ORD-measurements

CD and ORD measurements are a useful tool in studying configuration and conformation. The configuration of optically active 4,4 -dicarboxy-2,2, 5,5 -tetramethyl-3,3 -biselenienyl (1, X = Se) relative to its thiophene analog (1, X = S), was determined by reducing both to the corresponding 4,4 -dihydroxymethyl derivatives (2), which could be related to each other by the quasi-racemate method and by circular dichroism studies.15 Compounds 1 have also been related to 3,3, 6,6 -tetramethyl-2,2 -diphenic acid (3), and it was found that the levorotatory form of 1 (X = Se, S) and the dextrorotatory form of 3 have the -configuration.16... 

Starting with intermediate 145 (Scheme 26), 147 was prepared using dihydrocinnamoyl chloride, followed by catalytic hydrogenation and saponification of the ester group. The cyclization step was performed in the same manner as described above (see Scheme 27). The resulting product 148 was identical to the analogous derivative obtained from natural periphylline therefore, periphylline must possess structure 138 (775). The chirality of center-11 has been defined as S by ORD measurement in relation to the alkaloids chaenorhine and homaline (113). 

As seen in Figure 5.IB, the polymer forms a layered structure below the transition point, showing a well-developed system of SAXS peaks. Moreover, the ORD measurements (see Figure 5.2) exhibit drastic growth of the optic rotation in the IsoSm phase towards shorter wavelengths, in contrast to the proper isotropic melt of the same polymer above the transition point, suggesting some helix-like superstructural ordering in the mesophase with a pitch below 300 nm. That hypothesis was further supported with CD, dielectric spectroscopy, and UV-vis spectroscopy data. " Tlie critical importance of chirality for the formation of the IsoSm phase is also confirmed by... 

The crystal and molecular structure of [S,(Sas,5 as)]-( + )-83 has been determined . The structural analysis provided the absolute chirality of the cation and of the three stereogenic centres present, including the carbon of the ort/jo-metalated (S)-( — )-dimethyl-(a-methylbenzyl)amine, which had been established previously on the basis of CD and ORD measurements... 

Light-absorption and CD studies of hemocyanins from two different molluscan species showed several bands in the visible region characteristic also of other copper proteins. The greater resolving power of CD spectra yielded more accurate information than previous ORD measurements. d-d Transitions with distorted coordination sites could account for the absorption intensities observed without invoking charge transfer. By comparison of the CD data with those of peptide-Cu(II) complexes, the... 

CD studies of metal complexes (iron, copper) with human serum transferrin showed bands in the visible region (114) [earlier work in this field, mainly by ORD measurements is cited in Ref. (114)]. The binding of cupric or zinc ions to apotransferrin had no significant effect on the far ultraviolet CD (ORD) spectra (114). Similar results were also reported for chicken ovotransferrin (115). However, there were differences in the aromatic and other spectral regions up to 1000 nm between the CD spectra of the two copper transferrins indicating dissimilarities in the respective metal-binding sites (115). 

A considerable amount of work has been published on the optical activity of cytochrome c in both ferro and ferri states. As in other cases, earlier investigations were performed by ORD measurements. 

CD measurements in the range 205—500 nm were reported for cytochromes from Rhodospirillum rubrum and Rhodopseudomonas palustris under various conditions, and the relatively high helix content of about 63% was estimated by standard methods for both ferricytochromes (215) [see, however, Ref. (216)]. ORD measurements on Chromatium cytochrome c552, which contains two mesohemes and one flavin per molecule, showed complex behavior in the Soret region, indicating possible interaction between the hemes (217). 

ORD measurements in the Soret region of the carbon monoxide derivative of cytochrome oxidase showed a single Cotton effect near 430 nm, which indicated that only cytochrome a3 has an optically active transition, while the non-reacting cytochrome a subunit did not show measurable optical activity (249). By comparison of oxidation-reduction... 

ORD measurements on alkali-denatured cytochrome oxidase did not show Soret Cotton effects in the oxidized state, but a complex spectrum appeared at pH 11.6 in the reduced state, indicating heme-heme interactions. Polylysine-heme complexes were used as models (252). The optical activity of both oxidized and reduced heme a was measured in various solvents and under different conditions (253, 254). 

Early ORD measurements on beef liver catalase showed large Cotton effects in the Soret region, which disappeared upon denaturation (255). No evidence for previously reported (256) Cotton effects near 600 nm could be obtained (255). ORD and CD measurements on bovine liver catalase included also the liganded hemoprotein. Conformational changes in the protein, occurring upon ligand addition, were deduced from data in the ultraviolet region (257). 

According to ORD measurements of ferric HRP and its apoprotein, splitting of the heme appears to cause a reduction of the estimated a-helix content (260, 259). CD spectra of Japanese-radish peroxidase a have been interpreted as reduction of about 35% (upper limit) in the a-helix content upon removal of the heme with possible formation of / -structure. Differences between the oxidized and reduced forms of this peroxidase have been recorded (261) [see above, Myoglobin and Hemoglobin, ultraviolet region],... 

ORD measurements in the range 300—600 nm of the native enzyme showed Cotton effects due to the coenzymes (pyridoxal and pyridoxamine phosphate). These effects were absent in the apoenzyme, in the coenzymes alone, and at high substrate concentrations (357). CD data obtained for this enzyme were transformed to ORD curves, which were in good agreement with ORD data measured previously (358). 

CD spectra (200—350 nm) of calf thymus chromatin were compared with those of pure DNA in solution. Some of the differences observed (above approximately 250 nm) were attributed to conformational changes in the bound DNA, in which a large tilting of the bases may occur [(373) and refs, cited therein]. Previously, similar conclusions had been reached on the basis of ORD measurements on native nucleohistone and on nucleohistone dissociated either fully or partially into DNA and histone [(374) see also (375—379)]. CD studies on the state of DNA in native and partially deproteinized gander erythrocyte chromatin and of complexes of ethidium bromide with these systems were reported (380). 

ORD measurement, deg cm /dmol temperature (c.g., in Curie—Weiss expressions) metric ton triplet (spectra) triton... 

The symmetry of the bisphenethylisoquinoline molecule is such that reductive cleavage of 0,0-dimethylmelanthioidine (17) with sodium in liquid ammonia afforded almost exclusively the one phenolic isoquinoline 18 (12, 13) which showed a negative first Cotton effect. Previous knowledge (14, 15) of ORD measurement on tetrahydroiso-quinoline chromophores established the illustrated R-configuration and indicated that the molecule is in a head-to-tail arrangement. 

ORD measurements are commonly extended into the far-ultraviolet region where the Cotton effects characteristic of the a-helix (a trough at 233 m/z and a maximum near 200 m/z) (8, 56) are found. By analyzing the circular dichroic spectra of a-helical polypeptides, Holzwarth and Doty (24) have shown that three rotatoiy bands (the n1 — w transition at 222 m/z, the parallel-polarized w° — 7r exciton transition at 206 m/z, and the perpendicularly polarized t° — w exciton transition at 190 m/z) can account for these Cotton effects. When the polypeptide chain becomes disordered, only a single Cotton effect with a trough at 204 m/z is seen (8). 

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