Dual molecular tweezers extending from a nanohoop.

The field of nanohoops is mature enough that synthetic protocols exists to tune their size, composition (incorporation of heteroaromatic building blocks), connectivity ( linkages), and solubility in different media (hydrophobic hydrophilic). Here, we report an additional dimension incorporating the concept of fullerene tweezers into a nanohoop. The resulting hybrid nanohoop is highly strained at 77 kcal mol, possesses a quantum yield of 0.

Reversible dioxygen uptake at [Cu] clusters.

Dioxygen binding solely through non-covalent interactions is rare. In living systems, dioxygen transport takes place iron or copper-containing biological cofactors. Specifically, a reversible covalent interaction is established when O binds to the mono or polynuclear metal center.

Directing Molecular Weaving of Covalent Organic Frameworks and Their Dimensionality by Angular Control.

Although reticular chemistry has commonly utilized mutually embracing tetrahedral metal complexes as crossing points to generate three-dimensional molecularly woven structures, weaving in two dimensions remains largely unexplored. We report a new strategy to access 2D woven COFs by controlling the angle of the usually linear linker, resulting in the successful synthesis of a 2D woven pattern based on chain-link fence. The synthesis was accomplished by linking aldehyde-functionalized copper(I) bisphenanthroline complexes with bent 4,4'-oxydianiline building units.

Synthesis of Square Planar Cu Clusters.

Template-assisted synthesis of well-defined polynuclear clusters remains a challenge for [M ] square planar topologies. Herein, we present a tetraamine scaffold L(NH ) , where L is a rigidified resorcin[4]arene, to direct the formation of C -symmetric L(NH) Cu clusters with Cu-Cu distances around 2.7 Å, suggesting metal-metal direct interactions are operative since the sum of copper's van der Waals radii is 2.

Decarboxylative Cyclization of Proline with -Alkynylbenzaldehyde through an Unexploited 8π-Electrocyclization: A DFT Study.

We employed density functional theory (DFT) methods to investigate the most plausible mechanism of cyclization/ring expansion of proline with -alkynylbenzaldehyde. This one-pot reaction starts with the in situ formation of azomethine ylide, which can undergo three different reaction pathways to form the final product. Two mechanisms are based on nucleophilic addition and 4π-electrocyclization of the azomethine ylide, and our results indicate that the rate-determining step (RDS) of these two cyclizations are 40.

Nonspherical anion sequestration by C-H hydrogen bonding.

Macrocyclic arenes laid the foundations of supramolecular chemistry and their study established the fundamentals of noncovalent interactions. Advancing their frontier, here we designed rigidified resorcin[4]arenes that serve as hosts for large nonspherical anions. In one synthetic step, we vary the host's anion affinity properties by more than seven orders of magnitude.

Synthesis of Spiro[chromene-imidazo[1,2-]pyridin]-3'-imines via 6--dig Cyclization Reaction.

A transition-metal-free postmodification of the Groebke-Blackburn-Bienaymé (GBB) reaction for the synthesis of spiro[chromene-imidazo[1,2-]pyridin]-3'-imine was discovered. The unusual transformation represents the first example of activation and the reaction of the imidazole carbon atom. In this postcondensational modification, KO-Bu acts as a base, which, after the isomerization of an alkyne moiety to allene, causes the next unique nucleophilic reaction of the imidazole carbon atom that results in spirocyclic structures.

Regioselectivity in the Scholl Reaction: Mono and Double [7]Helicenes.

We employed the density functionaly theory (DFT)-predicted regioselectivity of the intramolecular Scholl reaction in phenanthrene and dibenzo[,]chrysene frameworks to obtain π-extended mono and double [7]helicenes, respectively. The formation of these helical structures occurs despite the buildup of a large strain energy up to 30 kcal/mol compared with their most stable isomers. The twisted and strained structures were characterized and analyzed by experimental (NMR, UV-vis, emission, electrochemistry, and single-crystal X-ray diffraction) techniques and were further supported by DFT calculations.

Tubularenes.

We report the synthesis and characterization of conjugated, conformationally rigid, and electroactive carbon-based nanotubes that we term tubularenes. These structures are constructed from a resorcin[ ]arene base. Cyclization of the conjugated aromatic nanotube is achieved in one-pot eight-fold C-C bond formation Suzuki-Miyaura cross-coupling.

Angular ladder-type -phenylenes: synthesis and electronic structural analysis.

Herein, we report the synthesis of two new series of angular (all-syn) ladder-type -[n]phenylenes (LMP, n = 3-8). One series contains keto groups at the termini bridges, denoted angular keto (AKn), the second contains alkyl groups at all bridge sp carbons, denoted angular alkyl (AAn). Their electronic and structural properties were delineated by a combination of electrochemistry and spectroscopic (UV-Vis and emission) methods and further supported by DFT calculations.

Conjugated Molecular Nanotubes.

Molecular compounds with permanent tubular architectures displaying radial π-conjugation are exceedingly rare. Their radial and axial delocalization presents them with unique optical and electronic properties, such as remarkable tuning of their Stokes shifts, and redox switching between global and local aromaticity. Although these tubular compounds display large internal void spaces, these attributes have not been extensively explored, thus presenting future opportunities in the development of materials.

Mechanism-Based Inactivation of Cytochrome P450 Enzymes: Computational Insights.

Mechanism-based inactivation (MBI) refers to the metabolic bioactivation of a xenobiotic by cytochrome P450s to a highly reactive intermediate which subsequently binds to the enzyme and leads to the quasi-irreversible or irreversible inhibition. Xenobiotics, mainly drugs with specific functional units, are the major sources of MBI. Two possible consequences of MBI by medicinal compounds are drug-drug interaction and severe toxicity that are observed and highlighted by clinical experiments.

Radially Oriented []Cyclo--phenylenes.

Molecular compounds with zigzag carbon nanotube geometries are exceedingly rare. Here we report the synthesis and characterization of carbon-based nanotubes with zigzag geometry, best described as radially oriented []cyclo--phenylenes, extending the tubularene family of compounds. By the incorporation of edge-sharing benzene rings into the tubularene's radial π-surface, we have uncovered the first step to give rise to the emergence of radial orbital distribution in zigzag nanorings.

Electron-Transfer-Induced Self-Assembly of a Molecular Tweezer Platform.

The design and synthesis of a new molecular tweezer (T-tmp) with electron-rich pincers are reported. The stable monocationic radicals and self-assembled dimeric radicals of this molecular tweezer platform were prepared by chemical oxidative titration. With the aid of DFT calculations, it was found that the dimeric radicals with syn-syn-syn conformer has the most stable structure, with the hole primarily delocalized between parallel stacked pyrenyl groups.

Redox-Induced Molecular Actuators: The Case of Oxy-Alternate Bridged Cyclotetraveratrylene.

We report a practical two-step approach for the synthesis of hybrid-bridge macrocyclic molecules that has been used to synthesize two novel oxy-alternate-bridged macrocyclic molecules, oxy-alternate cyclotetraveratrylene (CTTV) and oxy-alternate cyclohexaveratrylene (CHV). Electrochemistry, absorption spectroscopy, X-ray crystallography, and DFT calculations demonstrate that CTTV acts as a redox-induced molecular actuator, as its switches from the open conformation in the neutral state to the closed conformation in the cation-radical state.

Improving Performance of the SMD Solvation Model: Bondi Radii Improve Predicted Aqueous Solvation Free Energies of Ions and p Values of Thiols.

Calculation of the solvation free energy of ionic molecules is the principal source of errors in the quantum chemical evaluation of p values using implicit polarizable continuum solvent models. One of the important parameters affecting the performance of these models is the choice of atomic radii. Here, we assess the performance of the solvation model based on density (SMD) implicit solvation model employing SMD default radii (SMD) and Bondi radii (SMD-B), a set of empirical atomic radii developed based on the crystallographic data.

Highly Selective Synthesis of Pillar[ n]arene ( n = 5, 6).

An efficient and highly selective synthetic method toward the preparation of pillar[ n]arenes ( n = 5, 6) is reported, based upon a high solvent-dependent selectivity found in the condensation reaction between 1,4-dialkyloxybenzene and paraformaldehyde, involving methanesulfonic acid as catalyst. Pillar[6]arene (P6) is obtained as the major product when using chloroform as solvent, while in dichloromethane pillar[5]arene (P5) is the dominant product. Accordingly, a series of P5 and P6 have been selectively synthesized with excellent yield.

An Electron-Rich Calix[4]arene-Based Receptor with Unprecedented Binding Affinity for Nitric Oxide.

Calixarenes have found widespread application as building blocks for the design and synthesis of functional materials in host-guest chemistry. The ongoing desire to develop a detailed understanding of the nature of NO bonding to multichromophoric π-stacked assemblies led us to develop an electron-rich methoxy derivative of calix[4]arene (3), which we show exists as a single conformer in solution at ambient temperature. Here, we examine the redox properties of this derivative, generate its cation radical (3 ) using robust chemical oxidants, and determine the relative efficacy of its NO binding in comparison with model calixarenes.

An electron-transfer induced conformational transformation: from non-cofacial "sofa" to cofacial "boat" in cyclotetraveratrylene (CTTV) and formation of charge transfer complexes.

Electro-active polychromophoric assemblies that undergo clam-like electromechanic actuation represent an important class of organic functional materials. Here, we show that the readily available cyclotetraveratrylene (CTTV) undergoes oxidation-induced folding, consistent with interconversion from a non-cofacial "sofa" conformation to a cofacial "boat" conformer. It is found that the non-cofacial "sofa" conformer of CTTV forms stable electron donor-acceptor complexes with chloranil and DDQ.

Molecular Actuators in Action: Electron-Transfer-Induced Conformation Transformation in Cofacially Arrayed Polyfluorenes.

There is much current interest in the design of molecular actuators, which undergo reversible, controlled motion in response to an external stimulus (light, heat, oxidation, etc.). Here we describe the design and synthesis of a series of cofacially arrayed polyfluorenes (F nH m) with varied end-capping groups, which undergo redox-controlled electromechanical actuation.

The simulation of UV spectroscopy and electronic analysis of temozolomide and dacarbazine chemical decomposition to their metabolites.

The electronic features of anti-tumor agent, temozolomide, and its degradation products (MTIC and metabolite AIC) have been traced by means of UV absorption spectroscopy in vacuo and aqueous media. For comparison, electronic spectra of related structures and drugs (e.g.