2.	Nanobiotechnology for health-care
Keto-enol tautomerism of curcumin in the preparation of nanobiocomposites with fumed silica 
Kazakova O.O., Lipkovska N.O., Barvinchenko V.M. 
Chuiko Institute of Surface Chemistry, NAS of Ukraine,
17 General Naumov Str., Kyiv 03164, Ukraine,
E-mail: kazakova_olga@ukr.net

The plant polyphenol curcumin (Cur) has anti-inflammatory, antioxidant, neuroprotective, hepatoprotective and other properties. Its pharmacological activity largely depends on the ratio of its ketone (Cur-K) and enol (Cur-E) tautomeric forms, so understanding the dynamics of Cur tautomerization is fundamental in the development of drugs, dietary supplements and for predicting clinical reactions.

                              

                   Сur-К                                                        Сur –Е                                                        
The purpose of this work was complex quantum-chemical, sorption and spectral studies of the curcumin keto-enol tautomerism in the process of preparation of its nanobiocomposites with fumed silica (trademarks "Atoxil", "Polysorb") by the adsorption from water-ethanol solutions used in technology to increase the bioavailability of poorly soluble drugs.
  It was found that keto-enol tautomerism of Cur is observed in water-ethanol solutions. Cur-E exists at ethanol concentrations >50%, and with water addition the tautomeric equilibrium shifts towards Cur-K. Quantum-chemical calculations (solvation model SM 5.42 / 6-31G (d), GAMESSPLUS) of various curcumin isomers confirmed that in aqueous solution existence of Cur-K is more thermody-namically favorable. The ratio of ketone and enol forms depends also on the permittivity of water-ethanol solutions: at ε <45, curcumin exists only as  when at ε > 45 the relative amount of Cur-K increases proportionally to the solution permittivtiy. 
Curcumin tautomers adsorb on silica in different ways. At low curcumin concentrations in solution (<1.5 ∙ 10-4 M), a monolayer on the sorbent surface is formed only by the adsorption of Cur-E, apparently due to its linear structure.  Non planar Cur-K begins to adsorb only at Cur concentration > 1.5 ∙ 10-4 M as part of molecular assemblies – aggregates with coplanar geometry, which are formed in curcumin solutions. 
The found patterns make it possible to develop practical recommendations for the preparation and standardization of nanocomposites based on silica and Cur.