Degree Of Conformational Order Research Articles

Harnessing Conformational Disorder of Organic Cations for Efficient Blue Quasi‐2D Perovskite LEDs

AbstractDespite quasi‐2D perovskite offering great control over the optoelectronic properties, disordered organic cations are often perceived as detrimental to device performance, primarily affecting charge carrier mobility. However, it is proposed that such disordered organic cations‐enabled excellent excitonic properties can be beneficial for fabricating high‐efficiency perovskite light‐emitting diodes (PeLEDs) facilitated by reduced dielectric screening effect. Here, by incorporating acetamidinium bromide additives, the conformational disorder of organic cation is precisely manipulated and meticulously probed using sum frequency generation vibrational spectroscopy. Finally, a distinctive inverse relationship is elucidated between the degree of conformational order, characterized as relative structure ordering , and key performance metrics such as photoluminescence quantum yield and external quantum efficiency (EQE). By optimizing the configurational disorder, sky‐blue (485 nm) PeLEDs achieve a noteworthy EQE of 14.42% and exhibit significantly prolonged operational stability in open‐air conditions. This finding underscores the potential advantages of disordered organic cations in enhancing exciton properties and radiative recombination efficiency.

Diverse Native Ensembles Dictate the Differential Functional Responses of Nuclear Receptor Ligand-Binding Domains.

Native states of folded proteins are characterized by a large ensemble of conformations whose relative populations and interconversion dynamics determine the functional output. This is more apparent in transcription factors that have evolved to be inherently sensitive to small perturbations, thus fine-tuning gene expression. To explore the extent to which such functional features are imprinted on the folding landscape of transcription factor ligand-binding domains (LBDs), we characterize paralogous LBDs of the nuclear receptor (NR) family employing an energetically detailed and ensemble-based Ising-like statistical mechanical model. We find that the native ensembles of the LBDs from glucocorticoid receptor, PPAγ, and thyroid hormone receptor display a remarkable diversity in the width of the native wells, the number and nature of partially structured states, and hence the degree of conformational order. Monte Carlo simulations employing the full state representation of the ensemble highlight that many of the functional conformations coexist in equilibrium, whose relative populations are sensitive to both temperature and the strength of ligand binding. Allosteric modulation of the degree of structure at a coregulator binding site on ligand binding is shown to arise via a redistribution of populations in the native ensembles of glucocorticoid and PPAγ LBDs. Our results illustrate how functional requirements can drive the evolution of conformationally diverse native ensembles in paralogs.

How Phospholipid-Cholesterol Interactions Modulate Lipid Lateral Diffusion, as Revealed by Fluorescence Correlation Spectroscopy

Cholesterol is a key player in regulating physico-chemical properties of cellular membranes and, thereby, ensuring cell viability. In particular, lipid-cholesterol interactions may provide important information on the spatio-temporal organization of membrane components. Here, we apply confocal imaging and Fluorescence Correlation Spectroscopy (FCS) to Giant Unilamellar Vesicles (GUVs) composed of binary mixtures of lipids and cholesterol. The effect of cholesterol on lipid dynamics and molecular packing order of unsaturated, monounsaturated, fully saturated (with both low and high phase transition temperatures, Tm) glycero-phospholipids and sphingomyelin has been investigated. We show that, for unsaturated glycerophospholipids, the decrease of the lipid diffusion coefficient as a result of the interaction with cholesterol does not depend on the fatty acid chain length. However, the values of the diffusion coefficient change as a function of chain length. The monounsaturated phospholipid palmitoyl-oleoyl-phosphatidylcholine (POPC) exhibits a dynamic behavior very similar to the unsaturated dioleoyl-phosphatidylcholine (DOPC). By contrast, for saturated (low Tm) glycero-phospholipids, cholesterol causes a decrease of lipid mobility in a chain length-dependent manner. FCS can be employed as a valuable tool to study lipid-sterol interactions and their effect on lipid dynamics, molecular packing and degree of conformational order.

Temperature and pH Effects on the Coadsorption of Sodium Dodecyl Sulfate and Poly(ethylenimine)

The polar orientation and alkyl chain conformational ordering of sodium dodecyl sulfate (SDS) at the octadecanethiol/water hydrophobic interface have been investigated using sum frequency vibrational spectroscopy (SFS). The effects of different concentrations of the cationic polymer poly(ethylenimine), PEI, along with the solution pH and temperature have been determined. PEI was found to promote synergistic adsorption of ordered SDS at concentrations as low as 10 ppm at pH 6.0 through cooperative polymer/surfactant complex formation. At lower pH's and in the presence of the polymer stronger interfacial ordering of the surfactant was observed, attributed to increased protonation of PEI amino groups in acidic solutions and consequent decreases in the intersurfactant spacings of complexed SDS. SDS was found to be present at the hydrophobic surface at temperatures of up to 60 °C, although thermally induced motion of the surfactant chains resulted in a monotonic decrease in the degree of conformational order with rising temperature. In the presence of PEI the effect of temperature on the ordering of SDS, present predominantly in the form of a polymer/surfactant complex, was qualitatively similar.

Conformational analysis of receptor selective tachykinin analogs: senktide and septide.

The conformational behavior in solution of two receptor selective tachykinin agonists, senktide (succinyl-D-F-MeF-G-L-M-NH2) and septide (pQ-F-F-P-L-M-NH2) is described. Two dimensional cross relaxation NMR spectroscopy is used together with coupling constant data to obtain interproton distance constraints. These results are used in conjunction with semi-empirical energy computations to indicate favorable conformations. Senktide is found to have a high degree of conformational order which is attributed to rotational restriction associated with the N-methylation of phenylalanine. The lowest energy conformation in accord with the experimental interproton distances contains a beta-turn. Interproton distances indicate that septide exists as a random coil or in an extended chain conformation. Energy computations suggest that septide is primarily an extended chain with internal reorientation restricted by the proline residue. These results may be related to the selectivity of these peptides for different receptors, in that the analogs, with conformations more stable than tachykinins, are more receptor selective.