"Janus" Calixarenes: Double-Sided Molecular Linkers for Facile, Multianchor Point, Multifunctional, Surface Modification

Article abstract of DOI:10.1021/acs.langmuir.6b02222

We herein report the synthesis of novel "Janus" calix[4]arenes bearing four "molecular tethering" functional groups on either the upper or lower rims of the calixarene. These enable facile multipoint covalent attachment to electrode surfaces with monolayer coverage. The other rim of the calixarenes bear either four azide or four ethynyl functional groups, which are easily modified by the copper(I)-catalyzed azide-alkyne cycloaddition reaction (CuAAC), either pre- or postsurface modification, enabling these conical, nanocavity reactor sites to be decorated with a wide range of substrates to impart desired chemical properties. Redox active species decorating the peripheral rim are shown to be electrically connected by the calixarene to the electrode surface in either "up" or "down" orientations of the calixarene.

Full text of DOI:10.1021/acs.langmuir.6b02222

Subscriber access provided by CORNELL UNIVERSITY LIBRARY
Article
“Janus” calixarenes: double–sided molecular linkers for facile,
multi-anchor point, multi-functional, surface modification
James P. Buttress, David P. Day, James M. Courtney, Elliot J. Lawrence, David L. Hughes, Robin J. Blagg,
Alison Crossley, Susan E. Matthews, Carl Redshaw, Philip C. Bulman Page, and Gregory G. Wildgoose
Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.6b02222 • Publication Date (Web): 15 Jul 2016
Downloaded from http://pubs.acs.org on July 19, 2016
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Langmuir is published by the American Chemical Society. 1155 Sixteenth Street N.W.,
Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 17
Langmuir
1
2
3
4
5
6
7
8
9
“Janus” calixarenes: double–sided molecular linkers for fac-
ile, multi-anchor point, multi-functional, surface modification
James P. Buttress,[a] David P. Day,[a] James M. Courtney,[a] Elliot J. Lawrence,[a] David L. Hughes,[a] Robin J. Blagg,[a] Alison
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Crossley,[b] Susan E. Matthews,[c] Carl Redshaw,[d] Philip C. Bulman Page,[a]* and Gregory G. Wildgoose.[a]*
[a] School of Chemistry, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, United Kingdom.
[b] Department of Materials, Oxford University Begbroke Science Park, Sandy Lane, Yarnton, Oxford, OX5 1PF,
United Kingdom
[c] School of Pharmacy, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, United Kingdom
[d] Department of Chemistry, University of Hull, Cottingham Road, Hull, HU6 7RX, United Kingdom.
ABSTRACT: We herein report the synthesis of novel “Janus” calix[4]arenes bearing four “molecular tethering” funcꢀ
tional groups on either the upper or lower rims of the calixarene. These enable facile multiꢀpoint covalent attachment to
electrode surfaces with monolayer coverage. The other rim of the calixarenes bear either four azide or four ethynyl
functional groups, which are easily modified by the copper(I)ꢀcatalyzed azideꢀalkyne cycloaddition reaction (CuAAC),
either preꢀ or postꢀ surface modification, enabling these conical, nanocavity reactor sites to be decorated with a wide
range of substrates to impart desired chemical properties. Redox active species decorating the peripheral rim are
shown to be electrically connected by the calixarene to the electrode surface in either “up” or “down” orientations of the
calixarene.
Introduction
Heterogeneous support of surfaceꢀimmobilized species can
provide several advantages over homogenous systems,
such as being reusable, nonꢀleaching and nonꢀintrusive to
the systems they are employed within. When the heterogeꢀ
neous support is an electrode, such systems have found
myriad applications from medicinal devices1 and flow reacꢀ
tors2 to sensors.3,4,5 To date, the vast majority of surface
immobilization strategies employ an approach of “one atꢀ
tachment point per modifying molecular species”. While this
approach is often synthetically convenient, the disadꢀ
vantage is that if the molecular attachment to the surface is
broken under the reaction and/or electrolysis conditions,
then the modifying species may leach from the surface – a
common problem encountered in this research area. Leachꢀ
ing of the modifier from heterogeneous supports risks reꢀ
ducing lifetime and catalytic efficiency of the system or conꢀ
taminating the reaction solution/product mixture. Obviously
devising multiꢀpoint attachment strategies and incorporating
these into the synthesis of every individual molecule that
one might wish to support on a surface would be both laboꢀ
rious and impractical. Instead, we have devised a generic
macromolecular scaffold using modified calix[4]arenes that
serve as doubleꢀsided, conductive, molecular “sticky tape”,
which are facile to produce in gram quantities. Either the top
or bottom of the calixarene may be used to form fourꢀpoint
attachments to a surface while the other side is decorated
with up to four modifying species.6 We have dubbed these
“Janus” calixarenes after the twoꢀfaced Roman god.
Figure 1. (A) Structure of "Janus" calix[4]arene ("N" groups are
either azide or amine functionality). (B) Illustrates the cone structure
of "Janus" calixarene. (C) The calixarene immobilized onto a surꢀ
face by: (i) the lower rim; (ii) the upper rim.
Calix[4]arenes are multiꢀfunctionalizable macromolecules
made up of four aromatic subunits connected by methylene
linkers7. With suitable functional groups in place, caꢀ
lix[4]arenes can be locked into a coneꢀshaped geometry,
which – like the Greek vase (“calix”) they are named after –
have a wider upper rim and a narrower lower rim enclosing
a hydrophobic, nanometerꢀsized, central cavity (Figure 1).
Typically calixarenes are modified at two positions on the
aromatic rings: the lower rim positions, which are commonly
decorated with phenolic or ether groups, and the carbon
atoms para to these positions which form the upper rim. The
structural modification of calixarenes is an extensive area of
research that has been reviewed by several authors in reꢀ
cent years,8,9 with reports of upperꢀrim functionalization
ranging from the use of biomolecular species such as pepꢀ
tides for the binding of small molecules and ligands,10 ureaꢀ
modified calix[4]arenes that participate in hostꢀguest interꢀ
actions with target substrates,11 through to organometallic
ACS Paragon Plus Environment

Langmuir
Page 2 of 17
catalysts for polymerization reactions.12 Modification of the
question of how to attach the target modifying molecules to
1
2
3
4
5
6
7
8
lower rim of the calixarene structure, while less commonly
reported, has been shown to enable calix[4]arenes to act as
fluorescent reagents for sensing various anions and catiꢀ
ons.13 Furthermore, due to their unique 3D conical strucꢀ
ture, calix[4]arenes have been shown to form densely
packed monolayers on surfaces,14 a property that we wish
to exploit.
the calixarene in a way that is applicable for a wide a range
of different substrates. To this end, we report methods to
functionalize either the upper or lower rim of calix[4]arenes,
the rim not used for attachment to the surface, with either
azide or ethynyl moieties. Simple incorporation of alkyne or
azide groups onto the target substrate allows us to couple
the substrate to the calixarene tethers using the extremely
versatile copper(I) catalyzed alkyneꢀazide cycloaddition
(CuAAC) reaction.34 The substrate is then bound to the caꢀ
lixarene via a chemically and electrochemically robust triaꢀ
zole linkage.35,36 Furthermore we show that full modification
of each “Janus” calixarene with four modifying species can
be accomplished using the CuAAC approach either before
or, crucially, after the surface modification step.
Previous strategies to attach large macrocyclic substrates
such as calixarenes,15 resorcinarenes,16 and cyclodextrins17
to surfaces have predominantly focused on the spontaneꢀ
ous adsorption of their thiol derivatives onto gold. This highꢀ
ly adaptable method is effective for a large array of subꢀ
strates. However, this approach suffers one important limiꢀ
tation: the relatively weak goldꢀthiol bond is prone to cleavꢀ
age resulting in a lack of thermal stability18,19 and a relativeꢀ
ly narrow electrochemical window in which to operate.20
Furthermore this attachment strategy is only effective on
“coinage” metals such as platinum, nickel and gold. In order
to make our “Janus” calixarene approach universally appliꢀ
cable to the modification of both metallic and nonꢀmetallic
(e.g. ubiquitous and inexpensive graphitic supꢀ
ports/electrode surfaces) we have chosen two alternative
strategies: i) the reduction of aryldiazonium functionalities
incorporated into the calix[4]arenes; ii) the oxidation of lithioꢀ
activated alkyne moieties on the calix[4]arene. Either stratꢀ
egy is applicable to the modification of a range of metallic
and nonꢀmetallic surfaces21,22,23 and can be selected to
complement any redox sensitivity of the target modifying
species when attached to the “Janus” calixarene prior to
surface attachment.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Given the enormous scope of substrates that are amenable
to this approach, in this report we are focused on presenting
the synthesis, characterization and multiꢀpoint, robust, elecꢀ
trode surface modification of four different “Janus” caꢀ
lixarenes attached to the surface using two different strateꢀ
gies, and each bearing four identical functional groups on
either upper or lower rims comprising of: i) organic nitro
functionalities; ii) organometallic azideꢀfunctionalized ferroꢀ
cenyl moieties; iii) ethynylꢀfunctionalized ferrocenyl groups;
iv) organic 1ꢀethynylꢀ3,5ꢀbis(trifluoromethyl)benzene moieꢀ
ties. Substrates i)ꢀiii) are used to demonstrate that the aroꢀ
matic and unsaturated “Janus” calixarene linkers enable
electron transfer to redox active centers attached at either
the upper or lower rim of the calixarene. Substrate iv) is
used as an XPS label to aid in surface characterization and
to demonstrate that full functionalization of the “Janus” caꢀ
lixarenes can be readily achieved through CuAAC reactions
after surface attachment of the calixarene. Aside from preꢀ
senting synthetic routes to novel functionalized caꢀ
lix[4]arenes, including the first examples of tetraazido (upꢀ
per rim) functionalized calix[4]arenes, this report seeks to
demonstrate widespread applicability in providing a facile
method of covalently attaching more than one species
through more than one bond to a surface proffered by the
use of “Janus” calixarenes.
The electrochemical oneꢀelectron reduction of aryl diazoniꢀ
um salts (generating a reactive aryl radical intermediate with
loss of N2) was first reported by Pinson et al.24 in 1992 and
has gained significant interest since then.25,26 It is a highly
versatile method of immobilizing compounds to solid supꢀ
ports, as aryl diazonium salts are easily generated from the
corresponding aniline derivatives in either aqueous or nonꢀ
aqueous solvents. Similarly, the electroꢀgrafting process
can take place in either aqueous27 or organic media28 and
involves the formation of strong, robust C–C or C–metal
bonds. Bulk surface modification is also readily achievable
by chemical, rather than electrochemical, reduction of the
diazonium salts, e.g. by using hypophosphorous acid.29 The
only minor drawback of this approach is that simple precauꢀ
tions must be taken to avoid the formation of disorganized,
multilayer, films.30,31
Results and discussion
Suitable calix[4]arenes were synthesized for attachment to
a glassy carbon electrode (GCE) surface at either the upper
or lower rim. Once bound to the GCE surface, the exposed
face of the calixarene was designed for facile modification
using the copperꢀcatalyzed azide alkyne cycloaddition (Cuꢀ
AAC) reaction.
The alternative surface attachment protocol we have seꢀ
lected, involving the oxidation of lithioꢀactivated alkynes,
was first described by Geiger et al. in 2013.32 They initially
demonstrated that several reactive organometallic comꢀ
plexes bearing pendent propargyl groups (–CH2C≡CH)
could be electrografted onto carbon and precious metal
electrodes; in later work Geiger’s group has extended this
methodology to porphyrins.33 The oneꢀelectron oxidation of
either a terminal alkyne or lithioꢀalkyne results in the rapid
loss of H+ or Li+ respectively, to form the desired propargyl
radical intermediate for bond formation to the electrode surꢀ
face.33 Herein, we demonstrate that this approach can also
be extended to covalently attach calixarenes to electrode
surfaces.
Our starting material, pꢀtertꢀbutylcalix[4]arene 1, was Oꢀ
alkylated with four propargyl groups following Chetcuti’s
procedure.37 Attaching groups to the lower rim ensures that
the calix[4]arenes maintain a cone confirmation (confirmed
by the presence of two characteristic doublets in the 1Hꢀ
NMR spectra of every calix[4]arene studied, each correꢀ
sponding to 4 methylene protons in the region of ca. 2.7–4.6
ppm)38 throughout the synthesis. The ipsoꢀnitration to funcꢀ
tionalize the upper rim of the calixarene was conducted
using fuming nitric acid and glacial acetic acid.39 However,
attempting the nitration reaction without first protecting the
reactive terminal alkyne substituents failed to yield any of
the desired product. Therefore, the propargyl groups were
protected using tertꢀbutyldimethylsilyl (TBDMS) groups,
whereupon the nitration of the upper rim proceeded smoothꢀ
ly, leaving the alkyne groups intact. The nitro functionalities
Having selected two complementary and widely applicable
surface attachment strategies, we were only left with the
ACS Paragon Plus Environment

Page 3 of 17
Langmuir
were then reduced using SnCl2.2H2O40 in refluxing ethanol
to afford the novel cone-5,11,17,23ꢀtetraꢀaminoꢀ
performing the reduction in anhydrous acetonitrile using
[nBu4N][PF6] as electrolyte.42 During the first reductive scan
we observed a broad irreversible reduction at ꢀ0.35 V ver-
sus Ag/Ag+, corresponding to the oneꢀelectron reduction of
the diazonium salt to the phenyl radical, which then bonds
to the electrode surface. Subsequent scans exhibited a
large decrease in the background capacitance, suggesting
that the exposed rim of the calixarene, modified with large
silyl protecting groups, acts as a blocking layer to the elecꢀ
trode, passivating the surface (See Supporting Information
Figure S45). The passivation observed is consistent with
the electrografting of similar molecules in the literature. 30
1
2
3
4
5
6
7
8
25,26,27,28ꢀTBDMSꢀpropargylcalix[4]arene 6. Employing
the Sandmeyer reaction, 6 was converted into compound 7,
through formation of the corresponding tetradiazonium salt
by using sodium nitrite in dilute hydrochloric acid, and subꢀ
sequently performing a nucleophilic aromatic substitution
with sodium azide. Removal of the TBDMS protecting
groups using a solution of 1 M tetraꢀnꢀbutylammonium fluoꢀ
ride (TBAF) in THF afforded target molecule 8. TBAF was
also used to remove the TBDMS groups of molecule 4 to
give the unprotected 5,11,17,23ꢀtetraꢀnitroꢀ25,26,27,28ꢀ
propargylcalix[4]arene 5. This novel calix[4]arene is highly
versatile, with either rim being easily modifiable by the Cuꢀ
AAC reaction, affording us a very stable and functionalizaꢀ
ble scaffold surrounding a hydrophobic cavity.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Having electroꢀreduced the diazonium salt onto the GCE
surface, further functionalization was conducted using the
CuAAC reaction.43 The alkyne was deprotected using 1M
TBAF, and ferrocenyl methyl azide was added to the immoꢀ
bilized calixarenes in a “click” reaction generating a triazole
linker. This produced a ferroceneꢀmodified calixarene on the
surface of the GCE, as shown in figure 3A. In principle this
method can be adapted for a large array of substrates.
Models of all immobilized and post surfaceꢀmodified caꢀ
lix[4]arenes were also separately synthesized in solution
All novel compounds were fully characterized by mass
spectrometry, nuclear magnetic resonance (NMR) and IR
spectroscopy (see supporting information for more inforꢀ
mation). Only the final products require purification by flash
chromatography before being attached to the electrode surꢀ
face.
and fully characterized to show that they are indeed formed
under these conditions and that they maintain their cone
conformations (See Supporting Information, molecules 10
and 13).
Figure 2. Synthesis of cone-5,11,17,23ꢀtetraꢀazidoꢀ25,26,27,28ꢀ
propargylcalix[4]arene 8.
After attaching the ferrocene moieties by the CuAAC reacꢀ
tion, the electrode was thoroughly rinsed to remove any
physisorbed material (see Supporting Information). The
GCE was transferred to a fresh anhydrous electrochemical
cell containing 0.1 M [nBu4N][PF6] in 10 mL dichloroꢀ
methane. A wellꢀdefined reversible oxidation of the ferroꢀ
Attachment of “Janus” calixarenes by the upper rim
The surface of a GCE was modified with tetraaminoꢀ
calix[4]arene 6 to form a robust, versatile platform that can
be functionalized by a large array of substrates using the
CuAAC reaction. The immobilization of calix[4]arene 6 was
performed by the formation of its tetradiazonium salt, by
reaction of 6 with stoichiometric sodium nitrite in 1 M hydroꢀ
chloric acid. The diazonium salt was then reduced onto the
electrode surface either in situ41 or by isolating the salt and
cene moiety was observed, centered at 0.16 V vs. Cp2Fe0/+
,
as illustrated in figure 3B. It was noted that the peak current
corresponding to the reversible oxidation increases linearly
upon increasing the voltage scan rate from 50 ꢀ750 mV sꢀ1,
as shown in figure 3C. This result is clearly indicative of a
ACS Paragon Plus Environment

Langmuir
Page 4 of 17
surface–bound redox active species. In contrast, a redox
active species in solution would exhibit a massꢀtransport
limited diffusional response typified by a linear dependence
of peak current upon the square root of the voltage scan
rate. It is also important that over multiple scans the current
corresponding to the ferrocene redox couple did not deꢀ
crease, suggesting the surface adsorbed species is electroꢀ
chemically stable.
stirred for 20 minutes. Cyclic voltammetric characterization
1
2
3
4
5
6
7
8
of the solutions revealed a large irreversible anodic oxidaꢀ
tion wave present at 0.6 V vs Ag/Ag+ for both calix[4]arenes
5 and 8 (see Supporting Information Figure S46), correꢀ
sponding to the irreversible, oneꢀelectron oxidation of lithioꢀ
ethynyl groups on each calixarene.32 Next, a chronoamꢀ
perometric experiment was performed by holding the potenꢀ
tial of the working electrode beyond the onset of oxidation,
0.9 V vs. Ag/Ag+, for 300 s to electrograft substrates 5 and 8
separately onto different electrode surfaces. Note if the
electrografting is attempted without the addition of n-BuLi,
no oxidation is observed, suggesting that activation of the
alkyne groups is essential to facilitate attachment onto the
GCE.
The surface concentration, ϙ (mol cmꢀ2), of ferrocene atꢀ
tached to the GCE surface was calculated from the peak
areas. Assuming complete coupling of the ferrocenyl moieꢀ
ties to every available site on the calixarene, the surface
coverage of ferroceneꢀmodified calixarene was found to be
ϙ = 1.3 x10ꢀ10 mol cmꢀ2. Note that this assumption sets a
lower limit on the calculated surface coverage of the caꢀ
lixarene linkers. Nevertheless, this value indicates a packing
density of immobilized calixarenes on the surface of 0.78
calix nmꢀ2. This compares very favorably with the theoretical
maximum value for a hexagonally packed monolayer of
calixarenes (modelled as discs of diameter 11.6 Å derived
from crystallographic dimensions of structurally similar caꢀ
lixarenes) of 0.85 calix nmꢀ2,44 strongly supporting the forꢀ
mation of a complete monolayer of surface immobilized
calixarene linkers on the electrode surface. After formation
of the monolayer, we were able to functionalize the adꢀ
sorbed calixarenes with different organic and organometallic
substrates using the CuAAC reaction. These calixarenes
serve as excellent molecular tethers, connecting the redox
active moieties to the electrode surface, while ensuring
good electron conductivity between ferrocenyl units and the
electrode, and effectively blocking the electrode surface to
other redox active species that may be in solution.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
With calixarene 5 bound to the GCE, the electrode was
thoroughly rinsed to remove any physisorbed species and
placed into an aqueous electrochemical cell containing 10
mL 1 M hydrochloric acid and 1.0 M KCl. The cyclic voltꢀ
ammetry obtained from this system showed a large irreꢀ
versible reduction on the first scan at ꢀ0.52 V vs. SCE (peak
1 in Figure 4A), which corresponds to the chemically and
electrochemically irreversible fourꢀelectron, fourꢀproton reꢀ
duction of the nitro functional groups on the calix[4]arene.
After sweeping to potentials beyond this initial reduction and
then reversing the scan direction a new oxidation wave was
observed (peak 2). On further cycling, a new reduction peak
(peak 3) was observed corresponding to peak 2; reduction
peak 1 was no longer observed. This new, chemically and
electrochemically reversible system (peaks 2 and 3), cenꢀ
tered at 0.33 V vs. SCE, corresponds to the twoꢀelectron,
twoꢀproton arylhydroxylamine/arylnitroso redox couple. The
observed voltammetric behavior is characteristic of the reꢀ
dox chemistry of arylnitro groups, and confirms the presꢀ
ence of calix[4]arene 5 on the electrode surface. Next, the
voltage scan rate was varied between 50ꢀ750 mVsꢀ1 over
the quasiꢀreversible arylhydroxylamine/arylnitroso region
(figure 4B). Once again, the oxidative and reductive peak
currents were found to increase linearly with respect to the
voltage scan rate (Figure 4C), confirming that the caꢀ
lix[4]arene 5 is indeed bound to the electrode surface.
Figure 3. (A) Calix[4]arene 13 immobilized onto GCE surface. (B)
Overlaid cyclic voltammograms recorded in CH2Cl2/0.1
M
[nBu4N][PF6], at scan rates of 50ꢀ750 mVsꢀ1 for a GC electrode
modified with calixarene 6 after further modification with ferrocenyl
methyl azide moieties to form calix[4]arene 13 attached by the
upper rim. (C) Corresponding plot of peak current versus scan rate.
Attachment of “Janus” calixarenes by the lower rim
Attachment of calix[4]arenes 5 and 8 at the lower rim to a
GCE surface was achieved using the pendent propargyl
ether groups. The formation of ethynylꢀbased radicals, genꢀ
erated by anodic oxidation of “lithioꢀactivated” terminal
ethynyl groups,32 was used to electrochemically graft the
substrates onto the surface. Lithiation of each calix[4]arene
5 or 8 was conducted in an anhydrous electrochemical cell
containing a 0.1 M solution of [nBu4N][PF6] and 4 mM caꢀ
lixarene dissolved in 10 mL THF cooled to ꢀ78 oC. Dilute
(1.6 M) n-BuLi was added slowly to the reaction mixture and
Figure 4. (A) Overlaid cyclic voltammograms of a GC electrode
modified with 5 in 1 M HCl/1 M KCl, scan rate 0.1 V sꢀ1. (B) Correꢀ
sponding plot of peak current versus scan rate. (C) Overlaid cyclic
ACS Paragon Plus Environment

Page 5 of 17
Langmuir
voltammograms of the modified electrode recorded at 50ꢀ750 mVsꢀ1
over the reversible arylhydroxylamine/arylnitroso redox couple.
was conducted using a clean GCE that was modified with
calixarene 8 using the lithiation and electrografting methodꢀ
ology described above. Instead of using a redox active
probe we modified the immobilized calix[4]arene 8 molecuꢀ
lar tether with 1ꢀethynylꢀ3,5ꢀbis(trifluoromethyl)benzene,
following the CuAAC reaction protocol as described in the
Supporting Information. This introduces a fluorineꢀlabelled
probe onto the surface, whose presence is easily identified
by Xꢀray photoelectron spectroscopy. The modified GCE
was then thoroughly rinsed in a variety of solvents to reꢀ
move any physisorbed species and analyzed using XPS.
The full survey spectrum (See Supporting Information Figꢀ
ure S47) shows characteristic F1s and N1s signals from the
probe molecules in addition to C1s and O1s signals arising
from the GC surface. We also observed a small amount of
Cl2p and Si2p impurities introduced by the polishing steps
used to clean the electrode surface.
1
2
3
4
5
6
7
8
The GCE modified with tetraazidocalix[4]arene 8 was treatꢀ
ed with ethynyl ferrocene in the presence of Cu(I) to afford a
ferrocenylꢀmodified calixarene immobilized onto the elecꢀ
trode surface shown in figure 5C. The electrode was thorꢀ
oughly rinsed and transferred to an electrochemical cell
containing 0.1M [nBu4N][PF6] in dry dichloromethane. Cyclic
voltammetry was conducted at scan rates ranging from 50
mVsꢀ1 to 750 mVsꢀ1 (Figure 5A). We observed a nonꢀideal
reversible oxidation of the ferrocenyl moiety centered at ꢀ
0.27 vs. Cp2Fe0/+, where the peak current was again linearly
dependent on the voltage scan rate, again indicative of a
surface bound redox species (Figure 5B). Note, the waveꢀ
shape of the redox couple of the ferrocene moieties is nonꢀ
ideal, presumably, caused by the requirement for electrons
to hop over the propargylꢀether linkers and/or the lateral
interactions between charged centers around the upper rim.
Whereas, the sharp reductive signal is attributed to the reꢀ
lease of counter ions from the oxidized electrode surface,
during the reduction process. Furthermore, it is important
that the peak current remained constant over numerous
scans suggesting that the chemisorbed material remains
anchored to the electrode surface.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Strong evidence for the successful modification of the caꢀ
lixarenes after their surface immobilization onto the GCE is
given by the presence of the peaks observed at binding
energies of 399.7 eV and 688.3 eV (Figure 6). These correꢀ
spond to the N1s signal from the three nitrogen atoms in
each of the triazole rings and the F1s signal arising from the
six fluorine atoms in the CF3 groups of the 3,5ꢀ
(trifluoromethyl)benzene moieties respectively. Note that
had any unreacted azide groups been present on the GCE
surface, these would have given rise to two characteristic
nitrogen signals at 405 eV and 401 eV in a ratio of 1:2,45
which are not observed. Figure 6A shows that we observe
only one distinct triazole N1s signal, suggesting that we have
achieved complete modification of the calixarene molecular
tether at almost all available reactive sites using the CuAAC
reaction.
Further evidence in support of this claim is found in the ratio
between the observed N1s and F1s signals measured in the
XPS spectrum. After adjusting for the relative atomic sensiꢀ
tivity factors,46,47 the relative abundance of the two elements
on the surface of the GCE was found to be 1:1.9 (Nitroꢀ
gen:Fluorine). This is very close to the 1:2 ratio of nitroꢀ
gen:fluorine expected for complete modification of the surꢀ
face–bound
calixarene
with
1ꢀethynylꢀ3,5ꢀ
bis(trifluoromethyl)benzene moieties. Furthermore, the
“click” reaction was performed on calix[4]arene 7 under
similar conditions in solution to show that the molecule can
be readily synthesized and maintains its cone confirmation
(See Supporting Information Molecule 9).
Figure 5. (A) Overlaid cyclic voltammograms of a GCE modified
with, 8, after post surface modification in CH2Cl2/0.1 M NBu4PF6,
scan rate 0.05ꢀ0.75 mVsꢀ1. (B) Corresponding plot of peak current
vs. scan rate. (C) Structure of modified electrode surface
The surface concentration ϙ (mol cmꢀ2) of the ferrocene
groups attached to the GCE surface was calculated from
the oxidative and reductive peak areas to be ϙ = 5.6 x10ꢀ10
mol cmꢀ2. Assuming conversion of all the azide functional
groups into the triazoleꢀlinked ferrocene moieties, this corꢀ
responds to a surface coverage of 0.84 calix nmꢀ2. Again,
this value compares favorably with the theoretical value of
0.90 calix nmꢀ2 for a hexagonally packed monolayer of caꢀ
lix[4]arenes (assumed to be discs of diameter 11.3 Å, deꢀ
rived from the crystallographically determined dimensions of
5), indicating that we are able to attach a complete monoꢀ
layer of calixarene linkers covalently to a GCE. Furtherꢀ
more, this linker is shown to be easily functionalized on the
GCE surface at all four sites on the upper rim using the Cuꢀ
AAC reaction.
Figure 6. XPS spectra recorded over: (a) the N1s region; (b) the F1s
region of the modified GCE. (c) Structure of the functionalized caꢀ
lixarene attached to the GCE surface.
Experimental
XPS studies were also used to analyze the attachment and
postꢀsurface modifications of the calixarene linkers. This
Commercially available reagents were purchased from
SigmaꢀAldrich (Gillingham, UK) and used without further
ACS Paragon Plus Environment

Langmuir
Page 6 of 17
purification unless stated otherwise. Anhydrous reactions
butyldimethylsilyl chloride in THF was added dropwise, via
1
2
3
4
5
6
7
8
were performed under a dry nitrogen atmosphere (BOC
Gasses) using standard Schlenkꢀline techniques on a dual
manifold vacuum/inert gas line. All glassware was dried in
the oven overnight before use. Anhydrous solvents were
dried via distillation over either sodium/benzophenone (tetꢀ
rahydrofuran (THF) and diethyl ether) or calcium hydride
(dichloromethane (DCM)) under an inert nitrogen atmosꢀ
phere, and sparged with nitrogen gas to remove any trace
amounts of dissolved oxygen. Water used in aqueous elecꢀ
trochemical reactions was also thoroughly sparged with
nitrogen to remove dissolved oxygen prior to use. After any
surface modification the electrode was sonicated for 10
minutes in each of the following solvents, water, acetone
and dichloromethane before being allowed to dry.
cannula to the solution containing the deprotonated caꢀ
lixarene, 2. After complete addition, the flask was allowed to
warm to room temperature overnight. The reaction was then
quenched by the addition of a saturated solution of ammoꢀ
nium chloride (100 mL). The organic layer was separated,
and the aqueous layer washed with dichloromethane (100
mL). The organic extracts were combined, dried over
MgSO4, and remaining solvents removed in vacuo. The
product 3 was isolated as a light brown solid (12.0 g, 64%).
1H NMR (500 MHz, CDCl3): 0.09 (24H, s), 0.90 (36H, s),
1.06 (36 H, s), 3.12 (4H, d, J = 13 Hz), 4.52 (4H, d, J = 13
Hz), 4.83 (8H, s), 6.75 (8H, s). 13C NMR (125 MHz, CDCl3):
ꢀ4.5, 16.6, 26.3, 31.5, 32.7, 34.0, 61.4, 89.5, 103.6, 124.9,
134.8, 145.3, 152.1; IR (neat, ν / cmꢀ1): 2952, 2929, 2855,
2167 (alkyne), 1739, 1480, 1361, 1248, 1196, 1120, 1040;
HRMS: m/z: [M + NH4]+ Calcd for C80H120O4Si4, 1274.8607,
found 1274.8581
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Electrochemical measurements were performed under an
inert atmosphere using computerꢀcontrolled potentiostat
(Model PGSTAT 30, Autolab, Utrecht, The Netherlands)
using a standard three–electrode configuration: a glassy
carbon electrode (GCE) (BasiTechnicol, diameter 3 mm)
served as the workingꢀelectrode with a platinum wire counꢀ
ter electrode (99.99%, GoodFellow, Cambridge, U.K.) and
either a silver wire pseudoꢀreference electrode (99.99%,
GoodFellow, Cambridge, U.K.) or a saturated calomel elecꢀ
trode (Radiometer, Copenhagen, Denmark) used as the
reference electrode for nonꢀaqueous and aqueous electroꢀ
chemical measurements respectively. The working elecꢀ
trode surface was renewed by successive polishing with
diamond paste slurries of decreasing particle size ranging
from 3.0 ꢁm to 0.1 ꢁm (Kemmet, U.K.). The electrode was
sonicated in deionized water and rinsed with ethanol beꢀ
tween each polishing step to remove any adhered polishing
materials.
Synthesis of cone-5,11,17,23-tetra-nitro-25,26,27,28-
TBDMS-propargylcalix[4]arene 4. To a round bottom
flask, cooled to 0 °C, was added 3 (13 g, 10.4 mmol) disꢀ
solved in dichloromethane (130 mL) and glacial acetic acid
(130 mL). Using a glass syringe, 100% nitric acid (54 mL,
1.29 mol) was added dropwise at 0 °C. After complete addiꢀ
tion, the flask was allowed to warm to room temperature
overnight. The reaction was then poured into iced water
(200 mL), and the organic layer was separated by extracꢀ
tion. The aqueous layer was washed with dichloromethane
(50 mL x3), and the remaining organic phases were comꢀ
bined, dried with MgSO4, and remaining solvents were
evaporated in vacuo. Reꢀdissolving the resulting residue in
dichloromethane, followed by trituration with methanol
1
yielded 4 as a cream powder (4.6 g, 37%). H NMR (500
MHz, CDCl3): 0.08 (24H, s), 0.86 (36H, s), 3.44 (4H, d, J =
14 Hz), 4.66 (4H, d, J = 14 Hz), 4.91 (8H, s), 7.71 (8H, s).
13C NMR (125 MHz, CDCl3):ꢀ4.7, 16.5, 26.0, 32.3, 62.6,
93.4, 99.9, 124.2, 136.3, 144.0, 159.7; IR (neat, ν / cmꢀ1):
2952, 2885, 2857, 2929, 2179 (alkyne), 1738, 1714, 1587,
1524 (nitro asymmetric), 1462, 1345 (nitro symmetric),
1251, 1205, 1096; HRMS: m/z: [M + NH4]+ Calcd for
C80H120O4Si4, 1230.5501, found 1230.5497.
Flash chromatography was performed on silica gel (SiO2,
70ꢀ200 micron mesh 60 Å) purchased from Alfa Aesar. Thin
layer chromatograph was performed using silica gel 60 Å
F254 preꢀcoated plates.
Proton NMR (1H NMR) spectra were recorded using a
Bruker Avance DPXꢀ500 MHz spectrometer. The data is
reported as: s = singlet, d = doublet, t = triplet, q = quartet,
m = multiplet, br = broad; coupling constant(s) in Hz. Chemꢀ
ical shifts are reported in parts per million (ppm) relative to
CDCl3 (7.26 ppm). Carbon NMR (13C NMR) spectra were
recorded at 75 MHz and 125 MHz. Chemical shift is reportꢀ
ed in ppm relative to the carbon resonance of CDCl3 (77.00
ppm). IR spectra were recorded using a PerkinElmer µꢀATR
Spectrum II spectrometer. Xꢀray photoelectron spectroscoꢀ
py (XPS) was performed with a Thermo Scientific Kꢀalpha
instrument using monochromatic Al Xꢀrays. All spectra were
corrected relative to the graphitic C1s peak position (284.97
Synthesis of cone-5,11,17,23-tetra-nitro-25,26,27,28-
propargylcalix[4]arene 5. Calixarene 4 (1 g, 0.82 mmol)
was dissolved in a 1M solution of Tetraꢀnꢀbutylammonium
fluoride (TBAF) in THF (16.5 mL, 16.5 mmol) at room temꢀ
perature, the reaction was monitored by TLC. Once comꢀ
plete the reaction was quenched by the addition of cold
water (100 mL), and the product was extracted with diꢀ
chloromethane (3x 50 mL) washings of the aqueous layer.
The combined organic layers were then washed with water
(2x 100 mL), dried using MgSO4. The filtrate was concenꢀ
trated in vacuo, and the residue was purified using flash
chromatography (acetone/petroleum ether 1:4) to afford 5
as a pale yellowꢀorange solid (0.34 g, 55%). 1H NMR (500
MHz, CDCl3): 2.60 (4H, t, J = 2 Hz), 3.49 (4H, d, J = 14 Hz),
4.72 (4H, d, J = 14 Hz), 4.86 (8H, d, J = 2 Hz), 7.71 (8H, s).
13C NMR (125 MHz, CDCl3): 26.0, 62.6, 93.4, 99.9, 124.2,
136.3, 144.0, 159.7; IR (neat, ν / cmꢀ1): 3287, 3079, 2931,
2120 (alkyne), 1704, 1585, 1519 (nitro asymmetric), 1459,
1342 (nitro symmetric), 1202, 1093; HRMS: m/z: [M +
NH4]+ Calcd for C40H32N5O12, 774.2042, found
774.2044.
,
eV). Calix[4]arenes 148 49 and 237 where synthesized followꢀ
ing modified literature procedures full details in supporting
information.
Synthesis
of
cone-5,11,17,23-tetra-tert-butyl-
25,26,27,28-TBDMS-propargylcalix[4]arene 3. To a 3
necked 100 mL round bottom flask, tertꢀbutyldimethylsilyl
chloride (14.7 g, 97.5 mmol) was dissolved in anhydrous
THF (50 mL). In a separate flask 2 (12 g, 16.2 mmol) was
added and dissolved in anhydrous THF (100 mL), this was
then cooled to ꢀ78 °C, and over a period of 15 minutes lithiꢀ
um bis(trimethylsilyl)amide solution (1.0 M in THF, 100 mL,
97.5 mmol) was added, resulting in a dark brown reaction
mixture. After 30 mins the flask containing tertꢀ
Synthesis of cone-5,11,17,23-tetra-amino-25,26,27,28-
TBDMS-propargylcalix[4]arene 6. Calix[4]arene 5 (4 g,
ACS Paragon Plus Environment

Page 7 of 17
Langmuir
3.3 mmol) was dissolved in ethanol (200 mL), to which
by submerging the GCE stub in a stirring solution of 1 M
1
2
3
4
5
6
7
8
SnCl2.2H2O (40 g, 177 mmol) was added and stirred at
room temperature for 15 minutes. The reaction mixture was
then submitted to reflux for 48 h. After allowing the reaction
to cool to room temperature, 10% NaOH solution (200 mL)
was added to basify the reaction mixture. Extraction of the
aqueous layer with dichloromethane (3x 200 mL), followed
by drying of the organic extracts over MgSO4 and solvent
evaporation under reduced pressure afforded compound 6
as a light brown solid (2.05 g, 58%). 1H NMR (500 MHz,
CDCl3): 0.08 (24H, s), 0.90 (36H, s), 2.93 (4H, d, J = 13
Hz), 4.45 (4H, d, J = 13 Hz), 4.69 (8H, s), 6.11 (8H, s). 13C
NMR (125 MHz, CDCl3): ꢀ4.5, 16.6, 26.2, 31.1 (t, J = 167
Hz), 61.7, 89.4, 103.7, 115.6, 136.2, 141.2, 148.2; IR (neat,
ν / cmꢀ1): 3325 (amine), 2954, 2928, 2855, 2173 (alkyne),
1606 (amine), 1471, 1361, 1249, 1207, 1097; HRMS: m/z:
[M + H]+ Calcd for C64H93N4O4Si4, 1093.6267, found
1093.6269.
TBAF (10 mL) this reaction was ran for 14 hours. The elecꢀ
trode was removed from the solution and cleaned as deꢀ
scribed above. The CuAAC reaction of the unprotected alꢀ
kyne with ferrocenylmethyl azide was achieved by immersꢀ
ing the stub in a rapidly stirred solution containing copper(II)
sulfate (50 mg, 0.2 mmol) and sodium ascorbate (20 mg,
0.1 mmol) to this was added ethynyl ferrocene (10 mg, 0.05
mmol) dissolved in 2 mL dichloromethane, the reaction was
ran for 12 hours. The GCE was then removed from the soluꢀ
tion and cleaned before electrochemical analysis.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Post surface modification of immobilized calyx[4]arene
8. The post surface modification of molecule 8 was conꢀ
ducted by submerging the GCE stub in a rapidly stirring
solution containing copper(II) sulfate (50 mg, 0.2 mmol) and
sodium ascorbate (20 mg, 0.1 mmol) to this was added the
desired alkynyl (0.05 mol) dissolved in 2 mL dichloroꢀ
methane, the reaction was ran for 12 hours. The GCE was
then removed from the solution and cleaned before electroꢀ
chemical or XPS analysis.
Synthesis of cone-5,11,17,23-tetra-azido-25,26,27,28-
TBDMS-propargylcalix[4]arene 7. To a stirred solution of
6 (1.5 g, 1.37 mmol) in trifluoroacetic acid (TFA) (10 mL) at
0 °C a solution of NaNO2 (900 mg, 13 mmol) in cold water
was added dropwise, the mixture was stirred at 0 °C for 10
mins. After this time a solution of NaN3 (1.8 g, 26 mmol) in
cold water was added dropwise and the reaction mixture
was stirred at 0 °C for 45 mins. Dichloromethane (10 mL)
was then added and the reaction was allowed to warm up to
room temperature overnight. The reaction was diluted with
water and extracted with dichloromethane (3x 25 mL) washꢀ
ings of the aqueous layer. The combined organic layers
were dried over MgSO4, filtered and concentrated in vacuo.
The residue was purified using flash chromatography (ethyl
acetate/petroleum ether 1:10) to afford 7 as pale yellow
powder (1.0 g, 67 %). 1H NMR (500 MHz, CDCl3): 0.08 (s,
24H), 0.88 (s, 36H), 3.13 (d, J = 13.6 Hz, 4H), 4.53 (d, J =
13.6 Hz, 4H), 4.73 (s, 8H), 6.37 (s, 8H). 13C NMR (125
MHz, CDCl3): ꢀ4.58 16.53, 26.13, 61.96, 91.01, 101.97,
118.69, 134.78, 136.98, 152.12, IR (neat, ν / cmꢀ1): 2953,
2927, 2856, 2177 (alkyne), 2107 (azide), 1656, 1587, 1468,
1361, 1317, 1249, 1233, 1201, 1024; HRMS: m/z: [M +
NH4]+ Calcd for C64H88N13O4Si4, 1214.6154, found
1214.6153.
Conclusion
In summary we describe two methods to form a monolayer
of calix[4]arenes onto a GCE surface at either the upper or
lower rims. These immobilized molecules have proven to be
both chemically and electrochemically stable on an elecꢀ
trode surface, having up to four points of attachment to the
surface per calixarene linker. These linkers can be easily
functionalized by an array of substrates using the CuAAC
reaction either before or after surface attachment, with four
points of modification per calixarene. The use of biꢀ
functional “Janus” calixarenes offers a simple, yet highly
versatile route to robust, multiꢀattachmentꢀpoint functionaliꢀ
zation of surfaces for a wide range of potential chemical and
biological species, with applications ranging from analytical
sensors through to heterogeneous catalyst support.
ASSOCIATED CONTENT
Synthesis, electrode modification procedures and suppleꢀ
mentary figures. This material is available free of charge via
the Internet at http://pubs.acs.org.
Synthesis of cone-5,11,17,23-tetra-azido-25,26,27,28-
propargylcalix[4]arene 8. Calixarene 7 (750 mg, 0.63
mmol) was dissolved in a 1M solution of TBAF in THF (13
mL mL, 13 mmol) at room temperature, the reaction was
monitored by TLC. Once complete the reaction was
quenched by the addition of cold water (100 mL), and the
product was extracted with dichloromethane (3x 50 mL)
washings of the aqueous layer. The combined organic layꢀ
ers were then washed with water (2x 100 mL), dried using
MgSO4. The filtrate was concentrated in vacuo, and the
residue was purified using flash chromatography (aceꢀ
tone/petroleum 1:4) to afford 8 as a yellow solid (0.25 g,
54%). 1H NMR (500 MHz, CDCl3): 2.48 (t, J = 2.1 Hz, 1H),
3.17 (d, J = 13.8 Hz, 1H), 4.59 (d, J = 13.8 Hz, 1H), 4.70 (d,
J = 2.1 Hz, 2H), 6.39 (s, 2H). 13C NMR (125 MHz, CDCl3):
32.14, 61.63, 75.53, 79.88, 118.87, 135.10, 136.79, 152.41;
IR (neat, ν / cmꢀ1): 3295, 2921, 2195 (alkyne), 2104 (azide),
1587, 1529, 1467, 1366, 1314, 1232, 1201, 1001; HRMS:
m/z: [M + NH4]+ Calcd for C40H32N13O4, 758.2695, found
758.2689.
AUTHOR INFORMATION
Corresponding Authors
G.Wildgoose@uea.ac.uk
P.Page@uea.ac.uk
ACKNOWLEDGMENT
J.P.B. thanks the Leverhulme trust for financial support by
PhD grant and the University of East Anglia for use of faciliꢀ
ties. G.G.W. thanks the Royal Society for financial support
through a University Research Fellowship. We thank the
EPSRC UK National Crystallography Service at the Univerꢀ
sity of Southampton for collection of the crystallographic
data for compound 9. We acknowledge the use of the
EPSRC funded National Chemical Database Service hosted
by the Royal Society of Chemistry, and the EPSRC UK Naꢀ
tional Mass Spectrometry Facility (NMSF) at the University
of Swansea. The research leading to these results has reꢀ
ceived funding from the European Research Council under
the ERC Starting Grant Agreement No. 307061 (PiHOMER)
and ERC PoC Grant Agreement No. 604988 (FLPower).
Post surface modification of immobilized calyx[4]arene
6. Removal of the TBDMS protecting groups was conducted
ACS Paragon Plus Environment

Langmuir
Page 8 of 17
Ferri/ferrocyanide
calix[4]resorcinarenetetrathiolꢀModified
Electrode as a Study of Novel Electrode Modifying
Coatings for Use within ElectroꢀAnalytical Sensors.
J. Electroanal. Chem. 2003, 549 (SUPPL.), 119–
127.
Couple
at
a
Gold
REFERENCES
1
2
3
4
5
6
7
8
(1)
Zhang, Y.; Bai, Y.; Yan, B. Functionalized Carbon
Nanotubes for Potential Medicinal Applications.
Drug Discov. Today 2010, 15 (11ꢀ12), 428–435.
(2)
Tryba, B. Immobilization of TiO2 and FeꢀCꢀTiO2
Photocatalysts on the Cotton Material for
Application in a Flow Photocatalytic Reactor for
Decomposition of Phenol in Water. J. Hazard.
Mater. 2008, 151 (2ꢀ3), 623–627.
(17)
(18)
(19)
(20)
Nelles, G.; Weisser, M.; Back, R.; Wohlfart, P.;
Wenz, G.; MittlerꢀNeher, S. Controlled Orientation
of Cyclodextrin Derivatives Immobilized on Gold
Surfaces. J. Am. Chem. Soc. 1996, 118 (21), 5039–
5046.
9
(3)
Sljukić, B.; Banks, C. E.; Compton, R. G. Iron Oxide
Particles Are the Active Sites for Hydrogen
Peroxide Sensing at Multiwalled Carbon Nanotube
Modified Electrodes. Nano Lett. 2006, 6 (7), 1556–
1558.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Love, J. C.; Estroff, L. A.; Kriebel, J. K.; Nuzzo, R.
G.; Whitesides, G. M. SelfꢀAssembled Monolayers
of Thiolates on Methals as
Nanotechnology. Chem. Rev. 2005, 105, 1103–
1169.
a
Form of
(4)
(5)
(6)
Boopathi, M.; Won, M. S.; Shim, Y. B. A Sensor for
Acetaminophen in a Blood Medium Using a Cu(II)ꢀ
Conducting Polymer Complex Modified Electrode.
Anal. Chim. Acta 2004, 512 (2), 191–197.
Vericat, C.; Vela, M. E.; Benitez, G.; Carro, P.;
Salvarezza, R. C. SelfꢀAssembled Monolayers of
Thiols and Dithiols on Gold: New Challenges for a
WellꢀKnown System. Chem. Soc. Rev. 2010, 39 (5),
1805–1834.
Yemini, M.; Reches, M.; Gazit, E.; Rishpon, J.
Peptide NanotubeꢀModified Electrodes for Enzymeꢀ
Biosensor Applications. Anal. Chem. 2005, 77 (16),
5155–5159.
Wano, H.; Uosaki, K. In Situ Dynamic Monitoring of
Electrochemical
Reductive Desorption Processes of
Assembled Monolayer of Hexanethiol on a Au(111)
Surface in KOH Ethanol Solution by Scanning
Tunneling Microscopy. Langmuir 2005, 21 (9),
4024–4033.
Oxidative
Adsorption
and
Selfꢀ
a
Fiore, M.; Chambery, A.; Marra, A.; Dondoni, A.
Single and Dual Glycoside Clustering around
calix[4]arene Scaffolds via Click ThiolꢀEne Coupling
and AzideꢀAlkyne Cycloaddition. Org. Biomol.
Chem. 2009, 7 (19), 3910–3913.
(21)
(22)
(23)
Sheridan, M. V.; Lam, K.; Geiger, W. E.
Spontaneous Attachment of LithiumꢀActivated
Ferrocenylalkynes
(7)
Bohmer, V. Calixarenes , Macrocycles with (Almost)
Unlimited Possibilities. Angew. Chem. Int. Ed. Engl.
1995, 34, 713–745.
to
Carbon
and
Gold.
Electrochem. Commun. 2015, 52, 63–66.
(8)
Nimse, S. B.; Kim, T. Biological Applications of
Functionalized Calixarenes. Chem. Soc. Rev. 2013,
42, 366–386.
Kirkman, P. M.; Güell, A. G.; Cuharuc, A. S.; Unwin,
P. R. Spatial and Temporal Control of the
Diazonium Modification of sp2 Carbon Surfaces. J.
Am. Chem. Soc. 2014, 136 (1), 36–39.
(9)
Agrawal, Y. K.; Pancholi, J. P.; Vyas, J. M. Design
and Synthesis of Calixarene. J. Sci. Ind. Res. 2009,
68, 745–768.
Celiktas, A.; Ghanem, M. A.; Bartlett, P. N.
Modification of Nanostructured Gold Surfaces with
Organic Functional Groups Using Electrochemical
and SolidꢀPhase Synthesis Methodologies. J.
Electroanal. Chem. 2012, 670, 42–49.
(10)
Shuker, S. B.; Esterbrook, J.; Gonzalez, J. Solidꢀ
Phase Synthesis of a Novel Peptide Substituted
Calix[4]arene. Synlett 2001, 2, 210–213.
(11)
(12)
Julius, R. Host–guest Chemistry of Calixarene
Capsules. Chem. Commun. 2000, 8, 637–643.
(24)
(25)
Deiamar, M.; Hitmi, R.; Pinson, J.; Saveant, J. M.
Covalent Modification of Carbon Surfaces by
Grafting of Functionalized Aryl Radicals Produced
from Electrochemical Reduction of Diazonium Salts.
J. Am. Chem. Soc. 1992, 114 (114), 5884–5886.
Redshaw, C.; Walton, M.; Michiue, K.; Chao, Y.;
Walton, A.; Elo, P.; Sumerin, V.; Jiang, C.;
Elsegood, M. R. J. Vanadyl calix[6]arene
Complexes: Synthesis, Structural Studies and
Ethylene Homoꢀ(Coꢀ)Polymerization Capability.
Dalton Trans. 2015, 44 (27), 12292–12303.
Lagrost, C.; Noël, J.ꢀM.; Sjöberg, B.; Marsac, R.;
Zigah, D.; Bergamini, J.ꢀF.; Wang, A.; Rigaut, S.;
Hapiot, P. Flexible Strategy for Immobilizing Redoxꢀ
Active Compounds Using in Situ Generation of
Diazonium Salts. Investigations of the Blocking and
Catalytic Properties of the Layers. Langmuir 2009,
25 (21), 12742–12749.
(13)
Kim, J. S.; Quang, D. T. CalixareneꢀDerived
Fluorescent Probes. Chem. Rev. 2007, 107 (9),
3780–3799.
(14)
(15)
Lagrost, C.; Mattiuzzi, A.; Jabin, I.; Hapiot, P.;
Reinaud, O. European Patent EP 12164038, 2012.
(26)
(27)
Heald, C. G. R.; Wildgoose, G. G.; Jiang, L.; Jones,
T. G. J.; Compton, R. G. Chemical Derivatisation of
Multiwalled Carbon Nanotubes Using Diazonium
Salts. ChemPhysChem. 2004, 5 (11), 1794–1799.
Cormode, D. P.; Evans, A. J.; Davis, J. J.; Beer, P.
D. Amplification of Anion Sensing by Disulfide
Functionalized
Calixarene Receptors Adsorbed onto Gold
Surfaces. Dalton Trans. 2010, 39 (28), 6532–6541.
Ferrocene
and
Ferroceneꢀ
Corgier, B. P.; Marquette, C. A.; Blum, L. J.
DiazoniumꢀProtein Adducts for Graphite Electrode
Microarrays Modification: Direct and Addressed
Electrochemical Immobilization. J. Am. Chem. Soc.
2005, 127 (51), 18328–18332.
(16)
Collyer, S. D.; Davis, F.; Lucke, A.; Stirling, C. J. M.;
Higson, S. P. J. The Electrochemistry of the
ACS Paragon Plus Environment

Page 9 of 17
Langmuir
(28)
Kariuki, J. K.; McDermott, M. T. Formation of
Isomers of the Ethers and Esters of calix[4]arenes.
Tetrahedron 1983, 39 (3), 409–426.
1
2
3
4
5
6
7
8
Multilayers on Glassy Carbon Electrodes via the
Reduction of Diazonium Salts. Langmuir 2001, 17
(19), 5947–5951.
(39)
Reinhoudt, D. N.; Verboom, W.; Durie, A.; Egberink,
R. J. M.; Asfari, Z. Ipso Nitration of PꢀTertꢀButylcalix
Arenes. J. Org. Chem. 1992, 57, 1313–1316.
(29)
Pandurangappat, M.; Lawrence, N. S.; Compton, R.
G. Homogeneous Chemical Derivatisation of
Carbon Particles: A Novel Method for Funtionalising
Carbon Surfaces. Analyst 2002, 127 (12), 1568–
1571.
(40)
(41)
Bellamy, F. D.; Ou, K. Reduction of PꢀNitrobenzoic
Acid. Tetrahedron Lett. 1984, 25, 839–842.
Mattiuzzi, A.; Jabin, I.; Mangeney, C.; Roux, C.;
Reinaud, O.; Santos, L.; Bergamini, J.ꢀF.; Hapiot,
9
(30)
(31)
(32)
(33)
Leroux, Y. R.; Hapiot, P. Nanostructured
Monolayers on Carbon Substrates Prepared by
Electrografting of Protected Aryldiazonium Salts.
Chem. Mater. 2013, 25 (3), 489–495.
P.;
Lagrost,
C.
Electrografting
of
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
calix[4]arenediazonium Salts to Form Versatile
Robust Platforms for Spatially Controlled Surface
Functionalization. Nat. Commun. 2012, 3 (May),
1130.
Leroux, Y.; Fei, H.; Noël, J. Efficient Covalent
Modification of a Carbon Surface: Use of a Silyl
Protecting Group to Form an Active Monolayer. J.
Am. Chem. Soc. 2010, 132 (21), 14039–14041.
(42)
(43)
(44)
(45)
Laws, D. R.; Sheats, J.; Rheingold, A. L.; Geiger,
W. E. Organometallic Electrodes: Modification of
Electrode Surfaces through Cathodic Reduction of
Cyclopentadienyldiazonium Complexes of Cobalt
and Manganese. Langmuir 2010, 26 (18), 15010–
15021.
Sheridan, M. V; Lam, K.; Geiger, W. E. An Anodic
Method for Covalent Attachment of Molecules to
Electrodes through an Ethynyl Linkage. J. Am.
Chem. Soc. 2013, 135, 2939–2942.
Sayed, S. Y.; Bayat, A.; Kondratenko, M.; Leroux,
Y.; Hapiot, P.; McCreery, R. L. Bilayer Molecular
Sheridan, M. V; Lam, K.; Geiger, W. E. Covalent
Attachment of Porphyrins and Ferrocenes to
Electrode Surfaces through Direct Anodic Oxidation
of Terminal Ethynyl Groups. Angew. Chem. Int. Ed.
Engl. 2013, 52 (49), 12897–12900.
Electronics:
AllꢀCarbon
Electronic
Junctions
Containing Molecular Bilayers Made With “click”
chemistry. J. Am. Chem. Soc. 2013, 135 (35),
12972–12975.
(34)
(35)
Lee, L.; Brooksby, P. A.; Leroux, Y. R.; Hapiot, P.;
Downard, A. J. Mixed Monolayer Organic Films via
Sequential Electrografting from Aryldiazonium Ion
and Arylhydrazine Solutions. Langmuir 2013, 29 (9),
3133–3139.
Klimentová, J.; Vojtíšek, P. New Receptors for
Anions in Water: Synthesis, Characterization, Xꢀ
Ray Structures of New Derivatives of 5,11,17,23ꢀ
Tetraaminoꢀ25,26,27,28ꢀ
tetrapropyloxycalix[4]arene. J. Mol. Struct. 2007,
826 (1), 48–63.
Day, D. P.; Dann, T.; Hughes, D. L.; Oganesyan, V.
S.;
Steverding,
D.;
Wildgoose,
G.
G.
Collman, J. P.; Devaraj, N. K.; Eberspacher, T. P.
A.; Chidsey, C. E. D. Mixed AzideꢀTerminated
Monolayers: A Platform for Modifying Electrode
Surfaces. Langmuir 2006, 22 (6), 2457–2464.
Cymantrene−Triazole “Click” Products: Structural
Characterization and Electrochemical Properties.
Organometallics 2014, 33, 4687–4696.
(36)
(37)
Day, D. P.; Dann, T.; Blagg, R. J.; Wildgoose, G. G.
Synthesis and Characterization of Redox Active
Cyrhetrene–triazole Click Products. J. Organomet.
Chem. 2014, 770, 29–34.
(46)
(47)
(48)
National Institute of Standards and Technology
(NIST) http://srdata.nist.gov/xps/.
UK
Surface
Analysis
Forum
(UKSAF),
http://www.uksaf.org/data.html.
Chetcuti, M. J.; Devoille, A. M. J.; Othman, A. B.;
Souane, R.; Thuéry, P.; Vicens, J. Synthesis of
Monoꢀ, Diꢀ and TetraꢀAlkyne Functionalized
calix[4]arenes: Reactions of These Multipodal
Ligands with Dicobalt Octacarbonyl to Give
Complexes Which Contain up to Eight Cobalt
Atoms. Dalton Trans. 2009, 16 (16), 2999–3008.
Gutsche, C. D.; Iqbal,
M. PꢀTertꢀ
BUTYLCALIX[4]ARENE. Org. Synth. 1990, 68,
234–235.
(49)
Simaan, S.; Biali, S. E. Synthesis of PꢀTertꢀ
Butylcalix[4]arene Derivatives with TransꢀAlkyl
Substituents on Opposite Methylene Bridges. J.
Org. Chem 2003, 68, 3634–3639.
(38)
Gutsche, D. C.; Dhawan, B.; Levine, J. A.; Hyun No,
K.; Bauer, L. J. Calixarenes 9: Conformational
ACS Paragon Plus Environment

Langmuir
Page 10 of 17
SYNOPSIS TOC (Word Style “SN_Synopsis_TOC”). If you are submitting your paper to a journal that requires a
synopsis graphic and/or synopsis paragraph, see the Instructions for Authors on the journal’s homepage for a
description of what needs to be provided and for the size requirements of the artwork.
1
2
3
4
To format doubleꢀcolumn figures, schemes, charts, and tables, use the following instructions:
5
6
7
8
Place the insertion point where you want to change the number of columns
From the Insert menu, choose Break
Under Sections, choose Continuous
Make sure the insertion point is in the new section. From the Format menu, choose Columns
In the Number of Columns box, type 1
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Choose the OK button
Now your page is set up so that figures, schemes, charts, and tables can span two columns. These must appear
at the top of the page. Be sure to add another section break after the table and change it back to two columns
with a spacing of 0.33 in.
Table 1. Example of a Double-Column Table
Column 1
Column 2
Column 3
Column 4
Column 5
Column 6
Column 7
Column 8
Authors are required to submit a graphic entry for the Table of Contents (TOC) that, in conjunction with the manꢀ
uscript title, should give the reader a representative idea of one of the following: A key structure, reaction, equaꢀ
tion, concept, or theorem, etc., that is discussed in the manuscript. Consult the journal’s Instructions for Authors
for TOC graphic specifications.
Insert Table of Contents artwork here
ACS Paragon Plus Environment

Page 11 of 17
Langmuir
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 1. (A) Structure of "Janus" calix[4]arene ("N" groups are either azide or amine functionality). (B)
Illustrates the cone structure of "Janus" calixarene. (C) The calixarene immobilized onto a surface by: (i) the
lower rim; (ii) the upper rim.
84x34mm (300 x 300 DPI)
ACS Paragon Plus Environment

Langmuir
Page 12 of 17
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 2. Synthesis of cone-5,11,17,23-tetra-azido-25,26,27,28-propargylcalix[4]arene 8.
97x53mm (600 x 600 DPI)
ACS Paragon Plus Environment

Page 13 of 17
Langmuir
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 3. (A) Calix[4]arene 13 immobilized onto GCE surface. (B) Overlaid cyclic voltammograms recorded
in CH2Cl2/0.1 M [nBu4N][PF6], at scan rates of 50-750 mVs-1 for a GC electrode modified with calixarene 6
after further modification with ferrocenyl methyl azide moieties to form calix[4]arene 13 attached by the
upper rim. (C) Corresponding plot of peak current versus scan rate.
141x77mm (300 x 300 DPI)
ACS Paragon Plus Environment

Langmuir
Page 14 of 17
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 4. (A) Overlaid cyclic voltammograms of a GC electrode modified with 5 in 1 M HCl/1 M KCl, scan rate
0.1 V s-1. (B) Corresponding plot of peak current versus scan rate. (C) Overlaid cyclic voltammograms of
the modified electrode recorded at 50-750 mVs-1 over the reversible arylhydroxylamine/arylnitroso redox
couple.
79x74mm (300 x 300 DPI)
ACS Paragon Plus Environment

Page 15 of 17
Langmuir
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 5. (A) Overlaid cyclic voltammograms of a GCE modified with, 8, after post surface modification in
CH2Cl2/0.1 M NBu4PF6, scan rate 0.05-0.75 mVs-1. (B) Corresponding plot of peak current vs. scan rate.
(C) Structure of modified electrode surface
65x50mm (300 x 300 DPI)
ACS Paragon Plus Environment

Langmuir
Page 16 of 17
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 6. XPS spectra recorded over: (a) the N1s region; (b) the F1s region of the modified GCE. (c)
Structure of the functionalized calixarene attached to the GCE surface.
35x14mm (300 x 300 DPI)
ACS Paragon Plus Environment

Page 17 of 17
Langmuir
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
TOC image also found on last page of manuscript
83x29mm (300 x 300 DPI)
ACS Paragon Plus Environment