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1.
J Hosp Infect ; 152: 105-113, 2024 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-39094738

RESUMO

BACKGROUND: It is essential to refrain from unnecessary isolation measures indicated for patients identified with multidrug-resistant Gram-negative bacteria (MDR-GNB). AIM: To evaluate whether a pro-active follow-up strategy to discontinue isolation measures of patients identified with MDR-GNB (without carbapenemase production) resulted in reduced isolation days during hospitalization, compared to passive follow-up. METHODS: A comparison was made between active and passive follow-up strategies over a two-year period after first MDR-GNB identification. Patients could be declared negative after two consecutive negative screening cultures. Active follow-up patients received a questionnaire for screening cultures within six months of MDR-GNB identification. Of the 2208 patients included, 1424 patients (64.5%) underwent passive follow-up and 784 patients (35.5%) underwent active follow-up. FINDINGS: A significantly higher proportion of active follow-up patients who had sufficient (at least two) screening cultures were declared MDR-GNB negative compared to those with passive follow-up; 66.9% vs 20.6% (P < 0.001) for adult patients and 76.0% vs 17.1% (P < 0.001) for paediatric patients. A comparison between active follow-up patients with sufficient versus those with active follow-up but insufficient cultures revealed a reduction of isolation days for paediatric patients (median 10.6 vs 1.6 days; P = 0.031). Though this difference was not statistically significant for adults (median 5.3 vs 4.2 isolation days), there was a valuable decrease in the number of isolation days for both adult and paediatric patients under active follow-up with sufficient (≥2) cultures, indicating clinical relevance. CONCLUSION: We recommend an active follow-up strategy for patients identified with an MDR-GNB, to prevent further unneeded infection prevention measures.


Assuntos
Farmacorresistência Bacteriana Múltipla , Bactérias Gram-Negativas , Infecções por Bactérias Gram-Negativas , Isolamento de Pacientes , Humanos , Infecções por Bactérias Gram-Negativas/microbiologia , Infecções por Bactérias Gram-Negativas/prevenção & controle , Masculino , Feminino , Adulto , Pessoa de Meia-Idade , Bactérias Gram-Negativas/isolamento & purificação , Bactérias Gram-Negativas/efeitos dos fármacos , Bactérias Gram-Negativas/classificação , Idoso , Criança , Adolescente , Adulto Jovem , Pré-Escolar , Inquéritos e Questionários , Idoso de 80 Anos ou mais , Seguimentos , Controle de Infecções/métodos , Lactente
2.
Health Promot J Austr ; 35(4): 911-923, 2024 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-38566279

RESUMO

ISSUE ADDRESSED: Women are 'at-risk' population for failing to meet muscle strengthening guidelines. Health benefits specific to this exercise mode include maintenance of muscle mass, which is associated with reduced risk of chronic disease and falls. Of significance is the progressive decline in muscle strength exercise participation in women aged 35-54 in Australia. This period is critical for maintaining muscle strength as it establishes foundations for older women's engagement. This integrative review examined available evidence regarding factors influencing muscle strength exercise participation, specifically in women aged 35-54. METHODS: Seven databases were searched. Study inclusion criteria were: (1) peer reviewed, (2) English language, (3) sample populations of healthy female adults or general adult sample population differentiating females from males, (4) mean age between 35 and 54 years, (5) focused on muscle strength exercise and measured as the primary outcome factors of participation in muscle strength exercise. FINDINGS: Five of 1895 studies met inclusion criteria. Five key factors were associated with participation in muscle strength exercise of women aged 35-54 years: perceived time constraints; knowledge and education; modality and intensity; social support and behavioural strategies. CONCLUSIONS: Focused education on strength exercise and guidelines, plus initiatives and strategies that suit the needs of this cohort, are necessary to achieve health and wellbeing benefits. Responsive approaches by health professionals to these women's circumstances can potentially address current low participation levels. SO WHAT?: Creating conditions where health professionals respect a woman's exercise preferences can positively impact these women's musculoskeletal health into older age.


Assuntos
Exercício Físico , Força Muscular , Humanos , Feminino , Força Muscular/fisiologia , Pessoa de Meia-Idade , Adulto , Austrália , Apoio Social , Conhecimentos, Atitudes e Prática em Saúde
3.
J Am Chem Soc ; 146(8): 5067-5073, 2024 02 28.
Artigo em Inglês | MEDLINE | ID: mdl-38365186

RESUMO

The replacement of a functional group with its corresponding bioisostere is a widely employed tactic during drug discovery campaigns that allows medicinal chemists to improve the ADME properties of candidates while maintaining potency. However, the incorporation of bioisosteres typically requires lengthy de novo resynthesis of potential candidates, which represents a bottleneck in their broader evaluation. An alternative would be to directly convert a functional group into its corresponding bioisostere at a late stage. Herein, we report the realization of this approach through the conversion of aliphatic alcohols into the corresponding difluoromethylated analogues via the merger of benzoxazolium-mediated deoxygenation and copper-mediated C(sp3)-CF2H bond formation. The utility of this method is showcased in a variety of complex alcohols and drug compounds.


Assuntos
Descoberta de Drogas , Álcoois/química
4.
Science ; 382(6667): 191-197, 2023 Oct 13.
Artigo em Inglês | MEDLINE | ID: mdl-37824651

RESUMO

Second- and third-row transition metal complexes are widely employed in photocatalysis, whereas earth-abundant first-row transition metals have found only limited use because of the prohibitively fast decay of their excited states. We report an unforeseen reactivity mode for productive photocatalysis that uses cobalt polypyridyl complexes as photocatalysts by exploiting Marcus inverted region behavior that couples increases in excited-state energies with increased excited-state lifetimes. These cobalt (III) complexes can engage in bimolecular reactivity by virtue of their strong redox potentials and sufficiently long excited-state lifetimes, catalyzing oxidative C(sp2)-N coupling of aryl amides with challenging sterically hindered aryl boronic acids. More generally, the results imply that chromophores can be designed to increase excited-state lifetimes while simultaneously increasing excited-state energies, providing a pathway for the use of relatively abundant metals as photoredox catalysts.

5.
BMC Gastroenterol ; 23(1): 306, 2023 Sep 12.
Artigo em Inglês | MEDLINE | ID: mdl-37700260

RESUMO

BACKGROUND AND AIMS: Non-alcoholic fatty liver disease (NAFLD) has become the most common cause of chronic liver disease in wealthy societies, and is responsible for a significant rise in liver morbidity and mortality. Current treatments prioritise lifestyle interventions, predominantly diet and exercise management, but patients frequently fail to make the necessary behavioural adjustments. The current study seeks to identify those factors which influence patients' behaviour with respect to adherence to treatment regimes. METHODS: Novel areas of interest were investigated; locus of control, behavioural regulation and a range of mental health measures, due to their links to either poor lifestyle choices or abnormal eating as identified in previous literature. Data was gathered using self-report questionnaires, from 96 participants, who were split into three groups, NAFLD patients, non-NAFLD liver disease patients and healthy controls RESULTS: Data was analysed using a MANOVA, and followed up with a Tukey post-hoc test. Three factors were found to be significant by group; cognitive restraint, uncontrolled eating and SAPAS score (a measure of personality disorders). An association between personality disorders and NAFLD was identified. CONCLUSION: It is suggested that NAFLD patients are screened for personality disorders and, if identified, treated prior to the commencement of diet and exercise management.


Assuntos
Hepatopatia Gordurosa não Alcoólica , Humanos , Hepatopatia Gordurosa não Alcoólica/complicações , Saúde Mental , Estilo de Vida , Exercício Físico
7.
J Hosp Infect ; 128: 92-95, 2022 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-35944791

RESUMO

BACKGROUND: Surfaces in healthcare facilities can act as reservoirs of infection. Currently, no standardized protocol on when and how to sample hospital surfaces exists. AIM: A web-based questionnaire was devised to gain insight into current sampling practices and was distributed by email to a targeted infection prevention and control (IPC) audience. METHODS: The survey consisted of 26 questions on sample collection and processing for a number of healthcare relevant bacterial species. FINDINGS: The majority of respondents were clinical microbiologists or IPC practitioners, and 57.3% were from either the Netherlands, the United Kingdom, or Ireland. Respondents had high self-reported knowledge, but this was not consistent with response to certain questions. There was no consensus on sample sites, either within or between countries. Indirect sampling methods were preferred for all target microorganisms, and cotton and flocked swabs were the most popular methods. CONCLUSION: The results of our survey highlight the inconsistencies in environmental sampling between and within countries, and the need for guidance and consensus.


Assuntos
Controle de Infecções , Manejo de Espécimes , Hospitais , Humanos , Controle de Infecções/métodos , Irlanda , Inquéritos e Questionários
8.
Angew Chem Int Ed Engl ; 61(35): e202207150, 2022 08 26.
Artigo em Inglês | MEDLINE | ID: mdl-35727296

RESUMO

The rapid exploration of sp3 -enriched chemical space is facilitated by fragment-coupling technologies that utilize simple and abundant alkyl precursors, among which alcohols are a highly desirable, commercially accessible, and synthetically versatile class of substrate. Herein, we describe an operationally convenient, N-heterocyclic carbene (NHC)-mediated deoxygenative Giese-type addition of alcohol-derived alkyl radicals to electron-deficient alkenes under mild photocatalytic conditions. The fragment coupling accommodates a broad range of primary, secondary, and tertiary alcohol partners, as well as structurally varied Michael acceptors containing traditionally reactive sites, such as electrophilic or oxidizable moieties. We demonstrate the late-stage diversification of densely functionalized molecular architectures, including drugs and biomolecules, and we further telescope our protocol with metallaphotoredox cross-coupling for step-economic access to sp3 -rich complexity.


Assuntos
Álcoois , Alquilantes , Álcoois/química , Alquilação , Catálise , Oxirredução
9.
J Am Chem Soc ; 144(14): 6185-6192, 2022 04 13.
Artigo em Inglês | MEDLINE | ID: mdl-35353531

RESUMO

Alcohols and carboxylic acids are among the most commercially abundant, synthetically versatile, and operationally convenient functional groups in organic chemistry. Under visible light photoredox catalysis, these native synthetic handles readily undergo radical activation, and the resulting open-shell intermediates can subsequently participate in transition metal catalysis. In this report, we describe the C(sp3)-C(sp3) cross-coupling of alcohols and carboxylic acids through the dual combination of N-heterocyclic carbene (NHC)-mediated deoxygenation and hypervalent iodine-mediated decarboxylation. This mild and practical Ni-catalyzed radical-coupling protocol was employed to prepare a wide array of alkyl-alkyl cross-coupled products, including highly congested quaternary carbon centers from the corresponding tertiary alcohols or tertiary carboxylic acids. We demonstrate the synthetic applications of this methodology to alcohol C1-alkylation and formal homologation, as well as to the late-stage functionalization of drugs, natural products, and biomolecules.


Assuntos
Álcoois , Ácidos Carboxílicos , Alquilação , Carbono/química , Ácidos Carboxílicos/química , Catálise
10.
Chem Rev ; 122(2): 1485-1542, 2022 01 26.
Artigo em Inglês | MEDLINE | ID: mdl-34793128

RESUMO

The merger of photoredox catalysis with transition metal catalysis, termed metallaphotoredox catalysis, has become a mainstay in synthetic methodology over the past decade. Metallaphotoredox catalysis has combined the unparalleled capacity of transition metal catalysis for bond formation with the broad utility of photoinduced electron- and energy-transfer processes. Photocatalytic substrate activation has allowed the engagement of simple starting materials in metal-mediated bond-forming processes. Moreover, electron or energy transfer directly with key organometallic intermediates has provided novel activation modes entirely complementary to traditional catalytic platforms. This Review details and contextualizes the advancements in molecule construction brought forth by metallaphotocatalysis.


Assuntos
Elétrons , Elementos de Transição , Catálise , Níquel/química , Oxirredução
11.
J Intellect Disabil Res ; 65(12): 1085-1096, 2021 12.
Artigo em Inglês | MEDLINE | ID: mdl-34786786

RESUMO

BACKGROUND: Individuals with Down syndrome (DS) are at high risk for dementia, specifically Alzheimer's disease. However, many measures regularly used for the detection of dementia in the general population are not suitable for individuals with DS due in part to floor effects. Some measures, including the Severe Impairment Battery (SIB), Brief Praxis Test (BPT) and Dementia Scale for People with Learning Disabilities (DLD), have been used in clinical trials and other research with this population. Validity research is limited, particularly regarding the use of such tools for detection of prodromal dementia in the DS population. The current project presents baseline cross-sectional SIB, BPT and DLD performance in order to characterise their predictive utility in discriminating normal cognition, possible dementia and probable dementia in adult DS. METHOD: Baseline SIB, BPT and DLD performances from 100 individuals (no dementia = 68, possible dementia = 16 & probable dementia = 16) were examined from a longitudinal cohort of aging individuals with DS. Receiver operating characteristic curves investigated the accuracy of these measures in relation to consensus dementia diagnoses, diagnoses which demonstrated high percent agreement with the examining neurologist's independent diagnostic impression. RESULTS: The SIB and BPT exhibited fair discrimination ability for differentiating no/possible versus probable dementia [area under the curve (AUC) = 0.61 and 0.66, respectively]. The DLD exhibited good discrimination ability for differentiating no versus possible/probable dementia (AUC = 0.75) and further demonstrated better performance of the DLD Cognitive subscale compared with the DLD Social subscale (AUC = 0.77 and 0.67, respectively). CONCLUSIONS: Results suggest that the SIB, BPT and DLD are able to reasonably discriminate consensus dementia diagnoses in individuals with DS, supporting their continued use in the clinical assessment of dementia in DS. The general performance of these measures suggests that further work in the area of test development is needed to improve on the AUCs for dementia status discrimination in this unique population. At present, however, the current findings suggest that the DLD may be the best option for reliable identification of prodromal dementia in this population, reinforcing the importance of including informant behaviour ratings in assessment of cognition for adults with DS.


Assuntos
Doença de Alzheimer , Demência , Síndrome de Down , Deficiências da Aprendizagem , Adulto , Estudos Transversais , Demência/diagnóstico , Síndrome de Down/complicações , Síndrome de Down/diagnóstico , Humanos , Testes Neuropsicológicos
12.
J Hosp Infect ; 117: 182-183, 2021 11.
Artigo em Inglês | MEDLINE | ID: mdl-34118344
13.
Physiotherapy ; 112: 55-63, 2021 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-34051594

RESUMO

OBJECTIVE: To explore entry-level physiotherapy students' attitudes and beliefs relating to weight bias and stigmatisation in healthcare. DESIGN: Cross sectional survey of physiotherapy students. METHODS: All final year physiotherapy students (n = 215) enrolled in entry-level physiotherapy programmes in the Republic of Ireland were invited to participate. Each received a questionnaire, consisting of 72 questions, within four key sections. Descriptive statistics and frequencies were used to analyse the data. RESULTS: A response rate of 83% (179/215) was achieved. Whilst physiotherapy students, overall, had a positive attitude towards people with obesity, 29% had a negative attitude towards people with obesity, 24% had a negative attitude towards managing this population and most (74%) believed obesity was caused by behavioural and individual factors. Over one third of students (35%) reported that they would not be confident in managing patients with obesity and more than half (54%) felt treating patients with obesity was not worthwhile. CONCLUSION: This study provides preliminary findings to suggest that weight stigma-reduction efforts are warranted for physiotherapy students. Helping students to understand that obesity is a complex, chronic condition with multiple aspects requiring a multi-faceted approach to its management might be the first step towards dispelling these negative attitudes towards patients living with obesity. Inclusion of a formal obesity curriculum should perhaps now be part of the contemporary physiotherapy students' education.


Assuntos
Preconceito de Peso , Atitude , Atitude do Pessoal de Saúde , Estudos Transversais , Conhecimentos, Atitudes e Prática em Saúde , Humanos , Irlanda , Modalidades de Fisioterapia , Estudantes , Inquéritos e Questionários
14.
Sci Total Environ ; 791: 146409, 2021 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-33771395

RESUMO

There is increasing research interest in the application of the ecosystem services (ES) concept in the environmental risk assessment of chemicals to support formulating and operationalising regulatory environmental protection goals and making environmental risk assessment more policy- and value-relevant. This requires connecting ecosystem structure and processes to ecosystem function and henceforth to provision of ecosystem goods and services and their economic valuation. Ecological production functions (EPFs) may help to quantify these connections in a transparent manner and to predict ES provision based on function-related descriptors for service providing species, communities, ecosystems or habitats. We review scientific literature for EPFs to evaluate availability across provisioning and regulation and maintenance services (CICES v5.1 classification). We found quantitative production functions for nearly all ES, often complemented with economic valuation of physical or monetary flows. We studied the service providing units in these EPFs to evaluate the potential for extrapolation of toxicity data for test species obtained from standardised testing to ES provision. A broad taxonomic representation of service providers was established, but quantitative models directly linking standard test species to ES provision were extremely scarce. A pragmatic way to deal with this data gap would be the use of proxies for related taxa and stepwise functional extrapolation to ES provision and valuation, which we conclude possible for most ES. We suggest that EPFs may be used in defining specific protection goals (SPGs), and illustrate, using pollination as an example, the availability of information for the ecological entity and attribute dimensions of SPGs. Twenty-five pollination EPFs were compiled from the literature for biological entities ranging from 'colony' to 'habitat', with 75% referring to 'functional group'. With about equal representation of the attributes 'function', 'abundance' and 'diversity', SPGs for pollination therefore would seem best substantiated by EPFs at the level of functional group.


Assuntos
Ecossistema , Monitoramento Ambiental , Conservação dos Recursos Naturais , Polinização , Medição de Risco
15.
J Hosp Infect ; 109: 88-95, 2021 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-33359899

RESUMO

BACKGROUND: Isolation precautions are recommended when caring for patients identified with highly resistant micro-organisms (HRMOs). However, the direct costs of patients in isolation are largely unknown. AIM: To obtain detailed information on the daily direct costs associated with isolating patients identified with HRMOs. METHODS: This study was performed from November until December 2017 on a 12-bed surgical ward. This ward contained solely isolation rooms with anterooms. The daily direct costs of isolation were based on three cost items: (1) additional personal protective equipment (PPE), measured by counting the consumption of empty packaging materials; (2) cleaning and disinfection of the isolation room, based on the costs of an outsourced cleaning company; and (3) additional workload for healthcare workers, based on literature and multiplied by the average gross hourly salary of nurses. A distinction was made between the costs for strict isolation, contact-plus isolation, and contact isolation. FINDINGS: During the study period, 26 patients were nursed in isolation because of HRMO carriage. Time for donning and doffing of PPE was 31 min per day. The average daily direct costs of isolation were the least expensive for contact isolation (gown, gloves), €28/$31, and the most expensive for strict isolation (surgical mask, gloves, gown, cap), €41/$47. CONCLUSION: Using a novel, easy method to estimate consumption of PPE, we conclude that the daily direct costs of isolating a patient differ per type of isolation. Insight into the direct costs of isolation is of utmost importance when developing or updating infection prevention policies.


Assuntos
Infecção Hospitalar , Custos de Cuidados de Saúde , Controle de Infecções/economia , Isolamento de Pacientes/economia , Desinfecção , Pessoal de Saúde , Hospitais , Humanos , Máscaras , Equipamento de Proteção Individual , Roupa de Proteção , Carga de Trabalho
16.
PLoS One ; 15(10): e0240995, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-33112893

RESUMO

OBJECTIVE: The objective of this study was to identify risk factors for surgical site infection from digestive, thoracic and orthopaedic system surgeries using clinical and data-driven cut-off values. A second objective was to compare the identified risk factors in this study to risk factors identified in literature. SUMMARY BACKGROUND DATA: Retrospective data of 3 250 surgical procedures performed in large tertiary care hospital in The Netherlands during January 2013 to June 2014 were used. METHODS: Potential risk factors were identified using a literature scan and univariate analysis. A multivariate forward-step logistic regression model was used to identify risk factors. Standard medical cut-off values were compared with cut-offs determined from the data. RESULTS: For digestive, orthopaedic and thoracic system surgical procedures, the risk factors identified were preoperative temperature of ≥38°C and antibiotics used at the time of surgery. C-reactive protein and the duration of the surgery were identified as a risk factors for digestive surgical procedures. Being an adult (age ≥18) was identified as a protective effect for thoracic surgical procedures. Data-driven cut-off values were identified for temperature, age and CRP which can explain the SSI outcome up to 19.5% better than generic cut-off values. CONCLUSIONS: This study identified risk factors for digestive, orthopaedic and thoracic system surgical procedures and illustrated how data-driven cut-offs can add value in the process. Future studies should investigate if data-driven cut-offs can add value to explain the outcome being modelled and not solely rely on standard medical cut-off values to identify risk factors.


Assuntos
Procedimentos Ortopédicos/efeitos adversos , Infecção da Ferida Cirúrgica/etiologia , Adolescente , Feminino , Humanos , Masculino , Estudos Retrospectivos , Fatores de Risco , Adulto Jovem
17.
J Intellect Disabil Res ; 64(12): 934-945, 2020 12.
Artigo em Inglês | MEDLINE | ID: mdl-32996650

RESUMO

BACKGROUND: People with Down syndrome (DS) develop Alzheimer's disease (AD) at an earlier age of onset than those with sporadic AD. AD neuropathology is typically present in DS by 40 years of age with an onset of dementia approximately 10 years later. This early onset is due to the overexpression of amyloid precursor protein from the third copy of chromosome 21. Cerebrovascular neuropathology is thought to contribute in 40-60% of cases sporadic AD. However, the vascular contribution to dementia in people with DS has been relatively unexplored. We hypothesised that vascular perfusion is compromised in older adults with DS relative to younger individuals and is further exacerbated in those with dementia. METHOD: Cerebral blood flow (CBF) was measured using pulsed arterial spin labelling in 35 cognitively characterised adults with DS (26-65 years). DS participants were also compared with 15 control subjects without DS or dementia (26-65 years). Linear regression evaluated the difference in CBF across groups and diagnosis along with assessing the association between CBF and cognitive measures within the DS cohort. RESULTS: Cerebral blood flow was significantly lower among DS participants with probable AD compared with controls (P = 0.02) and DS participants with no dementia (P = 0.01). Within the DS cohort, CBF was significantly associated with the Severe Impairment Battery (SIB) measure and the Dementia Questionnaire for People with Learning Disabilities (DLD) rating (F3,25  = 5.13; P = 0.007). Both the SIB (ß = 0.74; t = 2.71; P = 0.01) and DLD (ß = -0.96; t = -3.87; P < 0.001) indicated greater impairment as global CBF decreased. Age was significantly associated with CBF among participants with DS. There was a non-linear effect of age, whereby CBF declined more rapidly after 45 years of age. CONCLUSIONS: This preliminary study of CBF in DS indicates that cerebrovascular pathology may be a significant contributor to dementia in DS. CBF was associated with diagnosis, cognition and age. Notably, CBF decreases at a greater rate after age 45 and may represent a significant prodromal event in AD progression.


Assuntos
Envelhecimento/fisiologia , Circulação Cerebrovascular/fisiologia , Demência/epidemiologia , Síndrome de Down/epidemiologia , Adulto , Idoso , Comorbidade , Demência/fisiopatologia , Síndrome de Down/fisiopatologia , Feminino , Humanos , Estudos Longitudinais , Masculino , Pessoa de Meia-Idade , Estados Unidos/epidemiologia
18.
J Am Chem Soc ; 142(27): 11691-11697, 2020 07 08.
Artigo em Inglês | MEDLINE | ID: mdl-32564602

RESUMO

Alkyl chlorides are bench-stable chemical feedstocks that remain among the most underutilized electrophile classes in transition metal catalysis. Overcoming intrinsic limitations of C(sp3)-Cl bond activation, we report the development of a novel organosilane reagent that can participate in chlorine atom abstraction under mild photocatalytic conditions. In particular, we describe the application of this mechanism to a dual nickel/photoredox catalytic protocol that enables the first cross-electrophile coupling of unactivated alkyl chlorides and aryl chlorides. Employing these low-toxicity, abundant, and commercially available organochloride building blocks, this methodology allows access to a broad array of highly functionalized C(sp2)-C(sp3) coupled adducts, including numerous drug analogues.


Assuntos
Hidrocarbonetos Clorados/química , Catálise , Estrutura Molecular , Níquel/química , Oxirredução , Processos Fotoquímicos
19.
J Phys Chem B ; 124(24): 5073-5078, 2020 06 18.
Artigo em Inglês | MEDLINE | ID: mdl-32432473

RESUMO

A study of the dynamics of a series of biphenyl compounds having varying chlorine levels was carried out. Increasing the chlorine content increases the glass transition temperature and makes the dynamics substantially more sensitive to density changes. Nonetheless, in the vicinity of their respective glass transitions, the different liquids display very similar extents of dynamic correlation and dynamic heterogeneity. The slight narrowing of the relaxation peak with increasing chlorine follows the general trend of the effect of increasing molecular polarity. This relationship between the peak breadth and dipole moment was reproduced in molecular dynamics simulations of a simplified model of the Aroclor molecule.

20.
J Phys Chem B ; 124(7): 1240-1244, 2020 Feb 20.
Artigo em Inglês | MEDLINE | ID: mdl-31999929

RESUMO

We examine the density scaling properties of two ionic materials, a classic aprotic low molecular weight ionic liquid, 1-butyl-3-methylimidazolium bis(perfluoroethylsulfonyl)imide ([BMIm][BETI]), and a polymeric ionic liquid, poly(3-methyl-1,2,3-triazolium bis(trifluoromethylsulfonyl)imide) (TPIL). Density scaling is known to apply rigorously to simple liquids lacking specific intermolecular associations such as hydrogen bonds. Previous work has found that ionic liquids conform to density scaling over limited ranges of temperature and pressure. In this work, we find that the dc-conductivity of [BMIm][BETI] accurately scales for density changes of 17%; however, there is a departure from scaling for TPIL for even more modest variations of temperature and pressure. The entropy of both ionic samples conforms to density scaling only if the scaling exponent is allowed to vary linearly with the magnitude of the entropy.

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