Front face fluorescence spectroscopy and visible spectroscopy coupled with chemometrics have the potential to characterise ripening of Cabernet Franc grapes

The potential of front-face spectroscopy for grape ripening dates discrimination was investigated on Cabernet Franc grapes from three parcels located on the Loire Valley and for six ripening dates. The 18 batches were analysed by front-face fluorescence spectroscopy and visible spectroscopy. The excitation spectra (250-310 nm, emission wavelength = 350 nm) were characterised by a shoulder at 280 nm. Grapes spectra were classified by factorial discriminant analysis (FDA). Ripening dates were well predicted by fluorescence spectra: grapes before veraison were separated from grapes after veraison and almost every ripening date was identified. The common spectroscopic space obtained by CCSWA showed that wavelengths corresponding to anthocyanin absorption in the visible were correlated to fluorescence wavelengths around the starting and ending points of the shoulder (263 and at 292 nm). Then, regression models were investigated to predict total soluble solids (TSS), total acidity, malvidin-3G, total anthocyanins and total phenolics content from visible and fluorescence spectra. To predict technological indicators (TSS and total acidity), the PLS model with visible spectra (RMSECV = 0.82°Brix or 0.96 g L⁻¹ H₂SO₄) was better than those with fluorescence one (RMSECV = 1.39°Brix or 2.06 g L⁻¹ H₂SO₄). For malvidin-3G and total anthocyanins, all and were superior to 0.90 and RMSECV were low. Visible and fluorescence spectroscopies succeeded in predicting anthocyanin content. Concerning total phenolic, the best prediction was provided by fluorescence spectroscopy.     

Design of dipicolinic acid ligands for the two-photon sensitized luminescence of europium complexes with optimized cross-sections

The multistep synthesis of an extensive series of push-pull donor-pi-conjugated dipicolinic acid ligands is described. The charge transfer character of the ligand can be tuned by changing the donor group (CH 2R, OR, SR, or NR 2) or the nature of the conjugated backbone (phenyl, phenylethynyl, naphtylethynyl, bis(phenylethynyl), or chalcone). The photophysical properties of related D 3 symmetric europium complexes (absorption and luminescence) were measured. Experiments using two-photon sensitized luminescence of a Eu (III) complex reveal large two-photon absorption (TPA) cross-section values (775 GM at 740 nm) in dichloromethane. Furthermore, some structure-property relationships can be derived from this systematic study, allowing an optimization of TPA properties of lanthanide complexes.     

Efficient sensitization of europium, ytterbium, and neodymium functionalized tris-dipicolinate lanthanide complexes through tunable charge-transfer excited states

A series of push-pull donor-pi-conjugated dipicolinic acid ligands and related tris-dipicolinate europium and lutetium complexes have been prepared. The ligands present broad absorption and emission transitions in the visible spectral range unambiguously assigned to charge-transfer transitions (CT) by means of time-dependent density functional theory calculations. The photophysical properties (absorption, emission, luminescence quantum yield, and lifetime) of the corresponding europium complexes were thoroughly investigated. Solvatochromism and temperature effects clearly confirm that Eu(III) sensitization directly occurs from the ligand CT state. In addition, modulation of the energy of the CT donating state by changing the nature of the donor fragment allows the optimal energy of the antennae for europium sensitization to be determined, and this optimal energy was found to be close to the (5)D 1 accepting state. Finally, this CT sensitization process has been successfully extended to near-infrared emitters (neodymium and ytterbium).     

Ab initio and QM/MM study of electron addition on the disulfide bond in thioredoxin

Thioredoxin controls the intracellular redox potential through a disulfide/dithiol couple. Under conditions of oxidative stress, this protein functions via one-electron exchange, in which formation of the disulfide radical anion occurs. Combined quantum mechanical (QM) and molecular mechanical (MM) calculations using two- and three-level ONIOM schemes were performed on the thioredoxin (Trx) protein of Chlamydomonas reinhardtii in its oxidized-disulfide and one-electron-reduced forms. In both cases, the active site disulfide moiety was described at the MP2(fc)/6-31+G(d) level, and larger regions of varying sizes around the active site were described at the B3LYP/6-31+G(d) level. The remainder of the 112 residues and 33 water molecules of the crystal structure (PDB entry 1EP7) were described by the AMBER force field. Adiabatic electron affinities were calculated for the disulfide bond in all systems. Separate QM or QM/QM calculations were performed on the QM regions to establish the role of the remainder of the protein on the active site properties. The radical anion species becomes more stable as the number of amide groups in the vicinity increases. One-electron reduction potentials were calculated for the small molecule models, and approximated for the protein for which the values are similar to the experimental one (approximately 0 V). This high reduction potential is due to interaction with the charged end of Lys40, as indicated by mutation in silico to norleucine. The inclusion of the protonated Asp30 side chain and a water molecule in the QM region leads to an increase in the electron affinity. Proton transfer from the Asp30 side chain to the Cys39 sulfur in the radical anion species is strongly disfavored. The radical anion is more stable than the protonated form, which is consistent with experimental results.     

Excited-State Reactivity of [Mn(im)(CO)3(phen)]+: A Structural Exploration

The electronic excited state reactivity of [Mn(im)(CO)₃(phen)]⁺ (phen = 1,10-phenanthroline; im = imidazole) ranging between 420 and 330 nm have been analyzed by means of relativistic spin–orbit time-dependent density functional theory and wavefunction approaches (state-average-complete-active-space self-consistent-field/multistate CAS second-order perturbation theory). Minimum energy conical intersection (MECI) structures and connecting pathways were explored using the artificial force induced reaction (AFIR) method. MECIs between the first and second singlet excited states (S₁/S₂-MECIs) were searched by the single-component AFIR (SC-AFIR) algorithm combined with the gradient projection type optimizer. The structural, electronic, and excited states properties of [Mn(im)(CO)₃(phen)]⁺ are compared to those of the Re(I) analogue [Re(im)(CO)₃(phen)]⁺. The high density of excited states and the presence of low-lying metal-centered states that characterize the Mn complex add complexity to the photophysics and open various dissociative channels for both the CO and imidazole ligands. © 2018 Wiley Periodicals, Inc.     

Modeling the Dynamics of Protein–Protein Interfaces,How and Why?

Protein–protein assemblies act as a key component in numerous cellular processes. Their accurate modeling at the atomic level remains a challenge for structural biology. To address this challenge, several docking and a handful of deep learning methodologies focus on modeling protein–protein interfaces. Although the outcome of these methods has been assessed using static reference structures, more and more data point to the fact that the interaction stability and specificity is encoded in the dynamics of these interfaces. Therefore, this dynamics information must be taken into account when modeling and assessing protein interactions at the atomistic scale. Expanding on this, our review initially focuses on the recent computational strategies aiming at investigating protein–protein interfaces in a dynamic fashion using enhanced sampling, multi-scale modeling, and experimental data integration. Then, we discuss how interface dynamics report on the function of protein assemblies in globular complexes, in fuzzy complexes containing intrinsically disordered proteins, as well as in active complexes, where chemical reactions take place across the protein–protein interface.