CASSCF/CAS-PT2 study of hole transfer in stacked DNA nucleobases

CASSCF and CAS-PT2 calculations are performed for the ground and excited states of radical cations consisting of two and three nucleobases. The generalized Mulliken-Hush approach is employed for estimating electronic couplings for hole transfer in the pi-stacks. We compare the CASSCF results with data obtained within Koopmans' approximation. The calculations show that an excess charge in the ground and excited states in the systems is quite localized on a single base both at the CASSCF level and in Koopmans' picture. However, the CASSCF calculations point to a larger degree of localization and, in line with this, smaller transition dipole moments. The agreement between the CAS-PT2 corrected energy gaps and the values estimated with Koopmans' theorem is better, with the CAS-PT2 calculations giving somewhat smaller gaps. Overall, both factors result in smaller CASSCF/CAS-PT2 couplings, which are reduced by up to 40% of the couplings calculated using Koopmans' approximation. The tabulated data can be used as benchmark values for the electronic couplings of stacked nucleobases. For the base trimers, comparison of the results obtained within two- and three-state models show that the multistate treatment should be applied to derive reliable estimates. Finally, the superexchange approach to estimate the donor acceptor electronic coupling in the stacks GAG and GTG is considered.     

Space Semi-Discretisations for a Stochastic Wave Equation

We study an approximation scheme for a nonlinear stochastic wave equation in one-dimensional space, driven by a spacetime white noise. The sequence of approximations is obtained by discretisation of the Laplacian operator. We prove L ^p -convergence to the solution of the equation and determine the rate of convergence. As a corollary, almost sure convergence, uniformly in time and space, is also obtained. Finally, the speed of convergence is tested numerically.⋆Supported by the grant BMF 2003-01345 from the Dirección General de Investigación, Ministerio de Ciencia y Tecnología, Spain.     

Structural insights for the design of new PPARgamma partial agonists with high binding affinity and low transactivation activity

Peroxisome Proliferator-Activated Receptor γ (PPARγ) full agonists are molecules with powerful insulin-sensitizing action that are used as antidiabetic drugs. Unfortunately, these compounds also present various side effects. Recent results suggest that effective PPARγ agonists should show a low transactivation activity but a high binding affinity to inhibit phosphorylation at Ser273. We use several structure activity relationship studies of synthetic PPARγ agonists to explore the different binding features of full and partial PPARγ agonists with the aim of differentiating the features needed for binding and those needed for the transactivation activity of PPARγ. Our results suggest that effective partial agonists should have a hydrophobic moiety and an acceptor site with an appropriate conformation to interact with arm II and establish a hydrogen bond with Ser342 or an equivalent residue at arm III. Despite the fact that interactions with arm I increase the binding affinity, this region should be avoided in order to not increase the transactivation activity of potential PPARγ partial agonists.     

Principal mappings of 3-dimensional Riemannian spaces into spaces of constant curvature

As is well-known, the Gauss theorem, according to which any 2-dimensional Riemannian metric can be mapped locally conformally into an euclidean space, does not hold in three dimensions. We define in this paper transformations of a new type, that we call principal. They map 3-dimensional spaces into spaces of constant curvature. We give a few explicit examples of principal transformations and we prove, at the linear approximation, that any metric deviating not too much from the euclidean metric can be mapped by a principal transformation into the euclidean metric.     

All bipartite entangled states are useful for information processing

The question of whether all entangled states can be used as a nonclassical resource has remained open so far. Here we provide a conclusive answer to this problem for the case of systems shared by two parties. We show that any entangled state can enhance the teleportation power of some other state. This holds even if the state is bound entangled.     

A removal lemma for systems of linear equations over finite fields

We prove a removal lemma for systems of linear equations over finite fields: let X ₁, …, X _m be subsets of the finite field F _q and let A be a (k × m) matrix with coefficients in F _q ; if the linear system Ax = b has o(q ^m−k ) solutions with x _i ∈ X _i , then we can eliminate all these solutions by deleting o(q) elements from each X _i . This extends a result of Green [Geometric and Functional Analysis 15 (2) (2005), 340–376] for a single linear equation in abelian groups to systems of linear equations. In particular, we also obtain an analogous result for systems of equations over integers, a result conjectured by Green. Our proof uses the colored version of the hypergraph Removal Lemma.     

Mechanistic studies on the conversion of dicobalt octacarbonyl into colloidal cobalt nanoparticles

In situ ATR-FTIR monitoring has allowed the direct study of the effect of additives (trioctylphosphine oxide [TOPO] and oleic acid) on the kinetics and rate of the thermal decomposition of dicobalt octacarbonyl leading to the formation of colloidal cobalt nanoparticles (CoCNPs). The study has shown that additives usually considered as simple surfactants influence the rate and kinetics of the decomposition of dicobalt octacarbonyl. Several of the initial intermediates connecting Co2(CO)8 with CoCNPs have been identified, and a tentative mechanism for the formation of the colloidal nanoparticles has been proposed.     

An extended conical intersection seam associated with a manifold of decay paths: excited-state intramolecular proton transfer in O-hydroxybenzaldehyde

O-Hydroxybenzaldehyde (OHBA) is a prototypical photoprotector exhibiting excited-state intramolecular proton transfer (ESIPT). Here we report how its photostability depends on an extended conical intersection seam associated with a manifold of decay paths. Thus, the photoreactivity of OHBA derives from a flat excited-state potential energy surface with barriers of only tenths of electronvolts between the reactant and several conical intersection structures that lead to different products: two isomers of a hydrogen-bonded intersection (HBI) that lead back to the enol reactant or to the tautomerized keto form in its Z conformation; an intersection (ZEI) that mediates the Z-E isomerization of the keto tautomer; and a twisted-pyramidalized one (TPI) that leads to an oxetene adduct. The intersection structures are connected to each other, forming a continuous seam, and the competition between the products depends on where the seam is accessed after the initial excitation. The overall picture must be also valid for the methyl salicylate and salicylic acid analogues of OHBA since it reflects the characteristics reported previously for MS and SA.     

A perspective on operational research prospects for agriculture

This paper discusses the future of operational research (OR) for the agricultural industries in a broad sense, including horticulture and viticulture during a period of increased pressure on natural resources. The authors use their experience in the field along with published literature, to draw insights into new opportunities for OR, and how the OR community might adapt to realise these opportunities best. Trends in demand for food security and biofuels, the quest for sustainability, information technology (IT), and commercial power create new opportunities to support strategic investment and operations management within both primary production and the related supply chains. To realise such potential, the agricultural OR community needs to improve management of stakeholder relations, interdisciplinary synthesis, and the successful application of OR.     

Characterization of winemaking yeast by cell number-size distribution analysis through flow field-flow fractionation with multi-wavelength turbidimetric detection

Yeasts are widely used in several areas of food industry, e.g. baking, beer brewing, and wine production. Interest in new analytical methods for quality control and characterization of yeast cells is thus increasing. The biophysical properties of yeast cells, among which cell size, are related to yeast cell capabilities to produce primary and secondary metabolites during the fermentation process. Biophysical properties of winemaking yeast strains can be screened by field-flow fractionation (FFF). In this work we present the use of flow FFF (FlFFF) with turbidimetric multi-wavelength detection for the number-size distribution analysis of different commercial winemaking yeast varieties. The use of a diode-array detector allows to apply to dispersed samples like yeast cells the recently developed method for number-size (or mass-size) analysis in flow-assisted separation techniques. Results for six commercial winemaking yeast strains are compared with data obtained by a standard method for cell sizing (Coulter counter). The method here proposed gives, at short analysis time, accurate information on the number of cells of a given size, and information on the total number of cells.