Molecular Weight Estimations

Analytical and test methods for the characterization of polyethylene and PP are also used for PB, PMP, and polymers of other higher a-olefins. The C-nmr method as well as k and Raman spectroscopic methods are all used to study the chemical stmcture and stereoregularity of polyolefin resins. In industry, polyolefin stereoregularity is usually estimated by the solvent—extraction method similar to that used for isotactic PP. Intrinsic viscosity measurements of dilute solutions in decahn and tetraHn at elevated temperatures can provide the basis for the molecular weight estimation of PB and PMP with the Mark-Houwiok equation, [rj] = KM. The constants K and d for several polyolefins are given in Table 8. 

Molecular weight Estimated 240,000-580,000 Formula Mixture of natural products Density 1.35-1.49 gml-1 Volatility NA... 

From neutron scattering measurements using different concentrations of D2O, an independent molecular weight estimate of 40.8 x 10 has been derived (Jacrot et al., 1983). 

Polyacrylamide gel electrophoresis revealed that these three mannanases were electrophoretically homogeneous. The molecular weights estimated by SDS-PAGE... 

The present experiments may be subject to some uncertainty in terms of molecular weight estimates and diffusion effects that could affect the exactness of these interpretations. The conclusion is reached that the experiments strongly suggest evidence for discontinuous topological quantification. In other words, the order and rate of fragment release is consistent with expectations based on fragment topology. 

Peptide toxins. Of all the toxins produced by freshwater cyanobacteria, the peptide toxins of Microcystis aeruginosa have received the most attention. All research on these peptide toxins indicates they are small, possibly cyclic, with molecular weights estimated at 1200 to 2600 (10,11). Recent work has become more definitive in the estimation of molecular weight and amino acid composition. In 1978 Elleman et al. (12) reported that they had isolated and characterized the peptide toxin of an Australian strain Microcystis which was a pentapeptide with a minimum molecular weight of 654. It consisted of equimolar amounts of alanine, tyrosine, methionine, glutamic and 3-methyl aspartic acid and methylamine. 

Anderson, M., Cawston, T. and Cheeseman, G. C. 1974. Molecular weight estimates of milk fat globule membrane protein-sodium dodecyl sulfate complexes by electrophoresis in gradient acrylamide gels. Biochem. J. 139, 653-660. 

Leach, B. S., Collawn, J. F. Jr. and Fish, W. W. 1980. Behavior of glycopolypeptides with empirical molecular weight estimation methods. 2. In random coils. Biochemistry 19, 5741-5747. 

Anderson, M., Cawston, T. and Cheeseman, G. C. 1974B. Molecular-weight estimates of... 

Previous studies (5-7) have clearly demonstrated that gel permeation chromatography of reduced linear randomly coiled polypeptide chains in GuHCl provides an accurate, dependable method for molecular weight estimation. 

The technique described here is finding increasingly widespread use for the resolution and molecular weight estimation of naturally occurring polypeptides. Its intended function is to supplement the classical exact techniques of molecular weight analysis and is not intended as an alternative procedure. Although we are aware of no instance in which invalid data have been obtained, the method can only be considered an approximate one since measurement involves calibration with secondary standards, and at present it is not suitable for precise theoretical analysis. 

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