Aggregate chirality

Simonyi M, Bikadi Z, Zsila F, and Deli J. 2003. Supramolecular exciton chirality of carotenoid aggregates. Chirality 15(8) 680-698. 

Chiral aggregates of 40 were subjected to multiple cycles of heating (50°C) and cooling (-10°C) to investigate the thermal stability of the aggregate chirality.29 In the CD spectra of the aggregates at 60%/40% THF/methanol, the bisignate Cotton effect observed at 20°C completely disappears at 50°C... 

In order to further experimentally probe the hard-core model of polysilane aggregate chirality, a series of poly-[(alkyl)alkylphenylsilylene]s, differing in phenyl ring-substituent position and chain length were synthesized, designed such that the polymer chain diameter, d, and helical pitch, p, in the hard-core model were varied.343... 

Before analysing the vortex effects on J-aggregates chirality it is worth recalling some peculiarities of this chemical system. 

In a solution of a chiral compound, the enantiomers should display identical physical properties, if any foreign optically active substance does not exist in the system. However, this notion holds true only in on ideal dilute solution. To the extent that there is some degree of solute aggregation, chiral dififerentiation of enantiomers may be possible without the aid of any foreign optically active substance. As Uskokovic and coworkers discovered in... 

Optical properties of cyanines can be usefiil for both chiral substituents/environments and also third-order nonlinear optical properties in polymer films. Methine-chain substituted die arbo cyanines have been prepared from a chiral dialdehyde (S)-(+)-2-j -butylmalonaldehyde [127473-57-8] (79), where the chiral properties are introduced via the chiral j -butyl group on the central methine carbon of the pentamethine (die arbo cyanine) chromophore. For a nonchiral oxadicarbocyanine, the dimeric aggregate form of the dye shows circular dichroism when trapped in y-cyclodextrin (80). Attempts to prepare polymers with carbocyanine repeat units (linked by flexible chains) gave oligomers with only two or three repeat units (81). However, these materials... 

Another chiral titanium reagent, 11, was developed by Corey et al. [17] (Scheme 1.24). The catalyst was prepared from chiral ris-N-sulfonyl-2-amino-l-indanol and titanium tetraisopropoxide with removal of 2-propanol, followed by treatment with one equivalent of SiCl4, to give the catalytically-active yellow solid. This catalyst is thought not to be a simple monomer, but rather an aggregated species, as suggested by NMR study. Catalyst 11 promotes the Diels-Alder reaction of a-bro-moacrolein with cyclopentadiene or isoprene. 

The second chirality enrichment mechanism operating in the solution is most likely that some heterochiral pairs of the 1 1 complex DBFOX/Ph-Ni(C104)2 are formed or they are further associated to form relatively stable racemic aggregation [58], while weak aggregation should result in the case of enantiopure 1 1 complex... 

In collaboration with Professor Collum and coworkers, 6Li NMR (including 13C-labeled acetylene 37 and 15N-labeled chiral modifier 46 experiments) and Li aggregation studies were implemented to assist in the understanding of some of the factors responsible for the stereoselective nature of this chemistry [35],... 

All labeled compounds including n-Bu6Li (from 6Li ingot) were prepared by us. When n-Bu6Li was added to a solution of cyclopropylacetylene (37) and chiral modifier 46 (1 1 ratio) in THF-pentane, the 6Li NMR at -125 °C (A) is shown in Figure 1.7. A few sets of aggregates could be identified. (See Ref [35a] for full assignment). 

Spano, F. C. 2009. Analysis of the UV/Vis and CD spectral line shapes of carotenoid assemblies Spectral signatures of chiral H-aggregates. J. Am. Soc. 131 4267-4278. 

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