M. A. Vicente

Glutamate receptors of the kainate type and synaptic transmission

Glutamic acid is an important excitatory neurotransmitter in the mammalian CNS. It has been established that synaptic transmission is mediated mostly by the ionotropic glutamate receptors AMPA and NMDA, with fast and slow kinetics, respectively. The recent demonstration in hippocampal neurones of a class of glutamate receptors that are activated by kainate and not by AMPA (that is, kainate-selective receptors) opens the possibility that receptors, others than those of the AMPA type, might also be involved in fast neurotransmission. The lack of specific pharmacological tools to dissect out AMPA from kainate receptors has hampered the functional study of kainate receptors. However, the recent finding that a 2,3-benzodiazepine (GYK153655) behaves as a selective antagonist of AMPA receptors allows us to address the question of the role of rapidly inactivating kainate receptors in synaptic transmission.

Weathering and decay of granitic rocks: its relation to their pore network

Abstract A study is presented on the pore size distribution in granites, both fresh and artifically aged by freezing/thawing cycles (−20/110°C), in the diameter range 0–25 nm, by nitrogen adsorption at −196°C. The pore size distribution found permits a plausible explanation for the behaviour shown by these materials during degradation processes associated to fluid flows through their pores (thermoclasty and gelifraction). If low porous granites are used, artificial ageing has only a minor, limited effect on their pore network; however, changes in pore size distribution (diameter

Assessment of chromatic changes due to artificial ageing and/or conservation treatments of sandstones

Villamayor sandstone (also known as ‘‘golden the construction of modern buildings. This stone has interesting ornamental properties, but its use also involves sandstone’’) has been widely used for construction in the city of Salamanca since Roman times. In the present certain drawbacks (a high degree of porosity, a high water imbibition coefficient, low mechanical resistance, etc.). study, the four most characteristic varieties of this material were used, considering the chromatic changes The aim of the chemical treatments to which it is sometimes subjected is to improve the properties that render brought about by consolidation and/or waterproofing treatments and by cycles of artificial ageing of natural it crumbly when challenged with humidity but without affecting its original aspect (colour, texture, etc.), thus stone and of stone subjected to these treatments. The treatments consisted of application of a consolidant at enabling it to be used in situations not normally possible, such as in window sills or any other parts of buildings different concentrations (RC 70 and 40% RC 70) and two consolidants plus waterproofing agents (RC 80 and RC where it would be exposed to frequent humidity or where 90). Artificial ageing was induced by 10 cycles of wetting/ the accumulation of water might lead to waterlogging. drying and freezing/thawing. The chromatic variations In the authors’ opinion, the treatment of this stone observed considering the E*, L*, a*, and b* parameters should not be undertaken unless absolutely necessary. were subjected to statistical analysis. q 1998 John Wiley & Their own experience and the abundant references in the Sons, Inc. Col Res Appl, 23, 46–51, 1998 literature suggest that in Mediterranean climates with a continental trend this sandstone, when properly used, gen

Color changes in the surface of granitic materials by consolidated and/or water repellent treatments

Color is one of the parameters to be monitored when determining the suitability of a protective or conservative treatment of stone. Application of a given treatment product should elicit the least possible effect in this parameter. Changes in color of five varieties of granite of highly varying characteristics due to their origin are studied in the present work. All the granites studied are widely used in buildings of historical interest in Avila (Spain). Some varieties are from unaltered facies (grey granites of different grain size), and have a very low degree of porosity, while other are from facies that have undergone strong natural weathering processes, and that display important mineralogical and physical changes. In this sense, the ochre variety of granite contains clays (smectite and some kaolinite); the white variety contains kaolinite and opal, and the red variety contains kaolinite, opal, and iron oxihydroxides. Fresh cut and artificially aged (with 25 cycles of freezing/thawing and cold/heat treatment) samples were treated with consolidant (RC80 or RC70) and/or water repellent (H224) agents. After the corresponding statistical treatment of data obtained, significant changes in ΔE were observed with the treatments given; such changes are more pronounced in unaged samples. Changes in ΔL (lightness), however, despite being noticeable, seem to have only a minor effect on ΔE, which seem to be more dependent on changes in Δa and Δb. This was more pronounced when the stone was treated with RC80 and then with H224.

Thermal studies of pharmaceutical-clay systems Part I. Montmorillonite-based systems

Abstract Pharmaceutical-clay systems, used as solar radiation shields, obtained by interaction of Na montmorillonite and several pharmaceuticals using two methods of preparation, have been studied. Samples have been prepared by melting the drug onto the clay or by intimate mixing and grinding of both. The shielding ability against solar radiation is improved by use of these preparation methods. Differential thermal analysis and thermogravimetric analysis confirm the steady substitution of water molecules from the interlayer space of the clay by drug molecules, as the amount of the latter is increased. The melting method seems to facilitate access of the drug into the interlayer space of the clay.

Determination of the origin and evolution of building stones as a function of their chemical composition using the inertia criterion based on an HJ-biplot

Abstract The aim of the present work is to determine the origin and background of 72 samples of four varieties of granite s.l. from quarries and different parts of the Cathedral Group Buildings of Avila (Spain) subject to different microenvironmental conditions. To do so, the results of the chemical analyses of major and trace elements of all samples were analysed statistically using the inertia method based on an HJ-biplot. Clusters of samples related to their origin, quarry or building were obtained. The statistical method employed is a useful tool for determining the origin of the stone located on different parts of the historical monument. This is of great interest when the stone needs to be replaced for maintenance and restoration purposes.

Thermal studies of pharmaceutical clay systems. Part II. Sepiolite-based systems

Pharmaceutical-clay systems, used as solar radiation shields, obtained by interaction of natural sepiolite and several pharmaceuticals using two methods of preparation (melting the drug onto the clay or by intimate mixing and grinding of both), have been studied. The shielding ability against solar radiation is improved by using these preparation methods. Differential thermal analysis and thermogravimetric analysis confirm displacement of water molecules adsorbed onto the clay surface by the pharmaceutical molecules. The grinding method seems to facilitate adsorption and dispersion of the drug onto the clay surface.

Interaction of N-methyl 8-hydroxy quinoline methyl sulphate with sepiolite

Abstract The adsorption of N-methyl 8-hydroxy quinoline methyl sulphate—a drug generally used to protect from sunburn—by natural and acid-treated sepiolite, has been investigated. Acid treatment led to partial dissolution of the fibres of the clay, mainly in the external surface of the crystallites. Incorporation of the drug decreased the amount of water adsorbed, leading to a strong interaction between the drug and the clay, but upon acid treatment the interaction seemed to weaken. Clay-drug complexes formed by adsorption from the drug aqueous solutions and by mechanical mixing of the components in the solid state served as good sunburn shields, as indicated by the spectra of these materials in the visible-ultraviolet range of the spectrum.

Removal of salts from granite by sepiolite

Abstract A study has been carried out on the extraction of salts from different types of granite using patent sepiolite formulation. The ability to remove salts greatly depends on the mineralogical compositions of the granites. Two types of equilibria are important: the absorption and/or adsorption of salts on the stone, and the partition of ions constituting the salt in the adsorbed state between the clay minerals in the rocks and that used as an extracting agent.

Application of Methyl Cinnamate/Montmorillonite as Ultraviolet Radiation Shelters

AbstractThe interaction of methyl cinnamate/montmorillonite samples prepared by melting the former onto the second or by joint grinding, has been studied by x-ray diffraction. differential thermal analysis, thermogravimetric analysis and Fourier-transform infrared spectroscopy. Formation of an interlayer compound has been observed, leading to an increase of 4.15 or 3.42 A (samples obtained by melting or grinding, respectively) in the basal spacing of the clay. Formation of such a complex leads to a displacement of molecular water from the interlayer space, as concluded from the thermal studies. No chemical change is observed in the methyl cinnamate molecule, as confirmed by infrared spectroscopy. The system prepared improve the shelter properties of the clay and the drug separately, mainly in the C zone of the ultraviolet spectrum (290-190 nm).