Vibrational population distribution of ground state BaO formed by the reaction Ba + O2

The vibrational population distribution of X ¹Σ(υ′' = 0 through ν′' = 7) BaO formed in the reaction Ba + O₂ at 0.3 torr has been measured by laser induced photoluminescence intensities. On the basis of the assumed similarity between the Ba + O₂ and Ba + N₂O reactions, these data suggest that a population inversion may exist between A ¹Σ(ν′ = 1) and X ¹Σ(υⁿ = 7) BaO formed in the latter reaction at ≈ 16 torr.     

Quantitation of acrylamide in food products by liquid chromatography/mass spectrometry

A simple and inexpensive liquid chromatography/mass spectrometry (LC/MS) method was developed for the quantitation of acrylamide in various food products. The method involved spiking the isotope-substituted internal standard (1-C13 acrylamide) onto 6.00 g of the food product, adding 40 mL distilled/deionized water, and heating at 65 degrees C for 30 min. Afterwards, 10 mL ethylene dichloride was added and the mixture was homogenized for 30 s and centrifuged at 2700 x g for 30 min, and then 8 g supernatant was extracted with 10, 5, and 5 mL portions of ethyl acetate. The extracts were combined, dried with sodium sulfate, and concentrated to 100-200 microL. Acrylamide was determined by analysis of the final extract on a single quadrupole, bench-top mass spectrometer with electrospray ionization, using a 2 mm id C18 column and monitoring m/z = 72 (acrylamide) and m/z = 73 (internal standard). For difficult food matrixes, such as coffee and cocoa, a solid-phase extraction cleanup step was incorporated to improve both chromatography and column lifetime. The method had a limit of quantitation of 10 ppb, and coefficients of determination (r2) for calibration curves were typically better than 0.998. Acceptable spike recovery results were achieved in 11 different food matrixes. Precision in potato chip analyses was 5-8% (relative standard deviation). This method provides an LC/MS alternative to the current LC/MS/MS methods and derivatization gas chromatography/mass spectrometry methods, and is applicable to difficult food products such as coffee, cocoa, and high-salt foods.     

Molecular imprinting made easy

A simple method of molecular imprinting is presented that uses a single cross-linking monomer N,O-bismethacryloyl ethanolamine (NOBE) along with template, initiator, and solvent. This formulation eliminates the need for additional functional monomers and empirical optimization of relative ratios of functional monomers, cross-linkers, and template. In fact, utilization of NOBE alone often provides molecularly imprinted polymers (MIPs) with higher performance than MIPs incorporating functional monomer (e.g., methacrylic acid).     

Characterization and genetic manipulation of peptide synthetases in Pseudomonas aeruginosa PAO1 in order to generate novel pyoverdines

PvdD, a nonribosomal peptide synthetase (NRPS) of Pseudomonas aeruginosa PAO1, incorporates two L-threonines into the siderophore pyoverdine. A pvdD mutant did not synthesize pyoverdine and lacked a high Mr iron-regulated cytoplasmic protein (IRCP). Analysis of other IRCPs and the P. aeruginosa genome enabled the remaining pyoverdine NRPSs to be identified. The pvdD mutation could be complemented in trans, enabling design of plasmid-based systems for the generation of novel pyoverdines. Introduction of a truncated pvdD gene resulted in attenuated forms of pyoverdine, and introduction of L-threonine-incorporating NRPSs from other organisms restored pyoverdine production to mutant cells. This is the first successful rational in vivo modification of NRPS modules outside of Bacillus subtilis. The systems employed did not allow incorporation of other residues into pyoverdine, indicating that there are multiple elements contributing toward substrate specificity in NRPSs.     

The self-consistent mean spherical approximation for the one-component plasma

The consequences of choosing the adjustable hard-core diameter in the mean spherical approximation for the one-component plasma so as to achieve thermodynamic consistency between the energy and compressibility equations are investigated. Such a choice is found to be possible only for >8.5 and, although the resulting correlation functions are discontinuous, the height of the main peak in the static structure factor is remarkably accurate. Two especially noteworthy aspects of the thermodynamic results are that the compressibility equation is much more accurate than in any previous approximation free of input from computer simulations and that the nonstatic part of the internal energy has a ^1/4 dependence in the strong coupling limit in agreement with Monte Carlo data.     

PHOTOLYSIS OF PHOSPHODIESTER BONDS IN PLASMID DNA BY HIGH INTENSITY UV LASER IRRADIATION

Abstract— The cleavage of phosphodiester bonds in DNA exposed to high intensity UV laser pulses in aerated aqueous solution has been investigated using a krypton fluoride excimer laser (248 nm) and bacterial plasmid DNA. The dependence of strand breakage on fluence and intensity has been studied in detail and shows that the process is non-linear with respect to intensity. The relationship between the quantum yield for strand breakage and intensity shows that the strand breakage reaction involves two-photon excitation of DNA bases. The quantum yield rises with intensity from a lower value of 7 times 10^-5 until a maximum value of 4.5 times 10^-4 is attained at intensities of 10¹¹ W m^-2 and above. This value is approximately fifty-fold higher than the quantum yield for strand breakage induced by exposure to low density UV irradiation (254 nm, 12 W m^-2). DNA sequencing experiments have shown that strand breakage occurs by the specific cleavage of the phosphodiester bond which lies immediately 3' to guanine residues in the DNA, leaving some alkali-labile remnant attached to the terminal phosphate. A mechanism for DNA strand breakage which involves the generation of guanine radical cations is proposed.     

PHOTOTROPISM IN PHYCOMYCES MUTANTS LACKING β-CAROTENE

Abstract. β-carotene and riboflavin are considered as the major candidates for the photoreceptor for physiological responses to blue light in Phycomyces and a number of other organisms. Mutants of Phycomyces blocked in all six steps of the biosynthesis of β-carotene from phytoene contain no detectable β-carotene (less than 4 times 10^-5 of wild-type amount) but exhibit phototropic responses identical to wild-type. Moreover, wild-type Phycomyces , while abundant in trans -β-carotene, contains no detectable cis -β-carotene, sometimes proposed as a photoreceptor candidate on the basis of the close similarity of the cis -species absorption spectrum in the near UV region to many action spectra for blue-light responses. These results indicate that β-carotene cannot be the photoreceptor for phototropism in Phycomyces.     

Synthesis,characterization, and properties of novel aromatic bispropenyl ethers

Aromatic bispropenyl ethers are a new class of highly reactive thermosetting monomers that have been prepared and characterized. Two synthetic routes to their preparation have been developed. The first of these involves the base-catalyzed isomerization of bisallyl ether precursors that gives predominantly the Z bispropenyl ether isomers. The second method employs tris(triphenylphosphine)ruthenium(II) dichloride as an isomerization catalyst and produces predominantly the E isomers. Using these methods, a number of bispropenyl ether monomers containing different aromatic groups have been synthesized. The cationic polymerization of these novel monomers to give crosslinked network polymers using diaryliodonium salts as photo and thermal initiators has been studied.     

Taming the rugged landscape: production, reordering, and stabilization of selected cluster inherent structures in the X13-nYn system

We present studies of the potential energy landscape of selected binary Lennard-Jones 13 atom clusters. The effect of adding selected impurity atoms to a homogeneous cluster is explored. We analyze the energy landscapes of the studied systems using disconnectivity graphs. The required inherent structures and transition states for the construction of disconnectivity graphs are found by combination of conjugate gradient and eigenvector-following methods. We show that it is possible to controllably induce new structures as well as reorder and stabilize existing structures that are characteristic of higher-lying minima. Moreover, it is shown that the selected structures can have experimentally relevant lifetimes.     

Reactions of some bromofluorobenzenes with copper(I) benzenethiolate

The reactions of copper(I) benzenethiolate with some bromofluorobenzenes have resulted in the replacement of the bromine by a phenylthio group. Combinations of this method and the reactions of sodium thiolates with fluorobenzenes have enabled various isomeric phenylthio substituted fluorobenzenes C₆H_xF_y(SR)_z to be prepared. The new products have been characterized by elemental analyses, mass, infrared, and fluorine NMR spectroscopy.