Authors:M. P. Sánchez -Sánchez, J. M. Salas -Peregrín, M. A. Romero -Molina, and J. Ruiz Sánchez
The following Zn(II), Cd(II), Hg(II) and Hg(I) complexes of 4-amino-1,6-dihydro-2-methylthio-5-nitroso-6-oxopyrimidine (MTH) have been prepared and their thermal behaviour studied by TG and DSC techniques: Zn(MT)2·3H2O, Cd(MT)·H2O. Cd(MTH)Cl2, Hg(MTH)Cl2 and Hg2(MT)(NO3). The dehydration and dehalogenation enthalpy values were calculated.
Authors:J. Ontiveros-Cuadras, A. Ruiz-Fernández, J. Sanchez-Cabeza, L. Wee-Kwong, and L. Pérez-Bernal
210Pb activities were analyzed in surface sediments from the Coatzacoalcos River (Gulf of Mexico) to evaluate its distribution
according to sediment grain size and in different geochemical compartments by using sequential extraction techniques. The
geochemical fractionation experiments provided compatible results: by using the Tessier’s method [<cite>1</cite>] more than 90% of the 210Pb activity in the samples was found the residual fraction (primary and secondary minerals) and the remaining (<10%) in the
iron and manganese oxides fraction of the sediments; whereas using the Huerta-Diaz and Morse method [<cite>2</cite>] the 210Pb content was found in comparative amounts in the reactive, the silicate, and the pyrite fractions (accounting together for
>80%), and the rest was found in the residual fraction. The grain size fractionation analyses showed that the 210Pb activities were mostly retained in the clay fraction, accounting up to 60–70% of the 210Pb total activity in the sediment sample and therefore, it is concluded that the separation of the clay fraction can be useful
to improve the analysis of low 210Pb content sediments for dating purposes.
Authors:P. Sánchez-Soto, M. Villacampa, J. Ginés, A. Ruiz-Conde, M. Avilés, and M. Arias
Several derivatives containing a new organic ring system, the tropane-6-spiro-5′-hydantoin structure (namely 8-alkyl-8-azabicyclo
[3.2.1.] octane-6-spiro-5′-imidazoline-2′,4′-diones) have been characterized by thermal (DSC and simultaneous DTA-TG-DTG)
and spectroscopic techniques (IR,1 H-NMR,13 C-NMR). X-ray powder diffraction and elemental analysis were applied for structural and molecular characterization. All the
compounds melt in the range 160–250°C and undergo decomposition with progressive mass loss after the solid-liquid thermal
transition with molecular degradation. It was found that tropane-6-spiro-5′-hydantoin derivatives with the hydantoin ring
in β position are thermally less stable than those containing this ring in α position.
Authors:P. Sánchez-Soto, J. Ginés, M. Arias, Cs. Novák, and A. Ruiz-Conde
This paper studies the effect of molecular mass on the melting temperature, enthalpy and entropy of hydroxy-terminated poly(ethylene oxide) (PEO). It aims to correlate the thermal behaviour of PEO polymers and their variation of molecular mass (MW). Samples ranging from 1500 to 200,000 isothermally treated at 373 K during 10 min, were investigated using DSC and Hot Stage Microscopy (HSM). On the basis of DSC and HSM results, melting temperatures were determined, and melting enthalpies and entropies were calculated. Considering the melting temperatures, it was found that the maximum or critical value of MW was found around 4000, and then these remain almost constant. This behaviour was interpreted assuming that lower MW fractions (MW<4000) crystallize in the form of extended chains and higher MW fractions (MW>4000), as folded chains. The melting enthalpies showed a scattering effect at least up to MW 35,000. It was difficult to obtain any relationship between melting enthalpies in J g–1 and MW. These variations seem to be of statistical nature. Corrected enthalpy data on a molar basis (kJ mol–1) exhibited a linear relationship with MW. Considering the solid—liquid equilibrium, the melting entropies (in kJ mol–1) were calculated. These values were more negative as compared with molar enthalpy increases. It was explained because the changes in melting temperatures are much smaller than those observed in the enthalpy values. Linear relationship between enthalpies andentropies as a function of MW was deduced.
Authors:J. Ginés, M. Arias, C. Novák, P. Sánchez-Soto, A. Ruiz-Conde, and E. Morillo
The formation of crystalline inclusion complex of triamterene with β-cyclodextrin (β-CD) was studied, evaluating the thermal
behaviour and dispersion state of this drug in different types of binary systems. Spray-drying and co-grinding (oscillating
mill) mixtures of triameterene with β-CD were prepared in 1∶1 molar ratio. The changes of crystalline properties of original
(untreated) triamterene, β-CD, and composites obtained by co-grinding and spray-drying were investigated in comparison with
those produced in simple physical mixtures. The thermal behaviour of the different samples was investigated using DTA. X-ray
diffraction was applied as a complementary technique. The results have been explained by formation of amorphous drug particles
on spray-drying samples and co-grinding or alternatively by means of a solid dispersion formation or a combination of these
two. A contamination effect by grinding media was also observed as increasing grinding time.
Authors:J. M. Ginés, M. J. Arias, A. M. Rabasco, C. Novák, A. Ruiz-Conde, and P. J. Sánchez-Soto
In the present study, the effect of the molecular weight and thermal treatments on commercial polyethylene glycols (PEG) samples used in the pharmaceutical processing technology, has been analyzed using DSC and HSM. The molecular weight of these polymers range from 1500 to 200000. Thermal investigations on the melting behavior of original PEG samples (as received from the manufacturer) showed only one single melting DSC endotherm effect before 373 K. This fact was associated to the presence of only one type of polymeric chain. Using standard conditions, PEG samples were solidified from the melt at 373 K, either by flash cooling (using liquid nitrogen and an ice bath) and by slow cooling, soaked and by slow cooling at room temperature. They were further studied by DSC. It was found that after cooling, PEG with molecular weight 1500 and 15000 showed DSC thermograms with a single endothermic peak. However, thermograms for PEG 4000 and 6000 produced a splitted melting endotherm. This fact was attributed to the presence of two types of chains, that are the folded and extended chains.
Authors:L. E. Garcia-Megias, E. Colacio-Rodriguez, A. Garcia-Rodriguez, J. Ruiz-Sanchez, and J. M. Salas-Peregrin
The thermal behaviour of 6-amino-5-formyluracil (HFU), 6-amino-1-methyl-5-formyluracil (1-MFU), 6-amino-3-methyl-5-formyluracil (3-HFU) and 6-amino-1,3-dimethyl-5-formyluracil (HDFU) is described. Only HDFU is shown to contain crystallization water. Dehydration and fusion enthalpy values have been calculated from the DSC curves. Likewise, the thermal behaviour of new complexes obtained by reaction between the above pyrimidine derivatives and Ni(II), Cu(II) and Pd(II) ions is reported.
Authors:E. T. Stepkowska, S. Yariv, J. L. Pérez-Rodríguez, A. Justo, A. Ruiz-Conde, and P. Sánchez-Soto
A dredged sludge was studied to investigate the influence of ageing and of pretreatment on its drying rate, water sorption/retention, thermal mass loss, XRD and microstructure (SEM).
Ageing caused change in particle thickness and specific surface, a gradual aggregation to form units of the size 10–50 μm, formation of macropores of similar size, unhomogeneity and fissures between aggregates and “super-aggregates”. Macropores were detectable by the initial drying rate especially at 45°C. They indicated a tendency of collapsing at a lower drying rate at 30°C. This is consistent with SEM observations. With ageing the aggregates were more compact and less sensitive to drying.
The aggregated system indicated a higher initial drying rate (higher permeability), whereas stirring induced a lower drying rate, favouring the formation of compact laminar structure.
XRD peak intensity was lowered with ageing due to decrease in crystallinity (stacking faults and/or decrease in crystallite size). The content of amorphous material was lowered as well, reducing water sorption/desorption, which indicated that the specific surface is lower.
From the suitable microstructure induced by ageing some new phases may form (feldspar, zeolites), preferably in the coarser fraction of the sludge. This is disturbed by stirring which operation expels also carbonates from the particle edges and this may reduce the structural strength of the sludge. In aged bentonite suspension a similar tendency was observed of formation of specific microstructures capable of phase transformation, e.g. to feldspar.