Self-assembling porphyrins and phthalocyanines for photoinduced charge separation and charge transport

Large π-conjugated compounds are promising building blocks for organic thin-film electronics such as organic light-emitting diodes, organic field-effect transistors, and organic photovoltaics. Utilization of porphyrins and phthalocyanines for this purpose is highly fascinating because of their excellent electric, photophysical, and electrochemical properties as well as intense self-assembling abilities arising from π-π stacking interactions. This paper focuses on fundamental aspects of self-assembled structures that have been obtained from porphyrin and phthalocyanine building blocks and more complex composites for photoinduced charge separation and charge transport toward the potential applications to organic thin-film electronics.     

Superconducting fullerene nanowhiskers

We synthesized superconducting fullerene nanowhiskers (C(60)NWs) by potassium (K) intercalation. They showed large superconducting volume fractions, as high as 80%. The superconducting transition temperature at 17 K was independent of the K content (x) in the range between 1.6 and 6.0 in K-doped C(60) nanowhiskers (K(x)C(60)NWs), while the superconducting volume fractions changed with x. The highest shielding fraction of a full shielding volume was observed in the material of K(3.3)C(60)NW by heating at 200 °C. On the other hand, that of a K-doped fullerene (K-C(60)) crystal was less than 1%. We report the superconducting behaviors of our newly synthesized K(x)C(60)NWs in comparison to those of K(x)C(60) crystals, which show superconductivity at 19 K in K(3)C(60). The lattice structures are also discussed, based on the x-ray diffraction (XRD) analyses.     

A molecular dynamics study of the lateral free energy profile of a pair of cholesterol molecules as a function of their distance in phospholipid bilayers

Free energy profile of a pair of cholesterol molecules in a leaflet of 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) bilayers in the liquid-crystalline phase has been calculated as a function of their lateral distance using a combination of NPT-constant atomistic molecular dynamics calculations (P = 1 atm and T = 310.15 K) and the thermodynamic integration method. The calculated free energy clearly shows that the two cholesterol molecules form a dimer separated by a distance of 1.0-1.5 nm in POPC bilayers. Well depth of the free energy profile is about 3.5 kJ/mol, which is comparable to the thermal energy k(B)T at 310.15 K. This indicates that the aggregation of cholesterol molecules in the bilayers depends on the temperature as well as the concentration of the system. The free energy function obtained here may be used as a reference when coarse grained potential model is investigated for this two-component system. Local structure of POPC molecules around two cholesterol molecules has also been investigated.     

Effects of bubble size on heat transfer enhancement by sub-millimeter bubbles for laminar natural convection along a vertical plate

Injection of sub-millimeter bubbles is considered a promising technique for enhancing natural convection heat transfer for liquids. So far, we have experimentally investigated heat transfer characteristics of laminar natural convection flows with sub-millimeter bubbles. However, the effects of the bubble size on the heat transfer have not yet been understood. The purpose of this study is to clarify the effects of the bubble size on the heat transfer enhancement for the laminar natural convection of water along a vertical heated plate with uniform heat flux. Temperature and velocity measurements, in which thermocouples and a particle tracking velocimetry technique are, respectively used, are conducted to investigate heat transfer and flow characteristics for different bubble sizes. Moreover, two-dimensional numerical simulations are performed to comprehensively understand the effects of bubble injection on the flow near the heated plate. The result shows that the ratio of the heat transfer coefficient with sub-millimeter-bubble injection to that without injection ranges from 1.3 to 2.2. The result also shows that for a constant bubble flow rate, the heat transfer coefficient ratio increases with a decrease in the mean bubble diameter. It is expected from our estimation based on both experimental data and simulation results that this increase results from an increase in the advection effect due to bubbles.     

Cu NMR/NQR Studies on Magnetism in Impurity/Hole-Doped Spin-Ladder Compounds

Cu nuclear magnetic resonance (NMR) spectra of impurities (Zn, Ni, and La)-doped spin-1/2 Heisenberg ladder compounds SrCu₂O₃ (Sr123) are broadened with Curie-like temperature (T) dependence. The spectra have been successfully fit by using a quasi-one-dimensional (Q1D) staggered polarization (SP) model. Such a SP has also revealed in Cu NMR measurements of Sr_14–x Ca _x Cu₂₄O₄₁ (Cax) with hole-doped ladders. The origin of possible 3D antiferromagnetic (AF) long-range ordering in (Zn and Ni)-doped Sr123 and Cax around x=12 at low T is considered to be similar. Once unpaired spins S ₀'s are induced and 3D interlayer interaction occurs, the localized spins couple in the whole system.     

Characterization of Natural Chromite Samples from Ophiolite Complexes in the Philippines by 57Fe Mössbauer Spectroscopy

Mössbauer spectroscopy was applied to natural chromite samples from ophiolite complexes in the Philippines. Chemical and structural characterization of the chromite samples was also carried out using X-ray absorption fine structure (XAFS), X-ray diffraction (XRD) and X-ray fluorescence spectrometry (XRF). The Mössbauer spectra of the samples consisted of quadrupole doublets ascribable to Fe³⁺ in octahedral site, Fe³⁺ in tetrahedral site, and Fe²⁺ in tetrahedral site. The relative percentage of Fe³⁺ and Fe²⁺ ions suggested that these Philippine samples were formed under relatively high oxygen fugacity.     

在6H-SiC衬底上用低压MOVPE法生长AlN和GaN的过程中用(AlN/GaN)多层缓冲层来控制残余应力

人们已提出用BAlGaN四元系材料制备紫外光谱区的光发射器件.GaN和AlN二元系是这种四元材料在器件应用中的基础材料.6H-SiC衬底在氮化物生长中因其晶格失配小是一大优势,而且SiC衬底的热膨胀系数也和AlN的很接近.然而,对于AlN外延层来说,需要控制其中的残余应力,因为在SiC衬底上直接生长的AlN外延层中存在着因晶格失配所产生的压缩应力.另一方面,在SiC衬底上直接生长的GaN外延层中存在着拉伸应力.这种拉伸应力起源于GaN比衬底有着更大的热膨胀系数.本文讨论了在6H-SiC衬底上生长的氮化物外延层中残余应力的类型、数量及控制.为此目的,提出了在6H-SiC衬底上,无论是生长AlN,还是生长GaN,都可以采用(GaN/AlN)多层缓冲层的办法,作为控制残余应力的有效方法.我们还讨论了AlN和GaN外延层的结晶质量和残余应力间的关系.     

Enhancement in age hardenability of sintered Ti–5Fe alloy by Zr addition processed by pulsed electric current sintering

The age-hardenable Ti–5Fe–5Zr (wt. %, 5Zr) alloy has been consolidated by pulsed electric current sintering, following a β solution treatment, and the results are compared with a Ti–5Fe (0Zr) alloy. The precipitation sequence measured at 640°C ageing is β?+?athermal ω?→?β?+?isothermal ω?→?β?+?α. At the peak hardness isothermal ω phase forms at 20?s of ageing. The Zr addition retards the precipitation kinetics of the α phase; as a result, the α phase nucleates at latest at 300?s ageing in the overaged state. Fe is partitioned into β, while it is depleted from the α phases. There is Zr enrichment near the α/β interface when the α phase precipitates due to a solute drag effect; the growth rate of the α phase in the 5Zr alloy is significantly reduced compared with that in the 0Zr alloy.     

Spin-projected QM/MM Free Energy Simulations for Oxidation Reaction of Guanine in B−DNA by Singlet Oxygen

Guanine is the most susceptible base to oxidation damage induced by reactive oxygen species including singlet oxygen (¹O₂, ¹Δ_g). We clarify whether the first step of guanine oxidation in B−DNA proceeds via either a zwitterionic or a diradical intermediate. The free energy profiles are calculated by means of a combined quantum mechanical and molecular mechanical (QM/MM) method coupled with the adaptive biasing force (ABF) method. To describe the open-shell electronic structure of ¹O₂ correctly, the broken-symmetry spin-unrestricted density functional theory (BS−UDFT) with an approximate spin projection (AP) correction is applied to the QM region. We find that the effect of spin contamination on the activation and reaction free energies is up to ∼8 kcal mol⁻¹, which is too large to be neglected. The QM(AP−ULC−BLYP)/MM-based free energy calculations also reveal that the reaction proceeds through a diradical transition state, followed by a conversion to a zwitterionic intermediate. Our computed activation energy of 5.2 kcal mol⁻¹ matches experimentally observed range (0∼6 kcal mol⁻¹).     

Enantioselective synthesis of (−)-elenolic acid and (−)-ajmalicine

A secoiridoid monoterpene (?)-elenolic acid and a representative heteroyohimbine alkaloid (?)-ajmalicine have been synthesized enantio- and stereoselectively using L-ethyl lactate as a chiral starting material.