New Insights on the Vibrational Dynamics of 2-Methoxy-, 4-Methoxy- and 4-Ethoxy-Benzaldehyde from INS Spectra and Periodic DFT Calculations

The dynamics of 2-methoxybenzaldehyde, 4-methoxybenzaldehyde, and 4-ethoxybenzaldehyde in the solid state are assessed through INS spectroscopy combined with periodic DFT calculations. In the absence of experimental data for 4-ethoxybenzaldehyde, a tentative crystal structure, based on its similarity with 4-methoxybenzaldehyde, is considered and evaluated. The excellent agreement between calculated and experimental spectra allows a confident assignment of the vibrational modes. Several spectral features in the INS spectra are unambiguously assigned and torsional potential barriers for the methyl groups are derived from experimental frequencies. The intramolecular nature of the potential energy barrier for methyl rotation about O–CH3 bonds compares with the one reported for torsion about saturated C–CH3 bonds. On the other hand, the intermolecular contribution to the potential energy barrier may represent 1/3 of the barrier height in these systems.

Co-opting propelling and perturbing appendages facilitates strenuous ground self-righting

Terrestrial animals must self-right when overturned on the ground. To do so, the discoid cockroach often pushes its wings against the ground to begin a somersault but rarely succeeds in completing it. As it repeatedly attempts this, it probabilistically rolls to the side to self-right. Here, we studied whether seemingly wasteful leg flailing in this process helps. Adding mass to increase hind leg flailing kinetic energy fluctuation increased the animal’s self-righting probability. We then developed a robot with similar, strenuous self-righting behavior and used it as a physical model for systematic experiments. As legs flailed more vigorously and wings opened more, self-righting became more probable. A potential energy landscape model revealed that, although wing opening did not generate sufficient kinetic energy to overcome the high pitch potential energy barrier, it reduced barriers for rolling, facilitating the small kinetic energy fluctuation from leg flailing to probabilistically overcome roll barriers to self-right.Impact statementWhen overturned terrestrial animals self-right on the ground, their seemingly wasteful yet ubiquitous flailing of appendages is crucial in providing kinetic energy fluctuation to probabilistically overcome potential energy barriers.

Microwheels on microroads: Enhanced translation on topographic surfaces

Microbot locomotion is challenging because of the reversible nature of microscale fluid flow, a limitation that can be overcome by breaking flowfield symmetry with a nearby surface. We have used this strategy with rotating wheel-shaped microbots, microwheels (μwheels), that roll on surfaces leading to enhanced propulsion and fast translation speeds. Despite this, studies to date on flat surfaces show that μwheels roll inefficiently with substantial slip. Taking inspiration from the mathematics of roads and wheels, we demonstrate that μwheel velocities can be significantly enhanced by changing microroad topography. Here, we observe that periodic bumps in the road can be used to enhance the traction between μwheels and nearby walls. Whereas continuous μwheel rotation with slip is observed on flat surfaces, a combination of rotation with slip and nonslip flip occurs when μwheels roll on surfaces with periodic features, resulting in up to fourfold enhancement in translation velocity. The unexpectedly fast rolling speed of μwheels on bumpy roads can be attributed to the hydrodynamic coupling between μwheels and road surface features, allowing nonslip rotation of entire wheels along one of their stationary edges. This road-wheel coupling can also be used to enhance μwheel sorting and separation where the gravitational potential energy barrier induced by topographic surfaces can lead to motion in only one direction and to different rolling speeds between isomeric wheels, allowing one to separate them not based on size but on symmetry.

Mechanistic insights into the phosphoryl transfer reaction in cyclin-dependent kinase 2: a QM/MM study

Cyclin-dependent kinase 2 (CDK2) is an important member of the CDK family exerting its most important function in the regulation of the cell cycle. It catalyzes the transfer of the gamma phosphate group from an ATP (adenosine triphosphate) molecule to a Serine/Threonine residue of a peptide substrate. Due to the importance of this enzyme, and protein kinases in general, a detailed understanding of the reaction mechanism is desired. Thus, in this work the phosphoryl transfer reaction catalyzed by CDK2 was revisited and studied by means of hybrid quantum mechanics/molecular mechanics (QM/MM) calculations. Our results show that the base-assisted mechanism is preferred over the substrate-assisted pathway, in agreement with a previous theoretical study. The base-assisted mechanism resulted to be dissociative, with a potential energy barrier of 14.3 kcal/mol, very close to the experimental derived value. An interesting feature of the mechanism is the proton transfer from Lys129 to the phosphoryl group at the second transition state, event that could be helping in neutralizing the charge on the phosphoryl group upon the absence of a second Mg2+ ion. Furthermore, important insights into the mechanisms in terms of bond order and charge analysis were provided. These descriptors helped to characterize the synchronicity of bond forming and breaking events, and to characterize charge transfer effects. Local interactions at the active site are key to modulate the charge distribution on the phosphoryl group and therefore alter its reactivity.

Hybrid-Bistable Vibration Energy Harvester With Adaptive Potential Well

Many common environmental vibration sources exhibit low and broad frequency spectra. In order to exploit such excitations, energy harvesting architectures utilizing nonlinearity, especially bistability, have been widely studied since the energetic interwell oscillations between their stable equilibria can provide enhanced power harvesting capability over a wider bandwidth compared to the linear counterpart. However, one of the limitations of these nonlinear architectures is that the interwell oscillation regime may not be activated for a low excitation level that is not strong enough to overcome the potential energy barrier, thus resulting in low amplitude intrawell response which provides poor energy harvesting performance. While the strategic integration of bistability and additional dynamic elements has shown potential to improve broadband energy harvesting performance by lowering the potential barrier, there is a clear opportunity to further improve the energy harvesting performance by extracting electrical power from the kinetic energy in the additional element that is induced when the potential barrier is lowered. To explore this opportunity and advance the state of the art, this research develops a novel hybrid bistable vibration energy harvesting system with a passive mechanism that not only adaptively lowers the potential energy barrier level to improve broadband performance but also exploits additional means to capture more usable electrical power. The proposed harvester is comprised of a cantilever beam with repulsive magnets, one attached at the free end and the other attached to a linear spring that is axially aligned with the cantilever (a spring-loaded magnet oscillator). This new approach capitalizes on the adaptive bistable potential that is passively realized by the spring-loaded magnet oscillator, which lowers the double-well potential energy barrier thereby facilitating the interwell oscillations of the cantilever across a broad range of excitation conditions, especially for low excitation amplitudes and frequencies. The interwell oscillation of the cantilever beam enhances not only the piezoelectric energy harvesting from the beam but also the electromagnetic energy harvesting from the spring-loaded magnet oscillator by inducing large amplitude vibrations of the magnet oscillator. Numerical investigations found that the proposed architecture yields significantly enhanced energy harvesting performance compared to the conventional bistable harvester with fixed magnet.

Measuring the potential energy barrier to lipid bilayer electroporation

Electroporation is a common tool for gene transfection, tumour ablation, sterilization and drug delivery. Using experimental methods, we explore the temperature dependence of electropore formation in a model membrane system (droplet-interface bilayers), using optical single-channel recording to image the real-time gating of individual electropores. We investigate the influence of the agarose substrate on electropores formed in this system. Furthermore, by examining the temperature-dependent kinetics of pore opening and closure we are able to estimate a barrier to pore opening in 1,2-diphytanoyl- sn -glycero-3-phosphocholine (DPhPC) membranes to be 25.0 ± 8.3 k B T , in agreement with previous predictions. Overall these measurements help support the toroidal model of membrane electroporation. This article is part of the themed issue ‘Membrane pores: from structure and assembly, to medicine and technology’.

Interfacial assembly structures and nanotribological properties of saccharic acids

The larger friction of the successfully constructed assembly of saccharic acid indicates the higher potential energy barrier at the interface.