275 research outputs found
Electron Shuttling in High-Valent Heterobimetallic NiFe-Porphyrin Dimers: Stabilization of Ni(III) and Fe-Phenoxyl Radicals
No full textA series of axially phenoxide-bound Ni(II)-Fe(III) heterobimetallic porphyrin dimers, as a synthetic mimic of the diheme enzyme MauG, have been synthesized, which upon 4e- oxidations revealed the oxidized complex involving porphyrin π-cation radicals, an Fe(III)-coordinated phenoxyl radical, and a Ni(III) center. Redox cooperativity and the extensive π-conjugation through the bridge make the oxidized complex behave like a single supramolecular entity having unpaired electrons spread over five magnetic centers. Several isoelectronic states for the oxidized Fe(por) center, i.e., Fe(IV)(por)(PhO•) ↔ Fe(IV)(por•+)(PhO) ↔ Fe(III)(por•+)(PhO•), are possible that can be in equilibrium with low-energy barriers between them. DFT studies demonstrate spin delocalization with a dramatic change in the Fe-OTyr bond upon oxidation, which thereby becomes an active modulator of various electronic states of high-valent intermediates in diheme enzymes, such as MauG and bacterial diheme cytochrome c peroxidase (bCcP), for their function
Depth of Investigation of Dipole-dipole, Noncolinear and Focused Geoelectric Arrays
No full textInvestigation depth of various DC geoelectric arrays has always been in the focus of interest of geoelectricians. According to its classical definition (Roy and Apparao 1971), the depth of investigation is the depth of the maximum response due to a horizontal thin-sheet embedded in a half-space, by using a given geoelectric array. On basis of the graph of the thin-sheet response as a function of the depth (from the so-called „depth of investigation characteristics” or DIC function) Edwards (1977) found more realistic to compute the medium depth than the depth of the maximum response. DIC functions have been known so far only for simple colinear arrays, the dipole equatorial array and two focused arrays. Here we provide a summary about the depth of investigation values of various dipole-dipole arrays (for parallel, perpendicular, radial, azimuthal ones), and for the most important noncolinear and focused arrays. Depth of investigation values are computed from both approaches. DIC functions (obtained by a new analytical
formula) are also presented, as illustrations. The analytical formula can be used to compute DIC function
of any surface geoelectric array. A systematic interpretation of the resulting depth of investigation values provides simple but useful thumb-rules for practical applications
Iridium catalyzed C-H activation/borylation of aromatic/heteroaromatic substrates and its application in small molecule synthesis
No full textCatalytic transformation of carbon–hydrogen bonds to other functional groups represents a long–standing challenge in homogeneous and heterogeneous catalysis. The Ir–catalyzed C—H activation/borylation has emerged as a useful method for synthesizing various aryl and heteroaryl boronic esters with regiochemistry complimentary to traditional methods and tolerant of various functional groups. The steric dominance of C—H activation/borylation has allowed for the synthesis of new aromatic building blocks which were previously unaccessible or hard to synthesize.The compatibility with Boc protecting groups allows for manipulating the regioselectivities for Ir–catalyzed borylations of nitrogen heterocycles. In addition, Ir–catalyzed borylations of protected amino acids are shown to be feasible for the first time, which augurs favorably for similar functionalizations of peptides. This work also established heat as a clean agent for Boc deprotection of BPin substituted heteroarenes.The halogen tolerance that is a hallmark of Ir C—H borylation makes it trivial to construct building blocks possessing halogen and boronate ester functionality. This unique feature of C—H borylation in combination with Suzuki coupling has allowed the synthesis of 2,3–diaryl and 3,5–diaryl thiophenes. DuP 697 a COX–2 inhibitor was synthesized in 5–steps with an overall 42% yield.Even though protolytic deborylation is an undesired side reaction in most coupling reactions, it was used to our advantage on diborylated substrates. C—H activation/borylation coupled with deborylation has proved to be powerful method in synthesizing pinacol boronic esters, with regiochemistry complementary to the previously known methods and tolerant of a variety of functional groups. The mildness and stereospecificity of the reactions has allowed us to use deuteration and deborylation on advanced molecules like pharmaceuticals.N–Methyliminodiacetic acid protection has been used to attenuate the reactivity of the diboron compounds. It has allowed us to desymmetrize diboron compounds generated from Ir–catalyzed C—H activation/borylation and Miyaura borylation. The selective coupling of BPin leaving the BMIDA intact allows for the iterative cross–coupling. The utility of these substrates with two or more reaction sites in multi transformations has been demonstrated. This allows for the synthesis of complex organic molecules from simple building blocks.Thesis (Ph. D.)--Michigan State University. Chemistry, 2010Includes bibliographical reference
Design and Development of 3-D Printed RDRA for Polarization Reconfigurability in C-band.
No full textIn this article, a 3D printed rectangular dielectric resonator antenna which is capable of polarization reconfiguration has been designed. Dielectric resonator is composed of environment friendly and biodegradable material, which is Polylactic Acid. In the proposed model, the polarization can be switch from a linear to a circular by changing the state of a switch, electonically. The antenna switch between two different polarizations: Linear polarization during OFF STATE and Left-hand circular polarization during ON STATE. The proposed 3D printed dielectric resonator antenna is designed to operate in C-band of microwave spectrum, with a broad effective bandwidth (overlapped impedance bandwidths of both states) of 14.542% with centre frequency at 5.845GHz and peak gain 5.5dBi. Further, validated simulated results with experiment and both results are in good agreement
Effect of the composition and heat of combustion of hydrocarbon fuels on gas turbine cycle performance.
No full textA procedure was developed for the calculation of gas turbine cycles using as fuels, a general hydrocarbon or Hydrogen. Computer programs were developed, to facilitate calculations, by suitably modifying the existing ones, developed by the National Research Council, Ottawa. Using these programs, the effect of changes in the fuel composition and heat of combustion on the performance of turbojet, turbofan,-turboprop and turboshaft cycles was studied. The performance of different fuels was compared with the standard fuel performance. On the basis of this study, the ranges of H/C ratio and heat of combustion of the fuel, within which the 'standard fuel approach' is reliable, was found. A simple modification of the approach was expected to be reliable within a wider range of fuel properties
STRUCTURE OF THE BAND SPECTRUM OF THE CuI MOLECULE: II. ROTATIONAL STRUCTURE OF THE <i>C</i> AND <i>D</i> SYSTEMS OF <sup>63</sup>Cu<sup>127</sup>I
No full text The C and D band systems of 63Cu127I, lying in the region 4 100–4 800 Å, have been photographed in emission under high resolution. Rotational analysis of the (0–0), (0–1), and (0–2) bands of the C system and the (0–0), (0–1), (0–2), and (0–3) bands of the D system has been made. The C and D systems are found to involve 1Σ (C1Σ)–1Σ(X1Σ)and 1Π(D1Π)–1Σ(X1Σ) transitions respectively. The Λ-type splitting in the D1Π state is small. The rotational constants obtained are as follows (cm−1 units):[Formula: see text] </jats:p
TNT Equivalency of Unconfined Aerosols of Propylene Oxide
No full textThe unconfined aerosols of propylene oxide (PO) are formed by dispersing the fuel in air. These aerosols undergo detonation by suitable initiation and produce high impulse blast. Tri-nitro Toluene (TNT) equivalence is an important parameter used to represent the power of explosive materials and compare their relative damage effects wrt TNT. The parameters commonly used for estimation of TNT equivalency are total energy of explosive source and properties of resulting blast wave, viz., blast peak overpressure and positive impulse. In the present study, the unconfined aerosols of 4.2 kg PO were formed by breaking open the cylindrical canister with the help of axially positioned central burster charge and then detonated using a secondary explosive charge after a preset time delay. The resulting blast profiles were recorded and the blast parameters were analysed. Being a non-ideal explosive source, the TNT equivalency depends on fraction of total energy utilised for blast formation, the rate of energy release, cloud dimensions, and concentration of fuel. Hence, various approaches based on energy release, experimental blast profiles, triangulated blast parameters, and ground reflected blast parameters were considered to determine the TNT equivalency of unconfined PO aerosols. It was observed that the TNT equivalency is not a single value but vary with distance. The paper provides various options for weapon designer to choose a suitable approach for considering TNT equivalency. The scaling laws established from the experimental data of unconfined aerosols of PO for blast peak over pressure and scaled impulse help in predicting the performance for different values of fuel weight and distance.Defence Science Journal, Vol. 64, No. 5, September 2014, pp.431-437, DOI:http://dx.doi.org/10.14429/dsj.64.685
Umpolung α‑Silylation of Cyclopropyl Acetates via Low-Temperature Catalytic C–C Activation
No full textWe
report a redox-neutral, catalytic C–C activation of cyclopropyl
acetates to produce silicon-containing five-membered heterocycles
in a highly regio- and chemoselective fashion. The umpolung α-selective
silylation leading to dioxasilolanes is opposed to contemporary β-selective
C–C functionalization protocols of cyclopropanols. Lewis base
activation of dioxasilolanes as α-silyl carbinol equivalents
undergoes the unconventional [1,2]-Brook rearrangement to form tertiary
alcohols. Notably, mechanistic studies indicate that an electrophilic
metal-π interaction harnessing highly fluorinated Tp(CF3)2Rh(nbd) catalyst permitted a low-temperature
C–C activation
Symmetry transition via tetravalent impurity and investigations on magnetic properties of Li0.5Fe2.5O4
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