23 research outputs found
Calcium Coordination Solids for pH-Triggered Release of Olsalazine
Calcium coordination solids were synthesized and evaluated for delivery of olsalazine (H_4olz), an anti-inflammatory compound used for treatment of ulcerative colitis. The materials include one-dimensional Ca(H_2olz)⋅4 H_2O chains, two-dimensional Ca(H_2olz)⋅2 H_2O sheets, and a three-dimensional metal-organic framework Ca(H_2olz)⋅2DMF (DMF=N,N-dimethylformamide). The framework undergoes structural changes in response to solvent, forming a dense Ca(H_2olz) phase when exposed to aqueous HCl. The compounds Ca(H_2olz)⋅x H_2O (x=0, 2, 4) were each pressed into pellets and exposed to simulated gastrointestinal fluids to mimic the passage of a pill from the acidic stomach to the pH-neutral intestines. All three calcium materials exhibited a delayed release of olsalazine relative to Na_2(H_2olz), the commercial formulation, illustrating how formulation of a drug within an extended coordination solid can serve to tune its solubility and performance
Water Enables Efficient CO2 Capture from Natural Gas Flue Emissions in an Oxidation-Resistant Diamine-Appended Metal-Organic Framework.
Supported by increasingly available reserves, natural gas is achieving greater adoption as a cleaner-burning alternative to coal in the power sector. As a result, carbon capture and sequestration from natural gas-fired power plants is an attractive strategy to mitigate global anthropogenic CO2 emissions. However, the separation of CO2 from other components in the flue streams of gas-fired power plants is particularly challenging due to the low CO2 partial pressure (∼40 mbar), which necessitates that candidate separation materials bind CO2 strongly at low partial pressures (≤4 mbar) to capture ≥90% of the emitted CO2. High partial pressures of O2 (120 mbar) and water (80 mbar) in these flue streams have also presented significant barriers to the deployment of new technologies for CO2 capture from gas-fired power plants. Here, we demonstrate that functionalization of the metal-organic framework Mg2(dobpdc) (dobpdc4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) with the cyclic diamine 2-(aminomethyl)piperidine (2-ampd) produces an adsorbent that is capable of ≥90% CO2 capture from a humid natural gas flue emission stream, as confirmed by breakthrough measurements. This material captures CO2 by a cooperative mechanism that enables access to a large CO2 cycling capacity with a small temperature swing (2.4 mmol CO2/g with ΔT = 100 °C). Significantly, multicomponent adsorption experiments, infrared spectroscopy, magic angle spinning solid-state NMR spectroscopy, and van der Waals-corrected density functional theory studies suggest that water enhances CO2 capture in 2-ampd-Mg2(dobpdc) through hydrogen-bonding interactions with the carbamate groups of the ammonium carbamate chains formed upon CO2 adsorption, thereby increasing the thermodynamic driving force for CO2 binding. In light of the exceptional thermal and oxidative stability of 2-ampd-Mg2(dobpdc), its high CO2 adsorption capacity, and its high CO2 capture rate from a simulated natural gas flue emission stream, this material is one of the most promising adsorbents to date for this important separation
Calcium Coordination Solids for pH-Triggered Release of Olsalazine
Calcium coordination solids were synthesized and evaluated for delivery of olsalazine (H_4olz), an anti-inflammatory compound used for treatment of ulcerative colitis. The materials include one-dimensional Ca(H_2olz)⋅4 H_2O chains, two-dimensional Ca(H_2olz)⋅2 H_2O sheets, and a three-dimensional metal-organic framework Ca(H_2olz)⋅2DMF (DMF=N,N-dimethylformamide). The framework undergoes structural changes in response to solvent, forming a dense Ca(H_2olz) phase when exposed to aqueous HCl. The compounds Ca(H_2olz)⋅x H_2O (x=0, 2, 4) were each pressed into pellets and exposed to simulated gastrointestinal fluids to mimic the passage of a pill from the acidic stomach to the pH-neutral intestines. All three calcium materials exhibited a delayed release of olsalazine relative to Na_2(H_2olz), the commercial formulation, illustrating how formulation of a drug within an extended coordination solid can serve to tune its solubility and performance
Olsalazine-Based Metal–Organic Frameworks as Biocompatible Platforms for H_2 Adsorption and Drug Delivery
The drug olsalazine (H_4olz) was employed as a ligand to synthesize a new series of mesoporous metal–organic frameworks that are expanded analogues of the well-known M_2(dobdc) materials (dobdc^4– = 2,5-dioxido-1,4-benzenedicarboxylate; M-MOF-74). The M_2(olz) frameworks (M = Mg, Fe, Co, Ni, and Zn) exhibit high surface areas with large hexagonal pore apertures that are approximately 27 Å in diameter. Variable temperature H_2 adsorption isotherms revealed strong adsorption at the open metal sites, and in situ infrared spectroscopy experiments on Mg_2(olz) and Ni_2(olz) were used to determine site-specific H_2 binding enthalpies. In addition to its capabilities for gas sorption, the highly biocompatible Mg_2(olz) framework was also evaluated as a platform for the delivery of olsalazine and other encapsulated therapeutics. The Mg_2(olz) material (86 wt % olsalazine) was shown to release the therapeutic linker through dissolution of the framework under simulated physiological conditions. Furthermore, Mg_2(olz) was used to encapsulate phenethylamine (PEA), a model drug for a broad class of bioactive compounds. Under simulated physiological conditions, Mg_2(olz)(PEA)_2 disassembled to release PEA from the pores and olsalazine from the framework itself, demonstrating that multiple therapeutic components can be delivered together at different rates. The low toxicity, high surface areas, and coordinatively unsaturated metal sites make these M_2(olz) materials promising for a range of potential applications, including drug delivery in the treatment of gastrointestinal diseases
Olsalazine-Based Metal–Organic Frameworks as Biocompatible Platforms for H_2 Adsorption and Drug Delivery
The drug olsalazine (H_4olz) was employed as a ligand to synthesize a new series of mesoporous metal–organic frameworks that are expanded analogues of the well-known M_2(dobdc) materials (dobdc^4– = 2,5-dioxido-1,4-benzenedicarboxylate; M-MOF-74). The M_2(olz) frameworks (M = Mg, Fe, Co, Ni, and Zn) exhibit high surface areas with large hexagonal pore apertures that are approximately 27 Å in diameter. Variable temperature H_2 adsorption isotherms revealed strong adsorption at the open metal sites, and in situ infrared spectroscopy experiments on Mg_2(olz) and Ni_2(olz) were used to determine site-specific H_2 binding enthalpies. In addition to its capabilities for gas sorption, the highly biocompatible Mg_2(olz) framework was also evaluated as a platform for the delivery of olsalazine and other encapsulated therapeutics. The Mg_2(olz) material (86 wt % olsalazine) was shown to release the therapeutic linker through dissolution of the framework under simulated physiological conditions. Furthermore, Mg_2(olz) was used to encapsulate phenethylamine (PEA), a model drug for a broad class of bioactive compounds. Under simulated physiological conditions, Mg_2(olz)(PEA)_2 disassembled to release PEA from the pores and olsalazine from the framework itself, demonstrating that multiple therapeutic components can be delivered together at different rates. The low toxicity, high surface areas, and coordinatively unsaturated metal sites make these M_2(olz) materials promising for a range of potential applications, including drug delivery in the treatment of gastrointestinal diseases
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Controlling Crystallization and Transport in Metal–Organic Frameworks
This dissertation documents efforts to control and take advantage of crystallization handles in metal–organic framework synthesis. Understanding fundamental processes during synthesis allows for directed, predictable control over crystallite size and shape, which is demonstrated to play a role in intracrystalline diffusion. Chapter 1 first introduces a summary of crystallization and transport in porous materials, including classical and non-classical models of crystallization, homogeneous and heterogeneous nucleation, and mass transfer resistances. The application of these concepts to metal–organic frameworks is presented alongside common synthetic strategies, coordination modulation and other strategies to control crystallite size and shape, and the potential for non-coordinating bases and buffers to help alleviate some complicating factors common to framework synthesis. Finally, because crystallite size and shape can control intracrystalline path lengths, an introduction to mass transfer resistances is given, including intracrystalline diffusion. Different methods of measuring diffusion in porous materials are presented, including the technique applied in this work, zero-length column chromatography (ZLC). Chapter 2 details success in deconvoluting solution equilibria during hydrothermal metal–organic framework synthesis. The use of non-coordinating bases and anions allows for generalizable increase in crystallite size. Further, non-coordinating buffers may be used during synthesis to add or subtract individual coordinating anions at a given pH. This strategy allows for tunable and predictable control over aspect ratio in a one-dimensional metal–organic framework. Chapter 3 describes the discovery and utilization of interfacial effects during hydrothermal synthesis to control crystalline phase and size. Controlling the interface between reaction vessel and solution via silanization is found to decrease morphological distribution, change the phase produced for stock solutions, and in some cases, increase crystallite volume by several orders of magnitude. Chapter 4 details the assembly and usage of a ZLC instrument capable of differentiating between different mass transfer resistances. Design considerations and instrument improvements are described. The instrument is used to probe CO2 diffusion within very large crystallites (up to 700 microns in length) of Zn2(dobdc), where surface resistances and defects are proposed to account for a lower diffusivity measured via ZLC versus pulsed-field gradient NMR. Synthetic control over Co2(dobdc) path length is demonstrated to bring about improved mass transfer resistances via path length control for the industrially important molecule m-xylene