Rapid-Scan Electron Paramagnetic Resonance of Highly Resolved Hyperfine Lines in Organic Radicals.

X-band (ca. 9 GHz) fluid solution rapid-scan electron paramagnetic resonance spectra are reported for radicals with multiline spectra and resolution of hyperfine lines as narrow as 30 mG. Highly-resolved spectra of 3-carbamoyl-2,2,5,5-tetramethylpyrrolidin-1-yloxy, diphenylnitroxide, galvinoxyl, and perylene cation radical with excellent signal-to-noise are shown, demonstrating the capabilities of the rapid-scan technique to characterize very small, well-resolved hyperfine couplings. To acquire high resolution spectra the signal bandwidth must be less than the resonator bandwidth. Signal bandwidth is inversely proportional to linewidth and proportional to scan rate. Resonator bandwidth is inversely proportional to resonator Q. Proper selection of scan rate and resonator Q is needed to achieve resolution of closely-spaced narrow EPR lines.

Mapping the Quebec dental workforce: ranking rural oral health disparities.

INTRODUCTION: Ensuring access to oral health services is crucial for improving the oral health of rural and remote populations. A logical step towards addressing oral health disparities and underutilization of services in rural areas is to ensure the availability of the dental workforce. Geographical information systems are valuable in examining workforce dispersion patterns and identifying priority areas requiring administrative and policy attention. The objective of this study was to examine and map the distribution patterns of the dental workforce in Quebec, Canada. METHODS: Utilizing the membership directory of Quebec Professional Orders (2009-2010), data on practice locations, practice types and license issue date for all active members of the Quebec dental workforce were obtained. This was followed by reverse geocoding of the geographic coordinates using a global positioning system visualizer to reveal textual locations. These locations were classified according to various degrees of rurality as defined by the 2006 Census Metropolitan Area and Census Agglomeration Influenced Zone typology, developed by Statistics Canada. Cartography layers were extracted from a geospatial database provided by Canada Natural Resources using ArcGIS 9.3. Descriptive and bivariate analyses were performed using SPSS v17 for Windows. RESULTS: Data analysis revealed statistically significant differences in the distribution of dental professionals in rural and urban areas (urban 59.4±19.4/100 000 vs rural 39.9±17.6/100 000; p<0.001). Approximately 90.3% of the dental workforce was located in urban zones, 1.3% in the zones strongly influenced by metropolitan area, 4.9% in the moderately influenced zones, while only 0.3% of the dental workforce was located in non-metropolitan-influenced zones. Urban zones such as Montreal, Quebec and Sherbrooke had the highest workforce availability (4-6 dentists for every 5000 inhabitants). Of a total of 447 specialist dentists in Quebec, only five were located in rural areas. CONCLUSIONS: This study concludes that there is a strong relationship between the degree of urbanization and the highest concentration of dental professionals. In addition, there is a lack of dental workforce availability, particularly specialists in rural Quebec. Further research is needed to examine and evaluate to what degree these distribution patterns might contribute to oral health outcomes of the rural population.

Development of a metal-ion-mediated base pair for electron transfer in DNA.

A new C-nucleoside structurally based on the hydroxyquinoline ligand was synthesized that is able to form stable pairs in DNA in both the absence and the presence of metal ions. The interactions between the metal centers in adjacent Cu(II)-mediated base pairs in DNA were probed by electron paramagnetic resonance (EPR) spectroscopy. The metal-metal distance falls into the range of previously reported values. Fluorescence studies with a donor-DNA-acceptor system indicate that photoinduced charge-transfer processes across these metal-ion-mediated base pairs in DNA occur more efficiently than over natural base pairs.

A synthetic two-spin quantum bit: g-engineered exchange-coupled biradical designed for controlled-NOT gate operations.

A quantum gate: A system of two coupled electron spins that is useful for simple quantum computing operations has been prepared by synthesis of a biradical 1 and co-crystallization with an isomorphous host molecule. The two weakly exchange-coupled quantum bits (target qubit blue and control qubit red) span four electron spin states. The electron spin transition is denoted by two black arrows.

The short-lived signaling state of the photoactive yellow protein photoreceptor revealed by combined structural probes.

The signaling state of the photoactive yellow protein (PYP) photoreceptor is transiently developed via isomerization of its blue-light-absorbing chromophore. The associated structural rearrangements have large amplitude but, due to its transient nature and chemical exchange reactions that complicate NMR detection, its accurate three-dimensional structure in solution has been elusive. Here we report on direct structural observation of the transient signaling state by combining double electron electron resonance spectroscopy (DEER), NMR, and time-resolved pump-probe X-ray solution scattering (TR-SAXS/WAXS). Measurement of distance distributions for doubly spin-labeled photoreceptor constructs using DEER spectroscopy suggests that the signaling state is well ordered and shows that interspin-label distances change reversibly up to 19 Å upon illumination. The SAXS/WAXS difference signal for the signaling state relative to the ground state indicates the transient formation of an ordered and rearranged conformation, which has an increased radius of gyration, an increased maximum dimension, and a reduced excluded volume. Dynamical annealing calculations using the DEER derived long-range distance restraints in combination with short-range distance information from (1)H-(15)N HSQC perturbation spectroscopy give strong indication for a rearrangement that places part of the N-terminal domain in contact with the exposed chromophore binding cleft while the terminal residues extend away from the core. Time-resolved global structural information from pump-probe TR-SAXS/WAXS data supports this conformation and allows subsequent structural refinement that includes the combined energy terms from DEER, NMR, and SAXS/WAXS together. The resulting ensemble simultaneously satisfies all restraints, and the inclusion of TR-SAXS/WAXS effectively reduces the uncertainty arising from the possible spin-label orientations. The observations are essentially compatible with reduced folding of the I(2)' state (also referred to as the 'pB' state) that is widely reported, but indicates it to be relatively ordered and rearranged. Furthermore, there is direct evidence for the repositioning of the N-terminal region in the I(2)' state, which is structurally modeled by dynamical annealing and refinement calculations.

Intracellular Protein-Lipid Interactions Studied by Rapid-Scan Electron Paramagnetic Resonance Spectroscopy.

Protein-membrane interactions play key roles in essential cellular processes; studying these interactions in the cell is a challenging task of modern biophysical chemistry. A prominent example is the interaction of human α-synuclein (αS) with negatively charged membranes. It has been well-studied in vitro, but in spite of the huge amount of lipid membranes in the crowded environment of biological cells, to date, no interactions have been detected in cells. Here, we use rapid-scan (RS) electron paramagnetic resonance (EPR) spectroscopy to study αS interactions with negatively charged vesicles in vitro and upon transfection of the protein and lipid vesicles into model cells, i.e., oocytes of Xenopus laevis. We show that protein-vesicle interactions are reflected in RS spectra in vitro and in cells, which enables time-resolved monitoring of protein-membrane interaction upon transfection into cells. Our data suggest binding of a small fraction of αS to endogenous membranes.

High field 27Al ENDOR reveals the coordination mode of Cu2+ in low Si/Al zeolites.

The siting of Cu2+ in zeolites with low exchange levels has been a subject for debate due to the lack of experimental evidence that provide directly the interaction between the Cu2+ ion and the zeolite framework. High field 27Al ENDOR provided highly resolved orientation selective ENDOR spectra from which both the 27Al hyperfine and quadrupole principal components and orientations relative to the g tensor principal axis system were determined for a dehydrated Cu2+ exchanged zeolite X with Si/Al = 1. The results show that all three Cu-Al distances in the six-member ring are equivalent, in contrast to DFT predictions using cluster models.