Chiral Recognition of Poly(N-isopropylacrylamide-co-(d or l)-N-tryptophan−acrylamide) with Methylated β-Cyclodextrin

Abstract

Chiral recognition is an important subject in biological, medical, or pharmaceutical systems. Focusing on natural amino acids, their optical purity or ee values normally are determined analytically with chiral columns. [1][2][3] Cyclodextrins (CDs) are chiral, naturally occurring cyclic oligosaccharides, which, due to the unique molecular structure, are able to form inclusion (host-guest) complexes with various polymers. 4,5 The first stereoselective inclusion of a whole polymer chain with CDs was shown by Tonelli et al., who demonstrated that only isotactic poly(3-hydroxy butyrate) can be included in a R-CD cavity, while atactic poly(3-hydroxy butyrate) cannot. 6 Accordingly, the enantioselective enclosing of isotactic polylactides with CD rings was published by Yui et al. in 2007. 7 We demonstrated recently that in the case of a free radical polymerization of a CD complexed N-methacryloyl-D,L-phenylalanine methyl ester racemic mixture the D-enantiomer polymerizes preferentially, whereas the L-enantiomer tends to accumulate in the solution. 8 Up to now, the enatioselective inclusion of chiral side groups of synthetic polymers with CD has not been investigated. Herein, we demonstrate the chiral recognition of the polymeric bound amino acid with RAMEB-CD (random methylated β-cyclodextrin). Generally, the glucose-based CDs might distinguish between native D-and L-amino acid enantiomers in aqueous media due to diastereomeric effects. 9-12 Thus, D-and L-tryptophan (D-and L-Trp) became the focus of our interest as chiral model compounds. It is an essential amino acid implemented in proteins with an aromatic moiety and therefore suitable to build inclusion complexes with RAMEB-CD. [13][14][15] Also, L-Trp is a precursor of serotonin, which is commonly used in pharmaceutical application as a tranquillizer. Furthermore, because of the presence of two functional domains, the amino and carboxylic groups D-and L-Trp are an interesting species for polymer synthesis.The D-and L-Trp-based monomers are synthesized when the amino groups of the amino acid are modified via condensation reaction, while the free carboxylic group, sensitive to pH value, still remains. The remarkable polymer properties based on poly-(N-isopropylacrylamide) (poly(NIPAAm)) induced us to select the NIPAAm as comonomer for direct copolymerization procedures. It is well-known that poly(NIPAAm) is a typical thermoresponsive polymer exhibiting a lower critical solution temperature (LCST) behavior in aqueous media at around 32 °C. 16 Above this critical temperature the polymer precipitates a stage that is reversible as soon as the temperature sinks below the LCST. The important feature is that the poly(NIPAAm) LCST value bears a tunable character due to the existence of a delicate

d-, l- and d,l-Tryptophan-Based Polyamidoamino Acids: pH-Dependent Structuring and Fluorescent Properties

“…In particular, poly- N -acryloyltryptophan was used in the determination of chiral interactions with 1,1-bis-2-naphthol [10]. Copolymers of N -acryloyltryptophan with other acrylamides [11] were employed in recognition studies [12,13,14]. The interaction of copolymeric poly- N -methacryloyltryptophan with β-cyclodextrin was investigated [15].…”

Synthesis and chiroptical properties of helical polyallenes bearing chiral cholesteryl pendant groups

“…The objectives of these research are not only to mimic the structure and function of biological helices, but also to widen their applications into many fields, as helical polymers can display optical activity based solely on their main‐chain helical conformation. In addition to their interesting helical structures, artificial helical polymers have been revealed to be useful materials in enantiomer separation, chiral recognition, and asymmetric catalysis . A typical example is the optically active helical poly(triphenylmethyl methacrylate) (PTrMA) developed by Okamoto and co‐workers, which shows excellent chiral recognition for a variety of racemic compounds and has been commercialized as a chiral stationary phase for high‐performance liquid chromatography (HPLC) …”

Molecular Recognition: Influence of Para‐Versus‐Meta‐Substituted Phenyl Moieties on the Swelling Degree of Macroscopic Polymeric Gels in Aqueous Cyclodextrin Solutions

“…Accordingly, molecular recognition of low‐ and high‐molecular‐weight organic substrates via host–guest complexes gained a lot of interest in the last decades . As an example, the use of cyclodextrins (CDs) for gel‐to‐gel attraction in the mm scale has been described .…”

“…[2][3][4][5] Accordingly, molecular recognition of low-and highmolecular-weight organic substrates via host-guest complexes gained a lot of interest in the last decades. [6][7][8][9][10] As an example, the use of cyclodextrins (CDs) for gel-to-gel attraction in the mm scale has been described. [ 11 ] Furthermore, CDs have been used for the formation of smart hydrogels by self-assembly of star-shaped supramolecular architectures [ 12 ] and the transition of nanogel-like micelles to nanovesicles.…”