Thermodynamic Control of Domain Swapping by Modulating the Helical Propensity in the Hinge Region of Myoglobin

Domain swapping is an exception to Anfinsen's dogma, and more than one structure can be produced from the same amino acid sequence by domain swapping. We have previously shown that myoglobin (Mb) can form a domain‐swapped dimer in which the hinge region is converted to a helical structure. In this study, we showed that domain‐swapped dimerization of Mb was achieved by a single Ala mutation of Gly at position 80. Multiple Ala mutations at positions 81 and 82 in addition to position 80 facilitated dimerization of Mb by stabilization of the dimeric states. Domain swapping tendencies correlated well with the helical propensity of the mutated residue in a series of Mb mutants with amino acids introduced to the hinge region. These findings demonstrate that a single mutation in the hinge loop to modify helical propensity can control oligomer formation, providing new ideas to create high‐order protein oligomers using domain swapping.     

Palladium‐Catalyzed C−H Iodination of Arenes by Means of Sulfinyl Directing Groups

C?H iodination of aromatic compounds has been accomplished with the aid of sulfinyl directing groups under palladium catalysis. The reaction proceeds selectively at the peri‐position of polycyclic aryl sulfoxides or at the ortho‐position of phenyl sulfoxides. The iodination products can be further converted via iterative catalytic cross‐coupling at the expense of the C?I and C?S bonds. Computational studies suggest that peri‐C?H palladation would proceed via a non‐directed pathway, wherein neither of the sulfur nor oxygen atom of the sulfinyl group coordinates to the palladium before and at the transition state.     

Discotic Liquid Crystals of Transition Metal Complexes, 19: Discotic Mesomorphism and Double Clearing Behavior of Octakis(dialkoxyphenyl)phthalocyanine Derivatives

Eight novel octakis(3,4-dialkoxyphenyl)- phthalocyanine derivatives, Cn-M (2, M=2H; 3, M=Ni; 4, M=Cu; a, decyloxy; b, undecyloxy; c, dodecyloxy), have been synthesized and characterized. It was found that each of the derivatives exhibits discotic liquid crystalline properties, and that each of the Cn–Cu (4) derivatives has two kinds of D_rd2( P 2₁/ a ) mesophases. These Cn–Cu (4a,b,c) and C₁₂–2H (2c) derivatives exhibit a unique double clearing behavior.     

Operating Limits for Stable Growth of Silicon Fibers with Diameter Less Than 150 μm by Modified μ-PD Method

The μ-PD method originally developed for oxide crystals has been modified and applied for filamentary silicon crystal growth. Our main modification of μ-PD method is concerned with an arrangement of melt permeable feeder which is inserted into the nozzle. The feeder finishes by a sharp tip the diameter of which (is almost the same as that of the desired semiconductor fiber, i.e., less than 150 μm. Silicon fibers were grown from the small liquid pool at the end of the feeder. Three types of crucible-die arrangement were designed and tested. The best results were obtained with the help of inclined insert made of graphite fibers because of its ability to quench oscillations and longer operation life. Fiber crystals, 100 μm in diameter and 70 mm in length, have been grown successfully. Small meniscus stability, operating limits of μ-PD method and silicon carbide formation during the growth process are discussed.     

NMR studies on the ligand exchange reactions between diaryl tellurides and phenyllithium: Detection of hypervalent triaryl tellurium ate complexes

Diaryl tellurides undergo rapid ligand exchange and disproportionation reactions on treatment with phenyllithium at −78°C. Triarylteliuranes [10-Te-3(C₃)]⁻ Li⁺ were identified as discrete intermediates during the reactions by ¹²⁵Te, ¹H, ¹³C, and CH-COSY NMR studies.     

Direct Oxidation of Propylene with Molecular Oxygen Over Ti-Modified Sulfated Zirconia Catalyst, 2. In Situ Diffuse Reflectance FT-IR Study

During the reaction of propylene with O₂, in situ Diffuse Reflectance FT-IR measurements were performed over Ti-modified SZ and SZ catalysts. Without O₂, the main bands characteristic of (branched) hydrocarbons, formed by oligomerization leading to, finally, carbonaceous residue, appeared within the range of 3900-2750 cm^-1, which was affected by the bands of surface OH groups. Investigation of these IR bands showed the role of molecular oxygen not only to limit the formation of carbonaceous species on the catalyst surface, but also to form oxygenates and these findings were in good agreement with the results of catalytic reaction.     

Module-based assembly of copper(II) chloranilate compounds: syntheses, crystal structures, and magnetic properties of [[Cu(2)(CA)(terpy)(2)][Cu(CA)(2)]](n)() and [[Cu(2)(CA)(terpy)(2)(dmso)(2)][Cu(CA)(2)(dmso)(2)](EtOH)](n)(H(2)CA = chloranilic acid, terpy = 2,2':6',2' '-terpyridine, dmso = dimethyl sulfoxide)

Two new copper(II) compounds of chloranilate and 2,2':6',2' '-terpyridine have been synthesized, and the structures have been solved by the single-crystal X-ray diffraction method. The crystal structure of [[Cu(2)(CA)(terpy)(2)][Cu(CA)(2)]](n)(1), where H(2)CA = chloranilic acid and terpy = 2,2':6',2' '-terpyridine, consists of two modules, the dimer unit [Cu(2)(CA)(terpy)(2)](2+) and the anionic mononuclear unit [Cu(CA)(2)](2)(-), forming an alternated chain. The chain is stabilized by semicoordinating and additional but efficient secondary bonding interactions. The crystal structure of [[Cu(2)(CA)(terpy)(2)(dmso)(2)][Cu(CA)(2)(dmso)(2)](EtOH)](n)(2), where dmso = dimethyl sulfoxide, consists of solvent molecules and two discrete modules, the dimer unit [Cu(2)(CA)(terpy)(2)(dmso)(2)](2+) and the anionic mononuclear unit [Cu(CA)(2)(dmso)(2)](2)(-). The dimer units form a layer by secondary bonding interactions, and the monomer units and ethanol molecules are introduced between the layers. The magnetic properties of 1 and 2 have been investigated in the temperature range 2.0-300 K. A weak ferromagnetic interaction was observed in 1, J(a) = 2.36 cm(-)(1) and zJ(b) = -0.68 cm(-)(1) while no exchange coupling was observed in 2.     

Short Radiative Lifetime and Non-Triplet Sensitization in Near-Infrared-Luminescent Yb(III) Complex with Tripodal Schiff Base

We prepared Ln(III) (Ln=Eu, Gd, and Yb) complexes with a tripodal Schiff base, tris[2-(5-methylsalicylideneimino)ethyl]amine (H₃L) and studied their photophysical properties. Upon ligand excitation, YbL showed Yb(III)-centered luminescence in the near-infrared region. While the overall quantum yield (0.60(1)%) of YbL in acetonitrile was moderate among the reported values for Yb(III) complexes, its radiative lifetime (0.33(2) ms) was significantly shorter than those reported previously. We propose that the ligand-to-metal charge-transfer (LMCT) state mediated the sensitization in YbL. The emission and excitation spectra of EuL indicated the participation of the LMCT state in the sensitization. The radiative lifetime (0.84(7) ms) for EuL in the solid state was rather short compared to those of reported Eu(III) complexes. Our results show that the Yb(III) complex with the Schiff base ligand has two features: the short radiative lifetime and the non-triplet sensitization path.