Molecular weights, exact

All have molecular weights of 226 to the nearest integer (C = 12, H = 1, S = 32), but the exact molecular weights differ slightly. A resolution of 2500 is necessary to separate molecules 1, 2 and 3 but 75,000 is required to separate molecule 4 from molecule 3 which explains why high resolution mass spectrometers are sdiiglit. 

Using the approximate formula weight of the simplest formula, determine the true molecular formula and the exact molecular weight. 

Reports exact molecular weight of a protein or part of a protein as determined by mass spectrometric methods Any comment that does not belong to any of the other defined... 

Table 3.1 A portion of the membership of the ALIS screening library, composed of NG LI 27A443 (library 3 in this table) and four other libraries, which yields DHFR ligand 1 (NCD-157, entry 11). Compounds of similar exact molecular weight (EMW) are distributed among the five pooled libraries to minimize mass overlap and simplify hit deconvolution. Reprinted from [40] with permission from Elsevier.

Although the chemical structure of cellulose is understood in detail, its supermolecular state, including its crystalline and fibrillar structure is still open to debate. Examples of incompletely solved problem areas are the exact molecular weight and polydispersity of native cellulose and the dimensions of the microfibrils. 

Use the technique described in Problem 12.1 to find the molecular formula of cortisone. Cortisone contains approximately 25 hydrogens. Make a table of possible molecular formulas for cortisone that have around 25 hydrogens and calculate the exact molecular weights corresponding to these formulas. 

The "comb" dispersing agent was a graft copolymer of polymethylmethacrylate-methacrylic acid (methoxypolyethylene oxide methacrylate) supplied by ICI Paints Division (Slough) and used as received. The exact molecular weight of the polymer is not known, but it is ejqpected to be in the region of 20-30,000 (as indicated by ICI Paints Division). The of the polyethylene chains was 750. 

The succinate dehydrogenase of yeast mitochondria was isolated by Singer et al. 15, 219) in 1957, and stated to have a molecular weight of 200,000 and an iron flavin ratio of 4 1, similar to the mammalian enzyme. These studies antedated, however, the purification of mammalian succinate dehydrogenase by Davis and Hatefi. Therefore, the exact molecular weight and composition of the yeast enzyme will have to be reexamined in light of present information. 

Difficulties for obtaining exact molecular weights also occur when taking the metal free products of TCB and some metal disulfides After GPC diagrams the molar masses correspond to 10 (Table 11). But from membrane osmometry, values near 2 10 were obtained. It was assumed that stiff Pc-structure will lead to a large effective hydrodynamic value which may explain the high GPC data. 

Data relating intrinsic viscosity and molecular weights are not available for any of the polymers of the dialkyl itaconates. Polymethyl methacrylate constants have been used to estimate molecular weights for the polydiethyl itaconates but the exactness of such an approximation is difficult to judge. While exact molecular weights cannot be... 

High mass-spectral resolution is often essential in structural work as the answers obtained with conventional low-resolution instruments may not always be unequivocal in terms of atomic composition in the studied molecules. While the resolution obtained in a GC/MS model on the individual chromatographic peaks is short of the typical values obtained under static conditions, it is frequently sufficient to yield the exact molecular weights. Due to the design features of double-focusing instruments, sensitivities are typically lower than those obtained with the conventional GC/MS instruments. 

In modem SEC, polymers of an exact molecular weight, such as proteins, and synthetic polymers of a narrow molecular weight distribution, are separated as narrow bands, but with low peak capacity (section 4.3.9.1), and only a few separated bands can be accommodated within the separation. But SEC is still a powerful exploratory method for the characterization of unknown samples, since it provides an overall view of sample composition in a predictable time with little method development (section 4.3.9.2). Polymers of a broad molecular weight range contain many components of similar size that cannot be resolved into individual species, and are eluted as a continuous band with a molecular size distribution that is characteristic of the polymer, for example. 

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