Electronic Structure of Cu(II) Complexes with N,N′-Disalicylidene-1,2-cyclohexanediamine and N,N′-Disalicylidenetrimethylenediamine

Summary.  The electronic absorption and X-ray photoelectron spectra of N,N′-disalicylidenetrimethylenediaminatocopper(II) ([Cu(saltn)]) and N,N′-disalicylidene-trans-1,2-cyclohexanediaminatocopper(II) ([Cu(salchx)]) were measured. From these results and from informations derived from MO calculations the electronic structure of the complexes was clarified. Each electronic absorption band which can be assigned to the ππ^ast; or ML/LMCT transition of [Cu(saltn)] or [Cu(salchx)] observed in the wavelength region of 450–200 nm appears at the almost same frequency as the corresponding band of N,N′-disalicylideneethylenediaminatocopper(II) ([Cu(salen)]) in solution. The LLCT bands (the intramolecular CT band between two π-electronic systems separated by saturated hydrocarbon chains such as ) also appear at nearly the same positions (ca. 245 nm) for [Cu(salchx)], [Cu(saltn)], and [Cu(salen)]. The locations of the dd transition and the intensity of the ML/LMCT transition of [Cu(saltn)] are significantly different from those of [Cu(salen)] and [Cu(salchx)]. These differences may arise from the strengths of the interaction between metal and ligand. Received August 21, 2001. Accepted (revised) October 20, 2001     

Luminescence tuning of imidazole-based lanthanide(III) complexes [Ln = Sm, Eu, Gd, Tb, Dy

To tune the lanthanide luminescence in related molecular structures, we synthesized and characterized a series of lanthanide complexes with imidazole-based ligands: two tripodal ligands, tris{[2-{(1-methylimidazol-2-yl)methylidene}amino]ethyl}amine (Me(3)L), and tris{[2-{(imidazol-4-yl)methylidene}amino]ethyl}amine (H(3)L), and the dipodal ligand bis{[2-{(imidazol-4-yl)methylidene}amino]ethyl}amine (H(2)L). The general formulas are [Ln(Me(3)L)(H(2)O)(2)](NO(3))(3)·3H(2)O (Ln = 3+ lanthanide ion: Sm (1), Eu (2), Gd (3), Tb (4), and Dy (5)), [Ln(H(3)L)(NO(3))](NO(3))(2)·MeOH (Ln(3+) = Sm (6), Eu (7), Gd (8), Tb (9), and Dy (10)), and [Ln(H(2)L)(NO(3))(2)(MeOH)](NO(3))·MeOH (Ln(3+) = Sm (11), Eu (12), Gd (13), Tb (14), and Dy (15)). Each lanthanide ion is 9-coordinate in the complexes with the Me(3)L and H(3)L ligands and 10-coordinate in the complexes with the H(2)L ligand, in which counter anion and solvent molecules are also coordinated. The complexes show a screw arrangement of ligands around the lanthanide ions, and their enantiomorphs form racemate crystals. Luminescence studies have been carried out on the solid and solution-state samples. The triplet energy levels of Me(3)L, H(3)L, and H(2)L are 21?000, 22?700, and 23?000 cm(-1), respectively, which were determined from the phosphorescence spectra of their Gd(3+) complexes. The Me(3)L ligand is an effective sensitizer for Sm(3+) and Eu(3+) ions. Efficient luminescence of Sm(3+), Eu(3+), Tb(3+), and Dy(3+) ions was observed in complexes with the H(3)L and H(2)L ligands. Ligand modification by changing imidazole groups alters their triplet energy, and results in different sensitizing ability towards lanthanide ions.     

Cascade‐ and Orthoamide‐Type Overman Rearrangements of Allylic Vicinal Diols

This article describes the details of two new types of Overman rearrangement from allylic vicinal diols. Starting from identical diols, both bis(imidate)s and cyclic orthoamides were selectively synthesized by simply changing the reaction conditions. Whilst exposure of the bis(imidate)s to thermal conditions initiated the double Overman rearrangement to introduce two identical nitrogen groups in a single operation (the cascade‐type Overman rearrangement), the reaction of cyclic orthoamides resulted in a single rearrangement (the orthoamide‐type Overman rearrangement). The newly generated allylic alcohols from the orthoamide‐type reaction can potentially undergo a variety of further transformations. For instance, we demonstrated an Overman/Claisen sequence in one pot. The most conspicuous feature of this method is that it offers precise control over the number of Overman rearrangements from the same allylic vicinal diols. This method also excludes the tedious protecting‐group manipulations of the homoallylic alcohols, which are necessary in conventional Overman rearrangements. All of the performed rearrangements proceeded in a completely diastereoselective fashion through a chair‐like transition state.     

Study on the Indirect Electrochemical Detection of Ammonium Ion with In Situ Electrogenerated Hypobromous Acid

The electrochemical oxidation of bromide in the presence of ammonium ion (NH ) was studied by cyclic voltammetry and UV‐vis spectroscopy. The experimental results suggested that the anodically generated bromine (Br₂) would be hydrolyzed to hypobromous acid (HBrO) at the pH range of 5–7 and was further disproportionate to hypobromite anion (BrO^?) when pH was larger than 7. Both HBrO and BrO^? were confirmed to be participated in the following homogeneous chemical reaction with the coexisted ammonium ion. However, HBrO is electroactive whereas BrO^‐ is electroinactive at carbon electrode. Based upon the reaction of HBrO with NH , an indirect electrochemical method was proposed for determination of NH with dual‐electrode configuration in phosphate buffer solution (pH 7), where HBrO was produced at a generator electrode and the excess HBrO was subsequently detected at a collector electrode after a reaction with NH in a batch solution or in a micro flow injection analytical (micro‐FIA) system by using an interdigitated array (IDA) Pt microelectrode and a carbon film ring‐disk electrode (CFRDE), respectively. The decreasing of reduction current at the collector electrode was proportional to the concentration NH in both systems, with the detection limit below 3.0 μM. This approach shows the advantage of highly selectivity even in presence of a large amount of coexisted cations, and was successfully applied for the determination of NH in environmental water samples.     

Preparation of poly(bis(trialkylammonium) 4,4′-oxydiphenylenepyromellitamate) films: A useful polyimide precursor film

A poly[bis(trialkylammonium) 4,4′-oxydiphenylenepyromellitamate] film not containing residual solvents was prepared first as a polyimide precursor film. The preparative method is composed of three process steps involving (1) polymerization of pyromellitic dianhydride with 4,4′-oxydianiline in a mixed solvent of tetrahydrofuran/methanol, (2) addition of a mixture of methanol/trialkylamine to the resulting poly(4,4′-oxydiphenylenepyromellitamic acid) solution, and (3) casting onto glass plates and drying. The salt formation between the poly(amic acid) and trialkylamines was confirmed first by spectroscopic methods. The dried salt film is thermally cured to produce the polyimide film with a reduced coefficient of thermal expansion (CTE). © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2493–2499, 1997     

Syntheses of pyrido[1,2-a][1,3,5]triazin-4-one C-deoxyribonucleosides

We achieved the syntheses of new C-deoxyribonucleosides bearing pyrido[1,2-a][1,3,5]triazin-4-one derivatives using palladium-catalyzed Heck-type coupling. Some of these C-deoxyribonucleosides were able to convert to phosphoramidite reagents, which can be used for DNA synthesizer. DNA oligomers including pyrido[1,2-a][1,3,5]triazin-4-one C-deoxyribonucleoside, which had 2-amino group were synthesized, and T_m values with a natural nucleoside were measured.     

Glucose oxidase-immobilized glass disks for imaging of D-glucose in acute brain slices.

A biotinylated glucose oxidase (bGOD)-immobilized glass disk was prepared for visualizing D-glucose fluxes in acute brain slices. A mouse hippocampal slice was placed on the bGOD disk and stimulated with a stimulant solution containing horseradish peroxidase (HRP) and a substrate DA-64, followed by capturing digital images of Bindschedler's Green (BG), an oxidized form of DA-64, with a CCD camera. The bGOD membranes responded proportionally to D-glucose, ranging from 2.0 to 5.0 mM. Sucrose, GABA, L-glutamic acid, L-aspartic acid, glycine, acetylcholine and L-ascorbic acid at 10 mM did not cause any responses. The D-glucose fluxes in mouse hippocampal slices stimulated by a hypoxia solution were neuronal region-dependent, i.e., dentate gyrus (DG), cornu ammonis 1 (CA1) and cornu ammonis 3 (CA3), while those stimulated by KCl was independent of the neuronal regions. The response of bGOD disks is discussed in terms of the principle, concentration dependence and selectivity.     

Crumpling transition of self-avoiding tethered membranes caused by screening

A system of D-dimensional self-avoiding tethered membranes embedded in a d-dimensional space is considered for the seni-dilute case. The effect of the screening is taken into account, and the crumpled phase diagram in the (d, D) plane is obtained. For D = 2, membranes are in the swollen crumpled phase. The possobility of a crumpling transition caused by the screening is discussed. The density dependences for some quantities such as the screening length and radius of gyration are obtained from a scaling argument.     

Observation of ultrahigh-energy cosmic rays with the ANITA balloon-borne radio interferometer

We report the observation of 16 cosmic ray events with a mean energy of 1.5 × 101? eV via radio pulses originating from the interaction of the cosmic ray air shower with the Antarctic geomagnetic field, a process known as geosynchrotron emission. We present measurements in the 300-900 MHz range, which are the first self-triggered, first ultrawide band, first far-field, and the highest energy sample of cosmic ray events collected with the radio technique. Their properties are inconsistent with current ground-based geosynchrotron models. The emission is 100% polarized in the plane perpendicular to the projected geomagnetic field. Fourteen events are seen to have a phase inversion due to reflection of the radio beam off the ice surface, and two additional events are seen directly from above the horizon. Based on a likelihood analysis, we estimate angular pointing precision of order 2° for the event arrival directions.     

Uncertainty quantification of a graphite nitridation experiment using a Bayesian approach

In this paper, a stochastic system based Bayesian approach is applied to estimate different model parameters and hence quantify the uncertainty of a graphite nitridation experiment. The Bayesian approach is robust due to its ability to characterize modeling uncertainties associated with the underlying system and is rigorous due to its exclusive foundation on the axioms of probability theory. We choose an experiment by Zhang et al. [1] whose main objective is to measure the reaction efficiency for the active nitridation of graphite by atomic nitrogen. To obtain the primary physical quantity of interest, we need to model and estimate the uncertainty of a number of other physical processes associated with the experimental setup. We use the Bayesian method to obtain posterior probability distributions of all the parameters relevant to the experiment while taking into account uncertainties in the inputs and the modeling errors. We use a recently developed stochastic simulation algorithm which allows for efficient sampling in the high-dimensional parameter space. We show that the predicted reaction efficiency of the graphite nitridation and its uncertainty is ∼3.1 ± 1.0 × 10⁻³ that is slightly larger than the ones deterministically obtained by Zhang et al. [1].