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S1
Electronic Supporting Information
Detailed study of interactions between eosin yellow and gemini pyridinium surfactants
Renu Sharma, Ajar Kamal and Rakesh Kumar Mahajan*
*Department of Chemistry, UGC-Centre for Advanced Studies-I, Guru Nanak Dev University,
Amritsar-143005, India
*To whom correspondence should be addressed:
e-mail: [email protected]; Fax: +91 183 2258820
Electronic Supplementary Material (ESI) for RSC Advances.This journal is © The Royal Society of Chemistry 2016
S2
Annexure SI
1. Methods
1.1 Conductivity measurements. The Conductivity measurements were carried out using a
digital Systronics conductivity meter model 306 with a dip-type conductivity cell at 298.15 K
having a cell constant of 1.01 cm-1
. All the solutions were prepared in deionised double distilled
water having specific conductivity of 2.0-3.0 µS cm-1
.
1.2 UV-visible measurements. The absorption spectra of eosin yellow (EY) and EY-gemini
pyridinium surfactants mixed systems were recorded on a UV-1800 Shimadzu
spectrophotometer with a quartz cuvette having a path length of 1 cm. The titrations were
performed at 298.15 K by successive additions of stock solutions of surfactants directly into the
quartz cuvette containing 2.0 mL of 0.001 mmol dm-3
EY solution. The spectra were recorded in
the range of 400-650 nm.
1.3 Fluorescence measurements. Fluorescence measurements were carried out using F-
1600 Hitachi spectrophotometer using a quartz cuvette having an optical length of 10 mm at
298.15 K. The emission spectrum of EY was recorded in the range of 530-650 nm at an
excitation wavelength of 518 nm. The titrations were performed same as done in UV-visible
measurements.
1.4 Voltammetric measurements. The voltammetric measurements were carried out on a
PC controlled CHI660D (Austin, USA) electrochemical workstation equipped with a
conventional three electrode system comprising of a working glassy electrode (3.0 mm in
diameter), a counter Pt wire and a reference Ag/AgCl electrode. All the solutions were
deoxygenated with N2 and working electrodes were polished with slurry of alumina powder.
These voltammetric measurements were carried out in the presence of 0.1 M KCl working as a
supporting electrolyte.
1.5 Potentiometric measurements. The potentiometric measurements were done by employing
an Equiptronics digital potentiometer, Model EQ-602 employing the following
electrochemical cell assembly:
Ag/AgCl 3M KCl Test Solution PVC
membrane
Internal Reference
Solution
3M KCl Ag/AgCl
S3
The neutral ion-pair complexes of gemini pyridinium surfactants and sodium
dodecylsulfate as [Cn-3(OH)-Cn] +DS ̄ , where n = 14, 16 were prepared by same procedure as
reported [1, 2]. Equimolar aqueous solutions of [Cn-3(OH)-Cn], n = 14, 16 and sodium
dodecylsulfate (SDS) were mixed and after continuous stirring for a considerable time, the white
precipitates of [Cn-3(OH)-Cn]+DS ̄ were obtained . The precipitates so obtained were washed
repeatedly with water to remove NaCl and recrystallized thrice from acetone. The PVC (176
mg), ion-pair (5 mg) and plasticizer (550 mg) were mixed and dissolved in minimum quantity of
THF. The resulting mixture was poured in 50-mm petri dish after removing the air-bubbles. The
solvent THF was allowed to evaporate at room temperature. The resulting membrane was cut to
required size and attached to PVC tubes with PVC glue and equilibrated in 1mM of respective
surfactant solution. The internal reference solution was 1mM of these surfactants in 1mM NaCl.
The given composition of the components used for membrane formation represents the best
system in terms of slope values, correlation coefficient, linear range and detection limit. The
EMF measurements were performed by titration method at 298.15 K in the presence of 1mM
NaCl solution.
1.6 Dynamic light scattering measurements. Dynamic light scattering measurements were
done using a Malvern Nano-ZS Zetasizer instrument employing a He-Ne laser (λ = 632 nm) at a
scattering angle of 173˚. The solutions of EY and EY-surfactants mixed systems were prepared
in doubly distilled water and filtered through a membrane filter with pore size of 0.45 μm prior
to each measurement. The temperature of the measurements was controlled to an accuracy of
±0.1°C using a built-in temperature controller.
S4
Annexure SII
The corrected absorbance (ΔA) represents the difference between the measured
absorbance (Aexp) and theoretical absorbance (Atheo) as per the equation (1) [3]
∆𝐴 = 𝐴𝑒𝑥𝑝 − 𝐴𝑡ℎ𝑒𝑜 (1)
Where Atheo is calculated taking into account the Beer-Lambert’s law i.e. the two
components do not interact with each other and hence the total absorbance of the mixture is
equal to the sum of their individual absorbances according to the equation (2)
𝐴𝑇ℎ𝑒𝑜 = 𝜀𝑆𝐶𝑆0𝑋𝑆 − 𝜀𝐷𝐶𝐷
0(1 − 𝑋𝑆) (2) (3)
Here εs and εD are the molar extinction coefficients and Cs0 and CD
0 are the concentrations
of the stock solutions of the gemini pyridinium surfactants and the dye, EY respectively,
whereas, Xs represents the volume fraction of gemini pyridinium surfactants. The formation of
dye-surfactant complexes makes the absorbance of the solution to satisfy the following equation
(3):
𝐴𝑒𝑥𝑝 = 𝜀𝑆𝐶𝑆 + 𝜀𝐷𝐶𝐷 + 𝜀𝑆−𝐷𝐶𝑆−𝐷 (3)
Where εS-D is the molar extinction coefficient of the complex (Dye-surf) and CS, CD and
CS-D are the concentrations of the respective species in the mixture.
S5
System C1(mmol dm-3
) C2 = cmc(mmol dm-3
)
[14-3(OH)-14] - 0.022
EY+[14-3(OH)-14] 0.001 0.017
[16-3(OH)-16] - 0.003
EY+[16-3(OH)-16] 0.001 0.002
EY + [14-3(OH)-14]
C / mmol dm-3
0.025a 0.002
b 0.010
b 0.025
b
Dh / nm 82.5 58.8 91.3 220.2
EY + [16-3(OH)-16]
C / mmol dm-3
0.003a 0.0005
b 0.0010
b 0.0030
b
Dh / nm 91.3 78.8 122.4 342.0
a In the absence of EY,
b in the presence of 0.001 mmol dm
-3 EY
Table S1. The concentration corresponding to ion-pair formation (C1), critical micelle
concentration C2 (cmc) of gemini pyridinium surfactants, [14-3(OH)-14] and [16-3(OH)-16]
surfactants in the absence and presence of EY determined from potentiometric measurements.
Table S2. Hydrodynamic diameters (Dh) for EY-gemini pyridinium surfactants mixed
systems at different concentration of gemini pyridinium surfactants, [14-3(OH)-14] and
[16-3(OH)-16] in the absence and presence of EY.
S6
0.0 1.0x10-6
2.0x10-6
3.0x10-6
4.0x10-6
5.0x10-6
0
10
20
30
40
50
C1
C2(cmc)
0.00 1.50x10-6
3.00x10-6
4.50x10-6
1.0
1.5
2.0
2.5
3.0
/
S
cm
-1
C / mol dm-3
/
S
cm
-1
0.0002 mmol dm-3
0.0005 mmol dm-3
0.0010 mmol dm-3
C / mol dm-3
[16-3(OH)-16]
Fig.S1 Variation of specific conductivity (κ) with molar concentration of gemini pyridinium
surfactant, [16-3(OH)-16] in the presence of varying amounts of EY and the inset shows the
variation of specific conductivity (κ) with molar concentration of pure [16-3(OH)-16] in
aqueous solution.
450 500 550 600
0.0
0.4
0.8
1.2
1.6
2.0
Ab
sorb
an
ce
Wavelength / nm
0.001 mmol dm-3
0.005 mmol dm-3
0.010 mmol dm-3
0.020 mmol dm-3
Fig.S2 UV-visible spectra of EY at different concentrations
S7
450 500 550 600
0.00
0.05
0.10
0.15
0.20
0.25
Ab
sorb
an
ce
Wavelength / nm
0.0000mmol dm-3
0.0002mmol dm-3
0.0004mmol dm-3
0.0006mmol dm-3
0.0007mmol dm-3
0.0009mmol dm-3
0.0010mmol dm-3
0.0015mmol dm-3
0.0020mmol dm-3
0.0030mmol dm-3
(A) [16-3(OH)-16]
Fig.S3 (A) UV-visible spectra of 0.001 mmol dm
-3 EY in the presence of increasing concentrations
of gemini pyridinium surfactant, [16-3(OH)-16] (B) Job’s plot depicting 1:1 stoichiometry of EY-
[16-3(OH)-16] mixed system.
0.0 0.2 0.4 0.6 0.8 1.0
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
0.1
Xsurf
A
(B) [16-3(OH)-16]
540 560 580 600 620 640
0
50
100
150
200
250
300
350
540 560 580 600 620 6400
1
2
3
4
5
6
7
8
Wavelength / nm
Flu
ore
scen
ce I
nte
nsi
ty
Wavelength / nm
Flu
oresc
en
ce I
nte
nsi
ty
Fig.S4 Fluorescence emission spectra of 0.001 mmol dm
-3 EY in the presence of increasing
concentrations of gemini pyridinium surfactant, [16-3(OH)-16].
S8
-1.4 -1.2 -1.0 -0.8
-1.0x10-5
-8.0x10-6
-6.0x10-6
-4.0x10-6
-2.0x10-6
0.0
2.0x10-6
(A) [16-3(OH)-16]
Potential / V
I p /
A
-1.4 -1.2 -1.0 -0.8
-1.0x10-5
-8.0x10-6
-6.0x10-6
-4.0x10-6
-2.0x10-6
(B) [16-3(OH)-16]
I p /
A
Potential / V
Fig.S5 (A) Cyclic voltammograms of EY in the presence of increasing concentrations of
gemini pyridinium surfactant, [16-3(OH)-16] (B) Differential pulse voltammograms of EY in
the presence of increasing concentrations of [16-3(OH)-16]
-1.4 -1.2 -1.0 -0.8
-1.0x10-5
-8.0x10-6
-6.0x10-6
-4.0x10-6
-2.0x10-6
0.0
2.0x10-6
(A) 0.005 mmol dm-3
[14-3(OH)-14] in EY
I p /
A
Potential / V
0.01 V
0.02 V
0.03 V
0.04 V
0.05 V
-1.4 -1.2 -1.0 -0.8
-6.0x10-6
-4.0x10-6
-2.0x10-6
0.0 (B) 0.010 mmol dm
-3
[14-3(OH)-14] in EO
Potential / V
0.01 V
0.02 V
0.03 V
0.04 V
0.05 V
I p /
A
-1.4 -1.2 -1.0 -0.8
-8.0x10-6
-6.0x10-6
-4.0x10-6
-2.0x10-6
0.0
2.0x10-6
(C) 0.030 mmol dm-3
[14-3(OH)-14] in EYI p
/ A
0.01 V
0.02 V
0.03 V
0.04 V
0.05 V
Potential / V
Fig.S6 Cyclic voltammogram (CV) of gemini pyridinium surfactants in EY at various scan rates (A)
0.005 mmol dm-3
[14-3(OH)-14] (B) 0.010 mmol dm-3
[14-3(OH)-14] (C) 0.030 mmol dm-3
[14-3(OH)-14].
S9
-1.4 -1.2 -1.0 -0.8
-1.0x10-5
-8.0x10-6
-6.0x10-6
-4.0x10-6
-2.0x10-6
0.0
2.0x10-6
(A) 0.0005 mmol dm-3
[16-3(OH)-16] in EY
I p /
A
Potential / V
0.01 V
0.02 V
0.03 V
0.04 V
0.05 V
-1.4 -1.2 -1.0 -0.8
-1.0x10-5
-8.0x10-6
-6.0x10-6
-4.0x10-6
-2.0x10-6
0.0
2.0x10-6
(B) 0.010 mmol dm-3
[16-3(OH)-16] in EY
0.01 V
0.02 V
0.03 V
0.04 V
0.05 VI p
/ A
Potential / V
-1.4 -1.2 -1.0 -0.8
-8.0x10-6
-6.0x10-6
-4.0x10-6
-2.0x10-6
0.0
2.0x10-6 (C) 0.0004 mmol dm
-3
[16-3(OH)-16] in EY
I p /
A
Potential / V
0.01 V
0.02 V
0.03 V
0.04 V
0.0 5.0x105
1.0x106
1.5x106
2.0x106
0.0
-5.0x105
-1.0x106
-1.5x106
1/C
1/
p
[14-3(OH)-14]
[16-3(OH)-16](B)
0.0 5.0x105
1.0x106
1.5x106
2.0x106
2.5x106
0
50
100
150
(A) [14-3(OH)-14]
[16-3(OH)-16]
1/C
1/
Fig.S8 Binding constant determination for the EY-gemini pyridinium surfactants mixed
systems using (A) changes in UV-visible spectra of EY (B) changes in the peak current of EY.
Fig.S7 Cyclic voltammogram (CV) of gemini pyridinium surfactants in EY at various scan rates (A)
0.0005 mmol dm-3
[16-3(OH)-16] (B) 0.0020 mmol dm-3
[16-3(OH)-16] (C) 0.0040 mmol dm-3
[16-3(OH)-16]
S10
-7.5 -7.0 -6.5 -6.0 -5.5
-0.20
-0.15
-0.10
-0.05
0.00
0.05[16-3(OH)-16]
0.000 mmol dm-3
0.001 mmol dm-3
EM
F /
V
log C / mol dm-3
(A)
-7.5 -7.0 -6.5 -6.0 -5.5
5.0x1011
5.5x1011
6.0x1011
6.5x1011
7.0x1011
7.5x1011
8.0x1011
8.5x1011
9.0x1011
9.5x1011
(B) [HEC16OPyBr]
v
log C / mol dm-3
Fig.S9 (A) EMF as a function of logarithm of molar concentration of gemini pyridinium
surfactant, [16-3(OH)-16] in the absence and presence of 0.001 mmol dm-3
EY (B) Binding
isotherms of binding parameter (v) versus logarithm of molar concentration of [16-3(OH)-16] in
the presence of 0.001 mmol dm-3
EY.
450 500 550 600
0.00
0.03
0.06
0.09
0.12
0.15
Ab
sorb
an
ce
Wavelength / nm
Fig.S10 Representative spectral decomposition stratergy for deconvolution of EY
absorbance spectra into Gaussian shapes.
S11
References
[1] A. Shaheen, I. Kaur, R.K Mahajan, Potentiometric studies of micellization behavior of
cationic surfactants in the presence of glycol additives and triblock polymer (Pluronic
F68), using surfactant-selective sensors based on neutral ion-pair complexes. Ind. Eng.
Chem. Res. 2007, 46, 4706-4709.
[2] R.K. Mahajan, A. Shaheen, Effects of various additives on the performance of a newly
developed PVC based potentiometric sensor for anionic surfactants. J. Colloid Interface
Sci. 2008, 326, 191-195.
[3] S. Gokturk, M. Tuncay, Dye-surfactant interaction in the pre-micellar region. J. Surf.
Deterg. 2003, 6, 325-330