Molecular weight determination procedure

Molecular weight determinations have been carried out with methyl-ethyl-, diethyl-, di-n-propyl-, pentamethylene-, and methylphenyl-diazirine. They gave monomeric molecular weights. The three last-named compounds gave the calculated C, H, and N values by the usual procedure of microanalysis. 

The acetyl derivative was prepared according to the procedure of Haworth and Streight.24 After 110 precipitations of a warm benzene solution with petroleum ether, a product rotating — 23.5° resulted. Cryoscopic molecular weight determinations in benzene solution gave an average value of 9517, corresponding to 30 to 31 D-fructose residues. 

The assessment of the rate of degradation follows a classic Arrhenius procedure. Yarns or specimens of film are exposed to water and steam at temperatures typically between 70 °C and 130 °C, followed by tensile testing and molecular weight determination, and the results are extrapolated to service temperatures [32]. There are however a number of uncertainties. Firstly, will steam above 100 °C and water below 100 °C have the same effect There appears to be a change in gradient at 90 °C extrapolation using all the... 

A molecular weight determination clearly showed that the second peak corresponded to 2-cyano-6-bromohexane (molecular weight 190.1) and not 2,6-dicyanohexane (molecular weight 136.2). This procedure for identification offers clear advantages over collecting the peak for identification by infrared or other techniques. 

Another widely used procedure for molecular weight determinations is gel electrophoresis, in which the migration of proteins is accomplished through an electrical field. To avoid shape effects on the rate of migration, as well as differences in net charge, most proteins may be rendered into a random coil con-... 

K. Weber and M. Osbom, Proteins and Sodium Dodecyl Sulfate Molecular Weight Determination on Polyacrylamide Gels and Related Procedures, in The Proteins, Vol. 1 (H. Neurath and R. L. Hill, Eds.), Academic Press, New York, 1975. 

Goring and Timell (5) determined the DP for native celluloses from several sources of plant material. They used a nitration isolation procedure that attempts to maximize the yield while minimizing the depolymerization of the cellulose. These molecular weight determinations, done by light-scattering experiments, indicate wood cellulose has a DP of at least 9,000-10,000, and possibly as high as 15,000. A DP of 10,000 would mean a linear chain length of approximately 5 xm in wood. 

In electrospray ionization, compounds with a mass in excess of 500 Da may be prone to the formation of multiple-charge ions, either in positive-ion or in negative-ion mode [22-23], The averaging algorithm [23-24] can be used for molecular-weight determination from an ion envelope of multiple-charge ions (Ch. 16.2.2). Various automated computer-based procedures for the deconvolution or transformation of the electrospray mass spectra of proteins have been introduced. 

Difructose anhydrides II and III were first reported by Jackson and McDonald." In both cases molecular weight determinations indicated a difructose anhydride molecule. Difructose anhydride III has been shown by the following procedure" to be 1,2 2,3 -di-D-fructofurano8e anhydride. 

Gel permeation chromatography (GPC) is essentially a process for the separation of polymer molecules according to their size. The separation occurs as the solute molecules in a flowing liquid move through a stationary bed of porous particles. The method has been used extensively in biochemistry to separate biological polymer molecules from small molecule contaminants (with the use of Sephadex column). Application of the method to synthetic polymer chemistry in the 1970s has revolutionized the procedures for polymer characterization and molecular weight determination. 

Materials. Three samples of poly-7-benzyl-L-glutamate were studied. Polymer I was obtained by polymerizing 7-benzyl A-carboxy-L-glutamate anhydride by sodium methoxide in DMF and polymer II by a similar polymerization using n-hexylamine as initiator. Both were purified by reprecipitation. The molecular weights determined from the viscosity-molecular weight ratio of Doty et al. (4) were 67,000 for polymer I and 21,000 for polymer II. Polymer III was a commercial sample (Pilot Chemical Co.) of molecular weight 275,000. All solvents were purified by standard laboratory procedures. 

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