Phosphodiester cleavage properties of copper(II) complexes of 1,4,7-triazacyclononane ligands bearing single alkyl guanidine pendants

Article abstract of DOI:10.1021/ic2019814

Three new metal-coordinating ligands, L¹·4HCl [1-(2-guanidinoethyl)-1,4,7-triazacyclononane tetrahydrochloride], L ²·4HCl [1-(3-guanidinopropyl)-1,4,7-triazacyclononane tetrahydrochloride], and L³·4HCl [1-(4-guanidinobutyl)-1,4,7- triazacyclononane tetrahydrochloride], have been prepared via the selective N-functionalization of 1,4,7-triazacyclononane (tacn) with ethylguanidine, propylguanidine, and butylguanidine pendants, respectively. Reaction of L ¹·4HCl with Cu(ClO₄)₂·6H ₂O in basic aqueous solution led to the crystallization of a monohydroxo-bridged binuclear copper(II) complex, [Cu₂L ¹₂(μ-OH)](ClO₄)₃·H ₂O (C1), while for L² and L³, mononuclear complexes of composition [Cu(L²H)Cl₂]Cl· (MeOH)_0.5· (H₂O)_0.5 (C2) and [Cu(L ³H)Cl₂]Cl· (DMF)_0.5· (H ₂O)_0.5 (C3) were crystallized from methanol and DMF solutions, respectively. X-ray crystallography revealed that in addition to a tacn ring from L¹ ligand, each copper(II) center in C1 is coordinated to a neutral guanidine pendant. In contrast, the guanidinium pendants in C2 and C3 are protonated and extend away from the Cu(II)-tacn units. Complex C1 features a single μ-hydroxo bridge between the two copper(II) centers, which mediates strong antiferromagnetic coupling between the metal centers. Complexes C2 and C3 cleave two model phosphodiesters, bis(p-nitrophenyl)phosphate (BNPP) and 2-hydroxypropyl-p-nitrophenylphosphate (HPNPP), more rapidly than C1, which displays similar reactivity to [Cu(tacn)(OH₂)₂] ²⁺. All three complexes cleave supercoiled plasmid DNA (pBR 322) at significantly faster rates than the corresponding bis(alkylguanidine) complexes and [Cu(tacn)(OH₂)₂]²⁺. The high DNA cleavage rate for C1 {k_obs = 1.30 (±0.01) × 10^-4 s^-1 vs 1.23 (±0.37) × 10^-5 s^-1 for [Cu(tacn)(OH₂)₂]²⁺ and 1.58 (±0.05) × 10^-5 s^-1 for the corresponding bis(ethylguanidine) analogue} indicates that the coordinated guanidine group in C1 may be displaced to allow for substrate binding/activation. Comparison of the phosphate ester cleavage properties of complexes C1-C3 with those of related complexes suggests some degree of cooperativity between the Cu(II) centers and the guanidinium groups.

Full text of DOI:10.1021/ic2019814

Article
pubs.acs.org/IC
Phosphodiester Cleavage Properties of Copper(II) Complexes of
,4,7-Triazacyclononane Ligands Bearing Single Alkyl Guanidine
Pendants
1
†
‡
†
†
†
†
Linda Tjioe, Tanmaya Joshi, Craig M. Forsyth, Boujemaa Moubaraki, Keith S. Murray,
,§
,∥
,†
Joel
̈
Brugger, Bim Graham,* and Leone Spiccia*
†
School of Chemistry, Monash University, Vic 3800, Australia
‡
School of Earth and Environmental Sciences, Centre of Tectonics, Resources and Exploration (TRaX), The University of Adelaide,
North Terrace, SA 5005, Australia
§
Department of Mineralogy, South Australian Museum, Adelaide, SA 5000, Australia
∥
Medicinal Chemistry and Drug Action, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Vic 3052,
Australia
*
S Supporting Information
1
ABSTRACT: Three new metal-coordinating ligands, L ·4HCl
1-(2-guanidinoethyl)-1,4,7-triazacyclononane tetrahydro-
[
2
chloride], L ·4HCl [1-(3-guanidinopropyl)-1,4,7-triazacyclo-
nonane tetrahydrochloride], and L ·4HCl [1-(4-guanidinobu-
3
tyl)-1,4,7-triazacyclononane tetrahydrochloride], have been
prepared via the selective N-functionalization of 1,4,7-
triazacyclononane (tacn) with ethylguanidine, propylguani-
dine, and butylguanidine pendants, respectively. Reaction of
1
L ·4HCl with Cu(ClO ) ·6H O in basic aqueous solution led
4
2
2
to the crystallization of a monohydroxo-bridged binuclear
copper(II) complex, [Cu L (μ-OH)](ClO ) ·H O (C1),
while for L and L , mononuclear complexes of composition [Cu(L H)Cl ]Cl·(MeOH) ·(H O) (C2) and [Cu(L H)Cl ]-
Cl·(DMF) ·(H O) (C3) were crystallized from methanol and DMF solutions, respectively. X-ray crystallography revealed
that in addition to a tacn ring from L ligand, each copper(II) center in C1 is coordinated to a neutral guanidine pendant. In
contrast, the guanidinium pendants in C2 and C3 are protonated and extend away from the Cu(II)−tacn units. Complex C1
features a single μ-hydroxo bridge between the two copper(II) centers, which mediates strong antiferromagnetic coupling
between the metal centers. Complexes C2 and C3 cleave two model phosphodiesters, bis(p-nitrophenyl)phosphate (BNPP) and
1
2
2
4
3
2
2
3
2
3
2
0.5
2
0.5
2
0.5
2
0.5
1
2
-hydroxypropyl-p-nitrophenylphosphate (HPNPP), more rapidly than C1, which displays similar reactivity to [Cu(tacn)-
2+
(
OH ) ] . All three complexes cleave supercoiled plasmid DNA (pBR 322) at significantly faster rates than the corresponding
bis(alkylguanidine) complexes and [Cu(tacn)(OH ) ] . The high DNA cleavage rate for C1 {k = 1.30 (±0.01) × 10
2 2
2
+
−4 −1
s
vs
2
2
obs
−5
−1
2+
−5 −1
1
.23 (±0.37) × 10
s
for [Cu(tacn)(OH ) ] and 1.58 (±0.05) × 10
s
for the corresponding bis(ethylguanidine)
2
2
analogue} indicates that the coordinated guanidine group in C1 may be displaced to allow for substrate binding/activation.
Comparison of the phosphate ester cleavage properties of complexes C1−C3 with those of related complexes suggests some
degree of cooperativity between the Cu(II) centers and the guanidinium groups.
INTRODUCTION
restriction enzymes in molecular biology research and as
nucleic acid-targeting therapeutics.
In the quest to generate cleavage agents with improved
reactivity, structural elaboration of simple metal chelates to
■
8
−28
A prominent area of research in coordination chemistry in
recent decades has been the development of low molecular
weight metal complexes that mimic the function of (ribo)-
include auxiliary groups that complement the hydrolytic action
1
−7
nuclease and phosphatase metallo-enzymes.
These studies
26,29−42
of the metal ion(s) has been undertaken.
Inspiration for
have sought to improve our knowledge of how these enzymes
work, as well as lend understanding to basic metal ion reactivity.
The development of complexes as “artificial nucleases” has also
been stimulated by realization that hydrolytically active metal
complexes (and their conjugates with various targeting agents)
may potentially find utility as robust, versatile replacements for
these designs comes from the enzymes themselves, which, in
addition to metal ions, contain amino acid residues at their
active sites that assist catalysis by activating the substrate,
Received: September 9, 2011
Published: December 22, 2011
©
2011 American Chemical Society
939
dx.doi.org/10.1021/ic2019814 | Inorg. Chem. 2012, 51, 939−953

Inorganic Chemistry
Article
promoting protonation/deprotonation processes, and stabiliz-
structures of the copper(II) complexes and the magnetic
properties of the hydroxo-bridged complex formed by L , we
4
3,44
1
ing transition states.
A good example is provided by the
well-studied enzyme, alkaline phosphatase (AP), which uses
two zinc centers, in conjunction with serine and arginine
residues, to promote the rapid cleavage of phosphate
have investigated the kinetics of cleavage of three phospho-
diester-containing compounds, namely, BNPP, HPNPP, and
pBR 322 plasmid DNA.
4
5
monoesters. The positively charged guanidinium group
present in arginine is postulated to assist with substrate
activation and transition state stabilization, while the serine
residue provides the attacking nucleophile, leading to the
formation of a phosphoseryl intermediate during the AP
catalytic cycle.
EXPERIMENTAL SECTION
Materials and Chemicals. Chemicals and solvents were of
reagent or analytical grade and were used as received unless otherwise
■
indicated. Distilled H O and high-performance liquid chromatography
2
grade chloroform were used throughout. Tetrahydrofuran (THF) was
dried over 4 Å molecular sieves and then freshly distilled from Na/
benzophenone prior to use. 1,4-bis(tert-Butoxycarbonyl)-1,4,7-triaza-
Complexes of ligands derived from the facially coordinating
macrocycle, 1,4,7-triazacyclononane (tacn), have featured
prominently in studies aimed at mimicking metallo-nuclease
and -phosphatase function. Pioneering work by Burstyn and co-
workers demonstrated that the copper(II)−tacn complex is
capable of promoting the cleavage-activated phosphate esters,
5
1
cyclononane and sodium 2-hydroxypropyl-p-nitrophenylphosphate
5
2,53
(
NaHPNPP)
were synthesized according to literature procedures.
The pBR 322 plasmid DNA was purchased from Promega
Corporation. Milli-Q water used for DNA cleavage was sterilized by
autoclaving, and all reaction solutions were prepared according to
standard sterile techniques. Deoxygenated water was prepared by
boiling distilled water under nitrogen for 4 h and cooling while
bubbling with nitrogen gas. High-purity nitrogen gas was used directly
from a reticulated system.
1
DNA, RNA, and peptides. Building on these seminal findings,
a number of research groups, including our own, have shown
that N-functionalization of tacn with various groups can
2
8,46−48
enhance cleavage rates.
Most recently, we reported
two series of tacn derivatives with appended guanidinium
pendant groups and their copper(II) complexes as nuclease
Instrumentation and Methods. Infrared spectra were recorded
as KBr disks using a Bruker Equinox FTIR spectrometer at 4.0 cm−
resolution, fitted with an ATR platform. Microanalyses were
performed by Campbell Microanalytical Service (Otago, New
1
4
9,50
mimics.
Some evidence for cooperativity between the
copper(II) centers and the guanidine pendants was obtained
for selected complex−substrate combinations, but the enhance-
ments in reaction rates were modest relative to the non-
1
13
Zealand). H NMR and C NMR spectra were recorded at 25 °C
in D O or CDCl (as listed) on a Bruker AC200, AM300, or DX400
2
3
spectrometer. Chemical shifts were recorded on the δ scale in parts per
million (ppm) and were calibrated using either tetramethylsilane
(TMS) or signals due to the residual protons of deuterated solvents.
2
+
functionalized complex [Cu(tacn)(OH ) ] . Most notably, a
2
2
complex incorporating a pair of propyl-linked guanidinium
2+
1
groups was significantly more active than [Cu(tacn)(OH ) ]
Abbreviations used to describe the resonances for H NMR spectra are
2
2
in accelerating the cleavage of bis(p-nitrophenyl)phosphate
as follows: s (singlet), d (doublet), t (triplet), q (quartet), m
(
multiplet), and br s (broad singlet). Low-resolution electrospray
(
(
BNPP) and 2-hydroxypropyl-p-nitrophenylphosphate
HPNPP) but only marginally more active in hydrolyzing
ionization mass spectra (ESI-MS) were measured with a Micromass
Platform II Quadrupole Mass Spectrometer fitted with an electrospray
source. The capillary voltage was set at 3.5 eV, and the cone voltage at
plasmid DNA, possibly due to unfavorable steric interactions
49
with the double-helix structure. On the other hand, a series of
complexes with single xylyl guanidinium pendants exhibited
much higher rates of nuclease cleavage than [Cu(tacn)-
3
5 V. Thin-layer chromatography (TLC) was performed using silica
gel 60 F-254 (Merck) plates with detection of species present by UV
irradiation or KMnO oxidation. UV−vis-NIR spectra were recorded
4
2+
(
OH ) ] but were on par in terms of their BNPP and
in 1 cm quartz cuvettes using Varian Cary Bio 300 or 5G
spectrophotometers. Agarose gel electrophoresis of plasmid DNA
cleavage products was performed using a Biorad Mini-Protean 3
Electrophoresis Module. Bands were visualized by UV light irradiation,
fluorescence imaged using an AlphaImager, and photographed with a
CCD camera. The gel photographs were analyzed with the aid of the
program ImageQuaNT version 4.1.
2
2
50
HPNPP reactivity. This was interpreted as evidence that the
more rigidly linked guanidinium groups in these complexes do
not interact with the phosphodiester group undergoing
cleavage but were able to enhance DNA binding by forming
favorable interactions with neighboring phosphodiester groups
within the sugar−phosphate backbone. As part of our
continued efforts to develop more efficient synthetic nucleases
through the combined use of metal ions and auxiliary functional
groups, we now report the synthesis, characterization, and
cleavage properties of the copper(II) complexes of three tacn
Caution: Although no problems were encountered in this work,
perchlorate salts are potentially explosive. They should be prepared in
small quantities and handled with care.
Syntheses. 1-(2-Phthalimidoethyl)-4,7-bis(tert-butoxycarbon-
yl)-1,4,7-triazacyclononane (1). A solution of 2-bromoethylphthali-
1
mide (0.370 g, 1.40 mmol) in CH CN (50 mL) was added dropwise
ligands featuring single alkyl guanidine pendants (Figure 1, L −
3
to a mixture of 1,4-bis(tert-butoxycarbonyl)-1,4,7-triazacyclononane
(
0
0.470 g, 1.40 mmol), K CO (0.470 g, 3.40 mmol), and KI (0.120 g,
.600 mmol) in CH CN (50 mL), and the resulting mixture was
3
2 3
stirred for 1 h at room temperature and then refluxed for 3 days. After
it was cooled to room temperature, the inorganic salts were filtered off,
and the solvent was removed under reduced pressure to yield 1 as a
1
2
3
1
Figure 1. Ligands, L , L , and L , prepared in this study as
yellow oil. Yield: 0.47 g (65%). H NMR (300 MHz, CDCl ): δ 1.34
3
t
tetrahydrochloride salts.
(s, 18H, Bu CH ), 2.74 (m, 6H, ethyl CH and tacn CH ), 3.15−3.37
m, 8H, tacn CH ), 3.65 (m, 2H, ethyl CH ), 7.65 (m, 2H, aromatic
CH), 7.85 (m, 2H, aromatic CH). C NMR (75 MHz, CDCl
3
2
2
(
2
2
L3). One of our goals was to maintain the enhanced reactivity
of the bis(alkylguanidinium) complexes toward simple
phosphodiester compounds, while reducing steric bulk to
improve access of the Cu(II) center to the sugar−phosphate
backbone of DNA with the expectation that nuclease activity
could be enhanced. In addition to determining the crystal
13
): δ
3
t
2
(
8.2 ( Bu CH ), 35.7, 39.7 (ethyl CH ), 47.8−53.7 (tacn CH ), 79.2
3
2
2
t
Bu quaternary C), 123.1, 131.8, 133.8 (aromatic CH), 155.3 (C
−
1
O), 168.0 (CO). IR (neat), υ (cm ): 3473w (υ ), 3058w
N−H
), 1682s (υ
(
1
υ
), 2974s (υ ), 1773s (υ
), 1456s,
C−H(aromatic)
C−H
CO
CO
393s, 1249s (υC−O), 1152s, 1018m, 986m, 868m, 773m, 720s, 620m.
+
+
ESI-MS (m/z): 503.3 (90%) [M + H] , 525.2 (10%) [M + Na] .
9
40
dx.doi.org/10.1021/ic2019814 | Inorg. Chem. 2012, 51, 939−953

Inorganic Chemistry
Article
−
1
1
-(3-Phthalimidopropyl)-4,7-bis(tert-butoxycarbonyl)-1,4,7-tria-
(cm ): 3371w (υN−H), 2975s (υC−H), 2932s (υC−H), 1692s (υ
),
CO
zacyclononane (2). Compound 2 was prepared in an identical manner
to 1 using 3-bromopropylphthalimide (0.450 g, 1.70 mmol), 1,4-
bis(tert-butoxycarbonyl)-1,4,7-triazacyclononane (0.550 g, 1.70 mmol),
K CO (0.470 g, 3.40 mmol), and KI (0.120 g, 0.600 mmol) in
1463s, 1416s, 1366s, 1249s (υC−O), 1155s, 989m, 860m, 772m. ESI-
MS (m/z): 401.4 (100%) [M + H] .
1-{2-[bis(tert-Butoxycarbonyl)guanidino]ethyl}-4,7-bis(tert-bu-
toxycarbonyl)-1,4,7-triazacyclononane (7). To a stirred solution of 4
+
2
3
CH CN (50 mL). The crude product was purified by column
(0.490 g, 1.30 mmol) in THF (20 mL) was added N,N′-Boc -1H-
3
2
chromatography (Merck Silica Gel 60, eluent: CH Cl /diethyl ether,
pyrazole-1-carboxamidine (0.410 g, 1.30 mmol) dissolved in THF (20
mL). The resulting solution was stirred at room temperature for 2
days. The solvent was then removed under reduced pressure, and the
residue was dissolved in CH Cl (50 mL). After it was washed with 0.1
2
2
7
/3 v/v), with the desired fraction having an R = 0.71. Yield: 0.55 g
f
1
t
(
63%). H NMR (300 MHz, CDCl ): δ 1.43 (s, 18H, Bu CH ), 1.80
3
3
(
m, 2H, ethyl CH ), 2.54−2.67 (m, 6H, ethyl CH and tacn ring
2
2
2
2
CH ), 3.29 (m, 4H, tacn ring CH ), 3.45 (m, 4H, tacn ring CH ), 3.75
M NaOH (3 × 30 mL), the organic fraction was dried with Na SO ,
2
2
2
2 4
(
m, 2H, ethyl CH ), 7.73 (m, 2H, aromatic CH), 7.85 (m, 2H,
and the solvent was removed under reduced pressure to yield the
crude product. Purification by column chromatography (Merck Silica
2
13
aromatic CH). C NMR (75 MHz, CDCl ): δ 27.1 (propyl CH ),
2
(
1
3
2
t
8.5 ( Bu CH ), 36.3 (propyl CH ), 49.3, 49.8, 50.2, 50.7, 53.8, 54.5
tacn CH ), 51.4 (propyl CH ), 79.4 ( Bu quaternary C), 123.1, 132.2,
Gel 60, eluent: 2% MeOH/CHCl ) yielded the pure product as a pale
3
2
3
t
1
yellow oil (R = 0.30). Yield: 0.54 g (67%). H NMR (300 MHz,
2
2
f
t
t
33.8 (aromatic CH), 155.7 (CO), 168.4 (CO). IR (neat), υ
CDCl ): δ 1.45 (s, 27H, Bu CH ), 1.49 (s, 9H, Bu CH ), 2.74 (m,
3
3
3
−1
(
cm ): 3469w (υ ), 3058w (υ
), 2973s (υ ), 1770s
6H, tacn CH and ethyl CH ), 3.30 (m, 4H, tacn CH ), 3.51 (m, 6H,
2 2 2
N−H
C−H(aromatic)
C−H
1
3
(υ
), 1714s (υ
), 1455s, 1393s, 1250s (υC−O), 1150s, 1037s,
tacn CH and ethyl CH ), 8.54 (t br, 1H, NH). C NMR (75 MHz,
CO
CO
2 2
t
t
t
9
H] .
90m, 860m, 773m, 720s, 620m. ESI-MS (m/z): 517.2 (100%) [M +
CDCl ): δ 28.0 ( Bu CH ), 28.2 ( Bu CH ), 28.5 ( Bu CH ), 39.4
3 3 3 3
+
(ethyl CH ), 49.6, 50.6, 54.5, 55.2 (tacn CH ), 56.2 (ethyl CH ), 79.0,
2
2
2
t
1
-(4-Phthalimidobutyl)-4,7-bis(tert-butoxycarbonyl)-1,4,7-triaza-
79.3, 82.9 ( Bu quaternary C), 126.0 (CN), 155.5, 156.0, 163.5
1
−1
cyclononane (3). The synthesis was as for 1. Yield: 65%. H NMR
(
1
4
CH ), 7.70 (m, 2H, aromatic CH), 7.85 (m, 2H, aromatic CH).
NMR (75 MHz, CDCl ): δ 26.3 (butyl CH ), 28.5 ( Bu CH ), 30.5,
(CO). IR (neat), υ (cm ): 3334s (υ ), 3131 m (υ ), 2973s
N−H
), 1634s (υ
N−H
), 1557s (υ
t
300 MHz, CDCl ): δ 1.45 (s, 20H, Bu CH and butyl CH ), 1.62−
(υ ), 1732s (υ
), 1662s (υ
),
CN
3
3
2
C−H
CO
CO
CO
.85 (m, 4H, butyl CH ), 2.54−2.63 (m, 4H, tacn ring CH ), 3.23 (m,
H, tacn ring CH ), 3.46 (m, 4H, tacn ring CH ), 3.73 (m, 2H, butyl
1455s, 1249s (υC−O), 1156s, 1056s, 988s, 918s, 859s. ESI-MS (m/z):
2
2
+
2
2
615.3 (100%) [M + H] .
13
C
1-{3-[bis(tert-Butoxycarbonyl)guanidino]propyl}-4,7-bis(tert-bu-
toxycarbonyl)-1,4,7-triazacyclononane (8). The synthesis was as for
2
t
3
2
3
3
7.9, (butyl CH ), 49.5, 49.7, 50.5, 50.9, 53.9, 54.0 (tacn CH ), 56.1
7, with purification by column chromatography (R
f
= 0.35). Yield:
): δ 1.47 (s, 27H, Bu CH ), 1.50 (s,
), 2.56
), 3.28 (m, 4H, tacn
), 8.33 (t br, 1H, NH).
C NMR (75 MHz, CDCl ): δ 27.6 (propyl CH ), 27.9, 28.2, 28.4
2
2
t
1
t
(
butyl CH ), 79.3 ( Bu quaternary C), 123.1, 132.2, 133.8 (aromatic
72%. H NMR (300 MHz, CDCl
3
3
2
−1
t
CH), 155.7 (CO), 168.4 (CO). IR (neat), υ (cm ): 3470w
9H, Bu CH
3
), 1.62 (s br, 1H, NH), 1.73 (m, 2H, propyl CH
), 2.65 (m, 4H, tacn CH
), 3.46 (m, 6H, tacn CH and propyl CH
2
(
(
υ
υ
), 3058w (υ
), 1714s (υ
), 2975s (υ ), 2935s, 2865s, 1771s
), 1463s, 1398s, 1250s (υC−O), 1171s, 1045m,
(m, 2H, propyl CH
2
2
N−H
CO
C−H(aromatic)
C−H
CH
CO
2
2
2
1
3
990m, 861m, 774m, 734s, 647m. ESI-MS (m/z): 531.3 (100%) [M +
3
2
+
t
H] .
-(2-Aminoethyl)-4,7-bis(tert-butoxycarbonyl)-1,4,7-triazacyclo-
( Bu CH ), 38.8 (propyl CH ), 49.3, 49.5, 50.4, 51.0, 53.8, 53.9 (tacn
3
2
t
1
CH ), 54.3 (propyl CH ), 78.8, 79.2, 82.8 ( Bu quaternary C), 153.1
2
2
−1
nonane (4). Hydrazine monohydrate (0.530 g, 10.0 mmol) was added
to a solution of 1 (0.750 g, 1.50 mmol) in EtOH (50 mL), and the
solution was heated at 50 °C for 4 h. After it was cooled to room
temperature, the white precipitate that formed was removed by
filtration, and the filtrate was evaporated to dryness to yield an oily
residue, which was dissolved in CH Cl (50 mL). After it was washed
(CN), 155.4, 156.0, 163.5 (CO). IR (neat), υ (cm ): 3334s
),
N−H N−H C−H C−H
(υ ), 3138m (υ ), 2921s (υ ), 2950s (υ ), 1732s (υ
CO
1662s (υ
), 1614s (υ
), 1574s (υ
), 1470s, 1455s, 1249s
CO
CO
CN
(υC−O), 1047s, 991s, 918s, 858s, 731s. ESI-MS (m/z): 629.1 (90%)
+
+
[M + H] , 651.1 (10%) [M + Na] .
2
2
1-{4-[bis(tert-Butoxycarbonyl)guanidino]butyl}-4,7-bis(tert-bu-
toxycarbonyl)-1,4,7-triazacyclononane (9). The synthesis was as for
with 1 M NaOH (2 × 50 mL) and dried with Na SO , the solvent was
2
4
removed under vacuum to yield 4 as a yellow oil. Yield: 0.45 g (80%).
7, with purification by column chromatography (R = 0.32). Yield:
f
1
t
1
t
H NMR (300 MHz, CDCl ): δ 1.46 (s, 18H, Bu CH ), 1.62 (s br,
71%. H NMR (300 MHz, CDCl ): δ 1.36 (s, 27H, Bu CH ), 1.39 (s,
3
3
3
3
t
2
H, NH ), 2.63 (m, 8H, ethyl CH and tacn CH ), 3.25−3.47 (m, 8H,
11H, Bu CH
butyl CH
(m, 6H, tacn CH
MHz, CDCl ): δ 24.9, 26.6 (butyl CH
40.6 (butyl CH ), 49.2, 49.5, 50.4, 51.0, 53.7, 54.0 (tacn CH
(butyl CH
3
and butyl CH
2
), 1.55 (m, 2H, butyl CH
2
), 2.41 (m, 2H,
), 3.16 (m, 4H, tacn CH ), 3.36
2 2
2
2
2
13
t
tacn CH ). C NMR (75 MHz, CDCl ): δ 28.5 ( Bu CH ), 40.1,
2
), 2.52 (m, 4H, tacn CH
2
3
3
1
3
(
ethyl CH ), 48.7, 49.8, 50.8, 51.2, 53.9, 54.5 (tacn CH ), 51.3 (ethyl
2
2
and butyl CH ), 8.21 (t br, 1H, NH). C NMR (75
2
2
2
t
−1
t
CH ), 79.6 ( Bu quaternary C), 155.6 (CO). IR (neat), υ (cm ):
3
2
), 27.8, 28.1, 28.3 ( Bu CH
),
3
), 56.1
3
1
369w (υ ), 2974s (υ ), 2933s (υ ), 1694s (υ
), 1463s,
2
2
N−H
C−H
C−H
CO
t
416s, 1366s, 1249s (υC−O), 1166s, 1100m, 990m, 860m, 773m. ESI-
2
), 78.9, 79.1, 82.7 ( Bu quaternary C), 153.0 (CN),
+
−1
MS (m/z): 373.3 (100%) [M + H] .
155.3, 155.9, 163.4 (CO). IR (neat), υ (cm ): 3332s (υN−H),
1
-(3-Aminopropyl)-4,7-bis(tert-butoxycarbonyl)-1,4,7-triazacy-
3139m (υN−H), 2977s (υC−H), 2933s (υC−H), 1695s (υCO), 1681s
1
clononane (5). The synthesis was as for 4. Yield: 73%. H NMR (300
(υ
), 1634s (υ
), 1555s (υ
), 1455s, 1252s (υC−O), 1157s,
CO
CO
CN
t
+
MHz, CDCl ): δ 1.31 (s br, 2H, NH ), 1.48 (s, 18H, Bu CH ), 1.52
1051s, 990s, 919s, 858s. ESI-MS (m/z): 643.2 (90%) [M + H] , 665.2
3
2
3
+
(
m, 2H, propyl CH ), 2.49 (m, 2H, propyl CH ), 2.58 (m, 4H, tacn
(10%) [M + Na] .
2
2
CH ), 2.68 (m, 2H, propyl CH ), 3.22 (m, 4H, tacn CH ), 3.41 (m,
1-(2-Guanidinoethyl)-1,4,7-triazacyclononane Tetrahydrochlor-
2
2
2
13
t
1
4
H, tacn CH2). C NMR (75 MHz, CDCl ): δ 28.4 ( Bu CH ), 31.7,
ide (L ·4HCl). Compound 7 (0.470 g, 0.770 mmol) was dissolved in
3
3
4
0.2 (propyl CH ) 49.3, 49.6, 50.4, 50.8, 53.6, 54.4 (tacn CH ), 51.4
a 1:1 (v/v) mixture of TFA and CH Cl (10 mL), and the solution was
2 2
2
2
t
(
(
1
8
propyl CH ), 79.3 ( Bu quaternary C), 155.5 (CO). IR (neat), υ
stirred at room temperature overnight. The solvent was then removed
under reduced pressure, and the resulting hygroscopic brown oil was
dissolved in a mixture of EtOH (5 mL) and concentrated HCl (2 mL).
The addition of diethyl ether (5 mL) produced a white precipitate,
which was collected by filtration, dissolved in a small volume of water,
and then freeze-dried to yield the product as a white solid. Yield: 0.12
g (71%). Microanalysis: calcd for C H N Cl : C, 27.3; H, 8.0; N,
2
−1
cm ): 3371w (υ ), 2975s (υ ), 2933s (υ ), 2861s (υ ),
N−H
C−H
C−H
C−H
690s (υ
), 1463s, 1414s, 1366s, 1249s (υC−O), 1174s, 1098s, 990s,
CO
+
60m, 773m, 620m. ESI-MS (m/z): 387.2 (100%) [M + H] .
1
-(4-Aminobutyl)-4,7-bis(tert-butoxycarbonyl)-1,4,7-triazacyclo-
1
nonane (6). The synthesis was as for 4. Yield: 81%. H NMR (300
t
MHz, CDCl ): δ 1.31 (s br, 2H, NH ), 1.45 (s, 22H, Bu CH and
3
2
3
9
31
6
4
1
butyl CH ), 2.47 (m, 2H, butyl CH ), 2.67 (m, 6H, tacn CH and
21.3; Cl, 34.5%. Found: C, 27.3; H, 7.6; N, 21.2; Cl, 35.8%. H NMR
2
2
2
13
butyl CH ), 3.24 (m, 4H, tacn CH ), 3.50 (m, 4H, tacn CH ).
C
(300 MHz, D O): δ 3.06 (t, 2H, ethyl CH ), 3.15 (m, 4H, tacn CH ),
2
2
2
2
2
2
t
NMR (75 MHz, CDCl ): δ 25.3 (butyl CH ), 28.5 ( Bu CH ), 31.5,
3.44 (m, 4H, tacn CH ), 3.51 (t, 2H, J = 7.2 Hz, ethyl CH ), 3.75 (s,
2 2
3
2
3
4
2.2 (butyl CH ), 49.6, 49.8, 50.6, 51.1, 53.9, 54.1 (tacn CH ), 56.6
4H, tacn CH2). 13C NMR (75 MHz, D O): δ 37.8 (ethyl CH ), 42.6,
2
2
2
2
t
(
butyl CH ), 79.4 ( Bu quaternary C), 155.7 (CO). IR (neat), υ
44.3, 47.9 (tacn CH ), 52.8 (ethyl CH ), 157.2 (CN). IR (KBr
2
2
2
9
41
dx.doi.org/10.1021/ic2019814 | Inorg. Chem. 2012, 51, 939−953

Inorganic Chemistry
Article
−
1
disk), υ (cm ): 3404s (υN−H), 2977s (υC−H), 2960s (υC−H), 1618s
), 1450m, 1230w, 1178w, 940w. ESI-MS (m/z): 108.2 (90%)
[
calculated spectra based on the model, the spectra for the individual
complexes, and formation constants for all of the species included in
the model. For the present study, activity coefficients were fixed to
unity (fixed ionic strength).
(υ
CN
2+
+
M + 2H] , 215.2 (10%) [M + H] .
1
-(3-Guanidinopropyl)-1,4,7-triazacyclononane Tetrahydro-
chloride (L ·4HCl). The synthesis was as for L ·4HCl. Yield: 78%.
Microanalysis: calcd for C H N Cl : C, 30.6; H, 7.8; N, 21.1; Cl,
3.2%. Found: C, 30.6; H, 7.6; N, 21.4; Cl, 33.8%. H NMR (300
MHz, D O): δ 1.94 (m, 2H, propyl CH ), 2.90 (m, 2H, propyl CH ),
2
1
Cleavage of Model Phosphate Esters. BNPP. These experi-
5
7,58
10
32
6
4
ments were conducted using established procedures.
Briefly, the
1
3
cleavage of BNPP by the Cu(II) complexes was measured at pH 7.0
2
2
2
(HEPES) and 9.0 (CHES) at T = 50 °C, by following the formation of
3
4
2
.11 (m, 4H, tacn CH ), 3.29 (t, 2H, J = 7.2 Hz, propyl CH ), 3.44 (m,
−1
−1
2
2
p-nitrophenoxide ion (λmax = 400 nm, εmax = 18700 M cm ) in
13
H, tacn CH ), 3.69 (s, 4H, tacn CH ). C NMR (75 MHz, D O): δ
2
2
2
solutions containing 0.1 mM BNPP, 2 mM Cu(II) complex, and 0.15
3.7, 39.5 (propyl CH ), 42.3, 43.9, 47.6 (tacn CH ), 52.2 (propyl
2
2
M NaClO . Absorbance measurements were commenced 2 min after
4
−1
CH ), 157.1 (CN). IR (KBr disk), υ (cm ): 3412s (υN−H), 2954s
2
mixing and were continued for 8000 min, with a reading taken every 5
min. As the complex was in large excess as compared to BNPP, the
time dependence of the appearance of NP (and cleavage of BNPP)
was modeled as a first-order process, and observed rate constants
(
(
υ
), 1610s (υ
), 1436m, 1172w, 1018w. ESI-MS (m/z): 115.2
C−H
CN
2+
+
90%) [M + 2H] , 229.2 (10%) [M + H] .
1
-(4-Guanidinobutyl)-1,4,7-triazacyclononane Tetrahydrochlor-
3
1
ide (L ·4HCl). The synthesis was as for L ·4HCl. Yield: 72%.
(
k
) were determined by fitting the data to the equation, Abs = A +
obs
−k
Microanalysis: calcd for C H N Cl : C, 30.3; H, 7.7; N, 19.0; Cl,
4.3%. Found: C, 30.5; H, 8.1; N, 19.4; Cl, 32.8%. H NMR (300
MHz, D O): δ 1.68 (m, 4H, butyl CH ), 2.94 (m, butyl CH ), 3.24
t
11
35
6
4
obs
Be , where A and B are constants.
1
3
HPNPP. These experiments were carried out in a similar manner to
the BNPP experiments. The cleavage of HPNPP by the Cu(II)
complexes was measured at pH 6.0 (MES), 7.0 (HEPES), and 9.0
2
2
2
(
m, 6H, tacn CH and butyl CH ), 3.41 (m, 4H, tacn CH ), 3.60 (s,
2
2
2
4
H, tacn CH2). 13C NMR (75 MHz, D O): δ 21.5, 26.0, 41.2 (butyl
2
(CHES) at T = 25 °C by following the release of the p-nitrophenoxide
CH ), 42.2, 43.2, 48.0 (tacn CH ), 55.2 (butyl CH ), 157.1 (CN).
2
2
2
ion in solutions containing 0.1 mM HPNPP, 2 mM Cu(II) complex,
−1
IR (KBr disk), υ (cm ): 3378s (υ ), 2977s (υ ), 2788s (υ ),
N−H
C−H
C−H
and 0.15 M NaClO , and k was determined as for the BNPP
4
obs
1
(
608s (υ
), 1503s, 1256w, 1160w, 968w. ESI-MS (m/z): 243.3
100%) [M + H] .
CN
+
cleavage studies.
DNA Cleavage Experiments. These experiments also followed
1
2
[
Cu L (μ−OH)] (ClO ) ·H O (C1). To a stirred aqueous solution (4
mL) of L ·4HCl (0.097 g, 0.250 mmol) was added Cu(ClO ) ·6H O
0.120 g, 0.290 mmol) dissolved in water (4 mL). The pH of solution
was adjusted to 9 with the addition of 1 M NaOH, resulting in a color
change to a darker blue and the precipitation of a small amount of
Cu(OH) , which was removed by filtration. The deep blue solution
was left to slowly evaporate in a crystallizing dish, eventually yielding
49,50
2
4 3
2
1
established procedures.
Reaction mixtures (total volume = 15 μL)
4
2
2
containing supercoiled pBR 322 plasmid DNA (38 μM base pair
concentration) and copper(II) complexes (75, 100, 150, 225, 300, 450,
and 600 μM) in 40 mM buffers (MES, HEPES, TAPS, and CHES) at
pH 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, and 9.0 were incubated in a water bath at
(
2
3
7 °C for periods of up to 48 h. The loading buffer was added to stop
the reactions at defined time periods, and the resulting solutions were
dark blue crystals of C1. Yield: 75 mg (34%). Microanalysis: calcd for
stored at −20 °C until just prior to analysis. The resulting solutions
Cu C H N O Cl : C, 24.3; H, 5.3; N, 18.9%. Found: C, 24.3; H,
2
18 47 12 14
3
−3
−1
−1
were loaded onto 1% agarose gels containing 1.0 μg dm ethidium
5
[
.2; N, 18.6%. UV−vis (H O): λ (nm) [εmax] (M cm ): 626
113], 987 [36]. IR bands (ATR) υ (cm ): 3446m (υO−H), 3378m,
242m, 3306m (υN−H), 2984w, 2884w (υC−H), 1615s (υ
359m, 1274w, 1065s br, 621s (υ
2
max
−1
bromide. The DNA fragments were separated by gel electrophoresis
[
70 V for 2 h in 1 × Tris-acetate EDTA (TAE) buffer]. Ethidium-
3
1
), 1464m,
CN
−
stained agarose gels were imaged, and the extent of supercoiled DNA
cleavage was determined via densitometric analysis of the visualized
bands using the volume quantification method. In all cases,
background fluorescence was determined by reference to a lane
containing no DNA. Supercoiled pBR 322 DNA intensity values were
multiplied by 1.42 to account for the increased ability of ethidium
bromide to intercalate into supercoiled DNA (form I) as compared to
).
ClO4
2
[
Cu(L H)Cl ]Cl·(MeOH) ·(H O) (C2). An aqueous solution (4
2 0.5 2 0.5
2
mL) of L ·4HCl (0.097 g, 0.230 mmol) was added to Cu-
(
ClO ) ·6H O (0.130 g, 0.280 mmol) dissolved in water (4 mL).
4
2
2
The adjustment of the pH to 9 with 1 M NaOH, followed by removal
of Cu(OH)2 by filtration, gave a deep blue solution, which was
evaporated to dryness. The residue was dissolved in MeOH, and the
product was crystallized by diffusion of diethyl ether into this solution.
Yield: 35 mg (36%). Microanalysis: calcd for CuC10.5H N OCl : C,
2
6,49,50
nicked DNA (form II).
The DNA cleavage data were fitted to a
obs
−k t
first-order expression, % DNA = A + Be , yielding the first-order
rate constant, kobs, for cleavage of form I DNA to produce form II.
DNA Cleavage Experiments in the Presence of Radical
Scavengers. Aliquots (5 μL) of aqueous solutions of scavenging
agents (30 mM KI, DMSO, BuOH, or NaN in 40 mM HEPES buffer
28
6
3
2
(
(
9.7; H, 6.7; N, 19.8%. Found: C, 29.6; H, 6.4; N, 20.1%. UV−vis
−1 −1
H O): λ (nm) [ε ] (M cm ): 618 [91], 957 [29]. IR bands
2 max max
−1
ATR) υ (cm ): 3246m, 3149m (υN−H), 2941w, 2874w (υC−H),
t
1
8
652s (υ
), 1450m, 1375w, 1280w, 1095w, 1023w, 954w, 888w,
CN
3
at pH 7.0) were added to the solutions of supercoiled DNA (5 μL,
113.5 μM base pair concentration) prior to the addition of complexes
C1, C2, and C3. The final reaction conditions were: [complex] = 150
μM, [scavenging agents] = 10 mM, and [DNA] = 38 μM base pair
concentration. Each solution was incubated at 37 °C for 6 h,
quenched, and analyzed according the procedures described above.
DNA Cleavage under Anaerobic Conditions. Experiments
under anaerobic condition were performed following the protocol
30w.
3
[
Cu(L H)Cl ]Cl·(DMF) ·(H O) (C3). The synthesis was as for C2,
2
0.5
2
0.5
3
except that L ·4HCl (0.100 g, 0.240 mmol) and Cu(ClO ) ·6H O
0.150 g, 0.280 mmol) were used. The product was crystallized by
dissolving the residue in N,N′-dimethylformamide and diffusing diethyl
ether into this solution. Yield: 38 mg (35%). Microanalysis: calcd for
CuC12.5H31.5N OCl : C, 32.7; H, 6.9; N, 19.8%. Found: C, 32.6; H,
4
2
2
(
6.5
3
−1
−1
6
[
.8; N, 20.2%. UV−vis (H O): λ (nm) [εmax] (M cm ): 620
103], 948 [35]. IR bands (ATR) υ (cm ): 3320m, 3262m, 3124m,
2
max
6
49,50
−1
reported by Burstyn and co-workers and in our previous work.
All
(
1
υN−H), 2931w, 2862w (υC−H), 1625s (υ ), 1492m, 1257w, 1161w,
039w, 960w, 869w, 757w, 633w.
Derivation of Protonation and Dimerization Constants.
other conditions were as for the cleavage experiments performed
under aerobic conditions in which final concentrations for the reaction
mixtures were 150 μM for complexes, 40 mM HEPES buffer, and 38
μM base pair concentration for supercoiled DNA.
CN
Equilibrium constants for protonation and dimerization reactions of
C1−C3 were derived from systematic series of spectra collected
X-ray Crystallography. Intensity data for blue crystals of C1 (0.20
3
3
(
(
400−1300 nm) at varying pH (∼4−12) and complex concentrations
5−15 mM). The series of spectra were analyzed using the BEEROZ
× 0.10 × 0.05 mm ), C2 (0.18 × 0.15 × 0.05 mm ), and C3 (0.15 ×
3
0.12 × 0.05 mm ) were collected at 123 K on a Bruker Apex II CCD
54
software. Briefly, this method employs constraints from mass balance
and mass action equations to test the speciation models for spectral
data sets containing many species and to derive formation constants
fitted with graphite monochromated Mo Kα radiation (0.71073 Å).
The data were collected to a maximum 2θ value of 55° (50° for C1,
the high angle data was dominated by noise [I/σ(I) < 1.0] and was
omitted) and processed using Bruker Apex II software package. Crystal
5
5,56
for the spectroscopically active species.
The analysis provides the
9
42
dx.doi.org/10.1021/ic2019814 | Inorg. Chem. 2012, 51, 939−953

Inorganic Chemistry
Article
1
2
3
a
Scheme 1. Synthesis of Hydrochloride Salts of Ligands L , L , and L
a
Reagents and conditions: (i) 2 equiv of Boc-ON, NEt , CHCl , RT, 8 h. (ii) Bromoalkylphthalimide, K CO , KI, CH CN, reflux, 3 days. (iii)
3
3
2
3
3
N H ·H O, EtOH, 50 °C, 4 h. (iv) N,N′-Boc -1H-pyrazole-1-carboxamidine, THF, RT, 2 days. (v) (a) TFA/CH Cl (1:1), RT, o/n; (b)
2
4
2
2
2
2
concentrated HCl.
parameters and details of the data collection are summarized in Table
S01 in the Supporting Information.
5
9,60
The structures of C1, C2, and C3 were solved using SHELX-97
and expanded using standard Fourier transform routines. All hydrogen
atoms were placed in idealized positions, except for the hydrogen
atoms on the nitrogen atoms, which were located on the Fourier
difference map. All nonhydrogen atoms were refined anisotropically.
RESULTS AND DISCUSSION
■
Preparation of Ligands and Complexes. Scheme 1
describes in detail the route employed to prepare the new
guanidine-bearing derivatives of tacn from the di-Boc-protected
5
1
1
tacn precursor (Boc tacn). Each of compounds 1−9 and L −
2
3
L ·4HCl were obtained in reasonable to high yields (60−80%),
and the identity of each was established by H and C NMR
spectroscopy and ESI-MS. The C NMR spectra of 7−9
exhibited signals at ca. 163.5 and 156.0 ppm, which were
1
13
1
3
assigned to the carbonyl type carbons of the Boc -guanidine
2
Figure 2. Thermal ellipsoid plot of the complex cation in C1
ellipsoids drawn at 50% probability). Atoms denoted i are generated
by symmetry (2 − x, y, 1/2 − z).
group. A signal at ca. 153 ppm, assigned to the CN moiety of
the guanidine group, further suggested that 7−9 had been
formed. This signal shifted to 157 ppm for the final ligands.
(
1
3
1
2+
3+
The copper(II) complexes of L −L , [Cu L (μ−OH)]-
Cu core in C1 with other [Cu (μ-OH) ] or [Cu (μ-OH)]
2 2 2
2
2
2
(
ClO ) (C1), [Cu(L H)Cl ]Cl·(MeOH) ·(H O) (C2),
and [Cu(L H)Cl ]Cl·(DMF) ·(H O) (C3) were prepared
cores indicates that the Cu−O distance lies within the usual
4
3
2
0.5
2
0.5
3
2
0.5
2
0.5
range [1.900(4)−2.019(3) Å] observed for such cores (Table
as described in the Experimental Section. The microanalyses
were consistent with these formula, and the IR spectra showed
1
). However, in comparison to the di-μ-hydroxo-bridged
complexes, a larger separation between the two Cu(II) centers
in C1 is an obvious outcome of the Cu−O−Cu angle being
more obtuse in the former (Table 1) and of the absence of a
second bridging hydroxo group. A similar Cu−O−Cu angle of
−1
NH vibrations in the 3240−3380 cm region and sharp υ
−
1
(
CN) vibrations at ca. 1620 cm attributable to the
guanidine pendant groups. Complex C1 also showed a broad
−1
OH vibration centered at 3446 cm and typical perchlorate
vibrations. The electronic spectra of C1−C3 measured in water
exhibited bands at ca. 620 and 950−990 nm, typical for square
1
35.2(3)° has previously been reported for an imidazole
im
3+
pendant-bearing Cu(II)−tacn complex, [Cu L (μ-OH)] ,
where the two metal centers were also connected by a
monohydroxo bridge.
2
2
61
pyramidal (SP) copper(II) complexes.
1
Crystallography. [Cu L (μ-OH)](ClO ) ·H O (C1). X-ray
2
2
4 3
2
The copper geometry in C1 is distorted SP. The τ value of
structural analysis revealed that C1 has two Cu(II) centers
linked by a single μ-hydroxo bridge (Figure 2). Only half of the
molecule resides in the asymmetric unit (ASU), while the other
half was generated by crystallographic symmetry about the μ-
hydroxo bridge. The two copper atoms are at a distance of
62
1
7%, calculated using the method described by Addison et al.,
indicates a slight degree of distortion from the ideal SP
geometry (τ = 0%) toward trigonal bipyramidal (TBP)
geometry (τ = 100%). As expected, the Cu(1)−N(3) distance
for the apical nitrogen atom [2.246(3) Å] is slightly longer than
the Cu−N(1) and N(2) bond lengths [2.032(3) Å and
3
.655(3) Å, making a nonlinear Cu−O−Cu angle of 139.8(2)°
about the hydroxo bridge vertex. Comparison of the Cu−OH−
9
43
dx.doi.org/10.1021/ic2019814 | Inorg. Chem. 2012, 51, 939−953

Inorganic Chemistry
Article
Table 1. Structural Data for Mono- and Di-μ-hydroxo-Bridged Cu(II)-tacn Complexes
a
complex
Cu−O (Å)
1.946(1)
Cu−O−Cu (deg)
refs
C1
139.8(2)
this work
[
[
Cu2Lim (μ-OH)]3+
1.913(4); 1.925(5)
1.900(4); 2.019(3)
135.2(3)
63
64
2
Cu3Lmes(μ-OH) (H O) ](ClO ) ·2H O
98.9(2)
2
2
2
4
4
2
1
.922(3); 2.015(3)
92.1(1)
mes
[
Cu (L ) (μ-OH) ](ClO ) ·2H O
1.957(3); 1.920(4)
94.7(1)
64
6
2
6
4
6
2
1
1
.954(3); 1.919(4)
.933(4); 1.969(4)
97.0(1)
98.7(2)
[
[
[
[
Cu (Me tacn) (μ-OH) ](ClO )
1.939(4); 1.936(4)
1.963(2)
100.1(2)
65
66
67
68
2
3
2
2
4 2
2
+
Cu (μ-OH)(μ-CH COO)(tacn) (μ-H O)]
114.3(2)
2
3
2
2
Cu2Lmx(μ-OH) ](BPh )
1.928(2); 1.931(2)
1.961(8); 1.975(8)
99.6(1)
2
4 2
Cu4Ldur(μ-OH) ](ClO )
97.9(4)
4
4 4
1
.936(7); 1.989(9)
95.7(4)
[
[
[
[
[
[
[
[
Cu (Butacn) (μ-OH) ](ClO )
1.929(2)
101.01(9)
101.1(3)
69
70
71
71
71
58
58
58
2
2
2
4 2
i
Cu (Fc Pr tacn) (μ-OH) ](ClO )
4 2
1.960(7); 1.946(7)
1.949(4); 1.924(5)
1.922(6); 1.951(6)
1.950(6); 1.933(6)
1.941(3); 1.952(3)
1.926 (3); 1.944 (3)
2
2
2
2
i
Cu (Bn tacn)(Bn tacn)(μ-OH) ](CF SO ) ·2( PrOH)
100.5(2);100.5(8)
100.9(3);102.7(3)
101.1(3);102.9(3)
97.9(1);97.9(1)
97.0(1);96.0(1)
95.8(1);96.1(1)
2
3
2
2
3
3 2
i
Cu ( Pr tacn) (μ-OH) ](BPh ) ·2THF
2
2
i
2
2
4 2
Cu (Bn Pr ) (μ-OH) ](CF SO )
2
2
2
2
3
3
2
Cu (μ-OH) (Me tacn) ](ClO )
4 2
2
2
2
2
Cu (μ -OH) (BnMe tacn) ](ClO )·H O
2
2
2
2
2
4
2
Cu (μ -OH) (cyanoBn tacn) ](ClO ) ·2H O
1.944(3); 1.945(3)
2
2
2
3
2
4
2
2
a
im
mes
Abbreviations: L , 1-(1-methylimidazol-2-ylmethyl)-1,4,7-triazacyclononane; L , 1,3,5-tris(1,4,7-triazacyclonon-1-ylmethyl)benzene; Me tacn,
3
mx
dur
1
,4,7-trimethyl-1,4,7-triazacyclononane; L , 1,3-bis(1,4,7-triazacyclonon-1-ylmethyl)benzene; L , 1,2,4,5-tetrakis(1,4,7-triazacyclonon-1-ylmethyl)-
i
benzene; Butacn, N-4-(but-1-ene)-1,4,7-triazacyclononane; Fc Pr tacn, 1-ferrocenylmethyl-4,7-diisopropyl-1,4,7-triazacyclononane; Bn tacn, 1,4,7-
tribenzyl-1,4,7-triazacyclononane; Bn tacn, 1,4-dibenzyl-1,4,7-triazacyclononane; Pr tacn, 1,4-diisopropyl-1,4,7-triazacyclononane; Bn Pr tacn, 1-
2
3
i
i
2
2
2
benzyl-4,7-diisopropyl-1,4,7-triazacyclononane; Me tacn, 1,4-dimethyl-1,4,7-triazacyclononane; BnMe tacn, 1-benzyl-4,7-dimethyl-1,4,7-triazacyclo-
2
2
nonane; and cyanoBn tacn, 1,4,7-tris(3-cyanobenzyl)-1,4,7-triazacyclononane.
3
2
.038(3) Å, respectively] that form the part of the basal plane
(Table 2). The oxygen atom, O(1), of the μ-hydroxo group and
a
Table 2. Selected Bond Lengths (Å) and Angles (°) for C1
Cu(1)−O(1)
Cu(1)−N(1)
Cu(1)−N(2)
Cu(1)−N(3)
Cu(1)−N(4)
1.946(1)
2.032(3)
2.038(3)
2.246(3)
1.996(3)
O(1)−Cu(1)−N(4)
O(1)−Cu(1)−N(1)
N(4)−Cu(1)−N(1)
O(1)−Cu(1)−N(2)
N(4)−Cu(1)−N(2)
N(1)−Cu(1)−N(2)
O(1)−Cu(1)−N(3)
N(4)−Cu(1)−N(3)
N(1)−Cu(1)−N(3)
N(2)−Cu(1)−N(3)
Cu(1)#2−O(1)−Cu(1)
98.7(1)
170.7(9)
82.8(1)
91.6(1)
160.5(1)
84.4(1)
105.6(1)
110.5(1)
82.3(1)
82.3(1)
139.8(2)
Figure 3. Relative orientation of the two Cu(II) SP coordination
polyhedra in C1 with the dihedral angle between the least-squares
basal planes indicated.
a
Symmetry transformations used to generate equivalent atoms: #1, −x
1, y, −z + 1/2; #2, −x + 2, y, −z + 1/2.
+
operation: 2 − x, y, 1/2 − z). The guanidine groups are
themselves skewed relative to each other (angle of 26.6°
between their least-squares planes) and further held in their
respective positions by hydrogen bonding with an oxygen atom
from the perchlorate anion present in the crystal lattice (Figure
the nitrogen atom, N(4), from the guanidine pendant complete
the basal plane, with Cu(1)−O(1) and Cu(1)−N(4) bond
distances of 1.946(1) and 1.996(3) Å, respectively. This type of
guanidine coordination mode was previously observed for the
Cu(II) complex of 1-ethyl-4,7-bis(ethylguanidine)-1,4,7-triaza-
4
9
cyclononane. As in our previous study, the high affinity of the
S01 in the Supporting Information and Table 3).
1
2
guanidine in L for copper(II) is highlighted by the fact that the
[Cu(L H)Cl
2
]Cl·(MeOH)0.5·(H
2
O)0.5 (C2). The crystal structure
Cu−N distance is shorter than those involving the macrocyclic
of C2 shows that the ASU contains two complex units,
distinguished within the crystal lattice by their relative distances
from a co-crystallized methanol molecule (Figure 4). The two
molecules are connected in a head-to-tail arrangement, due to
an intermolecular hydrogen-bonding interaction between them
[N(6)−H(6AN)···Cl(3): 3.262(2) Å, 162(2)°].
49
nitrogens, viz. 1.996(3) vs 2.032(3)−2.246(3) Å.
A least-squares analysis of the basal planes formed by atoms
N(1)/N(4)/O(1)/N(2) and their symmetry equivalents
reveals a dihedral angle of 61.75°, with the two guanidinium
pendants pointing away from each other (Figure 3). This may
be to minimize the steric and electrostatic repulsion between
these pendant and their symmetry equivalents (symmetry
The Cu(II) centers are five-coordinate and exhibit distorted
SP geometry, with τ = 10 and 13% for Cu(1) and Cu(2),
9
44
dx.doi.org/10.1021/ic2019814 | Inorg. Chem. 2012, 51, 939−953

Inorganic Chemistry
Article
a
Table 3. Hydrogen-Bonding Interactions in C1 (Å and °)
Table 4. Selected Bond Lengths (Å) and Angles (°) for C2
D−H···A
d(D−H) d(H···A)
d(D···A)
∠(DHA)
Cu(1)−N(1)
Cu(1)−N(2)
Cu(1)−N(3)
Cu(1)−Cl(1)
Cu(1)−Cl(2)
Cu(2)−N(8)
Cu(2)−N(7)
Cu(2)−N(9)
Cu(2)−Cl(4)
Cu(2)−Cl(3)
2.020(2)
2.038(2)
2.275(2)
2.2758(5)
2.2941(6)
2.020(2)
2.039(2)
2.265(2)
2.2855(5)
2.2922(5)
N(1)−Cu(1)−N(2)
N(1)−Cu(1)−N(3)
N(2)−Cu(1)−N(3)
N(1)−Cu(1)−Cl(1)
N(2)−Cu(1)−Cl(1)
N(3)−Cu(1)−Cl(1)
N(1)−Cu(1)−Cl(2)
N(2)−Cu(1)−Cl(2)
N(3)−Cu(1)−Cl(2)
Cl(1)−Cu(1)−Cl(2)
N(8)−Cu(2)−N(7)
N(8)−Cu(2)−N(9)
N(7)−Cu(2)−N(9)
N(8)−Cu(2)−Cl(4)
N(7)−Cu(2)−Cl(4)
N(9)−Cu(2)−Cl(4)
N(8)−Cu(2)−Cl(3)
N(7)−Cu(2)−Cl(3)
N(9)−Cu(2)−Cl(3)
Cl(4)−Cu(2)−Cl(3)
83.07(7)
83.17(6)
82.22(7)
164.83(5)
90.94(5)
109.90(4)
90.15(6)
170.92(5)
103.05(4)
94.13(2)
82.96(7)
82.50(7)
83.39(6)
88.82(5)
164.14(5)
109.04(4)
171.96(5)
91.04(5)
102.19(4)
95.70(2)
N(2)−H(2)···O(2)#3
N(3)−H(3)···O(3)#4
N(5)−H(5C)···O(5)
N(5)−H(5D)···O(6)#2
N(6)−H(6D)···O(7)#5
N(6)−H(6C)···O(1)
0.87(1)
0.87(1)
0.87(1)
0.88(1)
0.88(1)
0.88(1)
2.19(1)
2.33(1)
2.19(3)
2.32(2)
2.32(2)
2.36(3)
3.062(4)
3.190(5)
2.976(5)
3.158(5)
3.177(4)
2.925(4)
179(4)
168(3)
149(4)
160(3)
165(4)
122(3)
a
Symmetry transformations used to generate equivalent atoms: #1, −x
1, y, −z + 1/2; #2, −x + 2, y, −z + 1/2; #3, x − 1/2, y − 1/2, −z +
/2; #4, −x + 5/2, y − 1/2, z; and #5, x + 1, y, z.
+
1
a
Table 5. Hydrogen-Bonding Interactions in C2 (Å and °)
D−H···A
d(D−H) d(H···A) d(D···A)
∠(DHA)
N(5)−H(5BN)···O(1)
N(5)−H(5AN)···Cl(6)#1
N(6)−H(6AN)···Cl(3)
N(6)−H(6BN)···Cl(6)
O(1)−H(1O)···Cl(5)#2
N(4)−H(4N)···Cl(5)#2
N(12)−H(13N)···Cl(5)
N(10)−H(10N)···Cl(6)#3
N(12)−H(12N)···Cl(6)#3
N(1)−H(1N)···Cl(1)#4
N(8)−H(8N)···Cl(3)#5
N(11)−H(11N)···Cl(5)
0.80(3)
0.86(2)
0.84(2)
0.80(3)
0.84
2.12(3)
2.50(2)
2.45(2)
2.45(3)
2.34
2.900(3)
3.221(2)
3.262(2)
3.230(2)
3.070(2)
3.269(2)
3.205(2)
3.212(2)
3.212(2)
3.234(2)
3.270(2)
3.342(2)
166(3)
141(2)
162(2)
168(2)
146.2
0.77(2)
0.84(3)
0.87(2)
0.90(2)
0.76(2)
0.75(2)
0.90(3)
2.50(2)
2.41(3)
2.39(2)
2.38(2)
2.57(2)
2.59(2)
2.51(3)
175(2)
157(2)
158(2)
154(2)
147(2)
152(2)
154(2)
Figure 4. Thermal ellipsoid plot of the asymmetric unit of C2 showing
noncoordinating chloride anions and methanol molecule (ellipsoids
drawn at 50% probability; selected hydrogen atoms are omitted for
clarity; dashed bonds indicate intermolecular hydrogen-bonding
interactions).
a
Symmetry transformations used to generate equivalent atoms: #1, −x
+ 1, −y + 1, −z + 2; #2, x − 1, −y + 1/2, z − 1/2; #3, −x + 1, y − 1/2,
−z + 5/2; #4, x, −y + 1/2, z + 1/2; and #5, x, −y + 1/2, z − 1/2.
respectively. The base of the pyramid is defined by the two Cl
atoms, and the two secondary nitrogens [N(1)/N(2)/Cl(1)/
Cl(2) and N(7)/N(8)/Cl(4)/Cl(3) for Cu(1) and Cu(2),
respectively], while the apical site is occupied by the
macrocyclic nitrogen atom bearing the propyl guanidinium
pendant. The two sets of basal atoms have a mean deviation of
units in a head-to-tail fashion via hydrogen bonding. This
hydrogen-bonding network is extended in the third dimension
by the cocrystallized methanol molecule and chloride anions
present in the lattice. The chloride counteranions, Cl(6) and
Cl(5), serially link the protonated guanidine pendants in the
crystal lattice to each other by means of hydrogen bonds (Table
5). This network is further extended by hydrogen bonding with
the methanol molecule, which acts as hydrogen bond acceptor
to the guanidine protons and donor to the chloride anions.
0
.069 and 0.074 Å, respectively, from their least-squares planes,
with the two copper atoms, Cu(1) and Cu(2), lying out of the
plane by 0.20 and 0.19 Å, respectively.
3
The basal Cu−Cl distances, for example, Cu(1)−Cl(1) =
[Cu(L H)Cl ]Cl·(DMF) ·(H O) (C3). As for C2, the Cu(II)
2
0.5
2
0.5
2
.2758(5) Å and Cu(1)−Cl(2) = 2.2941(6) Å, are typical for
center in C3 lies in a distorted SP geometry (Figure 5), τ value
of 9%, comprised of three facially coordinating nitrogen atoms
from tacn and two chloride ligands. The secondary nitrogens,
N(1) and N(2), along with Cl(1) and Cl(2), define the basal
plane with the deviation from the least-squares plane being
0.042 Å. The tertiary nitrogen atom with the butylguanidinium
pendant attached forms the apex of the pyramid. The two Cu−
Cl basal distances and other bond angles and bond lengths are
61
such coordinate bonds. In both molecular units, the Cu−N
axial distance is elongated with respect to the Cu−N basal
9
distances by >0.20 Å (Table 4), as is typical for d Cu(II)
72
centers with a SP geometry. The bond angles around the
73−75
Cu(II) center are typical for Cu(II)−tacn derivatives.
In both molecular units, the propylguanidinium pendant is
protonated, with the pendant extending away from the metal
center and forming hydrogen-bonding interactions with the
chloro ligands (Figure S02 in the Supporting Information and
Table 5). As mentioned before, within the ASU, the
coordinated chloride ligand, Cl(3), connects the two cationic
6
1,72,75
within the expected ranges (Table 6).
The deviation of
the copper center from the least-squares basal plane toward the
apical nitrogen N(3) is 0.25 Å, which is slightly larger than in
C2.
9
45
dx.doi.org/10.1021/ic2019814 | Inorg. Chem. 2012, 51, 939−953

Inorganic Chemistry
Article
Figure 5. Thermal ellipsoid representation of C3 (ellipsoids drawn at
50% probability; hydrogen atoms on carbon and counteranions have
been omitted for clarity).
Table 6. Selected Bond Lengths (Å) and Angles (°) for C3
Cu(1)−N(1)
Cu(1)−N(2)
Cu(1)−N(3)
Cu(1)−Cl(1)
Cu(1)−Cl(2)
2.034(4)
2.021(3)
2.254(4)
2.264(1)
2.314(1)
N(2)−Cu(1)−N(1)
N(2)−Cu(1)−N(3)
N(1)−Cu(1)−N(3)
N(1)−Cu(1)−Cl(1)
N(2)−Cu(1)−Cl(1)
N(3)−Cu(1)−Cl(1)
N(1)−Cu(1)−Cl(2)
N(2)−Cu(1)−Cl(2)
N(3)−Cu(1)−Cl(2)
Cl(1)−Cu(1)−Cl(2)
83.3(2)
83.5(1)
Figure 6. Plot of μeff and χ (per Cu) vs temperature for complex C1.
M
82.2(2)
The solid lines were calculated using the parameter set given in the
text and are restricted to the 100−300 K region since this is the region
sensitive to J.
92.0(1)
168.3(1)
106.5(1)
163.1(1)
88.7(1)
76
centers.7 The data were fitted to the modified Bleaney−
7
Bowers given in eq 1, yielding the following parameters: g =
−
1
2
0
.01, J = −165 cm , and P (fraction of S = 1/2 monomer) =
111.71(4)
93.01(2)
.04, with a temperature-independent paramagnetism (Nα) per
−6
3
−1
Cu(II) of 64 × 10 cm mol . This large, negative value of J is
primarily due to strong antiferromagnetic coupling across the
Cu−O(H)−Cu bridge and is compatible with the Cu−O−Cu
bridge angle of 139.8(2)° and Cu···Cu separation of 3.655(3)
Å. While di-μ-hydroxo bridging is most common in Cu(II)
dimers, there is a small but growing number of singly OH-
bridged examples, and the present example fits nicely into the
magnetostructural correlations deduced from O(H) p-orbital
Similar to C2, the nitrogen atom N(4) on the charged
guanidinium pendant in C3 is not coordinated. The terminal
nitrogen on the guanidinium pendant forms charge-assisted
hydrogen bonds with one chloro ligand, which further forms
Cl···H−N hydrogen-bonding interactions with the secondary
amine nitrogen on the macrocycle [N(6)−H(6AN)···Cl(3):
.242(4) Å, 153(4)°; N(5)−H(5BN)···Cl(3): 3.181(5) Å,
59(4)°; N(1)−H(1N)···Cl(3)#1: 3.202(4) Å, 148(4)°, #1
denoting the symmetry operator (−x + 3/2, y, z − 1/2)]. This
creates a chloro ligand-mediated 1D-helical chain with the
molecules aligned in a head-to-tail arrangement in the crystal
lattice (Figure S03 in the Supporting Information and Table 7).
3
1
2
2
bridging between Cu(d ) orbitals arising from SP Cu
x −y
78
centers.
2
2
−1
Ng β ⎡
⎛−2J ⎞⎤
(1 − P)
χCu
=
3 + exp
⎜
⎟
⎢
⎥
kT ⎣
Ng β P
⎝ kT ⎠⎦
2
2
a
Table 7. Hydrogen-Bonding Interactions in C3 (Å and °)
+
+ Nα
4kT
(1)
D−H···A
d(D−H)
d(H···A)
d(D···A) ∠(DHA)
Aqueous Speciation. The results of the speciation
calculations based on systematic variations in the UV−vis
spectra are shown in Figure 7. Equilibrium constants for the
preferred models are listed in Table 8. For C1, principal
component analysis (PCA) suggests that a minimum of five
species are required to explain the individual data sets at fixed
concentration of C1. In practice, four species (as per speciation
N(1)−H(1N)···Cl(3)#1
N(2)−H(2N)···Cl(1)#2
N(6)−H(6AN)···Cl(3)
N(5)−H(5BN)···Cl(3)
0.83(5)
2.47(5)
2.54(3)
2.45(3)
2.33(5)
3.202(4)
3.339(3)
3.242(4)
3.181(5)
148(4)
154(4)
153(4)
159(4)
0.860(19)
0.858(19)
0.90(5)
a
Symmetry transformations used to generate equivalent atoms: #1, −x
+
3/2, y, z − 1/2; and #2, x − 1/2, −y + 1, z.
2
scheme in Figure 8) provided a good fit to the data: the χ value
Magnetic Properties of C1. Molar magnetic susceptibil-
corresponding to the absolute minimum was 3.25, and Δ
ities for C1 were measured in a field of 1 T over the
temperature range of 30−300 K. The variable temperature
magnetic moment plot (see Figure 6) shows a decrease in
magnetic moment with temperature, which is indicative of
strong antiferromagnetic coupling between the copper(II)
centers, mediated by the OH bridge. The 300 K value of
abs
(
largest difference between measured and calculated absorban-
ces) was 0.025 units. Because a binuclear complex crystallizes
from solutions of C1, we hypothesized that this complex might
also be important in solution. Consequently, we investigated
1
3+
the effect of [L Cu (OH)] on the overall fit. The preferred
2
2
2
model (Figure 7) (χ = 4.46; Δ = 0.028) is within the 90%
confidence range of the fit corresponding to the absolute
abs
1
.32 μ , per Cu(II), decreases with decreasing temperature and
B
reaches a value of ca. 0.5 μ at ca. 100 K, after which the
54,79
B
minimum
and shows the maximum amount of the
magnetic moment remains reasonably constant, the corre-
sponding susceptibilities (Figure 6) showing Curie-like
behavior. The increase in susceptibility observed between 100
and 30 K is most likely due to the presence of a monomeric
impurity”, which is a commonly observed in Cu(II) complexes
possessing antiferromagnetic interactions between the metal
binuclear complex among the fits within the 90% confidence
level relative to the absolute minimum.
For C2, PCA clearly indicates that a minimum of five species
are required to explain the UV−vis data set; this corresponds to
the number of complexes in the simplified speciation model in
Figure 9. The best-fit results using this model, shown in Figure
“
9
46
dx.doi.org/10.1021/ic2019814 | Inorg. Chem. 2012, 51, 939−953

Inorganic Chemistry
Article
Figure 7. Results of UV−vis titrations and quantitative spectral analysis for C1, C2, and C3. (a, c, e) Absorbance data at a fixed wavelength of 626
nm, as a function of pH (x-axis) and total complex concentration. Circles are measurements; lines were calculated using the speciation model. (b, d,
f) Distribution of species calculated from the quantitative analysis, calculated for complex concentrations of 5 (dashed lines) and 15 (plain lines)
mM; corresponding stability constants are shown in Table 8.
2
7
c,d (χ = 1.26; Δ = 0.028), indicate that the amounts of
confidence level for the solution corresponding to the absolute
abs
5
4,79
polynuclear species formed in this system are small.
minimum.
This solution was preferred because it displays
For C3, PCA reveals that a minimum of six species are
required to explain the UV−vis spectra. Our preferred model
the most reasonable spectra for the individual complexes
(Figure S04 in the Supporting Information). We note, in
particular, that in many fits the molar absorbance for
(
Figure 7f) contains seven species (based on the speciation
2
2+
scheme in Figure 9), but the spectra of the minor binuclear
[Cu L (OH) ] was similar to those of the mononuclear
2 2
3
4+
3
3
3+
complexes, [Cu (L H) (OH) ] and [Cu (L H)L (OH) ] ,
species, suggesting that the amount of polynuclear species at
pH ≥ 9 was overestimated. From the favored solution, it can be
inferred that <10% of species present at pH ≤ 8 are polynuclear
(Figure 7f).
Within the limits of measurement and fitting of spectropho-
tometric data, the concentration of binuclear complexes present
at the concentrations used is concluded to be low for C2 and
C3. As will be discussed further below, it then follows that
under the conditions of the kinetic experiments ([complex] of
2
2
2
2
2
were constrained to be equal during the fitting. As with the
other systems, the similarity in the spectra of the individual
complexes (Figure 7) results in some degrees of correlation
between the formation constants of some complexes. The χ2
value corresponding to the absolute minimum was 1.81 (Δ
=
abs
0
.067). For C3, the concentration of polynuclear complexes
was highly sensitive of the log K value; the favored solution
D
2
has a χ value of 2.07 (Δ = 0.070), which is within the 90%
abs
9
47
dx.doi.org/10.1021/ic2019814 | Inorg. Chem. 2012, 51, 939−953

Inorganic Chemistry
Article
Table 8. Proposed Protonation and Dimerization Constants
for C1−C3
dissolution, complicated equilibria will be established as
elucidated from the speciation studies.}
The slowest rates of cleavage were measured for complex C1,
1
3+
1
2+
+
(
L H)Cu(H O) = L Cu(H O) + H + H O
pKa1 = 5.6
pKa2 = 7.9
2+
2
2+
2
2
2
which displayed similar reactivity to [Cu(tacn)(OH ) ] . On
1
1
+
+
2 2
L Cu(H O) = L Cu(OH) + H
2
the basis of the crystal structure and the results of speciation
1
2+
1
+
1
2
3+
L Cu(H O) + L Cu(OH) = L Cu (HO) + H O
Log K = 2.9
2
2
2
d
studies, which correspond well to the complex bearing two
49
ethylguanidine pendants above pH 6, C1 exists in three major
L HCu(H O) = L HCu(H O)(OH) + H+
2
3+
2
2+
pKa1 = 6.5
pKa2 = 7.5
pKa3 = 10
2
2
2
1
2+
1
+
forms, [Cu(L )(OH )] , [Cu(L )(OH)] , and the dimer,
L HCu(H O)(OH) = L HCu(OH) + H+
2
2+
2
+
2
2
2
1
3+
1
+
[
[
Cu (L ) (μ-OH)] (Figure 7). Since for [Cu(L )(OH)] and
Cu (L ) (μ-OH)] the Cu(II) coordination sphere is
2
+
2
+
2 2
L HCu(OH) = L Cu(OH) + H
2
2
1
3+
2
+
2
2
2+
2
2
2
2
L Cu(OH)(OH ) = L Cu (OH) + 2H O
Log K = 1.4
2
2
2
d
comprised of four nitrogen donor from the ligand and an
oxygen from a hydroxo ligand, coordination of the substrate
would require displacement of the hydroxo ligand, which is
L HCu(H O) = L HCu(H O)(OH) + H+
3
3+
3
2+
pKa1 = 7.0
pKa2 = 8.9
pKa3 = 11.2
2
2
2
L HCu(H O)(OH) = L HCu(OH) + H+
3
2+
3
+
2
2
1
2+
3
+
3
+
bound more strongly than the aqua ligand in [Cu(L )(OH )] .
2
L HCu(OH) = L Cu(OH) + H
2
2
3
+
3
2+
Furthermore, even if binding occurs, no internal nucleophile
2
2
L Cu(OH)(OH ) = L Cu (OH) + 2H O
Log K = 2.3
2
2
2
2
2
4+
d
57,81
3
2+
3
(Cu−OH) is available to carry out the cleavage.
C1 can
L HCu(H O)(OH) = (L H) Cu (OH) + 2H O
Log K = 0.7
2
2
2
2
3+
2
d
3
4+
3
3
+ H+
therefore be considered to be surprisingly reactive. The rates of
(
L H) Cu (OH) = (L H)L Cu (OH)
Log K = 6.7
2
2
2
2
2
d
2+
cleavage are slower than for [Cu(tacn)(OH ) ] but much
2
2
faster than those of the Cu(II) complex of the ligand with two
2
mM for BNPP/HPNPP cleavage and 75−600 μM for DNA
2+
ethylguanidine pendants, [Cu(A)] , whose Cu(II) coordina-
cleavage), the concentration of binuclear complexes is even
smaller, such that they are unlikely to affect the rates of
cleavage.
49
tion sphere is saturated by the ligand donor atoms. For
HPNPP, the reaction rates are similar to those for [Cu(tacn)-
2+
(
OH ) ] , except at pH 6, where the rate of cleavage is faster
2
2
Cleavage of Model Phosphate Esters. The rate
constants for the cleavage of the model phosphodiesters,
BNPP and HPNPP, measured in the presence of C1−C3 at
different pH values are summarized in Tables 9 and 10,
together with data for related complexes. At all pH values and
for both substrates, the three complexes enhanced the rate of
cleavage well above background levels, particularly for the less
reactive DNA mimic, BNPP (HPNPP, like RNA, features a 2′-
OH group on the ribose ring that acts as an internal
nucleophile). In addition, the reaction rate increased with pH,
consistent with the proposed hydrolytic mechanism for
Cu(II)−tacn-based complexes, which features a Cu(II)-bound
for C1. At pH 6, about 50% of the complex exists as
1
3+
[
(L H)Cu(H O) ] and has a protonated guanidine pendant
2 2
that may assist the cleavage of HPNPP through hydrogen-
bonding/electrostatic interactions.
At pH 7, the rates of cleavage of BNPP and HNPP by C2
and C3 were faster than for C1 (5−10-fold) and [Cu(tacn)-
2
+
(
OH ) ] (3−5-fold), whereas at pH 9, the fastest rates were
2 2
observed for C3, the most active complex in the series. C3 is
also more active than complexes with more rigid xylyl-linked
2
+
2+
guanidinium groups, [Cu(C)(OH ) ] , [Cu(D)(OH ) ] ,
2
2
2 2
2+ 50
and [Cu(E)(OH ) ] . The guanidinium groups in C2 and
2
2
C3 appear to play an active role in cleavage. Assuming that
cleavage involves mono aqua-hydroxo species, as proposed by
1
1
hydroxide nucleophile as the active species. {For simplicity, in
Burstyn and co-workers, the charged pendants may be
the discussion of cleavage studies that follows, we refer to the
enhancing substrate binding and stabilizing transition states
parent complexes, C1−C3, but it should be emphasized that on
through electrostatic/hydrogen-bonding interactions. That the
Figure 8. Proposed protonation and dimerization equilibria for complex C1.
9
48
dx.doi.org/10.1021/ic2019814 | Inorg. Chem. 2012, 51, 939−953

Inorganic Chemistry
Article
Figure 9. Proposed protonation and dimerization equilibria for complexes C2 and C3.
guanidinium pendants contribute to activity is supported by the
fact that addition of a second propylguanidinium pendant to C2
leads to further increases in the rate of BNPP and HPNPP
confirmed through experiments performed in the presence of
various scavengers for reactive oxygen species (Figures S16−
S21 in the Supporting Information), as well as under anaerobic
conditions (Figures S22−S24 in the Supporting Information),
consistent with earlier observations for related Cu(II)−tacn-
2
+
cleavage (cf. C2 vs [Cu(B)(OH ) ] in Tables 9 and 10). It
2
2
should be noted, however, that the cleavage rates for C2 and
C3 fall within the range observed for di- and trialkylated tacn−
6
,49,50
based complexes.
5
7,58,75,80
copper(II) complexes.
The propyl derivative, C2, exhibited the highest rate of DNA
cleavage, being ca. 15 times more active than the Cu(II)−tacn
Cleavage of Plasmid DNA. The cleavage of pBR 322
plasmid DNA by complexes C1−C3 was studied as function of
pH and complex concentration, under aerobic and anaerobic
conditions, and in the presence of radical scavengers. The
results of these experiments are summarized in Figures 10−12
and S05−S26 in the Supporting Information and Tables 11 and
S02−S12 in the Supporting Information. Incubation of pBR
7
complex and accelerating cleavage by a factor of 2 × 10 relative
82
to the background rate. The varying rates of DNA cleavage by
the guanidine-bearing compounds indicate that DNA hydrol-
ysis may be driven by cooperativity between the Cu(II) center
and positively charged guanidinium group and that the degree
of cooperativity can be favorably altered by tuning the length
50
3
22 plasmid DNA with complexes C1, C2, and C3 converts the
supercoiled form (form I) to the singly nicked relaxed from
form II) and to the double-nicked linear form (form III)
and nature of the pendant. Complexes C1−C3 are all more
reactive than the analogues bearing two alkylguanidine
pendants, [Cu(A)]2+ and [Cu(B)(OH ) ] , indicating that
2+
(
2
2
toward the end of the 48 h incubation period (Figure 10). The
their reduced steric bulk probably allows better access of the
rate of cleavage was 5−15-fold faster than for nonfunctionalized
Cu(II) center to the sugar−phosphate backbone. In the case of
2
+
2+
[
Cu(tacn)(OH ) ] complex (see Table 11). For example,
[Cu(A)] , strong binding of the two guanidine pendants
2
2
incubation of pBR 322 plasmid DNA for 6 h at pH 7.0 in the
saturates the primary coordination sphere and also contributes
to the reduced reactivity of this complex.
presence of 150 μM C1−C3 converted 72−90% of the initial
2+
DNA to form II, cf., 20% for [Cu(tacn)(OH ) ] . Control
The enhanced rate of DNA cleavage by C1, when compared
to BNPP, is consistent with our previous results on phosphate
2
2
experiments confirmed that no measurable DNA cleavage
occurred when pBR 322 plasmid DNA was incubated with a
49
ester cleavage by the Cu(II)-bis-guanidinium tacn family,
1
50 μM concentration of either the nonmetalated ligands or
where it was postulated that, on introduction of DNA,
phosphodiester−guanidinium and phosphodiester−Cu(II) in-
teractions induce detachment and protonation of the
coordinated guanidines, leading to improved potency. For
C1, this would create a vacant site on the Cu(II) center for an
CuCl (see Figure S26 in the Supporting Information). This
indicates that the species active in DNA cleavage are (or are
2
derived from) complexes C1−C3. A predominantly hydrolytic
(
as opposed to redox-mediated) mode of cleavage was
9
49
dx.doi.org/10.1021/ic2019814 | Inorg. Chem. 2012, 51, 939−953

Inorganic Chemistry
Article
Table 9. First-Order Rate Constants for Hydrolysis of BNPP
a
by Copper(II) tacn-Based Complexes
1
06 kobs (s−1)
pH 7.0
0.0003
compd
pH 9.0
refs
this
control
work
57
this
work
this
work
this
work
2
+
[
[
Cu(tacn)(OH ) ]
1.71 ± 0.01
1.35 ± 0.09
6.3
2
2
1
3+
Cu L (μ-OH)] (C1)
7.9 ± 0.5
8.5 ± 0.5
19 ± 3
2
2
2
2+
[
Cu(L )(OH ) ] (C2)
7.0 ± 0.1
2
2
3
2+
[
Cu(L )(OH ) ] (C3)
10.2 ± 0.9
2
2
b
NRd
[
[
[
[
[
[
[
[
[
[
Cu(A)]2+
0.0100 ± 0.0003
72.4 ± 0.8
1.65 ± 0.03
2.36 ± 0.03
2.39 ± 0.04
12.4
49
49
2
+
Cu(B)(OH ) ]
63.5 ± 0.2
3.07 ± 0.08 50
7.02 ± 0.07 50
7.49 ± 0.05 50
2
2
2
+
Cu(C)(OH ) ]
2
2
2
+
Cu(D)(OH ) ]
2
2
2+
Cu(E)(OH ) ]
2
2
2
2
+
+
c
c
Cu(Me tacn)(OH )]
58
57
80
75
75
2
2
Cu(Me tacn)(OH )]
37
3
2
i
2+
c
Cu( Pr tacn)(OH )]
43
3
2
i
2+
c
Cu(Et Prtacn)(OH )]
14.3
2
i
Cu(PrNH Bn Prtacn)
0.48 ± 0.001
2
2
+
c
(
OH )]
2
i
2+
c
[
Cu(Bn Prtacn)(OH )]
15.3
70.1
75
58
2
[
Cu(BnMe tacn)
2
2
+
c
(
OH )]
2
a
Conditions used: [complex] = 2 mM, [BNPP] = 0.1 mM, [HEPES]
50 mM, I = 0.15 M, and T = 50 °C. Solutions were prepared by
dissolving samples of complexes C1−C3. Abbreviations: A, 1-ethyl-
,7-bis(2-guanidinoethyl)-1,4,7-triazacyclononane; B, 1-ethyl-4,7-bis(3-
guanidinopropyl)-1,4,7-triazacyclononane; C, 1-(o-guanidinoxylyl)-
,4,7-triazacyclononane; D, 1-(m-guanidinoxylyl)-1,4,7-triazacyclono-
=
Figure 10. Agarose gel showing cleavage of pBR 322 plasmid DNA
2+
(
38 μM bp) by [Cu(tacn)(OH ) ] and C1−C3 (150 μM) in
2
2
4
HEPES buffer (40 mM, pH 7.2) at 37 °C for various time intervals.
Lanes 1 and 2, DNA control; lanes 3 and 4, 1 h; lanes 5 and 6, 2 h;
lanes 7 and 8, 4 h; lanes 9 and 10, 6 h; lanes 11 and 12, 8 h; lanes 13
and 14, 16 h; lanes 15 and 16, 24 h; and lanes 17 and 18, 48 h.
1
nane; E, 1-(p-guanidinoxylyl)-1,4,7-triazacyclononane; Me tacn, 1,4-
2
dimethyl-1,4,7-triazacyclononane; Me tacn, 1,4,7-trimethyl-1,4,7-tria-
3
i
zacyclononane; Pr tacn, 1,4,7-triisopropyl-1,4,7-triazacyclononane;
Et Prtacn, 1-ethyl-4-isopropyl-1,4,7-triazacyclononane; Bn Prtacn, 1-
3
The extent of plasmid DNA cleavage by complexes C1−C3
was found to vary with pH and complex concentration in a very
similar fashion to that previously observed for the bis(alkylgua-
i
i
benzyl-4-isopropyl-1,4,7-triazacyclononane; BnMe tacn, 1-benzyl-4,7-
2
b
dimethyl-1,4,7-triazacyclononane Data were analyzed using initial rate
method, yielding kobs indirectly, which was further converted to a first-
49
50
nidine) and xylylguanidine complex series. The plots of
percentage cleavage versus [complex] and pH display a bell-like
profile (Figures 11 and 12), with an optimal rate of DNA
cleavage at a pH and [complex] of 7.0 and 150 μM,
respectively, similar to those reported previously for synthetic
c
order rate constant. Aquo complexes formed on dissolution in
d
d d
aqueous solution.
NR, no reaction.
incoming phosphodiester on the DNA substrate to bind and
activate.
5
7,58,75,80
nucleases.
a
Table 10. First-Order Rate Constants for Cleavage of HPNPP by Copper(II) tacn-Based Complexes
1
06 kobs (s−1)
compd
pH 6.0
0.019
pH 7.0
pH 9.0
0.81
refs
b
HPNPP only
0.012 ± 0.007
3.6 ± 0.2
this work
50
2
+
b
b
[
[
[
[
[
[
[
[
[
Cu(tacn)(OH ) ]
∼0.4
8.7 ± 1.0
7.53 ± 0.01
22.8 ± 0.3
45.7 ± 1.0
2
2
3+
1
Cu L (μ-OH)] (C1)
1.16 ± 0.02
1.83 ± 0.02
2.77 ± 0.03
1.46 ± 0.09
14 ± 2
14.1 ± 0.7
0.13 ± 0.06
32 ± 3
1.88 ± 0.03
2.74 ± 0.02
2.30 ± 0.03
this work
this work
this work
49
2
2
2
2+
Cu(L )(OH ) ] (C2)
2
2
3
2+
Cu(L )(OH ) ] (C3)
2
2
Cu(A)]2+
2
+
Cu(B)(OH ) ]
49
2
2
2
+
Cu(C)(OH ) ]
0.754 ± 0.007
1.51 ± 0.02
0.936 ± 0.006
3.27 ± 0.09
10.1 ± 0.6
9.55 ± 0.01
50
2
2
2
+
Cu(D)(OH ) ]
50
2
2
2
+
Cu(E)(OH ) ]
50
2
2
a
Conditions used: [complex] = 2 mM, [HPNPP] = 0.1 mM, [HEPES] = 50 mM, I = 0.15 M, and T = 25 °C. Solutions were prepared by dissolving
b
samples of complexes C1−C3. For abbreviations, see the footnotes to Table 9. Data were analyzed using initial rate method, yielding k directly.
Value at pH 6 has been corrected using the effective molar extinction coefficient.
obs
9
50
dx.doi.org/10.1021/ic2019814 | Inorg. Chem. 2012, 51, 939−953

Inorganic Chemistry
Article
Table 11. First-Order Rate Constants for Single-Strand
Cleavage of pBR 322 Plasmid DNA by Copper(II) tacn-
Based Complexes
For C1, the pH-dependent reactivity can be explained by
considering the different protonated forms of the complex at
pH 4.0−12.0 (Figure 7), each of which will have different DNA
cleavage activity, with the overall cleavage activity at any pH
being a cumulative effect of all the species coexisting in the
solution. With an increase in pH, the concentration of the less
a
5
−1
compd
10 k (s )
refs
obs
2
+
[
[
[
[
[
[
[
[
[
Cu(tacn)(OH ) ]
1.23 ± 0.37
13.03 ± 0.13
18.73 ± 0.19
5.51 ± 0.03
1.58 ± 0.05
2.53 ± 0.04
27.1 ± 0.28
8.15 ± 1.02
6.7 ± 0.3
49
2
2
1
3+
Cu L (μ−OH)] (C1)
this work
1
+
2
2
active form of C1, [Cu(L )(OH)] , increases. A nearly
saturated coordination environment around the Cu(II) center
and presence of a poor nucleophile make this species least
active, and as a result, reduced DNA cleavage activity is
observed at higher pH. In the case of C2 and C3, binuclear
complexes are unlikely to play a significant role in DNA
cleavage as the speciation studies (see Figure 7) indicate that
the concentration of these will be very small (a few % at most)
under the conditions of DNA cleavage (150−600 μM).
2
2+
Cu(L )(OH ) ] (C2)
this work
2
2
3
2+
Cu(L )(OH ) ] (C3)
this work
2
2
Cu(A)]2+
49
49
50
50
50
2
+
Cu(B)(OH ) ]
2
2
2
+
Cu(C)(OH ) ]
2
2
2
+
Cu(D)(OH ) ]
2
2
2+
Cu(E)(OH ) ]
2
2
a
Conditions used: [complex] = 150 μM, [pBR 322 plasmid] = 38 μM
bp, and [HEPES] = 40 mM (pH 7.0 at 37 °C). Data were analyzed
using first-order analysis, yielding kobs directly. Abbreviations: A, 1-
ethyl-4,7-bis(2-guanidinoethyl)-1,4,7-triazacyclononane; B, 1-ethyl-4,7-
bis(3-guanidinopropyl)-1,4,7-triazacyclononane; C, 1-(o-guanidinoxyl-
yl)-1,4,7-triazacyclononane; D, 1-(m-guanidinoxylyl)-1,4,7-triazacyclo-
Drawing comparisons from other phosphate diester hydro-
1,83,84
II
lyzing metal diaqua complexes,
the Cu -aqua-hydroxo
form of C2 and C3 should be most active in DNA cleavage.
Burstyn and co-workers have reported that the first pK for
a
2+
80
b
ligated water in the [Cu(tacn)(OH ) ] complex is ∼7.3.
Introduction of the guanidinium groups on the tacn ring has
been found to lower this value. Therefore, as the pH increases
above 7, mononuclear complexes will be converted into
dihydroxo complexes, [CuL (OH) ] and [CuL (OH) ]
2
2
nonane; and E, 1-(p-guanidinoxylyl)-1,4,7-triazacyclononane. [com-
c
plex] = 100 μM. [complex] = 144 μM.
85
2
2+
3
2+
2
2
(
see Figure 7), which leads to a decrease in the concentration
of active species and a concomitant decrease in DNA cleavage
rates.
The rates of DNA cleavage with [complex] (Figure 11) for
2+
C1−C3 and [Cu(tacn)(OH ) ] were found to reach a
2
2
maximum at ca. 150 μM and to then decrease as the
concentration of complex is increased further. Similar reactivity
profiles have been observed previously and concluded to be due
to the formation of increased amounts of the hydroxo-bridged
dimers, which bind DNA, blocking access of the cleavage-active
5
7,58,75,80
monomeric species.
However, as noted previously for
C2 and C3, the dimer concentration is predicted to be very low
under the DNA cleavage conditions. This prompts us to
propose an alternative explanation for the observed behavior.
The DNA cleavage experiments are conducted with an excess
of metal complex, some 2−15 times the DNA base pair
concentration, but the actual DNA concentration is in the
nanomolar range so that [complex] is >2000 higher than
Figure 11. Concentration dependence of cleavage of pBR 322 DNA
promoted by C1, C2, C3, and Cu -tacn in 40 mM HEPES (pH 7.0) at
II
37 °C over a 4 h period.
[
[
DNA] and in very large excess. Thus, it is conceivable that as
complex] increases, mononuclear forms of the complexes bind
to and/or electrostatically interact with more and more of the
exposed phosphate ester groups in DNA, thereby stabilizing it
against cleavage.
CONCLUSION
The copper(II) complexes of three tacn-based ligands with
■
1
2
single ethylguanidine (L ), propylguanidine (L ), and butylgua-
3
nidine (L ) pendant arms have been synthesized and
characterized. X-ray crystallography reveal that, under basic
1
conditions, L forms a monohydroxo-bridged binuclear copper-
(
II) complex (C1) in which the guanidine pendants coordinate
to the copper(II) centers, forming five-membered chelate rings.
2
3
In contrast, L and L yield mononuclear complexes (C2 and
C3) in which the guanidinium pendants remain protonated and
do not coordinate. Complexes C2 and C3 are more reactive
toward the simple phosphodiesters BNPP and HPNPP than
the analogues featuring xylyl-linked guanidine groups, suggest-
ing that the more flexible alkyl pendants allow the guanidinium
groups to better interact with the Cu(II)-bound phosphate
Figure 12. pH dependence of the cleavage of pBR 322 DNA
promoted by C1, C2, and C3 over a 4 h period ([DNA] = 38 μM bp,
[
complex] = 150 μM, and T = 37 °C).
9
51
dx.doi.org/10.1021/ic2019814 | Inorg. Chem. 2012, 51, 939−953

Inorganic Chemistry
Article
ester and assist with cleavage. Complex C1 displays lower
reactivity than C2 and C3 but is on par with the “parent” tacn
complex, indicating that the coordinated guanidine may partly
dissociate from the metal center to allow for substrate binding.
Complexes C1−C3 were all found to cleave plasmid DNA
(14) Baker, B. F.; Lot, S. S.; Kringle, J.; Cheng-Flournoy, S.; Villiet,
P.; Sasmor, H. M.; Siskowski, A. M.; Chappell, L. L.; Morrow, J. R.
Nucl. Acids. Res. 1999, 27, 1547−1551.
(
15) Perreault, D. M.; Ansyln, E. V. Angew. Chem., Int. Ed. 1997, 36,
32−450.
16) Cheng, C. C.; Rokita, S. E.; Burrows, C. J. Angew. Chem., Int. Ed.
993, 32, 277−278.
17) Friedel, M. G.; Pieck, J. C.; Klages, J.; Dauth, C.; Kessler, H.;
Carell, T. Chem.Eur. J. 2006, 12, 6081−6094.
4
(
1
(
2
+
II
faster than [Cu(tacn)(OH ) ] and the Cu −tacn bis(alkyl-
2
2
guanidine) complexes, indicating that they can better access the
sugar−phosphate backbone and that the guanidinium groups
likely act in concert with the copper(II) center to accelerate
cleavage. For all three complexes, a reduction in the rate of
DNA cleavage with increasing pH is attributed to the formation
of hydrolytically inactive complexes. The decrease in cleavage
rate with [complex], on the other hand, points to the possibility
that the amount of mononuclear complex bound to DNA
increases with concentration and that this stabilizes the DNA
against cleavage.
(
18) Mancin, F.; Tecilla, P. New J. Chem. 2007, 31, 800−817.
(19) Noll, D. M.; Mason, T. M.; Miller, P. S. Chem. Rev. 2006, 106,
277−301.
(20) Hettich, R.; Schneider, H.-J. J. Am. Chem. Soc. 1997, 119, 5638−
5
647.
(
21) Ren, R.; Yang, P.; Zheng, W.; Hua, Z. Inorg. Chem. 2000, 39,
454−5463.
22) Komiyama, M.; Kina, S.; Matsumura, K.; Sumaoka, J.; Tobey, S.;
5
(
Lynch, V. M.; Ansyln, E. V. J. Am. Chem. Soc. 2002, 124, 13731−
1
3736.
ASSOCIATED CONTENT
(23) Yang, M.-Y.; Richard, J. P.; Morrow, J. R. Chem. Commun. 2003,
■
2
(
832−2833.
*
S
Supporting Information
24) Worm, K.; Chu, F.; Matsumoto, K.; Best, M. D.; Lynch, V. M.;
Crystallographic files in CIF format; table of crystallographic
data (Table S01), figures showing H-bonding and unit cell
lattice of complexes C1−C3 (Figures S01−S03), UV−visible
titration data (Figure S04); agarose gel images of DNA cleavage
and kinetic profiles (Figures S05−S26 and Tables S02−S12),
and histograms showing extent of DNA cleavage in presence of
scavenging agents and under aerobic/anaerobic conditions
Ansyln, E. V. Chem.Eur. J. 2003, 9, 741−747.
(25) Jin, Y.; Cowan, J. A. J. Am. Chem. Soc. 2005, 127, 8408−8415.
(26) An, Y.; Tong, M.-L.; Ji, L.-N.; Mao, Z.-W. Dalton Trans. 2006,
2066−2071.
(27) Corneillie, T. M.; Whetstone, P. A.; Lee, K. C.; Wong, J. P.;
Meares, C. F. Bioconjugate Chem. 2004, 15, 1389−1391.
(28) Qian, J.; Gu, W.; Liu, H.; Gao, F.; Feng, L.; Yan, S.; Liao, D.;
Cheng, P. Dalton Trans. 2007, 1060−1066.
29) Kovari, E.; Heitker, J.; Kramer, R. J. Chem. Soc. Chem. Commun.
995, 1205−1206.
30) Kovari, E.; Kramer, R. J. Am. Chem. Soc. 1996, 118, 12704−
12709.
(
Figures S17, S19, S21, and S25). This material is available free
(
1
(
of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
(31) Jubian, V.; Dixon, R. P.; Hamilton, A. D. J. Am. Chem. Soc. 1992,
Corresponding Author
1
(
14, 1120−1121.
*
Fax: +61 3 9903 9582. E-mail: Bim.Graham@monash.edu
B.G.). Fax: +61 3 9905 4597. E-mail: Leone.Spiccia@monash.
edu (L.S.).
32) Dixon, R. P.; Geib, S. J.; Hamilton, A. D. J. Am. Chem. Soc. 1992,
(
114, 365−366.
(33) Jubian, V.; Veronese, A.; Dixon, R. P.; Hamilton, A. D. Angew.
Chem., Int. Ed. 1995, 34, 1237−1239.
(34) Muche, M.-S.; Goebel, M. W. Angew. Chem., Int. Ed. 1996, 35,
ACKNOWLEDGMENTS
■
2126−2129.
This work was supported by the Australian Research Council
through the Discovery Program. L.T. is the recipient of a
Monash Graduate Scholarship and Postgraduate Publication
Award.
(35) Ariga, K.; Ansyln, E. V. J. Org. Chem. 1992, 57, 417−419.
(36) Ait-Haddou, H.; Sumaoka, J.; Wiskur, S. J.; Folmer-Andersen, J.
F.; Ansyln, E. V. Angew. Chem., Int. Ed. 2002, 41, 4013−4016.
(37) Feng, G.; Mareque-Rivas, J. C.; de-Rosales, R. T. M.; Williams,
N. H. J. Am. Chem. Soc. 2005, 127, 13470−13471.
38) Feng, G.; Mareque-Rivas, J. C.; Williams, N. H. Chem. Commun.
2006, 1845−1847.
39) Chen, X. Q.; Wang, J. Y.; Sun, S. G.; Fan, J. L.; Wu, S.; Liu, J. F.;
(
REFERENCES
■
(
(
1) Hegg, E. L.; Burstyn, J. N. Coord. Chem. Rev. 1998, 173, 133−
Ma, S. J.; Zhang, L. Z.; Peng, X. J. Bioorg. Med. Chem. Lett. 2008, 18,
109−113.
(40) He, J.; Hu, P.; Wang, Y. J.; Tong, M.-L.; Sun, H. Z.; Mao, Z.-W.;
Ji, L.-N. Dalton Trans. 2008, 3207−3214.
165.
(
7
(
2) Yun, J. W.; Tanase, T.; Lippard, S. J. Inorg. Chem. 1996, 35,
590−7600.
3) Gomez-Tagle, P.; Yatsimirsky, A. K. J. Chem. Soc., Dalton Trans.
2
(
(
001, 2663−2670.
(41) Sheng, X.; Lu, X. M.; Chen, Y. T.; Lu, G.-Y.; Zhang, J. J.; Shao,
Y.; Liu, F.; Xu, Q. Chem.Eur. J. 2007, 13, 9703−9712.
(42) Shao, Y.; Sheng, X.; Li, Y.; Jia, Z. L.; Zhang, J. J.; Liu, F.; Lu, G.-
Y. Bioconjugate Chem. 2008, 19, 1840−1848.
4) Hay, R. W.; Govan, N. Polyhedron 1998, 17, 463−468.
5) Hegg, E. L.; Burstyn, J. N. J. Am. Chem. Soc. 1995, 117, 7015−
7016.
(
(
6) Hegg, E. L.; Burstyn, J. N. Inorg. Chem. 1996, 35, 7474−7481.
7) Hegg, E. L.; Deal, K. A.; Kiessling, L. L.; Burstyn, J. N. Inorg.
(43) Cotton, F. A.; Hazen, E. E. J.; Legg, M. Proc. Natl. Acad. Sci.
U.S.A. 1979, 76, 2551−2555.
Chem. 1997, 36, 1715−1718.
(
(44) Weber, D. J.; Meeker, A. K.; Mildvan, A. S. Biochemistry 1991,
30, 6103−6114.
8) Erkkila, K. E.; Odom, D. T.; Barton, J. K. Chem. Rev. 1999, 99,
2
(
777−2796.
(45) Wilcox, D. E. Chem. Rev. 1996, 96, 2435−2458.
(46) Sheng, X.; Guo, X.; Lu, M.-X.; Lu, G.-Y.; Shao, Y.; Liu, F.; Xu,
Q. Bioconjugate Chem. 2008, 19, 490−498.
9) Rajski, S. R.; Williams, R. M. Chem. Rev. 1998, 98, 2723−2796.
10) Burger, R. M. Chem. Rev. 1998, 98, 1153−1170.
11) Sherman, S. E.; Lippard, S. J. Chem. Rev. 1987, 87, 1153−1181.
12) Cowan, J. A. Curr. Opin. Chem. Biol. 2001, 5, 634−642.
13) Morrow, J. R.; Iranzo, O. Curr. Opin. Chem. Biol. 2004, 8, 192−
(
(
(
(
(47) Kim, J. H.; Youn, M. R.; Lee, Y.-A.; Kim, J. M.; Kim, S. K. Bull.
Korean Chem. Soc. 2007, 28, 263−270.
(48) Iranzo, O.; Elmer, T.; Richard, J. P.; Morrow, J. R. Inorg. Chem.
2003, 42, 7737−7746.
200.
9
52
dx.doi.org/10.1021/ic2019814 | Inorg. Chem. 2012, 51, 939−953

Inorganic Chemistry
Article
(
49) Tjioe, L.; Joshi, T.; Brugger, J.; Graham, B.; Spiccia, L. Inorg.
Chem. 2011, 50, 621−635.
50) Tjioe, L.; Meininger, A.; Joshi, T.; Graham, B.; Spiccia, L. Inorg.
Chem. 2011, 50, 4327−4339.
51) Kimura, S.; Bill, E.; Bothe, E.; Weyhermuller, T.; Wieghardt, K.
(81) Bazzicalupi, C.; Bencini, A.; Bonaccini, C.; Giorgi, C.; Gratteri,
P.; S., M.; Palumbo, M.; Simionato, A.; Sgrignani, J.; Sissi, C.;
Valtancoli, B. Inorg. Chem. 2008, 47, 5473−5484.
(
(82) Eigner, J.; Boedtker, H.; Michaels, G. Biochim. Biophys. Acta
1961, 51, 165−168.
(
(
(
83) Chin, J.; Zou, X. J. Am. Chem. Soc. 1988, 110, 223−225.
84) Chin, J.; Banaszczyk, M.; Jubian, V.; Zou, X. J. Am. Chem. Soc.
J. Am. Chem. Soc. 2001, 123, 6025−6039.
(
(
52) Brown, D. M.; Usher, D. A. J. Chem. Soc. 1965, 6558−6564.
53) Tsang, J. S.; Neverov, A. A.; Brown, R. S. J. Am. Chem. Soc. 2003,
1
(
989, 111, 186−190.
85) Aoki, S.; Iwaida, K.; Hanamoto, N.; Shiro, M.; Kimura, E. J. Am.
Chem. Soc. 2002, 124, 5256−5257.
1
(
25, 1559−1566.
54) Brugger, J. Comput. Geosci. 2007, 33, 248−261.
55) Brugger, J.; McPhail, D. C.; Black, J.; Spiccia, L. Geochim.
(
Cosmochim. Acta 2001, 65, 2691−2708.
56) Liu, W.; Etschmann, B.; Brugger, J.; Spiccia, L.; Foran, G.;
McInnes, B. Chem. Geol. 2006, 231, 326−349.
57) Fry, F.; Fischmann, A. J.; Belousoff, M. J.; Spiccia, L.; Brugger, J.
Inorg. Chem. 2005, 44, 941−950.
58) Belousoff, M. J.; Duriska, M. B.; Graham, B.; Batten, S. R.;
Moubaraki, B.; Murray, K. S.; Spiccia, L. Inorg. Chem. 2006, 47, 3746−
755.
59) Sheldrick, G. M. SHELXL-97; University of Gottingen:
Gottingen, Germany, 1997.
60) Sheldrick, G. M. SHELXS-97; University of Gottingen:
Gottingen, Germany, 1997.
61) Schwindinger, W. F.; Fawcett, T. G.; Lalancette, R. A.; Potenza,
J. A.; Schugar, H. J. Inorg. Chem. 1980, 19, 1379−1381.
62) Addison, A. W.; Rao, T. N.; Reedjik, J.; Rijin, J. V.; Verschoor,
G. C. J. Chem. Soc., Dalton Trans. 1984, 1349−1356.
63) Di Vaira, M.; Mani, F.; Stoppioni, P. Inorg. Chim. Acta 2000,
03, 61−69.
64) Graham, B.; Spiccia, L.; Fallon, G. D.; Hearn, M. T. W.; Mabbs,
F. E.; Moubaraki, B.; Murray, K. S. J. Chem. Soc., Dalton Trans. 2002,
226−1232.
65) Chaudhuri, P.; Ventur, D.; Wieghardt, K.; Peters, E., -M.; Peters,
K.; Simon, A. Angew. Chem., Int. Ed. 1985, 24, 57−59.
66) Elliot, D. J.; Martin, L. L.; Taylor, M. R. Acta Crystallogr., Sect. C
998, 54, 1259−1261.
67) Farrugia, L. J.; Lovatt, P. A.; Peacock, R. D. J. Chem. Soc., Dalton
Trans. 1997, 911−912.
68) Graham, B.; Hearn, M. T. W.; Junk, P. C.; Kepert, C. M.;
Mabbs, F. E.; Moubaraki, B.; Murray, K. S.; Spiccia, L. Inorg. Chem.
001, 40, 1536−1543.
69) Farrugia, L. J.; Lovatt, P. A.; Peacock, R. D. Inorg. Chim. Acta
996, 246, 343−348.
70) Evans, A. J.; Watkins, S. E.; Craig, D. C.; Colbran, S. B. J. Chem.
Soc., Dalton Trans. 2002, 983−994.
71) Mahapatra, S.; Halfen, J. A.; Wilkinson, E. C.; Pan, G.; Wang, X.;
(
(
(
3
(
(
(
(
(
3
(
1
(
(
1
(
(
2
(
1
(
(
Young, V. G. J.; Cramer, C. J.; Que, L. J.; Tolman, W. B. J. Am. Chem.
Soc. 1996, 118, 11555−11574.
(
72) Fry, F.; Spiccia, L.; Jensen, P.; Moubaraki, B.; Murray, K. S.;
Tieknik, E. D. T. Inorg. Chem. 2003, 42, 5594−5603.
73) Brudenell, S. J.; Spiccia, L.; Tieknik, E. D. T. Inorg. Chem. 1996,
5, 1974−1979.
74) Tei, L.; Bencini, A.; Blake, A. J.; Lippolis, V.; Perra, A.;
Valtancoli, B.; Wilson, C.; Schroder, M. Dalton Trans. 2004, 1934−
944.
75) Belousoff, M. J.; Battle, A. R.; Graham, B.; Spiccia, L. Polyhedron
007, 26, 344−355.
76) Kruger, P. E.; Moubaraki, B.; Fallon, G. D.; Murray, K. S. J.
(
3
(
1
(
2
(
Chem. Soc., Dalton Trans. 2000, 713−718.
(
(
77) Bleaney, B.; Bowers, K. D. Proc. R. Soc 1952, 214, 451−465.
78) Koval, I. A.; van der Schilden, K.; Schuitema, A. M.; Gamez, P.;
Belle, C.; Pierre, J.-L.; Luken, M.; Krebs, B.; Roubeau, O.; Reedjik, J.
Inorg. Chem. 2005, 44, 4372−4382.
(
79) Draper, N. R.; Smith, H. Applied Regression Analysis; Wiley: New
York, 1998.
80) Deck, K. M.; Tseng, T. A.; Burstyn, J. N. Inorg. Chem. 2002, 41,
69−677.
(
6
9
53
dx.doi.org/10.1021/ic2019814 | Inorg. Chem. 2012, 51, 939−953