One influential parameter which mediates interactions between many types of molecules and biological membranes stems from
the lumped contributions of the transmembrane potential, dipole potential and the difference in the surface potentials on
both sides of a membrane. With relevance to cell physiology, such electrical features of a biomembrane are prone to undergoing
changes as a result of interactions with the aqueous surrounding. Among the most useful tools devoted to exploring changes
of electrical parameters of a lipid membrane induced by certain extracellular ions, lipid composition, and embedded membrane
peptides and proteins, are spectroscopic imaging and the inner field compensation (IFC) method. In this work we layout the
principles of a fully computerized version of the IFC method, which makes it more readily available to users. As a direct
application, we deployed this improved version of the IFC method to time-resolve changes induced by alamethicin monomers upon
membrane dipole potential, following their aggregation within an artificial lipid membrane. Intriguingly, even prior crossing
the membrane core, the membrane-bound alamethicin monomers are shown to significantly increase the dipole potential of the
monolayer they reside in. Such data further emphasize the yet less-explored interplay between membrane-based protein and peptides,
and the membrane dipole potential. 相似文献
The topological changes that occur during coarsening of 2D and 3Dcellular structures, such as polycrystals, areinvestigated. Particular attention is given to the elimination ofgrain boundaries and grains with more than the minimum number oftopological elements. A thermodynamic criterion is introduced tofind out which topological transformations are favoured, based on theevaluation of the Gibbs free energy of the initial and finalconfigurations. In general, elimination of grains is possible only ifthe number of their neighbours is below a critical value, which maybe affected by geometry. 相似文献
In the Y—Bi system the formation heats were measured using a direct isoperibol calorimeter. The following values were found for the two known compounds: 相似文献
The development of synthetic routes to access stable, ultra-small (i.e. <5 nm) lead halide perovskite (LHP) quantum dots (QDs) is of fundamental and technological interest. The considerable challenges include the high solubility of the ionic LHPs in polar solvents and aggregation to form larger particles. Here, we demonstrate a simple and effective host–guest strategy for preparing ultra-small lead bromide perovskite QDs through the use of nano-sized MOFs that function as nucleating and host sites. Cr3O(OH)(H2O)2(terephthalate)3 (Cr-MIL-101), made of large mesopore-sized pseudo-spherical cages, allows fast and efficient diffusion of perovskite precursors within its pores, and promotes the formation of stable, ∼3 nm-wide lead bromide perovskite QDs. CsPbBr3, MAPbBr3 (MA+ = methylammonium), and (FA)PbBr3 (FA+ = formamidinium) QDs exhibit significantly blue-shifted emission maxima at 440 nm, 446 nm, and 450 nm, respectively, as expected for strongly confined perovskite QDs. Optical characterization and composite modelling confirm that the APbBr3 (A = Cs, MA, FA) QDs owe their stability within the MIL-101 nanocrystals to both short- and long-range interfacial interactions with the MOF pore walls.We demonstrate a simple and effective host–guest strategy for preparing ultra-small lead bromide perovskite QDs through the use of nano-sized MOFs that function as nucleating and host sites.相似文献
Kinetics of the reduction of 3-chloroacetophenone (CAF) with sodium borohydride (NaBH(4)) were followed by UV-vis spectroscopy at 27.0 degrees C in different reverse micellar media, toluene/BHDC/water and toluene/AOT/water, and compared with results in an isooctane/AOT/water reverse micellar system. AOT is sodium 1,4-bis-2-ethylhexylsulfosuccinate, and BHDC is benzyl-n-hexadecyl dimethylammonium chloride. The kinetic profiles were investigated as a function of variables such as surfactant and NaBH(4) concentration and the amount of water dispersed in the reverse micelles, W(0) = [H(2)O]/[surfactant]. In all cases, the first-order rate constant, k(obs), increases with the concentration of surfactant as a consequence of incorporating the substrate into the interface of the reverse micelles where the reaction takes place. The reaction is faster at the cationic interface than at the anionic one probably because the negative ion BH(4)(-) is part of the cationic interface. The effect of the external solvent on the reaction shows that reduction is favored in the isooctane/AOT/water reverse micellar system than that with an aromatic solvent. This is probably due to BH(4)(-) being more in the water pool of the toluene/AOT/water reverse micellar system. The kinetic profile upon water addition depends largely on the type of interface. In the BHDC system, k(obs) increases with W(0) in the whole range studied while in AOT the kinetic profile has a maximum at W(0) approximately 5, probably reflecting the fact that BH(4)(-) is part of the cationic interface while, in the anionic one, there is a strong interaction between water and the polar headgroup of AOT below W(0) = 5 and, above that, BH(4)(-) is repelled from the interface once the water pool has formed. Application of a kinetic model based on the pseudophase formalism, which considers the distribution of the ketone between the continuous medium and the interface and assumes that reaction takes place only at the interface, has enabled us to estimate rate constants at the interface of the reverse micellar systems. At W(0) < 10, it was considered that NaBH(4) is wholly at the interface and, at W(0) >/= 10, where there are free water molecules, also the partitioning between the interface and the water pool was taken into account. The results were used to evaluate CAF and NaBH(4) distribution constants between the different pseudophases as well as the second-order reaction rate constant of the reduction reaction in the micellar interface. 相似文献
An aneroid isoperibol calorimetric apparatus is described which is particularly suitable for measurement of the reaction heat among solids. Such an apparatus contains four calorimeters and allows to carry out differential measurements. Each calorimeter includes two small electric furnaces employed for heating the solid mixture until the reaction begins and for the successive electric calibrations, respectively. The temperature trend of each calorimeter is followed by 80 thermocouples in series. The instrument characteristics are briefly discussed. Examples of its employment in the alloy thermochemistry are given. 相似文献
An evaluation of the gas-phase ion chemistry of rotenone (1) by electrospray ionisation (ESI) mass spectrometry (MS) and tandem mass spectrometry (MS2) is presented, aiming at providing tools for its determination in natural and biological matrices. The behaviour of its cycloadducts with benzonitrile-N-oxide (2) and 2,4,6-trimethylbenzonitrile-N-oxide (3) was also evaluated and the MS data thus obtained have provided evidence into the mechanism of formation of the key product ion at m/z 192 which can be considered a marker in the MS and MS2 spectra of rotenone and its derivatives. 相似文献
This study further extends the scope of a previous paper [Y. Ferro and A. Allouche, J. Chem. Phys. 118, 10461 (2003)] on the reactivity of atomic Na with water to some other highly polar molecules known for their solvation properties connected to efficient hydrogen bonding. The solvation mechanisms of ammonia and methanol are compared to the hydration mechanism. It is shown that in the case of ammonia, the stability of the solvated system is only ensured by electrostatic interactions, whereas the methanol action is more similar to that of water. More specific attention is given to the solvation process of the valence 3s Na electron. The consequences on the chemical reactivity are analyzed: Whereas ammonia is nonreactive when interacting with atomic sodium, two chemical reactions are proposed for methanol. The first process is dehydrogenation and yields methoxy species and hydrogen. The other one is dehydration and the final products are methoxy species, but also methyl radical and water. The respective roles of electron solvation and hydrogen bonds network are analyzed in detail in view of the density of states of the reactive systems. 相似文献
The vapour pressures of cytosine and thymine were measured using the torsion-effusion technique. The sublimation processes of cytosine and thymine were investigated over the temperature ranges 480–553 K and 420–503 K, respectively. The following pressure—temperature equations were derived by least-squares treatment of the vapour pressure data The standard sublimation enthalpies were obtained by second-and third-law treatment of the experimental data and the values ΔH0298 = 167 ± 10 kJ mole?1 and ΔH0298 = 138 ± 10 kJ mole?1 were derived for cytosine and thymine, respectively. IR and Raman spectra were recorded in the gas phase in order to evaluate the thermodynamic functions of gaseous cytosine and thymine. 相似文献