Molecular Weights: The Key for Lyotropic Liquid Crystalline Phases of Poly-β-benzyl-l-aspartate

Abstract

Herein, we report the preparation of lyotropic liquid crystalline (LLC) phases of poly-β-benzyl-L-aspartate (PBLA), a polymer that has not been known to form LLC phases before. Compared to other L-configured polypeptides usually forming right-handed helices, PBLA forms left-handed helices. The LLC phase behavior was observed for PBLA in a specific range of molecular weights, exclusively. Living polymerization allowed for this excellent control over the molecular weight. Furthermore, the LLC phase was used as a host matrix for two chiral analytesisopinocampheol and β-pineneused as probes. The interaction between these probes and the polypeptide was measured indirectly using NMR spectroscopy by investigation of the resulting orientation of probes in general and the enantiodifferentiation of the chiral analytes in particular. By comparison of the orientation induced on the probes by PBLA and the well-known poly-β-benzyl-Lglutamate, the effect of side-chain flexibility and conformation of the polypeptides on the alignment process are discussed.

Multinuclear NMR in polypeptide liquid crystals: Three fertile decades of methodological developments and analytical challenges

“…More recently, new variants of enantiodiscriminating polypeptide-based polymers have been reported. For instance, we can mention systems made of poly-βphenethyl-L-aspartate (PPLA) [123], of poly-β-benzyl-L-aspartate (PBLA) [124], of poly-γ-pbiphenylmethyl-L-glutamate (PBPMLG) [125] as well as a co-polymer of phenethyl and benzylpolyaspartate [126]. Interestingly, the alignment process of PPLA or PBPMLG systems, for instance, change drastically (reversal point) as function of the temperature, thus providing two sets of [139] PPA-(L)-Phe SC CHCl 3 [140] PPA-(L)-Val SC CHCl 3 [141] Poly(isocyanopeptide) (L,L)-PIAF-OBn SC CHCl 3 [142] a Acronym generally used.…”

Light-Controlled Lyotropic Liquid Crystallinity of Polyaspartates

“…[a] C-CH 3 dipolar couplings calculated from corresponding C-H dipolar couplings according to a literature known relation 17 [b] calculated using scalar couplings taken from reference 8 [c] No fitting was performed, because D exp are zero within their estimated uncertainty ranges as expected in the absence of anisotropy. #1(-)-Z': -0.04 ± 0.04 --C10-H10 124.9 ± 0.1 0.0 ± 0.1 --C2-C10 [a] 0.00 ± 0.02 --…”

“…[a] C-CH 3 dipolar couplings calculated from corresponding C-H dipolar couplings according to a literature known relation 17 [b] calculated using scalar couplings taken from reference 8 [c] No fitting was performed, because D exp are zero within their estimated uncertainty ranges as expected in the absence of anisotropy. The centrifugation procedure is routinely applied in preparation of LLC based alignment media to obtain a homogeneous sample 9 and is used in this study for samples irradiated homogeneously.…”

“…Avg(F1+F2) denotes the average of both couplings being displayed. [c] calculated using scalar couplings taken from reference8…”

Light-Controlled Lyotropic Liquid Crystallinity of Polyaspartates

“…If these polymers were soluble in higher concentrations, their helical conformation would posses the necessary shape anisotropy to form lyotropic liquid crystalline solutions. From our previous investigations on poly-β-benzyl-L-aspartate (PBLA) 21 , we know that polyaspartate solubility can crucially depend on the polymer weight and, thus, we believed that solubility issues can be addressed similarly by utilisation of a controlled polymerisation protocol. To overcome the thermal instability of light-induced conformational changes of the polyaspartates mentioned 22 , we chose stable (o-F) 4 -azobenzene 23 instead of the unsubstituted azobenzene.…”