Yiwen Yang

β-adrenergic antagonists (β-blockers) with at least one chiral center are an exceedingly important class of drugs used mostly to treat cardiovascular diseases. At least 70 β-blockers have been investigated in history. However, only a few β-blockers, e.g., timolol, are clinically marketed as an optically pure enantiomer. Therefore, the separation of racemates of β-blockers is essential both in the laboratory and industry. Many approaches have been explored to obtain the single enantiomeric β-blocker, including high performance liquid chromatography, supercritical fluid chromatography and simulated moving bed chromatography. In this article, a review is presented on different chromatographic methods applied for the enantioseparation of β-blockers, covering high performance liquid chromatography (HPLC), supercritical fluid chromatography (SFC) and simulated moving bed chromatography (SMB).

Various toxic metal ions were successfully removed from solid matrix into supercritical CO₂ (scCO₂) by open-chain crown ether bridged diphosphates at 313.15 K and 20 MPa, these diphosphates with different ester side chains and different length of ethylene oxide bridge group are highly soluble in supercritical CO₂. The extraction efficiency (E%) of heavy metals is between 55 and 89%. Mulliken charge distribution of ligand’s P=O coordination group was calculated to indicate the stability of metal complex. The ligand structure effects and the rationale for different selectivity were discussed. In addition, binding property of these diphosphates towards the alkaline earth metals was further studied following the same extraction procedures. Alkaline earth metal ions Ca²⁺, Sr²⁺ and Ba²⁺ were extracted with E% at 49–74%, 50–73% and 16–64%, respectively. DFT calculations were performed to investigate the interaction energy of the complexes and the correlation with the E% was discussed.

The effective separation and utilization of high value-added unsaturated fatty acid methyl esters from model bio-oils could make full use of the biomass resources and greatly improve the economic feasibility of bio-fuels. Selective separation of unsaturated fatty acid methyl esters was performed by liquid–liquid extraction, using ionic liquids (ILs) as extractants in the presence of cosolvent. The results showed that the mixture of 1-ethyl-3-methylimidazolium dicyanamide ([EMIm][N(CN)₂]) and N,N-dimethylformamide (DMF) demonstrated excellent separation selectivity, reaching up to an outstanding value of 11.7, when the mole ratio of [EMIm][N(CN)₂] to DMF was 1 : 9, at least twice the value (5.6) using DMF as the extractant. In addition, the effects of the structure, the mole fraction of ILs, the feedstock concentration and temperature, on extraction equilibrium were studied. By calculating the fractional extraction, the feasibility of liquid–liquid extraction for practical application was confirmed.

The chiral separation of citalopram base by supercritical fluid chromatography on a semipreparative Chiralpak AD column was studied with the use of three alcohol‐type modifiers (methanol, ethanol, and 2‐propanol) with different volume percentages (5, 10, and 15%). The best separation was achieved when 10% 2‐propanol was used in the presence of 0.1% diethylamine as additive. Under these conditions, the resolution reached 2.15 and the selectivity was 1.388. In addition, other parameters that affected the retention and separation properties, i.e. temperature, pressure, and density, were studied in detail. At the same pressure, a decrease in the temperature improved the enantioselectivity as the experimental temperature range was below the isoelution temperature. However, the temperature dependence of the retention factor was complicated. As a rule, the retention factor decreased when the temperature increased at the same density. A satisfactory regression of the logarithm of the retention factor versus density and temperature was obtained using a simplified lattice‐fluid model. Surprisingly, the relationship between the Henry constant and density can be accurately correlated by using the same quadratic equation.