Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 51
Filtrar
1.
Proc Natl Acad Sci U S A ; 121(23): e2400727121, 2024 Jun 04.
Artigo em Inglês | MEDLINE | ID: mdl-38819998

RESUMO

Understanding the interplay between charge, nematic, and structural ordering tendencies in cuprate superconductors is critical to unraveling their complex phase diagram. Using pump-probe time-resolved resonant X-ray scattering on the (0 0 1) Bragg peak at the Cu [Formula: see text] and O [Formula: see text] resonances, we investigate nonequilibrium dynamics of [Formula: see text] nematic order and its association with both charge density wave (CDW) order and lattice dynamics in La[Formula: see text]Eu[Formula: see text]Sr[Formula: see text]CuO[Formula: see text]. The orbital selectivity of the resonant X-ray scattering cross-section allows nematicity dynamics associated with the planar O 2[Formula: see text] and Cu 3[Formula: see text] states to be distinguished from the response of anisotropic lattice distortions. A direct time-domain comparison of CDW translational-symmetry breaking and nematic rotational-symmetry breaking reveals that these broken symmetries remain closely linked in the photoexcited state, consistent with the stability of CDW topological defects in the investigated pump fluence regime.

2.
J Mol Evol ; 2024 Jul 17.
Artigo em Inglês | MEDLINE | ID: mdl-39020132

RESUMO

Current evidence suggests that some form of cellular organization arose well before the time of the last universal common ancestor (LUCA). Standard phylogenetic analyses have shown that several protein families associated with membrane translocation, membrane transport, and membrane bioenergetics were very likely present in the proteome of the LUCA. Despite these cellular systems emerging prior to the LUCA, extant archaea, bacteria, and eukaryotes have significant differences in cellular infrastructure and the molecular functions that support it, leading some researchers to argue that true cellularity did not evolve until after the LUCA. Here, we use recently reconstructed minimal proteomes of the LUCA as well as the last archaeal common ancestor (LACA) and the last bacterial common ancestor (LBCA) to characterize the evolution of cellular systems along the first branches of the tree of life. We find that a broad set of functions associated with cellular organization were already present by the time of the LUCA. The functional repertoires of the LACA and LBCA related to cellular organization nearly doubled along each branch following the divergence of the LUCA. These evolutionary trends created the foundation for similarities and differences in cellular organization between the taxonomic domains that are still observed today.

3.
Kidney Int ; 104(5): 995-1007, 2023 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-37598857

RESUMO

Autosomal dominant polycystic kidney disease (ADPKD) resulting from pathogenic variants in PKD1 and PKD2 is the most common form of PKD, but other genetic causes tied to primary cilia function have been identified. Biallelic pathogenic variants in the serine/threonine kinase NEK8 cause a syndromic ciliopathy with extra-kidney manifestations. Here we identify NEK8 as a disease gene for ADPKD in 12 families. Clinical evaluation was combined with functional studies using fibroblasts and tubuloids from affected individuals. Nek8 knockout mouse kidney epithelial (IMCD3) cells transfected with wild type or variant NEK8 were further used to study ciliogenesis, ciliary trafficking, kinase function, and DNA damage responses. Twenty-one affected monoallelic individuals uniformly exhibited cystic kidney disease (mostly neonatal) without consistent extra-kidney manifestations. Recurrent de novo mutations of the NEK8 missense variant p.Arg45Trp, including mosaicism, were seen in ten families. Missense variants elsewhere within the kinase domain (p.Ile150Met and p.Lys157Gln) were also identified. Functional studies demonstrated normal localization of the NEK8 protein to the proximal cilium and no consistent cilia formation defects in patient-derived cells. NEK8-wild type protein and all variant forms of the protein expressed in Nek8 knockout IMCD3 cells were localized to cilia and supported ciliogenesis. However, Nek8 knockout IMCD3 cells expressing NEK8-p.Arg45Trp and NEK8-p.Lys157Gln showed significantly decreased polycystin-2 but normal ANKS6 localization in cilia. Moreover, p.Arg45Trp NEK8 exhibited reduced kinase activity in vitro. In patient derived tubuloids and IMCD3 cells expressing NEK8-p.Arg45Trp, DNA damage signaling was increased compared to healthy passage-matched controls. Thus, we propose a dominant-negative effect for specific heterozygous missense variants in the NEK8 kinase domain as a new cause of PKD.


Assuntos
Doenças Renais Policísticas , Rim Policístico Autossômico Dominante , Animais , Humanos , Recém-Nascido , Camundongos , Proteínas de Transporte/metabolismo , Cílios/patologia , Rim/metabolismo , Mutação , Quinases Relacionadas a NIMA/genética , Quinases Relacionadas a NIMA/metabolismo , Doenças Renais Policísticas/genética , Rim Policístico Autossômico Dominante/patologia , Proteínas Serina-Treonina Quinases/genética , Proteínas Serina-Treonina Quinases/metabolismo , Serina/genética , Serina/metabolismo , Canais de Cátion TRPP/genética , Canais de Cátion TRPP/metabolismo
4.
Fam Process ; 62(2): 653-670, 2023 06.
Artigo em Inglês | MEDLINE | ID: mdl-35655389

RESUMO

Little research has examined the potential spillover of parenting difficulties in the coparental stepfamily subsystem. Using family systems theory as a guide, we longitudinally examined: (a) whether early parenting difficulties within stepfamilies persist 1 year later and (b) whether the parenting difficulties experienced by one partner impact the parenting difficulties of the other partner within remarriages. Copies of marriage licenses were used to identify remarried individuals. Surveys were mailed out, with follow-up surveys mailed a year later, resulting in a sample of 676 remarried couples (the majority of which were White and college educated). The sample was split into three groups, according to stepfamily constellation: (a) families with a stepfather and biological mother; (b) families with a biological father and a stepmother; and (c) families with both stepfathers and stepmothers. We estimated three different actor-partner interdependence models (APIM), one for each group. Consistent with family systems theory, our findings showed that parenting and stepparenting difficulties were interrelated, though gendered in effect. All parenting and stepparenting difficulties displayed actor effects, suggesting that parenting difficulties persist 1 year later. However, the only cross-spouse influences (partner effects) were such that the mother's parenting difficulties (of her own biological children) were predicted by the father's parenting and stepparenting difficulties, and these differed by stepfamily constellation. Implications regarding gendered expectations, the importance of the coparenting subsystem in stepfamilies, early establishment of parental boundaries, and the (potentially important) inclusion of the stepfather in the parenting dynamics are discussed.


Assuntos
Estrutura Familiar , Poder Familiar , Masculino , Criança , Feminino , Humanos , Pais , Pai , Mães
5.
Gynecol Oncol ; 165(3): 610-618, 2022 06.
Artigo em Inglês | MEDLINE | ID: mdl-35351333

RESUMO

OBJECTIVE: Personalised care requires the identification of modifiable risk factors so that interventions can be implemented rapidly following a gynaecological cancer diagnosis. Our objective was to determine what pre-treatment factors are associated with quality of life (QOL) at baseline (pre-treatment) and 12 months. METHODS: 1222 women with a confirmed diagnosis of endometrial, ovarian, cervical or vulvar cancer from 82 UK NHS hospitals agreed to complete questionnaires at baseline, three and 12 months. Questionnaires included measures of QOL, health, lifestyle, support and self-management. The primary outcome measure was QOL as measured by Quality of Life in Adult Cancer Survivors (QLACS). Sites provided clinical data at baseline, six and 12 months. Linear regression models were constructed to examine the association between baseline characteristics and QOL outcomes. RESULTS: QOL declined between baseline and 3 months, followed by an improvement at 12 months. Baseline (pre-treatment) factors associated with worse QOL at both baseline and 12 months were depression, anxiety, living in a more deprived area and comorbidities which limit daily activities, whereas higher self-efficacy and age of 50+ years were associated with better QOL. CONCLUSIONS: Depression, anxiety and self-efficacy are modifiable risk factors that can impact on QOL. Screening for these, and assessment of whether comorbidities limit daily activities, should be incorporated in a holistic needs assessment and interventions to improve self-efficacy should be made available. Care can then be personalised from the outset to enable all women with a gynaecological cancer the opportunity to have the best QOL.


Assuntos
Neoplasias dos Genitais Femininos , Qualidade de Vida , Adulto , Ansiedade/etiologia , Estudos de Coortes , Feminino , Neoplasias dos Genitais Femininos/diagnóstico , Neoplasias dos Genitais Femininos/epidemiologia , Neoplasias dos Genitais Femininos/terapia , Humanos , Pessoa de Meia-Idade , Inquéritos e Questionários , Reino Unido
6.
Am J Physiol Heart Circ Physiol ; 320(3): H1136-H1155, 2021 03 01.
Artigo em Inglês | MEDLINE | ID: mdl-33449851

RESUMO

Aging is associated with increased risk of cardiovascular and cerebrovascular events, which are preceded by early, negative remodeling of the vasculature. Low physical activity is a well-established risk factor associated with the incidence and development of disease. However, recent physical activity literature indicates the importance of considering the 24-h movement spectrum. Therefore, the purpose of this review was to examine the impact of the 24-h movement spectrum, specifically physical activity (aerobic and resistance training), sedentary behavior, and sleep, on cardiovascular and cerebrovascular outcomes in older adults, with a focus on recent evidence (<10 yr) and sex-based considerations. The review identifies that both aerobic training and being physically active (compared with sedentary) are associated with improvements in endothelial function, arterial stiffness, and cerebrovascular function. Additionally, there is evidence of sex-based differences in endothelial function: a blunted improvement in aerobic training in postmenopausal women compared with men. While minimal research has been conducted in older adults, resistance training does not appear to influence arterial stiffness. Poor sleep quantity or quality are associated with both impaired endothelial function and increased arterial stiffness. Finally, the review highlights mechanistic pathways involved in the regulation of vascular and cerebrovascular function, specifically the balance between pro- and antiatherogenic factors, which mediate the relationship between the 24-h movement spectrum and vascular outcomes. Finally, this review proposes future research directions: examining the role of duration and intensity of training, combining aerobic and resistance training, and exploration of sex-based differences in cardiovascular and cerebrovascular outcomes.


Assuntos
Ciclos de Atividade , Envelhecimento , Doenças Cardiovasculares/prevenção & controle , Remodelação Vascular , Fatores Etários , Doenças Cardiovasculares/etiologia , Doenças Cardiovasculares/fisiopatologia , Transtornos Cerebrovasculares/etiologia , Transtornos Cerebrovasculares/fisiopatologia , Transtornos Cerebrovasculares/prevenção & controle , Feminino , Nível de Saúde , Estilo de Vida Saudável , Humanos , Masculino , Fatores de Proteção , Treinamento Resistido , Medição de Risco , Fatores de Risco , Comportamento de Redução do Risco , Comportamento Sedentário , Fatores Sexuais , Sono , Fatores de Tempo
7.
Colorectal Dis ; 23(12): 3234-3250, 2021 12.
Artigo em Inglês | MEDLINE | ID: mdl-34679253

RESUMO

AIM: Depression experienced by people with colorectal cancer (CRC) is an important clinical problem affecting quality of life. Recognition of depression at key points in the pathway enables timely referral to support. This study aimed to examine depression before and 5 years after surgery to examine its prevalence and identify determinants. METHOD: The ColoREctal Wellbeing (CREW) study is a prospective UK cohort study involving 872 adults with nonmetastatic CRC recruited before surgery with curative intent. Questionnaires completed before surgery and 3, 9, 15, 24, 36, 48 and 60 months after surgery captured socio-demographics and assessed depression (Centre for Epidemiologic Studies Depression Scale, CES-D) and other psychosocial factors. Clinical details were also gathered. We present the prevalence of clinically significant depression (CES-D ≥ 20) over time and its predictors assessed before and 2 years after surgery. RESULTS: Before surgery, 21.0% of the cohort reported CES-D ≥ 20 reducing to 14.7% 5 years after surgery. Presurgery risk factors predicting subsequent depression were clinically significant depression and anxiety, previous mental health service use, low self-efficacy, poor health, having neoadjuvant treatment and low social support. Postsurgery risk factors at 2 years predicting subsequent depression were clinically significant depression, negative affect, cognitive dysfunction, accommodation type and poor health. CONCLUSION: Depression is highly pervasive in people with CRC, exceeding prevalence in the general population across follow-up. Our findings emphasize the need to screen and treat depression across the pathway. Our novel data highlight key risk factors of later depression at important and opportune time points: before surgery and at the end of routine surveillance. Early recognition and timely referral to appropriate support is vital to improve long-term psychological outcomes.


Assuntos
Neoplasias Colorretais , Qualidade de Vida , Adulto , Ansiedade , Estudos de Coortes , Neoplasias Colorretais/epidemiologia , Neoplasias Colorretais/cirurgia , Depressão/epidemiologia , Depressão/etiologia , Humanos , Prevalência , Estudos Prospectivos
8.
Opt Express ; 28(16): 23545-23553, 2020 Aug 03.
Artigo em Inglês | MEDLINE | ID: mdl-32752349

RESUMO

We design and realize an arrival time diagnostic for ultrashort X-ray pulses achieving unprecedented high sensitivity in the soft X-ray regime via cross-correlation with a ≈1550 nm optical laser. An interferometric detection scheme is combined with a multi-layer sample design to greatly improve the sensitivity of the measurement. We achieve up to 275% of relative signal change when exposed to 1.6 mJ/cm2 of soft X-rays at 530 eV, more than a hundred-fold improvement in sensitivity as compared to previously reported techniques. The resolution of the arrival time measurement is estimated to around 2.8 fs (rms). The demonstrated X-ray arrival time monitor paves the way for sub-10 fs-level timing jitter at high repetition rate X-ray facilities.

9.
Arterioscler Thromb Vasc Biol ; 39(10): 2168-2191, 2019 10.
Artigo em Inglês | MEDLINE | ID: mdl-31434495

RESUMO

OBJECTIVE: Endothelial cells (EC) in obese adipose tissue (AT) are exposed to a chronic proinflammatory environment that may induce a mesenchymal-like phenotype and altered function. The objective of this study was to establish whether endothelial-to-mesenchymal transition (EndoMT) is present in human AT in obesity and to investigate the effect of such transition on endothelial function and the endothelial particulate secretome represented by extracellular vesicles (EV). Approach and Results: We identified EndoMT in obese human AT depots by immunohistochemical co-localization of CD31 or vWF and α-SMA (alpha-smooth muscle actin). We showed that AT EC exposed in vitro to TGF-ß (tumor growth factor-ß), TNF-α (tumor necrosis factor-α), and IFN-γ (interferon-γ) undergo EndoMT with progressive loss of endothelial markers. The phenotypic change results in failure to maintain a tight barrier in culture, increased migration, and reduced angiogenesis. EndoMT also reduced mitochondrial oxidative phosphorylation and glycolytic capacity of EC. EVs produced by EC that underwent EndoMT dramatically reduced angiogenic capacity of the recipient naïve ECs without affecting their migration or proliferation. Proteomic analysis of EV produced by EC in the proinflammatory conditions showed presence of several pro-inflammatory and immune proteins along with an enrichment in angiogenic receptors. CONCLUSIONS: We demonstrated the presence of EndoMT in human AT in obesity. EndoMT in vitro resulted in production of EV that transferred some of the functional and metabolic features to recipient naïve EC. This result suggests that functional and molecular features of EC that underwent EndoMT in vivo can be disseminated in a paracrine or endocrine fashion and may induce endothelial dysfunction in distant vascular beds.


Assuntos
Tecido Adiposo/irrigação sanguínea , Transição Epitelial-Mesenquimal/genética , Neovascularização Patológica/genética , Obesidade/genética , Fator de Crescimento Transformador beta1/farmacologia , Tecido Adiposo/metabolismo , Análise de Variância , Biomarcadores/metabolismo , Estudos de Casos e Controles , Movimento Celular/genética , Proliferação de Células/genética , Células Cultivadas , Células Endoteliais/metabolismo , Transição Epitelial-Mesenquimal/efeitos dos fármacos , Citometria de Fluxo/métodos , Humanos , Obesidade/fisiopatologia , Proteômica/métodos
10.
Opt Lett ; 44(2): 243-246, 2019 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-30644871

RESUMO

The normalization of scattered intensity by incident flux is a crucial step in analyzing data from stochastic x-ray free electron laser sources and is complicated by non-linearities traditionally attributed to detector saturation. Here we show that such non-linearities can also arise when the sample spectra are non-uniform within the monochromator bandwidth. A method for modeling and removing this non-linearity using multivariate regression with shot-by-shot x-ray photon energy as an independent variable is presented. This approach demonstrates the benefit of event building and will allow for a reconsideration of data which has proven challenging to normalize.

11.
Chemistry ; 24(53): 14127-14136, 2018 Sep 20.
Artigo em Inglês | MEDLINE | ID: mdl-29573487

RESUMO

In an attempt to prepare new Fe catalysts for the dehydrocoupling of amine-boranes and to provide mechanistic insight, the paramagnetic FeII dimeric complex [Cp'FeI]2 (1) (Cp'=η5 -((1,2,4-tBu)3 C5 H2 )) was used as a precursor to a series of cyclopentadienyl FeII and FeIII mononuclear species. The complexes prepared were [Cp'Fe(η6 -Tol)][Cp'FeI2 ] (2) (Tol=C6 H5 Me), [Cp'Fe(η6 -Tol)][BArF4 ] (3) (BArF4 =[B(C6 H3 (m-CF3 )2 )4 ]- ), [N(nBu)4 ][Cp'FeI2 ] (4), Cp'FeI2 (5), and [Cp'Fe(MeCN)3 ][BArF4 ] (6). The electronic structure of the [Cp'FeI2 ]- anion in 2 and 4 was investigated by SQUID magnetometry, EPR spectroscopy and ab initio Complete Active Space Self Consistent Field-Spin Orbit (CASSCF-SO) calculations, and the studies revealed a strongly anisotropic S=2 ground state. Complexes 1-6 were investigated as catalysts for the dehydrocoupling of Me2 NH⋅BH3 (I) in THF at 20 °C to yield the cyclodiborazane product [Me2 N-BH2 ]2 (IV). Complexes 1-4 and 6 were active dehydrocoupling catalysts towards I (5 mol % loading), however 5 was inactive, and ultra-violet (UV) irradiation was required for the reaction mediated by 3. Complex 6 was found to be the most active precatalyst, reaching 80 % conversion to IV after 19 h at 22 °C. Dehydrocoupling of I by 1-4 proceeded via formation of the aminoborane Me2 N=BH2 (II) as the major intermediate, whereas for 6 the linear diborazane Me2 NH-BH2 -NMe2 -BH3 (III) could be detected, together with trace amounts of II. Reactions of 1 and 6 with Me3 N⋅BH3 were investigated in an attempt to identify Fe-based intermediates in the catalytic reactions. The σ-complex [Cp'Fe(MeCN)(κ2 -H2 BH⋅NMe2 H][BArF4 ] was proposed to initially form in dehydrocoupling reactions involving 6 based on ESI-MS (ESI=Electrospray Ionisation Mass Spectroscopy) and NMR spectroscopic evidence. The latter also suggests that these complexes function as precursors to iron hydrides which may be the true catalytic species.

12.
J Synchrotron Radiat ; 24(Pt 6): 1180-1186, 2017 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-29091061

RESUMO

A method for measuring resonant inelastic X-ray scattering based on the conversion of X-ray photons into photoelectrons is presented. The setup is compact, relies on commercially available detectors, and offers significant flexibility. This method is demonstrated at the Linac Coherent Light Source with ∼0.5 eV resolution at the cobalt L3-edge, with signal rates comparable with traditional grating spectrometers.

13.
J Gerontol Soc Work ; 60(8): 619-646, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-28929943

RESUMO

This study measured the need for formal alternative modes of transportation among older adults by applying traditional factors of the Behavioral Model. Survey participants who regularly drove were compared to those who could no longer drive. Race/ethnicity and self-reported health were significant predictors of perceived need for transportation services for both groups. However, income and service awareness were significant predictors only for drivers, while family proximity was a significant predictor only for non-drivers. Results suggest the importance of gaining a better understanding of the factors associated with need for senior-focused transportation services to more effectively plan such programs.


Assuntos
Condução de Veículo/normas , Avaliação das Necessidades , Meios de Transporte/métodos , Idoso , Idoso de 80 Anos ou mais , Feminino , Humanos , Renda/estatística & dados numéricos , Masculino , Pessoa de Meia-Idade , Análise Multivariada , Inquéritos e Questionários , Meios de Transporte/normas
14.
Opt Express ; 24(20): 22469-22480, 2016 Oct 03.
Artigo em Inglês | MEDLINE | ID: mdl-27828320

RESUMO

X-ray free electron lasers (XFELs) enable unprecedented new ways to study the electronic structure and dynamics of transition metal systems. L-edge absorption spectroscopy is a powerful technique for such studies and the feasibility of this method at XFELs for solutions and solids has been demonstrated. However, the required x-ray bandwidth is an order of magnitude narrower than that of self-amplified spontaneous emission (SASE), and additional monochromatization is needed. Here we compare L-edge x-ray absorption spectroscopy (XAS) of a prototypical transition metal system based on monochromatizing the SASE radiation of the linac coherent light source (LCLS) with a new technique based on self-seeding of LCLS. We demonstrate how L-edge XAS can be performed using the self-seeding scheme without the need of an additional beam line monochromator. We show how the spectral shape and pulse energy depend on the undulator setup and how this affects the x-ray spectroscopy measurements.

15.
J Synchrotron Radiat ; 22(3): 498-502, 2015 May.
Artigo em Inglês | MEDLINE | ID: mdl-25931059

RESUMO

The Soft X-ray Research instrument provides intense ultrashort X-ray pulses in the energy range 280-2000 eV. A diverse set of experimental stations may be installed to investigate a broad range of scientific topics such as ultrafast chemistry, highly correlated materials, magnetism, surface science, and matter under extreme conditions. A brief description of the main instrument components will be given, followed by some selected scientific highlights.

16.
J Synchrotron Radiat ; 22(3): 606-11, 2015 May.
Artigo em Inglês | MEDLINE | ID: mdl-25931075

RESUMO

A gas monitor detector was implemented and characterized at the Soft X-ray Research (SXR) instrument to measure the average, absolute and pulse-resolved photon flux of the LCLS beam in the energy range between 280 and 2000 eV. The detector is placed after the monochromator and addresses the need to provide reliable absolute pulse energy as well as pulse-resolved measurements for the various experiments at this instrument. This detector provides a reliable non-invasive measurement for determining flux levels on the samples in the downstream experimental chamber and for optimizing signal levels of secondary detectors and for the essential need of data normalization. The design, integration into the instrument and operation are described, and examples of its performance are given.

17.
J Synchrotron Radiat ; 22(3): 621-5, 2015 May.
Artigo em Inglês | MEDLINE | ID: mdl-25931077

RESUMO

This paper describes the development of new instrumentation at the Linac Coherent Light Source for conducting THz excitation experiments in an ultra high vacuum environment probed by soft X-ray diffraction. This consists of a cantilevered, fully motorized mirror system which can provide 600 kV cm(-1) electric field strengths across the sample and an X-ray detector that can span the full Ewald sphere with in-vacuum motion. The scientific applications motivated by this development, the details of the instrument, and spectra demonstrating the field strengths achieved using this newly developed system are discussed.

18.
Angew Chem Int Ed Engl ; 54(16): 4836-41, 2015 Apr 13.
Artigo em Inglês | MEDLINE | ID: mdl-25712707

RESUMO

The catalyst loading is the key to control the molecular weight of the polymer in the iron-catalyzed dehydropolymerization of phosphine-borane adducts. Studies showed that the reaction proceeds through a chain-growth coordination-insertion mechanism.

19.
J Am Chem Soc ; 136(8): 3048-64, 2014 Feb 26.
Artigo em Inglês | MEDLINE | ID: mdl-24527706

RESUMO

The readily available iron carbonyl complexes, [CpFe(CO)2]2 (1) and CpFe(CO)2I (2) (Cp = η-C5H5), were found to be efficient precatalysts for the dehydrocoupling/dehydrogenation of the amine-borane Me2NH·BH3 (3) to afford the cyclodiborazane [Me2N-BH2]2 (4), upon UV photoirradiation at ambient temperature. In situ analysis of the reaction mixtures by (11)B NMR spectroscopy indicated that different two-step mechanisms operate in each case. Thus, precatalyst 1 dehydrocoupled 3 via the aminoborane Me2N═BH2 (5) which then cyclodimerized to give 4 via an off-metal process. In contrast, the reaction with precatalyst 2 proceeded via Me2NH-BH2-NMe2-BH3 (6) as the key intermediate, affording 4 as the final product after a second metal-mediated step. The related complex Cp2Fe2(CO)3(MeCN) (7), formed by photoirradiation of 1 in MeCN, was found to be a substantially more active dehydrocoupling catalyst and not to require photoactivation, but otherwise operated via a two-step mechanism analogous to that for 1. Significantly, detailed mechanistic studies indicated that the active catalyst generated from precatalyst 7 was heterogeneous in nature and consisted of small iron nanoparticles (≤10 nm). Although more difficult to study, a similar process is highly likely to operate for precatalyst 1 under photoirradiation conditions. In contrast to the cases of 7 and 1, analogous experimental studies for the case of photoactivated Fe precatalyst 2 suggested that the active catalyst formed in this case was homogeneous. Experimental and computational DFT studies were used to explore the catalytic cycle which appears to involve amine-borane ligated [CpFe(CO)](+) as a key intermediate.

20.
Chemistry ; 20(52): 17624-34, 2014 Dec 22.
Artigo em Inglês | MEDLINE | ID: mdl-25358970

RESUMO

The modes of interaction of donor-stabilized Group 13 hydrides (E=Al, Ga) were investigated towards 14- and 16-electron transition-metal fragments. More electron-rich N-heterocyclic carbene-stabilized alanes/gallanes of the type NHC⋅EH3 (E=Al or Ga) exclusively generate κ(2) complexes of the type [M(CO)4 (κ(2)-H3 E⋅NHC)] with [M(CO)4 (COD)] (M=Cr, Mo), including the first κ(2) σ-gallane complexes. ß-Diketiminato ('nacnac')-stabilized systems, {HC(MeCNDipp)2 }EH2 , show more diverse reactivity towards Group 6 carbonyl reagents. For {HC(MeCNDipp)2 }AlH2, both κ(1) and κ(2) complexes were isolated, while [Cr(CO)4 (κ(2)-H2 Ga{(NDippCMe)2 CH})] is the only simple κ(2) adduct of the nacnac-stabilized gallane which can be trapped, albeit as a co-crystallite with the (dehydrogenated) gallylene system [Cr(CO)5 (Ga{(NDippCMe)2 CH})]. Reaction of [Co2 (CO)8] with {HC(MeCDippN)2 }AlH2 generates [(OC)3 Co(µ-H)2 Al{(NdippCme)2 CH}][Co(CO)4] (12), which while retaining direct AlH interactions, features a hitherto unprecedented degree of bond activation in a σ-alane complex.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA