Temperature and hydration dependence of proton MAS NMR spectra in MCM-41: model based on motion induced chemical shift averaging.

The proton MAS NMR spectra in MCM-41 at low hydration levels (less than hydration amounting to one water molecule per surface hydroxyl group) show complex proton resonance peak structures, with hydroxyl proton resonances seen in dry MCM-41 disappearing as water is introduced into the pores and new peaks appearing, representing water and hydrated silanol groups. Surface hydroxyl group-water molecule chemical exchange and chemical shift averaging brought about by a water molecule visiting different surface hydrogen bonding sites have been proposed as possible causes for the observed spectral changes. In this report a simple model based on chemical shift averaging, due to the making and breaking of hydrogen bonds as water molecules move on the MCM-41 surface, is shown to fully reproduce the NMR spectra, both as a function of hydration and temperature. Surface proton-water proton chemical exchange is not required in this model at low hydration levels.

Initial investigation on the use of MR spectroscopy and micro-MRI of GAFCHROMIC EBT radiotherapy film.

PURPOSE: This article presents an initial investigation of the efficacy of using 1H MRS and micro-MRI as analysis techniques for irradiated GAFCHROMIC EBT radiotherapy films. METHODS: GAFCHROMIC EBT radiotherapy film was irradiated with 6 MV x rays to known doses ranging from 5 to 1000 cGy. 24 h following irradiation 1H MRS measurements were performed to access the degree of post-irradiation polymer cross-linking. 2D 1H micro-MRI experiments were also performed for film irradiations of 0 and 300 cGy. RESULTS: Linear response of the 1H MRS linewidth to dose in the range from 0 to 400 cGy (R2 = 0.98) was observed. Such linearity is not seen when analyzed under conventional light analysis. The sensitivity of the film, as measured by the slope of the curve between 0 and 400 cGy, is 0.0042 +/- 0.0003 kHz/cGy, demonstrating the sensitivity of the 1H MRS technique used to analyze the film. The film saturates at a dose of approximately 900 cGy. Broadline 1H MRS provides a quantitative measure of the degree of polymerization of the film. CONCLUSIONS: A quantitative measurement of the degree of polymerization of GAFCHROMIC EBT film has been presented using 1H MRS. The saturation of the film at approximately 900 cGy is corroborated by that observed with light analysis. Further MR spectroscopic experiments are needed to investigate the response of the film to dose, allowing for a better understanding of the relationship between polymer cross-linking in the active layer.

Magnetic resonance imaging of cells overexpressing MagA, an endogenous contrast agent for live cell imaging.

Molecular imaging with magnetic resonance imaging (MRI) may benefit from the ferrimagnetic properties of magnetosomes, membrane-enclosed iron biominerals whose formation in magnetotactic bacteria is encoded by multiple genes. One such gene is MagA, a putative iron transporter. We have examined expression of MagA in mouse neuroblastoma N2A cells and characterized their response to iron loading and cellular imaging by MRI. MagA expression augmented both Prussian blue staining and the elemental iron content of N2A cells, without altering cell proliferation, in cultures grown in the presence of iron supplements. Despite evidence for iron incorporation in both MagA and a variant, MagAE137V, only MagA expression produced intracellular contrast detectable by MRI at 11 Tesla. We used this stable expression system to model a new sequence for cellular imaging with MRI, using the difference between gradient and spin echo images to distinguish cells from artifacts in the field of view. Our results show that MagA activity in mammalian cells responds to iron supplementation and functions as a contrast agent that can be deactivated by a single point mutation. We conclude that MagA is a candidate MRI reporter gene that can exploit more fully the superior resolution of MRI in noninvasive medical imaging.

Integration of DNA barcoding into an ongoing inventory of complex tropical biodiversity.

Inventory of the caterpillars, their food plants and parasitoids began in 1978 for today's Area de Conservacion Guanacaste (ACG), in northwestern Costa Rica. This complex mosaic of 120 000 ha of conserved and regenerating dry, cloud and rain forest over 0-2000 m elevation contains at least 10 000 species of non-leaf-mining caterpillars used by more than 5000 species of parasitoids. Several hundred thousand specimens of ACG-reared adult Lepidoptera and parasitoids have been intensively and extensively studied morphologically by many taxonomists, including most of the co-authors. DNA barcoding - the use of a standardized short mitochondrial DNA sequence to identify specimens and flush out undisclosed species - was added to the taxonomic identification process in 2003. Barcoding has been found to be extremely accurate during the identification of about 100 000 specimens of about 3500 morphologically defined species of adult moths, butterflies, tachinid flies, and parasitoid wasps. Less than 1% of the species have such similar barcodes that a molecularly based taxonomic identification is impossible. No specimen with a full barcode was misidentified when its barcode was compared with the barcode library. Also as expected from early trials, barcoding a series from all morphologically defined species, and correlating the morphological, ecological and barcode traits, has revealed many hundreds of overlooked presumptive species. Many but not all of these cryptic species can now be distinguished by subtle morphological and/or ecological traits previously ascribed to 'variation' or thought to be insignificant for species-level recognition. Adding DNA barcoding to the inventory has substantially improved the quality and depth of the inventory, and greatly multiplied the number of situations requiring further taxonomic work for resolution.