A series of supported 3% MoO x catalysts were synthesized by incipient-wetness impregnation of a 5–15% TaO x surface-modified γ-Al2O3 support. The catalysts were characterized by in situ spectroscopies (diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), Raman, UV–vis, X-ray absorption spectroscopy (XAS)) and multiple chemical probes (C2H4/C4H8 titration, C3H6-TPSR, steady-state propylene metathesis, NH3-IR adsorption). The supported tantalum oxide phase was present as surface TaO x sites on the γ-Al2O3 support that capped the Al2O3 surface hydroxyls. The change in available surface hydroxyls caused the subsequent anchoring of MoO x species to occur at different surface hydroxyls. This shifted the anchoring of MoO x species from basic (Al-OH) to neutral (Al2-OH) to more acidic (Al3-OH) surface hydroxyls as well as perturbation of the remaining alumina surface hydroxyls by the surface TaO x sites. The TaO x surface-modified γ-Al2O3 support increased the number of activated surface MoO x sites (Ns) by ∼6× and the turnover frequency (TOF) by ∼10×, resulting in an increased activity of ∼60×. It was found that the specific anchoring surface hydroxyls rather than the extent of oligomerization of the surface MoO x sites control the number of activated MoO x sites and TOF for propylene metathesis. No relationships between the nature of the surface Lewis/Brønsted acid sites and Ns and TOF were found to be present.

A series of supported ReO x catalysts were synthesized by incipient-wetness impregnation of perrhenic acid onto one component (Al2O3 and SiO2) and surface-modified mixed-oxide supports (SiO2/Al2O3, Al2O3/SiO2, and ZSM-5 (Si/Al = 15)), characterized with in situ molecular spectroscopy (Raman, DRIFTS, UV–vis, and XAS), and chemically probed (ammonia chemisorption, C2H4/C4H8-titration, C3H6-TPSR, and steady-state propylene self-metathesis). The initial dehydrated surface rhenia species were coordinated to the oxide supports as isolated Re7+O4 sites. For the Al-containing supports, dioxo surface (O)2Re­(−O)2 sites appear to be the preferred coordination. The number of activated surface ReO x sites during metathesis is determined by the oxide support ligands (3% ReO x /ZSM-5 > 3% ReO x /5% AlO x /SiO2 > 3% ReO x /5% SiO x /Al2O3 > 3% ReO x /Al2O3 ≈ 3% ReO x /SiO2). The specific activity (TOF) is also controlled by the oxide support ligands (3% ReO x /Al2O3 > 3% ReO x /5% SiO x /Al2O3 ≫ 3% ReO x /ZSM-5 ≈ 3% ReO x /5% AlO x /SiO2 ≫ 3% ReO x /SiO2). The overall propylene metathesis activity (N × TOF), however, is dominated by the number of activated sites (N). Consequently, the enhanced overall activity of surface ReO x supported on SiO2–Al2O3 mixed-oxide supports is related to the greater number of activated surface ReO x sites. The overall propylene metathesis activity was not related to the local surface ReO4 molecular structure or the strength of the Brønsted acid site, since the same rhenia structures appeared to be present on all of the active catalysts and the strengths of the Brønsted acid sites were comparable for all of the active catalysts, respectively.

A series of supported ReO x catalysts were investigated that allowed identifying the unique surface anchoring sites on oxide supports responsible for activating the surface ReO4 sites for propylene metathesis (the catalytic active site). The catalysts were synthesized by incipient-wetness impregnation of aqueous HReO4 onto the oxide supports (Al2O3, ZrO2, TiO2, SiO2, and CeO2), characterized under dehydrated and propylene metathesis reaction conditions with in situ spectroscopy (Raman, DRIFTS, UV–vis and NAP-XPS), and chemically probed (CH3CHCH2–TPSR, CH2CH2/CH3CHCHCH3 titration and steady-state self-metathesis of propylene to ethylene and 2-butene). The initially calcined supported rhenia species anchor as isolated surface Re7+O4 sites on the oxide supports by reacting with the surface hydroxyls (terminal S–OH, bridged S–OH–S, and tricoordinated S3–OH) of the oxide supports. The specific oxide support was found to control the number of activated sites (Al2O3 ≫ ZrO2 > CeO2 > TiO2 > SiO2) and propylene metathesis activity (Al2O3 ≫ ZrO2 ≫ TiO2 ∼ CeO2 ∼ SiO2), revealing that the oxide support action is a potent ligand for the surface ReO x sites. The activation and specific activity of the surface ReO x sites depend on several factors (nature of surface hydroxyls (S3–OH > S–OH–S > S–OH), coordination of the oxide support surface cation (ZrO7, AlO6, CeO4) and electronegativity of the oxide support cation (SiO2 > Al2O3 > TiO2 > ZrO2 > CeO2). No relationships exist between olefin metathesis activity and acid strength of surface Lewis and Brønsted sites. Prior studies primarily focused on supported ReO x /Al2O3, and the lack of examination of non-Al2O3 supported rhenia catalysts precluded comparison between efficient and inefficient olefin metathesis catalysts, which prevented identifying the catalytic active site for olefin metathesis by supported ReO x catalysts.

Liposomes have become increasingly common in the delivery of bioactive agents due to their ability to encapsulate hydrophobic and hydrophilic drugs with excellent biocompatibility. While commercial liposome formulations improve bioavailability of otherwise quickly eliminated or insoluble drugs, tailoring formulation properties for specific uses has become a focus of liposome research. Here, we report the design, synthesis, and characterization of two series of amphiphilic macromolecules (AMs), consisting of acylated polyol backbones conjugated to poly(ethylene glycol) (PEG) that can serve as the sole additives to stabilize and control hydrophilic molecule release rates from distearoylphosphatidylcholine (DSPC)-based liposomes. As compared to DSPC alone, all AMs enable liposome formation and stabilize their colloidal properties at low incorporation ratios, and the AM's degree of unsaturation and hydrophobe conformation have profound impacts on stability duration. The AM's chemical structures, particularly hydrophobe unsaturation, also impact the rate of hydrophilic drug release. Course-grained molecular dynamics simulations were utilized to better understand the influence of AM structure on lipid properties and potential liposomal stabilization. Results indicate that both hydrophobic domain structure and PEG density can be utilized to fine-tune liposome properties for the desired application. Collectively, AMs demonstrate the potential to simultaneously stabilize and control the release profile of hydrophilic cargo.