Real‐Time Interrogation of Aspirin Reactivity,Biochemistry, and Biodistribution by Hyperpolarized Magnetic Resonance Spectroscopy

Hyperpolarized magnetic resonance spectroscopy enables quantitative, non‐radioactive, real‐time measurement of imaging probe biodistribution and metabolism in vivo. Here, we investigate and report on the development and characterization of hyperpolarized acetylsalicylic acid (aspirin) and its use as a nuclear magnetic resonance (NMR) probe. Aspirin derivatives were synthesized with single‐ and double‐¹³C labels and hyperpolarized by dynamic nuclear polarization with 4.7 % and 3 % polarization, respectively. The longitudinal relaxation constants (T₁) for the labeled acetyl and carboxyl carbonyls were approximately 30 seconds, supporting in vivo imaging and spectroscopy applications. In vitro hydrolysis, transacetylation, and albumin binding of hyperpolarized aspirin were readily monitored in real time by ¹³C‐NMR spectroscopy. Hyperpolarized, double‐labeled aspirin was well tolerated in mice and could be observed by both ¹³C‐MR imaging and ¹³C‐NMR spectroscopy in vivo.     

First and Efficient Method for Reduction of Aliphatic and Aromatic Nitro Compounds with Zinc Borohydride as Pyridine Zinc Tetrahydroborato Complex: A New Stable Ligand‐Metal Borohydride

Pyridine zinc tetrahydroborate, [(Py)Zn(BH₄)₂], as a new stable ligand‐metal borohydride, is prepared quantitatively by complexation of 1:1 zinc borohydride and pyridine at room temperature. This reagent efficiently reduces different aromatic and aliphatic nitro compounds to their primary amines in refluxing THF. In addition, the reduction shows chemoselectivity for aliphatic nitro compounds over the aromatic nitro compounds.     

Slice profile optimization in arterial spin labeling using presaturation and optimized RF pulses

OBJECTIVE: An important source of error in arterial spin labeling (ASL) is incomplete static tissue subtraction due to imperfect slice profiles. This effect can be reduced by saturating the spins in the imaging area prior to labeling. In this study, the use of optimized presaturation is compared with the use of optimized RF pulses for minimizing this error. MATERIALS AND METHODS: Different methods for optimizing presaturation were simulated by numerical solution of the Bloch equation. Presaturation was optimized by changing the number of presaturation pulses, their position in the pulse sequence and the area of the crusher gradients following each saturation pulse. It was also investigated whether the use of optimized presaturation could reduce the tag gap needed to ensure complete static tissue subtraction. Simulation results were verified using phantom and in vivo studies at 3T. RESULTS: In proximal inversion with control for off-resonance effects, optimized presaturation could reduce the necessary tag gap to 15% of the imaging slab for experiments using standard RF pulses, while c-FOCI RF pulses could reduce it to 11%. In flow-sensitive alternating inversion recovery, a single presaturation pulse could reduce the inversion width to 122% of the imaging slab and neither multiple presaturation pulses nor optimized RF pulses could reduce it further. CONCLUSION: Optimized presaturation can reduce the necessary inversion width to the same level as if using optimized RF pulses and can, therefore, be used to optimize ASL sensitivity. Furthermore, optimized presaturation can reduce the B(1)-dependent sensitivity in static tissue subtraction.     

On the Generalization of Reissner Plate Theory to Laminated Plates,Part I: Theory

This is the first part of a two-part paper presenting the generalization of Reissner thick plate theory (Reissner in J. Math. Phys. 23:184–191, 1944) to laminated plates and its relation with the Bending-Gradient theory (Lebée and Sab in Int. J. Solids Struct. 48(20):2878–2888, 2011 and in Int. J. Solids Struct. 48(20):2889–2901, 2011). The original thick and homogeneous plate theory derived by Reissner (J. Math. Phys. 23:184–191, 1944) is based on the derivation of a statically compatible stress field and the application of the principle of minimum of complementary energy. The static variables of this model are the bending moment and the shear force. In the present paper, the rigorous extension of this theory to laminated plates is presented and leads to a new plate theory called Generalized-Reissner theory which involves the bending moment, its first and second gradients as static variables. When the plate is homogeneous or functionally graded, the original theory from Reissner is retrieved. In the second paper (Lebée and Sab, 2015), the Bending-Gradient theory is obtained from the Generalized-Reissner theory and comparison with an exact solution for the cylindrical bending of laminated plates is presented.     

Complementary Site-Selective Halogenation of Nitrogen-Containing (Hetero)Aromatics with Superacids

Site-selective functionalization of arenes that is complementary to classical aromatic substitution reactions remains a long-standing quest in organic synthesis. Exploiting the generation of halenium ion through oxidative process and the protonation of the nitrogen containing function in HF/SbF₅, the chlorination and iodination of classically inert Csp²−H bonds of aromatic amines occurs. Furthermore, the superacid-promoted (poly)protonation of the molecules acts as a protection, favoring the late-stage selective halogenation of natural alkaloids and active pharmaceutical ingredients     

Applicability of some mass spectrometric criteria for the confirmation of pesticide residues

This study was initiated to demonstrate the impact of tolerance intervals calculated based on experimental data and standard criteria on the capability to detect and identify pesticide residues by GC-MS in plant extract. The tolerance intervals specified by the current guidelines and standards (EU, EPA, ISO, EC) result in a large number of false negative values. The tolerance intervals calculated based on the actually measured ion ratios at 2 different probability levels did not provide a better estimate. Based on experimental findings a 2-phase procedure for confirmation of pesticide residues is recommended. The first screening phase comprises identification of those pesticide residues that are likely to be present avoiding false negatives as far as possible. Relatively large tolerance intervals, +/-30% of absolute ion abundances ratios, have to be used at this point. When 2 or 3 selected ion ratios are within the established tolerance intervals the residue is confirmed. When the ions detected still indicate the possible presence of a residue the result may be reported as tentatively identified. However, when the result would lead to regulatory action, second confirmatory phase has to be undertaken. This can be achieved with the same GC-MS equipment, by injecting matrix-matched standards of the suspected analyte, in order to compensate for matrix influence on ion ratios. Alternatively, methods using different physico-chemical properties of the compound have to be used. The choice of the technique depends on their availability, time and cost.     

Determination of pesticide residues in peaches by using gas chromatography and mass spectrometric detection

ABSTRACT

A multi-residue method using selected ion monitoring mode GC-MSD has been developed for the quantitative analysis of 30 widely used pesticides in fresh peaches produced in Swat Malakand, Pakistan. The planned methodology involved a sample extraction procedure using liquid-liquid partition with acetonitrile followed by a clean-up step based on solid-phase extraction (SPE). Method validation was performed in accordance with European Union guidelines. The European Union criteria (recovery 70–120%, RSD <20%) were met for majority of pesticides. For most of the pesticides, signal-to-noise ratios were good and background-corrected mass spectra often contained sufficient diagnostic to enable identity and confirmation. The limits of quantification (LOQs) were in the range 0.01–1.0 mg/kg. The above method was successfully applied to the analysis of peach samples (n = 30) from the field. Pesticide concentration in real peach samples was compared with the maximum residue levels (MRLs). Pesticide residues were detected in 73% of the peach samples. Most frequent residues were metalaxyl, α-cypermethrin, azoxystrobin, dimethoate, tebuconazol, λ-cyhalothrin and spiromesifin in peach samples.     

Facile synthesis of scheelite-type NdOsO4 directly grown on carbon cloth for oxygen evolution reaction

Journal of Solid State Electrochemistry - In the recent work, the scheelite-type ABO4&nbsp;compound (A = Nd and B = Os) is synthesized via a hydrothermal route directly...