Aggregation of Hydroxypropyl Methylcellulose Acetate Succinate under Its Dissolving pH and the Impact on Drug Supersaturation.

Hydroxypropyl methylcellulose acetate succinate (HPMC-AS) is one of the commonly selected polymers used in amorphous solid dispersions (ASD) with excellent capabilities to maintain aqueous supersaturation of poorly water-soluble drugs and inhibit their crystallization, but the underlying mechanisms remain elusive. In this study, posaconazole was chosen as the model drug to study the supersaturation maintaining and crystallization inhibition capabilities of different types of HPMC-AS under pH 5.5-7.5. We analyzed the HPMC-AS aggregation status in solution using combination of static and dynamic light scattering and observed higher polymer aggregation number when higher grade HPMC-AS or lower pH was used, which correlates well with prolonged drug supersaturation or crystallization inhibition. The amount of HPMC-AS coprecipitated with PSZ, a direct indicator of drug/HPMC-AS affinity, also showed positive correlation with the drug supersaturation and crystallization inhibition in the dissolution process. Therefore, we conclude that the aggregation behavior of HPMC-AS and the drug/HPMC-AS affinity are the key mechanisms that lead to posaconazole supersaturation and crystallization inhibition when HPMC-AS was applied.

Modulating lipid bilayer permeability and structure: Impact of hydrophobic chain length, C-3 hydroxyl group, and double bond in sphingosine.

Sphingosine, an amphiphilic molecule, plays a pivotal role as the core structure of sphingolipids, essential constituents of cell membranes. Its unique capability to enhance the permeability of lipid membranes profoundly influences crucial life processes. The molecular structure of sphingosine dictates its mode of entry into lipid bilayers and governs its interactions with lipids, thereby determining membrane permeability. However, the incomplete elucidation of the relationship between the molecular structure of sphingosine and the permeability of lipid membranes persists due to challenges associated with synthesizing sphingosine molecules. A series of sphingosine-derived molecules, featuring diverse hydrophobic chain lengths and distinct headgroup structure, were meticulously designed and successfully synthesized. These molecules were employed to investigate the permeability of large unilamellar vesicles, functioning as model lipid bilayers. With a decrease in the hydrophobic chain length of sphingosine from C15 to C11, the transient leakage ratio of vesicle contents escalated from âˆ¼ 13 % to âˆ¼ 28 %. Although the presence of double bond did not exert a pronounced influence on transient leakage, it significantly affected the continuous leakage ratio. Conversely, modifying the chirality of the C-3 hydroxyl group gives the opposite result. Notably, methylation at the C-3 hydroxyl significantly elevates transient leakage while suppressing the continuous leakage ratio. Additionally, sphingosines that significantly affect vesicle permeability tend to have a more pronounced impact on cell viability. Throughout this leakage process, the charge state of sphingosine-derived molecule aggregates in the solution emerged as a pivotal factor influencing vesicle permeability. Fluorescence lifetime experiments further revealed discernible variations in the effect of sphingosine molecular structure on the mobility of hydrophobic regions within lipid bilayers. These observed distinctions emphasize the impact of molecular structure on intermolecular interactions, extending to the microscopic architecture of membranes, and underscore the significance of subtle alterations in molecular structure and their associated aggregation behaviors in governing membrane permeability.

Insight into UV-induced simultaneous photocatalytic degradation of Ti3C2Tx MXene and reduction of U(VI).

With the development of MXene as the efficient adsorbent for U(VI), the tendency of MXene coming into contact with U(VI) in wastewaters increases. Motivated by UV light irradiation applied in wastewater treatments, the UV light induced photochemical co-transformation of Ti3C2Tx MXene and U(VI) is studied. To clarify the role of U(VI) induced Ti3C2Tx aggregation in phototransformation of Ti3C2Tx, the aggregation kinetics of Ti3C2Tx in the presence of various valent radioactive ions are investigated, obtaining the critical coagulation concentrations (CCC) of Ti3C2Tx for Cs+, Sr2+, UO22+, Eu3+, and Th4+. Besides, the colloidal stability of UV-induced Ti3C2Tx as a function of standing time is discussed. The results show that the aggregation behavior of Ti3C2Tx induced by radioactive ions follows the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory and the Schulze-Hardy rule. The UV irradiation will change the physicochemical properties and colloidal stabilities of Ti3C2Tx. Furthermore, the degradation of Ti3C2Tx can be accelerated by UV irradiation and further promoted by the presence of U(VI). The removal of U(VI) is highest in the case of Ti3C2Tx combined with UV irradiation via adsorption and reduction. This study provides an example demonstrating that the simultaneous transformation of Ti3C2Tx (adsorbent) and U(VI) (adsorbate) to mild toxic components.

Influence of Large Steric Hinderance Substituent Position on Conformation and Charge Transfer Process for Non-Fused Ring Acceptors.

To obtain stable and planar molecular geometry in non-fused electron acceptors, A4T-25 and A4T-26 are designed and synthesized by introducing the bulk 2,4,6-triisopropylphenyl side groups onto different positions of the central two thiophene units. A4T-25 and A4T-26 both show a narrow-bandgap of 1.39 and 1.46 eV, with highest occupied molecular orbital/lowest unoccupied molecular orbital levels of -5.56/-3.81 and -5.65/-3.83 eV, respectively, and the electrostatic potential distributions imply that they have strong electron-accepting capability. The single crystal structure analysis and the transfer integral calculation demonstrate that the much more compact π-π stacking in A4T-26 can promote efficient charge transportation compared to that in A4T-25. Therefore, the electron mobility of A4T-26 is obviously higher and more balanced than that of A4T-25. When blending the two acceptors with the same polymer donor PBDB-TF, the photovoltaic cell based on PBDB-TF:A4T-25 has an inadequate power conversion efficiency (PCE) of 7.83%, while the PBDB-TF:A4T-26-based one yields an enhanced PCE of 12.1%. Overall, this study offers an insight into the relationship between the fine-tuning of the molecular structure of non-fused ring acceptors and the corresponding charge transfer process in organic solar cells.

Effects of partial substitution of NaCl on myofibrillar protein properties from pearl mussel Hyriopsis cumingii muscle: Structural characteristics and aggregation behaviors.

The effects of NaCl and its partial substitutes (KCl, MgCl2 and CaCl2) on solubility, structural characteristics and aggregation behaviors of myofibrillar protein (MP) from pearl mussel muscle were investigated and compared. MP at 0.6 M NaCl was beneficial to protein unfolding and showed excellent potential functional properties. When NaCl was substituted in low level, MPs also showed good solubility and ordered microstructure as well as NaCl, especially MgCl2 and CaCl2, due to the unfolding of α-helical structures and subsequently exposed tyrosine residues and hydrophobic groups. However, the obviously increased disulfide bonds and hydrophobic interactions in high substitution level indicated the excessive non-sodium salts had negative effects on molecular rearrangement, leading to irregular and overly tight of microstructure. Thus, NaCl partially substituted by KCl, MgCl2 and CaCl2 in low substitution level is promising to improve functional properties of MP in low-sodium meat products.

Aggregation behaviors of thermo-responsive methylcellulose in water: A molecular dynamics simulation study.

The aggregation behaviors of methylcellulose (MC) in aqueous solution were investigated using all-atom molecular dynamic simulations (MD). The interactions between MC chains and water molecules at different temperatures were investigated by a series of MD analyses, such as the solvent accessible surface area, number of hydrogen bonds, radial distribution functions and the interaction energies. Constant temperature simulations and heating simulations of MC aqueous solution were carried out in this work. In the simulations at three constant temperatures (25 °C, 50 °C and 75 °C), the aggregation behaviors of MC chains were affected by the temperature. In the heating simulation (25 °C âˆ¼ 75 °C), temperature increases were accompanied by decreases in interactions between MC and water molecules, and by increases in interactions between MC chains, which led to the aggregation of MC chains. The degree of aggregation of MC chains increased with the rise of temperature.

Investigation of the structural, physicochemical properties, and aggregation behavior of lipopeptide biosurfactant produced by Acinetobacter junii B6.

In the present study the produced biosurfactant of Acinetobacter junii B6 (recently isolated from Iranian oil excavation site) were partially purified and identified by high performance thin layer chromatography (HPTLC), Fourier transform infrared spectroscopy (FTIR), and proton nuclear magnetic resonance (1H NMR). Elemental analysis of the biosurfactant by energy dispersive X-ray spectroscopy (EDS) revealed that the biosurfactant was anionic in nature. The physiochemical properties of the lipopeptide biosurfactant were evaluated by determination of its critical micelle concentration (CMC) and hydrophile-lipophile balance (HLB). The produced biosurfactant decreased the surface tension of water to 36mNm-1 with the CMC of approximately 300mg/l. Furthermore, the solubility properties of the biosurfactant (dissolved in phosphate-buffer saline solution, pH7.4) were investigated by turbidity examination, dynamic light scattering (DLS) measurements, and transmission electron microscopy (TEM) inspection. It could be concluded that the biosurfactant showed the spherical-shaped vesicles at a concentration higher than its CMC and the circular dichroism (CD) spectra showed that the secondary structure of the biosurfactant vesicles is dominated by the ß sheet.