Fluorine containing calcium aluminosilicate glasses are widely used for a number of
technological applications including dental cements, mould fluxes in steel making and in a variety
of glass-ceramic systems. Despite of their importance these systems remain quite poorly understood
with respect to their composition. To address this question a glass composition corresponding to the
equimolar binary system anorthite−fluorite (Ca2Al2Si2O8−CaF2) was chosen as a base point for two
series of compositions. One of the series is designed on the anorthite stoichiometry and considered
as classically charge balanced. Another series starts from the fluorine free composition of the
anorthite−lime (Ca2Al2Si2O8−CaO) stoichiometry and, therefore, is characterized by a disrupted
network with at least one non-bridging oxygen (NBO) attached to silicon. A multinuclear 19F, 27Al,
29Si solid state NMR study of the glasses was undertaken. It is shown that in both series fluorine is
predominantly coordinated by calcium, F−Ca(n), and in addition interacts with aluminium forming
Al−F−Ca(n) complexes, where n denotes the number of first neighbouring calcium cations. Small
amounts of high coordinated aluminium grows with increasing fluoride content in both glass series.
However, the high coordinated aluminium may not be solely due to the formation of the
Al−F−Ca(n) complexes. Glasses of the first series displayed systematic upfield shift of 29Si NMR
resonance while substituting fluoride for oxide, starting from the fluorine free composition. This
upfield shift is interpreted as the lack of cations in the network, due to formation of the F−Ca(n),
which drives silicon network to polymerize toward a higher Qn structure. Contrary to the first series,
the 29Si NMR resonance remains constant for fluorine containing compositions of the second series
but differs downfield from the initial anorthite glass. The latter is explained by the excess of cations
in the network due to addition of the fluorite resulting in formation of NBO on the silicon. Binding
of fluorine with silicon is considered negligible in these systems. Thus, fluorine and calcium both
define the degree of network polymerization and are considered as a cause for the changes in silicon
and aluminium networks.
A 2H Solid-State NMR Study of Lipid Clustering by Cationic Antimicrobial and Cell-Penetrating Peptides in Model Bacterial Membranes
