Search results for "Constants"
showing 10 items of 150 documents
Speciation of trialkyltin(IV) cations in natural fluids
2004
The hydrolysis of (CH(3))(3)Sn(+), (C(2)H(5))(3)Sn(+) and (C(3)H(7))(3)Sn(+) has been studied in a Synthetic Seawater (SSW) ionic medium simulating the major composition of natural seawater, at different salinities (5 less than or equal to S less than or equal to 45), and at t = 25 degreesC. Interactions with anionic components of SSW, considered as single sea salt, are determined by means of a complex formation model. By potentiometric measurements (ISE-H(+) and ISE-F(-) electrodes), the model has been extended to also consider interactions of organotins with carbonate and fluoride ions, which are other important components of seawater. Literature and new values of hydrolysis constants in …
Binding of acrylic and sulphonic polyanions by open-chain polyammonium cations
2000
Abstract The interactions between some acrylic and sulphonic polyanions and some protonated amines (diamines NH 2 -(CH 2 ) x -NH 2 , x =2,…,10; linear tri-, tetra-, penta- and hexa-amines) were studied potentiometrically in aqueous solution, at 25°C. For both types of polyanions AL 2 H i (L − , monomer of polyanion, A, amine) species are formed, with i =1,…, n ( n =number of amino groups in the amine). The stability of these species is strictly dependent on the polyammonium cation charge, and fairly independent of the type of amine (in diamine species maximum stability is observed for x =4, 5). Acrylic and sulphonic polyanion complexes are considerably stronger than analogous species formed…
Photoinduced electron transfer in supramolecular complexes of a π-extended viologen with porphyrin monomer and dimer
2012
A π-extended viologen has been synthesized, forming supramolecular complexes with a freebase tetraphenylporphyrin (H2TPP) and the cofacial porphyrin dimer with an anthracene spacer [H4(DPA)] through π–π interaction in benzonitrile (PhCN). Formation of the H2TPP-BHV2+ supramolecular complex was probed by UV-vis and fluorescence spectra. The fluorescence of H2TPP was strongly quenched by electron transfer from the singlet excited state (1H2TPP*) to BHV2+ in the supramolecular complex. The transient absorption spectrum of the charge-separated (CS) state (H2TPP•+ and BHV•+) was successfully detected by the laser flash photolysis measurements of the H2TPP-BHV2+ supramolecular complex in PhCN. Th…
ChemInform Abstract: Ternary Complexes of Cimetidine and Phenobarbital with Cu(II) in Methanolic Solution.
1986
The formation constants of the binary complexes Cu(CM)2+ and Cu(CM) 2 2+ as well as those of the ternary complexes Cu(CM)L + and Cu(CM)2 L + (CM=Cimetidine=N-Cyano-N′-methyl-N″[(5-methyl-1H-imidazol-4-yl)methyltioethyl]-guanidine; HL=Phenobarbital=5-ethyl-5-phenyl-barbituric acid) have been determined in 0.1 and 1.0 mol dm−3 NaClO4 methanol solutions at 25±0.2°C. The values of logX, log βstat.., and Δ logK confirm the stability of the ternary complexes.
Electrochemical determination of the stability of complexes formed by proton-ionizable ligands of 3,5-disubstituted 1H-pyrazole with phenethylamine
1999
The application of two extreme models for diffusion in two-component systems to electrochemically determine equilibrium constants is discussed. The application of cyclic voltammetric, diferential pulse and rotating-disc electrode voltammetric data to elucidate the stoichiometry and formation constant of complex species by applying a generalization of the molar-ratio method is described. Molar-ratio experiments permit the distinction between the limiting diffusive regimes. The values of the equilibrium stability constants for complexation of phenethylamine and phenethylammonium ions by a 26-membered dioxotetraester crown of 3,5-disubstituted 1H-pyrazole as free ligand 1[L] and as dipyrazolat…
Ternary complexes of cimetidine and phenobarbital with Cu(II) in methanolic solution
1986
The formation constants of the binary complexes Cu(CM)2+ and Cu(CM) 2 2+ as well as those of the ternary complexes Cu(CM)L + and Cu(CM)2 L + (CM=Cimetidine=N-Cyano-N′-methyl-N″[(5-methyl-1H-imidazol-4-yl)methyltioethyl]-guanidine; HL=Phenobarbital=5-ethyl-5-phenyl-barbituric acid) have been determined in 0.1 and 1.0 mol dm−3 NaClO4 methanol solutions at 25±0.2°C. The values of logX, log βstat.., and Δ logK confirm the stability of the ternary complexes.
Inf-sup conditions on convex cones and applications to limit load analysis
2019
The paper is devoted to a family of specific inf–sup conditions generated by tensor-valued functions on convex cones. First, we discuss the validity of such conditions and estimate the value of the respective constant. Then, the results are used to derive estimates of the distance to dual cones, which are required in the analysis of limit loads of perfectly plastic structures. The equivalence between the static and kinematic approaches to limit analysis is proven and computable majorants of the limit load are derived. Particular interest is paid to the Drucker–Prager yield criterion. The last section exposes a collection of numerical examples including basic geotechnical stability problems.…
Poincaré Type Inequalities for Vector Functions with Zero Mean Normal Traces on the Boundary and Applications to Interpolation Methods
2019
We consider inequalities of the Poincaré–Steklov type for subspaces of H1 -functions defined in a bounded domain Ω∈Rd with Lipschitz boundary ∂Ω . For scalar valued functions, the subspaces are defined by zero mean condition on ∂Ω or on a part of ∂Ω having positive d−1 measure. For vector valued functions, zero mean conditions are applied to normal components on plane faces of ∂Ω (or to averaged normal components on curvilinear faces). We find explicit and simply computable bounds of constants in the respective Poincaré type inequalities for domains typically used in finite element methods (triangles, quadrilaterals, tetrahedrons, prisms, pyramids, and domains composed of them). The second …
Complex-forming properties of peat humic acids from a raised bog profiles
2013
Abstract Humic substances (HS) belong to the most powerful complex-forming agents, significantly affecting major and trace element speciation in natural environment. Several authors have focused on humic–metal interactions, using differing methods and comparing humic substances on different sources. However, the intrinsic differences among the HS of different origin and the impact of humification degree on the complex formation between humic substances and metals have not received the necessary attention until now. The aim of this study is to determine the Cu(II) complexing capacity and stability constants of Cu(II) complexes of humic acids (HA) isolated from two well-characterized raised b…
Interplay of acidity and ionic liquid structure on the outcome of a heterocyclic rearrangement reaction
2021
The study of suitable probe reactions is a powerful tool to investigate the properties of nonconventional solvents such ionic liquids (ILs). In particular, we studied the acid-catalyzed mononuclear rearrangement of heterocycles (MHR) of the Z-phenylhydrazone of 5-amino-3-benzoyl-1,2,4-oxadiazole into the relevant 1,2,3-triazole, in solution of ILs by means of kinetic measurements. We chose as solvents six ILs differing both in the cation and anion, in the presence of five carboxylic and sulfonic acids as catalysts. For a useful comparison, the reaction was also performed in 1,4-dioxane and methanol. In general, the reaction occurs faster in ILs, compared to conventional solvents, according …