Comparison of activities of homogeneous Ti-based catalysts in the presence of methylaluminoxane (MAO) for synthesis of syndiotactic polystyrene by UV/visible spectroscopic study

The catalytic activities in syndiospecific polymerization of styrene in hydrocarbon using homogeneous Ti-based catalysts in the presence of methylaluminoxane (MAO) were investigated through UV/visible spectroscopic analysis. A strong UV absorption band of CpTiCl₃, itself, incipiently appeared at λ_max = 400 nm in toluene, followed by a bathochromic shift with its remarkable decrease by the addition of MAO. The absorption band intensity at λ_max = 400 nm arising from delocalization of π-electrons on the cyclopentadienyl ring decreased by methylation in the presence of MAO with regard to the mechanism for production of an active center (“cation-like”), for example, the change of the ionic nature. The intensity decrease at λ_max = 400 nm was suppressed over 2000 of the [Al]/[Ti] ratio. In the case of Ti(OC₄H₉)₄ having a σ-ligand, new and broad UV absorption bands were developed at λ_max = 340 nm and 410 nm in the presence of MAO in contrast with the CpTiCl₃/MAO system. Comparison between the relative absorption intensities at λ_max = 340 nm and 410 nm led to the determination of a maximum catalytic activity of Ti(OC₄H₉)₄ in the presence of MAO related to the polymerization yield. The maximum polymerization yield was observed with regard to the relative maximum value of the absorption intensity at λ_max = 410 nm with the [Al]/[Ti] ratio (500). From observation for polymorphism of the final products via differential scanning calorimetric analysis (DSC), the thermally unstable β-form seemed to be produced by the CpTiCl₃/MAO system independent of the MAO concentration, the Ti(OC₄H₉)₄/MAO system produced a thermally stable α-form in the low MAO concentration (up to 100 of the [Al]/[Ti] ratio), and a mixture of α- and/or β-forms over 200 of the [Al]/[Ti] ratio under our experimental conditions. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1733–1741, 1998     

Microstructure effect in the coupling reactions of polymeric organolithium compounds using chlorosilanes

The most important variable affecting the yield in the coupling reactions of polymeric organolithium compounds with chlorosilane compounds has been investigated through size-exclusion chromatographic (SEC) analysis. The coupling reaction of poly(styryl)lithium with dichlorodimethylsilane as a silane-coupling agent provided 44 wt % of the coupling yield. The coupling yield, depending on the chain end reactivity of active polymers, was not greatly affected. The addition of a Lewis base such as N,N,N′,N′-tetramethylethylenediamine (TMEDA) even after complete polymerization of the dienes in hydrocarbon seems to affect the coupling reaction, resulting in decreasing the yield. The 1,2- or 3,4-enchain contents in the polydiene backbones affected the reduction of the linking efficiency in the coupling of the poly(dienyl)lithiums with chlorosilanes as the linking agent. The linking yields of the active polymers including over 75 mol % of 1,2- or 3,4-enchainment on the polydiene segment were below 20 wt %. The linking yields exhibited a dependence not only on the steric requirement of the chain end, but also the microstructure of the polydiene segment. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1743–1753, 1998     

Syntheses and biological activities of α-methoxy-exo-3,6-epoxy-1,2,3,6-tetrahydrophthaloyl-5-fluorouracil and its polymers

The new monomer, α-methoxy-exo-3,6-epoxy-1,2,3,6-tetrahydrophthaloyl-5-fluorouracil (METFU), was synthesized by the reaction of 5-fluorouracil (5-FU) and exo-3,6-epoxy-1,2,3,6-tetrahydrophthalic anhydride (ETA) in order to prepare polymers containing 5-FU moiety. Poly(α-methoxy-exo-3,6-epoxy-1,2,3,6-tetrahydrophthaloyl-5-fluorouracil) [poly(METFU)], poly(α-methoxy-exo-3,6-epoxy-1,2,3,6-tetrahydrophthaloyl-5-fluorouraci-co-acrylic acid) [poly(METFU-co-AA)], and poly(α-methoxy-exo-3,6-epoxy-1,2,3,6-tetrahydrophthaloyl-5-fluorouracil-co-vinyl acetate) [poly(METFU-co- VAc)] were synthesized by photopolymerizations using 2,2-dimethoxy-2-phenylacetophenone (DMP) as an initiator. The synthesized METFU and the polymers were identified by FTIR and ¹H-NMR spectroscopies. The contents of METFU in poly(METFU-co-AA) and poly(METFU-co-VAc) determined by elemental analysis were 52 and 60 mol %, respectively. The average molecular weights and polydispersity indices determined with GPC were as follows: M n = 9,400, M w = 11,400 M w/M n = 1.21 for poly(METFU), M n = 14,400, M w = 26,800, M w/M n = 1.86 for poly(METFU-co-AA), and M n = 23,100, M w = 33,000, M w/M n = 1.43 for poly(METFU-co-VAc). The in vitro cytotoxicities of samples were evaluated with mouse mammary carcinoma (FM3A), mouse leukemia (P388), and human histiocytic lymphoma (U937) as cancer cell lines, and mouse liver cells (AC2F) as a normal cell line. The in vivo antitumor activities of synthesized polymers against mice bearing the sarcoma 180 tumor cell line were greater than those of 5-FU at concentrations of 0.8 and 80 mg/kg. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2177–2184, 1998     

Details of surface features in aromatic polyamide reverse osmosis membranes characterized by scanning electron and atomic force microscopy

In the present article, some new events on the surface morphology of the aromatic polyamide thin‐film‐composite (TFC) membranes were demonstrated in conjunction with their inherent chemical nature. In addition, the detailed, quantitative understanding of the microscopic surface features was shown to be essential in controlling the water permeability and eventually developing the high performance membranes. The surface roughness and the surface area were mainly affected by the existence or nonexistence of the crosslinking and/or the free amide groups not pertinent to the formation of the hydrogen bonding, which in turn contributed to the water permeability. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1429–1440, 1999     

Visible upconversion and infrared luminescence investigations of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> powders doped with Er<Superscript>3+</Superscript>, Yb<Superscript>3+</Superscript> and Zn<Superscript>2+</Superscript> ions

Alumina (Al₂O₃) powders doped with Er³⁺, Yb³⁺ and Zn²⁺ ions have been prepared by a low-temperature combustion synthesis technique. The phase purity and crystalline structure of the combustion products are confirmed by powder X-ray diffraction. An efficient frequency upconversion in the visible region and the emission in the infrared (IR) region respectively corresponding to the ²H_11/2, ⁴S_3/2→⁴I_15/2, ⁴F_9/2→⁴I_15/2 and ⁴I_13/2→⁴I_15/2 transitions upon direct excitation with a CW laser lasing at ∼980 nm are discussed. The enhancement observed in the intensity of the upconversion emission bands in the visible region and the emission band in the IR region due to the presence of Yb³⁺ and Zn²⁺ in Er³⁺:Al₂O₃ powders is reported and explained in detail.     

Metal-directed supramolecular assembly of metal(II) benzoates (M = Co,Ni, Cu,Zn, Mn,and Cd) with 4,4′-bipyridine: Effects of metal coordination modes and novel catalytic activities

Six polymeric metal(II)-benzoate complexes of formula [Co₂(O₂CPh)₄(4,4′-bpy)₂]_n (1-Co), [Ni(O₂CPh)₄(H₂O)₂(4,4′-bpy)]_n (2-Ni), [Cu₂(O₂CPh)₄(4,4′-bpy)]_n (3-Cu), [Zn₂(O₂CPh)₂(OH)₂(4,4′-bpy)₂]_n (4-Zn), [Zn₃(O₂CPh)₄(μ-OH)₂(4,4′-bpy)₂]_n (5-Zn), and [Cd₂(O₂CPh)₄(4,4′-bpy)₂]_n (6-Cd) have been synthesized and characterized (4,4′-bpy = 4,4′-bipyridine). 1-Co and 6-Cd show ladder-type double chains, 2-Ni does a helical structure, 3-Cu does a one-dimensional chain containing paddle-wheel units, 4-Zn does a zigzag chain, and 5-Zn does two-dimensional sheets. Since different structures provide different coordination geometry of each metal ion, it is clear that selection of appropriate metal ions can control the coordination geometry of each metal ion to form different crystal structures. Reactivity study of the compounds 1–7 for the transesterification of a variety of esters has shown that 4-Zn and 5-Zn are very efficient and the best among them. The catalyst 6-Cd containing Cd ion, well known as an inert metal ion for the ligand substitution, also catalyzed efficiently the transesterification of a variety of esters, and its reactivity is comparable to 4-Zn and 5-Zn. Moreover, the redox-active metal-containing polymers, 1-Co, 3-Cu, and 7-Mn, have shown efficient catalytic reactivities for the transesterification reactions, while 2-Ni has displayed a very slow conversion. The reactivities of the compounds used in this study are in the order of 5-Zn > 4-Zn > 6-Cd > 7-Mn ∼ 3-Cu > 1-Co > 2-Ni, indicating that the non-redox metal-containing compounds (5-Zn, 4-Zn, and 6-Cd) show better activity than the redox-active metal-containing compounds (7-Mn, 3-Cu, 1-Co, and 2-Ni). These results suggest that it is possible to tune the catalytic activities by changing from Zn to those metals such as Cd, a kinetically inert metal, or Cu, Mn, and Co, the redox-active metals.     

Real-time observation of temperature-dependent protein-protein interactions using real-time dual-color detection system

This study examined the ability of a real-time dual-color detection system to allow direct observations of the kinetics of temperature-dependent protein-protein interaction at a single-molecule level. The primary target protein was an Alexa Fluor^® 488-labeled actin conjugate, which had been pre-incubated with an unlabeled rabbit anti-actin antibody (IgG). The complementary fluorescent protein was Alexa Fluor^® 633-labeled goat anti-rabbit IgG antibody, which interacts with the rabbit anti-actin antibody (IgG) bound to the Alexa Fluor^® 488-labeled actin conjugate. The individual protein molecules labeled with different fluorescent dyes in solution were effectively focused, interacted with the other protein molecules at 500 aM, and detected directly in real-time using the dual-wavelength (λ_ex = 488 and 635 nm) laser-induced fluorescence detection system. The kinetics of the protein-protein interactions were examined at different temperatures (12-32 °C). At concentrations in the aM range, the number of bound complex molecules through the protein-protein interaction decreased gradually with time at a given temperature, and increased with decreasing temperature at a set time. A high concentration (above 500 pM) of the protein sample caused aggregation and nonspecific binding of the protein molecules, even though the protein molecules were not an example of complementary binding. The results demonstrated that the real-time kinetics of a protein-protein interaction could be analyzed effectively at the single-molecule level without any time delay using the real-time dual-color detection system.     

一维热传导方程热源反问题基于最小二乘法的正则化方法

研究一维热传导方程热源反问题.给出基于最小二乘支持向量机（LS-SVM）求解的半解析表达式,此外还给出一种参数调节方法以及算法稳定性的证明.数值实验表明该方法具有较高的数值精度和稳定性.     

Challenges in quantitative analyses for volatile organic compounds bound to lipocalins

In this communication, I describe the challenges in quantitative analyses for volatile organic compounds in mouse urine, which are primarily caused by the presence of the major urinary proteins, a lipocalin subfamily, that sequester volatile ligands. The analyses of volatile compounds in mouse urine have been performed since the late 1970s. However, none of them considered the binding interactions of the quantified compounds with the urinary proteins. Some volatile ligands are tightly bound to the proteins and may not be extracted completely by organic solvents. The amounts of volatile ligands measured by external standard calibration represent those of the unbound ligands in the headspace, not the total amounts in urine. Addition of internal standards displaces ligands bound to the proteins, resulting in a completely different volatile profile. Normalization of volatile compounds using relative peak area (or height) ratios may not be used in the conditions where displacement of ligands bound to the proteins occurs. Because of the unique chemical properties of mouse urine, I have not been able to find a good quantification method for the volatile compounds released from mouse urine. I hope that the identification of these issues will stimulate others to come up with novel approaches.     

Highly luminescent InP/GaP/ZnS nanocrystals and their application to white light-emitting diodes

Highly stable and luminescent InP/GaP/ZnS QDs with a maximum quantum yield of 85% were synthesized by in situ method. The GaP shell rendered passivation of the surface and removed the traps. TCSPC data showed an evidence for the GaP shell. InP/GaP/ZnS QDs show better stability than InP/ZnS. We studied the optical properties of white QD-LEDs corresponding to various QD concentrations. Among various concentrations, the white QD-LEDs with 0.5 mL of QDs exhibited a luminous efficiency of 54.71 lm/W, Ra of 80.56, and CCT of 7864 K.