1H NMR Study of the HCa2Nb3O10 Photocatalyst with Different Hydration Levels

The photocatalytic activity of layered perovskite-like oxides in water splitting reaction is dependent on the hydration level and species located in the interlayer slab: simple or complex cations as well as hydrogen-bonded or non-hydrogen-bonded H2O. To study proton localization and dynamics in the HCa2Nb3O10·yH2O photocatalyst with different hydration levels (hydrated—α-form, dehydrated—γ-form, and intermediate—β-form), complementary Nuclear Magnetic Resonance (NMR) techniques were applied. 1H Magic Angle Spinning NMR evidences the presence of different proton containing species in the interlayer slab depending on the hydration level. For α-form, HCa2Nb3O10·1.6H2O, 1H MAS NMR spectra reveal H3O+. Its molecular motion parameters were determined from 1H spin-lattice relaxation time in the rotating frame (T1ρ) using the Kohlrausch-Williams-Watts (KWW) correlation function with stretching exponent β = 0.28: Ea=0.2102 eV, τ0=9.01 × 10−12 s. For the β-form, HCa2Nb3O10·0.8H2O, the only 1H NMR line is the result of an exchange between lattice and non-hydrogen-bonded water protons. T1ρ(1/T) indicates the presence of two characteristic points (224 and 176 K), at which proton dynamics change. The γ-form, HCa2Nb3O10·0.1H2O, contains bulk water and interlayer H+ in regular sites. 1H NMR spectra suggest two inequivalent cation positions. The parameters of the proton motion, found within the KWW model, are as follows: Ea=0.2178 eV, τ0=8.29 × 10−10 s.

1H MAS NMR of Donor Pancreatic Tissue is a Useful Predictor of Islet Viability Prior to Islet Isolation

A significant limitation and cost to any clinical islet program is the related to processing human pancreas and not recovering significant numbers of viable islets for clinical transplantation. The development of an assay system that could be utilized and provide an index of cell and tissue viability before islet isolation would provide a major impact on the scientific aspects of organ preservation and a huge cost saving to any clinical islet transplantation program.Metabolomic analysis by 1H MAS NMR was used to assess samples of donor pancreatic tissue taken prior to islet isolation. A significant correlation was observed between the ratio of the combined integrals of the sugar (3.5-4.5 ppm) and choline (3.0-3.5 ppm) regions to the integrals of the CH3 (0.9 ppm) and CH2 (1.3 ppm) peaks of the 1H MAS NMR spectra of pancreatic tissue samples taken prior to islet isolation and the glucose responsiveness, a measure of islet viability, of the isolated islets (P<0.05). The effect of the two-layer (University of Wisconsin solution/perfluorochemical [UW/PFC]) cold-storage method, previously shown to restore ischemically damaged pancreases by increasing oxygenation, was also studied using 1H MAS NMR spectroscopy. PFC recovery of the donor pancreas also correlated with an increase in the combined integrals of the sugar and choline regions to the CH3 and CH2 peaks of the 1H MAS NMR spectra (P<0.05). In addition, significant differences in the integrals of the sugar region and CH2 peaks were observed between the pre- and post-PFC samples (P<0.05). These results support the notion that specific metabolites observed in 1H MAS NMR can be used as a means to assess reversible/irreversible tissue damage and offers a means to assess donor pancreatic tissue prior to islet isolation for transplantation.

Study of PtOx/TiO2 Photocatalysts in the Photocatalytic Reforming of Glycerol: The Role of Co-Catalyst Formation

In this study, relationships between preparation conditions, structure, and activity of Pt-containing TiO2 photocatalysts in photoinduced reforming of glycerol for H2 production were explored. Commercial Aerolyst® TiO2 (P25) and homemade TiO2 prepared by precipitation-aging method were used as semiconductors. Pt co-catalysts were prepared by incipient wetness impregnation from aqueous solution of Pt(NH3)4(NO3)2 and activated by calcination, high temperature hydrogen, or nitrogen treatments. The chemico-physical and structural properties were evaluated by XRD, 1H MAS NMR, ESR, XPS, TG-MS and TEM. The highest H2 evolution rate was observed over P25 based samples and the H2 treatment resulted in more active samples than the other co-catalyst formation methods. In all calcined samples, reduction of Pt occurred during the photocatalytic reaction. Platinum was more easily reducible in all of the P25 supported samples compared to those obtained from the more water-retentive homemade TiO2. This result was related to the negative effect of the adsorbed water content of the homemade TiO2 on Pt reduction and on particle growth during co-catalyst formation.