Search results for "MOLECULE"
showing 10 items of 5162 documents
Watching the photo-oxidation of a single aromatic hydrocarbon molecule
2001
International audience; The photooxidation of single dye molecules (see scheme) can be followed by confocal fluorescence microscopy. The self-sensitized reaction with singlet oxygen leads to a suite of products, which may be differentiated spectrally. Tentative structures for certain photoproducts have been obtained from quantum-chemical calculations.
Isoreticular two-dimensional magnetic coordination polymers prepared through pre-synthetic ligand functionalization
2018
Chemical functionalization is a powerful approach to tailor the physical and chemical properties of two-dimensional (2D) materials, increase their processability and stability, tune their functionalities and, even, create new 2D materials. This is typically achieved through post-synthetic functionalization by anchoring molecules on the surface of an exfoliated 2D crystal, but it inevitably alters the long-range structural order of the material. Here we present a pre-synthetic approach that allows the isolation of crystalline, robust and magnetic functionalized monolayers of coordination polymers. A series of five isostructural layered magnetic coordination polymers based on Fe(ii) centres a…
Fluorescence excitation and emission spectroscopy on single MEH-PPV chains at low temperature.
2008
Fluorescence emission and excitation spectra of single MEH-PPV polymer molecules dispersed in thin PMMA films have been recorded at 1.2 and 20 K. We observe single as well as multichromophore emission in single chain emission spectra, whereby the relative fractions depend on the two different molecular weights (50 and 350 kDa) studied. The molecular weight also affects the distribution of peak emission maxima, which is monomodal (bimodal) for the low (high) molecular weight. The appearance of an additional "red" subpopulation for the high molecular weight sample is attributed to interactions of multiple chromophores from a sufficiently flexible single chain. The comparison of emission spect…
Direct monitoring of spin state in dinuclear iron(II) coordination compounds
2001
So far there has been no direct method to determine the spin state of molecules in dinuclear iron(II) compounds. The molecular fractions of high-spin (HS) and low-spin (LS) species have been deduced from magnetic susceptibility and zero-field Mossbauer spectroscopy data irrespective of whether they belong to LS–LS, LS–HS and HS–HS pairs. However, the distinction of pairs becomes possible if Mossbauer measurements are carried out in an external magnetic field. The proposed method opens new possibilities in the study of spin crossover phenomena in dinuclear compounds.
Anisotropic Effect after Stretching of the Spin-Crossover Compound [Fe(II)(2,6-bis-(benzimidazol-2′-yl)pyridine)2] (C1O4)2 in Polyvinylalcohol Polyme…
1999
Abstract [Fe(II)(2,6-bis-(benzimidazol-2′-yl)-pyridine)2](C1O4)2 diffused into a poly(vinyl)alcohol polymer matrix, exhibits an thermally induced spin-crossover. After stretching the matrix, the compound orients itself in the matrix. Polarised UV/VIS spectra measured parallel and perpendicular to the stretching direction allowed to calculate the distortion of the molecule in the matrix by means of semi-empirical PPP SCF-CI calculations.
Multiple interactions between molecular and supramolecular ordering
1999
We report studies of the interplay among processes of molecular conformational changes, spinodal demixing of the solution, and molecular crosslinking involved in the physical gelation of a biopolysaccharide-water system. Multiple interactions and kinetic competition among these processes were studied under largely different absolute and relative values of their individual rates by appropriate choices of the quenching temperature at constant polymer concentration. Quenching temperature strongly affects the rate of growth but not the final value of the fractal dimension of the gel. Kinetic competition plays a central role in determining the final conformation of individual molecules and the s…
Classification of Complex Molecules
2009
Algorithms for classification and taxonomy based on criteria, e.g., information entropy and its production are proposed. In molecular classification, the feasibility of replacing a given molecule (e.g, anaesthetic) by similar ones in the composition of a complex drug is studied. Some local anaesthetics currently in use are classified using characteristic chemical properties of different portions of their molecules. In taxonomy, the detailed comparison of the sequences (primary structures) of biomolecules, proteins or nucleic acids, allows the reconstruction of a molecular phylogenetic tree for some species, e.g. the 1918 influenza virus. The method is applied to the classifications of: (1) …
Consecutive Selective Adsorption of Pentamidine and Phosphate Biomolecules on a Self-Assembled Layer: Reversible Formation of a Chemically Selective…
1996
In situ ellipsometric film thickness measurements, FT-IR external reflectance spectroscopy, and potentiometric measurements indicated that the amphiphile pentamidine (PAM), a bisbenzamidine, associated by self-assembly with a preformed self-assembled monolayer of a mercaptoalkanoic acid on gold. The structural properties of PAM and the nature of the substrate were ideal for the formation of a densely packed monolayer. This process was fully reversible, as demonstrated by changing the pH of the surrounding medium. Thus, disassembly−reassembly occurred when the pH was cycled between 8.7 and 3. The bilayer structure, featuring a positively charged amidinium surface, was subsequently used for s…
Coordination behavior of cinoxacine: Synthesis and crystal structure of tris (cinoxacinate) cobaltate(II) of sodium hexahydrate (HCx = 1-ethyl-4(1H) …
1991
The synthesis, crystal, and molecular structure of Co(Cx)3Na6H2O are reported. The Cobalt(II) compound crystallizes in the trigonal system, space group R 3 with Z = 6, in a cell of dimensions a= 18.688(7) (A), c= 20.142(6) A. Least-squares refinement of 1331 reflections [I≥3σ(I)] gave a final R = 0.088 for all observed reflections. The structure consists of anionic monomeric units of (Co(Cx)3−) and sodium cations. Three Cinoxacinate ions are chelated through Oceto and Ocarbox atoms. The Co(II) ion positioned on the third axis is bonded to six oxygen atoms in a slightly distorted octahedral environment.
TaNi 2 .05Te 3 , eine Verbindung mit “aufgefüllter” TaFe 1+ x Te 3 ‐Struktur
1994
TaNi2.05Te3, a Novel Telluride with “Stuffed” TaFe1+xTe3 Structure The novel metal-rich layer compound TaNi2.05Te3 was synthesized from the elements. Its structure contains TaNi2Te3 layers which are interconnected by Ni atoms on partially occupied tetragonal-pyramidal sites located between the layers. The title compound and the related telluride TaFe1.14Te3 form a pair of compounds differing only in the occupation or nonoccupation of one 3d-material atom site. Therefore, the structure of TaNi2.05Te3, which is stabilized by interstial Ni atoms, can be regarded as a “stuffed” TaFe1.14Te3 type. Pairs of compounds with a similar structural relationship seem to be of general importance in early …