Aromatic Guest Molecules Research Articles

Water Solubilization and Guest Molecule-Induced Fluorescence Changes of Porous Host Molecules via Complexing with Polysaccharide or Polypeptide.

To detect small aromatic molecules in water, we prepared functional host molecules based on water-soluble N,N'-bis(2-aminobenzophenone)-1,4,5,8-naphthalenetetracarboxylic diimide (1) and a solubilizing agent using a high-speed vibration milling apparatus. The fluorescence response of host 1-solubilizing agent complexes before and after extraction of small aromatic guest molecules was large and the fluorescence maxima were dependent on the small aromatic guest molecules.

Selective uptake and removal of aromatic and heterocyclic compounds by para-dicyanobenzene-linked, EFe3(CO)9-incorporated (E = Te, Se), semiconducting Cu chain polymers

The uptake and removal of volatile and toxic organic compounds is an important issue in modern industrial chemistry because these organic pollutants have long-term effects on public health and the global environment. In this work, we successfully synthesized two novel para-dicyanobenzene (p-DCB)-linked, EFe3(CO)9-incorporated (E = Te, Se) 1D polymers [EFe3(CO)9Cu2(p-DCB)1.5]n (E = Te, 1a; Se, 1b) from liquid-assisted grinding (LAG) of the di-Cu compounds [EFe3(CO)9Cu2(MeCN)2] with p-DCB. Polymers 1a and 1b had isomorphous structures with single- and double-p-DCB linkers alternatively connected to Cu atoms of EFe3(CO)9Cu2 (E = Te, Se) cores, in which two p-DCB of the double-p-DCB moiety were parallel-displaced with the π···π interaction on their benzene rings. The selective adsorption of C7−C10-alkyl aromatics, polycyclic aromatics, and heterocyclic compounds by 1a and 1b was accomplished via neat grinding or THF-aided LAG processes. These reactions led to the formation of the guest molecule (G)-intercalated products, i.e., 1a- and 1b-based polymers [EFe3(CO)9Cu2(p-DCB)1.5·(G)m]n [E = Te, 1a·mG; E = Se, 1b·mG; m = 0.5 or 1] and the THF-introduced single-p-DCB-bridged polymer [TeFe3(CO)9Cu2(p-DCB)·(THF)]n (2a·1THF). These adsorption activities of 1a and 1b were thoroughly evaluated by single-crystal and powder X-ray analysis and TGA and DSC measurement, where some C−H···π, π···π, and C−H···E (E = O, S) interactions between guest molecules and the p-DCB linkers were observed to stabilize polymer chains. The desorption of volatile heterocyclic (THF, furan, thiophene) or alkyl aromatic (toluene, m-xylene, mesitylene, durene) guest molecules to give the parent polymers 1a and 1b could be achieved by vacuum and recrystallization or stepwise LAG process in the Te system. Importantly, these EFe3(CO)9Cu2-incorporated (E = Te, Se) polymers 1a and 1b, as well as their host−guest adducts, exhibited semiconducting behaviors possessing tunable energy gaps (1.36−1.51 eV) with moderate electrical conductivities ((1.21−6.55)×10–7 S·cm–1), in which the guest molecules played a crucial role in modulating the electron transport in the solid state.

Stability and electronic properties of aromatic and heteroaromatic molecules for Guest@MOF complexes

A set of Guest@Host complexes formed by aromatic and heteroaromatic guest molecules encapsulated into the [Zn2(SDC)2(An2Py)] as host structure was computationally investigated. The stability of these complexes was characterized by energy decomposition and intermolecular interaction analysis, demonstrating the strong effect of dispersion forces and electrostatic interactions on the adsorption and interaction energy, being more stable the heteroaromatic cases. The electronic structure and semiconductor properties of Guest@MOF complexes have proved that heteroaromatic guest molecules allow band-gap tuning, depending on the electron donor and acceptor character of the guest molecules. Simulated absorption spectra of Guest@MOF complexes preserved the same profile because of the higher contribution of MOF, but heteroaromatic complexes displayed interesting cases of Charge−Transfer excitations, generating new bands at lower energy. The Charge−Transfer spectra have exhibited the active participation of the Guest molecule in Charge−Transfer excitations, but the electronic Redistribution has played the key role in the global spectrum of Guest@MOF complexes. Incorporating heteroaromatic guest molecules appeared as an outstanding strategy to tune-up the MOF electronic properties.

Heat-set supramolecular polymer gel and decomposition by guests

A degradable, heat-set fibrillar gel by supramolecular polymer in DMF based on stearic acid appended l-lysine, β-cyclodextrin and potassium carbonate has been developed. The heat-set stable, irreversible gel decomposed by aromatic guest molecules.

Aqueous Solutions of a Porous Host-Poly-L-lysine Complex with Information on Solids as Different Fluorescence by Guests.

N,N'-Dipyrid-3-yl-1,4,5,8-naphthalenediimide linked to two tris(pentafluorophenyl)borane (1) exhibits strong fluorescence emission in the solid state by the formation of a charge-transfer complex containing small aromatic guest molecules. Hydrophobic 1 was dissolved in water by mixing with poly-L-lysine (PLL) as a solubilizing agent. The 1-PLL complex could include small aromatic guest molecules in water, significantly increasing the fluorescence. The fluorescence maxima of 1 in aqueous solution and solid state were different depending on the guest molecule. Therefore, compound 1 was prepared as aqueous solution with information of fluorescence on solids by complexation with PLL.

Experimental X-ray and DFT Structural Analyses of M12L8 Poly-[n]-catenanes Using exo-Tridentate Ligands.

Despite their potential applications in host-guest chemistry, there are only five reported structures of poly-[n]-catenanes self-assembled by elusive M12L8 icosahedral nanocages. This small number of structures of M12L8 poly-[n]-catenanes is because self-assembly of large metal-organic cages (MOCs) with large windows allowing catenation by means of mechanical bonds is very challenging. Structural reports of M12L8 poly-[n]-catenanes are needed to increase our knowledge about the self-assembly and genesis of such materials. Poly-[n]-catenane (1·p-CT) self-assembly of interlocked M12L8 icosahedral cages (M = Zn(II) and L = 2,4,6-tris-(4-pyridyl)benzene (TPB)) including a new aromatic guest (p-chlorotoluene (p-CT)) is reported by single-crystal XRD. Despite the huge internal M12L8 voids (> 2500 Å3), p-CT is ordered, allowing a clear visualization of the relative host-guest positions. DFT calculations have been used to compute the electrostatic potential of the TPB ligand, and various aromatic guests (i.e., o-dichlorobenzene (o-DCB), p-chloroanisole (p-CA), and nitrobenzene (NBz)) included (ordered) within the M12L8 cages were determined by single-crystal XRD. The computed maps of electrostatic potential (MEPs) allow for the rationalization of the guest's inclusion seen in the 3D X-ray structures. Although more crystallographic X-ray structures and DFT analysis are needed to gain insights of guest inclusion in the large voids of M12L8 poly-[n]-catenanes, the reported combined experimental/DFT structural analyses approach can be exploited to use isostructural M12L8 poly-[n]-catenanes as hosts for molecular separation and could find applications in the crystalline sponge method developed by Fujita and co-workers. We also demonstrate, exploiting the instant synthesis method, in solution (i.e., o-DCB), and in the solid-state by neat grinding (i.e., without solvent), that the isostructural M12L8 poly-[n]-catenane self-assembled with 2,4,6-tris-(4-pyridyl)pyridine (TPP) ligand and ZnX2 (where X = Cl, Br, and I) can be kinetically synthesized as crystalline (yields ≈ 60%) and amorphous phases (yields ≈ 70%) in short time and large quantities. Despite the change in the aromatic nature at the center of the rigid exo-tridentate pyridine-based ligand (TPP vs TPB), the kinetic control gives the poly-[n]-catenanes selectively. The dynamic behavior of the TPP amorphous phases upon the uptake of aromatic guest molecules can be used in molecular separation applications like benzene derivatives.

Comparative study of inclusion complex formation between β-cyclodextrin (host) and aromatic diamines (guests) by mixing in hot water, co-precipitation, and solid-state grinding methods

Aromatic diamines are essential components of polyimide and many other thermosetting polymers. Recent attention has been growing on the threading of cyclodextrins (CDs) onto diamine monomers intended to improve the solubility in water and thermal stability of resultant polymers. The co-precipitation method is often used to isolate inclusion complexes (ICs) of aromatic diamines and other sparingly water-soluble aromatic guest molecules with β-CD. To find the viability of other methods, we studied IC formation between β-CD and some aromatic diamines by mixing in hot water, co-precipitation, and solid-state grinding. ICs formation in water was carried out by solid guest dispersion into the β-CD aqueous solution at 80 °C with high-speed magnetic stirring. In contrast, solid-state grinding was employed by adding a small amount of water to promote IC formation. Thus, ICs prepared by mixing in hot water and solid-state grinding methods were crystallized from water by cooling to 4 °C. Structures of the ICs in solution were confirmed by chemical shifts changes of cavity protons of β-CD in 1H NMR and the cross-peaks between aromatic protons and cavity protons in 1H-1H ROESY NMR. Job’s plot and NMR titration experiments were used to determine the stoichiometric ratio of host and guest in solution.

An atomistic view on the uptake of aromatic compounds by cyclodextrin immobilized on mesoporous silica

The effect of immobilized upbeta-cyclodextrin (bCD) molecules inside a mesoporous silica support on the uptake of benzene and p-nitrophenol from aqueous solution was investigated using all-atom molecular dynamics (MD) simulations. The calculated adsorption isotherms are discussed with respect to the free energies of binding for a 1:1 complex of bCD and the aromatic guest molecule. The adsorption capacity of the bCD-containing material significantly exceeds the amount corresponding to a 1:1 binding scenario, in agreement with experimental observations. Beside the formation of 1:2 and, to a lesser extent, 1:3 host:guest complexes, also host–host interactions on the surface as well as more unspecific host–guest interactions govern the adsorption process. The demonstrated feasibility of classical all-atom MD simulations to calculate liquid phase adsorption isotherms paves the way to a molecular interpretation of experimental data that are too complex to be described by empirical models.

Ternary Cocrystals with Large Soft Cavities: A 1,4-diiodotetrafluorobenzene (DITFB)⋅4-Biphenylpyridine N-oxide (BPNO) Host Assembled by Inclusion of Planar Aromatic Guests.

A large soft-cavity host composed of 1,4-diiodotetrafluorobenzene (DITFB) and 4-biphenylpyridine N-oxide (BPNO) is assembled under the mediation of a planar aromatic guest molecule (pyrene or perylene) through C-I⋅⋅⋅- O-N+ halogen bonds and π-hole⋅⋅⋅π bonds. Single-crystal X-ray diffraction reveals that guest molecules can be completely encapsulated in the four-layer host cavity to assemble ternary host-guest cocrystals; namely, Pyr@DITFB ⋅ BPNO and Per@DITFB ⋅ BPNO. The luminescence of these ternary cocrystals originates from their discrete guest molecules, which exhibit pure-blue and yellow emissions, respectively, that are localized at 425 nm and in the range of 485 to 578 nm, respectively. In addition, the contribution of different fragments to the stabilization of the crystal structure is estimated by computational chemistry. These cocrystals have significant potential for use in optical applications or materials, such as photonics or organic light-emitting diodes, respectively, that require to avoid the aggregation between luminophores.

Face-Directed Assembly of Molecular Cubes: In Situ Substitution of a Predetermined Concave Cluster.

Systematic design and self-assembly of metal-organic polyhedra with predictable configurations has been a long-standing challenge in crystal engineering. Herein a concave polyoxovanadate cluster, [V6 O6 (OCH3 )9 (SO4 )4 ]5- , which can be generated in situ under specific reaction conditions, is reported. Based on this cluster, a potential trivalent molecular building block, [V6 O6 (OCH3 )9 (SO4 )(CO2 )3 ]2- , can be obtained by the bridging-ligand-substitution strategy and it possesses appropriate angle information for the design of molecular cubes. Utilizing the face-directed assembly of the trivalent molecular building block and a diverse set of tetratopic carboxylate linkers, a series of metal-organic cubes (VMOC-1-VMOC-5) with the same topology but different functionalities and dimensions were designed and constructed. An inclusion study using VMOC-3 shows that they are potential molecular receptors for selective capture of size-matching polycyclic aromatic hydrocarbon guest molecules.

Face‐Directed Assembly of Molecular Cubes: In Situ Substitution of a Predetermined Concave Cluster

AbstractSystematic design and self‐assembly of metal–organic polyhedra with predictable configurations has been a long‐standing challenge in crystal engineering. Herein a concave polyoxovanadate cluster, [V6O6(OCH3)9(SO4)4]5−, which can be generated in situ under specific reaction conditions, is reported. Based on this cluster, a potential trivalent molecular building block, [V6O6(OCH3)9(SO4)(CO2)3]2−, can be obtained by the bridging‐ligand‐substitution strategy and it possesses appropriate angle information for the design of molecular cubes. Utilizing the face‐directed assembly of the trivalent molecular building block and a diverse set of tetratopic carboxylate linkers, a series of metal–organic cubes (VMOC‐1–VMOC‐5) with the same topology but different functionalities and dimensions were designed and constructed. An inclusion study using VMOC‐3 shows that they are potential molecular receptors for selective capture of size‐matching polycyclic aromatic hydrocarbon guest molecules.

Perylene Diimide Based Imine Cages for Inclusion of Aromatic Guest Molecules and Visible‐Light Photocatalysis

AbstractA strategy for the development of visible‐light‐sensitive organic cage structures is reported. Enantiomeric imine cages with optical and electrochemical properties are developed employing perylene diimide (PDI) and tetraphenylethene subunits using dynamic covalent imine chemistry. Polycyclic aromatic hydrocarbons are encapsulated efficiently in the imine cage, and the guests interact with PDI units via supramolecular π‐π interactions. Visible‐light‐driven Smiles rearrangement of 2‐aryloxybenzoic acids to aryl salicylates is achieved with high efficiency in the presence of the imine cage as the catalyst.

Role of Host–Guest Charge Transfer in Cyclodextrin Complexation: A Computational Study

Charge transfer (CT) was proposed to play a role in the cyclodextrin (CD) complexation with guest molecules. To elucidate the importance of CT interactions, here we used computational methods of quantum mechanics, docking, and molecular dynamics (MD) to investigate α-CD complexes with aromatic guest molecules of nitrobenzene, carboxybenzene, benzoate, 4-nitrophenol, and 4-nitrophenolate. Considering host–guest CT in the docking has more of a chance to search reasonable guest orientations relative to α-CD matching the experiment, compared to that without CT. The CT interaction enlarges the difference in binding affinities of varied guests, as evidenced from potential of mean force (PMF) MD calculations. Energy decomposition of the total enthalpy and entropy shows the CT influence on the binding reactions in detail and indicates that there are considerable compensating effects of individual contributions from the binding partners and surrounding water. Charge transfer reduces the total dipole of α-CD by 9% ...

Unsubstituted Oxacalix[n]arenes (n=4 and 8): A Conformational Study in Solution and Solid State and Interaction Studies with Aromatic Guests

AbstractWe present single crystal structures of unsubstituted oxacalix[4]arene and oxacalix[8]arene macrocycles and investigate the weak supramolecular interactions that govern their packing in the solid state. We further show that the unsubstituted oxacalix[4]arene shows weak complexation with two aromatic guest species, benzoic acid and ferrocene, in CDCl3, whereas the oxacalix[8]arene host does not complex with these guest molecules. We also present NMR titration experiments with non‐aromatic acids and DFT calculations that signify the importance of π‐π interactions for complexation with benzoic acid. Weak complexation is also observed between electron‐rich aromatic guest molecules and the unsubstituted oxacalix[4]arene host.

Host-guest complexation behaviour of emissive calix[3]naphthobipyrrole toward aromatic guests

ABSTRACTA new hexapyrrolic macrocycle composed of three naphthobipyrrole units has been synthesized which exhibited different emission changes with hydrogen pyrophosphate and benzoate ions. Phosphate ions caused red shifting of the fluorescence band of calixnaphthobipyrrole while benzoate ions resulted in quenching of the same. The fluorescence quenching was further utilized for investigating binding preferences of the probe with neutral aromatic guest molecules substituted with groups having varied electron withdrawing abilities. The extent of quenching with the neutral guests increased with the increasing electron deficiency on the aromatic ring of the guest. The fluorescence quenching has been ascribed to electron transfer from the host to the guest species.

An analysis of the interactions between folic acid and aromatic guest molecules.

The formation of complexes between folate and therapeutic drug molecules is well known. In this work, we attempted to elucidate the role of the aromatic rings of folate and drug molecules in interactions between both of these molecules. A detailed molecular simulation study was carried out to explore the associative behavior of folic acid with phenylalanine and tyrosine, which show fluorescence emission following the excitation of these molecules at 257nm and 274nm, respectively. Therefore, studies of fluorescence emission from phenylalanine and tyrosine were performed in this work. The results of these studies indicated that folic acid associates with phenylalanine and tyrosine with binding constants ranging from 1.46×104 to 2.66×104M-1. X-ray diffraction studies suggested that folic acid self-assembly is maintained in the presence of associative interactions of the folic acid with guest molecules. These results demonstrate that the aromatic rings in the structures of the folic acid and the therapeutic drug play an important role in the encapsulation of guest molecules through folate self-assembly.

A Kinetically Stable Macrocycle Self-Assembled in Water.

A macrocycle through a dynamic covalent approach relying on reversible hydrazone formation in acidic aqueous solutions at elevated temperatures is constructed. By decreasing the acidity of the solution and lowering the temperature, the structure becomes kinetically inert. The macrocycle is capable of hosting hydrophobic aromatic guest molecules in water.

Self-Assembly of Fluorinated Boronic Esters and 4,4′-Bipyridine into 2:1 N→B Adducts and Inclusion of Aromatic Guest Molecules in the Solid State: Application for the Separation of o,m,p-Xylene

A series of 2:1 fluorinated arylboronic ester adducts with 4,4′-bipyridine sustained by N→B dative bonds have been synthesized. The degree of fluorination in the arylboronic esters derived from catechol is shown to modulate the molecular conformation of the coordinated boronic ester moieties and the intermolecular interactions by means of C–H···F and F···F contacts that sustain the crystal lattices. The adduct derived from the catechol ester of 2,4-difluorophenylboronic acid was chosen to examine the formation of inclusion complexes with a large number of aromatic guests, affording solvates, cocrystals, and a cocrystal solvate. Six different crystal structure types with 1:1, 1:2, and 1:2:2 N→B adduct–guest ratios were observed, whose supramolecular organization is strongly influenced by the formation of sandwich-type complexes between the host and guest molecules. The host–guest interactions involve π···π interactions with the bipyridine linkers and additional contacts with the catecholate and B-arylF sub...

Tuning Light Emission towards White Light from a Naphthalenediimide-Based Entangled Metal-Organic Framework by Mixing Aromatic Guest Molecules

Taking advantage of the outstanding properties of a naphthalenediimide-based entangled porous coordination polymer, a simple strategy for the achievement of white light emission is herein presented. The dynamic structural transformation of the [Zn2(bdc)2(dpNDI)]n metal-organic framework enhances the interactions with aryl-guests giving rise to different luminescence colors upon UV (ultraviolet) illumination. Thus, through the rational selection of those small aromatic guest molecules with different electron donor substituents at the appropriate proportion, the emission color was tuned by mixture ratio of guest molecules and even white light emission was achieved. Furthermore, domains in large crystals with a complementary response to linearly polarized light were noticed.

Octahedral [Pd6 L8 ]12+ Metallosupramolecular Cages: Synthesis, Structures and Guest-Encapsulation Studies.

Four planar tripyridyl ligands (Ltripy ), 1,3,5-tris(pyridin-3-ylethynyl)benzene 1 a, 1,3,5-tris[4-(3-pyridyl)phenyl]benzene 2 a, and the hexyloxy chain functionalized derivatives 1,3,5-tris[(3-hexyloxy-5-pyridyl)ethynyl]benzene 1 b, and 1,3,5-tris[4-(3-hexyloxy-5-pyridyl)phenyl]benzene 2 b, were synthesized and used to generate a family of [Pd6 (Ltripy )8 ](BF4 )12 octahedral cages (Ltripy =1 a, b or 2 a, b). The ligands and cages were characterized using a combination of 1 H, 13 C, and DOSY nuclear magnetic resonance (NMR) spectroscopy, high resolution electrospray mass spectrometry (HR-ESI-MS), infrared (IR) spectroscopy, elemental analysis, and in three cases, X-ray crystallography. The molecular recognition properties of the cages with neutral and anionic guests were examined, in dimethyl sulfoxide (DMSO), using NMR spectroscopy, mass spectrometry and molecular modeling. No binding was observed with simple aliphatic and aromatic guest molecules. However, anionic sulfonates were found to interact with the octahedral cages and the binding interaction was size selective. The smaller [Pd6 (1 a, b)8 ]12+ cages were able to interact with three p-toluenesulfonate guest molecules while the larger [Pd6 (2 a, b)8 ]12+ systems could host four of the anionic guest molecules. To probe the importance of the hydrophobic effect, a mixed water-DMSO (1:1) solvent system was used to reexamine the binding of the neutral organic guests adamantane, anthracene, pyrene and 1,8-naphthalimide within the cages. In this solvent system all the guests except adamantane were observed to bind within the cavities of the cages. NMR spectroscopy and molecular modeling indicated that the cages bind multiple copies of the individual guests (between 3-6 guest molecules per cage).