Shorter Alkyl Chains Enhance Molecular Diffusion and Electron Transfer Kinetics between Photosensitisers and Catalysts in CO2-Reducing Photocatalytic Liposomes

Covalent functionalisation with alkyl tails is a common method for supporting molecular catalysts and photosensitisers onto lipid bilayers, but the influence of the alkyl chain length on the photocatalytic performances of the resulting liposomes is not well understood. In this work, we first prepared a series of rhenium-based CO₂-reduction catalysts [Re(4,4’-(C_nH_2n+1)₂-bpy)(CO)₃Cl] ( ReC_n ; 4,4’-(C_nH_2n+1)₂-bpy=4,4’-dialkyl-2,2’-bipyridine) and ruthenium-based photosensitisers [Ru(bpy)₂(4,4’-(C_nH_2n+1)₂-bpy)](PF₆)₂ ( RuC_n ) with different alkyl chain lengths (n=0, 9, 12, 15, 17, and 19). We then prepared a series of PEGylated DPPC liposomes containing RuC_n and ReC_n , hereafter noted C_n , to perform photocatalytic CO₂ reduction in the presence of sodium ascorbate. The photocatalytic performance of the C_n liposomes was found to depend on the alkyl tail length, as the turnover number for CO (TON) was inversely correlated to the alkyl chain length, with a more than fivefold higher CO production (TON=14.5) for the C₉ liposomes, compared to C₁₉ (TON=2.8). Based on immobilisation efficiency quantification, diffusion kinetics, and time-resolved spectroscopy, we identified the main reason for this trend: two types of membrane-bound RuC_n species can be found in the membrane, either deeply buried in the bilayer and diffusing slowly, or less buried with much faster diffusion kinetics. Our data suggest that the higher photocatalytic performance of the C₉ system is due to the higher fraction of the more mobile and less buried molecular species, which leads to enhanced electron transfer kinetics between RuC₉ and ReC₉ .     

D-Sorbitol Physical Properties Effects on Filaments Used by 3D Printing Process for Personalized Medicine

Fused filament fabrication (FFF) is a process used to manufacture oral forms adapted to the needs of patients. Polyethylene oxide (PEO) filaments were produced by hot melt extrusion (HME) to obtain a filament suitable for the production of amiodarone hydrochloride oral forms by FFF 3D printing. In order to produce personalized oral forms adapted to the patient characteristics, filaments used by FFF must be controlled in terms of mass homogeneity along filament. This work highlights the relation between filament mass homogeneity and its diameter. This is why the impact of filler excipients physical properties was studied. It has been showed that the particle’s size distribution of the filler can modify the filament diameter variability which has had an impact on the mass of oral forms produced by FFF. Through this work it was shown that D-Sorbitol from Carlo Erba allows to obtain a diameter variability of less than 2% due to its unique particle’s size distribution. Using the filament produced by HME and an innovating calibration method based on the filament length, it has been possible to carry out three dosages of 125 mg, 750 mg and 1000 mg by 3D printing with acceptable mass uniformity.     

Stereoretentive Palladium‐Catalyzed Arylation,Alkenylation, and Alkynylation of 1‐Thiosugars and Thiols Using Aminobiphenyl Palladacycle Precatalyst at Room Temperature

A general and efficient protocol for the palladium‐catalyzed functionalization of mono‐ and polyglycosyl thiols by using the palladacycle precatalyst G3‐XantPhos was developed. The C?S bond‐forming reaction was achieved rapidly at room temperature with various functionalized (hetero)aryl‐, alkenyl‐, and alkynyl halides. The functional group tolerance on the electrophilic partner is typically high and anomer selectivities of thioglycosides are high in all cases studied. New sulfur nucleophiles such as thiophenols, alkythiols, and thioaminoacids (cysteine) were also successfully coupled to lead to the most general and practical method yet reported for the functionalization of thiols.     

Mild and general methods for the palladium-catalyzed cyanation of aryl and heteroaryl chlorides

[reaction: see text] New methods for the palladium-catalyzed cyanation of aryl and heteroaryl chlorides have been developed, featuring sterically demanding, electron-rich phosphines. Highly challenging electron-rich aryl chlorides, in addition to electron-neutral and electron-deficient substrates, as well as nitrogen- and sulfur-containing heteroaryl chlorides can all undergo efficient cyanation under relatively mild conditions using readily available materials. In terms of substrate scope and temperature, these methods compare very favorably with the state-of-the-art cyanations of aryl chlorides.     

Protonation of a Biologically Relevant CuII μ‐Thiolate Complex: Ligand Dissociation or Formation of a Protonated CuI Disulfide Species?

The proton‐induced electron‐transfer reaction of a Cu^II μ‐thiolate complex to a Cu^I‐containing species has been investigated, both experimentally and computationally. The Cu^II μ‐thiolate complex [Cu^II₂( L^MeS )₂]²⁺ is isolated with the new pyridyl‐containing ligand L^MeSSL^Me , which can form both Cu^II thiolate and Cu^I disulfide complexes, depending on the solvent. Both the Cu^II and the Cu^I complexes show reactivity upon addition of protons. The multivalent tetranuclear complex [Cu^I₂Cu^II₂( LS )₂(CH₃CN)₆]⁴⁺ crystallizes after addition of two equivalents of strong acid to a solution containing the μ‐thiolate complex [Cu^II₂( LS )₂]²⁺ and is further analyzed in solution. This study shows that, upon addition of protons to the Cu^II thiolate compound, the ligand dissociates from the copper centers, in contrast to an earlier report describing redox isomerization to a Cu^I disulfide species that is protonated at the pyridyl moieties. Computational studies of the protonated Cu^II μ‐thiolate and Cu^I disulfide species with LSSL show that already upon addition of two equivalents of protons, ligand dissociation forming [Cu^I(CH₃CN)₄]⁺ and protonated ligand is energetically favored over conversion to a protonated Cu^I disulfide complex.     

Electronic structure analysis of electrochemical CO2 reduction by iron-porphyrins reveals basic requirements for design of catalysts bearing non-innocent ligands

Electrocatalytic CO₂ reduction is a possible solution to the increasing CO₂ concentration in the earth’s atmosphere, because it enables storage of energy while using the harmful CO₂ feedstock as a starting material. Notably, iron(ii) tetraphenylporphyrin, [Fe^II(TPP)]⁰ (TPP²⁻ = tetraphenylporphyrin tetra-anion diradical), and its derivatives have been established as one of the most promising families of homogeneous catalysts for CO₂ reduction into CO. Our earlier work has demonstrated that [Fe(TPP)]²⁻, a catalytically active species, is best described as an Fe(ii) center antiferromagnetically coupled with a TPP⁴⁻ diradical. In fact, [Fe(TPP)]²⁻ represents a prototypical example of a diverse array of highly efficient molecular catalysts that feature non-innocent ligands. To obtain valuable insights for future catalyst design, their outstanding catalytic performance warrants an investigation aimed at elucidating the role played by the ligand non-innocence in the reaction. To this end, the reactivity of [Fe(TPP)]²⁻ was first investigated in detail by using density functional theory calculations, and the theoretical results were then validated by reproducing available experimental kinetic and thermodynamic data. Further in-depth analyses pinpointed the electronic-structure feature of the non-innocent TPP ligand that is responsible for the high efficiency of the reaction. Finally, we analyzed the electronic-structure evolution found for the reactions catalyzed by ten related representative non-innocent systems. Our results revealed that for the reactions under consideration, the reducing equivalents are stored on the non-innocent ligand, while CO₂ functionalization takes place at the metal center. Therefore, all of the transformations invariably entail two synchronized electron-transfer events: (1) a metal-to-CO₂ transfer and (2) a ligand-to-metal electron transfer. The former is affected by σ-donation from the metal d_z² orbital to the CO₂ orbital, and the latter is facilitated by orbital coupling between the ligand and the metal center. Our results suggested that ligand non-innocence plays a fundamental role in stabilizing highly active intermediates while realizing high product selectivity for CO₂ reduction and that the metal–ligand cooperativity is essential to the high reaction kinetics. On the basis of these findings, we proposed fundamental requirements for design of catalysts with non-innocent ligands.

This computational study elucidates the role played by ligand non-innocence in CO₂ reduction on the basis of analyses of electronic structure evolution of highly efficient iron-tetraphenylporphyrin and ten other transition metal complexes, all bearing non-innocent ligands.     

Highly selective addition of cyclosilanes to alkynes enabling new conjugated materials

Main group organometallic compounds can exhibit unusual optical properties arising from hybrid σ,π-conjugation. While linear silanes are extensively studied, the shortage of methods for the controlled synthesis of well-defined cyclic materials has precluded the study of cyclic conjugation. Herein we report that Ru-catalyzed addition of cyclosilanes to aryl acetylenes (hydrosilylation) proceeds with high chemoselectivity, regioselectivity, and diastereoselectivity, affording complex organosilanes that absorb visible light. We further show that the hydrosilylation products are useful building blocks towards novel conjugated polymers.

Hybrid σ,π-conjugated cyclosilanes were synthesized via highly selective hydrosilylation and have shown great potentials as building blocks to construct novel conjugated polymers with control of tacticity.     

Mimicking Photosystem I with a Transmembrane Light Harvester and Energy Transfer-Induced Photoreduction in Phospholipid Bilayers

Photosystem I (PS I) is a transmembrane protein that assembles perpendicular to the membrane, and performs light harvesting, energy transfer, and electron transfer to a final, water-soluble electron acceptor. We present here a supramolecular model of it formed by a bicationic oligofluorene 1²⁺ bound to the bisanionic photoredox catalyst eosin Y (EY²⁻) in phospholipid bilayers. According to confocal microscopy, molecular modeling, and time dependent density functional theory calculations, 1²⁺ prefers to align perpendicularly to the lipid bilayer. In presence of EY²⁻, a strong complex is formed (K_a=2.1±0.1×10⁶ m ⁻¹), which upon excitation of 1²⁺ leads to efficient energy transfer to EY²⁻. Follow-up electron transfer from the excited state of EY²⁻ to the water-soluble electron donor EDTA was shown via UV–Vis absorption spectroscopy. Overall, controlled self-assembly and photochemistry within the membrane provides an unprecedented yet simple synthetic functional mimic of PS I.