Enhanced production of l(+)-lactic acid by floc-form culture of Rhizopus oryzae

A process to optimize l-lactic acid production from glucose by Rhizopus oryzae, based on sustaining floc morphology throughout the fermentation process, is herein performed. During the fermentation, supplementary ammonium sulfate was added intermittently to maintain the ammonia level of the culture medium always higher than 0.1 g/L. With replenish of nitrogen source, mycelia flocs did not aggregate, and the lactic acid production was optimized upon the fermentation being controlled at pH 4.3–4.5 by adding calcium carbonate slurry. In contrast, without supplementary addition of nitrogen source, mycelial clumps formed, resulting in a poor production of lactic acid. In the initial batch fermentation process, the final concentration of lactic acid produced was 109 g/L, with a yield (g lactic acid/g glucose consumed) of 0.87 and a productivity of 2.73 g/L h, using 125 g/L of glucose as substrate. For the first four cycles of repeated-batch fermentation, the average final concentration, the productivity and the yield of lactic acid were 113 g/L, 4.03 g/L h and 0.90, respectively.     

Triblock and star-block copolymers of N-(2-hydroxypropyl)methacrylamide or N-vinyl-2-pyrrolidone and D,L-lactide: synthesis and self-assembling properties in water

Novel A-B-A triblock and star-block amphiphilic copolymers, i.e. poly(N-(2-hydroxypropyl)methacrylamide)-block-poly(D,L-lactide)-block-poly(N-(2-hydroxypropyl)metha-crylamide), poly(N-vinyl-2-pyrrolidone)-block-poly(D,L-lactide)-block-poly(N-vinyl-2-pyrrolidone), star-poly(D,L-lactide)-block-poly(N-(2-hydroxypropyl)methacrylamide) and star-poly(D,L-lactide)-block-poly(N-vinylpyrrolidone), were synthesized and characterized. These polymers were prepared by free radical polymerization of N-(2-hydroxypropyl)methacrylamide and N-vinyl-2-pyrrolidone in the presence of either poly(D,L-lactide) dithiol or star-poly(D,L-lactide) tetrakis-thiol, both biodegradable macromolecular chain-transferring agents. All copolymers self-assembled in aqueous solution to form supramolecular aggregates of 20–180 nm in size. The critical aggregation concentration of the copolymers ranged from 5 to 24 mg/L, depending on their hydrophobicity. The partition equilibrium constant of pyrene in the hydrophobic core of micelles was between 0.71×10⁵ and 1.63×10⁵. The triblock copolymer micelles were loaded with two model poorly water-soluble drugs, namely, indomethacin (1.5–16.4% w/w) and paclitaxel (0.4–1.5% w/w), by a dialysis procedure. These triblock and star-block copolymers could prove useful as nanocarriers for the solubilization and delivery of hydrophobic drugs.     

Mathematical modelling of the solubility of supercritical CO2 in poly(l-lactide) and poly(d,l-lactide-co-glycolide)

Two mathematical models, Sanchez–Lacombe equation of state and the Perturbed-Chain Statistical Associating Fluid Theory were applied for modelling the phase equilibrium for the poly(l-lactide)–CO₂ and poly(d,l-lactide-co-glycolide)–CO₂ systems. Aspen Polymer Plus software was used. The results were compared with previously obtained experimental values for solubility. The solubility of scCO₂ in the two biodegradable polymers was calculated for three different temperatures (308, 313 and 323 K) in the pressure range (10–30 MPa). The characteristic parameters for the components and the binary interaction parameters for the models were optimized in order to obtain the best fit between the estimated and the experimental gas solubility data. The results suggest that both SL EOS and PC-SAFT are reliable models in describing the phase equilibrium of the PLLA–CO₂ and PLGA–CO₂ systems at the proposed working conditions.     

Technology update: Vacuum infusion

Vacuum, or resin, infusion techniques are becoming increasingly popular, especially in the marine industry where they can produce high quality boat hulls quickly and cleanly (see Reinforced Plastics' Marine Supplement, October 2003).     

Emulsion liquid membrane pertraction of L-lysine from dilute aqueous solutions by D2EHPA mobile carrier

The results of experimental studies on the batch extraction of L-lysine by emulsion liquid membrane are discussed and the capabilities of this method in the separation of solute from dilute aqueous solutions are shown. Studies on the extraction equilibrium for organic and aqueous phases were performed. The experimental results showed that the degree of extraction was increased by an increase in the pH of the feed phase, the concentration of [H⁺] in the internal phase, and concentration of the carrier in the organic phase. An optimum value of stirring speed was achieved. The rate of water swelling as an undesirable phenomenon was also measured.     

Interphex 2004: Conference programme

Interphex 2004 is split into four concurrent events offering pharmaceutical technology solutions, under the banner of the exhibition, and educational opportunities, under the banner of the conference. The four segments, which will run alongside each other, are: Pharma Manufacturing; Pharma Discovery; Pharma IT; and Pharma Sourcing & Services. A separate conference programme has been organised for each strand providing industry professionals with the chance to learn about the latest trends or to advance their career with accredited short courses. Education providers include the International Society of Pharmaceutical Engineers (IPSE) and the Institute for International Research (IIR), amongst others.Below we highlight some of the more relevant presentations for professionals involved in the field of filtration and separation. For more detailed information and a full conference program please visit the Interphex 2004 website (www.interphex.com)     

Interphex 2004: Exhibitor focus

The exhibition component of Interphex 2004 has attracted more than 950 exhibitors from around the globe. There are representatives from every conceivable pharmaceutical sector, including ethical/proprietary drugs, cosmetics, R&D, the biotech field, and full-scale manufacturing support. The various companies have been attracted to New York by the thousands and thousands of visitors and industry decision-makers who are expected to attend this year's event. A number of companies will be showcasing their latest filtration and separation equipment systems, accessories and process solutions for application in the pharmaceutical market. Below Filtration+Separation presents a selection of new products and systems that will be on display in New York, covering everything from vertical centrifuges, membrane filters and sanitary sieves, to disposable filtration solutions, filter housings, depth filtration systems, and metal detection devices for process flows. We hope our “Exhibitor Focus” section helps you to select the companies that will be of most interest to you.     

WFC9: Exhibitor focus

The WFC9 exhibition is an ideal opportunity for industry professionals to see the latest products and developments in the fields of filtration and separation. Approximately 50 companies are expected to attend the international exposition event in New Orleans, USA, on Monday 19 April to Wednesday 21 April. The 2^1/2 day exhibition runs alongside the short courses and technical presentations that make up the rest of the programme of the ninth World Filtration Congress (WFC9). Below Filtration+Separation presents a selection of new products and systems that will be on display at the Hyatt Regency hotel in New Orleans, covering everything from new netting, radial cartridge filters, membranes, porous metals, and testing/validation equipment to filter presses and antimicrobial filter media. We hope that our Exhibitor Focus section will help you to select the companies and organisations that will be of most interest to you.     

Refolding of recombinant N-acetyl-d-glucosamine 2-epimerase by a fed-batch process

N-Acetyl-d-glucosamine 2-epimerase is one of the key enzymes for the enzymatic synthesis of N-acetylneuraminic acid, a sialic acid and a critical precursor for the synthesis of some antiviral agents. Overexpression of the recombinant epimerase in Escherichia coli led to the formation of protein inclusion bodies. Refolding of guanidine HCl-solubilized protein by direct dilution resulted in the formation of soluble oligomers, mediated probably by hydrophobic interactions. The extent of aggregation of protein subunits into inactive oligomers could be efficiently reduced by employing fed-batch refolding process, in which the solubilized proteins were added continuously at a pre-determined rate. The yields of soluble proteins decreased with the feeding rates. The addition of glutathione into refolding buffer at certain stage of the refolding process could enhance the yield of soluble proteins more than two-fold, possibly by resolving the inadvertently formed disulfide bridges among the protein subunits that contain 10 cysteine residues each. Folding aids such as l-arginine and glycerol were found effective in increasing the yield of soluble proteins and the specific activity of the refolded proteins. Under the optimal condition, a specific activity of 0.47 IU/mg was obtained with an activity recovery yield of ca. 30%. The specific activity of the refolded proteins was significantly lower than that of the native protein, 1.23 IU/mg, indicating that more information concerning the 3D structure of native N-acetyl-d-glucosamine 2-epimerase and the role of its cofactor, ATP, for catalytic activity is needed for the development of a more efficient refolding process.     

Novel Poly(EThyleneAmidoAmine) (PETAA) dendrimers produced through a unique and highly efficient synthesis

Polyamidoamine (PAMAM) dendrimers have unique attributes that have led to their use in a wide variety of biomedical applications. However, the complex synthesis of this polymer leads to variations in the structure and consistency of the final product, and makes scale-up of manufacturing difficult. This has limited the clinical translation of PAMAM-based materials. Here we describe a rapid and highly efficient two-step method for the synthesis of novel Poly(EThyleneAmidoAmine) (PETAA) dendrimers that have many of the favorable characteristics of PAMAM dendrimers. Generation 0 (G0) to 5 (G5) PETAA dendrimers were synthesized using a 3-(bis(2-(2,2,2,-trifluoroacetamido)ethyl)amino)propanoic acid AB₂ (compound 1) building block via a divergent approach. An ethylenediamine core was coupled with the AB₂ building block via O-(7-Azabenzotriazol-1-yl)N,N,N’,N’-tetramethyluronium hexafluorophosphate (HATU) in the presence of diisopropylethyl amine to give a G0 trifluoroacetamide surface dendrimer. The G0 amine surface dendrimer was then obtained by treating the G0 trifluoroacetamide surface dendrimer with potassium carbonate. Repetitions of these two coupling/deprotection reactions were then used to build the dendrimer by coupling the surface amino groups to the carboxyl moiety of the AB₂ building block, followed by the deprotection step with potassium carbonate. The resulting PETAA dendrimers have the same number of surface primary amino groups, the same number of chemical bonds between the dendrimer core and the surface, and the same number of tertiary amino groups throughout the structures as similar generations of PAMAM dendrimers. In contrast, the structure of the PETAA dendrimers is more complete and more uniform than PAMAM dendrimers, especially at higher generations. This unique synthetic process for PETAA dendrimers also offers the potential for large-scale production, therefore providing inherently more uniform and complete structures for exacting biomedical applications.     

Titanium complexes based on aminodiol ligands for the ring opening polymerization of l- and d,l-lactide

A series of new titanium isopropoxide complexes (1-4-Ti(OⁱPr)₂ based on enantiopure (1-H₂), racemic (2-H₂), meso (3-H₂) and diastereomeric (4-H₂) aminodiol ligands have been prepared and tested as initiators for the ring opening polymerization (ROP) of l/rac-lactide in solution and in bulk conditions. All complexes were shown to have significant activity in solution at 70 °C and higher activity in bulk at 130 °C with a good control over the molar mass distribution and molecular weights. The complex derived from the racemic-aminodiol ligand gave partially heterotactic polylactide in ROP of rac-lactide and afforded atactic polylactide in the bulk, whereas all other complexes yielded atactic polylactides both in solution and in bulk. Ligand variation (chirality) in the complexes has little effect on either the activity or selectivity of the initiators. The polymerization kinetics using (1-Ti(OⁱPr)₂) as an initiator indicated a first order reaction with respect to the monomer concentration.     

In situ diagnostic of two-phase flow phenomena in polymer electrolyte fuel cells by neutron imaging: Part B. Material variations

The formation of liquid water in operating polymer electrolyte fuel cells (PEFC) of industrial and laboratory size has been investigated by in situ neutron imaging. The influence of the materials chosen for the structural components of the cell on droplet formation and transport in flow fields and on liquid formation in gas diffusion layers has been studied. The changing of the cathodic gas diffusion layer material allowed the relationship between materials, liquid accumulation, and electrochemical performance to be examined. It has been shown that material choice has considerable bearing on the presence of liquid inside the porous structures and the electrochemical characteristics. A simplified quasi one-dimensional cell with an active area of 25 cm² was used for materials comparison, and the results were related to technically relevant operating conditions - where inhomogeneities have to be considered - by subsequent examination of cells with an active area of 100 cm².     

Synthetic carbons activated with phosphoric acid: I. Surface chemistry and ion binding properties

Synthetic activated carbons were prepared by phosphoric acid activation of a styrene-divinylbenzene copolymer at various temperatures in the 400-1000 °C range. The resulting carbons were characterized by elemental analysis, cation-exchange capacity measurement, infrared spectroscopy, potentiometric titration with calculation of proton affinity spectra, and copper adsorption from solution. The results indicate that the synthetic carbons obtained possess acidic character and show cation-exchange properties similar to those of oxidized carbons. However, the acidic compounds arising from treatment with phosphoric acid are tightly bound to the carbon lattice and are chemically and thermally more stable than those introduced by oxidative treatments. The largest amount of cation-exchange surface groups is introduced after activation at 800 °C. Infrared investigations showed that phosphorus compounds may be polyphosphates bound to the carbon lattice. Proton affinity distribution curves calculated from potentiometric titration experiments showed four types of surface groups on synthetic phosphoric acid activated carbons. Among them phosphorus-containing groups are the most important for the adsorption of heavy metal ions (copper) from acid solutions. Thus, carbons activated with phosphoric acid may be regarded as prospective cation-exchangers for the removal of heavy metals from water solutions.     

Reactivity ratios for the copolymerization systems styrenep-ethoxystyrene and methyl methacrylatep-ethoxystyrene

Reactivity ratios for the systems $\text{styrene}\text{p-}\text{ethoxystyrene}$ and methyl $\text{methacrylate}\text{p-}\text{ethoxystyrene}$ have been determined at 50°C. The values found by the computational method of Tidwell and Mortimer were 1.08 and 0.74 for the first system, and 0.37 and 0.24 for the second; the 90% joint confidence limit envelopes were also calculated.     

In situ analysis of solvent/nonsolvent exchange and phase separation processes during the membrane formation of polylactides

Membrane formation of polylactides has been studied using in situ analysis techniques. An experimental method based on the use of dark ground optics and reflected light illumination is used to monitor the mass transfer and phase separation dynamics during for mation. Additionally, the phase separation and structure formation has been studied using optical microscopy. The results of the dark ground optics technique for the polymer/solvent/nonsolvent systems poly-L-lactide/chloroform/methanol and poly-DL-lactide/chloroform/methanol showed that the diffusion kinetics were similar for the semicrystalline poly-L-lactide (PLLA) and the amorphous poly-DL-lactide. The influence of the molecular weight of the polymers on the diffusion kinetics was found to be negligible. Increasing the polymer concentration of the casting solution decreased the rate of diffusion. The phase separation of poly-DL-lactide was studied with optical microscopy and found to proceed via liquid-liquid demixing. For poly-L-lactide solutions of relatively low concentration (5–6% w/w), phase separation proceeded via liquid-liquid demixing followed by crystallization. For more concentrated PLLA solutions, phase separation proceeded directly via solid-liquid demixing processes. Additionally, for 6% w/w solutions of poly-L-lactide in dioxane immersed in methanol, precipitation also occurred solely via solid-liquid demixing. © 1996 John Wiley & Sons, Inc.     

Feasibility study of using montmorillonite for stability enhancement of l-ascorbic acid

This study tended to construct new l-ascorbic acid (LAA) composites in low toxicity and high stability for feasible application. LAA is chemically very unstable, since it is easily oxidized into biologically inactive compounds naturally. Our finding showed that introduction of montmorillonite (MMT) could significantly attenuate its toxicity and to sustain the stability of LAA with economic feasibility for practical uses. In addition, as phosphoric acid was biologically compatible, it was used for the pretreatment of MMT to obtain a promising stabilization of LAA. Toxicity assessment also showed that MMT treated with low-concentration acids should be considered as biologically safe according to our assessment. Thus, using acid treated MMT to stabilize LAA in a long-term might be technically feasible for further uses.     

Synthesis, characterization, and conformational studies of N-t-butyloxycarbonyl-oligo-l-leucine methyl esters

The conformational properties of N-t-butyloxycarbonyl-oligo-l-leucine methyl esters were examined in anhydrous and aqueous organic solvents. This study demonstrates that these oligomers may exist in predominantly β-associated or unordered conformations depending upon the solvent. The β-structure, which appears at the pentamer in ethylene glycol (EG) and trifluoroethanol (TFE)-water (20:80 v/v), could be disrupted by dilution or by increasing the temperature. The stability of the β-structures was found to be lower than those formed by oligopeptides derived from l-isoleucine and l-valine and comparable to those formed by oligo-l-methionines.