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.     

On inversion of linear descriptor-variable control systems containing input derivatives

Linear control systems of the form E = Ax + Bv, y = Cx + Dv,are considered, where v is a column composed of the controlu and its first k derivatives, and E is a singular square matrix.This problem is this: find a system R = Fz + Gw, Lv = Hz + Jw,where w is some linear combination of y (the output of the originalsystem) and its derivatives. For the solution of this problem,a method (based on the use of matrix generalized inverse) isdeveloped that can be applied both to time-invariant and totime-varying systems. For the time-invariant case, a numericalprocedure is presented that either yields a system of the desiredform in which the coefficient matrices are of the smallest possibledimensions or shows that there is no such system.     

Theoretical study of rearrangements in water dimer and trimer

The global minimum and transition states for the acceptor-tunnelling, donor-acceptor interchange and bifurcation tunnelling rearrangements of the water dimer, and the single-flip, bifurcation and concerted proton transfer processes in the water trimer have been reinvestigated. Our analysis of the tunnelling splittings and spectroscopy is based on ab initio calculations at the computational level of second-order M?ller-Plesset (MP2) theory with basis sets of aug-cc-pVXZ quality (X = D, T, Q for the dimer; X = D, T for the trimer). In both water dimer and trimer, the binding energy, barrier heights, intermonomer distances, and harmonic frequencies converge smoothly as the size of the basis set increases. In the water dimer, the binding energy was evaluated as 5.09kcal mol^?1, while the activation energies are 0.52 (acceptor-tunnelling) 0.79 (donor-acceptor interchange), and 1.94 kcal mol^?1 (bifurcation tunnelling) at the MP2/aug-cc-pVQZ level. In the water trimer, the binding energy was evaluated as 16.29 kcal mol^?1, while the activation energies are 0.28 (single-flip), 2.34 (bifurcation), and 26.36 (proton transfer) kcal mol^?1 at the MP2/aug-cc-pVTZ level.     

AN INDIVIDUAL-BASED FISHERY MODEL AND ASSESSING FISHERY STABILITY

ABSTRACT. The stability of a fishery system was investigated using two forms of a stochastic computer simulation model that was individually based in terms of the fishing boats. Fish catch was partitioned among boats according to two catch processes: an unranked process in which all boats had equal ability to catch fish and a ranked catch model in which a boat's ability to catch fish depended on its wealth. Stock size, total catch, fleet size and individual boat wealth were modeled over a series of years. In the unranked catch model the fish stock size and fleet size were significantly more variable than in the ranked catch model.     

Analytical second derivatives for excited electronic states using the single excitation configuration interaction method: theory and application to benzo[a]pyrene and chalcone

A compact formulation and a semi-direct implementation are described of analytical second derivatives of the single excitation configuration interaction (CIS) energy. CPU time, memory usage and disc storage all scale with the same power of system size as the ground state Hartree—Fock (HF) method, with a coefficient only 2 to 3 times larger. Thus usually analytical excited state CIS frequencies are feasible when HF frequencies are feasible. As a computational example, analytical CIS/3-21G frequencies for benzo[a]pyrene are calculated more efficiently than with finite differences. As a chemical application, analytical CIS/6-31G^* frequencies are used to investigate non-planarity in the lowest π → π excited state of transchalcone.     

The velocity autocorrelation function and self-diffusion coefficient of fluids with steeply repulsive potentials

We consider the velocity autocorrelation function, vacf, or C_v(t) and self-diffusion coefficients, D, of steeply repulsive inverse power fluids (SRP) in which the particles interact with a pair potential, ? (r) = ?(σ/r)ⁿ. The C_v(t) are calculated numerically by molecular dynamics simulations. Accurate expressions for the short time expansion of C_v(t) to order O(t⁴) for n large are derived for this fluid. We propose novel expressions for C_v (t) that, for n large, spans the transition from the short time regime (expandable in even powers of time) and the longer time exponential-like regime characteristic of hard spheres. Inter alia we introduce relaxation times that characterize the duration of a collision and the decay of the velocity correlation within the mean-collision or Enskog-like relaxation time, T_E.     

THE USE OF TELESCOPING SPATIAL SCALES TO CAPTURE INSHORE TO SLOPE DYNAMICS IN MARINE ECOSYSTEM MODELING

Abstract Ecosystem processes function at many scales, and capturing these processes is a challenge for ecosystem models. Nevertheless, it is a necessary step for considering many management issues pertaining to shelf and coastal systems. In this paper, we explore one method of modeling large areas with a focus at a range of scales. We develop an ecosystem model that can be used for strategic management decision support by modeling the waters off southeastern Australia using a polygon telescoping approach, which incorporates fine‐scale detail at the coastal zone, increasing in scale to a very coarse scale in the offshore areas. This telescoping technique is a useful tool for incorporating a wide range of habitats at different scales into a single model.     

1H NMR investigation of the hetero-association of aromatic molecules in aqueous solution: factors involved in the stabilization of complexes of daunomycin and acridine drugs

Hetero-association of the anthracycline drug, daunomycin (DAU), with typical mutagens, the acridine dyes proflavine (PF) and acridine orange (AO), has been studied by 500 MHz ¹H NMR spectroscopy as a function of concentration and temperature in 0.1 mol dm^?3 phosphate buffered aqueous solutions at pD = 7.1. The results have been analysed in terms of a statistical-thermodynamical model of hetero-association of aromatic molecules, described previously [Davies, D. B., Veselkov, D. A., and Veselkov, A. N., 1999, Molec. Phys., 97, 439], but generalized in this work, so that there is no limitation on the magnitudes of the self-association constants of the interacting molecules. Expressions suitable for the analysis of NMR parameters of both components in the mixed solution have been developed enabling both the structural and thermodynamic properties of hetero-association to be determined. The magnitude of the equilibrium constant for hetero-association of PF + DAU is found to be substantially higher than the self-association constants of these molecules, whereas that for hetero-association of AO + DAU is intermediate between the equilibrium constants of self-association of AO and DAU. Intermolecular cross-peaks observed in 2D-ROESY spectra of PF + DAU mixed solutions are consistent with formation of a hetero-association complex in which an intermolecular hydrogen bond can form between either of the 3,6-diamino groups of the PF chromophore and the 9-MeCO group of DAU, which is in contrast to AO + DAU hetero-association, where such hydrogen bonds are unable to form. Quantitative structural and thermodynamical analysis of PF + DAU complexation is consistent with an intermolecular hydrogen bond contributing to the stability of the hetero-complex in aqueous solution. The NMR results show that hydrophobic interactions play a substantial role in the stabilization of the AO-DAU complex, characterized by a relatively small entropy change on complexation, compared to the PF-DAU hetero-complex, which is mainly stabilized by hydrogen bond and dispersive van der Waals interactions.     

Application of the elongation method to nonlinear optical properties: finite field approach for calculating static electric (hyper)polarizabilities

A novel finite-field approach for calculating electric (hyper)polarizabilities based on the elongation method is developed. The method was tested at the semi-empirical PM3 level by using three model systems: the hydrogen chain, the water chain and polyacetylene. The results satisfactorily reproduce the ‘exact’ MOPAC values. The most important advantage of this approach is the large saving of computer time since the dimension of the SCF equation remains the same regardless of the number of atoms in the system. Thus, it is a very useful tool to treat large systems. The method can also be applied to building up a chain containing an arbitrary sequence of monomers.     

Molecular dynamics study of the mobility in poly(butyl methacrylate) isomers

Molecular mobility is studied in poly(butyl methacrylate) isomers with molecular dynamics simulations in order to understand the role of the side chain steric hindrance on the β and δ relaxation mechanisms. The simulations suggest that in the temperature range studied the δ process is weakly influenced by the α process. Conversely, the β process seems to be significantly changed as compared with the low frequency regime. The results exposed also show evidence that the intramolecular cooperativity is higher in PnBMA than in PtBMA, which, could be related to the distance to the α-β crossover.