Two types of rhodium-catalyzed CS/CS metathesis reactions: formation of CS/CS bonds and CC/SS bonds

A rhodium complex catalyzes two types of single bond metathesis reactions of two CS bonds depending on the added ligand: CS/CS to CS/CS metathesis and CS/CS to CC/SS metathesis. In the presence of a catalytic amount of RhH(PPh₃)₄ and 1,1′-bis(diphenylphosphino)ferrocene (dppf), two 1-alkylthioalkynes exchange alkylthio groups to give equilibrium mixtures of four 1-alkylthioalkynes. When tris(p-methoxyphenyl)phosphine or diphenylmethylphosphine is used, 1,3-butadiynes are obtained.     

β-Galactosidase fluorescence probe with improved cellular accumulation based on a spirocyclized rhodol scaffold

We identified a rhodol bearing a hydroxymethyl group (HMDER) as a suitable scaffold for designing fluorescence probes for various hydrolases. HMDER shows strong fluorescence at physiological pH, but phenolic O-alkylation of HMDER results in a strong preference for the spirocyclic form, which has weak fluorescence. As a proof of concept, we utilized this finding to develop a new fluorescence probe for β-galactosidase. This probe has favorable characteristics for imaging in biological samples: it has good cellular permeability, and its hydrolysis product is well-retained intracellularly. It could rapidly and clearly visualize β-galactosidase activity in cultured cells and in Drosophila melanogaster tissue, which has rarely been achieved with previously reported fluorescence probes.     

Development of an Si-rhodamine-based far-red to near-infrared fluorescence probe selective for hypochlorous acid and its applications for biological imaging

A far-red to near-infrared (NIR) fluorescence probe, MMSiR, based on Si-rhodamine, was designed and synthesized for sensitive and selective detection of HOCl in real time. MMSiR and its oxidized product SMSiR have excellent properties, including pH-independence of fluorescence, high resistance to autoxidation and photobleaching, and good tissue penetration of far-red to NIR fluorescence emission. The value of MMSiR was confirmed by real-time imaging of phagocytosis using a fluorescence microscope. wsMMSiR, a more hydrophilic derivative of MMSiR, permitted effective in vivo imaging of HOCl generation in a mouse peritonitis model. This probe is expected to be a useful tool for investigating the wide range of biological functions of HOCl.     

A practical strategy to create near-infrared luminescent probes: conversion from fluorescein-based sensors

Luminescent lanthanide complexes incorporating Yb(3+) and Nd(3+) are attracting much attention as imaging agents, but there have been few practical methods to make responsive sensors with these complexes. Here, we introduce a general strategy to synthesize near-infrared luminescent probes by conjugating a Yb(3+) chelate to established fluorescein-based probes. As the first demonstration, we present a complex, based on the green-emitting probe DAF-4, that responds to nitric oxide (NO) in aqueous solution with a significant increase in luminescence intensity at 980 nm.     

A long-lived luminescent probe to sensitively detect arylamine N-acetyltransferase (NAT) activity of cells

Arylamine N-acetyltransferase (NAT) is an important phase II metabolizing enzyme that influences drug efficacy and adverse effects. Here, we report a long-lived luminescent lanthanide complex as a probe for NAT, employing an intraligand photoinduced electron transfer strategy. The probe shows approximately 100-fold increase of luminescence upon N-acetylation catalyzed by NAT, with relatively high specificity for NAT2 over NAT1. It is the first NAT probe that is suitable for sensitive, homogeneous, and rapid detection of NAT activity of recombinant enzyme or cell lysate, and is expected to be useful for drug discovery and clinical diagnosis.     

Rhodium-catalyzed interconversion between acid fluorides and thioesters controlled using heteroatom acceptors

A rhodium complex catalyzed the equilibrium acyl transfer reaction between acid fluorides and thioesters. In the presence of fluoride or thiolate acceptors, the reaction could be shifted to either product. RhH(PPh₃)₄-dppe catalyzed the reaction of acid fluorides and diorgano disulfides in the presence of triphenylphosphine giving thioesters, which was accompanied by triphenylphosphine difluoride. The same complex catalyzed the reaction of aryl thioesters and hexafluorobenzene giving acid fluorides, which was accompanied by 1,4-di(arylthio)-2,3,5,6-tetrafluorobenzenes.     

Design and Synthesis of a Highly Sensitive Off–On Fluorescent Chemosensor for Zinc Ions Utilizing Internal Charge Transfer

Fluorescence imaging is a powerful tool for the visualization of biological molecules in living cells, tissue slices, and whole bodies, and is important for elucidating biological phenomena. Furthermore, zinc (Zn²⁺) is the second most abundant heavy metal ion in the human body after iron, and detection of chelatable Zn²⁺ in biological studies has attracted much attention. Herein, we present a novel, highly sensitive off–on fluorescent chemosensor for Zn²⁺ by using the internal charge transfer (ICT) mechanism. The rationale of our approach to highly sensitive sensor molecules is as follows. If fluorescence can be completely quenched in the absence of Zn²⁺, chemosensors would offer a better signal‐to‐noise ratio. However, it is difficult to quench the fluorescence completely before Zn²⁺ binding, and most sensor molecules still show very weak fluorescence in the absence of Zn²⁺. But even though the sensor shows a weak fluorescence in the absence of Zn²⁺, this fluorescence can be further suppressed by selecting an excitation wavelength that is barely absorbed by the Zn²⁺‐free sensor molecule. Focusing on careful control of ICT within the 4‐amino‐1,8‐naphthalimide dye platform, we designed and synthesized a new chemosensor ( 1 ) that shows a pronounced fluorescence enhancement with a blueshift in the absorption spectrum upon addition of Zn²⁺. The usefulness of 1 for monitoring Zn²⁺ changes was confirmed in living HeLa cells. There have been several reports on 4‐amino‐1,8‐naphthalimide‐based fluorescent sensor molecules. However, 1 is the first Zn²⁺‐sensitive off–on fluorescent sensor molecule that employs the ICT mechanism; most off–on sensor molecules for Zn²⁺ employ the photoinduced electron transfer (PeT) mechanism.     

Difference sets over Galois rings with odd extension degrees and characteristic an even power of 2

We construct an infinite family of (2 ^ns , 2 ^{ns/2 -1}(2 ^ns/2?1), 2 ^{ns/2 -1}(2 ^{ns/2 -1} ?1)) difference sets over a Galois ring GR(2 ⁿ , s) with characteristic an even power n of 2 and an odd extension degree s. It makes a chain of difference sets preserving the structures when n increases and s is fixed. We introduce a new operation into GR(2 ⁿ , s). The Gauss sum associated with the multiplicative character defined by the subgroup with respect to the new operation plays an important role in the construction.     

Preparation, characterization and properties of novel covalently surface-functionalized zinc oxide nanoparticles

Novel covalently surface-modified zinc oxide (ZnO) nanoparticles (NP) (ZHIE) were successfully prepared, which have organic chains composed of hydrophilic amide and urethane linkages, and terminal amino groups on the surfaces, using zinc acetate monohydrate. FTIR spectroscopy, X-ray analysis and TEM observation suggested that the resultant ZHIE NPs have the mean sizes of about 10 nm in diameters, the organic chains linking the amino groups in the terminals and wurtzite crystal structure. UV-vis absorption spectrum of the ZHIE NPs in methanol showed maximum absorption band at 348 nm, supporting the TEM observations. Photoluminescent spectrum measurements depicted that the ZHIE NPs show broad visible emission band on the basis of trapped-electron emission. Cytotoxicity and phagocytosis assays suggested that the ZHIE NPs are noncytotoxic, and the ZHIE-labeled zymosan particles derived by conjugation of the ZHIE NPs with zymosan are internalized into the cells and generate fluorescence based on the ZHIE NPs.