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Institut für Anorganische und Angewandte Chemie
Dieter Rehder NMR 2 Polyoxometalates and
Biological Applications  PICB Winter
School Shanghai 5th-10th March 2007  
 
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Nuclei of interest in the context of
characterising polyoxometalates and modelling ion
transport
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Applications of 51V, 95Mo and 183W NMR
Characterising polyoxometalates
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Species differentiation by chemical shifts 51V
NMR of an aq. solution of 5 mM vanadate, pH 5.7
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H4V14PO425-
(Capped a-Keggin)
-506 (capping V)
1
1
1
-560, -582 (other V)
P
6
H6V15O423-
(Capped a-Keggin)
-531 (2 capping VO5)
-584, -597 (VO6)
V -507
C. L. Hill, Chem. Commun. 1993, 426
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A host-guest system based on a polyoxovanadate,
stabilised by a large cation
Bu4N4MeCN?V12O32
d(51V) -590 (4V) -598 (4V) -606 (4V)
W.V. Day et al. JACS 111 (1989) 5959
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From Keggin to Dawson
1
1
3
3
2
2
Remove 1, 2 and 3, and fuse
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183W NMR spectra of Dawson-type polyoxotungstates
P2MoW17O62n-
P
P
P2W18O62n-
R. Contant, Inorg. Chem. 1991, 30, 1695
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183W NMR spectra of polyoxotungstates MnAs4W40O1
40(28-n)-
M
Line which is strongly cation-dependent
O. Howarth, in Polyoxometalates 1994, 167
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Variable temperature 95Mo NMR spectra (molybdate
at pH 6)
MoO42- ? HMo7O245-
49 C
39 C
30 C
19 C
4 C
A.G. Wedd, Aust. J. Chem. 1984, 37, 1825
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Applications of 7Li and 23Na NMR Modeling ion
transport by porous polyoxomolybdates
in cooperation with Prof. Achim Müller
(Bielefeld) and Dr. Erhard Haupt (Hamburg)
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Why Li ?

• Lithium salts are used in the treatment of
• Bipolar disorder (manic depression)
• high blood pressure (hypertension)
• lacking blood supply (ischaemic injury)
• Viral infections

How does Li act?

• Competition with Na and K (disturbance of the
  Na/K balance)
• Inhibition of Mg2 activated enzymes in signal
  transduction (e.g. inositol-6-phosphatase)
• Modulation of the activity of Mg2 dependent
  enzymes in metabolic pathways (e.g. pyruvate
  kinase)

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7Li NMR - nuclear spin 3/2 - quadrupole
moment 4.5 fm2 - natural abundance 92.85 -
receptivity (1H 1) 0.6
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7Li NMR of erythrocytes (red blood cells) in the
presence of
Li outside
Li inside
0
5
Li(H2O)4
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Paramagnetic shift reagent
Dy3, 4f9 5 unpaired electrons, magnetic moment
10.65 BM
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Cell membrane with cation ion channel
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Ion channel - details
blue Protein
Na, K
O2- (of carboxy-lates or carbonyl)
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Porous Polyoxomolybdates Models for cellular
cation transport
Me2H2N44Li28MoVI(MoVI5O21)(H2O)612MoV2O4(SO4)
30?200H2O
Diameter ca. 3 nm 20 pores (0.42 nm ? ) and
channels, one cavity (containing water cluster)
Effective pore radius ca. 0.6 Å
Mo132O372(H2O)72(SO4)3072-
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Detail from the outer surface (viewed from the
interior)
2 Mo9O9 rings are linked together by a central
Mo2 unit
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Detail from the outer surface, showing one of the
pores in a lateral view, with a Na attached to 3
sulfates and 3 water molecules
(towards cavity of the capsule)
Mo132O372(H2O)72(SO4)3072-
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7Li NMR
in DMSO, concentration dependence
Li(dmso)x
Li?Mox
Li(H2O)4
Chem. Commun. 2005, 3912-3914
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7Li-2D-EXSY NMR
Mixing time 1.5 ms
Li(dmso)x ? Li?Mox
Li
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7Li-2D-EXSY NMR in the presence of guanidinium
cations
Li(dmso)x ? Li?Mox
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Li(dmso)x
7Li NMR in the presence of increasing amounts of
Dy3-triphosphate
no Dy3 added
External reference
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7Li NMR
23Na NMR
x 10
? Increasing c(Na) ?
Chem. Asian J. 2006, 76
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Essentially the same behaviour is observed for
K, Rb and Ca2
Ionic radii (coord. number 6) /
Å _______________________________ Li Na K Rb C
s Ca2 0.78 0.98 1.33 1.49 1.64 1.06
from close packing ion volumes
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Replacement of Li by K
Li(dmso)n
Li?Mox
Increasing c(K)
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Ca2 completely removes Li from internal capsule
sites
(excess) Ca2 added
no Ca2
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7Li NMR
in the presence of Cs no substantial exchange
Increasing c(Cs)
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Influence of water
Chem. Commun. 2005, 3912
Li(dmso/H2O)4 ? Li(H2O)x?Mox Equilibrium
accelerated by water
c(H2O)
2.5 M
0.26 M
0.16 M
dry
0.26 M (ca. 0.4)
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Summarising provisional assignments of lithium
sites