Tondo et al.
Article
Anion incorporation in zwitterionic micelles has been exam-
ined largely with simple sulfobetaines. We synthesized a new
zwitterionic surfactant, ImS3-14, with new physical-chemical
properties. It differs from other sulfobetaines in that it has very
low water solubility in the absence of salts and the cationic
imidazolium ring is rigid and unsymmetrical. We probed anion
effects by electrophoresis and spectrophotometric analysis of acid
dissociation of 1-hydroxy-2-naphthoic acid (HNA) and by fol-
lowing acid hydrolysis of 2-(p-heptoxyphenyl)-1,3-dioxolane
ppm: 10.26 s (1H), 8.03 s (1H), 7.68 s (1H), 4.87 t (2H), 4.53t (2H),
3.04 t (2H), 2.55 t (2H), 1.99 m (2 H), 1.33 m (22H), 0.94 t (3H).
Surface Tension Measurements. Surface tensions of
surfactant-water mixtures containing 0.08 M NaCl or NaClO
were measured by the du No u€ y ring method on a K8 tensiometer
4
(
KRUSS) at 25 ꢀC. Before each measurement, the ring was briefly
heated above a Bunsen burner until glowing. The vessel was
cleaned with chromic-sulfuric acid and boiling distilled water and
then flamed in a Bunsen burner. Surface tension measurements
were repeated twice with 1 mN m precision.
Fluorescence Measurements. Fluorescence quenching of
pyrene by DPC was monitored in a Varian Cary Eclipse spectro-
-1
3
(
HPD), and compared these effects to those in simple sulfobetaine
micelles.
-6
fluorimeter. The low probe concentration (2 ꢀ 10 M) avoided
excimer formation, and the quencher concentration was 2.44 ꢀ
-
5
-4
1
0
-2.31 ꢀ 10 M. The [pyrene]/[micelles] and [quencher]/
[micelles] ratios were low enough to ensure Poisson distri-
butions.
sion wavelength of 394 nm were used.
2
7-30
An excitation wavelength of 337 nm and an emis-
Kinetics and Spectrophotometric Titrations. All experi-
ments were made with a diode-array spectrophotometer, with a
thermostatted cell holder, in aqueous ImS3-14, and with 0.08 M
4
NaCl or NaClO , under conditions such that the spectroscopic
micellar acidity probe 1-hydroxy-2-naphtoic acid (HNA) and the
organic substrate 2-(p-heptoxyphenyl)-1,3-dioxolane (HPD) are
almost wholly micellar-bound and the surfactant concentration is
much higher than the critical micelle concentration (cmc). All pH
measurements were made with a Metrohm model 713 pH meter
calibrated with standard buffers, pH 7.00 and 4.00 (Carlo Erba),
Experimental Section
Materials. We used 1-hydroxy-2-naphthoic acid (HNA)
Sigma) as the UV-vis micellar acidity probe and pyrene
Aldrich) as the fluorescent probe indetermination of aggregation
numbers. The preparation and purification of 2-(p-heptoxy-
phenyl)-1,3-dioxolane (HPD) are described.
n-dodecylpyridinium salt (DPC) was synthesized as described
(
(
-5
at 25.0 ꢀC. A solution of HNA (8.0 ꢀ 10 M) was titrated with
2
3-25
HCl and NaOH, and the equilibrium dissociation was followed
spectrophotometrically at 358 nm. Hydrolysis of 2-(pheptoxy-
phenyl)-1,3-dioxolane (HPD) was followed at 286 nm, and reac-
tions were started by adding 30 μL of a stock solution of the
4-Carboxy-1-
2
6
1
(
8
1
mp189 ꢀC, dec.). H NMR spectrum(CDCl
3
, 400 MHz), δ, ppm:
.61 d (2H), 8.42 d (2H), 4.64 t (2H), 2.04 m (2H), 1.36 m (2H),
.25 m (16H), 0.88, t (3H). Sodium hydride, imidazole, 1-bromo-
substrate (1.1 mM) in water to 3 mL of reaction solution, giving
-5
1
.1 ꢀ 10 M substrate. Absorbance versus time data were stored
tetradecane, and other reagents were of analytical grade and were
used without further purification. The salts (NaCl and NaClO
directly on a microcomputer, and first order rate constants, kobs,
were estimated from linear plots of ln(A - A ) against time for at
4
)
¥
t
and solvents were dried by standard methods.
Synthesis of 1-Tetradecylimidazole. A solution of imida-
zole (16.3 g, 0.24 mol) in dry 1,4-dioxane (100 mL) was added to
50 mL ofasuspensionofoil-freesodiumhydride (5.8g, 0.24mol)
with stirring for 1 h at 90 ꢀC. A solution of 1-bromotetradecane
33.3 g, 0.12 mol) in 1,4-dioxane (100 mL) was then added
dropwise to the reaction solution, and the mixture was stirred
for 48 h at 90 ꢀC. The solvent was removed on a rotary evaporator
giving a yellow residue that was suspended in 500 mL of water,
least 90% of the reaction by using an iterative least-squares
program; correlation coefficients were >0.999 for all kinetic runs.
Capillary Electrophoresis. Experiments were conducted
1
3D
with an Agilent CE capillary electrophoresis system, with on-
column diode-array detection at 25 ꢀC, as previously de-
(
1,2,22
scribed,
and electropherograms were monitored at 272 nm.
Samples were introduced by hydrodynamic injection at 50 mbar/
s. Fused-silica capillaries (Polymicro Technologies) of total
5
length 60.0 cm, effective length 51.5 cm, and 50 μm i.d. were used.
The electrophoresis system was operated under normal polarity
and constant 30 kV. The capillary was conditioned by flushes of
followed by extraction with CH Cl
2
washing, and the organic layer was dried with anhydrous Na SO .
2 4
2
(4 ꢀ 70 mL) and brine
2 2
After removal of CH Cl , the resulting yellow oil was purified by
column chromatography (silica gel) with ethyl acetate as eluent,
giving 17.8 g (55.7%) of 1-tetradecylimidazole as a pale yellow oil.
νmax/cm IR (film): 3421, 3106, 2924, 2849. H NMR spectrum
CDCl , 400 MHz), δ, ppm: 7.46 s (1H), 7.05 s (1H), 6.90 s (1H),
.92 t (2H), 1.77 m (2H), 1.25 m (22H), 0.88, t (3H).
Synthesis of 3-(1-Tetradecyl-3-imidazolio)propanesulfo-
1
M NaOH (5 min), deionized water (5 min), and electrolyte
solution (10 min). Between experiments, the capillary was recon-
ditioned by a pressure flush with the electrolyte containing 3 mM
sodium borate (2 min). The mobility of the micelles was mon-
itored by following the migration of micellar-bound pyrene
-1
1
(
3
3
(
1 μM), and acetone (0.1%) was used as the electroosmotic flow
marker.
Computational Methods: Charges and Geometry Search.
nate (ImS3-14). A solution of 1,3-propanesultone (9.0 g, 0.074
mol) inacetone (80 mL) wasslowlyadded ina round-bottomflask
to 1-tetradecylimidazole (17.6 g, 0.067 mol) and acetone (80 mL)
at 0 ꢀC. The reaction mixture was then warmed to room tem-
perature and stirred for 5 days. Filtration gave a white powder
that was washed four times with fresh acetone, filtered, and dried
under vacuum at 50 ꢀC for 6 h giving 22.7 g (88.2%) of the
All computational calculations were made with the Gaussian 03
program. Structures of zwitterionic SB3-14 and ImS3-14 were
31
obtained by full geometry optimization at the HF/6-31þG(d)
32
level with the polarizable continuum model (PCM) adding an
aqueous-like environment to the system with the molecular cavity
-
1
zwitterion ImS3-14. ν /cm IR (film): 3471, 3428, 3133, 3079,
max
1
2
926, 2846, 1189, 1047. H NMR spectrum (CDCl3, 400 MHz), δ,
(27) Tachiya, M. Chem. Phys. Lett. 1975, 33, 289–292.
(28) Infelta, P. P.; Gratzel, M. J. Chem. Phys. 1979, 70, 179–190.
(29) Turro, N. J.; Yekta, A. J. Am. Chem. Soc. 1978, 100, 5951–5952.
(30) Rodriguez Prieto, M. F.; Rios Rodriguez, M. C.; Gonzalez, M. M.;
(
24) Ruzza, A. A.; Walter, M. R. K.; Nome, F.; Zanette, D. J. Phys. Chem. 1992,
Rios Rodriguez, A. M.; Mejuto Fernandez, J. C. J. Chem. Educ. 1995, 72, 662–663.
96, 1463–1467.
(31) Frisch, M. J. et al. Gaussian 03, revision D.01; Gaussian, Inc.: Pittsburgh, PA,
(
25) Fife, T. H.; Jao, L. K. J. Org. Chem. 1965, 30, 1492–1495.
2004.
(
26) Amhar, J.; Monnet, C.; Perchec, L. P.; Chevalier, Y. New J. Chem. 1993, 17,
(32) Cossi, M.; Barone, V.; Cammi, R.; Tomasi, J. J. Chem. Phys. Lett. 1996,
237–247.
255, 327–335.
Langmuir 2010, 26(20), 15754–15760
DOI: 10.1021/la102391e 15755