General synthesis and aggregation behaviour of a series of single-chain 1,ω-Bis(phosphocholines)

Article abstract of DOI:10.1002/chem.200601866

The synthesis and physicochemical characterisation of a series of polymethylene-1,ω-bis(phosphocholines) with even-numbered chain lengths between 22 and 32 carbon atoms is described. Two new synthetic strategies for the preparation of long-chain 1,ω-diols as hydrocarbon building blocks are presented. The temperature-dependent self-assembly of the single-chain bolaamphiphiles was investigated by cryo transmission electron microscopy (cryo-TEM), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR).

Full text of DOI:10.1002/chem.200601866

DOI: 10.1002/chem.200601866
General Synthesis and Aggregation Behaviour of a Series of Single-Chain
1,w-Bis(phosphocholines)
Simon Drescher,[a] Annette Meister,[b] Alfred Blume,[b] Gçran Karlsson,[c]
Mats Almgren,[c] and Bodo Dobner*[a]
Abstract: The synthesis and physicochemical characterisation of a series of poly-
methylene-1,w-bis(phosphocholines) with even-numbered chain lengths between
22 and 32 carbon atoms is described. Two new synthetic strategies for the prepara-
tion of long-chain 1,w-diols as hydrocarbon building blocks are presented. The
temperature-dependent self-assembly of the single-chain bolaamphiphiles was in-
vestigated by cryo transmission electron microscopy (cryo-TEM), differential scan-
ning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR).
Keywords: aggregation · alcohols ·
amphiphiles
methods
· lipids · synthetic
Introduction
of great interest in biotechnology and materials science. Be-
sides the more complex natural lipids and model systems[2,3]
single-chain bola compounds also exhibit interesting proper-
ties.[4] A bolalipid with only one hydrocarbon chain of
twenty two carbon atoms and phosphocholine head groups
at both ends of the hydrocarbon chain was found in plants
showing fungicidal activity.[5]
We recently reported the temperature-dependent aggrega-
tion behaviour of the symmetrical long-chain bolaamphi-
phile dotriacontane-1,32-bis(phosphocholine). Self-assembly
of this lipid is exclusively driven by hydrophobic interac-
tions. Formation of a dense network of nanofibres is ob-
served, which is responsible for very efficient gelation of
water.[6,7] Within these fibres, the molecules are arranged
side by side but twisted relative to each other due to the
bulky head groups. Above a transition temperature of about
508C, the fibres transform into smaller aggregates and the
gel character is lost.
Bolaamphiphiles occur naturally in the lipids of archaebac-
teria,[1] which represent the third kingdom of organisms be-
sides the prokaryotes and eukaryotes. The archaebacteria
thrive under extreme conditions, such as high salt concentra-
tions, anaerobic milieu and high temperatures with associat-
ed low pHvalues. Due to these living conditions their mem-
brane lipids are quite different from those of other organ-
isms; they exhibit branches in the hydrophobic chains, ether
bonds instead of the common ester bonds in the glycerol
backbone, and sn-2,3 stereochemistry. Whereas the mem-
branes of halophilic archaebacteria consist of monopolar
lipids, most of the membrane components of methanogenic
and thermoacidophilic archaebacteria are bipolar and have
two membrane-spanning chains. Especially these lipids are
Here we present a new general synthetic approach to this
class of interesting bolaamphiphiles with chain lengths of 22
to 32 carbon atoms. Polymethylene-1,w-bis(phosphocho-
lines) with even-numbered chains were prepared by double
phosphorylation of the corresponding 1,w-diols followed by
quaternisation. The temperature-dependent aggregation
properties of these new bis(phosphocholines) were investi-
gated by means of cryo-transmission electron microscopy
(cryo-TEM), differential scanning calorimetry (DSC) and
Fourier transform infrared spectroscopy (FTIR).
[a] S. Drescher, Prof. Dr. B. Dobner
Institute of Pharmacy
MLU Halle-Wittenberg
Wolfgang-Langenbeck-Strasse 4
06120 Halle/Saale (Germany)
Fax : (+49)0345-55-27018
E-mail: bodo.dobner@pharmazie.uni-halle.de
[b] Dr. A. Meister, Prof. Dr. A. Blume
Institute of Chemistry
MLU Halle-Wittenberg
Mühlpforte 1
06108 Halle/Saale (Germany)
[c] G. Karlsson, Prof. Dr. M. Almgren
Department of Physical and Analytical Chemistry
Uppsala University, Box 579, 75123 Uppsala (Sweden)
5300
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FULL PAPER
Results and Discussion
Synthetic methods: The synthesis of the bolalipids depends
on an effective and high-yield preparation of the corre-
sponding diols, which represent the hydrophobic part of the
bolalipids. Diols with 22 or more C atoms were already syn-
thesised by classical multistep procedures. These methods
include the preparation of cyclic enamines followed by bis-
acylation with dicarboxylic acid dichlorides, hydrolysis of en-
amino ketones and ring opening and Wolff–Kishner reduc-
Scheme 2. Formation of “short-chain” (3’) and “long-chain” (3’’) by-prod-
ucts during copper-catalysed bis-coupling. a) Mg, Et2O, reflux, 2 h; then
THF, Li2CuCl4, 08C, 3 h.
tion of bis
(oxo acid)s and then reduction with LiAlH4.[8,9]
G
Double Wittig reaction with bis-phosphorylides and w-func-
tionalised aldehydes or suitably functionalised phosphory-
lides and bis-aldehydes is also described in the literature.[10]
Both methods are expensive and preparation of the final re-
agents requires many steps.
Our investigations using reactive components with latent
functionality led to the target diols in only two steps and
high yield. Commercially available 11-bromoundec-1-ene
(1a) was transformed into the corresponding Grignard re-
agent. Reaction of this compound with 1,w-dibromoalkanes
2 in a ratio of 2:1 under catalysis with dilithium tetrachloro-
cuprate(II) according to the generally described procedure
yielded terminal dienes 3. The olefin structure is then simply
and nearly quantitatively converted to diols 4 by the known
hydroboration/oxidation procedure (Scheme 1). First at-
of 26 (3d) and 24 carbon atoms (3e) was prepared from
commercially available 8-bromooct-1-ene (1b). For the pu-
rification of the longer dienes (3b and 3c) the same proce-
dure as described above was used, whereas for shorter
chains (3d and 3e) methanol was used for precipitation in-
stead of acetone. We also found that filtration of the crude
product over silica gel with heptane before precipitation was
helpful. However, the product contained a few percent of
higher coupling products with longer chains (see 3’’ in
Scheme 2) resulting from dimerisation of the 1:1 product of
the Grignard reagent and the dibromide by transmetalla-
tion, already described in the pioneering work of Kochi
et al.[11] Some attempts were made to avoid this side reac-
tion, for example, by incubation of the Grignard reagent
with the catalyst, reaction at lower temperature and chang-
ing the sequence of addition of the reactants, but without
any effect on product composition.
tempts with 9-borabicyclo[3.3.1]nonane caused problems in
U
purification due to the similar polarity of the long-chain diol
and the cyclooctanediol resulting from the oxidation step.
Therefore, disiamylborane was the reagent of choice.
Another method for the preparation of long-chain bola-
diols, first published by Schill et al.[12] and some years ago by
another group,[13] uses 2:1 copper-catalysed Grignard bis-
coupling starting from the Grignard reagents of the tetrahy-
dropyranyl ethers of w-bromo alcohols and corresponding
1,w-dibromides. The authors did not describe the occurrence
of side products in their reactions. However, in our hands
we also found small amounts of the higher coupling prod-
ucts 3’’ when following the protocol of Mohr et al.[13]
In the synthesis of docosa-1,21-diene by homocoupling of
11-bromoundec-1-ene[14] with its Grignard reagent, forma-
tion of higher molecular weight compounds is not possible.
Thus our second strategy for the synthesis of the boladiols is
based on this 1:1 reaction. However long-chain w-bromo al-
kenes are not commercially available and the preparation of
these compounds is very expensive. The alternative route is
shown in Scheme 3 by homocoupling of compound 12 with
the Grignard reagent of this bromo compound under copper
catalysis. The w-bromo alcohols 11 and the corresponding
tetrahydropyranyl ethers 12 are also not commercially avail-
able, but they can be synthesised in a few effective steps
from commercially available and inexpensive lactones 5 or
dicarboxylic acids 8, as shown in Scheme 4. In contrast to
the synthesis via dienes and subsequent hydroboration the
crude bis(tetrahydropyranyl ether)s 13 resulting from the
coupling reaction were not purified but transformed into the
corresponding diols 4 by cleavage of the tetrahydropyranyl
Scheme 1. Synthesis of long-chain 1,w-diols by copper-catalysed bis-cou-
pling. a) Et2O, Mg, reflux, 2 h; then THF, Li2CuCl4, 08C, 3 h; b) THF,
BH3, 2-methylbut-2-ene, 08C; then EtOH, NaOH, H2O2, 508C, 2 h.
The synthesis of dotriaconta-1,31-diene 3a was already
described[6] and includes very simple purification by a pre-
cipitation step with acetone from diethyl ether/THF, where-
by the C22 homo-coupling product (see 3’ in Scheme 2)
could be separated. For the preparation of the dienes with
30 (3b) and 28 carbon atoms (3c) the same Grignard re-
agent was coupled with 1,8-dibromooctane (2b) and 1,6-di-
bromohexane (2c), respectively. The Grignard reagent for
the synthesis of the corresponding dienes with chain length
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B. Dobner et al.
acid dichloride and 2-chloro-1,3,2-dioxophospholanes or
phosphites were used under mild conditions. However, the
reaction did not proceed in a satisfactory way and the yield
was rather low even after long reaction times. The limiting
factor for these transformations was the insolubility of the
diols in the normally used solvents such as chloroform and
tetrahydrofuran. This problem could be solved by the fol-
lowing procedure in which the diol component, an excess of
b-bromoethylphosphoric acid dichloride and the base (trie-
thylamine, TEA) were first suspended in dry chloroform at
room temperature. Then the mixture was brought to a tem-
perature at which it became homogeneous (in the case of
long-chain diols up to 608C). The mixture was then cooled
to room temperature and no new precipitation occurred.
After 24 h at this temperature phosphorylation was com-
plete. According to other studies on bolaphospholipid syn-
thesis,[15,16] the classic reagent b-bromoethylphosphoric acid
dichloride was more efficient than the phospholane method.
The last step in the reaction was quarternisation (Scheme 5)
with a solution of trimethylamine in chloroform/acetonitrile/
ethanol.
Scheme 3. Synthesis of long-chain 1,w-diols by copper-catalysed homo-
coupling. a) THF, Mg, reflux, 3 h; then THF, Li2CuCl4, 08C, 3 h;
b) MeOH, pyridinium p-toluenesulfonate, reflux.
Scheme 5. Preparation of long-chain 1,w-bis(phosphocholines) by high-
temperature phosphorylation. a) CHCl3, bromoethylphosphoric acid di-
chloride, 45–608C; then THF, H2O, 2 h ; b) CHCl3, CH3CN, EtOH, N-
Scheme 4. Synthetic pathways for the preparation of w-bromo-1-[(tetra-
hydro-2H-pyran-2-yl)oxy]alkanes. a) MeOH, p-toluenesulfonic acid,
reflux, 24 h; b) CHCl3, methanesulfonyl chloride, reflux; then acetone,
LiBr, reflux; c) Et2O, LiAlH4, 08C; d) MeOH, H2SO4, reflux; e) Benzene,
HBr, water trap, reflux; f) CH2Cl2, dihydropyran, pyridinium p-toluene-
sulfonate, 24 h. * 12 f was prepared from commercially available 11-bro-
moundecan-1-ol 11 f.
A
Temperature-dependent aggregation: From recent investiga-
tions on the temperature-dependent aggregation of dotria-
contane-1,32-bis(phosphocholine), PC-C32-PC, synthesised
by copper-catalysed bis-coupling, we know that this bolaam-
phiphile forms long and flexible nanofibres with a diameter
that corresponds roughly to its molecular length.[7] A tem-
perature increase leads to disruption of the nanofibres until
small nanoparticles are formed at high temperature. This
temperature-induced change in aggregation was monitored
by electron microscopy, differential scanning calorimetry
(DSC) and FTIR spectroscopy. In the DSC curves at least
two distinct endothermic transitions are observed, one at
low temperature which is somehow connected to the break-
down of the nanofibres and the hydrogel, and a high-tem-
perature transition which occurs inside the stability range of
the nanoparticles and is presumably caused by further disor-
dering of the chains inside the nanoparticle.
protecting groups. These compounds were isolated and re-
crystallised from heptane in 55–65% yield, similarly to the
method described by Mohr et al.,[13] and they did not con-
tain any higher condensation product. Thus, this strategy is
preferred for the synthesis of long-chain diols.
In addition, we found that the high molecular weight by-
products 3’’ could be completely separated during the purifi-
cation of the final bis(phosphocholines) 15 by MPLC with a
gradient technique and chloroform/methanol/water as
eluent. Thus, we have developed two new effective ap-
proaches to the long-chain 1,w-diols 4 necessary for the
preparation of bolaphosphocholines 15a–f.
For the synthesis of bis-phosphocholines 15a–f, common
phosphorylating reagents such as b-bromoethylphosphoric
Since the self-assembly process of these bolaamphiphiles
is exclusively driven by hydrophobic interactions of the long
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Synthesis and Aggregation of 1,w-Bis(phosphocholines)
FULL PAPER
alkyl chain, the question arises of the minimal chain length
for which formation of fibres can be realised. With our new
synthetic strategy for symmetrical single-chain bolaamphi-
philes with different alkyl chain lengths, we were able to in-
vestigate the temperature dependent aggregation of bolaam-
phiphiles with 22 to 32 carbon atoms in the alkyl chain
(15a–f).
The DSC thermograms of bolaamphiphiles 15a–f (Fig-
ure 1A) show two endothermic transitions between 2 and
1008C. The first peak always has the largest latent heat. Fig-
ure 1B shows the dependence of both transition tempera-
tures on carbon chain length. With increasing carbon chain
length both transition temperatures shift to higher values by
an average of about 58C per additional CH2 group. Howev-
er, the temperature increase is not linear: the steepness de-
creases with increasing chain length (see Figure 1B). The
width of the first transition narrows with increasing chain
length. This also seems to be the case for the high-tempera-
ture transition. The transitions apparently become more co-
operative at longer chain length.
The transition enthalpies for both transitions are summar-
ised in Figure 1C. The chain-length dependence of both
transitions is quite unusual. The transition enthalpy DH1 for
the low-temperature transition first increases with increasing
alkyl chain length up to C26 and then decreases up to C32.
The C32 compound even has a lower transition enthalpy
than its C24 analogue. The transition enthalpy DH2 for the
high temperature transition does not follow the same
course. This high-temperature transition is very broad and
the transition enthalpy is not easily determined. Therefore,
the observed changes may not be significant. From these
data it is not clear what the cause for this peculiar change in
transition enthalpy is. It seems likely that the aggregation
behaviour could change when the chain length is decreased
below 24 carbon atoms. However, the transition tempera-
tures show the expected behaviour and no unusual devia-
tions.
Temperature-dependent aggregation of compounds 15a–f
was then monitored by cryo-TEM. Figure 2 shows electron
micrographs of dilute aqueous dispersions of 15c–e for dif-
ferent quenching temperatures, chosen according to the
transition temperatures of the bolaamphiphiles, as deter-
mined by DSC (see Figure 1). At 208C, 15a–d form a dense
network of long and flexible fibres with diameters that cor-
respond approximately to their molecular length (see Fig-
ure 2A and C; data for 15a,b not shown). For 15d addition-
al stiff and shorter rods of larger diameter can be seen (Fig-
ure 2D). Investigation of aggregates of 15e,f below the first
transition temperature (see Figure 1) was not possible be-
cause quenching of the samples starting from temperatures
below 108C could not be performed. At temperatures above
the first transition the fibres of bolaamphiphiles 15a–c trans-
form into spherical micelles (see Figure 2B; data for 15a,b
not shown). Whereas disc-like aggregates with diameters up
to 150 nm were observed for 15d (see Figure 2E), stiff and
short rods of larger diameter were obtained for 15e (data
not shown). Furthermore, we investigated 15e above the
Figure 1. A) DSC curves of 1,w-bis(phosphocholines) with chain lengths
of 32 to 22 carbon atoms (15a–f). B) Dependence of transition tempera-
tures (Tm1 and Tm2) carbon chain length. C) Dependence of the corre-
sponding transition enthalpies carbon chain length (the lines are guides
to the eye).
second transition temperature, where spherical aggregates
were found (see Figure 2F).
From these data we can conclude that the exclusive for-
mation of long and flexible fibres below and spherical mi-
celles above the first transition is realised for chains longer
than 26 carbon atoms. Shorter chain lengths lead to the for-
mation of different aggregates above the first transition,
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B. Dobner et al.
Figure 3. Wavenumber of the symmetrical methylene stretching vibra-
tional band as a function of temperature for dispersions containing
50 mgmLÀ1 of 1,w-bis(phosphocholines) with chain lengths of 32 to 22
carbon atoms (15a–f).
gauche ratio in the chain. The smaller shift for longer alkyl
chains indicates a slightly higher degree of order of the alkyl
chains in the aggregates of the new phase. When the second
transition temperature is passed, a further shift of the peak
position is observed, which is characteristic for highly disor-
dered molecules in small aggregates such as spherical mi-
celles for 15e.
The analysis of the change in frequency at the first main
transition shows the same tendency as the transition enthal-
py measured by DSC. With increasing chain length above
C26 the change in frequency decreases, as does the transition
enthalpy. Also the frequency change at the second transition
clearly decreases with increasing chain length, and the abso-
lute value of the CH2 vibrational frequency at high tempera-
ture is the lowest for the C32 compound. The FTIR data cor-
respond to the DSC data and show that the major contribu-
tion to the transition enthalpy comes from fluidisation of
the chains and not from contributions from head-group in-
teractions.
Figure 2. Cryo-TEM images of aqueous dispersions of 1 mgmLÀ1 1,w-bis-
(phosphocholines) quenched from different temperatures (with two dif-
ferent magnifications). The scale bar corresponds to 200 nm. A) 15c,
208C, flexible fibres; B) 15c, 458C, spherical micelles; C) 15d, 208C, flex-
ible fibres; D) 15d, 208C, stiff rods; E) 15d, 358C, discs and sheets;
F) 15e, 558C, spherical micelles.
ACHTREUNG
such as short and thick rods and disc-like structures. Obvi-
ously, a different packing of the bolaamphiphiles with their
large head groups and small cross-sectional area of the alkyl
chains is realised. Whereas fibres seem to be composed of
stretched molecules, which are slightly twisted relative to
each other and are stabilised by van der Waals interactions
of the alkyl chains,[6] shorter chains contribute less to the
stabilization of the fibre arrangement, and different packing
motives are preferred. A striking property of highly dilute
aqueous suspensions (1 mgmLÀ1) of polymethylene-1,w-bis-
A
Conclusion
scribed for PC-C32-PC.[6] Below the first transition tempera-
ture the fibres entangle, and water is trapped within the
fibre network, so that the suspension stops flowing.
Bolaphosphocholines were prepared from precursors syn-
thesised in two different ways. Long-chain diols can be syn-
thesised by the procedures of Schill et al.[12] and Mohr
et al.[13] We prepared these compounds as hydrophobic pre-
cursors for the synthesis of bolaphosphocholines by two new
strategies. The 2:1 bis-coupling of the Grignard reagent of
commercially available 11-bromoundec-1-ene or 8-bro-
mooct-1-ene with different 1,w-dibromides results in a high
yield of the diene containing a small amount of higher con-
densation products. These side products could be eliminated
by MPLC purification of the bis(phosphocholines). The al-
ternative route is 1:1 homocoupling of the corresponding w-
bromo-1-[(tetrahydro-2H-pyran-2-yl)oxy]alkanes of differ-
ent chain lengths, which avoids higher condensation prod-
The temperature-dependent course of the CH2 stretching
vibrational bands, investigated for aqueous suspensions
(50 mgmLÀ1) of 15a–f by FTIR spectroscopy, is summarised
in Figure 3. It shows two characteristic steps occurring at the
same temperatures at which transitions are observed by
DSC. The wavenumber of this band is an indicator for the
conformational order of the alkyl chain. Below the first
transition temperature, the peak position for 15a–e is ap-
proximately 2849.5 cmÀ1, which indicates relatively ordered
extended alkyl chains in all-trans conformation. During the
first transition the peak positions shift to significantly higher
values that are characteristic for a decrease in the trans/
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Synthesis and Aggregation of 1,w-Bis(phosphocholines)
FULL PAPER
mixture was poured into a cold saturated solution of ammonium chloride
(150 mL). The organic layer was separated and the aqueous phase was
extracted twice with diethyl ether (50 mL). The combined organic phases
were washed with water, dried over sodium sulfate, and concentrated to
dryness under reduced pressure. For purification the residue was filtered
over silica gel (100 g, 0.060–0.200 mm) with dry heptane (500 mL). Dry
THF/diethyl ether (1/1) was added to the residue until a clear solution
appeared. Dry acetone was added with stirring until no further precipita-
tion of the diene 3a–c occurred. In the case of C26 diene 3d and C24
diene 3e, dry methanol was used instead of acetone. The obtained precip-
itate was collected by filtration and dried in vacuo over phosphorus pent-
oxide.
ucts and results in yields comparable to those of Mohr
et al.[13] For the synthesis of the boladiols, this method is pre-
ferred. The phosphorylation of these diols to bolaphospho-
cholines is possible by using the conventional phosphoryla-
tion reagent used in phospholipid synthesis. The main prob-
lem was the insolubility of the diols in chloroform under the
usual reaction conditions, which could be solved by an initial
temperature increase at the beginning of the phosphoryla-
tion reaction.
With this development of a new synthetic strategy for
symmetrical single-chain bolaamphiphiles with different
alkyl chain lengths, we were able to investigate the tempera-
ture-dependent aggregation of bolaamphiphiles with 22 to
32 carbon atoms in the alkyl chain. For chains longer than
26 carbon atoms, flexible fibres are observed below the first
transition temperature. The fibres seem to be composed of
stretched molecules which are slightly twisted relative to
each other and are stabilised by van der Waals interactions
of the alkyl chains. Above the first transition temperature
these long-chain bolaamphiphiles form nanoparticles or
spherical micelles. For bolaphospholipids with shorter
chains, other types of aggregates are found above the first
transition temperature, namely, short and thick rods and
disc-like structures.
Dotriaconta-1,31-diene (3a): Yield: 7.8 g (87%); 1HNMR (400 MHz,
CDCl3, 278C): d=1.24–1.28 (m, 48H, =CHCH2CH2
A
CH=), 1.32–1.39 (m, 4H, =CHCH2CH2(CH2)24CH2CH2CH=), 1.99–2.05
AHCTREUNG
(q, 4H, 2”H2C=CHCH2), 4.88–5.00 (m, 4H, 2”H2C=), 5.74–5.85 ppm
(m, 2H, 2”=CH); ESI-MS: m/z: 446 [M+]; elemental analysis calcd (%)
for C32H62 (446.83): C 86.01, H13.99; found: C 86.01, H13.96.
Triaconta-1,29-diene (3b): Yield: 6.7 g (80%); 1HNMR (500 MHz,
CDCl3, 278C): d=1.24–1.28 (m, 44H, =CHCH2CH2
A
CH=), 1.33–1.39 (m, 4H, =CHCH2CH2(CH2)22CH2CH2CH=), 1.99–2.04
AHCTREUNG
(q, 4H, 2”H2C=CHCH2), 4.89–4.99 (m, 4H, 2”H2C=), 5.76–5.84 ppm
(m, 2H, 2”=CH); ESI-MS: m/z: 418 [M+]; elemental analysis calcd (%)
for C30H58 (418.78): C 86.04, H13.96; found: C 86.06, H13.76.
Octacosa-1,27-diene (3c): Yield: 5.9 g (75%); 1HNMR (400 MHz,
CDCl3, 278C): d=1.24–1.29 (m, 40H, =CHCH2CH2
A
CH=), 1.33–1.40 (m, 4H, =CHCH2CH2(CH2)20CH2CH2CH=), 1.99–2.05
AHCTREUNG
(q, 4H, 2”H2C=CHCH2), 4.89–5.00 (m, 4H, 2”H2C=), 5.75–5.85 ppm
(m, 2H, 2”=CH); ESI-MS: m/z: 390 [M+]; elemental analysis calcd (%)
for C28H54 (390.73): C 86.07, H13.93; found: C 85.90, H13.98.
Hexacosa-1,25-diene (3d): Yield: 5.9 g (82%); 1HNMR (500 MHz,
CDCl3, 278C): d=1.24–1.28 (m, 36H, =CHCH2CH2
A
Experimental Section
CH=), 1.33–1.38 (m, 4H, =CHCH2CH2(CH2)18CH2CH2CH=), 2.00–2.04
AHCTREUNG
(q, 4H, 2”H2C=CHCH2), 4.89–4.99 (m, 4H, 2”H2C=), 5.76–5.84 ppm
(m, 2H, 2”=CH); ESI-MS: m/z: 362 [M+]; elemental analysis calcd (%)
for C26H50 (362.67): C 86.10, H13.90; found: C 85.95, H13.88.
Tetracosa-1,23-diene (3e): Yield: 5.2 g (78%); 1HNMR (400 MHz,
General: The purity of all compounds was checked by TLC (Merck) and
the following eluents were applied: A=heptane, B=heptane/CHCl3 (4/
6), C=CHCl3/Et2O (8/2), D=CHCl3/MeOH/ammonia (50/50/15). The
chromatograms were developed with Bromothymol Blue[17] for non-phos-
phorus-containing compounds and Molybdenum Blue[18] for phosphorus-
containing compounds. Silica gel (Merck, 0.060–0.200 mm) was used for
column chromatography. The purification of the final bolaamphiphiles
was carried out by MPLC (Büchi) on silica gel (Merck, 0.032–0.060 mm).
Melting points were determined with a Boetius apparatus and are uncor-
CDCl3, 278C): d=1.23–1.27 (m, 32H, =CHCH2CH2
A
CH=), 1.32–1.39 (m, 4H, =CHCH2CH2(CH2)16CH2CH2CH=), 1.97–2.04
AHCTREUNG
(q, 4H, 2”H2C=CHCH2), 4.87–4.99 (m, 4H, 2”H2C=), 5.74–5.84 ppm
(m, 2H, 2”=CH); ESI-MS: m/z: 334 [M+]; elemental analysis calcd (%)
for C24H46 (334.62): C 86.14, H13.86; found: C 86.08, H13.91.
1
rected. Hand 13C NMR analyses were performed on a Varian Inova 500
16-Hydroxyhexadecanoic acid methyl ester (6a) and 15-hydroxypentade-
canoic acid methyl ester (6b) were prepared from the corresponding lac-
tones 5 according to the literature[20] and used without further characteri-
sation and purification.
or Varian Gemini 2000 NMR spectrometer with CDCl3 or CD3OD as in-
ternal standard. Mass spectrometric data were obtained with a Finnigan
mass spectrometer model MAT SSQ 710 C (ESI-MS) or were recorded
on an AMD 402 (70 eV) spectrometer. Elemental analyses were recorded
on a Leco CHNS-932. All solvents used were purified and dried. 11-Bro-
moundec-1-ene (1a), 8-bromooct-1-ene (1b), 1,10-dibromodecane (2a),
1,8-dibromooctane (2b), 1,6-dibromohexane (2c), hexadecanolide (5a),
pentadecanolide (5b), tetradecanedioic acid (8a), tridecanedioic acid
(8b), dodecanedioic acid (8c) and 11-bromoundecan-1-ol (11 f) were sup-
plied by Aldrich Co. b-Bromoethylphosphoric acid dichloride was pre-
pared according to the literature.[19]
16-Bromohexadecanoic acid methyl ester (7a) and 15-bromopentadeca-
noic acid methyl ester (7b) were prepared from the methyl esters 6 ac-
cording to the literature[21] and passed through a silica gel column with
heptane/chloroform as eluent. Methyl esters 7 were used without further
characterisation.
16-Bromohexadecane-1-ol (11a) and 15-bromopentadecane-1-ol (11b)
were prepared from methyl esters 7 according to the literature[22] by reac-
tion with lithium aluminium hydride in dry diethyl ether at 08C to avoid
reduction of the bromo substituent.
General procedure for the synthesis of terminal dienes 3 by Grignard
bis-coupling: A solution of 11-bromoundec-1-ene (1a, 14 g, 60 mmol) or
8-bromooct-1-ene (1b, 11.5 g, 60 mmol) in dry diethyl ether (50 mL) was
added dropwise under stirring to magnesium turnings (2.1 g, 85 mmol)
under argon atmosphere. After the exothermic reaction had subsided,
the mixture was heated at reflux for 2 h. The excess magnesium was re-
moved and the Grignard solution was concentrated under reduced pres-
sure at 108C. Dry THF (180 mL) was added to the oily residue at such a
rate that the temperature remained below 08C. Then dilithium tetrachlor-
ocuprate(II) (3.5 mL, 0.1m solution in THF, freshly prepared) was added
Tetradecane-1,14-diol (10a), tridecane-1,13-diol (10b) and dodecane-
1,12-diol (10c) were prepared from the corresponding dicarboxylic acids
8 by esterification with methanol/sulfuric acid to obtain the dimethyl
esters 9, which were reduced with lithium aluminium hydride by standard
procedures. Diols 10 were used without further characterisation and pu-
rification.
14-bromotetradecan-1-ol (11c), 13-bromotridecan-1-ol (11d) and 12-bro-
mododecan-1-ol (11e) were prepared from diols 10 according to the liter-
ature.[23]
with stirring followed by
a solution of the 1,w-dibromo alkane 2
(20 mmol) in dry THF (20 mL). After 20 min the mixture was diluted
with dry THF (20 mL) and stirring was continued for a further 3 h at
08C. For work-up diethyl ether (100 mL) was added and the resulting
Synthesis of w-bromo-1-[(tetrahydro-2H-pyran-2-yl)oxy]alkanes 12: w-
Bromo-1-[(tetrahydro-2H-pyran-2-yl)oxy]alkanes 12 were prepared from
the corresponding w-bromo alcohols 11 according to the literature.[24]
A
Chem. Eur. J. 2007, 13, 5300 – 5307
ꢀ 2007 Wiley-VCHVerlag GmbH& Co. KGaA, Weinheim
www.chemeurj.org
5305

B. Dobner et al.
solution of w-bromo alcohol 11 (50 mmol) and dihydropyran (7.6 g,
90 mmol) in dry methylene chloride (150 mL) was stirred at room tem-
perature. After 24 h water (150 mL) was added to the mixture and the or-
ganic layer was separated. The aqueous residue was extracted with meth-
ylene chloride (25 mL). The combined organic phases were washed with
water, dried over sodium sulfate and concentrated to dryness under re-
duced pressure. The crude residue was passed through a silica gel column
by using the gradient technique and heptane/diethyl ether as eluent to
obtain pure w-bromo-1-[(tetrahydro-2H-pyran-2-yl)oxy]alkanes 12 as oils
or white waxy substances in yields between 88 and 96% with respect to
w-bromo alcohols 11, or in yields between 41–52% relative to the corre-
sponding lactones 5 or dicarboxylic acids 8.
m/z (%): 426 (15) [M+], 390 (33) [M+À2H2O]; elemental analysis calcd
(%) for C28H58O2 (426.76): C 78.80, H13.70; found: C 78.78, H13.68.
Hexacosane-1,26-diol (4d): Yield: method A: 3.6 g (90%), method B:
4.5 g (60%); m.p. 106–1088C; 1HNMR (500 MHz, CDCl 3, 278C): d=
1.24–1.35 (m, 44H, HOCH2CH2
A
HOCH2CH2(CH2)22CH2CH2OH), 3.60–3.63 ppm (t, 4H, 2”HOCH2); MS
N
(70 eV): m/z (%): 398 (1) [M+], 362 (17) [M+À2H2O]; elemental analy-
sis calcd (%) for C26H54O2 (398.70): C 78.32, H13.65; found: C 78.19, H
13.59.
Tetracosane-1,24-diol (4e): Yield: method A: 3.2 g (85%); m.p. 102–
1038C; 1HNMR (500 MHz, CDCl
,
278C): d=1.23–1.34 (m, 40H,
3
HOCH2CH2
ACHTREUNG
General procedure for the synthesis of diols 4 by hydroboration/oxida-
tion of dienes 3 (method A): A 250-mL round-bottomed flask was filled
with 1m borane/THF complex (40 mL) under argon atmosphere and
cooled to À108C. A solution of 2-methylbut-2-ene (2m in THF, 40 mL)
was added dropwise at the same temperature. After stirring for 2 h at
08C, a solution of the diene 3 (10 mmol) in dry THF (40 mL) was intro-
duced dropwise and the mixture was stirred at room temperature for ap-
proximately 18–24 h till TLC (solvent system A) showed complete con-
version of the diene. For the oxidation ethanol (30 mL), 6n NaOH
(10 mL) and H2O2 (30%, 20 mL) were added slowly and the reaction
mixture was held for 3 h at 508C. After cooling to room temperature po-
tassium carbonate was added and the organic layer was separated. The
aqueous residue was washed twice with diethyl ether (50 mL). The com-
bined organic phases were dried over sodium sulfate and concentrated to
dryness under reduced pressure. The crude residue was recrystallised
from heptane and methanol to give the pure diols 4 as white crystals.
(CH2)20CH2CH2OH), 3.60–3.63 ppm (t, 4H, 2”HOCH2); MS (70 eV):
(%) for C24H50O2 (370.65): C 77.77, H13.60; found: C 77.68, H13.56.
Docosane-1,22-diol (4 f): Yield: method B: 4.2 g (65%); m.p. 96–988C;
1HNMR (500 MHz, CDCl 3, 278C): d=1.22–1.33 (m, 36H, HOCH2CH2-
A
1.52–1.56
(m,
4H,
HOCH2CH2-
A
m/z (%): 342 (2) [M+], 306 (20) [M+À2H2O]; elemental analysis calcd
(%) for C22H46O2 (342.60): C 77.13, H13.54; found: C 76.97, H13.50.
General procedure for the synthesis of the polymethylene-1,1’-diyl-
A
(1.93 g, 8 mmol) was poured into dry chloroform (20 mL) under cooling
with ice/water. A mixture of dry TEA (1.42 g, 14 mmol) and dry chloro-
form (20 mL) was added slowly with stirring, which was continued for
30 min at 08C. Diol 4 (1 mmol) was added as solid substance in one por-
tion. The suspension was heated until the solid was dissolved (max.
608C), than rapidly cooled to room temperature. Stirring was continued
for a further 24–48 h at room temperature. After TLC (solvent system C)
showed complete conversion of diol 4, crushed ice (40 mL) was added to
the solution and the mixture was stirred for a further 2 h. The organic
layer was separated and the aqueous phase was diluted with a cold satu-
rated solution of sodium chloride (50 mL) and then extracted twice with
chloroform (50 mL). The combined organic phases were concentrated
under reduced pressure and the oily residue was dissolved in THF/H2O
(9/1, 30 mL). After 1.5 h the solvent was evaporated and the oily residue
General procedure for the synthesis of diols 4 by Grignard homocoupling
of w-bromo-1-[(tetrahydro-2H-pyran-2-yl)oxy]alkanes 12 (method B): A
solution
of
w-bromo-1-[(tetrahydro-2H-pyran-2-yl)oxy]alkane
12
(22 mmol) in dry THF (50 mL) was added dropwise with stirring to mag-
nesium turnings (0.8 g, 33 mmol) under argon atmosphere. After the exo-
thermic reaction had subsided, the mixture was stirred at 558C for 3 h.
The excess magnesium was removed and the Grignard solution was
cooled to À58C. A freshly prepared solution of dilithium tetrachlorocu-
prate(II) (0.1m in THF, 3.5 mL) was added with stirring. After a solution
of the same w-bromo-1-[(tetrahydro-2H-pyran-2-yl)oxy]alkane 12
(19 mmol) in dry THF (50 mL) was added in one portion, stirring was
continued for further 3 h at 08C. For work-up diethyl ether (150 mL) was
added and the resulting mixture was poured into a cold saturated solu-
tion of ammonium chloride (150 mL). The organic layer was separated
and the aqueous phase was extracted twice with diethyl ether (50 mL).
The combined organic phases were washed with water, dried over
sodium sulfate and concentrated to dryness under reduced pressure. For
cleavage of the THP protecting groups the crude bis(tetrahydropyranyl
ether)s 13 were dissolved in dry methanol (100 mL) and heated under
reflux for 3 h with catalytic amounts of pyridinium p-toluene sulfonate.
The hot suspension was filtered and the white residue was recrystallised
from heptane to give the pure diols 4 as white crystals.
was transferred into
a mixture of chloroform (30 mL), acetonitrile
(30 mL) and an alcoholic solution of trimethylamine (10 mL, 4.2m). The
mixture was kept in a closed tube at 40–458C for 48–72 h. After TLC
(solvent system D) showed formation of the product, the mixture was
concentrated by evaporation of the solvent and the residue purified by
MPLC on silica gel by using the gradient technique and chloroform/
methanol/water as eluent. The bis(phosphocholines) 15 were dried in
vacuo over phosphorus pentoxide at room temperature for two days. For
physicochemical studies the products were dissolved in a small amount of
dry chloroform/methanol (1/1). Dry acetone was then added to precipi-
tate the white product. The precipitate was separated by centrifugation
and dried in vacuo over phosphorus pentoxide.
Dotriacontane-1,32-diol (4a): Yield: method A: 4.6 g (95%), method B:
5.8 g (63%); m.p. 115–1168C; 1HNMR (500 MHz, CDCl 3, 278C): d=
Dotriacontane-1,1’-diylbis[2-(trimethylammonio)ethylphosphate] (15a):
Yield: 0.49 g (60%); 1HNMR (400 MHz, CDCl 3/CD3OD, 278C): d=
1.24–1.34 (m, 56H, HOCH2CH2
G
1.15–1.22 (m, 56H; OCH2CH2
OCH2CH2(CH2)28CH2CH2O), 3.11 (s, 18H; 6”CH3), 3.47–3.51 (m, 4H;
2”NCH2CH2O), 3.72–3.77 (q, 4H; OCH2CH2(CH2)28CH2CH2O), 4.10–
U
HOCH2CH2(CH2)28CH2CH2OH), 3.61–3.63 ppm (t, 4H, 2”HOCH2); MS
G
AHCTREUNG
(70 eV): m/z (%): 482 (5) [M+], 446 (19) [M+À2H2O]; elemental analy-
sis calcd (%) for C32H66O2 (482.86): C 79.59, H13.78; found: C 79.40, H
13.71.
4.12 ppm (m, 4H; 2”NCH2CH2O); 13C NMR (100 MHz, CDCl3/CD3OD,
278C): d=25.65, 29.26, 29.45–29.52, 30.62, 30.70, 54.12, 54.15, 54.19,
58.63, 58.68, 65.72, 65.78, 66.44 ppm; ESI-MS: m/z: 813.8 [M++H], 835.7
[M++Na]; elemental analysis calcd (%) for C42H90N2O8P2·H2O: C 60.69,
H11.16, N 3.37; found: C 60.72, H11.23, N 3.53.
Triacontane-1,30-diol (4b): Yield: method A: 4.1 g (91%), method B:
4.8 g (55%); m.p. 112–1148C; 1HNMR (500 MHz, CDCl 3, 278C): d=
1.23–1.34 (m, 52H, HOCH2CH2
HOCH2CH2(CH2)26CH2CH2OH), 3.60–3.64 ppm (t, 4H, 2”HOCH2); MS
U
Triacontane-1,1’-diylbis[2-(trimethylammonio)ethylphosphate]
Yield: 0.46 g (58%); 1HNMR (400 MHz, CDCl 3/CD3OD, 278C): d=
1.09–1.19 (m, 52H, OCH2CH2(CH2)26CH2CH2O), 1.42–1.46 (m, 4H,
OCH2CH2(CH2)26CH2CH2O), 3.04 (s, 18H, 6”CH3), 3.40–3.42 (m, 4H,
2”NCH2CH2O), 3.66–3.70 (q, 4H, OCH2CH2
(15b):
AHCTREUNG
AHCTREUNG
(CH2)26CH2CH2O), 4.04–
Octacosane-1,28-diol (4c): Yield: method A: 3.7 g (87%); m.p. 109–
4.05 ppm (m, 4H, 2”NCH2CH2O); 13C NMR (100 MHz, CDCl3/CD3OD,
278C): d=25.94, 29.78, 54.39, 58.88, 58.94, 66.04, 66.10, 66.74 ppm; ESI-
MS: m/z: 785.8 [M++H], 807.7 [M++Na]; elemental analysis calcd (%)
1118C; 1HNMR (500 MHz, CDCl
,
278C): d=1.24–1.35 (m, 48H,
(CH2)24CH2CH2OH), 1.53–1.57 (m, 4H, HOCH2CH2-
(CH2)24CH2CH2OH), 3.60–3.63 ppm (t, 4H, 2”HOCH2); MS (70 eV):
3
HOCH2CH2
ACHTREUNG
ACHTREUNG
5306
www.chemeurj.org
ꢀ 2007 Wiley-VCHVerlag GmbH& Co. KGaA, Weinheim
Chem. Eur. J. 2007, 13, 5300 – 5307

Synthesis and Aggregation of 1,w-Bis(phosphocholines)
FULL PAPER
for C40H86N2O8P2·2H2O: C 58.51, H11.05, N 3.41; found: C 58.52, H
10.98, N 3.41.
8 min, 32 scans were recorded and accumulated. The corresponding spec-
tra of the solvent were subtracted from the obtained sample spectra by
using the OPUS software supplied by Bruker.
Octacosane-1,1’-diylbis[2-(trimethylammonio)ethylphosphate]
Yield: 0.47 g (62%); 1HNMR (400 MHz, CDCl 3/CD3OD, 278C): d=
1.01–1.15 (m, 48H, OCH2CH2(CH2)24CH2CH2O), 1.36–1.43 (m, 4H,
OCH2CH2(CH2)24CH2CH2O), 2.98 (s, 18H, 6”CH3), 3.34–3.36 (m, 4H,
2”NCH2CH2O), 3.61–3.66 (q, 4H, OCH2CH2
(15c):
AHCTREUNG
ACHTREUNG
A
Acknowledgements
4.02 ppm (m, 4H, 2”NCH2CH2O); ESI-MS: m/z: 757.8 [M++H], 779.4
[M++Na]; elemental analysis calcd (%) for C38H82N2O8P2·2H2O: C 57.55,
H10.93, N 3.53; found: C 57.59, H11.04, N 3.41.
This work was supported by grants from the Deutsche Forschungsge-
meinschaft (A.M., S.D., B.D. and A.B.) and from the Cluster of Excel-
lence “Nanostructured Materials” (B.D. and A.B.).
Hexacosane-1,1’-diylbis[2-(trimethylammonio)ethylphosphate]
Yield: 0.47 g (65%); 1HNMR (400 MHz, CDCl 3/CD3OD, 278C): d=
0.93–1.05 (m, 44H, OCH2CH2(CH2)22CH2CH2O), 1.26–1.33 (m, 4H,
OCH2CH2(CH2)22CH2CH2O), 2.88 (s, 18H, 6”CH3), 3.25–3.27 (m, 4H,
2”NCH2CH2O), 3.51–3.56 (q, 4H, OCH2CH2(CH2)22CH2CH2O), 3.89–
(15d):
AHCTREUNG
ACHTREUNG
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AHCTREUNG
3.90 ppm (m, 4H, 2”NCH2CH2O); ESI-MS: m/z: 730.0 [M++H], 751.9
[M++Na]; elemental analysis calcd (%) for C36H78N2O8P2·2H2O:
C
56.52, H10.81, N 3.66; found: C 56.54, H10.89, N 3.59.
Tetracosane-1,1’-diylbis[2-(trimethylammonio)ethylphosphate]
Yield: 0.42 g (60%); 1HNMR (400 MHz, CDCl 3/CD3OD, 278C): d=
0.89–0.99 (m, 40H, OCH2CH2(CH2)20CH2CH2O), 1.22–1.29 (m, 4H,
OCH2CH2(CH2)20CH2CH2O, 2.84 (s, 18H, 6”CH3), 3.21–3.23 (m, 4H, 2”
NCH2CH2O), 3.46–3.51 (q, 4H, OCH2CH2(CH2)20CH2CH2O), 3.83–
(15e):
AHCTREUNG
ACHTREUNG
AHCTREUNG
3.88 ppm (m, 4H, 2”NCH2CH2O); 13C NMR (100 MHz, CDCl3/CD3OD,
278C): d=25.46, 29.30, 30.41, 30.48, 53.58, 58.54, 58.59, 65.54, 65.60,
66.09, 66.12 ppm; ESI-MS: m/z: 701.8 [M++H], 723.7 [M++Na]; elemen-
tal analysis calcd (%) for C34H74N2O8P2·2H2O: C 55.41, H10.67, N 3.80;
found: C 55.53, H10.71, N 3.72.
Docosane-1,1’-diylbis[2-(trimethylammonio)ethylphosphate]
Yield: 0.36 g (54%); 1HNMR (400 MHz, CDCl 3/CD3OD, 278C): d=
0.86–0.94 (m, 36H, OCH2CH2(CH2)18CH2CH2O), 1.17–1.26 (m, 4H,
OCH2CH2(CH2)18CH2CH2O), 2.81 (s, 18H, 6”CH3), 3.17–3.20 (m, 4H,
2”NCH2CH2O), 3.42–3.47 (q, 4H, OCH2CH2
(15 f):
AHCTREUNG
ACHTREUNG
A
3.84 ppm (m, 4H, 2”NCH2CH2O); ESI-MS: m/z: 673.6 [M++H], 695.6
[M++Na]; elemental analysis calcd (%) for C32H70N2O8P2·2H2O: C 54.22,
H10.53, N 3.95; found: C 54.29, H10.56, N 3.83.
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coated with a perforated polymer film. Excess solution was then removed
with a filter paper to leave a thin film of the solution spanning the holes
of the polymer film on the EM grid. Vitrification of the thin film was
achieved by rapid plunging of the grid into liquid ethane held just above
its freezing point. The vitrified specimen was kept below 108 K during
both transfer to the microscope and investigation.
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DSC: DSC measurements were performed with a MicroCal VP-DSC dif-
ferential scanning calorimeter (MicroCal Inc., Northampton, MA, USA).
Before the measurements, the sample solution (1 mgmLÀ1) and the water
reference were degassed under vacuum while stirring. A heating rate of
208ChÀ1 was used and the measurements were performed in the temper-
ature interval from 2 to 1008C. To check the reproducibility, three con-
secutive scans of each sample were recorded. The reference thermogram
(water/water baseline) was subtracted from the thermograms of the sam-
ples and the DSC scans were evaluated with the MicroCal ORIGIN 5.0
software.
FTIR spectroscopy: Infrared spectra were measured on a Bruker Vector
22 Fourier transform spectrometer with a DTGS-detector operating at
2 cmÀ1 resolution. The sample with a concentration of 50 mgmLÀ1 was
placed between two BaF2 windows, which were separated by a 56 mm
spacer for measurements in D2O. IR spectra were measured every 28C in
the temperature range from 5 to 958C. After an equilibration time of
Received: December 22, 2006
Published online: March 23, 2007
Chem. Eur. J. 2007, 13, 5300 – 5307
ꢀ 2007 Wiley-VCHVerlag GmbH& Co. KGaA, Weinheim
www.chemeurj.org
5307