Rational Molecular Design towards Vis/NIR Absorption and Fluorescence by using Pyrrolopyrrole aza‐BODIPY and its Highly Conjugated Structures for Organic Photovoltaics

Pyrrolopyrrole aza‐BODIPY (PPAB) developed in our recent study from diketopyrrolopyrrole by titanium tetrachloride‐mediated Schiff‐base formation reaction with heteroaromatic amines is a highly potential chromophore due to its intense absorption and fluorescence in the visible region and high fluorescence quantum yield, which is greater than 0.8. To control the absorption and fluorescence of PPAB, particularly in the near‐infrared (NIR) region, further molecular design was performed using DFT calculations. This results in the postulation that the HOMO–LUMO gap of PPAB is perturbed by the heteroaromatic moieties and the aryl‐substituents. Based on this molecular design, a series of new PPAB molecules was synthesized, in which the largest redshifts of the absorption and fluorescence maxima up to 803 and 850 nm, respectively, were achieved for a PPAB consisting of benzothiazole rings and terthienyl substituents. In contrast to the sharp absorption of PPAB, a PPAB dimer, which was prepared by a cross‐coupling reaction of PPAB monomers, exhibited panchromatic absorption across the UV/Vis/NIR regions. With this series of PPAB chromophores in hand, a potential application of PPAB as an optoelectronic material was investigated. After identifying a suitable PPAB molecule for application in organic photovoltaic cells based on evaluation using time‐resolved microwave conductivity measurements, a maximized power conversion efficiency of 1.27 % was achieved.     

Synthesis and electronic structures of D2h-symmetry tetrabenzoporphyrins

A novel low-symmetry tetrabenzoporphine with D_2h symmetry (1) and its zinc complex (2) were prepared via mixed condensation reaction of 5,6-dimethyl phthalimide and 4,5,6,7-tetraphenyl phthalimide with sodium acetate in the presence of zinc acetate. The zinc complex 2 exhibited a split Q band at 640 and 623 nm and a single Soret band at 435 nm. The absorption spectra of 1 and 2 were calculated and analyzed using Hartree-Fock theory based on INDO/S Hamiltonian.     

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.     

Homogeneous Oligomeric Ligands Prepared via Radical Polymerization that Recognize and Neutralize a Target Peptide

Abiotic ligands that bind to specific biomolecules have attracted attention as substitutes for biomolecular ligands, such as antibodies and aptamers. Radical polymerization enables the production of robust polymeric ligands from inexpensive functional monomers. However, little has been reported about the production of monodispersed polymeric ligands. Herein, we present homogeneous ligands prepared via radical polymerization that recognize epitope sequences on a target peptide and neutralize the toxicity of the peptide. Taking advantage of controlled radical polymerization and separation, a library of multifunctional oligomers with discrete numbers of functional groups was prepared. Affinity screening revealed that the sequence specificity of the oligomer ligands strongly depended on the number of functional groups. The process reported here will become a general step for the development of abiotic ligands that recognize specific peptide sequences.     

Stereoselective Syntheses of all the Possible Stereoisomers of Coronafacic Acid

An efficient and stereoselective syntheses of all the possible stereoisomers of coronafacic acid (CFA) has been developed. The stereochemistries of C3a and C7a were controlled in a diastereoselective Diels-Alder type cycloaddition using a chiral auxiliary. CFA and 6-epi-CFA were synthesized by hydrogenation of a common intermediate. During the synthesis of 6-epi-CFA, we established that its cis-fused configuration is important for the introduction of C4-C5 double bond by dehydration. This report is the first practical synthesis of both 6-epi-CFA, and its enantiomer.     

Polymer‐Assisted Solution‐Phase Synthesis and Neurite‐Outgrowth‐Promoting Activity of 15‐Deoxy‐Δ12,14‐PGJ2 Derivatives

An efficient solution‐phase synthesis of rac‐15‐deoxy‐Δ^12,14‐PGJ₂ (15dPGJ₂) derivatives that contain variable α and ω chains based on a polymer‐assisted strategy and their neurite‐outgrowth‐promoting activity are described. The strategy for the synthesis of PGJ₂ derivatives involves the use of a vinyl iodide bearing cyclopentenone as a key intermediate, which undergoes Suzuki–Miyaura coupling and subsequent Lewis acid catalyzed aldol condensation for incorporation of the ω and α chains, respectively. For easy access to the PGJ₂ derivatives, a polymer‐supported catalyst and scavengers were adapted for use in these four diverse steps, in which workup and purification can be performed by simple filtration of the solid‐supported reagents. By using this methodology, we succeeded in the synthesis of 16 PGJ₂ derivatives with four alkyl boranes and four aldehydes. The neurite‐outgrowth‐promoting activity of the 16 synthetic compounds in PC12 cells revealed that the side‐chains play a major role in modulating their biological activity. The carboxylic acid on the α chain improved the biological activity, although it was not absolutely required. Furthermore, a PGJ₂ derivative with a phenyl moiety on the ω chain was found to exhibit an activity comparable to that of natural 15dPGJ₂.     

Biomimetic formation of gramicidin S by dimerization-cyclization of pentapeptide precursor on solid support

The biomimetic formation of gramicidin S, cyclo(-d-Phe-Pro-Val-Orn-Leu-)₂, by the dimerization and cyclization of pentapeptide precursor without the protection of δ-amino group of the Orn residue was examined on a solid support. The cyclization of H-d-Phe-Pro-Val-Orn-Leu-oxime on a resin with an oxime group of 0.62 mmol/g in 1,4-dioxane directly gave gramicidin S in a 50% yield. The dimerization-cyclization mode on the solid support was similar to that of the biosynthesis of gramicidin S on an enzyme.     

Monolithic silica spin column extraction and simultaneous derivatization of amphetamines and 3,4-methylenedioxyamphetamines in human urine for gas chromatographic-mass spectrometric detection

A simple, sensitive, and specific method with gas chromatography-mass spectrometry was developed for simultaneous extraction and derivatization of amphetamines (APs) and 3,4-methylenedioxyamphetamines (MDAs) in human urine by using a monolithic silica spin column. All the procedures, such as sample loading, washing, and elution were performed by centrifugation. APs and MDAs in urine were adsorbed on the monolithic silica and derivatized with propyl chloroformate in the column. Methamphetamine-d₅ was used as an internal standard. The linear ranges were 0.01-5.0 μg mL⁻¹ for methamphetamine (MA) and 3,4-methylenedioxymethamphetamine (MDMA) and 0.02-5.0 μg mL⁻¹ for amphetamine (AP) and 3,4-methylenedioxyamphetamine (MDA) (coefficient of correlation ≧0.995). The recovery of APs and MDAs in urine was 84-94%, and the relative standard deviation of the intra- and interday reproducibility for urine samples containing 0.1, 1.0, and 4.0 μg mL⁻¹ of APs and MDAs ranged from 1.4% to 13.6%. The lowest detection limit (signal-to-noise ratio ≧ 3) in urine was 5 ng mL⁻¹ for MA and MDMA and 10 ng mL⁻¹ for AP and MDA. The proposed method can be used to perform simultaneous extraction and derivatization on spin columns that have been loaded with a small quantity of solvent by using centrifugation.     

Luminescence enhancement of Eu, Ce co-doped Ba3Si5O13−δNδ phosphors

Host lattice Ba₃Si₅O_13−δN_δ oxonitridosilicates have been synthesized by the traditional solid state reaction method. The lattice structure is based on layers of vertex-linked SiO₄ tetrahedrons and Ba²⁺ ions, where each Ba²⁺ ion is coordinated by eight oxygen atoms forming distorted square antiprisms. Under an excitation wavelength of 365 nm, Ba₃Si₅O_13−δN_δ:Eu²⁺ and Ba₃Si₅O_13−δN_δ:Eu²⁺,Ce³⁺ show broad emission bands from about 400-620 nm, with maxima at about 480 nm and half-peak width of around 130 nm. The emission intensity is strongly enhanced by co-doping Ce³⁺ ions into the Ba₃Si₅O_13−δN_δ:Eu²⁺ phosphor, which could be explained by energy transfer. The excitation band from the near UV to the blue light region confirms the possibility that Ba₃Si₅O_13−δN_δ:Eu²⁺, Ce³⁺ could be used as a phosphor for white LEDs.     

Thermal [2+2] cycloaddition of morpholinoenamines with C60 via a single electron transfer

The thermal reaction of C(60) with five- and six-membered morpholinocycloalkenes in refluxing toluene exclusively gave the [2+2] cycloadducts in high yields. However, a seven-membered homologue sluggishly reacted with C(60) because of the increasing steric hindrance. This cycloaddition reaction is likely to proceed via a single electron transfer (SET), a radical-coupling, and subsequent ion cyclization rather than the prior proton transfer between the radical ions.