A Photochromic Azobenzene Peptidomimetic of a β-Turn Model Peptide Structure as a Conformational Switch

The insertion of azobenzene moiety in complex molecular protein or peptide systems can lead to molecular switches to be used to determine kinetics of folding/unfolding properties of secondary structures, such as α-helix, β-turn, or β-hairpin. In fact, in azobenzene, absorption of light induces a reversible trans ↔ cis isomerization, which in turns generates a strain or a structure relaxation in the chain that causes peptide folding/unfolding. In particular azobenzene may permit reversible conformational control of hairpin formation. In the present work a synthetic photochromic azobenzene amino acid derivative was incorporated as a turn element to modify the synthetic peptide [Pro7,Asn8,Thr10]CSF114 previously designed to fold as a type I β-turn structure in biomimetic HFA/water solution. In particular, the P-N-H fragment at positions 7–9, involved in a β-hairpin, was replaced by an azobenzene amino acid derivative (synthesized ad hoc) to investigate if the electronic properties of the novel peptidomimetic analog could induce variations in the isomerization process. The absorption spectra of the azopeptidomimetic analog of the type I β-turn structure and of the azobenzene amino acid as control were measured as a function of the irradiation time exciting into the respective first ππ* and nπ* transition bands. Isomerization of the azopeptidomimetic results strongly favored by exciting into the ππ* transition. Moreover, conformational changes induced by the cis↔ trans azopeptidomimetic switch were investigated by NMR in different solvents

Co(II)-Based single-ion magnets with 1,1 '-ferrocenediyl-bis(diphenylphosphine) metalloligands

Herein, we report on investigations of magnetic and spectroscopic properties of three heterobimetallic Fe(ii)-Co(ii) coordination compounds based on the tetracoordinate {CoP2X2} core encapsulated by dppf metalloligand, where X = Cl (1), Br (2), I (3), dppf = 1,1 '-ferrocenediyl -bis(diphenylphosphine). The analysis of static magnetic data has revealed the presence of axial magnetic anisotropy in compounds (1) and (2) and this was further confirmed by high-frequency electron spin resonance (HF-ESR) spectroscopy. Dynamic magnetic data confirmed that (1) and (2) behave as field-induced Single-Ion Magnets (SIMs). Together with bulk studies, we have also tested the possibility of depositing (2) as thick films on Au(111), glass, and polymeric acetate by drop-casting as well as thermal sublimation, a key aspect for the development of future devices embedding these magnetic objects

Thermal and light-induced spin transition in a nanometric film of a new high-vacuum processable spin crossover complex

Spin crossover complexes are among the most studied classes of molecular switches and have attracted considerable attention for their potential technological use as active units in new multifunctional devices. A fundamental step towards a practical implementation is their effective processability into thin films. Crucially, the physical property of technological interest shown by these materials in the bulk phase has to be retained once they are deposited on a solid surface. These conditions are not easily satisfied by most of the intrinsically fragile coordination compounds, either because the material processing methods can compromise their molecular structure, or the interaction between the molecule and the surface can induce drastic changes in the resulting properties. Herein, we report the identification of a novel high-vacuum processable spin-crossover complex, [Fe(qnal)2] (qnal = quinoline-naphthaldehyde), and the preparation of a 50 nm sublimated film of this molecular switch on gold. X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) were used to investigate the composition and the temperature- and light-induced spin-crossover of the deposited material, providing full evidence of the capability of this molecular system to be efficiently processed into nanometric films with retention of its switchable magnetic properties.Initiative d'excellence de l'Université de BordeauxMOLSPIN COS

A Photochromic Azobenzene Peptidomimetic of a β-Turn Model Peptide Structure as a Conformational Switch

International audienceThe insertion of azobenzene moiety in complex molecular protein or peptide systems can lead to molecular switches to be used to determine kinetics of folding/unfolding properties of secondary structures, such as α-helix, β-turn, or β-hairpin. In fact, in azobenzene, absorption of light induces a reversible trans ↔ cis isomerization, which in turns generates a strain or a structure relaxation in the chain that causes peptide folding/unfolding. In particular azobenzene may permit reversible conformational control of hairpin formation. In the present work a synthetic photochromic azobenzene amino acid derivative was incorporated as a turn element to modify the synthetic peptide [Pro7,Asn8,Thr10]CSF114 previously designed to fold as a type I β-turn structure in biomimetic HFA/water solution. In particular, the P-N-H fragment at positions 7–9, involved in a β-hairpin, was replaced by an azobenzene amino acid derivative (synthesized ad hoc) to investigate if the electronic properties of the novel peptidomimetic analog could induce variations in the isomerization process. The absorption spectra of the azopeptidomimetic analog of the type I β-turn structure and of the azobenzene amino acid as control were measured as a function of the irradiation time exciting into the respective first ππ* and nπ* transition bands. Isomerization of the azopeptidomimetic results strongly favored by exciting into the ππ* transition. Moreover, conformational changes induced by the cis↔ trans azopeptidomimetic switch were investigated by NMR in different solvents

Room temperature control of spin states in a thin film of a photochromic iron(ii) complex

Thin films of a molecular spin crossover iron(II) complex featuring a photochromic diarylethene-based ligand have been grown by sublimation in ultra-high vacuum on an Au(111) single crystal, and investigated by X-ray and UV photoelectron spectroscopies. Temperature-dependent studies demonstrate that the thermally induced spin crossover behaviour is preserved in thin films. The photochromic ligand deliberately integrated into the complex allows photoswitching of the spin states of this iron(II) complex at room temperature, and this photomagnetic effect is still observed in 5 nm thick sublimated films. Thus, this work opens new horizons and pushes bistable spin crossover systems closer to prospective applications in molecular electronics and molecular spintronics devices functioning at room temperature

Substrate-dependent spin crossover in an Fe( ii ) scorpionate complex

A new spin-crossover complex based on a heteroscorpionate ligand was synthesized and characterized. Thin films were grown by sublimation in an ultra-high vacuum on highly oriented pyrolytic graphite (HOPG) and on single crystal Au (111), and spectroscopically characterized using X-ray absorption and X-ray photoemission. Temperature-dependent experiments on sub-nanometric deposits demonstrated that the thermally induced spin-crossover is preserved at a sub-monolayer (0.7 ML) coverage on HOPG, while films with similar thickness lose the switching behaviour when deposited on a Au(111) surface. The system was unresponsive to light stimuli at low temperatures independently of the used substrate.Initiative d'excellence de l'Université de Bordeau

Substrate driven Spin Crossover in a Fe(II) scorpionate complex.

A new spin crossover complex based on a heteroscorpionate ligand was synthesized and characterized. Thin films were grown by sublimation in ultra-high vacuum on highly oriented pyrolytic graphite (HOPG) and on gold single crystal Au (111), and spectroscopically characterized through X-ray absorption and by X-ray photoemission. Temperature-dependent experiments on sub-nanometric deposits demonstrated that the thermally induced spin-crossover is preserved at a sub-monolayer (0.7 ML) coverage on HOPG, while deposits with similar thickness lose the switching behaviour on Au(111) surface. The system was unresponsive to light stimuli at low temperature indepently of the used substrate