Structural Information on Supramolecular Copper(II) ß-Diketonate Complexes from Atomic Force Microscopy and Analytical Ultracentrifugation.

Supramolecular Cu(II) complexes were prepared from two trifunctional ß-diketone ligands. The ligands (CH3Si(phacH)3 and CH3Si(phprH)3, represented by LH3) contain three aryl-ß-diketone moieties joined by an organosilicon group. The complexes have the empirical formula Cu3L2, as expected for combinations of Cu2+ and L3-. Several metal-organic polyhedra (MOPs) [Cu3L2]n are possible (n = 1-10); a dodecahedron (Cu30L20; n = 10; estimated diameter of ca. 5 nm) should be the most stable because its internal bond angles would come closest to ideal values. Atomic force microscopy (AFM), performed on samples deposited from solution onto mica substrates, revealed a distribution of sample heights in the 0.5-3.0 nm range. The most commonly observed heights were 0.5-1.5 nm, corresponding to the smallest possible molecules (Cu3L2, i.e., n = 1). Some molecular cubes (Cu12L8; ca. 2.5 nm) or larger molecules or aggregates may be present as well. Equilibrium analytical ultracentrifugation (AUC) was also used to probe the compounds. A previously reported reference compound, the molecular square Cu4(m-pbhx)4 (M = 2241 g mol-1), behaved well in AUC experiments in four nonpolar organic solvents. AUC data for the new tris(ß-diketonate) MOPs [Cu3L2]n in toluene and fluorobenzene did not agree well with the theoretical results for a single solute. The data were fit well by a two-solute model, but these results were not consistent in the two solvents used, and some run-to-run variability was noted even in the same solvent. Also, the calculated molecular weights differed significantly from those expected for [Cu3L2]n ([Cu3(CH3Si(phac)3)2]n, multiples of 1322 g mol-1; or [Cu3(CH3Si(phpr)3)2]n, multiples of 1490 g mol-1).

The use of gas chromatography - high resolution mass spectrometry for suspect screening and non-targeted analysis of per- and polyfluoroalkyl substances.

This study is a workflow development for the analysis, identification, and categorization of per- and polyfluoroalkyl substances (PFAS) using gas chromatography-high resolution mass spectrometry (GC-HRMS) with non-targeted analysis (NTA) and suspect screening techniques. The behavior of various PFAS in a GC-HRMS was studied with regards to retention indices, ionization susceptibility, fragmentation patterns, etc. A custom PFAS database was constructed from 141 diverse PFAS. The database contains mass spectra from electron ionization (EI) mode, as well as MS and MS/MS spectra from positive and negative chemical ionization (PCI and NCI, respectively) modes. Common fragments of PFAS were identified across a diverse set of 141 PFAS analyzed. A workflow for suspect screening of PFAS and partially fluorinated products of incomplete combustion/destruction (PICs/PIDs) was developed which utilized both the custom PFAS database and external databases. PFAS and other fluorinated compounds were identified in both a challenge sample (designed to test the identification workflow) and incineration samples suspected to contain PFAS and fluorinated PICs/PIDs. The challenge sample resulted in a 100% true positive rate (TPR) for PFAS which were present in the custom PFAS database. Several fluorinated species were tentatively identified in the incineration samples using the developed workflow.

Alternating magnetic field mediated release of fluorophores from magnetic nanoparticles by hysteretic heating.

This study explores the use of differential heating of magnetic nanoparticles with different sizes and compositions (MFe2O4 (M = Fe, Co)) for heteroplexed temporal controlled release of conjugated fluorophores from the surface of nanoparticles. By exploiting these differences, we were able to control the amount of hysteretic heating occurring with the distinct sets of magnetic nanoparticles using the same applied alternating magnetic field radio frequency (AMF-RF). Using thermally labile retro-Diels-Alder linkers conjugated to the surface of nanoparticles, the fluorescent payload from the different nanoparticles disengaged when sufficient energy was locally generated during hysteretic heating. 1H, 13C NMR, ESI-MS, and SIMS characterized the thermally responsive fluorescent cycloadducts used in this study; the Diels Alder cycloadducts were modeled using density functional theory (DFT) computations. The localized point heating of the different nanoparticle compositions drove the retro-Diels-Alder reaction at different times resulting in higher release rates of fluorophores from the CoFe2O4 compared to the Fe3O4 nanoparticles.