Design of a Photocatalytic [2+2] Cycloaddition Reaction Using Redox-Tag Strategy

The design of photocatalytic processes is important for a sustainable society. Key to these photocatalytic reactions is electron transfer. This article is focused on titanium dioxide photocatalyzed organic synthesis and the design of a new [2+2] cycloaddition reaction based on the electron transfer process. Electron transfer - not only between the substrate and the photocatalyst but also inter- and intramolecularly – is crucial for the reaction design. Radical cations were generated by the photocatalyst and trapped by alkenes. The resultant cyclobutyl radical cations were immediately reduced by the aryl rings via intramolecular electron transfer to obtain cyclobutane rings. The outcome of the reaction was controlled by substitution of the aryl ring and the linker connecting the aryl ring to the enol ether. The carefully designed substrates were highly effective for photocatalytic cycloaddition.     

Intramolecular Long‐Distance Nucleophilic Reactions as a Rapid Fluorogenic Switch Applicable to the Detection of Enzymatic Activity

Long‐distance intramolecular nucleophilic reactions are promising strategies for the design of fluorogenic probes to detect enzymatic activity involved in lysine modifications. However, such reactions have been challenging and hence have not been established. In this study, we have prepared fluorogenic peptides that induce intramolecular reactions between lysine nucleophiles and electrophiles in distal positions. These peptides contain a lysine and fluorescence‐quenched fluorophore with a carbonate ester, which triggers nucleophilic transesterification resulting in fluorogenic response. Transesterification occurred under mild aqueous conditions despite the presence of a long nine‐amino‐acid spacer between the lysine and fluorophore. In addition, one of the peptides showed the fastest reaction kinetics with a half‐life time of 3.7 min. Furthermore, the incorporation of this fluorogenic switch into the probes allowed rapid fluorogenic detection of histone deacetylase (HDAC) activity. These results indicate that the transesterification reaction has great potential for use as a general fluorogenic switch to monitor the activity of lysine‐targeting enzymes.     

Morphology and properties of globular polymeric materials in the solid state: A composite material of DNA with a cationic surfactant

The aim of the present study was to control entanglements in order to regulate the properties of polymeric solids. Initially, fabrication of polymeric solids with few entanglements was attempted. Films of the DNA–cationic surfactant, cetyltrimethylammonium bromide (CTAB) (DNA–CTA), were cast from ethanol solution at room temperature. Morphological examination of DNA–CTA complex films using atomic force microscopy (AFM) revealed that these films were constructed by particle‐like substances. Geometrical analysis of AFM images showed that the particle‐like substances were the aggregates of several DNA–CTA globules. Mechanical characterization suggested that there were fewer entanglements than with normal plastic films. Small angle X‐ray scattering experiments during annealing indicated that molecular motions were highly excited in the surface region of each particle. In conclusion, a globular polymeric film with fewer entanglements was fabricated. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 730–738