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41.
Piero Zanello Renato Seeber Bruno Crociani Marino Nicolini 《Transition Metal Chemistry》1980,5(1):45-48
Summary The electrochemical behaviour of a series of cationic platinum(II) isocyanide complexes has been studied in acetonitrile. All the tested compounds are oxidized at a platinum electrode via a two-electron process and reduced at a platinum or mercury electrode via two successive one-electron steps. The anodic step involves the formation of platinum(IV) complexes. The main reduction product formed in correspondence to the first cathodic process is a stable dimer platinum(I) containing bridging isocyanide ligands. Platinum(0) species are formed in the subsequent reduction step. 相似文献
42.
Tommaso Carofiglio Euro Solari Carlo Floriani Angiola Chiesi-Villa Corrado Rizzoli 《Polyhedron》1996,15(24):4435-4440
The UV-stabilizer 2-(2′-hydroxy-5′-methylphenyl)benzotriazole (Tinuvin P, LH) has been used as a monoanionic bidentate ligand for complexing oxocations. Displacement of acacH from [VO(acac)2] and [MoO2(acac)2] gave [*VO(acac)2*(μ-L)] (2) and [cis-O2Mo(acac)L] (3) respectively, as crystalline compounds. Their structure has been determined by an X-ray analysis showing the structural changes occurring upon coordination. The UV spectrum of Tinuvin P is significantly affected by complexation. 相似文献
43.
The kinetics of the process AuCl3(nu) + Cl−→ AuCl
4
−
+ nu (nu = one of a number of five-membered N-donor heterocycles covering a wide range of basicity, namely: oxazole, 2,4,5-trimethyloxazole,
thiazole, 5-methylthiazole, 4-methylthiazole, 4,5-dimethylthiazole, 2,4-dimethylthiazole, 2,4,5-trimethylthiazole, imidazole
and 2-methylimidazole) have been studied in methanol at 25 °C. The reactions follow the usual two-term rate law, rate = (k
1 + k
2[Cl−])[complex], observed in a square-planar substitution associative-mechanism. The second-order rate constants, k
2, indicate that the discriminating ability of Au(III) in these complexes is good and markedly influenced by the nature of the leaving group. A linear-free-energy relationship,
logk
2 = 0.53pK
a
+ constant, is observed between the rate constant and the basicity of the leaving group for its replacement by chloride.
The results are compared with data from the literature regarding a series of complexes of the type AuCl3(py) (py = one of a number of pyridines) reacting with the Cl− anion under the same experimental conditions. The reactivity depends not only upon ligand basicity but also upon the nature
of the ligand in the order: pyridines> five-membered heterocycles. Steric factor due to the presence of a single methyl group
ortho to the sp2 nitrogen atom in the ring has no influence on the rate of substitution while, surprisingly, when there are two ortho methyl groups a remarkable steric retardation effect is observable. The results are discussed in terms of reaction-profile
in the associative-substitution reaction and bonding interactions in the ground and transition states. 相似文献
44.
Bossée A Afonso C Fournier F Tasseau O Pepe C Bellier B Tabet JC 《Journal of mass spectrometry : JMS》2004,39(8):903-912
Peptide metallation with Cu2+ was explored in the negative ESI mode using an ion trap mass spectrometer. Under these conditions, the [(M-3H) + CuII]- species formed were investigated under low-energy collision-induced dissociation conditions. MS2 experiments indicate a very different behavior of CuII metallated complexes compared with [M-H]- species. CuII induces an easy loss of CO2 and specific side-chain cleavages (by radical losses) at the C-terminal residue, as observed previously by prompt 'in source' dissociation experiments. The loss of CO2 yields an unstable carbylide that leads to further dissociations involving the migration of a proton or a hydrogen radical (through the reduction of CuII). Multistage MS3 experiments were carried out to rationalize this behavior. Fragmentation pathways are proposed in order to explain the product ions observed. The side-chain radical loss at the C-terminus was demonstrated to be a consecutive process. Finally, evidence is provided that the specific side-chain cleavages can be used for the differentiation of Leu/Ile and Gln/Lys residues when they are located at the C-terminus. The existence of a zwitterionic form in the case of the anionic YGGFK-CuII complex is proposed. 相似文献
45.
Pozzoli L Bolzacchini E Van Dingenen R Hjiorth J Dentener F Perrone G Rindone B Librando V 《Annali di chimica》2003,93(4):447-456
The model BAGS (Boxmodel for Aerosol and Gasphase Simulations) has been developed. It is composed of two major modules: the first one describes the system of the chemical reactions in the gaseous phase, the second one calculates the aerosol chemical composition and the dimensional distribution of the particles. The boxmodel has been developed with the introduction of new chemical and physical processes, not previously included, in particular the formation of Secondary Organic Aerosol. The other implemented processes are a module for the dynamic of the particle population, nucleation, coagulation and dry deposition. The last phase of the work has been a check of the BAGS capabilities by a series of tests, that have permitted to compare it with other models (MAPS and MADM). The tests in particular have concerned the aerosol water content prediction, the photochemistry, the condensation of the inorganic compounds and the formation of Secondary Organic Aerosol. 相似文献
46.
Hydroboration of β-acetylenic alcohols followed by NaOH/H2O2 oxidation leads to hemiacetals of γ-aldols which are easily dehydrated to 2,3-dihydrofuran compounds. The reaction gives good yields with hindered alcohols and its stereochemistry may be controlled during the organometallic synthesis of the starting alcohol. 相似文献
47.
A large‐scale synthetic route to a variety of phosphaformamidines and phosphaformamidinates, a type of derivative that was not accessible by the methods previously known for preparing phosphaamidines and phosphaamidinates, is reported. Thermally stable ethyl N‐arylformimidates 1 (ArN?CH(OEt), Ar=2,4,6‐(Me)3Ph or 2,6‐(iPr)2Ph) readily reacted with lithium dialkyl‐ and diarylphosphanides to afford the corresponding N‐aryl phosphaformamidines in 80 and 60 % yield, respectively, whereas with lithium (aryl)(silyl)phosphanide, the N‐aryl‐N‐silylphosphaformamidine (60 % yield) was obtained. Addition of primary lithium arylphosphanides to 1 followed by addition of a stoichiometric amount of nBuLi gave rise to the respective phosphaformamidinates (70–88 % yield). Methanolysis of the products afforded the N‐aryl‐N‐hydrogenophosphaformamidines (90–95 % yield). The solid‐state structure of one of the phosphaformamidinates is also presented. 相似文献
48.
Bernatkova M Dvorakova H Andrioletti B Kral V Bour P 《The journal of physical chemistry. A》2005,109(24):5518-5526
Eight meso-aryl calixphyrin derivatives were synthesized and their conformational equilibria and transitions studied with temperature-dependent NMR spectroscopy. On the basis of density functional computations, several conformer species could be identified and observed changes in chemical shifts explained. In some compounds, the aryl group rotation and porphyrin ring flipping could be monitored independently, as their NMR coalescence temperatures were well-separated. Calculated relative conformer energies, transition barriers, and isotropic shieldings agree well with the experimental data. In the meso-substituted porhyrins (calixphyrins) the sp3 carbon atoms perturb their pi-electron system and significantly modify the molecular shape and the flexibility. Even when the conjugation of the pi-electron system was destroyed by the nonplanarity, far-range electronic induction effects still exist and influence chemical shielding and molecular geometry. The aryl functional groups moderately modify the structure of the calixphyrin ring and thus can be used for fine-tuning of the mechanical and chemical properties of these compounds. 相似文献
49.
Summary The determination of both high and low fluorine concentrations in concentrated phosphoric acid is complicated by the reaction of hydrofluoric acid with phosphoric acid to form monofluorophosphoric acid (MFP), the formation being favoured at high concentrations of phosphoric acid. Neutralization to pH 6–8, a condition suitable for the determination of fluoride with the fluoride electrode, gives low recoveries, since only free hydrogen fluoride is converted into fluoride ion, while MFP is not. The rates of formation and dissociation of MFP were studied and thermodynamic and kinetic parameters were determined. MFP formed in concentrated phosphoric acid can be hydrolysed completely by treatment of the sample with dilute hydrochloric acid and boiling briefly under reflux. EDTA is added to mask any potentially interfering metal ions. The results obtained for concentrated phosphoric acid, after dilution and prehydrolysis, were satisfactory for all the fluorine levels examined.
Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980. 相似文献
Bestimmung geringer Fluorgehalte in konzentrierter Phosphorsäure mit Hilfe der Fluorid-Elektrode
Zusammenfassung Die Bestimmung hoher und niedriger Fluorkonzentrationen in konz. Phosphorsäure wird durch die Reaktion der Flußsäure mit der Phosphorsäure zu Monofluorphosphorsäure (MPF) behindert, die in konz. Phosphorsäure begünstigt wird. Neutralisierung zu pH 6–8, die für die Bestimmung von Fluorid mit der Fluoridelektrode förderlich ist, gibt zu niedrige Resultate, da nur freier Fluorwasserstoff zu Fluoridion dissoziiert, nicht aber MFP. Die Anteile der Bildung und Dissoziation von MFP wurden untersucht, die thermischen und kinetischen Parameter bestimmt. In konz. Phosphorsäure gebildete MFP kann durch Behandlung der Probe mit verdünnter Salzsäure und kurzes Kochen unter Rückfluß vollständig hydrolysiert werden. Um störende Metallionen zu maskieren wird EDTA zugesetzt. Die nach Verdünnen und Hydrolyse der konz. Phosphorsäure erhaltenen Ergebnisse waren für alle untersuchten Größenordnungen von Fluor befriedigend.
Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980. 相似文献
50.
Ursula E. Spichiger Rudolf Eugster E. Haase G. Rumpf Peter Gehrig Angela Schmid Bruno Rusterholz Wilhelm Simon 《Fresenius' Journal of Analytical Chemistry》1991,341(12):727-731
Summary The selectivity of a new magnesium ionophore (ETH 7025) induced in membranes of different compositions is experimentally studied in view of the ion activities in human serum. The required selectivity coefficient against calcium for the application of an ion-selective magnesium electrode to human serum is calculated for the worst case. Other critical parameters for the application of a liquid PVC-based ion-selective membrane to undiluted human serum discussed are: the sensor lifetime which is related to the lipophilicity of the carrier as well as the ruggedness of the membrane against interactions with components of the relatively lipophilic sample. 相似文献