Rational design of boron dipyrromethene (BODIPY)-based photobleaching-resistant fluorophores applicable to a protein dynamics study

We studied the photobleaching of a library of boron dipyrromethene (BODIPY) derivatives with a range of electron densities, and found that the photobleaching rate is influenced by the electron-withdrawing capacity of the substituents. Electron-deficient BODIPYs generated less singlet oxygen, were less reactive to singlet oxygen, and were highly resistant to photobleaching. We confirmed the utility of one of these fluorophores, 2,6-diCO(2)R-BDP, for visualizing EGF receptor dynamics in cells expressing an SNAP-tagged EGF receptor.     

Retro‐Diels–Alder Approach to the Synthesis of π‐Expanded Azuliporphyrins and Their Porphyrinoid Aromaticity

Bicyclo[2.2.2]octadiene (BCOD) fused azuliporphyrins were synthesized by 3+1 porphyrin synthesis of azulitripyrranes with diformylpyrroles. Subsequent retro‐Diels–Alder reaction of the BCOD‐fused azuliporphyrins afforded azulibenzo‐, azulidibenzo‐, and azulitribenzoporphyrins 1 – 5 . NMR and UV/Vis spectra, as well as nucleus‐independent chemical shift (NICS) calculations revealed that 1 – 5 and their diprotonated dications exhibit relatively low porphyrinoid aromaticity, which was dependent on the position and number of fused benzene rings present.     

Development of Luciferin Analogues Bearing an Amino Group and Their Application as BRET Donors

We systematically synthesized bioluminogenic substrates bearing an amino group on benzothiazole, quinoline, naphthalene, and coumarin scaffolds. They emit bioluminescence in various colors: red, orange, yellow, and green. An amino‐substituted coumarylluciferin derivative, coumarylaminoluciferin (CAL), showed the shortest bioluminescence wavelength among substrates reported so far. Further, the fluorescence of CAL did not exhibit solvatochromism, which suggests that its bioluminescence is not susceptible to environmental factors. We applied CAL as an energy‐donor substrate for a bioluminescence resonance energy transfer (BRET) system with click beetle red luciferase (CBRluc), a mutant of firefly luciferase, as the energy‐donor enzyme and yellow fluorescent protein (YFP) as the energy‐acceptor fluorophore, and obtained a clearly bimodal bioluminescence spectrum. Stable bioluminescence that is not influenced by environmental factors is highly desirable for reliable measurements in biological assays.     

Complexed bridging ligand,Cu(bptap)2, as a ferromagnetic coupler

A novel complexed bridging ligand [Cu(bptap)2] which acts as a ferromagnetic coupler forms one dimensional chain consisting of tri-copper(II) [Cu2(Cu(bptap)2)]4+ units in which adjoining copper(II) ions are ferromagnetically coupled.     

Nickel-catalyzed cycloadditions of thiophthalic anhydrides with alkynes

Nickel-catalyzed cycloadditions have been developed where thiophthalic anhydrides react with alkynes to afford substituted sulfur-containing heterocyclic compounds. Selective formations of thioisocoumarins, benzothiophenes, and thiochromones were accomplished with three different reaction conditions.     

Integration of Chandrasekhar's integral equation

We solve Chandrasekhar's integration equation for radiative transfer in the plane-parallel atmosphere by iterative integration. The primary thrust in radiative transfer has been to solve the forward problem, i.e., to evaluate the radiance, given the optical thickness and the scattering phase function. In the area of satellite remote sensing, our problem is the inverse problem: to retrieve the surface reflectance and the optical thickness of the atmosphere from the radiance measured by satellites. In order to retrieve the optical thickness and the surface reflectance from the radiance at the top-of-the atmosphere (TOA), we should express the radiance at TOA “explicitly” in the optical thickness and the surface reflectance. Chandrasekhar formalized radiative transfer in the plane-parallel atmosphere in a simultaneous integral equation, and he obtained the second approximation. Since then no higher approximation has been reported. In this paper, we obtain the third approximation of the scattering function. We integrate functions derived from the second approximation in the integral interval from 1 to ∞ of the inverse of the cos of zenith angles. We can obtain the indefinite integral rather easily in the form of a series expansion. However, the integrals at the upper limit, ∞, are not yet known to us. We can assess the converged values of those series expansions at ∞ through calculus. For integration, we choose coupling pairs to avoid unnecessary terms in the outcome of integral and discover that the simultaneous integral equation can be deduced to the mere integral equation. Through algebraic calculation, we obtain the third approximation as a polynomial of the third degree in the atmospheric optical thickness.     

A solution of radiative transfer in isotropic plane-parallel atmosphere by integrating Milne equation

In this paper we solve the inversion problem of the radiative transfer process in the isotropic plane-parallel atmosphere by iterative integrations of the Milne integral equation. As a result, we obtain the scattering function in the form of a cubic polynomial in optical thickness. The author has already solved the same problem by iterative integrations of Chandrasekhar's integral equation. In the Milne integral equation, both the cosines of the viewing angles and the optical thickness are integral variables, while in Chandrasekhar's integral equation the cosines of the viewing angles are variables but the optical thickness is not. We derive several series of exponential-like functions as intermediate derivations. Their convergences are evaluated by the author's previous work in the solution of Chandrasekhar's integral equation. The truncated scattering function up to the third order in optical thickness thus obtained is identical to that obtained from Chandrasekhar's integral equation, though their apparent forms are different. Chandrasekhar pointed out that the solution of Chandrasekhar's integral equation does not have a uniqueness of solution. The Milne equation, in contrast, has been proven to have a unique solution. We discuss the uniqueness of the solution by these two methods.     

Methylenecyclopropane as C1 synthetic units: [1+4] cycloaddition via a nickel catalyst

Nickel-catalyzed reactions of methylenecyclopropanes and thioanhydrides afford sulfur-containing heterocyclic compounds via [1+4] cycloaddition. The reactions represent a new use for methylenecyclopropane as a possible one-carbon building block to replace carbon monoxide, isocyanides, and Fischer carbene complexes.     

Spin Ice-like Magnetic Relaxation of a Two-dimensional Network based on Manganese(III) Salen-type Single-Molecule Magnets

Spin ice is an exotic type of magnetism displayed by bulk rare-earth pyrochlore oxides. We discovered a spin ice-like magnetic relaxation of [{Mn(saltmen)}₄{Mn(CN)₆}](ClO₄)⋅13 H₂O (saltmen²⁻=N,N′-(1,1,2,2-tetramethylethylene)bis(salicylideneiminate)). This magnetic system can be considered as a two-dimensional network of Mn^III salen-type single-molecule magnets (SMMs) in which each SMM unit (S_T=4) has two orthogonally oriented axial anisotropies and is connected ferromagnetically through the [Mn(CN)₆]³⁻ unit (S=1). This work illustrates that a two-dimensional SMM network with competition between the ferromagnetic interaction and local noncollinear magnetic anisotropies on SMMs is a new type of magnetic system exhibiting slow relaxation of magnetization with a Davidson-Cole-type broad distribution of the relaxation time.