Mass transport at infinite regular arrays of microband electrodes was investigated theoretically and experimentally in unstirred solutions. Even in the absence of forced hydrodynamics, natural convection limits the convection-free domain up to which diffusion layers may expand. Hence, several regimes of mass transport may take place according to the electrode size, gap between electrodes, time scale of the experiment, and amplitude of natural convection. They were identified through simulation by establishing zone diagrams that allowed all relative contributions to mass transport to be delineated. Dynamic and steady-state regimes were compared to those achieved at single microband electrodes. These results were validated experimentally by monitoring the chronoamperometric responses of arrays with different ratios of electrode width to gap distance and by mapping steady-state concentration profiles above their surface through scanning electrochemical microscopy.
It takes two (photons) to tango: Single-turnover flash experiments showed that the flavoenzyme (6–4) photolyase uses a successive two-photon mechanism to repair the UV-induced T(6–4)T lesion in DNA (see picture). The intermediate (X) formed by the first photoreaction is likely to be the oxetane-bridged dimer T(ox)T. The enzyme could stabilize the normally short-lived T(ox)T, allowing repair to be completed by the second photoreaction.
The dynamics of water molecules within the hydration shell surrounding a biomolecule can have a crucial influence on its biochemical function. Characterizing their properties and the extent to which they differ from those of bulk water have thus been long-standing questions. Following a tutorial approach, we review the recent advances in this field and the different approaches which have probed the dynamical perturbation experienced by water in the vicinity of proteins or DNA. We discuss the molecular factors causing this perturbation, and describe how they change with temperature. We finally present more biologically relevant cases beyond the dilute aqueous situation. A special focus is on the jump model for water reorientation and hydrogen bond rearrangement.
Cell penetrating peptides induce membrane invaginations in cellular membranes. They induce negative membrane curvature by a metabolic energy independent pathway. This pathway also called 'Physical endocytosis' could be a new mechanism of cell penetrating peptide uptake
We propose a dynamic model that accounts for the photochemical behavior of the Spinach system, a recently described fluorescent probe for RNA imaging. We exploit the dynamic fluorogen exchange and the unprecedented photoconversion properties in a non-covalent fluorescence turn-on system to significantly improve signal-to-background ratio during long-term microscopy imaging.
Since infrared and luminescent spectroscopies are complementary for bio-detection and bio-imaging, such IR-luminescent SCoMPIs are of great potential and their multiple modalities open up wide prospects for cross correlative studies in biological media. Multimodal imaging is currently a fast expanding field. The elaboration of small molecule chemistry to target and image other organelles and biological macromolecules is likely to contribute substantially to our molecular-level understanding of chemical processes in cells.
Cell fate decisions and cellular functions are dictated by the spatiotemporal dynamics of molecular signaling networks. However, the techniques available to examine the spatiotemporal properties of these intracellular processes remain limited. Here we report a method to artificially control in space and time such signaling pathways using magnetic nanoparticles conjugated to key regulatory proteins.
Living systems rely on chains of energy transfer to maintain their metabolism from an energy source. This task requires functionally-identified components and organizations. However propagation of a sustained energy flux throughout a cascade of reaction cycles has never been reproduced at steady-state in a simple chemical system.
We showed, using first-principle molecular dynamics simulations, that the standard Marcus theory of charge transfer reaction in solution, relying on a linear solvent response approximation, and involving two parameters, the reorganization energy and the reaction free-energy parameter, may fail when the solvation has a different character in the reactant and product state. Such situation arise for even simple half oxydo- reduction reactions involving the Cu+/Cu2+ or Ag/Ag+ couples in water. We proposed theoretical extensions that exhibit the correct non-linear response behavior and reproduce the simulation results quantitatively, whereas Marcus theory breaks down.