12 research outputs found
The KetoâEnol Tautomerism of Biliverdin in Bacteriophytochrome: Could it Explain the Bathochromic Shift in the Pfr Form?
Phytochromes are ubiquitous photoreceptors found in plants, eukaryotic algae, bacteria and fungi. Particularly, when bacteriophytochrome is irradiated with light, a ZâtoâE (photo)isomerization takes place in the biliverdin chromophore as part of the PrâtoâPfr conversion. This photoisomerization is concomitant with a bathochromic shift in the Qâband. Based on experimental evidence, we studied a possible ketoâenol tautomerization of BV, as an alternative reaction channel after its photoisomerization. In this contribution, the noncatalyzed and waterâassisted reaction pathways for the lactamâlactim interconversion through consecutive ketoâenol tautomerization of a model BV species were studied deeply. It was found that in the absence of water molecules, the proton transfer reaction is unable to take place at normal conditions, due to large activation energies, and the endothermic formation of lactim derivatives prevents its occurrence. However, when a water molecule assists the process by catalyzing the proton transfer reaction, the activation free energy lowers considerably. The drastic lowering in the activation energy for the ketoâenol tautomerism is due to the stabilization of the water moiety through hydrogen bonds along the reaction coordinate. The absorption spectra were computed for all tautomers. It was found that the UVâvisible absorption bands are in reasonable agreement with the experimental data. Our results suggest that although the ketoâenol equilibrium is likely favoring the lactam tautomer, the equilibrium could eventually be shifted in favor of the lactim, as it has been reported to occur in the dark reversion mechanism of bathy phytochromes
The KetoâEnol Tautomerism of Biliverdin in Bacteriophytochrome: Could it Explain the Bathochromic Shift in the Pfr Form?
Phytochromes are ubiquitous photoreceptors found in plants, eukaryotic algae, bacteria and fungi. Particularly, when bacteriophytochrome is irradiated with light, a ZâtoâE (photo)isomerization takes place in the biliverdin chromophore as part of the PrâtoâPfr conversion. This photoisomerization is concomitant with a bathochromic shift in the Qâband. Based on experimental evidence, we studied a possible ketoâenol tautomerization of BV, as an alternative reaction channel after its photoisomerization. In this contribution, the noncatalyzed and waterâassisted reaction pathways for the lactamâlactim interconversion through consecutive ketoâenol tautomerization of a model BV species were studied deeply. It was found that in the absence of water molecules, the proton transfer reaction is unable to take place at normal conditions, due to large activation energies, and the endothermic formation of lactim derivatives prevents its occurrence. However, when a water molecule assists the process by catalyzing the proton transfer reaction, the activation free energy lowers considerably. The drastic lowering in the activation energy for the ketoâenol tautomerism is due to the stabilization of the water moiety through hydrogen bonds along the reaction coordinate. The absorption spectra were computed for all tautomers. It was found that the UVâvisible absorption bands are in reasonable agreement with the experimental data. Our results suggest that although the ketoâenol equilibrium is likely favoring the lactam tautomer, the equilibrium could eventually be shifted in favor of the lactim, as it has been reported to occur in the dark reversion mechanism of bathy phytochromes
Toward a Neutral Single-Component Amidinate Iodide Aluminum Catalyst for the COâ Fixation into Cyclic Carbonates
A new iodide aluminum complex ({AlI(ÎșâŽ-naphbam)}, 3) supported by a tetradentate amidinate ligand derived from a naphthalene-1,8-bisamidine precursor (naphbamH, 1) was obtained in quantitative yield via reaction of the corresponding methyl aluminum complex ({AlMe(ÎșâŽ-naphbam)}, 2) with 1 equiv of Iâ in CHâClâ at room temperature. Complexes 2 and 3 were tested and found to be active as catalysts for the cyclic carbonate formation from epoxides at 80 °C and 1 bar of COâ pressure. A first series of experiments were carried out with 1.5 mol % of the alkyl complex 2 and 1.5 mol % of tetrabutylammonium iodide (TBAI) as a cocatalyst; subsequently, the reactions were carried out with 1.5 mol % of iodide complex 3 as a single-component catalyst. Compound 3 is one of the first examples of a nonzwitterionic halide single-component aluminum catalyst producing cyclic carbonates. The full catalytic cycle with characterization of all minima and transition states was characterized by quantum chemistry calculations (QCCs) using density functional theory. QCCs on the reaction mechanism support a reaction pathway based on the exchange of the iodine contained in the catalyst by 1 equiv of epoxide, with subsequent attack of Iâ» to the epoxide moiety producing the ring opening of the epoxide. QCCs triggered new insights for the design of more active halide catalysts in future explorations of the field
Reaction Electronic Flux Perspective on the Mechanism of the Zimmerman Di-Ï-methane Rearrangement
The reaction electronic flux (REF) offers a powerful tool in the analysis of reaction mechanisms. Noteworthy, the relationship between aromaticity and REF can eventually reveal subtle electronic events associated with reactivity in aromatic systems. In this work, this relationship was studied for the triplet Zimmerman di-Ï-methane rearrangement. The aromaticity loss and gain taking place during the reaction is well acquainted by the REF, thus shedding light on the electronic nature of reactions involving dibenzobarrelenes
Trapping an Unusual Pentacoordinate Carbon Atom in a Neutral Trialuminum Complex
A neutral trialuminum complex incorporates a pentacoordinate carbon through a methylidene bridge linking the three metal atoms. The rigid electron-deficient Al3 core stabilizes thehypercoordinate carbon atom resulting in the shortest equatorial AlâC distance reported for such systems.</div
Air- andWater-Stable Heteroleptic Copper (I) Complexes Bearing Bis(indazol-1-yl)methane Ligands: Synthesis, Characterisation, and Computational Studies
A series of four novel heteroleptic Cu(I) complexes, bearing bis(1H-indazol-1-yl)methane
analogues as N,N ligands and DPEPhos as the P,P ligand, were synthesised in high yields under
mild conditions and characterised by spectroscopic and spectrometric techniques. In addition, the
position of the carboxymethyl substituent in the complexes and its effect on the electrochemical and
photophysical behaviour was evaluated. As expected, the homoleptic copper (I) complexes with the
N,N ligands showed air instability. In contrast, the obtained heteroleptic complexes were air- and
water-stable in solid and solution. All complexes displayed green-yellow luminescence in CH2Cl2
at room temperature due to ligand-centred (LC) phosphorescence in the case of the Cu(I) complex
with an unsubstituted N,N ligand and metal-to-ligand charge transfer (MLCT) phosphorescence for
the carboxymethyl-substituted complexes. Interestingly, proper substitution of the bis(1H-indazol-
1-yl)methane ligand enabled the achievement of a remarkable luminescent yield (2.5%) in solution,
showcasing the great potential of this novel class of copper(I) complexes for potential applications in
luminescent devices and/or photocatalysis
Reaction Electronic Flux Perspective on the Mechanism of the Zimmerman Di-Ï-methane Rearrangement
The
reaction electronic flux (REF) offers a powerful tool in the
analysis of reaction mechanisms. Noteworthy, the relationship between
aromaticity and REF can eventually reveal subtle electronic events
associated with reactivity in aromatic systems. In this work, this
relationship was studied for the triplet Zimmerman di-Ï-methane
rearrangement. The aromaticity loss and gain taking place during the
reaction is well acquainted by the REF, thus shedding light on the
electronic nature of reactions involving dibenzobarrelenes