Green-and-Red Photoluminescence from Si-Si and Ge-Ge Bonded Network Homopolymers and Copolymers

Recently, we found pure green photoluminescence (PL) at 540 nm (2.34 eV) in a vacuum, which is characteristic of a Si-Si bonded network polymer bearing n-butyl groups (organopolysilyne, SNP). SNP was carefully isolated as an orange-yellow solid by avoidance of contact with air and water in the polymer synthesis and PL measurement. This was in contrast with previous reports that SNPs carrying alkyl groups have a blue PL band around 450-480 nm. By applying the modified technique to a soluble Ge-Ge bonded network polymer carrying n-butyl groups (organopolygermyne, GNP), with much care in synthesising the polymer and measuring the PL, we found that GNP reveals a very brilliant red-coloured PL band at 690 nm (1.80 eV) in a vacuum at 77 K. This was in contrast with a previous report that GNP carrying n-hexyl groups has a green PL band at 560 nm (2.21 eV). On the other hand, soluble Si-Ge network copolymers (SGNPs) prepared in a similar way to SNP and GNP syntheses showed green-and-red dual PL bands at 540 nm and 690 nm. Based on analyses with IR, Raman, HR-TEM, XPS, EELS, UV-Vis and PL data, the dual emission was assumed to originate from the coexistence of Si and Ge domains (1-2 nm in diameter), possibly, in the same skeleton of SGNP.journal articl

Characteristics of turbulent square duct flows over porous media

application/pdfJournal of Fluid Mechanics. 2020, 884, P.A7journal articl

Observation of Initial Stage of Nano-Scale Au Thin Film on Si(111)7×7 Surface by the PLD Method

As an important information for fabrication of atomic scale Au thin film which is used for biosensors, we have observed morphology of Au particles absorbed on the Si(111)7x7 surface, which is supposed to be the initial stage of Au thin film formation. Au particles were adsorbed on the Si cleaned surface using PLD method, and the adsorbed particles were observed using the scanning tunneling microscope. As the number of laser shot was increased in the PLD method, size of the adsorbed particle became larger. The larger particle were seemed to form clusters which are aggregation of particles from which each particles are distinguished, so we call this type of clusters film-shaped clusters. In this work we have mainly analyzed this type of clusters. As a result the film-shaped clusters were found to have a structure of nearly monoatomic layer. The particles in the clusters were close gathered in nearly the 3-fold structure with an inter atomic distance of 0.864 nm. We proposed a model for the cluster structure by modifying Au(111) face so that the each observed particles consists of 3 Au atoms.departmental bulletin pape

損傷自己検知型デバイスの開発とそのシステム化に関する研究

textapplication/pdfdepartmental bulletin pape

Observation of B̅0→DsJ*(2317)+K- Decay

journal articl

Solar neutrino measurements in Super-Kamiokande-II

The results of the second phase of the Super-Kamiokande solar neutrino measurement are presented and compared to the first phase. The solar neutrino flux spectrum and time variation as well as oscillation results are statistically consistent with the first phase and do not show spectral distortion. The timedependent flux measurement of the combined first and second phases coincides with the full period of solar cycle 23 and shows no correlation with solar activity. The measured 8B total flux is (2:38± 0.05(stat.)/begin+0.16 // -0.15/end (sys.)) × 10^6 cm^{-2} s^{-1} and the day-night difference is found to be (-6.3 ±4.2(stat.)±3.7(sys.))%.There is no evidence of systematic tendencies between the first and second phases.journal articl

Effects of Mg²⁺ and the 2‘ OH of Guanosine on Steps Required for Substrate Binding and Reactivity with the <i>Tetrahymena</i> Ribozyme Reveal Several Local Folding Transitions^†

Transient kinetic studies with fluorescence detection were used to determine the effects of Mg2+ concentration and the 2‘ OH group of guanosine monophosphate, prG, substrate on various steps in the transesterification reaction of prG with 5‘ pyrene-labeled oligonucleotides as catalyzed by the L-21 ScaI ribozyme. The effect of increasing Mg2+ from 5 to 10 mM on the rate constants of association and dissociation of 5‘ pyrene-labeled CUCUA at 15 °C was measured. The rate constant of association increases about 3-fold to (8.7 ± 0.7) × 106 M-1 s-1 at 10 mM Mg2+. The rate constant for dissociation is 25 ± 4 s-1 at 10 mM Mg2+, within experimental error of the rate constant of 17 ± 5 s-1 measured at 5 mM Mg2+. This Mg2+ dependence is attributed to nonspecific binding of Mg2+ to the duplex helix. In the absence of prG, no docking of substrate is observed. The effect of Mg2+ concentration on rates for docking of 5‘ pyrene-labeled substrate, pyrCCUCUA, were measured at [Mg2+] ≥ 2 mM and at temperatures ≤ 20 °C, where optical melting curves indicate global folding is complete. Thus the rates monitor local folding steps important for catalytic function. Three and possibly four local cooperative transitions were induced by Mg2+. The fastest fluorescence transient, which is associated with substrate docking, changes from a quenching to an enhancement between 2 and 4 mM Mg2+, and its observed rate constant at pH 6.5 and 7.5 is about 1 s-1, independent of [Mg2+] when 4 ≤ [Mg2+] ≤ 15 mM. The slowest fluorescence transient, which is apparently associated with transesterification, has an observed rate constant that continues to increase when [Mg2+] ≥ 4 mM. In the presence of Ca2+, such that [Ca2+] + [Mg2+] = 15 mM, the observed rate constants of both transients are constant when 4 mM ≤ [Mg2+] ≤ 7 mM but double between 7 and 11 mM Mg2+. At pH 6.5 when 4 mM ≤ [Mg2+] ≤ 7 mM in the absence of Ca2+, there is also evidence for a third transient with a Mg2+-dependent observed rate constant that is intermediate between the observed rate constants of docking and transesterification. Thus these experiments reveal several separable, local folding transitions that are dependent on Mg2+ in a very cooperative manner and are important for function. When pdG is substituted for prG, no transesterification is observed, and fluorescence quenching is observed for 1−15 mM Mg2+. The switch from fluorescence enhancements with prG to quenching with pdG suggests the 2‘ OH of prG is important for proper positioning of substrate in the catalytic site

Consecutive GA Pairs Stabilize Medium-Size RNA Internal Loops^†

Internal loops in RNA are important for folding and function. Consecutive noncanonical pairs can form in internal loops having at least two nucleotides on each side. Thermodynamic and structural insights into such internal loops should improve approximations for their stabilities and predictions of secondary and three-dimensional structures. Most natural internal loops are purine rich. A series of oligoribonucleotides that form purine-rich internal loops of 5−10 nucleotides, including kink-turn loops, were studied by UV melting, exchangeable proton and phosphorus NMR. Three consecutive GA pairs with the motif or (i.e., closed on at least one side with a CG, UA, or UG pair with Y representing C or U and R representing A or G) stabilize internal loops having 6−10 nucleotides. Certain motifs with two consecutive GA pairs are also stabilizing. In internal loops with three or more nucleotides on each side, the motif has stability similar to . A revised model for predicting stabilities of internal loops with 6−10 nucleotides is derived by multiple linear regression. Loops with 2 × 3 nucleotides are predicted well by a previous thermodynamic model

Solution Structure of (rGCGGACGC)₂ by Two-Dimensional NMR and the Iterative Relaxation Matrix Approach^†

The three-dimensional solution structure of the RNA self-complementary duplex was derived from two-dimensional NMR and the iterative relaxation matrix approach. Each GA mismatch forms two hydrogen bonds:  A-NH6 to G-O6 and A-N1 to G-NH1 (imino). This is the first three-dimensional RNA structure with imino hydrogen-bonded tandem GA mismatches. This GA structure is totally different from the sheared tandem GA structure in which also has two hydrogen bonds:  A-N7 to G-NH2 and A-NH6 to G-N3 [SantaLucia, J., Jr., & Turner, D. H. (1993) Biochemistry 32, 12612−12623]. In particular, the sheared and imino GA mismatches produce a narrowing and widening of the backbone, respectively. The results show that substitutions of Watson−Crick base pairs can have dramatic effects on the three-dimensional structures of adjacent non-Watson−Crick paired regions; i.e., the structure depends on sequence context. Thus compensating substitutions in site-directed mutagenesis experiments may not always restore biological activities

C5-(1-Propynyl)-2‘-deoxy-Pyrimidines Enhance Mismatch Penalties of DNA:RNA Duplex Formation^†

UV melting experiments show that C5-(1-propynyl)ation of seven pyrimidines to give a fully propynylated oligodeoxynucleotide (PrODN) heptamer increases the thermodynamic stability of six Watson−Crick paired DNA:RNA duplexes by 8.2 kcal/mol, on average, at 37 °C. About 2.5 kcal/mol of this enhancement is due to long-range cooperativity between the propynylated pyrimidines, Yp's. On average, penalties for dUp:rG, dCp:rA, dUp:rC, and dCp:rC mismatches are enhanced by 2.9 kcal/mol in PrODN:RNA duplexes over those in unmodified duplexes. This results in penalties as large as 10 kcal/mol for a single mismatch. Removing a single propyne two base pairs away from a mismatch in a PrODN:RNA duplex eliminates the enhancement in specificity. Evidently, enhanced specificity is directly linked to long-range cooperativity between Yp's. In most cases, the enhanced specificity is larger for internal than for terminal mismatches. PrODN:RNA duplexes are destabilized by full phosphorothioate backbone substitution to give S-PrODN:RNA duplexes. The S-PrODN:RNA duplexes retain enhanced mismatch penalties, however. These results provide insight for utilizing long-range cooperativity and enhanced specificity to improve nucleic acid based probe and drug design