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CD Data (cd + data)
Selected AbstractsThe Alzheimer ,-peptide shows temperature-dependent transitions between left-handed 31 -helix, ,-strand and random coil secondary structuresFEBS JOURNAL, Issue 15 2005Jens Danielsson The temperature-induced structural transitions of the full length Alzheimer amyloid ,-peptide [A,(1,40) peptide] and fragments of it were studied using CD and 1H NMR spectroscopy. The full length peptide undergoes an overall transition from a state with a prominent population of left-handed 31 (polyproline II; PII)-helix at 0 °C to a random coil state at 60 °C, with an average ,H of 6.8 ± 1.4 kJ·mol,1 per residue, obtained by fitting a Zimm,Bragg model to the CD data. The transition is noncooperative for the shortest N-terminal fragment A,(1,9) and weakly cooperative for A,(1,40) and the longer fragments. By analysing the temperature-dependent 3JHNH, couplings and hydrodynamic radii obtained by NMR for A,(1,9) and A,(12,28), we found that the structure transition includes more than two states. The N-terminal hydrophilic A,(1,9) populates PII-like conformations at 0 °C, then when the temperature increases, conformations with dihedral angles moving towards ,-strand at 20 °C, and approaches random coil at 60 °C. The residues in the central hydrophobic (18,28) segment show varying behaviour, but there is a significant contribution of ,-strand-like conformations at all temperatures below 20 °C. The C-terminal (29,40) segment was not studied by NMR, but from CD difference spectra we concluded that it is mainly in a random coil conformation at all studied temperatures. These results on structural preferences and transitions of the segments in the monomeric form of A, may be related to the processes leading to the aggregation and formation of fibrils in the Alzheimer plaques. [source] Conformational changes of ,-lactoglobulin in sodium bis(2-ethylhexyl) sulfosuccinate reverse micellesFEBS JOURNAL, Issue 4 2004A fluorescence, CD study The effect of ,-lactoglobulin encapsulation in sodium bis(2-ethylhexyl) sulfosuccinate reverse micelles on the environment of protein and on Trp was analysed at different water contents (,0). CD data underlined the distortion of the ,-sheet and a less constrained tertiary structure as the ,0 increased, in agreement with a concomitant red shift and a decrease in the signal intensity obtained in steady-state fluorescence measurements. Fluorescence lifetimes, evaluated by biexponential analysis, were ,1 = 1.28 ns and ,2 = 3.36 ns in neutral water. In reverse micelles, decay-associated spectra indicated the occurrence of important environmental changes associated with ,0. Bimolecular fluorescence quenching by CCl4 and acrylamide was employed to analyse alterations in the accessibility of the two Trp residues in ,-lactoglobulin, induced by changes in ,0. The average bimolecular quenching constant <> was found not to depend on ,0, confirming the insolubility of this quencher in the aqueous interface, while <> increases with ,0. The drastic decrease with ,0 of kq, associated with the longest lifetime, , comparatively to the increase of , emphasizes the location of ,-lactoglobulin in the aqueous interfacial region especially at ,0,,10. The fact that (,0 = 30) , (water) also confirms the important conformational changes of encapsulated ,-lactoglobulin. [source] Formation of Human Telomeric G-quadruplex Structures Induced by the Quaternary Benzophenanthridine Alkaloids: Sanguinarine, Nitidine, and ChelerythrineCHINESE JOURNAL OF CHEMISTRY, Issue 5 2010Shu Yang Abstract The ligands which can facilitate the formation and stabilize G-quadruplex structures have attracted enormous attention due to their potential ability of inhibiting the telomerase activity and halting tumor cell proliferation. It is noteworthy that the abilities of the quaternary benzophenanthridine alkaloids (QBAs), the very important G-quadruplex binders, in inducing the formation of human telomeric DNA G-quadruplex structures, have not been reported. Herein, the interaction between single-strand human telomeric DNA and three QBAs: Sanguinarine (San), Nitidine (Nit) and Chelerythrine (Che), has been investigated. Although these molecules are very similar in structure, they exhibit significantly different abilities in inducing oligonucleotide d(TTAGGG)4 (HT4) to specific G-quadruplex structures. Our experimental results indicated that the best ligand San could convert HT4 into antiparallel G-quadruplex structure completely, followed by Nit, which could transform to mixed-type or hybrid G-quadruplex structure partially, whereas Che could only transform to antiparallel G-quadruplex structure in small quantities. The relative QBAs' inducing abilities as indicated by the CD data are in the order of San>Nit>Che. Further investigation revealed that the G-quadruplex structures from HT4 induced by QBAs are of intramolecular motif. And only sequences with certain length could be induced by QBAs because of their positive charges which could not attract short chain DNA molecules to close to each other and form intermolecular G-quadruplex. In addition, the factors that affect the interaction between HT4 and QBAs were discussed. It is proposed that the thickness of the molecular frame and the steric hindrance are the primary reasons why the subtle differences in QBAs' structure lead to their remarkable differences in inducing the formation of the G-quadruplex structures. [source] Circular dichroism of diglycosyl dichalcogenides in solution and solid state,CHIRALITY, Issue 3-4 2008Tibor Kurtán Abstract Solution and solid-state CD spectra of nine peracetylated and deacetalyted diglycosyl disulfides were measured to study the relationship between the low-energy CD transitions (n1,,*SS and n2,,*SS) and helicity of the inherently chiral disulfide chromophore as perturbed by chiral carbohydrate moieties. The solid-state CD spectra were directly correlated with the reported X-ray structures of Ac4GlcSSGlcAc4 and Ac4GlcSSGalAc4, and the CD data revealed that all the disulfides have M helicity with C1SSC1, dihedral angles ,90° < , < 0° both in solution and in the solid state. A TDDFT CD study was carried out on dimethyl diselenide which confirmed that the same quadrant rule is relevant between the signs of the low-energy CD transitions and the diselenide torsional angle as formulated previously for the disulfide chromophore. The CD spectra of Ac4GlcSeSeGlcAc4 measured in solution and in the solid state were correlated with its X-ray structure and reproduced well by TDDFT CD calculations performed on its tetra- O -acetyl derivative. Chirality, 2008. © 2007 Wiley-Liss, Inc. [source] Measurement of circular birefringence and circular dichroism of the single crystals of ,-(+)589 - and ,-(,)589 -tris(ethylenediamine)cobalt(III) triiodide monohydrate by the extended HAUP methodCHIRALITY, Issue 5 2004Ryo Matsuki Abstract We have achieved measuring four optical parameters simultaneously, namely, linear birefringence (LB), circular birefringence (CB), linear dichroism (LD), and circular dichroism (CD), of single crystals of ,-(+)589 - and ,-(,)589 -tris(ethylenediamine) cobalt(III) triiodide monohydrate (1) along the <001> plane at the fixed wavelength (514.5 nm). Such measurements are possible only when the High Accuracy Universal Polarimeter (HAUP) is employed; it is called the extended HAUP method. Our experimental results showed that both LB and LD of the ,-(+)589 -(1) crystal have the same magnitude as those of the ,-(,)589 -(1) crystal. It was also revealed for the first time that the CB data of crystals of ,-(+)589 -(1) and ,-(,)589 -(1) are almost of the same magnitude, but are of opposite sign, reflecting their opposite absolute configurations. On the other hand, although the CD data obtained for ,-(+)589 -(1) is almost three times larger than that for ,-(,)589 -(1,) these CD data are also opposite in sign, as expected from the opposite chirality of crystals. Chirality 16:286,293, 2004. © 2004 Wiley-Liss, Inc. [source] | ||||||||||