Comparison in enantioseparation performance of chiral stationary phases prepared from chitosans of different sources and molecular weights.

The aim of the present study was to compare the enantioseparation performance of chiral stationary phases (CSPs) which were derived from chitosans of different sources and molecular weights. Therefore, chitosans of shrimp and crab shells were prepared. The viscosity-average molecular weights of the chitosans both prepared from shrimp and crab shells were 2.8 × 105 and 1.4 × 105. The chitosans were isobutyrylated yielding isopropylcarbonyl chitosans which were then derivatized with 4-methylphenyl isocyanate to provide chitosan 3,6-bis(4-methylphenylcarbamate)-2-(isobutyrylamide)s. The chitosan 3,6-bis(4-methylphenylcarbamate)-2-(isobutyrylamide)s were used as chiral selectors (CSs) with which the corresponding CSPs were prepared. With the same chiral analytes and under the same mobile phase conditions, the enantioseparation capability of the CSPs was evaluated by high-performance liquid chromatography. In two CSs prepared from the same source, the one with higher molecular weight showed better enantioseparation capability; in two CSs prepared with the chitosans of the same molecular weight, the one derived from shrimp shell exhibited better performance. With regard to the two shrimp chitosan CSs, most of chiral analytes interacted more strongly with the one with lower molecular weight, and an opposite trend was found for the two crab chitosan CSs. Based on the results observed in the present study and in previous work, we believe that the influence of molecular weight on CSP enantioseparation performance is related to the substituent introduced in the CS molecule.

Are paediatric clinical practice guidelines trustworthy?

AIM: To assess the methodological and reporting quality of paediatric clinical practice guidelines (CPGs) in National Guideline Clearinghouse (NGC) using the Appraisal of Guidelines for Research and Evaluation (AGREE) II instrument and Reporting Items for Practice Guidelines in Healthcare (RIGHT) standard. METHODS: We identified all published CPGs through the NGC, and search records were screened in duplicate for inclusion. Two researchers evaluated the methodological and reporting quality of paediatric CPGs using the AGREE II instrument and RIGHT standard. STATA version 12.0 and SPSS version 22.0 software were used to analyse the related data. RESULTS: A total of 50 paediatric CPGs were included. The scores for all six domains by AGREE II instrument were presented as follows: scope and purpose (85.6 ± 9.59), stakeholder involvement (69.15 ± 19.32), rigour of development (73.19 ± 17.18), clarity of presentation (78.51 ± 14.36), applicability (54.61 ± 22.63) and editorial independence (68.42 ± 13.06). In the seven domains of the RIGHT standard, the reporting rate of the recommendation domain was the lowest (52.86%).The highest reporting rate was the other information domain, which was 68%.There was a high correlation between reporting the completeness of CPGs using the AGREE II instrument and RIGHT standard (r = 0.77, P < 0.001). CONCLUSIONS: The paediatric CPGs from NGC have good quality. There was a high correlation in the completeness of reporting for paediatric CPGs using the AGREE II instrument and RIGHT standard. It could be concluded that the CPGs of good methodological quality have good reporting quality. Maybe the researcher should effectively combine the AGREE II instrument and RIGHT standard in the development process of CPGs.

Structure screening and performance restoration of chiral separation materials based on chitosan derivatives.

In order to screen chiral selector structure and find structure-property relationship, ten chitosan 3,6-bis(phenylcarbamate)-2-(cyclopropylformamide)s were synthesized from which corresponding chiral stationary phases were prepared. Enantioseparation capability and mobile phase tolerability of the chiral stationary phases were evaluated. The chiral selectors with 3-chloro-4-methylphenyl, 4-chlorophenyl, 3-chlorophenyl, 3,5-dichlorophenyl and 4-trifluoromethoxyphenyl groups demonstrated powerful enantioseparation capability. Enantioseparation capability was found to be dependent on a match between the substituent at C2 and the one attached to phenyl group at C3/C6 of glucose unit in the chitosan derivatives. Moreover, the tolerability tests revealed that the developed chiral stationary phases were highly tolerable to pure ethyl acetate, pure acetone and n-hexane/tetrahydrofuran of various ratios. In addition, n-hexane/tetrahydrofuran was found to be a modifier to adjust suprastructure of the chitosan derivatives, resulting in an improvement or restoration in enantioseparation. This observation implies n-hexane/tetrahydrofuran may make a damaged chiral selector restore its enantioseparation capability.

Novel combined method of biosorption and chemical precipitation for recovery of Pb2+ from wastewater.

A novel combined biosorption-precipitation process has been designed and applied to recycle Pb2+ from low concentration lead containing wastewater. Pb2+ was firstly removed selectively from wastewater by pyromellitic dianhydride (PMDA) modified sugarcane bagasse (SB) fixed-bed column, and then, it was desorbed into the concentrated eluate and recycled by adding chemical precipitant. Adsorption performance of the column and optimum desorption and precipitation condition for Pb2+ were investigated in detail. Results showed that the as-prepared column could efficiently remove Pb2+ from aqueous solution and optimum condition for Pb2+ precipitation in eluate was at pH 3.0 and molar ratio of precipitant to Pb2+ of 5:1 by using Na3PO4 as precipitant. Recovery experiment illustrated that Pb2+ was selectively removed from wastewater containing ions of Pb2+, Zn2+, Cd2+, Ca2+, K+, and Na+ through competitive substitution adsorption on the modified SB, and mass ratio of the five metal ions in eluate was 96.8:0.7:0.7:0.7:0.5:0.5. Pb2+ in this concentrated and purified eluate solution was recycled efficiently by adding Na3PO4. The combined method had great potential in application of heavy metal recovery from wastewater.

High performance chiral separation materials based on chitosan bis(3,5-dimethylphenylcarbamate)-(alkyl urea)s.

Enantioseparation plays an important role for many fields and for pharmaceutical industry in particular. Chiral stationary phase (CSP) is the core of chiral liquid chromatography that effectively implements enantioseparation. In order to develop coated type CSPs with excellent enantioseparation capability and high tolerance against mobile phases, in this work, a series of chitosan bis(3,5-dimethylphenylcarbamate)-(alkyl urea)s were synthesized, which were coated on 3-aminopropyl silica gel to afford new CSPs. Owing to strong hydrogen bonds formed among the synthesized derivatives, the supra-structure of the derivatives should be highly ordered. Hence, these CSPs could provide excellent separation capability and could tolerate common organic solvents that are usually prohibited for coated type CSPs of cellulose and amylose derivatives. Therefore the newly prepared CSPs exhibited promising prospects for enantioseparation of chiral compounds.