General synthesis and aggregation behaviour of new single-chain bolaphospholipids: Variations in chain and headgroup structures

Article abstract of DOI:10.1002/chem.200800033

The chemical structures of polymethylene-1,ω-bis(phosphocholines) that self-assemble into nanofibres was modified on the one hand in the hydrophobic chain region, by introduction of sulfur and oxygen atoms, and on the other hand by variation of the polar

Full text of DOI:10.1002/chem.200800033

DOI: 10.1002/chem.200800033
General Synthesis and Aggregation Behaviour of New Single-Chain
Bolaphospholipids: Variations in Chain and Headgroup Structures
Simon Drescher,[a] Annette Meister,[b] Gesche Graf,[b] Gerd Hause,[c]
Alfred Blume,[b] and Bodo Dobner*[a]
Abstract: The chemical structures of
polymethylene-1,w-bis(phosphocho-
lines) that self-assemble into nanofi-
bres was modified on the one hand in
the hydrophobic chain region, by intro-
duction of sulfur and oxygen atoms,
and on the other hand by variation of
the polar headgroup structure with
functionalised tertiary amines. The
temperature-dependent self-assembly
of these novel bolaphospholipids into
nanofibres and spherical micelles was
investigated by differential scanning
calorimetry (DSC) and transmission
electron microscopy (TEM). The ther-
mal stabilities of the nanofibres strong-
ly depend on the chemical composi-
tions of the headgroups and of the hy-
drophobic chains. The insertion of new
functionalities in the headgroup region
by click chemistry makes these sub-
stances interesting for potential appli-
cations in bioscience and materials
Keywords: aggregation
philes lipids nanofibers
synthetic methods
·
amphi-
·
·
·
AHCTREsGNU cience.
Introduction
Recently, we reported the synthesis and temperature-de-
pendent aggregation behaviour of symmetrical single-chain
polymethylene-1,w-bis(phosphocholines) with hydrocarbon
chain lengths of 22 to 32 carbon atoms and two phosphocho-
line headgroups attached at both ends (PC-Cn-PC).[8] These
bolalipids self-assemble at room temperature into long
nanofibres that form a dense network, which gels water very
efficiently. Within the fibres, the molecules are arranged
side by side, but the bulky headgroups induce a twisted ar-
rangement, causing a helical superstructure of the fibres.[9–11]
Above a certain temperature, which depends on the length
of the alkyl chain, the nanofibres reversibly transform into
smaller aggregates such as spherical micelles or discs, and
the gel character of the aqueous solution is lost.
The self-assembly process of polymethylene-1,w-bis(phos-
phocholines) is exclusively driven by hydrophobic interac-
tions of the long alkyl chains, because the phosphocholine
headgroups cannot form intermolecular hydrogen bonds.
The question arose of whether the substitution of methylene
groups by sulfur or oxygen atoms would perturb this aggre-
gation process as a result of increased polarity, together with
the different binding angles and bond lengths relative to a
methylene group in a hydrocarbon chain. We therefore in-
serted oxygen and sulfur at certain positions in the alkyl
chain and investigated the influence of both atoms on the
aggregation behaviour.
A bolalipid is composed of two hydrophilic headgroups at-
tached to one or two hydrophobic spacers. The basic struc-
ture has its origin in the membrane lipids of certain species
of archaebacteria.[1] The membrane-spanning—and thus
membrane-stabilizing—properties of these bolalipids with
two alkyl chains make these molecules attractive candidates
for use in vesicular drug delivery systems or for the stabilisa-
tion of supported membrane biosensor devices.[2,3] Since
well defined, natural bolaphospholipids are difficult to iso-
late from natural membranes, considerable efforts have
been devoted to the synthesis of novel bipolar lipids.[4,5] Un-
expectedly, the simplification of these model compounds to
bipolar lipids with just one long alkyl chain gave rise to new
aggregate structures, such as nanofibres and nanoparticles of
self-assembled single-chain bolaphospholipids.[6,7]
[a] S. Drescher, Prof. Dr. B. Dobner
Institute of Pharmacy, MLU Halle-Wittenberg
Wolfgang-Langenbeck-Strasse 4, 06120 Halle/Saale (Germany)
Fax : (+49)345-55-27018
E-mail: bodo.dobner@pharmazie.uni-halle.de
[b] Dr. A. Meister, G. Graf, Prof. Dr. A. Blume
Institute of Chemistry, MLU Halle-Wittenberg
Mühlpforte 1, 06108 Halle/Saale (Germany)
[c] Dr. G. Hause
We have recently reported on bolaphospholipids with di-
methylammonio headgroups that self-assemble into nanofi-
Biocenter, MLU Halle-Wittenberg
Weinbergweg 22, 06120 Halle/Saale (Germany)
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FULL PAPER
bres that display higher thermal stability due to the forma-
tion of intermolecular hydrogen bonds between the head-
groups.[12] In this study we synthesised several bolaphospho-
lipids with further variations in the polar headgroup struc-
tures. We modified the choline headgroups with several
functional groups in order to scrutinise the size effect of the
headgroup on the aggregation behaviour and also to find
out the synthetic limits for the quarternisation reaction. In
addition, the functionalised choline headgroups are suitable
for further chemical modifications such as binding of fluo-
rescence labels or low-molecular-weight proteins.
In this work we present a general synthetic approach to
chain- and headgroup-modified dotriacontane-1,32-bis(phos-
phocholines). The temperature-dependent aggregation prop-
erties of these novel single-chain bolaphospholipids were in-
vestigated by differential scanning calorimetry (DSC), Fou-
ACHTREUNGrier transform infrared spectroscopy (FTIR), transmission
electron microscopy (TEM) and dynamic light scattering
(DLS).
Scheme 1. Synthesis of 1,w-bis(phosphocholines) with modified alkyl
chains. a) THF, potassium tert-butoxide, room temperature; b) THF,
NaH, reflux, 3 h; c) THF, 2-(11-bromoundecyloxy)tetrahydro-2H-pyran,
tetrabutylammonium iodide, reflux, 10–24 h; d) MeOH, pyridinium p-tol-
uenesulfonate, reflux, 3 h; e) CHCl3, bromoethylphosphoric acid dichlor-
ide, triethylamine, 24 h, room temperature; then THF, H2O, 2h ;
Results and Discussion
Synthetic methods: At first we prepared 1,w-bis(phospho-
cholines) with modified alkyl chains of a total chain length
of 32atoms for direct comparison with the well investigated
dotriacontane-1,32-diyl-bis[2-(trimethylammonio)ethylphos-
phate] 6a (Scheme 2, below).[9,10] For the synthesis of the
sulfur-containing compound 4a (PC-C32SS-PC), commer-
cially available octane-1,8-dithiol (1a) was deprotonated
with potassium tert-butoxide in tetrahydrofuran (THF) at
room temperature (Scheme 1). Treatment with 2-(11-bro-
moundecyloxy)tetrahydro-2H-pyran and catalytic amounts
of tetrabutylammonium iodide in THF resulted in the for-
mation of compound 2a in high yield (up to 90%). After re-
moval of the THP blocking groups under mild conditions
the 12,21-dithiadotriacontane-1,32-diol (3a) was trans-
formed into the corresponding 12,21-dithiadotriacontane-
1,32-diyl-bis[2-(trimethylammonio)ethylphosphate] (4a) in a
two-step procedure. For the phosphorylation reaction we
used the common b-bromoethylphosphoric acid dichloride
in combination with triethylamine (TEA) as basic additive.
This reagent was more efficient than 2-chloro-1,3,2-dioxo-
phospholane or other phosphites also used by others[13,14] in
bolaphospholipid synthesis. Initial heating at the beginning
of the phosphorylation reaction[8] was not necessary, because
of the higher solubility of the thia-modified diol 3a in
chloroform in relation to the unmodified diol 5. The final re-
action step was quarternisation with a solution of trimethyl-
amine in chloroform/acetonitrile/ethanol (Scheme 1).
f) CHCl3, CH3CN, EtOH, NCAHTRE(UGN CH3)3, 508C, 48 h.
the deprotonation of the two hydroxy groups required stron-
ger conditions, so treatment with sodium hydride in THF at
reflux and subsequent alkylation of 1b’ with 2-(11-bromoun-
decyloxy)tetrahydro-2H-pyran and catalytic amounts of tet-
rabutylammonium iodide gave compound 2b only, not unex-
pectedly, in moderate yields. The subsequent steps in reac-
tion were similar to the procedures described above
(Scheme 1), and the 12,21-dioxadotriacontane-1,32-diyl-
bis[2-(trimethylammonio)ethylphosphate] (4b) was obtained
in moderate yield (45%) based on the diol 3b.
Besides the chain modifications, our main attention was
focused on the variation of the headgroup structure. The
synthesis of dotriacontane-1,32-bis(phosphocholines) with
modified headgroups (6a–f) started from dotriacontane-
1,32-diol (5), which was esterified with the b-bromoethyl-
phosphoric acid dichloride used above in combination with
TEA to yield the corresponding bis(b-bromoethyl phospho-
ric acid ester) 5’. The introduction of the quarternary nitro-
gen atom was carried out, in contrast to the preparation of
compounds 4, with various tertiary amines including two
methyl groups and one larger residue (Scheme 2) in order to
find out the synthetic limits for the quarternisation reaction.
The reaction conditions and purification procedures were
similar to those described previously.[8]
The high yield of this thia-modified 1,32-bis(phosphocho-
line) 4a (up to 70%) relative to that obtained with the un-
modified 1,32-bis(phosphocholine) 6a[8] might also be due to
the lack of any need for heating during the phosphorylation
reaction.
For the first quarternisation reactions we used larger, tri-
alkylated amines such as N,N-dimethyl-N-ethylamine (6b),
N-allyl-N,N-dimethylamine (6c) and N,N-dimethyl-N-prop-
2-ynylamine (6d). Since these amines are commercially
available as pure liquids and not as solutions in ethanol, a
mixture of dry chloroform, acetonitrile and ethanol (3:3:1 v/
The synthesis of the oxygen-containing analogue 4b (PC-
C32OO-PC) started from octane-1,8-diol (1b). However,
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B. Dobner et al.
not possible due to the very similar chromatographic proper-
ties of the obtained products.
The functionalised choline headgroups of compounds 6c,
d and e were tested for coupling with different sulfur-con-
taining residues suitable for complexation of gold nanoparti-
cles. Such complexes are of great interest for electronic de-
vices. Depending on the structures of 6c–e, three methods—
photoaddition, click reactions and esterification with appro-
priate sulfur-containing reagents—were tested for an effec-
tive binding reaction.
We first attempted to use the allyl groups in compound
6c for UV-induced addition to diverse alkyl thiols as de-
scribed in the literature[15,16] (Scheme 3, top). In our hands,
however, the reaction failed to produce the corresponding
thioethers 7.
Scheme 2. Synthesis of dotriacontane-1,32-bis(phosphocholines) with
modified headgroups. a) CHCl3, bromoethylphosphoric acid dichloride,
triethylamine, 608C; then 24 h at room temperature; then THF, H2O, 2h ;
b) CHCl3, CH3CN, EtOH, (CH3)2NR, 508C, 48 h.
In another attempt the propynyl group in compound 6d
was used in a copper(I)-catalysed click reaction[17–19] with
azidomethyl phenyl sulfide as one example. For this, 6d was
dissolved in a small amount of water/ethanol (2:1 v/v), and
was then treated with the azide and catalytic amounts of a
copper(I) salt to provide compound 8 (PTTPC-C32-PTTPC)
in high yields (up to 75%). The catalyst was prepared in situ
by reduction of copper(II) salts with sodium ascorbate
(Scheme 3, middle). In addition, we found that the use of
20 mol% of copper(II) acetate[19] led to the best yields
during this reaction, relative those obtained with other cop-
per(II) salts such as copper sulfate.
v) was used instead of dry chloroform/acetonitrile[8] as sol-
vent for this reaction. We also worked strictly under argon
because of the sensitivity of the amines. The yields of the
obtained 1,32-bis(phosphocholines) 6b–d (45 to 55%) were
smaller than that of compound 6a.
Furthermore, we also used different heteroatom-substitut-
ed, trialkylated amines such as N,N-dimethylethanolamine,
N,N,N’,N’-tetramethylethylenediamine,
N,N,N’,N’-tetra-
ACHTREUNGmethylpropylenediamine and N,N-dimethylethylenediamine.
However, with increasing size of the amine the yields during
the quarternisation reaction became rather low (see
Table 1). Thus, for the quarter-
nisation
reaction
with
Table 1. Yields (based on the diol 5) of dotriacontane-1,32-bis(phosphocholines) 6 with modified headgroups.
N,N,N’,N’-tetramethylethylene-
diamine we obtained a marginal
yield of 25%, but for the reac-
[a]
Compound
Amine compound N
A
Yield [%]
6a (PC-C32-PC)
CH3
60[8]
6b (EPC-C32-EPC)
6c (APC-C32-APC)
CH2CH3
CH2CH=CH2
55
52
tion
methyl
could detect the desired
bis(phosphocholine) only by
with
N,N,N’,N’-tetra-
A
ACHTREUNGpropylenediamine
we
ꢀ
6d (PPC-C32-PPC)
CH2C CH
CH2CH2OH
45
50
25
6e (HEPC-C32-HEPC)
6 f (DMAEPC-C32-DMAEPC)
6g (DMAPPC-C32-DMAPPC)
6h (AEPC-C32-AEPC)
CH2CH2N
CH2CH2CH2N
CH2CH2NH2
A
ACHTREUNG
G
not determined[b]
not determined[c]
mass spectrometry, purification
by MPLC not being worthwhile
because of the very marginal
yields.
[a] Yield of isolated product. [b] Product was detectable by mass spectrometry but purification failed. [c] Re-
action resulted in mixtures—purification was not possible.
In addition, quarternisation
reactions with alkyl amines pos-
sessing two different reaction
centres (N,N-dimethylethanol-
ACHTREUNG
ACHTREUNG
ACHTREUNG
kylation was observed during
the quarternisation reaction.
However, the use of N,N-
dimethylethylACHTREUNGenediamine led to
a
mixture of secondary and
quarternary amines. The separa-
tion and purification of these
single compounds by MPLC
Scheme 3. a) H2O, EtOH, 6d, azidomethyl phenyl sulfide, sodium ascorbate, copper(II) acetate, room temper-
ature, 8–24 h; b) CCl4, (Æ)-a-lipoic acid, DCC, 30 min, room temperature; then CHCl3, DMSO, 6e, DMAP,
and a gradient technique was 508C, 48 h.
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New Bolaphospholipids
FULL PAPER
Furthermore, the additional hydroxy group in the choline
region of compound 6e was also suitable for reactions with
a broad spectrum of activated acids, such as lipoic acid.
Compound 6e was therefore converted into the lipid 9
(LAPC-C32-LAPC) by treatment with racemic lipoic acid,
N,N’-dicyclohexylcarbodiimide (DCC) and 4-(dimethylami-
no)pyridine (DMAP) as catalyst (Scheme 3, bottom). This
reaction led to bolaphospholipids with ester-modified head-
groups. The yield in that case was rather moderate, however,
but compound 9 was successfully tested for the fixation of
gold nanoparticles.[11]
By comparison of the yields and reaction procedures of
the functionalisation reactions discussed above we can con-
clude that the click chemistry entry is the method of choice
for coupling of various residues at the headgroup structure
of the bolaphosphocholines.
COMPASS force field in the Discover module from Materi-
als Studio (Accelrys, Inc.).
Whereas the oxygen atoms induce only a minor perturba-
À
tion in the all-trans conformation (C O 0.142nm and COC
À
113.58, relative to C C 0.153 nm and CCC 113.38), the sub-
stitution with sulfur atoms leads to two pronounced kinks
À
(C S 0.181 nm and CSC 96.18) in the chain. In addition, the
introduction of oxygen atoms increases the polarity in the
chain region to a greater extent than the introduction of
sulfur atoms.
The temperature-dependent aggregation behaviour of the
novel bolaphospholipids was investigated by differential
scanning calorimetry (DSC), transmission electron microsco-
py (TEM) and dynamic light scattering (DLS). Figure 1A
shows the DSC curve of PC-C32-PC, with two endothermic
transitions, one at 488C, associated with the breakdown of
the nanofibres, and a high-temperature transition at about
738C, which occurs inside the stability range of nanoparti-
cles.[8] Figure 1A also shows the DSC curves of the corre-
sponding bolaphospholipids with oxygen- and sulfur-contain-
ing chains (4a, 4b) for comparison. These two components
each exhibit only one endothermic peak at much lower tem-
perature: namely at 108C (4b) and 148C (4a). We presumed
that this transition was also due to a breakdown of nanofi-
bres and the formation of micelle-like aggregates, and show
later by TEM and DLS that this is indeed the case. We ob-
served a pronounced exothermic peak in the cooling curve
of 4a (data not shown), which indicates a reformation of the
fibres with almost no hysteresis.
Temperature-dependent aggregation: The conformational
consequences of substitution of two methylene groups with
oxygen or sulfur at positions C12 and C21 in the PC-C32-PC
chain are presented in the inset of Figure 1. These energy-
optimised structures were calculated with the aid of the
Figure 1B presents the CH2-stretching vibrational bands
of 4a below (58C) and above (208C) the transition tempera-
ture. The wavenumbers of the symmetric and antisymmetric
CH2-stretching vibrations provide a sensitive measure for
the conformational order of the chain. As a result of the in-
terruption of the long chain by S atoms, the continuous CH2
segments are much shorter than in the case of PC-C32-PC.
At 58C the symmetric stretching vibrational band shows a
wavenumber of 2850 cmÀ1, which is characteristic for an
almost all-trans conformation of the alkyl chain. Obviously,
the sulfur-containing chains can achieve a relatively dense
packing arrangement, despite the two pronounced kinks in
the chain separating the all-trans CH2-segments.
At 208C the symmetric stretching vibrational band has
shifted to 2853 cmÀ1, indicating that above the transition
temperature a significant proportion of gauche conformers
is present.
The DSC curve of the oxygen-containing bolaphospholi-
pid 4b shows one small, broad endothermic peak in the
heating curve. Since the disturbance of the all-trans confor-
mation of the chain by the oxygen atoms is smaller than in
the case of the sulfur atoms, their hydrophilic character ob-
viously has a stronger influence on the aggregation behav-
iour. One could assume that water penetrates into the chain
region, disturbing the self-assembly of 4b into nanofibres
and limiting their low-temperature stability.
Figure 1. A) DSC curves of aqueous suspensions of polymethylene-1,w-
bis(phosphocholines) with modified alkyl chains. The inset shows the hy-
drophobic chains (without headgroups) of the bolaphospholipids PC-
C32-PC (top), 4b with oxygen atoms in dark grey (middle), and 4a with
sulfur atoms in light grey (bottom). B) FTIR curves of an aqueous sus-
pension of 4a at 5 and 208C in the CH2-stretching vibrational region.
Chemical modification of the phosphocholine headgroup
with ethyl, allyl, propynyl and 2-(dimethylamino)ethyl moi-
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B. Dobner et al.
eties caused significantly lower transition temperatures than
in the case of PC-C32-PC (488C), which shows the strong in-
fluence of the headgroup size on the aggregation behaviour
(see Figure 2A). These bolaphospholipids are exclusively
stabilised by hydrophobic interactions of the alkyl chains,
and with increasing headgroup diameter from ethyl to 2-(di-
methylamino)ethyl moieties the transition temperatures are
shifted down to 47 and 42.58C, respectively. In contrast, the
transition temperature is shifted upwards (51.58C) for com-
pound 6e with 2-hydroxyethyl-modified headgroups. The
stabilizing effect of these headgroups on the fibres could be
due to the possibility of forming intermolecular hydrogen
bonds between the headgroups.
of the insolubility of this compound in water. For this mix-
ture the breakdown of the nanofibres occurred at a higher
temperature than with 6a, indicating a stabilizing effect of 9.
In the next step, TEM and DLS were used to characterise
the shapes of the formed aggregates. The TEM image of
stained (uranyl acetate) suspensions of the sulfur-modified
bolaphospholipid 4a shows nanofibres with non-uniform di-
ameters from 4 up to 10 nm when the sample was prepared
below the transition temperature of 148C (see Figure 3A).
The TEM image reflects the problems encountered by this
compound in achieving dense packing of the sulfur-contain-
Figure 2. DSC curves of aqueous suspensions of: A) dotriacontane-1,32-
bis(phosphocholines) with modified headgroups (6a–f) and B) bis(phos-
phocholines) 8, 9 and mixtures of both lipids with PC-C32-PC (6a).
Figure 2B shows the DSC curves of pure PTTPC-C32-
PTTPC (8) and of a mixture with PC-C32-PC (6a). The
strong shift in the transition temperature to lower values for
the pure compound is due to the increased size of the head-
group. In contrast, the 8/6a mixture with a low amount of 8
exhibits a higher transition temperature than pure 6a, indi-
cating a stabilizing effect of 8 on the nanofibres of 6a.
Figure 3. TEM images of aqueous stained (uranyl acetate) suspensions
(1 mgmLÀ1
)
of: A) PC-C32SS-PC (4a); B) PC-C32OO-PC (4b);
C) EPC-C32-EPC (6b); D) APC-C32-APC (6c); E) PPC-C32-PPC (6d);
F) HEPC-C32-HEPC (6e); G) DMAEPC-C32-DMAEPC (6 f);
H) PTTPC-C32-PTTPC (8); I) PTTPC-C32-PTTPC/PC-C32-PC (8/6a)
(1:10); K LAPC-C32-LAPC/PC-C32-PC (9/6a) (1:10). Samples were pre-
pared at 208C, except for A) at 58C, and B), H) and I) at 28C. The bar
corresponds to 50 nm.
The lipoic acid-modified bolalipid 9 could only be investi-
gated in a mixture with PC-C32-PC in a 1:10 ratio because
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New Bolaphospholipids
FULL PAPER
ing chains. As a consequence, the diameter of the nanofibres
can exceed the molecular length of about 5 nm. This would
mean that the headgroups are not in register any more.
The oxygen-modified bolaphospholipid 4b shows the for-
mation of short nanofibres of uniform diameter, indicating a
uniform packing of the chains at 28C (see Figure 3B).
For the bolaphospholipids 6b–f and 8, the formation of
long and flexible nanofibres was observed (see Figure 3C–
H). The bolaphospholipid mixtures 8/6a and 9/6a also show
long and flexible nanofibres, indicating that PC-C32-PC is
able to accommodate the larger headgroups of 8 and 9 (see
Figure 3I and K).
Above its first (or only) transition temperature, each in-
vestigated bolaphospholipid shows a nanofibre to micelle
transformation. The diameters of the formed spherical mi-
celles were determined by DLS. An example of an intensity
correlation function and the number-weighted size distribu-
tion of the formed aggregates is given in Figure 4 for com-
pound 6d.
Conclusion
In this work we have presented a general synthetic approach
to novel single-chain dotriacontane-1,32-bis(phosphocho-
lines) with modified chain and headgroup structures.
Oxygen and sulfur atoms were inserted at certain positions
in the alkyl chain with the aid of bis-alkylation reactions of
octane-1,8-diol or octane-1,8-dithiol with THP-protected 11-
bromoundecanol. The oxygen- and sulfur-containing bolali-
pids self-assembled into nanofibres that are less stable than
the unmodified bolalipid as a result of changes in the chain
conformation and the decreased hydrophobic character of
the chain.
The enlargement of the headgroup structures through the
use of various tertiary amines for the quarternisation reac-
tion was accompanied by some problems relating to the
chemical yields. In two cases the corresponding product was
not obtained in substantial amounts, due to the size or varia-
bility in the reaction centres of the amines used in the quar-
ternisation reaction. In all other cases we were able to iso-
late the corresponding bolalipids in good yields. The
physicoACHTREUcNG hemical characterisation of these compounds
showed either stabilizing or destabilizing effects of the
modified headgroups on the nanofibre structure, depending
on the size and the chemical composition of the attached
moieties. In all cases micellar-like aggregates were observed
at temperatures above the first endothermic transition.
The functionalised headgroup structures were successfully
used for further chemical modifications. In particular, the
functionalisation of the headgroup by click chemistry tech-
niques offers new possibilities for the use of nanofibres as
templates for the fixation of biological macromolecules or
metal or semiconductor nanoparticles.
Figure 4. Intensity correlation function of an aqueous suspension
(1 mgmLÀ1) of PPC-C32-PPC (6d) at 2 58C. The inset shows the number-
weighted size distribution.
Experimental Section
General: The purities of all compounds were checked by thin layer chro-
matography (TLC, Merck) with common eluents. The purification of the
final bolaamphiphiles was carried out by middle pressure liquid chroma-
tography (MPLC, Büchi) on silica gel (Merck, 0.032–0.060 mm). Melting
points were determined with a Boetius apparatus and are uncorrected.
Nuclear magnetic resonance (NMR) spectra were performed on a Varian
Inova 500 or a Varian Gemini 2000 NMR spectrometer with use of
CDCl3 or CD3OD as internal standard. Mass spectrometric data were ob-
tained with a Finnigan model MAT SSQ 710 C mass spectrometer (ESI-
MS) or were recorded on an AMD 402(70 eV) spectrometer. Elemental
analyses were recorded on a Leco CHNS-932instrument. All solvents
were used purified and dried. Commercially available reagents were sup-
plied by Aldrich, Co. and were used without further purification. b-Bro-
moethylphosphoric acid dichloride, 2-(11-bromoundecyloxy)tetrahydro-
2H-pyran and dotriacontane-1,32-diol were prepared according to the
The radii of the micellar-like aggregates of the bolaphos-
pholipids are summarised in Table 2.
Table 2. Radii of micelles, determined by DLS, of aqueous suspensions
(1 mgmLÀ1) of bolaphospholipids above the transition temperature.
Compound
T [8C]
r [nm]
4a (PC-C32SS-PC)
25
25
55
45
45
55
55
55
3.3Æ0.2
3.3Æ0.9
1.7Æ0.7
2.2Æ0.3
2.5Æ0.2
2.1Æ0.3
2.5Æ0.1
2.2Æ0.5
4b (PC-C32OO-PC)
6b (EPC-C32-EPC)
6c (APC-C32-APC)
6d (PPC-C32-PPC)
6d (PPC-C32-PPC)
6e (HEPC-C32-HEPC)
6 f (DMAEPC-C32-DMAEPC)
AHCTREUNG
literature.[8]
Synthesis of THP-blocked 1,32-diols with modified alkyl chains
2,2’-[(12,21-Dithiadotriacontane-1,32-diyl)oxy]bis(tetrahydro-2H-pyran)
(2a): Octane-1,8-dithiol (1a, 0.5 g, 2.8 mmol) diluted with dry THF
(25 mL) was placed in a round-bottomed flask under argon. Potassium
tert-butoxide (0.63 g, 5.6 mmol) was added, and the mixture was stirred
for 30 min at room temperature. A solution of 2-(11-bromoundecyl-
AHCTREoUNG xy)tetrahydro-2H-pyran (1.88 g, 5.6 mmol) in dry THF (25 mL) was
Chem. Eur. J. 2008, 14, 6796 – 6804
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
6801

B. Dobner et al.
added dropwise, and the mixture was heated under reflux for 10 h. For
the workup, diethyl ether (100 mL) was added, and the resulting mixture
was poured into a cold, saturated solution of sodium chloride (100 mL).
The organic layer was separated, and the aqueous phase was extracted
with diethyl ether (2”50 mL). The combined extracts were dried over
sodium sulfate and concentrated to dryness under reduced pressure. The
crude product was purified by MPLC by the gradient technique and with
heptane/diethyl ether to give the title compound as a white solid (1.73 g,
90%). 1H NMR (500 MHz, CDCl3, 2 78C): d=1.25–1.35 (m, 36H; 2”-
(40 mL) was added to the solution, and the mixture was stirred for a fur-
ther 2h. The organic layer was separated, and the aqueous phase was di-
luted with cold saturated sodium chloride (50 mL) and then extracted
twice with chloroform (50 mL). The combined organic phases were con-
centrated under reduced pressure, and the oily residue was dissolved in
THF/water (9:1, 30 mL). After 1 h the solvent was evaporated, and the
oily residue was transferred into a mixture of dry chloroform (25 mL),
dry acetonitrile (25 mL) and an ethanolic solution of trimethylamine
(10 mL, 4.2m). The mixture was kept in a closed tube at 508C for 48 h.
Afterwards the mixture was concentrated by evaporation of the solvent,
and the residue was purified by MPLC by the gradient technique and
with chloroform/methanol/water as eluent to give a bis(phosphocholine)
4, which was dried in vacuo over phosphorus pentoxide at room tempera-
ture for two days.
(CH2)
24H; 2”-CH
(CH2)2-), 2.46–2.50 (t, 8H; 2”-CH2SCH2-), 3.33–3.39, 3.68–3.74 (2”dt,
4H; 2”-OCH2A(CH2)10S-), 3.45–3.51, 3.83–3.88 (2”m, 4H; 2”-
CH2OCHOACHTREUNG(CH2)11S-), 4.55–4.56 ppm (m, 2H; -CH-); ESI-MS: m/z:
7A
ACHTREUNG(CH2)2ACHTREUNG(CH2)2-), 1.48–1.59, 1.66–1.73, 1.77–1.85 (3”m,
A
CHTREUNG
ACHTREUNG
CHTREUNG
709.8 [M+Na]+; elemental analysis calcd (%) for C40H78O4S2 (687.14): C
69.91, H 11.44, S 9.33; found: C 69.90, H 11.20, S 9.58.
12,21-Dithiadotriacontane-1,32-diyl-bis[2-(trimethylammonio)ethylphos-
phate] (4a): Yield: 0.59 g (70%); 1H NMR (400 MHz, CDCl3/CD3OD,
2,2’-[(12,21-Dioxadotriacontane-1,32-diyl)oxy]bis(tetrahydro-2H-pyran)
(2b): Sodium hydride (0.84 g, 21 mmol) suspended in dry THF (15 mL)
was placed in a round-bottomed flask under argon. A solution of octane-
1,8-diol (1b, 1.5 g, 10.3 mmol) in dry THF (25 mL) was added slowly, and
the mixture was stirred for 3 h under reflux. After the mixture had
cooled down to room temperature, a solution of 2-(11-bromoundecyl-
278C): d=1.20–1.32 (m, 36H; 2”-(CH2)
1.57 (m, 12H; 2”-OCH 2CH2A(CH2)7CH2CH2SCH2CH
(t, 8H; 2”-CH2SCH2-), 3.19 (s, 18H; 6”-CH3), 3.59–3.60 (m, 4H; 2”
NCH2CH2O-), 3.77–3.82(q, 4H; 2”-OC 2A(CH2)10S-), 4.16–4.22 ppm (m,
4H; 2”NCH2CH2O-); 13C NMR (100 MHz, CDCl3/CD3OD, 278C): d=
25.84 (2”-O(CH2)2CH2A(CH2)8S-), 28.74, 28.93, 29.00, 29.24, 29.40, 29.51,
29.54, 29.60, 29.66, 29.76 (2”-O(CH2)3A(CH2)7CH2SCH2A(CH2)3-), 30.86,
30.93 (2”-OCH2CH2A(CH2)9S-), 32.16, 32.20 (2”-CH2SCH2-), 54.36–54.42
(6”-CH3), 58.90, 58.95 (2”NCH2CH2O-), 65.72, 65.78 (2”-OCH2-
C
G
2ACHTREU(GN CH2)2-), 1.48–
N
CHTREUNG
N
CHTREUNG
ACHTREUNGoxy)tetrahydro-2H-pyran (6.7 g, 20 mmol) in dry THF (10 mL), together
G
U
CHTREUNG
with catalytic amounts of tetrabutylammonium iodide, were added, and
the mixture was headed under reflux for at least 24 h. For the workup, di-
ethyl ether (100 mL) was added, and the resulting mixture was poured
into a cold, saturated solution of sodium chloride (50 mL). The organic
layer was separated, and the aqueous phase was extracted with diethyl
ether (2”50 mL). The combined extracts were dried over sodium sulfate
and concentrated to dryness under reduced pressure. The crude product
was purified by MPLC by the gradient technique and with heptane/ether
as eluent to give 2b as a white solid (0.67 g, 10%). ESI-MS: m/z: 672.4
[M+NH3]+; elemental analysis calcd (%) for C40H78O6 (655.04): C 73.35,
H 12.00; found: C 73.31, H 11.84.
CTHREUNG
871.4 [M+Na]+; elemental analysis calcd (%) for C40H86N2O8P2S2·2H2O:
C 54.27, H 10.25, N 3.16, S 7.24; found: C 54.22, H 10.41, N 3.13, S 7.17.
12,21-Dioxadotriacontane-1,32-diyl-bis[2-(trimethylammonio)ethylphos-
phate] (4b): Yield: 0.37 g (45%); 1H NMR (400 MHz, CDCl3/CD3OD,
278C): d=1.09–1.14 (m, 36H; 2”-(CH2)
1.47 (m, 12H; 2”-OCH 2CH2A(CH2)7CH2CH2OCH2CH
18H; 6”-CH3), 3.21–3.24 (t, 8H; 2”-CH2OCH2-), 3.42–3.44 (m, 4H; 2”
NCH2CH2O-), 3.64–3.69 (q, 4H; 2”-OCH2A(CH2)10O-) 3.99–4.09 ppm (m,
4H; 2”NCH2CH2O-); 13C NMR (100 MHz, CDCl3/CD3OD, 278C): d=
25.65, 25.88, 26.01 (6”-O(CH2)2CH2-), 29.18, 29.29, 29.35, 29.45, 29.48,
29.53 (2”-O(CH2)3A(CH2)5CH2CH2CH2OCH2CH2CH2CH2-), 30.64, 30.70
(2”-OCH2CH2A(CH2)9O-), 54.10–54.16 (6”-CH3), 58.86, 58.89 (2”
NCH2CH2O-), 65.81, 65.86 (2”-OCH2A(CH2)10O-), 66.33 (2”NCH2CH2O-
7A
G
2ACHTREU(GN CH2)2-), 1.35–
C
CHTREUNG
CTHREUNG
Unmasking of hydroxy groups: A solution of a bis(tetrahydropyranyl)
ether 2 (2mmol) in dry methanol (100 mL) was heated under reflux for
3 h in the presence of catalytic amounts of pyridinium toluene-p-sulfo-
nate. The hot suspension was filtered off, and the white residue was re-
crystallised from heptane to provide a pure diol 3 as white crystals.
AHCTREUNG
A
CHTREUNG
CTHREUNG
CTHREUNG
), 70.75, 70.79 ppm (2”-CH2OCH2-); ESI-MS: m/z: 817.7 [M+H]+, 839.6
12,21-Dithiadotriacontane-1,32-diol (3a): Yield: 0.93 g (90%); m.p. 94–
[M+Na]+; elemental analysis calcd (%) for C40H86N2O10P2·2H2O:
C
1
958C; H NMR (400 MHz, CDCl3, 2 78C): d=1.26–1.37 (m, 36H; 2”HO-
56.31, H 10.64, N 3.28; found: C 56.12, H 10.86, N 3.21.
A
G
(CH2)2S
G
2CATHER(UNG CH2)2-), 1.52–1.59 (m, 12H; 2”HOCH2CH2-
A
CHTREUNG
General synthesis of headgroup-modified dotriacontane-1,32-bis(phos-
phocholines): b-Bromoethylphosphoric acid dichloride (1.93 g, 8 mmol)
was poured into dry chloroform (20 mL) with cooling (ice/water). A mix-
ture of dry triethylamine (1.42g, 14 mmol) and dry chloroform (20 mL)
was added slowly with stirring, which was continued at 08C for 30 min. A
diol 5 (0.48 g, 1 mmol) was added as a solid in one portion. The suspen-
sion was heated to 608C until the diol was dissolved, then rapidly cooled
to room temperature. Stirring at this temperature was continued for a
further 24–48 h. After TLC (chloroform/ether 8:2) showed complete con-
version of diol 6, crushed ice (40 mL) was added, and the mixture was
stirred for a further 2h. The organic layer was separated, and the aque-
ous phase was diluted with cold saturated sodium chloride solution
(50 mL) and then extracted twice with chloroform (50 mL). The com-
bined organic phases were concentrated under reduced pressure, and the
oily residue was dissolved in THF/water (9:1, 30 mL). After 1 h the sol-
vent was evaporated, and the oily residue was transferred under argon
into a mixture of dry chloroform (30 mL), dry acetonitrile (30 mL) and
dry ethanol (10 mL). The pure amine (20 mmol) was added slowly, and
the mixture was kept in a closed tube at 508C for 48 h. Afterwards the
mixture was concentrated by evaporation of the solvent, and the residue
was purified by MPLC by the gradient technique and with chloroform/
methanol/water as eluent to give the bis(phosphocholine) 6, which was
dried in vacuo over phosphorus pentoxide at room temperature for two
days.
G
CHTREUNG
T
U
CHTREUNG
CTHREUNG
HOCH2-); MS (70 eV): m/z (%): 518 (10) [M]+, 347 (16) [MÀC11H23O]+,
315 (100) [MÀC11H23OS]+, 144 (80) [MÀC22H46O2S]+; elemental analysis
calcd (%) for C30H62O2S2 (518.91): C 69.43, H 12.04, S 12.36; found: C
69.29, H 11.91, S 12.42.
12,21-Dioxadotriacontane-1,32-diol (3b): Yield: 0.29 g (60%); 1H NMR
(400 MHz, CDCl3, 2 78C): d=1.26–1.35 (m, 36H; 2”HO
(CH2)2O(CH2)2A(CH2)2-), 1.51–1.58 (m, 12H; 2”HOCH 2CH2-
(CH2)7CH2CH2OCH2CH (CH2)2-), 3.35–3.38 (t, 8H; 2”-CH2OCH2-),
ACHRTEU(NG CH2)2ACHRTE(UGN CH2)7-
G
U
CHTREUNG
A
2ACHTREUNG
3.60–3.63 ppm (t, 4H; 2”HOCH2-); MS (70 eV): m/z (%): 487 (3) [M]+,
315 (40) [MÀC11H23O]+, 297 (76) [MÀC11H25O2]+, 187 (42)
[MÀC19H39O2]+; ESI-MS: m/z: 488.2[ M+H]+, 509.6 [M+Na]+; elemen-
tal analysis calcd (%) for C30H62O4 (486.81): C 74.02, H 12.84; found: C
73.91, H 12.69.
Phosphorylation and quarternisation: b-Bromoethylphosphoric acid di-
chloride (1.93 g, 8 mmol) was poured into dry chloroform (20 mL) with
cooling (ice/water). A mixture of dry triethylamine (1.42g, 14 mmol) and
dry chloroform (20 mL) was added slowly with stirring, which was contin-
ued for 30 min at 08C. A diol 3 (1 mmol) was added as a solid in one por-
tion. The suspension was allowed to come to room temperature, and stir-
ring was continued at this temperature for a further 24–48 h. After TLC
(chloroform/ether 8:2) showed complete conversion of diol 3, crushed ice
Dotriacontane-1,32-diyl-bis[2-(N,N-dimethyl-N-ethylammonio]ethylphos-
phate] (6b): Yield: 0.46 g (55%); 1H NMR (400 MHz, CDCl3/CD3OD,
6802
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 6796 – 6804

New Bolaphospholipids
FULL PAPER
278C): d=1.24–1.38 (m, 62H; 2”-CH2CH3, -(CH2)
2A
G
by MPLC by the gradient technique and with chloroform/methanol/water
as eluent to give
(400 MHz, CDCl3, 2 78C): d=1.21–1.31 (m, 56H; -(CH2)
1.51–1.59 (m, 4H; -CH2CH2A(CH2)28CH2CH2-), 3.16 (s, 12H; 4”-CH3),
3.54–3.56 (m, 4H; 2”NCH2CH2O-), 3.81–3.86 (q, 4H; -OCH2-
(CH2)30CH2O-), 4.25–4.29 (m, 4H; 2”NCH2CH2O-), 4.76 (s, 4H; 2”
8 as a
white powder (17.9 mg, 75%). 1H NMR
1.57–1.63 (m, 4H; -CH2CH
3.45–3.49 (q, 4H; 2”-CH2CH3), 3.52–3.54 (m, 4H; 2”NCH2CH2O-),
2A
2CATHRE(UNG CH2)28CH2CH2-), 3.19 (s, 12H; 4”-CH3),
2ACHRTEU(GN CH2)28ACHTREUNG(CH2)2-),
3.82–3.86 (q, 4H; -OCH HCRTEN(UG CH2)30CH2O-), 4.17–4.21 ppm (m, 4H; 2”
CTHREUNG
NCH2CH2O-); ESI-MS: m/z: 841.8 [M+H]+, 863.6 [M+Na]+; elemental
analysis calcd (%) for C44H94N2O8P2·4H2O: C 57.79, H 11.26, N 3.07;
found: C 57.87, H 11.13, N 2.87.
AHCTREUNG
CCH2N), 5.70 (s, 4H; 2”SCH2N), 7.26–7.35 (m, 10H; 2”C6H5),
8.51 ppm (s, 2H; 2”C H); ESI-MS: m/z: 1192.2 [M+H]+, 1214.8
[M+Na]+; elemental analysis calcd (%) for C60H104N8O8P2S2·4H2O: C
57.03, H 8.93, N 8.87, S 5.07; found: C 57.33, H 9.05, N 8.62, S 4.81.
Dotriacontane-1,32-diyl-bis[2-(N-allyl-N,N-dimethylammonio)ethylphos-
phate] (6c): Yield: 0.45 g (52%); 1H NMR (400 MHz, CDCl3/CD3OD,
278C): d=1.17–1.31 (m, 56H; -(CH2)
-CH2CH2A(CH2)28CH2CH2-), 3.14 (s, 12H; 4”-CH3), 3.61–3.63 (m, 4H; 2”
NCH2CH2O-), 3.79–3.84 (q, 4H; -OCH2A(CH2)30CH2O-), 4.03–4.05 (d,
2ACHTRENUG(CH2)28CAHRTE(UGN CH2)2-), 1.53–1.60 (m, 4H;
CHTREUNG
Dotriacontane-1,32-diyl-bis{2-[N,N-dimethyl-N-(2-{[5-(1,2-dithiolan-3-yl)-
1-oxopentyl]oxy}ethyl)ammonio]ethylphosphate} (9): (Æ)-a-Lipoic acid
(0.24 g, 1.2 mmol) and DCC (0.12 g, 0.6 mmol), dissolved in dry tetra-
chloromethane (10 mL), were placed in a round-bottomed flask. The
mixture was stirred for 30 minutes at room temperature. The precipita-
tion was filtered off, and the solution was concentrated under reduced
pressure. DMAP (0.12g, 0.6 mmol), dissolved in dry chloroform (10 mL),
DMSO (5 mL) and compound 6e (50 mg, 57 mmol) were then added, and
the mixture was kept in a closed tube at 508C for 48 h. The crude prod-
uct was purified by MPLC by the gradient technique and with chloro-
form/methanol/water as eluent to give 9 as a white solid. Yield: 10.7 mg
(15%); ESI-MS: m/z: 1249.5 [M+H]+, 1271.5 [M+Na]+.
CTHREUNG
4H; 2”H2C=CHCH2N), 4.21–4.27 (m, 4H; 2”NCH2CH2O-), 5.69–5.73
(dd, 4H; 2” H2C=CHCH2N), 5.89–6.00 ppm (m, 2H; 2”H 2C=CHCH2N);
13C NMR (100 MHz, CDCl3/CD3OD, 278C): d=25.59 (2”-O
ACHTREUNG
A
N
ACHRTU(NEG CH2)3ACHTRENUG
CTHREUNG
A
67.75–67.79
(2”NCH2CH2O-),
123.82
129.46 ppm (H2C=CH-); ESI-MS: m/z: 866.6 [M+H]+, 887.8 [M+Na]+;
elemental analysis calcd (%) for C46H94N2O8P2·4H2O: C 58.95, H 10.97,
N 2.99; found: C 59.39, H 10.97, N 2.66.
Dotriacontane-1,32-diyl-bis[2-(N,N-dimethyl-N-propynylammonio)ethyl-
phosphate] (6d): Yield: 0.39 g (45%); 1H NMR (400 MHz, CDCl3/
Sample preparation: Homogenous dispersions of the bolalipids in water
were achieved by heating the aqueous mixture to 808C and vortexing.
CD3OD, 278C): d=1.11–1.21 (m, 56H; -(CH2)
(m, 4H; -CH2CH2A(CH2)28CH2CH2-), 2.91–2.92 (t, 2H; 2”HC=CCH2N),
3.11 (s, 12H; 4”-CH3), 3.51–3.53 (m, 4H; 2”NCH2CH2O-), 3.68–3.73 (q,
4H; -OCH2A(CH2)30CH2O-), 4.06–4.10 (m, 4H; 2”NCH2CH2O-), 4.22–
4.23 ppm (d, 2H; 2”HC=CCH2N); 13C NMR (100 MHz, CDCl3/CD3OD,
278C): d=25.80 (2”-O(CH2)2CH2A(CH2)13-), 29.01 (2”-O(CH2)15CH2-),
29.45–29.63 (2”-O(CH2)3A(CH2)12CH2-), 30.77, 30.84 (2”-OCH2CH2-
(CH2)14-), 51.49 (4”-CH3), 55.36 (2”HC=CCH2N), 58.72, 58.76 (2”
NCH2CH2O-), 64.35, 64.42(2”-O CH2A(CH2)15-), 65.93 (2”NCH2CH2O-),
2CAHTRUNEG(CH2)28CAHTRE(UGN CH2)2-), 1.43–1.50
CHTREUNG
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 heat-
ing rate of 20 KhÀ1 was used, and the measurements were performed in
the temperature interval from 2to 95 8C. To check the reproducibility,
three consecutive scans of each sample were recorded. The reference
thermogram (water/water baseline) was subtracted from the thermo-
grams of the samples, and the DSC scans were evaluated with the Micro-
Cal ORIGIN 7.0 program.
CHTREUNG
A
N
A
CHTREUNG
ACHTREUNG
CTHREUNG
71.33 (HC=C-), 81.20 ppm (HC=C-); ESI-MS: m/z: 861.5 [M+H]+, 883.5
[M+Na]+; elemental analysis calcd (%) for C46H90N2O8P2·4H2O:
59.20, H 10.59, N 3.00; found: C 59.43, H 10.44, N 2.97.
FTIR spectroscopy: Infrared spectra were measured on
Vector 22 Fourier transform spectrometer with a DTGS detector operat-
ing at 2cm À1 resolution. The sample, with a concentration of 50 mgmLÀ1
was placed between two BaF2 windows, separated by a 56 mm spacer, for
measurements in D2O. IR spectra were measured at 5 and 208C. After
an equilibration time of 8 min, 32scans were recorded and accumulated.
The corresponding spectra of the solvent were subtracted from the ob-
tained sample spectra with the aid of the OPUS software supplied by
Bruker.
a Bruker
Dotriacontane-1,32-diyl-bis{2-[N,N-dimethyl-N-(2-hydroxyethyl)ammo-
nio]ethylphosphate} (6e): Yield: 0.44 g (50%); 1H NMR (400 MHz,
,
CDCl3/CD3OD, 278C): d=0.93–1.05 (m, 56H; -(CH2)
1.26–1.33 (m, 4H; -CH2CH2A(CH2)28CH2CH2-), 2.91 (s, 12H; 4”-CH3),
3.21–3.24 (m, 4H; 2”NCH2CH2OP-), 3.34–3.36 (m, 4H; 2”
HOCH2CH2N), 3.50–3.55 (q, 4H; -OCH2A(CH2)30CH2O-), 3.64–3.67 (m,
2ACHTREU(NG CH2)28ACHRTE(UGN CH2)2-),
CTHREUNG
CTHREUNG
4H; 2”NCH2CH2OP-), 3.86–3.93 (m, 4H; 2”HOCH2CH2N); ESI-MS:
m/z: 873.8 [M+H]+, 896.0 [M+Na]+; elemental analysis calcd (%) for
C44H94N2O10P2·2H2O: C 58.12, H 10.87, N 3.08; found: C 58.03, H 10.95,
N 3.01.
TEM: The negatively stained samples were prepared by spreading the
bolalipid dispersion (5 mL) onto a Cu grid coated with a formvar film.
After 1 min of adsorption time, excess liquid was blotted off with filter
paper, and aqueous uranyl acetate (1%, 5 mL) was placed on the grid
and drained off after 1 min. The dried specimens were examined with a
Zeiss EM 900 transmission electron microscope.
Dotriacontane-1,32-diyl-bis{2-[N,N-dimethyl-N-(2-dimethylaminoethy-
l)ammonio]ethylphosphate} (6 f): Yield: 0.23 g (25%); 1H NMR
(400 MHz, CDCl3/CD3OD, 278C): d=1.06–1.17 (m, 56H; -(CH2)2-
A
G
(CH2)28CH2CH2-), 2.10 (s,
U
G
ACHTREUNG
G
CHTREUNG
DLS: The DLS experiments were performed with an ALV-NIBS-HPPS
particle sizer (ALV-Laser Vertriebsgesellschaft, mbH, Langen, Germa-
ny). The device was equipped with a 3 mW HeNe laser with a wave-
length of 632.8 nm. Because of the principle of noninvasive back scatter-
ing the scattering angle was 1738. All samples (1 mgmLÀ1) were freshly
prepared and then filtered through a membrane filter of 0.2 mm pore size
(at 808C) into quartz cuvettes (HELLMA GmbH & Co. KG, Muellheim,
Germany). Three individual measurements were performed for each
system to test the reproducibility. The experimental data were analysed
with the aid of the ALV-5000/E software based on the modified
CONTIN method,[20] with the temperature correction of the viscosity
being taken into account.
ACHTREUNG
CHTREUNG(CH2)30CH2O-), 4.00–4.04 (m, 4H; 2”NCH2CH2O-); ESI-
MS: m/z: 927.9 [M+H]+, 949.9 [M+Na]+; elemental analysis calcd (%)
for C48H104N4O8P2·4H2O: C 57.69, H 11.30, N 5.61; found: C, 57.95; H,
11.35; N, 5.42.
Further modifications of bis(phosphocholines)
Dotriacontane-1,32-diyl-bis[2-(N,N-dimethyl-N-{[1-(phenylthiomethyl)-
1,2,3-triazol-4-yl]methyl}ammonio)ethylphosphate] (8): Propynylcholine
(6d, 17.2mg, 20 mmol) and azidomethyl phenyl sulfide (6.6 mg, 40 mmol)
were suspended in a mixture of water and ethanol (2:1, 7.5 mL). Sodium
ascorbate (8 mmol, 0.4 mL of freshly prepared 20 mm solution in water)
was added, followed by copper(II) acetate monohydrate (4 mmol, 0.4 mL
of 10 mm solution in water). The heterogeneous mixture was stirred vigo-
rously for 8–24 h at room temperature. After TLC (chloroform/metha-
nol/ammonia 5:5:1) showed complete conversion of 6d, the mixture was
concentrated by evaporation of the solvent, and the residue was purified
Calculation of hydrophobic chain structures: The energy-optimised struc-
tures of hydrophobic chains with substituted oxygen and sulfur atoms
were calculated with the aid of the COMPASS force field in the Materi-
als Studio (Accelrys, Inc.) Discover module.
Chem. Eur. J. 2008, 14, 6796 – 6804
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
6803

B. Dobner et al.
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Received: January 8, 2008
Revised: April 11, 2008
Published online: June 11, 2008
6804
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