Mononuclear Cu(II) complex of an oxime ligand derived from N-Heterocyclic hydrazide: Synthesis, spectroscopy, electrochemistry, DFT calculations and catecholase activity

Article abstract of DOI:10.1016/j.molstruc.2019.05.072

A new oxime derivative N-heterocyclic hydrazide ligand, N'-[(1E,2E)-2-(hydroxyimino)-1-methylpropylidene]-2-[(4-methyl-5-phenyl-4H-1,2,4-triazol-3-l)thio] acetohydrazide (1) and its mononuclear copper(II) complex (1a) have been synthesized and characterized by using IR, UV–Vis, NMR and MALDI-TOF mass spectrometry. DFT-based molecular orbital energy calculations and electrochemical behaviors of the compounds have been also studied to explain redox potential of the compounds. The catecholase-mimetic activity of the Cu(II) complex (1a) has been investigated by monitoring the formation of 3,5-di-tert-butyl-benzoquinone from 3,5-di-tert-butylcatechol. Irreversible electrochemical ring-closing of the ligand by oxidation is proposed. Electrochemical ring-closing reaction is shielded by the coordination of Cu(II) to the oxime moiety of the ligand and the title complex undergoes quasi-reversible oxidation and irreversible reduction. Under aerobic conditions, the title copper(II) complex behaves as an effective catalyst towards oxidation of 3,5-di-tert-butylcatechol to its corresponding quinone derivative in MeOH. The turnover number was found as 100.1 h^?1.

Full text of DOI:10.1016/j.molstruc.2019.05.072

Accepted Manuscript
Mononuclear Cu(II) complex of an oxime ligand derived from N-Heterocyclic
hydrazide: Synthesis, spectroscopy, electrochemistry, DFT calculations and
catecholase activity
Ali Zengin, Kaan Karaoğlu, Mustafa Emirik, Emre Menteşe, Kerim Serbest
PII:
S0022-2860(19)30642-8
DOI:
https://doi.org/10.1016/j.molstruc.2019.05.072
MOLSTR 26579
Reference:
To appear in: Journal of Molecular Structure
Received Date: 22 February 2019
Revised Date: 17 May 2019
Accepted Date: 18 May 2019
Please cite this article as: A. Zengin, K. Karaoğlu, M. Emirik, E. Menteşe, K. Serbest, Mononuclear
Cu(II) complex of an oxime ligand derived from N-Heterocyclic hydrazide: Synthesis, spectroscopy,
electrochemistry, DFT calculations and catecholase activity, Journal of Molecular Structure (2019), doi:
https://doi.org/10.1016/j.molstruc.2019.05.072.
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ACCEPTED MANUSCRIPT
Mononuclear Cu(II) Complex of an Oxime Ligand Derived From N-
Heterocyclic Hydrazide: Synthesis, Spectroscopy, Electrochemistry, DFT
Calculations and Catecholase Activity
Ali Zengina, Kaan Karaoğlu b, Mustafa Emirikc, Emre Menteşec, and Kerim Serbest c,*
a Pazar Vocational School, Recep Tayyip Erdogan University, 53300 Pazar/Rize, Turkey
b
Vocational School of Technical Studies, Recep Tayyip Erdogan University, 53100
Rize, Turkey
c Department of Chemistry, Recep Tayyip Erdogan University, 53100 Rize, Turkey
Abstract
A new oxime derivative N-heterocyclic hydrazide ligand, N'-[(1E,2E)-2-(hydroxyimino)-1-
methylpropylidene]-2-[(4-methyl-5-phenyl-4H-1,2,4-triazol-3-l)thio] acetohydrazide (1) and
its mononuclear copper(II) complex (1a) have been synthesized and characterized by using
IR, UV-Vis, NMR and MALDI-TOF mass spectrometry. DFT-based molecular orbital energy
calculations and electrochemical behaviors of the compounds have been also studied to
explain redox potential of the compounds. The catecholase-mimetic activity of the Cu(II)
complex (1a) has been investigated by monitoring the formation of 3,5-di-tert-butyl-
benzoquinone from 3,5-di-tert-butylcatechol. Irreversible electrochemical ring-closing of the
ligand by oxidation is proposed. Electrochemical ring-closing reaction is shielded by the
coordination of Cu(II) to the oxime moiety of the ligand and the title complex undergoes
quasi-reversible oxidation and irreversible reduction. Under aerobic conditions, the title
copper(II) complex behaves as an effective catalyst towards oxidation of 3,5-di-tert-
butylcatechol to its corresponding quinone derivative in MeOH. The turnover number was
found as 100.1 h-1.
Keywords: Catecholase; Triazole; Vibrational analyses; DFT; Electrochemistry.
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______________________
*Corresponding author. Department of Chemistry, Recep Tayyip Erdogan University,
53100, Rize, Turkey Tel.: +90 464 2236126.
E-mail address: kerimserbest@yahoo.com (K.Serbest).
1. Introduction
Due to their bearing of hydroxyl (OH) and azomethine (C=N) group, the word “oxime”
is derived from the combination of the words “oxy” and “imine”. Oximes can form stable
complexes by the coordination to the metal ion.
The imine and oxyimine (oxime) ligands
and their coordination compounds have been found interesting by researchers for their
stability, biological activity [1–3], medicine [4], liquid crystals [5], electro optical sensors [6]
trace metal analysis [7], and catalysis [8–10]. Transition metal complexes having different
types of nuclearity have been investigated to obtain new more effective catalytic systems.
Copper is defined to be active center in many metaloenzymes [11]. Industrially, inexpensive
selective oxidation of alcohols to quinone is essential and the catechol oxidase as
antiferromagnetically coupled dinuclear Cu(II) system catalyzes the oxidation of catechols to
orthoquinones in aerobic condition. The copper complexes are good candidates and some
dicopper(II) complexes with catecholase like activity have been described to model the
dicopper active centre of catecholase [12–15] , but only a few reported literature that uses
monocopper(II) complexes of the oxime ligands as a catalyst for the oxidation of catechols to
orthoquinones [10,16–18].
Our research group has investigated more effective catalysts for oxidation of 3,5-
ditertiarybutyl catechol to the corresponding quinone derivative. So, novel Cu(II) complexes
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with new oxime ligands is needed for the advances in the development of effective catalysts.
In this study, we report the synthesis and characterization of an oxime ligand derived from N-
heterocyclic hydrazide and its copper(II) complex with catecholase mimetic activity.
2. Experimental
2.1. Materials and Methods
The synthesis of N'-[(1E,2E)-2-(hydroxyimino)-1-methylpropylidene]-2-[(4-methyl-5-
phenyl-4H-1,2,4-triazol-3-yl)thio]acetohydrazide (1) was carried out under an atmosphere of
dry, oxygen-free nitrogen, using standard Schlenk techniques. 2,3-Butanedione monoxime
(Alfa Aesar), copper(II) acetate (Merck) and all the solvents were of reagent grade and used
without
any
further
purification.
2-[(4-methyl-5-phenyl-4H-1,2,4-triazol-3-
yl)sulfanyl]acetohydrazide was synthesized in four steps by previously reported procedure
[19].
2.2. Measurements
Fourier transform infrared (FT-IR) spectra were recorded on a Perkin Elmer Spectrum
100 spectrometer equipped with an ATR apparatus. Elemental analyses were performed using
a LECO truspect analyzer at the Central Research Laboratory of Recep Tayyip Erdogan
(RTE) University. Mass spectra were recorded using Thermo Sci. TSQ Quantum Access
MAX Triple Stage Quadrupole mass spectrometer equipped with heated electrospray
ionization (H-ESI) probe at the Central Research Laboratory of RTE University for the
ligand. MALDI-TOF mass spectroscopy in a DHB matrix was investigated on a Bruker
microflex LT at the Gebze Institute of Technology for the complex. 1H and 13C NMR spectra
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were recorded on an Agilent Technologies 400/54 spectrometer at the Central Research
Laboratory of RTE University. UV–vis spectra were recorded on a SpectroScan 60DV UV-
vis. spectrophotometer.
2.3. Catecholase activity
The catalytic oxidation of 3,5-di-tert-butyl catechol (3,5-DTBC) to the corresponding o-
quinone (3,5-DTBQ) was selected as model reaction for screening catechol oxidase mimetic
activity. Catecholase mimetic activity was monitored spectrophotometrically by following the
absorbance increase of 3,5-di-tert-butylquinone at 400 nm under aerobic conditions. Because
of the good solubility of the complex as well as the substrate and its product, the catalytic
reactivity assays were performed in DMSO. In a typical experiment, 50 ꢀL of a solution of
copper complex was added to give a final concentration of 5.1×10-5 M in a quartz cuvette
containing 900 ꢀL of O2-saturated DMF solution of 3,5-DTBC (varying its concentration
from 1.67×10-4 to 8.63×10-3) and 50 ꢀL of aqueous TRIS pH 8.0 buffer (50 mM) at 24ºC. The
conversion of the reaction rate units from A/s to M/s was done using ε= 2818 M-1 cm-1 for
3,5-DTBQ in DMSO [20]. A kinetic treatment on the basis of the Michaelis-Menten approach
was applied and the results were evaluated from Lineweaver-Burk double-reciprocal plots.
2.4. Electrochemisty
Cyclic voltammograms (CV) were recorded by using Gamry Reference 3000
potentiostat controlled by an external PC. A three electrode system [BAS model
(Bioanalytical System Inc.) consisted of glassy carbon (GC) (3.0 mm diameter) disc electrode
as working electrode, a platinum wire counter electrode, and a Ag/AgCl (3.5 M KCl)
reference electrode solid cell stand] was used for CV measurements in DMSO. The
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electrochemical cells were deoxygenated by a stream of high purity nitrogen for 15 min
before running the experiment and the solution was protected from air by a blanket of
nitrogen during the experiment.
2.5. Computational Details
Density functional theory (DFT) calculations, as implemented in Gaussian 03 [21], were
used for all the theoretical calculations. The gas phase molecular structure and vibrational
frequencies were calculated by using the lanL2DZ effective potential (ECP) set of Hay and
Wadt [22] for copper atom and the standard 6–311ꢁ++ꢁG(d,p) basis set for C, H, N and O
atoms, respectively [23,24]. The absence of the imaginary frequencies confirms that the
optimized molecular structure is stable at a minimum on the potential energy surface. The
electronic excitations of compounds were calculated at the same level of theory by using
Time-Dependent Density Functional Theory (TDDFT) combined with conductor-like
polarizable continuum model (CPCM) in implicit solvent of DMSO [25]. Gaussview program
was used to visualize the geometric and electronic results of the computations [26].
GAUSSSUM 3.0 [27] was used to calculate the fractional contributions of ligand fragment
and metal ion to each molecular orbital to describe the excitation energies of UV-vis bands.
2.6. Synthesis of the ligand, (1)
A solution of 99% 2,3-butanedione monoxime (0.22 g, 2.2 mmol) in 10 mL anhydrous
ethanol was added dropwise to a solution of 2-[(4-methyl-5-phenyl-4H-1,2,4-triazol-3-
yl)sulfanyl]acetohydrazide (0.52 g, 2 mmol) in 20 mL anhydrous ethanol. The mixture was
stirred at 90 °C temperature under nitrogen atmosphere and the process was monitored by
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TLC (ethylacetate:ethanol 1:1 as mobile phase). After being stirred four days, the precipitate
was filtered, washed with ethanol, dried in oven at 50 °C.
Yield 0.25 g (37%). mp 210 °C (dec.). Color: Brooken white. Anal. Calc. for
C15H18N6O2S (M = 346.41): C, 52.01; H, 5.24; N, 24.26; Found: C, 52.12; H, 5.18; N,
24.08%. ESI-MS, m/z (%): 368.91 (100) [M+Na-H]+. FT-IR (cm-1): 3242 ν(-OH), 3164 ν(-
NH), 2960, 2880 νas/s(CH3), 1663 ν(C═O), 1606 ν(C═N), 1554 ν(-C═C-)/ β(-NH)/, 974
1
ν(N—O), 700,783 (mono subs.). H NMR δ (ppm): 11.61, 11.56 (s., 1H, -OH); 10.88,10.81
(s., 1H, -NH); 7.66 (s., 2H, Ar); 7.54 (s., 3H, Ar); 4.36, 4.09 (s., 2H, H2C—S); 3.61 (s., 3H,
H3C—N); 2.04, 1.94 (s., 6H, -CH3). UV-Vis. nm (ε, M-1 cm-1) in DMSO: 270 (433).
2.7. Synthesis of the Cu(II) complex, (1a)
A hot solution of copper(II) acetate (0.05 g; 0.3 mmol) in 10 mL anhydrous ethanol was
added to the hot suspension of the ligand (0.10 g; 0.3 mmol) in 20 mL anhydrous ethanol. The
mixture was stirred at 60 °C for 8 hours and then filtered to afford a green crude product,
washed with ethanol, and dried in oven 50 °C.
Yield 87 mg (62%), m.p.=220 °C (dec). Anal. Calc. for C17H20CuN6O4S (M=468.0): C,
43.63; H, 4.31; N, 17.96; Cu, 13.58. Found: C, 43.46; H, 4.19; N, 18.11%. MALDI-TOF MS,
m/z (%): 409.828 (69.85 a.u.) [M-CH3COO]+. FT-IR (cm-1): 3242 ν(-OH), 1622 νasym(COO-),
1498 ν(-C═C-)/ β(-NH)/, 1376 νsym(COO-), 987 ν(N—O), 700,783 (mono subs.). UV-Vis. nm
(ε, M-1 cm-1) in DMSO: 280 (24500), 402 (2430), 624 (232). ꢀeff (B.M.) = 1.62. Λ (ꢂ−1 cm2
mol−1) = 0.01.
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3. Results and Discussion
3.1. Structural characterizations
Theoretical calculations have been executed using GAMESS software in order to
produce structural parameters of the investigated compounds because crystals suitable for X-
ray diffraction were not be obtained. DFT optimized molecular structures are presented in
Figure 1. DFT calculations showed that oxime group of the free ligand (1) has E-isomer form
and coordination of the donor atoms of group leads transformation to the Z-form as expected.
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Figure 1. DFT optimized molecular structures of 1 (up) and 1a (down).
According to DFT calculations, Cu(II) complex prefers a distorted square pyramidal
geometry wherein one of the oxygen atoms from acetate ion lies in the square plane and the
other oxygen is at the apical position. Some selected bond length (Å) dihedral angles (°)
around Cu(II) center were tabulated in Table 1.
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Table 1. The selected bond lengths and dihedral angles 1a.
Bond
Length (Å)
2.019
Dihedral angle
O1─Cu─N3─N2
O4─N1─Cu─O2
O4─N1─Cu─O3
N2─C2─C3─N1
Degree (°)
0.432
O1─Cu
O2─Cu
O3─Cu
N1─Cu
N2─Cu
1.999
1.661
2.450
55.701
1.454
2.031
1.923
1
The H NMR spectra of the ligand (1) was taken in d6-dimethylsulfoxide (DMSO) and
the obtained data revealed that the free ligand in solution undergoes to tautomerisation (see
supplementary Fig. S1, 2). The NH and OH proton signal were split due to the tautomerism
and observed at 11.607, 11.564 ppm and 10.878, 10.813 ppm, respectively. The tautomeric
effect is stronger on the S-CH2 protons and they are observed at 4.36, 4.09 ppm as singlets.
All the integrating signal intensities are suitable with the structure of the ligand.
The experimental FT IR spectra of the ligand (1) and its Cu(II) complex (1a) have been
elucidated by means of theoretical calculations. Theoretical vibrational analysis have been
performed 6-311G(d, p) basis set and harmonic vibrational frequencies scaled by the factor
0.9688 [28]. Experimental and theoretical IR spectra of the compounds given in Figure 2. The
theoretically calculations were used for bands assignments of the experimental vibrational
spectra. In the experimental spectra of the ligand (1), the characteristic O─H, N─H, C=O and
C=N bands were observed at 3242, 3164, 1663, and 1606 cm-1, respectively
[8–10].
Theoretical frequency calculations were in accordance with the experimental data (Table 2),
except for O─H stretching vibration because of effect of intermolecular hydrogen bonding in
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solid state. For the Cu(II) complex (1a), O─H and C=N bands were only observed at 3408
and 1580 cm-1, respectively due to the fact that weak and sharp NH and very strong C=O
bands were disappeared.
In the IR spectrum of the Cu(II) complex, the carbonyl and NH vibrations were
disappeared. These signals disappeared confirmed that the ligand is coordinated to Cu(II) as
-
-
enolate form. The magnitude of ꢃ [νas (CO2 )- νs (CO2 )] in the complex is used as constituting
a diagnosis for probable binding mode of the acetate ion. The title Cu(II) complex shows a ꢃν
value of is 100 cm-1, which is quite similar to the corresponding bidentate values of acetates
[29]. So, bidentate coordination of acetate ion is tentatively assigned to this complex. This
suggestion is also good agreement in theoretically calculated value of acetate ion (Table S1).
100
A
0
B
80
C
D
4
8
60
40
20
A : 1 (exp.)
B : 1 (theo.)
C : 1a (exp.)
D : 1a (theo.)
4000
3500
3000
2500
2000
1500
1000
Wavenumber, cm-1
Figure 2. Experimental and theoretical IR spectra of 1 and 1a.
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In order to obtain information about the fundamental spectroscopic properties, TD-DFT
calculations have been performed in DMSO using CPCM. Experimental absorption band,
theoretical electronic transitions and their characters of 1 and 1a were tabulated in Table 2.
The experimental electronic spectrum of 1 showed an absorption bands at 258 nm (ε=90948
M-1 cm-1) an attributed as π→π* transition character. The band at 270 nm is theoretically
assigned as the following excitations at 270 nm due to contribution of HOMO → L+1 (94%),
at 274 nm due to contributions of H-1 → LUMO (62%), HOMO → LUMO (20%) and at 280
nm due to contribution of HOMO → LUMO (62%), H-1 → LUMO (20%) transitions.
Complex 1a shows absorption band for ligand based π–π*, π −d and d-d transitions
around 280 nm, 402 nm and 624 nm, respectively. The band at 280 nm is theoretically
assigned as the excitations at 277 nm due to contributions of HOMO(B) → L+2(B) (32%),
HOMO(A) → L+1(A) (31%) and the excitations at 306 nm due to contributions of H-9(B) →
LUMO(B) (25%), H-7(B) → LUMO(B) (15%) and interpreted as π→π* transitions. The peak
observed at 402 nm (calculated as 377, 402 and 415 nm) corresponds to HOMO(A) →
LUMO(A) and HOMO(B)→L+1(B) transitions. Considering that the HOMO(A) and
HOMO(B) are delocalized on the benzotriazole moiety and LUMO(A) and LUMO(B)+1 are
delocalized on the oxime moiety of the ligand, the band at 402 nm represents an interligand
charge transfer from benzotriazole group to oxime moiety of 1a. The weak peak observed at
624 nm can be separate two groups. The first one calculated as 567 and 590 nm corresponds
to HOMO(B) →LUMO(B) and is interpreted as π→d transition according to frontier orbital
analyses. The second one calculated as 726 nm is responsible for H-3(B), H-4(B)
→LUMO(B) transitions and can be attributed as d→d transition.
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Table 2. The experimental and theoretical electronic transitions with their possible
assignments for 1 and 1a.
Comp. Wavelength (nm)
Exp. Theo.
Major contribution
Character
π→π*
π→π*
π→π*
π→π*
π→π*
π→ π*
π→ π*
π→ π*
π → d
π → d
d → d
270
HOMO → L+1 (94%)
270
280
402
274
280
277
306
399
402
415
567
590
726
H-1 → LUMO (62%), HOMO → LUMO (20%)
HOMO → LUMO (62%), H-1 → LUMO (20%)
HOMO(B) → L+2(B) (32%), HOMO(A) → L+1(A) (31%)
H-9(B) → LUMO(B) (25%), H-7(B) → LUMO(B) (15%)
HOMO(A) → LUMO(A) (30%)
1
HOMO(B) →L+1(B) (89%)
1a
HOMO(A) →LUMO(A) (68%)
624
HOMO(B) →LUMO(B) (71%)
HOMO(B) →LUMO(B) (26%), H-7(B) →LUMO(B) (22%)
H-3(B) →LUMO(B) (33%), H-4(B) →LUMO(B) (20%)
3.2. Electrochemical studies
Cyclic voltammetry is used to investigate electrochemical properties of the compounds
in dichloromethane solution (5×10-3 M) containing 0.1 M tetra-n-butylammonium perchlorate
(TBAP, n-Bu4NClO4) in the potential range +1.5 to −2.5 V vs. Ag/AgCl reference electrode.
The electrochemical data were tabulated in Table 3 and voltammograms of compounds were
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given in Figure 3. Cyclic voltammograms (CVs) of ferrocene were recorded to establish
electrochemical stability and reversibility criteria in the same experimental conditions. The
formal standard potential (E0′) of Fc+/Fc under experimental conditions was calculated as
0.518 V vs. Ag/AgCl [ꢃEp (the anodic to cathodic peak-to-peak separation) = 0.087 V, Ipc/Ipa
(the cathodic-anodic peak ratio) = 1.07].
1.50E-04
1.00E-04
5.00E-05
0.00E+00
-5.00E-05
T2Ox
T2Ox-Cu
-1.00E-04
-1.50E-04
-2.00E-04
-2.50E-04
-3.00E-04
-3.50E-04
-2.5
-1.5
-0.5
0.5
1.5
V vs. Ag/AgCl
Figure 3. Cyclic voltammogram of 1 and 1a in DMSO containing 0.1 M n-Bu4NClO4 at 100
mV s-1 scan rate, c:5×10-3 M.
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H3C
NH
N
OH
CH3
N
S
S
N
CH3
N
O
-e-
CH3
OH
O
H3C
H3C
N
N
N
N
N
- H+
N
N
Figure 4. Proposed electrochemical ring-closing reaction of the 1 by oxidation.
As seen in surface plots of the HOMO and LUMO (Figure 5), the HOMO of the 1 is
mainly constituted by oxime part and the LUMO is constituted mainly by π–electron system
of the phenyl part. Removal of an electron from HOMO in highly polar aprotic medium such
as DMSO could cause polarization of the hydroxyl group of the oxime moiety and the
hydroxyl group leads ring-closing reaction as proposed in Figure 4 [30,31]. This radical then
undergoes further radical-molecule reactions. Because of weaker π*-acceptor properties of the
triazoles [32], additional electron to LUMO probably could not be transferred through triazole
to the structure. Because the oxidized and reduced species are unstable in the DMSO medium
on the cyclic voltammetry time scale, oxime ligand shows irreversible oxidation and reduction
electron transfer reactions.
The oxime displayed a oxidation peak without the corresponding cathodic waves on the
reverse scan, whereas Cu(II) complex gave a couple. Theoretical calculations showed that the
LUMO of 1a is mainly contributed by d-electrons of the Cu(II) center. Coordination of the
Cu(II) center to the oxime moiety acts as shield to the ring-closing reactions and molecule
gains quasi-reversible electrochemical properties. The voltammogram exhibits a redox couple
whose oxidation occurs at Epa = 0.707 V and reduction at Epc = 0.375 V. Copper complex also
shows an irreversible reduction wave at Epc = -2.335 V.
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1, HOMO
1, LUMO
1a, HOMO
1a, LUMO
Figure 5. Surface plots of HOMO and LUMO’s of the 1 and 1a.
Table 3. Electrochemical data for compounds.
Compound
1
Epa (V)a
Epc (V)a E0’ (V)b ∆E (V)c Ic/Ia
0.685
─
─
─
─
─
─
─
─
-0.646
0.707
0.375
0.541
0.332
0.27
1a
-2.335
─
─
─
─
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3.3. Kinetic Study
The catalytic oxidation of 3,5-DTBC has been studied as a model reaction for the
catecholase activity of catechol oxidase. Catalytic activity was monitored by following the
absorbance increase at 400 nm for 60 minutes in methanol media, adjusted to pH 8 with Tris-
HCl buffer (50 mM). Under aerobic conditions, saturation kinetics were found for the initial
rates versus the 3,5-DTBC concentrations Figure 6.
7
6
7x104
5
Equation
y = a + b*
0,9723
Adj. R-Square
Value
Intercept 11276,49657
Slope 28,36756
Standard Error
1228,05748
1,32663
6x104
5x104
4x104
3x104
2x104
F
F
4
3
2
1
5,0x102
1,0x103
1,5x103
2,0x103
1/[S]
0
0,000
0,002
0,004
0,006
0,008
0,010
[Substrate], M
Figure 6. Plot of rate vs. [3,5-DTBC] in presence of 1a in methanol; inset: Lineweaver-Burk
plot.
Michaelis-Menten model, originally developed for enzyme kinetics, was applied for
kinetic experiments. The kinetic parameters calculated by linear regression using the
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Lineweaver–Burk plot, gave reasonable straight lines, from which the parameters such as
maximum velocity (Vmax), rate constant for the dissociation of the complex–substrate
intermediate (the turnover number), and Michaelis binding constant (KM). As given in
Equation 1, the y-intercept of such a graph is equivalent to the inverse of Vmax; the x-intercept
of the graph represents −1/Km [33].
ꢀ
ꢂ
ꢄ[ꢅ]
ꢂ
ꢀ
ꢀ
ꢃ
ꢃ
=
=
+
ꢁ
ꢃꢆꢇ
ꢁ
ꢁ
ꢃꢆꢇ
[ꢅ]
ꢁ
ꢃꢆꢇ
[ꢅ]
Results were obtained from Lineweaver–Burk plot as vmax = 8.74×10-5 mol dm3 s-1 and
KM = 2.47×10-3 mol dm-3. The turnover number of 100.1 h-1 was compared with literature
data and as seen in Table 4, 1a has comparable higher turnover number than some reported
mononuclear copper(II) complexes.
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Table 4. Some reported turnover numbers of catecholase mimetic activities for mono- and di-
nuclear copper(II) complexes.
Complex
Turnover number (h-1)
Reference
[16]
6.00
11.16
13.32
[17]
mono-nuclear copper(II)
[18]
1.97
[13]
[12]
[12]
[14]
[15]
15.84
28.50
5470
di-nuclear copper(II)
1.56×104
4. Conclusion
Previously, we reported catecholase mimics which are dinuclear Cu(II) complexes of
ferrocenyl substituted heterocyclic ligands or mononouclear Cu(II) complex of oxime
derivative unsymmetrical azine ligand [10,34]. In this paper, we have reported a new oxime
derivative N-heterocyclic hydrazide ligand and its mononuclear Cu(II) complex and their
applications in catalytical field. The results of catalytic activity studies show that the Cu(II)
complex (1a) is an effective catalyst having turnover numbers (kcat) 100.1 h-1. The obtained
turnover number in this study is lower than our previously reported study, but higher than
some related oxime complexes [35].
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Acknowledgements
This work was supported by The Research Fund of Recep Tayyip Erdoğan University, Project
No: FDK-2018-965 (Rize/Turkey). The numerical calculations reported in this paper were
performed at TUBITAK ULAKBIM, High Performance and Grid Computing Center
(TRUBA Resources).
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Highlights
•
•
•
•
An oxime derivative hydrazide ligand and its Cu(II) complex have been synthesized.
DFT calculations were performed for vibrational assignments and electronic transitions.
The Cu(II) complex shows catecholase mimetic activity.
Electrochemical properties of compounds were investigated by CV.