Poly circular dichroism

Peculiar DNA architecture was demonstrated in 25% aqueous ethanol when DNA was complexed with series of cationic detergents in the presence of poly(glutamic acid) [124]. Electron microscopy and x-ray scattering demonstrated that DNA can pack cetyltrimethylammonium bromide molecules into rodlike micelles, which form a hexagonal lattice. Interestingly, circular dichroism spectroscopy revealed that in these complexes DNA adopts left-handed conformation. 

Fig. 25.—Circular Dichroism for Blocks of Poly(L-guIopyranuronate) Poly(o-...

Fig. 28.—Circular Dichroism of a Film of Poly(D-galactopyranuronic Acid). (Redrawn from Ref. 62.)...

Earlier studies using thermal denaturation analysis and spectrophotomet-ric titration with TxA T and CxC-C" containing DNA triplexes showed that coralyne binds strongly to these triplexes by intercalation and does not exhibit a significant sequence-selectivity [222]. In a later study by Morau Allen et al. [217], employing DNase footprinting, thermal denaturation analysis, UV-visible spectrophotometric titrations, circular dichroism and NMR spectroscopy, showed that coralyne is fully intercalated into TxA T triplex DNA whereas in C GxC triplex, it is partially intercalated due to electrostatic repulsion between the cationic alkaloid and the protonated cytosine [217]. Kepler et al. [223] demonstrated that coralyne intercalated to parallel triplex DNA but did not intercalate to antiparallel triplex DNA. Recently Hud and coworkers [219,224] demonstrated that duplex poly(dA) poly(dT) is trans-... 

The optically active poly(TrMA) shows a large optical activity and intense circular dichroism (CD) due both to the triphenylmethyl group, indicating that this group has a chiral propeller structure, and to the helicity. Poly(TrMA) of degree of polymerization (DP) over 80 is insoluble in common organic solvents. 

BMW Langeveld-Voss, R Janssen, MPT Christiaans, SCJ Meskers, HPJM Dekkers, and EW Meijer, Circular dichroism and circular polarization of photoluminescence of highly ordered poly 3,4-di[(5)-2-methylbutoxy]thiophene, J. Am. Chem. Soc., 118 4908 -909, 1996. 

A Marietta, D Gongalvcz, ON Oliveira Jr., RM Faria, and FEG Guimaraes, Circular dichroism and circularly polarized luminescence of highly oriented Langmuir-Blodgett films of poly(/j-phenylene vinylene), Synth. Met., 119 207-208, 2001. 

Empirical conformational energy calculations are performed on helical poly(2,3-quinoxaline)s to predict stable conformations. Two energy minimum conformations are found by varying the dihedral angle, y, between two adjacent quinoxaline units from 5 to 180°. Circular dichroism spectra are calculated for the two stable conformations (v - 45 and 135°) on the basis of exciton theory. 

Fig. 29. Circular dichroism spectra of poly(dG-m5dC) po]y(dG-m5dC) in 5 mitt Tris-HCl, pH 8.0, plus the following73 ...

In fact Schulz and co-workers (131,134), and Klabunovskii, Shvartsman and Petrov (55) report that the O. R. D. curves of poly-menthyl-acrylate, poly-bornyl-acrylate and poly-2-methyl-butyl-methacrylate show a maximum at about 300 mp, the wavelength corresponding to the maximum being related to the method of preparation of the polymer. Circular dichroism measurements seem advisable in order to confirm the existence of a Cotton effect postulated by the above authors in that wavelength range. 

In a more recent study using circular dichroism, Pflumm and Beychok (313) have fitted the observed curve for RNase-A (see Figs. 11c and d) weighted mixtures of the characteristic bands for helix from poly-L-glutamic acid and / structure from poly-L-lysine. The data are compatible with 11.5% helix and 33% / conformation. Ribonuclease-S and RNase-A have almost identical CD spectra from 198 to 300 nm. The spectrum of S-protein is markedly different from the other two. 

A photochromic polymer containing azobenzene units has also been prepared by modification of a naturally occurring microbial poly(E-L-lysine) (Scheme 5, Structure IX), and investigated by means of absorption and circular dichroism spectroscopy.1431 The structure of this polymer, however, does not correspond to those of polypeptides, which are poly(amide)s of a-amino acids, and therefore the results cannot be discussed in terms of the typical polypeptide structures (a-helix, P-structure, random coil) and their standard CD spectra. 

Bioactive macromolecules like peptides, proteins, and nucleic acids have been successfully embedded in planar LbL films. An important question is the retention of the bioactivity of the film-embedded biomolecules. The structural properties and stability of the LbL films formed from synthesized polypeptides of various amino acid sequences were recently reported [50]. The authors showed that control over the amino acid sequence enables control over non-covalent interpolypeptide interaction in the film, which determines the film properties. Haynie and coworkers showed by circular dichroism spectroscopy that the extent of adsorption of poly(L-glutamic acid) (PGA) and poly(L-lysine) (PLL) in the LbL films scales with the extent of secondary structure of the polypeptides in solution [51]. Boulmedais demonstrated that the secondary structure of the film composed of these polypeptides is the same as the peptide structure in the complex formed in solution [52], as found by Fourier transform IR spectroscopy (FUR). 

Blackwell and his co-workers have used circular dichroism spectroscopy to study the interactions of glycosaminoglycans with collagen, and with synthetic cationic polypeptides. In the absence of glycosaminoglycans, poly-L-lysine and poly-L-arginine exist in an extended charged coil conformation. Glycosaminoglycans bind to these cationic polypeptides and cause them to assume an a-helical conformation. In a series of systematic studies (76-83). Blackwell and his co-workers... 

Fig. 13 Circular dichroism spectra of poly(L-arginine) retinoate (a), poly(L-histidine) retinoate (b), and poly(L-lysine) retinoate (c). The complexes were prepared as films on quartz slides. Reprinted with permission from [142]. Copyright 2000 American Chemical Society...

FIGURE 3.4.2 Increments on circular dichroism spectra of secondary structure elements cx-helix (black solid line), (3-sheet (black dashed-dotted line), (3-turn (gray dashed line), poly-L-proline (gray solid line), and random coil (black dashed line). 

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