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- Bioactive glasses (2)
- NMR (2)
- Raman (2)
- 27Al nuclear magnetic resonance (1)
- Alumina (1)
- Bioactive coatings (1)
- C-13 isotopic labeling (1)
- Cellodextrins (1)
- Cellulose (1)
- Differential thermal analysis (1)
Aluminas resulting from sols prepared via a modified Yoldas procedure were studied with differential thermal analysis (DTA), differential thermal gravimetrie (DTG), 27Al nuclear magnetic resonance (27Al MAS NMR) and X-ray diffraction (XRD) concerning their thermal properties, aluminum speciation and phase content.
Hydrolysis of aluminum-sec-butoxide in aluminum nitrate solutions allowed to prepare stable sols with varying NO3-/Al molar ratios, solids contents and pH values. Resulting sols contained different aluminum species including also Al13 polycations. Sol preparation conditions also determined aluminum speciation in solid products obtained after thermal treatments of gels obtained from these sols. Al13 polycations and AlO5 species were found to play an important role for thermally induced transformation from amorphous products via eta-Al2O3 to alpha-Al2O3. Intermediately formed eta-Al2O3 promotes the phase transformation to alpha-Al2O3.
The supermolecular mechanism of the template-mediated oxidative polymerization of pyrrole is investigated in detail. It is shown for the first time that 2,5-bis(pyrrol-2-yl)pyrrolidyl complexes with aromatic sulfonic acids such as %#946;-naphtalenesulfonic acid or para-toluenesulfonic acid are formed in the early polymerization step. The crystalline acidbase complexes are isolated and their crystal structures are analyzed. A 2,5-bis(pyrrol-2-yl)pyrrolidyl cation is common to both complexes and forms an inner salt with the sulfonic acid anion. As concluded from NMR investigations the synthesis using sulfonic acids results in a high stereo selectivity with respect to the trans conformation of the pyrrolidyl ring compared with the classical synthesis routine of this compound using hydrochloric acid. The needle-like crystals of the complexes act as hard templates during the next step of the polymerization and result in tubular morphologies of the polypyrrole.
The results of a structural study combining NMR and Raman spectroscopy of several melt-derived glasses in the system Na2OMgOCaOP2O5SiO2 are presented. The Raman spectra show clear changes in the SiOSi vibrational modes (related to the bridging oxygen atoms, BO) and also verify the presence of non-bridging oxygen atoms (NBO), also named terminal oxygens. The intensity of the SiONBO stretching mode depends on the cation concentration. It can be concluded from the NMR studies that the MgO-containing samples have orthophosphate units charge-compensated by Ca2+ and Mg2+. The silicate matrix also contains both types of two-valent cations and consists of Q2 and Q1 units. Similarly, the Na2O-containing samples contain isolated orthophosphate units in a silicate matrix (Q2 and Q3 units), both charge-compensated by mixed cations Ca2+ and Na+. These experimental data were compared with theoretical parameters given by the Stevels model, which is a suitable tool for understanding bioactive behavior of these glasses. Furthermore, results of the in vitro tests carried out in simulated body fluids are presented and compared with both Raman and NMR structural data.
The results of a combined structural characterisation (XRD, IR, NMR, SEM, TEM) of a
phosphate containing Mg-Ca silicate and a phosphate containing Na-Ca silicate glass samples are
presented. The structural results are also compared with in vitro tests carried out in simulated body
fluids for checking bioactivity.
Silicon substituted Hydroxyapatite coatings were prepared by Pulsed Laser Deposition
from targets made of mixtures of Hydroxyapatite with Si powder at different concentrations. The
properties of the Si-HA coatings with several degrees of Si substitution were analyzed by different
techniques such as FTIR, XRD, XPS and solid-state NMR. It was found that the Si incorporation
causes an amorphization of the structure together with a loss of carbonate groups. Furthermore, the
Si atoms are incorporated in the form of SiO4
4- groups, and H(PO4)2- appears as the predominant
phosphate group.