Giacomo Martini

The dynamics of a nitroxide radical in water adsorbed on porous supports studied by ESR

Abstract The ESR of the neutral spin probe 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl in the study of its dynamics of water adsorbed onto silica gels with pore diameters in the range 4 to 100 nm is described. The correlation times for the motion and their activation energies were calculated from the ESR linewidth at different temperatures. The mobility of the spin probe decreases with decreasing pore size, thus reflecting an increase in the average viscosity of the adsorbed water. Different behaviors are shown by water in silica gels with pore diameters 10–100 nm and in silica gels with p.d. 4 nm. The results obtained with the nitroxide are compared with those obtained with Cu(II) and Mn(II) on the same supports, and discussed in terms of the nature of the adsorbed water.

The state of water adsorbed on silica gel as determined by ESR of transition metal ion probe

Abstract The electron spin resonance of the Mn(H2O)62+ ion in aqueous solution adsorbed on silica gels with narrow and wide pores has been used to investigate the properties of the water filling the pores as well as the solid-liquid interaction. The analysis of the electron spin relaxation rate has shown the occurrence of a decreased mobility of water inside narrow pores with respect to water inside the wide pores, where it behaves as bulk water. The existence of a distribution of correlation times for the motion of Mn(II) complexes in such systems has been interpreted in terms of a gradient of mobility of water from the surface to the middle of the pores. The ESR lineshape at 77°K has made it possible to evaluate the distance from the surface at which secondary interactions are effective on the paramagnetic probe. This distance was found to be 2–3 nm. Moreover, the lineshape analysis allowed an investigation of the freezing properties of water in the different regions in the pores.

ESR study on the interaction between a positively charged spin probe and the silica gel surface

Abstract The electron spin resonance lineshape of the positively charged 4-trimethylammonium-2,2,6,6-tetramethylpiperidine-1-oxyl nitroxide radical has been used for an investigation of the structural properties of water adsorbed on narrow-pore (4 nm diameter) silica gel. Different spectra were obtained from the radical in the different regions inside the pores, as a function of the distance from the surface. The radical showed slow-motion conditions in the first water layers near the surface (primary interaction region), while fast-motion conditions applied in the secondary interaction region. The partition constant of the radical between the two regions and the correlation times for the radicals motion have been calculated through a computer simulation in slow- and fast-motion conditions. The results have been compared with those obtained with other spin probes in similar systems.

Mobility of water molecules adsorbed into Y zeolites as studied by the electron spin resonance of the Cu(H2O)2+6 complex

Abstract Molecular motions in the liquid phase in the faujasite cavities of a fully hydrated Y zeolite have been studied by the electron spin relaxation of the copper ion.

Study of bradykinin conformation in the presence of model membrane by Nuclear Magnetic Resonance and molecular modelling

The conformation of bradykinin (BK), Arg1-Pro2-Pro3-Gly4-Phe5-Ser6-Pro7-Phe8-Arg9, was investigated by Nuclear Magnetic Resonance (NMR) spectroscopy and Monte Carlo simulation in two different media, i.e. in pure aqueous solution and in the presence of phospholipid vesicles. Monolamellar liposomes are a good model for biological membranes and mimic the environment experienced by bradykinin when interacting with G-protein coupled receptors (GPCRs). The NMR spectra showed that lipid bilayers induced a secondary structure in the otherwise inherently flexible peptide. The results of ensemble calculations revealed conformational changes occurring rapidly on the NMR time scale and allowed for the identification of different families of conformations that were averaged to reproduce the NMR observables. These structural results supported the hypothesis of the central role played by the peptide C-terminal domain in biological environments, and provided an explanation for the different biological behaviours observed for bradykinin

Electron spin relaxation of manganese (II) in solution

Abstract The electron spin resonance of Mn(II)in liquids and its implication as a paramagnetic probe are discussed. A motional model is proposed to account for

Electron spin relaxation and hyperfine line shape of manganese (II) in mixed‐solvent systems

The X‐band ESR line shape of the six hyperfine components of manganese (II) has been investigated both in pure and in mixed solvents. The procedure used by Luckhurst and Pedulli [G. R. Luckhurst and G. F. Pedulli, Mol. Phys. 22, 931 (1971)] to account for the removal of the spin degeneracy by the nonsecular terms in the spin Hamiltonian has been used to compute the line shape as a function of (D:D) and of τc. In mixed solvents, large deviations from the theoretical line shape are due to the presence of differently coordinated complexes. A criterion for the determination of the selective solvation has been established.

Surface effects toward the mobility of charged spin probes: ESR study of nitroxide solutions adsorbed on zeolites

Abstract A study concerning the surface effects of zeolites X and Y toward the mobility of charged nitroxides is reported. Because of their critical dimensions, the nitroxides were only able to enter the large faujasite cavities. The relaxation analysis allowed us to establish the existence of a decreased mobility of the water solutions of nitroxide adsorbed in the zeolitic cavities with respect to mobility in bulk water. The negative radical Tempyo − gave results on the status of water near the cavity center whereas the ESR spectra of the positive radical TempTMA + were largely affected by water layers near the cavity walls.

Changes in Erythrocyte Properties during the First Hours of Life: Electron Spin Resonance of Reacting Sulfydryl Groups

ABSTRACT: In an attempt to clarify the mechanism by which the red cells (RBC) of newborn infants are protected against oxidative agents, electron spin resonance (ESR) assays were carried out using the nitroxide radical 4-maleimide-2,2,6,6-tetramethylpiperidinyl-1-oxyl (Mal-6), a sulfydryl-reacting agent. The ESR assays were performed in 24 samples of cord blood, 20 samples of blood from 4-day-old infants, and eight samples of 8-h-old infants. The analyses were carried out on whole blood and washed erythrocytes were resuspended in buffered saline. The same experiments were performed in 10 blood samples from healthy adults as controls. Whole blood, before and after removing the buffy coat, and cell-free plasma were also examined by ESR assay. Cell-free plasma and buffy coats proved not to be appreciably involved in the Mal-6 behavior. The data of the ESR spectroscopy demonstrated a significantly slower reaction rate in the samples of cord blood and in blood of 8-h-old infants, compared to that of 4-day-old infants and adults. No significant differences in Mal-6 behavior could be detected between cord blood and 4-day-old infant blood in the results of ESR assays performed in washed red cells. Chemical determination of RBC-reacting sulfydryl groups and the assays of glutathione also demonstrated the absence of differences between cord blood and blood of 4-day-old infants. The results of our investigation suggest that the RBC-sulfydryl-reacting groups are less involved in the detoxification of oxidative agents during the first hours of life than in the following days. This peculiarity of RBC of younger infants appears to be due, to a considerable extent, to the modulation by plasma factors of the interactions between Mal-6 and RBC-reacting sulfydryl groups. Therefore, the changes in plasma components occurring during the first hours of life appear to modify the interactions between the RBC and the oxidative agents.

Electron spin resonance in surface science

Abstract This review deals with the recent applications of electron spin resonance spectroscopies in surface science. The following topics are considered: (i) adsorbed inorganic radicals; (ii) adsorbed organic radicals; (iii) paramagnetic species on zeolites and on other alumino-silicates; (iv) transition metal ions on catalyst surfaces; (v) micellar and other organized systems; (vi) Langmuir-Blodgett films and other thin films; and (vii) the surface effects on molecular motion of adsorbed species. A table is added to each section with references to the works published in the last few years. Particular attention is given to the combined use of conventional and advanced ESR spectroscopies with other recently developed surface techniques.