| Budget Amount *help |
¥13,600,000 (Direct Cost: ¥13,600,000)
Fiscal Year 2004: ¥2,400,000 (Direct Cost: ¥2,400,000)
Fiscal Year 2003: ¥11,200,000 (Direct Cost: ¥11,200,000)
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| Research Abstract |
The recent development of the statistical mechanics of polymers has clarified the principles underlying the memory of conformation by macromolecules. First, the polymer must be a heteropolymer, i.e., there should be more than one monomer species, so that some conformations are energetically more favorable than others. Second, the polymer must be condensed, in which case frustrations exist due to the interplay of chain connectivity and excluded volume. Third, the sequence of monomers must be selected as to minimize these frustrations. These three conditions allow the polymer to have its global energy minimum at one particular conformation, which thus can be said to be memorized. We investigated an experimental implementation of the above principles, albeit at a primitive level, in the synthesis of a weakly cross-linked polymer gel. The gel can memorize a part of its molecular conformation-specifically, spatial assemblies of certain groups of its monomers. they can interact with special
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additional so-called target molecules, not connected to the gel network, but having several negative charges each. These positively charged minority monomers can form ionic complexes with the negatively charged target molecules. In other words, they assemble into groups in which their interaction is mediated by the target molecules. Our major experimental strategy is to compare gels
which are post-cross-linked in the presence or in the absence of target molecules. We call these gels imprinted and random, respectively. We argue that, by doing post-crosslinking in the presence of target molecules, we suppress frustrations and thus approach the minimal frustration situation. We experimentally realized that a gel system in which frustrations exist and can be minimized, thus meeting two crucial criteria predicted to enable memory of conformations in polymers. The gels consist of a thermosensitive major monomer component and two minor components. One minor component is positively charged and will form complexes around negatively charged target molecules placed in solution. The complexes can be imprinted into the gel by then cross-linking the second minor component, which will form cross-links additional to those in the major polymer matrix. The complexes are destroyed and reformed upon swelling and reshrinking of the gels, showing that memorization has been achieved. Less
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