Search results for "Constants"
showing 10 items of 150 documents
On the determination of the intramolecular potential energy surface of polyatomic molecules: Hydrogen sulfide and formaldehyde as an illustration
2009
International audience; We present here an approach for determining the Hamiltonian of polyatomic molecules that allows one to successfully solve the problem of potential energy surface (PES) determination via construction and diagonalization of a Hamiltonian matrix of large dimension. In the suggested approach, the Hamiltonian is very simple and can be used both for any "normal" polyatomic molecule and for any isotopic species of a molecule. Molecules with two to four equivalent X-Y bonds are considered, and for illustration of the efficiency of the suggested approach, numerical calculations are made for the three-atomic (hydrogen sulfide) and four-atomic (formaldehyde) molecules.
Monitoring temporal changes in the spatial patterns of a Mediterranean shrubland using Landsat TM images
2001
Summary The overall goal of this study is to understand the structure and function of a Mediterranean shrubland at landscape scale by means of satellite images and GIS. Specifically, to assess the sensitivity of several spatial statistics to characterise landscape pattern, measure fragmentation and quantify the change through time. We study the landscape structure of a Mediterranean shrubland located in the east part of Spain (Valencia) and the change in spatial patterns of different shrubs types from 1984 to 1994. To accomplish these objectives, we used 10 Landsat™ images from 1984 to 1994 (except 1988) to which a geometric correction and an atmospheric normalization was applied. In additi…
Assignment of complex species by affinity capillary electrophoresis: The case of Th(IV)‐desferrioxamine B
2020
International audience; The electrophoretic mobility change of desferrioxamine B (DFO) was monitored by UV absorption spectrophotometry upon increasing the thorium(IV) concentration in the background electrolyte at two acidities ([HClO4]Tot = 0.0316 and 0.0100 M). These data enabled to assess the speciation model and to determine the equilibrium constant of [Th(DFO)H2]3+ at fixed ionic strength (I = 0.1 M (H,Na)ClO4). Affinity capillary electrophoresis (ACE) turned out to be most helpful in identifying the complexed species by ascertaining its charge and protonation state. The assignment of the correct stoichiometry relied on the reliable estimation of the electrophoretic mobility by assumi…
Quantitative parameters for the sequestering capacity of polyacrilates towards alkaline earth metal ions
2002
The complex formation constants of polyacrylic (PAA) ligands (1.4</=logN</=2.4, N=number of monomer units) with calcium and magnesium ions were determined in different ionic media at different ionic strengths, 0</=I</=1 mol l(-1), at t=25 degrees C. Experimental pH-metric data in the presence of Ca(2+) or Mg(2+) were firstly analysed in terms of apparent protonation constants, logK(H*), using the "three parameter model" proposed by Hogfeldt; differences in logK(H*), determined in different ionic media, were interpreted in terms of complex species formation. The only species present in the system M-PAA (M=Ca(2+) or Mg(2+)) is ML(2): attempts to find species of different stoichiometry were un…
The solution behavior of dopamine in the presence of mono and divalent cations: A thermodynamic investigation in different experimental conditions
2021
The interactions of dopamine [2-(3,4-Dihydroxyphenyl)ethylamine, (Dop-)] with methylmercury(II) (CH3Hg+), magnesium(II), calcium(II), and tin(II) were studied in NaCl(aq) at different ionic strengths and temperatures. Different speciation models were obtained, mainly characterized by mononuclear species. Only for Sn2+ we observed the formation of binuclear complexes (M2L2 and M2LOH (charge omitted for simplicity)
Antibiotic as Ligand. Coordinating Behavior of the Cephalexin Towards Zn(II) and Cd(II) Ions
1987
The complex formation equilibria of Zn(II) and Cd(II) with cephalexin have been studied through potentiometric titrations. Experimental data were analyzed using the least squares computer program SUPERQUAD. The stability constants were 1g beta ZnCEX+ = 2.40, 1g beta Zn(CEX)(OH) = -4.54, 1g beta CdCEX+ = 2.18, and 1g beta Cd(CEX)(OH) = -5.18 (I = 0.1 M NaNO3), CEX complexes of formulae Zn(CEX)2(3)H2O and Cd(CEX)(OH)H2O have been synthesized and characterized by elemental analysis, IR spectra, conductivity measurements, and electronic and NMR spectra. The thermal behavior of the synthesized compounds were studied by TGA and DTA. We conclude that the metal ion interacts with the amido group of…
A simple helical macrocyclic polyazapyridinophane as a stereoselective receptor of biologically important dicarboxylates under physiological conditio…
2007
The interaction of a synthetic enantiopure azamacrocyclic receptor (L) with biologically important chiral dicarboxylates (A, 1-7) has been studied by means of potentiometric titrations in 0.15 M NaCl aqueous solution in a wide pH range. This macrocycle forms strong complexes of the type [HnLA](n-2) (with n = 0-5). As a general trend, the binding is much tighter at basic or neutral pH than in acidic medium. Interestingly, nonprotected excitatory amino acids (Asp and Glu) are strongly bound even at acidic pH. Regarding selectivity, the receptor showed stereoselective binding toward those substrates bearing an H-bonding donor at Calpha, being S-selective in most of the cases, except for glutam…
Imidazolate bridged Cu(II)-Cu(II) and Cu(II)-Zn(II) complexes of a terpyridinophane azamacrocycle: a solution and solid state study.
2007
The dinuclear Cu2+ and Zn2+ as well as the mixed Cu2+-Zn2+ complexes of a 5,5''-pentaazaterpyridinophane ligand (L) are able to incorporate imidazolate (Im-) as a bridging ligand. The crystal structure of [Cu(2)L(Im)(Br)(H2O)](CF(3)SO(3))(2).3H2O (1) shows one copper coordinated by the three pyridine nitrogens of the terpyridine unit, one nitrogen of the imidazolate bridge (Im-) and one bromide anion occupying the axial position of a distorted square pyramid. The second copper atom is coordinated by the remaining imidazolate nitrogen, the three secondary nitrogens at the centre of the polyamine bridge and one water molecule that occupies the axial position. Magnetic measurements have been p…
What is the form of muscimol from fly agaric mushroom (Amanita muscaria) in water? An insight from NMR experiment supported by molecular modeling.
2020
ARTYKUŁ Z BADAŃ SPECJALNYCH
Protein isotope effects in dihydrofolate reductase from Geobacillus stearothermophilus show entropic-enthalpic compensatory effects on the rate const…
2014
Catalysis by dihydrofolate reductase from the moderately thermophilic bacterium Geobacillus stearothermophilus (BsDHFR) was investigated by isotope substitution of the enzyme. The enzyme kinetic isotope effect for hydride transfer was close to unity at physiological temperatures but increased with decreasing temperatures to a value of 1.65 at 5 °C. This behavior is opposite to that observed for DHFR from Escherichia coli (EcDHFR), where the enzyme kinetic isotope effect increased slightly with increasing temperature. These experimental results were reproduced in the framework of variational transition-state theory that includes a dynamical recrossing coefficient that varies with the mass of…