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.

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.

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.

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.

Synthesis of substituted phenylcarbamates of N-cyclobutylformylated chitosan and their application as chiral selectors in enantioseparation.

The goal of this study was to develop new chiral stationary phases (CSPs) with high chiral recognition capability and high compatibility with the so-called "nonstandard solvents". Seven new chitosan bis(phenylcarbamate)-(N-cyclobutylformamide) derivatives were synthesized from chitosan with high degree of deacetylation as a starting material. The corresponding chiral stationary phases (CSPs 1-7) were prepared with the chitosan derivatives as chiral selectors (CSs). The enantioseparation capability of CSPs 1-7 was evaluated by high performance liquid chromatography with nineteen analytes. In comparison with the CSPs of cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC) and amylose tris(3,5-dimethylphenylcarbamate) (ADMPC), the prepared CSPs generally demonstrated excellent enantioseparation capability, particularly for the CSP derived from chitosan bis(3-chloro-4-methylphenylcarbamate)-(N-cyclobutylformamide). Moreover, the CSPs in the present study could separate some analytes better, making them complementary for enantioseparations with the CSPs of CDMPC and ADMPC. The tolerability of the CSP with the best enantioseparation capability to organic solvents was investigated. The results showed that it could work in pure ethyl acetate, pure chloroform, and a normal phase containing 70% tetrahydrofuran, which are prevented from enantioseparation by the coating type CSPs of CDMPC and ADMPC. As these chitosan derivatives were almost insoluble in most organic solvents, the corresponding CSPs can work in a wide range of mobile phases. In addition, the influence of the position and electron effects of methyl and chloro groups introduced onto the CSs and the composition of mobile phases on enantioseparation was also discussed.

Chiral stationary phases based on chitosan bis(4-methylphenylcarbamate)-(alkoxyformamide).

Highly N-deacetylated chitosan was chosen as a natural chiral origin for the synthesis of the selectors of chiral stationary phases. Therefore, chitosan was firstly acylated by various alkyl chloroformates yielding chitosan alkoxyformamides, and then these resulting products were further derivatized with 4-methylphenyl isocyanate to afford chitosan bis(4-methylphenylcarbamate)-(alkoxyformamide). A series of chiral stationary phases was prepared by coating these derivatives on 3-aminopropyl silica gel. The content of the derivatives on the chiral stationary phases was nearly 20% by weight. The chiral stationary phases prepared from chitosan bis(4-methylphenylcarbamate)-(ethoxyformamide) and chitosan bis(4-methylphenylcarbamate)-(isopropoxyformamide) comparatively showed better enantioseparation capability than those prepared from chitosan bis(4-methylphenylcarbamate)-(n-pentoxyformamide) and chitosan bis(4-methylphenylcarbamate)-(benzoxyformamide). The tolerance against organic solvents of the chiral stationary phase of chitosan bis(4-methylphenylcarbamate)-(ethoxyformamide) was investigated, and the results revealed that this phase can work in 100% ethyl acetate and 100% chloroform mobile phases. Because as-synthesized chiral selectors did not dissolve in many common organic solvents, the corresponding chiral stationary phases can be utilized in a wider range of mobile phases in comparison with conventional coating type chiral stationary phases of cellulose and amylose derivatives.

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.

Enantioseparation characteristics of tadalafil and its intermediate on chitin derived chiral stationary phases.

Due to the low solubility and swelling properties of chitin bis(arylcarbamate) in most organic solvents, the chiral stationary phases (CSPs) prepared from chitin derivatives can be analyzed with a wide range of solvents. In order to develop new CSPs of chitin derivatives with halogen groups, chitin was derivatized with three different phenyl isocyanates to obtain chitin bis(4-trifluoromethoxyphenylcarbamate), chitin bis(3-chloro-4-methylphenylcarbamate) and chitin bis(4-chloro-3-trifluoromethylphenylcarbamate). Then, the three chitin derivatives were coated on macroporous 3-aminopropyl-functionalized silica gel to obtain three CSPs 1-3 respectively. These CSPs showed good enantioseparation capabilities towards tadalafil and its intermediate. Therefore, these CSPs are potentially applied for the enantioseparation and determination of tadalafil and its intermediate. It was also found that the retention times of some enantiomers were prolonged in the presence of their diastereoisomers or structural analogues and as a result, the resolution was improved to some extent. Hence, in the enantioseparation of a compound with two chiral centers, the resolution is hopefully improved by adding a diastereoisomer or a structural analogue.

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.

The comparison in enantioseparation ability of the chiral stationary phases with single and mixed selector--the selectors derived from two D-tartrates.

(2S,3S)-2,3-Bis(3,5-dimethylphenylcarbonyloxy)-3-(benzyloxycarbonyl)-propanoic acid and (2S,3S)-2,3-bis(1-naphthalenecarbonyloxy)-3-(benzyloxycarbonyl)-propanoic acid were synthesized from D-tartaric acid. These two compounds were chlorinated to afford two chiral selectors for chiral stationary phases (CSPs). The selectors were separately immobilized on aminated silica gel to give two single selector CSPs; and were simultaneously immobilized to obtain a mixed selector CSP. Comparing to the single selector CSPs, the mixed selector CSP bears the enhanced enantioseparation ability, suggesting that the two selectors in the mixed selector CSP are consistent for chiral recognition in most mobile phase conditions.

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.

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.

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.

Synthesis of dendrimer-type chiral stationary phases based on the selector of (1S,2R)-(+)-2-amino-1,2-diphenylethanol derivate and their enantioseparation evaluation by HPLC.

In our recent work, a series of dendritic chiral stationary phases (CSPs) were synthesized, in which the chiral selector was L-2-(p-toluenesulfonamido)-3-phenylpropionyl chloride (selector I), and the CSP derived from three-generation dendrimer showed the best separation ability. To further investigate the influence of the structures of dendrimer and chiral selector on enantioseparation ability, in this work, another series CSPs (CSPs 1-4) were prepared by immobilizing (1S,2R)-1,2-diphenyl-2-(3-phenylureido)ethyl 4-isocyanatophenylcarbamate (selector II) on one- to four-generation dendrimers that were prepared in previous work. CSPs 1 and 4 demonstrated the equivalent enantioseparation ability. CSPs 2 and 3 showed the best and poorest enantioseparation ability respectively. Basically, these two series of CSPs exhibited the equivalent enantioseparation ability although the chiral selectors were different. Considering the enantioseparation ability of the CSP derived from aminated silica gel and selector II is much better than that of the one derived from aminated silica gel and selector I, it is believed that the dendrimer conformation essentially impacts enantioseparation.

Preparation and enantioseparation of a mixed selector chiral stationary phase derived from benzoylated tartaric acid and 1,2-diphenylethylenediamine.

L-Dibenzoyl tartaric acid was mono-esterified with benzyl alcohol, and then chlorinated with SOCl(2) to give (2S,3S)-1-(benzyloxy)-4-chloro-1,4-dioxobutane-2,3-diyl dibenzoate (Selector 1). (1R,2R)-1,2-Diphenylethylenediamine was mono-functionalized with phenyl isocyanate and phenylene diisocyanate in sequence to give (1R,2R)-1,2-diphenyl-2-(3-phenylureido)ethyl 4- isocyanatophenylurea (Selector 2). Two brush-type chiral stationary phases (CSPs) of single selector were prepared by separately immobilizing selectors 1 and 2 on aminated silica gel. Selectors 1 and 2 were simultaneously immobilized on aminated silica gel to give a mixed selector CSP. The enantioseparation ability of these CSPs was studied. The CSP of selector 1 has strongest separation ability, while the enantioseparation ability of the mixed selector CSP is relatively lower.

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.

Immobilization of (1S,2R)-(+)-2-amino-1,2-diphenylethanol derivates on aminated silica gel with different linkages as chiral stationary phases and their enantioseparation evaluation by HPLC.

A chiral selector was prepared through the reaction between (1S,2R)-(+)-2-amino-1,2-diphenylethanol and phenyl isocyanate. This selector was immobilized on aminated silica gel, respectively, with bifunctional group linkers of 1,4-phenylene diisocyanate, methylene-di-p-phenyl diisocyanate, and terephthaloyl chloride to produce corresponding three chiral stationary phases. The prepared compounds and chiral stationary phases were characterized by FT-IR, elemental analysis, (1)H NMR, and solid-state (1)H NMR. The enantioseparation ability of these chiral stationary phases was evaluated with structurally various chiral compounds. The chiral stationary phase prepared with 1,4-phenylene diisocyanate as linker showed excellent enantioseparation ability. The influence of different linkages on the enantioseparation was discussed.

Chiral self-discrimination of the enantiomers of alpha-phenylethylamine derivatives in proton NMR.

Two types of chiral analytes, the urea and amide derivatives of alpha-phenylethylamine, were prepared. The effect of inter-molecular hydrogen-bonding interaction on self-discrimination of the enantiomers of analytes has been investigated using high-resolution (1)H NMR. It was found that the urea derivatives with double-hydrogen-bonding interaction exhibit not only the stronger hydrogen-bonding interaction but also better self-recognition abilities than the amide derivatives (except for one bearing two NO(2) groups). The present results suggest that double-hydrogen-bonding interaction promotes the self-discrimination ability of the chiral compounds.

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.