蛋白质分子量测定过程中的酸效应

在基质辅助激光解吸电离飞行时间质谱（MALDI-TOF-MS）和电喷雾质谱（ESI-MS）测定蛋白质分子分子量的过程中,适当提高样品的酸度,可提高分析测试的灵敏度。在选定最佳样品分子浓度的基础上,通过适当加入三氟乙酸（TFA）来调整测试样品的酸度,准确测定了标准蛋白质-溶菌酶（lysozyme）的分子量,并且对蛋白质分子在“软电离”质谱中,受酸效应的影响进行了初步探讨。     

粘度法测高分子化合物相对分子质量实验结果讨论

作为物理化学基础实验之一 ,粘度法是测定高分子化合物相对分子质量的一种简单易行的方法 ,其准确度能够满足许多情况下的要求。但在此实验中会遇到诸多对实验结果产生影响的因素 ,现在就我在用粘度法测定聚乙烯醇相对分子质量的实验中遇到的一些情况做一简单分析。1　实验过程　　实验中所用仪器有三管粘度计 ,停表及恒温槽装置一套 ;试剂为聚乙烯醇水溶液。实验过程如下[1] 。　　①于 30 .0 0± 0 .0 5℃的条件下恒温待测液和蒸馏水。　　②向粘度计中加入 1 0ｍＬ聚乙烯醇水溶液 ,质量浓度为 5.50 0 ｇ/Ｌ ,测定溶液自粘度计的中间管上…     

Relationship between Intrinsic Viscosity and Molecular Weight for Fractionated Cellulose

A relationship between intrinsic viscosity and molecular weight for fractionated cellulose is established. The exponent a of the Mark-Houwink equation is 0.80. The unperturbed dimensions of cellulose are discussed on the basis of the Stockmayer-Fixman and Kurata-Stockmayer viscometric theories, and it is determined that cellulose is not a very rigid macromolecule in nature. This conclusion disagrees with the results obtained by statistical mechanics procedures in which the restriction of β-glucose residues to the C1 conformation was kept. The steric hindrance factor, σ is about 2, and it seems to be independent of the substituents in cellulose if it is evaluated in both cellulose and cellulose derivatives from viscometric data. From statistical mechanics data reported in the literature, σ is estimated as 4.4 for cellulose and cellulose derivatives, such as cellulose nitrate, and this means that the steric hindrances of the substituents have little influence on the rigidity of cellulose derivatives. This view disagrees with the results obtained from the non-Newtonian behavior of cellulose and cellulose nitrate in dilute solutions. By applying the Noda-Hearst theory, the conclusion is reached that cellulose nitrate is a more extended macromolecule than cellulose.     

Determination of Polymer Molecular Weight by GPC in the Low Molecular Weight Region

Abstract

In order to determine the molecular weight of a polymer by GPC in the low MW region, a secondary calibration method can be established when polymer standards of the analysed polymer are not available (1). The efficiency of this method has been checked for the system poly(methyl methacrylate) (PMMA-methyl ethyl ketone (MEK) using polystyrene (PS) standards. When the solvent is poor for one of the polymers, limitations arise due to the secondary separation effects. Furthermore, a GPC method is proposed for the determination of the Dondos-Benoīt constants (A₁ A₂) which must be known for the above-mentioned calibration. This method uses either two or at least one polydisperse polymer sample.     

甲基丙烯酸三丁基锡酯与甲基丙烯酸甲酯共聚物的分子量测定和K、α值的订定

甲基丙烯酸三丁基锡酯与甲基丙烯酸甲酯共聚物的分子量测定和K、α值的订定     

凝胶色谱法测定顺丁橡胶平均分子量及其分布的研究

通过一系列的条件试验,包括样品浓度、样品量及流动相流速对柱效的影响,确定了最佳的凝胶色谱（ＧＰＣ）试验条件;采用普适校正法将聚苯乙烯（ＰＳ）标定曲线转换成顺丁橡胶（ＰＢ）标定曲线,并对Ｍａｒｋ－Ｈｏｕｗｉｎｋ方程式中Ｋ,α值的选择进行了讨论;采用４种分子量加宽方程对色谱柱加宽效应进行改正计算,通过比较,选定适合本试验系统的加宽效应的改正方法;用粘度法测得的顺丁橡胶特性粘度（η）吻合ＧＰＣ所测得特性粘度值,证明了方法的可靠性。     

Determination of Molecular Weight of PDPS Modified Copolymers

Molecular weight (MW) determinations of polydiphenylsiloxane‐co‐polydimethylsiloxane (PDPS/PDMS), polydiphenylsiloxane‐co‐polymethylphenylsiloxane (PDPS/PMPS) and polydiphenylsiloxane‐co‐polymethyl(3,3,3‐trifluoropropyl)siloxane (PDPS/PMFPS) statistical copolymers by gel permeation chromatography (GPC), GPC coupled differential viscometer (GPC‐DV) and light scattering (LS) techniques have been compared and discussed. The MW obtained by GPC‐DV in the PDPS/PDMS and the PDPS/PMPS series agreed with that obtained by LS very well. In PDPS/PDMS copolymers, it was found that the MW obtained by GPC was much lower than that obtained by GPC‐DV and LS, as Ph₂SiO) content is higher than 50 mol%. In PDPS/PMFPS copolymers, the MW obtained by GPC was far different from that obtained by GPC‐DV and the deviation decreased with increasing Ph₂SiO) mol%. The α values of the copolymers can be explained by the structure of the polymer in tetrahydrofuran (THF). Based on the relatively soluble copolymers, not only the differential refractive index increments (dn/dc) of PMPS, PDMS and PMFPS homopolymers but also that of the PDPS homopolymer in THF could be calculated by their corresponding copolymers.     

用MALDI-TOF-MS法快速测定天花粉蛋白分子量

采用ＭＡＬＤＩ－ＴＯＦ－ＭＳ法快速测定了天花粉蛋白的分子量,并讨论和对比了三种不同基质对其影响,认为用基质芥子酸是最佳适宜条件。实验结果表明本方法优于其它传统的测定生物大分子分子量方法。     

The Effect of Trifluoroacetic Acid on Molecular Weight Determination of Polyesters:An in Situ NMR Investigation

Due to the poor solubility of aromatic polyesters in common organic solvents,trifluoroacetic acid is usually used as a co-solvent to increase their solubility for characterizations.However,only few studies have reported the side reactions induced by it.We present here the application of in situ 1H-NMR techniques to explore its effect on the hydroxyl end-groups,which are usually used for the molecular weight determination of polyesters by end-group estimation method.Using bis(2-hydroxyethyl) terephthalate (BHET) as model compound,1H quantitative NMR results show the peak integration of hydroxyethyl end-groups decreased with time via a pseudo-first-order kinetics in d-trifluoroacetic acid/d-chloroform mixture solvent (1∶10,V∶V).This is due to the esterification of hydroxyethyl groups with trifluoroacetic acid,revealed by the 1H-13C gradient-enhanced heteronuclear multiple bond correlation (gHMBC) spectrum.The mixtures of dimethyl terephthalate and BHET with different molar ratios were used to represent poly(ethylene terephthalate) (PET) with different degrees of polymerization,and the effect of trifluoroacetic acid on the estimation of hydroxyethyl groups and subsequent molecular weight determination of polyesters was studied.Our results show that if a relative error of 5％ is allowed,the NMR measurements must be finished within 1.3 h of solution preparation at 25 ℃ in the mixture solvent.The results were confirmed in PET sample,while in poly(ethylene adipate),the obtained esterifaction constant is faster that those in aromatic system.The results can be applied to other polymer systems with alcohol functionalized groups,and used as a guideline for the characterization of polyesters and polyethers by end-group estimation method.     

超高效凝胶色谱法测定聚乙二醇衍生物的分子量及其分布

采用超高效聚合物色谱(APC)技术,以单甲氧基聚乙二醇丙醛(m PEG_p ALD)为代表,测定了聚乙二醇衍生物的相对分子质量及其分布和杂质含量,优选了色谱柱和流动相,考察了样品质量浓度变化以及溶解时间等对测定结果的影响。优化后3根超高效凝胶色谱柱串联,在柱温40℃,流动相95%甲醇,流速0.5m L/min,示差折光检测条件下,对m PEG_p ALD的分子量及其分布进行测定,同时得到杂质的相对含量。结果测得m PEG_p ALD主成分的重均分子量(Mw)为19 444,分布指数(D)为1.01;杂质1的Mw为38 703,D为1.01,含量为1.31%;杂质2的Mw为61 036,D为1.00,含量为0.70%。与常规凝胶渗透色谱(GPC)相比,该方法分辨率高,分析速度快,能快速测定m PEG_p ALD的相对分子量及其分布,并能得到其纯度和杂质含量,为其工艺研发、质量控制提供了科学的依据,同时也可用于其它PEG衍生物的相对分子量及其分布和纯度的测定。     

聚甲基丙烯酸己磺酸钠特性粘数与数均分子量关系

前文已报导了具有较好抗凝血性能的新型聚电解质,聚甲基丙烯酸己磺酸钠(PSSH-MA)的合成,用统计方法对盐存在时PSSHMA溶液的粘性研究及用小角激光光散射法测定的PSSHMA体系的特性粘数和重均分子量的关系。本文进一步用KNAUER膜渗透计测定了该体系的特性粘数与数均分子量的关系^[6],并进一步探讨聚电解质水溶液渗透压测定中的一些问题。     

一种简便渗透压法测定高聚物分子量

本工作采用一种改进的一膜两室渗透计和简便动态渗透压法测定了一系列聚合物的数均分子量,该法操作方便、快速、可靠,测定分子量相对误差在±5％以内。     

超高分子量聚苯乙烯的性能测定

聚苯乙烯(PS)制成高定向薄膜后可用于电视机、雷达、高频率电线等电器部件和发泡材料。其主要缺点是耐冲击强度低、耐温性差。大量的改性工作主要是通过混炼或共聚等方法制成非均聚物,其结果透明性不佳,而且生产工艺复杂、成本高。聚苯乙烯改性的另一个途径是提高其分子量,使_w达到4.0×10~5以上,形成超高分子量聚苯乙烯(UHMW PS)。     

基质辅助激光解析飞行时间质谱快速测定水解胶原蛋白粉分子量

应用基质辅助激光解析电离飞行时间质谱(MALDI-TOF-MS)快速测定了水解胶原蛋白粉的分子量.分别以α-氰基-4-羟基内桂酸、2,5-二羟基苯甲酸和芥子酸为基质,在正离子模式下对水解胶原蛋白粉分子质量分布进行测定.结果显示:芥子酸为最适宜基质,分析条件为线性方式和反射方式相结合,可准确、快速确定水解胶原蛋白粉的分子...     

从GPC和特性粘数计算高聚物各种平均相对分子质量的新方法

聚合物相对分子质量表征问题可以从ＧＰＣ数据和特性粘数较可靠地迅速解决，同时求出其烽均、粘均、重均，动力学平均相对分子质量及相对分子质量－特性粘数关联参数。为些须对以往方法作较大的改进，其关键是用迭代法进行特性粘数与相对分子质量的关联。方法经用聚甲基丙烯酸甲酯验证后用于聚碳酸亚乙酯（ＰＥＣ）和聚碳酸亚丙酯（ＰＰＣ）分别得到关系式。     

高分子量的聚L-谷氨酸的合成与表征

采用三乙胺为催化剂经过氨基酸羧酸酐单体的开环聚合和脱保护基, 制备了高分子量聚L-谷氨酸. 实验结果表明, 合成的高分子量聚L-谷氨酸黏均分子量控制在70 000~350 000左右. 单体和引发剂的摩尔比n(A)/n(I)大于50时, 分子量与n(A)/n(I)无关.     

Validation of an Analytical Method for the Simultaneous Determination of Hyaluronic Acid Concentration and Molecular Weight by Size-Exclusion Chromatography

The hyaluronic acid (HA) global market growth can be attributed to its use in medical, cosmetic, and pharmaceutical applications; thus, it is important to have validated, analytical methods to ensure confidence and security of its use (and to save time and resources). In this work, a size-exclusion chromatography method (HPLC-SEC) was validated to determine the concentration and molecular distribution of HA simultaneously. Analytical curves were developed for concentration and molecular weight in the ranges of 100–1000 mg/L and 0.011–2.200 MDa, respectively. The HPLC-SEC method showed repeatability and reproducibility greater than 98% and limits of detection and quantification of 12 and 42 mg/L, respectively, and was successfully applied to the analysis of HA from a bacterial culture, as well as cosmetic, and pharmaceutical products.     

Determination of Functionality and Molecular Weight Distribution by Orthogonal Chromatography

Abstract

During polymerization oligomers, telechelics and macromers with different endgroups are formed as a result of various mechanisms (starting, termination, cyclization. transfer reactions).

The characterization of the resulting products is possible by using orthogonal chromatography. In order to characterize 1,3,6-trioxocane polymers, synthesized in presence of benzyl alcohol, Liquid Adsorption Chromatography (LAC) under “critical conditions” is combined with Size-Exclusion Chromatography (SEC). This method includes a preparative chromatographic separation of the product which is followed by SEC and LAC under “critical conditions” and vice versa. Results advantages and problems of this type of orthogonal chromatography are discussed.     

Determination of Ascorbic Acid by Molecular Spectroscopic Techniques

The determination of ascorbic acid by spectrophotometry, chemiluminescence and fluorescence techniques, sorption–spectroscopy, and visual-test methods is considered. Data on the reagents in use, analytical ranges, detection limits, and interfering substances are presented. Special attention is focused on solid-phase reagents for the spectroscopic and rapid visual-test determination of ascorbic acid in various samples. The bibliography includes 65 references.