New Vanadium(v) Complexes with Salicylaldehyde Semicarbazone Derivatives: Synthesis, Characterization, and in vitro Insulin-Mimetic Activity - Crystal Structure of [VVO2(salicylaldehyde semicarbazone)]

Article abstract of DOI:10.1002/ejic.200300421

The new dioxo(semicarbazone)vanadium(v) complexes cis-VO₂L, where L = salicylaldehyde semicarbazone (L¹), salicylaldehyde 4-n-butylsemicarbazone (L²), or salicylaldehyde 4-(2-naphthyl)semicarbazone (L³), have been synthesized, characterized by ¹H and ¹³C NMR and FTIR spectroscopy and tested for bioactivity as potential insulin-mimetic agents. All dioxovanadium(v) complexes exhibited essentially no in vitro insulin-mimetic activity, but the VO₂L² complex developed activity in the presence of ascorbic acid, similar to that of vanadyl sulfate. The molecular structure of the novel complex VO₂L¹ has been solved by X-ray diffraction methods. It crystallizes in the tetragonal space group P4 ₂/n with a = 12.7674(7), c = 11.5308(5) A, and Z = 8. The vanadium atom is in a distorted square-pyramidal coordination, with L ¹ acting as a tridentate ligand through its azomethyne nitrogen atom, carbonyl oxygen atom and deprotonated phenol oxygen atom. The coordination sphere is completed by two oxo ligands at cis positions. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.

Full text of DOI:10.1002/ejic.200300421

FULL PAPER
New Vanadium( ) Complexes with Salicylaldehyde Semicarbazone Derivatives:
V
Synthesis, Characterization, and in vitro Insulin-Mimetic Activity ؊ Crystal
Structure of [VVO2(salicylaldehyde semicarbazone)]
[a]
[b]
[a]
[c]
[c]
´
´
Pabla Noblıa, Enrique J. Baran, Lucıa Otero, Patricia Draper, Hugo Cerecetto,
[c]
[d]
[e]
[f]
´
Mercedes Gonzalez, Oscar E. Piro, Eduardo E. Castellano, Toshifumi Inohara,
Yusuke Adachi,[f] Hiromu Sakurai,[f] and Dinorah Gambino*[a]
Keywords: Vanadium / Tridentate ligands / N,O,O ligands / Insulin-mimetic agents
The new dioxo(semicarbazone)vanadium(
V
) complexes cis-
complex VO2L1 has been solved by X-ray diffraction
VO2L, where L = salicylaldehyde semicarbazone (L1), salicyl-
methods. It crystallizes in the tetragonal space group P42/n
aldehyde 4-n-butylsemicarbazone (L2), or salicylaldehyde 4- with a = 12.7674(7), c = 11.5308(5) A, and Z = 8. The vana-
˚
(2-naphthyl)semicarbazone (L3), have been synthesized,
characterized by 1H and 13C NMR and FTIR spectroscopy
and tested for bioactivity as potential insulin-mimetic agents.
dium atom is in a distorted square-pyramidal coordination,
with L1 acting as a tridentate ligand through its azomethyne
nitrogen atom, carbonyl oxygen atom and deprotonated
phenol oxygen atom. The coordination sphere is completed
All dioxovanadium(V) complexes exhibited essentially no in
vitro insulin-mimetic activity, but the VO2L2 complex de- by two oxo ligands at cis positions.
veloped activity in the presence of ascorbic acid, similar to
that of vanadyl sulfate. The molecular structure of the novel
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2004)
Introduction
interesting ligands will help in furthering the inorganic
pharmacology of vanadium.[1]
In particular, the discovery of the insulin-like in vitro and
in vivo activity of oxovanadates() and oxovanadium()
compounds such as vanadyl sulfate has stimulated research
on vanadium compounds that may have promising appli-
cation in the treatment of non-insulin-dependent type-2
diabetes mellitus.[2Ϫ9] Different approaches have been at-
tempted to develop more potent and orally active va-
nadium-containing insulin enhancing agents.[10] Some va-
nadium complexes, such as bis(alkylmaltolato)oxovanadi-
um() ones, are promising candidates as oral complements
for insulin in the treatment of diabetes. Although such com-
plexes have shown pharmacological advantages (better gas-
trointestinal absorption, higher potency and less toxicity)
compared to the uncomplexed VOSO4, further improve-
ment in ligand design is needed, focusing on identifying new
vanadium compounds with increased potency and de-
creased toxicity.[11]
The interaction of simple vanadium species with ligand
groups bearing pharmacological activity, particularly those
with antitumoral and insulin-mimetic properties, is of grow-
ing interest. A more detailed physicochemical characteriz-
ation of vanadium compounds with pharmacologically
[a]
´
´
´
´
Catedra de Quımica Inorganica, Facultad de Quımica,
´
Universidad de la Republica,
Gral. Flores 2124, C. C. 1157, 11800 Montevideo, Uruguay
E-mail: dgambino@fq.edu.uy
[b]
[c]
[d]
´
´
Centro de Quımica Inorganica (CEQUINOR/CONICET-
UNLP), C. C. 962, Universidad Nacional de La Plata,
C. C. 67, 1900 La Plata, Argentina
´
´
´
Departamento de Quımica Organica, Facultad de Quımica Ϫ
´
Facultad de Ciencias, Universidad de la Republica,
´
Igua 4225, 11400 Montevideo, Uruguay
´
Departamento de Fısica and Instituto IFLP (CONICET),
Facultad de Ciencias Exactas, Universidad Nacional de La
Plata,
C. C. 67, 1900 La Plata, Argentina
[e]
[f]
´
Instituto de Fısica de Sa˜o Carlos, Universidade de Sa˜o Paulo,
Semicarbazones and thiosemicarbazones (Figure 1) show
a wide range of biological activities.[12Ϫ15] Although some
(thiosemicarbazone)vanadium complexes have been synthe-
sized and characterized, there are very few examples of the
analogous semicarbazone ligands.[12] To further discern the
chelating behaviour of semicarbazones of pharmacological
C. P. 369, 13560 Sa˜o Carlos (SP), Brazil
Department of Analytical and Bioinorganic Chemistry, Kyoto
Pharmaceutical University,
5 Nakauchi-cho, Misasagi, Yamashina-ku, Kyoto 607-8414,
Japan
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
322
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/ejic.200300421
Eur. J. Inorg. Chem. 2004, 322Ϫ328

New Vanadium(V) Complexes with Salicylaldehyde Semicarbazone Derivatives
FULL PAPER
Selected vibration bands of the free ligands and their va-
nadium complexes, which are useful for determining the li-
gand’s mode of coordination, are given in Table 1. The
shifts in the ν(CϭO) and the ν(CϭN) bands upon coordi-
nation are consistent with bidentate coordination of the se-
micarbazone portion of the ligand through the carbonyl
oxygen atom and azomethine nitrogen atom.[17,18] The third
coordination position is the deprotonated phenol oxygen;
thus the OϪH stretching band is not in the spectrum of the
complexes. In addition, the typical strong bands owing to
asymmetric and symmetric stretching modes of the cis-VO2
moiety are observed.[22]
Figure 1. General formula of semicarbazones (X ϭ O) and thiose-
micarbazones (X ϭ S)
interest,[16Ϫ18] a more detailed physicochemical characteriz-
ation of their vanadium complexes has been made, involv-
ing the synthesis, characterization and in vitro biological
evaluation as potential insulin-mimetic agents of a series
Table 1. Selected vibration bands of the ligands L and the VVO2L
ϩ
complexes (cmϪ1); ν: stretching; as: asymmetric, s: symmetric
of novel (semicarbazone)VO2 complexes with the general
formula cis-VVO2L. Selected ligands L are salicylaldehyde
semicarbazone derivatives bearing moieties with different
lipophilicity Ϫ a physicochemical property that determines
an adequate bioresponse of drugs, and is related to their
absorption, distribution, metabolism, elimination and tox-
icity.[19] The ligands L (Figure 2) are salicylaldehyde sem-
icarbazone (L1), salicylaldehyde 4-n-butylsemicarbazone
(L2) and salicylaldehyde 4-(2-naphthyl)semicarbazone (L3).
ϩ
Com- ν(CϭO) ν(CϭN) ν(CϪO) ν(OϪH) νas(VO2ϩ) νs(VO2
pound
)
VO2L1 1661
L1
1683
VO2L2 1645
L2
1651
VO2L3 1601
L3
1647
1606
1598
1577
1573
1560
1566
1557
1522
1473
1488
1508
1508
Ϫ
3422
Ϫ
3300
Ϫ
3307
908
Ϫ
933
Ϫ
907
Ϫ
933
Ϫ
912
Ϫ
889
Ϫ
NMR Studies
The NMR spectra show narrow signals typical of VV dia-
magnetic complexes. HETCOR experiments allowed us to
assign all of signals for the studied complexes. The 1H
NMR chemical shifts along with the chemical shift differ-
ences between each complex and the corresponding ligand,
expressed as ∆δ, are listed in Table 2. The formula in the
table shows the numbering scheme of the free ligands. The
1H NMR integrations and signal multiplicities agree with
the proposed formula. The three complexes show similar
1H and 13C chemical shifts for the salicylaldehyde semicar-
bazone common portion. When the ligand is coordinated,
the deshielding effect of the metal atom is apparent in some
Figure 2. Selected ligands: salicylaldehyde semicarbazone (L1),
salicylaldehyde 4-n-butylsemicarbazone (L2) and salicylaldehyde
4-(2-naphthyl)semicarbazone (L3)
Although almost no VVO2ϩ complex has shown good in-
sulin-enhancing properties, VV complexes may be reduced
in vivo to form potentially bioactive VIVO2ϩ complexes.[20]
In particular, vanadium() dipicolinate is an effective oral
agent in live animals.[21] Thus, it seemed interesting to test
the insulin-mimetic activity of the three novel complexes
reported here.
1
protons, causing a downfield shift of the corresponding H
1
NMR peaks. Upfield shifts in the H NMR spectra of the
signals of 4- and 6-H of the complexes could be the result
of ligand deprotonation upon coordination, due to the lack
of 7-H (Table 2).[18] The upfield shift of the signal of 3-H
could be due to the decreasing azomethine anisotropic ef-
fect in the coordinated form of L. When L is coordinated,
the azomethine moiety is fixed by the vanadium core in an
opposite spatial distribution to 3-H. Thus, after coordi-
nation, this proton is less affected by the magnetic aniso-
tropy of the CϭN double bond than in the free ligand.[23]
Results and Discussion
Three novel VV semicarbazone complexes have been syn-
thesized and characterized. Complexes with the formula
VVO2L, where L ϭ salicylaldehyde semicarbazone (L1), sal-
icylaldehyde 4-n-butylsemicarbazone (L2) or salicylaldehyde
4-(2-naphthyl)semicarbazone (L3), were prepared in good
yields and high purity. The analytical data agree with the
proposed formulae.
Structural Results
In contrast to VIVO2ϩ complexes, those of VO2L do not
Intramolecular bond lengths and angles around the metal
show electronic dϪd transitions in the visible region due to ion in VO2L1 (Table 3) and an ORTEP[24] drawing of the
the absence of d-electrons. Thus, the yellow color of the VV molecule (Figure 3) are shown here.
complexes arises from intense absorption tailing-in from the
The X-ray diffraction study shows that the complex
UV region, originating in OǞV charge transfer tran- VO2L1 consists of a discrete monomeric molecule. The va-
sitions.[22]
nadium() ion is in a distorted square-pyramidal environ-
Eur. J. Inorg. Chem. 2004, 322Ϫ328
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 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
323

D. Gambino et al.
FULL PAPER
1
Table 2. H NMR chemical shifts (δ, ppm) of VVO2L, with L ϭ L1, L2 and L3, in [D6]DMSO/D2O at 303 K
H
VVO2L1
δComplex
VVO2L2
δComplex
VVO2L3
δComplex
∆δ[a]
∆δL2
δLigand
δLigand
δLigand
∆δL1
0.44
Ϫ0.24
Ϫ0.02
0.21
Ϫ0.08
Ϫ
2.31
∆δL3
0.48
Ϫ
Ϫ0.02
Ϫ
Ϫ0.09
Ϫ
Ϫ0.77
0.75
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
0.09
Ϫ
Ϫ
Ϫ
Ϫ
1
3
4
5
6
7
8
10
11
12
13
14
15
17
18
20
21
22
23
25
8.14
7.72
6.81
7.16
6.87
9.85
10.19
8.58
7.48
6.79
7.37
6.79
not present
12.50
8.12
7.74
6.85
7.17
6.80
9.97
10.17
6.80
Ϫ
3.12
1.45
1.30
0.89
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
8.63
7.51
6.85
7.39
8.21
7.74
6.87
7.23
6.89
10.08
10.70
9.07
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
8.69
0.51
Ϫ0.23
0
0.22
0
Ϫ
Ϫ
1.55
Ϫ
0.08
0.04
0.03
0.01
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
[b]
6.85
[b]
6.80
6.80
not present
9.93
9.82
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
not present
not observed[c]
8.35
Ϫ
6.53
7.96
1.43
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
3.20
1.49
1.33
0.90
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
7.97
8.06
[d]
[b]
[d]
[b]
[b]
[b]
[b]
7.37
7.46
[d]
Ϫ
Ϫ
Ϫ
0.11
8.31
8.42
[a]
∆δ ϭ (δComplex Ϫ δLigand). [b] 7.30Ϫ7.90 ppm, as multiplet. [c] Owing to exchange with solvent protons. [d] 7.77Ϫ7.87 ppm, as multiplet.
ported for the cis-VO2 moiety in other complexes.[25] The
trans-ligandϪVϪligand angles are O1ϪVϪO2 147.9(2)°
and N3ϪVϪO12 148.7(2)° and the cis-ligandϪVϪligand
angles vary from 74.2(2) to 108.1(2)°.
˚
Table 3. Bond lengths [A] and angles [°] around the vanadium atom
in [VO2(salicylaldehyde semicarbazone)], VO2L1
VϪO(11)
VϪO(12)
VϪO(2)
VϪO(1)
VϪN(3)
1.622(4)
1.641(4)
1.894(4)
1.998(4)
2.154(5)
O(11)ϪVϪO(12)
O(11)ϪVϪO(2)
O(12)ϪVϪO(2)
O(11)ϪVϪO(1)
O(12)ϪVϪO(1)
O(2)ϪVϪO(1)
O(11)ϪVϪN(3)
O(12)ϪVϪN(3)
O(2)ϪVϪN(3)
O(1)ϪVϪN(3)
108.1(2)
105.1(2)
95.9(2)
101.8(2)
92.1(2)
The nitrogen atom and the three coordinated oxygen
atoms at the pyramid base are nearly in a plane (rms devi-
ation of NO3 atoms from the least-squares plane is 0.017
˚
˚
147.9(2) A) with the metal ion 0.401 A apart from this plane,
102.2(2)
148.7(2)
towards the axial oxo ligand.
The salicylaldehyde semicarbazone molecule is also
83.2(2)
nearly planar (rms deviation of ligand atoms from the least-
74.2(2)
˚
squares plane is 0.065 A) and subtends an angle of 5.8(1)°
with the NO3 plane. Of the possible isomeric forms for the
ment, coordinated at the pyramid basis to a salicylaldehyde ligand, the (E) isomer is preferred. The crystal is further
semicarbazone molecule that acts as a tridentate ligand stabilized by a net of medium-to-strong intermolecular
through its azomethine nitrogen atom [d(VϪN) ϭ 2.154(5) NϪH···O bonds, involving the terminal NH2 group of a
˚
A], and its carbonyl and deprotonated phenol oxygen atoms given ligand molecule and the phenol oxygen atom
˚
˚
˚
[VϪO distances of 1.998(4) and 1.894(4) A, respectively], [d(N1···O2Ј) ϭ 2.972 A, N1ϪH1A···O2 ϭ 174.9°] and the
˚
2.870 A,
and to an oxo ligand [d(VϪO) ϭ 1.641(4) A]. The fivefold equatorial oxo ligand [d(N1···O12ЈЈ)
ϭ
coordination is completed by another oxo ligand at the N1ϪH1B···O12ЈЈ ϭ 171.4°] of neighboring ligand mol-
˚
pyramid apex [d(VϪO) ϭ 1.622(4) A]. Both oxo ligands are ecules, and also the NϪH group in an NϪH···O bond with
˚
in cis positions. The average VϪO bond length and the axial oxo ligand [d(N2···O11ЈЈ)
OϪVϪO angle are quite similar to those previously re- N2ϪH2···O11ЈЈ ϭ 153.2°].
ϭ
2.723 A,
324
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Inorg. Chem. 2004, 322Ϫ328

New Vanadium(V) Complexes with Salicylaldehyde Semicarbazone Derivatives
FULL PAPER
Figure 3. [VO2(salicylaldehyde semicarbazone)] complex showing the labeling scheme of the non-H atoms and their displacement ellipsoids
at the 30% probability level
Figure 4. Inhibitory effects of VOSO4 and dioxovanadium() complexes with or without 1 m ascorbic acid on FFA release from isolated
rat adipocytes treated with epinephrine
addition of 1 m ascorbic acid to VOSO4 or VO2L2 com-
plex (VOSO4-asc and VO2L2-asc) significantly enhanced the
inhibitory effect of FFA release (Table 4, VOSO4-asc: 0.34
Ϯ 0.15 m, VO2L2-asc: 0.73 Ϯ 0.27 m). Thus, the in vitro
insulin-mimetic activity of VO2L2 was improved by the ad-
dition of the reducing agent ascorbic acid, even though it
remained lower than that of pure VOSO4 under the same
conditions.
Biological Activity of the Complexes
In vitro insulin-mimetic activities of the three dioxovana-
dium() complexes were examined, with or without 1 m
ascorbic acid, with regard to inhibition of FFA release from
isolated rat adipocytes treated with epinephrine (Figure 4).
Ascorbic acid exhibited essentially no inhibitory effect on
FFA release under the experimental conditions. The inhibi-
tory effects of dioxovanadium() complexes were compared
Upon addition of VOSO4 to the adipocytes under air, the
with those of VOSO4 as a positive control (IC50 ϭ 1.00 Ϯ vanadyl state was found to be oxidized during the 3 h of
0.27 m). In the absence of ascorbic acid, all dioxovanadi- incubation (unpublished results). Therefore, the addition of
um() complexes exhibited scarcely any inhibitory effects at ascorbic acid was thought to maintain the vanadyl state
concentrations of 10Ϫ4, 5 ϫ 10Ϫ4 and 10Ϫ3 . The in vitro during incubation, which in turn enhances the insulin-mi-
insulin-mimetic activities of the three dioxovanadium() metic activity of VOSO4. Interestingly, of the tested dioxo-
complexes were lower than that of VOSO4. However, the vanadium() complexes only VO2L2 exhibited insulin-mi-
Eur. J. Inorg. Chem. 2004, 322Ϫ328
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 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
325

D. Gambino et al.
FULL PAPER
With VVO2L1 re-oxidation of the VIV species occurred al-
most immediately under the experimental conditions tested.
Thus, NMR and spectrophotometric experiments
strongly indicate that ascorbic acid reduces VVO2L to a
VIVO2ϩL complex.
Table 4. Estimated IC50 values of the dioxovanadium() complexes
Compound
IC50 [m]
VOSO4
1.00 Ϯ 0.27
0.34 Ϯ 0.15[a]
none
VOSO4 ϩ ascorbic acid
In particular, the reduction of the VVO2L2 complex could
explain the enhancement in insulin-mimetic activity of this
complex in the presence of ascorbic acid.
VO2L1
VO2L1 ϩ ascorbic acid
VO2L2
none
none
VO2L2 ϩ ascorbic acid
VO2L3
0.73 Ϯ 0.22[b][c]
none
These results, together with those of the biological tests
in the presence of ascorbic acid, encouraged us to try to
synthesize and isolate the VIVL2 complex, which could
VO2L3 ϩ ascorbic acid
none
[a]
[b]
Significance at P Ͻ 0.05 vs. VOSO4. Significance at P Ͻ 0.05 show the desirable in vitro and/or in vivo insulin-mimetic
[c]
vs. VOSO4 ϩ ascorbic acid. Significance at P Ͻ 0.05 vs. VO2L2.
activity. We are thus extending our research to examine the
structure-activity relationship of these complexes Ϫ involv-
metic activity in the presence of ascorbic acid, although
spectroscopic experiments showed that all three complexes
were reduced by the addition of ascorbic acid, as described
below. These results suggest the importance of the interac-
tion between the reduced forms of the complexes and the
adipocytes, and that this interaction strongly depends on
the chemical nature of the ligands.
ing redox potentials, partition coefficients, stability con-
stants, molecular sizes and the elucidation of the chemical
structure of the reduced forms. The emerging results will be
the subject of a future publication.
Experimental Section
Reaction of VVO2L with Ascorbic Acid
Materials: All common laboratory chemicals were purchased from
The reaction of VVO2L2 with ascorbic acid was moni- commercial sources and used without further purification. 4-n-Bu-
tylsemicarbazide, 4-(2-naphthyl)semicarbazide and VIVO(acac)2,
1
tored by H NMR spectroscopy at 303 K in [D6]DMSO/
where acac ϭ acetylacetonate, were prepared according to well-
D2O. Immediately after the addition of ascorbic acid, the
established
literature
procedures.[27Ϫ29]
Vanadyl
sulfate
solution changed from yellow to dark-green and the narrow
signals characteristic of the VV diamagnetic complex were
converted into broad ones. This strongly suggests that dur-
ing the reaction the VVO2L2 complex is reduced by the asc-
orbic acid to a paramagnetic VIV species. Signals of free
L2 were not detected, indicating that the ligand remained
coordinated to the central atom in the VIV species.
(VOSO4·2.8H2O) and (ϩ)--ascorbic acid were purchased from
Wako Pure Chemical (Osaka, Japan). The purity of VOSO4·2.8H2O
was determined by chelatometry using Cu-Pan [Cu-1-(2-pyridyl-
azo-2-naphthol)]. Collagenase (Type II), bovine serum albumin
(BSA; fraction V) and (Ϯ)-epinephrine hydrochloride (adrenaline)
were obtained from Sigma Chemical (St. Louis, MO, USA). (ϩ)-
-Glucose was purchased from Nacalai Tesque, Inc. (Kyoto, Ja-
Similar conclusions arise from the spectrophotometric pan). Other reagents were of the highest purity commercially avail-
study of the reduction with ascorbic acid of VVO2L2 and
able.
VVO2L3, as previously reported for (maltol)- and (ethylmal-
Physicochemical Characterization: C, H, N analyses were per-
formed with a Carlo Erba Model EA1108 elemental analyzer.
tol)vanadium() complexes.[25] In each case, after addition
of the reducing agent a new band in the visible region near
670 nm was detected, which is attributable to a dϪd tran-
sition of the resulting VIV species.[22] After keeping the solu-
tion under air for 8 h, the new band disappeared gradually
and finally the initial spectrum was obtained (Figure 5).
FTIR spectra (4000Ϫ400 cmϪ1) were measured as KBr pellets with
a Bomen M102 instrument. Electronic spectra were recorded with
a Spectronic 3000 spectrophotometer. 1H and 13C NMR spectra of
the free ligands and of the complexes were recorded with a Bruker
DPX-400 instrument (at 400 and 100 MHz, respectively). Experi-
ments were performed at 303 K in [D6]DMSO/D2O (8:2) (stability
of the complexes in this medium had been tested previously). Het-
eronuclear correlation experiments (2D-HETCOR), HMQC (mul-
tiple quantum) and HMBC (multiple bond) were performed with
the same instrument. MS experiments of the free ligands were ob-
tained in the mass range 40Ϫ500 amu using a Shimadzu MSQP
1100 EX spectrometer with EI at 70 eV and a direct insertion
probe.
Syntheses of the Ligands: All reactions were carried out under ni-
trogen. An equimolar mixture of 2-hydroxybenzaldehyde (salicylal-
dehyde) and the corresponding semicarbazide was stirred with p-
TsOH (catalytic amounts) in dry toluene as solvent at room tem-
perature until no more carbonyl compound was detected (SiO2, 1%
MeOH in CH2Cl2). For L1 and L2 the resulting solid was collected
by filtration. For L3 the solution was concentrated in vacuo and
the solid was filtered off. The ligands were characterized by 1H and
13C NMR, IR and MS.
Figure 5. Electronic spectra (400Ϫ800 nm) of a 9.5 ϫ 10Ϫ4

DMSO solution of VVO2L2 (a) before and (b) immediately after
the addition of ascorbic acid, and (c) 20, (d) 60 and (e) 300 min
after the addition
326
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Eur. J. Inorg. Chem. 2004, 322Ϫ328

New Vanadium(V) Complexes with Salicylaldehyde Semicarbazone Derivatives
FULL PAPER
Syntheses of the Complexes: The VVO2L complexes were prepared
by boiling under reflux VIVO(acac)2 (100 mg, 0.375 mmol, acac ϭ
acetylacetonate) with L (0.375 mmol) in ethanol (10 mL) for 10 h.
prepared cells were filtered through sterilized cotton gauze and
were then washed with KRB buffer. Isolated rat adipocytes cells
(1.0Ϫ2.0 ϫ 106 cells/mL) were preincubated at 37 °C for 30 min
with various concentrations (10Ϫ4Ϫ10Ϫ3 ) of VOSO4 or dioxovan-
adate complexes in KRB buffer containing 2% dimethyl sulfoxide
(DMSO) with or without 1 m (ϩ)--ascorbic acid. The reaction
mixtures were then incubated at 37 °C for 3 h after the addition of
epinephrine (10Ϫ5 , adrenaline). The reactions were stopped by
soaking in ice/water and the resultant mixtures were centrifuged at
3000 rpm at 4 °C for 10 min. For the outer solution of the cells,
the FFA levels were determined with an FFA kit (NEFA C-test
Wako, Wako Pure Chemicals). In vitro insulin-mimetic effects of
the dioxovanadate complexes were evaluated by the apparent IC50
value (50% inhibitory concentration of the FFA released in each
system).
VVO2L1: VVO2L1 was filtered off from the hot solution as a yellow-
greenish solid. Yield 69 mg, 70%. Single yellow-greenish crystals,
suitable for X ray diffraction, were obtained by slow concentration
of an ethanolic solution at room temperature. C8H8N3O4V (261.1):
calcd. C 36.8, H 3.09, N 16.1; found C 37.1, H 3.41, N 15.8. UV/
1
Vis (MeOH): λmax ϭ 237, 278, 315 nm. H NMR: δ ϭ 6.79 (m, 2
H), 7.37 (t, 1 H), 7.48 (d, 1 H), 7.96 (br. s, 2 H), 8.58 (br. s, 1 H),
12.50 (br. s, 2 H) ppm. 13C NMR: δ ϭ 118.20, 119.30, 120.00,
133.00, 134.30, 150.0, 161.4, 164.20 ppm.
VVO2L2: VVO2L2 was obtained as a microcrystalline powder by
slow concentration of the reaction mixture at room temperature.
Yield 47 mg, 40%. C12H16N3O4V (317.2): calcd. C 45.4, H 5.08, N
13.2; found C 45.1, H 5.31, N 13.1. UV/Vis (MeOH): λmax ϭ 244,
Reaction of VVO2L with Ascorbic Acid: The reduction of VVO2L
by ascorbic acid was studied by electronic spectroscopy in DMSO
solution. Ascorbic acid (0.047 mmol, 8.3 mg) was added to a
VVO2L solution (9.5 ϫ 10Ϫ4 , 5.0 mL) (VVO2L/ascorbic acid, mo-
lar ratio 1:10). The spectrum of the resultant solution was meas-
ured in the range 400Ϫ800 nm both before and after the addition
and monitored with time until no bands were detected. The reac-
tion of VVO2L2 with ascorbic acid was also monitored by 1H NMR
at 303 K, by first dissolving VVO2L2 (0.032 mmol) in [D6]DMSO/
D2O (8:2) in an NMR tube. After purging the solution with nitro-
1
287, 359 nm. H NMR: δ ϭ 0.90 (t, 3 H), 1.33 (m, 2 H), 1.49 (m,
2 H), 3.20 (m, 2 H), 6.80 (d, 1 H), 6.85 (t, 1 H), 7.39 (t, 1 H), 7.51
(d, 1 H), 8.35 (br. s, 1 H), 8.63 (br. s, 1 H) ppm. 13C NMR: δ ϭ
14.40, 20.18, 31.86, 41.03, 118.66, 119.77, 120.31, 133.39, 134.65,
150.22, 160.59, 164.58 ppm.
VVO2L3: VVO2L3 was obtained as a yellow solid by slow concen-
tration of the reaction mixture at room temperature, after filtering
off the unreacted ligand from the hot solution. Yield 73 mg, 50%.
C18H14N3O4V (387.3): calcd. C 55.8, H 3.64, N 10.8; found C 55.5,
H 3.90, N 10.6. UV/Vis (MeOH): λmax ϭ 242, 283, 330 nm. 1H
NMR: δ ϭ 6.80 (br. t, 1 H), 6.85 (br. d, 1 H), 7.30Ϫ7.90 (m, 7 H),
8.06 (m, 1 H), 8.42 (br. s, 1 H), 8.69 (br. s, 1 H), 9.82 (br. s, 1 H),
9.93 (br. s, 1 H) ppm. 13C NMR: δ ϭ 116.90, 119.00, 120.10,
121.00, 121.75, 125.17, 127.29, 127.88, 128.34, 128.82, 129.26,
131.48, 134.28, 134.69, 137.59, 150.00, 159.66, 163.79 ppm.
1
gen for 5 min, the H NMR spectrum was measured. The ascorbic
acid (0.032 mmol) was then added in one portion, and the 1H
NMR spectrum measured again after keeping the mixture under
nitrogen for 30 min.
Acknowledgments
This work was supported by PEDECIBA, CSIC and CONICYT
of Uruguay, CONICET and ANPCyT of Argentine, TWAS,
FAPESP of Brazil and by the collaborative agreement between
CONICET of Argentina and CNPq of Brazil.
X-Ray Diffraction Data and Crystal Structure Determination and
Refinement: Crystal data, the data collection procedure, structure
determination methods and refinement results for VVO2L1 are sum-
marized in Table 5. The hydrogen atoms were included in the mo-
lecular model at stereochemical positions and refined with the rid-
ing model. CCDC-213179 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge at www.ccdc.cam.ac.uk/conts/retrieving.html [or from Cam-
bridge Crystallographic Data Centre, 12 Union Road, Cambridge
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327

D. Gambino et al.
Table 5. Crystal data and structure solution methods and refinement results for [(salicylaldehyde semicarbazone)VO2], VO2L1
FULL PAPER
Empirical formula
Formula mass
Temperature [K]
Low-temperature device
Cooling rate [K/h]
Crystal system
C8H8N3O4V
261.11
120(2)
Oxford Cryosystems
200
tetragonal
Space group
P42/n
[a]
˚
Unit cell dimensions [A]
a ϭ b ϭ 12.7674(7), c ϭ 11.5308(5)
1879.6(2)
8, 1.845
1.058
1056
3
˚
Volume [A ]
Z, calculated density [Mg/m3]
Absorption coefficient (µ) [mmϪ1
F(000)
]
Crystal size [mm]
Crystal color/shape
0.190 ϫ 0.055 ϫ 0.037
greenish-yellow/prism
KappaCCD/ϕ and ω
Mo-Kα, λ ϭ 0.71073
2.26 to 24.99
Diffractometer/scan type
˚
Radiation [A], graphite monochromator
␽ range for data collection [°]
Index ranges
Ϫ15Յ h Յ13, Ϫ14Յ k Յ15, Ϫ12Յ l Յ13
6324/1663 [R(int) ϭ 0.102]
94.7 (to ␽ ϭ 24.99°)
1329
Reflections collected/unique
Completeness [%]
Reflections observed [I Ͼ 2σ(I)]
Absorption correction
PLATON[29]
Max./min transm.
Data collection
0.964/0.884
COLLECT[30]
Data reduction and correction,[b] structure solution,[c] and
refinement[d] programs
DENZO and SCALEPACK,[31] SHELXS-97,[32]
SHELXL-97[33]
Refinement method
Weights w
Full-matrix least-squares on F2
[σ2(Fo ) ϩ (0.05P)2 ϩ 9.68P]Ϫ1
;
2
2
2
P ϭ [max(Fo , 0) ϩ 2Fc ]/3
1663/0/145
1.177
R1 ϭ 0.0623, wR2 ϭ 0.1674
R1 ϭ 0.0810, wR2 ϭ 0.1766
0.438/Ϫ0.668
Data/restraints/parameters
Goodness-of-fit on F2
Final R(ind.) [I Ͼ 2σ(I)][e]
R indices (all data)
Ϫ3
˚
Largest peak/hole [e·A
]
[a]
[b]
Least-squares refinement of the angular settings for 6324 reflections in the 2.26° Ͻ ␽ Ͻ 24.99° range.
Corrections: Lorentz,
[c]
[d]
polarization, and absorption. Neutral scattering factors and anomalous dispersion corrections.
Fourier methods. Final molecular model obtained by anisotropic full-matrix least-squares refinement of the non-hydrogen atoms.
indices defined as: R1 ϭ Σ||Fo| Ϫ |Fc||/Σ|Fo|, wR2 ϭ [Σw(Fo Ϫ Fc ) /Σw(Fo ) ]
Structure solved by Patterson and
[e]
R
2
2 2
2 2 1/2
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Published Online November 19, 2003
328
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