Functional evaluation of iron oxypyriporphyrin in protein heme pocket

The iron complex of oxypyriporphyrin, a porphyrinoid containing a keto-substituted pyridine, was coupled with apomyoglobin. The reconstituted ferric myoglobin was found to be five-coordinate without iron-bound water molecules. The anionic ligands such as CN (-) and N 3 (-) bound the myoglobin with high affinities, while neutral imidazole did not. The IR observation indicated that the azide complex was pure high-spin, although the corresponding native protein was in the spin-state equilibrium. The reduced myoglobin was five-coordinate but exhibited no measurable affinity for O 2. The affinity for CO was lowered down to 1/2400 as compared with native myoglobin. These anomalies were ascribed to the deformation in the iron coordination core after the replacement of one of the four pyrroles with a larger pyridine ring. The ligand binding analyses for the ferric and ferrous myoglobin suggest that the proximal histidine pulls the iron atom from the deformed core to reduce the interaction between the iron and exogenous ligands. Similarity of the reconstituted myoglobin with guanylate cyclase, a NO-responsive signaling hemoprotein, was pointed out.     

LOV-like flavin-Cys adduct formation by introducing a Cys residue in the BLUF domain of TePixD

BLUF and LOV are blue-light sensor domains that possess flavin as a common chromophore but exhibit distinct photoreactions. Ile66 located in the BLUF domain of a cyanobacterial photosensor protein, TePixD, was replaced with Cys to mimic the LOV domain. Light-induced Fourier transform infrared spectra of the I66C TePixD showed that a flavin-Cys adduct, typical of the photoinduced intermediates of LOV domains, was formed in the I66C BLUF domain. This result demonstrates that different types of flavin photoreactions can be realized in the same domain if key amino acids are properly arranged near the flavin and the domain structure itself is not a crucial factor to determine the photoreaction type.     

Artificial polymeric receptors on the cell surface promote the efficient cellular uptake of quantum dots

In our previous paper, secondary-amine appended cationic polymer 1 was used as a scaffold to display artificial receptors on a cell surface (R. Kamitani et al., ChemBioChem, 2009, 10, 230). This polymer can be retained on the cell surface for more than 30 min before being slowly internalized into the cells. In this study, our aim is to achieve the efficient internalization of quantum dots (QDs) into target cells via artificial receptors on the polymer. As a receptor molecule, N-acetylglucosamine (GlcNAc) moieties were introduced into the polymer, and GlcNAc binding protein-displaying QDs were used as a ligand. We found that ligand-presenting QDs could be internalized effectively into cells via polymer-mediated endocytosis, whereas QDs were not internalized into untreated cells. These data suggest that our method based on cell-surface engineering using polymers affords a new approach to the delivery of various poorly permeable nanoparticles into cells.     

Azide-Containing Phenolic Resin as a Negative Deep Uv Resist

A negative photoresist has been developed by partial esterification of poly(p-hydroxystyrene) with p-azidobenzenesulfonyl chloride. About 10% of esterification is sufficient to sensitize the polymer to light in the wavelength region between 240 and 300 nm. The dose required to insolubilize the polymer was 80 mJ/cm². The resolution capability is not as high as expected because of the swelling of photoinsolubilized resist films in an aqueous alkaline developer.     

Three-Step Spin State Transition and Hysteretic Proton Transfer in the Crystal of an Iron(II) Hydrazone Complex

A proton–electron coupling system, exhibiting unique bistability or multistability of the protonated state, is an attractive target for developing new switchable materials based on proton dynamics. Herein, we present an iron(II) hydrazone crystalline compound, which displays the stepwise transition and bistability of proton transfer at the crystal level. These phenomena are realized through the coupling with spin transition. Although the multi-step transition with hysteresis has been observed in various systems, the corresponding behavior of proton transfer has not been reported in crystalline systems; thus, the described iron(II) complex is the first example. Furthermore, because proton transfer occurs only in one of the two ligands and π electrons redistribute in it, the dipole moment of the iron(II) complexes changes with the proton transfer, wherein the total dipole moment in the crystal was canceled out owing to the antiferroelectric-like arrangement.     

Electrochemistry of monoazahemin reconstituted myoglobin at an indium oxide electrode

Monoazahemin reconstituted myoglobin was prepared and its electrochemical behavior was studied in comparison with native myoglobin. For both myoglobins well-defined voltammograms were clearly obtained at highly hydrophilic surfaces of indium oxide electrodes. Although monoazahemin showed a more positive redox potential than hemin (measured in methanol), monoazahemin reconstituted myoglobin showed a more negative redox potential than native myoglobin in a 50 mM bis-Tris buffer solution (pH 6.5), suggesting that for both native and reconstituted myoglobins the heme environment including proximal histidine as an axial ligand of the redox center plays an important role in determining the redox potential. Also, a unique electrochemical response of cyano-monoazahemin reconstituted myoglobin was demonstrated.     

An isocyanide probe for heme electronic structure: bis(tert-butylisocyanide) complex of diazaporphyrin showing a unique (dxy)2(dxz, dyz)3 ground state

Isocyanide-bound model hemes always adopt the (dxz, dyz)4(dxy)1 ground state, however, we have found that the replacement of porphyrin by diazaporphyrin leads to the formation of an unprecedented low-spin bis(tert-butylisocyanide) complex with the (dxy)2(dxz, dyz)3 ground state.     

Does bulk metallic glass of elemental Zr and Ti exist?

To verify the high-pressure formation of the bulk metallic glass in elemental Zr and Ti, which Zhang and Zhao [Nature (London) 430, 332 (2004)] and Y. Wang et al. [Phys. Rev. Lett. 95, 155501 (2005)] recently reported, the high-pressure states were investigated by our newly developed in situ angle-dispersive x-ray diffraction using a two-dimensional detector and x-ray transparent anvils. Despite the disappearance of all the Bragg peaks in the one-dimensional energy-dispersive data, two-dimensional angle-dispersive data showed several intense Bragg spots even at the conditions where the amorphization was reported. This finding suggests that Zr and Ti do not transform into an amorphous state, but that their grain size becomes large, which causes the missing Bragg peaks in energy-dispersive data.     

Photoelectron spectra of aminopyridines and cyanopyridines

Photoelectron spectra of 2?, 3?, and 4-aminopyridines and 2?, 3?, and 4? cyanopyridines were measured and assigned. The second highest occupied orbitals of the aminopyridines and 2? and 3-cyanopyridines and the highest occupied orbital of 4-cyanopyridine were concluded to be the lone pair orbital of the ring nitrogen.     

Role of heme propionates of myoglobin in vibrational energy relaxation

The role of heme propionates of myoglobin in vibrational energy relaxation was studied by time-resolved resonance Raman spectroscopy. Time-resolved anti-Stokes spectra were measured to monitor the vibrational energy relaxation of the heme. The decay rates of the band intensities were compared between wild-type myoglobin and etioheme-substituted myoglobin where the heme lacks hydrogen-bonding side chains. The decay rates of the anti-Stokes intensities of the latter were less than those of the former, providing strong support for a theoretical proposal that the propionates and their coupling to solvent bath play an important role in the dissipation of excess energy of the excited heme in solvated wild-type myoglobin.