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The corrosion behaviour of Ti alloy TA8-1, Cu alloy B19 and Cu are studied under simulated early deep geological conditions of Beishan, China. In the short-term experiment, the influence of temperature on the corrosion properties of the studied materials is investigated by electrochemical impedance spectroscopy (EIS), potentiodynamic polarisation and cyclic polarisation. In the long-term immersion tests, the evolution of corrosion behaviour is investigated by EIS, in combination with SEM, XPS and Raman analysis. The results show that Ti alloy TA8-1 has the minimum corrosion current density (10−7 A cm−2) and low pitting susceptibility, attributed to the formation of a thin passive film. Cu has the relatively high corrosion current density (∼10−5 A cm−2) and low pitting susceptibility. The corrosion resistance of the Cu2O/Cu2(OH)3Cl deposit layer is maintained during the two-month immersion test at 50°C. Severe localised corrosion occurs on the surface of B19 and the corrosion resistance deteriorates obviously during the immersion test.

Lysosomal polarity is considered a key indicator of lysosomal function due to its significant impact on membrane fluidity and enzymatic reactions in lysosomes. Monitoring lysosomal polarity can gain insight into the related physiological and pathological processes and develop new diagnostic methods. However, current fluorescent probes with lysosomal polarity response suffer from narrow linear range, photobleaching and complicated preparation. Herein, a ratiometric fluorescent probe (r-bCDs) for intracellular lysosomal polarity imaging is designed and constructed by amide bond assembly of polarity-sensitive red fluorescent carbon dots (rCDs) and referenced blue fluorescent carbon dots (bCDs). r-bCDs show a much wider linear range of polarity response (orientation polarizability Δf from 0.020 to 0.315) than other probes, and the interference of uneven distribution and instrument factors can be effectively eliminated by ratiometric fluorescent sensing. Imaging of intracellular lysosomal polarity with r-bCDs is implemented to observe the polarity variation caused by the change of cell state and the difference between cancer cells and normal cells. This work provides a promising tool for studying the related physiological and pathological processes and developing new diagnostic methods.

In this work, the photoelectrochemical (PEC) properties of TiO2 nanotube arrays (NTAs) were enhanced by forming heterostructures with non-substituted covalent organic frameworks (H-COFs) and fluoro...

On the basis of the Griess-Saltzman (GS) reaction, an optical device for nitric oxide (NO) detection in exhaled breath and atmosphere was developed by employing the light-emitting diode (LED, 560 nm) as the light source, light-to-voltage converter (LVC) as the detector, and porous polypropylene membrane tube (PPMT) as the cuvette. The PPMT was filled with GS reagents and covered with a coaxial jacket tube for gas collection and color reaction; two ends of the PPMT were connected with the LED and LVC to detect the change of light transmissivity in the wavelength range of 530 to 590 nm mainly. A gas absorber filled with GS reagents was installed prior to another absorber filled with KMnO4 solution to eliminate the interference of coexisting NO2. Under the optimized experimental conditions, the device achieved a limit of detection (3σ/k) of 4.4 ppbv for NO detection. The linearity range of this device was divided into two segments, i.e., 25 to 100 ppbv and 50 to 1000 ppbv, with both coefficients of determination > 0.99. The relative standard deviation was 2.7% (n = 9, c = 100 ppbv), and the analytical time was 5.5 min per detection. The minimum detectable quantity was decreased to 1.18 ng, which was ~ 100 times lower than the original GS method (115 ng). The present device was applied for determination of NO in exhaled breath, vehicle exhaust, and air. In addition to satisfactory spiking recoveries (i.e., 103% and 107%), the analytical results of the present device were in agreement with the results obtained by the standard method. These results assured the practicality of the developed device for NO detection in real environmental samples.

In this study, the application of carbon dots (CDs) modified NaYF4:Yb, Er nanoparticles (UCNPs@CDs) as the fluorescent nanoprobe for simultaneous detection of Fe2+ and Fe3+ was investigated. Fe3+ quantification (5–80 μmol L−1) was achieved, as a result of Fe3+ induced fluorescence quenching of UCNPs@CDs at 434 nm (under the 336 nm excitation). The chelate (Fe2+-phen) formed by Fe2+ and 1,10-phenanthroline had a broad absorption centered at 510 nm, due to inner filter effect (IFE), Fe2+ quantification (4–120 μmol L−1) was achieved as a result of (Fe2+-phen) induced fluorescence quenching of UCNPs@CDs at 545 nm (under the 980 nm excitation). The resultant UCNPs@CDs probe, with excellent anti-interference capability, favorable fluorescence stability, and convincing performance in real sample analysis, showed promising application in simultaneous detection of Fe2+ and Fe3+.

FeS2/TiO2 nanotube array composite films with clean, high efficiency, low cost and low consumption were prepared by electrochemical anodization and hydrothermal methods. The modification of FeS2 nanoparticles on the surface of TiO2 nanotube array film not only broadens the light absorption range of TiO2, but also improves the utilization ratio of visible light and the separation rate of photogenerated electron–hole pairs, which greatly improves the photoelectrochemical cathodic protection performance of TiO2 for 304 stainless steel (304SS). Under visible light irradiation, the open circuit potential of 304SS coupled with the FeS2/TiO2 nanocomposite films decreased from − 170 to − 700 mV, and the electrode potential can still maintained at − 400 mV after the light was turned off. Compared with pure TiO2 nanotube array film, FeS2/TiO2 nanocomposite film has better photoelectrochemical cathodic protection effect on 304SS in 3.5 wt% NaCl corrosion medium.

FeS2/TiO2 nanotube array composite films with clean, high efficiency, low cost and low consumption were prepared by electrochemical anodization and hydrothermal methods. The modification of FeS2 nanoparticles on the surface of TiO2 nanotube array film not only broadens the light absorption range of TiO2, but also improves the utilization ratio of visible light and the separation rate of photogenerated electron–hole pairs, which greatly improves the photoelectrochemical cathodic protection performance of TiO2 for 304 stainless steel (304SS). Under visible light irradiation, the open circuit potential of 304SS coupled with the FeS2/TiO2 nanocomposite films decreased from − 170 to − 700 mV, and the electrode potential can still maintained at − 400 mV after the light was turned off. Compared with pure TiO2 nanotube array film, FeS2/TiO2 nanocomposite film has better photoelectrochemical cathodic protection effect on 304SS in 3.5 wt% NaCl corrosion medium.

In this work, a superhydrophobic coating was developed by modifying pure epoxy resin with prepared sepiolite powder. The wettability, morphology, and composition of the superhydrophobic coating were characterized by contact angle measurement (CA), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD). The corrosion behavior of the coatings was investigated by electrochemical impedance spectroscopy (EIS), salt-spray test, and Scanning Kelvin Probe (SKP). The results showed that the composite coating had better corrosion performance than pure epoxy resin (EP) coating, and the composite coating showed super-hydrophobicity with a contact angle of 154.6o and a sliding angle of 3oafter sprayed with 5 wt% modified powder. The corrosion region of the damaged coating could be obviously restricted and the corrosive rate of the substrate was delayed and confirmed by SKP technology. The complete coating morphology was more conducive to enhancing the corrosion resistance of the sample.

Models for the corrosion of spent nuclear fuel (fission and actinide-doped uranium dioxide) provide the essential source term for the release of radionuclides from within a failed nuclear waste con...

The influence of γ-radiation in the presence of dissolved hydrogen on the corrosion of uranium dioxide has been compared to the electrochemical behavior of uranium dioxide in aqueous chloride solutions. Hydrogen atoms, produced either electrochemically or by water radiolysis were shown to reduce UV in the oxide leading to suppression of its corrosion. The removal of electrochemical polarization, and of hydrogen when γ-radiation was present, allowed re-oxidation of the uranium dioxide accompanied by the reformation of hydrogen. These results are consistent with published studies which show the corrosion of spent nuclear fuel can be suppressed in the presence of hydrogen. H2 effect in suppressing the corrosion of UO2-based materials without catalysis of noble metal particles is studied by producing H radicals electrochemically and radiolytically. Reactive H radicals produced by H2O reduction at cathodic potentials, lead to the reduction of UV states which are present due either to the DyIII doping or the non-stoichiometry within the UO2 based materials. When the cathodic potential is switched to open circuit, the relaxation of ECORR (corrosion potential) indicates that the electrochemically reduced surface is unstable. The combination of γ-irradiation and H2 can also lead to the reduction of UO2. In the absence of dissolved H2, a similar relaxation of ECORR indicates that reactive H radicals produced electrochemically or radiolytically are responsible for the reduction of the UO2 matrix.

This study investigated the effects of carbonation on the chloride binding of mortars containing simulated marine sand. Various admixtures were added, and metakaolin (MK), fly ash (FA), nano-Al2O3 (NA), and aluminum (A) were considered as supplementary cementitious materials (SCMs) for use in mortars. Changes in free chloride content, total chloride content, bound chloride content, chloride binding rates, and pH values as a function of mortar depth were analyzed, and the effects of carbonation on the hydration products were also assessed. The results indicated that in the place of cement, SCMs could significantly increase the carbonation zone depth in mortar. The chloride ions migrated outward and inward under accelerated carbonation conditions in the mortar, generating two peak values for the chloride content in the mortars. Consequently, the incorporation of SCMs was beneficial for chloride ion migration in mortars under carbonation. Additionally, the bound chloride content and chloride binding rates were initially extremely low, then gradually increased, and finally stabilized with increased depth in the mortars under carbonation. Furthermore, the incorporation of SCMs resulted in the decreased chloride binding capacity of the mortars under accelerated carbonation, and Friedel’s salt gradually decomposed with carbonation.

Concrete is a multi-phase, porous system. The pore structure has an important influence on the properties of the concrete. In this paper, a kind of fiber reinforced mortar was prepared with desert sand and its pore structure was studied. The MIP technique was used to investigate the pore structure characteristics between 1 nm and 500 μm (in diameter). Meanwhile, the μX-CT technique was used to study the pore structure characteristics above 200 μm. It was found that the total porosity tends to decrease first and then increase as the dosage of desert sand increased. The porosity decreased gradually from the upper to bottom area inside the sample, and the diameter of the air voids near the upper area became larger. After curing for 28 days, the compressive strength of fiber reinforced mortar reached the maximum when the content of desert sand was 50%. In conclusion, the appropriate amount of desert sand can reduce the porosity of the fiber reinforced mortar to some extent and the number of large size air voids can be significantly reduced, which improves the pore structure and the mechanical properties of the fiber reinforced mortar.

A model previously developed to predict the corrosion rate of spent fuel (UO 2 ) inside a failed waste container has been adapted to simulate the rates measured on a wide range of α-doped UO 2 and spent fuel specimens. This simulation confirms the validity of the model and demonstrates that the steady-state corrosion rate is controlled by the radiolytic production of H 2 O 2 (which has been shown to be the primary oxidant driving fuel corrosion), irrespective of the reactivity of the UO 2 matrix. The model was then used to determine the consequences of corrosion inside a failed container resealed by steel corrosion products. The possible accumulation of O 2 , produced by H 2 O 2 decomposition, was found to accelerate the corrosion rate in a closed system. However, the simultaneous accumulation of radiolytic H 2 , which is activated as a reductant on the noble metal ( e ) particles in the spent fuel, rapidly overcame this acceleration leading to the eventual suppression of the corrosion rate to insignificant values. Calculations also showed that, while the radiation dose rate, the H 2 O 2 decomposition ratio, and the surface coverage of e particles all influenced the short term corrosion rate, the influence of the radiolytically produced H 2 was the overwhelming influence in reducing the rate to negligible level (i.e., −20 mol m −2 s −1 ).

The influence of Gd-doping level and oxygen stoichiometry on the structural properties and electrochemical reactivity of U 1−y Gd y O 2±x have been investigated. The stoichiometry of UO 2 matrices with different Gd contents was determined using the lattice parameter obtained by XRD. The extent of lattice contraction, defined by a contraction factor, was found to be dependent on the stoichiometry. The surface morphologies exhibited differences in grain size which varied with stoichiometry and its influence on the U atom diffusivity during fabrication. The differences in grain size and, hence, the density of grain boundaries was reflected in variations in electrical conductivity, with hyperstoichiometric specimens with a low number of boundaries, yielding an increase in conductivity with increasing Gd content. Cyclic voltammetry showed that a variation in Gd content had only a minor influence on the electrochemical reactivity of stoichiometric U 1−y Gd y O 2 . By contrast, the reactivity of hypostoichiometric U 1−y Gd y O 2−x and hyperstoichiometric U 1−y Gd y O 2+x increased and decreased, respectively, with increasing Gd content. The formation of Gd-O v clusters in hyperstoichiometric U 1−y Gd y O 2+x has a more marked influence on reactivity than the accompanying changes in grain size and electrical conductivity.

A series of (U1−yGdy)O2 materials (y = 0, 0.01, 0.03, 0.05, 0.07 and 0.10) were characterized by X-ray diffractometry and Raman spectroscopy to determine the influence of GdIII doping on the structure of (U1−yGdy)O2 solid solutions. The XRD results show that, while the fluorite structure is maintained, Gd doping up to 10% leads to a contraction of the fluorite lattice. Raman spectroscopy shows GdIII doping distorts the fluorite lattice structure due to the formation of oxygen vacancies (Ov) and, possibly, MO8-type complexes, as a consequence of the differences in both the oxidation state and the ionic radius of Gd3+ compared to that of the U4+. The influence of Gd doping on the electrochemical reactivity of the (U1−yGdy)O2 specimens was shown to be minor, possibly due to a competition between the increase in the number of Ov and the contraction of the lattice.

A combination of electrochemical methods, X-ray photoelectron spectroscopy and current-sensing atomic force microscopy has been used to study the anodic reactivity of close-to-stoichiometric UO 2.002 , SIMFUEL, and Gd and Dy-doped UO 2 . Experiments were conducted in 0.1 mol L −1 NaCl solutions containing either bicarbonate/carbonate or phosphate at pH = 10. Anodic oxidation of the UO 2 matrix and its dissolution were both suppressed by doping, with the reactivities being in the order UO 2.002 > SIMFUEL > Gd-doped UO 2 > Dy-doped UO 2 . The onset of dissolution for SIMFUEL and the doped specimens was initiated by tetragonal distortions of the cubic matrix and was accompanied by a deeper more extensive oxidation of the UO 2 matrix. The composition of the surface of UO 2.002 was non-uniform, leading to the sub-thermodynamic oxidation and dissolution of more non-stoichiometric locations. Oxidation of the matrix was suppressed in phosphate solution and the onset of oxidation to U VI led to the formation of a protective uranyl phosphate layer. By contrast, in bicarbonate/carbonate solutions, U VI species were complexed by carbonate and dissolved.

The U 1−y Gd y O 2−x solid solutions with y = 0.005, 0.01, 0.03, 0.05 and 0.1 were characterized by Raman spectroscopy to investigate the defect structure induced by oxygen vacancies. The oxygen deficiencies of solid solutions were estimated by the relation between the doping level and a lattice parameter calculated from X-ray diffraction patterns. Raman mode shifts to higher wavenumber with increasing doping level showed that crystal lattice disorder due to oxygen vacancies. The frequency shifts and relative ratio of Raman modes were enabled to be the indicator for composition, defect and oxygen vacancy of U 1−y Gd y O 2−x solid solutions.

A 2-D model for the corrosion of spent nuclear fuel inside a failed nuclear waste container has been modified to determine the influence of various redox processes occurring within fractures in the fuel. The corrosion process is driven by reaction of the fuel with the dominant α radiolysis product, H2O2. A number of reactions are shown to moderate or suppress the corrosion rate, including H2O2 decomposition and a number of reactions involving dissolved H2 produced either by α radiolysis or by the corrosion of the steel container vessel. Both sources of H2 lead to the suppression of fuel corrosion, with their relative importance being determined by the radiation dose rate, the steel corrosion rate, and the dimensions of the fractures in the fuel. The combination of H2 from these two sources can effectively prevent corrosion when only micromolar quantities of H2 are present.

For the first time, a covalent organic framework TpBD was grown in situ on TiO2 nanotube arrays (NTAs), and the performance of the composite was investigated for the application of photoelectrochemical (PEC) cathodic protection. The synthesized TpBD/TiO2 NTA composite exhibited enhanced PEC cathodic protection performance under visible light. Coupled with the TpBD/TiO2 NTA photoanode, the photoinduced potential drop values for 304 stainless steel and Q235 carbon steel in 3.5 wt% NaCl solution were 910 and 370 mV, respectively. It was proposed that the enhanced PEC performance was due to the formation of a Z-scheme heterojunction between TpBD and TiO2.

A covalent organic framework (COF) modified carbon paste electrode (CPE) was used for the electrochemical detection of hazardous hydroquinone (HQ) and catechol (CC). Due to the advantages of TpBD-COF (large surface area, abundant functional groups and high chemical stability), rapid quantitative determination of HQ and CC was accomplished by differential pulse voltammetry (DPV). Under the optimal conditions, the resultant sensor showed an extended linear response range for HQ and CC (1–2000 μmol L−1), and the detection limits were 0.31 and 0.46 μmol L−1 (S/N = 3) respectively. The simultaneous determination of HQ and CC can be accomplished by data deconvolution. In binary solutions with one constant constituent concentration, a linear relationship was established between the deconvoluted peak current and concentration of the changing constituent. In addition, the electrochemical sensor showed strong anti-interference ability, good reproducibility (a relative standard deviation of 0.99% for HQ and 0.77% for CC, n = 5) and applicability in real sample detection (with spiking recoveries from 97.7% – 101.6% for HQ and 100.3% – 103.3% for CC). These results demonstrate that COF modified carbon materials are promising candidates for efficient electrochemical detection of phenolic compounds.

The photo-catalytic activity of TiO2 was greatly enhanced by co-sensitization with Ag and In2S3, and its application to protect 304 stainless steel from corrosion was reported. TiO2 nanotube arrays (TiO2 NTAs,) with large specific surface area and hollow nanostructures favored the immobilization of In2S3 and Ag. In2S3 as a narrow band gap semiconductor could broaden the light absorption range of TiO2. Surface plasmon resonance of Ag could accelerate the separation of photo-induced carriers generated from TiO2 and In2S3. The photo-induced potential drop of 304 stainless steel in NaCl solution measured 530 mV, and the photo-current density reached 45 µA/cm2 with visible light irradiation coupled with Ag and In2S3 co-sensitized TiO2 composite.

In this work, the photo-catalytic activity of TiO2 is considerably enhanced via sensitization with CdIn2S4, and its application for protecting Q235 from corrosion in splash zones is examined. TiO2 nanotube arrays (NTAs) are prepared on a flat Ti substrate via two-step anodization. CdIn2S4 is deposited on the surface of TiO2 NTAs by hydrothermal reaction. TiO2 NTAs with enormous specific surface areas and large-diameter hollow nanostructures are found to benefit the immobilization of CdIn2S4. As a narrow band gap semiconductor, CdIn2S4 is able to extend the light absorption range of TiO2, and the construction of an n&ndash, n type hetero-junction accelerates the separation of carriers. Strong solar light, which accelerates the corrosion of Q235 in the splash zone area, is converted into the necessary condition for protecting Q235 from corrosion. In this work, TiO2 is sensitized with MoS2 microspheres (MoS2/TiO2 nanocomposites), which were prepared on a flat Ti substrate via a two-step anodization and hydrothermal method, sequentially.

If nuclear waste containers in a deep geologic repository were to fail allowing groundwater to contact the spent fuel wasteform, the release of the great majority of radionuclides would be controlled by the corrosion rate of the UO 2 fuel matrix. This rate will be controlled by the redox conditions within the container established by the radiolytic decomposition of the ground water and the corrosion of the steel containment vessel. Extensive experimental research and model calculations, commonly employing electrochemical techniques and formulations, demonstrate that the fuel corrosion rate will be predominantly controlled by the reactivity of the fuel, the kinetics of oxidant (H 2 O 2 , O 2 ) reduction, and the scavenging of these oxidants by the products of steel corrosion (H 2 , Fe 2 + ).

A high-valent phosphoniomethylidyne tantalum complex [(C5Me4H)Ta( C-PPh3)( CH-PPh3)Cl] (3) was obtained via transylidation reactions of (C5Me4H)TaCl4 with 5 equivalents of the phosphorus ylide Ph3P = CH2. The addition of strong base Li(N(SiMe3)2 is beneficial to the transylidation reaction and improves the yield of complex 3. The ylide adduct complex [(C5Me4H)TaCl4(CH2PPh3)] (4) as the reaction intermediate was isolated through the reaction of (C5Me4H)TaCl4 with one equivalent of the phosphorus ylide Ph3P = CH2. Both complexes 3 and 4 were structurally characterized by X-ray single crystal diffraction. A comparison on the preparation and properties of the phosphoniomethylidyne tantalum complexes with different supporting ligands, [CpTa( C-PPh3)( CH-PPh3)Cl] (1) (Cp = cyclopentadieneyl ligand), [(C5Me4H)Ta( C-PPh3)( CH-PPh3)Cl] (3) (C5Me4H = tetramethylcyclopentadienyl ligand) (3) and [Cp⁎Ta( C-PPh3)( CH-PPh3)Cl] (2) (Cp⁎ = pentamethylcyclopentadienyl ligand) was discussed.

A 2-D model for the corrosion of spent nuclear fuel inside a failed nuclear waste container has been modified to determine the influence of various redox processes occurring within fractures in the fuel. The corrosion process is driven by reaction of the fuel with the dominant α radiolysis product, H

Dibenzylphenylphosphine in the reaction with CoMe(PMe 3 ) 4 afforded complex [(Me 3 P) 3 Co(( ortho -C 6 H 4 )∩P(C 6 H 5 )(CH 2 C 6 H 5 ))] ( 1 ) by C sp2 –H activation via ortho -metalation with P atom as anchoring group. An unexpected dinitrogen iron(II) complex [(Me 3 P) 2 (N 2 )Fe(( ortho -C 6 H 4 ) 2 ∩P(C 6 H 5 ))] ( 2 ) stabilized by two five-membered chelate rings as [CPC]-pincer ligand was formed through the reaction of dibenzylphenylphosphine with FeMe 2 (PMe 3 ) 4 via double C sp2 –H activation. The reactions of complexes 1 and 2 with carbon monoxide delivered carbonyl complexes [(Me 3 P)(CO) 2 Co(( ortho -C 6 H 4 )∩P(C 6 H 5 )(CH 2 C 6 H 5 ))] ( 3 ) and [(Me 3 P) 2 (CO)Fe(( ortho -C 6 H 4 ) 2 ∩P(C 6 H 5 ))] ( 4 ). An iodo methyl cobalt(III) complex [(Me 3 P) 2 (Me)(I)Co(( ortho -C 6 H 4 )∩P(C 6 H 5 )(CH 2 C 6 H 5 ))] ( 5 ) was isolated through the reaction of 1 with iodomethane. The structures of 1, 2, 3, 4 and 5 were determined by X-ray diffraction.

Reactions of 1,1'-bis(dipheny1phosphino)cobaltocene with Co(PMe(3))(4), Ni(PMe(3))(4), Fe(PMe(3))(4), Ni(COD)(2), FeMe(2)(PMe(3))(4) or NiMe(2)(PMe(3))(3) afford a series of novel dinuclear complexes [((Me(3)P)[lower bond 1 start]Co(η(5)-C(5)H(4)[upper bond 1 start]PPh(2)))((Me(3)P)M[upper bond 1 end](η(5)-C(5)H(4)P[lower bond 1 end]Ph(2)))] (M = Co(1), Ni(2) and Fe(3)) [Co(η(5)-C(5)H(4)[upper bond 1 start]PPh(2))(2)Ni[upper bond 1 end](COD)](4), [Co(η(5)-C(5)H(4)[upper bond 1 start]PPh(2))(2)Ni[upper bond 1 end](PMe(3))(2)] (5) and [((Me(3)P)[lower bond 1 start]Co(Me)(η(5)-C(5)H(4)[upper bond 1 start]PPh(2)))((Me(3)P)Fe[upper bond 1 end](Me)(η(5)-C(5)H(4)P[lower bond 1 end]Ph(2)))] (6). Reactions of 1,1'-bis(dipheny1phosphino)ferrocene with Ni(PMe(3))(4), NiMe(2)(PMe(3))(3), or Co(PMe(3))(4) gives rise to complexes [Fe(η(5)-C(5)H(4)[upper bond 1 start]PPh(2))(2)M[upper bond 1 end](PMe(3))(2)] (M = Ni (7), Co (8)). The complexes 1-8 were spectroscopically investigated and studied by X-ray single crystal diffraction. The possible reaction mechanisms and structural characteristics are discussed. Density functional theory (DFT) calculations strongly support the deductions.

Porins are trimers of beta-barrels that form channels for ions and other hydrophilic solutes in the outer membrane of Gram-negative bacteria. The X-ray structures of OmpF and PhoE show that each monomeric pore is constricted by an extracellular loop that folds into the channel vestibule, a motif that is highly conserved among bacterial porins. Electrostatic calculations have suggested that the distribution of ionizable groups at the constriction zone (or eyelet) may establish an intrinsic transverse electrostatic field across the pore, that is perpendicular to the pore axis. In order to study the role that electrostatic interactions between pore residues may have in porin function, we used spontaneous mutants and engineered site-directed mutants that have an altered charge distribution at the eyelet and compared their electrophysiological behavior with that of wild-type OmpC. We found that some mutations lead to changes in the spontaneous gating activity of OmpC porin channels. Changes in the concentration of permeant ions also altered this activity. These results suggest that the ionic interactions that exist between charged residues at the constriction zone of porin may play a role in the transitions between the channel's closed and open states.

Porins are trimeric channel-forming proteins of the outer membrane of Escherichia coli. Each subunit contains 16 beta-strands forming a transmembrane beta-barrel whose pore is constricted by the third extracellular loop (L3). We investigated the effects of site-directed mutations at two critical regions of the OmpC porin: (i) the D315A mutation targets a key component of a putative hydrogen bond network linking the L3 loop to the adjacent barrel wall and (ii) the D118Q, R174Q and R92Q mutations target putative salt bridges at the root of the L3 loop. We purified the outer membrane fractions obtained from each mutant and reconstituted them in liposomes suitable for electrophysiology. Patch clamp experiments showed that the frequency of spontaneous transitions between open and closed states is increased in the D315A, D118Q and R92Q mutants but unchanged in the R174Q mutant. These transitions are not driven by transmembrane voltage changes and represent the thermal oscillations between functionally distinct conformations. The asymmetric voltage-dependent inactivation of the channels is not affected by the mutations, however, suggesting different molecular mechanisms for the spontaneous and voltage-dependent gating processes. We propose that the positioning or flexibility of the L3 loop across the pore, as governed by the putative hydrogen-bond network and a salt bridge, play a role in determining the frequency of spontaneous channel gating.

In the title compound, [Co(C(20)H(18)P)I(C(3)H(9)P)(2)], the Co(II) atom has a distorted square-pyramidal geometry, the base of which is comprised of two trans PMe(3) groups, an I atom, and a C atom of the benzyl group. This benzyl group is tethered to the P atom at the apex of the pyramid, thereby forming a five-membered chelated Co-C-C-C-P ring.