Spectra circular dichroism

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. 

Fig. 6.—Measured Circular Dichroism Spectrum (-----), Calculated Circular Dichroism...

Fig. 11.—Circular Dichroism Spectrum for a Solid Film of Guar Galactomannan. (Redrawn from Ref. 24.)...

The Ca -ATPase has been crystallized in both conformations [119,152-155]. The two crystal forms are quite different [10,88-93,156-161], suggesting significant differences between the interactions of Ca -ATPase in the Ei and E2 conformations. Since the Ei-E2-transition does not involve changes in the circular dichroism spectrum of the Ca -ATPase [162], the structural differences between the two states presumably arise by hinge-like or sliding motions of domains rather than by a rearrangement of the secondary structure of the protein. 

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. 

Optical activity in metal complexes may also arise either if one of the ligands bound to the metal in the first co-ordination sphere is itself optically active or if the complex as a whole lacks a centre of inversion and a plane of symmetry. Thus all octahedral cts-complexes of the tris-or bis-chelate type have two isomeric forms related by a mirror plane, the d- and /-forms. These species have circular dichroism spectra of identical intensities but opposite in sign. The bands in the circular dichroism spectrum are, of course, modified if ligand exchange occurs but they are also exceedingly sensitive to the environment beyond the first co-ordination sphere. This effect has been used to obtain association constants for ion-pair formation. There also exists the possibility that, if such compounds display anti-tumour activity, only one of the mirror isomers will be effective. 

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. 

Because configurational information can be derived from optical rotatory dispersion and circular dichroism scans, considerable work has been conducted using these techniques to study the tetracyclines (32). The absolute configuration of CTC was determined using optical rotatory dispersion data (33) Spectral curves are presented in Figures 8 and 9. The circular dichroism spectrum is similar to that presented by Mitscher et al. (34), except that the values differ by a factor of about 1.5. In Table 3, data obtained by Mitscher and in FDA laboratories are compared. 

In addition to the effect of mutations at Phe-82 on the stability of the cytochrome c active site, the intense, negative Soret Cotton effect in the circular dichroism spectrum of ferricytochrome c is profoundly affected by the presence of non-aromatic amino acid residues at this position [115]. Recent examination of six position-82 iso-l-ferricytochrome c mutants establishes that while Tyr-82 exhibits a Soret CD spectrum closely similar to that of the wild-type protein, the intensity of the negative Soret Cotton affect varies with the identity of the residue at this position in the order Phe > Tyr > Gly > Ser = Ala > Leu > He, though the Ser, Ala, He, and Leu variants have effectively no negative Soret Cotton effect [108]. 

The heme moiety provides de novo designed heme proteins with an intrinsic and spectroscopically rich probe. The interaction of the amide bonds of the peptide or protein with the heme macrocycle provides for an induced circular dichroism spectrum indicative of protein-cofactor interactions. The strong optical properties of the heme macrocycle also make it suitable for resonance Raman spectroscopy. Aside from the heme macrocycle, the encapsulated metal ion itself provides a spectroscopic probe into its electronic structure via EPR spectroscopy and electrochemistry. These spectroscopic and electrochemical tools provide a strong quantitative base for the detailed evaluation of the relative successes of de novo heme proteins. 

Monomeric hemes possess a mirror plane and are hence achiral (151). Incorporation of the heme macrocycle into the anisotropic protein matrix distorts the heme environment, inducing a circular dichroism spectrum (57, 152, 153). From the design standpoint, the presence of an induced heme CD spectrum qualitatively confirms intimate communication between the heme and the surrounding protein matrix, which indicates the heme is most likely specifically bound. This spectroscopic signature serves as a first indication that the heme resides within the designed protein scaffold and has been used by various groups to... 

The a-hydroxydihydrochalcones are a small subclass of compounds found mainly in the Leguminosae. To their number can be added the new derivative 273, a constituent of extracts of the bark and wood of Eysenhardtia polystachyaP This species is already known as the source of the a-hydroxydihydrochalcone C-glucosides, coatline A and Comparison of the circular dichroism spectrum of 273 with that of related compounds allowed the configuration at C-a to be deduced as R (see Figure 16.14). Most known examples of p-hydro-xydihydrochalcones are also constituents of the Leguminosae, thus the isolation of 2, 4, 4, P-tetrahydroxy-6 -methoxydihydrochalcone (274) from the aerial parts of Vitex leptobotrys represents the first report of this type of compound in the Verbenaceae. Nel et al. have reported an improved method for the enantioselective synthesis of p-hydroxydihydrochal-cones. 

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. 26. Circular dichroism spectrum of double-stranded rice dwarf virus RNA in 0.15 M KF at 25 °C 861. The relative CD magnitudes of the two negative CD bands at 210 nm and 240 nm are used as a discriminator for the A and B forms...

The spectral data are described in the following way the position of the maximum of absorption (or in circular dichroism spectrum) in nanometer units, transition energy in electron volts corresponding to the position of maximum. The oscillator strengths or e x 10-3 values are given in parentheses. The letter s signifies a shoulder. 

M(A-A)3 complexes are optically active, and the problem can be remedied if a circular dichroism spectrum of one enantiomer can be measured and the sharp electronic lines identified. The bite and twist angles have very different effects on the rotational strengths. The twist angle has a marked effect that is quite plausible when one considers that a 60° twist causes conversion to the opposite enantiomer. Sign changes in the rotational strength can also occur at twist angles near / = 0°. 

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...

Isaksson, R., Rochester, J., Sandstrom, J., and Wistrand, L.-G. (1985) Resolution, circular dichroism spectrum, molecular structure, and absolute configuration of cis,trans-l,3-cyclooctadiene, J. Am. Chem. Soc. 107, 4074-4075. 

Fig. 7 Circular dichroism spectrum of tetracycline in methanol-water (90 10)...

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

The magnetic circular dichroism spectrum of thioxanthone and the circular dichroism spectrum of its inclusion complex with cyclodextrin have been measured and interpreted with the aid of PPP and CNDO/S calculations. The first jtJt state exhibits intramolecular charge transfer characteristics <1994JPC10432>. 

The shuttling process was confirmed by H NMR and NOE experiments, and significantly also resulted in changes in the circular dichroism spectrum, suggesting that the change in position also affected the influence of the chirality of the cyclodextrin upon the aromatic regions of the thread. 

Protein has a secondary structure a-helix, -structure or random chain. The contents of these components in the protein structure can be calculated on the basis of circular dichroism spectrum in the region of far-ultraviolet wavelength (around 220 nm),46 or amino acid sequences.47 Although these methods do not always reflect a secondary structure of protein, they are applicable to research on the structure of proteins, especially homologous proteins whose three-dimensional structures have not been shown. 

The circular dichroism spectrum of E. coli tryptophanase18 showed that the secondary structure of this enzyme seems to be predominantly a-helical. The a-helix content was estimated to be about 50% (Y. Kawata, unpublished results) by the method of Greenfield and Fasman.19 ... 

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