Pendant Hydrogen-Bond Donors in Cobalt Catalysts Independently Enhance CO_2 Reduction

The bioinspired incorporation of pendant proton donors into transition metal catalysts is a promising strategy for converting environmentally deleterious CO_2 to higher energy products. However, the mechanism of proton transfer in these systems is poorly understood. Herein, we present a series of cobalt complexes with varying pendant secondary and tertiary amines in the ligand framework with the aim of disentangling the roles of the first and second coordination spheres in CO_2 reduction catalysis. Electrochemical and kinetic studies indicate that the rate of catalysis shows a first-order dependence on acid, CO_2, and the number of pendant secondary amines, respectively. Density functional theory studies explain the experimentally observed trends and indicate that pendant secondary amines do not directly transfer protons to CO_2, but instead bind acid molecules from solution. Taken together, these results suggest a mechanism in which noncooperative pendant amines facilitate a hydrogen-bonding network that enables direct proton transfer from acid to the activated CO_2 substrate

Electronically Modified Cobalt Aminopyridine Complexes Reveal an Orthogonal Axis for Catalytic Optimization for CO₂ Reduction

The design of effective electrocatalysts for carbon dioxide reduction requires understanding the mechanistic underpinnings governing the binding, reduction, and protonation of CO₂. A critical aspect to understanding and tuning these factors for optimal catalysis revolves around controlling the electronic environments of the primary and secondary coordination sphere. Herein we report a series of para-substituted cobalt aminopyridine macrocyclic catalysts 2–4 capable of carrying out the electrochemical reduction of CO₂ to CO. Under catalytic conditions, complexes 2–4, as well as the unsubstituted cobalt aminopyridine complex 1, exhibit i_(cat)/i_p values ranging from 144 to 781. Complexes 2 and 4 exhibit a pronounced precatalytic wave suggestive of an ECEC mechanism. A Hammett analysis reveals that ligand modifications with electron-donating groups enhance catalysis (ρ < 0), indicative of positive charge buildup in the transition state. This trend also extends to the Co^(I/0) potential, where complexes possessing more negative E(CoI/0) reductions exhibit greater i_(cat)/i_p values. The reported modifications offer a synthetic lever to tune catalytic activity, orthogonal to our previous study of the role of pendant hydrogen bond donors

Proton-Assisted Reduction of CO_2 by Cobalt Aminopyridine Macrocycles

We report here the efficient reduction of CO_2 to CO by cobalt aminopyridine macrocycles. The effect of the pendant amines on catalysis was investigated. Several cobalt complexes based on the azacalix[4](2,6)pyridine framework with different substitutions on the pendant amine groups have been synthesized (R = H (1), Me (2), and allyl (3)), and their electrocatalytic properties were explored. Under an atmosphere of CO_2 and in the presence of weak Brønsted acids, large catalytic currents are observed for 1, corresponding to the reduction of CO_2 to CO with excellent Faradaic efficiency (98 ± 2%). In comparison, complexes 2 and 3 generate CO with TONs at least 300 times lower than 1, suggesting that the presence of the pendant NH moiety of the secondary amine is crucial for catalysis. Moreover, the presence of NH groups leads to a positive shift in the reduction potential of the Co^(I/0) couple, therefore decreasing the overpotential for CO_2 reduction

Pendant Hydrogen-Bond Donors in Cobalt Catalysts Independently Enhance CO_2 Reduction

The bioinspired incorporation of pendant proton donors into transition metal catalysts is a promising strategy for converting environmentally deleterious CO_2 to higher energy products. However, the mechanism of proton transfer in these systems is poorly understood. Herein, we present a series of cobalt complexes with varying pendant secondary and tertiary amines in the ligand framework with the aim of disentangling the roles of the first and second coordination spheres in CO_2 reduction catalysis. Electrochemical and kinetic studies indicate that the rate of catalysis shows a first-order dependence on acid, CO_2, and the number of pendant secondary amines, respectively. Density functional theory studies explain the experimentally observed trends and indicate that pendant secondary amines do not directly transfer protons to CO_2, but instead bind acid molecules from solution. Taken together, these results suggest a mechanism in which noncooperative pendant amines facilitate a hydrogen-bonding network that enables direct proton transfer from acid to the activated CO_2 substrate

Women’s access to and control over land in the current land administration system in two rural kebeles in Ada’a Woreda of Oromia Region

The study is designed to explore the status of rural women in access to and control over land in the current land administration system in two rural Kebeles in East Shewa Zone Ada’a Woreda of Oromia region on smallholder farmers’ landholding registration. The Ormia National Regional State Rural Land Administration and Use Proclamation and its implementation procedure are examined from a gender perspective in terms of ensuring rural women’s land holding rights and control they have over land. Historical overview on the land question in Ethiopia revealed that tenure systems evolved through historical periods. Land remained under men’s control throughout history and men’s control over land was strengthened by the rural land reform carried out by the Derg. This tenure reform applied rural land distribution using households as unit for rural land allocation and women were disadvantaged as most rural households were headed by men. The Oromia rural land proclamation is not discriminatory on basis of sex. However, policy gaps are evident in addressing women specific issues such as issues of FHHs and women under polygamous marriages. Gaps also exist between policy and implementation. Customary laws and practices have serious impacts on women’s land rights at the level of implementation. The research applied both quantitative and qualitative methods in view of feminist research methodology to properly address issues from a gender perspective. Survey of 318 households was conducted administering questionnaires in the quantitative method. The qualitative method applied was interviews with relevant Woreda office and Kebele LACs, focus group discussions with rural women, case stories and observation. Triangulation method is applied in data collection, data presentation and in analysis of findings. Study findings reveal that women’s access rights to land is less equal than legally provided. This study evidences gaps between policy and implementation. Customary laws and traditional practices generally have impacts on land access rights of single/unmarried, divorced, widowed women and on access rights of women in polygamous marriages. Women’s control over land is not efficiently addressed by the regional rural land policy. This is a significant policy drawback as women’s equal rights on land could not be achieved without gaining control over land. The land administration system in general and the land registration process in particular has not considered women’s participation in community activities and decision-making. Women are not represented in LACs and Sub-Committees in both Kebeles. Study findings indicate absence of autonomous institution as gap in addressing women’s issues in the land administration system. This study also revealed loose linkages between the rural land policy and other regional legislations like the regional family law which provides women’s equal rights on land in marriage and on its abandonment. This study forwards recommendation to address gender gaps identified to ensure women’s equal access to and control over land in the study area. The Oromia rural land proclamation needs revision from a gender perspective to address women’s specific issues and the land administration system should consider women’s participation in the process, their contribution to the system as well as their equal benefits from policy outcomes

Each to their own: skeletal muscles of different function use different biochemical strategies during aestivation at high temperature

Preservation of muscle morphology depends on a continuing regulatory balance between molecules that protect and molecules that damage muscle structural integrity. Excessive disruption of the biochemical balance that favours reactive oxygen species (ROS) in disused muscles may lead to oxidative stress, which in turn is associated with increased atrophic or apoptotic signalling and/or oxidative damage to the muscle and thus muscle disuse atrophy. Increases in the rate of oxygen consumption likely increase the overall generation of ROS in vivo. Temperature-induced increases in oxygen consumption rate occur in some muscles of ectotherms undergoing prolonged muscular disuse during aestivation. In the green-striped burrowing frog, Cyclorana alboguttata, both large jumping and small non-jumping muscles undergo atrophy seemingly commensurate with their rate of oxygen consumption during aestivation. However, because the extent of atrophy in these muscles is not enhanced at higher temperatures, despite a temperature-sensitive rate of oxygen consumption in the jumping muscle, we proposed that muscles are protected by biochemical means that, when mobilised at higher temperatures, inhibit atrophy. We proposed that the biochemical response to temperature would be muscle-specific. We examined the effect of temperature on the antioxidant and heat shock protein systems and determined the extent of oxidative damage to lipids and proteins in two functionally different skeletal muscles, the gastrocnemius (jumping muscle) and the iliofibularis (non-jumping muscle), by aestivating frogs at 24 and 30 degrees C for 6. months. We assayed small molecule antioxidant capacity, mitochondrial and cytosolic superoxide dismutase activities and Hsp70 concentrations to show that protective mechanisms in disused muscles are differentially regulated with respect to both temperature and aestivation. High aestivation temperature results in an antioxidant response in the metabolically temperature-sensitive jumping muscle. We assayed lipid peroxidation and protein oxidation to show that oxidative damage is apparent during aestivation and its pattern is muscle-specific, but unaffected by temperature. Consideration is given to how the complex responses of muscle biochemistry inform the different strategies muscles may use in regulating their oxidative environment during extended disuse and disuse at high temperature

Pendant Hydrogen-Bond Donors in Cobalt Catalysts Independently Enhance CO₂ Reduction

The bioinspired incorporation of pendant proton donors into transition metal catalysts is a promising strategy for converting environmentally deleterious CO₂ to higher energy products. However, the mechanism of proton transfer in these systems is poorly understood. Herein, we present a series of cobalt complexes with varying pendant secondary and tertiary amines in the ligand framework with the aim of disentangling the roles of the first and second coordination spheres in CO₂ reduction catalysis. Electrochemical and kinetic studies indicate that the rate of catalysis shows a first-order dependence on acid, CO₂, and the number of pendant secondary amines, respectively. Density functional theory studies explain the experimentally observed trends and indicate that pendant secondary amines do not directly transfer protons to CO₂, but instead bind acid molecules from solution. Taken together, these results suggest a mechanism in which noncooperative pendant amines facilitate a hydrogen-bonding network that enables direct proton transfer from acid to the activated CO₂ substrate

Proton-Assisted Reduction of CO₂ by Cobalt Aminopyridine Macrocycles

We report here the efficient reduction of CO₂ to CO by cobalt aminopyridine macrocycles. The effect of the pendant amines on catalysis was investigated. Several cobalt complexes based on the azacalix[4]­(2,6)­pyridine framework with different substitutions on the pendant amine groups have been synthesized (R = H (<b>1</b>), Me (<b>2</b>), and allyl (<b>3</b>)), and their electrocatalytic properties were explored. Under an atmosphere of CO₂ and in the presence of weak Brønsted acids, large catalytic currents are observed for <b>1</b>, corresponding to the reduction of CO₂ to CO with excellent Faradaic efficiency (98 ± 2%). In comparison, complexes <b>2</b> and <b>3</b> generate CO with TONs at least 300 times lower than <b>1</b>, suggesting that the presence of the pendant NH moiety of the secondary amine is crucial for catalysis. Moreover, the presence of NH groups leads to a positive shift in the reduction potential of the Co^I/0 couple, therefore decreasing the overpotential for CO₂ reduction

Pendant Hydrogen-Bond Donors in Cobalt Catalysts Independently Enhance CO₂ Reduction

The bioinspired incorporation of pendant proton donors into transition metal catalysts is a promising strategy for converting environmentally deleterious CO₂ to higher energy products. However, the mechanism of proton transfer in these systems is poorly understood. Herein, we present a series of cobalt complexes with varying pendant secondary and tertiary amines in the ligand framework with the aim of disentangling the roles of the first and second coordination spheres in CO₂ reduction catalysis. Electrochemical and kinetic studies indicate that the rate of catalysis shows a first-order dependence on acid, CO₂, and the number of pendant secondary amines, respectively. Density functional theory studies explain the experimentally observed trends and indicate that pendant secondary amines do not directly transfer protons to CO₂, but instead bind acid molecules from solution. Taken together, these results suggest a mechanism in which noncooperative pendant amines facilitate a hydrogen-bonding network that enables direct proton transfer from acid to the activated CO₂ substrate

Pendant Hydrogen-Bond Donors in Cobalt Catalysts Independently Enhance CO₂ Reduction

The bioinspired incorporation of pendant proton donors into transition metal catalysts is a promising strategy for converting environmentally deleterious CO₂ to higher energy products. However, the mechanism of proton transfer in these systems is poorly understood. Herein, we present a series of cobalt complexes with varying pendant secondary and tertiary amines in the ligand framework with the aim of disentangling the roles of the first and second coordination spheres in CO₂ reduction catalysis. Electrochemical and kinetic studies indicate that the rate of catalysis shows a first-order dependence on acid, CO₂, and the number of pendant secondary amines, respectively. Density functional theory studies explain the experimentally observed trends and indicate that pendant secondary amines do not directly transfer protons to CO₂, but instead bind acid molecules from solution. Taken together, these results suggest a mechanism in which noncooperative pendant amines facilitate a hydrogen-bonding network that enables direct proton transfer from acid to the activated CO₂ substrate