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1.
J Vet Med Educ ; 50(2): 205-216, 2023 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-35385371

RESUMO

Rotations in diverse, marginalized communities may offer health care students opportunities to develop cultural humility through different clinical experiences and activities. Through the actualization of cultural humility, veterinarians may offer accessible, affordable, culturally proficient, high-quality care to all their patients with a better understanding of how cultural differences affect the animal patient's health, well-being, and care. The purpose of this study was to explore whether participation in a community rotation in remote northern Indigenous communities promotes cultural humility among final-year veterinary students. Small groups of University of Calgary veterinary students travel annually to the Sahtu Settlement Area of the Northwest Territories, Canada, to participate in the Northern Community Health Rotation (NCHR). During the 4-week rotation, students spend 2.5 weeks providing veterinary services to domestic animals in five communities in the Sahtu. Eleven veterinary students who attended the NCHR between 2015 and 2020 answered exploratory open-ended questions in an online survey. Responses highlight areas of learning that contributed to their development of cultural humility. The rotation appears successful in increasing students' confidence working with people from diverse cultures, offering students opportunities to implement a client-centered approach, and advancing their capacity to recognize and challenge their preconceived biases about Indigenous cultures and animal ownership. These experiences are important to the acquisition of cultural humility for veterinary care providers.


Assuntos
Educação em Veterinária , Saúde Pública , Animais , Humanos , Saúde Pública/educação , Competência Cultural/educação , Estudantes , Aprendizagem
2.
Exp Astron (Dordr) ; 51(3): 1427-1440, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-34720416

RESUMO

Since 2015 the gravitational-wave observations of LIGO and Virgo have transformed our understanding of compact-object binaries. In the years to come, ground-based gravitational-wave observatories such as LIGO, Virgo, and their successors will increase in sensitivity, discovering thousands of stellar-mass binaries. In the 2030s, the space-based LISA will provide gravitational-wave observations of massive black holes binaries. Between the ∼ 10 -103 Hz band of ground-based observatories and the ∼ 1 0 - 4 -10- 1 Hz band of LISA lies the uncharted decihertz gravitational-wave band. We propose a Decihertz Observatory to study this frequency range, and to complement observations made by other detectors. Decihertz observatories are well suited to observation of intermediate-mass ( ∼ 1 0 2 -104 M ⊙) black holes; they will be able to detect stellar-mass binaries days to years before they merge, providing early warning of nearby binary neutron star mergers and measurements of the eccentricity of binary black holes, and they will enable new tests of general relativity and the Standard Model of particle physics. Here we summarise how a Decihertz Observatory could provide unique insights into how black holes form and evolve across cosmic time, improve prospects for both multimessenger astronomy and multiband gravitational-wave astronomy, and enable new probes of gravity, particle physics and cosmology.

3.
J Vet Med Educ ; 48(4): 477-484, 2021 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-33433304

RESUMO

To promote accessible veterinary care in the community and to help students refine their communication skills, the University of Calgary, Faculty of Veterinary Medicine (UCVM) partnered with the Calgary Urban Project Society (CUPS), a human services organization, to develop the UCVM-CUPS Pet Health Clinics. These clinics are a service-learning experience where third-year students provide services to those facing barriers to veterinary care in Calgary, Alberta. The clinics are offered at CUPS for 6 weeks at 1 day per week. Each student participates in one 4-hour lab; running two 90-minute appointments. In this mixed-methods article, the question was asked: How does a communication-based veterinary service learning program impact students' perception and knowledge of their skills and their perceived role in community outreach to underserved populations and their animals? All third-year veterinary students (N = 30) participated in the 2018 UCVM-CUPS Pet Health Clinics. Students completed a demographics survey, and a pre- and post-clinic questionnaire. Statistical analysis was used to compare pre- and post-clinic responses, and to determine relationships between questionnaire responses and the demographics survey data. Students were significantly more in agreement with statements that demonstrated confidence in their medical knowledge, technical abilities, and communication skills after participating in the program. There was significantly more disagreement to continue volunteering after graduation, but many planned on providing community outreach. Overall, students felt a strong sense of social responsibility and were motivated to help underserved populations. The findings suggest that communication-based, service-learning experiences are related to greater social awareness and enhance students' clinical skills including communication.


Assuntos
Educação em Veterinária , Animais , Competência Clínica , Currículo , Humanos , Aprendizagem , Estudantes
4.
Angew Chem Int Ed Engl ; 59(32): 13586-13590, 2020 Aug 03.
Artigo em Inglês | MEDLINE | ID: mdl-32392392

RESUMO

Homoleptic σ-bonded uranium-alkyl complexes have been a synthetic target since the Manhattan Project. The current study describes the synthesis and characterization of several unprecedented uranium-methyl complexes. Amongst these complexes, the first example of a homoleptic uranium-alkyl dimer, [Li(THF)4 ]2 [U2 (CH3 )10 ], as well as a seven-coordinate uranium-methyl monomer, {Li(OEt2 )Li(OEt2 )2 UMe7 Li}n were both crystallographically identified. The diversity of complexes reported herein provides critical insight into the structural diversity, electronic structure and bonding in uranium-alkyl chemistry.

5.
J Am Chem Soc ; 141(31): 12338-12345, 2019 08 07.
Artigo em Inglês | MEDLINE | ID: mdl-31304750

RESUMO

While iron-catalyzed C-H activation offers an attractive reaction methodology for organic transformations, the lack of molecular-level insight into the in situ formed and reactive iron species impedes continued reaction development. Herein, freeze-trapped 57Fe Mössbauer spectroscopy and single-crystal X-ray crystallography combined with reactivity studies are employed to define the key cyclometalated iron species active in triazole-assisted iron-catalyzed C-H activation. These studies provide the first direct experimental definition of an activated intermediate, which has been identified as the low-spin iron(II) complex [(sub-A)(dppbz)(THF)Fe]2(µ-MgX2), where sub-A is a deprotonated benzamide substrate. Reaction of this activated intermediate with additional diarylzinc leads to the formation of a cyclometalated iron(II)-aryl species, which upon reaction with oxidant, generates C-H arylated product at a catalytically relevant rate. Furthermore, pseudo-single-turnover reactions between catalytically relevant iron intermediates and excess nucleophile identify transmetalation as rate-determining, whereas C-H activation is shown to be facile under the reaction conditions.

6.
Inorg Chem ; 57(15): 9544-9553, 2018 Aug 06.
Artigo em Inglês | MEDLINE | ID: mdl-30040391

RESUMO

Treatment of both [CoCl( tBuPNP)] and [NiCl( tBuPNP)] ( tBuPNP = anion of 2,5-bis((di- tert-butylphosphino)methyl)pyrrole) with one equivalent of benzoquinone affords the corresponding chloride complexes containing a dehydrogenated PNP ligand, tBudPNP ( tBudPNP = anion of 2,5-bis((di- tert-butylphosphino)methylene)-2,5-dihydropyrrole). Dehydrogenation of PNP to dPNP results in minimal change to steric profile of the ligand but has important consequences for the resulting redox potentials of the metal complexes, resulting in the ability to isolate both [CoH( tBudPNP)] and [CoEt( tBudPNP)], which are more challenging (hydride) or not possible (ethyl) to prepare with the parent PNP ligand. Electrochemical measurements with both the Co and Ni dPNP species demonstrate a substantial shift in redox potentials for both the M(II/III) and M(II/I) couples. In the case of the former, oxidation to trivalent Co was found to be reversible, and subsequent reaction with AgSbF6 afforded a rare example of a square-planar Co(III) species. Corresponding reduction of [CoCl( tBudPNP)] with KC8 produced the diamagnetic Co(I) species, [Co(N2)( tBudPNP)]. Further reduction of the Co(I) complex was found to generate a pincer-based π-radical anion that demonstrated well-resolved EPR features to the four hydrogen atoms and lone nitrogen atom of the ligand with minor contributions from cobalt and coordinated N2. Changes in the electronic character of the PNP ligand upon dehydrogenation are proposed to result from loss of aromaticity in the pyrrole ligand, resulting in a more reducing central amido donor. DFT calculations on the Co(II) complexes were performed to shed further insight into the electronic structure of the pincer complexes.

7.
Living Rev Relativ ; 21(1): 2, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-29674941

RESUMO

Euclid is a European Space Agency medium-class mission selected for launch in 2020 within the cosmic vision 2015-2025 program. The main goal of Euclid is to understand the origin of the accelerated expansion of the universe. Euclid will explore the expansion history of the universe and the evolution of cosmic structures by measuring shapes and red-shifts of galaxies as well as the distribution of clusters of galaxies over a large fraction of the sky. Although the main driver for Euclid is the nature of dark energy, Euclid science covers a vast range of topics, from cosmology to galaxy evolution to planetary research. In this review we focus on cosmology and fundamental physics, with a strong emphasis on science beyond the current standard models. We discuss five broad topics: dark energy and modified gravity, dark matter, initial conditions, basic assumptions and questions of methodology in the data analysis. This review has been planned and carried out within Euclid's Theory Working Group and is meant to provide a guide to the scientific themes that will underlie the activity of the group during the preparation of the Euclid mission.

8.
Can Vet J ; 59(6): 668-672, 2018 06.
Artigo em Inglês | MEDLINE | ID: mdl-29910484

RESUMO

We reflect on our experiences providing veterinary services in 5 remote communities of the Sahtu Settlement Area in the Northwest Territories in February 2017. The evolving role of dogs and the social determinants of health that influence dog health in the communities are explored, including biology, physical environment, behavior, dog and human social factors, and access to veterinary care. The importance of continued exposure of veterinary professionals to different cultural perspectives in order to provide services that are culturally appropriate and effective is highlighted.


Vétérinaires du Nord : perspectives sur le rôle des vétérinaires en santé communautaire dans les collectivités du Nord. Nous examinons nos expériences lors de la prestation, en février 2017, de services vétérinaires dans cinq collectivités éloignées dans la région désignée du Sahtu des Territoires du Nord-Ouest. Nous explorons le rôle changeant des chiens et les déterminants sociaux de la santé qui influencent la santé canine dans les collectivités, notamment la biologie, le milieu physique, le comportement, les facteurs sociaux des chiens et des humains et l'accès aux soins vétérinaires. Nous soulignons l'importance de l'exposition continue des professionnels vétérinaires aux différentes perspectives culturelles afin de fournir des services qui sont efficaces et appropriés sur le plan culturel.(Traduit par Isabelle Vallières).


Assuntos
Cães , Médicos Veterinários , Animais , Educação em Veterinária , Conhecimentos, Atitudes e Prática em Saúde , Humanos , Indígenas Norte-Americanos , Territórios do Noroeste , Papel Profissional , Saúde Pública , População Rural , Estudantes , Medicina Veterinária/métodos
9.
Angew Chem Int Ed Engl ; 57(22): 6496-6500, 2018 05 28.
Artigo em Inglês | MEDLINE | ID: mdl-29624838

RESUMO

The use of N-methylpyrrolidone (NMP) as a co-solvent in ferric salt catalyzed cross-coupling reactions is crucial for achieving the highly selective, preparative scale formation of cross-coupled product in reactions utilizing alkyl Grignard reagents. Despite the critical importance of NMP, the molecular level effect of NMP on in situ formed and reactive iron species that enables effective catalysis remains undefined. Herein, we report the isolation and characterization of a novel trimethyliron(II) ferrate species, [Mg(NMP)6 ][FeMe3 ]2 (1), which forms as the major iron species in situ in reactions of Fe(acac)3 and MeMgBr under catalytically relevant conditions where NMP is employed as a co-solvent. Importantly, combined GC analysis and 57 Fe Mössbauer spectroscopic studies identified 1 as a highly reactive iron species for the selective formation generating cross-coupled product. These studies demonstrate that NMP does not directly interact with iron as a ligand in catalysis but, alternatively, interacts with the magnesium cations to preferentially stabilize the formation of 1 over [Fe8 Me12 ]- cluster generation, which occurs in the absence of NMP.


Assuntos
Brometos/química , Compostos Férricos/síntese química , Ferro/química , Compostos de Magnésio/química , Compostos Organometálicos/síntese química , Pirrolidinonas/química , Catálise , Compostos Férricos/química , Modelos Moleculares , Estrutura Molecular , Compostos Organometálicos/química , Sais/síntese química , Sais/química
10.
Inorg Chem ; 56(19): 11721-11728, 2017 Oct 02.
Artigo em Inglês | MEDLINE | ID: mdl-28898098

RESUMO

A combination of XAS, UV-vis, NMR, and EPR was used to examine the binding of a series of α-hydroxythiones to CoCA. All three appear to bind preferentially in their neutral, protonated forms. Two of the three clearly bind in a monodentate fashion, through the thione sulfur alone. Thiomaltol (TM) appears to show some orientational preference, on the basis of the NMR, while it appears that thiopyromeconic acid (TPMA) retains rotational freedom. In contrast, allothiomaltol (ATM), after initially binding in its neutral form, presumably through the thione sulfur, forms a final complex that is five-coordinate via bidentate coordination of ATM. On the basis of optical titrations, we speculate that this may be due to the lower initial pKa of ATM (8.3) relative to those of TM (9.0) and TPMA (9.5). Binding through the thione is shown to reduce the hydroxyl pKa by ∼0.7 pH unit on metal binding, bringing only ATM's pKa close to the pH of the experiment, facilitating deprotonation and subsequent coordination of the hydroxyl. The data predict the presence of a solvent-exchangeable proton on TM and TPMA, and Q-band 2-pulse ESEEM experiments on CoCA + TM suggest that the proton is present. ESE-detected EPR also showed a surprising frequency dependence, giving only a subset of the expected resonances at X-band.

11.
Living Rev Relativ ; 16(1): 6, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-29142500

RESUMO

Euclid is a European Space Agency medium-class mission selected for launch in 2019 within the Cosmic Vision 2015-2025 program. The main goal of Euclid is to understand the origin of the accelerated expansion of the universe. Euclid will explore the expansion history of the universe and the evolution of cosmic structures by measuring shapes and red-shifts of galaxies as well as the distribution of clusters of galaxies over a large fraction of the sky. Although the main driver for Euclid is the nature of dark energy, Euclid science covers a vast range of topics, from cosmology to galaxy evolution to planetary research. In this review we focus on cosmology and fundamental physics, with a strong emphasis on science beyond the current standard models. We discuss five broad topics: dark energy and modified gravity, dark matter, initial conditions, basic assumptions and questions of methodology in the data analysis. This review has been planned and carried out within Euclid's Theory Working Group and is meant to provide a guide to the scientific themes that will underlie the activity of the group during the preparation of the Euclid mission.

12.
Prev Vet Med ; 196: 105471, 2021 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-34509773

RESUMO

Access to veterinary services can have positive impacts on animal health and welfare, and on human mental and physical health and well-being; however, many communities worldwide lack access to such services. At their request, the 5 communities of the Sahtu Settlement Area, Northwest Territories, Canada, have received annual access to preventive veterinary services through the University of Calgary's Northern Community Health Rotation since 2008. To determine the reach of the program, we conducted a dog census in 2017. We then conducted a chart review of 11 years of dog medical records from 2008 to 2018 to evaluate how the reach of the program, the uptake of veterinary services, and dog population demographics, health and welfare measures changed over the duration of the program. In the chart review, we used either multi-level logistic regression or generalized linear models, to determine how seven variables, including age, sex, breed, body condition, deworming, vaccination, and sterilization status upon clinic entry, changed over the course of program delivery. Our results suggest that program reach, veterinary service uptake, and dog demographic, health and welfare measures improved over time. We observed high rabies vaccination coverage in some communities (48 %-83 % of the dog population) and moderate overall sterilization status (25 %-56 % of the dog population) with female dog sterilization more common than male (75 % of dogs leaving the 2017 clinics, compared to 43 %). Several dog demographic, health, and welfare measures, including age, body condition, and vaccination, deworming, and sterilization status, were significantly better in later years of the program (all p < 0.001). Differences among communities, both in dog population numbers from the 2017 census (40-89 dogs) and in the uptake of veterinary services in 2017 (48 %-83 % of the dog population), were notable. Vaccination uptake was directly related to clinic attendance, but sterilization was impacted by additional factors, including community members' acceptance of the procedure. Some unintended consequences were noted, however, including the potential effect of sterilization on the availability of traditional dog breeds in the communities. Overall, our study findings demonstrate that subsidized veterinary services provided over a regular and extended period of time benefit animal population demographics, health and welfare, and could have positive impacts on human well-being. The framework of community collaboration and long-term commitment developed through this program serves as a model for achieving common health goals among communities in need and veterinary service providers.


Assuntos
Bem-Estar do Animal , Doenças do Cão , Vacinação , Medicina Veterinária/economia , Animais , Doenças do Cão/prevenção & controle , Cães , Feminino , Masculino , Territórios do Noroeste , Saúde Pública , Raiva/prevenção & controle , Raiva/veterinária , Vacina Antirrábica/economia , Vacinação/economia , Vacinação/veterinária
13.
Chem Sci ; 12(27): 9398-9407, 2021 Jul 14.
Artigo em Inglês | MEDLINE | ID: mdl-34349913

RESUMO

Synthetic methods that utilise iron to facilitate C-H bond activation to yield new C-C and C-heteroatom bonds continue to attract significant interest. However, the development of these systems is still hampered by a limited molecular-level understanding of the key iron intermediates and reaction pathways that enable selective product formation. While recent studies have established the mechanism for iron-catalysed C-H arylation from aryl-nucleophiles, the underlying mechanistic pathway of iron-catalysed C-H activation/functionalisation systems which utilise electrophiles to establish C-C and C-heteroatom bonds has not been determined. The present study focuses on an iron-catalysed C-H allylation system, which utilises allyl chlorides as electrophiles to establish a C-allyl bond. Freeze-trapped inorganic spectroscopic methods (57Fe Mössbauer, EPR, and MCD) are combined with correlated reaction studies and kinetic analyses to reveal a unique and rapid reaction pathway by which the allyl electrophile reacts with a C-H activated iron intermediate. Supporting computational analysis defines this novel reaction coordinate as an inner-sphere radical process which features a partial iron-bisphosphine dissociation. Highlighting the role of the bisphosphine in this reaction pathway, a complementary study performed on the reaction of allyl electrophile with an analogous C-H activated intermediate bearing a more rigid bisphosphine ligand exhibits stifled yield and selectivity towards allylated product. An additional spectroscopic analysis of an iron-catalysed C-H amination system, which incorporates N-chloromorpholine as the C-N bond-forming electrophile, reveals a rapid reaction of electrophile with an analogous C-H activated iron intermediate consistent with the inner-sphere radical process defined for the C-H allylation system, demonstrating the prevalence of this novel reaction coordinate in this sub-class of iron-catalysed C-H functionalisation systems. Overall, these results provide a critical mechanistic foundation for the rational design and development of improved systems that are efficient, selective, and useful across a broad range of C-H functionalisations.

14.
Prev Vet Med ; 181: 105061, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32599372

RESUMO

Access to veterinary services in marginalized communities has important implications for people and animals around the world. Subsidized veterinary services are occasionally provided, however, they are seldom evaluated for their value to stakeholders and overall animal health. In 2017, we evaluated a decade-long veterinary program in four remote communities in the Sahtu Settlement Area of the Northwest Territories, Canada to understand if there were changes in dog husbandry and community perceptions of, and experiences with, dogs since an initial assessment at the beginning of the program in 2008. Using questionnaires and a dog census, we found a significant increase over time in dog health indicators, including the proportion of dogs that had received preventive veterinary care and had been sterilized. We documented significant changes in the described purpose of dogs, husbandry practices, experiences with dogs, and attitudes towards dogs and veterinary services. In 2017, respondents commonly described their dog(s) as companions and as part of their family. However, communities differed in the way dogs were housed and fed and in their attitudes towards dogs and dog-related issues. These inter-community differences are noteworthy as they impact service provision, uptake, and evaluation and must be taken into consideration in order to develop effective programs. Regular program evaluations are critical to check in with stakeholders, to ensure the program is meeting community needs, and to optimize effective use of resources.


Assuntos
Criação de Animais Domésticos/estatística & dados numéricos , Medicina Preventiva/estatística & dados numéricos , Avaliação de Programas e Projetos de Saúde/estatística & dados numéricos , Medicina Veterinária/estatística & dados numéricos , Bem-Estar do Animal , Animais , Cães , Territórios do Noroeste , População Rural , Estações do Ano
15.
Prev Vet Med ; 157: 59-69, 2018 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-30086850

RESUMO

The World Health Organization (WHO) and the World Organization for Animal Health (OIE) both recognize the importance of veterinary services in controlling zoonotic diseases, in preventing human injury, and in protecting the welfare of non-human animals. Furthermore, both organizations recommend regular evaluations of veterinary programs. Accordingly, we conducted a scoping review to collate the available peer-reviewed evaluations of subsidized small animal veterinary services in terms of the effects on animal and public health. We summarized the evaluation methods used, identified key journals in this disparate literature, and identified gaps in knowledge. CAB Abstracts, PubMed, and Scopus were searched, yielding 1441 records published between 2009 and 2016 for initial screening. After examining titles and keywords, abstracts, and finally full articles, we identified 32 relevant papers that evaluated 27 distinct programs. The global distribution was broad, with half of the papers evaluating programs in Africa or Asia, all of which were rabies vaccination programs targeting dogs. Three program evaluation categories were identified: zoonotic disease prevention (9 papers), animal welfare and control (9 papers), and One Health promotion (14 papers). Nearly three-quarters (72%) of the papers used more than one method for collecting data. The most common data sources were questionnaires (22 papers) and administrative records, such as medical charts (21 papers). The most common indicators used for animal health-related program assessments were the number of animals reached by the program (27 papers) and any changes in animal population demographics (22 papers). These indicators were found in all three types of program evaluations (i.e., zoonotic disease prevention, animal welfare/control, and One Health promotion). For public health-related program assessments, the most common indicators consisted of determining barriers to a veterinary program's success (13 papers), followed by costs of a program (11 papers), changes in perceived threats or nuisances (11 papers), and community knowledge of a zoonotic disease (11 papers). The small number of papers identified in this review, n = 32, underscores that comprehensive evaluations of subsidized veterinary services are uncommon in the peer-reviewed literature. Yet, when performed, such evaluations can help guide program delivery and future research. Given the high stakes and the high costs of subsidized veterinary services, greater efforts in program evaluation are warranted.


Assuntos
Bem-Estar do Animal , Saúde Global , Avaliação de Programas e Projetos de Saúde , Medicina Veterinária , Zoonoses/prevenção & controle , Animais , Humanos , Saúde Pública , Medicina Veterinária/economia , Medicina Veterinária/normas
16.
Chem Sci ; 9(41): 7931-7939, 2018 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-30429998

RESUMO

The first direct syntheses, structural characterizations, and reactivity studies of iron-phenyl species formed upon reaction of Fe(acac)3 and PhMgBr in THF are presented. Reaction of Fe(acac)3 with 4 equiv. PhMgBr in THF leads to the formation of [FePh2(µ-Ph)]2 2- at -80 °C, which can be stabilized through the addition of N-methylpyrrolidone. Alternatively, at -30 °C this reaction leads to the formation of the tetranuclear iron-phenyl cluster, Fe4(µ-Ph)6(THF)4. Further synthetic studies demonstrate that analogous tetranuclear iron clusters can be formed with both 4-F-PhMgBr and p-tolylMgBr, illustrating the generality of this structural motif for reactions of simple ferric salts and aryl Grignard reagents in THF. Additional studies isolate and define key iron species involved in the synthetic pathway leading to the formation of the tetranuclear iron-aryl species. While reaction studies demonstrate that [FePh2(µ-Ph)]2 2- is unreactive towards electrophile, Fe4(µ-Ph)6(THF)4 is found to rapidly react with bromocyclohexane to selectively form phenylcyclohexane. Based on this reactivity, a new catalytic reaction protocol has been developed that enables efficient cross-couplings using Fe4(µ-Ph)6(THF)4, circumventing the current need for additives such as TMEDA or supporting ligands to achieve effective cross-coupling of PhMgBr and a secondary alkyl halide.

17.
Chem Sci ; 8(2): 1369-1377, 2017 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-28451278

RESUMO

Calprotectin (CP) is an abundant metal-chelating protein involved in host defense, and the ability of human CP to bind Fe(ii) in a calcium-dependent manner was recently discovered. In the present study, near-infrared magnetic circular dichroism spectroscopy is employed to investigate the nature of Fe(ii) coordination at the two transition-metal-binding sites of CP that are a His3Asp motif (site 1) and a His6 motif (site 2). Upon the addition of sub-stoichiometric Fe(ii), a six-coordinate (6C) Fe(ii) center associated with site 2 is preferentially formed in the presence of excess Ca(ii). This site exhibits an exceptionally large ligand field (10Dq = 11 045 cm-1) for a non-heme Fe(ii) protein. Analysis of CP variants lacking residues of the His6 motif supports that CP coordinates Fe(ii) at site 2 by employing six His ligands. In the presence of greater than one equiv. of Fe(ii) or upon mutation of the His6 motif, the metal ion also binds at site 1 of CP to form a five-coordinate (5C) Fe(ii)-His3Asp motif that was previously unidentified in this system. Notably, the introduction of His-to-Ala mutations at the His6 motif results in a mixture of 6C (site 2) and 5C (site 1) signals in the presence of sub-stoichiometric Fe(ii). These results are consistent with a reduced Fe(ii)-binding affinity of site 2 as more weakly coordinating water-derived ligands complete the 6C site. In the absence of Ca(ii), both sites 1 and 2 are occupied upon addition of sub-stoichiometric Fe(ii), and a stronger ligand field is observed for the 5C site. These spectroscopic studies provide further evaluation of a unique non-heme Fe(ii)-His6 site for metalloproteins and support the notion that Ca(ii) ions influence the Fe(ii)-binding properties of CP.

18.
Dalton Trans ; 46(39): 13290-13299, 2017 Oct 10.
Artigo em Inglês | MEDLINE | ID: mdl-28766619

RESUMO

The combination of simple cobalt salts and N-heterocyclic carbene (NHC) ligands has been highly effective in C-H functionalization, hydroarylation and cross-coupling catalysis, though displaying a strong dependence on the identity of the NHC ligand. In addition, reactions effective with NHC ligands are often ineffective with phosphine ligands, further motivating the evaluation of the fundamental electronic structure and bonding differences in well-defined distorted tetrahedral Co(ii) complexes. Magnetic circular dichroism (MCD) studies indicate that Co(ii)-bisphosphines have larger ligand fields than Co(ii)-NHC complexes. Theoretical density functional theory (DFT) calculations were performed on an expanded set of L2CoCl2 complexes (L2 = NHC, bisphosphine and diamine) to study the electronic structure and relative ligation properties of NHCs compared to bisphosphine and diamine ligands. Mayer bond order and charge decomposition analyses indicate that NHC ligands are slightly stronger donor ligands than bisphosphines but also result in a weakening of Co-Cl bonds in a trans-like influence. From MCD and DFT studies, changing the NHC N-substituent has a larger effect on the ligand field of Co(ii)-NHC complexes than saturating the backbone. Overall, these studies provide detailed insight into the electronic structure and bonding effects in Co(ii) complexes with ligand types commonly explored in catalysis.

19.
Acta Crystallogr E Crystallogr Commun ; 71(Pt 12): m228-9, 2015 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-26870438

RESUMO

In the structure of the title complex, [Fe(C5H7O2)3] or Fe(acac)3, the asymmetric unit contains one mol-ecule in a general position. The coordination sphere of the Fe(III) atom is that of a slightly distorted octahedron. The crystal under investigation was a two-component pseudo-merohedral twin in the monoclinic system with a ß angle close to 90°. Twin law [100/0-10/00-1] reduced the R1 residual [I > 2σ(I)] from 0.0769 to 0.0312, and the mass ratio of twin components refined to 0.8913 (5):0.1087 (5). In the crystal, mol-ecules are arranged in sheets normal to [001] via non-classical C-H⋯O hydrogen bonding. No other significant inter-molecular inter-actions are observed. The structure is a new polymorph of Fe(acac)3 and is isotypic with one polymorph of its gallium analog.

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