Metal-dependent regioselective oxidative coupling of 5,10,15-triarylporphyrins with DDQ-Sc(OTf)3 and formation of an oxo-quinoidal porphyrin

[reaction: see text] Regioselectivity of the oxidative coupling of 5,10,15-triarylporphyrin metal complexes with DDQ-Sc(OTf)(3) was dependent on the central metal and meso-aryl substituent. Oxo-quinoidal porphyrin was obtained from Ni(II) porphyrin under the same conditions.     

Synthetic studies on carbapenem antibiotics from penicillins. IV. Stereoselective kinetic protonation of a chiral azetidinone enolate

A stereoselective kinetic protonation of the azetidinone enolate $\text{B}$ was studied and an efficient synthesis of$\text{2}$(cis) was achieved via aldol reaction of $\text{5}$ with acetone followed by the kinetic protonation with Ph₃SnH as proton source.     

Efficient excitation energy transfer in long meso-meso linked Zn(II) porphyrin arrays bearing a 5,15-bisphenylethynylated Zn(II) porphyrin acceptor

Electronically coupled porphyrin arrays are suitable for artificial light harvesting antenna in light of a large absorption cross-section and fast excitation energy transfer (EET). Along this line, an artificial energy transfer model system has been synthesized, comprising of an energy donating meso-meso linked Zn(II) porphyrin array and an energy accepting 5,15-bisphenylethynylated Zn(II) porphyrin linked via a 1,4-phenylene spacer. This includes an increasing number of porphyrins in the meso-meso linked Zn(II) porphyrin array, 1, 2, 3, 6, 12, and 24 (Z1A, Z2A, Z3A, Z6A, Z12A, and Z24A). The intramolecular singlet-singlet EET processes have been examined by means of the steady-state and time-resolved spectroscopic techniques. The steady-state fluorescence comes only from the acceptor moiety in Z1A-Z12A, indicating nearly the quantitative EET. In Z24A that has a molecular length of ca. 217 A, the fluorescence comes largely from the acceptor moiety but partly from the long donor array, indicating that the intramolecular EET is not quantitative. The transient absorption spectroscopy has provided the EET rates in real time scale: (2.5 ps)(-1) for Z1A, (3.3 ps)(-1) for Z2A, (5.5 ps)(-1) for Z3A, (21 ps)(-1) for Z6A, (63 ps)(-1) for Z12A, and (108 ps)(-1) for Z24A. These results have been well explained by a revised F?rster equation (Sumi formula), which takes into account an exciton extending coherently over several porphyrin pigments in the donor array, whose length is not much shorter than the average donor-acceptor distance. Advantages of such strongly coupled porphyrin arrays in light harvesting and transmission are emphasized in terms of fast EET and a large absorption cross-section for incident light.     

Asymmetric synthesis of permethric acid. stereochemistry of chiral copper carbenoid reaction

The most effective optical isomer (1$\text{R}$-$\text{cis}$) of permethric acid ($\text{2}$, R = H), a potent intermediate in the production of synthetic pyrethroid, was enantioselectively prepared.     

Imaging of enzyme activity by scanning electrochemical microscope equipped with a feedback control for substrate-probe distance

The enzymatic activity of diaphorase (Dp) immobilized on a solid substrate was characterized using a scanning electrochemical microscope (SECM) with shear force feedback to control the substrate-probe distance. The shear force between the substrate and the probe was monitored with a tuning fork-type quartz crystal and used as the feedback control to set the microelectrode probe close to the substrate surface. The sensitivity and the contrast of the SECM image were improved in the constant distance mode (distance, 50 nm) with the shear force feedback compared to the image in the constant height mode without the feedback. By using this system, the SECM and topographic images of the immobilized diaphorase were simultaneously measured. The microelectrode tip used in this study was ground aslant like a syringe needle in order to obtain the shaper topographic images. This shape was also effective for avoiding the interference during the diffusion of the enzyme substrates.     

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.     

Effect of conformational heterogeneity on excitation energy transfer efficiency in directly meso-meso linked Zn(II) porphyrin arrays

We have investigated the overall excitation energy relaxation dynamics in linear porphyrin arrays as well as the energy transport phenomena by attaching an energy acceptor to one end of a linear porphyrin array by using steady state and time-resolved spectroscopic measurements. We have revealed that the solvation dynamics as well as the conformational dynamics contributes significantly to the energy relaxation processes of linear porphyrin arrays. Consequently, long porphyrin arrays no longer serve as good energy transmission elements in donor-acceptor linked systems due to conformational heterogeneities which provide the non-radiative deactivation channels as energy quenchers.     

Thermal splitting of Bis-Cu(II) octaphyrin(1.1.1.1.1.1.1.1) into two Cu(II) porphyrins

When heated, bis-Cu(II) octaphyrin(1.1.1.1.1.1.1.1) is quantitatively split into two Cu(II) porphyrins both in solution and film states, which is accompanied by large absorption spectral changes.