Hydrophobic hydration driven self-assembly of Curcumin in water: Similarities to nucleation and growth under large metastability, and an analysis of water dynamics at heterogeneous surfaces

As the beneficial effects of curcumin have often been reported to be limited to its small concentrations, we have undertaken a study to find the aggregation properties of curcumin in water by varying the number of monomers. Our molecular dynamics simulation results show that the equilibrated structure is always an aggregated state with remarkable structural rearrangements as we vary the number of curcumin monomers from 4 to 16 monomers. We find that curcumin monomers form clusters in a very definite pattern where they tend to aggregate both in parallel and anti-parallel orientation of the phenyl rings, often seen in the formation of beta-sheet in proteins. A considerable enhancement in the population of parallel alignments is observed with increasing the system size from 12 to 16 curcumin monomers. Due to the prevalence of such parallel alignment for large system size, a more closely packed cluster is formed with maximum number of hydrophobic contacts. We also follow the pathway of cluster growth, in particular the transition from the initial segregated to the final aggregated state. We find the existence of a metastable structural intermediate involving a number of intermediate-sized clusters dispersed in the solution. The course of aggregation bears similarity to nucleation and growth in highly metastable state. The final aggregated form remains stable with total exclusion of water from its sequestered hydrophobic core. We also investigate water structure near the cluster surface along with their orientation. We find that water molecules form a distorted tetrahedral geometry in the 1st solvation layer of the cluster, interacting strongly with hydrophilic groups at the surface of curcumin. The dynamics of such quasi-bound water molecules near the surface of curcumin cluster is considerably slower than the bulk signifying a restricted motion as often found in protein hydration layer.Comment: 31 pages, 9 figure

Effect of Organic Acid-Modified Mesoporous Alumina toward Fluoride Ions Removal from Water

Mesoporous alumina (MA) was prepared via the sol–gel process at 40 °C/48 h followed by calcinations at 550 °C/5 h, in the absence of organic acids and in the presence of malic, tartaric, and citric acids (sample IDs: A-550, AM-550, AT-550, and AC-550, respectively). For fluoride ion adsorption on MA, the effects of different parameters such as contact time, concentration of adsorbate (F^– ions), pH, temperature, and competing ions were studied. The adsorption kinetics of fluoride ions followed the pseudo-second-order model. The prepared MA showed the maximum F^– ions adsorption capacity of 47.2, 49, 51.2, and 62.5 mg g^–1 for the samples A-550, AM-550, AT-550, and AC-550, respectively. The adsorption efficiency of MA followed the order AC-550 > AT-550 > AM-550 > A-550, corroborating to their BET surface area and pore volume. The competing anions (PO₄^3–, Cl^– and SO₄^2–) have a slight effect of reducing the F^– ions adsoption in the order of PO₄^3– > SO₄^2– > Cl^–. For interpretation of adsorption isotherms, both Langmuir and Freundlich models were used. The F^– ions adsorption efficiency remained almost the same up to 3 cycles of the regenerated MA

Molecular principles of recruitment and dynamics of guest proteins in liquid droplets

International audienceDespite the continuous discovery of host and guest proteins in membraneless organelles, complex host–guest interactions hinder the understanding of the molecular grammar governing liquid–liquid phase separation. In this study, we characterized the localization and dynamic properties of guest proteins in liquid droplets using single-molecule fluorescence microscopy. Eighteen guest proteins of different sizes, structures, and oligomeric states were examined in host p53 liquid droplets. Recruitment did not significantly depend on the structural properties of the guest proteins, but was moderately correlated with their length, total charge, and number of R and Y residues. In contrast, the diffusion of disordered guest proteins was comparable to that of host p53, whereas that of folded proteins varied widely. Molecular dynamics simulations suggest that folded proteins diffuse within the voids of the liquid droplet while interacting weakly with neighboring host proteins, whereas disordered proteins adapt their structures to form tight interactions with the host proteins. Our study provides insights into the key molecular principles of the localization and dynamics of guest proteins in liquid droplets