The generation of H2 from protons and electrons by complexes of cobalt has an extensive history. During the past decade, interest in this subject has increased as a result of developments in hydrogen ...generation that are driven electrochemically or photochemically. This article reviews the subject of hydrogen generation using Co complexes as catalysts and discusses the mechanistic implications of the systems studied for making H2. This article is part of a Special Issue entitled: Metals in Bioenergetics and Biomimetics Systems.
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•Photocatalytic systems using cobalt catalysts are examined.•Photocatalytic and electrocatalytic methods are discussed in detail.•Major mechanistic findings are presented.•Systems using integrated photosensitizer–catalyst systems are considered.•Semi-conductor based systems with cobalt catalysts are also examined.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A question of nobility: A biomimetic nickel thiolate complex (see scheme; TEA=triethylamine) exhibits unprecedented activity for the title reaction. By using a low concentration of a sacrificial ...donor, the system maintains significant activity for at least 60 hours. The enhanced stability of the system is ascribed to the ability to proceed through an oxidative quenching pathway.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The complex Co(bdt)2− (where bdt = 1,2-benzenedithiolate) is an active catalyst for the visible light driven reduction of protons from water when employed with Ru(bpy)3 2+ as the photosensitizer and ...ascorbic acid as the sacrificial electron donor. At pH 4.0, the system exhibits very high activity, achieving >2700 turnovers with respect to catalyst and an initial turnover rate of 880 mol H2/mol catalyst/h. The same complex is also an active electrocatalyst for proton reduction in 1:1 CH3CN/H2O in the presence of weak acids, with the onset of a catalytic wave at the reversible redox couple of −1.01 V vs Fc+/Fc. The cobalt–dithiolene complex Co(bdt)2− thus represents a highly active catalyst for both the electrocatalytic and photocatalytic reduction of protons in aqueous solutions.
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IJS, KILJ, NUK, PNG, UL, UM
Artificial photosynthesis (AP) is a promising method of converting solar energy into fuel (H ₂). Harnessing solar energy to generate H ₂ from H ⁺ is a crucial process in systems for artificial ...photosynthesis. Widespread application of a device for AP would rely on the use of platinum-free catalysts due to the scarcity of noble metals. Here we report a series of cobalt dithiolene complexes that are exceptionally active for the catalytic reduction of protons in aqueous solvent mixtures. All catalysts perform visible-light-driven reduction of protons from water when paired with Formula as the photosensitizer and ascorbic acid as the sacrificial donor. Photocatalysts with electron withdrawing groups exhibit the highest activity with turnovers up to 9,000 with respect to catalyst. The same complexes are also active electrocatalysts in 1∶1 acetonitrile/water. The electrocatalytic mechanism is proposed to be ECEC, where the Co dithiolene catalysts undergo rapid protonation once they are reduced to Formula. Subsequent reduction and reaction with H ⁺ lead to H ₂ formation. Cobalt dithiolene complexes thus represent a new group of active catalysts for the reduction of protons.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
Nerves enable cancer progression, as cancers have been shown to extend along nerves through the process of perineural invasion, which carries a poor prognosis. Furthermore, the innervation of some ...cancers promotes growth and metastases. It remains unclear, however, how nerves mechanistically contribute to cancer progression. Here, we demonstrated that Schwann cells promote cancer invasion through direct cancer cell contact. Histological evaluation of murine and human cancer specimens with perineural invasion uncovered a subpopulation of Schwann cells that associates with cancer cells. Coculture of cancer cells with dorsal root ganglion extracts revealed that Schwann cells direct cancer cells to migrate toward nerves and promote invasion in a contact-dependent manner. Upon contact, Schwann cells induced the formation of cancer cell protrusions in their direction and intercalated between the cancer cells, leading to cancer cell dispersion. The formation of these processes was dependent on Schwann cell expression of neural cell adhesion molecule 1 (NCAM1) and ultimately promoted perineural invasion. Moreover, NCAM1-deficient mice showed decreased neural invasion and less paralysis. Such Schwann cell behavior reflects normal Schwann cell programs that are typically activated in nerve repair but are instead exploited by cancer cells to promote perineural invasion and cancer progression.
A series of homogeneous Fe(
iii
) complexes were recently reported that are active for electrocatalytic hydrogen generation. Herein we report a naphthalene-terminated Fe(
iii
) complex for use in the ...functionalization of glassy carbon surfaces for electrocatalytic hydrogen generation with retention of catalytic activity.
A napthelene-terminated iron polypyridyl monophenolate catalyst was absorbed onto glassy carbon surfaces for electrocatalytic hydrogen generation.
We report the first example of a sulfinato Fe(III) complex acting as a highly active electrocatalyst for proton reduction. The sulfinate binds to the metal through oxygen, resulting in a ...seven-membered chelate ring that is likely hemilabile during catalysis. Proton reduction occurs at −1.57 V versus Fc/Fc+ in CH3CN with an i c/i p = 13 in CH3CN (k obs = 3300 s–1) and an overpotential of 800 mV. The catalysis is first order with respect to catalyst and second order with respect to trifluoracetic acid. An 11% increase in catalytic activity is observed in the presence of water, suggesting that sulfinate moieties are viable functional groups for aqueous proton reduction catalysts.
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IJS, KILJ, NUK, PNG, UL, UM
A series of Fe(III) complexes were recently reported that are stable and active electrocatalysts for reducing protons into hydrogen gas. Herein, we report the incorporation of these electrocatalysts ...into a photocatalytic system for hydrogen production. Hydrogen evolution is observed when these catalysts are paired with fluorescein (chromophore) and triethylamine (sacrificial electron source) in a 1:1 ethanol:water mixture. The photocatalytic system is highly active and stable, achieving TONs > 2100 (with respect to catalyst) after 24 h. Catalysis proceeds through a reductive quenching pathway with a quantum yield of over 3%.
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IJS, KILJ, NUK, PNG, UL, UM
Two cobalt(iii) complexes containing inexpensive Schiff-base ligands have been found to be active for proton reduction at low overpotentials. The dinitro and tetranitro derivatized Schiff-base ...complexes show catalytic activity at -0.96 V and -1.1 V vs. Fc
/Fc, respectively, resulting in overpotentials of 120 mV and 280 mV. Foot-of-the-wave analysis is used to examine the kinetic properties of these complexes, yielding a theoretical TOF
of up to 4100 s
. Experimental TOFs of 7 s
and 3 s
are observed. Catalytic Tafel plots are also presented in order to benchmark the relationship between turnover frequency and overpotential.
BACKGROUND:Retear and stiffness are not uncommon outcomes of rotator cuff repair. The purpose of this study was to evaluate the relationship between rotator cuff repair healing and shoulder ...stiffness.
METHODS:A total of 1,533 consecutive shoulders had an arthroscopic rotator cuff repair by a single surgeon. Patients assessed their shoulder stiffness using a Likert scale preoperatively and at 1, 6, 12, and 24 weeks (6 months) postoperatively, and examiners evaluated passive range of motion preoperatively and at 6, 12, and 24 weeks postoperatively. Repair integrity was determined by ultrasound evaluation at 6 months.
RESULTS:After rotator cuff repair, there was an overall significant loss of patient-ranked and examiner-assessed shoulder motion at 6 weeks compared with preoperative measurements (p < 0.0001), a partial recovery at 12 weeks, and a full recovery at 24 weeks. Shoulders that were stiff before surgery were more likely to be stiff at 6, 12, and, to a lesser extent, 24 weeks after surgery (r = 0.10 to 0.31; p < 0.0001). A stiffer shoulder at 6 and 12 weeks (but not 24 weeks) postoperatively correlated with better rotator cuff integrity at 6 months postoperatively (r = 0.11 to 0.18; p < 0.001). The retear rate of patients with ≤20° of external rotation at 6 weeks postoperatively was 7%, while the retear rate of patients with >20° of external rotation at 6 weeks was 15% (p < 0.001).
CONCLUSIONS:In patients who developed stiffness after surgery, a rotator cuff repair was more likely to heal.
LEVEL OF EVIDENCE:Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.
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