Why Is the Spontaneous Deprotonation of [Cu(uracil)2]2+ Complexes Accompanied by Enolization of the System?

The reaction‐force formalism is applied to carry out a detailed analysis of the mechanisms behind the enolization processes undergone by the complexes formed on interaction of uracil dimers with Cu²⁺ ions after spontaneous deprotonation of the resulting complexes. These enolization processes apparently involve a single proton transfer (PT) from an NH group to a carbonyl group of the same uracil moiety, which should involve a rather high activation barrier that prevents the process occurring. However, the reaction‐force, chemical‐potential, and electronic‐flux profiles unambiguously indicate that the actual mechanism involves three low‐barrier elementary steps, and this explains why enolization of the [Cu(uracil?H)(uracil)]⁺ complexes is a highly facile, assisted PT process. All of the observed PT processes show a typical profile for both the chemical potential and the electronic flux associated with the bond‐breaking and the bond‐formation processes.     

Computational Study of Proton Transfer in Tautomers of 3‐ and 5‐Hydroxypyrazole Assisted by Water

The tautomerism of 3‐ and 5‐hydroxypyrazole is studied at the B3LYP, CCSD and G3B3 computational levels, including the gas phase, PCM–water effects, and proton transfer assisted by water molecules. To understand the propensity of tautomerization, hydrogen‐bond acidity and basicity of neutral species is approached by means of correlations between donor/acceptor ability and H‐bond interaction energies. Tautomerism processes are highly dependent on the solvent environment, and a significant reduction of the transition barriers upon solvation is seen. In addition, the inclusion of a single water molecule to assist proton transfer decreases the barriers between tautomers. Although the second water molecule further reduces those barriers, its effect is less appreciable than the first one. Neutral species present more stable minima than anionic and cationic species, but relatively similar transition barriers to anionic tautomers.     

Conductivity‐Dependent Completion of Oxygen Reduction on Oxide Catalysts

The electric conductivity‐dependence of the number of electrons transferred during the oxygen reduction reaction is presented. Intensive properties, such as the number of electrons transferred, are difficult to be considered conductivity‐dependent. Four different perovskite oxide catalysts of different conductivities were investigated with varying carbon contents. More conductive environments surrounding active sites, achieved by more conductive catalysts (providing internal electric pathways) or higher carbon content (providing external electric pathways), resulted in higher number of electrons transferred toward more complete 4e reduction of oxygen, and also changed the rate‐determining steps from two‐step 2e process to a single‐step 1e process. Experimental evidence of the conductivity dependency was described by a microscopic ohmic polarization model based on effective potential localized nearby the active sites.     

Void‐Assisted Ion‐Paired Proton Transfer at Water–Ionic Liquid Interfaces

At the water–trihexyl(tetradecyl)phosphonium tris(pentafluoroethyl)trifluorophosphate ([P_14,6,6,6][FAP]) ionic liquid interface, the unusual electrochemical transfer behavior of protons (H⁺) and deuterium ions (D⁺) was identified. Alkali metal cations (such as Li⁺, Na⁺, K⁺) did not undergo this transfer. H⁺/D⁺ transfers were assisted by the hydrophobic counter anion of the ionic liquid, [FAP]^?, resulting in the formation of a mixed capacitive layer from the filling of the latent voids within the anisotropic ionic liquid structure. This phenomenon could impact areas such as proton‐coupled electron transfers, fuel cells, and hydrogen storage where ionic liquids are used as aprotic solvents.     

Effect of the π Bridge and Acceptor on Intramolecular Charge Transfer in Push–Pull Cationic Chromophores: An Ultrafast Spectroscopic and TD‐DFT Computational Study

Three (donor–π–acceptor)⁺ systems with a methyl pyridinium or quinolinium as the electron‐deficient group, a dimethyl amino as the electron‐donor group, and an ethylene or butadiene group as the spacer have been investigated in a joint spectroscopic and TD‐DFT computational study. A negative solvatochromism has been revealed in the absorption spectra, which implies a solution color change, and interpreted by considering the variation in the permanent dipole moment modulus and orientation upon photoexcitation. The fluorescence efficiency decreases upon increasing solvent polarity, in agreement with the excited‐state optimized geometries (planar in low‐polarity media and twisted in high‐polarity media). Femtosecond transient absorption has revealed the occurrence of a fast photoinduced intramolecular charge transfer (ICT) and the molecular factors that determine an efficient ICT. Considering the crucial role of the ICT in tuning the nonlinear optical (NLO) properties, these compounds can be considered promising NLO materials.     

Acceleration of Long‐Range Photoinduced Electron Transfer through DNA by Hydroxyquinolines as Artificial Base Pairs

The C‐nucleoside based on the hydroxyquinoline ligand (Hq) is complementary to itself and forms stable Hq–Hq pairs in double‐stranded DNA. These artificial Hq–Hq pairs may serve as artificial electron carriers for long‐range photoinduced electron transfer in DNA, as elucidated by a combination of gel electrophoretic analysis of irradiated samples and time‐resolved transient absorption spectroscopy. For this study, the Hq–Hq pair was combined with a DNA‐based donor–acceptor system consisting of 6‐N,N‐dimethylaminopyrene conjugated to 2′‐deoxyuridine as photoinducible electron donor, and methyl viologen attached to the 2′‐position of uridine as electron acceptor. The Hq radical anion was identified in the time‐resolved measurements and strand cleavage products support its role as an intermediate charge carrier. Hence, the Hq–Hq pair significantly enhances the electron hopping capability of DNA compared to natural DNA bases over long distances while keeping the self‐assembly properties as the most attractive feature of DNA as a supramolecular architecture.     

A novel quantitative model of cell cycle progression based on cyclin-dependent kinases activity and population balances

Cell cycle regulates proliferative cell capacity under normal or pathologic conditions, and in general it governs all in vivo/in vitro cell growth and proliferation processes. Mathematical simulation by means of reliable and predictive models represents an important tool to interpret experiment results, to facilitate the definition of the optimal operating conditions for in vitro cultivation, or to predict the effect of a specific drug in normal/pathologic mammalian cells. Along these lines, a novel model of cell cycle progression is proposed in this work. Specifically, it is based on a population balance (PB) approach that allows one to quantitatively describe cell cycle progression through the different phases experienced by each cell of the entire population during its own life. The transition between two consecutive cell cycle phases is simulated by taking advantage of the biochemical kinetic model developed by Gérard and Goldbeter (2009) which involves cyclin-dependent kinases (CDKs) whose regulation is achieved through a variety of mechanisms that include association with cyclins and protein inhibitors, phosphorylation–dephosphorylation, and cyclin synthesis or degradation. This biochemical model properly describes the entire cell cycle of mammalian cells by maintaining a sufficient level of detail useful to identify check point for transition and to estimate phase duration required by PB. Specific examples are discussed to illustrate the ability of the proposed model to simulate the effect of drugs for in vitro trials of interest in oncology, regenerative medicine and tissue engineering.     

Multicomponent Molecular Orbital–Climbing Image–Nudged Elastic Band Method to Analyze Chemical Reactions Including Nuclear Quantum Effect

To analyze the H/D isotope effects on hydrogen transfer reactions in XHCHCHCHY?XCHCHCHYH (X, Y=O, NH, or CH₂) including the nuclear quantum effect of proton and deuteron, we propose a multicomponent molecular orbital‐climbing image‐nudged elastic band (MC_MO–CI–NEB) method. We obtain not only transition state structures but also minimum‐energy paths (MEPs) on the MC_MO effective potential energy surface by using MC_MO–CI–NEB method. We find that nuclear quantum effect affects not only stationary‐point geometries but also MEPs and electronic structures in the reactions. We clearly demonstrate the importance of including nuclear quantum effects for H/D isotope effect on rate constants (k_H/k_D).     

An Electron Dynamics Mechanism of Charge Separation in the Initial‐Stage Dynamics of Photoinduced Water Splitting in XMnWater (X=OH,OCaH) and Electron–Proton Acceptors

An electron dynamics mechanism of charge separation in the initial stage of excited‐state reactions of the class of X?Mn?OH₂???A${ \to }$ X?Mn?OH???HA (X=OH or OCaH; A=N‐methylformamidine, guanidine, imidazole, or ammonia cluster) is reported. The dynamic effect of calcium doping is also revealed. This study provides a novel factor to be considered in designing efficient systems for photoinduced water splitting.