Application of ODMR to the study of DNA complexes of bisintercalating antibiotics and their biosynthesized derivatives

The DNA complexes of triostin A, echinomycin, and the monoquinoline (1QN) and bisquinoline (2QN) biosynthesized derivatives of echinomycin were investigated by optical detection of triplet-state magnetic resonance (ODMR) spectroscopy, with the quinoxaline and quinoline moieties of the DNA-binding peptides used as intrinsic probes. Plots of zero-field splitting (zfs)D parameter versus monitored wavelength revealed heterogeneity in the phosphorescence emission of echinomycin, triostin A, and 2QN ascribed to the occurrence of major and minor forms of the peptides in aqueous solution. ODMR results, in conjunction with findings from phosphorescence studies, indicate that the quinoxaline and quinoline chromophores of the major forms of the peptides are involved in aromatic stacking interactions in complexes with the natural DNAs fromMicrococcus lysodeikticus, Escherichia coli, and calf thymus as evidenced by red shifts in the phosphorescence 0,0 bands of the drugs, reductions in the phosphorescence lifetimes and zfsD andE parameters, and polarity reversal of the ODMR slow passage signals upon drug complexation. The reversal in ODMR signal polarity of echinomycin and 2QN is a consequence of changes in the triplet-state sublevel decay constants upon peptide binding to the natural DNAs. The extent of reduction of theD parameter for the major form of echinomycin, 2QN, and the quinoline moiety of 1QN upon complexation with polymeric DNAs was found to correlate with the binding affinities measured for these targets [1], but no correlation was found for the quinoxaline moiety of 1QN. Preliminary studies of triostin A-DNA complexes also revealed no correlation between the reduction in zfsD-value upon complexation and binding affinity, although the largest reductions inD-value among the peptides investigated in this report were exhibited by the poly(dG-dC)·poly(dG-dC) and natural DNA complexes of triostin A.     

Thermal interdiffusion in InGaAs/GaAs and GaAsSb/GaAs strained quantum wells as a function of doping density

We studied the thermal stability and interdiffusion of InGaAs/GaAs and GaAsSb/GaAs single quantum wells as a function of temperature for both Be and Si doping at various doping concentrations. The interdiffusion was monitored using the photoluminescence from the ground states of the valence- and conduction-band quantum wells. Using a Green's function method to solve the diffusion equation, assuming Fick's law behaviour, the evolution of the well shape during annealing was determined, and Schrödinger's equation was solved for this well shape to provide the ground-state energy levels of the system using the diffusion constant as the only fitting parameter. The validity of this model as applied to both systems is discussed.Strained Layer Structures Research Group.     

Domination of uniformly continuous semigroups

We prove that a bounded operator on a Banach lattice, satisfying a growth condition, is regular. Also, we prove that the generator of a C ₀-semigroup on such a lattice for which such an operator exists is bounded.     

Parity violation at neutron p-wave resonances of238U and232Th and related questions

Parity violation effects have been studied at 40 neutron p-wave resonances of the even-even nuclei²³⁸U and²³²Th. Of these 11 show parity violation effects larger than 2 standard deviations, making parity violation a rather common phenomenon. Parity mixing up to 10% has been found. The root-mean squared matrix elements for parity violation derived from these resonances are M=0.58 (+0.50/-0.25) meV for²³⁸U, respectively 1.39 (+0.35/-0.38) meV for²³²Th.     

A DISCRETE AGE STRUCTURED SI MODEL OF TRACHEAL MITE (Acarapis woodi (RENNIE)) INFESTATION OF HONEY BEES (Apis mellifera L.) AT THE COLONY LEVEL

This paper presents a discrete age structured SI model of tracheal mite (Acarapis woodi (Rennie)) infestation of honey bees (Apis mellifera L.) at the colony level. The model describes the elevated honey bee attrition during winter and predicts that winter brood rearing should promote colony survival by decreasing the colony's infestation and increasing the colony's population. The model also predicts that swarming and the artificial removal of part of the colony's forager honey bees should reduce the colony's infestation level.     

Protonated ethanol and its neutral counterparts

Collisionally activated dissociation and neutralization-reionization experiments reveal that protonation of ethanol leads to two distinct isomers, the classical ion CH₃CH₂OH⁺₂ and the proton-bound complex C₂H₄…H⁺…OH₂. The neutral counterpart of the latter is unstable, whereas that of the former can be produced in a bound state if the CH₃CH₂OH⁺₂ precursor ion is formed under low ion source pressure conditions and, thus, with higher internal energies. This suggests that there are substantial differences in the geometries of CH₃CH₂OH⁺₂ and the hypervalent CH₃CH₂OH₂ ·. This provides only a partial explanation for unusual isotope effects; C₂H₅OD₂ ·, CH₃CD₂OD₂ ·, and CD₃CH₂OD₂ · are substantially more stable than C₂D₅OD₂ · and C₂H₅OH₂ ·.     

Triggering GaAs lock-on switches with laser diode arrays

Progress toward the triggering of high-power photoconductive semiconductor switches (PCSSs) with laser diode arrays, is reported. An 850-W optical pulse from a laser diode array was used to trigger a 1.5-cm-long switch that delivered 8.5 MW to a 38.3-Ω load. Using 166-W arrays, it was possible to trigger a 2.5-mm-long switch delivering 1.2 MW with 600-ps rise-times at pulse repetition frequencies of 1 kHz. These 2.5-mm-long switches survived 10⁵ pulses at 1.0 MW levels. In single-pulse operation, up to 600 A was switched with laser diode arrays. The goal is to switch up to 5 kA in a single-shot mode and up to 100 MW repetitively at up to 10 kHz. At electric fields below 3 kV/cm GaAs switches are activated by creation of one electron-hole pair per photon. This linear mode demands high laser power and, after the light pulse, the carriers recombine in nanoseconds. At higher electric fields GaAs acts as a light-activated Zener diode. The laser light generates carriers as before, but the field induces gain such that the amount of light required to trigger the switch is reduced by a factor of up to 500. The gain continues until the field across the sample drops to a material-dependent lock-on field. The gain in the switch allows for the use of laser diodes     

The effect of dissipation on coherent quantum tunnelling in a double-well system: Two-level model using an adjoint equation approach

We examine the effect of dissipation on coherent quantum tunnelling between the two lowest levels of a double-well system using an adjoint equation approach developed previously in the treatment of quantum-optical problems. Dissipation is modelled by a linear coupling to a bath of harmonic oscillators. The high frequency portion of the bath is adiabatically eliminated using a cumulant expansion technique, which generates frequency renormalisation terms. Making a low temperature assumption, an approximate two-level model is developed in the form of three coupled stochastic differential equations. With a decorrelation approximation, the two-level equations can be solved to yield familiar results. However, the adjoint equation also permits the use of direct stochastic simulation as a means of solution, and simulations are carried out for a range of parameters. A comparison with the decorrelation approximation is made.