Interaction of Adjacent Amino Acids

Ramachandran plots display the dihedral angles of a single protein residue. We propose a crossed torsion angle plot called SSY‐plot between two neighboring amino acids and demonstrate that a special coherence motion can exist between some very special amino acid pairs leading to spontaneous unusual structures. A 6mer was extracted from a BBA polypeptide chain which in this plot shows two diagonal domains for the Ser‐Arg pair after some induction time. Other amino acid pairs in general do not show this kind of split domain. This shows that a special pair is required for stabilizing two distinct native structures in protein folding. We suggest that the existence of these two domains corresponds to a bifurcation between two different protein structures and that the special pair is the key to producing these two structures. These two different structures are produced spontaneously without an external agent.     

Enthalpic Interaction of Amino Acids with Ethanol in Aqueous Solutions at 25°C

The enthalpies of mixing aqueous ethanol solutions and with aqueous amino acid solutions (glycine, L-alanine, L-serine, L-threonine, and L-proline) and their respective enthalpies of dilution have been determined at 25^°C by a flow microcalorimetric system. The experimental data have been analyzed in terms of McMillan-Mayer formalism to obtain the enthalpic virial coefficients for heterotactic interaction. The results have been interpreted from the point of view of solute-solute interactions.     

Enthalpic Interaction of Amino Acids with 2-Chloroethanol in Aqueous Solutions at 298.15 K

The enthalpies of mixing have been determined for five kinds of aqueous amino acids solutions (glycine, L-alanine, L-valine, L-serine, and L-proline) with 2-chloroethanol by an LKB-2277 Bio Activity Monitor at 298.15 K. In addition, the enthalpies of dilution at 298.15 K of aqueous solutions containing the five kinds of amino acids and 2-chloroethanol have been obtained. The heterotactic enthalpic pairwise interaction coefficients of the virial expansion of excess enthalpy were evaluated and interpreted from the point of view of solute–solute interactions. In comparison with ethanol, 2-chloroethanol shows a stronger exothermic interaction with amino acids because of its hydrophilic Cl atom and a more acidic –OH group. Using the additivity groups concept by Savage and Wood (SWAG), contributions of each of functional group of the amino acids and ethanol and 2-chloroethanol have been estimated.     

Theoretical Studies on Complexes of Calcium Ion with Amino Acids

The complexes formed by calcium ion and 12 common amino acids were investigated systematically in the gas phase at the level of MP2/6-311＋＋G（d,p）//MP2/6-3 1G（d,p）.The results show that the salt-bridge structure is the most preferred motif for Ca2＋ binding aliphatic amino acids without heteroatom in the side chain,while charge-solvated（CS） structure is the most preferred motif for Ca2＋ binding other amino acids except for glutamine and lysine.IR spectra of Gln-Ca2＋ and Asn-Ca2＋ complexes were calculated and compared well with the available experiments.From the study in aqueous solution,the bidentate salt-bridge structure was determined to be the most favorable for all the twenty kinds of amino acids to chelate Ca2＋ to both the oxygen atoms of the negatively carboxylate group in the backbone.     

Interaction of Nonaromatic Amino Acids with Cyclodextrins in Aqueous Solution

Weak interactions of nonaromatic amino acids with - and -cyclodextrins in aqueous solutions at 298.15 K were studied calorimetrically. The structure and solvation of these compounds noticeably affect the thermodynamic characteristics of interparticle interactions.     

分光光度法研究氨基酸与四氯苯醌形成的荷移配合物

本文用分光光度法研究了5种氨基酸与四氯苯醌形成的荷移配合物.通过对影响配合物形成因素的研究,确立了以四氯苯醌形成荷移配合物的方法测定氨基酸的最佳反应条件,测定了反应平衡常数.讨论了配合物的组成.     

人参中氨基酸及多肽的研究

氨基酸及多肽是人参中重要成分之一。田中治,Gstirner等对人参根中氨基酸分析表明,主要有Arg、Lys、Ala、Ser、Tyr、Pro、Gly、Glu、Thr、Leu、Ile、Val、AspPhe、His等,也曾确定含半胱氨酸。我们分析了吉林省集安边条参各部位的氨基酸(见表1)表明,芦头和花蕾各检出16种;根检出15种;侧根、须根和叶各检出14种。     

两种非蛋白氨基酸的新功能: 与丙二醛相互反应的机制

丙二醛(MDA)是生物分子氧化的典型羰基中间体, 是脂质过氧化的典型终末产物. 这类活性羰基中间体引起组织蛋白的老化与恶化及DNA损伤. 牛磺酸在人体内具有非常广泛的生理功能, 而g-氨基丁酸(GABA)是神经系统的一种重要抑制性神经递质, 因此二者是两种很重要的非蛋白氨基酸. 研究了在生理条件下牛磺酸或GABA是否直接诱捕MDA从而保护组织蛋白不受伤害. 将牛磺酸或GABA与MDA在生理条件下温浴48 h, 经高效液相、质谱等分析手段分析, 发现牛磺酸或GABA与MDA直接反应, 通过HPLC分离, 都生成两种主产物, 一种是没有荧光的紫外吸收峰为274～278 nm 的产物, 一种是有荧光的产物, 这种类似脂褐素(Ex. 392～395 nm/Em. 456～364 nm)的荧光产物是1,4-二氢吡啶衍生物. 牛磺酸或GABA与MDA的反应表明它们在生理条件下具有清除活性羰基的功能, 而这种毒性羰基与很多羰基紧张相关的疾病及衰老有关.     

Interactions of Some Amino Acids with Aqueous Osmoprotectant Proline at 298.15 K: Volumetric and Calorimetric Studies

Apparent molar volumes of a homologous series of amino acids in aqueous proline solutions have been obtained from densities at 298.15 K, measured with a vibrating-tube digital densimeter. These data have been used to deduce the partial molar volumes of transfer from water to aqueous proline solutions; these partial molar volumes of transfer are found to be positive for glycine, alanine, α-amino-n-butyric acid and valine, whereas they are negative for leucine. The number of water molecules hydrated to the amino acids was estimated from the partial molar volume data. In order to supplement this information, enthalpies of transfer of aqueous amino acids from water to 0.1, 2.25 and 1 mol⋅dm⁻³ aqueous proline have been determined at 298.15 K using a VP-ITC titration calorimeter. The data on the partial molar volumes and enthalpies of transfer are discussed in terms of various interactions operating in the ternary mixtures of amino acids, water and proline.     

Thermodynamics of the Interaction of a Homologous Series of Amino Acids with Sorbitol

The apparent molar volumes V _2,φ , apparent molar isentropic compressibilities K _S,2,φ , and enthalpies of dilution of aqueous glycine, alanine, α-amino butyric acid, valine, and leucine have been determined in aqueous 1.0 and 2.0 mol⋅dm⁻³ sorbitol solutions at 298.15 K. These data have been used to calculate the infinite dilution standard partial molar volumes V_2,m⁰V_{2,m}^{0}, partial molar isentropic compressibilities K_S,2,m⁰K_{S,2,m}^{0}, and enthalpies of dilution Δ_dil H ⁰ of the amino acids in aqueous sorbitol, along with the standard partial molar quantities of transfer of the amino acids from water to aqueous sorbitol. The linear correlation of V_2,m⁰V_{2,m}^{0} for this homologous series of amino acids has been utilized to calculate the contribution to V₂⁰V_{2}^{0} of the charged end groups (NH₃⁺\mathrm{NH}_{3}^{+}, COO⁻), the CH₂ group, and other alkyl chains of the amino acids. The results for the standard partial molar volumes of transfer, compressibilites and enthalpies of dilution from water to aqueous sorbitol solutions have been correlated and interpreted in terms of ion–polar, ion–hydrophobic, and hydrophobic–hydrophobic group interactions. A comparison of these thermodynamic properties of transfer suggest that an enhancement of the hydrophilic/polar group interactions is operating in ternary systems of amino acid, sorbitol, and water.     

N-磷酰化氨基酸与核糖核苷反应的研究

研究了Ｎ－磷酰化氨基酸与核苷在水溶液中的反应，反应中能够同时生成小肽和小的寡核苷酸；不同的Ｎ－磷酰化氨基酸与不同的核苷之间的反应具有一定的选择性。     

Accurate Interaction Energies of CO2 with the 20 Naturally Occurring Amino Acids

We have performed a series of highly accurate calculations between CO₂ and the 20 naturally occurring amino acids for the investigation of the attractive noncovalent interactions. Different nucleophilic groups present in the amino acid structures were considered (α-NH₂, COOH, side groups), and the stronger binding sites were identified. A database of accurate reference interactions energies was compiled as computed by explicitly-correlated coupled-cluster singles-and-doubles, together with perturbative triples extrapolated to the complete-basis-set limit. The CCSD(F12)(T)/CBS reference values were used for comparing a variety of popular density functionals with different basis sets. Our results show that most density functionals with the triple-zeta basis set def2-TZVPP align with the CCSD(F12)(T)/CBS reference values, but errors range from 0.1 kcal/mol up to 1.0 kcal/mol.     

配位体交换树脂对中性氨基酸分离性能的研究

采用配位体交换树脂对中性氨基酸(Gly,Ala,Val和Leu)进行了分离,并与一般阳离子交换树脂的分离性能进行了比较,对淋洗剂、柱温等分离条件进行了实验;研究了树脂载体结构、功能基及配位中心离子对分离性能的影响。     

Effect of Basic Amino Acids on Nickel Ion Reduction at a Mercury Electrode

In a 0.02 M borax solution (pH 8.5), basic amino acids (arginine, lysine, and ornithine) react with Ni²⁺ to form a mono‐ligand complex that is reduced at a mercury electrode at about ?0.85 V vs. Ag|AgCl|KCl (3 M). At a long time scale (staircase voltammetry; scan rate<50 mV s^?1), the complex reduction is a catalytic (EC′) process, the rate‐determining step being the regeneration of the reducible species by the reaction of the amino acid with free Ni²⁺. At a short time scale (differential pulse voltammetry or higher scan rate staircase voltammetry), the reaction rate is controlled by the diffusion of the complex. Although the same kind of complexation occurs with either basic amino acids or glycine, the last one does not induce a similar process. The peculiar effect of basic amino acids is due to the side chain that causes the ligand molecule to adopt a favorable orientation at the electrode surface. The differential pulse voltammetry peak current is proportional to the total amino acid concentration over the concentration range from 2 to 100 μM. Hence a voltammetric method for arginine determination in nutritional supplements was developed and validated using HPLC as reference method.     

Colloidal Interaction at the Air-Liquid Interface

In this paper, we propose a model to analyze the stability of colloidal particles at the air-liquid interface. The proposed model for the colloidal particle interaction considers DLVO interactions and capillary, hydrophobic, and dipolar interactions between the particles. Typical values from the literature were assigned to most parameters included in the model. Numerical computation revealed the most important parameter in determining the total interaction is the density of dipoles at the external surface of the particles. We have found significant differences for the pair potential between hydrophobic and hydrophilic particles. Hydrophobic particles must aggregate in a principal minimum of the interaction potential curve while hydrophilic particles aggregate in a secondary minimum. Copyright 2000 Academic Press.     

铀酰与羧酸和肟基类配体相互作用的理论研究

深入了解各种功能基团与铀酰离子的络合行为有助于设计和开发高效海水提铀吸附剂. 本工作通过密度泛函理论(DFT)方法系统地研究了两种典型铀酰络合配体吡啶-2,6-二羧酸(H₂DPA)和戊二酰偕亚胺二肟(H₂A)与铀酰离子及碳酸根离子形成的配合物的结构、成键性质以及热力学稳定性. 研究结果表明, 所有配合物中, 配体与铀酰离子之间具有不同强度的共价相互作用. 由于H₂A配位时发生了质子重排, 而且配体的解离能较高, 使其更难与[UO₂(CO₃)₃]^4-发生取代反应, 因此H₂DPA配体是海水提铀中一种潜在的有效配体. 本工作的相关研究结果为海水提铀中高效吸附基团的设计和开发提供了理论线索.     

镧(Ⅲ)-氨基酸配合物的温度滴定量热法研究

稀土配合物因其特有的性质而日益受到人们的重视 [1] .对于稀土与氨基酸配合物的已有研究 [2 ,3] ,但尚未见到关于镧 ( )与不同种氨基酸配合反应的较系统的报道 .文献 [2 ,3]大多采用 p H电位法或其它非热化学方法 ,且大多只得到反应的平衡常数 ,而用滴定量热法直接测定其配合常数和反应焓变的研究尚未见报道 .用滴定热量法可同时测定配合反应的焓变和熵变 [4 ] ,而且在滴定量热过程中 ,反应体系基本上是一封闭体系 ,除了对体系的温度进行监测外 ,对反应体系没有其它任何干扰 ,因而可以减少外界因素的影响 ,从而减少测定的误差 .本文用滴…     

The Studies of the Reactions of 2, 4, 6-Triphenylpyrylium Tetrafluoroborate with Amino Acids

The reactions of triphenylpyrylium salt 1 with various amino acids were explored and compared. The reactions with most α-amino acids yielded decarboxylation products 2 viadecarboxylation. The reactions with glutamic acid, lysine and ACC (1-aminocyclopropyl-carboxylic acid) gave triphenylpyridine 8, dimer 9 and acid 5a-ace, respectively. The reactionswith β and γ-amino acids yielded triphenylpyridine by intramolecular elimination.     

芳香氨基酸在吸附树脂上的传质速度的研究

本文建立了测量芳香氨基酸在吸附树脂上传质速度的方法。引用Boyd方程模型测定了苯丙氨酸和酪氨酸的有效内扩散系数;研究了树脂结构与芳香氨基酸扩散速度之间的关系;同时考察了温度、pH值诸因素对扩散速度的影响。     

Impact of the Chirality and Curvature of Carbon Nanostructures on Their Interaction with Aromatics and Amino Acids

Understanding noncovalent interactions on the surfaces of carbon nanostructures (CNSs) is of fundamental importance and also has implications in nano‐ and biotechnology. The interactions of aromatic compounds such as benzene, naphthalene, and aromatic amino acids with CNSs of varying diameter, chirality, and curvature were systematically explored by using density functional theory. Planar graphene exhibits stronger binding affinity than curved carbon nanotubes (CNTs), whereas zigzag CNTs appear to show stronger binding affinity than armchair CNTs. For hydrocarbons, there exist two competing modes, namely, π–π stacking interactions and CH ??? π interactions, which bring the aromatic motifs into parallel and perpendicular dispositions with respect to the CNSs, respectively. Our results reveal that π–π stacking interactions override CH ??? π interactions in such cases. However, in the case of aromatic amino acids, π–π interactions can exist simultaneously along with a range of other interactions, including CH ??? π. The polarizability and HOMO energy of the CNSs were found to be the key factors that determine the binding energies. The HOMO–LUMO energy gaps of the CNSs were found to be undisturbed by the noncovalent functionalization of the aromatic molecules.