Colorimetric Detection of Spermine by the CuII Complex of Imine-Based Organic Nanoaggregates in Aqueous Medium

Article abstract of DOI:10.1002/ejic.201500489

A Schiff-base receptor bearing different functionalities was synthesized from dipicolinic acid hydrazide and characterized with several spectroscopic techniques. To explore its practical application as a sensor, the receptor was processed into organic nan

Full text of DOI:10.1002/ejic.201500489

FULL PAPER
DOI:10.1002/ejic.201500489
Colorimetric Detection of Spermine by the CuII Complex
of Imine-Based Organic Nanoaggregates in Aqueous
Medium
Shweta Chopra,[a][‡] Jasminder Singh,[b][‡] Harpreet Kaur,[a]
Ajnesh Singh,[b] Narinder Singh,*[b] and Navneet Kaur*[a]
Keywords: Colorimetry / Sensors / Biogenic amines / Nanoparticles / Schiff bases / Copper
A Schiff-base receptor bearing different functionalities was
synthesized from dipicolinic acid hydrazide and charac-
terized with several spectroscopic techniques. To explore its
practical application as a sensor, the receptor was processed
into organic nanoaggregates (O1) in aqueous medium by the
structure of the complex O1·Cu2+ thus formed was deter-
mined by single-crystal X-ray crystallography. Complex
O1·Cu2+ was further employed as a sensor for detection of
biogenic amines in aqueous medium, and showed selective
sensing of spermine with a detection limit of 7.62 nM. The
reprecipitation method. The O1 nanoaggregates were char- color change on addition of spermine to the complex can be
acterized by techniques such as dynamic light scattering and
TEM, and their recognition properties for metal ions were
seen with the naked eye. Moreover, stability in the physio-
logical pH range and negligible effect of ionic environment
investigated by fluorescence spectroscopy. The nanoaggre- provided the opportunity for real-time application of the sen-
gates showed selectivity for Cu2+ over other metal ions. The
sor in aqueous medium.
in permissible limits, but when present in excess they pose
a serious threat to human health, as several BAs have nu-
merous toxicological repercussions. For example, histamine,
tyramine, and phenylethylamine can cause a variety of
symptoms in the human body, such as nausea, rashes, ab-
dominal cramps, itching, burning, tingling, and hypoten-
sion. Putrescine and cadaverine are secondary amines that
cause food poisoning by enhancing the physiological effect
of histamine. Tyramine is also considered to cause hyper-
tension.[7–9] The amount of BA present in foodstuffs is used
as a quality index for their storage and to check for spoil-
age. Considering the extent of physiological and health ef-
fects caused by these BAs, their determination in various
foodstuffs, especially before packaging, is of major impor-
tance.[10] Various methods are available in the literature for
determination of amines, such as HPLC, electrophoresis,
and electrochemical techniques. These techniques require
expert handling and laborious interpretation.[8,11–13] On the
other hand, techniques such as UV/Vis absorption and
fluorescence spectroscopy do not require expert handling or
preparation of solutions.[14,15] Various receptors have been
devised for determination of biomolecules that form
hydrogen bonds with the receptors, but their use in aqueous
medium is a challenge owing to formation of hydrogen
bonds with water molecules instead of biomolecules.[16]
However, complexation of metal ions with the receptor pro-
vides a suitable alternative to determination through
hydrogen bonding, as it brings electrostatic interactions of
complexes with biomolecules into the picture.[17]
Introduction
Biogenic amines (BAs) are low molecular weight bio-
molecules and can be categorized as aliphatic (e.g., sperm-
ine, spermidine), aromatic (e.g., tyramine, phenylethyl-
amine), and heterocyclic (e.g., histamine, tryptamine) or-
ganic bases. BAs are found as physiological components of
several food products and are also generated by decarboxyl-
ation of amino acids present in the food by bacterial action.
In other words, the origin of BAs can be categorized as
endogenous or exogenous.[1–3] In the human body BAs are
formed by various metabolic process and are necessary in
diverse physiological functions. For example, spermine and
spermidine regulate growth, serotonin acts as a neural
transmitter, histamine and tyramine are inflammation
agents, and BAs are involved in cell-membrane equilibrium,
cell propagation, and the synthesis of RNA, DNA, and
various proteins.[4–6] Hence, BAs are of great physiological
importance and pose no threat to human health if present
[a] Centre for Nanoscience and Nanotechnology (UIEAST),
Panjab University,
Chandigarh 160014, India
E-mail: navneetkaur@pu.ac.in
www.puchd.ac.in
[b] Department of Chemistry, Indian Institute of Technology
Ropar (IIT Ropar),
Rupnagar, Panjab 140001, India
E-mail: nsingh@iitrpr.ac.in
www.iitrpr.ac.in
[‡] Both authors contributed equally.
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201500489.
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Keeping these perspectives in view, we synthesized recep- 15 nm (Figure 1). The fluorescence spectrum of O1 in aque-
tor 1 and converted it to organic nanoaggregates O1 by a ous solution showed marked differences to the emission
single-step reprecipitation method. These organic nano- profile of receptor 1 in an organic solution. Nanoaggregates
aggregates show good optical fluorescence properties and O1 are highly fluorescent at 515 nm, in contrast to their
form complexes selectively with copper ions. The complex predecessor 1, when excited at 353 nm (Figure 2). The ob-
O1·Cu2+ was used for analytical determination of BAs with
detection by UV/Vis absorption spectroscopy and the
naked eye.
Results and Discussion
Synthetic Procedure
Receptor 1 was obtained by condensation of dipicolinic
acid hydrazide[18] with salicylaldehyde in ethanol
(Scheme 1). The structure was confirmed by 1H and 13C
NMR spectroscopy, IR spectroscopy, CHN analysis, and
mass spectrometry (Figures S1–S4).
Scheme 1. Synthesis of receptor 1.
Figure 1. (a) TEM image and (b) DLS size distribution of nano-
aggregates of receptor 1 prepared in aqueous solution.
Nanoaggregate Formation
The practical applications of organic nanoparticles in ad-
vanced materials for, for example, drugs, display elements,
and cosmetics, which are due to their excellent solubility in
water and biodegradable nature, have opened great perspec-
tives in the fields of biology and green chemistry.[19–21] Their
size domain, which is quite different from that of inorganic
nanomaterials, ranges from a few tens of nanometers to a
few hundred nanometers. The optical properties of nano-
particles of molecules with flexible conformation are size-
dependent. Therefore, fabrication of organic nanoaggre-
gates of requisite size is of the utmost importance. Herein,
we utilized a single-step reprecipitation process for the fab-
rication of organic nanoparticles.[22] This process was car-
ried out by time-regulated injection of a solution of recep-
tor 1 in DMF to doubly-distilled water (100 mL) with son-
ication, which led to aggregation of receptor 1 and disper-
sion of nanoaggregates O1. Various solvent/water systems
were tried for nanoaggregation; the requisite size was ob-
tained with water/DMF (99/1, v/v). The formation of O1
was confirmed by dynamic light scattering (DLS) and
TEM, which showed a narrow size distribution around (1:99, v/v) and receptor 1 in DMF.
Figure 2. Emission profile of nanoaggregate O1 in DMF/water
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served differences are in accordance with aggregation-in- coordination around Cu(1) is trigonal-bipyramidal with
duced emission.[23,24]
ligation by three donor nitrogen atoms of 1 and two mono-
dentate nitrate ions. The other two copper ions, Cu(2) and
Cu(3), have square-pyramidal geometries. The five coordi-
nation sites of Cu(2) are filled by three oxygen and one
nitrogen atoms of ligand 1 and one oxygen atom of a coor-
dinated DMF ligand. The Cu(3) center has similar coordi-
nation to Cu(2), but here the fifth coordination site is occu-
pied by a coordinated water molecule. Selected bond
lengths and angles around the metal centers are listed in
Table S2.
Fluorescent Recognition of Cu2+
The binding ability of O1 with different metal ions was
tested. Fluorometric analysis of various metal ions (Li+,
Na+, K+, Cs+, Mg2+, Ca2+, Sr2+, Ba2+, Al3+, Cr3+, Mn2+
,
Fe3+, Co3+, Cu2+, Zn2+, Ag+, Cd2+, Pb2+, Hg2+; 50 μm
each) as their nitrate salts revealed that O1 (10 μm) can bind
Cu2+ ions selectively with fluorescence turn-off behavior
(Figure S5). To authenticate O1 as potential sensor for cop-
per ions, quantitative titration was performed by addition
of small aliquots of copper nitrate solution to a solution of
O1, which resulted in uniform quenching of fluorescence
intensity with good linearity in the range 0–70 μm, with a
lower detection limit of 7.9 nm, calculated by the 3σ
method.[25] The fluorescence quenching can be attributed to
complexation of O1 and Cu2+ in aqueous medium (Fig-
ure S6). Moreover, this quenching activity could be ex-
plained partly by considering the paramagnetic nature of
copper ions and partly by coordination of Cu2+ with donor
atoms of 1, which inhibits the charge-transfer process. The
structure of the complex formed between receptor 1 and
copper nitrate was fully characterized by single-crystal
XRD. To further authenticate the exclusive binding of cop-
per ion with the receptor, competitive binding was per-
formed (Figure S7), which revealed that that copper binds
exclusively with receptor 1 without any interference from
other metal ions.
Figure 4. Packing diagram of the copper complex viewed down the
a-axis.
Structure Description
The copper complex of 1 crystallizes in the triclinic crys-
tal system with space group P1. The asymmetric unit
consists of one molecule of the complex and three DMF
molecules as solvent of crystallization. The ORTEP with
atom-numbering scheme is shown in Figure 3.
When the packing of the complex is viewed down the a-
axis (Figure 4), a layered arrangement can be seen. These
layers are formed by 1D chains of the complex. The vacant
spaces between the 1D chains are filled by solvent mol-
ecules of crystallization. These solvent molecules interact
with each other and the 1D chains through extensive
hydrogen bonding (i.e., O–H···O and C–H···O/N hydrogen
bonds). The hydrogen-bonding parameters are listed in
Table S3. No other significant π–π stacking or C–H···π in-
teractions were observed.
¯
Recognition Study with BAs
The binding selectivity of O1·Cu2+ toward eight impor-
tant BAs (spermine, spermidine, tyramine, 2-phenylethyl-
amine, histamine, 1,2-diaminopropane, 1,4-diaminobutane,
and 1,5-diaminopentane; 100 µm each) in aqueous medium
was determined by UV/Vis spectrophotometry. The absorp-
tion spectrum exhibited a significant decrease in absorbance
at 397 nm and the appearance of new peak at 551 nm in
Figure 3. ORTEP of the copper complex of 1 with 40% probability the presence of spermine, and had clear isosbestic point at
thermal ellipsoids and atom-numbering scheme (solvent molecules
of crystallization are omitted for clarity).
439 nm during the titration experiment (Figure 5, a and b).
Whereas minor changes were produced by the other BAs,
The complex is a 1D coordination polymer in which tris- the change in absorption behavior due to spermine resulted
CuII units are repeated along the bc plane (Figure 4). The in a color change of the O1·Cu2+ solution from yellow to
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blue, which can be used for naked-eye detection of spermine
with O1·Cu2+ solution (Figure 6). The interaction of
spermine and change in color of the solution of O1·Cu2+
can be explained on the basis that complexation of the cop-
per ion with the of Schiff-base nitrogen atom[26] results in
its characteristic peak at 397 nm, while its decomplexation
on addition of spermine leads to disappearance of the peak,
and complexation of O1 with spermine leads to appearance
of a new peak at 551 nm.
Figure 6. Change in the color of O1·Cu2+ solution on addition of
100 μm BA in aqueous medium. (A1) O1·Cu2+ only, (A2) O1·Cu2+
+ spermine, (A3) O1·Cu2+ + spermidine, (A4) O1·Cu2+ + tyramine,
(B1) O1·Cu2+ + 2-phenylethylamine, (B2) O1·Cu2+ + histamine,
(B3) O1·Cu2+ + 1,2-diaminopropane, (B4) O1·Cu2+ + 1,4-diamino-
butane, (C1) O1·Cu2+ + 1,5-diaminopentane.
spermine was recorded. Response-time studies were per-
formed with additions of varying concentrations of sperm-
ine (0.2, 0.6, 1.0, and 1.4 mm) and the mixtures observed as
a function of time. The interaction occurred within the first
3 min, and afterwards no change in absorption profile was
observed up to 8 min (Figure 7).
Figure 7. Response-time plot of O1·Cu2+ and spermine at varying
concentrations of spermine (0.2, 0.6, 1.0, and 1.4 mm) in DMF/
water (1/99, v/v) solvent system (λmax = 551 nm).
Figure 5. (a) Change in the UV/Vis absorption profile of O1·Cu2+
complex in the presence of different BAs (spermine, spermidine,
tyramine, 2-phenylethylamine, histamine, 1,2-diaminopropane, 1,4-
diaminobutane, and 1,5-diaminopentane; 100 μm each). (b) Change
in the UV/Vis absorption profile of O1·Cu2+ complex with increas-
ing concentration of spermine in the range 0–100 μm in aqueous
medium. Inset: plot of absorbance as a function of the concentra-
tion of spermine in the range 0–1.6ϫ10–6 m at λmax = 551 nm.
Real-Sample Analysis
To test the applicability of the complex in real-time
analysis, artificial samples with known concentrations of
spermine were prepared. The prepared samples were
screened with the proposed sensor (Table 1).
Changes in the absorption intensity at 551 nm were lin-
ear with spermine concentration in the range of 0–
1.6ϫ10–6 m with a detection limit[25] for spermine of
7.62 nm. Additionally, O1·Cu2+ was found to be stable in
aqueous environments in the pH range of 6–11. No sub-
stantial effect of ionic concentration on the profile of
O1·Cu2+ was observed on successive addition of perchlo-
rate salt (0–100 equiv.), which is proof of its potential under
physiological conditions (Figures S8 and S9). To check its
use as a real-time tool for determination of spermine, the
Table 1. Real-sample analysis of artificially prepared samples of
spermine and percentage recoveries.
Sample
Concentration
added [μm]
Concentration
Recovery
[%]
of spermine[a] [μm]
1
2
3
1
1.5
2
0.95Ϯ0.02
1.47Ϯ0.01
1.96Ϯ0.05
95
98
98
time dependence of the interaction between O1·Cu2+ and [a] Mean of three determinations.
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crystallographic parameters, final R values, and refinement details
are provided in Table S1. CCDC 1055494 contains the supplemen-
tary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
It is evident from Table 1 that the proposed sensor can
determine spermine in solution with high accuracy and a
percentage recovery of more than 95% in all samples.
Synthesis of Nanoaggregates: Organic nanoparticles were obtained
by a single-step reprecipitation method. Working solutions of vari-
ous concentrations were prepared by dissolving receptor 1 in DMF.
The working solutions (0.5 mL) were used for formation of organic
nanoparticles by slow injection into water (100 mL) with a microsy-
ringe under sonication with continuous analysis of particle size by
a DLS probe. Of the several concentrations used, the best-sized
organic nanoparticles were formed at a concentration of 1 mm in
DMF (1 mL). The thus-obtained organic nanoparticles (O1) were
sonicated for a further 5 min while keeping the temperature of the
solution at 25Ϯ10 °C. Concentrations higher than the optimized
concentration led to settling of the prepared organic nanoparticles
due to agglomeration or large organic nanoparticles, even with con-
tinuous sonication. At concentrations lower than the optimum con-
centration, neither organic nanoparticles nor precipitates were
formed.
Conclusions
Organic nanoaggregates were developed for selective
chemosensing of spermine in aqueous medium. Contribut-
ing factors to the selective chemosensing of spermine are
the weakly fluorescent complex of O1·Cu2+ with spermine,
which induced changes in the color of the complex, and
the UV/Vis spectral profile of O1·Cu2+. Single-crystal XRD
confirmed the interactions between binding sites of 1 and
Cu2+. Selective determination of spermine was achieved
with a solution of O1·Cu2+, which had a detection limit of
7.62 nm in the concentration range of 0–1.6ϫ10–6 m.
Experimental Section
Recognition Studies: UV/Vis absorption and fluorometric spectral
profiles were recorded at 25Ϯ1 °C. The solutions were shaken suf-
ficiently and sonicated before recording the spectrum. The binding
behavior of O1 was first studied for various metal ions, and then
the complex of O2 with Cu2+ was used as a sensor by adding vari-
ous BAs (100 μm) to solutions of O1 (5 mL) in volumetric flasks.
Before recording the spectra, the volumetric flasks were allowed to
stand for 30 min. Titrations of O1·Cu2+ were performed by adding
a solution of spermine to volumetric flasks containing a solution
of O1·Cu2+ in aqueous medium. To determine the effect of ionic
strength, the spectra were recorded at different concentrations of
tetrabutylammonium perchlorate (0–100 equiv.). pH titrations were
performed to explore the effect of pH on the recognition behavior
by varying the acidity and basicity of the solution.
General Information: All chemicals used were of analytical grade
and were purchased from Sigma-Aldrich Co. 1H and 13C NMR
spectra were recorded with a JNM-ECS400 (JEOL) instrument op-
1
erating at 400 MHz for H and 100 MHz for 13C. IR spectra were
recorded with a Bruker Tensor 27 spectrometer on compounds in
the solid state as KBr disks or as neat samples. CHN analysis was
performed with a Flash EA 1112 elemental analyzer. UV/Vis spec-
tral profiles were recorded with a Spectroscan 30. The particle size
of nanoaggregates was determined by DLS with the external probe
of a Metrohm Microtrac Ultra Nanotrac particle size analyzer.
Fluorescence data were recorded with an RF-5301 PC spectrofluor-
ometer, and mass spectra were recorded with a Waters Micromass
Q-Tof mass spectrometer.
Synthesis of Receptor 1: Dipicolinic acid hydrazide (0.195 g,
1 mmol) and salicylaldehyde (0.244 g, 2.0 mmol) were heated to re-
flux in ethanol (50 mL). After 6 h, a yellow precipitate was ob-
tained. The precipitate was collected by filtration and washed with
Real-Sample Analysis: Three different samples with known concen-
trations of spermine were prepared to test the real-time application
of the proposed sensor.
1
ethanol, yield 72%. H NMR (400 MHz, CDCl3 + [D6]DMSO): δ
= 6.96–6.98 (m, 4 H, Ar), 7.34 (t, 2 H, Ar), 7.70 (d, 2 H, Ar), 8.29–
8.33 (m, 1 H, Ar), 8.37–8.39 (d, 2 H, Ar), 8.94 (s, 2 H,
N=CH),11.07 (s, 2 H, OH), 12.43 (s, 2 H, NH) ppm. 13C NMR
(100 MHz, CDCl3 + [D6]DMSO): δ = 116.5, 118.9, 119.6, 125.7,
Acknowledgments
This work was supported with research grant provided by Council
of Scientific and Industrial Research (CSIR), New Delhi [project
number 02(0216)/14/EMR-II] through project sanctioned to Dr.
Navneet Kaur and Ms. Shweta Chopra is thankful to University
Grants Commission (UGC), New Delhi for fellowships.
129.0, 131.8, 140.0, 148.0, 149.2, 157.5, 159.4 ppm. IR (KBr): ν =
˜
1682 (s), 2924 cm–1 (s). ESI-MS: m/z = 402.1 [M – H]+.
C21H17N5O4 (403.4): calcd. C 62.53, H 4.25, N 17.36; found C
62.48, H 4.31, N 17.41.
X-ray Crystallography: The diffraction data for single-crystal X-ray
structure analysis of the copper complex were collected at 293 K
with a Bruker X8 APEX II KAPPA CCD diffractometer by using
graphite-monochromatized Mo-Kα radiation (λ = 0.71073 Å). The
crystal was kept at 50 mm from the CCD, and measurements of
diffraction spots were obtained with a counting time of 10 s. The
APEX II program suite (Bruker, 2007) was employed for data re-
duction and multiscan absorption correction. The structure was
solved by direct methods with the SIR97 program,[27] and full-ma-
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Published Online: August 18, 2015
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