Sulfate-Templated 2D Anion-Layered Supramolecular Self-Assemblies

Article abstract of DOI:10.1016/j.chempr.2019.06.023

Anions are widespread in our world, and many anions carry out specific roles in nature, for both living and inanimate matter. Because these processes are often accompanied by specificity, when changes occur in these interactions, the results can be of har

Full text of DOI:10.1016/j.chempr.2019.06.023

Article
Sulfate-Templated 2D Anion-Layered
Supramolecular Self-Assemblies
Anna B. Aletti, Salvador Blasco,
Savyasachi J. Aramballi, Paul E.
Kruger, Thorfinnur
Gunnlaugsson
paul.kruger@canterbury.ac.nz (P.E.K.)
gunnlaut@tcd.ie (T.G.)
HIGHLIGHTS
Synthesis of urea-based tripodal
ligands, with propeller-like
appearance, is described
These structures form hydrogen
2À
bonding networks with SO4
These self-assemblies give rise to
highly ordered layered materials
The formation of hierarchical
structures, including nano-sized
particles, is observed
Tripodal N-methylated(1,3,5-benzene-tricarboxamide)-tris(phenylurea) BTA
ligands, possessing urea functionalities in the meta position, are able to form
extended self-assembly 2D networks via hydrogen bonding templated by sulfate
(SO42À). Studies in solution and in the solid state, as well as scanning electron
microscopy (SEM) on the self-assembly properties of the ligands showed that the
convergence also leads to the formation of hierarchical structures, including
porous films and spherical nano-sized particles, with the morphological outcome
being highly solvent dependent.
Aletti et al., Chem 5, 1–13
October 10, 2019 ª 2019 Published by Elsevier
Inc.
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Article
Sulfate-Templated 2D Anion-Layered
Supramolecular Self-Assemblies
Anna B. Aletti,1 Salvador Blasco,1,2 Savyasachi J. Aramballi,1 Paul E. Kruger,3,
*
and Thorfinnur Gunnlaugsson1,4,
*
SUMMARY
The Bigger Picture
Anions are widespread in our
world, and many anions carry out
specific roles in nature, for both
living and inanimate matter.
Because these processes are often
accompanied by specificity, when
changes occur in these
Using solution and solid-state analyses, we demonstrate that the tripodal N-methyl-
ated(1,3,5-benzene-tricarboxamide)-tris(phenylurea) BTA ligands, possessing urea
functionalities in the meta position, are able to form extended self-assembly 2D net-
works via hydrogen bonding templated by sulfate (SO42–). The divergence of the
urea binding sites confers a propeller-like conformation to the ligands and is key
to formation of the self-assemblies. Studies in solution and in the solid state as
well as scanning electron microscopy (SEM) on the self-assembly properties of the
ligands showed that the convergence also leads to the formation of hierarchical
structures, including porous films and spherical nano-sizedparticles;the morpholog-
ical outcome is highly solvent dependent.
interactions, the results can be of
harm to life and the environment.
For this reason, the study of the
noncovalent bonds of anions has
been of interest to scientists for
many years, with a focus on
INTRODUCTION
Supramolecular anion chemistry is a topical area of research with a large number of
organic and coordination structures developed for the recognition, sensing, and
transport of anions.1–3 Anions play a critical role as counter ions in the formation
of coordination networks and MOFs4 and in directing self-assembly processes,
such as in the formation of clusters,5 metallo-macrocyles and cages,6 helicates,7
knots,8 and mechanically interlocked structures.9 Their application in supramolecu-
lar gel formation is also well studied.10,11 In contrast, examples of anions directing
the formation of higher order organized self-assemblies and functional hierarchical
hydrogen bonding, imitating the
way proteins and enzymes can
interact with anions in nature.
A deep understanding of these
interactions is needed to
comprehend how their activity can
be actively used toward the
formation of hierarchical
assemblies to control their
functions and activities in their
environment.
materials from charge neutral organic building blocks is limited. Noteworthy exam-
12
ꢀ
ples include that of Basaric et al., who used phosphate to mediate the formation
of self-assembly structures from adamantane bisurea derivatives and that of Das
et al.13 who used carbonate to induce the formation of dimeric capsular hexagonal
assemblies. Recently, Bielawski et al.14 used bis-anions in the formation of anion
cross-linked soft materials, while Granja et al.15 formed higher order organized
self-assemblies of spherical aggregates from cyclic peptides. In the last decade,
several examples of anion coordination polymer (ACP) have also been developed
which normally give 1D structures16,17 and other anion based polymeric sys-
tems.18,19 In fact, anion supramolecular self-assembly chemistry has become an
import and fast growing area of research.20–22 The BTA (1,3,5-benzenetricarboxa-
mide) moiety is a tripodal building block that has been extensively used in the
formation of a range of supramolecular structures and materials.23 Recently,
Stefankiewicz et al. used BTA ligands in the formation of a large enantiopure nano-
The development of anion-
templated self-assemblies is of
interest for their potential in the
removal of hazardous and
polluting anions from the
environment using new improved
methodologies.
capsule as a host for C60.
24 We have recently shown that the BTA scaffold can form
anion-templated self-assembly cages using SO42– in 2:1 stoichiometry and self-sort-
ing self-assembled clusters with 4:4 stoichiometry.25 Here, we demonstrate that the
high coordination requirement of SO42– and its templating ability can be capitalized
upon in the formation of a supramolecular layered polymeric 2D network, and that
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Figure 1. Structure of Tripodal Ligands 1–3
(A) Structures of 1–3.
(B) The X-ray crystal structure of 2, viewed from the BTA core demonstrating the open propeller
conformation with divergent urea binding sites. Hydrogen atoms and solvent molecules omitted
for clarity.
these self-assemblies form nano-sized hierarchical aggregates in solution. We
demonstrate by using SEM imaging that the nature of the solvent mixture dictates
the way that these 2D networks aggregate to form higher-ordered hierarchical ma-
terials, the morphology of which are highly solvent dependent.
RESULTS AND DISCUSSION
Synthesis and Characterization
2–
Inspired by the ability of the SO4 anion to form anion-templated capsules, the
N-methylated BTA structures 1–3, Figure 1A, possessing three inner-core phenyl
urea groups substituted in the meta position were synthesized in three steps. Start-
ing from 1,3,5-benzenetricarbonyltrichloride and N-methyl-3-nitroaniline, which
were coupled to give a tripodal nitro precursor, which, once catalytically reduced
to the corresponding amine, was reacted with the relevant phenyl isocyanate to
give the desired ligands (see Scheme S1 and Supplemental Information for full de-
tails). Our objective was to investigate whether these ligands could be used to direct
self-assembly formation away from the ‘‘capsule’’ structure18 toward the formation of
higher-ordered hierarchical structures. Slow evaporation of DMSO and CH3CN so-
lutions of 2 and 3, respectively, resulted in the formation of diffraction-quality single
1School of Chemistry and AMBER (Advanced
Materials and BioEngineering Research) Centre,
crystals. The crystal structures are shown in Figures 2A–2D. Unfortunately, attempts
to grow suitable crystals of 1 failed. Ligand 2 crystallized in the triclinic P-1 space
group and showed the three N-methylamido groups of the BTA unit to be directed
away from the plane of the central benzene core (Figures 1B, 2A, and 2B). The three
amide oxygen atoms bend away from the plane defined by the central benzene ring
with torsion angles of ca. 43ꢀ for two arms and 62ꢀ for the third. The coplanar confor-
mation of two of the arms is further stabilized by low angle, ca. 120ꢀ, hydrogen
bonds between aromatic C–H donors, and the acceptor oxygen atom of the ureas
(Table S7). These interactions as well as p–p interactions stabilize the conformation
of 2,4-difluorophenyl moiety which, in principle, can rotate freely. These two ureas
are also engaged in hydrogen bonding with two DMSO molecules, reflecting solva-
tion of the potential binding site of the receptor. The third arm exhibits a wider angle
because of bifurcated intermolecular hydrogen bonding of the urea with another
arm of a neighboring molecule of 2. The crystals of 3 were also formed in the triclinic
P-1 space group, with the asymmetric unit containing one molecule of ligand and
Trinity College Dublin, The University of Dublin,
Dublin 2, Ireland
2Departamento de Quımica, Inorga´nica,
´
Universidad de Valencia, Instituto de Ciencia
Molecular, Edificio de Institutos de Paterna,
C/Catedra´tico Jose´ Beltra´n Martınez 2, Paterna,
´
Valencia 46980, Spain
3MacDiarmid Institute for Advanced Materials
and Nanotechnology, School of Physical and
Chemical Sciences, University of Canterbury,
Private Bag 4800, Christchurch 8041, New
Zealand
4Lead Contact
*Correspondence:
paul.kruger@canterbury.ac.nz (P.E.K.),
gunnlaut@tcd.ie (T.G.)
https://doi.org/10.1016/j.chempr.2019.06.023
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Figure 2. Crystal Structures of 2 and 3
Structure of 2. Shown in (A) is a capped stick representation demonstrating the open propeller
conformation, with divergent urea binding sites, that are involved in H-bond with 2 solvent
molecules (DMSO), and in (B) is the packing showing hydrogen bonding from one of the urea
groups NH to the BTA C=O on a neighboring molecule. Shown is the structure of 3: in (C) is a
capped stick representation showing the formation of internal hydrogen bond from one urea NH
and the Ortho NO2 group and in (D) is packing showing hydrogen bonding from two of the urea
groups NH (the one not involved in the intramolecular H-bond) to the BTA C=O on a neighboring
molecule. Hydrogen atoms omitted for clarity.
some solvent molecules. As was seen for 2, the central BTA moiety adopts a confor-
mation where all three amide oxygen atoms locate on the same side of the central
ring, and a range of different supramolecular interactions (intermolecular hydrogen
bonds, p–p stacking, and CH–p bonds) are evident in the crystal packing. Further-
more, an intramolecular hydrogen bond between the nitro-substituted distal phenyl
ring and urea NHs exists for all three arms (Figure 1C). We26 and others27 have
demonstrated such interactions in structurally similar urea-based receptors. As
was observed for 2, intermolecular hydrogen bonds between the arms of neigh-
boring molecules also exist in 3 and give rise to a 1D network in the crystallography
a axis (Figure 2D).
Anion Binding Studies
Anion Binding Studies in Solution
The solid-state analysis above demonstrated the presence of the anticipated open
‘‘propeller-like’’ conformation for both 2 and 3 and suggests that this preorganiza-
tion may be appropriate to form anion-templated networks. With this in mind, we
investigated the affinity of 1–3 for different anions (tetrabutyl-ammonium salts of
AcOÀ, SO42À, H2PO4À, and ClÀ)26 in CH3CN solution using UV-vis absorption spec-
troscopy. The absorption spectra consisted of a broad band at high energy for the
BTA core, and a shoulder for 1 and 2, or a band for 3, that was significantly red
shifted, because of internal charge transfer. All the anion titrations clearly demon-
strated that 1–3 participated in anion binding, with concomitant formation of
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different isosbestic points (Figures S58–S69). However, the overall changes were in
some cases relatively small, and the titration data could not be fit easily to give reli-
able anion binding constants (see Table S1 for fitting). Therefore, titrations were car-
ried out in DMSO-d6 solutions and followed using 1H NMR spectroscopy.
Full NMR characterization of 1–3 was completed using 2D NMR experiments (i.e.,
HMBC, C–H, and N–H HSQC) combined with selective 1H ROESY, which allowed
us to identify, and confidently monitor, the shift of each proton during the binding
events. Titration of these ligands with the aforementioned anions caused de-shield-
ing to occur in the urea proton resonances, indicating hydrogen bonding interaction
with the anions. From these changes, the anion binding stoichiometry and
constants could be determined using the non-linear regression analysis program
HypNMR.28,29 The analysis showed the formation of 1:1 complexes (ligand 1:
K
1:1 = 32, 200 and 8 MÀ1 for ClÀ, H2PO4À, and SO42À, respectively; for other ligands
see Table S2), while with AcO- ligands 2 and 3 formed the 1:1, and ligand 1 showed
the formation of two species, 1:1 and 1:3. This behavior is in line with the Hofmeister
series and the solvation of the anions. The formation of 1:1 complexes for ClÀ,
À
SO42À, and H2PO4 was also confirmed by MALDI-TOF analysis (Figures S37–
S41), with the isotopic distribution patterns matching those of the calculated spe-
cies. Unfortunately, ligand 1 was the only host that displayed sufficient solubility in
CD3CN for 1H NMR titrations to be carried out. In this media, all anions induced a
greater downfield shift in the urea proton resonances than seen in DMSO-d6 and
less selective binding was observed (SO42À and ClÀ showed shifts that were 2 and
4 times those seen in DMSO-d6) (Figure 3). This reflects their stronger interactions
in less competitive media (Table S3). These titrations were fit to the same binding
models as employed above, showing both 1:1 and 1:3 (L:A) stoichiometry for ClÀ,
2À
À
SO4 and H2PO4 (Table S3). Having determined the binding affinity of 1–3 and
possible species distributions, we next set out to investigate if these ligands, in
the presence of high-coordinating oxyanions, could be used to form extended
anion-templated self-assemblies as outlined above (in either solution or in the solid
state).
Solid-State Studies: Formation of Anion-Templated 2D Materials
2À
The crystallization of 1–3 in the presence tetrabutyl-ammonium salts of SO4
,
AcOÀ, H2PO4À, and ClÀ was carried out in both DMSO or CH3CN solutions, using
various methodologies. However, of these, only 2 in the presence of SO42À yielded
2À
crystals. The slow evaporation of DMSO or CH3CN solutions of 2 (in excess SO4
)
resulted, on both occasions, in the formation of crystals that were suitable for single
crystal X-ray diffraction analysis (Figure 2) and the structural details showed them to
be isostructural (Table S4). The complex of 2 with SO42À (2$SO42À) crystallized in the
trigonal R-3 space group, with each of the SO42À anions positioned on a hexagonal
axis, within a tight hydrogen binding pocket. The asymmetric unit contains 1/3 of a
molecule of 2, 1/6 of a SO42À anion. Solvent molecules and the counter cations were
present, however, these were disordered and not interacting with their host receptor
or guest anion. Each SO42À ion is surrounded by six urea groups, from six different
molecules of 2 (Figures 4A–4D) with a total of 12 hydrogen bonds (Figure 4D) with
N–H.O(S) bond lengths ranging from 1.923–2.240 A, with an average N–H.O
˚
bond length of 2.22 A (Table S10). Within the 2$SO42À assembly, each ligand binds
˚
2À
to three different SO4 ions (Figures 4B and 4C). This demonstrates that the high
coordination preference of the anion is fulfilled within this binding arrangement.30
In contrast to the structure of 2 (cf. Figure 2A), in 2$SO42À, all three 2,4-difluoro-
phenyl moieties are equally rotated at 77ꢀ with respect to the urea groups, the amide
carbonyls and the N-methyl groups pointing away from the central C3 axis, and it is
4
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Figure 3. 1H NMR Binding Studies of Ligand 1
(A–D) Binding isotherms of urea protons comparing results between CD3CN (blue) and DMSO-d6 (green) titration of 1 with (A) ClÀ, (B) CH3COOÀ, (C)
À
SO42À, (D) H2PO4
.
clear that the preorganization observed in 2 is to greater extent maintained in
2$SO42À, where 2 maintains its ‘‘propeller-like’’ conformation. The anion templation
2À
results in an overall C3 symmetry, which tessellates the ligands around the SO4
anion, resulting in the formation of an extended 2D layer along the ab plane. These
planes are stacked along the c axis, each one rotated +/À 120ꢀ with respect to sur-
rounding planes. This network is further stabilized by inter-ligand p–p stacking and
additional hydrogen bonding interactions. The p-stacking interactions differ from
the ligand crystal where face-to-face interactions were seen between distal phenyl
rings from the neighboring molecules. This places the ortho-fluorine atoms in one
of two sites within the structure, with a similar occupancy distribution to the ligand
crystal, where 32% has a potential aromatic CH.O(amide) hydrogen bond in place
2À
and 68% in the alternate conformation. The SO4 anion can be found in two
different orientations along the c axis, up or down, producing two crystallographi-
cally different oxygen atoms in axial or equatorial orientations. One of the ortho-
fluorine atoms is situated very close to this axis, so it has two symmetry generated
31
˚
F at 2.54(3) A, suggesting the possibility of a F–F interaction (Figure 4E), as we
have observed in other self-assembly structures.32 The above results demonstrate
that our design strategy has been successful, and that the ‘‘propeller-like’’
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2À
Figure 4. Crystal Structure of 2$SO4
(A) Packing details viewed down the c axis (only one layer shown) and schematic representation of the 2D network formed by the SO42À-templated self-
assembly of the propeller-like molecule.
2À
(B) Detail of a cluster formed by 6 molecules of 2 around 1 molecule of SO4
.
(C) Details of the interaction of 1 molecule of 2 interacting with three SO42À molecules.
(D) Detail of 1 molecule of SO42À interacting with 6 different molecules of 2.
(E) Details of the F–F interactions between three different molecules.
preorganization of 2 results in the formation of an extended 2D network upon bind-
ing to SO42À (Figure 4A). This is, to the best of our knowledge, the first example of
the use of SO42À anion to generate such a higher order 2D self-assembly in prefer-
ence to the more commonly seen capsule formation.24,25,33
Self-Aggregation Studies
Aggregates and hierarchical materials such as extended 2D and 3D networks are
formed because of inter- and intra- molecular supramolecular interactions and sol-
vent effects.23 Given that the 2$SO42À assembly gives rise to crystalline 2D networks,
6
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and that 1–3 and 1–3$SO42À, all have the ability to partake in such extended supra-
molecular network formation, we investigated the hierarchical formation for 1–3
in solution, both in the absence and presence of anions. 1H NMR dilution
studies (5 3 10À6 / 1 3 10À2 M) were first undertaken and these showed that in
DMSO-d6 only minor changes were observed for the free ligands. However,
2À
such dilution studies in the presence of SO4 clearly showed aggregation effects
occurring for 1$SO42À and 2$SO42À (Figures S81 and S85). In the case of 1, aggrega-
tion effects were seen in both CD3CN and CD3OD, with sharpening and shifts in key
resonances observed at higher concentrations (Figures S82–S83). Next, solutions of 1
(1 mM in DMSO, CH3CN, and CH3OH), 2, and 3 (in DMSO)34 were deposited on silica
plates; these were dried in vacuum and imaged using scanning electron microscopy
(SEM). The formation of thin films was observed in the SEM for 1–3 in DMSO (Fig-
ure S87) and for 1 CH3CN, Figure 5A. However, for ligand 1 in CH3OH, the formation
of micro-spherical aggregates of ca. 1–2 mm size was observed, Figure 5B.35 It is clear
from the SEM imaging that the solvent has a major effect on the supramolecular in-
teractions of these 2D structures, which results in the formation of the hierarchical
structures. While it is difficult to elucidate what self-assembly pathways these 2D
structures take to form these higher order structures, it is clear that the polarity,
and hydrogen bonding ability, of the solvent is an important factor. As 1 is hydropho-
bic in nature, we investigated the effect of H2O on the assembly process of 1 in
CH3OH by adding various aliquots of H2O to the 1mM solution of 1 in CH3OH above.
This instantly generated off-white precipitates that would remain dispersed in solu-
tion for days. Samples of these suspensions were analyzed by SEM and all showed
the formation of spheres, Figure 5C. However, unlike that seen from pure CH3OH so-
lution, these were more uniform and nano-sized (ca. 150–300 nm), demonstrating the
effect of water on the aggregation pathway, and that the ligand alone can form hier-
archical material. The formation of the spherical structures of 1 was also observed at
even lower concentrations. This prompted us to monitor their formation as a function
of both concentration of 1 (between 10À6 / 10À5 M) and in different H2O:CH3OH
compositions, using UV-vis absorption spectroscopy. The results showed that at
8 3 10À6 M concentration of 1, the aggregate formation instantaneously occurred
upon addition of H2O and the absorption of 1 at 263 nm, being initially slightly
blue shifted (0% / 50% H2O), was followed by a red shift (265 nm) with the formation
a broad shoulder (ꢁ300 nm) (Figure 5E). DLS studies of these samples confirmed their
monodispersed nature and size distribution between 150–350 nm (Figure 5F).
2À
Next, we investigated what effect SO4 (1 equiv) would have on such hierarchical
formations. The addition of SO42À to DMSO solutions of 1 and 3 resulted in the for-
mation of aggregates from deposited solutions, these clearly being formed as
discrete microspheres for 3 (Figure S88), while 1, consisted of ‘‘film’’ covered parti-
cles (Figure 6A). In contrast, 2 showed the formation of microcrystals within a film
structure (Figure 6C). Addition of H2O (50%) to these solutions showed the formation
of smooth spherical particles for 1 (Figure 6B) and 3 (Figure S88), while 2 showed a
spherical aggregate with a microcrystalline texture (Figure 6D). We also added
SO42À to preformed spheres of 1 in 1:1 CH3OH:H2O solutions causing the precipi-
tation of the microparticles. SEM imaging of these showed that further aggregation
of the spheres occurred (Figure 5D), giving rise to the formation of ‘‘coral’’-like ag-
gregates. This clearly demonstrates that the 2D self-assembly material forms alter-
native hierarchical structures in highly competitive hydrogen bonding media, which
could possibly be due to the combination of hydrophobic effects between the
layered material and the solvent, as well as a degree of hydrogen boning interac-
tions with the urea oxygen atoms. Although we have not been able to prove this
experimentally, it is clear that the polarity of the urea arms (e.g., due to the nature
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Figure 5. Self-Assembly Studies of 1 in CH3CN and CH3OH
(A–D) SEM images of self-assembled nanospheres of 1 in: (A) CH3CN (bar; 1 mm), (B) CH3OH (bar; 2 mm), (C) 1:1 CH3OH-H2O mixture (1 wt %) (bar;
200 nm), (D) 1:1 CH3OH -H2O mixture (1 wt %) and 3 equiv of SO42À (bar; 200 nm).
(E) UV-vis plot; (inset) plot of absorbance at 262 nm against H2O content in solution. Ligand concentration 8 3 10À6 M.
(F) Average particle size distribution determined using DLS technique from suspensions of ligand 1, prepared in CH3OH:H2O in different ratios (c = 8 3
10À6 M, at 25ꢀC).
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Figure 6. Self-Assembly Studies for 1 and 2 in DMSO
(A and B) SEM images of deposited solutions of 1. SO42À in: (A) DMSO (scale bar, 20 mm), (B) 1:1
DMSO-H2O (scale bar, 10 mm, inset = 1 mm).
(C and D) SEM images of deposited solutions of 2. SO42À in: (C) DMSO (scale bar, 2 mm), (D) 1:1
DMSO-H2O (scale bar, 2 mm).
of the substituents; e.g., CF3 versus F) allows us to gain some degree of tuning of the
morphological outcome.
Using ClÀ, AcOÀ, and H2PO4À caused similar effect (Figure S89). In contrast, SEM im-
ages of samples where SO42À was first added to a solution of 1 in CH3OH solution,
followed by the addition of H2O, gave no evidence of sphere formation, and only the
formation of films, similar to that seen above, was observed (Figure S90). These
studies showed that the self-assembly properties of the ligand would be highly
affected by the solvent, which can influence both the self-assembly of the free ligand
and of its SO42À complexes.36,37
Conclusions
In summary, we have demonstrated that supramolecular self-assembly networks and
aggregates, including uniform nano- and microspheres, can be formed from
N-methylated BTA structures possessing meta phenyl urea groups, in both the pres-
2À
ence and absence of SO42À. Using X-ray crystallography, we showed that 2$SO4
formed a 2D hydrogen bonded network, where each anion is bound in a symmetrical
way to six 2 ‘‘hosts’’. To the best of our knowledge, these are the first examples of
such SO42À based or connected supramolecular self-assembled structures hierarchi-
cal materials using BTA based urea ligands, demonstrating the powerful role anions
can have in generating novel functional material towing to its high coordination
requirement.
EXPERIMENTAL PROCEDURES
All solvents and chemicals were purchased from commercial sources and used
without further purification. Deuterated solvents used for NMR analysis (CD3CN,
DMSO-d6) were purchased and used as received. Silica chromatography was carried
out on a Teledyne Isco CombiFlash automated machine using pre-packed RediSep
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cartridges. Infrared spectra were recorded on a Perkin Elmer Spectrum One FT-IR
spectrometer fitted with a universal ATR sampling accessory. Melting points were
determined using an Electrothermal IA9100 digital melting point apparatus. Where
applicable, elemental analysis (CHN) was carried out by the School of Chemistry,
University College Dublin.
Mass Spectroscopy
Mass spectrometry was completed in the departmental mass spectrometry service
of the School of Chemistry, Trinity College Dublin. Electrospray mass spectra were
measured on a Micromass LCT spectrometer calibrated against a leucine enkephalin
standard. MALDI Q-ToF mass spectra were recorded on a MALDI Q-TOF Premier
(Waters Corporation, Micromass MS Technologies, Manchester, UK) and high-reso-
lution mass spectrometery was performed using Glu-Fib as an internal reference
(m/z = 1,570.677).
Dynamic Light Scattering
DLS measurements were made from back scatter in using Malvern Instrument
Zetasizer Nano Series at 25ꢀC in quartz cuvette with a path length of 10 mm. Statis-
tical distribution by intensity were determined using the instrument software with
standard deviations determined from triple replicate measurements. Samples
were prepared using HPLC-grade CH3OH and H2O filtered six times through a
0.45 mm syringe filters (Acrodisk, PTFE).
UV-Vis Absorption Studies
UV-visible absorption spectra were recorded using a Varian Cary 50 spectrophotom-
eter, a spectroscopic window of 450–200 nm was used for all spectra with
applied baseline correction from blank solvent. All UV-vis measurements were per-
formed at 298 K in CH3CN or DMSO:CH3CN (spectroscopic grade) solutions. UV-vis
absorption spectra were measured in 1 cm quartz cuvettes, except for the aggrega-
tion measurements for which 0.2 cm quartz cuvette was used. Baseline correction
was applied for all spectra. Spectroscopic solutions were prepared from stock solu-
tions using Pipetman Classic micropipettes (Gilson, Inc.).
Preparation of Solutions for UV-Vis Titrations with Anions
The TBA salts of the anions used in the titrations were of spectroscopic grade
and were purchased from Sigma Aldrich. All TBA salts were dried over P2O5 at
room temperature under vacuum. Solutions of these salts were prepared at varying
concentrations of ca. 0.1 M, 5 3 10À2 M, 1 3 10À2 M, and 1 3 10À3 M. Host solutions
of ca. 1 3 10À3 M were prepared and then diluted before titration (ca. 1 3 10À5 M).
1H NMR Studies
The 1H NMR spectra were recorded at either 400 or 600 MHz on Bruker instruments
(AV3-400 or AV2-600). 13C NMR spectra were recorded, on the same instruments, at
either 150.9 or 100.6 MHz, while 19F NMR spectra were recorded at 376.5 MHz. All
1
13C NMR spectra were decoupled from H, couplings to other nuclei are specified
where appropriate. All spectra were recorded in commercially sourced per-deuter-
ated solvents and referenced to residual proton signals of those solvents.
Recorded free-induction decay signals were Fourier-transformed and processed
using MestreNova v.6 without apodization and chemical shifts expressed in parts
per million (ppm/d) and coupling constants (J) in Hz. Residual solvent resonances
were used as the internal reference, while 2D spectra were graphically referenced.
All NMR spectra were carried out at 298 K.
10
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Please cite this article in press as: Aletti et al., Sulfate-Templated 2D Anion-Layered Supramolecular Self-Assemblies, Chem (2019), https://
doi.org/10.1016/j.chempr.2019.06.023
Preparation of Solutions for 1H NMR Titrations with Anions
Spectroscopic solutions were prepared from stock solutions using Pipetman Classic
micropipettes (Gilson, Inc.). The concentrations of these solutions were prepared in
deuterated solvent such that 2 mL would give ca. 0.1 molar equivalents of the anion.
Host solutions of 7 3 10À3 M were prepared by dissolving a known amount of host in
0.7 mL of deuterated solvent. All measurements were performed at 25ꢀC in CD3CN.
Receptors were titrated with a 100-fold more concentrated solution of the anion, as
1
TBA+ salt. After each addition of the titrant solution, the H-NMR spectrum was re-
corded. TBA salts were dried in vacuum over P2O5. The 1H NMR spectra were re-
corded at 400 MHz on Bruker instruments AV3-400.
SEM
Microscopy analysis of gel-aggregate samples by SEM was carried out using the
facilities of the Advanced Microscopy Laboratory (AML) in Trinity College Dublin.
Samples were prepared by a drop-casting methodology onto clean silicon wafers
(cleaned by sonication in HPLC-grade acetone followed by HPLC-grade propan-2-
ol) from glass Pasteur pipettes.24 The manually drop cast samples were dried over-
night in ambient conditions (a week in the case of DMSO solutions) and under high
vacuum for 2 h immediately prior to their imaging. Samples were coated with a
conductive Au layer, by sputtering, in order to improve contrast where static
charging interfered with the imaging. Low kV SEM was carried out using the Zeiss
ULTRA Plus using an SE2 detector.
X-Ray Crystallography
X-ray data were collected on a Rigaku Saturn 724 CCD Diffractometer using graphite-
˚
monochromated Mo-Ka radiation (l = 0.71073 A). The data were collected using Crystal-
clear-SM 1.4.0 software. Data integration, reduction, and correction for absorption and
polarization effects were all performed using Crystalclear-SM 1.4.0 software. Space
group determination was obtained using Crystal structure version 3.8. Data for structure
(2$SO42À).22 was collected on an APEX Duo diffractometer using Cu-Ka radiation
˚
(l = 1.54056 A). The data collection, integration, and reduction were made with Bruker
Apex II software. The structures were solved by direct methods (SHELXS-97) and refined
against all F2 data (SHELXL97). All H-atoms, except for N-H protons, were positioned
˚
geometrically and refined using a riding model with d(CHaro) = 0.95 A, Uiso = 1.2Ueq
˚
(C) for aromatic and 0.98 A, Uiso = 1.2Ueq (C) for CH3. N–H protons were found from
the difference map and fixed to the attached atoms with UH = 1.2UN. In some cases,
disorderedsolventmoleculeswereremovedusingSQUEEZE program fromthePLATON
crystallographic software.37
DATA AND CODE AVAILABILITY
X-ray crystallographic data can be obtained free of charge from the Cambridge
Crystallographic Data Center (www.ccdc.cam.ac.uk/data_request/cif) under access
numbers CCDC: Structure 2: 1874341; structure 2.SO4À: 1874342, and structure
3: 1874344.
SUPPLEMENTAL INFORMATION
Supplemental Information can be found online at https://doi.org/10.1016/j.chempr.
2019.06.023.
ACKNOWLEDGMENTS
Financial support from Science Foundation Ireland (SFI PI 2013 to T.G. and the Phase
II Funding [Research Centres Phase 2 12/RC/2278_P2] to the SFI AMBER Centre),
Chem 5, 1–13, October 10, 2019
11

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doi.org/10.1016/j.chempr.2019.06.023
School of Chemistry and the University of Dublin (Postgraduate Scholarship to A.A.),
Marie Skłodowska-Curie actions (MSCA to S.B.) is acknowledged. We acknowledge
Dr. Samuel Bradberry for continued support, fruitful discussions, and preparation of
the final manuscript. We would also like to thank Drs. J.E. O’Brien, M. Reuther, and
G. Hessman for helping with NMR and MS analysis and for their continuous support
of our research efforts.
AUTHOR CONTRIBUTIONS
A.B.A. carried out the synthesis, anion binding, and aggregation studies. Crystal
structures were solved by S.B. Samples for SEM were prepared by A.B.A. and
S.A.J., and images were collected by S.A.J. A.B.A. and T.G. co-wrote the manuscript
with support from all authors. All research was performed under the guidance and
supervision of T.G. and P.E.K.
DECLARATION OF INTERESTS
The authors declare no competing interests.
Received: October 25, 2018
Revised: December 6, 2018
Accepted: June 27, 2019
Published: July 25, 2019
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