A conjugated hydrogen bond receptor for attachment to gold

Article abstract of DOI:10.1007/s10847-010-9903-4

A fully conjugated host molecule (in order to allow conductivity) with a hydrogen bonding motif for molecular recognition (six hydrogen bonds in the Hamilton receptor array) on one end and a sulfur unit for immobilization on gold at the other end has been

Full text of DOI:10.1007/s10847-010-9903-4

J Incl Phenom Macrocycl Chem (2011) 71:239–242
DOI 10.1007/s10847-010-9903-4
SHORT COMMUNICATION
A conjugated hydrogen bond receptor for attachment to gold
•
Christian Glockner Ulrich Lu¨ning
Received: 6 September 2010 / Accepted: 6 November 2010 / Published online: 1 December 2010
ꢀ Springer Science+Business Media B.V. 2010
Abstract A fully conjugated host molecule (in order to
allow conductivity) with a hydrogen bonding motif for
molecular recognition (six hydrogen bonds in the Hamilton
receptor array) on one end and a sulfur unit for immobi-
lization on gold at the other end has been synthesized and
its binding to gold clusters has been investigated by fluo-
rescence spectroscopy.
be created easily during the production process of the
nanowire in a thin-film crack [4–6].
A molecular recognition reaction could be used to
bridge the nanoscopic gaps (at least partially). Immobili-
zation of host molecules within the nanogaps should pro-
vide a change in electric resistance of the whole nanowire
via partial bridging of the gaps, based on electron hopping
and tunneling. After the addition of suitable guest mole-
cules and formation of host–guest complexes in these gaps,
conductivity should increase even more due to further
bridging (see Fig. 3).
Keywords Colloidal gold ꢀ Gold surface ꢀ Hydrogen
bond ꢀ Molecular recognition ꢀ Nanoparticles ꢀ Thiol
With this approach, unlike the FET concept, it should be
possible not only to detect charged but also neutral mole-
cules, and a carefully chosen recognition site shall allow to
detect guest molecules selectively. Furthermore, nanowires
with nanogaps have an even higher surface-to-volume ratio
than ‘‘classic’’ nanowires and should therefore in general
provide even higher sensitivity.
Introduction
The strength of the sulfur–gold bond [2] between thiols and
this precious metal is exploited when gold surfaces or gold
nanoparticles are to be functionalized. Due to the excellent
conductance of gold, functionalized gold can be incorpo-
rated into microelectronic devices. During the last years,
nanowires have been functionalized and used as field effect
transistors (FETs) for detection of molecular species like
certain amino acids [3], for example. An inherent disad-
vantage with the FET concept, however, is that the desired
molecules must be charged to allow detection. An alter-
native might be the use of nanoscopic gold wires which
contain many nanoscopic gaps and are thus different from
what is usually referred to as a ‘‘nanowire’’. Such gaps can
In order to be able to change the conductivity of such a
nanowire by molecular recognition, a respective host
molecule has to be attached to a conducting moiety which
itself is able to bind to the surface of gold nanoclusters. As
an electrically conducting linker, an arylethyne backbone
was chosen [7] which carries a sulfur atom at one end and
can be coupled to the recognition site at the other terminus
for instance by a Sonogashira reaction (see Fig. 1).
One of the aryl rings in 1 carries a methyl group, as
described [7], hopefully increasing solubility. A V-shaped
‘‘Hamilton receptor’’ [8] for barbiturates such as 2 and
related molecules was chosen as the recognition site. This
host molecule recognizes its counterpart by formation of
six hydrogen bonds (Fig. 1, hydrogen bond donor and
acceptor atoms are printed bold). With a non-conjugated
linker, such a system has already been connected to a gold
surface by a thiol linkage [9].
Multiple hydrogen bonds, Part 7. Part 6: see [1].
C. Glockner ꢀ U. Lu¨ning (&)
Otto-Diels-Institut fu¨r Organische Chemie,
¨
Christian-Albrechts-Universitat zu Kiel,
Olshausenstr. 40, 24098 Kiel, Germany
e-mail: luening@oc.uni-kiel.de
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J Incl Phenom Macrocycl Chem (2011) 71:239–242
Fig. 1 Sulfur terminated
arylethyne analog of a
O
N
‘‘Hamilton receptor’’ 1 in
protected (1a) and deprotected
form (1b) for immobilization on
gold, and diethylbarbiturate (2)
which can be recognized via six
hydrogen bonds
O
O
N
N
H
H
H
N
N
O
O
N
N
H
H
RS
O
H
1
N
O
2
R = CH2CH2SiMe3
R = H
a
b
Experimental
to vendor: 3–6 nm) has been used. In a first set of mea-
surements, we investigated the adsorption of 1a onto gold
clusters (Fig. 2a), in a second set of experiments we
deprotected the sulfur unit by reaction of 1a with tetra-n-
butylammonium fluoride (TBAF) to give the free thiol 1b
(Fig. 2b). Fluorescence spectra were recorded of both
mixtures in concentrated and diluted form.
The arylethyne linker was synthesized as described [7],
thus containing the thiol unit protected as a trimethylsi-
lylethyl thioether. The Hamilton receptor was synthesized
as its 5-iodo derivative as described by Brammer [10].
These two fragments were joint by Sonogashira coupling,
and the resulting receptor 1a (Fig. 1) was isolated from the
product mixture by chromatography besides the Glaser
homocoupling product of the ethyne. 1a was fully char-
acterized, and its host properties were controlled by
1H NMR titration in chloroform at 298 K giving an asso-
ciation constant between 1a and diethylbarbiturate (2) of
When the solution of 1a was mixed with gold clusters,
fluorescence in the resulting spectrum decreased signifi-
cantly. This shows that binding of 1a to gold surfaces is
possible even in the protected form, which is predicted for
other thioethers by literature [12]. In the following exper-
iment, the mixture was diluted to one-third of its concen-
tration. If the molecules were bound strongly to the surface,
one would expect that fluorescence intensity decreased to
nearly one-third. This is not the case, consequently, 1a is
only physically adsorbed on gold nanoclusters and desorbs
upon dilution.
40000 M-1
.
Next, the interaction of the new Hamilton receptor with
gold surfaces was investigated. It is a well known fact [11]
that gold surfaces can quench the fluorescence of adsorbed
molecules, so we have used fluorescence spectroscopy to
prove that 1, which is a fluorophore, can bind to nanoscopic
gold. In this work, a commercially available colloidal gold
solution in toluene (diameter of the gold clusters according
But when the sulfur function in 1a was deprotected by
addition of TBAF to give the free thiol 1b, fluorescence
decreased upon dilution (Fig. 2).
75
(b)
(a)
150
50
25
0
100
50
0
350
375
400
425
350
375
400
425
/nm
/nm
Fig. 2 Fluorescence spectra: a straight curve (top): 1a (120 nmol L-1
in toluene), dotted curve: colloidal gold solution (0.005 % in toluene),
dashed curve: 1:1 mixture of 1a and gold solution (at least 70 surface
gold atoms per host molecule available), straight curve (bottom):
mixture diluted to one-third (toluene). b straight curves (from top to
bottom): diluted mixture of the first measurements (a) after the
addition of 1 mg of TBAF after 15 min, 40 min, 2 h, 15 h; dashed
curve: dilution again to one-third (toluene, after 15 h)
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J Incl Phenom Macrocycl Chem (2011) 71:239–242
241
a
b
Fig. 3 Schematic
representation of a single
nanowire gap in a conductivity
measurement setup. The
distance a after attachment of
conducting host molecules to
the gold clusters (in grey) is
considerably larger than the
remaining distance b when
conducting guests are bound.
The recognition domains are
shown schematically
n
n
n
S
n
(
n
)
(
n
)
S
Au
S
S
n
Au
S
(
)
(
)
n
n
S
n
n
n
Results and Discussion
(KBr) n~u/cm-1 = 3409, 3276, 2959 (aliph. CH), 2207
(C : C), 1676 (CONH), 1585 (C = O), 1499 (C = C),
1448, 1261, 1086, 800. 1H NMR (600 MHz; CDCl3):
d/ppm = 0.06 (9 H, s, SiMe3), 0.92–0.98 (8 H, m, SiCH2,
aliph. Me), 1.41 (4 H, mc, CH2CH2CH2Me), 1.72 (4 H, mc,
CH2CH2CH2Me),2.40(4H,t,J = 7.8 Hz, CH2CH2CH2Me),
2.49 (3 H, s, arom. Me), 2.99 (2 H, mc, SCH2), 7.22–7.25 (2 H,
m, Ar00-2,6-H), 7.31–7.34 (1 H, m, Ar0-6-H), 7.39 (1 H, mc,
Ar0-3-H),7.41–7.45(3H, m,Ar0-5-H, Ar00-3,5-H),7.73(2H,t,
J = 8.2 Hz, Pyr-4-H), 7.91 (2 H, br s, nBuCONH), 7.97 (2 H,
d, J = 8.4 Hz, Pyr-5-H), 8.00 (2 H, d, J = 8.2 Hz, Pyr-3-H),
8.16 (2 H, d, J = 1.9 Hz, Ar-4,6-H), 8.35 (1 H, t, J = 1.7 Hz,
Ar-2-H), 8.53 (2 H, br s, ArCONH). 13C NMR (150 MHz;
CDCl3): d/ppm = -1.74 [q, Si(Me3)3], 13.78 (q, aliph. Me),
16.69 (t, SiCH2), 20.63 (q, arom. Me), 22.34
(t, CH2CH2CH2Me), 27.42 (t, CH2CH2CH2Me), 28.94
(t, SCH2), 37.52 (t, CH2CH2CH2Me), 89.34 (s, Ar0CCAr00),
91.03 (s, ArCCAr0), 91.34 (s, Ar0CCAr00), 92.42 (s, ArCCAr0),
109.71 (d, Pyr-5-C), 110.31 (d, Pyr-3-C), 119.71 (s, Ar00-1-C),
121.75 (s, Ar0-4-C), 124.07 (s, Ar0-1-C), 125.17 (d, Ar-2-C),
125.36 (s, Ar-5-C), 127.82 (d, Ar00-3,5-C), 128.89 (d, Ar0-5-
C), 131.93 (d, Ar0-6-C), 132.06 (d, Ar0-3-C), 132.57 (d, Ar00-
2,6- C), 133.36 (d, Ar-4,6-C), 135.16 (s, Ar-1,3-C), 138.87
(s, Ar00-4-C), 140.52 (s, Ar0-2-C), 140.97 (d, Pyr-4-C), 149.15
(s, Pyr-6-C), 149.86 (s, Pyr-2-C), 163.73 (s, ArCONH),
171.83 (nBuCONH). ESI (MeOH): m/z = 863 (M??H,
21%), 879 (4, M??H ? O).
As a conclusion, we have synthesized a molecule 1 with a
conjugated p-system allowing molecular recognition of
cyanurates or barbiturates (e. g. 2). Its binding to gold
clusters in solution has been shown, next, it shall be
attached to gold clusters in nanowire gaps for conductivity
measurements (Fig. 3).
Synthesis and characterization of 5-(2-Methyl-4-{4-[2-
(trimethylsilyl)ethylsulfanyl]phenylethynyl}
phenylethynyl)-N,N0-bis(6-valeroylaminopyrid-2-yl)
isophthalic acid diamide 1a
5-Iod-N,N0-bis(6-valeroylaminopyrid-2-yl)isophthalic acid
diamide[10] (46.6 mg, 72.6 lmol), bis(dibenzylideneace-
tone)palladium(0) (4.1 mg, 7.1 lmol), triphenylphosphine
(10.5 mg, 40.1 lmol)andcopper(I)iodide(2.5 mg, 13 lmol)
were dissolved in dry N,N-dimethylformamide (20 mL) and
dry diisopropylamine (10 mL) under an atmosphere of
nitrogen and hydrogen (1:1). 1-Ethynyl-2-methyl-{[4-(2-(tri-
methylsilyl)ethylsulfanyl]phenylethynyl}benzene (21.3 mg,
61.2 lmol) indryN,N-dimethylformamide (5 mL)wasadded
and the mixture was heated for 4 d to 70 ꢁC. After the addition
of chloroform (50 mL) and aqueous sodium bicarbonate
(0.6 N, 50 mL), the layers were separated, and the aqueous
layer was extracted with chloroform (2 9 40 mL). The
combined extracts were dried with sodium sulfate, and the
solvent was evaporated under reduced pressure. The residue
was purified by column chromatography (silica gel, cyclo-
hexane/ethyl acetate, 3:2) to yield 12 mg (23%) of 1a. M.p.
95 ꢁC. (Found: C, 68.1; H, 6.3; N, 9.6; S, 3.6. Calc. for
C50H54N6O4SSi• H2O: C, 68.15; H, 6.4; N, 9.5; S, 3.6.). IR
Fluorescence measurements
All spectra have been recorded with a Perkin–Elmer LS 22
spectrometer. Excitation wavelength for all measurements
was 320 nm.
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Acknowledgement The support of the Deutsche Forschungsge-
meinschaft (Lu 378/15) is gratefully acknowledged.
6. Elbahri, M., Jebril, S., Wille, S., Adelung, R.: Simple ways to
complex nanowires and their application. Adv. Solid State Phys.
48, 27–38 (2009)
7. Yu, C.J., Chong, Y., Kayyem, J.F., Gozin, M.: Soluble ferrocene
conjugates for incorporation into self-assembled monolayers.
J. Org. Chem. 64, 2070–2079 (1999)
References
8. Chang, S.K., Hamilton, A.D.: Molecular recognition of biologi-
cally interesting substrates: synthesis of an artificial receptor for
barbiturates employing six hydrogen bonds. J. Am. Chem. Soc.
110, 1318–1319 (1988)
9. Motesharei, K., Myles, D.C.: Molecular recognition on func-
tionalized self-assembled monolayers of alkane thiols on gold.
J. Am. Chem. Soc. 120, 7328–7336 (1998)
¨
10. Brammer, S.: Ph.D. Thesis, Christian-Albrechts-Universitat zu
Kiel (2001)
11. Dulkeith, E., Morteani, A.C., Niedereichholz, T., Klar, T.A.,
Feldmann, J., Levi, S.A., van Veggel, F.C.J.M., Reinhoudt, D.N.,
1. Taubitz, J., Lu¨ning, U.: The AAAAꢀDDDD hydrogen bond
dimer. Synthesis of a soluble sulfurane as AAAA domain and
generation of a DDDD counter part. Aust. J. Chem. 62,
1550–1555 (2009)
2. Nuzzo, R.G., Fusco, F.A., Allara, D.L.: Spontaneously organised
molecular assemblies. J. Am. Chem. Soc. 109, 2358–2368 (1987)
3. Cui, Y., Wei, Q., Park, H., Lieber, C.M.: Nanowire nanosensors
for highly sensitive and selective detection of biological and
chemical species. Science 293, 1289–1292 (2001)
4. Adelung, R., Aktas, O.C., Franc, J., Biswas, A., Kunz, R., El-
bahri, M., Kanzow, J., Schu¨rmann, U., Faupel, F.: Strain-con-
trolled growth of nanowire within thin-film cracks. Nat. Mater. 3,
375–379 (2004)
¨
Moller, M., Gittins, D.I.: Fluorescence quenching of dye mole-
cules near gold nano particles: radiative and non radiative effects.
Phys. Rev. Lett. 89, 203002 (2002)
5. Jebril, S., Elbahri, M., Titazu, G., Subannajui, K., Essa, S.,
¨
12. Jung, C., Dannenberger, O., Xu, Y., Buck, M., Grunze, M.: Self
assembled monolayers from organic sulfur compounds: a com-
parison between sulfides, disulfides and thiols. Langmuir 14,
1103–1107 (1998)
Niebelschu¨tz, F., Rohlig, C.-C., Cimalla, V., Ambacher, O.,
Schmidt, B., Kabiraj, D., Avasti, D., Adelung, R.: Integration of
thin film fracture based nanowires into microchip fabrication.
Small 4, 2214–2221 (2008)
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