Automatic code generation for quantum chemistry applications

A unified, computer algebra system‐based scheme of code‐generation for computational quantum‐chemistry programs is presented. Generation of electron‐repulsion integrals and their derivatives as well as exchange‐correlation potential and its derivatives is discussed. Application to general‐purpose computing on graphics processing units is considered.     

Synthesis of α1-(Cbz-aminoalkyl)-α2-(hydroxyalkyl)phosphinic esters

A synthesis of α₁-(Cbz-aminoalkyl)-α₂-(hydroxyalkyl)phosphinic esters was achieved by the 1,2-addition of the appropriate aldehyde to Cbz-protected phosphinic analogues of amino acid esters in the presence of at least three equivalents of trimethylsilyl chloride and NEt₃. The complete deprotection of the product esters could be achieved in one step using 35% HBr in acetic acid.     

Preparation of stable AsBr4+ and I2As-PI3+ salts. Why didn't we succeed to prepare AsI4+ and As2X5+? A combined experimental and theoretical study

In analogy to our successful "PX2+" insertion reactions, an "AsX2+" insertion route was explored to obtain new arsenic halogen cations. Two new salts were prepared: AsBr4+[Al(OR)4]-, starting from AsBr3, Br2 and Ag[Al(OR)4], and I2As-PI3+[Al(OR)]4 from AsI3, PI3 and Ag[Al(OR)4](R=C(CF3)3). The first cation is formally a product of an "AsBr2+" insertion into the Br2 molecule and the latter clearly a "PI2+" insertion into the As-I bond of the AsI3 molecule. Both compounds were characterized by IR and NMR spectroscopy, the first also by its X-ray structure. Reactions of Ag[Al(OR)4] with AsI3 do not lead to ionization and AgI formation but rather lead to a marginally stable Ag(AsI3)2+[Al(OR)]4 salt. Despite many attempts we failed to prepare other PX-cation analogues such as AsI4+, As2X5+ and P4AsX2+(X=Br, I). To explain these negative results the thermodynamics of the formation of EX2+, EX4+ and E2X5+(E = As, P; X = Br, I) was carefully analyzed with MP2/TZVPP calculations and inclusion of entropy and solvation effects. We show that As2Br5+ is in very rapid equilibrium with AsBr2+ and AsBr3(DeltaGo((CH2Cl2))=+30 kJ mol(-1)). The extremely reactive AsBr2+ cation available in the equilibrium accounts for the observed decomposition of the [Al(OR)4]- anion. By contrast, the stability of AsI3 against Ag[Al(OR)4] appears to be kinetic and, if prepared by a suitable route, As2I5+ would be expected to have a stability intermediate between the known P2I5+ and P2Br5+.     

TiO2 phytate films as hosts and conduits for cytochrome c electrochemistry

Cytochrome c is accumulated into a film of TiO(2) nanoparticles and phytate by adsorption from an aqueous solution into the mesoporous structure. Stable voltammetric responses and high concentrations of redox protein within the TiO(2) phytate layer can be achieved. Two types of electrode systems are reported with (i) the modified TiO(2) phytate film between electrode and aqueous solution phase and (ii) the modified TiO(2) phytate film buried under a porous gold electrode ('porotrode'). The electrical conductivity of TiO(2) phytate films is measured and compared in the dry and in the wet state. Although in the dry state essentially insulating, the TiO(2) phytate film turns into an electrical conductor (with approximately 4 Omega cm specific resistivity assuming ohmic behaviour) when immersed in aqueous 0.1 M phosphate buffer solution at pH 7. The redox protein cytochrome c is therefore directly connected to the electrode via diffusion and migration of electrons in the three dimensional mesoporous TiO(2) phytate host structure. Electron transfer from cytochrome c to TiO(2) is proposed to be the rate-determining step for this conduction mechanism.     

A theoretical study on the formation of EX4+ and E2X5+(E = P, As; X = Br, I) from Ag+ and EX3/X2

The mechanism and the thermodynamics of the formation of EX2+, EX4+ and E2X5+ (E = As, P; X = Br, I) was carefully analyzed with MP2/TZVPP calculations and inclusion of entropy and solvation effects (COSMO model approximating CH2Cl2). Thus, as likely intermediates the complexes of Ag+ and one or two EX3 as well as EX3/X2 were optimized. The global minimum isomers of the Ag(EX3)2+ intermediates were found to be P-coordinated Ag(PI3)2+ and (BrPBr2)Ag(PBr3)+ but exclusively halogen coordinated Ag(X2AsX)2+ complexes. Similarly complicated is the situation for the Ag(EX3)(X2)+ intermediates: (I3E)Ag(I2)+, (BrAsBr2)Ag(Br2)+ and (Br3P)(Br-Br)Ag+ complexes were found to be the global minima. Based on all available results likely mechanisms for the formation of the known PX4+, AsBr4+, P2X5+ salts (X = Br, I) from these intermediates were proposed. An explanation for the failure to prepare an AsI4+ salt is also given.     

Rheological properties of nanopowder alumina coated with adsorbed fatty acids

The rheological properties of a nanosized alumina powder coated with fatty acid steric stabilizers of varying chain length were investigated. The storage and loss moduli of the complex modulus were measured to characterize the behavior of the flocculated systems. As chain length increased, there was a transition from an elastic response to fluid behavior. However, the fluid system developed elastic characteristics at relatively low volume fractions of 22%. The length of the steric barrier required to produce the fluid dispersion was estimated to be approximately 2 nm and correlates with attractive interactions on the order of the system thermal energy. Moreover, in the flocculated systems, the storage modulus was found to be higher than reported previously in the literature. These higher values were related to the additional attractive forces due to van der Waals attractions between the hydrocarbon tails of the adsorbed fatty acid layers.     

Spectrum analysis of U-doped LaBr3 single crystals. Part 1: crystal-field analysis

Single crystals of U³⁺:LaBr₃ were grown by the Bridgman-Stockbarger technique. High-resolution polarized absorption spectra of the crystals were recorded at 4.2 K in the 4000-50,000 cm⁻¹ range. Sixty-four experimental crystal-field energy levels of the U³⁺ ion were fitted to a semiempirical Hamiltonian employing free-ion, one-electron crystal-field as well as two-particle correlation crystal-field (CCF) operators with an r.m.s. deviation of 28 cm⁻¹. The performed analysis of the spectra enabled the determination of crystal-field parameters and assignment of the observed 5f³→5f³ transitions. The effects of selected CCF operators on the splitting of some specific U³⁺ multiplets have been investigated and the obtained values of Hamiltonian parameters are discussed and compared with those reported in previous analyses.     

Structurally heterogeneous electrode films of polyacrylamide and acrylamide/vinylpyridine copolymeric gels: Mediation of ascorbic acid oxidation

The surface chemistry, i.e. adsorption and surface phase formation, on Rh, Ir, Pt and Au single-crystal electrodes in 0.5 M H₂SO₄ has been studied in the potential range between 0 and 4 V vs. a standard hydrogen electrode by X-ray photoelectron spectroscopy and cyclic voltammetry. Both methods gave complementary results which were interpreted as potential-dependent changes from physisorption of water to adsorption of hydroxyl groups, hydroxide film formation, and eventual growth of thick adlayers of oxyhydroxide (Rh, Ir and Au) or hydroxide (Pt) with increasing applied voltage.     

New Insight on Carbon Dioxide-Mediated Hydrogen Production**

A new approach to hydrogen production from water is described. This simple method is based on carbon dioxide-mediated water decomposition under UV radiation. The water contained dissolved sodium hydroxide, and the solution was saturated with gaseous carbon dioxide. During saturation, the pH decreased from about 11.5 to 7–8. The formed bicarbonate and carbonate ions acted as scavengers for hydroxyl radicals, preventing the recombination of hydroxyl and hydrogen radicals and prioritizing hydrogen gas formation. In the presented method, not yet reported in the literature, hydrogen production is combined with carbon dioxide. For the best system with alkaline water (0.2 m NaOH) saturated with CO₂ under UV-C, the hydrogen production amounted to 0.6 μmol h⁻¹ during 24 h of radiation.     

Ochratoxin A and 2′R-Ochratoxin A in Selected Foodstuffs and Dietary Risk Assessment

The aim of this study was to estimate the contamination of grain coffee, roasted coffee, instant coffee, and cocoa purchased in local markets with ochratoxin A (OTA) and its isomerization product 2′R-ochratoxin A (2′R-OTA), and to assess risk of dietary exposure to the mycotoxins. OTA and 2′R-OTA content was determined using the HPLC chromatography with immunoaffinity columns dedicated to OTA. OTA levels found in all the tested samples were below the maximum limits specified in the European Commission Regulation EC 1881/2006. Average OTA concentrations calculated for positive samples of grain coffee/roasted coffee/instant coffee/cocoa were 0.94/0.79/3.00/0.95 µg/kg, with the concentration ranges: 0.57–1.97/0.44–2.29/0.40–5.15/0.48–1.97 µg/kg, respectively. Average 2′R-OTA concentrations calculated for positive samples of roasted coffee/instant coffee were 0.90/1.48 µg/kg, with concentration ranges: 0.40–1.26/1.00–2.12 µg/kg, respectively. In turn, diastereomer was not found in any of the tested cocoa samples. Daily intake of both mycotoxins with coffee/cocoa would be below the TDI value even if the consumed coffee/cocoa were contaminated with OTA/2′R-OTA at the highest levels found in this study. Up to now only a few papers on both OTA and 2′R-OTA in roasted food products are available in the literature, and this is the first study in Poland.