Nanoparticle-Based Tough Polymers with Crack-Propagation Resistance.

Although thin elastomer films of polymer nanoparticles are regarded as environmentally friendly materials, the low mechanical strength of the films limits their use in various applications. In the present study, we investigated the fracture resistance of latex films composed of acrylic nanoparticles where a small quantity of a rotaxane crosslinker was introduced. In contrast to conventional nanoparticle-based elastomers, the latex films composed of the rotaxane-crosslinked nanoparticles exhibited unusual crack propagation behavior; the direction of crack propagation changed from a direction parallel to the crack to one perpendicular to the crack, resulting in an increase in tear resistance.

Stacking interaction in the middle and at the end of a DNA helix studied with non-natural nucleotides.

Base stacking is important for the base pair interaction of a DNA duplex, DNA replication by polymerases, and single-stranded nucleotide overhangs. To study the mechanisms responsible for DNA stacking interactions, we measured the thermal stability of DNA duplexes containing a non-natural nucleotide tethered to a simple aromatic hydrocarbon group devoid of dipole moments and hydrogen bonding sites. The duplexes containing tetrahydrofuran were paired with a deoxyadenosine derivative (A/T base pair analog) or a deoxycytidine derivative (C/G base pair analog) and showed a lower stability than Watson-Crick base pairing, partly due to the loss of interbase hydrogen bonds.

Dynamics and energetics of the base flipping conformation studied with base pair-mimic nucleosides.

A base flipping conformation is found in many biological processes, including DNA repair and DNA and RNA modification processes. To investigate the dynamics and energetics of this unusual conformation in a double helix, base flipping induced by the base pair analogues of deoxyadenosine and deoxycytidine derivatives tethering a phenyl or naphthyl group was investigated. DNA strands bearing the base pair analogues stabilized the base flipping conformation of a complementary RNA, resulting in a site-specific hydrolysis by specific base catalysis.

Functionalization of DNA by the base pair-mimic nucleosides.

We developed the base pair-mimic nucleosides tethering the phenyl group and the naphtyl group, synthesized from deoxyadenosine (Aphe and Anaph) and deoxycytidine (Cphe and Cnaph). Structure and the thermal stability of the DNA duplexes containing the deoxyadenosine derivatives or the deoxycytidine ones in the middle of a DNA strand were obtained by the CD spectra and the UV melting curves. The DeltaGo37 values among DNA duplexes containing Aphe-A, Aphe-G, Aphe-C and Aphe-T pair differed only by 1.

The base-pairing ability of the base pair-mimic nucleosides.

The deoxyadenosine derivative tethering the phenyl group at N6 of deoxyadenosine (A(phe)) was previously found to have a property to stack strongly with adjacent nucleotide bases in a DNA duplex. On the other hand, it was also demonstrated that DNA polymerases selectively incorporated dTTP opposite A(phe) in a template DNA strand. These observations suggest that the conformation of A(phe) in solution differs from that during the DNA polymerase reaction.

Recognition of the base pair-mimic nucleosides by DNA polymerases.

We previously reported that the deoxyadenosine derivative tethering the phenyl group at the N6 position of deoxyadenosine, A(phe) stacked efficiently with the adjacent nucleotide bases at a DNA duplex terminus and in the middle of a DNA duplex. In contrast with the observations for A(phe), this study revealed that the phenyl group of the deoxycytidine derivative, C(phe) located outside the helix and allowed the base pair formation with guanine in a DNA duplex, although its phenyl group could stack with the adjacent DNA bases as efficient as A(phe). Klenow fragment of DNA polymerase I and T7 DNA polymerase selectively incorporated dTTP and dGTP opposite A(phe) and C(phe) in the template DNA, respectively, implying that the conformation of A(phe) differs between in the DNA polymerase and in solution.

DNA base flipping by a base pair-mimic nucleoside.

On the basis of non-covalent bond interactions in nucleic acids, we synthesized the deoxyadenosine derivatives tethering a phenyl group (X) and a naphthyl group (Z) by an amide linker, which mimic a Watson-Crick base pair. Circular dichroism spectra indicated that the duplexes containing X and Z formed a similar conformation regardless of the opposite nucleotide species (A, G, C, T and an abasic site analogue F), which was not observed for the natural duplexes. The values among the natural duplexes containing the A/A, A/G, A/C, A/T and A/F pairs differed by 5.

Site-selective RNA cleavage by DNA bearing a base pair-mimic nucleoside.

We have synthesized the deoxyadenosine derivative tethering a phenyl group (X), which mimics the Watson-Crick A/T base pair. The RNA/DNA hybrid duplexes containing X in the middle of the DNA sequence showed a similar thermal stability regardless of the ribonucleotide species (A, G, C, or U) opposite to X, probably because of the phenyl group stacking inside of the duplex accompanied by the opposite ribonucleotide base flipped in an extrahelical position. The RNA strand hybridized with the DNA strand bearing X was cleaved on the 3'-side of the ribonucleotide opposite to X in the presence of MgCl2, and the RNA sequence to be cleaved was not restricted.