Salicylic acid humidity effect

Glycerol is a widely used humectant and moisturizer in cosmetics, and considerable research has been done on its effect on the stratum corneum functionality (75). Glycerol was identified as an effective agent in the formation of lipid crystals under conditions of low humidity. The use of alpha- and beta-hydroxy acids on skin desquamation is now well established and widely practiced (76). New lipophilic variants of salicylic acid are reported to affect comeodesmolysis by acting on the whole stmcture of the comeodesmosomes. Alpha-hydroxy acids fractionate the cor-neodesmosomes only (77). 

Fig. 24 Effect of humidity on the salicylic acid content in aspirin-disintegrant mixtures at 120 days and 25°C (A, aspirin powder). (Adapted from Ref l)...

LLCs are promising candidates as probes for humidity sensors due to the distinct quenching effect of water molecules which can reversibly coordinate to lanthanide ions. The decrease in lifetime of the Dq transititMi of europiumflll) perchlorate was used for the determination of small amounts of water in DMF and DMSO [106]. Wang and Li have presented luminescent nanospheres for die determination of small amounts of water (0.05-3.0 vol%) in ethanol [107]. They coated silica nanoparticles with a thin layer of a salicylic acid-La /Tb " coordination compound. The green fluorescence peaking at 549 nm corresponds to the D4 transition of Tb and is strongly quenched by trace amounts of water. The nanoparticles can be excited at wavelengths around 350 nm. 

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