光控智能界面构建及其在生物中的应用 #

张隽佶，马文静*

（华东理工大学结构可控先进功能材料及其制备教育部重点实验室和精细化工研究所, 上海 200237）

2.02.02.0Key Laboratory for Advanced Materials and Institute of Fine Chemicals, East China University of Science & Technology, Shanghai 200237;Key Laboratory for Advanced Materials and Institute of Fine Chemicals, East China University of Science & Technology, Shanghai 200237华东理工大学结构可控先进功能材料及其制备教育部重点实验室和精细化工研究所, 上海 200237;华东理工大学结构可控先进功能材料及其制备教育部重点实验室和精细化工研究所, 上海 200237200237;13764263481;13764263481;上海市徐汇区梅陇路130号华东理工大学;zhangjunji@ecust.edu.cn;mwjwicky@163.com张隽佶（1985-），男，讲师，光控表界面行为研究;张隽佶;马文静ZHANG Junji;MA Wenjing张隽佶教育部博士点新教师基金 (20130074120002)2.02.02.02.02.02.02.02.02.02.02.02.0	1*|*期刊*|*(a) Balzani V, Gómez-López M, Stoddart J F. Molecular machines[J]. Accounts of Chemical Research, 1998, 31(7): 405-414. (b) Balzani V, Credi A, Raymo F M, et al. Artificial molecular machines[J]. Angewandte Chemie International Edition, 2000, 39(19): 3348-3391. 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Epimeric Monosaccharide-Quinone Hybrids on Gold Electrodes toward the Electrochemical Probing of Specific Carbohydrate-Protein Recognitions[J]. Journal of the American Chemical Society, 2011, 133(10): 3649-3657.<CR>28*|*期刊*|*Chandrasekaran V, Lindhorst T K. Sweet switches: azobenzene glycoconjugates synthesized by click chemistry[J]. Chemical Communications, 2012, 48(60): 7519-7521.<CR>29*|*期刊*|*Zhu L, Zhang D, Qu D, et al. Dual-controllable stepwise supramolecular interconversions[J]. Chemical Communications, 2010, 46(15): 2587-2589.<CR>30*|*期刊*|*Kai-Bin L; Yi Z; Huan W; Xiao-Peng H; He T; et al. hepatoma-selective imaging of heavy metal ions using a 光控智能界面构建及其在生物中的应用|Construction of Light Control Smart Interface and Its Application in Biology|教育部博士点新教师基金 (20130074120002)*|1|张隽佶|ZHANG Junji|华东理工大学结构可控先进功能材料及其制备教育部重点实验室和精细化工研究所, 上海 200237|Key Laboratory for Advanced Materials and Institute of Fine Chemicals, East China University of Science & Technology, Shanghai 200237|张隽佶（1985-），男，讲师，光控表界面行为研究|上海市徐汇区梅陇路130号华东理工大学|200237|zhangjunji@ecust.edu.cn|13764263481|13764263481<CR>|2|马文静|MA Wenjing|华东理工大学结构可控先进功能材料及其制备教育部重点实验室和精细化工研究所, 上海 200237|Key Laboratory for Advanced Materials and Institute of Fine Chemicals, East China University of Science & Technology, Shanghai 200237||||mwjwicky@163.com||

摘要：光控智能界面在光电子和传感器领域有着广泛的应用。使用光作为调控信号有很多优点，例如提供了更高的时间和空间分辨率，可以实现远程和非侵入性控制。当引入目标生物大分子例如肽类、DNA和小分子(包括叶酸衍生物和糖)来修饰光电开关，可以进一步增强智能表面的检测效率和特异性识别功能。在本文中，基于单糖(半乳糖和甘露糖)修饰的偶氮苯，我们构建了光控自组装单分子层，用电化学方法来检测偶氮的光控异构化性能，以及单糖对蛋白质选择性粘附性能。在紫外光和可见光的交替照射下，实现了电极表面单糖对选择性凝集素的高、低识别之间的相互转化。此外，cis-SAMs表面对选择性蛋白质具有低结合亲和力，对非选择性蛋白质几乎没有吸附作用，这可以应用于制备表面防污层，在实际应用可以避免不必要的表面污染和探针消耗。此外，所使用的电化学技术促进了基于智能表面的便携式设备的开发，在疫病诊断领域也有广阔的应用前景。

关键词：应用化学；光控；自组装单分子层；偶氮苯；单糖蛋白质识别

中图分类号：069

Construction of Light Control Smart Interface and Its Application in Biology

ZHANG Junji, MA Wenjing

(Key Laboratory for Advanced Materials and Institute of Fine Chemicals, East China University of Science & Technology, Shanghai 200237)

Abstract: Photoresponsive smart surfaces are promising candidates for a variety of applications in optoelectronics and sensing devices. The use of light as an order signal provides advantages of remote and noninvasive control with high temporal and spatial resolutions. Modification of the photoswitches with target biomacromolecules, such as peptides, DNA, and small molecules including folic acid derivatives and sugars, has recently become a popular strategy to empower the smart surfaces with an improved detection efficiency and specificity. Herein, we report the construction of photoswitchable self-assembled monolayers (SAMs) based on sugar (galactose/mannose)-decorated azobenzene derivatives and determine their photoswitchable, selective protein adhesion performances via electrochemistry. Under alternate UV/vis irradiation, interconvertible high/low recognition and binding affinity toward selective lectins (proteins that recognize sugars) are achieved. Furthermore, the cis-SAMs with a low binding affinity toward selective proteins also exhibit minimal response toward unselective protein, which offers the possibility in avoiding unwanted contamination and consumption of probes prior to functioning for practical applications. Besides, the electrochemical technique used facilitates the development of portable devices based on the smart surfaces for on-demand disease diagnosis.

Key words: Applied Chemistry; Photo-switching; Self-assembled monolayer; Azobenzene; Monosaccharide protein recognition

引言

光响应材料由于其非侵入性、绿色清洁以及拥有高分辨率等特点有助于实现准确的远程操控，这吸引了越来越多科学家的研究兴趣[1-4]。到目前为止，大多数对光控分子的研究都是在溶液相中实现，而溶液中分子是分散分布、随机定向的。为了将光可逆分子修饰到材料表面从而以便于发展实用设备，“智能表面”的出现引起了科学家的研究兴趣。这种智能表面的“智能”表现在可以从远程收到光信号的“指令”来执行指定任务。在过去十年里，智能表面通过主客体作用[5-6]、静电作用[7-8]以及简单的几何异构化效应[9-11]等使其具有“捕获与释放”功能、电催化和润湿性的可调控操作系统，并且在光致变色分子和光电子器件之间起到了重要的桥梁作用。除了在光电器件领域的应用，智能表面连接上生物配体(例如，核苷酸，肽，糖配体)也已成为一个不断扩大的研究领域，因为他们可以模仿基本的生理过程，如蛋白质-配体识别[12-16]，酶级联催化[16-17]，细菌杀伤[18-19]和细胞粘附等。将生物配体与光响应分子组合促进了具有先进性功能和智能操作的新一代表面材料的发展，例如光控可逆分子通过“ON-OFF”转换使智能表面实现对细胞可逆性粘附以及表面循环再利用的功能[20, 21]。

以前的研究中，通常利用包括红外反射吸收光谱[20]，荧光光谱学[22-23]，单细胞力谱学和其他生物测定如OD细菌生长测定[21]等光学谱图和力学谱作为监测智能表面的光控过程的手段。虽然实现了蛋白质、细胞粘附和细菌生长的高效光调控检测，但是需要笨重和昂贵的仪器并且耗费较长的检测时间。在我们的体系中，利用电化学方法(包括循环伏安法，差分脉冲伏安法和交流阻抗法)来检测智能表面的可逆性行为。与上述光谱表征方法相比，电化学在检测速度和精度方面显示了其独特的优点，并且实现了仪器的小型化设备的使用(实验过程只需要一个小型恒电位器与个人笔记本电脑相连接就可以检测)，其已经广泛用于饮用饮料检测和生物分析领域。此外，智能表面的另一个优点是智能表面在某些特定光信号下可以保持休眠状态(OFF状态)，在另外某些特定光信号激活下成光活化状态(ON状态)。基于我们设计的可控智能表面本身的优点和光指令非侵入性的特点，在实际材料的应用过程中有很大的应用前景。比如材料存储和输送期间将不会产生不必要的消耗或污染，实现一个清洁可控的材料设计理念。

研究发现，糖基化的荧光探针和智能表面可以靶向检测蛋白、表达糖受体的细胞和病原体，并且具有低的细胞毒性、高的特异性等优点[24-26]。本研究中，我们使用了两种单糖(如图1)[27]：半乳糖和甘露糖。其中半乳糖可以选择性地与花生凝集素(PNA)结合；甘露糖则可以选择性结合伴刀豆球蛋白(Con A)发生相互作用。我们合成了半乳糖基和甘露糖基拴系的偶氮苯并将其修饰在金电极，通过施加交替UV/vis构建一个可切换的ON-OFF表面。我们并对其在UV/vis光智能表面对凝集素的识别和粘附做了电化学分析。

图1 (A)半乳糖偶氮苯(Gal-Azo-SH)和甘露糖偶氮苯(Man-Azo-SH)的结构；(B)在休眠(非活动)和活化(工作)状态之间可逆吸附蛋白的智能表面

Fig. 1 (A) Structure of the Galactose-Azobenzene (Gal-Azo-SH) and Mannose-Azobenzene (Man-Azo-SH); (B) Photoswitching of the Smart Surface between Dormant (Inactive) and Activated (Working) States Towards Selective Protein Adhesion

实验部分

试剂和仪器

所有的试剂和化学药品都是在售化学品，测试所需的蛋白购买自Sigma-Aldrich。化合物的1H NMR和13C NMR核磁共振谱图采用Bruker DRX-400型核磁共振仪测定，以CDCl3为氘代试剂，以TMS为内标进行测定表征。使用365 nm手提紫外灯(UVP Inc., 115 V, 0.16 A)进行Azo-SAMs的紫外线照射，使用氙灯(LEO，中国深圳)进行可见光照射，光学滤波片(450 nm-700 nm)购买自东方科仪仪器有限公司(中国天津)。电化学测试所需的工作站CHI1220b购买自上海辰华仪器公司，所用的三电极体系为3 mm的圆盘金电极作为工作电极，铂丝电极为辅助电极，饱和甘汞电极作为参比电极来进行测试。所用的实验都是在室温下进行，在电化学测试之前的所有溶液都进行除氧操作。

合成路线及方法

偶氮苯衍生物的合成(compound 1和1’)此前有报道[28-29]。

图2 乙酰化半乳糖-偶氮苯硫醇前体的合成

Fig. 2 Synthesis of acetylated galactose-azobenzene thiol precursor

4-(3-N-全乙酰基半乳糖基三氮唑基)-甲氧基-4’-羟基-偶氮苯的合成(compound 2)

称取4-(丙炔氧基)-4’-羟基偶氮苯(400 mg, 1.59 mmol)和全乙酰化叠氮半乳糖(373 mg, 1.90 mmol)置于25 mL圆底烧瓶中，加入7 mL CH2Cl2溶解。在磁力搅拌下充分溶解后，同时滴加CuSO4水溶液 (1.5 mL, 3.18 mmol)，L-抗坏血酸钠水溶液(VcNa, 1.5 mL, 6.36 mmol)，反应物在室温下搅拌过夜。反应结束后利用TLC检测发现原料基本反应完全，过滤除去无机盐，旋蒸除去CH2Cl2得到粗产物。用柱层析纯化分离，用环已烷:乙酸乙酯=3:2(v/v)冲洗产物点，得到黄色固体，质量696 mg，产率为70%。1H NMR(400 MHz, CDCl3) δ 7.97(s, 1H), 7.84(d, J=8.8 Hz, 2H), 7.79(d, J=8.8 Hz, 2H), 7.05(d, J=9.0 Hz, 2H), 6.94(d, J=8.8 Hz, 2H), 5.57(s, 2H), 5.29(s, 1H), 5.27(m, 3H), 4.22(m, 3H), 2.23(s, 3H), 2.05(s, 3H), 2.02(s, 3H), 1.88(s, 3H). 13C NMR (100 MHz, CDCl3) δ 170.4, 169.8, 169.1, 147.5, 144.5, 141.1, 124.5, 124.2, 121.4, 115.9, 115.1, 86.3, 74.1, 70.8, 67.8, 66.8, 62.1, 61.2, 20.6, 20.5, 20.5, 20.2. TOF MS ES+ m/z: [M+1]+ calcd. for 625.2020, found 625.2012.

4-(3-N-全乙酰基半乳糖基三氮唑基)-甲氧基-4’-(6-溴烷氧基)-偶氮苯的合成(compound 3)

在50 mL三口烧瓶中，N2保护下，将化合物2 (500 mg, 0.80 mmol)，6-溴-1-己醇 (432 mg, 2.40 mmol)，三苯基膦 (629 mg, 2.40 mmol)溶解在10 mL干燥的四氢呋喃，在0 oC下滴加偶氮二甲酸二乙酯 (418 mg, 2.40 mmol)，搅拌1 h。然后将反应提到室温搅拌5 h，TLC跟踪反应进程，反应结束，蒸发浓缩除去四氢呋喃。柱层析分离得到黄色固体425 mg，产率67.5%。1H NMR (400 MHz, CDCl3) δ 7.89(d, J=7.88 Hz, 2H), 7.86(d, J=7.6 Hz, 2H), 7.52(s, 1H), 7.40(d, J=7.6 Hz, 2H), 7.00(d, J=8.8 Hz, 2H), 5.59(s, 2H), 5.39(d, J=3.6 Hz, 1H), 5.20(t, J=9.6 Hz, J=8.8 Hz, 1H), 4.9(m, 2H), 4.82(d, J=12.4 Hz,1H), 4.04(t, J=6.4 Hz, J=6.4Hz, 2H), 3.95(t, J=6.8 Hz, J=6.4 Hz, 1H), 3.43(t, J=7.2 Hz, J=5.6 Hz, 2H), 2.13(s, 3H), 2.04(s, 3H), 1.96(s, 3H), 1.88(s, 3H), 1.83(br, 2H), 1.52(br, 4H), 1.26(br, 2H). 13C NMR(100 MHz, CDCl3) δ 170.2, 169.9, 169.8, 168.8, 160.2, 156.9, 132.7, 131.9, 131.8, 128.3, 128.2, 85.9, 73.7, 70.6, 67.8, 66.9, 65.4, 63.6, 61.5, 40.7, 33.8, 32.4, 27.8, 24.9, 20.5, 20.3, 20.0. TOF MS ES+ m/z: [M+1]+ calcd. for 787.2064, found 787.2055.

4-(3-N-全乙酰基半乳糖基三氮唑基)-甲氧基-4’-(6-硫代乙酸基烷氧基)-偶氮苯的合成(compound 4)

称取化合物3 (300 mg, 0.38 mmol)和KSAc (52 mg, 0.46 mmol)置于50 mL圆底烧瓶中，加入5 mL DMF充分溶解，室温搅拌过夜。然后将反应混合物用二乙醚(100 mL)洗涤，合并有机相并用水(2×25 mL)洗涤，MgSO4干燥。过滤旋蒸得到粗产物。柱层析得到黄色固体262 mg，产率88%。1H NMR(400 MHz, CDCl3) δ 7.88(d, J=8.8 Hz, 2H), 7.86(d, J=8.0 Hz, 2H), 7.52(s, 1H), 7.40(d, J=8.4 Hz, 2H), 6.99(d, J=8.8 Hz, 2H), 5.59(s, 2H), 5.38(d, J=3.4 Hz, 1H), 5.20(m, 1H), 4.98(m, 1H), 4.82(d, J=12.8 Hz, 1H), 4.65(d, J=8.0 Hz, 1H), 4.14(d, J=6.4 Hz, 2H), 4.03(t, J=6.4 Hz, J=6.4 Hz, 2H), 2.88(t, J=7.6 Hz, J=7.2 Hz, 2H), 2.32(s,3H), 2.13(s, 3H), 2.04(s,3H), 1.96(s, 3H), 1.87(m, 2H), 1.62(m, 2H), 1.47(m, 4H). 13C NMR (100 MHz, CDCl3) δ 194.9 ,170.2 , 161.6 , 149.7 , 144.3 , 142.3 , 138.4 , 128.3 , 123.6 , 122.9 , 114.7 , 106.3 , 74.8 , 72.0 , 70.7 , 69.3 , 68.7 , 62.5 , 62.4 , 57.3 , 32.5 , 30.5 , 29.6 , 29.2 , 28.7 , 25.6 , 21 , 20.7. TOF MS ES+ m/z: [M+1]+ calcd. for 783.2785, found 783.2779.

图3 乙酰化甘露糖-偶氮苯硫醇前体的合成

Fig. 3 Synthesis of acetylated mannose-azobenzene thiol precursor

4-(4-全乙酰基甘露糖基甲基醚基三氮唑基)-甲基-4’-羟基-偶氮苯的合成(compound 3’)

称取化合物1’ (300 mg, 0.90 mmol)置于25 mL的圆底烧瓶中，加入4 mL CH3CN溶解。称取NaN3(129 mg, 1.98 mmol)溶于1 mL去离子水中，并将其溶液加入含有化合物4’的CH3CN溶液中。升温至80 oC搅拌反应过夜。反应结束后，冷却至室温，反应化合物用乙酸乙酯多次萃取水相，并用MgSO4干燥。减压蒸馏除去CH3CN直接用于下步反应。

称量4-(叠氮乙基)-4’-羟基偶氮苯(183 mg, 0.63 mmol)和丙炔氧基甘露糖苷(300 mg, 0.75 mmol)置于25 mL圆底烧瓶中，加入5 mL CH2Cl2，在磁力搅拌下充分溶解后，同时滴加CuSO4水溶液(1 mL, 1.24 mmol)，L-抗坏血酸钠水溶液(VcNa, 1 mL, 2.48 mmol)，反应物在室温下搅拌过夜。反应结束，过滤除去无机盐，旋转蒸发除去二氯甲烷得到粗产物。柱层析分离得到黄色固体，质量310 mg，产率79 %。1H NMR(400 MHz, CDCl3) δ 7.88(d. J=3.6 Hz, 2H), 7.86(d, J=4.2 Hz, 2H), 7.56(s, 1H), 7.43(d, J=8.4 Hz, 2H), 6.95(d, J=8.8 Hz, 2H),5.62(s, 2H), 5.23(m, 1H), 4.95(d, J=1.28 Hz, 1H), 5.30(s, 2H), 5.23(m, 1H), 4.95(d, J=1.28 Hz, 1H), 4.86(d, J=12.4 Hz, 1H), 4.67(d, J=12.4 Hz, 1H), 4.29(dd, J=5.2 Hz, J=5.2 Hz, 1H), 4.06(s, 1H), 2.15(s,3H), 2.11(s, 3H), 2.03(s, 3H), 1.97(s,3H). 13C NMR (100 MHz, CDCl3) δ 170.2, 161.2, 161.1, 145.8, 144.2, 142.9, 134.7, 123.7, 114.9, 111.8, 101.6, 97.9, 73.7, 70.6, 68.9, 67.4, 62.4, 61.6, 60.9, 34.8, 32.4, 31.4, 27.8, 24.9, 20.5. TOF MS ES+ m/z: [M+Na]+ calcd. for 801.2221, found 824.2142.TOF MS ES+ m/z: [M+1]+ calcd. for 639.2177, found 639.2166.

4-(4-全乙酰基甘露糖基甲基醚基三氮唑基)-甲基-4’-(6-溴烷氧基)-偶氮苯的合成(compound 4’)

在50 mL三口烧瓶中，N2保护下，将化合物3’(200 mg, 0.32 mmol)，6-溴-1-己醇(174 mg, 0.96 mmol)，三苯基膦(252 mg, 0.96 mmol)溶解在6 mL干燥的四氢呋喃，在0 oC下滴加偶氮二甲酸二乙酯(167 mg, 0.96 mmol)，搅拌1 h。然后将反应提到室温搅拌5 h，TLC跟踪反应进程，反应结束，旋转蒸发除去四氢呋喃。柱层析分离得到黄色固体176 mg，产率68.4%。1 H NMR(400 MHz, CDCl3) δ 7.89(d, J=8.8 Hz, 2H), 7.88(d, J=8.0 Hz, 2H), 7.56(s, 1H), 7.42(d, J=8.4 Hz, 2H), 7.00(d, J=8.8 Hz, 2H), 5.61(s, 2H), 5.30(s, 2H), 5.23(m, 1H), 4.97(d, J=1.28 Hz, 1H), 4.95(m, 1H), 4.86(d, J=12.4 Hz, 1H),4.84(d, J=12.4 Hz, 1H), 4.67(d, J=12.4 Hz, 1H), 4.29(dd, J=5.2 Hz, J=5.2 Hz, 1H), 4.07(t, J=7.0 Hz, J=7.0 Hz ,2H), 3.43(t, J=6.8 Hz, J=6.8 Hz, 2H), 2.14(s, 3H), 2.10(s, 3H), 2.02(s, 3H), 1.97(s, 3H), 1.87(m, 4H), 1.53(dr, 4H). 13C NMR (100 MHz, CDCl3) δ 170.2, 169.9, 169.6, 168.8, 160.2, 156.9, 152.2, 132.7, 131.9, 131.8, 131.6, 128.5, 128.3, 85.9, 73.7, 70.6, 67.9, 66.9, 65.4, 63.6, 61.9, 61.5, 33.8, 32.6, 32.4, 27.8, 24.9, 20.5, 20.3, 20.0. TOF MS ES+ m/z: [M+Na]+ calcd. for 801.2221, found 824.2142.

4-(4-全乙酰基甘露糖基甲基醚基三氮唑基)-甲基-4’-(6-硫代乙酸基烷氧基)-偶氮苯的合成(compound 5’)

在50 mL圆底烧瓶中，将化合物4’(150 mg, 0.18 mmol), KSAc(25 mg, 0.22 mmol)溶解在5 mL DMF中，室温搅拌过夜。然后将反应混合物用二乙醚(100 mL)洗涤，合并有机相并用水(2×25 mL)洗涤，MgSO4干燥。过滤蒸发旋蒸得到粗产物。柱层析得到黄色固体262 mg，产率88%。1H NMR(400 MHz, CDCl3) δ 7.83(d, J=7.2 Hz, 2H), 7.81(d, J=7.6 Hz, 2H), 7.48(s, 1H), 7.35(d, J=8.4 Hz, 2H), 6.92(d, 8.8 Hz, 2H), 5.54(s, 2H), 5.22(s, 2H), 5.15(dr, 1H), 5.00(m, 2H), 4.87(d, J=1.48 Hz, 1H), 4.76(d, J=12.4 Hz, 1Hz), 4.60(d, J=12.4 Hz, 1H), 4.21(dd, J=5.2 Hz, J=5.2 Hz, 1H), 3.93(t, J=7.0 Hz, J=7.0 Hz, 2H), 2.82(t, J=7.2 Hz, J=7.2 Hz, 2H), 2.26(s, 3H), 2.07(s, 3H), 2.04(s, 3H), 1.96(s, 3H), 1.90(s, 3H), 1.56(m, 4H), 1.41(m, 4H). 13C NMR (100 MHz, CDCl3) δ 169.9 , 169.7 , 160.9 , 151.7 , 145.7 , 143.4 , 127.9 , 127.6 , 123.9 , 122.3 , 121.9 , 113.7 , 95.7 , 69.4 , 67. 9 , 67.7 , 67.1 , 65.0 , 61.9 , 61.7 , 61.3 , 60.1 , 52.9 , 29.6 , 28.7 , 28.4 , 27.9 , 27.4 , 24.5. TOF MS ES+ m/z: [M+1]+ calcd. for 797.2942, found 797.2922.

单分子层的形成

首先将金电极表面抛光至镜面状态，然后在乙醇中超声3 min。然后将电极浸泡在Piranha溶液(98% H2SO4/30% H2O2 = 3:1 (v/v))中10 min，除去电极表面的有机物。然后将金电极浸泡在超纯水中超声30 s。通过在0.5 M H2SO4溶液中进行循环伏安测试来进行电化学清洁(抛光程序)以除去残留的杂质。具体参数设置如下：电位范围为-0.30至1.55 V，在新配置的0.5 M H2SO4溶液中，以0.1 V·s-1的扫描速率、0.001 V的电位间隔下进行，共需要扫描10次获得循环伏安图。关键步骤: 必须保证获得清洁、光滑的金电极表面，才能支持化合物与金电极表面的有效结合。在一个清洁金电极的典型循环伏安图中，特征性单尖锐金氧化物还原峰是位于相对于SCE约0.9 V的位置，而多个重叠的氧化峰出现在相对于SCE的1.2-1.5 V的范围内。

因为硫醇是相当容易被空气氧化的，全乙酰基保护的偶氮苯在脱保护后立即进行自组装实验。即将全乙酰基保护的偶氮苯溶解在乙醇中，加入催化量的甲醇钠，常温搅拌2 h，点板检测反应进程。旋蒸过后柱层析分离得到Gal-Azo-SH/Man-Azo-SH。然后将金电极泡在含有1 mM的混合硫醇溶液即Gal-Azo-SH/Man-Azo-SH和n-C6H13-SH(1:10，摩尔比)的乙醇溶液，在室温下在暗处放置约36小时进行单分子层自组装。然后用乙醇冲洗未组装在 电极上的硫醇，并在干燥的高纯氮气流中干燥。

光控实验

将组装完成的Azo-SAMs的电极浸泡在磷酸盐缓冲液 (PBS, 0.1 M, pH 7.0)中20 min，在交替的紫外光(365 nm)和可见光(> 450 nm)照射下，进行循环伏安法(CV)，示差脉冲伏安法(DPV)实验，所有电化学实验都是在[Fe(CN)6]3-/4-(1.0 mM)+ KCl(0.1 M)溶液中进行的，CV电位从-0.2至0.7 V(扫描速率：0.1 V·s-1)扫描，DPV电位从0至0.6 V。

蛋白附着

组装完成的单糖偶氮苯(Azo-SAMs)在相应浓度(0.1~10 μM)的凝集素的PBS缓冲液(0.1 M, pH 7.4)浸泡20 min，使金表面单糖吸附蛋白达到饱和状态，然后分别用PBS缓冲液(0.1 M, pH 7.4)和Milli-Q冲洗未吸附在电极表面的蛋白，然后再进行电化学测试。对于凝集素脱离过程，将上述电极浸入PBS缓冲液(0.1 M, pH 7.4)，并暴露于365 nm紫外光照射下15 min，然后用PBS缓冲液(0.1 M, pH 7.4)和Milli-Q冲洗掉脱附的蛋白。随后对该电极施加450-700 nm可见光照射30分钟再回到trans-SAMs。循环伏安法(CV)，示差脉冲伏安法(DPV)实验在[Fe(CN)6]3-/4-(1.0 mM)+ KCl(0.1 M)溶液中进行。将CV电位从-0.2扫描至0.7 V(扫描速率，0.1 V·s-1)，DPV电位从0到0.6 V。

结果讨论

trans/cis-Azo-SAM的电化学测试

本文采用循环伏安法(CV)，示差脉冲伏安法(DPV)两种测试方法，以[Fe(CN)6]3-/4-为氧化还原电对进行表面测试。如图4所示，不管在CV图还是DPV图中，Gal/Man-Azo-SAM表面电流比裸电极电流有明显的下降，这是因为单分子层组装在金电极表面后，阻碍了[Fe(CN)6]3−/4-氧化还原电对在电极表面的传导。当我们施加紫外光对trans-SAMs表面照射，使偶氮苯从反式光异构化成为顺式时，暴露在金电极表面的是疏水性偶氮苯结构，进一步阻碍了[Fe(CN)6]3−/4-氧化还原电对的传导，导致CV和DPV电流进一步降低，此时经过cis-SAMs表面的电流约是trans-SAMs的38.7%。

图4 Gal-Azo-SAM (A)和Man-Azo-SAM (C)光可逆CV图，DPV Gal-Azo-SAM (B) and Man-Azo-SAM (D) 光可逆DPV图

Fig. 4 CV plots of Gal-Azo-SAM (A) and Man-Azo-SAM (C) modified electrode monolayers after UV/Vis irradiation. DPV plots of Gal-Azo-SAM (B) and Man-Azo-SAM (D) after UV/Vis irradiation.

为了进一步研究表面单糖偶氮苯的光致异构性能，我们进行了接触角实验测试。在光异构化由顺式结构变为反式结构后，裸露在金电极最表面的基团由亲水性的单糖变为疏水性的偶氮苯(如图1)，阻碍了[Fe(CN)6]3−/4-氧化还原电对的传导。除此之外，顺式偶氮苯的偶极矩有了明显的增加，由反式0 debye变为顺式4.4 debye，这可能是阻止[Fe(CN)6]3−/4-氧化还原电对有效扩散到金表面的另外一个重要原因。为了验证光异构化前后电极表面亲水性的变化，我们对trans/cis-SAMs表面进行了接触角测试。结果如图5所示：半乳糖组装的偶氮苯光照前后接触角从52.6 ± 1.3°(trans) 变到61.1 ± 1.1°(cis)，而甘露糖组装的偶氮苯光照前后接触角从53.6 ± 1.1°(trans) 变到 60.7 ± 1.0°(cis)。测试结果表明光照前后金表面的亲水性发生了变化，从而也间接证明了光照前后电极上单糖的位置发生了变化。

图5 trans/cis-Gal-Azo-SAM和trans/cis-Man-Azo-SAM的静态水接触角

Fig. 5 Images of the static water contact angles on the trans/cis-Gal-Azo-SAM and

trans/cis-Man-Azo-SAM

trans/cis-Azo-SAM光控蛋白行为测试

如前文所述，单糖可以选择性地识别蛋白。我们用来构建智能表面的单糖偶氮苯具有半乳糖和甘露糖两种单糖，所以可以特异性地识别蛋白。当智能单糖偶氮苯表面处于trans-SAMs状态时，单糖裸露在电极表面的最外层，因为单糖可以特异性吸附某种蛋白，所以我们电极可以识别蛋白，此时我们的电极处于“工作”状态；而当单糖偶氮苯表面处于cis-SAMs状态时，单糖伸向电极单分子层内部，而偶氮苯裸露在电极最外层，因为偶氮苯不能特异性识别蛋白，所以此时我们的电极处于“休眠”状态。我们设计的智能单糖偶氮苯表面处于trans-SAMs状态时，单糖裸露在电极表面的最外层，因为单糖可以特异性吸附某种蛋白，所以我们电极可以识别蛋白，此时我们的电极处于“工作”状态；而当单糖偶氮苯表面处于cis-SAMs状态时，单糖伸向电极表面里面，而偶氮苯裸露在电极最外层，因为偶氮苯不能特异性识别蛋白，所以此时我们的电极处于“休眠”状态。

我们研究了trans/cis-SAMs两种不同界面对蛋白特异结合能力的差异。在光控条件下，将不同界面状态的单分子层对蛋白的吸附作用进行了DPV测试。如图6所示，trans-SAMs加入蛋白后(将PNA加入到Gal-Azo-SAM, Con A加入到Man-Azo-SAM)，峰电流相对于初始状态下降了60%，而cis-SAMs表面电流相对于初始状态下降了28%。这说明trans-SAMs表面相比于cis-SAMs表面对于识别蛋白的能力更灵敏。

我们通过加入蛋白后，对比trans-SAMs和cis-SAMs表面电流下降的百分比(Id = (I0 − Is)/I0，Id是电流下降的百分比，I0未加蛋白时的电流，Is是加过蛋白的电流)，如图6(E, F)所示，可以看出trans-SAMs表面是具有特异性识别和选择性识别功能的，而cis-SAMs表面是不能识别蛋白的。这是因为光异构化前后电极表面中单糖的位置由裸露在电极最表面变成伸向电极里面，此时裸露在电极最外层的偶氮苯不具有特异性识别蛋白的能力，所以此时的电极表面是“休眠”状态。

图6 trans-Gal-Azo SAM (A)和cis-Gal-Azo SAM 对PNA响应的DPV图，trans-Man-Azo SAM (C) and cis-Gal-Azo SAM (D)对Con A响应的DPV图。trans-/cis-Gal-Azo SAM (E)和trans-/cis-Man-Azo SAM (F) 表面加入各种蛋白时电流下降的百分比

Fig. 6 DPV plots of trans-Gal-Azo SAM (A) and cis-Gal-Azo SAM (B) with PNA. DPV response of trans-Man-Azo SAM (C) and cis-Gal-Azo SAM (D) with Con A. Percentage (%) of peak current decrease of trans-/cis-Gal-Azo SAM (E) and trans-/cis-Man-Azo SAM (F) upon addition of various selective or unselective proteins.

为了进一步研究trans-Gal/Man-Azo-SAMs表面对蛋白的特异性吸附的灵敏度，我们做了一组浓度梯度测试，在不同浓度的蛋白中(在pH 7.4, 0.1 M PBS中，浓度变化范围是从0.1到10 μM)，检测电极表面对蛋白吸附(trans-Gal-Azo-SAM对PNA的特异性吸附，trans-Man-Azo-SAM对Con A的特异性吸附)的电流值。如图7，我们可以观察到trans- SAMs表面对蛋白的检测有个非常好的线性关系，通过对trans-SAMs表面检测限的推算[30]，得出trans-Gal-Azo-SAM表面的检测限为113 nM，trans-Man-Azo-SAM表面的检测限为103 nM。

图7 (A) trans-Gal-Azo-SAM对不同浓度PNA的响应，(C) trans-Man-Azo-SAM 对不同浓度Con A的响应。trans-Gal-Azo-SAM (B)和trans-Man-Azo-SAM (D)以(I0-IS)/I0为函数的灵敏度曲线

Fig.7 DPV plots of (A) trans-Gal-Azo-SAM with various concentrations of PNA and (C) trans-Man-Azo-SAM with various concentrations of Con A. Plotting of protein sensitivity (I0-IS)/I0 of trans-Gal-Azo-SAM (B) and trans-Man-Azo-SAM (D) as a function of protein concentration.

光可逆trans/cis-Azo-SAM潜在应用前景

我们设计的智能表面除了可以实现在trans/cis-SAMs两种不同界面对蛋白的不同作用之外，还可以通过光控实现电极表面在“工作”和“休眠”之间自由切换。如图8所示，trans-Gal-Azo-SAM表面处于“工作”状态，可以特异性识别PNA，所以当与PNA作用后，电流出现了明显的下降；当此时用紫外光照射，使偶氮苯发生光异构化反应变成顺式结构后，此时电极表面的半乳糖位置发生改变，蛋白在随着单糖变化的过程中，因为空间位阻效应而被挤掉，此时由于蛋白的离开电极表面的电流恢复到接近cis-Gal-Azo-SAM表面时的大小，此时电极表面处于“休眠”状态。而我们可以通过可见光的照射，让偶氮苯由顺式变成反式结构，重新恢复电极表面“工作”的状态。同理trans-Man-Azo-SAM亦是如此。这类光可控的智能界面相比于传统的光敏智能界面，在保留了光控的条件外，实现了可重复利用。

图8 蛋白对光可逆(A)Gal-Azo-SAM和(B)Man-Azo-SAM 表面响应的DPV图

Fig. 8 DPVplots of the photo-reversibility of (A) Gal-Azo-SAM and (B) Man-Azo-SAM with protein.

结论

综上所述，我们构建了半乳糖偶氮苯(Gal-Azo-SH)和甘露糖偶氮苯 (Man-Azo-SH)两种智能光控单分子层电极。他们可以从不同的光中接受命令，执行特定的任务。而当智能表面处于trans-SAMs状态时，可以特异性识别蛋白，这样可以用来提取特定的蛋白。重要的是，智能表面处于cis-SAMs状态时，对特异性蛋白吸附量极少，而对于非特异性蛋白几乎没有吸附作用，故此时电极表面处于非活性状态，在实际应用中可以避免智能材料表面受到不必要的污染。

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基金项目：教育部博士点新教师基金 (20130074120002)

作者简介：张隽佶（1985-），男，讲师，光控表界面行为研究. E-mail: zhangjunji@ecust.edu.cn