Integrating UPLC-MS/MS with in Silico and in Vitro Screening Accelerates the Discovery of Active Compounds in Stephania epigaea.

Traditional Chinese medicines (TCMs) are popular in clinic because of their safety and efficacy. They contain abundant natural active compounds, which are important sources of new drug discovery. However, how to efficiently identify active compounds from complex ingredients remains a challenge. In this study, a method combining UHPLC-MS/MS characterization and in silico screening was developed to discover compounds with dopamine D2 receptor (D2R) activity in Stephania epigaea (S. epigaea). By combining the compounds identified in S. epigaea by UHPLC-MS/MS with reported compounds, a virtual library of 80 compounds was constructed for in silico screening. Potentially active compounds were chosen based on screening scores and subsequently tested for in vitro activity on a transfected cell line CHO-K1-D2 model using label-free cellular phenotypic assay. Three D2R agonists and five D2R antagonists were identified. (-)-Asimilobine, N-nornuciferine and (-)-roemerine were reported for the first time as D2R agonists, with EC50 values of 0.35 ± 0.04 µM, 1.37 ± 0.10 µM and 0.82 ± 0.22 µM, respectively. Their target specificity was validated by desensitization and antagonism assay. (-)-Isocorypalmine, (-)-tetrahydropalmatine, (-)-discretine, (+)-corydaline and (-)-roemeroline showed strong antagonistic activity on D2R with IC50 values of 92 ± 9.9 nM, 1.73 ± 0.13 µM, 0.34 ± 0.02 µM, 2.09 ± 0.22 µM and 0.85 ± 0.08 µM, respectively. Their kinetic binding profiles were characterized using co-stimulation assay and they were both D2R competitive antagonists. We docked these ligands with human D2R crystal structure and analyzed the structure-activity relationship of aporphine-type D2R agonists and protoberberine-type D2R antagonists. These results would help to elucidate the mechanism of action of S. epigaea for its analgesic and sedative efficacy and benefit for D2R drug design. This study demonstrated the potential of integrating UHPLC-MS/MS with in silico and in vitro screening for accelerating the discovery of active compounds from TCMs.

The severity assessment of Parkinson's disease based on plasma inflammatory factors and third ventricle width by transcranial sonography.

BACKGROUND: Predicting Parkinson's disease (PD) can provide patients with targeted therapies. However, disease severity can be roughly evaluated in clinical practice based on the patient's symptoms and signs. OBJECTIVE: The current study attempted to explore the factors linked with PD severity and construct a predictive model. METHOD: The PD patients and healthy controls were recruited from our study center while recording their basic demographic information. The serum inflammatory markers levels, such as Cystatin C (Cys C), C-reactive protein (CRP), RANTES (regulated on activation, normal T cell expressed and secreted), Interleukin-10 (IL-10), and Interleukin-6 (IL-6) were determined for all the participants. PD patients were categorized into early and mid-advanced groups based on the Hoehn and Yahr (H-Y) scale and evaluated using PD-related scales. LASSO logistic regression analysis (Model C) helped select variables based on clinical scale evaluations, serum inflammatory factor levels, and transcranial sonography measurements. The optimal harmonious model coefficient λ was determined via 10-fold cross-validation. Moreover, Model C was compared with multivariate (Model A) and stepwise (Model B) logistic regression. The area under the curve (AUC) of a receiver operator characteristic (ROC), brier score, calibration curve, and decision curve analysis (DCA) helped determine the discrimination and calibration of the predictive model, followed by configuring a forest plot and column chart. RESULTS: The study included 113 healthy individuals and 102 PD patients, with 26 early and 76 mid-advanced patients. Univariate analysis of variance screened out statistically significant differences among inflammatory markers Cys C and RANTES. The average Cys C level in the mid-advanced stage was significantly higher than in the early stage (p < 0.001) but not for RANTES (p = 0.740). The LASSO logistic regression model (λ.1se = 0.061) associated with UPDRS-I, UPDRS-II, UPDRS-III, HAMA, PDQ-39, and Cys C as the included independent variables revealed that the Model C discrimination and calibration (AUC = 0.968, Brier = 0.049) were superior to Model A (AUC = 0.926, Brier = 0.079) and Model B (AUC = 0.929, Brier = 0.071) models. CONCLUSION: The study results show multiple factors are linked with PD assessment. Moreover, the inflammatory marker Cys C and transcranial sonography measurement could objectively predict PD symptom severity, helping doctors monitor PD evolution in patients while targeting interventions.

An integrated strategy for the discovery of quality marker of Dactylicapnos scandens based on phytochemical analysis, network pharmacology and activity screening.

Dactylicapnos scandens (D. scandens) is an ethnic medicine commonly used for the treatment of analgesia. In this study, an integrated strategy was proposed for the quality evaluation of D. scandens based on "phytochemistry-network pharmacology-effectiveness-specificity" to discover and determine the quality marker (Q-marker) related to analgesia. First, phytochemical analysis was conducted using UPLC-Q-TOF-MS/MS and a self-built compound library, and 19 components were identified in D. scandens extracts. Next, the "compounds-targets" network was constructed to predict the relevant targets and compounds related to analgesia. Then, the analgesic activity of related compounds was verified through dynamic mass redistribution (DMR) assays on D2 and Mu receptors, and 5 components showed D2 antagonistic activity with IC50 values of 39.2 ± 14.7 µM, 5.46 ± 0.37 µM, 17.5 ± 1.61 µM, 7.89 ± 0.79 µM and 3.29 ± 0.73 µM, respectively. Subsequently, nine ingredients were selected as Q-markers in consideration of specificity, effectiveness and measurability, and their content was measured in 12 batches of D. scandens. Furthermore, the hierarchical cluster analysis and heatmap results indicated that the selected Q-marker could be used to discriminate D. scandens and that the content of Q-marker varied greatly in different batches. Our study shows that this strategy provides a useful method to discover the potential Q-markers of traditional Chinese medicine and offers a practical workflow for exploring the quality consistency of medicinal materials.

Decoloration and alkaloid enrichment of Dactylicapnos scandens extracts based on the use of strong anion-exchange resins in tandem with strong cation-exchange silica-based materials.

Alkaloids are natural bioactive ingredients but are usually present in low amounts in plant extracts. In addition, the dark color of plant extracts increases the difficulty in separation and identification of alkaloids. Therefore, effective decoloration and alkaloid enrichment methods are necessary for purification and further pharmacological studies of alkaloids. In this study, a simple and efficient strategy is developed for the decoloration and alkaloid enrichment of Dactylicapnos scandens (D. scandens) extracts. In feasibility experiments, we evaluated two anion-exchange resins and two cation-exchange silica-based materials with different functional groups using a standard mixture composed of alkaloids and nonalkaloids. By virtue of its high adsorbability of nonalkaloids, the strong anion-exchange resin PA408 is considered a better choice for the removal of nonalkaloids, and the strong cation-exchange silica-based material HSCX was selected for its great adsorption capacity for alkaloids. Furthermore, the optimized elution system was applied for the decoloration and alkaloid enrichment of D. scandens extracts. Nonalkaloid impurities in the extracts were removed by the use of PA408 in tandem with HSCX treatment, and the total alkaloid recovery, decoloration and impurity removal ratios are determined to be 98.74%, 81.45% and 87.33%, respectively. This strategy can contribute to further alkaloid purification and pharmacological profiling of D. scandens extracts, as well as other plants with medicinal value.

Highly Tough, Stretchable, and Solvent-Resistant Cellulose Nanocrystal Photonic Films for Mechanochromism and Actuator Properties.

Cellulose nanocrystals (CNCs)-derived photonic materials have confirmed great potential in producing renewable optical and engineering areas. However, it remains challenging to simultaneously possess toughness, strength, and multiple responses for developing high-performance sensors, intelligent coatings, flexible textiles, and multifunctional devices. Herein, the authors report a facile and robust strategy that poly(ethylene glycol) dimethacrylate (PEGDMA) can be converged into the chiral nematic structure of CNCs by ultraviolet-triggered free radical polymerization in an N,N-dimethylformamide solvent system. The resulting CNC-poly(PEGDMA) composite exhibits impressive strength (42 MPa), stretchability (104%), toughness (31 MJ m-3 ), and solvent resistance. Notably, it preserves vivid optical iridescence, displaying stretchable variation from red, yellow, to green responding to the applied mechanical stimuli. More interestingly, upon exposure to spraying moisture, it executes sensitive actuation (4.6° s-1 ) and multiple complex 3D deformation behaviors, accompanied by synergistic iridescent appearances. Due to its structural anisotropy of CNC with typical left-handedness, the actuation shows the capability to generate a high probability (63%) of right-handed helical shapes, mimicking a coiled tendril. The authors envision that this versatile system with sustainability, robustness, mechanochromism, and specific actuating ability will open a sustainable avenue in mechanical sensors, stretchable optics, intelligent actuators, and soft robots.

Highly Strong and Solvent-Resistant Cellulose Nanocrystal Photonic Films for Optical Coatings.

Cellulose nanocrystals (CNCs) are powerful photonic building blocks for the fabrication of biosourced colored films. A combination of the advantages of self-assembled CNCs and multiple templating agents offers access to the development of novel physicochemical sensors, structural coatings, and optic devices. However, due to the inherent brittleness and water instability of CNC-derived materials, their further applications are widely questionable and restrictive. Here, a soft polymer of poly(vinyl alcohol) (PVA) was introduced into the rigid CNC system to balance molecular interactions, whereafter two hard/soft nanocomposites were fastened through a cross-linking reaction of glutaraldehyde (GA), resulting in a highly flexible, water-stable, and chiral nematic CNC composite film through an evaporation-induced self-assembly technique. For a 1.5 wt % GA-cross-linked 70 wt % CNC loading film, its treatment with harsh hydrophilic exposure (soaking in a strong acid, strong base, and seawater) and various organic solvents show exceptional solvent-resistant abilities. Furthermore, the film can even withstand a weight of 167 g cm-2 without failure, which is a highly stiff and durable character. Importantly, the film remains a highly ordered chiral nematic organization, being able to act as a highly transparent substrate for selective reflection of left-handed circularly polarized light, preparing fully covered and patterned full-color coatings on various substrates. Our work paves the way for applications in low-cost, durable, and photonic cellulosic coatings.

Computer-Aided Rapid Establishment of Fingerprint of Xiaojin Capsule by HPLC.

Traditional Chinese medicine (TCM) formulas have a significant clinical efficacy, and the fingerprint technology has been widely accepted to fully reveal the quality of TCM. Whereas, it is a great challenge to establish the fingerprint chromatogram which can fully reflect every single herb material in a short time. In this study, we used Xiaojin capsule (XJC) as a case and developed a rapid fingerprint method based on increasing the column temperature and flow rate simultaneously combined with computer-aided. First, the elution gradient was optimized based on the retention parameters and peak shape parameters of the four linear gradients, and then, the column temperature and flow rate were increased simultaneously to shorten the analysis time. Next, the standard fingerprint chromatogram of XJC, which can reflect every herb material, was generated. Finally, quality markers were screened through unsupervised cluster analysis and supervised orthogonal partial least squares discrimination analysis. Combining computer-aided with increasing column temperature and flow rate simultaneously can develop the rapid method for establishing HPLC fingerprint of XJC, which can fully reflect every single herb material and provide comprehensive quality control. The strategy for establishing HPLC fingerprint of TCM formula could be applied to other traditional Chinese medicine formulas and herbal medicine.

Correction to: Combination of multi-model statistical analysis and quantitative fingerprinting in quality evaluation of Shuang-huang-lian oral liquid.

The authors would like to call the reader's attention to the fact that unfortunately there was a mistake in Table 1 of this contribution.

Combination of multi-model statistical analysis and quantitative fingerprinting in quality evaluation of Shuang-huang-lian oral liquid.

A model consisting of quantitative fingerprinting integrated with fundamental statistical analysis was established to carry out quality control analysis of Shuang-huang-lian (SHL) oral liquid. The quantitative fingerprinting approach was developed by systematic investigation of the chromatographic condition and optimization of a gradient using a complex sample analysis software system (CSASS). Five pivotal components from three traditional Chinese medicines of SHL oral liquid were determined at dual wavelengths, including phillyrin, baicalin, chlorogenic acid, neochlorogenic acid and cryptochlorogenic acid. Among them, neochlorogenic acid and cryptochlorogenic acid were quantified by quantitative analysis of multi-components with a single marker (QAMS) method. Further, the developed quantitative fingerprinting approach was validated. Good linearity with correlation coefficients (R2) higher than 0.9999 were achieved for phillyrin, baicalin and chlorogenic acid. Recoveries of the three analytes were between 96% and 108%. Relative standard deviation (RSD) values were below 3% regarding the stability and intra-day and inter-day precision. Besides, the feasibility of the QAMS method was verified by an external standard method (ESM) using 18 batches of SHL oral liquid. Fifty-nine batches of SHL oral liquid from nine manufacturers were then analyzed. Effective distinction was realized based on a linear principal component analysis (linear-PCA) model by the combination of the quantitative data and chromatographic fingerprinting. The linear-PCA model based on quantitative chromatographic fingerprinting exhibited great advantage over conventional similarity analysis to distinguish between different samples. The strategy provided a particularly simple and effective approach for quality evaluation of SHL oral liquid from various manufacturers. Graphical abstract.

[Preparation of macroporous silica and its application on polysaccharide derivative based chiral stationary phase].

In order to prepare 100-nm macroporous silica, spherical silica (5 µm in particle size, 10 nm in pore diameter) was treated by hydrothermal or baking methods. During hydrothermal treatment, 22 g/L NaF was added, which efficiently promoted the enlargement of pore diameters. By this method, the average pore diameter of silica reached 100 nm after heating for 48 h at 160℃ in an autoclave, but showed a poor size distribution. In the baking method, pore diameter enlargement was controlled by modifying the baking temperature, time, and the amount of double salt LiCl-NaCl added. The addition of 1.125 g LiCl·H2O and 0.75 g NaCl per 10 g silica and baking at 500℃ for 3-5 h yielded silica with 100-nm pore diameters. This method was more efficient, easier, and better in the product pore diameter distribution than hydrothermal treatment. The obtained silica was very similar to commercial Fuji-1000 gel. The macroporous silicas obtained from the hydrothermal and baking treatments were both modified with aminopropyl silane and coated by cellulose tri(3,5-dimethylphenyl carbamate) to prepare chiral stationary phases (CSPs). The CSP based on the baking-treated silica exhibited much better selectivity and resolution for enantiomers.

"Two-dimensional" molecularly imprinted solid-phase extraction coupled with crystallization and high performance liquid chromatography for fast semi-preparative purification of tannins from pomegranate husk extract.

In this study, "two dimensional" molecularly imprinted solid-phase extraction (2D-MIP-SPE) of semi-preparative grade was constructed to fast purify ellagitannins in pomegranate husk extract with the help of crystallization and reverse-phase liquid chromatgoraphy (RPLC). Ellagic acid and punicalagin imprinted polymers were synthesized in batch mode and two semi-preparative MIP-SPE columns were individually packed. After investigaing "functional complementation", 2D-MIP-SPE was constructed using ellagic acid MIP and punicalagin MIP-SPE as the first and second dimension, respectively. Then, pomegranate husk extract was fast divided into four fractions individually enriching in ellagic acid, granatin A, punicalagin and ellagic acid glucoside by 2D-MIP-SPE. With the aid of crystallization and RPLC, ellagic acid (13.5mg) and punicalagin (53.4mg) were fast obtained in 30min. Ellagic acid glucoside was purified to the purity near 100% with a recovery of 86.1%. Granatin A (92%) was directly obtained by 2D-MIP-SPE with the recovery of 81.8%. All above indicated that 2D-MIP-SPE was highly efficient in natural product purification. The concept of "functional complementation" was expected to be a useful tool in the construction of 2D-MIP-SPE.

Purification of high-purity glycyrrhizin from licorice using hydrophilic interaction solid phase extraction coupled with preparative reversed-phase liquid chromatography.

Glycyrrhizin (GA), a major bioactive compound in licorice, has been extensively used throughout the world as a medicine to treat chronic viral hepatitis and allergic dermatitis. In this study, a new method based on hydrophilic interaction solid phase extraction (HILIC-SPE) and preparative reversed-phase liquid chromatography (prep-RPLC) was developed to purify GA with high purity from the complex licorice extract. Via evaluation of retention behavior of GA and flavonoids in different commercially available columns, a hydrophilic column--Click XIon was finally chosen for the purification due to its excellent resolution toward GA and flavonoids under HILIC mode. To optimize the SPE elution conditions, relative factors including water content, pH and ionic strength had been investigated in chromatographic condition. The result indicated that the most appropriate water content was 30% and pH at 4.00, as well as salt concentration should be controlled at 5mM. In addition, the optimization revealed that GA experiences both hydrophilic interaction and ion-exchange interaction on the Click XIon material. According to the chromatographic evaluation, the optimized conditions were applied to HILIC-SPE to enrich GA from licorice, which leads to an increased content of GA from 13.67% to 64.22%. Finally, prep-RPLC was performed to obtain GA with purity higher than 99.00%，which demonstrating great prospect in large-scale preparation of GA.

Separation behavior of basic compounds on unbonded silicon oxynitride and silica high-performance liquid chromatography stationary phases with reversed-phase eluents.

Unbonded silicon oxynitride and silica high-performance liquid chromatography stationary phases have been evaluated and compared for the separation of basic compounds of differing molecular weight, pKa , and log D using aqueous/organic mobile phases. The influences of percentage of organic modifier, buffer pH, and concentration in the mobile phase on base retention were investigated on unbonded silicon oxynitride and silica phases. The results confirmed that unbonded silicon oxynitride and silica phases demonstrated excellent separation performance for model basic compounds and both the unbonded phases examined possessed a hydrophobic/adsorption and ion-exchange character. The silicon oxynitride stationary phase exhibited high hydrophilicity compared with silica with a reversed-phase mobile phase. An ion-exclusion-type mechanism becomes predominant for the separation of three aimed bases on the silicon oxynitride column at pH 2.8. Different from silicon oxynitride stationary phase, no obvious change for the retention time of three model bases on silica stationary phase at pH 2.8 can be observed.

Sequential enrichment of singly- and multiply-phosphorylated peptides with zwitterionic hydrophilic interaction chromatography material.

An interesting and novel method for the selective and sequential enrichment of singly- and multiply-phosphorylated peptides with a zwitterionic material "Click TE-Cys" is presented. Retention mechanisms between phosphopeptides and Click TE-Cys are systematically investigated by checking the influence of acetonitrile content, pH value, and buffer concentration on the retention of phosphopeptides. Both hydrophilic interaction and electrostatic interaction are involved in retention between phosphopeptides and Click TE-Cys. Based on these results, an optimized method is established for selective enrichment of phosphopeptides using Click TE-Cys. This method not only exhibits high selectivity for phosphopeptides, but also fractionates singly- and multiply-phosphorylated peptides into two fractions. This method was evaluated using relatively complex samples, including peptide mixtures of α-casein and bovine serum albumin (BSA) at a molar ratio of 1:10 and skim milk. This efficient and optimized protocol has great potential for enriching multiply-phosphorylated peptides and could be a valuable tool for specific enrichment of phosphopeptides in phosphoproteome analysis.

Hydrophilic-subtraction model for the characterization and comparison of hydrophilic interaction liquid chromatography columns.

Nowadays more and more hydrophilic interaction liquid chromatography (HILIC) columns with diverse functional groups have become commercially available, which pose a challenge to select an appropriate one. However, there is no universal model to provide guidance for selecting HILIC columns. To handle this problem, a retention model named "hydrophilic-subtraction model" was developed to characterize and compare HILIC columns. The hydrophilic-subtraction model, which was designed based on the widely recognized HILIC retention mechanisms including hydrophilic partitioning, hydrogen-bonding and electrostatic interactions, was established by the retention of 41 solutes with various properties on 8 representative HILIC columns. High correlation coefficients (R(2)≥0.990) and small standard deviations (SD≤0.041) indicated that this model correlated effectively the retention with solute descriptors and column parameters. To evaluate reliability of the model, the model was further applied to characterize 15 additional HILIC columns using 41 solutes. The results of multiple linear regression confirmed the significance of the model. The regression coefficients of the model were used to investigate retention mechanisms occurring in different chromatographic systems. Based on these regression coefficients, selectivities of HILIC stationary phases were exhibited intuitively by an angle graph and a spider diagram, which could be used as guidance for researchers to select appropriate columns for HILIC separation. Additionally, a rapid and convenient procedure was proposed for characterizing HILIC columns.

Evaluation of a silicon oxynitride hydrophilic interaction liquid chromatography column in saccharide and glycoside separations.

The retention characteristics of a silicon oxynitride stationary phase for carbohydrate separation were studied in hydrophilic interaction chromatography mode. Four saccharides including mono-, di-, and trisaccharides were employed to investigate the effects of water content and buffer concentration in the mobile phase on hydrophilic interaction liquid chromatography retention. For the tested saccharides, the silicon oxynitride column demonstrated excellent performance in terms of separation efficiency, hydrophilicity, and interesting separation selectivity for carbohydrates compared to the bare silica stationary phase. Finally, the silicon oxynitride hydrophilic interaction liquid chromatography column was employed in the separation of complex samples of fructooligosaccharides, saponins, and steviol glycoside from natural products. The resulting chromatograms demonstrated good separation efficiency and longer retention compared with silica, which further confirmed the advantages and potential application of silicon oxynitride stationary phase for hydrophilic interaction liquid chromatography separation.

Amide alkaloids from Scopolia tangutica.

Four new hydroxycinnamic acid amides, scotanamines A-D (1-4), and seven known alkaloids, including N (1),N (10)-di-dihydrocaffeoylspermidine (5), scopolamine (6), anisodamine (7), hyoscyamine (8), anisodine (9), caffeoylputrescine (10), and N (1)-caffeoyl-N (3)-dihydrocaffeoylspermidine (11), were obtained from the roots of Scopolia tangutica. The present study represents the first recognition of hydroxycinnamic acid amides containing putrescine or spermidine in S. tangutica. Compound 1, in particular, contains a moiety resulting from the condensation of nortropinone and putrescine. Compound 2 exhibited moderate agonist activity at the µ-opioid receptor (EC50=7.3 µM). Compound 2 was tested in vivo and induced analgesia in mice. The analgesic effect was recorded using the tail-flick assay and was reversed by naloxone.

A novel method for characterization and comparison of reversed-phase column selectivity.

Characterization of reverse-phase column selectivity is helpful for chromatographers to select an optimal column. A novel method, based on linear solvation energy relationships (LSERs) combined with fundamental retention equations, was developed to characterize and compare reversed-phase column selectivity. The retention times of 25 elaborately selected solutes on 12 reversed-phase columns were determined in three linear gradient elutions. Using these retention times, fundamental retention equations were acquired by a complex sample analysis software system (CSASS). When 0%, 10%, 20%, 30%, 40% and 50% acetonitrile were introduced into the fundamental retention equations, the corresponding retention factors were predicted and used to obtain LSER equations by multiple linear regression. In the gradient elution, the retention times of solutes could be accurately determined and the excessively long or short analysis time could be avoided. As the retention factor (lnkw) at a hypothetical 0% organic modifier closely reflected properties of columns, coefficients of LSERs equations obtained based on lnkw were employed to discuss the properties of different stationary phases. An angle and a spider diagram based on solvation energy vectors were used to compare selectivity differences between stationary phases, which provided a visual means for users to select appropriate columns with orthogonal or similar selectivity. These results of column selectivities were compared with those obtained by geometric orthogonality approach, and a consistent result was acquired. Finally, Click TE-CD and XCharge C18PN with highest difference in column selectivity were applied to the separation of Psoralea corylifolia extraction.

Evaluation and comparison of n-alkyl chain and polar ligand bonded stationary phases for protein separation in reversed-phase liquid chromatography.

Protein retention is very sensitive to the change of solvent composition in reversed-phase liquid chromatography for so called "on-off" mechanism, leading to difficulty in mobile phase optimization. In this study, a novel 3-chloropropyl trichlorosilane ligand bonded column was prepared for protein separation. The differences in retention characteristics between the 3-chloropropyl trichlorosilane ligand bonded column and n-alkyl chain modified (C2, C4, C8) stationary phases were elucidated by the retention equation l nk=a+cC(B). Retention parameters (a and c) of nine standard proteins with different molecular weights were calculated by using homemade software. Results showed that retention times of nine proteins were similar on four columns, but the 3-chloropropyl trichlorosilane ligand bonded column obtained the lowest retention parameter values of larger proteins. It meant that their retention behavior affected by acetonitrile concentration would be different due to lower |c| values. More specifically, protein elution windows were broader, and retentions were less sensitive to the change of acetonitrile concentration on the 3-chloropropyl trichlorosilane ligand bonded column than that on other columns. Meanwhile, the 3-chloropropyl trichlorosilane ligand bonded column displayed distinctive selectivity for some proteins. Our results indicated that stationary phase with polar ligand provided potential solutions to the "on-off" problem and optimization in protein separation.