Solvent Remodeling in Single-Chain Amphiphilic Heteropolymer Systems

Through molecular dynamics simulations, we demonstrate how single-chain nanoparticles (SCNPs) assembled via transient linkages in water can remodel in organic solvent. Methacrylate-based random heteropolymers (RHPs) have shown promise in an assortment of applications that harness their bio-inspired properties. While their molecular behavior has been broadly characterized in water, many newer applications include the use of organic solvent rather than bio-mimetic conditions in which the polymer assemblies, typically driven by the hydrophobic effect, are less well understood. Here, we examine a specific RHP system which forms compact globular morphologies in highly polar and non-polar environments while adopting extended conformations in solvents of intermediate polarity. We also demonstrate the pivotal role of electrostatic interactions between charge groups in low dielectric mediums. Finally, we compare high temperature anneal cycles to room temperature equilibrations to illuminate activation barriers to remodeling upon environmental changes.

Low-Energy Electron Elastic Collisions with Actinide Atoms Am, Cm, Bk, Es, No and Lr: Negative-Ion Formation

The rigorous Regge-pole method is used to investigate negative-ion formation in actinide atoms through electron elastic total cross sections (TCSs) calculation. The TCSs are found to be characterized generally by negative-ion formations, shape resonances and Ramsauer-Townsend(R-T) minima, and they exhibit both atomic and fullerene molecular behavior near the threshold. Additionally, a polarization-induced metastable cross section with a deep R-T minimum is identified near the threshold in the Am, Cm and Bk TCSs, which flips over to a shape resonance appearing very close to the threshold in the TCSs for Es, No and Lr. We attribute these new manifestations to size effects and orbital collapse significantly impacting the polarization interaction. From the TCSs unambiguous and reliable ground, metastable and excited states negative-ion binding energies (BEs) for Am−, Cm−, Bk−, Es−, No− and Lr− anions formed during the collisions are extracted and compared with existing electron affinities (EAs) of the atoms. The novelty of the Regge-pole approach is in the extraction of the negative-ion BEs from the TCSs. We conclude that the existing theoretical EAs of the actinide atoms and the recently measured EA of Th correspond to excited anionic BEs.

Abiotic Stress-Induced Molecular and Physiological Changes and Adaptive Mechanisms in Plants

Abiotic stress is the primary cause of crop loss worldwide, reducing average yields for most major crop plants by more than 50%. Among abiotic stress, drought, salinity, high temperature, and cold are major adverse environmental factors that limit the crop production and productivity by inhibiting the genetic potential of the plant. So, it leads to complete change of morphological, physiological, biochemical, and molecular behavior of the plants and modifies regular metabolism of life, thereby adversely affecting plant productivity. Major effects of the drought, salinity, extreme temperatures, and cold stress are often interconnected and form similar cellular damage. To adopt plants with various abiotic stresses, plants can initiate a number of molecular, cellular, and physiological changes in its system. Sensors are molecules that perceive the initial stress signal from the outside of the plant system and initiate a signaling cascade to transmit the signal and activate nuclear transcription factors to induce the expression of specific sets of genes. Understanding this molecular and physiological basis of plant responses produced because of abiotic stress will help in molecular and modern breeding applications toward developing improved stress-tolerant crops. This review presents an overview and implications of physiological and molecular aspects of main abiotic stress, i.e., drought, heat, salt, and cold. Potential strategies to improve abiotic tolerance in crops are discussed.

Molecular motion and tridimensional nanoscale localization of kindlin control integrin activation in focal adhesions

Focal adhesions (FAs) initiate chemical and mechanical signals involved in cell polarity, migration, proliferation and differentiation. Super-resolution microscopy revealed that FAs are organized at the nanoscale into functional layers from the lower plasma membrane to the upper actin cytoskeleton. Yet, how FAs proteins are guided into specific nano-layers to promote interaction with given targets is unknown. Using single protein tracking, super-resolution microscopy and functional assays, we link the molecular behavior and 3D nanoscale localization of kindlin with its function in integrin activation inside FAs. We show that immobilization of integrins in FAs depends on interaction with kindlin. Unlike talin, kindlin displays free diffusion along the plasma membrane outside and inside FAs. We demonstrate that the kindlin Pleckstrin Homology domain promotes membrane diffusion and localization to the membrane-proximal integrin nano-layer, necessary for kindlin enrichment and function in FAs. Using kindlin-deficient cells, we show that kindlin membrane localization and diffusion are crucial for integrin activation, cell spreading and FAs formation. Thus, kindlin uses a different route than talin to reach and activate integrins, providing a possible molecular basis for their complementarity during integrin activation.

On Catalytic Kinetics of Enzymes

Classical enzyme kinetic theories are summarized and linked with modern discoveries here. The sequential catalytic events along time axis by enzyme are analyzed at the molecular level, and by using master equations, this writing tries to connect the microscopic molecular behavior of enzyme to kinetic data (like velocity and catalytic coefficient k) obtained in experiment: 1/k = t equals to the sum of the times taken by the constituent individual steps. The relationships between catalytic coefficient k, catalytic rate or velocity, the amount of time taken by each step and physical or biochemical conditions of the system are discussed, and the perspective and hypothetic equations proposed here regarding diffusion, conformational change, chemical conversion, product release steps and the whole catalytic cycle provide an interpretation of previous experimental observations and can be testified by future experiments.