Optical rotatory dispersion spectrum

A. Circular Dichroism and Optical Rotatory Dispersion Spectra. 236... 

Bohren, C. F., 1977. Circular dichroism and optical rotatory dispersion spectra of arbitrarily shaped optically active particles, J. Theor. Biol., 65, 755-767. 

Recently, another red protein Buchanan, Lovenberg, and Rabinowitz 32) Mortenson 72) has been isolated in crystalline form from C. pasteurianum and certain of its properties determined Lovenberg and Sobel 67)). Lovenberg and Sobel 67) named it rubredoxin because of its color and properties of an electron carrier. They showed rubredoxin differed from ferredoxin in absorption spectrum, composition and redox potential. Rubredoxin contained no inorganic sulfide the recent demonstration 49) of the similarity of the optical rotatory dispersion spectra of rubredoxin and bacterial ferredoxin makes a further comparison of the properties of these proteins particularly interesting. 

The effect of pH on oligonucleotide conformation has been shown, for example, in an interesting study of absorption and optical rotatory dispersion spectra by Warshaw and Tinoco, 1965 and Cantor and Tinoco, 1965. Their study also shows that the conformations of (Gp, Ap)U are very different at pH 7 and they suggest that optical rotatory dispersion measurements can distinguish between trinucleotide sequence isomers. They do not discuss the application of their work to oligonucleotide fractionation but this would seem to be an interesting field for study. 

Fig. 10.—Optical Rotatory Dispersion Spectra, in Dioxane, of Two Diastereomers (m.p. 204° and 191°) of ortto-Dimercaptocyclohexanetetrol Trithiocarbonate, Di-0-isopropylidene Acetal.

The trithiocarbonates may prove useful as intermediates for the synthesis of sugar dithiols from epoxides. Ring opening by reductive cleavage with lithium aluminum hydride gives excellent results with aliphatic and ahcyclic trithiocarbonates. When both carbon atoms are secondary, the product is a iraws-dithiol for example, cyclohexene oxide, which is converted into a irans-trithiocarbonate, gives, on reduction, cyclo-hexane-1,2-dithiol. The reaction has been used in the cyclitol series for the preparation of 1,2-dithio-neo-inositol and 1,2-dithio-ir-inositol, from 1,2-anhydro-alZo-inositol. The inositol trithiocarbonates show pronounced Cotton effects in their optical rotatory-dispersion spectra. 

Fig. 2.—Ultraviolet Absorption Spectra, Optical Rotatory Dispersion Spectra, and Circular Dichroism Spectra of Methyl (Benzyl 2,3-Di-0-benzyl-4-deoxy-/3-L-threo-hex-4-enopyranosid)uronate (------) and its a Anonier (--------).

Fig. 4.—The Ultraviolet and Optical Rotatory Dispersion Spectra of the Dienol Ethers 181 and 182.

These compounds are, respectively 1 la,15(S)-dihydroxy-9-oxo-13-frans-prostenoic acid 15(S)-hydroxy-9-oxo-10,13-trans-prostadienoicacid 15(S)-hydroxy-9-oxo-8(12), 13-trans-prostadienoic acid 9a,lla,15(S)-trihydroxy-13-trans-prostenoic acid 9/S, lla,15(S)-trihydroxy-5-c/s,13-trans-prostadienoic acid and, 1 la,15(S)-dihydroxy-9-oxo-5-cIS,13- rans-prostadienoic acid. NMR and optical rotatory dispersion spectra have been determined for several of these compounds, and ultraviolet data have been given (Ramwell et al., 1968). 

Figure 9.3(B) depicts the absorption, circular dichroism and optical rotatory dispersion spectra of the mirror image of the hypothetical molecule considered in Figure 9.3(A). Note that vdille the absorption spectra in both cases are identical, the circular dichroism and optical rotatory dispersion spectra have changed signs. If a racemic mixture of this hypothetical compound is subjected to the above experiment, the absorption spectrum would still be identical but the circular dichroism and optical rotatory dispersion spectra would cancel out.

The cholesteric texture of a-PPEI scatters white light and produces dark lines. Consequently, the optical rotation has its origins primarily in the supramolecular helix and the contribution of the asymmetric molecules are negligible since isotropic solutions (1 mm thick or less) appear black under crossed polarized light and do not show any circular dichroic or optical rotatory dispersion spectra. The a-PPEI samples studied were polymerized from racemic monomer, and may be considered to be racemic mixtures of oppositely wound helices. 

The 7-substitued polymer is crystalline with a melting point of 62 °C whereas the corresponding racemic material cannot be crystallized (/ )-(+)-ethyl-6-acetylthio-3-methylthiohexanoate and (/ )-(-)-ethyl-6-acetylthio-4-methylthiohexanoate were prepared as model compounds (Scheme LVI). A comparison of their optical rotatory dispersion spectra with those of the polymers indicates that the conformations around the asymmetric centers are the same in both types of compound. The macromolecules are too flexible to assume conformational order in dilute solution. 

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