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61.
Sameh Daboussi Sophie Kazamias Kevin Cassou Olivier Guilbaud Moana Pittman Olivier Delmas Olivier Neveu Brigitte Cros Gilles Maynard David Ros 《Applied physics. B, Lasers and optics》2013,110(1):7-14
We calculate the field distribution based on the vector diffraction theory for a superposition of spirally phase shifted radially polarized beams. Twisted longitudinally polarized field is found in the focal region. The total intensity as well as the polarization components rotates around the beam axis near the focus. Calculation of the Poynting vector at the focal plane shows that the electromagnetic energy is redistributed between different polarization components. Nonzero value of transverse components of the Poynting vector implies the transverse flow of the energy in the focal region. 相似文献
62.
Jie Ren Dan Zhao Shi-Jie Wu Jie Wang Yun-Jing Jia Wen-Xin Li Hua-Jie Zhu Fei Cao Wan Li Charles U. Pittman Xiang-Jiu He 《Tetrahedron》2019,75(9):1194-1202
The absolute configuration of cepharanthine (1), a strongly bioactive bisbenzylisoquinoline alkaloid exhibiting 12 specific bioactivities without any reported negative side-effects, has been reassigned from (1R,1′S) to (1R,1′R) using quantum theory. The absolute configurations (ACs) of 13 other analogues of 1 were also systematically reassigned. Six quaternary salts were prepared from 1 and one exhibited strong anti-bacterial activity against Bacillus subtilis with MIC 0.31?μM, while Ciprofloxacin, the positive control medicine was 3.88?μM. This work established the critical importance of correlating chiroptical experimental spectra with their quantum mechanically predicted spectra for accurate stereogenic center assignments. 相似文献
63.
Liwei Cao Charles U. Pittman 《Journal of polymer science. Part A, Polymer chemistry》1999,37(15):2823-2840
Carbon black-supported sulfuric acid or BF3·Et2O-initiated polymerizations of 2-methylene-4,4,5,5-tetramethyl-1,3-dioxolane (1), 2-methylene-4-phenyl-1,3-dioxolane (2), and 2-methylene-4-isopropyl-5,5-dimethyl-1,3-dioxane (3) were performed. 1,2-Vinyl addition homopolymers of 1–3 were produced using carbon black-supported H2SO4 initiation at temperatures from 0°C to 60°C whereas both ring-opened and 1,2-vinyl structural units were present in the polymers using BF3·Et2O as an initiator. Cationic polymerizations of 2-methylene-1,3-dithiolane (4) and copolymerization of 4 with 2-methylene-4-(t-butyl)-1,3-dioxolane (5) were initiated with either carbon black-sulfuric acid or BF3·Et2O. Insoluble 1,2-vinyl addition homopolymers of 4 were obtained upon initiation with the supported acid or BF3·Et2O. A soluble copolymer of 2-methylene-1,3-dithiolane (4) and 4-(t-butyl)-2-methylene-1,3-dioxolane (5) was obtained upon BF3·Et2O initiation. This copolymer is composed of three structural units: a ring-opened dithioester unit, a 1,2-vinyl-polymerized 1,3-dithiolane unit, and a 1,2-vinyl polymerized 4-(t-butyl)-1,3-dioxolane unit. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2823–2840, 1999 相似文献
64.
Zhihong Wu Charles U. Pittman 《Journal of polymer science. Part A, Polymer chemistry》1998,36(6):873-881
BF3·OEt2-initiated polymerizations of 2-methylene-1,3-dioxepane gave polymers composed of both ring-retained and ring-opened structures. The ring-opening content increased with an increase in polymerization temperature. Poly(4,7-dimethyl-2-methylene-1,3-dioxepane) propagated slower during BF3·OEt2-initiated polymerization and had a lower ring-opened content than poly(2-methylene-1,3-dioxepane). The type of acid initiator used also affected the amount of ring opening observed. Stronger acids gave less ring opening. Attempted BF3·OEt2-initiated copolymerizations of these seven-membered ring cyclic ketene acetals with isobutyl vinyl ether at room temperature resulted in formation of the two homopolymers. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 873–881, 1998 相似文献
65.
Shen Ji George M. Crews Charles U. Pittman Yin Wang Ruicheng Ran 《Journal of polymer science. Part A, Polymer chemistry》1996,34(13):2543-2561
Ammeline–melamine–formaldehyde resins (AMF Resins) containing 5–100 mol % of ammeline, were synthesized by polymerization of the preformed sodium salt of ammeline, melamine, and formaldehyde in basic medium by three methods. These resins, when cured, constitute a new class of thermosets. The rate of hydroxymethylation of the amino groups of the ammeline salt with formaldehyde was somewhat larger then that of the amino groups on melamine. At higher pH values ammeline insolubility was not a problem. The AMF resin composition was approximately equal to the mol ratio of the components originally charged. Both ammeline and melamine were consumed over the entire reaction period. Thus, it is possible to make approximately uniform random ammeline-melamine-formaldehyde resins (AMF) with any mol ratio of ammeline salt to melamine. By controlling the pH of the solution from which the resins were isolated, the (SINGLE BOND) O− Na+/(SINGLE BOND) OH ratio could be varied. Resin melting points varied widely with the mol fraction of ammeline and the (SINGLE BOND) O− Na+/(SINGLE BOND) OH ratio. AMF resin solubilities, shelf lives, cloud points, and water tolerance depended upon the method of preparation, pH, and other factors. The sodium salt of ammeline was hydroxymethylated in water more readily than ammeline. More highly methylolated ammeline species were readily formed in solution but upon precipitation only bis-N-hydroxymethylammeline was isolated. © 1996 John Wiley & Sons, Inc. 相似文献
66.
A novel and efficient Ni-catalyzed aryl- and alkyl-selenation of imidazo[1,2-α]pyridines employing selenium powder has been developed for the first time. The significant advantages of this protocol are that it is an inexpensive nickel catalyst and exhibits broad functional-group compatibility and good reaction yields. 相似文献
67.
68.
Mitsuru Ueda Masami Takahashi Toshiyuki Suzuki Yoshio Imai Charles U. Pittman 《Journal of polymer science. Part A, Polymer chemistry》1983,21(4):1139-1149
α-Methylene-N-methylpyrrolidone (α-MMP) was synthesized and homopolymerized by bulk and solution methods. The poly(α-MMP) is readily soluble in water, methanol, methylene chloride, and dipolar aprotic solvents at room temperature. Thermogravimetric analysis of poly(α-MMP) showed a 10% weight loss at 330°C in air. The kinetics of α-MMP homopolymerization and copolymerization were investigated in acetonitrile, using azobisisobutyronitrile (AIBN) as an initiator. The rate of polymerization Rp could be expresed by Rp = k[AIBN]0.49[α-MMP]1.3. The overall activation energy was calculated to be 84.1 kj/mol. The relative reactivity ratios of α-MMP (M2) copolymerization with methyl methacrylate (r1 = 0.59, r2 = 0.26) in acetonitrile were obtained. Applying the Q-e scheme led to Q = 2.18 and e = 1.77. These Q and e values are larger than those for acrylamide derivatives. 相似文献
69.
Mitsuru Ueda Masahiko Yazawa Toshiyuki Suzuki Charles U. Pittman 《Journal of polymer science. Part A, Polymer chemistry》1986,24(12):3177-3189
Methylthiomethyl methacrylate (MtMA) was synthesized and homopolymerized in solution. The poly(MtMA) is readily soluble in benzene, acetone, tetrahydrofuran, and methylene chloride at room temperature. The values of K and a in the Mark–Houwink equation, [η] = KMa, were found to be K = 2.88 × 10–5 and a = 0.75 when M = Mw. The glass transition temperature of poly(MtMA) was observed to be 72°C by thermomechanical analysis. Intramolecular anhydride formation occurred when poly(MtMA) was heated to 250–300°C. The kinetics of MtMA homopolymerization was investigated in benzene, using azobisisobutyronitrile as initiator. The rate of polymerization Rp was expressed by Rp = k[AIBN]0.5[MtMA]1.05 and the overall activation energy was calculated to be 75.7 kJ/mol. The relative reactivity ratios of MtMA in styrene copolymerizations (r1 = 0.33, r2 = 0.55) were obtained. Applying the Q-e scheme led to Q = 1.07 and e = 0.51 for MtMA. 相似文献
70.
A quantitative analytical method, using high-performance liquid chromatography and ultraviolet detection, has been established for the determination of nefazodone (NEF) and its metabolites, m-chlorophenylpiperazine (mCPP),p-hydroxynefazodone (PHN), and hydroxynefazodone (HO-NEF), in human plasma. The fully automated, robotic procedure consisted of addition of internal standard (aprindine), extraction with butyl chloride, followed by phase separation, organic phase evaporation, reconstitution of the residue, and injection onto the chromatographic system. The limits of detection for NEF, mCPP, PHN, and HO-NEF were 5, 1, 10, and 5 ng/ml, respectively, at a signal-to-noise ratio of 4. The method had a linear range of 10-1000 ng/ml for NEF and HO-NEF, 20-2000 ng/ml for PHN, and 2.5-250 ng/ml for mCPP. Correlation coefficients of 0.996 or greater were obtained during validation and study sample analysis. 相似文献