Molecular Dynamics and Surface Interactions of Nickelocene Adsorbed on Silica: A Paramagnetic Solid-State NMR Study.

When grinding nickelocene with silica in the absence of a solvent at room temperature, it adsorbs on the surface within the pores. This has also been demonstrated visually by adsorbing green nickelocene in the pores of a large colorless silica gel specimen. While this dry adsorption and translational mobility of nickelocene within the pores is proven visually, the site-to-site mobility of the nickelocene molecules and their orientation toward the surface are not yet understood. In this contribution, mesoporous silica is used as the support material for a systematic solid-state NMR study of these issues. Paramagnetic 1H VT solid-state NMR and T1 relaxation times have been powerful tools for studying the dynamics of nickelocene on the silica surface. Herewith, the mobility of the surface-adsorbed nickelocene molecules in the pores could be quantified on the molecular scale. According to the obtained data, the nickelocene molecules move like a liquid on the surface. Isotropically moving molecules exchange places rapidly with surface-attached molecular states of nickelocene in a sample with submonolayer surface coverage. This finding is corroborated by a macroscopic visualization experiment. The states of the surface-attached horizontally oriented nickelocene molecules that are prevalent at temperatures below 200 K have been quantified. The temperature dependencies of the rate k in coordinates of ln(k) versus 1/T and ln(k/T) versus 1/T form ideal straight lines that allow the determination of the kinetic parameters Eact = 5.5 kcal/mol, A = 1.1 × 1010, ΔH‡ = 5.0 kcal/mol, and ΔS‡ = -15 eu. Investigating a sample with equal amounts of nickelocene and ferrocene in a submonolayer amount of 80% overall surface coverage shows that the different metallocenes mix on the molecular level on the silica surface.

Cardiac Toxicity After Craniospinal Irradiation: A Late Effect That May be Eliminated With Proton Therapy.

BACKGROUND: Craniospinal irradiation (CSI) is commonly required for pediatric patients with central nervous system malignancies. Traditionally, CSI is given using x-rays to deliver radiation to the brain and spine, exposing normal anterior structures, including heart, to unnecessary radiation. OBSERVATIONS: We present a patient treated with x-ray CSI for medulloblastoma with spinal metastasis (3600 cGy CSI with focal boost to 5000 cGy), who subsequently developed significant cardiac toxicity, likely related to radiation exposure. CONCLUSIONS: Spinal irradiation can cause significant cardiac risk due to exit dose through anterior structures. This toxicity may be avoided with proton therapy, which eliminates visceral exit dose.

Creating Solid Solutions of Metallocenes: Migration of Nickelocene into the Ferrocene Crystal Lattice in the Absence of a Solvent.

Ferrocene and nickelocene do not react with each other in solution; however, the large impact of the paramagnetic component on the ferrocene 1H NMR signal linewidth and relaxation times has been quantified. Co-crystallization of ferrocene and nickelocene at any ratio from a solvent can be explained with both pure substances crystallizing in the same space group P21/n. As a new phenomenon, when a ferrocene single crystal is exposed to polycrystalline nickelocene in the absence of a solvent, the nickelocene migrates into the ferrocene crystal lattice and a mixed crystal is formed that retains its macroscopic shape. This process has been proven visually by cutting the single crystal. Mixing polycrystalline ferrocene with polycrystalline nickelocene at different molar ratios with a mortar and pestle leads to crystalline solid solutions with the corresponding molar ratios of both components. This migration of one organometallic component into an existing crystal lattice of another at ambient temperature in the absence of a solvent has not been described previously. Paramagnetic 1H solid-state NMR spectroscopy of static and rotating samples of dry ferrocene/nickelocene mixtures at varying ratios is used to prove and quantify the mixing of both metallocenes at the molecular level. A single-crystal X-ray structure of a 50/50 mixed crystal corroborates the NMR results that nickelocene and ferrocene are randomly distributed in the lattice and that the space group P21/n is retained. All ferrocene molecules in the mixed crystal lattice show a broadening of their 1H wideline signals and residual magic-angle spinning (MAS) lines at ambient temperature. The broadening of the ferrocene signals correlates with the nickelocene content. 1H T1 relaxation time measurements for the signals of ferrocene in samples with different amounts of nickelocene corroborate the assumption that the signal broadening is due to paramagnetic dipole-dipole relaxation of ferrocene molecules in the vicinity of nickelocene. Spatially separated ferrocene and nickelocene powders in one rotor show the solid-state NMR characteristics of the individual polycrystalline metallocenes. The described formation of solid solutions of metallocenes in the absence of a solvent will open new pathways to homogeneously mixed nanoparticles with desired metal ratios and dual-atom catalysts.

Peer-led problem-based learning in interprofessional education of health professions students.

BACKGROUND: The role of peer teachers in interprofessional education has not been extensively studied. This study is designed to determine if peer-teacher-led problem-based seminars can influence medical and pharmacy students' perceptions of interprofessional education. METHODS: Undergraduate medical and pharmacy students participated in one-hour problem-based learning seminars held over the course of 16 weeks. A case-control study design was used to compare perceptions of interprofessional education between students who participated in seminars and students who did not participate in seminars. The validated Interdisciplinary Education Perception Scale (IEPS) was used to assess perceptions of interprofessional education and was distributed to medical and pharmacy students at the conclusion of 16 weeks of seminars. A two-tailed t-test was used to determine significance between groups. A survey was also distributed to all students regarding perceived barriers to involvement in interprofessional education training. RESULTS: In total, 97 students responded to IEPS (62 medical, 35 pharmacy). Data showed significantly higher perception of professional cooperation among medical students (p=0.006) and pharmacy students (p=0.02) who attended interprofessional seminars compared to those who did not attend. One hundred and nine students responded to the survey regarding perceived barriers to interprofessional education, with the two most common barriers being: 'I am not aware of interprofessional education opportunities' (61.5%) and 'I do not have time to participate' (52.3%). CONCLUSION: Based on this data we believe peer-teacher-led problem-based interprofessional seminars can be used to increase medical and pharmacy students' perceived need for professional cooperation. Currently, major barriers to interprofessional education involvement are awareness and time commitment. Undergraduate health professions education can incorporate student-led seminars to improve interprofessional education.