ABSTRACT
Tröger's base-embedded pillararenes (P[1]TB[3]A), which combine Tröger's base (TB) with dialkoxybenzene units, were prepared via a fragment-coupling macrocyclization strategy. The TB unit in macrocycle P[1]TB[3]A provides a fixed chiral source, while 1,4-alkoxybenzene segments flip quickly to change their arrangement, which could provide reversible conformational chirality for those macrocycles. This rare example of macrocycles holding both fixed and conformational chirality lays a good foundation for expanding pillararenes using the fixed chiral source.
ABSTRACT
The importance of molecular docking in drug discovery lies in the precise recognition between potential drug compounds and their target receptors, which is generally based on the computational method. However, it will become quite interesting if the rigid cavity structure of supramolecular macrocycles can precisely recognize a series of guests with specific fragments by mimicking molecular docking through co-crystallization experiments. Herein, we report a phenylphosphine oxide-bridged aromatic supramolecular macrocycle, F[3]A1-[P(O)Ph]3, which precisely recognizes benzonitrile derivatives through non-covalent interactions to form key-lock complexes by co-crystallization method. A total of 15 various benzonitrile derivatives as guest molecules are specifically bound by F[3]A1-[P(O)Ph]3 in co-crystal structures, respectively. Notably, among them, crisaborole (anti-dermatitis) and alectinib (anti-cancer) with the benzonitrile fragment, which are two commercial drug molecules approved by the U.S. Food and Drug Administration (FDA), could also form a key-lock complex with F[3]A1-[P(O)Ph]3 in the crystal state, respectively.
ABSTRACT
X-ray crystallography is the most reliable method for structure elucidation and absolute configuration determination of organic molecules based on their single-crystal forms. However, many analytes are hard to crystallize because of their low melting points (an oily state at room temperature) or conformational flexibility. Here, we report the crystallization of a macrocycle, CTX[P(O)Ph] (host), which is a cyclotrixylohydroquinoylene (CTX) derivative, with 26 oily organic molecules (guests), which is applied for the structural determination of the guest with X-ray crystallography. With the aid of the host, CTX[P(O)Ph], the guest molecules were well-ordered with full occupancy in crystal structures. In most cases, at least one guest structure without any disorder could be observed; solvent masking was not necessary for the single crystal X-ray structural analysis, and thus the structures of the guests could be successfully determined, and the absolute configuration could be assigned reliably for chiral guests with this method. The crystallization mechanism was further discussed from theoretical and experimental perspectives, suggesting that the negative electrostatic potential surface of CTX[P(O)Ph] and noncovalent interactions between the host and guest were crucial for the ordered arrangements of the guest.
ABSTRACT
Enantiomers of Tröger's base-based [3]arenes R6N-E[3] and S6N-E[3] were synthesized successfully as two optically pure Tröger's base-based macrocycles in which three Tröger's base subunits were incorporated. Among these Tröger's base-based[3]arenes, M[3] showed high absorption of iodine up to 4.02 g g-1 in vapor.
ABSTRACT
Chirality is ubiquitous in nature, ranging from a DNA helix to a biological macromolecule, snail's shell, and even a galaxy. However, the precise control of chirality at the nanoscale is a challenge due to the structure complexity of supramolecular assemblies, the small energy differences between different enantiomers, and the difficulty in obtaining polymorphic crystals. The planar chirality of water-soluble pillar[5]arenes (called WP5-Na with Na ions in the side chain) host triggered by the addition of chiral L-amino acid hydrochloride (L-AA-OEt) guests and acid/base is rationalized by the relative stability of different chiral isomers, being estimated by molecular dynamics (MD) simulations and quantum chemical calculations. As an increase in the pH value, the change from a positive to a negative value of the free energy difference (ΔG) between two conformations, pR-WP5-NaâL-AA-OEt and pS-WP5-NaâL-AA-OEt, suggests an inversed preference of the pS-WP5-Na conformer induced by the deprotonated L-arginine ethyl ester (L-Arg-OEt) at pH = 14, which is supported by the circular dichroism (CD) experiments. On the basis of 2256 WP5-NaâL-Ala-OEt and 3299 WP5-NaâL-Arg-OEt conformers sampled from MD, the gradient boosting regression (GBR) model exhibits a satisfactory performance (R2 = 0.91) in predicting the chirality of WP5-Na complexations using host-guest binding descriptors, including the geometry matching and binding sites and modes (electrostatics and hydrogen bonding). The machine learning model also performs well on external tests of different hosts (using different side chains and cavity sizes) with the addition of 22 other different guests, with the average chirality prediction accuracy of ML versus experimental CD determinations of 92.8%. The easily accessible host-guest features, binding position coordination and size matching between the cavity and guest, exhibit a close correlation to the chirality of different macrocyclic molecules, water-soluble pillar[6]arenes (WP6) versus WP5, in complexation with different amino acid guests. The exploration of efficient host-guest features in ML displays the great potential of building a large space of various assembled systems and accelerating the on-demand design of chiral supramolecular systems at the nanoscale.
ABSTRACT
The reduction of Fe(III) coupled with the oxidation of organic matter, primarily stimulated by dissimilatory iron-reducing bacteria (DIRB) under anoxic conditions, is a critical biogeochemical process in lacustrine sediments. Many single strains have been recovered and investigated, however, the changes in the diversity of culturable DIRB communities with sedimentary depth have not been fully revealed. In this study, 41 DIRB strains affiliated to ten genera of phylum Firmicutes, Actinobacteria, and Proteobacteria were isolated from the sediments of Taihu Lake at three depths (0-2 cm, 9-12 cm, and 40-42 cm), referring to distinct nutrient conditions. Fermentative metabolisms were identified in nine genera (except genus Stenotrophomonas). The DIRB community diversity and the microbial iron reduction (MIR) patterns vary in vertical profiles. The community abundance varied with the TOC contents in vertical profiles. The DIRB communities, containing 17 strains of 8 genera, were most diverse in the surface sediments (0-2 cm), where organic matter was most abundant among the three depths. 11 DIRB strains of five genera were identified in the 9-12 cm sediments with the lowest content of organic matter, while 13 strains of seven genera were identified in deep sediments (40-42 cm). Among the isolated strains, phylum Firmicutes dominated the DIRB communities at three depths, while its relative abundance increased with depth. Fe2+ ion was recognized as the dominant microbial ferrihydrite-reducing product of DIRB from 0 to 12 cm sediments. Instead, lepidocrocite and magnetite were the main MIR products of DIRB retrieved from 40 to 42 cm. The results indicate that the MIR driven by fermentative DIRB is crucial in lacustrine sediments and that the distribution of nutrients and iron (minerals) likely influences the diversity of DIRB communities in the lacustrine sediments.
Subject(s)
Ferric Compounds , Lakes , Ferric Compounds/metabolism , Lakes/microbiology , Geologic Sediments/chemistry , Iron/analysis , Bacteria/metabolism , Oxidation-Reduction , RNA, Ribosomal, 16SABSTRACT
Cuboid, a basic geometric structure, has been widely applied in architecture and mathematics. In chemistry, the introduction of cuboid structures always provides a specific structural shape, enhances the stability of the structure and improves the performance of materials. Herein, a simple strategy exploiting self-discrimination to construct a cuboid-stacking crystal material is proposed, in which a chiral macrocycle (TBBP) based on Tröger's base (TB) and benzophenone (BP) was synthesized as the building element of the cuboid. The cuboid is designed to be transformable compared with cuboid structures in previous work. For this reason, it is considered that the cuboid-stacking structure can be transformed through external stimulation. Iodine vapor is selected as the external stimulus to transform the cuboid-stacking structure due to the favorable interaction between iodine and the cuboid. The changes in the stacking mode of TBBP is studied by single-crystal X-ray diffraction (SCXRD) and powder X-ray diffraction (PXRD). To our surprise, this Tröger's base-based cuboid shows strong iodine adsorption capacity up to 3.43â g g-1 and exhibits potential as a crystal material for iodine adsorption.
Subject(s)
Gases , Iodine , Adsorption , Crystallography, X-Ray , X-Ray DiffractionABSTRACT
Controlling molecular motion is one of hot topics in the field of chemistry. Molecular rotors have wide applications in building nanomachines and functional materials, due to their controllable rotations. Hence, the development of novel rotor systems, controlled by external stimuli, is desirable. Pillar[n]arenes, a class of macrocycles, have a unique planar chirality, in which two stable conformational isomers pR and pS would interconvert by oxygen-through-the-annulus rotations of their hydroquinone rings. We observe the differential kinetic traits of planar chirality transformation in sodium carboxylate pillar[5]arene (WP5-Na) and ammonium carboxylate pillar[5]arene (WP5-NH4), which inspire us to construct a promising rotary platform in anionic pillar[5]arenes (WP5) skeletons. Herein, we demonstrate the non-negligible effect of counter cations on rotational barriers of hydroquinone rings in WP5, which enables a cation grease/brake rotor system. Applications of this tunable rotor system as fluorescence switch and anti-counterfeiting ink are further explored.
ABSTRACT
Iodine capture is of great significance for disposal of the hazardous radioactive iodine. CTX[P(O)Ph], one kind of censer-shaped macrocycle cyclotrixylohydroquinoylene (CTX) derivatives, was applied as an efficient iodine adsorbent. It showed satisfactory iodine adsorption capacity in vapor phase and could be reused without obvious adsorption capacity loss. Besides, the adsorbent could also uptake iodine in water. Fortunately, two iodine loading CTX[P(O)Ph] crystal structures were obtained under different conditions to explore the mechanism of iodine adsorption. This work provides a relatively rare example of iodine adsorption by macrocycle. It is promising that the results with crystal information might be meaningful for exploring and designing new kinds of iodine adsorbents.
ABSTRACT
On the basis of cyclotrixylohydroquinoylene (CTX), a novel water-soluble phospholate-based CTX derivative (WPCTX) was prepared with facile synthetic procedure and satisfying yield. Several model guest molecules were selected to investigate WPCTX's host-guest properties. Based on the study of the host and model guest complexation, a tetraphenylethylene derivative from model guest was employed as a guest molecule (G) to form WPCTXâG nanoparticles (NPs) with WPCTX through further supramolecular self-assembly in water. Moreover, a hydrophobic fluorescent dye, Eosin Y(ESY) or Nile red (NiR), was encapsulated in WPCTXâG NPs to construct two types of artificial light-harvesting systems. Their high antenna effect demonstrated such NPs successfully mimicked light-harvesting systems in nature.
Subject(s)
Fluorescent Dyes , Nanoparticles , Hydrophobic and Hydrophilic Interactions , WaterABSTRACT
In the aqueous solution, l-CySS-OMe induced pS-WP5 from racemic WP5. Upon the addition of dithiothreitol as a reducing reagent to the above system, pS-WP5 was then converted to pR-WP5 for the reason that l-CySS-OMe was reduced to l-Cys-OMe. Followed by the addition of H2O2 as an oxidation reagent, pR-WP5 was converted back to pS-WP5. The chiral conformational transferring process between pR-WP5 and pS-WP5 can be easily and visually observed by reading the CD signal.
ABSTRACT
Chirality at different levels is widely observed in nature, but the clue to connect it all together, and the way chirality transfers among different levels are still obscure. Herein, a l-/d-lysine-based self-assembly system was constructed, in which two-step chirality transfer among three different levels was observed in aqueous solution. The chirality originated from the point chirality of amino acid derivatives l-/d-PyLys hydrochloride, and was transferred to the planar conformational chirality of water-soluble pillar[5]arene pR-/pS-WP5. Then, with the aid of pR-/pS-WP5, nanoparticles were formed that exhibited L-/R-handed circularly polarized luminescence with a dissymmetry factor of up to ±0.001, arising from pyrene chiral excimers. This multilevel chirality transfer not only provides a perspective to trace potential clues, and to pursue certain ways by which the chirality transfers, but also offers a strategy to create controllable CPL emission in aqueous media.
Subject(s)
Luminescence , Nanoparticles , Amino Acids , Stereoisomerism , WaterABSTRACT
The Tröger's base derivative rac-TBPP was synthesized and separated into two enantiomers R 2N -TBPP and S 2N -TBPP by chiral column chromatography. These compounds show a strong circularly polarized luminescence with g lum values of +0.0021, and -0.0025, respectively. The second way to fabricate the rac-TBPP-based CPL-active material is to co-gel the fluorescent rac-TBPP with a chiral á´ -glutamic acid gelator DGG by co-assembly strategy. At the molar ratio of rac-TBPP/DGG = 1:80, the g lum value of the co-gel was about three times higher than the g lum values of R 2N -TBPP and S 2N -TBPP enantiomers. Interestingly, the CPL handedness of the rac-TBPP/DGG co-gel could be adjusted effectively by changing their stoichiometric ratios.
ABSTRACT
A stoichiometry-controlled chirality induction was successfully achieved through coassemblies of amphiphilic tetraphenylethylene derivative TPEA, γ-cyclodextrin (γ-CD), and water-soluble pillar[5]arene WP5 in aqueous solution. Stoichiometric variation of WP5 was found to be an effective strategy to induce topological transition between the pseudo[4]rotaxane and the vesicular form. Interestingly, the formation of pseudo[4]rotaxane triggered dual chirality induction from chiral γ-CD to TPEA (negative ICD1), and then, to dynamically racemic WP5 (positive ICD2), whereas both ICD1 and ICD2 were silent in the vesicular form.
Subject(s)
Biocompatible Materials/chemistry , Calixarenes/chemistry , Quaternary Ammonium Compounds/chemistry , Stilbenes/chemistry , gamma-Cyclodextrins/chemistry , Materials Testing , Molecular Structure , Particle Size , Solubility , Stereoisomerism , Water/chemistryABSTRACT
Chiral α-amino acids play critical roles in the metabolic process in nearly all life forms. So far, chiral recognition of α-amino acids has mainly focused on the determination of l/d enantiomers. Herein, selection of planar chiral conformations between water-soluble pillar[5]arene WP5 and pillar[6]arene WP6 was observed due to α-side chain or ethyl ester moieties of l-α-amino acid ethyl ester hydrochlorides binding with WP5 and WP6, respectively. Therefore, α-side chain and ethyl ester moieties of l-α-amino acid ethyl ester hydrochlorides were recognized by observing the induced CD signal and its inversion. This is a rare example of being able to detect the chiral region around α-carbon of a chiral α-amino acid molecule.
ABSTRACT
A crown-shaped cyclotriveratrylene (CTV) analogue with persubstituted arene units-namely, cyclotrixylohydroquinoylene (CTX)-was synthesized from tetrasubstituted o-xylohydroquinone. Importantly, a series of CTX derivatives were prepared by introducing second bridged methylene, phenylphosphine oxide, and dimethylsilyl at the middle rim, referred to as CTX[CH2], CTX[P(O)Ph], and CTX[SiMe2], respectively, with the completely locked crown conformation, leading to the formation of unique C3-symmetric Chinese censer-shaped pocket structures. In addition, the water-soluble CTX[CH2] derivative (WCTX[CH2]) was synthesized from CTX[CH2] by simple oxidation reaction with the modification at the upper rim, and its host-guest interaction with methyl viologen in water was investigated.
ABSTRACT
The competitive conformation chirality of dynamically racemic water-soluble pillar[5]arene WP5 can be induced by 19 different l-amino acid ethyl ester hydrochlorides. Among them, l-Arg-OEt and 18 other l-amino acid ethyl ester hydrochlorides can induce the opposite-handedness conformation of WP5. This was ascribed to the different binding models with a side-chain moiety or ethyl ester moiety of amino acids toward the cavity of WP5.
Subject(s)
Calixarenes/chemistry , Amino Acids , Circular Dichroism , Models, Molecular , Molecular Conformation , Solubility , Stereoisomerism , Water/chemistryABSTRACT
Planar-chiral pillar[5]arenes bearing ß-D-galactose substituents on both rims have been successfully synthesized and effectively separated by silica gel chromatography with a high yield. The obtained (S p )- and (R p )-ß-D-galactose functionalized pillar[5]arenes [(S p-D )-GP5 and (R p-D )-GP5] exhibit the S p and R p planar chirality. Furthermore, (S p-D )-GP5 and (R p-D )-GP5 can not racemize according to dynamic 1H NMR and CD spectra. Notably, GP5 is able to capture a guest molecule (DNS-CPT) to form a host-guest supramolecular amphiphile, which can further self-assemble into chiral nanoparticles with the S p and R p planar chirality of (S p-D )-GP5 and (R p-D )-GP5 still being retained, suggesting GP5 could be as reliable chiral sources to transfer the S p and R p planar chirality.
ABSTRACT
Three stereoisomers of Tröger's Base-based dimeric macrocycles Trögerophane 1 (T1) including one pair of enantiomers ( rac-T1) and one meso isomer ( R 2N S 2N -T1) were obtained and fully characterized by X-ray analysis. In the crystalline stacking state R 2N S 2N -T1 showed heterochiral self-sorting behavior along a axis with cofacial π-π stacking interactions, while rac-T1 showed heterochiral self-sorting behavior along c axis with slipped π-π stacking interactions, respectively. Meanwhile both of them showed homochiral self-sorting behavior along b axis as well as one pair of supramolecular helixes were formed in both cases. All the self-sorting behaviors are controlled by two chiral Tröger's Base units from neighboring molecules. To the best of our knowledge, such chiral self-sorting and supramolecular helixes of N-centered chiral superstructures is a rare example. In addition, R 2N S 2N -T1 and rac-T1 demonstrated different adsorption capacities toward the vapor of dichloromethane and acetone, respectively.
ABSTRACT
Two isomers of Tröger's base-linked cryptands 5a and 5b were synthesized, and both of them have two chiral N-centers, exhibiting rare diamond-like scaffolds. Particularly, when growing from the solution of rac-5a, a single enantiomer RNRN-5a was found in the crystal cell, revealing chiral self-sorting behaviour. However, when adding CF3COOH to protonate Tröger's base in the solution of rac-5a, two enantiomers were both formed in pairs in the crystal cell, exhibiting chiral self-discriminating behaviour.