Fe vibrational spectroscopy of myoglobin and cytochrome f

The Fe vibrational density of states (VDOS) has been determined for the heme proteins deoxymyoglobin, metmyoglobin, and cytochrome f in the oxidized and reduced states, using nuclear resonance vibrational spectroscopy (NRVS). For cytochrome f in particular, the NRVS spectrum is compared with multiwavelength resonance Raman spectra to identify those Raman modes with significant Fe displacement. Modes not seen by Raman due to optical selection rules appear in the NRVS spectrum. The mean Fe force constant extracted from the VDOS illustrates how Fe dynamics varies among these four monoheme proteins, and is correlated with oxidation and spin state trends seen in model heme compounds. The protein's contribution to Fe motion is dominant at low frequencies, where coupling to the backbone tightly constrains Fe displacements in cytochrome f, in contrast to enhanced heme flexibility in myoglobin.     

Frequency-selective homonuclear dipolar recoupling in solid state NMR

We introduce a new approach to frequency-selective homonuclear dipolar recoupling in solid state nuclear magnetic resonance (NMR) with magic-angle spinning (MAS). This approach, to which we give the acronym SEASHORE, employs alternating periods of double-quantum recoupling and chemical shift evolution to produce phase modulations of the recoupled dipole-dipole interactions that average out undesired couplings, leaving only dipole-dipole couplings between nuclear spins with a selected pair of NMR frequencies. In principle, SEASHORE is applicable to systems with arbitrary coupling strengths and arbitrary sets of NMR frequencies. Arbitrary MAS frequencies are also possible, subject only to restrictions imposed by the pulse sequence chosen for double-quantum recoupling. We demonstrate the efficacy of SEASHORE in experimental (13)C NMR measurements of frequency-selective polarization transfer in uniformly (15)N, (13)C-labeled L-valine powder and frequency-selective intermolecular polarization transfer in amyloid fibrils formed by a synthetic decapeptide containing uniformly (15)N, (13)C-labeled residues.     

Design of a photostabilizer having built-in antioxidant functionality and its utility in obtaining broad-spectrum sunscreen formulations

Di-2,2'-diethylhexyl-3,5-dimethoxy-4-hydroxy-benzylidenemalonate (INCI name diethylhexyl syringylidene malonate, DESM), the target photostabilizer, was synthesized in one step by condensation of 3,5-dimethoxy-4-hydroxy benzaldehyde (Syringaldehyde) with di-2,2'-diethylhexyl malonate. Photostability data in sunscreen formulations showed that DESM is photostable and improves the photostability of avobenzone significantly when compared to control (without a photostabilizer). Photostable broad-spectrum sunscreen formulations with high SPF (>30) have been achieved by combining avobenzone, DESM and UV-B sunscreens, such as homosalate, octisalate or other UV-B sunscreens. It seems that (a) triplet-state energy transfer from avobenzone to DESM and (b) scavenging of reactive species are responsible for the observed stabilization of avobenzone. In vitro study of the two formulations containing DESM clearly showed critical wavelength of well over 370 nm and can thus be categorized as broad-spectrum sunscreens. DESM does not have any contribution to in vivo SPF; instead it boosts SPF by about 5 units in high-SPF products. DESM was found to be an excellent singlet-oxygen quencher, thereby reducing photodegradation of avobenzone caused by singlet oxygen. In short, the multiplicity of effects and formulation benefits seen with DESM makes it an ideal choice as a unique antioxidant photostabilizer for a variety of cosmetic products targeting young and mature skin alike.     

Current reuse topology in UWB CMOS LNA

Low power low voltage operation is found to be the bottleneck of future CMOS system implementations. To comply with these constrains, a current reuse configuration is here reported to design UWB Low Noise Amplifiers (LNA). A resistive feedback topology is first proposed performing an 11.5 dB gain over a 2 to 9 GHz range. Consuming a 17 mW under 1.4 V, this circuit achieves a 4.45 dB minimum Noise Figure (NFmin). Current reuse approach is then combined with LC ladder technique to cover the upper band of European UWB—i.e. 6 to 10 GHz-. This second LNA provides a 12.2 dB, 4.4 dB NFmin, from 5.6 to 8.8 GHz. Operating under 1.6 V it solely consumes 5 mW. Considering a 1.2 V supply voltage case, the two circuits still exhibit a more than 9 and 11 dB gain respectively. Implemented in a 0.13 μm CMOS technology, silicon areas are 0.6 mm2 for resistive feedback amplifier, and 1 mm2 for LC ladder, with PADS.     

Large-scale screening of metal hydrides for hydrogen storage from first-principles calculations based on equilibrium reaction thermodynamics

Systematic thermodynamics calculations based on density functional theory-calculated energies for crystalline solids have been a useful complement to experimental studies of hydrogen storage in metal hydrides. We report the most comprehensive set of thermodynamics calculations for mixtures of light metal hydrides to date by performing grand canonical linear programming screening on a database of 359 compounds, including 147 compounds not previously examined by us. This database is used to categorize the reaction thermodynamics of all mixtures containing any four non-H elements among Al, B, C, Ca, K, Li, Mg, N, Na, Sc, Si, Ti, and V. Reactions are categorized according to the amount of H(2) that is released and the reaction's enthalpy. This approach identifies 74 distinct single step reactions having that a storage capacity >6 wt.% and zero temperature heats of reaction 15 ≤ΔU(0)≤ 75 kJ mol(-1) H(2). Many of these reactions, however, are likely to be problematic experimentally because of the role of refractory compounds, B(12)H(12)-containing compounds, or carbon. The single most promising reaction identified in this way involves LiNH(2)/LiH/KBH(4), storing 7.48 wt.% H(2) and having ΔU(0) = 43.6 kJ mol(-1) H(2). We also examined the complete range of reaction mixtures to identify multi-step reactions with useful properties; this yielded 23 multi-step reactions of potential interest.     

C-H bond arylations and benzylations on oxazol(in)es with a palladium catalyst of a secondary phosphine oxide

An air-stable, well-defined palladium complex derived from secondary phosphine oxide (SPO) (1-Ad)(2)P(O)H enabled efficient C-H bond functionalizations with ample scope, which set the stage for direct arylations and benzylations of (benz)oxazoles, as well as unprecedented palladium-catalyzed C-H bond arylations on nonaromatic oxazolines.     

Self-ordering of colloidal particles in shallow nanoscale surface corrugations

The influence of nanoscale out-of-plane roughness on the ordering of submicron spheres during evaporative deposition from colloidal suspension was examined using shallow corrugated substrates possessing optical wavelengths and nanoscale amplitude. Under conditions in which spheres were embedded in a liquid layer with thickness on the order of the sphere diameter, it was observed that the spheres overwhelmingly deposited in the valleys of the surface corrugations rather than on their peaks. This behavior persisted to surprisingly shallow corrugation amplitudes, sometimes 100 times smaller than the sphere diameter. An analysis of the capillary forces on the spheres explains this behavior and also yields a critical corrugation amplitude below which a substrate will appear "flat" to depositing spheres. The observation that substrate features significantly smaller than the sphere diameter can influence deposition morphology may lead to simple methods to create large domains of order in colloidal crystals.     

Some Critical Materials and Processing Issues in SiC Power Devices

There has been a rapid improvement in SiC materials and power devices during the last few years. However, the materials community has overlooked some critical issues, which may threaten the emergence of SiC power devices in the coming years. Some of these pressing materials and processing issues will be presented in this paper. The first issue deals with the possibility of process-induced bulk traps in SiC immediately under the SiC/SiO₂ interface, which may be involved in the reduction of effective inversion layer electron mobility in SiC metal–oxide–semiconductor field-effect transistor (MOSFETs). The second issue addresses the effect of recombination-induced stacking faults (SFs) in majority carrier devices such as MOSFETs, Schottky diodes, and junction field-effect transistors (JFETs). In the past it was assumed that the SFs only affect the bipolar devices such as PiN diodes and thyristors. However, most majority carrier devices have built-in p–n junction diodes, which can become forward biased during operation in a circuit. Thus, all high-voltage SiC devices are susceptible to this phenomenon.     

2 to 23 GHz BiFET low noise amplifier design flow and implementations in 0.25 μm SiGe BiCMOS technology

Two BiFET LNAs are here reported, implemented in a 0.25 μm BiCMOS technology from ST Microelectronics. First of them, dedicated to WCDMA standard, depicts a 15.5 and 2.85 dB, S₂₁ and noise figure (NF), respectively, under 2 mA current consumption. The second realization operates at 23 GHz for Mini-Link application. It provides a 14 dB gain and 7 dB at 22 GHz NF for an 8.2 mA current consumption under 2.5 V. Both circuits were designed according to a design flow, here depicted, based on input matching, NF and gain optimisation. A large part of the article also deals with high frequency layout considerations. Indeed useful techniques dedicated to integrated microstrip waveguides and RF inter-connections are proposed based on 3D electromagnetic field simulations.