Polydiacetylene vesicles functionalized with N-heterocyclic ligands for metal cation binding

Article abstract of DOI:10.1039/b918452j

Self assembled poly diacetylene (PDA) based blue vesicles LS-Terpy, LS-DPA, LS-DP and LS-DEA with metal chelating sites have been prepared and characterized. Their response to the presence of metal cations in buffered aqueous solution has been investigated by monitoring changes of colour, UV-Vis absorption and emission. The addition of zinc, manganese, cadmium, mercury or silver salts to solutions of the vesicles induces a colour change from blue to red observable by the naked eye, while the addition of other metal salts, containing ions like Li⁺, Na⁺, K⁺, Mg ²⁺, Ca²⁺, Cr²⁺, Ni²⁺, Fe ²⁺, Co²⁺, Cu²⁺ or Pb²⁺, failed to show any changes. The metal ion coordination selectivity of the ligands is slightly different for the vesicle surface immobilized ligands compared to the reported metal cation binding of the corresponding ligands in solution, which may be due to the special environment at the lipid-solution interface. The vesicles aggregate upon metal ion coordination to the embedded ligands as shown by dynamic light scattering (DLS) particle size analysis. The functionalized PDA vesicles retain their response to the presence of aqueous solutions of metal ions if immobilized in transparent polyvinyl alcohol films or on paper.

Full text of DOI:10.1039/b918452j

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PAPER
www.rsc.org/obc | Organic & Biomolecular Chemistry
Polydiacetylene vesicles functionalized with N-heterocyclic ligands for metal
cation binding†
D. Amilan Jose and Burkhard Ko¨nig*
Received 8th September 2009, Accepted 31st October 2009
First published as an Advance Article on the web 10th December 2009
DOI: 10.1039/b918452j
Self assembled poly diacetylene (PDA) based blue vesicles LS-Terpy, LS-DPA, LS-DP and LS-DEA
with metal chelating sites have been prepared and characterized. Their response to the presence of
metal cations in buffered aqueous solution has been investigated by monitoring changes of colour,
UV-Vis absorption and emission. The addition of zinc, manganese, cadmium, mercury or silver salts to
solutions of the vesicles induces a colour change from blue to red observable by the naked eye, while the
addition of other metal salts, containing ions like Li+, Na+, K+, Mg2+, Ca2+, Cr2+, Ni2+, Fe2+, Co2+, Cu2+
or Pb2+, failed to show any changes. The metal ion coordination selectivity of the ligands is slightly
different for the vesicle surface immobilized ligands compared to the reported metal cation binding of
the corresponding ligands in solution, which may be due to the special environment at the
lipid–solution interface. The vesicles aggregate upon metal ion coordination to the embedded ligands as
shown by dynamic light scattering (DLS) particle size analysis. The functionalized PDA vesicles retain
their response to the presence of aqueous solutions of metal ions if immobilized in transparent
polyvinyl alcohol films or on paper.
The selective coordination of metal ions to vesicles bearing
suitable amphiphilic ligands has been reported and in some
Vesicular particles have been employed in diverse applications
cases, it results in the formation of unusual complexes and
Introduction
remarkable changes in the lateral organization of the membrane.7
However, only a few reports describe the use of PDA based
materials for the recognition of cations at the vesicular interface,4b,8
and the examples are limited to alkali and alkali earth metal
cations. Thus we have prepared amphiphilic diacetylenes with
N-heterocyclic metal chelating head groups,9 which are suitable
for the coordination of transition metal cations, such as Zn2+,
Cd2+, Pb2+ and Hg2+. The functionalized amphiphilic diacetylenes
were self-assembled into vesicles and photopolymerized to give
PDA particles exhibiting transition metal cation affinity. The
composition of the vesicles was altered and their metal cation
binding selectivity was determined to reveal how their properties
can be modulated by varying the embedded ligands.
in biological research, due to their relative ease of preparation
and variability in composition.1 Interactions of hosts and guests
at vesicle surfaces resemble recognition processes at biological
membranes, including cell recognition, adhesion and fusion.
Synthetic receptor sites have been incorporated into self-assembled
monolayers or bilayer membranes,2 leading to extended function-
alized interfaces, which are able to interact with guest molecules or
ions from solution. Well defined self-assembly processes starting
from rather simple building blocks allow their easy preparation
and molecular recognition events in the special environment of
the lipid–solution interface may benefit from increased affinities
or altered selectivities compared to homogeneous solution.3
Polydiacetylene (PDA) is a particularly interesting material in
this respect, as diacetylene surfactants self assemble in water to
form vesicles that can be photopolymerized to generate PDA
in situ. PDA exhibits an intense colour change from blue to red
in response to external stimuli such as temperature, pH, ions,
solvent or mechanical stress.4 The colour change is visible by the
naked eye and easily monitored by UV absorption spectroscopy.
This unique colour transition has been widely used to monitor
binding processes at interfaces.5 Recently, we described receptor
modified PDA vesicles that respond to the presence of biologically
important anions like ATP and PPi.6
Result and discussion
Terpyridine (3, Terpy), di-(2-picolyl) amine (4, DPA) and di-
pyridine (5, DP) were used as N-heterocyclic head groups of
10, 12-pentacosodiyonic acid (1, PCDA) derived amphiphiles. A
derivative of diethyl amine (6, DEA) was prepared for comparison
(Fig. 1). The N-heterocyclic ligands are well known to form defined
complexes with many transition metal cations and have been
widely used for the preparation of coordination compounds and
molecular sensors.10 However, in many cases complex formation
requires non-aqueous conditions.
Institut fu¨r Organische Chemie, Universita¨t Regensburg, D-93040, Re-
gensburg, Germany. E-mail: burkhard.koenig@chemie.uni-regensburg.de;
Fax: +49-9419431717
† Electronic supplementary information (ESI) available: General methods
and material, 1H and 13C NMR spectra for new compounds, binding
studies and particle size distribution plots. See DOI: 10.1039/b918452j
Synthesis of PCDA monomers
The diacetylene amphiphiles 7, 8, 9 and 10 were prepared by
amide or ester formation as shown in Scheme 1. Compound
7 was prepared by reacting 2 with 3 in dry THF under ice
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Fig. 1 Structures of the ligands used as head groups for diacetylene amphiphiles.
Scheme 1 General synthesis of receptor modified amphiphilic diacetylene monomers.
cooling (Scheme 1a). Compounds 8 and 9 were prepared at room
temperature starting from compound 1 using DMAP and DCC
in dry DCM with good yields (Scheme 1b). Compound 10 was
prepared by amide formation at 0 ◦C and subsequent reflux
at 75 ◦C (Scheme 1c). All diacetylene amphiphiles 7, 8, 9 and
10 were characterized by standard analytical and spectroscopic
techniques and are very stable when stored under nitrogen in the
dark. Detailed experimental procedures and analytical data of the
compounds are provided in the experimental section.
10 : 90, respectively, was dissolved in dichloromethane in a 25 mL
round bottom flask. The solvent was evaporated by a stream of
N2 gas and an appropriate amount of buffered aqueous solution
(HEPES 10 mmol, pH = 7.2) was added to the flask to give the
desired concentration of the lipid (1 ¥ 10-3 M). This solution was
sonicated at 75–80 ◦C for 40 min. The resulting milky solution
was filtered through a syringe filter (pore size: 1 mm, filter: 15 mm)
while hot, the filtrate was cooled and stored at 0 ◦C overnight. The
self-assembled vesicles were polymerized at room temperature by
irradiating the solutions with light of 254 nm wavelength for 5
to 10 min, whereby the colourless vesicle solution turned blue.
The average size of the liposomes was 150–250 nm as determined
by dynamic light scattering (DLS). The stability of the vesicles
depends on the concentration of the vesicles. Highly concentrated
vesicle solutions are unstable and the vesicles will precipitate over
time. More diluted samples are very stable when stored at 4 ◦C
(> 3 month test period). Liposomes containing 7 are named
Vesicle preparation
A liposome solution containing unmodified 10,12-pentacosa-
diynoic acid (1, PCDA) and receptor modified PCDA i.e. 7, 8,
9, and 10 was prepared using an earlier reported procedure.5,11 Ac-
cording to that, a mixture containing the diacetylene amphiphiles
7, 8, 9 or 10 and diacetylene carboxylic acid 1 in a molar ratio of
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Table 1 Particle size of the prepared vesicles determined by dynamic light
scattering
alkaline earth and transition metal cations in buffered water
(HEPES, pH = 7.2, 10 mmol L-1).
Absorption spectra of 5 ¥ 10-5 M solutions of the blue coloured
vesicles in the absence and the presence of the metal salts were
recorded. The absorption spectra of the different functionalized
liposomes in the absence of any metal ion show absorption bands
at 640 and 589 nm. The colour response and the spectral change of
the functionalized liposomes was screened adding different alkali,
alkaline earth or transition metal ions like Li+, Na+, K+, Mg2+,
Ca2+, Cr2+, Fe2+, Co2+, Ni2+, Cu2+, Hg2+, Cd2+, Ag2+, Zn2+ and Pb2+.
Only in a few cases the absorption band at 640 nm completely
disappeared, the colour of the solution became red and the
intensity of the absorption at 589 and 543 nm increased. (Fig. 2).
Fig. 3 shows the visible colour changes induced by the different
metal cations added to an aqueous solution of the functionalized
vesicles and demonstrates that the blue to red colour transition of
the vesicles depends on the nature of metal cation.
Vesicles
Particle size in nm
LS-Terpy
LS-DPA
LS-DP
250 10
190 10
120 10
135 10
LS-DEA
LS-Terpy, liposomes containing 8 are named LS-DPA, liposomes
containing 9 are named LS-DP, and liposomes containing 10
are named LS-DEA, respectively (Fig. 1, ESI†). The metal ion
binding of the blue colour nanometre sized vesicles in solution
was monitored by UV-visible and emission spectroscopy. The
concentration of the final liposome solution was determined
following a literature described method.12
Particle size measurement
Dynamic light scattering (DLS) particle sizing measurements were
performed by a Zetasizer 3000 from Malvern instruments Ltd.
Malvern, UK. Vesicle solutions were diluted 5- to 6-fold and
measured at room temperature keeping a typical count rate at 30–
50 kcps. Each diameter value is an average result of continuous
measurements over 5 min. At least three measurements were
performed for each solution. The measured particle size values
are summarized in Table 1. The obtained values are in good
agreement with comparable liposomes that have been reported
earlier in literature.13 The two-component vesicles have an average
size of 250 nm. Upon UV irradiation, the vesicle size shrinks to
160–200 nm (Fig. 2, ESI†).
Fig. 3 Colour change of functionalized vesicle solutions (1 ¥ 10-4 M) in
water (HEPES buffer, pH = 7.2) upon addition of different metal salts (1 ¥
10-3 M) at room temperature. The solutions were allowed to equilibrate
for 5 min after the salt addition.
The colour change from blue to red was quantified by calculat-
ing the colorimetric response (CR, Table 2).5,14 A systematic change
in the UV-Vis spectra of LS-Terpy, LS-DPA, LS-DP and LS-DEA
associated with varying concentration of different metal ions are
shown in Fig. 4. Spectral and colour change reveal that LS-Terpy
has a slightly higher affinity for Zn2+ ions in water than for Cd2+,
Cu2+, Mn2+ and Hg2+ ions (Fig. 4); terpyridine-type ligands are
known to form stable complexes with zinc ions in the solid state.15
In vesicle solution Zn2+ ions displayed a fast response time (~1 min)
with a detection limit of 2.1 ¥ 10-6 M, which allows the colorimetric
detection of submillimolar concentrations of Zn2+ ions. Other
metal ions like Cd2+ and Hg2+ exhibit a slower response kinetic
and a full colour change is attained in approximately 3–5 min.
The order of metal ion selectivity is Zn2+ > Cd2+ > Hg2+ꢀCu2+or
Ni2+. The metal ion binding properties for LS-Terpy are consistent
with the previously reported results for simple terpyridine ligands.
Fig. 2 Change in absorption spectra of (a) LS-Terpy (1 ¥ 10-5 M) and
(b) LS-DEA (5 ¥ 10-5 M) with different metal ions in aqueous buffer solu-
tion. Chloride salts of Zn2+, Hg2+, Ni2+, Cu2+, Co2+, Cr2+, Mn2+, Mg2+, Ca2+
and nitrate salts of Cd2+, K+, Na+, Pb2+, Li+, Ag+ used for binding studies.
Metal ion binding
The metal ion binding properties of the vesicles LS-Terpy,
LS-DPA, LS-DP and LS-DEA were examined for several alkali,
Fig. 4 Comparative plot of the colorimetric response of receptors with
metals.
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Table 2 Colorimetric response (%CR) aof the receptors with different
Apparent binding constant (log Kapp) values of the vesicular
receptors were derived based on the changes in the absorption
spectra with respect to different concentration of metal salts
(Fig. 5, Fig. 6, Table 3) by using non-linear regression analysis
and assuming a 1 : 1 ligand to metal ion binding at the interface of
the vesicles.11,23
metal ions
Receptor
Cu2+
Cd2+ Mn2+ Zn2+ Ni2+
Hg2+ Ag+
Fe2+
LS-Terpy
LS-DPA
LS-DP
7
9
9
—
38
—
46.6
—
4
62.1
53.5
58.8
—
10
—
—
—
57.2
9.5
13.2
60.1
10
—
—
61
NDb
—
—
49.1
17.2
—
LS-DEA
—
a Li+, Na+, K+, Mg2+, Ca2+, Cr2+, Co2+ and Pb2+ ions did not show any
spectral changes to obtain CR values. b not determined due to high level
of precipitation.
Table 3 Apparent binding constant (log Kapp
vesicular receptors
)
avalues of the metal ion
Metal ion affinity (log Kapp
)
Receptor Cu2+ Cd2+ Mn2+
Zn2+ Ni2+
Fe2+
Hg2+ Ag+
b
LS-Terpy <1.0 5.1
—
5.8
4.3
6.1
—
<1.0
—
—
—
3.4
3.1
3.2
2.3
—
—
—
2.2
LS-DPA
LS-DP
—
—
—
<1.0 5.5
—
—
—
6.2
—
—
—
LS-DEA
—
a Li+, Na+, K+, Mg2+, Ca2+, Cr2+, Ni2+, Co2+, Cu2+ and Pb2+ ions did not
show any significant spectral changes for calculating binding constant.
b Not determined due to high level of precipitation.
However, contrary to a recent report,16 which shows preferable
Hg2+ binding for a terpyridine derivative in DMSO/water (1 : 3.5)
solution, our vesicle immobilized terpyridine ligand displays only
weak interactions with Hg2+ ions and strong binding of Zn2+ and
Cd2+ ions. Terpyridine ligands are known to form manganese
complexes in solution,17 but at the vesicular PDA interface it failed
to coordinate Mn2+ ions.
DPA ligands18 show nanomolar affinity to zinc ions at neutral
pH in the presence of high concentrations of other metal cations.19
LS-DPA discriminates manganese and zinc ions with apparent
log Kapp values of 5.5 and 4.3. The metal cation selectivity
observed for LS-DPA (Table 3) is consistent with the established
binding affinities of the DPA ligands. Ligand 5 (DP) is known
to coordinate with various metals ions in solution, like Mg2+,
Ca2+, Sr2+, Mn2+, Co2+, Cu2+, or Zn2+ under various conditions.20
However, embedded into a vesicle (LS-DP) the ligand responds
only to zinc and cadmium ions in water with nanomolar affinity
(Fig. 4). The metal ion binding selectivity is obviously affected by
the conditions at the lipid–solution interface.
LS-DEA shows a response to the presence of mercury or silver
ions (Table 3) at millimolar concentrations.21 Amide and urea NH
groups have been reported to interact with metal ions like Hg2+.22
To investigate the role of the NH group in LS-DEA for ion binding,
we synthesized the butyl-modified compound 11 for comparison.
Interestingly, vesicles prepared using compound 11 did not show
any significant spectral change with any metal ions tested. This
observation indicates that the amide NH groups are not significant
for the observed metal ion binding and the diethyl amine moiety
acts as a binding site for mercury and silver ions. This illustrates
that the coordination ability of ligands may change significantly at
the lipid-solution interface and a simple N,N-diethyl amino ligand
showing only weak interactions with metal ions in solution phase
can lead to strong ion responses at the vesicle interface.
Fig. 5 UV-visible titration of (a) LS-Terpy (1 ¥ 10-5 M) with zinc ions
(1 ¥ 10-6 M–2 ¥ 10-5 M) (b) LS-DEA (5 ¥ 10-5 M) with mercury ions (1 ¥
10-6 M–5 ¥ 10-2 M) in water, inset: change of absorbance maximum at
610 nm and 510 nm with respect to added Hg2+ ion.
Zinc ions lead to an immediate change in UV-Vis absorption
with all receptors except LS-DEA. Manganese ions induce changes
only with receptor LS-DPA and with a slow response time of
30 min to reach maximum colour change. Cadmium ions do not
induce spectral changes with receptors LS-DPA and LS-DEA, but
interact with LS-Terpy and LS-DP receptors. Mercury ions give
spectral changes in aqueous solution with all receptors, which is
strongest in the case of LS-DEA. We have also conducted control
binding experiments with PDA vesicles that were not modified
with metal ion coordinating groups. No changes in the absorption
spectra and colour of the solution were observed upon the addition
of metal ions. This confirms that the PDA vesicles modification
with metal ion binding ligands is responsible for the spectral and
colour change of the solution
EDTA-addition experiments were conducted to examine the
reversibility of the receptor-metal ion binding event. When EDTA
was added to the red solution of vesicles and metal ions the
spectral change is not reverted to its original blue form. This
result indicates that the metal ion induced colour change of the
vesicles from blue to red is not reversible. Irreversible response
behaviour of different sensors based on PDA is very common in
literature.24 In a control experiment, we have confirmed that EDTA
does not interact with the vesicles in the absence of any metals.
The colour transitions of PDA assemblies have been attributed
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Fig. 6 Titration curves of (a) LS-Terpy, (b) LS-DPA, (c) LS-DP and (d) LS-DEA with different metals in water at room temperature.
to conformational transitions in the conjugated (ene-yne) PDA
backbone, induced by structural perturbations.25,26
Upon addition of metal ions (metal ions which responded
colorimetrically: Zn2+, Mn2+, Cd2+, Hg2+ and Ag+) the emission
intensity centred at 600 nm increases about 20-fold. Other ions
like Li+, Na+, K+, Mg2+, Ca2+, Cr2+, Ni2+, Fe2+, Co2+, Cu2+ and
Pb2+ induced very little or no change in the emission intensity
(Fig. 7) upon addition to the vesicle solution. The relative emission
intensities of the vesicles with different metal cations are shown in
Fig. 3, ESI.†
Based on the observed spectral changes, the response of the
functionalized vesicles to the presence of metal cations can be
summarized as follows: LS-Terpy responds to the presence of zinc
and cadmium ions at nanomolar concentrations affinity, but fails
to respond to manganese ions as observed by others for terpyridine
ligands in homogeneous solutions. LS-DP is selective for zinc
and cadmium ions. LS-DPA responds to the presence of zinc
and manganese ions with high affinity, which is in accordance
to the properties of DPA ligands in solution. LS-DEA selectively
responds to the presence of mercury and silver ions, which is
typically not observed for DEA ligands in solution. Overall,
the incorporation of the ligands into the vesicles changes their
metal ion coordination ability: Different selectivities and increased
affinities compared to solution are observed.
Emission studies
Next, changes in the emission properties of the PDA vesicles in
response to the presence of metal cations were studied. Emission
spectra of the receptors LS-Terpy, LS-DPA, LS-DP and LS-DEA
(5 ¥ 10-5 M in 10 mM HEPES buffer, pH 7.2) show a very weak
emission band centred at 625 nm upon excitation at 510 nm
(Fig. 7).
Effect of metal ions on vesicular particle size
A solution of LS-DP (1 ¥ 10-4 M) was titrated with zinc ions,
and the size of the particles was measured after each addition.
Upon increasing amounts of zinc ions the observed size of the
LS-DP particles increased from 120 nm to ~2800 nm (Fig. 8)
indicating a metal ion induced aggregation.7e,27 The size of the
vesicular particles is not affected upon addition of non-binding
metal ions, such as manganese ions. The experiments reveal that
the aggregation depends on the metal ion binding to the interfaces
Fig. 7 Emission titration of (a) LS-DPA (5 ¥ 10-5 M) with different metal
cations (1 ¥ 10-3 M), (b) emission titration of LS-DPA (5 ¥ 10-5 M) with
manganese ions (1 ¥ 10-6 M–5 ¥ 10-3 M), (c) LS-DP (5 ¥ 10-5 M) with
different cations (1 ¥ 10-3 M), (d) emission titration of LS-DP (5 ¥ 10-5 M)
with zinc ions(1 ¥ 10-6 M–5 ¥ 10-3 M).
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colour change of the test papers from blue to red indicates the
binding of ions to the immobilized vesicle receptors (Fig. 9d).
Conclusions
A series of self assembled polydiacetylene vesicles LS-Terpy,
LS-DPA, LS-DP and LS-DEA has been prepared. The vesicles
display N-heterocyclic ligands at their surfaces and are stable
in solution for a long time if stored at 4 ◦C. Upon addition of
zinc, cadmium, manganese, silver or mercury salts to aqueous
solutions of the vesicles a visible colour change is observed. Metal
complex formation at the interface of the PDA vesicles leads to an
aggregation of the vesicles as confirmed by monitoring the particle
size. The vesicles retain their binding properties in transparent PVA
films and immobilized on paper.
Fig. 8 (a) DLS curves upon addition of Zn2+metal ion in to the LS-DP
(HEPES, pH = 7.2). (b) Particle size measurement of LS-DP with Mn2+
and Zn2+ ions.
of the vesicles. A schematic representation of the process is shown
in Fig. 4, ESI.†
The results show that coordination properties of typical
N-heterocyclic ligands can be transferred onto PDA vesicles by
embedded co-monomers bearing the ligands, but their specific
coordination ability changes at the lipid-solution interface. The
method is easily applied to almost any ligand and may find
applications in the development of analytical nanoparticles or
metal complex immobilization.
Vesicle immobilization in polyvinyl alcohol films and on paper
To investigate if the response of the functionalized vesicles to metal
cations is retained upon immobilization, transparent polyvinyl
alcohol films and coated papers with the polymerized vesicular
receptor were prepared. The blue coloured solution containing
functionalized vesicles was mixed with an aqueous 10 wt%
polyvinyl alcohol (PVA) solution (2 ml, 1 : 1, v/v%)28 and slowly
poured in a Petri dish to form a uniform layer.
Experimental section
After drying at room temperature for 36 h a thin film was formed
in the Petri dish. This blue-coloured transparent film was removed
from the dish (Fig. 9a) and used for binding studies. The metal
ion recognition property of the blue colour films was checked with
different metal ions. Films prepared using LS-DPA were dipped
into an aqueous solution containing zinc ions and within the few
minutes the colour of the film changed to red. However, the film
collapsed due to the water solubility of PVA films (Fig. 9b). In
the presence of non-binding metal ions the film colour remains
blue (Fig. 9c). To immobilize the functionalized vesicles on
water insoluble support, we coated papers with different vesicular
receptor following an earlier reported procedure.6 The obtained
test papers are stable in aqueous solution. The colorimetric
response of LS-Terpy, LS-DPA, LS-DP and LS-DEA coated
papers was examined in the presence of different metal ions. The
Thin layer chromatography (TLC) analyses were performed on
silica gel 60 F-254 with a 0.2 mm layer thickness; compound
detection by UV light at 254 nm/366 nm or ninhydrin staining
in EtOH. Column chromatography was performed on silica gel
(70–230 mesh) from Merck. Starting materials were purchased
from either Acros or Sigma-Aldrich and used without any further
purification. Commercially available solvents of standard quality
were used. Dry THF, which was prepared by distillation from
potassium. If otherwise stated, purification and drying was done
according to accepted general procedures.29
Synthesis and characterization of compounds
Compounds 230 and 331 were synthesised according to known
literature procedures. Other compounds are prepared by the
following synthetic protocols with good yield and purity.
Pentacosa-10,12-diynoic acid 4-[2,2¢;6¢,2¢¢]terpyridin-4¢-yl-
phenyl ester (7). Compound 3 (100 mg, 0.31 mmol) was
dissolved in dry THF under N2 atmosphere and compound 2
(122 mg, 0.32 mmol) and 0.25 mL of Et3N were added. This
◦
reaction mixture was stirred at 0 C overnight then the reaction
mixture was heated to reflux for 1 h. The white coloured salt
formed was filtered and the clear solution was evaporated
to dryness. The crude product was purified by silica column
chromatography using ethyl acetate and petroleum ether as the
eluent. The desired product 7 was collected as the first fraction in
the form of colourless solid. MP: 95–98 ◦C, Yield: 170 mg (75%).
3
1H-NMR (300 MHz, CDCl3): d (ppm) = 0.87 (t, J = 7.1 Hz, 3
3
H, CH3), 1.21 (m, 26 H, CH2), 1.51 (t, J = 7.5 Hz, 4 H, CH2),
1.77 (t, 3J = 7.4 Hz, 2 H, CH2), 2.25 (m, 3J = 7.1 Hz, 4 H), 2.61
(t, 3J = 7.4 Hz, 2 H, CH2), 7.25 (d, 2J = 8.2 Hz, 2 H, Ar–H), 7.35
Fig. 9 (a) Transparent blue colour PVA film with embedded LS-DPA
receptor (b) PVA film with embedded LS-DPA receptor in the presence
of zinc ions (c) with cadmium ions in water (d) test papers prepared from
different vesicular solutions in presence and absence of metal ions.
2
2
(t, J = 5.6 Hz, 2 H, Ar–H), 7.85 (d, J = 7.5 Hz, 2 H, Ar–H),
2
7.93 (d, 2 H, Ar–H), 8.67 (d, J = 7.5 Hz, 2 H, Ar–H), 8.71 (d,
2 H, Ar–H), 8.73 (d, 2 H, Ar–H). 13C-NMR (75 MHz, CDCl3):
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d (ppm) = 171.1,155.1, 154.9, 148.1, 136.4, 135.8, 134.9, 127.4,
122.9, 121.1, 120.4, 117.7, 64.30, 64.18, 33.4, 30.9, 29.9, 28.62,
28.60, 28.58, 28.45, 28.3, 28.1, 27.9, 27.8, 27.7, 27.32, 27.3, 21.7,
18.18, 13.11. Mass: ES-MS (DCM–MeOH+10mM NH4OAc),
m/z (%) = 681.4 (100) [MH+].
the second fraction◦in the form of colourless solid. Yield: 145 mg
1
(68%). MP: 82–85 C, H-NMR (300 MHz, CDCl3): d (ppm) =
3
0.75 (t, J = 7.1 Hz, 3 H, CH3), 1.08 (t, 6 H, CH3), 1.21 (m, 26
3
H, CH2), 1.38 (t, J = 7.5 Hz, 4 H, CH2), 1.49 (t, 2 H, CH2),
3
1.90 (m, 2 H, CH2), 2.11 (m, 6 H, CH2), 2.25 (t, J = 7.1 Hz,
2 H), 2.72–2.89 (m, 6 H, CH2), 3.37 (t, 3 H, –CH2), 5.48 (s, br,
1 H, NH). 13C-NMR (75 MHz, CDCl3): d (ppm): 173.98, 77.5,
77.4, 65.2, 65.20, 51.9, 49.38, 47.4, 47.3, 36.4, 35.5, 31.9, 30.7,
29.6, 29.6, 29.55, 29.52, 29.4, 29.3, 29.2, 29.13, 29.05, 28.9, 28.8,
28.7, 28.3, 28.3, 25.6, 22.6, 19.1, 19.12, 17.6, 14.1. MS: ESI-MS
(dichloromethane–MeOH+10mM NH4OAc), m/z (%) = 473.3
(100). HRMS (EI-MS): Calcd. for C31H56N2O [M+]: 472.4393.
Found 472.4386.
Pentacosa-10,12-diynoic acid bis-pyridin-2-ylmethyl-amide(8).
Compound 4 (125 mg, 0.63 mmol) was dissolved in dry
dichloromethane under N2 atmosphere, to this solution compound
1 (246.5 mg, 0.63 mmol), DMAP (76.8 mg, 0.63 mmol) and DCC
(144 mg, 0.7 m mol) was added. This reaction mixture was stirred
at room temperature for 24 h, and then the reaction mixture
was filtered and the clear solution was evaporated to dryness.
The crude product was purified by silica column chromatography
using dichloromethane and petroleum ether as the eluent. The
desired compound 8 was collected as colourless◦solid in the
second fraction. Yield: 230 mg (68%). MP: 95–100 C. 1H-NMR
Pentacosa-10,12-diynoic acid butylamide (11). Butyl amine 6a
(73 mg, 1 mmol) was dissolved in dry THF under N2 atmosphere,
to this solution compound 2 (393 mg, 1 mmol), dissolved in dry
THF and dry Et3N (0.2 ml) was added. This reaction mixture
was stirred at 0◦ C for 4 h and 16 h at room temperature.
Then the reaction mixture was filtered and the clear solution was
evaporated to dryness, the crude product was purified by silica
column chromatography using dichloromethane and petroleum
ether as the eluent. The desired product was collected as the second
fraction in the form of colourless solid. Yield: 400 mg (81%).
3
(300 MHz, CDCl3): d (ppm) = 0.81 (t, J = 7.1 Hz, 3 H, CH3),
3
1.40 (s, 26 H, CH2), 1.51 (t, J = 7.5 Hz, 4 H, CH2), 1.66 (t, 2
3
H, CH2), 2.21 (t, J = 7.1 Hz, 4 H), 2.42 (t, 2 H, –CH2), 4.73 (s,
2 H, CH2), 4.79 (s, 2H, CH2), 7.15–7.35 (m, 4 H, Py), 7.65 (t, 2
H, Py), 8.56–8.48 (dd, 2 H, Py). 13C-NMR (75 MHz, CDCl3): d
(ppm) = 174.15, 157.5, 156.9, 149.8, 148.8, 137.0, 122.6, 120.6,
65.2, 65.23, 54.02, 49.6, 33.1, 31.9, 29.6, 29.4, 29.36, 29.28, 29.23,
29.10, 28.94, 28.87, 28.78, 28.36, 28.31, 25.16, 22.7, 19.2, 14.1. MS:
ES-MS (DCM–MeOH+10mM NH4OAc), m/z(%) = 556.3(100)
[MH+]. HRMS (EI-MS): Calcd for C37H53N3O [M+]: 555.4189.
Found 555.4186.
3
1H-NMR (300 MHz, CDCl3): d (ppm) = 0.84 (t, J = 7.0 Hz,
3 H, CH3), 0.89 (t, 3 H, CH3), 1.15–1.32 (m, 28 H, CHz), 1.45 (m,
6 H, CH2), 1.55 (t, 3J = 7.2 Hz, 2 H, CH2), 2.09 (t, 3J = 7.6 Hz,
2 H), 2.20 (m, 4 H, CH2), 3.20 (t, 2 H, CH2), 5.42 (br, s, 1 H, NH).
13C-NMR (75 MHz, CDCl3): d (ppm) = 173.02, 77.61, 65.28,
65.22, 39.19, 36.90, 31.93, 31.77, 30.32, 29.64, 29.62, 29.66, 29.49,
29.36, 29.23, 29.17, 29.11, 28.92, 28.87, 28.75, 28.36, 28.29, 25.79,
22.70, 20.09, 19.22, 19.19, 14.14.
Pentacosa-10,12-diynoic acid di-pyridin-2-yl-amide (9). Com-
pound 9 was prepared by following the same method as above. 2,
2¢-Dipyridyl amine, 5 (100 mg, 0.58 mmol) was dissolved in dry
dichloromethane under N2 atmosphere, to this solution compound
1 (224 mg, 0.60 mmol), DMAP (73 mg. 0.60 mmol) and DCC
(123 mg, 0.60 m mol) were added. This reaction mixture was
stirred at room temperature for 32 h, and then the reaction mixture
was filtered and the clear solution was evaporated to dryness.
The crude product was purified by silica column chromatography
using dichloromethane and petroleum ether as the eluent. The
desired product was collected as the second fraction in the form
Acknowledgements
We thank the Deutsche Forschungsgemeinschaft for support of
this work. D.A.J. thanks the Alexander von Humboldt foundation
for a fellowship
1
of colourless solid. Yield: 250 mg (72%). H-NMR (300 MHz,
CDCl3): d (ppm) = 0.87 (t, 3J = 6.8 Hz, 3 H, CH3), 1.25–1.33 (m,
26 H, CH2), 1.51 (m, 24 H, CH2), 1.69 (t, 2 H, CH2), 2.23 (t, 3J =
6.8 Hz, 4 H), 2.40 (d, 2 H, J = 7.8 Hz, CH2), 6.87 (t, 2H, Ar–H),
7.62 (m, 4 H, Ar–H), 8.21 (t, 2 H, Ar–H). 13C-NMR (75 MHz,
CDCl3): d (ppm) = 173.4, 154.1, 148.0, 147.1, 138.1, 116.2, 112.1,
106.5, 77.6, 77.5, 65.3, 39.1, 29.7, 29.64, 29.62, 29.49, 29.36,
29.32, 29.23, 29.19, 28.96, 28.87, 28.82, 28.36, 25.38, 22.71, 19.21,
14.14. MS: ES-MS (DCM–MeOH+10mM NH4OAc), m/z(%) =
528.6(50) [MH+].
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The Royal Society of Chemistry 2010
©