Dextran hydration

Fakes et al. [1.152] evaluated the moisture sorption behavior of mannitol, anhydrous lactose, sucrose, D-(+)-trehalose, dextran 40 and povidine (PVP K24) as bulking agents. Mannitol was found to be crystalline and non-hygroscopic before and after freeze-drying with RM 0.1-0.3% w/w at 25 °C and 10-60% RH. Anhydrous lactose, sucrose and trehalose were crystalline and relatively non-hygroscopic with RM 0.86, 0.15 and 9.2% respectively. After freeze-drying they where amorphous with RM 1.6, 2.5 and 1.2%, respectively, and adsorbed moisture in an increasing RH atmosphere. Lactose adsorbed 10% water and formed its crystalline hydrate at 55% RH. 

The mechanical properties of single hydrated dextran microcapsules (< 10 pm in diameter) with an embedded model protein drug have also been measured by the micromanipulation technique, and the information obtained (such as the Young s modulus) was used to derive their average pore size based on a statistical rubber elasticity theory (Ward and Hadley, 1993) and furthermore to predict the protein release rate (Stenekes et al., 2000). 

There are at least four crystalline forms of cellulose, based on different packing of the primary chain (Blackwell, 1982), and three forms of granular starch, based on the packing of double helices (Noel et al., 1993). The differences are largely in the unit-cell dimensions and the crystallization and precipitation temperatures. One form of starch, precipitated with alcohol, is in a symmetrical molecular arrangement and is readily dispersible in cold water (Kerr, 1950). Mannan and dextran yield different crystals at low and high temperatures, and there was not only a polymorphic difference, but a conformational difference in cellulose (Quenin and Chanzy, 1987). Curdlan appears to have three polymorphs—anhydrous, hydrated, and annealed. 

The spacing is measured in separate experiments, as by use of X-ray diffraction. Furthermore, the force corresponding to the spacing is proportional to the osmotic pressure, which is, of course, also a function of the water activity. The water activity can be controlled conveniently by establishing osmotic equilibrium with a large volume of a solution of a polymer (e.g., dextran) at an appropriate concentration. This allows accurate specification of small osmotic pressures for water activities near unity, corresponding to the relatively small energies per water molecule associated with hydration forces. 

Recendy studies of this type have been extended to other systems especially to questions concerning the binding of polymer to cations in solution. Figure 3 shows the first order difference functions for two systems, Ni-PSS and Ca-Dextran in which the hydration structure of a cation has been studied and compared with the corresponding structure in the pure salt solution. 

From these observations it is possible to conclude that the ion, in all cases, remains bound to the same number of oxygens as the pure solution. The reduced intensity of the second (, H) peak is strong evidence that some water has been displaced firom the hydration sphere and has been replaced by the polymer/polyelectrolyte directly binding to the ion. In aU cases this leads to the reduction in the peak and predicts additional correlations further out due to the internal structure of the polymer/polyelectrolyte, for example, Ni-O-P correlations in Ni-ATP, Ni-O-S correlations in Ni-PSS and Ca-O-C correlations in Ca-dextran solutions. These correlations would all be consistent with the third observation above. 

Form liposomes by hydration of the film with either 1 mL of HBS pH 6.5 or 1 mL of HBS (pH 7.0) containing 10 mg/mL FITC dextran in case of rhodamine-PE labelled or DiD labelled liposomes, respectively. 

To prepare Rhodamine-labeled liposomes, add 0.5% Rhodamine-PE in standard formulation (Subheading 3.1, item 1) and hydrate lipid film with 40 mM FlTC-dextran in K-H buffer. Remove non-encapsulated FlTC-dextran with by gel-filtration on NAP column. 

Some polymers can be used as accelerators of nucleic acid hybridization. They sometimes produce background staining and are only recommended when the hybridization rate is low (small amounts of probe or target). Dextran sulfate is often used as an accelerator but polyethylene glycol (PEG 6000) and sodium polyacrylate have been shown to be valuable alternatives. These polymers probably act by exclusion of probe molecules from the volume occupied by the hydrated polymer which results in an effective increase in the probe concentration (Wetmur, 1975). The optimal probe concentration in membrane hybridization is considered to be about 10 cpm of probe/ml (1-10 ng/ml), but Amasino (1986) found a 2- to 10-fold reduction in the probe concentration to be optimal when 10% PEG was included (note that these effects may depend on the specific activity of the probe). These polymers do not act in a similar way and have their own characteristics. 

Composition Ferric oxide hydrate bonded to sucrose chelates with gluconate in a molar rate of 2 iron molecules to 1 gluconate molecule Complex of ferric hydroxide and dextran Complex of polynuclear iron hydroxide in sucrose... 

The free and complexed Cd (II) are separated by two 25 cm HPLC columns of Sephadex G-10 (a cross-linked dextran gel of 40-120 p bead diameter). The mobile phase was distilled deionized water. Sephadex G-10 xerogel has an exclusion limit 700, that is, it can be used to fractionate species of molecular weight less than 700. The larger Cd-fulvic acid complex is unretained and elutes before hydrated Cd (II). As with the phosphorus esters above, SEC is a viable method not only for separating these complexes for analysis but also for purification. 

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