Dextran, aqueous solution

Figure 5.10A shows three of the possible directions for membrane irradiation with US for the previously discussed dextran aqueous solution and Fig. 5.1 OB shows the resulting permeate flow as compared with the absence of US. An orthogonal direction of the flow relative to the US radiation was found to provide the best results on the other hand, a minimal effect was observed when the direction of US propagation opposed that of the permeate flow.

Figure 5.9. Influence of US frequency (A) and Intensity (B) on the permeate flux of a 1 wt% dextran aqueous solution at an operating pressure of 30 kPa and a feed flow- rate of 325 mllmln. (n) 28 kHz, (h) 45 kHz, (o) 100 kHz, ( ) without US and ( ) for water Irrespective of the frequency. (Reproduced with permission of Elsevier, Ref [92].)...

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).

Second Virial Coefficients and Interaction Parameter of Dextran Aqueous Solutions ... 

Biopolymer Extraction. Research interests involving new techniques for separation of biochemicals from fermentation broth and cell culture media have increased as biotechnology has grown. Most separation methods are limited to small-scale appHcations but recendy solvent extraction has been studied as a potential technique for continuous and large-scale production and the use of two-phase aqueous systems has received increasing attention (259). A range of enzymes have favorable partition properties in a system based on a PGE—dextran—salt solution (97) ... 

Recovery and Purification. The dalbaheptides are present in both the fermentation broth and the mycelial mass, from which they can be extracted with acetone or methanol, or by raising the pH of the harvested material, eg, to a pH of 10.5—11 for A47934 (16) (44) and A41030 (41) and actaplanin (Table 2) (28). A detailed review on the isolation of dalbaheptides has been written (14). Recovery from aqueous solution is made by ion pair (avoparcin) or butanol (teicoplanin) extraction. The described isolation schemes use ion-exchange matrices such as Dowex and Amberlite IR, acidic alumina, cross-linked polymeric adsorbents such as Diaion HP and Amberlite XAD, cation-exchange dextran gel (Sephadex), and polyamides in various sequences. Reverse-phase hplc, ion-exchange, or affinity resins may be used for further purification (14,89). 

Works where study the hydrodynamic properties of a biopolymers in aqueous solution at different temperatures are made by Guner (1999), and Guner Kibarer (2001) for dextran Ghen Tsaih (1998) and Kasaii (2008) for chitosan, Bohidar for gelatin (1998), and Monkos for serum proteins (1996,1997,1999, 2000, 2004 and 2005). 

Guner A. 1999. Unperturbed dimensions and theta temperature of dextran in aqueous solutions. Journal of Applied Polymer Science 72, 871-876. 

Amylose and dextran have been studied in aqueous solution as the xanthate derivatives. Dextran xanthate has no observable c.d., but amylose xanthate in aqueous solution has a complex c.d. that indicates an organized structure. 

Aqueous standard solutions are a source of certain difficulties In electrothermal atomic absorption spectrometry of trace metals In biological fluids The viscosities and surface tensions of aqueous standard solutions are substantially less than the viscosities and surface tensions of serum, blood and other proteln-contalnlng fluids These factors Introduce volumetric disparities In pipetting of standard solutions and body fluids, and also cause differences In penetration of these liquids Into porous graphite tubes or rods Preliminary treatment of porous graphite with xylene may help to minimize the differences of liquid penetration (53,67) A more satisfactory solution of this problem Is preparation of standards In aqueous solutions of metal-free dextran (50-60 g/llter), as first proposed by Pekarek et al ( ) for the standardization of serum chromium analyses This practice has been used successfully by the present author for standardization of analyses of serum nickel The standard solutions which are prepared In aqueous dextran resemble serum In regard to viscosity and surface tension Introduction of dextran-contalnlng standard solutions Is an Important contribution to electrothermal atomic absorption analysis of trace metals In body fluids. 

Dextran was chosen to study for the following reasons. First, it is water soluble allowing three dimensional modification employing aqueous solution and classical interfacial condensation routes. Second, it is readily available in industrial quantities. Third, it is available in a range of molecular weight allowing product modification to be studied as a function of dextran chain size. Fourth, it is generally considered to be an under-utilized natural feedstock. 

Solubility generally decreases with increase in chain size and extent of branching. The solubility of dextran can be divided into four groups — those that are readily soluble at room temperature in water, IMF, DMSO and dilute base those that have difficulty dissolving in water those that are soluble in aqueous solution only in the presence of base and, those that are soluble only under pressure, at high temperatures (> 100°C) and in the presence of base. Dextran B-512 readily dissolves in water and 6M, 2M glycine and 50% glucose aqueous solutions. 

Addition of an aqueous solution of PEG to a saturated aqueous solution of a-CD at room temperature did not lead to complex formation unless the average molecular weight of PEG exceeded 200 [46]. Moreover, carbohydrate polymers such as dextran and pullulan failed to precipitate complexes with PEG, and the same was true for amylose, glucose, methyl glucose, maltose, maltotriose, cyclodextrin derivatives, such as glucosyl-a-CD and maltosyl-a-CD, and water-soluble polymers of a-CD crosslinked by epichlorohydrin. These facts suggested to Harada et al. the direction for further research. 

The squaraine rotaxane tetracarboxylic acid 15a is soluble in aqueous solution at physiological pH and acts as an excellent fluorescent marker with extremely high photostability, which allows trafficking processes in cells to be monitored in realtime, with constant sample illumination, over many minutes. This type of real-time monitoring cannot be done with other available NIR fluorescent probes, such as the amphiphilic styryl dye KM4-64 and water-soluble dextran-Alexa 647 conjugate, because they are rapidly photobleached. 

Lindvall and Anderson (90) prepared an ill-defined complex by adding an aqueous solution of ferric chloride in small increments to a solution containing sorbitol, citric acid, and the dextran held at 60°. The pH of the solution was adjusted to approximately 7.5 after the addition of each aliquot of the iron. The resulting iron complex can be precipitated with... 

Bibette has used this method to study the effect of osmotic pressure on the stability of thin films in concentrated o/w emulsions [96], by means of an osmotic stress technique. The emulsion is contained in a dialysis bag, which is immersed in an aqueous solution of surfactant and dextran, a water-soluble polymer. The bag is permeable to water and surfactant, but impermeable to oil and polymer. The presence of the polymer causes water to be drawn out of the emulsion, increasing the phase volume ratio and the deformation of the dispersed droplets (Fig. 10). 

Pavlovskaya, G., Semenova, M., Tsapkina, E., Tolstoguzov V. (1993). The influence of dextran on the interfacial pressure of adsorbing layers of 1 IS globulin Viciafaba at the planar w-decane/aqueous solution interface. Food Hydrocolloids, 7, 1-10. 

Schaink, H.M., Smit, J.A.M. (2007). Protein-polysaccharide interactions the determination of the osmotic second virial coefficients in aqueous solutions of p-lactoglobulin and dextran. Food Hydrocolloids, 21, 1389-1396. 

Semenova, M.G., Belyakova, L.E., Polikarpov, Y.N., Antipova, A.S., Dickinson, E. (2009). Light scattering study of sodium caseinate + dextran sulfate in aqueous solution relationship to emulsion stability. Food Hydrocolloids, 23, 629-639. 

Light scattering study of sodium caseinate + dextran sulfate in aqueous solution relationship to emulsion stability. FoodHydrocolloids, 23, 629-639. 

Void volume is measured by passing a large, inert molecule through the column." Its elution volume is defined as F0. Blue Dextran 2000, a blue dye of molecular mass 2 X 106, is commonly used for this purpose. The volume Vm can be calculated from the measured column bed volume per gram of dry gel. For example, 1 g of dry Sephadex G-100 produces 15 to 20 mL of bed volume when swollen with aqueous solution. The solid phase occupies only 1 mL of the bed volume, so Vm is 14 to 19 mL, or 93-95% of the total column volume. Different solid phases produce widely varying column bed volumes when swollen with solvent. 

Dialysis studies122 of ofellulose and dextran in aqueous solutions of barium hydroxide, sodium hydroxide, and cadoxene (cadmium hydroxide in ethylenediamine) showed no difference in complexing ability between the two polysaccharides. Furthermore, in solutions having equal base normality, Ba2 , Na ,, nd Cd (ethylenediamine) had loughly equal complexing abilities. 

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