Local CO2 reservoir layer promotes rapid and selective electrochemical CO2 reduction

Electrochemical CO2 reduction reaction in aqueous electrolytes is a promising route to produce added-value chemicals and decrease carbon emissions. However, even in Gas-Diffusion Electrode devices, low aqueous CO2 solubility limits catalysis rate and selectivity. Here, we demonstrate that when assembled over a heterogeneous electrocatalyst, a film of nitrile-modified Metal-Organic Framework (MOF) acts as a remarkable CO2-solvation layer that increases its local concentration by ~27-fold compared to bulk electrolyte, reaching 0.82 M. When mounted on a Bi catalyst in a Gas Diffusion Electrode, the MOF drastically improves CO2-to-HCOOH conversion, reaching above 90% selectivity and partial HCOOH currents of 166 mA/cm2 (at -0.9 V vs RHE). The MOF also facilitates catalysis through stabilization of reaction intermediates, as identified by operando infrared spectroscopy and Density Functional Theory. Hence, the presented strategy provides new molecular means to enhance heterogeneous electrochemical CO2 reduction reaction, leading it closer to the requirements for practical implementation.

Regulation of Catalyst Immediate Environment Enables Acidic Electrochemical Benzyl Alcohol Oxidation to Benzaldehyde

Electrocatalytic alcohol oxidation in acid offers a promising alternative to the kinetically sluggish water oxidation reaction toward low-energy H2 generation. However, electrocatalysts driving active and selective acidic alcohol electrochemical transformation are still scarce. In this work, we demonstrate efficient alcohol-to-aldehyde conversion achieved by reticular chemistry-based modification of the catalyst's immediate environment. Specifically, coating a Bi-based electrocatalyst with a thin layer of metal-organic framework (MOF) substantially improves its performance toward benzyl alcohol electro-oxidation to benzaldehyde in a 0.1 M H2SO4 electrolyte. Detailed analysis reveals that the MOF adlayer influences catalysis by increasing the reactivity of surface hydroxides as well as weakening the catalyst-benzaldehyde binding strength. In turn, low-potential (0.65 V) cathodic H2 evolution was obtained through coupling it with anodic benzyl alcohol electro-oxidation. Consequently, the presented approach could be implemented in a wide range of electrocatalytic oxidation reactions for energy-conversion application.

Nickel-Iron-Modified 2D Metal-Organic Framework as a Tunable Precatalyst for Electrochemical Water Oxidation

Mixed-metal metal-organic framework (MOF)-based water oxidation precatalysts have aroused a great deal of attention due to their remarkable catalytic performance. Yet, despite significant advancement in this field, there is still a need to design new MOF platforms that allow simple and systematic control over the final catalyst's metal composition. Here, we show that a Zr-BTB 2D-MOF could be used to construct a series of Ni-Fe-based oxide hydroxide water oxidation precatalysts with diverse Ni-Fe compositions. In situ Raman spectroscopy characterization revealed that the MOF precatalysts could be electrochemically converted to the active catalysts (NiFeOOH). In turn, it was found that the highest water oxidation activity was obtained with a catalyst containing a 47:53 Ni:Fe molar ratio. Additionally, the obtained catalyst is also active toward electrochemical methanol oxidation, exhibiting high selectivity toward the formation of formic acid. Hence, these results could pave the way for the development of efficient electrocatalytic materials for a variety of oxidative reactions.

Electrostatic Secondary-Sphere Interactions That Facilitate Rapid and Selective Electrocatalytic CO2 Reduction in a Fe-Porphyrin-Based Metal-Organic Framework

Metal–organic frameworks (MOFs) are promising platforms for heterogeneous tethering of molecular CO₂ reduction electrocatalysts. Yet, to further understand electrocatalytic MOF systems, one also needs to consider their capability to fine‐tune the immediate chemical environment of the active site, and thus affect its overall catalytic operation. Here, we show that electrostatic secondary‐sphere functionalities enable substantial improvement of CO₂‐to‐CO conversion activity and selectivity. In situ Raman analysis reveal that immobilization of pendent positively‐charged groups adjacent to MOF‐residing Fe‐porphyrin catalysts, stabilize weakly‐bound CO intermediates, allowing their rapid release as catalytic products. Also, by varying the electrolyte's ionic strength, systematic regulation of electrostatic field magnitude was achieved, resulting in essentially 100 % CO selectivity. Thus, this concept provides a sensitive molecular‐handle that adjust heterogeneous electrocatalysis on demand.

Assembly of a Metal-Organic Framework (MOF) Membrane on a Solid Electrocatalyst: Introducing Molecular-Level Control Over Heterogeneous CO2 Reduction

Electrochemically active Metal‐Organic Frameworks (MOFs) have been progressively recognized for their use in solar fuel production schemes. Typically, they are utilized as platforms for heterogeneous tethering of exceptionally large concentration of molecular electrocatalysts onto electrodes. Yet so far, the potential influence of their extraordinary chemical modularity on electrocatalysis has been overlooked. Herein, we demonstrate that, when assembled on a solid Ag CO₂ reduction electrocatalyst, a non‐catalytic UiO‐66 MOF acts as a porous membrane that systematically tunes the active site's immediate chemical environment, leading to a drastic enhancement of electrocatalytic activity and selectivity. Electrochemical analysis shows that the MOF membrane improves catalytic performance through physical and electrostatic regulation of reactants delivery towards the catalytic sites. The MOF also stabilizes catalytic intermediates via modulation of active site's secondary coordination sphere. This concept can be expanded to a wide range of proton‐coupled electrochemical reactions, providing new means for precise, molecular‐level manipulation of heterogeneous solar fuels systems.

Electrochemically Driven Cation Exchange Enables the Rational Design of Active CO2 Reduction Electrocatalysts

Metal oxides or sulfides are considered to be one of the most promising CO₂ reduction reaction (CO₂ RR) precatalysts, owing to their electrochemical conversion in situ into highly active electrocatalytic species. However, further improvement of the performance requires new tools to gain fine control over the composition of the active species and its structural features [e.g., grain boundaries (GBs) and undercoordinated sites (USs)], directly from a predesigned template material. Herein, we describe a novel electrochemically driven cation exchange (ED-CE) method that enables the conversion of a predesigned CoS₂ template into a CO₂ RR catalyst, Cu₂ S. By means of ED-CE, the final Cu₂ S catalyst inherits the original 3 D morphology of CoS₂ , and preserves its high density of GBs. Additionally, the catalyst's phase structure, composition, and density of USs were precisely tuned, thus enabling rational design of active CO₂ RR sites. The obtained Cu₂ S catalyst achieved a CO₂ -to-formate Faradaic efficiency of over 87 % and a record high activity (among reported Cu-based catalysts). Hence, this study opens the way for utilization of ED-CE reactions to design advanced electrocatalysts.

Active-Site Modulation in an Fe-Porphyrin-Based Metal-Organic Framework through Ligand Axial Coordination: Accelerating Electrocatalysis and Charge-Transport Kinetics

The construction of artificial solar fuel generating systems requires the heterogenization of large quantities of catalytically active sites on electrodes. In that sense, metal–organic frameworks (MOFs) have been utilized to assemble unpreceded concentration of electrochemically active molecular catalysts to drive energy-conversion electrocatalytic reactions. However, despite recent advances in MOF-based electrocatalysis, so far no attempt has been made to exploit their unique chemical modularity in order to tailor the electrocatalytic function of MOF-anchored active sites at the molecular level. Here, we show that the axial coordination of electron-donating ligands to active MOF-installed Fe-porphyrins dramatically alters their electronic properties, accelerating the rates of both redox-based MOF conductivity and the electrocatalytic oxygen reduction reaction (ORR). Additionally, electrochemical characterizations show that in multiple proton-coupled electron transfer reactions MOF-based redox hopping is not the only factor that limits the overall electrocatalytic rate. Hence, future efforts to enhance the efficiency of electrocatalytic MOFs should also consider other important kinetic parameters such as the rate of proton-associated chemical steps as well as mass-transport rates of counterions, protons, and reactants toward catalytically active sites.

Spatially confined electrochemical conversion of metal-organic frameworks into metal-sulfides and their in situ electrocatalytic investigation via scanning electrochemical microscopy

There is an on-going search for new earth-abundant electrocatalytic materials, suitable for replacing noble-metals as efficient accelerators of energy-conversion reactions. In this regard, over the last few years, metal-organic framework (MOF)-converted materials have demonstrated promising electrocatalytic properties. Nevertheless, the discovery of new catalytic materials requires development of methods combining high-throughput synthesis and electrochemical-activity screening. To do so, here we couple the synthetical and the analytical virtues of scanning electrochemical microscopy (SECM). Namely, we first utilized an SECM tip electrode to induce spatially confined (μm-scale) electrochemical conversion of cobalt-based ZIF-67 MOFs into patterns of cobalt sulfide with a tuned chemical composition. In turn, the same SECM setup was used to map the H₂ evolution activity of the as-formed cobalt sulfide. Hence, the presented method should have great implications for future screening of new electrocatalytic materials for a variety of energy-related applications.

Pristine versus Pyrolyzed Metal-Organic Framework-based Oxygen Evolution Electrocatalysts: Evaluation of Intrinsic Activity Using Electrochemical Impedance Spectroscopy

Metal-organic frameworks (MOFs) have emerged as outstanding electrocatalysts for water oxidation. Commonly, MOFs are utilized for electrocatalytic water oxidation either in pristine or pyrolyzed form. Yet, despite significant advancements in their catalytic performance, further improvement requires new insights on the parameters influencing MOF-based catalysts activity. Here, we have conducted a detailed comparison between the intrinsic electrocatalytic properties of pristine and pyrolyzed Ni-Fe-based MOFs. Interestingly, although pristine MOF exhibits the maximum overall electrocatalytic performance, apparent turnover frequency (TOF) values (intrinsic activity) of all pyrolyzed MOFs exceeded the one of pristine MOF. Moreover, an upper-limit estimation of TOF was extracted using electrochemical impedance spectroscopy (EIS), by excluding IR-drops linked with the electrochemical cell. By doing so, EIS-extracted TOF values were 10-times higher compared to the apparent TOFs. Accordingly, a great leap in performance should still be expected for these catalysts, by designing conductive MOF-platforms having larger pore-diameters to reduce mass-transport limitations.

Immunological and virological effects of long term IL-2 therapy in HIV-1-infected patients

We report the long-term outcome of 27 HIV-infected patients treated for over 3 years with IL-2 and binucleoside analogues. These patients experienced a sustained increase in CD4 cells and a decrease of proviral DNA with infrequent IL-2 cycles. In three cases, virus could not be isolated from activated peripheral cells. A high frequency of HIV-1-specific memory CD4 T cells was found in the patients studied. IL-2 maintains specific effector cells and reduces the pool of infected cells in patients, albeit treated only with binucleosides.

Mechanism of action of 1-beta-D-2,6-diaminopurine dioxolane, a prodrug of the human immunodeficiency virus type 1 inhibitor 1-beta-D-dioxolane guanosine

(-)-beta-D-2,6-Diaminopurine dioxolane (DAPD), is a nucleoside reverse transcriptase (RT) inhibitor with activity against human immunodeficiency virus type 1 (HIV-1). DAPD, which was designed as a water-soluble prodrug, is deaminated by adenosine deaminase to give (-)-beta-D-dioxolane guanine (DXG). By using calf adenosine deaminase a K(m) value of 15 +/- 0.7 microM was determined for DAPD, which was similar to the K(m) value for adenosine. However, the k(cat) for DAPD was 540-fold slower than the k(cat) for adenosine. In CEM cells and peripheral blood mononuclear cells exposed to DAPD or DXG, only the 5'-triphosphate of DXG (DXG-TP) was detected. DXG-TP is a potent alternative substrate inhibitor of HIV-1 RT. Rapid transient kinetic studies show the efficiency of incorporation for DXG-TP to be lower than that measured for the natural substrate, 2'-deoxyguanosine 5'-triphosphate. DXG-TP is a weak inhibitor of human DNA polymerases alpha and beta. Against the large subunit of human DNA polymerase gamma a K(i) value of 4.3 +/- 0.4 microM was determined for DXG-TP. DXG showed little or no cytotoxicity and no mitochondrial toxicity at the concentrations tested.

Treatment of isografted 9L rat brain tumors with beta-5-o-carboranyl-2'-deoxyuridine neutron capture therapy

beta-5-o-Carboranyl-2'-deoxyuridine (D-CDU) is a nontoxic pyrimidine nucleoside analogue designed for boron neutron capture therapy of brain tumors. In vitro studies indicated that D-CDU accumulates to levels 92- and 117-fold higher than the extracellular concentration in rat 9L and human U-251 glioma cells, respectively, and persists for several hours at levels 5-fold higher than the extracellular concentration. Furthermore, D-CDU was not toxic to rats injected i.p. with up to 150 mg/kg. On the basis of these studies, D-CDU was evaluated as a neutron capture therapy agent using rats bearing stereotactically implanted intracranial 9L tumors at single i.p. doses of 30 mg/kg and 150 mg/kg of D-CDU (20% 10B enriched), given 2 h before irradiation with thermal neutrons. Boron concentrations in tumors 2 h after dosing were 2.3 +/- 1.6 and 7.4 +/- 1.3 micrograms boron/g tissue (mean +/- SD), corresponding to tumor/brain ratios of 11.5 +/- 3.6 and 6.8 +/- 2.0 micrograms boron/g tissue for the low and high doses, respectively. All untreated animals died within 28 days, whereas half survived at days 32, 55, and 38 for groups receiving neutrons only, 30 mg/kg D-CDU, and 150 mg/kg D-CDU, respectively. Odds ratios of all treatment groups differed significantly from the untreated group (P < 0.002; logrank test). The median survival time for the 30 mg/kg-treated group but not for the 150 mg/kg-treated group was significantly longer than for rats treated with neutrons only (P = 0.036), which may correlate with the decreased tumor selectivity for D-CDU observed at the higher dose. Additional pharmacodynamic studies are warranted to determine optimal dosing strategies for D-CDU.

Expression and biological activity of interleukin-1 receptors in mouse gamma/delta thymocytes during ontogeny

We have recently shown that the response of mouse thymocytes to interleukin (IL)-1 + IL-2 was maximal at birth and that the responding cells displayed a CD4-CD8- T cell receptor (TcR) gamma/delta + phenotype. Unexpectedly, despite their high proportion of gamma/delta + cells, fetal thymocyte populations responded only weakly to IL-1 + IL-2. In this report, we demonstrate that the discrepancy between the day 17.5 fetal and newborn sensitivities to the combined action of IL-1 and IL-2 is a consequence of the different patterns of high-affinity IL-1 receptor (IL-1R) expression displayed by these two cell subsets. Actually, high- and low-affinity IL-1R are found in TcR gamma/delta + newborn cells and, in contrast, only low-affinity IL-1R are detectable in day 17.5 fetal cells. Our binding and functional studies strongly support the hypothesis that high-affinity IL-1R on the one hand, and low-affinity ones on the other hand, are involved in the response to IL-1 + IL-2 of newborn and day 17.5 fetal thymocytes, respectively. In addition, the high-affinity IL-1R appear to be far more efficient than the low-affinity receptors in promoting IL-2 responsiveness of thymocytes.

Ontogeny of the response of mouse thymocytes to interleukin 1 and interleukin 2

In the present report we demonstrate that the in vitro proliferative response of the newborn thymocytes to interleukin (IL) 1 and IL 2, which is remarkably stronger than the adult thymocyte response, is associated with a considerable increase of CD4-CD8- cells expressing a gamma/delta T cell receptor (TcR). By polymerase chain reaction analysis we show that the V gamma gene segment usage in the adult and newborn responding cells reflects the developmentally regulated expression of the V gamma gene segments, suggesting that the increase in TcR gamma/delta+ cells results from the polyclonal expansion of pre-existing clones. Surprisingly, although the fetal thymocyte populations contain higher numbers of TcR gamma/delta+ cells than the adult and newborn ones, the highest proliferative response to IL 1 and IL 2 is obtained with the newborn thymocytes. Non mutually exclusive hypotheses are discussed to explain these results.

Cellular basis of the resistance of newborn mice to the pathogenic effects of anti-CD3 treatment

We have analysed the mechanisms underlying the differences in the susceptibilities of adult and newborn mice to the pathogenic effects of anti-CD3 mAbs. Our data show that the thymus cell number in adults is reduced by 93% 48 h after one single injection of 5 mg/kg of Ab whereas the same dose in newborns induces only a 30% decrease. In the adult, this effect is associated with a marked depletion of CD4+ CD8+ double positive (DP) cells and with the appearance of important areas of cell necrosis in the thymic cortex. In newborns, the DP cells are less affected and the thymic cortex does not present any cell necrosis even after an injection of 45 mg/kg of mAbs. Pre-treatment of adults with anti-CD4 and anti-CD8 Abs, while completely abolishing the toxic side-effects induced by anti-CD3 mAbs, does not protect the thymus from the depletion of DP cells. In vitro, anti-CD3 mAbs induce the proliferation of thymocytes and spleen cells from adults but not from newborns. Tumour necrosis factor-alpha (TNF alpha) is found in the serum of adults 90 min after injection of anti-CD3 but is never detected in the serum of anti-CD3 treated newborns. Taken together our data support the view that anti-CD3 mAbs act by two different mechanisms. The first one results from the binding of anti-CD3 on the CD3+ thymocytes which induces a direct toxicity for only the CD4+ CD8+ cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Bathymetry CuBr laser

The design and performance of a short-pulse high-repetition-rate CuBr laser suitable for bathymetry is described. The pulse width and peak power were 4.5 nsec and 30 kW, respectively, corresponding to 140 microJ/pulse. These conditions occurred at a repetition rate of 16 kHz and an overall efficiency of 0.14% within a compact long-lived sealed-off discharge.

Optical analysis of laser systems using interferometry

Previous methods of predicting focal spot parameters such as the Strehl ratio and encircled energy of large laser systems like the Los Alamos fusion CO(2) lasers involved the digitization of interference patterns of the optical components and propagation of the complex amplitude and phase of the wave front throughout the system. In the new approach described in this paper, the computational procedure has been extended to produce computer plots of the final emerging wave front. This enables direct comparison with the experimentally produced wave front of the total system and opens the way for optical analysis, design, and possible optimization of laser systems, especially CO(2) laser systems. The computational procedure and the Twyman-Green and Smartt IR interferometers constructed to verify this approach are described. The implications of the results are discussed.

Automatic target alignment of the Helios laser system

An automatic target-alignment technique for the Helios laser facility is reported and verified experimentally. The desired alignment condition is completely described by an autocollimation test. A computer program examines the autocollimated return pattern from the surrogate target and correctly describes any changes required in mirror orientation to yield optimum target alignment with either aberrated or misaligned beams. Automated on-line target alignment is thus shown to be feasible.

A Comparison of Lamps for Use in High Continuous Power Nd:YAG Lasers

The efficiency of krypton, xenon, and tungsten-iodine lamps for pumping Nd: YAG are compared both spectroscopically and by laser pumping. The relative pumping efficiencies of xenon and tungsten to krypton are 0.86 and 1.1, respectively. However, because the tungsten filament uses a higher percentage of its power in overcoming the laser threshold, the krypton lamp with its larger power density yielded the best over-all efficiency. An output power of 105 W was obtained at an input power of 3610 W for an over-all efficiency of 2.9%.

The spherical reflector for use in the optical pumping of lasers

The coupling of optical energy from a lamp into a laser rod using a spherical mirror enclosure has been analyzed using geometrical optics. The calculations indicate that about 75% coupling can be obtained for typical sized laser rods and spheres. Experimental results for a 3 mm x 30 mm Nd: Cr: YAG rod are given. Using external resonators, a slope efficiency of 1.15% and an output power of 3.4 W were observed for an input power of 870 W.

A high resolution rapid-scanning spectrometer

A Czerny-Turner type spectrometer has been designed and operated as a rapid scanning instrument by placing a rotating mirror near the exit slit. Using a helium-neon gas laser, resolution of 0.027 A has been measured at scanning rates of 0.4 A/microsec. Data have been taken with the scanning rate of 6 A/microsec, which could have been increased an order of magnitude if desired. A scanning range of 1-600 A depending on the grating and mirrors used has been obtained. Applications shown included the shift and shape of xenon spectral lines in a pulsed arc discharge. The associated electronics required for synchronization are included.