ortho-Substituted 2-Phenyldihydroazulene Photoswitches: Enhancing the Lifetime of the Photoisomer by ortho-Aryl Interactions

Photochromic molecules are systems that undergo a photoisomerization to high-energy isomers and are attractive for the storage of solar energy in a closed-energy cycle, for example, in molecular solar thermal energy storage systems. One challenge is to control the discharge time of the high-energy isomer. Here, we show that different substituents in the ortho position of a phenyl ring at C-2 of dihydroazulene (DHA-Ph) significantly increase the half-life of the metastable vinylheptafulvene (VHF-Ph) photoisomer; thus, the energy-releasing VHF-to-DHA back-reaction rises from minutes to days in comparison to the corresponding para- and meta-substituted systems. Systems with two photochromic DHA-Ph units connected by a diacetylene bridge either at the para, meta and ortho positions and corresponding to a linear or to a cross-conjugated pathway between the two photochromes are also presented. Here, the ortho substitution was found to compromise the switching properties. Thus, irradiation of ortho-bridged DHA-DHA resulted in degradation, probably due to the proximity of the different functional groups that can give rise to side-reactions.

An effect of positional isomerism of benzoic acid derivatives on antibacterial activity against Escherichia coli

This study demonstrated the effect of positional isomerism of benzoic acid derivatives against E. coli ATCC 700728 with the serotype O157. The addition of hydroxyl and methoxyl substituents weakened the effect of acids against E. coli with respect to benzoic acid (except 2-hydroxybenzoic). The connection of the hydroxyl group at the second carbon atom in the benzoic ring reduced the time needed to kill bacterial cells. Phenolic acids with methoxyl substitutes limited the biofilm formation by E. coli to a greater extent than hydroxyl derivatives. The most significant influence on the antibacterial activity of phenolic acids has the type of substituent attached to the benzoic ring, their number, and finally the number of carbon atoms at which the functional group is located.

Influence of Positional Isomerism on the Chiroptical Properties of Functional Aromatic Oligoamide Foldamers

A series of functionalized quinoline-based aromatic oligoamide foldamers were prepared in their two enantiomeric forms, comprising an enantiopure terminal camphanyl chiral inducer, which governed the adjacent (P-/M-) helical-handedness. Hierarchical chirality transfer was further investigated in chromophore-appended variants via a range of electronic and vibrational spectroscopic techniques, including circularly polarized luminescence, vibrational circular dichroism and fluorescence. Intense total and polarized photoluminescence (up to Φ_lum =0.39, g_lum =1.5×10^-3 ) was observed in the visible region from these modular multicomponent architectures and a significant influence of positional isomerism was evidenced. The optimal position of a fluorophore substituent on the quinoline hexamers was determined as being position 2 over position 6, as stronger chiroptical features were systematically observed with the 2-positioned derivatives.

Influence of ligand positional isomerism on the molecular and supramolecular structures of cobalt(II)-phenylimidazole complexes

In a study to evaluate the impact of flexible positional isomeric ligands on the coordination geometry and self-assembly process of 3d metal complexes, the synthesis of eight new cobalt(II) complexes with the 2-phenylimidazole (LH) and 5-phenylimidazole (L'H) ligands has been carried out. A variety of parameters/conditions have been probed using the general Co^II/X^-/LH or L'H (X^- = Cl^-, Br^-, I^-, NO₃^-, NCS^-, ClO₄^-, SO₄^2-) reaction system. Interestingly, X-ray analyses reveal two distinct groups of complexes: reactions with LH only lead to tetrahedral or quasi-tetrahedral complexes {i.e. [CoCl₂(LH)₂] (1), [CoI₂(LH)₂] (2), [Co(NO₃)₂(LH)₂] (3), [Co(NCS)₂(LH)₂] (4)}, whereas L'H favours octahedral coordination {i.e. [Co(L'H)₄(MeCN)(H₂O)]I₂ (5), [Co(L'H)₄(MeCN)(H₂O)](NO₃)₂ (6) and [Co(NCS)₂(L'H)₄)]·2MeOH (7·2MeOH)}. A tetrahedral [Co(NCS)₂(L'H)₂)] (8) complex was also concurrently isolated with complex 7. The effects of the positional isomeric ligands LH and L'H and of the coordinated inorganic anions on the stoichiometry and packing arrangements of the complexes are thoroughly discussed. The supramolecular assembly is firmly directed, in all types of complexes, by robust N-H...X (X = Cl, I, O or S) motifs, leading to varying dimensionalities (1D, 2D or 3D) and packing arrangements. The formation of these motifs has been activated by choosing appropriate anions X, acting as terminal ligands or counterions. At a second level of organization, additional subordinate C-H...X (X = Cl, I, O or S), C-H...π and π...π intermolecular interactions complement the rigidity of the complexes' packing towards compact 3D assemblies. Hirshfeld surface analyses provided insight into the intermolecular interactions, allowed quantification of the individual contact types and comparison between the complexes.

Hexadecenoic Fatty Acid Positional Isomers and De Novo PUFA Synthesis in Colon Cancer Cells

Palmitic acid metabolism involves delta-9 and delta-6 desaturase enzymes forming palmitoleic acid (9cis-16:1; n-7 series) and sapienic acid (6cis-16:1; n-10 series), respectively. The corresponding biological consequences and lipidomic research on these positional monounsaturated fatty acid (MUFA) isomers are under development. Furthermore, sapienic acid can bring to the de novo synthesis of the n-10 polyunsaturated fatty acid (PUFA) sebaleic acid (5cis,8cis-18:2), but such transformations in cancer cells are not known. The model of Caco-2 cell line was used to monitor sapienic acid supplementation (150 and 300 μM) and provide evidence of the formation of n-10 fatty acids as well as their incorporation at levels of membrane phospholipids and triglycerides. Comparison with palmitoleic and palmitic acids evidenced that lipid remodelling was influenced by the type of fatty acid and positional isomer, with an increase of 8cis-18:1, n-10 PUFA and a decrease of saturated fats in case of sapienic acid. Cholesteryl esters were formed only in cases with sapienic acid. Sapienic acid was the less toxic among the tested fatty acids, showing the highest EC₅₀s and inducing death only in 75% of cells at the highest concentration tested. Two-photon fluorescent microscopy with Laurdan as a fluorescent dye provided information on membrane fluidity, highlighting that sapienic acid increases the distribution of fluid regions, probably connected with the formation of 8cis-18:1 and the n-10 PUFA in cell lipidome. Our results bring evidence for MUFA positional isomers and de novo PUFA synthesis for developing lipidomic analysis and cancer research.