An electrochemical investigation of intermediates and processes involved in the catalytic reduction of dinitrogen by [HIPTN3N]Mo (HIPTN3N = (3,5-(2,4,6-i-Pr3C6H2)2C6H3NCH2CH2)3N)

The redox properties of [HIPTN(3)N]Mo complexes (where HIPTN(3)N = (3,5-(2,4,6-i-Pr(3)C(6)H(2))(2)C(6)H(3)NCH(2)CH(2))(3)N) involved in the catalytic dinitrogen reduction cycle were studied using cyclic voltammetry in fluorobenzene with Bu(4)NPF(6) as the electrolyte. MoN(2) (Mo = [HIPTN(3)N]Mo, E(1/2) = -1.96 V vs. Fc(+)/Fc at a Pt electrode), Mo≡N (E(1/2) = -2.68 V vs. Fc(+)/Fc (Pt)), and [Mo(NH(3))]BAr'(4) (Ar' = 3,5-(CF(3))(2)C(6)H(3), E(1/2) = -1.53 V vs. Fc(+)/Fc (Pt)) each undergo a chemically reversible one-electron reduction, while [Mo=NNH(2)]BAr'(4) (E(1/2) = -1.50 V vs. Fc(+)/Fc (Pt)) and [Mo=NH]BAr'(4) (E(1/2) = -1.26 V vs. Fc(+)/Fc (Pt)) each undergo a one-electron reduction with partial chemical reversibility. The acid employed in the catalytic reduction, [2,4,6-collidinium]BAr'(4), reduces irreversibly at -1.11 V vs. Fc(+)/Fc at Pt and at -2.10 V vs. Fc(+)/Fc at a glassy carbon electrode. The reduction peak potentials of the Mo complexes shift in the presence of acids. For example, the reduction peak for MoN(2) in the presence of [2,4,6-collidinium]BAr'(4) at a glassy carbon electrode shifts positively by 130 mV. The shift in reduction potential is explained in terms of reversible hydrogen bonding and/or protonation at a nitrogen site in Mo complexes. The significance of productive and unproductive proton-coupled electron transfer reactions in the catalytic dinitrogen reduction cycle is discussed.     

Role of bridging diamine linkers on the rate of ligand substitution in a series of dinuclear PtII complexes

A series of dinuclear platinum^II complexes of the type [{trans‐Pt(H₂O)(NH₃)₂}₂‐NH₂(CH₂)_nH₂N]⁴⁺ (where n = 2, 3, 4, and 6) were synthesized to investigate the influence of the bridging diamine linker on the reactivity of the platinum centers. The pK_a values were determined, and the rates of substitution of the aqua moieties by a series of neutral nucleophiles viz. thiourea, 1,3‐dimethyl‐2‐thiourea, and 1,1,3,3‐tetramethyl‐2‐thiourea were studied as a function of concentration and temperature. All reactions studied gave excellent fits to a single exponential and obeyed the simple rate law, k_obs=k₂[Nu]. Negative activation entropies support an associative mode of substitution. The results obtained suggest that the rate of substitution is definitely influenced by the length of the diamine chain, with the rate of substitution decreasing as the length of the diamine chain increases. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 202–210, 2006     

Photoproduction of π+ from9Be

The reaction⁹Be(γ, π ⁺)⁹Li has been studied with bremsstrahlung in the energy range 100–800 MeV employing the radioactivity method. The cross section curve deduced is compared with an impulse approximation calculation including a volume and a surface production model. In the energy region 200–300 MeV the experimental cross section, approximately 7 (μb, is best reproduced by the surface production model with a cut-off parameterr ₀ equal to 2.8 fm, i.e. somewhat larger than the r.m.s. radius of⁹Be.     

Large-eddy simulation of shock-turbulence interaction in supersonic diffuser flows

LES based on explicit filtering is used to study the shock train phenomenon in turbulent supersonic diffuser flows with circular cross-section and isothermal wall with an incoming pipe flow at friction Reynolds number 245 and centerline Mach number 1.7. Alternate regions of compression and expansion are found in the shock train which is followed by a shock-free ‘mixing’ region as observed in experiments and simulations in the literature. Turbulence amplification and local peaks in pressure-dilatation correlation are observed in the vicinity of the shocks. Low-frequency oscillations of the shock train are also observed.     

On the Debye‐Waller factor and Debye temperature of CdO nanoparticles

Theoretical calculation on the phonon dispersion of CdO nanoparticles at room temperature is reported here for the first time. The mean square amplitude, Debye–Waller factor and Debye temperature are calculated for CdO nanoparticles from the phonon spectrum and compared with the experimental results obtained from Rietveld refinement of XRD pattern of the CdO nanoparticles. The thermal stability of the nanoparticles is studied from both the experimental and theoretical calculations of melting point which is found to be 3686 K and 3951 K, respectively, greater than that of bulk CdO. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Scale directional distance function and its application to the measurement of eco-efficiency in the manufacturing sector

Directional distance function (DDF) is a recognized technique for measuring efficiency while incorporating undesirable outputs. This approach allows for desirable outputs to be expanded while undesirable outputs are contracted simultaneously. A drawback of the DDF approach is that the direction vector to the production boundary is fixed arbitrarily, which may not provide the best efficiency measure. Therefore, this study extends the previous framework of efficiency analysis to introduce a new slacks-based measure of efficiency called the scale directional distance function (SDDF) approach. This new approach determines the optimal direction to the frontier for each unit of analysis and provides dissimilar expansion and contraction factors to achieve a more reasonable eco-efficiency score. This new approach is employed to measure the eco-efficiency of the Malaysian manufacturing sector. In addition, the paper demonstrates the use of the new approach to establish target values for the reduction/expansion of outputs in order for the inefficient DMUs to achieve full eco-efficiency. The results indicate that Melaka, Pulau Pinang, Negeri Sembilan, Sabah, Sarawak and Labuan have attained full eco-efficiency while Terengganu is the least eco-efficient. The overall eco-efficiency of the manufacturing sector in Malaysia is 80.5 % with wide variations across the states.     

The effect of 19-electron formation constants on the electrochemistry and electron transfer induced substitution reactions of cyclopentadienylmetal halide complexes

The reduction of cyclopentadienylmetal halide complexes is generally considered to involve addition of an electron to an orbital that is antibonding with respect to the metal-halide bond. Subsequent metal-halide bond cleavage yields the halide and an organometallic radical. At inert electrodes, this radical is reduced further to an 18-electron anion. This series of reactions constitutes a prototypical ECE mechanism. Chemical reduction can be used to divert the radical into other pathways such as electron transfer chain catalyzed substitution. Attempts to initiate such reductively induced substitution reactions of CpFe(CO)₂I and Cp′Mo(CO)₃I give very different results, suggesting that these very similar complexes are reduced via substantially different mechanisms. Very likely, the molybdenum complex reacts via a DISP mechanism instead of ECE. The difference in electrochemical reduction mechanism as well as the different reactivity toward reductively induced substitution are explained in terms of a difference in the formation constants of 19-electron intermediates.     

Direct Infusion Electrospray Ionization – Ion Mobility – High Resolution Mass Spectrometry (DIESI-IM-HRMS) for Rapid Characterization of Potential Bioprocess Streams

Direct infusion electrospray ionization?-?ion mobility?-?high resolution mass spectrometry (DIESI-IM-HRMS) has been utilized as a rapid technique for the characterization of total molecular composition in "whole-sample" biomass hydrolysates and extracts. IM-HRMS data reveal a broad molecular weight distribution of sample components (up to 1100 m/z) and provide trendline isolation of feedstock components from those introduced "in process." Chemical formulas were obtained from HRMS exact mass measurements (with typical mass error less than 5 ppm) and were consistent with structural carbohydrates and other lignocellulosic degradation products. Analyte assignments are supported via IM-MS collision-cross-section measurements and trendline analysis (e.g., all carbohydrate oligomers identified in a corn stover hydrolysate were found to fall within 6% of an average trendline). These data represent the first report of collision cross sections for several negatively charged carbohydrates and other acidic species occurring natively in biomass hydrolysates.     

Combined Use of Post-Ion Mobility/Collision-Induced Dissociation and Chemometrics for b Fragment Ion Analysis

Although structural isomers may yield indistinguishable ion mobility (IM) arrival times and similar fragment ions in tandem mass spectrometry (MS), it is demonstrated that post-IM/collision-induced dissociation MS (post-IM/CID MS) combined with chemometrics can enable independent study of the IM-overlapped isomers. The new approach allowed us to investigate the propensity of selected b type fragment ions from AlaAlaAlaHisAlaAlaAla-NH₂ (AAA(His)AAA) heptapeptide to form different isomers. Principle component analysis (PCA) of the unresolved post-IM/CID profiles indicated the presence of two different isomer types for b₄ ⁺, b₅ ⁺, and b₆ ⁺ and a single isomer type for b₇ ⁺ fragments of AAA(His)AAA. We employed a simple-to-use interactive self-modeling mixture analysis (SIMPLISMA) to calculate the total IM profiles and CID mass spectra of b fragment isomers. The deconvoluted CID mass spectra showed discernible fragmentation patterns for the two isomers of b₄ ⁺, b₅ ⁺, and b₆ ⁺ fragments. Under our experimental conditions, calculated percentages of the “cyclic” isomers (at the 95 % confidence level for n = 3) for b₄ ⁺, b₅ ⁺, and b₆ ⁺ were 61 (± 5) %, 36 (± 5) %, and 48 (± 2) %, respectively. Results from the SIMPLISMA deconvolution of b₅ ⁺ species resembled the CID MS patterns of fully resolved IM profiles for the two b₅ ⁺ isomers. The “cyclic” isomers for each of the two-component b fragment ions were less susceptible to ion fragmentation than their “linear” counterparts.