Propeller, Linear, Cruciform and Stellate Spiro-bicarbazolium Salts.

A general synthetic approach to halogenated tetraaryl-ammonium salts has been developed and illustrated crystallographically. Bromide ammonium salts used as common synthetic intermediates together with Suzuki coupling of these bromides to a family of boronic acids provided a simplified strategy for arylation. Resolution of the C2 subset of spiro-bicarbazolium derivatives led to the first examples of enantiopure spiro-bicarbazoliums and the assignment of their absolute configuration by comparison of computational and experimental electronic circular dichroism (ECD) spectra. An ECD comparison with Prelog's spirobifluorenes is provided. The absolute configuration of the meta-bromide spiro-bicarbazolium salt was confirmed by anomalous scattering. Cruciform and stellate tetra-substituted salts provide a test of the limits of the methodology, and their structures suggest them to be candidates for MOF building blocks.

Reversible Photooxygenation of Anthracene Carboxyimide for Singlet Oxygen Formation: Mechanistic Study and Efficient Nitrite Detection.

Polycyclic aromatic endoperoxides are important sources of singlet oxygen (1 O2 ) and their formation from polyacenes is well established. Anthracene carboxyimides are of particular interest as they exhibit excellent antitumor activity and possess unique photochemical properties. However, the photooxygenation of the synthetically versatile anthracene carboxyimide moiety has not been reported due to its competing [4+4] photodimerization reaction. Herein, we describe the reversible photo-oxidation of an anthracene carboxyimide. X-ray crystallographic analysis surprisingly revealed the formation of a racemic mixture of chiral hydroperoxides, rather than the expected endoperoxide. The photoproduct undergoes both photo- and thermolysis to form 1 O2 . Activation parameters were derived for the thermolysis and the mechanisms of photooxygenation and thermolysis are discussed. The anthracene carboxyimide also showed high selectivity and sensitivity for nitrite anions in acidic aqueous media and possessed stimuli-responsive behaviour.

Cooperative Weak Dispersive Interactions Actuate Catalysis in a Shape-Selective Abiological Racemase.

A simple abiological host-guest system demonstrates racemase activity with catalytic rate enhancements of 104 without employing traditional functional groups. Cooperative weak interactions enhanced through shape-complementarity between the catalyst active site and the reaction transition state drive this activity, as proposed by Pauling for enzymes. In analogy to the Jencks' concept of catalytic antibodies, it is shown that a hapten resembling the planar transition state of the bowl inversion acts as a potent inhibitor of this catalytic process. In contrast, no substrate/product inhibition is detected, and a relatively weak binding of the substrate is observed (Ka ≈ 102 M-1 at 293 K). This simple box-and-bowl system demonstrates that shape selectivity arising from cooperative dispersive forces suffices for the emergence of a catalytic system with an enzyme-like thermodynamic profile.

The Unusual Photochromic and Hydrochromic Switching Behavior of Cellulose-Embedded 1,8-Naphthalimide-Viologen Derivatives in the Solid-State.

Stimuli-responsive chromic materials such as photochromics, hydrochromics, thermochromics, and electrochromics have a long history of capturing the attention of scientists due to their potential industrial applications and novelty in popular culture. However, hybrid chromic materials that combine two or more stimuli-triggered color changing properties are not so well known. Herein, we report a design strategy that has led to a series of emissive 1,8-naphthalimide-viologen dyads which exhibit unusual dual photochromic and hydrochromic switching behavior in the solid-state when embedded in a cellulose matrix. This behavior manifests as reversible solid state fluorescence hydrochromism upon changes in atmospheric relative humidity (RH), and reversible solid state photochromism upon generation of a cellulose-stabilized viologen radical cation. In this design strategy, the bipyridinium unit serves as both a water-sensitive receptor for the hydrochromic fluorophore-receptor system, and a photochromic group, capable of eliciting its own visible colorimetric response, generating a fluorescence quenching radical cation with prolonged exposure to ultraviolet (UV) light. These dyes can be inkjet-printed onto cellulose paper or drop-cast as cellulose powder-based films and can be unidirectionally cycled between three different states which can be characteristically visualized under UV light or visible light. The material's photochromism, hydrochromism, and underlying mechanism of action was investigated using computational analysis, dynamic vapor sorption/desorption isotherms, electron paramagnetic resonance spectroscopy, and variable humidity UV-Vis adsorption and fluorescence spectroscopies.

Enantiopure C5 Pentaindenocorannulenes: Chiral Graphenoid Materials.

Chiral carbon nanomaterials offer numerous prospects for material science. As a fundamental building block for non-planar graphenoid materials, pentaindenocorannulene (PIC) with its C5v symmetrical structure presents a platform for creation of supramolecular chiral carbon materials. Specifically, when uniformly penta-substituted on its periphery, PIC generates C5 symmetrical chiral buckybowls capable of columnar stacking. The synthesis and resolution of such PICs are achieved, assignment of absolute configuration is established by comparison of ECD and VCD spectra with theory, and material characterization is reported. Evidence for columnar stacking in solution and in the crystal is presented.

X-ray Crystallography and Unexpected Chiroptical Properties Reassign the Configuration of Haliclonadiamine.

Haliclonadiamine and papuamine are bis-indane marine natural products isolated from the marine sponge Haliclona sp. Their relative structures were previously reported to differ by inversion at only one of their eight shared stereocenters. Here X-ray crystallography shows the opposite to be true: papuamine has a 1R,3S,8R,9S,14S,15R,20S,22R configuration, while haliclonadiamine has a 1S,3R,8S,9R,14R,15S,20R,22R configuration. Paradoxically the ECD of each structure displays a negative Cotton effect. X-ray crystallography reveals the two structures adopt similar conformations of their 13-membered macrocyclic core that comprises a configurationally relevant diene. B97x-D/Def2-TZVPP-(MeOH)-calculated ECD supports the diene configuration with the macrocycle dominating the ECD Cotton effect for haliclonadiamine and papuamine. Additional crystallographic and chiroptical analyses of three sponge samples from geographically distant locations indicate this pair of natural products always exists as a configurationally related couple. The co-discovery of a biosynthetic precursor, halichondriamine C, present in these same Haliclona samples must be considered when discussing any biosynthetic pathway. Taken together, this work justifies a reassignment of haliclonadiamine's structure and opens the question of how this complex stereochemical relationship between haliclonadiamine and palauamine arises biosynthetically.

Classical and non-classical melatonin receptor agonist-directed micellization of bipyridinium-based supramolecular amphiphiles in water.

The addition of molecular recognition units into structures of amphiphiles is a means by which soft matter capable of undergoing template-directed micellization can be obtained. These supramolecular amphiphiles can bind with molecular templates using non-covalent bonding interactions, forming host-guest complexes that hold the amphiphiles together as they undergo micellization. In most cases, such templates are synthesized and designed for a specific molecular recognition motif. It is not clear, however, to what extent these types of amphiphile systems are responsive to members of a biologically derived class of molecular targets, for example, melatonin receptor agonists and their numerous isosteres. Herein, we describe the template-directed micellization and arrangement at the air-water interface of a bipyridinium-based gemini surfactant, driven by the influence of donor-acceptor CT interactions with a series of bioactive classical and non-classical melatonin isosteres. Under the conditions of templation by either 5-methoxytryptophol, N-acetylserotonin, N-acetyltryptamine, or the pharmaceutical agent agomelatine, favorable Gibbs free energies of micellization were observed with decreases in CMC by up to 70%, and concomitant increases of 28% in surface pressure, and decreases of 20% in contact angle versus untemplated solutions. Solid state thermochromic transition temperatures for inkjet-printed patterns of the templated amphiphile solutions were inversely correlated with trends observed for their respective CMCs, and exhibited no correlation to their binding constants. These findings contend for the generalizable use of melatonin receptor agonists as targets and/or templates for chemical systems, which rely on π-stacking donor-acceptor CT interactions in water to facilitate the actions of binding, sequestration, or template-directed self-assembly.

Fluorous Corannulenes: Ab initio Predictions and the Synthesis of sym-Pentafluorocorannulene.

Ten sym-penta and deca-X substituted corannulenes (1-10; X=H, F, CH3 , or CF3 ) define a library of fluorous compounds comprising high symmetry non-planar aromatic compunds. They provide a group of structurally similar, yet physically distinct structures manifesting special chemical behavior related to their degree of fluorination. Owing to their bowl forms, corannulene derivatives are distinct from planar polynuclear aromatic compounds; they have relatively high dipole moments, accept 1-4 electrons, and display room temperature fluorescence as well as low temp phosphorescence. Electronic structure theory predicts the bowl inversion barrier and physical properties. The syntheses of sym-pentafluorocorannulene by an efficient late stage fluorination affords a key derivative to calibrate predictions.

Transition-Metal Catalysis of Triene 6π Electrocyclization: The π-Complexation Strategy Realized.

Triene 6π electrocyclization, wherein a conjugated triene undergoes a concerted stereospecific cycloisomerization to a cyclohexadiene, is a reaction of great historical and practical significance. In order to circumvent limitations imposed by the normally harsh reaction conditions, chemists have long sought to develop catalytic variants based upon the activating power of metal-alkene coordination. Herein, we demonstrate the first successful implementation of such a strategy by utilizing [(C5 H5 )Ru(NCMe)3 ]PF6 as a precatalyst for the disrotatory 6π electrocyclization of highly substituted trienes that are resistant to thermal cyclization. Mechanistic and computational studies implicate hexahapto transition-metal coordination as responsible for lowering the energetic barrier to ring closure. This work establishes a foundation for the development of new catalysts for stereoselective electrocyclizations.

Synthesis of Modified Nucleoside Oligophosphates Simplified: Fast, Pure, and Protecting Group Free.

Phosphoramidite analogues of modified cyclotriphosphates provide a general and step-economical synthesis of nucleoside triphosphates and analogues on scale without the need for protecting groups. These reagents enable rapid access to pure nucleoside oligophosphates and a range of other analogues that were previously difficult to obtain (e.g., NH, CH2, CCl2, and CF2 replacements for O, phosphono- and phosphoimidazolides, -morpholidates, -azidates, and -fluoridates). DFT calculations demonstrate that the selectivity of the cyclotriphosphate opening reactions proceeds via an in-line substitution mechanism that displaces the least charged leaving group.

Corannurylene Pentapetalae.

Despite the great advances in the synthesis of diverse nonplanar graphenoids, investigations into the relationship between structural features and intermolecular interactions still present significant challenges. Herein, the novel nonplanar graphenoid structure, corannurylene pentapetalae (CRP), obtained via bottom-up syntheses of hybridization between perylene diimide (PDI) planar fragments and a corannulene curved core, is presented. Single crystal studies reveal a D5-symmetric as well as a C2-symmetric graphenoid corannurylene pentapetalae. The D5-symmetric structure has a unique honeycomb lattice with two chiral honeycomb layers alternately stacked, whereas the C2-symmetric CRP forms dimer units via π-π stacking. Transistor devices demonstrate that, without any π-π stacking, the honeycomb lattice of the D5-symmetric CRP has the potential to also facilitate electron transport.

Fivefold Symmetry and 2D Crystallization: Self-Assembly of the Buckybowl Pentaindenocorannulene on a Cu(100) Surface.

The modification of metal electrode surfaces with functional organic molecules is an important part of organic electronics. The interaction of the buckminsterfullerene fragment molecule pentaindenocorannulene with a Cu(100) surface is studied by scanning tunneling microscopy, dispersion-enabled density functional theory, and force field calculations. Experimental and theoretical methods suggest that two adjacent indeno groups become oriented parallel to the surface upon adsorption under mild distortion of the molecular frame. The binding mechanism between molecule and surface is dominated by strong electrostatic interaction owing to Pauli repulsion. Two-dimensional aggregation at room temperature leads to a single lattice structure in which all molecules are oriented unidirectionally. Their relative arrangement in the lattice suggests noncovalent intermolecular interaction through C-H⋅⋅⋅π bonding.

Acid-Induced Liberation of Polysubstituted Cyclopentadiene Ligands from Cyclopentadienyl Cobalt: A [2 + 2 + 1] Cycloaddition Route toward 1,2,4-Trisubstituted Cyclopentadienes.

Here, we report that trifluoroacetic acid (TFAH) induces demetallation and protodesilylation of the cyclopentadiene ligand in cobalt-η4-cyclopentadiene complexes of general formula [(η5-C5H5)Co(η4-exo-C(TMS)═C(SO2Ph)CH═CRCH(CO2Et))] (1-Ph, R = Ph; 1-ArtBu, R = p-C6H4tBu; 1-ArNMe2, R = p-C6H4NMe2; and 1-Me, R = Me). The trisubstituted cyclopentadiene products are isolated as a mixture of two tautomers, [(CH2C(SO2Ph)═CHC(CO2Et)═CR)] (8-R-A) and [(CH═C(SO2Ph)CH2C(CO2Et)═CR)] (8-R-B). The endo isomer, [(η5-C5H5)Co(η4-endo-C(TMS)═C(SO2Ph)CH═CPhCH(CO2Et))] (1-Ph-endo), also undergoes demetallation and protodesilylation to give 8-Ph-A and 8-Ph-B in excellent yield. The cobalt-cyclopentadiene complex, [(η5-C5H5)Co(η4-exo-C(TMS)═C(SO2Ph)CH═C(CO2Me)CH(CO2Et))] (1-CO2Me), undergoes demetallation and protodesilylation upon treatment with TFAH to give a hydrogen-bonded fulvenol (8-CO2Me). Liberation of the ethoxy-substituted cyclopentadiene ligand of [(η5-C5H5)Co(η4-exo-C(TMS)═C(SO2Ph)CH═C(OEt)CH(CO2Et))] (1-OEt) leads to formation of a cyclopentenone derivative (11). Thermolysis of 8-Ph-A/8-Ph-B in the presence of maleimide leads to a highly functionalized Diels-Alder adduct, whereas 8-Ph-A/8-Ph-B serves as precursors to trisubstituted ruthenocenes by in situ deprotonation and reaction with [(η5-C5R5)Ru(NCMe)3]PF6 (16-H, R = H; 16-Me, R = Me).

Melatonin-directed micellization: a case for tryptophan metabolites and their classical bioisosteres as templates for the self-assembly of bipyridinium-based supramolecular amphiphiles in water.

The bulk solution properties of amphiphilic formulations are derivative of their self-assembly into higher ordered supramolecular assemblies known as micelles and of their ordering at the air-water interface. Exerting control over the surface-active properties of amphiphiles and their propensity to aggregate in pure water is most often fine-tuned by covalent modification of their molecular structure. Nevertheless structural constraints which limit the performance of amphiphiles do emerge when trying to develop more sophisticated systems which undergo for example, shape-defined controlled assembly and/or respond to external stimuli. In this regard, the template-modulated assembly of the so-called "supramolecular amphiphiles" continues to make progress ordering molecules that otherwise have very little to no driving force to aggregate in a prescribed manner in aqueous solutions. Herein we describe the template-modulated micellization and ordering at the air-water interface of bipyridinium-based supramolecular amphiphiles triggered by host-guest interactions with high specificity for the neurotransmitter melatonin over its biosynthetic synthon l-tryptophan and the thermodynamic parameters governing the template-modulated micellization process. When bound to the bipyridinium units of micellized surfactant molecules, melatonin effectively serves as "molecular glue" capable of lowering the CMC by 52% as compared to untemplated solutions. Analysis of this system suggests that a hallmark of donor-acceptor template-modulated micellization in water is a strong positively correlated temperature dependence of the CMC and the absence of a U-shaped CMC-temperature curve. Our findings make a case for the incorporation of l-tryptophan-based metabolites and their classical synthetic pharmaceutical bioisosteres as potential targets/components of donor-acceptor CT-based supramolecular amphiphile systems/materials operating in water.

1,2,3- versus 1,2-Indeno Ring Fusions Influence Structure Property and Chirality of Corannulene Bowls.

Annulated corannulenes 3-5 form via distinct synthetic pathways: (i) Pd-catalyzed sp3 CH insertion, (ii) Pd-catalyzed aryl coupling, and (iii) silyl cation-promoted C-F activation/CH insertion. Crystal structure, redox, and photophysical studies elucidate the differing influence of 1,2,3- versus 1,2-indeno ring fusions. Mono and dianions of 3-5 are characterized. Resolution of 4 gives enantiopure forms, allowing assessment of the bowl-inversion barrier.

Correction: General optimization procedure towards the design of a new family of minimal parameter spin-component-scaled double-hybrid density functional theory.

Correction for 'General optimization procedure towards the design of a new family of minimal parameter spin-component-scaled double-hybrid density functional theory' by Loïc M. Roch and Kim K. Baldridge, Phys. Chem. Chem. Phys., 2017, 19, 26191-26200.

Chiral Atropisomeric Indenocorannulene Bowls: Critique of the Cahn-Ingold-Prelog Conception of Molecular Chirality.

Chiral corannulenes abound, but suffer generally from configurational lability associated with bowl-to-bowl inversion, thus obviating questions of stereogenicity and stereoelement construction. In contrast, peri-annulated corannulenes show greatly increased barriers for bowl-to-bowl inversion; specifically indenocorannulenes invert on a time scale too slow to observe by normal NMR methods and raise the possibility of creating chiral atropisomeric bowl-shaped aromatics. Two methods for preparing indenocorannulene from simple 2-haloarylcorannulenes-silyl cation C-F activation, and Pd-mediated C-Cl activation[5] -enable the synthesis of an array of such chiral atropisomeric indenocorannulenes. Resolution of the enantiomers by high-performance liquid chromatography over chiral support phases motivates the study of chiroptical properties, the assignment of absolute "Cartesian" configuration, and the assessment of configurational stability. These studies bring into question any systematic assignment of nontrivial stereoelements (i.e. not the molecule in its entirety) and refute any assertion of congruence between "Cahn-Ingold-Prelog elements" and the physical or "Cartesian" basis of chirality.

[3+3] Cyclocondensation of Disubstituted Biphenyl Dialdehydes: Access to Inherently Luminescent and Optically Active Hexa-substituted C3-Symmetric and Asymmetric Trianglimine Macrocycles.

A general synthetic route to inherently luminescent and optically active 6-fold substituted C3-symmetric and asymmetric biphenyl-based trianglimines has been developed. The synthesis of these hexa-substituted triangular macrocycles takes advantage of a convenient method for the synthesis of symmetrically and asymmetrically difunctionalized biphenyl dialdehydes through a convergent two-step aromatic nucleophilic substitution-one-pot Suzuki-coupling reaction protocol. A modular [3+3] diamine-dialdehyde cyclocondensation reaction between both the symmetrically and asymmetrically difunctionalized-4,4'-biphenyldialdehydes with enantiomerically pure (1R,2R)-1,2-diaminocyclohexane was employed to construct the hexa-substituted triangular macrocycles. B97-D/6-311G(2d,p) density functional theory determined structures and X-ray crystallographic analysis reveal that the six substituents appended to the biphenyl legs of the trianglimine macrocycles adopt an alternating conformation not unlike the 1,3,5-alternate conformation observed for calix[6]arenes. Reduction of the imine bonds using NaBH4 afforded the corresponding 6-fold substituted trianglamine without the need to alkylate the amine nitrogen atoms which could hinder their later use as metal coordination sites and without having to introduce asymmetric carbons.

General optimization procedure towards the design of a new family of minimal parameter spin-component-scaled double-hybrid density functional theory.

A general optimization procedure towards the development and implementation of a new family of minimal parameter spin-component-scaled double-hybrid (mSD) density functional theory (DFT) is presented. The nature of the proposed exchange-correlation functional establishes a methodology with minimal empiricism. This new family of double-hybrid (DH) density functionals is demonstrated using the PBEPBE functional, illustrating the optimization procedure to the mSD-PBEPBE method, and the performance characteristics shown for a set of non-covalent complexes covering a broad regime of weak interactions. With only two parameters, mSD-PBEPBE and its cost-effective counterpart, RI-mSD-PBEPBE, show a mean absolute error of ca. 0.4 kcal mol-1 averaged over 66 weak interacting systems. Following a successive 2D-grid refinement for a CBS extrapolation of the coefficients, the optimization procedure can be recommended for the design and implementation of a variety of additional DH methods using any of the plethora of currently available functionals.

On the Origins of Nonradiative Excited State Relaxation in Aryl Sulfoxides Relevant to Fluorescent Chemosensing.

We provide herein a mechanistic analysis of aryl sulfoxide excited state processes, inspired by our recent report of aryl sulfoxide based fluorescent chemosensors. The use of aryl sulfoxides as reporting elements in chemosensor development is a significant deviation from previous approaches, and thus warrants closer examination. We demonstrate that metal ion binding suppresses nonradiative excited state decay by blocking formation of a previously unrecognized charge transfer excited state, leading to fluorescence enhancement. This charge transfer state derives from the initially formed locally excited state followed by intramolecular charge transfer to form a sulfoxide radical cation/aryl radical anion pair. With the aid of computational studies, we map out ground and excited state potential energy surface details for aryl sulfoxides, and conclude that fluorescence enhancement is almost entirely the result of excited state effects. This work expands previous proposals that excited state pyramidal inversion is the major nonradiative decay pathway for aryl sulfoxides. We show that pyramidal inversion is indeed relevant, but that an additional and dominant nonradiative pathway must also exist. These conclusions have implications for the design of next generation sulfoxide based fluorescent chemosensors.