Chiral side chain

Trzaska and co-workers showed a similar propeller mechanism for the formation of helical columns from disclike metallomesogens (29-31).34 These metallomesogens also have C3 symmetry and 30 and 31 are provided with chiral side chains. In the hexagonal columnar mesophase these chiral side chains induce a Cotton effect in the chromophore of the helically arranged core. Heating the mesophase to the isotropic liquid results in the disappearance of the Cotton effect because of the loss of helical order. This effect illustrates the need for the molecules to be positionally ordered in order for the side-chain chirality to be transferred to the supramolecular column. 

There was no obvious explanation for the side-chain chirality of biopterin or its related aromatic pterin derivatives in the CD spectra. This fact requires that structural determination of all newly found pterins must be carried out by comparison with optically active authentic samples. Indeed, almost all compounds have been obtained as aromatic pterins through the exploration of naturally occurring rare pterins and their structures have been generally determined by chemical syntheses from sugar derivatives, as descried in Sect. 3.2. From the viewpoint of characteristic fluorescence emissions, the application of FDCD to the configurational analyses of aromatic pterin derivatives has been carried out in previous studies [64,65]. Since FDCD analysis of aromatic pterins is approximately 100 times more sensitive than normal... 

In the polymerization of the (—)-monomers with various ee s, enantiomer selection was observed though the selectivity was lower compared with that of the polymerization of IDPDMA.83-87 In this experiment, a nonlinear relation was observed between the ee of the monomer in the feed and the optical activity of the obtained polymer (Figure 6). This indicates that the optical activity of the polymer is not based only on the side chain chirality. Furthermore, the chirality of a one-handed helical part induced by a successive sequence of the (—)-monomeric units (monomeric units derived from a (—)-monomer) can overcome the opposite chiral induction by the sporadic (+)-monomeric units. In other words, once a one-handed helical radical comes under the influence of the (—)-monomeric units, an entering (+)-monomer becomes a part of the one-handed helix whose direction may be unfavorable to the chiral nature of the (+)-monomer. 

Side chain chiral polyn rs (34, in Fig. 24) have been produced via active ester synthesis, by using soluble and crosslinked samjdes of copoly(AOTcp-styrene) (unpublished work). The resulting chiral polymers are of considerable interest in separation technology, and as auxiliary n dia for asymmetric synthesis. Fluorescent labeled polymers, polyelectrolytes and hydrophobically modified ionomers (e.g. and 36), are also readily available via active ester synthesis. 

When the major gymnochrome B (275) was heated in pyridine at 160°C, it was partially converted into a diastereomer which exhibited a CD curve opposite in sign to that of 275. This implies that the two compounds are both configurational helixes (the configurations of the side-chain chiral centres cannot be modified by the thermal isomerization). The inversion of helicity is accompanied by a... 

In these isotactic polymers, the optical purity of the monomer affected the optical activity via the relationship to the excess helical sense of the polymer (Figure 1). ° In the case of isotactic poly((S)-4-methyl-l-hexene) (2) and poly((i )-3,7-dimethyl-l-octene) (3), an increase in the optical purity of the monomers resulted in an increase in the optical activity of the polymers in a nonlinear fashion the optical activity of the polymers leveled off when the optical purity of the monomer reached -80%. By contrast, in the case of isotactic poly((S)-5-methyl-l-heptene) (4), the relation was linear. These findings imply that the side-chain chiral centers of 4, which are separated from the main chain by three covalent bonds, may be too far from the main chain to affect the helical conformation. 

The majority of the ferrocene ligands have both planar (Cp ring with two different substituents) and central (in the side chain) chirality. A matched combination is very convenient for achieving high levels of asymmetric induction. From a structural point of view, chiral ferrocenyl diphosphines can be divided in two classes depending on the relative position (1,1 or 1,2) of the phosphorus donor atoms, which, in turn, may be attached to one or both cyclopentadienyl rings directly or via a spacer. 

Booth TD, Lough WJ, Saeed M, Noctor TAG, Wainer IW (1997) Enantioselective separation of enantiomeric amides on three amylose-based chiral stationary phases effects of backbone and carbamate side chain chiralities. Chirality 9 173-177... 

The preparation of enantiopure or enriched complexes possessing planar chirality has been accomplished either by resolution of racemic mixtures or by asymmetric syntheses. Reported methods for the resolution of planar chirality include both chemical and kinetic resolution procedures, whilst reported asymmetric syntheses of enantiomerically pure or enriched benchrotrenic complexes include enantioselective ort/io-deprotonations with chiral lithium amide bases, and the transfer of side chain chirality onto the arene ring mediated by diastereoselective orf/io-nucleophilic additions and o/tfeo-metalations. 

The side-chain chirality of (-)-biopterin (76) has been assembled from 2,3-O-cyclohexylidene-D-ribose as indicated in Scheme 18. ... 

By certain physical factors like thermal, ultraviolet irradiation, high pressure and other chemical parameters like organic solvents the helical pol5mers are easily denaturalized. A variety of helical polymers are synthesized, which include polyisocyanates, polyisocyanides, polychloral, polymethacrylates, polysilanes, polythiophenes, poly (p-phenylene)s, poly(l-methylpropargyl-ester)s, poly(phenylacetylene)s and poly (-unsaturated ketone) [18-24] (Fig. 1). Other polymers are whose optical activity is main chain or side chain chirality dependent e.g. amino-acid-based polymers are nontoxic, biocompatible and biodegradable. 

Dissymmetric systems shows exciton splitting of dichroic absorptions and optical activity and photochromic materials having NLO, photoresponsiveness and photorefractivity properties, which occurred due to the presence of azoaromatic and chiral functionalities in the polymers [62]. Finally, novel optically active multifunctional methacrylic copolymers were synthesized, which contained side-chains chiral moieties and linked to a photoconductive carbazolic and to a photochromic azoaromatic chromophores... 

Henceforth, the synthesis of multifunctional methaciylic copolymers with side-chains chiral moieties linked to a photochromic azoaromatic and to photo-conductive carbazolic chromophores based novel optically active polymers are very meaningful. 

L. Angiolini, R. Bozio, T. Dainese, L. Giorgini, A. Golemme, F. Mauriello, D. Pedron, R. Termine, Photoresponsive polymers containing side-chain chiral azocaibazole chro-mophores as multifunctional materials. Proc. SPIE 6653, 665305 (2007)... 

Side Chain Chiral Thermotropic Liquid Crystal Polymers... 

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