J. Galvez Alvarez

Use of topological descriptiors in chromatographic chiral separations

Abstract Studies of enantiomeric separations are reported, specifically the direct chromatographic separation of enantiomers using a chiral stationary phase by molecular topology. The results obtained show good correlation equations for the capacity factor, k ′, and the separation factor, α, for different set of compounds (hydantoins, aromatic α-amino acids and arylamides). Such equations may be useful for the selection of the optimum stationary and mobile phases for the separation of enantiomers. Futher, the correlation between topological descriptors and performance in chiral separations opens up a new approach to the design of chiral stationary phases.

Molecular topology and chromatographic retention parameters for benzodiazepines

Abstract The relationship between gas-liquid chromatographic (GLC) retention properties and R F values in thin-layer chromatography (TLC) with molecular connectivity indices, m X t , was investigated for a series of benzodiazepines using multiple correlation coefficients, standard errors of estimate, F -Snedecor function values and Students t -test as the criteria for best equation selection. Regression analyses show that the molecular connectivity model predicts the retention properties in GLC with the polar stationary phase OV-17 at 280°C and the R F values in TLC with the stationary phase silica gel. However, zero- or second-order connectivity indices alone are not sufficient; higher-order indices are shown to be necessary. The effect of the polarity of the mobile phases in TLC was also investigated.

Physico-chemical study of the radiopharmaceuticals 99mTc-DMSA, 99mTc-EDTA and 99mTc-DTPA interaction with plasmatic proteins

Abstract This report studies the binding rate of the radiopharmaceuticals 99m Tc-DTPA, 99m Tc-EDTA and 99m Tc-DMSA to plasmatic proteins. The proteins bind to the tested radiopharmaceuticals in the following sequence: 99m Tc-DTPA 99m Tc-DMSA(C 1 ) 99m Tc-EDTA 99m Tc-DMSA(C 2 ) where C 1 and C 2 represent two different Tc-DMSA complexes. The thermodynamic study suggests a quantitative relationship of radiopharmaceutical:protein = 1:1 and an almost nonexistent influence of the temperature, which means that the interacting forces in this process are relatively weak.

[99mTc]Ca-Phytate: Some colloidal characteristics related to the optimal preparation conditions

Abstract Some physico-chemical characteristics of the colloidal radiopharmaceutical [ 99 m Tc]Ca-phytate related to optimal preparation conditions have been studied. (1,2) It is demonstrated that the Ca 2+ -phytate stoichiometry is 6:1. Two different Ca-phytate colloids seem to be formed, mainly depending on the Ca 2+ :phytate molar ratio-one of low mycelar size for a 1:1 Ca 2+ :phytate molar ratio ( cmc ∗ = 5.10 −5 M ) , and another one, with a higher mycelar size for a 6:1 molar ratio (cmc = 8.10 −5 M). This last one it probably better for providing a good quality splenic uptake.

Stability of the radiopharmaceutical [99mTc]DMSA: Study of the ligand exchange reaction with [99Tc]EDTA

Abstract A kinetic study was made of the ligand exchange reaction between [ 99 m Tc]EDTA and DMSA. The results of this study indicate that this exchange reaction is closely related to temperature and pH. Kinetic and thermodynamic parameters demonstrate that both complexes—[ 99 m Tc]EDTA and [ 99 m Tc]DMSA—have a similar stability. Furthermore, the existence of an acid-basic catalysis for the global exchange reaction was established, and the catalytic parameters were calculated. These data were obtained by radiochromatography and visible spectrophotometry.

A Simple Algorithm for the Distinction of Reaction Mechanisms Based on the Measurement of Additive Properties

This study shows that, in a reacting system containing three compounds, previously identified, only one of them being a reactive, it is possible, through measures of global absorbance or any other additive property, to distinguish between different, very frequent reaction mechanisms, such as irreversible, reversible, consecutive, and simultaneous processes.

99mTc-tetracycline radiopharmaceutical: physical chemistry study related to the preparation and reaction products and thermodynamic stability.

Abstract The labelling of tetracycline hydrochloride with 99mTc at neutral pH, using Sn2+ as reducing agent, has been investigated by chromatography, using a 4:1:5 n-butanol: acetic acid:H2O mixture as developing agent, with Whatman paper No 3. In such conditions, reduced 99mTc remained at the origin, while labelled 99mTc migrates at R f ⋍ 0.6 . Radiochromatographic and u.v.-visible spectrophotometric results, demonstrated that the higher the tetracycline concentration the higher was the labelling of 99mTc to that ligand, obtaining a 50% labelling when the molar ratio of tetracycline: Sn2+ was approximately 20:1, independent of the Tc concentration level. The Tc oxidation state in the radiopharmaceutical is +4, deduced from iodimetric and radiometric techniques. Furthermore, it seems that time does not influence labelling, while pH does. The maximum labelling level occurs at physiological pH. The thermodynamic study performed with the radiopharmaceutical formation shows that the Tc-tetracycline complex has a 1:1 stoichiometry, thus a low stability constant (about 2 × 102).

Some aspects related to stability, critical concentrations and kinetics of flocculation of the calcium phytate colloid

Abstract As 99mTcCa phytate is an important radiopharmaceutical and its colloidal nature presents problems, we investigated some of them. This work describes the study of the colloidal behaviour of the calcium phytate colloid in terms of its formation, stability and kinetics of flocculation. The study of spontaneous, and centrifugation-induced flocculation allows the determination of two critical concentrations of sol flocculation. The titrations of calcium phytate colloid at different concentrations provide information on the colloidal formation conditions. Moreover, a study on flocculation kinetics was made by turbidity measurements.