Shunsuke Kuwahara

Combination of a new chiroptical probe and theoretical calculations for chirality detection of primary amines.

A method to determine absolute configurations of primary amines by combined use of a chiroptical probe 1 and theoretical calculations is reported. Probe 1 is linked to chiral primary amines yielding 1-amine conjugates, which exhibited exciton coupled circular dichroism in the m-quaterphenyl chromophores. The ratios between the P and M conformers of the 1-amine conjugates, which are calculated with DFT, were correlated highly with the sign and amplitude of the observed CD spectra.

Comparing various chiral dirhodium tetracarboxylates in the dirhodium method

Three enantiopure dirhodium tetracarboxylates are compared in their NMR properties to differentiate chiral ligands of various kinds (dirhodium method). The complex with four (S)-2-methoxy-2-(1-naphthyl) propionate (MalphaNP) residues (Rh2) is slightly better for strong donors than the complex with four Mosher acid anions (Rh1), but it is inferior for weak donors. On the other hand, the dirhodium tetracarboxylate complex with four (S)-N-phthaloyl-(S)-tert.-leucinate residues (Rh3) is generally more effective than Rh1. These results are explained by the estimated conformational behavior of the substituents within the equatorial acid residues and the anisotropy (ring-current) effect of aryl groups.

Synthesis and Photostability of Unimolecular Submersible Nanomachines: Toward Single-Molecule Tracking in Solution

The synthesis and photophysical properties of a series of photostable unimolecular submersible nanomachines (USNs) are reported as a first step toward the analysis of their trajectories in solution. The USNs have a light-driven rotatory motor for propulsion in solution and photostable cy5-COT fluorophores for their tracking. These cy5-COT fluorophores are found to provide an almost 2-fold increase in photostability compared to the previous USN versions and do not affect the rotation of the motor.

Double-armed and tetra-armed cyclen-based cryptands

Abstract Double-armed and tetra-armed cyclen-based cryptands (1a–1d and 2) that bridge two aromatic rings by diethyleneoxy and triethyleneoxy units were prepared. The CSI-MS of 1:1 mixtures ([Ag+]/[ligand]) indicated that these new cryptands form 1:1 complexes with Ag+. The log K values for the interaction between Ag+ and 2 was greater than those of 1a–1d, double-armed cyclens (3a–3c and 4), and tetra-armed cyclen (5). The Ag+-ion-induced 1H NMR spectral changes suggest that the Ag+–π interactions of the Ag+ complexes with the cryptands (1a–1d and 2) are stronger than those in Ag+/double-armed and tetra-armed cyclens. To visualise the Ag+−π interactions, the isosurfaces of the LUMO and HOMOs of the Ag+ complexes were calculated at the B3LYP/3–21G(*) theoretical level. The LUMO of the Ag+ ion is distorted by interaction with the HOMOs of the aromatic side arms. The calculations reveal Ag+−π interactions between the Ag+ ion and the aromatic side arms, and these are shown graphically.

Thermal E/Z Isomerization in First Generation Molecular Motors

Determination of a thermal E/ Z isomerization barrier of first generation molecular motors is reported. Stable ( E)-1a directly converts to stable ( Z)-1c without photochemical E/ Z isomerization. The activation Gibbs energy of the isomerization was determined to be 123 kJ mol-1 by circular dichroism spectral changes. Density functional theory calculations show that ( Z)-1c is ∼11.4 kJ mol-1 more stable than ( E)-1a.