Effect of pulse width and fluence of femtosecond laser on the size of nanobump array

Conical nanobump arrays were generated on gold thin film processed by interfering femtosecond laser. The transition of the height and diameter as functions of fluence and pulse width was investigated. When the fluence was 87 mJ/cm², the height and diameter were not so different at 350 fs or shorter pulse width. They decreased at longer pulse width, and no bump could be generated over 1.6 ps. The results suggest the decrease of size is due to the diffusion of electron to not-excited region, and due to heat conduction to not heated region or substrate, or change of absorbance of laser. At long pulse width of 2.4 ps and relatively higher fluence of 190 mJ/cm², nanobump had liquid-like structure as a stop motion of a water drop.     

Synthesis of a Stable N-Hetero-RhI-Metallacyclic Silanone

A novel N-hetero-Rh^I-metallacyclic silanone 2 has been synthesized. The silanone 2 , showing an extremely large dimerization energy (ΔG=+86.2 kcal mol⁻¹), displays considerable stability and persists in solution up to 60 °C. Above 120 °C, an intramolecular C_sp3−H insertion occurs slowly over a period of two weeks leading to the bicyclic silanol 5 . The exceptional stability of 2 , related to the unusual electronic and steric effects of Rh^I-substituent, should allow for a more profound study and understanding of these new species. Furthermore, the metallacyclic silanone 2 presents two reactive centers (Si=O and Rh), which can be involved depending upon the nature of reagents. Of particular interest, the reaction with H₂ starts with the hydrogenation of Rh^I center leading to the corresponding Rh^III-dihydride complex 7 and it undergoes a cis/trans-isomerization via a particular mechanism, demonstrating that addition-elimination processes can also happen for silanones just like for their carbon analogues!     

Design of a hybrid biosensor for enhanced phosphopeptide recognition based on a phosphoprotein binding domain coupled with a fluorescent chemosensor

Protein-based fluorescent biosensors with sufficient sensing specificity are useful analytical tools for detection of biologically important substances in complicated biological systems. Here, we present the design of a hybrid biosensor, specific for a bis-phosphorylated peptide, based on a natural phosphoprotein binding domain coupled with an artificial fluorescent chemosensor. The hybrid biosensor consists of a phosphoprotein binding domain, the WW domain, into which has been introduced a fluorescent stilbazole having Zn(II)-dipicolylamine (Dpa) as a phosphate binding motif. It showed strong binding affinity and high sensing selectivity toward a specific bis-phosphorylated peptide in the presence of various phosphate species such as the monophosphorylated peptide, ATP, and others. Detailed fluorescence titration experiments clearly indicate that the binding-induced fluorescence enhancement and the sensing selectivity were achieved by the cooperative action of both binding sites of the hybrid biosensor, i.e., the WW domain and the Zn(II)-Dpa chemosensor unit. Thus, it is clear that the tethered Zn(II)-Dpa-stilbazole unit operated not only as a fluorescence signal transducer, but also as a sub-binding site in the hybrid biosensor. Taking advantage of its selective sensing property, the hybrid biosensor was successfully applied to real-time and label-free fluorescence monitoring of a protein kinase-catalyzed phosphorylation.     

Kinetics of chain collapse in dilute polymer solutions: molecular weight and solvent dependences

The molecular weight and solvent dependences of the characteristic time of chain collapse were studied for poly(methyl methacrylate) (PMMA) of the molecular weight Mw=6.4x10(6) and 1.14x10(7) in pure acetonitrile (AcN) and in the mixed solvent of AcN+water (10 vol %). The size of PMMA chains was measured as a function of the time after the quench by static light scattering and the chain collapse processes were expressed by the plot of the expansion factor alpha2 vs ln t. The chain collapse in the mixed solvent AcN+water (10 vol %) was found to occur much faster than that in pure AcN, though the measurement of the former collapse process required several hours. In order to make a comparison between the rates of chain collapses, the fast chain collapse process was superposed on the slow one by scaling the time of the fast process as gammat. The scale factor gamma was determined by comparing the chain collapse processes of nearly the same equilibrium expansion factor with each other. Accordingly, the superposition of the collapse for Mw=6.4x10(6) on that for Mw=1.14x10(7) yielded gammam=4.0+/-0.6 for the process in AcN+water and 5.5+/-0.6 in AcN. The superposition of the chain collapse process in AcN+water on that in AcN yielded gammas=9.5+/-1.4 for Mw=6.4x10(6) and 12.0+/-1.8 for Mw=1.14x10(7). This analysis suggests that gammam and gammas are constant independent of each other. Thus, by assuming the molecular weight dependence of gammam approximately Mz, the characteristic time tauexp of chain collapse was conjectured as tauexp approximately kappaMz, where kappa reflects the nature of solvent species. The ratio of kappa for PMMA in AcN to that in AcN+water is given by gammas. The exponent was estimated to be z=2.4+/-0.7 for AcN+water and 3.0+/-0.7 for AcN. These values are compatible with the theoretical prediction z=3 based on a phenomenological model, though the observed characteristic times are longer by several orders of magnitude than those of the theoretical prediction.     

Fluorescent 3-methylene-2,3-dihydrochalcogenophenes incorporated in a rigid dibenzobarrelene skeleton

The fluorescent 3-methylene-2,3-dihydroselenophene derivative (Φ(F) = 0.86 in CH(2)Cl(2)) incorporated in a dibenzobarrelene skeleton was synthesized by the reaction of a four-membered selenaplatinacycle with dimethyl acetylenedicarboxylate (DMAD) or reaction of bis(dibenzobarrelenyl) diselenide with DMAD in the presence of Pd(PPh(3))(4) and PPh(3). A fluorescent sulfur homologue (Φ(F) = 1.0 in CH(2)Cl(2)) was also synthesized by the reaction of bis(dibenzobarrelenyl) disulfide with DMAD in the presence of Pd(PPh(3))(4). Selected chemical transformations of these diesters were also investigated.     

Photoexcited chemical wave in the ruthenium-catalyzed Belousov-Zhabotinsky reaction

The excitation of the photosensitive Belousov-Zhabotinsky (BZ) reaction induced by light stimulation was systematically investigated. A stepwise increase in the light intensity induced the excitation, whereas a stepwise decrease did not induce the excitation. The threshold values for the excitation were found to be a function of the initial and final light intensities, time variation in light intensity, and the concentration of NaBrO(3). The experimental results were qualitatively reproduced by a theoretical calculation based on a three-variable Oregonator model modified for the photosensitive BZ reaction. These results suggest that although the steady light irradiation is known to inhibit oscillation and chemical waves in the BZ system under almost all conditions, the stepwise increase in the light irradiation leads to the rapid production of an activator, resulting in the photoexcitation.     

Die optischen Aufheller Fraxin und Aesculin

The closely related glycosides fraxin and esculin have been isolated in pure form from an ash bark extract by gel permeation chromatography. This challenging separation is a prime example for the preparative value of a crosslinked dextran gel. Silicagel 60 only leads to pure esculin. The terms optical brighteners and fluorescence are discussed. All analytical spectra were recorded and are reproduced and interpreted either in the main part or in the supporting information. The project is a follow up of the recent book “Classics in Spectroscopy” by S. Berger und D. Sicker (Wiley‐VCH 2009).     

Dilemma game structure hidden in traffic flow at a bottleneck due to a 2 into 1 lane junction

Following Yamauchi’s study [A. Yamauchi, J. Tanimoto, A. Hagishima, H. Sagara, Dilemma game structure observed in traffic flow at a 2-to-1 lane junction, Physical Review E 79 (2009) 036104], we find that several social dilemma structures are represented by n-person Prisoner’s Dilemma (n-PD) games in certain traffic flow phases at a bottleneck caused by a lane-closing section. In this study, the stochastic Nishinari-Fukui-Schadschneider (S-NFS) model was adopted as a cellular automaton traffic model. In the system, two classes of driver-agents coexist: C-Agents (cooperative strategy) always driving in the first lane, and D-Agents (defective strategy) trying to drive in a lower-density lane, whether the first or the second lane. In relatively high-density flow phases, such as the metastable phase and the high-density phase, we found n-PD games, where D-Agents’ interruption into the first lane from the second just before the lane-closing section creates a heavier traffic jam, which reduces social efficiency. This could be solved by decreasing the interruption probability, which can be realized by a provision where drivers in the first lane firmly refuse interruptions.     

Photoinduced electron‐transfer reactions of tris(2,2′‐bipyridine)ruthenium(II)‐based carbonic anhydrase inhibitors tethering plural binding sites

Tris(2,2′‐bipyridine)ruthenium(II) complex‐based carbonic anhydrase (CA) inhibitors, [Ru(bpy)₂(bpydbs)]²⁺ {bpy = 2,2′‐bipyridine and bpydbs = 2,2′‐bipyridinyl‐4,4′‐dicarboxilic acid bis[(2‐{2‐[2‐(4‐sulfamoylbenzoylamino)ethoxy]ethoxy}ethyl)amide]} and [Ru(bpydbs)₃]²⁺, tethering plural benzenesulfonamide groups have been prepared. The CA catalytic activity was effectively suppressed by these synthetic [Ru(bpy)₂(bpydbs)]²⁺ and [Ru(bpydbs)₃]²⁺ inhibitors, and their dissociation constants at pH = 7.2 and at 25°C were determined to be K_I = 0.93 ± 0.02 μM and K_I = 0.24 ± 0.03 μM, respectively. Next, 2 photoinduced electron‐transfer (ET) systems comprising a Ru²⁺‐CA complex and an electron acceptor, such as chloropentaamminecobalt(III) ([CoCl(NH₃)₅]²⁺) or methylviologen (MV²⁺) were studied. In the presence of CA and a sacrificial electron acceptor, such as pentaamminechlorocobalt(III) complex, the photoexcited triplet state of ³([Ru(II)]²⁺)* was quenched through an intermolecular photoinduced ET mechanism. In case of the [Ru(bpydbs)₃]²⁺‐CA‐MV²⁺ system, the photoexcited triplet state of ³([Ru(bpydbs)₃]²⁺)* was quenched by sacrificial quencher through an intermolecular photoinduced ET mechanism, giving the oxidized [Ru(bpydbs)₃]³⁺. Then the following intramolecular ET from the amino acid residue, Tyr6, near the active site of CA proceeded. We observed a transient absorption around at 410 nm, arising from the formation of a Tyr^?+ in the [Ru(bpydbs)₃]²⁺‐CA‐MV²⁺ system. These artificial Ru(II)‐CA systems may clearly demonstrate both intermolecular and intramolecular photoinduced ET reactions of protein and could be one of the interesting models of the ET proteins. Their photophysical properties and the detailed ET mechanisms are discussed in order to clarify the multistep ET reactions.