Exciton recurrence motion in aggregate systems in the presence of quantized optical fields

The exciton dynamics of model aggregate systems, dimer, trimer, and pentamer, composed of two-state monomers is computationally investigated in the presence of three types of quantized optical fields, i.e., coherent, amplitude-squeezed, and phase-squeezed fields, in comparison with the case of classical laser fields. The constituent monomers are assumed to interact with each other by the dipole-dipole interaction, and the two-exciton model, which takes into account both the one- and two-exciton generations, is employed. As shown in previous studies, near-degenerate exciton states in the presence of a (near) resonant classical laser field create quantum superposition states and thus cause the spatial exciton recurrence motion after cutting the applied field. In contrast, continuously applied quantized optical fields turn out to induce similar exciton recurrence motions in the quiescent region between the collapse and revival behaviors of Rabi oscillation. The spatial features of exciton recurrence motions are shown to depend on the architecture of aggregates. It is also found that the coherent and amplitude-squeezed fields tend to induce longer-term exciton recurrence behavior than the phase-squeezed field. These features have a possibility for opening up a novel creation and control scheme of exciton recurrence motions in aggregate systems under the quantized optical fields.     

Measurement of hydrolysis kinetics of galactose-substituted fluorescein by β-galactosidase at the toluene–water interface by spinning microtube fluorometry

A new analytical technique, spinning microtube fluorometry (SMF), was developed and applied to the study of interfacial hydrolysis of 5-dodecanoylaminofluorescein di-β-D-galactopyranoside (C₁₂FDG) by β-galactosidase (β-gal) in the toluene–water system. The nonfluorescent lactone form of C₁₂FDG in the toluene phase was converted at the interface to 5-dodecanoylaminofluorescein (C₁₂F), which was fluorescent in the aqueous phase as a dianion at pH 7.3, though some part of C₁₂F was extracted into the toluene phase as its nonfluorescent lactone form. The distribution ratios of C₁₂FDG and C₁₂F at pH 7.3 were determined as 1.4×10² and 1.97, respectively. The interfacial adsorption constants from the toluene phase to the interface at pH 7.3 were 4.8×10⁻⁴ and 1.7×10⁻² dm for C₁₂FDG and C₁₂F, respectively. The kinetic experiments with the SMF method concluded that the rate-determining step of the enzymatic hydrolysis at the interface and in the aqueous phase was the 1:1 reaction of C₁₂FDG and β-gal and that the hydrolysis reaction rate constant at the interface at pH 7.3 was 1.84×10³ M⁻¹s⁻¹, almost equal to that in the aqueous solution, 1.76×10³ M⁻¹s⁻¹. Finally, the SMF method revealed that the contribution of the interfacial reaction to the overall hydrolysis reaction rate of the toluene–water system was as high as 97%.     

Scanning tunneling spectroscopic evidence of crossover transition in the two-impurity Kondo problem

To explore the crossover transition in the two-impurity Kondo problem, we calculate the differential conductance (dI / dV) corresponding to scanning tunneling spectroscopy (STS) measurements of a magnetic dimer adsorbed on a metal surface covered by a decoupling layer. With the aid of the numerical renormalization group (NRG) technique, we find that the peak structure of the dI / dV spectra near the Fermi level changes gradually as a function of the adatom separation and the coupling between the adatom localized spins and the metal surface conduction band. When the coupling becomes small, the peak disappears and, instead, a dip structure appears near the Fermi level. This dip structure is the manifestation of the strong antiferromagnetic correlation between the localized spins. We conclude that the gradual change of the dI / dV structure from a peak structure to a dip structure is an evidence of the crossover transition in the two-impurity Kondo problem.     

Wickerols A and B: novel anti-influenza virus diterpenes produced by Trichoderma atroviride FKI-3849

Wickerols A and B were produced by a fungus, Trichoderma atroviride FKI-3849. Wickerol A showed potent anti-influenza virus activity against strain A/PR/8/34 (H1N1), whereas wickerol B exhibited weaker impact. The anti-influenza virus spectrum between wickerols A and B was different. The cyclization mechanism of the wickerol carbon-skeleton was investigated by incorporation of ¹³C-labeled acetate. A pathway through the verticillyl cation was predicted.     

Synthesis of pyrrolophenanthridone alkaloid kalbretorine from indolecarboxylic acids via hypervalent iodine(III) mediated halodecarboxylation and reduction

The treatment of 8,9,10-trimethoxy-7H-pyrrolo[3,2,1-de]phenanthridine-4,5-dicarboxylic acid with phenyliodine diacetate and potassium iodide in tetrahydrofuran gave the corresponding 4,5-diiodo derivative, which was converted to kalbretorine via reduction, demethylation, followed by alkylation.     

Chiral recognition of 2-alkyl alcohols with porphyrin J-nanoaggregates at the liquid-liquid interface

The J-aggregate of diprotonated tetraphenylporphyrin (H(4)TPP(2+)) formed at the dodecane-water interface showed circular dichroism spectra corresponding to the chirality of 2-alkyl alcohols, longer than 2-butanol, added to the dodecane phase. The phenomenon suggested the preferential interaction between the nano-sized J-aggregates and the chiral alcohols at the interface, and provided a potential use of the J-nanoaggregate as a chiral recognition probe.     

Vibrational spectrum at a water surface: a hybrid quantum mechanics/molecular mechanics molecular dynamics approach

A hybrid quantum mechanics/molecular mechanics (QM/MM) molecular dynamics (MD) simulation is applied to the calculation of surface orientational structure and vibrational spectrum (second-order nonlinear susceptibility) at the vapor/water interface for the first time. The surface orientational structure of the QM water molecules is consistent with the previous MD studies, and the calculated susceptibility reproduces the experimentally reported one, supporting the previous results using the classical force field MD simulation. The present QM/MM MD simulation also demonstrates that the positive sign of the imaginary part of the second-order nonlinear susceptibility at the lower hydrogen bonding OH frequency region originates not from individual molecular orientational structure, but from cooperative electronic structure through the hydrogen bonding network.     

Density functional theory-based analysis on O2 molecular interaction with the tri-s-triazine-based graphitic carbon nitride

The structural and electronic properties of O₂ molecular adsorption on the Tri-s-triazine-based graphitic carbon nitride (g-C₃N₄) surface was investigated through first principles calculation based on density functional theory (DFT). Here, we show that the O₂ molecule is merely physisorbed on the surface of g-C₃N₄ through the interaction of its lowest unoccupied molecular orbital (LUMO) with the orbitals of the 2-coordinated nitrogen atoms of the surface. Though physisorbed, a stronger molecular adsorption was found as compared with its adsorption on pure graphene sheets. We also found that the O₂ molecule gains very small amount of electron charges from the surface, which, together with a stronger adsorption energy, may attribute to a more effective oxygen reduction reaction (ORR) site as compared with pure graphene. These results would then be important for reactions with intermediate surface oxidation step in a carbon and nitrogen-based catalyst, and could lead to realization of an effective materials design for surface application, e.g. towards a more efficient catalyst for the ORR on the cathode side of the proton exchange membrane fuel cell (PEMFC).     

The mechanism of H2 dissociation and adsorption on Mn-modified Ni(111) surface: A density functional theory-based investigation

The mechanism of H₂ dissociative adsorption on Mn-modified Ni(111) surface is investigated and explained using spin-polarized density functional theory (DFT). Potential energy surface (PES) is used to determine the efficient reaction pathway of H₂ on the surface. The dissociative adsorption of H₂ in the hollow sites with its center-of-mass (CM) positioned on top of Ni atom has low activation barrier. This is lower compared if its CM is on top of the Mn atom. The difference in the reactivity of H₂ with Ni and Mn as the CM is corroborated by the positions of the bonding and antibonding orbitals of H₂ as it approaches the surface which is verified from local density of states (LDOS). The greater density of states in the region around the Fermi level of the d_zz, d_xz, and d_yz orbitals of the Ni atom explains the low activation barrier obtained for the dissociation of H₂ on top of the Ni atom in the Mn-modified Ni(111) surface.     

Ring-Closing Metathesis of Ene-Ynamide: Application to the Synthesis of Medium-Sized Cyclic Dienamide

Summary: Ring-closing metathesis (RCM) of ene-ynamide, which could be applied to the synthesis of various heterocycles containing 7- and 8-membered rings, was investigated. Ene-ynamides are easily synthesized by the known method. When a toluene solution of ene-ynamide was stirred in the presence of a catalytic amount of second-generation ruthenium carbene complex 1 under an ethylene atmosphere, RCM proceeded smoothly to provide a heterocyclic compound having a diene moiety in good to high yield. A substituent of the ynamide moiety affected the yield of the cyclized product.