Why 1,2‑quinone derivatives are more stable than their 2,3‑analogues?

In this work, we have studied the relative stability of 1,2- and 2,3-quinones. While 1,2-quinones have a closed-shell singlet ground state, the ground state for the studied 2,3-isomers is open-shell singlet, except for 2,3-naphthaquinone that has a closed-shell singlet ground state. In all cases, 1,2-quinones are more stable than their 2,3-counterparts. We analyzed the reasons for the higher stability of the 1,2-isomers through energy decomposition analysis in the framework of Kohn–Sham molecular orbital theory. The results showed that we have to trace the origin of 1,2-quinones’ enhanced stability to the more efficient bonding in the π-electron system due to more favorable overlap between the SOMOπ of the ·C4n−2H2n–CH·· and ··CH–CO–CO· fragments in the 1,2-arrangement. Furthermore, whereas 1,2-quinones present a constant trend with their elongation for all analyzed properties (geometric, energetic, and electronic), 2,3-quinone derivatives present a substantial breaking in monotonicity.European Union in the framework of European Social Fund through the Warsaw University of Technology Development Programme. O.A. S., H. S. and T.M. K

Proteus sp. – an opportunistic bacterial pathogen – classification, swarming growth, clinical significance and virulence factors

The genus Proteus belongs to the Enterobacteriaceae family, where it is placed in the tribe Proteeae, together with the genera Morganella and Providencia. Currently, the genus Proteus consists of five species: P. mirabilis, P. vulgaris, P. penneri, P. hauseri and P. myxofaciens, as well as three unnamed Proteus genomospecies. The most defining characteristic of Proteus bacteria is a swarming phenomenon, a multicellular differentiation process of short rods to elongated swarmer cells. It allows population of bacteria to migrate on solid surface. Proteus bacteria inhabit the environment and are also present in the intestines of humans and animals. These microorganisms under favorable conditions cause a number of infections including urinary tract infections (UTIs), wound infections, meningitis in neonates or infants and rheumatoid arthritis. Therefore, Proteus is known as a bacterial opportunistic pathogen. It causes complicated UTIs with a higher frequency, compared to other uropathogens. Proteus infections are accompanied by a formation of urinary stones, containing struvite and carbonate apatite. The virulence of Proteus rods has been related to several factors including fimbriae, flagella, enzymes (urease - hydrolyzing urea to CO2 and NH3, proteases degrading antibodies, tissue matrix proteins and proteins of the complement system), iron acqusition systems and toxins: hemolysins, Proteus toxin agglutinin (Pta), as well as an endotoxin - lipopolysaccharide (LPS). Proteus rods form biofilm, particularly on the surface of urinary catheters, which can lead to serious consequences for patients. In this review we present factors involved in the regulation of swarming phenomenon, discuss the role of particular pathogenic features of Proteus spp., and characterize biofilm formation by these bacteria

(3+2)‐Cyclization Reactions of Unsaturated Phosphonites with Aldehydes and Thioketones

By exploiting the unique reactivity of ethynyl‐phosphonites we obtain novel P(V)‐containing five‐membered heterocycles via (3+2)‐cyclization reactions with aldehydes or cycloaliphatic thioketones in satisfactory to excellent yields. Whereas reactions with thioketones to yield 1,3‐thiaphospholes‐3‐oxides occur smoothly at room temperature with equimolar amounts of the starting materials in absence of any catalyst, the analogous conversions with aldehydes to generate 3‐oxides of 1,3‐oxaphospholes require addition of triethylamine as a base. We postulate a step‐wise (3+2)‐cyclization mechanism for the formation of the 1,3‐thiaphosphole ring based on DFT quantum chemical calculations. With this study, we introduce new cyclization reactions originating from unsaturated phosphonites as central synthetic building blocks to yield previously inaccessible stable phosphorus‐containing heterocycles with unexplored potential for the molecular sciences.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Alexander von Humboldt-Stiftung http://dx.doi.org/10.13039/100005156Peer Reviewe

Crystal structure of 3,6-bis­­(pyridin-2-yl)-1,4-di­hydro-1,2,4,5-tetra­zine

The structure of the title compound, C12H10N6, at 100 K has monoclinic (P21/n) symmetry. Crystals were obtained as a yellow solid by reduction of 3,6-bis­(pyridin-2-yl)-1,2,4,5-tetra­zine. The structure displays inter­molecular hydrogen bonding of the N—H⋯N type, ordering mol­ecules into infinite ribbons extending along the [100] direction.Funding for this research was provided by: Narodowe Centrum Nauki (grant No. 2015/19/B/ST4/01773); EFRD in Operational Programme Development of Eastern Poland 2007–2013, the Oxford Diffraction SuperNova DualSource diffractometer (award No. POPW.01.03.00-20-004/11)

Oxidation of 2-mercaptopyridine N-oxide upon iodine agent: structural and FT-IR studies on charge-assisted hydrogen bonds CAHB(+) and I…I halogen interactions in 2,2′-dithiobis(pyridine N-oxide) ionic cocrystal

2-Mercaptopyridine N-oxide (I) undergoes spontaneous dimerization to the disulfide form due to reaction with iodine acting as an oxidizing reagent. As a result, a di-N-oxide disulfide derivative of pyridine is obtained. During the process of crystallization, one of N-oxide groups undergoes protonation and a cation form of disulfide moiety cocrystallizes with I3 − counterion forming a salt structure. Therefore, in the crystalline state, the 2,2′-dithiobis(pyridine N-oxide) molecule exists in a not observed previously form of monocation. Interestingly, the protonated N-oxide group does not form hydrogen-bonded salt bridges (of the CAHB(±) type with I3 − anions) but prefers to be involved in intermolecular interactions with the unprotonated N-oxide group of the adjacent molecule This results in formation of intermolecular CAHB(+) hydrogen bridges finally linking molecules into infinite chains. The crystal structure is also stabilized by other various noncovalent interactions, including iodine...iodine and sulfur...iodine contacts

Comparison of Various Means of Evaluating Molecular Electrostatic Potentials for Noncovalent Interactions

The various heterodimers formed by a series of Lewis acids with NH3 as Lewis base are identified. Lewis acids include those that can form chalcogen (HSF and HSBr), pnicogen (H2PF and H2PBr), and tetrel (H3SiF and H3SiBr) bonds, as well as H‐bonds and halogen bonds. The molecular electrostatic potential (MEP) of each Lewis acid is considered in a number of ways. Pictorial versions show broad regions of positive and negative MEP, on surfaces that vary with respect to either the value of the chosen isopotential, or their distance from the nuclei. Specific points are identified where the MEP reaches a maximum on a particular isodensity surface (Vs,max). The locations and values of Vs,max were evaluated on different isodensity surfaces, and compared to the stabilities of the various equilibrium geometries. As the chosen isodensity is decreased, and the MEP maxima drift away from the molecule, some points maintain their angular positions with respect to the molecule, whereas others undergo a reorientation. The lowering isodensity also causes some of the maxima to disappear. In general, there is a fairly good correlation between the energetic ordering of the equilibrium structures and the values of Vs,max. A number of possible Lewis acid sites on the heteroaromatic imidazole ring were also considered and presents some cautions about application of Vs,max as the principal criterion for predicting equilibrium geometries. © 2017 Wiley Periodicals, Inc