Photochemical release of nitric oxide from a regenerable, sol-gel encapsulated Ru-salen-nitrosyl complex

Light activation leads to release of NO from a silicate sol-gel material SG-RuNO prepared from the ruthenium complex, [Ru(salen)(OH2)(NO)]+ (salen = N,N'-bis-(salicylidene)ethyl-enediaminato); after photochemical NO photolabilization, SG-RuNO can be regenerated from the spent material via the subsequent reaction with aqueous nitrite.     

High-resolution radiocarbon dating of prehistoric sites in southern Italy

A new facility for accelerator mass spectrometry radiocarbon dating has been put in operation at the University of Lecce in southern Italy. The general features of the facility are described, showing how by the use of electrostatic and magnetic analyzers the radiocarbon content in several kinds of sample materials can be measured. The performances of the system are also given in terms of precision, accuracy and background. The results of the radiocarbon dating of two prehistoric sites are also reported. PACS 93.85.+q     

Interaction of urea and urea derivatives with cyclohexamylose in aqueous solutions at 25°C

The interaction in water of urea, monomethylurea, monoethylurea, monopropylurea, and monobutylurea with -cyclodextrin(hexacycloamylose) was studied calorimetrically at 25°C. The results show that the last three substances form inclusion complexes with -cyclodextrin. The enthalpy and the association constants relative to the inclusion process were determined. The association constant values are low, indicating weak complexing that increases with increasing length of the alkyl chain. Urea and monomethylurea, on the other hand, do not form inclusion complexes. For these systems the calorimetric data were treated in terms of excess enthalpies, and the McMillan-Mayer approach was used to get an insight into the weak, non-bonding molecular interactions occurring in these solutions.Presented at the sixth Italian meeting on Calorimetry and Thermal Analysis (AICAT) held in Naples, December 4–7, 1984.     

Excess free energies and entropies of aqueous solutions of methyl-D-pyranosides at 25°C

The excess Gibbs free energies of four -methyl-D-aldopyranosides in water were determined at 25°C from isopiestic measurements. The excess entropies were obtained by subtracting the free energy values from the enthalpy data. The results show a remarkable enthalpy-entropy compensation. The positive sign of the excess free energies is interpreted as due to the favorable solute-solvent interactions that prevent the favorable solute-solute interaction. The signs and magnitudes of the pair interaction coefficients are attributed to the release of water from the hydration cospheres during the concentration process. The excess properties seem to depend, however, on the stereochemistry of the solutes. This effect is discussed and attributed to the different specific stabilities of the hydration shells.     

The Effects of Cosolvents on the Complexation of α-Cyclodextrin with Alkylated Substances. Calorimetric Studies at 25 °C

The formation of complexes of -cyclodextrin with 1,2-alkanediols, ,-alkanediols and some cycloalkanols has been studied calorimetrically at 25 °C in water, in 7 mol kg^-1 aqueous urea and in 3 mol kg^-1 aqueous glucose. When a complex is formed, calorimetry enables the calculation of both the enthalpy and the association constant, from which the free energy and the entropy of the process can be obtained. The forces involved in the association process are discussed in the light of the signs and values of the thermodynamic parameters obtained. The effect of the variation of the aqueous medium on the hydration of the interacting substances and the consequent changes in the association parameters have been investigated. As respect to water, complexes are less stable in urea and more stable in glucose. The analysis of the data shows that this is the result of a different enthalpy-entropy balance in the two solvent media. Deaquation of the interacting substances plays a major role in determining the stability of the inclusion complexes.     

Post‐Synthesis Stabilization of Germanosilicate Zeolites ITH,IWW, and UTL by Substitution of Ge for Al

Germanosilicate zeolites often suffer from low hydrothermal stability due to the high content of Ge. Herein, we investigated the post‐synthesis introduction of Al accompanied by stabilization of selected germanosilicates by degermanation/alumination treatments. The influence of chemical composition and topology of parent germanosilicate zeolites ( ITH , IWW , and UTL ) on the post‐synthesis incorporation of Al was studied. Alumination of ITH (Si/Ge=2–13) and IWW (Si/Ge=3–7) zeolites resulted in the partial substitution of Ge for Al (up to 80 %), which was enhanced with a decrease of Ge content in the parent zeolite. In contrast, in extra‐large pore zeolite UTL (Si/Ge=4–6) the hydrolysis of the interlayer Ge?O bonds dominated over substitution. The stabilization of zeolite UTL was achieved using a novel two‐step degermanation/alumination procedure by the partial post‐synthesis substitution of Ge for Si followed by alumination. This new method of stabilization and incorporation of strong acid sites may extend the utilization of germanosilicate zeolites, which has been until now been limited.     

Abstract capacitary estimates and the completeness and separability of certain classes of non-locally convex topological vector spaces

We are concerned with establishing completeness and separability criteria for large classes of topological vector spaces which are typically non-locally convex, including Lebesgue-like spaces, Lorentz spaces, Orlicz spaces, mixed-normed spaces, tent spaces, and discrete Triebel–Lizorkin and Besov spaces. For vector spaces of measurable functions we also derive pointwise convergence results. Our approach relies on abstract capacitary estimates and works in certain cases of interest even in the absence of a background measure space and/or of a vector space structure.     

Nanoscale Confinement Controls the Crystallization of Calcium Phosphate: Relevance to Bone Formation

A key feature of biomineralization processes is that they take place within confined volumes, in which the local environment can have significant effects on mineral formation. Herein, we investigate the influence of confinement on the formation mechanism and structure of calcium phosphate (CaP). This is of particular relevance to the formation of dentine and bone, structures of which are based on highly mineralized collagen fibrils. CaP was precipitated within 25–300 nm diameter, cylindrical pores of track etched and anodised alumina membranes under physiological conditions, in which this system enables systematic study of the effects of the pore size in the absence of a structural match between the matrix and the growing crystals. Our results show that the main products were polycrystalline hydroxapatite (HAP) rods, together with some single crystal octacalcium phosphate (OCP) rods. Notably, we demonstrate that these were generated though an intermediate amorphous calcium phosphate (ACP) phase, and that ACP is significantly stabilised in confinement. This effect may have significance to the mineralization of bone, which can occur through a transient ACP phase. We also show that orientation of the HAP comparable, or even superior to that seen in bone can be achieved through confinement effects alone. Although this simple experimental system cannot be considered, a direct mimic of the in vivo formation of ultrathin HAP platelets within collagen fibrils, our results show that the effects of physical confinement should not be neglected when considering the mechanisms of formation of structures, such as bones and teeth.