Aromatic properties of 8-hydroxyquinoline and its metal complexes

Abstract Chelatoaromaticity (aromaticity of chelate complexes) has been recently recognized as an important property influencing the stability of chelate compounds. In this paper, aromaticity of various forms of 8-hydroxyquinoline (anion, neutral molecule, zwitterion and cation) as well as its chelate complexes with magnesium and aluminium ions are investigated. Aromatic properties of these compounds are analyzed using several aromaticity indices based on energetic, geometric, magnetic and electronic physical manifestations of this phenomenon. Results of performed calculations have shown different aromatic properties for the two rings (pyridine and benzene) occurring in the studied ligand. Aromaticity of these rings in metal complexes of 8-hydroxyquinoline is significantly higher than that in corresponding ligand anion. This means that during complexation the aromaticity of the ligand increases and the chelatoaromatic effect stabilizes the studied metal complexes. In contrast, metallocyclic rings of studied metal complexes have non-aromatic properties, and, consequently, the metallocyclic ring is not stabilized by chelatoaromaticity. We conclude that, in the complex, every 8-hydroxyquinoline unit and the metal ion are separated p-electronic systems. </jats:p

Subunit-Selective Interrogation of CO Recombination in Carbonmonoxy Hemoglobin by Isotope-Edited Time-Resolved Resonance Raman Spectroscopy

Hemoglobin (Hb) is an allosteric tetrameric protein made up of αβ heterodimers. The α and β chains are similar, but are chemically and structurally distinct. To investigate dynamical differences between the chains, we have prepared tetramers in which the chains are isotopically distinguishable, via reconstitution with 15N-heme. Ligand recombination and heme structural evolution, following HbCO dissociation, was monitored with chain selectivity by resonance Raman (RR) spectroscopy. For α but not for β chains, the frequency of the ν4 porphyrin breathing mode increased on the microsecond time scale. This increase is a manifestation of proximal tension in the Hb T-state, and its time course is parallel to the formation of T contacts, as determined previously by UVRR spectroscopy. Despite the localization of proximal constraint in the α chains, geminate recombination was found to be equally probable in the two chains, with yields of 39 ± 2%. We discuss the possibility that this equivalence is coincidental, in the sense that it arises from the evolutionary pressure for cooperativity, or that it reflects mechanical coupling across the αβ interface, evidence for which has emerged from UVRR studies of site mutants

Vibrational and quantum-chemical study of pH dependent molecular structures of (hydroxypyridin-4-yl-methyl)phosphonic acid

Abstract Vibrational study of pH dependent molecular structures of (hydroxypyridin-4-yl-methyl)phosphonic acid is discussed based on experimental data and quantum-chemical calculations. A cationic, a zwitteranionic as well as mono-and dianionic forms of the acid are considered in our work. Equilibrium geometries, harmonic vibrational frequencies were calculated for all species of (hydroxypyridin-4-yl-methyl)phosphonic acid deprotonated in different way by using DFT (B3PW91) with 6-31G(d,p) basis set. The computed properties are compared to the experimental values. Additionally, charge distributions and aromaticity index were calculated for species studied here by using generalized atomic polar tensor (GAPT) and harmonic oscillator model of aromaticity (HOMA), respectively

Diamond-like carbon coatings formed by ionic methods for potential use in hip joint endoprostheses : preliminary studies

Zastosowanie supertwardych powłok węglowych dla poprawy własności trybologicznych układu główka- panewka endoprotezy stawu biodrowego może znacznie wydłużyć okres pracy endoprotezy. Metody jonowe (IBSD, IBAD) [1, 2] umożliwiają formowanie złożonych powłok ochronnych o doskonałej adhezji do podłoża, a poprzez odpowiednią strukturę warstwową powłok formowanych metodami jonowymi można w istotny sposób zmniejszyć naprężenia mechaniczne układu powłoka-podłoże. Własności biochemiczne i mechaniczne powłok formowanych metodami jo nowymi silnie zależą od przebiegu słabo poznanych procesów fizycznych zachodzących w trakcie formowania powłok. Celem niniejszej pracy było określenie struktury dwuwarstwowych powłok DLC-SiC oraz DLC-TiC oraz wstępna ocena ich biozgodności w hodowlach makrofagów i fibroblastów. Wielowarstwowe powłoki formowano dwuwiązkową metodą IBAD na powierzchniach płaskich próbek wykonanych ze stali lub ze stopu Ti-AI-V. Strukturę warstwową uformowanych powłok badano metodą RBS. Odporność korozyjną uformowanych powłok oceniono jako dobrą, a stopień przeżywalności komórek hodowanych na powierzchni próbek był wysoki.Super-hard carbon coatings improve tribological properties o f the head/cup system in the hip joint prostheses, and essentially extend their working time. The ionic methods (IBSD, IBAD) [1, 2] allow obtaining complex protective coatings with perfect adhesion to the substrate. Mechanical stresses on the substrate-coating interface can be minimized by applying appropriate layer structures. Biochemical and mechanical properties of coatings formed by the ionic methods strongly depend on, not fully understood, physical processes taking place upon deposition. The objective of this work was to determine the structure of the double-layer DLC-SiC and DLC-TiC coatings and to assess their biocompatibility in the macrophag and fibroblast cultures. The multilayer coatings were formed by a dualbeam IBAD method on flat surfaces of samples of stainless steel or Ti-AI-V alloy, and their layer structure was investigated by the RBS method. The resistance to chemical corrosion turned out good and the survival rate o f cells cultured on the coated surfaces was high