Endogenous chemical exchange saturation transfer (CEST) effects are always diluted by competing effects, such as direct water proton saturation (spillover) and semi-solid macromolecular magnetization transfer (MT). This leads to unwanted T2 and MT signal contributions that lessen the CEST signal specificity to the underlying biochemical exchange processes. A spillover correction is of special interest for clinical static field strengths and protons resonating near the water peak. This is the case for all endogenous CEST agents, such as amide proton transfer, –OH-CEST of glycosaminoglycans, glucose or myo-inositol, and amine exchange of creatine or glutamate. All CEST effects also appear to be scaled by the T1 relaxation time of water, as they are mediated by the water pool. This forms the motivation for simple metrics that correct the CEST signal. Based on eigenspace theory, we propose a novel magnetization transfer ratio (MTRRex), employing the inverse Z-spectrum, which eliminates spillover and semi-solid MT effects. This metric can be simply related to Rex, the exchange-dependent relaxation rate in the rotating frame, and ka, the inherent exchange rate. Furthermore, it can be scaled by the duty cycle, allowing for simple translation to clinical protocols. For verification, the amine proton exchange of creatine in solutions with different agar concentrations was studied experimentally at a clinical field strength of 3 T, where spillover effects are large. We demonstrate that spillover can be properly corrected and that quantitative evaluation of pH and creatine concentration is possible. This proves that MTRRex is a quantitative and biophysically specific CEST-MRI metric. Applied to acute stroke induced in rat brain, the corrected CEST signal shows significantly higher contrast between the stroke area and normal tissue, as well as less B1 dependence, than conventional approaches.

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Ionic liquids are gaining substantial interest as alternative reaction media. Despite the overwhelming amount of evidence suggesting a relationship between their structure and melting point, there still remains the problem of selectively choosing a particular ionic pair that will produce a liquid at room temperature. Ionic liquids based on 1-alkyl-3-methylimidazolium halides have been investigated using ab initio calculations utilizing Gaussian 98 and the 6-31G* and 6-31+G* basis sets. The calculated interaction energy was found to increase in magnitude with decreasing alkyl chain length at the Hartree−Fock level, although no trend was found to exist with increasing anionic radius. Correlations between melting point and interaction energy were investigated. Linear trends were found to exist in the 1-n-butyl-3-methylimidazolium (Bmim) halide series as well as the 1-alkyl-3-methylimidazolium iodide series.

There has been an explosion of interest in ionic liquids in the last five years that has resulted in the discovery of a vast number of new ionic liquids with a wide range of interesting applications. Although ionic liquids are invariably described as highly stable green solvents, thorough investigations quantifying their purity, stability, biodegradability, and toxicity have lagged behind the pace of other research in the area. This review addresses these key issues and summarizes the approaches that have been developed for recycling ionic liquids.

We present here a reassessment of our transition-metal free Suzuki-type coupling protocol. We believe that, although the reaction can be run without the need for addition of a metal catalyst, palladium contaminants down to a level of 50 ppb found in commercially available sodium carbonate are responsible for the generation of the biaryl rather than, as previously suggested, an alternative non-palladium-mediated pathway. We present a revised methodology for Suzuki couplings using ultralow palladium concentrations for use with aryl and vinyl boronic acids and discuss the effects of the purity of the boronic acid on the reaction.

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The biodegradability of a range of phosphonium ionic liquids (ILs) was assessed using the CO 2 headspace test (ISO 14593). Tetraalkylphosphonium cations in which one of the alkyl substituents contained ester, ether, alcohol or alkene functionality in order to promote biodegradation were targeted. These cations were paired with halide, triflimide and octylsulfate anions. In contrast to previously studied dialkylimidazolium and alkylpridinium ILs with incorporated ester moieties and octylsulfate anions, the phosphonium ILs showed relatively low levels of biodegradability. 902 496 8104; Tel: +1 902 496 8189 † Electronic supplementary information (ESI) available: 1 H, 13 C and 31 P NMR spectra of all novel phosphonium ionic liquids. See d P (121 MHz; DMSO d 6 ; 85% H 3 PO 4 ) 33.3; m/z (ESI, +ve) 327.3179 [(M-Br -) + requires 327.3175].This journal is

Purpose To evaluate the correlation between angiographic measures of Moyamoya disease and tissue-level impairment from measurements of tissue perfusion and cerebrovascular reactivity (CVR). Materials and Methods The relationship between perfusion-weighted arterial spin labeling (ASL) and hypercarbic blood oxygenation-level dependent (BOLD) CVR and time-to-peak (TTP) were compared with angiographically measured risk factors including arterial circulation time (ACT) and modified Suzuki Score (mSS) in patients (n=15) with Moyamoya disease. Results Hemodynamic contrasts provided information not apparent from structural or angiographic imaging. Mean z-statistics demonstrate that BOLD is significantly (P=0.017) higher in low mSS hemispheres (z-statistic=5.0±2.5) compared to high mSS hemispheres (z-statistic=3.7±1.7), implying that regions with less advanced stages of Moyamoya disease have higher reactivity. After correcting for multiple comparisons, a strong trend for a direct relationship (R=0.38; P=0.03) between BOLD TTP and ACT was observed, and a significant inverse relationship between CBF and ACT (R=−0.47; P=0.01) was found, demonstrating that BOLD and ASL contrasts reflect DSA measures of vascular compromise in Moyamoya disease, albeit with different sensitivity. Conclusion Correlative measures between angiography and hemodynamic methods suggest that BOLD and ASL could be used for expanding the diagnostic imaging infrastructure in Moyamoya patients and potentially tracking tissue response to revascularization.