Ratiometric and colorimetric "naked eye" selective detection of CN- ions by electron deficient Ni(II) porphyrins and their reversibility studies

Article abstract of DOI:10.1039/c5dt00937e

Highly electron deficient β-substituted Ni(II) porphyrins (1-5) were synthesized and utilized as novel sensors for selective rapid visual detection of CN^- ions. This article describes the single crystal X-ray structures, electronic spectral and electrochemical redox properties of these sensors. The ratiometric and colorimetric responses of these porphyrins were monitored by the change in optical absorption spectra. These sensors were found to be highly selective for cyanide ions with extremely high binding constants (10¹⁶-10⁸ M^-2) through axial ligation of CN^- ions and are able to detect <0.11 ppm of CN^- ions. 1-5 were recovered from 1-5·2CN^- adducts by acid treatment and reused without loss of sensing ability. CN^- binding strongly perturbs the redox properties of the parent porphyrin π-system. The applicability of 1-5 as practical visible colorimetric test kits for CN^- ions in aqueous and non-aqueous media has also been explored. The mode of binding was confirmed by single crystal X-ray, spectroscopic studies and DFT calculations.

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ARTICLE
Ratiometric Colorimetric “Naked eye” Selective
Detection of CN‒ ions by Electron Deficient Ni(II)
Porphyrins and their Reversibility Studies
Cite this: DOI: 10.1039/x0xx00000x
Ravi Kumar, Nivedita Chaudhri and Muniappan Sankar*
Received 00th January 2012,
Accepted 00th January 2012
Highly electron deficient β-substituted Ni(II) porphyrins (1-5) were synthesized and utilized as novel
sensors for selective rapid visual detection of CN‒ ions. This article describes the single crystal X-ray
structures, electronic spectral and electrochemical redox properties of these sensors. The ratiometric
and colorimetric responses of these porphyrins were monitored by change in optical absorption spectra.
These sensors were found to be highly selective for cyanide ions with extremely high binding constants
DOI: 10.1039/x0xx00000x
www.rsc.org/
(1016- 108 M-2) through axial ligation of CN‒ ions and are able to detect < 0.11 ppm of CN‒ ions.
recovered from
2CN‒ adduct by acid treatment and reused without loss of their sensing ability. CN‒
binding strongly perturbs the redox properties of parent porphyrin π-system. The applicability of as
1-5 were
1-5ꢀ
1-5
a practical visible colorimetric test kits for CN‒ ions in an aqueous and non-aqueous media have also
been explored. The mode of binding was confirmed by single crystal X-ray, spectroscopic studies and
DFT calculations.
sensors, which allows “naked eye” detection of CN‒ ions by
means of colour change.8ꢀ10 Various approaches to the novel
Introduction
The design of anion receptors with high selectivity has been the
subject of intensive research due to their potential applications
in environmental, clinical, chemical and biological sectors.1ꢀ3
Cyanide is one among the toxic anions; even as little as 0.5 ꢀ
3.5 mg cyanide per kg of body weight is lethal to humans
where it binds with cytochrome c inside the cells and interferes
the mitochondrial electron transport chain, thus inhibiting
cellular respiration causing hypoxia.4 Cyanide ions could be
absorbed through the lungs, skin, and gastrointestinal tract
leading to vomiting, convulsion, loss of consciousness, and
eventual death.5 Despite their toxicity, their outstanding
applications in various industrial processes6 including
electroplating, metallurgy, heap leaching of gold ore, polymer
synthesis, steel manufacturing and as raw materials for
synthetic fibers, resins and herbicides are inevitable, which
raises the risk for accidental or intentional release of cyanide
ions into environment as a toxic contaminant.6
colorimetric chemosensors for anions are chemodosimetric
method, displacement assay, nucleophilic addition to carbonyl
group or activated carbonꢀcarbon double bond, hostꢀguest
interactions through hydrogen bonding, anion induced
deprotonation etc.8ꢀ10 However, they do suffer with one or more
limitations such as poor selectivity especially in the presence of
fluoride or acetate ions. Most of the chemodosimeters are
irreversible, others require specific conditions, such as high
temperature or basic media, only works in an organic media,
complicated multiꢀstep synthesis.10 All these drawbacks
challenge us to fabricate
a unique reversible, specific,
colorimetric optical probe capable of ‘naked eye detection’ of
CN‒ ions with extremely low detection limits.
Porphyrinꢀbased receptors for anions have been constructed
through the derivatization of mesoꢀpositions11 having
appropriate binding pockets whereas only a few reports on βꢀ
functionalized porphyrins12 due to their synthetic difficulties.
Metalloporphyrins have been utilized for the detection of CNꢀ
ions due to intrinsic affinity of cyanide for many metals such as
zinc,7f,13aꢀd rhodium,13e and copper13f coordinated to porphyrins.
Recently, cyanide sensing through chemodosimetric method by
a new calix[4]pyrrole derivative,14a Pdꢀcalixphyrin,14b cobalt
corrins,14cꢀg and subphthalocyanine dye14h have been reported in
the literature. In general, square planar Ni(II) porphyrins
exhibited very weak axial ligation and extremely low binding
constants (β2 = 0.3 ꢀ 38 Mꢀ2) with nitrogenous bases.15 Herein,
All the above aspects demand an efficient sensing system to
monitor cyanide concentration from contaminant sources. A
variety of techniques have been developed for the determination
of cyanide, including ion chromatography, voltammetry,
amperometry, fluorometry, ion selective electrode and
potentiometry.7 But the primary disadvantage of these
techniques is the use of timeꢀconsuming procedures and
sophisticated instrumentation. Nowadays, the most attractive
approach focuses on highly selective colorimetric cyanide ion
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we are reporting an easy, rapid, reusable, selective and sensitive in Scheme 1 in the electronic supplementary information (ESI).
‘naked eye’ colorimetric cyanide ion sensing by highly electron These porphyrins were characterized by various spectroscopic
deficient planar and nonplanar βꢀsubstituted Ni(II) porphyrins techniques, elemental and single crystal XRD analyses.
(1ꢀ5
, Chart 1) with extremely high binding constants (β2 = 1016
ꢀ 108 Mꢀ2) through coordinative interactions for the first time in
porphyrin chemistry.
The representative absorption spectra of
in CH2Cl2 at 298 K (Fig. S1 in ESI). Table S1 in ESI lists the
electronic absorption spectral data of 1ꢀ5 in CH2Cl2.
10 nm red shift in the Soret band as compared to
1 and 3ꢀ5 were shown
3
1
exhibited
which is
attributed to the electron donating effect of methoxy
substituents. 1ꢀ3 exhibited considerable gain in the intensity of
the longest wavelength Qx(0,0) band relative to the Qx(1,0)
band due to extensive stabilization of a1u relative to a2u by
means of βꢀcyano substitution which leads to increased
transition probability of a2u to eg(π*) relative to a1u to eg(π*).16 4
has shown redꢀshifted optical absorption spectra (
Δλ = 9 ꢀ13
nm) as compared to due to electron withdrawing nature of
5
nitro group and increased nonplanarity induced by mixed
1
substitution. In H NMR spectra of 1ꢀ3, the βꢀpyrrole protons
exhibited a singlet at 8.74 ꢀ 8.81 ppm indicating the antipodal
positions of βꢀcyano groups (Figs. S2ꢀS4 in ESI).
Chart 1 Molecular structures of β-substituted Ni(II) porphyrins (1-5).
The Xꢀray quality single crystals of
obtained by direct diffusion of hexane into CHCl3/pyridine and
pure CHCl3 solutions of and , respectively. The single
crystals of were obtained by direct diffusion of hexane into
saturated toluene solution of and . The crystallographic data
1(Pyridine)2 and 3 were
1
3
4ꢀ5
4
5
of these porphyrins are listed in Table S2 in ESI. ORTEP top
and side views of these porphyrins are shown in Figs. 1 and S5
in ESI. The selected bond lengths and bond angles are given in
Table S3 in ESI. Notably,
conformation of porphyrin macrocyle (ꢁCβ = 0.06 ꢀ 0.07 Å and
ꢁ24 = 0.05 ꢀ 0.06 Å) whereas exhibited nonplanar
1 and 3 have shown planar
Fig. 1 The ORTEP diagrams showing (a) top and (b) side views of 1 with axial
coordination of pyridine molecules. In side view, the β-substituents and meso-
phenyl groups are not shown for clarity.
4ꢀ5
conformations with the displacements of βꢀpyrrole carbons,
ꢁCβ = ±0.9 Å and the 24 atoms core, ꢁ24 = ±0.53 Å, which is
attributed to the steric hindrance between βꢀsubstituents and
Results and Discussion
mesoꢀphenyl groups.17
1 and 3 exhibited longer CβʹꢀCβʹ bond
Synthesis and characterization
distance (1.37 Å) for βꢀpyrrole carbons having CN substituents
as compared to antipodal βꢀpyrrole carbons bearing no
substitution (CβꢀCβ = 1.32 Å) which is further supported by
increment in CβʹꢀCαʹꢀCm angle (125º) with concomitant
Ni(II) βꢀtetracyanoꢀmesoꢀtetraphenylporphyrins
prepared by nucleophilic substitution at βꢀpyrrole positions of
the tetrabromoporphyrins using modified literature methods16 as
(1ꢀ3) were
decrement in NʹꢀCαʹꢀCm (125.7º). Similarly,
4 and 5 exhibited
longer CβꢀCβ distance (1.35 Å) with increment in CβꢀCαꢀCm
Scheme 1 Synthetic route for the preparation of 1-3 via nucleophilic substitution
at β-pyrrole position.
shown in Scheme 1 and Ni(II) perhaloporphyrins (4ꢀ5) were
Fig. 2 Cyclic Voltammograms of 1-3 (a) and 4-5 (b) in CH2Cl2 containing 0.1 M
synthesized by direct substitution at βꢀpyrrole position of TBAPF6 as the supporting electrolyte using Ag/AgCl as reference electrode.
macrocyclic ring according to reported procedure12b as shown
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angle (~127º) with concomitant decrement in NꢀCαꢀCm (~124º), the form of TBA salts. Importantly, an additional remarkable
indicating severe steric repulsion between βꢀsubstituents which feature of these sensors was pinpointed, as their ability to
leads to nonplanar conformation of porphyrin macrocycle as specifically recognize cyanide in an admixture of anions.
compared planar porphyrins.17 The NꢀNiꢀN bond angles are have shown redꢀshifted UVꢀVisible spectra with colorimetric
exactly 180º for planar porphyrins ( and ) whereas these ‘naked eye’ detection of cyanide ions (green to yellow for
angles are deviated (171ꢀ172º) for porphyrins, and due to and reddish brown to green for ) whereas no observable shift
1ꢀ5
1ꢀ5
1
3
1ꢀ3
4
5
4ꢀ5
1
nonplanar conformation. The observed UVꢀVis and H NMR was found with other tested anions as shown in Figs. 3 and S6
spectroscopic data of these Ni(II) porphyrins is in accordance in ESI. 1ꢀ5 were titrated with CN‒ ions in toluene at 298 K and
with obtained single crystal Xꢀray structures.
monitored by UVꢀVis absorption spectroscopy. The broad Soret
of
upon addition of CN‒ ions is due to chargeꢀtransfer
transitions.19 The metal
ꢀorbital energies in metalloporphyrins
can be perturbed by the presence of axial ligands. Herein, the
electron deficient porphyrin πꢀsystem makes Ni(II) metal centre
to bind with highly basic cyanide (pKa = 9.3) ions.
1ꢀ5
To examine the effect of βꢀsusbtituents and nonplanarity of the
macrocyle on electrochemical redox potentials, we have carried
out cyclic voltammetric studies. Cyclic voltammograms of 1ꢀ5
in CH2Cl2 containing 0.1 M TBAPF6 as supporting electrolyte
are shown in Figure 2. The redox data (vs Ag/AgCl) is listed in
d
Table S4 in ESI. 1ꢀ5 exhibited one twoꢀelectron reversible UVꢀVis titration of
1 with cyanide ions is shown in Fig.4. Both
electrochemical oxidation and two successive oneꢀelectron the Soret (35 nm) and Q bands (77 nm) are shifted to longer
reductions. The first oxidation potentials of 1ꢀ3 exhibit wavelengths upon increasing the concentration of TABCN
300−480 mV anodic shift in comparison to NiTPP suggesting indicating the axial coordination of CN‒ ions to
1. For 1, wellꢀ
that each of the βꢀcyano group shifts ~130 mV anodically anchored isosbestic points were observed at 457, 526 and 647
which is due to the strong electronꢀwithdrawing nature of the βꢀ nm during the course of the cyanide binding experiment.
cyano substituents.15b,18 Further, the anodic shift in first Stoichiometry for
1
was established using Job’s plot (Fig. 4
oxidation of
4 and 5 as compared to NiTPP is ascribed to the inset) which has a maxima at a cyanide molar ratio of ~ 0.65
combined effect of electronꢀwithdrawing nature of nitro and indicating that
1
is capable of binding with 2 equivalents of
1
•2CN− adduct.
chloro substituents as well as the highly nonplanar CN‒ ions to form
conformation of macrocycle. The cathodic shift (80ꢀ150 mV) in
Similar UVꢀVis spectral profiles were observed for
2
2ꢀ3
ꢀ
5
with
was
first ring oxidation potentials of
2
ꢀ
3
in comparison to
ascribed to electron donating butyl and methoxy substituents
present at the mesoꢀphenyl rings of and , respectively. The
1 is
CN‒ ions as shown in Fig. S7 in ESI. Stoichiometry for
t
calculated using Job’s plot (Fig. S7 in ESI). The binding
constants for with cyanide ions were calculated using Hill
equation20 and the corresponding binding parameters are
presented in Table 1. The stoichiometry for and was
2
3
1ꢀ5
observed redox potentials indicate the highly electron deficient
nature of porphyrin πꢀsystem.16,18
4
5
confirmed by Hill plot as shown in insets of Fig. S7 in ESI. The
Hill plot shows a straight line between log[CN‒] and log(Aiꢀ
A0/AfꢀAi) having slope value 2, which indicates 1:2 (porphyrinꢀ
toꢀcyanide) stoichiometry. The magnitude of Hill coefficient (n)
Cyanide Sensing
The anion recognition properties of all synthesized porphyrins
(
1
ꢀ
5
) were studied in toluene with various anions, using UVꢀ
for
1ꢀ3 clearly reflects the extent of cooperativity between
Visible spectroscopy with the addition of the aliquot anion in
supramolecular binding events.3d,11b
Fig. 3 (Top) Colorimetric response of 1 with tested anions in toluene; (b) UV-Vis
(3.33 × 10-6 M) upon addition of excess TBA salts of tested anions in
Fig. 4 UV-visible spectral titrations of 1 (9.35 µM) upon addition of aliquots of
TBACN (0 - 0.03 M) in toluene, inset shows corresponding Job’s plot.
spectra of
toluene at 298 K.
1
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Notably, the plots of the absorbance changes (ꢁA) vs [CNꢀ]
Table 1. Binding constant dataa of Ni(II) porphyrins and their CNꢀ ion
detection limits in toluene at 298 K.
show sigmoidal curves, which indicate that cyanide ions bind to
Porphyrin
β2
r2
n
3.33
3.33
2.68
2
LOD (ppm)
0.108
0.108
0.104
0.062
m
2
2
2
2
2
1
2
3
4
5
3.86×1016
1.95×1016
6.70×1012
1.21×109
7.79×108
0.87
0.92
0.90
0.99
0.97
2
0.103
aWithin the error of ±0.04; n = Hill coefficient; LOD = Limit of detection; m
= Stiochiometry.
Ni(II) cyanoporphyrins (1ꢀ3) exhibited very high binding
constants, β2 (1016 ꢀ 1012 Mꢀ2) owing to their high electron
Fig. 6 (a) sigmoidal curve for 1-3
behaviour. (b) DPV (in V vs Ag/ AgCl) traces recorded for
, [CN-] vs ΔA indicating positive cooperative
(blue) and 1·2CN−(red)
deficient nature as compared to nonplanar perhaloporphyrins,
and
(109 – 108 Mꢀ2) as indicated by their reduction potentials
(Table S5 in ESI). The trend along the series of porphyrins
tracks the β2 values ( ), with the more electron
4
1
in CH2Cl2 containing 0.1 M TBAPF6 with a scan rate of 0.1 V/s at 298 K.
5
1
> 2 > 3 > 4 > 5
Table 2. Electrochemical first ring redox potentials (in mV vs Ag/AgCl)
upon addition of CNꢀ ions to 1ꢀ5 in CH2Cl2 containing 0.1 M TBAPF6 with a
scan rate of 0.1 V/s.
deficient porphyrins displaying larger Hill Coefficients (Table
1). The detection limits (LOD) for CN˗ ions were calculated in
presence of
able to detect as low as ~ 0.11 ppm solution of cyanide ions.
1ꢀ5
in toluene (Table 1).21 These porphyrins are
Porphyrin
Porphyrin (without CN‒)
Porphyrinꢀ2CN‒
1st Ox 1st Red
1st Ox
1st Red
Hence these sensors
cyanide ions.
1ꢀ5 were very selective and sensitive for
1
2
3
4
5
1480
1400
1332
1340
1280
ꢀ392
ꢀ416
ꢀ420
ꢀ630
ꢀ810
1132
1135
1000
820
ꢀ552
ꢀ675
ꢀ612
ꢀ860
ꢀ1102
Interestingly, the most commonly interfering anions especially
basic anions such as fluoride, acetate and dihydrogenphosphate
didn’t show any response with these sensors. The competition
experiments were performed to ascertain the selectivity of
synthesized porphyrins using two equivalents of cyanide ions
and 10 equivalents of interfering anions in toluene. The
783
1ꢀ3 in a cooperative manner as shown in Fig. 6a. Nevertheless,
in order to get further insight into the binding ability of these
representative bar graph observed for
which clearly demonstrate the tolerance of
1
is shown in Fig. 5,
towards these
sensors
1ꢀ5
with CN‒ ions, we have carried out differential
1
pulse voltammetric (DPV) studies of 1ꢀ5 with addition of
cyanide ions (Figs. 6b and S9 in ESI). The addition of cyanide
potentially interfering anions and thus can be used
quantitatively and selectively to detect cyanide ions. The
ions to
1 results a cathodic shift of 250 mV in first oxidation
similar results were observed for
ESI.
2ꢀ5 as shown in Figure S8 in
and 160 mV in first reduction which is expected upon going
from neutral porphyrin to dinegatively charged porphyrin
˗
adduct (1•2CN ). This shift in potential is further in consistent
with rising of HOMO (from DFT studies). Table 2 represents
the electrochemical first ring redox data of
absence of CN‒ ions.
1ꢀ5 in presence and
Reversibility Studies
To acknowledge the range of applicability, the reversibility and
reusability of the sensors are the key events that have to be
determined.22
was treated with 2 equivalents of cyanide ions
in toluene forming
1ꢀ5
1
˗
1
•2CN as visualized by colorimetric change
from green to yellow accompanied by UVꢀvisible spectral
changes as shown in Fig. 7. Switching off the cyanide ion
binding was carried out using TFA. As shown in the Fig.7, the
addition of aliquots of 1 mM solution of TFA in toluene to the
˗
solution containing 1•2CN adduct immediately restored to 1
with colorimetric change from yellow to green.
Fig. 5 Ratiometric absorbance changes (A473/A439) of
1
(1.01×10-5 M) on addition
of 2 equiv of CN- and 10 equiv of other anions. Green bars indicate the blank and To confirm the reusability, the resulting mixture was washed
in presence of other interfering anions, and red bars indicate the addition of CN-
to the interfering anions.
with water and dried over anhydrous Na2SO4. The recovered
was treated with 2 equivalents of CN‒ ions, which showed
1
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DCP)P and NiT(p
ꢀtButꢀPh)PBr4) with CN‒ ions and found no Visible spectral studies) was dried and distilled from sodiumꢀ
spectral changes (Fig. S23 in ESI) observed even with excess of benzophenone mixture.
CN˗ ions which clearly suggests that highly electron deficient
Instrumentation and methods
Optical absorption spectra were recorded on Agilent Cary 100
spectrophotometer using a pair of quartz cells of 10 mm path
1
length. H NMR spectra were recorded on Bruker AVANCE
500 MHz and JEOL ECX 400 MHz spectrometers in CDCl3.
MALDIꢀTOFꢀMS spectra were measured using a Bruker
UltrafleXtremeꢀTN MALDIꢀTOF/TOF spectrometer using
HABA as a matrix and ESI mass spectra were recorded on
Bruker Daltanics microTOF mass spectrometer in positive ion
mode using CH3CN as solvent. The Xꢀray quality single
Scheme 2 Schematic representation of CN‒ ions binding to
1-5 and their
reversibility in presence of trifluroacetic acid (TFA) followed by reusability after
water wash.
crystals of
of hexane into CHCl3/pyridine and pure CHCl3 solutions of
and , respectively. The single crystals of were obtained by
direct diffusion of hexane into saturated toluene solution of
and . Xꢀray quality single crystals of
CN− was obtained by
direct diffusion of ꢀhexane into the CHCl3 solution of
containing small amount of TBACN. Singleꢀcrystal XRD data
of and
CN− were collected on a Bruker ApexꢀII CCD
1(Pyridine)2 and 3 were obtained by direct diffusion
1
Ni(II)ꢀporphyrin metal centre is necessary for CN‒ ion
recognition. Further, it is revealed that the reduction potential
positive than ꢀ0.8 V makes them a suitable candidate for CN‒
ion detection (Fig. S24 and Table S5 in ESI). Based on our
experimental and theoretical studies, we are representing the
plausible mechanism of cyanide ion recognition and their
3
4ꢀ5
4
5
3ꢀ
n
3
1
,
3
ꢀ
5
3ꢀ
reversibility with TFA of 1ꢀ5 in Scheme 2.
diffractometer equipped with a liquid cryostat. The single
crystals obtained were mounted on mounting loops. All
diffraction data were collected using Bruker APEXII
Conclusions
diffractometer at 293
monochromated Mo α (λ = 0.71073 Å) by the ωꢀ2θ scan. The
structures were solved by direct methods by using SIR97 and
SHELXꢀ97.25 In case of , SQUEEZE procedure26
(Py)2 and
was implemented in order to correct electron density
contribution from disordered solvent molecules. The
crystallographic data of these Ni(II) porphyrins are summarized
K
equipped with graphiteꢀ
In summary, we have demonstrated that 1ꢀ5 displays a specific,
colorimetric and ratiometric response to cyanide ions over the
other coexisting anions in toluene. Highly electron deficient
planar porphyrins, 1ꢀ3 exhibit very high binding constants β2 (~
1016 ꢀ 1012 Mꢀ2) and bind with 2 equivalent of cyanide ions in a
highly cooperative fashion as compared to nonplanar
K
1
3
porphyrins
4
and
5
. Cyanide binding also perturbs the redox
2CN− adduct is
in Table S2 in ESI. CCDCꢀ1043611 (
1
(pyridine)2), 1043609
CN‒) contain
chemistry and each of the Ni(II) porphyrin
ꢀ
(
3
), 1043615 ( ), 1044025 ( ) and 1043610 (1ꢀ
4
5
much more easily oxidized than the parent porphyrin. These
porphyrins are being able to detect (LOD) < 0.11 ppm of
cyanide ions. The reversibility studies revealed that the sensors
the crystallographic supplementary data. The elemental
analyses were carried out using Elementarvario EL III
instrument. The ground state geometry optimization of
1 and 4
1ꢀ5 can be recoverable and reusable for cyanide detection
(with and without cyanide ions) in gas phase was carried out by
DFT calculations using B3LYP functional with LANL2DZ
basis set. Electrochemical measurements were carried out using
CH instrument (CH 620E). A three electrode assembly was
used consisted of a platinum button working electrode (2 mm
diameter), Ag/AgCl as a reference electrode and a platinum
without losing their sensing ability.
Experimental section
Materials
Pyrrole, benzaldehyde, Ni(OAc)2•4H2O, TFA, pyridine and
Na2SO4 were purchased from HiMedia, India and used as
wire as a counter electrode. The concentration of
1ꢀ5 was
maintained 1 mM. All measurements were performed in triple
̴
received. 4ꢀAnisaldehyde was purchased from SDFCL and pꢀ
distilled CH2Cl2 containing 0.1 M TBAPF6 as supporting
electrolyte which was degassed by Argon gas purging. For UVꢀ
Vis titrations, the concentrations of 1ꢀ5 were kept in the range
tBuꢀbenzaldehyde and copper(I) cyanide were purchased from
Alfa Aesar and used as received. All solvents employed in the
present work were of analytical grade and distilled or dried
before use. Silica gel (100 ꢀ 200 mesh) was purchased from
Rankem and used as received. TBAPF6 was recrystallised twice
with ethanol and dried at 50 ºC under vacuum for 3 days. The
tetrabutylammonium salts (TBAX, X = CN‒, F‒, Cl‒, Br‒, I‒,
of 9 ꢀ 13 µM throughout the experiments whereas the stock
solution of anions was maintained in between 4 to 8 mM as per
their need. The temperature inside the cell was 298±0.2 K. The
association constants (β2) and stoichiometry for anion binding
were calculated using Hill equation.20 The limit of detection
(LOD) values has been calculated by using the intercept of
plotted graph between (AminꢀA)/(AminꢀAmax) and log[Aꢀ].24 For
the practical utility of these sensors, the test strips were
‒
‒
‒
‒
‒
HSO4 ,OAc‒, H2PO4 , ClO4 , PF6 and NO3 ) were purchased
from Alfa Aesar and used as received. Dry CH2Cl2 for CV
studies was distilled thrice from CaH2 and the toluene (for UVꢀ
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prepared by cutting the Whatman filter paper (grade 1) and Research (CSIR), India, respectively for senior research
dipped in 1 mM toluene solution of for few seconds and fellowship.
dried. These test strips were dipped in different anion solutions
for 1ꢀ2 seconds. The colour change from green to yellow (
and brown to green ( ) were observed only with cyanide ions.
1ꢀ5
Notes and references
1ꢀ3)
4ꢀ5
Ravi Kumar, Nivedita Chaudhri and Muniappan Sankar*
The similar results were observed when these test strips were
exposed to neutral aqueous solution of tested anions.
Department of Chemistry, Indian Institute of Technology Roorkee,
Roorkee ꢀ 2476667, Uttrakhand, India
.
Eꢀmail: sankafcy@iitr.ac.in; Tel: +91ꢀ1332ꢀ28ꢀ4753; Fax: +91ꢀ1332ꢀ27ꢀ
General procedure for the Synthesis of Nickel(II) complexes of
βꢀtetracyanoꢀmesoꢀtetraphenylporphyrins (1ꢀ3):
3560.
1
†Electronic Supplementary Information (ESI) available: UVꢀVis and H
NiTPPBr4 (0.5 g, 0.507mmol) and copper(I)cyanide (1.816 g,
20.27mmol) were taken in 250 mL two neck RB. To this, 50
mL of pyridine was added and heated at 90 ºC for 24 hours
under argon atmosphere. At the end of this period, the reaction
mixture was cooled and filtered through Gꢀ4 sintered crucible
to remove excess copper cyanide. Solvent was removed under
vacuum and then the crude product was loaded on silica column
and purified using CHCl3 as eluent. The similar procedure was
NMR spectra, crystallographic and electrochemical redox data, UVꢀVis
titrations of
DPV traces in presence and absence of cyanide ions, DFT optimized
structures and their frontier molecular orbitals (FMOs) of
2CN‒
and CCDCꢀ1043609, 1043610, 1043611, 1043615 and 1044025.
2CN‒
See DOI: 10.1039/b000000x/
1ꢀ5 for cyanide ion sensing and their reversibility studies,
1, 4, 1ꢀ
4ꢀ
.
1
(a) N. H. Evans and P. D. Beer, Angew. Chem. Int. Ed., 2014, 53
,
,
employed for the preparation of
~ 40% in all cases ( ).
2ꢀ3. The yield was found to be
11716; (b) D. S. Kim and J. L. Sessler, Chem. Soc. Rev., 2015, 44
1ꢀ3
532; (c) V. V. Roznyatovskiy, C.ꢀH. Lee and J. L. Sessler, Chem.
Soc. Rev., 2013, 42, 1921; (d) P. D. Beer and P. A. Gale, Angew.
Chem. Int. Ed., 2001, 40, 486; (e) P. A. Gale and C. Caltagirone,
Chem. Soc. Rev., 2015 (DOI: 10.1039/c4cs00179f); (f) M. H Lee, J.
S. Kim and J. L. Sessler, Chem. Soc. Rev., 2015 (DOI:
10.1039/c4cs00280f); (h) J. W. Steed and J. L. Atwood,
Supramolecular Chemistry, Wiley, New York, 2000, pp. 198; (g) Y.
Kubo, M. Yamamoto, M. Ikeda, M. Takeuchi, S. Shinkai, S.
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(b) A. Bianchi, K. BowmanꢀJames and E. GarciaꢀEspana,
Supramolecular Chemistry of Anions, Ed., WileyꢀVCH, New York,
1997; (c) J. L. Sessler, P. A. Gale and W.ꢀS. Cho, Anion Receptor
Chemistry, RSC Publishing, Cambridge, UK, 2006; (d) L. C. Gilday,
N. G. White and P. D. Beer, Dalton Trans., 2012, 41, 7092.
NiTPP(CN)4 (1): UV/Vis (CH2Cl2): λmax (nm) (logε) 440
1
(5.10), 630(4.50). H NMR in CDCl3:
δ (ppm) 8.77 (s, 4H, βꢀ
pyrroleꢀH), 7.89ꢀ7.83 (m, 12H, mesoꢀoꢀ and mꢀphenylꢀH), 7.75ꢀ
7.71 (m, 8H, mesoꢀmꢀ and pꢀphenylꢀH). ESIꢀMS (m/z): found
771.9 [M+H]+, calcd. 771.2. Anal. Calcd for C48H24N8Ni: C,
74.73; H, 3.14; N, 14.53%. Found: C, 74.52; H, 3.39; N,
14.65%.
NiT(
445 (5.13), 632(4.47).1H NMR in CDCl3:
ꢀpyrroleꢀH), 7.77ꢀ7.70 (m, 16H, mesoꢀoꢀ and mꢀphenylꢀH),
p
ꢀtButꢀPh)P(CN)4 (2): UV/Vis (CH2Cl2): λmax (nm) (logε)
(ppm) 8.81 (s, 4H,
2
3
4
5
δ
β
t
1.54 (s, 36H, CH3 of But). ESIꢀMS (m/z): found 1020.7
[M+H
Na]+, calcd. 1020.0. Anal. Calcd for C64H56N8Ni: C,
ꢀ
77.19; H, 5.67; N, 11.25%. Found: C, 77.31; H, 5.50; N,
11.43%.
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(a) K.W. Kulig, Cyanide Toxicity, U.S. Department of Health and
Human Services, Atlanta, GA, 1991; (b) Z. Xu, X. Chen, H. N. Kim
and J. Yoon, Chem. Soc. Rev., 2010, 39, 127; (c) F. Wang, L. Wang,
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NiT(
(logε) 450 (5.07), 636(4.54). H NMR in CDCl3:
(s, 4H, ꢀpyrroleꢀH), 7.75 (d, 8H, = 8.5 Hz, mesoꢀoꢀphenylꢀ
H), 7.24 (d, 8H, = 8.5 Hz, mesoꢀmꢀphenylꢀH), 4.04 (s, 12H
OCH3 mesoꢀmꢀphenylꢀH). MALDIꢀTOFꢀMS (m/z): found
892.6 calcd. 892.6. Anal. Calcd for
[M+H]+,
C52H32N8O4Ni 0.5H2O: C, 69.35; H, 3.69; N, 12.44%. Found:
pꢀOMeꢀPh)P(CN)4 (3): UV/Vis (CH2Cl2): λmax (nm)
1
δ
(ppm) 8.74
β
J
J
,
ꢀ
C, 69.40; H, 3.78; N, 12.55%.
Acknowledgements
We are grateful for the financial support provided by Council of
Scientific and Industrial Research (01(2694)/12/EMRꢀII),
Science and Engineering Research Board (SB/FT/CSꢀ
015/2012) and Board of Research in Nuclear Science
(2012/37C/61/BRNS/2776). We sincerely thank Dr. Natarajan
Sampath, Department of Chemistry, SASTRA University,
Thanjavur, India for his kind help related to Xꢀray structure
analysis. RK and NC thank Ministry of Human Resource
development (MHRD) and Council of Scientific and Industrial
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DOI: 10.1039/C5DT00937E
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