Thermogravimetric Analysis and Mass Spectrometry Allow for Determination of Chemisorbed Reaction Products on Metal Organic Frameworks.

Thermogravimetric analysis (TGA) is a technique which can probe chemisorption of substrates onto metal organic frameworks. A TGA method was developed to examine the catalytic oxidation of S-nitrosoglutathione (GSNO) by the MOF H3[(Cu4Cl)3(BTTri)8] (abbr. Cu-BTTri; H3BTTri = 1,3,5-tris(1H-1,2,3-triazol-5-yl)benzene), yielding glutathione disulfide (GSSG) and nitric oxide (NO). Thermal analysis of reduced glutathione (GSH), GSSG, GSNO, and Cu-BTTri revealed thermal resolution of all four analytes through different thermal onset temperatures and weight percent changes. Two reaction systems were probed: an aerobic column flow reaction and an anaerobic solution batch reaction with gas agitation. In both systems, Cu-BTTri was reacted with a 1 mM GSH, GSSG, or GSNO solution, copiously rinsed with distilled-deionized water (dd-H2O), dried (25 °C, < 1 Torr), and assessed by TGA. Additionally, stock, effluent or supernatant, and rinse solutions for each glutathione derivative within each reaction system were assessed by mass spectrometry (MS) to inform on chemical transformations promoted by Cu-BTTri as well as relative analyte concentrations. Both reaction systems exhibited chemisorption of glutathione derivatives to the MOF by TGA. Mass spectrometry analyses revealed that in both systems, GSH was oxidized to GSSG, which chemisorbed to the MOF whereas GSSG remained unchanged during chemisorption. For GSNO, chemisorption to the MOF without reaction was observed in the aerobic column setup, whereas conversion to GSSG and subsequent chemisorption was observed in the anaerobic batch setup. These findings suggest that within this reaction system, GSSG is the primary adsorbent of concern with regards to strong binding to Cu-BTTri. Development of similar thermal methods could allow for the probing of MOF reactivity for a wide range of systems, informing on important considerations such as reduced catalytic efficiency from poisoning, recyclability, and loading capacities of contaminants or toxins with MOFs.

S-Nitrosoglutathione exhibits greater stability than S-nitroso-N-acetylpenicillamine under common laboratory conditions: A comparative stability study.

S-Nitrosothiols (RSNOs) such as S-nitrosoglutathione (GSNO) and S-nitroso-N-acetylpenicillamine (SNAP) are susceptible to decomposition by stimuli including heat, light, and trace metal ions. Using stepwise isothermal thermogravimetric analysis (TGA), we observed that NO-forming homolytic cleavage of the S-N bond occurs at 134.7 ±â€¯0.8 °C in GSNO and 132.8 ±â€¯0.9 °C in SNAP, contrasting with the value of 150 °C that has been previously reported for both RSNOs. Using mass spectrometry (MS), nuclear magnetic resonance (NMR), and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), we analyzed the decomposition products from TGA experiments. The organic product of GSNO decomposition was glutathione disulfide, while SNAP decomposed to form N-acetylpenicillamine disulfide as well as other products, including tri- and tetrasulfides. In addition, we assessed the relative solution stabilities of GSNO and SNAP under common laboratory conditions, which include variable temperature, pH, and light exposure with rigorous exclusion of trace metal ions by chelation. GSNO exhibited greater stability than SNAP over a 7-day period except in one instance. Both RSNOs demonstrated an inverse relationship between solution stability and temperature, with refrigeration considerably extending shelf life. A decrease in pH from 7.4 to 5.0 also enhanced the stability of both RSNOs. A further decrease in pH from 5.0 to 3.0 resulted in decreased stability for both RSNOs, and is notably the only occasion in which SNAP proved more stable than GSNO. After 1 h of exposure to overhead fluorescent lighting, both RSNOs displayed high susceptibility to light-induced decomposition. After 7 h, GSNO and SNAP decomposed 19.3 ±â€¯0.5% and 30 ±â€¯2%, respectively.

Nitric Oxide Generation from Endogenous Substrates Using Metal-Organic Frameworks: Inclusion within Poly(vinyl alcohol) Membranes To Investigate Reactivity and Therapeutic Potential.

Cu-BTTri (H3BTTri = 1,3,5-tris[1H-1,2,3-triazol-5-yl]benzene) is a water-stable, copper-based metal-organic framework (MOF) that exhibits the ability to generate therapeutic nitric oxide (NO) from S-nitrosothiols (RSNOs) available within the bloodstream. Immobilization of Cu-BTTri within a polymeric membrane may allow for localized NO generation at the blood-material interface. This work demonstrates that Cu-BTTri can be incorporated within hydrophilic membranes prepared from poly(vinyl alcohol) (PVA), a polymer that has been examined for numerous biomedical applications. Following immobilization, the ability of the MOF to produce NO from the endogenous RSNO S-nitrosoglutathione (GSNO) is not significantly inhibited. Poly(vinyl alcohol) membranes containing dispersions of Cu-BTTri were tested for their ability to promote NO release from a 10 µM initial GSNO concentration at pH 7.4 and 37 °C, and NO production was observed at levels associated with antithrombotic therapeutic effects without significant copper leaching (<1%). Over 3.5 ± 0.4 h, 10 wt % Cu-BTTri/PVA membranes converted 97 ± 6% of GSNO into NO, with a maximum NO flux of 0.20 ± 0.02 nmol·cm-2·min-1. Furthermore, it was observed for the first time that Cu-BTTri is capable of inducing NO production from GSNO under aerobic conditions. At pH 6.0, the NO-forming reaction of 10 wt % Cu-BTTri/PVA membrane was accelerated by 22%, while an opposite effect was observed in the case of aqueous copper(II) chloride. Reduced temperature (20 °C) and the presence of the thiol-blocking reagent N-ethylmaleimide (NEM) impair the NO-forming reaction of Cu-BTTri/PVA with GSNO, with both conditions resulting in a decreased NO yield of 16 ± 1% over 3.5 h. Collectively, these findings suggest that Cu-BTTri/PVA membranes may have therapeutic utility through their ability to generate NO from endogenous substrates. Moreover, this work provides a more comprehensive analysis of the parameters that influence Cu-BTTri efficacy, permitting optimization for potential medical applications.

Latent Porosity in Alkali-Metal M2B12F12 Salts: Structures and Rapid Room-Temperature Hydration/Dehydration Cycles.

Structures of the alkali-metal hydrates Li2(H2O)4Z, LiK(H2O)4Z, Na2(H2O)3Z, and Rb2(H2O)2Z, unit cell parameters for Rb2Z and Rb2(H2O)2Z, and the density functional theory (DFT)-optimized structures of K2Z, K2(H2O)2Z, Rb2Z, Rb2(H2O)2Z, Cs2Z, and Cs2(H2O)Z are reported (Z2- = B12F122-) and compared with previously reported X-ray structures of Na2(H2O)0,4Z, K2(H2O)0,2,4Z, and Cs2(H2O)Z. Unusually rapid room-temperature hydration/dehydration cycles of several M2Z/M2(H2O)nZ salt hydrate pairs, which were studied by isothermal gravimetry, are also reported. Finely ground samples of K2Z, Rb2Z, and Cs2Z, which are not microporous, exhibited latent porosity by undergoing hydration at 24-25 °C in the presence of 18 Torr of H2O(g) to K2(H2O)2Z, Rb2(H2O)2Z, and Cs2(H2O)Z in 18, 40, and 16 min, respectively. These hydrates were dehydrated at 24-25 °C in dry N2 to the original anhydrous M2Z compounds in 61, 25, and 76 min, respectively (the exact times varied from sample to sample depending on the particle size). The hydrate Na2(H2O)2Z also exhibited latent porosity by undergoing multiple 90 min cycles of hydration to Na2(H2O)3Z and dehydration back to Na2(H2O)2Z at 23 °C. For the K2Z, Rb2Z, and Cs2Z transformations, the maximum rate of hydration (rhmax) decreased, and the absolute value of the maximum rate of dehydration (rdmax) increased, as T increased. For K2Z ↔ K2(H2O)2Z hydration/dehydration cycles with the same sample, the ratio rhmax/rdmax decreased 26 times over 8.6 °C, from 3.7 at 23.4 °C to 0.14 at 32.0 °C. For Rb2Z ↔ Rb2(H2O)2Z cycles, rhmax/rdmax decreased from 0.88 at 23 °C to 0.23 at 27 °C. For Cs2Z ↔ Cs2(H2O)Z cycles, rhmax/rdmax decreased 20 times over 8 °C, from 6.7 at 24 °C to 0.34 at 32 °C. In addition, the reversible substitution of D2O for H2O in fully hydrated Rb2(H2O)2Z in the presence of N2/16 Torr of D2O(g) was complete in only 60 min at 23 °C.

Comparison of the Coordination of B12F122-, B12Cl122-, and B12H122- to Na+ in the Solid State: Crystal Structures and Thermal Behavior of Na2(B12F12), Na2(H2O)4(B12F12), Na2(B12Cl12), and Na2(H2O)6(B12Cl12).

The synthesis of high-purity Na2B12F12 and the crystal structures of Na2(B12F12) (5 K neutron powder diffraction (NPD)), Na2(H2O)4(B12F12) (120 K single-crystal X-ray diffraction (SC-XRD)), Na2(B12Cl12) (5 and 295 K NPD), and Na2(H2O)6(B12Cl12) (100 K SC-XRD) are reported. The compound Na2(H2O)4(B12F12) contains {[(Na(µ-H2O)2Na(µ-H2O)2)]2+}∞ infinite chains; the compound Na2(H2O)6(B12Cl12) contains discrete [(H2O)2Na(µ-H2O)2Na(H2O)2]2+ cations with OH···O hydrogen bonds linking the terminal H2O ligands. The structures of the two hydrates and the previously published structure of Na2(H2O)4(B12H12) are analyzed with respect to the relative coordinating ability of B12F122-, B12H122-, and B12Cl122- toward Na+ ions in the solid state (i.e., the relative ability of these anions to satisfy the valence of Na+). All three hydrated structures have distorted octahedral NaX2(H2O)4 coordination spheres (X = F, H, Cl). The sums of the four Na-O bond valence contributions are 71, 75, and 89% of the total bond valences for the X = F, H, and Cl hydrated compounds, respectively, demonstrating that the relative coordinating ability by this criterion is B12Cl122- ≪ B12H122- < B12F122-. Differential scanning calorimetry experiments demonstrate that Na2(B12F12) undergoes a reversible, presumably order-disorder, phase transition at ca. 560 K (287 °C), between the 529 and 730 K transition temperatures previously reported for Na2(B12H12) and Na2(B12Cl12), respectively. Thermogravimetric analysis demonstrates that Na2(H2O)4(B12F12) and Na2(H2O)6(B12Cl12) undergo partial dehydration at 25 °C to Na2(H2O)2(B12F12) and Na2(H2O)2(B12Cl12) in ca. 30 min and 2 h, respectively, and essentially complete dehydration to Na2(B12F12) and Na2(B12Cl12) within minutes at 150 and 75 °C, respectively (the remaining trace amounts of H2O, if any, were not quantified). The changes in structure upon dehydration and the different vapor pressures of H2O needed to fully hydrate the respective Na2(B12X12) compounds provide additional evidence that B12Cl122- is more weakly coordinating than B12F122- to Na+ in the solid state. Taken together, the results suggest that the anhydrous, halogenated closo-borane compounds Na2(B12F12) and Na2(B12Cl12), in appropriately modified forms, may be viable component materials for fast-ion-conducting solid electrolytes in future energy-storage devices.