Conformational restriction of flexible molecules in solution by a semirigid bis-porphyrin molecular tweezer

Binding Properties of a Dinuclear Zinc(II) Salen-Type Molecular Tweezer with a Flexible Spacer in the Formation of Lewis Acid-Base Adducts with Diamines

In this paper we report the binding properties, by combined 1H NMR, optical absorption, and fluorescence studies, of a molecular tweezer composed of two Zn(salen)-type Schiff-base units connected by a flexible spacer, towards a series of ditopic diamines having a strong Lewis basicity, with different chain length and rigidity. Except for the 1,2-diaminoethane, in all other cases the formation of stable 1:1 Lewis acid-base adducts with large binding constants is demonstrated. For α,ω-aliphatic diamines, binding constants progressively increase with the increasing length of the alkyl chain, thanks to the flexible nature of the spacer and the parallel decreased conformational strain upon binding. Stable adducts are also found even for short diamines with rigid molecular structures. Given their preorganized structure, these latter species are not subjected to loss of degrees of freedom. The binding characteristics of the tweezer have been exploited for the colorimetric and fluorometric selective and sensitive detection of piperazine.

Synthesis, characterization, DFT study, DNA/BSA-binding affinity, and cytotoxicity of some dinuclear and trinuclear gold(III) complexes

In this study, we have synthesized a series of dinuclear and trinuclear gold(III) complexes of the general formula [Au₂(N-N)Cl₆] (1-3) for dinuclear and [Au₃(N-N)₂Cl₈]⁺ (4-6) for trinuclear compounds, respectively, in which N-N is a bidentate ligand (1,4-diaminobutane; 1,6-diaminohexane or 1,8-diaminooctane). These complexes were characterized by elemental analysis, molar conductivity, and spectroscopic techniques (IR, UV-Vis, ¹H NMR, ESI-MS). We performed DFT calculations to get insight into the geometry of the studies complexes. DNA-binding studies were performed by UV-Vis spectrophotometry and fluorescence spectroscopy. The results of competitive reactions between gold(III) complexes and ethidium bromide (EB) towards DNA have shown that selected complexes can displace EB from DNA-EB adduct. In addition, these experiments confirm that polynuclear gold(III) complexes interact with DNA covalently or via intercalation. Furthermore, high values of binding constants of gold(III) complexes towards bovine serum albumin (BSA) protein indicate good binding affinity. In addition, redox stability of complexes in the presence of DNA/BSA was confirmed by cyclic voltammetry. Results of the interactions between gold(III) complexes with DNA/BSA were discussed in reference to molecular docking data obtain by Molegro virtual docker. The cytotoxic activity of synthesized gold(III) complexes was evaluated on human breast cancer cell line (MDA-MB-231), human colorectal cancer cell line (HCT-116), and normal human lung fibroblast cell line (MRC-5). All complexes dose-dependently reduced cancer and normal cells viabilities, with significant cytotoxic effects (IC₅₀ < 25 μM) for trinuclear gold(III) complexes (4, 5) on HCT-116 cells.

Porphyrin cage compounds based on glycoluril – from enzyme mimics to functional molecular machines

This Feature Article gives an overview of the application of glycoluril-based porphyrin cage compounds in host–guest chemistry, allosterically controlled self-assembly, biomimetic catalysis, and polymer encoding.

Hydrogenolysis of carbon–carbon σ-bonds using water catalysed by semi-rigid diiridium(iii) porphyrins

Semi-rigid diiridium(iii) porphyrins alkyls with m-xylyl and p-xylyl diether linkers were synthesized. They were found to be catalysts for the carbon–carbon σ-bond hydrogenolysis of [2.2]paracyclophane in neutral conditions using water as the hydrogen source.

Design of oxophilic metalloporphyrins: an experimental and DFT study of methanol binding

Experimental binding constants are matched with computations to identify optimal host–guest systems for ligands with oxygen-containing functional groups.

Synthesis and Properties of Bis-Porphyrin Molecular Tweezers: Effects of Spacer Flexibility on Binding and Supramolecular Chirogenesis

Ditopic binding of various dinitrogen compounds to three bisporphyrin molecular tweezers with spacers of varying conformational rigidity, incorporating the planar enediyne (1), the helical stiff stilbene (2), or the semi-rigid glycoluril motif fused to the porphyrins (3), are compared. Binding constants K_a = 10⁴–10⁶ M⁻¹ reveal subtle differences between these tweezers, that are discussed in terms of porphyrin dislocation modes. Exciton coupled circular dichroism (ECCD) of complexes with chiral dinitrogen guests provides experimental evidence for the conformational properties of the tweezers. The results are further supported and rationalized by conformational analysis.

Dimeric packing of molecular clips induced by interactions between π-systems

We report the first observation synthesis and X-ray structures of seven glycoluril clips that feature extended aromatic sidewalls; compounds 1 and 2 are the first examples of the out–out dimeric motif.

X-ray studies of conformation: observation of conformational polymorphism of a glycoluril clip

In this report, molecular modeling, X-ray crystallography and NMR spectroscopy were used to study the conformational behavior of a novel glycoluril based clip.

New approach for post-functionalization of meso-formylporphyrins

An approach for the transformation of formyl groups into areneimidazoles at a porphyrin substrate is developed, allowing straightforward design of new polytopic porphyrinoid compounds.