单晶表面上水-气转移反应动力学及可逆吸附的作用—─Monte Carlo 模拟研究

用二元方格网络表示Ｃｕ（１１１）单晶表面上吸附活性位构型，建立了一个水－气转移反应的蒙特卡罗模型；对水－气转移反应的动力学进行了模拟，并研究了可逆吸附在表面反应中的重要作用．当水的解离吸附为反应的决速步骤时，模拟得到的ＣＯ和Ｈ２Ｏ的反应级数与Ｃａｍｐｂｅｌ等的单晶实验结果一致．模拟研究还表明，可逆吸附不仅可以抑制催化剂表面同种吸附物种ｃｌｕｓｔｅｒ的形成，而且可以不断提供新的吸附活性位，从而使表面反应稳定进行得以维持．     

稳态同位素瞬变动力学分析*

稳态同位素瞬变动力学分析是研究非均相催化反应动力学和反应机理的有效方法。由该技术既可定性获取有关反应机理方面的信息, 又可得到包括不同反应吸附中间物种的量、覆盖度、表面寿命, 基元反应的速率常数, 活性位的数量及其分布等定量的原位动力学信息。本文就SSITKA 实验装置、反应器的选择、动力学参数的求取、反应机理的推断以及SSITKA 与原位FTIR 的有机结合等方面进行了综述。     

活性白土对油脂溶液中β-胡萝卜素的吸附热力学及动力学研究

探讨了活性白土(AAB)对油脂溶液中β-胡萝卜素的吸附热力学及动力学特征,AAB对β-胡萝卜素的吸附行为可用Langmuir和Freundlich等温式进行描述,相关性均较好,在高温条件下(75～95℃),AAB对β-胡萝卜素的吸附更符合Freundlich模型的吸附行为.分别采用拟一级反应乖拟二级反应模型描述了吸附动力学数据,表明AAB吸附β-胡萝卜素适合于拟二级吸附动力学行为,且高温有利于提高吸附量和吸附速率.AAB对β-胡萝卜素的吸附表现活化能E_a为38.673kJ/mol,表明整个吸附过程涉及到化学吸附作用;通过对吸附热力学参数△H、△S及△G的分析,表明吸附过程是自发进行且伴随着吸热及熵值的增加,吸附趋势随着温度的升高而有所增大.     

SH15树脂吸附胞二磷胆碱的热力学及动力学研究

静态条件下,研究了SH15树脂吸附水溶液中胞二磷胆碱(CDPC)的热力学和动力学特性.测定了不同温度下,热力学性质的变化.实验结果表明,SH15树脂对CDPC吸附平衡数据符合Langmmuir吸附等温方程,吸附过程为自发的物理吸附过程.考察了温度、溶液浓度、树脂粒径和搅拌速率对吸附过程的影响.运用动边界模型(MBM)描述了SH15树脂吸附CDPC的动力学过程,确定在实验条件范围内,SH15树脂吸附CDPC的吸附速度受颗粒扩散控制,并计算出吸附过程的表观活化能为9.73kJ/mol,反应级数为0.47,速率常数为0.0744,并推导出CDPC:在SH15树脂上的动力学总方程.     

大港沥青对正戊烷溶剂中卟啉钒化合物的吸附动力学研究

利用静态实验,研究了在正戊烷溶剂中,大港沥青质对卟啉钒模型化合物的吸附动力学,并对吸附机理进行了探讨。通过对吸附卟啉钒化合物前后的大港沥青质进行FT-ICR MS和元素(C/H/N/O)分析,发现大港沥青质上吸附了一定量的卟啉钒化合物。沥青质对卟啉钒的吸附过程受到沥青质的加入量(0.010 0和0.020 0 g)、戊烷溶液中初始卟啉钒的浓度(10和15μg/mL)以及吸附温度(15、20和25℃)等因素的影响。分别采用拟一级、拟二级、Elovich和粒子内扩散等方程对实验数据进行了拟合,结果发现沥青质对卟啉钒的吸附符合拟二级动力学方程。     

大港沥青对正戊烷溶剂中卟啉钒化合物的吸附动力学研究

利用静态实验,研究了在正戊烷溶剂中,大港沥青质对卟啉钒模型化合物的吸附动力学,并对吸附机理进行了探讨。通过对吸附卟啉钒化合物前后的大港沥青质进行FT-ICR MS和元素（C/H/N/O）分析,发现大港沥青质上吸附了一定量的卟啉钒化合物。沥青质对卟啉钒的吸附过程受到沥青质的加入量（0.010 0和0.020 0 g）、戊烷溶液中初始卟啉钒的浓度（10和15 μg/mL）以及吸附温度（15、20和25 ℃）等因素的影响。分别采用拟一级、拟二级、Elovich和粒子内扩散等方程对实验数据进行了拟合,结果发现沥青质对卟啉钒的吸附符合拟二级动力学方程。     

偕胺肟合铁(Ⅲ)纤维对还原棕BR染料的吸附

采用部分偕胺肟化的聚丙烯腈纤维与铁离子反应,形成偕胺肟合铁(Ⅲ)纤维,以此为吸附材料,吸附水溶液中的还原棕染料. 研究了其吸附反应条件、吸附规律及吸附反应动力学. 结果表明,pH值11.5～12.5、温度60 ℃和吸附时间60 min为最佳吸附反应条件. 偕胺肟合铁(Ⅲ)纤维对还原棕的吸附反应符合Langmuir方程和Freundlich等温吸附经验式. 采用不同初始浓度研究吸附时间与溶液浓度的关系,用微分法确定了反应级数和反应速率常数. 由不同温度下的速率常数,并结合Arrhenius方程求出了反应的活化能. 结果表明,偕胺肟合铁(Ⅲ)纤维对还原棕的吸附符合一级反应动力学特征,速率方程c=c_0e~(-kt),速率常数k=32.01e~(-E_a/RT),活化能E_a=11.55 kJ/mol.     

疏水层析蛋白质动力学与平衡过程的考察

疏水层析是分离生物大分子的常用技术之一，但对疏水层析中蛋白质吸附动力学和平衡过程的研究并不多见．本文对蛋白质疏水吸附动力学和平衡过程作了基本假设，并用实验进行了验证。制备了两种不同丁基密度的疏水琼脂糖介质，用其吸附牛血清白蛋白(BSA)以验证对疏水吸附动力学与平衡过程作的假设，考察了盐浓度及配基密度对蛋白质疏水吸附的影响．还对三种疏水性不同的蛋白质：核糖核酸酶、卵清蛋白和牛血清白蛋白的混合体系进行了分离性能的研究，获得了满意的分离效果．实验表明，蛋白质在疏水介质上的吸附动力学和平衡过程与所作假设相符，在实验条件下等温吸附线符合Langmuir吸附等温方程：研制的丁基琼脂糖疏水介质具有优良的使用性能。     

新型离子交换树脂CG-6对人凝血酶原复合物的吸附行为分析及研究

根据人凝血酶原复合物(Prothrombin Complex Concentrate,以下简称PCC)的性质,对合成的大孔阴离子交换树脂进行静态吸附研究,并与已经商品化的DEAE Sephadex A50、Streamline DEAE凝胶型离子交换树脂进行比较,筛选出吸附性能较优的CG-6树脂.通过静态吸附实验,测定了CG-6对PCC在不同温度下的吸附等温线、考察了吸附过程中的动力学和热力学行为并初步探讨了吸附机理.结果表明,吸附动力学可用拟二级速率方程来描述,计算值与实测值吻合较好.CG-6对PCC的吸附等温线可分为两段,在较低的平衡浓度下,吸附平衡符合Langmuir方程,温度的升高有利于平衡吸附量的增大,表明该吸附反应为一吸热过程.求出反应的焓变△H=115.1kJ/mo1,熵变△S分别为2.37J/mol·K(5℃)、20.97 J/mol·K(15℃)、23.11J/mol·K(20℃)、37.32J/mol·K(30℃),吉布斯自由能变化△G分别为-0.54kJ/mol(5℃)、-5.93kJ/mol(15℃)、-6.66kJ/mol(20℃)、-11.20kJ/mol(30℃).此外,除了离子交换,CG-6对PCC也有物理吸附现象.     

柏树锯末对废水中罗丹明B的吸附性能研究

本文研究了柏树锯末对模拟印染废水中罗丹明B的吸附性能,考察了溶液的pH值、吸附时间、锯末用量及染料溶液的初始浓度等条件对吸附效果的影响。结果表明:染料在柏树锯末上的吸附等温线较好地符合Freundlich方程,吸附动力学可以用拟二级动力学模型描述。通过Langmuir方程在318K下计算得到其最大单层吸附容量为35.93 mg.g-1。     

Investigations of the chemical homogeneity of solids

Chemical homogeneity is a relative property of solid-state materials; it depends not only on their ultimate purposes, but also on the parameters of the analytical procedure applied in the investigation. These features are often given inadequate attention in the characterization of solid materials. A statistical model for representative sampling is used here as the starting point to derive relationships which demonstrate quantitatively the increasing rigour of the homogeneity test with increasing spatial resolution and precision of the analytical procedure. It is also shown that chemical homogeneity can be confirmed at a calculated risk, when the tests do not show the material to be significantly inhomogeneous and when maximum permissible deviations in concentration can be given for a practical application.     

EXAFS and time-resolved laser fluorescence spectroscopy (TRLFS) investigations of the structure of Cm(III)/Eu(III) complexed with di(chlorophenyl)dithiophosphinic acid and different synergistic agents

The complexes of trivalent actinide curium (Cm(III)) with di(chlorophenyl)dithiophosphinic acid ((ClPh)2PSSH) and three different neutral complexing agents as synergists in tert-butylbenzene are studied by EXAFS and time-resolved laser fluorescence spectroscopy (TRLFS). The results are compared with those from the corresponding europium (Eu(III)) complexes. The aim of these investigations is to understand the chemical interactions responsible for the high selectivity of the synergistic systems of (ClPh)2PSSH and neutral complexing agents tri-n-octylphosphine oxide, tributylphosphate and tris(2-ethylhexyl)phosphate for trivalent actinide cations in liquid-liquid extraction. In our structural chemistry study, we find that the inner coordination sphere of extracted Cm(III) and Eu(III) complexes are different. In all complexes the (ClPh)2PSSH is bound to the metal cation in a bidentate fashion and the oxygen donor of the neutral complexing agent used as synergist is directly coordinated to the metal cation. Comparison of the Cm(III) and Eu(III) complexes shows that Cm(III) preferentially binds to the sulfur of (ClPh)2PSSH, whereas Eu(III) is preferentially bound to oxygen. A good selectivity in liquid-liquid extraction is correlated with a high ratio of the sulfur coordination number to oxygen coordination number. This leads to the conclusion that the observed differences in the coordination structure between Cm(III) and Eu(III) complexes play an important role in the selectivity of these extraction systems.     

Parameter Estimation for the Constant Capacitance Surface Complexation Model: Analysis of Parameter Interdependencies

Results of extensive application of the 2-pK constant capacitance surface complexation model (CCM) to surface charge data of a range of minerals in 0.1Melectrolytes are summarized where the program FITEQL has simultaneously been used to study the interdependence of the involved optimized parameters.To illustrate representative results, surface complexation and goodness of fit parameters are given as a function of the capacitance value (C). For all (ca. 150) tested data sets, one of three patterns is observed, two of which do not allow a unique parameter set to be obtained.The results indicate that the optimized site density parameter is relatively insensitive to a wide variation ofC; optimized site density is rather low in this range of (higher)Cand tends toward maximum proton uptake in the respective data set which in turn will be close to sometimes experimentally observed saturation levels. At low and with further decreasingCa steep increase of site density may occur; in this case, ΔpK_astrongly increases after a ΔpK_aminimum. Alternatively at lowC, ΔpK_amay continue to decrease and site density decreases simultaneously after a site density maximum. The observed patterns can be explained by the constraint ofCon the electrostatic correction factor.Linear correlation coefficients (which are very useful parameters but do not receive much attention) show that in the region of lowC, the optimized parameters become fully correlated, which finally causes nonconvergence in parameter optimization. In the region where the optimized site density is not significantly affected by a decrease inCthe optimized parameters are more weakly correlated. When site concentration is co-optimized high correlation between adjustable parameters suggests that it is preferable to have an estimate for this parameter.Overall, it can be stated that substantial difficulties were observed in the effort to obtain unique (and thus meaningful) parameters for the CCM in about 60% of the data sets treated.     

Preparation of Well‐Defined Antibody–Drug Conjugates through Glycan Remodeling and Strain‐Promoted Azide–Alkyne Cycloadditions

Antibody–drug conjugates hold considerable promise as anticancer agents, however, producing them remains a challenge and there is a need for mild, broadly applicable, site‐specific conjugation methods that yield homogenous products. It was envisaged that enzymatic remodeling of the oligosaccharides of an antibody would enable the introduction of reactive groups that can be exploited for the site‐specific attachment of cytotoxic drugs. This is based on the observation that glycosyltransferases often tolerate chemical modifications in their sugar nucleotide substrates, thus allowing the installation of reactive functionalities. An azide was incorporated because this functional group is virtually absent in biological systems and can be reacted by strain‐promoted alkyne–azide cycloaddition. This method, which does not require genetic engineering, was used to produce an anti‐CD22 antibody modified with doxorubicin to selectively target and kill lymphoma cells.     

Polydispersity effects and the interpretation of polymer adsorption isotherms

In many cases, polymer adsorption is studied by measuring adsorption isotherms. Quite often it is found that the results are at variance with theoretical predictions. However, usually these adsorption isotherms are interpreted in terms of a single polymeric solute. Most polymers used in experimental studies are polydisperse and should be treated as mixtures. It is well established that the larger molecules in such mixtures adsorb preferentially over the smaller ones. In this paper we show that many discrepancies between polymer adsorption theory and experiment (e.g., the rounded shape of isotherms, the dependence of the adsorbance on adsorbent concentration, and the lack of desorption upon dilution) can be attributed to polydispersity. A quantitative analysis enables us to calculate isotherms for a polymer of arbitrary molecular weight distribution, provided the dependency of the plateau adsorbance on molecular weight is known. Experiments supporting the theory are reported. The fact that polymers do not desorb upon dilution with solvent is often regarded as a proof that polymer adsorption is irreversible. We show that, if a polydisperse sample is in equilibrium with an adsorbing surface, no detectable desorption may take place upon dilution. Therefore, the adsorption of polymers might well be reversible, even if desorption experiments would indicate apparent irreversibility.     

用计算机模拟技术研究潜影形成机理 Ⅲ.化学增感对潜影形成的作用

继前文的潜影形成模型,对化学增感乳剂进行了计算机模拟研究。结果如下:(1)硫增感引入大的浅陷阱,可增加敏度与改善低照互易律失效;其空穴陷阱的作用则不是很有效。(2)金增感除了减小可显影中心的尺寸和增加抗氧化能力外,还应有另外的增感机理。Ag₂经金强化可以部分地转化为可显影中心。(3)还原增感斑与尺寸相同的曝光产生的银斑性质相同,曝光时大部分还原增感斑被破坏掉了,只有极少数有机会长大。还原增感斑的两个重要作用:提高了形成潜影的概率;消耗空穴或光解溴,使颗粒中的净剩电子增多。二者对潜影形成都有重要贡献。     

Protonation of different goethite surfaces--Unified models for NaNO3 and NaCl media

Acid-base titration data for two goethites samples in sodium nitrate and sodium chloride media are discussed. The data are modeled based on various surface complexation models in the framework of the multi site complexation (MUSIC) model. Various assumptions with respect to the goethite morphology are considered in determining the site density of the surface functional groups. The results from the various model applications are not statistically significant in terms of goodness of fit. More importantly, various published assumptions with respect to the goethite morphology (i.e., the contributions of different crystal planes and their repercussions on the "overall" site densities of the various surface functional groups) do not significantly affect the final model parameters within simple 1-pK approximations. The simultaneous fit of the chloride and nitrate data results in electrolyte binding constants, which are applicable over a wide range of electrolyte concentrations including mixtures of chloride and nitrate. Model parameters for the goethite sample with 90 m2/g specific surface area are in excellent agreement with parameters that were independently obtained by another group on different goethite titration data sets.     

Model of phase distribution of hydrophobic organic chemicals in cyclodextrin–water–air–solid sorbent systems as a function of salinity,temperature, and the presence of multiple CDs

Environmental and other applications of cyclodextrins (CD) often require usage of high concentration aqueous solutions of derivatized CDs. In an effort to reduce the costs, these studies also typically use technical grades where the purity of the CD solution and the degree of substitution has not been reported. Further, this grade of CD often included high levels of salt and it is commonly applied in high salinity systems. The mathematical models for water and air partitioning coefficients of hydrophobic organic chemicals (HOC) with CDs that have been used in these studies under-estimate the level of HOC within CDs. This is because those models (1) do not take into account that high concentrations of CDs result in significantly lower levels of water in solution and (2) they do not account for the reduction in HOC aqueous solubility due to the presence of salt. Further, because they have poor knowledge of the CD molar concentration in their solutions, it is difficult to draw comparisons between studies. Herein is developed a mathematical model where cyclodextrin is treated as a separate phase whose relative volume is calculated from its apparent molar volume in solution and the CD concentration of the solution. The model also accounts for the affects of temperature and the presence of salt in solution through inclusion of modified versions of the Van’t Hoff and Setschenow equations. With these capabilities, additional equations have been developed for calculating HOC phase distribution in air–water–CD–solid sorbent systems for a single HOC and between water and CD for a system containing multiple HOCs as well as multiple types of cyclodextrin.     

The effect of cryogenic sample cooling on X-ray absorption spectra

It is common for samples to be cooled to near liquid He temperature (4 K) during measurement of their X-ray absorption spectra (XAS). This procedure is believed to improve spectrum quality either by minimizing radiation damage, or by decreasing thermal motions of atoms. The actual benefits realized by cooling are rarely assessed, since that would require duplicate measurements at multiple temperatures, followed by duplicate data analyses. With a cryostat installed, it is difficult to measure room temperature or hotter spectra, which often requires removing the cryostat from the beam path.Here we investigate the effect of cooling and show that it is not globally useful in X-ray absorption spectroscopy. Photolysis does not occur, or its consequences are not controlled by cooling. Secondary photochemical damage is delayed and is remote from the absorption site. Thermal motions do not usually contribute significantly to disorder and consequent damping of EXAFS, either because vibrational amplitudes are small, or because static disorder and structural complexity affect EXAFS in the same way but more profoundly.The low probability of photochemical effects on XAS is in contrast to the situation with crystallography of biological specimens, where photochemical damage anywhere in the sample degrades the data set regardless of proximity to atoms of one specific element. Thermal disorder becomes important in certain types of samples and when the Debye-Waller factor is itself used as a tool. In most cases, it is more efficient to first measure room temperature spectra, and then repeat measurement using a cryostat of only those spectra where the objectives of the analysis justify an attempt to gain more information.     

Correlations Between Amino Acids at Different Sites in Local Sequences of Protein Fragments with Given Structural Patterns

Ample evidence suggests that the local structures of peptide fragments in native proteins are to some extent encoded by their local sequences. Detecting such local correlations is important but it is still an open question what would be the most appropriate method. This is partly because conventional sequence analyses treat amino acid preferences at each site of a protein sequence independently, while it is often the inter-site interactions that bring about local sequence-structure correlations. Here a new scheme is introduced to capture the correlation between amino acid preferences at different sites for different local structure types. A library of nine-residue fragments is constructed, and the fragments are divided into clusters based on their local structures. For each local structure cluster or type, chi-square tests are used to identify correlated preferences of amino acid combinations at pairs of sites. A score function is constructed including both the single site amino acid preferences and the dual-site amino acid combination preferences, which can be used to identify whether a sequence fragment would have a strong tendency to form a particular local structure in native proteins. The results show that, given a local structure pattern, dual-site amino acid combinations contain different information from single site amino acid preferences. Representative examples show that many of the statistically identified correlations agree with previously-proposed heuristic rules about local sequence-structure correlations, or are consistent with physical-chemical interactions required to stabilize particular local structures. Results also show that such dual-site correlations in the score function significantly improves the Z-score matching a sequence fragment to its native local structure relative to nonnative local structures, and certain local structure types are highly predictable from the local sequence alone if inter-site correlations are considered.