Circular dichroism determination

Since the adamantane ring system is composed of three interlocking cyclohexane rings, all in the perfect chair conformation, /3-sub stituted adamanta-nones are also ideal models for establishing quantitative substituent contributions to the optical rotatory dispersion of cyclohexanones in the undisturbed chair form. A variety of optically active /3-equatorial and /3-axial substituted adamantanones have been synthesized 18°-184) and their circular dichroism determined 184-185) jji generai) axial polar substituents (C02R, Cl,... 

Spectrophotometric Methods 8.6.1 Calorimetric Determinations 8.6.2 Ultraviolet Determinations 8.6.3 Fluorimetric Analysis 8.6.4 Infrared Determinations 8.6.5 Circular Dichroism Determination... 

The secondary stmcture of the plasminogen molecule, as determined by circular dichroism spectra, is 80% random coil, 20% beta-stmcture, and 0% alpha-helix. Electron microscopy has demonstrated the tertiary stmcture of plasminogen to be a 22- to 24-nm long spiral filament with a diameter of 2.2 to 2.4 nm. 

Optical rotation and circular dichroism have been used for die characterization of optically active polymers. They have been used to determine whether polymers are optically active and whether a secondary structure such as a helix exists. 

Circular Dichroism Measurements. The absolute configurations of the C6 chiral center in tetrahydrobiopterin cofactor and related compounds were determined by comparison of their circular dichroism (CD) spectra with those of... 

Small-angle X-ray scattering (SAXS), circular dichroism (CD), and UV spectroscopy at different temperatures were used to investigate the nature of calf-thymus DNA in aqueous solution, in the presence of [Me Sn] " (n = 1-3) species. The results demonstrate that the [MeSn(IV)] moiety does not influence the structure and conformation of the DNA double helix, and does not degrade DNA, as indicated by agarose gel electrophoresis. Inter alia, the radii of gyration, Rg, of the cross section of native calf-thymus DNA, determined by SAXS in aqueous solution in the presence of [Me Sn] " (n = 1-3) species are constant and independent of the nature and concentration of the [Me Sn] species. 

The determination of the absolute configuration of a carotenoid is only possible by circular dichroism (CD) measurement. The spectrum interpretation can only be done by comparison with reference or model compounds with known chiralities. The sample requirement is as low as 5 to 50 pg, but CD facilities are not so commonly available. Buchecker and Noack reported experimental aspects and discussion of the relationships of carotenoid structures and CD spectra. 

Because process mixtures are complex, specialized detectors may substitute for separation efficiency. One specialized detector is the array amperometric detector, which allows selective detection of electrochemically active compounds.23 Electrochemical array detectors are discussed in greater detail in Chapter 5. Many pharmaceutical compounds are chiral, so a detector capable of determining optical purity would be extremely useful in monitoring synthetic reactions. A double-beam circular dichroism detector using a laser as the source was used for the selective detection of chiral cobalt compounds.24 The double-beam, single-source construction reduces the limitations of flicker noise. Chemiluminescence of an ozonized mixture was used as the principle for a sulfur-selective detector used to analyze pesticides, proteins, and blood thiols from rat plasma.25 Chemiluminescence using bis (2,4, 6-trichlorophenyl) oxalate was used for the selective detection of catalytically reduced nitrated polycyclic aromatic hydrocarbons from diesel exhaust.26... 

Of the visible spectroscopic techniques, CD spectroscopy has seen the most rapid and dramatic growth. The far-UV circular dichroism spectrum of a protein is a direct reflection of its secondary structure [71]. An asymmetrical molecule, such as a protein macromolecule, exhibits circular dichroism because it absorbs circularly polarized light of one rotation differently from circularly polarized light of the other rotation. Therefore, the technique is useful in determining changes in secondary structure as a function of stability, thermal treatment, or freeze-thaw. 

The redox potentials of zinc-substituted phthalocyanines are shown to be linearly dependent on the total Hammett substituent constant.837 In 1987, Stillman and co-workers used the absorption and magnetic circular dichroism spectra of the zinc phthalocyanine and its 7r-cation-radical species to assign the observed bands on the basis of theoretical calculations. The neutral and oxidized zinc phthalocyanine complexes with cyanide, imidazole, and pyridine were used with the key factor in these studies the stability of the 7r-cation-radical species.838 The structure of zinc chloro(phthalocyaninato) has been determined and conductivity investigated.839... 

Determination of protein secondary structure has long been a major application of optical spectroscopic studies of biopolymers (Fasman, 1996 Havel, 1996 Mantsch and Chapman, 1996). These efforts have primarily sought to determine the average fractional amount of overall secondary structure, typically represented as helix and sheet contributions, which comprise the extended, coherent structural elements in well-structured proteins. In some cases further interpretations in terms of turns and specific helix and sheet segment types have developed. Only more limited applications of optical spectra to determination of tertiary structure have appeared, and these normally have used fluorescence or near-UV electronic circular dichroism (ECD) of aromatic residues to sense a change in the fold (Haas, 1995 Woody and Dunker, 1996). 

Mancini, F., Fiori, J., Bertucci, C., Cavrini, V., Bragieri, M., Zanotti, M.C., Liverani, A., Borzatta, V., Andrisano, V. (2004). Stereoselective determination of allethrin by two-dimensional achiral/chiral liquid chromatography with ultraviolet/circular dichroism detection. J. Chromatogr. A 1046, 67-73. 

Meadows F, Narayanan N, Patonay G (2000) Determination of protein-dye association by near infrared fluorescence-detected circular dichroism. Talanta 50 1149-1155... 

The absolute configuration of C-3 of the chromophore 459 of isopyoverdins was determined to be S from the circular dichroism (CD) spectrum (Cotton effect +242 nm, —290 nm, +358 nm) of 460 obtained from isopyoverdin by acidic hydrolysis <2001T1019>. Diorganotin(iv) complexes with 4//-pyrido[l,2-/z pyrimidin-4-ones 461 <1996AOM47>, complexes of 2-methyl- and 2-methyl-8-nitro-9-hydroxy-4//-pyrido[l,2-tf]pyrimidin-4-ones with Ag(i), Cu(ll), Ni(n), Co(n), and Mn(n) ions <2000RJD587>, 2,4-dimethyl-9-hydroxypyrido[l,2-tf]pyrimidinium perchlorate and its complexes with prasedynium, neodymium, samarium, and europium <2000RJD310> were characterized by UV spectroscopy. 

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... 

Optically active telluronium ylides were not obtained for a long time. Optically active diastereomeric telluronium ylides 7 were obtained for the first time in 1995 by fractional recrystallization of the diastereomeric mixture.19 The absolute configurations of the chiral telluronium ylides were determined by comparing their specific rotations and circular dichroism spectra with those of the corresponding selenonium ylide with known absolute configuration. The telluronium ylides were found to be much more stable toward racemization than the sulfonium and selenonium ylides (Scheme 4). 

---