We developed four types of naphthalene oligomer-based dyes showing intense circularly polarized luminescence (CPL). (1) A peri-xanthenoxanthene (PXX) with two naphthalene rings connected via a methylenedioxy bridge and a chiral axis displayed CPL. A bridged PXX dimer also showed CPL. The bridged structure adjusts the angle between the vectors of the electric and magnetic transition dipole moments, which is essential for showing CPL activity. (2) (R,R,R)-naphthalene tetramers possessing six fluorophores displayed excimer-CPL. The fluorophores form a twist excimer. The systematic study allowed us to find an empirical rule called the excimer chirality rule: right- and left-handed excimers exhibit (+)- and (−)-CPL, respectively. (3) Pyrenes sandwiched by (R)-2-hydroxybinaphthyls exhibited solvent-dependent inversion of the sign of CPL without a change in emission wavelength. The (−)- and (+)-CPL were detected in nonpolar and polar solvents, respectively. This switching property originates from the inversion of excimer chirality caused by the presence or absence of intermolecular hydrogen bonds in the excited state. (4) A binaphthyl-bipyridyl cyclic dyad exhibited ON/OFF properties in CPL by protonation/deprotonation. The switching properties resulted from an inversion of the bipyridyl axis mediated by intramolecular hydrogen bonds.
The recent depletion of fossil fuel resources has impelled industrial and academic researchers to search for alternative carbon sources. Developing sustainable resources/energy is one of the most urgent missions for human beings since the increasing resources/energy demand is in drastic conflict with the limited global fossil fuel storage. In another perspective, massive production of CO2 is inevitable and the fatal risk as far as fossil resources are continuously used as the only sources of carbon. Considerable effort has been invested in biotechnology and sustainable/green technologies to develop a chemical industry in which renewable energy resources complement dwindling fossil fuel sources for the new millennium. A round-table discussion of the US Department of Energy identified the top 30 value-added chemicals derived from biomass, which included various (poly)carboxylic acids and polyols. Non-biodegradable microplastics already plague our oceans and are destroying the world. It is really no secret. These chemicals exist in high oxidation and/or highly oxygenated/nitrogenated states, and thus, current state-of-the-art oxidation catalysts must be substantially modified so that new millennium catalysts could effectively promote the reduction and dehydration of such renewable resources. We have developed new molecular technologies based on well-elaborated metal complexes with PNNP tetradentate ligands for dehydration and reduction of unactivated amides, polycarboxylic acids, and CO2 using thermal or light energy. Those catalytic systems represent potentially sustainable methods for the production of alternative energy carriers/platform chemicals on a large scale. Herein, we offer a brief account on the development of molecular insights into mononuclear low-valent transition metal complexes for reduction of a range of renewable carbon resources.
The development of efficient synthetic methods of π-conjugated compounds by means of cross-coupling reactions are reported. Tetraarylethenes with four different substituents are synthetic targets. The Pt-catalyzed addition of diboron to alkynylsilanes to yield 1-aryl-1-silyl-2,2-diborylethenes with perfect stereoselectivity. Step by step chemoselective Suzuki-Miyaura couplings with aryl halides were performed to give a triarylsilylethene with perfect chemoselectivity. The silyl group was transformed to the aryl group with desilybromination, followed by Suzuki-Miyaura coupling, leading to the successful synthesis of the desired tetraarylated olefin. On the other hand, novel and versatile methods for the synthesis of various phenacene and thienophenacene derivatives by cross-coupling reactions were elucidated for application to organic field-effect transistors (OFETs) and organic photovoltaics (OPVs). As one of representative phenacenes, picene is a polycyclic aromatic hydrocarbon consisting of five fused benzene rings with a W-shape structure, which exhibits high hole mobility. We successfully found the synthetic route of various substituted picenes. In addition, the synthesis of phenanthro [1,2-b : 8,7-b’] dithiophene (PDT) was achieved by replacing two terminal phenyl rings in picene with thiophene rings. The fabricated OFET devices based on C12-PDT-2 displayed a quite high mobility of up to 5.6 cm2 V−1 s−1. In regard to OPV devices, PDT-fluorinated benzothiadiazole (BT) polymers possessing alkyl side chains showed the highest power conversion efficiencies (PCE) of 9.0%.
The opioid use disorder is a significant public health concern in the United States. There have been a large number of opioid overdose deaths and as a result, a public health emergency was declared in October 2017. This growing number of overdose deaths can in part be attributed to the increased frequency of fentanyl contamination in the United States heroin supply. Previously, our research group has published several examples of immunotherapy as an innovative treatment strategy for substance use disorders. This strategy provides immunoantagonistic protection from the drug without interacting with the drug’s target receptor(s). Moreover, antidrug vaccines produce a long-lasting blockade against the target drug without any of the side effects. Our research group has already developed heroin vaccine and fentanyl vaccine. In our efforts to further combat the opioid crisis as well as tackle the rampant emergence of fentanyl in the United States heroin supply, we questioned whether a heroin-fentanyl dual vaccine could be feasible. We examined the effects of “admixture vaccine of fentanyl and heroin hapten immunoconjugates” and “chemically contiguous heroin-fentanyl hapten conjugated vaccine” as dual vaccines against heroin contaminated with fentanyl. Herein, we detail the preparation of these vaccines and their biological evaluation.
Oligonucleotide-based therapeutics, such as antisense oligonucleotides and small interfering RNAs(siRNAs), are fast emerging as the next generation of chemotherapeutics. However, a major issue for oligonucleotide-based therapeutics involves effective intracellular delivery of the active molecules into the cells. Several methods such as lipid nanoparticle encapsulation and conjugation of functional molecules have been reported. As an alternative approach, the use of pro-oligonucleotides (pro-oligos) offers several advantages, including improved enzymatic stability, thereby avoiding the need for transfection reagents for the delivery of oligonucleotides into cells. We have developed several bio-labile protecting groups for the pro-oligos. This article describes the design and synthesis of bio-labile protecting groups and their application to pro-oligo type molecules for the development of oligonucleotide therapeutics.
Chalcogen bond is defined by an IUPAC commission as “net attractive interaction between an electrophilic region associated with a chalcogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity”. While this effect has long been examined in crystal engineering field, the focus of recent studies is shifted to its application in solution systems. This review summarizes three recent topics on neutral chalcogen bond donor which are conducted in organic solvent as well as water.
Site-selective functionalization of arenes is a long-standing issue in organic synthesis. Sulfonium salt formation of arenes by a SEAr reaction is one of the solutions of this challenge. These salts are ready to engage in various transformations such as cross-coupling reactions. This review summarizes the site-selective functionalizations of aromatic compounds by “sulfonium salt formation/coupling reaction”.
Ruthenium polypyridyl complexes have recently attracted much attention not only in organic chemistry but also in chemical biology because of their unique photophysical and photochemical properties by visible light irradiation. This review describes the recent developments in oligonucleotide chemistry using ruthenium polypyridyl complex-conjugated oligonucleotides.
Hippolachnin is a polyketide natural product isolated from the marine sponge Hippospongia lachnein in China 2013, which has shown highly potent antibacterial activities against several pathogenic fungi. It features a highly substituted cyclobutane, six contiguous stereocenters, one of which is quaternary carbon and bears an unusual array of four ethyl groups on its convex face. In this review, total syntheses of hippolachnin by four groups are described.