Author: Herr Dr. Amoneit
Last saved by: Gürbüzoglu, Meltem
Company: HP

Partition Constants and Distribution of Catechol in
Corn Oil/Tween20/Acidic Water Emulsions
Sonia Losada-Barreiro^1, ^*, Marlene Costa^2, Carlos Bravo-Díaz ^1, Fátima Paiva-Martins^2, Laurence S. Romsted^3
^1Fac. Química, Dpto Química Física, Universidad de Vigo, 36200, Vigo, Spain
^2Facultade de Química e Bioquímica, Universidade do Porto, Porto, Portugal
^3Chemistry Dpt., Rutgers, The State University of New Jersey, New Jersey, USA
*sonia@uvigo.es

The efficiency of antioxidants (AOs) in inhibiting lipid oxidation depends on their intrinsic reactivity against the radicals and their concentration at the reaction site. In emulsified systems, the reaction site is the interfacial region, but antioxidants may distribute between the oil, interfacial and aqueous regions of the emulsion. Thus, their concentration at the reaction site does not parallel their stoichiometric concentration and needs to be determined in the intact emulsions because of the physical impossibility of separating the interfacial from the aqueous and oil regions. Moreover, AO distribution depends on a number of factors such as their structure, HLB of the emulsifier, acidity and temperature.  Here we report on the distribution of catechol, CAT, in stripped corn oil-in-water emulsions prepared with acidic water and Tween 20. The distribution of CAT in emulsions is described by two partition constants, that between the oil-interfacial region, P_O^I, and that between the aqueous and interfacial region, P_W^I.[2] The partition constants P_O^I and P_W^I are obtained in the intact emulsions by employing a kinetic method that exploits the reaction between the hydrophobic 4-hexadecylbencenediazonium ion (16-ArN_2^+) and CAT. Experimental data are analyzed on the grounds of the pseudophase kinetic model.[1] Results indicate that CAT distributes between three regions. An increase in emulsifier concentration promotes the incorporation of CAT to the interfacial region of the emulsions, so that at the emulsifier volume fraction of 0.037, more than ∼70% is located in that region. Comparison of results with those obtained for different catechol derivatives indicate that the fraction of antioxidant in the interfacial region of the emulsions do not correlate with their polarity. Results should contribute to a better understanding of AOs efficiencies in emulsions.

[1] Romsted, L.S.; Bravo-Díaz, C., Modelling chemical reactivity in emulsions. Current Opinion in Colloid and Interface Science  2013, 18, 3-14.
[2] Losada-Barreiro, S.; Bravo-Díaz, C.; Costa, M.; Paiva-Martins, F., Distribution of catechol in emulsions. Journal of Physical Organic Chemistry 2014, 27, 290–296,