A robust approach to model-based classification based on trimming and constraints

Advances in Data Analysis and Classification - In a standard classification framework a set of trustworthy learning data are employed to build a decision rule, with the final aim of classifying...     

Gaussian parsimonious clustering models with covariates and a noise component

Advances in Data Analysis and Classification - We consider model-based clustering methods for continuous, correlated data that account for external information available in the presence of...     

Quantum computing methods for electronic states of the water molecule

ABSTRACT

We compare recently proposed methods to compute the electronic state energies of the water molecule on a quantum computer. The methods include the phase estimation algorithm based on Trotter decomposition, the phase estimation algorithm based on the direct implementation of the Hamiltonian, direct measurement based on the implementation of the Hamiltonian and a specific variational quantum eigensolver, Pairwise VQE. After deriving the Hamiltonian using STO-3G basis, we first explain how each method works and then compare the simulation results in terms of gate complexity and the number of measurements for the ground state of the water molecule with different O–H bond lengths. Moreover, we present the analytical analyses of the error and the gate-complexity for each method. While the required number of qubits for each method is almost the same, the number of gates and the error vary a lot. In conclusion, among methods based on the phase estimation algorithm, the second-order direct method provides the most efficient circuit implementations in terms of the gate complexity. Moreover, Pairwise VQE serves the most practical method for near-term applications on the current available quantum computers. Finally the possibility of extending the calculation to excited states and resonances is discussed.     

Hydrogen Atom Transfer-Mediated Domino Cyclisation Reaction to Access (Spiro)Quinazolinones

A radical domino cyclisation reaction of N-cyanamide alkenes, mediated by hydrogen atom transfer (HAT) has been developed. This method, using PhSiH₃ and catalytic Fe(acac)₃, allows for the synthesis of challenging (spiro)quinazolinone scaffolds from simple, tractable (hetero)aryl carboxylic acid and cyanamide building blocks.     

Synthesis and Structure of the Alkoxido-Titanium Pentamolybdate (nBu4N)3[(iPrO)TiMo5O18]: An Entry into Systematic TiMo5 Reactivity

The alkoxido-titanium pentamolybdate [(ⁱPrO)TiMo₅O₁₈]³⁻ (1) has been obtained as its tetrabutylammonium (TBA) salt by hydrolysis of a mixture containing (TBA)₂[Mo₂O₇], (TBA)₄[Mo₈O₂₆] and Ti(OⁱPr)₄ in MeCN and has been characterised by ¹H, ¹³C, ¹⁷O, ⁴⁹Ti and ⁹⁵Mo NMR and FTIR spectroscopy, electrospray ionisation mass spectrometry, elemental microanalysis and single-crystal X-ray crystallography. The Lindqvist-type structure is derived from [Mo₆O₁₉]²⁻ by replacement of {Mo=O}⁴⁺ by {(ⁱPrO)Ti}³⁺ and shows bond alternation in the TiMo₃O₄ rings, with average bond distances of 1.956(8) ? for Ti–O(Mo), 1.832(7) ? for Mo–O(Ti), 1.943(7) ? for Mo_eq–O(Mo_ax) and 1.910(6) ? for Mo_ax–O(Mo_eq), while the increase in charge results in a decrease in ¹⁷O NMR chemical shift for terminal Mo=O groups from δ 933 for [Mo₆O₁₉]²⁻ to δ 875 and 857 for 1 and a shift in ν_Mo=O from 951 cm⁻¹ for [Mo₆O₁₉]²⁻ to 930 cm⁻¹ for 1. The main peaks in the negative-ion electrospray ionisation mass spectrum of (TBA)₃ 1 could be assigned to ion aggregates containing 1 or fragments derived from 1, including {(TBA)₂[(ⁱPrO)TiMo₅O₁₈]}⁻, {(TBA)[(ⁱPrO)TiMo₅O₁₈]}²⁻, {(ⁱPrO)TiMo₂O₈}⁻, {TiMo₅O₁₈}²⁻, {TiMo₄O₁₅}²⁻ and {Mo₃O₁₀}²⁻.     

Reductions of challenging organic substrates by a nickel complex of a noninnocent crown carbene ligand

The first crown-tetracarbene complex of Ni(II) has been prepared, and its crystal structure determined. The complex can be reduced by Na/Hg, with an uptake of two electrons. The reduced complex reductively cleaves arenesulfonamides, including those derived from secondary aliphatic amines, and effects Birch reduction of anthracenes as well as reductive cleavage of stilbene oxides. Computational studies show that the orbital that receives electrons upon reduction of the complex 2 is predominantly based on the crown carbene ligand and also that the HOMO of the parent complex 2 is based on the ligand.     

Neutron activation analysis with pre- and post-irradiation chemical separation for the value assignments of Al, V, and Ni in the new bovine liver SRM 1577C

Instrumental neutron activation analysis as carried out at the National Institute of Standards and Technology (NIST) is inadequate for determining Al, Ni, and V at the levels found in the newly prepared Standard Reference Material^® (SRM) 1577c Bovine Liver. To overcome shortcomings in the value assignment, the authors initiated a cooperative approach using NAA with previously established chemical separation procedures and with significantly different neutron energy spectra to determine Al and V with pre-irradiation separation of the elements at NIST, and V and Ni with post-irradiation separation at the Nuclear Physics Institute ?e?. The determinations were confirmed with the analyses of several SRMs. The work supported the certification of mass fraction values for V and Ni in SRM 1577c.     

2-Aryl propionamides via 1,4-aryl radical migration from N-arylsulfonyl-2-bromopropionamides

Reaction of N-alkyl-N-arylsulfonyl-2-halo-propionamides with pentamethyldiethylenetriamine and either CuBr or CuCl leads to 2-aryl propionamides via initial radical generation, 1,4-aryl migration with loss of SO₂ and reduction of the intermediate amidyl radical in 40-99% yields.     

Photoproducts Formed in the Photoyellowing of Collagen in the Presence of a Fluorescent Whitening Agent

Fibrous proteins discolor on exposure to the UV component of sunlight. This effect is exacerbated in the presence of fluorescent whitening agents (FWAs), which are often applied to textiles to improve product brightness. Tryptophan photoproducts have been identified as significant contributors to protein photoyellowing; however, the role of non–tryptophan-derived chromophores is less clear. In this study bovine collagen, containing no tryptophan residues, was irradiated in the presence and absence of the stilbene-derived FWA, 4,4'-bis(2-sulfostyryl)biphenyl (DSBP) and photoproducts were identified using mass spectrometry. Photoyellowing was found to be dependent on the presence of the FWA, attributed to amplified generation of reactive oxygen species (ROS), particularly hydroxyl radicals and peroxynitrite. Four key proteinaceous photomodifications contributing directly to photoyellowing were located in irradiated collagen pretreated with DSBP, namely dopa, nitrophenylalanine, nitrotyrosine and nitrohistidine. This represents the first direct characterization of the three nitrated residues in the photoyellowing of an isolated fibrous protein, and implicates the ROS, peroxynitrite, as a key contributor to protein photoyellowing. Direct oxidative modification of the FWA itself was also observed. This study demonstrates that, even in the absence of tryptophan residues, significant photomodification of protein residues leading to chromophore formation occurs in the presence of an FWA.     

An EPR investigation of acetonitrile reactivity with superoxide radicals on polycrystalline TiO<Subscript>2</Subscript>

The interaction of acetonitrile with superoxide radicals over a polycrystalline TiO₂ (Degussa P25) surface was investigated using continuous-wave electron paramagnetic resonance (cw-EPR) spectroscopy. For the first time, a thermally unstable radical intermediate has been observed following the low-temperature exposure of acetonitrile to surface-adsorbed O₂⁻ radicals. The radical intermediate has been identified as an [O₂⁻···CH₃CN] type surface complex characterised by the g values of g ₁ = 2.031, g ₂ = 2.010 and g ₃ = 2.003. This surface complex is thermally unstable and decomposes at temperatures of T > 240 K. A second oxygen-centred species was also observed following acetonitrile adsorption, characterised by the spin Hamiltonian parameters of g ₁ = 2.028, g ₂ = 2.010, g ₃ = 2.004, A ₁ = 1.2 mT, A ₂ = 1.0 mT and A ₃ = 1.0 mT, and was assigned to a hydroperoxy radical (HO₂^•).