明胶大分子的照相性质研究——Ⅰ.明胶中的蛋氨酸砜及亚砜的测定

应用氨基酸分析仪对十六种国外明胶(大部分为IAG明胶)的氨基酸含量进行了测定,其中重点进行了蛋氨酸及其氧化产物含量的测定。测试结果表明:明胶中蛋氨酸含量随不同样品变化较大,亚砜含量一般较少,所有照相胶都含有砜,绝大多数胶样含有亚砜。     

照相明胶与化学增感剂相互作用的XPS研究

本文采用X射线光电子能谱技术研究了两种照相明胶与化学增感剂相互作用的机理.当两种照相明胶样品在HAuCl₄溶液中反应5min后,明胶中的蛋氨酸、蛋氨酸亚砜均被氧化为蛋氨酸砜.与此同时,明胶吸附的大部分Au³⁺被还原为Au⁺,并且Au⁺以络合形态存在于明胶之中.根据与AuCl₃反应之后明胶中Au³⁺与Au⁺的比例,法国明胶的还原性略高于包头明胶.添加到明胶中的Na₂S₂O₃能将明胶大分子所含的蛋氨酸亚砜全部还原为蛋氨酸.S₂O₃^2-、蛋氨酸和蛋氨酸砜可以稳定共存于明胶体系之中,外加的S₂O₃^2-的还原性高于明胶中蛋氨酸、蛋氨酸亚砜的还原性.添加Na₂S₂O₃后的两种照相明胶均可以将其溶胀吸附的Au³⁺全部还原为胶态金.此时,参与氧化还原反应的主要基团是S₂O₃^2-而非明胶中的蛋氨酸残基.由于Na₂S₂O₃的添加,照相明胶对AuCl₃的还原能力增强.     

在照相明胶层中金催化的铜无电沉积

利用X射线光电子能谱的原位氩离子束溅射和ESCA技术，研究了无电沉积前后照相明胶中硫元素化学形态的变化，对无电沉积所形成的导电膜进行了深度剖析，探讨了照相明胶层中金催化的铜无电沉积机理．结果表明：在酸性条件下（pH＝3．20），明胶大分子的蛋氨酸亚砜对AU3 仍具有较大的还原能力，明胶大分子的蛋氨酸、蛋氨酸亚砜将Au3 最终还原为胶态金，而蛋氨酸和蛋氨酸亚砜均被氧化为蛋氨酸砜．在无电沉积初期，胶态金作为催化中心引发铜的无电沉积，之后的反应为Cu2 在新生态铜的自催化下的还原沉积．在无电沉积过程的碱性条件下（pH＝12．50），明胶中的部分蛋氨酸砜又被甲醛还原为蛋氨酸．     

蛋氨酸与化学增感剂的相互作用机理

运用X射线光电子能谱 (XPS)的ESCA扫描技术研究了蛋氨酸与不同化学增感剂相互作用及其中的硫、金、碳和氧等元素的化学形态和相对含量的变化规律 .发现蛋氨酸与不同的化学增感剂的反应机理是不尽相同的 .蛋氨酸与S增感剂不会发生任何化学反应 ,它们可以稳定地共存于同一体系之中 ;蛋氨酸可以将全部Au3+ 增感剂还原为Au ,其自身部分被氧化为蛋氨酸亚砜 ,并且在其脱质子的羟基部位与Au形成Au -O -C结构的金属配合物 .向蛋氨酸体系中加入S +Au增感剂后 ,体系中的氧化还原反应发生在外加的Au3+ 和S2 O32 - 之间 ,此时蛋氨酸的作用是将被S增感剂还原的Au络合 ,亦形成Au -O -C结构的配合物 .     

蛋氨酸亚砜/蛋氨酸亚砜还原酶荧光检测研究进展

蛋白质蛋氨酸亚砜化是一种重要的氧化还原依赖的蛋白质翻译后修饰,不仅是氧化应激的重要标志物之一,也是一种蛋白质功能调控开关可影响活性氧信号转导,与一系列疾病尤其是神经退行性疾病的发生发展密切相关。 在许多生物体中,蛋氨酸亚砜还原酶是目前已经发现的唯一能将蛋白质蛋氨酸亚砜还原为蛋氨酸的物质,可以修复氧化损伤蛋白,恢复蛋白质功能,调控细胞氧还平衡,对相关疾病的治疗具有非常重要的意义。 本文重点介绍蛋氨酸亚砜和蛋氨酸亚砜还原酶的结构和催化机理,综述蛋氨酸亚砜和蛋氨酸亚砜还原酶荧光探针的部分研究进展,对该领域的研究前景进行展望。     

明胶大分子的照相性质研究 Ⅱ.明胶中蛋氨酸及其氧化物对明胶还原性影响的研究

通过对明胶中Met及其氧化物含量及明胶还原性能进行的测定,考察了Met及其氧化物(砜及亚砜)对明胶还原性的影响.结果表明:在还原性与Met含量之间存在着正相关性,并首次证明在还原性与Metson之间存在着反相关性.     

氯化银T-颗粒乳剂制备专用的氧化明胶的研究

以往的研究表明:低蛋氨酸含量的明胶能制得晶体形态比较高的高氯T-颗粒乳剂.本文用氧化方法进一步降低明胶中的蛋氨酸含量.明胶经氧化剂(H₂O₂)氧化能得到不同的氧化明胶.用电位法测定氧化明胶的还原性;用氨基酸分析仪测定它们的蛋氨酸含量;用SDS-PAGE电泳法测定它们不同结构的组份含量.结果表明,还原性及蛋氨酸含量随氧化剂加入量的多少而变化;但氧化明胶的分子量分布与原胶相比变化甚小.     

照相明胶中铁的化学形态研究

利用凝胶层析-电热石墨管炉原子吸收光谱法对照相明胶中铁的化学形态进行了研究。发现明胶中的铁主要与蛋白结合为大分子,同时也有少量小分子量蛋白铁和游离铁。当向明胶样品申加入微量无机铁盐后,铁仍以游离态存在,未与蛋白结合,因而随着明胶中铁含量明显降低,外界铁的污染必须加以特别注意。在照相乳剂制备中必须同时考虑明胶中铁总量及其存在的化学形态。     

蛋氨酸亚砜还原酶的结构特征及与神经退行性疾病的关系

蛋氨酸易被氧化为蛋氨酸亚砜,使生物体中氧化还原平衡失调,诱发各种疾病.蛋氨酸亚砜还原酶(Msrs)能将蛋氨酸亚砜还原成蛋氨酸,恢复蛋白的结构与功能,对调控多种氧化应激相关疾病具有重要作用.本文结合本课题组的研究结果,介绍了Msrs的分类进化、结构特征、催化机理和基因工程表达;综述了Msrs与衰老、帕金森病和阿尔茨海默病的关系,以探讨有关Msrs研究的发展方向和应用前景.     

高效液相色谱-柱前衍生化法测定饲料中的含硫氨基酸

发展了一种饲料中含硫氨基酸的检测方法。样品经过甲酸氧化,将其中的胱氨酸和蛋氨酸分别氧化为磺基丙氨酸和蛋氨酸砜;再经酸水解后,采用2,4-二硝基氟苯进行柱前衍生化,衍生物经高效液相色谱分析。使用Elite AAK C18色谱柱(250 mm×4.6 mm, 5 μm)分离;以0.05 mol/L乙酸钠和乙腈-水(50:50, v/v)为流动相,梯度洗脱,流速为1.2 mL/min;检测波长为360 nm;柱温为31 ℃。结果表明,胱氨酸在0.4～16.0 mg/L、蛋氨酸在0.7～29.6 mg/L范围内的线性相关系数分别为0.9999、0.9998;胱氨酸和蛋氨酸的定量限(信噪比(S/N)=10)分别为2.6 μg/kg和3.1 μg/kg;3次样品平行测定的胱氨酸和蛋氨酸含量的相对标准偏差(RSD)分别为0.79%和2.56%,加标回收率分别为100.28%～102.00%和105.72%～107.89%。该方法分析成本低,测定结果准确,灵敏度高,符合饲料中含硫氨基酸的检测要求。     

明胶大分子的还原性与抽提的关系

用不同抽提次序的一系列明胶样品,用电位法测定了它们的还原性,用氨基酸分析仪测定了蛋氟酸(Met)、蛋氨酸亚砜(Metsox)和砜(Metson)的含量,用SDS-PAGE电泳法测定了它们的不同构象组份的相对含量。发现:明胶的还原性随抽提次序的增加出现一极大值,而这个极大值与α₁,α₁+α₂和α₁/α₂的比值互呈正并行性的对应关系。仔细考察和对比α₁和α₂的一级构型表明:α₁比α₂含有较多的Met。这个极大值的出现,是与第2道抽提出来的明胶中含有较多的α₁组份(从而较多的Met)有关。     

Spin-mixing and the different spin states of ferric ion in tetragonal symmetry

We have used the wave functions generated from a strong crystal field model of ferric ion in complexes of tetragonal symmetry with spin-orbit coupling, to calculate the behavior of several localized properties of the ferric ion in parameter regions of different ground and low-lying ferric ion states. In the previous paper of this series we have shown with this model that ferric ion can exist in a doublet, sextet, quartet and substantially spin-mixed ground state. We have delineated such regions and described the changing nature of the wave functions. In the present study, we calculate the effective magnetic moments and their temperature dependence, the first order magnetic field energies, and the electric field gradients of ferric ion in these various spin states. Particular emphasis is placed on the properties of ferric ion in substantially spin-mixed states which have hitherto not been reported. Wherever possible, our results are compared with existing experimental data. In particular, with this model, we have been able to quantitatively account for the continuously varying values of magnetic moment for a series of 12 ferric hemoglobin derivatives, in the region from range of 5.92 to 2.26 Bohr magnetons.     

Doped gelatin films as a model matrix for molecular secondary ion mass spectrometry studies of biological soft tissue

Porcine gelatin films doped with a number of biological compounds at various concentrations and prepared by spin-casting have been used as model biological tissue matrices for studying organic ion emission in molecular secondary ion mass spectrometry. For many compounds, portions of the working curves were found to be linear over several orders of magnitude in concentration. Detection limits for the, analyzed compounds were in the parts per million range for several organic salt compounds but high (0.1 wt%) for others. Owing to the presence of a significant chemical background, the poorest detection limits were generally obtained from compounds with low molecular weights. Secondary ion yield matrix effects, indicated by a reduction in ionization efficiency at higher concentrations, were observed for several organic salt compounds.     

A comparative DFT study of Fe3+ and Fe2+ ions adsorption on (100) and (110) surfaces of pyrite: An electrochemical point of view

Pyrite acts as a catalyst in the mineral processing, and the speed of ferric ion reduction and mineral decomposition increases with increasing cathodic points. In this study, the ferric ion interaction on the (100) and (110) surfaces of pyrite was studied using the density functional theory calculations. The analysis of stability, density of states, and electron density were performed to understand the interaction between the ferric ion and pyrite surfaces. The results showed that pyrite surface is chemically active and tends to absorb ferric ion between two surface sulfur atoms. The hyperconjugation between the 3d orbital of ferric ion and the 3p or 3d orbitals of surface atoms provides the conditions for the Fe³⁺ ion adsorption. The molecular orbital (MO) and electron density analyses indicate that the 3p orbitals of S atoms play a more important role in bonds formations relative to the 3d orbitals. The (110) surface is more active, and the adsorption energy is larger than that of surface (100), which is the result of decreased cation coordination and the presence of sulfur at the surface. Subsequently, the interaction of the Fe²⁺ ion, as product of Fe³⁺ ion reduction and its competitor for adsorption, on the surfaces was studied. The Fe^{2 +} ion adsorbs stronger at the surface of (110), and the adsorption energies at (100) and (110) surfaces were obtained as −24 and −47 kcal/mol, respectively. In general, the Fe³⁺ ion is a stronger oxidizing agent than Fe²⁺ on pyrite surfaces.     

Eu2+掺杂硼酸盐系列发光晶体化学键参数的计算

利用复杂晶体化学键理论对Eu^2 掺杂的硼酸盐晶体Ba2LiB5O10,Ba2MgB2O6,Ba2Be2B2O6,BaLiBO3,SrB4O7和SrAl2B2O7的化学键参数进行了理论计算，结果表明，在不同的晶体中掺杂离子与配位原子间形成的共价键的键性是不同的，这种差异的产生是由于成键原子的性质、配位数以及键长的不同而造成的。     

Treatment of humic acids with ferric, aluminum, and chromium ions in water

The interaction of ferric, aluminum, and chromium ions with humic acids at different pH of mixture has been investigated. The concentration of metal ions, bound with humic acid is proportional to the concentration of metal ion in water solution at pH 3 at low metal ion concentrations. The ratio of the number of ferric ions, bound with humic acid, to the number of acidic groups in humic acid is more than 1.5 at high ferric ion concentration in solution. That is bound with the formation of dimers of ferric ions and their treatment with acidic groups of humic acid. The radius of particles formed in the reaction of humic acid with ferric ion does not depend on the pH and decreases in the reaction with chromium and aluminum ions at pH higher than 4. An increase of metal ion concentration leads to the increase of the particle radius at low metal ion concentration reaching the constant value at high metal ion concentration and pH 6.1.     

Comparison of thioethers and sulfoxides as axial ligands for N-acetylmicroperoxidase-8: implications for oxidation of methionine-80 in cytochrome c

Methionine-80 (Met-80) in mitochondrial cytochrome c (cyt c) can be oxidized to the corresponding sulfoxide by reactive oxygen species, a reaction of potential biological significance. As an approach to investigating how oxidation of Met-80 would influence its interactions with heme iron, we have examined binding of 2-(methylthio)ethanol (MTE) and dimethyl sulfoxide (DMSO), models for the side chains of Met and Met(SO), respectively, to ferrous and ferric N-acetylmicroperoxidase-8 (AcMP8). We find that DMSO coordinates 1.2 kcal/mol less strongly to Fe(III)-AcMP8 than does MTE, although both ligands form low-spin complexes. Comparison of spectroscopic data for the DMSO complex of Fe(III)-AcMP8 with published data for the Met(SO)-80 form of ferric cyt c allows us to conclude that Met(SO)-80 does not coordinate to iron in the latter. DMSO coordinates to Fe(II)-AcMP8 1.3 kcal/mol more strongly than does MTE, whereas Met-80 and Met(SO)-80 are reported to have approximately equal affinity for Fe(II) in cyt c. This result suggests that the steric environment near the heme iron in cyt c discriminates against coordination of Met(SO)-80. Vacuum quantum chemical density functional theory calculations confirm the greater affinity of the sulfoxide and show that coordination via oxygen is strongly favored. Resonance Raman spectroscopic data indicate that the preference for coordination via oxygen is maintained in solution. The computational data further indicate that the DMSO complex derives significant enthalpic stabilization from pi back-bonding but that iron to sulfur pi back-bonding does not make a significant contribution to bonding in the thioether complex.