Lanthanitin: A chiral nanoball encapsulating 18 lanthanum ions by ferritin-like assembly

Article abstract of DOI:10.1002/anie.200603622

(Figure Presented) A chiral supramolecule, obtained by self-assembly of 24 chiral ditopic carboxylate ligands, 18 La ions, and two carbonate anions, has been dubbed lanthanitin because of its structural resemblance to ferritin. The picture shows the molec

Full text of DOI:10.1002/anie.200603622

Communications
involving weak intermolecular forces, the much stronger
interactions between metal ions and polydentate organic
ligands make the contribution of weak interactions less
significant.[1,2] Thus, the number of factors to be considered
in the process is substantially decreased, and the outcome is
often predictable. Many efforts were successfully directed to
obtaining geometrically intriguing supramolecules such as
molecular polygons,[3] highly symmetrical cage molecules,[4]
and metal–organic frameworks[5] by rational design of metal–
ligand motifs. However, precise prediction of the outcome is
still not always possible, and there is more to be explored,
especially for the f-block elements because of their versatile
coordination numbers.[6] Potential applications of self-assem-
bled lanthanide-containing nanoparticles in catalytic reac-
tions, optoelectronics, and magnetic materials have attracted
much interest.[7] Despite intensive studies, enantiopure lan-
thanide coordination compounds still represent a formidable
challenge.[8]
We herein report a unique chiral lanthanum-containing
supramolecule, dubbed lanthanitin because it forms by
ferritin-like assembly.[9] In addition, its incorporation into a
chiral double helix in crystals in an unprecedented manner
constitutes a new class of crystal packing other than that of
the helicates.[10] Chiral ligands (S,S)-1H2 and (R,R)-1H2 (acid
forms of 1) used in this study were both synthesized from 4,4’-
dibromostilbene in optically pure form by taking advantage of
Sharpless asymmetric dihydroxylation (Scheme 1).[11] Chiral-
ity is introduced on the ethylene bridge. The ditopic carboxyl
groups on para positions of the aromatic rings will serve to
bridge various metal ions. Tying up the two hydroxyl groups
with a 1,1’-dimethylmethylene group eliminated the flexibility
of the molecule. Thus, the molecule has a fixed conformation
and a dihedral angle between the two benzoic acid groups of
about 808.
Colorless antiprismatic crystals of (S)-lanthanitin suitable
for X-ray diffraction were grown from a mixture of (S,S)-1H2
and LaCl3·6H2O in N,N’-diethylformamide (DEF) solution at
608C over two weeks (Figure 1a). X-ray crystallographic
studies revealed that the crystal belongs to the enantiomor-
phous space group P4122. The asymmetric unit containing a
trigonal arrangement of nine LaIII ions and 12 (S,S)-1 linking
ligands forms a supramolecular hemisphere. When the
crystallographic twofold symmetry is applied to the asym-
metric unit, two hemispheres fuse to form a spherical
molecule with a diameter of 3.0 nm.
Chiral Nanoballs
DOI: 10.1002/anie.200603622
Lanthanitin: A Chiral Nanoball Encapsulating 18
Lanthanum Ions by Ferritin-Like Assembly**
Kyung Seok Jeong, Young Shin Kim, Yun Ju Kim,
Eunsung Lee, Ji Hye Yoon, Won Hwa Park,
Young Woo Park, Seung-Joon Jeon, Zee Hwan Kim,
Jaheon Kim, and Nakcheol Jeong*
In self-assembly through metal–organic coordination chemis-
try, strong interaction between metal ions and polydentate
ligands is the primary driving force. Contrary to processes
[*] K. S. Jeong, Y. S. Kim, Y. J. Kim, W. H. Park, Y. W. Park, Prof. S.-J. Jeon,
Prof. Z. H. Kim, Prof. N. Jeong
Department ofChemistry
Twenty four ligands encompass the metal ions in a unit
having the formula [La18{(S,S)-1}24(CO3)2(H2O)32]2+ (Fig-
ure 1b). In the core of the molecule, two carbonate anions
(Figure 2) each bind three lanthanum ions. The presence of
the carbonate core as a seed is critical for the formation of
crystals, even though the origin of carbonate is not clear. It
may come from atmospheric carbon dioxide. This unusual
kind of nucleation was reported previously only in two cases,
one of which includes a GdIII complex.[12]
One of the most notable structural features of (S)-
lanthanitin is that the 18 LaIII ions form an octahedral
arrangement with six sets of three lanthanide ions. The three
LaIII ions in each set are arranged linearly with average
interatomic distances of 4.145 Š. These sets are, if we consider
Korea University
Seoul 136-701 (Korea)
Fax: (+82)2-3290-3121
E-mail: njeong@korea.ac.kr
E. Lee, J. H. Yoon, Prof. J. Kim
Department ofChemistry and CAMDRC
Soongsil University
Seoul 156-743 (Korea)
[**] N.J. thanks KOSEF (grant No. R02-2002-000-00128-0 ofthe Basic
Research Program), CMDS and Korea University for their financial
support. K.S.J., Y.S.K, and Y.J.K are grateful to BK21 program. J.K.
thanks the Korea Research Foundation for the grant (KRF 2003-070-
C00029).
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
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Chemie
ions in the core of the molecule and
their symmetry-related partners
form hydrogen bonds among them-
selves and leave no void space. The
LaIII ions on the second sphere,
{La(4), La(5), and La(6)}, have
eight oxygen atoms as ligands, all
of which are from carboxylates. The
coordination between LaIII and car-
boxylate exhibits three different
modes: monodentate, bis-monoden-
tate, and chelating, m-O tridentate,
except for one carboxylate group
(Figure 3). For the LaIII ions on the
third sphere, additional water mol-
ecules are required to complete the
respective coordination numbers
besides oxygen atoms from carbox-
ylates in bis-monodentate and
bidentate chelating modes.
Scheme 1. Preparation ofligands ( S,S)-1H2 and (R,R)-1H2. See the Supporting Information.
PTSA=para-toluenesulfonic acid.
Figure 1. a) Preparation oflanthanitin enantiomers. b) Molecular struc-
tures oflanthanitins with octahedral arrangement of18 La ions as
large blue balls and the central carbonate carbon atoms as small
green balls. Hydrogen atoms are omitted for clarity. Color code: C
gray, O red.
the asymmetric unit, {La(1),La(4),La(7)}, {La(2),La(5),La(8)},
and {La(3),La(6),La(9)} which together form a pyramidal
shape with a small triangle {La(1),La(2),La(3)} linked by a
carbonate anion at the apex (Figure 2b). The interplanar
distance among the sets is 1.90 Š. The outer lanthanum ions
{La(7),La(8),La(9)} and their twofold symmetry pairs define a
slightly distorted octahedron with an average edge length of
17.624 Š (16.818–18.794 Š).
The average diagonal distance between La vertices is
24.886 Š. Most LaIII ions in the hemisphere have a coordina-
tion number of eight, except for La(8) and La(9), which are
ten-coordinate (Figure 3). All three central lanthanum ions
located on the first sphere, {La(1), La(2), and La(3)}, are
coordinated by three kinds of ligands: two oxygen atoms of
Figure 2. a) ORTEP drawing ofthe crystallographic asymmetric unit of
(S)-lanthanitin, which is a halfofthe whole assembly as a result of
crystallographic twofold symmetry. b) The arrangement of the nine LaIII
ions in the asymmetric unit around the central carbonate ion with
interatomic distances in Š.
CO32À, four oxygen atoms from carboxylate in bis-mono-
dentate fashion, and two water molecules. The water mole-
cules are engaged in hydrogen bonds with adjacent water
molecules. All six water molecules are bound to three LaIII
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pseudo-twofold axes penetrate six sets of edges. The symme-
try of the molecule is close to point group O or crystallo-
graphic 432, because there is no inversion center due to the
chirality. Such an analogy to the well-known 432 molecular
symmetry of ferritin is rarely seen in synthetic supramole-
cules.
Interestingly, (S)-lanthanitin molecules form a right-
handed double helix with pitch length of 80.460 Š and
radius of 13.829 Š around the helical axis at (0.5,0.5,z)
(Figure 5a). (S)-Lanthanitin units contact each other through
1,1’-dimethylmethylene (DMM) groups. Two DMM groups
form a chiral cavity in which the two methyl groups of the
DMM moieties of neighboring balls are incorporated (Fig-
ure 5b and c). The hydrogen atoms on the stereogenic carbon
atoms are in good van der Waals contacts with the neighbor-
ing DMM groups.
Figure 3. Coordination environment ofthe La III atoms (blue) with
partial atomic numbering scheme is shown with only carboxylate
moieties (gray and pink), carbonate ions (green and pink), and
coordinating water molecules (red) for simplicity. The primed numbers
denote twofold-symmetry-related atoms. The 12 coordinating water
molecules attached to the central 6 La atoms, O(1W)–O(6W) and
O(1W’)–O(6W’) are drawn with thermal ellipsoids in the inset.
Possible hydrogen bonds are indicated as dotted red lines. One ofthe
carboxylate oxygen atoms, O(6D), is not bound to an La atom and
instead forms a hydrogen bond with O(9W).
To grasp the framework structure, the molecule can be
disassembled schematically into six La3[(S,S)-1]4 units which
are related with each other by pseudo-octahedral symmetry
(Figure 4a). Each unit is interconnected with another four
Figure 5. a) Double helices formed by the lanthanitins with 1.5 helical
turns. The two single helices are distinguished by blue and light brown
colors. (S)-Lanthanitin (left) forms a right-handed double helix, and
(R)-lanthanitin a left-handed one (right). b) Two lanthanitin molecules
in contact showing the boundary region. c) Two ligands from each
lanthanitin unit participate in the contact; the acetonide moieties
including the DMM groups ofthe ligands are drawn as space-iflling
models.
Figure 4. a) Schematic representation oflanthanitin which shows that
six sets ofLa 3(1)4 moieties come together around the central carbon-
ate ions to form the whole molecule. The 24 ligands are grouped into
six sets, drawn with different colors. b) Space-filling model of lanthani-
tin. Colors match those of(a). c) Structure ofbacterioef rritin (PDB
code: 1BFR). Twenty four subunits are grouped as six sets for
comparison with the arrangement ofligands in lanthanitin.
(R)-Lanthanitin, the chiral counterpart of (S)-lanthanitin,
was prepared by employing (R,R)-1H2 in place of (S,S)-1H2.
As we expected, (R)-lanthanitin belongs to space group
P4322, which forms an enantiomorphous pair with P4122 of
(S)-lanthanitin. Furthermore, (R)-lanthanitin also forms a
double helix in the crystal lattice, with opposite handedness
(Figure 5a). As confirmed by solid-state circular dichroism
(CD), the chirality derived from the ligands is preserved in
the crystals (Figure 6). Both (S)- and (R)-lanthanitin crystals
in KBr pellet give mirror-symmetrical CD spectra with
opposite signs, that is, each crystal has only one sense of
helical structure. In addition, although there is an example of
self-assembly of spherical colloids into single helical chains by
capillary forces,[13] it is very unusual that supramolecular
double helices are formed by discrete entities through
equatorial units by four organic ligands to form a completely
integrated assembly. This assembly pattern endows lanthani-
tin with a close structural resemblance to ferritin.[9] The
arrangement of the organic linkers in lanthanitin is the same
as that of the protein subunits in ferritin (Figure 4b and c).
Neglecting the minor distortions around the LaIII coordi-
nation sphere, the lanthanum ions are aligned along three
pseudomolecular fourfold rotational axes that pass through
the molecule. In addition, three pseudo-threefold axes
penetrate a set of trigonal-antiprismatic triangles, and six
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by direct methods and subsequent difference Fourier syntheses and
refined with the SHELXTL software package. A total of 211188
reflections were collected in the range 1.05 ꢀ q ꢀ 20.848, of which
32002 were independent and 22331 were observed (I > 2s(I)). All
stages of weighted full-matrix least-squares refinement were con-
ducted on F2o data and converged to give R1 = 0.0835 (I > 2s(I)),
wR2 = 0.2268 (all data), and GOF = 1.029. Most non-hydrogen atoms
were refined anisotropically, except for six atoms with nonpositive-
definite problems. Hydrogen atoms were generated with the ideal
geometry. The absolute configuration was confirmed by the Flack x
parameter of 0.060(19).
X-ray structural analysis of (R)-lanthanitin: prismatic colorless
crystal, 0.35 ” 0.30 ” 0.25 mm3, C466.5H505.5N1.5O207La18, M = 11945.6,
tetragonal, space group P4322 (No. 95), T= 130(2) K, a = 27.2922(6),
c = 79.728(3) Š,
V= 59386(4) Š3,
Z = 4,
1calcd = 1.336 gmÀ3
,
m(MoKa) = 1.345 mmÀ1. Final refinement converged to R1 = 0.0921
(I > 2s(I)), wR2 = 0.2341 (all data), GOF = 1.076, and a Flack
parameter of x = 0.13(3). CCDC 619112 ((S)-lanthanitin) and
619113 ((R)-lanthanitin) contain the supplementary crystallographic
data for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif.
Figure 6. CD data obtained from a transparent disk with a radius of
5 mm made from a mixture of crystalline lanthanitin (3 mg) and KBr
(100 mg). The inset shows the CD spectra ofthe ligands in methanol.
UV/Vis absorption spectra of various solutions were measured
between 800 and 200 nm with a Jasco UVIDEC 650 spectrophotom-
eter. CD spectra were recorded on a Jasco J-810 spectropolarimeter.
DRCD spectra were obtained by inserting a diffuse-reflectance
sphere in the optical path of the instrument. This J-810 was
specifically modified to allow simultaneous detection of LD (linear
dichroism) as a simple way to verify potential artifacts.
nondirectional van der Waals interactions. Usually most
artificial helices or double helices, denoted as helicates,
have been guided by relatively strong interactions such as
hydrogen bonds or coordination bonds.[14]
In conclusion, we have obtained novel supramolecules
containing lanthanum ions: (S) and (R)-lanthanitin, in which
many ligands work together to bind numerous metal ions and
form a spherical supramolecule with unique structural
resemblance to ferritin. Furthermore, the chiral supramole-
cules resulting from the use of enantiomerically pure ligands
form double helices in the crystal with a single handedness.
Various combinations of lanthanides and chiral ligands could
provide supramolecule lanthanide nanoparticles with poten-
tial optoelectronic, magnetic, and catalytic applications. Their
solution properties and applications will be subjects of future
study.
Received: September 5, 2006
Published online: November 17, 2006
Keywords: carboxylate ligands · helical structures · lanthanum ·
.
nanostructures · self-assembly
[1]B. Moulton, M. J. Zaworotko, Chem. Rev. 2001, 101, 1629.
[2]D. Caulder, K. N. Raymond, Acc. Chem. Res. 1999, 32, 975.
[3]a) L. R. MacGillivray, J. L. Atwood, Angew. Chem. 1999, 111,
1080; Angew. Chem. Int. Ed. 1999, 38, 1018; b) B. Olenyuk, J. A.
Whiteford, A. Fechtenkötter, P. J. Stang, Nature 1999, 398, 796;
c) P. J. Stang, B. Olenyuk, Acc. Chem. Res. 1997, 30, 502; d) H.
Jiang, W. Lin, J. Am. Chem. Soc. 2003, 125, 8084.
[4]a) N. Takeda, K. Umemoto, K. Yamaguchi, M. Fujita, Nature
1999, 398, 794; b) S. R. Seidel, P. J. Stang, Acc. Chem. Res. 2002,
35, 972.
[5]a) O. M. Yaghi, M. OꢀKeeffe, N. W. Ockwig, H. K. Chae, M.
Eddaoudi, J. Kim, Nature 2003, 423, 705; b) S. Kitagawa, R.
Kitaura, S. Noro, Angew. Chem. 2004, 116, 2388; Angew. Chem.
Int. Ed. 2004, 43, 2334.
Experimental Section
Synthesis of (S)- and (R)-lanthanitin: Ligands (S,S)-1H2 and (R,R)-
1H2 were prepared according to the methods described in the
Supporting Information.
A mixture of LaCl3·6H2O (0.010 g,
0.10 mmol) and (S,S)-1H2 or (R,R)-1H2 (0.010 g, 0.10 mmol) in DEF
(3 mL) and H2O (3 mL) was heated at 608C for two weeks. Colorless
prismatic crystals were obtained in 30% yield. The crystals were
sparingly soluble in water before sonication, and insoluble in common
organic solvents. Elemental analysis (%) calcd for (S)-lanthanitin
[La18(CO3)2(C19H16O6)24(H2O)32]CO3·20.5H2O·1.5DEF: C 46.90, H
4.27, N 0.18; found: C 46.90, H 4.11, N 0.15.
[6]a) Y. Zhou, M. Hong, X. Wu, Chem. Commun. 2006, 135; b) Z.
Zheng, Chem. Commun. 2001, 2521.
[7]a) K. Mikami, M. Terada, H. Matsuzawa, Angew. Chem. 2002,
114, 3704; Angew. Chem. Int. Ed. 2002, 41, 3554; b) M. Ziegler,
A. von Zelewsky, Coord. Chem. Rev. 1998, 177, 257; c) S. P.
Fricker, Chem. Soc. Rev., 2006, 35, 524; d) M. Bottrill, L. Kwok,
N. J. Long, Chem. Soc. Rev. 2006, 35, 557; e) D. Gatteschi, R.
Sessoli, Angew. Chem. 2003, 115, 278; Angew. Chem. Int. Ed.
2003, 42, 268.
X-ray structural analysis of (S)-lanthanitin: Prismatic colorless
crystal, 0.50 ” 0.30 ” 0.30 mm3, C466.5H505.5N1.5O207La18, M = 11945.6,
tetragonal, space group P4122 (No. 91), T= 243(2) K, a = 27.5037(10),
c = 80.460(3) Š, V= 60864(4) Š3, Z = 4, 1calcd = 1.304 gmÀ3
,
m-
(MoKa) = 1.312 mmÀ1. A crystal was attached to a glass capillary,
which was positioned in a N2(g) stream at 243(2) K after mounting on a
Bruker SMART CCD diffractometer equipped with a normal-focus
and graphite-monochromated Mo-target X-ray tube (l = 0.71073 Š).
A total of 1315 frames were collected, and integrated with the SAINT
software package with a narrow-frame algorithm. An absorption
correction was applied by using SADABS. The structure was solved
[8]With carboxylate ligands: a) O. Mamula, M. Lama, S. G. Telfer,
A. Nakamura, R. Kuroda, H. Stoeckli-Evans, R. Scopelitti,
Angew. Chem. 2005, 117, 2583; Angew. Chem. Int. Ed. 2005, 44,
2527. With bipyridine ligands: b) O. Mamula, A. von Zelewsky,
G. Bernardinelli, Angew. Chem. 1998, 110, 302; Angew. Chem.
Int. Ed. 1998, 37, 289; c) O. Mamula, T. Bark, A. von Zelewsky,
G. Bernardinelli, Angew. Chem. 1999, 111, 3129; Angew. Chem.
Angew. Chem. Int. Ed. 2006, 45, 8134 –8138
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
8137

Communications
Int. Ed. 1999, 38, 2945; d) O. Mamula, A. von Zelewsky, Coord.
Chem. Rev. 2003, 242, 87; e) L.-E. Perret-Aebi, A. von Zelewsky,
C. Dietrich-Buchecker, J.-P. Sauvage, Angew. Chem. 2004, 116,
4582; Angew. Chem. Int. Ed. 2004, 43, 4482.
[9]X. Liu, E. C. Theil, Acc. Chem. Res. 2005, 38, 167.
[10]a) M. Albrecht, Chem. Rev. 2001, 101, 3457; b) C. Piguet, G.
Bernardinelli, G. Hopfgartner, Chem. Rev. 1997, 97, 2005.
[11]H. C. Kolb, M. S. Van Nieuwenhze, K. B. Sharpless, Chem. Rev.
1994, 94, 2483.
[12]a) C. A. Chang, L. C. Francesconi, M. F. Malley, K. Kumar, J. Z.
Gougoutas, M. F. Tweedle, D. W. Lee, L. J. Wilson, Inorg. Chem.
1993, 32, 3501; b) X. Liang, J. A. Parkinson, S. Parsons, M.
Weishꢁupl, P. J. Sadler, Inorg. Chem. 2002, 41, 4539.
[13]Y. Yin, Y. Xia, J. Am. Chem. Soc. 2003, 125, 2048.
[14]a) G. W. Orr, L. J. Barbour, J. L. Atwood, Science 1999, 285,
1049; b) H. Engelkamp, S. Middelbeek, R. J. M. Nolte, Science
1999, 284, 785.
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