Self-organised nano-arrays of p-phosphonic acid functionalised higher order calixarenes

Article abstract of DOI:10.1039/b801256c

Water-soluble p-phosphonic acid calix[n]arenes (n = 5, 6 or 8) have been synthesized in five steps in overall 68, 66, 67% yield, respectively, by the recently developed procedure for p-phosphonic acid calix[4]arene. The hydrogen bonding prowess of the phosphonic acids dominates their self assembly into nano-arrays in both solution and the gas phase. In DMSO, nano-arrays of p-phosphonic acid calix[6]arene are stable for over 24 h, with the solvent molecules slowly disrupting the hydrogen bonded network affording solvated monomeric units. In the gas phase, nano-arrays of around 20 calixarene units were observed for the p-phosphonic acid calix[n]arenes using MALDI-TOF-MS, and ESI-MS revealed the presence of heteroleptic nano-arrays for a 1: 1 mixture of p-phosphonic acid calix[4,5]arenes. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

Full text of DOI:10.1039/b801256c

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www.rsc.org/njc | New Journal of Chemistry
Self-organised nano-arrays of p-phosphonic acid functionalised higher
order calixarenesw
Thomas E. Clark,a Mohamed Makha,*a Alexandre N. Sobolev,a Dian Su,b
Henry Rohrs,b Michael L. Gross,b Jerry L. Atwoodc and Colin L. Raston*a
Received (in Durham, UK) 23rd January 2008, Accepted 7th March 2008
First published as an Advance Article on the web 2nd May 2008
DOI: 10.1039/b801256c
Water-soluble p-phosphonic acid calix[n]arenes (n = 5, 6 or 8) have been synthesized in five steps
in overall 68, 66, 67% yield, respectively, by the recently developed procedure for p-phosphonic
acid calix[4]arene. The hydrogen bonding prowess of the phosphonic acids dominates their self
assembly into nano-arrays in both solution and the gas phase. In DMSO, nano-arrays of
p-phosphonic acid calix[6]arene are stable for over 24 h, with the solvent molecules slowly
disrupting the hydrogen bonded network affording solvated monomeric units. In the gas phase,
nano-arrays of around 20 calixarene units were observed for the p-phosphonic acid calix[n]arenes
using MALDI-TOF-MS, and ESI-MS revealed the presence of heteroleptic nano-arrays for a
1 : 1 mixture of p-phosphonic acid calix[4,5]arenes.
range of charge that the phosphonated calixarenes can build
up relative to the sulfonatocalixarenes. Moreover, they have
Introduction
Water-soluble calixarenes have a range of applications in
catalysis, for example, as well as acting as surfactants and
potential to forming nanoscale capsular assemblies via hydro-
gen or coordination bonding, and possibly acting as nano-
host molecules.1 Water solubility can be imparted by suitable
reaction vessels or selective carriers of guest molecules, as
established for other systems.9
A tetra-p-phosphonatocalix[4]arene has been shown to form
modification of the calixarene skeleton at either the upper or
lower rim with polar functionality such as dialkylamino,1e
carboxylic,2 sulfonic3 and phosphonic acid groups.4
discrete 1 : 1 molecular capsules with complementary tetra-
cationic calixarenes.10 The larger the pKa difference between
p-Sulfonato-calixarenes are the most widely studied class of
water-soluble calixarene due to their facile synthesis, high
the two pre-organized building blocks, the larger the binding
constant observed, up to 105
M
À1. Unfortunately no guest
solubility in aqueous media and their potential role in a
number of biological applications. For example, they have
been shown to be active ion-channel blockers,5 possess anti-
thrombotic and anti-viral activity,6 and solubilise a variety of
otherwise non-soluble drugs.7
inclusion was seen for any of the molecular capsules, which
have an internal volume capacity of 170–230 A3, and this is
possibly a consequence of the high stability of the capsule.11
There has also been much interest in the use of calix[4]arene
tetraphosphonates as amphiphilic receptor molecules for the
detection of proteins or cations at the air/water interface12 and
for the recognition of amino alcohols or uracil derivatives in
aqueous medium.13
Studies on the related p-phosphonatocalixarenes are limited
mainly due to the more challenging synthetic procedures
required to gain access to such compounds.8 Nevertheless,
there has been growing interest in the supramolecular chem-
istry of p-phosphonatocalixarenes. This relates to the in-
creased potential of self association of the conjugate acid
through hydrogen bonding of the diprotic phosphonic acid
groups relative to the monoprotic sulfonic acid groups of the
corresponding sulfonatocalixarenes, and also to the greater
We recently reported the five-step synthesis of p-phosphonic
acid calix[4]arene free of any lower rim substitution, and its self
assembly into remarkably stable nano-rafts.14 Using spinning disc
processing (SDP), we formed 3.0(3) and 20(2) nm nano-rafts in
water using acetonitrile as a stabilizer, whilst clusters of up to 20
calixarenes are observed in the gas phase using MALDI-TOF
mass spectrometry. The assignment of nano-rafts relates mainly
to the ability to form bilayer structures, either with or without a
layer of water molecules interposed between such layers. We now
report the synthesis of the higher order calixarenes, namely
p-phosphonic acid calix[n]arenes (n = 5, 6 or 8), thereby demon-
strating the versatility of the synthetic protocol that was estab-
lished for the sibling calix[4]arene analogue.14 We also report the
self-assembly of the calixarenes into nano-arrays in the gas and
solution phase, along with structural authentication using X-ray
diffraction of some of the intermediates en route to the formation
of the p-phosphonic acid calixarenes.
a School of Biomedical, Biomolecular and Chemical Sciences,
University of Western Australia, 35 Stirling Hwy, Crawley, W.A.
6009, Australia. E-mail: colin.raston@uwa.edu.au;
Fax: (+61) 86488 1005; Tel: (+61) 86488 3045
b Department of Chemistry, Washington University in St. Louis,
St. Louis, MO 63130, USA
c Department of Chemistry, University of Missouri-Columbia,
Columbia, MO 65211, USA
w Electronic supplementary information (ESI) available: A full de-
scription of the methods used, synthetic procedures for p-phosphonic
acid calix[6,8]arenes and crystal/refinement details for compounds 3c,
3d and 4d. CCDC reference numbers 669055–669059. For ESI and
crystallographic data in CIF or other electronic format see DOI:
10.1039/b801256c
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least soluble in benzonitrile, with calix[8]arene, 4c, being only
sparingly soluble at the reaction temperature of 180 1C. The
only purification required throughout the synthesis was a
simple flash chromatography on the crude phosphonate esters,
2d–4d. The phosphonic acids 2f–4f are highly soluble in water
and dimethyl sulfoxide (DMSO), moderately soluble in alco-
hols such as methanol and insoluble in common non-polar
organic solvents. Structure authentication by means of single-
crystal X-ray diffraction was performed on calixarenes 2c, 3c,
2d, 3d and 4d.16
Results and discussion
The synthesis of p-phosphonic acid calix[4]arene, 1f, has
previously been accomplished in five steps in 62% overall
yield from the commercially available p-H-calix[4]arene, 1a.14
The key development involved the use of a tetraacetoxy-p-
bromocalix[4]arene precursor, 1c, for the nickel-catalyzed
Arbuzov reaction8 to effect the aryl C–P bond formation. This
precursor was synthesized from a modified literature proce-
dure for octa-acetoxy-p-bromocalix[8]arene, 4c, which
involved bromination of p-H-calix[8]arene, 4a, using elemental
bromine followed by acetylation using acetic anhydride.15 It
was anticipated that the same procedure could be applied to
any of the p-H-calix[4,5,6,8]arenes, 1a–4a, respectively,
to produce the corresponding acetylated p-bromocalix-
[4,5,6,8]arenes, 1c–4c, respectively. Indeed this was the case
and the nickel-catalyzed Arbuzov reaction proceeded
smoothly with any of the acetylated p-bromocalix[4,5,6,8]-
arenes, 1c–4c, respectively, in excellent yield. The acetyl
groups were then removed quantitatively using potassium
hydroxide, and subsequent de-esterification of the phospho-
nate esters using bromotrimethylsilane (BTMS) was also
effected in quantitative yield. The yield over five steps for
preparing p-phosphonic acid calix[n]arenes (n = 5, 6 or 8),
2f–4f, were 68, 66 and 67%, respectively. It is noteworthy that
the earlier protocol en route for the synthesis of p-phosphonic
acid calix[4]arene8 is not applicable for higher-order calixar-
enes because of solubility issues (Scheme 1).14
The calix[8]arene, 4d, was recrystallized by slow evaporation
of a pure saturated solution from ethyl acetate–dichloro-
methane to afford colourless single crystals suitable for
X-ray diffraction studies. This yielded a solvent-free structure
ꢀ
in the space group P1 (Z = 1), albeit with substantial disorder
of the phosphonate groups. The calix[8]arene molecule adopts
a very compact spatial arrangement resulting from the orien-
tation of the aromatic rings relative to the bridging methylenes
whereby two acetyl and ethoxy groups occupy the available
space within the molecular cavity, Fig. 1(A).
The compact organisation of 4d based on the intramolecular
interactions of the acetyl and the ester ethoxy groups involves
two short H3CÁ Á ÁOQC distances of 3.44 and 3.70 A. There is
also a short H3CÁ Á ÁOQC distance of 3.04 A, and a short
H3CÁ Á ÁOQP distance of 3.86 A which is between adjacent
aromatic moieties. The dihedral angles between the plane of
the methylene bridges and bonded aromatic rings are 29.5 and
123.01 (Ph1–C1–Ph2), 74.1 and 75.81 (Ph2–C2–Ph3), 130.1
and 66.31 (Ph3–C3–Ph4), 67.4 and 124.71 (Ph4–C4–Ph1a) and
58.7 and 106.41 (Ph4a–C4a–Ph1). The molecules pack together
into a complex layered arrangement in the extended structure
parallel to the bc plane with numerous short contacts between
The nickel catalyzed Arbuzov reaction was sensitive to the
concentration of the reaction mixture with more concentrated
solutions producing higher yields. This can be seen for the
higher calix[6,8]arenes, 3c and 4c, respectively, which are the
Scheme 1 Synthesis of p-phosphonic acid calix[4,5,6,8]arenes, 1f–4f, starting from p-H-calix[4,5,6,8]arenes, 1a–4a. DMF = dimethylformamide,
Ac = acetyl, Et = ethyl, Ph = phenyl, THF = tetrahydrofuran, Me = methyl.
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Fig. 2 1H NMR (left) and 31P NMR (right) expansions between
8.0–6.8 and 19.0–14.0 ppm, respectively, for calix[6]arene 3f in
d6-DMSO: (A) 0 h, (B) 7 h, (C) 24 h.
due to aggregation thereby reducing the broad nature of the
signal. These nano-arrays take over 24 h to slowly dissociate
into solvated monomeric units. This is also confirmed by 31P
NMR, which shows one broad singlet increasing in intensity
and two sharp singlets decreasing in intensity over time. The
nano-array behaviour is attributed to residual acetonitrile from
the synthetic procedure orchestrating the nano-array assembly
by participating in hydrogen bonding and also by acting as a
stabilizer on the surface of the nano-arrays with the non-polar
methyl groups directed into the cavities of the calixarenes.
Previously calix[4]arene, 1f, was shown to form stable nano-
rafts in the gas phase using MALDI-TOF-MS with up to 20
calixarene units per raft.14 The assignment of nano-rafts in this
case comes from the availability of crystal structure data on the
extended structure, revealing a bi-layer arrangement which is
most likely prevalent in the gas phase. Hence the assignment of
the aggregates of the calixarene as nano-rafts is justified. For the
MALDI-TOF-MS studies herein, using the acidic matrix, 2,5-
dihydroxybenzoic acid (2,5-DHB), successive peaks out to 20-
mer and beyond were also observed for 2f–4f, Fig. 3(A)–(C).
This equates to nano-arrays of around 18–30 kDa for 2f–4f.
The nano-arrays for calix[5]arene, 2f, are likely to have
similar packing as that deduced for calix[4]arene, 1f, whereby
the calixarenes take on a bilayer arrangement within the nano-
rafts.18 This is reasonable as both calixarenes, 1f and 2f, adopt
the locked-cone conformation (1H NMR), and analogously
p-sulfonatocalix[5]arenes were shown to form bilayers in the
solid state.19 However, assignment of the nano-rafts comprised
of bi-layer organisation for 3f and 4f is not substantiated.
ESI-MS on a 1 : 1 mixture of 1f and 2f revealed the existence
of hetero-nano-arrays with mixed dimers, trimers and tetra-
mers being observed, Fig. 4(A)–(D).
Fig. 1 X-Ray crystal structure of phosphonate ester calix[8]arene, 4d.
(A) Compact packing of the acetyl and ethoxy groups in the molecular
cavity associated with inversion of the aromatic rings relative to the
bridging methylenes. (B) Partial packing of 4d within a layered
arrangement viewed down the a axis and depicted with different
atomic style for clarity. The following colour scheme is used: carbon
atoms – grey, oxygen atoms – red and phosphorus atoms – green.
Disordered phosphonate groups, and hydrogens have been removed
for clarity.
neighbouring calixarenes, H2CÁ Á ÁOQC 3.38 A, HCArÁ Á ÁOQC
3.29 A, CcentroidÁ Á ÁCH2 2.93 A, H2CÁ Á ÁOQP 3.65 A and
H3CÁ Á ÁOQP 3.30, 3.43 and 3.59 A, Fig. 1(B).
Self-assembled nano-rafts of p-phosphonic acid calix[4]-
arene, 1f, have remarkable stability in DMSO at room tem-
perature, slowly dissociating over the course of 36 h into
solvated monomeric units.14 This behaviour is also observed
for the calix[6]arene analogue, 3f, which is in contrast to tetra-
urea-calixarene dimers, which ‘‘denature’ within seconds upon
1
addition of a few mol% of DMSO.17 The H NMR spectrum
of a freshly prepared solution of 3f in d6-DMSO gave a broad
singlet and two doublets for the two equivalent aromatic
protons which are split by coupling to the single phosphorus
atom, Fig. 2(A)–(C). The broad singlet can be attributed to
conformationally flexible monomeric units of 3f on the NMR
time scale. The doublets are reminiscent of the those seen for
the analogous protons of the conformationally restricted
calix[4]arene, 1f. Thus the doublets herein can be attributed
to nano-arrays of 3f whereby the conformation of 3f is locked
It can be seen that mixed dimers comprised of one 1f and
one 2f with charges ranging from À1, À2 and À3 are observed
at m/z 1673, 836 and 557, respectively, Fig. 4(A). Mixed
trimers composed of two 1f and one 2f with charges À2 and
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under reduced pressure. After addition of 250 mL of methanol
the precipitate was filtered off and washed with methanol
(3 Â 40 mL) to yield 8.01 g (92%) of 2b as a pale brown solid.
1H NMR (CDCl3, 25 1C, 250 MHz) d 8.77 (s, 5H, OH), 7.31
(s, 10H, ArH), 3.75 (br s, 10H, ArCH2Ar).
5,11,17,23,29-Pentabromo-31,32,33,34,35-pentaacetoxycalix[5]-
arene (2c)
A mixture of 7.03 g (7.64 mmol) of 2b and 4.70 g (57.28 mmol)
of anhydrous sodium acetate in 60 mL of acetic anhydride was
refluxed for 4 h. After cooling to RT the solution was slowly
quenched with 80 mL of water. The precipitate was collected
by filtration and washed with methanol (3 Â 30 mL) to yield
7.43 g (86%) of 2c as a light green solid. Recrystallisation from
dichloromethane yielded X-ray quality single crystals, 2cÁ
3CH2Cl2Á2,25H2O, which were also submitted for micro-
analysis; mp 4270 1C (decomp.); IR (KBr) 2932 (w), 1764
(s), 1574 (m), 1458 (s), 1369 (m), 1208 (s), 1173 (s), 873 (m) cmÀ1
;
1H NMR (CDCl3, 25 1C, 500 MHz) d 7.76–6.68 (m, 10H, ArH),
4.02–3.02 (m, 10H, ArCH2Ar), 2.74–1.10 (m, 15H, CH3); 13C
NMR (CDCl3, 25 1C, 126 MHz) d168.80–167.81 (m),
147.72–145.06 (m), 135.88–130.24 (m), 119.91–118.36 (m),
34.91–33.09 (m), 31.69–29.89 (m), 20.99–18.61 (m); HRMS
(FAB) m/z calc. for [C45H35Br5O10 À H]À 1132.8028, found
1132.7952. Elemental analysis. Calc. (%) for C45H35Br5O10:
C 47.61, H 3.11. Found: C 47.41, H 3.02.
Crystal/refinement details for 2cÁ3CH2Cl2Á2.25H2O.
C48H45.5Br5Cl6O12.25, M = 1430.59, F(000) = 5668 e, mono-
clinic, C2/c, Z = 8, T = 100(2) K, a = 37.319(8),
b
=
15.438(5),
c = 21.720(6) A, b = 115.70(10)1,
Fig. 3 MALDI-TOF spectra showing nano-assemblies in the gas
phase for the p-phosphonic acids of (A) calix[5]arene, 2f, (B) calix[6]-
arene, 3f, and (C) calix[8]arene, 4f.
V = 11 276(5) A3, Dc = 1.685 g cmÀ3, mMo = 3.906 mmÀ1
,
sin(y/lmax) = 0.6427, N(unique) = 12 406 (merged from
38 911, Rint = 0.0723, Rsig = 0.0839), No (I 4 2s(I)) = 7523,
R = 0.0710, wR2 = 0.1600 (A, B = 0.06, 121.8), GOF =
1.034, |Drmax| = 0.9(1) e AÀ3. CCDC 669055.
À3 are observed at m/z 1208 and 805, respectively, Fig. 4(B),
and one 1f and two 2f with charges À2 and À3 are observed at
m/z 1301 and 867, respectively, Fig. 4(C). Finally a mixed
tetramer with composition of two 1f and two 2f of charge À3 is
also observed at m/z 1115, Fig. 4(D).
5,11,17,23,29-Penta(diethoxyphosphoryl)-31,32,33,34,35-
pentaacetoxycalix[5]arene (2d)
A solution of 3.87 g (3.43 mmol) of 2c and 0.56 g (4.28 mmol)
of NiCl2 in 20 mL of benzonitrile was treated dropwise with
7.34 mL (42.83 mmol) of P(OEt)3 under nitrogen at 190 1C.
The solution was stirred for 0.5 h and the volatiles removed
under reduced pressure to leave an orange residue. The residue
was purified by flash chromatography to yield 5.21 g of a light
yellow solid. Recrystallisation from toluene–hexane yielded
4.30 g (88%) of 2d as a white solid. Further recrystallisation
from toluene yielded X-ray quality single crystals, 2d, which
were also submitted for microanalysis. Rf = 0.43 (1 : 4
methanol–ethyl acetate); mp 253–255 1C; IR (KBr)
2985 (m), 2911 (w), 1763 (s), 1653 (w), 1457 (m), 1373 (m),
Experimental
All starting materials and solvents were obtained from com-
mercial suppliers and used without further purification except
otherwise noted. Acetonitrile was dried over 4 A molecular
sieves for 24 h and NiCl2Á6H2O was dried at 180 1C in vacuo
for 8 h before use. All moisture-sensitive reactions were
performed under a positive pressure of nitrogen. p-Phosphonic
acid calix[4]arene,14 p-H-calix[5]arene,20 p-H-calix[6]arene21
and p-H-calix[8]arene21 were prepared as described previously
in the literature.
1
1272 (m), 1020 (s), 966 (s), 796 (w), 605 (m) cmÀ1; H NMR
5, 11, 17, 23, 29-Pentabromo-31,32,33,34,35-pentahydroxycalix[5]-
arene (2b)
(CDCl3, 25 1C, 500 MHz) d8.12–7.01 (m, 10H, ArH),
4.46–3.24 (m, 30H, ArCH2Ar and POCH2), 2.82–0.87
(m, 45H, CH3 and POCH2CH3); 13C NMR (CDCl3, 25 1C,
126 MHz) d 167.93, 151.95–148.10 (m), 135.35–130.04 (m),
3.62 mL (70.73 mmol) of bromine in 50 mL of DMF was
added dropwise with stirring to a solution of 5.00 g
(9.43 mmol) of calix[5]arene, 2a, in 200 mL of DMF. The
solution was stirred for 4 h and the volatiles were removed
2
128.38–124.95 (m), 62.36 (d, JPÀC = 3.6 Hz), 35.69–
33.91 (m), 31.54–30.32 (m), 21.53–18.15 (m), 16.32
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Fig. 4 ESI mass spectra showing hetero-nano-arrays in the gas phase between 1f and 2f. (A) Hetero-dimer formation, 1fÁ2f. (B) Hetero-trimer
formation, (1f)2Á2f. (C) Hetero-trimer formation, 1fÁ(2f)2. (D) Hetero-tetramer formation, (1f)2Á(2f)2.
3
(d, JPÀC = 4.2 Hz); 31P NMR (CDCl3, 25 1C, 101 MHz) d
17.71; MS (ESI) m/z calc. for [C65H85O25P5 + Na]+
1443.3966, found 1443.4003. Elemental analysis. Calc. (%)
for C65H85O25P5Á0.65H2O: C 54.48, H 6.07. Found: C 54.21,
H 5.78.
pressure to yield 1.70 g (98%) of 2e as a white solid.
Recrystallisation from ethyl acetate–hexane yielded a white
solid suitable for microanalysis; mp 128–130 1C; IR (KBr)
3365 (br), 2984 (m), 2907 (m), 1653 (m), 1473 (m), 1394 (m),
1278 (m), 1022 (s), 966 (s), 795 (m) cmÀ1; 1H NMR (CDCl3, 25
1C, 500 MHz) d 9.03 (br s, 5H, OH), 7.66 (d, 10H, ArH, JPÀH
= 13.0 Hz), 4.28–3.62 (m, 30H, ArCH2Ar and POCH2), 1.23
(t, 30H, POCH2CH3, J = 7.0 Hz); 13C NMR (CDCl3, 25 1C,
Crystal/refinement details for 2d. C65H85O25P5, M = 1421.18,
ꢀ
F(000) = 1500 e, triclinic, P1, Z = 2, T = 100(2) K,
2
a = 12.9938(4), b = 16.3618(5), c = 18.4136(6) A, a =
100.825(3), b = 94.164(3), g = 112.261(3)1, V = 3513.2(7) A3,
Dc = 1.343 g cmÀ3, mCu = 1.873 mmÀ1, sin(y/lmax) = 0.5970,
N(unique) = 12 348 (merged from 41 009, Rint = 0.0483,
Rsig = 0.0599), No (I 4 2s(I)) = 7153, R = 0.0731, wR2 =
126 MHz) d 153.73, 133.32 (d, JPÀC = 10.7 Hz), 126.77 (d,
1
3JPÀC = 14.2 Hz), 121.20 (d, JPÀC = 190.1 Hz), 62.07 (d,
2JPÀC = 5.2 Hz), 30.96, 16.23 (d, 3JPÀC = 6.5 Hz); 31P NMR
(CDCl3, 25 1C, 101 MHz) d 19.21; MS (ESI) m/z calc. for
[C55H75O20P5 + Na]+ 1233.3438, found 1233.3505. Elemental
analysis. Calc. (%) for C55H75O20P5: C 54.55, H 6.24. Found:
C 54.56, H 6.05.
0.1995 (A, B = 0.145, 0), GOF = 1.008, |Drmax| = 1.63(9) e AÀ3
.
CCDC 669056.
5,11,17,23,29-Penta(diethoxyphosphoryl)-31,32,33,34,35-
pentahydroxycalix[5]arene (2e)
5,11,17,23,29-Penta(dihydroxyphosphoryl)-31,32,33,34,35-
pentahydroxycalix[5]arene (2f)
A mixture of 2.04 g (1.44 mmol) of 2d and 1.01 g (17.98 mmol)
of KOH in 50 mL of methanol, 50 mL of tetrahydrofuran and
50 mL of water was stirred for 4 h. The solvents were removed
under reduced pressure and the residue treated with 50 mL of
dichloromethane and 50 mL of 2 M HCl. The organic layer
was separated, washed with 2 M HCl (1 Â 25 mL), water (2 Â
25 mL), dried over MgSO4 and evaporated under reduced
3.53 mL (26.77 mmol) of bromotrimethylsilane was added to
1.62 g (1.34 mmol) of 2e in 50 mL of dry acetonitrile and the
solution was refluxed for 16 h. The volatiles were removed
under reduced pressure and the resulting residue was triturated
with 40 mL of acetonitrile and 2 mL of water. The
precipitate formed was filtered off and washed with aceto-
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nitrile (3 x 20 mL) to yield 1.23 g (99%) of 2f as a white solid.
Purification using the ion exchange resin, Dowex 50W yielded
a white solid suitable for microanalysis; mp 4280 1C
(decomp.); IR (KBr) 3393 (br), 2300 (br), 1597 (m), 1471 (s),
1385 (m), 1280 (m), 1124 (m), 950 (m), 874 (m) cmÀ1; 1H NMR
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(CDCl3, 25 1C, 600 MHz) d 7.42 (d, 10H, ArH, JPÀH
=
13.2 Hz), 5.35 (br s, COH/POH, shifts downfield with increas-
ing [H]+), 3.88 (s, 10H, ArCH2Ar); 13C NMR (DMSO-d6,
25 1C, 151 MHz) d 154.14, 131.74 (d, 2JPÀC = 10.3 Hz), 127.57
(d, 3JPÀC = 15.4 Hz), 124.58 (d, 1JPÀC = 186.1 Hz), 30.78; 31
P
NMR (DMSO-d6, 25 1C, 243 MHz) d 15.03; MS (ESI) m/z
calc. for [C35H35O20P5 + H]+ 931.05, found 931.13. Elemen-
tal analysis. Calc. (%) for C35H35O20P5Á1.25H2O: C 44.11, H
3.97. Found: C 44.31, H 4.18.
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We have successfully applied the synthetic procedure devel-
oped for p-phosphonic acid calix[4]arene to the higher-order
calixarenes, p-phosphonic acid calix[n]arenes (n = 5, 6 or 8) in
overall 68, 66 and 67% yield, respectively. These highly water-
soluble molecules assemble into nano-arrays both in solution
and the gas phase, and most certainly serve as a platform for
supramolecular chemistry and materials science, investigations
we are currently pursuing.
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Acknowledgements
We thank the ARC, NSF and NIH (grant P41RR000954) for
financial support of this work and to The University of
Western Australia for SIRF, GRST and PRT awards to
Thomas Clark.
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16 Cyrstal/refinement details for calixarenes 2c and 2d are reported in
the experimental section and details of 3c, 3d, and 4d are reported
in the ESIw.
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ꢀc
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