C2 Symmetry Research Articles

Water-regulated viscosity-plasticity phase transitions in a peptide self-assembled muscle-like hydrogel

The self-assembly of small molecules through non-covalent interactions is an emerging and promising strategy for building dynamic, stable, and large-scale structures. One remaining challenge is making the non-covalent interactions occur in the ideal positions to generate strength comparable to that of covalent bonds. This work shows that small molecule YAWF can self-assemble into a liquid-crystal hydrogel (LCH), the mechanical properties of which could be controlled by water. LCH can be used to construct stable solid threads with a length of over 1 meter by applying an external force on 2 µL of gel solution followed by water-regulated crystallization. These solid threads can support 250 times their weight. Cryogenic electron microscopy (Cryo-EM) analysis unravels the three-dimensional structure of the liquid-crystal fiber (elongated helix with C2 symmetry) at an atomic resolution. The multiscale mechanics of this material depend on the specificity of the molecular structure, and the water-controlled hierarchical and sophisticated self-assembly.

Cryo-EM SPRstructures of Salmonella typhimurium ArnC; the key enzyme in lipid-A modification conferring polymyxin resistance.

Polymyxins are last-resort antimicrobial peptides administered clinically against multi-drug resistant bacteria, specifically in the case of Gram-negative species. However, an increasing number of these pathogens employ a defense strategy that involves a relay of enzymes encoded by the pmrE (ugd) loci and the arnBCDTEF operon. The pathway modifies the lipid-A component of the outer membrane (OM) lipopolysaccharide (LPS) by adding a 4-amino-4-deoxy-l-arabinose (L-Ara4N) headgroup, which renders polymyxins ineffective. Here, we report the cryo-EM SPR structures of glycosyltransferase ArnC from Salmonella typhimurium determined in apo and UDP-bound forms at resolutions 2.75 Å and 3.8 Å, respectively. The structure of the ArnC protomer comprises three distinct regions: an N-terminal glycosyltransferase domain, transmembrane region, and the interface helices (IHs). ArnC forms a tetramer with C2 symmetry, where the C-terminal strand inserts into the adjacent protomer. This tetrameric state is further stabilized by two distinct interfaces formed by ArnC that form a network of hydrogen bonds and salt bridges. The binding of UDP induces conformational changes that stabilize the loop between residues H201 to S213, and part of the putative catalytic pocket formed by IH1 and IH2. The surface property analysis revealed a hydrophobic cavity formed by TM1 and TM2 in the apo state, which is disrupted upon UDP binding. The comparison of ArnC structures to their homologs GtrB and DPMS suggests the key residues involved in ArnC catalytic activity.

High-nitrogen-content energetic BNn+ (n = 4-16) clusters.

Nitrogen-rich materials have attracted considerable attention in recent years as potential high-energy-density materials (HEDMs). However, their metastability poses substantial challenges for synthesis under ambient conditions. Here, we employ a novel strategy to explore energetic and structural features of the nitrogen-rich BNn+ (n = 4-16) clusters by doping with the light non-metal boron. A series of boron-doped nitrogen clusters, with nitrogen content ranging from 83% to 96%, were obtained by laser ablation and analyzed via time-of-flight mass spectrometry. The results indicate that the BN6+ cluster is dominant in the mass spectrum, while the BN12+ cluster exhibits the highest abundance after cooling the cluster source with liquid nitrogen. To further confirm the experimental results, extensive structure searches for BNn+ (n = 4-16) clusters are conducted using the CALYPSO method and density functional theory (DFT) calculations. The calculations show that BN6+ (singlet) exhibits a planar [B(NN)3]+ three-branched geometry with D3h symmetry, while BN12+ (singlet) adopts a [(linear-N6)B(N3)2]+ branched geometry with C1 symmetry. Stability analyses reveal the relatively high structural stabilities of BN6+ and BN12+ clusters and agree well with the experimental findings. Notably, the gas-phase enthalpy of formation of the BN12+ cluster is remarkably high, -1385.10 kJ mol-1, suggesting its potential as a high-energy building block for HEDM construction. The present findings enhance the structural diversities of non-metal-doped nitrogen clusters, and offer new perspectives for the rational design and synthesis of nitrogen-rich energetic materials.

Reciprocal space mapping of ZnMgY face-centred icosahedral quasicrystals

The reciprocal lattice of face-centred icosahedral ZnMgY quasicrystals was investigated using X-ray diffractometry. A large-scale planar cut of the reciprocal ZnMgY lattice was recorded making use of a PIXcel area detector. The θ-2θ scans along the C5, C3 and C2 symmetry axes revealed numerous diffraction peaks with a large dynamical range of about 106. Low structure-factor diffraction peaks, corresponding to large complementary reciprocal lattice vectors g┴ up to g┴a = 24 (where a is the quasilattice constant), were observed, indicating a high structural quality of ZnMgY quasicrystals. A static linear phason strain was detected in one of the five investigated ZnMgY samples.

The Designs and Applications of Tetraphenylethylene Macrocycles and Cages.

Macrocycles and cages are very attractive for the development of functional materials due to their unique inner cavities. Building blocks with interesting functions and synthetic conveniences are especially attractive. Tetraphenylethylene (TPE) is such an entity with C2 symmetry and tetrakis-functional groups easily modifiable. As a typical aggregation-induced emission (AIE) active compound, TPE perfectly unites the functions of fluorescence and structural building blocks together. The unique marriage of the two roles into one component makes TPE an ideal platform for the development of functional molecular systems including macrocycles and cages. The TPE macrocycles and cages are not merely a simple combination of those two but also generate added values unseen in either component alone. The fluorescence properties of TPE in macrocycles/cages are greatly improved or modulated, which makes them more suitable for various applications compared to their linear counterparts. In this review, the chemistry and design principles of TPE macrocycles/cages are surveyed first. The unique properties of those compounds are also discussed to provide general guidance for their functionalization. A brief discussion of their applications focusing on the utilization of their unique fluorescence is also presented. In the last, outlooks and future perspectives of TPE macrocycles/cages are provided for further developments.

Multiorgan-on-a-chip for cancer drug pharmacokinetics-pharmacodynamics (PK-PD) modeling and simulations.

Cancer is one of the most common and fatal diseases worldwide and kills millions of people every year. Cancer drug resistance, lack of efficacy, and safety are significant problems in cancer patients. A multiorgan-on-a-chip (MOC) device consisting of breast and liver compartments was designed with AutoCAD software. The MOC molds were printed by a Formlabs Form 2 3D printer. MDA-MB-231, HepG2, and MCF-10A cells were used for the MOC experiments. The cell lines were cultured at 37°C with 5% CO2, and cell viability was assessed via Alamar blue dye to generate pharmacodynamics (PD) data. Drug concentrations from the cell culture media were analyzed via Agilent 1260 Infinity II HPLC with a Waters Symmetry C18 column and used to generate pharmacokinetics (PK) data. The PK and PD data were modeled and simulated by Monolix and Simulix software, respectively. The safety and efficacy of drug dosing regimens were compared, and the best dosing regimens were selected. This research designed and fabricated a unique MOC consisting of liver and breast compartments that overcomes the need for sealing or assembling. It was used for PK-PD modeling and simulations, and its functionality was proven experimentally. The new MOC will be helpful in preclinical trials to evaluate the efficacy and safety of drugs.

Mechanistic Insights into Dual NIR Emission from Cr-Doped Sc2O3 via First-Principles Calculations.

The emission of Cr-doped Sc2O3 (space group Ia3̅, No. 206) phosphor features a broad band in NIR-I (700-1000 nm) and another in NIR-II (1000-1700 nm), which is significant for spectral analysis and medical applications. Although Sc2O3 has two 6-coordinated Sc sites─the nearly octahedral site with S6 point-group symmetry (S6 site) and the highly distorted site with C2 symmetry (C2 site)─the origin of the dual-band emission remains widely debated. In this study, we performed first-principles calculations to investigate the properties of Cr and Ni dopants in Sc2O3, including preference in site occupation, valence state, ligand field strength, Stokes shift, and line shape. Our calibrated calculations conclusively determined that the NIR-I emission peak at 840 nm is due to Cr3+ at the S6 site. However, the broad NIR-II emission peaking at around 1280 nm cannot be attributed to Crq (q = +2, +3, +4) at either site, suggesting the presence of possible trace impurities and phases. Ni2+ ions at octahedral sites exhibit a narrow peak width and long lifetime, which contradict reported experimental observations. The Cr4+ ions at a tetrahedral site, similar to that in the phase of Sc2O3 with the space group Pna21 (No. 33), show the most consistent line shape and emission decay rates with experimental data. A systematic first-principles approach incorporating the line shape calculation can be useful to resolve the issues in identifying luminescent centers in systems involving intrinsic defects and dopants.

Unconventional Near‐equilibrium Nucleation of Graphene on Si‐terminated SiC(0001) Surface

The transfer‐free character of graphene growth on Silicon Carbide (SiC) makes it compatible with state‐of‐the‐art Si semi‐conductor technologies for directly fabricating high‐end electronics. Although significant progress has been achieved in epitaxial growth of graphene on SiC recently, the underlying nucleation mechanism remains elusive. Here, we present a theoretical study to elucidate graphene near‐equilibrium nucleation on Si‐terminated hexagonal‐SiC(0001) surface. It is found that the ultra‐large lattice mismatch between SiC(0001) surface and graphene and the highly localized electron distribution on SiC(0001) surface lead to a distinctive nucleation process: (i) Most of the magic carbon clusters on SiC(0001) show only C1 symmetry and are mainly composed of pentagonal rings; (ii) Two possible nucleation pathways are revealed, i.e, longitudinal and circular modes; (iii) Carbon clusters are more stable on flat terraces than near atomic step edges. Based on above findings, a graphene nucleation diagram on SiC(0001) is established and experimentally observed contradictories for graphene growth on SiC(0001) are answered. Our in‐depth understanding on graphene nucleation on SiC(0001) extends nucleation mechanisms of 2D crystals and will benefit high‐quality graphene growth on SiC(0001).

Unconventional Near-Equilibrium Nucleation of Graphene on Si-Terminated SiC(0001) Surface.

The transfer-free character of graphene growth on Silicon Carbide (SiC) makes it compatible with state-of-the-art Si semiconductor technologies for directly fabricating high-end electronics. Although significant progress has been achieved in epitaxial growth of graphene on SiC recently, the underlying nucleation mechanism remains elusive. Here, we present a theoretical study to elucidate graphene near-equilibrium nucleation on Si-terminated hexagonal-SiC(0001) surface. It is found that the ultra-large lattice mismatch between SiC(0001) surface and graphene and the highly localized electron distribution on SiC(0001) surface lead to a distinctive nucleation process: (i) Most of the magic carbon clusters on SiC(0001) show only C1 symmetry and are mainly composed of pentagonal rings; (ii) Two possible nucleation pathways are revealed, i.e., longitudinal and circular modes; (iii) Carbon clusters are more stable on flat terraces than near atomic step edges. Based on above findings, a graphene nucleation diagram on SiC(0001) is established and experimentally observed contradictories for graphene growth on SiC(0001) are answered. Our in-depth understanding on graphene nucleation on SiC(0001) extends nucleation mechanisms of 2D crystals and will benefit high-quality graphene growth on SiC(0001).

5]Helicene Based π-Conjugated Macrocycles with Persistent Figure-Eight and Möbius Shapes: Efficient Synthesis, Chiral Resolution and Bright Circularly Polarized Luminescence.

π-Conjugated chiral shape-persistent molecular nanocarbons hold great potential as chiroptical materials, though their synthesis remains a considerable challenge. Here, we present a simple approach using Suzuki coupling of a [5]helicene building block with various aromatic units, enabling the one-pot synthesis of a series of chiral macrocycles with persistent figure-eight and Möbius shapes. Single-crystal structures of 7 compounds were solved, and 22 enantiomers were separated by preparative chiral HPLC. A notable pyrene-bridged figure-eight macrocycle, with its rigid, fully π-conjugated and overcrowded structure, exhibited pure excimer emission and outstanding circularly polarized luminescence (CPL) properties, including a large dissymmetric factor (|glum|=3.8×10-2) and significant CPL brightness (BCPL=710.5 M-1cm-1). This method provides a versatile synthetic platform for producing various chiral D2-symmetric figure-eight macrocycles and singly or triply twisted Möbius macrocycles with C2 and D3 symmetry, offering tunable chiroptical properties for CPL applications.

5]Helicene Based π‐Conjugated Macrocycles with Persistent Figure‐Eight and Möbius Shapes: Efficient Synthesis, Chiral Resolution and Bright Circularly Polarized Luminescence

Abstractπ‐Conjugated chiral shape‐persistent molecular nanocarbons hold great potential as chiroptical materials, though their synthesis remains a considerable challenge. Here, we present a simple approach using Suzuki coupling of a [5]helicene building block with various aromatic units, enabling the one‐pot synthesis of a series of chiral macrocycles with persistent figure‐eight and Möbius shapes. Single‐crystal structures of 7 compounds were solved, and 22 enantiomers were separated by preparative chiral HPLC. A notable pyrene‐bridged figure‐eight macrocycle, with its rigid, fully π‐conjugated and overcrowded structure, exhibited pure excimer emission and outstanding circularly polarized luminescence (CPL) properties, including a large dissymmetric factor (|glum|=3.8×10−2) and significant CPL brightness (BCPL=710.5 M−1cm−1). This method provides a versatile synthetic platform for producing various chiral D2‐symmetric figure‐eight macrocycles and singly or triply twisted Möbius macrocycles with C2 and D3 symmetry, offering tunable chiroptical properties for CPL applications.

Merging bound states in the continuum-driven ultrahigh sensing figure of merit in all-dielectric metasurfaces.

Radiation-free photonic bound states in the continuum (BIC) in metasurfaces allow ultrahigh quality (Q) factor and strongly confined mode volume, which are extremely advantageous in the development of ultrasensitive microcavity sensors. However, the conventional isolated BICs are susceptible to failure due to symmetry breaking caused by fabrication imperfection and nonzero incident angle. Here, we propose a silicon nitride-based metasurface with multiple BIC merging. The merging of accidental BIC and symmetry-protected BIC can increase the Q-factor near the Brillouin zone Γ point and thus robustly induces a figure of merit (FOM) of refractive index sensing at small incident angles two orders of magnitude higher than that in isolated BIC configuration. Specifically, the FOM in merging BIC reaches 108 at a 2° incident angle. The BIC merging can be universally achieved in square lattices with C4 symmetry, and slower decay of Q-factor and higher FOM can further occur in hexagonal lattices benefiting from higher-order topological charges. The advantage of merging BIC is also maintained when considering in-plane and out-of-plane symmetry breaking. These results offer a unique design path for high-performance metasurface sensors and can be extended to other high-Q applications such as low-threshold lasers, nonlinear frequency conversion, and low-loss waveguides.

Solid-State NMR Analysis of the Dynamics of Cofactors: Comparison of Heliobacterial and Purple Bacterial Reaction Centers.

Photosynthetic reaction centers (RCs) serve as natural engines converting solar energy to chemical energy. Understanding the principles of efficient charge separation and light-induced electron transfer (ET) between the chlorophyll-type pigments might guide the synthesis for artificial photosynthetic systems. We present detailed insight into the dynamics at the atomic level using solid-state NMR techniques applied to the RCs of Heliobacillus (Hb.) mobilis (HbRCs) and the purple bacterium Rhodobacter (R.) sphaeroides (PbRCs). It is assumed that heliobacteria were among the first phototrophic organisms; therefore, their RC can be regarded as ancient. They are constructed homodimerically with perfect C2 symmetry, enabling ET over both branches of cofactors. Modern RCs of R. sphaeroides wild-type (WT) have higher redox power and are functionally highly asymmetric. The dynamics of the cofactors in both RCs has been explored using nuclear hyperpolarization, induced by the solid-state photochemically induced dynamic nuclear polarization (photo-CIDNP) effect. Based on the individual incorporation of 13C positions of the cofactors (through supplementation by 13C-δ-aminolevulinic acid), photo-CIDNP magic-angle spinning (MAS) NMR experiments provide access to the local dynamics of the cofactors along the ET path over a broad range of time scales. Theoretical analysis of the dynamic deformation of these macrocycles is also discussed in terms of function. The dynamics observed in HbRCs appears to be correlated to ET. The cofactors in PbRC are significantly less dynamic than those in the HbRC. Relevance for efficiency and redox properties are discussed.

Liquid Crystal Behavior of Uniform Short Rods Made from Computationally Designed Parallel Coiled Coil Building Blocks.

Parallel, homotetrameric coiled coils were computationally designed using 29 amino acid peptides. These parallel coiled coils, called "bundlemers", have C2 symmetry, with all N-termini displayed from one end of the nanoparticle and all C-termini from the opposite end. This anisotropic display of the peptide termini allowed for the functionalization of two sets of nanoparticles with either maleimide or thiol functionality at the N-terminal region of the constituent peptides. The thiol-Michael conjugation reaction between the N-terminal end of complementary bundlemer nanoparticles formed monodisperse, rigid bundlemer dimer, called "dibundlemer", rods. The constituent, individual bundlemer nanoparticles were characterized with small-angle X-ray scattering (SAXS), Förster resonance energy transfer (FRET), and circular dichroism (CD) spectroscopy to confirm the parallel assembly of the coiled coils, consistent with the computational design. The dibundlemer rods were characterized with SAXS to reveal the uniform dibundlemer nature of the rods. Optical birefringence is observed in concentrated samples of the rods, with polarized optical microscopy (POM) revealing a nematic liquid crystalline behavior.

Diamagnetic Precursor to Biradical by Means of a Thermal Trigger: A Head-to-Tail (N-O)2 Four-Membered Ring Formed in Naphthalene-1,8-diyl Bis(tert-butyl Nitroxide).

The title compound was synthesized, and ESR and magnetic analysis revealed diamagnetic properties below 400 K. The crystal structure analysis clarified that the molecule possesses an approximate C2 symmetry with a head-to-tail (N-O)2 four-membered ring. The N···O distances are 2.349(4) - 2.374(4) Å, belonging to the class found in diamagnetic phases of dimerized nitroxide materials. A zero-field splitting pattern appeared in the solid-state ESR around 440 K on heating. The density functional theory (DFT) calculations supported the formation of a biradical.

CuI/CuII Chiral Homoleptic Complexes: Study of Self‐Recognition and Self‐Discrimination

AbstractThe formation of ML2 homoleptic copper(I) and copper(II) complexes from bidentate chiral ligands with C2 symmetry, comprising three types of substituents (namely benzyl, indanyl and phenyl groups), was investigated. The formation of homochiral or heterochiral complexes can be influenced by the nature of the substituents and the geometry induced by the oxidation state of the metal. All the complexes were isolated and characterized, in particular in the solid state by X‐ray diffraction studies. In solution, cyclic voltammetry was used to study ligand association and discrimination induced by the CuI/CuII transition.

Synthesis, Structure, and Optical Property of Tris(biaryldiyl)metal Complexes Consisting of Group 9 Elements.

We report the synthesis and characterization of tris(biphenyl-2,2'-diyl)metal complexes of trivalent group 9 elements (1M, M = Co, Rh, Ir) and their nonplanarly π-extended analogs, tris(1,1'-binaphthyl-2,2'-diyl)metal complexes (2M, M = Rh, Ir). Single crystal X-ray crystallography reveals the distorted octahedral geometry with an approximate C3 symmetry of trianionic complexes 1M (M = Co, Rh, Ir) and 2M (M = Rh, Ir), which are contacted by three Li+ ions in the crystal. Complex 1Ir exhibits yellow luminescence in THF with a photoluminescence quantum yield (ΦPL) of up to 0.73, along with a distinctive photophysical property, namely, a concentration dependence of the emission wavelength from 530 to 580 nm. This is a characteristic property of 1Ir and has not been observed in its isoelectronic analog, tris(2-phenylpyridinato)iridium(III) (Ir(ppy)3). The concentration-dependent optical properties originate from the dissociation equilibria of Li+ ions from the anionic chromophore. Complex 2Ir also exhibits luminescence at 715 nm in THF, with a notable bathochromic shift from 1Ir through the π-extension. The findings offer insights into the photophysical properties of homoleptic organo-transition metal complexes, providing the foundation for the design of related transition metal complexes.

Complex Dance of Molecules in the Sky: Choreography of Intermolecular Structure and Dynamics in the Cyclopentene-CO2-H2O Hetero Ternary Cluster.

This study delves into driving forces behind the formation of a hetero ternary cluster consisting of volatile organic compounds from industrial or combustion sources, specifically cyclopentene, alongside greenhouse gases like carbon dioxide, and water vapor. While substantial progress has been made in understanding binary complexes, the structural intricacies of hetero ternary clusters remain largely uncharted. Our research characterized the cyclopentene-CO2-H2O hetero ternary cluster utilizing Fourier transform microwave spectroscopy. The observed isomer in the pulsed jet has CO2 and H2O aligning above the cyclopentene ring, with water undergoing an internal rotation approximately about its C2 symmetry axis. Theoretical analyses support these observations, identifying an O-H⋅⋅⋅π hydrogen bond and a secondary C⋅⋅⋅O tetrel bond within this cluster. This study marks a critical step towards comprehending the molecular dynamics and interactions of VOCs, greenhouse gases, and water in the atmosphere, paving the way for further investigations into their roles in climate dynamics and air quality.

Characterization of disulfide bridges containing cyclic peptide Linaclotide and its degradation products by using LC-HRMS/MS

Linaclotide (LINA) is a first-in-class guanylate cyclase agonist used for treating irritable bowel syndrome with constipation (IBS-C) and chronic idiopathic constipation. Stress degradation studies were performed to examine LINA's intrinsic stability, adhering to International Council for Harmonisation of Technical ICH) guidelines Q1A (R2). The current study endeavours to elucidate the stability behavior of LINA by exposing various stress conditions. A simple LC method was developed for effective separation of all LINA degradation products using a Waters Symmetry C18 column (150 ×4.6 mm, 3.5 µm) as the stationary phase. The generated degradation products were identified and characterized by using high-resolution mass spectrometry (LC-HRMS), MS/MS studies. The mechanistic fragmentation pathway for the seven degradation products was established and the chemical structure for the identified degradation products was elucidated. LINA was susceptible to degrade under acidic, basic, neutral, photolytic, and oxidative conditions. A total of three Pseudo DPs, DP-1, DP-2, and DP-3, were formed under acidic conditions while using methanol as the co-solvent. Additionally, degradation products (DPs) were identified: DP-4 formed under basic stress condition and DP-5 under neutral, thermal, and photolytic conditions. Furthermore, DP-6 and DP-7 were formed under oxidative stress condition. This study established the mechanistic fragmentation pathways and elucidated the chemical structures of the degradation products, offering valuable insights for generics and novel formulation drug development.

Solid-solution Er:(Sc,Y)2O3 transparent ceramics: Optical spectroscopy, inhomogeneous line broadening, C3i sites and mid-infrared laser operation

Rare-earth-doped transparent sesquioxide laser ceramics enable engineering of their gain bandwidths via solid-solution compositions exhibiting a strong inhomogeneous spectral line broadening. We report on a detailed spectroscopic study and the first mid-infrared laser operation of Erbium-doped yttria-scandia, (ScxY1−x)2O3, ceramics fabricated by vacuum sintering at 1750 °C from laser-ablated nanoparticles. The effect of the Sc fraction on the spectral and kinetic properties of Er3+ emission around 2.8 μm owing to the 4I11/2 → 4I13/2 is revealed. The inhomogeneous spectral line broadening leading to merging of individual Stark sub-levels of Er3+ multiplets is evidenced by low-temperature spectroscopy. An original method of quantifying the distribution of dopant Er3+ ions over C2 and C3i symmetry sites in the cubic bixbyite structure is suggested based on the transition probabilities derived by the Judd-Ofelt theory. In the parent Er:Y2O3 ceramic, the Er3+ ions nearly follow the ideal distribution with 3/4 of ions residing in C2 sites, and Sc addition skews it in favor of C3i sites. A continuous-wave Er:(Sc,Y)2O3 ceramic laser generated 312 mW at 2716 nm with a slope efficiency of 18.6 % and a laser threshold of 128 mW.