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J M Cabral

Publications and source records attributed to J M Cabral.

69 records · Page 4Linked to original sources
PubMed1991

Factor for correcting the ruthenium interference in instrumental neutron activation analysis of barium in uraniferous samples.

The fission spectral interference of ruthenium on the instrumental neutron activation analysis of barium in samples containing uranium is extensively discussed. In particular the dependence of the correction factor on the phi epi/phi th ratio is studied. An excellent agreement between experimental and calculated values is achieved. A procedure is suggested for the resolution of multiple interferences in the general case where uranium, barium and/or ruthenium are present in samples to be analysed.

Barium↗
PubMed1988

Local plasminogen activator and prostacyclin-like activity after partial venous occlusion--an experimental study in the dog.

After 90 min. of partial venous occlusion (40%) in dog's femoral vein plasminogen activator (t-PA) was decreased in the pre-occlusion segment and maintained in the post-occlusion segment. Prostacyclin-like activity (PLA) was maintained in the pre-, but increased in the post-occlusion segment. Treatment with heparin (loading dose-70/kg; IV perfusion-1 U/kg/min) did not affect pre-treatment pattern of t-PA or PLA in either segments. Treatment with aspirin (IV perfusion-2 mg/kg/min) promoted profound depression of PLA in both segments while t-PA remained unchanged. Treatment with lidocain (loading dose-1.5 mg/kg; IV perfusion 0.2 mg/kg/min) did not affect either PLA or t-PA in the pre-occlusion segment, but a decrease of these two activities was observed in the post-occlusion segment. We conclude that, since thrombin, prostaglandins and white blood cells were not responsible for all changes observed at t-PA and PLA vessel wall levels, it is justified, to evaluate the role of rheological factors as the probable determinant of these changes.

Animals↗
PubMed1986

Oxygen limitation on L-serine production in a hollow-fiber bioreactor.

Pseudomonas AM1 utilizes glycine and methanol to produce L-serine aerobically. The consumption of methanol in this bioconversion is stoichiometrically in excess of L-serine production. Consequently, the oxygen requirement associated with L-serine production is higher than expected for the conversion from glycine. One method of L-serine production investigated was a technique utilizing a hollow-fiber ultrafiltration cartridge as a bioreactor. Oxygen diffusion limitations appear to impede the consumption of methanol and, consequently, the production of L-serine in such a reactor. Methanol consumption data agree with predictions based on a hollow-fiber diffusion model.

Glycine↗
PubMedDate not supplied

Studies on the batch adsorption of plasmid DNA onto anion-exchange chromatographic supports.

The adsorption of a supercoiled 4.8 kbp plasmid onto quaternary ammonium anion-exchangers was studied in a finite bath. Equilibrium experiments were performed with pure plasmid, at 25 degrees C, using commercial Q-Sepharose matrices differing in particle diameter (High Performance, 34 microm; Fast Flow, 90 microm; and Big Beads, 200 microm) and a recently commercialized ion-exchanger, Streamline QXL (d(p) = 200 microm) at different salt concentrations (0.5, 0.7, and 1 M NaCl). Plasmid adsorption was found to follow second-order kinetics (Langmuir isotherm) with average association constants K(A) = 0.32+/-0.12 mL microg(-)(1) and K(A) = 0.25+/-0.15 mL microg(-1) at 0.5 and 0.7 M Nacl, respectively. The maximum binding capacities were not dependent on the ionic strength in the range 0.5-0.7 M but decreased with increasing particle diameter, suggesting that adsorption mainly occurs at the surface of the particles. No adsorption was found at 1 M NaCl. A nonporous model was applied to describe the uptake rate of plasmid onto Streamline QXL at 0.5 M NaCl. The overall process rate was controlled by mass transfer in the regions of low relative amounts of adsorbent (initial stages) and kinetically controlled in the later stages of the process for high relative amounts of adsorbent. The forward reaction rate constant (k(1) = 0.09+/-0.01 mL mg(-1) s(-1)) and film mass transfer coefficient (K(f) = (6 +/- 2) x 10(-4) cm s(-1)) were calculated. Simulations were performed to study the effect of the relative amount of adsorbent on the overall process rate, yield, and media capacity utilization.

Adsorption↗
PubMedDate not supplied

Liquid-liquid extraction of a recombinant protein with a reverse micelle phase.

Recombinant cytochrome b5 was extracted to a reversed micelle phase of a cationic surfactant (hexadecyltrimethylammonium bromide, CTAB) in cyclohexane/decanol and back-extracted to a fresh aqueous phase. Depending on the experimental conditions, i.e., temperature, pH, and ionic strength, the extraction is controlled by either hydrophobic (pH close to the pI and high ionic strength) or electrostatic (pH far from the pI and low ionic strength) interactions. The protein interacts strongly with the surfactant aggregate once it is extracted to the organic phase, and it is very difficult to back-extract it to a new aqueous phase.

Cetrimonium↗
PubMedDate not supplied

A multiphasic hollow fiber reactor for the whole-cell bioconversion of 2-methyl-1,3-propanediol to (r)-beta-hydroxyisobutyric acid.

This paper describes the bioconversion of 2-methyl-1,3-propanediol to (R)-beta-hydoxyisobutyric acid (HIBA) by Acetobacter ALEI in a hollow fiber membrane bioreaction system arrangement that allows the integration of three liquid phases: the aqueous bioconversion phase, the organic phase consisting of a solution of trioctyl phosphine oxide (TOPO) in isooctane, and the third phase consisting of a basic stripping solution that allows reextraction of HIBA from the organic phase. A comparison of HIBA mass transfer experiments was carried out in the membrane reactor with two and three phases for different pH and TOPO concentrations. The use of the three-phase arrangement allows the extraction of high quantities of HIBA from the aqueous medium (higher than 85%) independently of the pH, whereas in the two-phase system the percentage of HIBA extracted from the aqueous medium was lower, 42% in the best case, and strongly influenced by the pH. The percentage of the extractive agent TOPO in the organic phase influenced on the mass transfer rate in both bi- and triphasic arrangements. By simply integrating the re-extraction phase in the system it was possible to increase the extraction yield by 2-fold, reduce the amount of TOPO by 4-fold, and operate at the more favorable pH 4. A bioconversion experiment was done in these conditions (pH = 4, TOPO = 5%) to confirm the advantages of including the third stripping solution. Fed-batch operation of the triphasic membrane reactor was maintained for more than 20 h, reaching an HIBA concentration in the stripping solution of 29 g L(-)(1).

Acetobacter↗
PubMedDate not supplied

Optimization study of Escherichia coli TB1 cell disruption for cytochrome b5 recovery in a small-scale bead mill.

The recovery of a recombinant intracellular protein, cytochrome b5, from Escherichia coli TB1 cells was carried out by bead mill disintegration in a discontinuous small-scale instrument. This process was optimized by the use of experimental factorial design. Several parameters were studied: operating time, amount and size of beads, cellular suspension concentration, and presence of toluene and lysozyme. For the experimental conditions used, only the time of treatment and bead load had significant effects. The optimal values of these variables were found by applying the response surface methodology.

Cytochromes b5↗
PubMedDate not supplied

Development of process flow sheets for the purification of supercoiled plasmids for gene therapy applications.

Human clinical trial of gene therapy with nonviral vectors demands large amounts of pharmaceutical-grade plasmid DNA. Since standard molecular biology methods cannot be used for this purpose, there is a need for the development of processing methodologies for the large-scale production and purification of plasmids. This work describes several studies that were undertaken during the development of process flow-sheets for the downstream processing of supercoiled plasmids. Anion-exchange HPLC was used as a routine technique for monitoring plasmid purity in process streams. The use of RNase or high temperatures during alkaline lysis was proved unnecessary. Instead, RNA could be completely removed by performing sequentially clarification with a chaotropic salt, concentration with PEG, and ion-exchange and size-exclusion chromatography. Also, clarification of streams by precipitation was independent of the chaotropic salt used. Furthermore, by proceeding directly from cell lysis to chromatography it was possible to obtain plasmid with purity/quality identical to that of the one obtained when clarification and concentration were included in the process. This strategy has the advantage of increasing the overall process yield to 38%. The plasmid thus purified was depleted of RNA, chromosomal DNA, and proteins. Additionally, no animal-derived enzymes, alcohols, or toxic solvents were used, rendering validation potentially easier. The results described in this report also indicate that downstream processing times and costs can be considerably reduced without affecting plasmid purity.

Bioreactors↗