Anion transport and binding properties of N, N′-(phenylmethylene)dibenzamide based receptors

Article abstract of DOI:10.1080/10610278.2015.1034126

The anion transport and binding properties of a series of bis-amide based compounds have been studied in POPC lipid bilayers. The compounds display evidence of aggregation in solution with single crystal X-ray crystallographic analysis showing hydrogen bo

Full text of DOI:10.1080/10610278.2015.1034126

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Supramolecular Chemistry
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Anion transport and binding properties of NN′-
(phenylmethylene)dibenzamide based receptors
Harriet J. Clarkea, Wim Van Rossoma, Peter N. Hortona, Mark E. Lighta & Philip A. Galea
a Chemistry, University of Southampton, Southampton SO17 1BJ, UK
Published online: 27 Apr 2015.
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To cite this article: Harriet J. Clarke, Wim Van Rossom, Peter N. Horton, Mark E. Light & Philip A. Gale (2015): Anion
transport and binding properties of NN′-(phenylmethylene)dibenzamide based receptors, Supramolecular Chemistry, DOI:
10.1080/10610278.2015.1034126
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Supramolecular Chemistry, 2015
http://dx.doi.org/10.1080/10610278.2015.1034126
Anion transport and binding properties of N, N0-(phenylmethylene)dibenzamide based receptors
Harriet J. Clarke, Wim Van Rossom, Peter N. Horton, Mark E. Light and Philip A. Gale*
Chemistry, University of Southampton, Southampton SO17 1BJ, UK
(Received 12 March 2015; accepted 22 March 2015)
Dedicated to friend and mentor Professor Jonathan L. Sessler on the occasion of his 60th birthday.
The anion transport and binding properties of a series of bis-amide based compounds have been studied in POPC lipid
bilayers. The compounds display evidence of aggregation in solution with single crystal X-ray crystallographic analysis
showing hydrogen bonding between the amide substituents of adjacent receptors in the solid state.
Keywords: hydrogen bonding; anion transport; bis-amides; X-ray crystallography; anion complexation
Introduction
and is expected to increase the binding affinity of the
receptors for anions (3). Trifluoromethyl substituents have
been used previously to enhance the transport properties of
a variety of receptors by both enhancing the affinity of the
receptor for anions and increasing its lipophilicy (17).
Inorganic anions play important roles throughout biologi-
cal systems including regulating cellular pH, osmotic
balance and cell volume (1–3). The transport of anions,
such as chloride, bicarbonate and phosphate, across lipid
bilayers are key in maintaining chemical potentials across
lipid bilayers, driving metabolic processes and cell
signalling (2). Interest in developing synthetic anion
transporters with the future potential to combat ‘channe-
lopathies’, (4) diseases caused by malfunctioning anion
transport channels, has gained momentum in the last few
years, with many small molecule anion transporters
reported (5–8).
Experimental
Synthesis
N,N0-(phenylmethylene)dibenzamide (1)
General procedure adapted from the literature (16) –
Benzamide (476 mg, 3.9 mmol) and benzaldehyde
(203 mL, 2 mmol) were dissolved in dry DMF (8 mL).
TMSCl (507 mL, 4 mmol) was added as a catalyst and was
stirred at 508C for 18 h under nitrogen. A white precipitate
was formed with the addition of a few drops of water and
was purified by stirring with diethyl ether for 30 min. The
product was isolated using vacuum filtration. Yield 31%;
m.p. 218.0–220.08C. 1H NMR (400 MHz, DMSO-d6)
d ppm 9.05 (d, J ¼ 7.80 Hz, 2 H), 7.89–7.96 (m, 4 H),
7.53–7.62 (m, 2 H), 7.47–7.51(m, 6 H), 7.40 (t,
J ¼ 7.40 Hz, 2 H), 7.32 (t, J ¼ 7.40 1 H), 7.05 (t,
J ¼ 7.80 Hz, 1 H). 13C NMR (101 MHz, DMSO-d6) d
ppm 166.0 (CO), 140.8 (ArC), 134.3 (ArC), 132.0 (ArCH),
128.8 (ArCH), 128.8 (ArCH), 128.1 (ArCH), 128.0
(ArCH), 127.0 (ArCH), 59.2 (CH). LR-MS-ESIþ- (m/z):
353 [M þ Naþ]. HR-MS-ESIþ- (m/z): Calc.
C21H18N2NaO2 353.1260 [M þ Naþ]. Meas. 353.1255
[M þ Naþ]. Error 1.4 ppm.
Our research interests focus on designing new small
molecules containing hydrogen bond donors that function
as transmembrane anion transporters. Favourable anion
binding affinities and transport abilities of amides, ureas
and thioureas have been reported (9–13). QSAR studies
involving a series of simple thioureas have shown that
lipophilicity, molecular size and substituent effects
(Hammett constant) are important molecular parameters
that can be optimised to maximise transport efficiency
across simple lipid bilayers. Ureas and thioureas (14, 15)
have been found to form stable complexes with a range of
anions. Inspired by the effectiveness of the urea and
thiourea motifs in anion receptor, transporters and self-
assembling systems we report here the anion binding and
transport properties of a family of N, N0-(phenylmethy-
lene)dibenzamide (16) based receptors 1–7 (Figure 1).
These bisamide-based receptors, like urea, possess a
potentially parallel array of hydrogen bond donors. Nitro-
and trifluoromethyl substituents were chosen due to their
electron withdrawing properties, which is known to
increase the acidity of attached hydrogen bond donors
N,N0-(phenylmethylene)bis(4-nitrobenzamide) (2)
Using the general procedure with 4- nitrobenzamide
(662 mg, 3.9 mmol), benzaldehyde (203 mL, 2 mmol) and
TMSCl (507 mL, 4 mmol). Yield 44%; m.p. 253.1–
*Corresponding author. Email: philip.gale@soton.ac.uk
q 2015 The Author(s). Published by Taylor & Francis.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/Licenses/by/4.0/), which permits
unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

2
H.J. Clarke et al.
Figure 1. Bisamide based receptors 1–7.
254.48C. 1H NMR (400 MHz, DMSO-d6) d ppm 9.53
(d, J ¼ 7.21 Hz, 2 H), 8.33 (d, J ¼ 8.68 Hz, 4 H), 8.16
(d, J ¼ 8.68 Hz, 4 H), 7.52 (d, J ¼ 7.36 Hz, 2 H), 7.42
(t, J ¼ 7.38 Hz, 2 H), 7.36–7.37 (m, 1 H), 7.00
(t, J ¼ 7.27 Hz, 1 H). 13C NMR (101 MHz, DMSO-d6)
d ppm 164.8 (CO), 149.7 (ArC), 140.0 (ArC), 139.6 (ArC),
129.7 (ArCH), 128.8 (ArCH), 128.4 (ArCH), 127.3
(ArCH), 123.9 (ArCH), 59.9 (CH). LR-MS-ESIþ- (m/z):
421 [M þ Hþ]. HR-MS-ESIþ-(m/z): Calc. C21H16N4NaO6
443.0962 [M þ Naþ]. Meas. 443.0969 [M þ Naþ]. Error
1.6 ppm.
2 H), 7.74 (d, J ¼ 8.36 Hz, 2 H), 7.04 (t, J ¼ 7.09 Hz, 1 H).
13C NMR (101 MHz, DMSO-d6) d ppm) 165.0 (CO),
149.7 (ArC), 144.1 (ArC), 139.8 (ArC), 129.7 (ArCH),
129.1 (q, CF3), 128.2 (ArCH), 125.7 (ArC), 123.9 (ArCH),
123.3 (ArCH), 59.7 (CH). LR-MS-ESIþ- (m/z): 489
[M þ Hþ]. HR-MS-ESIþ-(m/z): Calc. C22H15F3N4NaO6
511.0836 [M þ Naþ]. Meas. 511.0845 [M þ Naþ]. Error
1.8 ppm.
N, N0-((3,5-bis(trifluoromethyl)phenyl)methylene)bis(4-
nitrobenzamide) (4)
Using the general procedure with 4-nitrobenzamide
(1.008 g, 6 mmol), 3,5-bis (trifluoromethyl)benzaldehyde
(500 mL, 3 mmol)) and TMSCl (770 mL, 6 mmol) in 10 mL
DMF. Yield 81 %; m.p. 283.2–285.18C. 1H NMR
(400 MHz, DMSO-d6) d ppm 9.68 (br d, J ¼ 6.85 Hz,
2 H), 8.35 (br d, J ¼ 8.56 Hz, 4 H), 8.26 (s, 2 H), 8.15 (br d,
N,N0-((4-(trifluoromethyl)phenyl)methylene)bis(4-
nitrobenzamide) (3)
Using the general procedure with 4-nitrobenzamide
(340 mg, 2 mmol), 4 (trifluoromethyl)benzaldehyde
(85 mL, 0.5 mmol)) and TMSCl (200 mL, 1 mmol). Yield
1
a
42%; m.p. 280.0–281.98C. H NMR (400 MHz, DMSO-
d6) d ppm 9.61 (d, J ¼ 7.09 Hz, 2 H), 8.35 (d, J ¼ 8.86 Hz,
J ¼ 8.44 Hz, 5 H) , 7.09 (br t, J ¼ 6.66 Hz, 1 H). 13C
NMR (101 MHz, DMSO-d6) d ppm 165.2 (CO), 149.8
(ArC), 142.8 (ArC), 139.6 (ArC), 130.8 (q, CF3), 129.7
4 H), 8.17 (d, J ¼ 8.86 Hz, 4 H), 7.79 (d, J ¼ 8.36 Hz,

Supramolecular Chemistry
3
(ArCH), 128.6 (ArC), 124.0 (ArCH), 122.6 (ArCH),
122.4 (ArCH), 59.7 (CH). LR-MS-ESI2- (m/z): 555[M-
Hþ]. HR-MS-ESIþ- (m/z): Calc. C23H14F6N4NaO6
579.0710 [M þ Naþ]. Meas.579.0715 [M þ Naþ]. Error
671.0810 [M þ Hþ]. Meas. 671.0806 [M þ Hþ]. Error
0.6 ppm.
a
N,N0-(phenylmethylene)bis(2,3,4,5,6-
pentafluorobenzamide) (7)
0.9 ppm. two overlapping signals singlet overlapping a
doublet.
2,3,4,5,6-Pentafluorobenzamide (842 mg, 4 mmol) and ben-
zaldehyde (203mL, 2 mmol) were dissolved in dry toluene
(5 mL). ZnCl2 (,5 mg) was added as a catalyst and the
reaction mixture was refluxed for 24 hours under nitrogen.
A white precipitate was formed over time and the product
was isolated using hot vacuum filtration washing with
N, N0-(phenylmethylene)bis(3,5-bis(trifluoromethyl)
benzamide) (5)
Using the general procedure with 3,5-bis(trifluoromethyl)
benzamide (600 mg, 2.3 mmol), benzaldehyde (138 mL,
1.2 mmol)) and TMSCl (296 mL, 2.3 mmol) in 10 mL
DMF. Recrystallised from EtOAC to give the product as a
1
diethyl ether. Yield 20 %; m.p. 253.0–256.08C. H NMR
(400 MHz, DMSO-d6) d ppm 9.95 (d, J ¼ 7.96Hz, 2 H),
7.46–7.48(m,4 H),7.38–7.42(m,1 H),6.90(t,J ¼ 7.94 Hz,
1 H). 13C NMR (101MHz, DMSO-d6) d ppm 156.7 (CO),
144.9 (ArC), 142.5 (ArC), 140.5 (ArC) 138.6 (ArC), 138.2
(ArC), 136.2 (ArC), 129.1 (ArCH), 128.9 (ArCH), 126.7
(ArCH), 112.5 (ArC), 58.6 (CH) LR-MS-ESI2- (m/z): 553
[M þ Naþ]. HR-MS-ESIþ-(m/z): Calc C21H9O2N2F10
511.0499 [M þ Hþ]. Meas 511.0511 [M þ Hþ], Error 2.3
ppm. Calc. C21H8O2N2NaF10 533.0318 [M þ Naþ]. Meas.
533.0330 [M þ Naþ]. Error 2.25 ppm.
1
white powder. Yield 66 %; m.p. 257.1–2598C. H NMR
(400 MHz, DMSO-d6) d ppm 9.73 (d, J ¼ 7.12 Hz, 2 H),
8.60 (s, 4 H), 8.35 (s, 2 H), 7.56 (d, J ¼ 7.34 Hz, 2 H), 7.44
(t, J ¼ 7.34 Hz, 2H) 7.36–7.40 (m, 1 H), 7.06 (t,
J ¼ 6.97 Hz, 1 H). 13C NMR (101 MHz, DMSO-d6) d
ppm 163.6 (CO), 139.1 (ArC), 136.4 (ArC), 130.9 (q,
CF3), 129.0 (br s, ArC), 128.6 (ArCH), 127.4 (ArCH),
125.6 (br s, ArCH), 124.9 (ArCH), 122.2 (ArCH), 60.3
(CH). LR-MS-ESIþ- (m/z): 602 [M þ Hþ]. HR-MS-ESIþ-
(m/z): Calc. C25H15F12N2O2 603.0936 [M þ Hþ]. Meas.
603.0927 [M þ Hþ]. Error 1.5 ppm.
Results and discussion
Binding studies were carried out in two solvent systems for
receptors 1–7 to determine their affinity for a variety of
different anions. After determination of the binding
stoichiometry, by Job plot analyses (18), stability constants
for chloride, bicarbonate and dihydrogen phosphate
complex formation were determined from fitting 1H
NMR titration data (following the downfield shift of the
amide NH) to 1:1 binding isotherms using winEQNMR2
(19). The association constants are shown in Table 1.
Titrations were performed using nitrate as the guest
anion but these showed little or no shift of the amide
NH and could not be fitted to a binding isotherm. The
general trend in association constants for receptors 1–7
indicates the binding affinity for chloride is low. The
compounds have a higher affinity for oxoanions
N,N0-((4-(trifluoromethyl)phenyl)methylene)bis(3,5-bis
(trifluoromethyl)benzamide) (6)
Using the general procedure with 3,5-bis(trifluoromethyl)
benzamide (1.03 mg, 4 mmol), 4- (trifluoromethyl) benzal-
dehyde (272 mL, 2 mmol)) and TMSCl (507 mL, 4 mmol).
Yield 8 %; m.p. 269.0–270.08C. 1H NMR (400 MHz,
DMSO-d6) d ppm 9.82 (d, J ¼ 6.96 Hz, 2 H), 8.60 (s, 4 H),
8.39 (s, 2 H), 7.77–7.86 (m, 4 H), 7.09 (t, J ¼ 6.86 Hz, 1 H).
13C NMR (101 MHz, DMSO-d6) d ppm 163.7 (CO), 143.7
(ArC), 136.2 (ArC), 130.9 (q, CF3), 129.0 (br s, ArC), 128.4
(ArCH), 127.6 (ArC), 125.8 (m, CF3), 124.9 (ArCH), 122.2
(ArCH), 119.5 (ArCH), 60.0 (CH). LR-MS-ESI2- (m/z):
669 [M-Hþ]. HR-MS-ESIþ-(m/z): Calc. C26H14N2O2F15
Table 1. Apparent stability constants (M21) in A) DMSO-d6/0.5 % water and B) 59.75 % acetonitrile-d3/39.75 % DMSO-d6/ 0.5 %
water.
1
2
3
4
5
6
7
Anion
A
B
A
B
A
B
A
B
A
B
A
B
A
B
Cl2
HCO23
H2PO24
19
275
370
46
550
296
19
771
2270
47
1680
1630
17
745
8290
67
18
796
1350
54
11
266
673
27
314
530
10
307
1320
49
,10
,10
a,b
c
c
c
c
c
c
c
3410
4030
4370
Notes: Guests were added as tetrabutylammonium salts, unless stated otherwise. All data was fitted to a 1:1 receptor:anion isotherm with WinEQNMR2.
a Peak broadening upon addition of the anionic guest.
b Guest was added as a tetraethylammium salt.
c No association constant could be calculated due disappearance of the NH signal upon addition of the anionic guest, most probably due to deprotonation of
the receptor.

4
H.J. Clarke et al.
particularly dihydrogen phosphate which is attributed to
the favourable binding mode in which presumably two
parallel hydrogen bonds are formed to the oxo-anion.
Upon addition of bicarbonate, peak broadening was
observed which in some cases precluded the elucidation of
an association constant.
Receptors 5 and 6, despite being highly fluorinated, do not
exhibit the greatest transport abilities and this is discussed
later.
Two transport mechanisms are possible, antiport
(Cl2=NO32 exchange) or symport (Naþ/Cl2 or Hþ/Cl2
co-transport). To rule out the latter, the standard POPC
Cl2=NO23 assay was repeated using both KCl and CsCl as
the encapsulated salt and this resulted in no significant
change in the chloride efflux (see ESI) – evidence that
does not support a metal co-transport mechanism.
To confirm the antiport mechanism and rule out the Hþ/
Cl2 symport mechanism, POPC vesicles were prepared
and suspended in Na2SO4. After addition of the transporter
there was little, if any, chloride efflux observed (see ESI),
this was expected due to the high dehydration penalty
involved in the transport of the hydrophilic sulfate anion
(21). This result indicated that an exchange process was
likely and no Hþ/Cl2 co-transport was occurring, this
assay was repeated and at 120 s a pulse of NaHCO3 was
added, switching on the chloride efflux via a chloride/
bicarbonate exchange process. Receptors 2–6 were less
effective as Cl2/HCO32 antiporters than Cl2=NO23
antiporters. For example, receptor 4 could only facilitate
ca. 30% release of chloride at the end of the experiment
(see Figure 3).
The transport ability of receptors 1–7 was investigated
using phospholipid vesicle based assays (20). Unilamellar
1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine
(POPC) vesicles were prepared with an internal solution
of 489 mM NaCl buffered to pH 7.2 with 5 mM sodium
phosphate salts, and were suspended in an external
solution of 489 mM NaNO3 buffered to pH 7.2 with 5 mM
sodium phosphate salts; to obtain a final lipid concen-
tration of 1 mM. The receptor was added as a DMSO
solution, 2 mol% with respect to the lipid, and the resulting
chloride efflux was measured using a chloride selective
electrode. At 300 s the vesicles were lysed with 50 mL
polyoxyethylene (8) lauryl ether detergent to give the 100
% chloride efflux and the results were calibrated using this
final electrode reading.
Figure 2 demonstrates the differing abilities of
receptors 1–7 to facilitate chloride efflux. Receptor 4
displays the most effective chloride transport across the
course of the experiment with .80% chloride efflux over
300 s. Increasing the fluorination of the central phenyl for
receptors 2–4 showed an increase in chloride efflux, which
supports previous studies that attributes this to the
increased lipophilicity of the transporter and therefore a
greater ability to partition into the lipid bilayer (17).
Quantification of the transport process for receptors 2–
6 was attempted by Hill analysis (22). Receptors 1 and 7
were excluded due to no measurable chloride transport at
2 mol% of receptor. EC50 values and effective receptor
concentration required to facilitate 50% chloride efflux
Figure 3. (Colour online) Chloride efflux facilitated by 1–7 at
2 mol% loading (with respect to lipid) from POPC vesicles
containing 450 mM NaCl buffered to pH 7.2 with 20 mM sodium
phosphate salts suspended in 162 mM Na2SO4 buffered to pH 7.2
with sodium phosphate salts. At 120 s a NaHCO3 solution was
added to give a 40-mM external concentration. To end the
experiment detergent was added to lyse the vesicles and this final
chloride efflux was used as 100% to calibrate the ion selective
electrode. Each point is an average of three runs.
Figure 2. (Colour online) Chloride efflux facilitated by 1–7 at
2 mol% loading (with respect to lipid) from POPC vesicles
containing 489 mM NaCl buffered to pH 7.2 with 5 mM sodium
phosphate salts suspended in 489 mM NaNO3 buffered to pH 7.2
with sodium phosphate salts. To end the experiment detergent
was added to lyse the vesicles and this final chloride efflux was
used as 100 % to calibrate the ion selective electrode. Each point
is an average of three runs.

Supramolecular Chemistry
Table 2. EC50 and Hill coefficient (n) values for receptors 2–6.
5
prepared with a 7:3 POPC:cholesterol composition and a
Cl2=NO23 assay was conducted. Cholesterol orders a lipid
bilayer resulting in less fluidity (30), so it would be
assumed for mobile carrier mechanisms that depend on
diffusion through the membrane, transport would be
reduced with this increase in viscosity.
Receptor
EC50
a
n
a
2
3
4
5
6
5.4
0.37
0.78
1.07
b
b
3.8c
2.5c
Receptors 2–4 exhibit the expected decrease in
activity, Figure 4 shows an increase in activity for receptor
6 and very little change in activity for receptor 5, this could
be indicative that their transport process is not a mobile
carrier mechanism; however, from U-tube tests (see ESI) a
channel formation was deemed unlikely. Haynes et al. (24)
reported similar increases in transport with cholesterol for
receptors containing highly lipophilic substituents such as
CF3. It is clear that delivery and partitioning into the lipid
membrane is affected by the presence of cholesterol and
the lipophilic nature of the receptor (31).
Notes: To an extent all receptors tested displayed signs of self aggregation
at higher concentrations, consistency of runs was hard to achieve and
therefore reported Hill analysis may be unreliable.
a Hill analysis not reliable due to low transport activity.
b Possible self aggregation of the receptor did not allow for consistent
results for Hill analysis.
c Hill analysis should be treated with caution due to poor fit and unusual
behaviour in testing.
after 270 s, can be found in Table 2. Hill coefficients (n)
were also calculated, giving an indication of the
stoichiometry for the transported complex (23).
Investigating the unusual concentration dependant
behaviour of these compounds further, a series of NMR
dilution experiments were performed to try to identify if
self-aggregation was a possibility in solution and hence
reducing the efficacy of chloride transport. Self-aggregates
typically have higher log P values and lower solubility
than their monomeric components which would explain
why receptors 5 and 6 exhibit more aggregate tendencies
(32). Typical NMR spectra of aggregators can show
changes in the number of signals present, indicative of
multiple aggregates species in solution. Additionally,
changes in chemical shifts (d ppm) may be detected
resulting from local environmental changes in the
Table 2 shows that compound 4 is quantitatively the
most efficient transporter with the lowest EC50 value.
Although Hill analysis was deemed unreliable and in some
cases, EC50 values could not be calculated, this was due to
unusual behaviour from all the receptors to varying
extents. When adding the receptor in DMSO solution, the
more concentrated the stock solution, the less consistent
the runs and in some cases the lower the chloride efflux,
despite the overall amount of receptor added being the
same. This effect was most apparent for receptors 5 and 6
it was also evident that these receptors possessed a
different transport profile. Figure 2 shows their transport
takes longer to begin following the addition of the receptor
to the system, giving more of a sigmoidal shape to the
curve, receptor 6 also displays a more sigmoidal shape in
the Hill plot. This behaviour has previously been noted by
Haynes et al. (24) which was attributed to the receptors
lying outside the optimum lipophilicity values proposed by
Saggiomo et al. (25) Receptors 5 and 6 possess log P
values of 5.1 and 5.44 respectively as calculated by VCC
labs, (26) which lie above the optimum lipophilicity values
proposed (log P < 4) (25). This would allow the slow start
to transport to be rationalised, as delivery through the
aqueous external solution is hindered. Another explanation
of the unusual concentration dependant results is the
possibility of self-aggregation of the receptors in solution
which is reported to be counterproductive to transport
efficacy (27, 28).
Hill coefficients for receptors 3 and 4 were both <1,
which is indicative of a mobile carrier mechanism, where
one receptor transports one anion across the bilayer.
Receptor 6 however has a Hill coefficient of 2.5, this
indicates that more than one receptor may be in contact
with the anion during the transport process, possibly the
formation of a cluster or aggregate that transports the
anion (29). To investigate this further, vesicles were
Figure 4. (Colour online) Chloride efflux facilitated by 2–6 at
2 mol% loading (with respect to lipid) from POPC: Cholesterol
(7:3) vesicles containing 489 mM NaCl buffered to pH 7.2 with
5 mM sodium phosphate salts suspended in 489 mM NaNO3
buffered to pH 7.2 with sodium phosphate salts. To end the
experiment detergent was added to lyse the vesicles and this final
chloride efflux was used as 100% to calibrate the ion selective
electrode. Each point is an average of three runs. DMSO was used
for the blank run.

6
H.J. Clarke et al.
Figure 5. (Colour online) NMR dilution studies: stack plots of spectra differing in concentration (1–100 mM) samples in DMSO- d6. (a)
Small upfield shift of proton Ha. (b) Small downfield shift of proton Hb.
magnetic field of the molecule if aggregates are formed.
Changes in the shape of the resonance peaks, typically
broadening, may indicate a change in the size and
tumbling rate of the species in solution (33). Proton NMR
spectra were obtained for receptors 1–7 at a range of
concentrations (1–100 mM). Inserts from the spectra of
receptor 5 can be seen in Figure 5. A small change in
chemical shift is evident for Ha and Hb.
Most of the receptors showed small, but noticeable,
changes in the chemical shifts for proton (Hb) and the N-H
protons (see ESI). Receptor 5 was the only one to show
significant changes for other proton shifts (Ha) and
receptor 4 displayed the least noticeable shifts, interest-
ingly, as this receptor showed the least concentration
dependence during vesicle studies and was the most
effective chloride transporter. The self-association of these
receptors in solution means that the association constant
determinations above will be dependent on concentration.
Therefore the association constants should be regarded as
apparent values only.
Receptors 2 and 6 were both isolated as crystalline
solids by slow evaporation at room temperature of
acetonitrile and DMSO solutions of the compounds
respectively.1 The structures of the compounds were
elucidated by single crystal X-ray diffraction. Figure 6
shows that in the solid state the receptors adopt a
conformation in which the NH hydrogen bond donors are
nearly parallel. The molecules form continuous hydrogen
Figure 6. (Colour online) (a) Uncomplexed receptors 2 and 6. (b) Self aggregation through hydrogen bonding to adjacent receptor
˚
molecules (distances in A).

Supramolecular Chemistry
7
(M ¼ 420.38): Orthorhombic, space group Pnma,
bonded arrays in the solid state via two NH· · ·O (1.96–
˚
˚
˚
a ¼ 16.5475(11) A, b ¼ 22.8442(16) A, c ¼ 4.9997(4) A
˚
2.00 A) interactions between the amide groups on adjacent
receptors.
3
˚
a ¼ 908, b ¼ 908, g ¼ 908, V ¼ 1890.0(2) A , Z ¼ 4,
T ¼ 100(2) K, m(MoKa) ¼ 0.111 mm21, Dcalc ¼ 1.477 g/
mm3, 10813 reflections measured (3.040 #2Q # 27.466),
2216 unique (Rint ¼ 0.0355) which were used in all
calculations. The final R1 was 0.0365 (I . 2s(I)) and wR2
was 0.0982 (all data).
Conclusions
A series of N, N0-(phenylmethylene)dibenzamide based
receptors were found to function as Cl2=NO32 and
Cl2=HCO23 antiporters, most likely by a mobile carrier
mechanism although evidence of aggregation in solution
was observed which complicated unambiguous determi-
nation of the transport mechanism. Self-aggregation was
supported by NMR dilution studies and was most apparent
in fluorinated receptor 5. The self-association properties of
this motif may effectively increase log P and hence
enhance the transport properties of the compounds.
Substituent effects and lipophilicity were found to be
important parameters involved in the binding and transport
abilities. One can envisage this hydrogen-bonding motif
being used instead of urea in a variety of self-assembled
structures due to the formation of two nearly linear
hydrogen-bonding interactions. We are continuing to
investigate the properties of this hydrogen-bonding array.
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Disclosure statement
´
Bradberry, S.J.; Gomez-Iglesias, P.; Soto-Cerrato, V.;
Perez-Tomas, R.; Gale, P.A. Chem. Sci. 2012, 3,
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´
No potential conflict of interest was reported by the authors.
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We thank the EPSRC for a DTP studentship (HJC), for access to
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Note
1. X-ray data were collected on
a Rigaku AFC 12
diffractometer mounted on Rigaku FR-Eþ Super Bright
High Flux rotating anode CCD diffractometer equipped with
VariMax high flux (HF) optics and Saturn 724 þ CCD
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Crystal data for receptor 6. CCDC 1053070, C26H13F15N2O2
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˚
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˚
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˚
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mm3, 16362 reflections measured (2.168 # Q # 31.993),
4347 unique (Rint ¼ 0.0253) which were used in all
calculations. The final R1 was 0.0581 (I . 2s(I)) and wR2
was 0.1431 (all data).
Crystal data for receptor 2. CCDC 1053071, C21H16N4O6

8
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Supramolecular Chemistry
9
Harriet J. Clarke, Wim Van Rossom, Peter N. Horton,
Mark E. Light and Philip A. Gale
Anion transport and binding properties of N, N0-
(phenylmethylene)dibenzamide based receptors
1–9