Research on the structure-surface adsorptive activity relationships of triazolyl glycolipid derivatives for mild steel in HCl

Article abstract of DOI:10.1016/j.carres.2012.03.006

Triazolyl glycolipid derivatives constructed via Cu^I-catalyzed azide-alkyne 1,3-dipolar cycloaddition reaction (Cue-AAC) represent a new range of carbohydrate-based scaffolds for use in many fields of the chemical research. Here the surface ads

Full text of DOI:10.1016/j.carres.2012.03.006

Carbohydrate Research 354 (2012) 32–39
Contents lists available at SciVerse ScienceDirect
Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
Research on the structure–surface adsorptive activity relationships
of triazolyl glycolipid derivatives for mild steel in HCl
⇑
⇑
Hai-Lin Zhang, Xiao-Peng He , Qiong Deng, Yi-Tao Long, Guo-Rong Chen , Kaixian Chen
Key Laboratory for Advanced Materials & Institute of Fine Chemicals, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, PR China
a r t i c l e i n f o
a b s t r a c t
Triazolyl glycolipid derivatives constructed via CuI-catalyzed azide-alkyne 1,3-dipolar cycloaddition reac-
tion (Cue-AAC) represent a new range of carbohydrate-based scaffolds for use in many fields of the chem-
ical research. Here the surface adsorptive ability of series of our previously prepared C1- or C6-triazole
linked gluco- and galactolipid derivatives for mild steel in 1 M HCl was studied via electrochemical
impedance spectroscopy (EIS). Results indicated that these monosaccharide–fatty acid conjugates are
weak inhibitors against HCl corrosion for mild steel. Moreover, some newly synthesized triazolyl
disaccharide (maltose)–fatty alcohol conjugates failed to display enhanced activity, meaning that the
structural enlargement of the sugar moiety does not favor the iron surface adsorption. However, a bis-
triazolyl glycolipid derivative, which was realized by introducing a benzenesulfonamide group via
Cue-AAC to the C6-position of a C1-triazolyl glucolipid analog, eventually showed significantly improved
adsorptive potency compared to that of its former counterparts. The corrosion inhibitive modality of this
compound for mild steel in HCl was subsequently studied via potentiodynamic polarization and thermo-
dynamic calculations.
Article history:
Received 4 February 2012
Received in revised form 6 March 2012
Accepted 7 March 2012
Available online 17 March 2012
Keywords:
Glycolipid
Cue-AAC
EIS
Corrosion
Inhibitor
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
the other hand, despite their abundance in nature, most of the
structurally simple amino acids lack essentially the potency for
During the everyday industrial washing and scaling processes of
various metallic equipments in acidic solutions, the presence of
corrosion inhibitors may necessarily assuage the excessive dissolu-
tion of heavy metals that harm both nature and our health. Due to
their structural versatility, easy accessibility and superior potency,
organic compounds are now frequently used in place of inorganic
materials for corrosion inhibition. However, despite the good
protective ability of the numerous identified small-molecule corro-
sion inhibitors for metals, the toxic nature of these compounds
embodying extensive polycyclic rings yet lowers their potential to-
ward industrialization.1 As a result, identification of environmen-
tally friendly corrosion inhibitors that simultaneously possess
admirable inhibitive potency becomes the mainstream of current
corrosion investigations.
Some natural products including amino acids and plant extracts
have been proposed, alternatively, as the green surrogates of pres-
ent corrosion inhibitors.2–5 Nevertheless, they also have limitations
that hamper the further commercialization. On the one hand, iso-
lation of products from natural resources may be of low efficiency
due to the long extraction time/step and poor isolated yields. On
metal surface adsorption. Therefore, the exertion of efficient chem-
ical modifications upon easily available natural metabolites could
become a promising strategy for acquiring potency-enhanced cor-
rosion inhibitors with potentially retained greenness.
Taking nature’s hint for the creation of her primary metabolites
such as polysaccharides, polynucleosides, and polypeptides,
Sharpless and co-workers coined ‘Click Chemistry’ a decade ago.6
This new synthetic concept prompts the exploration of efficient
carbon-heteroatom ligation reactions for the modular construction
of useful compound libraries in high yields without tedious
laboratorial workup. CuI-catalyzed azide-alkyne 1,3-dipolar
cycloaddition reaction (Cue-AAC)7–9 in forming the unique 1,4-
disubstituted 1,2,3-triazoles represents arguably the best para-
digm of click chemistry, and has realized the effective construction
of myriad functional compounds including triazole-functionalized
carbohydrate derivatives.10–23
Enlightened by this, we sought to synthesize triazole-modified
natural products as our strategy for the innovation of new
corrosion inhibitors. Since the sugar moiety in connection with a
triazole group is envisioned capable for metal surface adsorption,
while their lipid end could form presumably additional protective
films by generating lipid arrays over the surface, we report here a
research on the structure–surface adsorption activity relationships
of triazolyl glycolipids for mild steel in HCl. The adsorptive ability
⇑
Corresponding authors. Tel.: +86 21 64253016; fax: +86 21 64252758.
E-mail addresses: xphe@ecust.edu.cn (X.-P. He), mrs_guorongchen@ecust.edu.cn
(G.-R. Chen).
0008-6215/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.carres.2012.03.006

H.-L. Zhang et al. / Carbohydrate Research 354 (2012) 32–39
33
Table 1
of three series of our previously synthesized triazolyl monosaccha-
ride–fatty acid conjugates was first tested for mild steel in HCl via
electrochemical impedance spectroscopy (EIS).
EIS parameters for mild steel in 1 M HCl without (blank) and with compounds 1–27
Compd
Rs
(X
cm2)
Rct
(X
cm2)
CPE (l
F cmÀ2
)
n
g (%)
Blank
1
2
3
4
5
6
7
8
4.19
8.05
6.89
5.96
10.68
7.50
5.97
10.71
7.58
10.05
9.22
6.84
10.68
10.76
10.73
4.16
6.58
5.22
5.88
8.12
9.80
5.85
5.39
4.20
9.90
7.28
4.24
10.74
62.72
77.33
87.03
83.78
105.2
109.8
106.2
112.0
114.8
105.3
99.57
88.99
103.0
131.9
123.1
120.9
113.3
113.5
118.7
66.88
77.94
73.62
79.58
127.8
103.7
103.9
105.9
104.1
295.7
127.0
129.4
119.9
106.4
108.5
122.3
107.6
188.7
154.3
91.12
301.6
106.4
121.6
128.1
300.7
107.3
100.7
102.8
148.4
157.4
290.5
255.5
92.04
129.0
103.2
102.1
106.0
0.80
0.82
0.83
0.84
0.82
0.83
0.83
0.82
0.83
0.79
0.83
0.79
0.82
0.80
0.80
0.78
0.83
0.84
0.83
0.81
0.79
0.79
0.80
0.84
0.80
0.83
0.83
0.82
n.a.a
18.9
27.9
25.1
40.4
42.9
40.9
44.0
45.4
40.4
37.0
29.5
39.1
52.4
49.0
48.1
44.6
44.7
47.2
2. Results and discussion
Preparation of triazole-functionalized glycolipid derivatives has
been reported by several independent research groups.24–28 These
new carbohydrate–lipid conjugates have addressed interesting
properties through many interdisciplinary studies.
Recently, we have disclosed three series of novel C1- or C6-tri-
azole-linked monosaccharide–lipid conjugates constructed via
Cue-AAC, shown in Figure 1.26–28 A preliminary EIS study indicated
that the C1-substituted glycolipids 1–9 have good ability for gold
surface adsorption in CH2Cl2.26 As a result, we chose to measure
practically the surface adsorptive potency of these compounds,
and that of their C6-triazole-linked gluco- and galactolipid ana-
logues for the industrially frequently used mild steel in 1 M HCl
via EIS.
A conventional three-electrode assembly that comprises the
mild steel with 1.0 cm2 exposed surface area as the working elec-
trode, platinum foil as the counter electrode, and a saturated calo-
mel electrode (SCE) as the reference electrode, was used for
electrochemical experiments. The electrochemical process of these
electrodes in the absence and presence of compounds 1–27 (10À3
M) in 1 M HCl was examined via EIS at open-circuit potential and
the resulting Nyquist plots are given in Figure S-1.
According to the suited equivalent circuit model for these plots
(Fig. 7, Section 4), the corresponding impedance parameters
including solution resistance (Rs), charge transfer resistance (Rct),
constant phase element (CPE) and phase shift (n) were obtained
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
6.22
19.5
14.8
21.2
50.9
39.5
39.6
40.8
39.8
a
n.a. means not available.
in order to give a more accurate fit to the experimental results and
n can be described as a degree of surface roughness and non-homo-
geneity. The shape of the impedance curves for blank (HCl alone)
and that for all compounds features similarly a depressed semicir-
cle, which indicates that the corrosion was mainly controlled by
charge transfer. We thus illustrated their Rct values which may re-
flect the solidness of the molecular film formed by the compound
(if any) at the metal–solution interface in Figure 2 for a clearer
comparison.2–5,29–31
The triazolyl glycolipid derivatives that feature relatively short
lipid chains of 5C (1, 10, 19), 7C (2, 11, 20), and 9C (3, 12, 21) pos-
sess low Rct values comparable to that of the blank, and poor inhib-
itive efficiencies ranging from 15% to 39%. In contrast, their
analogues with prolonged lipid chains showed both slightly in-
and the inhibitive efficiencies (g) were calculated (Table 1), in
which CPE is frequently used in place of a double layer capacitance
HO
(CH2)n
Series 1:
O
1: n = 1; 2: n = 3; 3: n = 5
4: n = 8 5: n = 9; 6: n = 10
7: n = 11; 8: n = 12; 9: n = 14
HO
HO
O
O
1
N
HO
N
N
creased Rct and
g values. The C1- and C6-triazolyl glucolipid deriv-
N
atives 4–9 and 12–18 bearing alkyl chains of 12C–18C have similar
inhibitive efficiencies of around 45%. For the C6-triazolyl galactol-
ipid analogues 22–27, compound 23 with a 13C-alkyl chain exhib-
N
N
O
6
Series 2:
O
10: n = 1; 11: n = 3; 12: n = 5
13: n = 8; 14: n = 9; 15: n = 10
16: n = 11; 17: n = 12; 18: n = 14
ited the best efficiency (51%), whereas the
g values of its
HO
HO
counterparts 24–27 bearing further prolonged lipid chains lowered
modestly.
O
4
n(H2C)
Although it could seemingly be deduced that by coupling longer
lipid chains of >12C with the sugar moiety via Cue-AAC, the result-
ing surface protective ability of the triazolyl glycolipids can be in-
creased, there are yet no obvious structure–activity relationships
(SARs) available among the three series. Neither the substitution
position of the triazolyl lipid on the sugar scaffold (series 1 vs ser-
ies 2) nor the C4-epimeric identity between glucose and galactose
(series 2 vs series 3) is influential to their corrosion inhibitive
potency.
Since our previously synthesized triazolyl monosaccharide–
lipid conjugates failed to exhibit acceptable inhibitive potency
against HCl corrosion for mild steel, we attempted to further pre-
pare some disaccharide–lipid hybrids via Cue-AAC for evaluating
whether the enlargement of the sugar moiety would bring on po-
sitive impact. As shown in Scheme 1, a known azido peracetyl
OMe
N
OH
N
N
O
Series 3:
O
19: n = 1; 20: n = 3; 21: n = 5
22: n = 8; 23: n = 9; 24: n = 10
HO
HO
O
25
26
27
: n = 11; : n = 12; : n = 14
n(H2C)
OMe
OH
Figure 1. Previously synthesized C1- or C6-substituted triazolyl glycolipid
derivatives.

34
H.-L. Zhang et al. / Carbohydrate Research 354 (2012) 32–39
OAc
O
a
b
c
O
AcO
AcO
OAc
O
+
(CH2)n
a1: n = 1; a2: n = 3; a3: n = 7
O
OAc
AcO
N3
b
OAc
OH
O
HO
HO
OH
n(H2C)
i, ii
O
O
OH
O
HO
N
OH
N
28: n = 1 (82%)
N
29: n = 3 (86%); 30: n = 7 (79%)
Scheme 1. Reagents and conditions: (i) CuSO4Á5H2O, Na ascorbate, CH2Cl2/H2O; (ii)
MeOH/Et3N/H2O.
Figure 3. Nyquist plots of mild steel in 1 M HCl in the absence (blank) and presence
of 10À3 M triazolyl maltose–lipid conjugates.
Table 2
Figure 2. Collected Rct values of mild steel in the absence (blank) and presence of
compounds (a) 1–9; (b) 10–18; (c) 19–27.
EIS parameters for mild steel in 1 M HCl without (blank) and with compounds 28–30
Compd
Rs
(
X
cm2)
Rct
(X
cm2)
CPE (l
F cmÀ2
)
n
g (%)
Blank
28
29
4.19
8.23
6.83
4.48
62.72
102.5
103.2
115.2
295.7
112.1
117.1
97.71
0.80
0.83
0.84
0.83
n.a.a
38.8
39.2
45.6
maltose b32 and three propargyl fatty alcohols bearing alkyl chains
of 6C (a1), 8C (a2), and 12C (a3), respectively, were used for the
Cue-AAC. Under the action of Na ascorbate and CuSO4Á5H2O, the
desired 1,4-disubstituted triazolyl conjugates were obtained as
the unique products which were directly subject to deacetylation
in MeOH/Et3N/H2O by stirring over night. The desired triazole-con-
nected maltose–lipid hybrids 28–30 were acquired in high yields
of 80–86%.
The electrochemical process of mild steels in 1 M HCl in the
presence of these compounds (10À3 M) was then evaluated via
EIS. The resulting Nyquist plots are shown in Figure 3 and the EIS
parameters obtained from the same circuit model are listed in Ta-
ble 2. The capacitive curves of 28–30 displayed similar shape to
those of their monosaccharide counterparts (Fig. S-1), indicating
that the corrosion was likewise controlled by charge transfer.
30
a
n.a. means not available.
and galactolipid analogues. This demonstrates that enlargement of
the sugar moiety does not improve the surface adsorptive ability of
the triazolyl glycolipid derivatives.
Subsequently, we tended to introduce an additional functional
group to a monosaccharide-based glycolipid scaffold via Cue-AAC
in order to investigate whether such a structural modification
would be effective. As heteroatom-rich compounds are known as
preferred corrosion inhibitors due to their possession of lone pairs
to coordinate with metals that have available empty d-orbital, we
chose to introduce p-amino benzenesulfonamide (BSA) c that con-
tains simultaneously O, N, and S atoms, and a benzene ring that
may provide supplementary interactions with the metal surface,
to a known glycolipid derivative e1 (Scheme 2).24 Moreover, c
However, as depicted by their unfavorable Rct and
g values
(around 40%, Table 2) similar to those afforded by series 1–3 (Table
1), the triazolyl maltolipid derivatives prepared did not exhibit
markedly enhanced inhibitive potency with respect to their gluco-

H.-L. Zhang et al. / Carbohydrate Research 354 (2012) 32–39
35
was directly subject to a debenzylation under the action of PdCl2/
H2, affording the desired bis-triazolyl conjugate 31 with both a li-
pid chain and a BSA group attached on the sugar scaffold in 85%
yield. For study of the SAR, compound 32 with solely a triazolyl
BSA group on the C6-position of a methyl O-glucoside was synthe-
sized by Cue-AAC of the known 6-O-propargyl methyl O-glucoside
f34 with the azide d, and then debenzylation with PdCl2/H2 in a
two-step yield of 89%, while triazole-linked BSA–lipid conjugate
33 was synthesized via Cue-AAC of the propargyl lipid a3 with d
in a high yield of 92%. The EIS of the prepared compounds was
sequentially performed and the corresponding parameters were
calculated through the same circuit model (Fig. 7).
We first observe that c alone displayed very weak inhibitive ef-
fect in HCl for mild steel (Fig. 4 and Table 3). However, to our de-
light, the bis-triazole conjugate 31 eventually exhibited favorable
potency against the corrosion.
As shown in both Figure 4 and Table 3, the presence of bis-
triazole 31 in 1 M HCl resulted in a significantly improved Rct
O
S
O
S
Ref
H2N
NH2
N3
NH2
O
O
c
d
An additional
C6-modification
HO
O
(H2C)7
O
(H2C)7
N
HO
BnO
BnO
i-iv
O
O
O
HO
N
OH
N
OBn
N
N
N
e1
e
2 (71% over 4 steps)
(g = 87.3%) for mild steel in contrast with 13 and 30, two mono-
triazolyl analogues that exhibited the best potencies among the
former glycolipid series. In order to evaluate whether the triazolyl
BSA fragment functions dominantly in the context of the surface
adsorption of 31, the corrosion inhibitive profile of the mono-triaz-
olyl BSA–methyl O-glucoside conjugate 32 and that of the triazolyl
BSA–lipid conjugate 33 were also characterized via EIS (Fig. 4). As
shown in Table 3, the inhibitive potency of 32 is as weak as those of
O
S
N
N
H2N
N
O
v,vi
O
e2 + d
(H2C)7
N
HO
HO
the former mono-triazolyl lipid–sugar conjugates
(
g
= 40%)
31 (85% over
O
2 steps)
whereas that of 33 appeared to be only slightly better (
g
= 65%).
O
This clearly demonstrates that the additional Cue-AAC modifica-
tion performed in fabricating the bis-triazolyl derivative based on
a sugar scaffold is necessary for obtaining the adequate inhibitive
efficiency against HCl corrosion.
OH
N
N
Potentiodynamic polarization was then conducted under vari-
ous concentrations of 31 for elaboration of its potential inhibitive
mechanism and the resulting polarization curves are shown in
Fig. 5. Polarization parameters including corrosion potential (Ecorr),
anodic (ba) and cathodic (bc) Tafel slopes and corrosion current
density (icorr), and the calculated surface coverage rate (h) and inhi-
O
S
N
N
O
H2N
N
O
BnO
BnO
v,vi
O
O
bition efficiency (g) values are given in Table 4. Upon increase of
OMe
the inhibitor in the solution, both ba and bc values varied accord-
ingly and the icorr values decreased prominently. This means that
both the anodic metal dissolution of iron and the cathodic hydro-
HO
HO
O
32 (89% over
OBn
2 steps)
f
OMe
gen evolution reaction were inhibited by 31. Moreover, the
g value
(88.7%, Table 4) at the highest inhibitor concentration (10À3 M) ob-
tained from Tafel extrapolation is in a good agreement with that
obtained by EIS (87.3%, Table 3). The corrosion potential of mild
OH
O
S
N
N
N
v
H2N
a3 + d
O
O
33 (92%)
Scheme 2. Reagents and conditions: (i) TBDMSCl, DMAP, pyridine; (ii) NaH, BnBr,
DMF; (iii) AcCl, MeOH; (iv) NaH, propargyl bromide, DMF; (v) CuSO4Á5H2O, Na
ascorbate, CH2Cl2/H2O/acetone; (vi) PdCl2/H2, MeOH/CH2Cl2.
frequently occurs in many drug entities, demonstrating its safety
to human body.
As shown in Scheme 2, according to a literature method, p-azido
BSA d was acquired.33 A four-step sequence involving C6-silylation
with TBDMSCl, O-benzylation with BnBr and NaH, C6-desilylation
with AcCl, and then O-propargylation with propargyl bromide gave
the C6-propargylated 1-triazolyl glycolipid e2 in 71% yield.
Subsequent Cue-AAC of d with e2 led to a unique product which
Figure 4. Nyquist plots of mild steel in 1 M HCl in the absence (blank) and presence
of 10À3 M compounds.

36
H.-L. Zhang et al. / Carbohydrate Research 354 (2012) 32–39
Table 3
EIS parameters for mild steel in 1 M HCl without (blank) and with compounds c, 13
and 30–33
Compd
Rs
(X
cm2)
Rct
(X
cm2)
CPE (l
F cmÀ2
)
n
g (%)
Blank
c
4.19
5.24
10.76
4.48
3.90
7.38
7.08
62.72
86.92
131.9
115.2
494.7
104.5
177.9
295.7
250.9
121.6
97.71
55.03
122.9
159.9
0.80
0.79
0.80
0.83
0.83
0.82
0.80
n.a.a
27.8
52.4
45.6
87.3
40.0
64.7
13
30
31
32
33
a
n.a. means not available.
×
×
×
×
×
Figure 6. Langmuir isotherm of 31 adsorbing onto the mild steel surface in 1 M HCl
at 298 K.
Table 5
The calculated Kads and DG0 values for mild steel in 1 M HCl containing inhibitor 31
ads
at 298 K
G0ads (kJ molÀ1
À39.7
)
Compd
T (K)
Slope
1.12
Kads (MÀ1
)
D
31
298
166881.9
Meanwhile, it can be deduced that this inhibitor adopts both elec-
trostatic-adsorption and chemo-adsorption on the mild steel sur-
face in 1 M HCl, whereas the latter is privileged.30
Figure 5. Polarization curves of mild steel in 1 M HCl in the absence (blank) and
presence of various concentrations of compound 31.
3. Conclusion
To summarize, series of our previously prepared triazolyl glyco-
lipid derivatives were manifested not to be good corrosion inhibi-
tors for mild steel in 1 M HCl via EIS, whereas the successively
synthesized triazolyl disaccharide–lipid conjugates via Cue-AAC
also displayed weak potency for mild steel protection. This first im-
plies that the structural variations such as the change in the substi-
tution position of the triazolyl lipid on the sugar moiety, the
prolongation of the lipid chain and the enlargement of the sugar
ring do not enhance positively the corrosion inhibitive competency
of triazolyl glycolipid derivatives. A subsequent stepwise Cue-AAC
strategy by grafting an additional heteroatom-rich BSA group to a
‘pre-clicked’ glucolipid derivative led to, however, an admirable
inhibitor 31 with remarkably improved protective potency for mild
steel in HCl. Moreover, its analogues 32 with solely a triazolyl BSA
substituent on a methyl O-glucoside and the mono-triazolyl BSA–
lipid conjugate 33 exhibited markedly decreased potency, indicat-
ing that the triazolyl lipid and BSA functionalities together might
exert a synergistic effect in their surface adsorptive process. Polar-
ization and isotherm calculations eventually elaborated that 31 is a
mixed-type inhibitor and adopts mainly chemo-adsorption toward
the metal surface. This study would thus offer collectively new
steel in the presence of the inhibitor shifted by 2–18 mV as regards
that of the blank, which suggests that 31 behaves as a mixed-type
corrosion inhibitor for mild steel by first adsorbing on the metal
surface and then blocking the reaction sites of the metal surface
without affecting the anodic and cathodic reactions.29
Adsorption isotherm calculations were sequentially performed
to further assess the inhibitive mechanism of 31 by tentatively fit-
ting the above-obtained h values (Table 4) at various concentra-
tions (C) to Temkin, Frumkin, Freundluich, and Langmuir
isotherm models, respectively. The best correlation between the
experimental results and isotherm functions was obtained using
the Langmuir adsorption isotherm interpreted by the following
equation: C/h = 1/Kads + C (where Kads is the equilibrium constant
of the adsorption process). Plotting of C versus C/h resulted in a lin-
ear correlation (Fig. 6) and the standard free energy of adsorption
(G0ads
55.5)exp(À
)
was estimated by the following equation: Kads = (1/
D
G0ads/RT) (where 55.5 is the molar concentration of
water in the solution expressed in the molarity unit M). As shown
in Table 5, the
D
G0ads value (À39.7) obtained indicates that the
adsorption process of 31 to the surface is spontaneous and the
interaction of the adsorbed layer with the steel surface is stable.
Table 4
Polarization parameters for mild steel in 1 M HCl without (blank) and with various concentrations of compound 31
31 (M)
Ecorr (mV)
icorr
(
l
A cm2)
ba (mV decÀ1
)
Àbc (mV decÀ1
)
h
g (%)
Blank
À470.7
À488.2
À474.7
À478.6
À472.2
À472.8
654.2
203.9
140.2
106.9
88.44
74.18
191.9
106.7
77.78
101.8
77.91
78.59
194.4
157.9
159.5
151.9
159.3
158.4
n.aa
n.a.
1.0 Â 10À5
3.2 Â 10À5
1.0 Â 10À4
3.2 Â 10À4
1.0 Â 10À3
0.69
0.79
0.84
0.86
0.89
68.8
78.6
83.7
86.5
88.7
a
n.a. means not available.

H.-L. Zhang et al. / Carbohydrate Research 354 (2012) 32–39
37
insights into the future design and construction of triazolyl glyco-
lipid derivatives as potential corrosion inhibitors.
3.75 (t, J = 9.1 Hz, 1H), 3.71 (m, 1H), 3.69–3.60 (m, 3H), 3.49 (t,
J = 6.6 Hz, 2H), 3.47 (dd, J = 8.8, 3.7 Hz, 1H), 3.27 (t, J = 9.3 Hz,
1H), 1.56 (m, 2H), 1.26 (br s, 18H), 0.87 (t, J = 6.8 Hz, 3H); 13C
NMR (100 MHz, CDCl3 + CD3OH) d 144.6, 123.3, 100.9, 87.5, 77.7,
76.5, 73.5, 72.9, 72.2, 71.1, 69.5, 63.6, 60.9, 60.6, 57.8, 31.8, 29.6,
29.5, 29.5, 29.4, 29.3, 29.2, 25.9, 22.5, 17.9, 13.9; HR-ESI-MS m/z:
calcd for C27H49N3O11 + H 592.3445, found 592.3441.
4. Experimental section
4.1. Synthesis
Solvents were purified by standard procedures. Petroleum ether
(PE) used refers to the fraction boiling in the range 60–90 °C. 1H and
13C NMR spectra were recorded on a Bruker AM-400 spectrometer
in CDCl3, D2O or CD3OD solutions using TMS as the internal stan-
dard (chemical shifts in parts per million). Standard abbreviations
are used to describe the signal multiplicity. All reactions were mon-
itored by TLC (Yantai Marine Chemical Co. Ltd, China). High resolu-
tion mass spectra (HRMS) were recorded on a Waters LCT Premier
XE spectrometer using standard conditions (ESI, 70 eV). Analytical
HPLC was measured using Agilent 1100 Series equipment.
4.1.2. Synthesis of [1-(2,3,4-Tri-O-benzyl-6-O-propargyl-b-D-
glucopyranosyl)-1H-1,2,3-triazol-4-yl]methyl n-dodecyl ether
(e2)
To a well-stirred solution of e1 (400 mg, 0.93 mmol) in pyridine
(7 mL) at 0 °C were added TBDMSCl (196.4 mg, 1.30 mmol) and
DMAP (45.5 mg, 0.37 mmol). The mixture was then allowed to
reach rt and stirred for 6 h. The resulting mixture was concentrated
under reduced pressure and the residue was diluted with CH2Cl2
and washed successively with 1 N HCl and 5% aq NaHCO3. The
combined organic layer was dried over MgSO4 and concentrated
under reduced pressure to give a crude product which was dis-
4.1.1. General procedure for the synthesis of compounds 28–30
To a well-stirred biphasic solution of the per-O-acetylated gly-
cosyl azide (1 equiv) and the alkynyl ether (2 equiv) in CH2Cl2
(8–10 mL) and H2O (6 mL), were added CuSO4Á5H2O (1.5 equiv)
and sodium ascorbate (2.5 equiv), and this mixture was stirred at
rt for 6 h. The resulting mixture was diluted with CH2Cl2 and then
washed with brine. The combined organic layer was dried over
MgSO4 and then concentrated under reduced pressure to give a
crude residue which was directly dissolved in MeOH/Et3N/H2O
(8:1:1, V/V/V) and stirred overnight at rt. The resulting solution
was concentrated to dryness to give a thick syrup which was puri-
fied by column chromatography.
solved in DMF (8 mL). BnBr (443.8 lL, 3.72 mmol) was added and
the resulting solution was cooled to 0 °C, followed by addition of
60% NaH (148.8 mg, 3.72 mmol) in 3 batches. After stirring at rt
for 2 h, the reaction was quenched with MeOH (2 mL) and the mix-
ture was concentrated in vacuum. The residue was diluted with
EtOAc and washed successively with 1 N HCl and brine. The organ-
ic layer was combined, dried over MgSO4 and concentrated under
reduced pressure. The resulting crude residue was dissolved in
MeOH (12 mL) and cooled to 0 °C. AcCl (329.2 lL, 4.66 mmol)
was added dropwise and the mixture was stirred at rt for 1 h.
The resulting mixture was concentrated under reduced pressure
and the resulting residue was dissolved directly in DMF (8 mL), fol-
lowed by addition of propargyl bromide (109.3 lL, 1.40 mmol). The
4.1.1.1. (1-b-
ether (28).
D
-Maltosyl-1H-1,2,3-triazol-4-yl)methyl n-hexyl
From b (217.4 mg, 0.329 mmol) and a1 (92.2 mg,
resulting mixture was cooled to 0 °C and 60% NaH (56.0 mg,
1.40 mmol) was added. After stirring at rt for 6 h, H2O (8 mL)
was added and the mixture was concentrated under reduced pres-
sure. The resulting residue was diluted with EtOAc and washed
with brine. The combined organic layers were dried over MgSO4,
concentrated under reduced pressure and eventually purified by
column chromatography (petroleum ether–EtOAc, 6:1?2:1) to
give e2 (492.3 mg, 71.7% over 4 steps) as a white crystalline solid.
TLC: Rf = 0.60 (petroleum ether–EtOAc, 2:1). 1H NMR (400 MHz,
CDCl3) d 7.58 (s, 1H), 7.30–7.20 (m, 10H), 7.16–7.10 (m, 3H), 6.88
(dd, J = 6.6, 2.8 Hz, 2H), 5.51 (d, J = 9.1 Hz, 1H), 4.86 (s, 2H), 4.83
(d, J = 10.8 Hz, 1H), 4.68 (d, J = 10.8 Hz, 1H), 4.55 (dd, J = 15.2,
12.8 Hz, 2H), 4.41 (d, J = 10.5 Hz, 1H), 4.13 (dd, J = 15.9, 2.4 Hz,
1H), 4.03 (dd, J = 15.9, 2.3 Hz, 1H), 3.98 (dd, J = 16.0, 9.7 Hz, 2H),
3.81–3.71 (m, 3H), 3.67 (dd, J = 10.9, 1.5 Hz, 1H), 3.65–3.60 (m,
1H), 3.42 (t, J = 6.7 Hz, 2H), 2.31 (t, J = 2.3 Hz, 1H), 1.50 (m, 2H),
1.17 (br s, 18H), 0.81 (t, J = 6.8 Hz, 3H).
0.66 mmol), column chromatography (CH2Cl2–EtOH, 3:1?3:2)
afforded 28 as a white solid (137.3 mg, 82.2%). TLC: Rf = 0.60
(CH2Cl2–MeOH, 1:1). 1H NMR (400 MHz, D2O) d 8.28 (s, 1H), 5.80
(d, J = 8.5 Hz, 1H), 5.51 (d, J = 3.8 Hz, 1H), 4.70 (s, 2H), 4.09–4.00
(m, 2H), 3.95 (d, J = 12.0 Hz, 1H), 3.92–3.87 (m, 3H), 3.86 (d,
J = 13.4 Hz, 1H), 3.82–3.70 (m, 3H), 3.63 (dd, J = 10.0, 4.0 Hz, 1H),
3.61 (t, J = 6.8 Hz, 2H), 3.46 (t, J = 9.4 Hz, 1H), 1.59 (m, 2H), 1.36–
1.23 (br m, 6H), 0.86 (t, J = 6.8 Hz, 3H); 13C NMR (100 MHz, D2O)
d 144.5, 123.9, 99.9, 87.3, 77.5, 76.4, 76.2, 72.9, 72.8, 72.2, 71.8,
70.7, 69.3, 63.0, 60.5, 60.4, 31.4, 29.0, 25.3, 22.3, 13.5; HR-ESI-MS
m/z: calcd for C21H37N3O11 + H 508.2506, found 508.2504.
4.1.1.2. (1-b-
ether (29).
D
-Maltosyl-1H-1,2,3-triazol-4-yl)methyl n-octyl
From b (203.9 mg, 0.31 mmol) and a2 (103.7 mg,
0.62 mmol), column chromatography (CH2Cl2–EtOH, 3:1?3:2)
afforded 29 as a white solid (141.2 mg, 85.6%). TLC: Rf = 0.68
(CH2Cl2–MeOH, 1:1). 1H NMR (400 MHz, D2O) d 8.15 (s, 1H), 5.71
(d, J = 7.7 Hz, 1H), 5.45 (d, J = 3.0 Hz, 1H), 4.54 (s, 2H), 4.00 (m,
2H), 3.91–3.81 (m, 4H), 3.75 (m, 4H), 3.62 (dd, J = 10.0, 3.1 Hz,
1H), 3.53–3.42 (m, 3H), 1.57 (br s, 2H), 1.30 (br s, 10H), 0.89 (t,
J = 6.0 Hz, 3H); 13C NMR (100 MHz, D2O + CD3OH) d 144.6, 123.9,
100.2, 87.5, 77.7, 76.6, 73.1, 72.9, 72.3, 72.0, 70.9, 69.4, 63.4, 60.7,
60.6, 32.0, 29.6, 29.4, 26.1, 22.8, 14.0; HR-ESI-MS m/z: calcd for
4.1.3. Synthesis of 4-{4-[(4-n-Dodecyloxymethyl-1H-1,2,3-
triazol-1-yl)b-D-glucopyranosd-6-yloxy]methyl-1H-1,2,3-
triazol-1-yl} benzenesulfonamide (31)
To a well-stirred biphasic solution of e2 (106 mg, 0.14 mmol)
and d (42.7 mg, 0.22 mmol) in CH2Cl2/H2O/acetone (10:5:1, V/V/
V) were added CuSO4Á5H2O (107.6 mg, 0.43 mmol) and sodium
ascorbate (170.7 mg, 0.86 mmol), and the mixture was stirred at
30 °C for 6 h. The resulting mixture was then diluted with CH2Cl2
and washed with saturated aq ethylene diamine tetraacetic acid
(EDTA) and brine. The combined organic layer was dried over
MgSO4 and concentrated under reduced pressure to give a crude
residue. This was then dissolved in MeOH/CH2Cl2 (2:1, V/V) and
PdCl2 (10 mg, 0.0564 mmol) was added. The mixture was stirred
vigorously under hydrogen atmosphere at 35 °C for 1 h. The result-
ing mixture was then filtered and concentrated under reduced
pressure. The resulting crude residue was purified by column chro-
C23H41N3O11 + H 536.2819, found 536.2820.
4.1.1.3. (1-b-
ether (30).
D
-Maltosyl-1H-1,2,3-triazol-4-yl)methyl n-dodecyl
From b (177.5 mg, 0.27 mmol) and a3 (120.4 mg,
0.54 mmol), column chromatography (CH2Cl2–EtOH, 3:1?2:1)
afforded 30 as a white solid (124.6 mg, 78.6%). TLC: Rf = 0.69
(CH2Cl2–MeOH, 1:1). 1H NMR (400 MHz, CD3OD) d 8.15 (s, 1H),
5.62 (d, J = 9.1 Hz, 1H), 5.23 (d, J = 3.7 Hz, 1H), 4.57 (s, 2H), 3.94
(t, J = 9.1 Hz, 1H), 3.87 (dd, J = 14.5, 2.2 Hz, 2H), 3.82 (m, 2H),

38
H.-L. Zhang et al. / Carbohydrate Research 354 (2012) 32–39
matography (CH2Cl2–EtOH, 10:1?4:1) to give 31 (81.7 mg, 85.2%)
as a white solid. TLC: Rf = 0.57 (CH2Cl2–MeOH, 4:1). 1H NMR
(400 MHz, CD3OD) d 8.50 (s, 1H), 8.12 (s, 1H), 8.05 (d, J = 8.8 Hz,
2H), 7.95 (d, J = 8.7 Hz, 2H), 5.60 (d, J = 9.2 Hz, 1H), 4.69 (d,
J = 2.4 Hz, 2H), 4.54 (s, 2H), 3.96–3.88 (m, 2H), 3.81 (dd, J = 11.1,
5.3 Hz, 1H), 3.73 (dd, J = 8.1, 5.1 Hz, 1H), 3.60–3.52 (m, 2H), 3.47
(t, J = 6.6 Hz, 2H), 1.53 (m, 2H), 1.24 (br s, 18H), 0.86 (t, J = 6.8 Hz,
3H); 13C NMR (100 MHz, CD3OD) d 145.1, 140.5, 129.1, 124.4,
123.3, 121.5, 89.5, 79.9, 79.6, 79.2, 78.9, 78.4, 73.8, 71.9, 70.8,
70.7, 65.3, 64.6, 33.1, 30.8, 30.8, 30.8, 30.7, 30.6, 30.5, 27.2, 23.8,
14.6; HR-ESI-MS m/z: calcd for C30H47N7O8S + H 666.3285, found
666.3290; HPLC (tR = 4.5 min over 20 min of 100% methanol, purity
100%).
Figure 7. Electric circuit model for the EIS plots.
EtOH = 1:1, V/V). The electrochemical experiments were carried
out using a conventional three-electrode cell assembly at rt. Mild
steel strips with a 1.0 cm2 exposed surface area were used as work-
ing electrode, platinum foil was used as the counter electrode, and
a saturated calomel electrode (SCE) was used as the reference elec-
trode. The potentiodynamic polarization curves were obtained
from À250 mVSCE to +250 mVSCE (vs open circuit potential [OCP])
with a sweep rate of 0.5 mV/s on a CHI660C apparatus. EIS mea-
surements were carried out in 100 kHz to 10 mHz frequency range
at the steady OCP disturbed with an amplitude of 10 mV on a ZAH-
NER apparatus. The raw electrochemical data were collected and
analyzed by the electrochemical software ZSimpWin. The EIS
parameters were calculated using the following circuit model:
4.1.4. Synthesis of 4-[4-(Methyl a-D-glucopyranosid-6-
yloxy)methyl-1H-1,2,3-triazol-1-yl] benzenesulfonamide (32)
To a well-stirred biphasic solution of f (343 mg, 0.68 mmol) and
d (175.8 mg, 0.89 mmol) in CH2Cl2/H2O/Acetone (3:1:1, V/V/V)
were added CuSO4Á5H2O (221.5 mg, 0.89 mmol) and sodium ascor-
bate (351.5 mg, 1.77 mmol). After stirring at rt for 6 h, the resulting
mixture was diluted with CH2Cl2 (12 mL) and then washed with aq
EDTA and brine. The combined organic layer was dried over MgSO4
and then concentrated under reduced pressure to give a crude res-
idue. This was then dissolved in MeOH/CH2Cl2 (6:1, V/V) and PdCl2
(30.0 mg, 0.169 mmol) was added. The mixture was stirred vigor-
ously under hydrogen atmosphere at 35 °C for 40 min and the
resulting mixture was filtered and concentrated under reduced
pressure. The crude residue was purified by column chromatogra-
phy (CH2Cl2–MeOH, 8:1?3:1) to give 32 (261.9 mg, 89.1%) as a
white solid. TLC: Rf = 0.27 (CH2Cl2–MeOH, 4:1). 1H NMR
(400 MHz, CD3OD) d 8.60 (s, 1H), 8.05 (d, J = 8.4 Hz, 2H), 7.99 (d,
J = 8.4 Hz, 2H), 7.79 (br s, 2H), 4.74 (s, 2H), 4.66 (d, J = 3.4 Hz,
1H), 3.82 (d, J = 9.8 Hz, 1H), 3.77 (dd, J = 10.9, 4.6 Hz, 1H), 3.69–
3.64 (m, 1H), 3.62 (d, J = 9.3 Hz, 1H), 3.43 (d, J = 3.4 Hz, 1H), 3.40
(d, J = 3.3 Hz, 1H), 3.36 (s, 3H); 13C NMR (100 MHz, CD3OD) d
147.3, 145.1, 140.6, 129.2, 123.5, 121.7, 101.2, 79.7, 79.5, 79.3,
79.0, 75.1, 73.4, 72.4, 71.5, 71.0, 65.4, 56.0; HR-ESI-MS m/z: calcd
for C16H22N4O8S + H 431.1237, found 431.1238; HPLC (tR = 3.9 min
over 20 min of 100% methanol, purity 94.3%).
The inhibition efficiency (g, %) was calculated by g (%) =
(Rct À Rct0)/Rct  100 = (icorr0 À icorr)/icorr0  100, where Rct and Rct0
are the charge transfer resistances in the presence and absence
of the inhibitors and icorr and icorr0 are the polarization current den-
sities in the presence and absence of the inhibitors, respectively.
Acknowledgements
Generous funding is provided by the National Natural Science
Foundation of China (Grant 21176076), Shanghai Science and
Technology Community (Grant 10410702700) and the Fundamen-
tal Research Funds for the Central Universities (No. WK1013002).
X.-P. He is also supported by China Postdoctoral Science Founda-
tion (No. 2011M500069) and he warmly thanks the French Em-
bassy in PR China for a co-tutored doctoral program and his
French advisor Professor Juan Xie at ENS Cachan.
Supplementary data
4.1.5. Synthesis of 4-(4-n-dodecyloxymethyl-1H-1,2,3-triazol-1-
yl) benzenesulfonamide (33)
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.carres.2012.
03.006.
To a well-stirred biphasic solution of a3 (230.9 mg, 1.03 mmol)
and d (136 mg, 0.69 mmol) in CH2Cl2/acetone/H2O (3:3:2, V/V/V)
were added CuSO4Á5H2O (222.7 mg, 0.89 mmol) and sodium ascor-
bate (312.7 mg, 1.58 mmol). After stirring at rt for 12 h, the result-
ing mixture was condensed under reduced pressure to half volume,
diluted with CH2Cl2 and washed with aq EDTA and brine. The com-
bined organic layer was dried over MgSO4 and then concentrated
under reduced pressure to give a light yellow solid. Subsequent
recrystallization (petroleum ether/CH2Cl2/MeOH, 15:5:1) afforded
33 as a white solid (267.3 mg, 92.2%). TLC: Rf = 0.51 (petroleum
ether–EtOAc, 1:1). 1H NMR (400 MHz, CDCl3 + CD3OD) d 8.55 (s,
1H), 8.09 (d, J = 8.8 Hz, 2H), 8.03 (d, J = 8.8 Hz, 2H), 4.68 (s, 2H),
3.57 (t, J = 6.6 Hz, 2H), 1.62 (m, 2H), 1.26 (s, 18H), 0.88 (t,
J = 6.7 Hz, 3H); 13C NMR (100 MHz, CDCl3 + CD3OD + DMSO-d6) d
147.1, 144.6, 140.1, 128.7, 122.6, 121.2, 71.6, 64.4, 32.6, 30.4,
30.3, 30.3, 30.1, 30.0, 26.8, 23.4, 14.5; HR-ESI-MS m/z: calcd for
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