Preparation of hydrophilic molecularly imprinted polymers via bulk polymerization combined with hydrolysis of ester groups for selective recognition of iridoid glycosides.

Hydrophilic molecularly imprinted polymers (H-MIP) with molecular recognition ability for iridoid glycosides (IGs) have been obtained via bulk polymerization combined with hydrolysis of ester groups. H-MIP were characterized by Fourier transform infrared spectroscopy (FT-IR). The hydrophilcity was measured by the contact angle measurement and the water dispersion stability. The obtained H-MIP demonstrated high selectivity and specific binding ability to five IGs in aqueous media. The group extraction efficiency of molecular imprinted solid-phase extraction (MISPE) for five IGs was investigated, including loading sample, breakthrough volume, washing solvent, and elution solvent. Compared with non-imprinted solid-phase extraction (NISPE), the higher average recovery (95.5 %) of five IGs with lower relative standard deviations values (below 6.1 %) using MISPE combined with high-performance liquid chromatography (HPLC) were achieved at three spiked levels in three blank samples. Under the optimum MISPE conditions, the wide linear range with the correlation coefficient of R (2) ≥ 0.9950 for five IGs with low limits of detection (LOD) and quantification (LOQ) (0.01-0.08 and 0.03-0.27 µg mL(-1), respectively) were obtained. Chromatograms obtained using MISPE columns demonstrated that the matrix interference has been minimized and great interferences around IGs were also eliminated efficiently. These results indicated that the developed MISPE-HPLC method was selective, accurate, and applicable for the determination of IGs in water media. Graphical Abstract Preparation of hydrophilic molecularly imprinted polymers via bulk polymerization combined with hydrolysis of ester groups.

Preparative separation of cichoric acid from Echinacea purpurea by pH-zone-refining counter-current chromatography.

pH-zone-refining counter-current chromatography was successfully applied to the separation of cichoric acid from Echinacea Purpurea (L.) Moench. A 3.0 g quantity of sample was separated using the following two-phase solvent system: MtBE-CH3CN-water (4:1:5, v/v), 10 mM trifluoroacetic acid in organic stationary phase and 10 mM ammonia in aqueous mobile phase. The obtained fractions were analyzed by high-performance liquid chromatography and negative ion electrospray ionization mass spectrometry. Double separations were performed with the same solvent system yielding 563 mg cichoric acid at 95.6% purity.

Preparation of salvianolic acid A by the degradation reaction of salvianolic acid B in subcritical water integrated with pH-zone-refining counter-current chromatography.

Salvianolic acid A is the major bioactive compound in Danshen, however, due to the chemical instability and low content in Danshen, it is difficult to extract amount of salvianolic acid A. Therefore, this study was to establish an effective strategy for obtaining adequate amount of salvianolic acid A, subcritical water extraction was used to degrade salvianolic acid B and prepare salvianolic acid A. Different reaction conditions including temperature, time, concentration and pH value in subcritical water were investigated. Under 40mg/mL of reactant concentration, 180°C of temperature, 4.0 of pH value and 60min of reaction time, the highest yield rate of salvianolic acid A reached 34.86%. Then, the degradation products were successfully separated by pH-zone-refining counter-current chromatography with the solvent system Pet-EtAc-n-BuOH-H2O (2:3:1:9, v/v), where 10mM TFA was added in stationary phase and 10mM NH3·H2O in mobile phase. As a result, a total of 227.3mg of salvianolic acid A at 98.2% purity, 38.9mg of danshensu at 99.3% purity, 9.5mg of salvianolic acid D at 92.7% purity, and 32.8mg of protocatechuic aldehyde at 93.1% purity were obtained from 1.2g degradation products of salvianolic acid B by one-step purification. The results demonstrated that the combinative application of subcritical water and pH-zone-refining counter-current chromatography is a potential technique for the preparative separation of salvianolic acid A from salvianolic acid B.

Molecularly imprinted polymers with novel functional monomer for selective solid-phase extraction of gastrodin from the aqueous extract of Gastrodia elata.

Molecular imprinted polymers (MIPs) with high selectivity and affinity to gastrodin in water were designed using allyl 2,3,4,6-tetra-O-acetyl-glucopyranoside (TAGL) and 1,2,3,4,5-pentafluoro-6-vinylbenzene (PFVB) as novel functional monomers. Binding characterization of pre-polymerization complexes was researched by nuclear magnetic resonance (NMR) and the MIPs were characterized by scanning electron microscopy (SEM). The properties involving adsorption isotherm, adsorption kinetics and selective recognition capacity were evaluated. The MIPs/TAGL exhibited good site accessibility in which it only took 30min to achieve adsorption equilibrium and highly selective recognition for the template. Furthermore, the performance of the MIPs/TAGL as solid phase extraction material was investigated in detail and hot water at 50°C served as the eluting solvent. Pure gastrodin with the recovery of 76.6% was obtained from the aqueous extract of Gastrodia elata roots.

Effectively designed molecularly imprinted polymers for selective extraction of glabridin from Glycyrrhiza glabra L. residues by screening the library of non-imprinted polymers.

Molecularly imprinted polymers (MIPs) with high selectivity and affinity to glabridin were designed based on the screening results of the library of non-imprinted polymers (NIPs). The NIP library contained 48 polymers that were polymerized with the combinations of different functional monomers, cross-linkers, and porogenic solvents. The distribution coefficient (k) values were used to estimate the affinity of NIPs to glabridin. The corresponding MIPs of the best three NIPs were prepared. After evaluating the imprinting effects and selectivity of the three MIPs, the performance of the best MIP as solid phase extraction sorbent was investigated. Glabridin with percent recovery of 83 was obtained from the extract of Glycyrrhiza glabra L. (G. glabra L.) residues by molecularly imprinted solid phase extraction (MISPE). Thus, this material can be successfully used for the extraction and purification of glabridin from G. glabra L. residues.