Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Detection of Al3+ and Zn2+ ions by
-(5-methylthiazol-2-yliminomethyl)phenol
2
Nithi Phukan, Jubaraj B. Baruah ⁎
Department of Chemistry, Indian Institute of Technology Guwahati, North-Guwahati 781039, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Aluminium chloride catalyses hydrolysis of 2-(5-methylthiazol-2-yliminomethyl)phenol (1). This reaction can
be specifically used for detection of Al ions in the presence of various other ions from the characteristic emis-
Received 8 August 2013
Accepted 23 September 2013
Available online 1 October 2013
3+
sion at 446 nm (λex = 365 nm). On the other hand selective emission of 2-(5-methylthiazol-2-yliminomethyl)
2+
phenol on interaction with zinc ions at 490 nm (λex = 365 nm) can be used to detect Zn
ions. The role of
other ions such as Cu2+, Hg , and Sn in the detections are discussed.
2+
2+
Keywords:
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2013 Elsevier B.V. All rights reserved.
Catalytic hydrolysis
Schiff-base
3
+
Al ions
2
+
Zn ions
Fluorescence
2
+
solution of the ligand (2mL,10−5M) in methanol, it underwent hydrolysis
The Schiff bases are routinely used in analytical chemistry of Zn
3
+
3+
and Al ions [1–9]. On the other hand some of the zinc and aluminium
complexes are used as catalysts for hydrolysis of functional groups such
as imines and esters [10,11]. Aluminium is a toxic element [12–15], thus
detection of such element in the presence of relatively non-toxic
elements would be of interest. The stability of Schiff base ligands
towards hydrolysis in the presence of different ions is an important
issue in success of analytical chemistry [16], and can decide the stability
of modified surface such as multiwall carbon nano-tube [17–20]. How-
ever, hydrolysed or decomposed products from a Schiff base ligand may
also interact with metal ions giving characteristic signals such as colour
and emission. to make a selective detection process. The identification
of such degradable ligands which will release fluorescence active part
on decomposition would be of general interest. We depict here that
under ambient condition. The strong fluorescence shown by Al
ions
during the hydrolysis of ligand 1 has similarity to the fluorescence emis-
sion shown by Schiff base of 2-hydroxybenzaldehyde binding to biological
system in the presence of Al3 ions [23].
+
3
+
The catalytic hydrolysis reactions of 1 by Al ions are monitored in
the presence of different metal ions as well as by varying the concentra-
tion of metal ions. It may be mentioned that 2-hydroxybenzaldehyde
2
+
2+
interacts with other metal ions such as Zn and Sn ions which also
lead to identical emission as that of the Al3 ions at 446 nm. But
among these ions, only aluminium can hydrolyse ligand 1 in the
presence or absence of other metal ions, leading to specific detection
+
3
+
of aluminium by 1. The reaction of 1 with Al
was monitored by
1
3+
H-NMR by adding different proportions of Al ions and the ligand 1.
2
-(5-methylthiazol-2-yliminomethyl)phenol (1) (Fig. 1) shows dual
fluorescence emission peaks at 425 nm and 525 nm (λex = 365 nm); it
Since the 1H-NMR of the 2-hydroxybenzaldehyde is distinguishable
from the ligand, the formation of hydrolysed products from compound
1 is discerned (please refer to supporting information).
3
+
undergoes selective hydrolysis by Al
ions under neutral condition
and shows fluorescence emission at 446 nm by interactions of Al3
with one of the hydrolysed product. On the other hand it shows
characteristic fluorescence emission on interactions with Zn2 ions.
+
On the other hand, addition of Zn ions to a solution of the ligand 1
2+
leads to a strong emission peak at 490nm (Fig. 2C). This peak is attrib-
uted to 1:1 complex formation with the ligand. Such emission peak
+
2
+
2+
We have observed that 2-(5-methylthiazol-2-yliminomethyl)phenol
was not observed with other metal ions. The ions like Cd , Ca and
+
2+
(
1) [21] undergoes fast catalytic hydrolysis by Al3 ions to form 2-
Mg do not significantly change the fluorescence of the ligand 1. How-
ever, Cd2 ions cause slight enhancement of the peak at 425nm of the
ligand by effecting insignificantly the other emission of the ligand. The
characteristic emission at 490nm shown by zinc ion with 1, was not in-
+
hydroxybenzaldehyde and 2-amino-5-methylthiazole [22] which can be
monitored by fluorescence spectroscopy (Fig. 2A). The monitoring of the
reaction is possible as the hydrolysed product 2-hydroxybenzaldehyde in-
2
+
2+
2+
2+
2+
teracts with aluminium chloride results in emission at 446 nm (λex
=
terfered by the other metal ions such as Ni , Zn , Ni , Zn , Cu
,
3+
−2
2+
3+
+
+
3+
+
3
65 nm) (Fig. 2B). When 1 μL solution of Al (10 M) was added to a
Hg , In , Na , and Li . However, Al
ion is an exception to this,
upon addition of catalytic amount of Al ions under neutral condition
3
2
+
to a solution containing equimolar amount of 1 and Zn
ions, the
⁎
fluorescence emission at 490 nm decreases and a new emission peak