Helicity Inversion Research Articles

Five‐Fold Symmetric Pentaindolo‐ and Pentakis(benzoindolo)Corannulenes: Unique Structural Dynamics Derived from the Combination of Helical and Bowl Inversions

AbstractPeripherally π‐extended corannulenes bearing quintuple azahelicene units, 10 and 11, were prepared and their dynamic behaviors were studied experimentally and theoretically. The fused corannulenes were synthesized from sym‐pentabromocorannulene in three steps. X‐Ray diffraction analysis for 10 displayed a conformer possessing a P(M) bowl chirality and a PPMPM (PMPMM) helical chirality, which was found to be the most stable conformer(s). Variable‐temperature NMR measurements of 10 and 11 revealed that their structural isomers can be interconvertible in solution, depending on the steric congestion around the helical scaffolds. Automated search for conformers in the equilibrium and transition states by Artificial Force Induced Reaction (AFIR) method revealed their interconversion networks, including bowl‐inversion and helical‐inversion. This analysis indicated that the co‐existing corannulene and azahelicene moieties influence the conformational dynamics, which leads to mitigation of the activation energy barriers for isomerization.

Statistical Theory of Helical Twisting in Nematic Liquid Crystals Doped with Chiral Nanoparticles

A molecular field theory of the cholesteric ordering in nematic nanocomposites doped with chiral nanoparticles was developed taking into consideration chiral dispersion interaction between rod-like nanoparticles. It was shown that the inverse pitch of the cholesteric helical structure is proportional to the anisotropy of the effective polarizability and the anisotropy of the effective gyration tensor of a nanoparticle in the nematic host. The theory enables one to predict the helical sense inversion induced by a change of the low-frequency dielectric susceptibility of the nematic host phase. The components of the high-frequency effective polarizability and the effective optical activity of a gold rod-like nanoparticle in a particular nematic solvent were calculated numerically.

Dynamic Quarter‐Wave Metasurface for Efficient Helicity Inversion of Polarization Beyond the Single‐Layer Conversion Limit

AbstractTerahertz chiral sensing and polarization‐multiplexing communication demand subwavelength devices that dynamically invert polarization helicity. Metasurfaces can enhance anisotropy and fine tunability at subwavelength scales for this purpose. Although metasurfaces enabling deep modulation between orthogonal polarizations have been designed, they suffer from low conversion efficiencies. In this study, it is shown that the efficiency of conversion from linear to circular polarization by conventional single‐layer transmissive metasurfaces cannot exceed a fundamental limit. A dynamic reflective metasurface free from this limitation is then proposed. The device includes multilayer structures working as a terahertz quarter‐wave plate with switchable slow and fast axes. A phase transition of vanadium dioxide induces the necessary structural transformation of the metallic patterns. A practical fabrication method, based on the room‐temperature bonding technique of sapphires, is presented. Dynamic helicity inversion is demonstrated at 0.90 THz, with a conversion efficiency of over 80% that is beyond the fundamental limit of single‐layer transmissive metasurfaces (65%) and more than four times greater than that of previously reported devices.

Helicity inversion and generation of orthogonal, degenerate index states of generic C points

We discuss a technique to invert the helicity of generic C points and generate its orthogonal state of polarization in a single step through a fork grating (FG). It is experimentally demonstrated that the beam in each of its diffraction orders possesses a degenerate C point index state. The diffraction phenomenon reported is helicity-dependent, in which left and right-handed ellipse field singularities are separated. The orthogonal polarization state of the input singularity is produced in one of the first diffracted orders of the grating. For every singularity that the grating produces, its orthogonal polarization state is also available in one of its diffraction orders. In contrast to a half-wave plate, where helicity inversion is accompanied by index inversion, a FG inverts helicity without inverting the index. Therefore, a FG can be used to perform multi-functions under generic C point illumination.

Polymerization-Induced Helicity Inversion Driven by Stacking Modes and Self-Assembly Pathway Differentiation.

Regulating the mutual stacking arrangements is of great interest for understanding the origin of chirality at different hierarchical levels in nature. Different from molecular level chirality, the control and manipulation of hierarchical chirality in polymer systems is limited to the use of external factors as the energetically demanding switching stimulus. Herein, the first self-assembly strategy of polymerization-induced helicity inversion (PIHI), in which the controlled packing and dynamic stereomutation of azobenzene (Azo) building blocks are realized by in situ polymerization without any external stimulus, is reported. A multiple helicity inversion and intriguing helix-helix transition of polymeric supramolecular nanofibers occurs during polymerization, which is collectively confirmed to be mediated by the transition between functionality-oriented π-π stacking, H-, and J-aggregation. The studies further reveal that helicity inversion proceeds through a delicate interplay of the thermodynamically and kinetically controlled, pathway-dependent interconversion process, which should provide new insight into the origin and handedness control of helical nanostructures with desired chirality.

Dinuclear Au(I), Au(II) and Au(III) Complexes with (CF2 )n Chains: Insights into The Role of Aurophilic Interactions in the Au(I) Oxidation.

New dinuclear Au(I), Au(II) and Au(III) complexes containing (CF2)n bridging chains were obtained. Metallomacrocycles [Au2{μ‐(CF2)4}{μ‐diphosphine}] show an uncommon figure‐eight structure, the helicity inversion barrier of which is influenced by aurophilic interactions and steric constraints imposed by the diphosphine. Halogenation of LAu(CF2)4AuL (L=PPh3, PMe3, (dppf)1/2, (binap)1/2) gave [Au(II)]2 species, some of which display unprecedented folded structures with Au−Au bonds. Aurophilic interactions facilitate this oxidation process by preorganizing the starting [Au(I)]2 complexes and lowering its redox potential. The obtained [Au(II)]2 complexes undergo thermal or photochemical elimination of R3PAuX to give Au(III) perfluorinated auracycles. Evidence of a radical mechanism for these decomposition reactions was obtained.

Water-soluble polycarbodiimides and their cytotoxic and antifungal properties

We have successfully synthesized water-soluble neutral and polyelectrolyte helical polycarbodiimides and studied their biological properties. These polymers were prepared by decorating carbodiimide backbones with nonionic, hydrophilic functional groups such as dimethylamine, piperazine, and morpholine. Additionally, the 3° amines present in these functional groups were quaternized using methyl iodide as the alkylating agent to produce their ionic analogs. Polycarbodiimides were chosen as the base polymer used because of their facile chemical modification, pH tolerance in terms of both their helical conformations and degradation behaviors, and tunable helical inversion barriers. Hydrophilic side groups, such as morpholine, dimethylamine, and piperazine, can be used to balance the amphiphilic architecture of the polycarbodiimides along with lipophilic groups, such as alkyl side chains. A chiral R or S BINOL Ti(IV) isopropoxide catalyst was used to control the handedness of the polycarbodiimide helices in these studies. These ionic and neutral polycarbodiimides were subsequently studied for potential antimicrobial and cytotoxic properties. Poly[N-methyl-N’-2-morpholinoethylcarbodiimide], as an example, exhibited significant antifungal properties against Candida albicans. Also, Poly[N-methyl-N’-2-morpholinoethylcarbodiimide] showed significant inhibition of biofilm formation. This suggests that the polymer is a promising candidate for antifungal biomedical applications. Measuring cytotoxicity against urinary bladder cancer cells, poly[N-[3-(dimethylamino)propyl)]-N’-[3-(morpholino)propyl]carbodiimide] (S-cat) and poly[N-[3-(dimethylamino)propyl)]-N’-[3-(morpholino)propyl]carbodiimide]-MeI (S-cat) showed significantly low IC50 values. The IC50 values of poly[N-[3-(dimethylamino)propyl)]-N’-[3-(morpholino)propyl]carbodiimide] (S-cat) and Poly[N-[3-(dimethylamino)propyl)]-N’-[3-(morpholino)propyl]carbodiimide]-MeI (S-cat) are 3.50 μM and 1.27 μM, respectively. The significantly low cancer cell growth inhibition concentration implies the highest cytotoxicity of the polymers, suggesting potential applications as cancer therapeutics. These results also showed that the functionalization and chirality of polycarbodiimides modulate their anticancer and antifungal activity.

Spontaneous chiral self-assembly of CdSe@CdS nanorods

Spontaneous chiral self-assembly of CdSe@CdS nanorods

Switchable Aromatic Nanopore Structures: Functions and Applications.

Nanopore structures in nature play a crucial role in performing many sophisticated functions such as signal transduction, mass transport, ion channel, and enzyme reaction. Inspired by pore-forming proteins, considerable effort has been made to design self-assembling molecules that are able to form nanostructures with internal pores in aqueous media. These nanostructures offer ample opportunity for applications because their internal pores are able to perform a number of unique functions required for a confined nanospace. However, unlike nanopore assembly in nature, the synthetic nanopore structures are mostly based on a fixed pore that impedes performing adaptable regulation of properties to environmental change. This limitation can be overcome by integration of hydrophilic oligo(ethylene oxide) dendrons into aromatic building blocks for nanopore self-assembly, because the dendritic chains undergo large conformational changes triggered by environmental change. The transition of the oligoether chains triggers the aromatic nanopore assembly to undergo reversible pore deformation through closing, squeezing, and shape change without structural collapse. These switching properties allow the aromatic nanopore structures to perform adaptable, complex functions which are difficult to achieve using a fixed pore assembly.In this Account, we summarize our recent progress in the development of switchable nanopore structures by self-assembly of rigid aromatic amphiphiles grafted by hydrophilic oligo(ethylene oxide) dendrons in aqueous media. We show that combining oligoether chains into aromatic segments generates switchable aromatic nanopore structures in aqueous media such as hollow tubules, toroidal structures, and 2D porous sheets depending on the shape of the aromatic building block. Next, we discuss the chemical principle behind the switching motion of the aromatic nanopore structures triggered by external stimuli. We show that the internal pores of the aromatic nanostructures are able to undergo reversible switching between open-closed or expanded-contracted states triggered by external stimuli such as temperature, pH, and salts. In the case of toroidal structures, closed ring-like aromatic frameworks can be spirally open triggered by heat treatment, which spontaneously initiate helical polymerization. Additionally, we discuss switchable functions carried out by the aromatic nanopores such as driving helicity inversion of DNA, consecutive enzymatic action, reversible actuation of lipid vesicles, and pumping of captured guests out of internal pores. By understanding the underlying chemical principle required for dynamic mechanical motion, aromatic assembly can be exploited more broadly to create emergent nanopore structures with functions as complex as those of biological systems.

Quantum-Classical Simulation of Molecular Motors Driven Only by Light.

Molecular motors that exhibit controlled unidirectional rotation provide great prospects for many types of applications, including nanorobotics. Existing rotational motors have two key components: photoisomerization around a π-bond followed by a thermally activated helical inversion, the latter being the rate-determining step. We propose an alternative molecular system in which the rotation is caused by the electric coupling of chromophores. This is used to engineer the excited state energy surface and achieve unidirectional rotation using light as the only input and avoid the slow thermally activated step, potentially leading to much faster operational speeds. To test the working principle, we employ quantum-classical calculations to study the dynamics of such a system. We estimate that motors built on this principle should be able to work on a subnanosecond time scale for such a full rotation. We explore the parameter space of our model to guide the design of a molecule that can act as such a motor.

Thermoswitching of Helical Inversion of Dynamic Polyphenylacetylenes through cis-trans Isomerization of Amide Pendants

The cis-trans isomerization of amides plays a vital role in all kinds of structural changes and biological activities, involving protein folding, protein misfolding, and even protein molecular recognition. However, the helical inversion of synthetic macromolecules arising from the cis-trans isomerization of tertiary amides, as a good mimic of natural protein, has been rarely researched. Herein, we synthesized meta-disubstituted polyphenylacetylenes (PPAs) with different N-substituted tertiary amides as one of the pendants, poly{(−)-3-methoxycarbonyl-5-[N-methyl-N-(S)-(1-phenylethyl)carbamoyl]phenylacetylene}(sP-NMe) and poly{(−)-3-methoxycarbonyl-5-[N-propyl -N-(S)-(1-phenylethyl)carbamoyl]phenylacetylene} (sP-NPr). The cis-trans isomerization of amides was investigated by a combinational analysis of 1H/13C nuclear magnetic resonance (NMR), heteronuclear multiple quantum coherence (HMQC), variable-temperature NMR, Raman spectroscopy, ultraviolet–visible (UV–vis) spectroscopy, electronic circular dichroism (ECD), vibrational circular dichroism (VCD), and computer calculations. The substituted amide of sP-NMe favors the trans isomer at low temperatures, and the polyene main chain takes the right-handed helical conformation. When increasing the temperature, the ratio of the cis isomer in sP-NMe increases, which causes helical inversion. The screw sense of the polymer backbone of sP-NMe can be thermoreversibly switched upon tuning the cis-trans isomerization equilibrium of the tertiary amide pendant. In comparison, sP-NPr has the left-handed conformation with the majority of the cis isomer owing to the bulky propyl group, and cis-trans isomerization cannot induce helical inversion upon thermal treatment. The results reveal that helical inversion caused by the cis-trans isomerization of amide groups is highly dependent on the size of N-alkyl substituents.

Synthesis and Stereochemical Behavior of Dioxa[6]helicene Derivatives

AbstractWe constructed a helically chiral dioxa[6]helicene by assembling simple phenol building blocks by a combination of two simple reactions involving oxidative cross‐coupling followed by dehydrative cyclization. X‐ray analysis and density functional calculations (DFT) revealed that the compound dioxa[6]helicene has a helical structure that undergoes helical inversion rapidly at room temperature. We were able to detect the presence of resolvable helical isomers of (−)‐menthyloxycarbonyl derivative of dioxa[6]helicene by recording 1H NMR spectra below 0 °C. The investigations of photo physical properties by cyclic voltammetry, UV/Vis‐ and fluorescence properties with the aid of time‐dependent DFT calculations were undertaken.

Inverse Evolution of Helicity from the Molecular to the Macroscopic Level Based on N-Terminal Aromatic Amino Acids.

Precise control of the emergence of macroscopic helicity with specific handedness is promising in rationally designing chiral nanomaterials, but it is rather challenging. Herein, we present a protocol to address the transmission of helicity at a molecularly resolved level to a macroscopically resolved level, in which process supramolecular chirality undergoes an inversion. A series of N-terminal aromatic amino acids could self-assemble in water, enabling the occurrence of helicity at the molecularly resolved scale, evidenced by the single crystal structure and chiroptical responses. While it failed to transmit the helicity to the macroscopic scale for individual self-assembly, the coassembly with small organic binder through hydrogen bonding interactions allows for the emergence of helical structures at the nano/micrometer scale. Experimental and theoretical results demonstrate that the introduction of extra hydrogen bonds enables a moderate crystallinity of coassemblies with remaining one-dimensional orientation to enhance the helical growth. The transmission of helicity to higher levels by coassembly is accompanied by the helicity inversion, resulting from the exchange of hydrogen bonds. This study presents a rational protocol to precisely control the emergence of macroscopic helicity from molecularly resolved helicity with finely tailored handedness, providing a deeper understanding of the chirality origin in the assembled systems in order to facilitate the design and construction of functional chiral nanomaterials.

Front Cover: Construction of Helical Structures with Multiple Fused Anthracenes: Structures and Properties of Long Expanded Helicenes (Chem. Eur. J. 14/2021)

Helical structures are constructed by successive fusion of anthracene units in a helicene-like manner like a dragon rising in a spiral. In the derivatives with four or more anthracene units, interlayer π⋅⋅⋅π interactions play an important role in the structures and properties of the polycyclic aromatic hydrocarbons. The helical inversion occurred via multistep mechanisms at relatively high barriers. This molecular design is valuable as a new helical motif based on the expanded and conjugated π systems. More information can be found in the Communication by S. Toyota et al. on page 4548.

Quantitative study on helicity inversion in Majorana neutrino decays at the LHC

We report an analytical and numerical investigation into the impact of helicity inversion in LHC processes that do not conserve lepton number ($L$). As a case study, we focus on the production and decay of Majorana neutrinos ($N$) through on- and off-shell $W$ bosons in the phenomenological type I seesaw model. Using the Monte Carlo event generator madgraph5_amc@nlo in conjunction with the heavyn model libraries, we perform exact matrix element (ME) computations without the narrow width approximation. Despite helicity inversion appearing explicitly in MEs, we report the absence of helicity suppression of $L$-violating collider observables for $1\ensuremath{\rightarrow}4$ and $2\ensuremath{\rightarrow}4$ processes that are dominated by resonant $N$ production. We attribute this incongruity to the different scalings of 4-momenta and squared 4-momenta in MEs and squared MEs, with exact cancelations occurring in the latter when $N$ goes on-shell in the small-width limit. In off-shell regimes, total suppression/enhancement of $L$ violation can emerge. Implications for other neutrino mass models are discussed.

Helical Chirality Inversion of Poly(biphenylacetylene) with Hydroxyl Groups Induced by a Single Enantiomer and Memory of the Helices

The solvent- and temperature-driven high-/low-twist switch of the biphenyl moieties in a poly(biphenylacetylene) with hydroxyl groups [poly(BPhDHPA)] triggered the rapid helix inversion of the induced helices in poly(BPhDHPA) by a single enantiomer, and the induced helices under both high-twist and low-twist modes could be well memorized using achiral phenylmethanol. The addition of a small amount of polar solvent [e.g., dimethyl formamide (DMF), <10 vol %] to a toluene solution of l-menthol/poly(BPhDHPA) complex causes an immediate and complete inversion of the induced helices. Further analysis indicates that the biphenyl moieties in the complex take the high-twist structure in nonpolar solvents and low-twist structure in polar solvents. The helices induced under the high-twist mode in nonpolar solvents showed higher thermostability than helices induced under the low-twist mode in polar solvents. The chiral amplification following the “majority rule” under the low-twist mode is more efficient than that under the high-twist mode.

Index polarity inversion by helicity inversion in Stokes vortices

To describe the state of polarization (SOP) of light, the Stokes parameters are obtained using intensity measurements made at different component polarization states. Using these Stokes parameters, complex field distributions called Stokes fields can be synthesized, and the phase singularities present in these Stokes fields are called Stokes vortices. The SOP of a Stokes vortex can be either linear or circular at the singular point. Of the three types of Stokes vortices, only one of them has handedness associated with it. We show here that changing the handedness of this Stokes vortex results in index sign inversion for the other two types of Stokes vortices. To accomplish handedness inversion without Stokes index sign inversion, a new phase engineering method is introduced here. The current study may unfold applications in the optical chirality measurement and structured illumination microscopy.

Triskelion‐Shaped π‐Luminophores Bearing Coumarin: Syntheses, Structures, and Luminescence Properties

AbstractTriskelion‐shaped π‐luminophores bearing three coumarin units 1 a and 1 b were successfully synthesized by the intramolecular Ullmann coupling reaction of triphenyl benzene‐1,3,5‐tricarboxylate derivatives. X‐ray crystal structure analysis revealed that compound 1 adopts a unique curved and three‐blade propeller‐shaped structure. These crystals are a racemic mixture consisting of PPP‐ and MMM‐1 due to the helicity resulting from the steric hindrance. A computational study suggests that this helical inversion process between PPP‐ and MMM‐1 a occurs with comparative ease. The emission spectra of 1 a and 1 b in THF solution showed sharp emission bands at 454 nm and 492 nm, respectively. The Stokes shifts were relatively large at 7385 cm−1 and 6556 cm−1 due to their degenerate frontier molecular orbitals. A solution of 1 b in different organic solvents demonstrated solvatofluorochromism due to intramolecular charge transfer of the coumarin unit in the excited states. Interestingly, both triskelion‐shaped molecules formed aggregates in a mixture of THF‐H2O and exhibited aggregation‐induced emission enhancement characteristics.

Preparation of amylose-poly(methyl methacrylate) inclusion complex as a smart nanocarrier with switchable surface hydrophilicity

Amylose, as a linear biopolymer, tends to form helical inclusion complexes with suitable guest species. This is of great importance for a variety of applications, especially in the pharmaceutical and food industry. In this study, we propose an approach for the preparation of a novel inclusion complex with switchable surface hydrophilicity. For this purpose, amylose was first conjugated to ethylene diamine hydrophilic residues. Then, the short chains of the hydrophobic poly(methyl methacrylate, PMMA) were grafted onto the cavity of amylose through atom transfer radical polymerization (ATRP). According to CD spectroscopy results, the amylose-PMMA inclusion complexes displayed solvent-directed helical chirality inversion using either DMSO or water as a solvent. Fluorescence imaging, AFM and DLS techniques revealed the solvent-dependent surface hydrophilicity of the amylose-PMMA inclusion complex. Interestingly, its morphological studies displayed a central cavity, which makes it suitable for carrying cargoes in drug delivery applications. Obtaining the amylose-polymer inclusion complexes with tailorable hydrophilicity of both the exterior surface and the interior cavity can be of paramount importance for a wide variety of bio-applications.

Use of q-plate as a coupler.

A coupler is a device that allows interconversion of angular momentum of the optical beam among spin and orbital parts, without absorbing any angular momentum. In this paper, we demonstrate that a q-plate with q=1 can act as a coupler for any of the polarization distribution that can be represented by a point on a Poincare sphere (PS), or on a higher-order PS, or on a hybrid-order PS. A q-plate with any q-value can act as a coupler for polarization distribution that can be represented by an equatorial point on any of these spheres. It is also possible to find a q-plate with an appropriate q-value that can act as a creation or annihilation operator that raises or lowers the polarization singularity index. The q-plate being a coupler and made of half-wave plate segments, the singularity index change is concomitant with the helicity inversion of C-points. Interconversion of bright and dark C-points is possible by using a q-plate.