Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 152 (2016) 1–7

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Internal charge transfer based ratiometric interaction of anionic surfactant with calf thymus DNA bound cationic surfactant: Study I Abhijit Mukherjee a, Tandrima Chaudhuri a,⇑, Satya Priya Moulik b, Manas Banerjee c a

Department of Chemistry, Dr. Bhupendranath Dutta Smriti Mahavidyalaya, Burdwan 713407, India Centre for Surface Science, Department of Chemistry, Jadavpur University, Kolkata 700 032, India c Department of Chemistry, University of Burdwan, Burdwan 713104, WB, India b

h i g h l i g h t s

g r a p h i c a l a b s t r a c t

 Cationic surfactant CTAB binds with

Compaction and decompaction of DNA in presence of cationic and anionic surfactants, respectively. Decompaction produces N-DNA and catanionic amphiphile (CTA+ SD). N-DNA: Normal DNA; C-DNA: Complexed DNA.

DNA electrostatically.  CTAB–DNA forms a stable ground as well as excited state equilibrium.  Anionic surfactant SDS interact with cationic CTAB but not with DNA.  ICT based ratiometric interaction of SDS with DNA bound CTAB.

N-DNA

a r t i c l e

i n f o

Article history: Received 2 May 2015 Received in revised form 3 July 2015 Accepted 8 July 2015 Available online 9 July 2015 Keywords: DNA–CTAB isosbestic Isoemissives SDS–(DNA bound CTAB) interaction Dynamic quenching contribution CV

C-DNA

a b s t r a c t Cetyl trimethyl ammonium bromide (CTAB) binds calf thymus (ct-) DNA like anionic biopolymers electrostatically and established equilibrium both in the ground as well as in excited state in aqueous medium at pH 7. Anionic sodium dodecyl sulfate (SDS) does not show even hydrophobic interaction with ct-DNA at low concentration. On contrary, SDS can establish well defined equilibrium with DNA bound CTAB in ground state where the same CTAB–DNA isosbestic point reappears. First report of internal charge transfer (ICT) based binding of CTAB with ct-DNA as well as ICT based interaction of anionic SDS with DNA bound CTAB that shows dynamic quenching contribution also. The reappearance of anodic peak and slight increase in cathodic peak current with increasing concentration (at lower range) of anionic SDS, possibly reflect the release of CTAB from DNA bound CTAB by SDS. Ó 2015 Elsevier B.V. All rights reserved.

1. Introduction DNA, an anionic polymer can binds or interacts cationic lipids/surfactants in aqueous medium essentially by electrostatic ⇑ Corresponding author. E-mail address: [email protected] (T. Chaudhuri). http://dx.doi.org/10.1016/j.saa.2015.07.049 1386-1425/Ó 2015 Elsevier B.V. All rights reserved.

C-DNA

interaction [1,2]; hydrophobic or non-polar interaction has secondary contribution in the process depending on the length of the non-polar tail [3,4]. The elongated DNA helix as a result condenses and may end up into compact configuration, even to globular form [2–5]. The complexed product has potential for introduction into living cells [6–12]. The process is called transfection. Thus inconvenient transfer of the elongated gene into the cell

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could be achieved conveniently by condensation [13–17], a prospective process in gene therapy in the discipline of biotechnology. But the question remains regarding the removal of bound cationic lipid/surfactants from complexed/compact DNA. Using the concept of normal electrostatic interaction between a cationic and an anionic surfactant, the DNA bound cationic surfactant can be released from DNA like biopolymer. An attempt was taken though possibility of hydrophobic interaction between DNA and anionic surfactant also prevails [18]. Number of model studies with cetyl trimethyl ammonium bromide (CTAB) and other cationic surfactants and different types of DNA, employing dynamic light scattering (DLS), fluorescence, calorimetric, electrometric and viscometric techniques have been reported [4,19]. Even the role of difference in the tails as well as the head groups of cationic surfactants has been studied vigorously, so far [20], no ICT based ratiometric binding of any cationic surfactant with any DNA is reported till date. Again to the best of our knowledge no work is reported regarding the interaction of anionic surfactant with compact DNA bound cationic surfactant. Thus, the studies to release CTAB from DNA bound CTAB as well as for a better understanding of this important interaction phenomenon, interaction between cationic surfactant CTAB with calf thymus (ct-) DNA and of anionic surfactant SDS with DNA bound CTAB have been considered in this study. We have examined the interaction behavior of cetyl trimethyl ammonium bromide with ct-DNA as well as of sodium dodecyl sulfate with DNA bound CTAB in aqueous solution using absorption and fluorescence spectroscopy, and cyclic voltammetry. The results have been analyzed in the light of general as well as specific behavior of the surfactants. This is the first attempt of interaction of cetyl trimethyl ammonium bromide (CTAB) the cationic surfactant that was complexed with calf thymus DNA, using an anionic surfactant sodium dodecyl sulfate in aqueous medium Scheme 1.

2. Experimental 2.1. Materials The surfactants used cetyl trimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) was purchased from Sigma–Aldrich, USA. Calf thymus (ct-) DNA (2.0 nm diam. and average mol. wt. of the order of 107) was a product of Bangalore Gene, India. Tris HCl buffer of pH 7 in doubly distilled water with 10 mM NaCl was used in all preparations. The concentration of ct-DNA was determined in terms of phosphate group taking absorbance measurements at 260 nm and using molar extinction

N-DNA

coefficient of 6600 L mol1 cm1 at 30 °C. Entire experiments are done at room temperature (30 °C). 2.2. Methods and instruments used 2.2.1. Spectroscopic measurements Absorption (UV–vis) spectral measurements were performed on a Shimadzu UV 1800 spectrophotometer fitted with an electronic temperature controller unit (TCC-240A). The steady state fluorescence emission and excitation spectra were recorded with a Hitachi F-4500 spectro-fluorometer equipped with a temperature controlled cell holder. Temperature was controlled within ±0.1 K by circulating water from a constant temperature bath (Heto Holten, Denmark). For lifetime measurements, the samples were excited at 280 nm using a picosecond diode laser (IBH-NanoLED source N-280). The emission was collected at magic angle polarization using a Hamamatsu MCP Photomultiplier (Model R-3809U-50). The time-correlated single photon counting (TCSPC) set up consist of an Ortec 9327 pico-timing amplifier. The data was collected with a PCI-6602 interface card as a multi-channel analyzer. The typical Full Width at Half Maximum (FWHM) of the system response was about 820 ps. The variation in the fluorescence intensity with time was fitted with a triexponential function of the following form.

FðtÞ ¼

3 X ai exp ðt=si Þ

ð1Þ

i¼1

where ai and si are the amplitude and time constant, respectively, for the ith decay component. The concentration of pyrene was always kept constant at 4  107 mol L1. Both excitation and emission band slits were fixed at 5 nm for steady state emission. The excitation wavelength was selected at 260 nm for steady state emission study. Concentrations of surfactants were varied from 105 to 106 M for a given DNA concentration. 2.2.2. Cyclic voltammetry Electrochemical measurements were carried out with a CHI 600E electrochemical analyzer (USA made) in a conventional three-electrode system. The working and counter electrodes were Pt wire and Ag/AgCl (aq) was used as the reference electrode, respectively. Cyclic voltammetry experiment was carried out in 5 mM K3Fe(CN)6 + 0.1 M KCl or 50 mM tris HCl buffer solution (pH 7.0) containing 10 lM ct DNA. 20 mL, 105 M DNA solution was titrated with 104 M CTAB stock solution. A CTAB (10 lM)– DNA (10 lM) mixture was again titrated with 102 M SDS stock

C-DNA

C-DNA

Scheme 1. Schematic presentation of compaction and decompaction of DNA in presence of cationic and anionic surfactants, respectively. Decompaction produces N-DNA and catanionic amphiphile (CTA+ SD). N-DNA: Normal DNA; C-DNA: Complexed DNA.

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solution. Each CV measurement was taken after attaining equilibrium with electrodes in each case. 3. Results and discussions 3.1. Photophysical study The association or binding of the cationic surfactant CTAB with ct-DNA in tris HCl buffer of pH 7 was monitored by visible absorption spectroscopy. A fixed concentration DNA solution was titrated

with stock solution of CTAB. Along with the decrease in absorbance of DNA at 260 nm, absorption maxima of CTAB (at 202 nm) increases monotonously on titrating with CTAB (shown in Fig. 1a), giving rise to a set of isosbestic at the juncture (215 nm). Thus this ground state isosbestic formation between CTAB and calf thymus DNA clearly supports the binding equilibrium for formation of CTAB bound DNA in solution. This point clearly to the existence of equilibrium between two forms, viz., the solvated DNA and the CTAB bound DNA. At a very high concentration of CTAB the complexed surfactant bound form of the DNA exists almost

(a)

(b)

(c)

(d)

Fig. 1. Ground state titration of (a) DNA (50 lM) by CTAB in tris Hcl buffer at pH = 7. Concentration of CTAB: 4.2  105, 8.18  105, 1.17  104, 1.5  104, 1.8  104, 2.07  104, 2.33  104, 2.57  104, 2.79  104, 3  104, 3.19  104, 3.375  104, 3.54  104, 3.7  104, 3.85  104, 4  104, 4.13  104, 4.26  104, 4.38  104 M; titration of (b) DNA (50 lM) bound CTAB (45 lM) by SDS; concentration of SDS: 0.00, 4.2  105, 8.18  105, 1.17  104, 1.5  104, 1.8  104, 2.07  104, 2.33  104, 2.57  104, 2.79  104, 3  104, 3.19  104, 3.375  104, 3.54  104, 3.7  104, 3.85  104, 4  104, 4.13  104, 4.26  104, 4.38  104 M. Titration of (c) DNA (5  105 M) by SDS and of (d) CTAB (4.5  104 M) by SDS of same concentration as that of (b).

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Table 1 Ground and excited state photophysical parameters and formation constants (M1) data of the two complexes at 293 K. Isosbestic/iso-emissive points at (nm) Ground state

Excited state

(KD + KS)

KD = kqs0

KS

CTAB–DNA SDS–(CTAB + DNA) CTAB–SDS

215 215, 248, 279 209

359, 454 360a –

2.93  104 3.06  104 –

– 3.13  103 –

2.93  104 2.75  104 –

Not well defined.

3.1.1. Steady state emission study Till date excited state surfactant–DNA interaction was not so well established as both the starting materials are non-fluorescent. To study the excited state interaction a pyrene solution of fixed concentration (0.4 lM) was used as fluorescent dye and concentrations of surfactants were varied from 105 to 106 M for a given fixed DNA concentration (50 lM). Before going to observe the interaction of any pyrene mixture, simple excited state interaction of pyrene with ct-DNA (Fig. S1A) and pyrene with CTAB (Fig. S2A) were checked separately. Both DNA and CTAB exhibited huge quenching with Stern–Volmer constant (KSV) 5.44  104 M1 and 4.78  104 M1 respectively (Figs. S1B and S2B). Thus the ct-DNA interact pyrene with higher binding constant in excited state than CTAB. It is well known that there are intercalations of pyrene with DNA bases at the grooves [21,22]. Maximum quenching of fluorescence intensity of 0.4 lM pyrene was observed with 30 lM DNA and 45 lM CTAB separately. The fluorescence maxima of pyrene (0.4 lM) in DNA(50 lM) where free pyrene would no more available, suffered a systematic quenching with the increasing concentration of CTAB in the solution, as shown in Fig. 2a. Not only fluorescence intensity of pyrene–DNA mixture was quenched but also gave rise to set of two iso-emissive points with cationic surfactant CTAB (Table 1). This indicated the equilibrium of CTAB binds DNA in solution also exists in excited state and that was as stable as that of ground state. But when the DNA bound CTAB solution with same fixed pyrene

1000

(a)

800

Fluorescence intensity

exclusively in the solution and the absorption band is due to this species only. The interaction with this DNA bound CTAB, the CTAB–DNA mixture of fixed concentration was titrated with a stock solution of anionic surfactant SDS. This give rise to three sets of isosbestic points at 215 nm, 248 nm and 279.5 nm (Fig. 1b and Table 1). Now to understand this new equilibrium reaction between SDS and CTAB bound DNA, two blank titrations of (i) DNA with SDS and of (ii) free CTAB with SDS were done separately. When a fixed concentration DNA is titrated with SDS, no isosbestic is formed (Fig. 1c). But when a fixed concentration free CTAB solution is titrated with SDS, a new isosbestic at 209 nm is appeared (Fig. 1d). Thus Fig. 1b demonstrated entirely a different sort of interaction of SDS with the CTAB bound DNA solution. This also indicated that no free CTAB is available (as no isosbestic is obtained 209 nm) in case of the CTAB–DNA mixture titration. Again SDS being an anionic surfactant also no isosbestic is formed with the anionic biopolymer DNA, so the isosbestic points appeared (at 248 nm and 279.8 nm) in Fig. 1b surely indicated the interaction of SDS with CTAB bound DNA. Now the isosbestic at 215 nm (in Fig. 1b) that was appeared during CTAB–DNA titration in Fig. 1a, was reappeared, might be indicative of de-complexation of bound CTAB from DNA. Table 1 indicates multiple isosbestic points in different region of the spectra on interaction of the surfactants with calf thymus DNA in tris HCl buffer of pH 7. Thus as CTAB form stable equilibrium with the DNA to bind it, similarly anionic surfactant SDS also form stable equilibrium with free cationic surfactant CTAB as well as with DNA bound CTAB also.

600

400

200

0 325

350

375

400

425

450

475

500

Wavelength (nm)

1000

(b)

800

Fluorescence intensity

a

Binding constant (M1)

System

600

400

200

0 325

350

375

400

425

450

475

500

Wavelength (nm) Fig. 2. Fluorescence titration of (a) calf thymus DNA (50 lM) in presence of pyrene (0.4 lM) by CTAB; concentration of CTAB (M): 0.00, 4.76  106, 9.09  106, 1.3  105, 1.66  105, 2  105, 2.3  105, 2.5  105, 2.8  105, 3.1  105, 3.3  105, 3.54  105, 3.75  105, 3.93  105; titration of (b) DNA (50 lM) bound CTAB (45 lM) in presence of pyrene (0.4 lM) by SDS; concentration of SDS (M): 0.00, 4.76  106, 9.09  106, 1.3  105, 1.66  105, 2  105, 2.3  105, 2.5  105, 2.8  105, 3.1  105, 3.3  105, 3.54  105, 3.75  105, 3.93  105 M. kex = 260 nm.

concentration (0.4 lM) was titrated with anionic surfactant SDS, no well defined iso-emissives were formed as that of ground state (Fig. 2b). Only quenching of fluorescence took place. We have to mention here that this excited state equilibrium did not at all establish with SDS in the excited state (Table 1). 3.1.2. Time-resolved emission study The decay of the excited singlet state, measured in tris HCl buffer of pH 7 is found to follow tri-exponential kinetics (cf. Eq. (1)). The fluorescence intensity for a given k, is given by

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A. Mukherjee et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 152 (2016) 1–7 Table 2 Lifetimes of pyrene (0.4 lM) solution in DNA (50 lM) bound CTAB (45 lM) with increasing concentration of SDS. SDS (mM)

s1

s2 (ns)

0 0.02 0.04 0.06 0.08 0.1

9.59 8.64 7.79 7.84 7.97 7.89

(ns)

s3

a1

a2

a3

hsi

v2

12.00 12.79 13.92 14.86 16.46 17.43

82.80 79.15 74.06 71.65 68.56 66.45

5.20 8.06 12.02 13.49 14.98 16.12

120.64 117.05 105.35 103.39 98.53 92.57

1.08 1.10 1.20 1.19 1.18 1.20

(ns) 144.23 146.41 140.71 142.58 141.70 137.13

1.27 0.74 0.45 0.50 0.43 0.46

(a)

[SDS] (mM) 0 0.02 0.04 0.06 0.08 0.1

log(counts)

1000 100 IRF

0

1.35

(b)

200

400 Time (ns)

600

(DNA bound CTAB) with SDS DNA with CTAB

1.30

F 0 =F ¼ 1 þ ðK D þ K S þ K S K D ½QÞ½Q

ð5Þ

in Eq. (5), F0 and F are the fluorescence intensities of fluorophore in the absence and presence of quencher (Q) respectively. KD is the dynamic Stern–Volmer constant, which equals to the product of the fluorescence lifetime (s0) and the dynamic quenching rate constant (kq). KS is the static binding constant between the fluorophore and the quencher. If [Q] approaches zero, the Eq. (5) changes to Eq. (6).

F 0 =F ¼ 1 þ ðK D þ K S Þ½Q 

10 1

3.1.3. Determination of association constant As CTAB and SDS form stable ground state complexes with free DNA and with DNA bound CTAB respectively, so the observed fluorescence quenching would have mixed contribution in nature. The Stern–Volmer relationship (Eq. (5)) for a system with both dynamic and static components of quenching has been derived earlier [23].

1.25

τ0 = 120.64 ns

1.20

kq= 2.59 x10

1.15

10

-1 -1

M s

τ0/τ

1.10 1.05 1.00

ð6Þ

This means that the limiting slope of the Stern–Volmer plot is (KD + KS). In the present study, the Stern–Volmer relationships were studied in the fluorescence quenching of pyrene in DNA by CTAB and of pyrene in DNA–CTAB mixture by SDS. Both the two plots exhibited good linear correlations between F0/F and [Q] at low quencher concentration region. Therefore, from the slopes of the correlations at low quencher concentration region, the value of (KD + KS) for each compound could be easily determined. These results were summarized in Table 1. Table 1 show both the KD and KS values. The excited state static binding constant (KS) values follow the order KCTAB–DNA  KSDS–(CTAB–DNA). This order signified that CTAB binds DNA slightly more strongly than SDS binds (DNA bound CTAB). Fig. 4 shows the Stern–Volmer plot of both the systems. Thus it might be possible for SDS to bind the CTAB from DNA bound adduct still with high efficiency.

0.95

3.2. Cyclic voltammetry

0.90 0.85 0.80 10.0µ 20.0µ 30.0µ 40.0µ 50.0µ 60.0µ 70.0µ 80.0µ 90.0µ 100.0µ 110.0µ

[Surfactant] M Fig. 3. (a) Time resolved fluorescence decay profile of pyrene (0.4 lM) in DNA– CTAB (50 lM) mixture with increasing concentration of SDS. (b) Stern–Volmer plots of lifetime components with surfactant concentration.

Fk ¼

Z

Surfactant compounds are not so electro-active, Fe(CN)63/4 was used as an redox probe [24] to investigate the interactions of such surfactant molecules with ct-DNA. Cyclic voltammograms of changes of Fe(CN)63/4 on different concentrations of cationic surfactant CTAB at fixed concentration of ct-DNA were shown in (Fig. 5). As is evidence from Fig. 5a, the reduction peak currents

1

F k ðtÞdt

2.1

ð2Þ

0

DNA bound CTAB with SDS DNA with CTAB

2.0

Using Eq. (1) one can write

where ai and si are the amplitude and the time constant, respectively for the ith decay component. The percentage of contribution of individual decay components are calculated as following,

ai si Ai ¼ 100 X ai si

1.8

ð3Þ

ð4Þ

1.7 1.6

F0/F

F k ¼ a1 s1 þ a2 s2 þ a3 s3

1.9

1.5 1.4 1.3

i

Values of lifetimes (s) of pyrene in ct-DNA–CTAB mixture with increasing concentration of SDS at pH 7 were listed in Table 2. Fig. 3a shows the decay profile. It appears that the s-values decrease monotonously with increasing concentration of SDS showing a mixed quenching Fig. 3b. However the Stern–Volmer plot of lifetime of pyrene in DNA suffers no remarkable change with regard to the increasing concentration of CTAB demonstrate a purely static quenching in Fig. 3b.

1.2 1.1 1.0 0.0

5.0µ

10.0µ

15.0µ

20.0µ

25.0µ

30.0µ

[Surfactant] M Fig. 4. Stern–Volmer plots of DNA–CTAB and SDS–(DNA bound CTAB) interacting systems.

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A. Mukherjee et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 152 (2016) 1–7 9.90 μM CTAB 9.00 μM CTAB 8.25 μM CTAB 7.40 μM CTAB 6.54 μM CTAB 5.66 μM CTAB 4.76 μM CTAB 10 μM DNA

12.0µ

(a)

10.0µ 8.0µ 6.0µ

Current (A)

4.0µ 2.0µ 0.0 -2.0µ -4.0µ -6.0µ -8.0µ -10.0µ 0.0

0.2

0.4

0.6

0.8

1.0

1.2

Potential (V)

(b)

12.0µ

612.0 μM SDS 535.0 μM SDS 376.6 μM SDS 128.0 μM SDS 43.3 μM SDS (10 μM DNA + 10 μM CTAB) mixture

10.0µ 8.0µ 6.0µ

Current (A)

4.0µ 2.0µ 0.0 -2.0µ -4.0µ -6.0µ -8.0µ -10.0µ 0.0

0.2

0.4

0.6

0.8

1.0

1.2

Potential (V) Fig. 5. Cyclic voltammograms of (a) calf thymus DNA (10 lM) at different concentration of CTAB. Concentration of CTAB (M): 0.00, 4.76  106, 5.66  106, 6.54  106, 7.4  106, 8.25  106, 9  106 and 9.9  106; (b) CTAB (10 lM) bound DNA (10 lM), at different concentration of SDS. Concentration of SDS (M): 0.00, 4.33  105, 1.28  104, 3.765  104, 5.35  104 and 6.12  104.

Table 3 Electrochemical potentials of different free and mixture systems in aqueous medium. System

Oxidation potential (volt)

Reduction potential (volt)

ct-DNA (1  105 M) CTAB (1  104 M) SDS (1  102 M)

0.700 0.629 0.634

0.522 0.538 0.554

System

Oxidation potential (volt)

Reduction potential (volt)

(CTAB) M added to 10 lM DNA 4.76  106 5.66  106 6.54  106 7.40  106 8.25  106 9.00  106 9.90  106 1.07  105 1.15  105 1.23  105 1.30  105

0.698 0.726 0.747 0.749 0.758 – – – – – –

System

Reduction potential (volt)

Oxidation potential (volt)

(SDS) M added to (10 lM CTAB + 10 lM DNA) 0.493 0.511 0.498 0.503 0.482 0.479 0.471 0.466 0.460 0.470 0.470

(ipc) slightly increases with rapid decrease in oxidation peak current (ipa) accompanied an increase in the concentrations from 4.76  106 M to 1.3  105 M of CTAB. Ultimately at higher concentration of CTAB (1.3  105 M), the reversibility of voltammogram was lost with the decrease in anodic peak current. With

4.33  105 1.28  104 2.13  104 2.95  104 3.77  104 4.56  104 5.34  104 6.12  104

– 0.671 0.684 0.673 0.687 0.663 0.668 0.668

– – – – –

increasing concentration, cationic surfactant CTAB mainly neutralizes the net negative charges of DNA, thus decreases the ipa and simultaneously ipc increases slightly. From the phenomena above, it can be deduced that CTAB binds to DNA is mainly related to electrostatic interaction.

A. Mukherjee et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 152 (2016) 1–7

Fig. 5b, depicted the cyclic voltammograms of changes of resultant DNA bound CTAB on different concentration of anionic surfactant SDS. It was observed that with addition of anionic SDS at very low concentration, cathodic peak current suddenly diminished. As no reduction was taking place in such electron rich system. But with increasing concentration of SDS, anodic peak reappears with higher peak current that was vanished when ct-DNA bound with CTAB (in Fig. 5a). However at higher concentration of SDS (up to 4.56  104 M) cathodic peak current also increases slightly. But at further higher concentration of SDS (6.12  104 M) cathodic peak current decreases (shown in Fig. 5b). Liu et at. [18] show that this decrease in peak currents due to hydrophobic interaction between anionic surfactant and ds-DNA. The reappearance of anodic peak and slight increase in cathodic peak current with increasing concentration (at lower range) of anionic SDS, possibly reflect the release of CTAB from DNA bound CTAB. Clearly we can say that with the addition of anionic SDS to the compact neutralized DNA, initially at low concentration (43.3 lM SDS) ve charge density increases so cathodic peak current suddenly drops. This was what we have shown in Fig. 5b. But with further increase in SDS concentration, anionic SDS interacts with cationic CTAB to unbind it from DNA. As a result cationic CTAB released in solvent to interact with anionic SDS. Thus slight increase in cathodic peak current was observed along with rapid increase in anodic peak current shown in Fig. 5b at (128–612 lM) SDS. This ultimately indicates the release of DNA bound CTAB by SDS. Peak potentials of pure ct-DNA, pure CTAB, pure SDS along with their respective mixtures of variable concentrations are shown in Table 3. 4. Conclusion Cationic surfactant CTAB binds ct-DNA like anionic biopolymers electrostatically and established equilibrium both in the ground as well as in excited state in aqueous medium at pH 7. At low concentration anionic surfactant SDS does not show any hydrophobic interaction with ct-DNA. Though anionic SDS can establish another well defined equilibrium with CTAB bound DNA in ground state where the same CTAB–DNA isosbestic point reappears. Blank titration of SDS–CTAB and SDS–DNA justified the reappearance of anodic peak and slight increase in cathodic peak current with increasing concentration (at lower range) of anionic SDS, possibly reflect the release of CTAB from DNA bound CTAB by SDS both spectroscopically and electrochemically.

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Acknowledgments Abhijit Mukherjee acknowledges Mr. R. Mondal, IISER, Bhopal. Tandrima Chaudhuri and Abhijit Mukherjee thank the Department of Science and Technology, (DST), India for financial assistance through a Fast Track Project Grant, Ref. No. SB/FT/CS-121/2012, dated 22.11.2013. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.saa.2015.07.049. References [1] K. Shirahama, K. Takashima, N. Takisawa, Bull. Chem. Soc. Jpn. 60 (1987) 43. [2] K. Hayakawa, P. Santerre, J.C.T. Kwak, Biophys. Chem. 17 (1983) 175. [3] S.M. Mel’nikov, V.G. Sergeyev, K. Yoshikawa, J. Am. Chem. Soc. 117 (1995) 9951. [4] D. Matulis, I. Rouzina, V.A. Bloomfield, J. Am. Chem. Soc. 124 (2002) 7331. [5] H. Gershon, R. Ghirlando, S.B. Guttman, A. Minsky, Biochemistry 32 (1993) 7143. [6] Y.S. Mel’nikova, S.M. Mel’nikov, J.-E. Löfroth, Biophys. Chem. 81 (1999) 125. [7] D.L. Reimer, Y. Zhang, S. Kong, J.J. Wheeler, R.W. Graham, M.B. Bally, Biochemistry 34 (1995) 12877. [8] F.M.P. Wong, D.L. Remier, M.B. Bally, Biochemistry 35 (1996) 5756. [9] P.L. Felgner, Adv. Drug. Delivery Res. 5 (1990) 163. [10] X. Zhou, L. Huang, Biochim. Biophys. Acta 1189 (1994) 195. [11] H. Farhood, N. Serbina, L. Huang, Biochim. Biophys. Acta 1235 (1995) 289. [12] Y. Xu, F.C. Szoka, Biochemistry 35 (1996) 5616. [13] R. Banerjee, P.K. Das, G.V. Srilakshmi, A. Chaudhury, N.M. Rao, J. Med. Chem. 42 (1999) 4292. [14] P.L. Felgner, T.R. Gadek, M. Holm, R. Roman, H.W. Chan, M. Wenz, J.P. Northorp, G.M. Ringold, M. Danielsen, Proc. Natl. Acad. Sci. U.S.A. 84 (1987) 7413. [15] R.S. Singh, K. Mukherjee, R. Banerjee, A. Chaudhuri, S.K. Hait, S.P. Moulik, Y. Ramdas, A. Vijayalakshmi, N.M. Rao, Chem. Eur. J. 8 (2002) 900. [16] G. Caracciolo, D. Pozzi, R. Caminiti, A.C. Castellano, Eur. Phys. J. E. 10 (2013) 331. [17] V. Cherezov, H. Qiu, V. Pector, M. Vandenbranden, J.-M. Ruysschaert, M. Caffrey, Biophys. J. 82 (2002) 3105. [18] Q. Liu, J. Li, W. Tao, Y. Zhu, S. Yao, Bioelectrochemistry 70 (2007) 301. [19] A. Chatterjee, S.P. Moulik, Indian J. Biochem. Biophys. 42 (2005) 205. [20] R.S. Dias, L.M. Magno, A.J.M. Valente, D. Das, P.K. Das, S. Maiti, M.G. Miguel, B. Lindman, J. Phys. Chem. B 112 (2008) 14446. [21] K. Jumbri, M.B. Abdul Rahman, E. Abdulmalek, H. Ahmad, N.M. Micaelo, Phys. Chem. Chem. Phys. 16 (2014) 14036. [22] H. Wang, J.i. Wang, S. Zhang, Phys. Chem. Chem. Phys. 13 (2011) 3906. [23] J.R. Lakowicz, Principles of Fluorescence Spectroscopy, third ed., Springer, 2006. [24] K.J. Zhang, W.Y. Liu, Int. J. Electrochem. Sci. 6 (2011) 1669.

Internal charge transfer based ratiometric interaction of anionic surfactant with calf thymus DNA bound cationic surfactant: Study I.

Cetyl trimethyl ammonium bromide (CTAB) binds calf thymus (ct-) DNA like anionic biopolymers electrostatically and established equilibrium both in the...
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