Search results for "Tassi"

1982

Crown ethers derived from bicyclocalix[4]arenes as chromoionophores

2001

The synthesis of calix[4]arenes in which opposite phenolic units are connected by a poly(oxyethylene) bridge at the narrow rim and a 2,6-dimethylene-4-nitrophenol bridge at the wide rim is reported. For two derivatives with tetra- (4) and penta(oxyethylene) (5) bridges UV-Vis spectrophotometric studies were carried out in buffered solution in the presence of alkali metal ions. Their complexation was associated with changes in their UV-Vis spectra, especially with an increase of the absorption band at 450 nm. For 4 and 5 this was most intense in the presence of potassium and caesium ions, respectively, indicating that the calixarene with the shorter crown ether bridge is selective towards po…

The role of potassium and hydrogen ions in the Prussian Blue ⇆ Everitt's Salt process

1998

Cyclic voltammetry experiments have proved very useful in the knowledge and understanding of the role of the potassium and hydrogen ions during the Prussian Blue ⇄ Everitt's Salt process. While potassium ions act as a stoichiometric reactant, the hydrogen ions play a very important role in the kinetics of the electron-hopping process. The entropy change for the reaction PB ⇄ ES has proved to be dependent on the degree of crystallinity of the film, indicating that this entropy change is related to the fixation of inner counterions on the crystal structure of the films.

Electronic Perspective on the Electrochemistry of Prussian Blue Films

2009

The derivative of the voltabsommetric scans, together with previous nano-electrogravimetric and X-ray diffraction results, allow different electrochemical processes to be distinguished during the Prussian blue (PB) voltammetric scan. Potassium, proton, and hydrated proton counterions involved in PB electrochemistry are related here to the electrochemical reactions of specific Fe sites. Potassium counterions show two different sites for their insertion: one located in the crystalline framework and another in ferrocyanide vacancies. From the monitoring of electroactive Fe sites, the covalent-exchange model is suggested as one of the first approaches to explain the origin of the PB magnetic or…

Determination of tyrosine through a FIA-direct chemiluminescence procedure.

2003

A new FI-direct chemiluminescence method is proposed for the determination of tyrosine, based on the oxidation of the amino acid by K(3)Fe(CN)(6) in potassium hydroxide medium, at room temperature and enhanced by the presence of beta-cyclodextrin and formic acid. The dynamic range was linear over the range 1.0-10.0 mgl(-1). A large study of the influence of foreign compounds was performed, including amino acids; and, the method showed high selectivity. The reproducibility between days resulted in a rsd (in slope%) of 4.8 and the repeatability with a rsd (n=50, 10.0 mgl(-1)) of 3.1%, the LOD (s/n=3) was 50 mugl(-1) and sample throughput 98 h(-1).

Partialsynthese neuer Ergolinderivate aus Clavinalkoloiden, 5. Mitt. N-1- und N-6-mono- und disubstituierte Festuclavine

1985

Festuclavin (1), 6-Cyano-6-nor-1 (3), 6-Nor-1 (5) und 6-Allyl-6-nor-1 (7) lassen sich in flussigem Ammoniak mit Kalium und dem entsprechenden Iodid in ihre 1-Allyl- und 1-Propyl-Derivate uberfuhren. Die Darstellung von 7 aus 5 wird beschrieben. Partial Syntheses of New Ergoline Derivatives from Clavine Alkaloids, V: Festuclavines Mono- and Disubstituted at N-1 and N-6 Festuclavine (1), 6-cyano-6-nor-1 (3), 6-nor-1 (5) and 6-allyl-6-nor-1 (7) were converted to their 1-allyl- and 1-propyl derivatives with potassium and the corresponding iodide in ammonia. The preparation of 7 from 5 is described.

Ion transport through membranes: A computer experiment

1983

Abstract Gramicidin-A is a linear pentadecapeptide antibiotic, which forms transmembrane channels; these have a number of interesting conductance characteristics [1, 2 and Refs. therein], as for example high specific ion fluxes (a single channel carries about 10 7 sodium ions/sec at 25 °C, 1 M NaCl and 100 mV transmembrane d.d.p.) have a remarkable ion selectivity among the monovalent cations. The permeability ratios with respect to sodium were found to be in following order H + (150) > NH 4 + (8.9) > Cs + (5.8) > Rb + (5.5) > K + (3.9) > Na + (1.0) > Li + (0.33). The channel is impermeable to anions and to divalent cations and it exhibits saturation and maxima in conductance as a function …

Oxidative cyclization of aldehyde thiosemicarbazones induced by potassium ferricyanide and by tris(p-bromophenyl)amino hexachloroantimoniate. A joint…

2005

The oxidative ring closure reaction of some aryl-substituted thiosemicarbazones induced by "bona fide" one-electron abstracting agents was investigated, by means of both experimental and computational techniques. The corresponding 1,2,4-triazole derivatives were the only cyclization products observed. The occurrence of two slightly different mechanistic pathways for the reaction is discussed.

Synthesis of 4-amino-5-fluoropyrimidines and 5-amino-4-fluoropyrazoles from a β-fluoroenolate salt

2020

A synthesis of fluorinated pyrimidines under mild conditions from amidine hydrochlorides and the recently described potassium 2-cyano-2-fluoroethenolate was developed. A broad substrate scope was tested and mostly excellent yields were obtained. The synthesis of fluorinated aminopyrazoles from the same fluorinated precursor could be demonstrated but proceeded with lower efficiency.

Isobaric Vapor−Liquid Equilibrium for Ethanol + Water + Strontium Nitrate

1996

Isobaric vapor−liquid equilibrium for ethanol (1) + water (2) + potassium nitrate (3) at various concentrations of salt and with ethanol mole fractions from 0 to 0.642 has been measured at 100.0 kPa. The results were correlated by assuming that the salt was in ionic form and it was associated only with the water.