共查询到20条相似文献,搜索用时 15 毫秒
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本文测定了不同中和度聚丙烯酸在不同离子强度盐溶液中的特性粘数,研究了聚丙烯酸的分子形态及构象对聚合物浓度、电荷密度及溶液离子强度的依赖性,得到聚离子的构象变化与溶液盐浓度的对数成反比,与电荷密度的平方根成正比等规律。 相似文献
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端羟基芳香酯二醇扩链的聚氨酯-酯的DSC研究陈静,余学海,杨昌正(南京化工学院应化系南京210009)(南京大学化学系南京210093)关键词嵌段聚醚聚氨酯-酯,结晶性,微观相结构,差示扫描量热法,形态结构众所周知,聚氨酯嵌段共聚物是一类结构特殊、用... 相似文献
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LIGHT-INDUCED ABSORBANCE CHANGES IN PHYCOMYCES PHOTOMUTANTS 总被引:1,自引:0,他引:1
Abstract— Blue-light-induced absorbance changes indicating the reduction of a b -type cytochrome by a flavin photoreceptor have been reported elsewhere for Dictyostelium, Neurospora , and Phycomyces . On the basis of action spectra alone these absorbance changes were associated with the blue-light physiological photoresponses in the latter two organisms. We have investigated phototropically abnormal mutants of Phycomyces in order to determine if there were common defects in blue-light-induced absorbance changes and photophysiology. However, mutants representing four genes, madA, madB, madC , and madE , the first two of which are associated with early steps in the sensory pathway, showed blue-light-induced absorbance changes identical to those in a phototropically normal strain. A pigment kinetics model, which was used to interpret dose-response data, indicated a rather low quantum yield of 0.015 for the light-induced absorbance changes. Similar blue-light induced absorbance changes were observed in HeLa cells. These cells are derived from a human cervical carcinoma and are thus very unlikely to possess any natural photophysiology. Our results question the relevance of these blue-light-induced absorbance changes regarding the blue-light receptor for physiological responses in various organisms. 相似文献
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Abstract— Light induced absorbancy changes in Rhodopseudomonas sp. NHTC 133 are analogous to those observed in other photosynthetic bacteria, but all of the features in the light-induced difference spectrum (except those reflecting cytochrome oxidation) are shifted to greater wavelengths. This general shift is consistent with the fact that the bacteriochlorophyll of this organism (BChl b ) differs from the usual BChl in that its absorption bands are shifted to greater wavelengths.
The singlet excited state of P985 (the counterpart of the P870 of Rhodopseudomonas spheroides ) is not an energy sink relative to the major component of BChl b in vivo . The absorption maximum of P985 is at 985 mp, whereas that of CBhl b in vivo is at 1012 mμ. 相似文献
The singlet excited state of P985 (the counterpart of the P870 of Rhodopseudomonas spheroides ) is not an energy sink relative to the major component of BChl b in vivo . The absorption maximum of P985 is at 985 mp, whereas that of CBhl b in vivo is at 1012 mμ. 相似文献
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Feng-en Chen Ming-xiao Fu Fan Wang Bin Fan Gao-quan Shi 《高分子科学》2005,(6):681-685
Poly(p-phenylene) (PPP) films have been electrochemically deposited on mirrorlike stainless steel (SS) electrode surfaces by direct oxidation of benzene in boron trifluoride diethyl etherate (BFEE) solutions at a constant applied potential of 1.7 V (versus Ag/AgCl). The chain conformations of as-grown PPP films have been studied by Raman spectroscopy. The results demonstrated that high synthesis temperature favors the formation of planar PPP, and the conformation of planar PPP can be changed into torsional PPP by cooling treatment. 相似文献
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聚乙烯醇/聚乙烯基吡咯烷酮共混体系相容性研究 总被引:1,自引:1,他引:1
用DSC、FTIR、SAXS和测定Flory-Huggins相互作用参数等方法对聚乙二醇(PVA1)/聚乙烯基吡咯烷酮(PVP)共混体系的研究。结果表明,该体系具有完全互容的性质。共混物只有一个玻璃化转变温度。用DMSO作溶剂浇铸的膜光学透明。PVA1的长周期和片晶厚度均随PVP含量增加而增大,但后者增大的幅度比前者小得多,表明PVP和PVA1的非晶部分形成均相并夹入到球晶内部。共混物中PVP羰基吸收峰和PVA1的羟基吸收峰与相应均聚物相比,在红外光谱图中皆向低频方向迁移,迁移波数随第二组分含量的增加而增大。表明二者间有氢键生成。用平衡熔点计算的Flory-Huggins相互作用参数为-0.88。 相似文献
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聚乙烯醇水凝胶溶胀特性研究 总被引:30,自引:0,他引:30
在前文对聚乙烯醇水溶液冰冻凝胶化浓度依赖性研究基础上,对接触浓度(C)以上聚乙烯醇水溶液通过冰冻-融化处理,制得了一种含水率高达95~98%的水凝胶.系统研究了该水凝胶在蒸馏水中的溶胀及溶解特性.得到了一个与实验结果相吻合的溶胀动力学方程:Q1=Qe-(Qe-QO)/ekt,及平衡溶胀比Qe与浓度之间的定量关系:Qe=60.3-4.45×102C.发现当冰冻-融化次数N≤5时,平衡溶胀比Qe及溶解量W与冰冻-融化次数(N)间满足幂函数关系:Qe。W通过对聚乙烯醇水凝胶平衡溶胀比与经冰冻处理的聚乙烯醇水溶液特性粘数进行比较,发现反映链间氢键凝聚缠结效应与反映链内氢键凝聚缠结效应的定量指标具有等效性. 相似文献
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Poly(p-phenylene) (PPP) films have been electrochemically deposited on mirrorlike stainless steel (SS) electrode surfaces by direct oxidation of benzene in boron trifluoride diethyl etherate (BFEE) solutions at a constant applied potential of 1.7 V (versus Ag/AgCl). The chain conformations of as-grown PPP films have been studied by Raman spectroscopy. The results demonstrated that high synthesis temperature favors the formation of planar PPP, and the conformation of planar PPP can be changed into torsional PPP by cooling treatment. 相似文献
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《高分子科学杂志,A辑:纯化学与应用化学》2013,50(11):1265-1278
ABSTRACT The use of poly(3,4-epoxy-1-butene) (polyEPB) in photoinduced free radical polymerizations has been investigated. It was observed that the inclusion of polyEPB into these photopolymerizations has several beneficial effects. In combination with aromatic ketones, polyEPB functions as a hydrogen donor to form a highly effective photoinitiator for the polymerization of acrylate monomers. At the same time, polyEPB undergoes facile autoxidation that serves to mitigate inhibition effects due to oxygen during free radical photopolymerizations. PolyEPB is an effective chain transfer agent that tends to increase both the rate and conversion in photoinduced crosslinking polymerizations in which multifunctional monomers are employed. Lastly, polyEPB is a interesting matrix-modifying agent that becomes incorporated into the resin matrix during photopolymerization due to photoinduced grafting reactions. 相似文献
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Abstract— Mediation of the chronic effects of differences in environmental illumination on pineal photoreceptor and adjacent supporting cells was studied in two experiments using larval trout. Experiment 1 had 7 groups exposed to controlled lighting conditions for 14 months: (1) constant darkness (DD); (2) natural photocycles (LD) followed by constant light (LL); (3) natural photocycles (LD); (4) LD fluorescent light; (5) LD blue (400–525nm) light; (6) LD green (500–612nm) light; and (7) LD red (600–750 nm) light. In Experiment II the fish were exposed to LL for 27–28 days, following 10 months in DD and one of five surgical manipulations: (1) pineal masked; (2) pineal sham-masked; (3) blinded; (4) blinded + pineal masked; (5) blinded + pineal sham masked.
Nuclei and nucleoli of pineal receptor and supporting cells were largest in fish raised in DD. LL or LD cycles, and light of either narrow or broad spectral range, were not notably different in their chronic effects on receptor cell nuclei and nucleoli. However, supporting cell nuclei and nucleoli were smallest in LL. Blinding and pineal masking demonstrated that: (1) pineal receptor cell nuclei and nucleoli were affected by chronic incident light in the pineal region but not by photic or visual influences via the lateral eyes; and conversely, (2) pineal supporting cell nuclei and nucleoli were affected by chronic photic input only via the lateral eyes. The results suggest the possible presence of a cellular comparator system in which photic inputs from lateral eyes and pineal affect separately and respectively the adjacent supporting and receptor cells of the pineal organ. 相似文献
Nuclei and nucleoli of pineal receptor and supporting cells were largest in fish raised in DD. LL or LD cycles, and light of either narrow or broad spectral range, were not notably different in their chronic effects on receptor cell nuclei and nucleoli. However, supporting cell nuclei and nucleoli were smallest in LL. Blinding and pineal masking demonstrated that: (1) pineal receptor cell nuclei and nucleoli were affected by chronic incident light in the pineal region but not by photic or visual influences via the lateral eyes; and conversely, (2) pineal supporting cell nuclei and nucleoli were affected by chronic photic input only via the lateral eyes. The results suggest the possible presence of a cellular comparator system in which photic inputs from lateral eyes and pineal affect separately and respectively the adjacent supporting and receptor cells of the pineal organ. 相似文献
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MONITORING LIGHT-INDUCED CHANGES IN ISOLATED, INTACT EYE LENSES 总被引:1,自引:0,他引:1
Fluorescence spectral changes occurring upon irradiation with 300 nm light have been monitored in situ in isolated, intact, whole lenses from the eyes of several species. The findings corroborate observations on other individual constituent protein molecules in the solution state, and also reveal features attributable to the supramolecular protein assembly that exists in the whole lens. Irradiation of the lens with 300 nm light causes red shifts in the tryptophan emission spectrum, suggesting alterations in the protein packing in the lens. Intermolecular energy transfer from tryptophan to one of the photoproducts, presumably N-formylkynurenine (N-FK), occurs in the condensed-phase sample. The N-FK formed is photodegraded efficiently in the lens, indicating that the photodynamic effects of endogenous N-FK might not be as severe as has been thought. Species variation in the photoevents are evident, particularly in avian lenses that contain the variant δ-crystallin as the core protein. The photoinduced changes in the near-UV circular dichroism of δ-crystallin (which is α-helical, as opposed to the β-sheet structure of α-, β-, and -γ-crystallins), isolated from chicken lenses, are remarkably different from other crystallins. Irradiation of δ-crystallin leads to a drastic reduction of circular dichroism intensity in the 250–300 nm region, whereas no changes are seen in the peptide absorption band. 相似文献
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Abstract— We studied the ultrastructure of laterally illuminated stage I sporangiophores of Phycomyces blakesleeanus to determine whether the phototropic response had any structural correlate. Stimulated sporangiophores conserved the distinctive division into the four longitudinal zones described for state I, and showed no significant differences in the distribution of major organelles in the sides proximal and distal to the light source. On the other hand, apical vesicles were asymmetrically distributed, being present in lower numbers in the faster growing (distal) side of the sporangiophore. We suggest that this asymmetrical distribution reflects the differential utilization of vesicles necessary to sustain the corresponding growth rate of each side. Illumination therefore, must affect the rate of vesicle migration and utilization, more than their rate of synthesis. 相似文献
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热处理过程中聚酯长丝的形态变化 总被引:1,自引:0,他引:1
在自制的红外三因素处理机上~[1],用红外加热在定张力下对聚对苯二甲酸乙二酯(PET)成品长丝进行热处理(二次定型)。用X-光衍射(WAXS)、X-光小角散射(DAXS)、红外光谱(IR)和双折射方法,测定样品的热收缩、结晶度、晶粒尺寸和取向、非晶取向、长周期和链折叠带强度。所得形态参数的变化表明,处理温度在200℃以上时,张力不再阻碍链折叠。不同定张力样品的形态研究表明,存在阻碍链折叠的某个张力转折值。本文条件下,这个张力值为f_(critical)=0.066g/dtex 。张力大于此值,链折叠过程受阻。 相似文献
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H-W. Trissl 《Photochemistry and photobiology》1979,29(3):579-588
Abstract— A novel technique of capacitative coupling of oriented rhodopsin at a polar/apolar interface allows the time resolved investigation of conformational changes following a flash. Electric signals arise as a consequence of changes of the interface potential. A signal occurring within milliseconds behaves like the R2 -phase of the "early receptor potential" (= ERP). This response is interpreted as a conformational change of rhodopsin. No correlation of this signal is found to the spectroscopically defined metarhodopsin I-metarhodopsin II transition.
The temperature dependence of the conformational change coincides with the temperature dependence of the latency of the 'a-wave' of the electroretinogram, reported by Arden and Ikeda (1968). It is suggested that the command step of visual excitation is the conformational change and not one of the spectroscopically defined photolysis steps of rhodopsin.
Analysis of slower electrical signals following the fast response is in accordance with the model of a light-induced pore formation. 相似文献
The temperature dependence of the conformational change coincides with the temperature dependence of the latency of the 'a-wave' of the electroretinogram, reported by Arden and Ikeda (1968). It is suggested that the command step of visual excitation is the conformational change and not one of the spectroscopically defined photolysis steps of rhodopsin.
Analysis of slower electrical signals following the fast response is in accordance with the model of a light-induced pore formation. 相似文献
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Jordi Contreras J. Idris Jones 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-2):67-68
Abstract Various sulfides are easily oxidized selectively to the corresponding sulfoxides in quantitative yields by iodosylarene (ArIO) catalyzed by metalloporphyrin (TPPM(III)Cl (M [dbnd] Fe, Mn)). The oxidation system is demonstrated to be a possible model for monooxygenase in the study of the stereochemistry of these sulfoxides. Metalloporphyrin-iodosylarene can initially equilibrate with the oxometalloporphyrin (TPPM(V)=O·Cl) formed in situ. The initial process may involve one-electron transfer from the sulfide to the intermediate oxometalloporphyrin followed by coupling of two resulting charged products, and/or nucleophilic attack of sulfide on oxometalloporphyrin oxygen. The overall reactions are depicted by paths with different electron demands from the results of Hammett plots. 相似文献
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聚乙烯醇纤维轴向压缩变形结构研究 总被引:1,自引:0,他引:1
研究了具有不同分子链形态PVA纤维的轴向压缩变形结构 .结果表明 ,在具有带状结构的PVA纤维中 ,带状结构对纤维的轴向压缩变形行为有很大影响 .压缩变形后纤维中的带状结构仍然存在 ,但带状结构内的分子链与纤维轴发生倾斜 ,随压缩变形程度增大 ,在有利剪切应力发展的方向形成褶皱变形带 ,最后导致纤维中所有带状结构破坏 .X光衍射实验结果表明 ,对于具有带状结构的PVA纤维 ,( 1 0 1 ) [0 1 0 ]晶面系的滑移对其压缩变形过程有重要影响 相似文献