Electron-rich Guests Research Articles

Electron Rich Guest Regulated Enhanced CO2 Reduction in a Multivariate Porous Coordination Polymer

Electron Rich Guest Regulated Enhanced CO₂ Reduction in a Multivariate Porous Coordination Polymer

DNA Chimeras as Electrochemical Biosensors for Host-Guest Measurements in Blood.

Few sensing platforms have become ubiquitous to enable rapid and convenient measurements at the point-of-care. Those, however, are "one-off" technologies, meaning that they can only detect a single target and are hardly adaptable. In response, we plan to develop a sensing platform that can be extended to detect other classes of molecules and that affords rapid, convenient, continuous measurements directly in undiluted complex matrices. For this, we decided to rely on a host molecule that presents reversible interactions toward specific guest molecules to develop a new class of sensors that we coined "Electrochemical DNA-host chimeras". As a proof-of-concept for our sensor, we decided to use cyclobis(paraquat-p-phenylene) ("blue box") that we attached on an electrode-bound DNA to allow measurements of electron-rich guests such as dopamine and aspirin. Doing so allows to promote host-guest complex that could be quantified using blue box's electrochemistry. Because of this unique sensor architecture, we achieve, to our knowledge, the first reagentless, continuous and rapid (< 5 min) host-guest measurements in undiluted whole blood. We envision that given the library of electroactive host molecules that this will allow the development of a sensing platform for measurements of several classes of molecules in complex matrices at the point-of-care.

Ionic liquid-modified UiO-66-NH2 as sorbent of dispersive solid-phase extraction for rapid adsorption and enrichment of benzoylurea insecticides.

Ionic liquid (IL)-modified UiO-66-NH2 composite was prepared and used as sorbent of dispersed solid-phase extraction (dSPE) for extracting trace benzoylurea insecticides (BUs) from complex environmental matrices. The IL in framework endowed the prepared material had electropositive characteristics, which can produce interaction with electron rich guest molecules, such as BUs. The high thermal and chemical stability of UiO-66-NH2/IL enabled it to be reused for 16 times without significant reduction in adsorption performance. Due to the multiple forces including π-π, hydrogen bonding, and fluorine-fluorine interaction, UiO-66-NH2/IL showed good adsorption performance, short adsorption time (20 s) and rapid desorption ability (60 s) for BUs. Under the optimal conditions, the method exhibited wide linear range (0.02-500 ng mL-1) with correlation coefficient (R2) not worsethan 0.9928, high enrichment factor (252-300), and low detection limit (0.005-0.4 ng mL-1). The dispersed solid phase extraction coupling with high-performance liquid chromatography-diode array detector (dSPE-HPLC-DAD) was successfully used to detection of BUs in real environmental samples and satisfactory recoveries were obtained (80.5%±2.4-118%±3.2). The results indicated that UiO-66-NH2/IL composite can be a potential sorbent for the preconcentration of trace insecticidesin environmental samples.

The Green Box: Selenoviologen-Based Tetracationic Cyclophane for Electrochromism, Host–Guest Interactions, and Visible-Light Photocatalysis

The novel selenoviologen-based tetracationic cyclophanes (green boxes 3 and 5) with rigid electron-deficient cavities are synthesized via SN2 reactions in two steps. The green boxes exhibit good redox properties, narrow energy gaps, and strong absorption in the visible range (370-470 nm), especially for the green box 5 containing two selenoviologen (SeV2+) units. Meanwhile, the femtosecond transient absorption (fs-TA) reveals that the green boxes have a stabilized dicationic biradical, high efficiency of intramolecular charge transfer (ICT), and long-lived charge separation state due to the formation of cyclophane structure. Based on the excellent photophysical and redox properties, the green boxes are applied to electrochromic devices (ECDs) and visible-light-driven hydrogen production with a high H2 generation rate (34 μmol/h), turnover number (203), and apparent quantum yield (5.33 × 10-2). In addition, the host-guest recognitions are demonstrated between the green boxes and electron-rich guests (e.g., G1:1-naphthol and G2:platinum(II)-tethered naphthalene) in MeCN through C-H···π and π···π interactions. As a one-component system, the host-guest complexes of green box⊃G2 are successfully applied to visible-light photocatalytic hydrogen production due to the intramolecular electron transfer (IET) between platinum(II) of G2 and SeV2+ of the green box, which provides a simplified system for solar energy conversion.

Encapsulating electron-rich guest in a MOF host through donor-acceptor interaction for highly tunable luminescence

The rational construction and modulation of charge-transfer based fluorescence materials in host-guest systems by virtue of donor–acceptor interactions remains a challenge owing to the elaborate self-assembly process of acceptor and donor components. Taking into account the design principles of the host-guest system, a well-defined MOF with electron-deficient properties should be an ideal host for the building of charge-transfer based fluorescence materials. Herein, an electron-deficient MOF host, [Cd3(NDC)3(tpt)2(H2O)3] (1) (H2NDC = 1,4-naphthalenedicarboxylic acid, tpt = 2,4,6-tri(4-pyridinyl)-1,3,5-triazine), and a corresponding series of host-guest materials 1⊃guest (guest = phenanthrene for 2, anthracene for 3, pyrene for 4, triphenylene for 5) with charge-transfer based fluorescence were successfully fabricated via the donor–acceptor interactions. Profiting from the clear electron-rich guests to electron-deficient MOF framework charge transfer interactions, the host-guest materials exhibit color-tunable emission over a wide range by rational selection of guest molecules. Furthermore, the electronic structure calculations reveal that the multicolor emission of the newly synthesized MOF materials depends on the HOMO energy level/ionization potential of guests. This work provides a hopeful strategy for the assembly of various novel charge transfer fluorescent materials as potential luminophores.

The modulation effect of an electron-rich guest on the luminescence of naphthalene diimide-based metal–organic frameworks

A series of host–guest MOF materials were successfully fabricated by virtue of donor–acceptor interactions, which exhibit color-tunable emissions in a wide wavelength range by rational selection of guest molecules.

“Texas-Sized” Molecular Boxes: From Chemistry to Applications

The design and synthesis of novel macrocyclic host molecules continues to attract attention because such species play important roles in supramolecular chemistry. However, the discovery of new classes of macrocycles presents a considerable challenge due to the need to embody by design effective molecular recognition features, as well as ideally the development of synthetic routes that permit further functionalization. In 2010, we reported a new class of macrocyclic hosts: a set of tetracationic imidazolium macrocycles, which we termed “Texas-sized” molecular boxes (TxSBs) in homage to Stoddart’s classic “blue box” (CBPQT4+). Compared with the rigid blue box, the first generation TxSB displayed considerably greater conformational flexibility and a relatively large central cavity, making it a good host for a variety of electron-rich guests. In this review, we provide a comprehensive summary of TxSB chemistry, detailing our recent progress in the area of anion-responsive supramolecular self-assembly and applications of the underlying chemistry to water purification, information storage, and controlled drug release. Our objective is to provide not only a review of the fundamental findings, but also to outline future research directions where TxSBs and their constructs may have a role to play.

Boron-Nitrogen Double Tweezers Comprising Arylboronic Esters and Diamines: Self-Assembly in Solution and Adaptability as Hosts for Aromatic Guests in the Solid State.

The thermodynamic stability of 1 : 1 and 2 : 1 boron-nitrogen (B←N) adducts formed between aromatic boronic esters with mono- and diamines was studied in solution by NMR and UV-vis spectroscopy with association energies (ΔG°) ranging from -11 to -28 kJ mol-1 . The effect of different substituents in the boronic ester, the nature of the diamine linker, and the effect of the solvent was explored. Stable 2 : 1 B←N adducts with diamines such as 1,3-diaminopropane were produced in solutions of hydrogen-bonding acceptor solvents (acetonitrile and ethyl acetate), which can be isolated in the solid state as crystalline solvates, whereas the use of noncoordinating solvents such as 1,2-dichloroethane afforded mainly 1 : 1 B←N adducts. In suitable combinations, aromatic bis-pyridyl diamines produced stable 2 : 1 B←N adducts that were isolated either as solvent-free solids, solvates, or cocrystals. In these crystalline forms, double-tweezer hosts were observed with an exceptional syn/anti conformational guest-adaptability driven by simultaneous donor-acceptor and C-H⋅⋅⋅π interactions in the tweezer cavities, resembling preorganized covalent tweezer hosts. Interestingly, cocrystals with electron-rich guests such as tetrathiafulvalene and pyrene showed non-centrosymmetric crystal lattices with infinite π-stacked donor-acceptor columns.

Interaction of aromatic compounds and anions with naphthylimide-dansylamide fluorescent dyad: Experimental evidence of aryl C-H…π and aryl C-H…anion contacts and DFT calculations.

In this work the interaction of halide anions and simple aromatic compounds with a bichromophoric fluorescent dyad derived from 1,8-naphthalimide (NAPIM) and 5-(dimethylamino)naphthalene-1-sulfonyl (DANS) was studied using electronic spectroscopy, 1H, and 19F NMR spectroscopy and quantum chemistry modeling (b3lyp/def2-TZVP). The NAPIM-DANS dyad interacts with electron-rich guests with binding constants in the range of 6×103 to 8×103M-1 in CHCl3. The formed complexes are stabilized through aryl C-H … anion and aryl C-H … π interactions.

Engineering Donor-Acceptor Heterostructure Metal-Organic Framework Crystals for Photonic Logic Computation.

Photonic materials use photons as information carriers and offer the potential for unprecedented applications in optical and optoelectronic devices. In this study, we introduce a new strategy for photonic materials using metal-organic frameworks (MOFs) as the host for the rational construction of donor-acceptor (D-A) heterostructure crystals. We have engineered a rich library of heterostructure crystals using the MOF NKU-111 as a host. NKU-111 is based upon an electron-deficient tridentate ligand (acceptor) that can bind to various electron-rich guests (donors). The resulting heterocrystals exhibit spatially segregated multi-color emission resulting from the guest-dependent charge-transfer (CT) emission. Spatially effective mono-directional energy transfer results from tuning the energy gradient between adjacent domains through the selection of donor guest molecules, which suggests potential applications in integrated optical circuit devices, for example, photonic diodes, on-chip signal processing, optical logic gates.

Atropisomer-based construction of macrocyclic hosts that selectively recognize tryptophan from standard amino acids.

A syn-atropisomer of naphthalene diimide as a highly preorganized precursor was used to construct a type of trapezoid-shape macrocycle, namely 'trapezoid' molecular boxes (TBox). As supramolecular hosts, TBox can bind electron-rich guests and selectively recognize free tryptophan and tryptophanyl residues from 20 standard amino acids.

Solid-State Umbrella-type Inversion of a VO5 Square-Pyramidal Unit in a Bowl-type Dodecavanadate Induced by Insertion and Elimination of a Guest Molecule.

Design of cavities for a target molecule and the elucidation of the corresponding host-guest interactions are important for molecular manipulation. A discrete dodecavanadate bowl, [V12 O32 ]4- (V12), with an entrance diameter of 4.4 Å and an electron-rich guest at the center of the bowl, was stabilized by electrostatic interactions. A characteristic of V12 is a solid-state polytopal rearrangement during guest elimination and recapture. A guest-free dodecavanadate, [V12 O32 ]4- (V12-free), was prepared by removal of the guest from CH2 Cl2 -inserted V12 under vacuum at 50 °C. Single-crystal X-ray analysis revealed that one of the VO5 square pyramids at the bottom of V12-free was inverted to fill the void of the bowl cavity. The exposure of V12-free to the guest molecule vapors of CH2 Cl2 , 1,2-dichloroethane, MeNO2 , MeCN, and MeBr resulted in the selective insertion of the guest to reform the guest-inserted V12 structure. Whereas CO2 could be inserted in the V12 bowl, CH4 and CO could not.

Recognition Properties and Self-assembly of Planar [M(2-pyridyl-1,2,3-triazole)2 ]2+ Metallo-ligands.

Molecular recognition continues to be an area of keen interest for supramolecular chemists. The investigated [M(L)2 ]2+ metallo-ligands (M=PdII , PtII , L=2-(1-(pyridine-4-methyl)-1 H-1,2,3-triazol-4-yl)pyridine) form a planar cationic panel with vacant pyridyl binding sites. They interact with planar neutral aromatic guests through π-π and/or metallophilic interactions. In some cases, the metallo-ligands also interacted in the solid state with AgI either through coordination to the pendant pyridyl arms, or through metal-metal interactions, forming coordination polymers. We have therefore developed a system that reliably recognises a planar electron-rich guest in solution and in the solid state, and shows the potential to link the resultant host-guest adducts into extended solid-state structures. The facile synthesis and ready functionalisation of 2-pyridyl-1,2,3-triazole ligands through copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) "click" chemistry should allow for ready tuning of the electronic properties of adducts formed from these systems.

Nanographenes as electron-deficient cores of donor-acceptor systems

Conjugation of nanographenes (NGs) with electro-active molecules can establish donor-acceptor π-systems in which the former generally serve as the electron-donating moieties due to their electronic-rich nature. In contrast, here we report a series of reversed donor-acceptor structures are obtained by C–N coupling of electron-deficient perchlorinated NGs with electron-rich anilines. Selective amination at the vertexes of the NGs is unambiguously shown through X-ray crystallography. By varying the donating ability of the anilino groups, the optical and assembly properties of donor-acceptor NGs can be finely modulated. The electron-deficient concave core of the resulting conjugates can host electron-rich guest molecules by intermolecular donor-acceptor interactions and gives rise to charge-transfer supramolecular architectures.

Construction of π-Surface-Metalated Pillar[5]arenes which Bind Anions via Anion-π Interactions.

By simple ligand exchange of the cationic transition-metal complexes [(Cp*)M(acetone)3 ](OTf)2 (Cp*=pentamethylcyclopentadienyl and M=Ir or Rh) with pillar[5]arene, mono- and polynuclear pillar[5]arenes, a new class of metalated host molecules, is prepared. Single-crystal X-ray analysis shows that the charged transition-metal cations are directly bound to the outer π-surface of aromatic rings of pillar[5]arene. One of the triflate anions is deeply embedded within the cavity of the trinuclear pillar[5]arenes, which is different to the host-guest behavior of most pillar[5]arenes. DFT calculation of the electrostatic potential revealed that the metalated pillar[5]arenes featured an electron-deficient cavity due to the presence of the electron-withdrawing transition metals, thus allowing encapsulation of electron-rich guests mainly driven by anion-π interactions.

Novel calix[4]pyrrole assembly: Punctilious recognition of F− and Cu+2 ions

A new tetra hydroxyl methoxy substituted calix[4]pyrrole (HMCP) has been synthesized and found to form stable complex with F− ions and Cu+2 ions. The red-shift in absorption band of HMCP was observed due to the presence of both cation (Cu+2) and anion (F−). These results displayed that formation of the complex is mainly attributed to the charge–transfer interactions between HMCP with electron deficient pyrrole rings and the electron-rich guest ions. Molecular dynamics simulation predicts intermolecular H-bonds and van der Waals types of interaction for the complex formation of HMCP-Cu+2 and HMCP-F-.

ChemInform Abstract: Recent Advances in Molecular Recognition with Tetrathiafulvalene‐Based Receptors

AbstractReview: [46 refs.

From Packed "Sandwich" to "Russian Doll": Assembly by Charge-Transfer Interactions in Cucurbit[10]uril.

As the host possessing the largest cavity in the cucurbit[n]uril (CB[n]) family, CB[10] has previously displayed unusual recognition and assembly properties with guests but much remains to be explored. Herein, we present the recognition properties of CB[10] toward a series of bipyridinium guests including the tetracationic cyclophane known as blue box along with electron-rich guests and detail the influence of encapsulation on the charge-transfer interactions between guests. For the mono-bipyridinium guest (methylviologen, MV2+ ), CB[10] not only forms 1:1 and 1:2 inclusion complexes, but also enhances the charge-transfer interactions between methylviologen and dihydroxynaphthalene (HN) by mainly forming the 1:2:1 packed "sandwich" complex (CB[10]⋅2 MV2+ ⋅HN). For guest 1 with two bipyridinium units, an interesting conformational switching from linear to "U" shape is observed by adding catechol to the solution of CB[10] and the guest. For the tetracationic cyclophane-blue box, CB[10] forms a stable 1:1 inclusion complex; the two bipyridinium units tilt inside the cavity of CB[10] according to the X-ray crystal structure. Finally, a supramolecular "Russian doll" was built up by threading a guest through the cavities of both blue box and CB[10].

Networked Spin Cages: Tunable Magnetism and Lithium Ion Storage via Modulation of Spin-Electron Interactions.

A networked spin cage comprising infinite CoII6L4 cages arrays (where Co = Co(NCS)2 and L = 1,3,5-tri-(4-pyridyl)-verdazal radical) is synthesized and found to exhibit tunable magnetic and electrochemical properties via inclusion of guests. SQUID investigation reveals the coexistence of ferromagnetic and anti-ferromagnetic interactions between the Co(II) ion center and radical ligands. Inclusion of electron-deficient guests (e.g., tetracyanoethylene) dramatically enhances spin concentration and increases anti-ferromagnetic interactions due to the formation of charge-transfer complex between the host and the guest. In addition, introduction of electron-rich guests (e.g., tetrathiafulvalene) into the networked spin cages doubles the capacity for binding the lithium ions.

Programmed disassembly of supramolecular nanoparticles stabilized by heteroternary CB[8] host-guest interactions

Controlled release is an important determinant of the in-vivo performance of drug delivering nanoparticles (NPs). Therefore the control over and understanding of the release mechanism, e.g. by disassembly or degradation of the carrier, is essential for the optimization of NP formulations. This paper presents a supramolecular toolbox approach for the formation and UV-induced disassembly of supramolecular nanoparticles (SNPs) which are either exclusively stabilized by cucurbit[8]uril (CB[8])/methyl viologen (MV)/azobenzene (Azo) interactions or CB[8]/MV/naphthol (Np) interactions, or by a combination of both. Photoisomerization of the Azo units enables UV-triggered disassembly of the CB[8]/MV/Azo host-guest complex. Depending on the valency of the electron-rich guest moieties (Np or Azo), either SNPs with a UV-responsive shell or a UV-responsive core were formed by assembling SNPs using a mixture of Azo and Np bearing guest molecules. In contrast, non-responsive SNPs or SNPs which disintegrate at both the core and the shell were formed by using exclusively CB[8]/MV/Np or CB[8]/MV/Azo interactions, respectively.