Electro- and Solar-Driven Fuel Synthesis with First Row Transition Metal Complexes.

The synthesis of renewable fuels from abundant water or the greenhouse gas CO2 is a major step toward creating sustainable and scalable energy storage technologies. In the last few decades, much attention has focused on the development of nonprecious metal-based catalysts and, in more recent years, their integration in solid-state support materials and devices that operate in water. This review surveys the literature on 3d metal-based molecular catalysts and focuses on their immobilization on heterogeneous solid-state supports for electro-, photo-, and photoelectrocatalytic synthesis of fuels in aqueous media. The first sections highlight benchmark homogeneous systems using proton and CO2 reducing 3d transition metal catalysts as well as commonly employed methods for catalyst immobilization, including a discussion of supporting materials and anchoring groups. The subsequent sections elaborate on productive associations between molecular catalysts and a wide range of substrates based on carbon, quantum dots, metal oxide surfaces, and semiconductors. The molecule-material hybrid systems are organized as "dark" cathodes, colloidal photocatalysts, and photocathodes, and their figures of merit are discussed alongside system stability and catalyst integrity. The final section extends the scope of this review to prospects and challenges in targeting catalysis beyond "classical" H2 evolution and CO2 reduction to C1 products, by summarizing cases for higher-value products from N2 reduction, C x>1 products from CO2 utilization, and other reductive organic transformations.Christian Doppler Research Association (Austrian Federal Ministry of Science, Research and Economy and National Foundation for Research, Technology and Development), the OMV Group, the Woolf Fisher Trust (New Zealand), the Cambridge Trust (University of Cambridge), the EPSRC (IAA Follow on Fund), the ERC Consolidator Grant “MatEnSAP” (GAN 682833) and a Blavatnik Fellowshi

The role of Zn-OR and Zn-OH nucleophiles and the influence of para-substituents in the reactions of binuclear phosphatase mimetics

Analogues of the ligand 2,2'-(2-hydroxy-5-methyl-1,3-phenylene)bis(methylene)bis((pyridin-2-ylmethyl)azanediyl)diethanol (CH(3)H(3)L1) are described. Complexation of these analogues, 2,6-bis(((2-methoxyethyl)(pyridin-2-ylmethyl)amino)methyl)-4-methylphenol (CH(3)HL2), 4-bromo-2,6-bis(((2-methoxyethyl)(pyridin-2-ylmethyl)amino)methyl)phenol (BrHL2), 2,6-bis(((2-methoxyethyl)(pyridin-2-ylmethyl)amino)methyl)-4-nitrophenol (NO(2)HL2) and 4-methyl-2,6-bis(((2-phenoxyethyl)(pyridin-2-ylmethyl)amino)methyl)phenol (CH(3)HL3) with zinc(II) acetate afforded [Zn-2(CH(3)L2)(CH3COO)(2)](PF6), [Zn-2(NO(2)L2)(CH3COO)(2)](PF6), [Zn-2(BrL2)(CH3COO)(2)](PF6) and [Zn-2(CH(3)L3)(CH3COO)(2)](PF6), in addition to [Zn-4(CH(3)L2)(2)(NO2C6H5OPO3)(2)(H2O)(2)](PF6)(2) and [Zn-4(BrL2)(2)(PO3F)(2)(H2O)(2)](PF6)(2). The complexes were characterized using H-1 and C-13 NMR spectroscopy, mass spectrometry, microanalysis, and X-ray crystallography. The complexes contain either a coordinated methyl-(L2 ligands) or phenyl-(L3 ligand) ether, replacing the potentially nucleophilic coordinated alcohol in the previously reported complex [Zn-2(CH(3)HL1)(CH3COO)(H2O)](PF6). Functional studies of the zinc complexes with the substrate bis(2,4-dinitrophenyl) phosphate (BDNPP) showed them to be competent catalysts with, for example, [Zn-2(CH(3)L2)](+), k(cat) = 5.70 +/- 0.04 x 10(-3) s(-1) (K-m = 20.8 +/- 5.0 mM) and [Zn-2(CH(3)L3)](+), kcat = 3.60 +/- 0.04 x 10(-3) s(-1) (K-m = 18.9 +/- 3.5 mM). Catalytically relevant pK(a)s of 6.7 and 7.7 were observed for the zinc(II) complexes of CH(3)L2(-) and CH(3)L3(-), respectively. Electron donating para-substituents enhance the rate of hydrolysis of BDNPP such that k(cat) p-CH3 > p-Br > p-NO2. Use of a solvent mixture containing H2O18/H2O16 in the reaction with BDNPP showed that for [Zn-2(CH(3)L2)(CH3COO)(2)](PF6) and [Zn-2(NO(2)L2)(CH3COO)(2)](PF6), as well as [Zn-2(CH(3)HL1)(CH3COO)(H2O)](PF6), the O-18 label was incorporated in the product of the hydrolysis suggesting that the nucleophile involved in the hydrolysis reaction was a Zn-OH moiety. The results are discussed with respect to the potential nucleophilic species (coordinated deprotonated alcohol versus coordinated hydroxide)

Diet, physical exercise and cognitive behavioral training as a combined workplace based intervention to reduce body weight and increase physical capacity in health care workers - a randomized controlled trial

<p>Abstract</p> <p>Background</p> <p>Health care workers comprise a high-risk workgroup with respect to deterioration and early retirement. There is high prevalence of obesity and many of the workers are overweight. Together, these factors play a significant role in the health-related problems within this sector. The present study evaluates the effects of the first 3-months of a cluster randomized controlled lifestyle intervention among health care workers. The intervention addresses body weight, general health variables, physical capacity and musculoskeletal pain.</p> <p>Methods</p> <p>98 female, overweight health care workers were cluster-randomized to an intervention group or a reference group. The intervention consisted of an individually dietary plan with an energy deficit of 1200 kcal/day (15 min/hour), strengthening exercises (15 min/hour) and cognitive behavioral training (30 min/hour) during working hours 1 hour/week. Leisure time aerobic fitness was planned for 2 hour/week. The reference group was offered monthly oral presentations. Body weight, BMI, body fat percentage (bioimpedance), waist circumference, blood pressure, musculoskeletal pain, maximal oxygen uptake (maximal bicycle test), and isometric maximal muscle strength of 3 body regions were measured before and after the intervention period.</p> <p>Results</p> <p>In an intention-to-treat analysis from pre to post tests, the intervention group significantly reduced body weight with 3.6 kg (p < 0.001), BMI from 30.5 to 29.2 (p < 0.001), body fat percentage from 40.9 to 39.3 (p < 0.001), waist circumference from 99.7 to 95.5 cm (p < 0.001) and blood pressure from 134/85 to 127/80 mmHg (p < 0.001), with significant difference between the intervention and control group (p < 0.001) on all measures. No effect of intervention was found in musculoskeletal pain, maximal oxygen uptake and muscle strength, but on aerobic fitness.</p> <p>Conclusion</p> <p>The significantly reduced body weight, body fat, waist circumference and blood pressure as well as increased aerobic fitness in the intervention group show the great potential of workplace health promotion among this high-risk workgroup. Long-term effects of the intervention remain to be investigated.</p> <p>Trial registration</p> <p>ClinicalTrials.gov: <a href="http://www.clinicaltrials.gov/ct2/show/NCT01015716">NCT01015716</a></p

Ligand modifications modulate the mechanism of binuclear phosphatase biomimetics

Complexation of dimethyl-6,6'-(2-hydroxy-5-methyl-1,3-phenylene)bis(methylene)bis((2-hydroxyethyl) azanediyl)bis(methylene)dipicolinate (Me(2)H(3)L4) and 2,2'-(2-hydroxy-5-methyl-1,3-phenylene)bis(meth ylene)bis(((6-methylpyridin-2-yl)methy)azanediyl)diethanol (H(3)L5) with Zn(II) afforded the complexes [Zn-2(H(2)L4)(H2O)(2)](ClO4) and [Zn-2(H(2)L5)(CH3CO2)(H2O)](PF6)(2)center dot 2H(2)O, which were characterized by H-1 and C-13 NMR spectroscopy, mass spectrometry, microanalysis, and the former by X-ray crystallography. Functional studies of the zinc complexes with the substrate bis(2,4-dinitrophenyl)phosphate (BDNPP) showed the complexes to be competent catalysts with k(cat) = 3.52 +/- 0.03 x 10(-4) and 1.27 +/- 0.04 x 10(-3) s(-1) (K-m = 6.7 +/- 0.9; 13.8 +/- 1.5 mM), with catalytically relevant pK(a)s of 9.4 and 6.6, respectively. The pK(a) values are discussed with respect to the potential nucleophilic species and the effect of the donor environment. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved

Selective Photocatalytic CO₂ Reduction in Water through Anchoring of a Molecular Ni Catalyst on CdS Nanocrystals

Photocatalytic conversion of CO₂ into carbonaceous feedstock chemicals is a promising strategy to mitigate greenhouse gas emissions and simultaneously store solar energy in chemical form. Photocatalysts for this transformation are typically based on precious metals and operate in nonaqueous solvents to suppress competing H₂ generation. In this work, we demonstrate selective visible-light-driven CO₂ reduction in water using a synthetic photocatalyst system that is entirely free of precious metals. We present a series of self-assembled nickel terpyridine complexes as electrocatalysts for the reduction of CO₂ to CO in organic media. Immobilization on CdS quantum dots allows these catalysts to be active in purely aqueous solution and photocatalytically reduce CO₂ with >90% selectivity under UV-filtered simulated solar light irradiation (AM 1.5G, 100 mW cm^–2, λ > 400 nm, pH 6.7, 25 °C). Correlation between catalyst immobilization efficiency and product selectivity shows that anchoring the molecular catalyst on the semiconductor surface is key in controlling the selectivity for CO₂ reduction over H₂ evolution in aqueous solution

Weakly Coupled Biologically Relevant Cu^II₂(μ‑η¹:η¹‑O₂) <i>cis</i>-Peroxo Adduct that Binds Side-On to Additional Metal Ions

The ability of many copper metalloenzymes to activate O₂ and transfer it to organic substrates has motivated extensive attention in the literature. Investigations focusing on synthetic analogues have provided a detailed understanding of the structures of potential intermediates, thereby helping to guide mechanistic studies. We report herein a crystallographically characterized synthetic Cu^II₂(μ-η¹:η¹-O₂) complex exhibiting <i>cis</i>-peroxo bonding geometry, known in iron chemistry but previously unobserved for copper. Detailed investigation by UV–vis, resonance Raman, and infrared spectroscopies provides evidence for a significantly diminished copper–oxygen interaction (ε ≈ 3000 M^–1 cm^–1, ν_Cu–O = 437 cm^–1, ν_O–O = 799 cm^–1) relative to those in known ’coupled’ Cu₂O₂ species, consistent with magnetic measurements which show that the peroxide mediates only weak antiferromagnetic coupling (−2<i>J</i> = 144 cm^–1). These characteristics are comparable with those of a computationally predicted transition state for O₂ binding to type 3 copper centers, providing experimental evidence for the proposed mechanism of O₂ activation and supporting the biological relevance of the Cu^II₂(μ-η¹:η¹-O₂) <i>cis</i>-species. The peroxide bonding arrangement also allows binding of sodium cations, observed both in the solid state and in solution. Binding induces changes on an electronic level, as monitored by UV–vis spectroscopy (<i>K</i>_a = 1700 M^–1), reminiscent of redox-inactive metal binding by iron–oxygen species. The results presented highlight the analogous chemistry these reactive oxygen species undergo, with respect to both their mechanism of formation, and the molecular interactions in which they participate

Weakly Coupled Biologically Relevant Cu^II₂(μ‑η¹:η¹‑O₂) <i>cis</i>-Peroxo Adduct that Binds Side-On to Additional Metal Ions

The ability of many copper metalloenzymes to activate O₂ and transfer it to organic substrates has motivated extensive attention in the literature. Investigations focusing on synthetic analogues have provided a detailed understanding of the structures of potential intermediates, thereby helping to guide mechanistic studies. We report herein a crystallographically characterized synthetic Cu^II₂(μ-η¹:η¹-O₂) complex exhibiting <i>cis</i>-peroxo bonding geometry, known in iron chemistry but previously unobserved for copper. Detailed investigation by UV–vis, resonance Raman, and infrared spectroscopies provides evidence for a significantly diminished copper–oxygen interaction (ε ≈ 3000 M^–1 cm^–1, ν_Cu–O = 437 cm^–1, ν_O–O = 799 cm^–1) relative to those in known ’coupled’ Cu₂O₂ species, consistent with magnetic measurements which show that the peroxide mediates only weak antiferromagnetic coupling (−2<i>J</i> = 144 cm^–1). These characteristics are comparable with those of a computationally predicted transition state for O₂ binding to type 3 copper centers, providing experimental evidence for the proposed mechanism of O₂ activation and supporting the biological relevance of the Cu^II₂(μ-η¹:η¹-O₂) <i>cis</i>-species. The peroxide bonding arrangement also allows binding of sodium cations, observed both in the solid state and in solution. Binding induces changes on an electronic level, as monitored by UV–vis spectroscopy (<i>K</i>_a = 1700 M^–1), reminiscent of redox-inactive metal binding by iron–oxygen species. The results presented highlight the analogous chemistry these reactive oxygen species undergo, with respect to both their mechanism of formation, and the molecular interactions in which they participate

Imidazolium-modification enhances photocatalytic CO2 reduction on ZnSe quantum dots.

Colloidal photocatalysts can utilize solar light for the conversion of CO2 to carbon-based fuels, but controlling the product selectivity for CO2 reduction remains challenging, in particular in aqueous solution. Here, we present an organic surface modification strategy to tune the product selectivity of colloidal ZnSe quantum dots (QDs) towards photocatalytic CO2 reduction even in the absence of transition metal co-catalysts. Besides H2, imidazolium-modified ZnSe QDs evolve up to 2.4 mmolCO gZnSe -1 (TONQD > 370) after 10 h of visible light irradiation (AM 1.5G, λ > 400 nm) in aqueous ascorbate solution with a CO-selectivity of up to 20%. This represents a four-fold increase in CO-formation yield and 13-fold increase in CO-selectivity compared to non-functionalized ZnSe QDs. The binding of the thiolated imidazolium ligand to the QD surface is characterized quantitatively using 1H-NMR spectroscopy and isothermal titration calorimetry, revealing that a subset of 12 to 17 ligands interacts strongly with the QDs. Transient absorption spectroscopy reveals an influence of the ligand on the intrinsic charge carrier dynamics through passivating Zn surface sites. Density functional theory calculations indicate that the imidazolium capping ligand plays a key role in stabilizing the surface-bound *CO2 - intermediate, increasing the yield and selectivity toward CO production. Overall, this work unveils a powerful tool of using organic capping ligands to modify the chemical environment on colloids, thus enabling control over the product selectivity within photocatalyzed CO2 reduction

Imidazolium-modification enhances photocatalytic CO₂ reduction on ZnSe quantum dots.

Colloidal photocatalysts can utilize solar light for the conversion of CO2 to carbon-based fuels, but controlling the product selectivity for CO2 reduction remains challenging, in particular in aqueous solution. Here, we present an organic surface modification strategy to tune the product selectivity of colloidal ZnSe quantum dots (QDs) towards photocatalytic CO2 reduction even in the absence of transition metal co-catalysts. Besides H2, imidazolium-modified ZnSe QDs evolve up to 2.4 mmolCO gZnSe -1 (TONQD > 370) after 10 h of visible light irradiation (AM 1.5G, λ > 400 nm) in aqueous ascorbate solution with a CO-selectivity of up to 20%. This represents a four-fold increase in CO-formation yield and 13-fold increase in CO-selectivity compared to non-functionalized ZnSe QDs. The binding of the thiolated imidazolium ligand to the QD surface is characterized quantitatively using 1H-NMR spectroscopy and isothermal titration calorimetry, revealing that a subset of 12 to 17 ligands interacts strongly with the QDs. Transient absorption spectroscopy reveals an influence of the ligand on the intrinsic charge carrier dynamics through passivating Zn surface sites. Density functional theory calculations indicate that the imidazolium capping ligand plays a key role in stabilizing the surface-bound *CO2 - intermediate, increasing the yield and selectivity toward CO production. Overall, this work unveils a powerful tool of using organic capping ligands to modify the chemical environment on colloids, thus enabling control over the product selectivity within photocatalyzed CO2 reduction

Weight loss among female health care workers- a 1-year workplace based randomized controlled trial in the FINALE-health study

<p>Abstract</p> <p>Background</p> <p>Weight management constitutes a substantial problem particularly among groups of low socio-economic status. Interventions at work places may be a solution, but high quality worksite interventions documenting prolonged weight loss are lacking. This paper presents results of an intervention aimed to achieve a 12 months weight loss among overweight health care workers.</p> <p>Methods</p> <p>Ninety-eight overweight female health care workers were randomized into an intervention or a reference group. The intervention consisted of diet, physical exercise and cognitive behavioral training during working hours 1 hour/week. The reference group was offered monthly oral presentations. Several anthropometric measures, blood pressure, cardiorespiratory fitness, maximal muscle strength, and musculoskeletal pain were measured before and after the 12-months intervention period. Data were analyzed by intention-to-treat analysis.</p> <p>Results</p> <p>The intervention group significantly reduced body weight by 6 kg (p < 0.001), BMI by 2.2 (p < 0.001) and body fat percentage by 2.8 (p < 0.001). There were no statistical reductions in the control group, resulting in significant differences between the two groups over time.</p> <p>Conclusions</p> <p>The intervention generated substantial reductions in body weight, BMI and body fat percentage among overweight female health care workers over 12 months. The positive results support the workplace as an efficient arena for weight loss among overweight females.</p> <p>Trial registration</p> <p>NCT01015716.</p