Synthesis, X-ray, 1H-NMR and DFT analysis of the phthalimide–hydrazone probes as selective anion sensor

Article abstract of DOI:10.1080/10610278.2016.1264074

Two simple phthalimide–hydrazone probes with nitro groups were synthesised and characterised by NMR, FT-IR, HR-MS and single crystal X-ray crystallography. The synthesised receptors were evaluated for application in anion sensing. The receptors displayed strong, sensitive and selective colouration in the presence of cyanide ions by forming a stable complex with cyanide ion. The use of variable nitro groups helped in the elucidation of the mechanism of the complex formation. The ¹H NMR spectroscopy was used to support the mechanism of the complex formation. DFT methods were used to understand the stability of the complex with respect to the reactant. The absorbance data were also compared with the TD-DFT calculated excitation parameters. The experimental results were found to correlate well with the theoretical data.

Full text of DOI:10.1080/10610278.2016.1264074

Supramolecular Chemistry
ISSN: 1061-0278 (Print) 1029-0478 (Online) Journal homepage: http://www.tandfonline.com/loi/gsch20
Synthesis, X-ray, 1H-NMR and DFT analysis of the
phthalimide–hydrazone probes as selective anion
sensor
Priya Ranjan Sahoo, Kunal Prakash, Pragati Mishra, Palak Agarwal, Nikita
Gupta & Satish Kumar
To cite this article: Priya Ranjan Sahoo, Kunal Prakash, Pragati Mishra, Palak Agarwal,
Nikita Gupta & Satish Kumar (2016): Synthesis, X-ray, 1H-NMR and DFT analysis of the
phthalimide–hydrazone probes as selective anion sensor, Supramolecular Chemistry
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Date: 03 January 2017, At: 05:25

Supramolecular chemiStry, 2016
http://dx.doi.org/10.1080/10610278.2016.1264074
Synthesis, X-ray, 1H-NMR and DFT analysis of the phthalimide–hydrazone probes
as selective anion sensor
Priya Ranjan Sahoo, Kunal Prakash, Pragati Mishra, Palak Agarwal, Nikita Gupta and Satish Kumar
Department of chemistry, St. Stephen’s college, university enclave, Delhi, india
ABSTRACT
ARTICLE HISTORY
received 16 September 2016
accepted 20 November 2016
Two simple phthalimide–hydrazone probes with nitro groups were synthesised and characterised
by NMR, FT-IR, HR-MS and single crystal X-ray crystallography. The synthesised receptors were
evaluated for application in anion sensing. The receptors displayed strong, sensitive and selective
colouration in the presence of cyanide ions by forming a stable complex with cyanide ion. The use
of variable nitro groups helped in the elucidation of the mechanism of the complex formation. The
1H NMR spectroscopy was used to support the mechanism of the complex formation. DFT methods
were used to understand the stability of the complex with respect to the reactant. The absorbance
data were also compared with the TD-DFT calculated excitation parameters. The experimental
results were found to correlate well with the theoretical data.
KEYWORDS
phthalimide probe;
hydrazone; cyanide ion;
colorimetric detection; DFt
1. Introduction
Ubiquitous anions in small concentration play an essen-
tial role in many biological processes (1, 2). However, their
presence beyond permissible limit is detrimental to envi-
ronment and human health (3, 4). Therefore, serious envi-
ronmental remediation efforts are required to identify and
tackle the contaminated sites, which require a screening
protocol consisting of library of potential receptors (5).
Among the most abundant anionic pollutants, cyanide
ion is known to have devastated effect on humans, plants
as well as aquatic life (6–9). The widespread utilisation of
cyanide in the production of organic chemical industry
such as nylons and acrylics, etc. has further heightened
the environmental concerns (10). The toxicity of cyanide
ion is due to its tendency to irreversibly coordinate the
trivalent iron present in the cytochrome c oxidase, which
may result in a condition called hypoxia (11, 12). Synthetic
receptors capable of binding selectively the analytes of
interest is of huge significance (13–16). It is advantageous
that the receptor shows sensitive, naked eye colorimetric
response in the presence of suitable guest species for easy
and affordable identification under practical conditions
(17, 18). The general strategy for the detection of cyanide
ion includes interaction with metal ion present in pyridine
(19) or porphyrin core (20), quantum dots like CdSe (21,
22), boronic acid (23, 24), nucleophilic addition of cyanide
ion to the photochromic molecules such as spiropyran
(25) or naphthopyran (26) and the single electron trans-
fer reactions (27). A number of reports related to cyanide
detection with colorimetric response are available in the
literature (3, 11, 18, 28). For example, a rhodfluor derivative
displayed both colorimetric and fluorometric response in
the presence of cyanide ions (17). The reported chemosen-
sors for cyanide ions also include pyrrole-based receptors
(10), subphthalocyanines (29) and functionalised calix[4]
pyrrole (30).
In the recent past, there is a greater emphasis to
develop small but competent molecules with H-bond
motifs for anion sensing as strong anion binding is possi-
ble through H-bonding or electrostatic interactions (31).
Hydrogen bonding is considered as one of the absolute
CONTACT Satish Kumar
satish@ststephens.edu
Supplemental data for this article can be accessed http://doi.dx.org/10.1080/10610278.2016.1264074.
© 2016 informa uK limited, trading as taylor & Francis Group

2
P. R. SAHOO ET AL.
and prominent interaction in crystal stabilisation (32–36).
At the same time, hydrogen bond is also essential for
molecular interactions in the medicinal and biomedicinal
field (34, 37–39). Recent research report highlights the use
of phthalimide scaffolds in the areas of drug discovery
and drug development (40). Such type of frameworks are
potential agents as antimicrobial, antitubercular and anti-
diabetic markers (41, 42). The phthalimide derivatives and
hydrazone functional moiety with hydrogen bond donor
sites are also potential precursor for optical switches and
sensors for environmentally relevant anions (28, 43, 44).
It also help in tracing different anions in the agricultural
habitat and hinterland (45). The multiple donor sites make
these molecules more adaptable and adds significance as
chelating agents (46, 47).
performed. Single crystal data for receptor 1 and 2 was
recorded on an Oxford Diffraction, X-calibur-S single crys-
tal XRD machine.
2.3. UV–Vis studies
A solution of chelator 1 or 2 (1.0 mL, 5.0 × 10−5 M) was
mixed with tetrabutylammonium salts of different anions
−
−
−
−
(CN−, F−, OAc−, Cl−, Br−, I−, NO3, H2PO4, HSO4, PF6, PhO−,
1.0 mL, 5.0 × 10−5 M) in each experiment. The UV–visible
spectra of the solutions were recorded on an Ocean Optics
USB4000 UV–Visible spectrometer. Similarly, 2.0 mL solu-
tions of 1 and 2 (1.96 × 10−5 M) with different anions (CN−,
−
−
−
−
F−, OAc−, Cl−, Br−, I−, NO3, H2PO4, HSO4, PF6, PhO−, S2−, SH−,
ClO−4 = 1.96 × 10−5 M) in TRIS buffer (1.0 mM, pH 7.6) were
prepared in a cuvette. The absorbance was recorded on
an ocean Optics USB4000 UV–Visible spectrometer. For
titration experiments, a solution of the receptor 1 or 2
(2.0 mL, 2.5 × 10−5 M) was taken in a quartz cuvette and
titrated with a solution of tetrabutylammonium cyanide
(1.0 × 10−3 M) in DMSO.
In the present article, we are reporting the synthesis,
crystal structure, DFT and anion binding investigations of
nitro group flanked phthalimide–hydrazone probes. The
phthalimide–hydrazone probes can be used as a flexible
and promising framework for real-time monitoring of toxic
cyanide.
2. Experimental
2.4. Computations
2.1. Reagents
Calculations reported in this paper were performed using
the Gaussian 09 rev. A.02 program suite (49). The initial
geometry of the receptor 1 and 2 was generated using
Gaussview 5.01 program. The geometries generated using
Gaussview were optimised using DFT/B3LYP/6-31+G(d,p)
and MPW1PW91/6-31+G(d,p) methods. The presence
of local minimum state of the optimised structure was
established through the absence of negative frequency.
Polarisable continuum model (PCM) (50) was used to per-
form calculations in DMSO. TheTD-DFT/B3LYP/6-31+G(d,p)
and TD-DFT/MPW1PW91/6-31+G(d,p) were used to calcu-
late the electronic excitation parameters for receptors 1, 2
and their 1-CN, 2-CN complex.
The reagents used in the study such as o-phthaloyl chlo-
ride, 2, 4-dinitrophenylhydrazine (99%), 4-nitrophenyl-
hydrazine (98.5%), dichloromethane (99%, Anhydrous),
dimethylsulfoxide(>99%), triethylamine (99%), tetrabu-
tylammonium acetate (>98%), tetrabutylammonium
hydrogen sulfate (99.5%), tetrabutylammonium bromide
(99%), tetrabutylammonium dihydrogen phosphate
(99%), tetrabutylammonium fluoride (>98%) and TRIS-
Buffer (>99.9%) were purchased from Spectrochem, India.
Tetrabutylammonium hexafluorophosphate (99%), and
tetrabutylammonium nitrate (98+%) were purchased from
Alfa Aesar. Tetrabutylammonium cyanide (>95%) was pur-
chased from Sigma–Aldrich. Tetrabutylammonium iodide
(99%) and tetrabutylammonium chloride (99%) were pur-
chased from CDH India.
2.5. Synthesis
2.5.1. Synthesis of receptor 1 (51)
To a solution of 4-nitrophenylhydrazine (1.0 g, 6.53 mmol)
in a 100 mL round-bottom flask, dichloromethane (50 mL),
triethylamine (0.5 mL) were added. The reaction mixture
was stirred and o-phthaloyl chloride (0.36 mL, 2.78 mmol)
was added dropwise to the reaction mixture in the
round-bottom flask. The reaction mixture was allowed
to stir for 3 h. The precipitate obtained was filtered and
washed thoroughly with water. The product was recrys-
tallised twice using hot methanol and dried. Yield 68%.
m.p. 260–264 °C. FT-IR (KBr pellet, ν/cm−1): 3328, 2922,
2.2. Instruments
The 1H and 13C NMR spectra were recorded on a 400 MHz
Jeol ECX 400 NMR spectrometer. The NMR spectra were
recorded either in DMSO-d6 or CDCl3. The chemical shift
values of the signals are described in ppm relative to the
TMS signal or residual solvent signal. In cases where sol-
vent signal was used as reference, the solvent was assigned
a value reported in the literature (48). The IR spectrum
was recorded on a Perkin Elmer FT-IR-RXI spectrometer
(with DTGS detector) using KBr pellet and 16 scans were
1
1739, 1615, 1510, 1467, 1407, 1341, 1281 and 1234. H
NMR (400 MHz, CDCl3, δ): 11.64 (d, 1H, NH), 8.06 (d, H,

SUPRAMOLECULAR CHEMISTRY
3
Table 1. experimental detail for receptors 1 and 2.
Crystal data
1
2
chemical formula
Mr
crystal system, space group
temperature (K)
a, b, c (Å)
c14h9N3o4
283.24
orthorhombic, P212121
297
5.2001 (10), 8.8939 (19), 26.026 (7)
1203.7 (5)
4
mo Kα
0.12
0.03 × 0.02 × 0.02
c14h8N4o6
328.2
orthorhombic, Pna21
293
5.3924 (2), 19.5141 (10), 13.0349 (7)
1371.64 (12)
4
mo Kα
0.13
0.02 × 0.01 × 0.01
V (Å3)
Z
radiation type
μ (mm−1)
crystal size (mm)
Diffractometer
Xcalibur, Sapphire3
multi-scan CrysAlis PRO, agilent-2013
0.219, 1.000
Xcalibur, Sapphire3
multi-scan CrysAlis PRO, agilent-2013
0.861, 1.000
absorption correction
T
min, Tmax
No. of measured, independent and observed
[I > 2σ(I)] reflections
Rint
9273, 2247, 1683
17,658, 3467, 2661
0.074
0.605
0.068, 0.130, 1.09
2247
0.055
0.691
0.044, 0.097, 1.06
3467
(sin θ/λ)max (Å−1)
R[F2 > 2σ(F2)], wR(F2), S
No. of reflections
No. of parameters
No. of restraints
190
0
218
1
h-atom treatment
Δρmax, Δρmin (e Å−3)
absolute structure
h-atom parameters constrained
0.20, −0.18
Flack x determined using 425 quotients
[(I+)−(I−)]/[(I+)+(I−)] (52)
2.8 (10)
h-atom parameters constrained
0.15, −0.14
Flack x determined using 969 quotients
[(I+)−(I−)]/[(I+)+(I−)] (52)
0.0 (8)
absolute structure parameter
J = 9.2 Hz, ArH), 7.90–7.88 (m, 2H, ArH), 7.80–7.78 (m,
2H, ArH), 6.77 (d, 2H, J = 9.2 Hz, ArH). 13C NMR (100 MHz,
DMSO-d6): 167.6, 154.8, 137.9, 134.6, 130.3, 128.1, 125.6,
110.9. HR-MS: m/z = Calculated [M + H] 284.0671 found
[M + H] = 284.0662.
the ShelXT/direct method (54) structure solution program
and refined using ShelXL/least square (55) program. All the
non-hydrogen atoms in the receptor 1 and 2 were refined
anisotropically. All the aromatic H atoms were placed at
their calculated position (C–H = 0.93 Å) and treated using
a riding model with Uiso(H) = 1.2Ueq(C). The N–H atoms
in both 1 and 2 were located, fixed at N–H = 0.86 Å and
refined freely. Mercury software (56) was used to prepare
the graphics material for publication.
The crystallographic data for both the receptors (1 and
2) were deposited to the CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK. The copies of the data can be obtained free
of charge on request, by quoting the deposition numbers
1432915, 1420924 and the publication citation.
2.5.2. Synthesis of receptor 2
To a solution of 24-dinitrophenylhydrazine (1.0 g,
5.04 mmol) in a 100 mL round-bottom flask, dichlo-
romethane (50 mL), triethylamine (0.5 mL) were added.
The reaction mixture was stirred and o-phthaloyl chloride
(0.30 mL, 2.32 mmol) was added dropwise to the reaction
mixture in the round-bottom flask. The reaction mixture
was allowed to stir for 3 h. The precipitate obtained was
filtered and washed thoroughly with water. The product
was then recrystallised from hot methanol and dried. Yield
72%. m.p. 240–245 °C. FT-IR (KBr pellet, ν/cm−1): 3266, 2918,
1779, 1583, 1535, 1471, 1311 and 1257. 1H NMR (400 MHz,
DMSO-d6): δ = 11.27 (s, 1H, NH), 8.17 (d, 2H, J = 9.2 Hz, ArH),
8.01 (d, 1H, J = 8.4 Hz, ArH), 7.93 (t, 1H, J = 7.6 Hz, ArH),
7.75 (t, 1H, J = 7.6 Hz, ArH), 7.43 (d, 2H, J = 9.2 Hz, ArH). 13C
NMR (100 MHz, CDCl3, δ): 168.0, 155.2, 145.1, 137.6, 131.8,
131.1, 129.9, 128.8, 123.5, 116.3. HR-MS: (m/z) = Calculated
[M + H] 329.0522 found [M + H] = 329.0506.
3. Results and discussion
The phthalimide–hydrazone probes were synthesised as
per the Scheme 1 in 68–72% yield. The receptors were
characterised using IR, NMR, HRMS and single crystal X-ray
crystallography.
3.1. X-ray crystallography
The crystals of receptors 1 and 2, suitable for single crystal
X-ray crystallographic determination were grown through
slow evaporation of a methanolic solution. X-ray diffrac-
tion analysis revealed that the receptor 1 crystallised in
P212121 space group, while receptor 2 crystallised in Pna21
space group (Figure 1). The two aromatic units of both the
2.6. Crystal data
The detailed crystal data, collection and structure refine-
ment parameters for 1 and 2 are summarised inTable 1 (52).
Olex2 (53) GUI was employed to solve the structure using

4
P. R. SAHOO ET AL.
receptor 1 and 2 were observed to be almost orthogonal
to each other. In receptor 1, the two aromatic units dis-
played torsion angles of 98.35(3)° [C17-C18-C10-C16] and 49°
[C21-C11-C10-C16] with respect to each other, while in recep-
tor 2, the two aromatic units displayed torsion angles of
100.2(1)° [C21-C22-C20-C11] and 47.3(6)° [C24-C18-C12-C17] with
respect to each other. Both the receptor 1 and 2 displayed
similar N–N–C angles. The N4-N3-C10 angle was observed
to be 119.8(4)o in receptor 1, while N5-N9-C12 angle was
observed to be 120.57(3)° in receptor 2. A N–N–C angle
around ~120° in both the receptors (1 and 2) may allow the
N–H group to easily participate in intermolecular H-bond
formation or interact with an ionic species (Tables 2 and
3, Figure S1, Figure S2 ESI). The crystal packing revealed
the formation of intermolecular hydrogen bond in both
1 and 2 (Table 2, Figures S1 and S2). The intermolecular
x + 1, y, z) indicate that the former is stronger than the
latter. Unlike receptor 1, the crystal structure or receptor
2 displayed the intramolecular H-bonding (Table 3). The
crystal packing also revealed the presence of several weak
C–H…O and C–H…N interactions, which link the molecules
together into three-dimensional network (Tables 2 and 3,
Figures S1 and S2).
3.2. Naked eye detection
The synthesised receptors were evaluated through colori-
metric response for affinity towards different environmen-
tally and biologically important anions due to the presence
of the acidic N–H group available for intermolecular
H-bond formation in DMSO and DMSO:water (8:2, 1.0 mM
TRIS buffer, pH 7.6). Standard solutions of the receptors 1
and 2 (1.0 × 10−4 M) were prepared in DMSO and treated
with one equivalent tetrabutylammonium salts of different
i
hydrogen bonding was observed between N3–H3···O1 ((i)
ii
−x, y + 1/2, −z−3/2) and N3–H3···O2 ((ii) x + 1, y, z) in recep-
−
−
−
−
tor 1 (Table 2), while receptor 2 displayed intermolecular
anions (CN−, F−, OAc−, Cl−, Br−, I−,NO3
,
H2PO4
,
HSO4
,
PF6, S2−,
H-bond between O01 H09–N09 (Table 3). The parameters
SH−, ClO−4, PhO−) in DMSO. The colorimetric investigation
revealed that the receptor 1 and 2 can detect the presence
of cyanide ion selectively by displaying a colour change
visible to the naked eye (Figures 2 and 3). The addition
of tetrabutylammonium salt of cyanide ion to a solution
of 1 in DMSO produced the colour change of the solu-
tion from colourless to dark yellow, while the addition of
cyanide ions to receptor 2 in DMSO produced a colour
change from yellow to orange-red (Figure 3). The colour
change observed for receptor 1 in the presence of cyanide
….
i
ii
for N3–H3···O1 ((i) −x, y + 1/2, −z−3/2) and N3–H3···O2 ((ii)
Scheme 1. the synthesis route of the receptor 1 and 2.
Figure 1. (colour online) ortep view of crystal structure of the receptors 1 and 2 with displacement ellipsoids at the 50% probability
level.

SUPRAMOLECULAR CHEMISTRY
5
changes to light yellow with time. However, unlike recep-
tor 1, the colour change for receptor 2 was immediate
and no colour change with time was observed. No colour
change was observed in the solution of receptor 1 and 2
upon addition of other anions (Figures 2 and 3). When the
similar experiments were repeated to evaluate the affinity
of receptor 1 and 2 towards anions in DMSO:water (8:2,
1.0 mM TRIS buffer, pH 7.6), an immediate colour change
from colourless to light purple was observed for receptor
1 (Figure S3). The receptor 2 produced a colour change
from light yellow to dark yellowish-red in the presence of
cyanide ion (Figure S4). The colour change for both recep-
tors 1 and 2 remained unchanged with time. However,
no colour change was observed upon addition of other
Table 2. Short intermolecular contacts observed in receptor 1.
D–H···A
D–H (Å)
H···A (Å)
D···A (Å)
D–H···A (°)
−
−
−
−
i
anions (F−, OAc−, Cl−, Br−, I−,NO3
,
H2PO4 HSO4
ClO−4, PhO−). The observation indicated that the receptors
1 and 2 act as selective sensor of cyanide ions.
,
,
PF6, S2−, SH−,
N3–h3···o1ii
0.848(5)
0.848(5)
0.930(5)
0.930(5)
0.930(5)
0.930(5)
0.930(5)
0.930(5)
2.590(5)
2.641(5)
2.648(3)
2.602(4)
2.837(3)
2.403(5)
2.807(4)
2.448(5)
3.288(5)
3.365(6)
3.573(6)
2.854(6)
3.603(6)
2.702(7)
3.729(7)
2.730(7)
140.46(44)
144.21(45)
172.4(31)
96.10(31)
140.38(31)
98.49(34)
171.18(35)
97.50(34)
N3–h3···o2
iii
c8–h8···o1
c8–h8···N4
c14–h14···o1
c15–h15···o7iv
c19–h19···o5
c19–h19···o5
i
The observations also suggested that due to the pres-
ence of two electronegative groups in receptor 2 the N–H
proton is highly acidic and was easily abstracted by the
cyanide ions. The presence of two nitro groups intensified
the observed colour change. The nitro groups are known
to influence the charge separation in the receptors (57) and
help in the anion coordination (58). Anion coordination is
also attributed to hydrogen bond interactions (59) with the
binding sites consisting of a highly polarised N–H group
(16, 60). The anions may deprotonate highly polarised N–H
groups, which produce considerable electron delocalisa-
tion resulting in the colour change visible to naked eye
and shift in absorption band (61). In addition, the fact that
both receptors 1 and 2 selectively complex a less basic
cyanide ion in comparison to other anions indicate (pKa:
F− = 15, CN− = 12.9, OAc− = 12.6, Cl− = 1.8, Br− = 0.9) (62) that
the recognition event is dictated by factors such as pKa,
size, geometry and nucleophilicity of the anion. Although
similar change in colour was observed in a tweezer-shaped
receptor composed of two 24-dinitrophenylhydrazone
Symmetry codes: (i) −x, y + 1/2, −z−3/2; (ii) x + 1, y, z; (iii) x−1, y, z; (iv) x + 1/2,
−y−1/2, −z−1.
Table 3. Short intermolecular and intramolecular contacts
observed in receptor 2.
D–H···A
D–H (Å)
H···A (Å)
D···A (Å)
D–H···A (°)
i
N09–h09···o01
N09–h09···o02
N09–h09···N03
c13–h13···o07
c13–h13···o08
c19–h19···o04
c19–h19···N05
c19–h19···o07
c20–h20···o10
c23–h23···o07
c24–h24···o07
c24–h24···o08
0.924(3)
0.924(3)
0.924(3)
0.931(3)
0.931(3)
0.930(3)
0.930(3)
0.930(3)
0.930(3)
0.930(4)
0.930(4)
0.930(4)
2.529(2)
1.916(3)
2.905(4)
2.411(3)
2.338(3)
2.607(3)
2.478(3)
2.789(3)
2.457(3)
2.808(3)
2.879(3)
2.952(3)
3.048(2)
2.588(3)
2.905(3)
2.711(4)
2.659(3)
3.362(4)
2.793(4)
3.470(4)
2.730(4)
3.218(5)
3.571(5)
3.636(5)
115.90(5)
127.89(3)
102.12(2)
98.57(2)
99.79(2)
138.70(2)
99.94(2)
130.90(2)
96.95(2)
107.90(2)
132.23(2)
131.58(2)
ii
iii
iv
v
iv
Symmetry codes: (i) x−1/2, −y + 1/2, z; (ii) x + 1, y, z; (iii) −x + 2, −y + 1, z + 1/2;
(iv) x, y, z + 1; (v) x−1, y, z + 1.
Figure 2. (colouronline) colourchangeon addition of 1.0 equivalentof tetrabutylammoniumsaltof anions intoasolution of phthalimide
receptor 1 in DmSo (a) immediate change in colour, (b) colour of the solution after 1 min.
−
−
−
−
Notes: [1] = 2.5 × 10−5 m. From left to right; a = Free receptor, B = cN−, c = F−, D = oac−, e = cl−, F = Br−, G = i−, h = NO3, i = H2PO4, J = HSO4, K = PF6, l = pho−, m
= ClO−4, N = S2−, o = Sh−.
Figure 3. (colour online) colour change on addition of 1.0 equivalent of tetrabutylammonium anions into a solution of hydrazone
receptor 2 in DmSo.
−
−
−
−
Notes: [2] = 2.5 × 10−5 m. From left to right; a = Free receptor, B = cN−, c = F−, D = oac−, e = cl−, F = Br−, G = i−, h = NO3, i = H2PO4, J = HSO4, K = PF6, l = pho−, m
= ClO−4, N = S2−, o = Sh−.

6
P. R. SAHOO ET AL.
moieties, but the mechanism of complex formation differ
slightly (16). The complex formation in the tweezer-shaped
molecule with two 24-dinitrophenylhydrazone groups
involved additional step, which require displacement of
DMSO by cyanide ion. This vital step required for the for-
mation of complex was absent in the case of receptors 1
and 2. The design for the phthalimide–hydrazone probe
(1 and 2) is simple and comparable in efficiency to the
tweezer-shaped molecule reported in the literature (16).
band at 600 nm indicated a complex formation between
the cyanide ion and the receptor 1 through the H-bond
between N–H and CN− ion. The complex formation fur-
ther resulted in the abstraction of a proton by the cyanide
ion, which yielded the anion of the receptor 1 and HCN
as products. The process is slow enough to allow kinetic
measurement through UV–visible spectroscopy. The pro-
ton abstraction by anions in receptors with acidic hydro-
gen was reported earlier in the literature (63), which results
in the formation of a coloured species.
A similar absorbance band at ~485 nm was observed,
when a solution of the receptor 1 was treated with cyanide
ions under pH controlled conditions in DMSO: water (8:2,
1.0 mM Tris buffer, pH = 7.6) solvent system. The absence
of any change in the absorption spectra of the receptor
1 in the presence of other anions indicated the selectiv-
ity of the receptor 1 towards cyanide ion (Figure S8). No
change in absorbance with time was observed under pH
controlled conditions. The receptors (1 and 2) displayed a
bathochromic shift in the UV–visible, while the receptors
that recognise the cyanide ions through covalent linkage
with cyanide ion display a hypsochromic shift with respect
to their open coloured form (merocyanine form) (25, 26).
The colour change here is more intense in comparison
to the naphthopyran receptor (26) or spiropyran-based
receptors (25).
Similarly, the solution of receptor 2 in the presence of
one equivalent anions (tetrabutylammonium salt) was
analysed through UV–visible spectroscopy, a decrease in
intensity of the absorption band at 340 nm was observed,
while a band at 410 nm with shoulder at 480 nm increased
in intensity (Figure 5). No colour change was observed in
the presence of tetrabutylammonium salt of other anions
3.3. UV–visible studies
The process of complex formation between receptors (1
and 2) and cyanide ion was further explored using UV–
Visible spectroscopy. The UV–visible spectra of receptor 1
displayed an absorption band between 350 and 470 nm.
The addition of one equivalent cyanide ions into a solu-
tion of receptor 1, leads to the decrease in the receptor 1
absorption band at 420 nm and appearance of a new band
at 600 nm (Figure 4). The absorption band at 600 nm dis-
appeared with time with the appearance of a new band at
480 nm (Figure S5). No other anions produced any change
in the absorbance spectra of the receptor 1 (Figure 3). In
order to understand the observed spectral shift from 600
to 480 nm in DMSO for 1, a solution of receptor 1 was
treated with one equivalent of cyanide ion and the spec-
tra were recorded with time (Figure S5). The rate of dis-
appearance of band at 600 nm was plotted against time,
an exponential decay was observed (Figure S6). The shift
in absorption maxima from 600 to 480 nm followed first-
order reaction kinetics. The data obtained were applied to
first-order reaction kinetics and the rate constant for this
reaction was calculated (Figure S7). The appearance of a
Figure 5. (colour online) absorption spectra of 2([2] =
2.5 × 10−5 m) with 1.0 equivalent amounts of tetra-n-butyl
Figure 4. (colour online) absorption spectra of receptor 1 ([1] =
2.5 × 10−5 m) with 1.0 equivalent of tetrabutylammonium salt of
−
ammonium salt of various anions (cN−, F−, oac−, cl−, Br−, i−, NO3,
−
−
−
−
various anions (cN−, F−, oac−, cl−, Br−, i−, NO3, H2PO4, HSO4, PF6,
−
−
−
−
H2PO4, HSO4, PF6, pho−Na+ S2−, Sh−, ClO4, 2.5 × 10−5 m) in DmSo.
S2−, Sh−, ClO−4, 2.5 × 10−5 m) or Naoph in DmSo.
Note: For simplicity spectra of only few important anions are shown.
,
Note: For simplicity spectra of only few important anions are shown.

SUPRAMOLECULAR CHEMISTRY
7
−
−
−
−
(F−, OAc−, Cl−, Br−, I−,NO3,H2PO4,HSO4,PF6, PhO−, S2−, SH−,
ClO−4). Under pH controlled conditions, a spectral shift from
370 nm to 440 nm was observed in the absorption spectra
of receptor 2 upon addition of one equivalent cyanide ion
in DMSO:water (8:2, 1.0 mM TRIS, pH 7.6) (Figure S9). No
spectral shift in the absorption spectra was detected in
experimental data for both the receptors (1 and 2) were
tested against all the different type of binding equilibria
models shown in Scheme 2. The 1:1 binding model, which
utilises only equation 1 was observed to fit better with the
experimental data for both the receptors and provided
a logβ value of 4.379 0.005 (Figure S12) for receptor 1
and 4.8776 0.0475 (Figure S13) for receptor 2. The other
binding equilibria models, which consider equation 1 with
equation 2 or 3 or both did not provide a good fit between
the experimental and observed absorbance values. A high
logβ value of the association constant support the obser-
vation that the receptors 1 and 2 have a high affinity for
cyanide ion and receptor 2 forms a slightly stronger com-
plex with cyanide ion in comparison to the receptor 1. The
1:1 complex stoichiometry was further supported by Job’s
plot (Figures S14 and S15).
−
the presence of other anions (F−, OAc−, Cl−, Br−, I−, NO3,
−
−
−
H2PO4
,
HSO4
,
PF6, S2−, SH−, ClO4−, PhO−). The results indicate
that the receptor 2 can be used for selective detection of
cyanide ions.
To further evaluate the strength of complex between
the receptors (1 and 2) and cyanide ion, UV-Visible titration
experiments were performed in DMSO. Upon gradual addi-
tion of cyanide ion to the receptor 1 solution, the peak at
420 nm gradually reduced followed by the development of
a new peak at 600 nm, which gradually reduced in intensity
with time and a new band appeared at 480 nm (Figure
S10). Similarly, a solution of receptor 2 was titrated with
a solution of cyanide ions in DMSO. The gradual addition
of cyanide ions into a solution of receptor 2 in DMSO
results in the increase in absorption intensity of a band at
410 nm and a clearly distinguishable isosbestic point at
370 nm, which indicated the formation of a stable complex
between the receptor 2 and cyanide ion (Figure S11).
The experimental titration data were analysed using the
HypSpec program (64) to obtain the value of association
constant through nonlinear fit. Different binding equilib-
ria (Scheme 2) were considered between the receptors
(1 and 2) and cyanide ions. The experimental data were
either applied to single equilibria model 1:1 (A:B) using
only equation 1 or any of the multiple binding equilibria
models such as 1:1 (A:B)+1:2 (A:2B) model using equation
1 and 2, 1:1 (A:B)+2:1 (2A:B) model using equation 1 and
3 and (A:B)+1:2 (A:2B)+2:1 (2A:B) model using equation 12
and 3 to observe better data fit with HypSpec program.
The single equilibria model 1:1 (AB) considers that one
molecule of receptor binds to one molecule of the anion
(equation 1). The result of the analysis using HypSpec
provides association constant K11. The data can also be
applied to multiple equilibria model 1:1 (A:B)+2:1 (2A:B),
which consider equation 1 and 2, the result of the analy-
sis using HypSpec can provide both K11 and K21. Another
multiple binding model 1:1 (A:B)+1:2 (A:2B) consider
equation 1 and 3 for the calculations and the result of the
analysis using HypSpec can provide both K11 and K12. The
3.4. NMR studies
The 1H NMR spectra were used to further investigate the
interaction between the receptors and cyanide ions. The
1H NMR of receptor 2 and 2-CN complex indicates that
the –NH signal at δ11.27 ppm disappeared upon addition
of cyanide ions, while a new peak at δ8.27 ppm appeared.
1
A new signal at δ8.14 ppm was also seen in the H NMR
spectra of receptor 1 with cyanide ions (Figures 6 and S18).
The appearance of new signal may be attributed to the
formation of HCN complexed to the nitrogen atom of the
receptor molecule. The observation supports the deproto-
nation mechanism for the complex formation between the
receptors and the cyanide ion. The shielding of all 1H NMR
signals further supports the deprotonation in the presence
of cyanide ions (Figure 6).
3.5. Practical utility
To investigate the practical utility of the receptors 1 and 2,
the detection limit of the both receptors (1 and 2) towards
1
Figure 6. (colour online) partial h Nmr spectra of 2 and 2-cN
complex recorded in DmSo-d6.
Scheme 2. Binding models used to fit the experimental data.

8
P. R. SAHOO ET AL.
cyanide ion was determined using the method reported in
the literature (65). A plot was drawn between absorbance
and [CN−], which produced a linear change in absorbance
intensity on increasing cyanide ion concentration (Figures
S16 and S17). The slope (m) and the standard deviation (σ)
were used for the calculation of detection limit based on
3σ/m. A detection limit value of 5.18 μM for receptor 1 and
0.48 μM for receptor 2 was obtained using the experimen-
tal data. The detection limit value observed for receptor 1
is above the detection limit value (1.9 μM) recommended
by WHO (8) but lower than the EPA recommended limit of
cyanide concentration (7.8 μM) (66, 67) in drinking water.
The detection limit value obtained obtained for receptor
2 is lower than the concentration limit recommended
by WHO (1.9 μM) (8) and EPA (7.8 μM) (66, 67) in drinking
water. The detection limit value obtained for the recep-
tor 2 was comparable to the detection limit of the optical
(both colorimetric and fluorometric) sensors (19, 24, 68–73)
reported in the literature. It should also be noted that the
receptors reported in the literature often required light
to induce cyanide binding, while the receptors 1 and 2
displayed colour change without any requirement of
light or dark conditions (24–26, 68–71). Some receptors
reported for the detection of cyanide ions are employed
in the pure organic solvents, while the receptors 1 and
2 detected cyanide ions in both organic and aqueous
organic solvents (26, 74) with a comparable detection limit.
The limit of detection value indicated that the receptor 2 is
more sensitive and simple colorimetric sensor for cyanide
ion in comparison to the similar tweezer-shaped receptor
reported in the literature (16).
followed by treatment with a solution of cyanide ions
(1.0 × 10−5 M) in aqueous DMSO. A clear change in colour
visible to the naked eye was observed, which indicated
that both the receptors can be used for the detection of
cyanide ions (Figures 7 and 8).
3.6. Computational studies
To understand further the process of complex formation
between the receptors and the cyanide ions, DFT calcu-
lations were performed using the Gaussian 09 software
suite. DFT/B3LYP methods are successfully used to study
a number of processes, which include photochromism,
enzymatic process, catalysis employing zeolites, drug
design, solar energy and supramolecular chemistry
(75–79). However, in certain systems, DFT methods fail
to predict the ground state correctly (80). DFT methods
badly describe the dispersion interactions and are not
used to study the stacking or London-type interactions
(81–83). However, such failures are rare and DFT meth-
ods provide excellent results for certain supramolecular
systems (84, 85). The results of the study were compared
with new hybrid density functional model MPW1PW91.
The MPW1PW91 method is known to provide accurate
results for non-covalent interactions (86, 87). The structure
of the receptor 1, 2 and their complex with cyanide ion
were optimised using DFT/B3LYP/6-31+G(d,p) method.
The energies of the optimised geometries (Figure 9) are
listed in the Table 4.
The important geometrical parameters obtained
through the computational methods were compared with
the parameter obtained using X-ray crystallography data.
A good correlation between the geometrical parameters
(bond angles and bond lengths) calculated using DFT
methods and obtained through X-ray crystallographic data
To explore the practical applications of the synthesised
receptor, paper strips of receptors (1 & 2) were prepared
by dipping the filter paper strips in a solution of the recep-
tors (1.0 × 10−5 M). The paper strips were dried in the air,
Figure 7. (colour online) colour change on paper strip of receptor 1 on treatment with one equivalent tetrabutylammonium salt of
different anions in DmSo:water (8:2, 1.0 mm triS buffer, ph 7.6) [1] = 1.96 × 10−5 m. From left to right; a = Free receptor, B = cN−, c = F−,
−
−
−
−
−
D = oac−, e = cl−, F = Br−, G = i−, h = NO3, i = H2PO4, J = HSO4, K = PF6, l = pho−, m = ClO4¸ N = S2−, o = Sh−,= 1.96 × 10−5 m.
Figure 8. (colour online) colour change on paper strip of receptor 2 on treatment with one equivalent tetrabutylammonium salt of
different anions in DmSo:water (8:2, 1.0 mm triS buffer, ph 7.6) [2] = 1.96 × 10−5 m. From left to right; a = Free receptor, B = cN−, c = F−,
−
−
−
−
−
D = oac−, e = cl−, F = Br−, G = i−, h = H2PO4, i = HSO4, J = PF6, K = pho−, l = ClO4, m = S2−, N = Sh−, o = NO3 = 1.96 × 10−5 m.

SUPRAMOLECULAR CHEMISTRY
9
Figure 9. (colour online) the B3lyp/6-31+G(d,p) optimised geometries of the free receptors 1, 2 and their complex with the cyanide ion.
Table 4. the energy of the free receptors 1, 2 and their complex with cyanide ion calculated using DFt/B3lyp/6-31+G(d,p) and mpW1p-
W91/6-31+G(d,p) methods.
Energy (kcal/mol)
Total energy of free 1 or 2 + free
∆E = Ecomplex − Ereceptor − ECN−
B3LYP/6-31+G(d,p) (∆Esolv
)
MPW1PW91/6-31+G(d,p) (∆Esolv
)
CN− Ions B3LYP (MPW1PW91)
B3LYP (MPW1PW91)
Receptor
1
−630,031.58 (−13.99)
−688,342.24 (−46.59)
−758,361.19 (−14.32)
−816,674.66 (−46.46)
−629,880.40 (−13.70)
−688,169.21 (−46.72)
−758,178.80 (−13.63)
−816,470.24 (−46.47)
1+cN
2
−688,305.52 (−688,131.39)
−816,635.12 (−816,429.79)
−36.72 (−37.82)
−39.54 (−40.44)
2+cN
was observed, which indicated that the equation 5 pro-
vide the more stable geometry of the complex between
receptor and cyanide ion. Therefore, the DFT methods
supported the formation of a stable complex geometry,
where HCN is linked to receptor 1 and 2 through hydrogen
bond. It was concluded that cyanide ion first abstracts a
proton from the receptor followed by formation of H-bond
between negatively charged receptor and cyanide ion. The
energy difference calculated by MPW1PW91 and B3LYP
method differs only by 1 kcal/mol indicating that B3LYP
method can be used for such studies. The solvation energy
calculated using B3LYP and MPW1PW91 indicated that the
cyanide complex is further stabilised by polar solvent like
DMSO, which indicate the polar nature of the complex. The
theoretical investigations also suggested that the receptor
2 should form a more stable complex with cyanide ion in
comparison to the receptor 1. The greater stability of the
2-CN complex predicted by quantum chemical methods
corroborates the experimental results. The ratio of binding
constant value 2-CN/1-CN (1.11) and the calculated ratio
of ∆E2−CN/∆E1−CN (1.08B3LYP, 1.07 MPW1PW91) indicates a good
correlation between the experimentally observed data
and calculated data.
Scheme 3. equations representing the complexation models.
was observed. For example, the N3-N6-C9 angle in the recep-
tor 1 calculated using B3LYP (120.10°) and MPW1PW91
(120.20°) methods were observed to correlate well with
the angle observed in the same set of atoms (N4-N3-C10)
in the crystal structure (119.8(3)°). Similarly, The N-N-C
angle in the receptor 2 calculated using B3LYP (N5-N9-C13,
122.27°) and MPW1PW91 (N5-N9-C12, 121.99°) methods
were observed to correlate well with the angle observed
for the same set of atoms (N5-N9-C12) in the geometry
obtained through the crystal structure (120.57(4)°).
The energy of the free receptor and cyanide ion was
compared with the energy of the complex using equation
4 and 5 (Scheme 3).
Both equations indicated that both receptors 1 and
2 can form a stable complex with the cyanide ion. When
equation 4 was used for ∆E calculation using MPW1PW91
−
(∆E = Erec−H + ECN − Erec − EHCN), the equation 4 yielded a
value of −22.11 kcal/mol for receptor 1 and −25.39 kcal/mol
for receptor 2. When equation 5 was used for calculation of
∆E for the reaction, a value of −37.82 and −40.44 kcal/mol
To investigate the observed UV–visible spectra of the
receptor 1 and 2 on the addition of cyanide ions, calcu-
lations using TD-DFT/B3lYP/6-31+G(d,p) method were

10
P. R. SAHOO ET AL.
Figure 10. (colour online) energy diagrams depicting the main orbitals of receptors 1, 2 and their 1-cN, 2-cN complex, calculated using
the tD-DFt/B3lyp/6-31+G(d,p) method.
performed with Gaussian 09 software suite. The calculated
electronic excitation parameters are listed in the Table
S1 for receptors 1, 2 and their 1-CN and 2-CN complex.
The singlet electronic transition in receptor 1 was mainly
contributed by HOMO to LUMO (S0 to S1) orbitals for the
observed absorption band.TheTD-DFT/B3LYP/6-31+G(d,p)
calculated energy of HOMO to LUMO transition (2.86 eV,
433 nm) is close to the observed absorption band (420 nm,
Figure 4) in receptor 1. The singlet electronic excitations
in the receptor 1-CN complex were mainly contributed by
HOMO to LUMO (S0 to S1) and HOMO to LUMO+1 (S0 to S2)
orbitals (Figure 10, Table S1) which are responsible for the
observed absorption band (Figure 4). The energy (2.68 eV,
463.12 nm) of HOMO to LUMO+1 is close to the absorption
band observed in 1-CN complex (~450 nm, Figure 4). For
receptor 2, the singlet electronic excitations were mainly
contributed by HOMO to LUMO+1 (S0 to S1) and HOMO
to LUMO (S0 to S2) orbitals (Figure 10, Table S1), which are
responsible for the observed absorption bands (Figure 5).
The calculated energy for HOMO to LUMO+1 and HOMO
to LUMO transitions are close to the absorption bands in
receptor 2. The singlet electronic excitation in the receptor

SUPRAMOLECULAR CHEMISTRY
11
2-CN is mainly contributed by HOMO to LUMO (S0 to S1)
transition (Table S1, Figure 10). The energy of the HOMO
to LUMO transition energy (2.73 eV, 452.64 nm) correlates
well with the absorption band (centred around 450 nm,
Figure 5) observed in the 2-CN complex. When similar cal-
culations were performed with MPW1PW91/6-31+G(d,p),
no further improvement was observed. Similarly, when
the TD-DFT calculations were performed on the optimised
geometry of the negatively charged anion of receptor 1
and 2, the results did not correlate with the experimental
data.
Funding
This work was financially supported by UGC [number 41-
235/2012]; DST Science and Engineering Research Board
[number SB/FT/CS-054/2012].
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Acknowledgements
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Disclosure statement
No potential conflict of interest was reported by the authors.

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