Synthesis of 1,2,9,10-tetrakis(N-phenylamino)[2.2]metacyclophane by SmI2-mediated reductive coupling of diimine

SmI₂/HMPA-mediated double reductive coupling of N,N′-(m-xylylidene)dianiline affords 1,2,9,10-tetrakis(N-phenylamino)[2.2]metacyclophane in good yield.     

Synthesis of 3,9-dialkylguanines and their conversion into 3-alkylwyes,models for the fluorescent nucleosides from phenylalanine transfer ribonucleic acids

Synthesis of 3,9-dialkylguanines 5 has been accomplished by N-cyanation of 1-alkyl-5-(alkylamino)imidazole-4- carboxamides 3 followed by base-catalysed cyclisation. Cyclocondensation of 9-alkyl-3-methylguanines 5a, d, f with MeCOCH₂Br gave 3-alkylwyes 6, model compounds of the most probable structure for wyosine from Torulopsis utilis tRNA^Phe.     

Ruthenium(II) pyridylamine complexes with diimine ligands showing reversible photochemical and thermal structural change

Ruthenium(II)-TPA-diimine complexes, [Ru(TPA)(diimine)]2+ (TPA=tris(2-pyridylmethyl)amine; diimine=2,2'-bipyridine (bpy), 2,2'-bipyrimidine (bpm), 1,10-phenanthroline (phen)) were synthesized and characterized by spectroscopic and crystallographic methods. Their crystal structures demonstrate severe steric hindrance between the TPA and diimine ligands. They exhibit drastic structural changes on heating and photoirradiation at their MLCT bands, which involve partial dissociation of the tetradentate TPA ligand to exhibit a facially tridentate mode accompanied by structural change and solvent coordination to give [Ru(TPA)(diimine)(solvent)]2+ (solvent=acetonitrile, pyridine). The incoming solvent molecules are required to have pi-acceptor character, since sigma-donating solvent molecules do not coordinate. The thermal process is irreversible dissociation to give the solvent-bound complexes, which takes place by an interchange associative mechanism with large negative activation entropies. The photochemical process is a reversible reaction reaching a photostationary state, probably by a dissociative mechanism involving a five-coordinate intermediate to afford the same product as obtained in the thermal reaction. Quantum yields of the forward reactions to give dissociated products were lower than those of the backward reactions to recover the starting complexes. In the photochemical process, the conversions of the forward and backward reactions depend on the absorption coefficients of the starting materials and those of the products at certain wavelength, as well as the quantum yields of those reactions. The reversibility of the motions can be regulated by heating and by photoirradiation at certain wavelength for the recovery process. In the bpm system, we could achieve about 90 % recovery in thermal/photochemical structural interconversion.     

Nonequilibrium molecular dynamics simulations with a backward-forward trajectories sampling for multidimensional infrared spectroscopy of molecular vibrational modes

A full molecular dynamics (MD) simulation approach to calculate multidimensional third-order infrared (IR) signals of molecular vibrational modes is proposed. Third-order IR spectroscopy involves three-time intervals between three excitation and one probe pulses. The nonequilibrium MD (NEMD) simulation allows us to calculate molecular dipoles from nonequilibrium MD trajectories for different pulse configurations and sequences. While the conventional NEMD approach utilizes MD trajectories started from the initial equilibrium state, our approach does from the intermediate state of the third-order optical process, which leads to the doorway-window decomposition of nonlinear response functions. The decomposition is made before the second pump excitation for a two-dimensional case of IR photon echo measurement, while it is made after the second pump excitation for a three-dimensional case of three-pulse IR photon echo measurement. We show that the three-dimensional IR signals are efficiently calculated by using the MD trajectories backward and forward in time for the doorway and window functions, respectively. We examined the capability of the present approach by evaluating the signals of two- and three-dimensional IR vibrational spectroscopies for liquid hydrogen fluoride. The calculated signals might be explained by anharmonic Brownian model with the linear-linear and square-linear system-bath couplings which was used to discuss the inhomogeneous broadening and dephasing mechanism of vibrational motions. The predicted intermolecular librational spectra clearly reveal the unusually narrow inhomogeneous linewidth due to the one-dimensional character of HF molecule and the strong hydrogen bond network.     

Two-dimensional fifth-order Raman spectroscopy of liquid formamide: Experiment and Theory

The fifth-order two-dimensional (2D) Raman spectrum of liquid formamide has been obtained. The absolute signal levels, qualitative features, as well as quantitative aspects of the 2D spectrum are found to be in good agreement with recent molecular dynamics calculations. The most important singular feature is the relatively strong rephasing signal observed along the diagonal. This finding illustrates the more structured nature of the hydrogen bond network of liquid formamide in comparison with simple liquids as exemplified by CS(2). The theoretical calculations have been extended to include comparisons of different potentials that illustrate the sensitivity of the experiment to the anharmonic motions in the liquid state. The theoretical results point out the key features in the 2D spectrum that probe the essential details in the intermolecular potential. The experiment has been demonstrated to provide new insight into collective effects operating in hydrogen bonded liquids and opens up the exploration of other liquids with this approach.     

Phase transition and crystal growth of a titania layer on a titanium metal plate

Research on Chemical Intermediates - A titanium metal surface was heated with an alkali metal chloride in order to produce a phase transition from amorphous titania to crystalline titania on the...     

2′‐Amino‐3‐methoxy­pyrimidino­[5′,4′:16,17]­estra‐1,3,5(10),16‐tetraene

In the title compound, C₂₁H₂₅N₃O, the six‐membered ring that is fused to two other six‐membered rings in the estrane moiety adopts an envelope conformation. The compound shows intermolecular hydrogen bonding of the amine group to an N atom of the pyrimidine moiety, as well as weak intermolecular interactions involving H atoms in the hydro­phobic residue of the mol­ecule.