Dextran data

Comparison of two series of dextran data shows the importance of considering the spectra in terms of specific residue type. One... 

Figure 2. Molecular-weight dependence of the optical rotation of dextran. Data shown by (%) are taken from Turvey and Whelan (2).

The 20.4 kDa dextran had concentrations up to 166 g/L. QELSS spectra were bimodal, the slower mode corresponding to Dp of the 864 kDa dextrans. Data followed a simple exponential. Daivis, et al. [103] used QELSS and PFGNMR to measure Dp of 110 kDa polystyrene, M /M = 1.06 in 110 kDa polyvinylmethylether, M /Mn 1.3, in toluene. From Fig. 24a, the two physical techniques agree, except perhaps at the largest c. Stretched exponentials describe well each data set. 

Applying the same analysis to the dextran data, we note that for this polymer, the "SEC radius" shows poor agreement with the radius of gyration, but rather good agreement with the two values of Rg. 

Finally, we are left with the conclusion that there does not exist a single answer, for all random coil polymers, to the question we have posed. This has been attributed (ref. 73) to the rather unusual properties of PEG in aqueous solution, and it may be that the conclusions drawn from the dextran data will prove to be more typical of random coil polymers in solution. This conclusion also seems to supply an explanation for the discrepancies observed by Kuga (ref. 75) in using dextran and PEG as probes to determine pore size distributions of gel substances used in SEC, as well as the failure of data from these two polymers to fall on the same universal calibration curve (ref. 76). The discrepancies in the two sets of data (Figs I and 2 of reference 56) are quite dramatic. Thus we have three independent studies of these two polymers by three different methods of analysis and they all clearly show that the differences in hydrodynamic behavior of these two polymers are real, and not artifacts due to the method of analysis. 

Figure 8.1 Dg of polymers in aqueous solution, including (left vertical scale) ( ) 64.2 kDa dextran (data from Brown, et (O) 73, ( ) 148, (0) 278, and...

FIGURE 2.2 Selectivity curve of Superdex 7S, HR 10/30, as compared to a hypothetical single pore-size support. , experimental data from dextran fractions calculated for a SEC medium having a single pore radius of 60 A. [Reproduced from Hagel (1996), with permission.]... 

FIGURE 2.4 Calibration curve of dextran on Sephacryi S-300 SF. Calibration curves were calculated from one chromatogram of a broad MWD reference sample using data for the molecular mass distribution as obtained by a calibrated gel filtration column ( , upper curve) and on-line MALLS ( ). The calibration curve was found useful for estimating the size of globular proteins. [Reproduced from Hagel et al. (1993), with permission.]... 

Models based on Eqs. (47)-(50) have been used in the past to describe the disruption of unicellular micro-organisms and mammalian (hybridoma) cells [62]. The extent of cell disruption was measured in terms of loss of cell viability and was found to be dependent on both the level of stress (deformation) and the time of exposure (Fig. 25). All of the experiments were carried out in a cone and plate viscometer under laminar flow conditions by adding dextran to the solution. A critical condition for the rupture of the walls was defined in terms of shear deformation given by Eq. (44). Using micromanipulation techniques data were provided for the critical forces necessary to burst the cells (see Fig. 4)... 

Table I lists physical data for a number of the carbamate and ester derivatives of cellulose, chitin, amylose, amylopectin, and dextran synthesized as described in the Experimental Section. The solubility of the polysaccharide starting materials as well as that of the produced derivatives allows for macromolecular characterization through techniques including UV, NMR, IR, high pressure liquid chromatography, etc.

In one case, a small peptide with enzyme-like capability has been claimed. On the basis of model building and conformation studies, the peptide Glu-Phe-Ala-Ala-Glu-Glu-Phe-Ala-Ser-Phe was synthesized in the hope that the carboxyl groups in the center of the model would act like the carboxyl groups in lysozyme 17). The kinetic data in this article come from assays of cell wall lysis of M. lysodeikticus, chitin hydrolysis, and dextran hydrolysis. All of these assays are turbidimetric. Although details of the assay procedures were not given, the final equilibrium positions are apparently different for the reaction catalyzed by lysozyme and the reaction catalyzed by the decapeptide. Similar peptide models for proteases were made on the basis of empirical rules for predicting polypeptide conformations. These materials had no amidase activity and esterase activity only slightly better than that of histidine 59, 60). 

Assuming that all a-[l->6)-linkages are in the dextran backbone, our permethylation g.l.c.-m.s. data [which indicate that only the residues shown above are present in this series of dextrans) are consistent with a polymeric structure that is comb-like with side branches a single residue long. 

These three independent structural methods give data for all dextrans which are in accord with each other. The 27 dextrans studied represent 25 structues which differ in type or degree of branching. Such extensive cross-referencing of data give us increased confidence with regard to spectra-to-structure relationships. 

In contrast to the above data, which for dextrans and amyloses... 

A second example [IJ) is that of the anomeric spectral region of dextran B-742 fraction S, a polysaccharide for which per-methylation data indicate Structure 2, when n=0. This is an unusual polymer, as every backbone residue is 3-0-substituted. It is fortunate that this polymer exists, as the dextrans branching through 3,6-di-O-substituted residues present a problem in the anomeric spectral region, displaying only a single branching anomeric resonance in addition to the linear dextran resonance. 

Fig. 7 Log Ks ce values determined by CE in the presence of egg L-a-phosphati-dylcholine liposome (32) versus log Ks U C values obtained by ILC on 1-palmitoyl-2-oleoyl-sra-phosphocholine liposomes, with a second-degree correlation line (R2 = 1.00). (The log A. jic values were taken from Ref. 27 and were here corrected for the slight effect of the drug interaction with the dextran-grafted agarose gel [unpublished data].)...

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