Hydrogel Microchambers Integrated with Organic Electrodes for Efficient Electrical Stimulation of Human iPSC‐Derived Cardiomyocytes

A hydrogel‐based microchamber with organic electrodes for efficient electrical stimulations of human induced pluripotent stem cell‐derived cardiomyocytes (hiPSC‐CMs) is described. The microchamber is made from molecularly permeable, optically transparent, and electrically conductive polyvinyl alcohol (PVA) hydrogel and highly capacitive carbon electrode modified with poly(3,4‐ethylenedioxythiophene) (PEDOT). Spheroids of hiPSC‐CMs are cultured in microchambers, and electrically stimulated by the electrode for maturation. The large interfacial capacitance of the electrodes enables several days of electrical stimulation without generation of cytotoxic bubbles even when the electrodes are placed near the spheroids. The spheroids can be cultivated in the closed microchambers because of the permeated nutrients through the hydrogel, thus the spheroids are stably addressable and the culture medium around the sealed microchambers can be simply exchanged. Synchronized beating of the spheroids can be optically analyzed in situ, which makes it possible to selectively collect electrically responsive cells for further use. As the hydrogel is electrically conductive, the amount of electrical charge needed for maturing the spheroids can be reduced by configuring electrodes on the top and the bottom of the microchamber. The bioreactor will be useful for efficient production of matured hiPSC‐CMs for regenerative medicine and drug screening.     

Total Biosynthesis of Melleolides from Basidiomycota Fungi: Mechanistic Analysis of the Multifunctional GMC Oxidase Mld7

Mushroom terpenoids are biologically and chemically diverse fungal metabolites. Among them, melleolides are representative sesquiterpenoids with a characteristic protoilludane skeleton. In this study, we applied a recently established hot spot knock-in method to elucidate the biosynthetic pathway leading to 1α-hydroxymelleolide. The biosynthesis of the sesquiterpene core involves the cytochrome P450 catalyzing stepwise hydroxylation of the Δ⁶-protoilludene framework and a stereochemical inversion process at the C5 position catalyzed by short-chain dehydrogenase/reductase family proteins. The highlight of the biosynthesis is that the flavoprotein Mld7 catalyzes an oxidation-triggered double-bond shift accompanying dehydration and acyl-group-assisted substitution with two different nucleophiles at the C6 position to afford the Δ⁷-protoilludene derivatives, such as melleolide and armillarivin. The complex reaction mechanism was proposed by DFT calculations. Of particular importance is that product distribution is regulated by interaction with the cell membrane.     

The First Observation of the Temperature-Dependent Phenomenon of Muon Catalyzed Fusion in Solid D–T Mixtures

A systematic study on muon catalyzed fusion (μCF) was conducted in solid deuterium and tritium (D–T) mixture. A variety of experimental conditions were investigated, i.e., tritium concentrations from 20 to 70%, temperatures from 5 to 16 K. A preliminary analysis result suggests a steep decrease in the dtμ-molecule formation rate with decreasing temperature, and also an increase in the probability for a muon reactivation after an α-sticking phenomenon. This revised version was published online in August 2006 with corrections to the Cover Date.     

Precise measurement of hfs constant of the muonium substituted radical in cis-polyacetylene

The state of the muon in cis-polyacetylene was studied by muon spin rotation method under high transverse magnetic field. The most of the muons are found to be in muonium substituted radical state. The hyperfine coupling constant was determined to be 91 MHz with a line width of 10 MHz.     

Spin dynamics in crystalline and amorphous DyAg

Crystalline (cr-) Dyag [CsC] structure] orders antiferro-magnetically with T_N≅60K; amorphous (am-) DyAg ferro-magnetically with T_C≈-18K. We measured the longitudinal field (LF) μ⁺SR relaxation functions G_ZZ(t) for 5K<T<300K using surface muons. In the paramagnetic state. cr-DyAg gives an exponential G_ZZ (t) in the relaxation rate rising first slowly then more rapidlynear T_N; no decoupling is observed in LF up to 0.4T. In the ordered state we see a Lorentzian Kubo-Toyabe G_ZZ(t), becoming nearly static at the lowest temperatures. Its static width is very narrow (Δ≈-7 MHz), and full dceoupling is achieved here in 0.1 T. On approaching T_N, the fluctuation rate and the static width increase mootonically bt the field distribution remains Loratzian. A LF of 0.4T is then insufficient to quench the fast exponential relaxation. In paramagnetic am-DyAg, the μ⁺ depolarization is always much faster then in cr-DyAg. At lower temperatures it is better described by a root-exponential than an exponential G_ZZ(t). Below T_C an exponentially relaxing signal with 1/3 amplitude is seen. The decoupling effect of LF up to 0.4T was negligible at all temperatures.     

Muon spin relaxation for Ar+NO2 systems in transverse and longitudinal magnetic fields

Surface muons produced in UT-MSL were introduced into argon gas of 4.0±0.2 atm with NO₂ (0–30 ppm), and muonium signals were detected in the presence of a transverse (1.7–3.4 G) and a longitudinal magnetic field (0–3.5 kG) at 295±1 K. The cross section for the transverse relaxation was (11.0±1.0)×10⁻¹⁶ cm². The relaxation rates in different longitudinal magnetic fields show that the rate does not follow the conventional equation which assumes that the relaxation occurs mainly by spin-exchange interaction. Similar measurements were performed for the Mu+O₂ system. These findings indicate that chemical reactions contribute to these relaxation rates.     

μ+SR Study of Ordering Phenomena in the Heavy-Fermion State of Ce3Pd20Ge6

Magnetic and quadrupolar ordering phenomena in a Ce₃Pd₂₀Ge₆ single crystal have been investigated by muon spin rotation/relaxation (μ⁺SR) spectroscopy. We have observed spontaneous precession of muons in zero-field below T _N =0.7 K in the antiferromagnetic state. The precession frequency follows the power law: ν(T)=ν(0)(1−T/T _N ) ⁿ . The exponent n=0.43(2) is close to the mean-field value of 0.5. The muon longitudinal spin relaxation rate 1/T ₁ is found to be nearly independent of temperature in the range of 0.3 to 2 K, i.e., across either T _N or T _Q =1.2 K, the quadrupolar ordering temperature. Two likely mechanisms for the temperature independent behavior of 1/T ₁ are suggested. This revised version was published online in September 2006 with corrections to the Cover Date.     

First-Principles Theory of Muon and Muonium Trapping in the Protein Chain of Cytochrome c and Associated Hyperfine Interactions

The microscopic details of the electron transfer in cytochrome c (cyt c) are being investigated by the Muon Spin Relaxation (μSR) technique. We are using the Hartree–Fock Cluster Procedure to determine the most likely trapping sites for μ⁺ and muonium (Mu) in the protein chain, and have performed extensive calculations in single amino acid molecules of the protein chain of cyt c. The double-bonded oxygen atom of the carboxyl group was identified as the trapping site for both μ⁺ and Mu. Utilizing the wave functions we obtained from the Hartree–Fock calculations, we have determined the hyperfine field that the μ⁺ in Mu experiences while the latter is trapped at the oxygen. This revised version was published online in September 2006 with corrections to the Cover Date.