Silk, optical rotation

The first successful experiments were reported by Schwab [16] Cu, Ni and Pt on quartz HI were used to dehydrogenate racemic 2-butanol 23. At low conversions, a measurable optical rotation of the reaction solution indicated that one enantiomer of 23 had reacted preferentially (eeright-handed quartz gave the opposite optical rotation it was deduced that the chiral arrangement of the crystal was indeed responsible for this kinetic resolution (for a review see [8]). Later, natural fibres like silk fibroin H5 (Akabori [21]), polysaccharides H8 (Balandin [23]) and cellulose H12 (Harada [29]) were employed as chiral carriers or as protective polymer for several metals. With the exception of Pd/silk fibroin HS, where ee s up to 66% were reported, the optical yields observed for catalysts from natural or synthetic (H8, Hll. H13) chiral supports were very low and it was later found that the results observed with HS were not reproducible [4],... 

Polarimeters for measuring optical rotation are so sensitive that they can measure rotations to 0.001°, an important fact when only small amounts of sample are available. Ecdysone, for example, is an insect hormone that controls molting in the silk- j worm moth. When 7.00 mg ecdysone was dissolved in 1.00 mL chloroform and the solution was placed in a cel with a 2.00 cm pathlength, an observed rotation dT -I-0.087° was found. Calculate [a]n for ecdysone. 

The first report of enantioselective catalysis over metal catalysts was made in 1939 by Lipkin and Stewart who showed that hydrocinchonine / -methylcinnamate could be hydrogenated in ethanol over an Adams Pt catalyst to yield / -phenylbutyric acid which exhibited an optical rotation of 8%.89 Some 20 years later, Akabori and co-workers reported that Pd supported on silk-fibroin was enantioselective for compounds containing both C=N and C=C functionalities, yielding optical yields as high as 66%, although the origin of the enantioselectivity in these systems has never been clear.90 A further 20 years later, Orito and co-workers reported... 

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