The efficiency of ring-closing metathesis catalyzed by a Hoveyda–Grubbs type catalyst in water can be enhanced by addition of a chloride salt under neutral conditions. UV–vis spectroscopic study showed that a characteristic band of the catalyst around 380 nm remained over 16 h in the presence of KCl, whereas the band distinctly decreased in the absence of KCl. The disappearance of the band is ascribed to a displacement of a chloride ligand by a water molecule or a hydroxide anion. The spectral changes can be related to the metathesis activity. The experimental results indicate that avoidance of the chloride ligand loss is important to maintain the metathesis activity in water.

The excimer emission of pyrene is popularly employed for investigating the association between pyrene-labeled biomolecules or between pyrene-labeled places in a biomolecule. The property of pyrene excimer emission is affected by the fluctuation in ring stacking modes, which originates from the structural flexibilities of pyrene probes and/or of labeled places. Investigations of the excimer emission in terms of dynamics of pyrene stacking modes provide the detailed spatial information between pyrene-labeled places. In order to evaluate the effects of probe structures and fluctuation in pyrene-pyrene association modes on their emission properties on protein surface, three types of pyrene probe with different linker lengths were synthesized and conjugated to two cysteine residues in the A55C/C77S/V169C mutant of adenylate kinase (Adk), an enzyme that shows a structural transition between OPEN and CLOSED forms. In the CLOSED form of Adk labeled by a pyrene probe with a short linker, excimer emission was found to be predominated by the ground-state association of pyrenes. The pyrene stacking structure on the protein surface was successfully determined by an X-ray crystallographic analysis. However, the emission decay in the protein suggested the existence of several stacking orientations in solution. With the increase in the linker length, the effect of fluctuation in pyrene association modes on the spectral properties distinctly emerged at both ground and excited states. The combination of steady-state and time-resolved spectroscopic analyses is useful for differentiation in the origin of the excimer emission, which is essential for precisely understanding the interaction fashions between pyrene-labeled biomolecules.

Adenylate kinase shows a conformational transition (OPEN and CLOSED forms) during substrate binding and product release to mediate the phosphoryl transfer between ADP and ATP/AMP. The protein motional characteristics will be useful to construct switching systems of fluorophore properties caused by the catalytic cycle of the enzyme. This paper demonstrates in situ reversible switching of a fluorophore property driven by the conformational transition of the enzyme. The pyrene-conjugated mutant adenylate kinase is able to switch the monomer/excimer emission property of pyrene on addition of ADP or P(1)P(5)-di(adenosine-5')pentaphosphate (Ap5A, a transition state analog). The observation under the dilute condition (~0.1 μM) indicates that the emission spectral change was caused by the motion of a protein molecule and not led by protein-protein interactions through π-π stacking of pyrene rings. The switching can be reversibly conducted by using hexokinase-coupling reaction. The fashion of the changes in emission intensities at various ligand concentrations is different between ADP, Mg(2+)-bound ADP, and Mg(2+)-bound Ap5A. The emission property switching is repeatable by a sequential addition of a substrate in a one-pot process. It is proposed that the property of a synthetic molecule on the enzyme surface is switchable in response to the catalytic cycle of adenylate kinase.

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A wet-stretching technique was applied to chromophore-blended poly(vinyl alcohol) (PVA) films to control the agglomeration of chromophores and improve the triplet−triplet annihilation (TTA) photon upconversion (UC) performance of the solid-state system. By using the stretching technique, a maximum UC quantum yield of ∼3% and lowest threshold intensity of 90 mW/cm 2 were obtained under atmospheric conditions. It was found that a decrease in the crystallinity of the PVA matrix induced by stretching caused specific localization of the chromophores and accelerated triplet energy transfer and triplet exciton migration.