Provitamin D molecule as a unique connecting link                                                       from the nanoworld to the macroworld

Irina Terenetskaya 
Department of Optical Quantum Electronics, Institute of Physics, NAS of Ukraine. Prospect Nauki, 46, Kyiv-03039, Ukraine.
E-mail: teren@iop.kiev.ua

     It is well known that vitamin D3 synthesis in human skin originates with the UV photon absorption by the 7-dehydrocholesterol (7-DHC, provitamin D) molecule. It is amazing how the break of С-С bond in this nanoscale molecule causes vital consequences for human health. 
     Our study of the 7-DHC photoreaction in a LC matrix was inspired by the idea of its vizual observation, i.e. developing personal UV biodosimeter for direct assessment of the vitamin D synthetic capacity of a UV source in situ.
     This goal was attained using mixture of LC with 7-DHC in a wedge LC cell (by changing the number of Cano-Grangean bands) [1], then by the color change of a plane-parallel LC cell depending on a UV dose, and finally by the disclination line rotation in the LC theta-cell upon UV exposure [2].    
     Using 7-DHC as a chiral dopant, the chirality transfer effects under UV irradiation were investigated in detail. The principal difference between chiral properties of provitamin D photoisomers in the H-bonding LC was found indicating the formation of 7-DHC supramolecules. In addition, collective nature of previtamin D cis-trans isomerization was revealed in LC matrices due to the medium ordering which can be used in molecular circuits [3].
     The adsorption of 7-DHC was studied in detail on different surfaces. The island structure of 7-DHC films on the mica surface, self-organization of molecules and transformation of the film structure with time was detected using atomic force microscopy (AFM). The formation of Langmuir-Blodgett films and the LCs photo-alignment achieved by UV irradiation of the LC cell substrate with provitamin D adsorbed [4] are promising for flexible organic electronics and information storage.

1.	Terenetskaya I., Method of UV dosimetry and device for visual detection of bioactive UVB radiation // Ukrainian Patent.-2006,- № u 2006 00162.
2.	Kapinos P., Orlova T., Terenetskaya I., UV biodosimeter with visual detection of vitamin D synthesis using θ-cell // Mol.Cryst.Liq.Cryst.-2015.- 615.-P.1-8.
3.	Terenetskaya I., Orlova T., Collective character of previtamin D cis-trans isomerization in liquid-crystalline matrices // Mol.Cryst.Liq.Cryst.-2011.- 541.-P.96-103.
4.	Gvozdovskyy I., Orlova T., Terenetskaya I., UV induced photoalignment and colour change in nematic liquid crystals with provitamin D dopant, Mol. Cryst.Liq.Cryst.-2005.- 430.- P.199-203.