Fluorescence detected circular dichroism

Differential scattering of incident left and right circularly polarized light can be an important contribution to the circular dichroism of macromolecules. In principle both differential absorption and differential scattering of circularly polarized light contribute to circular dichroism, but differential scattering is increasingly important for particles whose dimensions are greater than 1/20th the wavelength of light. The scattering contribution is probably not important for unaggregated proteins and nucleic acids in solution. It can be very important for viruses, membranes, and other protein-nucleic acid complexes. Outside the absorption bands of the scattering, chiral particle, only differential scattering contributes to the circular dichroism. The sign and magnitude of the differential scattering is quantitatively related to the relative orientations and the distances between the scattering units of the particle. The interpretation of the circular differential scattering depends on a simple, classical method. Thus, in understanding a measured circular dichroism, it often will be easier to relate the differential scattering to the structure of a particle (such as a virus) than it is to relate the differential absorption to the structure. CD and optical rotatory dispersion (ORD) studies have been helpful in providing useful knowledge about the structure of biological macromolecules. These methods were limited originally to homogeneous solutions of macromolecules. More recently, they also have been applied to increasingly complex systems such as viruses (1, 2), erythrocytes (3, 4), nucleohistones (5, 6), DNA-polylysine complexes (7,8), DNA aggregates (9), chloroplasts (10), etc. (11). A remarkable common feature of many of these systems was the presence of anomalies in their CD and optical rotatory dispersion spectra. The CD spectra presented: (i) apparent differential absorption of circularly polarized light outside of the absorption bands (the CD signal at long wavelengths was slowly varying but non-zero; this longwavelength "tail" could be positive or negative); (ii) signals sensitive to the distance of the photomultiplier from the sample; and (iii) CD values 1 or 2 orders of magnitude larger than normal. Fig. 1 Recently, a new quantitative understanding of differential scattering of circularly polarized light has been obtained. We were able to relate the difference in scattering efficiency for incident left and right circularly polarized light to the detailed structure of the scattering particle (20-24). We have measured the angular dependence of this circular intensity differential scattering for a helix of known structure and obtained good agreement with theory (25). Thus, we now can explain the "anomalous" behavior of chiral macromolecules and aggregates. We find that the scattering "artifacts" can provide valuable information about the configuration (left-or right-handed) of the component particles.Here we will show how the differential scattering of left and right circularly polarized light ...

show abstract

“…6 is non-zero. This method can be called scattering-detected CD in analogy with fluorescence-detected CD (26). Molecular Parameters.…”

Section: El-er = (Al-ar) + (Sl -Sr))mentioning

confidence: 99%

Circular differential scattering can be an important part of the circular dichroism of macromolecules.

Bustamante¹,

Tinoco²,

Maestre³

1983

Proc. Natl. Acad. Sci. U.S.A.

165

149

View full text Add to dashboard Cite

show abstract

“…A spectrometer capable of measuring FDCD spectra was prepared from the Cary 60/6001 by the scheme of Turner et al (1974). Cooling of the cells was performed with an external bath (Neslab).…”

Section: Optical Titrationsmentioning

confidence: 99%

Structural effects on the circular dichroism of ethidium ion nucleic acid complexes

Dahl¹,

Pardi²,

Tinoco³

1982

Biochemistry

Self Cite

View full text Add to dashboard Cite

phosphates had larger formation constants than their deoxyriboanalogs. Above 300 tim, where only the dye absorbs light, the induced CD spectra of the complexes had bands at 510, 375, 330, and 307 tim, with the magnitude of the 307 tim band, per bound dye, being the largest and sequence dependent. The CD spectra down to 220 tim of some complexes were obtained by FDCD measurements; between 220 and 300 tim both the positions and the magnitudes of the bands were sequence dependent. At very low ionic strength, complexes of calf thymus DNA plus ethidium ion in different salt concentrations showed that the 307 tim CD magnitude increased with decreasing counterion concentration. Implications of the results for theories of the induced CD spectrum of the ethidium ion are discussed.

show abstract

“…In a preliminary communication TUR:\IER et al (409) reported that the signal-to-noise ratios in Iysozyme CPL spectrum is several times !arger than for L-tryptophan spectrum. This was not unexpected since one can find an analogaus behaviour in the corresponding CD spectra.…”

Section: Circular Polarization Of Luminescencementioning

confidence: 98%