Micellization of Lactosylammonium Surfactants with Different Counter

Article pubs.acs.org/jced

Micellization of Lactosylammonium Surfactants with Different Counter Ions and Their Interaction with DNA Lifei Zhang, Yanyan Dong, Xiaohong Zhang, and Xia Guo* School of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou, Jiangsu 225002, People’s Republic of China S Supporting Information *

ABSTRACT: So far, the studies about the physical chemical properties of sugar-based surfactants have been still unsystematic; most of the studies have been focused on nonionic sugar-based surfactants. In the present work, we studied the micellization of four lactose-based surfactants, with the same headgroup (lactosylammonium) and the same hydrophobic alkyl chain (dodecyl) but different counterions (malonate, adipate, propionate, and hexanoate), at 25.0 and/or 50.0 °C. We found that these four surfactants could decrease the surface tension of water to ca. 30 mN/m. When the number of carboxylate groups in the counterion was the same, the counterion having a shorter alkyl chain could lead to a smaller minimum area per surfactant molecule. Moreover, the surfactants with monocarboxylates as counterions had much lower critical micelle concentrations than those with dicarboxylates as counterions, and the micelles from the former surfactants had a lower counterion binding degree. The lactosylammonium surfactants could bind with DNA, and low content of the surfactant could decrease the CD signal of DNA, while high content of the surfactant could make DNA unfold somewhat. decrease the surface tension of water to ca. 30 mN/m at 25 °C, and the surfactant with malonate as the counterion had the greatest preference to be adsorbed at the water/air surface, while the surfactant with succinate as the counterion had the lowest critical micelle concentration. Moreover, the surfactant with malonate as the counterion interacted with DNA strongest and that with adipate as the counterion interacted with DNA weakest.25 It has been found that tumor cells exhibit dramatically increased glucose uptake and highly elevated rates of glycolysis.26 Many glycolipids have been identified as membrane receptors of various pathogeneous agents, and galactosylceramide and its analogues have been found to show high anti-HIV activities with low cytotoxicity.8,9 On the other hand, a successful gene therapy is dependent on the development of an efficient delivery vector for drug based on nucleic acid; nonviral vectors (typically based on cationic lipids or polymers) are preferred because of safety concerns with viral vectors.27 So a thorough understanding of cationic sugar-based surfactants and their interactions with DNA should be interesting and important for its potential application as a nucleic-based drug carrier. Considering the very limited report about cationic sugar-based surfactants, in the present study, we synthesized lactose-based cationic surfactants di(N-dodecyllactosylammonium) malonate, di(N-dodecyllactosylammonium) adipate, N-dodecyllactosylammonium propionate, and N-dodecyllactosylammonium hexanoate, with C1−O bond remaining intact and highly stable. Then, we studied their surface activities, micellization behavior, and interactions with DNA and also made a comparison with the properties for glucosylammonium reported recently.25

1. INTRODUCTION Glycolipids are amphiphiles comprising a sugar headgroup and alkyl chain. In the past few decades, sugar-based amphiphiles have been interesting due to their significance in areas of food, medicine, self-assembly, and molecular recognition in biological systems.1,2 So far, various aspects of synthetic methodologies have been developed to produce sugar-based surfactants with different sugar-head types, alkyl chains, and molecular architectures (such as gemini, trimeric, and bola structures).3−15 It has been found that sugar-based amphiphilic molecules can selfaggregate in nanometer range, forming micelles, vesicles, or a myriad of liquid crystal phases (from simple lamellar, hexagonal, or cubic phases to rippled and gel phases).12−20 The detailed structures of the phases are governed by the balance between the hydrophobic chain bulkiness and the headgroup interaction, including hydrogen bonding.21 In spite of these studies, the study of sugar-based surfactants is still relatively new. So far, most of the surfactants studied are nonionic; the reports about ionized sugar-based surfactants have been limited yet. When an amino group was attached to the C1 of a sugar moiety, the C1−O bond in the sugar-based amine surfactant was generally broken.8,9,22,23 It has been thought that the structural role of glycolipids could best be understood through a systematic examination of these molecules varying in the structures of headgroup and hydrocarbon chain,21 which should be a key step toward rational design of new glycolipid-based materials. Therefore, we24 recently studied the micellization of glucosylamine in the presence of carboxylic acids and found that carboxylic acid could control its aggregation behaviors in water and on DNA. Moreover, glucosylamine could form stable precipitates with dicarboxylic acid after 2 days of stirring, and the product was cationic surfactant glucosylammonium.25 It was found that glucosylammonium surfactants could © 2016 American Chemical Society

Received: December 13, 2015 Accepted: June 16, 2016 Published: July 6, 2016 2969

DOI: 10.1021/acs.jced.5b01057 J. Chem. Eng. Data 2016, 61, 2969−2978

Journal of Chemical & Engineering Data

Article

surfactant concentration. 1H NMR (600 MHz, D2O, ppm): δ 0.81 (t, 6H, J = 6.6 Hz, 2CH3), 1.23−1.61 (m, 40H, 2CH3(CH2)10), 2.55 (s, 2H, CO-CH2), 2.80−3.05 (m, 4H, 2NH2+-CH2); sugar moiety, 3.19−4.59 (m, 28H), 5.15 (d, 0.4 H, J = 3.8 Hz, H-1α). Elem. Anal. Calcd for C51H98O24N2·H2O: C, 53.68; H, 8.77; N, 2.46. Found: C, 53.75; H, 8.90; N, 2.37. Di(N-dodecyllactosylammonium) Adipate (2b). Yield: 40%. [α]D15: +3.79° (c, 0.085 mol·kg−1; H2O). 1H NMR (600 MHz, D2O, ppm): δ 0.78 (t, 6H, 2CH3), 1.21 (m, 36H, 2CH3(CH2)9), 1.49−1.65 (m, 8H, 2NH2+-CH2-CH2 and CO−CH2-CH2-CH2CH2-CO), 2.10 (s, 4H, 2CO-CH2), 2.86−2.97 (m, 4H, 2NH2+CH2); sugar moiety, 3.19−4.59 (m, 28H), 5.14 (d, 0.5 H, J = 3.8 Hz, H-1α). Elem. Anal. Calcd for C54H104O24N2·(1/2)H2O: C, 55.24; H, 8.95; N, 2.39. Found: C, 55.40; H, 9.18; N, 2.42. N-Dodecyllactosylammonium Propionate (3a). Yield: 48%. [α]D15: +21.05° (c, 0.082 mol·kg−1; DMSO). Here c 0.05 means the surfactant concentration is 0.05 g/mL. 1H NMR (600 MHz, D2O, ppm): δ 0.89 (t, 3H, J = 7.2 Hz, CH3), 1.08 (t, 3H, J = 7.5 Hz, CH3), 1.32 (m, 18H, CH3(CH2)9), 1.55−1.68 (m, 2H, NH2+-CH2−CH2), 2.19 (q, 2H, J = 7.4 Hz, CO-CH2), 2.64−2.97 (m, 2H, NH2+-CH2); sugar moiety, 3.08−4.58 (m, 14H), 5.18 (d, 0.3 H, J = 3.7 Hz, H-1α). Elem. Anal. Calcd for C27H53O12 N·(3/2)H2O: C, 53.11; H, 9.18; N, 2.30. Found: C, 53.00; H, 8.74; N, 2.02. N-Dodecyllactosylammonium Hexanoate (3b). Yield: 40%. [α]D16: +28.11° (c, 0.074 mol·kg−1; DMSO). 1H NMR (600 MHz, D2O, ppm): δ 0.84 (t, 3H, J = 7.0 Hz, CH3), 0.86 (t, 3H, J = 7.0 Hz, CH3), 1.26 (m, 22H, CH3(CH2)9 of dodecyl chain and CH3(CH2)2 of hexanoate), 1.51−1.64 (m, 4H, NH2+-CH2−CH2 and CO−CH2− CH2), 2.13 (t, 2H, J = 7.5 Hz, CO-CH2), 2.92 (m, 2H, NH2+-CH2); sugar moiety, 3.16−4.58 (m, 14H), 5.14 (d, 0.1 H, J = 3.7 Hz, H-1α). Elem. Anal. Calcd for C30H59O12N·3H2O: C, 53.02; H, 9.57; N, 2.06. Found: C, 53.00; H, 8.75; N, 1.93. 2.3. Sample Preparation. The solution of surfactant was prepared in water, and its concentration was expressed as the content of ammonium, symbolized as CN. The surfactant/DNA mixtures were prepared by adding the desired amounts of water

2. EXPERIMENTAL SECTION 2.1. Materials. Lactose, malonic acid, adipic acid, propionic acid, hexanoic acid, 1-dodecanamine, methanol, and ethanol were analytical grade from Sinopharm Chemical Reagent Co. Ltd. (Shanghai, China). Ethidium bromide (EB, molecular biology grade) and pyrene (98%) were bought from Sigma-Aldrich, St. Louis, MO, USA. The descriptions of the chemicals employed are summarized in Table 1. The DNA used in the present study is plasmid DNA PεcRNAP, a generous gift from Prof. M. E. Harris (Case Western Reserve University, Cleveland, OH, USA). PεcRNAP is used to generate Escherichia coli (E. coli) RNase P RNA by in vitro transcription, and it is coiled, having ca. 3000 bp.28 The water used was deionized. 2.2. Preparation of Lactosylammonium Surfactant. The synthesis of lactosylammonium surfactant was shown in Scheme 1. The detailed procedure was as follows. N-Dodecyllactosylamine (1) was prepared first based on previous works.29,30 To 2.0 mmol of lactose in 4 mL of distilled water was added 3.0 mmol of 1-dodecanamine in 8 mL of methanol. After 24 h of stirring at 25−30 °C, the mixture was heated to 45−50 °C for 3 h first and then cooled and filtered. The precipitate was purified by recrystallization from ethanol twice, and N-dodecyllactosylamine was obtained as white powder at yield of 54% (mp, 125−126 °C). Then, di(N-dodecyllactosylammonium) dicarboxylates (2a,b) and N-dodecyllactosylammonium monocarboxylates (3a,b) could be prepared stoichiometrically by adding 1 mmol of dicarboxylic acids (or 2 mmol of monocarboxylic acids) into 2 mmol of 1 in 48 mL of methanol. After 2 days of stirring at room temperature, methanol was removed and the precipitate was washed with acetone twice first and then with n-hexane. The products di(N-dodecyllactosylammonium) dicarboxylates (or N-dodecyllactosylammonium carboxylates) were dried under vacuum and obtained as pale-yellow solid. Since they were very hygroscopic, they were kept at −18 °C or lower. The structures of the products were checked by 1H NMR spectroscopy and elemental analysis. Di(N-dodecyllactosylammonium) Malonate (2a). Yield: 66%. [α]D16: +30.82° (c, 0.088 mol·kg−1; H2O). Here c means the Table 1. Sample Source and Purity

a

chemical name

source

purity (mass fraction)

purification method

lactose malonic acid adipic acid propionic acid hexanoic acid 1-dodecanamine methanol ethanol ethidium bromide pyrene di(N-dodecyllactosylammonium) malonate

Solarbio Life Sciences, PRCa Sinopharm Chemical Reagent Co., PRC Sinopharm Sinopharm Sinopharm Sinopharm Sinopharm Sinopharm Sigma Aldrich synthesis

analytical reagent 98.0% 99.5% 99.5% 99.5% chemically pure 99.5% 99.7% molecular biology grade powder 98% 98%

recrystallization

di(N-dodecyllactosylammonium) adipate

synthesis

98%

recrystallization

N-dodecyllactosylammonium propionate

synthesis

98%

recrystallization

N-dodecyllactosylammonium hexanoate

synthesis

98%

recrystallization

analysis method

1

H NMR and elemental analyses 1 H NMR and elemental analyses 1 H NMR and elemental analyseis 1 H NMR and elemental analyses

PRC = People’s Republic of China. 2970



Article

Scheme 1. Synthesis for N-Dodecyllactosylammonium Surfactant with Carboxylate as Counterion

measure the microenvironmental polarity of micelles. A Shimadzu F4500 fluorescence spectrophotometer was used to record the fluorescence spectra of pyrene, and the excitation wavelength was 336 nm. 2.8. EB Exclusion. Ethidium bromide (EB) and cationic species both can bind to DNA, and the competitive binding is utilized to study the interaction between DNA and cationic surfactant.32 The fluorescence spectra of EB were determined with a Shimadzu F4500 fluorescence spectrophotometer, and the excitation and emission wavelengths were 500 and 595 nm, respectively. 2.9. Circular Dichroism Spectroscopy. Circular dichroism (CD) experiments were carried out on a Jasco J-810 spectrometer. CD spectra were recorded between 220 and 320 nm, using a step interval of 0.5 nm, an integration time of 0.5 s, and a bandwidth of 1.0 nm. The scanning rate was 20 nm/min, and four scans were averaged. The path length of the quartz cuvette used was 1 cm.

and the stock solutions of surfactant and DNA successively in a test tube. The stock solution of DNA was prepared in water, and the DNA concentration was determined from the UV spectrum at 260 nm and expressed as nucleotide (1 μM nucleotide is ca. 330 μg/L). Unless indicated otherwise, all of the samples were equilibrated for 1 h at 25.0 ± 0.1 and/or 50.0 ± 0.1 °C before measurements. 2.4. Surface Tension Measurements. The surface tension of each surfactant solution was measured at 25.0 ± 0.1 and/or 50.0 ± 0.1 °C using pendant drop method on an optical contact angle measuring instrument (DataPhysics, Filderstadt, Germany). Each surface tension value (γ) was determined from at least six consistent measured values. The surface tension curve was repeated three times, and the relative standard uncertainty was 0.01. 2.5. Determination of Conductivity. A conductor meter (DDS-11A, Shanghai Weiye Apparatus Co., China) was used to measure the conducttivity of surfactant aqueous solution. Before measurement, the instrument was calibrated by 0.1 mol/L KCl solution. The measurement was carried out at 25.0 ± 0.1 and/or 50.0 ± 0.1 °C. 2.6. ζ-Potential Measurements. ζ potential characterization of micellar surface charge was carried out with a ZetaSizer Nano Series Nano ZS (Malvern Instruments). 2.7. Determination of Microenvironmental Polarity. Pyrene was chosen as the probe to determine the microenvironmental polarity of the system.31 It has five emission peaks, which are marked 1−5 from the shortest wavelength peak. The ratio (I1/I3) of the intensity for the first peak to that for the third one is sensitive to pyrene environment and can be used to

3. RESULTS It has been found that glucosylamine is unstable, labile to hydrolysis or isomerization in the aqueous solutions of acetic acid, HCl, and NaOH.29,30 Therefore, glucosamines or lactosamines have been generally produced (where the C1−O bond in the sugar moiety is broken).8,9,22,23 However, our previous study25 indicated that glucosylamine could form stable salts with dicarboxylic acids (malonic acid, succinic acid, and adipic acid) and the C1−O bond remained intact, but no precipitate could be 2971



Article

counterions are similar and remain almost unchanged when the temperature is increased from 25.0 to 50.0 °C. 3.1.2. Surface Tension Study. The equilibrium surface tension (γ) of the aqueous solution of lactosylammonium with dicarboxylate ion as counterion (2a,b) was measured at both 25.0 and 50.0 °C (Figure 2). The surface tension was decreased with increasing surfactant concentration first and then reached a plateau. The concentration at the break point was taken as the cmc (listed in Table 2). It can be seen from Figure 2 that 2a has a little higher cmc than 2b, similar to the result from Figure 1. The surface tension at the cmc (γcmc) was 28.4 (or 25.6) mN/m for 2a at 25.0 (or 50.0) °C and 33.0 (or 31.7) mN/m for 2b at 25.0 (or 50.0) °C. Therefore, the counterion malonate could lead to a lower γcmc than adipate. One may notice the difference between the surface-tensionbased cmc and the conductivity-based cmc for 2b at 50.0 °C. It should be mentioned here that various experimental methods may see different thresholds for micellization.34 The conductivity of the solution decreases at the cmc owing to the lower mobility of the larger micelles, while surface-tension-based cmc is measured because the surface tension is sensitive to the adsorption of surfactant at the surface, which sometimes could lead to the conductivity-based cmc being higher than the surface-tensionbased cmc.35−37 The saturated adsorption values (Γmax) and the minimum area per surfactant molecule (Amin) at the air/water surface were obtained from the slope of the plot of surface tension vs logarithm of surfactant concentration by using the Gibbs adsorption isotherm (eqs 3 and 4).34

obtained in the glucosylamine/monocarboxylic acid system. In the present study, we found that N-dodecyllactosylamine and carboxylic acids, including both monocarboxylic acids (propionic acid and hexanoic acid) and dicarboxylic acids (malonic acid and adipic acid), stoichiometrically gave stable salts N-dodecyllactosylammoniums as pale-yellow powder (section 2.2). Moreover, the optical rotations, conductivities, and surface tensions for their aqueous solutions remained almost unchanged with time (the longest experimental time spans for conductivity, surface tension, and optical rotation measurements were 16 days, 119 h, and 93 h). Thus, it is reasonable for us to study the micellization behavior of these lactosylammonium surfactants. 3.1. Micellization of Lactosylammonium Surfactant with Dicarboxylate as Counterion. 3.1.1. Conductance Study. Figure 1 shows the dependence of the conductivity (κ) of

Γmax = −

A min =

dγ 1 nRT d ln C

1 NA Γmax

(4) −1

lactosylammonium with dicarboxylate as counterion (2a,b) on its concentration at 25.0 and 50.0 °C, according to which, κ is increased rapidly first and then slowly with the increase of the concentration of surfactant. The inflection represents the critical micelle concentration (cmc; Table 2). It can be seen from Table 2 that the values of cmc at 25.0 °C are similar to those at 50.0 °C and the cmc with malonate as counterion is a little higher than that with adipate as counterion. Based on the slopes of the straight lines with surfactant concentrations lower and higher than cmc,33 the micelle ionization degree (α) and counterion binding degree (β) can be obtained from eqs 1 and (2) and are listed in Table 2. (1)

α = S2/S1

(2)

−1

Here R = 8.314 J·mol ·K , NA was Avogadro’s number, and n was set to be 2. Table 2 listed these parameters, from which we could know that 2a had a smaller Amin and a higher Γmax than 2b. C20 represented the surfactant concentration required to decrease the surface tension by 20 mN/m, and the cmc/C20 ratio was a measure of the tendency for surfactant to form aggregates relative to be adsorbed at the air/water surface.38 It could be seen from Table 2 that the surfactants 2a and 2b had a similar cmc/C20. 3.2. Micellization of Lactosylammonium with Monocarboxylate as Counterion. Due to the low solubilities of 3a and 3b at 25.0 °C, the experiments were conducted at 50.0 °C (Figures 3 and 4). The data were listed in Table 2. From Table 2, the surfactants with monocarboxylates as counterions (3a,b) had a much lower cmc compared with those having dicarboxylates as counterions (2a,b), and the cmc with propionate as counterion (3a) was lower than that with hexanoate as counterion (3b). In addition, the surfactant 3a had a lower cmc/C20 than 3b, which had a cmc/C20 similar to those of 2a and 2b. The micelle ionization degree (α) and counterion binding degree (β) for the surfactants were calculated according to eqs 1 and 2 and listed in Table 2. Compared with dicarboxylate ion, monocarboxylate ion could result in a much lower β, and the less carbon atoms the monocarboxylate had, the lower the value of β was. In addition, the mean ζ potentials for the micellar surface charges were found to be ca. 11−15 mV with malonate and

Figure 1. Dependence of the conductivity of surfactant aqueous solution on surfactant concentration at 25.0 (open symbols) and 50.0 °C (solid symbols). Surfactant: 2a (top) and 2b (bottom). The regression range can be seen from the straight line, and the regression constants exceed 0.99.

β=1−α

(3)

Here, S1 and S2 represent the slopes of the straight lines before and after the inflection, respectively. It can be seen from Table 2 that the values of α and β with the two dicarboxylates as 2972



Article

Table 2. Surface Activity of N-Dodecyllactosylammonium Surfactant in Watera

a b

surfactant

2a

2b

2a

2b

3a

3b

t/°C cmcb/(mmol·kg−1) cmcc/(mmol·kg−1) γcmc/(mN·m−1) Amin/(nm2·molecule−1) Γmax/(μmol·m−2) C20/(mmol·kg−1) cmc/C20 ζ potential/mV α β

25.0 8.85 8.36 28.4 0.50 3.34 1.95 4.29 11 0.13 0.87

25.0 7.68 7.08 33.0 0.64 2.60 1.54 4.60 15 0.13 0.87

50.0 8.98 8.51 25.6 0.58 2.87 1.88 4.53 10 0.12 0.88

50.0 7.70 5.40 31.7 0.73 2.27 1.29 4.19 13 0.14 0.86

50.0 1.47 1.31 29.8 0.39 4.21 0.63 2.08 33 0.86 0.14

50.0 3.42 3.35 26.2 0.63 2.65 0.77 4.35 26 0.51 0.49

Standard uncertainty u is u(t) = 0.1 °C, u(γcmc) = 0.5 mN/m, relative standard uncertainties ur are ur(cmc) = 0.1, and ur(Amin) = 0.07. conductivity-based cmc. csurface tension-based cmc.

Figure 2. Surface tension as a function of surfactant concentration in water at 25.0 (open symbols) and 50.0 °C (solid symbols). Surfactant: 2a (top) and 2b (bottom). The regression range can be seen from the straight line, and the regression constants exceed 0.99.

Figure 3. Conductivity (top) and surface tension (bottom) for the aqueous solution of 3a as a function of surfactant concentration at 50.0 °C. The regression range can be seen from the straight line, and the regression constants exceed 0.99.

adipate as the counterions and ca. 33 and 26 mV with propionate and hexanoate as the counterions, respectively, suggesting that these carboxylate ions should show different effects on shielding the surface charge. 3.3. Interaction between Lactosylammonium Surfactant and DNA. Pyrene has been widely used as a probe for the interactions between surfactant and polymers.31 The value of I1/I3 is sensitive to the polarity of the microenvironment where pyrene is located; it decreases with decreasing microenvironmental polarity. In surfactant aqueous solution, the apparent value of I1/I3 should be controlled by the contributions of I1/I3 for pyrene molecules located in the surfactant aggregates and in water. Open symbols in Figure 5 showed the I1/I3 of pyrene in lactosylammonium surfactant aqueous solution. It could be seen that as the surfactant concentration increased to a critical value, the I1/I3 began to decrease because pyrene started to move to hydrophobic sites (mostly due to premicelle formation) and the polarity of a hydrophobic medium was lower than that of an

aqueous medium. At the surfactant concentration above the cmc, the I1/I3 value stabilized as pyrene accumulated in the micelle hydrophobic moieties. In the presence of DNA, the apparent value of I1/I3 was controlled by the contributions of I1/I3 for pyrene molecules located in (1) surfactant aggregates on DNA, (2) pure surfactant aggregates, and (3) water. Compared with the case without DNA (Figure 5, open symbols), the I1/I3 ratio with DNA (Figure 5, solid symbols) began to decrease sharply when surfactant concentration was very low (C1). C1 should indicate the formation of the hydrophobic domain in solution. Since surfactant behaves like a separate phase when contacting with DNA,39−41 C1 should be defined as the cac (critical aggregation concentration) of surfactant on DNA. Owing to the electrostatic attraction between the oppositely charged surfactant molecules and DNA, the effective concentration of surfactant around DNA should be 2973



Article

hydrophobic the counterion (given the number of carboxylate ion was the same), the lower the cac value is. With the further increase of surfactant concentration, the I1/I3 ratio was decreased gradually for 2a/DNA and 3a/DNA systems and became close to that in the DNA-free solution; the two curves were finally almost overlapping (Figure 5a,c, solid symbols vs open symbols). The number of surfactant aggregates on DNA should be increased with surfactant concentration, resulting in more pyrene molecules incorporated into the aggregates. As a result, I1/I3 was decreased with increasing surfactant concentration. Moreover, surfactant molecules could aggregate in water when DNA was saturated with surfactant molecules, and thus, pyrene might transfer into the hydrophobic domain formed by the surfactant molecules. Therefore, the I1/I3 ratio gradually became coincident with that in DNA-free solution. As for 2b/DNA and 3b/DNA systems, at the surfactant content higher than C1, the I1/I3 ratio was decreased first with the increase of surfactant content, reaching a plateau at C2, and at the surfactant concentration higher than C3, the I1/I3 ratio was gradually close to that in the DNA-free solution, and finally, the two curves were almost overlapping (Figure 5b,d, solid symbols vs open symbols). Similar to the discussion for 2a/DNA and 3a/DNA systems, the decreased I1/I3 between C1 and C2 should be due to that more pyrene molecules could be incorporated into the surfactant aggregates on DNA (since with increasing surfactant concentration, more aggregates could form on DNA). Furthermore, once all (or most) pyrene molecules were located into the aggregates on DNA, the I1/I3 ratio should be almost unchanged (Figure 5b,d, at surfactant concentrations between C2 and C3). The change in I1/I3 at surfactant concentration higher than C3 should be due to the transfer of pyrene molecules into pure surfactant aggregates from surfactant aggregates on DNA, similar to the discussion for 2a/DNA and 3a/DNA systems. Compared with the case for 2a/DNA and

Figure 4. Conductivity (top) and surface tension (bottom) for the aqueous solution of 3b as a function of surfactant concentration at 50.0 °C. The regression range can be seen from the straight line, and the regression constants exceed 0.99.

higher than that in the bulk phase, so the cac of surfactant on DNA could be much lower than the cmc in the absence of DNA. According to Figure 5, it could be seen that the values of C1 for the 2a/DNA, 2b/DNA, 3a/DNA, and 3b/DNA systems were ca. 100, 40, 200, and 100 μM, respectively. Therefore, the stronger

Figure 5. Dependence of microenvironmental polarities for pyrene on surfactant concentration in the absence (symbol ○) and presence (symbol ■; 0.12 mmol·kg−1) of DNA. Surfactant: 2a (a), 2b (b), 3a (c), and 3b (d). 2974



Article

Figure 6. Fluorescence intensities (FL) of EB at 595 nm in surfactant aqueous solution (symbols ☆) and surfactant/DNA (0.12 mmol·kg−1) mixed solution (symbols △) with surfactant concentration. Symbols □ represent the fluorescence intensities of surfactant aqueous solutions. Surfactant: 2a (a), 2b (b), 3a (c), and 3b (d).

same, a shorter alkyl chain leads to a smaller Amin (Table 2, 2a vs 2b, and 3a vs 3b). We25 recently found that glucosylammonium with malonate as counterion had a bigger Amin than that with adipate as counterion. The comparison of these data may indicate the role of hydrogen bonding in the properties of lactosylammonium surfactants. Usually, the properties of surfactants are controlled mainly by electrostatic, van der Waals, hydrophobic, steric interactions and their delicate balance. Lactose is 1,4-β-disaccharide. Compared with glucose, the end galacto unit of lactose with an axial C4-OH and the glycosidic linkages modify and enhance the hydrogenbonding interaction within the hydrophilic region.21 The hydrogen bonding may weaken the electrostatic repulsion between ammonium groups. Therefore, the ammonium groups of lactosylammonium adsorbed at the air/water surface should bind less counterions than gluosylammonium. As a result, the Amin for 2a (or 2b) is not bigger than that for the glucosylammonium with the same counterion (i.e., 0.77 nm2 with malonate as counterion or 0.64 nm2 with adipate as counterion25) although lactose is bigger than glucose. Further, the difference in the values of Amin for lactosylammoniums should be due to the different abilities of the counterions to bind with an ammonium group. The hydration degree for −OOCCH2COO− (or −OOCCH2CH3) is higher than that for −OOC(CH2)4COO− (or −OOC(CH2)4CH3), making the tendency for −OOCCH2COO− (or −OOCCH2CH3) binding with lactosylammonium lower. As a result, the Amin for 2a (or 3a) is smaller than that for 2b (or 3b). As for glucosylammonium surfactant, the hydrogen bonding should be not so strong and may not weaken the repulsive force between the headgroups so effectively, and the binding between the headgroup and the counterion should play an important role in shielding the repulsive force between the headgroups. Therefore, the glucosylammonium with malonate as the counterion has

3a/DNA systems, the existence of the plateau for 2b/DNA and 3b/DNA systems might indicate that these two systems showed higher capability to solubilize pyrene molecules. Ethidium bromide (EB) is a cationic dye. It can intercalate into DNA molecules and emit strong fluorescence. The addition of surfactant into DNA/EB solution can decrease the fluorescence intensity rapidly at first, and then when the binding of surfactant to EB− DNA complex reaches equilibrium, the further increase of surfactant concentration changes the fluorescence intensity little.39 So EB can also be used to study the interaction of DNA with surfactants.32,42 In the present study, the fluorescence intensities for surfactant solution and EB/surfactant solution (symbols □ and ☆, Figure 6) were both very weak, and that for DNA/surfactant/EB solution was decreased with increasing surfactant concentration very fast first (symbols Δ, Figure 6), and when the concentration of surfactant reached 2.0 mmol·kg−1 for 2a/DNA and 2b/DNA systems and ca. 1.5 mmol·kg−1 for 3a and 3b/DNA systems, the fluorescence intensity was the lowest, dropping to ca. 10% of its initial value. When surfactant content became further higher, the fluorescence intensity was observed stronger, ca. 40% of the initial value for 2a/DNA and 2b/DNA systems at the surfactant content being ca. 8 mmol·kg−1 and ca. 50% of the initial value for 3a /DNA and 3b/DNA systems at the surfactant content being ca. 2.5−3.0 mmol·kg−1. Figure 7 showed the CD spectra of DNA. With the increase of surfactant content, the CD signals of DNA became decreased first (red curve vs black curve, Figure 7) and then strengthened somewhat (green and blue curves vs black curve).

4. DISCUSSION The four lactosylammonium surfactants could decrease the surface tension of water to ca. 30 mN/m (Figures 2−4 and Table 2). When the number of carboxylate groups in the counterion is the 2975



Article

Figure 7. CD spectra of DNA (0.12 mmol·kg−1) in surfactant aqueous solution. Surfactant: 2a (a), 2b (b), 3a (c), and 3b (d).

a bigger Amin than that with adipate as the counterion since the hydration degree for −OOCCH2COO− is higher than that for − OOC(CH2)4COO−.25 It was reported that nonionic surfactant N-dodecyl-N-lactobionylethylenediamine had an Amin of 0.39 nm214 and N-dodecyl-N-methyllactobionamide had an Amin of 0.42 nm2,12 similar to that for 3a, further indicating that the hydrogen bonding in lactosylammonium could shield the electrostatic repulsion very effectively. Since 2a has a smaller Amin than 2b, it is reasonable to think that molecules 2a should be packed more densely than 2b at the air/water surface and hence, 2a can decrease the surface tension to a lower value than 2b. However, one may notice that 3b decreases the surface tension more effectively than 3a although 3a is smaller than 3b. This may be due to the location of the counterion (i.e., hexanoate) at the surface, with its hydrophobic chain -(CH2)4CH3 into air. Among the four lactosylammoniums, 3a has the lowest cmc/C20 (Table 2). A higher cmc/C20 ratio indicates that the hydrophobic groups are less suitably oriented in the interior of the aggregates.38 Therefore, the surfactant 3a should have the greatest preference to aggregate in water among the four surfactants. Once the adsorption at the surface gets saturated, surfactant molecules will aggregate in the bulk. Generally, multivalent counterions can decrease the cmc of ionic surfactants more than monovalent counterions.43 cmc can also be decreased once charged headgroups of surfactants are linked with spacers (for example, -(CH2)n- group), due to the decreased repulsive force among the headgroups.13 However, as for the lactosylammonium surfactants in the present study, the surfactants with monocarboxylates as counterions (3a and 3b) have much lower values of cmc than those with dicarboxylates as counterions (2a and 2b, Table 2). From Table 2, 3a and 3b also have much lower values of β than 2a and 2b. This seems that a lower β may result in a lower cmc. Dicarboxylates have a higher negative charge density than monocarboxylates, and hence, the electrostatic attraction between

dicarboxylate ion and the headgroup is stronger. This should be bad for the lactosylammonium aggregation and increase cmc. When the counterion is monocarboxylate, the hydration degree for − OOCCH2CH3 should be higher than that for −OOC(CH2)4CH3 and, thus, −OOC(CH2)4CH3 may bind with lactosylammonium more strongly (due to both electrostatic interaction and hydrophobic interaction) and makes cmc higher. In addition, although the micelles from 2a and 2b have a similar β, the cmc for 2b is a little lower than that for 2a. This may be due to the hydrophobic interaction between -(CH2)4- of adipate and the hydrophobic chain of the surfactant. Moreover, the cmc value for lactosylammoniums is higher than that for glucosylammoniums, given the counterion is the same. This should be due to the higher hydrophilicity of the lactosyl group than the glucosyl group. The ζ potential for the micelle is also related to the value of β. The value of β for the micelle from 3a is the lowest, followed by that from 3b, and then from 2a and 2b. Correspondingly, the ζ potential for the micelle from 3a is the highest, ca. 33 mV, followed by that for the micelle from 3b, which is ca. 25 mV, and the micelles from 2a and 2b have the lowest positive surface charge (ca. 10−15 mV). The apparent I1/I3 ratio of pyrene in the surfactant/DNA system is controlled by the contributions of I1/I3 in water, in surfactant aggregates on DNA, and in pure surfactant aggregates. From Figure 5, the lactosylammonium surfactants should be easier to aggregate on DNA in the presence of higher hydrophobic counterion (since the cac for 2b (or 3b) is lower than that for 2a (or 3a)). This should be a result of competitive bindings of DNA and dicarboxylate (or monocarboxylate) group with lactosylammonium. Moreover, there is a plateau between C2 and C3 in Figure 5b,d, while I1/I3 is continuously decreased until the data with DNA become coincident with that without DNA (Figure 5a,c), suggesting that 2b/DNA and 3b/DNA systems show higher capability to solubilize pyrene molecules than 2a/DNA and 3a/DNA systems. 2976



■

It has been well-known that DNA can become compacted in the presence of cationic surfactants.39−41 According to Figures 6 and 7, this was true for lactosylammoniums at low content since low content of the surfactant could decrease the fluorescence intensity for EB and the CD signal of DNA. However, at high content, lactosylammoniums could make DNA unfold since the fluorescence intensity of EB and the CD signal of DNA both became strengthened. Recently, we studied the interaction of glucosylammonium with DNA, and the result showed that glucosylammonium only promoted DNA compacted. By combining these results, we argued that the more hydroxyl groups and stronger hydrogen bonding in the presence of lactosyl should play a key role. However, a detailed explanation needs more thorough and delicate experiments, which should be proceeded with in the future.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.5b01057. Conductivities, surface tensions, dependence of I1/I3 of pyrene on molality, fluorescence intensities, and 1H NMR spectra, (PDF)

■

REFERENCES

(1) Claesson, M.; Kjellin, U. R. M. Sugar Surfactants. In Encyclopaedia of Surface and Colloid Science; Marcel Dekker: New York, 2002; pp 4909−4925. (2) Dal Bó, A. G.; Soldi, V.; Giacomelli, F. C.; Jean, B.; PignotPaintrand, I.; Borsali, R.; Fort, S. Self-Assembled Carbohydrate-Based Micelles for Lectin Targeting. Soft Matter 2011, 7, 3453−3461. (3) Gao, C.; Millqvist-Fureby, A.; Whitcombe, M. J.; Vulfson, E. N. Regioselective Synthesis of Dimeric (Gemini) and Trimeric SugarBased Surfactants. J. Surfactants Deterg. 1999, 2, 293−302. (4) Laurent, P.; Razafindralambo, H.; Wathelet, B.; Blecker, C.; Wathelet, J. P.; Paquot, M. Synthesis and Surface-Active Properties of Uronic Amide Derivatives, Surfactants from Renewable Organic Raw Materials. J. Surfactants Deterg. 2011, 14, 51−63. (5) Imura, T.; Kawamura, D.; Morita, T.; Sato, S.; Fukuoka, T.; Yamagata, Y.; Takahashi, M.; Wada, K.; Kitamoto, D. Production of Sophorolipids from Non-edible Jatropha Oil by Stamerella Bombicola NBRC 10243 and Evaluation of Their Interfacial Properties. J. Oleo Sci. 2013, 62, 857−864. (6) Janek, T.; Łukaszewicz, M.; Krasowska, A. Identification and Characterization of Biosurfactants Produced by the Arctic Bacterium Pseudomonas Putida BD2. Colloids Surf., B 2013, 110, 379−386. (7) Gan, C. S.; Wang, H. S.; Zhao, Z. Z.; Yin, B. Sugar-Based Ester Quaternary Ammonium Compounds and Their Surfactant Properties. J. Surfactants Deterg. 2014, 17, 465−470. (8) Blanzat, M.; Perez, E.; Rico-Lattes, I.; Lattes, A. Synthesis and AntiHIV Activity of Catanionic Analogs of Galactosylceramide. New J. Chem. 1999, 23, 1063−1065. (9) Blanzat, M.; Perez, E.; Rico-Lattes, I.; Prome, D.; Prome, J. C.; Lattes, A. New Catanionic Glycolipids. 1. Synthesis, Characterization, and Biological Activity of Double-Chain and Gemini Catanionic Analogues of Galactosylceramide (galβ1cer). Langmuir 1999, 15, 6163−6169. (10) Schuster, T.; Schellenberger, S.; Friedrich, R.; Klapper, M.; Müllen, K. Branched Fluorinated Amphiphiles Based on Carbohydrates. J. Fluorine Chem. 2013, 154, 30−36. (11) Salman, S. M.; Heidelberg, T.; Tajuddin, H. A. B. N-Linked Glycolipids by Staudinger Coupling of Glycosylated Alkyl Diazides with Fatty Acids. Carbohydr. Res. 2013, 375, 55−62. (12) Wilk, K. A.; Syper, L.; Burczyk, B.; Maliszewska, I.; Jon, M.; Domagalska, B. W. Preparation and Properties of New Lactose-Based Surfactants. J. Surfactants Deterg. 2001, 4, 155−161. (13) Wilk, K. A.; Laska, U.; Zielińska, K.; Olszowski, A. Fluorescence Probe Studies upon Microenvironment Characteristics and Aggregation Properties of Gemini Sugar Surfactants in an Aquatic Environment. J. Photochem. Photobiol., A 2011, 219, 204−210. (14) Yoshimura, T.; Ishihara, K.; Esumi, K. Sugar-Based Gemini Surfactants with Peptide Bonds-Synthesis, Adsorption, Micellization, and Biodegradability. Langmuir 2005, 21, 10409−10415. (15) Bize, C.; Blanzat, M.; Rico-Lattes, I. Self-Assembled Structures of Catanionic Associations: How to Optimize Vesicle Formation? J. Surfactants Deterg. 2010, 13, 465−473. (16) Yoshimura, T.; Umezawa, S.; Fujino, A.; Torigoe, K.; Sakai, K.; Sakai, H.; Abe, M.; Esumi, K. Equilibrium Surface Tension, Dynamic Surface Tension, and Micellization Properties of Lactobionamide-Type Sugar-Based Gemini Surfactants. J. Oleo Sci. 2013, 62, 353−362. (17) Pasc-Banu, A.; Blanzat, M.; Belloni, M.; Perez, E.; Mingotaud, C.; Rico-Lattes, I.; Labrot, T.; Oda, R. Spontaneous Vesicles of Single-Chain Sugar-Based Fluorocarbon Surfactants. J. Fluorine Chem. 2005, 126, 33− 38. (18) Ahmad, N.; Ramsch, R.; Esquena, J.; Solans, C.; Tajuddin, H. A.; Hashim, R. Physicochemical Characterization of Natural-Like Branched-Chain Glycosides toward Formation of Hexosomes and Vesicles. Langmuir 2012, 28, 2395−2403. (19) Chester, M. A. Nomenclature of Glycolipids (IUPAC Recommendations 1997). Pure Appl. Chem. 1997, 69, 2475−2487. (20) Baccile, N.; Babonneau, F.; Jestin, J.; Pehau-Arnaudet, G.; Van Bogaert, I. Unusual, pH-Induced, Self-Assembly of Sophorolipid Biosurfactants. ACS Nano 2012, 6, 4763−4776.

5. CONCLUSION Four lactosylammonium surfactants were prepared in the present study, with the counterions being dicarboxylates (−OOCCH2COO− and −OOC(CH2)4COO−) and monocarboxylates (−OOCCH2CH3 and −OOC(CH2)4CH3). Hydrogen bonding, electrostatic interaction, hydrophobic interaction, and their delicate balance controlled the properties of the surfactants. As a result, the surfactants with monocarboxylates as counterions have much lower values of cmc and β than those with dicarboxylates as counterions, and when the number of carboxylate groups in the counterion is the same, a shorter alkyl chain leads to a smaller Amin. Moreover, dicarboxylate can shield the surface charge of lactosylammonium micelles more effectively than monocarboxylate. The counterion also affects the binding of surfactant with DNA; the lactosylammonium surfactant should be easier to aggregate on DNA in the presence of higher hydrophobic counterion. The aggregates formed by DNA and lactosylammonium with adipate and hexanoate as counterions show higher capability to solubilize pyrene molecules than those with malonate and propionate as counterions. Furthermore, a low content of the lactosylammonium could decrease the CD signal of DNA, while a high content of surfactant could make the CD signal recover somewhat.

■

Article

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.: +86-0514-87975590-9513. Fax: +86-0514-87975244. Funding

This study is supported by the National Natural Scientific Foundation of China (Grant Nos. 21073155 and 21373179), the Jiangsu Provincial Natural Scientific Foundation (Grant No. BK2010308), and a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD). Notes

The authors declare no competing financial interest. 2977



Article

(21) Hashim, R.; Sugimura, A.; Minamikawa, H.; Heidelberg, T. Nature-Like Synthetic Alkyl Branched-Chain Glycolipids: A Review on Chemical Structure and Self-Assembly Properties. Liq. Cryst. 2012, 39, 1−17. (22) Soussan, D.; Mille, C.; Blanzat, M.; Bordat, P.; Rico-Lattes, I. Sugar-Derived Tricatenar Catanionic Surfactant: Synthesis, SelfAssembly Properties, and Hydrophilic Probe Encapsulation by Vesicles. Langmuir 2008, 24, 2326−2330. (23) Vivares, D.; Soussan, E.; Blanzat, M.; Rico-Lattes, I. SugarDerived Tricatenar Catanionic Surfactant: Self-Assembly and Aggregation Behavior in the Cationic-Rich Side of the System. Langmuir 2008, 24, 9260−9267. (24) Wan, J.; Li, Y.; Li, Y.; Guo, X. Micellization of N-dodecylglucosylamine and Its Interaction with DNA in the Presence of Carboxylic Acid. Colloid Polym. Sci. 2015, 293, 2599−2608. (25) Li, Y. M.; Zhang, X. H.; Li, Y.; Li, C.; Guo, X. Micellization of Glucose-Based Surfactants with Different Counter Ions and Their Interaction with DNA. Colloids Surf., A 2014, 443, 224−232. (26) Luo, J.; Solimini, N. L.; Elledge, S. J. Principles of Cancer Therapy: Oncogene and Non-Oncogene Addiction. Cell 2009, 136, 823−837. (27) Guo, X.; Huang, L. Recent Advances in nonviral Vectors for Gene Delivery. Acc. Chem. Res. 2012, 45, 971−979 and references cited therein. (28) Guo, X.; Campbell, F. C.; Sun, L.; Christian, E. L.; Anderson, V. E.; Harris, M. E. RNA-Induced Folding and Stabilization of the C5 Protein during Assembly of the RNase P. J. Mol. Biol. 2006, 360, 190− 203. (29) Pigman, W.; Cleveland, E. A.; Couch, D. H.; Cleveland, J. H. Reactions of Carbohydrates with Nitrogenous Substances. I. Mutarotations of Some Glycosylamines. J. Am. Chem. Soc. 1951, 73, 1976− 1979. (30) Lockhoff, O.; Stadler, P. Syntheses of Glycosylamides as Glycolipid Analogs. Carbohydr. Res. 1998, 314, 13−24. (31) Wilk, K. A.; Laska, U.; Zielinska, K.; Olszowski, A. Fluorescence Probe Studies upon Microenvironment Characteristics and Aggregation Properties of Gemini Sugar Surfactants in an Aquatic Environment. J. Photochem. Photobiol., A 2011, 219, 204−210. (32) Dupuy, N.; Pasc, A.; Parant, S.; Fontanay, S.; Duval, R. E.; Gerardin, C. Amino-Ethoxilated Fuorinated Amphiphile: Synthesis, Self-Assembling Properties and Interactions with ssDNA. J. Fluorine Chem. 2012, 135, 330−338. (33) Liu, W.; Guo, X.; Guo, R. The Interaction between Hemoglobin and Two Surfactants with Different Charges. Int. J. Biol. Macromol. 2007, 41, 548−557 and references cited therein. (34) Hiemenz, P. C.; Rajagopalan, R. Principles of Colloid and Surface Chemistry, 3rd ed.; Marcel Dekker: New York, 1997. (35) Liang, Y.; Hu, Z.; Cao, D. Surface Adsorption and Aggregation Properties of Novel L-Lysine-Based Gemini Surfactants. J. Surfactants Deterg. 2014, 17, 693−701. (36) Patial, P.; Shaheen, A.; Ahmad, I. Synthesis of Ester Based Cationic Pyridinium Gemini Surfactants and Appraisal of Their Surface Active Properties. J. Surfactants Deterg. 2013, 16, 49−56. (37) Zhang, X.; Peng, X.; Ge, L.; Yu, L.; Liu, Z.; Guo, R. Micellization Behavior of the Ionic Liquid Lauryl Isoquinolinium Bromide in Aqueous Solution. Colloid Polym. Sci. 2014, 292, 1111−1120. (38) Rosen, M. J. Surfactants and Interfacial Phenomena, 2nd ed.; John Wiley & Sons: New York, 1989. (39) Zhao, X. F.; Shang, Y. Z.; Liu, H. L.; Hu, Y. Complexation of DNA with Cationic Gemini Surfactant in Aqueous Solution. J. Colloid Interface Sci. 2007, 314, 478−483. (40) Guo, X.; Li, H.; Zhang, F.; Zheng, S.; Guo, R. Aggregation of Single-Chained Cationic Surfactant Molecules into Vesicles Induced by Oligonucleotide. J. Colloid Interface Sci. 2008, 324, 185−191. (41) Dias, R. S.; Magno, L. M.; Valente, A.; Das, D.; Das, P. K.; Maiti, S.; Miguel, M. G.; Lindman, B. Interaction between DNA and Cationic Surfactants: Effect of DNA Conformation and Surfactant Headgroup. J. Phys. Chem. B 2008, 112, 14446−14452.

(42) Rudiuk, S.; Franceschi-Messant, S.; Chouini-Lalanne, N.; Perez, E.; Rico-Lattes, I. Modulation of Photo-Oxidative DNA Damage by Cationic Surfactant Complexation. Langmuir 2008, 24, 8452−8457. (43) Shinoda, K. Colloidal Surfactants: Some Physico-chemical Properties; Academic Press: New York, 1963; Chapter 1.

2978


Micellization of Lactosylammonium Surfactants with Different Counter

Recommend Documents