l-Proline-catalyzed intramolecular cyclization of 5-hydroxypentene to β-halogenated tetrahydrofuran

A series of β-bromo- and β-iodotetrahydrofurans was synthesized from the reaction mixture of 5-hydroxypentene, l-proline, NBS (or I₂) in THF at 0 °C for 10 min. This l-proline-catalyzed intramolecular cyclization provides a simple and efficient method for the preparation of β-halogenated tetrahydrofuran.     

Fumaric acid production in airlift loop reactor with porous sparger

Airlift loop reactors with porous spargers were investigated and used in the process of fumaric acid production byRhizopus oryzae ATCC 20344. In order to enhance oxygen mass transfer, which is very important for organic acid production, two kinds of porous spargers (stainless steel membrane tube and porcelain tube) were examined. Gas holdup, liquid circulation velocity, mixing time, bubble size, and bubble rise velocities were measured in a 50 L rectangular airlift loop reactor with different ratios of the cross-sectional area of the riser and downcomer. The local volumetric mass transfer coefficient (K_La) was also measured in the gas sparger zone. The results indicated that high K_La and excellent hydrodynamics can be obtained in the airlift loop reactor with a porous sparger. A 10 L laboratory airlift loop reactor was employed for the fumaric acid fermentation. Results showed that the turbulence of two-phase flow in the airlift loop reactor not only produced favorable conditions for mass transfer, but was also useful for forming and suspending small, well-distributed mycelial pellets (1ç2 mm). A production rate of up to 0.814 g/L/h and efficiency yield of 50.1% (w/w) was obtained in the airlift loop reactor. The performance was compared with the typical stirred tank fermentor fermentation results.

     

Adsorption of heavy metal ions by immobilized phytic acid

Applied Biochemistry and Biotechnology - Phytic acid (myoinositol hexaphosphate) or its calcium salt, phytate, is an important plant constituent. It accounts for up to 85% of total phosphorus in...     

Lactic acid fermentation and adsorption on PVP

Applied Biochemistry and Biotechnology - Lactic acid was produced by immobilizedLactobacillus delbreückii cells in a fixedbed reactor and then separated by a column packed with...     

Newton interpolation is efficient for approximation of linear functionals

Summary The Newton interpolation approach is developed for approximation of linear functionals. It is shown that in numerical interpolation and numerical differentiation, the Newton interpolation approach is more efficient than solving the Vandermonde systems.This work was supported in part by the United States Air Force under a grant AFOSR 76-3020     

Luminescence of the hydrolysis products of Th(IV)

Raising the pH of an aqueous solution of thorium nitrate results in the precipitation of a hydrated thorium oxide. At room temperature this material does not exhibit any emissive properties, but upon cooling to 77 K a strong green luminescence can be observed. The emission spectrum is fairly broad, and is characterized by an emission lifetime of 125 μs. Calcination of the hydrolysis product produces an anhydrous thorium oxide which is not luminescent at any temperature. Through the production of a series of mixed lanthanide/thorium hydrolysis products, it was established that the luminescent species was a clustered thorium compound. Sensitization of Eu(III) emission by the thorium hydrolysis product was observed.     

Spectrophotometric determination of nitrite with p-nitroaniline and 2-methyl-8-quinolinol in hexadecyl-trimethylammonium bromide solution

Nitrite ion at low concentrations is determined spectrophotometrically by diazotization of p-nitroaniline and coupling of the diazonium salt with 2-methyl-8-quinolinol. The resulting dye is solubilized in hexadecyltrimethylammonium bromide micelles. The molar absorptivity is 4.72 × 10⁴ l mol^-1 cm^-1, and the Sandell sensitivity is 9.7 × 10^-4 μg cm^-2. Some interferences are reported, and preconcentration by evaporation is evaluated. The solubility of hexadecyltrimethylammonium bromide in water was determined as a function of temperature; the Krafft point is 19.6°C. Salting-in of the surfactant by potassium nitrate is described.     

System development for aqueous gel permeation chromatography

To devise an improved gel permeation chromatography system for the analysis of macromolecules, with a strongly alkaline solution as eluent, three Fractogel TSK gels were investigated. Because primary standards are usually unavailable, calibration was achieved by using Benoit's universal procedure and polystyrene sulfonates, polyethylene glycols, and dextrans as secondary calibrants. Continuous monitoring of intrinsic viscosity resulted from coupling a viscodetector with a classical differential refractometer. It was found that column efficiency and fractionation range could be extended well beyond those of previously studied systems on a reasonably short period of analysis.     

Forced Kramers escape in single-molecule pulling experiments

The pulling-induced rupture of noncovalent bonds is studied by the overdamped Kramers theory with full account of a time-varying barrier. Mechanic pulling reduces the energy barrier and leads to loading-rate dependence of the rupture force F(u)(F(t)). Tested against Langevin dynamics, four distinct regimes are identified, including kinetic dominant, weak pulling, strong pulling, and mechanic pulling dominant. Asymptotic analyses show that F(u) approximately ln F(t) in weak pulling regime and becomes 1-(F(u)F(c)) approximately [ln(F(t))E(b)](23) in strong pulling regime. Kinetic informations such as activation energy E(b) and critical force F(c) were extracted from pulling experiments for biotin-streptavidin complex.