Electronic Circular Dichroism Imaging (ECDi) Casts a New Light on the Origin of Solid-State Chiroptical Properties

Solid-state ECD (ss-ECD) spectra of a model microcrystalline solid, finasteride, dispersed into a KCl pellet were recorded by using the synchrotron radiation source at the Diamond B23 beamline. Scanning a surface of 36 mm² with a step of 0.5 mm, we measured a set of ECD imaging (ECDi) spectra very different from each other and from the ss-ECD recorded with a bench-top instrument (1 cm² area). This is due to the anisotropic part of the ECD (ACD), which averages to zero in solution or on a large number of randomly oriented crystallites, but can otherwise be extremely large. Two-way singular value decomposition (SVD) analysis, through experimental and simulated TDDFT spectra, disclosed that the measured and theoretical principal components are in line with each other. This finding demonstrates that the observed isotropic ss-ECD spectrum is governed by the anisotropy of locally oriented crystals. It also introduces a new quality for ss-ECD measurements and opens a new future for probing and mapping chiral materials in the solid state such as active pharmaceutical ingredients (APIs).     

The Enantiomers of Trinorbornane and Derivatives Thereof

Herein, we report the synthesis of the enantiomers of trinorbornane, a tetracyclic saturated hydrocarbon with the chemical formula C₁₁H₁₆. The preparation of these rigid carbon scaffolds was enabled by the successful chiral separation of its tricyclic precursor, thus allowing the enantiomers to be synthesized through a reductive radical cyclization reaction. Assignment of the absolute conformation of the enantiomers was achieved through VCD experiments. Further, we report an alternative cyclization procedure providing access to hydroxyl and phenyl sulfone functionalized trinorbornanes.     

Polydimethylsiloxane–graphene oxide composite improving performance by ion beam irradiation

A hybrid film consisting of graphene oxide covered with poly(dimethylsiloxane) was prepared via spin coater and followed by thermal annealing to improve the bond strength of the polymerized systems. Direct patterning on both graphene oxide and hybrid graphene oxide–poly(dimethylsiloxane) foils by ion microbeam was performed to induce localized reduction in the ion irradiated material. It is well established that the ion irradiation of graphene oxide induces modifications in its electrical, mechanical, and optical properties and disorder in the carbon crystal structure and defect production. The presence of poly(dimethylsiloxane) can be useful as it confers flexibility to the produced pattern and oxygen permeability from the graphene oxide surface. Rutherford backscattered spectroscopy and elastic recoil detection analysis were performed to evaluate the compositional changes in the composite. Atomic force microscopy studied the pattern fidelity. The electrical conductivity of the hybrid material was used to evaluate the changes induced during the proton irradiation of the material.     

Electrochemical and Spectroscopic Study of EuIII and EuII Coordination in the 1-Ethyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide Ionic Liquid

Separation processes based on room temperature ionic liquids (RTIL) and electrochemical refining are promising strategies for the recovery of lanthanides from primary ores and electronic waste. However, they require the speciation of dissolved elements to be known with accuracy. In the present study, Eu coordination and Eu^III/Eu^II electrochemical behavior as a function of water content in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIm][NTf₂]) was investigated using UV–visible spectrophotometry, time-resolved laser fluorescence spectroscopy, electrochemistry, and X-ray absorption spectroscopy. In situ measurements were performed in spectroelectrochemical cells. Under anhydrous conditions, Eu^III and Eu^II were complexed by NTf₂, forming Eu−O and Eu−(N,O) bonds with the anion sulfoxide function and N atoms, respectively. This complexation resulted in a greater stability of Eu^II, and in quasi-reversible oxidation–reduction with an E₀’ potential of 0.18 V versus the ferrocenium/ferrocene (Fc⁺/Fc) couple. Upon increasing water content, progressive incorporation of water in the Eu^III coordination sphere occurred. This led to reversible oxidation–reduction reactions, but also to a decrease in stability of the +II oxidation state (E₀’=−0.45 V vs. Fc⁺/Fc in RTIL containing 1300 mm water).     

Distinct Helical Molecular Orbitals through Conformational Lock**

Several theoretical studies have proposed strategies to generate helical molecular orbitals (Hel-MOs) in [n]cumulenes and oligoynes. While chiral even-[n] cumulenes feature Hel-MOs, odd-[n] cumulenes may also present them if the terminal groups lie in different planes. However, the proposed systems have been either experimentally unfeasible or resulted in opposite pseudo-degenerated Hel-MOs. We hereby demonstrate the introduction of a remarkable energy difference between helical orbitals of opposite twist by fixing the torsion angle between the terminal groups in butadiyne fragments. To experimentally lock the conformation of the terminal groups, we designed and synthesized cyclic architectures by combining acetylenes with chiral spirobifluorenes. The high stability of these systems with distinct helical orbitals allowed their isolation and full characterization. In our view, these results constitute a step further in the development of real systems presenting helical molecular orbitals.     

Preparation of items for a textile proficiency testing scheme

Accreditation and Quality Assurance - One of the fundamental stages in planning and developing any interlaboratory comparison is the selection and preparation of the test items to be distributed to...     

Helicene Monomers and Dimers: Chiral Chromophores Featuring Strong Circularly Polarized Luminescence

The synthesis and chiroptical properties of a series of enantiomerically pure, C₂-symmetrical carbo[6]helicene dimers are reported. Two helicene cores are connected through a buta-1,3-diyne-1,4-diyl linker or a heteroaromatic bridge and bear arylethynyl substituents at their 15-positions. This ensures the possibility of extended electronic communication throughout the whole molecule. The new chromophores exhibit intense ECD spectra with strong bands in the UV/Vis region well above 400 nm. The anisotropy factor g_abs (defined as Δϵ/ϵ) reaches values up to 0.047, which are unusually large for single organic molecules. They also display blue fluorescence, with good quantum yields (Φ_f∼0.25). The emitted light is circularly polarized to an outstanding extent: in some cases, the luminescence dissymmetry factor g_lum=2(I_L−I_R)/(I_L+I_R) attains values of |0.025|. To the best of our knowledge, such values are among the highest ever reported for non-aggregated organic fluorophores.