Scanning electrochemical microscopy study of the solid--solid interconversion of TCNQ to phase I and phase II CuTCNQ

The reduction of 7,7,8,8-tetracyanoquinodimethane (TCNQ) crystals attached to a glassy carbon electrode in the presence of Cu2+(aq) to form CuTCNQ(s) has been investigated using scanning electrochemical microscopy in the substrate generation tip collection mode and shown to involve a generation of soluble TCNQ−(aq). The subsequent oxidation of CuTCNQ does not involve simple expulsion of Cu+ into solution but a soluble complex attributed to Cu2+TCNQ−(aq). Mechanistic insights relative to the electrochemical conversion of CuTCNQ phase I into phase II by repetitive cycling of potential and electrochemical formation of KTCNQ have also been established

Modification of chemical reactivity by cyclodextrins. Observation of moderate effects on Norrish type I and type II photobehavior

The photochemistry and photophysics of organic molecules in organized assemblies are being studied with great interest in order to understand the features controlling the selectivity in the photoreactions brought about by these media.l These studies have paved the way to an intriguing number of possibilities by which photoreactivity can be modified. In this connection, we have investigated the photobehavior of a number of phenyl alkyl ketones and cu,cu-dimethylphenyl alkyl ketones (Scheme I) incorporated in the hydrophobic interior of cyclodextrin cavities.

Polarographic and redox potential studies on copper(I) and copper(II) and their complexes. Part III. Copper (I and II)-ethylene diamine and edta complexes and theory of formation of step reduction waves in cupric copper systems

Polarographic and redox potential measurements on the cupric and cuprous complexes of ethylenediamine and EDTA have been carried out. From the ratio of the stability constants of the cupric and cuprous complexes, and the stability constant of the cupric complex, the stability constant of the cuprous-ethylenediamine complex is obtained. In the case of the EDTA complex it has been possible to obtain only βic/β2ous from the equilibrium concentrations of the cuprous and cupric complexes and the disproportionation constant. The inequalities for the appearance of step reduction waves have been given. The values of the stability constants of the cupric and cuprous complexes determined by the polarographic-redox potential method have been used to explain the appearance of step reduction waves in some systems and the non-appearance in other systems.

Polarographic and redox potential studies on copper(I) and copper(II) and their complexes. Part I. Copper(I and II)-ammonia and methylamine complexes

The equilibrium between cuprous ion, cupric ion and metallic copper has been studied using polarographic and redox potential measurements, by reducing cupric ion with copper gauze until equilibrium. Using the well-defined anodic diffusion current plateau, an amperometric method for estimating cuprous copper based on the titration of cuprous ion with dichromate or permanganate has been developed. The diffusion current constant and the disproportionation constant of cuprous ion and the standard potential for the reduction reaction of Cu2+ → Cu+ have been determined. Polarograms have been taken after reducing cupric complexes of ammonia and methylamine with copper until equilibrium. In the case of the copper-ammonia system, reduction to the cuprous state is practically complete while in the case of the cupric-methylamine system, the first cathodic wave occurs to some extent. A new method, called the polarographic-redox potential method, for determining the stability constants of cuprous and cupric complexes has been developed. The method depends upon the determination of the concentration of complexes by polarographic wave heights, and free cupric anc cuprous ions by redox potentials. The stability constants of the following complexes have been obtained: Cu(NH3)2+4, Cu(NH3)+2, Cu(CH3NH2)2(OH)2, Cu(CH3NH2)+2. The stability constants determined by the new method and the half-wave potential shift method agree and the value for the cupric-ammonia complex is in good agreement with Bjerrum method, indicating the reliability of this method.

Diversity in Functional Organization of Class I and Class II Biotin Protein Ligase

The cell envelope of Mycobacterium tuberculosis (M. tuberculosis) is composed of a variety of lipids including mycolic acids, sulpholipids, lipoarabinomannans, etc., which impart rigidity crucial for its survival and pathogenesis. Acyl CoA carboxylase (ACC) provides malonyl-CoA and methylmalonyl-CoA, committed precursors for fatty acid and essential for mycolic acid synthesis respectively. Biotin Protein Ligase (BPL/BirA) activates apo-biotin carboxyl carrier protein (BCCP) by biotinylating it to an active holo-BCCP. A minimal peptide (Schatz), an efficient substrate for Escherichia coli BirA, failed to serve as substrate for M. tuberculosis Biotin Protein Ligase (MtBPL). MtBPL specifically biotinylates homologous BCCP domain, MtBCCP87, but not EcBCCP87. This is a unique feature of MtBPL as EcBirA lacks such a stringent substrate specificity. This feature is also reflected in the lack of self/promiscuous biotinylation by MtBPL. The N-terminus/HTH domain of EcBirA has the selfbiotinable lysine residue that is inhibited in the presence of Schatz peptide, a peptide designed to act as a universal acceptor for EcBirA. This suggests that when biotin is limiting, EcBirA preferentially catalyzes, biotinylation of BCCP over selfbiotinylation. R118G mutant of EcBirA showed enhanced self and promiscuous biotinylation but its homologue, R69A MtBPL did not exhibit these properties. The catalytic domain of MtBPL was characterized further by limited proteolysis. Holo-MtBPL is protected from proteolysis by biotinyl-59 AMP, an intermediate of MtBPL catalyzed reaction. In contrast, apo-MtBPL is completely digested by trypsin within 20 min of co-incubation. Substrate selectivity and inability to promote self biotinylation are exquisite features of MtBPL and are a consequence of the unique molecular mechanism of an enzyme adapted for the high turnover of fatty acid biosynthesis.

Mode I and Mode II Crack Tip Asymptotic Fields with Strain Gradient Effects

The strain gradient effect becomes significant when the size of fracture process zone around a crack tip is comparable to the intrinsic material length l, typically of the order of microns. Using the new strain gradient deformation theory given by Chen and Wang, the asymptotic fields near a crack tip in an elastic-plastic material with strain gradient effects are investigated. It is established that the dominant strain field is irrotational. For mode I plane stress crack tip asymptotic field, the stress asymptotic field and the couple stress asymptotic field can not exist simultaneously. In the stress dominated asymptotic field, the angular distributions of stresses are consistent with the classical plane stress HRR field; In the couple stress dominated asymptotic field, the angular distributions of couple stresses are consistent with that obtained by Huang et al. For mode II plane stress and plane strain crack tip asymptotic fields, only the stress-dominated asymptotic fields exist. The couple stress asymptotic field is less singular than the stress asymptotic fields. The stress asymptotic fields are the same as mode II plane stress and plane strain HRR fields, respectively. The increase in stresses is not observed in strain gradient plasticity for mode I and mode II, because the present theory is based only on the rotational gradient of deformation and the crack tip asymptotic fields are irrotational and dominated by the stretching gradient.

Radio frequency studies of surface resistance and critical magnetic field of type I and type II superconductors

The surface resistance and the critical magnetic field of lead electroplated on copper were studied at 205 MHz in a half-wave coaxial resonator. The observed surface resistance at a low field level below 4.2°K could be well described by the BCS surface resistance with the addition of a temperature independent residual resistance. The available experimental data suggest that the major fraction of the residual resistance in the present experiment was due to the presence of an oxide layer on the surface. At higher magnetic field levels the surface resistance was found to be enhanced due to surface imperfections.

The attainable rf critical magnetic field between 2.2°K and T_c of lead was found to be limited not by the thermodynamic critical field but rather by the superheating field predicted by the one-dimensional Ginzburg-Landau theory. The observed rf critical field was very close to the expected superheating field, particularly in the higher reduced temperature range, but showed somewhat stronger temperature dependence than the expected superheating field in the lower reduced temperature range.

The rf critical magnetic field was also studied at 90 MHz for pure tin and indium, and for a series of SnIn and InBi alloys spanning both type I and type II superconductivity. The samples were spherical with typical diameters of 1-2 mm and a helical resonator was used to generate the rf magnetic field in the measurement. The results of pure samples of tin and indium showed that a vortex-like nucleation of the normal phase was responsible for the superconducting-to-normal phase transition in the rf field at temperatures up to about 0.98-0.99 T_c' where the ideal superheating limit was being reached. The results of the alloy samples showed that the attainable rf critical fields near T_c were well described by the superheating field predicted by the one-dimensional GL theory in both the type I and type II regimes. The measurement was also made at 300 MHz resulting in no significant change in the rf critical field. Thus it was inferred that the nucleation time of the normal phase, once the critical field was reached, was small compared with the rf period in this frequency range.

Liver genomic responses to ciguatoxin: evidence for activation of Phase I and Phase II detoxification pathways following an acute hypothermic response in mice

Ciguatoxins (CTX) are polyether neurotoxins that target voltage-gated sodium channels and are responsible for ciguatera, the most common fish-borne food poisoning in humans. This study characterizes the global transcriptional response of mouse liver to a symptomatic dose (0.26 ng/g) of the highly potent Pacific ciguatoxin-1 (P-CTX-1). At 1 h post-exposure 2.4% of features on a 44K whole genome array were differentially expressed (p ≤ 0.0001), increasing to 5.2% at 4 h and decreasing to 1.4% by 24 h post-CTX exposure. Data were filtered (|fold change| ≥ 1.5 and p ≤ 0.0001 in at least one time point) and a trend set of 1550 genes were used for further analysis. Early gene expression was likely influenced prominently by an acute 4°C decline in core body temperature by 1 h, which resolved by 8 h following exposure. An initial downregulation of 32 different solute carriers, many involved in sodium transport, was observed. Differential gene expression in pathways involving eicosanoid biosynthesis and cholesterol homeostasis was also noted. Cytochrome P450s (Cyps) were of particular interest due to their role in xenobiotic metabolism. Twenty-seven genes, mostly members of Cyp2 and Cyp4 families, showed significant changes in expression. Many Cyps underwent an initial downregulation at 1 h but were quickly and strongly upregulated at 4 and 24 h post-exposure. In addition to Cyps, increases in several glutathione S-transferases were observed, an indication that both phase I and phase II metabolic reactions are involved in the hepatic response to CTX in mice.

1987 ecosystem view of management research in the Myakka River: review of Phase I and Phase II reports

This memorandum has four parts. The first is a review and partial synthesis of Phase 1 and Phase 2 Reports by Dr. Ernest Estevez of the Mote Marine Laboratory to the Board of County Commissioners of Sarasota County, Florida. The review and synthesis emphasizes identification of the most important aspects of the structure of the Myakka system in terms of forcing functions, biological components, and major energy flows. In this context, the dominant primary producers, dominant fish species and food habits, and major environmental variables were of articular interest. A major focus of the review and synthesis was on the river zonations provided in the report and based on salinity and various biological indicators. The second part of this memorandum is a review of a draft report by Mote Marine Laboratory on evaluation of potential water quality impacts on the Myakka River from proposed activities in the watershed. This Memorandum's third part is a review of resource-management related ecosystem models in the context of possible future models of the Myakka River Ecosystem. The final part of this memorandum is proposed future work as an extension of the initial reports.

Photophysics of Re(I) and Ru(II) diimine complexes covalently linked to pyrene: Contributions from intra-ligand charge transfer states

The photophysical properties of Ru(II) and Re(I) polypyridyl complexes including a bis-bipyridyl pyrene ligand are presented. The complexes ([(bpy)(2)Ru](2)bpb)(4+) and [(CO)(3)ReCl(bpb)] (bpy = 2,2'-bipyridine, bpb = 1,6-bis-(4-(2,2'-bipyrid-yl)-pyrene) were designed with the intent of examining intramolecular energy migration between MLCT states localized on the metal complexes and pyrene-localized (3)(pi-pi) states. Absorption spectroscopy of both complexes containing the bpb ligand reveals that in addition to the MLCT and the pyrene-centered (1)(pi-pi) transitions, a new absorption band is observed near 400 nm for both complexes. Absorption spectral data for the Re(I) complex strongly suggest the presence of a pyrene(pi) to bpy(pi) intraligand charge transfer (ILCT) transition. Emission spectra at room temperature and at 77 K are almost identical for the Ru(II) and Re(I) complexes containing the bpb ligand. The (3)MLCT emission of related bipyridyl compounds lacking the pyrene is observed at higher energy than for the pyrene-containing complexes, ([(bpy)(2)Ru](2)bpb)(4+) and [(CO(3)ReCl(bpb)]. The Ru(II) complex emits at room temperature with a remarkably long lifetime (130 micros in degassed DMSO). This emission is also strongly sensitive to oxygen and is almost entirely quenched in an aerated solution. In addition, excited-state absorption spectra exhibit features not consistent with (3)MLCT or (3)(pi-pi) states of the parent chromophores. The combined characteristics suggest the emission arises from either (3)(pi-pi) or (3)ILCT states or a state with mixed parentage.

Versatile N,C,N coordination behavior of a monoanionic aryldiamine ligand in ruthenium(II) complexes: Syntheses and crystal structures of [Ru-II(C6H3(CH(2)NMe(2))(2)-2,6)X(L)] (L equals norbornadiene, X=Cl, SO3CF3; L=PPh(3), X=I) and [Ru-II{C6H3(CH(2)NMe(2))(2)-2,6}(2,2':6:2''-terpyridine)]Cl

The monoanionic ligand [C6H3(CH(2)NMe(2))(2)-2,6](-), a potentially terdentate N,C,N bonding system, has been employed to synthesize a series of new ruthenium(II) complexes [Ru{C6H3(CH(2)NMe(2))(2)-2,6}X(L)] (L = PPh(3) X = Cl (2a), I (2b); L = norbornadiene (nbd), X = Cl (4), eta(1)-OSO2CF3 (5)) and [Ru{C6H3(CH(2)NMe(2))(2)-2,6}(2,2':6',2 ''-terpyridine)]Cl (3). X-ray crystal structures of 2b and 3-5 have been determined, in which the N,C,N coordination geometry with respect to the metal center is found to differ considerably. In each complex the aryldiamine ligand is terdentate, eta(3)-N,C,N-bonded as a six electron donor system. However, depending on the other ligands in the Ru(II) coordination sphere, this ligand demonstrates considerable flexibility in adopting coordination geometries which range from meridional in 3 through pseudomeridional in 2b to pseudofacial in 4 and 5. In the structures of 4 and 5 significant distortions of the aryl ring, involving bending of the six-membered ring into a boatlike conformation, are found. The different combinations of the N,C,N ligand with sets of other ligands lead to a range of metal geometries, i.e. square pyramidal in 2b, octahedral in 3, and bicapped tetrahedral in 4 and 5.

An investigation of Mode I and Mode II fracture toughness enhancement using aligned carbon nanotubes forests at the crack interface

A novel approach for introducing aligned multi-walled carbon nanotubes (MWCNTs) in a carbon-fibre composite pre-impregnated (prepreg) laminate, to improve the through-thickness fracture toughness, is presented. Carbon nanotube (CNT) 'forests' were grown on a silicon substrate with a thermal oxide layer, using a chemical vapour deposition (CVD) process. The forests were then transferred to a pre-cured laminate interface, using a combination of pressure and heat, while maintaining through-thickness CNT alignment. Standard Mode I and four-point bend end-notched flexure Mode II tests were undertaken on a set of specimens and compared with pristine specimens. Mode I fracture toughness for T700/M21 laminates was improved by an average of 31% while for T700/SE84LV specimens, an improvement of 61% was observed. Only T700/M21 specimens were tested in Mode II which yielded an average fracture toughness improvement of 161%. Scanning Electron Microscopy (SEM) showed good wetting of the CNT forest as well as evidence of penetration of the forest into the adjacent plies. © 2013 Elsevier Ltd.