Propeller Conformation Research Articles

Synthesis and Analysis of (γ,γ',γ''-Trifluoro)neopentyl (TFNP) Aryl Ethers as a Polar Fluoroaliphatic Motif.

A route is developed to (γ,γ',γ'''-trifluoro)neopentyl (TFNP) aryl ethers to extend the methods for the introduction of the tert-butyl group, carrying a fluorine on each of the methyl substituents. The route combines neopentyltosylate 3 with phenols and thiophenols to give efficient substitution reactions to the corresponding TFNP aryl ethers. The three C-F bonds adopt a helical propeller conformation as revealed by computation and single crystal X-ray structure analysis. The LogPs of TFNP ethers are lower (more hydrophilic) than their neopentyl analogues. The metabolism of selected TFNP ethers was explored in the fungus Cunninghamella elegans.

Controlled Self-Assembly, Isomerism, and Guest Uptake/Release of Charge-Reversible Lanthanide-Organic Octahedral Cages.

Charge plays a crucial role in the function of molecular and supramolecular systems, but coordination hosts capable of orthogonal charge regulation remain elusive so far. In this study, we report the condition-dependent self-assembly of charge-reversible lanthanide-organic tetra-capped octahedral cages, i.e., [Ln6(H3L)4]6+ and [Ln6L4]6-, from a series of lanthanide ions (Ln3+; Ln = Lu, Yb, Eu) and a tritopic tetradentate acylhydrazone ligand (H6L) featuring multiple deprotonation states and propeller conformations. While direct self-assembly under basic conditions produced a mixture of various ΔxΛ6-x-[Ln6L4]6- (x = 0-6) stereoisomers, racemic Δ6- and Λ6-[Ln6L4]6- could be exclusively obtained from the first self-assembly of Δ6- and Λ6-[Ln6(H3L)4]6+ under neutral conditions followed by post-assembly deprotonation. Rich isomerism on the tetra-capped octahedral cages arising from the coupling between the metal-centered Δ/Λ chirality and the ligand conformations has been discussed based on X-ray single-crystal structures of the C3-symmetric Δ3Λ3-Ln6L4 and T-symmetric Δ6/Λ6-Ln6L4 complexes. Host-guest studies confirmed that positively charged rac-Δ6/Λ6-[Ln6(H3L)4]6+ could bind anionic sulfonates, and negatively charged rac-Δ6/Λ6-[Ln6L4]6- exhibited strong encapsulation ability toward ammonium guests, where acid/base-triggered guest uptake/release could be realized taking advantage of the charge reversibility of the cage. Moreover, photophysical studies revealed visible-light-sensitized and guest-encapsulation-enhanced NIR emissions on the rac-Δ6/Λ6-Yb6L4 cage. This work not only enriches the library of functional lanthanide-organic cages but also provides a promising candidate with charge reversibility for the development of smart supramolecular materials.

α‐Cyano Triaryl[3]radialene: Unsymmetrical Stereo‐configuration, Clustering‐enhanced Excimer Emission, and Radical‐involved Multimodal Information Switching

Abstract[3]Radialene has a peculiar topology and cross‐conjugation system, representing a unique molecular scaffold in organic materials. Herein, we report a special class of stereoisomeric α‐cyano triaryl[3]radialenes (CTRs) that show concentration‐caused quenching in solution but emit red‐shifted and enhanced luminescence in the crystalline state. Clustering of multiple cyano groups and their through‐space interactions with the [3]radialene ring significantly extend π‐electron communication meanwhile rigidifying the propeller conformation multivalently, thus playing a key role behind the state‐dependent luminescence. These radialenes with a substantial electron affinity undergo a reversible electron transfer transition to anionic radicals with good stability, showing switching of photoabsorption, photoluminescence and electron spin resonance (ESR) signal. We also established proof‐of‐concept applications of CTRs for multimodal information encryption and chemical sensing.

α-Cyano Triaryl[3]radialene: Unsymmetrical Stereo-configuration, Clustering-enhanced Excimer Emission, and Radical-involved Multimodal Information Switching.

[3]Radialene has a peculiar topology and cross-conjugation system, representing a unique molecular scaffold in organic materials. Herein, we report a special class of stereoisomeric α-cyano triaryl[3]radialenes (CTRs) that show concentration-caused quenching in solution but emit red-shifted and enhanced luminescence in the crystalline state. Clustering of multiple cyano groups and their through-space interactions with the [3]radialene ring significantly extend π-electron communication meanwhile rigidifying the propeller conformation multivalently, thus playing a key role behind the state-dependent luminescence. These radialenes with a substantial electron affinity undergo a reversible electron transfer transition to anionic radicals with good stability, showing switching of photoabsorption, photoluminescence and electron spin resonance (ESR) signal. We also established proof-of-concept applications of CTRs for multimodal information encryption and chemical sensing.

Inducing Propeller Chirality in Triaryl Boranes with Chiral Amines.

Stabilization of chiral propeller conformations in triaryl compounds is challenging due to generally low racemization barriers. Nonetheless, it was recently found that chiral conformational preferences can be induced to triaryl boranes by incorporating point-chiral alkylether chains to the aryl blades and subsequently locking the structure with ammonia. A four-point interaction, meaning that the cooperative effects of Lewis-adduct formation and three hydrogen bonds, was proposed as stabilizing mechanism. Herein, it was shown that three such strong interactions suffice to introduce a preferential propeller handedness. Although DFT calculations predict no noteworthy preferences for either P- or M-chiral propellers for some of the investigated triarylborane-amine adducts that were prepared with chiral primary amines, vibrational circular dichroism (VCD) spectroscopic characterizations revealed that there is indeed a measurable excess of one propeller handedness. Furthermore, the steric demand of the amine was found to play a key role in the induction process and especially in preventing blade rotations.

Understanding the Interactions between Triolein and Cosolvent Binary Mixtures Using Molecular Dynamics Simulations

Biodiesel is one of the emerging renewable sources of energy to replace fossil-fuel-based resources. It is produced by a transesterification reaction in which a triglyceride reacts with methanol in the presence of a catalyst. The reaction is slow because of the low solubility of methanol in triglycerides, which results in low concentrations of methanol available to react with triglyceride. To speed up the reaction, cosolvents are added to create a single phase which helps to improve the concentration of methanol in the triglyceride phase. In this study, molecular dynamics simulations are used to help understand the role of cosolvents in the solvation of triglyceride (triolein). Six binary mixtures of triolein/cosolvent were used to study the solvation of triolein at 298.15 K. Results of 100 ns simulations at constant temperature and pressure to simulate mixing experiments show that in the first 10 ns all the binary mixtures remain largely unmixed. However, for the cosolvents that are fully miscible with triolein, the partial densities across the simulation boxes show that the systems are fully mixed in the final 10 ns. Some solvents were found to interact strongly with the polar part of triolein, while others interacted with the aliphatic part. The radial distribution functions and clustering of the solvents around triolein were also used as indicators for solvation. The presence of cosolvents also influenced the conformation of triolein molecules. In the presence of solvents that solubilize it, triolein preferred a propeller conformation but took up a trident conformation when there is less or no solubilization. The results show that tetrahydrofuran is the best solvent at solubilizing triolein, followed by cyclopentyl methyl ether, diethyl ether, and hexane. With 1,4-dioxane, the solubility improves with an increase in temperature. The miscibility of a solvent in triolein is aided by its ability to interact with both the polar and nonpolar parts of triolein.

Emerging Designs of Aggregation-Induced Emission Agents for Enhanced Phototherapy Applications

Emerging Designs of Aggregation-Induced Emission Agents for Enhanced Phototherapy Applications

Molecular structure controlled self-assembly of pyridine appended fluorophores: multi-stimuli fluorescence responses and fabricating rewritable/self-erasable fluorescent platforms

Pyridine appended structural isomers showed a planar or propeller conformation dependent molecular self-assembly, fluorescent polymorphs, stimuli-responsive fluorescence switching and halochromism.

Chiral Molecular Propellers of Triarylborane Ammonia Adducts.

Chiral molecular propeller conformations have been induced to various triaryl structures including trityl derivatives and triaryl boranes. For borane–amine adducts, such induced propeller chirality has not been reported yet due to the low energy barrier for racemization in common triarylboranes such as B(C6H5)3 or B(C6F5)3. Herein, we demonstrate that point chirality in side chains of chiral triarylborane–ammonia adducts, which feature intramolecular hydrogen bonds in addition to the dative N→B bond, can efficiently be transferred to triarylborane propeller chirality. Employing X‐ray crystallography and ECD/VCD spectroscopy for structural characterizations, we investigate three examples with different steric demands of the incorporated chiral alkoxy side groups. We elucidate the conformational preferences of the molecular propellers. Furthermore, we show that computationally predicted conformational preferences obtained for the isolated, only implicitly solvated molecules are actually opposite to the experimentally observed ones.

A C2-symmetric triple [5]helicene based on N-annulated triperylene hexaimide for chiroptical electronics

Two diastereoisomers (NTPH-P and NTPH-T1) as a C 2-symmetric triple [5]helicene based on N -annulated triperylene hexaimide were synthesized. Aided by nuclear magnetic resonance spectroscopy (NMR) and theoretical calculations, NTPH-P was assigned to three-blade propeller conformation while NTPH-T1 tended to exhibit twisted conformation with pyrrole ring fusing on a bowl-shaped PDI foil. Characterized by circular dichroism (CD) and circular polarized luminescence (CPL) measurements, the enantiomerically pure NTPH-P exhibited fairly good chiral activities both in the absorption and emission range with dissymmetry factors | g abs| of 4.1×10−3 and | g lum| of 1.2×10−3. The diastereoisomers were further employed as acceptors for organic solar cells with distinct PCEs of 8.11% and 5.24% for NTPH-P and NTPH-T1 based devices, respectively, signifying the prospects in chiroptical electronics by designing molecularly defined aromatics.

On the Origin of the Conformationally Non-Interconvertable Isomers of Bisphenyldirhodium(III) Caprolactamate

A plausible explanation for the unprecedented formation of two conformational isomers of bisphenyldirhodium(III) caprolactamate is presented. The presence of acetic acid during the coupling process leading to the formation of bisphenyldirhodium(III) caprolactamate is shown to increase the propeller conformer at the expense of the biplanar conformer, Acetic acid is also found to catalyze the decomposition of bisphenyldirhodium(III) caprolactamate with the propeller conformation reacting at a rate that is more than ten times greater than that for the biplanar conformation. We speculate that protonation of one of the caprolactamate ligands changes the orientation of the phenyl ring in its approach to rhodium in the product-forming step of the arylation reaction leading to the formation of the two conformational isomers.

DNA-Decorated, Helically Twisted Nanoribbons: A Scaffold for the Fabrication of One-Dimensional, Chiral, Plasmonic Nanostructures.

Crafting of chiral plasmonic nanostructures is extremely important and challenging. DNA-directed organization of nanoparticle on a chiral template is the most appealing strategy for this purpose. Herein, we report a supramolecular approach for the design of DNA-decorated, helically twisted nanoribbons through the amphiphilicity-driven self-assembly of a new class of amphiphiles derived from DNA and hexaphenylbenzene (HPB). The ribbons are self-assembled in a lamellar fashion through the hydrophobic interactions of HPB. The transfer of molecular chirality of ssDNA into the HPB core results in the bias of one of the chiral propeller conformations for HPB and induces a helical twist into the lamellar packing, and leads to the formation of DNA-wrapped nanoribbons with M-helicity. The potential of the ribbon to act as a reversible template for the 1D chiral organization of plasmonic nanomaterials through DNA hybridization is demonstrated.

DNA‐Decorated, Helically Twisted Nanoribbons: A Scaffold for the Fabrication of One‐Dimensional, Chiral, Plasmonic Nanostructures

AbstractCrafting of chiral plasmonic nanostructures is extremely important and challenging. DNA‐directed organization of nanoparticle on a chiral template is the most appealing strategy for this purpose. Herein, we report a supramolecular approach for the design of DNA‐decorated, helically twisted nanoribbons through the amphiphilicity‐driven self‐assembly of a new class of amphiphiles derived from DNA and hexaphenylbenzene (HPB). The ribbons are self‐assembled in a lamellar fashion through the hydrophobic interactions of HPB. The transfer of molecular chirality of ssDNA into the HPB core results in the bias of one of the chiral propeller conformations for HPB and induces a helical twist into the lamellar packing, and leads to the formation of DNA‐wrapped nanoribbons with M‐helicity. The potential of the ribbon to act as a reversible template for the 1D chiral organization of plasmonic nanomaterials through DNA hybridization is demonstrated.

Synthesis of Anion-Mixed Crystals of Assembled Complexes Bridged by 1,2-Bis(4-pyridyl)ethane and the Ligand Field of Fe(NCS)(NCBH3) Unit

Abstract Anion-mixed iron(II) assembled complexes using NCS and NCBH3 as anionic ligand and bridged by 1,2-bis(4-pyridyl)ethane (bpe) are synthesized under several conditions for various ratios of NCS to NCBH3. Elemental analysis showed that the experimentally observed fractions of NCS tend to be more than those in the preparation. Some structures are determined by using single crystal X-ray structural analysis. Powder X-ray diffraction patterns are compared among the anion-mixed crystals. 57Fe Mössbauer spectroscopy reveals that a new doublet appears and it is different from the doublets of Fe(NCS)2 and Fe(NCBH3)2 units and the relative area of this new doublet reaches maximum when the fraction of NCS is around 1.0 per each iron, suggesting that the new doublet is ascribed to an Fe(NCS)(NCBH3) unit. Corresponding anion-mixed complexes enclathrating p-dichlorobenzene (p-DCB) are synthesized. Superconducting quantum interference device (SQUID) measurement and Mössbauer spectroscopy reveal that the complexes show spin-crossover (SCO) phenomenon and the relative area of the low-spin state is more than the expected value. The existence of Fe(NCS)(NCBH3) is supported by the results of SQUID measurement and density functional theory (DFT) calculation. Ligand field splitting strength of Fe(NCS)(NCBH3) unit is estimated to be intermediate between Fe(NCS)2 and Fe(NCBH3)2 units. Complexes enclathrating p-DCB display propeller conformation of bpe around the iron atom, while complexes without a guest molecule have distorted propeller conformation of bpe around the iron atom. It is suggested that such difference determines whether the SCO is on or off.

Stereospecific Winding of Polycyclic Aromatic Hydrocarbons into Trinacria Propellers.

The stereospecific trimerization of enantiomerically pure binaphthols with hexakis(bromomethyl)benzene gives access in one step to enantiomerically pure molecular propellers, in which three binaphthyl rings are held together with dioxecine rings. X-ray diffraction analysis revealed that three out the six naphthyl moieties are folded in a (EF)3 -type arrangement held by three intramolecular C-H⋅⋅⋅π interactions. This slips outward the three remaining naphthyl rings in a blade-like fashion, just like in three-folded propeller components. This peculiar conformation shows striking similarity to the mythological Sicilian symbol of Trinacria, from which the name "trinacria propeller" derives. The propeller conformation is also preserved in chlorinated solutions, as displayed by the presence of a peak at 4.7 ppm typical of an aromatic proton resonance engaged in a C-H⋅⋅⋅π interaction. The denaturation of the propeller-like conformation is obtained at high temperature, corresponding to activation energy for the ring inversion of ca. 18.2 kcal mol-1 . Notably, halide-functionalized molecular propellers exposing I-atoms at the leading and trailing edges could be prepared stereo- and regiospecifically by choosing the relevant iodo-bearing BINOL derivative.

Determinants for Tight and Selective Binding of a Medicinal Dicarbene Gold(I) Complex to a Telomeric DNA G-Quadruplex: a Joint ESI MS and XRD Investigation.

The dicarbene gold(I) complex [Au(9-methylcaffein-8-ylidene)2 ]BF4 is an exceptional organometallic compound of profound interest as a prospective anticancer agent. This gold(I) complex was previously reported to be highly cytotoxic toward various cancer cell lines in vitro and behaves as a selective G-quadruplex stabilizer. Interactions of the gold complex with various telomeric DNA models have been analyzed by a combined ESI MS and X-ray diffraction (XRD) approach. ESI MS measurements confirmed formation of stable adducts between the intact gold(I) complex and Tel 23 DNA sequence. The crystal structure of the adduct formed between [Au(9-methylcaffein-8-ylidene)2 ](+) and Tel 23 DNA G-quadruplex was solved. Tel 23 maintains a characteristic propeller conformation while binding three gold(I) dicarbene moieties at two distinct sites. Stacking interactions appear to drive noncovalent binding of the gold(I) complex. The structural basis for tight gold(I) complex/G-quadruplex recognition and its selectivity are described.

Determinants for Tight and Selective Binding of a Medicinal Dicarbene Gold(I) Complex to a Telomeric DNA G‐Quadruplex: a Joint ESI MS and XRD Investigation

AbstractThe dicarbene gold(I) complex [Au(9‐methylcaffein‐8‐ylidene)2]BF4 is an exceptional organometallic compound of profound interest as a prospective anticancer agent. This gold(I) complex was previously reported to be highly cytotoxic toward various cancer cell lines in vitro and behaves as a selective G‐quadruplex stabilizer. Interactions of the gold complex with various telomeric DNA models have been analyzed by a combined ESI MS and X‐ray diffraction (XRD) approach. ESI MS measurements confirmed formation of stable adducts between the intact gold(I) complex and Tel 23 DNA sequence. The crystal structure of the adduct formed between [Au(9‐methylcaffein‐8‐ylidene)2]+ and Tel 23 DNA G‐quadruplex was solved. Tel 23 maintains a characteristic propeller conformation while binding three gold(I) dicarbene moieties at two distinct sites. Stacking interactions appear to drive noncovalent binding of the gold(I) complex. The structural basis for tight gold(I) complex/G‐quadruplex recognition and its selectivity are described.

Dynamic propeller conformation for the unprecedentedly high degree of chiral amplification of supramolecular helices.

An unprecedentedly high degree of chiral amplification of supramolecular helices in a sergeants and soldiers system was realized using a propeller-shaped molecule, triphenylamine (TPA), as the monomer. One sergeant controlled the handedness of 500 soldiers in supramolecular helices. We further demonstrated that a TPA derivative could switch its role from sergeant to soldier and vice versa depending on its partners. These achievements could be realized using the dynamic propeller conformation of TPA and provide new insights into supramolecular assemblies and the supramolecular chiral amplification of helices.

3-Benzhydryl-1,3,4-thiadiazole-2(3H)-thione

In the title compound, C15H12N2S2, the two phenyl rings and the planar (r.m.s. deviation = 0.002 Å) thia­diazole ring adopt a propeller conformation about the central C—H axis with H—C—C—C(phen­yl) torsion angles of 44 and 42° and an H—C—N—C(thia­diazole) torsion angle of 28°. Intra­molecular C—H⋯S and C—H⋯N contacts are observed. In the crystal, centrosymmetrically related mol­ecules associate through C—H⋯π inter­actions. These are connected into a supra­molecular chain along [101] by C—H⋯N inter­actions.

Polyethylene glycol binding alters human telomere G-quadruplex structure by conformational selection

Polyethylene glycols (PEGs) are widely used to perturb the conformations of nucleic acids, including G-quadruplexes. The mechanism by which PEG alters G-quadruplex conformation is poorly understood. We describe here studies designed to determine how PEG and other co-solutes affect the conformation of the human telomeric quadruplex. Osmotic stress studies using acetonitrile and ethylene glycol show that conversion of the ‘hybrid’ conformation to an all-parallel ‘propeller’ conformation is accompanied by the release of about 17 water molecules per quadruplex and is energetically unfavorable in pure aqueous solutions. Sedimentation velocity experiments show that the propeller form is hydrodynamically larger than hybrid forms, ruling out a crowding mechanism for the conversion by PEG. PEGs do not alter water activity sufficiently to perturb quadruplex hydration by osmotic stress. PEG titration experiments are most consistent with a conformational selection mechanism in which PEG binds more strongly to the propeller conformation, and binding is coupled to the conformational transition between forms. Molecular dynamics simulations show that PEG binding to the propeller form is sterically feasible and energetically favorable. We conclude that PEG does not act by crowding and is a poor mimic of the intranuclear environment, keeping open the question of the physiologically relevant quadruplex conformation.