Dynamic modeling of an immobilized cell reactor

A mathematical model has been developed to describe the dynamic aerobic reaction occurring in a semibatch type of mixed flow reactor, containing cells immobilized in gel beads. This modeling is an extension of that developed in our previous study, for an immobilized cell reactor involving ethanol fermentation. In contrast to anaerobic reactions such as ethanol fermentation, (wherein the influent substrate concentration can be set at any desired level), aeration becomes necessary to provide additional substrate (oxygen) for most aerobic reactions occurring in immobilized cell reactors. Tobacco cell cultivation was chosen as a representative aerobic reaction, and the effect of aeration was assessed in terms of the volumetric coefficient of oxygen from gas to liquid phases.     

Cyclic Triradicals Composed of Iminonitroxide–Gold(I) with Intramolecular Ferromagnetic Interactions

A triangular gold(iminonitroxide‐2‐ide) trimer complex ( 5 ) was prepared and investigated to determine its magnetic properties. The results showed that the metalloid triradical is highly stable, even in solution under aerated conditions. The intramolecular exchange interaction of 5 was found to be positive (J_intra/k_B≈+29 K), thus showing that 5 is in a quartet ground state. In addition, a silver sandwich complex ( 5 ‐Ag⁺‐ 5 ) was prepared and its electronic and magnetic properties were also clarified.     

A Kinetically Stabilized Nitrogen-Doped Triangulene Cation: Stable and NIR Fluorescent Diradical Cation with Triplet Ground State

A kinetically-stabilized nitrogen-doped triangulene cation derivative has been synthesized and isolated as the stable diradical with a triplet ground state that exhibits near-infrared emission. As was the case for a triangulene derivative we previously synthesized, the triplet ground state with a large singlet-triplet energy gap was experimentally confirmed by magnetic measurements. In contrast to the triangulene derivative, the nitrogen-doped triangulene cation derivative is highly stable even in solution under air and exhibits near-infrared absorption and emission because the alternancy symmetry of triangulene is broken by the nitrogen cation. Breaking the alternancy symmetry of triplet alternant hydrocarbon diradicals by a nitrogen cation would therefore be an effective strategy to create stable diradicals possessing magnetic properties similar to the parent hydrocarbons but with different electrochemical and photophysical properties.     

Magnetic interaction of tri- and di-oxytriphenylamine radical cation FeCl4 salts

The tetrachloroferrates of the 2,2':6',2':6',6-trioxytriphenylamine (TOT.+.FeCl4-) and 2,2':6',2'-dioxytriphenylamine (DOT.+.FeCl4-) radical cations were prepared, and their structures, magnetic properties, and the relationship between them were investigated. The TOT.+ moiety had a highly planar structure and packed as a dimer surrounded by tetrachroferrates, which also formed a dimer structure. The magnetic properties of TOT.+.FeCl4- were characterized by strong (2J/kB=approximately -1.3x10(3) K, H=-2JS1/2.S1/2) and weak (2J/kB=-1.76 K, H=-2JS5/2.S5/2) antiferromagnetic interactions due to the (TOT.+)2 and (FeCl4-)2 structures, respectively. DOT.+ had a twisted form and no dimer formation was observed between the DOT.+'s and FeCl4-'s. Instead, short contacts between the DOT.+ and chlorine atoms and between the DOT.+'s producing a DOT.+ chain were observed. The magnetic properties of DOT.+.FeCl4- were characterized by a 3D magnetic phase transition to an antiferromagnet with TN=approximately 8 K.     

Ab initio and DFT studies of the spin-orbit and spin-spin contributions to the zero-field splitting tensors of triplet nitrenes with aryl scaffolds

Spin-orbit and spin-spin contributions to the zero-field splitting (ZFS) tensors (D tensors) of spin-triplet phenyl-, naphthyl-, and anthryl-nitrenes in their ground state are investigated by quantum chemical calculations, focusing on the effects of the ring size and substituted position of nitrene on the D tensor. A hybrid CASSCF/MRMP2 approach to the spin-orbit term of the D tensor (D(SO) tensor), which was recently proposed by us, has shown that the spin-orbit contribution to the entire D value, termed the ZFS parameter or fine-structure constant, is about 10% in all the arylnitrenes under study and less depends on the size and connectivity of the aryl groups. Order of the absolute values for D(SO) can be explained by the perturbation on the energy level and spatial distributions of π-SOMO through the orbital interaction between SOMO of the nitrene moiety and frontier orbitals of the aryl scaffolds. Spin-spin contribution to the D tensor (D(SS) tensor) has been calculated in terms of the McWeeny-Mizuno equation with the DFT/EPR-II spin densities. The D(SS) value calculated with the RO-B3LYP spin density agrees well with the D(Exptl) -D(SO) reference value in phenylnitrene, but agreement with the reference value gradually becomes worse as the D value decreases. Exchange-correlation functional dependence on the D(SS) tensor has been explored with standard 23 exchange-correlation functionals in both RO- and U-DFT methodologies, and the RO-HCTH/407 method gives the best agreement with the D(Exptl) -D(SO) reference value. Significant exchange-correlation functional dependence is observed in spin-delocalized systems such as 9-anthrylnitrene (6). By employing the hybrid CASSCF/MRMP2 approach and the McWeeny-Mizuno equation combined with the RO-HCTH/407/EPR-II//U-HCTH/407/6-31G* spin densities for D(SO) and D(SS), respectively, a quantitative agreement with the experiment is achieved with errors less than 10% in all the arylnitrenes under study. Guidelines to the putative approaches to D(SS) tensor calculations are given.     

Tandem arrays of TEMPO and nitronyl nitroxide radicals with designed arrangements on DNA

Herein we describe one-dimensional electron-spin arrays consisting of two different organic radicals with the designed arrangement based on the DNA sequence. Two mismatch-binding ligands carrying 2,2,6,6-tetramethylpiperidine N-oxide (TEMPO) and nitronyl nitroxide selectively bind to the predetermined sites on double stranded DNA. By using the two mismatch-binding ligands carrying the organic radicals as the glue for DNA, electron-spin assembly could be successfully synchronized with the hybridization. Periodically and tandemly arranged, two kinds of organic radical molecules at designed positions might be useful for an approach to build up scalable qubits of electron-spin-based quantum computing. The approach using DNA nanostructures as a scaffold to assembly functional small molecules can afford one of the promising ways for the future application of DNA nanostructures and nanotechnology.     

What Factors Determine Hierarchical Structure of Microbial Cellulose – Interplay among Physics,Chemistry and Biology –

A microbial cellulose film (pellicle), prepared by Acetorbactor xylinum, is a supramolecule system, absorbing a huge amount of water (99% by weight). To elucidate the affinity to water, we investigated the hierarchical structure in a pellicle by using ultra-small-angle and small-angle neutron scattering, observing a wide range of length scales from nm to µm. We successfully determined mass fractal dimensions for the amorphous structure, which hierarchically varies local concentration fluctuations, bundle and network, appeared as the length scale increases. On a basis of these findings, we discuss to address a question what factors determine the hierarchy in the microbial cellulose. This is a new topic of soft matter science, regarded as reaction-induced self-assembly in a non-equilibrium open system, therein soft matter physics, biochemistry and cell biology crucially interplay.     

Self-assembly via a complex phase transition in mixtures of polystyrene-block -polybutadiene block copolymer and poly(methyl vinyl ether)

The self-assembly of a binary mixture of polystyreneblock-polybutadiene (SB) and poly(methyl vinyl ether) (PVME) was studied by transmission electron microscopy and time-resolved light scattering. The self-assembly studied involved first microphase separation, in which a microdomain structure composed of polybutadiene block chains (PB) was formed in a matrix composed of polystyrene block chains (PS) and PVME homopolymers, and subsequently macrophase separation of the PVME from the microdomain phase of SB. The microphase separation was induced in a film preparation process using a solution cast method at room temperature. The macrophase separation was induced by rapidly heating the film specimens to above a critical temperature where PVME and PS undergo spinodal decomposition (SD). This complex phase transition, involving microphase separation followed by macrophase separation, was found to generate a superlattice structure (or a modulated structure) with two characteristic spacings: A_macro associated with the SD and A_micro associated with the microphase separation, both being generally time-dependent. The growth of the “macrodomains” was found to be pinned at A_macro ˜ 840 nm due to the elastic effect of the microdomain structure. The microdomain structure with A_micro ˜ 57 nm was found to undergo a morphological transition (a transition between two ordered phases of block copolymers) as a consequence of the local composition change of the two polymers induced by the SD.