甘氨酸在N,N-二甲基甲酰胺水溶液中的体积性质

用Anton Paar型55精密数字密度计测定了甘氨酸在N,N-二甲基甲酰胺(DMF)水溶液中的密度,计算了甘氨酸的表观摩尔体积、极限偏摩尔体积、迁移偏摩尔体积和理论水化数,讨论了DMF的结构对甘氨酸迁移偏摩尔体积和理论水化数的影响。结果表明,甘氨酸在DMF水溶液中的迁移偏摩尔体积为正值,并且随着溶液浓度增大而增大。在DMF水溶液中的理论水化数比在纯水中的小,并且随着DMF浓度的增大而减小。把上述计算结果与在N,N-二甲基乙酰胺(DMA)水溶液中的实验结果进行了比较。     

三种氨基酸从水到DMSO水溶液的迁移焓研究

用微量量热法测定甘氨酸、L-丙氨酸、L-丝氨酸在二甲基亚砜(DMSO)水溶液中的溶解焓, 计算得到三种氨基酸从水到DMSO水溶液的迁移焓, 根据共球交盖模型对氨基酸与DMSO在水溶液中的相互作用进行讨论, 并与前期的氨基酸在尿素水溶液体系中的迁移焓进行比较. 结果显示, 氨基酸与共溶剂分子之间产生的静电相互作用以及亲水-亲水相互作用对氨基酸迁移焓有负贡献, 而亲水-疏水、疏水-疏水相互作用对氨基酸迁移焓有正贡献. 与尿素水溶液中氨基酸迁移焓的绝对值随尿素浓度的增加而增加, 并规律性地出现多个变化点的情况不同, 氨基酸从水到DMSO水溶液的迁移焓随DMSO浓度的增加而线性增加. 这种差异反映了尿素与DMSO及其水溶液结构的不同, 为认识尿素在水溶液中的缔合作用提供了对比依据.     

DMA水溶液的1H NMR研究

测量了N，N-二甲基乙酰胺(DMA)水溶液体系不同温度下全浓度范围的^1H NMR数据，对体系中的缔合情况进行了讨论。应用化学缔合模型求得了各缔合平衡常数K和缔合平衡的△H，结合N，N-二甲基甲酰胺(DMF)和N-甲基乙酰胺(NMA)水溶液的研究结果，发现酰胺自身结构和酰胺浓度是影响酰胺水溶液性质的主要因素。     

气相色谱法测定水中4种酰胺类化合物含量

采用气相色谱法同时测定水中N,N′-二甲基甲酰胺、N,N′-二甲基乙酰胺、N-甲基甲酰胺和N-甲基乙酰胺等4种酰胺类化合物的含量。柱流量为5mL·min-1,起始柱温为80℃。用DB-FFAP石英毛细管色谱柱分离,火焰离子化检测器检测。4种酰胺类化合物在一定的质量浓度范围内与其峰面积呈线性关系,方法的检出限在0.03~0.06 mg·L-1之间。加标回收率在92.3%~103%之间,测定值的相对标准偏差(n=6)在0.30%~2.7%之间。     

丝氨酸在醇-水溶液中的溶解焓

用RD-496III双热流精密微热量计测量了L-丝氨酸在纯水以及异丙醇、1,2-丙二醇和丙三醇水溶液中的溶解焓, 并计算了从水到醇-水溶液中的迁移焓. 实验发现, L-丝氨酸在水及醇-水溶液中的溶解焓都是正值, 它从水到醇-水溶液中的迁移焓也都是正值, 并且基本上随着醇浓度的增加而增加, 说明在溶解过程中, 溶质与混合溶剂分子的部分去水化吸热过程占主要地位. 另外, 实验还发现L-丝氨酸从水到异丙醇水溶液中的迁移焓大于在1,2-丙二醇水溶液中的, 更大于在丙三醇水溶液中的, 这是由于羟基的减少导致了疏水-亲水作用的增加和亲水-亲水作用的减弱.     

微波辅助萃取/气相色谱-串联质谱法同时测定皮革及其制品中5种限用酰胺类溶剂的残留量

建立了同时测定皮革及其制品中5种限用酰胺类溶剂残留量的气相色谱-串联质谱分析方法。以甲醇为萃取溶剂,微波萃取皮革及其制品中残留的限用酰胺类溶剂,萃取物经固相萃取柱净化后,进行气相色谱-串联质谱分析,外标法定量。在优化条件下,甲酰胺、N-甲基甲酰胺、N,N-二甲基甲酰胺、N-甲基乙酰胺、N,N-二甲基乙酰胺的定量下限(LOQ,S/N=10)分别为20,10,1,20,3μg/kg。在3个不同加标水平下,方法的平均加标回收率为81.4%~86.9%,相对标准偏差(RSD,n=9)为4.5%~8.7%。该方法简便快速,灵敏度高,定量下限远小于REACH法规的限量要求,可完全满足皮革及其制品中限用酰胺类溶剂残留量检测工作的要求。     

溶剂分子对甲酰胺及其衍生物分子内氢转移催化作用的研究

在B3LYP/6-311+ +G* * 水平下,通过计算所形成二元团簇的能量来研究水、氨、甲醇、氟化氢等溶剂分子对甲酰胺及其衍生物分子内氢原子转移的催化作用.简单描绘了在有水、氨、甲醇和氟化氢等溶剂分子存在时,甲酰胺及其衍生物分子内氢原子转移的过程.结果表明,当有水、氨、甲醇、氟化氢等溶剂分子存在时,从甲酰胺甲酰胺酸转变的能垒会降低.而且不同的溶剂分子对甲酰胺(FA)、 N-甲基甲酰胺(MF)和N,N-二甲基甲酰胺(DMF)的催化能力各不相同.在这四种溶剂分子中,氟化氢的催化作用最强.     

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     

碱基腺嘌呤与多肽酰胺间氢键作用的最佳位点

正确理解核酸碱基和蛋白质多肽间的作用机制有助于人们利用这些生物分子有效地进行分子设计,进而制备具有特殊纳米结构和功能的生物分子材料.本文优化得到了碱基腺嘌呤与N-甲基乙酰胺、甘氨酸二肽、丙氨酸二肽形成的20个氢键复合物的结构并计算了结合能,探讨了腺嘌呤与多肽酰胺间氢键作用的最佳位点.研究发现:腺嘌呤可以使用两个不同位点(A1位点和A2位点)与N-甲基乙酰胺形成N―H…N型或者N―H…O=C型氢键复合物,腺嘌呤使用A1位点与N-甲基乙酰胺形成的N―H…N型氢键复合物更稳定;二肽分子可以使用主链上两个不同位点(丙氨酸的Ala7位点和Ala5位点或者甘氨酸的Gly7位点和Gly5位点)与腺嘌呤形成含有N―H…N和N―H…O=C两条氢键的复合物,二肽分子使用Ala7或Gly7位点与腺嘌呤形成的氢键复合物更稳定;腺嘌呤与多肽间的氢键作用强于其与N-甲基乙酰胺的作用.基于分子中的原子理论与自然键轨道计算结果分析了氢键作用的本质.     

310.15K时蛋白质模型化合物与二元醇在水溶液中的异系焓相互作用

利用2277热活性检测仪的流动量热系统测量蛋白质模型化合物(甘氨酸、丙基酸、N,N-二甲基甲酰胺(DMF)和N,N-二甲基乙酰胺(DMA))与二元醇(1,3-丁二醇和2,3-丁二醇)的混合过程焓变以及各自的稀释焓;依据McMillan-Mayer理论对实验数据进行分析,获得310.15K时水溶液中蛋白质模型化合物与二元醇异构体分子的异系焓相互作用系数(hxy,hxxy,hxyy).结果表明,hxy值均为正值,此过程吸热效应占主导作用,并且hxy(DMA)hxy(丙氨酸)hxy(甘氨酸)hxy(DMF)和hxy(2,3-丁二醇)hxy(1,3-丁二醇).根据结果讨论了溶质-溶质相互作用和溶质-溶剂相互作用情况,阐明了二元醇官能团相对位置的变化对hxy值的影响,发现DMF或DMA与二元醇之间有较强的氢键作用,由于DMF分子共振结构有较好的可极化性,DMF与二元醇的氢键作用被进一步加强.     

Densities, Specific Heat Capacities, Apparent and Partial Molar Volumes and Heat Capacities of Glycine in?Aqueous Solutions of Formamide, Acetamide, and?N,N-Dimethylacetamide at T=298.15?K and?Ambient Pressure

Apparent molar volumes (V _2,φ ) and heat capacities (C _p2,φ ) of glycine in known concentrations (1.0, 2.0, 4.0, 6.0, and 8.0 mol⋅kg⁻¹) of aqueous formamide (FM), acetamide (AM), and N,N-dimethylacetamide (DMA) solutions at T=298.15 K have been calculated from relative density and specific heat capacity measurements. These measurements were completed using a vibrating-tube flow densimeter and a Picker flow microcalorimeter, respectively. The concentration dependences of the apparent molar data have been used to calculate standard partial molar properties. The latter values have been combined with previously published standard partial molar volumes and heat capacities for glycine in water to calculate volumes and heat capacities associated with the transfer of glycine from water to the investigated aqueous amide solutions, D[`(V)]<sub>2,tr</sub><sup>o</sup>\Delta\overline{V}_{\mathrm{2,tr}}^{\mathrm{o}} and D[`(C)]_p2,tr^o\Delta\overline{C}_{p\mathrm{2,tr}}^{\mathrm{o}} respectively. Calculated values for D[`(V)]<sub>2,tr</sub><sup>o</sup>\Delta\overline{V}_{\mathrm{2,tr}}^{\mathrm{o}} and D[`(C)]_p2,tr^o\Delta\overline{C}_{p\mathrm{2,tr}}^{\mathrm{o}} are positive for all investigated concentrations of aqueous FM and AM solutions. However, values for D[`(C)]_p2,tr^o\Delta\overline{C}_{p\mathrm{2,tr}}^{\mathrm{o}} associated with aqueous DMA solutions are found to be negative. The reported transfer properties increase with increasing co-solute (amide) concentration. This observation is discussed in terms of solute + co-solute interactions. The transfer properties have also been used to estimate interaction coefficients.     

Thermochemical Study of Solvation of Aliphatic Carboxamides in Aqueous Formamide Solutions

The entahlpies of solution of formamide, acetamide, and propionamide in aqueous formamide solutions (formamide concentration 8 mol kg^-1) at 298.15 K were measured. The entahlpies of transfer of amides from water to the mixed aqueous-organic solvent were calculated and compared with published data on the enthalpies of transfer of amides into aqueous urea solutions. The opposite trend in variation of the enthalpies of transfer of amides in these systems with increasing concentration of the nonaqueous component is due to different proton-donor power of formamide and urea relative to water. The enthalpy coefficients of pair interaction of amides with formamide in ternary aqueous solutions were calculated. Their positive values are due to endothermic interaction with formamide of the alkyl groups of amide molecules. The relative hydrophobicity of amides with different degrees of substitution of the amide group was estimated.     

甘氨酸从水到有机物水溶液的迁移焓研究

蛋白质是各种生物形态结构和生命活动所依赖的物质基础,在水溶液中蛋白质天然结构的稳定性归结于氨基酸残基之间以及与溶液中其它组分的相互作用．天然环境中存在的众多物质对蛋白质的溶解度、变性行为和解缔等都有很大的影响．为深入了解蛋白质折叠与解折叠过程中的物理化学现象,以氨基酸、肽、酰胺及其衍生物作为蛋白质模型分子的热力学研究引起了广泛重视．     

Freezing temperatures and enthalpies of dilution of aqueous solutions of amides. Gibbs energies and enthalpies of interaction of the N,N-dimethylamide group in aqueous solutions

Enthalpies of dilution, freezing temperatures, and densities of aqueous solutions of N,N-dimethylacetamide and N,N-dimethylpropionamide have been measured. Freezing temperatures of dilute aqueous solutions of formamide and N,N-dimethylformamide have also been measured. These data yield the pairwise molecular Gibbs energies and enthalpies of interaction: these have been treated according to a group additivity principle to give pairwise functional group Gibbs energies and enthalpies of interaction. The results indicate that substitution on the amide nitrogen may increase the Gibbs energy and enthalpy of interaction of the amide group with itself in an aqueous environment but the effect if present is small.     

DMF-H_2O缔合体系的~1HNMR研究

DMF水溶液是一种生物分子水溶液的简单生化模型。测量了DMF-H_2O体系不同 温度下全浓度范围的~1H NMR数据，对体系中的缔合情况进行了讨论，基于H_2O, H_2O·DMF, (H_2O)_2和(DMF)_2·H_2O的缔合平衡建立了化学缔合模型，采用最 小二乘法拟合实验数据，联合遗传算法和Levenberg-Marquardt算法对模型参数进 行全局寻优求解得不同温度的缔合平衡常数K，再根据不同温度的K求得缔合平衡的 ΔH和ΔS。为了更好地理解DMF水溶液中分子间的相互作用，还测量了298 K下DMF- CCl_4和DMF-BuOH体系全浓度范围的~1H NMR数据作为比较，结合NMR的基本原理对 各DMF溶液体系~1H NMR的实验现象进行了分析和解释，认为水溶液的特殊结构、氢 键和DMF酰胺基的共轭体系是影响DMF-H_2O体系~1H NMR的主要因素。     

Enthalpies of transfer of amino acids from water to aqueous solutions of formamide

Enthalpies of solution of glycine, l-alanine, l-serine in water and aqueous solutions of formamide were measured at 298.15 K. Transfer enthalpies of amino acids from water to aqueous solutions of formamide were derived and interpreted qualitatively with hydration co-sphere overlap model. The results show that the structure interaction between formamide and zwitterionic head-group and hydrophilic side chain of amino acids make a negative contribution to transfer enthalpy, while that with the hydrophobic side chain is positive. In the solvent composition range studied, transfer enthalpies decrease overall with the increasing concentration of formamide, with the relative order of l-serine < glycine < l-alanine.     

The enthalpies of interaction of glycine with some amides and ureas in water at 25°C

Measurement of solution enthalpyiesof glycine in aqueous solutions of formamide (F), N-methylformamide (NMF), N,N-dimethylformamide (DMF), monomethylurea (MMU), 1,3-diethylurea (DEU) and tetramethylurea (TMU) at 25°C have been undertaken. On the basis of the results, enthalpic coefficients of heterotactic interactions between a glycine zwitterion and a molecule of organic substance in aqueous solutions have been calculated. Using the additivity of groups concept by Savage and Wood (SWAG), contributions of each functional group of studied amides and ureas have been estimated. In this model a zwitterion of glycine has been considered as an individual equal to a single functional group.     

Thermochemistry of the dissolution of DL-α-alanyl-DL-norleucine in aqueous solutions of amides at 298.15 K

Enthalpies of the dissolution of DL-α-alanyl-DL-norleucine are determined by calorimetry in aqueous solutions of formamide (FA), N-methylformamide (MFA), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMA) at a concentration of amides of x ₂ = 0–0.4 molar parts and T = 298.15 K. Standard values of enthalpies of dissolution Δ_sol H ^o and Δ_tr H ^o of DL-α-alanyl-DL-norleucine transfer from water to binary solvent are calculated, along with the enthalpy coefficients of pair interactions h _xy of DL-α-alanyl-DL-norleucine with amide molecules. The effect of the composition of water-organic mixtures and the structure of amides on the enthalpy characteristics of dissolution and transition of DL-α-alanyl-DL-norleucine is considered. Quantitative estimates of the contributions to energy from DL-α-alanyl-DL-norleucine-amides pair interactions determined by the polarity, polarizability, and electron acceptor and electron donor ability of organic cosolvents are given using the Kamlet-Taft correlation equation.     

Thermodynamic Parameters of Solvation and Complexing of Copper(II) Nitrate and Nickel(II) Nitrate in Water + Acetamide Mixtures at 298.15 K

The heats of mixing of aqueous solutions of copper(II) or nickel(II) nitrate in water + acetamide (AA) mixtures in the existing range of amide concentrations have been studied. A rise in the amide concentration enhances solvation more strongly in copper(II) salt solutions. Data are analyzed with reference to previous results on the enthalpies of transfer of the salts studied in water + formamide (FA) and water + N,N-dimethylformamide (DMF) mixtures. Electronic absorbance spectra have been recorded at a fixed electrolyte concentration for all thermochemically studied systems, and a linear correlation has been found between the enthalpy of transfer of Cu(NO₃)₂ and the optical density of the solution. The enhanced solvation of copper(II) nitrate in aqueous acetamide is due to inner-sphere interactions between the cation and acetamide; that of nickel(II) nitrate is more due to outer-sphere interactions.     

Hydration of simple amides. FTIR spectra of HDO and theoretical studies

The hydration of formamide (F), N-methylformamide (NMF), N,N-dimethylformamide (DMF), acetamide (A), N-methylacetamide (NMA), and N,N-dimethylacetamide (DMA) has been studied in aqueous solutions by means of FTIR spectra of HDO isotopically diluted in H2O. The difference spectra procedure has been applied to remove the contribution of bulk water and thus to separate the spectra of solute-affected HDO. To facilitate the interpretation of obtained spectral results, DFT calculations of aqueous amide clusters were performed. Molecular dynamics (MD) simulation for the cis and trans forms of NMA was also carried out for the SPC model of water. Infrared spectra reveal that only two to three water molecules from the surrounding of the amides are statistically affected, from among ca. 30 molecules present in the first hydration sphere. The structural-energetic characteristic of these solute-affected water molecules differs only slightly from that in the bulk and corresponds to the clathrate-like hydrogen-bonded cage typical for hydrophobic hydration, with the possible exception of F. MD simulations confirm such organization of water molecules in the first hydration sphere of NMA and indicate a practical lack of orientation and energetic effects beyond this sphere. The geometry of hydrogen-bonded water molecules in the first hydration sphere is very similar to that in the bulk phase, but MD simulations have affirmed subtle differences recognized by the spectral method and enabled their understanding. The spectral data and simulations results are highly compatible. In the case of F, NMF, and A, there is a visible spectral effect of water interactions with N-H groups, which have destabilizing influence on the amides hydration shell. There is no spectral sign of such interaction for NMA as the solute. The energetic stability of water H-bonds in the amide hydration sphere and in the bulk fulfills the order: NMA > DMA > A > NMF > bulk > DMF > F. Microscopic parameters of water organization around the amides obtained from the spectra, which have been used in the hydration model based on volumetric data, confirm the more hydrophobic character of the first three amides in this sequence. The increased stability of the hydration sphere of NMA relative to DMA and of NMF relative to DMF seems to have its origin in different geometries, and so the stability, of water cages containing the amides.