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Development of hot-melt extrusion as a novel technique for the ...

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3.5 Intermolecular interactions <strong>of</strong> <strong>hot</strong>-<strong>melt</strong> extrudates3.5.1 Molecular modellingDepending on <strong>the</strong> initial positioning <strong>of</strong> <strong>the</strong> PRP molecule, two hydrogen bondingpatterns were identified (Fig. 6.4) after energy optimisation at <strong>the</strong> B3LYP 6-31G* level usingGaussian09 [23, 24] . Both <strong>the</strong> hydroxyl group and amine group within <strong>the</strong> drug molecule could<strong>for</strong>m strong hydrogen bonds with <strong>the</strong> monomer, <strong>as</strong> indicated by <strong>the</strong> optimal distancesbetween <strong>the</strong> H-bond donor and acceptor. Fur<strong>the</strong>rmore, <strong>the</strong> chloride ion w<strong>as</strong> placed within <strong>the</strong>proximity <strong>of</strong> <strong>the</strong> H bonds in structures. After re-optimisation, <strong>the</strong> H-bonding interaction<strong>for</strong>med with <strong>the</strong> hydroxyl group w<strong>as</strong> broken due to <strong>the</strong> presence <strong>of</strong> <strong>the</strong> chloride ion while <strong>the</strong>H-bond interaction with <strong>the</strong> amine group w<strong>as</strong> not affected (Fig. 6.4) There<strong>for</strong>e, calculationsindicate that <strong>the</strong> hydrogen bond identified b<strong>as</strong>ed on PRP, DPD, L100 and L100-55<strong>for</strong>mulations is most likely <strong>for</strong>med between <strong>the</strong> amine group <strong>of</strong> <strong>the</strong> drug molecule and <strong>the</strong>carbonyl groups <strong>of</strong> <strong>the</strong> polymer.Fig. 6.4: Molecular modelling <strong>of</strong> drugs/polymers (Gaussian 09).3.5.2 X-ray p<strong>hot</strong>oelectron spectroscopy (XPS)The surface elemental ratios <strong>of</strong> PRP, DPD, polymers and <strong>the</strong> extruded <strong>for</strong>mulationsdetermined experimentally by XPS [25] are shown in Table 6.1 and are compared with <strong>the</strong><strong>the</strong>oretical values derived from <strong>the</strong> structural <strong>for</strong>mula [26] . The experimental results were in114 | P a g e

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