Planar Chirality Research Articles

Synthesis of terminus-decorated aza[9]helicenes: control of interlayer interaction

Abstract Azahelicenes are intriguing luminescent materials with a planar chirality. The properties of aza[9]helicene can be perturbed by attaching substituent at the termini. The impact of the terminal decoration has been investigated in view of structural and electronic aspects, leading to the control of interlayer interaction.

Symmetry and planar chirality measured with a log-polar transformation in a transmission electron microscope

Symmetry and planar chirality measured with a log-polar transformation in a transmission electron microscope

Ultrasound‐induced circularly polarized luminescence based on homochiral aggregation of clothespin‐shaped Pt(II) complexes

AbstractUltrasound‐induced circularly polarized luminescence (CPL) was achieved using planar chiral, binuclear clothespin‐shaped trans‐bis(salicylaldiminato)platinum(II) complexes. Solutions of the clothespin‐shaped platinum(II) complexes anti‐1a–c in cyclohexane immediately transformed into stable gels upon brief ultrasound irradiation. The ultrasound gels exhibited intense phosphorescent emissions at room temperature, whereas none of the solution exhibited significant emissions under UV light illumination. Interestingly, gels prepared from optically pure complexes exhibited CPL activity at room temperature with an anisotropy factor of |glum| = 1.5–2.6 × 10−3. The emissive gels were readily converted to the original non‐emissive solution upon heating and cooling to room temperature and could be gelled again by ultrasound irradiation. In addition, chromogenic control from green to red emission can be achieved simply by introducing MeO groups at different positions on the aromatic rings.

DNA-mediated assembly of Au bipyramids into anisotropic light emitting kagome superlattices.

Colloidal crystal engineering with DNA allows one to design diverse superlattices with tunable lattice symmetry, composition, and spacing. Most of these structures follow the complementary contact model, maximizing DNA hybridization on building blocks and producing relatively close-packed lattices. Here, low-symmetry kagome superlattices are assembled from DNA-modified gold bipyramids that can engage only in partial DNA surface matching. The bipyramid dimensions and DNA length can be engineered for two different superlattices with rhombohedral unit cells, including one composed of a periodic stacking of kagome lattices. Enabled by the partial facet alignment, the kagome lattices exhibit lattice distortion, bipyramid twisting, and planar chirality. When conjugated with Cy-5 dyes, the kagome lattices serve as cavities with high-density optical states and large Purcell factors along lateral directions, leading to strong dipole radiation along the z axis and facet-dependent light emission. Such complex optical properties make these materials attractive for lasers, displays, and quantum sensing constructs.

Theoretical Study on Photo‐Induced Copper Autoredox Construction of Chiral Amines

AbstractDensity functional theory (DFT) calculations were conducted to investigate the photo‐induced copper‐catalyzed C−N coupling reaction for the synthesis of chiral tertiary amines. The ligands′ effects on the metal center and the factors determining regioselectivity in chiral tertiary amine formation were examined. The computational results revealed that the oxidative quenching process involved in the photocatalytic redox cycle via CuI‐CuI*‐CuII‐CuIII transitions. Throughout the reaction, four key processes occurred: C−Br bond activation, ligand exchange, amide ion/Br ion exchange, and C−N coupling. Among these steps, alkyl radical generation through single electron transfer was identified as the rate‐determining step with an energy barrier of 13.9 kcal/mol. The chelating diphosphine ligand improved copper‘s reducibility and its capacity to activate the C−Br bond by charge transfer when exposed to visible light (CT). Copper's own redox process was facilitated by interactions between diphosphine and diamine ligands. Finally, when combined with oxygen, this catalyst system formed a chiral plane CuII‐O1‐N1‐N2‐N3 essential for enantioselective product formation.

A Pillararene-Based Cavitand: Synthesis and Solid-State Capsular Assemblies Induced by Linear Alkanes with Specific Lengths.

Herein, a novel pillararene-based cavitand with fixed planar chirality was synthesized by the SuFEx reaction. As demonstrated by single crystal X-ray analysis, host-guest capsules involving this cavitand and linear alkanes with specific lengths are observed in the solid state. The formation of each capsule is driven by hydrogen bonding interactions between a linear alkane molecule and two cavitand molecules, as well as noncovalent interactions between the two cavitand molecules in this capsule.

Synthesis, Structure, and Resolution of Functionalized Oxacalix[4]arenes with Planar Chirality via Dynamic SNAr Reaction

A pair of racemic oxacalix[4]arenes featuring planar chirality and a mesomer with a symmetric plane were conveniently synthesized under mild conditions via a one‐pot dynamic SNAr reaction and separated in 20% and 49% yields, respectively. X‐ray single crystal analyses confirmed their structures unambiguously. The racemic mixture could further be resolved using HPLC on a chiral column. Time‐dependent products distribution and interconversion between products with CsF as a catalyst were revealed by 1H NMR studies, convincing the dynamic nature of SNAr reaction.

Self-Assembled Pure Covalent Tubes Exhibiting Circularly Polarized Luminescence.

Here, we successfully synthesized four structurally analogous, self-assembled chiral molecular tubes with relatively high yields. This achievement involved the condensation of six equivalents of enantiomerically pure trans-cyclohexane-1,2-diamine (trans-CHDA) and three equivalents of the corresponding tetraformyl precursor. Each precursor was equipped with a luminescent linker terminated by two m-phthalaldehyde units. Even though these tetraformyl precursors are barely soluble in almost all organic solvents, the molecular tubes are highly soluble in nonpolar solvents such as chloroform, allowing us to fully characterize them in solution. The stereo-chirality of the chiral bisamino building blocks endows the frameworks of molecular tubes with planar chirality. As a consequence, all of these molecular tubes exhibit circularly polarized luminescence (CPL) with relatively large dissymmetry values |glum| up to 7×10-3, providing an efficient method for synthesizing CPL-active materials.

Self‐Assembled Pure Covalent Tubes Exhibiting Circularly Polarized Luminescence

AbstractHere, we successfully synthesized four structurally analogous, self‐assembled chiral molecular tubes with relatively high yields. This achievement involved the condensation of six equivalents of enantiomerically pure trans‐cyclohexane‐1,2‐diamine (trans‐CHDA) and three equivalents of the corresponding tetraformyl precursor. Each precursor was equipped with a luminescent linker terminated by two m‐phthalaldehyde units. Even though these tetraformyl precursors are barely soluble in almost all organic solvents, the molecular tubes are highly soluble in nonpolar solvents such as chloroform, allowing us to fully characterize them in solution. The stereo‐chirality of the chiral bisamino building blocks endows the frameworks of molecular tubes with planar chirality. As a consequence, all of these molecular tubes exhibit circularly polarized luminescence (CPL) with relatively large dissymmetry values |glum| up to 7×10−3, providing an efficient method for synthesizing CPL‐active materials.

The Triceptide Maturase OscB Catalyzes Uniform Cyclophane Topology and Accepts Diverse Gly-Rich Precursor Peptides.

Triceptides are a class of ribosomally synthesized and post-translationally modified peptides defined by an aromatic C(sp2) to Cβ(sp3) bond. The Gly-rich repeat family of triceptide maturases (TIGR04261) are paired with precursor peptides (TIGR04260) containing a Gly-rich core peptide. These maturases are prevalent in cyanobacteria and catalyze cyclophane formation on multiple Ω1-X2-X3 motifs (Ω1 = Trp and Phe) of the Gly-rich precursor peptide. The topology of the individual rings has not been completely elucidated, and the promiscuity of these enzymes is not known. In this study, we characterized all the cyclophane rings formed by the triceptide maturase OscB and show the ring topology is uniform with respect to the substitution at Trp-C7 and the atropisomerism (planar chirality). Additionally, the enzyme OscB demonstrated substrate promiscuity on Gly-rich precursors and can accommodate a diverse array of engineered sequences. These findings highlight the versatility and implications for using OscB as a biocatalyst for producing polycyclophane-containing peptides for biotechnological applications.

Chirality Sensing of Cryptochiral Guests with Prism[n]arenes.

Optical chirality sensing has gained significant attention in recent years. Within this field, the quest for stereodynamic chiroptical probes capable of detecting cryptochiral guests presents a formidable challenge. Macrocycles exhibiting planar chirality have emerged as promising candidates for amplifying the chirality of cryptochiral guests. In this study, we demonstrate that the formation of host-guest complexes between cryptochiral molecules and planar chiral prismarenes triggers electronic circular dichroism (ECD) signals via host-guest complexation-induced chirality amplification. The absolute configuration of the most stable chiral macrocyclic host-guest complex has been established by resorting to both exciton model and DFT computations. Furthermore, we demonstrated that this supramolecular chirality sensing system can be employed to determine the enantiomeric composition of scalemic mixtures by measuring the ECD bands intensity. The information described here opens the way for the use of prismarenes as stereodynamic probes for sensing of cryptochiral guests.

Synthesis of Planar Chiral Ferrocenes by Catalytic Desymmetrization Reactions

Synthesis of Planar Chiral Ferrocenes by Catalytic Desymmetrization Reactions

Unraveling planar chirality in pillar[5]arenes

Pillar[5]arenes have attracted considerable interests in the areas of supramolecular chemistry, material science and stereochemistry. However, they likely encounter a challenge in obtaining stable enantiomers due to the presence of rotational single bonds in the cavity structure, instead leading to a high predisposition to racemization. This review summarizes approaches that have been developed to address this issue by effectively constraining their free rotation, including the introduction of bulky substituents and formation of mechanical interlock structures. The controllable flipping behavior of chiral bismacrocycles with pillar[5]arenes as the core is reviewed under the stimulation of external environment. Moreover, we will discuss the application areas that rely on the planar chirality of pillar[5]arene, such as circularly polarized luminescence, molecular recognition, and chiral organic nanotubes.

Polymers of Intrinsic Microporosity Containing [2.2]Paracyclophane Moieties: Synthesis and Gas Sorption Properties

AbstractThe unique structure of [2.2]paracyclophane (PCP) with its rigidity, stability, and planar chirality has gained significant attention in polymer and material research. In this work, the incorporation of amino‐functionalized PCPs within polymers of intrinsic microporosity (PIMs) is reported for the first time. Three different PCP‐PIMs were prepared via a Tröger's base formation mechanism, and their structures characterized via solid‐state NMR, MALDI‐TOF, and SEM. Their porosity was evaluated using gas adsorption (N2 and CO2) based on theoretical calculations such as Brunauer–Emmett–Teller (BET), NLDFT pore size distribution (PSD) and ideal IAST CO2/N2 selectivity (15/85), a crucial separation when considering the capture of CO2 from flue gas. The surface areas were found to be between 200–230 m2 g−1 while the selectivity for CO2/N2 ranged from 46 to 70.

Synthesis and Chiroptical Properties of Cyclic Anthraquinodimethane Dimer Using Au-Templated Method

Abstract Cyclic anthraquinodimethane (AQD) dimer with a highly constrained structure was synthesized by using the Au-templated method. X-ray diffraction analysis and UV-Vis spectroscopy revealed that the AQD skeleton adopts a deeply folded structure and exhibits red-shifted absorptions in the dimer compared to those in non-cyclized monomeric AQD. Due to the rigid and constrained structure, both enantiomers of the cyclic AQD dimer with planar chirality can be isolated and show strong circular dichroism signals. It is demonstrated that the Au-templated method is a valuable way to access a highly constrained cyclic structure with AQD skeletons.

Synthesis of Planar Chiral Compounds Containing α-Amino Phosphonates for Antiplant Virus Applications against Potato Virus Y.

An unprecedented study of the application of planar chiral compounds in antiviral pesticide development is reported. A class of multifunctional planar chiral ferrocene derivatives bearing α-amino phosphonate moieties was synthesized. These compounds, exhibiting superior optical purities, were subsequently subjected to antiviral evaluations against the notable plant pathogen potato virus Y (PVY). The influence of the absolute configurations of the planar chiral compounds on their antiviral bioactivities was significant. A number of these enantiomerically enriched planar chiral molecules demonstrated superior anti-PVY activities. Specifically, compound (Sp, R)-9n displayed extraordinary curative activities against PVY, with a 50% maximal effective concentration (EC50) of 216.11 μg/mL, surpassing the efficacy of ningnanmycin (NNM, 272.74 μg/mL). The protective activities of compound (Sp, R)-9n had an EC50 value of 152.78 μg/mL, which was better than that of NNM (413.22 μg/mL). The molecular docking and defense enzyme activity tests were carried out using the planar chiral molecules bearing different absolute configurations to investigate the mechanism of their antiviral activities against PVY. (Sp, R)-9n, (Sp, R)-9o, and NMM all showed stronger affinities to the PVY-CP than the (Rp, S)-9n. Investigations into the mechanisms revealed that the planar chiral configurations of the compounds played pivotal roles in the interactions between the PVY-CP molecules and could augment the activities of the defense enzymes. This study contributes substantial insights into the role of planar chirality in defending plants against viral infections.

Chiral Stacking Identification of Two-Dimensional Triclinic Crystals Enabled by Machine Learning.

Chiral materials possess broken inversion and mirror symmetry and show great potential in the application of next-generation optic, electronic, and spintronic devices. Two-dimensional (2D) chiral crystals have planar chirality, which is nonsuperimposable on their 2D enantiomers by any rotation about the axis perpendicular to the substrate. The degree of freedom to construct vertical stacking of 2D monolayer enantiomers offers the possibility of chiral manipulation for designed properties by creating multilayers with either a racemic or enantiomerically pure stacking order. However, the rapid recognition of the relative proportion of two enantiomers becomes demanding due to the complexity of stacking orders of 2D chiral crystals. Here, we report the unambiguous identification of racemic and enantiomerically pure stackings for layered ReSe2 and ReS2 using circular polarized Raman spectroscopy. The chiral Raman response is successfully manipulated by the enantiomer proportion, and the stacking orders of multilayer ReSe2 and ReS2 can be completely clarified with the help of second harmonic generation and scanning transmission electron microscopy measurements. Finally, we trained an artificial intelligent Spectra Classification Assistant to predict the chirality and the complete crystallographic structures of multilayer ReSe2 from a single circular polarized Raman spectrum with the accuracy reaching 0.9417 ± 0.0059.

Design, synthesis and Anti-PVY activity of planar chiral thiourea derivatives incorporated with [2.2]Paracyclophane.

Potato virus Y (PVY) is a prominent representative of plant viruses. It can inflict severe damage upon Solanaceae plants, leading to global dissemination and substantial economic losses. To discover new antiviral agents, a class of planar chiral thiourea molecules through the key step of N-heterocyclic carbene-catalyzed nitrile formation reaction was synthesized with excellent optical purities for antiviral evaluations against plant virus PVY. The absolute configurations of the planar chiral compounds exhibited obvious distinctions in the anti-PVY activities. Notability, compound (S)-4u exhibited remarkable curative activities against PVY, with a half maximal effective concentration (EC50) of 349.3 μg mL-1, which was lower than that of the ningnanmycin (NNM) (EC50 = 400.8 μg mL-1). Additionally, The EC50 value for the protective effects of (S)-4u was 146.2 μg mL-1, which was superior to that of NNM (276.4 μg mL-1). Furthermore, the mechanism-of-action of enantiomers of planar chiral compound 4u was investigated through molecular docking, defensive enzyme activity tests and chlorophyll content tests. Biological mechanism studies have demonstrated that the configuration of planar chiral target compounds plays a crucial role in the molecular interaction with PVY-CP, enhancing the activity of defense enzymes and affecting chlorophyll content. The current study has provided significant insights into the roles played by planar chiralities in plant protection against viruses. This paves the way for the development of novel green pesticides bearing planar chiralities with excellent optical purities. © 2024 Society of Chemical Industry.

2.2]Paracyclophanes: From Selective Functionalization to Optical Properties

AbstractSince their discovery, [2.2]paracyclophane (pCp) and its derivatives have fascinated the scientific community due to their original molecular architecture and unusual electronic behavior. Over the years, significant efforts have been devoted to the development of substituted pCps for a variety of applications in different fields, ranging from organic synthesis and asymmetric catalysis to polymer chemistry and material science. This review describes a series of useful approaches that allow chemists to selectively decorate pCps, control the planar chirality that these molecules can display as soon as they are functionalized, and tune their photophysical behaviors. For each of these aspects of paracyclophane chemistry, selected examples of major advances are presented, and possible directions for future research are outlined. The application of pCp as central core for the development of uncommon 3D luminophores is finally highlighted. Emphasis is placed on the potential use of planar chiral luminescent paracyclophanes as antennas or ligands for the design of multifunctional lanthanide complexes, a quite underdeveloped but highly promising area for future research endeavors.

Targeted isolation of antiviral cinnamoylphloroglucinol-terpene adducts from Cleistocalyx operculatus by building blocks-based molecular networking approach

The building blocks-based molecular network (BBMN) strategy was applied to the phytochemical investigation of Cleistocalyx operculatus, leading to the targeted isolation of eighteen novel cinnamoylphloroglucinol-terpene adducts (CPTAs) with diverse skeleton types (cleistoperones A–R, 1–18). Their structures including absolute configurations were determined by extensive spectroscopic methods, quantum chemical calculations, and single-crystal X-ray crystallographic experiments. Cleistoperone A (1), consisting of a cinnamoylphloroglucinol motif and two linear monoterpene moieties, represents an unprecedented macrocyclic CPTA, whose densely functionalized tricyclo[15.3.1.03,8]heneicosane bridge ring skeleton contains an enolizable β,β′-triketone system and two different kinds of stereogenic elements (including five point and three planar chiralities). Cleistoperones B and C (2 and 3) are two new skeletal CPTAs with an unusual coupling pattern between the (nor)monoterpene moiety and the cinnamoyl chain of the cinnamoylphloroglucinol unit. Cleistoperone D (4) possesses an unprecedented cage-like 6/6/6/4/6-fused heteropentacyclic scaffold. The plausible biosynthetic pathways for 1–18 were also proposed. Notably, compounds 1, 4, 7, 8, and 18 exhibited significant antiviral activity against respiratory syncytial virus (RSV). The most potent one, cleistoperone A (1) with IC50 value of 1.71 ± 0.61 μmol/L, could effectively inhibit virus replication via affecting the Akt/mTOR/p70S6K signaling pathway.