C O M M U N I C A T I O N S
Figure 4. Emission spectra of 1 as water is added to the solution. The
concentration of each spectrum is identical. The inset shows emission of 1
near the upper and lower limit concentrations of leakage experiments.
Figure 3. Graph showing the percentage of lysed vesicles over time as
the concentration of 1 is increased. 100% lysis was determined by the
addition of 50 µL of 0.2% Triton X-100.
extended, or all trans, backbone is favored over other conformations
because of the substitution pattern of P and NP groups. A helical
conformation in which the NP groups fold in the interior while P
side chains are exposed to the solvated exterior cannot be ruled
out at this time; however, the observed emission spectra are different
from those reported for helical PPEs.11
We report the synthesis of new PPE derivatives containing polar
cationic and nonpolar alkyl groups. These groups are patterned to
favor an extended conformation and produce facially amphiphilic
polymers. Langmuir and emission experiments are in agreement
with an extended amphiphilic structure. Vesicle leakage experiments
indicate that these polymers are membrane active. From these
preliminary observations and others in the literature,5,7 it can be
expected that polymers with facially ionic amphiphilicity will
organize into interesting supramolecular structures.
two extended oligomers were performed in Materials Studio and
gave an area of 44.7 Å2. The modeled orientation assumes the
polymer molecules are standing up with their aromatic rings
perpendicular to the water surface. In this configuration, the polar
cationic amine salts are immersed in the water layer and the
hydrophobic alkyl chains completely removed from the aqueous
surface.
Langmuir experiments indicate that this polymer is highly
amphiphilic and prefers to form monolayers at the air-water
interface. The surface activity of this cationic polymer was explored
further by monitoring the disruption of phospholipid vesicles.3
Large unilamellar vesicles (LUV) with 10 mol % excess negative
charge were prepared by reverse phase evaporation of a SOPS:
SOPC (1:9) solution.9 Leakage of calcein was monitored at 515
nm as a function of polymer concentration and is shown in Figure
3. The rate and percentage of lysed LUVs as measured by calcein
leakage increases as the concentration of 1 is increased. Initially
the rate of leakage is fast but slows down as less free polymer is
left in solution. The ability of these polymers to induce calcein
leakage from anionic LUV confirms their surface active nature.
Higher polymer concentration experiments suffered from polymer
aggregation.
Acknowledgment. Financial support for this work is gratefully
acknowledged from the National Science Foundation through
MRSEC at UMass. We thank Professor Hsu for use of the Langmuir
trough and Daniel J. Duffy.
Supporting Information Available: Experimental procedures and
compound characterization (PDF). This material is available free of
On the basis of the design of 1, we also expected that the polymer
could self-assemble in aqueous solution.7 In fact, it appears from
the LUV leakage experiments that this is true. To investigate if 1
is aggregated in aqueous solution, we monitored the emission
spectra as a function of water composition starting with neat DMSO.
The emission spectra shown in Figure 4 were obtained as a function
of water composition. The concentration of the sample was kept
constant to directly observe the effect on quantum yield. It can be
seen from Figure 4 that the intensity of emission decreases with
increasing water concentration and the band is broadened and
slightly red-shifted. The insert in Figure 4 shows the emission
spectra taken at concentrations from the leakage experiments and
are very similar to the 90% water spectrum. These observations
are in agreement with intermolecular aggregation of polymer chains
in an extended conformation as the water content is increased.4,10
The slight red-shift indicates tight packing of the chromophores
does not occur in the aggregate. Spectra taken in CHCl3 or THF as
solvent give emission maxima close to that observed for DMSO
((2 nm), indicating that the observed change with water addition
is not related simply to solvent polarity. The formation of an
References
(1) Eisenberg, D.; Weiss, R. M.; Terwillinger, T. C. Proc. Natl. Acad. Sci.
U.S.A. 1984, 81, 140-144.
(2) DeGrado, W. F.; Lear, J. D. J. Am. Chem. Soc. 1985, 107, 7684-7689.
(3) Tew, G. N.; Lui, D.; Chen, B.; Doerksen, R. J.; Kaplan, J.; Carroll, P. J.;
Klein, M. L.; DeGrado, W. F. Proc. Natl. Acad. Sci U.S.A. 2002, 99,
5110-5114.
(4) Kim, J.; Swager, T. M. Nature 2001, 411, 1030-1034.
(5) Nelson, J. C.; Saven, J. G.; Moore, J. S.; Wolynes, P. G. Science 1997,
277, 1793-1795.
(6) Reitzel, N.; Greve, D. R.; Kjaer, K.; Howes, P. B.; Jayaraman, M.; Savoy,
S.; McCullough, R. D.; McDevitt, J. T.; Bjornholm, T. J. Am. Chem. Soc.
2000, 122, 5788-5800. Bo, Z.; Rabe, J. P.; Schulter, A. D. Angew. Chem.,
Int. Ed. 1999, 38, 2370-2372.
(7) Bockstaller, M.; Kohler, W.; Wegner, G.; Vlassopoulos, D.; Fytas, G.
Macromolecules 2001, 34, 6359-6366.
(8) Giesa, R. J. Macromol. Sci., ReV. Macromol. Chem. Phys. 1996, 36, 631-
670. Bunz, U. H. F. Chem. ReV. 2000, 100, 1605-1644.
(9) Wilschut, J.; Duzgunes, N.; Fraley, R.; Papahadjopoulos D. Biochemistry
1980, 19, 6011-6021.
(10) Halkyard, C. E.; Rampey, M. E.; Kloppenburg, L.; Studer-Martinez, S.
L.; Bunz, U. H. F. Macromolecules, 1998, 31, 8655-8659.
(11) Prince, R. B.; Saven, J. G.; Wolynes, P. G.; Moore, J. S. J. Am. Chem.
Soc. 1999, 121, 3114-3121.
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