Diapositivo 1

1

Oxygen Solubility in Perfluorocarbon
Emulsions M.G. Freire1, A.M.A. Dias1, M.A.Z.
Coelho2, I.M.Marrucho1, J.A.P. Coutinho1 1CICECO,
Departamento de Química, Universidade de Aveiro,
3810-193, Aveiro, Portugal 2Departamento de
Engenharia Bioquímica, EQ / UFRJ, Bloco E,
Lab.113, 21949-900, Rio de Janeiro, Brasil
Perfluorocarbons (PFCs) are highly fluorinated,
inert organic compounds that can dissolve large
volumes of respiratory gases. PFCs are immiscible
with aqueous systems, including biological
fluids, and they must be converted to an
emulsified form to be safely injected into the
blood vasculature as blood substitutes or to be
used as oxygen vectors in biological reactors
1.   The scope of this study is to determine
the oxygen solubility in concentrated
perfluorocarbon in water emulsions at 310 K (the
human body temperature). To guarantee longer
emulsion stability these oil-in-water emulsions
were prepared in the presence of a surfactant. To
study the effect of the perfluorocarbon and of
the surfactant in the oxygen solubility, two
perfluorocarbons were used n-perfluorohexane and
perfluorodecalin in combination with three
nonionic surfactants Lecithin, Span 20 and
Pluronic F-68. The concentrations used were 50
(w/v) for the perfluorocarbons and 5 (w/v) for
the surfactant. An adaptation of a precise and
expedite enzymatic method for measuring the
oxygen content in the oil in water emulsions was
developed. The solubility of oxygen in the
concentrated emulsions was correlated with each
one of the pure perfluorocarbons and with the
pure water and conclusions were drawn.
The composition of the emulsions studied is
detailed in Table 1
Table 1. Composition of the studied emulsions
The studied emulsions were saturated with oxygen,
by bubbling compressed air in it during 30 min
before the analysis. The aspect of the emulsions
after preparation is illustrated in Figure 2.
For measuring the oxygen content in the
perfluorocarbon emulsions a precise and expedite
method is proposed. This method is based in the
oxidation of glucose by molecular oxygen
catalyzed by glucose oxidase and is commonly used
for glucose determination when oxygen in excess
is present. The method was adapted to measure the
molecular oxygen when glucose is in excess, and
can be described by the following equations

Figure 2. Emulsions 1-6 after sonication
The oxygen content measured in the
perfluorocarbon emulsions using the enzymatic
method and the values expected by adding the
oxygen content of pure water and PFC phases are
presented in Table 2.
In order to calculate the amount of oxygen
present in each emulsion, related to glucose that
has been oxidized, the color intensity of the
oxidized o-Dianisidine in the samples, was
measured at 540 nm. In Figure 1, the intensity of
the pink color against the control in the
enzymatic method is presented.

• If the solubility of oxygen in water and in each
  perfluorocarbon is considered independently the
  corresponding oxygen values are larger than those
  found with the enzymatic method and it is more
  pronounced in the n-perfluorohexane emulsions.
  This fact possibly indicates presence of a
  mechanism that hinders the dissolution of the
  oxygen in the emulsion.
• The solubility of water in the used PFCs was
  measured in our laboratory with a Karl Fischer
  titrator, Metrohm, model 737 KF Coulometer, at
  298.2 K, obtaining (1.460.04).10-3 mol.L-1 for
  water in n-perfluorohexane and (1.300.09).10-3
  mol.L-1 for water in perfluorodecalin. Water
  solubility in PFCs is in the same order of
  magnitude of the solubility of oxygen in the
  studied emulsions.
• The small extent of the solubilization of PFCs in
  water cannot be considered as one of the
  mechanisms that obstruct the solubility of oxygen
  in the aqueous phase of the emulsion. On the
  other hand, the solubility of water in pure
  liquid PFCs occurs in great extent and must be
  considered as a possible interference that
  decreases the solubility of oxygen in the
  emulsions.

Figure 1. Intensity of the pink color against the
control in the enzymatic method
1 Riess JG, Fluorocarbon based Oxygen
Delivery, Basic Principles and Product
Development, in Blood Susbstitutes Principles,
Products and Clinical Trials, Vol II, Ed. Karger
landes Systems, Switzerland, 1998 2 Dias AMA,
Freire MG, Coutinho JAP, Marrucho IM, Fluid Phase
Equilibria (in press) 3 DIPPR, Thermophysical
Properties Database, 1998 The authors thank
financial support from Fundação para a Ciência e
a Tecnologia, Portugal (POCTI/EQU/44427/2002)
and from FAPERJ and CNPq, Brasil M. G. Freire
acknowledges the scholarship SFRH / BD / 14134 /
2003