First principles study of 2D layered organohalide tin perovskites

This article describes the structure and the electronic properties of a series of layered perovskites of a general formula (A+)2(SnX4)-2 where X = I, Br and A+ is an organic cation, either formamidinium, 1-methylimidazolium, or phenylethylammonium. For each system, two conformations are considered, with eclipsed or staggered stacking of the adjacent inorganic layers. Geometry optimizations are performed at the density functional theory level with generalized gradient approximation (GGA) functional and semiempirical correction for dispersion energies; band profiles and bandgaps are computed including both spin orbit coupling (SOC) and correlation (GW) effects through an additive scheme. The theoretical procedures are validated by reproducing the experimental data of a well known 3D tin iodide perovskite. The results, combined with the calculations previously reported on PbI4 analogues, allow us to discuss the effect of cation, metal, and halide substitution in these systems and in particular to explore the possibility of changing the electronic bandgap as required by different applications. The balance of SOC and GW effects depends on the chemical nature of the studied perovskites and strongly influences the value of the simulated bandgap

Embedding monomers and dimers of sulfonamide antibiotics into high silica zeolite Y: an experimental and computational study of the tautomeric forms involved

This work is a second step towards the systematic study of the embedding of sulfonamide antibiotics into a synthetic high silica zeolite Y (HSZ-Y) with hydrophobic properties. In the previous paper [Braschi et al., Langmuir 2010, 31, 9524], the irreversible adsorption from water into HSZ-Y of three sulfonamides was studied by enlightening the host-guest interactions and, in the case of the smallest sized sulfadiazine, the guest-guest interactions of dimeric species inside the zeolite cage. Here the HSZ-Y was loaded with six sulfonamides, namely: sulfanilamide, sulfapyridine, sulfathiazole, sulfadimethoxine, sulfadoxine and sulfamerazine. With the exception of sulfanilamide, which showed scarce affinity for HSZ-Y (maximum loading 3% zeolite dry weight), the other sulfa drugs adsorbed at ca. 28% zeolite dry weight on average, and this is relevant for both water depollution and drug delivery issues. The low affinity of sulfanilamide for HSZ-Y was ascribed to its high hydrophilicity (water solubility 15-40 times higher than other drugs). The most stable tautomeric (amide or imide) form of each antibiotic adsorbed in zeolite Y was proposed by means of IR and solid state NMR spectroscopy augmented by computational modelling. The small dimensions and favourable stabilization energy allow the embedding of imidic and amidic dimers of sulfathiazole and sulfapyridine, respectively, inside the zeolite cage whereas the remaining sulfa drugs adsorbed in monomeric amidic form

Optimizing the relaxivity of MRI probes at high magnetic field strengths with binuclear GdIIIComplexes

The key criteria to optimize the relaxivity of a Gd(III) contrast agent at high fields (defined as the region 65 1.5 T) can be summarized as follows: (i) the occurrence of a rotational correlation time \u3c4R in the range of ca. 0.2\u20130.5 ns; (ii) the rate of water exchange is not critical, but a \u3c4M < 100 ns is preferred; (iii) a relevant contribution from water molecules in the second sphere of hydration. In addition, the use of macrocycle-based systems ensures the formation of thermodynamically and kinetically stable Gd(III) complexes. Binuclear Gd(III) complexes could potentially meet these requirements. Their efficiency depends primarily on the degree of flexibility of the linker connecting the two monomeric units, the absence of local motions and the presence of contribution from the second sphere water molecules. With the aim to maximize relaxivity (per Gd) over a wide range of magnetic field strengths, two binuclear Gd(III) chelates derived from the well-known macrocyclic systems DOTA-monopropionamide and HPDO3A (Gd2L1 and Gd2L2, respectively) were synthesized through a multistep synthesis. Chemical Exchange Saturation Transfer (CEST) experiments carried out on Eu2L2 at different pH showed the occurrence of a CEST effect at acidic pH that disappears at neutral pH, associated with the deprotonation of the hydroxyl groups. Then, a complete 1H and 17O NMR relaxometric study was carried out in order to evaluate the parameters that govern the relaxivity associated with these complexes. The relaxivities of Gd2L1 and Gd2L2 (20 MHz, 298 K) are 8.7 and 9.5 mM 121 s 121, respectively, +77% and +106% higher than the relaxivity values of the corresponding mononuclear GdDOTAMAP-En and GdHPDO3A complexes. A significant contribution of second sphere water molecules was accounted for the strong relaxivity enhancement of Gd2L2. MR phantom images of the dinuclear complexes compared to GdHPDO3A, recorded at 7 T, confirmed the superiority of Gd2L2. Finally, ab initio (DFT) calculations were performed to obtain information about the solution structure of the dinuclear complexes

Semi-Rigid (Aminomethyl) Piperidine-Based Pentadentate Ligands for Mn(II) Complexation

Two pentadentate ligands built on the 2-aminomethylpiperidine structure and bearing two tertiary amino and three oxygen donors (three carboxylates in the case of AMPTA and two carboxylates and one phenolate for AMPDA-HB) were developed for Mn(II) complexation. Equilibrium studies on the ligands and the Mn(II) complexes were carried out using pH potentiometry, 1H-NMR spectroscopy and UV-vis spectrophotometry. The Mn complexes that were formed by the two ligands were more stable than the Mn complexes of other pentadentate ligands but with a lower pMn than Mn(EDTA) and Mn(CDTA) (pMn for Mn(AMPTA) = 7.89 and for Mn(AMPDA-HB) = 7.07). 1H and 17O-NMR relaxometric studies showed that the two Mn-complexes were q = 1 with a relaxivity value of 3.3 mM-1 s-1 for Mn(AMPTA) and 3.4 mM-1 s-1 for Mn(AMPDA-HB) at 20 MHz and 298 K. Finally, the geometries of the two complexes were optimized at the DFT level, finding an octahedral coordination environment around the Mn2+ ion, and MD simulations were performed to monitor the distance between the Mn2+ ion and the oxygen of the coordinated water molecule to estimate its residence time, which was in good agreement with that determined using the 17O NMR data

A Porous Carbon with Excellent Gas Storage Properties from Recycled Polystyrene

In this paper, we describe the synthesis and gas adsorption properties of a porous carbonaceous material, obtained from commercial expanded polystyrene. The first step consists of the Friedel-Craft reaction of the dissolved polystyrene chains with a bridging agent to form a highly-crosslinked polymer, with permanent porosity of 0.7 cm 3 /g; then, this polymer is treated with potassium hydroxide at a high temperature to produce a carbon material with a porous volume larger than 1.4 cm 3 / g and a distribution of ultramicro-, micro-, and mesopores. After characterization of the porous carbon and determination of the bulk density, the methane uptake was measured using a volumetric apparatus to pressures up to 30 bar. The equilibrium adsorption isotherm obtained is among the highest ever reported for this kind of material. The interest of this product lies both in its excellent performance and in the virtually costless starting material

Photoemission study of ferrocenes: insights into the electronic structure of Si-based hybrid materials

We present here the results of synchrotron radiation-excited UV-photoemission investigation and DFT calculations on vinylferrocene (VFC), a redox molecule suitable for applications in molecular electronics. A detailed assignment is discussed of the valence photoelectron spectra (UPS), which provides new data on the electronic structure and offers a partial re-interpretation of previous assignments on VFC based on theoretical and experimental evidences. Furthermore, the present results can allow for a meaningful comparison of photoemission results from the corresponding hybrid obtained by covalently attaching VFC to Si oriented surfaces. © 2008 IOP Publishing Ltd

Influence of silicodactyly in the preparation of hybrid materials

The organic&#8315;inorganic hybrid materials have attracted great attention due to their improved or unusual properties that open promising applications in different areas such as optics, electronics, energy, environment, biology, medicine and heterogeneous catalysis. Different types of silicodactyl platforms grafted on silica inorganic supports can be used to synthesize hybrid materials. A careful evaluation of the dactyly of the organic precursors, normally alkoxysilanes, and of the type of interaction with the inorganic supports is presented. In fact, depending on the hydrophilicity of the silica surface (e.g., number and density of surface silanols) as well as on the grafting conditions, the hydrolysis and condensation reaction of the silylated moieties can involve only one or two out of three alkoxysilane groups. The influence of silicodactyly in the preparation of organic-inorganic silica-based hybrids is studied by TGA, 29Si, 1H and 13C solid-state NMR and FTIR spectroscopies, with the support of Molecular Dynamics calculations. Computational studies are used to forecast the influence of the different grafting configurations on the tendency of the silane to stick on the inorganic surface

Influence of Pore Size in Benzoin Condensation of Furfural Using Heterogenized Benzimidazole Organocatalysts

A designed N-heterocyclic carbene (NHC) catalyst was covalently anchored on a range of mesoporous and hierarchical supports, to study the influence of pore size in the benzoin condensation of furfural. The structural and spectroscopic characteristics of the anchored catalysts were investigated, also with the help of molecular dynamics simulations, in order to rationalize the degree of stability and recyclability of the heterogenized organocatalysts. Quantitative yields (99 %) and complete recyclability were maintained after several cycles, vindicating the design rationale

Structure and stability of 7-mercapto-4-methylcoumarin self-assembled monolayers on gold: an experimental and computational analysis

Self-assembled monolayers (SAM) of 7-mercapto-4-methylcoumarin (MMC) on a flat gold surface were studied by molecular dynamics (MD) simulations, reference-free grazing incidence X-ray fluorescence (GIXRF) and X-ray photoelectron spectroscopy (XPS), to determine the maximum monolayer density and to investigate the nature of the molecule/surface interface. In particular, the protonation state of the sulfur atom upon adsorption was analyzed, since some recent literature presented evidence for physisorbed thiols (preserving the S-H bond), unlike the common picture of chemisorbed thiyls (losing the hydrogen). MD with a specifically tailored force field was used to simulate either thiol or thiyl monolayers with increasing number of molecules, to determine the maximum dynamically stable densities. This result was refined by computing the monolayer chemical potential as a function of the density with the bennet acceptance ratio method, based again on MD simulations. The monolayer density was also measured with GIXRF, which provided the absolute quantification of the number of sulfur atoms in a dense self-assembled monolayer (SAM) on flat gold surfaces. The sulfur core level binding energies in the same monolayers were measured by XPS, fitting the recorded spectra with the binding energies proposed in the literature for free or adsorbed thiols and thiyls, to get insight on the nature of the molecular species present in the layer. The comparison of theoretical and experimental SAM densities, and the XPS analysis strongly support the picture of a monolayer formed by chemisorbed, dissociated thiyls