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PubMed2002

Synthesis and characterization of the SO(2)N(3)(-), (SO(2))(2)N(3)(-), and SO(3)N(3)(-) anions.

SO(2) solutions of azide anions are bright yellow, and their Raman spectra indicate the presence of covalently bound azide. Removal of the solvent at -64 degrees C from CsN(3) or N(CH(3))(4)N(3) solutions produces yellow (SO(2))(2)N(3)(-) salts. Above -64 degrees C, these salts lose 1 mol of SO(2), resulting in white SO(2)N(3)(-) salts that are marginally stable at room temperature and thermally decompose to the corresponding azides and SO(2). These anions were characterized by vibrational and (14)N NMR spectroscopy and theoretical calculations. Slow loss of the solvent by diffusion through the walls of a sealed Teflon tube containing a sample of CsSO(2)N(3) in SO(2) resulted in white and yellowish single crystals that were identified by X-ray diffraction as CsSO(2)N(3).CsSO(3)N(3) with a = 9.542(2) A, b = 6.2189(14) A, c = 10.342(2) A, and beta = 114.958(4) degrees in the monoclinic space group P2(1)/m, Z = 2, and Cs(2)S(2)O(5).Cs(2)S(2)O(7).SO(2), respectively. Pure CsSO(3)N(3) was also prepared and characterized by vibrational spectroscopy. The S-N bond in SO(2)N(3)(-) is much weaker than that in SO(3)N(3)(-), resulting in decreased thermal stability, an increase in the S-N bond distance by 0.23 A, and an increased tendency to undergo rotational disorder. This marked difference is due to SO(3) being a much stronger Lewis acid (pF(-) value of 7.83) than SO(2) (pF(-) value of 3.99), thus forming a stronger S-N bond with the Lewis base N(3)(-). The geometry of the free gaseous SO(2)N(3)(-) anion was calculated at the RHF, MP2, B3LYP, and CCSD(T) levels. The results show that only the correlated methods correctly reproduce the experimentally observed orientation of the SO(2) group.

Journal Article↗
PubMed1999

Diffusion of dialkylnitrosamines into the rat esophagus as a factor in esophageal carcinogenesis.

To indicate how readily nitrosamines (NAms) diffuse into the esophagus, we measured diffusion rate (flux) through rat esophagus of dialkyl-NAms using side-by-side diffusion apparatuses. Mucosal and serosal flux at 37 degrees C of two NAms, each at 50 microM, was followed for 90 min by gas chromatography-thermal energy analysis of NAms in the receiver chamber. Mucosal flux of one or two NAms at a time gave identical results. Mucosal flux was highest for the strong esophageal carcinogens methyl-n-amyl-NAm (MNAN) and methylbenzyl-NAm. Mucosal esophageal flux of 11 NAms was 18-280 times faster and flux of two NAms through skin was 13-28 times faster than that predicted for skin from the molecular weights and octanol:water partition coefficients, which were also measured. Mucosal: serosal flux ratio was correlated (P < 0.05) with esophageal carcinogenicity and molecular weight. For seven NAms tested for carcinogenicity by Druckrey et al. [(1967) Z. Krebsforsch., 69, 103-201], mucosal flux was correlated with esophageal carcinogenicity with borderline significance (P = 0.07). The MNAN:dipropyl-NAm ratio for mucosal esophageal flux was unaffected when rats were treated with phenethylisothiocyanate and was similar to that for forestomach, indicating no involvement by cytochromes P450. Mucosal esophageal flux of MNAN and dimethyl-NAm was reduced by >90% on enzymic removal of the stratum corneum, was unaffected by 0.1 mM verapamil and was inhibited 67-94% by 1.0 mM KCN and 82-93% by 0.23% ethanol. NAm flux through rat skin and jejunum was 5-17% of that through esophagus. Flux through skin increased 5-13 times after enzymic or mechanical removal of the epidermis; the histology probably explained this difference from esophagus. Hence, NAms could be quite rapidly absorbed by human esophagus when NAm-containing foods or beverages are swallowed, the esophageal carcinogenicity of NAms may be partly determined by their esophageal flux and NAm flux probably occurs by passive diffusion.

Animals↗
PubMed1988

Putative photoacoustic damage in skin induced by pulsed ArF excimer laser.

Argon-fluoride excimer laser ablation of guinea pig stratum corneum causes deeper tissue damage than expected for thermal or photochemical mechanisms, suggesting that photoacoustic waves have a role in tissue damage. Laser irradiation (193 nm, 14-ns pulse) at two different radiant exposures, 62 and 156 mJ/cm2 per pulse, was used to ablate the 15-microns-thick stratum corneum of the skin. Light and electron microscopy of immediate biopsies demonstrated damage to fibroblasts as deep as 88 and 220 microns, respectively, below the ablation site. These depths are far in excess of the optical penetration depth of 193-nm light (1/e depth = 1.5 micron). The damage is unlikely to be due to a photochemical mechanism because (a) the photons will not penetrate to these depths, (b) it is a long distance for toxic photoproducts to diffuse, and (c) damage is proportional to laser pulse intensity and not the total dose that accumulates in the residual tissue; therefore, reciprocity does not hold. Damage due to a thermal mechanism is not expected because there is not sufficient energy deposited in the tissue to cause significant heating at such depths. The damage is most likely due to a photoacoustic mechanism because (a) photoacoustic waves can propagate deep into tissue, (b) the depth of damage increases with increasing laser pulse intensity rather than with increasing total residual energy, and (c) the effects are immediate. These effects should be considered in the evaluation of short pulse, high peak power laser-tissue interactions.

Animals↗
PubMedDate not supplied

'Trouble-shooting' microwave accelerated procedures in histology and histochemistry: understanding and dealing with artefacts, errors and hazards.

Heating by microwave irradiation (microwaving) is a controllable way to accelerate most processes of diffusion and many chemical reactions occurring in histoprocessing and histochemistry. Consequently, microwaving can be particularly time-saving. However, apart from desirable accelerations, unwanted diffusions and reactions may also occur. These can generate artefacts such as extraction of tissue components, chemical alterations of cellular content, and decomposition of thermally labile staining reagents. Artefacts may arise at all stages of histoprocessing, from fixation, through embedding, to staining. Whereas all artefacts result from heating, some specifically involve microwave ovens; e.g. irregular heating due to inhomogeneities in the microwave field, and ageing of the magnetron. Microwaving can involve certain hazards. Most of them also arise in conventional ovens, but a few are unique to microwave ovens; for example, aqueous contents heating faster than glass containers, and sparking due to labels written in pencil. The 'trouble-shooting' of microwave procedures requires an understanding of the nature of the heating process and of the procedure in question. In order to achieve this, the development and application of 'trouble-shooting' charts for commonly used procedures is both recommended and illustrated.

Histocytochemistry↗
PubMed2005

Implications of the effects of viscosity, macromolecular crowding, and temperature for the transient interaction between cytochrome f and plastocyanin from the cyanobacterium Phormidium laminosum.

The reaction between cytochrome f and plastocyanin is a central feature of the photosynthetic electron-transport system of all oxygenic organisms. We have studied the reaction in solution to understand how the very weak binding between the two proteins from Phormidium laminosum can nevertheless lead to fast rates of electron transfer. In a previous publication [Schlarb-Ridley, B. G., et al. (2003) Biochemistry 42, 4057-4063], we suggested that the reaction is diffusion-controlled because of a strong effect of viscosity of the medium. The effects of viscosity and temperature have now been examined in detail. High molecular mass viscogens (Ficoll 70 and Dextran 70), which might mimic in vivo conditions, had little effect up to a relative viscosity of 4. Low molecular mass viscogens (ethane diol, glycerol, and sucrose) strongly decreased the bimolecular rate constant (k(2)) over a similar viscosity range. The effects correlated well with the viscosities of the solutions of the three reagents but not with their dielectric constants or molalities. A power law dependence of k(2) on viscosity suggested that k(2) depends on two viscosity-sensitive reactions in series, while the reverse reactions are little affected by viscosity. The results were incompatible with diffusion control of the overall reaction. Determination of the effect of temperature on k(2) gave an activation enthalpy, DeltaH(++) = 45 kJ mol(-)(1), which is also incompatible with diffusion control. The results were interpreted in terms of a model in which the stable form of the protein-protein complex requires further thermal activation to be competent for electron transfer.

Cyanobacteria↗
PubMed1997

Synthesis and Characterization of Cs(5)Sb(8)S(18)(HCO(3)): A New Layered Phase Containing Interstitial Cations and Anions.

A new pseudoternary phase, Cs(5)Sb(8)S(18)(HCO(3)), was prepared from supercritical ammonia at 160 degrees C over 4 days using stoichiometric quantities of Cs(2)CO(3), Sb(2)S(3), and S(8). Red parallelepipeds of the title phase crystallize in the centrosymmetric monoclinic space group C2/c, with a = 27.064(3) Å, b = 11.634(4) Å, c = 12.642(3) Å, beta = 97.45(2) degrees, and Z = 4. The compound has a layered structure, with the layers formed from ribbons of condensed psi-SbS(4) trigonal bipyramids linked via S(3)(2)(-) chains, and both Cs(+) and HCO(3)(-) ions between the layers, giving rise to the formula Cs(5)Sb(8)S(12)(S(3))(2)(HCO(3)). Each layer is approximately 10 Å thick, with two layers per unit cell. The condensation of the group 15/16 building blocks into ribbons is the result of a combination of edge- and vertex-shared antimony(III) sulfide pseudo trigonal bipyramids. In this phase, the S(3) chains always link adjacent ribbons via apical coordination sites on the antimony atoms. The open cavities created by the linking trisulfide dianions between neighboring ribbons accommodate the antimony lone pairs and two unique cesium cations. A third cesium cation is located between layers. Unique to this compound, the anionic antimony sulfide layers are separated not only by cesium cations but also by bicarbonate anions. Results derived from infrared spectroscopy, diffuse reflectance, bond valence sums, and magnetic susceptibility measurements support the formulation of this compound as an electron-precise, wide-bandgap material. Thermal stability studies of Cs(5)Sb(8)S(18)(HCO(3)) are also discussed.

Journal Article↗
PubMed2006

Electron transport dynamics in a room-temperature Au nanoparticle molten salt.

A room-temperature Au38 nanoparticle polyether melt has been prepared by exchanging poly(ethylene glycol) (PEG) thiolate ligands, HS-C6-PEG163, into the organic protecting monolayer of Au38(PhC2)24 nanoparticles. Spectral and electrochemical properties verify that the Au38 core size is preserved during the exchange. Adding LiClO4 electrolyte, free PEG plasticizer, and/or partitioned CO2 leads to an ionically conductive nanoparticle melt, on which voltammetric, chronoamperometric, and impedance measurements have been made, respectively, of the rates of electron and ion transport in the melt. Electron transport occurs by electron self-exchange reactions, or electron hopping, between diffusively relatively immobile Au38(0) and Au38(1+) nanoparticles. The rates of physical diffusion of electrolyte ions (diffusion coefficients DCION) are obtained from ionic conductivities. The measured rates of electron and of electrolyte ion transport are very similar, as are their thermal activation energy barriers, observations that are consistent with a recently introduced ion atmosphere relaxation model describing control of electron transfer in semisolid ion and electron-conductive media. The model has been previously demonstrated using a variety of metal complex polyether melts; the present results extend it to electron transfers between Au nanoparticles. In ion atmosphere relaxation control, measured rates and energy barriers for electron transfer are not intrinsic values but are instead characteristic of competition between back-electron transfer caused by a Coulombic disequilibrium resulting from an electron transfer and relaxation of counterions around donor-acceptor reaction partners so as to reachieve local electroneutrality.

Journal Article↗
PubMed2004

A combination of micro-porous membrane liquid-gas extraction and solid-phase trapping for ultra trace determination of benzene in urine.

A method was developed for the determination of benzene in urine. The sample was pumped through the donor channel of a membrane extraction unit with a micro-porous membrane, separating the donor channel from an identical acceptor channel purged with nitrogen. The analyte reached the acceptor channel by diffusion through the membrane and was then swept by the carrier to a solid sorbent tube, where it was trapped. The analyte was subsequently thermally desorbed and analyzed by gas chromatography (GC) with mass selective detection (MS). After optimization, the recovery was close to quantitative, or 95%. Purging the membrane unit with pure water in between the samples eliminated any memory effects. The linearity was good in the concentration range examined (20-4000 ng l(-1)), with a correlation coefficient of 0.9996. The repeatability at 50 ng l(-1) and 400 ng l(-1) was 1.4% and 1.2%, respectively. The limit of detection was 12 ng l(-1) and the limit of quantification 35 ng l(-1). This enables assessment of benzene exposures of occupationally exposed subjects, of smokers and the majority of the general population. The developed method can be easily automated.

Benzene↗
PubMed1980

Photochemical dimerization of parinaric acid in lipid bilayers.

Parinaric acid (9,11,13,15-octadecatetraenoic acid), a conjugated tetraene fatty acid, undergoes a second-order photochemical reaction in phospholipid bilayers. The reaction results in the loss of the characteristic absorption of this chromophore and the development of new absorption demonstrating the presence of a triene chromophore. The progress of this reaction is easily monitored by measurement of the decrease in the fluorescence intensity from a uniformly illuminated sample. The reaction rate measured in this way is sensitive to the thermal phase transition of the bilayer and to the presence of cholesterol. The relationship of the second-order rate constant to the lipid diffusion coefficient is discussed. This relationship differs from that previously used for the analysis of similar photochemical processes.

Journal Article↗
PubMed1996

Rapid genotypic confirmation of methicillin resistance.

Detection of phenotypic methicillin resistance in Staphylococcus aureus clinical strains by conventional disk diffusion testing is fraught with problems. We used gene amplification of the mecA locus by polymerase chain reaction (PCR), in conjunction with a capillary/air thermal cycler, to overcome both the inaccuracy of phenotypic methods and the lengthy processing times required for previous genotypic methods. The rapid PCR method correctly identified methicillin resistance in a consecutive series of 30 S. aureus isolates when compared with routine and reference phenotypic methods. The shorter processing time and smaller reagent volumes required for the air thermal cycler make same-day determination of methicillin resistance in clinical isolates feasible for diagnostic laboratories.

DNA, Bacterial↗
PubMed1985

Exposure treatment of the burned patient--a computer simulation of the thermal environment and its effect on evaporation and heat loss.

The influence of the thermal environment on evaporation and heat loss from burned tissue has been studied in order to optimise conditions for treatment of severely burned patients. Diffusion resistances have been defined to describe movement of water vapour through the skin and away from the body surface. These have been evaluated from experiments on a water phantom and from data on evaporation rates from burned tissue and normal skin. Results show that the diffusion resistance for burned tissue is less than one tenth of that for normal skin, but changes substantially during the development of an eschar. Evaporation is promoted by a high skin temperature and a low relative humidity, but not by raising the ambient air temperature. Blowing warm dry air over a burn wound will enhance evaporation and reduce heat loss, encouraging the rapid formation of a dry eschar to provide a barrier against infection. Selective irradiation of burned tissue with low levels of radiant energy can be used to compensate for local heat losses, and allow the air temperature in the treatment room to be kept at a level comfortable for the patient and nursing staff.

Body Temperature Regulation↗
PubMed2000

Long jumps in the strong-collision model

The jump-length probability distribution for a classical particle diffusing in a periodic potential is calculated in the framework of a strong-collision model, where each collision of the particle with the thermal bath reequilibrates the velocity. Exact numerical results are obtained by the matrix-continued-fraction method, and two different analytical approximations are developed. In the first approximations it is assumed that an activated particle is always retrapped in the cell where it suffers the first collision; in the second approximation it is assumed that only the collisions giving a final total energy which is lower than the activation barrier are effective for retrapping. This second analytical approximation is in excellent agreement with the numerical data.

Journal Article↗
PubMed2000

Direct observation of electromigration of Si magic clusters on Si(111) surfaces.

Using scanning tunneling microscopy, we have observed electromigration of Si on Si(111)-(7x7) surfaces and have identified the diffusion species to be Si magic clusters. Effects of the directed motion along the direction of the heating current in electromigration and those in thermal migration are determined separately and quantitatively. We also observe the preferential filling of two-dimensional (2D) Si craters and the preferential detachment of Si magic clusters from the edges of 2D Si islands near the cathode side. The driving force for this anisotropic behavior is much stronger than previously recognized.

Journal Article↗
PubMed2003

Lévy flights in inhomogeneous media.

We investigate the impact of external periodic potentials on superdiffusive random walks known as Lévy flights and show that even strongly superdiffusive transport is substantially affected by the external field. Unlike ordinary random walks, Lévy flights are surprisingly sensitive to the shape of the potential while their asymptotic behavior ceases to depend on the Lévy index mu. Our analysis is based on a novel generalization of the Fokker-Planck equation suitable for systems in thermal equilibrium. Thus, the results presented are applicable to the large class of situations in which superdiffusion is caused by topological complexity, such as diffusion on folded polymers and scale-free networks.

Journal Article↗
PubMed2006

Current noise in the vicinity of the 2D superconductor-insulator quantum critical point.

Systems near to quantum critical points show universal scaling in response to external probes. We consider whether this scaling is reflected in their out-of-equilibrium fluctuations. We study current noise in the metallic state at the z=1 quantum critical point between a superconductor and an insulator in two dimensions. Using a Boltzmann-Langevin approach within a 1/N expansion, we show that the current noise obeys a universal scaling form S_{j}=TPhi[T/T_{eff}(E)], with T_{eff} proportional, variantsqrt[E]. This treatment recovers Johnson noise in thermal equilibrium and S_{j} proportional, variantsqrt[E] at strong electric fields. The latter differs significantly from both the shot noise in conventional metals (diffusive Fermi liquids) and the free carrier result, due to strong correlations between the critical bosonic excitations. Current-noise measurements could therefore help clarify the physics of the destruction of superconductivity in thin film superconductors.

Journal Article↗
PubMed1998

Convective heat transfer around an infant head.

Knowledge of heat and mass transfer between an infant and his environment is necessary to control hospital care conditions, or understand a pathology as Sudden Infant Death Syndrome (SIDS). This paper precises the particular importance of the heat transfer over the head and quantifies the influence of various parameters on natural convection heat transfer.

Bedding and Linens↗
PubMed2005

Improvement of NaNO2-oxidizing activity in Nitrobacter vulgaris by coentrapment in polyacrylamide containing polydimethylsiloxane copolymer and DEAE-sephadex.

Removal of nitrite and nitrate from drinking water has attracted great attention in recent years because of the human health risk induced by the exposure to contaminated groundwater and surface water. We have therefore tested a model nitrite oxidation system by coentrapping the NaNO2 oxidizer Nitrobacter vulgaris with polydimethylsiloxane (PDMS) copolymer and DEAE-Sephadex in a polyacrylamide gel. The copolymer and the anion exchanger facilitate the diffusion of oxygen and NaNO2, respectively, into the gel matrix. To test the nitrite-oxidizing activity, the entrapped cells were coupled to a thermal sensor. Coentrapment of 5% (wt/vol) DEAE-Sephadex with Nitrobacter vulgaris increased the nitrite-oxidizing activity by a factor of 3.7 compared to entrapped cells alone, and by the addition of 0.86% (wt/vol) artificial oxygen carrier PDMS copolymer increased the activity further to 4.3 times higher. Operational and storage stability of the coentrapped N.vulgaris also improved. This suggests that this enhanced immobilized cell system can also be used for nitrite oxidation to nitrate in drinking water as an on-line thermally monitored bioreactor.

Acrylic Resins↗
PubMed2004

Recent developments, characteristics, and potential applications of electrochemical biosensors.

The objective of this study is to analyze the technical importance, performance, techniques, advantages, and disadvantages of the biosensors in general and of the electrochemical biosensors in particular. A product of reaction diffuses to the transducer in the first generation biosensors (based on Clark biosensors). The mediated biosensors or second generation biosensors use specific mediators between the reaction and the transducer to improve sensitivity. The second generation biosensors involve two steps: first, there is a redox reaction between enzyme and substrate that is reoxidized by the mediator, and eventually the mediator is oxidized by the electrode. No normal product or mediator diffusion is directly involved in the third generation biosensors, direct biosensors. Based on the type of transducer, current biosensors are divided into optical, mass, thermal, and electrochemical sensors. They are used in medical diagnostics, food quality controls, environmental monitoring, and other applications. These biosensors are also grouped under two broad categories of sensors: direct and indirect detection systems. Moreover, these systems could be further grouped into continuous or batch operation. Therefore, amperometric biosensors and their current applications are focused on more in detail since they are the most commonly used biosensors in monitoring and diagnosing tests in clinical analysis. Problems related to the commercialization of medical, environmental, and industrial biosensors as well as their performance characteristics, their competitiveness in comparison to the conventional analytical tools, and their costs determine the future development of these biosensors.

Biosensing Techniques↗