Molecular weight derivation

The molecular weights calculated in this way agree very closely with the so-called chemical molecular weights, derived from chemical analysis, and the method therefore rivals the latter in accuracy, without the attendant complications attaching to chemical operations with pure substances. 

MSTFA Most volatile by-products of all. Particularly useful for the separation of low molecular weight derivatives in the presence of excess reagent. 

Equations have been derived which relate G(scission) and G(crosslinking) to changes in Mn, Mw and Mz. Crosslinking produces branched molecules and the relative hydrodynamic volume (per mass unit) decreases compared with linear molecules. Therefore, molecular weights derived from viscometry and gel permeation chromatography will be subject to error. 

Marder, V. J., Shulman, N. R., and Carroll, W. R. (1969). High molecular weight derivatives of human fibrinogen produced by plasmin. J. Biol. Chem. 244, 2111-2119. 

In vitro studies have shown that dextran sulfate inhibits HIV binding, replication and syncytium formation, probably because they interfere with the ionic interaction between cell surface components such as CD4 or sulfated polysaccharides and positively charged amino acids concentrated in the V3 region of HIV gpl20 [ 127-129]. Again, low molecular weight derivatives with... 

While 3-H-3-phenyldiazirine was reported to be unstable on storage as a neat liquid (Smith and Knowles, 1975), its stability was improved in hexane solution at —20°C. Higher molecular weight derivatives of this compound have been stored for months in solution at —80°C without decomposition. 

Flocculants— The need to separate undesired. solid particles finely suspended in aqueous effluents, which is particularly relevant in wa.stewater treatment, the paper industry, etc.," - requires the use of water-soluble macromolecules, which arc mostly ionic in character and capable of interacting with the suspended material. With high-molecular-weight derivatives, the presence of a suitable content of ionogenic moieties as well as their uniform distribution along the polymeric chains are important in order to obtain the best performance of the flocculant, which should not completely cover the surface of the dispersed particles. 

To 10 mL of the stock solution of 2,4-dinitrophenylhydrazine in phosphoric acid add about 0.1 g of the compound to be tested. Ten milliliters of the 0.1 M solution contains 1 millimole (0.001 mole) of the reagent. If the compound to be tested has a molecular weight of 100 then 0.1 g is 1 millimole. Warm the reaction mixture for a few minutes in a water bath and then let crystallization proceed. Collect the product by suction filtration (Fig. 1), wash the crystals with a large amount of water to remove all phosphoric acid, press a piece of moist litmus paper on to the crystals, and if they are acidic wash them with more water. Press the product as dry as possible between sheets of filter paper and recrystallize from ethanol. Occasionally a high-molecular-weight derivative won t dissolve in a reasonable quantity (20 mL) of ethanol. In that case cool the hot suspension and isolate the crystals by suction filtration. The boiling ethanol treatment removes impurities so that an accurate melting point can be obtained on the isolated material. 

Chu BCF, Whiteley JM. High molecular weight derivatives of methotrexate as chemotherapeutic agents. Mol Pharmacol 1977 13 80-88. 

Chu BCF, Whiteley JM. Control of solid tumor metastases with a high molecular weight derivative of methotrexate. J Natl Cancer Inst 1979 62 79-82. 

Although GTP demonstrates the fundamental characteristics of a living polymerization, namely narrow molecular weight distribution, control of molecular weight derived from the monomer/initiator stoichiometry, and the... 

Ultraviolet absorbers are the most widely utilized of the photostabilizers. Most common UV absorbers are low molecular weight derivatives of o-hydroxybenzophe-none, o -hydroxybenzotriazole, or o-hydroxyphenyl salicylate [3], Most polymers are sensitive to UV radiation between 300 and 360 nm. They absorb UV radiation through their structure structural irregularities or impurities also have an effect [3], Table 4.1 shows some activation spectra for some typical polymers [3], Individual polymers absorb UV radiation within specific wave length regions, exhibiting activation spectra maxima at the wavelength where each is most vulnerable to photo-oxidation [4],... 

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