Correlations of Thermodynamic Properties of Aqueous Amino Acid-Electrolyte Mixtures

Suitable equations have been proposed to correlate thermodynamic properties, like mean ion activity coefficients, volumes and compressibilities, of amino acids in electrolyte solutions. An amino acid–electrolyte–water interaction parameter is extracted from the regression of the amino acid property values in aqueous electrolyte solution that is then transferred to an expression to correlate the properties of the electrolyte in mixtures. The single interaction parameter can successfully correlate the published data on mean ion activity coefficients, apparent molar volumes and compressibilities of amino acids as well as of electrolytes in their aqueous mixtures. The equations are tested against the large number of experimental data sets available in the literature.     

Infrared spectra and molar absorption coefficients of the 20 alpha amino acids in aqueous solutions in the spectral range from 1800 to 500 cm(-1)

In this work, we present the absorption spectra and molar coefficients of all 20 amino acids in aqueous solutions down to 500 cm(-1). The spectral region between 1200 and 500 cm(-1) was yet disregarded for protein infrared spectroscopy, mainly due to the strong H(2)O absorption. Absorption spectra were obtained mainly for physiological relevant pH region. Intense bands for aromatic amino acids, histidine and such with OH group could clearly be identified throughout the given spectral region. For sulfur-containing amino acids cysteine and methionine some strong bands besides the weak carbon-sulfur stretching vibration was shown. Effects of aqueous solution environment, pH, protonation states were discussed, together with previously reported data from theoretical approaches. With this complete set of spectral information application to proteins in the whole mid infrared region could be described precise and the potential of the lower spectral region to study typical cofactor ligands like histidine, shown.     

Density and viscosity of α-amino acids in aqueous solutions of cetyltrimethylammonium bromide

The densities and viscosities of aqueous solution of cetyltrimethylammonium bromide (0.01 mol kg⁻¹) (CTAB) and solutions of CTAB containing amino acids, viz., glycine, l-serine, and l-valine (0.01–0.05 mol kg⁻¹), were determined in the temperature range 298.15—313.15 K. Apparent molar volumes of the amino acids were calculated from the density and viscosity values. The calculated apparent molar volumes were used to calculate standard partial molar volumes (-V ₂⁰) and standard partial molar volumes of transfer of amino acids from water to an aqueous solution of CTAB. The viscosity values were used for the calculation of the viscosity coefficients A and B in the Jones—Dole equation. The linear dependences of -V ₂⁰ and B on the number of carbon atoms in the alkyl chains of the amino acids were found. The results obtained were used in analysis of hydrophilic-hydrophilic, hydrophilic-hydrophobic, and hydrophobic-hydrophobic interactions that occur during dissolution of amino acids in an aqueous solution of CTAB.     

Viscosities and apparent molar volumes of some amino acids in water and in 6M guanidine hydrochloride at 25°C

Apparent molar volumes and viscosity B- and D- coefficients of amino acids glycine, valine, proline, serine and arginine have been determined in water and in aqueous 6M guanidine hydrochloride (GuHCl) solution at 25°C. Transfer volumes and transfer viscosity B-coefficients were evaluated for the amino acids studied in going from water to 6M GuHCl. These transfer properties which were all positive were interpreted in terms of strong interactions of GuHCl molecules with the charged centers of amino acid molecules. A comparison of results obtained in this work for GuHCl and those obtained from literature for urea has shown that GuHCl has stronger interactions than urea with amino acids. This finding explained the previous experimental observations on GuHCl being a stronger denaturing agent than urea for proteins.     

α-氨基酸-丁醇-水三元体系中分子间的异系焓相互作用

利用2277热活性检测仪的流动测量系统获得了298.15K时甘氨酸、L-丙氨酸、L-缬氨酸和L-脯氨酸分别与n-丁醇在水溶液中混合过程的焓变以及各自的稀释焓,依据McMillan-Mayer理论关联得到异系焓相互作用系数,讨论了不同氨基酸与n-丁醇分子的作用机理.对hxy值分析结果表明,不同氨基酸与n-丁醇分子间的异系焓作用系数的大小主要取决于氨基酸分子结构的差异,氨基酸的不同侧基(非极性或极性)对焓作用系数有着不同的贡献,焓作用系数值的相对大小最终取决于各基团之间竞争平衡的结果.脯氨酸特殊的五元吡咯环结构对hxy值有较大的正贡献;n-丁醇的疏水性比尿素或甲脲大得多.     

脂肪族α-氨基酸疏水自缔合作用的流动微量热法研究

建立了水溶液中脂肪族α- 氨基酸疏水自缔合相互作用的化学模型, 根据模型方程对由精密流动微量热法测得的α- 氨基酸水溶液的稀释焓数据进行回归分析, 得到等步自缔合作用的平衡常数(K)、焓变(ΔHm)和熵变(ΔSm)等热力学参数, 发现焓、熵之间存在很好的补偿关系. 同时计算了溶液中水的偏摩尔过量熵(SE1), 并根据脂肪族α- 氨基酸的水化模型对结果进行了讨论. 建立的化学模型参数能在一定程度上解释McMillan- Mayer模型中的同系焓作用系数的物理意义.     

三种氨基酸在尿素水溶液中的体积性质

精密密度法详细测定甘氨酸、L-丙氨酸、L-丝氨酸在尿素水溶液中的表观摩尔体积,计算了三种氨基酸从水到尿素水溶液的迁移偏摩尔体积,结合前期的氨基酸从水到尿素水溶液的迁移焓,探讨尿素水溶液的结构特点及其对氨基酸与尿素在水溶液中相互作用的影响。结果表明,尿素分子在水溶液中自缔合,引起溶剂结构的变化并削弱其与氨基酸分子的结构相互作用,造成氨基酸从水到尿素水溶液的迁移偏摩尔体积和迁移焓随尿素浓度的增加而出现多个变化点,这一效应随着氨基酸疏水性的增强而增大,表明氨基酸的疏水性越强,其与尿素相互作用引起的去水化作用越明显。     

Quantitative gas-liquid chromatography of non-protein amino acids.

The quantitative gas--liquid chromatographic analysis of non-protein amino acids, in the presence of protein amino acids, is described. The amino acids were determined as their N-trifluoroacetyl n-butyl esters on an ethylene glycol adipate column. The relative molar responses of 38 amino acids are reported.     

Simultaneous Quantitation of Amino Acid Mixtures using Clustering Agents

A method that uses the abundances of large clusters formed in electrospray ionization to determine the solution-phase molar fractions of amino acids in multi-component mixtures is demonstrated. For solutions containing either four or 10 amino acids, the relative abundances of protonated molecules differed from their solution-phase molar fractions by up to 30-fold and 100-fold, respectively. For the four-component mixtures, the molar fractions determined from the abundances of larger clusters consisting of 19 or more molecules were within 25% of the solution-phase molar fractions, indicating that the abundances and compositions of these clusters reflect the relative concentrations of these amino acids in solution, and that ionization and detection biases are significantly reduced. Lower accuracy was obtained for the 10-component mixtures where values determined from the cluster abundances were typically within a factor of three of their solution molar fractions. The lower accuracy of this method with the more complex mixtures may be due to specific clustering effects owing to the heterogeneity as a result of significantly different physical properties of the components, or it may be the result of lower S/N for the more heterogeneous clusters and not including the low-abundance more highly heterogeneous clusters in this analysis. Although not as accurate as using traditional standards, this clustering method may find applications when suitable standards are not readily available.     

COMPARATIVE PHOTOCHEMICAL ANALYSIS OF HIGHLY PURIFIED 124 KILODALTON OAT and RYE PHYTOCHROMES in vitro

Abstract A direct comparison of the photochemical interconversions between red (P_r-) and far-red (P_fr-) absorbing forms of highly-purified 124 kDa oat and rye phytochromes under identical experimental conditions was performed. In two different buffer systems at 5°C, the quantum yields for the P_r to P_tr and P_fr to P_r phototransformations under constant red and far-red illumination, φ _r and φ_fr respectively, were determined to be 0.152-0.154 and 0.060-0.065 for oat preparations and 0.172-0.174 and 0.074-0.078 for rye preparations. These values as well as the wavelength dependence of the photoequilibrium produced under continuous illumination throughout the visible and near-ultraviolet spectrum were based on the absorption spectra of the two phytochrome preparations and revised molar absorption coefficients. The molar absorption coefficients were estimated by quantitative amino acid analysis and shown to be identical for the two monocot phytochromes (i.e. 132 mM ⁻¹ cm⁻¹ at the red absorption maximum for the P_r form). Because these measurements were performed under identical experimental conditions, including buffer, temperature, light fluence rate, and instrumentation, the differences observed must reflect structural features inherent to the two different monocotyledonous phytochromes.     

Synthesis and optical properties of new chalcones containing 4-[bis(2-hydroxyethyl)amino]phenyl fragment

New chalcones with 4-[bis(2-hydroxyethyl)amino] phenyl fragment were obtained from 4-[bis(2-acetoxyethyl) amino]- benzaldehyde by the Claisen–Schmidt reaction. From their UV-VIS absorption and emission spectra, optical band gap values were calculated based on the Stokes shifts as well as the molar absorption coefficients and fluorescence quantum yields were estimated. The dependence of the absorption and emission maxima on solvent polarity and pH was evaluated.     

Partial molar volumes of l-alanine,dl-serine,dl-threonine,l-histidine,glycine, and glycylglycine in water,NaCl, and DMSO aqueous solutions at T = 298.15 K

The apparent molar volumes of l-alanine, dl-serine, dl-threonine, l-histidine, glycine, and glycylglycine in water and in the aqueous solutions of NaCl and DMSO with various concentrations at T = 298.15 K have been measured by the precise vibrating-tube digital densimeter. The calculated partial molar volumes at infinite dilution have been used to obtain corresponding transfer volumes from water to various solutions. The experimental results show that the standard partial molar volumes of the above amino acids and peptide at the dilute DMSO aqueous solutions are very close to those in water. However, the volumes show several types of variations with the increase of the concentrations of DMSO due to different types of side chain of amino acids, which should be discussed specifically. The NaCl changes considerably the infinite dilution standard partial molar volumes of the above amino acids and peptide in the aqueous solutions. The infinite dilution standard partial molar volumes of the each amino acids and peptide increase with the concentrations of NaCl. The experimental results have been rationalized by a cosphere overlap model.     

碱性氨基酸离子交换平衡特性的研究

研究了碱性氨基酸与001×7阳离子交换树脂的离子交换平衡特性。测定了001×7树脂对碱性氨基酸两种价态离子的选择性吸附系数,并考察了pH和碱性氨基酸的浓度对平衡吸附量的影响,确定了离子交换的最佳pH 和碱性氨基酸的浓度。     

甘氨酸和L-丝氨酸在LiNO3, NaNO3和KNO3水溶液中的体积性质

用Anton Paar DMA 55精密数字密度计测定了甘氨酸和L-丝氨酸在LiNO3, NaNO3和KNO3水溶液中的密度, 计算了氨基酸的表观摩尔体积、极限偏摩尔体积、迁移偏摩尔体积、理论水化数和体积作用系数. 根据静电相互作用和结构水合作用模型讨论了氨基酸的侧链和阳离子的性质对迁移偏摩尔体积的影响. 结果表明, 甘氨酸和L-丝氨酸在3种硝酸盐水溶液中的迁移体积均为正值, 并且随着盐溶液浓度的增大而增大. 氨基酸两性离子端基和阴阳离子间的静电作用对迁移体积的贡献是主要的, 静电作用削弱了两性离子带电中心对周围水分子的电致收缩效应, 造成氨基酸的理论水化数随盐溶液浓度的增加而减小. L-丝氨酸的侧链与离子之间的亲水-亲水相互作用对迁移体积有小的正贡献, 使得在同一种盐溶液中L-丝氨酸的迁移体积较甘氨酸的大. 同一种氨基酸在NaNO3和KNO3水溶液中的迁移体积较在LiNO3水溶液中的大, 主要是由于Li＋难以去水化. 在低浓度的盐溶液中氨基酸与盐之间的相互作用以1∶1形式为主, 随着溶液浓度的增大, 1∶2形式的相互作用逐渐增大     

Are the integrated absorption coefficients temperature dependent? FT-NIR study of the first overtone of the OH stretching mode of octanoic acid

The integrated molar absorption coefficients of the first overtone of an OH stretching mode of free octanoic acid were determined through a series of FT-NIR measurements in a CCl₄ solution at different temperatures. A few methods of calculation of the molar absorption coefficient were applied; the results were compared and discussed. It was shown that not all of the methods can be applied for the calculation if the plot of Beer's law does not pass through the origin. The results clearly show that the integrated molar absorption coefficient is strongly temperature dependent; its value increases approximately 0.6 dm³ mol⁻¹ cm⁻¹ per one degree and the use of a constant value of the coefficient through a temperature range may lead to significant errors.     

212.8 nm laser photolysis of aromatic and aliphatic amino acids and related peptides.

The comparison of the photochemical properties of three aromatic and five aliphatic amino acids and three dipeptides was carried out using 212.8 nm laser irradiation and high performance liquid chromatography. The photochemical sensitivity, photolysis quantum yield and quantum yield of peptide bond scission were determined. Two-photon absorption coefficients of solvent (liquid water) and cell windows material (fused silica) at lambda = 212.8 nm were established.     

反相高效液相色谱用于寄生虫中氨基酸含量的测定

 为了对寄生虫病进行有效的防治 ,采用柱前衍生、反相高效液相色谱分离、紫外吸收定量法对中国 7个地区马来丝虫及马来丝虫幼虫氨基酸的组成和含量进行了测定。结果表明 :不同地区的马来丝虫中各氨基酸的含量存在着一定的差别 ,幼虫的氨基酸含量明显低于成虫的相应氨基酸含量。此方法简便、准确 ,在研究寄生虫的种内分化、种下分类和生长、发育、代谢等生命活动方面具有重要的意义。     

氨基酸在水或氯化钾水溶液中体积性质的研究

在298.15K和常压下利用密度法测定了十几种α-氨基酸在水或氯化钾水溶液中的表观摩尔体积, 由此得到了各氨基酸的偏摩尔体积和其相应的转移偏摩尔体积,以及氨基酸中侧链对其偏摩尔体积的贡献值。从理论上计算了各氨基酸在上述溶液浓度的增加而增大; 氨基酸共溶质间的相互作用以1:1形式为主; 氨基酸的水化数随盐浓度的增加而减小。对所得结果进行了定性讨论。     

甘氨酸在尿素、甲脲及二甲脲水溶液中的体积性质

用精密数字密度计测定了甘氨酸在不同质量分数的尿素、甲脲和二甲脲水溶液中的密度,计算了甘氨酸的极限偏摩尔体积、迁移偏摩尔体积、理论水化数和体积作用系数,讨论了溶剂组成变化对甘氨酸迁移偏摩尔体积和理论水化数的影响.结果表明,甘氨酸与尿素及烷脲分子间的相互作用主要以1:1的形式为主.尿素、甲脲、二甲脲分子与氨基酸荷电中心的直接相互作用,削弱了两性离子带电中心对周围水分子的电致收缩效应,造成了理论水化数随溶液浓度的增加而减小.     

甘氨酸、L-丙氨酸和L-丝氨酸在尿素水溶液中的体积性质

蛋白质的折叠与解折叠、稳定性、变性行为和酶的活性等都受到环境中其它各种物质影响.作为蛋白质模型分子,氨基酸在混合溶液中的热力学研究近年来引起了广泛重视.尿素在生物体系中的独特地位主要表现在:它是水结构的破坏者,同时又是许多球状蛋白的变性剂.然而,尿素对球状蛋白的变性作用尚未达成共识.