Amperometric Glucose Determination by Means of Glucose Oxidase Immobilized on a Cellulose Acetate Film: Dependence on the Immobilization Procedures

Glucose microelectrodes were prepared by immobilizing glucose oxidase onto a cellulose acetate film coating a platinum wire. Hexamethylenediamine (HMDA) and Glutaraldehyde (GA) were employed as spacer and coupling agent, respectively. Sensitivities and linear response ranges were studied as a function of the relative amounts of HMDA and GA. The best sensitivity was found when HMDA and GA were 5% and 2.5% in aqueous solutions, respectively. Taking as a reference the functioning of this biosensor, the roles of HMDA and GA percentages appear to be opposed when the extension of the linear response range is considered. Indeed, an increase of one unit in HMDA percentage (from 5 to 6 %) induces an increase in the extension of the linear response range equal to that obtained with a decrease of one unit of GA percentage (from 2.5 to 1.5%).     

Aziridines—XVI: Etude des conformations privilegiees cycle aromatique-petit cycle dans les C-aryl aziridines N-non-substituees

The preferred conformation of phenyl-2 aziridine involves the phenyl ring nearly bisecting the plane of the small ring (maximum conjugation). As the steric hindrance due to substituents on the aromatic ring is more substantial, the aromatic ring moves towards a perpendical plane. Good agreement between experimental (IR and NMR) and theoretical studies of the syn-anti configurational equilibrium of NH in these compounds is demonstrated. The analysis of the total electronic populations clarifies an understanding of the variation of the charge transfer small ring?aromatic cycle as a function of the aromatic nucleus.     

Soliton dynamics in alternating trans-polyacetylene and in stacked systems

The influence of substitutional disorder, of random forces and of energy dissipation on solitons in alternating trans-polyacetylene using the Su-Schrieffer-Heeger Hamiltonian is discussed. Double ionization in polyene chains was also investigated. Further soliton dynamics within a full Pariser-Parr-Pople Hamiltonian for trans-polyacetylene are presented. The presence of conformational solitons in stacked systems is shown numerically in a polyformamide model system. Possible relations to DNA and carcinogenesis are briefly reviewed.     

Stereoselectivity and chiral recognition in copper(I) olefin complexes with a chiral diamine

Trigonal copper(I) complexes of the chiral bidentate ligand (1S,2S)-N,N'-Bis-(mesitylmethyl)-1,2-diphenyl-1,2-ethanediamine ((S,S)-1) have been prepared with hydrocarbon olefins, as well as with allylic alcohols and ethers. The stereochemistry of the complexes has been investigated by 1H NMR spectroscopy and by combined quantum mechanics and molecular mechanics (QM/MM) computational methods. The coordinated chiral nitrogen atoms can display equal (R, R) or opposite (R, S) configuration, the latter being disfavored if steric hindrance is present above and below the coordination plane. Although the complexes exist as rapidly equilibrated mixtures of stereoisomers, one of these is often dominant, and prochiral olefins are coordinated with high enantioface selection. In addition, the [(S,S)-1]-Cu+ fragment selectively recognizes the R enantiomer of secondary allylic alcohols and ethers, as confirmed by the X-ray crystal structure analysis of the adduct with (R)-1-buten-3-ol. The reasons for the observed selectivities have been elucidated, and lead to some implications which are consistent with the enantioselection observed in catalytic cyclopropanation reactions promoted by copper complexes of the same ligand.     

Studies on the V2O5?TiO2 system, V. Equilibrium pressures

The oxygen equilibrium pressures from pure V₂O₅ and co-precipitated V₂O₅–TiO₂ system were measured in the range of 200–450 °C. The behavior of the equilibrium pressure with changes of temperature of the samples with and without TiO₂ is attributed to Ti⁴⁺ interaction with the V₂O₅ lattice.

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V₂O₅ - V₂O₅–TiO₂ 200–450°C. TiO₂ Ti⁺⁴ V₂O₅.

     

Double resonance observation of the (2ν3, E) state in methane

By using the double resonance technique we have observed the infrared inactive (2ν₃, E) level in methane. The experimental value of the vibrational energy (6043.8 cm^?1) is in good agreement with recent calculations based on the “local mode” model.     

Sodium ibuprofen dihydrate and anhydrous

(R,S)-(±)-ibuprofen sodium salt (racemate) dihydrate (SID) was dehydrated and the physicochemical properties of SID and the anhydrous forms (SIA) were compared by different analytical techniques (scanning electron microscopy, helium pychnometry, differential scanning calorimetry, X-ray powder diffractometry). The dehydration of SID, followed by thermogravimetry in isothermal conditions, allowed to calculate the activation energy of the dehydration process and to predict the mechanism of dehydration. Dehydration occurred in one step and the activation energy was rather low, indicating the ease of water removal from the crystal. The mechanism of dehydration followed a three dimensional diffusion (Jander equation). Similarly to the dehydration, the hydration process was followed under isothermal conditions by exposing the anhydrous powder at 64% RH at different temperatures. The mechanism of hydration was governed by a two dimensional diffusion and the energy associated to the process was very low, indicating the ease of crystal hydration. The driving force for the hydration is higher than that for the dehydration. From a thermodynamic point of view this fact may explain why the hydrated form is more stable than the anhydrous one. Solubilities, determined at different temperatures in water and in phosphate buffer (pH 6.8), showed that SID is more soluble in water than SIA for temperatures higher than approximately 283 K. On the contrary, in phosphate buffer SIA is always more soluble than SID in the temperature range considered for the experiments. Drug release reflects the solubility in water and phosphate buffer previously reported.     

Alkaline Hydrolytic Pathway of the Antitumor Drug,Cyclophosphamide

Abstract

In an attempt to clarify the alkaline hydrolytic pathway of the antitumor agent, cyclophosphamide (CP), the time course of its degradation was monitored by ³¹P NMR in 0.5 M KOH solution. After 16 hr at 25°C. 70% of CP is hydrolyzed (t_½ 9 hr) leading to a mixture of 8 phosphorated compounds. among them only 4 represented more than 5% of the initial CP. The chemical shifts and the intensities of these compounds were as follows: 1 1 .1 ppm. 30% of the initial CP (compound 1); 9.5 ppm, 12% (compound 2); 6.4 ppm, 9% (unknown) and 4.8 ppm, 9% (compound 3). The structures of compounds 1–3 were identified by NMR (13C and IH) and mass spectrometry after their isolation. The major degradation compound formed, the nine-membered ring compound I, was also observed during CP hydrolysis at neutral or moderately acid pHsill and was detected in urine of patients treated with CP[2] Compounds 2 and 3 were also formed during the hydrolysis of compound I in 0.5 M KOH solution. Based on the formation in time of the 31P NMR signals in KOH solutions of CP and compound I, the following scheme was established for the major degradation alkaline pathway of CP.     

Alkaline Hydrolysis of the Cytostatic Drug,Ifosfamide, and its N-Dechloroethylated Metabolites

Abstract

I fosfamide (IF) is an alkylating antitumor agent used in the treatment of solid tumors. Up to 50% of IF administered to patients undergoes an oxidative N-dealkylation reaction resulting in the loss or one, other or both chloroethyl side chain(s) to produce 2- or 3-dechloioethylIF (ZDCIF, 3DCIF) or 2,3-didechloroethyllF (DDCIF). The hydrolytic pathway of these four oxazaphosphorines has been studied earlier but only at acidic and neutral pHs^[l] In the present work, we monitored their time courses of hydrolysis at basic pHs using phosphorus-3 1 NMR. The structures of the compounds formed were determined by NMR (13C and 1H) and mass spectrometry. The results are reported in the following scheme.