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Three series of dibenzo[ a, c]phenazines were prepared in an order to assess the impact of side chain position on the phase stability of columnar liquid crystals. Each series was composed of four isomeric compounds differing only in the disposition of hexyloxy and decyloxy chains around the central aromatic core, giving rise to electronically similar compounds with varying shapes and symmetries. The substitution pattern was found to have a moderate effect on the clearing transition of the liquid crystal but a larger impact on the melting temperatures. These observations suggest a viable strategy for controlling the phase range of liquid crystals via judicious choice of peripheral chain structure and location. [ABSTRACT FROM AUTHOR]

We report the synthesis and mesophase characterization of a series of novel hexaalkoxydibenzanthracenes to probe the effect of side-chain length variation and substituents on the mesophase temperature range. A series of hexaalkoxydibenz[ a, c]anthracenes ( 2a- 2i) with varying chain lengths were prepared by Suzuki coupling of the appropriate boronate ester with the corresponding dialkoxydibromonaphthalenes, followed by oxidative cyclization. Compounds 2a- 2i were also brominated in the 10 and 13 positions to yield the corresponding dibromo series, 4a- 4i. While none of the compounds, 2a- 2i, exhibited columnar mesophases, all of the compounds in series 4a- 4i did exhibit columnar phases over broad temperature ranges. To further investigate the effect of substituents on the mesomorphic properties of hexaalkoxydibenzanthracenes, we also prepared iodo-substituted 8, nitro-substituted 9, and amino-substituted 10. A comparison of the mesophase temperature range with previously reported compounds 3- 7 shows that electron-withdrawing groups promote the formation of stable mesophases. However, our results also suggest that the substituents affect mesophase stability by participating in intermolecular contacts within the columnar stacks of the mesophase. [ABSTRACT FROM AUTHOR]

We recently introduced a technique, termed SAD-REDOR, for recoupling residual dipolar couplings in a single-domain polymer-stabilized liquid crystal (PSLC) undergoing magic-angle spinning (MAS). The experiment was demonstrated with 1H–15N dipolar couplings in a small molecule. Here, we show the applicability of the technique to a strongly aligned protein and we describe a novel two-dimensional experiment to generate in-phase and anti-phase (IPAP) doublets in the 1H dimension of an HSQC NMR spectrum. This pulse sequence, SAD-IPAP, was tested on a sample of 15N-labeled ubiquitin (5 mmol/L) in a polyacrylamide-stabilized Pf1 phage liquid crystal (20 mg/mL). 15N–1H residual dipolar couplings (RDCs) were measured with the SAD-IPAP pulse sequence at spinning speeds of 1000 and 1250 Hz. RDSs were also measured using the conventional HSQC-IPAP method in a sample of 15N-ubiquitin dissolved in a solution of Pf1 phage (1 mg/mL). The resulting RDCs were fitted to the solution structure of ubiquitin to estimate the alignment tensor and to determine the accuracy of the measured couplings. The results highlight the benefits of SAD-REDOR for the measurement of RDCs in strongly aligned macromolecules. [ABSTRACT FROM AUTHOR]