We report on femto- to nanosecond studies of the excited state intermolecular proton transfer (ESPT) reaction of trisodium 8-hydroxypyrene-1,3,6-trisulfonate (pyranine, HPTS) with the human serum albumin (HSA) protein. The formed robust 1:1 complexes (K(eq) = (2.6 ± 0.1) × 10(6) M(-1)) show both photoacid (∼430 nm) and conjugated photobase (∼500 nm) emissions of the caged HPTS in its protonated structure. The proton-transfer reactions in these complexes proceed in a large time window, spanning from 150 fs to ∼1.2 ns. The ultrafast component reflects a direct H-bond breaking and making in the robust complexes, involving the carboxylate groups of the amino acids, while the slowest one is arising from the slow dynamics of the so-called biological water. Additional time constants of the caged photoacid to give the conjugated photobase are observed, assigned to the ESPT reaction within "loose" complexes (3 to tens of picoseconds), and 130 ps and 1.2 ns due to the slow dynamics of the water molecules around the protein residues and involved in the proton transfer. The fs-ns anisotropy measurements confirm the robustness of the HPTS:HSA complexes. Our results indicate that, even though robust 1:1 complexes between HPTS and the HSA are formed, the system is heterogeneous, due to different possible interactions of the dye with the inside/outside parts of the protein. Furthermore, we find lower values of the initial anisotropy (r(0)) in the protein (0.33) and in γ-CD (0.28) in comparison with buffered aqueous solution (0.385). We propose that caging HPTS by the HSA protein and by the cyclodextrin affects the electronic redistribution in a different degree of mixing between the (1)L(a) and (1)L(b) states in the formed deprotonated form, for which the interactions of the sulfonate groups with the surroundings should play a key role.

We present here direct experimental evidence of the magnetic polarization of Zn atoms in ZnO nanoparticles capped with different materials by means of x-ray magnetic circular dichroism ͑XMCD͒. Our results demonstrate that the magnetism in this material is intrinsic and relays in the ZnO conduction band. The analysis of both x-ray absorption spectroscopy and XMCD signals points out the formation of a well-defined interface between ZnO and the capping molecule in which the exotic magnetism arises at the hybridized band formed among Zn and the bonding atom of the molecule. The magnetic properties of these systems should critically depend on the details of this interface which may offer a new insight into the different observations for seemingly identical materials.

In this work, we present a sol–gel synthesis of ε-Fe2O3 nano and microparticles stabilized in silica thin films. Thanks to the relatively high size of the synthesized particles, we have been able to discriminate the Raman signal of the ε- and α-Fe2O3 phases, thus presenting the first Confocal Raman Microscopy study of isolated ε-Fe2O3 particles. The vibrational modes of each phase are identified at room temperature. The phase transition from ε- to α-Fe2O3 and the morphological modifications are analyzed as a function of the in situ output laser power. A complete study of the Raman spectra for ε-Fe2O3 particles has been performed for a wide range of temperatures (80–570 K). The phonon frequencies and line widths show a behavior in which the contributions from lattice thermal expansion and anharmonic interactions have to be considered. We have also identified a two-magnon mode in the ε-Fe2O3 phase. Its intensity increases close to the Néel transition (TN) and persists well above it. This observation could be one of the few experimental examples of a paramagnon, i.e., a magnetic excitation in a paramagnetic state.

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We present a novel and easy synthetic path to prepare ε-Fe2O3 (∼90%) with a small portion of α-Fe2O3 nanoparticles embedded in an amorphous silica matrix.

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