Characterization of flocculation for cell removal from fermentation broth via polyelectrolyte addition is commonly based on qualitative methods such as physical appearance of the floc. The use of zeta potential as a quantitative measure of floc character was evaluated as an indicator of optimal polymer addition. Zeta potential was found to increase with increasing cationic polyelectrolyte dosage, but never reached zero regardless of the total amount of polymer added, indicating flocculation occurs at least partially through a bridging type mechanism. Experiments were conducted using various polymer concentrations (25-75 g/L) and dosing methods (batch, incremental and continuous addition) that resulted in variable overall polymer requirements to achieve optimum flocculation. Zeta potential was found to be constant at optimal floc character regardless of the total amount of polymer added, polymer concentration, or method of polymer addition. Experiments with two additional types of fermentation broth also showed characteristic zeta potentials at optimal flocculation. Polymer requirements to achieve a particular floc character can vary greatly, depending on polymer dosing conditions and fermentation batch. The effect of polymer dosing conditions on the polymer requirement to obtain optimal floc character was evaluated. Polymer dosing method and calcium concentration were both found to have a significant effect (P < 0.0001) with continuous polymer addition and high calcium concentration requiring less polymer than did batch polymer addition and low calcium concentration, respectively. Polymer dosing concentration did not significantly affect polymer requirement for optimal flocculation.
Diffusion-limited interactions between benziland anthracene-labeled polystyrene were studied by phosphorescence quenching in polystyrene-toluene solutions. Values of the bimolecular diffusion-limited quenching rate constant, kq, were obtained by measuring the benzil phosphorescence lifetime as a function of anthracene moiety concentration and applying a Stern-Volmer analysis. In the case of interactions of benzil with anthracene which was labeled randomly to phenyl groups along the polystyrene chain (RAPS), kq is approximately one-third the value of kq for the benzil-anthracene interaction over a broad range of unlabeled polystyrene concentration, from 0 to at least 400 g/L. This indicates that the physics controlling the polystyrene concentration dependence of the benzil-anthracene interaction also controls the polystyrene concentration dependence of the benzil-RAPS interaction in toluene solution. For both interactions, the Vrentas-Duda free volume theory for D" the solvent self-diffusion coefficient, predicts quantitatively the polymer concentration dependence of feq, with feq/Aqo = DJD& where the subscript 0 denotes the value at zero polymer concentration. In contrast to the significant effect of polymer concentration, kq was found to have little dependence on the polymer molecular weight. Benzil-RAPS interactions are compared to interactions of benzil with anthracene which is labeled at the terminus of the polystrene chain (TAPS), showing that the differences in the photophysical properties of RAPS and TAPS should be considered, along with other factors, in making conclusions about the effect of anthracene moiety placement on these interactions.
The purpose of this study was to assess certain pharmaceutical attributes of guar galactomannan, a hydrocolloid polysaccharide obtained from the endosperm of the leguminous plant Cyamopsis tetragonolobus (L.), following purification using both literature procedures and new processes. Experiments were performed to measure viscosity, hydration rate, tablet hardness, and dissolution profiles of guar galactomannan both before and after purification. The viscosity of an aqueous 1% purified galactomannan solution is typically 40-50% higher than its unpurified guar galactomannan precursor. The hydration rate of an aqueous 1% purified galactomannan solution increases by 100% after purification. These physicochemical changes resulted in improvements in pharmaceutical properties such as better stir speed independence in both tablet and capsule dissolution profiles and improved tablet hardness. For instance, time to 50% dissolution of ranitidine HCl from capsules containing unpurified guar gum was 0.4 and 1.8 hr at 20 and 40 rpm, respectively, using USP Apparatus II. Using the same amount of purified guar gum and the same conditions (20 and 40 rpm), these values were increased to 2.9 and 3.8 hr, respectively. These data demonstrate a reduced effect of changing agitation conditions and the need for less guar gum to sustain the release of a water-soluble drug. Tablet hardness of purified guar gum (particle size < 75 microns) was about 7 kP and the same unpurified guar gum of equal particle size and hydration gave a hardness of less than 1 kP.
There is widespread use of biomolecules in fabric care applications with laundry detergent formulations employing enzymes for improved cleaning.[1] However, long-term stabilization of enzymes in detergents presents unique challenges.[2]The hostile environment of detergents often leads to aggregation, precipitation, denaturation, and loss of activity of enzymes. [3] Consequently, an approach to stabilize biomolecules in detergents and subsequently release them through the use of a change in the osmolarity (or water content) of the medium as a trigger mechanism during the washing process remains a particularly attractive goal. Here, we report on an organosilica sol-gel system that exhibits unique osmotically triggered volume changes and is able to release encapsulated biomolecules with respect to variations in the osmolarity of the medium. We show that these porous glasses act as osmoresponsive materials, which selectively release biomolecules when placed in a low-osmolality medium. Furthermore, a particularly remarkable feature of this system is that the osmotically generated volume changes of the gels are reversible and can be efficiently modulated by simply changing the environmental conditions. Immobilization and controlled release of biomolecules provides an exquisite strategy in practical applications of proteins and enzymes. [4,5] The use of environmental stimuli as triggers for controlled release has been extensively investigated and there are many approaches based on different physicochemical stimuli as triggers. [6][7][8] In this context, the stabilization and release of encapsulated entities by changes in the osmolality of the medium represents a unique mechanism for externally controlled release. As such, the design of materials systems that can utilize osmotically regulated control mechanisms for controlled release remains a particularly attractive goal. This is especially important in the context of enzymes in detergents, since with alkaline proteases [9,10] -which are used extensively in liquid-detergent formulations [11,12] -the innate activity of these enzymes causes autolytic degradation of isolated enzymes in the basic environment of typical detergent formulations. [13,14] In this paper, we report osmotically regulated release of biomolecules from organosilica gels that exhibit volume changes depending upon the osmolarity of the medium, and demonstrate the feasibility of using osmotically triggered release as a control mechanism for release of encapsulated biomolecules. The porous sol-gels act as reversible osmoresponsive materials that shrink in a high-osmolarity medium and swell when placed in a medium with high water content. A particularly remarkable feature of these gels is their ability to preferentially release encapsulated entities in a water-rich medium.The gels used in this study made by hydrolysis of bis [3-(trimethoxysilyl)propyl] ethylenediamine (enTMOS) precursor are characterized by environmental sensitivity, and have been shown to undergo volume changes in response to different st...
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