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A.Z. El-Sonbati et al. / Journal of Molecular Liquids 218 (2016) 400–420
In addition to the two bifurcated inter/intramolecular OH–N hydro-
Pi ¼ −χ
ð6Þ
ð7Þ
gen bonds (Scheme 1C and D), two more intermolecular hydrogen bond-
ing interactions are observed between nitrogen atom of azomethine
group and phenolic hydroxyl hydrogen oxygen atom. This additional
H-bonding does not influence the intramolecular distance which
shows a band at a lower frequency than the intermolecular interaction.
The reason for this behavior might be the additional H-bond which influ-
ences the hydrogen bonding ability of the hydroxyl group by electronic
and/or steric factors. The overall structure of the dimer is close to planar
with a slight shift of the two quinoline units from the plane. The dimer is
able to dissociate, while the intermolecular interaction can only be
broken if appropriate hydrogen bond acceptors are attached then acting
as competitors to the quinoline nitrogen atoms.
The two hydroxyquinoline units of the dimer (Scheme 1F) are in one
plane. The intermolecular (I) as well as intramolecular (II) hydrogen
bonding occurs between the hydroxyl group and the quinoline nitrogen
atom. The intermolecular hydrogen bond distance is shorter than the
intramolecular one. This observation was also reported for other 8-
hydroxyquinoline dimers and might be due to an unfavored small
O–H–N angle for the intramolecular interaction [31,32].
As shown in Table 1, the values of yield (%) and melting point are
related to the nature of the p-substituent as they increase according to
the following order p-(NO2 N Cl N H N CH3 N OCH3). This can be attribut-
ed to the fact that the effective charge increased due to the electron
withdrawing p-substituent (HL4 and HL5) while it decreased by the
electrons donating character of (HL1 and HL2). This is in accordance
with that expected from Hammett's constant (σR) as shown in Fig. 2,
correlate the yield (%) and/or melting point values with σR it is clear
that all these values increase with increasing σR.
1
S ¼
2η
ω ¼ Pi2=2η
ð8Þ
ð9Þ
ΔNmax ¼ −Pi=η:
The azo form (B) is more reactive than azo form (A) (Scheme 1) as
reflected from energy gap values (Table 2). The value of Et for ligands
HL1, HL2, HL3, HL4 and HL5 is found 2.386, 2.576, 2.696, 2.327 and
3.135 eV, respectively. The value of Et for Ru(III) complexes (1–3) is
found 2.259, 3.003 and 0.491 eV, respectively. It was found that the
complex (3) is more stable than the other complexes.
3.3. Molecular docking study
The molecular docking is a key tool in computer drug design [26].
The focus of molecular docking is to simulate the molecular recognition
process. Molecular docking aims to achieve an optimized conformation
for both the protein and drug with relative orientation between them
such that the free energy of the overall system is minimized [27].
The results of molecular docking between ligands (HLn) and receptor
of prostate cancer mutant 2q7k-hormone showed a possible arrangement
between ligands and receptor (2q7k). A docking study showing a favor-
able interaction between ligands and the receptor (2q7k) and the calcu-
lated energy are listed in Table 4 and Fig. 7. 2D plot curves of docking
with ligands are shown in Fig. 8. This interaction could activate apoptosis
in cancer cell energy of interactions with ligands. Binding energies are the
most widely used mode of measuring binding affinity of ligands. Thus, de-
crease in binding energy due to mutation will increase the binding affinity
of the ligands toward the receptor.
The measured molar conductance values of 10−3 M solutions of
the prepared Ru(III) complexes in DMF were found to be in the range of
26–50 Ω−1 mol−1 cm2 which is in agreement with the non-electrolytic
nature of the complexes. The non-electrolytic nature of the prepared
complexes can be accounted by the deprotonation of the phenolic OH of
the ligands when it is coordinated to Ru(III).
3.4. Mass spectra
3.2. Geometrical structure of the ligands
The electron impact mass spectrum of ligand (HL3) is recorded and
investigated at 70 eV of electron energy. It is obvious that the molecular
ion peaks are in good agreement with their suggested empirical formula
as indicated from elemental analysis (Table 1). The mass spectrum
fragmentation mode of ligand (HL3) shows the exact mass of 249 corre-
sponding to the formula C15H11N3O (Fig. 9). The ion of m/z = 249
undergoes fragmentation to a stable peak at m/z = 172 by losing C6H5
atoms (structure I) as shown in Scheme 2. The loss of N2 leads to the
fragmentation with m/z = 144 (structure II). The loss of CHO atoms
leads to the fragmentation with m/z = 115 (structure III). A breakdown
of the backbone of HL3 ligand gives the fragment (IV).
The molecular structures of the ligands (HLn) and Ru(III) complexes
are optimized by HF method with 3-21G basis set. Primary calculations
reveal that the form (B) is more stable and reactive than forms (A) and
(A') (Scheme 1). The calculated molecular structures for HLn and Ru(III)
complexes are shown in Figs. 3 and 4. Selected geometric parameters
bond lengths and bond angles of HLn and Ru(III) complexes are listed
in Tables S1–S8 in the supplementary (azo form (B)).
Molecular structures (HOMO & LUMO) for HLn and Ru(III) com-
plexes are presented in Figs. 5 and 6. The HOMO–LUMO energy gap
(Et), which is an important stability index, is applied to develop theoret-
ical models for explaining the structure and conformation barriers in
many molecular systems. The smaller is the value of Et, the more is
the reactivity of the compound [33]. The calculated quantum chemical
parameters are given in Tables 2 and 3. Additional parameters such as
separation energies (Et), absolute electronegativities (χ), chemical
potentials (Pi), absolute hardness (η), absolute softness (σ), global elec-
trophilicity (ω), global softness (S) and additional electronic charge
(ΔNmax) are calculated according to the following equations [34,35]:
3.5. X-ray diffraction analysis
Single crystals of the ligands and their complexes could not be
prepared to get the XRD and hence the powder diffraction data were ob-
tained for structural characterization. Structure determination by X-ray
powder diffraction data has gone through a recent surge since it has
become important to get to the structural information of materials,
which do not yield good quality single crystals.
Et ¼ ELUMO−EHOMO
ð2Þ
ð3Þ
The X-ray diffraction (XRD) patterns of HL3 ligand and its complex (2)
in powder form are shown in Figs. 10 and 11. The XRD patterns show that
the ligand (HL3) has a polycrystalline nature and complex (2) is
completely amorphous. The calculated crystal system of HL3 ligand is
found to be monoclinic with space group P21/A. The estimated lattice pa-
rameters are found to be 20.4710 Å, 18.8150 Å, 19.9590 Å, 90.0°, 92.7° and
90.0° for a, b, c, α, β and γ, respectively. The inter-planar spacing (d) and
Miller indices (hkl) which are estimated by CRYSFIRE are listed in Table 5.
The average crystallite size (S) is calculated according to Scherer's
−ðEHOMO þ ELUMO
Þ
χ ¼
2
ELUMO−EHOMO
η ¼
ð4Þ
ð5Þ
2
σ ¼ 1=η
El-Sonbati
