Over the past decades, polymer mechanochemistry has focused on the development and application of advanced force application methods to better understand the mechanochemical response of ...mechanophores. In this regard, techniques such as ultrasonication and single‐molecule force spectroscopy (SMFS) are used to activate and detect up to thousands of chemical events within a polymer single chain, allowing the researchers to probe the mechanochemical reactivity of these stress‐responsive motifs. Here, the most recent contributions of the single‐molecule force spectroscopy technique to this field are presented, putting emphasis on the fundamental parameters of the technique for triggering specific force responses and on the description of force–extension curves measured for single‐ and multi‐mechanophore polymers. Moreover, new contributions of microscopy‐based techniques in the field of polymer mechanochemistry, as well as the potential application of single‐chain nanoparticles as mechanoresponsive materials, are highlighted.
Single‐molecule force spectroscopy (SMFS) is a key experimental technique to accurately measure and elucidate the mechanisms behind the activation of mechanophores, as the force required to activate a variety of mechanoactive moieties. SMFS can help to understand the properties of mechanophores by complementing macroscopic experiments and provide molecular‐level knowledge about chemical mechanisms governing the behavior of mechanophores.
Programmed cell death (PCD) is an integral part of plant development and of responses to abiotic stress or pathogens. Although the morphology of plant PCD is, in some cases, well characterised and ...molecular mechanisms controlling plant PCD are beginning to emerge, there is still confusion about the classification of PCD in plants. Here we suggest a classification based on morphological criteria. According to this classification, the use of the term 'apoptosis' is not justified in plants, but at least two classes of PCD can be distinguished: vacuolar cell death and necrosis. During vacuolar cell death, the cell contents are removed by a combination of autophagy-like process and release of hydrolases from collapsed lytic vacuoles. Necrosis is characterised by early rupture of the plasma membrane, shrinkage of the protoplast and absence of vacuolar cell death features. Vacuolar cell death is common during tissue and organ formation and elimination, whereas necrosis is typically found under abiotic stress. Some examples of plant PCD cannot be ascribed to either major class and are therefore classified as separate modalities. These are PCD associated with the hypersensitive response to biotrophic pathogens, which can express features of both necrosis and vacuolar cell death, PCD in starchy cereal endosperm and during self-incompatibility. The present classification is not static, but will be subject to further revision, especially when specific biochemical pathways are better defined.
Resting-state fMRI was first described by Biswal et al in 1995 and has since then been widely used in both healthy subjects and patients with various neurologic, neurosurgical, and psychiatric ...disorders. As opposed to paradigm- or task-based functional MR imaging, resting-state fMRI does not require subjects to perform any specific task. The low-frequency oscillations of the resting-state fMRI signal have been shown to relate to the spontaneous neural activity. There are many ways to analyze resting-state fMRI data. In this review article, we will briefly describe a few of these and highlight the advantages and limitations of each. This description is to facilitate the adoption and use of resting-state fMRI in the clinical setting, helping neuroradiologists become familiar with these techniques and applying them for the care of patients with neurologic and psychiatric diseases.
Confined at the nanoscale level, polymers crystallize much slower than in bulk, and in some cases the formation of ordered structures results inhibited for extremely long experimental time scales. ...Here, we report on the thickness dependence of the cold crystallization of thin poly(l-lactide) (PLLA) films (<300 nm), capped between two aluminum (Al) layers. The crystallization kinetics was monitored by means of dielectric relaxation spectroscopy, following the reduction in dielectric strength during annealing in isothermal experiments. We exploited a recently developed analytical method assessing the impact of irreversible chain adsorption and permitting to disentangle finite size and interfacial effects. In line with previous literature, the conversion time increased upon reduction of the thickness and crystallization was inhibited in films thinner than 10 nm. Moreover, we analyzed the thickness dependence of the dielectric strength and obtained the gradient in segmental mobility inside our capped films. We conclude that irreversible adsorption of chains onto the Al electrodes ultimately leads to a reduction in molecular mobility compared to the bulk.
This work presents the molecular dynamics of both fully amorphous and semicrystalline poly(butylene 2,5-furanoate) (PBF). Broadband dielectric spectroscopy experiments were combined with temperature ...modulated differential scanning calorimetry measurements. The results showed that the subglass molecular dynamics is characterized by the existence of two dielectric relaxation processes, being the faster one associated to the glycolic subunit, whereas the slower relaxation was assigned to the link in between the ester group and the furan ring. Crystallization affected differently the contribution of these two components. Additionally, crystallization had a stronger effect on the α relaxation process, related to the segmental dynamics of the amorphous phase. In the semicrystalline state, the PBF amorphous phase was described as being composed by different fractions, including a completely rigid one, with distinctly slower mobilities and reduced contributions to the dielectric relaxation, compared to the fully amorphous polymer.
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•Local and segmental dynamics of poly(butylene 2,5-furanoate) (PBF) were studied.•Local dynamics showed a broad relaxation, described by two processes respectively related to the more mobile subunit and to the stiffer moiety.•Amorphous phase mobility depended on the glycol subunit length, while the fragility was mainly correlated to the acid moiety.•Cold crystallization led to a slowdown of the segmental dynamics and concomitant reduced dielectric relaxation strength.•The amorphous phase of semicrystalline PBF was described using different fractions, including a completely rigid fraction.
Polymer nanostructures were developed on fully bio-based poly(trimethylene furanoate) (PTF) films, by using the technique of Laser Induced Periodic Surface Structures (LIPSS). We found that ...irradiation times between 1 and 8 min allowed the formation of periodic and nanometric ripples, when using an UV pulsed laser source at a fluence of 8 mJ/cm2. The wrinkled surfaces were studied by a combined macro- and nanoscale approach. We evaluated possible physicochemical changes taking place on the polymer surface after irradiation by infrared spectroscopy, contact angle measurements and atomic force microscopy. The macroscopic properties of PTF showed almost no changes after nanostructure formation, differently from the results previously found for the terephthalic counterparts, as poly(ethylene terephthalate), PET, and poly(trimethylene terephthalate), PTT. At the nanoscale, the surface mechanical properties of the nanostructured PTF were found to be improved, as evidenced by force spectroscopy measurements. In particular, stiffer surfaces characterized by an increased Young's modulus were measured for the nanostructured sample.
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•Formation of poly(trimethylene 2,5-furanoate) nanostructures by laser irradiation.•Combined macro- and nanoscale approach for the evaluation of the films' physical properties.•PTF showed almost no changes in its macroscopical properties after nanostructure formation.•Nanomechanical measurements indicated an improvement of the PTF mechanical response after wrinkling.
Achieving an understanding of how apoptosis/PCD (programmed cell death) is integrated within cellular responses to environmental and intracellular signals is a daunting task. From the sensation of a ...stimulus to the point of no return, a programme of cell death must engage specific pro-death components, whose effects can in turn be enhanced or repressed by downstream regulatory factors. In recent years, considerable progress has been made in our understanding of how components involved in these processes function. We now know that some of the factors involved in PCD networks have ancient origins that pre-date multicellularity and, indeed, eukaryotes themselves. A subject attracting much attention is the role that the actin cytoskeleton, itself a cellular component with ancient origins, plays in cell death regulation. Actin, a key cellular component, has an established role as a cellular sensor, with reorganization and alterations in actin dynamics being a well known consequence of signalling. A range of studies have revealed that actin also plays a key role in apoptosis/PCD regulation. Evidence implicating actin as a regulator of eukaryotic cell death has emerged from studies from the Animal, Plant and Fungal Kingdoms. Here we review recent data that provide evidence for an active, functional role for actin in determining whether PCD is triggered and executed, and discuss these findings within the context of regulation of actin dynamics.
Great progress has been made in our understanding of pollen-pistil interactions and self-incompatibility (SI) in flowering plants in the last few decades. This book covers a broad spectrum of ...research into SI, with accounts by internationally renowned scientists. It comprises two sections: Evolution and Population Genetics of SI, Molecular and Cell Biology of SI Systems. The reader will gain an insight into the diversity and complexity of these polymorphic cell-cell recognition and rejection systems. Heteromorphic and homomorphic SI systems and our current understanding of the evolution and phylogeny of these systems, based on the most recent molecular sequence data, are covered. Further, the book presents major advances in our knowledge of the pistil and pollen S-determinants and other unlinked components involved in SI, as well as the apparently diverse cellular regulatory mechanisms utilised to ensure inhibition of "self" pollen.
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