L. García-Río et al.
ꢀ
2
was studied using a concentration of amino acid of 5.010 m referred to
the volume of the droplet. For these experiments the microemulsions
were prepared using an aqueous solution of amino acid with a concentra-
[24] a) C. Gonzµlez-Blanco, L. J. Rodríguez, M. M. Velµzquez, Langmuir
1997, 13, 1938–1945; b) G.-W. Zhou, G.-Z. Li, W.-J. Chen, Langmuir
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183.
ꢀ
2
tion of 5.0010 m. An equal concentration of NaOH was added to this
solution to guarantee that the carboxyl group would be deprotonated.
The piperazine solutions were prepared in an aqueous medium, so that
the concentration of piperazine referred to the aqueous microdroplet was
0
.10m. The solutions of DEC were prepared in isooctane and were added
ꢀ
2
to the reaction mixture so that [DEC]=2.5010 m. In all the experi-
ments the temperature remained constant at (25.0ꢃ0.1)8C. The kinetic
absorbance versus time data always fit the first-order integrated rate
equation satisfactorily (r>0.999); in what follows,
k
obs denotes the
[28] Given the microheterogeneous character of the reaction medium it
is necessary to differentiate between concentrations referred to the
total volume of the system and concentrations referred to the
volume of the phase. We will always use a nomenclature in which
pseudo-first-order rate constant. We were able to reproduce the rate con-
stants with an error margin of ꢃ5%. In all cases we verified that the
final spectrum of the product of the reaction coincided with another ob-
tained in pure water, guaranteeing that the presence of the microemul-
sions did not alter the product of the reaction. A compilation of the ki-
netic data is supplied as Supporting Information.
w
i
o
[S] , [S] and [S] denote the concentrations of the substrate in the
w
i
o
aqueous microdroplet referred to the volume of the aqueous micro-
droplet; the substrate concentration in the interface referred to the
volume of the interface and substrate concentration in the continu-
ous medium referred to the volume of the continuous medium. The
concentrations written with just a subindex will always be referred
to the total volume of the system: [S] , [S] and [S] correspond to
w
i
o
the substrate concentrations in the aqueous microdroplet, the inter-
face and the continuous medium respectively, referred in all cases to
the total volume of the system.
Acknowledgements
[
[
[
29] L. García-Río, E. Iglesias, J. R. Leis, M. E. PeÇa, J. Phys. Chem.
Financial support from Ministerio de Ciencia y Tecnología (Project
BQU2002-01184) and Xunta de Galicia (PGIDT03-PXIC20905PN and
PGIDIT04TMT209003PR) is gratefully acknowledged.
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31] There is a large body of studies showing the validity of the droplet
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the compartmentalization of the reagents and hence the validity of
the kinetic model. See for example the photon correlation spectros-
copy studies showing the existence of a good correlation between
the Stokes radii of AOT/Isooctane/Water ternary systems with W
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