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1.
碳酸钙结晶对胃蛋白酶二级结构的影响   总被引:1,自引:0,他引:1  
本文通过傅里叶变换红外光谱及退卷积、曲线拟合等技术研究了碳酸钙结晶对胃蛋白酶二级结构的影响 ,结果表明 :在纯的胃蛋白酶中 ,α 螺旋、 β 折叠、转角及无规卷曲等四种结构的含量分别为2 4 38% ,2 9 91% ,39 2 2 % ,6 4 9% ;而在CaCO3 胃蛋白酶溶液中 ,四种结构的含量分别为 2 0 9% ,93 30 4 % ,4 6 0 %和 0 0 0 6 %。由此可以看出 :碳酸钙晶体的形成使胃蛋白酶的α 螺旋结构减少 ,β 折叠结构增多 ,本文讨论了这种变化的本质。  相似文献   

2.
用低温高分辨FTIR研究了EG系列乙烯-辛烯共聚物,通过对亚甲基rocking band的表征。结果表明,在支链不进入晶格的情况下,主链上支链的引入仍能引起晶格结构的变化,这种变化表现在正交晶格内分子链的距离的变化,二面角的变化和结晶规整程度的变化,并且发现不同的结晶过程对晶格的变化有不同的影响。  相似文献   

3.
Two different types of calcium fluoride (CaF2) particles were incorporated into a poly(ethylene terephthalate) (PET) matrix, fine particles (~350 nm), and nanoparticles (~70 nm). Both of them were synthesized by a chemical precipitation method using triethanolamine (TEA) as stabilizer. To obtain the nanoparticles, a greater amount of TEA was added during the synthesis in order to limit their growth. Therefore, unlike the fine particles, nanoparticles contained a greater amount of the stabilizer. Once CaF2 particles were obtained, the composite materials were prepared by melt-blending PET and particles at different filler loadings. The influence of both kinds of particles on the non-isothermal crystallization behavior of PET was investigated by using differential scanning calorimetry and field emission scanning electron microscopy. The Jeziorny-modified Avrami equation was applied to describe the kinetics of the non-isothermal crystallization, and several parameters were analyzed (half-crystallization time, Avrami exponent, and rate constant). According to the results, it is clear that CaF2 particles act as nucleating agents, accelerating the crystallization rate of PET. However, the effect on the crystallization rate was more noticeable with the addition of the fine particles where the surface plays an important role for epitaxial crystallization, while the addition of the nanoparticles with an organic surface coating resulted in a crystallization behavior similar to the observed for PET.  相似文献   

4.
徐君  邓风 《波谱学杂志》2007,24(3):368-370
介绍了一些常规固体核磁共振的技术的发展状况, 并综述了固体核磁共振在多孔材料中的应用情况, 其中包括沸石分子筛酸性和结构表征以及目前在分子筛合成机理研究中的应用进展. 本文的主要内容是利用固体核磁共振结合其它表征技术研究了一类介孔固体酸催化材料的酸性以及两种微孔磷铝分子筛的合成晶化过程.  利用有机聚合物为模板剂合成出两种介孔复合氧化物MoOx/ZrO2与WOx/ZrO2固体酸材料. 并对其进行了物理化学性质的表征. 研究发现它们在较高的焙烧温度下仍保持有较高的比表面积及规整的孔径. 利用固体核磁共振技术及DFT计算的方法发现在介孔WOx/ZrO2及MoOx/ZrO2表面存在两种类型的Br[AKo¨D]nsted酸位, 其酸强度强于传统的HZSM-5分子筛, 与典型的固体强酸硫酸锆相当, 但弱于100%的硫酸. 借助于理论计算清楚地揭示了酸性位的具体结构和酸强度信息, 且计算结果与实验结果符合得非常好. 除了弱酸性的Zr-OH基团外, 在介孔氧化锆表面存在大量的Lewis酸位(配位不饱和的Zr4+). 在引入Mo或W物种后, Mo-OH或W-OH与不饱和的Zr4+配位产生作为Br[AKo¨D]nsted酸位的桥式Mo-OH-Zr(或W-OH-Zr)羟基, 并且导致氧化锆表面Lewis酸位的大量减少. 利用理论计算证实了单聚或多聚体形式的桥式Mo-OH-Zr(或W-OH-Zr)羟基是强Br[AKo¨D]nsted酸性位产生的根源, 同时提出了酸性位形成的机理. 利用水热晶化法合成了AlPO4-5和MgAPO-36两种具有重要工业潜在应用价值的分子筛材料并用固体核磁共振技术结合X射线衍射、傅里叶红外、高分辨电子显微镜等技术研究了它们的详细晶化过程. 研究发现在HF存在条件下加热120 min后具有AFI类型的骨架晶化开始. 此时31P NMR谱中在δ -22与 δ -29处出现两个来源于骨架P-O-Al单元的信号, 19F NMR谱中在 δ -120处出现来源于骨架F-Alpen-O-P单元的信号, 证实了晶体骨架开始形成. 另外, 凝胶中五配位Al(F-Alpen-O-P)的出现是分子筛晶化开始的另一个标志. 利用27Al→31P HETCOR、 31P{27Al} TRAPDOR及1H→31P CP/MAS等双共振实验详细研究了初始凝胶相及晶化开始时凝胶相的结构, 在120 min加热凝胶中区分出具有不同化学环境的配位P原子, 提出了详细的晶化过程机理.  对于另一种具有高活性的镁取代的MgAPO-36分子筛催化材料, XRD发现在第二阶段423 K时, 加热1.5 h后骨架晶化开始. 31P NMR证实此时凝胶相中形成了P-O-Al及Mg-O-P骨架单元, 此后(2 h)凝胶相中出现半晶相的棒状颗粒. 并最终晶化为不规则球状的MgAPO 36晶体(18 h后). 利用27Al→31P HETCOR及1H→31P CP/MAS分析了中间凝胶相的微观结构并利用31P{27Al} TRAPDOR NMR技术研究骨架晶化开始时凝胶相中P(nAl) (n=1~4)的配位结构, 得出了5种具有不同配位状态的微观化学环境, 提出了详细的晶化过程机理.  相似文献   

5.
6.
Poly(m-aminophenol) was synthesized chemically from aqueous solutions of the monomer meta-aminophenol (mAP) in the initially acidic or basic medium by using ammonium persulfate as an oxidant. The polymer (PmAPA) synthesized in initially aqueous HCl medium was insoluble in organic solvents even after dedoping, while the polymer (PmAPB) synthesized in initially aqueous NaOH solution was found to be soluble in high pH water, dimethyl sulfoxide (DMSO), and dimethylformamide. It was possible to obtain a stable, free-standing film from the DMSO solution of PmAPB but, due to insolubility and infusibility, film casting was not possible for PmAPA. The synthesized polymers were characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analyses, X-ray diffraction spectroscopy, and four-probe DC electrical conductivity. A ladder-type structure was formed during the chemical polymerization of mAP in aqueous HCl, while a hydroxyl derivative of polyaniline was obtained in aqueous NaOH. The conductivity of sulfuric acid-doped PmAPB was 104 times higher than that of in situ HCl-doped PmAPA. An explanation of the difference in properties of both polymers is given based on molecular modeling.  相似文献   

7.
In the present study, we investigated the influences of polymerization and crosslinking technologies on the branched-chain structures, crystallization behaviors, and gel networks of two types of low-density polyethylenes, LDPE1 and LDPE2, polymerized under different polymerization conditions in commercial large-capacity production lines. High temperature 13C NMR analysis suggests that the molar contents of both long-chain branches and short-chain branches of LDPE2 were markedly higher than those of LDPE1 due to a higher polymerization temperature for LDPE2. The high content of chain branches of LDPE2 leads to its relatively higher storage modulus, entanglement density, and gel content, as indicated by dynamic mechanical analysis. In addition, when the crosslinking temperature reached 180°C, the LDPE2 crosslinked with 2 wt% dicumylperoxide (XLPE2-D2) displayed a relatively wider processing time window and a faster crosslinking rate than XLPE1-D2. Successive self-nucleation and annealing fractionation indicated that increasing the concentration of dicumylperoxide can improve the crosslinking degree, but resulted in lower crystallinity and thinner lamellar crystals.  相似文献   

8.
实验通过使用YBF-2型热导率测定仪测量不同厚度橡胶盘的热导率,并采用控制变量法,从而探究橡胶盘厚度对固体热导率测量的影响,发现橡胶盘越厚,热导率测量值的误差越大。所以在做固体热导率的实验时橡胶盘的厚度越薄越好。  相似文献   

9.
For styrene-butadiene rubber (SBR) compounds filled with the same volume fraction of carbon black (CB), precipitated silica and carbon–silica dual phase filler (CSDPF), filler-rubber interactions were investigated thru bound rubber content (BRC) of the compounds and solid-state 1H low-field nuclear magnetic resonance (NMR) spectroscopy. The results indicated that the BRC of the compound was highly related to the amount of surface area for interaction between filler and rubber, while the solid-state 1H low-field NMR spectroscopy was an effective method to evaluate the intensity of filler-rubber interaction. The silica-filled compound showed the highest BRC, whereas the CB-filled compound had the strongest filler-rubber interfacial interaction, verified by NMR transverse relaxation. The strain sweep measurements of the compounds were conducted thru a rubber process analyzer; the results showed that the CSDPF-filled compound presented the lowest Payne effect, which is mainly related to the weakened filler network structure in polymer matrix. The temperature sweep measurement, tested by dynamic mechanical thermal analysis, indicated that the glass transition temperature did not change when SBR was filled with different fillers, whereas the storage modulus in rubbery state and the tanδ peak height were greatly affected by the filler network structure of composites.  相似文献   

10.
羟基磷灰石结晶对牛血清白蛋白二级结构影响的光谱研究   总被引:2,自引:1,他引:1  
通过圆二色谱(CD)及傅里叶变换红外光谱及退卷积、曲线拟合等技术研究了羟基磷灰石结晶对牛血清白蛋白二级结构的影响。CD谱结果表明,在纯的牛血清白蛋白中,α-螺旋、β-折叠、β-转角及无规则卷曲等4种结构的含量分别为56.8%, 5.8%, 14.1%, 23.9%;而在羟基磷灰石/牛血清白蛋白溶液中,4种结构的含量分别为25.4%, 25.0%, 20.0%和29.7%, 红外光谱结果与其一致。由此可以看出, 晶体的形成使牛血清白蛋白的α-螺旋结构含量减少,β-折叠结构含量增多,且随着反应时间的进行α-螺旋结构减少越来越明显,β-折叠结构增加越来越多,表明在溶液中部分α-螺旋结构转变为β-折叠结构。文章对这种变化的本质进行了初步探讨。  相似文献   

11.
Poly(lactic acid) (PLA)/talc composites containing different contents of talc were prepared by melt blending. Multiple properties of the prepared composites were investigated including mechanical, rheological and crystallization as well as foaming properties. Tensile test results indicated that the mechanical properties of the composite with 3% wt. talc showed significant reinforcement and toughening effect. When the talc content reached 10%, Young's modulus of the composite was increased by 35% compared with pure PLA. The morphological results showed that the talc layers were partially delaminated and uniformly dispersed in the PLA matrix at low loading. Differential scanning calorimetry (DSC) and polarized optical microscopy (POM) results indicated that 3% wt. talc significantly increased the crystallinity of the PLA matrix. The thermogravimetric analysis (TGA) results demonstrated that the thermal stability of PLA/talc composites was enhanced as well. Moreover, talc at low loading could act as a plasticizer in the polymer flow, which was investigated by rheological tests. The batch foaming experiments revealed that 3% wt. talc loading had the most notable heterogeneous nucleation effect, with the cell size decreasing from 15.4 μm for neat PLA to 8.5 μm and the cell density increasing by 298%.  相似文献   

12.
Among the many material performance properties of vulcanized elastomers for tire tread application, rolling resistance and wet traction are particularly important since both greatly impact fuel efficiency and traction of a vehicle. Rolling resistance and wet traction are generally negatively correlated, i.e., with the increase in rolling resistance of a tire, its wet traction decreases. Silica nanofillers are often used for achieving the desired balance of wet traction and rolling resistance. However, the high cost of silica limits its wide spread application. In this research we studied the effects of using fillers with different aspect ratios (calculated by dividing the long dimension of a filler by its short dimension) on the performance of vulcanized styrene butadiene rubber (SBR), a common rubber for tire tread application. Three high aspect ratio fillers were used: aragonite calcium carbonate, wollastonite and carbon nanofiber. For comparison purpose, spherical silica filler was also included. We found that the high aspect ratio fillers were efficient in improving the wet traction and rolling resistance as well as enhancing the mechanical energy dissipation of SBR. Among the three high aspect ratio fillers studied, wollastonite provided the best wet traction and rolling resistance balance due to its high aspect ratio and compatibility with the base rubber. The effects of fillers induced crosslinking on the dynamic performance were also discussed.  相似文献   

13.
Spray characteristics and their spatial distribution have been investigated experimentally for sprays generated by the breakup of thin liquid sheets in co‐flowing air streams. The spray characteristics such as droplet mean and fluctuation velocity and Sauter mean diameter have been measured by using phase Doppler anemometry under various liquid and air flow conditions at the nozzle exit. The results show that at a given spray cross section the droplet axial mean velocity has a maximum value at the spray center, and decreases towards the edge of the spray; whereas the Sauter mean diameter has a minimum value at the center and increases monotonically towards the spray periphery. Data analysis indicates that sufficiently downstream of the nozzle exit the droplet mean velocity attains a jet‐like self‐similar distribution in the transverse direction, and such universal distribution is also observed for the turbulent fluctuation velocity and turbulent intensity, although it is achieved further downstream compared to the mean velocity profile. The Sauter mean diameter at the spray center has a complex variation in the downstream direction due to secondary atomization at high air velocity near the nozzle exit and droplet entrainment, migration and possible coalescence farther downstream.  相似文献   

14.
In this paper, interfacial structure induced development of crystallization behavior of polypropylene (PP)/polyolefin elastomer (POE)/barium sulfate (BaSO4) ternary composites was studied by DSC. Two kinds of PP (copolymer and homopolymer) were used. The compatibility between PP and POE had a distinct influence on nucleation and crystal growth of PP in PP/POE binary composites. The crystallization rate of PP homopolymer increased because of the heterogeneous nucleation by POE, while the crystallinity of PP homopolymer decreased because of an inhibition effect of the hexane side chains in POE. BaSO4 particles acted as heterogeneous nucleating agents of PP in ternary composites. The dispersion of BaSO4, controlled by interfacial design, had a distinct influence on the nucleation activity of BaSO4 in ternary composites. Interfacial structure had the same effect on nucleation activity of BaSO4 particles and crystallization rate of PP matrix in PP copolymer ternary composites as those in PP homopolymer ternary composites.  相似文献   

15.
Polystyrene (PS)/organoclay nanocomposites were prepared via free radical suspension polymerization. Two kinds of organoclay were used, labeled KT and KD, modified by trimethyloctadecyl ammonium (TM) and dimethyldioctadecyl ammonium (DM) ions, respectively. Nanocomposites containing various amounts of both of the organoclay nanoparticles (1, 3, and 5 wt%) were prepared. The wide angle X-ray diffraction (WAXD) results revealed intercalation in both of the nanocomposites. The greatest improvement in thermal stability of the nanocomposites was achieved with 5 wt% of organo-MMT for both of the clays. The nanocomposite containing 3 wt% of KT organo-MMT showed the greatest improvement of storage modulus. When the organoclay content exceeded 3 wt%, the storage moduli decreased compared to the nanocomposite filled with 3 wt% of the organoclay. D-spacing calculations using Bragg's law and WAXD data showed that the KT and KD nanoparticles were intercalated within the PS matrix, but with different extents of intercalation. The styrene conversions of the as-polymerized nanocomposite samples were obtained by a gravimetric method. The results showed that conversion decreased with incorporation of organoclay in the reaction recipe. Particle size was also increased by increasing nanoclay content.  相似文献   

16.
聚3-羟基丁酸酯(PHB)是微生物细胞在其生长的特定时期在胞内合成的具有相应生物功能的聚羟基烷酸酯类物质, 是一种具有潜在的广泛应用前景的生物可降解的高分子材料. 由于天然的PHB其较高的结晶度和较窄的温度处理范围,它在应用过程中受到较大的局限性. 人们将结构相似的单体3-羟基戊酸(HV)与3-羟基丁酸(HB)共聚形成共聚物(PHBV)以后, 显著改善了PHB的物理机械性能,譬如:冲击强度和韧性有所增加,而硬度脆性有一定程度的下降. 人们虽然在这些降解高分子材料的开发、制备和物理机械性能以及这些材料的应用等方面有很多研究,但是有关分子水平的问题并未得到系统的探索. 因此,针对这些分子基础问题(结构域特征和分子动力学等)做了一些初步的研究.  全氟磺酸树脂(Nafion)是杜邦公司生产的一种燃料电池电极薄膜材料,其较低的使用温度(<100℃)严重地限制了它的应用范围. 人们发现,当把层状硅酸盐(蒙脱土)和Nafion合成为有机无机纳米复合材料之后,在一定程度上提高了它的使用温度. 虽然这种复合材料很容易合成出来并且已经运用到了实际工业应用之中,但是这种热稳定性提高的原因却不甚清楚. 通过固体NMR等分析方法从微观相互作用方面来认识这种宏观性能改善的原因.  使用固体13C CP MAS、13C SPE MAS NMR以及XRD方法测定了PHB和两种PHBV的结晶度(Xc),发现随着HV的引入它们的Xc 逐渐减小. 研究同时发现在测量Xc 的这几种方法中13C SPE MAS NMR误差较小. 实验中我们利用质子弛豫诱导谱编辑(PRISE)、质子自旋扩散(Spin-diffusion)等固体NMR技术研究了PHB以及不同含量HV的PHBV的结构域特征和相应结构域的运动性. 实验结果表明随着HV含量的增加,它们的非晶相结构域尺寸增大,晶相结构域尺寸减小,可以看出HV的引入导致PHB的结构域特征的变化是其宏观性能改善的原因.  进一步通过低分辨固体NMR测量了PHB和PHBV的变温质子弛豫时间(T1, T, T2), 然后通过理论拟合获得了它们不同运动状态的分子运动相关频率(τc)和分子活化能(Ea)等动力学信息,研究发现随着HV含量的增加,分子运动加快,活化能减小,在分子水平上认识了HV的引入使得PHB宏观性能改善的微观原因.  通过溶胶凝胶法合成了燃料电池电极薄膜(Nafion)和层状硅酸盐(蒙脱土)纳米复合材料来提高Nafion的使用温度,FT-IR和29Si MAS NMR实验结果表明在杂化材料中虽然质子化的十二烷基胺修饰的蒙脱土(MMT)的引入没有导致MMT的骨架结构发生明显变化,而且Nafion也没有插入到MMT的层间,但是TGA分析表明杂化材料中的Nafion的热稳定性比纯的Nafion高. 通过一系列固体NMR技术包括19F MAS、1H-13C CP MAS NMR和1H-13C HETCOR 2D NMR实验初步证实了这种材料的热稳定性的提高可能是由于MMT表面吸附的NH+3与Nafion侧链上的SO-3之间存在较强的静电相互作用,初步可以认为这种相互作用是导致电极材料性能改善的原因.  相似文献   

17.
The sequential structure, isothermal crystallization, tensile property, and degradation behavior of poly(ethylene terephthalate-co-ethylene oxide-co-lactide) (ETOLA) copolyester based on melt transesterification of poly(ethylene terephthalate) with poly(ethylene oxide) and oligo(lactic acid) was investigated. The degree of randomness was calculated to be 0.38, showing the incorporation of poly(ethylene oxide) (PEO) blocks into the homogeneous sequences of ethylene terephthalate (ET) and lactide (LA) units. The isothermal crystallization kinetics results revealed that the crystallization activation energy of the copolyester calculated using the Arrhenius’ equation was lower than that reported for poly(ethylene terephthalate) (PET), indicating that the addition of PEO and LA units into PET retarded the crystallization of PET. The copolyester exhibited the same crystal structure at different crystallization temperatures, similar to that of PET homopolymer, based on wide angle X-ray diffraction results. The size of the spherulites of ETOLA increased with crystallization temperature. The increase of crystallization temperature reduced the elongation at break of the copolyesters, as well as the enzymatic degradation.  相似文献   

18.
The effect of planar interfaces on nucleation (namely, on the work of critical cluster formation and their shape) is studied both for crystallization and melting. Advancing an approach formulated about 150 years ago by J. W. Gibbs for liquid phase formation at planar liquid–liquid interfaces, we show that nucleation of liquids in the crystal at crystal–vapor planar interfaces proceeds as a rule with a much higher rate compared to nucleation in the bulk of the crystal. Provided the surface tensions crystal–liquid (σcl), liquid–vapor (σlv), and crystal–vapor (σcv) obey the condition σcv=σcl+σlv, the work of critical cluster formation tends to zero; in the range σcv<σcl+σlv, it is less than one half of the work of critical cluster formation for bulk nucleation. The existence of a liquid–vapor planar interface modifies the work of critical cluster formation in crystal nucleation in liquids to a much less significant degree. The work of critical crystal cluster formation is larger than one half of the bulk value of the work of critical cluster formation, reaching this limit at σcv=σcl+σlv. The shape of the critical clusters can be described in both cases by spherical caps with a radius, R, and a width parameter, h. This parameter, h, is the distance from the cutting plane (coinciding with the crystal–vapor and liquid–vapor planar interface, respectively) to the top of the spherical cap. It varies for nucleation of a liquid in a crystal in the range (h/R)1 and for crystal nucleation in a liquid in the range 2(h/R)1. At σcv=σcl+σlv, the ratio (h/R) of the critical cluster for nucleation in melting tends to zero ((h/R)0). At the same condition, the critical crystallite has the shape of a sphere located tangentially to the liquid–vapor interface inside the liquid ((h/R)2). We present experimental data which confirm the results of the theoretical analysis, and potential further developments of the theoretical approach developed here are anticipated.  相似文献   

19.
The reversible thermal behavior of a non-entangled semicrystalline polymer, poly(dimethylsiloxane), PDMS, was investigated in the presence of sub-micron particles. Filled polymer systems of this type are characterized by a large surface-to-volume ratio but lack the external confinement that is typical for a thin film geometry. Differential-scanning calorimetry (DSC) measurements indicate that the presence of the nanometric solid additives enhances the crystallization rate as compared to native PDMS melts. Different types of additives and surface interactions resulted in a similar effect, suggesting that the origin of the enhanced crystallinity is non-specific. The effect is attributed to entropic interactions in the boundary layer.  相似文献   

20.
PTT/EPDM-g-MA (80/20 w/w) nanocomposites were prepared by melt mixing of poly(trimethylene terephthalate) (PTT), ethylene-propylene-diene copolymer grafted with maleic anhydride (EPDM-g-MA), and organoclay. The blend nanocomposites show typical sea-island morphologies. The nonisothermal crystallization kinetics of pure PTT and 80/20 (w/w) PTT/EPDM-g-MA blends with various amounts of the clay were extensively studied by differential scanning calorimetry (DSC). The Avrami, Ozawa, and Mo methods were used to describe the nonisothermal crystallization process of pure PTT and 80/20 (w/w) PTT/EPDM-g-MA blends with various amounts of the clay. Avrami analysis results show that the crystallization rates of 80/20 (w/w) PTT/EPDM-g-MA blends with the clay were faster than those of pure PTT or PTT/EPDM-g-MA blends without clay, which indicates that the clay particles promote crystallization effectively, in agreement with the Mo analysis results. Ozawa analysis can describe the nonisothermal crystallization of pure PTT very well but was rather inapplicable to the 80/20 (w/w) PTT/EPDM-g-MA blends with various amounts of the clay.  相似文献   

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