M. Ikram et al. / Thermochimica Acta 562 (2013) 22–28
23
NH(Lys)
O
NH(Lys)
O
N-succinyl-l-phenylalanine-p-nitroanilide (prepared in buffer) at
final concentration of 0.4 mM. The change in absorbance was con-
tinuously monitored at 410 nm.
Ligand
O
O
OH2
N(His)
-H O
2
OH
N(His)
2
N(His)
Ni(1)(2)Ni
HO
Ni(1)
(2)Ni
N(His)
N(His)
H O
2
HO
Ligand
2.3. Crystal structure determination
N(His)
N(His)
N(His)
Suitable single crystal for X-ray structural analyses of H-QMP
Scheme 1. Mechanism of interaction of inhibitors with urease.
were mounted on a glass fiber, and the respective data were
collected on Oxford diffractometer (graphite-monochromated Mo
opportunities for inducing substrate chirality and reorientations in
geometry around the metal center thereby tuning electronic con-
figuration of the metal center [17–21]. Schiff bases have been also
found to enhance the solubility and stability of either homoge-
neous or heterogeneous catalysts [22–27]. Herein we report the
synthesis and crystal structure of a monoanionic ligand. Apart
from it the same metal complexes were also tested for their ␣-
chymotrypsin inhibitory activities. ␣-Chymotrypsin (EC 3.4.21.1),
a protease, which is secreted from pancreas, catalyzes the break-
down of polypeptide and proteins. If the precursor of chymotrypsin,
the chymotrypsinogens is cleaved to form active enzyme before
the target side, then it digest the tissues inside body such as in
cases of pancreatitis [28,29]. ␣-Chymotrypsin has been found to be
involved in clearance of ulcer, digesting damaged tissue and debris
in the infected site [20–29]. Therefore a drug which is active against
urease activities and inactive against ␣-chymotrypsin may help in
healing the peptic ulcers, etc. very efficiently. Here we are reporting
the structural details of H-QMP along with thermal degradation
studies in continuation to our previous work reported [30]. The
thermal data was used for the calculation of kinetic and thermody-
namic parameters. All the compounds were also studied for their
urease and ␣-chymotrypsin inhibitory activities. Nickel complex
was found to be much more active than the standard drug.
K␣ radiation, ꢁ = 0.71073 A˚ ) at 298 K. The structures were solved
with the olex2.solve [31] refined against all data by full-matrix
least-squares methods on F2 (SHELXL-97) [32]. All non-hydrogen-
atoms were refined with anisotropic displacement parameters. The
hydrogen atoms were refined isotropically on calculated positions
3
their pivot atoms for terminal sp carbon atoms and 1.2 times for all
other carbon atoms. Crystallographic details are given in the sup-
plementary information file. CCDC-885677 (H-QMP) data can be
obtained free of charge from the Cambridge Crystallographic Data
Center via www.ccdc.cam.ac.uk/data request/cif.
2.4. Docking
The molecular docking of the inhibitor with the 3D crystal struc-
ture of urease from Bacillus pasteurii downloaded from protein data
bank (PDB code: 4UBP) was performed with AutoDock Vina pro-
gram [33]. Autodock Tool was used to remove water molecules and
non-standard protein residues from the urease enzyme. The polar
hydrogens were added and charges were assigned with Gasteiger
method. The active sites were defined and the structure of the
enzyme as receptor in the required pdbqt format was saved. The
docking site on the receptor macromolecule was defined by fixing
the grid box with the dimensions 40 × 40 × 40 A˚ with grid spacing
2
. Experimental
of 0.375 A˚ centered on Ni841 in the active site of the protein.
The detailed synthesis and characterization can be found in our
earlier report [16]. The codes assigned to the compounds follow the
trend given below:
3
. TG–DTA analysis
The TG–DTA analyses were carried out using TG/DTA Diamond
2
-[(E)-(quinolin-3-ylimino)methyl]phenol (H-QMP)
◦
−1
model by Perkin Elmer at heating rate 10 C min
in tempera-
Bis(2-[(E)-(quinolin-3-ylimino)methyl]phenolato)nickel(II) (1)
Bis(2-[(E)-(quinolin-3-ylimino)methyl]phenolato)cobalt(II) (2)
◦
ture range 30–1000 C under static air. Specific mass of samples
were contained in ceramic pans crucibles adjusted on platform
support giving a proportional signal to recorder, observed by com-
puter interface and the results were plotted in the form of mass loss
of sample vs. temperature for TG and microvolts vs. temperature
for DTA. All the results were referenced to thermal decomposi-
tion of alumina. The activation energies of all the samples were
calculated using Horowitz–Metzger method [34]. It was found
2
-[(E)-(quinolin-3-ylimino)methyl]
phenolatoacetatoaquocopper(II) (3)
-[(E)-(quinolin-3-ylimino)methyl]
phenolatoacetatoaquozinc(II) (4).
2
2
.1. Urease inhibition assay
f
f
that linear plots can be obtained while ln ln(Wo − W )/(W − W )
t
t
Exact 25 L of enzyme (jack bean urease) solution and 5 L
{
where Wo = initial mass taken, W = weight remaining at a given
temperature, W = final weight} were plotted against ꢂ {where
of test compounds (0.5 mM concentration) were incubated with
f
t
◦
5
5 L of buffers containing 100 mM urea for 15 min at 30 C in each
ꢂ = Tc − Ts}. The slope of the straight line was used to calculate the
well of 96-well plates. Ammonia production was measured as a
urease activity by indophenol method. Final volumes were main-
tained as 200 L by adding 45 L phenol reagent (1%, w/v phenol
and 0.005%, w/v sodium nitroprussside), and 70 L of alkali reagent
activation energy through the expression (1):
∗
E
Slope =
(1)
RTs2
(
0.5%, w/v NaOH and 0.1% active chloride NaOCl) to each well. Using
Order of decomposition was calculated from the relationship
between reaction order and concentration at maximum slope [34].
Thermodynamic parameters of activation were evaluated by using
the following expressions (2)–(4), respectively [35]:
a microplate reader (Molecular Devices, CA, USA), the increase in
absorbance was measured at 630 nm after 50 min at pH 6.8 [27,28].
2
.2. ˛-Chymotrypsin inhibition assay
ꢀ
ꢁ
Ah
∗
ꢀ
S
= 2.303 log
R
(2)
kBTs
This was performed in 50 mM Tris–HCl buffer pH 7.6 with
1
0 mM CaCl according to Cannell et al. [29] with the slight modifi-
∗
∗
2
ꢀ
H
= ꢀE − RT
(3)
(4)
cation. ␣-Chymotrypsin (12 units/mL prepared in buffer) with the
various concentrations of test compound (prepared in DMSO) was
incubated at 30 C for 25 min. The reaction was started by adding
∗
∗
= ꢀH − TꢀS∗
ꢀ
G
◦