Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 131
Filtrar
1.
Inj Prev ; 29(5): 425-430, 2023 10.
Artigo em Inglês | MEDLINE | ID: mdl-37500503

RESUMO

OBJECTIVE: Evaluate the impact of a broadened theoretical and empirical model of community engagement aimed at coastal drowning prevention via relationship building between lifeguards and beachgoers through the delivery of skill development sessions on the beach. SETTING: A lifeguard-patrolled beach in Lorne, Victoria, Australia, during the 2023 peak summer holiday season. METHODS: In total, 12 skill development sessions were delivered by teams of lifeguards and risk researchers to beachgoers. Sessions were codesigned by the research team and shared with lifeguards beforehand to review and include lifeguards' interpretations of localised risk during delivery. In total, 85 survey interviews were conducted with self-selecting beachgoers post participation. RESULTS: In total, 79 participants (93%) enjoyed participating in the session(s) and 77 participants (91%) reported learning something new. Learning how to identify rip current (n=59) and escape a rip current (n=40) were the two most commonly learnt skills. Participants' intended changes in future beachgoing behaviours (n=46) include asking lifeguards at patrolled beaches how to identify site-specific (rip current) risk (n=11) and attempting to identify a rip current before entering the water (n=10). The spillover effects of participation include sharing what participants had learnt with family and friends. CONCLUSIONS: Creating a dialogic model of collaboration via participatory community engagements between lifeguards and researchers with the beachgoing public can successfully prompt learning drowning prevention skills. These skills are required when navigating dynamic coastal hazards at unpatrolled beaches. Supporting lifeguards and life-savers to provide skill development expands the ways that life-saving services can engage the public, including measurement of lifeguards' contributions to coastal drowning prevention.


Assuntos
Afogamento , Humanos , Afogamento/prevenção & controle , Vitória/epidemiologia
2.
Appetite ; 180: 106312, 2023 01 01.
Artigo em Inglês | MEDLINE | ID: mdl-36150553

RESUMO

Nutrition labels and ecolabels can support consumers to make healthier and more sustainable choices, and the former is now widespread. But there is no information on the impact of ecolabels in the presence of nutrition labels. The aims of this study were primarily to examine whether (1) ecolabels are effective at promoting sustainable purchasing behaviour if presented alongside nutrition labels; (2) and secondarily, whether nutrition labels are effective at promoting healthier purchasing if presented alongside ecolabels. Participants (N = 2730) visited an experimental online supermarket platform, and were randomised to see products with (1) environmental impact labels only; (2) nutrition (NutriScore) labels only; (3) both environmental and nutrition labels; (4) no labels. Linear regressions compared the mean environmental impact scores (EIS; primary outcome) and health scores of products in participants' shopping baskets across each condition. Compared to control (no labels) there were significant reductions in the EIS when environmental impact labels were presented: Alone (-1.3, 95%CI: -2.3 to -0.4) or With nutrition labels (-2.0, 95%CI: -2.9 to -1.0), with no evidence of differences in effectiveness between these two conditions. There was no evidence of an impact of nutrition labels on either the EIS or the healthiness of purchases, both when nutrition labels were shown alone and when ecolabels were also present. Environmental impact labels may be effective at encouraging more sustainable purchases alone or when used alongside nutrition labels. This adds to the evidence base on the feasibility and effectiveness of environmental impact labelling as an important measure to change dietary behaviour to improve planetary health.


Assuntos
Rotulagem de Alimentos , Nível de Saúde , Humanos , Meio Ambiente
3.
Int J Behav Nutr Phys Act ; 19(1): 9, 2022 01 31.
Artigo em Inglês | MEDLINE | ID: mdl-35094694

RESUMO

BACKGROUND: Increasing the availability of lower energy-density foods is a promising intervention to encourage healthier food purchasing but few studies have examined the effect of increasing availability of meat-free meals to promote more sustainable purchasing. We report three studies, all examining the impact of altering the availability of meat-free meals on meal selection. METHODS: Study 1 (a natural experiment in one university cafeteria) examined the impact of altering the ratio of meat-free meals (one meat-free and two meat, to two meat-free and one meat) on weekly sales of meals containing meat. Study 2 (a natural experiment in 18 worksite cafeterias) examined the impact on meat-free meal sales of a menu change designed to increase the availability of meat-free meals. Study 3 (an online study of 2205 UK-representative adults) compared meal selections when participants were randomised to ranges comprised of (a) one meat-free, three meat options; (b) two meat-free, two meat; or (c) three meat-free, one meat. RESULTS: Study 1 suggested a significant decrease in the proportion of sales of meat options when the availability of meat-free options increased (- 19.9 percentage points; 95%CIs:-25.2,-14.6), with no evidence of changes to meat-based meal sales in other university cafeterias during the same period. Findings from Study 2 were mixed: multilevel regressions found no evidence of an increase in meat-free meals following the menu change (2.3 percentage points; 95%CIs: - 1.3,5.9), while interrupted time-series analyses suggested sales did increase (2.3; 95%CIs: 0.4,4.2), but implementation of the planned change was limited. In Study 3 reducing meat-free options from 50 to 25% reduced participants' selection of meat-free options (odds ratio 0.35; 95%CIs: 0.26,0.46), while increasing meat-free options from 50 to 75% increased meat-free selections (odds ratio 2.43; 95%CIs: 1.94,3.04). There was no evidence effects were moderated by gender, socioeconomic status or usual meat consumption. CONCLUSION: Increasing the availability of meat-free options is effective at reducing meat selection and purchasing for different ratios of meat to meat-free options. The magnitude of the effect is uncertain, but with no evidence of differences in response by demographic groups when directly tested. TRIAL REGISTRATION: Study 3: Open Science Framework; https://osf.io/ze9c6 ; 6/8/2020.


Assuntos
Preferências Alimentares , Refeições , Adulto , Comércio , Comportamento do Consumidor , Humanos , Carne
4.
Inorg Chem ; 61(29): 11165-11172, 2022 Jul 25.
Artigo em Inglês | MEDLINE | ID: mdl-35829761

RESUMO

Weakening and cleaving N-H bonds is crucial for improving molecular ammonia (NH3) oxidation catalysts. We report the synthesis and H-atom-abstraction reaction of bis(ammonia)chromium porphyrin complexes Cr(TPP)(NH3)2 and Cr(TMP)(NH3)2 (TPP = 5,10,15,20-tetraphenyl-meso-porphyrin and TMP = 5,10,15,20-tetramesityl-meso-porphyrin) using bulky aryloxyl radicals. The triple H-atom-abstraction reaction results in the formation of CrV(por)(≡N), with the nitride derived from NH3, as indicated by UV-vis and IR and single-crystal structural determination of Cr(TPP)(≡N). Subsequent oxidation of this chromium(V) nitrido complex results in the formation of CrIII(por), with scission of the Cr≡N bond. Computational analysis illustrates the progression from CrII to CrV and evaluates the energetics of abstracting H atoms from CrII-NH3 to generate CrV≡N. The formation and isolation of CrV(por)(≡N) illustrates the stability of these species and the need to chemically activate the nitride ligand for atom transfer or N-N coupling reactivity.

5.
Eur J Nutr ; 61(5): 2615-2626, 2022 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-35244757

RESUMO

PURPOSE: A reduction in meat intake is recommended to meet health and environmental sustainability goals. This study aimed to evaluate the effectiveness of an online self-regulation intervention to reduce meat consumption. METHODS: One hundred and fifty one adult meat eaters were randomised 1:1 to a multi-component self-regulation intervention or an information-only control. The study lasted 9 weeks (1-week self-monitoring; 4-week active intervention; and 4-week maintenance phase). The intervention included goal-setting, self-monitoring, action-planning, and health and environmental feedback. Meat intake was estimated through daily questionnaires in weeks 1, 5 and 9. The primary outcome was change in meat consumption from baseline to five weeks. Secondary outcomes included change from baseline to nine weeks and change in red and processed meat intake. We used linear regression models to assess the effectiveness of all the above outcomes. RESULTS: Across the whole sample, meat intake was 226 g/day at baseline, 118 g/day at five weeks, and 114 g/day at nine weeks. At five weeks, the intervention led to a 40 g/day (95%CI - 11.6,- 67.5, P = 0.006) reduction in meat intake, including a 35 g/day (95%CI - 7.7, - 61.7, P = 0.012) reduction in red and processed meat, relative to control. There were no significant differences in meat reduction after the four-week maintenance phase (- 12 g/day intervention vs control, 95% CI 19.1, - 43.4, P = 0.443). Participants said the intervention was informative and eye-opening. CONCLUSION: The intervention was popular among participants and helped achieve initial reductions in meat intake, but the longer-term reductions did not exceed control. TRIAL REGISTRATION: ClinicalTrials.gov NCT04961216, 14th July 2021, retrospectively registered.


Assuntos
Carne , Autocontrole , Adulto , Humanos , Inquéritos e Questionários
6.
Appetite ; 169: 105824, 2022 02 01.
Artigo em Inglês | MEDLINE | ID: mdl-34826525

RESUMO

Perceptions of social norms around eating behavior can influence food choices. Communicating information about how others are changing their eating behavior over time (dynamic descriptive social norms) may motivate individuals to change their own food selection and consumption. Following a four-week baseline period, 22 in-store restaurants of a major retail chain across the UK were randomized to display a dynamic descriptive social norm message intended to motivate a shift from meat-to plant-based meals either during the first two, or last two weeks of the four-week study period. A linear regression model showed there was no evidence of an effect of the intervention (ß = -0.022, p = .978, 95% CIs: -1.63, 1.58) on the percentage sales of meat- vs plant-based dishes. Fidelity checks indicated that adherence to the intervention procedure was often low, with inconsistencies in the placement and display of the intervention message. In four stores with high fidelity the estimated impact of the intervention was not materially different. The lack of apparent effectiveness of the intervention may reflect poor efficacy of the intervention or limitations in its implementation in a complex food purchasing environment. The challenges highlighted by this study should be considered in future design and evaluation of field trials in real-world settings.


Assuntos
Restaurantes , Normas Sociais , Estudos Cross-Over , Humanos , Refeições , Carne
7.
J Med Internet Res ; 24(12): e37389, 2022 12 12.
Artigo em Inglês | MEDLINE | ID: mdl-36508245

RESUMO

BACKGROUND: There is an urgent need to reduce society's meat consumption to help mitigate climate change and reduce noncommunicable diseases. OBJECTIVE: This study aimed to investigate changes in meat intake after participation in an online, multicomponent, self-regulation intervention. METHODS: We conducted a pre-post observational study among adult meat eaters in the United Kingdom who signed up to a website offering support based on self-regulation theory to reduce meat consumption. The program lasted 9 weeks (including a 1-week baseline phase, a 4-week active intervention phase, and a 4-week maintenance phase), comprising self-monitoring, goal setting, action planning, and health and environmental feedback. Meat intake was estimated during weeks 1, 5, and 9 using a 7-day meat frequency questionnaire. We analyzed the change in mean daily meat intake from baseline to week 5 and week 9 among those reporting data using a hierarchical linear mixed model. We assessed changes in attitudes toward meat consumption by questionnaire and considered the acceptability and feasibility of the intervention. RESULTS: The baseline cohort consisted of 289 participants, of whom 77 were analyzed at week 5 (26.6% of the baseline sample) and 55 at week 9 (71.4% of the week 5 sample). We observed large reductions in meat intake at 5 and 9 weeks: -57 (95% CI -70 to -43) g/day (P<.001) and -49 (95% CI -64 to -34) g/day (P<.001), respectively. Participants' meat-free self-efficacy increased, meat-eating identities moved toward reduced-meat and non-meat-eating identities, and perceptions of meat consumption as the social norm reduced. Participants who completed the study reported high engagement and satisfaction with the intervention. CONCLUSIONS: Among people motivated to engage, this online self-regulation program may lead to large reductions in meat intake for more than 2 months, with promising signs of a change in meat-eating identity toward more plant-based diets. This digital behavior change intervention could be offered to complement population-level interventions to support reduction of meat consumption.


Assuntos
Dieta , Autocontrole , Adulto , Humanos , Estudos de Coortes , Inquéritos e Questionários , Autoeficácia
8.
PLoS Med ; 18(7): e1003715, 2021 07.
Artigo em Inglês | MEDLINE | ID: mdl-34264943

RESUMO

BACKGROUND: Reducing meat consumption could bring health and environmental benefits, but there is little research to date on effective interventions to achieve this. A non-randomised controlled intervention study was used to evaluate whether prominent positioning of meat-free products in the meat aisle was associated with a change in weekly mean sales of meat and meat-free products. METHODS AND FINDINGS: Weekly sales data were obtained from 108 stores: 20 intervention stores that moved a selection of 26 meat-free products into a newly created meat-free bay within the meat aisle and 88 matched control stores. The primary outcome analysis used a hierarchical negative binomial model to compare changes in weekly sales (units) of meat products sold in intervention versus control stores during the main intervention period (Phase I: February 2019 to April 2019). Interrupted time series analysis was also used to evaluate the effects of the Phase I intervention. Moreover, 8 of the 20 stores enhanced the intervention from August 2019 onwards (Phase II intervention) by adding a second bay of meat-free products into the meat aisle, which was evaluated following the same analytical methods. During the Phase I intervention, sales of meat products (units/store/week) decreased in intervention (approximately -6%) and control stores (-5%) without significant differences (incidence rate ratio [IRR] 1.01 [95% CI 0.95-1.07]. Sales of meat-free products increased significantly more in the intervention (+31%) compared to the control stores (+6%; IRR 1.43 [95% CI 1.30-1.57]), mostly due to increased sales of meat-free burgers, mince, and sausages. Consistent results were observed in interrupted time series analyses where the effect of the Phase II intervention was significant in intervention versus control stores. CONCLUSIONS: Prominent positioning of meat-free products into the meat aisle in a supermarket was not effective in reducing sales of meat products, but successfully increased sales of meat-free alternatives in the longer term. A preregistered protocol (https://osf.io/qmz3a/) was completed and fully available before data analysis.


Assuntos
Comportamento Alimentar , Preferências Alimentares , Produtos da Carne , Supermercados , Promoção da Saúde , Humanos , Análise de Séries Temporais Interrompida , Reino Unido
9.
Soft Matter ; 17(24): 5921-5931, 2021 Jun 28.
Artigo em Inglês | MEDLINE | ID: mdl-34041514

RESUMO

The organization of microtubules (MTs) is critical for cells during interphase and mitosis. During mitotic spindle assembly, MTs are made and organized around chromosomes in a process regulated by RanGTP. The role of RanGTP has been explored in Xenopus egg extracts, which are not limited by a cell membrane. Here, we investigated whether cell-sized confinements affect the assembly of RanGTP-induced MT networks in Xenopus egg extracts. We used microfluidics to encapsulate extracts within monodisperse extract-in-oil droplets. Importantly, we find that the architecture of Ran-induced MT networks depends on the droplet diameter and the Ran concentration, and differs from structures formed in bulk extracts. Our results highlight that both MT nucleation and physical confinement play critical roles in determining the spatial organization of the MT cytoskeleton.


Assuntos
Fuso Acromático , Proteínas de Xenopus , Proteínas Associadas aos Microtúbulos/metabolismo , Microtúbulos/metabolismo , Proteínas de Xenopus/metabolismo , Proteína ran de Ligação ao GTP/metabolismo
10.
Risk Anal ; 41(10): 1782-1794, 2021 10.
Artigo em Inglês | MEDLINE | ID: mdl-33521963

RESUMO

Risk tends to be conceptualized at the individual scale, with global risk communication and governance efforts fixated on an individual's knowledge and behavior. While individuals are undoubtedly influenced by those who surround them, such human-human interactions tend to be excluded from empirical and field-based analyses of risk taking. This study diverges from prevailing analyses of risk as an individualized phenomenon, exploring the collective and relational practices that influence risk while fishing from hazardous rocky coasts. The aim is to counter the near-universal tendency to individualize risk in empirical analyses by instead using a mixed-methodology that can quantify and enable consideration of collective responses to risk, in real-time. We demonstrate that both rock fishing practice and many of the high-risk events that emerge while rock fishing are managed collectively. Compared to the tendency to individualize risk, we demonstrate that collective responses to risk are more representative of how risk is experienced and acted upon, with implications for risk management in countless contexts.

11.
Environ Behav ; 53(8): 891-925, 2021 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-34456340

RESUMO

This review assessed the effects of environmental labels on consumers' demand for more sustainable food products. Six electronic databases were searched for experimental studies of ecolabels and food choices. We followed standard Cochrane methods and results were synthesized using vote counting. Fifty-six studies (N = 42,768 participants, 76 interventions) were included. Outcomes comprised selection (n = 14), purchase (n = 40) and consumption (n = 2). The ecolabel was presented as text (n = 36), logo (n = 13) or combination (n = 27). Message types included: organic (n = 25), environmentally sustainable (n = 27), greenhouse gas emissions (n = 17), and assorted "other" message types (n = 7). Ecolabels were tested in actual (n = 15) and hypothetical (n = 41) environments. Thirty-nine studies received an unclear or high RoB rating. Sixty comparisons favored the intervention and 16 favored control. Ecolabeling with a variety of messages and formats was associated with the selection and purchase of more sustainable food products.

12.
J Am Chem Soc ; 142(42): 17845-17858, 2020 10 21.
Artigo em Inglês | MEDLINE | ID: mdl-32977718

RESUMO

Oxidation of ammonia by molecular complexes is a burgeoning area of research, with critical scientific challenges that must be addressed. A fundamental understanding of individual reaction steps is needed, particularly for cleavage of N-H bonds and formation of N-N bonds. This Perspective evaluates the challenges of designing molecular catalysts for oxidation of ammonia and highlights recent key contributions to realizing the goals of viable energy storage and retrieval based on the N-H bonds of ammonia in a carbon-free energy cycle.

13.
Eat Weight Disord ; 25(6): 1573-1582, 2020 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31654288

RESUMO

PURPOSE: Examine the prevalence and potential relationships among food addiction (FA)-as measured by Yale Food Addiction Scale 2.0 (YFAS 2.0), eating disorders (ED)-as measured by Eating Disorder Diagnostic Scale (EDDS)-and exercise dependence (EXD)-as measured by Questionnaire to Diagnose Exercise Dependence in Endurance Sports (FESA), for the first time worldwide, in amateur endurance athletes. METHODS: A total of 1022 German-speaking endurance athletes (44% male, Ø 36 years, Ø BMI 23 kg/m2) replied to an online questionnaire consisting of demographics, related parameters, and the German versions of YFAS 2.0, EDDS, and FESA. RESULTS: Prevalence of FA, ED, and EXD was 6.2, 6.5, and 30.5%. The probability for FA increases with BMI, thoughts about food and EXD score, and decreases with age and when an ED is present. People with FA and people with ED vs. people with both, FA&ED, differed significantly in this cohort. Strong significant relationships were found between FA and EXD (X2 (1) = 15.117, p < 0.001, n = 1022). CONCLUSIONS: A considerable number of amateur endurance athletes may suffer from FA. The association between FA and EXD is stronger than between ED and EXD, indicating FA as a potentially more relevant subject-than ED-for prevention or therapy in people with EXD. Further studies are needed to investigate parameters and relationships between the possibly involved types of ED, FA, and EXD. LEVEL OF EVIDENCE: Level III, well-designed cohort analytic study.


Assuntos
Transtornos da Alimentação e da Ingestão de Alimentos , Dependência de Alimentos , Atletas , Exercício Físico , Transtornos da Alimentação e da Ingestão de Alimentos/epidemiologia , Feminino , Humanos , Masculino , Inquéritos e Questionários
14.
J Biol Chem ; 292(28): 11618-11630, 2017 07 14.
Artigo em Inglês | MEDLINE | ID: mdl-28546429

RESUMO

The nuclear receptor retinoid acid receptor-related orphan receptor γt (RORγt) is a master regulator of the Th17/IL-17 pathway that plays crucial roles in the pathogenesis of autoimmunity. RORγt has recently emerged as a highly promising target for treatment of a number of autoimmune diseases. Through high-throughput screening, we previously identified several classes of inverse agonists for RORγt. Here, we report the crystal structures for the ligand-binding domain of RORγt in both apo and ligand-bound states. We show that apo RORγt adopts an active conformation capable of recruiting coactivator peptides and present a detailed analysis of the structural determinants that stabilize helix 12 (H12) of RORγt in the active state in the absence of a ligand. The structures of ligand-bound RORγt reveal that binding of the inverse agonists disrupts critical interactions that stabilize H12. This destabilizing effect is supported by ab initio calculations and experimentally by a normalized crystallographic B-factor analysis. Of note, the H12 destabilization in the active state shifts the conformational equilibrium of RORγt toward an inactive state, which underlies the molecular mechanism of action for the inverse agonists reported here. Our findings highlight that nuclear receptor structure and function are dictated by a dynamic conformational equilibrium and that subtle changes in ligand structures can shift this equilibrium in opposite directions, leading to a functional switch from agonists to inverse agonists.


Assuntos
Anti-Inflamatórios não Esteroides/farmacologia , Agonismo Inverso de Drogas , Modelos Moleculares , Membro 3 do Grupo F da Subfamília 1 de Receptores Nucleares/antagonistas & inibidores , Anti-Inflamatórios não Esteroides/química , Anti-Inflamatórios não Esteroides/metabolismo , Apoproteínas/antagonistas & inibidores , Apoproteínas/química , Apoproteínas/genética , Apoproteínas/metabolismo , Sítios de Ligação , Ligação Competitiva , Células Cultivadas , Genes Reporter/efeitos dos fármacos , Células HEK293 , Humanos , Interleucina-17/antagonistas & inibidores , Interleucina-17/metabolismo , Ligantes , Conformação Molecular , Membro 3 do Grupo F da Subfamília 1 de Receptores Nucleares/química , Membro 3 do Grupo F da Subfamília 1 de Receptores Nucleares/genética , Membro 3 do Grupo F da Subfamília 1 de Receptores Nucleares/metabolismo , Fragmentos de Peptídeos/antagonistas & inibidores , Fragmentos de Peptídeos/química , Fragmentos de Peptídeos/genética , Fragmentos de Peptídeos/metabolismo , Fenilalanina/análogos & derivados , Fenilalanina/química , Fenilalanina/metabolismo , Fenilalanina/farmacologia , Compostos de Fenilureia/química , Compostos de Fenilureia/metabolismo , Compostos de Fenilureia/farmacologia , Conformação Proteica , Domínios e Motivos de Interação entre Proteínas , Redobramento de Proteína , Estabilidade Proteica , Proteínas Recombinantes de Fusão/química , Proteínas Recombinantes de Fusão/metabolismo , Células Th17/efeitos dos fármacos , Células Th17/metabolismo
15.
J Am Chem Soc ; 140(17): 5696-5700, 2018 05 02.
Artigo em Inglês | MEDLINE | ID: mdl-29676578

RESUMO

One-electron reduction of Cu3EL (L3- = tris(ß-diketiminate)cyclophane, and E = S, Se) affords [Cu3EL]-, which reacts with CO2 to yield exclusively C2O42- (95% yield, TON = 24) and regenerate Cu3EL. Stopped-flow UV/visible data support an A→B mechanism under pseudo-first-order conditions ( kobs, 298K = 115(2) s-1), which is 106 larger than those for reported copper complexes. The kobs values are dependent on the countercation and solvent (e.g., kobs is greater for [K(18-crown-6)]+ vs (Ph3P)2N+, and there is a 20-fold decrease in kobs in THF vs DMF). Our results suggest a mechanism in which cations and solvent influence the stability of the transition state.

16.
Chemistry ; 24(22): 5962-5966, 2018 Apr 17.
Artigo em Inglês | MEDLINE | ID: mdl-29437249

RESUMO

The divalent cobalt complex of the diprotic pincer ligand bis-pyrazolylpyridine, (H2 L)CoCl2 , is dehydrohalogenated twice by LiN(SiMe3 )2 in the presence of PEt3 to give monomeric S=1/2 LCo(PEt3 )2 (1), fully characterized in the solid-state and solution as a square pyramidal monomer with a long axial Co-P bond. This 17-electron species reacts in time of mixing with N2 O to form L2 Co2 (µ-OPEt3 ) (2)+3 OPEt3 , the former the first example of phosphine oxide bridging two transition metals. The same products are formed from O2 , and divalent cobalt persists even in the presence of excess oxidant. Species (2) catalyzes oxygen atom transfer (OAT) for generation of O=PEt3 from PEt3 from either N2 O or O2 . Bridging and terminal cobalt oxo intermediates are suggested, and the electron donor power, and potential redox activity of the dianionic pincer ligand is emphasized.

17.
Chemistry ; 24(59): 15852-15858, 2018 Oct 22.
Artigo em Inglês | MEDLINE | ID: mdl-30028543

RESUMO

The formation of metal-ligand coordination networks on surfaces that contain redox isomers is a topic of considerable interest and is important for bifunctional metallochemistry, including heterogeneous catalysis. Towards this end, a tetrazine with two electron withdrawing pyrimidinyl substituents was co-deposited with platinum metal on the Au(100) surface. In a 2:1 metal:ligand ratio, only half of the platinum is oxidized to the +2 oxidation state, with the remainder coordinating to the ligand without charge transfer, as Pt0 . The resultant Pt0 /PtII mixed valence structure is thought to form due to the aversion of the ligand towards a four-electron reduction and the strong preference of Pt towards 0 and +2 oxidation states. These results were confirmed through a series of experiments varying the on-surface metal:ligand stoichiometry in the redox assembly formed: added oxidant does not oxidize the already complexed Pt0 . Scanning tunneling microscopy reveals irregular chain structures that are attributed to the mixture of Pt valence states, each with distinct local coordination geometries. Density functional theory calculations give further detail about these local geometries. These results demonstrate the formation of a mixture of valence states in on-surface redox assembly of metal-organic networks that extends the library of single-site metal structures for surface chemistry and catalysis. Redox-isomeric Pt0 versus Pt2+ surface structures can coexist in this ligand environment.

18.
Inorg Chem ; 57(10): 6176-6185, 2018 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-29741888

RESUMO

The bis-pyrazolato pyridine complex LCo(PEt3)2 serves as a masked form of three-coordinate CoII and shows diverse reactivity in its reaction with several potential outer sphere oxidants and oxygen atom transfer reagents. N-Methylmorpholine N-oxide (NMO) oxidizes coordinated PEt3 from LCo(PEt3)2, but the final cobalt product is still divalent cobalt, in LCo(NMO)2. The thermodynamics of a variety of oxygen atom transfer reagents, including NMO, are calculated by density functional theory, to rank their oxidizing power. Oxidation of LCo(PEt3)2 with AgOTf in the presence of LiCl as a trapping nucleophile forms the unusual aggregate [LCo(PEt3)2Cl(LiOTf)2]2 held together by Li+ binding to very nucleophilic chloride on Co(III) and triflate binding to those Li+. In contrast, Cp2Fe+ effects oxidation to trivalent cobalt, to form (HL)Co(PEt3)2Cl+; proton and the chloride originate from solvent in a rare example of CH2Cl2 dehydrochlorination. An unexpected noncomplementary redox reaction is reported involving attack by 2e reductant PEt3 nucleophile on carbon of the 1e oxidant radical Cp2Fe+, forming a P-C bond and H+; this reaction competes in the reaction of LCo(PEt3)2 with Cp2Fe+.

19.
Inorg Chem ; 57(18): 11361-11368, 2018 Sep 17.
Artigo em Inglês | MEDLINE | ID: mdl-29791149

RESUMO

Oxygenation of a tricopper(I) cyclophanate (1) affords reactive transients competent for C-H bond activation and O atom transfer to various substrates (including toluene, dihydroanthracene, and ethylmethylsulfide) based on 1H NMR, gas chromatography/mass spectrometry (MS), and electrospray ionization (ESI)/MS data. Low product yields (<1%) are determined for C-H activation substrates (e.g, toluene, ethylbenzene), which we attribute to competitive ligand oxidation. The combined stopped-flow UV/visible, electron paramagnetic resonance, ESI/MS, 1H NMR, and density functional theory (DFT) results for reaction of 1 with O2 are consistent with transient peroxo- and di(oxo)-bridged intermediates. DFT calculations elucidate a concerted proton-coupled electron transfer from toluene to the di(µ-oxo) intermediate and subsequent radical rebound as the C-H activation mechanism. Our results support a multicopper oxidase-like mechanism for O2 activation by 1, traversing species similar to the coplanar Cu3O2 unit in the peroxy and native intermediates.

20.
Inorg Chem ; 57(18): 11382-11392, 2018 Sep 17.
Artigo em Inglês | MEDLINE | ID: mdl-30160943

RESUMO

Reaction of the tricopper(I)-dinitrogen tris(ß-diketiminate) cyclophane, Cu3(N2)L, with O-atom-transfer reagents or elemental Se affords the oxido-bridged tricopper complex Cu3(µ3-O)L (2) or the corresponding Cu3(µ3-Se)L (4), respectively. For 2 and 4, incorporation of the bridging chalcogen donor was supported by electrospray ionization mass spectrometry and K-edge X-ray absorption spectroscopy (XAS) data. Cu L2,3-edge X-ray absorption data quantify 49.5% Cu 3d character in the lowest unoccupied molecular orbital of 2, with Cu 3d participation decreasing to 33.0% in 4 and 40.8% in the related sulfide cluster Cu3(µ3-S)L (3). Multiedge XAS and UV/visible/near-IR spectra are employed to benchmark density functional theory calculations, which describe the copper-chalcogen interactions as highly covalent across the series of [Cu3(µ-E)]3+ clusters. This result highlights that the metal-ligand covalency is not reserved for more formally oxidized metal centers (i.e., CuIII + O2- vs CuII + O-) but rather is a significant contributor even at more typical ligand-field cases (i.e., Cu3II/II/I + E2-). This bonding is reminiscent of that observed in p-block elements rather than in early-transition-metal complexes.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA