Parameterization of a potential function for the Ca2+ −Ne and Ca2+ −N2 interactions using high-level ab initio data

Ab initio calculations have been carried out at the CCSD(T)/aug-cc-pVTZ level on di-nitrogen and neon interacting with a calcium (II) cation. The interaction of nitrogen with the Ca²⁺ cation is examined for end-on and side-on approaches. The two adjustable parameters in the TrAZ potential (A ^Ca2+-Ne , b ^Ca2+-Ne ) are fitted to the Ca²⁺-Ne potential energy curve and combination rules are then applied in reverse to get A ^Ca2+-Ca2+ , b ^Ca2+-Ca2+ . Combining these with values of A^NN, 6^NN enables the Ca²⁺-N₂ potential energy curves to be predicted a priori. Agreement with the ab initio data is found to improve dramatically when the anisotropy of the nitrogen polarizability is included in the induced interaction energy. Other combination rules are tried but are not found to have an impact on the agreement between the a priori potential and the ab initio data     

A study of the adsorption of the amphiphilic penicillins cloxacillin and dicloxacillin onto human serum albumin using surface tension isotherms

The interaction of human serum albumin (HSA) with two structurally similar anionic amphiphilic penicillins, cloxacillin and dicloxacillin, at 25 °C has been examined by surface tension measurements under conditions at which the HSA molecule was positively (pH 4.5) or negatively charged (pH 7.4). Measurements were at fixed HSA concentrations (0.0125 and 0.125% w/v) and at drug concentrations over a range including, where possible, the critical micelle concentration (cmc). Interaction between anionic drugs and positively charged HSA at pH 7.4 resulted in an increase of the cmc of each drug as a consequence of its removal from solution by adsorption. Limited data for cloxacillin at pH 4.5 indicated an apparent decrease of the cmc in the presence of HSA suggesting a facilitation of the aggregation by association with the protein. Changes in the surface tension-log (drug concentration) plots in the presence of HSA have been discussed in terms of the adsorption of drug at the air-solution and protein-solution interfaces. Standard free energy changes associated with the micellization of both drugs and their adsorption at the air-solution interface have been calculated and compared.     

Polarizabilities and excitation energies from the multiplicative Kohn-Sham (MKS) approach

The conventional Kohn-Sham expressions for the static isotropic polarizability and vertical excitation energy are evaluated using Kohn-Sham orbitals and eigenvalues determined directly from theoretical electron densities. For a series of small molecules, polarizabilities determined from wavefunction-based BD(T) electron densities differ, on average, by about 2% from conventional BD(T) polarizabilities when the LDA exchange-correlation integrand is used in the electric Hessian matrix. Also polarizabilities determined from Kohn-Sham densities, using the B97-2 hybrid functional, are close to the conventional B97-2 values. To quantify the dependence on the choice of exchange-correlation integrand, calculations are performed also using the HCTH integrand. Rydberg excitation energies determined from BD(T) and B97-2 densities exhibit errors due to inaccuracies in the asymptotic exchange-correlation potential. This category of excitation energy is relatively insensitive to the choice of exchange-correlation integrand; valence excitations can be more sensitive.     

Multidimensional Reconstruction by Set-valued Approximations

Some generalizations of the notion of univariate data interpolationare presented, inducing the concept of set-valued interpolationin a general metric space. Consequently methods for univariateinterpolation or smoothing of multidimensional geometrical dataare suggested. In particular the application of these methodsto 3-D body recognition from cross-sectional data is discussed.Preliminary analysis of the interpolation process is presentedand the capability of reconstructing bodies of complex topologiesis exemplified.     

Travelling waves in model reacting flows with reversible kinetics

The authors study the existence of wavefront-type travellingwave solutions in the Fickett-Majda model of viscous reactiveflow when the chemistry is modelled by a reversible chemicalreaction. The problem is reduced to proving the existence ofa heteroclinic orbit, in a two-dimensional phase space, connectingtwo critical points that represent the equilibrium states atplus and minus infinity. Reactions in which the forward reactioncan be either endothermic or exothermic are examined, and itis shown that compression waves must be accompanied by a shiftin the equilibrium composition in the endothermic direction,while rarefac-tions are accompanied by a shift in the exothermicdirection. Although compression waves occur on a larger parameterdomain, there are regimes where the rarefactions appear. Finally,the stability of an equilibrium state under small perturbationsis discussed.     

Optimal driving strategy for a solar car on a level road

Every three years, solar cars from all over the world come toAustralia to participate in the World Solar Challenge. In 1993there were 52 cars in the race. Five cars finished within fivedays, each one breaking the previous race record and achievingan average speed exceeding 70 km/h. The performance of thesecars depends on many factors: power, aerodynamics, tractionefficiency, weight, reliability, and (not least of all) drivingstrategy. On a level road, the optimal driving strategy foran ideal car is essentially a speed-holding strategy. For areal car with inefficient energy storage, however, there aretwo distinct holding speeds. The lower speed is held when solarpower is low and must be supplemented from stored energy. Theupper speed is held when solar poler is high, and excess energyis stored.     

PHOTOINDUCED ELECTRON TRANSFER ACROSS LIPID BILAYERS CONTAINING MAGNESIUM OCTAETHYLPORPHYRIN

Both photoinitiated (thermodynamically downhill) and photodriven (thermodynamically uphill) electron transfer reactions across lipid bilayers are sensitized by magnesium octaethyl porphyrin (MgOEP). It is shown that the reaction mechanism is via reduction of photoexcited MgOEP at the reducing (ascorbate) side of the bilayer and the charge carrier is likely the neutral protonated MgOEP anion. The MgOEP cation (or its neutral form) does not contribute to charge passage across the bilayer even though it is readily formed at the acceptor (ferricyanide or methyl viologen) side of the membrane. Photoelectric measurements on planar bilayers show that the time constant for reduction of excited MgOEP is about 10 microseconds with 10 mM ascorbate. The membrane transport of the mediator appears to be rate limiting when the reaction is photoinitiated and the interfacial reaction appears to be limiting when the reaction is photodriven. The quantum yield of the process is about 0.1 in the latter case and about 0.02 in the former. The former yield is increased to about 0.15 in the presence of a redox mediator, duroquinone. In these systems, the magnesium porphyrin is both sensitizer and trans membrane redox mediator.     

MODULATION BY THIOLS OF THE MEROCYANINE 540-SENSITIZED PHOTOLYSIS OF LEUKEMIA CELLS, RED CELLS, AND Herpes simplex VIRUS TYPE 1

This paper reports on the role of endogenous and exogenous thiols in the merocyanine 540 (MC 540)-sensitized photoirradiation of L1210 leukemia cells, human erythrocytes, and human Herpes simplex virus type 1. Several measures taken to decrease the intracellular content of glutathione enhanced the cells' sensitivity to MC 540-sensitized photoirradiation while stimulation of glutathione biosynthesis or supplementation of the extracellular or extraviral thiol content decreased the photosensitivity of cells and viruses. Taken together, these data suggest that endogenous and exogenous thiols can modulate the sensitivity of cells and enveloped viruses to MC 540-sensitized photoirradiation. They also pose new questions as to the mechanism of MC 540-sensitized photolysis.