Association capacity of ribose bis(thiosemicarbazonato)-copper(II) with nitric oxide

Article abstract of DOI:10.1080/15533170500360180

The stability constant for copper(II) complex with ribose bis(thiosemicarbazone) (log K = 18.46 ± 0.15) was determined from UV-Vis data using LETAGROP program. Its interaction with nitric oxide was studied by spectroscopic and electrochemical techniques. This interaction was observed in the UV-Vis spectra as a shoulder around 350 nm and an isosbestic point at 420 nm. The corresponding equilibrium constant was calculated and the obtained value (log K = 8.68 ± 0.12), indicates the formation of a stable nitrosyl complex. Copper(II) bis(thiosemicarbazonato) complex was immobilized on a gold electrode, as demonstrated by cyclic voltammetric studies and used for NO recognition. The reduction of NO coordinated to the copper centre was observed at a potential around -700mV. Copyright

Full text of DOI:10.1080/15533170500360180

This article was downloaded by: [134.117.10.200]
On: 15 March 2015, At: 05:33
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,
37-41 Mortimer Street, London W1T 3JH, UK
Synthesis and Reactivity in Inorganic, Metal-Organic,
and Nano-Metal Chemistry
Publication details, including instructions for authors and subscription information:
http://www.tandfonline.com/loi/lsrt20
Association Capacity of Ribose
Bis(Thiosemicarbazonato)Copper(II) with Nitric Oxide
Talkmore Ngarivhume a , Alicia Díaz b , Roberto Cao b , Mayreli Ortiz b & Iliana Sánchez b
a Chemistry Department , Bindura University of Science Education , Zimbabwe
b Laboratorio de Bioinorgánica, Facultad de Química , Universidad de La Havana , La
Havana , Cuba
Published online: 31 Jan 2012.
To cite this article: Talkmore Ngarivhume , Alicia Díaz , Roberto Cao , Mayreli Ortiz & Iliana Sánchez (2005) Association
Capacity of Ribose Bis(Thiosemicarbazonato)Copper(II) with Nitric Oxide, Synthesis and Reactivity in Inorganic, Metal-Organic,
and Nano-Metal Chemistry, 35:10, 795-800, DOI: 10.1080/15533170500360180
To link to this article: http://dx.doi.org/10.1080/15533170500360180
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained
in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no
representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the
Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and
are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and
should be independently verified with primary sources of information. Taylor and Francis shall not be liable for
any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever
or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of
the Content.
This article may be used for research, teaching, and private study purposes. Any substantial or systematic
reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any
form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://
www.tandfonline.com/page/terms-and-conditions

Synthesis and Reactivity in Inorganic, Metal-Organic and Nano-Metal Chemistry, 35:795–800, 2005
Copyright # 2005 Taylor & Francis, Inc.
ISSN: 1553-3174 print/1532-2440 online
DOI: 10.1080/15533170500360180
Association Capacity of Ribose Bis(Thiosemicarbazonato)-
Copper(II) with Nitric Oxide
Talkmore Ngarivhume
Chemistry Department, Bindura University of Science Education, Zimbabwe
´
´
Alicia Dıaz, Roberto Cao, Mayreli Ortiz, and Iliana Sanchez
Laboratorio de Bioinorganica, Facultad de Quımica, Universidad de La Havana, La Havana, Cuba
´
´
with divalent first transition metals. For that reason, we
The stability constant for copper(II) complex with ribose studied copper(II) bis(thiosemicarbazonato) of different
bis(thiosemicarbazone) (log K 5 18.46 + 0.15) was determined
from UV-Vis data using LETAGROP program. Its interaction
with nitric oxide was studied by spectroscopic and electrochemical
techniques. This interaction was observed in the UV-Vis spectra as
a shoulder around 350 nm and an isosbestic point at 420 nm. The
monosaccharide derivatives to obtain complexes with higher
water solubility and potentially improved biological activity
´
(Dıaz et al., 1997, 1998a, 1999). In this sense it is important
to point out that copper(II) complexes with 3-deoxy-D-
corresponding equilibrium constant was calculated and the erythro-hexos-2-ulose bis(thiosemicarbazones) were reported
obtained value (log K 5 8.68 + 0.12), indicates the formation of
a stable nitrosyl complex. Copper(II) bis(thiosemicarbazonato)
complex was immobilized on a gold electrode, as demonstrated
by cyclic voltammetric studies and used for NO recognition. The
reduction of NO coordinated to the copper centre was observed
at a potential around 2700 mV.
to present antitumoral activity (Horton and Nichol, 1987).
The comparison of the EPR parameters obtained in
polycrystalline state and frozen DMF solution of ribose
bis(thiosemicarbazonato)copper(II) (Scheme 1), Cu(RibTSC-
2H), suggested a significant apical interaction with solvent
´
molecules (Dıaz et al., 1997). The obtained distortion factor
(f) was around 113 cm, indicative of a slight distortion out of
the relatively rigid plane of the complex. This consideration
served to explain why when Cu(RibTSC-2H) was studied as
Keywords bis(thiosemicarbazone), copper(II) complexes, nitric
oxide, self-assembled monolayer
a SOD mimic a very low activity was observed (IC50
ꢀ
´
100 mM) (Dıaz et al., 1999) as predicted before (Diaz et al.,
1998a). The carbohydrate moiety apparently has no negative
effect on the SOD-like activity since for copper(II) complexes
with monosaccharide derived monothiosemicarbazones the
INTRODUCTION
Biological properties of thiosemicarbazones have been
studied since 1956, when Brockman (1956) reported the
antitumoral properties of 2-formylpyridine thiosemicarbazone.
A series of a-(N)-heterocyclic carboxaldehyde thiosemicarba-
zones was later studied for their antitumoral activity (French
and Blanz, 1965) and since then, this and other biological prop-
erties of thiosemicabazones have been reported (West et al.,
1991). Bis(thiosemicarbazones) are tetradentate k4-N,N,S,S
ligands that form stable and highly hydrophobic complexes
´
corresponding activity is 100-fold higher (Dıaz et al., 1998b).
The coordination of nitric oxide, a small radical with very
important biological properties (Moncada et al., 1991), by
´
copper(II) dithiocarbamate complexes (Dıaz et al., 2003)
stimulated us to study Cu(RibTSC-2H) as a NO scavenger.
Here we report the formation constant of Cu(RibTSC-2H)
and its interaction in aqueous solution with nitric oxide, NO,
studied by spectroscopic and electrochemical techniques.
Received 25 August 2005; accepted 9 September 2005.
T. N. wishes to thank the Zimbabwe–Cuba teacher training
program (1999) and the Bindura University of Science Education.
The University of Havana under Grant AM 21-2000 supported part
of this work.
Address correspondence to Roberto Cao, Laboratory of Bioinor-
ganic Chemistry, Faculty of Chemistry, University of Havana,
Havana 10400, Cuba. E-mail: cao@fq.uh.cu
EXPERIMENTAL SECTION
General Procedures
All reagents were purchased from Merck (Germany) and
were of analytical grade. Ribose bis(thiosemicarbazone) and
its copper(II) complex were synthesized with the same
´
procedure reported previously (Dıaz et al., 1997). Saturated
795

796
T. NGARIVHUME ET AL.
1
The tautomeric equilibrium of RibTSC was studied by H-
and 13C NMR. 34.6 mg of RibTSC were dissolved in 0.5 ml
of DMSO-d6 and the 1H- and 13C NMR spectra were
recorded. This process was repeated after the addition of one
and two equivalents of NaOD and followed by the neutraliz-
ation of the RibTSC solution with two equivalents of CF3OOH.
Electronic spectra were registered after different aliquots
(10 mL–1100 mL) of RibTSC (52 mM) were added to an
aqueous solution of CuCl2 (52 mM). The absorbance at differ-
ent wavelengths was introduced in the SPEFO version of
LETAGROP program and the stability constant of
[Cu(RibTSC-2H)] calculated.
SCH. 1.
aqueous solutions of nitric oxide were obtained by generating
the gas from the reaction of metallic copper with 5M nitric
acid using Schlenk techniques. The reaction was performed in
a Schlenk flask and the gas was purified by passing it through
five traps containing 50% NaOH solutions. The purified gas
was receipted in a Schlenk flask containing 20 mL of cold
water, through which it was bubbled. A thin Teflon hose was
connected into the NO aqueous solution through the side arm
of the flask. Teflon stopcocks were used to isolate each part
of the Schlenk system when necessary. The whole system,
tightly isolated from air, was previously deoxygenated by
passing pure nitrogen for no less than one hour. Once the NO
aqueous solution was obtained the Schlenk flask was discon-
nected and then installed in a thermostatted bath at 293.00(5)
K and the Teflon hose was connected to an Orion automatic
microburette (model microBU2031) and purged.
Interaction of Cu(RibTSC-2H) with NO Studied
Spectrophotometrically
Electronic spectra were made after successive additions of
10 mL aliquots of saturated aqueous solution of NO (2 mM)
in 7.4 phosphate buffer solution (0.06 M) at 293.0 K to 2 mL
of deoxygenated 94.9 mM aqueous solution of Cu(RibTSC-
2H) at 1.5 min intervals, using Wavescan Repeat Scan
facility. The recorded absorbances at different wavelengths
were introduced in the SPEFO version of LETAGROP
program and the stability constant of the Cu(RibTSC-2H)-
NO adduct was calculated.
Electrochemical Studies
Electrochemical studies were carried out with a Yanaco
P-900 cyclic polarograph coupled to a Graphted WX1000
X–Y recorder using a standard three-cell holder. Glassy
carbon or modified gold bead, Pt and Ag/AgCl were used as
working, counter and reference electrodes, respectively. All
solutions were previously deoxygenated with oxygen-free
nitrogen. Tetra-n-butylammonium tetrafluoroborate (0.2 M)
was used as supporting electrolyte. The cyclic voltammogram
of Cu(RibTSC-2H) (10 mM in DMSO) was recorded. The gold
electrode was prepared by annealing the tip of a one mm
diameter and 5 cm long gold wire (99.99%), previously
cleaned overnight with nitric acid (68%). The gold bead was
then electrochemically pre-treated in HClO4 (0.1 M) at 2.1 V
until gold(III) oxide formation (red colour). The electrode
was cleaned with HCl (0.1 M) and thoroughly rinsed with
water. The geometric area of the bead was calculated using
[Ru(NH3)6]Cl3 as previously described by Kaifer (1995). The
freshly pre-treated gold surface was modified by its immersion
Spectroscopy
The electronic spectra were recorded on an Ultraspec III
spectrophotometer (Pharmacia) interfaced with a micro-
computer for data acquisition. The temperature of the cell
(293.0 K) was controlled by a Peltier controller system of
Pharmacia (Autofill III) connected to the spectrophotometer
and the data were processed by Origin (version 5) and SPEFO
(Sillen and Warnquist, 1969; Sanchiz et al., 1997) version of
´
the LETAGROP software (Sillen and Whiteker, 1969).
The NMR spectra were recorded on a Bruker AC 250 F
spectrometer that operates at a frequency of 250.13 MHz
(1H) and 62.89 MHz (13C).
Equilibria Studied by Electronic and NMR Spectroscopy
KClO4 (0.25 M) was used as inert electrolyte. Since the into an oxygen-free DMSO solution of 10 mM RibTSC for
RibTSC is not fairly soluble in water, the determinations 72 h, followed by its interaction with a 0.2 mM DMSO
were made in a mixture of DMSO (4%) in water. 0.37 mM solution of CuCl2 for 24 h. The double-modified electrode
aqueous solutions of RibTSC in excess of HClO4 (0.1089 M) was thoroughly rinsed with doubly distilled water and
were prepared. NaOH (0.1 M) aliquots of 25 mL (up to ethanol. Its cyclic voltammograms were performed in 1 M
1100 mL) were added for a final volume of 25 mL. The Na2SO4 solution between 2200 to 700 mV. The electrochemi-
electronic spectra were registered after each addition. The cal behaviour after bubbling with NO was studied. NO was also
acid constant of RibTSC was obtained after processing generated ‘in situ’ from the interaction of NaNO2 (10 mM)
selected data with SPEFO version of LETAGROP program.
with H2SO4 (12.3 mM).

ASSOCIATION CAPACITY OF RIBOSE BIS(THIOSEMICARBAZONATO)COPPER(II) WITH NO
797
RESULTS AND DISCUSSION
When the acid-base equilibrium of RibTSC (in DMSO-d6)
was studied by NMR two signals at 10.83 and 11.68 ppm for
the N2-H protons were observed. Both signals strongly
decrease in intensity and become much wider upon addition
of one equivalent of NaOD and completely disappear when
the second equivalent of NaOD is added. The initial
spectrum is restored when two equivalents of CF3COOH are
added. On the other hand, the 13C NMR spectra of RibTSC
did not change once the experiment was concluded indicating
a high stability of the ligand under such conditions.
A previous report on the spectroscopic data, particularly
1H-RMN, 1H-1H COSY, and NOE-DIFF, and computer struc-
ture modelling indicated that the TSC moieties of the free
´
RibTSC ligand are both in E-configuration (Dıaz et al.,
1997). When this ligand coordinates to copper(II) as a tetraden-
tate NSSN ligand it adopts a Z-configuration forming a rigid
and only slightly distorted square plane, as suggest by EPR
spectroscopy studies in solid state and DMF solution. An
apical interaction of the solvent with the copper centre was
observed, probably favoured by H-bond interactions with the
hydroxyl groups of the carbohydrate moiety (Diaz et al.,
1997). Due to the interaction of these later groups with
water, and that the sulphur atoms are oriented inwards,
Cu(RibTSC-2H) is water-soluble, more than the ligand itself.
The high resemblance observed by NMR between both
N2-H protons and the relatively high deviation in the
obtained pKa value, explains why only one constant could be
determined.
The addition of different aliquots of RibTSC to a CuCl2
solution provoked the appearance and increase in intensity of
a band at 467 nm, as depicted in Figure 2. The stability
constant of Cu(RibTSC-2H) was calculated from these
spectral data using the SPEFO version of the LETAGROP
Spectrophotometric Studies
The visible spectra of RibTSC titrated with NaOH present program. The obtained value corresponded to log K ¼
an isosbestic point at 350 nm (Figure 1). At pH values lower 18.46 + 0.15, similar to that reported for Cu(GluTSC-2H)
than 9.2 a maximum at 331 nm is recorded, while for very (log K ¼ 20.65 + 0.06) (Signorella et al., 1999). The
basic solutions (pH . 11) this maximum is shifted to obtained stability constant indicates that Cu(RibTSC-2H) is
368 nm. The maximum at 331 nm decreases in intensity with highly stable, as expected, and can be submitted to study its
each addition of NaOH, while the contrary occurs for the interaction with NO.
maximum at 368 nm. The pKa calculated from these spectral
The coordination of NO to a copper(II) dithiocarbamate
data using the SPEFO version of the LETAGROP program complex was previously reported where the Cu(II)-S bond
´
reported a value of 11.82 + 0.17. This result is in good agree- was considered to play an important role (Dıaz et al., 2003).
ment with those reported by Beraldo (1986) and Petering For that reason, the interaction of Cu(RibTSC-2H) with
(1979) (11.50 + 0.2 and 10.97, respectively) for 2-formylpyr- NO(aq) was considered possible. The effect of the addition
idine thiosemicarbazone in aqueous solutions in the presence of aliquots of NO saturated aqueous solutions (7.4 phosphate
of 0.5% DMSO, obtained by spectrophotometric methods. buffer) to Cu(RibTSC-2H)(aq) was followed spectrophotome-
Signorella et al. (1999) reported pKa values (10.11 + 0.02 trically. The band assigned to the ligand at 302 nm (p-pꢀ)
and 10.23 + 0.01) obtained by a potentiometric method in increased only slightly in intensity. This variation can not be
30% v/v dioxane-water for glucose bis(thiosemicarbazone) attributed to interactions of NO with the ligand, such as
(GluTSC), a ligand very similar to RibTSC.
formation of adducts with nucleophiles (amines, sulphides
FIG. 1. Spectrophotometric titration (293.0 K) of RibTSC (HClO4 in excess) FIG. 2. Electronic spectra (293.0 K) when aliquots of RibTSC (52 mM) were
with NaOH; isosbestic point at 350 nm. added to an aqueous solution of CuCl2 (52 mM).

798
T. NGARIVHUME ET AL.
and thiols) (Lee et al., 2002). To affirm this, the possible irreversible peak at-500 mV (vs. Ag/AgCl) was observed.
RibTSC-NO interaction was studied spectrophotometrically This peak was assigned to the reductive desorption of
and only a partial decomposition of the ligand was observed RibTSC and indicates that a stable SAM was formed on the
at relatively high concentrations of NO.
A decrease in the absorbance of the band with maximum at
gold bead.
The CV of [Ru(NH3)6]Cl3 with both a clean and modified
467 nm (d-d) was observed when NO aliquots were added to (with RibTSC) gold bead, as working electrodes, were
Cu(RibTSC-2H). At the same time, a shoulder around recorded. An appreciable decrease in the intensity of both
350 nm and an isosbestic point at 420 nm were observed anodic and cathodic waves for the Ru(III)/Ru(II) pair was
(Figure 3). When the Cu(RibTSC-2H)-NO system was observed for the modified electrode when both CV were
purged with pure nitrogen gas or heated up to 333 K the compared. This observation confirms that the SAM was
spectrum corresponding to Cu(RibTSC-2H), free of NO, was formed in the bead modified with RibTSC. Its molecular
recovered. The isosbestic point and these later results are surface was determined (G ¼ 3 nmol/cm2) using the peak
indicative that a reversible NO-Cu(RibTSC-2H) interaction area of the reductive desorption curve.
took place. Similar spectrophotometric results for interactions Once demonstrated that RibTSC was chemisorbed on the
of copper(II) dithiocarbamate complexes with NO were gold electrode surface, the modified electrode was immersed
´
previously reported (Dıaz et al., 2003). The UV data into a DMSO solution of CuCl2 for 24 h. The obtained
obtained after each addition of NO were processed by the double-modified electrode was then studied by cyclic voltam-
SPEFO-LETAGROP program and the stability constant of metry from 2200 mV to 700 V in 1 M Na2SO4. Two redox
the Cu(RibTSC-2H)-NO adduct was obtained: log K ¼ peaks (Ec ¼ 180 mV and Ea ¼ 320 mV) were observed
8.68 + 0.12. This value is in good agreements with previous (Figure 4a), that can be attributed to the Cu(II)/Cu(I) pair of
reports for others nitrosyl copper complex and indicates that copper(II) coordinated to the ligand self-assembled on the elec-
´
a stable mononitrosyl complex was formed (Dıaz et al., trode. These values indicate the presence of Cu(II) in the
2003; Mederos et al., 2003).
double-modified electrode and areclose to those obtained for
the Cu(RibTSC-2H) complex in DMSO (Ec ¼ 280 mV and
Ea ¼ 360 mV) using a clean gold electrode. The observed simi-
larity between the values of the redox peaks of the Cu(RibTSC-
2H) complex in DMSO and the double-modified gold electrode
suggests that in the later Cu(II) is coordinated to the self-
assembled ligand in a similar way as in Cu(RibTSC-2H). In
the double-modified electrode both of sulphur atoms (or only
one) should be associated to the gold surface forming a
Au(I)-S(thioenol) bond. The association of only one sulphur
atom to Au should permit a stronger p-interaction of the
other one with Cu(II). On the other hand, the double interaction
of each sulphur atom with Au and coordinated Cu(II), as
depicted in Figure 4b, could also be possible.
Electrochemical Studies
The interaction of Cu(RibTSC-2H) with NO in aqueous
solution was also studied by cyclic voltammetry. A thioceto-
thioenolic equilibrium is present in mono- and bis(thiosemicar-
bazone) solutions. Taking this into consideration, the formation
of a self-assembled monolayer (SAM) of RibTSC through its
thioenolic groups on a gold electrode bead was studied. For
this the gold bead, previously treated and cleaned, was
immersed into a RibTSC solution (DMSO) for 72 h. The
cyclic voltammogram (CV) of the resulting modified gold
electrode in KOH (0.5 moL21) was recorded and an intense
When the double-modified gold electrode was immersed
into a NO aqueous solution and its CV recorded a new
cathodic wave was observed at 2720 mV (Figure 5), which
3
can be assigned to the NO þ e2 ! NO2 reduction (Farmer
FIG. 4. Cyclic voltammogram of the double-modified gold electrode in a
Na2SO4 (1M) solution (a); and its schematic representation (b). ( N, C,
S, O, W H).
FIG 3. Electronic spectra (293.0 K) of Cu(RibTSC-2H) (94,9 mM) for
different additions of NO saturated aqueous solution. Inset are the spectra for
Cu(RibTSC-2H) 46.5 mM.

ASSOCIATION CAPACITY OF RIBOSE BIS(THIOSEMICARBAZONATO)COPPER(II) WITH NO
799
A double-modified gold electrode was prepared by the self-
assembly of RibTSC, presumably through its thioenolic
groups, and the further coordination of copper(II). Electroche-
mically such coordination resulted to be similar to that in
Cu(RibTSC-2H). Electrochemical responses of the double-
modified electrode were observed when it was introduced
into a NO-containing solution. An intense cathodic wave,
assigned to reduction of NO was observed with double-
modified electrode. The results obtained in this work permit
to analyze Cu(RibTSC-2H) as a potential NO scavenger and
the double-modified electrode as a NO sensor.
REFERENCES
Beraldo, H.; Tosi, L. Spectroscopic studies of metal complexes con-
taining p-delocalized sulfur ligands. The pre-resonance Raman
spectra of the antitumor agent 2-formylpyridine thiosemicarbazone
and its Cu(II) and Zn(II) complexes. Inorg. Chim. Acta 1986, 125,
173–182.
´
Brauner, P.; Sillen, L. G.; Whiteker, R. High-speed computers as a
supplement to graphical methods. IX. Adjustment for systematic
experimental errors and other group parameters in LETAGROP.
Applications to potentiometric titrations. Arkiv Kemi 1969, 31,
365–376.
FIG. 5. Cyclic voltammogram of the double-modified gold electrode in a
Na2SO4 (1 M) solution saturated with NO.
Brockman, R. W.; Thompson, J. R.; Bell, M. J.; Skipper, H. E. The
carcinostatic activity of a-(N)-heterocyclic carboxaldehyde thiose-
micarbazone. Cancer Res. 1956, 16, 167–169.
and Sulc, 2005), only possible when NO is coordinated to a
metallic centre in one of its forms.
´
´
Dıaz, A.; Cao, R.; Fragoso, A.; Sanchez, I. Interpretation of the SOD-
like activity of series of copper(II) complexes with thiosemicarba-
zones. Inorg. Chem. Commun. 1999, 2 (8), 358–360.
The double-modified electrode was also introduced in a
solution containing NaNO2 to which H2SO4 was added to
generate NO (between 6 mM and 15 mM). Under such con-
ditions the intensity of the cathodic wave at 2720 mV was
observed to be sensitive to the concentration of NO. Practically
no shift in the Cu(II)/Cu(I) pair was observed as a consequence
of the interaction with NO. Nevertheless, a small increase in
the intensity of the anodic wave (Cu(I) ! Cu(II)) was
observed for each cycle. This observation is an indication
that the coordination of NO by the Cu(II) centre could
provoke its reduction with the formation of a Cu(I)-NOþ
´
Dıaz, A.; Pogni, R.; Cao, R.; Basosi, R. EPR characterization of a
series of mono- and bisthiosemicarbazone copper(II) complexes.
Inorg. Chim. Acta 1998a, 275, 552–556.
´
Dıaz, A.; Fragoso, A.; Cao, R.; Verez, V. Synthesis and SOD-like
activity of monosaccharide derived thiosemicarbazones.
Carbohydr. Chem. 1998b, 17, 293–303.
´ ´
Dıaz, A.; Garcıa, I.; Cao, R.; Beraldo, H.; Salberg, M. M.; West, D. X.;
´
Gonzalez, L.; Ochoa, E. Ribose, galactose and glucose bis(thiose-
micarbazone) complexes of copper (II) and nickel (II). Polyhedron
1997, 16, 3549–3555.
´
bond, as observed before (Dıaz et al., 2003; Mederos et al.,
´
´
Dıaz, A.; Ortiz, M.; Sanchez, I.; Cao, R.; Mederos, A.; Sanchiz, J.;
Brito, F. Interactions of nitric oxide with copper(II) dithiocarba-
mates in aqueous solution. J. Inorg. Biochem. 2003, 95, 283–290.
French, F. A.; Blanz, E. The carcinostatic activity of alpha-(N) hetero-
cyclic carboxaldehyde thiosemicarbazones. I. Isoquinoline-1-car-
boxaldehyde thiosemicarbazone. J. Cancer Res. 1965, 14,
1454–1456.
2003). The great similarity in the UV-Vis spectra of the
Cu(RibTSC–2H) – NO interaction with that reported before
for copper(II) dithiocarbamate complexes also supports this
suggestion. The results reported here permit to suggest the
possibility of using the double-modified electrode as a NO
sensor. Further work in this direction is in progress at our lab.
Farmer, P. J.; Sulc, F. J. Coordination chemistry of the HNO ligand
with hemes and synthetic coordination complexes. Inorg.
Biochem 2005, 99, 166–184.
CONCLUSIONS
Horton, D.; Nichol, R. Facile synthesis of 3-deoxyaldos-2-ulose-
bis(thiosemicarbazones). Carbohydr. Res. 1987, 168, 295–300.
Kaifer, E. A.; Rojas, T. M.; Koniger, R.; Stoddart, J. F. Supported
monolayers containing preformed binding sites. synthesis and
interfacial binding properties of a thiolated P-cyclodextrin deriva-
tive. J. Am. Chem. Soc. 1995, 117, 336–343.
The determined high stability of Cu(RibTSC-2H) in
solution made possible the study of its interactions with
nitric oxide by spectrophotometric and voltammometric deter-
minations. The coordination of NO to Cu(RibTSC-2H) was
expressed spectrophotometrically as a shoulder at 350 nm
and an isobestic point at 420 nm and the obtained equilibrium
constant indicates the formation of a stable mononitrosyl
complex, [Cu(RibTSC-2H)NO].
Lee, J.; Chen, L.; West, A. H.; Richter-Addo, G. B. Interactions of
organic nitroso compounds with metals. Chem. Rev. 2002, 102,
1019–1065.

800
T. NGARIVHUME ET AL.
Moncada, S.; Palmer, R. M. J.; Higgis, E. A. Nitric oxide: Physiology,
pathophysiology, and pharmacology. Pharmacol. Rev. 1991, 43,
109–142.
crystal structure of sodium aqua(4-chloro-1,2-phenylenediamine-
N,N,N0,N0-tetraacetato)ferrate(III)-water (1/1.5). Inorg. Chem.
1997, 36, 4108–4114.
´
Mederos, A.; Cachapa, A.; Hernandez-Molina, R. M.; Armas, T.; Signorella, S.; Palopoli, C.; Frutos, A.; Escandar, G.; Tanase, T.;
´
Gili, P.; Sokolov, M.; Gonzalez-Platas, J.; Brito, F. Theoretical
Sala, L. F. 3-Deoxy-D-erythro-hexos-2-ulose bis(thiosemicarba-
zone) copper(II) chelate. Studies in solution and in the solid
state. Can. J. Chem. 1999, 77 (9), 1492–1497.
and spectrophotometrical study of the interaction of nitric oxide
with copper(II) dithiocarbamates. Inorg. Chem. Commun. 2003,
6, 498–502.
´
Sillen, L. G.; Warnqvist, B. Application of LETAGROP to spectro-
Petering, D. H. J.; Knight, J. M.; Whelan, H. Electronic substituent
effects upon properties of 5-substituted-2-formylpyridine thiose-
micarbazones and their metal complexes. Inorg. Biochem. 1979, West, D. X.; Padhye, S. B.; Sonawane, P. B. Structural and
photometric data, for testing models and adjusting equilibrium
constants. Arkiv Kemi 1969, 31, 377–390.
11, 327–338.
physical correlations in the biological properties of
transition metal heterocyclic thiosemicarbazone and S-
alkyldithiocarbazate complexes. Structure Bonding 1991, 76,
4–50.
Sanchiz, J.; Dominguez, S.; Mederos, A.; Brito, F.; Arrieta, J. M. Tet-
ramethyl carboxylic acids derived from o-phenylenediamines as
sequestering agents for iron(III): Thermodynamic studies. X-ray