通过荧光共振能量转移（FRET）研究洞察非共价核心交联嵌段共聚物胶束,Macromolecules

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通过荧光共振能量转移（FRET）研究洞察非共价核心交联嵌段共聚物胶束
Macromolecules ( IF 5.1 ) Pub Date : 2015-05-08 00:00:00 , DOI: 10.1021/acs.macromol.5b00559
Priya Rajdev ₁ , Dipankar Basak ₁ , Suhrit Ghosh ₁

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由于两亲性聚合物能够产生具有容器特性的多种自组装结构，可用于应对生物医学应用中日益严峻的挑战，因此两性聚合物已成为一类重要的材料。因此，从应用角度出发，对它们的聚集特性的深入了解从根本上来说很重要。在本文中，我们描述了利用荧光共振能量转移（FRET）作为阐明两亲嵌段共聚物聚集体在非常低的聚合物浓度（〜10 ^–7 M）下的各种物理性能的强大工具，否则使用其他常用方法难以实现显微镜，散射或基于外部探针的光谱技术等技术。我们合成了基于PEO-的预聚物b -PMMA-合作-PHEMA，随后利用HEMA单元的羟基与绿色（D）或红色（A）荧光染料（适用于FRET的D–A对）共价连接，得到D和A标记的两亲聚合物这些发色团在两种聚合物的疏水嵌段中具有相似的空间分布。胶束聚集体中红色和绿色标记的聚合物的共组装可产生高效的FRET，而当它们保持单体状态时则未观察到FRET。通过混合两种聚合物的预先形成的聚集体或通过在单体混合物中诱导聚集，通过溶剂，浓度，时间和pH依赖的FRET研究来研究胶束化过程。与现有的看法相反，我们的研究表明动力学异常缓慢（混合时间> 50小时），临界聚集浓度非常低（<10^–7M），对良溶剂具有极高的耐受性，并且令人着迷的溶剂引起的溶胀，然后由这种相当简单的二嵌段共聚物分解胶束聚集体。我们明确显示了为什么基于FRET的工具在其他技术中能脱颖而出，以非常精确的浓度在非常稀的浓度下精确探测胶束聚集体的这种详细物理特征，否则这似乎是一项相当困难的任务。更有趣的是，通过提供疏水嵌段中存在的少数未反应的OH基团之间通过H键进行非共价核心交联的证据，我们为这些胶束的异常高稳定性提供了理论依据。当通过在酸性pH下质子化或通过乙酰基保护羟基来提高此参数时，FRET研究表明胶束聚集的动力学非常快，

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Insights into Noncovalently Core Cross-Linked Block Copolymer Micelles by Fluorescence Resonance Energy Transfer (FRET) Studies

Amphiphilic polymers have emerged as an important class of materials owing to their ability to produce a diverse range of self-assembled structures with container properties that can be used to address growing challenges in biomedical applications. Thus, in-depth understanding on their aggregation properties is important fundamentally as well as from an application viewpoint. In this article we describe utilization of fluorescence resonance energy transfer (FRET) as a powerful tool to elucidate various physical properties of amphiphilic block copolymer aggregates at very low polymer concentration (∼10^–7 M) which otherwise are difficult to achieve using other commonly used techniques such as microscopy, scattering, or external probe based spectroscopic techniques. We synthesized a prepolymer based on PEO-b-PMMA-co-PHEMA and subsequently utilized the hydroxy groups of the HEMA units to covalently attach with either a green (D) or a red (A) fluorescent dye (D–A pair suitable for FRET) to get D- and A-labeled amphiphilic polymers with similar spatial distribution of these chromophores in the hydrophobic block of the two polymers. Coassembly of red and green labeled polymers in micellar aggregates results in highly efficient FRET while no FRET is observed when they remain as unimer. This was exploited to study the micellization process by solvent, concentration, time, and pH dependent FRET studies either by mixing preformed aggregates of the two polymers or by inducing aggregation in mixture of unimers. Contrary to existing perception, our studies revealed exceptionally slow dynamics (mixing time >50 h), very low critical aggregation concentration (<10^–7 M), remarkably high tolerance to good solvent, and intriguing solvent induced swelling followed by disassembly of the micellar aggregate from this rather simple diblock copolymer. We explicitly show why the FRET based tool stands out among other techniques to probe such detail physical characteristics of micellar aggregates with precision at very dilute concentration which otherwise appears to be a rather difficult task. More interestingly, we provide the rationale behind the exceptionally high stability of these micelles by providing evidence of noncovalent core cross-linking by H-bonding among the few unreacted OH groups present in the hydrophobic block. When this parameter was lifted off by either protonation at acidic pH or protecting the hydroxyl group by acetyl group, FRET studies showed very fast dynamics of the micellar aggregations, confirming the free OH groups in the hydrophobic domain are responsible for noncovalent core cross-linking leading to the unusual stability of the micelles.

更新日期：2015-05-08

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