8392
J. Kim et al. / Tetrahedron 64 (2008) 8389–8393
then CH
repeatedly with CH
over Na SO . After removal of the solvent, the resulting oil was
purified by column chromatography on silica gel using CH Cl
MeOH (19:1) as an eluent to yield 4 as a pale yellow oil (1.2 g, 48%).
2
Cl
2
and H
2
O were added. The aqueous layer was extracted
the tips were immersed again in a 1 mM aqueous solution of 6-
2
2
Cl . The combined organic phases were dried
mercapto-1-hexanol for 12 h. The cantilever was then rinsed with
deionized water and ethanol. AFM measurements were carried out
with a NanoScope IIIa multimode AFM (Digital Instrument) utiliz-
ing a liquid cell (Digital Instrument). The uploading rate was 9.6 nN/
s. The quantitative analysis of the observed individual pull-off
events was performed for 300 force curves at 10 different positions
of 1-anchored SAM. The noise level of the forces measured with the
apparatus was estimated to be ꢂ20 pN from the baseline of force
curves near its pull-off point. Only the forces larger than 30 pN
were included for the quantitative force analysis, considering the
noise level originating from the inherent vibration of the AFM
cantilever occurring in the pull-off events.
2
4
2
2
/
4.2.2. Compound 5
2 2
A solution of DCC (210 mg, 1.02 mmol) in CH Cl was added to
a solution of 4 (500 mg, 1.00 mmol), thioctic acid (210 mg,
.02 mmol), and DMAP (25 mg, 0.20 mmol) in CH Cl . The reaction
1
2
2
mixture was stirred for 14 h. After removal of the solvent, the
resulting oil was purified by column chromatography on silica gel
using n-hex/EA (1:1) as an eluent to yield 5 as pale yellow oil
(
3
(
500 mg, 78%). 1H NMR (500 MHz, CDCl
.35–3.02 (14H, br), 2.51–2.41 (1H, m), 2.25–2.15 (2H, m), 1.98–1.91
1H, m), 1.78–1.55 (8H, m), 1.53–1.37 (31H, br); C NMR (125 MHz,
3
)
d
¼3.62–3.53 (1H, m),
4.5. SPR experiment for measuring surface density of 3 on an
Au substrate
13
CDCl
3
)
d
¼172.8, 156.5, 156.0, 79.7, 78.9, 56.4, 46.7, 46.2, 44.3, 43.8,
4
3.4, 40.2, 38.5, 37.4, 36.6, 35.5, 34.7, 28.9, 28.5, 27.7, 26.1, 25.5;
Surface plasmon resonance (SPR) experiments were carried out
þ
ꢃ
HRMS-FAB m/z: [MþH] calcd for C33
H
63
N
4
O
7
S
2
: 691.4138, found
at 25 C using a BIACore 2000 and Pioneer Sensor Chip J1 (plain
6
91.4130.
gold surface), which has a gold substrate with a size of 7ꢀ7 mm.
SPR measures the angle of light (q) reflected from the backside of
4
.2.3. Compound 3
To a solution of 5 (500 mg, 0.72 mmol) in methanol (5 mL),
the gold substrate that is a minimum in intensity. Changes in this
angle (Dq) are linearly related to the index of refraction of the so-
lution above the surface and therefore to the density of adsorbed
ꢃ
acetyl chloride (1 mL) was added slowly at 0 C. After stirring for
1
and acetonitrile. Removal of the solvent yielded 3 as a white solid
ꢃ
2
h, white precipitate was filtered off and washed with methanol
molecules (Dq of 0.10 ¼1 ng/mm ¼1000 RU). SPR experiments
ꢁ
1
were performed at the constant flow rate of 10
m
L min over gold
ꢃ
1
ꢃ
(
(
360 mg, 98%). Mp >240 C; H NMR (500 MHz, D
1H, m), 3.31 (2H, t, J¼6.5 Hz), 3.20–3.22 (2H, m), 3.16 (2H, t,
2
O)
d
¼3.72–3.75
surfaces at 25 C.
J¼6.5 Hz), 3.12 (8H, t, J¼7.5 Hz), 2.45–2.55 (1H, m), 2.29 (2H, t,
Acknowledgements
J¼7.0 Hz), 2.03–2.16 (H, m), 1.96–2.03 (1H, m), 1.86–1.95 (2H, m),
13
1
.80 (5H, s), 1.55–1.72 (3H, m), 1.38–1.46 (2H, m); C NMR
We gratefully acknowledge the Creative Research Initiative
Program of the Korean Ministry of Science and Technology and the
Brain Korea 21 Program of the Korean Ministry of Education for
support of this work.
(
3
[
125 MHz, D
2
O)
d
¼177.8, 57.0, 47.4, 47.3, 45.5, 44.9, 40.7, 38.5, 36.9,
Mꢁ3HClþH] calcd for C18 OS : 391.2565, found 391.2570.
.3. Preparation of 1-anchored self-assembled monolayer
6.3, 35.8, 34.0, 28.3, 26.1, 25.3, 24.1, 23.2; HRMS-FAB m/z:
þ
H
39
N
4
2
4
Supplementary data
(
SAM) on gold
SPR sensorgram of 3 on an Au substrate, FTIR spectra of SAM of 2
on gold and 1-anchored SAM, and histograms of rupture forces
obtained in control experiments are presented as supplementary
4
.3.1. SAM of 2 on gold
Gold substrates were prepared by evaporating 2 nm of Ti as an
adhesion layer, followed by 250 nm Au onto silicon (100) wafer. A
gold substrate (10ꢀ10 mm) was cleaned by freshly prepared pira-
nha solution for 3 min, then rinsed thoroughly with deionized
water and dried in vacuum for 1 h. The cleaned Au substrate was
immersed in ethanol (10 mL) solution of 2 (102 mg, 0.1 mmol) for 1
day. The substrate was washed with ethanol several times and
dried under a stream of nitrogen to produce SAM of 2 on gold with
allyl terminal groups.
References and notes
1. (a) Lehn, J. M. Supramolecular Chemistry: Concepts and Perspectives; VCH:
Weinheim, 1995; (b) Reinhoudt, D. N. Supramolecular Materials; Wiley: New
York, NY, 1999; (c) Buckingham, A. D.; Legon, A. C.; Roberts, S. M. Principles of
Molecular Recognition; Blackie: London, 1993.
2. Phizieky, E. M.; Fields, S. Microbiol. Rev. 1995, 59, 94–123.
4
.3.2. 1-Anchored SAM on gold
The SAM of 2 on gold was immersed in CH Cl (10 mL) solution
2 2
3. (a) Gaub, H.; Engel, A. J. Struct. Biol. 1997, 119, 83–237; (b) Baumgartner, W.;
Hinterdorfer, P.; Ness, W.; Raab, A.; Vestweber, D.; Schindler, H.; Drenckhahn, D.
Proc. Natl. Acad. Sci. U.S.A. 2000, 9, 4005–4010.
0
0
0
containing [Cl
2
P(Cy)
3
(IMes)Ru(]CHPh)] (IMes¼1,3-(2 ,4 ,6 -tri-
4
. (a) Lee, G. U.; Chrisey, L. A.; Colton, R. J. Science 1994, 266, 771–773; (b) Moy,
V. T.; Florin, E.-L.; Rief, M.; Lehmann, H.; Ludwig, M.; Gaub, H. E.; Dornmair, K.
Proc. SPIE-Int. Soc. Opt. Eng. 1995, 2384, 2–12.
methylphenyl)imidazol-2-ylidene) (second generation Grubbs cata-
lyst) (8.5 mg, 0.010 mmol) at rt for 5 min. The resulting substrate
5. (a) Florin, E.-L.; Moy, V. T.; Gaub, H. E. Science 1994, 264, 415–417; (b) Moy, V. T.;
Florin, E.-L.; Gaub, H. E. Science 1994, 266, 257–259.
was thoroughly washed with CH
a freshly prepared DMF (10 mL) solution containing 1 (15 mg,
.0090 mmol) at rt for 10 min. The gold substrate was rinsed with
2 2
Cl and then immersed in
6. (a) Sch o¨ nherr, H.; Beulen, M. W. J.; B u¨ gler, J.; Huskens, J.; van Veggel, F. C. J. M.;
Reinhoudt, D. N.; Vansco, G. J. J. Am. Chem. Soc. 2000, 122, 4963–4967; (b)
Zapotoczny, S.; Auletta, T.; de Jong, M. R.; Sch o¨ nherr, H.; Huskens, J.; van Veggel,
F. C. J. M.; Reinhoudt, D. N.; Vansco, G. J. Langmuir 2002, 18, 6988–6994; (c)
Auletta, T.; de Jong, M. R.; Mulder, A.; van Veggel, F. C. J. M.; Huskens, J.;
Reinhoudt, D. N.; Zou, S.; Zapotoczny, S.; Sch o¨ nherr, H.; Vansco, G. J.; Kuipers, L.
J. Am. Chem. Soc. 2004, 126, 1577–1584.
0
DMF and ethanol for several times and dried under a stream of
nitrogen to produce 1-anchored SAM on gold. Its FTIR spectrum is
shown in Figure S2.
7
. Kado, S.; Kimura, K. J. Am. Chem. Soc. 2003, 125, 4560–4564.
4
.4. AFM measurement and tip modification
8
9
. Frisbie, C. D.; Skulason, H. J. Am. Chem. Soc. 2002, 124, 15125–15133.
. Kim, J.; Liu, Y.; Ahn, S. J.; Zauscher, S.; Karty, J. M.; Yamanaka, Y.; Craig, S. L. Adv.
Mater. 2005, 17, 1749–1753.
Triangular-shaped,
gold-coated,
¼0.16 Nm , Olympus) were immersed in a 1 mM aqueous so-
lution of 3 for 12 h. After thoroughly rinsing with deionized water,
silicon
nitride
tips
10. Reviews: (a) Mock, W. L. Top. Curr. Chem. 1995, 175, 1–24; (b) Lee, J. W.; Samal,
ꢁ1
(k
c
S.; Selvapalam, N.; Kim, H.-J.; Kim, K. Acc. Chem. Res. 2003, 36, 621–630; (c) Kim,
K.; Kim, H.-J. Encyclopedia of Supramolecular Chemistry; Atwood, J. L., Steed, J. W.,