Dechlorination of poly(vinyl chloride) using NaOH in ethylene glycol under atmospheric pressure

A solution of NaOH dissolved in ethylene glycol (EG) was effective in the dechlorination of poly(vinyl chloride) (PVC) at atmospheric pressure. The degree of dechlorination increased with increasing temperature, reaching a maximum of 97.8% at 190 °C. The dechlorination proceeded under chemical control and exhibited first-order kinetics with an apparent activation energy of 170 kJ mol⁻¹. The apparent rate constant for dechlorination in 1.0 M NaOH/EG was approximately 150 times greater than that in 1.0 M NaOH/H₂O. In addition, dechlorination was faster at atmospheric pressure in NaOH/EG than under high pressure in NaOH/H₂O. The dechlorination reaction occurs via a combination of E2 and S_N2 mechanisms.     

Fluorescence determination of N-acetylaspartic acid in the rat cerebrum homogenate using high-performance liquid chromatography with pre-column fluorescence derivatization

N-acetyl-L-aspartic acid (NAA) is an endogenous compound, and its brain concentration is suggested to be altered in neurological disorders. In the present study, a fluorescence determination method for NAA was developed by employing reversed-phase high-performance liquid chromatography (HPLC) with pre-column fluorescence derivatization using 4-N,N-dimethylaminosulfonyl-7-N-(2-aminoethyl)amino-2,1,3-benzoxadiazole (DBD-ED). Using methylsuccinic acid as the internal standard, a linear calibration curve for NAA was constructed in the range 125-1000 microM (n=3). The detection limit on the column was approximately 5.0 fmol (signal-to-noise ratio 3). The proposed HPLC method was applied to determine NAA in the rat cerebrum homogenate. Cerebrum NAA was successfully determined using 10 microL of the homogenate, and the validation data for the proposed HPLC method demonstrated satisfactory results. Intra- and inter-day precision and accuracy were within 1.1-7.0 and -8.1-6.3%, respectively. The concentration of NAA in the male rat cerebrum (13 weeks old) was 84+/-4.6 micromol/mg protein (n=3).     

Switchable antenna: a star-shaped ruthenium/osmium tetranuclear complex with azobis(bipyridine) bridging ligands

A star-shaped Ru/Os tetranuclear complex, in which a central Os unit is linked to three peripheral Ru units by 4,4'-azobis(2,2'-bipyridine) (azobpy) bridging ligands, was prepared to examine the unique photodynamics regulated by its redox state. The Ru/Os tetranuclear complex exhibits Ru-based luminescence at 77 K, whereas the three-electron reduction (one for each azobpy) of the Ru/Os complex results in luminescence from the Os unit. The photoexcited state of the Ru/Os complex rapidly decays into low energy metal-to-ligand charge-transfer states, in which the excited electron is localized in the azobpy ligand in the form of azobpy(.-). Upon the one-electron reduction of the azobpy ligands, the above-mentioned low-energy states become unavailable to the photoexcited complex. As a result, an energy transfer from the Ru-based excited state to the Os-based excited state becomes possible. Ultrafast transient absorption measurements revealed that the energy transfer process consists of two steps; intramolecular electron transfer from the terminal bipyridine ligand (bpy(.-)) to form azobpy(2-) followed by a metal-to-metal electron transfer. Thus, the Ru/Os tetranuclear complex collects light energy into the central Os unit depending on the redox state of the bridging ligands, qualifying as a switchable antenna.     

In situ observation of the formation of Si clathrate Ba8Si46 at high pressures and high temperatures

X-ray diffraction measurements at high pressures and high temperatures revealed that Si clathrate Ba 8Si 46 is formed by a solid-phase reaction of an 8:30 molar mixture of SrSi 2-phase BaSi 2 and Si after BaSi 2 undergoes the BaSi 2-to-EuGe 2 and the EuGe 2-to-SrSi 2 transitions. The volume reduction during the formation of Ba 8Si 46 is the largest, 7.6%, among the observed transitions. On the other hand, an 8:30 molar mixture of SrSi 2-phase SrSi 2 and Si does not result in the formation of Sr 8Si 46 at high pressures and high temperatures; only SrSi 2 transforms from the SrSi 2 phase into the alpha-ThSi 2 phase, and Si remains in the diamond phase.     

Uncovering the physical origin of the difference between aliphatic chain and aromatic ring in the "hydrophobic" effects on partial molar volume

The partial molar volume changes in the transfer of several hydrophobic molecules, which are composed of aromatic rings and an aliphatic chain of different lengths, from carbon tetrachloride to water (DeltaV(hyd)) are calculated using the three-dimensional interaction site model theory of molecular solvation. The theory reproduces recent experimental observations: the addition of a methyl group decreases DeltaV(hyd); in contrast, the addition of an aromatic ring increases DeltaV(hyd). The discrepancy is found to originate from the difference between chain and ring structures rather than that between aliphaticity and aromaticity. Furthermore, a general rule of the variation in DeltaV(hyd) due to the addition of a hydrocarbon is found through the theoretical analysis. An outward addition at the trans position, which is to form chain structure, decreases DeltaV(hyd), while an inward addition at the cis position, which is to form ring structure, increases DeltaV(hyd). This is explained in terms of solvent packing rather than the so-called hydrophobic hydration. The present findings argue against the traditional idea that the hydrophobic hydration can be represented by the observed values of DeltaV(hyd).     

Determination of kynurenine levels in rat plasma by high-performance liquid chromatography with pre-column fluorescence derivatization

Kynurenine (KYN), a tryptophan metabolite, is a crucial compound for modulating neurotransmission because it can be metabolized in vivo into both quinolinic acid and kynurenic acid, which are the agonist and antagonist, respectively, of N-methyl-d-aspartate receptor. For the highly sensitive detection of KYN by high-performance liquid chromatography (HPLC), a fluorescence derivatization of KYN with a benzofurazan-type fluorogenic reagent, 4-N,N-dimethylaminosulfonyl-7-fluoro-2,1,3-benzoxadiazole (DBD-F) was investigated in the present study. KYN was derivatized with DBD-F (DBD-KYN) at 60 °C for 30 min, and separated on an octadecylsilica column with a gradient elution of the mobile phase, which consists of 0.1% formic acid in acetonitrile/methanol/water. DBD-KYN was detected fluorimetrically at 553 nm with an excitation wavelength of 431 nm. The limits of detection and quantification were approximately 0.30 pmol [signal-to-noise ratio (S/N) 3] and 1.0 pmol (S/N, 10) on column, respectively. Plasma KYN levels were successfully determined using 10 μL of rat plasma with satisfactory precision and accuracy. Intra- and inter-day precisions and accuracies were 1.7-6.8%, and −10 to 9.6%, respectively. KYN levels in plasma of male Sprague-Dawley rats (7 weeks old) were approximately 2.4 ± 0.32 μmol L⁻¹ (n = 4). The proposed HPLC method was applied to determine KYN levels in the plasma of ketamine-treated rats—the animal model of schizophrenia.     

Synthesis and characterization of titanium alkyl, oxo, and diene complexes bearing a SiMe2-bridged phenoxy-cyclopentadienyl ligand and their catalytic performance for copolymerization of ethylene and 1-hexene

A series of titanium complexes bearing a SiMe₂-bridged phenoxy-cyclopentadienyl ligand were synthesized and characterized, and their catalytic behavior for copolymerization of ethylene and 1-hexene was investigated. Treatment of dimethylsilyl(2,3,4,5-tetramethylcyclopentadienyl)(3-tert-butyl-5-methyl-2-phenoxy)-titanium dichloride (1) with appropriate nucleophiles afforded dimethoxy complex 2, dimethyl complex 3, and dibenzyl complex 4. Standing a toluene solution of 2 in air afforded a dinuclear μ-oxo complex 5 as a single isomer. 1,3-Diene complexes 6-8 were prepared by reaction of 1 with the corresponding 1,3-dienes in the presence of 2 equiv. of n-BuLi. X-ray analysis of 1,4-diphenyl-1,3-butadiene complex 6 revealed that the diene ligand coordinates to titanium in s-cis fashion with a prone orientation. The newly prepared titanium complexes were applied to copolymerization of ethylene and 1-hexene upon activation with AlⁱBu₃ and [C₆H₅NMe₂H][B(C₆F₅)₄]. It was found that the alkyl complexes 3-4 and the diene complexes 6-8 showed higher activities than 1 at elevated temperature.     

Nitrile-promoted Rh-catalyzed intermolecular hydroacylation of olefins with salicylaldehyde

Rh-catalyzed intermolecular hydroacylation between salicylaldehyde and alkenylnitriles proceeded at room temperature to preferentially give normal-hydroacylated products. Addition of CH3CN and NaOAc accelerated the Rh-catalyzed hydroacylation of monoolefins to exclusively produce the normal-hydroacylated products under mild reaction conditions. Plausible mechanisms for the regioselections are also described.