The complexation activity of NADO with various metal ions in an ethanolic solution is specifically studied by means of fluorescent spectra. The NADO exhibits a significant fluorescence enhancement at 469 nm in presence of Al3 þ due to the formation of a complex.
Trang 1Original Article
J Jone Celestinaa, L Alphonsea, P Tharmaraja,*, C.D Sheelab
a PG and Research Department of Chemistry, Thiagarajar College, Madurai 625009, Tamilnadu, India
b PG and Research Department of Chemistry, The American College, Madurai 625002, Tamilnadu, India
a r t i c l e i n f o
Article history:
Received 31 January 2019
Received in revised form
26 April 2019
Accepted 8 May 2019
Available online 16 May 2019
Keywords:
Fluorescent sensor
Colorimetric
Aluminium ion
Triazine
Schiff base
a b s t r a c t
This paper deals with a newfluorescent assay of Al3þions with (2,20 -(6-((4-nitrophenyl)amino)-1,3,5-triazine-2,4-diyl) bis(hydrazine-2-yl-1-ylidene)) bis(indolin-3-one) (NADO) containing triazine moiety developed over other commonly coexisting metal ions The complexation activity of NADO with various metal ions in an ethanolic solution is specifically studied by means of fluorescent spectra The NADO exhibits a significant fluorescence enhancement at 469 nm in presence of Al3þdue to the formation of a complex Under an optimized condition the detection limit is found to be 0.09mM As the concentration
of Al3þis increased, thefluorescence intensity gradually increases due to the formation of the complex The 1:1 binding stoichiometry between Al3þand NADO is confirmed by the Job's plot and the HR-LCMS mass spectrum of the metal complex
© 2019 Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an
open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)
1 Introduction
Aluminum being the third most abundant element has its
widespread use in light alloy, textiles and in treatment of water
Al3þremains in blood and tissues for a very long time before it is
excreted in the urine World Health Organization holds the view
that the average daily human intake of aluminum is about 3e10 mg
Human body tolerates an uptake up to 7 mg/kg of the body weight
per week Aluminum in excess would lead to environmental
contamination and could be toxic to human health since it impedes
calcium metabolism, thereby causing Osteomalacia, influences the
ingestion of iron in blood and also decreases the liver and kidney
functions Excess accumulation of Al3þleads to impairment of the
central nervous system, which is associated with the pathology of
dementia, anemia, Parkinson's disease, Alzheimer's disease and
dialysis[1,2]
It is, therefore, desirable to detect and sense Al3þions and to
control their impact in biosphere In previous reports,
Zheng-qiang Li and co-workers have reported several detection methods
for Al3þions among whichfluorescence detection offers several
advantages such as high sensitivity, a facile analysis, an intrinsic
selectivity and the capacity for rapid, real-time monitoring compared to other methods[3,4] Schiff base acts as a good op-tical andfluorescent sensor due to its photophysical properties Triazine Schiff base, formed with active carbonyls and amines, will enhance the property offluorescence on complexation It has been considered in variousfields of chemistry due to its specific properties like co-ordination ability which makes them appli-cable as afluorescent sensor in catalysts and in biological fields
In view of these facts, we designed the receptor as the target sensor that could strongly bind the metal ions through Schiff base moiety[5,6] In the present study, a functionalized triazine de-rivative, as afluorescent Al3 þsensor, is developed with a lowest detection limit of 0.09 mM Our results exhibit an enhanced fluorescence emission in ethanolic solution upon the addition of
Al3þions[6]
2 Experimental 2.1 Materials All the needed chemicals were purchased from sigma Aldrich India and were used without further purification The metal chlo-ride salts were purchased from Merck chemicals Ethanol was purchased commercially and was further purified by a distillation method Melting point of the synthesized ligand and its metal
* Corresponding author.
E-mail address: rajtc1962@gmail.com (P Tharmaraj).
Peer review under responsibility of Vietnam National University, Hanoi.
Contents lists available atScienceDirect Journal of Science: Advanced Materials and Devices
j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / j s a m d
https://doi.org/10.1016/j.jsamd.2019.05.001
2468-2179/© 2019 Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license ( http://
Journal of Science: Advanced Materials and Devices 4 (2019) 237e244
Trang 2complex were analyzed by an electrical heating method at using
capillary tubes
2.2 Characterization
The1H NMR and13C NMR was recorded using a 400 MHz Bruker
NMR instrument A FT-IR spectrometer in the range
4000e400 cm1was used to record the spectra using a KBr pellet
The LCMS and HR-LCMS mass spectra were recorded in the Bruker
mass spectrometer using acetonitrile as the solvent Absorption
and emission properties of NADO with different metal ions were
recorded in UV-Visible Jasco (V-530) and FP-6200
Spectropho-tometer instruments
2.3 Synthesis of NADO
The triazine Schiff base ligand was prepared using ethanol
4-nitroaniline (0.50 g, 2 mmol) in acetone, was stirred with
cyanu-ric chloride under ice cold condition for about 4 h and the yellow
solid obtained wasfiltered and dried The precipitate obtained was
allowed to stir for an hour with hydrazine hydrate to get (a) 4,
6-dihydrazinyl-N-(4-nitrophenyl)-1,3,5-triazine-2 amine To the dried precipitate (0.20 g, 1 mmol), Isatin (b) (0.24 g, 2 mmol) in ethanol was gradually added at 80C and refluxed for 24 h As a completion of the reaction, a dark yellow precipitate NADO (c) starts separating out It is shown inFig.S1 The precipitate obtained was collected byfiltration and washed several times with ethanol and dried in vacuum It was purified by column chromatography using neutral alumina in a mixture of (Ethyl acetate/Hexane) 2.4 Synthesis of Al3þ-NADO complex
The complex was prepared using an ethanolic solution of AlCl3 (0.15 g, 1 mmol) and an ethanolic solution of NADO (0.32 g, 1 mmol)
in 1:1 (ligand:metal) molar ratio by refluxing for two hours as shown inFig.S2 The obtained precipitate was washed with abso-lute ethanol and dried
2.5 Job's plot measurements NADO (1 mg) and 0.1 mg of AlCl3are dissolved in ethanol The solution mixture is taken and poured into the glass vials Different
Table 1
Physical and analytical data of NADO and [Al(NADO)Cl]Cl 2 complex.
Compound M.W g/mol1 Colour Calculated (Found) (%) M.p (C)
C 25 H 17 N 11 O 4 (NADO) 535.47 Yellow 56.08 (56.05) 3.20 (3.18) 11.95 (11.88) 28.77 (28.79) e 195e198 C [Al(NADO)Cl]Cl 2 667.10 Dark Yellow 50.14 (50.16) 3.03 (3.04) 25.73 (25.70) 22.01 (21.98) (4.51)
4.53
254e256 C
Fig 1 (a) UVevis spectrum of ligand (NADO), (b) UVevis spectra of NADO (20mM) after addition of metal cations and anions (c) UVevis spectra of NADO after adding (0.10e0.90)
mM of Al3þion.
Trang 3concentrations (0.1e1.0mM) of AlCl3 are added to the vials
con-taining the NADO and shaked for getting clear solutions After
shaking the solution is transferred into the UV-visible cuvette and
the UVevis absorption spectrum is taken using UV-visible
spec-trophotometer between the ranges 200 nme800 nm at room
temperature
2.6 Elemental analysis and conductivity measurements
The synthesized NADO and [Al(NADO)Cl]Cl2complex was
ob-tained in good yield with high purity The data of the complex
confirms the formation of 1:1 (M:L) coordination Al3 þwith NADO
as shown inTable 1 The percentage of C,H,N was measured in a
Vario EL- III CHNS Analyzer Melting points of the synthesized
NADO and its [Al(NADO)Cl]Cl2 complexes were analyzed in the
buchi melting point analyzer The electrolytic conductance of the
synthesized complex was studied with the help of the
con-ductometer with ethanol as the solvent Initially the cell constant
value is 1
3 Results and discussion
3.1 Absorption studies of NADO
The sensing property of NADO with different metal cations was
investigated by preparing stock solutions of NADO (1 103mM)
and metal cations in anhydrous ethanol[7]and its coordination
properties with various metal cations were measured by the
UVeVis Spectrometer The free NADO showed maximum
ab-sorption bands at 268 nm (37,313 cm1) and 326 nm
(30,675 cm1)which are due to thep/p*transition[8]as shown
inFig 1(a) When the metal ions were added to the NADO, there
was no specific change observed with the metal cations and
an-ions like (Zn2þ, Ni2þ, Fe2þ, Fe3þ, Cu2þ, Al3þ, Co2þ, Mg2þ, Ca2þ, Bi2þ,
Hg2þ, As2þ, Cr3þ, CO3 , SO
4 , PO
4 , NO3, NO2 and Cr
2O7 ) except for Al3þwhich gave a new band with increasing intensity
at 515 nm (19,417 cm1) corresponding to the3A2g(F)/3T1g(P) transition and at 657 nm (15,220 cm1) corresponding to the
4T1g(F)/4A2g(F) region as clearly shown inFig 1(b)[9e11] The
Table 2
UV-Vis spectral data of NADO and [Al(NADO)Cl]Cl 2 complex.
Compounds Frequency
cm1
Transition Geometry Electrolytic
conductance S/m NADO 30,675
37,313
[Al(NADO)Cl]Cl 2 19,417
15,220
3 A 2g (F)/ 3 T 1g (P)
4 T 1g (F)/ 4 A 2g (F)
distorted octahedral
173
Fig 2 (a) Emission spectra of NADO with different metal ions and (b) Emission intensity at 469 nm as a function of Al3þat different concentrations (0.10e0.80mM).
Fig 3 FT-IR Spectrum of NADO.
Fig 4 FT-IR Spectrum of the complex [Al(NADO)Cl]Cl 2 J.J Celestina et al / Journal of Science: Advanced Materials and Devices 4 (2019) 237e244 239
Trang 4latter transition might be due to the formation of a distorted
octahedral complex of Al3þwith NADO[1]as presented inTable 2
Though Zn2þgave a small shift in the absorbance it is considered
negligible and it is not because of the complex formation [12]
The interference experiments clearly show that Zn2þ has no
interference in selectively detecting Al3þ In Fig 1(c) with increasing equivalents of Al3þadded to the solution of NADO, the concentration of Al3þincreases with the consecutive decrease in the concentration of NADO which confirms the presence of the
Al3þcomplex in equilibrium with the free NADO A well-defined isosbestic point at 401 nm clearly confirms the complex forma-tion of Al3þwith the NADO resulting in a red shift[13,18,34] 3.2 Fluorescent studies of NADO
The selective ability of NADO towards Al3þinfluorescence in the presence of various metal ions was investigated in ethanol, as shown inFig 2(a) Free NADO showed weakfluorescence emission bands due tofluorescent quenching by lone pair of electrons from oxygen and nitrogen atoms, which results in the photo-induced electron transfer (PET) [14] When Al3þ ions were added, the fluorescence intensity of the ligand at 469 nm was enhanced without any spectral changes which indicates a high selectivity of NADO for Al3þions by means of chelation[11,15]Upon addition of (Zn2þ, Ni2þ, Fe2þ, Fe3þ, Cu2þ, Al3þ, Co2þ, Mg2þ, Ca2þ, Bi2þ, Hg2þ,
As2þ, Cr3þ, CO3, SO4, PO4, NO3, NO2and Cr2O7) ions into NADO, no obviousfluorescence response could be observed except for Zn2þand Fe2þwhich ions slightly increased the emission in-tensity with little interference in detecting Al3þ The Fluorescence response of the NADO to various concentrations of Al3þ (0.10e0.80mM) showed a gradual increase in intensity[12,34]as shown inFig 2(b) At 0.80mM the maximum precipitation occurs
Table 3
Infrared spectral data of the compound NADO and the [Al(NADO)Cl]Cl 2 complex.
Compound nC¼N cm 1 nC¼N cm 1 triazine ring nN-H cm1 nAl-N cm1 nAl-O cm1 nC-N cm1
Fig 5 Jobs Plot for determining the stoichiometry of NADO and Al3þin ethanol.
3þ
Trang 5The interference studies clearly show the selective sensing ability of
Al3þ ion compared with that of other cations with the highest
fluorescence intensity at 469 nm It underlines the excellent
spec-ificity to Al3 þ.
3.3 FT-IR spectral studies
InFig 3, the NADO has a broad absorption band in the region of
3139 cm1due to thee NH stretching vibration[12] This band is
slightly shifted by the formation of the Al3þcomplex and a new
band appears at 3129 cm1[16e18]which indicates the formation
of a metal complex with nitrogen present in the NH group that is
present in NADO[19,20] The sharp intense band in the region of
1324 cm1in the ligand is attributed to the carbonyl C-N stretching vibration and it was shifted to higher frequency 1327 cm1for the
Al3þcomplex The band at 1401 cm1is characteristic of triazine moiety which is shifted to 1398 cm1 The sharp peak at 749 cm1 strongly supports the bond formation nAl-O of metal through carbonyl oxygen of the Schiff base ligand to the Al3þion[20,21] The metal complex formation was further confirmed by the appearance of sharp peaks at 568 cm1nAl-N in the spectrum of the metal complex inFig 4which is assignable to stretching vi-brations[22] The coordination through azomethine nitrogen was supported by the shifting ofnC¼ N towards higher frequencies
Fig 7 HOMO and LUMO energy levels of NADO and [Al(NADO)Cl]Cl 2 J.J Celestina et al / Journal of Science: Advanced Materials and Devices 4 (2019) 237e244 241
Trang 6with respect to that observed at 1626 cm1in the free ligand while
the new shifted peak appears at 1590 cm1in the metal complex
given inTable 3 [11,16,23] The absence of the carbonyl amide band
at 1660 cm1 in NADO is a strong evidence for amidoeimido
tautomerism which takes place before complexation It is also
correlated by the decrease in the NH bending vibrations of the Al3þ
metal complex with NADO and by the presence of a new peak at
1589 cm1in the spectrum of the Al3þNADO complex[24] In the
metal complex, the bands shifts to lower frequency indicate that
the tautomerism is inhibited in the Al3þ complex and that the
imine nitrogen and carbonyl oxygen are involved in the
coordi-nation to the metal[25]
3.4 NMR and mass spectral studies
To understand the binding mode of NADO with Al3þ, a1H NMR
spectrum analysis is done in DMSO-d6 Thefine spectra of the
NADO and Al3þmetal complex are shown inFig.S3andFig.S4 The
1H NMR spectrum of NADO shows the characteristic imine peak at
8.11 ppm and the aromatic protons are centered from 6.96 ppm to
7.87 ppm The1H NMR spectrum of the Al3þcomplex shows the
merging of two singlet peaks at 6.98 ppm, a doublet at 7.6 ppm
and they are downshifted[26] A peak at 8.2 ppm undergoes a
downshift as well Complexation of NADO with Al3þ was
confirmed by the shifted proton peaks towards lower magnetic
fields due to the reduction of the electron density upon
coordi-nation to the metal ion[27e31].13C NMR spectrum of NADO as
given inFig.S5also confirms the formation of NADO The Mass
spectrum of the NADO and Al3þare examined by LCMS and
HR-LCMS mass spectrum analysis using acetonitrile as the solvent
[32,33].Fig S6clearly confirms the formation of the NADO with
the observed m/z peak at 536.53 (Mþ H)þ[34,35] The observed
m/z peak for NADO in the presence of Al3þat 666.06 (M-H)-peak
is attributed to the [NADO] [Al (NADO)Cl]Cl2complex (calculated: 667.01)[36e39]and is shown inFig S7 The mass data, therefore, confirm the binding of Al3þto ligand with 1:1 stoichiometry[16] The conductivity measurement value of 173 S/m corresponds to the proposed structure with two chlorine ions present outside the coordination sphere in the metal complex (Fig 6)
3.5 Theoretical studies
In order to support the results obtained from the1H- NMR and HR-LCMS mass spectral analysis, an optimization of the structures
of both NADO and [Al (NADO)Cl]Cl2were performed at the hybrid basic sets B3LYP/6-3 g(d) level in the Gaussian program The ob-tained result is in accordance with the results of the NMR and Mass spectral data[40] The optimized results exposed an octahedral structure It is found that [Al (NADO)Cl]Cl2is better stabilized than NADO The energy gap of HOMO and LUMO of NADO and the Al3þ complex is (DE¼ 3.5919 eV andDE¼ 2.4038 eV) The value of the
Al3þ complex is found to be comparatively lower than that of NADO, indicating a bathochromic shift towards longer wavelength
in the absorption spectrum In the optimized structure of the Al3þ NADO complex HOMO as given in Fig 7, electrons are mostly occupied in the ligand rings whereas, on the other hand, LUMO electrons are occupied both by the ligand rings and the Al center In view of these results, ICT (intramolecular charge transfer) is taking place efficiently in the mechanism of forming the Al3 þcomplex[41] (Fig 8)
3.6 Stoichiometry and binding mechanism of NADO with Al3þ The binding mechanism of NADOe Al3þwas studied by fluo-rescence spectral changes, by mass spectrometry[42]and by1H NMR and FT-IR spectral studies[38] Free NADO, which has poor fluorescence, is enhanced by the isomerization of C¼N (azomethine carbon and hydrogen) double bond in the excited state[36]by Al3þ metal on stable chelation Increase influorescence takes place and the Photo Induced Electron Transfer (PET) is inhibited (when the metal gets binded to NADO, the PET is stopped) InFig 2, NADO, as such being low influorescence because of intramolecular photo-induced electron transfer, on rapid addition of Al3þ shows enhancedfluorescence Thus the enhancement in fluorescence ul-timately leads to the complex formation[11] The detection limit (DL) of NADO to Al3þ was found to be lowest with the value of 0.09mM compared with the recent literatures as given inTable 4 The binding stoichiometry of ligand NADO to Al3þwas calculated
by the Job's method on the basis offluorescence emission spec-trum InFig 5thefluorescence intensity at 469 nm exhibited a maximum mole fraction at 0.50 demonstrating a possible 1:1 binding stoichiometry between Al3þand NADO
3.7 Effect of pH onfluorescence in presence of Al3 þwith NADO
To observe the binding interaction of NADO with Al3þ at different pH's, both acidic and basic pH solutions were used The interaction between NADO and the Al3þion was investigated at a
Fig 8 Effect of pH on [Al(NADO)Cl]Cl 2 complex.
Table 4
Detailed comparison of lod of various Al3þsensors by fluorescence responses.
Probe Selectivity Method Solvent LR Lod (mM) Ref
Naphthol- Quinoline Fluorescent chemosensor Al3þ Fluorescence DMF 0-16 equivalence 1.0mM [15]
Fluorescent chemosensor Al3þ Fluorescence DMSO 0.1e0.5mM 0.1mM [12]
Amphiphilic Carbon dots Al3þ Fluorescence Ethanol 8e20mM 1.1mM [30]
Fluorescent chemosensor Al3þ Fluorescence CH 3 OH/Water 0.5e10mM 0.43mM [36]
Triazine schiff base Al3þ Fluorescence Ethanol 0.1e0.8mM 0.09mM Present work
Trang 7pH range from 2 to 14[26] The pH of the solution was adjusted
using either NaOH or HCl solutions [32] This experiment was
carried out at afixed concentration of the NADO and Al3þas 20mM
and 200mM respectively in ethanol As shown inFig 8initially the
fluorescence is low and increases with increase in pH[42], it attains
a maximum intensity of 469 nm at pH 8 and again starts to decrease
in highly basic pH This is due to the precipitation of Aluminium
hydroxide[19] Thus, the [Al (NADO)Cl]Cl2has a higher intensity
value at pH 8 and the intensity starts to decrease at higher basic pH
4 Conclusion
In this work, a novel triazine based Schiff base, NADO as a
fluorescent sensor is developed and its ability of sensing for a wide
range of metal ions is studied NADO showed a significant
enhancement influorescence intensity after adding Al3 þions It can
operate as an efficient sensor in the detection of Al3þ The NADO
displayed a better selectivity for Al3þthan that of other competitive
metal ions The detection limit is low with the value of 0.09mM The
coordination of NADO with Al3þwas confirmed by mass spectrum
and Job's plot analysis and the coordination was found to be the 1:1
stoichiometry On the basis of the results, NADO could be applied
for the selective detection and recognition of Al3þpresent in the
environment It can be utilized for various applications
Acknowledgements
The authors thank the Management of Thiagarajar College
Madurai for providing the analytical facilities
Appendix A Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.jsamd.2019.05.001
References
fluorescent chemosensor based on PET and ESIPT in aqueous solution,
colorimetric chemosensor for selective detection of aluminum in aqueous
N.T Crespo-Velasco, M.A Mu noz-Hern andez, Synthesis and characterization
of aluminum complexes incorporating Schiff base ligands derived from
[(2-hydroxy-1-naphthaldehyde)-3-isatin]-bishydrazone, J Enzym Inhib Med Chem 22
a colorimetric sensor for iron in aqueous solution, Sens Actuators, B 215
fluo-rescent chemosensor for high selectivity and sensitivity of aluminum ions,
Fluorescent chemosensor based-on naphtholequinoline for selective
Recent advances in luminescent heavy metal complexes for sensing, Coord.
chemo-sensor for cobalt ions in a near perfect aqueous solution, Sens Actuators, B
27Al) NMR] and mass spectrometric studies of aluminium(III) complexes containing O- and N-chelating Schiff bases, Main Group Met Chem 38 (2015)
ligand complexes of cobalt(III) phenanthroline/bipyridyl and benzoylhy-drazones, their DNA binding and antimicrobial activity, J Inorg Biochem 99
L Wen, Z Wenping, X Jianping, J Chun, Water-soluble and highly selective fluorescent sensor from naphthol aldehyde-tris derivate for aluminium ion
sensor for Zn(II) and Al(III) and colorimetric sensor for Fe(II) and Fe(III), Sens.
“Offe OneOff” Sensor for Sequential Detection of Aluminum and Acetate/
Isatin-Schiff base copper(II) complexes and their influence on cellular
colori-metric sensor for Fe(III) and Fe(II) based on a novel 8-hydroxyquinoline
J.J Celestina et al / Journal of Science: Advanced Materials and Devices 4 (2019) 237e244 243
Trang 8[37] V.K Gupta, A.K Singh, M.R Ganjali, P Norouzi, F Faridbod, N Mergua,
Comparative study of colorimetric sensors based on newly synthesized Schiff
1-(2-pyridylazo)-2-naphthol for the detection of aluminium(III) ions, Sens Actuators, B 209
in aqueous medium: experimental and theoretical studies, Sens Acutators, B
one chemosensor for the highly sensitive and selective detection of zinc, RSC