Temperature and current coefficients of lasing wavelength in tunable diode laser spectroscopy

The factors determining temperature and current coefficients of lasing wavelength are investigated and discussed under monitoring CO₂-gas absorption spectra. The diffusion rate of Joule heating at the active layer to the surrounding region is observed by monitoring the change in the junction voltage, which is a function of temperature and the wavelength (frequency) deviation under sinusoidal current modulation. Based on the experimental results, the time interval of monitoring the wavelength after changing the ambient temperature or injected current (scanning rate) has to be constant at least to eliminate the monitoring error induced by the deviation of lasing wavelength, though the temperature and current coefficients of lasing wavelength differ with the rate.     

Kinetic and theoretical studies on alkaline ethanolysis of 4-nitrophenyl salicylate: effect of alkali metal ions on reactivity and mechanism

Pseudo-first-order rate constants (k(obsd)) for reactions of 4-nitrophenyl salicylate (7) with alkali metal ethoxides (EtOM, M = K, Na, and Li) in anhydrous ethanol have been measured spectrophotometrically. Interestingly, the k(obsd) value decreases significantly as the concentration of EtOM increases. Because the phenolic moiety of substrate 7 would be deprotonated and exist as an anionic form (i.e., 7(-)) under kinetic conditions, the ground-state stabilization of 7(-) through formation of a six-membered cyclic complex with M(+) (i.e., 8) is proposed to be responsible for the decreasing k(obsd) trend. The k(obsd) value at a given concentration of EtOK increases steeply upon addition of [18]crown-6 ether (18C6) up to [18C6]/[EtOK] = 1 in the reaction mixture and then remains relatively constant thereafter. In contrast, k(obsd) decreases upon addition of salts (e.g., LiClO(4) or KSCN) to the reaction mixture, which indicates that M(+) ions inhibit the reaction. However, in the presence of 18C6, the k(obsd) value is independent of the concentration of EtOK but remains constant, which indicates that the reaction proceeds through a unimolecular mechanism in the presence of the complexing agent. Although two conceivable unimolecular pathways (formation of ketene 9 and lactone 10) can account for the kinetic results, the reaction has been concluded to proceed via formation of ketene 9 as the reactive intermediate on the basis of theoretical calculations.     

Regioselective carbon-carbon bond cleavage in the oxidation of cyclopropenylcarbinols

The strained double bond of cyclopropenylcarbinols undergoes a facile oxidation reaction to lead to unsaturated carbonyl derivatives. The distribution of the formed products depends on the relative stability of carbon-centered radical species, and the Sharpless kinetic resolution leads to enantiomerically pure Baylis-Hillman enal adducts.     

Tetraquark-based analysis and predictions of the cross sections and distributions for the processes e+e-→Υ(1S)(π+π-,K+K-,ηπ0) near Υ(5S)

We calculate the cross sections and final state distributions for the processes e(+)e(-)→Υ(1S)×(π(+)π(-),K(+)K(-),ηπ(0)) near the Υ(5S) resonance based on the tetraquark hypothesis. This framework is used to analyze the data on the Υ(1S)π(+)π(-) and Υ(1S)K(+)K(-) final states [K.?F. Chen et al. (Belle Collaboration), Phys. Rev. Lett. 100, 112001 (2008); I. Adachi et al. (Belle Collaboration), Phys. Rev. D 82, 091106 (2010).], yielding good fits. Dimeson invariant-mass spectra in these processes are shown to be dominated by the corresponding light scalar and tensor states. The resulting correlations among the cross sections are worked out. We also predict σ(e(+)e(-)→Υ(1S)K(+)K(-))/σ(e(+)e(-)→Υ(1S)K(0)K(0))=1/4. These features provide crucial tests of the tetraquark framework and can be searched for in the currently available and forthcoming data from the B factories.     

Characterization of a glucose sensor prepared by electropolymerization of pyrroles containing a tris-bipyridine osmium complex.

A glucose sensor was developed by electrocopolymerization using pyrroles containing a tris-bipyridine (bpy) osmium complex (Os-py), pyrrole (py), pyrrole propanoic acid (PPA) and glucose oxidase (GOx) to improve the key performance characteristics, such as the sensitivity, selectivity, and long-term stability. Tris-bipyridine osmium pyrrole complexes with four different methylene moieties were utilized to correlate the methylene length with the glucose sensor performance. The electrocatalytic response of glucose was clearly observed at electrodes modified with Os-py, except for the electrode immobilized with the Os-py complex containing the shortest methylene moiety. The current response to glucose increased up to a concentration of 100 mmol dm(-3). The electrocatalytic response to glucose at the [Os(bpy)(2)(py(6)-bpy)](2+/3+)/py/PPA/GOx electrode was stable for more than 100 days. Dissolved oxygen and potential interference compounds (ascorbic acid, uric acid, and acetaminophen) minimally perturbed the current response to glucose at the [Os(DM-bpy)(2)(py(6)-bpy)](2+/3+)/py/PPA/GOx electrode. Based on these results, a longer methylene moiety appears to improve the performance characteristics of a glucose sensor fabricated via the electropolymerization of tris-bipyridine osmium pyrrole complexes.     

Effects of lysophospholipids on membrane order of phosphatidylcholine

Lysophospholipids are known to play a role in a wide range of cellular processes involving membrane–protein or membrane–membrane interactions; however lysolipids–lamellar lipids interactions remain unclear. The effects of lysolipids on membrane order and dynamics were examined using optical birefringence and fluorescence techniques. We found that lysophosphatidic acid (LPA) induces a considerable disorder in chain orientation for synthetic lipid of dimyristoyl-phosphatidylcholines (DMPC), whereas a slight order for natural lipid of egg yolk phosphatidylcholine (Egg-PC), e.g. the chain order decreases by 10% at 0.1 mole ratio for DMPC in comparison with the membranes without LPA and increases by 3.4% at 0.09 mole ratio for Egg-PC. Also, membrane fluidity corresponds with the change in the chain disorder, namely, the fluidity increases for DMPC membranes, while decreases for Egg-PC membranes by addition of LPA. The difference in the effects of LPA is interpreted by a difference in the chain packing between the synthetic and the natural lipid bilayers. LPA can be incorporated into natural lipid membranes without disturbance, and readjusts itself to a more favorable hydrophobic match with the bilayers. Lysophophatidylcholine (LPC) also induces a disorder in DMPC membranes, but the decrease in chain order is only half compared with that for LPA.     

UV protection and singlet oxygen quenching activity of aloesaponarin I

The UV protection and singlet oxygen quenching of aloesaponarin I have been studied by means of laser spectroscopy. The excited-state intramolecular proton transfer that provides the UV protection takes place along only one of the molecule's two intramolecular hydrogen bonds, and this can be understood by considering the nodal pattern of the wave function. The functional groups participating in the excited-state intramolecular proton transfer also play important roles in the singlet oxygen quenching. Aloesaponarin I has a quenching rate constant larger than that of vitamin E and has a long duration of action due to its resistance to UV degradation and chemical attacks by singlet oxygen and free radicals.     

Artificial DNAs based on alkynyl C-nucleosides as a superior scaffold for homo- and heteroexcimer emissions

DNA-like fluorescent oligomers composed of alkynyl beta-D-ribofuranosides bearing pyrene, perylene, and anthracene as a fluorophore were synthesized by solid-phase DNA synthesis. The fluorescent oligomers possess the defined number and order of the fluorophores. In these oligomers, the adjacent fluorophores efficiently interact with each other by hydrophobic interactions in their electronic ground states in a face-to-face fashion. The predominant excimer emissions were observed from not only the homooligomers (pyrene-pyrene and perylene-perylene systems) but also the heterooligomers (pyrene-perylene, pyrene-anthracene, and perylene-anthracene systems) in aqueous media.     

Brønsted basicities of diamines in the gas phase, acetonitrile, and tetrahydrofuran

A comprehensive basicity study of alpha,omega-alkanediamines and related bases has been carried out. Basicities in acetonitrile (AN, pK(a) values), tetrahydrofuran (THF, pK(alpha) values), and gas phase (GP, GB values), were measured for 16, 14, and 9 diamine bases and for several related monoamines. In addition the gas-phase basicities and equilibrium geometries were computed for 19 diamino bases and several related monoamines at the DFT B3LYP 6-311+G** level. The effects of the different factors (intrinsic basicity of the amino groups, formation of intramolecular hydrogen bonds, and molecular strain) determining the diamine basicities were estimated by using the method of isodesmic reactions. The results are discussed in terms of molecular structure and solvation effects. The GP basicity is determined by the molecular size and polarizability, the extent of alkylation, and the energy effect of intramolecular hydrogen bond formation in the protonated base. The basicity trends in the solvents differ very much from those in GP: 1) The solvents severely compress the basicity range of the bases studied (3.5 times for the 1,3-propanediamine family in AN, and 7 times in THF), and 2) while stepwise alkylation of the basicity center leads to a steady basicity increase in the gas phase, the picture is complex in the solvents. Significant differences are also evident between THF and AN. The high hydrogen bond acceptor strength of THF leads to this solvent favoring the bases with "naked" protonation centers. In particular, the basicity order of N-methylated 1,3-propanediamines is practically inverse to that in the gas phase. The picture in AN is intermediate between that of GP and THF.     

Amino substituted bisketenes: generation, structure, and reactivity

Hitherto unknown diamino-substituted bisketenes with both free (14) and tethered (16) amino substituents have been generated by using laser flash photolysis for ring opening of the corresponding cyclobutenediones. The time-resolved kinetics of ring closure of the amino bisketenes back to the cyclobutenediones were measured by IR or UV spectroscopy, and give first-order rate constants which vary by a factor of 7.5x10(4), and the bis(Me2N) bisketene 14 is the most reactive in ring closure that has been reported. Rate constants for ring closure of these and previously observed bisketenes vary by a factor of 10(13). The dialkylamino bisketenes 16 (R=Me, n-Bu) with tethered substituents and restricted geometries are less reactive than the bis(Me2N) bisketene 14 by factors of 1700 and 540, respectively. Computational results obtained with DFT methods suggest angle strain in the tethered cyclobutenediones 15 inhibits facile cyclization of bisketenes 16.