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The objective of this research was to develop a high-performance flexible silica aerogel composite for thermal insulation under high-temperature and thermal–force coupling conditions. Based on synthesis of flexible silica aerogels with methyltrimethoxysilane as the precursor, flexible silica aerogel composites were developed by wet-impregnating ceramic fiber felt. Morphology, microstructure, chemical structure, hydrophobicity, and compression performance evolutions of the flexible silica aerogels and their composite counterparts with temperature revealed that the resulting flexible silica aerogel samples have excellent stability at 900 °C. Flexible silica aerogel composites show 100 and 70% recovery with 50% strain after treatment at 500 and 900 °C, respectively. Thermal insulation performance of the flexible silica aerogel composites was comprehensively studied from different aspects, including thermal conductivity, thermal shield behavior under high-temperature and thermal–force coupling conditions, and thermal shock resistance. Thermal conductivities of the flexible silica aerogel composite at 25–1100 °C are lower than those of most reported aerogel composites. Coupling of force under high temperature leads to degradation of thermal insulation performance, owing to deformation with compression. The synthesis method of the flexible silica aerogel is facile and inspiring, and the flexible silica aerogel composites have promising prospects in thermal insulation under high-temperature and thermal-stress coupling conditions, such as suppressing thermal runaway propagation of lithium-ion batteries. [ABSTRACT FROM AUTHOR]

To improve the therapeutic efficacy of breast cancer (BC), an intelligent tri-responsive vehicle based on core–shell structured gold nanorods (GNR)@mesoporous SiO2 (MS)@hyaluronic acid (HA) is proposed for controlled delivery of methotrexate (MTX). The characterization of the resultant GNR@MS@HA is systematically investigated. GNR is used for photothermal conversion under near-infrared light (NIR) irradiation, and the produced hyperthermia can lead to the ablation of cancer cells. MTX can be encapsulated in the mesopores of MS with the aid of HA, which is grafted to the surface of aminated MS (MS-NH2) through amidation reaction. The proposed vehicle can be used for MTX release in the tri-response of pH, NIR, and hyaluronidase (HAase) and integrates photothermal therapy and chemotherapy so as to improve the inhibition rate of cancer cells. The results of cell viability experiments demonstrate that the developed tri-responsive vehicle displays excellent biocompatibility to L929 mouse fibroblasts while exhibiting high chemo-photothermal synergistic therapy efficiency against murine BC cells (4T1). [ABSTRACT FROM AUTHOR]

Developing the ability to 3D printvarious classes of materials possessing distinct properties couldenable the freeform generation of active electronics in unique functional,interwoven architectures. Achieving seamless integration of diversematerials with 3D printing is a significant challenge that requiresovercoming discrepancies in material properties in addition to ensuringthat all the materials are compatible with the 3D printing process.To date, 3D printing has been limited to specific plastics, passiveconductors, and a few biological materials. Here, we show that diverseclasses of materials can be 3D printed and fully integrated into devicecomponents with active properties. Specifically, we demonstrate theseamless interweaving of five different materials, including (1) emissivesemiconducting inorganic nanoparticles, (2) an elastomeric matrix,(3) organic polymers as charge transport layers, (4) solid and liquidmetal leads, and (5) a UV-adhesive transparent substrate layer. Asa proof of concept for demonstrating the integrated functionalityof these materials, we 3D printed quantum dot-based light-emittingdiodes (QD-LEDs) that exhibit pure and tunable color emission properties.By further incorporating the 3D scanning of surface topologies, wedemonstrate the ability to conformally print devices onto curvilinearsurfaces, such as contact lenses. Finally, we show that novel architecturesthat are not easily accessed using standard microfabrication techniquescan be constructed, by 3D printing a 2 × 2 × 2 cube of encapsulatedLEDs, in which every component of the cube and electronics are 3Dprinted. Overall, these results suggest that 3D printing is more versatilethan has been demonstrated to date and is capable of integrating manydistinct classes of materials. [ABSTRACT FROM AUTHOR]

Treatment of the o-hydroxyaryl imidazoliumproligands(2-OH-3,5-tBu2C6H2)(R)(C3H3N2)+Br–(R = iPr (1a), tBu (1b), Ph(1c), Mes (1d)) with 3 equiv of Ag2O afforded the corresponding silver complexes 2a–d. The subsequent metal-exchange reactions with [(p-cymene)RuCl2]2at room temperatureyielded the desired o-aryloxide-N-heterocyclic carbene p-cymene ruthenium complexes 3a–din nearly quantitative yields. All the complexes were characterizedby 1H and 13C NMR, high-resolution mass spectrometry(HRMS), and elemental analysis. The molecular structure of complex 3bwas determined by single-crystal X-ray diffraction analysis.The ring-opening metathesis polymerization (ROMP) of norbornene (NBE)with 3a–dwas studied. Among them,complex 3dshowed high activity and efficiency towardROMP of NBE at 85 °C without the need for any cocatalyst, andpolymers with very high molecular weight (>106) andnarrowmolecular weight distributions were obtained. This complex can alsocatalyze the alternating copolymerization of NBE and cyclooctene (COE). [ABSTRACT FROM AUTHOR]

Although covalent organic frameworks (COFs) accompanied by electrochemiluminescence (ECL) behavior have been introduced in recent years, they are still rarely applied for ECL-based enantioselective sensing, especially giving high recognition efficiency. In the current study, an achiral ionic COF comprised of the pyridinium unit is synthesized in the linkage of the carbon-nitrogen cation bond through the Zincke reaction. Interestingly, the synthesized ionic COF can generate clear ECL owing to the presence of electroactive species. Then, the ECL-active achiral COF is employed to absorb the chiral Co(III) complex for enantioselective sensing. As a result, the developed ECL sensor displays discriminative responses toward amino alcohol enantiomers. When the chiral Co(III) complex with ( R )-configuration is used, the examined ( S )-amino alcohols result in ECL enhancement, whereas ( R )-amino alcohols lead to ECL quenching. The maximum ECL intensity ratio between ( S )- and ( R )-amino alcohols is up to 47.7. In addition, the recognition mechanism is investigated in detail. Finally, a good linear relation between enantiomeric composition and ECL intensity is developed and appropriate for the accurate analysis of the enantiomeric purities of unknown samples. In short, we believe that this study constructs an effective strategy to combine the respective advantages of COFs and ECL for high-efficiency enantioselective sensing.

Nowadays, covalent-organic frameworks (COFs) integrated with the electrochemiluminescence (ECL) behavior are highly desired owing to the significant advantages including multifunctionality, high sensitivity, and low background noise. Here, two ionic COFs (iCOFs) consisting of the anthryl-extended viologen as the backbone were designed and synthesized via the Zincke reaction. It is found for the first time that the as-prepared iCOFs accompanied by potassium persulfate as the coreactant can provide a clear ECL response in a water-bearing medium. The maximum ECL emissions of the iCOFs were in agreement with the photoluminescence spectra. Besides, cyclic voltammetry and electron paramagnetic resonance measurements reveal that the pyridinium unit was electrochemically reduced to afford the free radical. Then, it reacted with SO 4 ·- to generate the excited-state [iCOF]*. Finally, [iCOF]* quickly returned to its ground state coupled with a clear ECL emission, yielding a maximum ECL quantum efficiency of 23.4% compared with tris(2,2'-bipyridyl) ruthenium(II) as the benchmark. In brief, the current study opens a way to develop a kind of ECL emitter that holds great potential in sensing, imaging, and light-emitting devices.

To date, achieving enantioselective electroanalysis for electrochemically silent chiral molecules is still highly desired. Here, an ionic covalent organic framework (COF) consisting of the pyridinium cation was derived from the tripyridinium Zincke salt and 1,4-phenylenediamine in a one-pot reaction. The electrochemical measurements revealed that the ionic backbone contributed to the electron transfer with a low charge transfer resistance. Besides, the π-π + interaction between the pyridinium cation and ferrocenyl unit can promote the absorption of electroactive chiral ferrocenyl reagents into the hole of COF, so as to afford the electrochemical signals by themselves, replacing the testing enantiomers. As a result, the electroactive complex used as an electrochemical platform was highly effective at enantiomerically recognizing amino alcohols (prolinol, valinol, leucinol, and alaninol) and amino acids (methionine, serine, and penicillamine), giving the ratios of current intensity between l- and d-enantiomers in the range of 1.46-1.72. Moreover, the density functional theory calculations determined the possible intermolecular interactions between the testing enantiomers and chiral selector: namely, hydrogen bonds and electrostatic attractions. Overall, the present work offers an effective strategy to enlarge the electrochemical scope for chiral recognition based on electroactive chiral COFs.

Although several studies related with the electrochemiluminescence (ECL) technique have been reported for chiral discrimination, it still has to face some limitations, namely, complex synthetic pathways and a relatively low recognition efficiency. Herein, this study introduces a facile strategy for the synthesis of ECL-active chiral covalent organic frameworks (COFs) employed as a chiral recognition platform. In this artificial structure, ruthenium(II) coordinated with the dipyridyl unit of the COF and enantiopure cyclohexane-1,2-diamine was harnessed as the ECL-active unit, which gave strong ECL emission in the presence of the coreactant reagent (K 2 S 2 O 8 ). When the as-prepared COF was used as a chiral ECL-active platform, clear discrimination was observed in the response of the ECL intensity toward l- and d-enantiomers of amino acids, including tryptophan, leucine, methionine, threonine, and histidine. The biggest ratio of the ECL intensity between different configurations was up to 1.75. More importantly, a good linear relationship between the enantiomeric composition and the ECL intensity was established, which was successfully employed to determine the unknown enantiomeric compositions of the real samples. In brief, we believe that the proposed ECL-based chiral platform provides an important reference for the determination of the configuration and enantiomeric compositions.

Chiral analysis is of significant importance for living organisms since chirality is the fundamental phenomenon in nature. In this work, a bifunctional electrochemiluminescent (ECL) platform is constructed for chiral discrimination and chiral sensing. 3-Mercaptopropionic acid-functionalized CdSe quantum dots (CdSe QDs) are combined with aminated TiO 2 nanotubes (NH 2 -TiNTs) via amidation. The resultant CdSe QDs/TiNTs display significantly enhanced ECL signals due to the synergistic effect between CdSe QDs and TiNTs, which are then used for the chiral discrimination of the isomers of nine chiral amino acids (AAs) in the presence of d-AA oxidase (DAAO). DAAO can selectively catalyze the oxidation of d-AAs to generate H 2 O 2 , which acts as the coreaction reagent and triggers the ECL signals of CdSe QDs/TiNTs, and thus, the isomers of the nine chiral AAs can be effectively discriminated. In addition, the as-constructed ECL platform can also be used for the sensitive detection of d-AAs in the presence of DAAO with a wide linear range and a low limit of detection. These findings suggest that the CdSe QDs/TiNTs can work as a bifunctional ECL platform (chiral discrimination and chiral sensing), which might be an advanced ECL platform for biomedical applications.

At present, chiral electroanalysis of nonelectroactive chiral compounds still remains a challenge because they cannot provide an electrochemical signal by themselves. Here, a strategy based on a competitive self-assembly interaction of a ferrocene (Fc) unit and the testing isomers entering into the cavity of β-cyclodextrin (β-CD) was carried out for chiral electroanalysis. First of all, the Fc derivative was directly bridged to silica microspheres, followed by inclusion into the cavity of β-CD. As expected, once it was modified onto the surface of a carbon working electrode as an electrochemical sensor, SiO 2 @Fc-CD-WE, its differential pulse voltammetry signal would markedly decrease compared with the uncovered Fc. Next, when l- and d-isomers of amino acids that included histidine, threonine, phenylalanine, and glutamic acid were examined using SiO 2 @Fc-CD-WE, it showed an enantioselective entry of amino acids into the cavity of β-cyclodextrin instead of Fc, resulting in the release of Fc with signal enhancement. For histidine, glutamic acid, and threonine, l-isomers showed a higher peak current response compared with d-isomers. The peak current ratios between l- and d-isomers were 2.88, 1.21, and 1.40, respectively. At the same time, the opposite phenomenon occurred for phenylalanine with a peak current ratio of 3.19 between d- and l-isomers. In summary, we are assured that the recognition strategy based on the supramolecular interaction can enlarge the detection range of chiral compounds by electrochemical analysis.

In the past, various chiral isomers accompanied by electroactive units have been distinguished using electrochemical techniques, which can produce electrochemical signals by themselves. However, it is still difficult to use an electrochemical technique to detect nonelectroactive samples. To address this bottleneck, an electroactive chiral polymer ( S , S )- p -CVB-Fc that contains one redox-active ferrocene unit was designed and synthesized in this study. The electroactive polymer can give electrochemical signals as an alternative to the tested chiral samples, regardless of whether the isomers have electroactive units. Then, it was fixed on the surface of a glassy carbon electrode as an electrochemical chiral sensor. When nonelectroactive amino acids including proline, threonine, and alanine were examined by the sensor, clear discrimination in the response of peak current could be observed toward l- and d-isomers at pH 6.5. The peak current ratios ( I L / I D ) for proline and alanine were 1.47 and 1.48, respectively. In contrast, for threonine, the d-isomer exhibited a higher peak current than the l -isomer with a ratio of 2.59. In summary, the results ensure that the current work can enlarge the testing scope of chiral samples in the field of chiral electroanalysis using an electroactive sensor.

π-Conjugated porphyrins have aroused particular attention for nanofabrication and biomimics; however, little attention has been paid to porphyrins-based chiral analysis owing to the achiral feature of porphyrins. Here, we demonstrated a chiral self-assembly of achiral porphyrin induced by l- and d-lysine (l- and d-Lys), and the resultant porphyrin self-assembly exhibited alterable morphologies depending on the inducer used (l- or d-Lys). The supramolecular chirality of the self-assembly was characterized by circular dichroism (CD) spectra, confirming successful transfer of molecular chirality from l- and d-Lys to the self-assembly. The enantioselective property of the chiral self-assembly was also investigated by using tryptophan (Trp) isomers as the model, and the results indicated that the developed chiral self-assembly showed significantly higher affinity toward l-Trp than d-Trp. Also in this work, the l-/d-Lys-induced chiral self-assembly of porphyrin and the supramolecular interaction between the self-assembly and l-/d-Trp were also studied by density functional theory (DFT).

The first sulfhydryl-directed iridium-catalyzed C-H/diazo coupling and tandem annulation of naphthalene-1-thiols has been developed. The framework of naphtho[1,8- bc ]thiopyrans was constructed in a one-step reaction with good yields. This transformation provides a practical synthetic route for the widely used naphtho[1,8- bc ]thiopyran derivatives.

Polyimide (PI) aerogels were successfully synthesized via a straightforward sol-gel process under room temperature along with the supercritical CO 2 drying method using 4-amino- N-methylbenzamide and 3,3',4,4'-biphenyltetracarboxylic dianhydride. 1,3,5-Triaminophenoxybenzene was used as the cross-linker. The chemical structure, pore structure, morphology, thermal performance, CO 2 adsorption, and mechanical performance of PI aerogels were investigated. The as-prepared PI aerogels had low bulk densities (0.091-0.167 g/cm 3 ), low shrinkages (9.73-17.36%), low thermal conductivities (0.0307-0.0341 W/m·K), high specific surface areas (449.76-538.19 m 2 /g), small pore diameter (10.37-22.41 nm), high thermal stability (onset of decomposition above 560 °C), and excellent mechanical property. The CO 2 adsorption capacities of PI aerogels were substantially higher than the values of the previous porous materials reported under the similar conditions, and the CO 2 uptake capacity was as high as 31.19 cm 3 /g at 25 °C and 1.0 bar. The resulting PI aerogels could be potentially used as thermal insulators and CO 2 adsorbents.

Polypyrrole (PPy) was synthesized by a galvanostatic method using (1 S)-(+)-10-camphorsulfonic acid ((+)-CSA) as the dopant, and the produced PPy was further overoxidized in a solution of (+)-CSA. A chiral microenvironment was successfully formed in the overoxidized PPy (OPPy) as a result of the synergistic effects of overoxidation and (+)-CSA, resulting in a twisted helical architecture of the OPPy chains. The formation of optically active OPPy was confirmed from aspects of its morphology (SEM and AFM) and circular-dichroism (CD) spectra. Finally, an electrochemical chirality sensor was fabricated on the basis of the resultant OPPy, which exhibited excellent biomolecular homochirality in the discrimination of tryptophan (Trp) enantiomers.

Here, a novel fluorescent chiral poly(ionic liquid) ( S)-PCIL-4 with nonconjugated backbone is designed and synthesized in the control of micelle through free-radical polymerization, whose fluorescence emission maximum is at λ em,max = 430 nm. It is observed that polymers with spatially proximate units (phenyl group and pyridinium cation) have photoluminescence through spatial π-π and ion-π interaction. Then, ( S)-PCIL-4 can be served as a fluorescent turn off/on sensor for chiral recognition of phenylalaninol and tryptophan in the presence of Cu(II). For example, when ( S)-PCIL-4-Cu(II) is treated with ( R/ S)-phenylalaninol, it will exhibit different fluorescence responses. Values of the enantiomeric fluorescence difference ratio for phenylalaninol and tryptophan are 1.10 and 1.08, respectively. In brief, we believe that the approach opens up a possible pathway to prepare a variety of fluorescent polymers with nonconjugated backbone and proves to be desirable in further application.

Molecular self-assemblies offer a promising strategy for the synthesis of advanced materials for the construction of novel chiral sensing systems, and latest innovations on such self-assemblies are focused on simple building blocks in biology such as nucleic acids, lipids, and peptides. Herein, the self-assemblies of diphenylalanine (FF) and oxalic acid (OA) were prepared as the chiral sensing device for the recognition of tryptophan (Trp) isomers. Interestingly, the self-assemblies composed of OA and FF with different charging states (neutral, positively charged, and negatively charged) exhibited quite different morphologies, resulting in significantly different chiral recognition ability toward the Trp isomers. Also, in this work, the temperature sensitivity and chiral selectivity of the proposed FF-OA self-assemblies were also studied. From a practical point of view, the FF-OA self-assemblies were finally applied for the determination of precise levels of d-Trp in the racemic mixture of Trp isomers.

A quinine (QN)-based chiral sensing platform with alterable enantioselectivity is constructed for electrochemical chiral recognition of tryptophan (Trp) isomers. The electrochemical signals of l- and d-Trp on the QN modified electrode depend closely on temperature, and more particularly are reversed at certain temperatures, which could be attributed to the temperature-sensitive H-bonds and π-π interactions between QN and the Trp isomers. The mechanisms of the reverse chiral recognition are investigated by density functional theory (DFT), variable-temperature UV spectra, and variable-temperature 1 H NMR spectra. In addition, the chiral recognition is highly specific to the isomers of Trp compared with other chiral amino acids. This study is the first example showing how temperature influences the reverse recognition of electrochemical chiral interfaces.

Polysaccharides of sodium carboxymethyl cellulose (CMC) and chitosan (CS) were integrated together via amidation reactions between the carboxyl groups on sodium CMC and the amino groups on CS. Compared with individual sodium CMC and CS, the integrated polysaccharides with a mass ratio of 1:1, CMC-CS (1:1), exhibited a three-dimensional (3D) porous network structure, resulting in a significantly enhanced hydrophility due to the exposed polar functional groups in the CMC-CS (1:1). Chiral interfaces were constructed with the integrated polysaccharides and used for electrochemical enantiorecognition of tryptophan (Trp) isomers. The CMC-CS (1:1) chiral interfaces exhibited excellent selectivity toward the Trp isomers owing to the highly hydrophilic feature of CMC-CS (1:1) and the different steric hindrance during the formation of H bonds between Trp isomers and CMC-CS (1:1). Also, the optimization in the preparation of integrated polysaccharides such as mass ratio and combination mode (amidation or electrostatic interactions) was investigated. The CMC-CS (1:1) presented the ability of determining the percentage of d-Trp in racemic mixtures, and thus, the proposed electrochemical chiral interfaces could be regarded as a potential biosensing platform for enantiorecognition of chiral compounds.

The ability to assemble nanomaterials, such as quantum dots, enables the creation of functional devices that present unique optical and electronic properties. For instance, light-emitting diodes with exceptional color purity can be printed via the evaporative-driven assembly of quantum dots. Nevertheless, current studies of the colloidal deposition of quantum dots have been limited to the surfaces of a planar substrate. Here, we investigate the evaporation-driven assembly of quantum dots inside a confined cylindrical geometry. Specifically, we observe distinct deposition patterns, such as banding structures along the length of a capillary tube. Such coating behavior can be influenced by the evaporation speed as well as the concentration of quantum dots. Understanding the factors governing the coating process can provide a means to control the assembly of quantum dots inside a capillary tube, ultimately enabling the creation of novel photonic devices.

Inspired by the double helix structure of DNA, a simple enantioselective system based on chitosan (CS) was employed for electrochemical enantiorecognition of tryptophan (Trp) isomers. The recognition mechanism was proposed from the supramolecular point of view, which was further verified by the recognition of Trp isomers with sulfonated CS (SCS). The SCS-based chiral system presented the ability of indicating the percentage of d-Trp in racemic mixture, extending future applications of the electrochemical chiral system based on natural polysaccharides.

The development of methods for achieving precise spatiotemporal control over chemical and biomolecular gradients could enable significant advances in areas such as synthetic tissue engineering, biotic-abiotic interfaces, and bionanotechnology. Living organisms guide tissue development through highly orchestrated gradients of biomolecules that direct cell growth, migration, and differentiation. While numerous methods have been developed to manipulate and implement biomolecular gradients, integrating gradients into multiplexed, three-dimensional (3D) matrices remains a critical challenge. Here we present a method to 3D print stimuli-responsive core/shell capsules for programmable release of multiplexed gradients within hydrogel matrices. These capsules are composed of an aqueous core, which can be formulated to maintain the activity of payload biomolecules, and a poly(lactic-co-glycolic) acid (PLGA, an FDA approved polymer) shell. Importantly, the shell can be loaded with plasmonic gold nanorods (AuNRs), which permits selective rupturing of the capsule when irradiated with a laser wavelength specifically determined by the lengths of the nanorods. This precise control over space, time, and selectivity allows for the ability to pattern 2D and 3D multiplexed arrays of enzyme-loaded capsules along with tunable laser-triggered rupture and release of active enzymes into a hydrogel ambient. The advantages of this 3D printing-based method include (1) highly monodisperse capsules, (2) efficient encapsulation of biomolecular payloads, (3) precise spatial patterning of capsule arrays, (4) "on the fly" programmable reconfiguration of gradients, and (5) versatility for incorporation in hierarchical architectures. Indeed, 3D printing of programmable release capsules may represent a powerful new tool to enable spatiotemporal control over biomolecular gradients.

Chronic myeloid leukemia (CML) is a malignant clone disease of hematopoietic stem cells. At present, the most effective therapy for CML is bone marrow transplantation, but this procedure is expensive, and it is often difficult to find appropriately matched bone marrow donors. As an alternative to marrow transplantation, a more effective anticancer drug should be developed to cure the disease; in addition, an effective system to evaluate the activity of the drug needs to be developed. Herein, we present a novel antileukemia drug evaluation method based on a multisignal amplified photoelectrochemical sensing platform that monitors the activity of caspase-3, a known marker of cell apoptosis. Manganese-doped CdS@ZnS core-shell nanoparticles (Mn:CdS@ZnS) were synthesized via a simple wet chemical method, which provided a stable photocurrent signal. A DEVD-biotin peptide and streptavidin-labeled alkaline phosphatise (SA-ALP) were immobilized successively at these nanoparticles through amide bonding and through specific interaction between biotin and streptavidin, respectively. The photocurrent of this sensing platform improved as the ALP hydrolyzed the substrate 2-phospho-l-ascorbic acid (AAP) to ascorbic acid (AA), a more efficient electron donor. The activity of caspase-3 was detected using this sensing platform, and thus, the efficacy of nilotinib for targeting K562 CML cells could be evaluated. The results indicate that nilotinib can effectively induce apoptosis of the K562 cells. This sensing platform exhibited sensitive, reproductive, and stable performance in studying the nilotinib-induced apoptosis of K562 CML cells, and the platform could be utilized to evaluate other anticancer drugs.

A poly(l-glutamic acid)/β-cyclodextrin (P-l-Glu/β-CD)-modified glassy carbon electrode (GCE) was prepared by electrochemical polymerization of l-glutamic acid on GCE and subsequent self-assembly of β-CD onto the obtained P-l-Glu. Electrochemical recognition of tryptophan (Trp) enantiomers with the P-l-Glu/β-CD was investigated by differential pulse voltammetry (DPV), and the results show that Trp enantiomers can be effectively recognized at the P-l-Glu/β-CD-modified GCE. It is also interesting to find that temperature plays a crucial role in the enantioselective recognition, which is evidenced by the variable-temperature UV spectra of the inclusion complexes of Trp enantiomers and β-CD. Under optimum conditions, the oxidation peak current ratio of l-Trp to d-Trp could reach 2.30, which is attributed to the stereoselectivity of β-CD to the enantiomeric pair of Trp.