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by J.E. Simão
265-269
DOI: DOI: 10.4152/pea.198803265
Influence of the water content in mixed water - acetonitrile solvents upon the kinetics and mechanisms of decomposition and stabilization reactions at the illuminated n - Ga As/TMPD interface.
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by S. Lingier, W.P. Gomes
85-104
DOI: DOI: 10.4152/pea.198802085
The competition between the anodic oxidation of the illuminated n-GaAs electrode and that of tetramethyl-p-phenylenediamine (TKPD) was studied by rotating ring-disk voltammetry as a function of the photo-current density, the TMPD concentration, the pH and the solvent composition, i.e. the water to acetonitrile ratio. From the results, it is concluded that decreasing the water content of the water-acetonitrile mixture influences the kinetics in the sense of improving the stability of the phctoelectrode, and that the subsequent electrochemical decomposition steps may involve either a free hole or a surface intermediate as the mobile surface species, depending on the composition of the electrolyte. These medium effects lead to a better insight into the structure of the decomposition intermediates of GaAs and into their chemical interactions with the solvent.
Polarographic Studies on Mixed Ligand Complexes of Cadmium -1 Methylimidazole - Oxalate System.
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by Gamal B. Mohamed, A. M. Ahmed
105-115
DOI: DOI: 10.4152/pea.198802105
The over-all formation constants of the mixed ligand complexes of 1-methylimidazole (l-Melm) and oxalate (Oxal) with cadmium (II) have been studied polarographically at constant ionic strength, p = 2.0, (NaN03) and pH 8 at 25 + 0.1°C. The reduction of the complexes at a dropping mercury electrode,DME, is reversible and diffusion controlled. The constants for three mixed complexes of Cd(II) are log = 4.0 for Cd(l-Melm)(Oxal), log p12 = 4.4
for Cd(l-Melm) (Oxal)2 and log p2± = 5.9 for Cd(l-Melm)2 (Oxal). The tendency of a ligand to add to a complex and to substitute another ligand was compared.
Novas Complexonas Derivadas de Poliazamacrociclos: Ácido 1, 4, 8, 12 - Tetra-Azaciclopentadecano - N, N', N", N'" – Tetracético.
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by Rita Delgado, J.J.R. Fraústo da Silva
117-133
DOI: DOI: 10.4152/pea.198802117
In the present paper we present the results of a study of the complexes of 1,4,8,12-tetra--azacyclopentadecane-N,N',N';N'''-tetracetic acid (cPENTA) which was synthesized in our laboratory. The stability constants of the complexes of Ca, Sr, Ba, Co, Ni, Cu and Zn and the thermodynamic functions for the formation of the complexes of Ni , Cu and Zn have been determined. The sequence of protonation of the ligand is discussed on the basis of the results of a NMR study and the structure of the complexes of nickel and cobalt is analysed in terms of their respective electronic spectra and of the calculated fractions of the ionic and covalent contributions of the enthalpy changes on formation of these complexes.
Electroreduction of Methyl Isocyanide at Thiomolybdato-Derived Centres: Evidence for an Active Role of Sulphur.
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by Sílvia S.P.R. Almeida, J.J.R. Fraústo da Silva, Rudolf Herrmann et al.
135-140
DOI: DOI: 10.4152/pea.198802135
Reaction of [MoS^][PPh^]^ with methyl isocyanide (CNMe) affords species formulated as [Mo0S,(SCNMe)0][PPh.] or [Mo„S,(CNMe)(CNH)(SCN)][PPh.] in which the isocyanide or the derived ligands undergo cathodic CN bond cleavage to give ammonia, methane and ethylene, in processes involving sulphur as a reductant of the substrate.
Recent Advances in Direct Potentiometry in Organic and Mixed Solvents
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by G. J. Kakabadse, M. Al-Aziz, N. F. N. Al-Yawer et al.
5-25
DOI: DOI: 10.4152/pea.198801005
The behaviour of ions in organic and mixed solvents is illustrated by a number of examples. Systematic study of the effect of solvent on potentials of cells with ion-selective electrodes led to the development by Kakabadse and co-workers of a new technique in direct potentiometry, viz. the ion isoconcentration technique (IICT). In IICT, concentration of solvent is varied and that of indicator ion is kept constant. Many simple mixtures show under ion isoconcentration conditions a systematic change of cell potential with variation in the concentration of organic solvent, providing a graphical method for the rapid determination of, (a) individual organic solvents in simple mixtures, and (b) residual water in organic solvents.
A laboratory prototype monitor for the continuous determination of ethanol in cider and sherry, using the fluoride isoconcentration technique (FICT), is described.
Electrochemical Behaviour of the Mesoinic Heterocycle: Anhidro l-Amino-5-Phenyl-2-Mercapto-l,3, 4-Triazolo-(3,2-c)-Quinazolin-4-ium
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by F. Martinez-Ortiz, J. Vera, M.A. Esteso
27-40
DOI: DOI: 10.4152/pea.198801027
An electrochemical study on the mesoionic heterocycle mentioned above is carried out, using dc polarography, cyclic voltammetry and controlled potential electrolysis . A reduction mechanism
with a consumption of four electrons in each polarographic wave is proposed. On the other hand, we detect a kinetic response of CE type caused by an equilibrium between hydrolysis products ot the heterocycle.
Temperature Effect on Polarogra-phic Behaviour of Co(II) and Zn(II) 2:1 Complexes with Paludrine
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by C. Sanz Box, C. Monleón Ombuena, F. Vicente Pedrós
41-50
DOI: DOI: 10.4152/pea.198801041
The polarographic reduction of Zn(II> and Co(II) complexes with paludrine has been studied in moderated acid media. The Zn(II) 2:1 complex shows two well defined waves. The Co(II) 2:1 complex shows only one wave. Arrhenius activation energies, obtained from diffusion currents of np, dp, aci , aca, KT and K-L- polarograms, show that all cathodic and anodic processes are controlled by diffusion. The mechanism of these processes is proposed.
The Effect of Adatoms on the Reversibility of some Redox Couples
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by Inês T.E. Fonseca, A.C. Marin
51-68
DOI: DOI: 10.4152/pea.198801051
Cyclic voltammetric studies were performed for six redox couples at a Pt electrode, in the absence and in the presence of Bi, Pb and Cd adatoms. Standard rate constants were evaluated for all the systems in the absence and in the presence of adatoms.
Whenever a catalytic effect was obtained the effect of coverage was studied in a quantitative way.It was found that the rate constant increases initially rapidly and then passes through a maximum or reaches a constant value, at coverages of the order of a monolayer. For all the systems the influence of the adatoms decreases in the order Bi > Pb > Cd.
Eléctrodo Sensível ao Anião 5,5-Dietilbarbiturato com Membrana de PVC sem Solução de Referência Interna com Sensor de Tetraoctilamónio em 2-Nitrofeniloctiléter
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by José L. F. C. Lima, M. Conceição B. S. M. Montenegro et al.
69-76
DOI: DOI: 10.4152/pea.198801069
Structure-Reactivity Relationships in Homogenous Electron Transfer Reactions
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by David B. Rorabacher
157-159
DOI: doi: 10.4152/pea.198703157
The Multi-Step Character of Electrode Reactions: Effects of Solvation, Complexation and Double-Layer Interactions
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by M. Sluyters-Rehbach, J. H. Sluyters
161-164
DOI: doi: 10.4152/pea.198703161
Membrane Electrodes of Herbicidal and Pharmaceutical Interest
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by J. D. R. Thomas
165-165
DOI: doi: 10.4152/pea.198703165
Influence of the Surface Structure of Metal Electrodes on Double Layer Parameters and the Reaction Kinetics
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by Antoinette Hamelin
166-166
DOI: doi: 10.4152/pea.198703166
by Jan Przyluski
167-169
DOI: doi: 10.4152/pea.198703167
Utilidade das Curvas de Histerese para a Determinação do Efeito da Temperatura nas Características de Resposta dos ESIs
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by M. T. S. D. Vasconcelos, A. A. S.C. Machado
171-173
DOI: doi: 10.4152/pea.198703171
Some Problems Related to the Reduction Charge in Potentiodynamic Studies of Passivating Films
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by S. R. Biaggio, N. Bocchi, C. V. D'Alkaine
175-178
DOI: doi: 10.4152/pea.198703175
Electrochemical Study of Isocyanide Derivatives of Ferrocene and of their Complexes with the {Cr(CO)5} Centre
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by T. EL-Shihi, F. Siglmuller, R. Herrmann et al.
179-185
DOI: doi: 10.4152/pea.198703179
Within our broad interest on the study of the redox and electronic (1) properties of coordination compounds by electrochemical methods, we embarked upon the investigation of the redox behaviour of series of ferrocene derivatives, FcX [where Fc stands for FeCn^-Cj-H) (n5-C H)]f with different types of (2) substituents (X); the latter may ligate an aromatic ring through, for instance, a sp or an unsaturated sp hybridized C atom, and some homo- and hetero-annular disubstituted ferrocenes have also been investigated. However, in this preliminary communication, we wish to report the results we have obtained with a type of substituents we are particularly interested from a coordination point of view: that with the isocyan functional group. In the ferrocene derivatives under study, CNR [J_; R=Fc (a), CH2FC (b)or CH(Men)Fc (c) where Men=(lR,2S,5R)-2-isopropyl-5-methylcyclohexyl], the isocyan group is prone to coordination to a metal centre and the derived ferrocenyl--isocyanide complexes [Cr(CO)^(CNR)] (2) can be prepared by reaction of the former with [Cr(CO) (thf)].
The Cathodic Cleavage of the 4-Nitrobenzyloxy-carbonyl Group from Amine Derivatives in Aprotic Conditions
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by H. L. S. Maia, M. J. Medeiros, M. I. Montenegro et al.
187-190
DOI: doi: 10.4152/pea.198703187
by A. M. Mota, M. L. Simões Gonçalves, M. M. Correia dos Santos
191-196
DOI: doi: 10.4152/pea.198703191