We have studied the interaction of K atoms with the surface of polycrystalline alkaline-earth metal oxides (MgO, CaO, SrO) by means of CW- and Pulsed-EPR, UV-Vis-NIR spectroscopies and DFT cluster model calculations. The K adsorption site is proposed to be an anionic reverse corner formed at the intersection of two steps, where K binds by more than 1 eV, resulting in thermally stable species up to about 400 K. The bonding has small covalent and large polarization contributions, and the K atom remains neutral, with one unpaired electron in the valence shell. The interaction results in strong modifications of the K electronic wave function which are directly reflected by the hyperfine coupling constant, (K)a(iso). This is found to be a very efficient "probe" to measure the degree of metal-oxide interaction which directly depends on the substrate basicity. These results provide an original and general model of the early stages of the metal-support interaction in the case of ionic oxides.

The application of the stochastic genetic algorithm (GA) in conjunction with the deterministic Powell search to analysis of the multicomponent powder EPR spectra based on computer simulation is described. This approach allows for automated extraction of the magnetic parameters and relative abundances of the component signals, from the nonlinear least-squares fitting of experimental spectra, with minimum outside intervention. The efficiency and robustness of GA alone and its hybrid variant with the Powell method was demonstrated using complex simulated and real EPR data sets. The unique capacity of the genetic algorithm for locating global minima, subsequently refined by the Powell method, allowed for successful fitting of the spectra. The influence of the population size, mutation, and crossover rates on the performance of GA was also investigated.

The adsorption of NO onto copper-exchanged ZSM-5 zeolite has been studied by EPR spectroscopy. A distinct Cu+−NO species possessing an end-on η bent structure has been identified. Its EPR spectrum with a well-defined superhyperfine coupling with 63,65Cu nuclei and hyperfine coupling with 14N was interpreted in terms of completely anisotropic g and hyperfine tensors with noncoincident axes (monoclinic symmetry). The spin Hamiltonian parameters of this adduct have been analyzed in detail, leading to a semiquantitative molecular orbital correlation picture of the complex. The model developed shows that the unpaired electron resides mainly on the angularly coordinated NO and the copper superhyperfine structure arises from delocalization of the unpaired electron density onto Cu a‘ orbitals (3d z 2 , 3d xz , and 4s). The total spin density on copper is found to be equal to 0.2 and is shared among 3d z 2 (0.079), 3d xz (0.021), and 4s (0.1) orbitals. The remaining part of the unpaired electron density is localized on nitrogen (0.55) and oxygen (0.25) atoms. The bonding interaction involves essentially an overlap of Cu 3d z 2 and 3d xz with an antibonding 2p π* and a lone pair n orbital of the NO ligand as well as a 3d yz overlap with a second orthogonal NO 2p π* orbital. The appropriate molecular orbital diagram has been devised to account for the EPR data. The model is consistent with the observed magnetic properties of the investigated adducts and satisfactorily explains the previously unrecognized complex source of hyperfine couplings. The implications of this coordination mode on the possible molecular mechanism of the catalytic decomposition of NO over Cu/ZSM-5 catalysts are discussed.

The interaction between metal nanoparticles and bacteria belongs to the central issues in a dynamically growing bionanotechnological research. Herein, we investigated the adhesion efficiency of gold nanoparticles (30 nm) for various bacterial strains, both Gram-positive (Bacillus subtilis, Staphylococcus carnosus) and Gram-negative (Neisseria subflava, Stenotrophomonas maltophilia). The thorough microscopic (SEM/TEM) observations revealed that the nanoparticles do not penetrate into the bacterial cells but adhere to the walls. Large differences in the adhered nanoparticles amount were observed for the investigated strains (B. subtilis >> S. carnosus > N. subflava > S. maltophilia). A direct correlation between the number of the attached nanoparticles and the ζ-potential of the bacterial strains was found, and the results were rationalized in terms of the DLVO model. The calculated DLVO energy profiles revealed that the activation barriers for the adhesion process are rather small (1.45-1.55 kT), and the primary energy minima of 120-170 kT are favorable for the effective adsorption process. The established linear correlation between the nanoparticles adhered to the cell surface and the size of the critical volume around the bacterial cell, where the attraction forces dominate, implies that the observed dramatic differences in the attachment efficiency result from the availability of the nanoparticles in the critical volume of the surrounding suspensions. Owing to non-specific interactions governed by the ζ-potential mainly, the obtained results can be readily extended for the other bacteria-nanoparticle systems, providing a rational background for future advances in bacteria detection and thorough characterization via SERS method as well as for nanoparticles assemblies towards nanoelectronics.

DFT calculations of the molecular structure of the intrazeolite η 1 {CuNO} 11 adduct and the 14 N and 17 O hyperfine and 63 Cu superhyperfine coupling constants were performed and compared with previous EPR results. The calculations confirmed the choice of signs adopted in the previous analysis of the experimental data and the character of the SOMO. The influence of the basis set and the exchange-correlation functional on the HFCC and the spin-density distribution was investigated and briefly discussed. The global repartition of the spin density over Cu (F ) 0.11), N(F ) 0.58), and O (F ) 0.34) atoms determined from the Mulliken population analysis compared well with the experiment. The 14 N hyperfine tensor was successfully reproduced with the LanL2DZ basis and BPW91 functional, whereas in the case of the 63 Cu superhyperfine dipolar tensor T the agreement, except for that of the T zz component, was less satisfactory because of an overestimated polarization of the 3d yz orbital, regardless of the computation level. For the calculation of a iso (Cu), because LanL2DZ treats inner electrons with the effective core potential, a 6-311G(df) basis set appeared to be the most appropriate, leading to excellent agreement between the experimental and calculated values.

Periodic spin unrestricted DFT-PW91+U calculations together with ab initio thermodynamic modeling were used to study the structure, defects, and stability of different terminations of the (100) surface of cobalt spinel under various redox conditions imposed by different oxygen partial pressure and temperature. Three terminations containing under-stoichiometric (100)-O, stoichiometric (100)-S, and overstoichiometric (100)-R amount of cobalt ions were analyzed, and their atomic and defect structure, reconstruction, and stability were elucidated. For the most stable (100)-S and (100)-O facets, formation of cationic and anionic vacancies was examined, and a surface redox state diagram of possible spinel (100) terminations in the stoichiometry range from Co 2.75 O 4 to Co 3 O 3.75 was constructed and discussed in detail. The results revealed that the bare (100)-S surface is the most stable at temperatures and pressures of typical catalytic processes (T ∼ 200°C to ∼500°C, p O2 /p°∼ 0.001 to ∼1). In more reducing conditions (T > 600°C and p O2 /p°< 0.0001), the (100)-S facet is readily reduced by formation of oxygen vacancies, whereas in the oxidizing conditions (T < 200°C and p O2 /p°> 10), coexistence of (100)-S and (100)-O terminations was revealed. Formation of the oxygen vacancies involves reduction of the octahedral trivalent cobalt and is accompanied by migration of the divalent tetrahedral cobalt into empty, interstitial octahedral positions. It was also found that the constituent octahedral Co cation proximal to the interstitial cobalt adopts a low spin configuration in contrast to the distal one that preserves its surface high spin state. In the case of the Co depleted surfaces, the octahedral vacancies are thermodynamically disfavored with respect to the tetrahedral ones in the whole range of the examined T and p O2 values. The obtained theoretical results, supported by TPD-O 2 and TG experiments, show that the octahedral cobalt ions are directly involved in the redox processes of Co 3 O 4 .

The adsorption of molecular oxygen ͑enriched with 17 O) onto high surface area MgO has been studied by electron paramagnetic resonance ͑EPR͒ spectroscopy. The oxide surface was pretreated in such a way so that surface trapped electron F S ϩ ͑H͒ centers are produced. Subsequent dioxygen adsorption results in an electron transfer reaction from F S ϩ ͑H͒ centers to O 2 , producing a surface stabilized superoxide (O 2 Ϫ) anion. The resulting EPR spectrum of the paramagnetic anion is complicated by the simultaneous presence of a high number of ''normal'' hyperfine lines along the principal axes and also by several off-axis extra features which have complicated previous interpretations of the A yy and A zz components. By adopting a suitable adsorption procedure which suppresses the superoxide speciation, using a highly crystalline MgO material and controlling the isotopomer composition through appropriate 17 O enrichments, the resolution of the EPR spectrum has been dramatically improved. Analysis of the 1 H superhyperfine structure (͉A H ͉/␤ e g ϭ͓3.9,2.2,1.3͔G), resulting from a dipolar interaction between the adsorbed O 2 Ϫ anion and a neighboring OH group, and positions of the extra absorption lines in the spectrum, have provided us with auxiliary sources of information to determine for the first time the complete 17 O hyperfine tensor (A O /␤ e gϭ͓Ϫ76.36,7.18,8.24͔ G͒. The tensor has been analyzed in detail using a localized spin model. The spin density is shared among the 2p x (0.495), 2p x y (Ϫ0.024) and 2s(0.011) orbitals. The total spin density on O 2 Ϫ indicates that a complete surface electron transfer from the F S ϩ ͑H͒ center to dioxygen occurs upon adsorption, in line with recent ab initio calculations.

In this paper we present a theoretical study of water sorption on cobalt spinel nanocrystals by means of plane-wave periodic density functional theory (DFT) calculations jointly with statistical thermodynamics. The three most stable (100), (110), and (111) planes exposed by Co 3 O 4 were considered, and their stabilization upon water adsorption is discussed in detail. The calculated changes in free enthalpy of the investigated system under different hydration conditions along with the Wulff construction were used to predict the rhombicuboctahedral equilibrium morphology of cobalt spinel nanocrystals in different conditions, which corresponds very well to the experimental transmission electron microscopic (TEM) images. Two-dimensional surface coverage versus temperature and pressure diagrams were constructed for each of the examined (100), (110), and (111) planes to illustrate water adsorption processes in a concise way.