Victor Borovkov

Chiral self-assembled supramolecular networks offer great potential for new chiral materials. We report the predictable self-assembly of metalloporphyrins with chiral cyclohexanohemicucurbit[n]urils (cycHC[6] and cycHC[8]), where cycHC[n] chirality is transferred to achiral porphyrins in solution and the solid state. Solvent and porphyrin substituents directed the formation of 31 novel complexes characterized by single-crystal X-ray diffraction. All complexes feature metal-urea coordination centers, with architectures ranging from discrete complexes to 1D, helical 1D, and 2D square-grid coordination polymers, governed by the shape and binding strength of cycHC[n]s. Noncovalent interaction analysis highlighted van der Waals interactions alongside metal-oxygen coordination. In solution, binding strengths ranged from 690 to 1,840,000 M^-1, while electronic circular dichroism (ECD) g-factors remained consistent. Solid-state measurements revealed a 10-fold increase in induced ECD intensity in the Soret region, attributed to chiral aggregation and interporphyrin exciton coupling. Vibrational circular dichroism showed chirality induction in the infrared range, with the g-factor of cycHC[6] carbonyl signals increasing 10-fold upon complexation. These results demonstrate the robustness of hemicucurbituril-metalloporphyrin supramolecular systems for developing advanced chiral sensing materials.

Chiral self-assembled supramolecular networks have high potential for the synthesis of new chiral materials. We present here the highly predictable self-assembly of metalloporphyrins with chiral cyclohexanohemicucurbit[n]urils (cycHC[6] and cycHC[8]), where the chirality of cycHCs is imprinted onto achiral porphyrins in both solution and the solid-phase. Diverse coordination environments, influenced by solvents and porphyrin substituents, led to the characterization of 32 novel complexes by single crystal X-ray diffraction. All complexes are based on metal-urea coordination centers, while their structural variability—ranging from discrete complexes to 1D-, helical 1D-, and 2D-square-grid coordination polymers—is governed by the shape and binding strength of cycHCs, as well as induced dipole - interactions of the porphyrins. In solution, the binding strength of the complexes varied significantly, from 690 to 1,840,000 M⁻¹, while the g-factors of electronic circular dichroism (ECD) remained consistent across porphyrins. Solid-state measurements revealed a ten-fold increase in the induced ECD intensity in the Soret band region compared to solution, attributed to chiral aggregation and interporphyrin exciton coupling. Vibrational circular dichroism studies demonstrated chirality induction in the infrared absorbance range, with the g-factor of cycHC[6] carbonyl signals increasing ten-fold upon complexation. This work highlights the robustness of hemicucurbituril–metalloporphyrin chiral supramolecular systems for the development of advanced sensing applications.

Electronic circular dichroism (ECD) spectroscopy is a widely employed method for studying chiral analysis, requiring the presence of a chromophore close to a chiral centre. Porphyrinoids are found to be one of the best chromophoric systems serving for this purpose and enabling the application of ECD spectroscopy for chirality determination across diverse classes of organic compounds. Consequently, it is crucial to understand the induction mechanisms of ECD in the porphyrin‐based complexes. The present study explores systematically the influence of secondary chromophores, bonded to an achiral zinc porphyrin or to chiral guest molecules, on the B‐region of ECD spectra using the time‐dependent density functional theory (TD‐DFT) calculations. The study analyses the impact of change in both the conformation of achiral porphyrin (host) and change in position and conformation of chiral organic molecule (guest) on the B‐band of ECD spectra (energy, intensity, sign of Cotton effect). Finally, conclusions made on model complexes are applied to published experimental data, contributing to a deeper understanding of various factors influencing ECD spectra in chiral systems. In addition, a computer program aimed to help rationalise ECD spectra by visualizing corresponding orbital energies, rotatory strengths, electric and magnetic transition moments, and angles between them, is presented.

The development of chiral receptors for discriminating the configuration of the analyte of interest is increasingly urgent in view of monitoring pollution in water and waste liquids. Here, we investigate an easy protocol to immobilize the desired non-water-soluble receptors inside a water-dispersible chiral nanoplatform made of silica. This approach induces chirality in the receptors and Here, we investigate an easy protocol to immobilize the desired non-water-soluble receptors inside a water-dispersible chiral nanoplatform made of silica. This approach induces chirality in the receptors and makes the dye@nanohelix system disperse in a suspension of water without aggregation. We noted strong induction and amplification of chiroptical activity in both achiral and chiral (proline-based or hemicucurbituril-based) porphyrin derivatives with and without zinc ions once confined and organized in nanometer silica helices. The results clearly demonstrated that the organization-induced chirality amplification of porphyrins dominates the molecular chirality, and the amplification is more efficient for more flexible porphyrins (especially free-base and achiral).

Hemicucurbiturils are members of the single-bridged cucurbituril family, formed through templated synthesis in a single step

Invited for the cover of this issue are the groups of Irina Osadchuk at Tallinn University of Technology and Mathias Senge at Trinity College Dublin. The image depicts how a porphyrin with two guest molecules (R)‐camphor sulfonic acid is irradiated with UV‐visible light to measure and simulate ECD and UV‐Vis spectra. Read the full text of the article at 10.1002/chem.202301408.

The determination of molecular stereochemistry and absolute configuration is an important part of modern chemistry, pharmacology, and biology. Electronic circular dichroism (ECD) spectroscopy is a widely used tool for chirality assignment, especially with porphyrin macrocycles employed as reporter chromophores. However, the mechanisms of induced ECD in porphyrin complexes are yet to be comprehensively rationalized. In this work, the ECD spectra of a sterically hindered hexa‐cationic porphyrin with two camphorsulfonic acids in dichloromethane and chloroform were experimentally measured and computationally analyzed. The influence of geometric factors such as the position of chiral guest molecules, distortion of the porphyrin macrocycle, and orientation of aromatic and non‐aromatic peripheral substituents on the ECD spectra was theoretically studied. Various potential pitfalls, such as a lack of significant conformations and accidental agreement of experimental and simulated spectra, are considered and discussed.

Enantiorecognition of a chiral analyte usually requires the ability to respond with high specificity to one of the two enantiomers of a chiral compound. However, in most cases, chiral sensors have chemical sensitivity toward both enantiomers, showing differences only in the intensity of responses. Furthermore, specific chiral receptors are obtained with high synthetic efforts and have limited structural versatility. These facts hinder the implementation of chiral sensors in many potential applications. Here, we utilize the presence of both enantiomers of each receptor to introduce a novel normalization that allows the enantio-recognition of compounds even when single sensors are not specific for one enantiomer of a target analyte. For this purpose, a novel protocol that permits the fabrication of a large set of enantiomeric receptor pairs with low synthetic efforts by combining metalloporphyrins with (R,R)- and (S,S)-cyclohexanohemicucurbit[8]uril is developed. The potentialities of this approach are investigated by an array of four pairs of enantiomeric sensors fabricated using quartz microbalances since gravimetric sensors are intrinsically non-selective toward the mechanism of interaction of analytes and receptors. Albeit the weak enantioselectivity of single sensors toward limonene and 1-phenylethylamine, the normalization allows the correct identification of these enantiomers in the vapor phase indifferent to their concentration. Remarkably, the achiral metalloporphyrin choice influences the enantioselective properties, opening the way to easily obtain a large library of chiral receptors that can be implemented in actual sensor arrays. These enantioselective electronic noses and tongues may have a potential striking impact in many medical, agrochemical, and environmental fields.