Successive phase transitions of <Emphasis Type="Italic">p</Emphasis>-methylbenzyl alcohol crystal studied by X-ray and adiabatic calorimetry

Summary Crystal structures of the room-temperature (RT) and low-temperature (LT) phases of p-methylbenzyl alcohol were reexamined by single-crystal X-ray diffraction method while paying special attention to detect structural disorder in the RT phase involved in successive structural phase transitions at 179 and 210 K. In the RT phase at 250 K, positional disorder of oxygen atoms was detected in contrast to the previous structure report. The structure of the LT phase coincided to the previous one. Heat capacities were measured by adiabatic calorimetry below 350 K, which covers the structural phase transitions and fusion at 331.87 K. The structural phase transitions were of first-order and required long time for completion. The combined magnitude of entropies of transition was ca. 5 J K^-1 mol^-1, a part of which can be ascribed to the positional disorder observed in the structure analysis. Standard thermodynamic functions are tabulated below 350 K.     

Molecular Design Rule of Phthalocyanine Dyes for Highly Efficient Near‐IR Performance in Dye‐Sensitized Solar Cells

A series of zinc–phthalocyanine sensitizers ( PcS16 – 18 ) with different adsorption sites have been designed and synthesized in order to investigate the dependence of adsorption‐site structures on the solar‐cell performances in zinc–phthalocyanine based dye‐sensitized solar cells. The change of adsorption site affected the electron injection efficiency from the photoexcited dye into the nanocrystalline TiO₂ semiconductor, as monitored by picosecond time‐resolved fluorescence spectroscopy. The zinc–phthalocyanine sensitizer PcS18 , possessing one carboxylic acid directly attached to the ZnPc ring and six 2,6‐diisopropylphenoxy units, showed a record power conversion efficiency value of 5.9 % when used as a light‐harvesting dye on a TiO₂ electrode under one simulated solar condition.     

Distinctive Properties of Dark Reversion Kinetics between Two Red/Green‐Type Cyanobacteriochromes and their Application in the Photoregulation of cAMP Synthesis

Cyanobacteriochromes (CBCRs) are photoreceptors that bind to a linear tetrapyrrole within a conserved cGMP‐phosphodiesterase/adenylate cyclase/FhlA (GAF) domain and exhibit reversible photoconversion. Red/green‐type CBCR GAF domains that photoconvert between red‐ (Pr) and green‐absorbing (Pg) forms occur widely in various cyanobacteria. A putative phototaxis regulator, AnPixJ, contains multiple red/green‐type CBCR GAF domains. We previously reported that AnPixJ's second domain (AnPixJg2) but not its fourth domain (AnPixJg4) shows red/green reversible photoconversion. Herein, we found that AnPixJg4 showed Pr‐to‐Pg photoconversion and rapid Pg‐to‐Pr dark reversion, whereas AnPixJg2 showed a barely detectable dark reversion. Site‐directed mutagenesis revealed the involvement of six residues in Pg stability. Replacement at the Leu294/Ile660 positions of AnPixJg2/AnPixJg4 showed the highest influence on dark reversion kinetics. AnPixJg2_DR6, wherein the six residues of AnPixJg2 were entirely replaced with those of AnPixJg4, showed a 300‐fold faster dark reversion than that of the wild type. We constructed chimeric proteins by fusing the GAF domains with adenylate cyclase catalytic regions, such as AnPixJg2‐AC, AnPixJg4‐AC and AnPixJg2_DR6‐AC. We detected successful enzymatic activation under red light for both AnPixJg2‐AC and AnPixJg2_DR6‐AC, and repression under green light for AnPixJg2‐AC and under dark incubation for AnPixJg2_DR6‐AC. These results provide platforms to develop cAMP synthetic optogenetic tools.     

Three putative photosensory light, oxygen or voltage (LOV) domains with distinct biochemical properties from the filamentous cyanobacterium Anabaena sp. PCC 7120

Light, oxygen or voltage (LOV) domains function as blue-light sensors in the phototropin family of photoreceptors found in plants, algae and bacteria. We detected putative LOV domains (Alr3170-LOV, All2875-LOV and Alr1229-LOV) in the genome of a filamentous cyanobacterium, Anabaena sp. PCC 7120. These cyanobacterial LOV domains are closely clustered with the known LOV domains. Alr3170-LOV and A112875-LOV carry the conserved cysteine residue unique to the photoactive LOV, whereas Alr1229-LOV does not. We expressed these three LOV domains in Escherichia coli and purified them. In fact, Alr3170-LOV and A112875-LOV that are conserved in Nostoc punctiforme, a related species, bound flavin mononucleotide and showed spectral changes unique to known LOV domains on illumination with blue light. Alr3170-LOV was completely photoreduced and dark reversion was slow, whereas A112875-LOV was slowly photoreduced and dark reversion was rapid. For comparison, AvA112875-LOV in a closely related A. variabilis was also studied as a homolog of A112875-LOV. Finally, we observed that Alr1229-LOV that is not conserved in N. punctiforme showed no flavin binding.     

Size-controlled and monodisperse enzyme-encapsulated chitosan microspheres developed by the SPG membrane emulsification technique

The amphiphilic gradient copolymers of 2,2,2-trifluoroethyl methacrylate (TFEMA) and acrylic acid (AA) have been synthesized by using amphiphilic RAFT agent via emulsifier-free emulsion polymerization with a starved feed method of adding TFEMA. Different cosolvents are added into polymerization system to inhibit AA's homopolymerization of in aqueous phase. RAFT polymerization kinetics under different reaction conditions are discussed in detail. (1)H NMR results indicate that the obtained copolymer has a chain structure with AA segments gradually changing to TFEMA segments. The copolymer latexes exhibit good pH stability (pH value from 5 to 14) and Ca(2+) stability. The self-assembly behavior of gradient copolymers in selective solvents are observed and studied by transmission electron microscopy. All the copolymers can form spherical micelles, but the homogeneity and size of micelles are different.     

On the accelerated iterative method for estimating the optimum overrelaxation parameter

This paper is concerned with the iterative method for estimating the optimum overrelaxation parameter. The improved power method (IP method) with the greatest rate of convergence is derived and compared with the Chebyshev polynomial iterative method (CP method) and the other iterative methods. Two algorithms (algorithms A and B) based on the IP method are presented. Some numerical results are shown.