温控近红外光谱用于胺类化合物氢键相互作用研究

氢键对于蛋白质等生物分子的结构与功能具有重要影响.基于近红外光谱对含氢基团的高灵敏响应及其温度效应,研究了脂肪胺中氮氢基团的结构及相互作用.采用独立成分分析对不同温度、不同浓度样品的光谱进行分析,得到光谱中的三种独立成分,分别对应于氮氢基团的非氢键键合、线型氢键键合和环状氢键键合三种结构形式.随着温度的升高,两种键合形式的氮氢基团逐步转化为非氢键键合形式.环状键合的氮氢基团先解离为线型键合形式,再解离为非氢键键合形式.随着脂肪伯胺侧链的增长,NH基团的光谱吸收受温度影响减弱,且线型键合形式受温度的影响较环状键合形式小.     

碱性二苯基萘基甲烷染料褪色分光光度法测定藻酸钠

在B-R缓冲溶液中,藻酸钠与维多利亚蓝4R、维多利亚蓝B、夜蓝等碱性二苯基萘基甲烷染料发生反应,形成结合产物,染料发生明显的褪色.对于不同染料,最大褪色波长分别位于612 nm(维多利亚蓝4R体系)、616 nm(维多利亚蓝B体系)、614 nm(夜蓝体系).体系吸光度的降低与藻酸钠的质量浓度成正比.藻酸钠的质量浓度在5.0 mg·L-1(维多利亚蓝4R体系)、3.0 mg·L-1(维多利亚蓝B体系)、3.0 mg·L-1(夜蓝体系)以内符合比耳定律,摩尔吸光率根据染料的不同在4.8×106～9.5×106 L·mol-1·cm-1之间,其中以维多利亚蓝4R体系最为灵敏,对藻酸钠的检出限为21 μg·L-1.以维多利亚蓝4R体系为例研究共存物质的影响,表明方法选择性好.此法用于面条样品中藻酸钠的分析测定,结果满意.     

绿色木霉纤维素酶分子侧链构象与侧链环境特征的研究

运用拉曼光谱分析技术能够揭示蛋白质分子基团振动特征,本文对绿色木霉(Triclwderrna viride)纤维素酶中的CBH Ⅱ在固态以及两种pH值的液态中酶分子的侧链构象与侧链环境状态进行了拉曼分析。结果揭示了CBHⅡ中胱氮酸的CαCβ-S-S’-Cα'Cβ'基团和C-S键,蛋氮酸(甲硫氮酸)的CαCβ-Cr-SC基团,HCβ-CγS基团和C-S键,以及半胱氮酸的HCβ-CγS基团和C-S键的构象特征。实验还证明14个色氮酸是部分暴露的,C2-C3-Cβ-Cβ侧链的扭转角[x^2.1]形式多样。在pH6．0和固体样品中,酶蛋白中酪氮酸均为强氢键供体,两种样品各有20．3％、25．1％是暴露于溶剂的。而pH8．0水溶液中酪氮酸酚羟基成键能力特点是既可做氢键供体,又可做氢键受体,它们有80％是暴露于溶剂的。     

高效液相色谱法测定椰油酰基谷氨酸钠中的月桂酰基谷氨酸含量

建立了高效液相色谱法(HPLC)测定表面活性剂椰油酰基谷氨酸及其钠盐中月桂酰基谷氨酸含量以及不同碳链酰基谷氨酸相对含量的分析方法。采用甲醇作溶剂,涡旋混合器溶解样品,经Agilent TC-C_(18)(250 mm×4.6 mm×5μm)色谱柱分离,以乙腈-0.002 mol/L硫酸水溶液为流动相,梯度洗脱,用紫外检测器在203 nm处检测。该方法的线性范围为0.050~2.0 mg/m L,检出限(S/N=3)为0.015 mg/m L,回收率为92.0%~101%。方法快速、准确、重现性好,可用于不同质量椰油酰基谷氨酸及其盐的测定,为此类原料的质量控制提供了有效的技术参考。     

取代基对N—H…O＝C氢键三聚体中氢键强度的影响

使用MP2方法研究了氢键三聚体中N-H…O=C氢键强度,探讨了氢键受体分子中不同取代基对N-H…O=C氢键强度的影响.研究表明,不同取代基对氢键三聚体中N-H…O=C氢键强度的影响是不同的:取代基为供电子基团,氢键键长r(H…O)缩短,氢键强度增强;取代基为吸电子基团,氢键键长r(H…O)伸长,氢键强度减弱.自然键轨道(NBO)分析表明,N-H…O=C氢键强度越强,氢键中氢原子的正电荷越多,氧原子的负电荷越多,质子供体和受体分子间的电荷转移越多.供电子基团使N-H…O=C氢键中氧原子的孤对电子n(O)对N-H的反键轨道σ~*(N-H)的二阶相互作用稳定化能增加,吸电子基团使这种二阶相互作用稳定化能减小.取代基对与其相近的N-H…O=C氢键影响更大.     

取代基对1-甲基尿嘧啶与N-甲基乙酰胺氢键复合物中氢键强度的影响

使用密度泛函理论B3LYP方法和二阶微扰理论MP2方法对由1-甲基尿嘧啶与N-甲基乙酰胺所形成的氢键复合物中的氢键强度进行了理论研究, 探讨了不同取代基取代氢键受体分子1-甲基尿嘧啶中的氢原子对氢键强度的影响和氢键的协同性. 研究表明: 供电子取代基使N－H…O＝C氢键键长r(H…O)缩短, 氢键强度增强; 吸电子取代基使N－H…O＝C氢键键长r(H…O)伸长, 氢键强度减弱. 自然键轨道(NBO)分析表明: 供电子基团使参与形成氢键的氢原子的正电荷增加, 使氧原子的负电荷增加, 使质子供体和受体分子间的电荷转移量增多; 吸电子基团则相反. 供电子基团使N－H…O＝C氢键中氧原子的孤对电子轨道n(O)对N－H的反键轨道σ^*(N－H)的二阶相互作用稳定化能增强, 吸电子基团使这种二阶相互作用稳定化能减弱. 取代基对与其相近的N－H…O＝C氢键影响更大.     

聚(L-谷氨酸)水凝胶的Diels-Alder制备及其生物分子响应性研究

报道了一种含有二硫键的聚L-氨基酸共价交联网络,制备了能对含巯基生物分子与蛋白酶产生响应的新型聚L-氨基酸水凝胶.通过二硫键将降冰片烯基团键合在聚(L-谷氨酸)侧链,所得到的聚合物与末端修饰四嗪基团的四臂聚乙二醇在水溶液中混合,通过降冰片烯与四嗪基团之间发生Diels-Alder反应形成分子间共价交联,获得了聚(L-谷氨酸)/聚乙二醇水凝胶.研究了水凝胶在含巯基生物活性分子谷胱甘肽(GSH)作用下的性质变化.结果表明,2种官能化聚合物混合后可快速形成稳定的水凝胶,其力学性质随聚合物浓度、2种聚合物比例和降冰片烯基团的取代度的改变而变化.体外降解实验结果表明,在GSH或弹性蛋白酶存在的条件下,水凝胶的降解速率显著增加.同时,经GSH处理的水凝胶机械强度也显著降低.大鼠体内实验表明,在交联点引入GSH响应性的二硫键会明显加速聚氨基酸水凝胶的体内降解.进一步体外细胞实验与组织学分析结果表明,所获得聚氨基酸/聚乙二醇水凝胶具有良好的体外细胞相容性和动物体内组织相容性.     

取代基对N-H…O=C氢键三聚体中氢键强度的影响

使用MP2方法研究了氢键三聚体中N—H…O=C氢键强度, 探讨了氢键受体分子中不同取代基对N—H…O=C氢键强度的影响. 研究表明, 不同取代基对氢键三聚体中N—H…O=C氢键强度的影响是不同的: 取代基为供电子基团, 氢键键长r(H…O)缩短, 氢键强度增强; 取代基为吸电子基团, 氢键键长r(H…O)伸长, 氢键强度减弱. 自然键轨道(NBO)分析表明, N—H…O=C氢键强度越强, 氢键中氢原子的正电荷越多, 氧原子的负电荷越多, 质子供体和受体分子间的电荷转移越多. 供电子基团使N—H…O=C氢键中氧原子的孤对电子n(O)对N—H的反键轨道滓*(N—H)的二阶相互作用稳定化能增加, 吸电子基团使这种二阶相互作用稳定化能减小. 取代基对与其相近的N—H…O=C氢键影响更大.     

苯砜基羧酸酯类急性毒性的QSAR研究

采用密度泛函理论方法, 在B3LYP/6-31G(d)理论水平下, 计算了56种苯砜基羧酸酯类化合物的量子化学参数. 计算结果表明, 酯基连接的烷烃链亲水性越小, 毒性越大; 苯环连接的取代基亲水性越大, 毒性越大; 分子的体积越大, 毒性越小; 分子产生氢键的能力越大, 毒性越小; 分子最高占据轨道能量越高, 毒性越大.     

以磁纳米粒为核的pH敏感型聚谷氨酸树状分子药物载体

报道了一种新的肽类树枝状分子改性磁性纳米药物载体.以天然氨基酸L-谷氨酸为原料,通过收敛法合成了聚(L-谷氨酸)树状分子,将多巴胺配体键合到聚(L-谷氨酸)树状分子上,用核磁(1H-NMR)、质谱(MS)对合成出的树状分子配体进行了表征,然后通过配体交换对四氧化三铁磁纳米粒表面进行多功能化.以阿霉素为模型药物通过pH敏...     

Crystallization Control by Additives: Molecular Recognition. Application to the Determination Of L-Glutamic Acid Using L-Lysine as Substrate

Abstract

The effects of 19 amino acids on the crystallization of L-Asparagine and L-Lysine have been comparatively studied with analytical purposes. A very simple nephelometric procedure is used for determination of L-Glutamic acid, based on its inhibitory action on the crystallization of L-Lysine. The obtention of supersaturated solutions of L-Lysine was accomplished by means of the change in the solvent composition. Thus, the addition of isopropanol to stable aqueous solutions of this amino acid, allows to obtain unstable supersaturated solutions. The method suffers from very few interferences. The method was also applied to the determination of L-Glutamic acid in pharmaceutical products.     

Syntheses and Structures of Three Cobalt Metal-organic Frameworks with 3-（Sulfonyl-glycine）benzoic Acid

Three new coordination networks based on a versatile and unsymmetric building block 3-（sulfonyl-glycine）benzoic acid （HAL） ligand and inorganic Co（Ⅱ） salt, [Co（HL）（bipy）2]. ClO4·1.5H2O （1）, [Co3（L）2（H2O）6]·4H2O （2） and [Co（HL）（bpp）（H2O）2]·2H2O （3） （bipy = 2,2-bipyridine, bpp = 1,3-bi（4-pyridyl）propane）, have been synthesized in aqueous media and structurally characterized by single-crystal X-ray diffraction. Reaction of Co salt with H3L afforded a neutral 1D alternating chain, which shows a 3-D supramolecular network through hydrogen bonds. When the auxiliary 2,2-bipyridine is used, a mononuclear unit is constructed; if using auxiliary ligand bpp, a neutral 1-D uniform chain is obtained and further extended into a 3-D supramolecular structure through versatile hydrogen bonds. The H3L ligand in 1 adopts a bidentate chelating coordination mode while that in 2 and 3 assumes a pentadentate bridging and a bis-monodentate bridging modes, respectively. This work and our previous work evidently demonstrate that the structures vary with altering the second ligands.     

Thermodynamic and functional properties of legumin (11S globulin from Vicia faba) in the presence of small-molecule surfactants: effect of temperature and pH

We report on the effect of a set of water-dispersible small-molecule surfactants (the main and the longest-hydrocarbon components of which are a citric acid ester of monostearate, a sodium salt of stearol-lactoyl lactic acid, and a polyglycerol ester of stearic acid) on molecular, thermodynamic, and functional properties of the major storage protein of broad beans (Vicia faba) legumin in different molecular states (native, heated, and acid-denatured). The interaction between legumin and the surfactants has been characterized by a combination of thermodynamic methods, namely, mixing calorimetry and multiangle laser static and dynamic light scattering. It was found that hydrogen bonds, electrostatic interactions, and hydrophobic contacts provided a basis for the interactions between the surfactants and both the native and the denatured protein in aqueous medium. Intensive association of the protein molecules in a bulk aqueous medium in the presence of the surfactants was revealed by static and dynamic laser light scattering. In consequence of this, both the surface activity and the gel-forming ability of legumin increased markedly, which has been shown by tensiometry, estimation of protein foaming capacity, and steady-state viscometry. A likely molecular mechanism underlying the effects of small-molecule surfactants on legumin structure-forming properties at the interface and in a bulk aqueous medium is discussed.     

氨基酸侧链与氧化鸟嘌呤碱基对体系的氢键作用

应用量子化学方法,分别在气相和水溶液中对氨基酸侧链与氧化鸟嘌呤碱基对(8-oxo-G∶C)形成的三体复合物的氢键键能、几何结构、电荷分布及二阶稳定化能进行了研究.结果表明,水溶液的存在削弱了复合物中的氢键强度,电荷分布变化明显,水溶液中形成氢键位点的电荷变化量约为气相中的10倍,而几何结构变化不明显、对于酶与DNA之间的相互作用的研究需在水溶液中进行.水溶液对带电三体复合物中8-oxo-G∶C与氨基酸侧链间的氢键有较大影响,键能平均减小了69.23 k J/mol,不带电复合物仅减小了3.60k J/mol.水溶液中三体复合物中8-oxo-G∶C间的氢键受侧链的影响不大,且与侧链带电与否无关,带电复合物和不带电复合物的氢键强度分别减小了24.57和30.05 k J/mol,且二阶稳定化能越大,其对应的氢键键长越短.     

Explanation of Ionic Sequences in Various Phenomena. VI. The Formation and Destruction of Helices in Bovine Plasma Albumin in Neutral and Acidic Solutions

Abstract

The structure of bovine plasma albumin (BPA) was examined by optical rotatory dispersion studies at both low (pH 1.5 and 2.0) and high (pH 9.0) pH values in various aqueous salt solutions. The resulting cationic sequences were compared to those observed by Pedersen for values of the sedimentation constant. At pH 9.0 the destruction of the “helix” produces an acidic sequence. The relative pH position of the “helix” transition, the fact that addition of salt increases the apparent helical content of BPA, and the observed acidic-type of sequence rule out the possibility of (1)ionic bonds between carboxylate and ?-amino groups, (2) hydrophobic bonds, or (3) hydrogen bonds between peptide linkages as major contributing forces in the formation of the helix. The stability of the “helix” in BPA between pH 3.0 and 9.0 must therefore be due to hydrogen bonds between carboxylate ions and hydroxyl groups such as those of serine, threonine, and tyrosine. Repulsive forces between the positively charged groups on BPA strengthen these bonds by preventing the expanded form of BPA from collapsing. At pH 2.0 two types of sequences were observed: The s⁰ _{20, w}, [α]_D and a₀ values gave an acidic-type cationic sequence. The b₀ (helix content), λ_c and [λ]₂₃₃ values gave essentially a nonpolar sequence. The nonpolar or hydrophobic salting-out sequences show that the formation of hydrophobic bonds at pH 2.0 hinders the formation of the helix or folded structure. The acidic sequences show that hydrogen bonds between carboxylic acid groups stabilize both the apparent helix or helices and the intermolecular aggregation of the BPA molecules. From a comparison of the S⁰ ₂₀,w values and the helical content of BPA at pH 9.0 it is also concluded that the formation of these apparent helices or folded structures expands or stiffens the BPA molecule.     

Monte Carlo simulations of the hydrophobic effect in aqueous electrolyte solutions

The hydrophobic interaction between two methane molecules in salt-free and high salt-containing aqueous solutions and the structure in such solutions have been investigated using an atomistic model solved by Monte Carlo simulations. Monovalent salt representing NaCl and divalent salt with the same nonelectrostatic properties as the monovalent salt have been used to examine the influence of the valence of the salt species. In salt-free solution the effective interaction between the two methane molecules displayed a global minimum at close contact of the two methane molecules and a solvent-separated secondary minimum. In 3 and 5 M monovalent salt solution the potential of mean force became slightly more attractive, and in a 3 M divalent salt solution the attraction became considerably stronger. The structure of the aqueous solutions was determined by radial distribution functions and angular probability functions. The distortion of the native water structure increased with ion valence. The increase of the hydrophobic attraction was associated with (i) a breakdown of the tetrahedral structure formed by neighboring water molecules and of the hydrogen bonds between them and (i) the concomitant increase of the solution density.     

Molecular aggregates in aqueous solutions of bile acid salts. Molecular dynamics simulation study

The aggregation behavior of two bile acid salts (i.e., sodium cholate and sodium deoxycholate) has been studied in their aqueous solutions of three different concentrations (i.e., 30, 90,and 300 mM) by means of molecular dynamics computer simulations. To let the systems reach thermodynamic equilibrium, rather long simulations have been performed: the equilibration period, lasting for 20-50 ns, has been followed by a 20 ns long production phase, during which the average size of the bile aggregates (regarded to be the slowest varying observable) has already fluctuated around a constant value. The production phase of the runs has been about an order of magnitude longer than the average lifetime of both the monomeric bile ions and the bonds that link two neighboring bile ions together to be part of the same aggregate. This has allowed the bile ions belonging to various aggregates to be in a dynamic equilibrium with the isolated monomers. The observed aggregation behavior of the studied bile ions has been found to be in good qualitative agreement with experimental findings. The analysis of the results has revealed that, due to their molecular structure, which is markedly different from that of the ordinary aliphatic surfactants, the bile ions form rather different aggregates than the usual spherical micelles. In the lowest concentration solution studied, the bile ions only form small oligomers. In the case of deoxycholate, these oligomers, such as the ordinary micelles, are kept together by hydrophobic interactions, whereas in the sodium cholate system, small hydrogen-bonded aggregates (mostly dimers) are also present. In the highest concentration systems, the bile ions form large secondary micelles, which are kept together both by hydrophobic interactions and by hydrogen bonds. Namely, in these secondary micelles, small hydrophobic primary micelles are linked together via the formation of hydrogen bonds between their hydrophilic outer surfaces.     

Effects of l-arginine on aggregates of fatty-acid/potassium soap in the aqueous media

In the present study, we investigated the effects of l-arginine on aggregates of fatty acid/fatty soap in the aqueous media as a function of pH, by means of hydrogen ion titration, viscoelastic measurement, cryo-transmission electron microscopy and phase contrast microscopy. We found out that l-arginine effectively inhibits the oil droplet growth of oleic acid or octanoic acid. The effect is explained in terms of the adsorption of arginine at the microscopic drop surface, or at the oil/water microinterface through the hydrophobic effect assisted by the hydrogen bonds between carboxyl group of fatty acid and carboxylate of arginine. As to the crystallization of lauric acid at temperatures below the melting point of the hydrocarbon chain, arginine is not effective. In addition, we also found out that the strong binding of arginine cation to anionic oleate micells induces the dominant micellar growth. l-arginine has been used in many refolding systems to suppress protein aggregation. These effects of l-arginine on the aggregates of fatty acid/fatty soap in the aqueous media observed in the present study is expected to form a basis to the specific function displayed in the protein refolding.     

Asp-Gly based peptides confined at the surface of cationic gemini surfactant aggregates

Cationic gemini surfactants complexed with anionic oligoglycine-aspartate (called gemini peptides hereafter) were synthesized, and their aggregation behaviors were studied. The effects of the hydrophobic chain length (C10-C22) and the length of the oligoglycine (0-4) were investigated, and it was clearly shown by critical micellar concentration, Krafft temperature, and isothermal surface pressure measurements that the hydrophobic effect and interpeptidic interaction influence the aggregation behavior in a cooperative manner. Below their Krafft temperatures, some of them formed both hydro- and organogels with three-dimensional networks and the Fourier transform infrared measurements show the presence of interpeptidic hydrogen bonds.     

298.1 K时脂肪酸钠盐对定组成水溶液中非水组分活度系数的影响

本文报告了298.1 K下甲酸钠(C_1), 乙酸钠(C_2)、丙酸钠(C_3)、丁酸钠(C_4)、戊酸钠(C_5)、已酸钠(C_6)和庚酸钠(C_7)七个盐对水溶液中乙醇、丙酮和乙腈三个溶质的活度系数的影响。实验方法是, 固定水溶液中乙醇、丙酮和乙腈的浓度(摩尔分数约为0.05), 用气相色谱法检测不同盐浓度下平衡气相中溶质分压的变化, 从而得出溶质的盐效应活度系数γ。本文给出了一个可以连续取样的气液平衡装置的设计。由实验结果可见, 不同碳链大小的脂肪酸根离子的盐效应作用差别很大。C_1、C_2的盐效应主要由于静电作用; 对C_3、C_4盐, 除静电作用外,它们的疏水基与溶质疏水基的相互作用对盐效应有显著影响; C_5、C_6和C_7的盐效应则反映了疏水离子的特色, 疏水水化、疏水相互作用、疏水离子形成的聚集体与不同官能团的特定相互作用等几项因素, 导致儿个溶质盐效应的差异。