A. L. Zubov

Poly(vinyl alcohol) cryogels employed as matrices for cell immobilization. 2. Entrapped cells resemble porous fillers in their effects on the properties of PVA-cryogel carrier

Abstract Poly(vinyl alcohol) cryogels which are prepared by freeze-thawing of concentrated aqueous solutions of the polymer are used as carriers for cell immobilization. Biomass entrapment causes a variation in the mechanical properties of the composites obtained. With rheological testing and scanning electron microscopy, it was shown that cells which manifested the reinforcing action in respect to the carrier resembled in their “physical behavior” simple model inorganic fillers of definite porosity. This porosity allows macromolecules of gel-forming polymer to penetrate into the inner regions of the particles and promote the formation of tight contacts between the matrix and dispersed phase, such as entrapped cells in particular. The immobilized cultures and model fillers were as follows: Citrobacter intermedius, Zymomonasas mobilis , and Pseudomonas sp. bacteria, Saccharomyces cerevisiae native and modified yeast cells, titanium dioxide, silica gels, and controlled pore glass.

Swelling behavior of poly(vinyl alcohol) cryogels employed as matrices for cell immobilization

Abstract Poly(vinyl alcohol) cryogels are prepared from aqueous solutions of the polymer by freezing and thawing and are employed as matrices for cell immobilization. The swelling behavior of these macroporous gel carriers in pure water and in solutions of certain compounds (salts, amino acids, and glucose) was studied to elucidate the osmotic properties of the cryogels during long-term exposure to aqueous media. It was shown that after the initial sol fraction was washed out, the residual gel matrix possessed high stability even at extreme pH conditions (acid or alkali concentration up to 1.0 mol l −1 ) or in the presence of strong chaotropic salts such as sodium rhodanide. Although the macroporous supermolecular structure of the carriers under consideration underwent certain changes as a result of aging processes during prolonged washing of the gel, the high porous morphology of the material was retained.

Study of cryostructuration of polymer systems. XII. Poly(vinyl alcohol) cryogels: Influence of low-molecular electrolytes

The influence of the presence of low-molecular electrolytes in initial solutions of poly(vinyl alcohol) (PVA) on the results of cryotropic gelation of the polymer (gelation caused by the freezing thawing) and on the swelling characteristics of PVA cryogels prepared in a salt-free medium were studied. The reinforcing ability of the electrolytes with respect to the gel strength for both alkaline element cations and simple low-molecular anions has been shown to be in agreement with the positions of these ions in corresponding lyotropic (Hofmeister) series. Namely, the ions (chaotropic ones), which are capable to interfere the H-bonding, disturbed somewhat the cryotropic gel-formation of PVA and facilitated the marked additional swelling of cryogels preliminary prepared in pure water medium, whereas the ions (antichaotropic ones), which are capable to promote the H-bonding, caused the formation of reinforced cryogels and resulted in the shrinking of cryogels prepared without salt additives. More pronounced effects were observed for anions as compared with cations. Some anomalous swelling behavior of PVA cryogel in Cs+-containing solutions was supposed to be associated with the formation of weak chelates. In addition to antichaotropic inorganic salts like NaF, rather high salting-out effects in respect to PVA were exhibited by wellsoluble amino acid salts: glycine zwitter-ions, lysine monochlorohydrate, and monosodium aspartate.

Use of PVA-cryogel entrappedCitrobacter intermedius cells for continuous production of 3-fluoro-L-tyrosine

SummaryThe cells ofCitrobacter intermedius (containing L-tyrosine phenol lyase which catalyses the synthesis of 3-fluoro-L-tyrosine fromo-fluorophenol, pyruvate and ammonia) were entrapped into 10% poly(vinyl alcohol) cryogel beads. Cryogenic immobilization resulted in a moderate increase of the synthetic activity of the cells. During continuous operation for one month in a packed bed column reactor the productivity of the immobilized biocatalyst decreased by 30%.

Production of ethanol from molasses at 45 °C using Kluyveromyces marxianus IMB3 immobilized in calcium alginate gels and poly(vinyl alcohol) cryogel

Abstract The thermotolerant, ethanol-producing yeast strain Kluyveromyces marxianus IMB3 has been immobilized in calcium alginate gel and poly(vinyl alcohol) cryogel (PVAC) beads. The immobilized preparations were used as biocatalyst in fed-batch reactor systems for prolonged periods. The substrate utilized in each case consisted of sugar cane molasses diluted to yield a sugar load of 140 g/l. During the first cycle the maximum ethanol concentration produced by the alginate system was 57 g/l, representing 80% of the maximum theoretical yield. In the system employing the PVAC-immobilized biocatalyst, ethanol production increased to a maximum of 52–53 g/l, representing 73% of the maximum theoretical yield. In both cases, maximum ethanol concentration was achieved within a 72-hour period. When each system was operated on a fed-batch basis for a prolonged period of time the average ethanol concentrations produced in the alginate- and the PVAC-immobilized systems were 21 and 45 g/l, respectively. The results suggest that the PVAC-based immobilization system may provide a more practical alternative to alginate for the production of ethanol by K. marxianus IMB3 in continuous or semi-continuous fermentation systems.