Microbial sensors of ultraviolet radiation based on recA’::lux fusions

Escherichia coli strains containing plasmid-borne fusions of the recA promoter-operator region to the Vibrio fischeri lux genes were previously shown to increase their luminescence in the presence of DNA damage hazards, and thus to be useful for genotoxicant detection. The present study expands previous work by demonstrating and investigating the luminescent response of these strains to ultraviolet radiation. Several genetic variants of the basic recA'::lux design were examined, including a tolC modification of membrane efflux capacity, a chromosomal integration of the recA'::lux fusion, a different lux reporter (Photorhabdus luminescens instead of V. fischeri, allowing the assay to be run at 37 degrees C), and a different host bacterium (Salmonella typhimurium instead of E. coli). Generally, two modifications provided the fastest responses: the use of the S. typhimurium host or the P. luminescens lux reporter. Highest sensitivity, however, was demonstrated in an E. coli strain in which a single copy of the V. fischeri lux fusion was integrated into the bacterial chromosome.     

Relation between the free energy and the direct correlation function in the mean spherical approximation

It is shown that the direct correlation function of a mixture of hard ions in the mean spherical approximation (MSA) can be expressed in terms of overlap functions of charged spherical shells. In particular, if the system is a mixture of pairs of ions of equal size and opposite charge, then the MSA direct correlation function is given by the electrostatic energy of a pair of charged shells, of radius equal to the radius of the hard ion plus 1/(2). This direct correlation function can be derived from a free energy functional, and a simple extension to nonuniform systems is given.     

New prostaglandin (PGF) derivatives from the soft coral Lobophyton depressum

Four PGF derivatives (15S)-PGF_2α-11-acetate methyl ester ($\text{1}$a), the 18-acetoxy derivative of compound $\text{1}$a ($\text{2}$a) as well as their two corresponding free carboxylic acids ($\text{1}$b) & $\text{2}$b) were isolated from a soft-coral and their structure elucidated, mainly on basis of their spectral data.     

Latrunculins: NMR study,two new toxins and a synthetic approach

A complete ¹H and ¹³C NMR assignment of one of the latrunculins (B) was accomplished with the aid of 2D NMR COSY and CH shift-correlation experiments. The various H-H Coupling constants have been datermined and a conformation of the macrolide and the tetrahydropyran (THP) ring suggested on basis of the J-values and measured NOE's. The absolute configuration of latrunculin-A($\text{1}$) was determined on the grounds of its earlier X-Ray analysis, and a chemical degradation to a known compound. Two novel latrunculins, -C($\text{3}$) and -D($\text{4}$), were isolated from the Red Sea sponge $\text{L. magnifica}$ and their structures elucidated. Starting with L-cysteine a synthon for the latrunculins has been synthesized.     

Fragmentation channels of large multicharged clusters

We address unifying features of fragmentation channels driven by long-range Coulomb or pseudo-Coulomb forces in clusters, nuclei, droplets, and optical molasses. We studied the energetics, fragmentation patterns, and dynamics of multicharged (A+)n (n=55, 135, 321) clusters. In Morse clusters the variation of the range of the pair-potential induced changes in the cluster surface energy and in the fissibility parameter X=E(Coulomb)2E(surface). X was varied in the range of X=1-8 for short-range interactions and of X=0.1-1.0 for long-range interactions. Metastable cluster configurations were prepared by vertical ionization of the neutral clusters and by subsequent structural equilibration. The energetics of these metastable ionic clusters was described in terms of the liquid drop model, with the coefficients of the volume and surface energies depending linearly on the Morse band dissociation energy. Molecular-dynamics simulations established two distinct fragmentation patterns of multicharged clusters that involve cluster fission into a small number of large, multicharged clusters for X<1 and Coulomb explosion into a large number of individual ions and small ionic fragments for X>1. The Rayleigh instability limit X=1 separates between spatially anisotropic fission and spatially isotropic Coulomb explosion. Distinct features of the fragmentation energetics and dynamics were unveiled. For fission of n=55 clusters, large kinetic and internal energies of the large fragments are exhibited and the characteristic fragmentation time is approximately 700 fs, while for Coulomb explosion the major energy content of the small fragments involves kinetic energy and the characteristic fragmentation time of approximately 300 fs is shorter. The Rayleigh (X=1) limit, leading to isotropic Coulomb explosion, is transcended by a marked enhancement of the Coulomb energy, which is realized for extremely ionized clusters in ultraintense laser fields, or by a dramatic reduction of the surface energy as is the case for the expansion of optical molasses.     

Matter–wave interference and deflection of tripeptides decorated with fluorinated alkyl chains

Studies of neutral biomolecules in the gas phase allow for the study of molecular properties in the absence of solvent and charge effects, thus complementing spectroscopic and analytical methods in solution or in ion traps. Some properties, such as the static electronic susceptibility, are best accessed in experiments that act on the motion of the neutral molecules in an electric field. Here, we screen seven peptides for their thermal stability and electron impact ionizability. We identify two tripeptides as sufficiently volatile and thermostable to be evaporated and interfered in the long‐baseline universal matter‐wave interferometer. Monitoring the deflection of the interferometric molecular nanopattern in a tailored external electric field allows us to measure the static molecular susceptibility of Ala–Trp–Ala and Ala–Ala–Trp bearing fluorinated alkyl chains at C‐ and N‐termini. The respective values are and .     

2 kW, M2 < 10 radially polarized beams from aberration-compensated rod-based Nd:YAG lasers

Radially polarized light in a 2.1 kW, good quality beam was obtained from a Nd:YAG rod-based master oscillator power amplifier. Several techniques were utilized: a pure radially polarized oscillator, efficient pump chambers, external compensation of lower-order aberrations, and higher-order aberration compensation by pairing of pump chambers.     

Folding of elongated proteins: conventional or anomalous?

The complexity of the mechanisms by which proteins fold has been shown by many studies to be governed by their native-state topologies. This was manifested in the ability of the native topology-based model to capture folding mechanisms and the success of folding rate predictions based on various topological measures, such as the contact order. However, while the finer details of topological complexity have been thoroughly examined and related to folding kinetics, simpler characteristics of the protein, such as its overall shape, have been largely disregarded. In this study, we investigated the folding of proteins with an unusual elongated geometry that differs substantially from the common globular structure. To study the effect of the elongation degree on the folding kinetics, we used repeat proteins, which become more elongated as they include more repeating units. Some of these have apparently anomalous experimental folding kinetics, with rates that are often less than expected on the basis of rates for globular proteins possessing similar topological complexity. Using experimental folding rates and a larger set of rates obtained from simulations, we have shown that as the protein becomes increasingly elongated, its folding kinetics becomes slower and deviates more from the rate expected on the basis of topology measures fitted for globular proteins. The observed slow kinetics is a result of a more complex pathway in which stable intermediates composed of several consecutive repeats can appear. We thus propose a novel measure, an elongation-sensitive contact order, that takes into account both the extent of elongation and the topological complexity of the protein. This new measure resolves the apparent discrimination between the folding of globular and elongated repeat proteins. Our study extends the current capabilities of folding-rate predictions by unifying the kinetics of repeat and globular proteins.     

Universality of melting and freezing indicators and additivity of melting curves

The assumption of universality of some melting and freezing indicators, in the context of approximate models of the liquid and the solid, gives rise to simple semi-empirical melting equations that describe additivity of melting curves. The melting equations are exact in the high temperature limit and give reasonably accurate results also near the triple point. They find many applications including quantum corrections to the melting curve.