Showing papers by "David S. Cannell published in 1975"
TL;DR: In this paper, measurements of the long-range correlation length along the critical isochore were made using two different light-scattering techniques and cover the temperature range $4.016 and $1.223.
Abstract: Results are reported of measurements of the long-range correlation length $\ensuremath{\xi}$, made along the critical isochore. The measurements were made using two different light-scattering techniques and cover the temperature range $4.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}\ensuremath{\le}\frac{T}{{T}_{c}}\ensuremath{-}1\ensuremath{\le}3.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$. All of the results are accurately fit by the expression $\ensuremath{\xi}=2.016{(\frac{T}{{T}_{c}}\ensuremath{-}1)}^{\ensuremath{-}0.621}$ \AA{}. Measurements of the isothermal compressibility ${\ensuremath{\kappa}}_{T}$, in the temperature range $1.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}\ensuremath{\le}\frac{T}{{T}_{c}}\ensuremath{-}1\ensuremath{\le}3.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$ are also reported and yield the result ${\ensuremath{\kappa}}_{T}=1.327\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}{(\frac{T}{{T}_{c}}\ensuremath{-}1)}^{\ensuremath{-}1.223}$ ${\mathrm{cm}}^{2}$/dyn. From these measurements the value of the exponent $\ensuremath{\eta}$ may be deduced as 0.03 \ifmmode\pm\else\textpm\fi{} 0.03. The measured values of $\ensuremath{\xi}$ are used to interpret existing measurements of the Rayleigh linewidth in terms of mode-mode coupling theories. Experimental results are also presented which indicate that stirring may be used to eliminate gravitationally induced density gradients near the critical point without affecting the fluid's critical properties.
38 citations
TL;DR: It is indicated that ATCase experiences an increase in frictional coefficient of approximately 4% due to succinate and carbamyl phosphate, and that any change in the enzyme's partial specific volume under these conditions is less than about 0.3%.
Abstract: Employing a differential optical mixing spectrometer, we have determined that the translational diffusion coefficient (DT) of aspartate transcarbamylase (AT-Case) decreases by (41 plus or minus 06)% in the presence of succinate and carbamyl phosphate This result, combined with the change in the sedimentation coefficient determined by Gerhart and Schachman (1968) and repeated by us in the present work indicates that ATCase experiences an increase in frictional coefficient of approximately 4% due to succinate and carbamyl phosphate, and that any change in the enzyme's partial specific volume (v) under these conditions is less than about 03% We have also measured (DT)20,w for ATCase as (375 plus of minus 011) x 10-7 cm2/sec Combining this with our measured value of s20,2-o for ATCase of (117 plus or minus 02) x 10-13 sec and the calculated value of v of 0738 cm3/g (Rosenbusch and Weber, 1971), we have determined the molecular weight of ATCase as (29 plus of minus 01) x 10-5 We have also observed the ATCase dimer and find that at a dimer concentration of 06 mg/ml the value of s20,w for the dimer is 158 x 10-13 sec and that this value decreases by (40 plus or minus 05)% upon the addition of succinate and carbamyl phosphate, a behavior essentially identical with that of the monomer
25 citations
14 citations
TL;DR: In this article, a differential optical mixing laser spectrometer capable of the direct measurement of the difference in the spectra of the light scattered by two solutions of macromolecules is presented.
Abstract: We present the design and development of a differential laser spectrometer capable of the accurate measurement of very small changes in the translational diffusion coefficients (DT) of macromolecules. Since DT depends solely on the translational frictional coefficient of a macromolecule, this parameter is a direct measure of macromolecular conformation, and thus detection of small changes in the translational diffusion coefficient can reveal very slight conformational alterations. The differential laser probe we present is a differential optical mixing laser spectrometer capable of the direct measurement of the difference in the spectra of the light scattered by two solutions of macromolecules and hence, the difference in the translational diffusion coefficients of the macromolecular species under investigation. In its present form, the instrument has a precision of 3 parts in 103, that is, the differential laser probe can measure a change in DT of 3% with a precision of 10%. Discussion is provided for th...
8 citations