Synthesis and characterization of cadmium complexes with phosphorylated ligands

Article abstract of DOI:10.1081/SIM-100002236

Complexes of cadmium(II) with phosphorylated ligands were studied in the solid state. One of these ligands is phosphocreatine (HPCR), an important natural compound and the others are diisopropylphosphorylguanidine (DPG) and diisopropylphosphorylthiourea (

Full text of DOI:10.1081/SIM-100002236

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SYNTHESIS AND CHARACTERIZATION OF CADMIUM
COMPLEXES WITH PHOSPHORYLATED LIGANDS
Judith Felcman a , Damiana C. N. Lopes a , Renata A. Cattapan a & Claudio A. Téllez Soto
b
a Department of Chemistry , Pontifícia Universidade Católica de Rio de Janeiro , Rua
Marquês de S. Vicente, 225, Rio de Janeiro, RJ, 22453-900, Brazil
b Department of Chemistry , Universidade Federal , Fluminense, Niterói, Brazil
Published online: 15 Feb 2007.
To cite this article: Judith Felcman , Damiana C. N. Lopes , Renata A. Cattapan & Claudio A. Téllez Soto (2001)
SYNTHESIS AND CHARACTERIZATION OF CADMIUM COMPLEXES WITH PHOSPHORYLATED LIGANDS, Synthesis and Reactivity in
Inorganic and Metal-Organic Chemistry, 31:3, 507-516, DOI: 10.1081/SIM-100002236
To link to this article: http://dx.doi.org/10.1081/SIM-100002236
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SYNTH. REACT. INORG. MET.-ORG. CHEM., 31(3), 507–516 (2001)
SYNTHESIS AND CHARACTERIZATION
OF CADMIUM COMPLEXES WITH
PHOSPHORYLATED LIGANDS
Judith Felcman,∗,1 Damiana C. N. Lopes,1
Renata A. Cattapan,1 and Claudio A. Te´llez Soto2
1Department of Chemistry, Pontif´ıcia Universidade Cato´lica
do Rio de Janeiro, Rua Marqueˆs de S. Vicente, 225,
22453-900, Rio de Janeiro, RJ, Brazil
2Department of Chemistry, Universidade Federal
Fluminense, Nitero´i, Brazil
ABSTRACT
Complexesofcadmium(II)withphosphorylatedligandswere
studied in the solid state. One of these ligands is phosphocrea-
tine (HPCR), an important natural compound and the others are
diisopropylphosphorylguanidine (DPG) and diisopropylphospho-
rylthiourea (DPT). The complexes were synthesized and charac-
terized by elemental and thermogravimetric analyses and IR and
Raman spectroscopy. The formed complexes are: [Cd(PCr)Cl]2,
Cd(DPG)Cl2 and [Cd(DPT)3Cl]Cl. In the HPCR and DPG com-
plexes, Cd(II) is bound through the oxygen of the phosphoryl group
and the nitrogen of the guanidine group and in the DPT complexes
through the sulfur atom.
∗Corresponding author. E-mail: felcman@rdc.puc-rio.br
507
Copyright ꢀ 2001 by Marcel Dekker, Inc.
www.dekker.com
C

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FELCMAN ET AL.
INTRODUCTION
Phosphorylated compounds perform many biological functions (1). They
participate in hydrolytic and enzymatic biochemical processes (2). The cleav-
age occurring in natural compounds releasing phosphates provides the energy
required by living organisms for muscular movement, synthesis of complex bio-
logical molecules and transport of solutes against concentration gradients (3). On
the other hand, hydrolytic cleavage releasing alkyl groups is important clinically
since alkylating agents are used in cancer therapy. One example is cyclophos-
phamide, which requires enzymatic activation in the liver to perform its role (4).
The hydrolysis of phosphocreatine (HPCR, Figure 1) to creatine (CR), which
is catalyzed by creatinekinase (CK) allows the transfer of high-energy phosphate
groups to ADP (5,6). Muscles of vertebrates contain very high amounts of HPCR
and CK.
This phosphagen system (hydrolysis of HPCR) quickly regenerates ATP and
buffers transient changes in the ATP-free ADP ratio. At the same time it provides
inorganic phosphate for glycolysis, oxidative phosphorylation and other regulatory
functions. Furthermore, inthelastdecadeitwasdemonstratedthatHPCRpossesses
important pharmaceutical properties, being employed for the treatment of acute
ischemic diseases (7).
O
P
NH
C
H
H
HO
HO
C
N
H
N
COOH
H
H PCR
O
P
NH
RO
C
N
NH2
RO
H
DPG
O
P
S
RO
RO
C
N
NH2
H
DPT
HPCR = Phosphocreatine
DPG = Diisopropylphosphorylguanidine
DPT= Diisopropylphosphorylthiourea
R = isopropyl group
Figure 1. Structures of the ligands.

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CADMIUM COMPLEXES
509
Cadmium is known to be a toxic metal and a potent inhibitor of neuromuscu-
lar enzymes. This element can cause several undesirable effects in human beings
including carcinogenesis, mutagenesis, oxidative stress and alterations in the an-
tioxidant system resulting in toxicity to liver, kidneys, brain, lungs, heart, testes
and the nervous system. It may react with groups present in the proteins such as
S-H, S-S, OH, COO−, NR2 (8–10) and with phosphates (11). However, according
to recent studies, it seems that under conditions where zinc is scarce, some marine
organisms produce a cadmium-specific carbonic anhydrase (12). Thus, in spite of
its toxicity cadmium may have a biological function. For these reasons, we decided
to study cadmium complexes with HPCR and other similar ligands in solution and
in the solid state (Figure 1).
Besides HPCR, we chose the ligands diisopropylphosphorylguanidine
(DPG) and diisopropylphosphorylthiourea (DPT) to compare their binding sites.
The structure of these three ligands can be seen in Figure 1.
RESULTS AND DISCUSSION
As it can be observed in Figure 1, all three ligands have one possible coordi-
nation site in common: the oxygen of the phosphonate. DPT also has a sulfur atom
and in DPG the latter one is substituted by the nitrogen of the guanidine group.
Besides, the phosphate and guanidine, HPCR has one carboxylate group being all
potential binding sites for metals.
Synthesis
The formation of the complexes may be represented by the following general
equations:
2CdCl2 + 2 HPCR →[Cd(PCR)Cl]2, + 2H+ + 2Cl−
CdCl2 + DPG → Cd(DPG)Cl2
CdCl2 + 3DPT →[Cd(DPT)3Cl]Cl.
The yields of the three complexes are all about 50%. The composition of the
complexes can be seen in Table I.
Spectroscopic Data
The IR and Raman spectra of the ligands and their cadmium complexes
were used to assign the various groups and compare the shifts due to
complexation. Some bands of the ligands and their cadmium complexes are listed

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FELCMAN ET AL.
Table I. The Analytical Data for Cadmium Complexes
[Cd(PCR)Cl]2 Cd(DPG)Cl2 [Cd(DPT)3Cl]Cl
Compound
(CdC4H9N3O5PCl)2 CdC7H18N3O3PCl2 [CdC21H51N6O9P3S3 Cl]Cl
%C Found (Calc)
%H Found (Calc)
%N Found (Calc)
%O Found (Calc)
%S Found (Calc)
%Cd Found (Calc)
%Cl Found (Calc)
%P Found (Calc)
F.W.
13.6 (13.4)
2.7 (2.8)
11.6 (11.7)
22.0 (22.3)
–
32.2 (31.2)
9.5 (9.9)
8.4 (8.7)
715
20.7 (20.7)
4.5 (4.4)
10.2 (10.3)
11.9 (11.8)
–
27.7 (27.6)
17.2 (17.5)
7.8 (7.7)
406
28.7 (27.9)
5.5 (5.6)
9.6 (9.3)
15.5 (15.9)
10.2 (10.6)
12.3 (12.4)
7.6 (7.9)
10.6 (10.3)
903
D.T. (◦C)
285
280
240
% Yield
49
52
48
in Table II. The spectral assignments for DPG were studied by our group ear-
lier (13). All of these values were compared to those found in the literature
(14).
When DPG is not bound to any metal, the PO group binds with the NH of
the guanidine group through an intermolecular hydrogen bond (15). This hydro-
gen bond is broken on coordinating to cadmium. This can be seen by the shift of
ν(PO)as to higher frequencies. On the other hand, ν(PO)s of the Cd(DPG)Cl2 com-
plex shifts to lower frequencies indicating coordination through this group. The
==
C N bands also shift to lower frequencies. In the case of HPCR and [Cd(PCR)Cl]2,
all of these bands are similar and the bands related to the carboxylic group also
shift to higher frequencies suggesting that the ligands DPG and HPCR bind
to cadmium through the oxygen of the phosphonates and the nitrogen of the
guanidine group. However, additional spectroscopic evidence (e.g. NMR) will
be required before the binding mode of these ligands is unambiguously demon-
strated. We also found the presence of Cd-N and Cd-O bands in the far-IR
region.
==
== –
DPT differs from DPG because it has a C S group in place of a C N H
==
–
group. The absence of shifted bands in−t1he region of C N and of P O and the
==
presence of a band for C S at 1099 cm in DPT that disappears in the complex
–
(16) demonstrates that sulfur is the donor atom in [Cd(DPT)3Cl]Cl. The ν(Cd S)
band could not be found in the IR spectrum. Only in the Raman spectrum it was
possible to attribute ν = 360 cm−1 to ν(Cd S). Weak Cd-S bands in far-IR are a
–
characteristic behavior of thioureas systems (17,18).
–
It is also possible to see that the ν(Cd Cl) bands of Cd(DPG)Cl2 and [Cd
(DPT)3Cl]Cl are at higher frequencies (217 and 223 cm−1) than that of [Cd(PCR)

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511
Table II. Some IR Spectral Assignments (cm−1) for HPCR, DPG, DPT, and Their Cad-
mium Complexes
DPG Cd(DPG)Cl2 HPCR [Cd(PCR)Cl]2 DPT [Cd(DPT)3Cl]Cl
ν(NH)
3436 w
3311 vw
3171 vw
3441 w
3320 vw 3291 w
3184 vw
1557 w
–
3413 w
3390 w
3320 vw
3350 m
3269 w
3170 m
–
3349 m
3269 w
3171 m
–
==
ν(C N) 1602 m
1675 m
–
1642 w
==
ν(C S)
–
–
1099 vw
–
ν(PO)
1187νas
1005νs m 997νs w
w
1205νas
w
1169νas
984νs w
1619νas
w
w
1194νas
945νs vw 1003νs w
1715νas
w
1223νas
w
1222νas w
998νs m
ν(COO)−
–
–
w
–
–
–
1446νs vw 1500νs w
–
ν(Cd Cl)
–
304 vw
300 R
217 R
210 vw
355 vw
354 R
246 w
244 R
–
–
308 vw
187 vw
223 R
–
ν(Cd N)
–
–
–
–
–
–
407 vw
385 R
264 vw
275 R
–
–
–
–
–
–
–
ν(Cd O)
–
ν(Cd S)
360 R
vw = very weak; w = weak; m = medium; R = Raman.
Cl]2, (187 cm−1) indicating a terminal chloride in Cd(DPG)Cl2 and [Cd(DPT)3Cl]
Cl and a bridging chloride in [Cd(PCR)Cl]2, (14).
Thermogravimetric Analysis
The decomposition of the complexes, Cd(DPG)Cl2, [Cd(PCR)Cl]2 and [Cd
(DPT)3Cl]Cl, were observed by TG analysis. They showed that Cd(DPG)Cl2 was
stable up to 280◦C. At this temperature it begins to decompose releasing the oxygen
atoms and the isopropyl gr◦oups bound to them. At 440◦C it loses PNH and from
== –
this temperature up to 900 C the cleavage continues, losing N C NH2. At this
temperaturetheremainingresidueisCd, ClandO. Thecomplex[Cd(PCR)Cl]2 was
stable up to 285◦C, again indicating similar coordination sites for the cadmium
complexes with DPG and HPCR. At this temperature it begins to decompose
releasing the OH groups and at 710◦C it loses one creatine group. Up to 900◦C
it loses the other creatine group bonded to a phosphorus atom. At 900◦C 2Cd,
2Cl, 2O and P remain as residue. The complex [Cd(DPT)3Cl]Cl has a completely
different behavior. It loses 68% of its weight at 240◦C and this means that it loses

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FELCMAN ET AL.
Table III. Mass of Residue (%) After TG Analysis of the Cadmium Complexes
Temperature Weight Loss Experimental (g)
Probable
Fragment lost
Compound
Range (◦C)
(%)
(Calculated)
[Cd(PCR)Cl]2
20–285
285–710
710–900
>900
8.93
17.76
21.64
51.67
Residue
63.87 (68)
126.96 (129)
154.72 (160)
369.46 (358)
4 OH
creatine group
P-creatine group
2Cd, 2Cl, 2O, P
Residue
Cd(HDPG)Cl2
[Cd(HDPT)3Cl]Cl
20–280
280–440
440–900
>900
27.56
12.00
18.76
41.69
111.88 (118)
48.70 (46)
76.15 (77.5)
169.26 (163.5)
2 C3H7O
PNH
== –
N C NH2 + Cl
Cd, Cl, O
Residue
20–240
240–540
540–605
>605
68.35
10.53
16.67
4.45
617.22 (624)
95.05 (96)
150.53 (147.5)
40.18
3 DPT but S
3 S
Cd, Cl
Ash, Residue
all of the three DPT molecules but the sulfur atoms, which still remain bound to
cadmium. At 540◦C it loses the three sulfur atoms and at 605◦C it decomposes the
remaining Cd and Cl and there is only a small residue left. The residual mass loss
data are given in Table III.
EXPERIMENTAL
Materials
All chemicals used were analytical-grade. CdCl2.H2O and Ag(NO3) were
obtained from Merck, Darmstadt, and HPCR (as the dissodium salt) from Sigma.
DPG and DPT were synthesized following a known procedure (19). The solvents
usedtopreparethecadmiumandligandsolutionsforthesynthesisofthecomplexes
were methanol, ethanol and acetone (Merck Darmstadt).
Synthesis of [Cd(PCR)Cl]2
The [Cd(PCR)Cl]2 complex was prepared according to the following pro-
cess: A CdCl2.H2O solution (1 mmol, 201.32 mg dissolved in 10 mL of ethanol)
was added drop-wise, using a dropping funnel to a HPCR solution (1 mmol, 255.1
mg dissolved in 10 mL of methanol). The resulting mixture was stirred at room

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513
temperature for concentration due to evaporation. After approximately 20 hours,
the volume of the solution was concentrated to 5 mL. The white precipitated com-
plex was then filtered and dried at room temperature in a desiccator over silica.
The resulting solid was analytically pure.
Synthesis of Cd(DPG)Cl2
The Cd(DPG)Cl2 complex was prepared according to the following process:
A CdCl2.H2O solution (1 mmol, 201.32 mg dissolved in 10 mL of ethanol) was
added drop-wise, using a dropping funnel, to a DPG solution (1 mmol, 223 mg
dissolved in 10 mL of acetone). The resulting mixture was stirred at room tempera-
ture to partially evaporate the solvent. After approximately 20 hours, the volume of
the solution was concentrated to 5 mL. The white precipitated complex was then
filtered and dried at room temperature in a desiccator over silica. The resulting
solid was analytically pure.
Synthesis of [Cd(DPT)3Cl]Cl
The [Cd(DPT)3Cl]Cl complex was prepared according to the following pro-
cess: A CdCl2.H2O solution (1 mmol, 201.32 mg dissolved in 10 mL of ethanol)
was added drop-wise, using a dropping funnel, to a DPT solution (1 mmol, 240 mg
dissolved in 10 mL of 1:1 acetone:ethanol). Due to the poor solubility of DPT,
its solutions were prepared with the aid of ultrasound. The resulting mixture was
stirred at room temperature to partially evaporate the solvent. After approximately
20 hours, the volume of the solution was concentrated to 5 mL. The white precipi-
tated complex was then filtered and dried at room temperature in a desiccator over
silica. The resulting solid was analytically pure.
Elemental Analyses
–
The CHNS O determinations were performed using a model EA 1110 el-
emental analyzer (CE Instruments) and cadmium was determined by atomic ab-
sorption spectrometry using a model 5 Varian Techtron spectrometer. The chloride
content was determined by titration with AgNO3. Phosphorus was determined by
difference.
Spectroscopic Measurements
The infrared spectra were carried out using a model FT-IR 2000 Perkin
Elmer spectrophotometer. Samples were prepared as KBr pellets for the range of

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FELCMAN ET AL.
4000–370 cm−1 and polyethylene ones for the range of 710–30 cm−1. The Raman
spectra were carried out on a Nicolet 950 FT-Raman.
Thermogravimetric Analysis
Thermogravimetric analyses were performed with a Perkin-Elmer TGA 7.
The temperature range used was from 20 to 900◦C, with a scanning rate of
10.0◦C.min−1 in a nitrogen atmosphere.
CONCLUSIONS
The coordination site proposed for Cd(DPG)Cl2 and [Cd(PCR)Cl]2 are the
oxygen of the phosphate and one nitrogen atom of the guanidine group (see
Figure 2). In the Cd(DPG)Cl2 complex the other positions are occupied by two
OH
O
HO
O
P
C
C
O
Cl
Cl
O
P
N
H
Cd
H
Cd
H
H
N
RO
OR
O
N
C
N
P
Cl
Cl
N
H
H
Cd
H
N
H
H
N
H
H
C
NH
C
HOOC
COOH
H2N
[Cd(PCR)Cl]2
Cd(DPG)Cl2
+
RO
O
H
C
RO
P
N
C
NH2
S
Cl
S
RO
RO
P
O
N
Cl−
Cd
S
NH2
C
N
H
P
H2N
RO
H
O
RO
[Cd(DPT) Cl]Cl
3
R = isopropyl group
Figure 2. Suggested structures of the complexes.

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CADMIUM COMPLEXES
515
chloride ions. In the [Cd(PCR)Cl]2 complex the two chlorides bridge two
monomeric molecules of the complex.
In the case of the [Cd(DPT)3Cl]Cl complex the proposed structure involves
monodentate behavior of the ligand. Three molecules of DPT bind to cadmium
through the sulfur atom; the fourth position is occupied by a chloride ion, forming
a cationic complex that is neutralized by another chloride.
The binding of Cd(II) through the phosphoramidate in HPCR and other
ligands inhibits its cleavage and does not permit HPCR to perform its biological
role.
ACKNOWLEDGMENT
The authors thank CNPq (Conselho Nacional de Pesquisa e Desenvolvi-
mento), Brazil, for their financial support.
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Received August 17, 2000
Accepted February 2, 2001
Referee I: S. O. Grim
Referee II: D. A. Knight

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