【作者】 王伟；

【导师】 张艳；

【作者基本信息】 南京大学 ， 化学、有机化学， 2014， 博士

【摘要】 光活性分子在一定波长的光诱导下发生的不可逆的化学转化及在不同波长光照下发生的可逆的结构或构型变化都是光化学研究中的重要内容。基于光活性分子在光诱导下的化学结构或构型变化,光化学研究也从对于光反应本身的阐释逐步拓展到了对于能够用于能源、环境及生物体系等领域中的光活性分子的发现及其在光调控等方面应用的探索。光活性分子在激发态下可通过与热反应条件下完全不同的途径发生特殊的化学反应,可为很多在热反应中难以获取的有机化合物提供有效的合成途径;一些在光照下发生可逆的结构或构型变化的光活性分子可被用作"光开关"来对复杂的生物体系实现动态的光调控;某些可在光照条件下迅速发生化学键断裂或重排的光活性分子则已被发展成为在生物体系研究中具有重要功能的封端化合物的光敏性保护基团,这些都是光活性分子在化学及多学科交叉研究中的重要性的体现。本论文工作主要针对两类光活性分子,一类是能够在光诱导下被有效激发生成nπ*或ππ*激发三重态从而与含有双键的物种发生反应的对醌类化合物;另一类则是在不同波长的光照下可发生可逆的开环/关环反应的吲哚啉螺吡喃类化合物。基于这两类光活性分子,本论文工作主要分以下四个部分:1.对醌在光诱导下与具有环张力的特殊烯烃环丙叉环丙烷的反应及其合成应用探索。本部分工作主要研究了不同的对醌类光活性分子在光诱导下与环丙叉环丙烷(BCP)的反应规律,通过一系列对醌(包括苯醌、萘醌、蒽醌和萘并[2,3-b]呋喃-4,9-二酮)与BCP之间的光化学反应,合成了一系列具有螺环丙烷环结构的多环化合物。对醌激发三重态的性质(nπ*或者ππ*激发三重态)及环丙烷在反应过程中可能发生的开环反应,导致对醌与BCP的光反应产物具有多样性。在反应中,我们不仅得到了初级产物氧杂环丁烷和环丁烷类化合物(由对醌激发三重态的性质决定),而且得到了环丙烷开环重排的次级产物。我们还发现在9,10-蒽醌与BCP的光反应中,Paterno-Buchi 1,4-双基中间体经历的新的反应途径,得到新型的加成-重排产物。本章所研究的对醌与BCP的光化学反应中,有些可能发展成为合成具有环丙烷结构的多环化合物的有用的手段。2.吲哚啉螺吡喃类光活性分子在水溶液中的反向光致变色反应(reverse photochromism)研究。本部分工作深入研究了具有不同取代基团的吲哚啉螺吡喃类光活性分子在水溶液中、不同的pH条件下,通过光照及加热条件实现的可逆的结构转化。我们通过将不同的基团引入吲哚啉螺吡喃分子中的不同位点以及引入芳香体系更大的萘环,得到四种吲哚啉螺吡喃分子SPⅠ、SPⅡ、SPⅢ和SPⅣ。通过吸收光谱和HPLC对化合物的转化过程进行监测,我们发现这四种螺环的光活性分子中,SPⅠ、SPⅡ和SPⅣ在水溶液中经适度加热后可迅速转变为相应的开环结构MCⅠ、MCⅡ和MCⅣ,这些开环结构在可见光照射下又可以迅速转变回螺环结构,这一可逆的结构变化可重复发生多次。而SPⅢ在水溶液中则没有这种反向光致变色反应发生。本章研究为我们在后续的两章研究中选用合适的光活性分子对超分子自组装体系进行可逆的调控奠定了基础。3.吲哚啉螺吡喃类光活性分子在短肽自组装体系的可逆调控中的应用。在本部分工作中我们通过将在第二部分工作中筛选出的在水溶液中具有反向光致变色效应的SPI及SPIV分别修饰在短肽的链端,研究通过这些光活性分子的异构化反应对合成短肽在水溶液中的自组装性质可进行的调控。实验结果表明,修饰短肽在水中的自组装性质主要决定于吲哚啉螺吡喃的结构以及短肽序列与吲哚啉螺吡喃的连接方式。短肽序列连接在吲哚啉螺吡喃分子SPⅠ或SPⅣ的5’-位时,得到的短肽在水溶液中经过加热促使的反向光致变色效应转变成MCⅠ或MCⅣ修饰的短肽后,可以在水中通过超分子自组装作用形成纳米纤维的网络进而成为超分子水凝胶。并且MCⅠ或MCⅣ修饰的短肽自组装成的水凝胶具有光敏性,经可见光照射后,可以转变为溶液;得到的溶液经加热,冷却后可以再次形成水凝胶。因此可以通过吲哚啉螺吡喃与短肽连接,可以实现光和热可逆的调控短肽分子的自组装性质。4.吲哚啉螺吡喃SPI在调控糖胺及PNA寡聚物等生物活性小分子自组装性质中的应用。在本部分工作中我们对于SPI的应用进行了进一部分探索,通过多种合成方法,我们成功的将SPI修饰在包括糖胺及PNA寡聚物等生物活性分子上,进而对这些分子的自组装性质进行了测试,发现SPI修饰的糖胺转变为相应的MCI结构后可以在中性的水溶液中自组装成为微结构为纳米纤维的超分子水凝胶。当把SPI与PNA寡聚物相连时,我们发现当PNA上碱基序列为A-A或T-T时,相应的开环型分子也可以在较高浓度下自组装成为水凝胶。这些由平面型的MCI修饰的小分子所形成的水凝胶都具有光敏性,在可见光照射下由于平面型的MCI转变为螺环的SPI,因此自组装被破坏,形成的水凝胶逐渐转变为溶液。更多还原

【Abstract】 Photo-induced reactions including the irreversible chemical transformations and the reversible structure or conformation changes are important topics in photochemistry.Photo-induced reactions via the excited states of the substrates usually proceed through different reaction pathways form those of thermal reactions,which may lead to the formation of complex framework that are difficult to obtain by conventional synthetic approaches based on thermal reactions.The reversible structure or conformation change of phot-active molecules upon irradiation with light of different wavelengths has greatly expanded the applications of photo-active molecules as "photo-switches" to realize dynamic modulation in biological system.Photoactive molecules that can undergo fast bond-cleavage reactions upon light irradiation have been used as photo-labile protecting groups in "caged compounds"which have found wide applications in biological studies.In this dissertation,we studied the irreversible photo-reactions of para-quinones and the reversible structure change of spiropyrans to explore their applications as "photo-switches".The main work in this dissertation was included in the following four parts:1.Photo-induced reactions of para-quinones with the strained alkene bicyclopropylidene.Photo-induced reactions of different para-quinones including benzoquinones,naphthoquinones,anthraquinones and naphtho[2,3-b]furan-4,9-dione with bicyclopropylidene(BCP)were investigated.Diverse polycyclic products bearing spiropropyl moiety were obtained via the photocycloaddition followed by various ring arrangements.The nature of the excited state of quinones(nπ*or ππ*triplet state)and the ring-opening reaction of cyclopropane ring during the reaction process led to the diversity of the products.Besides of the primary products oxetanes and cyclobutanes(depending on the nature of the excited states of para-quinones),secondary products from the ring-opening reactions of cyclopropane rings followed with rearrangement reactions were also obtained.In the reaction between 9,10-anthraquinone with BCP,an unprecedented reaction pathway was observed via the Paterno-Buchi 1,4-diradical intermediate leading to the formation of the novel addition-rearrangement product.Some of the photoreactions between para-quinones with BCP also hold potentials as useful synthetic protocol to prepare polycyclic compounds with the spiropolycyclic framework.2.Reversible isomerizations of spiropyrans indued by light/heat in aqueous solution.Four types of spiropyrans(SPⅠ,SPⅡ,SPⅢ and SPⅣ)were synthesized and studied with respect to their isomerization with the merocyanine(MC)form upon light irradiation or heating in aqueous solution at different pH.The isomerization procees was monitored by UV-vis spectra and HPLC analysis.Three of the four SPs(SPⅠ,SPⅡ and SPⅣ)were found to undergo fast isomerization leading to the ring-open(MCⅠ,MCⅡ and MCⅣ)in aqueous solution upon moderate heating.All the MC forms were able to be rapidly converted into their SP counterparts upon visible light irradiation.The reverse photochromism of SPⅠ,SPⅡ and SPⅣ in aqueous solution makes it possible to use these moieties in the construction of self-asembling systems that were able to be reversibly modulated with light/heat.3.Application of spiropyrans in reversible modulation of self-assembly system based on short peptides.Short peptides with 6-8 amido acid residues were linked with SPⅠ,SPⅡ or SPⅣ on the N terminal or C-termial to get photo-sensitive peptides.Upon reverse photochromism of the SP-peptides to form MC-short peptides,the self-assembling properties of the peptides were investigated in detail.Most of the short peptides linked with MCⅠ or MCⅣ were able to self-assemble into fibrous network to form supramolecular hydrogels.But none of the short peptides linked to MCⅡ showed hydrogelation ability.The hydrogels formed by the MCⅠ or MCⅣmodified peptides underwent gel to solution phase transition upon visible light irradiation to induce the change from MC-peptides to SP-peptides.The resulted solution containing large portions of SP-peptides upon proper heating for "reverse"photochromism of the SP moiety was able to form supramolecular hydrogel again."Smart" hydrogel with multi-responses was also constructed through the proper combination of the MC moiety and short peptides with specific sequence.4.Spiropyran modified glycosyamines and PNA oligomers.Using SPI and SPII linked with carboxylic acid,we further modified several types of bioactive molecules including glycosaymine and PNA oligomers with this photo-active moiety.Upon reverse photochromism to transform the SP moiety to the planar MC moiety,the self-assembling properties of the modified glycosaymine and PNA oligomers were investigated.We found that glycosyamines linked with MCI were able to self-assemble to form supramolecular hydrogels at neutral pH.PNA oligomers A-A and T-T linked with MCI were also able to gel water but with relatively high concentration.None of the MCII linked molecules showed hydrogelations ability.The hydrogel formed by MCI-glycosyamine or MCI-PNA oligomer all showed photoresponse upon irradiation with visible light.更多还原