Requirements in structure for chiral recognition of chitosan derivatives.

In order to investigate the influence of a minor variation in structure of N-acyl chitosan derivatives on enantioseparation, chiral selectors (CSs) of chitosan 3,6-bis(phenylcarbamate)-2-(phenylacetamide)s and chitosan 3,6-bis(phenylcarbamate)-2-(cyclohexylacetamide)s were synthesized. The corresponding chiral stationary phases (N-PhAc CSPs and N-cHeAc CSPs) were also prepared, respectively, with the two series of CSs. Enantioseparation results revealed that the N-PhAc CSPs were better than the N-cHeAc ones in enantioseparation. Thus, benzyl group (Bn) at C2 should be more preferable to enantioseparation than cyclohexylmethyl (cyclohexyl-CH2-) at the same position. Because N-PhAc CSPs exhibited higher enantioseparation capability than chitosan 3,6-bis(phenylcarbamate)-2-(benzamide) based CSPs (N-Bz CSPs), the Bn should also be more beneficial to enantioseparation than phenyl group (Ph) at C2 in N-Bz CSPs. In addition, it was found that, the cyclohexyl group at C2 in chitosan 3,6-bis(phenylcarbamate)-2-(cyclohexylformamide) CSPs was better than cyclohexyl-CH2- in N-cHeAc CSPs to enantioseparation. In a word, a minor variation at C2 of chitosan derivatives significantly affected enantioseparation. After the prepared CSPs were stood for six months, their enantioseparation capabilities were changed obviously, and the changes were probably related to nature, position and number of a substituent on Ph connected to carbamates at C3 and C6 of the CSs.

Conversion of azidoamylose to ureidoamylose carbamates in one-pot reactions.

In order to covert azidoamylose into ureidoamylose derivatives in a facile way, 6-azido-6-deoxyamylose was reacted with triphenylphosphine, and then with water and a phenyl isocyanate in turn. The obtained product was amylose 2,3-bis(phenylcarbamate)-6-deoxy-6-(phenylurea), which was synthesized through three reactions in a one-pot method. The essential point to ensure the method be successful was that the water should be fed at an appropriate amount. The prepared amylose 2,3-bis(phenylcarbamate)-6-deoxy-6-(phenylurea)s were characterized by FT-IR, 1H NMR and elemental analysis, substantiating the reduction of the azido group and the subsequent derivatization of the resulted amino group and the hydroxyl group in amylose were fully performed. In addition, the amylose 2,3-bis(phenylcarbamate)-6-deoxy-6-(phenylurea)s were coated on macroporous 3-aminopropyl silica gel to afford chiral stationary phases (CSPs) for high-performance liquid chromatography. The enantioseparations of the CSPs were evaluated, and the results indicated that the CSPs possessed chiral recognition ability towards some chiral compounds.

Chiral separation materials based on derivatives of 6-amino-6-deoxyamylose.

In order to develop new type of chiral separation materials, in this study, 6-amino-6-deoxyamylose was used as chiral starting material with which 10 derivatives were synthesized. The amino group in 6-amino-6-deoxyamylose was selectively acylated and then the hydroxyl groups were carbamoylated yielding amylose 6-amido-6-deoxy-2,3-bis(phenylcarbamate)s, which were employed as chiral selectors (CSs) for chiral stationary phases of high-performance liquid chromatography. The resulted 6-amido-6-deoxyamyloses and amylose 6-amido-6-deoxy-2,3-bis(phenylcarbamate)s were characterized by IR, 1 H NMR, and elemental analysis. Enantioseparation evaluations indicated that most of the CSs demonstrated a moderate chiral recognition capability. The 6-nonphenyl (6-nonPh) CS of amylose 6-cyclohexylformamido-6-deoxy-2,3-bis(3,5-dimethylphenylcarbamate) showed the highest enantioselectivity towards the tested chiral analytes; the phenyl-heterogeneous (Ph-hetero) CS of amylose 6-(4-methylbenzamido)-6-deoxy-2,3-bis(3,5-dimethylphenylcarbamate) baseline separated the most chiral analytes; the phenyl-homogeneous (Ph-homo) CS of amylose 6-(3,5-dimethylbenzamido)-6-deoxy-2,3-bis(3,5-dimethylphenylcarbamate) also exhibited a good enantioseparation capability among the developed CSs. Regarding Ph-hetero CSs, the enantioselectivity depended on the combination of the substituent at 6-position and that at 2- and 3-positions; as for Ph-homo CSs, the enantioselectivity was related to the substituent at 2-, 3-, and 6-positions; with respect to 6-nonPh CSs, the retention factor of most analytes on the corresponding CSPs was lower than that on Ph-hetero and Ph-homo CSPs in the same mobile phases, indicating π-π interactions did occur during enantioseparation. Although the substituent at 6-position could not provide π-π interactions, the 6-nonPh CSs demonstrated an equivalent or even higher enantioselectivity compared with the Ph-homo and Ph-hetero CSs.

The interactions between chiral analytes and chitosan-based chiral stationary phases during enantioseparation.

The goal of the present study was to disclose the interactions between chitosan-type chiral selectors (CSs) and chiral analytes during enantioseparation. Hence, six chitosan 3,6-bis(phenylcarbamate)-2-(cyclohexylmethylurea)s were synthesized and characterized. These chitosan derivatives were employed as CSs with which the corresponding coated-type chiral stationary phases (CSPs) were prepared. According to the nature and position of the substituents on the phenyl group, the CSs and CSPs were divided into three sets. The counterparts of the three sets were 3,5-diMe versus 3,5-diCl, 4-Me versus 4-Cl and 3-Me versus 3-Cl. The enantioseparation capability of the CSPs was evaluated with high-performance liquid chromatography. The CSPs demonstrated a good enantioseparation capability to the tested chiral analytes. In enantioselectivity, the CSs with 3,5-diCl and with 4-Me roughly were better than the counterparts with 3,5-diMe and with 4-Cl respectively. The CS with 3-Me enantiomerically recognized more analytes than the one with 3-Cl, but showed lower separation factors in more enantioseparations. The acidity of the amide hydrogen in the phenylcarbamates was investigated with density functional theory calculations and 1H NMR measurements. The trend of the acidity variation with different substituents on the phenyl group was confirmed by the retention factors of acetone on the CSPs. Compared the retention factors of analytes on every set of the counterparts, the formation of hydrogen bond (HB) in enantioseparation could be outlined as follows: when the CSs interacted with chiral analytes without reactive hydrogen but with lone paired electrons, the carbamate N‒Hs in the CSs were HB donors and the analytes were HB acceptors; if the CSs interacted with analytes with a reactive hydrogen, the role of the CSs in HB formation was related to the acidity of the reactive hydrogen; the patterns of HB formation between the CSs and analytes were also impacted by compositions of mobile phases, in addition to the nature, number and position of substituents on the phenyl group. Based on the discussion, chiral recognition mechanism could be understood in more detail. Besides, the strategy to improve enantioseparation capability of a CSP by introducing a substituent onto phenyl group was clarified and further comprehended.

Probing Activity Enhancement of Photothermal Catalyst under Near-Infrared Irradiation.

Exploring highly efficient catalysts with excellent photothermal conversion and further unveiling their catalytic mechanism are of significant importance for photothermal catalysis technologies, but there remain grand challenges to these activities. Herein, we fabricate a nest-like photothermal nanocatalyst with Pd decorated on a N-doped carbon functionalized Bi2S3 nanosphere (Bi2S3@NC@Pd). Given its well-dispersed ultrafine Pd nanoparticles and the excellent photothermal heating ability of support material, the Bi2S3@NC@Pd composite exhibits a superior activity and photothermal conversion property to commercial Pd/C catalyst for hydrogenation of organic dyes upon exposure to near-infrared (NIR) light irradiation. In addition, the photothermal effect (temperature rise) and activity enhancement of the heterogeneous catalysis system are further probed by comparing the reaction rate with and without the NIR light irradiation. Furthermore, the catalytic behaviors of the Bi2S3@NC@Pd catalyst under conventional and photothermal heating are investigated at the same reaction temperature. This work not only improves our fundamental understanding of the catalytic behavior in heterogeneous liquid-solid reaction systems under near-infrared irradiation but also may promote the design of catalysts with photothermally promoted activity.

Preparation of 6-amino-6-deoxy cellulose and its derivatives used as chiral separation materials.

In order to find a facile and practical method to synthesize amino cellulose in bulk with high regional selectivity and high degree of substitution, the reaction conditions to brominate cellulose and to reduce azido group were carefully studied and some interesting phenomena were observed. With the optimized method, 6-amino-6-deoxy cellulose could be easily prepared with very simple separation techniques. The degree of substitution of the amino group amounted to 0.97 which was determined by 1H NMR spectrum of 6-benzamido-6-deoxy cellulose. Moreover, the amino group was evidenced to be at the C6 of glucose unit by 1H-1H COSY NMR and 1H-13C HSQC NMR spectra. In addition, three cellulose 6-acetamido-6-deoxy-2,3-bis(phenylcarbamate)s were prepared from the 6-amino-6-deoxy cellulose prepared with the techniques optimized in the present study. The developed cellulose derivatives were used as chiral selectors with which chiral stationary phases (CSPs) were prepared. The CSPs exhibited enantioseparation power to some chiral compounds.

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.

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.

Incidence of second-time lateral patellar dislocation is associated with anatomic factors, age and injury patterns of medial patellofemoral ligament in first-time lateral patellar dislocation: a prospective magnetic resonance imaging study with 5-year follow-up.

PURPOSE: To examine the predictors of the second-time lateral patellar dislocation (LPD) in patients after acute first-time LPD in a 5-year follow-up. METHODS: Data were collected prospectively from patients after acute first-time LPD with conservative treatment. Factors included sex, age at the first-time LPD, anatomical variants [trochlear dysplasia, patellar height, tibial tuberosity-trochlear groove (TT-TG) distance], and injury patterns of medial patellofemoral ligament (MPFL) in acute first-time LPD. Logistic regression was carried out to identify the independent risk factors for the incidence of the second-time LPD. RESULTS: The incidence rate of a second-time LPD was 35.5% (59 of 166) in the 5-year follow-up. Univariate analysis revealed significant differences in the incidence rate of the second-time LPD among age at the first-time LPD (P = 0.04), trochlear dysplasia (P = 0.003), patella height (P = 0.017) and the TT-TG distance (P = 0.027). Risk factors for the second-time LPD were age < 18 years at the first-time LPD [odds ratio (OR) 4.088], low-grade trochlear dysplasia (OR 7.214), high-grade trochlear dysplasia (OR 18.945), patella alta (OR 8.416), elevated TT-TG distance (OR 12.742), complete MPFL tear at its isolated femoral-side (OR 6.04) and complete combined MPFL tear (OR 5.851). CONCLUSIONS: Trochlear dysplasia, elevated TT-TG distance, patella alta, age < 18 years at the first-time LPD, complete MPFL tear at its isolated femoral-side and complete combined MPFL tear in the first-time LPD are independently associated with a higher incidence rate of the second-time LPD. LEVEL OF EVIDENCE: III.

Performances comparison of enantiomeric separation materials prepared from shrimp and crab shells.

Previously reported studies demonstrate that many chitin/chitosan derivatives are promising for enantioseparation of chiral compounds. The aim of the present study is to investigate influence of the chitin sources on performances of the chitosan type enantiomeric separation materials. Therefore, the chitosans were prepared from crab and shrimp shells, from which two sets of chiral selector, i.e. chitosan bis(3,5-dimethylphenylcarbamate)-(octanamide)s and chitosan bis(3,5-dichlorophenylcarbamate)-(octanamide)s were synthesized. The chitosan bis(3,5-dimethylphenylcarbamate)-(octanamide)s, respectively, derived from crab and shrimp shells were close in swelling capacity and enantioseparation capability, and the same feature was found for the other two chiral selectors of chitosan bis(3,5-dichlorophenylcarbamate)-(octanamide). On the other hand, although most of the chiral analytes were eluted out in the same elution order, there were two analytes were in reversed elution orders when separated by the two chiral stationary phases of chitosan bis(3,5-dichlorophenylcarbamate)-(octanamide). Based on the observed results, we conclude that enantiomeric separation materials may be developed either with shrimp chitin or crab chitin, depending on the source accessibility.

A high-performance chiral selector derived from chitosan (p-methylbenzylurea) for efficient enantiomer separation.

N-Methoxycarbonyl chitosan was prepared by selectively modifying the amino group at the 2-position of chitosan with methyl chloroformate, which was further functionalized with p-methylbenzylamine to produce chitosan (p-methylbenzylurea). Then, the hydroxyl groups at the 3- and 6-positions of the glucose skeleton were modified with various phenyl isocyanates, affording a series of chitosan 3,6-bis(arylcarbamate)-2-(p-methylbenzylurea)s, which were characterized and proposed as chiral selectors for enantiomer separation. Nineteen racemates, most of which are drugs or intermediates for drugs, were selected as the model analytes to evaluate the enantioseparation performance. The structure-performance relationship of the chiral selectors was investigated in detail. It was found that the methyl-substituted chiral selectors possessed more preferable enantioseparation performance compared with the chloro-substituted ones, and the chiral selectors containing a methyl substituent at the 4-position of the benzene ring showed the best chiral recognition and separation ability with 17 racemates being recognized and 13 racemates being baseline separated. The prepared chiral separation materials derived from these chiral selectors exhibited favorable solvent tolerance towards ethyl acetate, acetone, chloroform and a low proportion of tetrahydrofuran in normal phase. To sum up, this work provided a useful reference for the design and preparation of high-performance chiral separation materials for efficient enantiomer separation.

The Correlation between the Injury Patterns of the Medial Patellofemoral Ligament in an Acute First-Time Lateral Patellar Dislocation on MR Imaging and the Incidence of a Second-Time Lateral Patellar Dislocation.

Objective: To evaluate the correlation between the injury patterns of the medial patellofemoral ligament (MPFL) on magnetic resonance imaging in an acute first-time lateral patellar dislocation (LPD) and incidence of a second-time LPD. Materials and Methods: Magnetic resonance images were prospectively analyzed in 147 patients after an acute first-time LPD with identical nonoperative management. The injury patterns of MPFL in acute first-time LPDs were grouped by location and severity for the analysis of the incidence of second-time LPD in a 5-year follow-up. Independent t tests, chi-square tests and Kruskal-Wallis tests were performed as appropriate. Results: Forty-six cases (46/147, 31.3%) of second-time LPD were present at the 5-year follow-up. Fourteen (14/62, 22.6%) and 31 cases (31/80, 38.8%) were present in the partial and complete MPFL tear subgroups, respectively. Twenty-five cases (25/65, 38.5%), 11 cases (11/26, 42.3%), and 8 cases (8/47, 17%) were present in the isolated femoral-side MPFL tear (FEM), combined MPFL tear (COM), and isolated patellar-side MPFL tear (PAT) subgroups, respectively. Compared with the partial MPFL tears, complete tears showed higher incidence of a second-time LPD (p = 0.04). The time interval between the two LPDs was shorter in the complete MPFL tear subgroup (24.2 months) than in the partial tear subgroup (36.9 months, p = 0.001). Compared with the PAT subgroup, the FEM and COM subgroups showed a higher incidence of a second-time LPD (p = 0.025). The time intervals between the two LPDs were shorter in the FEM and COM subgroups (20.8 months and 19.2 months) than in the PAT subgroup (32.5 months, p = 0.049). Conclusion: A complete MPFL tear, isolated femoral-side tear and combined tear in a first-time LPD predispose a second-time LPD.

Correlation analysis between injury patterns of medial patellofemoral ligament and vastus medialis obliquus after acute first-time lateral patellar dislocation.

PURPOSE: To evaluate the correlation between injury patterns of the medial patellofemoral ligament (MPFL) and vastus medialis obliquus (VMO) after acute first-time lateral patellar dislocation (LPD) in adults. METHODS: Magnetic resonance imaging (MRI) was prospectively performed in 132 consecutive adults with acute first-time LPD. Images were acquired and evaluated using standardized protocols. Injury patterns of MPFL were grouped by location and severity for analysis of the prevalence of VMO injury. RESULTS: MRI demonstrated VMO injury in 63 (47.7%) patients. Twenty (38.5%) and 43 cases (56.6%) were present in partial and complete MPFL tear subgroups, respectively. Compared with partial MPFL tears, complete tears showed a higher prevalence of VMO injury (P = 0.044). The mean coronal (28.5 mm) and mean sagittal VMO elevations (20.7 mm) were higher in the complete MPFL tear subgroup than in the partial tear subgroup (19.8 mm, P = 0.005; 11.9 mm, P < 0.001). No correlations were identified between the prevalence of VMO injury and location subgroups of MPFL injury (n.s.). Mean VMO elevations were higher in isolated femoral-side (FEM) and combined MPFL tear (COM) subgroups (mean coronal VMO elevation of 29 mm and mean sagittal VMO elevation of 20.8 mm in the FEM subgroup; mean coronal VMO elevation of 29.6 mm and mean sagittal VMO elevation of 23.1 mm in the COM subgroup) than in the isolated patellar-side MPFL tear (PAT) subgroup (P = 0.022, P < 0.001) (mean coronal VMO elevation of 20.7 mm and mean sagittal VMO elevation of 10.6 mm). CONCLUSIONS: Complete MPFL tear predisposes to VMO injury and has a higher elevation of torn VMO after acute first-time LPD in adults. Isolated femoral-side and combined MPFL tears predispose to higher elevation of torn VMO. LEVEL OF EVIDENCE: IV.

Performance comparison of chiral separation materials derived from N-cyclohexylcarbonyl and N-hexanoyl chitosans.

Chitosan bis(phenylcarbamate)-(N-cyclohexylformamide)s and chitosan bis(phenylcarbamate)-(N-hexanamide)s were synthesized as chiral selectors for enantiomeric separation. Since two types of substituents with different structures were, respectively, introduced onto the 2-position and the 3-/6-positions of the glucose skeleton in the chitosans through a "heterogeneous" modification pathway, the enantioseparation performances of the chiral selectors could be improved. Influence of the type and position of the substituents on chiral recognition and enantioseparation abilities was studied in detail, and the structural dependence on enantioseparation performance was particularly demonstrated. It was found that methyl- and chloro-substituted chitosan bis(phenylcarbamate)-(N-hexanamide)s possessed comparable enantioseparation performances, whereas chloro-substituted chitosan bis(phenylcarbamate)-(N-cyclohexylformamide)s exhibited much more powerful chiral recognition and enantioseparation abilities than the methyl-substituted ones. Among all the prepared chiral selectors, those with the combination of the cyclohexyl group at the 2-position of the glucose skeleton in the chitosan derivatives and the chlorophenyl group at the 3-/6-positions seemed to be more preferable for enantiomeric separation. As a result, the chitosan bis(3,4-dichlorophenylcarbamate)-(N-cyclohexylformamide) possessed the best enantioseparation performance. The solvent tolerability of the prepared chiral selectors was also investigated in the present study. Compared with the classical coated-type chiral separation materials derived from cellulose/amylose derivatives, the N-cyclohexylcarbonyl and N-hexanoyl chitosans based chiral stationary phases were observed to possess more favorable solvent tolerability, thus possibly widening their applications for various practical enantioseparations.

High-performance chiral stationary phases based on chitosan derivatives with a branched-chain alkyl urea.

In this study, two series of chitosan 3,6-bis(arylcarbamate)-2-(isobutylurea)s and corresponding coated-type chiral stationary phases (CSPs) were prepared from two kinds of chitosans with different molecular weights. Most of the prepared CSPs demonstrated better enantioseparation performance than the homemade CSP of cellulose tris(3,5-dimethylphenylcarbamate). The CSPs of chitosan 3,6-bis(4-methylphenylcarbamate)-2-(isobutylurea) with higher molecular weight and chitosan 3,6-bis(3-chloro-4-methylphenylcarbamate)-2-(isobutylurea) with lower molecular weight possessed outstanding chiral recognition abilities which were at least as good as that of the commercialized CSP of Chiralcel OD-H towards the tested chiral analytes. Except for the two CSPs derived from chitosan 3,6-bis(4-methylphenylcarbamate)-2-(isobutylurea)s, the CSPs (the first class) with the chiral selectors of lower molecular weight provided better enantioseparations than the ones (the second class) with the chiral selectors of higher molecular weight. On the other hand, the chiral selectors of the first class CSPs showed higher swelling capacities in organic solvents than the ones of the second class. All prepared CSPs could be analyzed with a wider range of mobile phases, in which some "unusual organic solvents" such as ethyl acetate, chloroform and THF etc. could be used as additives. According to separation performance and tolerance against organic solvents, we concluded that the chitosan derivatives with branched-chain alkyl urea at 2-C of glucosamine residue were preferable to be used as chiral selectors for enantiomeric separation.

Structural dependence on the property of chiral stationary phases derived from chitosan bis(arylcarbamate)-(amide)s.

The goal of present study was to investigate the structural dependence of chitosan derivatives on enantioseparation and mobile phase tolerance of the corresponding chiral packing materials for liquid chromatography. Hence, a series of chitosan bis(arylcarbamate)-(n-pentyl amide)s and the related chiral stationary phases (CSPs) were prepared from chitosans with different molecular weights. Because of the H-bond formed via CH3-π interaction, the CSP bearing methyl substituent exhibited high tolerance than the ones bearing dichloro substituents. The CSP derived from the chitosan bis(3,5-dichlorophenylcarbamate)-(n-pentyl amide) with a higher molecular weight possessed high tolerance to mobile phases, whereas the enantioseparation capability of this CSP was not as good as that of the one prepared from the chitosan derivative with a lower molecular weight. Therefore, enantioseparation capability and mobile phase tolerance have to be counterbalanced in designing chiral selectors for the CSPs derived from chitosan bis(arylcarbamate)-(amide)s.

Enantioseparation characteristics of the chiral stationary phases based on natural and regenerated chitins.

Natural and regenerated chitins were derivatized with 3,5-dimethyphenyl isocyanate. The corresponding chiral stationary phases were prepared by coating the resulting chitin derivatives on 3-aminopropyl silica gel. The swelling capacity of the chitin derivatives, enantioseparation capability, as well as eluents tolerance of the chiral stationary phases were evaluated. The results demonstrated no remarkable difference in enantioseparation capability between natural and regenerated chitins based chiral stationary phases. The similar enantioseparation characteristics of two chiral stationary phases could be understood by comparing the IR spectra of related chitin derivatives. The one of the two chiral stationary phases prepared by coating the chitin derivative with a lower molecular weight generally provided better enantioseparations. All chiral stationary phases can work in 100% chloroform, 100% ethyl acetate, 100% acetone, and the mobile phases containing a certain amount of tetrahydrofuran. The chiral stationary phase prepared from the chitin derivative with the highest swelling capacity exhibited better enantioseparations than others. This chiral stationary phase was damaged by flushing with 100% tetrahydrofuran, however, the enantioseparation capability was recovered again after the column was allowed to stand for 1 month. Furthermore, the recovered chiral stationary phase provided better enantioseparations for some chiral analytes than before.

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.

N-Acylated chitosan bis(arylcarbamate)s: A class of promising chiral separation materials with powerful enantioseparation capability and high eluents tolerability.

In order to comprehensively understand the influence of coordination of the substituent at 2-position with those at 3- and 6-positions on the properties of chitosan derivatives, a series of chitosan 3,6-bis(arylcarbamate)-2-(amide)s (CACAs) and the related chiral stationary phases (CSPs) were prepared and reported in the present study. Specifically, chitosan was N-acylated with carboxylic acid anhydrides, and then further derivatized with various aryl isocyanates to afford CACAs, from which a class of coated-type CSPs were prepared. When the substituent introduced on the acyl group at 2-position and those on the phenyl group of the carbamates at 3- and 6-positions were fittingly combined, these prepared CACAs based CSPs would exhibit powerful chiral recognition ability, further resulting in a class of promising chiral separation materials with excellent enantioseparation performance. Meanwhile, these newly developed materials with suitable molecular weight also bear a high tolerability towards organic solvents, even including pure tetrahydrofuran, thus broadening their application in enantiomeric separation.

Eluent Tolerance and Enantioseparation Recovery of Chiral Packing Materials Based on Chitosan Bis(Phenylcarbamate)-(n-Octyl Urea)s for High Performance Liquid Chromatography.

The goal of the present work was to study the influence of the swelling of chitosan derivatives on the enantioseparation and the separation performance recovery of chiral stationary phases (CSPs) based on these derivatives. Therefore, six chitosan bis(phenylcarbamate)-(n-octyl urea)s were synthesized, which were coated on macroporous 3-aminopropyl silica gel affording new CSPs. Most of the CSPs demonstrated strong enantioseparation capability for the tested chiral compounds. The swelling capacity of the chitosan bis(phenylcarbamate)-(n-octyl urea)s in ethyl acetate, acetone and tetrahydrofuran (THF) was evaluated. Among the chitosan derivatives, the chitosan bis(3,5-dichlorophenylcarbamate)-(n-octyl urea) polymer showed the highest swelling capacity in ethyl acetate and THF. The polymer-based CSPs could be utilized with pure ethyl acetate and a normal phase containing 70% THF, but was damaged by pure THF. On the other hand, the separation performance of the damaged CSP could be recovered after it was allowed to stand for a period of time. The observations are important for the development and application of polysaccharide derivative-based CSPs.