Abstract The total energy, dipole moment and electron densities for each possible rotational conformation about the Cpy-S bonds of di-2-pyridyl disulfide were evaluated by using the semi-quantitative CNDO/2 method. The conformations in which the pyridine rings are coplanar with the valency plane of the bonded sulfur atom (cis-cis, cis-trans and trans-trans) were predicted to be the most favored ones. Results of the theoretical study, when compared to some experimental determinations such as dipole moment and variable temperature pmr spectra, provided evidence that easy interconversion between these conformations can occur. 相似文献
The Co7(AlePy)2 polyoxometalate, which encloses a {(PW9)2CoII7} core covalently bound to two free aminopyridine groups through bisphosphonate ligands ( AlePy ), has been isolated. It can be used as a precursor, allowing the synthesis of heterometallic hybrid compounds, as illustrated by the characterization of cobalt/zinc ( Co7(AlePyZn)2 ), cobalt/palladium ( Co7(AlePyPd)2 ), and cobalt/platinum ( Co7(AlePyPt)2 ) species. A composite based on the water‐insoluble precious metal‐free Co7(AlePyZn)2 compound and the low‐cost carbon material Vulcan XC‐72 has been selected as a cathode material ( Co7Zn/C ) for oxygen reduction reaction studies. The electrocatalytic performances of the Co7Zn/C hybrids were assessed at neutral and basic pH, showing that Co7Zn/C exhibits high selectivity for the four‐electron reduction of O2. Moreover, its durability is superior to that of a commercial Pt/C catalyst with 20 % loading. Also, comparative studies performed in the presence of methanol have indicated that Co7Zn/C has a much better tolerance to the crossover effect than Pt/C . Altogether, these results indicate for the first time that, even in neutral media, polyoxometalate/carbon composites can represent low‐cost oxygen reduction catalysts that can function stably, for a long time, and with high performance. 相似文献
The crystal structures of 3-methylpiperid-1-ylmethane-1,1-diphosphonic (2), 4-methylpiperid-1-ylmethane-1,1-diphosphonic (3), 2-ethylpiperid-1-ylmethane-1,1-diphosphonic (4), and 2-methylpiperid-1-ylmethane-1,1-diphosphonic (5) acids have been determined and are discussed with respect to their molecular organization and crystal-packing preferences. The chair conformation, predominant also in solution, favors equatorial positioning of the bulky substituents of the heterocyclic N and C atoms. The molecular geometry also provides access to intramolecular hydrogen-bond formation between the axial protons located on the nitrogen atoms, as well as the carbon atoms closest to it, and phosphonic/phosphonate oxygen atoms. The molecules preferably arrange in monolayers, observed in all crystals with an exception of 3. The layers are held in place in the third direction through van der Waals interactions. The analysis of two-dimensional hydrogen-bonded networks is concentrated on revealing how the substituent's topology of the molecule affects the solid-state organization in well-defined structures and is aimed at unraveling the consequences and the possible conformational changes by stepwise network disruption upon crystal dissolution in water. The solution NMR studies are focused on revealing the role that the topochemistry of the substituent plays for the stereodynamics in 2-5. It is demonstrated that in contrast to piperid-1-ylmethane-1,1-diphosphonic acid (1), in which the ring inversion/rotation around the C-N bond concerted with the N-H...O hydrogen-bond breaking/formation process leads to a mixture of two interconverting conformers, the concerted N-H...O breaking/rotation/N-H...O formation process in 2 and 3 allows for a predominance of one conformer in solution. However, placement of a substituent at 2-position in the ring hampers the rotation around the C-N bond; this makes 4 and 5 significantly less flexible relative to compounds 1-3. In addition, both compounds 4 and 5 are proved to exist as a mixture of two conformers, the equilibrium of which in acidic solution is shifted towards the conformer found in solid state. In alkaline solutions of 4 and 5, the equilibrium is shifted towards the conformer that is forced by the flipping of the heterocyclic ring. These results correlate well with recently documented differences in the biological potency of this group of compounds. 相似文献
Gelatin nanoparticles can be tuned with respect to their drug loading efficiency, degradation rate, and release kinetics, which renders these drug carriers highly suitable for a wide variety of biomedical applications. The ease of functionalization has rendered gelatin an interesting candidate material to introduce specific motifs for selective targeting to specific organs, but gelatin nanoparticles have not yet been modified to increase their affinity to mineralized tissue. By means of conjugating bone‐targeting alendronate to biocompatible gelatin nanoparticles, a simple method is developed for the preparation of gelatin nanoparticles which exhibit strong affinity to mineralized surfaces. It has been shown that the degree of alendronate functionalization can be tuned by controlling the glutaraldehyde crosslinking density, the molar ratio between alendronate and glutaraldehyde, as well as the pH of the conjugation reaction. Moreover, it has been shown that the affinity of gelatin nanoparticles to calcium phosphate increases considerably upon functionalization with alendronate. In summary, gelatin nanoparticles have been developed, which exhibit great potential for use in bone‐specific drug delivery and regenerative medicine.
Pamidronate is a bisphosphonate that is effective in treating bone disease including osteopenia and osteoporosis in adults. A sensitive and reliable method for the analysis of pamidronate in whole blood and urine is key to the development of this drug for use in children. A previously described method for pamidronate analysis serum and urine did not consistently detect the drug at satisfactory levels in whole blood. The procedure involves co-precipitation of the bisphosphonates with calcium phosphate, pre-column derivitization with fluorescamine, HPLC utilizing a Nucleosil C(18) column, and fluorescence detection with excitation at 395 nm and emission at 480 nm.Changes to the original protocol included the use of a new internal standard (alendronate), the optimization of the concentration of ethylenediaminetetraacetic acid (EDTA) for dissolving the precipitate, and the elimination of the acidification step prior to deproteinization. The optimum EDTA concentration, which had a significant effect on the labeling capability of fluorescamine, was determined to be 20 mm.A good separation between pamidronate and alendronate was achieved using a heated (40 degrees C ) Nucleosil C(18), 10 micro m particle size column. The mobile phase was an aqueous solution of 1 mm Na(2)EDTA-methanol (97:3, v/v) adjusted to pH 6.5 using a fl ow-rate of 1 mL/min. Fluorescence detection was set at 395 nm for excitation and at 480 nm for emission. The limit of quantitation for pamidronate was 0.5 micro g/mL in whole blood and 0.1 micro g/mL in urine. The method was applied to both whole blood and urine samples from pediatric patients. 相似文献