A metal-mediated base pair with a [2+1] coordination environment

Article abstract of DOI:10.1002/ejic.201301491

A silver(I)-mediated base pair based on azole-derived ligands only was devised. The base pair comprises the monodentate imidazole nucleoside and a nucleoside carrying the new bidentate ligand 4-[(1H-1,2,4-triazol-1-yl)methyl]-1H-1,2,3-triazole. The silver

Full text of DOI:10.1002/ejic.201301491

SHORT COMMUNICATION
DOI:10.1002/ejic.201301491
A Metal-Mediated Base Pair with a [2+1] Coordination
Environment
Tim Richters[a] and Jens Müller*[a]
Keywords: Bioinorganic chemistry / DNA / Silver / Triazoles / Metal-mediated base pairs
A
silver(I)-mediated base pair based on azole-derived
plex comprising the new base pair is stabilized by 6 °C upon
ligands only was devised. The base pair comprises the mono- binding one equivalent of silver(I). CD spectroscopy was
dentate imidazole nucleoside and a nucleoside carrying the
new bidentate ligand 4-[(1H-1,2,4-triazol-1-yl)methyl]-1H-
1,2,3-triazole. The silver(I) ion is hence coordinated in a tri-
gonal planar [2+1] environment. A representative DNA du-
used to confirm that the duplex adopts the canonical B-type
conformation. The base pair represents the first example of
a metal-mediated base pair with a [2+1] coordination envi-
ronment.
Introduction
chemistry.[2] Nonetheless, a site-specific introduction of
transition metal ions is not trivial. A particularly interesting
concept is the introduction of transition metal ions into the
center of a nucleic acid duplex by forming metal-mediated
base pairs. In this artificial base pairing system, the hydro-
gen bonds between complementary nucleobases are for-
mally replaced by coordinative bonds to metal ions
(Scheme 1).[3]
Nucleic acids, and in particular DNA, have emerged as
important supramolecular scaffolds for the three-dimen-
sional arrangement of functional molecules.[1] While most
of these functional molecules are based on purely organic
moieties,[1b] the incorporation of metal complexes is gaining
more and more attention.[1a] It is well known that metal
ions are involved in almost every aspect of nucleic acid
Scheme 1. Representation of a DNA duplex with hydrogen-bond-mediated and artificial metal-mediated base pairs. Adapted with per-
mission from ref.[3b] Copyright Wiley-VCH Verlag GmbH & Co. KGaA.
In most examples, the ligands involved in metal-mediated
base pairs are artificial nucleobases. Nonetheless, several ex-
amples exist in which natural nucleobases such as thymine,
cytosine, or uracil represent the basis of a metal-mediated
[a] Westfälische Wilhelms-Universität Münster, Institut für
Anorganische und Analytische Chemie,
Corrensstr. 28/30, 48149 Münster, Germany
E-mail: mueller.j@uni-muenster.de
www.muellerlab.org
Eur. J. Inorg. Chem. 2014, 437–441
437
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
SHORT COMMUNICATION
base pair.[4] The combination of metal-based functionality
Results and Discussion
and self-assembling properties makes these metal–DNA
conjugates attractive targets for chemists. Various applica-
tions are feasible,[3a] for example in sensing[5a–5d] or other
uses based on the improved charge-transfer properties of
DNA upon metalation.[5e,5f]
Scheme 3 shows the synthesis of the nucleoside carrying
the new bidentate ligand tritri {4-[(1H-1,2,4-triazol-1-yl)-
methyl]-1H-1,2,3-triazole}. Reaction of 1-propargyl-1H-
1,2,4-triazole with a 2-deoxy-β-d-glycosyl azide gives the
desired toluoyl-protected nucleoside 1. After deprotection,
free nucleoside 2 was converted to phosphoramidite 4 in
a two-step synthesis. The phosphoramidite was used as a
building block in automated solid-phase DNA synthesis.
The oligonucleotide duplex under investigation is shown in
Scheme 4. The same sequences – albeit with other artificial
nucleobases – had been chosen in previous studies,[10] which
enables a comparison with other metal-mediated base pairs.
We have established various nucleic acid systems with
metal-mediated base pairs derived from azole ligands,[6] in-
cluding extensive studies with model nucleobases.[7] For ex-
ample, the first structure determination of a nucleic acid
with contiguous metal-mediated base pairs is based on
imidazole–AgI–imidazole base pairs.[8] It was shown that
neighboring base pairs of this type form in a cooperative
manner.[9] Consequently, we set out to develop azole-based
metal-mediated base pairs further. In particular, we aimed
at devising a new base-pairing system with a trigonal planar
coordination geometry of the central metal ion. This geom-
etry should be achieved by combining one bidentate and
one monodentate ligand. As the use of azole-based ligands
had been very successful in the past, we devised the new
bidentate ligand in a way to comprise two triazole moieties
(tritri). Accordingly, the well-established imidazole nucleo-
side (imi) was planned to function as the monodentate
ligand (Scheme 2). Alternatively, a pyrimidine nucleobase
(cytosine, thymine) was considered as the monodentate
ligand.
Scheme 4. Sequence of the oligonucleotide duplex under investiga-
tion (X = tritri, Y = imi, cytosine, or thymine).
To determine the melting temperature (Tm) of the oligo-
nucleotide duplexes, temperature-dependent UV spectra
were recorded. It is anticipated that the formation of a
stable metal-mediated base pair leads to an increase in Tm
due to the additional stabilization brought forward by the
coordinative bonds. For reference purposes, related DNA
sequences comprising canonical base pairs only had been
investigated previously. The addition of AgI to these du-
plexes led to an increase in Tm of 2.5–3.5 °C, which was
explained by nonspecific binding events due to an electro-
static interaction between the positively charged metal ion
and the negatively charged DNA backbone.[10b] Hence, only
ΔTm values significantly larger than 3.5 °C can be consid-
ered as evidence for the formation of a stable metal-medi-
Scheme 2. Metal-mediated base pair with trigonal planar [2+1] co-
ordination environment brought about by the ligands tritri and imi. ated base pair. Table 1 lists the increase in melting tempera-
Scheme 3. Synthesis of phosphoramidite 4: a) THF/2-propanol/H2O, CuSO4, sodium ascorbate, 12 h, r.t. (Tol: p-toluoyl); b) MeOH, NH3,
18 h, r.t.; c) dimethoxytrityl chloride (DMT-Cl), 4-(dimethylamino)pyridine (DMAP), pyridine, 3 h, r.t.; d) 2-cyanoethyl N,N-diisoprop-
ylchlorophosphoramidite (CEDIP-Cl), diisopropylethylamine (DIPEA), CH2Cl2, 30 min, r.t.
Eur. J. Inorg. Chem. 2014, 437–441
438
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
SHORT COMMUNICATION
ture (ΔTm) for the three DNA duplexes under investigation
upon the addition of one equivalent of various transition
metal ions.
Table 1. Melting temperatures of DNA duplexes comprising the
bidentate ligand tritri (X) and
a complementary imidazole,
thymine, or cytosine (Y) in the presence of one equivalent of
various transition metal ions.[a]
Y = imidazole
Y = cytosine
Y = thymine
ΔTm /°C
Mn+
Tm /°C
ΔTm /°C Tm /°C ΔTm /°C Tm /°C
–
21.7
27.7
21.8
21.8
21.6
21.6
21.6
21.7
21.7
21.8
21.7
–
21.6
23.0
n.d.
22.2
n.d.
n.d.
n.d.
22.1
n.d.
22.8
n.d.
–
23.0
25.0
–
AgI
+ 6.0
+ 0.1
+ 0.1
– 0.1
– 0.1
– 0.1
Ϯ0.0
Ϯ0.0
+ 0.1
Ϯ0.0
+ 1.4
n.d.
+ 0.6
n.d.
n.d.
n.d.
+ 0.5
n.d.
+ 1.2
n.d.
+ 2.0
n.d.
– 0.3
n.d.
n.d.
n.d.
+ 0.1
n.d.
+ 0.3
n.d.
AuIII
CuII
CoIII
CrIII
FeII
HgII
MnII
NiII
ZnII
n.d.
22.7
n.d.
n.d.
n.d.
23.1
n.d.
23.3
n.d.
Figure 1. Melting curves of the DNA duplex comprising one
tritri:imi base pair in the absence (black) and presence (red) of one
equivalent of silver(I). The increase in melting temperature can
clearly be discerned [Anorm = (A – Amin)/(Amax – Amin) at 260 nm].
bility constant for the binding of AgI to a tritri:imi mispair
has the same order of magnitude as that for an imi:imi mis-
pair [K = 3(1)ϫ106 m–1].[9]
[a] Conditions: 1 µm oligonucleotide duplex, 150 mm NaClO4, 5 µm
MOPS (pH 6.8), 1 µm metal salt. The estimated standard deviation
of Tm amounts to 1 °C.
CD spectroscopy was applied to prove that the incorpo-
ration of the silver(I) ion into the DNA duplex does not
induce any major conformational change. The CD spectra
of the duplex in the absence and presence of one equivalent
of silver(I) are shown in Figure 2. The two spectra overlap
significantly. The CD spectra clearly demonstrate that the
duplex adopts the canonical B-DNA conformation,[13] de-
spite the presence of the artificial nucleobases. In fact, be-
low 300 nm the CD spectra perfectly overlap with those of
the same DNA sequence comprising a homo base pair of
6-(2Ј-furyl)-purine.[10b] Above 300 nm, the CD spectra of
the DNA containing 6-(2Ј-furyl)-purine display additional
Cotton effects due to the presence of the furyl moiety. The
CD spectrum of the duplex with the tritri–AgI–imi base
pair shows a slight deviation around 308 nm from the CD
spectrum of the silver(I)-free duplex. It is tempting to
speculate that this weak positive Cotton effect indicates a
structural movement of the tritri ligand within the duplex
to better accommodate the silver(I) ion. However, because
of the weakness of the signal, no final conclusion can be
drawn at this stage.
It can clearly be discerned that only one of the three pos-
sible combinations (tritri:imi, tritri:cytosine, tritri:thymine)
is capable of forming a stable silver(I)-mediated base pair,
namely tritri–AgI–imi, as evidenced by a ΔTm of 6 °C. The
melting curves of this duplex in the absence and in the pres-
ence of one equivalent of silver(I) are shown in Figure 1.
None of the other transition metal ions under investigation
had a significant effect on the melting temperature. The ad-
dition of the chelating ligand EDTA to the duplex does not
lead to removal of the AgI from the metal-mediated base
pair. As expected, silver(I) with its d10 electronic configura-
tion seems to be the least selective metal ion in terms of
preferred coordination geometry. This behavior has also be-
come evident in other previously reported silver(I)-contain-
ing DNA systems such as the silver(I)-stabilized triple helix
with a tricoordinate metal ion ([1+1+1] coordination)[11] or
the silver(I)-mediated base pair proposed to possess a six-
fold coordinated metal ion ([3+3] coordination).[12] None-
theless, the tritri–AgI–imi base pair reported herein is the
first example for a [2+1] coordination environment in a
metal-mediated base pair.
Compared with other metal-mediated base pairs pre-
viously introduced into the same DNA sequence,[10] the
tritri–AgI–imi base pair is the most stable one. The silver(I)-
mediated base pair formed from dipicolylamine and imid-
azole (with a [3+1] coordination environment of the metal
ion), the most stable one in a series of dipicolylamine–AgI–
azole base pairs, stabilizes the duplex by 5.7 °C (and hence
a bit less than tritri–AgI–imi).[10a] Moreover, homo base
pairs of artificial nucleosides bearing a 6-(2Ј-thienyl)-purine
or 6-(2Ј-furyl)-purine ligand incorporated into the DNA
duplex shown in Scheme 4 did not seem to bind silver(I) at
all.[10b] The increase in Tm upon the formation of the tritri–
AgI–imi base pair is the same as that of the previously es-
tablished imi–AgI–imi base pair (albeit in a different se-
Figure 2. CD spectra of the DNA duplex comprising one tritri:imi
base pair in the absence (black) and presence (red) of one equiva-
quence context).[9] Hence, it can be estimated that the sta- lent of silver(I).
Eur. J. Inorg. Chem. 2014, 437–441
439
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
SHORT COMMUNICATION
(400 MHz, CDCl3): δ = 8.14 (s, 1 H, H5*), 7.93 [d, 2 H, Hmeta(Tol)],
7.90 (s, 1 H, H3*), 7.84 [d, 2 H, Hmeta(Tol)], 7.82 (s, 1 H, H5), 7.24
[m, 4 H, Hortho(Tol)], 6.45 (t, 1 H, H1Ј), 5.75 (d, 1 H, H3Ј), 5.39
(m, 2 H, CH2), 4.65 (q, 1 H, H4Ј), 4.61 (dd, 2 H, H5Ј, H5ЈЈ), 3.19
(dt, 1 H, H2Ј or H2ЈЈ), 2.86 (ddd, 1 H, H2Ј or H2ЈЈ), 2.43 [s, 3 H,
CH3(Tol)], 2.41 [s, 3 H, CH3(Tol)] ppm. 13C NMR (100 MHz,
CDCl3): δ = 166.1 (C=O), 164.9 (C=O), 152.2 (C3*), 144.6 (Tol),
144.2 (Tol), 143.3 (C4), 142.1 (C5*), 129.8 (Tol), 129.7 (Tol), 129.3
(Tol), 126.6 (Tol), 126.3 (Tol), 122.0 (C5), 118.9 (C5), 89.1 (C1Ј),
83.9 (C4Ј), 74.7 (C3Ј), 63.9 (C5Ј), 44.8 (CH2), 38.3 (C2Ј), 21.7
[CH3(Tol)] ppm. C26H26N6O5 (502.52): calcd. C 62.14, H 5.20, N
16.72; found C 62.17, H 5.21, N 16.47. HRMS: calcd. for [M +
Na]+ 525.1862; found 525.1858.
Conclusions
An artificial nucleoside that combines one 1,2,4-triazole
entity with one 1,2,3-triazole moiety has been devised with
the bidentate ligand tritri. This nucleoside forms a stable
silver(I)-mediated base pair with a complementary imid-
azole nucleoside. The canonical pyrimidine nucleosides are
not able to form metal-mediated base pairs with tritri.
Moreover, silver(I) is the only transition metal ion that was
found to stabilize the tritri:imi base pair. The resulting
tritri–AgI–imi system represents the first metal-mediated
base pair with a [2+1] coordination environment. A DNA
duplex comprising such a base pair is stabilized by 6 °C
with respect to the metal-free duplex. The only previous
example for a silver(I) coordinated in a trigonal planar
fashion inside DNA is a triple helix with a [1+1+1] coordi-
nation environment.[11] For that system, a stabilization of
only 2 °C has been reported despite the use of excess sil-
ver(I). Hence, the tritri–AgI–imi base pair is significantly
more stable than any previously reported DNA system with
trigonally coordinated silver(I). By introducing the [2+1]
coordination environment, the scope of metal-mediated
base pairs is extended also towards tricoordinate metal ions.
Free Nucleoside 2: Compound 1 (3.34 g, 6.64 mmol) was dissolved
in a mixture of methanol (100 mL) and aqueous NH3 (50 mL).
After stirring overnight at room temperature the solvent was evapo-
rated, and the crude solid was purified by column chromatography
to obtain the desired product 2 as a white solid (1.68 g; 6.29 mmol,
1
95%). H NMR (400 MHz, CD3OD): δ = 8.59 (s, 1 H, H5*), 8.29
(s, 1 H, H3*), 8.01 (s, 1 H, H5), 6.44 (t, 1 H, H1Ј), 5.60 (s, 2 H,
CH2), 4.56 (q, 1 H, H3Ј), 4.05 (q, 1 H, H4Ј), 3.74 (dd, 1 H, H5Ј or
H5ЈЈ), 3.65 (dd, 1 H, H5Ј or H5ЈЈ), 2.79 (m, 1 H, H2Ј or H2ЈЈ),
2.54 (m, 1 H, H2Ј or H2ЈЈ) ppm. 13C NMR (100 MHz, CD3OD):
δ = 152.5 (C3*), 145.1 (C5*), 130.5 (C4), 124.1 (C5), 90.3 (C1Ј),
89.7 (C4Ј), 72.1 (C3Ј), 63.1 (C5Ј), 45.4 (CH2), 41.7 (C2Ј) ppm.
C10H14N6O3 (266.26) for 2·0.25H2O: calcd. C 44.34, H 5.40, N
31.05; found C 44.10, H 5.19, N 30.84. HRMS: calcd. for [M +
Na]+ 289.1025; found 289.1016.
Experimental Section
General: DNA syntheses were performed in the DMT-off mode
with a K&A Laborgeräte H8 DNA/RNA synthesizer by following
standard protocols according to a recently published procedure.[10b]
The oligonucleotides were identified by MALDI-TOF mass spec-
trometry [purine-rich sequence: calcd. for (M + H)+ 4118 Da,
found 4121 Da; pyrimidine-rich sequence with Y = imi: calcd. for
(M + H)+ 3744 Da, found 3745 Da; pyrimidine-rich sequence with
Y = C: calcd. for (M + H)+ 3787 Da, found 3788 Da; pyrimidine-
rich sequence with Y = T: calcd. for (M + H)+ 3802 Da, found
3803 Da]. MALDI-TOF mass spectra were recorded with a Bruker
Reflex IV instrument by using a 3-hydroxypicolinic acid/ammo-
nium citrate matrix and applying a commercially available oligonu-
cleotide with a molecular mass of 4577 Da as internal reference.
NMR spectra were recorded with Bruker Avance(I) 400 and Bruker
Avance(III) 400 spectrometers at 300 K. Chemical shifts were refer-
enced to residual CD3OH (CD3OD, δ = 4.78 ppm) or TMS
(CDCl3, δ = 0 ppm). UV/Vis spectra were recorded with a Varian
CARY BIO 100 spectrophotometer. CD spectra were recorded at
10 °C with a Jasco J-815 spectrometer. The CD spectra were
smoothed, and a manual baseline correction was applied. 2-Deoxy-
3,5-di-O-(p-toluoyl)-β-d-erythro-pentafuranosyl azide and 1-pro-
pargyl-1H-1,2,4-triazole were prepared according to literature pro-
cedures.[14]
DMT-protected tritri Nucleoside 3: Compound
2
(1.67 g,
6.29 mmol) was co-evaporated thrice with dry pyridine (20 mL)
and then dissolved in dry pyridine (50 mL). To this reaction mix-
ture were added catalytic amounts of DMAP under an argon atmo-
sphere, followed by the addition of DMT-Cl (2.94 g, 7.55 mmol).
The mixture was stirred for 3 h at room temperature. The solution
was diluted with CH2Cl2 (100 mL) and washed with water (3ϫ
20 mL). The organic phase was dried (Na2SO4), and the solvents
were evaporated to dryness. The crude product was purified with
column chromatography to obtain 3 as a white foam (3.14 g,
1
5.53 mmol, 88%). H NMR (400 MHz, CDCl3): δ = 8.03 (s, 1 H,
H5), 7.84 (d, 2 H, H3*, H5*), 7.33 (m, 2 H, DMT), 7.25–7.19 (m,
7 H, DMT), 6.79 (d, 2 H, DMT), 6.32 (t, 1 H, H1Ј), 5.27 (d, 2 H,
CH2), 4.63 (m, 1 H, H3Ј), 4.13 (m, 1 H, H4Ј), 3.77 (s, 6 H, O-CH3),
3.31 (m, 2 H, H5Ј, H5ЈЈ), 2.80 (m, 1 H, H2Ј or H2ЈЈ), 2.53 (m, 1
H, H2Ј or H2ЈЈ) ppm. 13C NMR (100 MHz, CDCl3): δ = 158.5
(DMT), 151.6 (C3*), 144.4 (C5*), 143.0 (DMT), 141.4 (C4), 135.5
(DMT), 135.4 (DMT), 130.0 (DMT), 129.3 (DMT), 128.4 (DMT),
128.1 (DMT), 127.8 (DMT), 126.9 (DMT), 121.9 (C5), 113.1
(DMT), 88.8 (C1Ј), 86.6 (C4Ј), 70.8 (C3Ј), 63.2 (C5Ј), 55.2 (OCH3),
44.6 (CH2), 40.8 (C2Ј) ppm. HRMS: calcd. for [M + Na]+
591.2332; found 591.2334.
Toluoyl-Protected tritri Nucleoside 1: To a mixture of 1-propargyl-
1H-1,2,4-triazole (964 mg, 9.63 mmol) and 2-deoxy-3,5-di-O-(-p-
toluoyl)-β-d-erythro-pentafuranosyl azide (3.17 g, 8.03 mmol) in
Orthogonally Protected tritri Nucleoside 4: Compound 3 (724 mg,
1.27 mmol) was dissolved in freshly distilled CH2Cl2 (35 mL). To
this solution were added DIPEA (650 μL, 3.82 mmol) and CEDIP-
Cl (568 μL, 2.55 mmol) under an argon atmosphere. After 30 min
of stirring at room temperature the mixture was diluted with
EtOAc (75 mL). The organic phase was washed with saturated
aqueous NaHCO3 solution (30 mL) and dried (MgSO4). The solu-
tion was concentrated to dryness. Column chromatography gave 4
THF/2-propanol (40 mL, 4:1) were added
a solution of
CuSO4·5H2O (402 mg, 1.61 mmol) in H2O (8 mL) and sodium as-
corbate (636 mg, 3.21 mmol). After stirring for 12 h at room tem-
perature, the reaction was quenched by addition of EtOAc
(150 mL). The organic layer was washed with aqueous EDTA solu-
tion (0.5%) until the aqueous layer was colorless. The organic
phase was dried (MgSO4). After filtration the solvent was removed.
The crude product was purified by column chromatography, and 1
1
as a yellowish oil (887 mg, 1.15 mmol, 90%). H NMR (400 MHz,
CDCl3): δ = 7.96 (s, 1 H, H5), 7.79 (s, 2 H, H5*, H3*), 7.27 (m, 2
H, DMT), 7.20–7.12 (m, 8 H, DMT), 6.72 (m, 2 H, DMT), 6.28
(t, 1 H, H1Ј), 5.22 (m, 2 H, CH2), 4.67 (m, 1 H, H3Ј), 4.16 (m, 1
1
was obtained as a white solid (3.34 g, 6.65 mmol, 83%). H NMR
Eur. J. Inorg. Chem. 2014, 437–441
440
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
SHORT COMMUNICATION
ids Res. 2013, 41, 4345–4359; c) B. Y.-W. Man, D. S.-H. Chan,
H. Yang, S.-W. Ang, F. Yang, S.-C. Yan, C.-M. Ho, P. Wu, C.-
M. Che, C.-H. Leung, D.-L. Ma, Chem. Commun. 2010, 46,
8534–8536; d) D. S.-H. Chan, H.-M. Lee, C.-M. Che, C.-H.
Leung, D.-L. Ma, Chem. Commun. 2009, 7479–7481; e) T.
Ehrenschwender, W. Schmucker, C. Wellner, T. Augenstein, P.
Carl, J. Harmer, F. Breher, H.-A. Wagenknecht, Chem. Eur. J.
2013, 19, 12547–12552; f) S. Liu, G. H. Clever, Y. Takezawa,
M. Kaneko, K. Tanaka, X. Guo, M. Shionoya, Angew. Chem.
2011, 123, 9048; Angew. Chem. Int. Ed. 2011, 50, 8886–8890.
[6] a) J. Müller, D. Böhme, P. Lax, M. Morell Cerdà, M. Roitzsch,
Chem. Eur. J. 2005, 11, 6246–6253; b) D. Böhme, N. Düpre,
D. A. Megger, J. Müller, Inorg. Chem. 2007, 46, 10114–10119.
[7] D. A. Megger, J. Kösters, A. Hepp, J. Müller, Eur. J. Inorg.
Chem. 2010, 4859–4864.
H, H4Ј), 3.79–3.63 [m, 8 H, OCH3, CH(CH3)2], 3.49 (m, 2 H,
CH2CN), 3.23 (m, 2 H, H5Ј, H5ЈЈ), 2.78 (m, 1 H, H2Ј or H2ЈЈ),
2.61 (m, 1 H, H2Ј or H2ЈЈ), 2.53 (t, 2 H, OCH2), 1.10–1.00 [m, 12
H, CH(CH3)2] ppm. 31P {H} NMR (162 MHz, CDCl3): δ = 149.4,
149.1 ppm. HRMS: calcd. for [M
791.3405.
+
Na]+ 791.3410; found
Acknowledgments
We thank Dr. Olga Krug for helpful discussions at the inception
of this project.
[1] a) T. J. Bandy, A. Brewer, J. R. Burns, G. Marth, T. Nguyen,
E. Stulz, Chem. Soc. Rev. 2011, 40, 138–148; b) R. Varghese,
H.-A. Wagenknecht, Chem. Commun. 2009, 2615–2624.
[2] J. Müller, Metallomics 2010, 2, 318–327.
[3] a) P. Scharf, J. Müller, ChemPlusChem 2013, 78, 20–34; b) J.
Müller, Eur. J. Inorg. Chem. 2008, 3749–3763; c) Y. Takezawa,
[8] a) S. Kumbhar, S. Johannsen, R. K. O. Sigel, M. P. Waller, J.
Müller, J. Inorg. Biochem. 2013, 127, 203–210; b) S. Johannsen,
N. Megger, D. Böhme, R. K. O. Sigel, J. Müller, Nat. Chem.
2010, 2, 229–234.
[9] K. Petrovec, B. J. Ravoo, J. Müller, Chem. Commun. 2012, 48,
11844–11846.
M. Shionoya, Acc. Chem. Res. 2012, 45, 2066–2076; d) G. H. [10] a) K. Seubert, C. Fonseca Guerra, F. M. Bickelhaupt, J. Müller,
Clever, M. Shionoya, Coord. Chem. Rev. 2010, 254, 2391–2402;
e) G. H. Clever, C. Kaul, T. Carell, Angew. Chem. 2007, 119,
6340–6350; Angew. Chem. Int. Ed. 2007, 46, 6226–6236.
[4] a) D. A. Megger, N. Megger, J. Müller, Met. Ions Life Sci. 2012,
10, 295–317; b) S. Johannsen, S. Paulus, N. Düpre, J. Müller,
R. K. O. Sigel, J. Inorg. Biochem. 2008, 102, 1141–1151; c)
D. A. Megger, C. Fonseca Guerra, F. M. Bickelhaupt, J.
Müller, J. Inorg. Biochem. 2011, 105, 1398–1404; d) A. Ono, H.
Torigoe, Y. Tanaka, I. Okamoto, Chem. Soc. Rev. 2011, 40,
5855–5866.
Chem. Commun. 2011, 47, 11041–11043; b) I. Sinha, J. Kösters,
A. Hepp, J. Müller, Dalton Trans. 2013, 42, 16080–16089.
[11] K. Tanaka, Y. Yamada, M. Shionoya, J. Am. Chem. Soc. 2002,
124, 8802–8803.
[12] N. Zimmermann, E. Meggers, P. G. Schultz, J. Am. Chem. Soc.
2002, 124, 13684–13685.
[13] D. M. Gray, R. L. Ratliff, M. R. Vaughan, Methods Enzymol.
1992, 211, 389–406.
ˇ
[14] a) A. Stimac, J. Kobe, Carbohydr. Res. 2000, 329, 317–314; b)
Y. Gao, H. Gao, C. Piekarski, J. M. Shreeve, Eur. J. Inorg.
Chem. 2007, 4965–4972.
[5] a) D.-L. Ma, H.-Z. He, K.-H. Leung, H.-J. Zhong, D. S.-H.
Chan, C.-H. Leung, Chem. Soc. Rev. 2013, 42, 3427–3440; b)
H.-Z. He, D. S.-H. Chan, C.-H. Leung, D.-L. Ma, Nucleic Ac-
Received: November 27, 2013
Published Online: January 2, 2014
Eur. J. Inorg. Chem. 2014, 437–441
441
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim