Amino acid/crown ether hybrid materials: how charge affects liquid crystalline self-assembly

Abstract

To probe the influence of electrostatic interactions on the mesomorphic self-assembly and phase behaviour of hybrid liquid crystals a series of crown ether/tyrosine hybrid systems was prepared by Steglich esterification of alkyl N-(tert-butoxycarbonyl)-l-tyrosinates with 4-carboxybenzo[15]crown-5 and 4-carboxybenzo[18]crown-6. The obtained derivatives allowed further manipulations at the NH functional group and complexation of the crown ether unit with NaI to give neutral or charged hybrid materials. All compounds were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X-ray diffraction (XRD) measurements. Neither the variation of the N-protecting group, introduction of charge at the N-terminus nor anion exchange (Cl vs. I) resulted in mesomorphism. In contrast, N-Boc-protected and unprotected hybrids formed rectangular columnar (Col) mesophases with phase widths up to 35 K. NaI complexation switched these neutral thermotropic derivatives into ionic liquid crystals (ILCs) and induced a change of mesophase type from Col to smectic A (SmA). A comparison of experimentally obtained layer distances and theoretically calculated molecular lengths indicated bilayer SmA formation with interdigitated alkyl chains. Packing models for both mesophase types are proposed and discussed with respect to stabilizing interactions.

Novel Luminescent Diazafluorenone Liquid Crystals

“…Although this distance is larger than the expected value of 3.5 Å for π–π interactions with face-to-face stacking, it should be noted that the single crystal X-ray data revealed π–π distances of 3.4–4.0 Å for diazafluorenone DAF­(OC6) 2 with the shortest chains and 3.6–4.0 Å for homologue DAF­(OC12) 2 . Furthermore, similar distances have been reported for other columnar liquid crystals. − For example, Matsumoto rationalized experimental values of 4.1 Å for Col ro phases by the edge-to-edge type stacking of the mesogens in the column …”

Comparison of the Mesomorphic Behaviour of 1:1 and 1:2 Mixtures of Charged Gay-Berne GB(4.4,20.0,1,1) and Lennard-Jones Particles

“…Finally, we note that a general effect of increasing the charge, for a given packing fraction, is to increase the stability of the isotropic mixed phase, and therefore to destabilize the ionic liquid mesophases. This result has been also experimentally confirmed recently by Laschat and co-workers [54]: the authors investigated a series of amino acid/crown ether ionic LCs and found that increasing the charge is detrimental for the stability of ionic LC phases.…”

Power of Tyrosine Assembly in Microtubule Stabilization and Neuroprotection Fueled by Phenol Appendages

“…Moreover, many naturally occurring and synthesized molecules with a phenolic −OH moiety like in neurotransmitter molecules such as dopamine and ferulic acid have been reported to possess neuroprotective effects, − but none of the studies directly or indirectly have explored the importance of phenolic −OH in neuroprotection and their possible cross talk with tubulin or microtubule. Talking about phenolic −OH, several groups have already reported tyrosine analogues with effective biological activity, and this is one of the hot arenas in current research among the chemical biologists. − To address this fundamental aspect and to provide more detailed understanding in this article, we have designed novel tripodal molecules based on the 1,3,5-triazine core with trisubstitution of tyrosine (Y), phenylalanine (F), and serine (S), named as TY3, TF3, and TS3, respectively. Among the three molecules, TY3 and TF3 bind close to the taxol binding pocket of tubulin.…”