Excited state tracking during the relaxation of coordination compounds

The ability to locate minima on electronic excited states (ESs) potential energy surfaces both in the case of bright and dark states is crucial for a full understanding of photochemical reactions. This task has become a standard practice for small- to medium-sized organic chromophores thanks to the constant developments in the field of computational photochemistry. However, this remains a very challenging effort when it comes to the optimization of ESs of transition metal complexes (TMCs), not only due to the presence of several electronic ESs close in energy, but also due to the complex nature of the ESs involved. In this article, we present a simple yet powerful method to follow an ES of interest during a structural optimization in the case of TMCs, based on the use of a compact hole-particle representation of the electronic transition, namely the natural transition orbitals (NTOs). State tracking using NTOs is unambiguously accomplished by computing the mono-electronic wave function overlap between consecutive steps of the optimization. Here, we demonstrate that this simple but robust procedure works not only in the case of the cytosine but also in the case of the ES optimization of a ruthenium nitrosyl complex which is very problematic with standard approaches. © 2019 The Authors. Journal of Computational Chemistry published by Wiley Periodicals, Inc.     

Homogeneous hydrogels made with acrylic acid,acrylamide and chemically functionalized carbon nanotubes

Carbon nanotubes (CNTs) chemically functionalized were used to synthesize a series of novel nanocomposite hydrogels by in situ polymerization with acrylic acid (AA) and acrylamide (AM). A novel strategy was developed to prepare these hydrogels. CNTs were functionalized following a three-step chemical procedure: (i) purified carbon nanotubes (CNTs_p) were partially surface oxidized to obtain CNTs with hydroxyl, carbonyl and carboxyl groups on their sidewalls (CNTs_oxi), (ii) CNTs_oxi were reacted with oxalyl chloride to obtain CNTs functionalized with acyl chloride groups (CNTs_OCl), and (iii) CNTs_OCl were reacted with acrylic acid (AA). The product, AA modified CNTs_OCl (CNTs_OCl-AA) was used to prepare the (CNTs_OCl-AA-AM) nanocomposite hydrogels, where anhydride groups were tethered to the surface of the CNTs_OCl-AA. The swelling process in water was evaluated as a consequence of the anhydride group hydrolysis, which broke some chemical links between CNTs_OCl-AA and crosslinked AA-AM network. Equilibrium-swelling values of all hydrogels increased as the content of AA increased and were larger for AA-AM hydrogels than for CNTs_OCl-AA-AM nanocomposite hydrogels. Young’s moduli of CNTs_OCl-AA-AM nanocomposite hydrogels prepared with 1 or 2?wt.% AA, reached larger values than those measured for AA-AM hydrogels. This tendency was reversed when the AA content was raised to 3?wt.%.     

Hierarchical Functionalized Polymeric‐Ceramic Coatings on Mg‐Ca Alloys for Biodegradable Implant Applications

Magnesium‐based implants present several advantages for clinical applications, in particular due to their biocompatibility and degradability. However, degradation products can affect negatively the cell activity. In this work, a combined coating strategy to control the implant degradation and cell regulation processes is evaluated, including plasma electrolytic oxidation (PEO) that produces a 13 µm‐thick Ca, P, and Si containing ceramic coating with surface porosity, and breath figures (BF) approach that produces a porous polymeric poly(ε‐caprolactone) surface. The degradation of PCL‐PEO‐coated Mg hierarchical scaffold can be tailored to promote cell adhesion and proliferation into the porous structure. As a result, cell culture can colonize the inner PEO‐ceramic coating structure where higher amount of bioelements are present. The Mg/PEO/PCL/BF scaffolds exhibit equally good or better premyoblast cell adhesion and proliferation compared with Ti CP control. The biological behavior of this new hierarchical functionalized scaffold can improve the implantation success in bone and cardiovascular clinical applications.     

Reversible Optical Writing and Data Storage in an Anthracene‐Loaded Metal–Organic Framework

Metal–organic frameworks (MOFs) enable the design of host–guest systems with specific properties. In this work, we show how the confinement of anthracene in a well‐chosen MOF host leads to reversible yellow‐to‐purple photoswitching of the fluorescence emission. This behavior has not been observed before for anthracene, either in pure form or adsorbed in other porous hosts. The photoresponse of the host–guest system is caused by the photodimerization of anthracene, which is greatly facilitated by the pore geometry, connectivity, and volume as well as the structural flexibility of the MOF host. The photoswitching behavior was used to fabricate photopatternable and erasable surfaces that, in combination with data encryption and decryption, hold promise in product authentication and secure communication applications.     

Role of reaction atmosphere in preparation of potassium tantalate through sol–gel method

Potassium tantalate (KT) thin films and powders of both K₂Ta₂O₆ (KT pyrochlore) and KTaO₃ (KT perovskite) structures were prepared by means of chemical solution deposition method using Si(111) with ZnO and MgO buffer layers as a substrate. The influence of reaction atmosphere on reaction pathway and phase composition for both KT powders, and KT thin films has been studied mainly by means of powder diffraction and infrared spectroscopy. When an oxygen flow instead of static air atmosphere has been used the process of pyrolysis in oxygen runs over much narrower temperature interval (200–300 °C), relatively to air atmosphere (200–600 °C) and almost no (in case of powders), or no (in case of thin films) pyrochlore intermediate phase has been detected in comparison with treatment in air, where the pyrochlore phase is stable at temperatures 500–600 °C (powders). KT perovskite phase starts to crystallize at temperatures 50° and 150 °C lower compared to air atmosphere in case of powders and thin films, respectively. Microstructure formed by near-columnar grains and small grains of equiaxed shape was observed in films treated in oxygen and air atmosphere, respectively.     

Divalent cations reduce the pH sensitivity of OmpF channel inducing the pK(a) shift of key acidic residues

In contrast to the highly-selective channels of neurophysiology employing mostly the exclusion mechanism, different factors account for the selectivity of large channels. Elucidation of these factors is essential for understanding the permeation mechanisms in ion channels and their regulation in vivo. The interaction between divalent cations and a protein channel, the bacterial porin OmpF, has been investigated paying attention to the channel selectivity and its dependence on the solution pH. Unlike the experiments performed in salts of monovalent cations, the channel is now practically insensitive to pH, being anion selective all over the pH range considered. Electrostatic calculations based on the available structural data suggest that the binding of divalent cations has two main effects: (i) the pK(a) values of key ionizable groups differ significantly from those of the isolated groups in solution and (ii) the cation binding has a decisive impact on the effective electric charge regulating the channel selectivity. A simple molecular model based on statistical thermodynamics provides additional qualitative explanations to the experimental findings that could also be useful for other related systems like synthetic nanopores, ion exchange membranes, and polyelectrolyte multilayers.     

The O((1)D) + H2 (X (1)Σ+, v, j) → OH(X (2)Π, v', j') + H((2)S) reaction at low collision energy: when a simple statistical description of the dynamics works

In this communication, we highlight that statistical approaches for chemical reactions describe reasonably well the low energy dynamics of the title process. Consequently, such methods prove to be valuable to compute rate constants from low to room temperatures. Results are compared with experiment and recent precise quantum wave packet calculations [J. Phys. Chem. A, 2009, 113, 5285].     

Studies on Immobilization and Partial Characterization of Lipases from Wheat Seeds (<Emphasis Type="Italic">Triticum aestivum</Emphasis>)

The objective of this study was to provide some features on immobilization and partial characterization of lipases from wheat seeds. The optimum pH and temperature were found to be 5.5 and 32–37 °C, respectively. The stability of the concentrated enzymatic extract to high temperatures (25, 35, 45, and 55 °C) showed that the incubation of the extract at 55 °C led to its complete inactivation. The concentrated enzymatic extract kept 90% of its hydrolytic and esterification activities until 70 and 40 days of storage at 4 °C, respectively. The extract presented higher hydrolytic specificity to substrates of medium and long chains and higher esterification affinity to fatty acids of short and medium chains and alcohols with two and three carbon atoms. After the immobilization process using activated coal and sodium alginate as supports, an enhancement of about threefold in lipase activity was observed. The development of the present work permitted us to point out some characteristics of lipases from wheat seeds necessary for the proposition of new future industrial applications for this important biocatalyst.