In this work we present, to our knowledge for the first time, the results of a transient infrared spectroscopic study of the photoinduced valence tautomerism process in cobaltdioxolene complexes with ...sub-picosecond time resolution. The molecular systems investigated were Co(tpa)(diox)PF
6
(
1
) and Co(Me
3
tpa)(diox)PF
6
(
2
), where diox = 3,5-di-
tert
-butyl-1,2-dioxolene; tpa = tris(2-pyridylmethyl)amine and Me
3
tpa its 6-methylated analogue. Complex (
1
) is present in solution as ls-Co
III
(catecholate) (
1-CAT
), while (
2
) as hs-Co
II
(semiquinonate) (
2-SQ
). DFT calculation of the harmonic frequencies for (
1
) and (
2
) allowed us to identify the vibrational markers of catecholate and semiquinonate redox isomers. Irradiation with 405 and 810 nm pulses (35 fs) of (
1-CAT
) induces the formation of an intermediate excited species from which the ground state population is recovered with a time constant of 1.5 0.3 ns. Comparing the 1 ns transient infrared spectrum with the experimental difference spectrum FTIR
(
2-SQ
)
FTIR
(
1-CAT
)
and with the calculated difference spectrum IR
c
(
1-SQ
)
IR
c
(
1-CAT
)
we are able to unequivocally identify the long lived species as the semiquinonate redox isomer of (
1
). On the other hand, no evidence of photoconversion is observed upon irradiation of (
2
) with 405 nm. Temporal evolution of transient spectra was analyzed with the combined approach consisting of singular values decomposition and global fitting (global analysis). After 405 and 810 nm excitation of (
1-CAT
), the semiquinonate excited species is formed on an ultrafast time scale (<200 fs) and cools down within the first 50 ps. Excitation of (
2-SQ
) with 405 nm wavelength produces a short lived excited state in which the semiquinonate nature of dioxolene is preserved and the ground state recovery is completed within 30 ps.
Characterization of the photoinduced valence tautomerism process in cobaltdioxolene complexes using transient infrared spectroscopy.
Two-dimensional electronic spectroscopy (2DES) is an incisive tool for disentangling excited state energies and dynamics in the condensed phase by directly mapping out the correlation between ...excitation and emission frequencies as a function of time. Despite its enhanced frequency resolution, the spectral window of detection is limited to the laser bandwidth, which has often hindered the visualization of full electronic energy relaxation pathways spread over the entire visible region. Here, we describe a high-sensitivity, ultrabroadband 2DES apparatus. We report a new combination of a simple and robust setup for increased spectral bandwidth and shot-to-shot detection. We utilize 8-fs supercontinuum pulses generated by gas filamentation spanning the entire visible region (450 - 800 nm), which allows for a simultaneous interrogation of electronic transitions over a 200-nm bandwidth, and an all-reflective interferometric delay system with angled nanopositioner stages achieves interferometric precision in coherence time control without introducing wavelength-dependent dispersion to the ultrabroadband spectrum. To address deterioration of detection sensitivity due to the inherent instability of ultrabroadband sources, we introduce a 5-kHz shot-to-shot, dual chopping acquisition scheme by combining a high-speed line-scan camera and two optical choppers to remove scatter contributions from the signal. Comparison of 2D spectra acquired by shot-to-shot detection and averaged detection shows a 15-fold improvement in the signal-to-noise ratio. This is the first direct quantification of detection sensitivity on a filamentation-based ultrabroadband 2DES apparatus.
Growing evidence supports the suggestion that the peripheral immune system plays a role in different pathologies associated with cognitive impairment, such as vascular dementia (VD) or Alzheimer's ...disease (AD). The aim of this review is to summarize, within the peripheral immune system, the implications of different types of myeloid cells in AD and VD, with a special focus on post‐stroke cognitive impairment and dementia (PSCID). We will review the contributions of the myeloid lineage, from peripheral cells (neutrophils, platelets, monocytes and monocyte‐derived macrophages) to central nervous system (CNS)‐associated cells (perivascular macrophages and microglia). Finally, we will evaluate different potential strategies for pharmacological modulation of pathological processes mediated by myeloid cell subsets, with an emphasis on neutrophils, their interaction with platelets and the process of immunothrombosis that triggers neutrophil‐dependent capillary stall and hypoperfusion, as possible effector mechanisms that may pave the way to novel therapeutic avenues to stop dementia, the epidemic of our time.
LINKED ARTICLES
This article is part of a themed issue From Alzheimer's Disease to Vascular Dementia: Different Roads Leading to Cognitive Decline. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.6/issuetoc
The excited-state dynamics of a diketopyrrolopyrrole (DPP) derivative with push–pull substituents has been investigated in a variety of solvents and at the dodecane/water and dodecane/heavy-water ...interfaces using a combination of ultrafast spectroscopic techniques, including transient electronic absorption and time-resolved surface second-harmonic generation. Whereas the photophysics of a nonpolar DPP analogue is mostly independent of the solvent, the fluorescence decay of the push–pull DPP accelerates strongly by going from aprotic to protic solvents. As this effect increases with the polarity and the hydrogen-bond-donating ability of the solvent, it is attributed to the occurrence of H-bond-assisted nonradiative deactivation induced by the charge-transfer character of the excited state that favors the coupling of the molecule to the H-bond network of the solvent. At the dodecane/water interface, the excited-state lifetime is longer by a factor of ca. 20 than that estimated in pure water and increases further by a factor of about 3 when going to the dodecane/heavy-water interface. This isotope effect, that is more than twice as strong as that measured in bulk solutions, and molecular dynamic simulations indicate that the slowing down of the dynamics at the interface cannot be solely ascribed to a reduced accessibility of the DPP molecule to the aqueous phase. The slower excited-state decay is rather assigned to the conjunction of several effects, such as the strengthening of the H-bond network formed by the interfacial water molecules and the lower local polarity of the interfacial region.
The aim of the present work was to establish a cure‐prediction via dielectric analysis (DEA) for a bisphenol A diglycidyl ether (DGEBA) epoxy cured with an imidazolium‐based ionic liquid EMIMN(CN)2. ...Ionic liquids caught increasingly attention in the composite industry due to their potential use as efficient latent curing agent and hence possible optimization of production cycles. Dielectric analysis is a promising tool for mass‐scale composite production for monitoring cure and as feedback control system, however a profound correlation to thermal and rheological properties is necessary. For this purpose, complementary cure kinetic modeling of the neat system was first carried out via differential scanning calorimetry (DSC) to allow the prediction of the degree of cure and glass transition temperature Tg during the curing cycle. The focus laid on the comparison between isoconversional and model‐based prediction and the influence of the implementation of the diffusion factor. Dielectric measurements were conducted and afterwards a cure prediction based on these results was established. Problems with ionic liquids as curing agent along with using DEA as characterization method were addressed. Consequently, to verify the previously obtained outcome, dielectric analysis was conducted to real‐time monitor the crosslinking during the resin transfer molding (RTM) process. Sufficient agreement to theoretical cure prediction based on DSC and DEA results with actual conversion during RTM was observed.
Purpose
The purpose of this study is to analyze and assess the impact of cooperative learning in the acquisition of generic skills in teaching students.
Design/methodology/approach
The methodology ...underlying this research has a qualitative orientation. An ad hoc questionnaire has been used as an instrument, in addition to a team notebook, and the observation as procedure to analyze the perceptions of the students in the process.
Findings
The main results indicate that thanks to the active methodologies, more specifically, the cooperative learning, students develop and improve transferable skills, such as negotiation, leadership, teamwork, reflection, etc. Similarly, the authors have observed improvements in the classroom environment and their social interactions.
Research limitations/implications
The limitations and possible implications of this study are in the direction of analyzing the implemented cooperative learning methodology techniques to observe the existence of differences in learning. Moreover, they are also related to the analyzing of individual implications for teamwork to assess group learning and its influence on motivation and teamwork. Finally, they are related to the analysis of the involvement of observation and self-regulatory mechanisms in the teamwork learning.
Practical implications
With this research, the authors incise in the necessary methodological change in universities, responding to the demands of the European Higher Education Area (EHEA) and highlight the importance of using active methodologies.
Social implications
Cooperative learning is an effective teacher training tool for future teachers who will have to develop in an interpersonal context and, in turn, will teach students who need to acquire a personal and social skills.
Originality/value
This paper evaluates the impact of using active methodologies and how they contribute to the development of transversal or generic competencies in a real context of university learning.
The proposed methodology is based on the preconcentration of Pb2+ on oxidized carbon xerogel, a porous material of low density and high surface area. Adsorbed Pb2+ was eluted with HCl, followed by ...complexion with dithizone in ethanol–water solution and determined by UV–visible spectrophotometry in a continuous flow system (FI). Variables such as pH, type of eluent, eluent concentration, type of complexing solvent, concentration of complexing reagent and flow rates were optimized. The proposed system reached an enrichment factor of 50, with 5mL of sample. Detection limit was of 0.9μgL−1, with a precision of 7.8% (n=10). The proposed system was successfully applied to the determination of Pb in tap water from San Juan City, Argentina.
•A FI-SPE-UV system has been designed for Pb determination.•Oxidized carbon xerogel is introduced for the first time in online SPE procedures.•Oxidized carbon xerogel showed quantitative Pb retention.•Good Pb kinetic desorption from carbon xerogel allowed high enrichment factors.•Method sensibility was compatible with maximum Pb concentrations in waters established by WHO.
As one of the most necessary skills of the 21st century for problem solving, critical thinking should be taught and included in the curriculum of those schools in which inclusivity towards all their ...students is a priority. From this perspective, this study presents the educational implications for the teaching and evaluation of this skill. In addition, teachers' perceptions regarding the teaching methods used, evaluation techniques and limitations that they encounter at the moment of enhancing the critical thinking of their students are analysed. A descriptive-comprehensive research with a qualitative approach was adopted, with data collected from interviews with 10 primary education teachers in the Spanish educational system. The analysis suggests that, although there is some knowledge on the part of teachers about critical thinking skills, most of them are not able to respond to this learning need. They highlight the technique of joint discussion and interactions between teams as among the effective tools for fostering critical thinking skills. Notably, these teachers have referred to the existence of certain relationships between critical thinking and equitable and quality education.
The fluorescence quantum yield of a red naphthalenediimide dye (rNDI) with amino and Br core substituents has been found to decrease by a factor of almost 2 by going from S1 ← S0 to S2 ← S0 ...excitation. Time-resolved spectroscopic measurements reveal that this deviation from the Kasha–Vavilov’s rule is due to an ultrafast, < 200 fs, intersystem-crossing (ISC) from the S2 state to the triplet manifold, due to the ππ* → nπ* character of the transition and to the presence of the heavy Br atom. In non-core substituted naphthalenediimide (pNDI), ISC is slower, ∼2 ps, and was found to be reversible on a time scale shorter than that of vibrational cooling. The fluorescence and triplet quantum yields of rNDI, thus, can be substantially changed by a simple variation of the excitation wavelength.
PDF
