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Interfacial assembled Langmuir films of isomeric lipid derivative: Effect of hydrogen bond and chirality transfer
Colloids and Surfaces A xxx (xxxx) xxxx
Contents lists available at ScienceDirect
Colloids and Surfaces A journal homepage: www.elsevier.com/locate/colsurfa
Interfacial assembled Langmuir films of isomeric lipid derivative: Effect of hydrogen bond and chirality transfer Xiufeng Wanga,*, Pengfei Duanb, Minghua Liuc,* a
College of Science, China University of Petroleum (East China), Qingdao 266580, Shandong, PR China CAS Key Laboratory of Nanosystem and Hierarchy Fabrication, National Center for Nanoscience and Technology, Beijing 100190, PR China c CAS Key Laboratory of Colloid, Interface and Chemical Thermodynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, PR China b
G R A P H I C A L A B S T R A C T
A R T I C LE I N FO
A B S T R A C T
Keywords: Isomeric effect Langmuir-Blodgett film Assemble Supramolecular chirality
The assembled behaviors of three isomeric L-glutamic lipid derivatives at the water/air interface are different via Langmuir-Blodgett method. Various nanostructures were formed by different mode of hydrogen bond. In the mode of intramolecular hydrogen bond interaction, relative long and thin nanowire appeared. If intermolecular hydrogen bond interaction plays an important role, short nanorod nanostructures were obtained. While both intra- and inter-molecular hydrogen bond interactions exist, the morphology exhibits the mixture of nanowire and nanosheet. In the case of tetrakis (4-sulfonatonphenyl)-porphine (TPPS) added to the subphase, the nanostructures of self-assembly change obviously and achiral TPPS can be induced to appear supramolecular chirality, which due to the interaction between TPPS and the chiral lipid. And the opposite supramolecular chirality ascribed to TPPS can be induced by the origin chirality of lipids.
1. Introduction Langmuir-Blodgett technique offers an opportunity for water-insoluble amphiphiles, especially the surfactants and lipids, to assemble into organized thin film at the air/water interface in nano or microscale level [1–5]. The packing of LB monolayer can be fabricated in
⁎
appropriate conditions, such as surface pressure, temperature, compressing speed, type of subphases, and so on. Various well-defined organized nanostructures were usually obtained [6–10], as a result of building blocks are confined in a two dimension via Langmuir-Blodgett method. Then a slight change or modification of molecules may affect the interactions at the interface, different morphology and properties
Corresponding authors. E-mail addresses: [email protected] (X. Wang), [email protected] (M. Liu).
https://doi.org/10.1016/j.colsurfa.2019.124280 Received 10 October 2019; Received in revised form 21 November 2019; Accepted 25 November 2019 Available online 26 November 2019 0927-7757/ © 2019 Elsevier B.V. All rights reserved.
Please cite this article as: Xiufeng Wang, Pengfei Duan and Minghua Liu, Colloids and Surfaces A, https://doi.org/10.1016/j.colsurfa.2019.124280
Colloids and Surfaces A xxx (xxxx) xxxx
X. Wang, et al.
Fig. 1. Chemical structure of L-glutamic lipids 2PLG, 3PLG and 4PLG, and TPPS. The surface pressure-area (π-A) isotherms of 2PLG (a), 3PLG (b) and 4PLG (c) monolayers in subphase water (A) and TPPS solution (B).
10−5 M, pH value is 3) were selected as subphases.
on the interfacial assemblies are expected [11–13]. Through ingenious molecule design, appropriate and effective combine different noncovalent interaction like H-bond, π-π or hydrophobic interaction, can facilitate assembly at the air/water interface with expectant functions [14–18]. However, there are still relatively few investigations of different hydrogen bond type effect on interfacial assembly. When the molecules arrange in an orderly manner at the air/water interface, certain new properties beyond those in bulk phase could be expected. In this work, the assemble behavior of three isomeric L-glutamic lipid derivatives at the air-water interface are different from their formation of gels in organic solvents. The three isomers have been reported [19], which can form organogels in DMSO and self-assembled into different nanostructures of nanofiber, nanotwist and nanotube, respectively. In the present work, we report that three isomeric L-glutamic lipid derivatives Langmuir-Blodgett film in subphase of ultrapure water and TPPS solution. Though molecular structures of three isomers are similar, different hydrogen bond interaction for isomers resulted in absolutely distinct assembly at the air/water interface. The morphology and characteristics of isomers self-assembly were studied, and the induced chirality of porphyrin was observed, which realize the transfer of supramolecular chirality at the air/water interface.
2.2. Monolayer and multilayers preparation The surface pressure-molecular area (π-A) isotherms were measured on a KSV minitrough (KSV 1100, Helsinki, Finland). The chloroform solution of 2PLG, 3PLG, and 4PLG (0.5 mM) were spread on ultrapure water and TPPS aqueous solution subphase. The pH value of ultrapure water is 5.80 to 6.00. The pH of water subphase and TPPS subphase was adjusted to 3.0 using 1 M hydrochloric acid, in order to avoid the aggregation of TPPS. After evaporating the solvent for 20 min, the surface pressure-area isotherms were recorded with the constant compression speed of 5 mm/min at 20.0 ± 0.2℃. One-layer LB film was obtained using a vertical dipping method with an upstroke speed of 2 mm/min, and transferred onto freshly cleaved mica for AFM measurement. The multilayers were transferred at 15 mN/m by a horizontal lifting method onto CaF2 crystal substrates for UV–vis, CD and FT-IR spectroscopy measurements. 2.3. Characterization
2. Experimental
AFM images were recorded by Nanoscope IIIa multimode system (Santa Barbara, CA) and VEECO Dimension 3100 Atomic Force Microscope (Bruker Nano, Germany) with silicon nitride cantilever probes in the tapping mode. All AFM images have no image processing except flattening. UV–vis and CD spectra are measured by JASCO UV550 and JASCO J-810 CD spectrophotometer. Fourier transform-infrared (FTIR) studies were performed on Bruker Tensor-27 spectrophotometer with a wavenumber resolution of 4 cm−1 in the range of 1000−4000 cm−1 at room temperature.
2.1. Materials Tetrakis (4-sulfonatonphenyl)-porphine (TPPS) were purchased from TCI and used without further purification. Ultrapure water (18.2 MΩ cm) was obtained from the Milli-Q system and used as subphase or subphase solvent. Ultrapure water with pH 3 and Tetrakis (4-sulfonatonphenyl)-porphine (TPPS) water solution (the concentration is 1 × 2
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3. Results and discussion
and more assembled AFM images could be found in Figure S1-S6, in which assemblies with larger scale verify the uniformity. Although the ortho-, meta- and para- substituent position of pyridine show in the isomeric PLG, the self-assembly at water/air interface exhibit prodigious differences. 2PLG form long and thin nanofiber, with the average width of 16 nm around, which was calculated as the method showed in Figure S7. 3PLG form blend of nanowire and nanosheet structure, and the nanowire structure resemble 2PLG. However, 4PLG self-assemble into disparate nanostructure. It shows short and fat stick, which stack tightly (Fig. 2c). And the height of these ordered nanostructure mainly ranges from 0.88 nm to 1.87 nm, as showed in Figure S8. Interestingly, when the subphase is TPPS solution, the morphology varies a lot. 2PLG/TPPS is sticklike structure, which looks like the initial long nanowire change to a shorter and wider one. Keeping under observation of these short sticklike structures, we discover most of the sticks are folded. From Figure S9, the average height of sticks is 3.47 nm, and the folds is about 1.82 nm. Even if one stick is not folded, it inclines to stack with the other and forms folded-like structure, so we can see accordant morphology as a whole. For 3PLG/TPPS, short sticklike structure appears with a little folded-like structure. Like 3PLG, the images are very difficult to capture at high resolution, and the nanostructures are all mixture, which probably relates with the different hydrogen bond mode of 3PLG. For 4PLG/TPPS, larger aggregation appears, and petaline-like nanostructures are formed. It can be inferred that the interaction between 4PLG and TPPS is stronger than the others.
3.1. Surface pressure–area isotherms of the spreading films with different subphase The surface pressure-area (π-A) isotherms of different PLG monolayers are shown in Fig. 1. These isotherms make difference in the limit molecule area. When the subphase is ultrapure water, the limit molecule area of 4PLG is the largest, and the 2PLG’s is the smallest. However, while the subphase exchanges to the TPPS aqueous solution (the concentration is 1 × 10−5 M), the trend of limit molecule area is similar, but the distinction becomes narrower. At the same time, it is obvious to find the increased molecular areas for 3PLG and 4PLG on TPPS subphase, owing to the electrostatic interaction between 3PLG (4PLG) in monolayer and TPPS in the subphase, which enlarge the area of hydrophile group. Whereas, the limit molecule areas of 2PLG in these two cases are nearly the same, due to the existence of intramolecular Hbond in 2PLG, which prevents further interacting with TPPS to a certain extent. 3.2. Morphological investigation of the transferred one-layer LB films To get further insight into morphologies formed at the air/water interface, one-layer LB film was investigated by AFM measurement. From the π-A isotherms of different isomer, the surface pressure was selected at 15 mN/m, therefore, different transferred one-layer LB films were prepared. Fig. 2 shows the AFM images of the one-layer film on mica surface,
Fig. 2. AFM images of (a) 2PLG, (b) 3PLG, (c) 4PLG monolayer film in the subphase of water, (d) 2PLG, (e) 3PLG, (f) 4PLG in the subphase of TPPS aqueous solution. 3
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Fig. 3. FTIR spectra of the PLG transferred LS films in the subphase of water (A), and PLG/TPPS complex LS films in TPPS solution (B): (a) 2PLG/TPPS, (b) 3PLG/ TPPS and (c) 4PLG/TPPS.
3.3. Spectra of transferred multilayer LS films
same time, the blue shift of the peak at around 425 nm corresponds to the H-aggregation of the TPPS [23]. From the UV–vis spectrum, it is suggested that TPPS forms J-aggregate mostly. The measurement of CD Spectra is considered as an important method to research the stereochemistry of organic compounds. As a special kind of absorption spectrum, CD is very sensitive to the chirality of molecule assemblies. PLG multilayers reveal different CD signal, as showed in Fig. 4A, a negative Cotton effect is observed in 2PLG assembly, while 3PLG and 4PLG show a positive Cotton effect. TPPS molecule itself is not chiral, because there is no chiral center in it. But, in Fig. 4B, the absorption region of TPPS exhibits chirality. Distinct Cotton effects are found at about 490 and 720 nm in the transferred films. At about 490 nm, the strong CD signals indicate that the chirality is attributed to the J-aggregate of the TPPS [23,24]. Interestingly, compare with the region of 200–300 nm, opposite Cotton effect appears in the CD spectrum, positive Cotton effect can be observed in 2PLG and 3PLG at about 490 and 720 nm, and negative Cotton effect can be observed in 4PLG. It is explained as the chirality of PLG molecule in the low wavelength transfers to TPPS molecule in the larger wavelength [25]. The chirality of original achiral TPPS was induced by chiral PLG with orderly arrangement. As the Scheme 1 showed, PLG self-assemble with one kind of chirality in the interface, when TPPS come to act on PLG, TPPS can assemble following the trace of PLG, which progress is similar to the DNA transcription. The difference of these isomeric PLG is intermolecular interaction, which exhibits different surface pression-area (π-A) isotherms and characterization of the transferred films. For 2PLG, H-bond interaction, especially intramolecular H-bond plays a vital role in their self-assembly, meanwhile the strong π-π interaction between pyridine rings make it self-assemble into long ones and look comparatively perfect from AFM images in Fig. 2a. The intramolecular H-bond interaction of 3PLG is weaker than 2PLG. Perhaps due to both intramolecular and intermolecular H-bond interaction exist competitively in the 3PLG selfassembly, 3PLG forms less perfect structure, there are plenty of little parts without uniform size. For 4PLG, intermolecular H-bond and stronger π-π interaction exist at the same time, which make 4PLG molecule arrange tightly, and fold in some case as showed in Fig. 2c. CD signal of 4PLG at short wavelength scale is different from others, could be explained by the strong π-π interaction. When TPPS was added to the subphase, interaction of the isomeric PLG changed. For 2PLG, though interaction with TPPS is week, π-π interaction is strong and plays a leading role, whose case is similar to 4PLG in water subphase, result in their AFM images are similar (Fig. 2c, d). By the same token, 3PLG and 4PLG in TPPS subphase, π-π interaction also plays a great
In order to study the hydrogen bond pattern of the assembly, FTIR spectra were monitored. 100 layers PLG transferred LS films were prepared in water subphase, and 50-layer transferred LS films were prepared in TPPS subphase. For 2PLG, two NeH stretching vibration peaks appear at 3394 and 3307 cm−1 in Fig. 3A. The peak at 3394 cm−1 could be ascribed to the NeH stretching vibration of the amide group which attached to the pyridine ring, and can generate intramolecular hydrogen bond with pyridine nitrogen to from a five-membered ring. The remarkable shift of the NeH stretching vibrations to higher wavenumber was observed than 3/4PLG. Further evidence of formation intramolecular hydrogen bond stems from the vibrations of amide region. Comparing with 3PLG and 4PLG, the amide I band of 2PLG shifted to higher wavenumber and the amide II band shifted to lower wavenumber, indicated the intramolecular hydrogen bond formed. In TPPS subphase, various PLG molecules can interact with TPPS, then the interaction affects the hydrogen bond and diminishes the type of hydrogen bond. All the NeH stretching vibration bands appear around 3299 cm−1, and there are not significantly different in amide I and amide II. As is well known, the CH2 vibration band is regarded as an impactful diagnosis of the alkyl chains packing. CH2 asymmetric and symmetric stretching vibrations of 2915 and 2849 cm–1 indicated that the alkyl chains adopt an all-trans zigzag conformation. In addition, the intensity of the band at 2915 cm–1 is stronger than 2849 cm–1, suggesting the alkyl chains are vertical to the film surface. These bands did not change when the subphase was turned into TPPS solution, indicated that the packing of the alkyl chains is also vertical to the film plane with an all-trans conformation. Fig. 4C shows the UV–vis spectra of the transferred LS film, each multilayer film is transferred 100 layers PLG. The UV–vis spectrum of 2PLG LS film shows a shoulder absorption at 220 nm and an absorption peak at 265 nm, ascribed to the π-π* transition of pyridyl group. And the absorption of 3PLG is not very obvious, which could be observed at around 260 nm. For 4PLG, the absorption band of π-π* transition shift to 236 nm and 258 nm. It is indicated that π-π interaction appeared stronger in 4PLG assembly than others. Fig. 4D shows the UV–vis spectra of the transferred LS film, each multilayer film is transferred 50 layers PLG and TPPS complex. In addition to characteristic absorption peak of pyridyl group, the absorption of TPPS appears. Theoretically, at 432 nm and 640 nm, it showed the Soret band and Q-band of TPPS in the aqueous solution [20]. In the complex LS film, Soret and Q-bands can be observed to have a large red shift, at around 490 and 704 nm, which come from the formation J-aggregate of TPPS [21–23]. At the 4
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Fig. 4. CD spectra (A) and UV–vis spectra (C) of PLG transferred LS film: (a) 2PLG, (b) 3PLG and (c) 4PLG; and the CD (B) and UV–vis spectra (D) of PLG/TPPS complex transferred LS film: (a) 2PLG/TPPS, (b) 3PLG/TPPS and (c) 4PLG/TPPS.
Scheme 1. The illustration of hydrogen bond in different isomeric PLG, and the interaction between PLG and TPPS. 5
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role and TPPS forms J-aggregation, lead to aggregate stronger than that in the water subphase.
[3] K. Ariga, T. Mori, J. Li, Langmuir Nanoarchitectonics from basic to frontier, Langmuir 35 (2019) 3585–3599. [4] T. Li, K. Lilja, R.J. Morris, G.B. Brandani, Langmuir–blodgett technique for anisotropic colloids: young investigator perspective, J. Colloid Interface Sci. 540 (2019) 420–438. [5] K. Ariga, Chapter 1.2 - Langmuir-Blodgett films for nanoarchitectoncs, in: K. Ariga, M. Aono (Eds.), Advanced Supramolecular Nanoarchitectonics, William Andrew Publishing, 2019, pp. 17–29. [6] S. Zhang, H.-L. Wang, M. Chen, D.-J. Qian, Monolayers and Langmuir–Blodgett films of Fe2+-mediated polyelectrolyte with viologen derivatives as linkers at the air–water interface, Colloid Surf. A: Physicochem. Eng. Asp. 384 (2011) 561–569. [7] F. Xie, C. Zhuo, C. Hu, M.H. Liu, Evolution of nanoflowers and nanospheres of zinc bisporphyrinate tweezers at the air/water interface, Langmuir 33 (2017) 3694–3701. [8] K. Ma, R. Wang, T. Jiao, J. Zhou, L. Zhang, J. Li, Z. Bai, Q. Peng, Preparation and aggregate state regulation of co-assembly graphene oxide-porphyrin composite Langmuir films via surface-modified graphene oxide sheets, Colloid Surf. A: Physicochem. Eng. Asp. 584 (2020) 124023. [9] K. Ma, W. Chen, T. Jiao, X. Jin, Y. Sang, D. Yang, J. Zhou, M. Liu, P. Duan, Boosting the circularly polarized luminescence of small organic molecules via multi-dimensional morphology control, Chem. Sci. 10 (2019) 6821–6827. [10] K. Ariga, V. Malgras, Q. Ji, M.B. Zakaria, Y. Yamauchi, Coordination nanoarchitectonics at interfaces between supramolecular and materials chemistry, Coord. Chem. Rev. 320–321 (2016) 139–152. [11] A.R. Tao, J. Huang, P. Yang, Langmuir− Blodgettry of nanocrystals and nanowires, Acc. Chem. Res. 41 (2008) 1662–1673. [12] X. Huang, C. Li, S. Jiang, X. Wang, B. Zhang, M. Liu, Self-assembled spiral nanoarchitecture and supramolecular chirality in Langmuir-Blodgett films of an achiral amphiphilic barbituric acid, J. Am. Chem. Soc. 126 (2004) 1322–1323. [13] Y. Wang, G. Wen, S. Pispas, S. Yang, K. You, Effects of subphase pH, temperature and ionic strength on the aggregation behavior of PnBA-b-PAA at the air/water interface, J. Colloid Interface Sci. 512 (2018) 862–870. [14] J. Yuan, M. Liu, Chiral molecular assemblies from a novel achiral amphiphilic 2(heptadecyl) naphtha [2, 3] imidazole through interfacial coordination, J. Am. Chem. Soc. 125 (2003) 5051–5056. [15] C. Spitz, S. Dähne, A. Ouart, H.-W. Abraham, Proof of chirality of J-aggregates spontaneously and enantioselectively generated from achiral dyes, J. Phys. Chem. B 104 (2000) 8664–8669. [16] Y. He, R. Wang, T. Jiao, X. Yan, M. Wang, L. Zhang, Z. Bai, Q. Zhang, Q. Peng, Facile preparation of self-assembled layered double hydroxide-based composite dye films as new chemical gas sensors, ACS Sustainable Chem. Eng. 7 (2019) 10888–10899. [17] J.-F. Lemineur, N. Saci, A.M. Ritcey, Impact of concentration and capping ligand length on the organization of metal nanoparticles in Langmuir-Blodgett surface micelles and nanostrands, Colloid Surf. A: Physicochem. Eng. Asp. 498 (2016) 88–97. [18] G. Lin, W. Lu, Self-assembly of hydrophobic gold nanoparticles and adhesion property of their assembled monolayer films, J. Colloid Interface Sci. 501 (2017) 241–247. [19] Y. Gao, T. Jiao, R. Xing, L. Zhang, J. Zhou, Q. Peng, Construction and self-assembly of beta-cyclodextrin derivative composite Langmuir films: host-guest reaction and nanostructures, Colloid Surf. A: Physicochem. Eng. Asp. 533 (2017) 68–75. [20] P. Duan, X. Zhu, M. Liu, Isomeric effect in the self-assembly of pyridine-containing L-glutamic lipid: substituent position controlled morphology and supramolecular chirality, Chem. Commun. 47 (2011) 5569–5571. [21] N.C. Maiti, M. Ravikanth, S. Mazumdar, N. Periasamy, Fluorescence dynamics of noncovalently linked porphyrin dimers, and aggregates, J. Phys. Chem. 99 (47) (1995) 17192–17197. [22] J.M. Ribo, Z. El-Hachemi, O. Arteaga, A. Canillas, J. Crusats, Hydrodynamic effects in soft-matter self-assembly: the case of J-aggregates of amphiphilic porphyrins, Chem. Rec. 17 (2017) 713–724. [23] Q. Wang, L. Zhang, D. Yang, T. Li, M. Liu, Chiral signs of TPPS co-assemblies with chiral gelators: role of molecular and supramolecular chirality, Chem. Commun. 52 (2016) 12434–12437. [24] J.M. Ribó, J. Crusats, J.-A. Farrera, M.L. Valero, Aggregation in water solutions of tetrasodium diprotonated meso-tetrakis (4-sulfonatophenyl) porphyrin, J. Chem. Soc. Chem. Commun. 6 (1994) 681–682. [25] R. Lauceri, A. Raudino, L.M. Scolaro, N. Micali, R. Purrello, From achiral porphyrins to template-imprinted chiral aggregates and further. Self-replication of chiral memory from scratch, J. Am. Chem. Soc. 124 (2002) 894–895.
4. Conclusion Both the intramolecular or intermolecular hydrogen bond and π-π interaction of pyridine ring, have influence upon the self-assembly of isomeric PLG at water/air interface. In water subphase, 2PLG self-assemble into nanowire via intramolecular hydrogen bond mainly. Both intramolecular and intermolecular hydrogen bonds play a role in 3PLG assembling. And the intermolecular hydrogen bond of 4PLG link adjacent molecules and enhance the packing of pyridine rings, coinciding with the UV–vis spectra. In CD spectrum of 4PLG, the Cotton effect appeared at longer wavelength scale, different from 2PLG and 3PLG. In TPPS subphase, the complex between PLG and TPPS was formed immediately by electrostatic interaction. Due to the ordered packing of PLG at water/air interface, TPPS form J aggregates. The chirality of PLG assembly transferred to TPPS aggregates, and the CD signals were induced in the complex film successfully. This study deepens the understanding of chirality transfer and chiral supramolecular assembly, which will help to design new chiral materials. Author contribution X. Wang designed and performed the experiments, analyzed the experimental data and wrote the paper; P. Duan analyzed the data; M. Liu conceived the idea and revised the paper. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements This work was supported by the National Natural Science Foundation of China (21603276, 51673050, 91856115, 21890734), the Fundamental Research Funds for the Central Universities (19CX02060A), and Qingdao applied basic research project (17-1-1-74jch). Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.colsurfa.2019.124280. References [1] K. Ariga, Y. Yamauchi, T. Mori, J.P. Hill, 25th anniversary article: what can be done with the langmuir-blodgett method? Recent developments and its critical role in materials science, Adv. Mater. 25 (2013) 6477–6512. [2] L. Zhang, J. Yuan, M. Liu, Supramolecular chirality of achiral TPPS complexed with chiral molecular films, J. Phys. Chem. B 107 (2003) 12768–12773.
6
Contents lists available at ScienceDirect
Colloids and Surfaces A journal homepage: www.elsevier.com/locate/colsurfa
Interfacial assembled Langmuir films of isomeric lipid derivative: Effect of hydrogen bond and chirality transfer Xiufeng Wanga,*, Pengfei Duanb, Minghua Liuc,* a
College of Science, China University of Petroleum (East China), Qingdao 266580, Shandong, PR China CAS Key Laboratory of Nanosystem and Hierarchy Fabrication, National Center for Nanoscience and Technology, Beijing 100190, PR China c CAS Key Laboratory of Colloid, Interface and Chemical Thermodynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, PR China b
G R A P H I C A L A B S T R A C T
A R T I C LE I N FO
A B S T R A C T
Keywords: Isomeric effect Langmuir-Blodgett film Assemble Supramolecular chirality
The assembled behaviors of three isomeric L-glutamic lipid derivatives at the water/air interface are different via Langmuir-Blodgett method. Various nanostructures were formed by different mode of hydrogen bond. In the mode of intramolecular hydrogen bond interaction, relative long and thin nanowire appeared. If intermolecular hydrogen bond interaction plays an important role, short nanorod nanostructures were obtained. While both intra- and inter-molecular hydrogen bond interactions exist, the morphology exhibits the mixture of nanowire and nanosheet. In the case of tetrakis (4-sulfonatonphenyl)-porphine (TPPS) added to the subphase, the nanostructures of self-assembly change obviously and achiral TPPS can be induced to appear supramolecular chirality, which due to the interaction between TPPS and the chiral lipid. And the opposite supramolecular chirality ascribed to TPPS can be induced by the origin chirality of lipids.
1. Introduction Langmuir-Blodgett technique offers an opportunity for water-insoluble amphiphiles, especially the surfactants and lipids, to assemble into organized thin film at the air/water interface in nano or microscale level [1–5]. The packing of LB monolayer can be fabricated in
⁎
appropriate conditions, such as surface pressure, temperature, compressing speed, type of subphases, and so on. Various well-defined organized nanostructures were usually obtained [6–10], as a result of building blocks are confined in a two dimension via Langmuir-Blodgett method. Then a slight change or modification of molecules may affect the interactions at the interface, different morphology and properties
Corresponding authors. E-mail addresses: [email protected] (X. Wang), [email protected] (M. Liu).
https://doi.org/10.1016/j.colsurfa.2019.124280 Received 10 October 2019; Received in revised form 21 November 2019; Accepted 25 November 2019 Available online 26 November 2019 0927-7757/ © 2019 Elsevier B.V. All rights reserved.
Please cite this article as: Xiufeng Wang, Pengfei Duan and Minghua Liu, Colloids and Surfaces A, https://doi.org/10.1016/j.colsurfa.2019.124280
Colloids and Surfaces A xxx (xxxx) xxxx
X. Wang, et al.
Fig. 1. Chemical structure of L-glutamic lipids 2PLG, 3PLG and 4PLG, and TPPS. The surface pressure-area (π-A) isotherms of 2PLG (a), 3PLG (b) and 4PLG (c) monolayers in subphase water (A) and TPPS solution (B).
10−5 M, pH value is 3) were selected as subphases.
on the interfacial assemblies are expected [11–13]. Through ingenious molecule design, appropriate and effective combine different noncovalent interaction like H-bond, π-π or hydrophobic interaction, can facilitate assembly at the air/water interface with expectant functions [14–18]. However, there are still relatively few investigations of different hydrogen bond type effect on interfacial assembly. When the molecules arrange in an orderly manner at the air/water interface, certain new properties beyond those in bulk phase could be expected. In this work, the assemble behavior of three isomeric L-glutamic lipid derivatives at the air-water interface are different from their formation of gels in organic solvents. The three isomers have been reported [19], which can form organogels in DMSO and self-assembled into different nanostructures of nanofiber, nanotwist and nanotube, respectively. In the present work, we report that three isomeric L-glutamic lipid derivatives Langmuir-Blodgett film in subphase of ultrapure water and TPPS solution. Though molecular structures of three isomers are similar, different hydrogen bond interaction for isomers resulted in absolutely distinct assembly at the air/water interface. The morphology and characteristics of isomers self-assembly were studied, and the induced chirality of porphyrin was observed, which realize the transfer of supramolecular chirality at the air/water interface.
2.2. Monolayer and multilayers preparation The surface pressure-molecular area (π-A) isotherms were measured on a KSV minitrough (KSV 1100, Helsinki, Finland). The chloroform solution of 2PLG, 3PLG, and 4PLG (0.5 mM) were spread on ultrapure water and TPPS aqueous solution subphase. The pH value of ultrapure water is 5.80 to 6.00. The pH of water subphase and TPPS subphase was adjusted to 3.0 using 1 M hydrochloric acid, in order to avoid the aggregation of TPPS. After evaporating the solvent for 20 min, the surface pressure-area isotherms were recorded with the constant compression speed of 5 mm/min at 20.0 ± 0.2℃. One-layer LB film was obtained using a vertical dipping method with an upstroke speed of 2 mm/min, and transferred onto freshly cleaved mica for AFM measurement. The multilayers were transferred at 15 mN/m by a horizontal lifting method onto CaF2 crystal substrates for UV–vis, CD and FT-IR spectroscopy measurements. 2.3. Characterization
2. Experimental
AFM images were recorded by Nanoscope IIIa multimode system (Santa Barbara, CA) and VEECO Dimension 3100 Atomic Force Microscope (Bruker Nano, Germany) with silicon nitride cantilever probes in the tapping mode. All AFM images have no image processing except flattening. UV–vis and CD spectra are measured by JASCO UV550 and JASCO J-810 CD spectrophotometer. Fourier transform-infrared (FTIR) studies were performed on Bruker Tensor-27 spectrophotometer with a wavenumber resolution of 4 cm−1 in the range of 1000−4000 cm−1 at room temperature.
2.1. Materials Tetrakis (4-sulfonatonphenyl)-porphine (TPPS) were purchased from TCI and used without further purification. Ultrapure water (18.2 MΩ cm) was obtained from the Milli-Q system and used as subphase or subphase solvent. Ultrapure water with pH 3 and Tetrakis (4-sulfonatonphenyl)-porphine (TPPS) water solution (the concentration is 1 × 2
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3. Results and discussion
and more assembled AFM images could be found in Figure S1-S6, in which assemblies with larger scale verify the uniformity. Although the ortho-, meta- and para- substituent position of pyridine show in the isomeric PLG, the self-assembly at water/air interface exhibit prodigious differences. 2PLG form long and thin nanofiber, with the average width of 16 nm around, which was calculated as the method showed in Figure S7. 3PLG form blend of nanowire and nanosheet structure, and the nanowire structure resemble 2PLG. However, 4PLG self-assemble into disparate nanostructure. It shows short and fat stick, which stack tightly (Fig. 2c). And the height of these ordered nanostructure mainly ranges from 0.88 nm to 1.87 nm, as showed in Figure S8. Interestingly, when the subphase is TPPS solution, the morphology varies a lot. 2PLG/TPPS is sticklike structure, which looks like the initial long nanowire change to a shorter and wider one. Keeping under observation of these short sticklike structures, we discover most of the sticks are folded. From Figure S9, the average height of sticks is 3.47 nm, and the folds is about 1.82 nm. Even if one stick is not folded, it inclines to stack with the other and forms folded-like structure, so we can see accordant morphology as a whole. For 3PLG/TPPS, short sticklike structure appears with a little folded-like structure. Like 3PLG, the images are very difficult to capture at high resolution, and the nanostructures are all mixture, which probably relates with the different hydrogen bond mode of 3PLG. For 4PLG/TPPS, larger aggregation appears, and petaline-like nanostructures are formed. It can be inferred that the interaction between 4PLG and TPPS is stronger than the others.
3.1. Surface pressure–area isotherms of the spreading films with different subphase The surface pressure-area (π-A) isotherms of different PLG monolayers are shown in Fig. 1. These isotherms make difference in the limit molecule area. When the subphase is ultrapure water, the limit molecule area of 4PLG is the largest, and the 2PLG’s is the smallest. However, while the subphase exchanges to the TPPS aqueous solution (the concentration is 1 × 10−5 M), the trend of limit molecule area is similar, but the distinction becomes narrower. At the same time, it is obvious to find the increased molecular areas for 3PLG and 4PLG on TPPS subphase, owing to the electrostatic interaction between 3PLG (4PLG) in monolayer and TPPS in the subphase, which enlarge the area of hydrophile group. Whereas, the limit molecule areas of 2PLG in these two cases are nearly the same, due to the existence of intramolecular Hbond in 2PLG, which prevents further interacting with TPPS to a certain extent. 3.2. Morphological investigation of the transferred one-layer LB films To get further insight into morphologies formed at the air/water interface, one-layer LB film was investigated by AFM measurement. From the π-A isotherms of different isomer, the surface pressure was selected at 15 mN/m, therefore, different transferred one-layer LB films were prepared. Fig. 2 shows the AFM images of the one-layer film on mica surface,
Fig. 2. AFM images of (a) 2PLG, (b) 3PLG, (c) 4PLG monolayer film in the subphase of water, (d) 2PLG, (e) 3PLG, (f) 4PLG in the subphase of TPPS aqueous solution. 3
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Fig. 3. FTIR spectra of the PLG transferred LS films in the subphase of water (A), and PLG/TPPS complex LS films in TPPS solution (B): (a) 2PLG/TPPS, (b) 3PLG/ TPPS and (c) 4PLG/TPPS.
3.3. Spectra of transferred multilayer LS films
same time, the blue shift of the peak at around 425 nm corresponds to the H-aggregation of the TPPS [23]. From the UV–vis spectrum, it is suggested that TPPS forms J-aggregate mostly. The measurement of CD Spectra is considered as an important method to research the stereochemistry of organic compounds. As a special kind of absorption spectrum, CD is very sensitive to the chirality of molecule assemblies. PLG multilayers reveal different CD signal, as showed in Fig. 4A, a negative Cotton effect is observed in 2PLG assembly, while 3PLG and 4PLG show a positive Cotton effect. TPPS molecule itself is not chiral, because there is no chiral center in it. But, in Fig. 4B, the absorption region of TPPS exhibits chirality. Distinct Cotton effects are found at about 490 and 720 nm in the transferred films. At about 490 nm, the strong CD signals indicate that the chirality is attributed to the J-aggregate of the TPPS [23,24]. Interestingly, compare with the region of 200–300 nm, opposite Cotton effect appears in the CD spectrum, positive Cotton effect can be observed in 2PLG and 3PLG at about 490 and 720 nm, and negative Cotton effect can be observed in 4PLG. It is explained as the chirality of PLG molecule in the low wavelength transfers to TPPS molecule in the larger wavelength [25]. The chirality of original achiral TPPS was induced by chiral PLG with orderly arrangement. As the Scheme 1 showed, PLG self-assemble with one kind of chirality in the interface, when TPPS come to act on PLG, TPPS can assemble following the trace of PLG, which progress is similar to the DNA transcription. The difference of these isomeric PLG is intermolecular interaction, which exhibits different surface pression-area (π-A) isotherms and characterization of the transferred films. For 2PLG, H-bond interaction, especially intramolecular H-bond plays a vital role in their self-assembly, meanwhile the strong π-π interaction between pyridine rings make it self-assemble into long ones and look comparatively perfect from AFM images in Fig. 2a. The intramolecular H-bond interaction of 3PLG is weaker than 2PLG. Perhaps due to both intramolecular and intermolecular H-bond interaction exist competitively in the 3PLG selfassembly, 3PLG forms less perfect structure, there are plenty of little parts without uniform size. For 4PLG, intermolecular H-bond and stronger π-π interaction exist at the same time, which make 4PLG molecule arrange tightly, and fold in some case as showed in Fig. 2c. CD signal of 4PLG at short wavelength scale is different from others, could be explained by the strong π-π interaction. When TPPS was added to the subphase, interaction of the isomeric PLG changed. For 2PLG, though interaction with TPPS is week, π-π interaction is strong and plays a leading role, whose case is similar to 4PLG in water subphase, result in their AFM images are similar (Fig. 2c, d). By the same token, 3PLG and 4PLG in TPPS subphase, π-π interaction also plays a great
In order to study the hydrogen bond pattern of the assembly, FTIR spectra were monitored. 100 layers PLG transferred LS films were prepared in water subphase, and 50-layer transferred LS films were prepared in TPPS subphase. For 2PLG, two NeH stretching vibration peaks appear at 3394 and 3307 cm−1 in Fig. 3A. The peak at 3394 cm−1 could be ascribed to the NeH stretching vibration of the amide group which attached to the pyridine ring, and can generate intramolecular hydrogen bond with pyridine nitrogen to from a five-membered ring. The remarkable shift of the NeH stretching vibrations to higher wavenumber was observed than 3/4PLG. Further evidence of formation intramolecular hydrogen bond stems from the vibrations of amide region. Comparing with 3PLG and 4PLG, the amide I band of 2PLG shifted to higher wavenumber and the amide II band shifted to lower wavenumber, indicated the intramolecular hydrogen bond formed. In TPPS subphase, various PLG molecules can interact with TPPS, then the interaction affects the hydrogen bond and diminishes the type of hydrogen bond. All the NeH stretching vibration bands appear around 3299 cm−1, and there are not significantly different in amide I and amide II. As is well known, the CH2 vibration band is regarded as an impactful diagnosis of the alkyl chains packing. CH2 asymmetric and symmetric stretching vibrations of 2915 and 2849 cm–1 indicated that the alkyl chains adopt an all-trans zigzag conformation. In addition, the intensity of the band at 2915 cm–1 is stronger than 2849 cm–1, suggesting the alkyl chains are vertical to the film surface. These bands did not change when the subphase was turned into TPPS solution, indicated that the packing of the alkyl chains is also vertical to the film plane with an all-trans conformation. Fig. 4C shows the UV–vis spectra of the transferred LS film, each multilayer film is transferred 100 layers PLG. The UV–vis spectrum of 2PLG LS film shows a shoulder absorption at 220 nm and an absorption peak at 265 nm, ascribed to the π-π* transition of pyridyl group. And the absorption of 3PLG is not very obvious, which could be observed at around 260 nm. For 4PLG, the absorption band of π-π* transition shift to 236 nm and 258 nm. It is indicated that π-π interaction appeared stronger in 4PLG assembly than others. Fig. 4D shows the UV–vis spectra of the transferred LS film, each multilayer film is transferred 50 layers PLG and TPPS complex. In addition to characteristic absorption peak of pyridyl group, the absorption of TPPS appears. Theoretically, at 432 nm and 640 nm, it showed the Soret band and Q-band of TPPS in the aqueous solution [20]. In the complex LS film, Soret and Q-bands can be observed to have a large red shift, at around 490 and 704 nm, which come from the formation J-aggregate of TPPS [21–23]. At the 4
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Fig. 4. CD spectra (A) and UV–vis spectra (C) of PLG transferred LS film: (a) 2PLG, (b) 3PLG and (c) 4PLG; and the CD (B) and UV–vis spectra (D) of PLG/TPPS complex transferred LS film: (a) 2PLG/TPPS, (b) 3PLG/TPPS and (c) 4PLG/TPPS.
Scheme 1. The illustration of hydrogen bond in different isomeric PLG, and the interaction between PLG and TPPS. 5
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role and TPPS forms J-aggregation, lead to aggregate stronger than that in the water subphase.
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4. Conclusion Both the intramolecular or intermolecular hydrogen bond and π-π interaction of pyridine ring, have influence upon the self-assembly of isomeric PLG at water/air interface. In water subphase, 2PLG self-assemble into nanowire via intramolecular hydrogen bond mainly. Both intramolecular and intermolecular hydrogen bonds play a role in 3PLG assembling. And the intermolecular hydrogen bond of 4PLG link adjacent molecules and enhance the packing of pyridine rings, coinciding with the UV–vis spectra. In CD spectrum of 4PLG, the Cotton effect appeared at longer wavelength scale, different from 2PLG and 3PLG. In TPPS subphase, the complex between PLG and TPPS was formed immediately by electrostatic interaction. Due to the ordered packing of PLG at water/air interface, TPPS form J aggregates. The chirality of PLG assembly transferred to TPPS aggregates, and the CD signals were induced in the complex film successfully. This study deepens the understanding of chirality transfer and chiral supramolecular assembly, which will help to design new chiral materials. Author contribution X. Wang designed and performed the experiments, analyzed the experimental data and wrote the paper; P. Duan analyzed the data; M. Liu conceived the idea and revised the paper. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements This work was supported by the National Natural Science Foundation of China (21603276, 51673050, 91856115, 21890734), the Fundamental Research Funds for the Central Universities (19CX02060A), and Qingdao applied basic research project (17-1-1-74jch). Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.colsurfa.2019.124280. References [1] K. Ariga, Y. Yamauchi, T. Mori, J.P. Hill, 25th anniversary article: what can be done with the langmuir-blodgett method? Recent developments and its critical role in materials science, Adv. Mater. 25 (2013) 6477–6512. [2] L. Zhang, J. Yuan, M. Liu, Supramolecular chirality of achiral TPPS complexed with chiral molecular films, J. Phys. Chem. B 107 (2003) 12768–12773.
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