Development and Characterization of Novel Bigel-Based 1,4-Naphthoquinones for Topical Application with Antioxidant Potential

Discovering new antioxidant agents and optimizing their processing is a necessity to treat skin diseases. The assessment of quality and antioxidant activity of topical formulations based on 5,8-dihydroxy-1,4-naphthoquinone (M1) and 2,3-dichloro-5,8-dihydroxy-1,4-naphthoquinone (M2) was carried out for the first time for this purpose. Stability studies including evaluation of pH, viscosity, microscopic observation, and microbiological quality were determined. M1 and M2 were examined for their antioxidant capacities after their incorporation into bigels. Obtained data suggested that BG-M1 and BG-M2 have a good quality, a natural pH of the skin (4.5–6.0), and no sign of microbial development. Sensory analysis was also performed, and no negative assessment of unpleasant bigel properties was found. M1 and M2 have shown antioxidant activity toward DPPH radical (data are expressed as IC₅₀), 19 × 10⁻³ mg/mL for M1 and 35 × 10⁻³ mg/mL for M2, respectively. After their formulations, they have maintained this ability, for BG-M1 = 3.0 and BG-M2 = 1.1 mg/mL. Also, they demonstrated interesting ABTS scavenging with 1.5 × 10⁻³ and 2.5 × 10⁻³ mg/mL for M1 and M2, respectively. They kept this potential after formulation, since, BG-M1 = 1.7 mg/mL and BG-M2 = 4.9 mg/mL. Likewise, pure molecules revealed notable β-carotene bleaching inhibition (0.3 and 0.1 mg/mL for M1 and M2, respectively), which was maintained after their formulation into bigels (2.9 and 10.3 mg/mL for BG-M1 and BG-M2, respectively). These developed bigels maintaining the antioxidant potential of M1 and M2 could be used as the provision of a barrier to protect skin.