First example of the ring-opening transformation of thiazolidines to iminothiols on gold surface

Article abstract of DOI:10.1016/j.mencom.2009.03.013

A new way to construction of the self-assembling monolayers on gold surfaces based on ring opening reactions of thiazolidines to iminothiols followed by Au-S bond formation has been proposed.

Full text of DOI:10.1016/j.mencom.2009.03.013

Mendeleev
Communications
Mendeleev Commun., 2009, 19, 92–93
First example of the ring-opening transformation
of thiazolidines to iminothiols on gold surface
Alexander G. Majouga,a Elena K. Beloglazkina,*a Ivan V. Yudin,a
Rustem D. Rakhimov,a Andrei N. Khlobystovb and Nikolai V. Zyka
a Department of Chemistry, M. V. Lomonosov Moscow State University, 119991 Moscow, Russian Federation.
Fax: +7 495 939 0290; e-mail: beloglazki@mail.ru
b School of Chemistry, University of Nottingham, Nottingham, NG7 2RD, UK.
Fax: +44 (0) 115 95 1356; e-mail: Andrei.Khlobystov@nottingham.ac.uk
DOI: 10.1016/j.mencom.2009.03.013
A new way to construction of the self-assembling monolayers on gold surfaces based on ring opening reactions of thiazolidines to
iminothiols followed by Au–S bond formation has been proposed.
The formation of the self-assembling monolayer (SAM) of
R1
sulfur-containing compounds on metal surfaces (such as gold
and silver) has been a topic of great interest during the past
decade. The majority of these investigations have been focused on
the self-assembly of various alkanethiols and dialkyl disulfides.1
It has been demonstrated that sulfides,2 thiophenols,3 xanto-
genates,4 thioureas5 and other sulfur-containing molecules form
monolayers on gold surface. The SAMs on the solid surface
are of interest for application ranging from molecular sensing
devices to molecular electronics and nonlinear optical materials.6
It is generally accepted that the thiolate monolayers resulting
from the self-assembly of thiols and disulfides are indistin-
guishable.7 One factor that has led to the predominant use of
thiols as the reagent of choice for the formation of SAMs is that
thiols have much higher solubilities than disulfides. The low
solubility of disulfides makes them difficult to use in solution,
and their precipitation has been noted as a marked source of multi-
layer contamination of the substrate if the conditions of the
sample preparation are not controlled carefully.8
R1
O
H
EtOH
R2
+
S
NH
H2N
SH
R2
1 R1 = H, R2 = Ph
2 R1 = H, R2 = 4-MeOC6H4
3 R1 = COOMe, R2 = α-Py
Scheme 2 Synthetic route to the thiazolidines.
surface the adsorption bands of NH are disappeared and C=N
adsorption bands at ~1620 cm–1 are observed.
Compounds 1–3 were studied by cyclic voltammetry (CV)
and rotating disk electrode (RDE) techniques on gold electrode
in anhydrous MeCN with 0.05 M Bu4NBF4 as the supporting
electrolyte.† The electrochemical oxidation and reduction poten-
tials are given in Table 1.
The first reduction step of 1–3 takes place at potentials
between –0.14 and –1.47 V and presumably involves the sulfur
Here we describe a new method for the preparation of self-
assembling monolayers on gold surface based on chemisorption
of iminothiols. Iminothiols are non-cyclic form of the thiazo-
lidines (Scheme 1).
Table 1 Electrochemical oxidation and reduction potentials for compounds
1–3, as measured by Au (SAM) or Pt (solution) electrode. The values after
slash marks refer to peak potentials relevant to reverse scans of CV curves.
EOx/V (Au electrode –
Compound for SAM; Pt electrode – for for SAM; Pt electrode – for
ERed/V (Au electrode –
S
NH
HS
N
10–3 M MeCN solution)
1 (solution) 0.99/ 0.77; 1.83
1 (SAM) 1.84
2 (solution) 1.20/ 0.76; 1.86/ 1.50; 2.60
2 (SAM) 1.74/ 1.28; 2.46
3 (solution) 0.56/ 0.30; 1.56/ 0.86
10–3 M MeCN solution)
R
R
–1.47; 1.73
–1.03/ –0.67
–1.14; –2.14
–0.82/ –0.74
–1.36; –1.74/ 1.60
–0.70/ –0.64; –1.74/ 1.52
Scheme 1
The synthetic route to the thiazolidines is summarized in
Scheme 2. The ligands were prepared in one step from the
corresponding aromatic or heterocyclic aldehyde and amino-
ethane thiol.9 Obtained compounds 1–3 are stable at storage
and soluble in most of the common solvents.
We studied the effectiveness of adsorption of compounds
1–3 from solutions on the surface of a gold electrode. It is
expected that the cyclic form, which prevalently exists in
solution, presumably transforms into an acyclic iminothiol form
during the adsorption of molecules 1–3 on the gold surface,
forming the covalent S–Au bond. Electrochemical (Figure 1,
Table 1) and FT-IR spectroscopic measurements confirm this
transformation.
3 (SAM)
1.65/ 0.97
†
Electrochemical studies were performed using a PI-50-1.1 potentiostat
on Pt (d = 2 mm) or Au (d = 1 mm) electrode. Polycrystalline Au
electrode was polished with a diamond slurry and sonicated for 10 min
in water. The supporting electrolyte was an 0.05 M Bu4NBF4 solution,
and the reference electrode was an Ag | AgCl | KCl (sat.) electrode.
A potential scan rate was 200 (CV) or 20 mV s–1 (RDE), 2800 rpm. All
measurements were made under argon; samples were dissolved in a
preliminarily deaerated solvent. The SAMs of 1–3 were fabricated by
immersing the Au electrode in a 10–3 M acetonitrile solution of a test
compound for at least 24 h. Then, the electrode was rinsed several times
with MeCN, dried in air, and transferred into the pure supporting
electrolyte; after that, CV curves were recorded.
The IR spectra of compounds 1–3 in KBr exhibit NH-adsorp-
tion bonds at ~3230 cm–1. For the same compounds on the gold
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© 2009 Mendeleev Communications. All rights reserved.

Mendeleev Commun., 2009, 19, 92–93
atom, yielding in the electrochemically stable radical anion, a
result that is consistent with previously reported electrochemical
reduction of sulfides.10
The first oxidation step of 1–3 in the solution takes place at
potentials between 0.56 and –1.20 V and presumably involves
the NH group.11 Compound 3', which has no NH group,
oxidized at higher anodic potential. The potential of the second
oxidation peak lies in the region of oxidation potentials of
organic sulfides.10
S
SH
N
R2
R2
N
H
R1
R1
1–3
1'–3'
– 1e
+ 1e
0.56–1.20 V
(–1.14)–(–1.47) V
S
S
Au
electrode
R2
R2
N
N
H
R1
R1
As we can see in Table 1, the oxidation of 1 adsorbed on
the gold electrode surface is retarded and the reduction is
facilitated. This data indicates that compounds 1–3 adsorbed
on the electrode surface may have a structure different from
that in solution. It is evident that both oxidation and reduction
of the adsorbed forms of 1–3 involve the imine fragment. Based
on the electrochemical data obtained for 1–3, we can propose
a scheme of processes occurring at the surface of the gold
electrode, assuming that these compounds are adsorbed in the
open iminothiol form rather than the cyclic thiazolidine form.
The driving force of this process may be the formation of a
thiol self-assembled monolayer during the adsorption of 1–3
in their open forms 1'–3'.
R2
R2
R1
R2
N
N
R1
N
R1
S
S
S
Au
Au
Au
– 1e
1.56–1.84 V
+ 1e
(–0.70)–(–1.03) V
S
S
R2 + Au0
R2 + Au0
N
N
R1
R1
During the reverse of potential after +1.5 V, the corresponding
oxidation anodic peak at a potential of EpRed ~ –0.6 V displaying
the anion RS– is observed (Figure 1).12
– 1e
0.64–0.74 V
S
(a)
R2
N
R1
Scheme 3
This work was supported by the Russian Foundation for Basic
Research (project no. 07-03-00584) and by the Russian Science
Welfare Social Fund.
–2.0
0.0
2.0
E/V
References
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Figure 1 Cyclic voltammograms (0.05 M Bu4NBF4, 20 °C) of (a) com-
pound 1 in MeCN solution (Pt electrode, concentration 10–3 mol dm–3) and
(b) compound 1 adsorbed on Au electrode.
10 A. P. Tomilov, Yu. M. Kargin and I. N. Chernykh, Elektrokhimiya
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Summarizing, the following scheme of the processes taking
place under oxidation and reduction of compounds 1–3 in the
solution and on the Au electrode surface may be proposed
(Scheme 3).
Generalizing the results, we can conclude that we found a
new way to construction of the self-assembling monolayers on
gold surfaces based on ring opening reaction of thiazolidines to
iminothiols followed by Au–S bond formation. This conclu-
sion has been made on the basis of electrochemical and IR
spectroscopy data.
12 J. Simonet, M. Carriou and H. Lund, Liebigs Ann. Chem., 1981, 1665.
Received: 12th September 2009; Com. 09/3214
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