Magnetic Field Effect on the Cathodic Potential Oscillation of Zinc Electrode in Alkaline Solution

The magnetic field effect (0?C0.47?T) on cathodic potential oscillation of a zinc cathode in an alkaline solution was studied. By applying a magnetic field, the oscillation interval increased. The oscillation was quenched at 0.47?T. In situ bore-scope observation of the cathode during electrolysis in magnetic fields revealed that the solution convection induced by the Lorentz force causes the observed effect.     

OXIDATION OF ORGANIC SULFUR COMPOUNDS WITH DINITROGEN TETROXIDE

Abstract

Symmetrical disulfides were known to be oxidized with excess N₂O₄ to the corresponding sulfonic anhydride in good yields. We have found that the oxidation of methyl phenyl disufide or an intermediate, phenyl methanethiolsulfinate undergoes via forming the unstable intermediate, i.e. the thionitrite, which are derived by the cleavage of sulfur-sulfur bond of the subsrates. The oxidation products were symmetrical disulfides, thiolsulfonates, and sulfonic acids which were undoubtedly derived from the scission of sulfur-sulfur bond.     

Determination of lead in solution by solid phase extraction, elution, and spectrophotometric detection using 4-(2-pyridylazo)-resorcinol

Lead (+2) was selectively adsorbed on a solid phase extraction (SPE) gel (molecular recognition technology, MRT), quantitatively extracted, and spectrophotometrically determined as the Pb(II)-PAR (4-(2-pyridylazo)-resorcinol) complex. The linear range was 0.01 to 0.75 mg L^?1 and the detection limit was 6.4 µg L^?1. The MRT-SPE allows selective Pb(II) extraction from complex ion-rich matrices, which is difficult with other techniques. Interference from common matrix ions such as Fe²⁺, Ni²⁺, Cu²⁺ or Co²⁺ is minimized.      

Quenched Large Deviations for Multidimensional Random Walk in Random Environment with Holding Times

We consider a random walk in random environment with random holding times, that is, the random walk jumping to one of its nearest neighbors with some transition probability after a random holding time. Both the transition probabilities and the laws of the holding times are randomly distributed over the integer lattice. Our main result is a quenched large deviation principle for the position of the random walk. The rate function is given by the Legendre transform of the so-called Lyapunov exponents for the Laplace transform of the first passage time. By using this representation, we derive some asymptotics of the rate function in some special cases.     

Assembly of 3D Coordination Polymers from 2D Sheets by [2+2] Cycloaddition Reaction

The synthesis of three 2D interdigitated Zn^II coordination polymers (CPs), by using three monotopic ligands containing C?C bonds, is reported. Among these, two CPs with 4spy (4‐styryl pyridine) and 2F‐4spy (a 2′‐fluoro derivative of 4spy) ligands showed quantitative formation of cyclobutane rings, thus demonstrating a unique synthetic procedure to synthesize metal–organic frameworks (MOFs) by using this photochemical reaction. Interestingly, these compounds can also be synthesized by mechanochemical grinding procedures by using Zn(OAc)₂. In contrast, Zn(NO₃)₂ did not yield the required product, unlike in the solution route. In addition, compounds with 4vpy (4‐vinylpyridine), 4spy and 2F‐4spy ligands created different units in the CPs; 4vpy and 2F‐4spy furnished paddle wheel units, whereas 4spy yielded tetrahedral Zn^II repeating units. Furthermore, the change in coordination geometry manifests in the photoluminescence properties, attributed to the difference in charge‐transfer and ligand‐centered fluorescent phenomenon.     

Selective and sensitive determination of lipoyllysine (protein-bound alpha-lipoic acid) in biological specimens by high-performance liquid chromatography with fluorescence detection

The direct determination of lipoyllysine (LLys) in proteins was carried out by reversed-phase high-performance liquid chromatography with fluorescence (FL) detection. The proteins containing α-lipoic acid (LA) were first hydrolyzed with several enzymes such as pronase E and subtilisin A. The disulfide bond (-S-S-) in LLys liberated from the enzyme digestion was reduced with tris(2-carboxyethyl)phosphine to the thiol form (-SH). The reduced LLys was then labeled with ammonium 4-fluoro-2,1,3-benzoxadiazole-7-sulfonate (SBD-F) at 50 °C for 1 h. The resulting fluorophore, SBD-LLys, was separated by reversed-phase chromatography and fluorometrically detected at 510 nm (excitation at 380 nm). The calibration curve obtained from the peak areas versus the injection amounts of LLys showed a good linearity. The limits of detection and quantification of LLys on the chromatogram were approximately 0.13 pmol (signal-to-noise ratio (S/N) = 3) and 0.44 pmol (S/N = 10), respectively. A good recovery (98.9-107.1%) and precision (R.S.D.: 4.49-17.2%) of LLys were also obtained using the present procedure. The proposed method was used for the determination of LLys in spinach and animal tissues. The FL derivative was completely separated without any interference by endogenous substances in the sample and sensitively detected by the fluorimetry. The assay values of LLys per 1 g wet tissues were 3.67 μg (kidney), 1.97 μg (liver), 2.09 μg (heart), 0.59 μg (brain), 0.30 μg (lung), 0.38 μg (pancreas), and 0.20 μg (spleen). The direct determination of LLys in protein using the FL labeling method is reported for the first time.     

Synthesis and structure-activity relationships of potent 1-(2-substituted-aminoacetyl)-4-fluoro-2-cyanopyrrolidine dipeptidyl peptidase IV inhibitors

Dipeptidyl peptidase IV (DPP-IV) inhibitors have attracted attention as potential drugs for use in the treatment of type 2 diabetes because they prevent the degradation of glucagon-like peptide-1 (GLP-1) and extend its duration of action. We previously reported that 2-cyano-4-fluoropyrrolidines act as potent DPP-IV inhibitors and have been modifying the 1-position of pyrrolidine to obtain more useful inhibitors. An L-tert-butylglycine derivative was found to be a stable and potent DPP-IV inhibitor that exhibits a glucose lowering effect in vivo. Here, we report the synthesis of and biological data on the aforementioned derivatives.     

Mechanism of hydride donor generation using a Ru(II) complex containing an NAD+ model ligand: pulse and steady-state radiolysis studies

The mechanistic pathways of formation of the NADH-like [Ru(bpy) 2(pbnHH)] (2+) species from [Ru(bpy)2(pbn)](2+) were studied in an aqueous medium. Formation of the one-electron-reduced species as a result of reduction by a solvated electron (k=3.0 x 10(10) M(-1) s(-1)) or CO2(*-) (k=4.6 x 10(9) M(-1) s(-1)) or reductive quenching of an MLCT excited state by 1,4-diazabicyclo[2.2.2]octane (k=1.1 x 10(9) M(-1) s(-1)) is followed by protonation of the reduced species (p K a = 11). Dimerization (k7a=2.2 x 10(8) M(-1) s(-1)) of the singly reduced protonated species, [Ru(bpy) 2(pbnH(*))](2+), followed by disproportionation of the dimer as well as the cross reaction between the singly reduced protonated and nonprotonated species (k8= 1.2 x 10(8) M(-1) s(-1)) results in the formation of the final [Ru(bpy)2(pbnHH)](2+) product together with an equal amount of the starting complex, [Ru(bpy)2(pbn)](2+). At 0.2 degrees C, a dimeric intermediate, most likely a pi-stacking dimer, was observed that decomposes thermally to form an equimolar mixture of [Ru(bpy)2(pbnHH)](2+) and [Ru(bpy)2(pbn)](2+) (pH<9). The absence of a significant kinetic isotope effect in the disproportionation reaction of [Ru(bpy)2(pbnH(*))](2+) and its conjugate base (pH>9) indicates that disproportionation occurs by a stepwise pathway of electron transfer followed by proton transfer.     

Three-component coupling using arynes and aminosilanes for ortho-selective double functionalization of aromatic skeletons

Arynes were found to couple with aminosilanes and carbonyl compounds in the presence of benzoic acid to provide 2-aminobenzhydrols. Sulfonylimines could also be applied to the reaction, enabling amino and aminomethyl moieties to be incorporated into contiguous positions of aromatic skeletons. Only a small amount of the three-component coupling product was obtained in the absence of benzoic acid, which confirms its vital role in the present reaction.     

Efficiency of visual peak detection in X‐ray photoelectron spectra

We report initial results of a VAMAS/TWA2 project to evaluate procedures for automated peak detection in X‐ray photoelectron spectra. As a reference for investigations of the efficiency of automated peak‐detection software, we report the efficiency of visual peak detection in three test spectra. It was found that (i) characteristics of analysts are grouped into four categories using principal component analysis (PCA); the first participant group to detect large numbers of peaks for the three test spectra, the second one to detect small numbers of peaks for them, the third one to detect similar numbers of peaks, and the fourth one to detect a relatively large number of peaks for one of them and small numbers for two of them, (ii) scattering of detected peak numbers seems to depend on detection of medium‐intensity peaks because of participants' subjectivity or ambivalence for judgment of intensity, and (iii) the peaks that are detected by the analysts with a detectability more than 75% almost correspond to the peak signal‐to‐noise(S/N) ratio of more than 10 in logarithmic expression. Copyright © 2008 John Wiley & Sons, Ltd.