Growth of narrowly dispersed porphyrin nanowires and their hierarchical assembly into macroscopic columns

The self-assembly of amphiphilic (porphyrin)Sn 1 in an aqueous Pluronic F127 media results in the formation of narrowly dispersed nanowires. Variation of aqueous Pluronic concentrations allows for a systematic variation of porphyrin nanowire lengths while keeping their widths constant. These nanowires can be further assembled into secondary macroscopic columns.     

High resolution electron energy loss spectroscopy of fatty acids prepared by langmuir-blodgett techniques on polycrystalline silver

The surface of monomolecular layers of fatty acids prepared by Langmuir-Blodgett methods on polycrystalline silver has been studied by High Resolution Electron Energy Loss Spectroscopy (HREELS). Results demonstrate HREELS sensitivity to large molecules in molecular organizates on polycrystalline substrates. Spectra are interpreted in comparison with infrared vibrational data; results allow differentiation of degrees of unsaturation. The carbonyl vibration loss is observed as a weak feature, explained as due to the orientation of the fatty acid heads “down” on the subtrate surface approximately 20 Å from the scattering interaction.     

An Efficient One‐Pot Synthesis of Bis Butenolides

3,3′,4,4′‐Tetramethyl‐5,5′‐dioxo‐2,2′‐bifuran‐2,2′(5H,5′H) diyl diacetate was obtained from the reaction between 2,3‐dimethyl maleic anhydride and acetic anhydride in the presence of zinc in toluene. This easy synthetic route gave bis butenolide in excellent yield.     

Thermochemical properties of HxNO molecules and ions from ab initio electronic structure theory

Coupled-cluster calculations through noniterative triple excitations were used to compute optimized structures, atomization energies at 0 K, and heats of formation at 0 and 298 K for NH2O, HNOH, NH2O-, NH2OH+, NH3OH+, HNO-, and HON. These molecules are important in the gas-phase oxidation of NH3, as well as its solution-phase chemistry. The O-H, N-H, and N-O bond energies of these molecules are given and compared. The N-H and O-H bond energies are quite low, and, for NH2OH, the O-H bond is weaker than the N-H bond (by 7.5 kcal/mol). The energetics for a variety of ionic chemical processes in the gas phase, including the electron affinities of NH2O and HNO, the proton affinities of NH2O and NH2OH, and the acidities of NH2OH and NH2O, are given. The compounds are weak bases and weak acids in the gas phase. Solvation effects were included at the PCM and COSMO levels. The COSMO model gave better values than the PCM model. The relative values for pKa for NH2O and NH2OH are in good agreement with the experimental values, showing both compounds to be very strong bases in aqueous solution with NH2OH being the stronger base by 1.8 pK units at the COSMO level, compared to the experimental pK difference of 1.1+/-0.3 pK units. We predict that NH2OH+ will not be formed in aqueous solution, because it is a very strong acid. Based on the known acidity of NH3OH+, we predict pKa(NH2OH+)=-5.4 at the COSMO level, which is in good agreement with the experimental estimate of pKa(NH2OH+)=-7+/-2.     

Direct determination of calcium,copper, iron,magnesium, manganese and zinc in amniotic fluid samples using inductively coupled plasma-atomic emission spectrometry

An inductively coupled plasma-atomic emission spectrometric method is reported for the determination of calcium, copper, iron, manganese, magnesium and zinc. Samples are introduced directly when a sheath gas device is used. An external calibration procedure is used. The standards are prepared in a matrix composed of 0.5% (w/v) albumin and 0.76% (w/v) sodium chloride. The procedure was evaluated with a standard reference material (NBS SRM 909 Human Serum); all the values obtained are in agreement with the certified values. Results obtained for the determination of zinc, calcium, magnesium, copper, iron and manganese in amniotic fluid samples are reported.     

The stick-slip problem for a round jet

Summary The stick-slip problem for a round jet studied in Part I gives a good approximation for the swell of a low speed jet when the surface tension is large but it fails when the surface tension is small. In this paper a new stick-slip problem (II) is defined and solved using matched eigenfunction expansions. The new problem reduces to that solved in Part I when the surface tension is large and gives good results in the case of zero and small surface tension.With 18 figures     

Simulating surface tension with smoothed particle hydrodynamics

A method for simulating two‐phase flows including surface tension is presented. The approach is based upon smoothed particle hydrodynamics (SPH). The fully Lagrangian nature of SPH maintains sharp fluid–fluid interfaces without employing high‐order advection schemes or explicit interface reconstruction. Several possible implementations of surface tension force are suggested and compared. The numerical stability of the method is investigated and optimal choices for numerical parameters are identified. Comparisons with a grid‐based volume of fluid method for two‐dimensional flows are excellent. The methods presented here apply to problems involving interfaces of arbitrary shape undergoing fragmentation and coalescence within a two‐phase system and readily extend to three‐dimensional problems. Boundary conditions at a solid surface, high viscosity and density ratios, and the simulation of free‐surface flows are not addressed. Copyright © 2000 John Wiley & Sons, Ltd.     

Monomorphisms and epimorphisms in homotopy theory

A natural question to ask in any category ζ is whether a morphismf; X → Y in ζ which is simultaneously mono and epi is actually an equivalence. In this paper, we study this question for the category ℋ whose objects are pointed, path-connectedCW-spaces and whose morphisms are pointed homotopy classes of maps. We also continue our study of Hopfian and co-Hopfian objects of ℋ initiated in a recent joint paper with Peter Hilton. To the memory of my brother-in-law, Professor Jacob Feinstein     

Separation of Trp-Arg and Arg-Trp using G-quartet-forming DNA oligonucleotides in open-tubular capillary electrochromatography

DNA oligonucleotides that form intramolecular G-quartet structures were investigated as stationary phase reagents for separation of mixtures of the isomeric dipeptides Trp-Arg and Arg-Trp in open-tubular capillary electrochromatography (OTCEC). The oligonucleotides included a thrombin-binding aptamer that forms a biplanar G-quartet structure and an oligonucleotide that forms a 4-plane G-quartet structure. Fluorescence, circular dichroism and UV-visible absorbance spectroscopies were used in batch solution studies to indicate interactions between the dipeptides and the biplanar G-quartet structure. Results for OTCEC separations were compared with results obtained for capillary zone electrophoresis separations on a bare capillary. Temperature studies suggest that resolution is improved when the G-quartet structure is partially destabilized, but control experiments in which potassium chloride was not included in the mobile phase indicate that the G-quartet structure nevertheless plays a role in the separations.