A novel strategy for chromogenic chemosensors highly selective toward cyanide based on its reaction with 4-(2,4-dinitrobenzylideneamino)benzenes or 2,4-dinitrostilbenes

Article abstract of DOI:10.1016/j.saa.2014.10.041

N-(2,4-dinitrobenzylidene)-4-methoxyaniline (1), 4-(N,N-dimethylamine)-N-(2,4-dinitrobenzylidene) aniline (2), 2,4-dinitro-4′-methoxystilbene (3), and 2,4-dinitro-4′-(dimethylamino)stilbene (4) were synthesized and studied in dimethyl sulfoxide in a novel strategy as anionic chromogenic chemosensors. The color of the solutions of these compounds changed only in the presence of cyanide. The kinetic studies were performed with compounds 1-3 in an excess of cyanide. Higher second-order rate constant values were obtained for the compounds containing a methoxy group in relation to the compounds with a dimethylamino substituent, since the methoxy group donates electronic density to the 2,4-dinitrophenyl electron-accepting group less easily compared with the dimethylamino group. Stilbenes generally have greater structural rigidity than imines, facilitating the action of the substituents through the mesomeric effect. The data obtained indicate that the anion acts as a nucleophile, being responsible for C=N bond breaking. The C=C bridge is not broken in the stilbene dyes, but cyanide performs a nucleophilic attack on the 2,4-dinitrophenyl group.

Full text of DOI:10.1016/j.saa.2014.10.041

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
A novel strategy for chromogenic chemosensors highly
selective toward cyanide based on its reaction with
4-(2,4-dinitrobenzylideneamino)benzenes or 2,4-dinitrostilbenes
⇑
Renata S. Heying, Leandro G. Nandi, Adailton J. Bortoluzzi, Vanderlei G. Machado
Departamento de Química, Universidade Federal de Santa Catarina, UFSC, Florianópolis, SC 88040-900, Brazil
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
ꢀ
A novel anionic chromogenic
chemosensor is proposed.
The imines studied are chromogenic
chemosensors highly selective
toward CNꢁ.
ꢀ
ꢀ
The anion acts as a nucleophile, being
responsible for C@N bond breaking.
C@C bridge is not broken in the
stilbenes: CNꢁ attacks on the 2,4-
dinitrophenyl group.
ꢀ
The crystal structure of one imine
was determined by X-ray diffraction.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 June 2014
Received in revised form 9 October 2014
Accepted 15 October 2014
Available online xxxx
N-(2,4-dinitrobenzylidene)-4-methoxyaniline (1), 4-(N,N-dimethylamine)-N-(2,4-dinitrobenzylidene)
aniline (2), 2,4-dinitro-40-methoxystilbene (3), and 2,4-dinitro-40-(dimethylamino)stilbene (4) were syn-
thesized and studied in dimethyl sulfoxide in a novel strategy as anionic chromogenic chemosensors. The
color of the solutions of these compounds changed only in the presence of cyanide. The kinetic studies
were performed with compounds 1–3 in an excess of cyanide. Higher second-order rate constant values
were obtained for the compounds containing a methoxy group in relation to the compounds with a
dimethylamino substituent, since the methoxy group donates electronic density to the 2,4-dinitrophenyl
electron-accepting group less easily compared with the dimethylamino group. Stilbenes generally have
greater structural rigidity than imines, facilitating the action of the substituents through the mesomeric
effect. The data obtained indicate that the anion acts as a nucleophile, being responsible for C@N bond
breaking. The C@C bridge is not broken in the stilbene dyes, but cyanide performs a nucleophilic attack
on the 2,4-dinitrophenyl group.
Keywords:
Chromogenic chemosensors
Naked-eye detection
Cyanide
Displacement assay
Chemodosimeters
Ó 2014 Elsevier B.V. All rights reserved.
Introduction
sents an important target analyte to be detected due to its many
industrial applications and considering the risk that it poses to
The recognition and detection of anionic species has been
extensively studied in recent years [1–6]. Many chromogenic
chemosensors have been developed for the selective visual and
quantitative detection of anions [7–17]. In this regard, CNꢁ repre-
human health, being lethal in very small amounts because it inhib-
its the mitochondrial electron transport chain due to its strong
binding to the active site of cytochrome-oxidase [18–20]. Some
roots and fruit seeds release CNꢁ through hydrolysis [21] and also
some neurotoxic agents [22–24] deliver CNꢁ through hydrolysis
[25], highlighting the importance of the development of optical
chemosensors for CNꢁ detection [26–29].
⇑
Corresponding author. Tel.: +55 48 3721 4542; fax: +55 48 3721 6852.
E-mail address: vanderlei.machado@ufsc.br (V.G. Machado).
http://dx.doi.org/10.1016/j.saa.2014.10.041
1386-1425/Ó 2014 Elsevier B.V. All rights reserved.
Please cite this article in press as: R.S. Heying et al., A novel strategy for chromogenic chemosensors highly selective toward cyanide based on its reaction
with 4-(2,4-dinitrobenzylideneamino)benzenes or 2,4-dinitrostilbenes, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014),
http://dx.doi.org/10.1016/j.saa.2014.10.041

2
R.S. Heying et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2014) xxx–xxx
Many strategies have been used to detect CNꢁ, these being gen-
d = doublet, dd = double doublet), coupling constants (Hz) and inte-
gration. Infrared (IR) spectra were obtained on a Shimadzu model
Prestige-21 spectrophotometer, with KBr pellets. High-resolution
mass spectra were obtained with an electrospray ionization-quad-
rupole time-of-flight mass spectrometer (HR ESI-MS QTOF) or
Atmospheric Pressure Photoionization Source (HR APPI-MS QTOF).
erally based on acid–base equilibrium [11,30–33], the formation of
cyanide complexes [34–39] and the development of chemodosi-
meters, which are systems able to interact with the anion through
irreversible reactions [11,13,40–42]. The design of a chemodosime-
ter requires the connection of at least two functional units: the
reaction site (responsible for the interaction of the device with
the analyte); and a signalizing unit (which provides the optical
signal indicating the presence of the analyte). Several strategies
have been applied to the design of chemodosimeters for CNꢁ and
systems based on the nucleophilic addition of this anion to the
imine group have been recently reported [43–45].
In this paper, N-(2,4-dinitrobenzylidene)-4-methoxyaniline (1;
Scheme 1) was synthesized and studied in a novel strategy as an
anionic chromogenic chemosensor in dimethyl sulfoxide (DMSO).
Compound 1 was found to be highly selective toward CNꢁ in rela-
tion to other anions, but the mechanism of action differed from that
reported for other imine detection systems [43–46], since we
observed that the anion breaks the C@N bond, leading to the forma-
tion of colored species. Therefore, a detailed analysis of this process
was carried out by studying three other compounds (Scheme 1),
4-(N,N-dimethylamine)-N-(2,4-dinitrobenzylidene)aniline (2), 2,4-
dinitro-40-methoxystilbene (3), and 2,4-dinitro-40-(dimethyl-
amino)stilbene (4). UV–vis and mechanistic studies involving the
compounds were performed and are described herein.
Synthesis
N-(2,4-Dinitrobenzylidene)-4-methoxyaniline (1)
2,4-Dinitrobenzaldehyde (0.150 g, 0.76 mmol) and p-anisidine
(0.094 g, 0.76 mmol) were dissolved, with magnetic stirring, in
methanol (5 mL). A drop of acetic acid was added and the reaction
mixture was stirred for 4 h. A yellow solid was formed, which was
filtered and recrystallized from methanol, yielding 0.094 g (41%) of
the product; m.p. obtained: 131.4–131.5 °C (m.p. lit. [48]: 131 °C);
ꢀ
IR (KBr, m
max/cmꢁ1): 3018–3000 (CAH), 1522 (C@C), 1502 (C@N),
N@O (1346); 1H NMR (400 MHz, DMSO-d6) d/ppm: 8.96 (s, 1H),
8.80 (d, 1H, J = 2.3 Hz), 8.62 (dd, 1H, J = 8.6 and 2.3 Hz), 8.42 (d,
1H, J = 8.6 Hz), 7.40 (d, 2H, J = 9.0 Hz), 7.05 (d, 2H, J = 9.0 Hz), 3.79
(s, 3H). 13C NMR (100 MHz, DMSO-d6) d/ppm: 159.27, 152.11,
148.71, 147.86, 142.57, 135.20, 130.87, 127.60, 123.22, 120.07,
114.62, 55.39. HRMS (ESI, TOF): m/z calcd. for
C14H12N3O5
[M + H]+ 302.0771, found 302.0777.
4-(N,N-Dimethylamine)-N-(2,4-dinitrobenzylidene)aniline (2)
Experimental section
N,N-dimethyl-p-nitrosoaniline
N,N-dimethylaniline (15 mL) and concentrated HCl (50 mL)
were placed in a round-bottomed flask. The temperature of the
system was lowered to 5 °C using a glass bath. A solution of sodium
nitrite (10.0 g) in 15 mL of distilled water was prepared and added
to the solution containing N,N-dimethylaniline, keeping the tem-
perature at a maximum of 8 °C. After mixing, the reaction mixture
was left to stand for one hour. The product was filtered and recrys-
tallized in ethanol, providing 8.42 g (47.7%) of the product; m.p.
obtained: 84.6–85.4 °C (m.p. lit. [49]: 85 °C).
Materials
All chemicals used were high-purity commercial reagents. The
DMSO (HPLC grade, Sigma–Aldrich) was stored on molecular sieves
(Aldrich) [47]. Karl-Fischer titration was performed with the sol-
vent and demonstrated the presence of water in a concentration
of 5.1 ꢂ 10ꢁ3 mol Lꢁ1 (0.04% water). Tetra-n-butylammonium
hydroxide was purchased from Sigma–Aldrich. All anions (HSOꢁ4 ,
H2POꢁ4 , NO3ꢁ, CNꢁ, CH3COOꢁ, Fꢁ, Clꢁ, Brꢁ, and Iꢁ) were used as
tetra-n-butylammonium salts with purity greater than 97–99%.
The anions were purchased from Fluka (Fꢁ, >97%; Clꢁ, >98%;
NO3ꢁ, >97%; H2PO4ꢁ, >97%), Vetec (Brꢁ, >99%; Iꢁ, >99%; HSOꢁ4 ,
>99%) and Sigma–Aldrich (CH3COOꢁ, >97%) and were dried over
phosphorous pentoxide under vacuum before use.
Reduction of N,N-dimethyl-p-nitrosoaniline
N,N-dimethyl-p-nitrosoaniline (1.0 g, 9.98 mmol) and granu-
lated tin (2.0 g, 25 mmol) were mixed in a round-bottomed flask.
Concentrated HCl (10 mL) was then carefully added and the system
was refluxed for 11 h and 30 min. The end product was filtered and
recrystallized in methanol, providing 0.489 g (53.9%) of the prod-
uct; m.p. obtained: 50.3–51.9 °C (m.p. lit. [49]: 54 °C).
Instrumentation
UV–vis spectra and kinetic runs were carried out on an HP
8452A spectrophotometer equipped with a thermostated bath,
employing a 1-cm quartz cuvette. The maxima of the UV–vis spec-
tra (kmax) were calculated from the first derivative of the absorp-
tion spectrum. Melting points were obtained on a Kofler hot
stage and were uncorrected. The NMR spectra were recorded on
a Varian AS-400 spectrometer. Chemical shifts were recorded in
ppm with the solvent resonance as the internal standard. Data
are reported as follows: chemical shift, multiplicity (s = singlet,
Preparation of compound 2
2,4-Dinitrobenzaldehyde (0.150 g, 0.76 mmol) and N1,N1-
dimethylbenzene-1,4-diamine (0.105 g, 0.76 mmol) were placed
in a beaker and mixed with 20 mL of ethanol and 3 drops of acetic
acid. The reaction mixture was stirred for 4 h. The black solid
obtained was filtered and recrystallized from propan-2-ol, yielding
0.046 g (19.4%) of the product; m.p. obtained: 205.0–205.8 °C (m.p.
N
O2
N
O2
N
O2
N
O2
N
R
R
:
1 R
H
3
OC
:
3 R
H
3
=
=
OC
=
=
:
2 R
N
(CH
)
4:
R
(CH )
N
3 2
3
2
Scheme 1. Molecular structures of the compounds studied herein.
Please cite this article in press as: R.S. Heying et al., A novel strategy for chromogenic chemosensors highly selective toward cyanide based on its reaction
with 4-(2,4-dinitrobenzylideneamino)benzenes or 2,4-dinitrostilbenes, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014),
http://dx.doi.org/10.1016/j.saa.2014.10.041

R.S. Heying et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2014) xxx–xxx
3
m
max/cmꢁ1): 3093–2968 (CAH), 1518
Table 1
lit.[50]: 211 °C); IR (KBr,
(C@C), 1458 (C@N), 1345 (N@O); 1H NMR (400 MHz, CDCl3) d/
ppm: 9.04 (s, 1H), 8.85 (d, 1H, J = 2.3 Hz), 8.65 (d, 1H, J = 8.6 Hz),
8.46 (dd, 1H, J = 8.6 and 2.3 Hz), 7.41 (d, 2H, J = 9.0 Hz), 6.74 (d,
2H, J = 9.0 Hz), 3.04 (s, 6H). 13C NMR (100 MHz, CDCl3) d/ppm:
150.79, 148.37, 147.48, 145.83, 138.61, 136.75, 130.56, 126.96,
123.87, 120.40, 112.45, 40.51. HRMS (ESI, TOF): m/z calcd. for
Crystallographic data and structure refinement for 1.
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
C14H11N3O5
301.26
173 K
0.71073 Å
Triclinic
Pı
¯
C
15H15N4O4 [M + H]+ 315.1088, found 315.1087.
Unit cell dimensions
a = 7.4230 (2) Å
b = 11.8287 (4) Å
c = 15.6458 (6) Å
2,4-Dinitro-40-methoxystilbene (3)
Volume
1336.55 (8) Å3
2,4-Dinitrotoluene (0.250 g, 1.37 mmol) and p-anisaldehyde
(0.187 g, 1.37 mmol) were mixed in the presence of pyrrolidine
(0.085 g, 1.20 mmol) in a 50 mL round-bottomed flask. The system
was kept under magnetic stirring and heated using an oil bath at
90 °C for 30 min. The orange solid obtained was filtered, washed
with ice-cold water, and recrystallized from ethanol, yielding
0.798 g (68.8%) of the product; m.p. obtained: 159.6–160.4 °C
Z
4
Density (calculated)
Absorption coefficient
F (000)
Crystal size
h range for data collection
Index ranges
Reflections collected
Independent reflections
Absorption correction
Refinement method
Data/restraints/parameters
GOOF on F2
1.497 mg mꢁ3
0.12 mmꢁ1
624
0.30 ꢂ 0.16 ꢂ 0.06 mm
2.2–32.5°
h = ꢁ11 ? 11, k = ꢁ17 ? 17, l = ꢁ23 ? 23
24,067
9645
None
(m.p. lit. [51]: 163 °C); IR (KBr,
m
max/cmꢁ1): 3101–2933 (CAH),
1531 (C@C), 1513 (C@N), 1336 (N@O); 1H NMR (400 MHz,
DMSO-d6) d/ppm: 8.71 (s, 1H, J4 = 2.0 Hz), 8.46 (dd, 1H,
J3 = 8.8 Hz; J4 = 2.0 Hz), 8.23 (d, 1H, J3 = 8.8 Hz), 7.63 (d, 2H,
J3 = 8.6 Hz), 7.59 (d, 1H, J3 = 16.2 Hz), 7.36 (d, 1H, J3 = 16.2 Hz),
7.01 (d, 2H, J3 = 8.6 Hz), 3.79 (s, 3H). 13C NMR (100 MHz, DMSO-
d6) d/ppm: 160.42, 146.85, 145.25, 137.97, 137.31, 129.18,
128.66, 128.32, 127.0, 120.30, 118.33, 114.38, 55.25. HRMS (APPI,
Least-squares matrix: full
9645/0/399
1.02
R1 = 0.0463; wR2 = 0.1248
R1 = 0.0704; wR2 = 0.1419
0.39 e Åꢁ3 and ꢁ0.27 e Åꢁ3
Final R indices [I > 2
R indices (all data)
Largest diff. peak and hole
r
(I)]
TOF): m/z calcd. for
301.08186.
C
15H13N2O5 [M + H]+ 301.08190, found
UV–vis studies
A solution of each compound was prepared in DMSO in a con-
2,4-Dinitro-4’-(dimethylamino)stilbene (4)
centration of 5.0 ꢂ 10ꢁ5 mol Lꢁ1. This solution was then used to
2,4-Dinitrotoluene (552 mg, 3.70 mmol) and p-(dimethyl-
amino)benzaldehyde (0.671 g, 3.68 mmol) were mixed in a 50 mL
round-bottomed flask in the presence of pyrrolidine (0.254 g,
3.60 mmol). The system was kept under magnetic stirring and
heated in an oil bath (90 °C) for 30 min. The dark-red solid product
formed was filtered, washed with ice-cold water, and recrystallized
from ethanol, yielding 0.144 g (35.4%) of the product; m.p. obtained:
prepare the solutions of each anion in
a concentration of
2.78 ꢂ 10ꢁ3 mol Lꢁ1, using 5 mL flasks, and the colors of the solu-
tions were compared. These solutions were transferred to cuvettes
hermetically closed with rubber stoppers in order to minimize the
evaporation of the solvent and to avoid the entrance of water into
the system, and the UV–vis spectra were obtained (10 min for the
solutions containing CNꢁ).
175.2–175.7 °C (m.p. lit. [52]: 181 °C); IR (KBr, m
max/cmꢁ1): 3086–
2899 (CAH), 1523 (C@C), 1331 (N@O); 1H NMR (400 MHz, DMSO-
d6) d/ppm: 8.68 (s, 1H, J4 = 2.3 Hz), 8.40 (dd, 1H, J3 = 9.0 Hz;
J4 = 2.3 Hz), 8.22 (d, 1H, J3 = 9.0 Hz), 7.59 (d, 1H, J3 = 16.0 Hz), 7.50
(d, 2H, J3 = 8.6 Hz), 7.24 (d, 1H, J3 = 16.0 Hz), 6.75 (d, 2H,
J3 = 8.6 Hz), 2.98 (s, 6H). 13C NMR (100 MHz, CDCl3) d/ppm:
151.08, 146.58, 144.87, 139.48, 138.80, 129.34, 127.62, 126.62,
124.13, 120.92, 115.75, 112.42, 40.44. HRMS (ESI, TOF): m/z calcd.
for C16H16N3O4 [M + H]+ 314.1135, found 314.1132.
Titration experiments were performed with the solutions of 1
and of CNꢁ prepared as described above. The flask containing the
stock anion solution was closed with a rubber stopper and the
titration was carried out by adding small volumes of the salt solu-
tion with a microsyringe to a closed quartz cuvette containing the
solution of 1. The UV–vis spectra were obtained after each addition
and the absorbance values were collected at 360 and 400 nm. The
detection and quantification limits were obtained according to the
procedure reported in the literature [57–59].
Single-crystal X-ray structure determination
A prismatic yellow crystal of 1 with dimensions of 0.30–0.16–
0.06 mm3 was selected for crystallographic analysis. X-ray diffrac-
tion data were recorded on a Bruker APX-II DUO diffractometer
equipped with an APEX II CCD area detector using graphite-mono-
Kinetic studies involving compounds 1–3
Kinetic runs were carried out under first-order conditions with
at least an excess of tetra-n-butylammonium cyanide (between
1.5 ꢂ 10ꢁ3 and 2.7 ꢂ 10ꢁ3 mol Lꢁ1). A stock solution of each com-
pound (3.7 ꢂ 10ꢁ3 mol Lꢁ1) was prepared in DMSO. All reactions
were initiated mixing a small volume from the stock solution of
each compound in a hermetically closed 3 cm3 quartz-stoppered
cuvette (10 mm path length) containing 2 mL of DMSO. The final
concentration of the compounds was 5.0 ꢂ 10ꢁ5 mol Lꢁ1 in all
kinetic experiments. After the thermal equilibrium was reached,
a small volume of a stock solution of CNꢁ in DMSO was added to
the cuvette and the kinetic data were collected after an interval
of 5 s. The reaction was monitored through the change in absor-
bance (A) at 340 nm for 1 and 3 and 500 nm for 2. All reactions
gave strict first-order kinetics over more than five half-lives. The
kobs values were obtained from linear plots of ln(A1 ꢁ At) as a
function of time for at least 90% of the reaction using an iterative
chromated Mo K
were recorded by
a
x
(k = 0.71073 Å) at 173 K. The diffraction frames
and / scans using APEX2 [53] and data reduc-
tion procedure was performed using the SAINT and SADABS pro-
grams [54]. The structure was solved and refined with SHELXS97
and SHELXL2013 software [55], respectively. All non-hydrogen
atoms were refined anisotropically. Hydrogen atoms attached to
C atoms were placed at their idealized positions using standard
geometric criteria. ORTEP plot was performed with PLATON soft-
ware [56]. Further crystallographic information is presented in
Table 1.
Full tables containing the crystallographic data (except struc-
ture factors) were deposited at Cambridge Structural Database
(CCDC 977072) and these data are available free of charge at
www.ccdc.cam.ac.uk.
Please cite this article in press as: R.S. Heying et al., A novel strategy for chromogenic chemosensors highly selective toward cyanide based on its reaction
with 4-(2,4-dinitrobenzylideneamino)benzenes or 2,4-dinitrostilbenes, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014),
http://dx.doi.org/10.1016/j.saa.2014.10.041

4
R.S. Heying et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2014) xxx–xxx
least-squares program; correlation coefficients (r2) were >0.998 for
all kinetic runs.
angles are very close to each other. The N3AC7 bond length
[1.2581(15)Å] is slightly shorter than for a typical C@N bond
(1.28 Å) [61,62], which reflects the influence of the electronegative
2,4-dinitrophenyl ring.
The activation parameters were determined from the kobs val-
ues varying the temperature, by reacting compounds 1–3
(5 ꢂ 10ꢁ5 mol Lꢁ1) in DMSO with CNꢁ in a concentration of
2.52 ꢂ 10ꢁ3 mol Lꢁ1 in the cuvette. Arrhenius plots were used to
obtain the Ea values while the entropies and enthalpies of activa-
tion were calculated through the Eyring equation (Eq. (1)) [60],
by means of a plot of ln(kobsh/kBT) as a function of 1/T. All r2 values
Naked-eye detection and UV–vis study of the reaction of the
compounds with CNꢁ
Fig. 2 shows the behavior of solutions of compounds 1–4 in
DMSO in the presence of various anions. Solutions of 1 and 3 are
yellow while those of 2 and 4 are red. When several anions (HSO4-
ꢁ, H2POꢁ4 , NO3ꢁ, CNꢁ, CH3COOꢁ, Fꢁ, Clꢁ, Brꢁ, and Iꢁ) are individually
added to solutions of the compounds, only CNꢁ is responsible for
the change in the color of the solutions of all compounds studied,
with a change to orange observed for 1 and 3 and to light brown
for compounds 2 and 4. The change in the color is not immediately
observed, being visually perceived after 3 min and achieving the
complete change within 10 min.
were >0.99, with standard deviations below 9 ꢂ 10ꢁ2
.
lnðkobsh=kBTÞ ¼
D
S#=R ꢁ
D
H#=RT
ð1Þ
1H NMR studies of the reaction products
Five milligrams of 1 or 3 were placed in an NMR tube and
0.6 mL of DMSO-d6 was added. For 1, a ten-fold excess of CNꢁ in
relation to the compound was added to the tube in order to guar-
antee the complete reaction. In the case of 3 two experiments were
performed, with one and two equivalents of CNꢁ added in relation
to the compound. The 1H NMR spectra were obtained after 1 h at
room temperature.
Fig. 3 shows the UV–vis spectra of the compounds in DMSO in
the absence and in the presence of CNꢁ. The spectra for the com-
pounds in the absence of DMSO have a similar profile, a shift only
occurring in the bands with maxima at wavelengths (kmax
)
between 398 and 498 nm (Table S3). Also, it was observed that 2
and 4 exhibit bands with higher kmax in comparison with 1 and
3. The electronic transitions responsible for these bands are
Calculations
p
?
p⁄, with a charge-transfer character; however, the dimethyl-
All constants were calculated through the fitting of least-
squares regression curves using the program ORIGINÒ 6.1.
amino substituent can provide a considerably higher increase in
the electronic density of the aromatic ring electron donor moiety
in comparison with the methoxy group. Thus, the electron donor
aromatic system with the dimethylamino group has a much
greater electronic density to transfer to the electron acceptor
Results and discussion
X-ray structure characterization of compound 1
group. The values for the molar absorptivities (emax) for the imines
(1 and 2) are lower than the values observed for the stilbenes (3
and 4). These differences suggest that with the change in the con-
jugated bridge from C@N to C@C the system as a whole becomes
more rigid, facilitating the charge transfer through the mesomeric
effect and thus increasing the probability for the occurrence of the
electronic transition.
Compound 1 crystallized in the triclinic system, space group Pı.
¯
The main bond distances and torsion angles are presented in
Tables S1 and S2, respectively. Two independent molecules of 1
were found in the asymmetric unit (Fig. 1), exhibiting slight differ-
ences in their conformations, which can be evidenced by different
C2AC1AC7AN3 torsion angles of 179.29(11)° and 170.08(11)° and
by the interplanar angles between the 2,4-dinitrophenyl and
4-methoxyphenyl rings of 7.92(4)° and 10.20(3)°. If the equivalent
atoms for the two conformers are compared, the bond lengths and
With the addition of CNꢁ to the solutions containing each com-
pound, changes in their UV–vis spectra were observed. For 1
(Fig. 3A), the analysis of the spectra reveals that the band at
kmax = 400 nm related to 1 decreased over time after the addition
of CNꢁ, simultaneously with the appearance of a new band at
kmax = 360 nm and with an increase in the absorbance in the region
between 450 nm and 550 nm. In addition, two isosbestic points
can be clearly noted at 392 nm and 448 nm. For the other imine
(2, Fig. 3B), analysis of the UV–vis spectra over time shows that
on addition of CNꢁ to the solution the band related to the com-
pound at kmax = 500 nm is gradually reduced simultaneously with
the appearance of another band with a maximum at 385 nm and
at the same time an isosbestic point at 442 nm. For 3 (Fig. 3C),
the band at kmax = 400 nm decreases with the addition of CNꢁ
while in the regions of 300–359 nm and 465–600 nm the absor-
bance increased with two isosbestic points observed at 359 and
465 nm. With the addition of CNꢁ to the solution of the stilbene
4 (Fig. 3D) it was observed that the band at kmax = 372 nm, related
to the compound, shows a decrease simultaneously with the
appearance of a new band at kmax = 487 nm, with an isosbestic
point being clearly observed at 419 nm.
Fig. 4A shows the influence of CNꢁ on the UV–vis spectra for 1
in DMSO, a decrease in the band at kmax = 400 nm also being
observed with an increase in the c(CNꢁ), simultaneously with the
appearance of a band at kmax = 360 nm. Fig. 4B shows the depen-
dence of the 360 and 400 nm absorbance ratios (Abs360/Abs400
)
for 1 on the c(CNꢁ). The linear range of the titration curve (insert
Fig. 1. ORTEP diagram of 1. Ellipsoids are drawn at 50% probability level.
in Fig. 4) allowed the determination of the detection and quantifi-
Please cite this article in press as: R.S. Heying et al., A novel strategy for chromogenic chemosensors highly selective toward cyanide based on its reaction
with 4-(2,4-dinitrobenzylideneamino)benzenes or 2,4-dinitrostilbenes, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014),
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R.S. Heying et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2014) xxx–xxx
5
Fig. 2. Solutions of 1 (A), 2 (B), 3 (C), and 4 (D) in DMSO in the absence (a) and in the presence of (b) HSOꢁ4 , (c) H2POꢁ4 , (d) NOꢁ3 , (e) CNꢁ, (f) CH3COOꢁ, (g) Fꢁ, (h) Clꢁ, (i) Brꢁ, and
(j) Iꢁ. The photographs were taken 10 min after the addition of the anions.
cation limits [63,64], these being 9.07 ꢂ 10ꢁ6 and 3.02 ꢂ 10ꢁ5
group. The dimethylamino group increases, through resonance,
the electronic density of the 2,4-dinitrophenyl group, making the
latter less reactive, which reduces its ability to interact with the
nucleophile. If the imines (1 and 2) are compared with the stilb-
enes (3 and 4), the data suggest that the low k2 values for the stilb-
enes may be related to the greater structural rigidity of these
molecules in comparison to the imines, facilitating the action of
the substituents through the mesomeric effect.
mol Lꢁ1, respectively.
Kinetic studies for compounds 1–3 in DMSO in the presence of CNꢁ
The kinetic studies were performed with compounds 1–3 in
DMSO in the presence of an excess of CNꢁ in order to obtain kinetic
first-order conditions. These studies were not conducted with 4
since its reaction with CNꢁ is very slow and thus it is not suitable
for application in a chemosensor. For compounds 1–3 a good fit
was obtained using the first-order equation, which was used to
obtain the kobs values. These rate constants were used to obtain
k2 and the activation parameters for the studied reactions.
Fig. 5 shows plots of kobs as a function of c(CNꢁ) for the reaction
of compounds 1–3 with CNꢁ in DMSO at 25 °C. The data show a lin-
ear relationship between kobs values and the anion concentrations.
A linear fit of the data allowed the k2 values for each system to be
obtained through the angular coefficients.
Table 2 shows the k2 values and respective correlation coeffi-
cients (r2) obtained for the reactions involving compounds 1–3.
The higher k2 value for the compounds possessing a methoxy
group (1 and 3) in relation to those with a dimethylamino substi-
tuent (2 and 4) is due to the fact that the ability of the methoxy
group to donate electronic density to the 2,4-dinitrophenyl elec-
tron-accepting group is lower than that of the dimethylamino
The activation parameters were obtained for the reaction of
compounds 1–3 in DMSO with CNꢁ. Fig. 6 shows the effect of the
temperature on the kobs values for the compounds studied, more
specifically the Arrhenius plots (ln(kobs) versus 1/T), which were
used to obtain the Ea values. The use of the Eyring treatment (kobs-
h/kBT versus 1/T) allowed the
to be obtained. Table 3 shows the activation parameters calculated
for the compounds. Analysis of the
H– and S– values indicates
D D
H– and S– values for the reactions
D
D
that entropic and enthalpic factors are important to the formation
of the activated complex of the reaction. The lowest Ea value was
obtained for 1, in agreement with the fact that the reaction of this
compound with CNꢁ led to the highest k2 value. The data show that
(a) the imines react faster than the stilbenes when they have the
same substituent and (b) the compounds with the methoxy substi-
tuent react faster than the compounds with the dimethylamino
group when the same class of compounds (imine or stilbene) is
considered.
Please cite this article in press as: R.S. Heying et al., A novel strategy for chromogenic chemosensors highly selective toward cyanide based on its reaction
with 4-(2,4-dinitrobenzylideneamino)benzenes or 2,4-dinitrostilbenes, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014),
http://dx.doi.org/10.1016/j.saa.2014.10.041

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R.S. Heying et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2014) xxx–xxx
0,8
0,6
0,4
0,2
4,5
(A)
4,0
3,5
3,0
2,5
0,0
1,0
0,8
0,6
0,4
0,2
0,0
2,0
k
(B)
1,5
1,0
0,5
1,2
1,0
0,8
0,6
0,4
0,2
0,0
1,4
1,2
1,0
0,8
0,6
0,4
0,2
0,0
1,4
1,6
1,8
2,0
2,2
2,4
2,6
2,8
(C)
(D)
c
(CN-) (10-3 mol L-1)
Fig. 5. First-order rate constants for the reaction of 1 (j), 2 ( ), and 3 ( ) with CNꢁ
in DMSO at 25 °C as a function of c (CNꢁ).
Table 2
Second-order rate constants for the reaction of compounds 1–3 with CNꢁ in DMSO at
25 °C.
Compound
k2 (L molꢁ1 sꢁ1
)
r2
1
2
3
2.03
0.69
0.25
0.9995
0.9922
0.9980
300
350
400
450
500
550
600
Wavelength (nm)
Fig. 3. UV–vis spectra for solutions of 1 (A), 2 (B), 3 (C), and 4 (D) in DMSO at 25 °C
before and after the addition of CNꢁ. The last spectrum was collected after 10 min of
reaction.
related to the hydrogens of the ring containing the nitro groups
are not observed after the reaction with CNꢁ, which indicates the
nucleophilic attack of the anion on the ring. The signals related
to the ring containing the methoxy group exhibited the same pat-
tern observed before the reaction, although displaced, indicating
that this ring remains intact. A comparison of the data with the
1H NMR spectrum for p-anisidine (Fig. 7C), which was the reactant
used in the synthesis of 1, indicates the coincidence of the two
doublets centered at d 6.50 and 6.63 (aromatic hydrogens) and of
1H NMR studies on the reaction of 1 and 3 in the presence of CNꢁ
Fig. 7 shows the 1H NMR spectra for 1 in DMSO-d6 in the
absence (Fig. 7A) and in the presence of CNꢁ after 1 h of reaction
(Fig. 7B). A comparison of the spectra reveals that the signals
1.8
1.4
A
B
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
1.2
1.0
0.90
0.85
0.80
0.75
0.8
0.70
0
1
2
3
4
c(CN-) (10-4mol L-1
)
300
400
500
600
0.0
0.5
1.0
1.5
2.0
c(CN-) (10-3mol L-1)
Wavelength (nm)
Fig. 4. (A) Influence of the addition of increasing amounts of CNꢁ on the UV–vis spectra of 1 (5.0 ꢂ 10ꢁ5 mol Lꢁ1) in DMSO at 25 °C. The final concentration of CNꢁ was
1.8 ꢂ 10ꢁ3 mol Lꢁ1. (B) Titration curve for 1 using the variations in the 360 nm and 400 nm absorbance ratio for the compound with the addition of CNꢁ. The insert shows the
linear range of the ratiometric titration curve, which was used to estimate the detection and quantification limits.
Please cite this article in press as: R.S. Heying et al., A novel strategy for chromogenic chemosensors highly selective toward cyanide based on its reaction
with 4-(2,4-dinitrobenzylideneamino)benzenes or 2,4-dinitrostilbenes, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014),
http://dx.doi.org/10.1016/j.saa.2014.10.041

R.S. Heying et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2014) xxx–xxx
7
-3,5
-4,0
-4,5
-5,0
-5,5
-6,0
-6,5
-7,0
-7,5
-8,0
k
3,1
3,2
3,3
3,4
3,5
T -1(10-3K-1)
Fig. 8. Solutions of 1 in DMSO in the absence (a) and in the presence of (b) CNꢁ, (c)
CNꢁ + Cu+, and (d) CNꢁ + Cu2+. The metal ions were added 10 min after the mixture
of 1 with CNꢁ and the photograph was taken immediately.
Fig. 6. Influence of temperature on kobs values for the reaction of 1 (j), 2 ( ), and 3
(
) with CNꢁ in DMSO. The concentrations of each compound and CNꢁ were
5 ꢂ 10ꢁ5 and 2.52 ꢂ 10ꢁ3 mol Lꢁ1, respectively.
In solution, Cu2+ reacts with CNꢁ in excess to form firstly CuCN
and cyanogen (CN)2 [65] and secondly complexes with a high sta-
Table 3
Activation parameters for the reaction of compounds 1–3 with CNꢁ in DMSO.
bility constant, such as [Cu(CN)2]ꢁ, [Cu(CN)3]2ꢁ, and [Cu(CN)4]3ꢁ
,
Compound
Ea (kJ molꢁ1
)
D
H– (kJ molꢁ1
)
D
S– (J molꢁ1 Kꢁ1
)
r2
the species commonly found being [Cu(CN)2]ꢁ (K = 1 ꢂ 1024) and
[Cu(CN)4]3ꢁ (K = 1 ꢂ 1030) [66–70]. Some anionic chemosensors
based on displacement assays were carried out considering these
experimental findings [26,34,71–74]. It was observed that on addi-
tion of Cu2+ to the products of the reaction of 1 and CNꢁ in DMSO
the solution immediately recovers its yellow color (Fig. 8). UV–vis
spectra obtained for 1 in DMSO and of the product of the reaction
of 1 with CNꢁ in the presence of Cu2+ are similar, suggesting that
this reaction is reversible. Cu2+ is a paramagnetic species which
cannot be used in NMR studies. Therefore, the Cu+ ion was added
to the products of the reaction and, interestingly, this experiment
showed that the metal ion causes a return to the original system,
that is, before the addition of CNꢁ, and the 1H NMR spectrum
immediately after the addition of Cu+ (Fig. 7D) is essentially the
same as that for 1 (Fig. 7A).
1
2
3
40.5
57.2
63.6
37.9
53.8
58.2
ꢁ163
ꢁ118
ꢁ112
0.9951
0.9960
0.9860
4 4
(a)
(b)
4
3 3
2 2
1 1
3
2
1
The analysis of the spectra for compound 3 in the absence and
in the presence of CNꢁ (Fig. 9) verifies that in the stilbenes the C@C
bridge is not broken. Therefore, only the attack of CNꢁ on the 2,4-
dinitrophenyl group of compound 3 occurs. However, well-defined
(c)
(d)
(a)
9.0
8.4
7.8 7.4 7.0
6.4
5.8
5.2
4.6
3
δ (ppm)
Fig. 7. 1H NMR spectra (in DMSO-d6) for (a) 1, (b) 1 and CNꢁ after 1 h of reaction, (c)
p-anisidine, and (d) 1 + CNꢁ + Cu+, the metal ion being added after 1 h of the
mixture of 1 with CNꢁ.
(b)
2
the singlets at d 3.60 (AOCH3) and 4.57 (ANH2) with the signals in
Fig. 7B. This means that the C@N bond in 1 is broken in the pres-
ence of CNꢁ with the generation of p-anisidine and a product other
than 2,4-dinitrobenzaldehyde. Since aromatic hydrogens and the
aldehyde hydrogen of 2,4-dinitrobenzaldehyde could not be
observed, the data suggest that the CNꢁ attacks the 2,4-dinitro-
phenyl group and also the carbonyl in the compound nucleophili-
cally, forming several products, because the reaction does not
occur on the ring at a certain position. An 1H NMR spectrum of
2,4-dinitrobenzaldehyde in the presence of CNꢁ revealed a pattern
similar to that observed in the reaction of 1 with CNꢁ (see Figs. S23
and S24).
(c)
1
8.5
8.0
7.5
7.0
(ppm)
6.5
6.0
5.5
5.0
δ
Fig. 9. 1H NMR spectra (in DMSO-d6) for (a) 3, (b) 3 with one equivalent of CNꢁ, and
(c) 3 with two equivalents of CNꢁ after 1 h of reaction.
Please cite this article in press as: R.S. Heying et al., A novel strategy for chromogenic chemosensors highly selective toward cyanide based on its reaction
with 4-(2,4-dinitrobenzylideneamino)benzenes or 2,4-dinitrostilbenes, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014),
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R.S. Heying et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2014) xxx–xxx
(a)
N
O2
N
O2
N
C
O
C
+
N
C
N
O2
+
H
C
C
N
H
H2N
H
O
O2
3
N
O
O
N
+
-
u
C
N
C
A
(b)
N
O2
N
O2
N
C
N
O2
H
N
O2
3
+
H
C
3
N
C
O
B
Scheme 2. Representation of the reaction of (a) 1 and (b) 3 with CNꢁ in DMSO.
signals related to the hydrogens of the ring that was not attacked
by CNꢁ were not observed. This is due to the fact that as the
C@C bond is not broken and the cyano group does not attack the
2,4-dinitro ring at a certain position (various products being gener-
ated), which is responsible for the shifting of the signals for all of
the hydrogen atoms in the molecule.
anion acts as a nucleophile, being added to the strongly electro-
philic carbon atom of the C@N bond. Subsequently, the C@N bond
is broken, leading to the formation of products with a different
color compared with the starting reactant. This system exhibited
reversibility with the addition of copper ions, which also allows
the use of the 1-CNꢁ ensemble as a chromogenic chemosensor
for the detection of this metal ion, similarly to the displacement
assays found in the literature. Since it is possible to connect the
2,4-dinitrophenyl group, via an imine bridge, to other aromatic
groups which are potentially fluorogenic or chromogenic, the sys-
tem described herein is conceptually interesting for the develop-
Mechanism involved in the reaction of the compounds with CNꢁ
Scheme 2 represents the reactions of 1 (a) and 3 (b) with CNꢁ in
DMSO. The experimental data suggest that the first step in the
reaction of 1 with CNꢁ involves a nucleophilic attack of the anion
on the compound, although it was not possible to verify whether
this attack is on the C@N bond or on the 2,4-dinitrophenyl group
in the compound, but one of these two possibilities should corre-
spond to the rate-determining step of the reaction. Subsequently,
in a sequence of reversible steps, this intermediate is transformed
into the products of the reaction, p-anisidine and other products,
having the molecular structure A. This reaction occurs due to the
presence of water in the medium, even in small amounts. In fact,
even with the use of water-free DMSO water is always introduced
in the system with the addition of the CNꢁ salt. The attack of CNꢁ
on the 2,4-dinitrophenyl ring of the compound generated a very
complicated set of signals on the NMR spectrum in the range cor-
responding to the aromatic hydrogens. Since a similar pattern was
observed on the NMR spectrum for 2,4-dinitrobenzaldehyde
(Figs. S23 and S24) and also that for compound 3, the CNꢁ data sug-
gest that the nucleophilic attack of CNꢁ on the 2,4-dinitrophenyl
ring of the compounds did not occur at a defined position, leading
to the formation of various products, represented by structure A, as
suggested from an analysis of the NMR data, these being responsi-
ble for the orange color observed in solution. The addition of the
Cu+ ion to the system containing A species caused the removal of
the reversibly bonded CNꢁ, with the formation of 2,4-dinitrobenz-
aldehyde, which reacted with p-anisidine to regenerate compound
1. Scheme 2(b) represents the reaction between 3 and CNꢁ in
DMSO. When the chemosensor is a stilbene the CNꢁ only attacks
the 2,4-dinitrophenyl group nucleophilically, generating the prod-
ucts represented by the structure B, which are responsible for the
color change in solution. In this case, the products of the reaction
are sufficiently stable and the process cannot be reversed with
the use of the copper ion.
ment of efficient optical devices for the detection of CNꢁ and Cu2+
.
Acknowledgements
The financial support of the Brazilian Conselho Nacional de
Desenvolvimento Científico e Tecnológico (CNPq), Coordenação
de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Labo-
ratório Central de Biologia Molecular (CEBIME/UFSC) and UFSC is
gratefully acknowledged.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2014.10.041.
References
[1] M.A. Saeed, D.R. Powell, M.A. Hossain, Tetrahedron Lett. 51 (2010) 4904–4907.
[2] V.G. Marini, L.M. Zimmermann, V.G. Machado, Spectrochim. Acta A 75 (2010)
799–806.
[3] W. Huang, Y. Li, Z. Yang, H. Lin, H. Lin, Spectrochim. Acta A 79 (2011) 471–475.
[4] K. Ghosh, S.S. Ali, S. Joardar, Tetrahedron Lett. 53 (2012) 2054–2058.
[5] V. Reena, S. Suganya, S. Velmathi, J. Fluorine Chem. 153 (2013) 89–95.
[6] P. Zhang, B.-B. Shi, T.-B. Wei, Y.-M. Zhang, Q. Lin, H. Yao, X.-M. You, Dyes
Pigments 99 (2013) 857–862.
[7] S. Erdemir, O. Kocyigit, O. Alici, S. Malkondu, Tetrahedron Lett. 54 (2013) 613–
617.
[8] M.E. Moragues, L.E. Santos-Figueroa, T. Ábalos, F. Sancenón, R. Martínez-
Máñez, Tetrahedron Lett. 53 (2012) 5110–5113.
[9] A. Agostini, M. Milani, R. Martínez-Máñez, M. Licchelli, J. Soto, F. Sancenón,
Chem. Asian J. 7 (2012) 2040–2044.
[10] J.J. Park, Y.-H. Kim, C. Kim, J. Kang, Tetrahedron Lett. 52 (2011) 2759–2763.
[11] L.M. Zimmermann-Dimer, V.G. Machado, Quim. Nova 31 (2008) 2134–2146.
[12] L.E. Santos-Figueroa, M.E. Moragues, E. Climent, A. Agostini, R. Martínez-
Máñez, F. Sancenón, Chem. Soc. Rev. 42 (2013) 3489–3613.
[13] Y. Yang, Q. Zhao, W. Feng, F. Li, Chem. Rev. 113 (2012) 192–270.
[14] M.E. Moragues, R. Martínez-Máñez, F. Sancenón, Chem. Soc. Rev. 40 (2011)
2593–2643.
[15] J.M. Garcia, F.C. Garcia, F. Serna, J.L. de la Pena, Polym. Rev. 51 (2011) 341–390.
[16] G.J. Mohr, Anal. Bioanal. Chem. 386 (2006) 1201–1214.
[17] R. Martínez-Máñez, F. Sancenón, Chem. Rev. 103 (2003) 4419–4476.
[18] J. Lv, Z. Zhang, J. Li, L. Luo, Forensic Sci. Int. 148 (2005) 15–19.
Conclusions
The experiments allowed the observation of the high selectivity
of 1 in the detection of CNꢁ in DMSO, due to a process in which the
Please cite this article in press as: R.S. Heying et al., A novel strategy for chromogenic chemosensors highly selective toward cyanide based on its reaction
with 4-(2,4-dinitrobenzylideneamino)benzenes or 2,4-dinitrostilbenes, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014),
http://dx.doi.org/10.1016/j.saa.2014.10.041

R.S. Heying et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2014) xxx–xxx
9
[19] L. Nelson, J. Emerg. Nurs. 32 (2006) S8–S11.
[48] K. Osowska, O.Š. Miljanic´, J. Am. Chem. Soc. 133 (2010) 724–727.
[20] F.H. Zelder, C. Männel-Croisé, CHIMIA 63 (2009) 58–62.
[21] C. Agatemor, Elec. J. Env. Agric. Food Chem. 8 (2009) 195–200.
[22] T.J. Dale, J. Rebek, J. Am. Chem. Soc 128 (2006) 4500–4501.
[23] S. Royo, R. Martínez-Máñez, F. Sancenón, A.M. Costero, M. Parra, S. Gil, Chem.
Commun. (2007) 4839–4847.
[49] A.I. Vogel, B.S. Furniss, Vogel’s Textbook of Practical Organic Chemistry,
Longman, 1989.
[50] F. Barrow, F.J. Thorneycroft, J. Chem. Soc. (1939) 769–773.
[51] S. Saravanan, P.C. Srinivasan, Synth. Comm. 31 (2001) 823–826.
[52] H.B. Nisbet, J. Chem. Soc. (1927) 2081–2086.
[24] M. Burnworth, S.J. Rowan, C. Weder, Chem. Eur. J. 13 (2007) 7828–7836.
[25] Y.C. Yang, J.A. Baker, J.R. Ward, Chem. Rev. 92 (1992) 1729–1743.
[26] S. He, S.T. Iacono, S.M. Budy, A.E. Dennis, D.W. Smith, R.C. Smith, J. Mater.
Chem. 18 (2008) 1970–1976.
[53] APEX II, in: Data Collection Software, Bruker AXS Inc.: Madison, WI, 2005–
2011.
[54] Bruker, SADABS, APEX2 and SAINT, in, Bruker AXS Inc., Madison, Wisconsin,
USA, 2009.
[27] T.J. Dale, J. Rebek, Angew. Chem. Int. Ed. 48 (2009) 7850–7852.
[28] R. Gotor, A.M. Costero, S. Gil, M. Parra, R. Martínez-Máñez, F. Sancenón, Chem.
Eur. J. 17 (2011) (1997) 11994–11997.
[29] S. Royo, A.M. Costero, M. Parra, S. Gil, R. Martínez-Máñez, F. Sancenón, Chem.
Eur. J. 17 (2011) 6931–6934.
[30] D.-G. Cho, J.L. Sessler, Chem. Soc. Rev. 38 (2009) 1647–1662.
[31] E.V. Anslyn, J. Org. Chem. 72 (2007) 687–699.
[32] C.R. Nicoleti, V.G. Marini, L.M. Zimmermann, V.G. Machado, J. Braz. Chem. Soc.
23 (2012) 1488–1500.
[55] G. Sheldrick, Acta Crystallogr. Sect. A 64 (2008) 112–122.
[56] A. Spek, J. Appl. Crystallogr. 36 (2003) 7–13.
[57] M. Zhu, M. Yuan, X. Liu, J. Xu, J. Lv, C. Huang, H. Liu, Y. Li, S. Wang, D. Zhu, Org.
Lett. 10 (2008) 1481–1484.
[58] J. Isaad, A. El Achari, F. Malek, Dyes Pigments 97 (2013) 134–140.
[59] J. Isaad, A. El Achari, Tetrahedron 67 (2011) 5678–5685.
[60] S.R. Logan, Fundamentals of Chemical Kinetics, Longman Group Limited, 1996.
[61] J. March, Advanced Organic Chemistry: Reactions, Mechanisms, and Structure,
Wiley, 1985.
[33] L.G. Nandi, C.R. Nicoleti, I.C. Bellettini, V.G. Machado, Anal. Chem. 86 (2014)
4653–4656.
[62] F.H. Allen, O. Kennard, D.G. Watson, L. Brammer, A.G. Orpen, R. Taylor, J. Chem.
Soc., Perkin Trans. 2 (1987). S1–S19.
[34] C.R. Nicoleti, D.N. Garcia, L.E. da Silva, I.M. Begnini, R.A. Rebelo, A.C. Joussef,
V.G. Machado, J. Fluoresc. 22 (2012) 1033–1046.
[63] D.A. Skoog, Fundamentals of Analytical Chemistry (2004). Thomson-Brooks/
Cole.
[35] X. Lou, D. Ou, Q. Li, Z. Li, Chem. Commun. 48 (2012) 8462–8477.
[36] A. Helal, S. Kim, H.S. Kim, Bull. Korean Chem. Soc. 32 (2011) 3123–3126.
[37] S. Park, H.-J. Kim, Sens. Actuat. B-Chem. 168 (2012) 376–380.
[38] Y.-Y. Guo, X.-L. Tang, F.-P. Hou, J. Wu, W. Dou, W.-W. Qin, J.-X. Ru, G.-L. Zhang,
W.-S. Liu, X.-J. Yao, Sens. Actuat. B-Chem. 181 (2013) 202–208.
[39] P. Kaur, S. Kaur, K. Singh, Inorg. Chem. Comm. 12 (2009) 978–981.
[40] D.T. Quang, J.S. Kim, Chem. Rev. 110 (2010) 6280–6301.
[41] J.J. Du, M.M. Hu, J.L. Fan, X.J. Peng, Chem. Soc. Rev. 41 (2012) 4511–4535.
[42] M.Y. Chae, A.W. Czarnik, J. Am. Chem. Soc 114 (1992) 9704–9705.
[43] Y. Sun, Y. Liu, M. Chen, W. Guo, Talanta 80 (2009) 996–1000.
[44] J. Yoshino, N. Kano, T. Kawashima, J. Org. Chem. 74 (2009) 7496–7503.
[45] J.Y. Noh, I.H. Hwang, H. Kim, E.J. Song, K.B. Kim, C. Kim, Bull. Korean Chem. Soc.
34 (2013) 1985–1989.
[64] J. Isaad, A. El Achari, Tetrahedron 67 (2011) 4939–4947.
[65] F.A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry, fifth ed., Wiley-
Interscience, New York, 1988.
[66] A. Katagiri, S. Yoshimura, S. Yoshizawa, Inorg. Chem. 20 (1981) 4143–4147.
[67] K. Kurnia, D.E. Giles, P.M. May, P. Singh, G.T. Hefter, Talanta 43 (1996) 2045–
2051.
[68] G.C. Lukey, J.S.J. van Deventer, S.T. Huntington, R.L. Chowdhury, D.C. Shallcross,
Hydrometallurgy 53 (1999) 233–244.
[69] J. Lu, D.B. Dreisinger, W.C. Cooper, Hydrometallurgy 66 (2002) 23–36.
[70] L.-B. Li, S.-J. Ji, Y. Liu, Chin. J. Chem. 26 (2008) 979–982.
[71] X. Lou, L. Zhang, J. Qin, Z. Li, Chem. Commun. (2008) 5848–5850.
[72] Z.A. Li, X. Lou, H. Yu, Z. Li, J. Qin, Macromolecules 41 (2008) 7433–7439.
[73] Q. Zeng, P. Cai, Z. Li, J. Qin, B.Z. Tang, Chem. Commun. (2008) 1094–1096.
[74] S.-Y. Chung, S.-W. Nam, J. Lim, S. Park, J. Yoon, Chem. Commun. (2009) 2866–
2868.
[46] S. Sharma, M.S. Hundal, G. Hundal, Org. Biomol. Chem. 11 (2013) 654–661.
[47] D.B.G. Williams, M. Lawton, J. Org. Chem. 75 (2010) 8351–8354.
Please cite this article in press as: R.S. Heying et al., A novel strategy for chromogenic chemosensors highly selective toward cyanide based on its reaction
with 4-(2,4-dinitrobenzylideneamino)benzenes or 2,4-dinitrostilbenes, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014),
http://dx.doi.org/10.1016/j.saa.2014.10.041