Liquid Membrane Oscillation of Water/Oil/Water System Containing TTAB and Recognition to Amino Acids

Transcription

1 CHEM. RES. CHINESE UNIVERSITIES 2009, 25(4), Liquid Membrane Oscillation of Water/Oil/Water System Containing TTAB and Recognition to Amino Acids ZHOU Li 1*, TANG Jiao-ning 2, LIU Bo 1 and WU Yi-guang 1 1. College of Chemistry and Chemical Engineering, 2. College of Materials Science and Engineering, Shenzhen University, Shenzhen , P. R. China Abstract The liquid membrane oscillation of a novel water(aqueous tetradecyl trimethyl ammoniumbromide, TTAB and alcohol solution)/oil(picric acid in chloroform solution)/water(aqueous glucose solution) system was investigated by means of a homemade device. The results show that the water(aqueous 7 mmol/l TTAB and 0.5 mol/l n-propanol solution)/oil(0.5 mmol/l icric acid in chloroform solution)/water(0.1 mol/l glucose solution) system performed sustained and stable oscillation at 30 C. The oscillation curve under optimized conditions is considered to be referent. Several oscillation curves were accumulated with the addition of different amino acids. The results showed that the novel system can recognize the added amino acids such as L-tryptophan, L-tyrosine, and D,L-tyrosine. And there is corresponding relationship between the change of curve shape and the quantity of amino acid added. Keywords Liquid membrane; Oscillation; Surfactant; Tetradecyl trimethyl ammoniumbromide; Amino acid Article ID (2009) Introduction In the life process the substance s metabolism usually performs as the electrochemical process. The important biological shift phenomena such as nerve impulse, heartbeat, brain rhythm and so on frequently take place in the mode of biomembrane oscillation [1]. Because of the complexity in biomembrane s component, structure and function, the observation and research in situ and at any moment are extremely difficult. The liquid membrane containing surfactant supply the simplest model for observing the oscillatory phenomenon, understanding the membrane dynamics and studying the relative electrochemistry [2]. The liquid membrane oscillation between two immiscible phases can be applied to simulating the electron transfer process in biomembrane; therefore the molecular recognition based on unique potential oscillation can be applied to simulating taste, olfaction and other physiological process, and chemical analysis. Thus the liquid membrane oscillation has aroused a widespread interest [3 7]. Dupeyrat et al. [8] first discovered the liquid membrane oscillator in 1978, whereafter many scholars joined this research. Two main mechanisms were proposed for liquid membrane oscillation. Marangoni effect based on interface hydrodynamics proposed by Dupeyra et al. [8] considers that the periodic interface oscillation is due to the alternate process of molecular convection, molecular diffusion, interface adsorption and desorption. And chemical reaction theory proposed by Yoshikawa et al. [9] considers that the surfactant and its coordinator(for example: picric acid) form ion pair complex on the interface. That greatly reduces surfactant s solubility in the aqueous phase, and obviously increases its solubility in the organic phase. When the surfactant on interface aggregates to a certain extent, the surfactant ion pair complex passes through the contact surface into organic phase, thus the periodic oscillation occurs [9]. Until now, only limited liquid membrane systems has been studied. The real mechanism for liquid membrane oscillation is still uncertain, and the experiment was generally carried out at room temperature [1 12]. In this work, a novel water(aqueous tetradecyl trimethyl ammoniumbromide, TTAB and alcohol solution)/oil(picric acid in chloroform solution)/water(aqueous glucose solution) liquid membrane oscillation system was established. By using a homemade device, the potential varieties at the interface of various liquid membranes were recorded via altering the concentrations of TTAB and picric acid, the types of alcohol and organic solvents, the temperature and other factors, and the sustained and *Corresponding author. zhoulili@szu.edu.cn Received November 21, 2008; accepted March 24, Supported by the Open Research Fund of Shenzhen Key Laboratory of Functional Polymer, China.

2 No.4 ZHOU Li et al. 523 rhythmic oscillations were observed, and the results were discussed. Based on the reliable basis curve of liquid membrane oscillation, the recognition of amino acids was also studied. 2 Experimental The homemade device is shown in Fig.1. First, 15 ml of an organic solution containing picric acid (with different concentrations as described later) was added into a beaker of 5 cm i.d. to form organic phase A. The hollow glass tube of 1 cm i.d.(fig.1, G) was immersed in the center of the organic solution with an immersion depth of less than 5 mm. Second, 30 ml of an aqueous D-glucose solution(0.1 mol/l) was added into the beaker carefully outside the hollow tube to form the aqueous phase B. Third, 2.6 ml of an aqueous TTAB solution(with different concentrations as described later) and 0.5 mol/l of alcohol were added to the inner tube very slowly via a injector to form another aqueous phase C. Potential measurement was made by using two salt bridges (Fig.1, F) which one end was placed very close to the interfaces, and another end was immersed in a 3 mol/l aqueous KCl solution(fig.1, E). The potential was measured with two platinum electrodes(fig.1, D). The recorded data were then collected by a computer via an LK1100 electrochemical analyzer. It is necessary to operate precisely in the experiment, and the results are the oscillation curves repeated at least 3 times. Fig.1 Schematic representation of experimental apparatus A: Organic solution containing picric acid; B: aqueous glucose solution; C: aqueous CTAB and alcohol solution; D: platinum electrode; E: aqueous KCl saturated solution; F: KCl bridge; G: glass tube. 3 Results and Discussion 3.1 Establishment of Novel Liquid Membrane Oscillation System The novel liquid membrane oscillation system was composed of water(aqueous tetradecyl trimethyl ammoniumbromide, TTAB and alcohol solution)/oil (picric acid in chloroform solution)/water(aqueous glucose solution). In order to obtain the optimized oscillation conditions, the oscillation curves of various liquid membranes were investigated at different temperature via altering the concentrations of TTAB and picric acid, types of alcohol and other organic solvents [13] Effect of TTAB Concentration The experiments show that no oscillation occurred below 3 mmol/l. Oscillation frequency and duration increase as TTAB concentration increases, but amplitude reduces as TTAB concentration increases further. With the observed phenomenon and the characteristics of the oscillation curve, the nature of liquid membrane oscillation can be explained by Marangoni effect combined with chemical reaction theory [14]. Therefore, the reduce of amplitude(as TTAB concentration increase further) can be considered to be the decrease of the transfer quantity of ion pair complex and the increase of the direct molecular convection due to excess TTAB Effect of Concentration of Picric Acid The experiments show that oscillation frequency, amplitude and duration increase as the concentration of picric acid reduces. If organic phase contained no picric acid, irregular vibration appeared [14]. This implies that picric acid with a certain concentration promotes sustained and steady oscillation. But a higher concentration of picric acid makes no sustained and steady oscillation. Perhaps it reduces the TTAB solubility in the organic phase Effect of Organic Phase The liquid membrane oscillation with chloroform, nitromethane, and the mixed organic solution of nitromethane and chloroform(volume ratio 1/1 and 3/7) as organic phases was investigated, respectively. Among these cases, oscillation curves with chloroform and nitromethane as organic phase possess greater amplitude, more sustained and steady oscillation. Compared with nitromethane, chloroform performs better. Because interface tension with chloroform and nitromethane as organic phase is higher than that with the mixed organic solution as organic phase, we speculate that the system with chloroform and nitromethane as organic phase becomes easy to deviate from equilibrium Effect of Alcohol The experiments show that the oscillation frequency and amplitude of systems with propanol or

3 524 CHEM. RES. CHINESE UNIVERSITIES Vol.25 butanol are higher than those of the others. It implies that alcohols with a certain length of carbon chain promote the solution of TTAB in organic phase, and then favor continuous oscillation Effect of Temperature The experiments show that the oscillation frequency increases and the oscillation duration reduces as the temperature increases. The oscillation amplitude is relatively strong at 30 C. Here oscillation frequency corresponds the shift period; the oscillation amplitude corresponds the shift quantity each time; and the duration corresponds the balance time achieved. Theoretically, the increase in temperature results in faster movement, shorter balance time, higher oscillation frequency(namely shorter shift period), and then the lower shift quantity of each transfer(namely shorter oscillation amplitude). These were confirmed by above experimental results. Therefore, temperature mainly affects the transfer rate of the surfactant. The comprehensive effect of above 5 factors on the curve of liquid membrane oscillation, the optimized conditions were selected: water phase C: aqueous 7 mmol/l TTAB and 0.5 mol/l n-propanol solution; oil phase: 0.5 mmol/l picric acid in chloroform; water phase B: 0.1 mol/l glucose solution; at 30 C. The corresponding oscillation curve performs high frequency, long duration and good stability, as shown in Fig Recognition of the Liquid Membrane Oscillation System to L-Tyrosine The oscillation curve under optimized conditions is considered to be referent. Several oscillation curves were accumulated with the addition of 1, 3 and 5 mmol/l L-tyrosine, respectively, to aqueous phase C, as shown in Fig.3. The curves display clearly that the vibration systems with L-tyrosine have greater oscillation frequency and oscillation amplitude in early stage, smaller oscillation frequency and oscillation amplitude in middle stage, and high-frequency-smallamplitude stability oscillation in later stage. As the concentration of L-tyrosine increases, the earlier frequency and amplitude increase, and later oscillation of high-frequency-small-amplitude delays. Fig.3 E-t oscillation curves of L-tyrosine with different concentrations c/(mmol L 1 ): (A) 0; (B) 1; (C) 3; (D); Recognition of the Liquid Membrane Oscillation System to D,L-Tyrosine Several oscillation curves were accumulated with the addition of 1, 3 and 5 mmol/l D,L-tyrosine, respectively, to aqueous phase C under optimized conditions, as shown in Fig.4. The characteristic of oscillation curves with D,L-tyrosine is that the oscillation frequency remains basically unchanged in early stage, and then the frequency reduces with the increase in Fig. 2 Optimized E-t oscillation curve 30 C, 7 mmol/l of TTAB, pure chloroform, 0.5 mmol/l of picric acid, 0.5 mol/l of 1-propanol. 3.2 Recognition of the Liquid Membrane Oscillation System to Amino Acid Fig.4 E-t oscillation curves of D,L-tyrosine with different concentrations c/(mmol L 1 ): (A) 0; (B) 1; (C) 3; (D) 5.

4 No.4 ZHOU Li et al. 525 the amplitude. And the greater the concentration of D,L-tyrosine, the sooner the low-frequency oscillation appears Recognition of the Liquid Membrane Oscillation System to L-Tryptophan Several oscillation curves were accumulated with the addition of 1, 3 and 5 mmol/l of L-tryptophan respectively to aqueous phase C under optimized conditions, as shown in Fig.5. The characteristic of oscillation curves of vibration system with the L-tryptophan is that the oscillation frequency increases in initial stage, then the oscillation frequency reduces. As the concentration of L-tryptophan increases, the frequency of pre-oscillation increases, and the duration of high-frequency oscillation extends. Fig.5 E-t oscillation curves of L-tryptophan with different concentrations c/(mmol L 1 ): (A) 0; (B) 1; (C) 3; (D) 5. In the above experiments, it is worth noting that upon the addition of 1 mmol/l amino acid, three different types of amino acids presented similar oscillation, that is, there is high-frequency small-amplitude oscillation all in later stage. This indicates that the system is not appropriate to recognize different types of amino acids when the concentration of amino acid is low. The several oscillation curves were accumulated with the addition of 3 mmol/l of L-tryptophan, L-tyrosine, and D,L-tyrosine, respectively, to aqueous phase C, as shown in Fig.6. These oscillation curves were obviously different from each other. Thus, this liquid membrane oscillation system can be applied to recognize amino acids. Theoretically, perhaps the chemical reaction between the carboxylate group of the amino acid and amino group of surfactant occurs at interface, the surfactant monolayer is destroyed [15]. The competition between diffusion process Fig.6 E-t oscillation curves with different types of amino acids (A) Referent; (B) (D) with addition of 3 mmol/l of L-tyrosine, D,L-tyrosine and L-tryptophan, respectively. and chemical reaction causes the change of surfactant concentration, thus causes the change of amplitude, frequency, or induction period of liquid membrane oscillation. Furthermore, the change value of amplitude, frequency, or induction period is linearly realted with the quantity of amino acid added. Therefore, various amino acids can be recognized according to the curve shape with various amplitude, frequency, or induction period, and the quantitative analysis of an amino acid can be executed according to the change value of amplitude, frequency, or induction period. References [1] Gao J. Z., Dai H. X., Chen H., et al., Chin. Chem. Lett., 2007, 18(3), 309 [2] Srividhya J., Gopinathan M. S., J. Phys. Chem., 2003, 107(6), 1438 [3] Yoshikawa K., Shoji M., Nakata S., et al., Langmuir, 1988, 4(3), 759 [4] Yoshidome T., Higashi T., Kamata S., Chem. Lett., 2000, 5, 550 [5] Szpakowska M., Czaplicka I., Nagy O. B., Phys. Chem. A, 2006, 110, 7286 [6] Kovalchuk N. M., Vollhard D., J. Phys. Chem. B, 2006, 110(20), 9774 [7] Maeda K., Nagami S., Yoshida Y., et al., J. Electroanal. Chem., 2001, 496, 124 [8] Dupeyrat M., Nakache E., Bioelectrochemistry and Bioenergetics, 1978, 5, 134 [9] Yoshikawa K., Matsubara Y., J. Am. Chem. Soc., 1984, 106(16), 4423 [10] Kovalchuk N. M., Vollhardt D., Colloids and Surfaces A: Physicochem. Eng. Aspects, 2007, 309, 231 [11] Szpakowska M., Czaplicka I., Nagy O. B., Biophysical Chemistry, 2006, 120, 148 [12] Takehito O., Hiroshi S., Satoka A., et al., J. Colloid Interface Sci., 2007, 305, 195 [13] Zhou L., Tang J. N., Liu B., et al., Chin. Chem. Lett., 2008, 19(7), 871 [14] Zhou L., Tang J. N., Peng J. H., et al., J. Chem. Ind. Eng., 2007, 58(9), 2293 [15] Li H. X., Lu J., Li P. H., Chin. Sci. Bulletin, 1998, 43(3), 265

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6 CHEM. RES. CHINESE UNIVERSITIES 2009, 25(4), *Corresponding author. Received November 21, 2008; accepted March 24, Supported by the Open Research Fund of Shenzhen Key Laboratory of Functional Polymer, China.