Preparation and structural characterization of oxovanadium(V) complexes with Schiff bases and their inhibition studies on Helicobacter pylori urease

Article abstract of DOI:10.1080/00958972.2011.625021

A series of structurally similar dinuclear oxovanadium(V) complexes, [VO²L]² (L=L¹= 2-[(2-methylaminoethylimino) methyl]phenolate (1); L=L²=2-[(2-ethylaminoethylimino) methyl]phenolate (2); L=L³=2-[(2

Full text of DOI:10.1080/00958972.2011.625021

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Preparation and structural
characterization of oxovanadium(V)
complexes with Schiff bases and their
inhibition studies on Helicobacter
pylori urease
Zhong-Lu You a , Hui Sun a , Bo-Wen Ding a , Yu-Ping Ma a , Mei
Zhang a & Dong-Mei Xian a
a Department of Chemistry and Chemical Engineering , Liaoning
Normal University , Huanghe Road 850#, Dalian 116029, P.R. China
Published online: 03 Oct 2011.
To cite this article: Zhong-Lu You , Hui Sun , Bo-Wen Ding , Yu-Ping Ma , Mei Zhang & Dong-Mei Xian
(2011) Preparation and structural characterization of oxovanadium(V) complexes with Schiff bases
and their inhibition studies on Helicobacter pylori urease, Journal of Coordination Chemistry, 64:20,
3510-3520, DOI: 10.1080/00958972.2011.625021
To link to this article: http://dx.doi.org/10.1080/00958972.2011.625021
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Journal of Coordination Chemistry
Vol. 64, No. 20, 20 October 2011, 3510–3520
Preparation and structural characterization of oxovanadium(V)
complexes with Schiff bases and their inhibition studies on
Helicobacter pylori urease
ZHONG-LU YOU*, HUI SUN, BO-WEN DING, YU-PING MA,
MEI ZHANG and DONG-MEI XIAN
Department of Chemistry and Chemical Engineering, Liaoning Normal University,
Huanghe Road 850#, Dalian 116029, P.R. China
(Received 29 June 2011; in final form 30 August 2011)
A series of structurally similar dinuclear oxovanadium(V) complexes, [VO2L]2 (L ¼ L1 ¼
2-[(2-methylaminoethylimino)methyl]phenolate
(1);
L ¼ L2 ¼ 2-[(2-ethylaminoethylimino)
methyl]phenolate (2); L ¼ L3 ¼ 2-[(2-isopropylaminoethylimino)methyl]phenolate (3)), has
been synthesized and characterized by physico-chemical methods and single-crystal X-ray
diffraction. The V in each complex is octahedral, with three donors of L and one oxo defining
the equatorial plane, and with two oxos occupying the axial positions. The complexes were
tested for their urease inhibitory activities. The inhibition rate (%) of 1, 2, and 3 at
100 mmol Lꢀ1 on urease are 67 ꢁ 1, 53.5 ꢁ 0.9, and 44 ꢁ 1. The relationship between structures
of the complexes and the urease inhibitory activities indicates that shorter terminal groups of
the complexes have stronger activities against urease. Molecular docking study of the
complexes with the Helicobacter pylori urease was performed.
Keywords: Schiff base; Oxovanadium(V) complex; Crystal structure; Urease inhibition
1. Introduction
Schiff bases have received much attention in coordination and biological chemistry
[1–3]. Vanadium complexes have been reported to have interesting biological activities
such as normalizing high blood glucose levels and acting as models of haloperoxidases
[4–6]. Ara and co-workers [7] reported that binuclear vanadium(IV) complexes possess
interesting urease inhibitory activities. Our group indicated that mononuclear
oxovanadium(V) complexes with Schiff bases also possess effective urease inhibitory
activities [8]. To investigate the activities of binuclear vanadium complexes with Schiff
bases, a series of binuclear oxovanadium(V) complexes, [VO2L]2 (L ¼ L1 ¼ 2-[(2-
methylaminoethylimino)methyl]phenolate (1); L ¼ L2 ¼ 2-[(2-ethylaminoethylimino)
methyl]phenolate (2); L ¼ L3 ¼ 2-[(2-isopropylaminoethylimino)methyl]phenolate (3);
scheme 1), has been synthesized and structurally characterized. The urease inhibitory
*Corresponding author. Email: youzhonglu@yahoo.com.cn
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2011 Taylor & Francis
http://dx.doi.org/10.1080/00958972.2011.625021

Oxovanadium(V) Schiff bases
3511
H
N
R
N
O
Scheme 1. The Schiff bases. R ¼ methyl for L1, ethyl for L2, isopropyl for L3.
activities of the complexes and the molecular docking analysis of the complexes with
Helicobacter pylori urease were investigated.
2. Experimental
2.1. General methods and materials
Starting materials, reagents, and solvents were purchased from commercial suppliers in
AR grade and used without purification. Elemental analyses were performed on a
Perkin-Elmer 240C elemental analyzer. IR spectra were recorded on a Jasco FT/IR-
.
4000 spectrometer as KBr pellets from 4000 to 200 cmꢀ1 1H NMR spectra were
recorded on a Bruker AVANCE 400 MHz spectrometer with tetramethylsilane as the
internal reference. Molar conductance was measured with a Shanghai DDS-11A
conductometer. X-ray diffraction was carried out on a Bruker SMART 1000 CCD
diffractometer. The Schiff bases HL1, HL2, and HL3 were prepared according to the
literature method [9].
2.2. Synthesis of the complexes
[VO2L1]2 (1): A methanolic solution (30 mL) of VO(acac)2 (0.27 g, 1.0 mmol) was added
to a methanolic solution (20 mL) of HL1 (0.18 g, 1.0 mmol) with stirring. The mixture
was stirred at room temperature for 30 min to give a brown solution. The resulting
solution was allowed to stand in air for a week until 5 mL of the solvent remained.
Brown block-shaped crystals of 1 suitable for X-ray single-crystal diffraction formed at
the bottom of the vessel. The crystals were isolated, washed three times with cold
methanol, and dried in air. Yield 62%. IR data (cmꢀ1): 3246 (sh, m), 1649 (s), 1598 (m),
1549 (m), 1471 (m), 1451 (s), 1390 (w), 1333 (w), 1327 (s), 1202 (w), 1147 (w), 1122 (w),
1087 (w), 1031 (w), 1012 (w), 934 (s), 845 (s), 798 (w), 754 (m), 623 (m), 533 (w), 461 (w),
445 (w), 399 (w), 373 (w), 342 (w), 303 (w). Anal. Calcd for C20H26N4O6V2: C, 46.2;
H, 5.0; N, 10.8. Found (%): C, 46.5; H, 5.2; N, 10.6.
[VO2L2]2 (2): Complex 2 was synthesized by the same method as described for 1, with
HL1 replaced by HL2 (0.19 g, 1.0 mmol). Brown block-shaped single crystals of 2 were
isolated after a week, washed three times with cold MeOH, and dried in air. Yield 53%.
IR data (cmꢀ1): 3221 (sh, m), 1634 (s), 1601 (m), 1549 (m), 1472 (m), 1448 (s), 1394 (w),
1338 (w), 1292 (s), 1207 (w), 1151 (w), 1127 (w), 1088 (w), 1064 (m), 1020 (m), 929 (s),
846 (s), 805 (w), 760 (m), 623 (m), 553 (w), 465 (w), 446 (w), 393 (w), 378 (w) 350 (w),

3512
Z.-L. You et al.
Table 1. Crystallographic and experimental data for 1–3.
Complex
1
2
3
Empirical formula
Formula weight
Crystal system
Space group
C
520.3
Monoclinic
P21/c
20H26N4O6V2
C22H30N4O6V2
548.4
Triclinic
C24H34N4O6V2
576.4
Triclinic
ꢀ
ꢀ
P1
P1
ꢂ
˚
Unit cell dimensions (A, )
a
b
c
ꢁ
ꢂ
ꢃ
6.678(2)
11.955(3)
13.830(3)
90
92.161(3)
90
1103.3(5), 2
1.566
0.892
536
2364
7.685(1)
8.848(2)
10.634(2)
66.098(2)
72.935(2)
66.981(2)
600.6(2), 1
1.516
0.823
284
2403
2222
9.377(1)
9.510(1)
15.489(2)
74.535(2)
76.866(2)
77.901(1)
1279.9(3), 2
1.496
0.777
600
5413
3757
3
˚
Volume (A ), Z
Calculated density (g cmꢀ3
)
Absorption coefficient (Mo-Ka) (mmꢀ1
F(000)
)
Independent reflections
Observed reflections (I ꢃ 2ꢄ(I))
Min. and max. transmission
Parameters
1972
0.795 and 0.801
150
0.790 and 0.808
158
0.842 and 0.848
335
Restraints
1
1.042
0.0539, 0.1414
0.0633, 0.1477
1
1.063
0.0315, 0.0830
0.0343, 0.0847
2
1.056
0.0522, 0.1295
0.0782, 0.1443
Goodness-of-fit on F2
R1, wR2 [I ꢃ 2ꢄ(I)]a
R1, wR2 (all data)a
aR1 ¼ Fo ꢀ Fc/Fo, wR2 ¼ ½ÆwðFo2 ꢀ Fc2Þ=ÆwðFo2Þ ꢄ
.
2
1=2
302 (w). Anal. Calcd for C22H30N4O6V2: C, 48.2; H, 5.5; N, 10.2. Found (%): C, 48.0;
H, 5.6; N, 10.4.
[VO2L3]2 (3): Complex 3 was synthesized by the same method as described for 1, with
HL1 replaced by HL3 (0.21 g, 1.0 mmol). The brown block-shaped single crystals of 3
were isolated after a week, washed three times with cold MeOH, and dried in air. Yield
71%. IR data (cmꢀ1): 3221 (sh, m), 1644 (s), 1597 (m), 1549 (m), 1471 (m), 1448 (s),
1395 (w), 1325 (w), 1294 (s), 1204 (w), 1150 (w), 1125 (w), 1080 (w), 1028 (m), 931 (s),
855 (s), 768 (w), 621 (m), 551 (w), 459 (w), 426 (w), 377 (w), 345 (w). Anal. Calcd for
C24H34N4O6V2: C, 50.0; H, 5.9; N, 9.7. Found (%): C, 49.7; H, 6.0; N, 9.8.
2.3. X-ray crystallography
Diffraction intensities for the complexes were collected at 298(2) K using a Bruker
SMART 1000 CCD area-detector diffractometer with Mo-Ka radiation
˚
(ꢀ ¼ 0.71073 A). The collected data were reduced with SAINT [10], and multi-scan
absorption correction was performed using SADABS [11]. The structures were solved
by direct methods. The complexes were refined against F2 by full-matrix least-squares
using the SHELXTL package [12]. All non-hydrogen atoms were refined anisotrop-
ically. The amino hydrogen atoms in the complexes are located from difference Fourier
˚
maps and refined isotropically, with N–H distances restrained to 0.90(1) A. The
remaining hydrogen atoms were placed in calculated positions and constrained to ride
on their parent atoms. The crystallographic data for the complexes are summarized in
table 1. Selected bond lengths and angles are given in table 2.

Oxovanadium(V) Schiff bases
3513
ꢂ
˚
Table 2. Selected bond lengths (A) and angles ( ) for 1–3.
1
V1–O1
V1–O3
V1–N2
1.920(2)
1.669(2)
2.143(3)
V1–O2
V1–N1
V1–O3i
1.611(2)
2.153(3)
2.312(2)
O2–V1–O3
O3–V1–O1
O3–V1–N2
O2–V1–N1
O1–V1–N1
O2–V1–O3i
O1–V1–O3i
N1–V1–O3i
105.7(1)
O2–V1–O1
O2–V1–N2
O1–V1–N2
O3–V1–N1
N2–V1–N1
O3–V1–O3i
N2–V1–O3i
102.3(1)
98.7(1)
92.8(1)
95.4(1)
84.9(1)
171.5(1)
84.0(1)
79.2(1)
94.0(1)
156.6(1)
157.1(1)
76.8(1)
78.7(1)
78.4(1)
2
V1–O1
V1–O3
V1–N2
1.907(1)
2.385(1)
2.149(2)
V1–O2
V1–N1
V1–O3ii
1.612(2)
2.158(2)
1.665(1)
O2–V1–O3
O3ii–V1–O1
O3ii–V1–N2
O2–V1–N1
O1–V1–N1
O2–V1–O3
O1–V1–O3
N1–V1–O3
107.8(1)
O2–V1–O1
O2–V1–N2
O1–V1–N2
O3ii–V1–N1
N2–V1–N1
O3ii–V1–O3
N2–V1–O3
102.6(1)
98.7(1)
92.0(1)
97.3(1)
84.9(1)
169.8(1)
84.4(1)
75.7(1)
92.5(1)
157.8(1)
153.0(1)
77.0(1)
78.0(1)
78.8(1)
3
V1–O1
V1–O3
V1–N2
1.913(2)
1.609(2)
2.171(3)
V1–O2
V1–N1
V1–O2iii
1.666(2)
2.154(3)
2.410(3)
O3–V1–O2
O2–V1–O1
O2–V1–N1
O3–V1–N2
O1–V1–N2
O3–V1–O2iii
O1–V1–O2iii
N2–V1–O2iii
108.9(1)
O3–V1–O1
O3–V1–N1
O1–V1–N1
O2–V1–N2
N1–V1–N2
O2–V1–O2iii
N1–V1–O2iii
100.1(1)
99.1(1)
154.2(1)
95.5(1)
156.6(1)
170.2(1)
84.6(1)
77.6(1)
95.6(1)
84.2(1)
92.1(1)
77.1(1)
78.5(1)
76.3(1)
i
Symmetry codes: 2 ꢀ x, 2 ꢀ y, 1 ꢀ z; ii1 ꢀ x, ꢀy, 1 ꢀ z; iii1 ꢀ x, 1 ꢀ y, 1 ꢀ z.
2.4. Urease inhibitory activity assay
Helicobacter pylori (ATCC 43504; American Type Culture Collection, Manassas, VA)
was grown in brucella broth supplemented with 10% heat-inactivated horse serum for
24 h at 37ꢂC under microaerobic conditions (5% O2, 10% CO2, and 85% N2). The
method of preparation of H. pylori urease by Mao et al. [13] was followed. Briefly,
broth cultures (50 mL, 2.0 ꢅ 108 CFU mLꢀ1) were centrifuged (5000 g, 4ꢂC) to collect
the bacteria, and after washing twice with phosphate-buffered saline (pH 7.4), the H.
pylori precipitate was stored at ꢀ80ꢂC. While the H. pylori was returned to room
temperature, and mixed with 3 mL of distilled water and protease inhibitors, sonication
was performed for 60 s. Following centrifugation (15,000 g, 4ꢂC), the supernatant was
desalted through SephadexG–25 column (PD–10 columns, Amersham-Pharmacia
Biotech, Uppsala, Sweden). The resultant crude urease solution was added to an
equal volume of glycerol and stored at 4ꢂC until use in the experiment. The mixture,

3514
Z.-L. You et al.
containing 25 mL (4U) of H. pylori urease and 25 mL of the test compound, was pre-
incubated for 3 h at room temperature in a 96-well assay plate. Urease activity was
determined for three parallel times by measuring ammonia production using the
indophenol method as described by Weatherburn [14].
2.5. Molecular docking study
Molecular docking of the complexes into the 3-D X-ray structures of H. pylori urease
structure (entry 1E9Y in the Protein Data Bank) was carried out by using the
AutoDock 4.2 software as implemented through the graphical user interface
AutoDockTools (ADT 1.5.4). The graphical user interface AutoDockTools was
employed to setup the enzymes: all hydrogen atoms were added, Gasteiger charges were
calculated, and non-polar hydrogen atoms were merged to carbon atoms. The Ni initial
˚
parameters are set as r ¼ 1.170 A, q ¼ þ 2.0, and van der Waals well depth of
0.100 kcalmolꢀ1 [15]. The molecules of 1 and 2, and the V1 molecule of 3 were
transferred to pdb files with the program ChemBio3D. The pdb files were further
transferred to pdbqt files with AutoDockTools.
AutoDockTools was used to generate the docking input files. In all docking, a grid
box with a size of 70 ꢅ 60 ꢅ 60 points in x, y, and z directions was built, the maps were
centered on the original ligand molecule in the catalytic site of the protein. A grid
˚
spacing of 0.375 A and a distances-dependent function of the dielectric constant were
used for the calculation of the energy map. 100 runs were generated by using
Lamarckian genetic algorithm searches. Default settings were used with an initial
population of 50 randomly placed individuals, a maximum number of 2.5 ꢅ 106 energy
evaluations, and a maximum number of 2.7 ꢅ 104 generations. A mutation rate of 0.02
and a crossover rate of 0.8 were chosen. The results of the most favorable free energy of
binding were selected as the resultant complex structures.
3. Results and discussion
3.1. Chemistry
The Schiff bases were synthesized by the reaction of salicylaldehyde with N-alkylethane-
1,2-diamine in absolute methanol, with high yields and purity. The complexes were
synthesized by reaction of the Schiff bases with VO(acac)2 in a molar ratio of 1 : 1 in
methanol. Single crystals were obtained by slow evaporation of methanolic solutions of
the complexes. All complexes are stable in air at room temperature. Molar conductivities
of the complexes in MeOH at 10ꢀ3 molLꢀ1 are 24 ꢁꢀ1 cm2 molꢀ1 for 1, 22 ꢁꢀ1 cm2 molꢀ1
for 2, and 16 ꢁꢀ1 cm2 molꢀ1 for 3, and at concentration of 10ꢀ2 molLꢀ1 are
172 ꢁꢀ1 cm2 molꢀ1 for 1, 160 ꢁꢀ1 cm2 molꢀ1 for 2, and 135 ꢁꢀ1 cm2 molꢀ1 for 3,
indicating the non-electrolytic nature of the complexes in solution [16]. When
compared with the mononuclear oxovanadium(V) complexes derived from similar
Schiff bases [8, 17, 18], the secondary amine groups are essential for the dimeric
structures.

Oxovanadium(V) Schiff bases
3.2. Structure description of the complexes
3515
The molecular structures of 1, 2, and 3 are shown in figures 1, 2, and 3, respectively.
X-ray crystallography reveals that the complexes are similar centrosymmetric dimeric
oxovanadium(V) compounds. The difference among the complexes is different Schiff-
base ligands. Complex 1 is isostructural with that (10) reported by Mokry and Carrano
[19], b0ut with different space groups. The obvious difference between the structures of 1
0
˚
˚
and 1 is the lengths of the apical bonds (2.312(2) A for 1 and 2.437(2) A for 1 ),
0
˚
˚
following with the shorter V ꢆ ꢆ ꢆ V distance in 1 (3.106(1) A) than that in 1 (3.225(1) A).
Figure 1. Perspective view of the molecular structure of 1 with the atom labeling scheme. The thermal
ellipsoids are drawn at the 30% probability level.
Figure 2. Perspective view of the molecular structure of 2 with the atom labeling scheme. The thermal
ellipsoids are drawn at the 30% probability level.

3516
Z.-L. You et al.
The slight difference of the apical bonds leads to the distinct molecular packing modes
of the compounds (figure 4). In the molecular packing of 1, the molecules are stacked
with no obvious short contacts, while in 2, the molecules are linked via non-typical
intermolecular C–H ꢆ ꢆ ꢆ O hydrogen bonds, leading to formation of 2-D sheets parallel
˚
˚
to the ab plane. The V ꢆ ꢆ ꢆ V distances are 3.179(1) A for 2, 3.195(1) and 3.191(1) A for 3.
Each V in the complexes is six-coordinate through three bonds to oxo groups and
through three bonds to the tridentate Schiff-base ligand, forming an octahedral
geometry. The distances between V1 and O3 in 1 and 2, V1 and O2 and V2 and O5 in 3
˚
are in the range 1.658(2)–1.669(2) A, indicating they are typical V¼O bonds. O3 in 1
and 2, O2 and O5 atoms in 3 are bridging groups. The coordinate bond lengths in the
complexes are comparable to each other. Distortion of the octahedral coordination can
be observed by the coordinate bond angles, ranging from 76.8(1) to 105.7(1)ꢂ (1),
77.0(1) to 107.8(1)ꢂ (2), and 76.0(1) to 108.9(1)ꢂ for the perpendicular angles, and from
156.6(1) to 171.5(1)ꢂ (1), 153.0(1) to 169.8(1)ꢂ (2), and 153.4(1) to 170.4(1)ꢂ (3) for the
Figure 3. Perspective view of the molecular structure of 3 with the atom labeling scheme. The thermal
ellipsoids are drawn at the 30% probability level.
Figure 4. The molecular packing of 1 (left) and 10 (right) viewed along the a-axis. Intermolecular C–H ꢆ ꢆ ꢆ O
hydrogen bonds are drawn as dashed lines.

Oxovanadium(V) Schiff bases
3517
Table 3. Inhibition of urease by the tested materials.
Tested materials
Inhibition ratea (%)
IC50 (mmol L ꢀ 1
)
1
2
67.3 ꢁ 1.3
53.5 ꢁ 0.9
44.4 ꢁ 1.2
12.7 ꢁ 1.5
8.3 ꢁ 0.9
71.2 ꢁ 3.5
86.7 ꢁ 2.1
3
–
–
–
–
HL1
HL2
HL3
6.5 ꢁ 1.2
Vanadyl sulfate
AHA
22.3 ꢁ 2.7
207.1 ꢁ 3.1
90.2 ꢁ 3.7
43.1 ꢁ 2.7
aThe concentration of the tested material is 100 mmol Lꢀ1
.
diagonal angles. In each complex, there are two intramolecular N–H ꢆ ꢆ ꢆ O hydrogen
bonds in the dimeric molecule.
3.3. IR spectra
Weak and broad absorptions centered at 3425 cmꢀ1 indicate the presence of phenol
groups in the Schiff bases and are absent in the complexes. Strong absorption bands at
1615–1618 cmꢀ1 in spectra of the Schiff bases assigned to the azomethine ꢅ(C¼N) [20]
shift to higher wavenumbers in the complexes, 1634–1649 cmꢀ1, attributed to
coordination of imine nitrogen to vanadium. The middle absorption bands of Ar–O
in the Schiff bases at 1223–1280 cmꢀ1 [21] are located at lower frequencies for the
complexes, namely 1202 cmꢀ1 for 1, 1207 cmꢀ1 for 2, and 1204 cmꢀ1 for 3. The strong
absorptions at 930 cmꢀ1 and 850 cmꢀ1 are assigned to V¼O vibrations.
The close resemblance of the shape and the positions of the bands suggest similar
coordination modes for the complexes, in accord with structural features.
3.4. Pharmacology
The results of urease inhibition are summarized in table 3. Acetohydroxamic acid (AHA)
was used as a reference. The complexes exhibited moderate to effective inhibition. The
complexes inhibit urease in the order 1 4 2 4 3. The IC50 values (71 ꢁ 3 mmol Lꢀ1 for 1
and 87 ꢁ 2 mmol Lꢀ1 for 2) were determined since they have effective urease inhibitory
activities. The results indicate that the inhibitory activities of the complexes are much
better than vanadyl sulfate with an IC50 value of 207 ꢁ 3 mmol Lꢀ1. However, when
compared with AHA, the activities of the complexes are relatively weak. Considering
that the difference of the structures is only the terminal alkyl of the Schiff base, namely
methyl for 1, ethyl for 2, and isopropyl for 3, it is easy to conclude that the shorter the
terminal groups of the Schiff base, the stronger the urease inhibitory activities of the
oxovanadium(V) complexes. The results are in accord with that reported previously [22].
3.5. Molecular docking study
Molecular docking was performed to investigate the binding effects between the
complexes and the active sites of the H. pylori urease. In the X-ray structure available

3518
Z.-L. You et al.
Figure 5. Binding mode of 1 with H. pylori urease. Left: only the interacting residues are displayed.
The interactions are shown as dashed spheres. Right: the enzyme is shown as surface. The complex is shown
as sticks.
Figure 6. Binding mode of 2 with H. pylori urease. Left: only the interacting residues are displayed. The
interactions are shown as dashed spheres. Right: the enzyme is shown as surface. The complex is shown as
sticks.
for the native H. pylori urease, two nickels were coordinated by His136, His138,
Kcx219, His248, His274, Asp362, and water, while in the AHA-inhibited urease, water
molecules were replaced by AHA [23]. To understand the inhibitory activity of the
complexes, molecular docking of the complexes into the AHA-binding site of the urease
was performed on the binding model based on the H. pylori urease complex structure
(1E9Y.pdb). The binding models of the complexes and the urease are depicted in
figures 5–7, revealing that the complex molecules fit in the active pocket of the urease.
The binding energy of the complexes with urease are ꢀ6.75 kcalmolꢀ1 for 1,
ꢀ6.32 kcalmolꢀ1 for 2, and ꢀ5.86 kcalmolꢀ1 for 3, lower than that of the AHA
(ꢀ5.01 kcalmolꢀ1). The results of the molecular docking study agree with the inhibitory
order of 1 4 2 4 3, and could explain the activity of the complexes against H. pylori
urease.

Oxovanadium(V) Schiff bases
3519
Figure 7. Binding mode of 3 with H. pylori urease. Left: only the interacting residues are displayed.
The interactions are shown as dashed spheres. Right: the enzyme is shown as surface. The complex is shown
as sticks.
4. Conclusion
This study reports the synthesis and structures of three dimeric oxovanadium(V)
complexes with similar Schiff bases. The complexes show from moderate to effective
inhibitory activities against H. pylori urease. The structure–activity relationship
indicates that shorter terminal groups of the Schiff-base ligands have stronger urease
inhibitory activities of the oxovanadium(V) complexes. The complexes may be used in
the treatment of infections caused by urease producing bacteria.
Supplementary material
CCDC 830072 (1), 830073 (2), and 830074 (3) contain the supplementary crystallo-
graphic data for this article. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; Fax: (þ44) 1223-336-033; or
E-mail: deposit@ccdc.cam.ac.uk.
Acknowledgments
This work was financially supported by the National Science Foundation of China
(Project No. 20901036).
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