Isatin N-phenylsemicarbazone: Effect of substituents and concentration on anion sensing selectivity and sensitivity

Article abstract of DOI:10.1039/c4ra04847d

The effect of substituent and concentration on anion sensing selectivity and sensitivity of nine new easily synthesized isatin N-phenylsemicarbazone E-isomer sensors IIIa-XIa was investigated. The substantial difference between the association constants for IIIa-XIa interaction with strongly and weakly basic anions allows detection of F^- or CH₃COO^- anions even at high weakly basic anion excess. Substitution in position 5- of the isatin ring and para-substitution on the phenyl ring in the phenylsemicarbazide chain influence sensor:anion complex stoichiometry and thus also sensor sensitivity. Detection limits of 3-4 × 10^-7 mol dm^-3 for F^- and CH₃COO^- anions by sensors IVa and Va bearing electron-withdrawing substituents are among the lowest published detection limits for these anions in organic solvents. The high selectivity and sensitivity of sensor VIa allows confident F^- detection at tolerated fluoride drinking-water level. The solution dilution leads to a dramatic change in sensor selectivity. Consequently, one E-isomer can be used to sense both strongly and weakly basic anions. On the other side, higher sensor solution concentrations increase the F^- and CH₃COO^- anion detection range, similar to the additional Z-isomer utilization. This journal is

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Isatin
N-phenylsemicarbazone:
Effect
of
substituent and concentration on anion sensing
selectivity and sensitivity
Cite this: DOI: 10.1039/x0xx00000x
Marek Cigáň*, Klaudia Jakusová, Jana Donovalová, Vojtech Szöcs and Anton Gáplovský
Received 00th January 2012,
Accepted 00th January 2012
The effect of substituent and concentration on anion sensing selectivity and sensitivity of nine
DOI: 10.1039/x0xx00000x
new easily synthesized isatin N-phenylsemicarbazone E-isomer sensors IIIa
-XIa was
investigated. The substantial difference between the association constants for IIIa-XIa interaction
www.rsc.org/
with strongly and weakly basic anions allows detection of F- or CH3COO- anions even at high
weakly basic anion excess. Substitution in position 5- of the isatin ring and para- substitution on
the phenyl ring in the phenylsemicarbazide chain influence sensor:anion complex stoichiometry
and thus also sensor sensitivity. Detection limits of 3-4×10-7 mol dm-3 for F- and CH3COO- anions
by sensors IVa and Va bearing electron-withdrawing substituents are among the lowest
published detection limits for these anions in organic solvents. The high selectivity and sensitivity
of sensor VIa allows confident F- detection at tolerated fluoride drinking-water level. The solution
dilution leads to dramatic change in sensor selectivity. Consequently, one E-isomer can be used
to sense both strongly and weakly basic anions. On the other side, higher sensor solution
concentrations increase F- and CH3COO- anion detection range, similar to the additional Z-
isomer utilization.
Introduction
isatin-3-4-phenyl(semicarbazone) I and N-methylisatin-3-4-
phenyl(semicarbazone) II as sensors influenced the equilibrium
ratio of the individual sensor tautomeric forms in the liquid
phase.
Ion and neutral molecule recognition and signalling are
currently amongst the most intense emerging areas of
supramolecular chemistry. While anions play a very important
role in many chemical and biological processes, their
identification and quantification are quite complex; especially
in biological systems. One way to overcome this problem is to
utilize new optical receptors specifically designed for individual
anions. Supramolecular chemistry has focused on the
development of selective colorimetric or fluorescent anion
sensors for the last twenty years 1-4, and researches including
Wenzel, Chudzinski, Bergamaschi, Jiménez, Martínez-Máñez
and Gale continue this work.5-10
The E- and Z- sensor isomers differed in sensitivity,
selectivity and sensing mechanism. UV-Vis spectroscopy
readily determined the equilibrium ratio of the individual
tautomeric forms affected by; (1) the inter- and intra-
molecular
interaction
modulation
of
isatinphenylsemicarbazone molecules by anion induced
changes in receptor molecule solvation shells and (2) the
sensor-anion interaction with urea hydrogens. Appropriate
selection of experimental conditions resulted in a high degree
of sensor selectivity for some investigated anions. Sensors Ia
-
Anions and receptors interact together particularly through
hydrogen bonding interactions.4,11-14 Due to the facile synthesis
and easily-tunable NH acidity, amides, ureas and thioureas
persist as the most widely employed hydrogen bond donor
groups in anion receptor systems.10
IIb provided both excellent signal to noise ratio and wide
detection range. Detection of F- or CH3COO- anions at high
weakly-basic anion excess was also possible. Furthermore, due
to excellent E isomer sensitivity in organic media, these
isomers can be used for F- or CH3COO- sensing in semi-aqueous
media. The photodegradation of E-isomer anion sensors Ia and
IIa due to light initiated E-Z isomerization may complicate the
anion detection, therefore care should be taken when
interpreting data for quantitative determination of anions
using Ia and IIa E-isomers. However, photochemical E-Z
Anion induced tautomerism and the light and thermally
initiated mutual E- and Z-isomer transformations of two
efficient and easily synthesized isatin N-phenylsemicarbazone
colorimetric sensors were investigated in our recent three
studies (ESI Scheme S1†).15-17 Therein, the interaction of F-,
-
-
AcO-, H2PO4 , Br- and HSO4 anions with E- and Z-isomers of
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DOI: 10.1039/C4RA04847D
isomerization efficiency is relatively low at ФE-Z
<
0.01, and Results and Discussion
this allows reliable detection of strongly basic anions using Ia
or IIa. In addition, the easy E-isomer transformation to the
corresponding Z-isomer and the utilization of both isomers
significantly increases the detection range for F- and CH3COO-
anions valid for Ia or IIa in organic media from 10-6-10-4 mol
dm-3 to 10-6-10-2 mol dm-3 of F- or CH3COO-. Although zero
efficiency of back photochemical Z-E isomerization excludes
Sensor Selectivity
Anion presence affects the degree of IIIa
the DMF solution through intermolecular interactions.16 In the
presence of strongly basic anions (F- and CH3COO-), the IIIa
XIa
-
XIa self-association in
-
E-isomers transform from their self-associate hydrazide
A (keto) form to hydrazonolate (enolate) form B (Scheme 2).
This transformation is accompanied by a decrease in
absorption intensity at approximately 330 nm and increased
absorption at approximately 410 nm (Fig. 1 and ESI Figs. S1†,
S2†).
the use of isatinphenylsemicarbazones
I and II as molecular
switches, the absence of thermally initiated E-Z isomerization
and both photochemically and thermally initiated back Z-E
isomerizations in strongly interacting polar solvents are
beneficial for Ia and IIa E-isomer application in chemical
actinometry.
Strongly basic anions influence the solvation shell of the E-
isomer self-associate, and this interaction leads to formation
of the non-associated hydrazide. Concurrently, strongly basic
anions interact mostly with the highly acidic NH hydrogen of
hydrazide resulting in hydrazonol formation. This is sharply
contrasted with most urea and thiourea based sensors which
interact with CH3COO- in double hydrogen bonding to the Y-
shaped urea/thiourea moiety.9,18,19,… The reason for this
anomalous isatin N-phenylsemicarbazones behaviour is the
lower energy of its s-cis, s-trans –NHCONH– structural
fragment conformation compared to the Y-shaped s-trans, s-
trans –NHCONH– arrangement.17
Scheme 2. Presumed interaction of derivatives Ia and IIIa-XIa with F- (or
CH3COO-) anions during Ia solution titration with TBA+F- (or TBA+CH3COO-).
Herein, the substituent and dilution effect on anion sensing
of nine new isatin N-phenylsemicarbazone E-isomers IIIa
reported (Scheme 1); including the determination of light
initiated E-Z isomerization quantum yield (ФE-Z The
-XIa is
).
properties of these nine sensors with various substituents in
position 5- of the isatin or in the phenyl ring para- position are
compared with those for the unsubstituted Ia E-isomer. This
research is necessary for practical application of these
compounds as anion sensors and also for development and
design of new effective anion sensors. In addition, concepts of
sensing selectivity, sensitivity, detection range and detection
limit for these colorimetric sensors, together with
mathematical analysis of the well-known relation for
association constants Kass determination, are discussed in this
paper.
Fig. 1. Evolution of the UV-VIS spectrum of isatin N-phenylsemicarbazone E-
isomer IVa in DMF during IVa solution titration with TBA+CH3COO-
(cIVa = 1×10-4 mol dm-3; cCH3COO- = 0 mol dm-3, 1×10-5 mol dm-3, 2×10-5 mol dm-
3, 3×10-5 mol dm-3, 4×10-5 mol dm-3, 5×10-5 mol dm-3, 1×10-4 mol dm-3, 5×10-
4 mol dm-3, 1×10-3 mol dm-3 and 1×10-2 mol dm-3).
Similar to the result observed for Ia, the addition of weakly
-
basic anions such as Br- and HSO4 shifts the tautomeric
hydrazide/hydrazonol equilibrium for all substituted IIIa-XIa
derivatives to the hydrazide form A. Absortion band intensity
at approximately 410 nm decreases in the presence of these
anions in contrast to the F- and CH3COO- effect (ESI Fig. S3†,
S4†).
Scheme 1. Molecular structure of studied isatin N-phenylsemicarbazones
IIIa-XIa.
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Because the anion-receptor 1:1 Kass constants higher than second hydrazide molecule is stabilized by the solvent as
105 cannot be determined precisely by UV-VIS spectroscopy hydrazonol form. The tendency to form 2:1 complexes
(see Appendix A), sensor selectivity was investigated in therefore correlates fairly well with the hydrazonol form
DMF:H2O (9:1; v/v) solvent mixture (Table 1; ESI Fig. S5†, S6†). stabilization by solvation that increases in isatin N-
However, the large Kass sensitivity to additional anion-receptor phenylsemicarbazones with electron-withdrawing substituents
interactions in the high anion concentration region does not (ESI Figs. S8†, S9†).
allow correct selectivity comparison for IIIa
-
XIa sensors from
Substantial difference between the Kass values for IIIa-XIa
their Kass values alone (see Appendix B).
interaction with strongly and weakly basic anions allows
Interestingly, the –CN, –Br and –OCF3 electron-withdrawing detection of F- and CH3COO- anions even at high weakly basic
-
substituents in VIa
,
IXa and Xa
anion excess (Kass=101-102 for Br- or HSO4 anions).
Table 1. Association constants Kass (mol-1 dm3) of the studied E-isomers of
isatin N-phenylsemicarbazones Ia and IIIa-XIa with anions in DMF at 298.16
K.
Sensor Sensitivity
Sensitivity denotes sensor ability to detect an analyte at a
specified concentration. Sensor sensitivity depends not only on
sensor-anion interaction strength (Kass) but also on sensor
signal changes following anion-binding.
Association constants –Kass
Anion
Compd
F-
R2
CH3COO-
R2
The sensitivity of isatin N-phenylsemicarbazone IIIa
-XIa E-
(6.7 ± 0.2) × 103
(5.2 ± 0.2) × 103
(1.6 ± 0.5) × 104
(7.7 ± 0.2) × 103
Ia
0.9963
0.9906
0.9673
0.9934
isomers was compared by introducing the Γ sensitivity
parameter which describes detection-wavelength absorbance
IIIa
IVa
Va
changes in the presence of 1 equivalent of anion.
(1.2 ± 0.1) × 104
(2.9 ± 0.7) × 104
(5.6 ± 1.8) × 104
(5.3 ± 0.1) × 103
(5.4 ± 0.8) × 103
0.9810
0.9421
0.9869
0.9784
0.9853
(1.2 ± 0.1) × 104
(2.2 ± 0.3) × 104
0.9864
0.9710
Substitution in position 5- of the isatin ring and para-
substitution in the phenylsemicarbazide chain phenyl ring
influence
electron-withdrawing substituents increase the
sensitivity value, increase correlates rather with the sensor
Γ
value (Fig. 2 and ESI Fig. S10†). Although mainly
VIa
VIIa
VIIIa
(8.6 ± 4.1) × 106a 0.9581
Γ
sensor
Γ
(9.0 ± 0.6) × 103
(1.2 ± 0.0) × 104
0.9898
0.9874
ability to form 2:1 complexes than with the increasing strength
of electron-withdrawing group. However, the absence of
sensitivity icrease in Xa forming the most stable 2:1 complex
(Table 1) and the sensitivity order change in DMF compared to
DMF:H2O solvent mixture point out the complexity of
sensor/sensor, sensor/anion and sensor/solvent interactions
(Fig. 2 and ESI Fig. S10†). Combination of these processes
creates the complexity of resultant substituent influence on
sensor sensitivity.
IXa
Xa
(5.1 ± 0.6) × 104
(5.7 ± 3.2) × 107a
(2.4 ± 0.1) × 103
0.9942
0.9663
0.9967
(4.8 ± 2.3) × 107a 0.9728
(1.7 ± 0.9) × 108a 0.9574
(1.3 ± 0.1) × 104
XIa
0.9697
– sensor:anion 2:1 complex – Kass in mol-2 dm6; cE-isomer
1×10-4 mol-1 dm3; R2 – coefficient of determination (average
=
a
value)
change the sensor:anion binding stoichiometry to 2:1 and thus
further complicates IIIa-XIa Kass comparison. In these cases,
one anion binds two sensor molecules (Table 1; ESI Fig. S7†).
Despite the above mentioned complexities encountered in
Kass determination for 1:1 IIIa
basic anions, the Kass values higher than 1×104 for IIIa
and IIIa
XIa:CH3COO- 1:1 complexes and the Kass above 1×107
-
XIa complexes with strongly
-
XIa:F-
-
for sensor:anion 2:1 complexes indicate exceptionally strong F-
and CH3COO- anion binding. Therefore, strongly basic anion
addition leads rather to the NH group deprotonation than to
the
hydrazide/hydrazonol tautomeric equilibrium shift
resulting in sensor:hydrazonol 1:1 complex formation bounded
by one hydrogen bond (as we assumed in our previous
article).16 Absorbance increase at 410 nm during titration
process in non-polar CHCl3, where the hydrazonol is not
formed, supports this conclusion.
Fig. 2. The sensitivity Γ (to 1 equiv. of A-) of the studied E-isomers of isatin
N-phenylsemicarbazones Ia and IIIa-XIa at 410 nm for anions in DMF:H2O
(9:1; v/v) solvent mixture at 298.16 K (cE-isomer = 1 × 10-4 mol-1 dm3 for F- and
CH3COO- sensing and cE-isomer = 1 × 10-5 mol-1 dm3 for Br- and HSO4- sensing).
In the case of sensor:anion 2:1 complexes, one aggregate
(dimer) molecule is transformed to hydrazonolate B and the
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The IIIa
DOI: 10.1039/C4RA04847D
-
XIa E-isomer sensitivity for weakly basic Br- and these anions in organic solvent.20-23 At 10-5 mol dm-3 sensor
HSO4 anions at 10-5 mol dm-3 sensor concentration in solution concentration,
the tautomeric hydrazide-hydrazonol
is almost 1000-times lower than for F- and CH3COO- anions.
equilibrium is completely shifted to the hydrazonol side, and
Detection limit (3 /S) is the lowest concentration level isatin N-phenylsemicarbazones can be used as sensors for
determined statistically different from a blank with 99% weakly basic anions. Sensor solution dilution thus leads to
confidence and quantification limit (10 /S) is the level above dramatic change in sensor selectivity. Therefore, the one E-
which quantitative results are obtained with a specified degree isomer can be used for both strongly and weakly basic anion
-
σ
σ
-
of confidence. The calculated detection and quantification detection. The determined 3σ
/S for Br- and HSO4 anions in
-
limits for F-, CH3COO-, Br- and HSO4 anions using the most DMF for some isatin N-phenylsemicarbazone sensors is
important isatin N-phenylsemicarbazone E-isomer sensors highlighted in Table 2. Their values are in the 0.2-0.4 mmol dm-
from the Ia
/S for strongly basic F- and CH3COO- anions by sensors IVa
-
XIa set are summarized in Table 2. The determined 3 range.
3
σ
and Va are amongst the lowest published detection limits for
Table 2. Detection (3σ/S) and quantification (10σ/S) limits in ꢀmol dm-3 for selected anions using the most important isatin N-phenylsemicarbazone E-isomer
sensors from the Ia-XIa set in DMF at 298.16 K (refer to absorbance at 410 nm).
3σ/S [ꢀM]
10σ/S [ꢀM]
-
-
F-
CH3COO-
Br-
HSO4
F-
CH3COO-
Br-
HSO4
Anion
Compd
Ia
IVa
Va
VIa
VIIa
IXa
Xa
XIa
(a)
(a)
(b)
(b)
(a)
(a)
(b)
(b)
0.7
0.4
0.3
1.0
0.5
-
-
-
280
290
-
-
-
-
2.3
1.3
1.1
3.2
1.6
-
-
-
930
960
-
-
-
-
0.3
1.0
0.6
0.9
1.3
-
200
-
-
-
-
280
-
1.0
3.5
2.0
3.0
4.5
-
680
-
-
-
-
930
-
-
-
320
220
-
-
1100
720
-
-
ꢀM = ꢀmol dm-3 = 10-6 mol dm-3; a – cE-isomer = 1 × 10-4 mol-1 dm3; b –cE-isomer = 1 × 10-5 mol-1 dm3
Detection Range
0.005-100 equivalent of isatin N-phenylsemicarbazone (from
5×10-7- 10-4 mol dm-3 to 5×10-7- 10-2 mol dm-3 of F- and CH3COO-
)(Figs. 3 and S11†). The photochemical E-Z isomerization
Detection range is an important factor in anion sensing. The
utilization of Z-isomers with lower sensitivity can significantly
increase the F- or CH3COO- anion detection range valid for IIIa
efficiency for IIIa
similar to the situation in the unsubstituted Ia E-isomer and it
allows IIIa XIa reliable detection of strong basic anions (ESI
Table S1†).
-XIa is relatively low at ФE-Z < 0.01. This is
-
XIa in organic media from approximately 0.005-1 equivalent to
-
Fig. 3. CH3COO- anion detection range and the sensitivity of Xa-E- and Xb-Z-
isomer sensors.
Fig. 4. CH3COO- anion detection range increase using E-isomer sensor IVa
accomplished by sensor concentration increase and simultaneous decrease
in optical path length.
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Furthermore, the ФE-Z values for substituted IIIa
-
XIa E-
The determined low detection limit 3
/S = 4.3×10-6 mol dm-3) for F- anions in 9:1 DMF:H2O
σ
/S = 1.3×10-6 mol
isomers at 10-4 mol dm-3 concentration are approximately 2- dm-3 (10
σ
fold lower than for the unsubstituted Ia E-isomer. ФE-Z mixture by sensor VIa allows the confident F- detection at the
decrease following electron-withdrawing substitution in tolerated fluoride level of 1.5 mg L-1 (0.17 mmol dm-3) in
position 5- of the isatin ring and also in para- position on the drinking water. On the other side, E-isomer IXa with low 3σ/S
phenyl ring is connected with the enhanced tendency towards = 1.4×10-6 mol dm-3 for CH3COO- in 9:1 DMF:H2O mixture can
hydrazonol formation (ESI Figs. S8†, S9†).15 Unexpected ФE-Z be a useful sensor for CH3COO- determination in biological
decrease following also electron-donating substitution is samples with low F- concentration. However, because the
probably linked to the enhanced aggregate variability. Neither addition of strongly basic OH- anions has the same effect as F-
excitation nor solution heating Z-isomers led to back or CH3COO- anion addition, care must be taken when
conversion to the corresponding E-isomers; similar to the interpreting data in semi-aqueous media from aqueous
-
2-
situation in the unsubstituted Ia Z-isomer.
Sensor concentration increase and simultaneous optical equilibrium may also play an important role.
path length decrease also increase E- isomer sensors IIIa XIa
samples at pH above 10.16 In addition, the CO2(g)/HCO3 /CO3
-
anion detection range (Fig. 4). Although increased IVa
concentration decreases sensor sensitivity, it allows acetate Conclusion
anion detection range increase from 3×10-7-5×10-5 mol dm-3 to
This paper investigated the effect of substituent and
concentration on anion sensing selectivity and sensitivity of
nine new easily synthesized isatin N-phenylsemicarbazone E-
3×10-7-1×10-3 mol dm-3 CH3COO-.
isomer sensors IIIa-XIa
.
Anion detection in aqueous media
Although the large Kass sensitivity to additional anion-
receptor interactions in the high anion concentration region
Detection of anions in aqueous environments is currently one
of the most interesting target in the chemosensor field.19
However, this is unachievable for most designs relying on
hydrogen bonding, since even minute amounts of water
disrupt these interactions. Moreover, sensor molecules are
often such complex constructs that several synthetic steps are
required for their preparation.10,20,...
does not allow correct selectivity comparison for IIIa-XIa
sensors from their Kass values, it can be concluded that the Kass
values higher than 1×104 in DMF:H2O (9:1; v/v) solvent mixture
and Kass higher than 1×107 for 2:1 anion-sensor interactions
indicate exceptionally strong F- and CH3COO- anion binding.
Addition of strongly basic anion leads to the NH group
deprotonation and not to the sensor:hydrazonol 1:1 complex
formation that we assumed in our previous article. In the case
of sensor:anion 2:1 complexes, one aggregate (dimer)
molecule is deprotonated to hydrazonolate B and the second
hydrazide molecule is stabilized by solvation as the hydrazonol
form. The tendency to form 2:1 complexes correlates fairly
well with the hydrazonol form stabilization that increases in
isatin N-phenylsemicarbazones with electron-withdrawing
substituents. Substantial difference between the Kass values for
E-isomers IIIa
condensation of
phenylsemicarbazide in high reaction yield. Due to excellent
-
XIa are synthesized in a one step facile
isatine with the corresponding
IIIa-XIa E-isomer sensitivity in organic media, these isomers
can also be used for F- or CH3COO- sensing in semi-aqueous
media (Fig. 5).
IIIa-XIa interaction with strongly and weakly basic anions
allows the detection of F- or CH3COO- anions even at high
weakly basic anion excess. Although mainly electron-
withdrawing substituents increase the sensor sensitivity
(Γ parameter), Γ increase correlates rather with the sensor
ability to form 2:1 complexes than with the increasing strength
of electron-withdrawing group.
Although photodegradation of IIIa-XIa E-isomer anion
sensors due to light initiated E-Z isomerization can complicate
anion detection, the photochemical efficiency for substituted
IIIa-
XIa E-isomers at 10-4 mol dm-3 concentration is even
approximately 2-fold lower than for the unsubstituted Ia E-
isomer, and this allows reliable detection of strong basic
anions. Moreover, utilization of both E- and Z-isomers
Fig. 5. Evolution of the UV-VIS spectrum of isatin N-phenylsemicarbazone E-
isomer IVa in DMF:H2O 9:1 solvent mixture during IVa solution titration with
TBA+ CH3COO- (cIa = 1×10-4 mol dm-3; cF- = 0 mol dm-3, 1×10-5 mol dm-3, 5×10-5
mol dm-3, 1×10-4 mol dm-3, 2×10-4 mol dm-3, 3×10-4 mol dm-3, 5×10-4 mol dm-
3, 7×10-4 mol dm-3, 1×10-3 mol dm-3 and 1×10-2 mol dm-3).
increases the F- and CH3COO- anion detection range for IIIa
-XIa
in organic media from approximately 5×10-7- 1×10-4 mol dm-3
to 5×10-7-10-2 mol dm-3. A further efficient method of
increasing anion detection range up to 10-3 mol dm-3 for IIIa
-
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Fig. A2. A= f(cA-) curve behaviour at boundary conditions (Alim = const = 2.5;
csensor = 1×10-4 mol dm-3).
XIa E-isomer sensors is simultaneous sensor concentration
increase and optical pathway length decrease.
Sensor VIa’s low detection limit for F- anions in 9:1
DMF:H2O mixture and the simultaneous absence of detectable
CH3COO- anion levels allow confident F- detection at tolerated
drinking-water fluoride level.
2
2
(c0 + 1/ K ass + cA-
)
− 4c0 cA-
=
(1/Kass - c0 + cA-
)
+ 4c0 / Kass
.
(A2)
Further, the bracketed term in equation (A2) can be multiplied
Appendix A. Behaviour of the A = f(cA-) function.
by unity (×
[
… + √ ]
/
[
… + √ ]), which gives:
A= f(cA-) curve behaviour at boundary conditions (Alim = const
or Kass = const, respectively) and sensor concentration of 1×10-
2cA-
A = A0 + (Alim − A0 )
4
mol dm-3 is depicted in Figs. A1 and A2. Fig. A2 shows that
2
c0 +1/ Kass + cA-
+
(1/ Kass − c0 + cA-
)
+ 4c0 / Kass
.
steepness of the A= f(cA-) curve and thus sensor sensitivity are
directly linked to the Kass value for the sensor:anion 1:1
complex describing sensor selectivity; particularly in the low
Kass region. However, A= f(cA-) curve steepness does not
(A3)
Because the complex fraction on the right side of Eq.(A3) is
always positive for arbitrary Kass 0, it is clear that the Alim-A0
depend on further Kass increase in the high log Kass >5 region.
>
term determines the A vs. cA- behaviour. When Alim-A0
Therefore, Kass higher than 105 cannot be determined precisely
by UV-VIS spectroscopy.
> 0,
then A is the ascending function of cA-; and vice-versa.
The A= f(cA-) function, described by Eq. (A1),
Because the complex fraction on the right side of Eq.(A3) is
always positive for arbitrary Kass 0, it is clear that the Alim-A0
>
term determines the A vs. cA- behaviour. When Alim-A0
A = A0 +1/2c0 (Alim - A0 )
[
c0 + cA- +1/Kass
-
(c0 + cA- +1/Kass )2 - 4c0cA-
]
> 0,
, (A1)
then A is the ascending function of cA-; and vice-versa.
For small cA- values (cA-
→0), Eq. (A3) can be rewritten as
can be easily modified in a simple manoeuvre: The radicand in
(the complex fraction behave as x/( c0 + 1/Kass)):
this equation is positive for arbitrary Kass >0 (and Kass is always
higher than 0) because:
(
Alim − A0
c0 +1/ Kass
)
cA−
A = A0 +
.
(A4)
Therefore, for small cA- values, the steepness of the A= f(cA-)
curve directly indicating the sensor sensitivity is expressed as:
(
A
− A0
)
.
lim
c0 +1/ Kass
(A5)
This expression clearly indicates that if the sensor
concentration c0 is sufficiently higher than the inverted Kass
value (c0 >> 1/ Kass), sensor sensitivity is directly described by
the (Alim-A0)/c0 ratio and does not depend on Kass value; as
previously mentioned.
Fig. A1. A= f(cA-) curve behaviour at boundary conditions (Kass = const = 1×106
mol-1 dm3; csensor = 1×10-4 mol dm-3).
Appendix B. Complexities in Kass determination.
The Kass value strongly depends on sensor absorbance increase
at high anion concentration above 1 equivalent, despite similar
slope sensitivity in the initial low concentration portion of the
A = f(cA-) curve (Fig. A3).
However, absorbance at anion concentration above 1
equivalent can be influenced by additional anion-sensor
interactions, and these influences distort Kass value
determination. For example, F- concentration above 1
6 | J. Name., 2012, 00, 1-3
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ARTICLE
DOI: 10.1039/C4RA04847D
equivalent leads to loss of the intramolecular hydrogen bond the case of Xb Z-isomer, the filtrate was evaporated and the
in the E-isomer Ia structure and simultaneous hydrazonolate C residue was purified by column chromatography using silica
formation (ESI Scheme S2†).16 This structural change results in gel as the stacionary phase and hexol (a mixture of
hydrazonolate B absorption band hypsochromic shift in E- methylpentanes and hexane; ϕr
isomer Ia UV-VIS absorption spectra at 410 nm. However, as the mobile phase.
∼ 2:1)/ethyl acetate (ϕr = 2:3)
absorbance at 410 nm further increases up to the 10 sensor
For further data on the synthesis and characterization of
equivalent and significantly affects the sensor Kass value (ESI semicarbazones Ia and IIIa-XIa, see ESI Synthesis†.
Fig. S12†).
Spectroscopic measurements
Electronic absorption spectra were obtained on a HP 8452A
diode array spectrophotometer (Hewlett Packard, USA). The
N,N-dimethylformamide (DMF) solvent was UV-spectroscopy
grade (Uvasol, Merck, Germany), and DMF was dried with
CaH2 and distilled under reduced pressure. All photochemical
measurements were performed at 25°C in the dark, with only
405 nm LED diodes Thorlabs as light sources with optical
power of P = 6 mW.
Titration experiments
MATERIALS
All anions in the titration experimentswere added in the form
of tetrabutylammonium (TBA+) salts purchased from Sigma-
Aldrich (USA), and used without further purification.
Fig. A3. Kass value dependence on sensor absorbance increase at anion
concentration over 1 equivalent (cA- > 1×10-4 mol dm-3) for the 1:1 IXa:F-
anion-receptor complex. The red squares depict experimental values, the
black square is the model point, and red (black) line shows non-linear fitting.
GENERAL METHOD
All titration experiments were carried out in DMF or
DMF:distilled H2O solvent mixture (ϕr = 9:1) at 298.16 K. The
This large Kass sensitivity to additional anion-receptor
IIIa
anion solutions of F-, AcO-, Br- or HSO4 to obtain 1
mol.dm-3 or 1 10-5 mol.dm-3 sensor concentrations of the
resultant solution. The titration process in the anion
concentration range of 1
10-5 mol.dm-3 to 1 10-2 mol.dm-3 was
-XIa sensor solutions were titrated with the corresponding
interactions in the high anion concentration region does not
-
×
10-4
allow correct selectivity comparison for IIIa-XIa sensors from
×
their Kass values alone. Moreover, both the lower correlation
coefficient for 1:1 complex and Job’s plot indicate sensor:anion
2:1 complex stoichiometry in some cases, and this further
×
×
monitored by UV-VIS spectroscopy (in a 1 cm cuvette; 0.1 cm
complicates IIIa-XIa Kass comparison (Table 1; ESI Figs. S7†).
cuvette was used to increase the detection range).
A
SSOCIATION CONSTANT DETERMINATIONS
Experimental Section
Synthesis
The anion-receptor association constants Kass of the studied
isatinphenylsemicarbazones with the particular anions in 1:1
complex stoichiometry were determined using the well-known
relation describing the complex anion concentration:25
Semicarbazides were prepared using a modified procedure
from the literature [24]. Phenyl chloroformate (20 mmol) was
added dropwise to a mixture of aniline (20 mmol), pyridine (20
mmol) and dry CH2Cl2 (40 mL) in an ice-water bath and stirred
at room temperature for 18 hours. The mixture was then
evaporated under reduced pressure and the residue was
poured into saturated NaCl for salting out. The precipitate was
filtered, dried, and stirred in hydrazine hydrate (80%, 10 ml) at
room temperature for 4hours and then filtered off and
recrystallized from ethanol.
1/ 2
A
lim − A0
2c0
2
A = A0 +
[
c0 + cA- +1/ Kass
−
[(
c0 + cA- +1/ Kass
)
− 4c0cA-
]
]
,
(1)
where:
A0
is
the
absorbance
is the
of
free
isatinphenylsemicarbazone,
A
isatin
N-
phenylsemicarbazone absorbance measured after anion
addition, Alim is the isatinphenylsemicarbazone absorbance
measured with excess of the particular anion, c0 is the overall
concentration of isatinphenylsemicarbazone and cA- is the
overall concentration of the added anion A-.
General procedure: A solution of phenylsemicarbazide (6
mmol) in hot absolute EtOH (25 mL) was added to a solution of
R-substituted isatine (6 mmol) in hot absolute ethanol (50 mL);
R = –H (Sigma-Aldrich), –Br (Acros Organics), –OCF3 (Sigma-
Aldrich) and –CH3 (Sigma-Aldrich). The reaction mixture was
refluxed for 2 hours and the desired product precipitated. In
For further data on the association constant for
sensor:anion 1:1 and 2:1 complexes, and determination of the
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Organic & BiomolecVuielawrArCtichleeOmnliinsetry
ARTICLE
DOI: 10.1039/C4RA04847D
detection and quantification limits for semicarbazones IIIa-XIa
,
9
L.E. Santos-Figueroa, M.E. Moragues, E. Climent, A. Agostini, R.
Martínez-Máñez, F. Sancenón, Chem. Soc. Rev., 2013, 42, 3489-
3613, http://dx.doi.org/10.1039/c3cs60316d.
see ESI Titraꢀon experiments†.
10 P.A. Gale, N. Busschaert, C.J.E. Haynes, L.E. Karagiannidis, I.L. Kirby,
Chem. Soc. Rev., 2014, http://dx.doi.org/10.1039/c3cs60316d.
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168, 318-328, http://dx.doi.org/10.1016/j.snb.2012.04.029.
Light initiated E-Z isomerization
GENERAL PROCEDURE
Photochemical measurements were performed using the
apparatus described elsewhere (Fig.7 in Refrence 26 without 12 S.L.A. Kumar, M.S. Kumar, P.B. Sreeja, A. Sreekanth, Spectrochim.
ultrasonic horn H and lens L1 and using Ocean Optics SD 2000
diode array spectrophotometer). The light sources were four
Acta
A,
2013,
113
,
123-129,
http://dx.doi.org/10.1016/j.saa.2013.04.103.
405 nm LED diodes Thorlabs with overall incident photon flux 13 S.O. Kang, R.A. Begum, K. Bowman-James, Angew. Chem. Int. Ed.
I0=5.6 0.1 2006, 45, 7882-7894, http://dx.doi.org/10.1002/anie.200602006.
10-4 mol s-1 dm-3. Molar extinction coefficients of E-
isomers are higher than for Z-isomers at this wavelength.15 The 14 S. Hu, Y. Guo, J. Xu, S. Shao, Spectrochim. Acta A, 2009, 72, 1043-
actual compound concentrations in air-saturated solutions 1046, http://dx.doi.org/10.1016/j.saa.2008.12.042.
during irradiation in a 1 cm quartz fluorescence cuvette were 15 K. Jakusová, M. Cigáň, J. Donovalová, M. Gáplovský, R. Sokolík, A.
±
×
measured spectrophotometrically in right-angle arrangement
(HP 8452A), and LED light sources were turned off during
Gáplovský, J. Photochem. Photobiol. A Chem., 2014, accepted
manuscript.
concentration measurements. The incident concentration of 16 K. Jakusová, J. Donovalová, M. Cigáň, M. Gaplovský, V. Garaj, A.
the studied E-isomers was c0 =1.10-4 mol.dm-3.
Gaplovský, Spectrochim. Acta A, 2014, 123
,
421-429,
For further data on E-Z isomerization quantum yield (ΦE-Z
determination for isatinphenylsemicarbazone E-isomers IIIa
XIa in DMF solution, see ESI Light initiated E-Z isomerizaꢀon†.
)
http://dx.doi.org/10.1016/j.saa.2013.12.073.
-
17 K. Jakusová, J. Donovalová, M. Gaplovský, M. Cigáň, H. Stankovičová,
A. Gaplovský, J. Phys. Org. Chem., 2013, 26
,
805-813,
http://dx.doi.org/10.1002/poc.3164.
Acknowledgments
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The authors greatly appreciate the financial support provided
http://dx.doi:10.1016/j.ccr.2006.08.017.
by VEGA Grant Agency (Grant No. 1/1126/11)
.
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Notes and references
*Faculty of Natural Sciences, Institute of Chemistry, Comenius
University, Mlynská dolina CH-2, SK-842 15 Bratislava, Slovakia.
E-Mail: cigan@fns.uniba.sk
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additional data for Experimental section, Schemes S1, S2, Tables S1,
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8 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/C4RA04847D
Isatin N-phenylsemicarbazone: Effect of substituent and concentration on anion
sensing selectivity and sensitivity
Marek Cigáň, Klaudia Jakusová, Jana Donovalová, Vojtech Szöcs and Anton Gáplovský
Efficient and easily synthesized sensors for F- or CH3COO- anion sensing
in semiꢀaqueous media based on ketoꢀenol/enolate equilibria