Optical Rotatory Dispersion and Circular Dichroism

Except for measurement of optical rotation at single wavelengths chiroptical properties of carotenoids have only been studied during the last decade. 

In a fundamental paper on ORD spectra of carotenoids Bartlett et al. (20) classified chiral carotenoids into homodichiral (with two identical chiral end groups), heterodichiral (with two different chiral end groups) and monochiral (with one chiral and one achiral end group) carotenoids. They advanced an additivity hypothesis, stating that the ORD contribution from each end group was additive. 

By this approach the absolute configuration of carotenoids such as (27 ,2 7 )-P,P-carotene-2,2 -diol [(33), R=OH], see Fig. 2, and of (35,3 5)-astaxanthin (28) (after LiAlHU reduction) has been assigned (7,118) and subsequently proved by independent methods (38, 116). In accordance with the conformational rule esterification or glycosidation of a hydroxy group (21, 88) of a P-ring or replacement of a 2-hydroxy group in p,e- or y-rings with methyl or isopentenyl substituents has little effect on the 

Triple bonds in the 7(70 position greatly reduce the Cotton effect of a chiral cyclohexene ring. This is exemplified by the CD spectra of alloxanthin (31) 20, 21) and (35,3 iS)-7,8,708 -tetradehydroastaxanthin (34) 21). 

Substituent effects in chiral aliphatic end groups on CD spectra are not yet fully explored, but appear to be more complex than in cyclohexene derivatives 28, 107,153). 

Theoretically, the phenomena of optical activity can be described with the tools already developed. A photon (wave packet) with wave vector k is scattered from polarization ni k) to n2 k) (and the same energy) with probability amplitude 

For the case of minimal absorption the photon in the forward direction will have the polarization vector ni(k) — n2 k) L, where 

In order to compare this result with the expressions commonly used in the theory of optical rotation , the long-wavelength limit is considered, i.e., Eq. (6.45) is used to write 

The average over molecular orientations, or equivalently over photon propagation directions, appropriate for gaseous samples or liquid solutions, yields 

As kc Rv, lv))kc = iefm) pi,-,lv))kc and the angular momentum I defines the magnetic dipole moment operator M = e/2mc)l, it holds that 

The configuration of the localized iron binding area in adrenal and testis non-heme iron proteins could be extensively studied by measuring the optical rotatory dispersion (ORD) and circular dichroism (CD). The ORD properties of various non-heme iron containing proteins were reported by Vallee and Ulmer (67). 

Adrenal and testis non-heme iron proteins equally exhibit extrinsic multiple Cotton effects with three distinct maxima. The peaks of adrenodoxin appaer at 530 mp, 480 mp, and 360 mp and the troughs at 580 mp and 400 mp (Fig. 4). The peaks of testis protein appear at 530 mp, 475 mp, and 355 mp and the troughs at 580 mp and 390 mp. The characteristics of the principal effects in the above two proteins and spinach ferredoxin are summarized in Table 6. 

Dramatic change in the ORD occurs upon enzymatic reduction with NADPH and adrenodoxin reductase under anaerobic conditions as shown in Fig. 4. The dispersion displays a fairly plain pattern in the visible range, although the peak of the principal effect appears to shift to shorter wave length, whereas the peak near 350 mp is not affected. 

Upon simple aeration, the original dispersion appears to be regained. Similar changes in the dispersion can be observed on chemical reduction with dithionite. 

Upon reduction, the spectra change markedly. The maxima of reduced adrenodoxin occur at 400 mp and 590 mp with shoulders. Those of reduced spinach ferredoxin appear at 415 mp and 590 mp with shoulders. The 0 s of reduced adrenodoxin at 400 mp, and of reduced spinach ferredoxin at 415 mp are 6,500 and 22,000 deg-cm2/dmole respectively. To be noted here is the fact that there is no obvious counterpart of visible absorption to correspond to the CD components at 400 mp or 415 mp. 

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P. Crabbe, Top..Stereochem. 1 93 (1967) C. Djerassi, Optical Rotatory Dispersion, McGraw-Hill, New Vbrk, 1960 P. Crabbe, Optical Rotatory Dispersion and Circular Dichroism in Organic Chemistry, Holden D, San Francisco, 1965 E. Chamey, The Molecular Basis of Optical Activity. Optical Rotatory Dispersion and Circular Dichroism, John Wiley Sons, New Vbrk, 1979. 

P. Crabbe, Optical Rotatory Dispersion and Circular Dichroism in Organic Chemistry, Holden-Day, Inc., San Francsico, 1965, p. 166. 

Optical Rotatory Dispersion and Circular Dichroism Spectra. 181... 

C. Djerassi, Optical Rotatory Dispersion Applications to Organic Chemistry (New York, McGraw-Hill, 1960) L. Velluz, M. Legrand, and M. Grosjean, Optical Circular Dichroism, Principles, Measurements, and Applications (Weinheim, Verlag Chemie, 1965) and G. Snatzke (ed.), Optical Rotatory Dispersion and Circular Dichroism in Organic Chemistry (London, Heyden Son, 1967). 

Because configurational information can be derived from optical rotatory dispersion and circular dichroism scans, considerable work has been conducted using these techniques to study the tetracyclines (32). The absolute configuration of CTC was determined using optical rotatory dispersion data (33) Spectral curves are presented in Figures 8 and 9. The circular dichroism spectrum is similar to that presented by Mitscher et al. (34), except that the values differ by a factor of about 1.5. In Table 3, data obtained by Mitscher and in FDA laboratories are compared. 

Iizuka, E., and Yang,J. T. (1966). Optical rotatory dispersion and circular dichroism of the beta-form of silk fibroin in solution. Proc. Natl. Acad. Sci. USA 55, 1175-1182. 

The optical purity of the phosphonate (123)148 and the absolute configuration of the phosphonium bromide (124)149 have been established. Optical rotatory dispersion and circular dichroism have been used in stereochemical studies of phospholipids150 and adenosine-5 -triphosphate.151... 

Salvwkm, P. and Ciaidelli, F. An Introduction to Chiroptical Technique Basic Principles, Definitions and Applications," In Optical Rotatory Dispersion and Circular Dichroism Ciaidelli, F. Savadori, P., Eds. Heyden London, 1973 pp. 3-24. 

Fundamental Aspects and Recent Developments in Optical Rotatory Dispersion and Circular Dichroism, F. Ciardelli, P. Salvadori, Eds., Heyden, London 1973. 

If two different three-dimensional arrangements in space of the atoms in a molecule are interconvertible merely by free rotation about bonds, they are called conformations if not, configurations.l85 Configurations represent isomers that can be separated, as previously discussed in this chapter. Conformations represent conformers, which are rapidly interconvertible and thus nonseparable. The terms conformational isomer and rotamer are sometimes used instead of conformer. A number of methods have been used to determine conformations.186 These include x-ray and electron diffraction, ir, Raman, uv, nmr,187 and microwave spectra,188 photoelectron spectroscopy,189 supersonic molecular jet spectroscopy,190 and optical rotatory dispersion and circular dichroism measurements.191 Some of these methods are useful only for solids. It must be kept in mind that the conformation of a molecule in the solid state is not necessarily the same as in solution.192 Conformations can be calculated by a method called molecular mechanics (p. 149). 

Optical rotation, optical rotatory dispersion and circular dichroism. 

E. Charney, The Molecular Basis of Optical Activity. Optical Rotatory Dispersion and Circular Dichroism, Wiley, New York, 1979. 

For example W. Klyne (1960). Optical rotatory dispersion and the study of organic structures , in Advances in Organic Chemistry. Eds R. A. Raphael, E. C. Taylor, H. Wynberg. New York Interscience, Vol. 1, p. 239 Optical Rotatory Dispersion and Circular Dichroism in Organic Chemistry (1967). Ed. G. Snatzke. London Heyden and Son P. Crabbe and A. C. Parker (1972). Optical rotatory dispersion and circular dichroism , in Techniques of Chemistry. Eds A. Weissberger and B. W. Rossiter. New York Wiley, Vol. 1, Part IIIc, p. 183. 

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