共查询到18条相似文献,搜索用时 187 毫秒
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利用差示扫描量热法(DSC)研究了溶菌酶在不同浓度的添加剂(蔗糖、葡萄糖、果糖、甘露醇)和不同浓度的磷酸盐缓冲液影响下的热变性过程,并用等转化率法对该过程进行了分析.变性温度Tm随扫描速率和添加剂浓度的增加而提高,随磷酸盐缓冲液浓度的增加而降低.磷酸盐加速了溶菌酶的变性过程,降低了溶菌酶的热稳定性,而添加剂则增强了溶菌酶的热稳定性.在添加剂存在的条件下,溶菌酶变性过程部分为聚集不可逆过程,部分则可逆.等转化率法表明溶菌酶在所有条件下,其表观活化能在不同的转化率下并未保持不变,而是随转化率增大而减小,说明了一个简单的反应机理并不能用来描述溶菌酶的变性过程,其过程并不是标准两态可逆过程,而是一个涉及多种蛋白质状态的复杂过程. 相似文献
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用差示扫描量热计对低水含量蛋白质热变性的研究——“热变性前新峰”的证实 总被引:1,自引:0,他引:1
本文继发现水合牛血清白蛋白存在低温区吸热峰之后,迸一步测定了11个厂家生产的7种高纯低水含量蛋白质的DSC加热扫描曲线.证实在热变性峰之前的低温区无一例外都有一个明显可辨的小吸热峰,我们将它命名为“热变性前新峰”(Pre-thermodenaturation new peak).结果表明“热变性前新峰”的出现是低水含量蛋白质的共性.对新峰规律和机制的研究将有助于人们深入理解蛋白质的变性过程、肽链折叠途径、分子的缔合、解缔合及其溶剂效应。 相似文献
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用差示扫描量热法及热台显微镜法研究了Schiff碱类向列液晶PEBAB及PBAPB的熔融与清亮过程.给出PEBAB的Tm=378.53K,△Hm=26.48±0.20kJ/mol,△Sm=69.96±0.53J/K.mol,Tc=399.80K,△Hc=929±53J/mol,△Sc=2.32±0.13J/K.mol;对于PBAPB,Tm(II)=352.86K,Tm(I)=354.74K,Tc=384.54K,△Hc=866±25J/mol,△Sc=2.25±0.07J/K.mol.在通过二次加热法消除熔前效应后,得到△Hm(I+II)=12.36±0.17kJ/mol,它不随升温速率改变而变化.本工作测得的清亮焓,在3%的偏差范围内符合平均场理论要求;△H1/△H2=T1/T2;所得清亮熵也与大多数向列型液晶相近.在PBAPB中,在318K左右,还观察到固→固相变等情况,相变焓是13.96±0.35kJ/mol. 相似文献
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本文采用差示扫描量热法(DSC),研究了水合醛缩酶在含水量h从0.08g/g至2.28g/g范围内的热变性行为。实验结果表明,当h=0.08g/g时,水合醛缩酶样品的温度扫描热谱图呈现了两个吸热峰,其中低温峰很小,高温峰很大。随着h的增大,低温峰变得更小,高温峰则出现了分峰现象。当h=0.22g/g时,低温峰消失,高温峰则分裂成了两个独立的吸热峰。随着h的继续增大,其中前峰的位置不断移向低温,直至h_0.65g/g时,才不再变化。后峰的位置则始终保持不变。当再进行第二次温度扫描时,前峰消失,而后峰却能再现。本文给出了两峰在不同含水量时的转变温度、转变焓和转变焓之和,以及它们与含水量的关系。最后,对上述诸峰的起因作了分析讨论,认为低温峰可能起因于水合醛缩酶结晶的熔化作用,前峰和后峰可能起因于醛缩酶中两种A亚基的热变性。 相似文献
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N-烷基壳聚糖玻璃化转变温度的研究 总被引:1,自引:0,他引:1
采用差示扫描量热(DSC)法和热释电流(TSC)法研究了N-烷基壳聚糖的玻璃化转变行为. DSC法中采用二次扫描以消除溶剂和热历史的影响, 并利用物理老化方法来增强N-烷基壳聚糖在DSC曲线上的玻璃化转变区域的热焓吸热峰, 以克服DSC法的不灵敏性. 两种研究方法的结果一致表明, 三种N-烷基壳聚糖的玻璃化转变均发生在110~150 ℃温区内;取代的柔性烷基越大, 玻璃化转变温度(Tg)越低;但N-甲基壳聚糖例外, 其Tg略高于壳聚糖, 空间阻碍在这里起决定的作用. 相似文献
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采用粘度法确定了聚4-乙烯基吡啶(P4VP)在乙醇/水混合溶剂中的临界交迭浓度c*, 分别在稀溶液与亚浓溶液浓度范围内, 采用光谱法与电导滴定法研究了P4VP与Cu(II)离子的配合过程及配合物的结构, 通过红外光谱(FTIR)对配合物的化学结构进行了表征, 并用差示扫描量热法(DSC)测定了配合物的热性能. 结果表明, 对于相对分子质量为1.06×105的P4VP, 其c*为15 mmol8226;L8722;1(按P4VP中的链节量计算). 在稀溶液中P4VP与Cu(II)离子形成可溶性的分子内配合物, 表观配位数为9~10;在亚浓溶液中, P4VP与Cu(II)离子发生分子间配合作用, 由于配位交联, 形成不溶性的配合物P4VP-Cu(II), 配位数为3. P4VP与Cu(II)离子形成配合物后, 玻璃化温度明显提高. 相似文献
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调制差示扫描量热法研究玻璃化转变温度 总被引:3,自引:0,他引:3
对比了DSC与MDSC试验技术的差别, 列举了MDSC的优点,MDSC不但可以给出普通DSC的所有信息,而且给出更多的普通DSC无法提供的信息。MDSC特别适合于复杂转变、弱的转变分析,可以寻找出隐藏在熔融及结晶过程中的玻璃化转变。MDSC对于试验条件的选择比较苛刻,在选择好基本的试验参数的前提下,还需要设置调制周期、调制振幅等参数。 相似文献
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Anna Michnik Katarzyna Michalik Zofia Drzazga 《Journal of Thermal Analysis and Calorimetry》2005,80(2):399-406
Summary The effect of pH on the thermal denaturation of BSA containing fatty acids was studied by use of differential scanning calorimetry (DSC). Thermal scanning of BSA aqueous solutions gave various types of DSC curves depending on the protein concentration and on the pH. The broad bimodal endothermic transition was suggested to be connected with loose protein structure in contradistinction to single peak for compact molecule structure. The propensity toward precipitation at pH conditions ranging from 3.8 to 5 was observed. A scan-rate independent and partly reversible behavior of the thermal heating of BSA was found. Deconvolution of DSC traces in non-two-state model with assumption of two- or three-component transition allowed to study the effect of pH on different parts of BSA molecule. 相似文献
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Phase transitions of polycrystalline [Fe(H2O)6](ClO4)3 and [Cr(H2O)6](ClO4)3 studied by DSC 总被引:1,自引:0,他引:1
Mikuli E. Grad B. Zaremba K. Wróbel S. 《Journal of Thermal Analysis and Calorimetry》2004,76(3):719-726
The effects of heat treatment on soymilk protein denaturation were studied by differential scanning calorimetry (DSC) and
electrophoresis. Transition behavior of soymilk was studied by DSC. Three endotherms were found in DSC heating curves; the
transition observed at around 70°C is attributed to the denaturation of 7S (b-conglycinin) and the transition at around 90°C
is to 11S (glycinin). The denaturation temperature increased with the increasing soymilk protein content. The change of electrophoretic
patterns after heat treatments indicated that soy proteins were dissociated into subunits, some of which coalesced. When the
heating temperature is below their denaturation temperature, the protein fractions cannot completely be denatured even after
heat exposure for extended periods of time.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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Lammert A. M. Lammert R. M. Schmidt S. J. 《Journal of Thermal Analysis and Calorimetry》1999,55(3):949-975
The physical aging characteristics of maltose glasses aged at two temperatures below the glass transition temperature, Tg, (Tg-10°C and Tg-20°C) from 5 to 10 000 min were measured by standard differential scanning calorimetry (SDSC) and modulated differential
scanning calorimetry (MDSC). The experimentally measured instrumental Tg, the calculated Tg, and the excess enthalpy values were obtained for aged glasses using both DSC methods. The development of excess enthalpy
as a function of aging time, as measured by both SDSC and MDSC, was fit using the Cowie and Ferguson and Tool-Narayanswamy-Moynihan
models. The change in the Tg values and the development of the excess enthalpy resulting from physical aging measured by the two DSC methods are discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Li-Fen Wang 《European Polymer Journal》2005,41(2):293-301
Differential scanning calorimetry (DSC) and temperature modulated DSC (MDSC) have been applied to investigate the thermal behaviors of fluorinated polyurethanes (FPU), which were obtained using 2,2,3,3-tetrafluoro-1, 4-butanediol as the chain extender and based on various soft segments—polytetramethyl oxides (PTMO) with molecular weights of 650, 1000, 1400 and 2000. An exothermic peak and/or multiple melting endotherms were observed during the heating to melting temperature of soft and hard segments. Attributed to the simultaneous recrystallization and melting processes during heating, these features have been confirmed via MDSC, where an endotherm and an exotherm were noted in reversing and non-reversing components of the heat flow. Separating the non-reversing components from the reversing curves, the dependencies of polyurethane morphology on the length of the soft segment could be clarified using MDSC analysis. Soft segment lengthening significantly influences the morphology of soft segment domains in FPUs. The phase separation and crystallinity of the soft segment increased with its length. However, soft segment length exerted a minor influence on the dissociation temperature of the short-range ordered hard segment domain and on the melting temperature of hard segment crystals. Examination of the heats of melting based on the quasi-isothermal MDSC experiments indicated that the crystallinity of hard segment domains declined with increasing soft segment length. 相似文献
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Zumailan A. Denis G. Dargent E. Saiter J. M. Grenet J. 《Journal of Thermal Analysis and Calorimetry》2002,68(1):5-13
PET films uniaxially drawn in hot water are studied by means of conventional DSC and modulated DSC (MDSC).Glass transition
is studied by MDSC which allows to access the glass transition temperature T
g and the variations of ΔC
p=C
p1−C
pg (difference between thermal capacity in the liquid-like and glassy states at T=T
g). Variations of T
g with the water content (which act as plasticizer) and with the drawing (which rigidifies the amorphous phase) are discussed
with regard to the structure engaged in these materials. The increments of ΔC
p at T
g are also interpreted using a three phases model and the 'strong-fragile’ glass former liquid concept. We show that the ‘fragility’
of the medium increases due to the conjugated effects of deformation and water sorption as soon as a strain induced crystalline
phase is obtained. Then, ‘fragility’ decreases drastically with the occurring rigid amorphous phase.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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Karger-Kocsis J. Shang P. P. Moskala E. J. 《Journal of Thermal Analysis and Calorimetry》1999,55(1):21-28
The tensile loading-induced necking in notched specimens of an amorphous copolyester (aCOP) was studied by modulated differential
scanning calorimetry (MDSC). It was shown that necking occurred by cold drawing since the enthalpy of cold crystallization
and that of the subsequent melting agreed fairly with each other. Increasing deformation in the necking zone and increasing
deformation rate of the specimens shifted the onset of cold crystallization toward lower temperatures and yielded a slightly
higher glass transition temperature (Tg). This was attributed to the molecular orientation caused by mechanical loading. The finding that the melting contained a
non-reversing part was considered as appearance of possible microcrystallinity. The Tg range was strongly influenced by the deformation rate and reflects the thermomechanical history of the samples accordingly.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献