XII Iberian Meeting of Electrochemistry XVI Meeting of the ...

XII Iberian Meeting of Electrochemistry & XVI Meeting of the Portuguese Electrochemical Society PA 05
The effects of lithium, potassium and cesium ions on
the diffusion behaviour of caffeine in aqueous solutions
Victor M.M. Lobo 1 , Cecilia I.A.V. Santos 2 , Miguel A. Esteso 2 , Marisa C.F.
Barros 1 , Ana C.F. Ribeiro 1
1 Department of Chemistry, University of Coimbra, 3004 - 535 Coimbra, Portugal
vlobo@ci.uc.pt
Caffeine is naturally occurring in some beverages and is also used as a
pharmacological agent which is a central nervous system stimulant [1-3]. The
interactions of metal ions with caffeine (3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-
dione) are of major biological interest, due to the fact these complexes play a dominant
role in many biochemical interactions [1-3]. Currently, diffusion coefficients of caffeine
[4] in aqueous solutions and their dependence on media composition (e.g., pH, ionic
strength and metal ions) have been poorly characterized, even though these transport
parameters are necessary to obtain a satisfactory understanding of the tumor/drug
interactions.
H 3C
O
N
H 3C
N
N
O
N
CH 3
Figure 1 caffeine
The present communication intends to be a contribution in filling this gap. In this
work, we present ternary diffusion coefficients D 11 , D 22 , D 12 and D 21 for the ternary
systems (potassium chloride/caffeine, lithium chloride/caffeine, and caesium
chloride/caffeine), for the range of concentrations of each component between 0.0001 M
and 0.010 M at 298.15 K, using a specially designed apparatus built for experimentally
measuring diffusion coefficients based on the Taylor technique. Comparing the main
coefficients D 11 and D 22 and the binary diffusion coefficients of each component, and
using the values of cross coefficients D 12 and D 21 , we can take conclusions about the
influence of the caffeine solutes in diffusion of these salts. Also from the ratios D 21 /D 11
and D 12 / D 22, it is possible to obtain information concerning the number of moles of each
component transported per mole of the other component driven by its own concentration
gradient. We believe that our results will provide guidance for a better understanding of
the physicochemical behavior of these important pharmaceutical systems in aqueous
solutions.
Acknowledgments: We are also grateful to Prof. Pierandrea Lo Nostro from the Department of
Chemistry of University Firenze, Italy, for his valuable help of the interpretation on the diffusion
coefficients of these 3 component systems.
References
[1] Nafisi, S.; Shamloo, D. S.; Mohajerani, N.; Omidi, A.J. Mol. Struct. 2002, 608, 1.
[2] Nafisi, S.; Monajemi, M.; Ebrahimi, S. J. Mol. Struct. 2004, 705, 35.
[3] Food Chem. 2004, 84, 383.
[4] Ribeiro, A. C. F.; Santos, C. I. A. V.; Lobo, V. M. M.; Cabral, A. M. T. D. P. V.; Veiga, F. J.
B.; Esteso, M. A.J. Chem. Eng. Data 2009, 54, 115.
September, 811, 2010. ISEL - Lisbon 60