Helicity induction

Figure 45 Cartoon showing temperature-dependent Si chain helical induction by PTrMA block.333 Adapted with permission from Sanji, T. Takase, K. Sakurai, H. J. Am. Chem. Soc. 2001, 123, 12690-12691, 2001 American Chemical Society.

The use of disulfide linked di-a-helical peptides for the self-assembly of a heme-peptide model compounds has also been explored by Benson et al. (109). Conceptually analogous to the larger heme-protein systems utilized by Dutton and co-workers, to be detailed later, the incorporation of C4 S5mimetric Co(III)-porphyrins, based on coproporphyrin and octaethylporphyrin, resulted in helical induction comparable to that observed in the covalent PSM systems. 

S.J. George et al., Helicity induction and amplification in an oligo(p-phenylenevinylene) assembly through hydrogen-bonded chiral acids. Angew. Chem. Int. Ed. 46, 8206-8211 (2007)... 

Fig. 14 Schematic illustration of helicity induction on poly(phenylacetylene)s upon com-plexation with chiral compounds...

This section mainly describes our studies of the helicity induction on poly(phenylacetylene)s through noncovalent chiral interactions together with other interesting chiroptical properties of helical polymers and oligomers. 

Fig. 17 Schematic illustration of helicity induction on 34 upon complexation with a small amount of L-Ala HCIO4 (a). Titration curves of 34 with L-Ala HCIO4 in acetonitrile at 25 and - 10 °C (b). Changes in ICD intensity (Ae2nd) of 34 versus the % ee of L-Ala- HC104 during the complexation with 34 in acetonitrile at 25 and - 10 °C (c). (Reprinted with permission from [88], Copyright 2003 American Chemical Society)...

The macromolecular helicity induced in poly(phenylacetylene)s 28-30 (Fig. 14) upon complexation with chiral amines is dynamic in nature, and therefore, the ICD due to the helical chirality immediately disappears when exposed to a stronger acid such as trifluoroacetic acid. However, during the intensive exploration of the helicity induction and chirality amplification mechanism of the poly(phenylacetylene)s, such an induced helical chirality of 28-30 by an optically active amine such as (R)-39 has been found to be maintained, namely memorized , when the chiral amine is completely removed and replaced by various achiral amines, for example, 71 and 72 for 28 and diamines such as ethylenediamine for 29 and 30 in... 

Fig. 25 a Schematic illustration of helicity induction in 28 upon complexation with (R)-39 and memory of the induced macromolecular helicity after replacement by achiral amines (71, 72). b CD spectra of the 28-(J )-39 complex (solid line) and the isolated 28 by SEC fractionation using a DMSO solution containing an achiral amine 71 as the eluent (dashed line) in DMSO. (Reproduced with permission from [128]. Copyright 2004 American Chemical Society)... 

The noncovalent helicity induction and chiral memory concept is versatile enough to produce and maintain either a right- or left-handed helix because the helix-sense is predetermined by the chirality of the enantiomeric amines used. Consequently, the opposite enantiomeric helicity induction and the memory requires the opposite enantiomeric amine, followed by replacement with achiral amines. However, both mirror-image enantiomeric helices can be produced with a high efficiency from a helical poly(phenylacetylene) induced by a single enantiomer (Fig. 26) [129]. This dual memory of enantiomeric... 

Fig. 29 a Schematic illustration of a helicity induction in 44-Na upon complexation with (S)-77 and memory of the induced macromolecular helicity after complete removal of (S)-77. b Syn-anti configurational isomerization of the C = N double bond of polyisocyanide backbone... 

V. CHIRALITY OR HELICITY INDUCTION ON ACHIRAL PHOTORESPONSIVE POLYMER FILMS BY CIRCULAR POLARIZED LIGHT... 

Helicity induction was also realized for polyphosphazene derivative 109 using R) -1 -phenethylamine (110) as the chiral additive.193... 

Homopolymers and block copolymers of poly(2,3-quinoxaline)s containing functional side chains (85) have been prepared employing the Pd(II)-catalyzed helix-sense-selective polymerization.233 235 Recently is was reported that side chains can be modified without the quenching of the living site of the polymer.236-237 The helical induction by the 1,1 -binaphth-2-ylpalladium(II) complexes has been investigated in detail, mainly using NMR techniques. 

M. Mathews, N. Tamaoki, Reversibly tunable helicity induction and inversion in liquid crystal self-assembly by a planar chiropdc trigger molecule. Chem. Commun. 3609-3611 (2009)... 

Figure 6 Schematic illustration of a preferred-handed helicity induction in achiral st-PMMA in the presence of Ceo with (S)- or (R)-PEA, memory of the induced helicity after removal of PEA, and subsequent optically active stereocomplex formation after the addition of it-PMMA, resulting from replacement of the encapsulated Ceo molecules by it-PMMA strands. Reproduced with permission from Yashima, E. Maeda, K. lida, H. etal. Chem. Rev. 2009, 109, 6102. Copyright 2009 American Chemical Society.

Single-handed helicity induction was also achieved in gels and films of polyphenylacetylene derivatives. Gels obtained by copolymerization of (4-carboxyphenyl)acetylene with a bis(phe-nylacetylene) or by cross-linking of 168 responded to chirality to nonracemic amines in DMSO and alkaline water. Compound 174 formed an optically active gel upon complexation with optically active bis (amino acid)s. A cast film of 168 exhibited ICD in response to the chirality of liquid and solid chiral amines. Polydiacetylenes with a 4-carboxyIphenyI functions also showed ICD in the presence of optically active amines in dispersion and in the solid state. Helicity induction was also realized for polyphosphazene derivative 185 as (P)-phenethylamine as the chiral additive. ... 

Also the N-N transition was observed in a compensated system, in which another non-photoresponsive chiral dopant 10 with opposite helicity induction was used to compensate the HTP of the photoresponsive dopant 11 to form a compensated N phase. Reversible phase transition between the compensated N phase and cholesteric phase can be achieved by photo switching the chiral dopant between the two states [49] (Fig. 5.11). 

Yashima, E. Maeda, K. Helicity induction on optically inactive polyacetylenes and polyphosphazenes. In Synthetic Macromolecules with Higher Structural Order, Kahn, T. I. M., Ed. ACS Symposium Series 812 American Chemical Society Washington, DC, 2002 pp 41-53. 

Sato, M. A. Maeda, K. Onouchi, H. Yashima, E. Synthesis and macromolecular helicity induction of a stereoregular polyacetylene bearing a carboxy group with natural amino acids in water. Macromolecules 2000, 33, 4616 618. 

Zagres, W., Hall, J., and Lehn, J.-M. (1991) Helicity induction in helicate selforganisation from chiral tris(bipyridine) ligand strands, Helv. Chim. Acta, 1843-1852. 

Figure 6.5 (a) Schematic representation of the macromolecular helicity induction on poly(1 -co-5 ) upon complexation with L-alanine. The achiral fullerene and crown ether pendants represented by yellow and blue rings for clarity arrange in a helical array along the one-handed helical polymer backbone induced by noncovalent chiral interactions with L-alanine. (b) CD spectra of poly(1o.i-co-5o,) with L- and o-Ala HClO ([Ala-HCl04]/[poly(1o.,-co-5o,)] = 2) in dichloromethane-acetonitrile (8/2, v/v) at 25... 

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