A. Rauf et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 138 (2015) 58–66
59
class is the prime objective of medicinal chemists [6]. Some of their
derivatives from various amine and carbonyl derivatives have been
reported to possess genotoxicity and antimicrobial activities [7,8].
Schiff bases containing hydroxyl group have received the utmost
attention of chemists and physicists due to their special photochro-
mic/thermochromic characteristics and electrochemical applica-
tions [9–11]. These pH dependent proton exchanging compounds
are also applied in the designing of different molecular electronic
devices [12]. Moreover, hydroxyl-substituted Schiff bases possess
antioxidant activities [13]. Metal complexes of these bases are
also fascinating due to their environmental importance [14,15].
Some Schiff bases have been documented to protect metals from
aggressive medium by adsorption at metals surfaces [16–18].
Based on these considerations we synthesized a new Schiff base,
and voltammetric response of the analytes. The electrochemical
studies were carried out in nitrogen saturated solutions using
lAutolab running with GPES 4.9 software, Eco-Chemie, the Nether-
lands. A glassy carbon electrode (GCE) with electro-sensing area of
2
0.063 cm was used as working electrode. Ag/AgCl (3 M KCl) and
platinum wire were used as reference and counter electrodes.
The electrode surface was polished by 0.3 lm alumina powder fol-
lowed by thorough rinsing with bidistillated water. Stock solutions
(2 mM) of BPIMN and CPIMN were prepared in analytical grade
ethanol. Fresh working solutions were prepared in 50% ethanol
and 50% BRB as supporting electrolyte. For reproducible experi-
mental results, the clean GC electrode was used to place in sup-
porting electrolyte solution and various cyclic voltammograms
were recorded until the achievement of a steady state baseline
voltammogram. Differential pulse voltammetry (DPV) was carried
1
-((4-bromophenylimino) methyl) naphthalen-2-ol (BPIMN) and
À1
characterized by a variety of techniques.
out at a scan rate of 5 mV s . For square wave voltammetry, a scan
À1
Schiff bases find use as catalyst for oxygenation, hydrolysis,
electro-reduction and decomposition of various compounds. The
electrochemical study is envisioned to provide highly valuable
information about the catalytic processes since catalytic conver-
sions are frequently accompanied by change in oxidation state of
the central metal and structure of the complex. Knowledge of elec-
tronic and steric effects to control the redox chemistry of these
metal complexes may prove critical in the design of new catalysts
rate of 100 mV s was fixed by setting 20 Hz frequency and 5 mV
potential increments. For computational studies, GAUSSIAN 03W
package was used. The geometric optimization of BPIMN and
CPIMN was done by density functional theory at B3LYP and
3-21G minimal bases set. The most stable conformation was used
for the measurement of charge distribution and energy calcula-
tions of HOMO and LUMO. The reason for the selection of
DFT/3-21G was its success in charge and energy calculations as
testified by other investigators [21].
[
19,20]. As Schiff bases are highly biologically active compounds,
so pH dependent photometric and voltammetric studies of two
unexplored derivatives of this class were carried out getting useful
insights about their role in cellular milieu.
Synthesis of 1-((4-bromophenylimino) methyl) naphthalen-2-ol
The novel Schiff base was synthesized by reacting 2-hydrox-
ynaphthaldehyde (0.03 mmol, 5.0 mg) and 4-chloroaniline
Experimental
(
0.03 mmol, 5.16 mg) in dry ethanol (Scheme 1). The obtained yel-
low crystalline solid was cooled, filtered and recrystallized in mix-
ture of chloroform and pet ether (3:1). The formation of BPIMN
Chemicals
was ensured from the following data:
2
-Hydroxy-1-naphthaldehyde, 4-bromoaniline and 4-chloroan-
À1
C
17
H
12NOBr: Yield 75%, M.p. 162.5–164 °C, FT-IR (cm ): 1615.6
iline were purchased from Aldrich, USA. The solvents like toluene,
chloroform, hexane and ethanol were obtained from Merck, Ger-
many and dried before use by following the standard reported pro-
cedures. p-Nitrophenyl phosphate hexahydrate, diethanolamine
and magnesium chloride were purchased from Sigma Aldrich and
used as received. Human serum was used as a source of alkaline
phosphatase.
1
m
1
(C@N), 3387
m(OH)phenolic, H NMR d (ppm): 9.15 {1H, CH@N},
1
3
5.05 {1H, OH}, C NMR d (ppm): 168.6 {CH@N}, 155.7 {C-OH}.
Synthesis of 1-((4-chlorophenylimino) methyl) naphthalen-2-ol
The Schiff base ligand, abbreviated as CPIMN was synthesized
and recrystallized by the method reported in literature [22]. The
yield and spectroscopic data of CPIMN are given below:
Instrumentation
À1
C
17
H
12NOCl: Yield 75%, M.p. 157–160 °C, FT-IR (cm ): 1620
1
m
(C@N), 3399 m(OH)phenolic, H NMR d (ppm): 9.40 {1H, CH@N},
15.25 {1H, OH}, C NMR d (ppm): 168.5 {CH@N}, 155.8 {C-OH}.
Melting points were determined using Gallen Kamp apparatus.
Infrared measurements (4000–400 cm ) were performed on ther-
1
3
À1
moscientific NICOLET 6700 FTIR spectrophotometer. Multinuclear
1
13
(
H and C NMR) spectra were recorded in solution on Bruker
X-ray structure determination
ARX 300 MHz using tetramethylsilane (TMS) as internal reference.
UV–Visible 1601 Shimadzu spectrophotometer with measurement
wavelength range of 200–800 nm was used for electronic absorp-
tion studies. Briton Robinson (BR) universal buffer of wide pH
range was used for studying the effect pH on the photometric
Suitable single crystals of BPIMN and CPIMN were selected and
mounted on a Microstar diffractometer. The crystal was kept at
100 K during data collection. The structure was solved with the
olex2 using Charge Flipping program [23] and refined with XL
CHO
NH2
HO
OH
C H OH
N
2
5
+
stirr 1 hr
X
X
X=Br, Cl
Scheme 1. Synthesis of 1-((4-bromophenylimino) methyl) naphthalen-2-ol and 1-((4-chlorophenylimino)methyl)naphthalen-2-ol.
Rauf, Abdur
