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

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

Thermodynamically metastable thiocyanato coordination polymer that shows slow relaxations of the magnetization

Reaction of cobalt thiocyanate with 4-acetylpyridine leads to the formation of [Co­(NCS)₂(4-acetylpyridine)₂]_<i>n</i> (<b>3/I</b>). In its crystal structure the Co cations are connected by pairs of μ-1,3-bridging thiocyanato ligands into dimers that are further connected into layers by single anionic ligands. DTA-TG measurements of Co­(NCS)₂(4-acetyl-pyridine)₄ (<b>1</b>) led to the formation of <b>3/I</b>. In contrast, when the hydrate Co­(NCS)₂(4-acetyl-pyridine)₂(H₂O)₂ (<b>2</b>) is decomposed, a mixture of <b>3/I</b> and a thermodynamically metastable form <b>3/II</b> is obtained. Further investigations reveal that thermal annealing of <b>2</b> leads to the formation of <b>3/II</b>, that contains only traces of the stable form <b>3/I</b>. DSC and temperature dependent X-ray powder diffraction (XRPD) measurements prove that <b>3/II</b> transforms into <b>3/I</b> on heating. The crystal structure of <b>3/II</b> was determined ab initio from XRPD data. In its crystal structure the Co cations are linked by pairs of bridging thiocyanato anions into a 1D coordination polymer, and thus, <b>3/II</b> is an isomer of <b>3/I</b>. Magnetic measurements disclose that the stable form <b>3/I</b> only shows paramagnetism without any magnetic anomaly down to 2 K. In contrast, the metastable form <b>3/II</b> shows ferromagnetic behavior. The phase transition into ordered state at <i>T</i>_c = 3.8 K was confirmed by specific heat measurements. Alternating current susceptibility measurements show frequency dependent maxima in χ′ and χ″, which is indicative for a slow relaxation of the magnetization

Influence of Metal Substitution on the Pressure-Induced Phase Change in Flexible Zeolitic Imidazolate Frameworks

Metal–organic frameworks that display step-shaped adsorption profiles arising from discrete pressure-induced phase changes are promising materials for applications in both high-capacity gas storage and energy-efficient gas separations. The thorough investigation of such materials through chemical diversification, gas adsorption measurements, and in situ structural characterization is therefore crucial for broadening their utility. We examine a series of isoreticular, flexible zeolitic imidazolate frameworks (ZIFs) of the type M(bim)2 (SOD; M = Zn (ZIF-7), Co (ZIF-9), Cd (CdIF-13); bim– = benzimidazolate), and elucidate the effects of metal substitution on the pressure-responsive phase changes and the resulting CO2 and CH4 step positions, pre-step uptakes, and step capacities. Using ZIF-7 as a benchmark, we reexamine the poorly understood structural transition responsible for its adsorption steps and, through high-pressure adsorption measurements, verify that it displays a step in its CH4 adsorption isotherms. The ZIF-9 material is shown to undergo an analogous phase change, yielding adsorption steps for CO2 and CH4 with similar profiles and capacities to ZIF-7, but with shifted threshold pressures. Further, the Cd2+ analogue CdIF-13 is reported here for the first time, and shown to display adsorption behavior distinct from both ZIF-7 and ZIF-9, with negligible pre-step adsorption, a ~50% increase in CO2 and CH4 capacity, and dramatically higher threshold adsorption pressures. Remarkably, a single-crystal-to-single-crystal phase change to a pore-gated phase is also achieved with CdIF-13, providing insight into the phase change that yields step-shaped adsorption in these flexible ZIFs. Finally, we show that the endothermic phase change of these frameworks provides intrinsic heat management during gas adsorption. </p

A Diaminopropane-Appended Metal-Organic Framework Enabling Efficient CO2 Capture from Coal Flue Gas via a Mixed Adsorption Mechanism.

A new diamine-functionalized metal-organic framework comprised of 2,2-dimethyl-1,3-diaminopropane (dmpn) appended to the Mg2+ sites lining the channels of Mg2(dobpdc) (dobpdc4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) is characterized for the removal of CO2 from the flue gas emissions of coal-fired power plants. Unique to members of this promising class of adsorbents, dmpn-Mg2(dobpdc) displays facile step-shaped adsorption of CO2 from coal flue gas at 40 °C and near complete CO2 desorption upon heating to 100 °C, enabling a high CO2 working capacity (2.42 mmol/g, 9.1 wt %) with a modest 60 °C temperature swing. Evaluation of the thermodynamic parameters of adsorption for dmpn-Mg2(dobpdc) suggests that the narrow temperature swing of its CO2 adsorption steps is due to the high magnitude of its differential enthalpy of adsorption (Δhads = -73 ± 1 kJ/mol), with a larger than expected entropic penalty for CO2 adsorption (Δsads = -204 ± 4 J/mol·K) positioning the step in the optimal range for carbon capture from coal flue gas. In addition, thermogravimetric analysis and breakthrough experiments indicate that, in contrast to many adsorbents, dmpn-Mg2(dobpdc) captures CO2 effectively in the presence of water and can be subjected to 1000 humid adsorption/desorption cycles with minimal degradation. Solid-state 13C NMR spectra and single-crystal X-ray diffraction structures of the Zn analogue reveal that this material adsorbs CO2 via formation of both ammonium carbamates and carbamic acid pairs, the latter of which are crystallographically verified for the first time in a porous material. Taken together, these properties render dmpn-Mg2(dobpdc) one of the most promising adsorbents for carbon capture applications