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ORIGINAL ARTICLE
Effect of Sonication on the Thermotropic Behavior of DODABVesicles Studied by Fluorescence Probe Solubilization
Eloi Feitosa • Carlos Roberto Benatti •
Marcio Jose Tiera
Received: 3 November 2008 / Accepted: 7 September 2009 / Published online: 12 December 2009
� AOCS 2009
Abstract The effect of sonication on fluorescence probe
solubilization in cationic vesicles of dioctadecyldimethy-
lammonium bromide (DODAB) was investigated by
steady-state fluorescence of pyrene (Py), trans-diphenyl-
polyenes—diphenylbutadiene (DPB), diphenylhexatriene
(DPH), and their corresponding 4,40-dialkyl derivatives
4B4A and 4H4A fluorescence probes. The data indicate
that sonication affects the bilayer polarity, the melting
temperature (Tm), and the cooperativity of the melting
process due to changes in vesicle morphology. The effect
of temperature on the fluorescence intensity and yielding
Uf and anisotropy \r[ shows that the ionizable probes
4B4A and 4H4A are solubilized close to the vesicle
interfaces, whereas the non-ionizable DPH and DPB are
deeper in the bilayers. Py solubilization indicates that
sonicated vesicles exhibit less densely packed bilayers.
Keywords DODAB � Pyrene � trans-Diphenylpolyenes �Fluorescence anisotropy � Melting temperature �Cationic vesicles
Abbreviations
DODAB Dioctadecyldimethylammonium bromide
DSC Differential scanning calorimetry
DPB 1,4-Diphenyl-1,3-butadiene
DPH 1,6-Diphenyl-1,3,5-hexatriene
ESR Electron spin resonance
I1/I3 Ratio between the intensities of the first and the
third vibronic peaks
If Total fluorescence intensity
Py Pyrene
\r[ Steady-state anisotropy
t-Dpo trans-Diphenylpolyenes
Tm Melting temperature
Uf Fluorescence quantum yield
Introduction
Vesicles are dynamic structures formed by the competition
of the attractive and repulsive interactions between the
polar and apolar portions of lipids, and are characterized by
a packing parameter (v/al) close to unity [1]. Vesicles
contain inner–outer interfaces where the hydrophilic head
groups are located, and an oil-like thin layer made up by
the hydrocarbon chains. The lipid bilayer can host apolar
solutes and small polar compounds can be entrapped in the
inner aqueous compartment, which allows transport studies
[2]. In excess water, double-chain lipids, such as DODAB,
self-assemble as large unilamellar vesicles commonly used
to mimic biological membranes and function as vehicles
for drug delivery [3, 4].
Vesicle properties, such as stability, permeability,
melting temperature, degree of ionization and size, among
others, depend on the chemical composition of the lipids
ionic, strength, temperature, pH, and method of vesicle
preparation [3–10]. It has been reported that sonicated
aqueous dispersions of a DODAB consist of one population
of bilayer fragments (RH = 8.5 nm) and another
E. Feitosa (&)
Physics Department, IBILCE/UNESP, Rua Cristovao Colombo
2265, Sao Jose do Rio Preto, SP 15054-000, Brazil
e-mail: [email protected]
C. R. Benatti
Physics Institute, USP, Sao Paulo, SP, Brazil
M. J. Tiera
Chemistry and Geoscience Department, IBILCE/UNESP,
Sao Jose do Rio Preto, SP, Brazil
123
J Surfact Deterg (2010) 13:273–280
DOI 10.1007/s11743-009-1169-8
population of vesicles (RH = 22 nm) [9], while spontane-
ous DODAB aqueous dispersions contain two populations
of vesicles with RH = 80 and 337 nm [10]. Such structures
provide different solubilization compartments for small
probe molecules for spectroscopic studies.
Typical vesicles exhibit a gel to the liquid–crystalline
state transition at a well-defined melting temperature (Tm)
[11]. Below Tm the lipid chains are in a more extended
(gel) state, whereas above Tm they are in a more flexible
(liquid–crystalline) state. The cooperativity of the phase
transition may be influenced by the lipid structural char-
acteristics as the head-group or hydrocarbon chain com-
position and length [11], counterion type [12] as well as by
the method of vesicle preparation [13]. A great effort has
been made to understand better the effects of the lipid
structure and composition and the bulk characteristics on
the vesicle Tm as well as the correlation between the vesicle
structure and general properties [12–18]. For example, the
bilayer barrier to water or small inorganic molecules is
higher above than below Tm owing to different lipid
packing constrains, and additives in general affect Tm and
thus the vesicle permeability [18].
Fluorescence spectroscopy is useful for investigating
microenvironments in vesicle bilayers whose local vis-
cosity and polarity influence the fluorescence response of
solubilized probes [14, 19–21]. Fluorescence spectra of the
probes give information about the bilayer organization and
state of the lipid chains [19]. In the particular case of the
trans-diphenylpolyene (t-Dpo) derivatives the excited
fluorophores solubilized in the bilayer are isomerized and
the competition between the fluorescence and the fluoro-
phore photoisomerization results in a decrease in the total
fluorescence intensity [14, 20]. Above Tm, in the liquid–
crystalline state, the higher mobility of the probes favors
photoisomerization yielding a decrease in the total fluo-
rescence intensity (If), quantum yield (Uf) and anisotropy
(\r[), that can be monitored as a function of temperature
to obtain the vesicle Tm. The ratio of the fluorescence
intensities of the first (I1) to the third (I3) vibronic bands of
the Py emission spectrum has also been widely used to
characterize the polarity of vesicle bilayers [19, 21].
In this communication, a number of trans-diphenyl-
polyenes (t-Dpo) fluorescent probes were used to study the
effect of sonication on the thermotropic behavior of
DODAB vesicles. The data reported is thus complementary
to those previously reported by Feitosa and Brown [9] and
Benatti et al. [4] who investigated bath-sonicated DODAB
vesicles by light scattering and electron spin resonance,
respectively. Brito and Marques [5] and Feitosa et al. [18]
also reported data on differential scanning calorimetry
(DSC) for tip- and bath-sonicated DODAB vesicles.
It is known that sonication and extrusion [17, 18, 22]
yield formation of lens-shaped DODAB vesicles. The
amount of these structures depends on sonication power
and time [17, 22], as well as on the nominal diameter of the
extrusion membrane: the smaller the membrane pore
diameter, the more lens-shaped vesicles are formed [22].
Since bath-sonication is less powerful than tip-sonication, a
lower number of lens-like vesicles is expected in the
former.
The right choice of spectroscopic probe is thus impor-
tant for the investigation of the thermal behavior of vesicles
since it can be solubilized in different bilayer sites. t-Dpo
are planar molecules with a high probability of being
incorporated at the vesicle interfaces or within the bilayer
[14, 20, 23, 24]. Although the probes in the vesicles may be
distributed throughout different sites with different polar-
ity, the spectra represent an average of the emission char-
acteristic of the microenvironment felt by the probes.
These probes have been used before to investigate DODAB
and DODAC (dioctadecyldimethylammonium chloride)
spontaneous vesicles [23, 24], and here they help us to gain
insight into the effect of sonication on the thermal behavior
of DODAB vesicles.
Experimental Section
The fluorescence measurements were made using pyrene
(Py) and 1,4-diphenyl-1,3-butadiene (DPB), 1,6-diphenyl-
1,3,5-hexatriene (DPH), and their 4,40-dialkyl- derivatives
(4B4A and 4H4A) as fluorescence probes, whose chemical
structures are shown in Fig. 1.
DODAB was used as purchased from Eastman Kodak.
DPH (Aldrich) was recrystallized twice from acetone, and
DPB was recrystallized three times from benzene/alcohol
as described [20, 25, 26]. 4H4A and 4B4A were synthe-
sized as reported [26]. Py (Aldrich Chemical Co.) was used
as received. Milli-Q Plus high quality water was used in
sample preparations.
Fig. 1 Chemical structures of the fluorescence probes used in this
work
274 J Surfact Deterg (2010) 13:273–280
123
Vesicle Preparation
Spontaneously formed vesicle dispersions were prepared
by simply mixing DODAB (1 mM) in water at 55 �C, as
reported [10]. After preparation, the samples were cooled
to room temperature and stored at this temperature for at
least 24 h before the fluorescence measurements. Bath-
sonicated vesicles were prepared by 90-min sonication of
the DODAB dispersions at 55 �C using a bath sonicator
(Microsonic SX-10).
The Probe Incorporation
Solutions of DPH and DPB in cyclohexane and Py, 4H4A
and 4B4A in chloroform were prepared. The incorporation
of these probes in the vesicle compartments were made by
placing a known amount of the probe organic solution on
the bottom of a glass flask followed by evaporating the
organic solvent under a N2 stream to form a lipid film. The
previously prepared vesicle dispersions were then added to
the probe-containing flask and the dispersions were kept
stirring overnight. The probed vesicles were prepared at
very low amphiphile/probe molar ratios, like 200:1 or
250:1.
Fluorescence Measurements
The data were collected using a Hitachi F-4500 spectro-
fluorometer. In order to check reproducibility, the experi-
ments were measured two times and the mean values were
used to construct the diagrams.
Anisotropy and Quantum Yields
Anisotropy measurements were performed in the range of
15–66 �C. A time interval of 20 min between two
measurements was necessary to ensure the temperature
equilibrium of the solution. The temperature of the
water-jacketed cell holder in the spectrophotometer was
controlled by circulating water connected to a bath circu-
lator (Fisher-Scientific). All measurements were performed
at 1.0 mM DODAB for the sonicated or 0.5 mM for the
non-sonicated vesicles to minimize scattering effects. The
fluorescence spectra were obtained in the wavelength range
of 370–550 nm.
Fluorescence quantum yield (Uf) was obtained by
exciting the probes at 360 nm for DPH and 4H4A, and
321 nm for DPB and 4B4A. At these wavelengths, we
measured the absorbance of the probes in the vesicle and
reference solutions. Ur for DPB and DPH in cyclohexane
(reference samples) at 25 �C is 0.44 and 0.80, respectively
[25]. Uf was obtained from the fluorescence spectra
according to Eq. 1 [20]:
Uf ¼ Ur
Ar
As
� Fs
Fr
� �ð1Þ
where As (Ar) and Fs (Fr) are, respectively, the solution
(reference) absorbance at the excitation wavelength and the
area under the emission spectra.
The fluorescence anisotropy \r[ was calculated using
the equation [27]
\r ¼ IVV � GIVH
IVV þ 2GIVH
[ ð2Þ
where G = IHV/IHH is an instrumental factor and IVV, IVH,
IHV and IHH account for the measured emission intensities
polarized in the vertical or horizontal detection planes upon
excitation with vertical or horizontally polarized light.
The I1/I3 Ratio of the Pyrene Vibronic Bands
Emission spectra of Py in DODAB vesicles were obtained
at 90� to the excitation radiation. The excitation wave-
length was 310 nm and the excitation and emission slit
widths were adjusted to a resolution of 2.5 nm. The Py
emission spectra were obtained around 550 nm in the
absence of dimmers, and the I1/I3 ratio obtained, which is
sensitive to the polarity of the microenvironment [19, 21,
28].
Results and Discussion
The properties of DODAB vesicles, including size, struc-
ture (e.g., whether uni- or multilamellar), degree of
counterion dissociation and polydispersity, depend on the
sample preparation protocol [4, 5, 8–10, 15, 17, 18, 22, 29–
32]. The t-Dpo probes incorporated in vesicles give
information on the thermotropic behavior and melting
temperature, Tm. They incorporate randomly in the vesicle
bilayer and, upon excitation, have their fluorescence
quantum yield and anisotropy changed according to the
conformational state of the lipid chains [25]. At room
temperature, DODAB chains are in the gel state, while
above Tm & 43 �C they are in the liquid–crystalline state.
The melting temperature, as well as the transition coop-
erativity, decreases when the dispersion is sonicated owing
to changes in vesicle size and morphology, as shown
below, what is in good agreement with data from the lit-
erature [4, 5, 18, 30].
Quantum Yield Results
Figure 2 depicts typical fluorescence emission spectra of
4H4A in sonicated DODAB vesicles at 16, 35 and 61 �C,
showing a decrease in the fluorescence intensity when the
J Surfact Deterg (2010) 13:273–280 275
123
temperature is raised, indicating that the lipid chains
acquire higher mobility on increasing temperature.
The effect of temperature on the quantum yield (Uf) of
4B4A and 4H4A in sonicated and non-sonicated DODAB
dispersions is shown in Fig. 3a–d. For both probes Uf
decreases linearly with temperature, and Tm can be
obtained from the intercept of the fitting curves. The
curves for 4B4A give Tm = 43.4 and 47.3 �C, for soni-
cated and non-sonicated DODAB vesicles, respectively
(Fig. 3c and d), while those for 4H4A yield Tm = 43.5 �C
for sonicated and two intercepts for non-sonicated dis-
persions: Tp = 35.6 �C and Tm = 41 �C (Fig. 3a and b,
respectively).
This value for Tp is in good agreement with the pre-
transition temperature for non-sonicated DODAB vesicles
obtained by DSC [18]. Furthermore, sonicated DODAB
exhibit no pre-transition temperature [18]. ESR data [4]
indicated that non-sonicated DODAB has a tighter bilayer
packing than sonicated vesicles, indicating that 4H4A is
solubilized along the hydrocarbon chains perpendicular to
the vesicle interfaces, allowing it to monitor both the pre-
and main transition temperatures.
On heating the samples, as the temperature approaches
Tm, Uf varies differently for 4B4A and 4H4A, suggesting
that these probes are incorporated in different sites of the
vesicle bilayers. Above Tm the probe isomerization
increases yielding a linear decrease in Uf at a rate that
depends on the probe structure and solubilization. Similar
result was also reported by Allen et al. for 4B4A and 4H4A
solubilized in phospholipid liposomes [20] and in mixtures
of cationic lipids with co-surfactants [23, 24]. It was also
observed that an increase in the separation length between
the phenyl groups of t-Dpo reduces the probe ability to be
aligned with the hydrocarbon chains, thus explaining the
different accommodation of these probes in the bilayer
giving different fluorescence signals [20]. Deviation in the
Uf curves may be related not only to the probe chemical
structure but also to the vesicle size, lipid packing and the
vesicle architecture as a result of sonication.
Anisotropy Results
Figure 4 shows the anisotropy \r[ as a function of tem-
perature for DPB, 4B4A, DPH and 4H4A in sonicated and
non-sonicated DODAB vesicles. Relative to the ionizable
4H4A or 4B4A, the non-ionizable DPH and DPB incor-
porate deeper into the bilayer, thus exhibiting a higher
mobility and lower \r[. For all vesicle dispersions, the
anisotropy of 4B4A is larger than DPB which displays a
higher mobility below and above Tm. It is expected that the
charged carboxylic group favors the solubilization of 4B4A
closer to the vesicle interfaces whereas DPB is deeper into
the bilayer. The same behavior was observed for the pair
DPH and 4H4A in DODAB (Fig. 4a and b) or in
phospholipid vesicles [20].
The anisotropy of the pair DPH and 4H4A in DODAB
dispersions (Fig. 4c and d) does not vary much when the
temperature is raised to ca. 35 �C, but decreases sharply
beyond this temperature and around Tm, which was taken at
the mid point of this variation. The sharpness of the jump
in the anisotropy curve increases when the vesicle size is
augmented, meaning that the cooperativity of the melting
process increases with the vesicle size.
Figure 5 illustrates the effect of sonication on the
cooperativity of the melting transition of DODAB vesicles.
The change in melting temperature, together with the shape
of the transition curve, suggests that DODAB is packed
differently in the sonicated and non-sonicated vesicles.
Accordingly, the larger the vesicle size, the more compact
is the bilayer and the more cooperative is the transition, and
consequently the higher is Tm, in good agreement with the
effect of size on Tm in extruded DODAB vesicles investi-
gated by DSC [18]. Moreover, according to ESR [4] and
dynamic light scattering [9] studies, the sonicated DODAB
dispersions have two populations of aggregates, a highly
fluid and another with low mobility relative to the non-
sonicated dispersions that exhibit more homogeneous lipid
distributions. These two populations together may reduce
the transition cooperativity.
Tables 1 and 2 summarize the Tm values for sonicated
and non-sonicated DODAB vesicles obtained from
Figs. 3, 4, 5. The Tm obtained from the anisotropy of
4B4A and 4H4A are quite the same, indicating that these
probes are submitted to similar strains. The Tm obtained
from the Uf curves is slightly larger than that obtained by
anisotropy. Overall, different methods may give different
Tm since different correlation may exist between the
melting transition and the physical phenomenon exploited
400 450 500 550
200
400
600
800
15.8 35.4 61.2 °C
I f
λ (nm)
Fig. 2 Typical fluorescence emission spectra of 4H4A in DODAB/
water sonicated dispersions at selected temperatures
276 J Surfact Deterg (2010) 13:273–280
123
by these methods. For all probes and methods used in this
work, however, Tm is higher for non-sonicated than for
sonicated vesicles, as expected and reported for
dipalmitoylphosphatidylcholine [33] and DODAB soni-
cated [4, 5] and extruded [18] vesicles studied by DSC or
ESR.
0.6
0.7
0.8
0.9
1.0 (a) (c)
(d)(b)0.0
0.2
0.4
0.6
0.8
1.0
10 20 30 40 50 60 700.4
0.5
0.6
0.7
0.8
0.9
1.0
10 20 30 40 50 60 700.0
0.2
0.4
0.6
0.8
1.0
T (oC)
Φ f (no
rmal
ized
)
Fig. 3 Effect of temperature on
the fluorescence quantum yield
for 4H4A (a and b) and 4B4A
(c and d) in DODAB sonicated
and non-sonicated vesicles
0.00
0.07
0.14
0.21
0.28
0.35
0.42
(a) (c)
(d)(b)0.15
0.18
0.21
0.24
0.27
0.30
10 20 30 40 50 60 700.00
0.07
0.14
0.21
0.28
0.35
T (oC)
< r >
10 20 30 40 50 60 700.12
0.16
0.20
0.24
0.28
0.32
DPH
4H4A
DPB
4B4A
Sonic. Sonic.
DPH
DPB
4B4A
4H4A
Fig. 4 Effect of temperature on
the fluorescence anisotropy of
DPH, 4H4A, DPB and 4B4A in
sonicated (a and c) and non-
sonicated (b and d) DODAB
vesicles, as indicated
J Surfact Deterg (2010) 13:273–280 277
123
The Tm values of DODAB in sonicated and non-soni-
cated dispersions obtained by anisotropy of DPH or 4H4A
thus corroborate the general trend of Tm to increase with
vesicle size. For sonicated dispersions Tm lies between 37
and 40 �C according to the DPH/4H4A and DPB/4B4A
pair fluorescence, respectively, whereas for non-sonicated
dispersions Tm obtained by anisotropy is close to 40 �C.
Such a small difference in Tm obtained by quantum yield
and anisotropy is due to the differing sensitivity of the
monitored parameters since Uf reflects small changes in the
probe molecular geometry and strains the probes undergo
[20], whereas any deviation in \r[ from its maximum
value indicates tumbling of the probe about its long axis,
which is influenced mainly by the fluorescence character-
istics of the molecules as well as the surrounding moiety.
I1/I3 Ratio of the Py Vibronic Bands
Py exhibits a fine structure in the fluorescence spectra of its
monomers in aqueous solution. The intensity of the first Py
emission peak enhances with the solvent polarity, whereas
the third peak shows a minimal intensity variation. Thus,
the intensity ratio I1/I3 gives information on the measure-
ment polarity of the Py microenvironment. In general, it is
assumed that Py incorporates deeply into the bilayer [34].
However, Abuin et al. [35] reported that Py solubilizes near
the bilayer interface, in good accordance with the data
reported here.
Previous ESR [4], DSC [18, 30] and fluorescence [30]
results indicate that the thermal behavior of DODAB
vesicles depends on the way samples are prepared, that
is, on the vesicle architecture. Figure 6 shows the effect
of DODAB concentration in sonicated and non-sonicated
dispersions on the I1/I3 ratio of Py 10-6 M, at 25 �C.
I1/I3 decreases to a minimum of 1.3 and 1.5 for DODAB
concentrations around 0.1 and 0.6 mM for sonicated and
non-sonicated dispersions, respectively, indicating that Py
is deeper into the bilayer of sonicated than non-sonicated
vesicles. The fluorescence anisotropy together with our
previous ESR results [4] indicates that the bilayers are
less densely packed and the transition is less cooperative
for sonicated than non-sonicated DODAB dispersions. In
the latter, the transition is sharper due to deeper Py
solubilization in the bilayer of sonicated vesicles, giving
lower polarity signals. The tighter packing of the bilayers
in non-sonicated vesicles has to do with the location of
the Py molecules that are more exposed to the solvent
(polar) molecules, erroneously indicating a more polar
environment. These results are in agreement with those
of ESR reported previously [4]. The tighter packing of
non-sonicated vesicles reduces the number of water
molecules at the bilayer interfaces, thus decreasing the
polarity of the interface region relative to the sonicated
vesicles.
Concluding Remarks
The fluorescence data presented in this communication,
together with previously reported results (Refs. [4, 18, 30])
indicate that the thermotropic behavior of DODAB vesicles
depends on the way vesicles are prepared. Accordingly,
sonication results in smaller vesicles with smaller Tm and a
less cooperative melting transition as reported here and
elsewhere [5, 9, 18].
The Tm data for sonicated DODAB vesicles here
reported are in good agreement with previously reported
values obtained by other techniques [4, 29–32]. Small
deviations in the experimentally obtained Tm may be
10 20 30 40 50 60 700.00
0.07
0.14
0.21
0.28
0.35
sonicated non-sonicated
< r >
T ( °C)
Fig. 5 Effect of temperature on the fluorescence anisotropy of DPH
in DODAB sonicated and non-sonicated vesicles. Curves re-plotted
from Fig. 4
Table 1 Melting temperature (Tm) obtained from fluorescence
quantum yield of 4B4A and 4H4A in sonicated and non-sonicated
DODAB vesicles
Sample 4B4A 4H4A
Sonicated 43.4 — 43.5
Non-sonicated 48.4 35.6 41.2
Table 2 Melting temperature (Tm) obtained by fluorescence anisot-
ropy of DPB, 4B4A, DPH and 4H4A in sonicated and non-sonicated
DODAB vesicles
Sample DPH DPB 4H4A 4B4A
Sonicated 37.3 35.3 38.1 39.8
Non-sonicated 40.7 39.1 39.3 40.3
278 J Surfact Deterg (2010) 13:273–280
123
attributed the different vesicle preparation protocols, lipid
source, solvent conditions or method to obtain Tm.
The melting temperature is an important property that
can be monitored by different techniques to characterize
and control the quality of vesicle dispersions. Fluorescence
gives, in addition to Tm, information on the lipid packing
into vesicles prepared by sonication or other methods that
can be used for different purposes.
Acknowledgments E.F. thanks CNPq and FAPESP. Dr. Laerte
Miola is acknowledged for kindly supplying the t-Dpo probes.
References
1. Israelachvili J (1992) Intermolecular and surface forces, 2nd edn.
Academic Press, New York
2. Groth C, Tollgerdt K, Nyden M (2006) Diffusion of solutes in
highly concentrated vesicle solutions from cationic surfactants
effects of chain saturation and ester function. Colloid Surf A
Physicochem Eng Aspects 281:23–34
3. Feitosa E, Jansson J, Lindman B (2006) The effect of chain
length on the melting temperature and size of dialkyldimethy-
lammonium bromide vesicles. Chem Phys Lipids 142:128–132
4. Benatti CR, Feitosa E, Fernandez RM, Lamy MT (2001) Struc-
tural and thermal characterization of dioctadecyldimethylammo-
nium bromide dispersions by spin labels. Chem Phys Lipids
111:93–104
5. Brito RO, Marques EF (2005) Neat DODAB vesicles: Effect of
sonication time on the phase transition thermodynamic parame-
ters and its relation with incomplete chain freezing. Chem Phys
Lipids 137:18–28
6. Kano K, Romero A, Djermouni B, Ache HJ, Fendler JH (1979)
Characterization of surfactant vesicles as membrane mimetic
agents. 2. Temperature-dependent changes of the turbidity, vis-
cosity, fluorescence polarization of 2-methylanthracene, and
positron annihilation in sonicated dioctadecyldimethylammonium
chloride. J Am Chem Soc 101:4030–4037
7. Carmona-Ribeiro AM, Hix S (1991) pH effects on properties of
dihexadecyl phosphate vesicles. J Phys Chem 95:1812–1817
8. Carmona-Ribeiro AM (1992) Synthetic amphiphile vesicles.
Chem Soc Rev 21:209–214
9. Feitosa E, Brown W (1997) Fragment and vesicle structures in
sonicated dispersions of dioctadecyldimethylammonium bro-
mide. Langmuir 13:4810–4815
10. Feitosa E, Karlsson G, Edwards K (2006) Extruded vesicles of
dioctadecyldimethylammonium bromide and chloride investi-
gated by light scattering and cryogenic transmission electron
microscopy. Chem Phys Lipids 140:66–74
11. Attwood D, Florence AT (1985) Surfactant systems: their
chemistry, pharmacy and biology. Chapman and Hall, New York
12. Feitosa E, Alves F (2008) The role of counterion on the ther-
motropic phase behavior of DODAB and DODAC vesicles.
Chem Phys Lipids 156:13–16
13. Marsh D, Watts A, Knowles PF (1977) Cooperativity of the phase
transition in single- and multibilayer lipid vesicles. Biochim
Biophys Acta 465:500–514
14. Allen MT, Miola L, Suddaby BR, Whitten DG (1987) Fluores-
cent stilbene, diene and triene surfactants as probes of reactivity
in amylose inclusion complexes. Tetrahedron 43:1477–1484
15. Fendler JH (1980) Surfactant vesicles as membrane mimetic
agents: characterization and utilization. Acc Chem Res 13:7–13
16. Blok MC, van Deenen LL, De Gier J (1976) Effect of the gel to
liquid crystalline phase transition on the osmotic behaviour of
phosphatidylcholine liposomes. Biochim Biophys Acta 433:1–12
17. Andersson M, Hammarstrom L, Edwards K (1995) Effect of
bilayer phase transitions on vesicle structure and its influence on
the kinetics of viologen reduction. J Phys Chem 99:14531–
14538
18. Feitosa E, Barreleiro PCA, Olofsson G (2000) Phase transition in
dioctadecyldimethylammonium bromide and chloride vesicles
prepared by different methods Chem. Phys Lipids 105:201–213
19. Kalyanasundaram K (1987) Photochemistry in microheteroge-
nous systems. Academic Press, New York, p 194
20. Allen MT, Miola L, Whitten DG (1988) Host-guest interactions:
a fluorescence investigation of the solubilization of diphenyl-
polyene solute molecules in lipid bilayers. J Am Chem Soc
110:3198–3206
21. Winnik FM (1993) Photophysics of preassociated pyrenes in
aqueous polymer solutions and in other organized media. Chem
Rev 93:587–614
22. Lopes A, Edwards K, Feitosa E (2008) Extruded vesicles of
dioctadecyldimethylammonium bromide and chloride investi-
gated by light scattering and cryogenic transmission electron
microscopy. J Colloid Interface Sci 322:582–588
23. Feitosa E, Bonassi NM, Loh W (2006) Vesicle-micelle transition
in mixtures of dioctadecyldimethylammonium chloride and bro-
mide with nonionic and zwitterionic surfactants. Langmuir
22:4512–4517
24. Barreleiro PCA, Olofsson G, Bonassi NM, Feitosa E (2002)
Interaction of octaethylene glycol n-dodecyl monoether with
dioctadecyldimethylammonium bromide and chloride vesicles.
Langmuir 18:1024–1029
25. Allen MT, Miola L, Whitten DG (1987) Temperature effects on
fluorescence in diphenylpolyene derivatives: structure- and sub-
stituent-dependent changes in mechanisms and rates for nonra-
diative decay. J Phys Chem 91:6099–6102
26. Velsko SP, Fleming GR (1982) Photochemical isomerization in
solution. Photophysics of diphenyl butadiene. J Chem Phys
76:3553–3562
27. Lakowicz JR (1983) Principles of fluorescence spectroscopy, 2nd
edn. Plenum Publishing Corporation, New York
28. Kalyanasundaram K, Thomas JK (1977) Environmental effects
on vibronic band intensities in pyrene monomer fluorescence and
0.0 0.2 0.4 0.6 0.8 1.01.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
sonicated non-sonicated
I 1/I3
[DODAB] (mM)
Fig. 6 Effect of DODAB concentration on the I1/I3 ratio of the
vibronic peaks of Py in bath-sonicated (circles) and non-sonicated
(triangles) DODAB vesicles, at 25 �C
J Surfact Deterg (2010) 13:273–280 279
123
their application in studies of micellar systems. J Am Chem Soc
99:2039–2044
29. Cocquyt J, Olsson U, Olofsson G, der Meeren PV (2004) Tem-
perature quenched DODAB dispersions: fluid and solid state
coexistence and complex formation with oppositely charged
surfactants. Langmuir 20:3906–3912
30. Benatti CR, Tiera MJ, Feitosa E, Orlofsson G (1999) Phase
behavior of synthetic amphiphile vesicles investigated by calo-
rimetry and fluorescence methods. Thermochimica Acta
328:137–142
31. Feitosa E, Barreleiro PCA (2004) The effect of ionic strength on
the structural organization of dioctadecyldimethylammonium
bromide in aqueous solution. Prog Colloid Polym Sci 128:163–
168
32. Alves FR, Zaniquelli MED, Loh W, Castanheira EMS, Real
Oliveira MECD, Feitosa E (2007) Vesicle–micelle transition in
aqueous mixtures of the cationic dioctadecyldimethylammonium
and octadecyltrimethylammonium bromide surfactants. J Colloid
Interface Sci 316:132–139
33. Lichtenberg D, Freire E, Schmidt CF, Barenholz Y, Felgner PL,
Thompson TE (1981) Effect of surface curvature on stability,
thermodynamic behavior, and osmotic activity of dipalmitoyl-
phosphatidylcholine single lamellar vesicles. Biochemistry
20:3462–3467
34. Kodama T, Ohta A, Toda K, Katada T, Asakawa T, Miyagishi S
(2006) Fluorescence-probe study of vesicle and micelle forma-
tions in a binary cationic surfactants system. Colloids Surf A
Physicochem Eng Aspects 277:20–26
35. Abuin E, Lissi E, Aravena D, Zanocco A, Macuer M (1988) A
fluorescent probe study of the effect of size on the properties of
dioctadecyldimethylammonium chloride vesicles. J Colloid
Inteface Sci 122:201–208
Author Biographies
Eloi Feitosa received his PhD in physical chemistry from Sao Paulo
State University, Brazil, where he is currently Adjunct Professor. His
main research interests are association colloids, micelles, vesicles and
microemulsions, polymer-containing systems and phase behavior of
polymer and surfactant systems.
Carlos Roberto Benatti received his MS and PhD at Sao Paulo State
University, Brazil, under the supervision of Dr. E. Feitosa on cationic
vesicle systems. His main interest is on the characterization and
application of cationic liposomes.
Marcio Jose Tiera received his PhD degree in physical chemistry
from Sao Paulo State University, where he is currently a Research
Professor. His main research interests are the synthesis and charac-
terization of surfactants and polymer in colloidal systems.
280 J Surfact Deterg (2010) 13:273–280
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