To be dinuclear or not: Z-DNA induction by nickel complexes

Article abstract of DOI:10.1002/chem.200600737

The left-handed Z-DNA has been identified as a gene regulating element. Therefore the generation of ZDNA through metal complexes might be an innovative way for the regulation of gene expression. Use of the new dinuclear complex N,N,N',N'-tetrakis-[2(3,5-dimethylpyrazol-l-yl)ethylJ-l,3propylenediamine- bis(nickel(II) dinitrate) (2) reversibly induced Z-DNA formation. However, when a 1:1 ratio of metal/dinucleating ligand was used as a control, the midpoint of the B- to Z-DNA transition was at the same nickel concentration as in case of the dinuclear complex. The novel mononuclear analogue, N-methyl-N,N-bis-[2(3,5- dimethylpyrazol-l-yl)ethyl]aminenickel(II)-dinitrate (3) was inducing the Z-DNA at a similar ratio versus nucleotides as free nickel(II) itself. For the first time, proton and nickel binding constants for the bis-[2-(pyrazol-lyl)ethyl] amine ligand system are reported and discussed. Both nickel complexes 2 and 3 were structurally characterized by single crystal analysis. Furthermore, the synthesis of the two new ligands, N,N,N',N,'-tetrakis-[2-(3,5-dimethylpyrazol-l- yl)ethyl]-l,2-propylenediamine (4) and N-methyl-N,N-bis-[2(3,5-dimethylpyrazol- l-yl)ethyl]amine (5) is described. The two major synthetic pathways leading to polypyrazoyl amines in general are critically discussed with respect to yield, reproducibility and handling of the intermediates.

Full text of DOI:10.1002/chem.200600737

FULL PAPER
DOI: 10.1002/chem.200600737
To Be Dinuclear or Not: Z-DNA Induction by Nickel Complexes
Bernhard Spingler* and Philipp M. Antoni[a]
Abstract: The left-handed Z-DNA has
been identified as a gene regulating el-
ement. Therefore the generation of Z-
DNA through metal complexes might
be an innovative way for the regulation
of gene expression. Use of the new di-
nuclear complex N,N,N’,N’-tetrakis-[2-
(3,5-dimethylpyrazol-1-yl)ethyl]-1,3-
dinuclear complex. The novel mononu-
plexes 2 and 3 were structurally charac-
terized by single crystal analysis. Fur-
thermore, the synthesis of the two new
ligands, N,N,N’,N’-tetrakis-[2-(3,5-dime-
thylpyrazol-1-yl)ethyl]-1,2-propylenedi-
amine (4) and N-methyl-N,N-bis-[2-
(3,5-dimethylpyrazol-1-yl)ethyl]amine
(5) is described. The two major syn-
thetic pathways leading to polypyrazoyl
amines in general are critically dis-
cussed with respect to yield, reproduci-
bility and handling of the intermedi-
ates.
clear analogue, N-methyl-N,N-bis-[2-
(3,5-dimethylpyrazol-1-yl)ethyl]amine-
nickel(II)-dinitrate (3) was inducing
the Z-DNA at a similar ratio versus
nucleotides as free nickel(II) itself. For
the first time, proton and nickel bind-
ing constants for the bis-[2-(pyrazol-1-
yl)ethyl]amine ligand system are re-
ported and discussed. Both nickel com-
propylenediamine-bis(nickel(II) dini-
N
trate) (2) reversibly induced Z-DNA
formation. However, when a 1:1 ratio
of metal/dinucleating ligand was used
as a control, the midpoint of the B- to
Z-DNA transition was at the same
nickel concentration as in case of the
Keywords: bioinorganic chemistry ·
DNA structures · metal complexes ·
N ligands · nickel
Introduction
regulating element,[10] our interest focused on the conditions
which lead to its formation starting from B-DNA. In Z-
DNA, the N7 of guanine is exposed to the solvent.[11] Bind-
ing of nickel ions[12] or nickel complexes[13] to this atom in-
duces the conformational change from B- to Z-DNA.
During our studies aimed at a better understanding the fac-
tors which influence the formation of the left-handed Z-
DNA,[12] we proposed that both metal centres of a dinuclear
complex might act in a synergistic way to induce Z-DNA at
a lower metal-to-nucleobase ratio than their mononuclear
analogues.[14,15] This concept has been realized in our recent
The binding of first- or second-row transition metal com-
plexes to nucleobases has been studied for a long time. In
most cases, a hydrophobic ligand binds to one of the DNA
grooves or an extended aromatic system of the metal com-
plex intercalates between the base pairs.[1,2] Contrarily, the
inner-sphere coordination of first- or second-row transition
metals to either phosphates and/or nucleobases has been
studied less intensively.[3–5] Here, the subsequent reactions
after the initial binding, such as phosphate diester hydroly-
sis[6] or oxidation promoted by metal complexes,[7] are of
special interest.
work of bis-12
[ane]N3 complexes.[16] The ideal dinuclear
A
system to induce Z-DNA should have the following proper-
ties:
The left-handed Z-form of oligonucleotides was first ob-
served at high salt concentrations, but in the mean time,
transition metals[8] as well as proteins[9] were also found to
induce the Z-form. Since Z-DNA was found to be a gene
*
each metal cation should have at least one labile coordi-
nation site, thereby allowing inner-sphere binding;
*
the metal-to-metal distance should be between 5 and
7 Š;
[a] Dr. B. Spingler, P. M. Antoni
University of Zürich, Winterthurerstrasse 190
8057 Zürich (Switzerland)
*
the bridging ligand with 2 should contain sterically rather
demanding chelating moieties to enforce preferential se-
lectivity for Z-DNA versus B-DNA.
Fax : (+41)44-635-6803
E-mail: spingler@aci.unizh.ch
Following a search on the Cambridge Structure Database,[17]
we selected dinickel complex 1 as an additional promising
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author.
Chem. Eur. J. 2007, 13, 6617 – 6622
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
6617

compound fulfilling the above-mentioned criteria. The Ni–
Ni distance in the crystal structure of 1 was 6.453(1) Š,[18]
though this value was expected to change upon rotation of
the ligand to accommodate the syn coordination of the
metals to the DNA major groove. In order to further ex-
plore the chemistry of complexes such as 1, we synthesised
the new dinuclear complex 2 and for comparison the mono-
nuclear complex 3 (Figure 1). They are based on the novel
Scheme 1. Retrosynthetic analysis for bis-[2-(pyrazol-1-yl)ethyl]amines.
instead directly reacted with an excess of potassium pyrazo-
late. This procedure had two advantages: the highly vesicant
bis-(2-chloroethyl) ammonium salts are much less volatile
than their free bases and the formation of side products
such as piperazine derivatives through dimerisation was
completely suppressed.
Figure 1. Nickel complexes studied.
The synthetic route for bis-(2-chloroethyl)amine turned
out to be highly efficient and reproducible. The new ligands
N,N,N’,N’-tetrakis-[2-(3,5-dimethylpyrazol-1-yl)ethyl]1,2-pro-
pylenediamime (4) and N-methyl-N,N-bis-[2-(3,5-dimethyl-
pyrazol-1-yl)ethyl]amine (5) were synthesized on a multi-
gramm scale from commercial available chemicals in two
and three steps in an overall yield of 86 and 72%, respec-
tively. The ligands were treated with two or one equivalents
dinucleating ligand N,N,N’,N’-tetrakis-[2-(3,5-dimethylpyra-
zol-1-yl)ethyl]1,2-propylenediamime (4) and the new mono-
nucleating ligand N-methyl-N,N-bis-[2-(3,5-dimethylpyrazol-
1-yl)ethyl]amine (5). In this paper, we report the synthesis
and characterisation of compounds 2–5, as well as their re-
versible interactions with polyd(GC) with respect to the B-
to Z-DNA transition. For the first time, proton and nickel
binding constants of the bis-[2-(pyrazol-1-yl)ethyl]amine
ligand system are reported and discussed. In addition, we
critically evaluate the various synthetic pathways leading to
polypyrazoyl ligands such as 4 and 5.
of Ni(NO3)2 to yield compounds 2 and 3. In both cases,
A
single crystals were grown by vapor diffusion of methanolic
solutions against tetrahydropyran. Both structures show a
distorted octahedral coordination geometry around the
nickel centers (Figures 2 and 3). The distortion is mainly
caused by the chelating mode of a nitrate molecule. As de-
scribed before for dinickel complex 1, the bis-[2-(3,5-dime-
thylpyrazol-1-yl)ethyl]amine units coordinate to the metal in
a facial fashion.[18] The Ni–Ni distance of 6.7698(6) Š in 2 is
a little bit longer than in the case of the ethylene bridged 1
(6.453(1) Š).
Results and Discussion
Two different synthetic pathways leading to bis-[2-(pyrazol-
1-yl)ethyl]amines have been described in the literature thus
far (Scheme 1).[19–21] 2-(3,5-Dimethylpyrazol-1-yl)ethanol
was transformed into its tosy-
late derivative, which was then
used to alkylate aliphatic
amines.[19] We first followed
this route, but found that the
yield of the tosylation step was
rather low and the amine alky-
lation was not reproducible.
Thus we turned to another ap-
proach starting from diethanol-
amine derivatives. These were
treated with thionyl chloride to
yield aza analogues of mustard
gas. As described in the litera-
ture,[20,21] the bis-(2-chloroeth-
yl) ammonium salts were not
isolated as their free bases, but
Figure 2. ORTEP plot of 2·
vent molecules were omitted for clarity.
N
G
6618
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ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2007, 13, 6617 – 6622

Z-DNA Induction by Nickel Complexes
FULL PAPER
Figure 3. ORTEP plot of 3·H2O, ellipsoids drawn at 50% probability. Hy-
drogen atoms were omitted for clarity
Figure 5. Experimental CD titration of polyd(GC) with either 2, 3 or the
1:1 adduct of Ni
A
lated fitting curves for the B- to Z-DNA transition.
Both complexes 2 and 3 as well as ligands 4 and 5 were
tested for their ability to induce Z-DNA formation by titrat-
ing polyd(GC) with solutions containing either 2, 3, 4 or 5.
As a control as to whether the dinuclear complex 2 remains
Table 1. Induction of Z-DNA by Ni
A
G
intact, the 1:1 adduct of Ni(NO3)2 and 4 was also tested. The
A
and 4, 3, 4, or 5.
transformation from B- to Z-DNA was followed by circular
dichroism (CD) and UV/Vis spectroscopy at room tempera-
ture at a pH 7. Addition of complexes 2 and 3 as well as the
Compound
Equivalents of metals/ligands
needed for the midpoint of the
transition from B- to Z-DNA
Ni
(NO3)2
(NO3)2]/4[b] 1:1
0.48[12]
0.26(1)
0.28(1)
0.49(1)
no transition
no transition
1:1 adduct of Ni(NO3)2 and 4 (Figure 4 and Figure S1in the
N
N
ACHTREUNG
N
(NO3)2(5)]ꢀ3[a]
4
5
[a] Preformed complexes. [b] Formed in situ, before addition to the
DNA.
in water at a submillimolar concentration complex 2 is loos-
ing one of its two nickel cations to yield a 1:1 nickel/ligand 4
complex. The better efficiency of either 2 or the 1:1 adduct
of Ni(NO3)2 and 4 might come from the formation of macro-
A
chelate complex of nickel coordinating to N7 and the terna-
ry free amine of the previous second binding side, which is
protonated at pH 7 (Figure 6). An UV/Vis titration was at-
tempted to directly study the behaviour of complex 2 in the
same aqueous solution, in which the circular dichroism stud-
ies were performed (1m m cacodylate buffer, pH 7). Howev-
er, the poor solubility of ligand 4 in water and the low ex-
tinction coefficient of complex 2 impeded our efforts to in-
dependently study its identity at the submillimolar concen-
trations of the CD experiment. Pettinari and co-workers
have studied the UV/Vis properties of bispyrazoylmethane
metal complexes in the organic solvents, such as acetoni-
trile.[24]
Figure 4. CD spectra showing the B- to Z-DNA transition induced by the
1:1 adduct of Ni(NO3)2 and 4. Conditions: 1m m sodium cacodylate,
0.1m m polyd(GC).
ACHTREUNG
Supporting Information), but not the ligands 4 and 5 (Figure
S2, Supporting Information), induced Z-DNA with its char-
acteristic positive band at 269 nm and a negative band at
293 nm.[22] The transition from B- to Z-DNA was followed
at 255 nm (Figure 5). The midpoint of the transitions, ex-
pressed in units of metal ions per DNA phosphates,[23] were
determined to be 0.26(1) for 2, 0.28(1) for the 1:1 adduct of
Ni
complex 3 showed a comparable efficiency for Z-DNA in-
duction as Ni(NO3)2 which had a midpoint of the transition
at 0.48 equivalents.[12] The preformed dinuclear complex 2
and the 1:1 adduct of Ni(NO3)2 both induced the Z-DNA at
G
Additional amounts of complex 2 or the 1:1 adduct of Ni-
(NO3)2 and 4 to polyd(GC) already in the Z-form trans-
U
formed the DNA to yet another known left-handed confor-
mation, previously denoted as either Z’- or U-DNA (Fig-
ures 4 and 5). After addition of total 0.7 equivalents of 2, no
further change in the CD signal could be detected. The tran-
sition from Z- to Z’-DNA, with its characteristic isosbestic
half the nickel concentration compared with nickel nitrate
alone. A model to explain this behaviour would include that
Chem. Eur. J. 2007, 13, 6617 – 6622
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
6619

B. Spingler and P. M. Antoni
Conclusion
Two new ligands N,N,N’,N’-tetrakis-[2-(3,5-dimethylpyrazol-
1-yl)ethyl]-1,2-propylenediamime (4) and N-methyl-N,N-bis-
[2-(3,5-dimethylpyrazol-1-yl)ethyl]amine (5) were synthe-
sized on a multigram scale from commercially available
chemicals in two and three steps in an overall yield of 86
and 72%, respectively. The synthetic pathway via the N,N-
bis-(2-chloroethyl)ammonium salts proved to be not only
high-yielding but also perfectly reproducible. These two ad-
vantages, not present in the alternative synthetic path via
the tosylate route (Scheme 1), outweighed the handling of
the reactive intermediates.
Two novel complexes have been described herein: dinu-
clear N,N,N’,N’-tetrakis-[2-(3,5-dimethylpyrazol-1-yl)ethyl]-
1,3-propylenediamine-bis(nickel(II) dinitrate) (2) and its
G
mononuclear analogue, N-methyl-N,N-bis-[2-(3,5-dimethyl-
pyrazol-1-yl)ethyl]amine-nickel(II) dinitrate (3). Z-DNA
could be induced by either using the preformed dinuclear
complex 2 or the 1:1 adduct of Ni(NO3)2 at the half the
G
nickel concentration of either nickel nitrate or the mononu-
clear complex 3 alone. Determination of the proton and
nickel binding constants of 4 and 5 indicated that they are
rather weakly coordinating to nickel. From these results, it
is difficult to predict an active species in case of 4 for the
ternary system DNA–nickel–ligand 4. One possibility is that
complex 2 looses one of its two nickel cations to yield a 1:1
nickel/ligand 4 complex. The better efficiency of either 2 or
Figure 6. Postulated interaction between Z-DNA and the 1:1 adduct of
Ni2+ and 4.
the 1:1 adduct of Ni
(NO3)2 and 4 versus either Ni2+ alone or
G
complex 3 was explained by the formation of a macroche-
late of the nickel coordinating to N7 of guanosine and a hy-
drogen bridge between a DNA phosphate and the ternary
protonated amine of the former second binding side of
ligand 4 (Figure 6). Higher concentrations of either 2 or the
point at 268 nm and bathochromic shift of 5 nm of the posi-
tive signal at around 270 nm, had previously been observed
when concentrations of either cobalt hexammine or ethanol
were increased.[25–27] The formation of Z-DNA could be re-
versed by addition of a slight excess of EDTA (Figure S3,
Supporting Information).
1:1 adduct of Ni
A
rare Z’-DNA conformation.
To gain further insight in the behaviour of ligands 4 and
5, we studied their proton and nickel binding constants. Due
to the limited solubility of the ligands at submillimolar con-
centrations in pure aqueous electrolyte solutions, experi-
ments were performed in 40% isopropanol for 4 and 40%
methanol for 5 as organic cosolvents. The results of the titra-
tions are shown in Table 2. Both ligands are coordinating
the nickel rather weakly under the experimental conditions.
Experimental Section
General: All chemicals except polyd(GC) were purchased from Aldrich
or Fluka (Buchs, CH) and used without further purification. Poly d(GC)
was purchased from GE Healthcare (formerly Amersham Biosciences)
and used as received. The ligand syntheses were performed under a nitro-
gen atmosphere. The reactions were monitored by thin-layer chromatog-
raphy (TLC) on 0.25 mm Merck silica gel aluminium plates (60 F254) or
aluminium oxide pre-coated plastic sheets (alox N/UV254) using UV light
or Schlittler reagent[28] as a visualising agent. Column chromatography
was performed on silica gel (particle size 0.040–0.063 mm) or aluminium
oxide (basic, 0.05–0.15 mm, pH 9.5ꢁ0.5). Elemental analyses were per-
formed on a Leco CHNS-932 elemental analyser. Electrospray Ionisation
(ESI) mass spectra were recorded on a Merck Hitachi M-8000 spectrom-
eter. NMR spectra were recorded on a Varian Mercury 200 MHz or
Gemini 300 MHz spectrometer. The chemical shifts are relative to residu-
al solvent protons as reference.
Table 2. Proton and nickel binding constants of 4 and 5.
4
5
proton
binding
constants
b1 =10.56ꢁ0.02
b2 =16.85ꢁ0.03
b3 =20.87ꢁ0.04
b4 =24.0ꢁ0.1
b1 =4.5ꢁ0.1
b1 =6.10ꢁ0.02
b2 ꢂ8.1
nickel
binding
constants
b1 =2.8ꢁ0.2
Circular dichroism measurements were performed using a Jasco J-810
spectropolarimeter equipped with a Jasco PFD-4255 Peltier temperature
controller. The spectra were smoothed with the help of the program
ORIGIN. The calculation of the transition midpoints was done following
(product: [Ni(4)]2+
b2 =12ꢁ0.5
)
(product: [Ni(5)]2+
)
(product: )
[NiH(4)]3+
A
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Chem. Eur. J. 2007, 13, 6617 – 6622

Z-DNA Induction by Nickel Complexes
FULL PAPER
the Hill equation. y0 and y1 were set to the minimum and maximum
due to the high reactivity of this nitrogen mustard analogue. The crude
material was used without further purification.
spectrocopic responses of the observed transition.[29,30]
Crystallography: Crystallographic data were collected on a Stoe IPDS
diffractometer at 183(2) K using a graphite-monochromated MoKa radia-
tion (l=0.71073 Š). Suitable crystals were covered with Paratone N oil,
mounted on top of a glass fiber and immediately transferred to the dif-
fractometer. Eight thousand reflections distributed over the whole limit-
ing sphere were selected by the program SELECT and used for unit cell
parameter refinement with the program CELL.[31] Data were collected
for Lorentz and polarisation effects as well as for absorption (numerical).
Structures were solved with direct methods using SHELXS-97[32] or
SIR97[33] and were refined by full-matrix least-squares methods on F2
with SHELXL-97.[34] The program PLATON was used to check whether
higher symmetry was present.[35] Selected crystallographic data is shown
in Table 3.
WARNING: Analogues of N,N-di-(2-chloroethyl)amines are highly toxic
and powerful vesicants! Cleaning of all glassware exposed to every reac-
tion product was done with a 3% solution of Na2S2O3 in water.[20,36]
N,N,N’,N’-Tetrakis-[2-(3,5-dimethylpyrazol-1-yl)ethyl]-1,2-propylenedi-
amime (4): A solution of 3,5-dimethylpyrazole (6.06 g, 63 mmol) in dry
diethyleneglycol dimethylether (100 mL) was stirred with potassium
(2.5 g, 63 mmol) at 708C until all metal was dissolved.[37] Compound 7
(4.05 g, 12.6 mmol) was added to this solution at 258C and the resulting
solution was stirred at 1108C for 4 d. The solvent was removed on a
rotary evaporator, final traces of solvent were removed by adding water
to the oil and reducing the volume in vacuo. The compound was purified
by dissolving the crude material in dichloromethane, filtering through
Celite and washing with ethanol. Excess pyrazole was removed by subli-
mation at 808C and 0.1mbar. Further purification was achieved by chro-
matography on aluminiumoxide (98% dichloromethane/2% isopropa-
nol). Fractions with an Rf value of 0.09 were combined to yield the oily
product (3.71g, 6.6 mmol, 53%). 1H NMR (200 MHz, [D4]MeOH, 258C):
d=1.5 (brm, 2H, CH2CH2CH2), 2.12 (s, 12H, pyrazol-CH3), 2.21(s, 12H,
Table 3. Crystallographic data of 2·C5H10O·C2H3N and 3·H2O.
2·C5H10O·C2H3N
3·H2O
formula
Mr
C38H63N15Ni2O13
1055.45
C15H26N7NiO7
475.14
pyrazol-CH3), 2.38 (m, 4H, CH2CH2CH2), 2.74 (t, 3J=6.8 Hz, 8H,
3
NCH2CH2N
(s, 4H, CH
(C3(pyrazol)CH3), 13.03 (C5
(NCH2CH2N(pyrazol)), 53.84 (CH2CH2CH2), 55.45 (NCH2CH2N-
(pyrazol)), 105.99 (CH(pyrazol)), 141.42 (C3(pyrazol)), 148.66 (C5-
(pyrazol)); ESI-MS: m/z (%): 563 (100) [M+H]+; elemental analysis
(pyrazol)), 3.92 (t, J=6.6 Hz, 8H, CH2N
U
color/habit
crystal system
space group
a [Š]
b [Š]
c [Š]
blue plate
triclinic
P1
blue plate
monoclinic
P21
8.4648(4)
9.5669(6)
13.0389(6)
90
95.863(5)
90
1050.4(1)
2
AHCTREUNG
¯
U
ACHTREUNG
AHCTREUNG
8.5748(6)
15.570(1)
19.0251(12)
77.975(7)
83.622(8)
88.939(8)
2468.3(3)
2
U
A
ACHTREUNG
AHCTREUNG
calcd (%) for C31H50N10: C 66.16, H 8.95, N 24.89; found: C 65.95, H
8.94, N 24.59.
a [8]
b [8]
g [8]
N-Methyl-N,N-bis-(2-chloroethyl)-ammonium chloride (8): N-Methyldie-
thanolamine (5.4 g, 45 mmol) was added dropwise to a solution contain-
ing thionylchloride (11.6 mL, 100 mmol) and toluene (50 mL). The solu-
tion was heated under reflux for 3 h at 1008C. The solvent was removed
under vacuum. No analysis was made due to the reactivity of this nitro-
gen mustard analogue. The crude material was used without further pu-
rification. See WARNING mentioned above!!!
V [Š3]
Z
1calcd [gcmꢃ3
]
1.420
0.837
1.502
0.976
m [mmꢃ1
]
reflections measured
reflections observed [I > 2s(I)]
Flack parameter
13616
10595
–
3205
2631
0.07(2)
0.0461/0.1371
N-Methyl-N,N-bis-[2-(3,5-dimethylpyrazol-1-yl)ethyl]amine (5): A solu-
tion of 3,5-dimethylpyrazole (14.28 g, 150 mmol) in dry diethyleneglycol
dimethylether (200 mL) was stirred with potassium (6 g, 150 mmol) at
708C until the metal had dissolved.[37] To this solution, compound 8
(7.06 g, 45 mmol) was added in one portion. This solution was stirred at
1208C for 4 d. The solvent was removed under vacuum and the residue
was purified by chromatography on aluminium oxide (1.5% isopropanol/
98.5% dichloromethane). The fractions with an Rf value of 0.24 were
combined to yield the product (8.32 g, 30 mmol, 67%). 1H NMR
(200 MHz, [D4]MeOH, 258C): d=2.13 (s, 6H, CH3), 2.18 (s, 6H, CH3),
2.29 (s, 3H, NCH3), 2.72 (t, 3J=6.7 Hz, 4H, CH2), 3.94 (t, 3J=6.7 Hz,
4H, CH2), 5.77 ppm (s, 2H, CH); 13C NMR (50 MHz, [D4]MeOH, 258C):
R1/wR2 [I > 2s(I)]
0.0555/0.1639
CCDC-282007 and -282008 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.
Synthesis of mono- and dinucleating ligands
N,N,N’,N’-Tetrakis-(2-hydroxyethyl)-1,3-diamino-propane (6):[20] 1,3-Di-
bromopropane (80 mmol, 16.15 g) and N,N-diethanolamine (160 mmol,
16.61 g) were added to a round bottom flask containing a a solution of
K2CO3 (80 mmol, 11.06 g) in ethanol (150 mL). The mixture was stirred
and heated under reflux for 64 h. After cooling down to room tempera-
ture, chloroform (50 mL) was added and the solution was stirred for an-
other 12 h. The mixture was filtered and the solid precipitate was thor-
oughly washed with chloroform. The combined filtrates were concentrat-
ed in vacuo to give a colorless oil. The crude material was purified by
chromatography on silica gel (methanol with 10% concentrated ammo-
nia/dichloromethane 1:4). Fractions with an Rf value of 0.34 were com-
bined to yield the product (16.95 g, 67.7 mmol, 85%). 1H NMR
(200 MHz, [D4]MeOH, 258C): d=1.67 (br quint, 2H, CH2CH2CH2), 2.67
(m, 12H, NCH2), 3.62 ppm (t, 3J=5.8 Hz, 8H, CH2OH); 13C NMR
(50 MHz, [D4]MeOH, 258C): d=25.21(CH 2CH2CH2), 54.06
(CH2CH2CH2), 57.63 (CH2CH2OH), 60.73 ppm (CH2OH); ESI-MS: m/z
(%): 250 (100) [M+]; elemental analysis calcd (%) for C11H26N2O4·H2O:
C 49.23, H 10.52, N 10.44; found: C 49.38, H 10.87, N 10.15.
d=11.04 (C3
(pyrazol)), 47.65 (NCH2CH2N
(pyrazol)), 141.47 (C3(pyrazol)), 148.64 ppm (C5
C
G
U
ACHTREUNG
G
A
N,N,N’,N’-Tetrakis-[2-(3,5-dimethylpyrazol-1-yl)ethyl]-1,3-propylenedi-
amine-bis
ACHTREUNG
added to a solution containing Ni
AHCTREUNG
trimethyl orthoformate (27 mmol, 2.92 mL) in methanol (1mL). This
mixture was equilibrated versus diethyl ether by vapour diffusion.[18]
After one week, diethyl ether was removed and hexane was added into
the outer glass. This mixture was again equilibrated, the precipitated crys-
tals were dissolved in other solvents to grow single crystals. Blue crystals
were grown in an acetonitrile solution versus tetrahydrofuran, single crys-
tals suitable for X-ray analysis by slow vapour diffusion of a methanol so-
lution versus tetrahydropyran. ESI-MS: m/z (%): 292 (100) [li-
N,N,N’,N’-Tetrakis-(2-chloroethyl)-1,3-propylene-diammonium dichloride
(7): Compound 6 (12 mmol, 3 g) was dissolved in toluene (5 mL) and
added dropwise during 1h to a solution of thionyl chloride (54 mmol,
6.42 g) in toluene (30 mL). The mixture was stirred and heated under
reflux for 2 h. The solvent was removed in vacuo. No analysis was made
gand+2H]2+
(NO3)2+H2O]+;
,
583 (90) [ligand+H]+, 816 (15) [ligand+2Ni+
elemental
analysis
calcd
(%)
for
Chem. Eur. J. 2007, 13, 6617 – 6622
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
6621

B. Spingler and P. M. Antoni
C31H50N14O12Ni2·H2O·2THF: C 42.96, H 6.29, N 17.98; found: C 42.98, H
6.55, N 18.36.
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N-Methyl-N,N-bis-[2-(3,5-dimethylpyrazol-1-yl)ethyl]amine-nickel(II) ni-
trate (3): Compound 5 (100 mg, 0.36 mmol) was added to a solution of
Ni
(NO3)2·6H2O (105 mg, 0.36 mmol) and trimethyl orthoformate[18]
G
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[23] Using metal equivalents as units instead of complex equivalents
allows to directly compare the efficiency of the mono- and dinuclear
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(2.92 mL, 27 mmol) in methanol (1mL). Blue crystals were grown in an
acetonitrile solution versus tetrahydrofuran, single crystals suitable for X-
ray analysis by slow vapour diffusion of a methanol solution versus tetra-
hydropyran. ESI-MS: m/z (%): 276 (100) [ligand+H]+, 446 (27) [li-
gand+Ni+NO3+CH3OH+H2O]+; elemental analysis calcd (%) for
C15H25N7NiO6: C 39.33, H 5.50, N 21.40; found: C 39.70, H 5.09, N 21.28.
CD measurements: CD titrations of polyd(GC) with 2, 3, 1:1 adduct of 4
and Ni(NO3)2, 4, and 5 were performed as follows: A 0.1m m polyd(GC)
G
solution in 1m m sodium cacodylate buffer (pH 7) was titrated with vari-
ous aliquots of 1m m solutions of the metal complexes 2, 3, the 1:1 adduct
of Ni(NO3)2 and 4 as well as ligands 4 and 5 in the same buffer. The sam-
U
ples were warmed to 608C for 5 min and then cooled down to 258C for
the CD measurements. The CD spectra were smoothed by adjacent aver-
aging.
Binding constants determination: The proton and nickel binding con-
stants of 4 and 5 were determined as follows: The pH titrations were car-
ried out on a Metrohm potentiograph E 356 at 258C in 0.1m NaNO3 con-
taining 40% isopropanol for 4 and 40% methanol for 5. The titration
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rithmic values of the ionic product of water (pKW) in the presence of the
organic cosolvents were taken from the literature[40, 41] and corrected for
the ionic strength using Specific Interaction Theory (SIT).[42] The deter-
mination of metal binding constants was performed analogously in the
presence of two (in case of 4) or one (in case of 5) equivalents of nickel.
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[34] SHELXL97-2, Program for the Refinement of Crystal Structures,
G. M. Sheldrick, Version 97-2, University of Gçttingen (Germany),
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Acknowledgements
This work was supported by the Swiss National Science Foundation. We
thank the whole Alberto group, Dr. B. Knobloch and Professor R. K. O.
Sigel for valuable discussions. We further thank N. Agorastos for the
ESI-MS analyses and H. Spring for the elemental analyses. We express
our sincere thanks to the valuable suggestions made by an anonymous
referee.
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Received: May 26, 2006
Revised: March 14, 2007
Published online: May 22, 2007
6622
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Chem. Eur. J. 2007, 13, 6617 – 6622