S. Ciampi and J. J. Gooding et al.
1.7 Hz, 2H), 7.61 (dd, J=4.4, 1.7 Hz, 2H), 6.73 (brs, 1H), 3.59–3.52 (m,
2H), 3.46 (t, J=6.4 Hz, 2H), 1.95–1.87 ppm (m, 2H); 13C NMR
(75.5 MHz, CDCl3): d=165.79, 150.69, 141.64, 120.98, 49.81, 38.25,
28.63 ppm; IR (NaCl): n˜ =3291, 3067, 2936, 2876, 2099, 1651, 1548, 1309,
X-ray photoelectron spectroscopy measurements: X-ray photoelectron
spectroscopy data were acquired using an ESCALAB 220iXL spectrome-
ter with a monochromatic AlKa source (1486.6 eV), hemispherical ana-
lyzer and multichannel detector (6 detectors). Spectra were recorded in
normal emission with the analyzing chamber operating below 10ꢁ9 mbar
and selecting a spot size of approximately 1 mm2. The incidence angle
was set to 588 to the analyzer lens. The resolution of the spectrometer is
about 0.6 eV as measured from the Ag 3d5/2 signal (full width at half max-
imum, fwhm) with a 20 eV pass energy. Survey scans were carried out
over 1100–0 eV range with a 1.0 eV step size, a 100 ms dwell time, and
analyzer pass energy of 100 eV. High-resolution scans were run with
0.1 eV step size, dwell time of 100 ms and the analyzer pass energy set to
20 eV. After background subtraction using the Shirley routine, spectra
were fitted with a convolution of Lorentzian and Gaussian profiles as
previously reported.[8a] All energies are reported as binding energies in
eV and referenced to the C 1s signal (corrected to 285.0 eV). When de-
tected, the monolayer coverage of oxidized silicon was calculated directly
from the oxidized/bulk Si 2p peak area ratio according to the method de-
scribed by Webb and co-workers for very thin oxide overlayers.[47]
1262, 1161, 1110, 1066, 1000, 848 cmꢁ1
.
d) 3-Chloropropyl isonicotinate (D): Triethylamine (5.1 g, 50.3 mmol) was
added in portions over a 30 min period to a stirred suspension of com-
pound B (3.1 g, 17.4 mmol) and 3-chloropropanol (2.14 g, 22.6 mmol) in
anhydrous tetrahydrofuran (ca. 50 mL), while stirring under argon. The
suspension was stirred at room temperature under an argon atmosphere
for 14 h. Filtration through Celite and evaporation of the solvent in
vacuo afforded the crude compound D as a dark orange oil. Purification
of the crude material by column chromatography (ethyl acetate/light pe-
troleum, 1:1) gave the ester D as a colorless oil (1.9 g, 55%). 1H NMR
(300 MHz, CDCl3): d=8.79 (d, J=6.0 Hz, 2H), 7.84 (d, J=6.0 Hz, 2H),
4.53 (t, J=6.2 Hz, 2H), 3.68 (t, J=6.1 Hz, 2H), 2.28–2.24 ppm (m, 2H);
13C NMR (75.5 MHz, CDCl3): d=165.04, 150.68, 137.36, 122.98, 62.68,
41.86, 35.07 ppm; IR (NaCl): : n˜ =3401, 2966, 2361, 1730, 1654, 1598,
1562, 1408, 1281, 1126, 1063, 993 cmꢁ1
.
Electrochemical measurements: All the electrochemical measurements on
the putative pyridine-ligated assembly were performed under an argon
atmosphere in degassed electrolytes (20 mm sodium phosphate buffer,
pH 7.0) not containing cytc.
e) 3-Azidopropyl isonicotinate (3): A solution of compound D (900 mg,
4.51 mmol) and sodium azide (1.46 g, 22.5 mmol) in N,N-dimethylforma-
mide (10 mL) was stirred at 1008C for 24 h under an argon atmosphere.
The mixture was evaporated in vacuo, and the resulting residue was sus-
pended in ethyl acetate (ca. 100 mL). The suspension produced was fil-
tered, and the filtrate was concentrated in vacuo. The crude product was
purified by column chromatography (ethyl acetate/light petroleum, 3:5)
All electrochemical experiments were preformed in a conventional PTFE
three-electrode cell with the modified silicon surface as the working elec-
trode, a platinum mesh as the counter electrode, and silver/silver chloride
in 3m sodium chloride as the reference electrode. A rectilinear cross-sec-
tion gasket defined the geometric area of the working electrode to
18.1 mm2. Ohmic contact between the silicon substrate and a copper
plate was ensured by rapidly rubbing a gallium indium eutectic onto a
close series of marks (emery paper) aimed to expose the bulk of the sili-
con electrodes. The cell was enclosed in a grounded Faraday cage during
all measurements. Electrolyte solutions were prepared with Milli-Qꢅ
water, purged with argon gas before electrochemical measurements, and
kept under an argon atmosphere during the course of the experiment.
Cyclic voltammetry (CV) was performed using a Solartron 1287 potentio-
stat/galvanostat (Farnborough, UK). All potentials are reported versus
the reference electrode. The uncompensated solution resistance for the
electrochemical cell was about 2–2.5 kW, resulting in an uncompensated
iR for the CV data less than 1 mV for the highest currents measured in
this work. Impedance measurements were performed with a Solartron
1255B (Farnborough, UK) frequency response analyzer interfaced to a
Solartron 1287 potentiostat/galvanostat module. Impedance data were
collected at 60 frequencies in the frequency range from 0.1 Hz to
0.1 MHz. An ac potential amplitude of 15 mV root mean square was
added to the dc potential of the working electrode (Edc). The impedance
measurements were performed at a dc potential equal to the apparent
formal potential as determined by cyclic voltammetry experiments. Both
the in-phase (Z’) and out-of-phase impedance (Z’’) were extracted at the
same time from the data and analyzed with the ZView 3.1 and ZPlot
softwares (Scribner Associates, Inc.). Electrochemical experiments were
performed at room temperature (23ꢀ28C).
to give the substituted azide
3 as a colourless oil (545 mg, 59%).
1H NMR (300 MHz, CDCl3): d=8.79 (d, J=4.9 Hz, 2H), 7.84 (d, J=
4.9 Hz, 2H), 4.46 (t, J=6.2 Hz, 2H), 3.49 (t, J=6.6 Hz, 2H), 2.11–
2.02 ppm (m, 2H). 13C NMR (75.5 MHz, CDCl3): d=165.12, 150.83,
137.29, 122.95, 62.86, 48.31, 28.28 ppm. IR (NaCl): : n˜ =3333, 2949, 2879,
2098, 1733, 1563, 1457, 1346, 1281, 1128, 1063 cmꢁ1
.
Surface modification: Assembly of the isonicotinic acid-functionalized
surfaces 2 and 3 followed synthetic procedures depicted in Scheme 1.
Assembly of monolayers of 1,8-nonadiyne (surface 1): Assembly of the
acetylenylated SiACHTUNGTRENNUNG(100) surface by covalent attachment of the diyne 1 fol-
lowed a previously reported procedure.[8a, 9] After modification, the silicon
wafers were rinsed several times with dichloromethane, ethanol and
water before being either analyzed or further reacted with the azide mol-
ecules 2 and 3.
Attachment of azide molecules 2 and 3 to the acetylenyl surface (surfa-
ces 2 and 3): In a typical “click” procedure, the following were added to
a reaction vial containing the alkyne-functionalized silicon surface (sur-
face 1): 1) the azide molecule (2 or 3, 10 mm, 2-propanol/water, 2:1), 2)
copper(II) sulfate pentahydrate (1 mol% relative to the azide) and 3)
sodium ascorbate (10 mol% relative to the azide). Reactions were car-
ried out at room temperature, in the dark, without excluding air from the
reaction environment and stopped after 24 h by removal of the modified
sample from the reaction vessel.[45] The prepared surface-bound [1,2,3]-
triazoles samples (surfaces 2 and 3) were rinsed consecutively with copi-
ous amounts of water, ethanol, and dichlorometane and then rested at
room temperature for a 12 h period in a 0.05% (w/v) ethylenediamine-
ACHTUNGTRENNUNGtetraacetic acid solution (pH 7.4). Samples were then rinsed with copious
amounts water before being either analyzed or further reacted.
Cytochrome c immobilization: The coordination of cytc onto the isonico-
tinic acid modified electrodes followed a procedure analogous to that of
Waldeck and co-worker on gold surfaces.[14f] In brief, the modified silicon
surface (either surface 1, surface 2 or surface 3) was immersed in a de-
gassed (purged with argon gas) 100 mm cytc and 20 mm sodium phosphate
buffer (pH 7.0) solution for 45 min.[14e] The electrode was then removed
from the solution, rinsed with 20 mm sodium phosphate buffer (pH 7.0)
and mounted into an electrochemical cell.
Acknowledgements
This research was supported by the Australian research Councilꢁs Discov-
ery Projects funding Scheme (project number DP0772356).
electronics: From Theory to Applications (Eds.: I. Willner, E. Katz),
Wiley-VCH, Weinheim, 2005, pp. 35–97.
Surface characterization
Contact angle goniometry: Water contact angles were determined on a
Ramꢇ-Hart 200-F1 goniometer and images were processed with the LB-
ADSA software.[46] Samples were prepared in triplicate with three sepa-
rate spots being measured for each sample.
5966
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 5961 – 5968