Mendeleev
Communications
Mendeleev Commun., 2007, 17, 82–84
Ambidextrous ‘hybrid’ fluorinated zwitterionic geminis:
self-assembly in both organic and aqueous media
†
Andrey Peresypkin,* Caroline Clavel and Fredric M. Menger
Department of Chemistry, Emory University, 1515 Pierce Drive, Atlanta, GA 30322, USA
DOI: 10.1016/j.mencom.2007.03.009
‘Hybrid’ fluorinated zwitterionic gemini surfactants have been shown to self-assemble in both organic and aqueous media thus
being an example of ambidextrous amphiphiles. As a result of these properties, these compounds are attractive targets both from
the academic standpoint and in industrial applications.
The term ‘gemini surfactant’ denotes a class of amphiphilic
molecules with a general structure shown below.
31P), IR, HRMS and EA and appeared as white hygroscopic
solids soluble in alcoholic and halogenated solvents.
1
Examples of synthesized compounds along with their respec-
tive abbreviated symbols (which should be self-explanatory) are
Hydrocarbon
Ion Spacer Ion
Hydrocarbon
shown in Scheme 2 and include F C –C
; F C –C14–22;
8
2
14–22
6 2
F C –C
; HF C –C
; HF C –C
; F C –C ; F C –
7
1
14–22
6
1
14–22
4
1
14–18 6 2 8–12 7 1
Since the name of geminis in 1991, they have been shown
to have far superior properties as compared to conventional
surfactants, showing up to 100 times lower critical micellar con-
centrations and significantly improved surface activity. Gemini
surfactants have found use in various industrial applications
C8–12; HF C –C8–12. Note that the fluorinated chains are always
on the phosphate side of the geminis.
6 1
When F C –C was hydrated with water (electroformation
6
2
18
6
method), giant unilamellar vesicles were formed [Figure 1(a)].
Formation of vesicles from these amphiphiles in water was
expected if past hydrocarbon analogues were any guide. How-
ever, to our surprise, when F C –C was smeared on the micro-
(drug encapsulation, enhanced oil recovery, preparation of high-
porosity materials, etc.) and have entertained scientific minds in
6
2
18
multiple academic research groups due to their ‘unconven-
tional’ behavior and properties.
scope slide followed by immersion in toluene, long bilayer
tubules (reminiscent of myelin figures formed upon hydration
of phospholipids) were observed, as shown in Figure 1(b). To
ensure reproducible preparations, smeared solids were necessary
to expose to a mist of water or high relative humidity (> 70% RH)
for a few minutes prior to addition of an appropriate organic
solvent (cyclohexane, hexane, toluene, chlorocyclohexane or
dodecane). It is quite important for the solid gemini to be
‘prehydrated’ before organic solvent is added. Thus, if an organic
solvent was added to a dry solid, then only a few tubules were
observed. On the other hand, if a solid gemini was ‘prehydrated’
prior to the treatment with an organic solvent, a large number
of tubules were reproducibly observed. Thus, F C –C can
2
Most of the work in the area of gemini surfactants focused
on symmetrical geminis (i.e., both chains and polar groups
were identical), and the effects on asymmetry on self-assembly
and other properties have not been well understood. One of the
first examples of asymmetrical geminis with different chain
lengths was reported to be a family of bis(quaternary ammo-
nium) geminis. When dissolved in aqueous media, asymmetrical
(
n-2-m) geminis displayed a transition from spherical micelles
to various tubular structures depending on the length of the
hydrocarbon tails. On the other hand, very asymmetrical geminis
3
formed small spherical micelles only.
6
2
18
In an attempt to gain better understanding of the effect of
asymmetry on aggregation properties, we turned our attention
towards zwitterionic geminis whose general structure is shown
in Scheme 1.4 The ‘tunability’ of the overall chain length
and asymmetry made the zwitterionic geminis attractive candi-
dates for studying aggregation properties as a function of
structural variations. Thus, a ‘structural phase diagram’ was
constructed (consisting of over 40 geminis with varying hydro-
carbon chains) produced some unusual and surprising results:
small structural differences led to various morphological changes
in water including formation of gels, micelles, coacervates and
vesicles.5
be called an ambidextrous amphiphile; i.e., it aggregates into
bilayer assemblies in both aqueous and non-polar organic media.
Bilayer morphologies were obtained with several other geminis
including F C –C
; F C –C
; F C –C
; HF C –C14–22;
8
2
14–22
6
2
14–22
7
1
14–22 6 1
HF C –C14–18. When a water-soluble dye (Lucifer Yellow) was
4
1
sprayed onto to F C –C followed by addition of cyclohexane,
6
2
20
O
O
P
O
Cl
,
Et N, i
O
O
3
R OH
F
RF
P
O
O
(crude)
Intrigued by these findings, we turned our attention to partially
fluorinated ‘hybrid’ analogues. The synthesis of ‘hybrid’ zwitter-
ionic gemini surfactants was performed in two steps starting from
the appropriate fluorinated alcohols, as shown in Scheme 1.
O
Me
N
R NMe , ii
H
2
RF
O
P
O
(CH )
RH
2 2
O
Me
1
13
19
R = fluorinated tail
F
RH = hydrogenated tail
All compounds were fully characterized by NMR ( H, C, F,
†
A former student of the Higher Chemical College of the RAS (1992–
999). Current address: Merck and Co., Rahway, NJ, USA 07065. E-mail:
Scheme 1 Synthesis of a family of ‘hybrid’ zwitterionic geminis. Reagents
and conditions: THF (anh.), 0 °C, 5 min, room temperature, 4 h, Ar; ii,
MeCN (anh.) or DMF (anh.), 65–70 °C, 2 days, Ar.
1
andrey_peresypkin@merck.com.
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