Rotaxane-Based Molecular Muscles Bruns, Carson J; Stoddart, J. Fraser
Accounts of chemical research,
07/2014, Letnik:
47, Številka:
7
Journal Article
Recenzirano
Conspectus More than two decades of investigating the chemistry of bistable mechanically interlocked molecules (MIMs), such as rotaxanes and catenanes, has led to the advent of numerous molecular ...switches that express controlled translational or circumrotational movement on the nanoscale. Directed motion at this scale is an essential feature of many biomolecular assemblies known as molecular machines, which carry out essential life-sustaining functions of the cell. It follows that the use of bistable MIMs as artificial molecular machines (AMMs) has been long anticipated. This objective is rarely achieved, however, because of challenges associated with coupling the directed motions of mechanical switches with other systems on which they can perform work. A natural source of inspiration for designing AMMs is muscle tissue, since it is a material that relies on the hierarchical organization of molecular machines (myosin) and filaments (actin) to produce the force and motion that underpin locomotion, circulation, digestion, and many other essential life processes in humans and other animals. Muscle is characterized at both microscopic and macroscopic length scales by its ability to generate forces that vary the distance between two points at the expense of chemical energy. Artificial muscles that mimic this ability are highly sought for applications involving the transduction of mechanical energy. Rotaxane-based molecular switches are excellent candidates for artificial muscles because their architectures intrinsically possess movable filamentous molecular components. In this Account, we describe (i) the different types of rotaxane “molecular muscle” architectures that express contractile and extensile motion, (ii) the molecular recognition motifs and corresponding stimuli that have been used to actuate them, and (iii) the progress made on integrating and scaling up these motions for potential applications. We identify three types of rotaxane muscles, namely, “daisy chain”, “press”, and “cage” rotaxanes, and discuss their mechanical actuation driven by ions, pH, light, solvents, and redox stimuli. Different applications of these rotaxane-based molecular muscles are possible at various length scales. On a molecular level, they have been harnessed to create adjustable receptors and to control electronic communication between chemical species. On the mesoscale, they have been incorporated into artificial muscle materials that amplify their concerted motions and forces, making future applications at macroscopic length scales look feasible. We emphasize how rotaxanes constitute a remarkably versatile platform for directing force and motion, owing to the wide range of stimuli that can be used to actuate them and their diverse modes of mechanical switching as dictated by the stereochemistry of their mechanical bonds, that is, their mechanostereochemistry. We hope that this Account will serve as an exposition that sets the stage for new applications and materials that exploit the capabilities of rotaxanes to transduce mechanical energy and help in paving the path going forward to genuine AMMs.
Let’s motor through the fog of molecular machine terminology, not only by defining our own words clearly, but by embracing the coexistence of multiple meanings in a rational and structured manner.
Hunger and chronic undernourishment impact over 800 million people, which translates to ≈10.7% of the world's population. While countries are increasingly making efforts to reduce poverty and hunger ...by pursuing sustainable energy and agricultural practices, a third of the food produced around the globe still is wasted and never consumed. Reducing food shortages is vital in this effort and is often addressed by the development of genetically modified produce or chemical additives and inedible coatings, which create additional health and environmental concerns. Herein, a multifunctional bio‐nanocomposite comprised largely of egg‐derived polymers and cellulose nanomaterials as a conformal coating onto fresh produce that slows down food decay by retarding ripening, dehydration, and microbial invasion is reported. The coating is edible, washable, and made from readily available inexpensive or waste materials, which makes it a promising economic alternative to commercially available fruit coatings and a solution to combat food wastage that is rampant in the world.
A conformal bio‐nanocomposite coating based on cellulose nanocrystals and poly(albumen) is developed that increases the shelf‐life of fresh produce by retarding ripening, dehydration, and microbial attack. The coating is edible, easily washable, and made from readily available inexpensive materials, which makes it a promising solution to combat food wastage.
Effective interventions are needed to improve brain function in mild cognitive impairment (MCI), an early stage of Alzheimer's disease (AD). The posterior cingulate cortex (PCC)/precuneus is a hub of ...the default mode network (DMN) and is preferentially vulnerable to disruption of functional connectivity in MCI and AD.
We investigated whether 12 weeks of aerobic exercise could enhance functional connectivity of the PCC/precuneus in MCI and healthy elders.
Sixteen MCI and 16 healthy elders (age range = 60-88) engaged in a supervised 12-week walking exercise intervention. Functional MRI was acquired at rest; the PCC/precuneus was used as a seed for correlated brain activity maps.
A linear mixed effects model revealed a significant interaction in the right parietal lobe: the MCI group showed increased connectivity while the healthy elders showed decreased connectivity. In addition, both groups showed increased connectivity with the left postcentral gyrus. Comparing pre to post intervention changes within each group, the MCI group showed increased connectivity in 10 regions spanning frontal, parietal, temporal and insular lobes, and the cerebellum. Healthy elders did not demonstrate any significant connectivity changes.
The observed results show increased functional connectivity of the PCC/precuneus in individuals with MCI after 12 weeks of moderate intensity walking exercise training. The protective effects of exercise training on cognition may be realized through the enhancement of neural recruitment mechanisms, which may possibly increase cognitive reserve. Whether these effects of exercise training may delay further cognitive decline in patients diagnosed with MCI remains to be demonstrated.
To determine the relationship between the amount and intensity of physical activity performed by older adults in North America (United States and Canada) and their depression and anxiety symptoms ...while currently under social distancing guidelines (SDG) for the COVID-19 pandemic.
Descriptive cross-sectional study.
Online survey conducted between April 9 and April 30, 2020, during the COVD-19 pandemic.
About 1,046 older adults over the age of 50 who live in North America.
Participants were asked about their basic demographic information, current health status, and the impact of the current SDG on their subjective state of mental health. Participants completed the Physical Activity Scale for the Elderly, to determine the amount and intensity of physical activity performed, as well as both the Geriatric Depression Scale and Geriatric Anxiety Scale, to ascertain the extent of their depression and anxiety-like symptoms.
Ninety-seven percent of participants indicated that they adhered to current SDG "Most of the time" or "Strictly." Participants who performed greater levels of physical activity experienced lower levels of depression-like symptoms when age, sex, and education were accounted for; however, no relationship between physical activity and anxiety-like symptoms was found. A hierarchical regression analysis that incorporated the intensity of physical activity performed (light, moderate, and vigorous) in the model indicated that greater light and strenuous activity, but not moderate, predicted lower depression-like symptoms.
These results suggest that performing even light physical activity during the COVID-19 pandemic may help alleviate some of the negative mental health impacts that older adults may be experiencing while isolated and adhering to SDG during the COVID-19 pandemic.
Exercise training has been associated with greater cerebral blood flow (CBF) in cognitively normal older adults (CN). Alterations in CBF, including compensatory perfusion in the prefrontal cortex, ...may facilitate changes to the brain's neural infrastructure.
To examine the effects of a 12-week aerobic exercise intervention on resting CBF and cognition in CN and those with mild cognitive impairment (MCI). We hypothesized individuals with MCI (versus CN) would exhibit greater whole brain CBF at baseline and that exercise would mitigate these differences. We also expected CBF changes to parallel cognitive improvements.
Before and after a 12-week exercise intervention, 18 CN and 17 MCI participants (aged 61-88) underwent aerobic fitness testing, neuropsychological assessment, and an MRI scan. Perfusion-weighted images were collected using a GE 3T MR system. Repeated measures analyses of covariance were used to test within- and between-group differences over time, followed by post-hoc analyses to examine links between CBF changes and cognitive improvement.
At baseline, individuals with MCI (versus CN) exhibited significantly elevated perfusion in the left insula. Twelve weeks of aerobic exercise reversed this discrepancy. Additionally, exercise improved working memory (measured by the Rey Auditory Verbal Learning Test) and verbal fluency (measured by the Controlled Oral Word Association Test) and differentially altered CBF depending on cognitive status. Among those with MCI, decreased CBF in the left insula and anterior cingulate cortex was associated with improved verbal fluency.
Exercise training alters CBF and improves cognitive performance in older adults with and without cognitive impairment. Future studies must evaluate the mediating effects of CBF on the association between exercise training and cognition.
Calorie restriction (CR) extends life span in diverse species. Mitochondria play a key role in CR adaptation; however, the molecular details remain elusive. We developed and applied a quantitative ...mass spectrometry method to probe the liver mitochondrial acetyl-proteome during CR versus control diet in mice that were wild-type or lacked the protein deacetylase SIRT3. Quantification of 3,285 acetylation sites—2,193 from mitochondrial proteins—rendered a comprehensive atlas of the acetyl-proteome and enabled global site-specific, relative acetyl occupancy measurements between all four experimental conditions. Bioinformatic and biochemical analyses provided additional support for the effects of specific acetylation on mitochondrial protein function. Our results (1) reveal widespread reprogramming of mitochondrial protein acetylation in response to CR and SIRT3, (2) identify three biochemically distinct classes of acetylation sites, and (3) provide evidence that SIRT3 is a prominent regulator in CR adaptation by coordinately deacetylating proteins involved in diverse pathways of metabolism and mitochondrial maintenance.
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► MS quantifies 1,578 mitochondrial acetyl sites altered during CR and loss of SIRT3 ► SIRT3 functions as a prominent regulator in CR adaptation ► CR and SIRT3 regulate previously unrecognized processes in mitochondria ► We provide an acetylation atlas for understanding mitochondrial regulation in CR
Tunable solid-state fluorescent materials are ideal for applications in security printing technologies. A document possesses a high level of security if its encrypted information can be authenticated ...without being decoded, while also being resistant to counterfeiting. Herein, we describe a heterorotaxane with tunable solid-state fluorescent emissions enabled through reversible manipulation of its aggregation by supramolecular encapsulation. The dynamic nature of this fluorescent material is based on a complex set of equilibria, whose fluorescence output depends non-linearly on the chemical inputs and the composition of the paper. By applying this system in fluorescent security inks, the information encoded in polychromic images can be protected in such a way that it is close to impossible to reverse engineer, as well as being easy to verify. This system constitutes a unique application of responsive complex equilibria in the form of a cryptographic algorithm that protects valuable information printed using tunable solid-state fluorescent materials.
Notwithstanding the significant practical importance of hematite, α‐Fe2O3, the complete assignment and understanding of the Raman spectrum acquired on this crystalline solid are uncertain. Above all, ...only one of the two external Eg phonons arising from the Γ point has been resolved and hence assigned. It is well known that the Eg mode at 294 cm−1 has been attributed to one of the two external phonons arising from the Γ point. To this end, we have undertaken studies to examine the polarized Raman scattering on a pure single crystal to gain a better understanding and assignment of phonons arising from the Γ point in the Raman spectrum of hematite. Here, we resolve and assign the previously unidentified external Eg phonon at 245 cm−1 and, additionally, confirm that the band at 294 cm−1 is an external Eg phonon, in the first‐order Raman spectrum of hematite. Further, our polarized Raman spectra display interesting polarization behavior of the 2LO mode at 1320 cm−1, where this band is only Raman active in ei||es polarization configurations.
The Eg mode at 294 cm−1 has been attributed to one of the two external modes in the Raman spectrum of hematite. However, the other external mode has not yet been resolved and hence assigned. We undertook polarized Raman spectroscopic measurements on single‐crystal hematite to shed light on the unknown external mode. On the basis of polarization measurements, we attribute the external modes involving rotations and translations of entire Fe2O3 units to the Eg phonons at 245 and 295 cm−1.
Polycyclic aromatic hydrocarbons (PAHs) are promising nanocarbon materials with diverse optoelectronic properties, yet they also pose concerning environmental and health risks. Despite the ubiquity ...of PAHs in the environment (crude oil, emissions, and biomass), most supermolecules rely on heteroatoms for stability. We discovered and characterized a family of all-hydrocarbon, all-π-conjugated
n
cycloparaphenylene-PAH host-guest complexes. We built a theoretical framework to rapidly select these complexes and predict their stabilities, driven exclusively by CH−π interactions. More than a dozen complexes were confirmed experimentally and assembled directly from commercially available compounds. This motif offers a versatile way to combine the advantageous properties of organic semiconductors with the rich dynamic, stereochemical, stimulus-responsive, and stress-dissipative behavior of host-guest complexes, while creating new opportunities for bespoke PAH separation or remediation materials.
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