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The development of the cyanobiphenyls for display applications was one of the most important technological advances of the 20th century. Here, we present a personal account of how advances in biphenyl science (synthesis and application) influenced the development of discotic liquid crystals. We focus on those based on triphenylene, the most widely studied discotic core. The search for nematic discotics proved to be challenging with relatively few early examples being reported. In examples of symmetrically hexasubstituted triphenylenes, a ring of peripheral aryl ester or alkynylaryl substituents provides effective steric blocking to columnar assembly – the face-to-face molecular arrangement that is observed in the majority of triphenylene discotics. The synthetic challenges associated with early triphenylene synthesis have now been largely overcome. Efficient oxidative trimerisation of dialkoxybenzenes gave direct access to materials with high purity and at scale. The intermediates can be manipulated through deprotection and elaboration, a pathway that allowed synthesis of lyotropic (Nc) systems among others. The combination of modern cross-coupling chemistry with oxidative processes has proved versatile, leading to synthesis of unsymmetrical monomeric and dimeric systems. Dimeric systems linked by rigid bridges have been identified as a separate class of materials that show strong tendency for nematic mesophase formation. [ABSTRACT FROM AUTHOR]

Therapeutic microbubbles (thMBs) contain drug-filled liposomes linked to microbubbles and targeted to vascular proteins. Upon the application of a destructive ultrasound trigger, drug uptake to tumour is improved. However, the structure of thMBs currently uses powerful non-covalent bonding of biotin with avidin-based proteins to link both the liposome to the microbubble (MB) and to bind the targeting antibody to the liposome–MB complex. This linkage is not currently FDA-approved, and therefore, an alternative, maleimide–thiol linkage, that is currently used in antibody–drug conjugates was examined. In a systematic manner, vascular endothelial growth factor receptor 2 (VEGFR2)-targeted MBs and thMBs using both types of linkages were examined for their ability to specifically bind to VEGFR2 in vitro and for their ultrasound imaging properties in vivo. Both showed equivalence in the production of the thMB structure, in vitro specificity of binding and safety profiles. In vivo imaging showed subtle differences for thMBs where biotin thMBs had a faster wash-in rate than thiol thMBs, but thiol thMBs were longer-lived. The drug delivery to tumours was also equivalent, but interestingly, thiol thMBs altered the biodistribution of delivery away from the lungs and towards the liver compared to biotin thMBs, which is an improvement in biosafety. [ABSTRACT FROM AUTHOR]

A new approach to the synthesis of derivatives of the perchlorinated tritryl radical is described. It relies on the fact that, under the conditions required to fully chlorinate the ortho positions of a triarylmethane, there is only minimal substitution of aryl fluorine by chlorine and then on the fact that, in the mixed Cl/F substituted triarylmethanes obtained, it is possible to selectively substitute the fluorine‐bearing positions using the sodium salt of n‐hexanol in n‐hexanol/dimethylsulfoxide. The meta‐hexyloxy derivatives obtained are much more soluble and photostable than the parent perchlorotrityl radical. For example, the introduction of four meta‐hexyloxy substituents gives a radical where, under white light illumination, the lifetime is improved by a factor of almost 104. The photostability of the radical, the lifetime of the excited state and the fluorescence all decrease as the number of meta‐hexyloxy substituents is increased. The improvements in solubility and in photostability observed should help in creating a more diverse range of perchlorotrityl radical derivatives and in the development of new applications. [ABSTRACT FROM AUTHOR]

The inner membrane of Escherichia coli, overexpressing an ubiquinol oxidase, cytochrome [bo.sub.3] ([cbo.sub.3]), was 'tethered' in a planar configuration to a gold electrode. Electron transfer to [cbo.sub.3] was achieved via native ubiquinol-8 or added ubiquinol-10, and impedance spectroscopy was used to characterize the diffusion properties of the ubiquinol/ubiquinone in the tethered membrane system. Spectra were obtained at varying direct current (DC) potentials covering the potential window in which the voltammetric catalytic wave of [cbo.sub.3] is visible. These spectra were compared to those obtained after addition of a potent inhibitor of [cbo.sub.3], cyanide, and the difference in impedance was analyzed using a derived equivalent circuit, which is similar to that of open finite-length diffusion (OFLD) or the finite Warburg circuit, but with the boundary conditions modified to account for the fact that ubiquinol reoxidation is limited by enzyme activity. Analysis of the impedance spectra of the tethered membrane system gave kinetic parameters that are consistent with values obtained using cyclic voltammetry. Importantly, the diffusion rate of ubiquinone ([10.sup.-13]-[10.sup.-12] [cm.sup.2]/s) was found to be orders of magnitude lower than accepted values for lateral diffusion ([10.sup.-8]-[10.sup.-7] [cm.sup.2]/ s). It is hypothesized that this result represent perpendicular diffusion of quinone across the membrane, corresponding to a 'flip' time between 0.05 and 1 s.

Various studies including the surface plasmon resonance (SPR) and electrochemical impedance spectroscopy (EIS) are conducted to develop a new electrode surface that enables the characterization of redox-active membrane enzymes in a native-like environment. The results show that most of the cytochrome bo(sub 3) on the surface of the Escherichia cell is catalytically active and hence retains its integrity during immobilization.

The applications of a mercury-supported biomimetric membrane obtained by an analogous procedure using triethyleneoxythiol (EO3) and hexaethyleneoxythiol are presented. The result shows that a polyethyleneoxythiol anchored to a hanging mercury drop electrode, with a self-assembled phospholipid bilayer on top, constitutes a valid experimental model of a biomembrane.

The steady state and time resolved phophysical properties of a novel self-assembling lyotropic discotic liquid crystal, 2,3,6,7,10,11-hexa-(1,4,7-trioxaoctyl)-triphenylene (TP^EO2M) are reported. Findings indicate that this lyotropic system has an order of magnitude higher concentration of intrinsic traps in the isotropic phase than its thermotropic analogues display in the columnar mesophase.

Research was conducted to examine the orientation of the headgroup of phosphatidylinositol in a model biomembrane as determined by neutron diffraction. The derivatives of the sodium salt of dimyristoylphosphatidyliositol were synthesized and specifically deuterated in the headgroup. The depth of each deuterium (hydrogen) within the bilayer were determined to be plus or minus 0.5 angstrom which gave the orientation of the inositol ring.

A study demonstrates the use of the micro-patterning of thiol-terminated lipophilic self-assembled monolayers to support planar lipid bilayer membranes which satisfy the critical criteria required for use as potential biosensors. This new method involving the integration of microcontact printing and self-assembly of lipid vesicles enables the construction of a tethered biomimetic membrane. Experimental methods and results are discussed.

Isotropic phase de-wetting of discotic liquid crystals on a surface patterned with alternating ~5-10 μm wide wetting and de-wetting stripes results in the formation of long narrow droplets. On slow cooling into the columnar phase, the liquid crystal aligns such that the columns lie either across or along the stripes. However, if the stripes are wider and/or the cooling rate is too fast, defects appear. When there are many such defects, the result is complex zigzag and wavy line optical textures, which are reminiscent of the egg and dart friezes associated with classical architecture. To a first approximation, all of these patterns can be seen as joined up fragments of developable domains in which the columns either circle a defect or propagate in a straight line. They are built up from motifs that involve bend but not splay or twist deformations; deformations that leave the two-dimensional lattice of the columnar phase unchanged. As is shown, these basic circular and straight-line motifs can be combined in a variety of different ways along the stripe but, in all of these, it is found that the defects alternate from side to side. [ABSTRACT FROM AUTHOR]

Construction of the triphenylene nucleus via the oxidative coupling of phenyl and biphenyl residues is the vital step in the synthesis of main-chain, triphenylene-based discotic-liquid-crystalline polymers. Demethylation of 2,7-dimethoxy-3,6,10, 11-tetrakis(hexyloxy)triphenylene, followed by condensation with 1, 11-dibromoundecane generates a 2,7-linked main chain polymer, having an average molecular weight of 24,000 and Dh mesophase range of 98-118 degrees Celsius. Low-angle X-ray crystallography, differential thermal analysis and polarizing microscopy help characterize these polymers.

The presence of 1% (w/w) of methylbenzene thiol coated gold nanoparticles increases the conductivity of the discotic liquid crystal 2,3,6,7,10,11-hexakis(hexyloxy)triphenylene (HAT6) by about two orders of magnitude in all three phases (crystal, columnar liquid crystal, and isotropic liquid). However, when a field (above a certain critical value) is applied to the isotropic phase, the conductivity rapidly increases by another three or four orders of magnitude after which the higher conductivity is maintained regardless of phase, field, or temperature. This increase in conductivity is attributed to the formation of chains of gold nanoparticles. A similar phenomenon is observed for 1% (w/w) gold nanoparticles in the isotropic phase of hexadecane. However, the liquid crystal/nanoparticle mixture preserves its high conductivity when it is cooled into the crystalline phase whereas that of the hexadecane/nanoparticle mixture is lost. In hexadecane, crystal grain boundaries are expected to form in a random fashion and this disrupts the conductive pathways. However, if HAT6 crystallizes via the homeotropically aligned columnar phase, the grain boundaries form predominantly surface to surface (electrode to electrode) so that the conductive nanoparticle chains are trapped in a stabilizing solid matrix. [ABSTRACT FROM AUTHOR]

Hole transport has been investigated by the time-of-flight method for the hexagonal columnar phase of a discogen containing a strongly dipolar nitro substituent; 1-nitro-2,3,6,7,10,11-hexakis(hexyloxy)triphenylene (HAT6-NO2). Unlike the corresponding unsubstituted system, 2,3,6,7,10,11-hexakis(hexyloxy)triphenylene (HAT6), and unlike most other liquid crystals, the mobility in HAT-NO2 depends strongly on both electric field and temperature. As in amorphous solids there is disorder dominated hopping and the mobility can be modeled using an energy disorder parameter, σ of just over 100 meV. Compared to HAT6, the disorder in HAT6-NO2 is enhanced because of the strong dipole of the nitro group. [ABSTRACT FROM AUTHOR]

The ESR spectrum of a non-Kekule polynuclear aromatic compound is presented. The compound comes from triangulene which is a pi biradical. Pi biradicals present difficulty in writing structures wherein each pi electron is paired with one on a neighboring carbon. It was shown that triangulene has a pair of nondisjoint degenerate nonbonding molecular orbitals and as such should have a triplet ground state.

The fabrication of mixtures of organic functionalized methylbenzene thiol gold nanoparticles with the discotic liquid crystal 2,3,6,7,10,11-hexakis(hexyloxy)triphenylene (HAT6) and hexadecane is described. The increase in conductivity is attributed to the formation of chains of gold nanoparticles, which is retained when the nanoparticle mixture is cooled into crystalline phase while it is lost for isotropic phase of hexadecane.

Thiol-on-gold self-assembled monolayers (SAMs) that can be photodetected by using soft ultraviolet (UV) irradiation to yield C[O.sub.2]H functionalized surfaces are reported. The results from infrared studies have shown that the long chain protected residues reorganize and shield the functional COOH groups, thereby reducing the hydrophilic character of the surface.