Formation and dissociation of synthetic hetero-double-helix complex in aqueous solutions: significant effect of water content on dynamics of structural change.

Tsukasa Sawato,Ryosuke Yuzawa,Higashi Kobayashi,Nozomi Saito,Masahiko Yamaguchi

doi:10.1039/c9ra06073a

Tsukasa Sawato, Ryosuke Yuzawa + Show 3 more

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https://doi.org/10.1039/c9ra06073a

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Abstract

A 1 : 1 mixture of the ethynylhelicene pseudoenantiomers (M)-tetramer and (P)-pentamer, which possess hydrophilic terminal tri(ethyleneglycol) (TEG) groups, changes their structures in the water–THF (10 μM) solvent system between dissociated random-coils and an associated hetero-double-helix upon heating and cooling. A small change in water content between 30 and 33% significantly affects the dynamics of structural changes. At 30% water content, heating to 60 °C causes rapid formation of random-coil and cooling to 10 °C causes the rapid formation of hetero-double-helix, accompanied by repeated changes in Δε at 369 nm between 0 and −2000 cm−1 M−1. Heating and cooling experiments at constant rates between 60 and 10 °C resulted in sigmoidal curves in Δε/temperature profiles, which indicate rapid structural changes. Different phenomena occurred at 33% water content. Heating to 60 °C and cooling to 0 °C initially induced changes in Δε between 0 and −2000 cm−1 M−1, and repeated cycles gradually reduced the range between 0 and −500 cm−1 M−1. Heating and cooling experiments at constant rates between 60 and 10 °C caused small changes in Δε, and repeated cycles at 10 °C gradually increased Δε to −500 cm−1 M−1. These phenomena involved rapid changes in molecular structure and slow structural changes in the water–THF solvent system. The sharp switching of the dynamics of structural changes at water content between 30 and 33% indicated discontinuous structural changes in the hydration of TEG and/or in water clusters in the vicinity of oligomer molecules.

Highlights

The hetero-double-helix, derived from linear molecules with two different structures, plays pivotal roles in biological doublestranded DNA, which dissociates and associates in water for gene regulation and expression to occur.[1,2] the development of hetero-double-helix from synthetic molecules in aqueous solution is attractive, because it promotes the understanding and control of such biological events as well as provides novel functional materials.[3]
The experiment was conducted using a 100 mM solution, and circular dichroism (CD) spectra obtained at 10 C were very similar to those of the 10 mM solution (Fig. S7†), which indicated that the CD spectrum with D3 reaching À1500 cmÀ1 MÀ1 showed the equilibrium shi ed to B
An important role of water in the type-1 and type-2 behaviors was con rmed by experiments in THF without water, in which dissociated 2A persisted without formation of B upon heating and cooling (Fig. S4†). These results indicate a sharp switching in dynamics of the structural changes of the (M)-1/(P)-2 mixture at water contents between 30 and 33% owing to the type-1 and -2 behaviors

Summary

Introduction

The hetero-double-helix, derived from linear molecules with two different structures, plays pivotal roles in biological doublestranded DNA, which dissociates and associates in water for gene regulation and expression to occur.[1,2] the development of hetero-double-helix from synthetic molecules in aqueous solution is attractive, because it promotes the understanding and control of such biological events as well as provides novel functional materials.[3] water-soluble synthetic homo-double-helices have recently been developed[4,5,6,7,8] as dimeric aggregates derived from linear molecules with the same structure, the synthesis and dynamic properties of the water-soluble hetero-double-helix have not yet been studied. To develop a water-soluble synthetic hetero-double-helix, the presence of hydrophilic groups is essential. It was found that mixtures of the ethynylhelicene pseudoenantiomers (M)-oligomer and (P)-oligomer with different helicene numbers formed hetero-double-helix in organic solvents.[10,11,12] In this study, a water-soluble heterodouble-helix was developed employing a mixture of pseudoenantiomers ethynylhelicene (M)-tetramer (M)-1 and (P)-pentamer (P)-2, which possess terminal hydrophilic TEG groups (Fig. 1b)

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