Water Dimer under Electric Fields: An Ab Initio Investigation up to Quantum Accuracy.

It is well-established that strong electric fields (EFs) can align water dipoles, partially order the H-bond network of liquid water, and induce water splitting and proton transfers. To illuminate the fundamental behavior of water under external EFs, we present the first benchmark, to the best of our knowledge, of DFT calculations of the water dimer exposed to intense EFs against coupled cluster calculations. The analyses of the vibrational Stark effect and electron density provide a consistent picture of the intermolecular charge transfer effects driven along the H-bond by the increasing applied field at all theory levels. However, our findings prove that at extreme field regimes (∼1-2 V/Å) DFT calculations significantly exaggerate by ∼10-30% the field-induced strengthening of the H-bond, both within the GGA, hybrid GGA, and hybrid meta-GGA approximations. Notably, a linear correlation emerges between the vibrational Stark effect on OH stretching and H-bond strengthening: a 1 kcal mol-1 increase corresponds to an 80 cm-1 red-shift in OH stretching frequency.

Experimental and computational study on morin and its complexes with Mg2+, Mn2+, Zn2+, and Al3+: Coordination and antioxidant properties.

Morin (MRN), an intriguing bioflavonol, has received increasing interest for its antioxidant properties, as have its metal complexes (Mz+-MRN). Understanding their antioxidant behavior is critical to assess their pharmaceutical, nutraceutical potential, and therapeutic impact in the design of advanced antioxidant drugs. To this end, knowing the speciation of different H+-MRN and Mz+-MRN is pivotal to understand and compare their antioxidant ability. In this work, the protonation constant values of MRN under physiological ionic strength and temperature conditions (I = 0.15 mol L-1 and t = 37 °C), determined by UV-vis spectrophotometric titrations, are introduced. Thus, a reliable speciation model on H+-MRN species in aqueous solution is presented, which exhibits five stable forms depending on pH, supplemented by quantum-mechanical calculations useful to determine the proton affinities of each functional group and corresponding deprotonation order. Furthermore, potentiometry and UV-vis spectrophotometry have been exploited to determine the thermodynamic interaction parameters of MRN with different metal cations (Mg2+, Mn2+, Zn2+, Al3+). The antioxidant ability of H+-MRN and Mz+-MRN has been evaluated by the 2,2'-diphenyl-1-benzopyran-4-one (DPPH) method, and the Zn2+-MRN system has proven to afford the most potent antioxidant effect. Ab initio molecular dynamics simulations of Mz+-MRN species at all possible chelation sites and under explicit water solvation allowed for the fine characterization not only of the metal chelation modalities of MRN in explicit water, but also of the role played by the local water environment around the metal cations. Those microscopic patterns reveal to be informative on the different antioxidant capabilities recorded experimentally.

New modes in non-invasive ventilation.

Non-invasive ventilation is useful to treat some forms of respiratory failure. Hence, the number of patients receiving this treatment is steadily increasing. Considerable conceptual and technical progress has been made in the last years by manufacturers concerning this technique. This includes new features committed to improve its effectiveness as well as patient-ventilator interactions. The goal of this review is to deal with latest advances in ventilatory modes and features available for non-invasive ventilation. We present a comprehensive analysis of new modes of ventilator assistance committed to treat respiratory failure (hybrid modes) and central and complex sleep apnea (adaptive servo ventilation), and of new modes of triggering and cycling (neurally adjusted ventilatory assist). Technical aspects, modes of operation and settings of these new features as well as an exhaustive review of published data, their benefits and limits, and the potential place of these devices in clinical practice, are discussed.