Vibrational relaxation of hydrogen fluorides: HF(ν = 1) + F → HF(ν = 0) + F

The deexcitation rate constant of HF(ν = 1) + F → HF(ν = 0) + F is calculated over the temperature range 100–3000 K based on the collision model of FH + F in an operator calculus approach. At temperatures above 1500 K, the rate constant is very large with the magnitude of 10¹³ cm³/mol s. From 100 to 1500 K, the rate constant increases by two orders of magnitude.     

Study of the effect of stabilizer on the degradation of poly(vinyl chloride) by pyrolysis–gas chromatography

The effect of stabilizer on the thermal degradation of poly(vinyl chloride) was studied by means of pyrolysis–gas chromatography. The stabilizers used in this study were dibutyltin dilaurate, dibutyltin bis(n-dodecyl mercaptide), barium stearate, and zinc stearate. PVC containing these stabilizers was degraded in a stream of nitrogen at temperatures ranging from 350 to 570°C. It was found that observed drastic reduction of benzene yield from the PVC containing zinc stearate had a close correlation with the formation of crosslinking structures.     

Preparation of palladium complexes of 1,3-di(2-pyridyl)propane derivatives and their use in norbornene polymerization

A variety of neutral palladium(II) complexes [Pd(L–L)Cl₂] containing 1,3-di(2-pyridyl)propane (1), 1,3-bis(2-pyridyl)-2-pentylpropane (2), 1,3-bis(2-pyridyl)-2-phenylpropane (3a), 1,3-bis(2-pyridyl)-2-tolylpropane (4), and 1,3-bis(2-pyridyl)-2-ferrocenylpropane (5) as chelate ligands (L–L) have been synthesized. The crystal structures of 1,3-diphenyl-2,4-di-pyridin-2-yl-butan-1-ol (3b), 5, [(2)PdCl₂], [(4)PdCl₂], and [(5)PdCl₂] have been determined and show a square planar geometry at palladium(II). The neutral complexes were tested in the polymerization of norbornene and copolymerization of norbornene with norbornene derivatives. The complex bearing the pentyl group exhibited high reactivity to give up to 5.9×10⁵ in molecular weight for the homopolymerization. When [(4)PdCl₂] or [(5)PdCl₂] was used as a catalyst, homopolymers insoluble at 150 °C in trichlorobenzene were obtained. However, copolymerization of norbornene with norbornene derivatives 8a–d catalyzed by [(4)PdCl₂] gave soluble copolymers with molecular weights up to 5.1×10⁵.     

Fluorescence quenching of three molecular weight fractions of a soil fulvic acid by UO(2)(II)

A soil fulvic acid isolated from a Korean forest was divided into three different molecular weight fractions (F1: less than 220 Da; F2: 220-1000 Da; and F3: 1000-4000 Da) by gel filtration chromatography and the fractions were studied by synchronous fluorescence (SyF) spectroscopy. Analysis of the SyF spectra for the fulvic acid fractions showed that the fractions with molecules of larger sizes have a higher content of condensed aromatic compounds. The information about their interaction with UO(2)(II) ions in an aqueous solution (100 mg l(-1) of fulvic acid, in 0.1 M NaClO(4) at pH 3.5) was obtained from the measurement of SyF spectra at increasing concentrations of metal ions. Self-modeling mixture analysis of the quenching spectra gives two distinct peak components having a maximum peak position of 386 (type I) and 498 nm (type II) for all the size-fractionated fulvic acids. From the analysis of the quenching profiles of the peaks, using a non-linear method, the concentration of binding sites (C(L)), and the corresponding stability constants (logK) were calculated. The stability constants of the UO(2)(II)-fulvate complexes ranged from 4.10 to 5.33, and increased with higher molecular weight fractions, which indicates a stronger affinity for UO(2)(II) in the fraction with molecules of larger size.     

Synthesis and characterization of carboxylate-bridged copper(II) dinuclear complex

The dinuclear copper(II) complex {[Cu(pmea)Cl][Cu(H₂O)₃Cl]}(Cl)·H₂O (1) (pmea =bis(2-pyridylmethyl)amino-2-ethanoic acid) has been synthesized and characterized. It crystallizes in the monoclinic system P2₁/c, a = 9.0057(11), b = 28.031(3), c = 8.5669(10) Å, β = 104.267(2)°, V = 2095.9(4) ų, Z = 4. Crystal structure of 1 reveals a syn-anti carboxylate-bridged dinuclear complex, in which the coordination environment around each copper atom exhibits a distorted square-pyramid. Magnetic susceptibility measurement for 1 exhibits a weak intermolecular antiferromagnetic exchange interaction with 2J = −1.17(9) cm⁻¹. The cyclic voltammogram of 1 gives one oxidation and two reduction processes.     

Correlations between photoluminescence and Hall mobility in GaN/sapphire grown by metalorganic chemical vapor deposition

We have investigated photoluminescence (PL) and electron Hall mobility for unintentionally doped GaN epitaxial layers grown by low-pressure metalorganic chemical vapor deposition on c-plane Al₂O₃ substrates. Four GaN films having identical dislocation density but remarkably different electron Hall mobility were exploited. At low temperature (12 K), a PL line associated with a bound exciton was observed and strong correlations were found between the Hall mobility and the PL intensity of the exciton transition. That is, relative PL intensity of the bound exciton to a donor-bound exciton monotonously increased with decreasing the electron mobility of the GaN films. This correlation was interpreted in terms of electrical compensation. Efforts to find the chemical origin of the PL line led to the conclusion that the BE line originated neither from threading dislocations nor from extrinsic point defects. Intrinsic acceptors such as Ga vacancy and GaN anti-site were suspected as plausible origin.     

Synthesis and characterization of fully rodlike poly(4,4′‐biphenylene pyromellitimide)s with various short side groups

Fully rodlike poly(4,4‐biphenylene pyromellitimide) (PMDA–BZ) is so brittle in spite of its extremely high modulus. In this study, the brittleness was attempted to be improved without a significant sacrifice of the high modulus by incorporating short side groups. For this, benzidine monomers, which contain methyl, methoxy, fluoro, and trifluoromethyl at the 2,2′‐positions, were synthesized and then used for polycondensation reactions with pyromellitic dianhydride in N‐methyl‐2‐pyrrolidone, producing soluble poly(amic acids)s. The synthesized poly(amic acid)s were converted to the fully rodlike polyimides in films by a conventional spin‐coating on substrates, soft bake, and thermal imidization. The brittleness of PMDA–BZ was successfully healed with a small portion of sacrifice in the modulus by incorporating methyl, methoxy, and trifluoromethyl groups but could not be healed by the fluoro side group. The improvement in the brittleness might be contributed from the chain mobility and lateral chain packing order enhanced by the incorporation of the side groups, which are evident on the measured structures and properties. The structure and other properties were detected to be influenced by the incorporated side groups. The detailed structures and properties were interpreted by considering roles of side groups and the correlation between structure and properties, respectively. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 937–957, 1999     

18:0 Lyso PC Derived by Bioactivity-Based Molecular Networking from Lentil Mutant Lines and Its Effects on High-Fat Diet-Induced Obese Mice

Lentil (Lens culinaris; Fabaceae), one of the major pulse crops in the world, is an important source of proteins, prebiotics, lipids, and essential minerals as well as functional components such as flavonoids, polyphenols, and phenolic acids. To improve crop nutritional and medicinal traits, hybridization and mutation are widely used in plant breeding research. In this study, mutant lentil populations were generated by γ-irradiation for the development of new cultivars by inducing genetic diversity. Molecular networking via Global Natural Product Social Molecular Networking web platform and dipeptidyl peptide-IV inhibitor screening assay were utilized as tools for structure-based discovery of active components in active mutant lines selected among the lentil population. The bioactivity-based molecular networking analysis resulted in the annotation of the molecular class of phosphatidylcholine (PC) from the most active mutant line. Among PCs, 1-stearoyl-2-hydroxy-sn-glycero-3-phosphocholine (18:0 Lyso PC) was selected for further in vivo study of anti-obesity effect in a high-fat diet (HFD)-induced obese mouse model. The administration of 18:0 Lyso PC not only prevented body weight gain and decreased relative gonadal adipose tissue weight, but also attenuated the levels of total cholesterol, triglycerides, low-density lipoprotein cholesterol, and leptin in the sera of HFD-induced obese mice. Additionally, 18:0 Lyso PC treatment inhibited the increase of adipocyte area and crown-like structures in adipose tissue. Therefore, these results suggest that 18:0 Lyso PC is a potential compound to have protective effects against obesity, improving obese phenotype induced by HFD.     

Aminolysis of aryl dithio-2-thiophenates and dithio-2-furoates in acetonitrile

The aminolyses of the title substrates with anilines and benzylamines are investigated in acetonitrile. A clean second-order kinetics is obtained with a first-order rate law in the amine concentration, which is uncomplicated by the fast proton transfer step. The large magnitude of ρ_Z (ρ_1g) as well as ρ_X (ρ_nuc) together with relatively large positive ρ_XZ values is consistent with a stepwise mechanism in which thiophenolate ion expulsion from the intermediate is rate limiting. For the reactions of aryl dithio-2-thiophenates with benzylamines the magnitude of ρ_X and ρ_Z values is relatively smaller suggesting that both the addition and expulsion of thiophenolate are partially rate determining. Relatively large secondary kinetic isotope effects, k_H/k_D≥1.7, with deuterated nucleophiles, support involvement a concurrent proton transfer to the departing thiophenolate ion in the transition state. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 849–857, 1998