Synthesis and evaluation of novel tetrapropoxycalix[4]arene enones and cinnamates for protection from ultraviolet radiation

A series of novel calix[4]arene enones (5–7) and cinnamates (12–14) have been synthesized and evaluated for ensuring protection from ultraviolet radiation (UVR). Spectroscopic analyses has revealed that compound 6 absorbs ultraviolet radiations between 280 and 350 nm with an absorption maximum at 312 nm. Its molar absorption coefficient (ε) (>5 × 104 M−1 cm−1) and bandwidth are larger than those for the commercially used sun protectants (oxybenzone (OB), 2-ethylhexyl 4-methoxycinnamate (OMC) and avobenzone). The in vitro Sun Protection Factor (SPF) measurement revealed an SPF of 5.2 at 2% concentration of 6 in home made emulsion formulations while combination of 2% each of 6 and OMC gave an SPF of 8.8. Lower sun protection seems to be compensated by significant protection from more harmful UVA radiations (UVA/UVB absorbance ratio of 0.62).

Graphical abstractPotential of using substituted calix[4]arene enones for sun protection has been investigated.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Functionalized calixarenes can function as useful UV-A and UV-B sun protectants. ► Rapid conformational isomerization of calixarenes can be deployed for better dissipation of absorbed energy. ► Formulations developed from calixarenes function analogous to currently used UVA protectant, avobenzone. ► Synergistic action of calixarenes and octylmethoxycinnamate (OMC) in Sun Protection Factor (SPF) analysis has been observed.