Circular dichroism measurements

Infrared, nuclear magnetic resonance, ultraviolet, optical rotary dispersion and circular dichroism measurements have been used for the spectral analysis of thiiranes. A few steroidal thiiranes have been reported to possess infrared absorption in the range from 580 to 700 cm The intermediate thiocyanate derivatives (RSCN) have a strong sharp peak at 2130-2160 cm the isomeric isothiocyanate (RNCS) shows a much stronger but broad band at 2040-2180 cm. ... 

Circular Dichroism Measurements. The absolute configurations of the C6 chiral center in tetrahydrobiopterin cofactor and related compounds were determined by comparison of their circular dichroism (CD) spectra with those of... 

Compounds 167-171 outlined in Fig. 43 form another series of diboronic acids that form complexes with mono- and disaccharides. In these cases the asymmetrical immobilization of chromophoric functional groups, e.g., aromatic rings in 167-170 or Fe -complexation with the related boronate 171, can be analyzed by circular dichroism measurements [256-262]. 

Fig. 43. Compounds 167-171 form a series of diboronic acids for the complexation of saccharides with functional groups that permit analysis by circular dichroism measurements...

The conformational changes which have been described so far are probably all relatively small local changes in the structure of H,K-ATPase. This has been confirmed by Mitchell et al. [101] who demonstrated by Fourier transform infrared spectroscopy that a gross change in the protein secondary structure does not occur upon a conformational change from Ei to 3. Circular dichroism measurements, however [102,103], indicated an increase in a-helical structure upon addition of ATP to H,K-ATPase in the presence of Mg and... 

Circular dichroism measurements on soluble Sup35pN and NM domains indicate a largely unfolded structure (Glover et al, 1997 King et al., 1997). 

Circular Dichroism Measurements. Circular dichroism measurements were carried out by using a Cary model 6002 spectro-polarimeter calibrated with d-10 camphor sulfonic acid. All measurements were run at room temperature in the same 1 cm, quartz cell over the near-ultraviolet region (250-330 nm). 

If two different three-dimensional arrangements in space of the atoms in a molecule are interconvertible merely by free rotation about bonds, they are called conformations if not, configurations.l85 Configurations represent isomers that can be separated, as previously discussed in this chapter. Conformations represent conformers, which are rapidly interconvertible and thus nonseparable. The terms conformational isomer and rotamer are sometimes used instead of conformer. A number of methods have been used to determine conformations.186 These include x-ray and electron diffraction, ir, Raman, uv, nmr,187 and microwave spectra,188 photoelectron spectroscopy,189 supersonic molecular jet spectroscopy,190 and optical rotatory dispersion and circular dichroism measurements.191 Some of these methods are useful only for solids. It must be kept in mind that the conformation of a molecule in the solid state is not necessarily the same as in solution.192 Conformations can be calculated by a method called molecular mechanics (p. 149). 

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. 

The method is less powerful in characterizing proteins lacking tryptophan, for reasons mentioned earlier (see Support Protocol), and does not apply at all to the rare proteins that lack tyrosine as well. Near-UV circular dichroism measurements (unit 7.6) can still be of considerable value for proteins containing tyrosine and, in both cases, both far-UV circular dichroism and urea-gradient gel electrophoresis (unit 7.4) provide powerful contributions to characterization. 

Nuclease behaves like a typical globular protein in aqueous solution when examined by classic hydrodynamic methods (40) or by measurements of rotational relaxation times for the dimethylaminonaphth-alene sulfonyl derivative (48)- Its intrinsic viscosity, approximately 0.025 dl/g is also consistent with such a conformation. Measurements of its optical rotatory properties, either by estimation of the Moffitt parameter b , or the mean residue rotation at 233 nin, indicate that approximately 15-18% of the polypeptide backbone is in the -helical conformation (47, 48). A similar value is calculated from circular dichroism measurements (48). These estimations agree very closely with the amount of helix actually observed in the electron density map of nuclease, which is discussed in Chapter 7 by Cotton and Hazen, this volume, and Arnone et al. (49). One can state with some assurance, therefore, that the structure of the average molecule of nuclease in neutral, aqueous solution is at least grossly similar to that in the crystalline state. As will be discussed below, this similarity extends to the unique sensitivity to tryptic digestion of a region of the sequence in the presence of ligands (47, 48), which can easily be seen in the solid state as a rather anomalous protrusion from the body of the molecule (19, 49). 

Several theoretical studies concluded that the two bands originate from electronic transitions from one ground state to two excited states [47-51,55], The D3-symmetry conformation was confirmed by an X-ray diffraction study of crystal samples [56], resonance Raman studies [46,51,57], and magnetic circular dichroism measurements [55], Yet, no C2-symmetry conformation has been identified yet. 

FIGURE 11.15 Resolution of the protein folding of a-apolactalbumin. (a) Detection of changes in protein secondary structure (far-UV circular dichroism measurements), (b) Detection of changes in protein tertiary structure (near-UV circular dichroism measurements), (c) Complete description of protein folding. Resolution of the row-wise data set formed by near-UV (Dj) and far-UV (D2) circular dichroism measurements. Solid line native conformation, dash-dotted line intermediate conformation, dotted line unfolded conformation. 

Another important property is polarization. SR is plane polarized when viewed in the plane of the particle trajectory and elliptically polarized above or below this plane. The polarization is of crucial importance to the study of the spatial distribution and spin of the ejected photoelectrons, and to VUV magnetic circular dichroism measurements. 

Polavarapu PL (1989) New developments in Fourier-transform infrared vibrational circular-dichroism measurements. Appl Spectrosc 43 1295-1297... 

Malon P, Keiderling TA (1996) Spinning quarter-wave plate polarization modulator test of feasibility for vibrational circular dichroism measurements. Appl Spectrosc 50 669-674... 

Cao XL, Dukor RK, Nafie LA (2008) Reduction of linear birefringence in vibrational circular dichroism measurement use of a rotating half-wave plate. Theor Chem Acc 119 69-79... 

Haraday T, Kuroday R (2002) Circular dichroism measurement of a protein in dried thin films. Chem Lett 326-327... 

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