Assembly and Characterization of Ternary SV−DNA−TMPyP Complex

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Assembly and Characterization of Ternary SV-DNA-TMPyP Complex Langmuir-Blodgett Films Xiaodong Chen,† Lin Li,‡ and Minghua Liu*,† Laboratory of Colloid and Interface Science, Center for Molecular Science, Institute of Chemistry, the Chinese Academy of Sciences, Beijing, 100080, People’s Republic of China, and State Key Laboratory of Polymer Physics and Chemistry, Center for Molecular Science, Institute of Chemistry, the Chinese Academy of Sciences, Beijing, 100080, People’s Republic of China Received December 8, 2001. In Final Form: April 2, 2002 Ternary complex Langmuir-Blodgett (LB) films containing 1,1′-dioctadecyl-4,4′-bipyridinium (SV), deoxyribonucleic acid (DNA), and 5,10,15,20-tetrakis(4-N-methylpyridyl)porphine tetra(p-toluenesulfonate) (TMPyP) were assembled in two ways. One was assembled by depositing the complex monolayer of SV/DNA/TMPyP, which was in situ formed through the adsorption of aqueous subphase containing DNA and TMPyP onto the spreading SV monolayer (type I). Another was obtained by reacting the preformed SV/DNA LB film with TMPyP in aqueous solution (type II). A series of methods, such as surface pressurearea isotherms, atomic force microscopy (AFM), polarized UV-vis spectra, circular dichroism (CD), X-ray diffraction (XRD), and fluorescence lifetime measurements, were used to characterize these ternary LB films. The isotherm measurement indicated that stable complex monolayers could be formed at the airwater interface through the adsorption between SV and DNA or DNA/TMPyP. AFM showed different morphologies of type I and type II LB films. Through a series of characterizations on the LB films, it has been found that TMPyP can intercalate and electrostatically bind to DNA and orient differently in type I and type II LB films. Fluorescence lifetime measurements of the LB films indicated that in the type I LB film electron and/or energy transfer occurred predominantly between the SV and intercalated TMPyP, while in the type II LB film the transfer was predominantly between the SV and electrostatically bound TMPyP. Research showed that the deposition sequence or fabrication method plays an important role in the assembling of ternary LB systems. This method provides a way to fabricate DNA-based molecular assemblies in a controlled and precise manner.

Introduction Recently, research in the area of DNA-based molecular assemblies has attracted much interest because of its relevance to applications in biosensors,1 gene delivery,2 and specific molecular recognition.3 Moreover, the DNA can be used as a block for constructing nanoscaled structures4 or as a template for the preparation of nanomaterials.5 Through electrostatic interactions between the phosphate groups along the DNA backbone and the synthetic charged compounds, DNA-surfactant complexes assembled as gene delivery systems have been the subject of many studies.2 Seeman et al.4 first reported the * To whom correspondence may be addressed. Tel: (0086)-1062569563. Fax: (0086)-10-62569564. Email: [email protected]. † Laboratory of Colloid and Interface Science. ‡ State Key Laboratory of Polymer Physics and Chemistry. (1) (a) Anderson, M. L. M. Nucleic Acid Hybridization, 1st ed.; Springer-Verlag; New York, 1998. (b) Chan, V.; Graves, D. J.; McKenzie, S. E. Biophys. J. 1995, 69, 2243. (c) Englisch, U.; Gauss, D. H. Angew. Chem., Int. Ed. Engl. 1991, 30, 613. (d) Carvana, D. J.; Heller, A. J. Am. Chem. Soc. 1999, 121, 769. (2) (a) Radler, J. O.; Koltover, I.; Saldit, T.; Safinya, C. R. Science 1997, 275, 810. (b) Koltover, I.; Saldit, T.; Radler, J. O.; Safinya, C. R. Science 1998, 281, 78. (c) Huebner, S.; Battersby, B. J.; Grimm, R.; Cevc, G. Biophys. J. 1999, 76, 3158. (c) Melnikov, S. M.; Lindman, B. Langmuir 1999, 15, 1923. (d) Sergeyev, V. G.; Pyshkina, O. A.; Lezov, A. V.; Melnikov, A. B.; Ryumtsev, E. I.; Zezi, A. B.; Kabanov, V. A. Langmuir 1999, 15, 4434. (3) (a) Higashi, N.; Takahashi, M.; Niwa, M. Langmuir 1999, 15, 111. (c) Higashi, N.; Inoue, T.; Niwa, M. Chem. Commun. 1997, 1507. (4) (a) Seeman, N. C. Acc. Chem. Res. 1997, 30, 357. (b) Winfree, E.; Liu, F.; Wenzier, L. A.; Seeman, N. C. Nature 1998, 394, 539. (5) (a) Storhoff, J. J.; Mirkin, C. A. Chem. Rev. 1999, 99, 1849. (b) Mirkin, C. A.; Letdinger, R. L.; Mucic, R. C.; Storhoff, J. J. Nature 1996, 382, 607. (c) Alivisatos, A. P.; Johnsson, K. P.; Peng, X.; Wilson, T. E.; Loweth, C. J.; Bruchez, M. P.; Schultz, P. G. Nature 1996, 382, 609. (d) Braun, E.; Eichen, E.; Sivan, U.; Ben-Yoseph, G. Nature 1998, 391, 775.

preparation of two-dimensional DNA complex mesoscopic structures based on DNAs molecular recognition properties. By using a surface DNA-immobilization reaction and a self-assembly monolayer, some groups have investigated DNA hybridization,6 DNA microarray7 or orientation,8 DNA polymerases binding,9 and enantiomeric binding.3 Investigations on the electron transfer, dye intercalation, and amplified spontaneous emission of the DNA-surfactant complex assembled films have also be reported.10 Using the layer-by-layer method, DNA can also be assembled onto solid substrates, and some properties have been reported.11 As demonstrated in numerous studies over recent decades, the Langmuir-Blodgett (LB) tech(6) Satjapipat, M.; Sanedrin, R.; Zhou, F. Langmuir 2001, 17, 7637. (7) Smith, E. A.; Wanat, M. J.; Cheng, Y.; Barreira, S. V. P.; Frutos, A. G.; Corn, R. M. Langmuir 2001, 17, 2502. (8) (a) Huang, E.; Zhou, F.; Deng, Le. Langmuir 2000, 16, 3272. (b) Schouten, S.; Stroeve, P.; Longo, M. L. Langmuir 1999, 15, 8133. (9) Tsoi, P.; Yang, J.; Sun, Y.; Sui, S.; Yang, M. Langmuir 2000, 16, 6590. (10) (a) Ijiro, K.; Okahata, Y. J. Chem. Soc., Chem. Commun. 1992, 1339. (b) Okahata, Y.; Ijiro, K.; Matsuzaki, Y. Langmuir 1993, 9, 19. (c) Ijiro, K.; Shimomura, M.; Tanaka, M.; Nakamura, H.; Hasebe, K. Thin Solid Films 1996, 284-285, 780. (d) Machida, S.; Morisada, M.; Horie, K.; Okahata, Y. Polym. J. 1999, 31, 1179. (e) Shimomura, M.; Matsuoka, H.; Nakamura, F.; Ikeda, T.; Fukasawa, T.; Hasebe, K.; Sawadaishi, T.; Karthaus, O.; Ijiro, K. Polym. J. 1999, 31, 1115. (f) Kawabe, Y.; Wang, L.; Horinouchi, S.; Ogata, N. Adv. Mater. 2000, 12, 1281. (g) Wang, L.; Yoshida, J.; Ogata, N.; Sasaki, S.; Kajiyama, T. Chem. Mater. 2001, 13, 1273. (h) Nakayama, H.; Ohno, H.; Okahata, Y. Chem. Commun. 2001, 2300. (i) Tanaka, K.; Okahata, Y. J. Am. Chem. Soc. 1996, 118, 10679. (j) Okahata, Y.; Kobayashi, T.; Tanaka, K.; Shimomura, M. J. Am. Chem. Soc. 1998, 120, 6165. (11) (a) Sukhorukov, G. B.; Mo¨hwald, H.; Decher, G.; Lvov, Y. M. Thin Solid Films 1996, 284-285, 220. (b) Decher, G. Science 1997, 277, 1232. (c) Lang, J.; Liu, M. J. Phys. Chem. B 1999, 103, 11393. (d) Liu, M.; Yamashita, K. Science in China, Series B 1999, 42, 567. (e) Chen, X.; Lang, J.; Liu, M. Thin Solid Films, in press.

10.1021/la015718m CCC: $22.00 © 2002 American Chemical Society Published on Web 05/02/2002

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Chart 1. Molecular Structures of TMPyP and SV

nique proves to be a very powerful tool for building ultrathin organic films with well-controlled structure and thickness.12 This technique can also be used to fabricate DNA complex films. Okahata et al. investigated the orientation13a and conformation13b of DNA in the LB film. We also studied the interactions of a positively charged amphiphilic thiacarbocyanine monolayer with DNA at the air-water interface.14 However, these investigations have mainly been concerned with the assembly of binary compositions and few works have focused on the ternary assembly based on DNA.13a The effect of a third component on the structure of DNA assemblies and the effect of the assembling sequences on the structure and the properties of the ternary DNA assemblies have not been achieved yet. By taking advantage of the double helical structure of DNA together with its anionic properties, this paper investigates the assembly of ternary LB films containing a positively charged viologen derivative (SV), DNA, and a water-soluble cationic dye (TMPyP). The ternary DNA complex monolayer and LB films were achieved in two ways. The assembly, structures, and properties of the ternary monolayers and LB films were characterized by the surface pressure-area isotherms, atomic force microscopy (AFM), UV-vis, polarized UV-vis, and circular dichroism (CD) spectra, X-ray diffraction (XRD), and fluorescence lifetime measurements.

Chen et al. Preparation of Complex Monolayer. Measurements of surface pressure-area (π-A) isotherms and the deposition of LB films were carried out using a computer-controlled KSV1100 film balance system (KSV instruments, Helsinki, Finland). The trough surface and the moving barrier were coated with Teflon. The DNA and TMPyP were dissolved in the subphase of Millipore-Q water. After a SV CHCl3/DMSO [24:1 (v/v)] solution was spread for 45 min, a monolayer was compressed and the π-A isotherms were measured with a compressed speed of 7.5 cm2/min. For each isotherm measurement, 0.250 mL of SV solution was spread on the surface. Monolayers were transferred to a freshly cleaved mica surface or quartz plate by a vertical dipping method at a pressure of 20 mN/m. Assembling of the Ternary LB Films. To clarify the effect of the different assembly methods or deposition sequences on the structures and properties of the ternary LB films, the LB films were assembled in two ways, defined as type I and type II, as illustrated in Scheme 1. For type I, SV was spread on the subphase containing a mixture of DNA and TMPyP. The ternary LB film was fabricated by depositing the ternary monolayer of SV/DNA/TMPyP, which is in situ formed through the adsorption of an aqueous subphase containing DNA and TMPyP onto the spreading SV monolayer. For type II, the preformed SV/DNA LB film was immersed into 1 mM TMPyP aqueous solution for 3 h at room temperature, producing another ternary LB film. Transfer ratios revealed that both type I and SV/DNA LB films were Z-type. Atomic Force Microscopy Imaging. AFM images of the monolayers deposited onto freshly cleaved mica surfaces were recorded by a Digital Instrument Nanoscope III Multimode system (Santa Barbara, CA) with a silicon cantilever (resonance frequency 300 kHz, spring constant 35 N/m) using the tapping mode. AFM images are shown in the height mode without any image processing except flattening. Spectral Measurements. A JASCO UV-530 spectrophotometer was used for the polarized UV-vis absorption measurements and a polarizer (Hitachi Mode 650-0155) was placed in front of the LB films. CD spectra of the films were recorded with a JASCO 720 system. Florescence Lifetime Measurements. Fluorescence lifetimes of the complex films were measured by a Horiba timeresolved single photon-counting system (NAES-1100, Hitachi, Japan). The fluorescence lifetimes were determined from the data on the fluorescence transient waveform of the film to be tested, and the lamp waveform data were obtained using the least-squares iterative deconvolution method and then analyzed using exponential fits. Errors in the lifetimes are less than 5%. The range of χ2 (chi-square) is from 1.0 to 1.3. X-ray Diffraction Measurements. X-ray diffractions of the deposited LB films were obtained using a Hitachi Natural D/MaxγB X-ray diffractometer (Japan) with Cu KR (λ ) 1.54 Å) radiation.

Results and Discussion Experimental Section Materials. Sodium salt of DNA from salmon spermary (Wako Pure Chemical Industries. Ltd.) and 1,1′-dioctadecyl-4,4′-bipyridinium perchlorate (SV) (Nippon Kankoh Shikiso Kenkyusho, Okayama, Japan) were used without further purification. The concentration of DNA was obtained via absorption measurements using a molar extinction coefficient,  ) 1.31 × 104 M-1 cm-1, at the maximum 260 nm (i.e., DNA concentrations are reported in molar base pairs).15 5,10,15,20-Tetrakis(4-N-methylpyridyl)porphine tetra(p-toluenesulfonate) (TMPyP) was purchased from Dojindo Laboratories. The structures of TMPyP and SV are shown in Chart 1. Deionized Millipore-Q water (18 MΩ‚cm) was used in all cases. (12) (a) Roberts, G. G. Langmuir-Blodgett Films; Plenum: New York, 1990. (b) Ulman, A. An Introduction to Ultrathin Organic Films from Langmuir-Blodgett to Self-assembly; Academic Press: New York, 1991. (13) (a) Okahata, Y.; Kobayashi, T.; Tanaka, K. Langmuir 1996, 12, 1326. (b) Kago, K.; Matsuoka, H.; Yoshitome, R.; Yamaoka, H.; Ijiro, K.; Shimomura, M. Langmuir 1999, 15, 5193. (14) Liu, M.; Lang, J.; Nakahara, H. Colloids Surf., A 2000, 175, 153. (15) Wells, R. D.; Larson, J. E.; Grant, R. C.; Shortle, B. E.; Cantor, C. R. J. Mol. Biol. 1970, 54, 465.

Formation of Complex Monolayers at the AirWater Interface. Complex monolayers of SV/DNA/ TMPyP were formed at the air-water interface by adsorption from the aqueous subphase of the water-soluble components, i.e., DNA and TMPyP, onto the monolayer of SV. To characterize the interactions of DNA and TMPyP with SV, the surface pressure-area (π-A) isotherms of SV on different subphases were measured. The π-A isotherms of SV on pure water, aqueous DNA solution (1.0 × 10-5 mol/L), and aqueous DNA solution (1.0 × 10-5 mol/L) with an intercalating dye (TMPyP, 5.0 × 10-7 mol/ L) (refer to DNA/TMPyP solution in the following) are shown in Figure 1. In the case of the SV monolayer on the plain water surface, the onset of the surface pressure was observed at 1.29 nm2/molecule, and the monolayer was a typical condensed type. When the subphase contained DNA, the onset of the surface pressure appeared at 1.99 nm2/ molecule. When DNA and TMPyP were simultaneously contained in the subphase, the onset of the surface

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Scheme 1. The Preparation Process of the Two Types of LB Films

Figure 1. π-A isotherms of SV (a) on pure water, (b) on a DNA solution (1.0 × 10-5 mol/L), and (c) on a DNA solution (1.0 × 10-5 mol/L) with TMPyP (5.0 × 10-7 mol/L).

pressure appeared at 1.86 nm2/molecule. By extrapolation of the linear part of the isotherms to zero surface pressure, limiting areas of 1.11, 1.55, and 1.57 nm2/molecule can be obtained for the monolayers on pure water, DNA solution, and DNA/TMPyP solution. The headgroup of SV can be regarded as a box. On the basis of the CPK model, its size was estimated to be 0.72 × 0.44 × 0.34 nm3. Taking the van der Waals radius into account, it is suggested that the headgroup of SV is orientated with its long axis nearly parallel to the water surface. As shown in Figure 1, the π-A isotherms of SV on the DNA subphase and on the DNA/TMPyP subphase are more expanded than that on the pure water surface. This provides clear evidence for the complex formation between the SV monolayer and DNA or DNA/TMPyP at the air-water interface. Since the SV monolayer is positively charged and the DNA is negatively charged, it is suggested that the complex formation in the monolayer is mainly due to the electrostatic interactions. In addition, when comparing the isotherm of the SV monolayer on DNA with that on DNA/ TMPyP solution, smaller molecular areas are observed in the case of the DNA/TMPyP subphase. This suggests that

the monolayer becomes densely packed due to the addition of TMPyP into the DNA. AFM Images of Complex LB Films (One Layer) at the Mica Surface. To properly understand the effect of a third component on the structure of assemblies, the morphologies of the SV, SV/DNA, and type I and type II one-layer LB films were studied in details using AFM. Panels a and b of Figure 2 show the AFM images of SV and SV/DNA LB films on the freshly cleaved mica surface. For the SV LB film, randomly distributed small and large aggregated domains were found, which indicated that the SV itself aggregated easily on the water surface. However, when there was DNA in the subphase, well-ordered stripes were observed, which were distinctly different from the morphology of SV in the absence of DNA. These stripes aligned in the same direction and occurred parallel to the dipping direction of the film. In addition, the width of the stripes was the same, which was approximately 80-85 nm. These ordered stripes indicated that an ordered pattern could be obtained through the interfacial adsorption of the DNA on the amphiphilic SV monolayer. Also, the horizontal distance between the two stripes was approximately 55-60 nm. The height profile shows the height of the monolayer to be approximately 3.2 nm. On the basis of the CPK model of SV, the thickness of the SV layer is approximately 2.1 nm. DNA is reported to have a diameter of 2.0 nm. Therefore, it can be assumed that one layer of SV/DNA LB films consists of one layer of SV and one layer of DNA molecule (further discussion will be provided in the X-ray diffraction section of this paper). For type I and type II complex LB films, although containing identified components, they exhibited different morphologies, as shown in panels c and d of Figure 2. When DNA and TMPyP are simultaneously contained in the subphase, the transferred type I monolayer showed a netlike morphology (Figure 2c). The stripes became thinner and straighter than those in the SV/DNA monolayer. The morphology (Figure 2d) of the type II monolayer was distinctly different from the morphology of SV/DNA LB film in the absence of TMPyP. The stripe was kept, but it became more flexible. Also, the stripes were higher than those observed in the absence of TMPyP.

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Figure 2. AFM images of complex LB films (one layer) on a freshly cleaved mica sheet: (a) SV; (b) SV/DNA; (c) type I; (d) type II.

Figure 3. X-ray diffraction patterns of LB films of (a) SV, (b) SV/DNA, and (c) type I.

It is clear that the surface morphologies of the ternary type I and type II LB films are different. To clarify such differences further and to investigate the effects of these differences on the properties of the formed molecular assemblies, two ternary LB films were fabricated and characterized using a series of methods. XRD of the Complex LB Films. Figure 3 shows the XRD patterns of the LB films of SV, SV/DNA, and type I. For the LB film of SV transferred from the water surface, only one broad shoulder was observed at 2θ ) 4.30°, resulting in a layer spacing of d ) 2.05 nm. Because SV was deposited as a Z-type LB film, this value can be considered as the thickness of one layer. For the SV/DNA complex LB film transferred from the subphase containing DNA, a layer distance of 3.15 nm is obtained, which is

very close to the result of AFM (see above). Therefore, it can be concluded that the complex film is composed of one SV monolayer and one DNA layer. In addition, it can be seen that the thickness of the DNA layer in the complex film is 1.1 nm. This thickness is reasonable for a DNA layer in a dried state and comparable to those reported by other groups using X-ray reflectometry (1.1 nm)13b and atomic force microscopy (1.1 nm).16 For type I LB film transferred from the subphase containing DNA and TMPyP, the first-order Bragg reflection was observed at 2θ ) 1.54° and resulted in a layer spacing of d ) 4.6 nm. Considering the layer thickness of the SV/DNA LB film, the TMPyP layer thickness was 1.45 nm. TMPyP is a square molecule, with side and diagonal length of 1.3 and 1.8 nm. Therefore, the TMPyP molecules must be orientated with their diagonal axis tilted and/or partially inserted into the DNA layer. However, for a type II LB film, no Bragg diffraction peak was observed, which indicates that the ternary LB film of type II is less regular than the type I LB film. This result reveals that the structures of ternary LB films containing the same substances are different. Polarized UV-vis Spectra of the Ternary LB Films. The ratio of the absorbance for s-polarized light to p-polarized light, As/Ap, directly relates to the angular distribution of the transition dipoles in multilayer assemblies. The ratio reveals the chromophore orientation of organic dyes in LB films. For porphyrin molecules, the two transition dipoles lie in the molecular plane at an angle of 90° along the axis through the pyrrole nitrogens at opposite positions. The polarization direction of the π-π* Soret band is parallel to the molecular plane. To estimate the average tilted angle of the porphyrin and understand the effect of TMPyP on the two ternary LB (16) Shaiu, W.-L.; Vesenka, J.; Jondle, D.; Henderson, E.; Larson, D. D. J. Vac. Sci. Technol., A 1993, 11, 820.

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Figure 4. Polarized UV-vis spectra of type I (a, b) and type II (c, d) LB films. Incidence angle was 45°. The inset in this figure indicates the geometrical definitions. Table 1. Ratios of the s-Polarized to p-Polarized Absorbances of the Soret Band in the UV-vis Spectra of the Two Ternary LB Films at Incidence Angles of 0° and 45° As/Ap LB films

(β′ ) 0)

(β′ ) 45°)

θ (deg)

type I type II

0.98 0.98

1.06 1.18

45 27.4

films, the polarized UV-vis spectra of the two ternary LB films were measured on the quartz plates at incidence angles of 0° and 45°. For the incidence angle of 0°, no distinct anisotropy was observed for the two ternary LB films. For the incidence angle of 45°, however, the absorbance of the Soret bands decreased considerably upon changing the polarization direction of light from spolarized (parallel to the dipping direction) to p-polarized (perpendicular to the dipping direction), as shown in Figure 4. The ratios of the absorbance of the Soret band observed with s-(As) and p-(Ap) polarized light were obtained for the two LB films, as shown in Table 1. According to the Yoneyama equation17 and assuming the refractive index (n) of the films is 1.5, the angle between the porphyrin macrocycle plane in the LB films and the quartz substrate was estimated to be 45° for the type I and 27.4° for the type II LB film. This suggests that the orientations of porphyrin macrocycle in the two LB films are different. CD Spectra of the Ternary LB Films. It has been reported that DNA can take the A, B, and C forms in aqueous solutions.18 The DNA used in the current experiments takes the B form in the aqueous solution. For the LB film of type I, a negative valley at 251 nm and a negative peak at 291 nm were observed (as shown in Figure 5). For the type II LB film, a similar Cotton effect was observed at 255 and 296 nm. Considering the CD spectrum of SV/ DNA LB film, the DNA conformation must not have changed after interacting with TMPyP, and the righthanded double helix structure of DNA was retained in these films. The CD spectra of native DNA in ethanolic solution or dry DNA cast films from aqueous solutions in air is known to change depending on the ethanol concentration in water or water moisture in air due to slight changes of the base pair stacking forms (A, B, or C form) in the stranded structure.18,19 The CD spectra of the (17) Yoneyama, M.; Sugi, M.; Saito, M. Jpn. J. Appl. Phys. 1985, 25, 961. (18) Hanlon, S.; Brudno, S.; Wu, T. T.; Wolf, B. Biochemistry 1975, 14, 1648.

Figure 5. CD spectra of LB films of (a) SV/DNA, (b) type I, and (c) type II.

complex LB films were similar to those of the C form of native DNA in aqueous solution in the presence of high salts,18 high ethanol concentration,20 or DNA-lipid complex in the chloroform solution (at low water content).10a,10i Dickerson21 reported that water molecules were important in the formation of the B structure of DNA, in which water molecules interact with oxygen molecules of ribose and phosphate and minor or major grooves of the DNA strands. Thus, it suggests that the conformation of DNA in these complex LB films takes C form in air. From the visible range of CD spectra, a negative CD band was found in the visible range 443 nm for type I LB film and 448 nm for the type II LB film (as shown in Figure 5). These spectra are due to the induced CD spectra of TMPyP with DNA, although such spectra did not appear for TMPyP in the absence of DNA. This means that an orientation structure of TMPyP formed along the DNA double helix in the ternary LB films and a partial TMPyP macrocycle was intercalated22 into the DNA layer in both types of LB films Fluorescence Lifetime Measurements of the Ternary LB Films. To further understand the effect of the assembling method on the properties of the ternary LB films, the fluorescence decay of the two ternary LB films was measured, as show in Figure 6. Both of the decay curves of the LB films can be fitted using a doubleexponential function, and two lifetimes can be obtained, as shown in Table 2. For the type I LB film, the lifetimes of the two components were 7.49 and 2.08 ns, while for the type II LB film, the lifetimes were 9.25 and 1.27 ns. It has been reported that the fluorescence lifetimes of TMPyP are 10 and 1.7 ns in aqueous solution,23 and we also found that the fluorescence lifetimes of TMPyP were 9.22 and 2.26 ns in the DNA film without the viologen. In addition, the long-lived component is attributed to the intercalated TMPyP and the short-lived one is attributed to the externally bound TMPyP.23 This can also be applied to the ternary LB films. The long-lived component can be attributed to the intercalated TMPyP, while the short(19) Ivanov, V. I.; Minchenkova, L. E.; Schyokina, A. K.; Poledtayev, A. Y. Biopolymers 1973, 12, 89. (20) Girod, J. C.; Johnson, W. C., Jr.; Huntinggton, S. K.; Maestre, M. F. Biochemistry 1973, 12, 5092. (21) Prive, G. G.; Heinmann, U.; Chandrasegaren, S.; Kan, L.-S.; Kopra, M. L.; Dickerson, R. E. Science, 1987, 238, 498. (22) (a) Fiel, R. J.; Howard, J. C.; Mark, E. H.; Datta Gupta, N. Nucleic Acids Res. 1979, 6, 3093. (b) Pasternack, R. F.; Gibbs, E. J.; Villafranca, J. J. Biochemistry 1983, 22, 2406. (c) Hudson, B. P.; Sou, J.; Berger, D. J.; McMillin, D. R. J. Am. Chem. Soc. 1992, 114, 8997. (23) (a) Liu, Y.; Koningstein, J. A.; Yevdokimov, Y. Can. J. Chem. 1991, 69, 1791. (b) Shen, Y.; Myslinski, P.; Treszczanowicz, T.; Liu, Y.; Koningstein, J. A. J. Phys. Chem. 1992, 96, 7782.

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TMPyP.24,25 Therefore, it can be concluded that in type I LB film electron and/or energy transfer occurred predominantly between the SV and intercalated TMPyP, while it is preferred between the SV and electrostatically bound TMPyP in type II LB film. Conclusions

Figure 6. The fluorescence decay profile for (a) type I and (b) type II LB films. Excitation was made at 440 nm, and fluorescence was detected at 660 nm. The normalized instrumental response curve is given as (c). Table 2. Fluorescence Lifetimes of the DNA Complex Systemsa complex system

τl (ns)

Al (%)

τs (ns)

As (%)

χ2

type I type II TMPyP/PAH/DNA DNA/TMPyP (aq)b

7.49 9.25 9.22 10

68.3 62.9 57.1 1.7

2.08 1.27 2.26

31.7 37.1 42.9

1.10 1.23 1.10

a Entries to the columns are as follows: τ and τ are the lifetime s l of the short- and long-lived components of the decay; As and Al are the amplitudes of the short- and long-lived components. b Reference 23.

lived one can be attributed to the electrostatically bound TMPyP in the ternary LB films. Compared to the lifetimes of TMPyP in the ternary LB films with those in DNA film without viologen, it is interesting to note that in the case of type I LB film, the long-lived component is efficiently quenched, in which the lifetime changes from 9.22 to 7.49 ns, while the short-lived component slightly decreases. In the case of type II LB film, the situation is the opposite; i.e., the short-lived component is efficiently quenched, while the long-lived component experiences minimal quenching. The diminishing of the lifetime of the TMPyP in the existence of viologen is usually the result of the electron and/or energy transfer between the viologen and

By taking advantage of the LB technique in controlling the lateral diffusion and deposition sequences and using the unique properties of DNA molecule, two kinds of ternary LB films containing the same composition of SV, DNA, and TMPyP were successfully fabricated. Type I LB film was fabricated by depositing the complex monolayer of SV/DNA/TMPyP, through the in situ adsorption of the aqueous solution containing DNA and TMPyP onto the spreading SV monolayer. Type II LB film was obtained by immersing the preformed SV/DNA LB film with TMPyP in the aqueous solution. Thus, a different deposition sequence or different fabrication method can greatly affect the morphologies and properties of the ternary LB film, which provides a way to fabricate DNA-based molecular assemblies in a controlled and precise manner. The deposition sequence or fabrication method plays an important role in fabricating complicated supramolecular systems. Acknowledgment. This project is supported by the Outstanding Youth Fund, the Major State Basic Research Development Program (Grant. No. G2000078103), National Natural Science Foundation of China (Grant. No. 29992590-3), and the fund from the Chinese Academy of Sciences. LA015718M (24) Examination of redox potentials of the viologen and TMPyP was with the following equation: ∆G° ) e[E°(TMPyP+/TMPyP) E°(V2+/V+)] - ∆E00. E°(V2+/V+) and E°(TMPyP+/TMPyP) are the reduction potential for viologen and the ground state of porphyrin, and ∆E00 represents the energy of the singlet excited state of TMPyP. The estimated redox potential for (V2+/V+) is -0.44 V26 and for (TMPyP+/ TMPyP) is +1.3 V.27 The excited singlet state energy for porphyrin is 1.83 eV27 (all the values are vs NHE). Then ∆G° ) -0.09 eV. This is a consequence, at least in part, of the poor thermodynamic driving force for light-induced electron transfer between SV and TMPyP. (25) Brun, A. M., Harriman, A. J. Am. Chem. Soc. 1994, 116, 10383. (26) Fromherz, P.; Rieger, B. J. Am. Chem. Soc. 1986, 108, 5361. (27) Kalyanasundaram, K.; Neumann-Spallart, M. J. Phys. Chem. 1982, 86, 5163.