多壁碳纳米管键合硅胶固定相的保留机理研究

制备了3种不同键合量的多壁碳纳米管键合硅胶固定相。以芳香族化合物为目标分析物,甲醇-水为流动相,分别考察了其在不同流动相比例、流速、柱温条件下,酸性、中性、碱性化合物的色谱保留行为,并通过计算分离过程中焓变、熵变和吉布斯自由能等热力学参数,探讨了色谱柱的保留机理。结果表明,碳纳米管键合硅胶与未键合的硅胶固定相分离对氨基苯磺酸和尿嘧啶时,因碳纳米管的加入增强了其疏水作用,保留机理与反相色谱柱相似。而分离中性化合物时,因加入的碳纳米管引入π-π作用,增强了对化合物的保留,有效地提高了色谱柱的柱效。碳纳米管的加入使溶质分子在固定相上的保留增强,溶质分子从杂乱无序排列转为有序排列,且溶质分子在不同碳纳米管键合量的色谱柱上的保留并非由单一机理支配,而是由多种作用相互协同的结果,这使碳纳米管键合硅胶固定相在分离和固相萃取领域展现出良好的应用前景。     

Direct Chiral Separation of γ-Schizandrin Enantiomers by RP-HPLC Using Chiralcel OD-RH

采用反相手性色谱柱Chiralcel OD-RH(纤维素3,5-二甲基苯基氨基甲酸酯涂敷在5μm硅胶上)建立了五味子乙素对映体的反相高效液相色谱拆分方法.考察了流动相组成、柱温和流速对五味子乙素手性对映体拆分的影响.以甲醇-水(90∶10)为流动相,流速0.5 mL/min,柱温20℃,检测波长254 nm,在Chiralcel OD-RH手性柱上成功拆分了五味子乙素对映体,其中R-构型先出峰.用Ink对1/T作图得到的Van’t Hoff曲线具有良好线性,相关系数(r)均大于0.99,计算了对映体与固定相相互作用的焓变以及焓变差值和熵变差值等热力学参数.结果显示,五味子乙素对映体的拆分过程为焓控过程,即氢键、π-π及偶极-偶极等作用方式对对映体的拆分起重要作用.     

Chiralcel OD-RH直接拆分五味子乙素对映体

采用反相手性色谱柱Chiralcel OD-RH(纤维素3,5二甲基苯基氨基甲酸酯涂敷在5 μm硅胶上)建立了五味子乙素对映体的反相高效液相色谱拆分方法。考察了流动相组成、柱温和流速对五味子乙素手性对映体拆分的影响。以甲醇-水(90∶10)为流动相,流速0.5 mL/min,柱温20 ℃,检测波长254 nm,在Chiralcel OD-RH手性柱上成功拆分了五味子乙素对映体,其中R-构型先出峰。用lnk对1/T作图得到的Van-t Hoff曲线具有良好线性,相关系数（r）均大于0.99,计算了对映体与固定相相互作用的焓变以及焓变差值和熵变差值等热力学参数。结果显示,五味子乙素对映体的拆分过程为焓控过程,即氢键、π-π及偶极-偶极等作用方式对对映体的拆分起重要作用。     

联苯类对映体在纤维素类手性固定相上的高效液 相色谱法直接拆分

涂敷纤维素-三(3,5-二甲基苯基氨基甲酸酯)于自制的球形氨丙基硅胶上,制备了手性固定相。用该固定相直接拆分了一系列外消旋联苯类保肝药物。考察了柱温和流动相中乙醇含量对样品的保留和立体选择性的影响,升高柱温或增大流动相中乙醇含量都会使对映体的保留因子和分离因子降低。氨考察榈的分离因子的对数与温度的倒数成线性关系。确定了对映体从流动相传递到固定相的吉布斯自由能变之差值、焓变之差值及熵变之差值。     

液相色谱过量热力学函数变化规律性探讨

本文从溶液热力学和色谱理论推导出过量热力学函数与色谱参数间的关系, 测定了苯的同系物在液-液分配过程中, 过量焓变等函数与流动相组成、样品碳数的线性关系,并求得经验方程式. 同时研究了不同样品焓变和熵变的线性补偿规律. 并试图从溶液理论进行计算.     

高效金属有机骨架气相色谱固定相的理性设计北大核心CSCD

金属有机骨架材料(MOFs)由金属离子或金属簇与有机配体组装而成,其中多变的金属中心和有机配体使其具有高度可调性,这为调控高效气相色谱分离性能奠定了良好的结构基础。热力学作用力是描述分析物与固定相相互作用的基本指标,保留因子、麦氏常数、焓变与熵变等热力学值可以反映热力学作用力的相对大小。在微观层面上,可以通过设计MOFs孔隙内的多元作用力以开展热力学性质的研究,如设计金属亲和性、π-π相互作用、极性、手性位点等,这些热力学作用力可为分离具有微小差异的分析物提供有利环境。在动力学方面,MOFs的孔径大小与形状、颗粒尺寸、堆积模式对分析物的动力学扩散速率有着重要的影响,从改善分析物的动力学扩散角度出发,通过选择合适的孔径尺寸与形状、降低MOFs的颗粒尺寸、调控MOFs的堆积模式等手段,均可以提高气相色谱固定相的分离性能。根据色谱动力学统一方程和范蒂姆特方程计算扩散系数、理论塔板高度等动力学值,可有效评价色谱峰峰形和色谱柱柱效。在分离过程中,分析物的热力学作用力和动力学效应是协同作用的,且缺一不可。因此,本文从热力学与动力学两个角度提出了构建高效MOFs气相色谱固定相的设计思路,希望能为相关领域的研究提供一定帮助。     

磺化杯[4]芳烃与双正电荷季铵盐的键合作用

采用核磁波谱和等温微量热滴定等手段研究了磺化杯[4]芳烃与3个双正电荷季铵盐相互作用的键合比、 键合模式以及热力学参数. 结果表明, 磺化杯[4]芳烃与3个双正电荷季铵盐以不同的键合模式形成1: 1络合物, 其键合常数均超过10⁵ L/mol, 键合作用主要由焓变驱动, 同时伴随着微弱的正负熵变.     

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.     

甲氨蝶呤与牛血清白蛋白相互作用的光谱和分子对接研究

利用紫外-可见吸收光谱法、傅立叶红外光谱法和分子对接技术研究了抗癌药物甲氨蝶呤与牛血清白蛋白的相互作用。紫外光谱发现,在298 K和308 K,甲氨蝶呤与牛血清白蛋白结合常数分别为5.28×105L/mol和6.14×105L/mol,通过热力学计算得到反应的焓变和熵变。热力学函数说明甲氨蝶呤与牛血清白蛋白之间的作用力主要为疏水作用力。红外光谱表明甲氨蝶呤与牛血清白蛋白分子中氨基酸残基的硫及氮原子形成键合作用。结合AutoDock 4.2分子对接软件模拟研究了二者的键合模式和键合机制,表明甲氨蝶呤与牛血清白蛋白的相互作用力主要是疏水作用。     

姜黄素键合硅胶固定相的制备、表征及色谱性能

通过γ-［(2,3)-环氧丙氧］丙基三甲氧基硅烷(KH-560)偶联剂将具有抗菌功能的植物有效成分姜黄素键合到硅胶上,制备了姜黄素液相色谱键合硅胶固定相(CCSP)。采用元素分析、红外光谱和热分析对该固定相结构进行了表征。以甲醇和水为二元流动相,不同的中性、酸性和碱性化合物为溶质探针,并用ODS柱作参比,对固定相的色谱性能及保留机理进行了研究。研究结果表明,姜黄素键合固定相不仅具有良好的反相色谱性能,同时由于配体结构中所含有的基团形成了含芳环的共轭体系,从而引入了n-π和π-π作用位点,所含的羟基和β-二羰基与溶质之间存在偶极-偶极和氢键作用,与ODS相比,该固定相在极性化合物分离中占优势,且分析速度较快。     

高效液相色谱-串联质谱法结合多糖衍生物手性固定相拆分氰戊菊酯

建立了以多糖衍生物为手性固定相的高效液相色谱-串联质谱(HPLC-MS/MS)直接拆分氰戊菊酯对映体的方法。在反相液相色谱条件下,考察了手性固定相的种类、流动相组成、柱温、流速对氰戊菊酯4个立体异构体分离的影响。同时,利用热力学方法对氰戊菊酯的立体异构体与固定相之间的色谱保留和分离的热力学机理进行了探讨。结果表明:采用Lux Cellulose-3(纤维素-三(4-甲基苯甲酸酯))手性色谱柱,在以流动相为乙腈-水(5 mmol/L甲酸铵)=(55:45,V:V)流速0.4 mL/min,柱温30℃的条件下,可在14 mins内实现氰戊菊酯4个立体异构体的基线分离。拓展了HPLC-MS/MS在菊酯类手性农药对映体分离及检测上的应用。     

Effects of temperature on retention of chiral compounds on a ristocetin A chiral stationary phase

The isocratic retention of enantiomers of chiral analytes, i.e. tryptophan, 1,2,3,4-tetrahydroisoquinoline and gamma-butyrolac tone analogs, was studied on a ristocetin A chiral stationary phase at different temperatures and with different mobile phase compositions, using the reversed-phase, polar-organic and normal-phase modes. By variation of the both mobile phase composition and the temperature, baseline separations could be achieved for these enantiomers. The retention factors and selectivity factors for the enantiomers of all investigated compounds decreased with increasing temperature. The natural logarithms of the retention factors (ln k) of the investigated compounds depended linearly on the inverse of temperature (1/T). van't Hoff plots afforded thermodynamic parameters, such as the apparent change in enthalpy (deltaH(o)), the apparent change in entropy (deltaS(o)) and the apparent change in Gibbs free energy (deltaG(o) ) for the transfer of analyte from the mobile to the stationary phase. The thermodynamic parameters (deltaH(o), deltaS(o) and deltaG(o)) were calculated in order to promote an understanding of the thermodynamic driving forces for retention in this chromatographic system.     

Determination of methylamphetamine and related compounds in human urine by high performance liquid chromatography/electrospray/mass spectrometry

The influence of tetrabutylammonium (TBA) as a hydrophobic charged additive of the mobile phase was investigated in a chromatographic system involving d,l-dansyl amino acids as the test solute enantiomers and immobilized human serum albumin as the chiral stationary phase. By varying the column temperature, van't Hoff plots for solute retention and enantioselectivity were performed and thermodynamic parameters were calculated. An enthalpy-entropy compensation study revealed that the type of interaction between the analyte and stationary phase was independent of TBA concentration in the eluent. The counterion dependence on retention indicated that the coulombic interactions between dansyl amino acid and the site II binding cavity were of crucial importance in this association process. Also, the increasing variations of chiral discrimination with a TBA addition were attributed, by an analysis of the thermodynamic parameter trends, to a great facilitation of enantioselective H-bonding between solute and polar residues at the cavity rim.     

An assessment of the retention behaviour of polycyclic aromatic hydrocarbons on reversed phase stationary phases--thermodynamic behaviour on C18 and phenyl-type surfaces

The thermodynamic retention behaviour of a linear series of polycyclic aromatic hydrocarbons (PAHs) was investigated on C18 and selected phenyl-type reversed-phase stationary phases, namely C18, C18 Aqua, Propyl-phenyl and Synergi polar-RP stationary phases, using methanol mobile phases. The Propyl-phenyl stationary phase, despite having the lowest surface coverage, was found to exhibit significantly larger enthalpic interactions to the other Phenyl-type phase (Synergi polar-RP) even though this had a much higher surface coverage. This indicated that stronger interactions between the PAHs and the stationary phase ligands were occurring on the Propyl-phenyl phase. Evaluation of the elution band profile of the PAHs in the aqueous methanol mobile phase revealed fairly symmetrical bands for the C18, C18 Aqua and Synergi polar-RP, but severe peak tailing on the Propyl-phenyl phase. A change in mobile phase from methanol to acetonitrile improved the peak shape of the PAHs on the Propyl-phenyl phase, leading to the assumption that unfavourable pi-pi interactions were occurring between the electron-rich PAHs and the electron-rich phenyl rings of the Propyl-phenyl phase.     

Characterisation of reversed-phase stationary phases for the liquid chromatographic analysis of basic pharmaceuticals by thermodynamic data

This paper describes the characterisation of reversed-phase liquid chromatography (RPLC) columns using thermodynamic measurements. Retention versus 1/T data were used to construct Van't Hoff plots. The slope of these plots indicates the standard enthalpy of transfer of the analyte from the mobile to the stationary phase. The standard entropy can be calculated from the intercept. Van't Hoff plots were linear for the investigated RPLC columns, meaning that for basic analytes over the temperature range studied no changes in the retention mechanism occurred. Enthalpies and entropies of transfer of basic analytes from the mobile to the stationary phase revealed information about the types of interaction of protonated and neutral compounds with the stationary phases. However, a clear view using the present set of basic compounds on how these thermodynamic data may explain the observed substantial differences in peak symmetry cannot be given. It is considered that addition of N,N-dimethyloctylamine (DMOA) to the eluent will results in a dynamically coating of the stationary phase. Addition of DMOA to the eluent resulted for protonated basic compounds in a reduction of both enthalpy and entropy. In practice, with DMOA in the eluent symmetrical peaks were obtained. It is assumed that this is due to blocking residual silanols and/or ion exclusion effects.     

温度对蛋白和β-环糊精手性固定相拆分对映体的影响

 采用三聚氯氰为活化剂分别合成了牛血清白蛋白 (BSA)、人血清白蛋白 (HSA)和 β 环糊精手性固定相 ,研究了温度在色氨酸 ,华法令 ,酮基布洛芬和丹酰化苏氨酸手性拆分中的影响。结果表明 ,在蛋白手性固定相上对映体间的熵变对色氨酸 ,华法令和酮基布洛芬的拆分有很大的影响 ,而丹酰化苏氨酸对映体在 β 环糊精手性固定相上的拆分为典型的焓控过程 ,与蛋白柱有着不同的热力学特性。由于键合方式不同 ,色氨酸在我们合成的BSA手性固定相上的最佳分离温度为 35℃左右 ,而不是文献报道的以戊二醛为活化剂的 2 4℃。     

分子烙印聚合物的结构表征及手性拆分中的热力学研究

考察了一系列分子烙印聚合物的热稳定性和孔结构,探讨了孔结构与手性选择性的关系。计算了手性分离过程中的某些热力学参数的变化,发现分子烙印聚合物上的手性分离是一个焓控制的过程,热力学参数的变化同烙印分子的结构有关。     

Cyclofructan 6 based stationary phases for hydrophilic interaction liquid chromatography

New stationary phases for hydrophilic interaction liquid chromatography (HILIC) were synthesized by covalently attaching native cyclofructan 6 (CF6) to silica gel. The chromatographic characteristics of the new stationary phases were evaluated and compared to three different types of commercial HILIC columns. The CF6 columns produced considerably different retention and selectivity patterns for various classes of polar analytes, including nucleic acid compounds, xanthines, β-blockers, salicylic acid and its derivatives, and maltooligosaccharides. Univariate optimization approaches were examined including organic modifier (acetonitrile) contents and buffer pH and salt concentration. The thermodynamic characteristic of the CF6 stationary phase was investigated by considering the column temperature effect on retention and utilizing van't Hoff plots. CF6 based stationary phases appear to have exceptionally broad applicability for HILIC mode separations.     

Chitin as Stationary Phase in Thin-Layer Chromatography–Application of Chromatographic Process Optimization Theory for Chitin Layers

Abstract

This paper describes initial of two basic theories of adsorption thin-layer chromatography potimization namely thermodynamic adsorption theory and theory based on mass action law, so called Snyder s theory in chromatographic systems containing chitin as stationary phase on wchich various amino acids were chromatographed. The results obtained were comparable to those obtained for analogous chromatographic systems containing silica gel as stationary phase. Comparison of applicability of these theories for well investigated silica gel and for not enough investigate chitin will permit to draw introductory conclusions about the processes carrying in the chromatographic systems containing chitin as stationary phase.     

Chiral separations of pesticide enantiomers by high-performance liquid chromatography using cellulose triphenylcarbamate chiral stationary phase

The direct chiral separations of pesticide enantiomers by high-performance liquid chromatography by applying self-prepared cellulose triphenylcarbamate chiral stationary phase are performed. The mobile phase is n-hexane modified by isopropanol as a polar modifier. Nine chiral pesticides (benalaxyl, vinclozolin, diclofop-methyl, tebuconazole, quizalofop-ethyl, hexaconazole, lactofen, isocarbophos, and paclobutrazol) show enantioselectivity on the chiral stationary phase. An online circular dichrorism detector is used for identifying the pesticide enantiomers. The influences of the volume content of isopropanol and column temperature on the separations are investigated. The thermodynamic parameters related to the chiral distinguish mechanisms are also calculated.