Inhibitory effect of different product analogues on β-alanine synthase: A thermodynamic and fluorescence analysis

The enzyme N-carbamoyl-β-alanine amidohydrolase catalyse the hydrolysis of N-carbamoyl-β-alanine or N-carbamoyl-β-aminoisobutyric acid to β-alanine or 3-aminoisobutyric acid, under the release of carbon-dioxide and ammonia. This work studies the inhibition of N-carbamoyl-β-alanine amidohydrolase from Agrobacterium tumefaciens C58 (Atβcar) by different carboxylic acid compounds that differ in number of carbons, and position and size of ramification, while the binding thermodynamics of the inhibitors are studied by isothermal titration calorimetry (ITC) and fluorescence. From the binding constants and inhibition studies, we conclude that propionate is the most efficient inhibitor among those tested. Substitution of the linear alkyl acids in positions 2 and 3 resulted in a drastic decrease of the affinity. The thermodynamic parameters show that a conformational change is triggered upon ligand binding. Binding enthalpy ΔH_b is negative in all cases for all ligands, and thus, Van der Waals interactions and hydrogen bonding are most probably the major sources for this term. The process is entropically favoured at all temperatures and pH studied, most probably due to the liberation of water molecules accompanying the conformational change of the enzyme.     

A hybrid genetic algorithm for the resource-constrained project scheduling problem

In this paper we propose a Hybrid Genetic Algorithm (HGA) for the Resource-Constrained Project Scheduling Problem (RCPSP). HGA introduces several changes in the GA paradigm: a crossover operator specific for the RCPSP; a local improvement operator that is applied to all generated schedules; a new way to select the parents to be combined; and a two-phase strategy by which the second phase re-starts the evolution from a neighbour’s population of the best schedule found in the first phase. The computational results show that HGA is a fast and high quality algorithm that outperforms all state-of-the-art algorithms for the RCPSP known by the authors of this paper for the instance sets j60 and j120. And that it is competitive with other state-of-the-art heuristics for the instance set j30.     

Exotic electronic phases in the second Landau level

Recent experiments have shown that two-dimensional electron systems with an externally applied magnetic field are an extremely rich ground for many-body physics. In particular, when only two of the Landau levels (LL) are filled an intricate magnetoresistance is found. This result stems from an interesting competition of electronic phases such as fractional quantum Hall liquids, reentrant integer Hall states, and unique quantized states at even denominator LL filling factors. We present a brief review of the transport properties of these electronic phases and discuss in detail the effects of an added in-plane magnetic field.     

Versatile binding properties of di-pyridyl ligands with Cu(II) complexes: The syntheses,structural characterization and thermal analysis of six new species

A novel series of 4,4′-bipyridine- and 1,2-bis(4-pyridyl)ethane-Cu(II) complexes were synthesized using a variety of amine ligands (DPA = di(2-pyridylmethyl)amine, Medpt = 3,3′-diamino-N-methyldipropylamine, Hbpca = bis(2-pyridylcarbonyl)amine, TPA = tris(2-pyridylmethyl)amine) and cyclen = 1,4,7,10-tetraazacyclododecane). Different complexes were obtained including mononuclear [Cu(cyclen)(4,4′-bipy)](ClO₄)₂ (1), dinuclear {[Cu(μ₂-bpca)(4,4′-bipy)(H₂O)]ClO₄}₂ (2), [Cu₂(DPA)₂(μ₂-4,4′-bipy)(ClO₄)₄)]·H₂O (3), [Cu₂(cyclen)₂(μ₂-bpe)](ClO₄)₄ (4) and [Cu₂(TPA)₂(μ₂-bpe)](ClO₄)₄ (5) and the 1-D polymer, {[Cu(Medpt)(μ₂-4,4′-bipy)](ClO₄)₂}_n (6). In the 1–6 samples, cooling up to 100 K produces only the expected, minor, changes in cell constants given no space group changes. Therefore, data for the 100 K structures are reported only. Single-crystal X-ray crystallography reveals the monodentate coordination of the 4,4′-bipy in 1 and 2, and the bridged nature of the di-pyridyl ligands in the dinuclear complexes 2–5 and in the polymeric complex 6. In this series, structures 3–6 consist of the 4,4′-bipy or bpe bridging the two Cu(II) centers, the coordination by the tri- or the tetra-N donors of the amine, and the ClO₄^? groups as counter ions in 4–6 complexes. In the complexes 3–6, the Cu···Cu distances across the bridged di-pyridyl ligands were found to be greater than 11 Å. The magnetic properties of complex 3 reveal no evidence for magnetic coupling between the two Cu(II) centers (J = ?0.58 cm^?1).     

Chemoenzymatic synthesis of optically active Mugetanol isomers: use of lipases and oxidoreductases in fragrance chemistry

Straightforward synthetic strategies for the preparation of optically active Mugetanol isomers have been developed through different independent chemoenzymatic routes implying the use of either alcohol dehydrogenases in aqueous media or lipases in organic solvents coupled with a catalytic hydrogenation process. Among the alcohol dehydrogenases tested, ADH RS1 showed the best activities in the bioreduction of 4-isopropylacetophenone. The lipase from Pseudomonas cepacia (PSL-C I) reached high activity values in the lipase-catalyzed transesterification of 4-isopropylphenyl)ethanol, while Candida antarctica lipase B showed the best stereopreference in the acetylation of 4-isopropylcyclohexylethanol.     

An overlooked property of plot methods

An interesting and often overlooked property of the MLR least-squares method is discussed. Here it is shown how the observed vs. calculated and calculated vs. observed plots, which are usually presented as equivalent, in fact they are not. Due to the inherent properties of the MLR procedure, it is shown that the slope of the calculated vs. observed plot is r ², as the slope of the experimental vs. calculated plot is just 1. This behaviour also has direct consequences to the corresponding residual plots.     

Insertion of lattice-valued and hedgehog-valued functions

Problems of inserting lattice-valued functions are investigated. We provide an analogue of the classical insertion theorem of Lane [Proc. Amer. Math. Soc. 49 (1975) 90-94] for L-valued functions where L is a ?-separable completely distributive lattice (i.e. L admits a countable join-dense subset which is free of completely join-irreducible elements). As a corollary we get an L-version of the Katětov-Tong insertion theorem due to Liu and Luo [Topology Appl. 45 (1992) 173-188] (our proof is different and much simpler). We show that ?-separable completely distributive lattices are closed under the formation of countable products. In particular, the Hilbert cube is a ?-separable completely distributive lattice and some join-dense subset is shown to be both order and topologically isomorphic to the hedgehog J(ω) with appropriately defined topology. This done, we deduce an insertion theorem for J(ω)-valued functions which is independent of that of Blair and Swardson [Indian J. Math. 29 (1987) 229-250]. Also, we provide an iff criterion for inserting a pair of semicontinuous function which yields, among others, a characterization of hereditarily normal spaces.     

Determination of the entropy of formation of the Pt(111)∣ perchloric acid solution interface. Estimation of the entropy of adsorbed hydrogen and OH species

The entropy of formation of the interface between a Pt(111) electrode and a 0.1-M HClO₄ solution is calculated here for the first time from the temperature dependence of total charge vs potential curves following a thermodynamic analysis based on the electrocapillary equation. From this quantity, the absolute entropies of specifically adsorbed species (hydrogen and OH) can be estimated. The present method is an alternative treatment of data that overcomes some of the limitations involved in the approach that uses a generalized isotherm. However, it requires additional experimental data: the temperature coefficient of the potential of zero total charge of the working electrode and the temperature coefficient of the reference electrode. Comparison of the results obtained by both approaches shows that, for hydrogen adsorption, the agreement is reasonable, but the differences are larger for OH adsorption, thus showing the limitations inherent in the treatment based on the generalized isotherm. Dedicated to Professor Oleg Petrii on the occasion of his 70th birthday on August 24, 2007.     

A tabu thresholding algorithm for arc crossing minimization in bipartite graphs

Acyclic directed graphs are commonly used to model complex systems. The most important criterion to obtain a readable map of an acyclic graph is that of minimizing the number of arc crossings. In this paper, we present a heuristic for solving the problem of minimizing the number of arc crossings in a bipartite graph. It consists of a novel and easier implementation of fundamental tabu search ideas without explicit use of memory structures (a tabu thresholding approach). Computational results are reported on a set of 250 randomly generated test problems. Our algorithm has been compared with the two best heuristics published in the literature and with the optimal solutions for the test problems, size permitting.This research was partially supported by the C.I.C.Y.T. with code tap92-0639.