Measurement of an autoionizing triplet state in D2 by photoexcitation of a neutralized ion beam

Neutralized ion beam techniques have been extended to observe the laser ionization spectrum of the c ³Π_u state of D₂. The autoionizing triplet→nd Rydberg series has been observed. From the break in the continuous ionization signal the ionization energy of the c ³Π_u state is found to be 3.675±0.020 eV.     

Syntheses,structures, and characterization of new lead(II)-tellurium(IV)-oxide halides: Pb3Te2O6X2 and Pb3TeO4X2 (X = Cl or Br)

The syntheses, structures, and characterization of four new lead(II)-tellurium(IV)-oxide halides, Pb(3)Te(2)O(6)X(2) and Pb(3)TeO(4)X(2) (X = Cl or Br) are reported. The materials are synthesized by solid-state techniques, using Pb(3)O(2)Cl(2) or Pb(3)O(2)Br(2) and TeO(2) as reagents. The compounds have three-dimensional structural topologies consisting of lead-oxide halide polyhedra connected to tellurium oxide groups. In addition, the Pb(2+) and Te(4+) cations are in asymmetric coordination environments attributable to their stereoactive lone pair. We also demonstrate that Pb(3)Te(2)O(6)X(2) and Pb(2)TeO(4)X(2) can be interconverted reversibly through the loss or addition of TeO(2). X-ray data: Pb(3)Te(2)O(6)Cl(2), monoclinic, space group C2/m (No. 12), a = 16.4417(11) A, b = 5.6295(4) A, c = 10.8894(7) A, beta = 103.0130(10) degrees, Z = 4; Pb(3)Te(2)O(6)Br(2), monoclinic, space group C2/m (No. 12), a = 16.8911(8) A, b = 5.6804(2) A, c = 11.0418(5) A, beta = 104.253(2) degrees, Z = 4; Pb(3)TeO(4)Cl(2), orthorhombic, space group Bmmb (No. 63), a = 5.576(1) A, b = 5.559(1) A, c = 12.4929(6) A, Z = 4; Pb(3)TeO(4)Br(2), orthorhombic, space group Bmmb (No. 63), a = 5.6434(4) A, b = 5.6434(5) A, c = 12.9172(6) A, Z = 4.     

Nuclear magnetic resonance and optosensing properties of di-2-thienyl ketone p-nitrophenylhydrazone (DSKNPH) in non-aqueous media

The compound di-2-thienyl ketone p-nitrophenylhydrazone (DSKNPH) melting point 168-170 °C was isolated in good yield from the reaction between di-2-thienyl ketone (DSK) and p-nitrophenylhydrazine in refluxing ethanol containing a few drop of concentrated HCl. Nuclear magnetic resonance studies on DSKNPH in non-aqueous solvents revealed strong solvent and temperature dependence due to solvent-solute interactions. Optical measurements on DSKNPH in DMSO in the presence and absence of KPF₆ gave extinction coefficients of 83,300±2000 and 25,600±2000 M⁻¹ cm⁻¹ at 612 and 427 nm at 295 K. In CH₂Cl₂, extinction coefficient of 34,000±2000 M⁻¹ cm⁻¹ was calculated at 422 nm. When DMSO solutions of DSKNPH were allowed to interact with DMSO solutions of NaBH₄ the low energy electronic state becomes favorable and when DMSO solutions of DSPKNPH where allowed to interact with DMSO solutions of KPF₆ or NaBF₄, the high energy electronic state becomes favorable. The reversible BH₄⁻/BF₄⁻ interconversion points to physical interactions between these species and DSKNPH and hints to the possible use of DSKNPH as a spectrophotometric sensor for a variety of physical and chemical stimuli. Thermo-optical measurements on DSKNPH in DMSO confirmed the reversible interconversion between the high and low energy electronic states of DSKNPH and allowed for the calculations of the thermodynamic activation parameters of DSKNPH. Changes in enthalpy (ΔH^∅) of +57.67±4.20; 27.15±0.90 kJ mol⁻¹, entropy (ΔS^∅) of +160±12.88; 83±2.91 J mol⁻¹ and free energy (ΔG^∅) of −8.52±0.40; 2.66±0.25 kJ mol⁻¹ were calculated at 295 K in the absence and presence of NaBH₄, respectively. Manipulation of the equilibrium distribution of the high and low energy electronic states of DSKNPH allowed for the use of these systems (DSKNPH and surrounding solvent molecules) as molecular sensors for group I and II metal ions. Group I and II metal ions in concentrations as low as 1.00×10⁻⁵ M can be detected and determined using DSKNPH in DMSO.     

Film-Pore Diffusion Control for the Batch Sorption of Cadmium Ions from Effluent onto Bone Char

The sorption equilibrium and kinetics of cadmium ions from aqueous solution onto bone char have been studied. Equilibrium isotherms for the sorption system were correlated by Langmuir and bi-Langmuir equations. The application of the bi-Langmuir equation was developed because the mechanistic analysis in this research indicated that cadmium removal occurs ion exchange and physical adsorption onto different surface sites. The bi-Langmuir equation provides a better fit to the experimental data. In addition, the removal rates of cadmium ions based on the Langmuir models have been investigated. The effective diffusivity was calculated using the effects of initial metal ion concentration and bone char mass. Two mass-transport models based on film-pore diffusion control have been applied to analyze the concentration decay curves. The film and pore diffusion coefficients using an analytical equation are equal to 1.26x10(-3) cm/s and 5.06x10(-7) cm(2)/s, respectively. The pore diffusion coefficient obtained from the numerical method is 4.89x10(-7) cm(2)/s. A sensitivity analysis showed that the film-pore diffusion model and constant effective diffusivity could be used to describe the mass-transport mechanism of the sorption system with a high degree of correlation. Copyright 2001 Academic Press.     

New 2-methyl-6-alkylamino-5,8-quinolinequinones and 1,2,3,4-tetrahydro derivatives

The syntheses of six new 2-methyl-6-alkylamino-5,8-quinolinequinones, three 1,2,3,4-tetrahydro-5,8-quinolinequinones, and 7-(2′,6′,10′-trimethylundecyl)-6-hydroxy-5,8-quinolinequinone are described as potential antimetabolites of coenzyme Q and as potential antimalarial agents. The six 2-methyl-6-alkylamino-5,8-quinolinequinones were prepared by a six-step synthesis. 2-Methyl-6-methoxy-8-nitroquinoline was prepared from 2-nitro-4-methoxyaniline and crotonaldehyde by a Skraup reaction. Raney nickel reduction gave 2-methyl-6-metboxy-8-aminoquinoline, which upon diazotization followed by dithionite reduction yielded 2-methyl-6-methoxy-5,8-diaminoquinoline. Subsequent dichromate oxidation gave 2-methyl-6-methoxy-5,8-quinolinequinone, which yielded the corresponding 2-methyl-6-alkylamino-5,8-quinolinequinone in good yield when treated with the appropriate alkylamine. The telrahydro-5,8-quinolinequinones were prepared by catalytic hydrogenation of the appropriate 5,8-quinolinequinones at elevated H₂ pressure followed by air oxidation of the reduction product. 7-(2′,6′,10′-Trimethylundecyl)-6-hydroxy-5,8-quinolinequinone was synthesized by radical alkylation of 6-hydroxy-5,8-quinolinequinone by thermal decomposition of di-3,7,11-trimethyldodecanoyl peroxide, which was prepared by a multistep procedure from farnesol. Of the five new 2-methyl-6-alkylamino-5,8-quinoline-quinones tested against P. berghei in mice (blood schizonticidal test), only 2-methyl-6-cycloheptylamino-5,8-quinolinequinone was active (T-C = 6.1 at 320 mg./kg.). Both 7-(2′,6′,10′-trimelhytundecyl)-6-hydroxy-5,8-quinolinequinone and the tetrahydro derivatives were inactive in this same test system.     

A new linked scan for reversed geometry mass spectrometers

A new linked scan is described by which fragmentations occurring in the second field free region of a two sector instrument can be monitored. The scan can be used only if the first stage allows selection of ions according to their masses. The magnetic sector and electric sector are scanned in unison so that the product B²E is maintained constant. A spectrum of all parents of a preselected daughter ion is obtained and the resolution depends only on the mass resolution of the magnetic sector.     

The effect of density on the properties of short chain fluids

We incorporate density dependence into continuum Born-Green-Yvon (BGY) theory through calculation of the end-to-end intramolecular correlation function. Whereas in previous studies we had only performed this calculation for the case of an isolated (zero-density) square-well chain of m segments (3相似文献   

Use of parallel synthesis to probe structure-activity relationships among 12-helical beta-peptides: evidence of a limit on antimicrobial activity

We report structure-activity trends among helix-forming beta-amino acid oligomers that are intended to mimic alpha-helical host-defense peptides. Parallel synthesis of two small, focused beta-peptide libraries allowed us to identify relatively short (11-residue) beta-peptides that display antimicrobial activity. These beta-peptides exhibit selectivity for bacteria relative to human red blood cells. A large hydrophobic helical surface is necessary for antimicrobial activity. Longer analogues (16 residues) of the most active library members were prepared and evaluated. Some of these longer beta-peptides showed very good antimicrobial activity, but none was more active than a previously reported beta-peptide [Porter, E. A.; Wang, X.; Lee, H.-S.; Weisblum, B.; Gellman, S. H. Nature 2000, 404, 565]. The extensive literature on alpha-helical host-defense peptides and related alpha-peptides indicates that such molecules are seldom active at concentrations below 1 microg/mL, and our results suggest that amphiphilic helical beta-peptides are subject to a comparable limit.