Spectrofluorimetric Analysis of Interaction of Benzo(a) Pyrene and Surfactant Micelles
Shuchi Gupta1*, Seema Acharya2
1Professor, Manda Institute of Technology, Bikaner.
2Professor and Head, Department of Chemistry, Jai Narayan Vyas University, Jodhpur, Rajasthan.
*Corresponding Author E-mail: shuchigoyal2002@gmail.com
ABSTRACT:
Benzo (a) pyrene belongs to a class of Polycyclic aromatic hydrocarbon (PAH) that serves as micro pollutants in the environment. It has been reported as probable carcinogen in humans. PAHs has low water solubility. Solubility of PAHs can be increased by using surfactants to reduce surface tension and interfacial tension. The solubilization of Benzo (a) pyrene solubilizate into the micellar core of certain surfactants have been studied and analyzed with the help of Fluorescence spectroscopy. The increase in fluorescence intensity on addition of surfactant can be attributed to the increase in quantum efficiency suggests that the surfactants have solubilized the suspended molecule .The solubilization phenomenon was also confirmed by absorption spectral studies and light scattering measurements. Theoretical parameters were also determined; the calculated results are in fair agreement with the experimental results. This proves the validity of work done.
KEYWORDS: Solubilization, Polycyclic Aromatic Hydrocarbons (PAHs), Light Scattering, Fluorescence, Absorption Spectral Studies.
INTRODUCTION:
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants generated from both natural and anthropogenic processes and pose a serious concern to the health of aquatic life and humans through bioaccumulation1,2. In last few years an increased attention on research related to organic pollutants such as PAHs can be observed3-5. Polycyclic aromatic hydrocarbons (PAHs) are highly toxic chemicals. Their high hydrophobicity contributes to their low aqueous solubility and persistence in the environment. Consequently, effective techniques are needed to increase their bioavailability and to monitor their existence in the environment.
Benzo (a) pyrene is a condensed 5 ring hydrocarbon. It is highly carcinogenic polycyclic aromatic hydrocarbon (PAH) widely present in nature and derived from several natural and anthropogenic sources. Benzo (a) pyrene is highly fluorescent; therefore, fluorescence techniques can serve as a better analytical method, because of its high sensitivity, selectivity and simplicity.
Solubilization is a partition process of organic substances between an aqueous and a micellar phase. This process can be affected by many factors, including the properties of surfactants and solubilizates, as well as some environmental factors.Surfactants possess a wide range of applicability. They are among the most versatile products of the chemical industry. In aqueous systems, the addition of surfactant enables two immiscible liquids to become soluble in one another. This striking phenomenon is attributed to the unique structure of the surfactant molecules. Surfactants are chemicals possessing a hydrophobic core and a hydrophilic outer surface. Surfactant molecules, when above their critical micelle concentration (CMC), form aggregates in water, called “micelles”. An important property of micelles is their capability to promote the solubility of solvophobic molecules by trapping them in energetically favorable microenvironments via a process known as “solubilization”6. A considerable amount of research has quantified the efficiency of surfactants. However, most of those research studies focus on a single kind of surfactant, such as nonionic surfactants7 or anionic surfactants8. It is known that luminescence characteristics of luminophores change considerably in the presence of micelles of surfactants compared with an aqueous medium9. The extent of micellar solubilization depends on many factors, including surfactant structure, aggregation number, micelle geometry, ionic strength, temperature, and the size and chemistry of the solubilizate.Quantitative studies on the solubilization capacities of surfactants and effects of various parameters on the solubilization capacity of surfactants could be found in the literatures10-12. Bernardez and his group13,14 studied the solubilization of two PAHs in fivenon-ionic surfactants and determined that the solubilization rate depends on chemical structure of PAHs and type of surfactants. The present paper incorporate the studies on the solubilization of Benzo(a) pyrene in presence of certain surfactants at their critical micellar concentration or marginally above the critical micellar concentration, employing fluorescence, absorptionand light scattering spectral studies. The results have been interpreted from the Calculations of molar extinction coefficient and quantum yields of Benzo(a) pyrene fluorescence in various micellar media.
MATERIAL AND METHODS:
All fluorometric, absorption and light scattering experiments were carried out with the following three instruments:
1 Perkin-Elmer Fluorescence Spectrophotometer Model No. 204 A with a synchronized model no. 056 Strip Chart Recorder.
2 Hewlett Packard (HP) 8452 A diode array spectrophotometer.
3 Brice- Phoenix Universal Light Scattering Photometer Model No. 2000.
The stock solution of analytically pure benzo[a]pyrene (Sigma Chemicals) was prepared in distilled ethanol due to its low solubility in water. A 10-3 M solution was dilutedupto 10-5 M by adding water, ethanol or surfactant solution.
All the surfactants used were either of sigma (USA) or BDH product. The following surfactants were employed.
A. Nonionic:
PolyoxyethyleneTertoctyl Phenol (TX-100) PolyoxyethyleneSorbitanMonolauriate (Tween-80) and PolyoxyethyleneSorbitanMonopalmitate (Tween-40).
B. Cationic:
Cetyltrimethyl Ammonium Bromide (CTAB), Cetylpyridinium Chloride (CPC) and Cetylpyridinium Bromide (CPB).
C. Anionic:
Dodecylbenzene sodium sulphonate (DBSS), Dioctylsodium Sulphosuccinate (DSSS) and Sodiumlauryl Sulphate (SLS).
The purity of surfactant was checked by determining their CMC values with the help of surface tension measurement, employing drop weight method. By using appropriate equations, various spectral parameters like quantum yield and molar extinction coefficient were calculated in micellar media at different concentrations and stokes shift were calculated at different concentrations of the compound. The absolute fluorescence quantum yield of the compound relative to anthracene solution is taken as standard and sample from the area of the fluorescence spectrum were recorded over the whole range of emission under identical conditions.
RESULT AND DISCUSSION:
The excitation spectrum was taken by keeping the emission monochromator at maximum fluorescence wavelength, showed wavelength of maximum excitation at 410nm.the emission spectrum taken by keeping the excitation monochromator at 410 nm showed wavelength of maximum emission at 500nm.
During initial addition of nonionic surfactant an enhancement in fluorescence intensity accompanied by a blue shift of 10 nm was observed. On further increasing concentration of surfactant decrease in the fluorescence intensity accompanied by blue shift of 35-40 nm was observed. The anionic surfactants employed were DBSS, DSSS and SLS. With the addition of anionic surfactant, initially an increase in the fluorescence intensity was observed followed by decrease in the fluorescence intensity. Fluorescence Emission Spectra of benzo[a]Pyrene in DSSS is given in Fig.1.
On initial addition of cationic surfactant (0.001% to 0.01%) enhancement in the fluorescence intensity with a gradual blue shift of 15nm in the λem was observed. On further increasing the surfactant concentration in the solution, a pronounced decrease in fluorescence intensity at the shifted λem occurred. The minimum and maximum fluorescence intensity in absence and presence of nonionic, anionic and cationic surfactants are given in Table 1
Table 1: Relative fluorescence emission intensity (F.I.) of the benzo[a]pyrene (1x 10-5M) with different surfactants
λex=410nm, λem=500nm nm, P.M. Gain=2 Sensitivity Range=0.1
|
S. No. |
% of Brij-35 |
F.I |
λem |
% of DSSS |
F.I |
λem |
% of CPC |
F.I |
λem |
|
1 |
0.00 |
44 |
500 |
0.00 |
44 |
500 |
0.00 |
44 |
500 |
|
2 |
0.001 |
57 |
490 |
0.003 |
50 |
490 |
0.003 |
64 |
490 |
|
3 |
0.01 |
41 |
460 |
0.01 |
35 |
490 |
0.005 |
54 |
485-490 |
|
4 |
0.1 |
27 |
460 |
0.03 |
35 |
490 |
0.09 |
31 |
485-490 |
|
5 |
0.5 |
18 |
460 |
0.09 |
22 |
485-490 |
0.4 |
11 |
485 |
|
a. 1x 10-5 M BENZO (a) PYRENE b. -do- + 0.003% DSSS c. -do- + 0.01% -do- d. -do- + 0.09% -do- |
|
|
Fig. 1. Fluorescence Emission Spectra
|
a. 1x 10-4 M BENZO (a) PYRENE b. -do- + 0.01% CPC c. -do- + 0.05% -do- d. -do- + 0.1% -do- |
|
|
Fig.2. Absorption Spectra
The absorption spectrum of a solution of 1 x 10-4M Benzo (a) pyrene displayed peaks at 406 nm and 418 nm. During initial addition of nonionic surfactant (0.001% to 0.01%) decrease in the absorbance was observed. On further addition of surfactant (0.03% to 0.07%) enhancement in absorption was observed at both the peak positions. On the addition of anionic surfactants a continuous decrease in the absorbance was noticed. All anionic surfactants behave similarly. On addition of cationic surfactants absorbance first decreased and then increased without any shift in the peak position. Absorption Spectra of Benzo (a) pyrene in CPC is shown in fig. 2.The light scattering studies of Benzo (a) pyrene were made at an angle of 90° to the incident light.
During addition of each surfactant, there occurred a sharp decrease in the galvanometer deflection with increase in surfactant concentration. The nonionic surfactants showed the maximum deflection. The concentration required to reach the minimum value of scattering flux was different for each surfactant. The results are given in Fig. 3.The solubilization efficiency depends on many factors like type and structure of surfactants, type of solubilizates, mixing ratio of surfactants and so on15.Nonionic surfactants, because of their low CMC, are better solubilizing agents than ionics and the order of solubilizing power is nonionic>cationic >anionic for surfactants with same chain lengths.
The solubilization of cationic than anionics of the same hydrocarbon chain length, may be due to looser packing of the surfactant molecules in the micelles16absorption is less sensitive to its environment as compared to fluorescence, thus, the absorption spectra are less affected on adding surfactants as compared to fluorescence spectra. However the results obtained here, support those with fluorescence studies. The molar extinction coefficient log ε values of the compound in different micellar media follow the same trend as their emission intensity. Enhancement in the fluorescence intensity of the compound on adding surfactant can be attributed to the increase in the quantum efficiency of fluorescence. Thus, increase in quantum yield suggests that the surfactants have solubilized the suspended molecule of Benzo (a) pyrene in solution.
Fig.3. Plot of % Nonionic Surfactants Vs Scattering Intensity
CONCLUSION:
After interpreting and comparing the results obtained for Benzo (a) pyrene, it is found that the theoretical calculated spectral parameters like molar extinction coefficient log ε , stokes’ shifts and quantum yield φFare in fair agreement with experiment results. Thus, an understanding of the process of solubilization is expected to helps understanding the interplay of the different favourable and unfavourable forces guiding micellization. The solubilization process finds extensive application in the industrial, pharmaceutical and biochemical and agro-chemical fields. This proves the validity of the work done.
ACKNOWLEDGEMENT:
The authors are grateful to the authorities of Jai Narayan Vyas University, Jodhpur, Rajasthan for the facilities.
CONFLICT OF INTEREST:
The authors declare no conflict of interest.
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Received on 22.04.2018 Modified on 26.04.2018
Accepted on 30.04.2018 © AJRC All right reserved
Asian J. Research Chem. 2018; 11(3):633-636.
DOI:10.5958/0974-4150.2018.00113.X