Rotational decay constant of tobacco mosaic virus by depolarized photon-correlation spectroscopy
✍ Scribed by John C. Thomas; Guy C. Fletcher
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1978
- Tongue
- English
- Weight
- 251 KB
- Volume
- 17
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
In recent years a number of reports of rotational decay times for tobacco mosaic virus (TMV), determined by dynamic light scattering, have appeared in the literature.14 Three of these determination^^-^ used the method of zero-angle depolarized light scattering, while the fourth' extracted the rotational component of TMV from the intensity-fluctuation spectrum for polarized, finite-angle light scattering by fitting the spectrum with two Lorentzians to accommodate both the translational and the rotational diffusion. Although the method of depolarized light scattering should, in principle, provide a less ambiguous value for rotational decay times by removing the contribution of translational diffusion to the intensity fluctuations, variations in the reported values of the rotational decay constant are still apparent. Indeed, Schurr and Schmitz3 have commented on the large dispersion in these published values, and also on the large variability in the aggregation properties of TMV preparations. In view of this, we thought it worthwile to communicate the results of some recent depolarized light-scattering experiments on TMV.
The light-scattering spectrometer used in this work is similar to that of Schurr and Schmitz? the only differences being the addition of a quarter-wave plate after the first polarizer and the use of photon correlation rather than photocurrent correlation. The quarter-wave plate was included to compensate for unwanted birefringence of the various optical components and gave a significant improvement in the extinction of the primary beam. Despite this improvement, it was not possible to extinguish the primary beam completely with no scattering solution present. This unextinguished background was found to have the polarization of the analyzer; that is, it has the same polarization as the wanted depolarized signal.
With the first polarizer aligned parallel to the laser beam, the analyzer and quarter-wave plate were adjusted successively to give the best extinction of the forward scattered beam. This was done with the scattering solution present. The forward scattered light transmitted through the analyzer was imaged onto an EM1 9863 photomultiplier tube and the normalized single-clipped photocount autocorrelation function was determined by a Hewlett-Packard HP-2100s minicomputer using batch processing.