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1.
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
2.
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
3.
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
4.
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
5.
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
6.
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.

8.
Curr Dev Nutr ; 8(6): 103777, 2024 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-38911321

RESUMO

In 2021, 32% of adult meat consumers in Scotland exceeded the 70 g/d recommended limit of red and red processed meat (RPM) intake. We analyzed RPM consumption behaviors among adults in the Scottish Health Survey (2021) to better understand this consumer group. Consumers were categorized into low, medium, and high consumers, and overall, mean intake was 66 g/d. Males and individuals living in the most deprived areas were most likely to be high consumers (45% compared with 30% for males compared with females, respectively, and 44% compared with 32% for those in the most compared with least deprived areas, respectively). Dinners accounted for the majority of intake among high (55%) and medium (52%) consumers, whereas low consumers distributed intake between lunch (40%) and dinner (48%). Across all groups, consumption was highest on Sundays, and majority of RPM was purchased at supermarkets. Beef dishes and sandwiches were primary contributors among high and medium consumers. These insights can inform the design of effective strategies and policies aligned with meat reduction targets. For instance, strategies focusing on modifying traditional meat-centric dishes and sandwiches could be impactful.

9.
Nutrients ; 14(3)2022 Jan 18.
Artigo em Inglês | MEDLINE | ID: mdl-35276771

RESUMO

Food diaries are used to estimate meat intake at an individual level but it is unclear whether simpler methods would provide similar results. This study assessed the agreement between 7 day food diaries in which composite dishes were disaggregated to assess meat content (reference method), and two simpler methods: (1) frequency meal counts from 7 day food diaries; and (2) 7 day dietary recalls, each using standard estimated portion sizes. We compared data from a randomized controlled trial testing a meat reduction intervention. We used Bland-Altman plots to assess the level of agreement between methods at baseline and linear mixed-effects models to compare estimates of intervention effectiveness. At baseline, participants consumed 132 g/d (±75) of total meat; frequency meal counts and dietary recalls underestimated this by an average of 30 and 34 g/day, respectively. This was partially explained by an underestimation of the assumed portion size. The two simpler methods also underestimated the effect of the intervention, relative to control, though the significant effect of the intervention was unchanged. Simpler methods underestimated absolute meat intake but may be suitable for use in studies to measure the change in meat intake in individuals over time.


Assuntos
Carne , Avaliação Nutricional , Adulto , Registros de Dieta , Inquéritos sobre Dietas , Humanos , Carne/análise , Reino Unido
10.
Am J Clin Nutr ; 115(5): 1357-1366, 2022 05 01.
Artigo em Inglês | MEDLINE | ID: mdl-34958364

RESUMO

BACKGROUND: Reducing meat consumption could protect the environment and human health. OBJECTIVES: We tested the impact of a behavioral intervention to reduce meat consumption. METHODS: Adult volunteers who regularly consumed meat were recruited from the general public and randomized 1:1 to an intervention or control condition. The intervention comprised free meat substitutes for 4 weeks, information about the benefits of eating less meat, success stories, and recipes. The control group received no intervention or advice on dietary change. The primary outcome was daily meat consumption after 4 weeks, assessed by a 7-day food diary, and repeated after 8 weeks as a secondary outcome. Other secondary and exploratory outcomes included the consumption of meat substitutes, cardiovascular risk factors, psychosocial variables related to meat consumption, and the nutritional composition of the diet. We also estimated the intervention's environmental impact. We evaluated the intervention using generalized linear mixed-effects models. RESULTS: Between June 2018 and October 2019, 115 participants were randomized. The baseline meat consumption values were 134 g/d in the control group and 130 g/d in the intervention group. Relative to the control condition, the intervention reduced meat consumption at 4 weeks by 63 g/d (95% CI: 44-82; P < 0.0001; n = 114) and at 8 weeks by 39 g/d (95% CI: 16-62; P = 0.0009; n = 113), adjusting for sex and baseline consumption. The intervention significantly increased the consumption of meat substitutes without changing the intakes of other principal food groups. The intervention increased intentions, positive attitudes, perceived control, and subjective norms of eating a low-meat diet and using meat substitutes, and decreased attachment to meat. At 8 weeks, 55% of intervention recipients identified as meat eaters, compared to 89% of participants in the control group. CONCLUSIONS: A behavioral program involving free meat substitutes can reduce meat intake and change psychosocial constructs consistent with a sustained reduction in meat intake.


Assuntos
Dieta , Carne , Adulto , Registros de Dieta , Humanos
11.
Obes Rev ; 23(1): e13355, 2022 01.
Artigo em Inglês | MEDLINE | ID: mdl-34672069

RESUMO

People with serious mental illness (SMI) have identified barriers to engaging in behavioral weight management interventions (BWMIs). We assessed whether BWMIs that addressed these barriers were more effective. First, we systematically reviewed qualitative literature and used a thematic analysis to identify the characteristics of BWMIs that promote engagement for adults with SMI. Second, we systematically reviewed randomized controlled trials (RCTs) of BWMIs in adults with SMI. Data on the characteristics that promoted engagement and weight outcomes were extracted. We then used a crisp-set qualitative comparative analysis (CsQCA) to identify which characteristics were associated with weight loss. For the qualitative review, 20 studies in 515 people with SMI were analyzed and nine characteristics were reported to promote engagement in BWMIs. For the systematic review, 34 RCTs testing 36 interventions in 4305 participants were included. The active interventions resulted in more weight loss (mean = -4.37 to +1 kg at 6 weeks to 18 months follow-up) compared with controls (-1.64 to +3.08 kg). The CsQCA showed BWMIs that offered regular contact, tools to support enactment, and tailored materials were associated with effectiveness. As these are all supplementary strategies, it may be possible to augment BWMIs available for the general population to engage people with SMI.


Assuntos
Transtornos Mentais , Terapia Nutricional , Adulto , Terapia Comportamental , Humanos , Transtornos Mentais/terapia
12.
Sci Total Environ ; 807(Pt 3): 151041, 2022 Feb 10.
Artigo em Inglês | MEDLINE | ID: mdl-34673070

RESUMO

A global transformation towards sustainable food systems is crucial for delivering on climate change mitigation targets worldwide. In high- and middle-income settings, plant-based meat and dairy alternatives present potential substitutes for animal sourced foods, and a pathway to transition to more sustainable diets. We examined plant-based alternative foods (PBAF) consumption trends in the UK by analysing repeated cross-sectional food consumption data from the National Diet and Nutrition Survey 2008-2019. Dietary data for 15,655 individuals aged 1.5 years and over were analysed to assess aggregate change in intake of PBAF and six other food groups that play a role in transformative dietary change. Characteristics associated with consumption of PBAF were explored using logistic regression, and consumption patterns in high and low meat consumers were explored by examining intake of potential animal product substitute food groups. The proportion of individuals reporting consumption of any PBAFs increased from 6.7% in 2008-2011, to 13.1% in 2017-2019 (p < 0.01). Compared to 2008-2011 PBAF consumption rose by 115% in 2017-2019 (p < 0.01). Females were 46% more likely than males to report consumption of PBAF (p < 0.01). Millennials (age 24-39 years) were the most likely generation to report PBAF consumption (p < 0.01 compared to generation Z (age 11-23 years) and traditionalists (age 75+ years)), as were individuals of the highest income tertile (p < 0.01). Among "low meat consumers", PBAF consumption was on average higher than "high meat consumers" (18.6 g versus 4.8 g PBAF per day, p < 0.01). Our results support the hypothesis of a pivotal role of PBAF in the transition towards sustainable food systems in the UK, by demonstrating they are becoming increasingly popular among UK consumers. This highlights the urgent need to assess in detail the environmental and health impacts of large scale and population-wide consumption of PBAF in comparison to their animal-based equivalents.


Assuntos
Dieta/tendências , Programas Governamentais , Carne , Plantas , Adolescente , Adulto , Idoso , Animais , Criança , Estudos Transversais , Feminino , Humanos , Masculino , Reino Unido , Adulto Jovem
13.
Front Psychol ; 13: 974830, 2022.
Artigo em Inglês | MEDLINE | ID: mdl-36312106

RESUMO

Referent groups can moderate the perception of social norms and individuals' likelihood to model these norms in food choice contexts, including vegetable intake and reduced meat consumption. The present study investigated whether having a close vs. a distant social group as the referent changed perceptions of social norms around making healthy and eco-friendly food choices. It also assessed whether these changes were associated with a difference in the health and environmental impacts of food choice in a virtual grocery shopping task. A nationally representative sample of UK adults (N = 2,488) reported their perceptions of making healthy and eco-friendly food choices being the norm among people they share meals with (close referent group) and most people in the UK (distant referent group). The former was more commonly perceived to be making both healthy (Z = -12.0, p < 0.001) and eco-friendly (Z = -13.27, p < 0.001) food choices than the latter. Perceptions of norms referring to the close group were significantly associated with the environmental (ß = -0.90, 95% CIs: -1.49, -0.28) and health (ß = -0.38 p < 0.05, 95% CIs: -0.68, -0.08) impacts of participants' food choices in a virtual shopping task. No such relationship was found for norms referring to the distant group for both environmental (ß =0.43, p > 0.05, 95% CIs: -1.12, 0.25) and health (ß = -0.06, p > 0.05, 95% CIs: -0.37, 0.25) impacts. Framing social norms around making healthy and eco-friendly food choices to refer to a close referent group may change their perceptions and ability to encourage sustainable and healthy food purchasing.

14.
PLoS One ; 17(11): e0272800, 2022.
Artigo em Inglês | MEDLINE | ID: mdl-36327277

RESUMO

Providing consumers with product-specific environmental impact information for food products (ecolabels) may promote more sustainable purchasing, needed to meet global environmental targets. Two UK studies investigated the effectiveness of different ecolabels using an experimental online supermarket platform. Study 1 (N = 1051 participants) compared three labels against control (no label), while Study 2 (N = 4979) tested four designs against control. Study 1 found significant reductions in the environmental impact score (EIS) for all labels compared to control (labels presented: values for four environmental indicators [-3.9 percentiles, 95%CIs: -5.2,-2.6]; a composite score [taking values from A to E; -3.9, 95%CIs: -5.2,-2.5]; or both together [-3.2, 95%CIs: -4.5,-1.9]). Study 2 showed significant reductions in EIS compared to control for A-E labels [-2.3, 95%CIs: -3.0,-1.5], coloured globes with A-E scores [-3.2, 95%CIs:-3.9,-2.4], and red globes highlighting 'worse' products [-3.2, 95%CIs:-3.9,-2.5]. There was no evidence that green globes highlighting 'better' products were effective [-0.5, 95%CIs:-1.3,0.2]. Providing ecolabels is a promising intervention to promote the selection of more sustainable products.


Assuntos
Rotulagem de Alimentos , Supermercados , Humanos , Comportamento do Consumidor , Alimentos , Preferências Alimentares , Meio Ambiente , Ensaios Clínicos Controlados Aleatórios como Assunto
15.
Nutrients ; 13(3)2021 Mar 12.
Artigo em Inglês | MEDLINE | ID: mdl-33809192

RESUMO

Reliable and valid measurements of meat intake are needed to advance understanding of its health effects and to evaluate interventions to reduce meat consumption. Here, we describe the development and reliability of the Oxford Meat Frequency Questionnaire (MFQ). It asks individuals to report the number of servings of meat and seafood products they consumed in the last 24 h and is administered daily over 7 days. The MFQ combines food portion size data from the UK Food Standards Agency with estimates of meat content in composite dishes from the UK's National Diet and Nutrition Survey. Adults who self-reported to eat meat (n = 129) completed a 3-week web-based test-retest reliability study assessing the MFQ twice, with a wash-out week in the middle. Two-way random intraclass correlation coefficients (ICC) revealed moderate to good agreement on all meat outcomes (total meat ICC = 0.716; minimum-maximum individual components = 0.531-0.680), except for fish and seafood (ICC = 0.257). Participants reported finding the questionnaire easy to use and, on average, completed it in less than 2 min. This new MFQ offers a quick, acceptable, and reliable method to measure changes in an individual's meat intake in a UK population.


Assuntos
Inquéritos sobre Dietas/métodos , Carne , Adolescente , Adulto , Idoso , Dieta/estatística & dados numéricos , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Reprodutibilidade dos Testes , Alimentos Marinhos , Inquéritos e Questionários , Reino Unido , Adulto Jovem
16.
Lancet Planet Health ; 5(10): e699-e708, 2021 10.
Artigo em Inglês | MEDLINE | ID: mdl-34627474

RESUMO

BACKGROUND: High meat consumption, particularly red meat and processed meat, negatively affects our health, while meat production is one of the largest contributors to global warming and environmental degradation. The aim of our study was to explore trends in meat consumption within the UK and the associated changes in environmental impact. We also aimed to identify any differences in intake associated with gender, ethnicity, socioeconomic status, and year of birth. METHODS: Our study aimed to describe consumption of red, white, and processed meat within the UK, using data from the National Diet and Nutrition Survey rolling programme (2008-09 to 2018-19), and the associated changes in environmental impact. Meat consumption was based on disaggregated meat data, from 4 day food diaries that excluded all non-meat components of composite dishes. For each year surveyed, trends for meat intake were reported as mean grams per capita per day and linear-regression models were used to test for trends. We used multivariable linear-regression models to examine differences among consumers, as a percentage of food energy, by gender, ethnicity, equivalised household income, and year of birth. FINDINGS: From 2008 to 2019, average meat consumption per capita per day decreased from 103·7 g (SE 2·3) to 86·3 g (2·9) per day (ptrend<0·0001), including an absolute reduction in red-meat consumption of 13·7 g (ptrend<0·0001), an absolute reduction in processed meat consumption of 7·0 g (ptrend<0·0001), and a 3·2 g increase (ptrend=0·0027) in white-meat consumption. Collectively, these changes were associated with a significant reduction in all six environmental indicators over the whole period. The two middle birth-year groups (people born in 1960-79 and 1980-99) and White individuals were the highest meat consumers. Meat intake increased over time among people born after 1999, was unchanged among Asian and Asian British populations, and decreased in all other population subgroups. We found no difference in intake with gender or household income. INTERPRETATION: Despite the overall reduction in meat intake, reaching meat-consumption targets that align with sustainable diets will require a substantial acceleration of this trend. FUNDING: The Wellcome Trust, Our Planet Our Health programme (Livestock, Environment, and People).


Assuntos
Dieta , Carne , Promoção da Saúde , Humanos , Pessoa de Meia-Idade , Inquéritos Nutricionais , Reino Unido
17.
J Am Chem Soc ; 130(4): 1163-70, 2008 Jan 30.
Artigo em Inglês | MEDLINE | ID: mdl-18179207

RESUMO

The DNA light-switch complex [Ru(bpy)2(tpphz)]2+ (1, bpy = 2,2'-bipyridine, tpphz = tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2''',3'''-j]phenazine) is luminescent when bound to DNA and in organic solvents and weakly emissive in water. To date, light-switch behavior by transition metal complexes has generally been regarded as confirmation of DNA intercalation. In contrast, the present work demonstrates that the nonintercalating bimetallic complex [(bpy)2Ru(tpphz)Ru(bpy)2]4+ (2) behaves as a DNA light-switch. Weak emission from the 3MLCT excited state of 2 is observed in water with lambda(em) = 623 nm (phi(em) = 1.4 x 10(-4)), and a red shift (lambda(em) = 702 nm) and 40-fold increase in intensity are observed upon addition of 100 microM calf thymus DNA (ct-DNA). Addition of increasing concentrations of 2 to 1 mM herring sperm DNA does not result in an increase in the viscosity of the solution, indicating that the complex is not an intercalator. Additionally, experiments were conducted to ensure that the emission enhancement did not arise from threading intercalation of the complex. The in situ generation of 2 intercalated between the base pairs of ct-DNA in a threading fashion, however, exhibits emission maximum at 685 nm, which is blue-shifted from that of surface-bound 2. DFT calculations show low-lying orbitals in 2 that are expected to exhibit nonemissive character when contributing to the MLCT state, in accord with the lower emission intensity observed for 2 relative to that for 1. To our knowledge, the present work is the first example of a nonintercalating light-switch metal complex, thus showing that light-switch behavior cannot be used exclusively as confirmation of intercalation.


Assuntos
DNA/química , Substâncias Intercalantes/farmacologia , Luz , Animais , Bovinos , Eletroquímica/métodos , Peixes , Concentração de Íons de Hidrogênio , Ligantes , Espectroscopia de Ressonância Magnética , Masculino , Conformação de Ácido Nucleico , Espermatozoides/metabolismo , Timo/metabolismo , Zinco/química
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