Reactivity of cobaloxime bound to polystyrene chain by carbon–cobalt σ bond

The (alkyl)-bis(dimethylglyoximato)pyridinecobalt attached to polychloromethylstyrene by a cobalt–carbon bond was prepared by the reaction of Co(II)(DH)₂Py with polychloromethylstyrene in benzene. The fraction of p-vinylbenzyl·Co(DH)₂Py introduced to the polymer was 8.1 and 2.1 mole %. The photodecomposition of the polymer-bonded cobaloxime was investigated by following the change of the visible spectrum. The rate constant k_dec of the polymer-bonded cobaloxime was 1.1 × 10^?2 sec^?1 in benzene; it is one-fourth of that of its monomeric analog, benzyl·Co(DH)₂Py. The k_dec values of the cobaloximes were also measured in benzene–dimethyl sulfoxide mixed solvents, and the polymer effects were discussed. The dependence of the photodecomposition on energy of the irradiation light was investigated, and it was found that the absorption band near 470 nm is important for the photodecomposition of the cobalt–carbon bond. Spectroscopic measurements of the ligand exchange reaction of polymer-bonded cobaloxime with pyridine in dimethyl sulfoxide gave a larger equilibrium constant (1.2 × 10⁴ liter/mole) than that of benzyl·Co(DH)₂Py (9.4 × 10² liter/mole). The kinetic data of the ligand exchange reaction indicated that the larger equilibrium constant for the polymeric system is due to the smaller rate constant of the reverse reaction. The thermodynamic parameters were also obtained.     

Consideration on peak shape in a batch-type chemiluminescence detection cell for capillary electrophoresis

Peak areas, peak heights, and apparent theoretical plate numbers were examined as a function of sample injection times by use of the batch-type CL detection cell. Comparing the experimental data with those obtained by absorption detector, some considerations were carried out about the peak shape. The peak shape in CL detection was influenced by not only concentration distribution of sample in a sample zone but also sample diffusion and CL reaction at the capillary outlet. The sample injection time of ca. 35 s was recommended for the present CE with CL detector. The injection time much influenced peak shape as well as sensitivity in the CL detection cell.     

Biphenyl ether and biphenyl quinolizidine lactone alkaloids from Heimia salicifolia

Three new biphenyl ether quinolizidine lactone alkaloids (1–3) and 13 new biphenyl quinolizidine lactone alkaloids (4–16) were isolated from Heimia salicifolia (Lythraceae) together with seven known alkaloids. Their structures were determined by spectroscopic analyses and chemical conversions.     

Theoretical study on dependence of hyperpolarizability of one‐dimensional ring system on the delocalization transition

We calculate the optical properties such as the polarization, the (hyper)polarizabilities, the critical vector potential, etc., in terms of the non‐Hermitian Anderson model of a 6‐site ring model. The dependence of the optical properties on the delocalization transition is investigated. It is found that all the total optical properties nonlinearly increase with the increase of the delocalization. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

Improved accuracy for Raman spectroscopic determination of polyethylene property by optimization of measurement temperature and elucidation of its origin by multiple perturbation two-dimensional correlation spectroscopy

A novel strategy is demonstrated to improve the accuracy for determination of polyethylene (PE) density using Raman spectroscopy by optimizing the temperature of sample measurement. Spectral features associated with the conformation change of the polymer induced by temperature may provide valuable information to quantify important polymer properties such as density. To evaluate possible existence of an optimal temperature providing improved quantitative accuracy, Raman spectra of PE pellets with different densities were collected at eight different temperatures from 30 to 100 °C at 10 °C intervals. Using the spectral datasets collected at each temperature, partial least squares (PLS) models were developed using the reference PE density values determined by a standard density gradient method at 23 °C. Interestingly, the most accurate determination of density was realized at 70 °C. Multiple perturbation two-dimensional (MP2D) correlation analysis and differential scanning calorimetry (DSC) were used to examine the origin of improved accuracy at 70 °C. From these analyses, the pre-melt behavior of the PE samples was identified below their melting temperatures. Structural variations induced at the pre-melt stages enhance Raman spectral selectivity among the samples, thereby providing more accurate determination of PE density. The MP2D correlation analysis revealed the unforeseen thermal behavior of PE samples and successfully explained the improved accuracy at 70 °C.     

A stereochemical investigation of 2-methyl- and 2,5-dimethyl-3-phenyl-1,3-oxazolidines using NMR

The stereochemical properties of two 2-methyl-3-phenyl-1,3-oxazolidines and two of its 5-methyl substituted and four of its 2,5-dimethyl substituted derivatives have been investigated by pmr and cmr methods. The compounds of 2,5-dimethyl-3-phenyl-1,3-oxazolidines exist in isomeric cis and trans forms at the two methyl groups on the heterocyclic ring.     

Electrophoretic analysis of quinone anion radicals in acetonitrile solutions using an on-line radical generator

We have investigated analysis of anion radicals of phenanthrenequinone (PhQ) and anthraquinone (AQ) using acetonitrile-capillary electrophoresis (CE) under anaerobic conditions. PhQ and AQ have relatively high negative reduction potentials meaning that their anion radicals are re-oxidized quite readily by the surrounding O(2) to disappear during analysis and we failed to detect them with our previous system. In this work, we have developed an on-line system combining a unique electrolysis cell for generation of the radicals and a CE unit to keep the analysis system free from external O(2) molecules and to reduce analysis time remarkably. As a result, electrophoretic detection of the anion radicals of PhQ and AQ has been achieved. Furthermore, we have observed hydrogen-bonding interaction between the anion radicals and dimethylurea (DMU) using the present system and have indicated a characteristic interaction of the anion radical of PhQ as an ortho-quinone with DMU.     

First asymmetric total synthesis of tetrodotoxin

Tetrodotoxin, a toxic principle of puffer fish poisoning, is one of the most famous marine natural products because of the complex structure having many functional groups and its potent biological activity leading to death. Since the structure elucidation in 1964, this toxin has been recognized as a formidable target molecule for total synthesis. We have recently achieved the first asymmetric total synthesis from 2-acetoxy-tri-O-acetyl-d-glucal as a chiral starting material. The highly hydroxylated cyclohexane ring was constructed by Claisen rearrangement and regioselective hydroxylations of an acetone moiety and an intramolecular directed aldol condensation of the precursor having methyl ketone with dihydroxyacetone, which was synthesized through Sonogashira coupling. Installation of nitrogen functionality was unsuccessful through an attempted Overman rearrangement. We, therefore, employed a new intramolecular conjugate addition strategy between the carbamate and unsaturated ester groups. The alpha-hydroxyl lactone moiety was synthesized through an intramolecular epoxide opening by the Z-enolate of aldehyde, which was followed by oxidation-reduction of the resulting cyclic vinyl ether. The lactone was then converted to a protected ortho ester, and then gunanidinylation was followed by cleavage of the 1,2-glycol to give the fully protected tetrodotoxin. Selection of the protective groups has finally led us to accomplish the total synthesis of tetrodotoxin in an enantiomerically pure form. All the stereogenic centers were controlled with high selectivity, and the hydroxyl groups were differently protected to discriminate for the future analogue synthesis of a bioorganic program. The synthetic tetrodotoxin was purified by ion exchange chromatography and characterized to be identical with the natural compound.     

Regioselective allylmetalation of allenes with tetraallylmanganate or allylmagnesium chloride under MnCl2 catalysis

[reaction: see text] Treatment of allenes with tetraallylmanganate provides allylated products with high regioselectivity. A catalytic amount of MnCl(2) combined with allylmagnesium chloride also achieves efficient allylmetalation of allenes. The resulting alkenylmagnesium species react with various electrophiles. In the presence of molecular oxygen, the alkenylmagnesium undergoes diallylation reaction. A cyclization reaction of 1,2,6-heptatriene with tetraallylmanganate is also described.     

One Dimensional Face-to-Face Stacking of Anderson–Evans [Cr(OH)6Mo6O18]3− Polyoxometalate Anion: Synthesis, Structure, and Physical Properties of (BEDT-TTF)4[Cr(OH)6Mo6O18]⋅2H2O

The synthesis, structural and magnetic characterizations of a new charge transfer salt (BEDT-TTF)₄[Cr(OH)₆Mo₆O₁₈]2H₂O based on the planar paramagnetic Anderson–Evans polyoxometalate are reported. Structural parameters: T=293 K, triclinic (P ), a=5.9545(2) Å, b=16.3767(6) Å, c=21.8643(6) Å, =110.829(2)°, =91.262(2)°, =98.129(1)°, Z=1, R=0.0540. The crystal structure is characterized by a face-to-face stacking of the anions giving rise to a one-dimensional inorganic chain which develops along the a direction. The organic layers contain two crystallographically independent BEDT-TTF dimers that form alternating stacks along the b direction. This organic chain is perpendicular to the inorganic chains. The charges on BEDT-TTF dimers are deduced to +1.2(1) and +1.7(1) on the basis of the intramolecular bond lengths. The EPR spectrum at 2.5 K is characterized by the superposition of BEDT-TTF⁺ and [Cr^III(OH)₆Mo₆O₁₈]^3– signals. The static susceptibility can be fitted by the Curie–Weiss law down to 1.9 K and the magnetic moment at 300 K is estimated to 4.21 _B , suggesting the uncorrelated spin system with BEDT-TTF⁺ (S=1/2) and Cr^III (S=3/2) ions. This interpretion is consistent with the charge disproportionation on BEDT-TTF dimers along the stack, which is supported by the refined molecular structure and is closely related to the insulating behavior (<10^–9Scm^–1 at RT).