Intermolecular interaction energies in molecular crystals: comparison and agreement of localized Møller-Plesset 2, dispersion-corrected density functional, and classical empirical two-body calculations.

A comparative analysis of the intermolecular energy for a data set including 60 molecular crystals with a large variety of functional groups has been carried out using three different computational approaches: (i) a method based on a physically meaningful empirical partition of the interaction energy (PIXEL), (ii) density functional methods with a posteriori empirical correction for the dispersion interactions (DFT-D), and (iii) a full periodic ab initio quantum mechanical method based on Møller-Plesset perturbation theory for the electron correlation using localized crystal orbitals (LMP2). Due to the large computational cost, LMP2 calculations have been restricted to a subset of seven molecular crystal comprising benzene, formic acid, formamide, succinic anhydride, urea, oxalic acid, and nitroguanidine, and the results compared with PIXEL and DFT-D data as well as with the experimental data show excellent agreement among all adopted methods. This shows that both DFT-D and PIXEL approaches are robust predictive tools for studying molecular crystals.

Electron beam radiation effects on UHMWPE: an EPR study.

Electron paramagnetic resonance (EPR) technique has been employed to detect and characterise a series of different radical species generated in ultra-high molecular weight polyethylene (UHMWPE) via electron beam irradiation. Three different radical species have been found and assigned on the basis of their EPR spectra and of the related computer simulations. A secondary alkyl species, the prevalent one, is present immediately after irradiation, an allyl species appears only 24 h after irradiation when the alkyl species disappears.

Pyrolysis-GC/MS for the identification of macromolecular components in historical recipes.

Analytical pyrolysis with thermally assisted hydrolysis and methylation was employed to investigate ancient ointments collected from Spanish vessels coming from the sixteenth century pharmacies. The ointments were reproduced on the basis of historical recipes and characterization was made in comparison with real samples. Characteristic markers indicate the presence of beeswax, of animal and plant lipids, and of natural resins.

The iron-related molecular toxicity mechanism of synthetic asbestos nanofibres: a model study for high-aspect-ratio nanoparticles.

Asbestos shares with carbon nanotubes some morphological and physico-chemical features. An asbestos-like behaviour has been recently reported by some authors, though the mechanism of toxicity may be very different. To identify at the atomic level the source of toxicity in asbestos, the effect of progressive iron loading on a synthetic iron-free model nanofibre previously found non-toxic in cellular tests was studied.

Structural and spectroscopic investigation of ZnS nanoparticles grown in quaternary reverse micelles.

ZnS nanoparticles were synthesized in four component "water in oil" microemulsions formed by a cationic surfactant (cetyltrimethylammonium bromide, CTAB), a cosurfactant (pentanol or butanol), n-hexane and water. The effect of various parameters (nature of cosurfactant, water/surfactant W(0), and alcohol/surfactant P(0)) on the formation and stability of ZnS nanoparticles was investigated thoroughly. UV-Vis spectroscopy was employed to directly follow the formation of ZnS systems in the microemulsions.

Vitamin E-stabilized UHMWPE for total joint implants: a review.

Background: Osteolysis due to wear of UHMWPE limits the longevity of joint arthroplasty. Oxidative degradation of UHMWPE gamma-sterilized in air increases its wear while decreasing mechanical strength. Vitamin E stabilization of UHMWPE was proposed to improve oxidation resistance while maintaining wear resistance and fatigue strength.

Gas-phase phenol methylation over Mg/Me/O (Me = Al, Cr, Fe) catalysts: mechanistic implications due to different acid-base and dehydrogenating properties.

This contribution reports about an in situ FT-IR investigation and the catalytic reactivity of Mg/Me(3+) mixed oxides (Me = Cr, Fe, or Al; Mg/Me = 2, atomic ratio) in the gas-phase methylation of phenol with methanol. It is the second of two papers concerning the mentioned systems, and its purpose is twofold: to confute the classic and not accurate theory concerning the reaction mechanism, and to propose a novel interpretation based on the combined use of catalytic tests and in situ molecular spectroscopy. Results here reported highlight that: (i) the reaction mechanism in phenol methylation, when catalysed by basic systems, is not a classical electrophylic substitution, as generally reported in the literature, but proceeds through the formation of formaldehyde as an intermediate, and (ii) the catalytic behaviour in respect to both methanol and phenol reactants is strictly dependent on catalyst features.

Spectroscopic CW-EPR and HYSCORE investigations of Cu(2+) and O(2)(-) species in copper doped nanoporous calcium aluminate (12CaO.7Al(2)O(3)).

Continuous wave (CW) and pulse electron paramagnetic resonance in a variant of hyperfine sublevel correlation spectroscopy (HYSCORE) were used for obtaining structural information concerning speciation and local environment of alien Cu(2+) and native O(2)(-) ions encaged in copper doped nanoporous 12CaO.7Al(2)O(3) (mayenite). The samples were prepared by a solid-state reaction and characterized by means of XRD, SEM, and Raman techniques.

Synergistic behavior of bimetallic rhenium cluster catalysts: spectroscopic investigation into the nature of the active site.

Single-site Re nanoparticles were produced by anchoring dirhenium organometallic clusters on to the inner walls of mesoporous silica. The presence of oxophilic atoms (Sb or Bi) is essential to obtain well dispersed Re(0) centers. The interaction between the organometallic cluster and the silica support is critical for the generation of well-defined and isolated Re(0) single sites.

Photoactive hybrid nanomaterials: indocyanine immobilized in mesoporous MCM-41 for "in-cell" bioimaging.

Mesoporous silica nanoparticles are being explored as versatile tools for various biomedical and biotechnological applications including disease diagnosis, drug delivery, and intracellular imaging. In this paper, the synthesis and characterization of a fluorescent hybrid mesoporous silica nanomaterial, which is noncytotoxic and shows great potential for "in-cell" bioimaging applications, will be described. The hybrid mesoporous material has been obtained by confining highly fluorescent organic dyes, belonging to the indocyanine family, within the channels of mesoporous MCM-41.

On the compatibility criteria for protein encapsulation inside mesoporous materials.

The properties of the enzyme pepsin, relevant to its incorporation inside the channels of mesoporous silica materials in the preparation of bioinorganic hybrids, are highlighted by molecular dynamics simulations of aqueous solutions of the protein under conditions optimal for encapsulation in SBA-15. The protein size, shape, flexibility and surface properties are calculated with the aim of deriving general accessibility/compatibility criteria favouring encapsulation inside mesoporous systems.

Differential repression by the transcription factor REST/NRSF of the various Ca2+ signalling mechanisms in pheochromocytoma PC12 cells.

Expression of the nerve cell phenotype is orchestrated by the REST/NRSF transcription repressor, working on hundreds of genes recognized at a specific regulatory binding sequence. Most PC12 clones, the most frequently employed neuronal model, maintain low levels of REST; however a few, defective of neurosecretion, express high levels. To investigate the role of REST in Ca2+ signalling we studied the [Ca2+](i) changes in single cells of four clones, two wild-type and two defective, pre-treated for 5 days with NGF.

Direct evidence of adsorption induced Cr(II) mobility on the SiO(2) surface upon complexation by CO.

In situ, temperature dependent, XAFS proved that Cr(II) grafted on SiO(2) is extracted from the surface upon CO adsorption at 100 K: DeltaR(Cr-O) = +0.08 A. CO adsorption evolves into two coverage dependent steps: (i) displacement of weak siloxane ligands (non-classical carbonyls); (ii) relaxation of R(Cr-O) surface bond, R(Cr-CO) optimization and transformation into classical carbonyls.

Advances in identification of plant gums in cultural heritage by thermally assisted hydrolysis and methylation.

Plant gums are present in works of art as binding media for watercolours and adhesives for cellulosic substrates. Thermally assisted hydrolysis and methylation (THM) in combination with analytical pyrolysis coupled to GC/MS has been applied to the characterisation of plant gums typically used in artworks. THM products from standard samples of arabic gum, tragacanth gum and cherry gum were characterised.

Fate of antibacterial spiramycin in river waters.

Spiramycin, a widely used veterinary macrolide antibiotic, was found at traceable levels (nanograms per litre range) in Po River water (N-Italy). The aqueous environmental fate of this antibiotic compound was studied through drug decomposition, the identification of the main and secondary transformation products (TPs), assessment of mineralisation and the investigation of drug TPs toxicity. Initially, laboratory experiments were performed, with the aim of stimulating the antibacterial transformation processes followed in aquatic systems.

Response of CPO-27-Ni towards CO, N2 and C2H4.

Coordinatively unsaturated Ni(2+) atoms in CPO-27-Ni form linear adducts with molecular nitrogen. The framework responds to the adsorption-modifying vibrational properties and local structure around adsorbing sites. The present paper deals with a fundamental infrared (IR) study of the interaction of gases on a microporous adsorbent metallorganic framework CPO-27-Ni containing, after solvent removal, coordinatively unsaturated Ni(2+) atoms [Dietzel et al.

Stability and reactivity of grafted Cr(CO)3 species on MOF linkers: a computational study.

The possibility to modulate Cr(CO)(3) properties by grafting it onto metal-organic framework (MOF) linkers of different natures has been investigated using density functional methods. MOF linkers were modeled using clusters constituted by benzene rings doubly substituted in the para position. The effect of the electron-donor or electron-acceptor nature of benzene substituents on the stability of the (eta(6)-arene)Cr(CO)(3) adduct and on the shift of the CO bands has been considered.

Positive ion chemistry of SiH4/NF3 gaseous mixtures studied by ion trap mass spectrometry.

The positive ion chemistry occurring in silane/nitrogen trifluoride gaseous mixtures has been investigated by ion trap mass spectrometry. Reaction sequences and rate constants have been determined for the processes involving the primary ions SiH(n)(+) (n = 0-3) and NF(x)(+) (x = 1-3) and the secondary ions obtained from their reactions with SiH(4) and NF(3). The SiH(n)(+) efficiently react with NF(3) and undergo cascades of abstraction and scrambling reactions which form the fluorinated and perfluorinated cations SiHF(m)(+) (m = 1, 2), SiH(2)F(+) and SiF(x)(+) (x = 0-3).

Normal vibrational analysis of the syndiotactic polystyrene s(2/1)2 helix.

The full vibrational spectra of the gamma, delta, and epsilon crystalline phases of syndiotactic polystyrene (sPS), i.e., phases presenting the s(2/1)2 helical conformation, have been experimentally determined and compared with that calculated at the B3LYP/6-31G(d,p) level of theory for an infinite helix.

Reactivity of Ti(IV) species hosted in TS-1 towards H2O2-H2O solutions investigated by ab initio cluster and periodic approaches combined with experimental XANES and EXAFS data: a review and new highlights.

This work is intended to underline how the most-advanced experimental and theoretical physical chemistry tools must be used synergistically to understand the reactivity of Ti-silicalite-1 (TS-1) in an important number of low-temperature oxidation reactions with aqueous H(2)O(2) as the oxidant. Literature results are carefully reviewed and accompanied with new, unpublished highlights of both experimental and computational origin. The first part of this work is devoted to a discussion of the defective nature of the material and to the synergic role played by Si vacancies and Ti insertion in the framework.

FTIR spectroscopy and thermodynamics of hydrogen adsorbed in a cross-linked polymer.

The adsorption of H(2) in a cross-linked poly(styrene-co-divinylbenzene) (St-DVB) microporous polymer (BET surface area 920 m(2) g(-1)) is studied by volumetric and gravimetric methods, FTIR spectroscopy at variable temperature (300-14 K) and ab initio calculations. At 77 K the polymer reversibly stores up to 1.3 mass% H(2) at a pressure of 1 bar and 1.

Partially hydroxylated polycrystalline ionic oxides: a new route toward electron-rich surfaces.

Charge traps at the surface of oxide materials play a fundamental role in various chemical processes, such as the activation of supported metal clusters. In this study, combining electron paramagnetic resonance with cluster model DFT calculations, we show that excess electrons at the surface of MgO, CaO, and SrO polycrystalline materials can be generated by preparing weakly hydroxylated surfaces followed by deposition of small amounts of alkali metals. The residual OH groups present on specific sites of the partially dehydroxylated surface act as stable traps for electrons donated by the alkali metal (Na in this case) which forms a Na+ ion distant from the trapped electron.

Direct observation and modelling of ordered hydrogen adsorption and catalyzed ortho-para conversion on ETS-10 titanosilicate material.

Hydrogen physisorption on porous high surface materials is investigated for the purpose of hydrogen storage and hydrogen separation, because of its simplicity and intrinsic reversibility. For these purposes, the understanding of the binding of dihydrogen to materials, of the structure of the adsorbed phase and of the ortho-para conversion during thermal and pressure cycles are crucial for the development of new hydrogen adsorbents. We report the direct observation by IR spectroscopic methods of structured hydrogen adsorption on a porous titanosilicate (ETS-10), with resolution of the kinetics of the ortho-para transition, and an interpretation of the structure of the adsorbed phase based on classical atomistic simulations.