Formation of double helix self-assembled monolayers of ethynylhelicene oligomer disulfides on gold surfaces

Article abstract of DOI:10.1016/j.tet.2011.06.024

Optically active ethynylhelicene pentamers and hexamers linked by disulfide bonds were synthesized. They formed self-assembled monolayers (SAMs) with double helix structure on gold surfaces, which were analyzed by infrared reflection-absorption spectroscopy (IR-RAS), quartz crystal microbalance (QCM), surface plasmon resonance (SPR), and circular dichroism (CD). Double helix SAMs could be formed on gold surfaces either from double helices or random coils in solution. The double helices on the surface were more stable than in solution. This result suggested the presence of strong intercomplex interactions between double helix complexes on the surface.

Full text of DOI:10.1016/j.tet.2011.06.024

Tetrahedron 67 (2011) 5972e5978
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Formation of double helix self-assembled monolayers of ethynylhelicene oligomer
disulfides on gold surfaces
Koji Yamamoto a, Hiroki Sugiura a, Ryo Amemiya a, Haruo Aikawa b, Zengjian An c,
,
c
,
c
,
,d
Masahiko Yamaguchi a , Masashi Mizukami d, Kazue Kurihara c
*
a Department of Organic Chemistry, Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba 6-3, Sendai 980-8578, Japan
b International Advanced Research and Education Organization, Tohoku University, Aoba 6-3, Sendai 980-8577, Japan
c WPI Advanced Institute for Materials Research, Tohoku University, Aoba 6-3, Sendai 980-8577, Japan
d Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba, Sendai 980-8577, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 May 2011
Received in revised form 9 June 2011
Accepted 10 June 2011
Available online 16 June 2011
Optically active ethynylhelicene pentamers and hexamers linked by disulfide bonds were synthesized.
They formed self-assembled monolayers (SAMs) with double helix structure on gold surfaces, which
were analyzed by infrared reflection-absorption spectroscopy (IR-RAS), quartz crystal microbalance
(QCM), surface plasmon resonance (SPR), and circular dichroism (CD). Double helix SAMs could be
formed on gold surfaces either from double helices or random coils in solution. The double helices on the
surface were more stable than in solution. This result suggested the presence of strong intercomplex
interactions between double helix complexes on the surface.
Keywords:
Ethynylhelicene oligomer
Double helix
Ó 2011 Elsevier Ltd. All rights reserved.
Self-assembled monolayer
Thermal stability
Intercomplex interaction
1. Introduction
m-phenylene formed double helices in organic solvents.7,8 Ethy-
nylhelicene oligomers reversibly changed their structures between
Grafting simple small organic molecules, in general alka-
nethiols, on gold surfaces by metalesulfide bonds is a well-
established method to form self-assembled monolayers (SAMs)
on solid surfaces.1 If SAMs can be formed by multifunctional or-
ganic macromolecules possessing thiol groups, surface materials
with various functions can be obtained. Attempts have been made
using DNA, which reversibly forms double helices. However, elec-
tronic repulsions between DNA molecules resulted in low surface
densities of the molecules,2 and densely coated monolayers on gold
surfaces have been obtained only in exceptional cases.3,4 Synthetic
oligomers, which can form double helices, have recently been de-
veloped,5,6 and it was of interest to examine functional SAMs made
from such macromolecules. The SAM formation study of synthetic
double helix macromolecules double helices, however, has been
challenging, owing to the difficulty in forming and detecting the
double helix structures on solid surfaces.
random coil and double helix, and both the stability of double helix
and the unfolding process were affected by temperature, concen-
tration, and solvent. The structural change could be conveniently
detected by CD, taking advantage of extremely large changes in D3
values extending over three orders of magnitude.
It was of interest to determine whether such multifunctional
macromolecules can form SAMs on gold surfaces through a single
metal thiolate bond, which is a very small part of the macromole-
cule. Double helix formation on a solid surface may be detected by
taking advantage of the very large D3 values of the double helix
itself. Described in this report are the synthesis and SAM formation
of the ethynylhelicene oligomers with disulfide linkages. The for-
mation of double helices on gold surfaces was analyzed by CD as
well as infrared reflection-absorption spectroscopy (IR-RAS), quartz
crystal microbalance (QCM), and surface plasmon resonance (SPR).
We previously reported that optically active ethynylhelicene
oligomers containing 1,12-dimethylbenzo[c]phenanthrene and
2. Results and discussion
2.1. Synthesis
Disulfides (P)-1, (P)-2, and (P)-3 were synthesized from trimer
(P)-4, pentamer (P)-5, and hexamer (P)-6, respectively, possessing
* Corresponding author. Tel.: þ81 22 795 6812; fax: þ81 22 795 6811; e-mail
address: yama@mail.pharm.tohoku.ac.jp (M. Yamaguchi).
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.06.024

K. Yamamoto et al. / Tetrahedron 67 (2011) 5972e5978
5973
organothio terminal groups, which in turn were obtained by a one-
direction oligomer synthesis starting from (P)-7 (Scheme 1). The
coupling and deprotection sequences of (P)-7 with building block
(P)-8 gave trimer (P)-9, pentamer (P)-10, and hexamer (P)-11. Then,
the reaction with 1-(3-bromopropyl)-4-iodobenzene 12 converted
these oligomers to 3-bromopropylated derivatives, which were
reacted with potassium thioacetate, affording thioesters (P)-4, (P)-
5, and (P)-6. Dethioacetylation and oxidation to disulfides of the
thioesters were conducted by treating the thioesters in toluene/
pyrrolidine mixture under oxygen atmosphere at room tempera-
ture for 2 h, and (P)-1, (P)-2, and (P)-3 were obtained in 88, 65, and
61% yield, respectively.
(P)-2 (0.1 mM), and (P)-3 (0.1 mM) in trifluoromethylbenzene at
room temperature for 24 h. The plates were washed with tri-
fluoromethylbenzene and dried by argon blowing. IR-RAS analyses
of (P)-1, (P)-2, and (P)-3 grafted plates exhibited CeH bond
stretching at 2856, 2927, and 2956 cmꢀ1, and carbonyl absorption
at 1728 cmꢀ1 (Fig.1), which confirmed the adsorption of (P)-1, (P)-2,
and (P)-3 on the surface.
Fig. 1. IR-RAS spectra of monolayers on a gold surface. SAMs were prepared by im-
mersion in solution of (a), (b) (P)-1 (0.1 mM toluene), (c), (d) (P)-2 (0.1 mM tri-
fluoromethylbenzene), and (e) and (f) (P)-3 (0.1 mM trifluoromethylbenzene) at rt for
24 h. After 24 h, the plates were washed with (a), (b) toluene, (c), (d), (e), and (f)
trifluoromethylbenzene and dried by nitrogen blowing.
The transmission CD spectrawereobtained for quartz plates with
an 8-nm-thick gold layer.9 The plate obtained by immersion in (P)-1
solution did not show appreciable peaks, whereas (P)-2 and (P)-3
plates exhibited a positive Cotton effect at 364 nm and a negative
effect at 325 nm (Fig. 2). These spectra were very similar in shape to
those of (P)-2 and (P)-3 in trifluoromethylbenzene (Fig. S4), and
indicated the formation of double helices on the surface. The lack of
Scheme 1. Synthesis of (P)-1, (P)-2, and (P)-3. Conditions: (a) (P)-8, [Pd2(dba)3]$CHCl3,
CuI, Mes3P, Ph3P, n-Bu4NI, NEt3, DMF/THF, 45 ꢁC; (b) Bu4NF, THF, 0 ꢁC; (c) 1-(3-
bromopropyl)-4-iodobenzene 12, [Pd2(dba)3]$CHCl3, CuI, Mes3P, Ph3P, n-Bu4NI, NEt3,
DMF/THF, 45 ꢁC; (d) KSAc, DMA/THF, rt; (e) toluene/pyrrolidine, rt, O2.
dba¼dibenzylideneacetone, DMF¼N,N-dimethylformamide, Mes¼mesityl, Tf¼tri-
fluoromethanesulfonyl, Ac¼acetyl, DMA¼N,N-dimethylacetoamide.
The disulfides (P)-2 and (P)-3 formed intramolecular double
helices in trifluoromethylbenzene (0.1 mM) as indicated by their
typical CD spectra as well as VPO analysis (Figs. S2 and S3), and (P)-
1 was likely to be in the random coil state under the same condi-
tions, as indicated by the CD spectra (Fig. S4).
2.2. Double helix monolayer formation
Fig. 2. CD spectra of SAMs of (P)-1, (P)-2, and (P)-3 grafted gold-coated quartz plates.
SAMs were prepared by immersion in solution of (P)-1 (0.05 mM tri-
fluoromethylbenzene), (P)-2, and (P)-3 (0.1 mM trifluoromethylbenzene) at rt for 24 h.
Glass plates (1 mm thick) coated with a 200e250-nm-thick gold
layer were immersed in solutions of the disulfides (P)-1 (0.05 mM),

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K. Yamamoto et al. / Tetrahedron 67 (2011) 5972e5978
a Cotton effect for the (P)-1 plate was due to the random coil state of
this compound on the surface as well as in solution. It should be
emphasized that the surface double helix structure of (P)-2 and (P)-3
could be detected by CD. Such observation of surface monolayer
macromolecules by CD has not been reported before, and the ad-
vantage of the extremelystrong Cottoneffects of (P)-2 and (P)-3 with
the double helix form was used in the analysis.
suggestion that a monolayer of double helix (P)-2 and (P)-3 formed
on the gold surface.
The surface analyses indicated the dense monolayer formation
of (P)-2 and (P)-3 with double helix structures on the gold surface.
Assuming homogeneous surfaces, the double helix structure was
estimated to be 4e5 nm in height with 3 nm in diameter, which are
reasonable dimensions for the molecules.
Ethynylhelicene octamer (P)-13 lacking the disulfide group
formed double helix in trifluoromethylbenzene at 1 mM.8 A gold
plate was immersed in the trifluoromethylbenzene solution of (P)-
13, and this plate showed no Cotton effect (Fig. S5). The result
suggested that oligomers (P)-1, (P)-2, and (P)-3 were adsorbed on
the gold surface by covalent SeAu bonds.
Quartz crystal microbalance (QCM) analyses were conducted for
gold electrodes treated with (P)-2 or (P)-3 in order to determine the
amount of compounds on the surface: (P)-2, 57ꢂ6 ng on 0.392 cm2
plate; (P)-3, 61ꢂ6 ng on 0.392 cm2 plate. From these results, the
values of the area per molecule on the surface were estimated: (P)-
2, 6.5ꢂ0.6 nm2/molecule; (P)-3, 7.3ꢂ0.6 nm2/molecule. Assuming
cylindrical structures of the double helix, diameters were calcu-
lated: (P)-2, 2.8ꢂ0.2 nm; (P)-3, 3.0ꢂ0.2 nm. These values were
consistent with dense monolayer formation of these compounds on
the gold surface (Table 1).
2.3. Grafting of oligomer in random coil state
In these experiments, the grafting of (P)-2 and (P)-3 on gold (P)-
2 and (P)-3 formed double helix structures. Then, it was of interest
to compare grafting of (P)-2 and (P)-3 in a random coil state. Quartz
plates with 8-nm-thick gold layers were immersed in a THF solu-
tion of (P)-2 (0.1 mM, 20 ꢁC) for 24 h, in which (P)-2 was in random
coil state (Fig. S6a). The CD spectra of the plate was identical to that
obtained by grafting in trifluoromethylbenzene, in which (P)-2
adopted a double helix structure. The result showed that (P)-2 was
grafted with a double helix structure on the surface from the so-
lution of random coil as well as of double helix (Fig. 4a). Similarly,
SAMs of (P)-3 were prepared by immersion in a THF solution of (P)-
3 (0.1 mM, 20 ꢁC), in which (P)-3 was an approximately 1:3 mixture
of double helix and random coil as indicated by CD (Fig. S6b). The
CD spectra of SAMs prepared from THF solution were again iden-
tical to that prepared from trifluoromethylbenzene solution
(Fig. 4b). Since trimer (P)-1 was adsorbed on the surface in a ran-
dom coil state, random coils of (P)-2 and (P)-3 could be also grafted.
Random coils of (P)-2 and (P)-3 probably converted into a double
helix on the surface. Strong interactions between the double helix
complexes on the surface might have promoted double helix for-
mation of initially grafted random coils of (P)-2 and (P)-3.
Table 1
Results of QCM analysis. SAMs were prepared by immersion in solution of (P)-2 or
(P)-3 (0.1 mM trifluoromethylbenzene) at rt for 24 h. After 24 h, the plates were
washed with chloroform
(P)-2
(P)-3
D
D
f (Hz)
42ꢂ5
46ꢂ5
m (ng/0.392 cm2)
57ꢂ6
61ꢂ6
Area per molecule (nm2/molecule)
Diameter (nm)
6.5ꢂ0.6
2.8ꢂ0.2
7.3ꢂ0.6
3.0ꢂ0.2
The presence of such strong intercomplex interactions was also
suggested by attempted mixed grafting experiments of these
compounds with an alkanethiol. Plates with gold layers were im-
mersed in trifluoromethylbenzene solutions of (P)-2 or (P)-3
(0.1 mM) and 1-decanethiol (20 mM). CD spectra (Fig. 5) and IR-RAS
spectra (Figs. 1 and S7) of the plates did not markedly change
Surface plasmon resonance (SPR) analyses were conducted to
determine the thickness of the double helices on the gold layer (ca.
50 nm) on glass (Fig. 3). The thickness was determined by curve
fitting the calculated and experimental SPR reflectivity curve: (P)-2,
3.9ꢂ0.1 nm; (P)-3, 4.5ꢂ0.3 nm. The height of the longer oligomer
(P)-3 was slightly greater than that of (P)-2, which supported the
Fig. 3. Calculated (red line) and experimental (dotted line) SPR reflectivity curve for
a bare gold layer and a gold layer covered by a (upper) (P)-2 and (bottom) (P)-3
monolayer. SAMs were prepared by immersion in solution of (P)-2 or (P)-3 (0.1 mM
trifluoromethylbenzene) at rt for 24 h. After 24 h, the plates were washed with
chloroform and dried by nitrogen blowing.
Fig. 4. CD spectra of SAM of (a) (P)-2 and (b) (P)-3 on gold. SAMs were prepared by
immersion in solution of (P)-2 (0.1 mM) (a, blue line) in tetrahydrofuran, (a, red line) in
trifluoromethylbenzene, or (P)-3 (0.1 mM) (b, blue line) in tetrahydrofuran, (b, red line)
in trifluoromethylbenzene at 20 ꢁC for 24 h.

K. Yamamoto et al. / Tetrahedron 67 (2011) 5972e5978
5975
(0.1 mM), (P)-2 and (P)-3 unfolded to random coils by heating at
60e90 ꢁC (Fig. S8). These results showed that the double helix was
more stable on the gold surface than in solution, which may again
be ascribed to strong intercomplex interactions between the dou-
ble helix (P)-2 and (P)-3 on the surface.
3. Conclusion
To summarize, ethynylhelicene trimer, pentamer, and hexamer,
all with a disulfide moiety, were synthesized and formed dense
double helix monolayers on gold surfaces. These results are a no-
table example of grafting multifunctional macromolecules by thi-
olate linkage. CD was effective to probe the structure of these
compounds on the solid surface. These compounds formed double
helical SAMs on gold surfaces either from double helices or random
coils in solution. The presence of strong intercomplex interactions
on the surface was suggested.
4. Experimental section
4.1. General methods
Elemental analyses were conducted with a Yanaco CHN CORDER
MT-6 and a Yanaco HNS-15/HSU-20. Optical rotations were mea-
sured on a JASCO DIP-340 digital polarimeter. IR spectra were
measured on a JASCO FT/IR-400 spectrophotometer. 1H NMR and
13C NMR spectra were recorded on a Varian Mercury (400 MHz),
a Brucker AM-600 (600 MHz) or a JEOL JNM-ECA600 (600 MHz)
with tetramethylsilane as an internal standard, and the abbrevia-
tions of signal patterns are follows: s, singlet; d, doublet; t, triplet;
q, quartet; quint, quintet; m, multiplet. 13C NMR spectra taken in
Fig. 5. CD spectra of gold plates prepared by immersion in the mixture of the oligomer
(0.1 mM) and 1-decanethiol (x mM) in trifluoromethylbenzene for 24 h at rt (a) (P)-2
(0.1 mM) and 1-decanethiol (blue line) x¼0 and (red line) x¼20. (b) (P)-3 (0.1 mM) and
1-decanethiol (blue line) x¼0 and (red line) x¼20.
compared with those of the plates obtained from (P)-2 or (P)-3.
Despite the large difference between the concentration of (P)-2/(P)-
3 and 1-decanethiol, very small amounts of 1-dcanethiol were
adsorbed on the surface, if any (Figs. 5 and S6). This could be
explained by strong intercomplex interactions between the double
helices on the gold surface.
CDCl3 (d 77.0) were referenced to the residual solvents. Low- and
High-resolution mass spectra were recorded on a JEOL JMS DX-303
or a JEOL JMS AX-700 spectrometer. MALDI-TOF MS spectra were
recorded on a Perseptive Biosystems VoyagerÔ DE using a-cyano-
2.4. Thermal stability of double helix on gold surface
4-hydroxycinnamic acid as the matrix. CD and UV/vis spectra were
measured on a JASCO J-720 spectropolarimeter. Vapor pressure
osmometry (VPO) was conducted with a Knauer vapor pressure
osmometer K-7000 molecular weight apparatus using benzil as
a standard. Gel permeation chromatography (GPC) was conducted
with Recycling Preparative HPLC LC-908 or LC-918 (Japan Analytical
Industry, Co. Ltd.). Vacuum evaporation of gold was conducted by
a vacuum evaporator V-KS200 (Osaka vacuum) or small vacuum
evaporator VPC-260F (ULVAC kiko, Inc.).
Changing the structure of (P)-2 and (P)-3 on the gold surface was
attempted. When (P)-2 and (P)-3 on gold were heated at 80 ꢁC for
2 h and 6 h, respectively, the CD spectra showed essentially no
change (Fig. 6). On the other hand, in chloroform, toluene, and THF
4.2. Synthesis and characterization
4.2.1. 1-(3-Bromopropyl)-4-iodobenzene 12. To a mixture of 3-(4-
iodophenyl)propan-1-ol (195 mg, 0.743 mmol), triphenylphos-
phine (234 mg, 0.892 mmol), and dichloromethane (8 mL) was
added carbon tetrabromide (259 mg, 0.780 mmol) at 0 ꢁC, and the
mixture was stirred for 1 h at room temperature. The solvent was
removed under reduced pressure, and silica gel chromatography
gave the title compound (246 mg, quant.) as colorless oil. LRMS (EI,
70 eV) m/z 326 (Mþþ2, 75%), 324 (Mþ, 76%), 217 (Mþꢀ(CH2)2Br,
100%). HRMS m/z calcd for C9H10BrI: 323.9011. Found 323.9006. IR
(KBr) 2931, 2856 cmꢀ1. 1H NMR (400 MHz, CDCl3)
d 2.13 (2H, quint,
J¼6.8 Hz), 2.72 (2H, t, J¼7.3 Hz), 3.37 (2H, t, J¼6.6 Hz), 6.95 (2H, d,
J¼8.1 Hz), 7.60 (2H, d, J¼8.1 Hz). 13C NMR (100 MHz, CDCl3)
d 32.9,
33.5, 33.9, 91.2, 130.5, 137.4, 140.0.
4.2.2. Acetylthio trimer (P)-4. Under an argon atmosphere, a mix-
ture of tris(dibenzylideneacetone)dipalladium(0) chloroform ad-
duct (11.2 mg, 0.0108 mmol), cuprous iodide (24.6 mg, 0.129 mmol),
trimesitylphosphine (25.1 mg, 0.0645 mmol), tetrabutylammo-
nium iodide (317.7 mg, 0.860 mmol), triethylamine (0.3 mL), and
Fig. 6. CD spectra of SAM plates of (P)-2 (upper) and (P)-3 (bottom) on gold surfaces
before and after heating at 80 ꢁC.

5976
K. Yamamoto et al. / Tetrahedron 67 (2011) 5972e5978
N,N-dimethylformamide (3 mL) was freeze-evacuated three times
in flask A. In flask B, a mixture of (P)-910 (67.2 mg, 0.0430 mmol)
and 12 (15.4 mg, 0.0473 mmol) in tetrahydrofuran (3 mL) was
freeze-evacuated three times, and was added dropwise to flask A.
The mixture was stirred for 2 h at 45 ꢁC. The reaction was quenched
by adding saturated aqueous ammonium chloride, the organic
materials were extracted with toluene. The organic layer was
washed with brine, and dried over magnesium sulfate. The solvents
were evaporated under reduced pressure, and separation by silica
gel chromatography gave a mixture. The mixture was dissolved in
tetrahydrofuran (2 mL) and N,N-dimethylacetoamide (2 mL), and
potassium thioacetate (75.4 mg, 0.660 mmol) was added. The
mixture was stirred for 13 h at room temperature. The reaction was
quenched by adding water, and the organic materials were
extracted with toluene. The organic solvents were evaporated un-
der reduced pressure, and separation by recycling GPC gave (P)-4
(34.9 mg, 0.0199 mmol, 46% for two steps). Mp 128e130 ꢁC (chlo-
131.08, 131.11, 131.2, 131.48, 131.52, 131.9, 132.1, 132.18, 132.23,
132.26, 132.4, 132.8, 135.8, 136.8, 136.85, 136.93, 136.95, 138.29,
138.31, 142.0, 165.5, 166.4.
4.2.4. Acetylthio pentamer (P)-5. Under an argon atmosphere,
a mixture of tris(dibenzylideneacetone)dipalladium(0) chloroform
adduct (34.2 mg, 0.033 mmol), cuprous iodide (74.3 mg,
0.390 mmol), triphenylphosphine (51.4 mg, 0.196 mmol), trimes-
itylphosphine (76.2 mg, 0.196 mmol), tetrabutylammonium iodide
(960.4 mg, 2.600 mmol), triethylamine (1 mL), and N,N-dime-
thylformamide (10 mL) was freeze-evacuated three times in flask A.
In flask B, a mixture of (P)-1010 (350 mg, 0.173 mmol) and 12
(56.2 mg, 0.173 mmol) in tetrahydrofuran (10 mL) was freeze-
evacuated three times, and was added dropwise to flask A. The
mixture was stirred for 2 h at 45 ꢁC. The reaction was quenched by
adding saturated aqueous ammonium chloride, the organic mate-
rials were extracted with toluene. The organic layer was washed
with brine, and dried over magnesium sulfate. The solvents were
evaporated under reduced pressure, and separation by silica gel
chromatography gave a mixture. The mixture was dissolved in
tetrahydrofuran (15 mL) and N,N-dimethylacetoamide (15 mL), and
potassium thioacetate (494.0 mg, 4.325 mmol) was added. The
mixture was stirred for 12 h at room temperature. The reaction was
quenched by adding water, and the organic materials were
extracted with toluene. The solvents were removed under reduced
pressure, and separation by recycling GPC gave (P)-5 (289.4 mg,
0.133 mmol, 77% for two steps). Mp 154e156 ꢁC (chloroform/
roform/methanol). [
a
]
23 ꢀ549 (c 1.00, chloroform). MALDI-TOF MS
D
12
m/z calcd for
C
13C1H110O7S: 1755.8. Found: 1755.0. IR (KBr)
124
1723, 1686 cmꢀ1. Anal. Calcd for C125H110O7S: C, 85.48; H, 6.31%.
Found: C, 85.64; H, 6.44%. 1H NMR (600 MHz, CDCl3)
d
0.86 (6H, t,
J¼6.9 Hz), 1.20e1.45 (24H, m), 1.48e1.55 (4H, m), 1.86 (4H, quint,
J¼7.2 Hz), 1.92 (2H, quint, J¼7.6 Hz), 1.977 (6H, s), 1.981 (6H, s), 2.00
(6H, s), 2.35 (3H, s), 2.75 (2H, t, J¼7.6 Hz), 2.92 (2H, t, J¼7.4 Hz), 3.98
(3H, s), 4.43 (4H, t, J¼6.5 Hz), 7.24 (2H, d, J¼7.9 Hz), 7.45e7.55 (7H,
m), 7.64 (2H, d, J¼7.9 Hz), 7.66e7.77 (6H, m), 7.89 (1H, d, J¼7.6 Hz),
8.03 (1H, d, J¼7.9 Hz), 8.08 (1H, s), 8.11 (1H, s), 8.13 (1H, s), 8.14 (1H,
s), 8.16 (2H, s), 8.20e8.22 (2H, m), 8.36e8.40 (5H, m), 8.51e8.59
methanol). [
after dissolution). MALDI-TOF MS m/z calcd for
a
]
23 þ3807 (c 0.10, trifluoromethylbenzene, within 1 h
D
(6H, m). 13C NMR (150 MHz, CDCl3)
d
14.1, 22.7, 23.2, 26.1, 28.5, 28.8,
C
13C2H186O11S:
205
12
29.31, 29.34, 29.6, 30.7, 30.9, 31.9, 34.8, 52.3, 65.8, 87.3, 88.6, 89.33,
89.35, 89.37, 89.45, 92.9, 92.99, 93.02, 93.04, 93.7, 94.9, 119.7, 119.8,
119.86, 119.88, 120.1, 120.7, 121.0, 123.59, 123.65, 123.75, 123.81,
124.31, 124.33, 124.4, 126.5, 126.7, 126.8, 126.95, 126.98, 127.0, 128.6,
129.1, 129.22, 129.24, 129.28, 129.31, 129.4, 129.7, 129.88, 129.93,
130.6, 130.99, 131.03, 131.07, 131.09, 131.2, 131.5, 131.8, 132.1, 132.17,
132.23, 132.25, 132.4, 132.8, 135.8, 136.8, 136.87, 136.90, 136.95,
138.3, 141.9, 165.4, 166.4, 195.7.
2881.4. Found: 3443.9. UV/vis (trifluoromethylbenzene, 5 mM,
within 5 min after dissolution)
fluoromethylbenzene, 3
l
(
3
) 335 nm (2.3ꢃ105). CD (tri-
m
M, within 5 min after dissolution) l (D3)
326 nm (ꢀ890), 364 nm (1420), 390 nm (760). IR (KBr) 2204, 1722,
1693 cmꢀ1. Anal. Calcd for C207H186O11S: C, 86.27; H, 6.51; S, 1.11%.
Found: C, 86.18; H, 6.76; S, 1.21%. 1H NMR (600 MHz, CDCl3, mM,
observed at 60 ꢁC after heated for 15 min)
d
0.83 (12H, t, J¼6.9 Hz),
1.20e1.42 (48H, m), 1.46e1.52 (8H, m), 1.81e1.86 (8H, m), 1.92 (2H,
quint, J¼7.4 Hz), 1.942 (3H, s), 1.948 (6H, s), 1.952 (3H, s), 1.97 (12H,
s), 1.98 (6H, s), 2.33 (3H, s), 2.73 (2H, t, J¼7.4 Hz), 2.90 (2H, t,
J¼7.5 Hz), 3.95 (3H, s), 4.39e4.42 (8H, m), 7.22 (2H, d, J¼8.1 Hz),
7.41e7.49 (11H, m), 7.61 (2H, d, J¼8.1 Hz), 7.64e7.74 (10H, m), 7.86
(1H, ddd, J¼7.8, 1.8, 1.2 Hz), 8.03 (1H, ddd, J¼7.8, 1.8, 1.2 Hz), 8.05
(1H, s), 8.08 (1H, s), 8.095 (1H, s), 8.104 (1H, s), 8.131 (2H, s), 8.133
(2H, s), 8.15 (2H, s), 8.18e8.20 (4H, m), 8.33e8.36 (9H, m),
8.49e8.56 (10H, m). 13C NMR (150 MHz, CDCl3 mM, observed at
4.2.3. Trimer Disulfide (P)-1. Under an oxygen atmosphere, to
a solution of (P)-4 (32.2 mg, 0.0183 mmol) in toluene (2 mL) was
added pyrrolidine (2 mL) at room temperature. After being stirred
at room temperature for 3.5 h, the reaction was quenched by added
2 M aqueous hydrochloric acid. The organic materials were
extracted with toluene. The organic layer was washed with water
and brine, dried over magnesium sulfate. The solvents were re-
moved under reduced pressure, and separation by recycling GPC
gave (P)-1 (27.7 mg, 0.0081 mmol, 88%). Mp 168e170 ꢁC (chloro-
60 ꢁC after heated for 30 min)
d 14.0, 22.6, 23.1, 26.1, 28.6, 28.9,
29.29, 29.34, 29.6, 30.5, 30.9, 31.9, 34.9, 52.2, 65.8, 87.4, 88.8, 89.5,
89.6, 93.0, 93.08, 93.14, 93.8, 95.0, 119.9, 120.0, 120.1, 120.3, 120.9,
121.2, 123.7, 123.9, 124.0, 124.5, 124.6, 126.6, 126.9, 127.0, 127.1,
128.2, 128.6, 128.7, 129.05, 129.14, 129.2, 129.26, 129.28, 129.33,
129.5, 129.7, 129.96, 130.03, 130.9, 131.17, 131.23, 131.8, 131.9, 132.3,
132.38, 132.44, 132.6, 132.9, 135.8, 136.9, 137.00, 137.03, 137.05,
137.09, 138.3, 142.0, 165.4, 166.4, 195.3.
form/methanol). [
a
]
26 ꢀ579 (c 0.10, chloroform). MALDI-TOF MS m/
12
z calcd for
C
244
13DC2H214O12S2: 3425.6. Found: 3425.4. UV/vis
(trifluoromethylbenzene, 0.05 mM)
(trifluoromethylbenzene, 0.05 mM)
l
(3
) 341 nm (2.5ꢃ105). CD
l (D3) 336 nm (80), 388 nm
(ꢀ140). IR (KBr) 2202, 1722 cmꢀ1. Anal. Calcd for C246H214O12S2: C,
86.23; H, 6.30%. Found: C, 86.02; H, 6.57%. 1H NMR (600 MHz,
CDCl3) d 0.83e0.88 (12H, m), 1.20e1.55 (56H, m), 1.82e1.89 (8H, m),
1.94 (9H, m), 1.97 (9H, s), 1.978 (9H, s), 1.986 (9H, s), 2.07 (4H, quint,
J¼7.4 Hz), 2.72 (4H, t, J¼7.2 Hz), 2.78 (4H, t, J¼7.8 Hz), 3.97 (6H, s),
4.42 (8H, m), 7.24 (4H, d, J¼7.2 Hz), 7.42e7.54 (14H, m), 7.62e7.76
(16H, m), 7.88 (2H, dt, J¼7.6, 1.4 Hz), 8.03 (2H, s), 8.04e8.08 (4H, m),
8.09 (2H, s), 8.11 (3H, s), 8.12 (3H, s), 8.17 (2H, t, J¼1.6 Hz), 8.19 (2H,
t, J¼1.6 Hz), 8.32e8.39 (10H, m), 8.48e8.57 (12H, m). 13C NMR
4.2.5. Pentamer disulfide (P)-2. Under an oxygen atmosphere, to
a solution of (P)-5 (28.1 mg, 9.8 mmol) in toluene (2 mL) was added
pyrrolidine (2 mL) at room temperature. After being stirred at room
temperature for 1.5 h, the reaction was quenched by added 2 M
aqueous hydrochloric acid, and the organic materials were extracted
with toluene. The organic layer was washed with water and brine,
dried over magnesium sulfate. The solvents were removed under
reduced pressure, and separation by recycling GPC gave (P)-2
(150 MHz, CDCl3)
d 14.1, 22.7, 23.2, 26.1, 28.8, 29.31, 29.34, 29.6,
30.4, 31.9, 34.4, 38.1, 52.3, 65.8, 87.4, 88.6, 89.3, 89.36, 89.44, 92.9,
92.99, 93.01, 93.05, 93.7, 94.9, 119.7, 119.8, 119.86, 119.89, 120.1,
120.6, 121.0, 123.57, 123.65, 123.7, 123.8, 124.30, 124.34, 124.36,
126.4, 126.7, 126.8, 126.9, 126.97, 126.99, 127.04, 128.6, 128.7, 129.1,
129.19, 129.24, 129.3, 129.5, 129.7, 129.88, 129.93, 130.6, 131.00,
(17.9 mg, 6.3 m
mol, 65%). Mp 179e181 ꢁC (chloroform/methanol).
[
a
]
23 þ4190 (c 0.10, trifluoromethylbenzene, within 1 h after disso-
D
12
lution). MALDI-TOF MS m/z calcd for
C
13C4H366O20S2: 5676.7.
406
Found: 3443.9. UV/vis (trifluoromethylbenzene, 3 mM, within 5 min

K. Yamamoto et al. / Tetrahedron 67 (2011) 5972e5978
5977
after dissolution)
fluoromethylbenzene, 3
l
(
3
)
332 nm (4.2ꢃ105). CD (tri-
d 14.0, 22.6, 23.1, 26.1, 28.6, 28.9, 29.29, 29.34, 29.6, 29.7, 30.5, 30.9,
m
M, within 5 min after dissolution)
l
(D3
)
31.9, 34.9, 52.2, 65.8, 87.4, 88.8, 89.5, 89.6, 93.0, 93.1, 93.8, 95.0,
119.9, 120.0, 120.1, 120.3, 120.9, 121.2, 123.7, 123.9, 124.0, 124.5,
124.6, 126.6, 126.9, 127.0, 127.1, 128.6, 128.7, 129.1, 129.23, 129.24,
129.28, 129.32, 129.5, 129.7, 129.96, 130.03, 130.9, 131.2, 131.3, 131.8,
131.9, 132.3, 132.4, 132.6, 132.9, 135.8, 136.9, 136.94, 136.99, 137.04,
137.1, 138.3, 142.0, 165.4, 166.4, 195.3.
326 nm (ꢀ2200), 364 nm (3450), 390 nm (1950). IR (KBr) 2205,
1722 cmꢀ1. Anal. Calcd for C410H366O20S2: C, 86.74; H, 6.50; S, 1.13%.
Found: C, 86.47; H, 6.53; S, 1.41%. 1H NMR (600 MHz, CDCl3, mM,
observed at 60 ꢁC after heated at 60 ꢁC for 15 min)
d 0.82e0.90 (24H,
m), 1.20e1.53 (112H, m), 1.84 (16H, quint, J¼7.2 Hz), 1.94e1.99 (60H,
m), 2.06 (4H, quint, J¼7.4 Hz), 2.72 (4H, t, J¼7.2 Hz), 2.78 (4H, t,
J¼7.8 Hz), 3.96 (6H, s), 4.39e4.43 (16H, m), 7.23 (4H, d, J¼8.4 Hz),
7.43e7.50 (22H, m), 7.62 (4H, d, J¼8.4 Hz), 7.61e7.72 (20H, m), 7.85
(2H, ddd, J¼8.4, 1.8, 1.2 Hz), 7.99 (2H, s), 8.03 (2H, s), 8.03 (2H, ddd,
J¼6.6, 1.8, 1.2 Hz), 8.07 (2H, s), 8.09 (2H, s), 8.09 (2H, s), 8.10e8.12
(10H, m), 8.14 (2H, dd, J¼1.8, 1.2 Hz), 8.17e8.18 (6H, m), 8.31 (2H, t,
J¼1.8,1.2 Hz), 8.32 (2H, t, J¼1.8,1.2 Hz), 8.34e8.35 (12H, m), 8.36 (2H,
dd, J¼1.8,1.2 Hz), 8.48e8.55 (20H, m).13C NMR (150 MHz, CDCl3 mM,
4.2.7. Hexamer disulfide (P)-3. Under an oxygen atmosphere, to
a solution of (P)-6 (56.9 mg, 0.0165 mmol) in toluene (3 mL) was
added pyrrolidine (3 mL) at room temperature. After being stirred
at room temperature for 3 h, the reaction was quenched by added
2 M aqueous hydrochloric acid, and the organic materials were
extracted with toluene. The organic layer was washed with water
and brine, dried over magnesium sulfate. The solvents were re-
moved under reduced pressure, and separation by recycling GPC
observed at 60 ꢁC after heated at 60 ꢁC for 30 min)
d 14.0, 22.6, 23.1,
26.1, 28.9, 29.30, 29.34, 29.6, 29.7, 30.4, 31.9, 34.5, 38.4, 52.2, 65.8,
87.5, 88.8, 89.5, 89.6, 93.0, 93.09, 93.14, 93.8, 95.0, 96.2, 119.8, 120.0,
120.1, 120.3, 120.9, 121.2, 123.6, 123.75, 123.84, 124.0, 124.49, 124.53,
126.6, 126.8, 126.9, 127.0, 127.1, 128.6, 128.7, 129.0, 129.1, 129.26,
129.33, 129.5, 129.7, 129.96, 130.01, 131.17, 131.22, 131.3, 131.76,
131.82, 131.9, 132.3, 132.38, 132.44, 132.6, 132.9, 135.8, 136.9, 137.0,
137.1, 138.3, 142.1, 165.4, 166.4.
gave (P)-3 (34.1 mg, 0.0101 mmol, 61%). Mp 184e186 ꢁC (chloro-
23
form/methanol).
[
a]
þ4873 (c 0.10, trifluoromethylbenzene,
D
within 1 h after dissolution). MALDI-TOF MS m/z calcd for
C
488
13C4H442O24S2: 6801.3. Found: 3443.9. UV/vis (tri-
12
fluoromethylbenzene, 3 mM, within 5 min after dissolution) l (3)
331 nm (4.8ꢃ105). CD (trifluoromethylbenzene, 3
mM, within 5 min
D3) 326 nm (ꢀ2180), 366 nm (4310), 390 nm
after dissolution)
l
(
(2610). IR (KBr) 2208, 1724 cmꢀ1. Anal. Calcd for C488H442O20S2: C,
86.86; H, 6.55; S, 0.94%. Found: C, 86.88; H, 6.73; S, 1.00%. 1H NMR
(600 MHz, CDCl3, 2 mM, observed at 60 ꢁC after heated for 3 h)
4.2.6. Acetylthio hexamer (P)-6. Under an argon atmosphere,
a mixture of tris(dibenzylideneacetone)dipalladium(0) chloroform
adduct (12.8 mg, 0.0124 mmol), cuprous iodide (28.4 mg,
0.149 mmol), triphenylphosphine (19.5 mg, 0.0743 mmol), tri-
mesitylphosphine (28.9 mg, 0.0743 mmol), tetrabutylammonium
iodide (365.7 mg, 0.990 mmol), triethylamine (0.4 mL), and N,N-
dimethylformamide (2 mL) was freeze-evacuated three times in
flask A. In flask B, a mixture of (P)-1110 (161.1 mg, 0.0495 mmol) and
12 (21.4 mg, 0.0658 mmol) in tetrahydrofuran (6 mL) was freeze-
evacuated three times, and was added dropwise to flask A. The
mixture was stirred for 2 h at 45 ꢁC. The reaction was quenched by
adding saturated aqueous ammonium chloride, the organic mate-
rials were extracted with toluene. The organic layer was washed
with brine, and dried over magnesium sulfate. The solvents were
evaporated under reduced pressure, and separation by silica gel
chromatography gave a mixture. The mixture was dissolved in
tetrahydrofuran (7 mL) and N,N-dimethylacetoamide (7 mL), and
potassium thioacetate (141.6 mg, 1.24 mmol) was added. The
mixture was stirred for 12 h at room temperature. The reaction was
quenched by adding water, and the organic materials were
extracted with toluene. The organic solvents were evaporated un-
der reduced pressure, and separation by recycling GPC gave (P)-6
d
0.82e0.90 (30H, m), 1.20e1.70 (140H, m), 1.84 (20H, quint,
J¼7.4 Hz), 1.94e2.01 (72H, m), 2.05 (4H, quint, J¼7.4 Hz), 2.72 (4H, t,
J¼7.2 Hz), 2.77 (4H, t, J¼7.6 Hz), 3.95 (3H, s), 4.41 (20H, t, J¼6.8 Hz),
7.22 (4H, d, J¼8.1 Hz), 7.40e7.51 (26H, m), 7.62 (4H, d, J¼8.1 Hz),
7.63e7.72 (24H, m), 7.85 (2H, ddd, J¼7.7, 1.5, 1.3 Hz), 7.99 (2H, s),
8.02 (2H, s), 8.03 (2H, ddd, J¼7.9, 1.6, 1.2 Hz), 8.06 (2H, s), 8.07 (2H,
s), 8.08 (2H, s), 8.10 (12H, s), 8.13 (2H, dd, J¼1.8, 1.6 Hz), 8.16e8.17
(8H, m), 8.30e8.35 (22H, m), 8.48e8.54 (24H, m). 13C NMR
(150 MHz, CDCl3 2 mM, observed at 60 ꢁC after heated for 3 h)
d
14.0, 22.7, 23.1, 26.1, 28.9, 29.3, 29.4, 29.6, 29.7, 30.5, 31.9, 34.5,
38.4, 52.2, 65.8, 88.8, 89.5, 93.09, 93.14, 93.8, 95.0, 120.0, 120.1,
120.3, 123.7, 124.0, 124.5, 126.6, 126.8, 126.9, 127.0, 127.1, 128.6,
128.7, 129.1, 129.2, 129.26, 129.32, 129.5, 129.7, 130.0, 130.9, 131.15,
131.22, 131.8, 131.9, 132.38, 132.43, 132.9, 135.8, 136.9, 137.0, 138.3,
142.1, 165.4, 166.4.
4.3. Preparation of gold substrate
Gold substrates for IR-RAS measurements were prepared by
vapor deposition of chromium (5e7 nm) as adhesion layer and then
gold (99.99%, 200e250 nm) on a slide glass. Gold substrates for SPR
measurements were prepared by vapor deposition of gold (ca.
50 nm) on a slide glass. In the case of gold substrates for CD mea-
surements, gold (8 nm) was deposited on a quartz substrate.
(108.6 mg, 0.0317 mmol, 64% for two steps). Mp 152e154 ꢁC
(chloroform/methanol).
23
[
a
]
þ4038
(c
0.10,
tri-
D
fluoromethylbenzene, within 1 h after dissolution). MALDI-TOF MS
m/z calcd for
C
13C2H224O13S: 3443.7. Found: 3443.9. UV/vis
12
246
(trifluoromethylbenzene, 5 mM, within 5 min after dissolution) l (3)
332 nm (2.5ꢃ105). CD (trifluoromethylbenzene, 5
m
M, within 5 min
4.4. Preparation of self-assembled monolayer of (P)-1 on gold
after dissolution)
l
(
D3) 326 nm (ꢀ1380), 365 nm (2130), 390 nm
(1280). IR (KBr) 2206, 1722, 1692 cmꢀ1
.
Anal. Calcd for
The gold substrate (for IR-RAS or CD measurement) was im-
mersed in 0.05 mM trifluoromethylbenzene solution of (P)-1 at
20 ꢁC for 24 h. The substrate was removed from the solution, im-
mediately rinsed with trifluoromethylbenzene, and blown dried
with argon or nitrogen.
C248H224O13S: C, 86.48; H, 6.55; S, 0.93%. Found: C, 86.51; H, 6.76; S,
1.00%. 1H NMR (600 MHz, CDCl3, mM, observed at 60 ꢁC after
heated for 15 min)
d
0.85 (15H, t, J¼6.9 Hz), 1.23e1.38 (50H, m), 1.41
(10H, quint, J¼7.4 Hz), 1.50 (10H, quint, J¼7.5 Hz), 1.94 (2H, quint,
J¼7.4 Hz), 1.97 (15H, s), 1.99 (21H, s), 2.33 (3H, s), 2.74 (2H, t,
J¼7.4 Hz), 2.92 (2H, t, J¼7.4 Hz), 3.96 (3H, s), 4.40e4.43 (10H, m),
7.21 (2H, d, J¼8.1 Hz), 7.44e7.49 (13H, m), 7.61 (2H, d, J¼8.1 Hz),
7.65 (1H, dd, J¼7.9, 7.2 Hz), 7.67e7.73 (11H, m), 7.85 (1H, ddd, J¼7.5,
1.5, 1.3 Hz), 8.03 (1H, s), 8.03 (1H, ddd, J¼7.7, 1.6, 1.3 Hz), 8.07 (1H, s),
8.09 (1H, s), 8.09 (1H, s), 8.11 (4H, s), 8.12 (4H, s), 8.17e8.18 (5H, m),
8.33e8.35 (10H, m), 8.36 (1H, s), 8.49e8.55 (12H, m). 13C NMR
(150 MHz, CDCl3 mM, observed at 60 ꢁC after heated for 30 min)
4.5. Preparation of self-assembled monolayer of (P)-2 or (P)-3
on gold
Gold substrate (for IR-RAS or CD measurement) was immersed
in 0.1 mM trifluoromethylbenzene solution of the (P)-2 or (P)-3 at
20 ꢁC for 24 h. The substrate was removed from the solution, im-
mediately rinsed with trifluoromethylbenzene, and blown dried

5978
K. Yamamoto et al. / Tetrahedron 67 (2011) 5972e5978
with argon or nitrogen. No change of CD spectra was observed by
washing (Fig. S1).
4.10. Attempted preparation of the mixed monolayer on gold
The gold substrate (for IR-RAS or CD measurement) was im-
mersed in the mixture of (P)-2 or (P)-3 (0.1 mM) and decanethiol
(20 mM) in trifluoromethylbenzene at 20 ꢁC for 24 h. The substrate
was removed from the solution, immediately rinsed with tri-
fluoromethylbenzene, and blown dried with argon or nitrogen.
Trifluoromethylbenzene used in this experiment was degassed by
freeze-evacuation three times before preparation of the thiol
solution.
4.6. Infrared reflection-absorption spectroscopy (IR-RAS)
Analysis was performed on an FTIR Spectrum One (Per-
kineElmer) with a mercury/cadmium/tellurium (MCT) detector.
The IR-RAS measurements used 100 scans of interferogram accu-
mulations with the bare gold substrate as reference. The optical
path was purged with dry air before and during measurements. A
reflection attachment, at an incident angle of 70ꢁ, together with
a polarizer was used.
Acknowledgements
4.7. Surface plasmon resonance (SPR) spectroscopy
This work was financially supported by a Grant-in-Aid for Sci-
entific Research (No. 22790003), the GCOE program, and the WPI
Initiative from JSPS. K.Y. and Z.A. express their appreciation for fi-
nancial support from WPI-AIMR. H.A. expresses his appreciation for
the financial support from International Advanced Research and
Education Organization.
Surface plasmon resonance spectra were taken with SPR spec-
trometer (JEL-001, R-DEC Co., Ltd.). The SPR setup was based on the
configuration introduced by Kretschmann and Raether.11 Normal
refractive index glass (n¼1.52) slides was used. The substrate was
pressed against a 45ꢁ prism (n¼1.52) with index-matching oil be-
tween the substrate glass and prism. Using a p-polarized HeNe
Supplementary data
laser (
l¼632.8 nm) as the light source, the intensity of the beam
reflected at the gold interface was detected by a photodiode de-
tector, and recorded as a function of the incidence angle for ‘an-
gular-scan’ measurements. All sample cells and tubes were made of
Teflon, which was resistant to most organic solvents. Fitting of SPR
data was performed with the program Winspall (version 3.0.2.0
release: 0.1, Max-Planck-Institut fuer Polymerforschung). The
thickness and the complex refractive index of gold layer were de-
termined by curve fitting of the SPR data of bare gold in air. SAM
formation was initiated by injection of (P)-2 or (P)-3 solution
(0.1 mM trifluoromethylbenzene solution) into the cell. The ad-
sorption was continued for 24 h, after which the surface was rinsed
with chloroform, and blown dried with nitrogen. The SPR mea-
surements were carried out in air for determination of the thick-
ness of the SAMs. All measurements were performed at room
temperature.
Supplementary data associated with this article can be found in
the online version, at doi:10.1016/j.tet.2011.06.024. These data in-
clude MOL file and InChIKey of the most important compounds
described in this article.
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Quartz Crystal Microbalances, BAS Co., Tokyo, Japan) was employed
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resonance frequency. The both sides of the Au electrode of the QCM
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mersed into trifluoromethylbenzene solution of (P)-2 or (P)-3
(0.1 mM) for 24 h. After washing with chloroform, the QCM was
dried in a vacuum, and the mass change was calculated from the
frequency shift.
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Gold substrate (for CD measurement) was immersed in 0.1 mM
tetrahydrofuran solution of the (P)-2 or (P)-3 at 20 ꢁC for 24 h. The
substrate was removed from the solution, immediately rinsed with
trifluoromethylbenzene, and blown dried with argon.