Production of single-chain variable fragment antibody (scFv) in fed-batch and continuous culture of Pichia pastoris by two different methanol feeding methods

This study examined the effects of two methods of methanol feeding, DO-stat and methanol concentration control, in fed-batch and continuous cultures of Pichia pastoris on cell growth and single-chain variable fragment antibody (scFv) expression. By maintaining the methanol concentration at 3.9 g l(-1) in fed-batch culture, a scFv concentration of 198 mg l(-1) was obtained. In continuous culture using both methanol feeding methods, the scFv concentration in the fermentation broth increased with a decreasing dilution rate. A maximum scFv concentration of 810 mg l(-1) at a dilution rate of 0.0094 h(-1) was obtained by maintaining the methanol concentration at 3.9 g l(-1). Although the specific methanol consumption rate was the same for both methods, the specific productivity of scFv was higher in methanol concentration control from 0.0094 to 0.049 h(-1) than it was in DO-stat control. Therefore, continuous culture with methanol feeding by the concentration control method shows promise for the industrial scale production of recombinant proteins by Pichia pastoris.     

Thermochromism in an organic crystal based on the coexistence of sigma- and pi-dimers

Transition-metal complexes and organic radical molecules can be used to make electric conductors and ferromagnets, the optical properties of which can be controlled by changing temperature and are used as molecular switches and sensors. Whereas a number of organic radicals in solution show temperature-dependent optical properties, such behaviour in crystalline forms is more rare. Here, we show a fully reversible continuous thermochromism with a unique mechanism in purely organic crystals of diazaphenalenyl radical. This behaviour is based on changes in the diazaphenalenyl dimers coexisting in the crystal. From the X-ray crystal structure analyses and temperature-dependent visible spectra, we conclude the presence of a thermal equilibrium between sigma-bonded and pi-bonded dimers, which are separated by 2.62(6) kcal mol(-1). This conclusion is supported by room-temperature electron spin resonance spectra of the solid, which showed signals that are attributable to a thermally accessible triplet state of the pi-dimer structure. This proves the coexistence of two dimers of different bonding natures in the crystal, causing it to demonstrate thermometer-like behaviour.     

Residual Stress within Metallic Model Made by Selective Laser Melting Process

In order to improve the mechanical properties and the dimensional accuracy of the steel model produced by the selective laser melting process, the distribution of residual stress within the model is measured, and some methods for reducing the residual stress are proposed. The experimental results show that a large tensile stress remains in the surface layer of the model. Heat treatment at 600 and 700 °C for one hour reduces the residual stress effectively by about 70%. Re-scanning of laser and heating of the powder bed decrease the tensile stress by 55% and 40%, respectively.