MECHANISMS OF 1,2-DIOXETANE DECOMPOSITION: THE ROLE OF ELECTRON TRANSFER

Abstract— The chemiluminescence from the cleavage of a number of 1,6-diaryl-2,5,7,8-tetraoxabicyclo[4.2.0]octanes 1 has been examined. The ease of oxidation of (object) the aryl moiety strongly influences both the stability and chemiluminescence efficiency of these 1,2-dioxetanes. When Ar is difficult to oxidize, 1 is comparable in stability to simple. alkyl-substituted 1,2-dioxe-tanes and affords triplet excited states in moderate yield. Both biradical and concerted cleavage mechanisms have been suggested to explain this behavior. However, when Ar is a readily oxidized group, 1 is substantially destahilized and gives excited singlet states in high yield. In this instance 1 is analogous to a number of bioluminescent systems. Cleavage mechanisms involving intramolecular electron transfer are proposed to account for this observation. In certain cases thermolysis of 1 occurs by both types of mechanism in competition, and the electron transfer mechanism may be selectively catalyzed by polar, protic media.     

Über „Lithovanadate”︁: Zur Kenntnis von Rb2[LiVO4] und Cs2[LiVO4]

On ?Lithovanadates”?: Rb₂[LiVO₄] and Cs₂[LiVO₄] By heating of well ground mixtures of the binary oxides [A₂O, Li₂O, V₂O₅, A : Li: V = 2.2 : 1.1 : 1.0 (A = Rb, Cs); Ni-tube, 750° 25 d] we obtained Rb₂[LiVO₄] and Cs₂[LiVO₄] colourless, orthorhombic single crystals. We found a new type of ?Lithovanadate”?-structure: space group Cmc2₁; a = 587.9(1), b = 1170.1(1), c = 793.3(1) pm, Z = 4 (A = Rb) bzw. a = 610.5(1), b = 1222.6(3), c = 815.5(2) pm, Z = 4 (A = Cs). The structure was determined by four-circle diffractometer data [MoKα -radiation; 997 from 1157 I₀(hkl), R = 7.75%, R_w = 5.54% (A = Rb); 686 from 686 I₀(hkl), R = 6.97%, R_w = 4.20% (A = Cs)] parameters see text. The Madelung part of Lattice Energy, MAPLE, and Effective Coordination Numbers, ECoN, these via Mean Fictive Ionic Radii, MEFIR, have been calculated.     

Highly selective asymmetric hydrogenation using a three hindered quadrant bisphosphine rhodium catalyst

A concise synthesis of both enantiomers of ligand 2 and rhodium complex 5 is presented. The crux of the synthesis is a chiral HPLC separation of the enantiomers of 4. Rhodium complex 5 possesses three hindered quadrants in the steric environment within which a substrate binds. Evidence is presented that this configuration leads to high enantioselectivity (>99% ee) for rhodium-catalyzed asymmetric hydrogenation of alpha-acetamido dehydroamino acids, 6a-e. High enantioselectivities are also reported for the hydrogenation of a substrate precursor, 8, of pharmaceutical candidate, pregabalin. Advantages for large-scale hydrogenation of 8 using catalyst 5a vs Rh-Me-DuPhos are discussed.     

Near-perfect imaging in a focusing system based on a left-handed-material plate

This Letter deals with the investigation of the electromagnetic radiation focusing using a plane-parallel plate of a material with negative real parts of the permittivity and permeability. The reasons are demonstrated for the restriction of the limiting attainable resolution of the system. The possibility of obtaining the separated images of sources the distance between which is much less than the wavelength is confirmed theoretically and experimentally.     

Novel ‘Nano in Nano’ Composites for Sustained Drug Delivery: Biodegradable Nanoparticles Encapsulated into Nanofiber Non‐Wovens

Novel ‘nano in nano’ composites consisting of biodegradable polymer nanoparticles incorporated into polymer nanofibers may efficiently modulate drug delivery. This is shown here using a combination of model compound‐loaded biodegradable nanoparticles encapsulated in electrospun fibers. The dye coumarin 6 is used as model compound for a drug in order to simulate drug release from loaded poly(lactide‐co‐glycolide) nanoparticles. Dye release from the nanoparticles occurs immediately in aqueous solution. Dye‐loaded nanoparticles which are encapsulated by electrospun polymer nanofibers display a significantly retarded release.

     

Development of a Miniaturized Energy Converter Without Moving Parts

New developments in portable electrical and mechanical devices have created demand for increasing amounts of energy and thus new ways of supplying energy. The high energy density of hydrocarbon fuels are a possible way to solve this issue. This paper deals with the development of an adapted thermodynamic concept for a micro energy converter based on the thermoelectric effect. Developing a PowerMEMS device that does not contain any moving parts is the main design feature. In the proposed concept liquid hydrocarbon fuel, such as methanol, is evaporated in a micro evaporator, mixed with air, and combusted in a micro combustion chamber. The combustion process is assisted by catalytically coated microfibers. Electrical power can be generated by a thermoelectric generator, which is located between the hot combustion zone and the cold micro evaporator. This arrangement leads to large temperature differences between hot and cold junctions, which is necessary for efficient thermoelectric energy conversion and hence power generation. For a more detailed investigation of thermal boundary conditions and interior thermal management, in-situ temperature measurements of the combustor walls are performed using thermographic phosphors.     

Line Shift Investigations for Different Isotopomers of Carbon Monoxide

Line shift coefficients for five lines of five different isotopomers in the fundamental band of CO in the spectral region near 2058 cm⁻¹were measured using a three channel lead salt diode laser spectrometer. The study includes the linesP(3) of¹³C¹⁷O,R(3) of¹³C¹⁸O,P(9) of¹²C¹⁸O,P(10) of¹³C¹⁶O, andP(21) of¹²C¹⁶O, and covers collisions with N₂, O₂, H₂, D₂, He, Ne, Ar, Kr, and Xe. Line shifts of the isotopomers¹³C¹⁶O,¹²C¹⁸O,¹³C¹⁸O, and¹³C¹⁷O were determined for the first time. Within the experimental uncertainty no significant dependence of the shift effect on the isotopomer was found. TheR-branch line under study shows a smaller line shift coefficient than aP-branch line with a similar rotational quantum number. With increasing mass of the noble gas perturber the absolute size of the shift coefficient increases. Moreover self- and nitrogen-broadening coefficients for the isotopomer lines were determined. Compared to previous measurements no significant deviations between different isotopomers were observed.     

Hydrogenation of C=C and C=N Bonds of the Amide-Imine Ligand in the Metal Coordination Sphere in the Reaction of Yttrium Bis(alkyl) Complex [2,6-iso-Pr2C6H3NC(=CH2)C(Me)=NC6H3-iso-Pr2-2,6]Y(CH2SiMe3)2(THF) with Molecular Hydrogen

Russian Journal of Coordination Chemistry - On treatment of the yttrium bis(alkyl) complex [ArNC(=CH2)C(Me)=NAr]Y(CH2SiMe3)2(THF) (I, Ar = C6H3-iso-Pr2-2.6) containing an amide-imine ligand, with...     

Simultaneous Measurements of Temperature and CO Concentration in Stagnation Stabilized Flames

An impinging jet burner was developed to investigate flame-wall interactions (FWI) using laser based diagnostics. CO concentrations were measured with two-photon laser-induced fluorescence (LIF) in combination with coherent anti-Stokes Raman spectroscopy (CARS) gas phase temperature measurements. Besides being the principal factor in chemical kinetics, temperature data is required to correct the CO LIF data for various factors like density variation, quenching and variation in the Boltzmann population. Phosphor thermometry was used to determine surface temperatures of the wall and to estimate the heat flux. In an parameter study Reynolds numbers and fuel equivalence ratio were varied.     

An enantioselective synthesis of (S)-(+)-3-aminomethyl-5-methylhexanoic acid via asymmetric hydrogenation

A concise enantioselective synthesis of (S)-(+)-3-aminomethyl-5-methylhexanoic acid (1, Pregabalin) has been developed. The key step is the asymmetric hydrogenation of a 3-cyano-5-methylhex-3-enoic acid salt 2 with a rhodium Me-DuPHOS catalyst, providing the desired (S)-3-cyano-5-methylhexanoate 3 in very high ee. Subsequent hydrogenation of the nitrile 3 with a heterogeneous nickel catalyst provides Pregabalin 1 in excellent overall yield and purity.