Dextran molecular weight dependence

The colloid osmotic pressure of aqueous dextran solutions can be regulated by molecular weight and concentration of the solute [52]. Dissolved dextran in low concentrations possesses Newtonian flow characteristics [45]. The relationship between viscosity and concentration is shown in Fig. 6 for different dextran fractions [52]. The molecular weight dependence of the intrinsic viscosity can be estimated by several equations [37,46,53]. 

Ogiso, T., Paku, T., Masahiro, I. and Tanino, T. Mechanism of the enhancement effect of n-octyUP-D-thioglucoside on the transdermal penetration of fluorescein isothiocyanate-labeled dextrans and the molecular weight dependence of water-... 

Hanatani, K. Takada, K. Yoshida, N. Nakasuji, M. Morishita, Y. Yasako, K. Fujita, T. Yamamoto, A. Muranishi, S. Molecular weight-dependent lymphatic transfer of fluorescein isothiocyanate-labeled dextrans after intrapulmonary administration and effects of various absorption enhancers on the lymphatic transfer of drugs in rats. J. Drug Targeting 1995, 3, 263-271. 

Fig. 4. Molecular-weight dependence of effective vascular permeability. Vascular permeability to 150,000 MW dextran (D150) is about one order of magnitude higher in tumor vessels than in the host tissue (data from Gerlowski and Jain, 1986). Even though albumin has a lower molecular weight ( 70,000), because of its globular configuration, it has a lower permeability than D150 (Yuan et al., 1993). Liposomes with diameters between 80 and 100 nm have even lower permeability in the tumor (Yuan et al., 1994).

Fig. 7. Molecular weight dependence of diffusivity. (a) The effective diffusion coefficient, D, has been plotted as a function of molecular weight for dextrans (Nugent and Jain, 1984a, b Gerlowski and Jain, 1986), albumin (Nugent and Jain, 1984a, b), and IgG (Clauss and Jain, 1990) in water, normal tissue, and tumor tissue. Symbols , dextran, aqueous O, bovine serum albumin, aqueous O, rabbit IgG, tumor , dextran, normal tissue , bovine serum albumin normal tissue , rabbit IgG, normal tissue. The half-filled symbols refer to the tumor data, (b) The effective diffusion coefficient plotted versus the Stokes-Einstein radius. Symbols as in (a) plus X, sodium fluorescein, tumor +, sodium fluorescein, normal tissue. (From Clauss and Jain, 1990, with permission.) Currently, we are measuring diffusion coefficient of molecules and particles larger than 50 A in radius.

What is the minimum degree of polymerization necessary for dextran to exhibit properties characteristic of a typical polymer This question should be resolved by examining the molecular weight dependence of its solution properties, although this may be subject to the limitation that native dextran is not a linear polymer but a branched one. The optical rotation data in Figure 2 demonstrate the transition from oligomer to polymer aroxmd the... 

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

Figure 3. Molecular-weight dependence of intrinsic viscosity of dextran in water (O) and methanol-water mixture with a methanol mole fraction of 0.228 (9) at 25°C (4, 21)t (a) log [r]] — log plots (b) Stockmayer-Fixman plots.

Figure 4. Molecular-weight dependence of excess thermodynamic functions of dextran aqueous solutions at 37°C (9) excess virial coefficient, B (O) excess enthalpy coefficient, Bh (excess entropy coefficient, Bs (16).

Figure 5. Molecular-weight dependence of partial specific compressibility and bound water of dextran at 25°C (21)...

The retention of PVP, dextran, PHPMA in RES has been reported several times to be molecular-weight dependent Earlier studies with i.v. administered... 

The main problem of determination of molecular weight distribution (MWD) of dextrans (polysachaiides which ai e used as active substances for infusion medicines) is low robustness of the existing method. It means that obtained results are strongly dependent on controlled and uncontrolled pai ameters of chromatographic system standai d substances for calibration loading on columns etc. It has been shoved on practical examples. 

Maximum labelling of heparin with F-D was achieved at 5 hours at 25 °C, pH 8.4. In the case of heparin, the efficiency of labelling was not dependent on molecular weight, but solely a function of the ratio of the concentrations of labelling reagent to monosaccharide subunit in the reaction mixture. Similar results were encountered in the labelling of dextrans of different molecular weight (9). 

Morimoto et al. [33] demonstrated that the ocular absorption of hydrophilic compounds over a wide range of molecular weights could be increased by 2 and 10 mM sodium taurocholate and sodium taurodeoxycholate in a dose-dependent manner. The compounds were glutathione (307 Da), 6-carboxyfluorescein (376 Da), FTTC-dextran (4 kDa), and insulin (5.7 kDa). Of the two bile salts, sodium taurodeoxycholate was more effective. At 10 mM, this bile salt increased the permeability of 6-carboxyfluorescein from 0.02% to 11%, glutathione from 0.08% to 6%, FITC-dextran from 0% to 0.07%, and insulin from 0.06% to 3.8%. Sodium taurocholate, on the other hand, increased the permeability to 0.13%, 0.38%, 0.0011%, and 0.14%, respectively. Taurodeoxycholate was more effective than taurocholate in the nasal epithelium as well [202], This difference in activities can possibly be attributed to their micelle-forming capability, which is higher for taurodeoxycholate, a dihydroxy bile salt [190],... 

Dextran Gels Proteins and nucleotides can be separated by using cross-linked dextran gels available in various types and particle sizes. The molecular weight of dextran-gels vary considerably depending upon the extent of cross-linked nature. 

They are most commonly used plasma expanders. It is polysaccharide isolated from beet sugar which is formed by the action of Leuconstec mesenteroides. It is available in mainly two forms depending upon the molecular weight. Dextran 70 (mol. wt. 70,000) available in 6% solution and Dextran 40 (mol. wt. 40,000) available in 10% solution. They are infused intravenously in the treatment of shock. Dextran 40 acts more rapidly than dextran 70. It decreases the blood viscosity and prevents the sludging of RBC s. Dextran 70 remains in circulation for longer period (upto 24 hrs) and is slowly excreted by glomerular filtration. 

In some cases, but not in others, the concentration of the sample has been found to have a small effect on the elution volume, and, consequently, on Kd. Winzor and Nichol40 noted a slight increase in the elution volumes of certain proteins on Sephadex G-100 as the sample concentration was increased from 1 to 12 mg per ml, but no such effect was observed with a dextran of Mw (weight-average molecular weight) 500,000. The effect observed with the proteins was ascribed to dependence of their migration rates on the concentration. 

Therefore, while the independence of dextran diffusion on molecular weight is approximately established at high concentrations, the applicability of Eq. (15) in expressing Dcoop directly as a function of C is in doubt in this case since the predictions of the concentration dependence of Dcoop are not upheld with this material. 

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