Molecular mass in daltons

The actual mass of a single atom of 12C is defined as 12 daltons, one dalton being 1.661 x 10-24 g. The mass of a molecule can be given in daltons (Da) or kilodaltons (kDa). This molecular mass in daltons is numerically equivalent to the relative molecular mass (Mj) or molecular weight (MW)a and also to the molar mass (g/mol). However, it is not correct to use the dalton for the unitless quantity Mr. Masses of structures such as chromosomes, ribosomes, mitochondria, viruses, and whole cells as well as macromolecules can be given in daltons. b... 

Here c(r) is the concentration c at the radial position r (measured from the centrifuge axis), a is the radial distance of the meniscus, M is the molecular mass in daltons, and v is the partial specific volume in ml/gram. For most proteins v varies from 0.69-0.75. It is the reciprocal of the density of the particle. Rho (p) is the density (g/ml) of the solvent. A plot of log c(r) against r2 is a straight line of slope M (1 -up) / 2RT. The computer can also accommodate mixtures of proteins of... 

Figure 6.3 Effects of hydrocarbon chain modifications on melting points of similar-sized cuticular lipids. When lipids melt, the absorption frequency of C-H symmetric stretching vibrations increases from -2849 cm1 to -2854 cm4. From right to left, compounds are (chemical change relative to n-alkane, molecular mass in daltons) filled circles, n-dotnacontane (no change, 450) open circles, palmitic acid myristyl ester (wax ester, 452) filled triangles, 13-methylhentriacontane (methyl-branched alkane, 450) open triangles, (Z)-13-tritriacontene (double bond, 462) filled squares, 9,13-dimethylhentriacontane (2 methyl branches, 464) open squares, oleic acid oleyl ester (2 double bonds and an ester link, 532). Data from Gibbs and Pomonis (1995) and Patel el al. (2001).

An odd number of nitrogen atoms brings about an odd molecular mass in daltons such as is defined in mass spectrometry NH3 17, CH3NH2 31, and so on. Thus, in the case of an odd number of nitrogens, the earlier rule must be inverted for the ion, the mass parity is the same as the electron parity. 

Insulin, a small protein of molecular mass 6000 daltons, is composed of two chains designated A and B. There are no reduced cysteine residues in insulin, but it contains three essential disulfide bonds two that crosslink the A and B chains, and one internal to the A chain to stabilize the overall tertiary stmcture. These disulfide bonds are cleaved in the presence of excess AuX4, leaving A and B chains that have cysteine residues that have become oxidized to sulfonic adds [119]. With smaller amounts of AuX4, a single disulfide bond will be attacked to form sulfinic acid [119]. The reaction is second order for AuCU while AuBr4 reacts too quickly for accurate monitoring. 

The higher the molecular mass, the slower a substance is absorbed from the gastrointestinal tract. Assuming sufficient aqueous and lipid solubility, substances with molecular mass less than 300 daltons are typically well absorbed. Those with molecular mass ranging from 300 to 500 daltons are not as readily absorbed, and substances with molecular mass in the thousands are poorly absorbed, if at all (D Souza, 1990). 

Mr, relative molecular mass (molecular weight in dalton)... 

Fig. 1 Chemical structures, exact mass in Dalton, and molecular formula of selected typical APs...

Vesicles have molecular masses in the order of 10 -10 daltons. Van der Waals attraction between such gigantic solutes is very large. Nevertheless, vesicles do not precipitate but stay in solution, because the ultrathin membranes undulate. 

More recently Weidmann and Doll [27] have shown that the craze dimensions decrease markedly in PMMA at low molecular masses. In a study of the molecular mass dependence of fracture surfaces in the same pol3mier, Kusy and Turner [28] could observe no interference colours for a viscosity average molecular mass of less than 90 000 daltons, concluding that there was a dramatic decrease in the size... 

Different samples exhibit different levels of response to FAB, and, with a mixture of components, it is feasible that not all will be detected. In some cases, the minor components of a sample appear more prominently in the mass spectrum than the major ones. Despite these limitations, FAB is in widespread use and is an excellent technique for determining the molecular masses of peptides up to 10,000 Daltons, with an accuracy of 0.5 Da. 

For permeation of flavor, aroma, and solvent molecules another metric combination of units is more useful, namely, (kg-m)/(m -sPa). In this unit the permeant quantity has mass units. This is consistent with the common practice of describing these materials. Permeabihty values in these units often carry a cumbersome exponent hence, a modified unit, an MZU (10 ° kgm)/(m -s-Pa), is used herein. The conversion from this permeabihty unit to the preferred unit for small molecules depends on the molecular weight of the permeant. Equation 4 expresses the relationship where MW is the molecular weight of the permeant in daltons (g/mol). 

For a polypeptide chain of 100 residues in length, a rather modest size, the number of possible sequences is 20 , or because 20 = lO, lO unique possibilities. These numbers are more than astronomical Because an average protein molecule of 100 residues would have a mass of 13,800 daltons (average molecular mass of an amino acid residue = 138), lO such molecules would have amass of 1.38 X lO " daltons. The mass of the observable universe is estimated to be 10 proton masses (about 10 daltons). Thus, the universe lacks enough material to make just one molecule of each possible polypeptide sequence for a protein only 100 residues in length. 

The degradation of nicotine has been examined extensively in Arthrobacter nicotinovorans (oxydans) in which it is mediated by a plasmid (Brandsch et al. 1982 Schenk et al. 1998). In strain P34, the hrst metabolite was 6-hydroxynicotine, and experiments with 02 and H2 0 showed that the oxygen in the hydroxyl group was derived from H2O (Hochstein and Dalton 1965). Nicotine dehydrogenase has a molecular mass of 120,000 and contains FAD, Mo, Fe, and acid-labile sulfur (Freudenberg et al. 1988). Degradation involves a series of reactions ... 

From the above considerations, it appears that chain length is a main characteristic of polymers. Natural macromolecules, particularly in living bodies, can exhibit exact lengths, thus exact molecular masses. For instance haemoglobin molecular mass is known to within one dalton. However, a synthetic polymer... 

A comprehensive study of KDO 8-phosphate synthetase has been reported by Ray.137 The author purified the enzyme 450-fold from crude extracts of Escherichia coli B cells. The synthetase has a molecular mass of 90,000 6,000 daltons and is composed of three identical subunits having an apparent molecular mass of32,000 4,000 daltons. Two pH optima were observed, one being at pH 4.0-6.0 in succinate buffer, and the other, at pH 9.0 in glycine buffer. The isoelectric point of the enzyme is 5.1. The enzyme has an apparent KM for D-arabinose 5-phosphate of 20 pM and an apparent KM for enolpyruvate phosphate of 6 pM. 

The molecular mass has units termed daltons (Da), after the famous English chemist John Dalton (1766-1848). Eor example, the molecular mass of insulin might be said to be about 6000 daltons. However, this designation does not add much to understanding the concept of molecular size and we shall delete the dalton unit in all that follows. 

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