Studies toward an ideal fluorescence method to measure palladium in functionalized organic molecules: effects of sodium borohydride, temperature, phosphine ligand, and phosphate ions on kinetics

Residual metals in fine chemicals are currently detected by using inductively coupled plasma mass spectrometry, which requires expensive instrumentation and does not have high-throughput capabilities. Although fluorescent probes can be amenable to high-throughput analyses of metals, the utility of such analyses is limited due to the lack of generality. Herein, we report a significant improvement (≈19-fold) to our previously reported catalysis-based fluorescent probe for palladium. Specifically, we found that slightly elevated temperature dramatically improved the generality of the method and that the deallylation reaction of the nonfluorescent compound 1 was accelerated by phosphate ions in aqueous media. This method was capable of detecting 0.2 ppb palladium. We demonstrated reasonably accurate palladium detection in various active pharmaceutical ingredients and highly functionalized organic compounds.     

High rate performance of lithium manganese nitride and oxynitride as negative electrodes in lithium batteries

The performance of Li_7.9MnN_3.2O_1.6 and Li₇MnN₄ as electrode materials in lithium batteries was analyzed. At 1C rate, capacities of 180 and 230 mAh/g, respectively, were obtained after 50 cycles. If the first charge is done at 0.1C, outstanding capacities of 120–135 mAh/g are observed after 100 cycles at 5C. More lithium can be removed during the charge at 0.1C, leading to a large amount of lithium vacancies that enhance mobility and rate capability. It is proposed that incomplete filling of the vacancies occurs upon cycling, so that the mobility remains high. This performance compares well to that of Li₄Ti₅O₁₂.     

Prediction of viscosity for molecular fluids at experimentally accessible shear rates using the transient time correlation function formalism

Nonequilibrium molecular dynamics (NEMD) simulations were performed and the transient time correlation function (TTCF) method applied to calculate the shear viscosity of n-decane. Using the TTCF method we were able to calculate the viscosity at shear rate orders of magnitude lower than is possible by direct NEMD simulation alone. For the first time for a molecular fluid, we were able to simulate shear rates accessible by experimental measurements, which are typically performed at shear rates well below those accessible by NEMD simulation. The TTCF method allows us to close the gap between the lowest shear rates accessible by MD simulation and the highest shear rates possible in experimental studies. Additionally a multiple time step method for Gaussian thermostatted SLLOD equations of motion was developed following earlier work [G. A. Pan et al., J. Chem. Phys. 122, 4114 (2005)] for atomic fluids.     

BF3-activated oxidation of alkanes by MnO4 -

The oxidation of alkanes and arylalkanes by KMnO(4) in CH(3)CN is greatly accelerated by the presence of just a few equivalents of BF(3), the reaction occurring readily at room temperature. Carbonyl compounds are the predominant products in the oxidation of secondary C-H bonds. Spectrophotometric and kinetics studies show that BF(3) forms an adduct with KMnO(4) in CH(3)CN, [BF(3).MnO(4)](-), which is the active species responsible for the oxidation of C-H bonds. The rate constant for the oxidation of toluene by [BF(3).MnO(4)](-) is over 7 orders of magnitude faster than by MnO(4)(-) alone. The kinetic isotope effects for the oxidation of cyclohexane, toluene, and ethylbenzene at 25.0 degrees C are as follows: k(C6H12)/k(C6D12) = 5.3 +/- 0.6, k(C7H8)/k(C7D8) = 6.8 +/- 0.5, k(C8H10)/k(C8D10) = 7.1 +/- 0.5. The rate-limiting step for all of these reactions is most likely hydrogen-atom transfer from the substrate to an oxo group of the adduct. A good linear correlation between log(rate constant) and C-H bond energies of the hydrocarbons is found. The accelerating effect of BF(3) on the oxidation of methane by MnO(4)(-) has been studied computationally by the Density Functional Theory (DFT) method. A significant decrease in the reaction barrier results from BF(3) coordination to MnO(4)(-). The BF(3) coordination increases the ability of the Mn metal center to achieve a d(1) Mn(VI) electron configuration in the transition state. Calculations also indicate that the species [2BF(3).MnO(4)](-) is more reactive than [BF(3).MnO(4)](-).     

Assigning carbon-13 NMR spectra to crystal structures by the INADEQUATE pulse sequence and first principles computation: a case study of two forms of testosterone

A (13)C CPMAS NMR experiment at high field (11.7 T) has produced significantly improved dispersion for the alpha form of testosterone, allowing revisions and extensions to be made to the assignments. Correlations shown by an INADEQUATE two-dimensional spectrum, recorded at 16.5 T, have allowed the components of most of the doublet signals to be grouped into two sets (for the two crystallographically independent molecules). First-principles computations, employing a fully solid-state approach, have been used to obtain values for the crystallographic splittings, which are discussed in relation to the experimental values. This procedure enables assignments to the two groups to be suggested for all but one of the remaining doublet signals. It also allows the two sets of signals to be identified specifically to the two independent molecules in the crystal structure. Computations were also carried out for the beta form of testosterone (a dihydrate). The shift differences between the alpha and beta forms were compared with the experimental data, with encouraging results. Comparisons were also made between computed and experimental shielding anisotropies and asymmetries for three of the carbons of the alpha form. The methodology has a high potential for future applications, though more examples need to be evaluated before general conclusions can be drawn.     

Impact of Statistical Multiplexing on Voice Quality in Cellular Networks

This paper examines the quality of transmission of voice over cellular, packet-switched networks. The medium access mechanism in the uplink is simulated under various statistical multiplexing scenarios in order to assess the effect of front-end clipping on voice quality. Moreover, the simulation is implemented in a real-time demonstration platform utilized to acquire subjective indicators of voice quality by performing Mean Opinion Score (MOS) tests. Results from the MOS tests are reported, and an analysis of the obtained speech samples is presented. Finally, the results are summarized and potential further directions for the simulation tool and the speech models are discussed.     

Perturbing the Hofmeister series: a steroid-based anion receptor with preorganised quaternary ammonium and H-bond donor groups

Preorganised urea groups moderate the anion-exchange properties of cationic receptor 2, favouring halide extraction and promoting anion transport through a bulk liquid membrane.