P1-F_4S-P1 is evident by comparing the ^(19)F NMR spectra of the complexes between P1-F_4S-P1 and two different but related DNA dodecamers, d(CGCAAATTTGCG) and d(CGCTTTAAAGCG). P1-F_4S-P1 binds more strongly to the former dodecamer with an association constant of approximately 1 X 10^3 M^-1

Synthesis and Structure of Sn₁₄Cl₆(CH₂SiMe₃)₁₂: Toward Nanoclusters of 4‑Coordinate α‑Sn

Orange crystals of a Sn₁₄ cluster have been isolated in up to 22% yield from a reaction between Me₃Si­CH₂­SnCl₃, SnCl₄, and LiAlH₄. The structure determined by single crystal X-ray diffraction shows three unique Sn atoms in a 6:6:2 ratio, with all Sn atoms 4-coordinate, similar to the tetrahedral bonding in elemental gray Sn. The solid state ¹¹⁷Sn MAS NMR spectrum shows the three types of distinct Sn atoms in the expected 3:3:1 intensity ratio with respective chemical shifts of 87.9, −66.6, and −607.1 ppm relative to Me₄Sn. The chemical shift of the two Sn atoms without ligands (bonded only to Sn), at −607.1 ppm, is the most upfield, and is the closest to the chemical shift, reported here, of bulk gray tin (−910 ppm). First-principles density functional theory calculations of the chemical shielding tensors corroborate this assignment. While the core coordination is distorted from the ideal tetrahedral arrangement in the diamond structure of gray tin, this Sn₁₄ cluster, as the largest reported cluster with all 4-coordinate Sn, represents a major incremental step toward being able to prepare atomically precise nanoparticles of gray tin