Trends in bulk electron-structural features of early transition-metal carbides

A detailed and systematic density-functional theory (DFT) study of a series of early transition-metal carbides (TMC's) in the NaCl structure is presented. The focus is on the trends in the electronic structure and nature of bonding, which are essential for the understanding of the reactivity of TMC's. The employed approach is based on a thorough complementary analysis of the electron density differences, the density of states (DOS), the band structure, and the real-space wave functions to gain insight into the bonding of this class of materials and get a more detailed picture of it than previously achieved, as the trend study allows for a systematic identification of the bond character along the different bands. Our approach confirms the presence of both the well-known TM--C and TM--TM bonds and, more importantly, it shows the existence and significance of direct C--C bonds in all investigated TMC's, which are frequently neglected but have been recently identified in some cases [Solid State Commun. 121, 411 (2002); Phys. Rev. B 75, 235438 (2007)]. New information on the spatial extent of the bonds, their \textit{k}-space location within the band structure, and their importance for the bulk cohesion is provided. Trends in covalency and ionicity are presented. The resulting electron-structural trends are analyzed and discussed within a two-level model

Atomic and molecular adsorption on transition-metal carbide (111) surfaces from density-functional theory: A trend study of surface electronic factors

This study explores atomic and molecular adsorption on a number of early transition-metal carbides (TMC's) by means of density-functional theory calculations. Trend studies are conducted with respect to both period and group in the periodic table, choosing the substrates ScC, TiC, VC, ZrC, NbC, delta-MoC, TaC, and WC and the adsorbates H, B, C, N, O, F, NH, NH2, and NH3. Trends in adsorption strength are explained in terms of surface electronic factors, by correlating the calculated adsorption energy values with the calculated surface electronic structures. The results are rationalized with use of a concerted-coupling model (CCM), which has previously been applied succesfully to the description of adsorption on TiC(111) and TiN(111) surfaces [Solid State Commun. 141, 48 (2007)]. First, the clean TMC(111) surfaces are characterized by calculating surface energies, surface relaxations, Bader charges, and surface-localized densities of states (DOS's). Detailed comparisons between surface and bulk DOS's reveal the existence of transition-metal localized SR's (TMSR's) in the pseudogap and of several C-localized SR's (CSR's) in the upper valence band on all considered TMC(111) surfaces. Then, atomic and molecular adsorption energies, geometries, and charge transfers are presented. An analysis of the adsorbate-induced changes in surface DOS's reveals a presence of both adsorbate--TMSR and adsorbate--CSR's interactions, of varying strengths depending on the surface and the adsorbate. These variations are correlated to the variations in adsorption energies. The results are used to generalize the content and applications of the previously proposed CCM to this larger class of substrates and adsorbates. Implications for other classes of materials, for catalysis, and for other surface processes are discussed

Nature of Versatile Chemisorption on TiC(111) and TiN(111) Surfaces

Density-functional calculations on the polar TiX(111) (X = C, N) surfaces show (i) for clean surfaces, strong Ti3d-derived surface resonances (SR's) at the Fermi level and X2p-derived SR's deep in the upper valence band and (ii) for adatoms in periods 1-3, pyramidic trends in atomic adsorption energies, peaking at oxygen (9 eV). A concerted-coupling model, where adatom states couple to both kinds of SR's in a concerted way, describes the adsorption. The chemisorption versatility and the general nature of the model indicate ramifications and predictive abilities in, e.g., growth and catalysis.Comment: 5 pages, 4 figures, submitted to Physical Review Letters (2006

Nature of Chemisorption on Titanium Carbide and Nitride

Extensive density-functional calculations are performed to understand atomic chemisorption on the TiC(111) and TiN(111) surfaces, in particular the calculated pyramid-shaped trends in the adsorption energies for second- and third-period adatoms. Our previously proposed concerted-coupling model for chemisorption on TiC(111) is tested against new results for adsorption on TiN(111) and found to apply on this surface as well, thus reflecting both similarities and differences in electronic structure between the two compounds.Comment: 7 pages, 4 figures, conference proceeding presented at IWSP-2005 (Polanica Zdoj, Poland, 2005), submitted to Surf. Sci. (2005

Trends in Atomic Adsorption on Titanium Carbide and Nitride

Extensive density-functional calculations on atomic chemisorption of H, B, C, N, O, F, Al, Si, P, S, and Cl on the polar TiC(111) and TiN(111) yield similar adsorption trends for the two surfaces: (i) pyramid-like adsorption-energy trends along the adatom periods; (ii) strongest adsorption for O, C, N, S, and F; (iii) large adsorption variety; (iv) record-high adsorption energy for O (8.4-8.8 eV). However, a stronger adsorption on TiN is found for elements on the left of the periodic table and on TiC for elements on the right. The results support that a concerted-coupling model, proposed for chemisorption on TiC, applies also to TiN.Comment: 5 pages, 4 figures, 2 tables, conference proceeding presented at ECOSS-23 (Berlin, 2005), submitted to Surf. Sci. (2005

Protamine-like proteins have bactericidal activity. The first evidence in Mytilus galloprovincialis.

The major acid-soluble protein components of the mussel Mytilus galloprovincialis sperm chromatin consist of the protamine-like proteins PL-II, PL-III and PL-IV, an intermediate group of sperm nuclear basic proteins between histones and protamines. The aim of this study was to investigate the bactericidal activity of these proteins since, to date, there are reports on bactericidal activity of protamines and histones, but not on protamine-like proteins. We tested the bactericidal activity of these proteins against Gram-positive bacteria: Enterococcus faecalis and two different strains of Staphylococcus aureus, as well as Gram-negative bacteria: Proteus mirabilis, Proteus vulgaris, Pseudomonas aeruginosa, Salmonella typhmurium, Enterobacter aerogenes, Enterobacter cloacae, and Escherichia coli. Clinical isolates of the same bacterial species were also used to compare their sensitivity to these proteins. The results show that Mytilus galloprovincialis protamine-like proteins exhibited bactericidal activity against all bacterial strains tested with different minimum bactericidal concentration values, ranging from 15.7 to 250 µg/mL. Furthermore, these proteins were active against some bacterial strains tested that are resistant to conventional antibiotics. These proteins showed very low toxicity as judged by red blood cell lysis and viability MTT assays and seem to act both at the membrane level and within the bacterial cell. We also tested the bactericidal activity of the product obtained from an in vitro model of gastrointestinal digestion of protamine-like proteins on a Gram-positive and a Gram-negative strain, and obtained the same results with respect to undigested protamine-like proteins on the Gram-positive bacterium. These results provide the first evidence of bactericidal activity of protamine-like-proteins

Proarrhythmia assessment in treatment with hydroxychloroquine and azithromycin hospitalized elderly COVID-19 patients - our experience

The aim of our study was to characterize the repolarization disorders propensity induced by drug-drug interaction. In this observational retrospective study, we report our experience on all elderly patients with ascertained diagnosis of coronavirus disease 2019 through nasopharyngeal swab with real time-polymerase chain reaction at our Pugliese-Ciaccio hospital in Catanzaro, who received hydroxychloroquine (HCQ), with or without azithromycin (AZY). 33 hospitalized patients were examined. We calculated QT value, cQT, QT dispersion, and cQT dispersion and examined possible progression on the basal electrocardiogram (T0) and after the insertion of the drug (T1). The QT value is increased by T0 vs T1 (370±40.74 vs 420±36.91 ms; P=0.000), as well as the cQT value (408±25.40 vs 451.54±58.81; P=0.003), the QT dispersion (QTd: 36.36±14.53 vs 50.90±13.12 ms; P=0.000); the dispersion of cQTc (cQTd 46.27±18.72 vs 63.18±21.93 ms; P=0.001). The ΔQT was 37.44±44.09 while the ΔcQT was 32.01±56.47). The main determinant of QTc prolongation is the number of drug at risk of prolongation of the QT that could influence the ventricular repolarization phase. The use of HCQ in combination with AZY, in patients suffering from severe acute respiratory syndrome-related coronavirus-2, can favor the onset of serious side effects, even potentially fatal. Finally, the measures of QTd and cQTd confirmed additional electrocardiographic parameters useful in identifying patients being treated with drugs at risk of potential adverse arrhythmic events following drug interaction