In aging carbon‐depleted cultures of an industrial b‐lactam‐producing strain of Penicillium chrysogenum the fragmentation and autolysis of mycelia was coupled with high production of NH3 (71.6 mM) and oxalate (37.8 mM) and low production of b‐lactam (0.24 mM). Round‐ended hyphal fragments consisting of two cells were found to be the dominant surviving forms, and addition of an extra dose of glucose in the autolytic phase reversed the biomass degradation by reinitiating cell growth.
The complexation of the cationic, water soluble ammonium pillar [6]arene was investigated with Dapoxyl sodium sulfonate. Large fluorescence enhancement was observed upon partial inclusion and the resulting complex was used as the first pillararene-based indicator displacement system for the selective recognition of adenosine-5'-triphosphate.
The two most promising approaches for preparing solid contacts (SCs) for polymeric membrane based ion‐selective electrodes (ISEs) are based on the use of large surface areas conducting materials with high capacitance (e. g., various carbon nanotubes) and redox active materials (e. g. conducting polymers). While many of the essential requirements for the potential stability of SCISEs were addressed, the E0 reproducibility and its predictability, that would enable single use of such electrodes without calibration is still a challenge, i. e., the fabrication of electrodes with sufficiently close E0 and slope values to enable the characterization of large fabrication batches through the calibration of only a small number of electrodes. The most generic solution seems to be the adjustment of the E0 potential by polarization prior to the application of the ion‐selective membrane. This approach proved to be successful in case of conducting polymer‐based solid contacts, but has to be still explored for capacitive solid contact based ISEs, which is the purpose of this paper. We have chosen a well‐established highly lipophilic multi‐walled carbon nanotube (MWCNT), i. e. octadecane modified MWCNT (OD‐MWCNT), that is investigated in the comparative context of a similarly lipophilic conducting polymer solid contact (a perfluorinated alkanoate side chain functionalized poly(3,4‐ethylenedioxythiophene)). While, the OD‐MWCNT based SCISEs had inherently small standard deviation of their E0 values (less than 5 mV) this could be further improved by external polarization and short circuiting the SCISEs.
Methylotrophic yeast Pichia pastoris is an ideal host organism for recombinant protein production. However, adequate methanol feed is still a critical point of successful product formation in P. pastoris Mut 5 fermentations. Three methanol feed strategies were tested: an organic vapor sensor, a dissolved oxygen controlled methanol addition and a predetermined model, as well. The organic vapor sensor proved to be unsuitable for methanol concentration measurements when samples were taken from the head space of the bioreactor, but may have the potential to substitute expensive gas analyzers in methanol fed-batch with a suitable selector submerged into the fermentation media. Dissolved oxygen and substrate consumption did not show strict mathematical relation. However, drop of dissolved oxygen tension for periodic methanol addition may be applied for the determination of the substrate concentration in the media. The rate of methanol consumption shows peaks at 0.45 and 0.95% (v/v) substrate concentrations. The rate of the specific methanol consumption of our model organism was determined. Based on the value of 0.023 h`, which is significantly less than suggested by earlier experiments, a successful predetermined methanol feed strategy was set up.
Solid-contact ion-selective electrodes (SCISEs) can overcome essential limitations of their counterparts based on liquid contacts. However, attaining a highly reproducible and predictable E 0 , especially between different fabrication batches, turned out to be difficult even with the most established solid-contact materials, i.e., conducting polymers and large-surface-area conducting materials (e.g., carbon nanotubes), that otherwise possess excellent potential stability. An appropriate batch-to-batch E 0 reproducibility of SCISEs besides aiding the rapid quality control of the electrode manufacturing process is at the core of their “calibration-free” application, which is perhaps the last major challenge for their routine use as single-use “disposable” or wearable potentiometric sensors. Therefore, here, we propose a new class of solid-contact material based on the covalent functionalization of multiwalled carbon nanotubes (MWCNTs) with a chemically stable redox molecule, (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO). This material combines the advantages of (i) the large double-layer capacitance of MWCNT layers, (ii) the adjustable redox couple ratio provided by the TEMPO moiety, (iii) the covalent confinement of the redox couple, and (iv) the hydrophobicity of the components to achieve the potential reproducibility and stability for demanding applications. The TEMPO-MWCNT-based SC potassium ion-selective electrodes (K + -SCISEs) showed excellent analytical performance and potential stability with no sign of an aqueous layer formation beneath the ion-selective membrane nor sensitivity toward O 2 , CO 2 , and light. A major convenience of the fabrication procedure is the E 0 adjustment of the K + -SCISEs by the polarization of the TEMPO-MWCNT suspension prior to its use as solid contact. While most E 0 reproducibility studies are limited to a single fabrication batch of SCISEs, the use of prepolarized TEMPO-MWCNT resulted also in an outstanding batch-to-batch potential reproducibility. We were also able to overcome the hydration-related potential drifts for the use of SCISEs without prior conditioning and to feature application for accurate K + measurements in undiluted blood serum.
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