Revisiting the Perfluorinated Trityl Cation

Although ultimately not isolable for X-ray structural characterization, the free perfluorinated trityl cation was shown to be observable in neat triflic acid, which represents milder conditions than previous reports of this cation in “magic acid” or oleum. A triflate-bound species could be generated in organic solvents using stoichiometric amounts of triflic acid and was shown to be synthetically viable for hydride abstraction from Et₃SiH. It was demonstrated that the para-position on the -C₆F₅ rings is the primary point of attack for decomposition of the cation.     

Sound transmission at low frequencies through the walls of distorted circular ducts

A theoretical treatment of sound transmission through the walls of distorted circular ducts is given, for plane mode transmission within the duct. The transmission mechanism is essentially that of “mode coupling”, whereby higher structural modes in the duct walls are excited, because of the wall distortion, by the internal sound field. The theory is in two parts: an approximate analytical model for the structural response of the walls to the internal sound field, and a structural radiation model. Computed results, based on the theory, are compared to measurements on “long-seam” air conditioning ducts. Where the duct geometry can be reliably specified, reasonably good agreement is obtained between theoretical and experimental data. It is concluded that mode coupling effects serve to account for the discrepancies between ideal and observed behaviour in sound transmission through duct walls.     

Sounds, source levels, and associated behavior of humpback whales, southeast Alaska

Humpback whales in Southeast Alaskan waters produced five categories of sounds: moans, grunts, pulse trains, blowhole-associated sounds, and surface impacts. Frequencies (Hz) of moans and grunts were 20-1900. Major energy in low-frequency pulse trains was in a band of 25-80 Hz with pulse duration of 300-400 ms. Blowhole-associated sounds, recorded as transiting whales encountered one another, were of two types: shrieks, 555-2000 Hz, and trumpetlike horn blasts with fundamental at 414 Hz (median). Pulses and spread spectrum noise were associated with gas bubble formation and explosive bursts, respectively, in connection with spiral feeding maneuvers. Surface impacts resulted from fluke or flipper slaps in sequences of 3-21 sounds. Source levels ranged from 162 (low-frequency pulse trains) to 192 dB (surface impacts), re: 1 microPa, 1 m. Songs, commonly heard on winter breeding grounds, were absent from our recordings. Feeding and perhaps certain other whale activities can be monitored based on sound production.     

Determination of anthracycline purity in patient samples and identification of in vitro chemical reduction products by application of a multi-diode array high-speed spectrophotometric detector

We describe the application of a high-speed spectrophotometric detector and high-performance liquid chromatography to the determination of anthracycline purity in extracted patient specimens and to the identification of chemical reduction products. Blood contained pure anthracyclines whilst in urine, tissue and tumour there was evidence of co-eluting endogenous peaks and complexation. Aerobic reduction yielded two main products: a C13 alcohol and a fully reduced, non-fluorescent, yellow hydroquinone. Anaerobic reduction in the presence of DNA yielded a 7-deoxyaglycone metabolite end product instead of the fully reduced hydroquinone. Eight other separate chromatographic species were identified, all of which showed unique absorbance characteristics, having a visible lambda max at 530 nm and being coloured purple/blue.     

Characterization of titanium dioxide nanoparticles using molecular dynamics simulations

Molecular dynamics simulations of titanium dioxide nanoparticles in the three commonly occurring phases (anatase, brookite, and rutile) are reported. The structural properties inferred by simulated X-ray diffraction patterns of the nanoparticles were investigated. The titanium-oxygen bond length as a function of size, phase, and temperature was determined and was found to be dependent on the coordination environment of the titanium and independent of phase and size. The equilibrium Ti-O bond length is 1.86 A for a four-coordinated titanium ion, 1.92 A for a five-coordinated titanium ion, and 1.94 A for an octahedral titanium ion. Smaller nanoparticles are characterized by a higher fraction of titanium ions that are four and five coordinated, due to the larger surface area-to-volume ratios. The surface energies for anatase, rutile, and brookite particles were reported. The surface energy of the nanoparticle increases and approaches a constant value as the particle gets bigger. The surface energies of small rutile particles are higher than that for anatase particles of a similar size, consistent with anatase being the more stable phase of nanocrystalline titanium dioxide.     

Electrochemical reduction of uracil in dimethyl sulfoxide: Autoprotonation of the anion radical

The electrochemical reduction of uracil in dimethyl sulfoxide was investigated, using d.c.and a.c. polarography, cyclic voltammetry, and controlled potential electrolysis. Uracil is reduced in a one-electron step (E_1/2=?2.3 V); the apparent number of electrons transferred (n) decreases from one at infinite dilution to one-half at concentrations above 1mM. The concentration dependent n-value is due to proton transfer by the parent compound to the radical anion formed on reduction. Such a proton transfer, which has been observed for 2-hydroxypyrimidine, deactivates part of the uracil, which would otherwise be available for reduction, by formation of the more difficultly reducible conjugate base. The uracil anion forms insoluble mercury salts, producing two oxidation waves (E_1/2 of ?0.1 and ?0.3 V); the latter wave is due to formation of a passivating film on the electrode. Digital simulations indicate that the protonation rate exceeds 10⁵M^?1 s^?1 and that, at low uracil concentration, some of the free radical formed on protonation is further reduced. At concentrations exceeding 1 mM, all of the free radical dimerizes. The effect of added acids and base on the electrochemical behavior is described.     

Equation of state and liquid-vapor equilibria of one- and two-Yukawa hard-sphere chain fluids: theory and simulation

The accuracy of several theories for the thermodynamic properties of the Yukawa hard-sphere chain fluid are studied. In particular, we consider the polymer mean spherical approximation (PMSA), the dimer version of thermodynamic perturbation theory (TPTD), and the statistical associating fluid theory for potentials of variable attractive range (SAFT-VR). Since the original version of SAFT-VR for Yukawa fluids is restricted to the case of one-Yukawa tail, we have extended SAFT-VR to treat chain fluids with two-Yukawa tails. The predictions of these theories are compared with Monte Carlo (MC) simulation data for the pressure and phase behavior of the chain fluid of different length with one- and two-Yukawa tails. We find that overall the PMSA and TPTD give more accurate predictions than SAFT-VR, and that the PMSA is slightly more accurate than TPTD.     

Potentiometric determination of lead with DTPA in the presence of large amounts of aluminium

Lead can be titrated accurately in the presence of aluminium with diethylenetriaminepenta-acetic acid, with a silver electrode system for detection of the end-point. The method is very suitable for analysis of lead glasses.     

Effect of temperature on the adsorption of water in porous carbons

We report experimental and simulation studies to investigate the effect of temperature on the adsorption isotherms for water in carbons. Adsorption isotherms are measured by a gravimetric technique in carbon-fiber monoliths at 378 and 423 K and studied by molecular simulation in ideal carbon pores in the temperature range 298-600 K. Experimental adsorption isotherms show a gradual water uptake, as the pressure increases, and narrow adsorption-desorption hysteresis loops. In contrast, simulated adsorption isotherms at room temperature are characterized by negligible uptake at low pressures, sudden and complete pore filling once a threshold pressure is reached, and wide adsorption-desorption hysteresis loops. As the temperature increases, the relative pressure at which pore filling occurs increases and the size of the hysteresis loop decreases. Experimental adsorption-desorption hysteresis loops are narrower than those from simulation. Discrepancies between simulation and experimental results are attributed to heterogeneities in chemical composition, pore connectivity, and nonuniform pore-size distribution, which are not accounted for in the simulation model. The hysteresis phase diagram for confined water is obtained by recording the pressure-density conditions that bound the simulated hysteresis loop at each temperature. We find that the hysteresis critical temperature, i.e., the lowest temperature at which no hysteresis is detected, can be hundreds of degrees lower than the vapor-liquid critical temperature for bulk model water. The properties of confined water are discussed with the aid of simulation snapshots and by analyzing the structure of the confined fluid.