Universal Reaction Mechanism of Boronic Acids with Diols in Aqueous Solution: Kinetics and the Basic Concept of a Conditional Formation Constant

To establish a detailed reaction mechanism for the condensation between a boronic acid, RB(OH)₂, and a diol, H₂L, in aqueous solution, the acid dissociation constants (${K{{{\rm BL}\hfill \atop {\rm a}\hfill}}}$ ) of boronic acid diol esters (HBLs) were determined based on the well‐established concept of conditional formation constants of metal complexes. The pK_a values of HBLs were 2.30, 2.77, and 2.00 for the reaction systems, 2,4‐difluorophenylboronic acid and chromotropic acid, 3‐nitrophenylboronic acid and alizarin red S, and phenylboronic acid and alizarin red S, respectively. A general and precise reaction mechanism of RB(OH)₂ with H₂L in aqueous solution, which can serve as a universal reaction mechanism for RB(OH)₂ and H₂L, was proposed on the basis of (a) the relative kinetic reactivities of the RB(OH)₂ and its conjugate base, that is, the boronate ion, toward H₂L, and (b) the determined pK_a values of HBLs. The use of the conditional formation constant, K′, based on the main reaction: RB(OH)₂+H₂L ${{\mathop \leftrightarrow \limits ^{K{_{1}}}_{}}}$ RB(L)(OH)^?+H₃O⁺ instead of the binding constant has been proposed for the general reaction of uncomplexed boronic acid species (B′) with uncomplexed diol species (L′) to form boronic acid diol complex species (esters, BL′) in aqueous solution at pH 5–11: B′+L′ ${{\mathop \leftrightarrow \limits ^{K{^\prime}}_{}}}$ BL′. The proposed reaction mechanism explains perfectly the formation of boronic acid diol ester in aqueous solution.     

Diketopyrrolopyrrole J‐Aggregates Formed by Self‐Organization with DNA

Bis(2‐thienyl)diketopyrrolopyrrole with two Zn^II‐cyclens (ZnCyc‐DPP) was designed and synthesized to evaluate the selective binding of Zn^II‐cyclen with thymine base in single‐strand DNA as a tool for the construction of a highly ordered multichromophore system on DNAs. Through UV/Vis titrations, gel filtration chromatography, and circular dichroism spectroscopy, ZnCyc‐DPP formed J‐type DPP aggregates with oligo‐dT_n DNAs. The DPP aggregates absorbed on a gold electrode exhibited good photocurrent responses. The present results show that binding Zn^II‐cyclen–chromophore conjugates and thymine bases together is a powerful tool for preparing DNA‐templated multichromophoric systems with specific functions.     

The p53‐Dependent Expression of Frataxin Controls 5‐Aminolevulinic Acid‐Induced Accumulation of Protoporphyrin IX and Photo‐Damage in Cancerous Cells

Mitochondrial frataxin is involved in various functions such as iron homeostasis, iron–sulfur cluster biogenesis, the protection from oxidative stress and apoptosis and acts as a tumor suppressor protein. We now show that the expression of frataxin is stimulated in a p53‐dependent manner and prove that frataxin is a direct p53 target gene by showing that the p53‐responsive element in the promoter of the mouse frataxin gene is bound by p53. The bacterial expression of human frataxin stimulated maturation of human ferrochelatase, which catalyzes the insertion of iron into protoporphyrin at the last step of heme biosynthesis. Overexpression of frataxin in human cancer A431 and HeLa cells lowered 5‐aminolevulinic acid(ALA)‐induced accumulation of protoporphyrin and induced resistance to ALA‐induced photo‐damage, whereas p53 silencing with siRNA in non tumor HEK293T cells down‐regulated the expression of frataxin and increased the accumulation of protoporphyrin. Thus, the decrease of the expression of frataxin unregulated by p53 in tumor cells enhances ALA‐induced photo‐damage, by down‐regulation of mitochondrial functions.     

Characteristics of pure silica core single-mode fiber

Single-mode fibers with low attenuation and sufficient reliability are especially important for long-span optical transmission systems. Conventionally, GeO₂ has been added to the fiber core region in order to make a refractive index difference between the core and cladding. However, the addition of GeO₂ increases Rayleigh scattering loss [1], and deteriorates the chemical stability against hydrogen atmosphere and γ-ray irradiation to bring about an increase in attenuation. [2][3] Therefore, pure silica core single-mode fiber was considered to be an ideal type of fiber, and it was succeeded in being fabricated by utilizing fluorine containing SiO₂ cladding.     

Synthesis of 2,5-diaryloxazoles through van Leusen reaction and copper-mediated direct arylation

The direct arylation of 5-aryloxazoles, prepared by the van Leusen reaction, with various aryl iodides is effectively promoted by a system of CuI combined with PPh₃ and Na₂CO₃ as a ligand and a base, respectively, in DMF to produce the corresponding 2,5-diaryloxazoles in good yields.     

Phospholipid-linked coumarin: a fluorescent probe for sensing hydroxyl radicals in lipid membranes.

A fluorescent probe, DPPEC (1,2-dipalmitoylglycerophosphorylethanolamine labeled with coumarin) was developed for detecting hydroxyl radical (*OH) in lipid membranes. The coumarin moiety contributes to the fluorescent detection of *OH and the phospholipids moiety gives a driving force to localize the probe in lipid membranes. DPPEC in liposomal membranes rapidly reacted with *OH and increased the fluorescence intensity, depending on the concentration of *OH. The increase in the fluorescence intensity induced by *OH was effectively suppressed by the addition of DMSO. The probe exhibited a higher fluorescence response to *OH over other reactive oxygen species, such as hydrogen peroxide, nitric oxide, peroxynitrite, alkylperoxyl radical, and hypochlorite. DPPEC would be useful as a new type of fluorescent probe that can localize in lipid membranes and detect *OH efficiently.     

An abundance of invariant polynomials satisfying the Riemann hypothesis

In 1999, Iwan Duursma defined the zeta function for a linear code as a generating function of its Hamming weight enumerator. It can also be defined for other homogeneous polynomials not corresponding to existing codes. If the homogeneous polynomial is invariant under the MacWilliams transform, then its zeta function satisfies a functional equation and we can formulate an analogue of the Riemann hypothesis. As far as existing codes are concerned, the Riemann hypothesis is believed to be closely related to the extremal property.In this article, we show there are abundant polynomials invariant by the MacWilliams transform which satisfy the Riemann hypothesis. The proof is carried out by explicit construction of such polynomials. To prove the Riemann hypothesis for a certain class of invariant polynomials, we establish an analogue of the Eneström-Kakeya theorem.     

Construction and evaluation of a miniature electron ion coincidence analyzer mounted on a conflat flange with an outer diameter of 114 mm.

We have developed a miniature electron ion coincidence (EICO) analyzer mounted on a conflat flange with an outer diameter of 114 mm. It consists of a cylindrical mirror analyzer (CMA), a time-of-flight ion mass spectrometer (TOF-MS), a commercially available linear motion feed through, and a tilt adjustment mechanism. Each sample surface was irradiated by synchrotron radiation, and the energies of emitted electrons were analyzed and detected by the CMA, while desorbed ions were collected by the TOF-MS in coincidence with the electrons. The performance of the EICO analyzer was tested by measuring the Auger-electron H+ photoion coincidence spectrum of condensed water at 4a1 <-- O 1s resonance.     

Organized-polymerization in micelle formed by diblock macromonomers

Vinylbenzyl-terminated poly[styrene(S)-b-isoprene(I)] AB type diblock macromonomers were prepared by the direct coupling of corresponding living diblock anions with a large excess of p-chloromethylstyrene (CMS). The end group functionality of these diblock macromonomers was close to unity. Diblock macromonomers showed a narrow polydispersity (M?_w/M?_n = 1.04–1.09). Free radical polymerizations were carried out in micelle formed by diblock macromonomers. We also studied the formation of (AB)_n type star block copolymers by means of micro-gelation between diblock macromonomer and ethylene glycol dimethacrylate as a linking agent. © 1993 John Wiley & Sons, Inc.     

Structural and Thermal Characteristics of Nickel Dioxide Derived from LiNiO2

We report the structural and thermal characteristics of highly delithiated (lithium extracted) compounds Li_xNiO₂, which can be called “nickel dioxide.” We obtained Li_0.10NiO₂ and Li_0.04NiO₂ by treating LiNiO₂ with sulfuric acid. Both products contained phases with NiO₂ stacking similar to cadmium chloride (O3-type), but the latter also included a phase with NiO₂ stacking similar to cadmium iodide (O1-type). We examined their thermal behavior using high temperature X-ray diffraction analysis together with thermogravimetric analysis and found that novel polymorphs, with similar chemical compositions but different structures, were obtained by heating them at appropriate temperatures. We discuss these results together with those for Li_xNiO₂ obtained by electrochemical delithiation. We also report acid-treated products derived from Li_0.93Ni_1.07O₂.