Decarboxylation of 2,2'-bipyridinyl-4,4'-dicarboxylic acid diethyl ester during microwave synthesis of the corresponding trichelated ruthenium complex

Microwave reaction of RuCl3 with 2,2'-bipyridinyl-4,4'-dicarboxylic acid diethyl ester (debpy) in ethylene glycol generated Ru(bpy)3(2+) instead of the expected Ru(debpy)3(2+). Gas chromatography-mass spectrometry analysis of the headspace revealed CO2, and Ru(bpy)3(2+) was recovered from the filtrate. Further experiments suggest that RuCl3 decarboxylates debpy during microwave synthesis.     

Synthesis and hydrogenation of bis(imino)pyridine iron imides

Treatment of the iron bis(dinitrogen) complex, (iPrPDI)Fe(N2)2 (iPrPDI = (2,6-iPr2C6H3N=CMe)2C5H3N), with a series of aryl azides resulted in loss of 3 equiv of N2 and formation of the corresponding four-coordinate iron imide compounds, (iPrPDI)Fe(NAr). These complexes, two of which (Ar = 2,6-iPr2-C6H3 and 2,4,6-Me3-C6H2) have been characterized by X-ray diffraction, are significantly distorted from planarity. The metrical parameters in combination with M?ssbauer spectroscopic and SQUID magnetic data suggest an intermediate spin iron(III) center antiferromagnetically coupled to a ligand-centered radical. Nitrene group transfer has been accomplished by addition of 1 atm of CO, yielding aryl isocyanates, ArNCO, and (iPrPDI)Fe(CO)2. Hydrogenation of the more sterically hindered members of the series furnished free aniline and the previously reported iron dihydrogen complex. Catalytic aryl azide hydrogenation has also been achieved, and the observed relative rates are consistent with N-H bond formation as the rate-determining step in aniline formation.     

Mössbauer studies of the iron-sulfur cluster-free hydrogenase: the electronic state of the mononuclear Fe active site

The iron-sulfur cluster-free hydrogenase (Hmd) from methanogenic archaea harbors an iron-containing, light-sensitive cofactor of still unknown structure as prosthetic group. The enzyme is reversibly inhibited by CO and cyanide and is EPR silent. We report here on M?ssbauer spectra of the (57)Fe-labeled enzyme and of the isolated cofactor. The spectrum of the holoenzyme measured at 80 K revealed a doublet peak with an isomer shift delta = 0.06 mm.s(-)(1) and a quadrupole splitting of DeltaE(Q) = 0.65 mm.s(-)(1) (at pH 8.0). The signal intensity corresponded to the enzyme concentration assuming 1 Fe per mol active site. Upon addition of CO or cyanide to the enzyme, the isomer shift decreased to -0.03 mm.s(-)(1) and -0.00(1) mm.s(-)(1), and the quadrupole splitting increased to 1.38 mm.s(-)(1) and 1.75 mm.s(-)(1), respectively. The three spectra could be perfectly simulated assuming the presence of only one type of iron in Hmd. The low isomer shift is characteristic for Fe in a low oxidation state (0, +1, +2). When the spectra of the holoenzyme and of the CO- or cyanide-inhibited enzyme were measured at 4 K in a magnetic field of 4 and 7 T, the spectra obtained could be simulated assuming the presence of only the external magnetic field, which excludes that the iron in the active site of Hmd is Fe(I), high-spin Fe(0), or high-spin Fe(II). M?ssbauer spectra of the isolated Hmd cofactor are also reported.     

Performance of nonrelativistic and quasi-relativistic hybrid DFT for the prediction of electric and magnetic hyperfine parameters in 57Fe Mössbauer spectra

57Fe electric and magnetic hyperfine parameters were calculated for a series of 10 iron model complexes, covering a wide range of oxidation and spin states. Employing the B3LYP hybrid method, results from nonrelativistic density functional theory (DFT) and quasi-relativistic DFT within the zero-order regular approximation (ZORA) were compared. Electron densities at the iron nuclei were calculated and correlated with experimental isomer shifts. It was shown that the fit parameters do not depend on a specific training set of iron complexes and are, therefore, more universal than might be expected. The nonrelativistic and quasi-relativistic electron densities gave fit parameters of similar quality; the ZORA densities are only shifted by a factor of 1.32, upward in the direction of the four-component Dirac-Fock value. From a correlation of calculated electric field gradients and experimental quadrupole splittings, the value of the 57Fe nuclear quadrupole moment was redetermined to a value of 0.16 barn, in good agreement with other studies. The ZORA approach gave no additional improvement of the calculated quadrupole splittings in comparison to the nonrelativistic approach. The comparison of the calculated and measured 57Fe isotropic hyperfine coupling constants (hfcc's) revealed that both the ZORA approach and the inclusion of spin-orbit contributions lead to better agreement between theory and experiment in comparison to the nonrelativistic results. For all iron complexes with small spin-orbit contributions (high-spin ferric and ferryl systems), a distinct underestimation of the isotropic hfcc's was found. Scaling factors of 1.81 (nonrelativistic DFT) and 1.69 (ZORA) are suggested. The calculated 57Fe isotropic hfcc's of the remaining model systems (low-spin ferric and high-spin ferrous systems) contain 10-50% second-order contributions and were found to be in reasonable agreement with the experimental results. This is assumed to be the consequence of error cancellation because g-tensor calculations for these systems are of poor quality with the existing DFT approaches. Excellent agreement between theory and experiment was found for the 57Fe anisotropic hfcc's. Finally, all of the obtained fit parameters were used for an application study of the [Fe(H2O)6]3+ ion. The calculated spectroscopic data are in good agreement with the Mossbauer and electron paramagnetic resonance results discussed in detail in a forthcoming paper.     

Full wave electromagnetics for simulating high speed quantum well laser diode modulation

A unique discretization scheme that couples Maxwell’s full wave vector field equations self-consistently with nonlinear charge and energy transport is presented. The scheme is used to simulate laser modulation achieved in a simple electrically pumped quantum well laser diode by dynamically heating the degenerate quantum charge gases with high frequency radiation.     

High performance GaAs MESFETs with molecular implanted and optimized lowly-doped drain structure for maximized speed, gain and breakdown performance

GaAs MESFETs with novel lowly-doped drain structures have been developed utilizing molecular implants of silicon trifluoride. Short-channel effects in the 1/4 μm enhancement- and depletion-mode transistors have been suppressed with drain-induced barrier height lowering of less than 70 mV/V and pinch-off voltage shifts of less than 220 mV as the gate length was scaled from 1.0 to 1/4 μm. The 3-terminal breakdown, the transconductance to output conductance ratio, and the unity current gain, cut-off frequency were simultaneously optimized. The E-mode device possessed breakdown of >10 V, G_m · R_ds > 9.5, F_t > 55 GHz, and nominal on-resistance of 2.1 Ω mm while the D-mode device had breakdown >10 V, G_m · R_ds > 6.0, F_t > 45 GHz, and nominal on-resistance of 1.9 Ω mm. These optimized transistors enabled the realization of a variety of low-power digital and high-power mixed signal circuits, using 3-level source-coupled transistor and common-mode logic, such as laser and electro-optic drivers, highly integrated transceivers, multiplexers, demultiplexers, and clock data recover circuits.     

Dual-purpose gas chromatographic injection device for pressurized liquid and gas injection

A dual-purpose gas chromatographic injection device, capable of injecting pressurized liquid sample of up to 5000 psig and gas sample with a volume as high as 5000 μL, has been successfully developed and implemented. The injection device is synergized by the effectiveness of a classical flash vaporization of a syringe injection and the reliability of a proven rotary valve. Depending on the matrix involved, this injection device employs either a commercially available four-port internal valve for liquid sampling or a six-port external valve for gas sampling, a modified removable needle used in standard liquid syringe, and an auxiliary flow stream that can be either mechanical or electronic flow controlled for solute transfer. For pressurized liquid, the device was found suitable of up to nC₁₆ hydrocarbon with no observable carry-over despite the injection device was operating at ambient temperature. A relative standard deviation of less than 2% (n = 20) was obtained for hydrocarbon compounds ranging from nC₈ to nC₁₆. For gas injection, the device performed well even under difficult chromatographic conditions such as with a low column inlet pressure of less than 1 psig. A relative standard deviation of less than 0.5% (n = 10) was obtained for reactive sulfur compounds such as alkyl mercaptans. The device can be operated manually or automated with pneumatic or electrical actuator, is platform neutral, and can be moved amongst instruments without hardware modification as well as implemented for on-line or in situ applications. In this paper, the utility of the device was also demonstrated with selected GC applications of industrial significance.     

产品可靠性的重新下降？

不久前，我们的行业遇到了元件可靠性问题，大批量产品用户发现美国公司的存储器IC的故障率比日本同类产品高。通过努力，现在各类IC都很可靠，硬IC故障也很少。我们的其它元件．比如无源元件、印线电路板等，情况也大多是如此。