Increasing the flexoelastic ratio of liquid crystals using highly fluorinated ester-linked bimesogens.

We present experimental results on the bulk flexoelectric coefficients e and effective elastic coefficients K of non-symmetric bimesogenic liquid crystals when the number of terminal and lateral fluoro substituents is increased. These coefficients are of importance because the flexoelastic ratio e/K governs the magnitude of flexoelectro-optic switching in chiral nematic liquid crystals. The study is carried out for two different types of linkage in the flexible spacer chain that connects the separate mesogenic units: these are either an ether or an ester unit. It is found that increasing the number of fluorine atoms on the mesogenic units typically leads to a small increase in e and a decrease in K, resulting in an enhancement of e/K. The most dramatic increase in e/K, however, is observed when the linking group is changed from ether to ester units, which can largely be attributed to an increase in e. Increasing the number of fluorine atoms does, however, increase the viscoelastic ratio and therefore leads to a concomitant increase in the response time. This is observed for both types of linkage, although the ester-linked compounds exhibit smaller viscoelastic ratios compared with their ether-linked counterparts. Highly fluorinated ester-linked compounds are also found to exhibit lower transition temperatures and dielectric anisotropies. As a result, these compounds are promising materials for use in electro-optic devices.

Measurement of the Interaction Between Recombinant I-domain from Integrin alpha 2 beta 1 and a Triple Helical Collagen Peptide with the GFOGER Binding Motif Using Molecular Force Spectroscopy.

The role of the collagen-platelet interaction is of crucial importance to the haemostatic response during both injury and pathogenesis of the blood vessel wall. Of particular interest is the high affinity interaction of the platelet transmembrane receptor, alpha 2 beta 1, responsible for firm attachment of platelets to collagen at and around injury sites. We employ single molecule force spectroscopy (SMFS) using the atomic force microscope (AFM) to study the interaction of the I-domain from integrin alpha 2 beta 1 with a synthetic collagen related triple-helical peptide containing the high-affinity integrin-binding GFOGER motif, and a control peptide lacking this sequence, referred to as GPP. By utilising synthetic peptides in this manner we are able to study at the molecular level subtleties that would otherwise be lost when considering cell-to-collagen matrix interactions using ensemble techniques. We demonstrate for the first time the complexity of this interaction as illustrated by the complex multi-peaked force spectra and confirm specificity using control blocking experiments. In addition we observe specific interaction of the GPP peptide sequence with the I-domain. We propose a model to explain these observations.