Circular dichroism spectrum solution

These y9 -peptides are not expected to adopt a 3i4-helical conformation in an aqueous environment because of the destabihzing effect of cationic charges. The circular dichroism spectrum of a non-labeled analog of 165 does not display the characteristic signature of the 3i4-helix in aqueous solution however it is highly hehcoidal in MeOH. 

The u.v.-visible spectrum of the 4-hydroxy-2,2,6,6-tetramethyl-piperidine-N-oxyl-methyl-cobinamide is very similar to methyl-cobin-amide itself and as a result this technique cannot be used to rigorously identify the spin labeled derivative. The spin labeled compound does show a spectral change with pH between pH 7.0 and pH 2.0 which methyl-cobinamide does not exhibit. Despite the similarities between methyl-cobinamide and nitroxylmethylcobinamide, the circular dichroism spectrum of the two derivatives are quite different. Fig. 23 shows the marked difference in C. D. spectra of 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, methylcobinamide, and a methylcobinamide solution containing an equimolar amount of uncoordinated nitroxide. 

A mixture consisting of aniline ( 0.2 g) and (lS)-(+) camphorsulfonic acid (3.48 g) was dissolved in 10 ml of water and then treated with five separate portions of 0.1 g of ammonium peroxydisulfate dissolved in 1 ml water. Each successive portion was added when the solution turned from blue to green while the reaction mixture was maintained at 20°C. After the additions were completed the mixture was centrifuged and the product washed with water. The circular dichroism spectrum of the product suspensed in water indicated a molar ellipticity of about 90 x 103 deg-cm2/dmol. Transmission electron micrographs showed that the product had a nanofibrous structure with fiber diameters from 30 to 70 nm and had a length of several hundred nanometers. 

Fig. 6. Geiser and Giidel s axial circular dichroism spectrum of [A-Cr(en),] [A-Ir(en)3]Cl6 KC1 6H20 at 8 K [37], The wavenumber scale is the same as in Fig. 5. The dotted line represents the room temperature solution spectrum of [A-Cr(en)3]3 +. The peak in the center with a slightly negative Ae was assigned as an electronic origin...

Fig. 9 Circular dichroism spectrum of the magnesium complex of tetracycline in aqueous solution...

There have been detailed studies on the electronic absorption spectrum of the gas, and the magnetic circular dichroism spectrum has also been recorded and assigned 577,578,580 such spectra were also obtained for the aqueous solution.581 The electronic spectrum of the solid in an argon matrix at 20 K was measured and assigned.580 An energy level diagram was constructed on the basis of the... 

Aqueous solutions of the enantiomers of asyw-cfs-[Co(edda)(en)]Cl are stable to racemization at room temperature. The circular dichroism spectrum of the (-) isomer in water shows (Ae) 485 nm(-2.24), 357 nm (+0.89). The absolute configuration of the closely related (7 )-l,2-diaminopropane [(-)-pn] isomer, asym-cA-[Co(edda)[(-)-pn] ]C1, has been determined by x-ray crystallography.The results of this study confirm the absolute configuration assigned to the two. sym-cfs-[Co(edda)(en)]Cl enantiomers on the basis of their circular-dichroism spectra. ... 

The appearance of the difference e — in the argument of the hyperbolic tangent shows that the sign of the circular dichroism depends upon whether the transition is polarized parallel or perpendicular to the long molecular axis of the solute molecules. The circular dichroism spectrum therefore yields in a very simple way information on the relative polarization directions of optical transitions. 

We therefore carried out a series of studies on the circular dichroism spectrum of poly(i -oxypropylene) in a number of solvents in the vacuum ultraviolet region under the cooperation with W.C. Johnson, Oregon State University. In the circular dichroism(CD) spectra of poly(/ -oxypropylene), two CD bands were observed for cyclohexane, acetonitrile, and trifluoroethanol(TFE) solutions. 

We want to be able to deduce the conformation of a polymer in solution from its measured circular dichroism spectrum. For a linear polymer each ordered conformation must be a helix. The limiting cases for a helix are a straight line and a circle. A helix of identical residues is characterized by very few parameters. These are the radius of the helix, the rise per residue (the distance along the helix axis) and the number of residues per turn. A few examples will make this clear. A planar, all trans polyene will have a radius of zero (the helix is a straight line), a rise of 1.44 A and one residue per turn. A polypeptide a-helix has a radius of 2.28 A at the a-carbon, a rise per residue of 1.50 A and 3.6 residues per turn. One strand of a polynucleotide helix in the Watson-Crick B-form of DNA has a radius of 5.72 A at Cr of deoxyribose, a rise per residue of 3.4 A and 10 residues per turn. 

Similarly to the isotropic absorption spectrum (i.e., recorded using non-polar-ized light), the circular dichroism spectrum of a chemical species in solution is constituted by bands. There is, however, an important difference between absorption and CD spectra while the former exhibit only positive signals, the latter can show both positive and negative signals, because CD bands are due to absorption differences (Fig. 6.5). 

Circular dichroism (c.d.) spectroscopy measures the difference in absorption between left- and right-circularly polarized light by an asymmetric molecule. The spectrum results from the interaction between neighboring groups, and is thus extremely sensitive to the conformation of a molecule. Because the method may be applied to molecules in solution, it has become popular for monitoring the structure of biological molecules as a function of solvent conditions. 

The influence of adsorption on the structure of a -chymotrypsin is shown in Fig. 10, where the circular dichroism (CD) spectrum of the protein in solution is compared with that of the protein adsorbed on Teflon and silica. Because of absorbance in the far UV by the aromatic styrene, it is impossible to obtain reliable CD spectra of proteins adsorbed on PS and PS- (EO)8. The CD spectrum of a protein reflects its composition of secondary structural elements (a -helices, / -sheets). The spectrum of dissolved a-chymotrypsin is indicative of a low content of or-helices and a high content of //-sheets. After adsorption at the silica surface, the CD spectrum is shifted, but the shift is much more pronounced when the protein was adsorbed at the Teflon surface. The shifts are in opposite directions for the hydrophobic and hydrophilic surfaces, respectively. The spectrum of the protein on the hydrophilic surface of silica indicates a decrease in ordered secondary structure, i.e., the polypeptide chain in the protein has an increased random structure and, hence, a larger conformational entropy. Adsorption on the hydrophobic Teflon surface induces the formation of ordered structural elements, notably an increase in the content of O -helices (cfi, the discussion in Sect. 3.1.4). 

Unique inclusion behavior in reflection of the induced-fit binding mechanism is observed when an organic stock solution of octopus cyclophane 3 is injected into an aqueous medium containing ANS for the host-guest complexation study [17], A circular dichroism (CD) spectrum does not undergo any change for 3 upon complexation with ANS, indicating that the conformation around l-... 

Fig. 28a and b. Circular dichroism spectra of calf thymus DNA at pH 7 (27 °C) in aqueous solutions of varying concentrations of LiCl (a) and NH4C1 (b) 72). The molar concentrations are printed above each spectrum. The decrease in the CD magnitude of the positive band at 275 nm demonstrates the transformation from the B to C form... 

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