Chiral recognition by enantioselective liquid chromatography: Mechanisms and modern chiral stationary phases

An overview of the state-of-the-art in LC enantiomer separation is presented. This tutorial review is mainly focused on mechanisms of chiral recognition and enantiomer distinction of popular chiral selectors and corresponding chiral stationary phases including discussions of thermodynamics, additivity principle of binding increments, site-selective thermodynamics, extrathermodynamic approaches, methods employed for the investigation of dominating intermolecular interactions and complex structures such as spectroscopic methods (IR, NMR), X-ray diffraction and computational methods. Modern chiral stationary phases are discussed with particular focus on those that are commercially available and broadly used. It is attempted to provide the reader with vivid images of molecular recognition mechanisms of selected chiral selector–selectand pairs on basis of solid-state X-ray crystal structures and simulated computer models, respectively. Such snapshot images illustrated in this communication unfortunately cannot account for the molecular dynamics of the real world, but are supposed to be helpful for the understanding. The exploding number of papers about applications of various chiral stationary phases in numerous fields of enantiomer separations is not covered systematically.     

RSM and ANN modeling-based optimization approach for the development of ultrasound-assisted liposome encapsulation of piceid

Piceid, a naturally occurring derivative of resveratrol found in many plants, has recently been considered as a potential nutraceutical. However, its poorly water-soluble property could cause a coupled problem of biological activities concerning drug dispersion and absorption in human body, which is still unsolved now. Liposome, a well-known aqueous carrier for water-insoluble ingredients, is commonly applied in drug delivery systems. In this study, a feasible approach for solving the problem is that the targeted piceid was encapsulated into a liposomal formula as aqueous substrate to overcome its poor water-solubility. The encapsulation process was assisted by ultrasound, with investigation of lipid content, ultrasound power and ultrasound time, for controlling encapsulation efficiency (E.E%), absolute loading (A.L%) and particle size (PS). Moreover, both RSM and ANN methodologies were further applied to optimize the ultrasound-assisted encapsulation process. The data indicated that the most important effects on the encapsulation performance were found to be of lipid content followed by ultrasound time and ultrasound power. The maximum E.E% (75.82%) and A.L% (2.37%) were exhibited by ultrasound assistance with the parameters of 160 mg lipid content, ultrasound time for 24 min and ultrasound power of 90 W. By methodological aspects of processing, the predicted E.E% and A.L% were respectively in good agreement with the experimental results for both RSM and ANN. Moreover, RMSE, R² and AAD statistics were further used to compare the prediction abilities of RSM and ANN based on the validation data set. The results indicated that the prediction accuracy of ANN was better than that of RSM. In conclusion, ultrasound-assisted liposome encapsulation can be an efficient strategy for producing well-soluble/dispersed piceid, which could be further applied to promote human health by increased efficiency of biological absorption, and the process of ultrasound-mediated liposome encapsulation can be well established by a methodological approach using either RSM or ANN, but it is worth mentioning that the ANN model used here showed the superiority over RSM for predicting and optimizing encapsulation.     

Highly sensitive optical humidity probe

A highly sensitive optical humidity probe based on reflectance measurements has been developed using Nafion^®-crystal violet (CV) films. This sensor can be used to calibrate relative humidity (RH) in the range 0-0.25% with a detection limit (blank signal + 3σ_b, where σ_b = the standard deviation (S.D.) of the blank signal) of 0.018% RH (∼4.37 ppm) and exhibited low hysteresis. The sensor films were fully reversible in dry nitrogen and reversal times were shown to be dependent on exposure time and % RH. The response to 1% RH was highly reproducible (S.D. = 1.67%, number of samples (n) = 5). Hydrogen chloride gas did not interfere with the response of the sensor to RH but did reduce sensor reversal times. This sensor displayed sufficient sensitivity that it could be used to detect ppm levels of moisture in process gases such as nitrogen and HCl.     

Polarography and artificial neural network for the simultaneous determination of nalidixic acid and its main metabolite (7-hydroxymethylnalidixic acid)

Nalidixic acid (NA) and its main metabolite, 7-hydroxymethylnalidixic acid (OH-NA), are simultaneously determined by applying artificial neural networks (ANNs), to their square wave voltammetric signals. The scores of a PCR model, built with the voltammetric data of a set of standard samples, recorded between −0.70 and −1.0 V, are used as training set for the net for each compound. The trained nets (ANNs) are used for the simultaneous determination of NA and OH-NA in urine. The recovery values are comprised between 91 and 109% for NA and between 82 and 112% for OH-NA, being these results better than the results obtained by application of partial least squares (PLS) multivariate calibration.     

人工神经网络法预测核苷及核酸碱基的疏水分配系数

用人工神经网络方法预测核苷及核酸碱基一类化合物的ｌｇＰ值,预测精度显著优于ＢｌｇＰ法和ＡｌｇＰ法,根据预测结果讨论了分子内氢健及分子构象柔顺性对这类化合物疏水性的影响。     

HIV-1逆转录酶抑制剂2-氨基6-苯磺酰基苄腈及其类似物活性OSAR研究

首先利用半经验AM I量子化学方法计算了54个2-氨基-6-苯磺酰基苄腈及其类似物的物理化学、电子结构、指示变量等共28个参数,然后使用偏最小二乘,穷举回归和混沌遗传乘法训练的人工神经网络方法建立了这些参数和其抑制H IV-1逆转录酶活性之间的定量构效关系模型,为设计、合成更高生物活性的该类化合物提供了理论参考。     

有机化合物热力学性质的预测(Ⅲ)——人工神经网络法预测烷烃的生成焓

采用分子子图编码方法将烷烃的分子子图码作为人工神经网络(ANN)的输入参数 ,对烷烃的生成焓进行预测 ,取得了满意的结果 ,其拟合方程的回归系数达到 0 .9845     

基于BP-ANN和PLS的近红外光谱无损检测李果实品质的研究

可溶性固形物(SSC)和可滴定总酸(TA)含量是影响李果实品质的重要指标,经典的破坏性检测方法不适用于果实按品质分级,近红外光谱(NIRS)检测方法具有速度快、操作简便、可无损检测果实品质。为实现NIRS无损快速检测安哥诺李果实可溶性固形物和可滴定总酸含量,利用NIRS采集李果实的漫反射光谱,同时采用糖度计测定安哥诺李果实的SSC,采用滴定法测定了李果实TA含量,使用杠杆值和F概率值剔除异常样品,采用软件优化结合人工筛选光谱波段,使用了消除常数偏移量、减去一条直线、矢量归一化(SNV)、最大-最小归一化、多元散射校正(MSC)、一阶和二阶导数结合平滑处理、一阶导数结合减去一条直线和平滑处理、以及一阶导数结合SNV或MSC校正等光谱预处理方法,分别采用偏最小二乘法(PLS)和主成分分析结合反向传播人工神经网络(BP-ANN)建立李果实SSC、 TA的定量分析模型。结果表明,李果实SSC和TA的最佳PLS建模效果波段范围分别为4 000～8 852和4 605～6 523 cm^-1。SSC的PLS模型的最佳光谱预处理方法为MSC校正,最佳模型校正相关系数(R_...     

计算分子中原子净电荷的新方法及芳烃亲电取代反应定位效应的定量处理

本文提出一种简捷计算分子中原子净电荷的新方法。用这种方法计算了２３种一元取代苯的原子净电荷。计算所得苯环上碳原子净电荷与其￣（１３）Ｃ－ＮＭＲ化学位移有良好的线性关系。利用苯环上碳原子净电荷及立体参数作为输入参数，应用人工神经网络方法预报２４种一元取代苯硝化反应的邻、间、对位产物产率，结果良好。