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901.
902.
研究了采用低场脉冲核磁共振(NMR)测定二醋酸纤维素丝束油剂的新方法,给出NMR法测定二醋酸纤维素丝束油荆含量的标准曲线。同时对NMR法测量二醋酸纤维素丝束油荆不确定度进行了评估。结果表明,NMR法具有分析速度快、无污染、无损伤和准确度高的优点,适合于二醋酸纤维素丝束油荆的分析。 相似文献
903.
Luis C. Mendes Andrea D. Tedesco Mauro S. Miranda Marcia R. Benzi Beatriz S. Chagas 《Polymer Testing》2005,24(8):963-968
In this third work, we evaluated the degree of conversion (DC) versus depth of dental filling composite named Prodigy Condensable™ using infrared spectroscopy. Confirming previous results, there was a gradual reduction of DC with increasing depth but the composite exhibited extreme values of DC, an upper value (45.9%) on the surface and a lower one (6.1%) at a depth of 5 mm. The composite presented the worst performance among materials studied. The composite formulation was 80% of inorganic fillers and BisfenolA/dimethacrylate (BisGMA) (18%)/triethyleneglycoldimethacrylate (TEGDMA) (2.0%) as monomers. As stated before, type/ratio/viscosity of monomers and type, amount, size and size distribution of fillers all together had an important role in the cure reaction contributing to the final performance of the composite. 相似文献
904.
K. Laihia A. Valkonen E. Kolehmainen R. Suontamo M. Nissinen V. Nikiforov S. Selivanov 《Journal of Molecular Structure》2005,754(1-3):77-84
The 1H and 13C NMR chemical shifts for six toxaphene congeners: 2-exo,3-endo,6-exo,8,9,10-hexachloro- (1), 2-exo,3-endo,5-exo,9,9,10,10-heptachloro- (2), 2-exo,3-endo,6-exo,8,9,10,10-heptachloro- (3), 2-exo,3-endo,5-exo,6-endo,8,9,10-heptachloro- (4), 2-exo,3-endo,5-exo,6-endo,8,9,9,10-octachlorobornane (5) and 2,5-endo,6-exo,8,9,9,10,10-octachloro-2-bornene (6) are reported. Their chemical shift assignments have been obtained by means of Pulsed Field Gradient (PFG) Double Quantum Filtered (DQF) 1H,1H correlation spectroscopy (COSY), PFG 1H,13C Heteronuclear Multiple Quantum Coherence (HMQC) and PFG 1H,13C Heteronuclear Multiple Bond Correlation (HMBC) experiments. A single crystal X-ray structural analysis was made for compounds 1, 3, 4 and 6. The prevalences of two octachlorobornene rotamers (6a,6b) were elucidated by ab initio MO method and single point DFT/GIAO calculations for 13C chemical shifts. Theoretical calculations proved that the single crystal structure of 6 corresponds its most stable conformer in solution. 相似文献
905.
1,3-丙二胺邻苯二酚钼钨手性八面体配合物的仿生合成、晶体结构以及与ATP作用的液相NMR研究 总被引:1,自引:0,他引:1
合成了1,3-丙二胺邻苯二酚钼钨手性八面体配合物(NH3CH2CH2CH2NH2)2[Mo0.4W0.6O2(C6H4O2)2],并对其进行了单晶结构解析,研究了其与ATP作用的液相NMR谱.该晶体属正交晶系,空间群为Pcan.晶胞参数a=0.7501(2)nm,b=2.3994(7)nm,c=1.2178(4)nm,Z=4.[Mo0.4W0.6O2(C6H4O2)2]2-的配位几何构型为手性八面体,晶体为外消旋体.配位阴离子中MoW中心金属离子除了与两个端基O配位形成cis-MO键外,同时还分别与两个邻苯二酚配位基团的的氧原子配位,形成4个M-Ob(M=Mo,W)键,构成两个五元环.利用1HNMR,13CNMR,31PNMR以及1H-15NHMBC对标题配合物及其与ATP在D2O溶剂中的作用进行了研究,发现标题配合物的MoW中心金属离子在纯D2O溶剂中被还原成+5价,但与ATP混合后转化为+6价,且与原配位基邻苯二酚发生解离.解离后的[MO2]2+最大可能与腺嘌呤上的氨基N原子配位,而此配位可能是其抗癌抗肿瘤活性的主要作用机理之一. 相似文献
906.
The miscibility and thermal properties of poly(N‐phenyl‐2‐hydroxytrimethylene amine)/poly(N‐vinyl pyrrolidone) (PHA/PVP) blends were examined by using differential scanning calorimetry (DSC), high‐resolution solid‐state nuclear magnetic resonance (NMR) techniques, and thermogravimetric analysis (TGA). It was found that PHA is miscible with PVP, as shown by the existence of a single composition‐dependent glass transition temperature (Tg) in the whole composition range. The DSC results, together with the 13C crosspolarization (CP)/magic angle spinning (MAS)/high‐power dipolar decoupling (DD) spectra of the blends, revealed that there exist rather strong intermolecular interactions between PHA and PVP. The increase in hydrogen bonding and in Tg of the blends was found to broaden the line width of CH—OH carbon resonance of PHA. The measurement of the relaxation time showed that the PHA/PVP blends are homogeneous at least on the scale of 1–2 nm. The proton spin‐lattice relaxation in both the laboratory frame and the rotating frame were studied as a function of the blend composition, and it was found that blending did not appreciably affect the spectral densities of motion (sub‐Tg relaxation) in the mid‐MHz and mid‐KHz frequency ranges. Thermogravimetric analysis showed that PHA has rather good thermal stability, and the thermal stability of the blend can be further improved with increasing PVP content. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 237–245, 1999 相似文献
907.
Gaio Paradossi Francesca Cavalieri Donatella Capitani Vittorio Crescenzi 《Journal of Polymer Science.Polymer Physics》1999,37(12):1225-1233
In this paper, we report on the physicochemical characterization of hydrogels recently obtained by crosslinking poly (vinylalcohol), PVA, with telechelic PVA (telPVA, bearing terminal aldehydic groups) via acetalization in aqueous solution. These gels were studied by equilibrium swelling, compression modulus measurements, and proton relaxometry experiments. Swelling and compression modulus data allow to estimate the average molecular weight of PVA chain between crosslinks, the average mesh size of the networks, and the polymer–solvent interaction parameter χ1. The average mesh size of PVA‐telPVA compares well with domain dimensions of diffusionally confined water as detected by NMR relaxometry. Proton relaxometry also showed different network domains in which water is compartmentalized, indicating a complex heterogeneity. The study of the temperature behavior of the nuclear spin–spin relaxation times of the confined water was also considered. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1225–1233, 1999 相似文献
908.
Douglas R. Robello Teresa D. Eldridge Michael T. Swanson 《Journal of polymer science. Part A, Polymer chemistry》1999,37(24):4570-4581
Polycyanoacrylates were found to be inherently unstable. Even in the absence of a deliberately added strong base, their molecular weights decreased drastically on standing in solution in accord with observations by Ryan and McCann (Makromol Chem Rapid Commun 1996, 17, 217). The initial high molecular weight polymer disappeared over the course of a few hours in solution and was replaced by a much lower molecular weight material. For polymers made by anionic polymerization, the entire sample degraded, but for polymers made by free-radical polymerization, only a portion of the sample was affected. This behavior was consistent with the mechanism proposed by Ryan and McCann, in which the polymer chains are in dynamic equilibrium with their monomers and the polymer degrades from its chain terminus. Surprisingly, the degradation in molecular weight even occurred slowly in the solid state. The degradation was inhibited by acids and could be prevented by free-radical copolymerization with small amounts of more stable monomers. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4570–4581, 1999 相似文献
909.
Coordination Chemistry of P‐rich Phosphanes and Silylphosphanes. XVII [1] [Co(g5‐Me5C5)(g3‐tBu2PPCH–CH3)] from [Co(g5‐Me5C5)(g2‐C2H4)2] and tBu2P–P=P(Me)tBu2 [Co(η5‐Me5C5)(η3‐tBu2PPCH–CH3)] 1 is formed in the reaction of [Co(η5‐Me5C5)(η2‐C2H4)2] 2 with tBu2P–P 4 (generated from tBu2P–P=P(Me)tBu2 3 ) by elimination of one C2H4 ligand and coupling of the phosphinophosphinidene with the second one. The structure of 1 is proven by 31P, 13C, 1H NMR spectra and the X‐ray structure analysis. Within the ligand tBu2P1P2C1H–CH3 in 1 , the angle P1–P2–C1 amounts to 90°. The Co, P1, P2, C1 atoms in 1 look like a „butterfly”︁. The reaction of 2 with a mixture of tBu2P–P=P(Me)tBu2 3 and tBu–C?P 5 yields [Co(η5‐Me5C5){η4‐(tBuCP)2}] 6 and 1 . While 6 is spontaneously formed, 1 appears only after complete consumption of 5 . 相似文献
910.
H. Binder R. Kellner K. Vaas M. Hein F. Baumann M. Wanner R. Winter W. Kaim W. Hnle Y. Grin U. Wedig M. Schultheiss R. K. Kremer H. G. von Schnering O. Groeger G. Engelhardt 《无机化学与普通化学杂志》1999,625(7):1059-1072
Halogenation of nido-B10H14 with C2H2Cl4, C2Cl6, Br2, or I2, produces by cluster degradation the (2 n)-closo-clusters B9X9 (X = Cl, Br, I). The synthesis of salts of the perhalogenated radical anions of the type (2 n + 1)-closo-[B9X9]· – and of the corresponding dianions (2 n + 2)-closo-[B9X9]2– from neutral B9X9 is described [n is the number of cluster atoms; (2 n), (2 n + 1), and (2 n + 2) is the number of cluster electrons]. Molecular and crystal structures of B9Cl9, B9Br9, [(C6H5)4P][B9Br9] · CH2Cl2, and [(C4H9)4N]2[B9Br9] · CH2Cl2 have been determined via X-ray diffraction. All three oxidation states of the cluster retain the tricapped trigonal prism. The reduction of the clusters B9X9 was shown by cyclic voltammetry in CH2Cl2 to proceed via two successive one-electron reversible steps, separated by at least 0.4 V. The paramagnetic radical anions [B9X9]· – (X = Cl, Br) were further characterized by magnetic susceptibility measurements of [Cp2Fe][B9X9] and [Cp2Co][B9X9], respectively. The EPR spectra of [B9X9]· – (X = Cl, Br, I) in glassy frozen CH2Cl2 solutions showed increasing g anisotropy for the heavier halogen derivatives, illustrating significant halogen participation at the singly occupied MO. The 11B NMR spectra of CD2Cl2 solutions of the neutral clusters B9X9 exhibit only one sharp resonance, indicating that the boron atoms are highly fluxional in solution. In contrast, two different boron resonances as expected for a rigid tricapped trigonal prism are clearly observed for the [B9X9]2– dianions in solutions and for solid B9Br9 in the 11B MAS NMR spectra. Temperature dependent 11B MAS NMR experiments on B9Br9 and [B9Br9]2– in the solid state show a reversible coalescence of the two resonances at higher temperature. 11B MAS NMR spectra and DTA measurements of [B9Br9]2– showed a phase transition. 相似文献