Formation of Metal‐Assisted Stable Double Helices in Dimers of Cyclic Bis‐Tetrapyrroles that Exhibit Spring‐Like Motion

Bidipyrrin‐bridged macrocycles, prepared from Ni^II‐bridged dipyrrin‐based nanorings by intramolecular oxidative biaryl coupling reactions, yielded [2+4]‐type Zn^II‐assisted stable twisted‐ring dimers comprising two double helices. These [2+4]‐type metal complexes can be optically resolved by chiral HPLC and exhibit tunable electronic and optical properties as a result of spring‐like motions. The double helices behave as glue to connect two macrocycles and as the screws of hinges to form thermally responsive synchronized spring systems.     

Characterization of mitochondria isolated from normal and ischemic hearts in rats utilizing atomic force microscopy

Mitochondria play critical roles in both the life and the death of cardiac myocytes. Various factors, such as the loss of ATP synthesis and increase of ATP hydrolysis, impairment in ionic homeostasis, formation of reactive oxygen species (ROS), and release of proapoptotic proteins are related to the generation of irreversible damage. It has been proposed that the release of cytochrome c is caused by a swelling of the mitochondrial matrix triggered by the apoptotic stimuli. However, there is a controversy about whether or not the mitochondria, indeed, swell during apoptosis. The major advantages of atomic force microscopy (AFM) over conventional optical and electron microscopes for bio-imaging include the fact that no special coating and vacuum are required and imaging can be done in all environments--air, vacuum or aqueous conditions. In addition, AFM force-distance curve measurements have become a fundamental tool in the fields of surface chemistry, biochemistry, and material science. In this study, we used AFM to observe the morphological and property changes in heart mitochondria that were isolated from a rat myocardial infarction model. From the shape parameters of the mitochondria in the AFM topographic image, it seemed that myocardial infarction caused the mitochondrial swelling. Also, the results of force-distance measurements showed that the adhesion force of heart mitochondria was significantly decreased by myocardial in infarction. Therefore, we suggested that myocardial infarction might be the cause of mitochondrial swelling and the changes in outer membrane of heart mitochondria.     

Mechanical characteristics and morphological effect of complex crossed structure in biomaterials: fracture mechanics and microstructure of chalky layer in oyster shell

The complex crossed structures with a polymorph of calcite, termed a chalky layer, which make up much of the shell of an oyster, are composed of flames and leaflets. Two layers, folia and the chalky layer in the giant Pacific oyster (Crassostrea gigas) were examined using SEM (scanning electron microscope), micro-area-XRD (X-ray diffraction) and FT-IR (Fourier transform infrared spectrometer) to determine their morphologies and component characteristics. The chalky layer was also tested using microindentation to assess its mechanical properties, and a microcrack was generated to study the fracture mechanism of the chalky layer. From an analysis of the secondary protein structure, it was shown that the ordered structures of the two layers, α-helix and β-structure, are similar but that the unordered structures are different. Moreover, the foliated rods at the interface of the chalky layer play a key role in the crystal growth of the chalky layers. Comparing the morphology and the preferred orientation of foliated laths, the advantages of the relatively high density and low hardness of the chalky layer have interesting implications regarding the development of sophisticated complex composites.     

A hexacyclic ent-trachylobane diterpenoid possessing an oxetane ring from Mitrephora glabra

[chemical reaction: see text]. Three new ent-trachylobane diterpenoids (1-3) were isolated and structures elucidated from Mitrephora glabra Scheff. (Annonaceae). Mitrephorone A (1) possesses a hexacyclic ring system with adjacent ketone moieties and an oxetane ring, both of which are unprecedented among trachylobanes. All compounds were evaluated for cytotoxicity against a panel of cancer cells, where 1 displayed the most potent and broadest activity, and against a battery of antimicrobial assays, where all compounds were approximately equipotent.     

Porphyrin‐Ryleneimide Hybrids: Low‐Bandgap Acceptors in Energy‐Transfer Cassettes

Energy‐transfer cassettes consisting of naphthaleneimide‐fused metalloporphyrin acceptors (M=Zn and Pd) and BODIPY donors have been designed and synthesized. These systems have rigid pseudo‐tetrahedral structures with a donor‐acceptor separation of ca. 17.5 Å. Spectroscopic investigations, including femtosecond transient absorption measurements, showed efficient excitation energy transfer (EET) occurring according to the Förster mechanism. Strong fluorescence of the donor units and significant spectral overlap of the donor and acceptor subunits are prerequisites for the efficient EET in these systems.     

The aftermath of the interplay between the endoplasmic reticulum stress response and redox signaling

The endoplasmic reticulum (ER) is an essential organelle of eukaryotic cells. Its main functions include protein synthesis, proper protein folding, protein modification, and the transportation of synthesized proteins. Any perturbations in ER function, such as increased demand for protein folding or the accumulation of unfolded or misfolded proteins in the ER lumen, lead to a stress response called the unfolded protein response (UPR). The primary aim of the UPR is to restore cellular homeostasis; however, it triggers apoptotic signaling during prolonged stress. The core mechanisms of the ER stress response, the failure to respond to cellular stress, and the final fate of the cell are not yet clear. Here, we discuss cellular fate during ER stress, cross talk between the ER and mitochondria and its significance, and conditions that can trigger ER stress response failure. We also describe how the redox environment affects the ER stress response, and vice versa, and the aftermath of the ER stress response, integrating a discussion on redox imbalance-induced ER stress response failure progressing to cell death and dynamic pathophysiological changes.Subject terms: Mechanisms of disease, Cell biology     

A polymeric photobase generator containing oxime–urethane groups: Crosslinking reaction and application to negative photoresist

A polymeric photobase generator containing oxime–urethane groups was prepared by copolymerization of methyl methacrylate and methacryloxyethyl benzophenoneoxime urethane, and its photo and thermal crosslinking reaction after irradiation was examined from the measurement of UV and IR absorption spectral changes, insoluble fraction, and molecular weight changes. The photo‐crosslinking reaction of the copolymer film was more efficient when irradiations were carried out with 310 nm UV light in the presence of benzophenone than with 254 nm UV light without the addition of benzophenone. The crosslinking reaction increased after postexposure baking (PEB), and this thermal crosslinking reaction mechanism was studied from the identification of the photolysis products of a model compound, benzophenoneoxime phenylurethane, by a high‐performance liquid chromatography. The results indicate that the thermal crosslinking reaction of the copolymer after PEB is due to the formation of urea‐type chemical bonds. Resist properties of the copolymer were examined from the measurement of normalized thickness and micropattern development. A negative tone image with a resolution of 2 μm was obtained with this copolymer, having a sensitivity (D) of 1200 mJ/cm² and contrast (γ_n) of 1.31, when irradiation was carried out with 310 nm UV light in the presence of benzophenone following chloroform development. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 975–984, 2004     

Versatile Photophysical Properties of meso‐Aryl‐Substituted Subporphyrins: Dipolar and Octupolar Charge‐Transfer Interactions

Donor–acceptor systems based on subporphyrins with nitro and amino substituents at meta and para positions of the meso‐phenyl groups were synthesized and their photophysical properties have been systematically investigated. These molecules show two types of charge‐transfer interactions, that is, from center to periphery and periphery to center depending on the peripheral substitution, in which the subporphyrin moiety plays a dual role as both donor and acceptor. Based on the solvent‐polarity‐dependent photophysical properties, we have shown that the fluorescence emission of para isomers originates from the solvatochromic, dipolar, symmetry‐broken, and relaxed excited states, whereas the non‐solvatochromic fluorescence of meta isomers is of the octupolar type with false symmetry breaking. The restricted meso‐(4‐aminophenyl) rotation at low temperature prevents the intramolecular charge‐transfer (ICT)‐forming process. The two‐photon absorption (TPA) cross‐section values were determined by photoexcitation at 800 nm in nonpolar toluene and polar acetonitrile solvents to see the effect of ICT on the TPA processes. The large enhancement in the TPA cross‐section value of approximately 3200 GM (1 GM=10^?50 cm⁴ s photon^?1) with donor–acceptor substitution has been attributed to the octupolar effect and ICT interactions. A correlation was found between the electron‐donating/‐withdrawing abilities of the peripheral groups and the TPA cross‐section values, that is, p‐aminophenyl>m‐aminophenyl>nitrophenyl. The increased stability of octupolar ICT interactions in highly polar solvents enhances the TPA cross‐section value by a factor of approximately 2 and 4, respectively, for p‐amino‐ and m‐nitrophenyl‐substituted subporphyrins. On the other hand, the stabilization of the symmetry‐broken, dipolar ICT state gives rise to a negligible impact on the TPA processes.     

Assemblies of supramolecular porphyrin dimers in pentagonal and hexagonal arrays exhibiting light-harvesting antenna function

Porphyrin-based supramolecular macrocyclic arrays were synthesized as mimics of photosynthetic light-harvesting (LH) antennae. Pentameric and hexameric macrocyclic porphyrin arrays EP5 and EP6 were constructed by complementary coordination of m-bis(ethynylene)phenylene-linked zinc-imidazolylporphyrin Zn-EP-Zn. The proton NMR spectra of noncovalently linked N-EP5 and N-EP6 indicate fast rotation of the porphyrin moieties along the ethyne axis. These macrocycles were covalently linked and identified as C-EP5 (6832 Da) and C-EP6 (8199 Da) by mass spectrometry. Fluorescence quantum yields of C-EP2 (10.0%), C-EP5 (10.1%), and C-EP6 (11.0%), even larger than that of the unit coordination dimer C-EP1 (9.3%), were significantly increased from those of the series without the ethynylene linkage. The order of increasing fluorescence quantum yields was parallel to that of decreasing fluorescence lifetimes (C-EP1 (1.65 ns), C-EP2 (1.45 ns), C-EP5 (1.42 ns), and C-EP6 (1.38 ns)), indicating that the radiative decay rate kF increased relative to the other decay rates with an increase in the number of ring components. Based on the exciton-exciton annihilation and anisotropy depolarization times, the excitation energy hopping (EEH) times in these macrocyclic systems were obtained as 21 ps for C-EP5 and 12.8 ps for C-EP6. EEH times depend strongly on the orientation factor of the component transition dipoles in the macrocyclic arrays. The hexagonal macrocyclic array with an orientation of better transition dipole coupling resulted in faster EEH time compared to the pentagonal one.