Association-induced optical activity

Polyisocyanates have attracted much attention owing to their liquid crystalline properties, stiff-chain solution characteristics, and induced optical activities associated with helical chain conformation (Scheme 8). Pattern and Novak [39]... 

Reorientations of the coenzyme associated with the enzymatic catalytic cycle were first proposed by Ivanov and Karpeisky64 for aspartate transaminase on the basis of general topochemical considerations and studies of induced optical activity. Torchinsky and Koreneva65,66 found that induced optical activity of PLP bound to the transaminase is... 

In a series of works, Tokura and coworkers have systematically studied the CD induced in a number of carboxylic acids through their association with optically active amines [14-17]. Salts of 1 1 stoichiometry were formed as contact ion pairs, with limiting values normally being obtained for the observed ellipticities at equivalent molar amounts. The degree of salt formation could be related to the polarity of the solvent medium, as has been summarized in Table 1. The data in the table illustrate that, as the degree of solvent polarity increases, the limiting ellipticity induced in the carboxylate carbonyl band decreases. 

Cobalt(lll).—Complexes. Ammine complexes. Optical activity can be induced in the complexes [Co(NH3) ] and [Cofenlj] by means of outer-sphere association with chiral anions, e.g. (- - )-tartrate. Circular dichroism is observed in the d-d bands of the cations and it is suggested that this is due to (a) direct interaction between the chiral anion and the metal f/-orbitals and (b) the preferred conformation adopted by the inner-sphere ligands in the presence of a helical outer-sphere ligand. 

Circular Dichroism Studies of the Optical Activity Induced in Achiral Molecules Through Association with Chiral Substances... 

The circular dichroism induced in achiral compounds upon complexation with a chiral material can be used to characterize the nature of the interaction responsible for the association. Studies of this type may be conveniently classified as being the optical activity induced upon dissolution of a solute in a chiral solvent, through association of the species of interest with a co-dissolved chiral solute, or through association of the solute with chiral polymers. 

Optical Activity Induced Upon Association of an Achiral Solute with a Chiral Solute... 

OPTICAL ACTIVITY INDUCED UPON ASSOCIATION OF AN ACHIRAL... 

Photoresponsive membranes of cellulose-2,4-diacetate incorporating 6-nitro-l, 3, 3 -trimethylspiro-(2H-l-benzopyran-2,2 -indoline) have been prepared and chiroptical and fluorescence properties of optically active co-polymers of acenaphthalene with methyl acrylate/methacrylate have been investigated. Marked optical activity is induced in the aromatic units only for the co-polymer with methyl methacrylate. This difference in behaviour is associated with an overall higher main-chain flexibility and conformational freedom in acrylates compared with methacrylates. Photoisomerization in polyurethanes containing azo-links has been found to be dependent upon the thermal history of the polymer, and photoisomerization of linoleic acid and... 

So far, optical rotations of compounds have been discussed where the optical activity is associated with the particular structure of the cyclopropane ring. This means that the rotations are generated by a chiral arrangement of (achiral) ligands attached to the (achiral) molecular skeleton. For certain substituent patterns of I, in particular, the rotations are induced by atomic asymmetry. This is true for III and IV. The effect of the (achiral) cyclopropane moiety (viewed as a ligand) on open-chain molecules with an asymmetric carbon atom can be seen from the rotations of (S)-( —)-l-methyl-1-(1-ethoxyethyl) cyclopropane (80) and its counterpart 81 with only acyclic substituents. ... 

If one analyzes the rotation of D-a-(methylenecyclopropyl)glycine (82) the optical activity must come from (at least) four sources. One rotation contribution is associated with the atomic asymmetry of the open-chain moiety (methylenecyclopropane being viewed as a ligand). On the other hand, optical activity will also be induced by the asymmetric carbon atom of the ring and the asymmetry in the electron density distribution of the exocyclic double bond system (with diastereotopic faces). Finally also helix optical activity may be operative. The example of 82 demonstrates the complexity of the optical rotation of an apparently simple cyclopropane derivative. Further discussions of optical rotations of similar compounds, therefore, will cling to only the qualitative level. 

The first reported circular dichroism (CD) study of chiral PPy s was by Delabouglise and Gamier105 on the polymers 4 (R = CH2OH, CHMc2, and Ph), in which a series of amino acids are covalently bound at the 3-position of each pyrrole ring. They exhibit a CD band at ca. 470 nm associated with the absorption band at 460 nm. This optical activity is believed to be induced by the presence of the chiral amino acid substituents, leading to the adoption of a one-handed helical structure by the PPy chains. 

Achieving sufficient lattice hardening is important for several reasons in addition to securing necessary thermal stability for the poling-induced electro-optic activity [27-31,100-102]. As noted in the previous section, photochemical stability and optical loss (associated with material processing) are frequently strongly dependent on lattice hardness. 

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