Kinetics of MTO-catalyzed olefin epoxidation in ambient temperature ionic liquids: UV/Vis and 2H NMR study

The kinetics of oxygen-atom transfer from the peroxo complexes of methyltrioxorhenium (MTO) to alkenes in ionic liquids have been investigated. Noncatalytic conversions of alkenes to epoxide were monitored by UV/Vis at 360 nm, where the monoperoxorhenium (mpRe) and diperoxorhenium (dpRe) complexes absorb. Water- and peroxide-free dpRe was prepared in situ by the reaction of MTO and urea hydrogen peroxide (UHP) in dry THF. The observed biexponential time profiles in conjunction with kinetic modeling allow the assignment of the fast step to the reaction of olefin with dpRe (k4) and the slow step to the analogous reaction with mpRe (k3). In most of the tudied ionic liquids, k4 approximately 5 x k3. 2H NMR experiments conducted with [D3]dpRe under non-steady-state conditions confirm the speciation of the catalytic system in ionic liquids and assert the validity of the UV/Vis kinetics. Deuteriated alkenes were used to study the catalytic epoxidation and dihydroxylation of alkenes by 2H NMR spectroscopy. The values of k4 for alpha-methylstyrene in several ionic liquids exceed what is observed in acetonitrile by an order of magnitude. While the rate of olefin epoxidation is unaffected by the nature of the ionic liquid cation, a discernible kinetic effect is observed with coordinating anions such as nitrate.     

Kinetics and mechanistic studies of anticarcinogenic bisperoxovanadium(V) compounds: ligand substitution reactions at physiological pH and relevance to DNA interactions

Bisperoxovanadium(V) compounds with bidentate ligands have shown tumor growth inhibition by cleaving DNA. The kinetics and mechanisms of ligand substitution reactions of two bisperoxovanadium(V) compounds [VO(O(2))(2)(bpy)](-) (bpVbpy) and [VO(O(2))(2)(phen)](-) (bpVphen) with entering ligands picolinic acid (pic) and dipicolinic acid (dipic) at physiological pH are reported, and its relevance to their DNA-cleavage activities are discussed. The products of the ligand substitution reactions with pic and dipic are the monoperoxo complexes [VO(O(2))(pic)(2)](-) and [VO(O(2))(dipic)(H(2)O)](-), respectively. (51)V NMR experiments indicate that bpVphen is substantially more inert in aqueous solution than bpVbpy. As a result, bpVbpy is more prone to ligand substitution and subsequent conversion to monoperoxo species. The rate of reaction for bpVbpy was faster than that of bpVphen by an order of magnitude, indicating that the ancillary ligand plays an important role in ligand substitution reactions. The ligand substitution reactions of bpVbpy feature first-order dependence on both [pic](T) and [dipic](T) whereas the substitution kinetics of bpVphen feature saturation behavior with dipic. The substitution reactions of both bpVbpy and bpVphen with pic showed first-order dependence on [H(+)] whereas no acid dependence was observed for the reactions with dipic. Hydrogen peroxide was determined to be a competitive inhibitor with respect to dipic. The ligand substitution reaction mechanisms and the rate laws consistent with these results are presented. The substitution reactions with pic and dipic proceed through different mechanisms; the substitution reactions with dipic proceed via solvolysis as the first step in the mechanisms whereas the reactions with pic bypass solvolysis to go through a mixed ligand monoperoxo vanadium intermediate.     

Dynamic model of a flying manipulator with two highly flexible links

Nonlinear dynamic model of a flying manipulator with two revolute joints and two highly flexible links is obtained using Hamilton’s principle. Flying base of the manipulator is a rigid body. Stress is treated three dimensionally in the isotropic linearly-elastic links, but the in-plane and out-of-plane warpings of the links’ cross-sections are neglected. Although the links’ cross-sections undergo negligible elastic orientation, their models are more accurate than a nonlinear 3D Euler–Bernoulli beam. Tension, compression, twisting and spatial deflections of each link are coupled to each other by some nonlinear terms including two new ones. In the issue of flying flexible-link manipulators new terminologies, namely forward/inverse kinetics instead of forward/inverse kinematics are suggested, since determination of position and orientation of the end-effector is coupled to the partial differential motion equations.     

Non-isothermal lubrication problem with Tresca fluid–solid interface law. Part II Asymptotic behavior of weak solutions

We study in this paper the asymptotic analysis of an incompressible Newtonian and non-isothermal problem, when one dimension of the fluid domain tends to zero. We prove the strong convergence of the unknowns which are the temperature, the velocity and the pressure of the fluid, we obtain the limit problem with the specific Reynolds equation, and we also prove the uniqueness of the limit temperature velocity and pressure distributions.     

Regio- and stereoselective synthesis of functionalized oxazolidin-2-ones from the reaction of α-epoxyketones with urea

A regio- and stereoselective synthesis of functionalized 4,5-disubstituted oxazolidin-2-ones is reported with moderate to good yields from the reaction of α-epoxyketones with urea in the presence of p-toluenesulfonic acid as the catalyst.     

Design optimisation of erbium-doped fibre ring laser through numerical simulation

Erbium-doped fibre ring laser is modelled, incorporating the effects of ion pairs, using the propagation and rate equations of a homogeneous, two-level medium. The numerical model has been obtained by developing a spectral analysis of erbium-doped fibre amplifiers. This approach is modified to account for the cyclical propagation of the field in the ring laser. Numerical simulations provide interesting information on the spectral behaviour as well as important parameters for device analysis and design, mainly the lasing wavelength and output power.     

Synthesis of N'-(1-pyridin-2-ylmethylene)-2-furohydrazide and its application in construction of a highly selective PVC-based membrane sensor for La(III) ions.

A highly La(III) ion-selective PVC membrane sensor based on N'-(1-pyridin-2-ylmethylene)-2-furohydrazide (NPYFH) as an excellent sensing material was successfully developed. The electrode shows a good selectivity for La(III) ion with respect to most common cations including alkali, alkaline earth, transition and heavy metal ions. The proposed sensor exhibits a wide linear response with slope of 19.2 +/- 0.6 mV per decade over the concentration range of 1.0 x 10(-6) - 1.0 x 10(-1) M, and a detection limit of 7.0 x 10(-7) M of La(III) ions. The sensor response is independent of pH in the range of 3.5-10.0. The proposed electrode was applied as an indicator electrode in potentiometric titration of La(III) ion with EDTA.     

A stabilized tunable dual wavelength erbium-doped fiber laser with equal output power

Tunable dual-wavelength erbium-doped fiber laser with good stability is experimentally demonstrated. Output power of as high as +5.26 dBm is obtained in dual ring configuration. Both laser output can be tuned to as closed as 0.8 nm spacing between each other, with tuning range of 31.33 nm. The stability of both outputs was tested that results in less than ±0.8 dB and ±0.01 nm in power and wavelength fluctuation, respectively.     

Single-stage gain-clamped L-band EDFA with C-band ASE saturating tone

We demonstrate a single-stage gain-clamped L-band Erbium-doped fiber amplifier with 1480 nm pump wavelength. The gain-clamping technique is achieved by utilizing the backward propagation of C-band amplified spontaneous emission (ASE). This unwanted noise is reflected back into the optical amplifier and its intensity is adjusted using the variable optical attenuator. The C-band ASE sets the population inversion level along the Erbium doped-fiber and limits the L-band signal amplification to a specific value. The whole optical bandwidth in L-band can be employed for signal amplification since the saturating tone is out of the band. The gain dynamic range of 11.7 dB is obtained between 21.7 and 10.0 dB with noise figure of less than 5.5 dB for signal power up to 2 dBm.