163 research outputs found
Groupe de recherche Reber : Département de chimie, Université de Montréal
Ce rapport présente les membres du groupe de 1991 à 2023
Metal-ligand bonding in six-coordinate d-block complexes probed by luminescence spectroscopy at variable pressure
Luminescence spectra measured at variable pressure can reveal unique insight
on ground- and emitting state properties of transition metal compounds. This chapter
summarizes illustrative results for chromium(III) complexes with the d3 electron
configuration and oxo complexes of rhenium(V) and molybdenum(IV) with the d2
configuration. Their luminescence transitions only involve electronic configuration
changes within the t2 (O point group) molecular orbitals, leading to narrow spin-flip bands
and broad bands with vibronic structure for the chromium(III) and metal-oxo complexes,
respectively
On the spectrum of hypergraphs
Here we study the spectral properties of an underlying weighted graph of a
non-uniform hypergraph by introducing different connectivity matrices, such as
adjacency, Laplacian and normalized Laplacian matrices. We show that different
structural properties of a hypergrpah, can be well studied using spectral
properties of these matrices. Connectivity of a hypergraph is also investigated
by the eigenvalues of these operators. Spectral radii of the same are bounded
by the degrees of a hypergraph. The diameter of a hypergraph is also bounded by
the eigenvalues of its connectivity matrices. We characterize different
properties of a regular hypergraph characterized by the spectrum. Strong
(vertex) chromatic number of a hypergraph is bounded by the eigenvalues.
Cheeger constant on a hypergraph is defined and we show that it can be bounded
by the smallest nontrivial eigenvalues of Laplacian matrix and normalized
Laplacian matrix, respectively, of a connected hypergraph. We also show an
approach to study random walk on a (non-uniform) hypergraph that can be
performed by analyzing the spectrum of transition probability operator which is
defined on that hypergraph. Ricci curvature on hypergraphs is introduced in two
different ways. We show that if the Laplace operator, , on a hypergraph
satisfies a curvature-dimension type inequality
with and then any non-zero eigenvalue of can be bounded below by . Eigenvalues of a normalized Laplacian operator defined on a connected
hypergraph can be bounded by the Ollivier's Ricci curvature of the hypergraph
Bulk or surface grafted silylated Ru(ii) complexes on silica as luminescent nanomaterials
A series of Ru(II) complexes with monosilylated-dipyridine ligand have been synthesized and fully characterized and were then covalently attached to silica nanoparticles. Two types of hybrids were obtained depending on the experimental procedure. In the first approach, metal complexes were incorporated inside the silica nanoparticles leaving a free hydroxylated silica surface for further functionalization. These silica based nanohybrids are similar to the well known nanoparticles encapsulating [Ru(bpy)3]2+ complexes preventing the release of the dye when used in aqueous or organic solutions. Size and luminescence properties vary throughout the series of metal complexes. The second approach leads to ruthenium(II) complexes covalently attached to the silica nanoparticle surface via hydrolysis and condensation of the ethoxysilyl group with silanol sites of Ludox type silica nanoparticles. This leads to the grafting of a monolayer for complexes with the monoethoxysilyl dipyridine ligand. In contrast, the complexes with triethoxysilyl ligands can lead to small amounts of oligomers, but their quantity is limited by the sterical constraints imposed by the molecular structure. The size of the hybrids depends on the starting particles. 29Si and 13C solid state NMR are used to characterize silica surface properties whereas TEM and SEM confirm nanosize and morphology of the hybrids. The complexes and the nanohybrids are luminescent, with variations for ruthenium(II) complexes that are covalently incorporated or grafted on the silica surfac
Gene Expression during Survival of Escherichia coli O157:H7 in Soil and Water
The in vitro survival of Escherichia coli O157:H7 at 15°C
under two experimental conditions (sterile soil and sterile natural water) was examined. DNA microarrays of the entire set of E. coli O157:H7 genes were used to measure the genomic expression patterns after 14 days. Although the populations declined, some E. coli O157:H7 cells survived in sterile stream water up to 234 days and in sterile soil for up to 179 days. Cells incubated in soil microcosms for 14 days expressed genes for antibiotic resistance, biosynthesis, DNA replication and modification, metabolism, phages, transposons, plasmids, pathogenesis and virulence, antibiotic resistance, ribosomal proteins, the stress response, transcription, translation, and transport and binding proteins at significantly higher levels than cells grown in Luria broth. These results suggest that E. coli O157:H7 may develop a different phenotype during transport through the environment. Furthermore, this pathogen may become more resistant to antibiotics making subsequent infections more difficult to treat
Unconventional field induced phases in a quantum magnet formed by free radical tetramers
We report experimental and theoretical studies on the magnetic and
thermodynamic properties of NIT-2Py, a free radical-based organic magnet. From
magnetization and specific heat measurements we establish the temperature
versus magnetic field phase diagram which includes two Bose-Einstein
condensates (BEC) and an infrequent half magnetization plateau. Calculations
based on density functional theory demonstrates that magnetically this system
can be mapped to a quasi-two-dimensional structure of weakly coupled tetramers.
Density matrix renormalization group calculations show the unusual
characteristics of the BECs where the spins forming the low-field condensate
are different than those participating in the high-field one.Comment: 12 pages, 12 figure
LGM glaciations in the northeastern Anatolian mountains: New insights
Barhal Valley belongs to the Çoruh Valley System in the Kaçkar Mountains of northeastern Anatolia. This 13 km long valley is located to the south of the main weather divide and to the east of Mt. Kaçkar, with the highest peak of the mountain range being 3932 m. Today, source of an average yearly precipitation of 2000 mm of moisture is the Black Sea, situated approximately 40 km to the north of the study site. Glaciers of the Last Glacial Maximum (LGM) descended directly from Mt. Kaçkar and reached an altitude of ca. 1850 m a.s.l. (above sea level). In this study, we are exploring whether the position of Barhal Valley to the south of the main weather divide and its east–west orientation have an influence on the existence and expansion of paleoglaciers. Here, we present 32 new cosmogenic 36Cl dates on erratic boulders from the Çoruh Valley System. We reconstructed three geomorphologically well-contained glacier advances in the Barhal Valley, namely at 34.0 ± 2.3 ka, 22.2 ± 2.6 ka, and 18.3 ± 1.7 ka within the time window of the global LGM. Field evidence shows that the glacier of the 18.3 ± 1.7 ka advance disappeared rapidly and that by the latest time, at 15.6 ± 1.8 ka, the upper cirques were ice-free. No evidence for Lateglacial glacier fluctuations was found, and the Neoglacial activity is restricted to the cirques with rock glaciers. A range of 2700 to 3000 m for the Equilibrium Line Altitude (ELA) at the LGM was reported based on modeling of the glacial morphology. We determined that the most likely position of the LGM ELA in the Çoruh Valley System was at 2900 m a.s.l. We suggest an alternative moisture source to the direct transport from the Black Sea for the ice accumulation in the Eastern Black See Mountains. The shift of the Polar Front and of the Siberian High Pressure System to the south during the LGM resulted in the domination of easterly airflow to the Caucasus and Kaçkar Mountains with moisture from expanded lakes in central–western Siberia and from the enlarged Aral- and Caspian Seas
- …