Interaction dye cristal violet with Surfactants in Aqueous Media

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J Solution Chem (2007) 36: 563–571
DOI 10.1007/s10953-007-9133-6
O R I G I NA L PA P E R
Spectroscopic Investigations on the Interaction of Crystal
Violet with Nonionic Micelles of Brij and Igepal
Surfactants in Aqueous Media
Stephanie A. Moore · Karen M. Glenn ·
Rama M. Palepu
Received: 14 August 2006 / Accepted: 8 September 2006 /
Published online: 31 March 2007
© Springer Science+Business Media, LLC 2007
Abstract The behavior of the triphenylmethane dye crystal violet in aqueous solutions con-
taining polyoxyethylene nonionic surfactants was investigated using absorption and fluo-
rescence spectroscopic techniques. The interactions of the dye were examined in micellar
media in order to prevent dye aggregation and to ensure maximum dye and surfactant inter-
action. The relative fluorescence enhancements and the binding constants of the dye to the
surfactant micelles were determined. The micropolarities of the micellar environment sensed
by the pyrene probe were estimated from the I1/I3 intensity ratios of the fluorescence spec-
tra of pyrene. The fluorescence quenching of pyrene by hexadecylpyridinium chloride was
investigated in aqueous surfactant mixtures at a fixed concentration of surfactant in order to
determine the aggregation numbers. Attempts were made to correlate the binding constants
obtained in this investigation to various micellar parameters.
Keywords Fluorescence spectroscopy · Crystal violet · POE surfactant · Igepal
surfactants · Aggregation number · Stokes shift
1 Introduction
Triphenylmethane (TPM) dyes are an important class of commercial dyes that have potential
applications in the textile industry as sensitizers for photoconductivity and in medicine as
antibacterial and sterilization agents during blood transfusions [1–6]. The TPM dyes are
characterized by their intense colors, which include vivid reds, blues, greens and violets.
Due to the wide range of applications, the TPM dyes are often found in wastewaters and
some of these dyes have been found to be carcinogenic and genotoxic [7, 8]; therefore, it
is essential to detect these dyes at low concentrations. Currently, research is in progress to
employ nonionic surfactants to detect trace quantities of these dyes and to remove them from
wastewater [9–11].
S.A. Moore · K.M. Glenn · R.M. Palepu (�)
Department of Chemistry, St. Francis Xavier University, Antigonish, Canada B2G 2W5
e-mail: rpalepu@stfx.ca
564 J Solution Chem (2007) 36: 563–571
Among the TPM dyes, crystal violet (CV), the tris(p-(dimethylamino)phenyl)methyl ion,
is one of the more widely investigated dyes in terms of its molecular structure [2], electronic
states [12] and the relaxation dynamics of the electronic states [13, 14]. In neat aqueous
solutions, CV is known to fluoresce weakly due to the rapid rotation of the phenyl rings,
thereby providing a non-radiative decay path for the excited singlet state [15, 16]. The flu-
orescence quantum yields and lifetimes are known to increase when the dye is present in
rigid media and when it binds to polymer-like substrates and surfactants [17, 18].
In the present investigation, the effects of the addition of two classes of nonionic poly-
oxyethylene (POE) surfactants on the spectral properties of CV have been examined as a
function of the surfactant concentration. The binding constant, KM [19], and relative flu-
orescence intensity increase, Imax/I o, were determined. The static fluorescence quenching
method outlined by Yetka and Turro [20, 21] was employed to determine the aggregation
numbers. Pyrene was used as a fluorescence probe and hexadecylpyridinium chloride (CPCl)
was employed as a quencher in order to determine the aggregation numbers. The micropolar-
ity of the environment sensed by the pyrene was determined with the I1/I3 ratio method [22].
Rationalization of these results has been attempted.
2 Experimental Details
The nonionic polyoxyethylene (POE) chain surfactants Brij 35 {polyoxyethylene (23) lau-
ryl ether}, Brij 58 {polyoxyethylene (20) cetyl ether}, Brij 78 {polyoxyethylene (20) stearyl
ether}, Brij 98 {polyoxyethylene (20) oleyl ether}, Brij 700 {polyoxyethylene (100) cetyl
ether}, Igepal CO-630 {polyoxyethylene (9) nonylphenyl ether}, Igepal CO-720 {poly-
oxyethylene (12) nonylphenyl ether}, Igepal CO-890 {polyoxyethylene (40) nonylphenyl
ether}, Igepal CO-990 {polyoxyethylene (100) nonylphenyl ether}, Igepal DM-970 {poly-
oxyethylene (150) dinonylphenyl ether}, POE 12 TDE {polyoxyethylene (12) tridecyl
ether}, and POE 18 TDE {polyoxyethylene (18) tridecyl ether} were obtained from Aldrich,
and were used as received. The crystal violet was obtained from Fisher Scientific Company.
Hexadecylpyridinium chloride (CPCl) was obtained from Aldrich and was recrystallized
from acetone. The pyrene was obtained from Aldrich (99%, optical grade) and was purified
by repeated crystallization that was followed by sublimation. Doubly deionized water was
used to prepare the solutions.
Concentrations of CV of the order of 1 × 10−6 mol·L−1 were used in all experiments
to avoid dimerization of the dye. For the determination of aggregation numbers, the pyrene
concentration was kept at 1×10−6 mol·L−1 and the quencher concentration was varied from
0 to 0.6 mmol·L−1 [21].
2.1 Instrumentation
Absorption spectra were recorded on a Varian Cary 100 double beam UV-visible spectropho-
tometer. The scan range was 350 to 650 nm and identical 1 cm quartz cuvettes were used.
The fluorescence spectra were measured using a JY Horiba Spex Fluoromax-3 Fluorimeter
with a 1 cm quartz cuvette. The excitation wavelength for pyrene was 330 nm and the spec-
tra were scanned in the range of 335 to 385 nm. The excitation and emission bandwidths
were 2.00 and 1.00 nm, respectively. The dye CV was excited at 590 nm and the emission
range 600 to 670 nm was scanned. The excitation and emission bandwidths were 7.00 and
9.00 nm, respectively. Triplicate measurements were made and mean values were accepted
for the data analysis.
J Solution Chem (2007) 36: 563–571 565
3 Results and Discussion
3.1 Absorption Spectra
The maximum absorbance wavelength, λa, of the aqueous dye solutions occurred at
590.0 nm. A shoulder peak was also observed in these spectra that may be due to differ-
ent isomers in equilibrium [14, 23]. The origin of the shoulder was interpreted by assuming
the existence of two fundamental isomers, one with a propeller structure (D3 symmetry) for
the ground state and the other one with a pyramidal structure (C3 symmetry) in which three
bonds of the central atom are bent (Scheme 1).
Ionic surfactants are known to disturb the equilibrium between isomers [2]. In the present
study, it was observed that the nonionic micelles enhanced the absorbance intensity of the
shoulder peak at 550 nm. The absorbance intensity of the main peak was also enhanced, but
not to the same extent (Table 1). Similar observations were made for TPM dyes in the pres-
ence of polymers [19]. When a nonionic surfactant was present, there was a shift in λa to a
longer wavelength that ranged from 596.0 to 598.0 nm, depending upon the surfactant used.
Also, in the presence of the surfactant, the absorbance values at the maximum wavelength
increased. Values of λa for the aqueous dye solutions in the absence and presence of various
surfactants are shown in Table 1.
The red shift in the wavelength of the absorption maximum and the increase in intensity
of the peak can be attributed to interactions between the dye and nonionic micelles, with the
non-polar portion of the dye being localized in the hydrophobic core of the micelle, whereas
the polar portion resides in the poly(oxyethylene) head group region.
3.2 Fluorescence Spectra
The addition of a surfactant to an aqueous dye solution (above the cmc) caused an increase
in the fluorescence intensity (Fig. 1) until a maximum intensity, Imax, was reached (see
Fig. 2). The observed increase in intensity may be attributed to the interaction of the dye
with the nonionic micelles and the media also becomesmore viscous in micellar media. The
TPM dyes are weakly fluorescent because there is no hindrance in the rotation of the phenyl
rings [16], making the relaxation process very fast. The fluorescence and quantum yields are
significantly higher in viscous media or when the dye binds to a substrate, thus preventing
the fast rotational relaxation process from occurring. Values of the relative fluorescence
Scheme 1
566 J Solution Chem (2007) 36: 563–571
Table 1 Maximum wavelength and absorbance values for crystal violet (CV) in various media, along with
the relative increase in absorbance of the main peak, Asurf/Ao, shoulder peak, Assurf /Aso, and fluorescence
intensity, Imax/Io, for the nonionic POE surfactants
Solution Absorbance λa/nm Asurf/Ao Assurf/Aso Imax/Io
Aqueous CV 0.688 590 1.00 1.00 1.0
Brij 35 0.742 597 1.08 1.13 7.0
Brij 58 0.742 596 1.08 1.14 5.4
Brij 78 0.741 597 1.08 1.12 9.9
Brij 98 0.736 597 1.07 1.11 7.5
Brij 700 0.739 597 1.07 1.15 7.5
Igepal CO-630 0.764 598 1.11 1.19 17.3
Igepal CO-720 0.719 598 1.05 1.08 15.0
Igepal CO-890 0.704 597 1.02 1.07 15.6
Igepal CO-990 0.713 598 1.04 1.08 10.1
Igepal DM-970 0.694 597 1.01 1.05 11.6
POE 12 TDE 0.769 596 1.12 1.14 6.1
POE 18 TDE 0.719 596 1.05 1.08 6.0
Figure 1 Fluorescence emission
spectra of CV in the presence of
different concentrations of Igepal
CO-630: a 0 mmol·L−1; b 0.5
mmol·L−1; c 1.25 mmol·L−1; d
2 mmol·L−1; e 2.5 mmol·L−1; f
3.75 mmol·L−1; g 5 mmol·L−1;
h 7.5 mmol·L−1; i 10
mmol·L−1; j 17.5 mmol·L−1; k
25 mmol·L−1
increase, Imax/I o, are presented in Table 1 for the aqueous dye solution in the absence and
presence of surfactant.
The fluorescence intensity reaches a plateau at a sufficiently high concentration of surfac-
tant, indicating that all of the dye is interacting with the surfactant micelles. In this study the
surfactant concentrations were kept well above the cmc to maximize the interaction between
the CV dye and the surfactants, as well as to prevent the dye from self-aggregating.
Because both a change in the maximum emission wavelength and higher values of
Imax/I o were observed for aqueous CV solutions in the presence of surfactants, we assume
that the dye binds to the micellar aggregates of the surfactants. Assuming that the relative
increase in fluorescence intensity of the dye in the presence of non-ionic surfactants is due
to formation of an excited-state complex, the magnitude of the binding constant, KM, can
J Solution Chem (2007) 36: 563–571 567
Figure 2 Plot of fluorescence intensity versus [surfactant] (mmol·L−1) for: A Brij 58; B Igepal CO-990;
C POE 12 TDE
be estimated using the following equation [19]:
Imax − Io
It − Io = 1 +
1
KM[M] , (1)
where Imax is the limiting fluorescence intensity at higher micellar concentration, I o is the
fluorescence intensity in the absence of micelles, I t is the fluorescence intensity at an inter-
mediate micellar concentration, KM is the binding constant, and [M] is the concentration of
micelles present. Therefore, from a plot of (Imax − I o)/(I t − I o) versus 1/[M], the binding
constant can be determined from the slope.
The concentration of micelles can be established using the following relation:
[M] = [S] − cmc
Nagg
, (2)
where [S] is the total surfactant concentration and N agg is the aggregation number for that
surfactant. Because the surfactant concentration is much higher than the cmc value, Eq. 2
can be simplified to:
[M] = [S]
Nagg
. (3)
The aggregation numbers for the Brij series, POE 12 TDE and POE 18 TDE were deter-
mined by employing the static quenching method as outlined by Turro and Yetka [20]. The
aggregation numbers for the Igepal series were taken from our previous investigation [24].
568 J Solution Chem (2007) 36: 563–571
Table 2 I1/I3 ratios, aggregation numbers, Nagg, binding constants, KM, and Stokes shift, �ν, for various
surfactants
Solution [surfactant]/mmol·L−1 Nagg KM/L·mol−1 I1/I3 �ν/cm−1
Aqueous CV 0 – – – 1022
Brij 35 50 36 5171 1.28 945
Brij 58 50 39 2438 1.26 960
Brij 78 50 34 1250 1.26 1027
Brij 98 50 37 2502 1.19 967
Brij 700 20 76 16059 1.26 900
Igepal CO-630 50 42 769 1.36 751
Igepal CO-720 50 31 769 1.36 761
Igepal CO-890 50 26 305 1.41 712
Igepal CO-990 25 38 2836 1.37 912
Igepal DM-970 25 27 3845 1.26 932
POE 12 TDE 18 55 20790 1.26 966
POE 18 TDE 13 36 17301 1.30 956
The values of N agg for each surfactant are presented in Table 2. Employing these values
of N agg, the values of [M] were obtained and representative plots of (Imax − I o)/(I t − I o)
versus 1/[M] are presented in Fig. 3.
The binding constants were evaluated from the slopes of the plots and their values are
presented in Table 2. The estimated error in KM was found to be approximately ±3%. No
obvious correlation was observed between the binding constant values and their aggrega-
tion numbers, the number of ethylene oxide groups, or the number of carbon atoms in the
alkyl chain for the Brij and polyoxyethylene tridecyl ether series. In view of the varying
chain lengths and the number of ethylene oxide groups in the Brij series, the KM values
were correlated with the hydrophilic–lipophilic balance (HLB) values as depicted in Fig. 4a.
However, for the Igepal series the binding constants were correlated with the number of eth-
ylene oxide groups as they differ in the number of ethylene oxide groups only while the
hydrophobic chain length remains the same, except for Igepal DM-970 (Fig. 4b).
The binding of the dye to the micelles is due to hydrophobic interactions, which was fur-
ther verified by employing alkali halides to study the salting-out effect for these surfactant–
dye solutions [25]. It was found that the relative fluorescence intensities of the surfactant
solutions increased between 1.05 and 1.30 times when NaCl was present. Other salts, in-
cluding LiCl, KCl and CsCl, were also employed, and it was found that LiCl was the best
salting-out agent because the relative increase in fluorescence intensity was the greatest for
LiCl. KCl and CsCl were less effective in this regard than NaCl. The presence of complex
formation is further substantiated by the decrease in the rates of alkaline fading of CV in the
presence of micelles [26].
Values of the micropolarity of the environment sensed by pyrene were obtained using
the ratio of the intensity of the first peak to the intensity of the third peak (the I1/I3 ratio)
from the pyrene fluorescence spectra. The first peak results from a weak forbidden transition
that shows a strong dependence on the solvent polarity, whereas the third peak in the pyrene
spectrum results from a strong allowed transition that exhibits very little dependence on the
J Solution Chem (2007) 36: 563–571 569
Figure 3 Plot of (Imax −Io)/(I t −Io) versus 1/[micelles] (mmol·L−1) from which KM can be determined
for: A Brij 700; B Brij 35; C Igepal CO-990
Figure 4 A Plot of KM versus HLB for the Brij series of surfactants; B plot of KM versus the number EO
groups present for the Igepal series of surfactants
solvent polarity [20, 21]. The values of the I1/I3 ratios are listed in Table 2 and were found
to be similar for all of the surfactant solutions studied.
From the absorbance and emission spectra, the Stokes shift (cm−1) values were deter-
mined as follows:
�ν = νa − νf, (4)
570 J Solution Chem (2007) 36: 563–571
Figure 5 Plot of KM versus �ν¯ for: A the Igepal series of surfactants; B the Brij series of surfactants
where �ν is the Stokes shift and νa and νf are the wave numbers (in cm−1) at the maxima
of the absorption and the emission (fluorescence) spectra, respectively, for the same tran-
sition [27]. The calculated �ν values are listed in Table 2 and, for the Igepal series, the
magnitude of the Stokes shift increased with the degree of association of the dye with the
micelles (Fig. 5a). However, the opposite trend was observed for the Brij series (Fig. 5b),
which is intriguing and merits further investigation.
4 Conclusions
It was observed that the addition of a surfactant to crystal violet aqueoussolutions caused
a red-shift to occur in the wavelength of maximum fluorescence intensity along with an
initial increase in the absorbance. The fluorescence intensities also increased with increasing
concentration of the surfactant, which may be attributed to a dye–micelle interaction.
The binding constants of the dye with the micelles were determined and, for Igepal series,
the values of the binding constants depend on the number of ethylene oxide groups. How-
ever, for the Brij series, no such dependency was observed. For this series of surfactants
the binding constant values were correlated with their HLB values. Values of the binding
constants were also found to be related to the Stokes shift for the Brij and Igepal series of
surfactants.
The aggregation numbers, relative fluorescence intensities, and I1/I3 ratios were deter-
mined, but no obvious trend was observed between the binding constants and the micellar
parameters.
Acknowledgements R.P. acknowledges generous support from NSERC in the form of a Discovery Grant.
K.G. and S.M. are both grateful for the award of an USRA (2004) from NSERC.
References
1. Duxbury, D.-F.: The photochemistry and photophysics of triphenylmethane dyes in solids and liquid-
media. Chem. Rev. 93, 381–443 (1993)
2. Duxbury, D.-F. The sensitized fading of o-triphenylmethane dyes in polymer films. Dye Pigment 25,
179–204 (1994)
3. De, S., Girigoswami, A., Mandal, S.: Enhanced fluorescence of triphenylmethane dyes in aqueous sur-
factant solutions at supramicellar concentrations—Effect of added electrolyte. Spectrochim. Acta A 58,
2547–2555 (2002)
J Solution Chem (2007) 36: 563–571 571
4. Fessard, V., Godard, T., Huet, S., Mourot, A., Poul, J.M.: Mutagenicity of malachite green and leucoma-
lachite green in in vitro tests. J. Appl. Toxicol. 19, 421–430 (1999)
5. Sarkar, M., Poddar, S.: Studies on the interaction of surfactants with cationic dyes by absorption spec-
troscopy. J. Colloid Interface Sci. 221, 181–185 (2000)
6. de Santana, H., Dam, Z., Corio, P., El Haber, F., Louarn, G.: Preparation and characterization of Sers-
active substrates: A study of the crystal violet adsorption on Ag nano particles. Quim. Nova 29, 194–199
(2006)
7. Pearce, C.-I., Lloyd, J.R., Guthrie, J.T.: The removal of colour from textile waste water using whole
bacteria cells: A Review. Dye Pigment 58, 179–196 (2003)
8. Srivastava, S., Sinha, R., Roy, D.: Toxicological effects of malachite green. Aquat. Toxicolog. 66, 319–
329 (2004)
9. Materna, K., Schaadt, A., Bart, H.J., Szymanowski, J.: Dynamics of surfactant rich phase separation from
solutions containing non-ionic and zwitterionic surfactants. Colloids Surfaces A 254, 223–229 (2005)
10. Janos, P., Smidova, V.: Effects of surfactants on the adsorptive removal of basic dyes from water using
organo mineral sorbent–iron humate. J. Colloid Interface Sci. 291, 19–27 (2005)
11. Adak, A., Bandyopadhyay, M., Pal, A.: Fixed bed column study for the removal of crystal violet dye
from aquatic environment by surfactant-modified alumina. Dye Pigment 69, 245–251 (2006)
12. Lueck, H.-B., McHale, J.L., Edwards, W.D.: Symmetry-breaking solvent effects on the electronic struc-
ture and spectra of a series of triphenylmethane dyes. J. Am. Chem. Soc. 114, 2342–2348 (1992)
13. Martin, M.-M., Plaza, P., Meyer, Y.H.: Transient spectroscopy of triphenylmethane derivatives following
subpicosecond and irradiation. Chem. Phys. 153, 297–303 (1991)
14. Martin, M.-M., Plaza, P., Meyer, Y.H.: Ultrafast conformational relaxation of triphenylmethane dyes—
Spectral characterization. J. Phys. Chem. B 95, 9310–9314 (1991)
15. Doust, T.: Picosecond fluorescence decay kinetics of crystal violet in low-viscosity solvents. Chem. Phys.
Lett. 96, 522–525 (1983)
16. Ben-Amotz, D., Jeanloz, R., Harris, C.B.: Ground and excited-state torsional dyanamics of triphenyl-
methane dye in low-viscosity solvents. Chem. Phys. Lett. 119, 305–311 (1985)
17. Bapstista, M., Indig, G.L.: Effect of BSA Binding on photophysical and photochemical properties of
triphenylmethane dyes. J. Phys. Chem. B 102, 4678–4688 (1998)
18. Jones II, G., Oh, G., Goswami, K.: The photochemistry of triarylmethane dyes bound to polyelectrolytes:
Photo induced electron transfer involving bound dye monomers and dimers. J. Photochem. Photobiol. A
57, 65–80 (1991)
19. Almgrem, M., Greiser, F., Thomas, J.K.: Dynamics and static aspects of solubilization of neutral arenes
in ionic micellar solutions. J. Am. Chem. Soc. 101, 279–291 (1979)
20. Turro, N.-J., Yekta, A.J.: Luminescent probes for detergent solutions: A simple procedure for determi-
nation of the mean aggregation number of micelles. J. Am. Chem. Soc. 100, 5951–5952 (1978)
21. Yekta, A., Aikawa, M., Turro, N.J.: Photoluminescence methods for evaluation of solubilization parame-
ters and dynamics or micellar aggregates. Limiting cases which allow estimation of partition coefficients,
aggregation numbers, entrance and exit rates. J. Chem. Phys. Lett. 63, 543–548 (1979)
22. Guibault, G.-G.: Practical Fluorescence, 2nd edn. Marcel Dekker, New York (1990)
23. Lewis, G.-N., Magel, T.T., Lipkin, D.: Isomers of crystal violet ion: Absorption and re-emission of light.
J. Am. Chem. Soc. 64, 1774–1782 (1942)
24. Moore, S., Palepu, R.: Spectroscopic investigation on the interaction of an anionic probe with nonionic
micelles of Igepal surfactants in aqueous media. Mol. Phys. 104, 3155–3158 (2006)
25. Long, F.-A., McDevitt, W.F.: Activity coefficients of non-electrolyte solutions in aqueous salt solutions.
Chem. Rev. 51, 119–196 (1952)
26. Palepu, R.: Unpublished results (2006)
27. Lackowicz, J.R.: Principles of Fluorescence Spectroscopy. Plenum, New York (1983)
	Spectroscopic Investigations on the Interaction of Crystal Violet with Nonionic Micelles of Brij and Igepal Surfactants in Aqueous Media
	Abstract
	Introduction
	Experimental Details
	Instrumentation
	Results and Discussion
	Absorption Spectra
	Fluorescence Spectra
	Conclusions
	Acknowledgements
	References