A facile avenue to fabricate micrometer‐sized chiral (L ‐, D ‐) and meso‐like (dl ‐) SiO2 materials with unique structures by using crystalline complexes (cPEI/tart), composed of comblike polyethyleneimine (cPEI) and L ‐, D ‐, or dl ‐tartaric acid, respectively, as catalytic templates is reported. Interestingly, both chiral crystalline complexes appeared as regularly left‐ and right‐twisted bundle structures about 10 μm in length and about 5 μm in diameter, whereas the dl ‐form occurred as circular structures with about 10 μm diameter. Subsequently, SiO2@cPEI/tart hybrids with high silica content (>55.0 wt %) were prepared by stirring a mixture containing tetramethoxysilane (TMOS) and the aggregates of the crystalline complexes in water. The chiral SiO2 hybrids and calcined chiral SiO2 showed very strong CD signals and a nanofiber‐based morphology on their surface, whereas dl ‐SiO2 showed no CD activity and a nanosheet‐packed disklike shape. Furthermore, metallic silver nanoparticles (Ag NPs) were encapsulated in each silica hybrid to obtain chiral (D and L forms) and meso‐like (dl form) Ag@SiO2 composites. Also, the reaction between L ‐cysteine (Lcys) and these Ag@SiO2 composites was preliminarily investigated. Only chiral L ‐ and D ‐Ag@SiO2 composites promoted the reaction between Lcys and Ag NPs to produce a molecular [Ag–Lcys]n complex with remarkable exciton chirality, whereas the reaction hardly occurred in the case of meso‐like (dl ‐) Ag@SiO2 composite. 相似文献
The interaction of PEGylated poly(amino acid)s with their biological targets depends on their chemical nature and spatial arrangement of their building blocks. The synthesis, self‐assembly, and DNA complexation of ABC terblock copolymers consisting of poly(ethylene glycol), (PEG), poly(l ‐lysine), and poly(l ‐leucine), are reported. Block copolymers are produced by a metal‐free, living ring‐opening polymerization of respective amino acid N‐carboxyanhydrides using amino‐terminated PEG as macroinitiator: (PEG‐b‐p(l ‐Lys)x‐b‐p(l ‐Leu)y, PEG‐b‐p(l ‐Leu)x‐b‐p(l ‐Lys)y, and PEG‐b‐p((l ‐Lys)x‐co‐p(l ‐Leu)y). Sizes of self‐assembled nanoparticles depend on the formation method. The nanoprecipitation method proves useful for copolymers with the poly(l ‐lysine) block protected as trifluoroacetate, effective diameters range between 92 and 132 nm, while direct dissolution in distilled water is suitable for the deprotected copolymers, yielding effective diameters between 52 and 173 nm. Critical micelle concentration (CMC) analyses corroborate particle size analyses and show a distinct impact of the molecular architecture; the lowest CMC (8 µg mL−1) is observed when the poly(l ‐leucine) segment forms the C‐block and the hydrophilic, disassembly driving poly(l ‐lysine) segment is short. DNA complexation, evaluated by gel motility and RiboGreen analyses, depends strongly on the molecular architecture. A more efficient DNA complexation is observed when poly(l ‐lysine) and poly(l ‐leucine) form individual blocks as opposed to them forming a copolymer. 相似文献
Homochiral metal–organic framework (MOF) membranes have been recently reported for chiral separations. However, only a few high‐quality homochiral polycrystalline MOF membranes have been fabricated due to the difficulty in crystallization of a chiral MOF layer without defects on porous substrates. Alternatively, mixed matrix membranes (MMMs), which combine potential advantages of MOFs and polymers, have been widely demonstrated for gas separation and water purification. Here we report novel homochiral MOF–polymer MMMs for efficient chiral separation. Homochirality was successfully incorporated into achiral MIL‐53‐NH2 nanocrystals by post‐synthetic modification with amino acids, such as l ‐histidine (l ‐His) and l ‐glutamic acid (l ‐Glu). The MIL‐53‐NH‐l ‐His and MIL‐53‐NH‐l ‐Glu nanocrystals were then embedded into polyethersulfone (PES) matrix to form homochiral MMMs, which exhibited excellent enantioselectivity for racemic 1‐phenylethanol with the highest enantiomeric excess value up to 100 %. This work, as an example, demonstrates the feasibility of fabricating diverse large‐scale homochiral MOF‐based MMMs for chiral separation. 相似文献
In this study, a series of chiral stationary phases based on N‐[(4‐methylphenyl)sulfonyl]‐l ‐leucine amide, whose enantiorecognition property has never been studied, were synthesized. Their enantioseparation abilities were chromatographically evaluated by 67 enantiomers. The chiral stationary phase derived from N‐[(4‐methylphenyl)sulfonyl]‐l ‐leucine showed much better enantioselectivities than that based on N‐(4‐methylbenzoyl)‐l ‐leucine amide. The construction of C2 symmetric chiral structure greatly improved the enantiorecognition performance of the stationary phase. The C2 symmetric chiral stationary phase exhibited superior enantioresolutions to other chiral stationary phases for most of the chiral analytes, especially for the chiral analytes with C2 symmetric structures. By comparing the enantioseparations of the enantiomers with similar structures, the importance of hydrogen bond interaction, π–π interaction, and steric hindrance on enantiorecognition was elucidated. The enantiorecognition mechanism of trans‐N,N′‐(1,2‐diphenyl‐1,2‐ethanediyl)bis‐acetamide, which had an excellent separation factor on the C2 symmetric chiral stationary phase, was investigated by 1H‐NMR spectroscopy and 2D 1H‐1H nuclear overhauser enhancement spectroscopy. 相似文献
(+)‐(1S)‐1,1′‐Binaphthalene‐2,2′‐diyl hydrogen phosphate (bnppa) is one of the useful optical selectors. To disclose the molecular mechanism by which bnppa recognizes aliphatic L ‐α‐amino acids and separates them by fractional crystallization, X‐ray analyses of bnppa and of its salts with L ‐alanine, L ‐valine, L ‐norvaline, and L ‐norleucine have been undertaken. All the amino acids adopt energetically favorable conformations in the crystal structures. The conformations and the packing patterns of bnppa in these crystal structures are very similar. The bnppa molecules are packed in a specific way to form hydrophobic and hydrophilic layers that are well separated. Between bnppa molecules, at the interface of these hydrophobic and hydrophilic layers, a space with chirality is formed. This space, designated as chiral space, recognizes the optically active amino acids. The packing of bnppa is mainly governed by intermolecular CH⋅⋅⋅π interactions between naphthalene moieties. The chiral space is responsible for the molecular recognition by bnppa allowing fractional crystallization of the L ‐α‐amino acids. 相似文献
Chirality is one of the most fascinating and ubiquitous features in nature, especially in biological systems. The effects of chiral surfaces, especially in combination with degradable materials of good biocompatibility, on stem cell behaviors has not yet been tackled. In this communication, the chiral monomers N‐acryloyl‐l (d )‐valine (l (d )‐AV) are synthesized and are polymerized to obtain chiral (l (d )‐PAV‐SH) oligomers, which are covalently immobilized onto electron‐deficient poly(propylene fumarate) polyurethane (PPFU) via Michael addition. The PPFU‐l ‐PAV can interact more strongly and actively with bone marrow stem cells (BMSCs) than PPFU‐d ‐PAV, leading to a larger cell spreading area, faster migration velocity, and stronger osteodifferentiation tendency.
In this report, we describe our recent work on the development of a new family of chiral heteroleptic digold(I) metalloligands with mixed diphosphine and d ‐penicillaminate (d ‐pen), [Au2(dppx)(d ‐pen‐S)2]2– (dppx = PPh2(CH2)nPPh2, n = 1–5) and their application for the construction of chiral multinuclear and metallosupramolecular structures. The reactions of the metalloligands with 3d metal ions produce a variety of chiral heterobimetallic structures retaining the digold(I) metalloligand structure, ranging from discrete trinuclear to infinite helix structures that depend on the type of dppx. In addition, monophosphine and triphosphine analogues of the metalloligands were designed, and their coordination behavior is discussed to show the essential properties and potential extensibility of this class of metalloligands. 相似文献
Collection of two optically pure enantiomers in a single crystallization process can significantly increase the chiral separation efficiency but this is difficult to realize. Now a self‐reporting strategy is presented for visualizing the crystallization process by a dyed self‐assembled inhibitor made from the copolymers with tri(ethylene glycol)‐grafting polymethylsiloxane as the main chain and poly(N6‐methacryloyl‐l ‐lysine) as side chains. When applied with seeds together for the fractional crystallization of conglomerates, the inhibitors can label the formation of the secondary crystals and guide the complete separation process of two enantiomers with colorless crystals as the first product and red crystals as the second. This method leads to high optical purity of d /l ‐Asn?H2O (99.9 % ee for d ‐crystals and 99.5 % for l ‐crystals) in a single crystallization process. It requires a small amount of additives and shows excellent recyclability. 相似文献
Amino acid ionic liquids (AAILs) with l ‐lysine (l ‐Lys) as anion were synthesized and applied as new chiral ligands in Zn(II) complexes for chiral ligand‐exchange CE. After effective optimization, baseline enantioseparation of seven pairs of dansylated amino acids was achieved with a buffer of 100.0 mM boric acid, 5.0 mM ammonium acetate, 3.0 mM ZnSO4, and 6.0 mM [C6mim][l ‐Lys] at pH 8.2. To validate the unique behavior of AAILs, a comparative study between the performance of Zn(II)‐l ‐Lys and Zn(II)‐[C6mim][l ‐Lys] systems was conducted. In Zn(II)‐[C6mim][l ‐Lys] system, it has been found that the improved chiral resolution could be obtained and the migration times of the three test samples were markedly prolonged. Then the separation mechanism was further discussed. The role of [C6mim][l ‐Lys] indicated clearly that the synthesized AAILs could be used as chiral ligands and would have potential utilization in separation science in future. 相似文献
Nanomaterials with enzyme‐mimetic activities are possible alternatives to natural enzymes. Mimicking enzymatic enantioselectivity remains a great challenge. Herein, we report that cysteine‐derived chiral carbon dots (CDs) can mimic topoisomerase I to mediate topological rearrangement of supercoiled DNA enantioselectively. d ‐CDs can more effectively catalyze the topological transition of plasmid DNA from supercoiled to nicked open‐circular configuration than l ‐CDs. Experiments suggest the underlying mechanism: d ‐CDs intercalatively bind with DNA double helix more strongly than l ‐CDs; the intercalative CDs can catalyze the production of hydroxyl radicals to cleave phosphate backbone in one strand of the double helix, leading to topological rearrangement of supercoiled DNA. Molecular dynamics (MD) simulation show that the stronger affinity for hydrogen‐bond formation and hydrophobic interaction between d ‐cysteine and DNA than that of l ‐cysteine is the origin of enantioselectivity. 相似文献
The chromatographic retention mechanism describing relationship between retention factor and concentration of Cu2+(l ‐phenylalanine)2 using chiral ligand mobile phase was investigated and eight mandelic acid derivatives were enantioseparated by chiral ligand exchange chromatography. The relationship between retention factor and concentration of the Cu2+(l ‐phenylalanine)2 complex was proven to be in conformity with chromatographic retention mechanism in which chiral discrimination occurred both in mobile and stationary phase. Different copper(II) salts, chiral ligands, organic modifier, pH of aqueous phase, and conventional temperature on retention behavior were optimized. Eight racemates were successfully enantioseparated on a common reversed‐phase column with an optimized mobile phase composed of 6 mmol/L of l ‐phenylalanine or N,N‐dimethyl‐l ‐phenylalanine and 3 mmol/Lof copper(II) acetate or copper(II) sulfate aqueous solution and methanol. 相似文献
The preparation of star‐shaped poly(γ‐benzyl‐L ‐glutamate)s by the ring‐opening polymerization of N‐carboxy anhydride γ‐benzyl‐L ‐glutamate (BLG‐NCA) with hexakis(4‐aminomethylphenoxy)‐ ( 4 ) and hexakis(4‐aminophenoxy)cyclotriphosphazenes ( 6 ), and the conformation of resulting polymers has been studied. The six amino groups in 4 can initiate the polymerization of BLG‐NCA to give star‐shaped polyglutamates ( 7 ) with narrow molecular weight distributions (Mw/Mn = 1.10–1.33). For the polymerization of BLG‐NCA with 6 , however, a high ratio of [BLG‐MCA]/[ 6 ] was required to obtain star‐shaped polyglutamates ( 8 ). The conformation of 7 changed from a β‐sheet form to a right‐handed α‐helix form, depending on the degree of polymerization per chain (DPn/6). The helix content of hexa‐armed poly (γ‐benzyl‐L ‐glutamate‐co‐L ‐glutamic acid)s ( 9 ), prepared by partial hydrolysis of 7 , increased significantly compared with that of the corresponding linear analogue ( 10 ). As increasing of helix content of 9 , the fluorescence spectra of 8‐anilino‐1‐naphthalenesulfonic acid (ANS), a fluorescence probe, shifted to a short wavelength accompanied by the enhancement of intensity, suggesting that star‐shaped polymers are liable to form hydrophobic domains. From these results and the structural feature of the cyclotriphosphazene core, the formation of a 3α‐helix bundle structure of polyglutamates on both sides of the phosphazene ring has been suggested.