Insights into the interactions of Sulfamethoxazole with organized

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Interface Components: Nanoparticles, Colloids, Emulsions, Surfactants, Proteins, Polymers

Insights into the interactions of Sulfamethoxazole with organized assemblies of ionic and non-ionic surfactants Aparna D Saraf, Shweta Sharma, and Shilpee Sachar Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.8b02814 • Publication Date (Web): 01 Nov 2018 Downloaded from http://pubs.acs.org on November 1, 2018

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Langmuir

Insights into the interactions of Sulfamethoxazole with organized assemblies of ionic and non-ionic surfactants

Aparna Saraf a, Shweta Sharma b and Shilpee Sachar a* a

Department of Chemistry, University of Mumbai, Vidyanagari, Santacruz (E), Mumbai

400098, India b Institute

of Forensic Science & Criminology, Panjab University, Chandigarh, 160 014, India

* Author to whom correspondence should be addressed. Email: [email protected], [email protected] Tel: +91-22-26543594 Fax: +91-22-26528547

ABSTRACT This work reports the physicochemical behavior of antibiotic drug Sulfamethoxazole (SMX) in presence of different surfactants, viz., CTAB, DTAB, DDAB, SDS, NaDOC, Tween 80 and Tween 20. The drug-surfactant systems were studied by UV-Visible and fluorescence spectroscopy to assess the binding constants (Kb), partition coefficient (Kx), free energy of partition (∆Gp), aggregation number (Nagg) as well as quenching constant (Ksv). Solubilization studies were done to understand the encapsulation efficiency of the system, which was found to increase as a function of CTAB concentration. Surface tension measurements enabled us to determine the change in cmc as well as to calculate the variation in surface parameters of surfactant in presence of drug viz., surface pressure (π), surface excess concentration (γmax) and minimum area (Amin). In addition, UV-Visible, fluorescence and circular dichroism studies were done to check the effects of surfactant based SMX formulation on serum proteins. Keywords: Physiochemical behavior, Sulfamethoxazole, Surfactants, Solubility measurements

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INTRODUCTION A rational drug designing aims towards a formulation with minimum drug degradation, enhanced dissolution, targeted action along with enhanced bioavailability of the drug. Most of the promising drugs from the new generation of antibiotics suffer from low aqueous solubility, low penetration, poor bioavailability, low stability and hence low therapeutic efficacy. This along with increasing frequency of antibiotic-resistant bacteria has become a challenge for medicinal chemist. In addition, with natural product screening and chemical synthetic routes for a new antibiotic moiety, attempts should also be made for improving the efficacy of existing promising antibiotics by choosing different excipients like surfactants, sugars and nanoparticles in association with the desired drug in order to develop effective formulations which can facilitate the therapeutic action. Surfactant micelles are found to facilitate drug absorption along with shielding of the active drug molecules from the adverse environmental conditions. The study on molecular-level interactions between the drug and micelles can be used to predict several pharmacokinetic and pharmacological properties of drugs viz., transport, bio distribution, accumulations and therefore their efficacy. When sufficient amount of a surfactant is dissolved in water, the surfactant molecules form colloidal clusters (micelles) of various shapes in which the polar head groups point outwards and hydrophobic ends point towards the core of the micelle. The threshold concentration at which the formation of micelle begins is known as critical micelle concentration (cmc). Micellar core is capable of incorporating hydrophobic substances present in the system. In past, various ionic surfactants like CTAB, DTAB, TTAB, SDS, SLS, AOS, LAS alone and their mixtures have been studied in association with various poorly water soluble drugs, viz., Ibuprofen [1,2], Naringenin [3], Danazol [4], Gliclazide [5] etc. Non-ionic surfactants viz., Brij 35 [1], Tween 80 [5] have also been studied in association with poorly soluble drugs for enhancing their solubility.

Figure 1: Molecular structure of Sulfamethoxazole


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Sulfamethoxazole (SMX) (fig. 1) belonging to class Sulfonamides is an FDA approved drug which is one of the most frequently used antibiotic in combination with the trimethoprim. It is found in the blood as protein-bound, unbound, metabolized form and as conjugated form viz., N-glucuronide conjugate. The free form of the SMX is found to be the therapeutically active form. At pH values above 5.6, it is predominantly anionic, below 1.7 it is positively charged and in between it is uncharged. The drug is able to combine with bacterial cell and hence efficient in inactivating toxic proteins but its poor aqueous solubility results in severe side effects and hence limits its usage. Studies have been reported in past to improve its therapeutic index alone [6] and along with Trimethoprim (TMP) [7] via complexation approach using metal complexes [6], cyclodextrins [8, 9] and surfactants [9]. SMX showed a higher affinity towards β-CD and HP β-CD, and TMP showed a higher tendency of complexation with γ-CD. Also, the solubility of TMP showed higher enhancement than that of SMX in presence of sodium dodecyl sulfate surfactant. Its association with cationic benzalkonium chloride surfactants has also been studied using 1HNMR and conductivity measurements [10]. SMX was found to be solubilize in the outer micellar portions. Gemini surfactants have also been studied in association with SMX via adsorption isotherms, mainly to study the extent of SMX adsorption on micellar surface for effective removal antibiotics from the waste water [11]. SMX alone and in combination with TMP has also been studied in association with nanoparticles for developing a targeted delivery formulation [12, 13]. Reports suggested successful loading of SMX on nano modalities via different protocols. To investigate its fate in vivo, interactions of Sulfamethoxazole along with Sulfanilamide (SAM) were studied with serum proteins and nucleobases using molecular docking investigation, UV-Visible and fluorescence studies [14]. Very few micellar formulations have been studied in association with SMX and thus due to the paucity of information, the present study focusses on studying SMX with various classes of surfactants in order to find a suitable micellar core for SMX solubilization. Micellar solubilization of drugs can arise due to hydrophobic and/or electrostatic interactions. Surfactants from ionic (CTAB, DTAB, DDAB, SDS, NaDOC) and non-ionic classes (Tween 80, Tween 20) were comprehensively studied in association with SMX via UVVisible, fluorescence, and surface tension measurements. Being the major transport proteins, serum albumins are widely investigated with administered therapeutic formulations. Drug-protein interactions not only affect drug distribution but can bring conformational changes in the proteins which can trigger toxicity and hence affect the in vivo fate of the formulations. Circular dichroism studies were done to study conformational changes in BSA in presence of the SMX-Surfactant systems. The study provides insights into


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the association of SMX with different surfactants (CTAB, DTAB, DDAB, SDS, NaDOC, Tween 80 and Tween 20). The findings would, in turn, serve as an integral knowledge for the design of more competent surfactant-based drug formulations for SMX with an improved prolonged efficacy of the drug. MATERIALS AND METHOD Materials Sulfamethoxazole (SMX), Fatty acid free Bovine Serum Albumin (BSA), Cetyl Trimethyl Ammonium Bromide (CTAB), Dodecyl Trimethyl Ammonium Bromide (DTAB), Didodecyl Dimethyl Ammonium Bromide (DDAB), Sodium Dodecyl Sulfate (SDS), Sodium Deoxy Cholate (NaDOC), Tween 80, Tween 20, Sodium phosphate dibasic and Sodium phosphate monobasic with purity ≥98% were procured from Sigma-Aldrich. Pyrene with 98% purity was obtained from Alfa aeser. All the chemicals were of analytical grade and used without further purifications. The experiments were performed in phosphate buffer (pH 7.4). Double distilled water was used for the entire study. UV-Visible studies The effects of various types of surfactant on the absorption spectrum of SMX were studied using UV-2450 Shimadzu UV-VIS spectrophotometer with quartz-cuvettes of 1 cm path length at 298 K in the wavelength range of 200-800 nm. The concentration of surfactants was varied from pre to post micellar concentration viz., 0.1 mM to 20 mM for CTAB (cmcaq = 0.98 mM), 1 mM to 25 mM for DTAB (cmcaq = 14 mM), 0.01 mM to 1 mM for DDAB (cmcaq = 0.08 mM), 0.001 mM to 1 mM for Tween 80 (cmcaq = 0.023 mM), 0.01 mM to 0.2 mM for Tween 20 (cmcaq = 0.064 mM), 1 mM to 20 mM for SDS (cmcaq = 8.6 mM) and 1 mM to 10 mM for NaDOC (cmcaq = 2 mM). In all the experiments concentration of the SMX was kept constant at 0.1 mM. Entire experiments were performed in phosphate buffer (pH 7.4). Each set was carried out in triplicate and standard deviations are represented by the error bars in the graphs. Fluorescence studies All

the

fluorescence

experiments

were

done

on

a

RF-5301PC

Shimadzu

Spectrofluorophotometer at 298 K. The experiments were performed with a quartz cell of 1cm path length. For fluorescence measurements, the concentration of pyrene was kept constant at 1mM. SMX concentration was varied from 0.02 mM to 0.2 mM and concentration of surfactants was kept constant at 20 mM for CTAB, 25 mM for DTAB and 1 mM for Tween 80. The excitation wavelength was selected at 335 nm to selectively excite pyrene probe and corresponding emission spectra were recorded in the range of 345 nm to 600 nm. Excitation


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and emission slit widths were fixed at 5 nm. Each set was carried out in triplicate and standard deviations are represented by the error bars in the graphs. Protein Interactions Absorption spectra and fluorescence quenching studies of BSA (1 mg/mL) were recorded in presence of increasing concentration of SMX (0 mM to 0.1 mM) with the constant concentration of CTAB (20 mM), DTAB (25 mM) and Tween 80 (1 mM). For the fluorescence analysis, excitation and emission slit width were fixed at 5nm in the wavelength range of 287 nm to 500 nm with excitation wavelength at 277 nm. Each set was carried out in triplicate and standard deviations are represented by the error bars in the graphs. Circular Dichroism spectra in the far UV CD (190-260 nm) and near UV CD (260-360 nm) regions were obtained on JASCO J-815 CD spectrometer at 298 K for observing the alterations in the secondary and tertiary structure of the serum protein (BSA). The spectropolarimeter was thoroughly purged with N2 gas before starting the experiment. Each spectrum was baseline corrected and was taken as an average of three accumulations at a scan rate of 100 nm/min with a response time of 1 second. The secondary and tertiary structures of BSA were observed in absence and presence of SMX, CTAB and Tween 80 using cuvettes of 1 cm path length. SMX concentration was kept constant at 0.1 mM, CTAB, DTAB and Tween 80 concentrations were kept constant at 20 mM, 25 mM and 0.1 mM respectively for the CD studies. The concentration of BSA used was 0.3 x 10-6 mol/dm3 for Far UV and 15 x 10-6 mol/dm3 for near UV CD experiments. The molar ellipticity was calculated and plotted against the wavelength. To check the structural changes in BSA, the study was done for 48 hrs. Solubility measurement Phase-solubility studies of SMX in CTAB were carried out according to the Higuchi-Connors procedure [15]. 0.1 g of SMX was placed in each flask containing different concentrations (pre to post) of CTAB in phosphate buffer (pH 7.4). The flasks were stirred at 298 K for 24 h to achieve the equilibrium. Appropriate aliquots were then withdrawn, filtered and subsequently diluted with buffer (pH 7.4). The total concentration of the drug in the filtrate was analyzed by UV absorbance studies. A control assay was performed in the absence of surfactant which was used for the construction of a calibration curve. Each set was carried out in triplicate. Standard deviations are represented by the error bars in the graphs. Surface Tension studies Interfacial tension was measured by pendant drop method using 260-F4 rame-hart goniometer at 298 K. Critical micelle concentration and surface properties of CTAB were determined in the absence and in presence of a constant concentration of SMX (0.1 mM) in phosphate buffer


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(pH 7.4). Each set was carried out in triplicate and standard deviations are represented by the error bars in the graphs. RESULTS AND DISCUSSION Electronic Absorption studies Figure S1 (a) shows the absorption spectrum of varying concentration of SMX in pH 7.4. It indicates absorption maxima at 256 nm with a molar extinction coefficient of 31755 mol−1dm3cm−1 (R2: 0.9998) obtained from the plot of absorbance vs SMX concentration [inset fig S1 (a)]. Figure 2 (a) shows the absorption spectra of SMX in presence of varying concentrations of CTAB. It was observed that as the surfactant concentration increases the absorbance increases slightly with the shift in maxima from 256 nm to 260 nm. This observed red shift [inset fig 2 (a)] and the increase in absorbance clearly indicates the interaction between negatively charged SMX and positively charged CTAB moieties. The wavelength shift was found to be maximum for CTAB in comparison to DTAB [inset fig. 2 (b)]. A slight increase in absorbance with no shift in wavelength was observed in presence of Tween 80 [fig. 2 (c)]. No significant changes were observed in presence of SDS [fig. 2 (d)], DDAB, NaDOC and Tween 20 based systems [fig. S1 (b, c, d)] which point towards very weak interactions. Thus, the extent of binding between SMX-CTAB/DTAB/Tween 80 was evaluated using Bensi-Hilbrand equation [16] 1 ∆A

1

1

(1)

= At ― A0 + Kb[S](At ― A0)

Where, A and A0 are the values of absorbance of SMX in presence and absence of surfactants respectively, At is absorbance of SMX bound to surfactant micelles, [S] is the concentration of surfactant, ∆A is differential absorbance, and Kb is binding constant. Binding constant was found to be maximum for SMX-Tween 80 system [(1.88 ±0.1) x 104 M1]

in comparison to SMX-CTAB [(0.12 ±0.03) x 104 M-1] and SMX-DTAB [(0.01 ±0.001) x

104 M-1] [Table S1]. These values are in accordance with other drug-surfactant systems studied in the past [17].


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Figure 2: UV spectrum of [a]: SMX (0.1mM) in presence of varying concentration of CTAB (0.1 mM to 20 mM) inset: Bensi-Hilbrand plot of SMX-CTAB system [b]: SMX (0.1 mM) in presence of varying concentration of DTAB (1 mM to 25 mM) inset: Bensi-Hilbrand plot of SMX-DTAB system [c]: SMX (0.1 mM) in presence of varying concentration of Tween 80 (0.001 mM to 1 mM) inset: Bensi-Hilbrand plot of SMX-Tween 80 system [d]: SMX (0.1 mM) in presence of varying concentration of SDS (1 mM to 20 mM) in phosphate buffer (pH 7.4) at 298 K.

Partition Coefficient Partition coefficient (Kx) of SMX was evaluated between water and micellar pseudo-phase. It is the ratio of the concentration of drug molecules in the micelle to that in bulk aqueous solution. The partition coefficient parameter is important not only in elucidating the mechanism of solubilization, but also helps to understand how a drug is partitioned through biological membranes within the living body. The partition coefficient was obtained from the following equation [18, 19]: 1 ∆A

1

nw

(2)

= ∆A∞ + Kx∆A∞([S] + Ct ― cmc)

Where, A = A-A0, A = Ab-A0.


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A, A0 and Ab are the absorbance values of SMX in presence of surfactants, in absence of surfactants and the absorbance due to the formation of drug-surfactant complex respectively, CT is the total concentration of SMX, [S] is the concentration of surfactant, nw is the molarity of water (55.5 M) and Kx is the partition coefficient. The plot of 1/∆A vs 1/ ([S] +Ct-cmc) are shown in fig S2 (a, b, c) for SMX-CTAB, SMX-DTAB and SMX-Tween 80 systems. The values for Kx were found to be 3.29 (±0.2) x 106, 2.14 (±0.3) x 105 and 1.44 (±0.1) x 104 for the SMX-CTAB, SMX-Tween 80 and SMX-DTAB systems respectively (Table S1), which is in accordance with the literature values for drug-surfactant systems [19]. Drug partitioned between the micellar and water phases as a result of the hydrophobic or electrostatic interactions. The high positive value for the SMX-CTAB system in comparison to the SMXTween 80 and SMX-DTAB systems suggests that the electrostatic interaction plays a major role along with the hydrophobic interactions, as under working conditions SMX is negatively charged. This drives negatively charged SMX to partition or solubilize more in the CTAB micelles. The standard free energy change for the transfer of SMX from water to micellar phase (∆Gx0) was evaluated using the following equation: ∆Gx0 = -RTlnKx

(3)

Where, R is universal gas constant, T is temperature. ∆Gx for the systems SMX-CTAB, SMXTween 80 and SMX-DTAB was found to be -33 kJmol-1, -27 kJmol-1 and -21 kJmol-1 respectively. The negative value indicates that SMX partitioning between the micellar and the bulk water phases happens spontaneously. Fluorescence studies The molecular association and dynamics between SMX and surfactants were monitored by changes in the fluorescence emission of the probe (pyrene) as SMX is a very weak fluorescent drug. Relative intensity of I and III emission bands of pyrene is related to environment polarity and thus can give specific information on the absence or presence of micellar or other hydrophobic domains [20]. With increasing concentrations of SMX in presence of CTAB, DTAB and Tween 80 [fig. 3 (a, b, c)], a decrease in I1 and I3 peaks of pyrene emission spectra were observed. This indicates that the environment surrounding the pyrene get changed which is a result of the association of quencher (SMX) with the micelles. The aggregation numbers were also determined from the fluorescence results using the following equation [21]: I0

[Q]

(4)

ln I = [M]


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Where, [M] =

[S]T ― cmc

(5)

Nagg

[M] here, represents the micellar concentration and [Q] is the quencher concentration, I represents the intensities in the presence and I0 represents the intensities in absence of quencher, [S] T is the concentration of surfactant and Nagg is the micellar aggregation number. The slope of Eq. (4) is used to calculate aggregation number [fig. S3 (a), (b)]. The aggregation numbers for the SMX-CTAB and SMX-DTAB system were found to be 61 (±1), 54 (±2) respectively (Table S1). The decrease in fluorescence intensity with increasing SMX concentration points strongly towards the electrostatic interactions. The values of aggregation number show a minor increase in the case of SMX-CTAB/DTAB systems in comparison to the aggregation number of surfactants alone [22, 23]. This can be visualized as the presence of SMX on the palisade layer of the surfactant that results in more compact and stable aggregates as the hydrophobic part of the drug is distributed towards the non-polar part of the CTAB whereas the ionic part of the drug interacts with the head group of the surfactant. No significant quenching was observed for SMX-Tween 80 system and hence Nagg was not calculated. The quenching constant for SMX-CTAB and SMX-DTAB systems were evaluated using Stern-Volmer equation, F0 F

(6)

= 1 + 𝐾𝑠𝑣[Q]

Where, F represents the fluorescence intensities in the presence and F0 represents the intensities in absence of quencher concentration [Q]. Ksv is Stern-Volmer quenching constant which assesses the bimolecular quenching and decay as it is the product of rate constant of the quenching process and lifetime of the probe in the absence of quenching. Plot of F0/F vs [Q] for SMX–CTAB and SMX–DTAB systems are shown in inset of fig. 3 (a, b,) respectively. The values of Ksv were found to be 4.53 (±0.002) x 103 M-1 and 6.87 (±0.02) x 103 M-1 for SMX– CTAB and SMX–DTAB systems respectively (Table S1).


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Figure 3: Fluorescence spectra of [a]: Pyrene (1 mM) in presence of CTAB (20 mM) at varying concentrations of SMX (0.02 mM to 0.2 mM) inset: plot of ln F0/F vs [Q] [b]: Pyrene (1 mM) in presence of DTAB (25 mM) at varying concentrations of SMX (0.02 mM to 0.2 mM) inset: plot of ln F0/F vs [Q] [c]: Pyrene (1 mM) in presence of Tween 80 at varying concentrations of SMX (0.02 mM to 0.2 mM) in phosphate buffer (pH 7.4) at 298 K.

Protein Interactions UV-VIS studies The increase in the concentration of SMX causes enhancement in absorbance of BSA with a blue shift in wavelength (from 277 to 261 nm) in BSA-SMX-CTAB system [fig. 4 (a)], BSASMX-DTAB system [fig. 4 (b)] and BSA-SMX-Tween 80 system [fig. 4 (c)].This may be due to the formation of SMX-BSA ground-state complex in presence of CTAB, DTAB and Tween 80, which point towards the decrease in polarity around Tryptophan residues that again confirms binding between SMX-CTAB/DTAB/Tween 80 and BSA systems. The extent of binding between BSA-SMX-CTAB/DTAB/Tween 80 was evaluated using Bensi-Hilbrand relation (eq. 1). Plot of 1/∆A vs 1/[S] for BSA-SMX-CTAB, BSA-SMX-DTAB and BSA-SMX-Tween 80 systems are shown in inset of fig. 4 (a, b and c) respectively. Binding constant was found to be maximum for BSA-SMX-CTAB system [(1.28 ±0.001) x 102 M-1] in


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comparison to BSA-SMX-DTAB [(1.18 ±0.03) x 102 M-1] and BSA-SMX-Tween 80 [(0.92 ±0.003) x 102 M-1] (Table S2). Fluorescence studies The intrinsic fluorescence of BSA is essentially due to Tryptophan, which is sensitive to any polarity change in the microenvironment. Fluorescence of BSA gradually decreased with the increasing concentration of SMX in presence of CTAB [fig. 5 (a)] and DTAB [fig. 5 (b)]. A significant shift in the emission maximum wavelength (343-334 nm) was also observed, indicating SMX-BSA interaction that also supports quenching of intrinsic fluorescence. In BSA-SMX-Tween 80 [fig. 5 (c)] system, quenching was observed without a significant shift in the emission wavelength of the BSA. The fluorescence results obtained were analyzed using the Stern -Volmer relation (eq. 6). Plot of F0/F vs [Q] shown slightly upward curvature hence, the data was further analyzed by employing the modified Stern–Volmer equation shown below [24], F0

1

F0 ― F

1

(7)

= faKsv[Q] + fa

where, F and F0 are the fluorescence intensities of the protein in the presence and absence of SMX, respectively; Ksv is the modified Stern–Volmer quenching constant, [Q] is the concentration of the quencher and fa is the fraction of accessible tryptophan. The plot of Fo/(Fo−F) vs 1/[Q] [Inset in fig. 5 (a), (b) and(c)] indicate a linear trend. The value of fa was found to be 1.11 for BSA-SMX–CTAB, 0.96 for BSA-SMX–DTAB and 1.14 for BSA-SMX– Tween 80. Corresponding Ksv values are 30.0 (±0.003) M-1, 28.65 (±0.09) M-1and 18.93 (±0.001) M-1 respectively (Table S2). Analysis of binding equilibria: If it is assumed that there are similar and independent binding sites in the biomolecule, for static quenching interaction, the binding constant, K and the number of binding sites, n can be calculated using the equation [25], log

F0 - F F

(8)

= logK + nlog[Q]

From the linear plot of log (Fo−F)/F vs log [Q], the values of K and n were obtained from the intercept and slope, respectively [fig. S4 (a), (b) and (c)] (Table S2). Values of K for the BSASMX-CTAB, BSA-SMX-DTAB and BSA-SMX-Tween 80 systems were found to be 6.60 (±0.01) x105 M-1, 1.34 (±0.01) x103 M-1 and 3.09 (±0.02) x105 M-1 respectively. n value for the BSA-SMX-CTAB system was 1.3 which is greater than BSA-SMX-DTAB (0.9) and BSASMX-Tween 80 (1.2) systems. From the values of n, it may be inferred that there is one independent binding site on BSA for SMX in presence of CTAB, DTAB and Tween 80.


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The value of ∆G◦ was calculated using the equation given below, ∆G0 = ―2.303RTlogK

(9)

∆G◦ value for the BSA-SMX-CTAB system BSA-SMX-DTAB and BSA-SMX-Tween 80 systems was found to be -33.58 kJM-1, -18.07 kJM-1 and -31.68 kJM-1 respectively. The negative values of the ∆G0 indicate that the processes were spontaneous.

Figure 4: UV spectrum of [a]: BSA in presence of CTAB (20 mM) at varying concentrations of SMX (0.02 mM to 0.1 mM) inset: Bensi-Hilbrand plot [b]: BSA in presence of DTAB (25 mM) at varying concentrations of SMX (0.02 mM to 0.1 mM) inset: Bensi-Hilbrand plot [c]: BSA in presence of Tween 80 (1 mM) at varying concentrations of SMX (0.02 mM to 0.1 mM) inset: Bensi-Hilbrand plot in phosphate buffer (pH 7.4) at 298K


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Figure 5: Fluorescence spectra of [a]: BSA in presence of CTAB (20 mM) at varying concentrations of SMX (0.02 mM to 0.1 mM) inset: Modified Stern-volmer plot [b]: BSA in presence of DTAB (25 mM) at varying concentrations of SMX (0.02 mM to 0.1 mM) inset: Modified Stern-volmer plot [c]: BSA in presence of Tween 80 (1 mM) at varying concentrations of SMX (0.02 mM to 0.1 mM) inset: Modified Stern-volmer plot in phosphate buffer (pH 7.4) at 298 K.

Denaturation studies In the far UV region native BSA showed two negative minima at 208 nm (corresponding to π→π* transition for α helix) and 222 nm (corresponding to n→π* transition for both α helix and random coil) which are characteristic of the α-helical structure of proteins [26, 27]. This replicates helical conformation of the protein and any change in the α-helix can thus be seen via changes in the CD spectra. Near UV CD spectrum helps to detect the tertiary structural changes in protein due to unfolding. The secondary and tertiary structures of BSA were observed in the presence and absence of SMX, CTAB, DTAB and Tween 80 [Fig. 6 (a-f)] systems via accompanying changes in molecular ellipticity in the far and near UV regions. BSA in presence of SMX and Tween 80 shows stable secondary structure even after 48hrs, while the presence of CTAB and DTAB along with the drug changes the secondary structure of the protein. These changes can be attributed to partial rupture of intra chain hydrophobic


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interactions between the polypeptides leading to the expanding of polypeptide and unfolding of BSA. The near UV spectrum indicates minor changes in tertiary structures of BSA in presence of DTAB after 48 hrs, however the BSA structure was maintained in presence of CTAB and Tween 80 even after 48 hrs and thus confirming long-term biocompatibility of these systems.

Figure 6: [a] Far UV [b] near UV CD spectrum of protein in presence of SMX (0.1 mM)at constant concentration of CTAB (20 mM) [c] Far UV [d] near UV CD spectrum of protein in presence of SMX (0.1 mM) at constant concentration of DTAB (25 mM) [e] Far UV [f] near UV CD spectrum of protein in presence of SMX (0.1 mM) at constant concentration of Tween 80 (0.1 mM) in phosphate buffer (pH 7.4) at 298 K.


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Micellar Solubilization of SMX in CTAB From the UV-Visible and Fluorescence spectroscopic observations it was found that interactions between SMX and cationic surfactants are predominantly dominant. As changes in the near UV CD spectra were observed in DTAB system, thus further studies were done only for SMX-CTAB systems. Figure 6 shows the solubility change of SMX as a function of CTAB concentration which indicates that, above the cmc, the solubility of the drug increased with the increase in surfactant concentration. Solubilization effect of CTAB on SMX is stronger and this behavior is a consequence of the electrostatic interactions between the positively charged surfactant CTAB and anionic drug SMX, along with the hydrophobic interactions. Drug encapsulation efficiency (EE, %) was determined from solubility measurements, based on the weight ratio of the amount of SMX in micelles to the initial amount of drug added [28]. Encapsulation Efficiency =

amount of SMX in micelles Initial amount of SMX added

(10)

Encapsulation efficiency of SMX was found to increase as a function of CTAB concentration as shown in fig. 7 (b).

Figure 7 (a): Solubility curve (b): Encapsulation efficiency of SMX as a function of CTAB concentration in phosphate buffer (pH 7.4) at 298K.

Interfacial Phenomenon Surface tensiometry is an effective technique for studying the surface phenomenon of surfactants and macromolecules. The plot of surface tension (γ) vs log [C] in the presence and absence of SMX is given in figure 8. The cmc of CTAB in buffer solution (PH 7.4) was found to be 1.0 × 10−3 mol dm−3. The cmc of the surfactant in the presence of SMX shifted towards a higher concentration (1.8 × 10−3 mol dm−3) which is an indication of the utilization of surfactant monomers in binding with SMX which leads to delayed micellization. The slope of the


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tensiometric profile near the cmc is a measure of interfacial adsorption efficacy of the surfactant which was quantified by the Gibbs surface excess (γmax) [29-31] and is given by: 1

δγ (δlogC )

(11)

γmax = ― 2.303RTn

where γ is the surface tension of the solution, R is the universal gas constant (8.314 JK−1 mol−1), T is the temperature in the absolute scale, C is the concentration of the surfactant in solution and n is a constant which depends on the number of species constituting the surfactant and in the present case it is equal to 1due to presence of high ionic strength of the buffer solution used. The minimum area of exclusion per molecule at the saturated air/solution interface (Amin) is given by: 1018

(12)

Amin = NAγmax Where NA is Avogadro's number. The surface pressure at the cmc (πcmc) were obtained from the following equation:

(13)

πCMC = γ0 ― γCMC

Where γ0 and γCMC are the surface tensions of pure solvent and at the cmc, respectively. The interfacial parameters of the CTAB in the absence and presence of SMX are given in Table 1. Lower surface tension for the SMX-CTAB system than that of CTAB alone, indicates an interaction between the SMX and CTAB, which ultimately leads to the increase in γmax. The higher γmax and hence lower Amin values obtained for SMX-CTAB system compared to CTAB (in absence of SMX) indicates a more compact monolayer. Strong electrostatic interactions along with the hydrophobic interactions creates a pull for the negatively charged SMX moieties towards the micellar interface. This leads to the increase in surface excess concentration which in turn decrease the area per molecule at the interface in presence of SMX. This can be visualized as the closely packed SMX molecules with their orientation perpendicular to the interface. The increase in surface pressure of CTAB (πcmc) in presence of SMX again point towards the adsorption of SMX at the air/solution interface. Table 1: Values of γmax, πCMC, CMC evaluate from surface tension measurements:

SMX(M)

`

CMC[CTAB]

γmax

Amin

Πcmc

x10-3 (M)

x106 (mol/m2)

(nm2)

(mNm-1)

0

1.0

5.06

0.327

27.83

0.1× 10−3

1.8

6.11

0.271

30.38


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Figure 8: Variation of surface tension as a function of CTAB concentration in phosphate buffer (pH 7.4) at 298 K.

CONCLUSIONS The present work addresses the important need for a quantitative understanding of the solubilization and partitioning of antibacterial drug SMX in different micellar media. The associations of CTAB, DTAB, DDAB, SDS, NaDOC, Tween 80 and Tween 20 were analyzed with SMX via UV-Visible and fluorescence studies. The binding was found to be greater in case of CTAB, DTAB and Tween 80 systems at physiological pH 7.4. Large values of the partition coefficient for SMX in CTAB micelles [3.29 (±0.2) x 106] showed spontaneous partitioning of drug molecules from aqueous media to cationic CTAB micellar media in comparison to DTAB [1.44 (±0.1) x 104] and Tween 80 [2.14 (±0.3) x 105] systems. Another interesting point is that SMX-CTAB system showed strongest binding with transport serum proteins (BSA) whereas weak interactions were observed for Tween 80 based systems. Also, changes in the tertiary structure of BSA were observed in presence of SMX-DTAB systems. CTAB based SMX formulations are thus found to be stronger and long-term biocompatible. Solubility studies confirms the high solubility and increasing encapsulation efficiency of SMX with increasing CTAB concentrations. Surface properties viz. surface excess concentration γmax, minimum area per molecule Amin and surface pressure Πcmc provides better understanding about the location of SMX in CTAB micelles. The findings will contribute insights in understanding biomolecular interactions between surfactants with SMX, which can aid the design of a competent biocompatible SMX


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formulation. The future of such studies lies in understanding the interaction of a variety of drugs with different excipients quantitatively in order to gain insights into the functional groups responsible for interaction/partitioning, and hence deriving guidelines for target-oriented synthesis of new drugs formulations. ACKNOWLEDGEMENTS The authors acknowledge the financial support of University Grant Commission in the terms of Non-NET Fellowship. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Supporting Information (i)

UV spectra of [a]: SMX (0.02 mM to 0.1 mM) inset: calibration graph of SMX [b]: SMX (0.1 mM) in presence of varying concentration of DDAB (0.01 mM to 1 mM) [c]: SMX (0.1 mM) in presence of varying concentration of NaDOC (1 mM to 10 mM) [d]: SMX (0.1 mM) in presence of varying concentration of Tween 20 in (1 mM to 0.2 mM) phosphate buffer (pH 7.4) at 298 K (Figure S1).

(ii)

Plot of 1/∆A vs 1/ ([S] + Ct-CMC) for [a]: SMX-CTAB system [b]: SMX-DTAB system [c]: SMX-Tween 80 system (Figure S2).

(iii)

Plot of ln I0/I vs [Q] for the aggregation number of [a]: SMX-CTAB system [b] SMX-DTAB system in phosphate buffer (pH 7.4) at 298 K (Figure S3).

(iv)

Plot of log F0-F/F vs log Q for the BSA at varying concentrations of SMX [a]: in presence of CTAB (20 mM) [b]: in presence of DTAB (25 mM) [c]: in presence of Tween 80 (1 mM) in phosphate buffer (pH 7.4) at 298 K (Figure S4).

(v)

Values of binding constant (Kb), Partition coefficient (Kx), Agregation no. (Nagg) and Quenching constant (Ksv) for SMX-Surfactant systems. (Table S1)

(vi)

Values of binding constant (Kb), Quenching constant (Ksv), Equilibrium constant (K) and no. of binding sites (n) for BSA-SMX-Surfactant systems. (Table S2)


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REFERENCES 1. Jabbari, M.; Teymoori, F. An insight into effect of micelle-forming surfactants on aqueous solubilization and octanol/water partition coefficient of the drugs gemfibrozil and ibuprofen. J Mol Liq. 2018, 262, 1-7. 2. Rangel-Yagui, C. O.; Hsu, H. W. L.; Pessoa-Jr, A.; Tavares, L. C. Micellar solubilization of ibuprofen – influence of surfactant head groups on the extent of solubilization, Braz. J. Pharm. Sci. 2005, 41, 237–246. 3. Jabbari, M.; Jabbari, A. Antioxidant potential and DPPH radical scavenging kinetics of water-insoluble flavonoid naringenin in aqueous solution of micelles. Colloids Surf A Physicochem Eng Asp. 2016, 489, 392-399. 4. Vinarov, Z.; Katev, V.; Radeva, D.; Tcholakova, S.; Denkov, N. D. Micellar solubilization of poorly water-soluble drugs: effect of surfactant and solubilizate molecular structure. Drug Dev. Ind. Pharm. 2018, 44, 677–686. 5. Seedher, N.; Kanojia, M. Micellar Solubilization of Some Poorly Soluble Antidiabetic Drugs: A Technical Note. AAPS PharmSciTech. 2008, 9, 431-436. 6. Mondelli, M.; Pavan, F.; de Souza, P. C.; Leite, C. Q.; Ellena, J.; Nascimento, O. R.; Facchin, G.; Torre, M. H. Study of a series of cobalt(II) sulfonamide complexes: Synthesis, spectroscopic characterization, and microbiological evaluation against M. tuberculosis. Crystal structure of [Co(sulfamethoxazole)2(H2O)2].H2O. J Mol Struct. 2013, 1036, 180–187. 7. Markopoulou, C. K.; Malliou, E. T.; Koundourellis, J. E. Chemometric and derivative methods as flexible spectrophotometric approaches for dissolution and assaying tests in multicomponent tablets. Farmaco. 2004, 59, 627–636. 8. Varghese, B.; Suliman, F. O.; Hajri, A. A.; Al Bishri, N. S. S.; Al-Rwashda, N. Spectral and theoretical study on complexation of sulfamethoxazole with β- and HP βcyclodextrins in binary and ternary systems. Spectrochim. Acta A. 2018, 190, 392–401. 9. Gokturk, S.; Caliskan,E.; Talman, R. Y.; Var. A Study on Solubilization of Poorly Soluble Drugs by Cyclodextrins and Micelles: Complexation and Binding Characteristics of Sulfamethoxazole and Trimethoprim. ScientificWorldJournal. 2011, 2012, 1-12. 10. Farias, T.; de Menorval, L. C.; Zajac, J.; Rivera, A. Solubilization of drugs by cationic surfactants micelles: Conductivity and 1H NMR experiments. Colloids Surf A Physicochem Eng Asp. 2009, 345, 51–57.


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11. Wang, J.; Gao, M.; Ding, F.; Shen, T. Organo-vermiculites modified by heating and gemini pyridinium surfactants: Preparation, characterization and sulfamethoxazole adsorption. Colloids Surf A Physicochem Eng Asp. 2018, 546, 143-152. 12. Fariasa, T.; Charles de Menorval, L.; Zajac, J.; Rivera, A. Adsolubilization of drugs onto natural clinoptilolite modified by adsorption of cationic surfactants. Colloids Surf B Biointerfaces. 2010, 76, 421–426. 13. Martinez-Costa, J. I.; Leyva-Ramos, R.; Padilla-Ortega, E.; Aragon-Pina, A.; CarralesAlvarado, D. H. Antagonistic, synergistic and non-interactive competitive sorption of sulfamethoxazole-trimethoprim and sulfamethoxazole cadmium (ii) on a hybrid clay nanosorbent. Sci Total Environ. 2018, 640, 1241–1250. 14. Rajendiran, N.; Thulasidhasan, J. Interaction of sulfanilamide and sulfamethoxazole with bovine serum albumin and adenine: Spectroscopic and molecular docking investigations. Spectrochim Acta A. 2015, 144, 183-191. 15. Faustino, C.; Seraﬁm, C.; Ferreira, I.; Pinheiro, L.; Calado, A. Solubilization power of an amino acid-based gemini surfactant towards the hydrophobic drug amphotericin B. Colloids Surf A Physicochem Eng Asp. 2015, 480, 426–432. 16. Mahajan, S.; Mahajan, R. K. Interactions of phenothiazine drugs with bile salts: Micellization and binding studies. J Colloid Interface Sci. 2012, 387, 194–204. 17. Usman, M.; Siddiq, M. Surface and micellar properties of Chloroquine Diphosphate and its interactions with surfactants and Human Serum Albumin. J Chem Thermodyn. 2013, 58, 359–366. 18. Enache, M.; Toader, A. M.; Enache, M. I. Mitoxantrone-Surfactant Interactions: A Physicochemical Overview. MOLECULES. 2016, 27, 1356-1373. 19. Enache, M.; Toader, A. M.; Neacsu, V.; Ionita, G.; Enache, M. I. Spectroscopic Investigation of the Interaction of the Anticancer Drug Mitoxantrone with Sodium Taurodeoxycholate (NaTDC) and Sodium Taurocholate (NaTC) Bile Salts. MOLECULES. 2017, 22, 1079-1097. 20. Mukhija, A.; Kishore, N. Drug partitioning in individual and mixed micelles and interaction with protein upon delivery form micellar media. J Mol Liq. 2018, 265, 115. 21. Azum, N.; Rub, M.A.; Asiri, A. M. Analysis of surface and bulk properties of amphiphilic drug ibuprofen and surfactant mixture in the absence and presence of electrolyte. Colloids Surf B Biointerfaces. 2014, 121, 158–164.


Page 20 of 22

Page 21 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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22. Pisarcik, M.; Devinsky, F.; Pupak, M. Determination of micelle aggregation numbers of alkyl trimethyl ammonium bromide and sodium dodecyl sulfate surfactants using time-resolved fluorescence quenching. Open Chem. 2015, 13, 922–931. 23. Stam, J. V.; Depaemelaere, S.; De Schryver, F. C. Micellar Aggregation Numbers - a Fluorescence Study. J Chem Ed. chem. 1998, 75, 93-99. 24. Wang, G.; Wang, D.; Li, X.; Lu, Y. Exploring the binding mechanism of dihydropyrimidinones to human serum albumin: Spectroscopic and molecular modeling techniques. Colloids Surf B Biointerfaces. 2011, 84, 272–279. 25. Shahabadi, N.; Hadidi, S.; Feizi, F. Study on the interaction of antiviral drug ‘Tenofovir’ with human serum albumin by spectral and molecular modeling methods. Spectrochim Acta A. Mol Biomol Spectrosc. 2015, 138, 169–175. 26. Joseph, D.; Sachar, S.; Kishore, N; Chandra, S. Mechanistic insights into the interactions of magnetic nanoparticles with bovine serum albumin in presence of surfactants. Colloids Surf B Biointerfaces. 2015, 135, 596–603. 27. B. Sandhya; Hegde, A. H.; Kalanur, S.S.; Katrahalli, U.; J. Seetharamappa. Interaction of triprolidine hydrochloride with serum albumins: Thermodynamic and binding characteristics, and influence of site probes. J Pharm Biomed Anal. 2011, 54, 1180– 1186. 28. Singh, C.; Kumar, P. Solid Dispersion Incorporated Microcapsules: Predictive Tools for Improve the Half Life and Dissolution Rate of Pioglitazone Hydrochloride. Am. J. Med. Sci. 2013, 1, 57-70. 29. Branco, M. A.; Pinheiro, L.; Faustino, C. Amino acid-based cationic gemini surfactant– protein interactions. Colloids Surf A Physicochem Eng Asp. 2015, 480, 105–112. 30. Usman, M.; Rashid, M. A.; Mansha, A.; Siddiq, M. Thermodynamic solution properties of pefloxacin mesylate and its interactions with organized assemblies of anionic surfactant, sodium dodecyl sulphate. Thermochim Acta. 2013, 573, 18–24. 31. Ali, M. S.; Al-Lohedan, H. A. Interaction of biocompatible sugar based surfactant ndodecyl β-D-maltoside with lysozyme. J Mol Liq. 2015, 209, 662–668.


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“For Table of Contents Only” Insights into the interactions of Sulfamethoxazole with organized assemblies of ionic and non-ionic surfactants Aparna Saraf a, Shweta Sharma b and Shilpee Sachar a* a

Department of Chemistry, University of Mumbai, Vidyanagari, Santacruz (E), Mumbai

400098, India b Institute

of Forensic Science & Criminology, Panjab University, Chandigarh, 160 014, India

* Author to whom correspondence should be addressed. Email: [email protected], [email protected] Tel: +91-22-26543594 Fax: +91-22-26528547


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Insights into the interactions of Sulfamethoxazole with organized

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