Dynamic Light Scattering Based Microrheology of End-Functionalised Triblock Copolymer Solutions.

Nano-sized particles functionalised with short single-stranded (ss)DNAs can act as detectors of complementary DNA strands. Here we consider tri-block-copolymer-based, self-assembling DNA-coated nanoparticles. The copolymers are chemically linked to the DNA strands via azide (N3) groups. The micelles aggregate when they are linked with complementary ssDNA. The advantage of such block-copolymer-based systems is that they are easy to make. Here we show that DNA functionalisation results in inter-micellar attraction, but that N3-groups that have not reacted with the DNA detector strands also change the phase behaviour of the tri-block polymer solution. We studied the triblock copolymer, Pluronic® F108, which forms spherical micelles in aqueous solutions upon heating. We find that the triblock chains ending with either an N3 or N3-DNA complex show a dramatic change in phase behaviour. In particular, the N3-functionalisation causes the chain ends to cluster below the critical micelle temperature (CMT) of pure F108, forming flower-micelles with the N3-groups at the core, while the PPO groups are exposed to the solvent. Above the CMT, we see an inversion with the PPO chains forming the micellar core, while the N3-groups are now aggregating on the periphery, inducing an attraction between the micelles. Our results demonstrate that, due to the two competing self-assembling mechanisms, the system can form transient hydrogels.

On the role of flexibility in linker-mediated DNA hydrogels.

Three-dimensional DNA networks, composed of tri- or higher valent nanostars with sticky, single-stranded DNA overhangs, have been previously studied in the context of designing thermally responsive, viscoelastic hydrogels. In this work, we use linker-mediated gels, where the sticky ends of two trivalent nanostars are connected through the complementary sticky ends of a linear DNA duplex. We can design this connection to be either rigid or flexible by introducing flexible, non-binding bases. The additional flexibility provided by these non-binding bases influences the effective elasticity of the percolating gel formed at low temperatures. Here we show that by choosing the right length of the linear duplex and non-binding flexible joints, we obtain a completely different phase behaviour to that observed for rigid linkers. In particular, we use dynamic light scattering as a microrheological tool to monitor the self-assembly of DNA nanostars with linear linkers as a function of temperature. While we observe classical gelation when using rigid linkers, the presence of flexible joints leads to a cluster fluid with a much-reduced viscosity. Using both the oxDNA model and a coarse-grained simulation to investigate the nanostar-linker topology, we hypothesise on the possible structure formed by the DNA clusters. Moreover, we present a systematic study of the strong viscosity increase of aqueous solutions in the presence of these DNA building blocks.

Antigonadal and endocrine-disrupting activities of lambda cyhalothrin in female rats and its attenuation by taurine.

Lambda cyhalothrin (LCT) is a type II pyrethroid with a wide range of agricultural, industrial, and household uses. Taurine is a nonprotein sulfur containing amino acid as well as a well-known antioxidant and has valuable clinical applications in the detoxification of xenobiotics. The present study evaluated the effect of LCT on the reproductive and endocrine systems of female rats and determined whether taurine might alter these effects. Sexually mature female rats were administered LCT at two different dosages (6.3 mg/kg BW and 11.33 mg/kg BW) once daily by oral gavage for 14 consecutive days with the pretreatment of taurine (50 mg kg-1 BW). LCT treatment resulted in diminished adrenal cholesterol, ovarian 3ß- and 17ß-hydroxysteroid dehydrogenase (HSD) activity with increased ovarian cholesterol, adrenal 3ß- and 17ß-HSD activity. Furthermore, protein and mRNA expressions of ovarian 17ß-HSD and steroidogenic acute regulatory protein were also decreased. Hormonal imbalance was evident by concurrent reduction in the gonadotropic hormone, estradiol, and progesterone levels in LCT-treated rats. These rats also demonstrated the histopathological evidence of degenerative changes in the ovaries. Pretreatment of taurine attenuated the LCT-induced changes.