Spectroscopic investigation on proton transfer reaction in the complex of 2-aminopyridine with 2, 6-dichloro-4-nitrophenol in different solvents

Article abstract of DOI:10.1016/j.molliq.2010.11.012

Proton transfer (PT) reaction between 2-aminopyridine (2AP) with 2,6-dichloro-4-nitrophenol (DCNP) has been investigated spectrophotometrically in methanol (MeOH), acetonitrile (AN) and acetonitrile with 1,2-dichloroethane binary mixtures (1:1, ANDEI) and (3:1, ANDEII). A long wavelength band in the range 395-424 nm due to the proton transfer complex formation has been recorded. The formation constants of the PT-reaction (K_PT) have been estimated using Benesi-Hildebrand equation. It has been found that K_PT recorded larger value in AN than MeOH and binary mixtures. This result was interpreted in terms of solvatochromic parameters like, solvent polarizability (π^*), hydrogen bond donor (α), and hydrogen bond acceptor (β). The molecular composition of the PT-complex has been identified by Job's and photometric titration methods where 1:1 complex is formed. Based on the rapidity and simplicity of the PT-reaction as well as the stability and simple composition of the formed complex, a rapid, accurate and sensitive spectrophotometric method for determination of 2AP was proposed. In addition, the solid PT-complex (2AP-DCNP) has been isolated and characterized using elemental analyses and FTIR measurements.

Full text of DOI:10.1016/j.molliq.2010.11.012

Journal of Molecular Liquids 158 (2011) 161–165
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Spectroscopic investigation on proton transfer reaction in the complex of
2-aminopyridine with 2, 6-dichloro-4-nitrophenol in different solvents
a
Khairia M. Al-Ahmary a, Moustafa M. Habeeb b, , Eman A. Al-Solmy
⁎
a
Chemistry Department, Faculty of Science, King Abdul-Aziz University, Jeddah, Kingdom of Saudi Arabia
Chemistry Department, Faculty of Education, Alexandria University, Alexandria, Egypt
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Proton transfer (PT) reaction between 2-aminopyridine (2AP) with 2,6-dichloro-4-nitrophenol (DCNP) has
been investigated spectrophotometrically in methanol (MeOH), acetonitrile (AN) and acetonitrile with
1,2-dichloroethane binary mixtures (1:1, ANDEI) and (3:1, ANDEII). A long wavelength band in the range
395–424 nm due to the proton transfer complex formation has been recorded. The formation constants of the
PT-reaction (KPT) have been estimated using Benesi–Hildebrand equation. It has been found that KPT recorded
larger value in AN than MeOH and binary mixtures. This result was interpreted in terms of solvatochromic
Received 2 September 2010
Received in revised form 20 November 2010
Accepted 29 November 2010
Available online 8 December 2010
Keywords:
⁎
parameters like, solvent polarizability (π ), hydrogen bond donor (α), and hydrogen bond acceptor (β). The
2-Aminopyridine
2,6-Dichloro-4-nitrophenol
UV–Vis
molecular composition of the PT-complex has been identified by Job's and photometric titration methods where
1:1 complex is formed. Based on the rapidity and simplicity of the PT-reaction as well as the stability and simple
composition of the formed complex, a rapid, accurate and sensitive spectrophotometric method for
determination of 2AP was proposed. In addition, the solid PT-complex (2AP-DCNP) has been isolated and
characterized using elemental analyses and FTIR measurements.
FTIR
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
teroxicam which are non-steroided antiflammatory drugs that used in
musculo-skeletal and joint disorders [19]. Moreover, aminopyridines
Proton transfer is one of the most investigated chemical reactions in
chemistry and biochemistry [1–4]. They play an important role in
various chemical and biological processes like stabilizing biomolecular
structures [5], controlling the speed of enzymatic reactions [6] as well as
constructing supramolecular structures [7].
Complexes of phenols with nitrogen and oxygen bases belong to the
most frequently investigated H-bonded and proton transfer systems.
These complexes have been investigated by many experimental and
theoretical studies. Several physical properties of H-bonded complexes,
e.g. excess of dipole moment (Δμ), change of 1H, 13C, 15N chemical shifts
(Δδ) and 35Cl NQR frequency when plotted against ΔpKa (pKa (BH+)−
pKa (AH)), a sigmoidal titration curves are obtained which were usually
treated as evidence of the proton transfer equilibrium [8–11]. This
equilibrium is strongly affected by the properties of the proton donor,
proton acceptor and solvent polarity [12,13].
are commonly present in synthetic and natural products [20]. They
form repeated moiety in many large molecules with interesting
photophysical, electrochemical and catalytic applications [21].
In connectivity with our work on proton transfer reactions [22–24]
and due to the industrial, biological and pharmaceutical applications
of aminopyridines, we wish to report in the present article our finding
on the spectroscopic studies of the proton transfer complex formed
0.8
0.6
0.4
0.2
0.0
10
5
Aminopyridines are bioactive N-heterocyclic tertiary amines,
which increase the strength of the nerve signal by blocking of the
voltage-dependent K+ channel [14,15]. Also, aminopyridines have
been proposed as drugs for the treatment of many diseases such as
antithrombus drugs and antimicrobial agents [16–18]. In particular,
2-aminopyridine is one of the potential impurities in piroxicam and
1
330
360
390
420
450
480
510
540
Wavelength (nm)
Fig. 1. Electronic spectra of 1:1 complex of 1×10−4 M DCNP with various concentra-
tions of 2AP in AN: (1) 2×10−5, (2) 4×10−5, (3) 6×10−5, (4) 8×10−5, (5) 1×10−4
(6) 1.×210−4, (7) 1.4×10−4, (8) 1.6×10−4, (9) 1.8×10−4 and (10) 2×10−4 M.
,
⁎
Corresponding author. Tel./fax: +002035453988.
E-mail address: mostafah2002@yahoo.com (M.M. Habeeb).
0167-7322/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molliq.2010.11.012

162
K.M. Al-Ahmary et al. / Journal of Molecular Liquids 158 (2011) 161–165
1.0
0.8
0.6
0.4
0.2
0.0
10
5
1
330
360
390
420
450
480
510
540
Wavelength (nm)
Fig. 2. Electronic spectra of 1:1 complex of 1×10−4 M DCNP with various concentra-
tions of 2AP in MeOH: (1) 1×10− 5 (2) 2×10−5 (3) 3×10−5 (4) 4×10−5
, , , ,
(5) 5×10−5, (6) 6×10−5, (7) 7×10−5, (8) 8×10−5, (9) 9×10−5 and (10) 1×10−4 M.
Fig. 3. Job's plot of 1:1 complex of 2AP with DCNP in AN.
between 2AP as proton acceptor and DCNP as proton donor in
different solvents. The formation constant of the formed complex KPT
has been calculated. The solvation effect on KPT was discussed and
evaluated. Based on the rapidity and simplicity of the studied proton
transfer reaction, we proposed in this work a sensitive and accurate
spectrophotometric method for determination of 2AP in different
solvents. In addition, the solid PT-complex (2AP-DCNP) has been
isolated and characterized using elemental analyses and FTIR
measurements.
2.2. Chemicals
All chemicals used were of analytical grade. 2-aminopyridine was
supplied by Acros organic, 2,6-dichloro-4-nitrophenol was supplied
by Fluka. Acetonitrile and methanol were supplied by PAI-ACS. KBr
was spectroscopic grade supplied by Aldrich.
2.3. Preparation of the solid 1:1complex between 2AP with DCNP
The solid PT-complex (1:1) between 2AP and DCNP was prepared
by mixing equimolar amounts of 2AP with DCNP in acetonitrile. The
resulting complex solution was allowed to evaporate slowly at room
temperature where the complex was isolated as yellow crystals. The
separated complex was filtered off, washed well with acetonitrile and
dried over calcium chloride for 24 h. Anal. Calc. for (DCNP-2AP)
2. Experimental
2.1. Physical measurements
2.1.1. Electronic spectra
C11H9Cl2N3O3 complex: C, 43.73%; H, 3.00%; N, 13.19%. Found: C,
The electronic spectra were recorded in the region 700–250 nm
using UV–Vis Shimadzu UV-1601 spectrophotometer connected to
Shimadzu TCC-ZUOA temperature controller unit (Japan).
43.64%; H, 3.20%; N, 13.19%. MP. 174–176 °C.
3. Results and discussion
3.1. Electronic spectra
2.1.2. Infrared spectra
The infrared spectra were measured as KBr discs on Bruker-Tensor
37 Fourier transform infrared spectrophotometer (USA), evacuated to
avoid water and CO2 absorption.
The conversion of phenol in to the corresponding phenolate results
in the bathochromic shifts of 1La and 1Lb bands and an increase in εmax
[25]. When a phenol forms proton transfer complex, the electronic
spectrum resembles that of the phenolate ion. The electronic spectra
of the proton transfer complexes of DCNP with various nitrogen bases
were reported by Szafran et al. in different solvents where the
phenolate ion of DCNP exhibited absorption band near 425 nm [9].
2.1.3. Elemental analyses
C, H and N contents were determined with the Micro analyzer
Perkin Elmer 2400 (USA).
Cl
-
O
H
H
+
N
OH
N
O
N
Cl
DCNP
2AP
HB
Cl
-
H
H
O
+
NH
O
N
N
O
Cl
PT
Scheme 1. Proton transfer equilibrium of 2AP-DCNP complex.

K.M. Al-Ahmary et al. / Journal of Molecular Liquids 158 (2011) 161–165
163
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Table 1
AN
MeOH
ANDEI
Formation constant, molar extinction coefficient and wavelength of 1:1 complex of 2AP
with DCNP in different solvents.
Solvent
K
PT ×10−4
ε
PT ×10−4
λmax
L moL−1
L mol−1 cm−1
nm
AN
14.93 2.08
1.43 0.34
2.02 0.32
5.82 0.54
1.21 0.11
2.28 0.21
1.06 0.03
0.88 0.09
424
396
423
423
MeOH
ANDEI
ANDEII
[29] plots where two straight lines are produced intercepting at 1:1
ratio (proton donor: proton acceptor). Accordingly we can conclude
from Figs. 3 and 4 that the PT-complex is formed based on a 1:1
stoichiometric ratio.
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.3. Formation constant of 1:1 complex of 2AP with DCNP (KPT
)
CDCNP / C2AP
Based on the formation of 1:1 proton transfer complex, Benesi–
Hildebrand equation has been applied to estimate the proton transfer
formation constant KPT between 2AP and DCNP in different solvents
[30].
Fig. 4. Photometric titration curves of 1:1 complex of 2AP with DCNP in different
solvents.
Figs. 1 and 2 represent the electronic absorption spectra of the proton
transfer reaction between different concentrations of 2AP with
1×10−4 mol.L−1 DCNP in different solvents. A new band in the
range 395–424 nm due to the π–π* transition of the formed
PT-complex was observed. The increase in the intensity of absorbance
with increasing 2AP concentration suggests that the prototropic
equilibrium (Scheme 1) is shifted toward the hydrogen-bonded
ion-pair O−…HN+. It seems that the high basicity of 2AP (pK=6.86)
[26] as well as the high acidity of DCNP (pKa=3.55) [27] are
responsible for this situation. It is worth to mention that the blank
used has the same concentration of DCNP to eliminate the possible
overlap that may arise between the complex band and that of DCNP.
-
-
-
-
C dC a
A
1
C d + C a
¼
þ
KPT εPT
εPT
where C°d and C°a are the initial concentrations of the proton donor
and proton acceptor respectively, and A is the absorbance of the PT-
-
-
C dC a
band. Plotting
versus (C°d+C°a) for the formed PT-complex,
A
straight lines were obtained supporting our conclusion of the
formation of the 1:1 complex (Fig. 5). From the slopes and intercepts
of the plots, one can calculate KPT and the molecular extinction
coefficients ꢀPT. The results are compiled in Table 1. As one observes in
Table 1 both KPT and ꢀPT recorded high values confirming the
formation of stable complex. An important finding from Table 1 is
the highest value of KPT in acetonitrile compared with those in
methanol and binary mixtures. It seems that methanol exhibited dual
roles in the studied PT-reaction through solvation of both 2AP as
hydrogen bond donor (α=0.98) and DCNP as hydrogen bond
acceptor (β=0.66) [31]. Under this condition, the competition
among different molecular species resulting from a hydrogen-
bonding interaction between the solute and solvent molecules
becomes inevitable which hinders the PT-interaction between 2AP
3.2. Composition of the PT-complex
Job's method [28] of continuous variation was used to identify the
composition of the formed PT-complex between 2AP with DCNP in
different solvents. The plots of the absorbance against the mole
fraction of DCNP were presented in Fig. 3 where the maximum
absorbance was recorded at mole fraction 0.5 indicating the formation
of 1:1 PT-complex. Fig. 4 represents the spectrophotometric titration
with DCNP and consequently decreases KPT
.
5e-8
AN
MeOH
ANDEI
1.2
AN
MeOH
ANDEI
4e-8
1.0
3e-8
2e-8
1e-8
0
0.8
0.6
0.4
0.2
0.0
0.00010
0.00015
0.00020
0.00025
0.00030
0.00035
0
2
4
6
8
10
o
C
o
+ C
2AP
DCNP
C2APµg mL-1
Fig. 5. Spectral determination of formation constants and molar extinction coefficients
of 1:1 complex of 2AP with DCNP in different solvents.
Fig. 6. Beer's law curves of 1:1 complex of 2AP with DCNP in different solvents.

164
K.M. Al-Ahmary et al. / Journal of Molecular Liquids 158 (2011) 161–165
Table 2
Quantitative parameters of 1:1 complex of 2AP with DCNP in different solvents.
Parameter
AN
MeOH
ANDEI
ANDEII
Beer's law limits, μg ml−1
Limit of detection, μg ml−1
Limit of quantification, μg ml−1
Regression equation
0.19–9.41
0.08
0.27
0.19–9.41
0.11
0.37
0.19–9.41
0.20
0.62
0.47–9.41
0.27
0.90
Y*=0.077 X +0.035
Y*=0.144 X +0.035
Y*=0.056 X +0.044
Y*=0.042 X+0.046
Intercept, a
Slope, b
Confidence interval of intercept, α
Confidence interval of slope, β
Correlation coefficient, R2
0.035
0.077
0.001
0.0007
0.99
0.035
0.144
0.002
0.0014
0.99
0.044
0.056
0.002
0.0018
0.99
0.046
0.042
0.002
0.0013
0.99
*Y is the absorbance for concentration, X in μg mL−1
.
Concerning acetonitrile, it seems that its high polarity is the
predominating factor (π =0.75) [31] which increases KPT. To confirm
values confirming excellent linearity between the absorbance and
concentration, Table 2.
⁎
this assumption, the PT-reaction was carried out in the binary
mixtures ANDEI and ACDEII, respectively. It has been found that in
ANDEI KPT is reduced up to 87% while in ANDEII is reduced up to 61%
confirming that the polarizability of AN is the leading parameter in
this case.
The accuracy of the method was established by performing
analysis of solutions containing four different amounts (within Beer's
law limits) of 2AP and measuring the absorbance of their PT-
complexes with DCNP in all solvents. The concentration of 2AP was
determined from the regression equation and then calculated the
recovery percentages, the standard deviation S, and relative standard
deviation RSD. The recovery percentages recorder values near 100%
with RSD ranging from 0.91 to 2.90 confirming high accuracy and
precision of the proposed method, Table 3.
3.4. Application of the studied PT-reaction
3.4.1. Optimization of reaction time and temperature
The effect of temperature on the PT-reaction was studied by
following the absorbance of the PT-complexes resulting from mixing
1.0×10−4 mol L−1 DCNP with various concentrations of 2AP. It has
been found that 20 °C is the optimum temperature where the
absorbance of the PT-complex recorded the highest and constant
value. In addition, the complex was stable for more than 2 h.
Comparison of the difference between the mean and true value
(X− −μ) [33] with the largest difference that could be executed as a
ꢀtS
pffiffiffi
result of indeterminate error
has been carried out and the results
n
were collected in Table 3. It has been found that (X− −μ)were less
ꢀtS
pffiffiffi
than
indicating that no significant difference exists between the
n
mean and true values.
3.4.2. Analytical data
Based on the formation of 1:1 PT-complex between DCNP and 2AP,
we proposed in this section a simple, rapid and accurate spectropho-
tometric method for determination of 2AP. Hence, under the optimum
reaction conditions Beer's plot at various 1:1 molar ratios between
2AP and DCNP was constructed (Fig. 6). The regression equations in
different solvents were calculated by the least square method. In all
cases Beer's law plots were linear with very small intercepts, slopes
and good correlation coefficients in the general concentration range
(0.18 to 9.41) μg mL− 1, Table 2. The limits of detection and
quantification were calculated according to the IUPAC definition
[32]. The calculated values were listed in Table 2. They recorded small
values confirming high accuracy of the method. It has been found also
that the confidence intervals of intercept and slope recorded small
3.5. Infrared Spectra of 1:1 complex of 2AP with DCNP
The formation of 1:1 complex between 2AP with DCNP was
ascertained from a comparison of the i.r. spectra of complex with that
of 2AP and DCNP. The FTIR spectrum of the complex is shown in Fig. 7
where the asymmetric stretching vibration of the amino group is
broadened and appeared at 3445 cm−1. On the other hand, the
symmetrical stretching vibration is also broadened and shifted to
lower frequency at 3171 cm−1 compared with 3290 cm−1 in the i.r.
Spectrum of 2-aminopyridin [34]. The disturbance of the amino group
vibrations strongly confirms the formation of the PT-complex
between the phenolic and amino groups of the proton donor and
Table 3
Precision and accuracy of the analytical method.
tS
pffiffi
Solvent
AN
Amount taken μg mL−1
Amount found μg mL−1
Rec.%
X
SD
RSD
2.90
jX−μj
ꢀ
Confidence limits
n
3.29
5.18
6.12
8.00
5.18
6.12
7.06
8.00
3.29
5.18
6.12
7.06
3.29
6.12
7.06
8.00
3.45
5.15
6.03
7.88
5.22
6.12
7.02
8.12
3.37
5.24
6.16
6.94
3.29
6.23
7.14
8.00
104.65
99.57
98.62
98.53
100.87
99.99
100.34
2.91
0.34
4.63
100.34 4.63
MeOH
ANDEI
ANDEII
100.45
100.62
100.74
0.90
1.70
0.92
0.89
1.70
0.91
0.45
0.62
0.74
1.43
2.71
1.46
100.45 1.43
100.62 3.77
100.74 1.46
99.47
101.48
102.37
101.14
100.66
98.30
99.99
101.85
101.13
99.97
t=3.182 for n=4 at 95% confidence level.
SD=standard deviation, RSD=relative standard deviation.

K.M. Al-Ahmary et al. / Journal of Molecular Liquids 158 (2011) 161–165
165
References
[1] A. Muller, H. Ratajczak, W. Junge, E. Diemann (Eds.), Electron and Proton Transfer
in Chemistry and Biology, Elsevier, Amsterdam, 1992.
[2] H. Ratajczak, H. Orville-Thomas (Eds.), Molecular Interactions, vols. 1–3, Wiley,
Chichester, 1980.
[3] G. Zundel, Advances in Chemical Physics, vol. 3, Wiley, New York, 2000.
[4] L. Sobczyk, Ber. Bunsen Ges Phys. Chem. 102 (1998) 377.
[5] S. Deechongkit, H. Nguyen, E.T. Powers, P.E. Dawson, M. Gruebele, J.W. Kelly,
Nature 430 (2004) 101.
[6] G. Gregoire, C. Jouvet, C. Dedonder, A.L. Sobolewski, J. Chem. Phys. 324 (2006) 398.
[7] Yu.E. Alexeev, B.I. Kharisov, T.C. Hermandez, A.D. Garnovski, Coord. Chem. Rev.
254 (2010) 794.
[8] Z. Dega-Szafran, E. Sokolowska, J. Mol. Struct. 565 (2001) 17.
[9] Z. Dega- Szafran, M. Szafran, E. Sokolowska, M. Grundwald-Wyspianska, J. Mol.
Struct. 614 (2002) 189.
[10] M.M. Habeeb, Pol. J. Chem. 77 (2003) 1.
[11] M.M. Habeeb, Appl. Spectrosc. Rev. 32 (1997) 103.
[12] M.M. Habeeb, H.A. Alwakil, A. El-Dissouky, N.M. Refat, J. Chem. Res. S 200 (2001).
[13] P. Simunek, V. Machacek, Dyes Pigm. 86 (2010) 197.
[14] J. Melgo, M. Lemeignan, F. Peradejordi, P. Lechat, J. Pharmacol. Paris 16 (Suppl. II)
(1985) 109.
[15] C. Carlsoom, I. Rosen, E. Nilsson, Acta Anaesthesiol. Scand. 27 (1993) 87.
[16] J.I. Segal, B.S. Brunnemann, Pharmacotherapy 17 (1997) 415.
[17] A.G. Amr, A.M. Mohamed, S.F. Mohamed, N.A. Abdel-Hafez, A. Hammam, Bioorg.
Med. Chem. 14 (2006) 5488.
[18] I.O. Zhuravel, S.M. Kovalenko, A.V. Ivachtchenko, K.V. Balakin, V. Kazmirchuk,
Bioorg. Med. Chem. Lett. 5 (2005) 5483.
[19] K. Parfitt (Ed.), Martindale, The Extra Pharmacopoeia, 32nd ed., Pharmaceutical
Press, London, 1999, p. 48,49.
Fig. 7. FTIR spectrum of solid 1:1 complex of 2AP with DCNP in the range 4000–400 cm−1
.
proton acceptor. In addition, a weak band was recorded at 1612 cm−1
which can be ascribed to the asymmetric deformation of N+H3
vibration. One can also observe (Fig. 7) the presence of abroad and
intense absorption in the 1600–800 cm−1 region. Its center of gravity
ν
H lies at 1220 cm−1 which is characteristic of the hydrogen-bonded
ion pair (O−….H3N+) [35]. Moreover, the vibrational bands of the
complex were shifted compared with those of the reactants. The
stretching vibrations υC=Cand υC=Nare shifted to 1614 and
1562 cm−1 compared with 1595 and 1559 cm−1 for 2AP. Further-
more, the stretching vibrations of υCl are shifted to 848 and 898 cm−1
compared with 808 and 896 cm−1 for DCNP. These shifts also confirm
the formation of the PT-complex (2AP-DCNP).
[20] A. Goel, V.J. Ram, Tetrahydron 65 (2009) 7865.
[21] N.A. Al-Hashimy, Y.A. Hussein, Spectrochim. Acta, Part A 75 (2010) 198.
[22] M.M. Habeeb, A.S. Al-Attas, M.T. Basha, J. Mol. Liq. 150 (2009) 56.
[23] M.M. Habeeb, R.M. Alghanmi, JCED 55 (2010) 930.
[24] R.M. Alghanmi, M.M. Habeeb, AJC 3 (2010) 257.
[25] H.H. Jaffe, M. Orhin, Theory and Application of Ultraviolet Spectroscopy, Wiley,
New York, 1965.
[26] N.A. Caballero, F.J. Malendez, C. Munoz- Caro, A. Nino, Biophys. Chem. 124 (2006)
155.
[27] E.P. Serjeant, B. Dempsey, Ionization Constants of Organic Acids in Aqueous
Solutions, Pergamon Press, Oxford, 1979.
4. Conclusion
[28] P. Job, Advanced Physicochemical Experimental: London, 1964.
[29] D.A. Skoog, Principal of Instrumental Analysis, 3rd ed., Sunder College Publisher,
New York, 1985.
[30] H. Benesi, J. Hildebrand, J. Am. Chem. Soc. 71 (1949) 2703.
[31] N.S. Moyon, A.K. Chandra, S. Mitra, J. Phys. Chem. A114 (2010) 60.
[32] M.H. Irving, T.S. Freiser, West. IUPAC Compendium of Analytical Nomenclature
Definitive Rules, Pergamon Press, Oxford, 1981.
[33] J.C. Miller, N.A. Miller, Statistics for Analytical Chemistry, 2nd ed, Ellis Horwood
Ltd., England, 1988.
[34] N. Singh, A. Ahmad, J. Mol. Struct. 977 (2010) 197.
[35] J. Kalenik, I. Majerz, L. Sobczyk, E. Grech, M.M. Habeeb, J. Chem. Soc. Faraday Trans.
I 85 (1989) 3187.
The present article introduced a spectral study on the PT-complex
formation between 2AP with DCNP in different solvents where 1:1 PT-
complex (proton donor: proton acceptor) was formed. Based on the
simplicity and rapidity of the PT-reaction, a simple, rapid and accurate
spectrophotometric method for determination of 2AP was proposed.
Beer's law was obeyed in the concentration range 0.19–9.41 μg mL−1
with small values of both the limit of detection and limit of
quantification. Moreover, the solid PT-complex was isolated and
characterized by means of elemental analyses and FTIR measurements.
These measurements confirmed that the interaction site with the OH of
DCNP is the amino group of 2AP rather than the ring nitrogen.