The effect of the topological structure; that is, the network heterogeneity, of hydrophobically modified, slightly acidic hydrogels on the binding and release of low molar mass drugs has been studied using ibuprofen and ephedrine as model compounds with varying water solubility. The difference in the heterogeneity of the gels has been produced by the choice of the hydrophobe copolymerized into the polymer network. The effect of the drug loading on the release kinetics has been investigated as well. The release of hydrophobic ibuprofen was slower from a strongly aggregated heterogeneous gel than from a more homogeneous one, because of the strong hydrophobic interaction between ibuprofen and the heterogeneous hydrogel. The release of hydrophilic ephedrine from the homogeneous gel with an initial drug content of 30 wt % of dry polymer showed negative time dependence, indicating that during and after the swelling of the gel, ephedrine started to bind to the polymer. However, the release of ephedrine from a heterogeneous hydrogel increased with time. This shows that the heterogeneous, aggregated polymer binds the hydrophobic substance more strongly than the homogeneous one does, and that the homogeneous network has higher affinity for the basic hydrophilic substance than the heterogeneous one does. The loading contents of ibuprofen and ephedrine affect the release rates in different ways because of the different binding and release mechanisms. The number of binding sites accessible for ephedrine inside the polymer network is assumed to change upon the swelling of the gel.
Summary
Ozonations of methylpyranosides, as model compounds for cellulose, were performed in unbuffered
aqueous solution at room temperature. The degradation of the pyranosides was followed spectrophotometrically
and with high-performance liquid chromatography (HPLC) as a function of ozonation time.
The substrates studied were the α- and β-anomers of methyl-D-glucopyranoside, methyl-D-mannopyranoside
and methyl-D-xylopyranoside. Methyl-α-D-xylopyranoside degraded more slowly than the other
compounds, whereas the rate of degradation was fastest for methyl-β-D-mannopyranoside. In general
the degradation of the α-anomers was slower than that of the corresponding β-anomers. HPLC and gas
chromatography—mass selective (GC-MS) analyses of the ozonated glucopyranoside samples showed
that monosaccharides, lactones, furanosides and acidic compounds are formed during ozonation.
A lignin-carbohydrate complex (LCC), containing a D-xylose unit connected to an aromatic part
through a βglycosidic bond, was used as a model compound for lignocellulosic pulp. The degradation
of this compound during ozonation was also investigated. The results from UV analyses showed that the
reaction was extremely fast at the beginning and that the degradation of benzene structures in the lignin
mimicking part of the LCC was very rapid. The degradation of the carbohydrate part was slower. This
suggests that lignin provides some protection for the cellulose in lignin-containing pulps against attack
by ozone. IR and NMR analyses of the freeze-dried ozonated LCC samples showed further that C=O
structures are produced during ozonation.
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