Simulations of time-dependent fluorescence in nano-confined solvents

The time-dependent fluorescence of a model diatomic molecule with a charge-transfer electronic transition in confined solvents has been simulated. The effect of confining the solvent is examined by comparing results for solutions contained within hydrophobic spherical cavities of varying size (radii of 10-20 angstroms). In previous work [J. Chem. Phys. 118, 6618 (2002)] it was found that the solute position in the cavity critically affects the absorption and fluorescence spectra and their dependence on cavity size. Here we examine the effect of cavity size on the time-dependent fluorescence, a common experimental probe of solvent dynamics. The present results confirm a prediction that motion of the solute in the cavity after excitation can be important in the time-dependent fluorescence. The effects of solvent density are also considered. The results are discussed in the context of interpreting time-dependent fluorescence measurements of confined solvent systems.     

Reactor for prechromatographic fusion reactions

An improved design of a reactor for alkaline fusion as a preliminary to chromatographic analysis is described. The reactor allows the use of a significantly reduced sample size, minimizes leakages and facilitates the removal of the reaction products. The use of the reactor is demonstrated by the analysis of several polyester samples exhibiting increased hydrolytic stability.     

Molecular sieving of lambda phage DNA in polyacrylamide solutions as a function of the molecular weight of the polymer.

Electrophoresis of lambda phage DNA was carried out in solutions at various concentrations of uncrosslinked polyacrylamide of 0.6, 1, 5 and 9 x 10(6) molecular weight (Mw) with narrow Mw distribution. By inspection of mobilities in the various concentration ranges, it appears that mobilities decrease, and retardation increases, with increasing Mw. The relation between electrophoretic retardation and the Mw of the polymer was also interpreted (i) in the manner previously applied to nonlinear Ferguson plots and compatible with the Ogston model; and (ii) empirically, on the basis of the first derivatives of the functions describing the Ferguson plots at the polymer concentrations used. Interpretation (i) shows that the retardation increases linearly in the order of 0.6, 1, 5 and 9 x 10(6) Mw of polyacrylamide. Interpretation (ii) shows a nonlinear increase of retardation in the Mw range 5 to 9 x 10(6), and a decrease in retardation as Mw is raised from 0.6 to 5.0 x 10(6). Hypothetically, interpretation (ii) can be explained mechanistically by a progressive change, as the polymer size is increased, from a collision with the surface of the polymer fiber to one occurring after permeation in the interior of a random-coiled fiber. Interpretation (i) may fail to detect that change due to the large difference between DNA mobility in solutions of the smallest polymer and the free mobility. DNA peak detection in all of the four size classes of polyacrylamide in solution is limited to relatively narrow ranges of polymer concentration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Separation of rare earth elements from uranium by solvent extraction and ion exchange

The detection limit of⁹⁹Tc in (,) radio-activation analysis was determined in the presence of molybdenum and compared with that of⁹⁹Tc in pure materials in the previous paper. The isotopic ratio of molybdenum in a⁹⁹Mo–^99mTc generator column could be simultaneously determined by photon activation analysis.     

Contribution to the systematics of r0-derived molecular structure determinations from rotational parameters

This work investigates and enumerates the types of molecular structure that can, in principle, be obtained when moments of inertia, planar moments, or rotational constants or different forms of their isotopic differences are least-squares fitted to the respective experimental ground state values. Ther ₀-structure, ther ₀-derived pseudo-Kraitchman structuresr _I andr _B, and an inequality relation between them are discussed. A least-squares treatment that tries to determine not only the set of structural parameters but also constant, i.e., isotope-independent, rovibrational contributions to the moments of inertia or rotational constants is possible and merits preference. It is shown that the resulting structures are, however, identical with the formerr orr _B-structures, respectively.     

Heavy metals in human urinary calculi

Summary Heavy metals are incorporated in human urinary calculi during a complex pathological process. The trace metals cadmium, lead, chromium, nickel and mercury are determined with regard to significance in pathogenesis and therapy. The amounts of cadmium, lead and chromium were determined as well directly in the solid sample as after chemical digestion by Zeeman-GFAAS. Both analyzing techniques show corresponding results. Nickel could be determined after chemical digestion only, while mercury was determined by a solid sampling technique. The evaluation of the results of trace metal analysis in the pilot study of 11 urinary calculi showed increased amounts of lead and cadmium compared to the results of tartar and salivary calculi.     

Simultaneous determination of p-hydroxylated and dihydrodiol metabolites of phenytoin in urine by high-performance liquid chromatography

Accurate urinary measurements of the two major metabolites of phenytoin, 5-(p-hydroxyphenyl)-5-phenylhydantoin (p-HPPH) and 5-(3,4-dihydroxy-cyclohexa-1,5-dienyl)-5-phenylhydantoin (dihydrodiol, DHD), are necessary for pharmacokinetic and drug-interaction studies of this commonly used antiepileptic drug. We describe a simple, rapid, acid hydrolysis, with liquid-liquid extraction and simultaneous isocratic reversed-phase high-performance liquid chromatography of p-HPPH and 5-(m-hydroxyphenyl)-5-phenylhydantoin (m-HPPH) (hydrolytic end product of DHD). p-HPPH and m-HPPH were quantitated against their separate respective internal standards of alphenal and tolylbarb. The mobile phase consisted of water-dioxane-tetrahydrofuran (80:15:5, v/v/v) at 2 ml/min and at 50 degrees C, with detection at 225 nm. Baseline separation was achieved by use of a 16 cm x 3.9 mm Nova-Pak C18 column and total analysis time of 12 min. p-HPPH and m-HPPH concentrations ranged from 10 to 200 and from 2 to 30 micrograms/ml, respectively, with between-day coefficients of variations of 3.3-4.5% and 2.2-5.1% for controls. All standard curves were linear with r values greater than 0.993. The DHD concentration was determined by multiplying m-HPPH concentrations by 2.3.     

Composition of lipids of the grain of opaque-2 maize

It has been established that the change in the composition of the total lipids and the fall in the fatty acid content depend on the initial maize genotype. A decrease in the amount of unsaponifiable substances in the grain of mutants is accompanied by qualitative changes in the composition regardless of the nature of the genotype.Scientific-Research Institute of Biology Dnepropetrovsk State university. Translated from Khimiya Prirodnykh Soedinenii. No. 3. pp. 360–363. May–June, 1988.     

Gallium-, Indium-Mangan- und Thallium-Rhenium-Carbonylverbindungen

Gallium-, Indium-Manganese-, and Thallium-Rhenium Carbonyl Compounds Compounds of type Na{Cl_4?nM[Mn(CO)₅]_n} (M ? Ga, In; n = 1, 2, 3) were prepared by reaction of the Lewis acids MCl₃ and NaMn(CO)₅. Instead of the sodium salts were obtained the compounds (C₃H₇CO₂)₂InMn(CO)₄L (Indium atom with the coordination number 5) from Indium(III) butyrate with two carboxylate groups bonded as chelate ligands and NaMn(CO)₄L [L ? CO, P(C₆H₅)₃] in the molar ratio 1:1. By reacting TlCl with NaRe(CO)₅ i.r. spectroscopic measurements of the solution pointed out the intermediate product TlRe(CO)₅, which was unstable against a disproportionation reaction into Tl and Tl[Re(CO)₅]₃. The last named compound delivered as a thermal decomposition product Re₂(CO)₈[μ-TlRe(CO)₅]₂. I.r. bands of the new compounds were assigned.     

Degradation of aromatic compounds in ground-water, and methods of sample preservation

The degradation of acenaphthylene, acenaphthene, 2-methylnaphthalene, 2-methylindene, 3-methylindene and indene in water solutions was studied. These compounds at the 25-150 mug/l. level were almost totally degraded at ambient temperature within three days. The microbial population responsible for the degradation occurs naturally in ground-water taken from an aquifer in Ames, Iowa, which is contaminated with coal-tar products. These unidentified micro-organisms adapt readily to other waters when used as an inoculant for the degradation of aromatic compounds. The preservation of water to prevent such degradation was also investigated. Filtration through a 0.45-mum filter was found the most effective procedure for preserving the hydrocarbons in these waters.