Study on the Kinetics of Non-isothermal Dehydration of Alkaline Earth Metal Selenites

The dehydration kinetics of crystallohydrates of beryllium, magnesium and calcium selenites were studied under non-isothermal conditions. The values of the activation energy of dehydration, the pre-exponential factor in Arrhenius equation and the change of entropy for the formation of the activated complex were calculated using the calculation procedure of Coats and Redfern. Thermal stability and activation energy of dehydration of the crystallohydrates were found to increase by the same order. The relationships observed were interpreted using Klopman’s generalized perturbation theory of chemical reactivity. The same theory was applied to explain the differences in the IR spectra of the selenite crystallohydrates studied.     

Eptastigmine,nicotinamide and nicotinic acid determination using an inhibition enzyme sensor; application to pharmaceutical analysis

An enzyme inhibition biosensor, developed in our laboratory and previously used for the analysis of compounds with anticholinesterase activity (e.g. physostigmine, neostigmine, pyridostigmine nicotine and organophosphorus compounds) has now been tested for the analysis of another recently synthesized cholinesterase inhibitor, i.e. eptastigmine. In addition nicotinic acid and nicotinamide, although displaying weaker inhibition properties, were also tested in pharmaceutical products using the same inhibition enzyme sensor. The biosensor consisted of a hydrogen peroxide amperometric electrode coupled to a functionalised nylon membrane chemically bonding both the enzymes butyrylcholinesterase and choline oxidase; a butyrylcholine standard solution in glycine buffer acted as substrate. The response of the system to all the inhibitors considered was characterised completely and the analysis of several pharmaceutical formulations containing nicotinamide or nicotinic acid was also performed.     

The CuII−CuI−Cu0(Hg) system in the presence of benzotriazole: Part II. A chronocoulometric investigation

Both the oxidation of Cu⁰ at dropping amalgam electrodes immersed in solutions of benzotriazole (BTA) and the reduction of Cu^II at a dropping mercury electrode from BTA solutions have been investigated by the single potential-step chronocoulometric technique. The dependence of the charge Q(t) flowing as a consequence of a given potential jump E_i→E_f upon the initial and final potentials E_i and E_f, as well as upon the time t elapsed from the instant of the potential jump provides direct evidence for the presence of a single adsorbed monolayer of a Cu^I compound on a mercury electrode immersed in a Cu^II solution containing BTA, at applied potentials positive to ≈?0.4 V/SCE. Analogous measurements carried out at dropping amalgam electrodes reveal the presence of a single adsorbed monolayer of a Cu^I compound, or else of an adsorbed multilayer, depending on the potential range investigated. The results of the chronocoulometric measurements are in agreement with those of the polarographic measurements of Part I.     

Harmonic oscillator tensors in contact transformation theory

The application of contact transformation theory to the perturbed harmonic oscillator is reexamined in the light of the harmonic oscillator tensors previously presented. It is found that the recasting of the formalism of this problem in terms of harmonic oscillator tensors results in great simplifications, most of which stem from the introduction of the additional algebraic quantum numbers (l, m). The order of magnitude of each fragment of the Hamiltonian is easily recognizable, and the diagonal and nondiagonal parts contained therein are readily identifiable. The determination of the contact transformation operator is reduced to a simple formula. First, an analysis is made for a single mode of vibration, and it is subsequently extended to a multimode case. The perturbed diatomic vibrator is presented as an example.     

Multistep mass spectrometry of heterocyclic amines in a quadrupole ion trap mass analyser

The fragmentation of heterocyclic amines (HAs) in an ion trap was studied by means of the infusion of methanolic solutions containing the compounds under assay, and using an atmospheric pressure chemical ionization (APCI) as ion source. The MS(n) spectra obtained for compounds included in the same family, either aminoimidazoazaarenes (AIAs) or carbolines, were compared in order to propose fragmentation pathways for each HA. Moreover, labelled AIAs were used to establish the mechanisms. The protonated molecule was always obtained, but subsequent fragmentation was different for both families. In the case of AIAs, major product ions came from the fragmentation of the aminoimidazole moiety, thus the base peak in MS(2) corresponded to the loss of the methyl group, and losses of C(2)NH(3) and CN(2)H(2) were also observed. Further fragmentation occurred in the heterocyclic rings, mainly with losses of HCN and CH(3)CN. For carbolines, the most important product ions came from the loss of ammonia, except for harman and norharman, the loss of a methyl group for methylated carbolines or the loss of diverse fragments from the heterocyclic rings. In some cases, ion-molecule reactions into the ion trap were observed. For instance, for AalphaC or MeAalphaC one ion originating from these reactions corresponded to the base peak.     

XAS investigation of tantalum and niobium in nanostructured TiO2 anatase

Sol-gel routes were used to prepare Ta 10 at% and Nb 5 at% and 10 at% doped titania nanosized powders. When fired between 410°C and 850°C the doped titania powders are in the anatase phase; further heating up to 1050°C is required to obtain the rutile phase. The presence of dopant atoms delays the rate of transformation as compared with pure titania powders. Doping also affects the rate of grain growth and increases the conductance response to gas. To better understand the role played by dopant atoms in inhibiting both phase transformation to rutile and grain growth, X-ray Absorption Spectroscopy measurements were performed at the L_III-L_I absorption edges of Ta and Nb K absorption edge. Analysis was restricted to the anatase phase because the transformation to rutile phase, obtained by firing at 1050°C, is accompanied by the formation of undesired Ta and Nb oxides (Ta₂O₅ and Nb₂TiO₇, respectively). Extended X-ray Absorption Fine Structure and X-ray Absorption Near-Edge Spectroscopy analysis results indicate that in nanostructured anatase both tantalum and niobium atoms substitute Ti cations with +5 valence state.     

Metal-cinnamic acids interactions. Part III. Synthesis and study of copper(II) complexes of 3, 4- and 3, 5-dimenthoxycinnamic acid

Summary Copper(II) complexes derived from substituted cinnamic acids 3, 4-dimethoxycinnamic acid (3, 4-DMCH) and 3, 5-dimethoxycinnamic acid (3, 5-DMCH), of the formula [Cu(3, 4-DMC)₂]·H₂O (1), [Cu(3, 5-DMC)₂]·H₂O (2) were prepared. The magnetic properties of the complexes suggest dimeric structures typical of copper(II) acetate monohydrate-like complexes. X-band e.s.r. spectra of polycrystalline samples at low temperature are typical of triplet state systems S=1. Their ability to catalyze the aerial oxidation of 3, 5-di-t-butylcatechol was measured spectrophotometrically at 30°C. The complexes are models for oxidases.     

Testing equality in lisp-like environments

A function is presented to test equality between lists. In any case the function requires at most one single traversal of the lists and behaves as follows:

1. if there are no cycles, it works as standardEQU AL functions;
2. if there are cycles, it does not give information about equality, but it can detect cycles, i.e. it signals which lists are cyclic.

A simplified version of the function is also considered which is always at least as efficient as standardEQU AL; it grants protection against cycles without signaling them. A coroutine organized version of the function is shown.     

2‐Chloro‐4,5‐dihydroimidazole,Part X. Revisiting route to N‐heteroarylimidazolidin‐2‐ones

The ureidation reactions of 2‐ and 4‐picoline N‐oxides with 2‐chloro‐4,5‐dihydroimidazole are described. A mechanism of novel thioureidation reaction of 4‐picoline N‐oxide with 2‐(4,5‐dihydro‐1H‐imidazol‐2‐ylthioxy)‐4,5‐dihydro‐1H‐imidazole is proposed. Structural assignment is confirmed by ¹H and ¹³C nmr as well as by X‐ray crystallography.