Apolar 2‐alkoxyalkoxy‐substituted nematic liquid crystals

The synthesis is reported of a series of apolar nematic liquid crystals incorporating an alkoxyalkoxy chain attached in a terminal position to the molecular core. The dependence of the mesomorphism and phase transition temperatures on the nature of the terminal chain with one, two or three oxygen atoms was studied. Some compounds with a completely alicyclic molecular core and a terminal 2‐methoxyethoxy chain exhibit a nematic phase with a low melting point, birefringence and viscosity and a relatively high clearing point in the absence of smectic phases. They do not to absorb light in the near UV and may be useful as components of UV‐stable nematic mixtures for use in photoluminescent liquid crystal displays. The presence of the methoxyethoxy chain leads to a relatively large dipole moment perpendicular to the molecular long axis.     

Diruthenium dithiolato cyanides: basic reactivity studies and a post hoc examination of nature's choice of Fe versus Ru for hydrogenogenesis

The reaction of Ru2(S2C3H6)(CO)6 (1) with 2 equiv of Et4NCN yielded (Et4N)2[Ru2(S2C3H6)(CN)2(CO)4], (Et4N)2[3], which was shown crystallographically to consist of a face-sharing bioctahedron with the cyanide ligands in the axial positions, trans to the Ru-Ru bond. Competition experiments showed that 1 underwent cyanation >100x more rapidly than the analogous Fe2(S2C3H6)(CO)6. Furthermore, Ru2(S2C3H6)(CO)6 underwent dicyanation faster than [Ru2(S2C3H6)(CN)(CO)5]-, implicating a highly electrophilic intermediate [Ru2(S2C3H6)(mu-CO)(CN)(CO)5]-. Ru2(S2C3H6)(CO)6 (1) is noticeably more basic than the diiron compound, as demonstrated by the generation of [Ru2(S2C3H6)(mu-H)(CO)6]+, [1H]+. In contrast to 1, the complex [1H]+ is unstable in MeCN solution and converts to [Ru2(S2C3H6)(mu-H)(CO)5(MeCN)]+. (Et4N)2[3] was shown to protonate with HOAc (pKa = 22.3, MeCN) and, slowly, with MeOH and H2O. Dicyanide [3]2- is stable toward excess acid, unlike the diiron complex; it slowly forms the coordination polymer [Ru2(S2C3H6)(mu-H)(CN)(CNH)(CO)4]n, which can be deprotonated with Et3N to regenerate [H3]-. Electrochemical experiments demonstrate that [3H]- catalyzes proton reduction at -1.8 V vs Ag/AgCl. In contrast to [3]2-, the CO ligands in [3H]- undergo displacement. For example, PMe3 and [3H]- react to produce [Ru2(S2C3H6)(mu-H)(CN)2(CO)3(PMe3)]-. Oxidation of (Et4N)2[3] with 1 equiv of Cp2Fe+ gave a mixture of [Ru2(S2C3H6)(mu-CO)(CN)3(CO)3]- and [Ru2(S2C3H6)(CN)(CO)5]-, via a proposed [Ru2]2(mu-CN) intermediate. Overall, the ruthenium analogues of the diiron dithiolates exhibit reactivity highly reminiscent of the diiron species, but the products are more robust and the catalytic properties appear to be less promising.     

Interaction of the glycoalkaloid tomatine with DMPC and sterol monolayers studied by surface pressure measurements and Brewster angle microscopy

The interaction of the glycoalkaloid tomatine with monolayers of dimyristoylphosphatidylcholine (DMPC) and cholesterol, as well as other selected sterols, has been investigated using surface pressure measurements at constant area and Brewster angle microscopy (BAM). The interaction of tomatine with sterol monolayers is found to vary with the structure of the sterol. The interaction of tomatine with cholesterol-containing monolayers results in a surface pressure increase accompanied by the appearance of a mottled texture. Morphological changes are observed that suggest the formation of tomatine-cholesterol complexes that aggregate at the water-air interface. No morphology change observable by BAM is observed for monolayers containing epicholesterol, suggesting that the stereochemistry of hydrogen bonding between the sterol and the sugar units on tomatine is of particular significance. Strong interactions are observed with cholestanol- and coprostanol-containing monolayers, and BAM reveals formation of spiked aggregates upon interaction with 7:3 mole ratio DMPC/coprostanol mixed monolayers. More modest surface pressure changes are observed for cholestenone- and epicoprostanol-containing monolayers. A much smaller surface pressure increase is observed when tomatine is injected beneath a pure DMPC monolayer.     

A new chiral lanthanide NMR probe for the determination of the enantiomeric purity of alpha-hydroxy acids and the absolute configuration of alpha-amino acids in water

A water-soluble, enantiopure lanthanide complex, SSS-[Ln x L3], has been assessed as an effective chiral derivatizing agent for the determination of the enantiomeric purity of alpha-hydroxy acids in aqueous solution. The complex displays superior chemical shift non-equivalence (DeltaDeltadelta approximately 2-11 ppm) for the diastereomeric resonances of interest compared to lanthanide shift reagents reported in the literature (DeltaDeltadelta <0.1 ppm, typically). 1H NMR studies have also revealed that SSS-[Ln x L3] can be used to determine the absolute configuration of alpha-amino acids at physiological pH, in water. The ability of SSS-[Ln x L3] to signal anion binding and, in particular, to distinguish between diastereomers through optical techniques such as lanthanide luminescence and circular dichroism has also been assessed.     

Synthesis of arenediynes via the vinylidenecarbene-acetylene rearrangement

A convenient method for the two-step synthesis of arenediynes from 1,2-arenedialdehydes is reported. Dibromomethylenation of dialdehydes under Corey-Fuchs conditions (CBr₄, Ph₃P, Zn) provides the tetrabromides in excellent yields. Treatment of the tetrabromides with n-BuLi or LDA affords 3,4-unsaturated 1,5-diynes, the key structural moiety present in several naturally occurring antitumour antibiotics, in varying yields. The key intermediates in these transformations appear to be vinylidenecarbenes or carbenoids, generated in situ via metal-halogen exchange and elimination.     

The effect of terminal chain modifications on the mesomorphic properties of 4,4′-disubstituted diphenyldiacetylenes

The typical sidewalls produced in the fabrication of protrusion electrodes are proposed to create a low voltage (4.5 V_rms) and high transmittance (93%) blue-phase liquid crystal display (BP-LCD). The tilted electrodes produce a strong horizontal electrical field that reduces the operating voltage considerably. The common problem of the ‘dead zones’ is solved by reflecting the light onto the electrodes. In order to estimate the phase retardation of the reflected light, a ray tracing simulation program for anisotropic mediums has been developed. The proposed device is more competitive than vertical field switching based BP-LCD and also, has the advantages of protruded in-plane-switching structures. These facts make this technology a potential candidate for the next generation of BP-LCDs.