ABSTRACT Micellar solubilization is a powerful alternative for dissolving hydrophobic compounds in aqueous environment. Fluorescence and absorption spectroscopy are the two techniques used to monitor the micellar solubilization studies of p-amino benzoic acid (PABA). PABA is an aromatic compound with acidic functional group, is non essential nutrient, used as a sunscreen. Externally, it prevents sunburn and skin cancer from UV light. The emission intensity of PABA is significantly enhanced in nonionic and anionic micellar media and decreased in cationic micellar media of different surfactants. The solubilizing action of the surfactant has also been determined by theoretical calculated spectral parameters like empirical fluorescence coefficient, quantum yield, molar absorption coefficient and stokes&apos; shift value. The fluorescence as well as the theoretically calculated spectral data have been used to characterize the heteroenvironment of the micelles in terms of their polarity, probe solubilization site and critical micellar concentration (CMC). This article briefly discusses the importance of surfactants in biological system model as well as the use of micelles in pharmacy as an important tool that finds numerous applications

Rekha Soni

Seema Acharya

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Vol. 6 | No.1 | 24-28 | January-March | 2013 
ISSN: 0974-1496 | e-ISSN: 0976-0083 | CODEN: RJCABP 
http://www.rasayanjournal.com 
http://www.rasayanjournal.co.in 
 
STUDY OF p- AMINO BENZOIC ACID BY FLUORESCENCE                                                                            Seema Acharya and Rekha Soni 
INTERACTION OF p- AMINO BENZOIC ACID (PABA) WITH 
IONIC AND NONIONIC MICELLES BY FLUORESCENCE 
 
Seema Acharya and Rekha Soni* 
Department of Chemistry, Jai Narain Vyas University, Jodhpur (Raj.) India 
*E-mail:  rekhasoni1984@gmail.com 
 
ABSTRACT 
Micellar solubilization is a powerful alternative for dissolving hydrophobic compounds in aqueous environment. 
Fluorescence and absorption spectroscopy are the two techniques used to monitor the micellar solubilization studies 
of p-amino benzoic acid (PABA). PABA is an aromatic compound with acidic functional group, is non essential 
nutrient, used as a sunscreen. Externally, it prevents sunburn and skin cancer from UV light. The emission intensity 
of PABA is significantly enhanced in nonionic and anionic micellar media and decreased in cationic micellar media 
of different surfactants. The solubilizing action of the surfactant has also been determined by theoretical calculated 
spectral parameters like empirical fluorescence coefficient, quantum yield, molar absorption coefficient and stokes’ 
shift value. The fluorescence as well as the theoretically calculated spectral data have been used to characterize the 
heteroenvironment of the micelles in terms of their polarity, probe solubilization site and critical micellar 
concentration (CMC). This article briefly discusses the importance of surfactants in biological system model as well 
as the use of micelles in pharmacy as an important tool that finds numerous applications. 
Keywords: PABA, fluorescence, absorbance, micelles. 
© 2013 RASĀYAN. All rights reserved. 
 
INTRODUCTION 
By spectroscopic studies, it has been explained that different solubilized molecules are found in different 
regions of micelles1,2. Surfactants are known to play a vital role in many processes of interest in both 
fundamental and applied science. The formation of colloid sized clusters in solutions known as micelle, 
have particular significance in pharmacy because of their ability to increase the solubility of sparingly 
soluble substances in water
3
. The most striking feature of micelles is the ability to solubilize a variety of  
compounds in its different regions
4
. Nadine Arnand et al. studied the influence of pH, surfactant and 
synergic agent on the luminescent properties of terbium chelated with PABA and other benzoic acid 
derivatives in aqueous solution
5
. Milton studied the absorption spectra of the azo derivatives of PABA 
and also analyzed the effect of pH and salt added to it
6
. S.I. Akberova
 
studied PABA as an inducer of 
endogenous interferon and regulator and displays a virucidal, synergistic antiviral effect when combined 
with chemical drug and of a direct anticoagulant
7
. S Thiele-Bruhn et al. analyzed the PABA by soil 
absorption which is found in environment as an antibiotic
8
. Hanafi Tanojo et al. investigated the 
interdependence of the fluorescence intensity and pH of PABA solution in various acid-base mixtures9. 
M. Carlson and R.D. Thomson determined PABA in pharmaceuticals by HPLC
10
. Shaw et al. studied 
photoreactions of PABA in presence and absence of oxygen using light at 254nm and greater than 290 
nm
11
. ES Lianidou and PC Toannou explained the spectroscopic determination of PABA in biological 
fluids by use of Tb-sensitized luminescence
12
. J.H. Turnbull et al. studied the effect of β-cyclodextrin on 
the luminescence of PABA13. 
 
EXPERIMENTAL 
The fluorescence studies were made with Perkin-Elmer Fluorescence Spectrophotometer model 204A 
with a silica cell of 1 cm path length. All experiments were carried out at room temperature. Absorption 
spectra of PABA were taken on double beam specord UV-Vis spectrophotometer. 
 
Vol. 6 | No.1 | 24-28 | January-March | 2013 
 
STUDY OF p- AMINO BENZOIC ACID BY FLUORESCENCE                                                                            Seema Acharya and Rekha Soni 25 
The stock solution of analytically pure PABA was prepared in double distilled water keeping the final 
concentration of compound at 2 x 10
-5
 M and 1 x 10
-4
 M for fluorescence and absorption spectra 
respectively. All the surfactants used were either of Sigma (USA) or BDH (UK) products. 
 
The following surfactants were employed- 
(A) Nonionic surfactants 
   (i) Polyoxyethylene tert-octyl phenol (TX - 100) 
   (ii) Polyoxyethylene sorbitain monolaurate (Tween – 20) 
   (iii) Polyoxyethylene sorbitain monooleate (Tween - 80) 
 
(B) Anionic surfactants 
    (i) Dodecylbenzene sodium sulphonate (DBSS) 
    (ii) Dioctyl sodium sulphosuccinate (DSSS) 
    (iii) Sodium lauryl sulphate (SLS) 
 
(C) Cationic surfactants 
     (i) Cetylpyridinium chloride (CPC). 
     (ii) Cetytrimethyl ammonium bromide (CTAB) 
     (iii) Myristyltrimethyl ammonium bromide (MTAB) 
 
Table-1: Fluorescence intensity of p-amino benzoic acid (PABA) in presence and absence of surfactants. 
λex = 280nm                    P.M. Gain = 2 
                                       λem = 345 mn    Sensitivity Range = 1 
 
S.No. Nature of surfactant Range of conc. used 
(%) 
Fluorescence intensity 
in absence of 
surfactants 
Maximum 
fluorescence 
intensity 
1. 
2. 
3. 
4. 
5. 
6. 
7. 
8. 
9. 
TX-100 
Tween – 20 
Tween – 80 
DBSS 
DSSS 
SLS 
CPC 
CTAB 
MTAB 
0.03 
0.5 
0.5 
0.5 
0.5 
0.5 
0.5 
0.5 
0.5 
30 
30 
30 
30 
30 
30 
30 
30 
30 
Out of scale 
37 
38 
44 
40 
49 
30 
33 
36 
 
Table -2: Absorbance Maxima (λmax) , Molar Extinction Coefficient (log ε),Fluorescence Emission (λem) and 
Quantum yield ( fφ ) values of PABAat different concentrations of TX- 100 
 
The purity of the surfactants was checked by determining their CMC values with help of surface tension 
measurements, employing drop weight method. The values thus obtained coincided with the reported 
values. The absolute fluorescence quantum yield of the compound was calculated relative to anthracene 
S.N. % of 
TX-100 (w/v) 
λmax 
(nm) 
logε 
(dm
3
 mol
-1
 cm
-1
)) 
λem 
(nm) 
fφ  
1. 
2. 
3. 
4. 
5. 
6. 
7. 
0.000 
0.003 
0.005 
0.007 
0.01 
0.03 
0.05 
275 
275 
275 
270 
265 
265 
265 
4.7412 
4.7853 
4.7983 
4.8286 
4.8564 
4.9156 
4.9597 
345 
340 
335-340 
330-335 
305-310 
305-310 
305-310 
0.07109 
0.10091 
0.10091 
0.13531 
0.13740 
0.13740 
0.13740 
 
Vol. 6 | No.1 | 24-28 | January-March | 2013 
 
STUDY OF p- AMINO BENZOIC ACID BY FLUORESCENCE                                                                            Seema Acharya and Rekha Soni 26 
solution as standard. Fluorescence emission obtained is in the same range as that of the compound. 
Approximate corrections were made to compensate for the different absorptions of the compounds and 
the standard. Each time the total intensity of fluorescence emission was measured for the standard and the 
sample from the area of the fluorescence spectrum recorded over the whole range of emission, under 
identical conditions. 
 
RESULTS AND DISCUSSION 
p-Amino benzoic acid (PABA) in its aqueous solution showed a maximum emission wavelength at 345 
nm. The maximum excitation peak intensity appeared at 280 nm. 
              
 
 
 
Fig.-1: Influence of addition of TX-100 on fluorescence intensity of 2x10
-5
 M PABA solution 
 
 
 
 
 
Fig.-2: Influence of addition of SLS on fluorescence intensity of 2x10
-5
 M PABA solution 
 
 
Vol. 6 | No.1 | 24-28 | January-March | 2013 
 
STUDY OF p- AMINO BENZOIC ACID BY FLUORESCENCE                                                                            Seema Acharya and Rekha Soni 27 
All the nonionic surfactants caused an enhancement in peak value of fluorescence intensity. There is a 
blue shift of 30-35 nm in case of TX-100 and 2-3 nm in case of Tween-20 and Tween -80. Influence of 
addition of TX-100 on fluorescence intensity of 2 x 10
-5
 M PABA solution is shown in Fig. 1. The 
fluorescence intensity of PABA increased on adding anionic surfactants to it. Out of all, the three anionics 
employed only higher concentration of SLS and DBSS showed 2-3 nm red shift in peak position. 
Influence of addition of SLS on fluorescence intensity of 2 x 10-
5 
M, PABA solution is shown in Fig.2. 
Cationic surfactants caused no shift in peak position. CPC sharply decreased emission intensity whereas 
CTAB and MTAB at lower concentration slightly increased emission intensity and at their higher 
concentration it decreased. The enhancement in emission intensity was found to be minimum in cationic 
micellar media. The minimum and maximum fluorescence intensity in absence and presence of all three 
classes of surfactants is given Table-1. 
The absorption spectra gave a peak at 275 nm. The absorbance increased on increasing the concentration 
of nonionic and anionic surfactants. For nonionic surfactants absorbance increased in TX-100 with a blue 
shift of 5-10 nm. Cationics showed parallelism with the fluorescence intensity. The calculated 
fluorescence quantum yield data of surfactant added PABA solution show parallelism with change in 
fluorescence intensity of the compound. With nonionic surfactants, the value of fluorescence quantum 
yield increased continuously. Similarly anionic surfactants also increased the value of fluorescence 
quantum yield ( fφ ) of PABA. The Molar Extinction Coefficient ( log ε ) calculation data also show 
gradual increase with increase in concentration enhanced, was obtained for TX- 100, which has been 
supported by absorbance, log ε  and fφ  values. The changes in the theoretical spectral data are shown in 
Table 2. 
The results indicate that nonionic surfactants had a stronger enhancement on fluorescence and absorption 
behaviour of PABA. The maximum fluorescence enhancement was obtained for TX- 100 which has been 
supported by absorbance, log ε  and fφ  Values.  The results so obtained can be explained in a better 
manner by considering oblate  ellipsoidal model for TX-100. The octaphenyl group and the 
polyoxyethylene group of TX-100 can separate each layer packs well. This model predicts the 
hydrophobic and less fluid interior of the TX-100 micelle. This fact has also been supported by Kano et 
al14. Both the anionic and cationic surfactants increased the emission intensity slowly. The ionic micelles 
have higher polarity which may be asserted to the loose fluctuating and disordered structure of these 
micelles. Here in ionic micellar media, the hydrophilic solubilizate must leave its aggregate and exclude 
water molecule inside the ionic micelle. These processes cause slow solubilization. The blue shift 
observed may be attributed to the protic nature solvent, as hydrogen-donor solvent-interaction takes place 
between solubilizate and solvent. This may also be because of the difference in solvation energy of the 
solute in the ground and excited state. The shift here may be explained as resulting from greater 
contribution of the mesomeric forms of lower energy to the excited state. The absorption spectra are less 
affected on adding surfactants as absorption is less sensitive to its environment as compared to 
fluorescence. Sufficiently large value of log ε  is assigned to π-π*   transitions. The enhancement of 
fluorescence of PABA in TX–100 can be attributed to the increase in quantum efficiency of fluorescence. 
Furthermore, the quantum yield is higher in nonpolar medium because of the lesser effect of the other 
deactivation processes which compete with fluorescence.15 Thus the increased fφ  values showed that the 
micelles have been possibly adsorbed on to the dispersed microcrystal of PABA. The molecules of PABA 
have been subsequently solubilized by incorporation into the interior nonpolar core of the micelles. The 
presence of a nucleophillic pyridine ring in CPC causes a continuous decreasing effect in emission 
intensity and behaves differently from other cationics which have linear alkyl and aryl groups. 
As PABA is a pharmaceutically important, the present kind of study of micellar solubilization of PABA 
molecules is of great important. It signifies faster transport of PABA molecules requisite to the site of 
action by the processes of micellization followed by solubilization, the process which otherwise would 
have been a slow one. 
 
Vol. 6 | No.1 | 24-28 | January-March | 2013 
 
STUDY OF p- AMINO BENZOIC ACID BY FLUORESCENCE                                                                            Seema Acharya and Rekha Soni 28 
Thus, one can generalize the present physical understanding to the study the phenomenon of micellar 
solubilization. It has pharmacological application as the solubilizate PABA is analytically and 
pharmacologically important for medical research. 
 
ACKNOWLEDGEMENTS 
The authors are thankful to Head of the Department of Chemistry, J.N. Vyas University, Jodhpur for 
providing necessary research facilities. 
 
REFERENCES 
1. J.H. Fendler and L.K. Patterson, J. Phys. Chem., 75, 3907 (1971). 
2. B. Svens and B. Rosenholm, J. Colloid, Interfac. Sci., 44, 495 (1975). 
3. S. Mall, G. Buckton and D.A. Rawlins, J. Pharm. Sci, 85(1), 75 (1996). 
4. K. Shinoda, T. Nalkagava, B. Tanarnushi and T. Isemura, Colloidal Surfactant,Academic Press, New 
York. 
5. N. Arnand and J. Geoges, Laboratoire des Sciences Analytiques, The Royal Soc. Chem Anal., 125, 
1487, (2000). 
6. M. Tabachnick and H. Sobotka The J. Biol. Chem., 237, 7 (1959). 
7. S.I. Akberova,, Biol. Bull., 29(4), 2002. 
8. S. Thiele-Bruhn, T. Seibicke, H.R. Schutten and, Leinweber J. Environ. Qual . 33, 1331 (2004). 
9. H. Tanoja, H. E. Junginger and H. E. Bodde, J. Appl. Microbiol., 78, 209 (2008). 
10. M. Carlson, R.D. Thompson, J Liquid Chromato. and Related Techn., 10, 997 (1987). 
11. A.A. Shaw, L.A. Wainschel, M.D. Shetler Photochem. Photobiol., 55(5), 647 (1992). 
12. E.S. Lianidou and Ioannou, Clinical Chem., 42, 1659 (1996) 
13. J.H. Turnbull and R.G. Walker, Il Nuovo Climento B. 63, 441 (1981). 
14. K. Kano, H. Goto, T. Ogawa., Chem. Lett., 653 (1981). 
15. R.J. Robinson and E.A. Dennis, Acc. Chem. Res., 16, 257 (1983).  
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INTERACTION OF p-AMINO BENZOIC ACID (PABA) WITH IONIC AND NONIONIC MICELLES BY FLUORESCENCE

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INTERACTION OF p-AMINO BENZOIC ACID (PABA) WITH IONIC AND NONIONIC MICELLES BY FLUORESCENCE

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