RESUMO
This work reports a basic microflow system capable of performing multistep supramolecular polymerization. In this system, injection of the monomer, directional supramolecular copolymerization, removal of the unreacted monomer, and purification of the product supramolecular diblock copolymers are realized along a three-stream flow. When injecting a supramolecular polymer into the central stream of the three-stream flow, the supramolecular polymerization always occurs in the central flow, with the two lateral flows serving as supply and removal lines for the monomer. Employing two kinds of perylene bisimide derivatives as monomers, we confirmed that the reaction occurred selectively at the forward-facing terminus of the supramolecular polymer, along with recovery of the unreacted monomer, ultimately leading to a high-purity supramolecular diblock copolymer. Diblock copolymers are basic units for preparing multicomponent supramolecular block copolymers. Thus, connecting the present system in series would, in principle, result in a "microplant" capable of producing supramolecular polymers having desired inner complexity.
RESUMO
Although directional chain reactions are common in nature's self-assembly processes and in covalent polymerizations, it has been challenging to perform such processes in artificial one-dimensional self-assembling systems. In this paper, we describe a system, employing perylene bisimide (PBI) derivatives as monomers, for selectively activating one end of a supramolecular polymer during its growth and, thereby, realizing directional supramolecular polymerization. Upon introduction of a solution containing only a single PBI monomer into the microflow channel, nucleation was induced spontaneously. The dependency of the aggregation efficiency on the flow rate suggested that the shear force facilitated collisions among the monomers to overcome the activation energy required for nucleation. Next, by introducing a solution containing both monomer and polymer, we investigated how the shear force influenced the monomer-polymer interactions. In situ fluorescence spectra and linear dichroism revealed that growth of the polymers was accelerated only when they were oriented under the influence of shear stress. Upon linear motion of the oriented polymer, polymer growth at that single end became predominant relative to the nucleation of freely diffusing monomers. When applying this strategy to a two-monomer system, the second (less active) monomer reacted selectively at the forward-facing terminus of the first polymer, leading to the creation of a diblock copolymer through formation of a molecular heterojunction. This strategy-friction-induced activation of a single end of a polymer-should be applicable more generally to directional supramolecular block copolymerizations of various functional molecules, allowing molecular heterojunctions to be made at desired positions in a polymer.
RESUMO
The nymphalid butterfly Araschnia burejana and the papilionid butterfly Papilio xuthus exhibit seasonal diphenism comprising spring-morphs that develop from diapause pupae and summer-morphs that develop from non-diapause pupae. The development of seasonal morphs in A. burejana is regulated by the timing of secretion of ecdysteroids for adult development, whereas that in P. xuthus is regulated by the secretion of summer-morph-producing hormone, which is present in the brains and is under control of the photoperiod. We investigated whether a cerebral factor derived from brains plays a significant role in the regulation of seasonal morph development in A. burejana using surgical operations. Pairs of chilled diapause pupae that had been chilled for more than 3 months at 4°C were joined surgically to each other and then developed into spring-morph or spring-like-morph adults. Chilled diapause pupae that were joined with 1-day-old non-diapause pupae developed into summer-morph or summer-like-morph adults. When the brains of non-diapause pupae were removed surgically 6-8 hr after pupation with and without injection of 20-hydroxyecdysone, a large portion of them developed into spring-morph or spring-like-morph adults, respectively. Furthermore, 90% of non-diapause pupae developed into spring-morph or spring-like-morph adults when the neck was ligated within 5 min after pupation. These results indicated that a cerebral factor showing summer-morph-producing hormone activity, which is secreted from the brain in the early pupal stage, in addition to 20-hydroxyecdysone for adult development, play a significant role in the determination of summer-morph development in non-diapause pupae of A. burejana.
