Circular dichroism natural

Tanaka, J., Ozeki-Minakata, K., Ogura, F., and Nakagawa, M. Absolute configuration of a coupled chromophore system by exciton analysis of circular dichroism. Nature, Phys. Set. (London) 241, 22-23 (1973). 

Goldbeck R A, Kim-Shapiro D B and Kliger D S 1997 Fast natural and magnetic circular dichroism Annu. Rev. Rhys. Chem. 48 453-79... 

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. 

Recently, peptoid-based mimics of both SP-C and SP-B have been designed to adopt helical secondary structures, and also mimic (to varying degrees) the sequence patterning of hydrophobic and polar residues found in the natural surfactant proteins. Peptoid-based SP-C mimics of up to 22 monomers in length, were synthesized and characterized by in vitro experimental methods [67, 68] (Fig. 1.8). The secondary structure of all molecules was assessed by circular dichroism and found to be helical. The surface activities of these peptoids, in comparison to the actual SP peptides described above, were characterized by surfactometry using... 

Natural circular dichroism (optical activity). Although circular dichroism spectra are most difficult to interpret in terms of electronic structure and stereochemistry, they are so very sensitive to perturbations from the environment that they have provided useful ways of detecting changes in biopolymers and in complexes particularly those remote from the first co-ordination sphere of metal complexes, that are not readily apparent in the absorption spectrum (22). It is useful to distinguish between two origins of the rotational strength of absorption bands. 

The noncovalent binding of a series of oxo-squaraine dyes 9a-e to BSA was evaluated by measurement of absorption, emission, and circular dichroism [63]. The magnitude of the association constants (Ks) for the dye-BSA complexes depended on the nature of the side chains and ranged from 34 x 103 to 1 x 107 M-1. Depending on the side chains, the Ks increase in the order [R1 = R2 = butyl-phthalimide] < R1 = R2 = cetyl] <[RJ = R2 = ethyl] <<[R = butyl-phthalimide, R2 = butyl-sulfonate] <<[RJ = R2 = butyl-sulfonate]. These dyes seem to interact mainly with a hydrophobic cavity on BSA. However, the association constants Ks increase substantially when the side chains are selected from butyl sulfonate. 

While it is tempting to explain regulatory and cosolvent effects on the basis of conformational changes favorable or unfavorable to enzyme activity, it is much more difficult to demonstrate the actual involvement, amount, and structural details of such changes. Experimental evidence consists in most cases of bits and pieces provided by techniques such as absorption and fluorescence spectroscopy, circular dichroism, and magnetic circular dichroism. These tools work in solution (and, when desired, at subzero temperatures) to investigate not simply empty enzymes but enzyme—substrate intermediates. However, even with this information, the conformational basis of enzyme activity remains more postulated than demonstrated at the ball and stick level, and in spite of data about the number and sequence of intermediates, definition of their approximate nature, rate constants, and identification of the types of catalysis involved, full explanation of any particular reaction cannot be given and rests on speculative hypothesis. 

The primary motivation for the development and application of vibrational optical activity lies in the enhanced stereochemical sensitivity that it provides in relation to its two parent spectroscopies, electronic optical activity and ordinary vibrational spectroscopy. Over the past 25 years, optical rotatory dispersion and more recently electronic circular dichroism have provided useful stereochemical information regarding the structure of chiral molecules and polymers in solution however, the detail provided by these spectra has been limited by the broad and diffuse nature of the spectral bands and the difficulty of accurately modeling the spectra theoretically. 

If the incoming light is polarised, any chiral features of the molecule that absorbs will be highlighted—in particular changes in such chiral features, e.g. when the protein is unfolding, these features will stand out. The secondary stmctural elements of proteins are chiral in their nature. This phenomenon can be followed with the so-called circular dichroism (CD). ... 

The observation of natural ORD or CD requires lack of symmetry in the molecule, but any molecule may exhibit magnetic circular dichroism (MCD). It constitutes a molecular analogy for the Zeeman effect in atomic spectra. Measurements in this area may well reveal substituent interactions which are masked in normal UV spectra. Extensive definitive papers of great interest which well illustrate this have appeared on MCD of pyridine derivatives, measured in cyclohexane, acetonitrile, and alcohol or aqueous acidic solutions for protonated... 

Stephens PJ, Pan JJ, Krohn K. Determination of the Absolute Configurations of Pharmacological Natural Products via Density Functional Theory Calculations of Vibrational Circular Dichroism The New Cytotoxic Iridoid Piismatomerin. Journal of Organic Chemistry 2007 72(20) 7641-7649. 

Ettinger, M.J., Timasheff, S.N. (1971a). Optical activity of insulin. I. On the nature of the circular dichroism bands. Biochemistry, 10, 824—830. 

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