Polyimide Dendrimers Containing Multiple Electron Donor–Acceptor Units and Their Unique Photophysical Properties

A high‐yielding synthesis of a series of polyimide dendrimers, including decacyclene‐ and perylene‐containing dendrimer D6 , in which two types of polyimide dyes are present, is reported. In these constructs, the branching unit is represented by trisphenylamine, and the solubilizing chains by N‐9‐heptadecanyl‐substituted perylene diimides. The photophysical properties of the dendrimers have been studied by absorption, steady‐state, and time‐resolved emission spectroscopy and pump–probe transient absorption spectroscopy. Photoinduced charge‐separated (CS) states are formed on the femtosecond timescale upon visible excitation. In particular, in D6 , two different CS states can be formed, involving different subunits that decays independently with different lifetimes (ca. 10–100 ps).     

In Situ Microfocus Chemical Computed Tomography of the Composition of a Single Catalyst Particle During Hydrogenation of Nitrobenzene in the Liquid Phase

Heterogeneous catalysis performed in the liquid phase is an important type of catalytic process which is rarely studied in situ. Using microfocus X‐ray fluorescence and X‐ray diffraction computed tomography (μ‐XRF‐CT, μ‐XRD‐CT) in combination with X‐ray absorption near‐edge spectroscopy (XANES), we have determined the active state of a Mo‐promoted Pt/C catalyst (NanoSelect) for the liquid‐phase hydrogenation of nitrobenzene under standard operating conditions. First, μ‐XRF‐CT and μ‐XRD‐CT reveal the active state of Pt catalyst to be reduced, noncrystalline, and evenly dispersed across the support surface. Second, imaging of the Pt and Mo distribution reveals they are highly stable on the support and not prone to leaching during the reaction. This study demonstrates the ability of chemical computed tomography to image the nature and spatial distribution of catalysts under reaction conditions.     

On the modularity of elliptic curves over -adic exercises

We complete the proof that every elliptic curve over the rational numbers is modular.

     

Flow injection with chemical reaction interface-isotope ratio mass spectrometry: an alternative to off-line combustion for detecting low levels of enriched 13C in mass balance studies

We have evaluated the potential of flow injection chemical reaction interface isotope-ratio mass spectrometry to replace radioactive labeling techniques in material balance studies. A sample is flow injected and transmitted through a desolvation system followed by combustion to form ¹³CO₂ with a microwave-powered chemical reaction interface. We can detect trace amounts of a ¹³C-labeled drug (3′-azido-3′-deoxythymidine, AZT) in urine or feces. Our ability to quantify less than 100 ng/mL of excess ¹³C (∼1 μg/mL of ¹³C-labeled AZT) from a sample equivalent to 10 μL of urine is superior to previous detection limits for ¹³C in urine that use off-line combustion methods. Parallel studies using ¹⁴C-labeled AZT showed that our stable isotope method provides comparable percent excretion data for urine and feces. These results support previous findings that mass balance studies could be carried out with isotope-ratio mass spectrometer, here using doses as low as 1–2 mg/kg.     

URANS simulations for a high-speed transom stern ship with breaking waves

An exploratory study of high-speed surface ship flows is performed to identify modelling and numerical issues, to test the predictive capability of an unsteady RANS method for such flows, to explain flow features observed experimentally, and to document results obtained in conjunction with the 2005 ONR Wave Breaking Workshop. Simulations are performed for a high-speed transom stern ship (R/V Athena I) at three speeds Froude number (Fr) = 0.25, 0.43 and 0.62 with the URANS code CFDSHIP-IOWA, which utilizes a single-phase level set method for free surface modelling. The two largest Fr are considered to be high-speed cases and exhibit strong breaking plunging bow waves. Structured overset grids are used for local refinement of the unsteady transom flow at medium speed and for small scale breaking bow and transom waves at high-speeds. All simulations are performed in a time accurate manner and an examination of time histories of resistance and free surface contours is used to assess the degree to which the solutions reach a steady state. The medium speed simulation shows a classical steady Kelvin wave pattern without breaking and a wetted naturally unsteady transom flow with shedding of vortices from the transom corner. At higher speeds, the solutions reach an essentially steady state and display intense bow wave breaking with repeated reconnection of the plunging breaker with the free surface, resulting in multiple free surface scars. The high-speed simulations also show a dry transom and an inboard breaking wave, followed by outboard breaking waves downstream. In comparison to an earlier dataset, resistance is well predicted over the three speeds. The free surface predictions are compared with recent measurements at the two lowest speeds and show good agreement for both non-breaking and breaking waves.     

Reactions of 1,1,3,3-tetrakis(dimethylamino)-1λ5,3λ5-diphosphete with diphenylchlorophosphane and methyl iodide

1,1,3,3-Tetrakis(dimethylamino)-1λ⁵,3λ⁵-diphosphete, 1, reacts with diphenylchlorophosphane to yield 1,1,3,3-tetrakis(dimethylamino)-4-diphenylphosphanyl-1,2-dihydro-3λ⁵-[1,3]diphosphetium chloride, 2, or, depending on the reaction conditions, the isomer compound 3. The cation of 2 is deprotonated by LiN[Si(CH₃)₃]₂ to give the diphenylphosphanyl-substituted derivative of 1, i.e., compound 4. Methyl iodide adds to 1 to form 1,1,3,3-tetrakis(dimethylamino)-4-methyl-1,2-dihydro-3λ⁵-[1,3]diphosphetium iodide, 6. Deprotonation of 6 with n-butyllithium leads to the monomethyl derivative of 1, i.e., compound 7. Physical properties, NMR spectra, and mass spectra of compounds 2–4, 6, and 7 are described. The results of the X-ray structural analysis of 6 are reported and discussed. © 1996 John Wiley & Sons, Inc.     

Di­aqua­tris­(pentane‐2,4‐dionato‐O,O′)­holmium(III) mono­hydrate and di­aqua­tris­(pentane‐2,4‐dionato‐O,O′)holmium(III) 4‐hydroxy­pentan‐2‐one solvate dihydrate

The structures of the title compounds, [Ho(C₅H₇O₂)₃(H₂O)₂]·H₂O and [Ho(C₅H₇O₂)₃(H₂O)₂]·C₅H₈O₂·2H₂O, both show an eight‐coordinate holmium(III) ion in a square antiprismatic configuration. The packing of these structures consists of an infinite two‐dimensional network of hydrogen‐bonded mol­ecules. In both structures, the same hydrogen‐bonded chain of Ho^III complexes is found.     

Lipase-Catalyzed Synthesis of Carboxylic Amides: Nitrogen Nucleophiles as Acyl Acceptor

 The lipase-catalyzed aminolysis of carboxylic esters is a fairly general reaction that has been performed with a wide range of esters and amines, generally in anhydrous organic media to avoid undesirable hydrolysis of the ester. Alternatively, carboxylic amides can be synthesized by lipase mediated condensation of carboxylic acids and amines if an excess of either reactant is avoided. Chiral carboxylic esters have been resolved by lipase-catalyzed aminolysis. In the majority of these resolutions, Candida antarctica lipase B has been employed as the catalyst. A range of chiral amines has been resolved by lipase mediated acylation, using mainly the lipases from C. antarctica (B type) and Pseudomonas species. The enantiorecognition was frequently found to depend critically on the acylating agent and the reaction medium.     

Surface-induced dissociation in tandem quadrupole mass spectrometers: A comparison of three designs

Three different devices that-can be used for surface-induced dissociation (SID) m tandem quadrupole instruments are compared here. The designs were compared by examining the fragmentation of several compounds including benzene, W(CO)₆, and (CH₃)₄N⁺. These studies show that SID can be readily implemented on a variety of tandem quadrupoIe instruments and that the spectra obtained with the in-line and 90° instruments are similar. Evidence is presented that confirms that high average internal energies and narrow distributions of internal energy are available by this technique. Efficiencies for fragmentation of odd-electron ions are on the order of those previously reported by others. The overall SID efficiency for even-electron ions is higher than that for odd-electron ions of similar structure.