Enzyme electrode studies of glucose oxidase modified with a redox mediator

Glucose oxidase modified by the covalent attachment of ferrocenecarboxylic acid or ferrocene-acetic acid groups undergoes direct oxidation at metal electrodes. Studies of the comparative stability of the two modified enzymes on storage and on electrochemical cycling show that the material modified with ferroceneacetic acid is the more stable. Amperometric studies of enzyme electrodes based on these modified forms of glucose oxidase show that their application in practical biosensors is severely limited by the poor stability of the oxidized form of the covalently attached ferrocene mediator. A comparison of the results obtained with the native enzyme and with that modified with ferroceneacetic acid, for the oxidation of glucose, d-mannose, 2-deoxy-d-glucose, d-xylose and d-galactose, suggests that the modification procedure has little effect on the selectivity of the enzyme.     

An application of a damage constitutive model to concrete at high temperature and prediction of spalling

A characteristic feature of concrete under uniaxial compression is the development of cracks parallel to the loading direction. A damage constitutive model proposed by Ortiz [Ortiz, M., 1985. A constitutive theory for the inelastic behaviour of concrete. Mech. Mater. 4, 67–93] can predict the transverse tensile stress responsible for these cracks by considering the interaction between the aggregate and the mortar and the development of damage in the latter. When concrete is exposed to high temperature, as is the case during fire, the failure mode is thermal spalling. In order to improve the prediction of the stresses involved in this failure Ortiz’s model is extended to account for the effects of high temperature. Published experimental results for uniaxial and biaxial compression at high temperatures are used to calibrate the temperature dependence of some of the material properties. The transient creep strain is accounted for by modifying the constrained thermal strain. The stress analysis is coupled with hygro-thermal analysis of heat, mass transfer and pore pressure build-up. The effect of pore pressure on the damage evolution is modeled by applying a body force in the stress analysis module proportional to the pressure gradient. A numerical example of concrete under fire is solved and the computed results are discussed. Spalling is predicted when the damage variable reaches its maximum value of unity. The predicted depth and time of spalling for a range of variation of permeability and initial liquid water content are presented. They are in good agreement with published experimental results.     

Single-photon diode by exploiting the photon polarization in a waveguide

A single-photon optical diode operates on individual photons and allows unidirectional propagation of photons. By exploiting the unique polarization configuration in a waveguide, we show here that a single-photon optical diode can be accomplished by coupling a quantum impurity to a passive, linear optical waveguide which possesses a locally planar, circular polarization. We further show that the diode provides a near unitary contrast for an input pulse with finite frequency bandwidth and can be implemented in a variety of types of waveguides. Moreover, the performance of the diode is not sensitive to the intrinsic dissipation of the quantum impurity.     

Probing the differential effects of infrared light sources IR1072 and IR880 on human lymphocytes: evidence of selective cytoprotection by IR1072

Light therapy, both laser and LED, have been shown to provide clinical benefit in many therapeutic arenas. The effects of IR1072 and IR880 were investigated, using a range of single and multiple irradiation protocols, for their effect on freshly prepared human lymphocytes stimulated with phytohemagglutinin. Viable cell numbers remained significantly higher after irradiation with IR1072 and were significantly lower after IR880 irradiation compared to untreated controls, following a daily single irradiation over a 5-day period. Cell numbers were significantly higher after pre-treatment with IR1072 and exposure to UVA, compared to cells treated with UVA only. Cells irradiated twice on Day 3 post-harvest with various wavebands confirm on Day 5, an increase in % cell viability after IR1072, and IR1072 alternating with IR1268 irradiation, and a decrease in % cell viability after IR880 irradiation alone. Further, wavebands tested displayed no significant differences compared to the control. Cells were collected after exposure on Days 3 and 5 with IR1072 and IR880 treatments and protein levels were compared using quantitative immunoblotting probed with an anti-iNOS antibody. Following IR1072, but not IR880, treatment there was a 4.9+/-2.1-fold higher iNOS protein expression in treated cells compared to the control on Day 5 post-treatment.     

Directionally oriented LB films of an OPE derivative: assembly, characterization, and electrical properties

Langmuir films have been fabricated from 4-[4'-(4'-thioacetyl-phenyleneethynylene)-phenyleneethynylene]-aniline (NOPES) after cleavage of the thioacetyl protecting group. Characterization by surface pressure vs area per molecule isotherms and Brewster angle microscopy reveal the formation of a high quality monolayer at the air-water interface. One layer Langmuir-Blodgett (LB) films were readily fabricated by the transfer of the NOPES Langmuir film onto solid substrates. X-ray photoelectron spectroscopy (XPS), surface polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS), and quartz crystal microbalance (QCM) experiments conclusively demonstrate the formation of one layer LB films in which the functional group associated with binding to the substrate can be tailored by the film transfer conditions. Using LB methods this molecule could be transferred to gold samples with either the amine or thiol group attached to the gold surface. The amine group is directly attached to the gold substrate (Au-NH(2)-OPE-SH) when the substrate is initially immersed in the subphase and withdrawn during the transfer process; in contrast, monomolecular films in which the thiolate group is attached to the gold substrate (Au-S-OPE-NH(2)) are obtained when the substrate is initially out of the subphase and immersed during the transfer process. The morphology of these films was analyzed by atomic force microscopy (AFM), showing the formation of homogeneous layers. Film homogeneity was confirmed by cyclic voltammetry, which revealed a large passivation of gold electrodes covered by NOPES monolayers. Electrical properties for both polar orientated junctions have been investigated by scanning tunnelling microscopy (STM), with both orientations featuring a nonrectifying behavior.     

Study on the Development of Catalyst System for the Novel Rearrangement Reaction of Bicyclic Ketal Compound

A novel rearrangement of bicyclic ketals was investigated by using AcCl-NaI and MgBr₂-Ac₂O. Mono- and diacetylated products were isolated from these catalyst systems. Details of the chemistry are discussed.     

A Simple Propellane Synthesis

A dianion-mediated dialkylation reaction provides ready access to a heterocyclic propellane. The methodology should provide a general entry into a variety of similar systems.     

Quaternary Centers by Nickel‐Catalyzed Cross‐Coupling of Tertiary Carboxylic Acids and (Hetero)Aryl Zinc Reagents

This work bridges a gap in the cross‐coupling of aliphatic redox‐active esters with aryl zinc reagents. Previously limited to primary, secondary, and specialized tertiary centers, a new protocol has been devised to enable the coupling of general tertiary systems using nickel catalysis. The scope of this operationally simple method is broad, and it can be used to simplify the synthesis of medicinally relevant motifs bearing quaternary centers.     

MS2Assign,automated assignment and nomenclature of tandem mass spectra of chemically crosslinked peptides

In a previous report (Young et al., Proc. Natl. Acad. Sci. U.S.A. 2000, 97, 5802-5806), we provided a proof-of-principle for fold recognition of proteins using a homobifunctional amine-specific chemical crosslinking reagent in combination with mass spectrometry analysis and homology modeling. In this current work, we propose a systematic nomenclature to describe the types of peptides that are generated after proteolysis of crosslinked proteins, their fragmentation by tandem mass spectrometry, and an automated algorithm for MS/MS spectral assignment called "MS2Assign." Several examples are provided from crosslinked peptides and proteins including HIV-integrase, cytochrome c, ribonuclease A, myoglobin, cytidine 5-monophosphate N-acetylneuraminic acid synthetase, and the peptide thymopentin. Tandem mass spectra were obtained from various crosslinked peptides using post source decay MALDI-TOF and collision induced dissociation on a quadrupole-TOF instrument, along with their automated interpretation using MS2Assign. A variety of possible outcomes are described and categorized according to the number of modified lysines and/or peptide chains involved, as well as the presence of singly modified (dead-end) lysine residues. In addition, the proteolysis and chromatographic conditions necessary for optimized crosslinked peptide recovery are presented.