若干温敏高分子的单分子力谱研究
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摘要
聚合物种类繁多,其中有些部分是具有刺激响应性质的,响应因素有pH、光、温度、电磁场等等。其中,温敏聚合物的研究显得格外突出。温敏聚合物会随温度变化而发生聚合物分子内、分子间以及聚合物分子与溶剂分子间作用力的改变,导致材料宏观性质的改变。
温敏聚合物有一个主要的特性—最低临界溶解温度(Lower Critical Solution Temperature)。当温度高于该温敏聚合物的LCST时,溶解于水中的聚合物将析出,出现沉淀现象。溶于水中的温敏聚合物将与水分子形成氢键。由于受到分子链构象的限制,分子链在完全伸展的情况下每重复单元上的结合水分子的数量将比在自由卷曲状态下少很多。因此当我们利用原子力显微镜(AFM)来拉伸温敏聚合物分子时,聚合物链上的结合水将逐渐的减少,链周围的水分子结构将被迫进行重新排列,而这个水分子重排过程需要消耗一定的能量。因此在水中拉伸链时消耗的能量包括了克服分子链固有弹性的能量消耗以及水分子重排的能量消耗。通过实验,我们得到了以下几点结论：
1.利用AFM拉伸温敏聚合物分子可以表明在水中拉伸聚合物时将会有水分子重排现象产生,并可以通过计算获得水分子重排所消耗的能量；
2.温敏聚合物的LCST会随着侧链疏水性的增加而变小；
3.温敏聚合物的LCST与水分子重排所消耗的能量大小之间没有明显关联；
4.发现了在有机溶剂中,以C-C为主链的各种聚合物分子表现出其本征弹性,而侧链结构对其弹性基本不产生影响。
Some polymers are responsive to the external stimuli, such as pH, light, temperature and electromagnetic field. LCST (Lower Critical Solution Temperature) is a very important property of thermally sensitive polymers. When the temperature is higher than LCST, thermally sensitive polymer dissolved in water will undergo a phase transition. In the free state, the polymer molecules will form hydrogen bonds with water molecules. Because of the limitations in chain conformation, there would be much more bound water molecules in the free coil state than in the completely stretched state. That is to say, when stretched by an AFM, the polymer chain would lose bound water gradually during the stretching process. Thus, these structured water molecules around the polymer chain are forced to undergo rearrangement upon stretching, which would cost energy. We obtain several conclusions through single-molecule force measurements:
1. We find that there is a water rearrangement upon chain stretching. We have calculated the energy for this water rearrangement.
2. The stronger hydrophobic side groups will result in the lower LCST.
3. There is no clear correlation between LCST and the energy needed for the water rearrangement.
4. The inherent stretching elasticity of a single polymer chain with carbon-carbon backbone in nonpolar solvent shows that the side groups have no evident influence on the inherent elasticity.
温敏聚合物有一个主要的特性—最低临界溶解温度(Lower Critical Solution Temperature)。当温度高于该温敏聚合物的LCST时,溶解于水中的聚合物将析出,出现沉淀现象。溶于水中的温敏聚合物将与水分子形成氢键。由于受到分子链构象的限制,分子链在完全伸展的情况下每重复单元上的结合水分子的数量将比在自由卷曲状态下少很多。因此当我们利用原子力显微镜(AFM)来拉伸温敏聚合物分子时,聚合物链上的结合水将逐渐的减少,链周围的水分子结构将被迫进行重新排列,而这个水分子重排过程需要消耗一定的能量。因此在水中拉伸链时消耗的能量包括了克服分子链固有弹性的能量消耗以及水分子重排的能量消耗。通过实验,我们得到了以下几点结论：
1.利用AFM拉伸温敏聚合物分子可以表明在水中拉伸聚合物时将会有水分子重排现象产生,并可以通过计算获得水分子重排所消耗的能量；
2.温敏聚合物的LCST会随着侧链疏水性的增加而变小；
3.温敏聚合物的LCST与水分子重排所消耗的能量大小之间没有明显关联；
4.发现了在有机溶剂中,以C-C为主链的各种聚合物分子表现出其本征弹性,而侧链结构对其弹性基本不产生影响。
Some polymers are responsive to the external stimuli, such as pH, light, temperature and electromagnetic field. LCST (Lower Critical Solution Temperature) is a very important property of thermally sensitive polymers. When the temperature is higher than LCST, thermally sensitive polymer dissolved in water will undergo a phase transition. In the free state, the polymer molecules will form hydrogen bonds with water molecules. Because of the limitations in chain conformation, there would be much more bound water molecules in the free coil state than in the completely stretched state. That is to say, when stretched by an AFM, the polymer chain would lose bound water gradually during the stretching process. Thus, these structured water molecules around the polymer chain are forced to undergo rearrangement upon stretching, which would cost energy. We obtain several conclusions through single-molecule force measurements:
1. We find that there is a water rearrangement upon chain stretching. We have calculated the energy for this water rearrangement.
2. The stronger hydrophobic side groups will result in the lower LCST.
3. There is no clear correlation between LCST and the energy needed for the water rearrangement.
4. The inherent stretching elasticity of a single polymer chain with carbon-carbon backbone in nonpolar solvent shows that the side groups have no evident influence on the inherent elasticity.
引文
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[2]Jeong B, Gutowska A. Lessons from nature:stimuliresponsive polymers and their biomedical applications. Trends. Biotechnol.[J],2002,20 (7):305-311
[3]Alarco'n C d 1 H, Pennadam S, Alexander C. Stimuli responsive polymers for biomedical applications. Chem. Soc. Rev.[J],2005,34:276-285
[4]Kikuchi A, Okano T. Pulsatile drug release control using hydrogels. Adv. Drug. Deliver. Rev.[J],2002,54:53-77
[5]Kim E J, Cho S H, Yuk S H. Polymeric microspheres composed of pH/temperature-sensitive polymer complex. Biomaterials[J],2001,22:2495-2499
[6]Chung J E, Yokoyama M, Okano T. Inner core segment design for drug delivery control of thermo-responsive polymeric micelles. J. Control. Release[J],2000,65:93-103
[7]Shah S S, Wertheim J, Wang C T, et al. Polymer-drug conjugates:manipulating drug delivery kinetics using model LCST systems. J. Control. Release[J],1997,45:95-101
[8]Carter S, Rimmer S, Rutkaite R, et al. Highly Branched Poly(N-isopropylacrylamide) for Use in Protein Purification. Biomacromolecules[J],2006,7:1124-1130
[9]Lu Y, Proch S, Schrinner M, et al. Thermosensitive core-shell microgel as a "nanoreactor" for catalytic active metal nanoparticles. J. Mater. Chem.[J],2009,19: 3955-3961
[10]Lu Y, Mei Y, Ballauff M, et al. Thermosensitive Core-Shell Particles as Carrier Systems for Metallic Nanoparticles. J. Phys. Chem. B[J],2006,110:3930-3937
[11]Zhao Z, Yin L, Yuan G, et al. Layer-by-Layer Assembly of Two Temperature-Responsive Homopolymers at Neutral pH and the Temperature-Dependent Solubility of the Multilayer Film. Langmuir[J],2012,28:2704-2709
[12]Steitz R, Leiner V, Tauer K, et al. Temperature-induced changes in polyelectrolyte films at the solid-liquid interface. Appl. Phys. A-Mater.[J],2002,74:519-521
[13]Serpe M J, Jones C D, Lyon L A. Layer-by-Layer Deposition of Thermoresponsive Microgel Thin Films. Langmuir[J],2003.19 (21):8759-8764
[14]Browne W, Feringa B L. Making molecular machines work. Nature Nanotech.[J],2006, 1:25-35
[15]Cui S, Pang X, Zhang S, et al. Unexpected Temperature-Dependent Single Chain Mechanics of Poly(N-isopropyl-acrylamide) in Water. Langmuir[J],2012,28: 5151-5157
[16]Kobayashi J, Kikuchi A, Sakai K, et al. Cross-Linked Thermoresponsive Anionic Polymer-Grafted Surfaces To Separate Bioactive Basic Peptides. Anal. Chem.[J],2003, 75:3244-3249
[17]Cheng X, Wang Y, Hanein Y, et al. Novel cell patterning using microheater-controlled thermoresponsive plasma films. J. Biomed. Mater. Res. A[J],2004,70A (2):159-168
[18]Hinrichs W L J, Schuurmans-Nieuwenbroek N M E, Wetering P v d, et al. Thermosensitive polymers as carriers for DNA delivery. J. Control. Release[J],1999,60: 249-259
[19]Chilkoti A, Chen G, Stayton P S, et al. Site-Specific Conjugation of a Temperature-Sensitive Polymer to a Genetically-Engineered Protein. Bioconjugafe. Chem.[J],1994,5:504-507
[20]张文科,王驰,张希.单分子力谱.科学通报[J],2003,48：1113-1126
[21]Giannotti M I, Vancso G J. Interrogation of Single Synthetic Polymer Chains and Polysaccharides by AFM-Based Force Spectroscopy. Chem.Phys.Chem.[J],2007,8 (16): 2290-2307
[22]Zlatanova J, Lindsay S M, Leuba S H. Single molecule force spectroscopy in biology using the atomic force microscope. Prog. Biophys. Mol. Bio.[J],2000,74 (1-2):37-61
[23]Hugel T, Seitz M. The study of molecular interactions by AFM force spectroscopy. Macromol. Rapid Commun.[J],2001,22:989-1016
[24]Hinterdorfer P, Dufrene Y F. Detection and localization of single molecular recognition events using atomic force microscopy. Nat. Meth.[J],2006,3 (5):347-355
[25]Butt H-J, Cappella B, Kappl M. Force measurements with the atomic force microscope: Technique, interpretation and applications. SURF. SCI. REP.[J],2005,59 (1-6):1-152
[26]Zhang W, Zhang X. Single molecule mechanochemistry of macromolecules. Prog. Polym. Sci.[J],2003,28 (8):1271-1295
[27]Sader J E. Frequency response of cantilever beams immersed in viscous fluids with applications to the atomic force microscope. J. Appl. Phys.[J],1998,84 (1):64-76
[28]Hutter J L, Bechhoefer J. Calibration of atomic-force microscope tips Rev. Sci. Instrum.[J],1993,64(7):1868-1873
[29]Sader J E, Larson I, Mulvaney P, et al. Method for the calibration of atomic force microscope cantilevers. Rev. Sci. Instrum.[J],1995,66 (7):3789-3798
[30]Sader J E, Chon J W M, Mulvaney P. Calibration of rectangular atomic force microscope cantilevers. Rev. Sci. Instrum.[J],1999,70 (10):3967-3969
[31]Senden T, Ducker W. Experimental Determination of Spring Constants in Atomic Force Microscopy. Langmuir[J],1994,10 (4):1003-1004
[32]Cleveland J P, Manne S, Bocek D, et al. A nondestructive method for determining the spring constant of cantilevers for scanning force microscopy. Rev. Sci. Instrum.[J],1993, 64 (2):403-405
[33]Neumeister J M, Ducker W A. Lateral, normal, and longitudinal spring constants of atomic force microscopy cantilevers. Rev. Sci. Instrum.[J],1994,65 (8):2527-2531
[34]Fisher T E, Oberhauser A F, Carrion-Vazquez M, et al. The study of protein mechanics with the atomic force microscope. Trends. Biotechnol. [J],1999,24 (10):379-384
[35]Zhang W, Zou S, Wang C, et al. Single Polymer Chain Elongation of Poly(N-isopropylacrylamide) and Poly(acrylamide) by Atomic Force Microscopy. J. Phys. Chem. B[J],2000,104 (44):10258-10264
[36]Wang C, Shi W, Zhang W, et al. Force Spectroscopy Study on Poly(acrylamide) Derivatives:Effects of Substitutes and Buffers on Single-Chain Elasticity. NANO LETTERS[J],2002,2:1169-1172
[37]Xue W, Huglin M B, Jones T G J. Parameters Affecting the Lower Critical Solution Temperature of Linear and Crosslinked Poly(N-ethylacrylamide) in Aqueous Media. Macromol. Chem. Phys.[J],2003,204:1956-1965
[38]Idziak I, Avoce D, Lessard D, et al. Thermosensitivity of Aqueous Solutions of Poly(N,N-diethylacrylamide). Macromolecules[J],1999,32:1260-1263
[39]Djokpe E, Vogt W. N-Isopropylacrylamide and N-Isopropylmethacryl-amide:Cloud Points of Mixtures and Copolymers. Macromol. Chem. Phys.[J],2001,202 (5):750-757
[40]Boutris C, Chatzi E G, Kiparissides C. Characterization of the LCST behaviour of aqueous poly(N-isopropylacrylamide) solutions by thermal and cloud point techniques. Polymer[J],1997,38:2567-2570
[41]Wang X, Wu C. Light-Scattering Study of Coil-to-Globule Transition of a Poly(N-isopropylacrylamide) Chain in Deuterated Water. Macromolecules[J],1999,32: 4299-4301
[42]Wu C, Zhou S. Laser Light Scattering Study of the Phase Transition of Poly(N4sopropylacrylamide) in Water.1. Single Chain. Macromolecules[J],1995,28: 8381-8387
[43]Zhou S, Fan S, Au-yeung S C F, et al. Light-scattering studies of poly(N-isopropylacrylamide) in tetrahydrofuran and aqueous solution. Polymer[J],1995, 36 (7):1341-1346
[44]Kubota K, Fujishige S, Ando I. Single-chain transition of poly(N-isopropylacrylamide) in water. J. Phys. Chem.[J],1990,94 (12):5154-5158
[45]Schild H G, Tirrell D A. Microcalorimetric detection of lower critical solution temperatures in aqueous polymer solutions. J. Phys. Chem.[J],1990,94 (10):4352-4356
[46]Schild H G, Tirrell D A. Interaction of poly(N-isopropylacrylamide) with sodium n-alkyl sulfates in aqueous solution. Langmuir[J],1991,7 (4):665-671
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