Liquid crystal elastomer–nanoparticle systems for actuation

Liquid crystal elastomers (LCE) are currently of great interest due to conjoining of mesogenic ordering and rubber elasticity, exhibited in their large spontaneous thermally stimulated changes in shape. It has been shown that nanoparticles (nanotubes, photo-isomerisable dyes, magnetic nanoparticles) can be incorporated into these LCE networks to create a more sensitive network to external stimuli (i.e. strain or stress, optical, electrical, electro-thermal, magnetic). Here, we briefly summarise the current state of LCE–nanoparticle systems and explain in detail one system utilising carbon nanoparticles integrated at surfaces that may be used for electro-thermal heating of LCE systems

Electric-Field Effects on the [FeFe]-Hydrogenase Active Site

The effect of a homogeneous electric field—as exerted by the protein environment and by an electrode potential—on the reactivity of the active site of [FeFe] hydrogenases is unravelled by density functional theory calculations.ISSN:1359-7345ISSN:1364-548

Activation Barriers of Oxygen Transformation at the Active Site of [FeFe] Hydrogenases

Oxygen activation at the active sites of [FeFe] hydrogenases has been proposed to be the initial step of irreversible oxygen-induced inhibition of these enzymes. On the basis of a first theoretical study into the thermodynamics of O₂ activation [<i>Inorg. Chem.</i> <b>2009</b>, 48, 7127] we here investigate the kinetics of possible reaction paths at the distal iron atom of the active site by means of density functional theory. A sequence of steps is proposed to either form a reactive oxygen species (ROS) or fully reduce O₂ to water. In this reaction cascade, two branching points are identified where water formation directly competes with harmful oxygen activation reactions. The latter are water formation by O–O bond cleavage of a hydrogen peroxide-bound intermediate competing with H₂O₂ dissociation and CO₂ formation by a putative iron-oxo species competing with protonation of the iron-oxo species to form a hydroxyo ligand. Furthermore, we show that proton transfer to activated oxygen is fast and that proton supply to the active site is vital to prevent ROS dissociation. If sufficiently many reduction equivalents are available, oxygen activation reactions are accelerated, and oxygen reduction to water becomes possible

Photo-crosslinked side-chain liquid-crystalline elastomers for microsystems

Photo-crosslinkable side-chain liquid-crystalline polymers (LCPs) containing photoreactive benzophenone cores are synthesized in order to obtain their corresponding side-chain liquid-crystalline elastomers (LCEs). This strategic synthesis allows thin elastomeric films and their integration into microsystems for actuators and micromachines to be obtained. As an example of this principle, a gripper was developed. The position of its arms can be changed by applying voltages from 1.5 to 3.5 V at different rates. Small changes in the liquid-crystalline elastomer film cause strains of up to 150% in the microdevice and the capacity to move up to 400 times its own mass due to the nematic-to-isotropic transformation