反相液相色谱中计量置换线性参数logI的热力学特征

依据液相色谱中溶质计量置换保留模型及线性参数 log I(与 1mol溶质对固定相的亲和势大小有关的常数 ) ,通过作图得知非极性和极性小分子溶质及生物大分子的 log I与绝对温度的倒数 1/T,以及小分子溶质的log I与其在正辛醇 -水中分配系数的对数 log Po/ w呈线性关系 ,从两方面进一步证明了 log I具有热力学平衡常数的性质。基于小分子溶质、生物大分子的 log I和分配系数大小的差别 ,对两者在反相液相色谱中的保留对柱长的依赖关系给予了定量的说明     

MECC保留值与logP的相关性

研究了不同有机改性剂下胶束电动毛细管色谱 (MECC)中电中性化合物的保留值与其正辛醇 水分配系数 (logP)间的相关性。结果表明 :溶质在MECC中的保留值 (logk′)与logP的相关性决定于MECC体系在分配行为上与正辛醇 水体系的相似性 ,用logk′w 代替logk′并不能改善相关性 ;溶质的受质子碱性是影响相关性的最主要的溶质性质 ;使用有机改性剂可以调节溶质在MECC体系中的分配行为接近于正辛醇 水体系 ,THF是调节溶质受质子碱性的影响的最佳有机改性剂 ;要使MECC体系在溶质分配行为上全面接近于正辛醇 水体系 ,同时加入两种作用相互补充的有机改性剂可能是更好的方法     

反相液相色谱中计量置换线性参数logI的热力学特征

 依据液相色谱中溶质计量置换保留模型及线性参数logI(与1mol溶质对固定相的亲和势大小有关的常数),通过作图得知非极性和极性小分子溶质及生物大分子的logI与绝对温度的倒数1/T,以及小分子溶质的logI与其在正辛醇-水中分配系数的对数logPo/w呈线性关系,从两方面进一步证明了logI具有热力学平衡常数的性质。基于小分子溶质、生物大分子的logI和分配系数大小的差别,对两者在反相液相色谱中的保留对柱长的依赖关系给予了定量的说明。     

用SEC柱和胶束流动相分离小分子的模型

 使用体积排阻色谱 (SEC)柱和胶束流动相成功地分离了一些小分子化合物 ,给出了分离模型。这种分离方式是基于胶束和水相在色谱过程中的不同迁移以及溶质在胶束和水相间的不同分配而实现的 ,其分离的机制与胶束电动色谱 (micellar electrokinetic chromatography,MEKC)十分相似。理论处理的结果表明 ,溶质的保留体积与胶束浓度有关 ;通过溶质的保留体积可得到溶质在胶束和水相间的分配系数。还采用了两种不同的 SEC柱分离了一些脂肪醇 ,验证了这一理论模型 ,测定了它们的分配系数 ,结果表明两种柱测得的小分子醇在胶束和水相中的分配系数具有较好的一致。     

氨基酸在乙醇/磷酸氢二钾双水相体系中分配行为

研究了5种结构和性质各异的氨基酸(谷氨酸,半胱氨酸,苯丙氨酸,赖氨酸,精氨酸)在亲水性有机溶剂乙醇和磷酸盐溶液形成的乙醇/K2HPO4双水相体系中的分配行为及其影响因素。当双水相体系中乙醇的质量分数从22%增加到30%时,半胱氨酸和苯丙氨酸的分配系数明显增大,其它三种氨基酸的分配系数变化幅度不大;当磷酸盐的质量分数从14%增加到22%时,氨基酸的分配系数的变化均不明显;双水相体系的pH值对氨基酸的分配系数影响较大,当pH增加时,5种氨基酸的分配系数均增加,但是当pH约为9.5时,苯丙氨酸、半胱氨酸的分配系数接近相等但与其它3种氨基酸的分配系数相差较多,当pH为6.0~8.0时,苯丙氨酸的分配系数远远大于另外4种氨基酸。氨基酸的支链结构中含有非极性基团将导致其分配系数的增加。     

RE对耐候钢溶质再分配的影响

为研究RE对耐候钢中各元素偏析的影响,进行了不同RE含量的耐候钢定向凝固实验,拉速为15μm.s-1,观察了RE对耐候钢定向凝固试样糊状区的影响,并用电子探针定量分析了耐候钢中各元素的溶质分配系数。结果表明,钢中加入RE可以抑制枝晶生长,细化枝晶,有利于二次枝晶的生长,可以促进等轴晶的生成。RE原子在晶界的富集可以抑制溶质元素在固液界面的析出,提高各元素的非平衡溶质分配系数,可以有效减轻耐候钢的宏观偏析。     

应用反向传播神经网络预测化合物脑血分配系数

选用27种三维结构性质描述符对脑血分配系数预测建立神经网络模型.网络模型选用典型的适合函数逼近的两层结构神经网络对脑血分配系数(lgBB,BB为脑血浓度比)进行预测,计算中采用的模型具有一个双曲正切型激活函数的隐含层和一个线性激活函数的输出层.计算表明,使用小心选择的反向传播神经网络模型对化合物脑血分配系数具有较好的预测能力.     

纳米白藜芦醇脂质体的制备及分配系数测定

采用薄膜旋转蒸发-超声法制备了纳米白藜芦醇脂质体(RES-Lip),并用透射电子显微镜(TEM)和动态光散射技术(DLS)对产物进行表征;测定了膜材比(卵磷脂与胆固醇质量比m PC:m Chol=5:1,8:1,10:1,12:1)和药脂比(药物与卵磷脂质量比m RES:m PC=1:25,1:40,1:50,1:60)对RES-Lip脂质体-水分配系数(Plip/w)的影响,以及油-水分配系数(lg P_(o/w))和脂质体-水分配系数(lgP_(lip/w))随p H值的变化趋势,计算了RES-Lip中药物与磷脂双分子膜之间的吉布斯自由能。结果表明,实验中所制备的RES-Lip呈球形囊泡结构,粒径约为100 nm;当膜材比和药脂比分别为10:1和1:40时,lgP_(lip/w)最大,说明此时RES与磷脂膜间的综合作用力最大;RES-Lip的分配系数(lg P_(o/w)和lgP_(lip/w))随体系p H的变化趋势相同,说明RES与磷脂膜的作用力中以疏水作用为主,氢键、静电作用为辅;RES-Lip中RES与脂质体膜之间的吉布斯自由能为-17.07 k J·mol~(-1)。     

以BPO引发苯乙烯反向ATRP水分散体系中催化剂、乳化剂等在水/油两相分配系数的测定

在以过氧化二苯甲酰(BPO)为引发剂、1,10-邻二氮菲(phen)为催化剂配体、十二烷基磺酸钠(SLS)为乳化剂,水分散体系中进行的苯乙烯(St)的反向原子转移自由基聚合体系中,系统地分析了CuBr2/phen络合物、CuBr/phen络合物、SLS和phen在St/水两相中的分配行为,发现CuBr2/phen络合物、CuBr/phen络合物的两相分配系数对温度有一定的依赖性,结合所得的两相分配系数,从理论上分析了CuBr/CuBr2/phen/BPO乳液聚合体系中的"活性"/可控乳液聚合活性种的数目,较详细的讨论了水分散体系中反向ATRP反应的机理,并通过分相后的本体聚合实验,佐证了测得的催化体系的两相分配系数具有一定的指导意义.     

水溶液中氯化铯与糖(D-葡萄糖、D-果糖和蔗糖)相互作用的热力学参数研究(298.15K)

用钾离子选择性电极为测量电极,氯离子选择性电极为参比电极,设计组成无液接电池,用于氯化铯-糖(葡萄糖、果糖及蔗糖)-水三元体系中组分之间弱相互作用的热力学性质研究.通过测量电池的电动势获得氯化铯在糖水溶液中的活度系数,根据Scatchard理论推测出糖在氯化铯水溶液中的活度系数.通过Mcmillan-Mayer理论将体系的过量热力学函数与溶液中溶质的相互作用参数相关联,获得氯化铯与糖在水溶液中相互作用的吉布斯自由能参数及盐效应常数.运用结构相互作用模型、糖的羟基水化效应及色散能理论,探讨体系中溶质-溶质、溶质-溶剂间的相互作用及糖的立体结构和金属离子体积对热力学参数的影响.     

Mathematical model of computer-programmed intermittent dual countercurrent chromatography applied to hydrostatic and hydrodynamic equilibrium systems

Dual high-speed countercurrent chromatography (dual CCC) literally permits countercurrent flow of two immiscible solvent phases continuously through the coiled column for separation of solutes according to their partition coefficients. Application of this technique has been successfully demonstrated by separation of analytes by gas–liquid and liquid–liquid two-phase systems. However, the method cannot be directly applied to the system with a set of coiled columns connected in series, since the countercurrent process is interrupted at the junction between the columns. However, this problem can be solved by intermittent dual CCC by eluting each phase alternately through the opposite ends of the separation column. This mode of application has an advantage over the conventional dual CCC in that the method can be applied to all types of CCC systems including hydrostatic equilibrium systems such as toroidal coil CCC and centrifugal partition chromatography. Recently, the application of this method to high-speed CCC (hydrodynamic system) has been demonstrated for separation of natural products by Hewitson et al. using a set of conventional multilayer coil separation columns connected in series. Here, we have developed a mathematical model for this intermittent dual CCC system to predict retention time of the analytes, and using a simplified model system the validity of the model is justified by a series of basic studies on both hydrodynamic and hydrostatic CCC systems with a computer-programmed single sliding valve. The present method has been successfully applied to spiral tube assembly high-speed CCC (hydrodynamic system) and toroidal coil CCC (hydrostatic system) for separation of DNP-amino acid samples with two biphasic solvent systems composed of hexane–ethyl acetate–methanol–0.1 M hydrochloric acid (1:1:1:1 and 4:5:4:5, v/v).     

Efficient lipase-catalyzed synthesis of new lipid antioxidants based on a catechol structure

Lipid antioxidants phenolic saturated fatty acid esters were synthesized in high yields and short reaction times using the corresponding ethyl fatty acid esters, lipase from Candida Antarctica, vacuum and no solvent. Phenolic esters with mono- and polyunsaturated fatty acids (EPA and DHA) were also prepared.     

Counter-current chromatography using hexane/surfactant-containing water solvent systems

We developed a n-hexane/surfactant-containing water solvent system in counter-current chromatography (CCC) in order to separate hydrophobic compounds. By using the upper phase as the mobile phase, we have separated steroid samples. Retention times of steroids progesterone and delta4-androstene-3,17-dione increased slightly by increasing the concentration below the critical micellar concentration (CMC) of surfactant sodium 1-heptanesulfonate. However, the retention times increased drastically while the SHS concentrations were above the CMC. The partition of these two steroids in the two phases was significantly dependent on the interaction with micelles. Aromatic hydrocarbons were not retained by the lower phase no matter what the surfactant concentrations were. Their hydrophobic interaction with n-hexane greatly exceeded that with the micellar solution. The retention times of esters, however, were only slightly affected by the surfactant addition even above the CMC. The weaker interaction between esters and the micellar solution was probably due to their higher polarity. The micellar solvent systems provide an alternative way for hydrophobic sample separations in CCC, but the performance is limited.     

pH dependence of the hydrophobicity of beta-blocker amine compounds measured by counter-current chromatography

The octanol-water partition coefficients (Poct) of 17 antiadrenergic beta-blocker compounds were determined by counter-current chromatography (CCC). Since CCC uses a biphasic liquid system, the octanol-water liquid system was used with essentially an octanol stationary phase and aqueous buffer mobile phase. The Poct coefficients were obtained directly without any extrapolation. The measured Poct values were in the 0.0015-4070 range (-2.8 < log Poct < 3.6). Since the beta-blocking agents are ionizable compounds, the Poct values obtained were strongly dependent on the aqueous-phase pH. The apparent Poct coefficients of the beta-blockers were determined at three different pH values (approximately 3, 7 and 11) using 0.01 M ammonium phosphate buffers saturated with octanol. A model allowed us to obtain the molecular and ionic Poct value using the solute pKa with these three experimental octanol-water coefficients. Often, the Poct coefficients of the molecular forms obtained with the CCC method differ significantly from computed literature values and/or experimental values obtained by extrapolation. Relationships between biological properties and hydrophobicity were also examined.     

An interesting two‐phase solvent system and its use in preparative isolation of aconitines from aconite roots by counter‐current chromatography

Two‐phase solvent system plays crucial role in successful separation of organic compounds using counter‐current chromatography (CCC). An interesting two‐phase solvent system, composed of chloroform/ethyl acetate/methanol/water, is reported here, in which both phases contain sufficient organic solvents to balance their dissolving capacities. Adjusting the solvent system to get satisfactory partition coefficients (K values) for target compounds becomes relatively simple. This solvent system succeeded in sample preparation of aconitine (8.07 mg, 93.69%), hypaconitine (7.74 mg, 93.17%), mesaconitine (1.95 mg, 94.52%) from raw aconite roots (102.24 mg, crude extract), benzoylmesaconine (34.79 mg, 98.67%) from processed aconite roots (400.01 mg, crude extract), and yunaconitine (253.59 mg, 98.65%) from a crude extract of Aconitum forrestii (326.69 mg, crude extract).     

Countercurrent Chromatography for the Measurement of the Hydrophobicity of Sulfonamide Amphoteric Compounds

Octanol-water partition coefficients (P _o/w ) of 17 sulfonamides (SAs) were determined by countercurrent chromatography (CCC). The measured P _o/w values were in the 0.002–46 range (–2.65 < log P _o/w < 1.7). The lipophility of these compounds depends on the pH showing a maximum for intermediate values. The apparent P _o/w coefficients of SAs were obtained at 5 pH values: 2, 3, 5, 7 and 11, using 0.01 M ammonium phosphate octanol saturated buffers. A theoretical model linking these values with pH for amphoteric compounds was checked and verified. Often the P _o/w coefficients of the molecular forms obtained with the CCC method differ significantly from literature values obtained using softwares and/or from experimental values calculated with extrapolation. The CCC method allows also the determination of the P _o/w coefficients of the ionic forms of the SAs, cationic forms at low pH values and anionic forms at elevated pHs. The acidity constants were also estimated using the theoretical model. Relationships between SA retention factors obtained by RPLC and hydrophobicity were also discussed.     

Nuclear magnetic resonance-based solvent system selection for counter-current chromatography separation of compounds present in the same high-performance liquid chromatography peak: Flavonoids in barley seedlings as an example

Partition coefficient is a key parameter for counter-current chromatography separation. High-performance liquid chromatography (HPLC) is the most commonly used tool for the screening of partition coefficients. However, HPLC technology is not applicable to the compounds present in the same chromatographic peak. Nuclear magnetic resonance (NMR) technology could easily distinguish compounds according to their characteristic absorption even if they exist in the same HPLC peak. In this study, two flavonoids present in the same HPLC peak were successfully purified by counter-current chromatography with a solvent system screened by NMR to show the great potential of NMR technology in the screening of the partition coefficient of co-efflux compounds. Through NMR screening, an optimized ethyl acetate/n-buthanol/water (7:3:10, v/v/v) system was applied in this study. As a result, two flavonoids, including 4.8 mg of 3′-methoxyl-6′’’-O-feruloylsaponarin and 9.8 mg of 6′’’-O-feruloylsaponarin were separated from 15 mg of the mixture. There is only one methoxy group difference between the two flavonoids. This study provides a new strategy for the screening of counter-current chromatography solvent systems and broadens the application scope of counter-current chromatography.     

Strategies of solvent system selection for the isolation of flavonoids by countercurrent chromatography

Flavonoids form a large class of important naturally occurring bioactive compounds. Their isolation and purification from natural sources can sometimes be very difficult and time‐consuming when traditional phytochemical techniques are used. Countercurrent chromatography (CCC), a support‐free liquid–liquid partition chromatography technique, is very useful for the isolation of polar compounds and its use is increasing in the natural products field. In this paper, we propose strategies of solvent system selection for the isolation of flavonoids by CCC, based on data from the literature, plus incorporation of own practical experiences. The selected references report the isolation of over 300 different flavonoid compounds from more than 100 plant species, using 40 different solvent systems, showing the versatility of this technique. The solvent system hexane‐ethylacetate‐methanol‐water is proposed as a starting point for the separation of samples containing free flavonoids, as it was cited in more than 60% of the papers. A “fine tuning” step is proposed at each level of this solvent family. Other modifications include exchanging the alcohol in the system as well as introducing a fifth solvent. The solvent system ethyl‐acetate‐butanol‐water is proposed as the starting point for glycosylated flavonoids. Other solvent systems are also discussed. The use of gradients is proposed for samples containing both free and glycosylated flavonoids, as the polarity window is larger in these cases. High‐speed countercurrent chromatography was used in 89% of the reviewed data.