作为“绿色”化学纳米级反应容器的线性-树枝状超分子复合物。富勒烯C60与多环芳烃在水介质中的狄尔斯-阿尔德反应。

Linear-dendritic supramolecular complexes as nanoscale reaction vessels for "green" chemistry. Diels-Alder reactions between fullerene C60 and polycyclic aromatic hydrocarbons in aqueous medium.

作者信息

Simonyan Arsen, Gitsov Ivan

机构信息

Department of Chemistry, College of Environmental Science and Forestry, State University of New York, Syracuse, New York 13210, USA.

出版信息

Langmuir. 2008 Oct 21;24(20):11431-41. doi: 10.1021/la801593y. Epub 2008 Sep 10.

DOI:10.1021/la801593y

PMID:18781794

Abstract

This study describes the first Diels-Alder (DA) reaction performed in aqueous medium with highly hydrophobic compounds-fullerene (C 60) as the dienophile and anthracene (An) or tetracene (Tet) as the dienes, respectively. The reactions are performed in nanocontainers, constructed by self-assembly of linear-dendritic amphiphilic copolymers with poly(ethylene glycol), PEG or poly(ethylene oxide), PEO as the hydrophilic blocks and poly(benzyl ether) monodendrons as the hydrophobic fragments: G3PEO13k, dG3 and dG2. Comparative studies under identical conditions are carried out with an amphiphilic linear-linear copolymer, poly(styrene)1800- block-PEO2100, PSt-PEO, and the nonionic surfactant Igepal CO-720, IP720. The binding affinity of supermolecules built of these amphiphiles toward the DA reagents decreases in the following order: G3PEO13k > dG3 > PSt-PEO > dG2 > IP720. The kinetic constant of binding is evaluated for tetracene and decreases in a similar fashion: 5 x 10 (-7) M/min (G3PEO13k), through 4 x 10 (-7) M/min (PSt-PEO) down to 1.5 x 10 (-7) M/min for IP720. The mobility of substrates encapsulated in the micellar core, estimated by pyrene fluorescence decay, is 95-121 ns for the micelles of the linear-dendritic copolymers and notably higher for PSt-PEO (152 ns), revealing the much denser interior of the linear analogue. The apparent kinetic constant for the DA reaction of C 60 and Tet within the G3PEO13k supermolecule in aqueous medium is markedly higher than in organic solvent (toluene), 208 vs 1.82 M /min. With G3PEO13k the conversions reach 49% for the DA reaction between C 60 and An, and 55% for C 60 and Tet. Besides the monoadduct (26.5% yield) the reaction with An produces exclusively increasing amounts of D 2 h -symmetric antipodal bis-adduct, whose yield reaches up to 22.5% after 48 h. In addition to the environmentally friendly conditions notable advantages of the synthetic strategy described are the extended stability of the linear-dendritic nanovessels, the easy collection of the products formed, and the recovery and reuse of unreacted reagents and linear-dendritic copolymers.

摘要

本研究描述了首次在水介质中进行的狄尔斯-阿尔德（DA）反应，其中以高度疏水的化合物富勒烯（C60）作为亲双烯体，分别以蒽（An）或并四苯（Tet）作为双烯体。反应在纳米容器中进行，这些纳米容器由线性-树枝状两亲共聚物与聚乙二醇（PEG）或聚环氧乙烷（PEO）自组装构建而成，其中PEG或PEO作为亲水链段，聚苄基醚单树枝状分子作为疏水片段：G3PEO13k、dG3和dG2。在相同条件下，用两亲性线性-线性共聚物聚（苯乙烯）1800-嵌段-PEO2100（PSt-PEO）和非离子表面活性剂Igepal CO-720（IP720）进行了对比研究。由这些两亲物构建的超分子对DA试剂的结合亲和力按以下顺序降低：G3PEO13k＞dG3＞PSt-PEO＞dG2＞IP720。评估了并四苯的结合动力学常数，其也以类似方式降低：5×10⁻⁷M/min（G3PEO13k），经4×10⁻⁷M/min（PSt-PEO）降至IP720的1.5×10⁻⁷M/min。通过芘荧光衰减估计，包裹在胶束核中的底物的迁移率对于线性-树枝状共聚物的胶束为95 - 121纳秒，而对于PSt-PEO则明显更高（152纳秒），这表明线性类似物的内部结构更致密。在水介质中，G3PEO13k超分子内C60与Tet的DA反应的表观动力学常数明显高于在有机溶剂（甲苯）中的值，分别为208对1.82M/min。对于G3PEO13k，C60与An之间的DA反应转化率达到49%，C60与Tet之间的反应转化率达到55%。除了单加合物（产率26.5%）外，与An的反应仅产生数量不断增加的具有D2h对称的对映双加合物，其产率在48小时后达到22.5%。除了环境友好的条件外，所描述的合成策略的显著优点还包括线性-树枝状纳米容器的稳定性增强、所形成产物的易于收集以及未反应试剂和线性-树枝状共聚物的回收和再利用。