Izumi Iwakura

Total syntheses of coronatines by exo-selective Diels–Alder reaction and their biological activities on stomatal opening

The natural phytotoxin coronatine, which is composed of two individual parts, coronafacic acid and coronamic acid, exhibits various promising biological activities similar to jasmonic acid. Interestingly, coronatine induces stomatal opening involving the swelling of guard cells in which jasmonic acid is not involved as an endogenous regulator. We established syntheses of four stereoisomers of coronatine employing the exo-selective Diels–Alder reaction as a key step. Remarkable differences in stomatal opening activity were observed between enantiomers of coronatine. This result strongly suggests that the stereo structure of coronatine is very important for its stomatal opening activity. In addition, SAR studies suggested that coronatine operates as a molecular mimic of jasmonyl-L-isoleucine in plant guard cells.

Direct observation of molecular structural change during intersystem crossing by real-time spectroscopy with a few optical cycle laser.

Ultrafast spectroscopy by a sub-5 fs pulse laser was applied to the simultaneous study of electronic relaxation and vibrational dynamics in Ru(II)(TPP)(CO). The electronic lifetimes of (1)Q(x(1,0))(pi,pi*) and (1)Q(x(0,0))(pi,pi*) were determined to be 230 +/- 70 fs and 1150 +/- 260 fs, respectively. The spectrogram shows the time dependent changes in the vibrational spectrum associated with the spin state change from the Franck-Condon state in the excited singlet state to the triplet state via the curve crossing point between the singlet and triplet potential surfaces. The time constant of the intersystem crossing process was determined to be about 1.0 ps from observed electronic relaxation and vibrational dynamics reflecting the transition from the singlet to triplet electronic excited state.

The Reaction Mechanism of Claisen Rearrangement Obtained by Transition State Spectroscopy and Single Direct-Dynamics Trajectory

Chemical bond breaking and formation during chemical reactions can be observed using “transition state spectroscopy”. Comparing the measurement result of the transition state spectroscopy with the simulation result of single direct-dynamics trajectory, we have elucidated the reaction dynamics of Claisen rearrangement of allyl vinyl ether. Observed the reaction of the neat sample liquid, we have estimated the time constants of transformation from straight-chain structure to aromatic-like six-membered ring structure forming the C1-C6 bond. The result clarifies that the reaction proceeds via three steps taking longer time than expected from the gas phase calculation. This finding provides new hypothesis and discussions, helping the development of the field of reaction mechanism analysis.

The relation between the symmetry of vibrational modes and the potential curve displacement associated with electronic transition studied by using real-time vibrational spectroscopy

The relation between the vibronic coupling strength of the vibronic state combined with the optical transitions with short pulses and the symmetry of the coupled vibrational modes was studied by using multi-wavelength vibrational real-time spectroscopy. A pump–probe experiment of thiophene oligomers using 6.7 fs pulsed laser as an ultrashort pulse light source and a multi-channel lock-in amplifier as a broadband detector was performed to obtain simultaneously the real-time traces at 128 wavelengths. At all wavelengths, the absorbance changes were plotted against pump–probe delay time, which was between −200 and 2000 fs. The vibronic coupling in both the ground and excited states was classified into two types: the displaced (D) type with displaced potential surfaces and the non-displaced (ND) type with non-displaced potential surfaces between the two electronic studies. The D and ND types were found to be related to inversion anti-symmetric and symmetric molecular vibrations, respectively, with respect to the center of the pseudo-inversion symmetry of the molecule. The symmetry center is located at the middle point of the bond connecting the two quinoid-type thiophene rings. It was shown that multi-wavelength measurement of the vibrational real-time spectroscopy provides information on the mechanism of vibronic coupling in the process of transition from the ground state to the excited state and that between the two excited states.

Manganese and cobalt 3-oxobutylideneaminato complexes: Design and application for enantioselective reactions

Abstract The optically active 3-oxobutylideneaminato transition-metal complexes have been developed as efficient catalysts for a variety of enantioselective reactions; e.g. the corresponding manganese(III) complexes catalyzed the enantioselective aerobic epoxidation of unfunctionalized olefins, and the corresponding cobalt complexes have been developed for the enantioselective borohydride reduction of various carbonyl compounds. The cobalt complexes could also be employed for the catalytic enantioselective cyclopropanation with diazoacetates and the Lewis acid catalyses such as the hetero Diels–Alder reaction, carbonyl–ene reaction, and 1,3-dipolar cycloaddition of nitrones. In the presence of the cobalt complex, the Henry reaction proceeded with a high enantioselectivity, and the enantioselective chemical fixation of carbon dioxide to obtain the optically active cyclic carbonate. In these Lewis acid catalyses, the valence of cobalt and the counter anion have significant effects on the reaction rate and stereoselectivity.

Triazoyl-phenyl linker system enhancing the aqueous solubility of a molecular probe and its efficiency in affinity labeling of a target protein for jasmonate glucoside.

In methods employing molecular probes to explore the targets of bioactive small molecules, long or rigid linker moieties are thought to be critical factors for efficient tagging of target protein. We previously reported the synthesis of a jasmonate glucoside probe with a highly rigid linker consisting of a triazoyl-phenyl (TAzP) moiety, and this probe demonstrated effective target tagging. Here we compare the TAzP probe with other rigid or flexible probes with respect to target tagging efficiency, hydrophobic parameters, aqueous solubility, and dihedral angles around the biaryl linkage by a combination of empirical and calculation methods. The rigid biaryl linkage of the TAzP probe has a skewed conformation that influences its aqueous solubility. Such features that include rigidness and good aqueous solubility resulted in highly efficient target tagging. These findings provide a promising guideline toward designing of better linkers for improving molecular probe performance.

Excitonic and vibrational nonlinear processes in a polydiacetylene studied by a few-cycle pulse laser

High-density excitation of exciton induces the faster decay of absorbance change due to exciton–exciton interaction originated from the Auger recombination process. Experimental results clarified the dynamics of the exciton and the bimolecular quenching rate and the jump rate of exciton were determined to be 5.2×10−9 cm3 s−1 and 5.2×10−9 s−1, respectively. The intensity modulation of electronic transition under high-density excitation with sub-5-fs pulse was analyzed to observe the Fourier power spectrum of the molecular vibration modes and revealed the existence of a combination tone (2726 cm−1) of the C–C (1241 cm−1) and the C=C (1485 cm−1) stretching modes. This indicates that the highly excited state induced by the Auger process results in the fusion of vibrational quantum states. Difference frequency generation of the vibrational modes also takes place in the same process due to the fission of the vibrational quanta stimulated by the interaction of the two vibrational modes. It was also found that the intensities of several prominent peaks corresponding to the modes of C=C and C–C stretching were proportional to the squared intensity of the probe pulse. Furthermore, the frequencies of the modes were shifted to low frequencies at high probe intensity. The process can be considered to be fifth-order cascaded Raman scattering via real excitation of vibronic excitons.

Pulsed Nd:YAG laser induced high throughput stereospecific [2 + 2] cycloaddition of highly organized 1,2-bis(4-pyridyl)ethylene in a supramolecular scaffold

The 3rd harmonic generation in a Nd:YAG pulsed laser induces the high throughput [2 + 2] cycloaddition of 1,2-bis(4-pyridyl)ethylene that assemble itself tightly into a face-to-face manner around the Yb3+ octaaqua complex via hydrogen bonds, without damaging the cyclobutyl ring-containing products.

Transient process spectroscopy for the direct observation of inter-molecular photo-dissociation

Transient process spectroscopy has previously been thought to be applicable only to the analysis of intra-molecular processes. Two metal ion bridges used in the present work have allowed us to visualize real-time variations of the molecular vibration frequencies during photo-disproportionation inside bimolecule aggregates, which directly shows transient inter-molecular reactions.

[N,N′-Bis(2-methoxy­carbonyl-3-oxo­butyl­idene)­ethyl­enediaminato-κ4O,N,N′,O′]­cobalt(II)

The title compound, [Co(C14H18N2O6)], is the first structurally characterized example of a β-ketoiminato CoII complex without axial ligands. It adopts a square-planar cis-[CoN2O2] coordination geometry, and lies on a mirror plane. The planar complexes are stacked along 21 screw axes parallel to b to form columns, the Co⋯Co distance in the column being 3.5213 (2) A.