Synthesis and structural characterization of complexes of a DO3A-conjugated triphenylphosphonium cation with diagnostically important metal ions

Article abstract of DOI:10.1021/ic7010452

To understand the coordination chemistry of a DO3A-conjugated triphenylphosphonium (TPP) cation, triphenyl(4-((4,7,10-tris(carboxymethyl)-1,4, 7,10-tetraazacyclododecan-1-yl)methyl)benzyl)phosphonium (DO3A-xy-TPP), with diagnostically important metal ions, In(DO3A-xy-TPP)⁺, Ga(DO3A-xy-TPP)⁺, and Mn(DO3A-xy-TPP) were prepared by reacting DO3A-xy-TPP with 1 equiv of the respective metal salt. All three complexes have been characterized by elemental analysis, IR, ESI-MS, NMR methods (for In(DO3A-xy-TPP)⁺ and Ga(DO3A-xy-TPP)⁺), and X-ray crystallography. Results from HPLC concordance experiments show that ¹¹¹In(DO3A-xy-TPP)⁺ and In(DO3A-xy-TPP)⁺ have the same composition. The solid-state structures of In(DO3A-xy-TPP)⁺ and Mn(DO3A-xy-TPP) are very similar with DO3A being heptadentate in bonding to In(III) and Mn(II) in a monocapped octahedral coordination geometry. Because of the smaller size of Ga(III), the DO3A in Ga(DO3A-xy-TPP)⁺ is only hexadentate with four amine-N and two carboxylate-O atoms bonding to Ga(III). One carboxylic acid group in DO3A is deprotonated to balance the positive charge of Ga(III). The coordination geometry of Ga(DO3A-xy-TPP)⁺ is best described as a distorted octahedron. The NMR data shows that the coordinated DO3A in In(DO3A-xy-TPP)⁺ and Ga(DO3A-xy-TPP)⁺ is symmetrical in aqueous solution. There is no dissociation of the acetate chelating arms in In(DO3A-xy-TPP)⁺ and Ga(DO3A-xy-TPP)⁺, providing indirect evidence for the high solution stability of ¹¹¹In(DO3A-xy-TPP)⁺ and ⁶⁸Ga(DO3A-xy-TPP) ⁺.

Full text of DOI:10.1021/ic7010452

Inorg. Chem. 2007, 46, 8988−8997
Synthesis and Structural Characterization of Complexes of a
DO3A-Conjugated Triphenylphosphonium Cation with Diagnostically
Important Metal Ions
Chang-Tong Yang,† Yongxin Li,‡ and Shuang Liu*,†
School of Health Sciences, Purdue UniVersity, West Lafayette, Indiana 47907, and School of
Physical and Mathematical Sciences, Nanyang Technological UniVersity, Singapore
Received May 29, 2007
To understand the coordination chemistry of a DO3A-conjugated triphenylphosphonium (TPP) cation, triphenyl(4-
((4,7,10-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecan-1-yl)methyl)benzyl)phosphonium (DO3A-xy-TPP), with
diagnostically important metal ions, In(DO3A-xy-TPP)+, Ga(DO3A-xy-TPP)+, and Mn(DO3A-xy-TPP) were prepared
by reacting DO3A-xy-TPP with 1 equiv of the respective metal salt. All three complexes have been characterized
by elemental analysis, IR, ESI-MS, NMR methods (for In(DO3A-xy-TPP)+ and Ga(DO3A-xy-TPP)+), and X-ray
crystallography. Results from HPLC concordance experiments show that 111In(DO3A-xy-TPP)+ and In(DO3A-xy-
TPP)+ have the same composition. The solid-state structures of In(DO3A-xy-TPP)+ and Mn(DO3A-xy-TPP) are
very similar with DO3A being heptadentate in bonding to In(III) and Mn(II) in a monocapped octahedral coordination
geometry. Because of the smaller size of Ga(III), the DO3A in Ga(DO3A-xy-TPP)+ is only hexadentate with four
amine-N and two carboxylate-O atoms bonding to Ga(III). One carboxylic acid group in DO3A is deprotonated to
balance the positive charge of Ga(III). The coordination geometry of Ga(DO3A-xy-TPP)+ is best described as a
distorted octahedron. The NMR data shows that the coordinated DO3A in In(DO3A-xy-TPP)+ and Ga(DO3A-xy-
TPP)+ is symmetrical in aqueous solution. There is no dissociation of the acetate chelating arms in In(DO3A-xy-
TPP)+ and Ga(DO3A-xy-TPP)+, providing indirect evidence for the high solution stability of 111In(DO3A-xy-TPP)+
and 68Ga(DO3A-xy-TPP)+.
Introduction
kidney epithelial cell line was approximately 60 mV (163
mV in tumor cells vs 104 mV in normal cells). The
observation that the enhanced mitochondrial transmembrane
potential is prevalent in the tumor-cell phenotype provides
the conceptual basis for development of mitochondrial-
targeting diagnostic and therapeutic pharmaceuticals.1-3,10-13
Measurement of mitochondrial transmembrane potential
(∆Ψm) provides the most comprehensive reflection of
Alteration in the electric component or mitochondrial
membrane potential (∆Ψm) is an important characteristic of
cancer caused directly by mitochondrial dysfunction, such
as DNA mutation and oxidative stress.1-4 It has been reported
that the mitochondrial transmembrane potential in carcinoma
cells is significantly higher than that in normal epithelial
cells.5-9 For example, the difference in ∆Ψm between the
CX-1 colon carcinoma cells and the control green monkey
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* To whom correspondence should be addressed. Phone: 765-494-0236.
Fax: 765-496-1377. E-mail: lius@pharmacy.purdue.edu.
† Purdue University.
‡ Nanyang Technological University.
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8988 Inorganic Chemistry, Vol. 46, No. 21, 2007
10.1021/ic7010452 CCC: $37.00
© 2007 American Chemical Society
Published on Web 09/05/2007

DO3A-Conjugated Triphenylphosphonium Complexes
Figure 1. DO3A-conjugated TPP analogs and their radiometal complexes useful for imaging tumors.
mitochondrial bioenergetic function primarily because it
depends directly on proper integration of diverse metabolic
pathways that converge at mitochondria. Because plasma and
mitochondrial transmembrane potentials are negative, delo-
calized cationic molecules with appropriate structural features
are driven electrophoretically through these membranes and
tend to accumulate inside the energized mitochondria.1-4,11
For example, lipophilic cations, such as rhodamine-123 and
3H-tetraphenylphosphonium (3H-TPP), have been widely
used to measure mitochondrial potentials in tumor cells.1,14-16
According to the Nernst equation, the 60 mV difference in
∆Ψm between carcinoma and control epithelial cell is
theoretically sufficient to account for a 10-fold greater
accumulation of cationic compounds in carcinoma mito-
chondria than in those of normal cells.1-4,11 In addition, the
plasma membrane potential (30-90 mV) also preconcen-
trates the cationic species relative to the external medium,
thus affecting the cytoplasmic concentration of these com-
pounds and their availability for mitochondrial uptake.
Recently, several groups reported the use of radiolabeled
triphenylphosphonium (TPP) cations, such as 4-(18F-benzyl)-
triphenylphosphonium (Figure 1, 18F-BzTPP), as positron-
emission tomography (PET) potential radiotracers for tumor
tumor uptake than 99mTc-Sestamibi, its tumor selectivity is
very poor with the tumor/heart ratio being <0.2.19,23 In
3
addition, H-TPP is not suitable for imaging purposes. The
high uptake of 18F-BzTPP in the heart and liver may also
impose a significant challenge for its clinical applications
in the diagnosis of cancer in the chest and abdominal regions.
Thus, there is an urgent need for new radiotracers that have
high tumor selectivity and are able to provide information
of mitochondrial bioenergetic function in tumors by monitor-
ing mitochondrial potential in a noninvasive fashion.
Previously, we reported several 64Cu-labeled triphenylphos-
phonium (TPP) cations, such as 64Cu(DO3A-xy-TPP) (Figure
1, DO3A-xy-TPP ) triphenyl(4-((4,7,10-tris(carboxymethyl)-
1,4,7,10-tetraazacyclododecan-1-yl)methyl)benzyl)phospho-
nium), as new radiotracers for imaging tumors by positron-
emission tomography (PET).26 The TPP moiety acts as the
“mitochondrion-targeting biomolecule” to carry 64Cu into
tumor cells.26 DO3A is used as the bifunctional chelator
because it is able to form highly stable radiometal chelates
with radionuclides, such as 64Cu and 68Ga for PET, 111In for
single-photon emission computed tomography (SPECT), and
90Y and 177Lu for radiotherapy. Biodistribution and microPET
imaging studies have demonstrated that the 64Cu-labeled TPP
cations are able to localize in tumors with high tumor uptake
(2-3.5% ID/g) and high tumor selectivity (tumor/heart ratio
≈ 5:1 at 2 h postinjection, as compared to tumor/heart ratio
being <0.2 during the 2 h study period for 99mTc-Sestamibi).
The high tumor selectivity of the 64Cu-labeled TPP cations
is related to their low lipophilicity.26 The in vitro assay data
show that 64Cu(DO3A-xy-TPP) is able to localize in mito-
chondria of U87MG glioma cells. The 111In-labeled TPP
cations also have high tumor uptake, but their tumor
selectivity is not as good as that of their 64Cu analogs.27
In our previous report,26 we described the synthesis of Cu-
(DO3A-xy-TPP) as part of the characterization of 64Cu-
labeled TPP cations. However, we were not able to obtain
crystals of Cu(DO3A-xy-TPP) suitable for structural deter-
mination by X-ray crystallography. To understand the
coordination chemistry of DO3A-conjugated TPP cations
3
and heart imaging.17-25 Even though H-tetraphenylphos-
3
phonium (Figure 1, H-TPP) was reported to have a better
(13) Jakobs, S. Biochim. Biophys. Acta 2006, 1763, 561-575.
(14) Lichtshtein, D.; Kaback, H. R.; Blume, A. J. Proc. Natl. Acad. Sci.
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Biol. Med. 1994, 38, 521-526.
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F.; Frost, J. J.; Hare, J. M. J. Nucl. Med. 2006, 47, 1359-1366.
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Radiopharm. 2005, 48, 131-137.
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878-886.
Inorganic Chemistry, Vol. 46, No. 21, 2007 8989

Yang et al.
vacuum overnight before being submitted for elemental analysis.
The yield was 64.4 mg (∼67.6%). The HPLC retention time was
14.8 min with a purity of >95%. IR (cm-1, KBr pellet): δ 1632.7
(s, νCdO), 1726.6 (s, νCdO), 3441.3 (bs, νO-H). ESI-MS: m/z )
with diagnostically important metals and the impact of
radiometal chelates on biological properties of the radiola-
beled TPP cations, we prepared In(III), Ga(III), and Mn(II)
complexes of DO3A-xy-TPP. We are interested in the Ga-
(III) and In(III) complexes because of their potential ap-
plications as PET (68Ga) and SPECT (67Ga and 111In)
radiotracers. The Mn(II) complex is particularly interesting
because of its potential as a magnetic resonance imaging
(MRI) contrast agent and its similarity to its Cu(II) analog
with respect to molecular charge. In this report, we present
the synthesis and structural characterization of M(DO3A-
xy-TPP)+ (M ) Ga and In) and Mn(DO3A-xy-TPP). The
main objective of this study is to determine their structures
in both the solid state and solution. Biodistribution and
imaging data for 64Cu-labeled TPP cations has been described
previously.26 Biological evaluation for the 111In-labeled TPP
cations will be reported as a separate account.27
1
777.02 for [M + H]+ (778.50 calcd for [C40H45GaN4O6P]+). H
and 13C NMR data are listed in Table 1. 31P NMR (D2O, 300 Hz,
25 °C): δ 26.3 (s, 1P). Anal. Calcd For C40H46GaN5O9‚(CH3)2-
CO‚3H2O: C, 54.16; H, 6.06; N, 7.35. Found: C, 54.42; H, 5.93;
N, 7.02.
Mn(DO3A-xy-TPP). Mn(DO3A-xy-TPP) was prepared using
MnCl2 (12.5 mg, 0.1 mmol) according to the same procedure for
In(DO3A-xy-TPP)(OAc). Slow diffusion of methanol into the
reaction mixture afforded colorless crystals suitable for X-ray
crystallography. The solid was separated and dried under vacuum
before being submitted for elemental analysis. The yield was 61.7
mg (∼71.2%). A sample was analyzed by HPLC. The retention
time was 16.8 min with a purity of >95%. IR (cm-1, KBr pellet):
1637.1 (s, νCdO), 3429.3 (bs, νO-H). ESI-MS: m/z ) 764.09 for
[M + H]+ (763.72 calcd for [C40H45MnN4O6P]). Anal. Calcd for
C40H45MnN4O6P‚4H2O‚CH3OH: C, 54.46; H, 7.03; N, 5.72.
Found: C, 54.24; H, 6.71; N, 5.70.
Experimental Section
111In(DO3A-xy-TPP)+. NH4OAc buffer (0.5 mL, 0.1 M, pH 6.9)
containing 50 µg of the DO3A-xy-TPP and 0.10 mL of 111InCl3
solution (0.2-2.0 mCi) in 0.05 N HCl were added to a clean 3 mL
plastic vial. The mixture was heated at 100 °C for 30 min. After
the mixture was cooled to room temperature, a sample of the
resulting solution was analyzed by radio-HPLC. The HPLC
retention time was 14.7 min. The HPLC concordance experiment
was performed by injection of the HPLC-purified 111In(DO3A-xy-
TPP)+ and In(DO3A-xy-TPP)+ sequentially under the same chro-
matographic conditions.
Materials and Instruments. Chemicals were obtained from
Sigma/Aldrich (St. Louis, MO). 1,4,7,10-Tetraazacyclododecane-
4,7,10-tris(t-butyl acetate) (DO3A(OBu-t)3) was purchased from
Macrocyclics Inc. (Dallas, TX). NMR (1H, 13C, 31P, 1H-1H COSY,
HMQC, HSQC, HMBC, and NOESY) data were obtained using
Bruker DRX 300 MHz and Bruker Avance 500 MHz FT NMR
spectrometers. Chemical shifts are reported in parts per million
(ppm) relative to TMS. Infrared (IR) spectra were recorded on a
Perkin-Elmer FT-IR spectrometer. Mass spectra were collected
using positive mode on a Finnigan LCQ classic mass spectrometer,
School of Pharmacy, Purdue University. Elemental analysis was
performed by Dr. H. Daniel Lee using a Perkin-Elmer Series III
analyzer, Department of Chemistry, Purdue University.
HPLC Method. The HPLC method used a UV-vis detector (λ
) 254 nm), a â-ram IN-US detector, and a Zorbax Rx-C18 column
(4.6 mm × 150 mm, 300 Å pore size). The flow rate was 1 mL/
min with the mobile phase being isocratic with 80% solvent A (10
mM ammonium acetate) and 20% solvent B (acetonitrile) at 0-5
min, followed by a gradient mobile phase going from 20% B at 5
min to 60% B at 20 min.
In(DO3A-xy-TPP)(OAc). DO3A-xy-TPP was prepared accord-
ing to the procedure described in our previous report.26 DO3A-xy-
TPP (71.1 mg, 0.1 mmol) and In(OAc)3 (29.1 mg, 0.1 mmol) were
dissolved in 0.2 mL of NH4OAc buffer (0.5 M, pH ) 6.0). The
mixture was stirred and heated at 100 °C for 30 min. After filtration,
the filtrate was transferred into a clean 5 mL vial. Slow diffusion
of acetone into the reaction mixture produced colorless crystals
suitable for X-ray crystallography. The solid was separated by
filtration and dried under vacuum overnight before being submitted
for elemental analysis. The yield was 52.2 mg (∼63.5%). A sample
was analyzed by HPLC. The HPLC retention time was 14.7 min
with a purity of >95%. IR (cm-1, KBr pellet): 1629.6 (s, νCdO),
3435.2 (bs, νO-H). ESI-MS: m/z ) 823.16 for [M + H]+ (823.60
calcd for [C40H45InN4O6P]+). The 1H and 13C NMR data are listed
in Table 1. 31P NMR (D2O, 500 Hz, 25 °C): δ 19.5 (s, 1P). Anal.
Calcd for C42H48InN4O8P‚(CH3)2CO‚3H2O: C, 54.32; H, 6.03; N,
5.63. Found: C, 54.68; H, 6.19; N, 5.76.
X-ray Crystallographic Analysis. Crystallographic data for In-
(DO3A-xy-TPP)(OAc)‚7.5H2O‚(CH3)2CO, Ga(DO3A-xy-TPP)-
(NO3)‚6H2O‚(CH3)2CO, and Mn(DO3A-xy-TPP)‚4H2O‚CH3OH
were collected on a Nonius Kappa CCD diffractometer and are
listed in Table 2. Crystals were mounted on a glass fiber in a random
orientation. Preliminary examination and data collection were
performed using graphite-monochromated Mo KR radiation (λ )
0.71073 Å). Cell constants for data collection were obtained from
least-squares refinement, using the setting angles of 23 636 reflec-
tions in the range of 2 < λ < 25° for In(DO3A-xy-TPP)(OAc)‚
7.5H2O‚(CH3)2CO. A total of 23 636 reflections were collected,
and 9031 reflections were unique. Lorentz and polarization cor-
rections were applied to the data. The linear absorption coefficient
is 5.6 cm-1 for Mo KR radiation. An empirical absorption correction
using SCALEPACK28 was applied. The structure was solved by
direct methods using Charge Flipping29 in PLUTON.30 There are
eight oxygen atom positions of water molecules found in In(DO3A-
xy-TPP)(OAc)‚7.5H2O‚(CH3)2CO, seven of which have full oc-
cupancies, while one has fractional occupancy. For Ga(DO3A-xy-
TPP)(NO3)‚6H2O‚(CH3)2CO, cell constants for data collection were
obtained from least-squares refinement, using the setting angles of
18 858 reflections in the range of 3 < λ < 27°. The refined
mosaicity from DENZO/SCALEPACK28 was 0.34°, indicating good
crystal quality. A total of 18 858 reflections were collected, of which
8697 were unique. Frames were integrated with DENZO-SMN.28
Lorentz and polarization corrections were applied to the data. The
linear absorption coefficient is 7.0 cm-1 for Mo KR radiation. An
empirical absorption correction using SCALEPACK28 was applied.
Ga(DO3A-xy-TPP)(NO3). Ga(DO3A-xy-TPP)(NO3) was pre-
pared using Ga(NO3)3‚H2O (27.3 mg, 0.1 mmol) according to the
same procedure for In(DO3A-xy-TPP)(OAc). Slow diffusion of
acetone into the reaction mixture produced colorless crystals suitable
for X-ray crystallography. The solid was separated and dried under
(28) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307.
(29) Oszlanyi, G.; Suto, A. Acta Crystallogr. 2004, A60, 134.
(30) Spek, A. L. PLATON, Molecular Graphics Program; University of
Utrecht: Utrecht, The Netherlands, 1991.
8990 Inorganic Chemistry, Vol. 46, No. 21, 2007

DO3A-Conjugated Triphenylphosphonium Complexes
Table 1. 1H and 13C NMR Data (500 Hz) for In(DO3A-xy-TPP)+ and Ga(DO3A-xy-TPP)+a
In(DO3A-xy-TPP)+
Ga(DO3A-xy-TPP)+
H (mult., JHH
position
δH (mult., JHH
)
δC
δ
)
δC
1
2
178.2
60.1
173.1
62.5
3.53 (s)
3.54 (s)
3, 3′
4, 4′
5, 5′
3.09 (m), 3.33 (m)
3.04 (m), 3.25 (m)
3.62 (AB quartet)
54.8
54.8
61.5
3.26 (m), 4.02 (m)
3.35 (m), 3.51 (m)
3.85 (AB quartet)
53.8
56.2
58.7
6, 6′
7, 7′
8, 8′
9
177.9
53.5
49.1
173.0
56.5
53.3
3.04 (m), 3.29 (m)
2.69 (m)
3.96 (s)
3.35 (m), 3.51 (m)
2.89 (m), 3.39 (m)
3.92 (s)
58.9
63.5
10
132.6
134.9
133.7
131.0
31.7 (d)
119.7(d)
136.6
132.5
137.7
132.5
136.6
129.9
131.2
130.5
128.2
28.6 (d)
116.3
133.3
129.1
134.4
129.1
133.3
11, 11′
12, 12′
13
7.11 (d, 9.8 Hz)
7.00 (d, 9.8 Hz)
7.20 (d, 9.8 Hz)
6.96 (d, 9.8 Hz)
14
4.78 (d, 9.8 Hz)
4.78 (d, 9.8 Hz)
15, 15′,15′′
16, 16′, 16′′
17, 17′, 17′′
18, 18′, 18′′
19, 19′, 19′′
20, 20′, 20′′
7.65 (m)
7.65 (m)
7.86 (t)
7.65 (m)
7.65 (m)
7.57 (m)
7.57 (m)
7.78 (m)
7.57 (m)
7.57 (m)
1
a Both H and 13C NMR spectra were recorded in D2O at 25 °C.
The structure was solved by direct methods using SIR2004.31
Refinement was performed on a LINUX PC using SHELX-97.32
There were six O atom positions of lattice water molecules found
in Ga(DO3A-xy-TPP)+. No hydrogen atom was included for these
oxygen atoms, for which only the isotropic thermal parameter was
refined. Crystallographic drawings were done using programs
ORTEP33 and PLUTON.30 For Mn(DO3A-xy-TPP)‚4H2O‚CH3OH,
the cell constants for data collection were obtained from least-
squares refinement, using the setting angles of 26 583 reflections
in the range of 2 < λ < 26°. A total of 26 583 reflections were
collected, and 6443 reflections were unique. Lorentz and polariza-
tion corrections were applied to the data. The linear absorption
coefficient is 4.1 cm-1 for Mo KR radiation. An empirical
absorption correction using SCALEPACK28 was applied. The
structure was solved by direct methods using SIR2004.31 Refine-
ment was performed on a LINUX PC using SHELX-97.32 Crystal-
lographic drawings were done using programs ORTEP.33
Results
Synthesis. In this study, we prepared Ga(DO3A-xy-TPP)+,
In(DO3A-xy-TPP)+, and Mn(DO3A-xy-TPP) by reacting
DO3A-xy-TPP with 1 equiv of the respective metal salt in
0.5 M ammonium acetate buffer (pH 6). Heating was needed
to complete the reaction. Ga(DO3A-xy-TPP)+ and In(DO3A-
xy-TPP)+ were designed as model compounds for 67/68Ga-
(DO3A-xy-TPP)+ and 111In(DO3A-xy-TPP)+, respectively.
Mn(DO3A-xy-TPP) was prepared because of its potential
as a MRI contrast agent and its similarity to the Cu(II) analog
with respect to molecular charge and lipophilicity.26 Both
In(DO3A-xy-TPP)+ and Ga(DO3A-xy-TPP)+ were isolated
as the complex cations with acetate and nitrate as counterions,
respectively. Mn(DO3A-xy-TPP) was obtained as the zwit-
terion salt. All three compounds have been characterized by
IR, ESI-MS, HPLC, elemental analysis, and X-ray crystal-
lography. In(DO3A-xy-TPP)+ and Ga(DO3A-xy-TPP)+ have
(31) Burla, M. C.; Caliandro, R.; Camalli, M.; Carrozzini, B.; Cascarano,
G. L.; Caro, L. De; Giacovazzo, C.; Polidori, G.; Spagna, R. J. Appl.
Crystallogr. 2005, 38, 381.
(32) Sheldrick, G. M. SHELXL 97, A Program for Crystal Structure
Refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(33) Johnson, C. K. ORTEPII; Report ORNL-5138; Oak Ridge National
Laboratory: Oak Ridge, TN, 1976.
Inorganic Chemistry, Vol. 46, No. 21, 2007 8991

Yang et al.
Table 2. Selected Crystallographic Data and Structure Refinements
Details for In(DO3A-xy-TPP)(OAc)‚7.5H2O‚(CH3)2CO,
Ga(DO3A-xy-TPP)(NO3)‚6H2O‚(CH3)2CO, and
Mn(DO3A-xy-TPP)‚4H2O‚CH3OH
C45H69InN4O16.5
P
C43H64GaN5O16P C41H57MnN4O11P
fw
1075.83
1007.71
867.84
space
group
P1h (No. 2)
Pca21 (No. 29)
P21/c (No. 14)
λ (Å)
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
Mo KR (0.71073) Mo KR (0.71073) Mo KR (0.71073)
10.7779(9)
16.3040(17)
16.4520(18)
103.482(6)
106.939(6)
104.783(6)
2522.0(4)
2
28.9585(9)
12.8899(9)
19.1761(10)
17.1960(13)
90
103.84(4)
90
8.15090(10)
19.6548(6)
90
90
90
4639.3(2)
4
4127.0(5)
4
dcalcd
1.417
1.443
1.397
(g/cm3)
T (K)
150
0.572
0.788, 0.932
150
0.696
0.812, 0.773
150
0.406
0.954, 0.985
µ (mm-1
transm
coeff
)
R(Fo)
Rw(Fo )
0.056a
0.135b
0.043a
0.094b
0.069a
0.161b
2
a R ) ∑||Fo| - |Fc||/∑|Fo| for Fo2 > 2σ(Fo ). b Rw ) [∑w(|Fo | - |Fc2|)2/
2
2
2 2
∑w|Fo | ]1/2
.
also been studied by NMR spectroscopic methods (1H, 13C,
1
31P, H-1H COSY, HSQC, HMQC, HMBC, and NOESY)
to determine their solution structures.
IR and ESI-MS. The IR spectrum of In(DO3A-xy-TPP)-
(OAc) shows a strong and broad band at 3435 cm-1 attributed
to νO-H of the crystallization water molecules and a strong
band at 1630 cm-1 from the coordinated carboxylate groups.
Upon coordination, stretching frequencies from the carboxy-
lic groups (νCdO ≈ 1730 cm-1) undergo a significant “red-
shift” (∼100 cm-1). The IR spectra of complexes Ga(DO3A-
xy-TPP)(NO3) and Mn(DO3A-xy-TPP) also show broad
bands at 3441 and 3429 cm-1, respectively, attributed to
crystallization water molecules and strong bands at 1633
cm-1 for Ga(DO3A-xy-TPP)(NO3) and 1637 cm-1 for Mn-
(DO3A-xy-TPP) attributed to the coordinated carboxylate
groups. A strong band at 1727 cm-1 was observed for the
uncoordinated carboxylate group in Ga(DO3A-xy-TPP)-
(NO3). Two strong bands at 1300 and 1412 cm-1 are typical
Figure 2. Representative HPLC chromatograms of Ga(DO3A-xy-TPP)+,
In(DO3A-xy-TPP)+, and Mn(DO3A-xy-TPP).
Mn(DO3A-xy-TPP) (16.8 min). Obviously, Ga(DO3A-xy-
TPP)+ and In(DO3A-xy-TPP)+ with the +1 overall molec-
ular charge are more hydrophilic (shorter HPLC retention
time) than Mn(DO3A-xy-TPP) in the zwitterion form. The
HPLC retention time of Mn(DO3A-xy-TPP) is very close
to that of Cu(DO3A-xy-TPP) (17.2 min) under identical
chromatographic conditions.26
-
of non-coordinating NO3 counterions in Ga(DO3A-xy-
TPP)(NO3). The ESI-MS of In(DO3A-xy-TPP)(OAc) shows
a molecular ion at m/z ) 823.16 for [M + H]+, while the
ESI-MS of Ga(DO3A-xy-TPP)(NO3) has the molecular ion
at m/z ) 777.02 for [M + H]+. Mn(DO3A-xy-TPP) displays
the molecular ion at m/z ) 764.09 for [M + H]+ in its ESI
mass spectrum.
HPLC Analysis. The same HPLC method was used to
determine relative lipophilicity of Ga(DO3A-xy-TPP)+, In-
(DO3A-xy-TPP)+, and Mn(DO3A-xy-TPP). Figure 2 il-
lustrates their representative HPLC chromatograms. The
presence of a single peak in the region of interest suggests
that they exist in solution as a single or “averaged” species
under the chromatographic conditions used in this study. The
HPLC retention times for In(DO3A-xy-TPP)+ and Ga-
(DO3A-xy-TPP)+ are almost identical (14.5 and 14.7 min,
respectively), but they are significantly shorter than that of
HPLC Concordance Experiment. The HPLC concor-
dance experiment was performed using HPLC-purified
111In(DO3A-xy-TPP) and In(DO3A-xy-TPP). Figure 3 shows
HPLC chromatograms of In(DO3A-xy-TPP)+ (top) and 111
-
In(DO3A-xy-TPP)+ (bottom) under the same chromato-
graphic conditions. Since they share almost identical HPLC
retention times, we believe that 111In(DO3A-xy-TPP)+ and
In(DO3A-xy-TPP)+ have the same composition at both tracer
and macroscopic levels.
Structure of In(DO3A-xy-TPP)+. Figure 4 illustrates an
ORTEP view of In(DO3A-xy-TPP)+. There are two In-
(DO3A-xy-TPP)(OAc) molecules in each unit cell, along
with eight crystallization water molecules and one acetone
8992 Inorganic Chemistry, Vol. 46, No. 21, 2007

DO3A-Conjugated Triphenylphosphonium Complexes
O(71), O(101), from the carboxylate groups. The atom N(7)
caps the triangular face formed by N(4), N(10), and O(71).
In(DO3A-xy-TPP)+ has a symmetry plane that is defined
by four atoms: N(1), In(51), N(7), and O(71). The structure
of In(DO3A-xy-TPP)+ is very similar to those of Na[In(L1)]-
(NO3)(H2O)(C2H5OH)‚2.65H2O (H3L1 ) tris(2′-hydroxy-
benzylaminoethyl)amine)34 and [In(DO3A)]‚2H2O‚MeOH.35
Table 3 lists selected In-N and In-O bond distances and
selected bond angles in In(DO3A-xy-TPP)+. The average
In-N bond length is 2.374 Å (In(51)-N(1) ) 2.375(4) Å,
In(51)-N(4) ) 2.399(4) Å, In(51)-N(10) ) 2.327(4) Å,
In(51)-N(7) ) 2.395(4) Å), which is close to that (average
In-N distance ) 2.356 Å) of In(DO3A)‚2H2O‚MeOH35 and
is slightly shorter than that (average In-N distance ) 2.430
Å) of In(DOTA-AA) (DOTA-AA ) 1,4,7,10-tetraazacy-
clododecane-1,4,7,10-tetraacetic acid mono(p-aminoanilide))
because of its smaller coordination number.36 The average
In-O bond length is 2.174 Å (In(51)-O(41) ) 2.159(3) Å,
In(51)-O(71) ) 2.162(3) Å, and In(51)-O(101) ) 2.202-
(3) Å), which is comparable to that observed in In(DO3A)‚
2H2O‚MeOH (average In-O distance ) 2.181 Å),35 but it
is shorter than that of In(DOTA-AA) (average In-O distance
) 2.2191 Å).36 The N(7) amine-nitrogen atom caps the
triangular face formed by N(4), N(10), and O(71), leading
to the enlarged triangular face (O(71)-In(51)-N(4)) 114.19-
(13)°, N(10)-In(51)-N(4) ) 120.38(14)°, O(71)-In(51)-
N(10) ) 103.51(14)°) and the reduced triangular face formed
by N(1), O(41), and O(101) (O(41)-In(51)-N(1) ) 86.06-
(13)°, O(101)-In(51)-N(1) ) 86.55(13)°, and O(41)-In-
(51)-O(101) ) 84.51(12)°). The In(51)-N(7) bond distance
is 2.395(4) Å, which is significantly shorter than that (In-
(1)-N(7) ) 2.752(4) Å) in Na[In(L1)](NO3)(H2O)(C2H5-
OH)‚2.65H2O.34
Figure 3. HPLC concordance for In(DO3A-xy-TPP)+ (top) and 111In-
(DO3A-xy-TPP)+ (bottom). Their identical HPLC retention times suggest
that 111In(DO3A-xy-TPP)+ and In(DO3A-xy-TPP)+ have the same com-
position.
Table 3. Selected Bond Distances (Å) and Bond Angles (deg) in
In(DO3A-xy-TPP)(OAc)‚7.5H2O‚(CH3)2CO
atom 1
atom 2
distance
In51
In51
In51
In51
In51
In51
In51
O41
O71
O101
N10
N1
2.159(3)
2.162(3)
2.202(3)
2.327(3)
2.375(3)
2.395(3)
2.399(3)
N7
N4
Structure of Ga(DO3A-xy-TPP)+. Figure 5 shows the
ORTEP view of Ga(DO3A-xy-TPP)+. In each unit cell, there
are four Ga(DO3A-xy-TPP)(NO3) molecules, along with six
crystallization water molecules and one acetone surrounding
each Ga(DO3A-xy-TPP)(NO3). The coordinated DO3A is
hexadentate with four amine-N and two carboxylate-O donor
atoms bonding to Ga(III) due to its smaller size than that of
In(III). The remaining acetic acid group is uncoordinated and
deprotonated to balance the positive charge of Ga(III). The
coordination geometry around the Ga(III) is best described
as a distorted octahedron with N(4), N(10), O(41), and
O(101) forming the equatorial plane and N(1) and N(7)
occupying the remaining two axial positions. The structure
of Ga(DO3A-xy-TPP)+ is very similar to that reported for
Ga(DOTA-D-PheNH2) (DOTA-D-PheNH2 ) 1,4,7,10-tet-
raazacyclododecane-4,7,10-tricarboxymethyl-1-yl-acetyl-D-
Phe-NH2),37 Ga(HDOTA)‚5.5H2O (DOTA ) 1,4,7,10-
tetraazacyclododecane-4,7,10-triacetic acid),38 [Ga(Brbad)]-
atom 1
atom 2
atom 3
angle
O41
O41
O71
O41
O71
O101
O41
O71
O101
N10
O41
O71
O101
N10
N1
In51
In51
In51
In51
In51
In51
In51
In51
In51
In51
In51
In51
In51
In51
In51
In51
In51
In51
In51
In51
In51
O71
O101
O101
N10
N10
N10
N1
N1
N1
N1
N7
N7
N7
N7
N7
N4
N4
N4
N4
87.22(14)
84.51(12)
79.45(13)
152.56(14)
103.51(14)
73.04(13)
86.06(13)
164.99(14)
86.55(13)
77.22(14)
131.71(14)
73.31(15)
131.84(13)
75.72(14)
120.82(14)
75.61(14)
114.19(13)
154.85(14)
120.38(14)
77.00(13)
73.30(14)
O41
O71
O101
N10
N1
N4
N4
N7
(34) Liu, S.; Rettig, S. J.; Orvig, C. Inorg. Chem. 1992, 26, 5400.
(35) Riesen, A.; Kaden, T. A.; Ritter, W.; Ma¨cke, H. R. Chem. Commun.
1989, 460.
(36) Liu, S.; He, Z.; Hsieh, W.-Y.; Fanwick, P. E. Inorg. Chem. 2003, 42,
8831.
(37) Heppler, A.; Froidevaux, S.; Ma¨cke, H. R.; Jermann, E.; Be´he´, M.;
Powell, P.; Hennig, M. Chem.sEur. J. 1999, 5, 1974.
(38) Viola, N. A.; Rarig, Jr., R. S.; Ouellette, W.; Doyle, R. P. Polyhedron
2006, 25, 3457.
surrounding each In(DO3A-xy-TPP)+. DO3A acts as a
heptadentate ligand in bonding to In(III) with four amine-N
and three carboxylate-O donor atoms. The coordination
geometry in In(DO3A-xy-TPP)+ is best described as a
monocapped octahedron, in which there are three amine-N
atoms, N(1), N(4), N(10), and three oxygen atoms, O(41),
Inorganic Chemistry, Vol. 46, No. 21, 2007 8993

Yang et al.
Figure 4. ORTEP drawing of In(DO3A-xy-TPP)+. Ellipoids are at 50% probability. Crystallization molecules and hydrogen atoms are omitted for the sake
of clarity.
Figure 5. ORTEP drawing of Ga(DO3A-xy-TPP)+. Ellipoids are at 50% probability. Crystallization molecules and hydrogen atoms are omitted for the
sake of clarity.
Table 4. Selected Bond Distances (Å) and Bond Angles (deg) in
ClO4‚DMSO (H2Brbad ) 1,10-bis(2-hydroxy-5-bromoben-
Ga(DO3A-xy-TPP)(NO3)‚6H2O‚(CH3)2CO
zyl)-1,4,7,10-tetraazadecane),39 and [Ga(HL3)]Cl‚CHCl3 (H3-
atom 1
atom 2
distance
L3 ) tris(5′-bromo-2′-hydroxybenzylaminoethyl)amine).34
There is a symmetry plane that is defined by N(1), Ga(1),
and N(7) and that divides the coordinated DO3A moiety into
two identical parts. As a result, the bond angle N(10)-Ga-
(1)-N(7) (83.35(11)°) is almost identical to that of N(4)-
Ga(1)-N(7) (83.52(12)°), while the bond angle N(10)-
Ga(1)-N(1) (82.72(11)°) is very close to the angle N(4)-
Ga(1)-N(1) (83.10(12)°).
Ga1
Ga1
Ga1
Ga1
Ga1
Ga1
O41
O101
N4
N10
N7
1.926(2)
1.934(3)
2.115(3)
2.122(3)
2.125(3)
2.147(2)
N1
atom 1
atom 2
atom 3
angle
O41
O41
O10
O41
O10
N4
O41
O101
N4
N10
O41
O101
N4
N10
N7
Ga1
Ga1
Ga1
Ga1
Ga1
Ga1
Ga1
Ga1
Ga1
Ga1
Ga1
Ga1
Ga1
Ga1
Ga1
O101
N4
N4
N10
N10
N10
N7
N7
N7
N7
N1
84.95(12)
84.17(11)
168.95(11)
168.13(11)
83.25(12)
107.67(11)
97.49(10)
99.82(11)
83.52(12)
83.35(11)
99.95(9)
Table 4 lists the selected bond distances and bond angles
in Ga(DO3A-xy-TPP)+. The average Ga-N bond length is
2.127 Å (Ga(1)-N(4) ) 2.115(3) Å, Ga(1)-N(10) ) 2.122-
(3) Å, Ga(1)-N(7) ) 2.125(3) Å, Ga(1)-N(1) ) 2.147(2)
Å), which is very similar to those of Ga(HDOTA)‚5.5H2O
(average Ga-N distance ) 2.123 Å),38 [Ga(Brbad)]ClO4‚
DMSO (average Ga-N distance ) 2.112 Å),39 and [Ga-
(HL3)]Cl‚CHCl3 (average Ga-N distance ) 2.113 Å)34 and
is slightly shorter than that of Ga(DOTA-D-PheNH2) (aver-
age Ga-N distance ) 2.141 Å).37 The equatorial Ga-N
bonds (2.125(3) and 2.147(2) Å) are slightly longer than the
axial ones (2.115(3) and 2.122(3) Å). The average Ga-O
bond length is 1.930 Å (Ga(1)-O(41) ) 1.926(2) Å, Ga-
(1)-O(101) ) 1.934(3) Å), which is very close to that of
Ga(HDOTA)‚5.5H2O (1.935 Å)38 and slightly longer than
that of [Ga(Brbad)]ClO4‚DMSO (1.913 Å),39 [Ga(HL3)]Cl‚
CHCl3 (1.901 Å)34, and Ga(DOTA-D-PheNH2) (1.918 Å).37
N1
N1
N1
N1
96.91(12)
83.10(12)
82.72(11)
156.76(11)
Structure of Mn(DO3A-xy-TPP). A representative ORTEP
view of Mn(DO3A-xy-TPP) is shown in Figure 6. Crystal-
lization water molecules and hydrogen atoms are omitted
for the sake of clarity. In general, there are four Mn(DO3A-
xy-TPP) molecules in each unit cell, along with four
crystallization water molecules and one methanol molecule
surrounding each Mn(DO3A-xy-TPP). Like that in In(DO3A-
xy-TPP)+, the DO3A is heptadentate with all four amine-N
(39) Wong, E.; Liu, S.; Lu¨gger, T.; Hahn, F. E.; Orvig, C. Inorg. Chem.
1995, 34, 93.
8994 Inorganic Chemistry, Vol. 46, No. 21, 2007

DO3A-Conjugated Triphenylphosphonium Complexes
Mn-O bond length is 2.182 Å (Mn-O(43) ) 2.196(3) Å,
Mn-O(73) ) 2.190(3) Å, Mn-O(103) ) 2.161(3) Å), which
is slightly shorter than that of [Mn(EDTB)(Ac)](Ac)‚C2H5-
OH (EDTB ) N,N,N′,N′-tetrakis(2′-benzimidazolylmethyl)-
1,2-ethanediamine).41 The Mn-N(7) bond distance is 2.455-
(3) Å with N(7) capping the triangular face formed by N(4),
N(10), O(73), which leads to an increase of the triangular
face (N(4)-Mn-O(73) ) 110.85(12)°, N(4)-Mn-N(10) )
116.45(12)°, N(10)-Mn-O(73) ) 107.81(12)°) and a
decrease of the triangular face formed by N(1), O(43), and
O(103) (N(1)-Mn-O(43) ) 90.23(12)°, N(1)-Mn-O(103)
) 82.34(11)°, O(103)-Mn-O(43) ) 87.98(10)°) in the
octahedron. The coordination numbers of the Mn(II) com-
plexes range from four to eight.44 Seven-coordinated
Mn(II) complexes normally have the coordination geometry
of either monocapped octahedron or a pentagonal bi-
pyramid.39-43,45-47
Figure 6. ORTEP drawing of Mn(DO3A-xy-TPP). Ellipoids are at 50%
probability. Crystallization water molecules and hydrogen atoms are omitted
for the sake of clarity.
Table 5. Selected Bond Distances (Å) and Bond Angles (deg) in
Mn(DO3A-xy-TPP)‚4H2O‚CH3OH
atom 1
atom 2
distance
Mn
Mn
Mn
Mn
Mn
Mn
Mn
O103
O73
O43
N4
N10
N1
2.161(3)
2.190(3)
2.196(3)
2.379(3)
2.421(3)
2.447(3)
2.455(3)
NMR for In(DO3A-xy-TPP)+ and Ga(DO3A-xy-TPP)+.
Since 111In(DO3A-xy-TPP)+ and 67/68Ga(DO3A-xy-TPP)+ are
used as radiotracers in biological systems, it is necessary to
study their solution properties (structure, isomerism, and
stability) in aqueous solution. The solution structures of In-
(DO3A-xy-TPP)+ and Ga(DO3A-xy-TPP)+ were elucidated
using NMR methods (1H, 13C, 1H-1H COSY, HSQC,
HMQC, HMBC, and NOESY), while isomerism and stability
were monitored by variable-temperature 1H NMR spectros-
N7
atom 1
atom 2
atom 3
angle
O103
O103
O73
O103
O73
O43
O103
O73
O43
N4
O103
O73
O43
N4
N10
O103
O73
O43
N4
Mn
Mn
Mn
Mn
Mn
Mn
Mn
Mn
Mn
Mn
Mn
Mn
Mn
Mn
Mn
Mn
Mn
Mn
Mn
Mn
O73
O43
O43
N4
N4
N4
N10
N10
N10
N10
N1
N1
N1
N1
N1
N7
N7
N7
N7
89.64(11)
87.98(10)
84.66(11)
150.19(11)
110.85(12)
73.29(11)
74.55(11)
107.81(12)
158.14(11)
116.45(12)
82.34(11)
170.65(11)
90.23(11)
74.94(11)
74.75(11)
134.40(11)
71.13(11)
128.75(11)
74.43(11)
72.98(11)
1
copy. Table 1 summarizes H NMR and 13C NMR data for
In(DO3A-xy-TPP)+ and Ga(DO3A-xy-TPP)+ in D2O at
25 °C. Assignments of resonance signals from the phenyl,
p-xylene, and acetate groups were based on results from the
1H-1H COSY, NOESY, HSQC, and HMQC experiments
at 25 °C (Figures SI-SVI). The assignment of resonance
signals from protons of the cyclen backbone was tentative
because many of them are superimposed.
1
Figure 7 shows the aliphatic region of H NMR spectra
of In(DO3A-xy-TPP)+ in D2O at 5 (top) and 25 °C (bottom).
The doublet at 4.73 ppm is assigned to H14 and H14′ of the
PCH2C6H4 moiety. Splitting is caused by coupling from the
phosphonium-P. The singlet at 3.96 ppm is from H9 and
H9′ of the NCH2C6H4 moiety. The singlet at 3.53 is from
H2a and H2b in the acetate chelating arm attached to N(7).
The AB quartet at ∼3.6 ppm is assigned to H5a, H5b, H5a′,
and H5b′ of the two opposite acetate chelating arms. The
multiplets at 3.33 and 3.09 ppm are tentatively assigned to
H3a, H3a′, H3b, and H3b′ of the macrocycle. The multiplets
at 3.25 and 3.04 ppm are most likely from eight methylene
protons (H4, H4′, H7, and H7′), while the broad peak at 2.69
ppm is probably from the other methylene protons (H8a,
N10
N7
and three carboxylate-O atoms bonding to the Mn(II). There
is a symmetry plane defined by N(1), Mn, N(7), and O(71)
in the coordinated DO3A. The coordination geometry of Mn-
(DO3A-xy-TPP) is very similar to that of In(DO3A-xy-
TPP)+. Three amine-N atoms, N(1), N(4), and N(10), and
three carboxylate-O atoms, O(43), O(73), and O(103), form
the distorted octahedron. The remaining amine-N atom, N(7),
caps the triangular face formed by N(4), N(10), and O(73).
Table 5 lists selected Mn-N and Mn-O bond distances
and selected bond angles in the coordination sphere of Mn-
(DO3A-xy-TPP). The average Mn-N bond length is 2.426
Å (Mn-N(1) ) 2.447(3) Å, Mn-N(4) ) 2.379(3) Å, Mn-
N(10) ) 2.421(3) Å, Mn-N(7) ) 2.455(3) Å), which is in
agreement with those previously reported.40,41 The average
(42) Viossat, V.; Lemoine, P.; Dayan, E.; Dung, N.-H.; Voissat, B.
Polyhedron 2003, 22, 1461.
(43) Oki, A. R.; Gogineni, P.; Yurchenko, M.; Young, V. G., Jr Inorg.
Chim. Acta 1997, 257, 279.
(44) Baldeau, S. M.; Slinn, C. H.; Krebs, B.; Rompel, A. Inorg. Chim.
Acta 2004, 357, 3295.
(45) Platas-Iglesias, C.; Vaiana, L.; Esteban-Go´mez, David.; Avecilla, F.;
Real, J. A.; Blas, A. de; Rodr´ıguez-Blas, T. Inorg. Chem. 2005, 44,
9704.
(40) Luo, Y.; Zhang, J.; Lu, L.; Qian, M.; Wang, X.; Yang, X. Transition
Met. Chem. 2002, 27, 469.
(41) Liao, Z.-R.; Zheng, X.-F.; Luo, B.-S.; Shen, L.-R.; Li, D.-F.; Liu, H.-
L.; Zhao, W. Polyhedron 2001, 20, 2813.
(46) Ghachtouli, S. E.; Mohamadou, A.; Barbier, J.-P. Inorg. Chim. Acta
2005, 358, 3873.
(47) Coronado, E.; Gala´n-Mascaro´s, J. R.; Mart´ı-Gastaldo, C.; Mart´ınez,
A. M. Dalton Trans. 2006, 3294.
Inorganic Chemistry, Vol. 46, No. 21, 2007 8995

Yang et al.
1
Figure 7. Aliphatic region of the H NMR spectra of In(DO3A-xy-TPP)+ in D2O at 5 (top) and 25 °C (bottom).
1
Figure 8. Aliphatic region of the H NMR spectra of Ga(DO3A-xy-TPP)+ in D2O at 25 (top) and 65 °C (bottom).
H8a′, H8b, and H8b′) of the cyclen macrocycle. As the
temperature increases from 5 to 25 °C, all signals become
sharper with no significant change in their chemical shifts.
are from remaining four methylene protons (H8a, H8a′, H8b,
and H8b′) on the macrocyclic framework. As the temperature
increases from 25 to 65 °C, all proton resonance signals
remain the same, except for the multiplet at 4.0 ppm, which
shifted to 3.9 ppm probably because of rapid inversion of
ethylenic groups on the cyclen macrocycle.
1
Figure 8 shows the aliphatic region of H NMR spectra
of Ga(DO3A-xy-TPP)+ in D2O at 25 (top) and 65 °C
(bottom). The doublet at 4.78 ppm is assigned to H14 and
H14′ of the PCH2C6H4 moiety. The singlet at 3.92 ppm is
from H9 and H9′ of the NCH2C6H4 moiety. The singlet at
3.49 is assigned to methylene protons (H2a and H2b) in the
uncoordinated acetate group. The AB quartet at ∼3.85 ppm
are from four methylene protons (H5a and H5′) in the two
opposite acetate chelating arms due to the asymmetric nature
of Ga(DO3A-xy-TPP)+. The multiplets at 4.02 and 3.26 ppm
are tentatively assigned to methylene protons (H3a, H3a′,
H3b, and H3b′) of the cyclen macrocycle. The multiplets at
3.35 and 3.51 ppm are from eight methylene protons (H4,
H4′, H7, and H7′) and the multiplets at 2.89 and 3.39 ppm
Discussion
This report describes synthesis and structural characteriza-
tion of Ga(DO3A-xy-TPP)+, In(DO3A-xy-TPP)+, and Mn-
(DO3A-xy-TPP). The most important finding from this study
is that the bonding mode of DO3A depends largely on the
size of metal ion. For example, the ionic radius of In(III) is
0.92 Å,48 and DO3A is heptadentate in In(DO3A-xy-TPP)+.
Mn(II) has an ionic radius of 0.90 Å, and the coordination
(48) Shannon, R. D. Acta Crystallogr. 1976, A32, 751.
8996 Inorganic Chemistry, Vol. 46, No. 21, 2007

DO3A-Conjugated Triphenylphosphonium Complexes
geometry around Mn(II) in Mn(DO3A-xy-TPP) is almost
identical to that in In(DO3A-xy-TPP)+, despite their charge
difference. Ga(III) has a much smaller ionic radius (0.62 Å).48
As a result, coordinated DO3A is hexadentate with one
acetate group remaining deprotonated in Ga(DO3A-xy-
TPP)+. The overall molecular charge of Ga(DO3A-xy-TPP)+
is the same as that of In(DO3A-xy-TPP)+.
Conclusion
In conclusion, Ga(DO3A-xy-TPP)+, In(DO3A-xy-TPP)+,
and Mn(DO3A-xy-TPP) have been prepared and character-
ized by elemental analysis, spectroscopic methods, and X-ray
crystallography. In the solid state, DO3A uses all of its seven
donor atoms (N4O3) in bonding to In(III) or Mn(II), while it
is only hexadentate in bonding to Ga(III) with four amine-N
and only two carboxylate-O donor atoms. The NMR data
clearly demonstrate that the coordinated DO3A in In(DO3A-
xy-TPP)+ and Ga(DO3A-xy-TPP)+ is symmetrical in aque-
ous solution. The variable-temperature 1H NMR data reveal
no dissociation of the two acetate chelating arms in Ga-
(DO3A-xy-TPP)+, which remains rigid in aqueous solution
even at temperatures over 65 °C.
Another important finding from this study is that Ga-
(DO3A-xy-TPP)+ and In(DO3A-xy-TPP)+ are more hydro-
philic than Mn(DO3A-xy-TPP), the HPLC retention time of
which is very close to that of Cu(DO3A-xy-TPP).26 This
suggests that Cu(DO3A-xy-TPP) may also exist in solution
as its zwitterion form as observed in Mn(DO3A-xy-TPP),
despite their difference in coordination number resulting from
the smaller ionic radius of Cu(II) (0.67 Å) than Mn(II) (0.90
Å).48 Because the ionic radius of Cu(II) is very close to that
of Ga(III) (0.62 Å),48 we believe that the coordinated DO3A
in Cu(DO3A-xy-TPP) is most likely hexadentate with one
acetate group being deprotonated to balance to cationic
charge from the TPP moiety. Evaluation of radiometal chelate
and overall molecular charge on biological properties of the
radiolabeled TPP cation is still in progress, and the results
from these studies will be reported elsewhere.
The solution structure of In(DO3A-xy-TPP)+ and Ga-
(DO3A-xy-TPP)+ is important for understanding the coor-
dination chemistry of DO3A-conjugated TPP cations with
67/68Ga and 111In at the tracer level. On the basis of HPLC
concordance experiments, it is concluded that 111In(DO3A-
xy-TPP)+ and In(DO3A-xy-TPP)+ have the same composi-
tion because of their identical HPLC retention times (Figure
3). In(DO3A-xy-TPP)+ remains symmetrical in aqueous
solution. This conclusion is supported by the fact that the
proton resonance signals from the NCH2C6H4 moiety and
the acetate arm attached to N(7) appear as two singlets at
3.96 and 3.53 ppm, respectively. The presence of the AB
quartet at ∼3.62 ppm clearly indicates that all three car-
boxylate-O donors are firmly bonded to In(III). If these
carboxylate-O donors were dissociated, there would have
been three singlets: one from the central acetate group, one
from the NCH2C6H4 moiety, and one from the two remaining
acetate arms.
This symmetrical structure Ga(DO3A-xy-TPP)+ is also
maintained in solution as evidenced by the presence of two
singlets at 3.92 and 3.54 ppm from the NCH2C6H4 moiety
and the acetate arm attached to N(7), respectively. Since the
two methylene hydrogens of the coordinated acetate chelating
arms experience different chemical environments, it is not
surprising that they appear as the AB quartet at ∼3.65 ppm.
The two coordinated carboxylate-O donor atoms remain
firmly bonded to Ga(III) even at 65 °C (Figure 4), suggesting
that 68Ga(DO3A-xy-TPP)+ might have a very high in vivo
solution stability as observed for 68Ga(DOTA-D-Phe-
NH2)+.37
Acknowledgment. Acknowledgement is made to Dr.
Huaping Mo for his help with NMR data analysis and to
Dr. Philip E. Fanwick, Department of Chemistry, Purdue
University, for X-ray crystallography of In(DO3A-xy-
TPP)(OAc)‚7.5H2O‚(CH3)2CO, Ga(DO3A-xy-TPP)(NO3)‚
6H2O‚(CH3)2CO, and Mn(DO3A-xy-TPP)‚4H2O‚CH3OH.
This work is supported, in part, by Purdue University and
research grants (1R01 CA115883-01A2 (S.L.)) from National
Cancer Institute (NCI), (BCTR0503947 (S.L.)) the Susan G.
Komen Breast Cancer Foundation, (AHA0555659Z (S.L.))
the Greater Midwest Affiliate of American Heart Association,
(R21 EB003419-02 (S.L.)) National Institute of Biomedical
Imaging and Bioengineering (NIBIB), and (R21 HL083961-
01) National Heart, Lung, and Blood Institute (NHLBI).
1
Comparison of the H NMR spectra (Figures 7 and 8) of
In(DO3A-xy-TPP)+ and Ga(DO3A-xy-TPP)+ reveals certain
similarities in the splitting patterns for H2, H5, H9, and H14,
as well as significant differences in chemical shifts of H3,
H4, H7, and H8. The fact that both H3a and H8a have
1
significantly different chemical shifts (Table 1) in the H
NMR spectra of In(DO3A-xy-TPP)+ and Ga(DO3A-xy-
TPP)+ strongly suggests that they might have different
solution structures as those observed in the solid state
(Figures 4 and 5). It is important to note that the most
common coordination number for In(III) is 6 or 7, while the
coordination number of Ga(III) is predominantly 6 because
of its smaller ionic radius.34,35,38,39,48 Therefore, it is reasonable
to believe that the solution structure of Ga(DO3A-xy-TPP)+
is the same as that in the solid state (Figure 5) with one
acetate chelating arm being uncoordinated.
Supporting Information Available: X-ray crystallographic files
are in CIF format for the reported structures In(DO3A-xy-TPP)-
(OAc)‚7.5H2O‚(CH3)2CO, Ga(DO3A-xy-TPP)(NO3)‚6H2O‚(CH3)2-
CO, and Mn(DO3A-xy-TPP)‚4H2O‚CH3OH and 2D NMR spectra
for In(DO3A-xy-TPP)+ and Ga(DO3A-xy-TPP)+. This material is
available free of charge via the Internet at http://pubs.acs.org.
IC7010452
Inorganic Chemistry, Vol. 46, No. 21, 2007 8997