Abstract
Powerful antioxidant α-lipoic acid (LA) is easily degraded under light and heating. This creates difficulties in its manufacture, storage and reduces efficiency and safety of the drug. The purpose of this work was to synthesize novel silica-based composites of LA and evaluate their ability to increase photo and thermal stability of the drug. It was assumed that the drug stabilization can be achieved due to LA-silica interactions. Therefore, the composites of LA with unmodified and organomodified silica matrixes were synthesized by sol-gel method at the synthesis pH below or above the pKa of the drug. The effects of silica matrix modification and the synthesis pH on the LA-silica interactions and kinetics of photo and thermal degradation of LA in the composites were studied. The nature of the interactions was revealed by FTIR spectroscopy. It was found that the rate of thermal degradation of the drug in the composites was significantly lower compared to free LA and mainly determined by the LA-silica interactions. However, photodegradation of LA in the composites under UV irradiation was either close to that for free drug or significantly more rapid. It was shown that kinetics of photodegradation was independent of the interactions and likely determined by physical properties of surface of the composite particles (porosity and reflectivity). The most promising composites for further development of novel silica-based formulations were identified.
Highlights
A significant scientific and technological interest has focused on drug-silica materials, which have been identified as potentially effective drug delivery systems (DDS)
We focused on the effects of sol-gel synthesis pH and silica matrix modification on the photo and thermal stability of lipoic acid (LA) in the silica-based composites
LA was used as the racemic mixture of two enantiomers (R-(+)-LA and S-(−)-LA), because it is presented in the pharmaceuticals and nutraceuticals in most cases
Summary
A significant scientific and technological interest has focused on drug-silica materials, which have been identified as potentially effective drug delivery systems (DDS). The DDS can improve the administration and efficacy of pharmaceutical compounds. AZthaenngcaeptsaul.la[2ti4o]nreopforLtAed itnhastielinccaapmsautleartiiaolns oafnpdroftoeramseaitniosnilicoaf smilaictrai-xbasisgendifciocamnptloysiintecrceaanseledadthteormpraelpsatarabtiiloitny ooff nthoeveenl ozyraml efo. Modification results in altering properties of silica matrixes, e.g., hItydisrowpehlillikcnitoyw/hnydthroapt hmoobdiciiftiyc,aatcioidn-boafsseilpicraopmerattireisxeasndwsiuthrfvacaericohuasrgfue;nic.eti.o, tnhaelirgsrouurfpasceinreflaucetinvcietys. Ounpotnhefoormthaertiohnanodf ,thseiliccoamspuorfsaictee ccaannleaalsdotoioinniczreeaastincghaantgtriancgtivpeHordureeputolsitvhee dprruogto-snialitcioanin/dteerparcotitoonnsatiinonthoefcsoimlapnooslsite(Ss.i–TOakHin),gaisnwtoeallccaosuinntcothrpeoinrafoterdmaactiiodn-biansdeicsautrefdacaebofuvne,ctiniotnhael pgrreosuepnst.wTohrker,ethfoerceo, mapcohsaitnegseofiLnAthweithpHunmmoeddiifiuemd suilpicoanmfaotrrmixaatsiownelolfasththeecmomatrpioxseistemocadnifieledawd ittho increasing attractive or repulsive drug-silica interactions in the composites. Taking into account the Pharmaceutics 2020, 12, 228 different organic groups were synthesized by the sol-gel method at the synthesis pH below or above the pKa of the acid (pKa LA 4.7–5.1 [11]). We focused on the effects of sol-gel synthesis pH and silica matrix modification on the photo and thermal stability of LA in the silica-based composites. LA was used as the racemic mixture of two enantiomers (R-(+)-LA and S-(−)-LA), because it is presented in the pharmaceuticals and nutraceuticals in most cases
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