Synthesis of new acyclic schiff base oxovanadium(IV) complexes and their electrochemical, catecholase, and antimicrobial studies of minimum inhibitory concentration

Article abstract of DOI:10.1080/15533174.2015.1031040

Catalytically active complexes containing [VO(IV)L] were synthesized by using Schiff base ligands L^1-5 and vanadyl sulfate. Ligands L^1-5 were obtained by the condensation of 5-methylsalicylaldehyde with diethylene triamine (L¹

Full text of DOI:10.1080/15533174.2015.1031040

Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry (2015) 45, 1647–1654
Copyright © Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2015.1031040
Synthesis of New Acyclic Schiff Base Oxovanadium(IV)
Complexes and Their Electrochemical, Catecholase, and
Antimicrobial Studies of Minimum Inhibitory Concentration
A. VIJAYARAJ1, R. PRABU1, R. SURESH1, N. MATHIVANAN2, and V. NARAYANAN1
1Department of Inorganic Chemistry, School of Chemical Sciences, University of Madras, Guindy Maraimalai Campus, Chennai, India
2Centre for Advanced Studies in Botany, University of Madras, Guindy Maraimalai Campus, Chennai, India
Received 3 February 2012; accepted 24 January 2013
Catalytically active complexes containing [VO(IV)L] were synthesized by using Schiff base ligands L1–5 and vanadyl sulfate. Ligands
L1–5 were obtained by the condensation of 5-methylsalicylaldehyde with diethylene triamine (L1), tris(2-aminoethyl)amine (L2),
triethylene tetramine (L3), N,N-bis(3-aminopropyl)ethylenediamine (L4) and N,N- bis(aminopropyl) piperazine (L5). All the
complexes were characterized by elemental and spectral analysis. ESR spectra for the mononuclear [VO(IV)L] complexes show eight
lines, square pyramidal geometry. Room temperature magnetic moment for the complexes was around 1.73 B.M. Electrochemical
and catalytic studies of the complexes were compared on the basis of chain length of the imine compartment. All the [VO(IV)L1–5
complexes were screened antibacterial activity of MIC.
]
Keywords: Schiff base ligands, vanadyl(IV) complexes, cyclic voltammetry, catecholase activity, antimicrobial activity
Introduction
frequently accompanied by the change in the structure of the
complex and the oxidation state of the metal however; the
The importance of the Schiff base is due its versatile nature. electrochemical approaches for these purposes have not been
A number of Schiff bases exhibit biological activities[1,2] such fully explored. Henze et al.[18] in 1911 first reported the role
as antifungal, antibacterial, antitumor, anti-inflammatory, of vanadium in nitrogen fixation and become established in
and antipyretic, among others. Some of them have been used 1989 through investigations carried on nitrogen fixation
as complexing agents[3,4] and powerful corrosion inhibitors.[5] group. Julieta Gradinaru et al.[19] reported Ni(II), Cu(II), Zn
Acyclic Schiff base ligands and their metal complexes have (II), and VO(II) Schiff base complexes from 1-phenylbutane-
attracted great and growing interest in chemistry and biology 1,3-dione mono-S-methylisothiosemicarbazone with o-
for many years due to their facile synthesis and wide applica- hydroxybenzaldehyde that exhibit NLO property. Kianfar
tions.[6–8] Studies on complexes of acyclic Schiff base ligands et al.[20] reported the electrochemical activity of VO(IV)
with different size, number, and donor atoms for coordina- Schiff base complexes, salen type of aldehydes with diamine.
tion with a variety of metal centers have been reported.[9–11]
In 2011, we have reported Cu(II) Schiff base complexes.[21]
The study of the chemistry of vanadium occurs as an The present work deals with the influence of ligand modifica-
“essential trace” element in diverse living forms.[12–14] The tion on spectral, electrochemical, catecholase and antimicro-
vast majority of work has occurred more recently. Vanadium bial studies, reporting the synthesis and characterization of
is naturally occur in mushrooms as well and is required as an acyclic mononuclear vanadyl complexes.
essential cofactor in certain haloperoxidases and nitroge-
nases.[15] While vanadium is suspected to be an critical trace
element for humans,[16] as vanadate, it is known to affect
Experimental
phosphate metabolism and various forms of vanadium have
proven to have insulin mimetic effects.[17] The electrochemi-
Physical Measurements
cal methods also provide highly valuable information regard-
ing catalytic processes since catalytic conversions are
Elemental analysis of the complexes is obtained using a Haer-
eus CHN rapid analyzer. IR spectra were recorded on a
Perkin Elmer FT-IR 8300 series spectrophotometer on KBr
disks from 4000 to 400 cm¡1 1H NMR spectra were
.
Address correspondence to Dr. V. Narayanan, Associate Profes-
sor, Department of Inorganic Chemistry, University of Madras,
Guindy Maraimalai Campus, Chennai – 600 025, Tamil Nadu,
India. E-mail: vnnara@yahoo.co.in
recorded using a JEOL GSX 400MHz NMR spectrometer.
Deuterated chloroform (CDCl3) is used as the solvent. Tetra-
methylsilane (TMS) is used as an internal standard. ESI

1648
Vijayaraj et al.
Mass spectra were obtained on a JEOL DX-303 mass spec- dimethyl formamide, triethylenetetramine, diethylenetri-
trometer. Electronic spectral studies were carried out on a amine, and VOSO4.2H2O were purchased from Qualigens.
Perkin Elmer 320 spectrophotometer. Cyclic voltammograms TBAP (tetra(n-butyl)ammonium perchlorate) used as sup-
were obtained on a CHI-600A electrochemical analyzer porting electrolyte in electrochemical measurements was pur-
under oxygen-free conditions using a three-electrode cell in chased from Fluka and recrystallized from hot methanol. N,
which a glassy carbon electrode was the working electrode, a N-bis-(3-aminopropyl) piperazine, N,N-bis-(3-aminopropyl)
saturated Ag/AgCl electrode was the reference electrode and ethylene diamine and tris-(2-aminoethyl)amine were pur-
platinum wire was the auxiliary electrode. A ferrocene/ferro- chased from Aldrich.
cenium couple was used as an internal standard and E1/2 of
the ferrocene/ferrocenium (Fc/FcC) couple under the experi-
Bacterial pathogens
mental condition was 470 mV. Tetra(n-butyl)ammonium
perchlorate (TBAP) 1 £ 10¡1 M was used as the supporting The bacterial pathogens Escherichia coli, Salmonella typhi,
electrolyte. Room temperature magnetic moments were mea- and Streptococcus faecalis were obtained from CAS in Bot-
sured on a PAR vibrating sample magnetometer (VSM) any, University of Madras.
Model-155. X-band EPR spectra were recorded in DMF at
25ꢀC on a Varian EPR-E 112 spectrometer using diphenylpi-
Synthesis of metal complexes
crylhydrazine (DPPH) as the reference. Catalytic oxidation
of catechol to o-quinone by the vanadium complexes was Ligand L1, L2, L3, L4, and L5 were synthesized by following
studied in 10¡3 mol L¡1 DMF solutions. The reactions were our previous report[25a,25b] (Scheme 1). An absolute methanol
followed spectrophotometrically with the strongest absorp- solution containing VOSO4.2H2O (0.036 g, 0.1 mmol) was
tion of o-quinone at 390 nm and monitoring the increase in added drop-wise to a stirring solution of L1 (0.0339 g,
absorbance. A plot of log (A /A -At) versus time was 0.1 mmol) in 20 mL of absolute methanol. The solution was
1
1
made for each complex and rate constants for the catalytic refluxed for 8 h and the reaction is shown in Scheme 2. On
oxidations were calculated.
cooling the solution, green color microcrystals are formed,
which were filtered and washed with methanol followed by
diethyl ether and dried in vacuum. The crude product was
recrystallized from methanol and acetonitrile (1:3, v/v). [VO
(IV)L2], [VO(IV)L3], [VO(IV)L4], and [VO(IV)L5] were syn-
thesized by following the previous procedure using L2
(0.038 g, 0.1 mmol), L3 (0.0382 g, 0.1 mmol), L4 (0.0426 g,
0.1 mmol), and L5 (0.0468 g, 0.1 mmol) instead of L1. All
the vanadium (IV) complexes are neutral.
Antimicrobial Studies
Minimum inhibitory concentration
The minimum inhibitory concentration of the vanadium
complexes was done by Resazurin reduction assay in 96 well
microtitre plates according to the Yashodharan Kumaras-
amy et al.[22] method.
Preparation of Resazurin solution[23]
Synthesis of [VO(IV)L1]
The Resazurin solution was prepared by dissolving a 270 mg
tablet of resazurin in 40 mL of sterile distilled water. It is vor-
texed to get a complete dissolved homogenous solution.
Green solid. Yield: (65%). m.p.: 322ꢀC (dec). Anal. Calcd. for
[C20H23VN3O3]: C, 62.60; H, 6.74; N, 9.15; V, 11.09. Found:
C, 61.78; H, 6.69; N, 9.11; V,10.83%. ESI MS: (m/z) 405.33,
calcd. av. m/z 403.34. Selected IR data (KBr) (n, cm¡1):
1125 n(CꢁꢁO), 939 [n (VDO)],1630 n(CDN),630 n(MꢁꢁN),
439 n(MꢁꢁO).
Resazurin reduction assay
The MIC by Resazurin reduction assay was done in sterile
96-well plates. A volume of 200 mL of test material in 10%
(v/v) DMSO was pipetted into the first row of the plate. To
all other wells 100 mL of nutrient broth was added. Twofold
serial dilutions were performed using a pipette. Tips were dis-
carded after use such that each well had 100 mL of the test
material in serial dilutions. 10 mL of resazurin indicator solu-
tion was added to each well. Finally, 10 mL of bacterial sus-
pension (5 £ 106 cfu/mL) was added to each well to achieve
a concentration of 5 £ 105 cfu/mL. The antibiotic ampicillin
serves as positive control in serial dilution. All the plates were
incubated at 37ꢀC for 18–24 h. The color change was then
assessed visually. The color changes from purple to pink or
colorless were recorded as reduction of dye by the viable
bacteria.
Synthesis of [VO(IV)L2]
Green solid was obtained. Yield: (81%). m.p.:331ꢀC (dec).
Anal. Calcd. for [C22H28VN4O3]: C, 62.02; H, 7.21; N, 11.13;
V, 10.10. Found: C, 61.22; H, 7.08; N, 11.03; V, 10.07%. ESI
MS: (m/z) 445.87, calcd. av. m/z 446.41. Selected IR data
(KBr) (n, cm¡1): 1127 n(C-O), 958 [n (VDO)], 1623 n(CDN),
626 n(M-N), 444 n(M-O).
Synthesis of [VO(IV)L3]
Green solid was obtained. Yield: (71%). m.p.: 325ꢀC (dec).
Anal. Calcd. for [C22H28VN4O3]: C, 62.24; H, 6.83; N, 11.17;
V, 10.16. Found: C, 62.15; H, 6.75; N, 11.13; V, 9.96%. ESI
MS: (m/z 448.15, calcd. av. m/z 447.42. Selected IR data
Chemicals and Reagents
5-methylsalicylaldehyde[24] was prepared following the litera- (KBr) (n, cm¡1): 1126 n(C-O), 937 [n (VDO)],1629
ture method. Analytical grade methanol, acetonitrile, n(CDN),664 n(MꢁꢁN), 451 n(M-O).

New Acyclic Schiff Base Oxovanadium(IV) Complexes
1649
Sch. 1. Schematic diagram for the synthesis of ligands.
Synthesis of [VO(IV)L4]
3000 cm¡1 due to the aromatic CꢁꢁH stretching vibration.
5-methy1salicylaldehyde shows
a
sharp band at
Green solid was obtained. Yield: (79%). m.p.: 335ꢀC (dec).
Anal. Calcd. for [C24H32VN4O3]: C, 63.26; H, 7.58; N, 10.54;
V, 9.58. Found: C, 62.66; H, 7.30; N, 9.82; V, 9.44%. ESI
MS: (m/z) 472.20, Calcd. av. m/z 473.46. Selected IR data
(KBr) (n, cm¡1): 1300 n(CꢁꢁO), 977 [n (VDO)],1628
n(CDN),556 n(M-N), 424 n(MꢁꢁO).
1655 cm¡1 corresponding to n(¡CHO). Ligands and com-
plexes show a sharp band at 1620–1640 cm¡1 due to the
presence of CDN group and the absence of n(CDO) band
[26–31]
in the complexes indicate Schiff base condensation.
.
A strong band at 1260 cm¡1 in the free Schiff bases has
been assigned to phenolic C–O stretching. Upon complex-
ation, this band shifts to higher frequency (1300 cm¡1
)
Synthesis of [VO(IV)L5]
showing coordination through phenolic oxygen.[32] For
the complexes, bands at 930–980 cm¡1 could be assigned
to the -(VDO) bond.[33] Other weak bands at lower fre-
quency could be assigned to -(M–N) bond. In the proton
NMR spectra of all the vanadium(IV) complexes the peak
due to phenolic OH group is absent. This indicates that
Green solid was obtained. Yield: (61%). m.p.: 341ꢀC (dec).
Anal. Calcd. for [C26H34VN4O3]: C, 64.62; H, 7.59; N, 10.05;
V, 9.14. Found: C, 64.11; H, 7.41; N, 10.01; V, 09.01%. ESI
MS: (m/z 499.27, Calcd. av. m/z 501.12. Selected IR data
(KBr) (n, cm¡1): 1130 n(C-O), 964 [n (VDO)], 1624 n(CDN),
534 n(M-N), 469 n(M-O).
the
phenolic
protons
are
deprotonated
during
complexation.
ESI Mass Spectral Analysis
Results and Discussion
The ESI mass spectra of mono nuclear complexes [VO(IV)
L1], [VO(IV)L2], [VO(IV)L4], and [VO(IV)L5] show the
Spectroscopic Studies
The FT-IR spectra of the ligands show a broad band molecular ion peak (MC) at m/z D 405.33, 445.87, 472.20,
around 3400 cm¡1 due to the presence of the phenolic and 499.27, respectively. The spectra show some prominent
OH group. Absence of a peak around 3400 cm¡1 in all peaks corresponding to the various fragments of the com-
the complexes indicates the absence of n(¡OH) due to plexes. The ESI mass spectra of mononuclear complexes
deprotonation followed by complexation. The spectra of [VO(IV)L2] are shown in Figure 1 and the ESI mass spectra
all the complexes are dominated by bands at 2930– of the other three complexes are given in Figure S1.

1650
Vijayaraj et al.
Sch. 2. Schematic diagram for the synthesis of complexes.
Electronic Spectra
y2 dxy) and 2A1 2B2 (dz2 dxy) may be overlapping
with the other lower wavelength bands observed in the
region 350–400 nm. A red shift in the λmax value of d-d
band[35] with increase in the chain length between imine
nitrogen has been observed. This red shift may be due
to the distortion from planar geometry as the chain
length increases. Moderately intense band observed in
the region of 350–400 nm is associated with ligand to
Electronic spectra of all the complexes were obtained
in DMF medium. The electronic spectra of all the com-
plexes show a single weak d-d band in region 663–
2
692 nm due to E 2B2 (dxz,dyz dxy) transition asso-
ciated with square-pyramidal geometry[34] around the
VO2C ion. The other transitions due to B1 2B2 (dx2-
2
Fig. 1. ESI-mass spectrum of [VO(IV)L2] Complex m/z 445.87[MH¡], Calculated 446.41.

New Acyclic Schiff Base Oxovanadium(IV) Complexes
1651
Table 1. Electronic spectral data for [VO(IV)L1–5] complexes
Table 2. ESR Spectral data for [VO(IV)L1–5] complexes
λmax (nm) (e/M¡1 cm¡1
)
Sl.No.
Complexes
g
g
?
A
A
?
meff BM
jj
jj
1.
2.
3.
4.
5.
[VO(IV)L1]
[VO(IV)L2]
[VO(IV)L3]
[VO(IV)L4]
[VO(IV)L5]
1.97
2.00
2.05
2.00
2.04
1.99
2.01
2.10
2.03
2.09
160.2
161.2
162.3
161.3
162.2
49.2
49.3
49.1
49.2
49.4
1.69
1.70
1.72
1.71
1.74
Sl. No.
Complexes
dꢁꢁd
Charge transfer
1.
2.
3.
4.
5.
[VO(IV)L1]
[VO(IV)L2]
[VO(IV)L3]
[VO(IV)L4]
[VO(IV)L5]
663(118)
674(107)
679(92)
683(85)
692(69)
380(14900), 295(27500)
395(12200), 295 (27400)
385(14600), 270(28100)
375(15100), 265(28500)
350(16700), 290(27200)
electron has to be in b2g (dxy, 2B2 ground state) orbital
metal charge transfer transition. An intense band localized on metal, thus excluding the possibility of its
observed in the region 260–300 nm is associated with direct interaction with the ligand. The observed order (AII
intra ligand transition. The electronic spectral data are D 160.2 > A┴ D 49.2; g┴ D 1.99 > gII D 1.97) indicates
given in Table 1.
ESR Spectra
The ESR spectra of the vanadyl complexes, recorded in
DMSO solution at 300 and 77 K, spectra shown
in Figure 2. [VO(IV)L2] complex is given in Figure S2a.
The isotropic ESR parameters for [VO(IV)L1] giso D 1.97
and Aiso D 101 can be calculated from the position spac-
ing of the resonance lines from the room temperature
solution spectrum of the complex. The ESR spectra of all
the complexes show a typical eight-line pattern, due to
hyperfine splitting of the V nucleus (I D 7/2). This indi-
cates that a single vanadium ion is present in the molecule
(i.e., it is a monomer). From the anisotropic spectrum, the
anisotropic parameters were calculated and the data are
given in Table 2.
All the mononuclear vanadium complexes show well-
resolved axial anisotropy with eight line pattern with g <
k
g
and A >>A┴, a relationship characteristic of an axi-
?
k
ally compressed d1 configuration. Ligand nitrogen or
xy
hydrogen super hyperfine splittings are not observed on
the vanadium line. This indicates that the unpaired
Fig. 3. (A) Voltammograms of mononuclear [VO(IV)L1–5] com-
plexes: (a) [VO(IV)L1], (b) VO(IV)L2], (c) [VO(IV)L3], (d) [VO
(IV)L4], and (e) [VO(IV)L5] (reduction process). (B) Cyclic
voltammograms of the mononuclear [VO(IV)L1–5] complexes:
(a) [VO(IV)L1], (b) [VO(IV)L2], (c) [VO(IV)L3], (d) [VO(IV)L4],
and (e) [VO(IV)L5] (oxidation process).
Fig. 2. ESR spectra of the macrocyclic mononuclear complex
[VO(IV)L1].

1652
Vijayaraj et al.
Table 3. Electrochemical dataa and catecholase activity datab for the[VO(IV)L1–5] complexes
aReduction
Oxidation
bRate constant (k) £ 10¡3 min¡1
Complexes
potentialE1pc (V)
potentialE1pa (V)
[catecholase activity]
[VO(IV)L1]
[VO(IV)L2]
[VO(IV)L3]
[VO(IV)L4]
[VO(IV)L5]
–2.00
–1.80
–1.70
–1.60
–1.35
0.25
0.33
0.35
0.38
0.44
3.611
6.222
8.277
12.555
17.500
aMeasured by CV at 50 mV s¡1 scan rate. E versus Ag/AgCl conditions: GC working electrode and Ag/AgCl reference electrodes; supporting electrolyte
TBAP; concentration of complex 1£10¡3 M, concentration of TBAP 1£10¡1 M.
bMeasured spectrophotometrically in DMF. Concentration of the complexes: 1 £10¡3 M. Concentration of o-quinine: 1 £10¡1 M.
that the unpaired electron is present in the dxy orbital with Kinetic Studies
square-pyramidal geometry around the [VO(IV)]
Oxidation of pyrocatechol (catecholase activity)
chelates.[36–38]
The catecholase activity of the vanadium(IV) complexes
synthesized in the present work was carried out using
pyrocatechol as the convenient model substrate for the
Electrochemistry of the Complexes
identification of functional models for the metallo
Reduction process at negative potential
enzymes.[41] For this purpose, 10¡3 mol dm¡3 solutions of
The electrochemical properties of the mononuclear com-
plexes were studied by cyclic voltammetry in DMF solution
containing TBAP as supporting electrolyte in the potential
range of –0.20 to –2.75 V. The cyclicvoltammograms are
given in Figure 3a. The electrochemical data of vanadium
(IV) complexes are given in Table 3. Generally the electro-
chemical properties of the complexes depend on a number of
factors such as chelate ring/size, axial ligation, degree and
distribution of unsaturation and substitution pattern in the
chelate ring. Each voltammogram shows one electron irre-
versible reduction wave at a negative potential in the range of
–2.00 to –1.35 V. The controlled potential electrolysis carried
out at 100 mV more negative than the reduction wave con-
veys the consumption of one electron per molecule. It is very
interesting to compare the electrochemical behavior of [VO
(IV)L] complexes. The reduction potential shifts towards
anodic direction for the complexes [VO(IV)L1] to [VO(IV)L5]
from –2.00 to –1.35 V, as the number of methylene groups
increases.[39,40] This shows that, as the number of methylene
groups between the imine nitrogen (chain length) increases,
the entire acyclic ring becomes more flexible, which causes a
distortion of the geometry of the vanadium(IV) complexes
and makes the system more flexible.
complexes in dimethylformamide were treated with 100
equivalents of pyrocatechol in the presence of air. The
course of the reaction was followed spectrophotometri-
cally at 390 nm for nearly 45 min at regular time intervals
of 5 min. The slope was determined by the method of ini-
tial rates by monitoring the growth of the 390 nm band of
the product o-quinone. A linear relationship for initial
rate and the complex concentration obtained for the
vanadium(IV) complexes shows a first-order dependence
on the complex concentration for the systems.
Plots of log (A /A -At) versus time for catecholase
1
1
activity of the [VO(IV)L] complexes are obtained and
shown in Figure 4. The inset in Figure 4 shows the time
dependent growth of o-quinone chromophore in the pres-
ence of [VO(IV)L5]. The observed initial rate constant
Oxidation process at positive potential
The electrochemical properties of the mononuclear com-
plexes were studied by cyclic voltammetry in DMF solution
containing TBAP as supporting electrolyte in the potential
range of 0.00–0.70 V. The cyclic voltammograms are given
in Figure 3b. The electrochemical data of vanadium(IV)
complexes are given in Table 3. The oxidation potential shifts
towards more positive direction for the complexes [VO(IV)
L1] to [VO(IV)L5] from 0.25 to 0.44 V as the number of meth-
ylene group is increased. This is because as the ring size
increases the flexibility increases and the planarity of the
complexes decreases and hence the electrochemical oxidation
process occurs with difficulty.
Fig. 4. Catecholase activity of the [VO(IV)L1–5] complexes: (a)
[VO(IV)L1], (b) [VO(IV)L2], (c) [VO(IV)L3], (d) [VO(IV)L4], and
(e) [VO(IV)L5] The inset is the time dependent growth of o-qui-
nine chromophore in the presence of [VO(IV)L2].

New Acyclic Schiff Base Oxovanadium(IV) Complexes
1653
Table 4. Antibacterial activity data of [VO(IV)L1–5] complexes
spectrum of [VO(IV)L] complexes indicates square pyramidal
geometry, and there is a red shift due to the increase in the
chain length. Cyclic voltammograms exhibit one electron
quasireversible process. The reduction potential shifts less
negative potential on increasing chain length and oxidation
potential shifts more positive potential on increasing chain
length. All the [VO(IV)L] complexes show good catalytic
activity on increasing the chain length. Increase in the chain
length causes a greater distortion of the geometry of the com-
plexes. This flexibility in the geometry may favor the
observed higher rate of the reaction. The complex shows
remarkable activity against three bacterial pathogens. Com-
plex [VO(IV)L5] have highest activity against Streptococcus
faecalis, E. coli, and Salmonella typhi. All the studies of the
complexes agree well with the established trend.
MIC (mg/mL)
Bacterial pathogens
Streptococcus
faecalis
Salmonella
typhi
Test complexes
E. coli
[VO(IV)L1]
[VO(IV)L2]
[VO(IV)L3]
[VO(IV)L4]
[VO(IV)L5]
Ampicillin
50
6.25
12.5
6.25
6.25
1.56
50
25
12.5
6.25
3.12
3.12
25
50
25
12.5
6.25
3.12
value for vanadium(IV) complexes is given in Table 3.
The complex [VO(IV)L5] has higher catalytic activity
(17.500 £ 10¡3 min¡1) than the complex [VO(IV)L4]
(12.555 £ 10¡3 min¡1) which in turn is higher than the
vanadium(IV) complex [VO(IV)L1] (3.611 £ 10¡3 min¡1).
The order of activity of the complexes is the following:
Funding
Financial support from CSIR, New Delhi is gratefully
acknowledged.
Â
Ã
Â
Ã
Â
Ã
VOðIVÞL5 > VOðIVÞL4 > VOðIVÞL3
>
Supplementary Material
Â
Ã
Â
Ã
VOðIVÞL2 > VOðIVÞL1
Supplemental data for this article can be accessed at the pub-
lisher’s website. SI mass spectrum of [VO(IV)L1], [VO(IV)
L4], and [VO(IV)L5], are given in Figure S1a–S1c. ESR spec-
tra of the [VO(IV)L2] complex are given in Figure S2a and
Antimicrobial activity (minimum inhibitory concentration)
of complexes [VO(IV)L1–5] (MIC sterile disk photos are given
in Figure S3) are given as supplementary material.
From the results it is observed that the rate of oxidation of
catecholase to o-quinone has increased as the chain length
increases. The catecholase activity of complex containing lon-
ger carbon chain in the imine compartment is higher than
that of the complex containing lesser carbon chain in the
imine compartment, which is due to flexibility resulting from
distortion of the coordination sphere. Increase in the chain
length causes a greater distortion of the geometry of the com-
plexes. This geometry may favor the observed higher rate of
the reaction.
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The vanadium complex [VO(IV)L1] 1 to [VO(IV)L5] showed
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in the assay wells denotes the inhibition of the bacterial
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