Very low‐angle light scattering. A characterization method for high‐molecular‐weight DNA
1976; Wiley; Volume: 15; Issue: 7 Linguagem: Inglês
10.1002/bip.1976.360150705
ISSN1097-0282
AutoresHarold Levine, Robert J. Fiel, Fred W. Billmeyer,
Tópico(s)Electrostatics and Colloid Interactions
ResumoAbstract A very low‐angle light‐scattering photometer is described with respect to optical features, scattering cell, correction factors, and absolute calibration in the angular range 2°–35°. An improved microfiltration apparatus was used to obtain essentially dust‐free aqueous solutions for very low‐angle light scattering. The instrument was calibrated with silicotungstic acid, an absolute molecular‐weight standard, and the calibration was confirmed with the use of several secondary standards. Very low‐angle light‐scattering measurements were made to determine the weight‐average molecular weight M̄ r and z ‐average radius of gyration R g , z of a commerical preparation of calf‐thymus DNA. Microfiltration of the solutions allowed measurements down to 6°. The value M̄ r = 20.0 × 10 6 obtained by extrapolating 6°–9° data to 0° is more than three times that from 30°–75° data (6.38 × 10 6 ) but ∼20% smaller than that from 10–35° data (23.7 × 10 6 ). The experimental errors in M̄ r and R g , z are estimated to be ±8% and ±14%, respectively. Combined 6°–75° data from two photometers fit well a theoretical scattering curve for a model wormlike coil of the same M̄ r as the DNA sample.
Referência(s)