Stabilizacija askorbilpalmitata v lamelarnih tekočih kristalih

Badovinac, Maja (author), Gosenca Matjaž, Mirjam (mentor), Roškar, Robert (comentor)

Askorbilpalmitat (AP) je amfifilni derivat vitamina C, ki izkazuje večjo stabilnost in enostavnejše prodiranje v kožo, vendar je njegova stabilnost zaradi hitre oksidacije, nezadovoljiva. Namen magistrskega dela je izboljšati kemijsko stabilnost AP, vgrajenega v lamelarne tekoče kristale za dermalno uporabo. Ovrednotili smo dva različna pristopa za povečanje stabilnosti AP, in sicer dodatek antioksidantov ali povišanje koncentracije AP. V prvem delu smo v okviru preliminarne študije (2 tedna) testirali vpliv dodatka antioksidantov (vitamin C in E, koencim Q10, kvercetin, butilhidroksitoluen, propilgalat), različnih koncentracij AP (5 % in 10 % napram 1 % (m/m)) na stabilnost AP v dveh sistemih tekočih kristalov s konstantnim razmerjem med lipofilno fazo in emulgatorsko zmesjo ob različnem deležu vodne faze (T1 z najmanjšim deležem vode ter T8 z največjim deležem vode). V sisteme z dodanim antioksidantom smo vgradili 1 % (m/m) antioksidanta in 1 % (m/m) AP. Preliminarno stabilnostno študijo smo izvedli v klimatski komori pri 40 °C in 75 % RV, kjer so bili vzorci zaščiteni pred svetlobo, ter vrednotili stabilnost AP s pomočjo tekočinske kromatografije ob času 0 in 2 tedna. Ugotovili smo, da je bil AP najstabilnejši pri obeh višjih koncentracijah in sočasni vgradnji vitamina C v primeru 1 % (m/m) AP. Na podlagi preliminarnih rezultatov smo nadalje zasnovali in izvedli stabilnostno študijo pri višjih koncentracijah AP ali ob dodatku vitamina C v tekočih kristalih z različno kvantitativno sestavo, in sicer v tekočih kristalih z naraščajočim deležem vode (TK1, TK3, TK5 in TK8) in primerjalno v SMES (zmes olja in emulgatorjev brez dodane vode). Vzorce smo shranjevali v klimatski komori pri 40 °C in 75 % RV in določali upad vsebnosti AP s tekočinsko kromatografijo znotraj 8 tednov. Ugotovili smo, da stabilnost AP z nižanjem deleža vode narašča. Najbolj optimalno stabilnost smo po osmih tednih dosegli v TK1 in SMES-u pri višjih koncentracijah AP ali ob dodatku antioksidanta vitamina C. Ker lahko večji delež vgrajenega AP ali dodatek antioksidantov vpliva na mikrostrukturo, smo mikrostrukturo tekočih kristalov, vključenih v stabilnostno študijo, dodatno pregledali pod polarizacijskim mikroskopom ter potrdili njihovo lamelarno strukturo. Zaključimo lahko, da smo z vgradnjo višjih koncentracij AP in dodatkom vitamina C v tekoče kristale z manjšim deležem vode, dosegli uspešno stabilizacijo AP.

• Language: Slovenian
• Keywords: askorbilpalmitat, liotropni tekoči kristali, stabilnost, antioksidanti, vitamin C
• Work type: Master's thesis/paper
• Organization: FFA - Faculty of Pharmacy
• Year: 2021
• PID: 20.500.12556/RUL-131500
• Publication date in RUL: 29.09.2021

Secondary language

• Language: English
• Title: Stabilization of ascorbyl palmitate in lamellar liquid crystals

Abstract

Ascorbyl palmitate (AP) is an amphiphilic derivative of vitamin C, which shows greater stability and easier penetration into the skin, but its stability is still insufficient due to rapid oxidation. The aim of master’s thesis is to improve the chemical stability of AP incorporated in lamellar liquid crystals for dermal application. Two different approaches to increase the stability of AP were evaluated, the addition of antioxidants or increasing the AP concentration. Firstly, the effect of antioxidants (vitamins C and E, coenzyme Q10, quercetin, butylhydroxytoluene, propyl gallate) and different concentrations of AP (5% and 10% vs. 1% (w/w)) on the stability of AP in two liquid crystal systems was tested within preliminary study (2 weeks). Liquid crystals had a constant ratio between lipophilic phase and emulsifier mixture at different proportions of aqueous phase (T1 with the lowest and T8 with the highest proportion of water). In the systems with added antioxidant, 1% (w/w) antioxidant and 1% (w/w) AP had been incorporated. A preliminary stability study was carried out at 40 °C and 75 % relative humidity, where the samples were protected from light, and the stability of AP was evaluated by liquid chromatography at 0 and 2 weeks. AP was most stable at both higher AP concentrations and with the additional incorporation of vitamin C in the case of 1% (w/w) AP. Based on the preliminary results, a stability study was further designed and carried out at either higher concentrations of AP or with the addition of vitamin C in liquid crystals. The tested liquid crystals differ in their quantitative composition, namely the water content was increasing from TK1, TK3, TK5 to TK8, comparatively the stability was evaluated also in SMES (mixture of oil and emulsifiers with no added water). The samples were stored at 40 °C and 75 % relative humidity and the decrease in concentration of AP was determined by liquid chromatography within 8 weeks. As determined, the stability of AP increased with decreasing water content. The most optimal stability was observed after 8 weeks in TK1 and SMES at higher AP concentrations or with the addition of the antioxidant vitamin C. Because the addition of antioxidants or increasing the concentration of AP influence the microstructure, the microstructure of the liquid crystals included in the stability study was examined under a polarized microscope and the lamellar structure was confirmed. It can be concluded that by incorporating higher concentrations of AP and the addition of vitamin C to the liquid crystals with a lower proportion of water, successful stabilization of AP was achieved.

• Keywords: ascorbyl palmitate, lyotropic liquid crystals, stability, antioxidants, vitamin C